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ENDOCRINOLOGÍAY NUTRICIÓN

Órgano de la Sociedad Española de Endocrinología y Nutrición

Volumen 54, Monográfico 6, Julio 2007

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8.° SIMPOSIO CIENTÍFICO

NUEVAS APROXIMACIONES AL SÍNDROMEMETABÓLICO

Director invitado:

Dr. José Antonio Gutiérrez

Incluida en EMBASE/Excerpta Medicawww.doyma.es/endo www.seenweb.org

María de Molina 3, 1.º – 28006 Madrid – Tel.: 91 781 50 70 Fax 91 781 50 79 – Correo electrónico: [email protected] - www.fundacionlilly.com

Sumario

8.° SIMPOSIO CIENTÍFICO

NUEVAS APROXIMACIONES AL SÍNDROME METABÓLICO

Director invitado: Dr. José Antonio Gutiérrez

Introducción 1 J.A. Gutiérrez

Factores genéticos y ambientales 3 N. Stefandeterminantes de los lípidos intrahepáticos

Hábitos dietéticos, peso corporal y resistencia 5 G. Marchesini and R. Marzocchia la insulina en la enfermedad por hígado graso no alcohólico

Estrategias para la valoración de la 8 A.J. McCulloughesteatohepatitis no alcohólica

Objetivos terapéuticos y estado actual del 14 P. Charatcharoenwitthaya tratamiento de la enfermedad por hígado and K.D. Lindorgraso no alcohólico

Resistencia a la insulina y síndrome 17 J.M. Fernández-Realinflamatorio cardiovascular crónico

El aporte de macronutrientes induce el estrés 20 P. Dandonaoxidativo e inflamatorio, mientras que la insulina suprime la generación de especies reactivas del oxígeno (ROS) y la inflamación

Fibrinólisis y síndrome metabólico 22 M.C. Alessi and I. Juhan-Vague

Disfunción endotelial en el síndrome metabólico 25 A. Avogaro

Síndromes de obesidad humana monogénica 28 I. Sadaf Farooqi

Complicaciones metabólicas asociadas con 32 P. Arnerla obesidad: un problema del tejido adiposo

Experiencia DRECE 35 M.A. Rubio, en representación del grupo DRECE

En el camino para detener la progresión del 37 J.F. Carosíndrome metabólico

Síndrome metabólico y riesgo cardiovascular 40 R. Carmena


Este suplemento ha sido patrocinado por Fundación Lilly.

Esta publicación refleja conclusiones, hallazgos y comentarios propios de los autores y se mencionanestudios clínicos que podrían contener indicaciones/posologías/formas de administración de produc-tos no autorizadas actualmente en España. Se recuerda que cualquier fármaco mencionado deberá serutilizado de acuerdo con la Ficha Técnica vigente en España.

Contents

8th SCIENTIFIC SYMPOSIUM

NEW APPROACHES TO THE METABOLIC SYNDROME

Invited editor: Dr. José Antonio Gutiérrez

Introduction 1 J.A. Gutiérrez

Genetic and environmental determinants 3 N. Stefan of intrahepatic lipids

Dietary habits, body weight and insulin 5 G. Marchesini and R. Marzocchiresistance in nonalcoholic fatty liver disease

Strategies for the evaluation of nonalcoholic 8 A.J. McCulloughsteatohepatitis

Targets for therapy and current status 14 P. Charatcharoenwitthaya of treatment of nonalcoholic fatty liver disease and K.D. Lindor

Insulin resistance and chronic cardiovascular 17 J.M. Fernández-Realinflammatory syndrome

Macronutrient intake induces oxidative 20 P. Dandonaand inflammatory stress while insulin causes suppression of ROS generation and inflammation

Fibrinolysis and the metabolic syndrome 22 M.C. Alessi and I. Juhan-Vague

Endothelial dysfunction in the metabolic 25 A. Avogaro syndrome

Monogenic human obesity syndromes 28 I Sadaf Farooqi

Metabolic complications associated with 32 P. Arner obesity–an adipose tissue problem

The DRECE study experience 35 M.A. Rubio, on behalf of the Diet and Risk of Cardiovascular Diseases in Spain Study (DRECE) group

On the trail to arrest the progression 37 J.F. Caro of the metabolic syndrome

Metabolic syndrome and cardiovascular risk 40 R. Carmena


This supplement has been sponsored by Fundación Lilly.

This publication shows the conclusions, findings and comments of the authors and mentions clinical stud-ies that could have indications/dosages/administration forms of currently unauthorized medicinal prod-ucts in Spain. It is stressed that any drug mentioned should be used in accordance with the Data Sheetin force in Spain.

Endocrinol Nutr. 2007;54 Supl 6:1-2 1

Three years ago, at the 2nd Fundación Lilly Scientific Sym-posium entitled “The Metabolic Syndrome on its 80th anniver-sary”, we remembered the merits and honoured the memoriesof two physicians, Eskil Kylin, from Goteborg and GregorioMarañón, from Madrid. They both presented eighty years befo-re, patients in which high arterial blood pressure and glucoseintolerance or diabetes mellitus of adult type were coincident inone clinical picture, suggesting a common mechanism for de-velopment.

Eskil Kylin (1889-1975), was a Swedish specialist in in-ternal medicine, most of his time working as a head of de-partment at the general hospital in Jönköping, southern Swe-den. He interested himself in every aspect of arterialhypertension, but most of all the close associations betweenhypertension and diabetes mellitus as well as other metabolicdisorders. In his early publication from 1923 (Zeitschrift furInnere Medizin) he delineated a metabolic syndrome, inclu-ding hyperglycemia, arterial hypertension and hyperurice-mia. From his papers it is clear that he often referred to simi-lar works and hypotheses from the great Spanishendocrinologist Gregorio Marañón (1887-1960). Thereforeboth Kylin and Marañón should be jointly acknowledged fortheir early and accurate views on what, passed the time,would be recognized as the metabolic syndrome (MetS).

The frequent simultaneous presence of obesity, hyperlipide-mia, diabetes mellitus and arterial hypertension was first descri-bed in 1965 by Avogaro et al. In this work, they reported thehigh risk of coronary artery disease in carriers of this cluster ofmetabolic and vascular abnormalities. The association of thesefactors was subsequently described in 1977 by Haller et al, whofirst used the term “Metabolic Syndrome” and described the as-sociation with atherosclerosis. In 1980 Vague suggested theconcept that fat mass per se has little effect on the progressionfrom obesity to diabetes mellitus, but it is the predominance offat in the upper part of the body that leads to diabetes mellitusand atherosclerosis. As a matter of fact, insulin and cortisol se-cretion in obese patients are correlated with central obesity. La-ter on, the coining by Reaven in 1988 of the term “SyndromeX” renewed the impetus to conduct research concerning thissyndrome. In his description of this syndrome, Reaven conside-red the following abnormalities: resistance to insulin-stimulatedglucose uptake, glucose intolerance, hyperinsulinemia, increa-sed VLDL triglycerides, decreased HDL cholesterol, and arte-rial hypertension. Other metabolic abnormalities that have beenconsidered as part of the syndrome include abnormal weight orweight distribution, inflammation, microalbuminuria, hyperuri-cemia, and abnormalities of fibrinolysis and of coagulation.

Today, the term “Metabolic Syndrome” is generally used toindicate a clinical situation in which different degrees of arterialhypertension, impaired glucose tolerance, atherogenic dyslipide-mia, central fat accumulation, insulin resistance, as well as proth-rombotic and proinflammatory states, cluster together in thesame individual. Such a concurrence of disorders increases theprobability of suffering from cardiovascular disease or type 2diabetes mellitus, possibly more than what the sum of the singlerisk factors would predict. Sometimes, the “whole” really is gre-ater than the “sum” of its parts. Such is the case with MetS.

During the last decade, the MetS has progressively becomea major public health problem both in wealthy societies and indeveloping countries. MetS is now approaching epidemic pro-portions worldwide. A total 115 million individuals suffer fromthis syndrome in the US, Japan, France, Germany, Italy, Spainand the UK, a number which is set to increase rapidly, fuelledby the rising obesity and diabetes mellitus epidemic. Its sprea-ding prevalence is strictly associated with the adoption of a“westernized” lifestyle, characterized by lack of physical acti-vity, excessive food intake, a combination of factors leading tooverweight and obesity. In fact, obesity, particularly visceralobesity, seems to be a major determinant of insulin resistance,hence preparing the path to the clustering of metabolic andnon-metabolic factors embraced under the descriptive term ofMetS. Significant though it is, the MetS patient population re-mains poorly diagnosed.

The prevalence of MetS depends on gender and several so-cioeconomic, ethnic and geographic factors. It is estimated inthe USA to be approximately 22.7% of the general populationwith important differences between ethnic groups within thesame socio-geographic areas1, whereas in Europe MetS preva-lence results in 23% and 12% for male and female populations,respectively, with ample north-south and east-west geographicvariations2. To appreciate the whole impact of the problem onpopulation health, it must be considered that not only cardio-vascular mortality but all-cause mortality are increased in peo-ple with the MetS3. And what is even a matter of greater con-cern the prevalence of MetS in children and adolescence is onthe increase worldwide.

This reality is requiring an increasing effort of the scientificcommunity in detecting the etiopathogenic mechanisms and,consequently, to elaborate interventional initiatives to counte-ract such escalating health crisis. This mounting involvementof the biomedical community is well represented by the expo-nential trend in the number of scientific papers on “metabolic”and “insulin resistance” syndromes published in the literaturein the last 3 decades.

IntroductionJOSÉ ANTONIO GUTIÉRREZ

Pathways leading directly from adiposity to the genesis ofdislipidemia and arterial hypertension have been elucidated.Recent knowledge implies a role for fat-derived “adipokines”,including TNFα and adiponectin, as pathogenic contributorsor protective factors. Current therapies include diet and exerci-se as well as agents indicated for the treatment of individualcomponents of the syndrome. Future therapies may accruefrom the aggressive pursuit of newer molecular drug targetsthat have the potential to prevent or treat multiple aspects ofthe MetS.

Aim of this symposium was to provide the participants withfirst-hand cutting-edge information (from molecular pathophy-siology to genetic epidemiology) on a crucial component of theMetS as obesity, but also on the newer components, such as in-flammation molecules, prothrombotic state, endothelial dys-function or non-alcoholic fatty liver disease.

A special effort has been done to present a completeand updated overview, enriched with several original con-tributions that we are confident fulfilled all participants’

expectations in this 8th Fundación Lilly Scientific Sympo-sium.

REFERENCES

1. Park YW, Zhu S, Palaniappan L, Heshka S, Carnethon MR,Heymsfield SB. The metabolic syndrome: prevalence and asso-ciated risk factor findings in the US population from the ThirdNational Health and Nutrition Examination Survey, 1988-1994.Arch Intern Med. 2003;163:427-36.

2. The European Group for the Study of Insulin Resistance(EGIR). The frequency of the WHO metabolic syndrome in Eu-ropean cohorts, and an alternative definition of the insulin resis-tance syndrome. Diab Metab. 2002;28:364-76.

3. Lakka HM, Laaksonen DE, Lakka TA, Niskanen LK, Kumpu-salo E, Tuomilehto J, et al. The metabolic syndrome and totaland cardiovascular disease mortality in middle-aged men.JAMA. 2002;288:2709-16.

Gutiérrez JA. Introduction

2 Endocrinol Nutr. 2007;54 Supl 6:1-2


Nuevas aproximaciones al síndrome metabólico

Genetic and environmentaldeterminants of intrahepaticlipidsNORBERT STEFAN

Endocrinology, Metabolism and Pathobiochemistry. University ofTübingen. Germany.

There is increasing evidence that the clinical disorder termed nonalco-holic fatty liver disease (NAFLD) is closely associated with the metabo-lic syndrome1. It is currently under investigation whether NAFLD repre-sents a major risk factor for type 2 diabetes mellitus and cardiovasculardisease. Several pathophysiologic mechanisms may underlie the develop-ment of NAFLD. Among them insulin resistance of peripheral tissues,hepatic insulin resistance and an imbalance in serum adipocytokines arethe predominant ones. Recently genetic variability in candidate genes oflipid metabolism was identified to be closely associated with the accumu-lation of intrahepatic lipids.

It is accepted that an imbalance between the enzymes that promote up-take and synthesis of fatty acids and those that promote the oxidation andexport of fatty acids exists, and that this results in NAFLD. This imbalan-ce may be caused by whole-body insulin resistance. Insulin resistance,particularly insulin resistance of the adipose tissue leads to increase in li-polysis, which results in increased circulating fatty acids.

Another factor contributing to lipid storage in the liver may be hyperin-sulinemia. It results from insulin resistance and may lead to increased up-take and storage of fatty acids in hepatocytes. Insulin is stimulatory tosynthesis of glycogen in the liver. However, as glycogen accumulates tohigh levels (roughly 5% of liver mass), further synthesis is strongly sup-pressed. When the liver is saturated with glycogen, any additional glucosetaken up by hepatocytes is shunted into pathways leading to synthesis offatty acids. Thus, insulin resistance of the adipose tissue may be the pri-mary factor leading to increase in fatty acid release into the portal vein, re-sulting in hepatic steatosis and consecutively in hepatic insulin resistan-ce2,3. Fatty acids in parallel increase insulin resistance of the skeletalmuscle leading to hyperglycemia followed by hyperinsulinemia (fig. 1).

A different mechanism has begun to emerge from studies of mice withtargeted gene mutations, namely that the liver and the beta-cells are pri-mary sites of insulin resistance4. Liver-specific insulin receptor knockoutmice exhibit insulin resistance, severe glucose intolerance, and a failureof insulin to suppress hepatic glucose production. In addition regulationof hepatic gene expression was impaired5. These alterations are paralleledby hyperinsulinemia due to a combination of increased insulin secretionand decreased insulin clearance. These mice also showed further charac-teristics of the metabolic syndrome including alterations in lipid metabo-lism. LIRKO mice had a threefold increase in low-density lipoproteincholesterol compared with the control mice, with normal total cholesteroland high-density lipoprotein cholesterol6.

Based on other knock-out and transgenic animal models an importantrole of the insulin receptor-protein 2, sterol regulatory element-bindingprotein 1c, suppressors of cytokine signalling in the liver for the accumu-lation of fat in the liver was also found. These data suggest that impairedinsulin signalling in the liver results in accumulation of fat in hepatocy-tes.

In humans, imaging procedures such as computed tomographic scan-ning, magnetic resonance tomography (MRT) and proton magnetic reso-nance spectroscopy (1HMRS) are adequate tools for non-invasive detec-

Correspondence: Dr. N. [email protected]

tion and classification of NAFLD. Particularly early and non-invasive detection of NAFLD when serum liver enzymes arenot elevated yet, may be important for early intervention toprevent disturbances in glucose and lipid metabolism.

With 1HMRS and MRT we could investigate the role ofvisceral adipose tissue, adipocytokines and genetic variabi-lity in the pathophysiology of NAFLD. We found that vis-ceral fat was a strong determinant of fatty liver both in ma-les and in females7. Adiponectin, the adipocytokine that hasmultiple beneficial effects on glucose and lipid metabolism,was also found to play an important role for NAFLD. Adi-ponectin plasma levels were not only associated with liverfat in cross-sectional analyses but adiponectin plasma levelsat baseline also predicted change in liver fat during a li-festyle intervention in obese subjects. Further we found thatpolymorphisms in the adiponectin receptor-1 gene are alsopredictive for the change in insulin sensitivity and liver fat8.

We also identified a polymorphism in the hepatic lipase geneto predict fatty liver. Moreover, we could show that this effectwas modulated by the important Pro12Ala polymorphism in theperoxisome proliferator-activated receptor-γ2 gene9.

In summary, NAFLD is associated with characteristics ofthe metabolic syndrome. Whether it is a primary pathophy-siologic state of the liver or secondary to peripheral insulinresistance and/or an imbalance in plasma adipokines (fig. 1)is still under investigation. Nevertheless, early screening ofsubjects for this phenotype, while the complete picture of

the metabolic syndrome was not manifested, is necessary toearly direct these subjects toward an intervention. This in-cludes lifestyle intervention with diet and increase in physi-cal activity and possibly pharmacological therapy.

REFERENCES

1. Angulo P. Nonalcoholic fatty liver disease. N Engl J Med.2002;346:1221-31.

2. Bergman RN. Non-esterified fatty acids and the liver: why is insulin se-creted into the portal vein? Diabetologia. 2000;43:946-52.

3. Hotamisligil GS. Molecular mechanisms of insulin resistance and therole of the adipocyte. Int J Obes Relat Metab Disord. 2000;24 Suppl4:S237.

4. Accili D. Lilly lecture 2003: the struggle for mastery in insulin action:from triumvirate to republic. Diabetes. 2004;53:1633-42.

5. Michael MD, Kulkarni RN, Postic C, Previs SF, Shulman GI, MagnusonMA, et al. Loss of insulin signaling in hepatocytes leads to severe insulinresistance and progressive hepatic dysfunction. Mol Cell. 2000;6:87-97.

6. Cohen SE, Tseng YH, Michael MD, Kahn CR. Effects of insulin-sensiti-sing agents in mice with hepatic insulin resistance. Diabetologia.2004;47:407-11.

7. Thamer C, Machann J, Haap M, Stefan N, Heller E, Schnodt B, et al. In-trahepatic lipids are predicted by visceral adipose tissue mass in healthysubjects. Diabetes Care. 2004;27:2726-9.

8. Stefan N, Machicao F, Staiger H, Machann J, Schick F, Tschritter O, et al.Polymorphisms in the gene encoding adiponectin receptor 1 are associatedwith insulin resistance and high liver fat. Diabetologia. 2005;48:2282-91.

9. Stefan N, Schafer S, Machicao F, Machann J, Schick F, Claussen CD, etal. Liver fat and insulin resistance are independently associated with the–514C>T polymorphism of the hepatic lipase gene. J Clin EndocrinolMetab. 2005;90:4238-43.

Stefan N. Genetic and environmental determinants of intrahepatic lipids


Insulin

Insulin Resistance

Lipolysis Glucoseutilization

FFAGlucose

Hyperinsulinemia

Pathophysiology ofNAFLD

Visceral Adipose TissueGeneticsDietary Fatty AcidsAdipocytokinesCapacity of Lipid Oxidation(Physical Fitness)

Increased Glucose Production

Release of more saturated FFAs

Release of other Factors affectinginsulin Sensitivity and Insulinsecretion?

Fatty Liver

Fig. 1. In insulin resistance there is increased lipolysis in adipose tissue. Fatty acid flux from adipose tissue is elevated in these conditions,and free fatty acids (FFA) released by lipolysis of plasma triglyceride-rich lipoproteins are diverted from adipose tissue to other organs asthe liver. Increased FFA flux to the liver increases the hepatocyte fatty acid pool size. In parallel insulin resistance of glucose disposal in-creases glycemia resulting in elevated insulin secretion and hyperinsulienmia. In the presence of hepatic hyperinsulinemia/insulin resistan-ce, hepatic lipogenesis is increased and esterification of incoming fatty acids is relatively favoured over oxidation. Furthermore visceraladipose tissue, genetics, diet, adipocytokines and physical fitness are strong and partially primary predictors of fat accumulation in the li-ver. This results in increased glucose production, increased release of fatty acids and other factors affecting insulin sensitivity and insulinsecretion. This in turn results in increased plasma levels of FFA and glucose that aggravate fat accumulation in the liver.



Dietary habits, body weight and insulin resistance innonalcoholic fatty liver diseaseGIULIO MARCHESINI AND REBECCA MARZOCCHI

“Alma Mater Studiorum” University of Bologna. Bologna. Italy.

Correspondence: Dr. G. Marchesini.E-mail: [email protected]

Nonalcoholic fatty liver disease (NAFLD) includes a wide spectrum ofhepatic alterations of metabolic origin, significantly associated with themetabolic syndrome (MS) and its individual features1. A lot of data sup-port this association: a high proportion of NAFLD patients have MS as asystemic disease, and a high proportion of cases with MS have NAFLDas its specific hepatic disease. Both conditions have common pathogenicmechanism(s) and share the same complications and treatment2.

The sequence of events leading to liver fat accumulation and diseaseprogression are not completely understood; a possible unified theory isdepicted in the figure 1. Genetic and acquired factors contribute the first“hit”, leading to hepatic fat deposition through accelerated lipolysis andincreased hepatic flux of free fatty acids, mainly derived from the visce-ral adipose tissue, through mechanism(s) which are incompletely unders-tood. Insulin resistance has a pivotal role, favoring fatty acid (FFA) fluxfrom adipose tissue to the liver and driving hepatic triglyceride produc-tion. Hyperinsulinemia and hyperglycemia also promote de novo lipoge-nesis, and in turn both hepatic triglyceride accumulation and high circula-ting FFA levels contribute to hepatic and peripheral insulin resistance.Accordingly, patients with NAFLD are more insulin resistant than age,gender and body mass index (BMI) matched controls without hepatic ste-atosis3. When tested by the “glucose clamp” technique, nearly allNAFLD patients demonstrate a lower-than-normal insulin-mediated glu-cose disposal, and there is evidence that the severity of liver disease is as-sociated with progressively increased insulin resistance4. This defect, ho-wever, is not limited to overweight/obese subjects. A recent study innon-diabetic, non obese NAFLD patients pointed that also normal weightNAFLD cases are characterized by a reduced insulin activity on both glu-cose and lipid metabolism5. Peripheral glucose disposal was markedlydecreased in a 2-step euglycemic insulin clamp at the low and high insu-lin doses, due to impaired glucose oxidation and glycogen synthesis.Compared with controls, glycerol appearance and lipid oxidation weresignificantly increased in the basal state, and were suppressed by insulinto a lower extent. Lipid oxidation was significantly related to endogenousglucose production (EGP), glucose disposal, the extent of hepatic steato-sis, and LDL oxidability. The correlation existing between hepatic steato-sis and lipid oxidation suggests that fat accumulation can result from anincreased lipid delivery to the liver, due to a reduced antilipolytic effectof insulin in adipose tissue coupled with defects in re-esterification, pro-moting enhanced oxidation. Steatosis per se may generate insulin resis-tance, further contributing to metabolic imbalance. Tikkainen et al com-pared subjects with high and low liver fat, selected on the basis of similarBMI, subcutaneous and visceral fat6. High liver fat was associated withhigher insulin, a marker of insulin resistance, as well as higher triglyceri-

des and lower whole-body insulin sensitivity. High liver fatis also associated with normal EGP in the basal state, but lo-wer-than-normal suppression of both EGP and lipolysis du-ring hyperinsulinemia, in keeping with hepatic insulin resis-tance7.

Liver fat does not simply reflect fat stores, but is pro-bably regulated by dietary fat. Compared with subjects withlow liver fat, subjects with high liver fat submitted to aweight loss showed a larger decrease in hepatic fat and amore marked decrease in insulin concentration8. In a studycarried out by a magnetic resonance imaging and protonmagnetic resonance spectroscopy, Thomas et al9 reportedthat intra-hepatocellular lipids increase by 22% for any 1%increase in total adipose tissue, by 21% for any 1% increasein subcutaneous adipose tissue, and by 104% for 1% increa-se in intra-abdominal adipose tissue.

Hepatic lipid accumulation is not the sole factor responsi-ble for hepatocellular injury. Increased hepatic FFA oxida-tion can generate oxygen radicals promoting lipid peroxida-tion, cytokine secretion and mitochondrial dysfunction.FFAs may also cause hepatocyte apoptosis, the final mecha-nism of cellular injury in NAFLD.

Diet may be partly responsible for steatosis and oxidativestress. In animals, the liver has been shown to have a highcapacity to accumulate triglycerides, and the size of this

pool can change several folds within hours. Recent studiesin humans have shown that up to 20% of dietary fatty acidsare secreted as VLDL triglycerides within 6 hours after ameal. The habitual diet of NASH patients is rich in satura-ted fat and cholesterol and poor in polyunsaturated fat, fi-ber, and vitamin C and E, and is associated with a lowersensitivity to insulin and with other aspect of the metabolicsyndrome10. In overweight non-diabetic women, changes indietary fat content can change liver fat, independently ofany change in body weight, free fatty acid concentration, in-tra-abdominal or subcutaneous fat mass, or rate of carbohy-drate, lipid or protein oxidation11. Reducing dietary fat from36% to 16% systematically reduces the percentage of hepa-tic fat content, which is systematically increased by cros-sing-over to a diet containing 56% fat. Changes in liver fatwere paralleled by changes in fasting serum insulin concen-tration.

The major breakthrough in the relation between diet, in-sulin resistance and liver fat is a very recent study, first sho-wing that the amount of fat in the diet regulates the hepaticexpression of endocannabinoid receptors. Endocannabi-noids (anandamide) are novel lipid mediators that modulateappetitive behavior, increasing consumption of palatablesubstance, through the activation of central cannabinoid(CB1) receptors, involved in the development of obesity12.This receptor is widely expressed, in hepatocytes and in adi-pocytes, as well as in the hypothalamus, limbic forebrain,and peripheral sensory nerve terminals. CB1 stimulation af-fects fat metabolism by regulating the level of adiponectin,by increasing lipoprotein lipase activity, and by contrastingthe activity of leptin. Osei-Hyiaman et al13 demonstratedthat endocannabinoids also target the liver, where activationof CB1 results in increased de novo fatty acids synthesis th-rough the induction of the lipogenic transcription factor ste-roid regulatory element binding protein-1c (SREBP-1c) andits target enzymes acetyl-CoA carboxylase-1 and fatty acidssynthase. A high fat diet increases hepatic anandamideowing to a major reduction in its degradation by fatty acidamidohydrolase, the enzyme responsible for the metabolismof anandamide. The activation of this pathway by endoge-nous anandamide in the liver has a key role in the develop-ment of diet-induced obesity and fatty liver. These findingssuggest that CB1 antagonists may be effective not only asanti-obesity agents, but also in preventing/reversing the de-velopment of fatty liver and its progression to cirrhosis ofmetabolic origin.

REFERENCES

1. Marchesini G, Bugianesi E, Forlani G, Cerrelli F, Lenzi M, Manini R,et al. Nonalcoholic fatty liver, steatohepatitis, and the metabolic syn-drome. Hepatology. 2003;37:917-23.

2. Eckel RH, Grundy SM, Zimmet PZ. The metabolic syndrome. Lancet.2005;365:1415-28.

3. Marchesini G, Brizi M, Bianchi G, Tomassetti S, Bugianesi E, LenziM, et al. Nonalcoholic fatty liver disease: a feature of the metabolicsyndrome. Diabetes. 2001;50:1844-50.

4. Sanyal AJ, Campbell-Sargent C, Mirshahi F, Rizzo WB, Contos MJ,Sterling RK, et al. Nonalcoholic steatohepatitis: association of insulinresistance and mitochondrial abnormalities. Gastroenterology.2001;120:1183-92.

5. Bugianesi E, Gastaldelli A, Vanni E, Gambino R, Cassader M, Baldi S,et al. Insulin resistance in non-diabetic patients with non-alcoholic fattyliver disease: sites and mechanisms. Diabetologia. 2005;48:634-42.

6. Tiikkainen M, Tamminen M, Hakkinen AM, Bergholm R, VehkavaaraS, Halavaara J, et al. Liver-fat accumulation and insulin resistance inobese women with previous gestational diabetes. Obes Res.2002;10:859-67.

7. Seppala-Lindroos A, Vehkavaara S, Hakkinen AM, Goto T, Westerbac-ka J, Sovijarvi A, et al. Fat accumulation in the liver is associated withdefects in insulin suppression of glucose production and serum free

Marchesini G et al. Dietary habits, body weight and insulin resistance in nonalcoholic fatty liver disease


Lifestyle Genes

Excessdietary fat

Excesscalories

Lowexercise

Obesity

Hepaticinsulin

resistance

Whole-bodyinsulin

resistance

High FFAflux

Hyper-glycemia

Hyper-insulinemia

Oxidativestress

Pro-fibrogenicactivity

FattyLiver

CirrhosisHCCNASH

Fig. 1. Proposed mechanism(s) leading from lifestyle to fatty li-ver disease, steatohepatitis, cirrhosis and hepatocellular carcino-ma. Note the central role of hepatic and whole-body insulin resis-tance and the potential contribution of genetic traits. FFA: freefatty acids; HCC: hepato cellular carcinoma; NASH: nonalcoho-lic steatohepatitis.

fatty acids independent of obesity in normal men. J Clin EndocrinolMetab. 2002;87:3023-8.

8. Tiikkainen M, Bergholm R, Vehkavaara S, Rissanen A, Hakkinen AM,Tamminen M, et al. Effects of identical weight loss on body composi-tion and features of insulin resistance in obese women with high andlow liver fat content. Diabetes. 2003;52:701-7.

9. Thomas EL, Hamilton G, Patel N, O’Dwyer R, Dore CJ, Goldin RD, etal. Hepatic triglyceride content and its relation to body adiposity: amagnetic resonance imaging and proton magnetic resonance spectros-copy study. Gut. 2005;54:122-7.

10. Musso G, Gambino R, De Michieli F, Cassader M, Rizzetto M, Duraz-zo M, et al. Dietary habits and their relations to insulin resistance and

postprandial lipemia in nonalcoholic steatohepatitis. Hepatology.2003;37:909-16.

11. Westerbacka J, Lammi K, Hakkinen AM, Rissanen A, Salminen I, AroA, et al. Dietary fat content modifies liver fat in overweight non-diabe-tic subjects. J Clin Endocrinol Metab. 2005;90:2804-9.

12. Williams CM, Kirkham TC. Anandamide induces overeating: media-tion by central cannabinoid (CB1) receptors. Psychopharmacology(Berl). 1999;143:315-7.

13. Osei-Hyiaman D, DePetrillo M, Pacher P, Liu J, Radaeva S, Batkai S,et al. Endocannabinoid activation at hepatic CB1 receptors stimulatesfatty acid synthesis and contributes to diet-induced obesity. J Clin In-vest. 2005;115:1298-305.

Marchesini G et al. Dietary habits, body weight and insulin resistance in nonalcoholic fatty liver disease




Strategies for the evaluation ofnonalcoholic steatohepatitisARTHUR J. MCCULLOUGH

Division of Gastroenterology. The Schwartz Center forMetabolism and Nutrition. MetroHealth Medical Center. CaseUniversity. Cleveland. Ohio. United States of America.

Correspondence: Dr. A. McCullough.E-mail: [email protected]

Non alcoholic fatty liver disease (NAFLD) is a disease of our genera-tion. This disease currently impacts virtually all fields of clinical medici-ne and will continue to do so. NAFLD is the most common form of chro-nic liver disease in Western societies and its prevalence is increasing inall other areas of the world as well1. NAFLD and its most severe form —nonalcoholic steatohepatitis (NASH)— are common, expensive to so-ciety, adversely affect quality of life and cause cirrhosis and liver relateddeath in a significant but still imprecisely known percentage of patients.

The available data, which are based on screening population studiesusing the diagnostic modalities of ultrasound and liver function tests,now indicate the prevalence rate for both NAFLD and NASH have incre-ased from previous estimates. They are now estimated to be in the rangeof 17-33% for NAFLD and 5.7-16.5% for NASH. Because NAFLD andNASH are associated with insulin resistance and obesity, these prevalen-ce rates are expected to increase world wide concurrent with the pande-mic of obesity and type 2 diabetes mellitus.

The importance of these observations stems from the fact that NASHis a progressive fibrotic disease, in which cirrhosis and liver related deathoccur in up to 20% and 12% of these patients, respectively over a 10 yearperiod. This is of particular concern given the increasing recognition ofNAFLD in children. Therefore, the diagnosis of this disease has becomean extremely relevant topic in clinical hepatology.

DEFINITION OF NAFLD

When discussing the diagnosis of NAFLD it is important to define pre-cisely this disease.

Histology

It should be emphasized that NASH should be considered as the mostsevere form of a larger spectrum of NAFLD with histologic findings ran-ging from fat alone to fat plus inflammation to fat plus hepatocyte injury(ballooning degeneration) with or without fibrosis, polymorpho nuclearcells or Mallory hyaline. Only fat plus hepatocyte injury with or withoutfibrosis should be considered NASH. The significance of these histologiccategories rests not only on the fact that the prevalence varies by histo-logy with steatosis alone with or without inflammation being more com-mon than NASH, but clinical outcomes also vary by histologic category.Therefore, it is important to reliably distinguish NASH from other histo-logic types of NAFLD.

As shown in figure 1, cirrhosis develops in 15-25% of NASH patients2-5

and once developed, 40% of these patients may experience a liver related

death over a 10-year period5 with mortality rates similar to6

or worse than7 cirrhosis associated with hepatitis C. NASHis also now considered the major cause of cryptogenic cirr-hosis8. NASH associated cirrhosis can also decompensateinto subacute liver failure9, progress to hepatocellular carci-noma10-14 and re-occur post-transplantation15,16.

In contrast, steatosis alone is reported to have a more benignclinical course5,17,18, although progression of fibrosis in cirrho-sis has occurred in 3% of those patients with steatosis alone5.

Definition of nonalcoholic

By definition, excessive alcohol consumption excludesthe diagnosis of NAFLD. However, the definition of exces-sive has been elusive and a wide range of alcohol has beenallowed in previous reports19,20. Early studies allowed no al-cohol use4,21,22 while more recent studies have allowed 40 gweekly3,23 or up to 140 and 210 g weekly for women andmen respectively5,17,21,24-26. Confounding this issue is a re-cent study describing endogenous alcohol production inNASH patients related to the degree of obesity27 as well asthe protective effect of moderate alcohol intake in the pre-vention of diabetes mellitus28 and the development ofNASH in morbidly obese patients undergoing bariatric sur-gery29. Although there is no consensus regarding the defini-tion of “nonalcoholic” in NAFLD patients, it seems reaso-nable to exclude patients from this diagnosis if current orpast (within 5 years) daily alcohol intake has exceededmore than 10 g in women and 20 g in men. However, recent

data suggest remote or cumulative alcohol use is associatedwith NASH in up to 15% of patients30. Since there is no cli-nical feature or laboratory test sufficiently sensitive to de-tect this amount of alcohol intake, a careful history from thepatient, the patient’s family and other health care providersinvolved in the patient’s management is paramount31.

DIAGNOSIS OF NAFLD

It should be emphasized that this discussion deals predo-minantly with NAFLD associated with insulin resistanceand the metabolic syndrome. This form of NAFLD is oftenreferred to as primary NAFLD. Other secondary forms,which must be sought and excluded from the diagnosis ofprimary NAFLD, are provided.

Clinical presentation

History

The most common presentation is the patient with abnor-mal enzymes often performed during routine screening orfor an abnormal ultrasound, which was performed for abdo-minal pain. However, the typical patient will be asympto-matic, although some patients will complain of right upperquadrant pain or progressive fatigue. The fatigue is usuallyvague and thought related to distention of Glisson’scapsule32. Other entities associated with NAFLD and insulin

McCullough AJ. Strategies for the evaluation of nonalcoholic steatohepatitis


TABLE 1. Patient demographics

Author (year) n Age (years) Female (%) Diabetes mellitus (%) Obese (%) Hyperlipidemia (%)

Ludwig (1980) 20 54 65 25 90 67Diehl (1988) 3 52 81 55 71 —Lee (1989) 49 53 78 51 69 4Powell (1990) 42 49 83 36 93 81Bacon (1994) 33 47 42 21 39 21Pinto (1996) 32 — 75 34 47 28Laurin (1996) 40 48 73 28 70 28Matteoni (1999) 132 53 53 33 70 92Angulo (1999) 144 51 67 28 60 27Cortez-Pinto (1999) 30 48 57 33 80 63Willner (2001) 90 51 51 46 87 61Chitturi (2002) 66 47 41 39 57 82Marchesini (2003) 304 42 17 7 25 3

NATURAL HISTORY OF NASH

NASH CIRRHOSIS LIVER RELATED DEATH

20% 30-40%

HCC POST-OLTXSub-Acute

RecurrenceFailure

Fig. 1. Natural history of nonalcoholic steatohepatitis. HCC: hepatocellular carcinoma; OLTX: orthotopic liver transplan-tation; NASH: nonalcoholic steatohepatitis.

resistance include Obstructive Sleep Apnea and PolycysticOvary Syndrome (PCOS)33.

Physical examination

In the absence of cirrhosis, most patients usually have anunremarkable physical exam. Hepatomegaly may be presentin 50% of patients27. The majority of patients will be over-weight [body mass index (BMI) > 25] or have increasedvisceral adiposity and an increased waist circumference32. IfPCOS is present, female patients may have hirsutism andincreased acne. Attention should be paid to fat distributionbecause either congenital or drug indured lipodystrophiesmay be present.

Intermittent dysconjugate gaze34 and acanthosis nigrans35,which result from mitochondrial injury36 and insulin resis-tance, respectively, may also be present. When present thetypical stigmata of chronic liver disease; including spidertelangectasia, caput medusa, ascites, palmar erythema, andgynecomastia, suggest the likelihood of cirrhosis.

Patient demographics

Table 1 provides patient demographic information obtai-ned from a number of different studies2-5,22,23,37-43. Most ca-ses of NAFLD occur in the fifth and sixth decades of life,although of considerable concern is the occurrence ofNAFLD in children44-47. Ten of the studies in table 1 descri-be an overall patient demographic consistent with the origi-nal typical NAFLD patient21. Cases occurred more fre-quently in females (51% to 83%), and there was a highprevalence in both type 2 diabetes mellitus (28% to 55%)and obesity (47% to 90%). The prevalence of dyslipidemicdisorders is highly variable, ranging between 4% and 92%.It is important to emphasize, however, that three stu-dies2,42,43 indicate that the typical clinical profile needs to beexpanded to include male patients with normal weight andwithout abnormalities in either glucose nor lipid metabo-lism. In fact, such male patients existed in the other studieslisted in table 1 but were not the majority and were notemphasized. Although there appears to be little differencehistologically between the expanded and original profiles,one report found male patients to have less steatosis andmore stainable iron on liver biopsy than females25.

Nonalcoholic fatty liver disease has been reported in allethnic groups, with preliminary data48 suggesting an overrepresentation of Caucasians and Hispanics. A cross-sectio-nal study suggested a low prevalence of NAFLD amongAfrican Americans49, but the National Health and NutritionExamination Survey (NHANES) III indicates that NAFLDmay be more common in African Americans than in Cauca-sians50. There may be a familial component also. Onestudy38 found 16 of 90 patients with NAFLD had a first-de-gree relative with the disease also. Another study51 foundthat among eight families, 18 family members were affec-ted.

Serum chemistries

Increase aminotransferase activities are the most commonabnormality reported in patients with NASH5,38,51-59.Usually, ALT or AST are elevated only mildly to modera-tely in the range of a two- to fivefold elevation2,3,5,23,53,56.

Alkaline phosphatase may be abnormally elevated two-to threefold, in fewer than half of patients2,5,21,23,60,61. Serumalbumin levels are almost always normal, and bilirubin le-vels are rarely abnormal2,38, unless cirrhosis has developed.

Many studies have reported elevated serum ferritin in ap-proximately 50% of NAFLD patients23,38,62,63, without evi-

dence of hepatic iron overload. Two studies25,26 noted thatheterozygosity for the HFE gene is increased in NAFLD pa-tients, with a trend toward more severe hepatic fibrosis inNASH patients with a genetic basis for hepatic iron overlo-ad. The authors acknowledged, however, that hepatic ironoverload occurred in only a minority of their NASH pa-tients.

The AST/ALT ratio is reported to be less than 1 in 65%to 90% of NAFLD patients5,22,23,64-68. When the AST/ALTratio is greater that 1, it suggests that there is an advancedfibrotic form of NAFLD5,23. However, this ratio is almostnever greater than 254.

Hematologic measurements are usually normal, unlesscirrhosis has led to hypersplenism. Several small selectedcase studies have reported positive tests for antinuclear anti-body in 10% to 46% of patients with NAFLD4,17,38,64-71. Thesignificance of this observation is unclear, however.

Finally, it should be emphasized that data questioning theaccuracy of standard liver function tests have been repor-ted53,72-74. Although liver function tests usually are elevatedmildly in NAFLD75,76, values can be normal, and the degreeof abnormalities does not correlate with the degree of stea-tosis or fibrosis77,78. What is considered an abnormal valuealso has been questioned, since the normal limits for ALTin population studies have been revised downward, with va-lues individualized by gender and for individuals with obe-sity or the metabolic syndrome59. However there are limita-tions in the accuracy of serum chemistries for diagnosingfatty liver. The limitations of this approach has been discus-sed53,72-74 and include the following: a) lack of specificity; b)although normally mildly elevated19,75,76, liver function tests(LFT) can be normal in NAFLD77,78; c) serum LFT’s do notcorrelate with the degree of steatosis or fibrosis77,78, and d)the normal limits for ALT have been revised downward andindividualized by gender for patients with NAFLD as wellas individuals with obesity or with a dysmetabolic syndro-me59.

Radiologic methods

Ultrasound, CT scan, magnetic resonance imaging(MRI), and proton magnetic spectroscopy (1H MRS) haveall been used to assess hepatic fat deposition in the liver79-88.While some studies have described superiority of a particu-lar modality80,82,84,87, a recent study79 demonstrated ultra-sound, CT scan and MRI have similar diagnostic accuracyfor quantitating the severity of steatosis when fat depositionis > 33% of the liver volume. 1H MRS has greater sensiti-vity that the other 3 modalities and has been shown to de-tect as little as 5% fat deposition in the liver80. MRI is use-ful for confirming the nature of hepatic steatosis when itoccurs focally rather that its usual diffuse pattern89 and cali-brated CT scans may be useful in monitoring hepatic fatcontent over time81. However, differences between NASHand steatosis are not apparent with any of the radiologicmodalities79,85. Even though two studies90,91 have evaluatedtest characteristics for ultrasound and found that ultrasoundleads to an incorrect diagnosis of fatty liver in 15-33% ofpatients, the most recent data as well as cost considera-tions53, have made ultrasound the most common radiologicmodality used for evaluating hepatic steatosis.

LIVER BIOPSY

Although radiologic techniques and serum liver functiontests are useful, they remain only indirect surrogate markersof fatty liver. Liver biopsy is the only currently availablemethod for differentiating NASH from steatosis with or wit-



hout inflammation79,82, despite the issue of sampling error.However, the role of liver biopsy remains unclear with itsadvantages and disadvantages.

There are a number of certain situations that a liverbiopsy has significant clinical importance. These include:suspected subreptitions alcohol use, a positive anti nuclearantibody, possible medication effect, unexplained elevatedserum ferritin concentrations, or positive serology for hepa-titis C.

PREDICTORS OF ADVANCED FIBROSIS

In addition to histology (the presence or absence ofNASH), a number of risk factors have been identified aspredictors for the development of progressive fibrosis andcirrhosis. These include: obesity23,93,94, diabetes mellitus5,23,93,age23,94,95, arterial hypertension29, AST/ALT ratio23,56,96,triglycerides, elevated ALT29,39, iron25, extent of steatosis56,and the grade of inflammation23,93,94.

Table 2 displays combinations of the strongest predictivefactors along with their acronyms that have been used bydifferent investigators to predict fibrosis in patients withfatty liver23,29,94,96. The presence of either obesity and/or type2 diabetes mellitus are the most robust predictors offibrosis5,23,39,94,96. Age (> 45 or 50) is also a strong predictivefactor for cirrhosis5,23,93,96, which probably reflects the dura-tion of time that steatosis is at risk for a subsequent secondhit. An elevated ALT level29,94, an AST/ALT ratio > 0.823,96,arterial hypertension29,39, triglycerides94 and a high insulinresistance index29.

Data from the BARD or BARG acronyms (table 2), forexample, would predict a patient with fatty liver on ultra-sound who is < 45 years old, has neither obesity or diabetesand an AST/ALT ratio < 0.8, has only a minimal risk fordeveloping significant fibrosis. In contrast, almost twothirds of patients with diabetes or obesity, age > 45 years,and an AST/ALT ratio > 0.8 will have significant fibrosis.

This information can be used to determine the usefulnessof performing a liver biopsy in patients with fatty liver bytargeting a population with a high likelihood for havingNASH.

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TABLE 2. Prediction acronyms for advanced fibrosis in NAFLD

BARD BARG BAAT HAIR

BMI X X XAGE X X XAST/ALT X XALT X XDIABETES XHgA1C XTG’S XHYPERTENSTION XINSULIN RESISTANCE X

INDEX

BAAT: BMI (≥ 50), ALT (≥ 2 × normal), and triglycerides (TG’s) (≥ 1.7mmol/l); BARD: BMI (≥ 30), Age (≥ 45), Ratio of AST/ALT (≥ 1), and dia-betes mellitus; BARG: BMI (≥ 28), Age (≥ 50), Ratio of AST/ALT (≥ 0.8),and HgA1C (≥ 5.2); HAIR: Hypertension, ALT (> 4), and Insulin resistance(≥ 5.0 defined by Quicki).



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83. Levenson H, Greensite F, Hoefs J, Frilous L, Appelgate G, Silva E,et al. Fatty infiltration of the liver. Quantification with phase-contrastMR imaging at 1.5 T vs. biopsy. AJR Am J Roentgenol. 1991;156:307-12.

84. Mendler MH, Bouillet P, LeSidaner A, Lavoine E, Labrousse F, Saute-reau D, et al. Dual energy CT in the diagnosis and quantification offatty liver-limited clinical value in comparison to ultrasound and single-energy CT, with special reference to iron overload. J Hepatol.1998;28:785-79.

85. Siegelman ES, Rosen MA. Imaging of hepatic steatosis. Semin Liv Dis.2001;21:71-80.

86. Longo R, Pollesello P, Ricci C. Proton MR spectroscopy in quantitativein vivo determination of fat content in human liver steatosis. J MagnReson Imag. 1995;4:281-5.

87. Jacobs JE, Birnbaum BA, Shapira MA, Langlotz CP, Slosman F, Rube-sin SE, et al. Diagnostic criteria for fatty infiltration of the liver on con-trast enhanced helical CT. AJR Am J Roentgenol. 1998;171:659-64.

88. Hulcrantz R, Gabrielson N. Patients with persistent elevation of amino-transferases: Investigation with ultrasonography, radionuclide imagingand liver biopsy. J Intern Med. 1993;232:7-12.

89. Mitchell DG. Focal manifestations of diffuse liver disease at MR Ima-ging. Radiology 1992;185:1-11.

90. Zweiman B, Parrott CM, Graif Y, David M, Lessin SR. Quantitative es-timation of attenuation in ultrasound video images: correlation with his-tology in diffuse liver disease. Invest Radiol. 2000;35:319-24.

91. Graif M, Yanuka M, Baraz M. Quantitative estimation of attenuation inultrasound video images: Correlation with histology in diffuse liver di-sease. Invest Radiol. 2000;35:319-24.

92. Bianchi L. Liver biopsy in elevated liver function tests? An old ques-tion revisited. J Hepatol. 2001;35:290-4.

93. Wanless IR, Lentz JS. Fatty liver hepatitis (steatohepatitis) and obesity:

An autopsy study with analysis of risk factors. Hepatology. 1990;12:1106-10.

94. Ratzui V, Giral P, Charlotte F, Bruckert E, Thibault V, Theodoron I, et al.Liver fibrosis in overweight patients. Gastroenterology. 2000; 118:1117-23.

95. Garcia-Monzon C, Martin-Perez E, Iacono OL. Characterization of pat-hogenic and prognositc factors of non alcoholic steatohepatitis associa-ted with obesity. J Hepatol. 2000;33:716-24.

96. Harrison SA, Oliver DA, Torgerson S, Paul H, Neuschwander BA.NASH: Clinical assessment of 501 patients from two separate academicmedical centers with validation of a clinical scoring system for advan-ced hepatic fibrosis. Hepatology. 2003;34 Suppl;A511.





Targets for therapy and currentstatus of treatment ofnonalcoholic fatty liver diseasePHUNCHAI CHARATCHAROENWITTHAYA AND KEITH D. LINDOR

Division of Gastroenterology and Hepatology. Mayo Clinic.Rochester, MN. United States of America.

Correspondence: Dr. K.D. Lindor.E-mail: [email protected]

Nonalcoholic fatty liver disease (NAFLD) is emerging as a commoncause of chronic liver disease in Western countries. NAFLD is conside-red the hepatic manifestation of the metabolic syndrome, a cluster of me-tabolic abnormalities related to insulin resistance, including obesity, hy-perglycemia, dyslipidemia, and hypertension. NAFLD is more frequentamong people with diabetes and obesity, and it is almost universal amongmorbidly obese people with diabetes. Steatohepatitis is present in 18.5%of markedly obese patients and 2.7% of lean patients1. A recent cohortstudy clearly demonstrated chronological ordering between body weightgain, hypertransaminasemia, and insulin resistance-related clinical featu-res in a healthy population2. NAFLD incorporates a wide spectrum of li-ver change ranging from simple steatosis to steatosis plus necroinflam-matory activity (nonalcoholic steatohepatitis or NASH), to cirrhosis andultimately liver failure. Some clinical variables have been identified aspredictors for advanced fibrotic disease including obesity, diabetes, age >45 years and aspartate aminotransferase (AST)/alanine aminotransferase(ALT) ratio > 1. The risk of cirrhosis-related death or hospitalization ap-pears to be increased among persons with a central fat distribution thatmight be related to insulin resistance and hepatic steatosis3. Patients withNAFLD and diabetes are at risk for the development of aggressive outco-me, such as cirrhosis and mortality.

PATHOGENESIS

Several hypotheses have been proposed to explain the pathogenesis ofNAFLD. The most accepted theory is the “two hit” hypothesis, in whichthe first hit involves the development of hepatic steatosis, rendering theliver more susceptible to a second, as yet undefined, hit, resulting in moresevere liver damage (fig. 1). Current evidence points toward insulin resis-tance playing a key role, since it may influence several intracellular meta-bolic pathways. As a result of insulin resistance, there is increased freefatty acids (FFA) flux to the liver. Impairment of fatty acid oxidation ordecreasing apolipoprotein formation or microsomal formation of VLDL,which allows triglycerides to accumulate in the liver also occurs. Theprogression of steatosis to steatohepatitis is associated with increasingoxidative stress within hepatocytes. Hepatocytes handle the increasedFFA load by increasing FFA β-oxidation, thus contributing to generationof reactive oxygen species with subsequent cytokine induction (i.e.TNFα) that eventually leads to mitochondrial dysfunction.

TREATMENT

Treatment strategies for NAFLD have been focused on improvementin underlying insulin sensitivity, the management of associated meta-

bolic conditions, and protection of the liver from oxidati-ve stress. Pharmacotherapy should be aimed to slow theprogression of NAFLD and is therefore restricted to thosepatients with NASH, at highest risk of developing com-plications.

Weight reduction with diet and exercise leads to impro-ved insulin sensitivity and therefore should be an initialapproach in the management of patients with NASH. Ho-wever, there are no randomized clinical trials of weightcontrol as treatment for NAFLD. The National Heart,Lung and Blood Institute (NHLBI) and National Instituteof Diabetes and Digestive Kidney (NIDDK) expert panelclinical guideline for weight loss recommended that theinitial target for weight loss should be 10% of baselineweight within a period of 6 months. This is can be achie-ved by losing approximately 1-2 lb/week. Huang et al4

demonstrated that one-year intense nutritional counselingfor improving insulin sensitivity resulted in histologicalimprovement in NASH patients with mean weight reduc-tion of 2.9 kg.

Recently, bariatric surgery for morbidly obesity has beco-me more popular. Restrictive procedure (gastric bypass,gastroplasty) to achieve weight loss are safer than malab-sorptive procedures (jejunoileal bypass). Dixon et al5 obtai-ned repeat liver biopsies in 23 obese patients with NASHwho underwent laparoscopic adjustable gastric banding forweight loss. After losing a mean of 34 kg within 25.6months, NASH resolved in 82% of these patients. Majorimprovement was seen in steatosis, necroinflammation andfibrosis5.

Pharmacological agents used for weight reduction havealso been evaluated in small trials. Orlistat, a reversible in-hibitor of gastric and pancreatic lipases, is currently appro-ved for weight loss. Small pilot study conducted on obesepatients with NASH has demonstrated significant improve-ment in serum aminotransferases, hepatic steatosis, necroin-flammatory activity, and fibrosis6.

Clofibrate revealed no significant biochemical or histolo-gical improvement in 16 NASH patients treated for 12months7. Gemfibrozil was evaluated in a short duration,randomized trial of 46 NASH patients, demonstrating signi-ficant biochemical improvement compared with no treat-ment8.

Thiazolidinediones improve insulin sensitivity by acti-vating the peroxisome proliferators-activated receptorgamma and have shown promise in pilot studies involving

patients with NASH, although weight gain has been atroublesome side effect. Troglitazone was withdrawnfrom the market because of hepatotoxicity. The second-generation thiazolidinediones, rosiglitazone and pioglita-zone appear to be safer. Rosiglitazone has been evaluatedin an open-label trial of 4 mg twice daily for 48 weeks in30 NASH patients9. Insulin sensitivity and ALT levelsimproved significantly with post-treatment biopsy sho-wing a significant improvement of necroinflammatory ac-tivity and perisinusoidal fibrosis. Recently, a randomizedplacebo-controlled, multicenter clinical trial with pioglita-zone in 40 patients appears to confirm the beneficial ef-fects of thiazolidinediones in NASH10.

Metformin improves insulin sensitivity through decrea-sed hepatic glucose and triglyceride production. An open la-beled study of metformin 20 mg/kg for 1 year in 15NAFLD patients demonstrated a transient improvement inserum aminotransferase levels and insulin sensitivity remai-ned steady without further improvement11. Recently, anopen-label randomized trial of metformin 2 g/day for 12months versus either vitamin E 800 IU/day or a prescripti-ve, weight-reducing diet in 55 NAFLD patients showed thatlong-term metformin treatment significantly reduce averageALT levels and increased the chances to have ALT withinthe normal range as well as histological improvement incomparison to control treatment12.

Given the role of oxidative stress in the pathogenesis ofNASH, numerous studies have focused on the used of antio-xidants for NASH treatment. A small pilot study in adultNASH patients treated with vitamin E 300 mg/day for oneyear showed significant biochemical and histological im-provement13. Subsequently in a placebo-controlled trial,NASH patients were treated with vitamin E 1,000 IU/dayplus vitamin C 1,000 mg/day for 6 months in comparisonwith placebo that showed decreased fibrosis within the tre-atment groups, whereas there was no significant differencein necroinflammation or fibrosis when comparing betweengroups14.

Ursodeoxycholic acid (UDCA), the non-hepatotoxic epi-mer of chenodeoxycholic acid, has multiple hepatoprotecti-ve activities as well as immunological effects. Early pilotstudies of UDCA in NASH patients revealed promising re-sults, however, a recent multicenter, randomized trial in 166NASH patients demonstrated that UDCA 13-15 mg/kg/dayfor 2 years led to no significant difference in the biochemi-cal or histological improvement between the UDCA andplacebo groups15.

Betaine, N-acetylcysteine, pentoxyphylline, and lorsartanhave shown promise in small pilot trials. Other promisingpotentially useful nutritional approaches to NAFLD patientsinclude metadoxine, folic acid, alanine, oligofructose, ome-ga 3 fats, acarbose, and probiotics. Further studies to assesspotential beneficial effects of these novel findings are wa-rranted.

CONCLUSIONS

A better understanding of the pathogenesis leading to fataccumulation and oxidative balance impairment in steatoticlivers is greatly expected to improve the therapeutic appro-ach of NAFLD. Currently, treatment is limited to weight re-duction and the control of associated metabolic conditions.Attractive pharmacological therapy with insulin-sensitizingagents and antioxidants hold promise, but only small short-term pilot studies have been assessed. Further studies are re-quired to identify agents with adequately powered randomi-zed controlled trials evaluating fibrotic progression orclinical complication as end points.

Charatcharoenwitthaya P et al. Targets for therapy and current status of treatment of nonalcoholic fatty liver disease

Normal LiverOverfeeding Steatosis

(vulnerable)

Insulin resistance

Oxidative stress

1st hit

2nd hit

SteatohepatitisFibrosis

Fig. 1. “Two-hit” hypothesis: the first hit involves the developmentof hepatic steatosis, rendering the liver more susceptible to a se-cond hit resulting in more severe liver damage.


REFERENCES

1. Wanless IR, Lentz JS. Fatty liver hepatitis (steatohepatitis) and obesity: anautopsy study with analysis of risk factors. Hepatology. 1990;12: 1106-10.

2. Suzuki A, Angulo P, Lymp J, St Sauver J, Muto A, Okada T, et al. Ch-ronological development of elevated aminotransferases in a nonalcoho-lic population. Hepatology. 2005;41:64-71.

3. Ioannou GN, Weiss NS, Boyko EJ, Kowdley KV, Kahn SE, CarithersRL, et al. Is central obesity associated with cirrhosis-related death orhospitalization? A population-based, cohort study. Clin GastroenterolHepatol. 2005;3:67-74.

4. Huang MA, Greenson JK, Chao C, Anderson L, Peterman D, JacobsonJ, et al. One-year intense nutritional counseling results in histologicalimprovement in patients with non-alcoholic steatohepatitis: a pilotstudy. Am J Gastroenterol. 2005;100:1072-81.

5. Dixon JB, Bhathal PS, Hughes NR, O’Brien PE. Nonalcoholic fatty li-ver disease: Improvement in liver histological analysis with weightloss. Hepatology. 2004;39:1647-54.

6. Harrison SA, Fincke C, Helinski D, Torgerson S, Hayashi P. A pilotstudy of orlistat treatment in obese, non-alcoholic steatohepatitis pa-tients. Aliment Pharmacol Ther. 2004;20:623-8.

7. Laurin J, Lindor KD, Crippin JS, Gossard A, Gores GJ, Ludwig J, et al.Ursodeoxycholic acid or clofibrate in the treatment of non-alcohol-in-duced steatohepatitis: a pilot study. Hepatology. 1996;23:1464-7.

8. Basaranoglu M, Acbay O, Sonsuz A. A controlled trial of gemfibrozilin the treatment of patients with nonalcoholic steatohepatitis. J Hepatol.1999;31:384.

9. Neuschwander-Tetri BA, Brunt EM, Wehmeier KR, Oliver D, BaconBR. Improved nonalcoholic steatohepatitis after 48 weeks of treatmentwith the PPAR-gamma ligand rosiglitazone. Hepatology. 2003;38:1008-17.

10. Harrison S, Belfort R, Brown K, Darland C, Flrich J, Flrieke C, et al. Adouble-blind, placebo-controlled trial of pioglitazone in the treatment ofnon-alcoholic steatohepatitis (NASH) [abstract]. Gastroenterology.2005;128 Suppl 2:A681.

11. Nair S, Diehl AM, Wiseman M, Farr GH Jr, Perrillo RP. Metformin inthe treatment of non-alcoholic steatohepatitis: a pilot open label trial.Aliment Pharmacol Ther. 2004;20:23-8.

12. Bugianesi E, Gentilcore E, Manini R, Natale S, Vanni E, Villanova N,et al. A randomized controlled trial of metformin versus vitamin E orprescriptive diet in nonalcoholic fatty liver disease. Am J Gastroenterol.2005;100:1082-90.

13. Hasegawa T, Yoneda M, Nakamura K, Makino I, Terano A. Plasmatransforming growth factor-beta1 level and efficacy of alpha-tocopherolin patients with non-alcoholic steatohepatitis: a pilot study. AlimentPharmacol Ther. 2001;15:1667-72.

14. Harrison SA, Torgerson S, Hayashi P, Ward J, Schenker S. Vitamin Eand vitamin C treatment improves fibrosis in patients with nonalcoholicsteatohepatitis. Am J Gastroenterol. 2003;98:2485-90.

15. Lindor KD, Kowdley KV, Heathcote EJ, Harrison ME, Jorgensen R,Angulo P, et al. Ursodeoxycholic acid for treatment of nonalcoholicsteatohepatitis: results of a randomized trial. Hepatology. 2004;39:770-8.

Charatcharoenwitthaya P et al. Targets for therapy and current status of treatment of nonalcoholic fatty liver disease




Insulin resistance and chroniccardiovascular inflammatorysyndromeJOSÉ MANUEL FERNÁNDEZ-REAL

Unit of Diabetes, Endocrinology and Nutrition. HospitalUniversitari de Girona. Girona. Spain.

Correspondence: Dr. J.M. Fernández-Real.E-mail: [email protected]

Globalization of occidental way of life is leading to increasing preva-lence of obesity and type 2 diabetes, the greatest pandemy of the XXICentury. Obesity-associated insulin resistance has an important role inacute phase response and inflammatory pathways1-3. Chronic subclinicalinflammation develops in subjects with abdominal obesity and has beenproposed as a part of the metabolic syndrome4. The study of the factorswhich regulate the acute phase response in apparently healthy obese sub-jects has yielded consistent results implicating cytokines and growth fac-tors in the pathophysiology of obesity, insulin resistance and its compli-cations1-3.

It should be kept in mind that humans live in close association withvast numbers of microorganisms that are present on the external and in-ternal surfaces of our body. The ability to mount a prominent inflamma-tory response to pathogens confers a continuous advantage in our fightagainst pathogens. All metazoan organisms have evolved complex immu-ne defense systems, used to repel invasive microbes that would parasitizeor kill them. Innate immunity is the most universal and the most rapidlyacting. Most organisms survive through innate immune mechanisms alo-ne. After any trauma or infection, the organisms mount a homeostaticresponse to injury called acute-phase response, a highly complex process(fig. 1)5,6. In the acute phase, the acute phase response is protective be-cause it counteracts the effects of injury and improves survival. A conti-nous and permanent equilibrium exists between proinflammatory factorsand anti-inflammatory molecules. The maintainance of this equilibriumwill be very important for an adequate eradication of injury without chro-nification of the process.

Long-term exposure to stressful stimuli (mucositis, aging, increased fatintake, periodontitis…) may result in disease (insulin resistance, atheros-clerosis) rather than repair (fig. 1)7.

There exist two arms of innate immunity: the sensing arm (those me-chanisms involved in the continuous sensing and perception of infection)and the effector arm, the sophisticated processes aimed at eradicate infec-tion and tissue repair. Each of these arms may be subdivided in humoraland cellular processes tightly coordinated in the inflammatory process5,6.This system constitutes the first line of body’s defense and is constitutedby different barriers (epithelia, adipose tissue), and different blood andtissue components as macrophages, and neutrophils. This innate immunesystem generates the acute phase response in which different acute phaseproteins and cytokines are produced in response to different aggressionsas infections and traumatisms.

EFFERENT ARM OF INNATE IMMUNITY ANDINSULIN ACTION

From a historical point of view, the cellular effector armwas the first to be characterized and the best understood inthis context. The discovery that TNFα was expressed inadipose tissue and modulated insulin action in animal mo-dels is perhaps the cornerstone that led to an in-depth know-ledge of the interactions between immune system and meta-bolism8.

It is not enough for the host to sense microbes. It mustkill microbes as well. In vertebrates, innate immunity is lar-gely dependent upon myeloid cells: professional immu-nocytes that engulf and destroy pathogens5,6. Myeloid cellsinclude mononuclear phagocytes and polymorphonuclearphagocytes. The mononuclear phagocytes are the macrop-hages, derived from blood monocytes. A higher peripheralwhite blood cell count has been associated with insulin re-sistance and with atherosclerosis8. Peripheral white bloodcell count correlated significantly with insulin-mediatedglucose disposal during an euglycemic clamp9. In subse-quent studies, it was demonstrated that neutrophil andlymphocyte count correlated positively with several compo-nents of the insulin resistance syndrome, and that plasma in-sulin concentration was specifically associated with thenumber of lymphocytes and monocytes10.

In a recent study we substantiated these relationships atthe molecular level, providing evidence that a particular de-fense against infection bacterial and permeability increasingprotein (BPI) runs in parallel to insulin sensitivity amonghealthy subjects11. We found that circulating BPI concentra-tion was significant different across categories of glucosetolerance: BPI was significantly lower in patients with type2 diabetes. In subjects with glucose intolerance we foundthe strongest associations between plasma BPI and centralobesity, glucose metabolism, insulin sensitivity and compo-nents of the metabolic syndrome.

We also tested the functional significance of these fin-dings. Bioactive lipopolysaccharide (LPS) was significantlyand negatively associated with circulating BPI concentration.This finding suggests that, with decreasing BPI, the ability tobuffer LPS is impaired. We further substantiate this hypothe-sis by studying the effects of the insulin sensitizer-metforminon circulating BPI. In patients receiving metformin, but notin those receiving placebo, we observed improved insulinsensitivity and raised circulating BPI concomitantly11. Howcan all these associations be explained? Insulin action maylead to increased plasma BPI concentration. A recent studyhas demonstrated that insulin is a strong regulator of the mainneutrophil functions in nondiabetic, healthy subjects12. Thecellular functions of human neutrophil, including bactericidalactivity require energy derived from glucose. Whereas insulindoes not stimulate hexose transport in this immune cell, pre-vious reports have clearly shown that this hormone is able toregulate glucose metabolism in neutrophils13,14.

CELLULAR SENSING OF THE AFFERENT ARM OFINNATE IMMUNITY

The chronic inflammatory process of insulin resistance istriggered and sustained by unknown factors. Among thecandidate triggers are oxidized or enzymatically modifiedlow-density lipoproteins, heat shock proteins, and infectiouspathogens. Interestingly, in the last years it has become cle-ar that all these triggers and ligands could be recognizedand sensed by the same cell and the same receptor.

Macrophages (again) play a primary role in host defenseagainst infection, utilizing a range of receptors to recognizemicrobes by opsonic as well as direct interactions. The term“pathogen-associated molecular patterns” (PAMPs) was coi-ned to describe those microbial principles that triggered an in-nate immune response5,6. PAMPs were said to act via “patternrecognition receptors” (PRR)5,6, i.e. those sensors that couldrecognize a pattern on a microbe. Binding of targets via PRRresults in phagocytosis and killing. Macrophages express abroad repertoire of PRR (e.g., scavenger and lectin-like). Inthis sense, the amount of lipid retained in macrophages duringthe atherosclerotic process depends on the unregulated uptakeof oxidized lipoproteins by scavenger receptors, counterbalan-ced by degradation and cholesterol efflux. This scavenger re-ceptor also plays a major role in microbial uptake in the ab-sence of opsonins. The principal signaling receptors of theinnate immune system —through which the greater part of thehost awareness of infection is processed— are the toll-like re-ceptors (TLR) family of transmembrane molecules. The bestunderstood TLR, both in terms of ligand binding and signaltransduction, is the lipopolysaccharide (LPS) receptor, TLR4.

INTERPRETATION

Evolution pressures have led to survival of the fittest in-dividuals, those with genetics that allows the best defenseagainst infection and periods of famine. The evolutive ad-vantages of increased inflammatory responses, hypersecre-tion of proinflammatory cytokines (TNFα, interleukin [IL]-1β, IL-6, IL-18), or decreased anti-inflammatory molecules(adiponectin, certain TNFα isoforms, sCD14, etc.), wouldlead to chronic inflammation conditions, such as obesityand type 2 diabetes, leading to cardiovascular disease2.

Increasing evidence is reported according to which chro-nic inflammation precedes these conditions. The knowledgeof how these metabolic pathways interact with the inflam-matory cascade will facilitate new therapeutic approaches.Anti-inflammatory drugs are only the first step of this newapproach.

Fernández-Real JM. Insulin resistance and chronic cardiovascular inflammatory syndrome


Intense exercise Chronic infections(periodontitis, etc.)

Acute phase responseTrauma

Sepsis

Cytokines

Acute phase changesInsuline resistance

Alterations in carbohydrate metabolismHyperlipidemia

Tobacco

Aging

Obesity

Fig. 1. Different lesions and injuries constitute the triggers of in-flammation and acute phase response.

REFERENCES

1. Pickup JC, Crook MA. Is type II diabetes a disease of the innate immu-ne system? Diabetologia. 1998;41:1241-8.

2. Fernández-Real JM, Ricart W. Insulin resistance and inflammation inan evolutionary perspective. The contribution of cytokinegenotype/phenotype to thriftiness. Diabetologia. 1999;42:1367-74.

3. Fernández-Real JM, Ricart W. Insulin resistance and chronic cardiovas-cular inflammatory syndrome. Endocr Rev. 2003;24:278-301.

4. Festa A, D’Agostino R Jr, Howard G, Mykkanen L, Tracy RP, HaffnerSM. Chronic subclinical inflammation as part of the insulin resistancesyndrome: the Insulin Resistance Atherosclerosis Study (IRAS). Circu-lation. 2000;102:42-7.

5. Beutler B. Innate immunity: an overview. Mol Immunol. 2004;40:845-59.6. Janeway, CA Jr, Medzhitov R. Innate immune recognition. Ann Rev

Immunol. 2002;20:197-216.7. Munford RS. Statins and the acute phase response. N Engl J Med.

2001;344:2016-8.8. Hotamisligil GS, Shargill NS, Spiegelman BM. Adipose expression of

tumor necrosis factor-alpha: direct role in obesity-linked insulin resis-tance. Science. 1993;259:87-91.

9. Facchini F, Hollenbeck CB, Chen YN, Chen YD, Reaven HM. De-monstration of a relationship between white blood cell count, insulin re-sistance, and several risk factors for coronary heart disease in women. JIntern Med. 1992;232:267-72.

10. Targher G, Seidell JC, Tonoli M, Muggeo M, De Sandre G, Cigolini M.The white blood cell count: its relationship to plasma insulin and othercardiovascular risk factors in healthy male individuals. J Intern Med.1996;239:435-41.

11. Gubern C, López-Bermejo A, Biarnés J, Vendrell J, Ricart W, Fernández-Real JM. Natural antibiotics and insulin sensitivity: the role of bactericidaland permeability increasing protein (BPI). Diabetes. 2006;55:216-24.

12. Walrand S, Guillet C, Boirie Y, Vasson MP. In vivo evidences that in-sulin regulates human polymorphonuclear neutrophil functions. J Leu-koc Biol. 2004;76:1104-10.

13. Furukawa S, Saito H, Matsuda T, Inoue T, Fukatsu K, Han I, et al. Re-lative effects of glucose and glutamine on reactive oxygen intermediateproduction by neutrophils. Shock. 2000;13:274-8.

14. Munroe JF, Shipp JC. Glucose metabolism in leucocytes from patientswith diabetes mellitus, with and without hypercholesteremia. Diabetes.1965;14:584-90.

Fernández-Real JM. Insulin resistance and chronic cardiovascular inflammatory syndrome




Macronutrient intake inducesoxidative and inflammatorystress while insulin causessuppression of reactive oxygenspecies generation and inflammationPARESH DANDONA

Division of Endocrinology and Metabolism. State University ofNew York at Buffalo. Diabetes-Endocrinology Center of WesternNew York. Kaleida Health/Millard Fillmore Hospital. Buffalo. NewYork. United States of America.

Correspondence: Dr. P. Dandona.E-mail: [email protected]

Following our original observation that the intake of 75 g of glucose innormal subjects induces an increase in reactive oxygen species (ROS) ge-neration by mononuclear cells (MNC), we have shown that glucose, equi-caloric amounts of fat (eaten as cream) and a mixed fast food meal (900calories) induce not only an increase in ROS generation by MNC but alsocause an increase in p47 phox expression. In addition, there is an increasein intranuclear NF-κB binding, a fall in IkBa expression and an increasein IKKa and IKKb expression. There is a concomitant increase in TNFαmRNA in the MNC. Two other pro-inflammatory transcription factors,activator protein-1 (AP-1) and early growth response-1 (Egr-1), were alsoinduced by glucose intake. There was an increase in matrix metallopro-teinases (MMP) MMP-2, MMP-9, tissue factor (TF) and Plasminogen ac-tivator inhibitor-1 (PAI-1).

Thus, there occurs a comprehensive oxidative and inflammatory stressresponse following macronutrient intake. Consistent with this concept,the state of obesity, associated with increased macronutrient intake, ischaracterized by an increase in oxidative stress and chronic low grade in-flammation. As would be expected, caloric restriction in the obese resultsin a marked reduction in ROS generation by MNC and other indices ofoxidative stress, like lipid peroxidation and protein carbonylation. A 48hour fast in normal subjects leads to a reduction in ROS generation by50% and a parallel reduction in p47phox. In contrast to macronutrient in-take, a low dose insulin infusion (2 units per hour), results in a significantreduction in ROS generation by MNC, p47phox expression, intranuclearNF-κB binding with an increase in IkBa expression (fig. 1). In addition,there is a suppression of AP-1 and Egr-1, MMP-2, MMP-9, PAI-1 andTF. The anti-inflammatory effect of insulin was further confirmed by inpatients with acute myocardial infarction who were treated with a lowdose insulin infusion in addition to the standard thrombolytic therapy. In-sulin infusion led to a significant fall in C-reactive protein (CRP), serumamyloid (SAA), PAI-1, MMP-1 and oxidative stress. In addition, insulinhad a significant suppressive effect on the increase in plasma creatine ki-nase (CK), CK-MB and myoglobin concentrations in these patients, con-sistent with a cardioprotective action. This effect of insulin on CRP andSAA has now been confirmed both in acute myocardial infarction and inpatients undergoing coronary artery bypass surgery.

These facts allow us to conclude that there exists a novel relationshipbetween macronutrient intake and insulin, the hormone secreted in res-ponse to macronutrient intake. This relationship extends beyond the clas-

sical paradigm involving metabolic mechanisms only. It en-compasses oxidative and inflammatory stress following ma-cronutrient intake and the suppression of these processeswith insulin, the hormone which is secreted in response tomacronutrient intake (fig. 2).

We are now engaged in a) the investigation of foodswhich are least likely cause oxidative and inflammatorystress. Alcohol, orange juice and a high fiber and fruit con-taining meal do not cause oxidative of inflammatory stress,and b) the use of insulin as an anti-inflammatory, cardiopro-tective and neuroprotective agent in acute myocardial in-farction and stroke.

RECOMMENDED REFERENCES

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Iwakura K, Ito H, Ikushima M, Kawano S, Okamura A, Asano K. Associa-tion between hyperglycemia and the no-reflow phenomenon in patientswith acute myocardial infarction. J Am Coll Cardiol. 2003;41:1-7.

Foo K, Cooper J, Deaner A, Knight C, Suliman A, Ranjadayalan K. A sin-gle serum glucose measurement predicts adverse outcomes across thewhole range of acute coronary syndromes. Heart. 2003;89:512-6.

Capes SE, Hunt D, Malmberg K, Gerstein HC. Stress hyperglycaemia andincreased risk of death after myocardial infarction in patients with andwithout diabetes: a systematic overview. Lancet. 200;355:773-8.

Capes SE, Hunt D, Malmberg K, Pathak P, Gerstein HC. Stress hyperglyce-mia and prognosis of stroke in nondiabetic and diabetic patients: a syste-matic overview. Stroke. 2001;32:2426-32.

Toni D, De Michele M, Fiorelli M, Bastianello S, Camerlingo M, SacchettiML, et al. Influence of hyperglycaemia on infarct size and clinical outco-me of acute ischemic stroke patients with intracranial arterial occlusion,J Neurol Sci. 1994;123:129-33.

Williams LS, Rotich J, Qi R, Fineberg N, Espay A, Bruno A, et al. Effectsof admission hyperglycemia on mortality and costs in acute ischemicstroke. Neurology. 2002;59:67-71.

Furnary AP, Gao G, Grunkemeier GL, Wu Y, Zerr KJ, Bookin SO, et al.Continuous insulin infusion reduces mortality in patients with diabetesundergoing coronary artery bypass grafting. J Thorac Cardiovasc Surg.2003;125:1007-21.

Umpierrez GE, Isaacs SD, Bazargan N, You X, Thaler LM, Kitabchi AE.Hyperglycemia: an independent marker of in-hospital mortality in pa-tients with undiagnosed diabetes. J Clin Endocrinol Metab. 2002;87:978-82.

Van den Berghe G, Wouters P, Weekers F, Verwaest C, Bruyninckx F,Schetz M, et al. Intensive insulin therapy in the surgical intensive careunit. N Engl J Med. 2001;345:1359–67.

Krinsley JS. Effect of an intensive glucose management protocol on themortality of critically ill adult patients. Mayo Clin Proc. 2004;79:992-1000.

Diaz R, Paolasso EA, Piegas LS, Tajer CD, Moreno MG, Corvalan R, et al.Metabolic modulation of acute myocardial infarction. The ECLA (Estu-dios Cardiologicos Latinoamerica) Collaborative Group. Circulation.1998;98:2227-34.

Malmberg K, Ryden L, Hamsten A, Herlitz J, Waldenstrom A, Wedel H.Mortality prediction in diabetic patients with myocardial infarction:experiences from the DIGAMI study. Cardiovasc Res. 1997;34:248-53.

Van der Horst I, Zijlstra F, Van’t Hof A, Doggen C, De Boer M, Suryapra-nata H, et al. Glucose-insulin-potassium infusion in patients treated withprimary angioplasty for acute myocardial infarction. J Am Coll Cardiol.2003;42:784-91.

Baeuerle PA, Baltimore D. NF-kappa B: ten years after. Cell. 1996;87:13-20.

Barnes PJ, KarinM. Nuclear factor-kappaB: a pivotal transcription factor inchronic inflammatory diseases. N Engl J Med. 1997;336:1066-71.

Mercurio F, Zhu H, Murray BW, Shevchenko A, Bennett BL, Li J, et al.IKK-1 and IKK-2: cytokine-activated IkappaB kinases essential for NF-kappaB activation. Science. 1997;278:860-6.

Dandora P, Aljada A, Mohanty P. The anti-inflammatory and potential anti-atherogenic effect of insulin: a new paradigm. Diabetologia. 2002;45:924-30.

Dandona P. Macronutrient intake induces oxidative and inflammatory stress while insulin causes suppression of ROS generation and inflammation

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GlucoseMacronutrients

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The New Paradigm

Fig. 2. Relationship between macronutrient intake, insulin, andoxidative/inflammatory stress. Adapted from: Dandona et al. AP-1: activator protein-1; Egr-l: early growth response-1; NF-κB:nuclear factor Kappa-B; T2D: thiazolidimedromas.




Fibrinolysis and the metabolicsyndromeMARIE-CHRISTINE ALESSI AND IRÈNE JUHAN-VAGUE

Inserm U626. Faculty of Medicine. Marseille. France.

Correspondence: Dr. M.C. Alessi.E-mail: [email protected]

The purpose of this talk was to update understanding about the connec-tion between fibrinolysis, mainly plasminogen activator inhibitor 1 (PAI-1) and the metabolic syndrome. Fibrinolysis is a controlled enzymaticcascade that, when activated, generates a trypsin like protease, plasmin.Remarkably, the same enzyme functions in blood to breakdown fibrinand maintain vessel patency and in tissues to breakdown extracellularmatrix and control cell adhesion and migration. That is to say that thissystem is broadly used in human physiopathology. Activation of this sys-tem is accomplished by the release of two plasminogen activators fromcell, tPA and uPA, in response to signals such as inflammation. The regu-lation of fibrinolysis is achieved primarily by PAI-1 which prevents theescape of this potentially destructive protease system. It is quite easy topropose that excess of PAI-1 could contribute to the atherothromboticprocess by increasing fîbrin and extracellular matrix deposit into the vas-cular wall. This has been well demonstrated in mice. For example, trans-genic mice that express a stable form of human PAI-1 develop spontane-ous coronary arterial thrombosis. These mice exhibit a high level ofcirculating PAI-1 and most of them developed spontaneous occlusions ofcoronary arteries after six months evolution, with histological evidence of subendocardial infarction1. In humans, plasma PAI-1 levels have beenassociated with risk of developing coronary events. Remarkably the po-wer of the association was strongly reduced after adjustment for the fac-tors which belong to the metabolic syndrome2. Thus, it appears that mostof the predictive ability of PAI-1 on cardiovascular events in humans de-pends on the metabolic syndrome. The link between PAI-1 and the meta-bolic syndrome was established many years ago. We have previouslyshown that the more severe the metabolic syndrome with a high numberof criteria, the higher the level of plasma PAI-13. From the nuclear fami-lies of the Stanislas Cohort, we have quantified this association and ob-served that the metabolic syndrome explained a major part of PAI-1 va-riability, this relationship being stronger in males than in females (45 vs26%)4. Attempts to understand the mechanisms leading to the increase inplasma PAI-1 levels in the metabolic syndrome come up against the com-plexity of this syndrome. The first approach was to propose that the me-tabolic disturbances observed during the metabolic syndrome directly af-fect PAI-1 synthesis. Most cell culture experiments confirm thathyperinsulinemia, excess of free fatty acid, angiotensin II, cortisol di-rectly increase PAI-1 synthesis. But clinical observations do not alwayssupport such a direct effect. Although PAI-1 belongs to the serpin group,it does not hold all its properties. PAI-1 gene expression is inducible andhas the features of an immediate early gene. It is short lived and synthesi-sed by a wide variety of cells and tissues on condition that the environ-ment is favourable. The main environmental conditions found in the lite-rature are inflammation and tissue remodelling. By transposing these

situations to the metabolic syndrome one can ask oneselfwhether the subinflammatory state, well described duringobesity, explains the increase in plasma PAI-1 levels and/orwhether the remodelling of adipose tissue explains the PAI-1 increase observed. From 1996 until today several groupshave connected adipose tissue to PAI-1. A PAI-1 produc-tion by adipocyte cell lines, human adipose tissue explantshas been described. Using immunohistochemistry and insitu hybridization we found PAI-1 antigen mainly localizedin the stromal compartment of the adipose tissue5. PAI-1antigen was detected in purely stromal area and was alsofound in small cells in direct contact with adipocytes as mo-nocytes (or macrophages). The pattern of PAI-1 localisationdiffers from that observed for von Willebrand factor (vWF)antigen and from leptin. Double labelling confirmed thatfew small cells in close contact with adipocytes expressedboth PAI-1 and CD14, a monocyte marker. During humanadipocyte differentiation we observed a transitory increasein the production of PAI-1 antigen but we found a conti-nuous decrease in PAI-1 mRNA despite the presence of in-sulin and dexamethasone in the medium5. Using freshly co-llected tissues we have separated mature adipocytes fromstromal cells and found PAI-1 mRNA mainly in the stromalfraction of the tissue6. These results are in accordance withthose of Fain et al7, who find a PAI-1 release by adipocytesat levels far lower than those of non fat cells.

Accumulation of fat in the central part of the body is oneof the features of the metabolic syndrome. Rather than aglobal fat accumulation the metabolic syndrome is the wit-ness of fat redistribution. This fat redistribution is thoughtto reflect a deficiency in the peripheral fat storage processwith a reorientation of fat in ectopic territories such as vis-ceral fat, liver, muscle, vessels causing lipoapoptosis, lipo-toxicity. Several groups have stressed the exclusive associa-tion between high plasma PAI-1 levels and visceral obesity.For example the change in plasma PAI-1 levels during aweight reducing program was well correlated with that ofthe visceral but not that of the subcutaneous fat depot8. Fatredistribution has also been recognized in patients with HIVinfection associated with the features of the metabolic syn-drome. Interestingly in this population the only significantpredictor of PAI-1 was the waist to hip ratio although it par-tially explains the rise in PAI-19. This prompted us to exa-mine the PAI-1 expression in ectopic fat depots mainly thevisceral adipose tissue and the liver. We found that ectopicvisceral expressed 5 fold more PAI-1 than subcutaneous tis-sue5. Ectopic fat accumulation in human liver was also as-sociated with a strong expression of PAI-1 close to fat10. Allthese results suggest that circulating PAI-1 levels are notclosely dependent on fat mass but reflect rather a fat redis-tribution and could be considered as a biomarker of the ec-topic fat storage state. But several questions remainedunanswered: is there a direct ectopic fat mass effect, an in-direct connection between ectopic fat and PAI-1 through amediator or a common ground with a parallel evolution ofPAI-1 and ectopic fat without true connection? Literaturehas supplied some data on the intervention of possible me-diators. For a long time inflammatory cytokines and growthfactors have been shown to play a key role in PAI-1 regula-tion mainly in vitro. TNF and TGFβ1 appeared to be candi-dates of choice. Indeed TNF has been involved in the me-chanism of insulin resistance. TGFβ1 represents an inducerof choice in the context of tissue remodelling. The group ofLoskutoff was the first to emphasize the potential contribu-tion of TNF in PAI-1 regulation during obesity. In ob/obmice, deletion of both TNF receptors (RI and RII) led tosignificant reduction of plasma PAI-1 as well as adipose tis-sue PAI-1 mRNA levels. In these animals the use of TNF

neutralizing antibodies leads to an immediate decrease inplasma PAI-1 level proving a direct link between TNF andPAI-1 during obesity11. The invalidation of both TNF recep-tors decreases TGFβ expression in the adipose tissue, sug-gesting that the TNF and TGFβ pathways are connectedwithin adipose tissue and could both control PAI-1 expres-sion. In humans similar associations were evidenced. Wefound, within the adipose tissue, a strong relationship bet-ween both TNF Rs, TGFβ, and PAI-112,13. This result rein-forces the possible connection between the TNF/TGFβpathway and PAI-1 within adipose tissue. Thus the increa-sed PAI-1 expression observed during the metabolic syn-drome may reflect a particular kind of inflammatory statelocalized in ectopic fat tissues and in response to tissue ag-gression. Apart from the contribution of the inflammatoryprocess we could not exclude the contribution of other indu-cers involved at the same time. Clinical observations havehighlighted the link between glucocorticoids and obesity.We have previously shown that dexamethasone and cortisolare potent inducers of PAI-1 synthesis by 3T3 cells and hu-man adipose tissue14. Interestingly cortisol can be producedwithin the adipose tissue through the action of the 11β-hy-droxysteroid dehydrogenase (11β-HSD). The only isoformexpressed in adipose tissue, acts predominantly as an oxore-ductase to generate cortisol from inactive cortisone. Its ex-pression is elevated in the visceral tissue. We observed thatthe expression levels of this enzyme followed the same evo-lution of PAI-1. Using adipose tissue explants we found thatcortisol and inactive cortisone stimulated PAI-1 secretion,but coincubation with a specific 11β-HSD inhibitor preven-ted the effect of cortisone whereas this effect was not pro-duced with cortisol. This suggests that the local conversionof cortisone to cortisol may be involved in the increase ofPAI-1 expression in adipose tissue.

The contribution of PAI-1 to the development of the me-tabolic syndrome has been recently proposed. Several stu-dies have indicated this direction. High PAI-1 levels mayhelp to identify a high-risk population with the potential toprevent both atherosclerotic disease and type 2 diabetes. In-deed, Festa et al15 showed that high plasma PAI-1 levelspredict the development of diabetes. Interestingly in a logis-tic regression model that included a lot of parameters incre-ased PAI-1 levels still remained significantly related to inci-dent type 2 diabetes (OR [95% CI] for 1 SD increase, 1.61[1.20-2.16]; p = 0.002). A direct connection between PAI-1and the action of insulin has been shown in vitro. Additionof vitronectin to fibroblasts cooperates with insulin to indu-ce protein kinase B phosphorylation. PAI-1 was able to pre-vent this cooperation in a vitronectin-dependent manner16.We thus suspect that PAI-1 may interfere with insulin sig-nalling in adipocyte and may control the development ofobesity or the metabolic syndrome. A first result was thatobtained by the group of Liang et al17. Wild type and PAI-1deficient adipocytes were used after 10 days of differentia-tion. It was shown that PAI-1 deficiency enhanced glucoseuptake at the basal state and under insulin stimulation. Inte-restingly the same group studied the effect of PAI-1 on adi-pocyte differentiation. Inhibition of PAI-1 with a neutrali-zing antibody promoted 3T3 adipocyte differentiation.Similar results were obtained with PAI-1 deficient adipocy-tes although less pronounced. Conversely overexpression ofPAI-1 by adenovirus-mediated gene transfer inhibited diffe-rentiation. Differentiation markers were controlled in para-llel. PAI-1 deficiency increased expression of CCAAT/en-hancer binding protein alpha, CEBPa and fatty acid bindingprotein (aP2). Remarkebly PAI-1 deficiency was able toprevent the deleterious effect of TNF on insulin sensitivity.So in the light of these results an interesting aim was then to

Alessi MC et al. Fibrinolysis and the metabolic syndrome


look at these effects starting from the whole organism. Ourgroup was interested in the analysis of the effect of PAI-1excess. Mice overexpressing murine PAI-1 (PAI-1 Tg) un-der the control of the aP2 promoter were constructed in or-der to develop a model with high PAI-1 expression withinadipose tissue. This model has not only increased adiposetissue PAI-1 levels but led to 10 fold higher plasma PAI-1antigen levels. Under high fat diet (HFD) transgenic miceexhibited a lower feeding efficiency with a significant lowerbody weight after 15 weeks HFD18. This leads to the con-clusion that PAI-1 overexpression has impaired adipose tis-sue growth. This result could be in accordance with the ef-fect of PAI-1 on adipocyte differentiation but thispossibility needs to be confirmed. We then looked at themetabolic parameters in these mice. It appears that the PAI-1 overexpression worsens the metabolic profile. Transgenicmice maintained on standard fat diet exhibit higher insulinand triglyceride levels despite lower body fat. Glucose andinsulin tolerance tests did not reveal significant differencesbetween both genotypes. We then performed euglycemicclamp and again we did not find any difference between thegroups. More precise analysis at the tissues levels have beenplanned. Due to the improvement of insulin sensitivity in-duced by PAI-1 inhibition in vitro one could expect thatPAI-1 deficiency will lead to higher subcutaneous fat accu-mulation in vivo. Surprisingly two groups found that fat ac-cumulation was prevented in mice lacking PAI-1 in two dif-ferent kinds of models a nutritionally induced19 and agenetic20 murine model of obesity. The protection againstobesity was linked to an increase in metabolic rate, totalenergy expenditure and thermogenesis. Unfortunately ourgroup did not reproduce these results in two different seriesof a nutritionally induced obesity21,22. However we observedthat pharmacological inhibition of active PAI-1 improvesinsulin sensitivity in mice. A synthetic low molecularweight PAI-1 inhibitor was added to the food of wild typemice for 4 weeks. Addition of this inhibitor did not signifi-cantly affect total body fat. After insulin injection glycemiawas lower in treated animals suggesting higher insulin sen-sitivity in treated mice23. Overall these data support the con-cept that PAI inhibition has the potential to reduce obesityand its complications and may represent a new interestingtherapeutic target.

REFERENCES

1. Eren M, Painter CA, Atkinson JB, Declerck PJ, Vaughan DE. Age-de-pendent spontaneous coronary arterial thrombosis in transgenic micethat express a stable form of human plasminogen activator inhibitor-1.Circulation. 2002;106:491-6.

2. Juhan-Vague I, Pyke SD, Alessi MC, Jespersen J, Haverkate F, Thomp-son SG. Fibrinolytic factors and the risk of myocardial infarction orsudden death in patients with angina pectoris. ECAT Study Group. Eu-ropean Concerted Action on Thrombosis and Disabilities. Circulation.1996;94:2057-63.

3. Fontbonne A, Charles MA, Juhan-Vague I, Bard JM, Andre P, Isnard F,et al. The effect of metformin on the metabolic abnormalities associatedwith upper-body fat distribution. BIGPRO Study Group. Diabetes Care.1996;19:920-6.

4. Henry M, Tregouet DA, Alessi MC, Aillaud MF, Visvikis S, Siest G, etal. Metabolic determinants are much more important than genetic poly-

morphisms in determining the PAI-1 activity and antigen plasma con-centrations: a family study with part of the Stanislas Cohort. Arterios-cler Thromb Vasc Biol. 1998;18:84-91.

5. Bastelica D, Morange P, Berthet B, Borghi H, Lacroix O, Grino M, etal. Stromal cells are the main plasminogen activator inhibitor-1-produ-cing cells in human fat: evidence of differences between visceral andsubcutaneous deposits. Arterioscler Thromb Vasc Biol. 2002;22:173-8.

6. Alessi MC, Peiretti F, Morange P, Henry M, Nalbone G, Juhan-VagueI. Production of plasminogen activator inhibitor 1 by human adiposetissue: possible link between visceral fat accumulation and vascular di-sease. Diabetes. 1997;46:860-7.

7. Fain JN, Madan AK, Hiler ML, Cheema P, Bahouth SW. Comparisonof the release of adipokines by adipose tissue, adipose tissue matrix,and adipocytes from visceral and subcutaneous abdominal adipose tis-sues of obese humans. Endocrinology. 2004;145:2273-82.

8. Janand-Delenne B, Chagnaud C, Raccah D, Alessi MC, Juhan-Vague I,Vague P. Visceral fat as a main determinant of plasminogen activatorinhibitor 1 level in women. Int J Obes Relat Metab Disord. 1998;22:312-7.

9. Hadigan C, Meigs JB, Rabe J, D’Agostino RB, Wilson PW, Lipinska I,et al; Framingham Heart Study. Increased PAI-1 and tPA antigen levelsare reduced with metformin therapy in HIV-infected patients with fatredistribution and insulin resistance. J Clin Endocrinol Metab.2001;86:939-43.

10. Alessi MC, Bastelica D, Mavri A, Morange P, Berthet B, Grino M, etal. Plasma PAI-1 levels are more strongly related to liver steatosis thanto adipose tissue accumulation. Arterioscler Thromb Vasc Biol.2003;23:1262-8.

11. Samad F, Uysal KT, Wiesbrock SM, Pandey M, Hotamisligil GS, Los-kutoff DJ. Tumor necrosis factor alpha is a key component in the obe-sity-linked elevation of plasminogen activator inhibitor 1. Proc NatlAcad Sci U S A. 1999;96:6902-7.

12. Bastelica D, Mavri A, Verdier M, Berthet B, Juhan-Vague I, AlessiMC. Relationships between fibrinolytic and inflammatory parametersin human adipose tissue: strong contribution of TNF alpha receptors toPAI-1 levels. Thromb Haemost. 2002;88:481-7.

13. Alessi MC, Bastelica D, Morange P, Berthet B, Leduc I, Verdier M, etal. Plasminogen activator inhibitor 1, transforming growth factor-beta1,and BMI are closely associated in human adipose tissue during morbidobesity. Diabetes. 2000;49:1374-80.

14. Morange PE, Aubert J, Peiretti F, Lijnen HR, Vague P, Verdier M, etal. Glucocorticoids and insulin promote plasminogen activator inhibitor1 production by human adipose tissue. Diabetes. 1999;48:890-5.

15. Festa A, D’Agostino R Jr, Rich SS, Jenny NS, Tracy RP, Haffner SM.Promoter (4G/5G) plasminogen activator inhibitor-1 genotype and plas-minogen activator inhibitor-1 levels in blacks, Hispanics, and non-His-panic whites: the Insulin Resistance Atherosclerosis Study. Circulation.2003;107:2422-7.

16. Lopez-Alemany R, Redondo JM, Nagamine Y, Munoz-Canoves P.Plasminogen activator inhibitor type-1 inhibits insulin signaling bycompeting with alphavbeta3 integrin for vitronectin binding. Eur J Bio-chem. 2003;270:814-21.

17. Liang X, Kanjanabuch T, Mao S, Hao CM, Tang TW, Declerck PJ, etal. Plasminogen activator inhibitor-1 modulates adipocyte differentia-tion. Am J Physiol Endocrinol Metab. 2006;209:E103-13.

18. Lijnen HR, Maquoi E, Morange P, Voros G, Van Hoef B, Kopp F, et al.Nutritionally induced obesity is attenuated in transgenic mice overex-pressing plasminogen activator inhibitor-1. Arterioscler Thromb VascBiol. 2003;23:78-84.

19. Ma LJ, Mao SL, Taylor KL, Kanjanabuch T, Guan Y, Zhang Y, et al.Prevention of obesity and insulin resistance in mice lacking plasmino-gen activator inhibitor 1. Diabetes. 2004;53:336-46.

20. Schafer K, Fujisawa K, Konstantinides S, Loskutoff DJ. Disruption ofthe plasminogen activator inhibitor 1 gene reduces the adiposity andimproves the metabolic profile of genetically obese and diabetic ob/obmice. FASEB J. 2001;15:1840-2.

21. Morange PE, Lijnen HR, Alessi MC, Kopp F, Collen D, Juhan-Vague I.Influence of PAI-1 on adipose tissue growth and metabolic parametersin a murine model of diet-induced obesity. Arterioscler Thromb VascBiol. 2000;20:1150-4.

22. Lijnen HR. Effect of plasminogen activator inhibitor-1 deficiency on nu-tritionally-induced obesity in mice. Thromb Haemost. 2005;93:816-9.

23. Lijnen HR, Alessi MC, Van Hoef B, Collen D, Juhan-Vague I. On therole of plasminogen activator inhibitor-1 in adipose tissue developmentand insulin resistance in mice. J Thromb Haemost. 2005;3:1174-9.

Alessi MC et al. Fibrinolysis and the metabolic syndrome




Endothelial dysfunction in the metabolic syndrome ANGELO AVOGARO

Department of Clinical and Experimental Medicine. Division ofMetabolic Diseases. School of Medicine. University of Padova.Padova. Italy.

Correspondence: Dr. A. Avogaro.E-mail: [email protected]

The metabolic syndrome (MS) has reached epidemic proportions1.Substantial clinical and experimental studies suggest that key compo-nents of the MS include, in addition to National Cholesterol EducationProgram (NCEP) criteria, chronic inflammation, procoagulation, and im-paired fibrinolysis. The metabolic hallmark of MS is the presence of in-sulin resistance, i.e., a decreased sensitivity or responsiveness of periphe-ral tissue to the metabolic action of insulin. Insulin resistance per se andall the components of the MS are associated with altered functions of theendothelium, a dynamic autocrine/paracrine organ, that regulates vascu-lar tone and the interaction of the vessel wall with circulating substancesand blood cells. Endothelial cells secrete an array of mediators which canalternatively mediate either vasoconstriction or vasodilation. Nitric oxide(NO) is the major contributor to endothelium-dependent relaxation inconduit arteries. The MS substantially impairs the vasodilating propertiesof the endothelium and leads to the endothelial dysfunction which canthus be considered the first step in the progression of cardiovascular dise-ase (CVD).

If we assume that the measurement of endothelial function represents asurrogate of endothelial NO availability, then endothelium dependent va-sodilation could provide prognostic information in terms of future cardio-vascular events, as clearly shown by several independent groups2.

Oxidative stress is the common mechanistic damage by risk factorsof the MS. Oxidation reactions are crucial in all the events that lead toatherogenesis, including endothelial dysfunction. The effect of oxygenderived free radicals (ROS) on vascular function depends critically onthe amounts produced: when formed in low amounts ROS can act asintracellular second messengers, modulating the responses as growthof vascular smooth muscle cells and fibroblasts3. Higher amounts ofROS can cause DNA damage, significant toxicity, or even cell apopto-sis. Moreover, under the effect of risk factors, endothelial NO synthase(eNOS) becomes uncoupled and O2

∑– is made rather than NO. In en-dothelium exposed to agents that damage the vasculature there is sti-mulation of several enzymes that can produce ROS: among these enzy-mes, nicotinamide adenine dinucleotide/NADPH oxidase is a majorvascular source of ROS4. Hyperglycemia is the major causal factor inthe development of diabetic vascular complications and can mediatetheir adverse effects through multiple pathways. One of those mecha-nisms is the activation of protein kinases (PKC) by hyperglycemia-in-duced increases in diacylglycerol (DAG) level, partly due to de novosynthesis5. There is increasing evidence that PKC activation is impor-tant in diabetes-related endothelial dysfunction: impaired NO-vasodi-

lation and increases endothelin-1 (ET-1) release involvedPKC-mediated inhibition of eNOS; this is confirmed alsoby the observations showing that PKC inhibition restoresnormal blood flow. Glucose-induced PKC activation alsomediates endothelial membrane permeability; overexpres-sion of the isoforms β2 and ∆ of PKC in the retina increa-se gene and protein expression of ET-1 in the retina6.PKC activation also mediates the overexpression of adhe-sion molecules such as intercellular adhesion molecule(ICAM), vascular cell adhesion molecule (VCAM) and E-selectin. PKC also play a crucial role in mediating vascu-lar smooth muscle cell contractility thus mediating vascu-lar vasoconstriction in response to risk factors such ashyperglycemia. It has also been shown that an inappro-priate production of asymmetric dimethylarginine(ADMA) can alter endothelial function in patients withtype 2 diabetes: this endogenous competitor for NOS in-creases after a fatty meal in type 2 diabetics and its circu-lating levels correlate with a reduction of vascular func-tion7.

Beside hyperglycemia, regional body fat distribution hasa major influence on metabolic and cardiovascular risk fac-tors. Many prospective studies have shown that increasedabdominal fat accumulation is an independent risk factor forCAD, hypertension, stroke, and type 2 diabetes. The stronglink between increased abdominal fat and hyperinsulinemia,insulin resistance, elevated plasma free fatty acid (FFA) le-vels, hypertension, predisposition to thrombosis, hyper-triglyceridemia, small, dense LDL particles, and reducedHDL has been recognized for decades and characterizes thiscondition by widespread vascular dysfunction. Nonethelessseveral studies show that obesity is independently associa-ted with endothelial dysfunction, in humans. The link bet-ween central obesity and endothelial function is further sup-ported by the observation that insulin sensitivity is partlydetermined by the ability of endothelium to produce NO.Thus the haemodynamic resistance of endothelium to insu-lin in terms of NO production would further aggravate me-tabolic insulin resistance and in general metabolic/hae-modynamic coupling8.

In hypertension there is activation of the renin-angioten-sin system, a vasoconstrictor effect of angiotensin II and themineralocorticoid effects of aldosterone. Angiotensin II hasbeen shown to stimulate O2 generation; it has also the capa-bility to stimulate cell hypertrophy induced by angiotensintype 1 (AT1) receptor. Therefore in hypertension there is acondition of widespread oxidative stress that ultimately le-ads to endothelial dysfunction9.

In vivo studies have convincingly shown that hyperten-sion is associated with reduced endothelial function: defectshave been detected either by infusing acetylcholine (Ach),methacholine, or by applying shear stress. Alterations in en-dothelial function have been shown at the conduit arterieslevel, in the microcirculation and in the subcutaneous circu-lation. Thus hypertension, a component of the MS, contri-butes significantly to the alteration of endothelial functionin patients with this condition.

The atherogenic dyslipidemia associated with MS is cha-racterized by hypertriglyceridemia, increase in VLDL se-cretion from the liver, increase in atherogenic small denselow density lipoprotein (LDL), and a decrease in antiathero-genic high density lipoprotein (HDL) cholesterol. High le-vels of LDL and the parallel low level of HDL generateROS. In turn, oxidised LDL reduce NO synthesis and relea-se, and can cause enhanced destruction of NO10. Increasedtriglyceride concentration in the MS has also an importantnegative effect on endothelial function. There is evidencethat the postprandial rather than the fasting triglyceride con-centration play a negative role on endothelial function: thisphysiological phenomenon reflects changes in the composi-tion and concentration of plasma lipoproteins that occur af-ter ingesting a fatty meal.

Several studies in diabetic patients support the conclusionthat postprandial hyperglycemia is a more powerful riskfactor of cardiovascular disease than fasting hyperglycemiaitself11. It has been shown that an oxidative mechanism me-diates endothelial activation induced by postprandial hyper-lipidemia and hyperglycemia. This negative influence onendothelial function has been reported in both normal anddiabetic subjects. Myocardial contrast echocardiography

Avogaro A. Endothelial dysfunction in the metabolic syndrome


Fructose UDP-GlcNAc PKC AGE

NAD(P)H, X/XO, Mitho, Uncoupled NOS

Reactive Oxygen Species

Endothelial cells

1. Apoptosis2. Adhesion molecules3. Vascular permeability

1. Growth2. Migration

3. Matrix regulation

Vascular SmoothMuscle Cells

Fig. 1. Mechamisms underlying the glucose-induced generation ofoxidative stress in the endothelial cells. AGE: advanced glycationendproducts; Mitho: mithocondria-generated reactive oxygen spe-cies; PCK: protein kinase E; X/XO: xanthine oxidoreductase.

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Fig. 2. Significant reduction of endothelial precursor cells (EPCs)in patients with peripheral vascular disease (PVD) and metabolicsyndrome (MS). CTRL: control

using microbubbles may offer an approach to the noninvasi-ve detection of endothelial disease using clinical ultrasoundimaging techniques. We have shown that postprandial hy-perglycemia determines myocardial perfusion defects intype 2 diabetic patients12. These are secondary to deteriora-tion in microvascular function causing a decrease in myo-cardial blood volume.

Each component of the MS alters the integrity of endot-helium: however, this has the capability to renew itself atleast partly through the action of the so-called endothelialprecursor cells (EPCs), a subset of bone marrow-derivedcells capable of originating mature endothelial cells13. EPCsare believed to localize specifically at site of ischemia, whe-re they should increase blood vessel growth: EPC ability toimprove blood supply in peripheral and myocardial ische-mia has been demonstrated in several experimental models.A substantial reduction in circulating EPCs has been de-monstrated by our group in patients with MS14. Thus, EPCreduction and dysfunction may be involved both in endothe-lial dysfunction, as an earlier event in the atherogenetic pro-cess, and in impaired collateralization in the presence ofvascular obstruction by a plaque, as an advanced event lea-ding to clinical manifestation of the atherosclerotic disease.Multiple, interrelated mechanisms contribute to endothelialcell dysfunction in insulin resistance. All traditional riskfactors for coronary heart disease (CHD), including insulinresistance, induce endothelial dysfunction which is the firstkey step in the pathogenesis of atherosclerotic lesions. Sin-ce patients with MS are at particular risk for developingCHD, endothelial dysfunction must be either prevented orcorrected by modifying lifestyle and, if this is not adequate,by correcting each single risk factor without establishinghierarchic priority15.

REFERENCES

1. Haffner S, Taegtmeyer H. Epidemic obesity and the metabolic syndro-me. Circulation. 2003;108:1541-5.

2. Landmesser U, Hornig B, Drexler H. Endothelial function: a critical de-terminant in atherosclerosis? Circulation. 2004;109 Suppl 1:II27-33.

3. Droge W. Free radicals in the physiological control of cell function.Physiol Rev. 2002;82:47-95.

4. Griendling KK, FitzGerald GA. Oxidative stress and cardiovascular in-jury: Part I: basic mechanisms and in vivo monitoring of ROS. Circula-tion. 2003;108:1912-6.

5. Sheetz MJ, King GL. Molecular understanding of hyperglycemia’s ad-verse effects for diabetic complications. JAMA. 2002;288:2579-88.

6. Ceolotto G, Gallo A, Miola M, Sartori M, Trevisan R, Del Prato S, etal. Protein kinase C activity is acutely regulated by plasma glucose con-centration in human monocytes in vivo. Diabetes. 1999;48:1316-22.

7. Fard A, Tuck CH, Donis JA, Sciacca R, Di Tullio MR, Wu HD, et al.Acute elevations of plasma asymmetric dimethylarginine and impairedendothelial function in response to a high-fat meal in patients with type2 diabetes. Arterioscler Thromb Vasc Biol. 2000;20:2039-44.

8. Steinberg HO, Chaker H, Leaming R, Johnson A, Brechtel G, BaronAD. Obesity/insulin resistance is associated with endothelial dysfunc-tion. Implications for the syndrome of insulin resistance. J Clin Invest.1996;97:2601-10.

9. Taddei S, Salvetti A. Endothelial dysfunction in essential hypertension:clinical implications. J Hypertens. 2002;20:1671-4.

10. Stokes KY, Cooper D, Tailor A, Granger DN. Hypercholesterolemiapromotes inflammation and microvascular dysfunction: role of nitricoxide and superoxide. Free Radic Biol Med. 2002;33:1026-36.

11. Ceriello A. The post-prandial state and cardiovascular disease: relevan-ce to diabetes mellitus. Diabetes Metab Res Rev 2000;16:125-32.

12. Scognamiglio R, Negut C, De Kreutzenberg SV, Tiengo A, Avogaro A.Postprandial myocardial perfusion in healthy subjects and in type 2 dia-betic patients. Circulation. 2005;112:179-84.

13. Urbich C, Dimmeler S. Endothelial progenitor cells: characterizationand role in vascular biology. Circ Res. 2004;95:343-53.

14. Fadini GP, Miorin M, Facco M, Bonamico S, Baesso I, Grego F, et al.Circulating endothelial progenitor cells are reduced in peripheral vascu-lar complications of type 2 diabetes mellitus. J Am Coll Cardiol.2005;45:1449-57.

15. Gaede P, Vedel P, Larsen N, Jensen GV, Parving HH, Pedersen O.Multifactorial intervention and cardiovascular disease in patients withtype 2 diabetes. N Engl J Med. 2003;348:383-93.

Avogaro A. Endothelial dysfunction in the metabolic syndrome




Monogenic human obesitysyndromesI SADAF FAROOQI

University Departments of Medicine and Clinical Biochemistry.Cambridge Institute for Medical Research: Addenbrooke’sHospital. Cambridge. United Kingdom.

Correspondence: Dr. I.S. Farooqi.E-mail: [email protected]

Over the past decade we have witnessed a major increase in the scaleof scientific activity devoted to the study of energy balance and obesity.This explosion of interest has, to a large extent, been driven by the identi-fication of genes responsible for murine obesity syndromes, and the no-vel physiological pathways revealed by those genetic discoveries.

We and others have also recently identified several single gene defectscausing severe human obesity. Many of these defects have been in mole-cules identical or similar to those identified as a cause of obesity in ro-dents. I will consider the human monogenic obesity syndromes that havebeen characterized to date and discuss how far such observations supportthe physiological role of these molecules in the regulation of human bodyweight and neuroendocrine function.

INTRODUCTION

The concept that body fat mass is homeostatically regulated emergedin the 1950s1 and was supported by the hypothalamic lesioning studies ofHetherington et al2 and Anand et al3 and the parabiosis experiments ofHervey4. The subsequent emergence of several murine genetic models ofobesity5, and their study in parabiosis experiments by Coleman6 led to theconsolidation of the concept that a circulating factor might be involved inthe mediation of energy homeostasis. However, it was not until the 1990swhen the precise molecular basis for the agouti, ob/ob, db/db and fat/fatmouse emerged, that the molecular components of an energy balance re-gulatory network began to be pieced together7. The use of gene targetingtechnology has gone on to demonstrate the critical roles of certain otherkey molecules such as the melanocortin 4 receptor (MC4R)8 and melaninconcentrating hormone (MCH)9,10 in that network.

A critical question raised by these discoveries is the extent to whichthese regulatory pathways are operating in the control of human bodyweight. Over the past few years a number of novel monogenic disorderscausing human obesity have emerged11. In many cases the mutations arefound in components of the regulatory pathways identified in rodents.

CONGENITAL LEPTIN DEFICIENCY

In 1997, we reported two severely obese cousins from a highly consan-guineous family of Pakistani origin12. Both children had undetectable le-vels of serum leptin and were found to be homozygous for a frameshiftmutation in the ob gene (∆G133), which resulted in a truncated proteinthat was not secreted12,13. We have since identified three further affectedindividuals from two other families14 (and unpublished observations) whoare also homozygous for the same mutation in the leptin gene. All the fa-milies are of Pakistani origin but not known to be related over five gene-

rations. A large Turkish family who carry a homozygousmissense mutation have also been described15. All subjectsin these families are characterised by severe early onsetobesity and intense hyperphagia14,16,17. Hyperinsulinaemiaand an advanced bone-age are also common features14,16.Some of the Turkish subjects are adults with hypogonado-tropic hypogonadism17. Although normal pubertal develop-ment did not occur there was some evidence of a delayedbut spontaneous pubertal development in one person17.

We demonstrated that children with leptin deficiency hadprofound abnormalities of T cell number and function14,consistent with high rates of childhood infection and a highreported rate of childhood mortality from infection in obeseTurkish subjects17. However, there are some phenotypeswhere the parallels between human and mouse are not asclear-cut. Thus, while ob/ob mice are stunted18, it appearsthat growth retardation is not a feature of human leptin defi-ciency14,16, although abnormalities of dynamic growth hor-mone secretion have been reported in one human subject17.ob/ob mice have marked activation of the hypothalamic pi-tuitary adrenal axis with very elevated corticosterone le-vels19. In humans, abnormalities of cortisol secretion are, ifpresent at all, much more subtle14. The contribution of redu-ced energy expenditure to the obesity of the ob/ob mouse isreasonably well established20. In leptin deficient humans wefound no detectable changes in resting or free-living energyexpenditure14, although it was not possible to examine howsuch systems adapted to stressors such as cold. Ozata et al17

reported abnormalities of sympathetic nerve function in lep-tin deficient humans consistent with defects in the efferentsympathetic limb of thermogenesis.

RESPONSE TO LEPTIN THERAPY

Recently we reported the dramatic and beneficial effectsof daily subcutaneous injections of leptin reducing bodyweight and fat mass in three congenitally leptin deficientchildren14. We have recently commenced therapy in the ot-her two children and seen comparably beneficial results(personal observations). All children showed a response toinitial leptin doses (that were) designed to produce plasmaleptin levels at only 10% of those predicted by height andweight (i.e. approximately 0.01 mg/kg of lean body mass)14.

The major effect of leptin was on appetite with normali-sation of hyperphagia. Leptin therapy reduced energy intakeduring an 18 MJ ad libitum test meal by up to 84% (5 MJingested pre-treatment vs 0.8 MJ post-treatment in the childwith the greatest response)14. We were unable to demonstra-te a major effect of leptin on basal metabolic rate or free-li-ving energy expenditure14, but, as weight loss by other me-ans is associated with a decrease in (BMR) basal metabolicrate21, the fact that energy expenditure did not fall in ourleptin deficient subjects is notable.

The administration of leptin permitted progression of ap-propriately timed pubertal development in the single childof appropriate age and did not cause the early onset of pu-berty in the younger children14. Free thyroxine and TSH le-vels, although in the normal range before treatment, hadconsistently increased at the earliest post-treatment timepoint and subsequently stabilized at this elevated level14.These findings are consistent with evidence from animalmodels that leptin influences TRH release from the hypot-halamus22-24 and from studies illustrating the effect of leptindeficiency on TSH pulsatility in humans25.

Throughout the trial of leptin administration, weight losscontinued in all subjects, albeit with refractory periodswhich were overcome by increases in leptin dose14. The fa-milies in the UK harbour a mutation which leads to a pre-

maturely truncated form of leptin and thus wild-type leptinis a novel antigen to them. Thus, all subjects developedanti-leptin antibodies after ~6 weeks of leptin therapy,which interfered with interpretation of serum leptin levelsand in some cases were capable of neutralising leptin in abioassay14. These antibodies are the likely cause of refrac-tory periods occurring during therapy. The fluctuating natu-re of the antibodies probably reflects the complicating fac-tor that leptin deficiency is itself an immuno-deficientstate26,27 and administration of leptin leads to a change fromthe secretion of predominantly Th2 to Th1 cytokines, whichmay directly influence antibody production.

Is there a heterozygous phenotype?

The major question with respect to the potential therapeu-tic use of leptin in more common forms of obesity relates tothe shape of the leptin dose response curve. We have clearlyshown that at the lower end of plasma leptin levels, raisingleptin levels from undetectable to detectable has profoundeffects on appetite and weight14. Heymsfield et al adminis-tered supraphysiological doses (0.1-0.3 mg/kg body weight)of leptin to obese subjects for 28 weeks28. On average, sub-jects lost significant weight, but the extent of weight lossand the variability between subjects has led many to conclu-de that the leptin resistance of common obesity cannot beusefully overcome by leptin supplementation, at least whenadministered peripherally. We studied the heterozygous re-latives of our leptin deficient subjects. Serum leptin levelsin the heterozygous subjects were found to be significantlylower than expected for % body fat and they had a higherprevalence of obesity than seen in a control population ofsimilar age, sex and ethnicity29. Additionally, % body fatwas higher than predicted from their height and weight inthe heterozygous subjects compared to control subjects ofthe same ethnicity29. These findings closely parallel those inheterozygous ob- and db/- mice30,31. These data provide furt-her support for the possibility that leptin can produce a gra-ded response in terms of body composition across a broadrange of plasma concentrations.

All heterozygous subjects had normal thyroid functionand appropriate gonadotropins, normal development of se-condary sexual characteristics, normal menstrual cycles andfertility suggesting that low leptin levels are sufficient topreserve these functions29. This is consistent with the dataof Ioffe et al32 who demonstrated that several of the neuro-endocrine features associated with leptin deficiency wereabolished in low level leptin transgenic mice, which werefertile with normal corticosterone levels.

Our findings in the heterozygous individuals have somepotential implications for the treatment of common forms ofobesity. Whilst serum leptin concentrations correlate positi-vely with fat mass, there is considerable inter-individual va-riation at any particular fat mass. Leptin is inappropriatelylow in some obese individuals and the relative hypoleptine-mia in these subjects may be actively contributing to theirobesity and may be responsive to leptin therapy33. Heyms-field et al28 found no relationship between baseline plasmaleptin levels and therapeutic response, however, study sub-jects were not preselected for relative hypoleptinemia. Atherapeutic trial in a subgroup of subjects selected for dis-proportionately low circulating leptin levels would be ofgreat interest.

LEPTIN RECEPTOR DEFICIENCY

A mutation in the leptin receptor has been reported in oneconsanguineous family with three affected subjects34. Af-

Farooqi IS. Monogenic human obesity syndromes


fected individuals were found to be homozygous for a mu-tation that truncates the receptor before the transmembranedomain. The mutant receptor ectodomain is shed from cellsand circulates bound to leptin. The phenotype has similari-ties to that of leptin deficiency. Leptin receptor deficientsubjects were also of normal birthweight but exhibited rapidweight gain in the first few months of life, with severe hy-perphagia and aggressive behaviour when food was de-nied34. Basal temperature and resting metabolic rate werenormal, cortisol levels were in the normal range and all in-dividuals were normoglycaemic with mildly elevated plas-ma insulins similar to leptin-deficient subjects.

POMC

Two unrelated obese German children have been repor-ted with homozygous or compound heterozygous mutationsin POMC (pro-opiomelanocortin)35. Both children were hy-perphagic and developed early-onset obesity presumablydue to impaired melanocortin signalling in the hypothala-mus35. Presentation was in neonatal life with adrenal crisisdue to isolated ACTH deficiency (POMC is a precursor ofACTH in the pituitary). The children had pale skin and redhair due to the lack of MSH function at melanocortin 1 re-ceptors in the skin35. Three further subjects with homozy-gous or compound heterozygous complete loss of functionmutations of the POMC gene have been described36. Re-cently, a number of groups have identified a heterozygousmissense mutation (Arg236Gly) in POMC that disrupts thedibasic amino acid processing site between β-MSH and β-endorphin37-39. This results in an aberrant β-MSH/β-endorp-hin fusion peptide which binds to MC4R (melanocortin 4receptor) with an affinity identical to that of α- and β-MSHbut has a markedly reduced ability to activate the receptor37.Therefore, this cleavage site mutation in POMC may confersusceptibility to obesity through a novel molecular mecha-nism.

PROHORMONE CONVERTASE 1 DEFICIENCY

Further evidence for the role of the melanocortin systemin the regulation of body weight in humans comes from thedescription of a 47 year old woman with severe childhoodobesity, abnormal glucose homeostasis, very low plasma in-sulin but with elevated levels of proinsulin, hypogonadotro-pic hypogonadism and hypocortisolaemia associated withincreased levels of POMC40. She was found to be a com-pound heterozygote for mutations in prohormone converta-se 1, which cleaves prohormones at pairs of basic aminoacids, leaving C-terminal basic residues that are excised bycarboxypeptidase E (CPE)40. Although the inability to clea-ve POMC is a likely mechanism for obesity in these pa-tients, PC1 cleaves a number of other neuropeptides in thehypothalamus including glucagon-like-peptide 1, whichmay influence feeding behaviour. The phenotype of thesesubjects is very similar to that seen in the CPE deficientfat/fat mouse41 implicating this part of the pathway may beimportant in the control of body weight in humans.

HUMAN MC4R DEFICIENCY

Of the five known melanocortin receptors, the melano-cortin 4 receptor (MC4R) has been most closely linked tocontrol energy balance in rodents42. Mice homozygous for adeleted MC4 receptor become severely obese; heterozygo-tes have body weights intermediate between wild type andhomozygote null animals8. In 1998, two groups reported he-terozygous mutations in the MC4 receptor in humans which

were associated with dominantly inherited obesity43,44. Sincethen, heterozygous mutations in MC4R have been reportedin obese humans from various ethnic groups45-47.

We have studied over 500 severely obese probands andfound that approximately 5-6% have pathogenic MC4R mu-tations that are non-conservative in nature, not found incontrol subjects from the background population and co-se-gregate with obesity in families48. MC4R deficiency repre-sents the commonest known monogenic cause of humanobesity. Some studies have observed a lower prevalenceand this may be explained by the differing prevalence incertain ethnic groups although it is more likely to reflect thelater onset and reduced severity of obesity of the subjects inthese studies49.

We have now studied over 100 MC4R mutant carriers inour clinical research facility. Alongside the increase in fatmass, MC4R mutant subjects also have an increase in leanmass that is not seen in leptin deficiency48. Linear growth ofthese subjects is striking with affected children having aheight standard deviation score (SDS) of +2 compared topopulation standards (mean height SDS of other obese chil-dren in our cohort ± 0.5)48. MC4R deficient subjects alsohave higher levels of fasting insulin than age, sex and BMISDS matched children48. The accelerated linear growth andthe disproportionate early hyperinsulinaemia are consistentwith observations in the MC4R KO mouse50.

Affected subjects are objectively hyperphagic, but this isnot as severe as that seen with leptin deficiency48. Of parti-cular note is the finding that the severity of receptor dys-function seen in in vitro assays can predict the amount offood ingested at a test meal by the subject harbouring thatparticular mutation.

We have studied in detail the signalling properties ofmany of these mutant receptors and this information shouldhelp to advance the understanding of structure/function re-lationships within the receptor51. Importantly, we have beenunable to demonstrate evidence for dominant negativity as-sociated with these mutants, which suggests that MC4Rmutations are more likely to result in a phenotype throughhaploinsufficiency51.

SUMMARY

The identification of molecules that control food intakehas generated new targets for drug development in the treat-ment of obesity and related disorders. These considerationsindicate that an expanded ability to diagnose the pathophy-siological basis of human obesity will have direct applica-tions to its treatment. A more detailed understanding of themolecular pathogenesis of human obesity may ultimatelyguide treatment of affected individuals.

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9. Shimada M, Tritos NA, Lowell BB, Flier JS, Maratos-Flier E. Micelacking melanin-concentrating hormone are hypophagic and lean. Natu-re. 1998;396:670-4.

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11. Barsh GS, Farooqi IS, O’Rahilly S. Genetics of body-weight regulation.Nature. 2000;404:644-51.

12. Montague CT, Farooqi IS, Whitehead JP, Soos MA, Rau H, WarehamNJ, et al. Congenital leptin deficiency is associated with severe early-onset obesity in humans. Nature. 1997;387:903-8.

13. Rau H, Reaves BJ, O’Rahilly S, Whitehead JP. Truncated human leptin(delta133) associated with extreme obesity undergoes proteasomal de-gradation after defective intracellular transport. Endocrinology.1999;140:1718-23.

14. Farooqi IS, Matarese G, Lord GM, Keogh JM, Lawrence E, Agwu C, etal. Beneficial effects of leptin on obesity, T cell hyporesponsiveness,and neuroendocrine/metabolic dysfunction of human congenital leptindeficiency. J Clin Invest. 2002;110:1093-103.

15. Strobel A, Issad T, Camoin L, Ozata M, Strosberg AD. A leptin mis-sense mutation associated with hypogonadism and morbid obesity. NatGenet. 1998;18:213-5.

16. Farooqi IS, Jebb SA, Langmack G, Lawrence E, Cheetham CH, Prenti-ce AM, et al. Effects of recombinant leptin therapy in a child with con-genital leptin deficiency. N Engl J Med. 1999;341:879-84.

17. Ozata M, Ozdemir IC, Licinio J. Human leptin deficiency caused by amissense mutation: multiple endocrine defects, decreased sympathetictone, and immune system dysfunction indicate new targets for leptin ac-tion, greater central than peripheral resistance to the effects of leptin,and spontaneous correction of leptin-mediated defects. J Clin Endocri-nol Metab. 1999;84:3686-95.

18. Dubuc PU, Carlisle HJ. Food restriction normalizes somatic growth anddiabetes in adrenalectomized ob/ob mice. Am J Physiol. 1988;255:R787-93.

19. Dubuc PU. Basal corticosterone levels of young og/ob mice. Horm Me-tab Res. 1977;9:95-7.

20. Trayhurn P, Thurlby PL, James WPT. Thermogenic defect in pre-obeseob/ob mice. Nature. 1977;266:60-2.

21. Rosenbaum M, Murphy EM, Heymsfield SB, Matthews DE, Leibel RL.Low dose leptin administration reverses effects of sustained weight-re-duction on energy expenditure and circulating concentrations of thyroidhormones. J Clin Endocrinol Metab. 2002;87:2391-4.

22. Legradi G, Emerson CH, Ahima RS, Flier JS, Lechan RM. Leptin pre-vents fasting-induced suppression of prothyrotropin-releasing hormonemessenger ribonucleic acid in neurons of the hypothalamic paraventri-cular nucleus. Endocrinology. 1997;138:2569-76.

23. Nillni EA, Vaslet C, Harris M, Hollenberg A, Bjorbak C, Flier JS. Lep-tin regulates prothyrotropin-releasing hormone biosynthesis. Evidencefor direct and indirect pathways. J Biol Chem. 2000;275:36124-33.

24. Harris M, Aschkenasi C, Elias CF, Chandrankunnel A, Nillni EA,Bjøorbaek C, et al. Transcriptional regulation of the thyrotropin-relea-sing hormone gene by leptin and melanocortin signaling. J Clin Invest.2001;107:111-20.

25. Mantzoros CS, Ozata M, Negrao AB, et al. Synchronicity of frequentlysampled thyrotropin (TSH) and leptin concentrations in healthy adultsand leptin-deficient subjects: evidence for possible partial TSH regula-tion by leptin in humans. J Clin Endocrinol Metab. 2001;86:3284-91.

26. Lord GM, Matarese G, Howard JK, Baker RJ, Bloom SR, Lechler RI.Leptin modulates the T-cell immune response and reverses starvation-induced immunosuppression. Nature. 1998;394:897-901.

27. Matarese G. Leptin and the immune system: how nutritional status in-fluences the immune response. Eur Cytokine Netw. 2000;11:7-14.

28. Heymsfield SB, Greenberg AS, Fujioka K, Dixon RM, Kushner R,Hunt T, et al. Recombinant leptin for weight loss in obese and leanadults: a randomized, controlled, dose-escalation trial. JAMA.1999;282:1568-75.

29. Farooqi IS, Keogh JM, Kamath S, Jones S, Gibson WT, Trussell R, etal. Partial leptin deficiency and human adiposity. Nature. 2001;414:34-5.

30. Coleman DL. Obesity genes: beneficial effects in heterozygous mice.Science. 1979;203:663-5.

31. Chung WK, Belfi K, Chua M, Wiley J, Mackintosh R, Nicolson M, etal. Heterozygosity for Lep(ob) or Lepr(db) affects body compositionand leptin homeostasis in adult mice. Am J Physiol. 1998;274:R985-90.

32. Ioffe E, Moon B, Connolly E, Friedman JM. Abnormal regulation ofthe leptin gene in the pathogenesis of obesity. Proc Natl Acad Sci U SA. 1998;95:11852-7.

33. Ravussin E, Pratley RE, Maffei M, Wang H, Friedman JM, Bennett PH,et al. Relatively low plasma leptin concentrations precede weight gainin Pima Indians. Nat Med. 1997;3:238-40.

34. Clement K, Vaisse C, Lahlou N, Cabrol S, Pelloux V, Cassuto D, et al.A mutation in the human leptin receptor gene causes obesity and pitui-tary dysfunction. Nature. 1998;392:398-401.

35. Krude H, Biebermann H, Luck W, Horn R, Brabant G, Gruters A. Se-vere early-onset obesity, adrenal insufficiency and red hair pigmenta-tion caused by POMC mutations in humans. Nat Genet. 1998;19:155-7.

36. Krude H, Gruters A. Implications of proopiomelanocortin (POMC) mu-tations in humans: the POMC deficiency syndrome. Trends EndocrinolMetab. 2000;11:15-22.

37. Challis BG, Pritchard LE, Creemers JW, Delplanque J, Keogh JM,Luan L, et al. A missense mutation disrupting a dibasic prohormoneprocessing site in pro-opiomelanocortin (POMC) increases susceptibi-lity to early-onset obesity through a novel molecular mechanism. HumMol Genet. 2002;11:1997-2004.

38. Del Giudice EM, Cirillo G, Santoro N, D’Urso L, Carbone MT, DiToro R, et al. Molecular screening of the proopiomelanocortin (POMC)gene in Italian obese children: report of three new mutations. Int J ObesRelat Metab Disord. 2001;25:61-7.

39. Echwald SM, Sorensen TI, Andersen T, Tybjaerg-Hansen A, ClausenJO, Pedersen O. Mutational analysis of the proopiomelanocortin genein Caucasians with early onset obesity. Int J Obes Relat Metab Disord.1999;23:293-8.

40. Jackson RS, Creemers JW, Ohagi S, Raffin-Sanson ML, Sanders L,Montague CT, et al. Obesity and impaired prohormone processing asso-ciated with mutations in the human prohormone convertase 1 gene. NatGenet. 1997;16:303-6.

41. Naggert JK, Fricker LD, Varlamov O, Nishina PM, Rouille Y, SteinerDF, et al. Hyperproinsulinaemia in obese fat/fat mice associated with acarboxypeptidase E mutation which reduces enzyme activity. Nat Ge-net. 1995;10:135-42.

42. Yeo GS, Farooqi IS, Challis BG, Jackson RS, O’Rahilly S. The role ofmelanocortin signalling in the control of body weight: evidence fromhuman and murine genetic models. QJM. 2000;93:7-14.

43. Yeo GS, Farooqi IS, Aminian S, Halsall DJ, Stanhope RG, O’Rahilly S.A frameshift mutation in MC4R associated with dominantly inheritedhuman obesity. Nat Genet. 1998;20:111-2.

44. Vaisse C, Clement K, Guy-Grand B, Froguel P. A frameshift mutationin human MC4R is associated with a dominant form of obesity. Nat Ge-net. 1998;20:113-4.

45. Farooqi IS, Yeo GS, Keogh JM, Aminian S, Jebb SA, Butler G, et al.Dominant and recessive inheritance of morbid obesity associated withmelanocortin 4 receptor deficiency. J Clin Invest. 2000;106:271-9.

46. Vaisse C, Clement K, Durand E, Hercberg S, Guy-Grand B, Froguel P.Melanocortin-4 receptor mutations are a frequent and heterogeneouscause of morbid obesity. J Clin Invest. 2000;106:253-62.

47. Hinney A, Schmidt A, Nottebom K, Heibült O, Becker I, Ziegler A, etal. Several mutations in the melanocortin-4 receptor gene including anonsense and a frameshift mutation associated with dominantly inheri-ted obesity in humans. J Clin Endocrinol Metab. 1999;84:1483-6.

48. Farooqi IS, Keogh JM, Yeo GS, Lank EJ, Cheetham T, O’Rahilly S.Clinical spectrum of obesity and mutations in the melanocortin 4 recep-tor gene. N Engl J Med. 2003;348:1085-95.

49. Jacobson P, Ukkola O, Rankinen T, et al. Melanocortin 4 receptor se-quence variations are seldom a cause of human obesity: the SwedishObese Subjects, the HERITAGE Family Study, and a Memphis cohort.J Clin Endocrinol Metab. 2002;87:4442-6.

50. Fan W, Dinulescu DM, Butler AA, Zhou J, Marks DL, Cone RD. Thecentral melanocortin system can directly regulate serum insulin levels.Endocrinology. 2000;141:3072-9.

51. Yeo GS, Lank EJ, Farooqi IS, Keogh J, Challis BG, O’Rahilly S. Muta-tions in the human melanocortin-4 receptor gene associated with severefamilial obesity disrupts receptor function through multiple molecularmechanisms. Hum Mol Genet. 2003;12:561-74.





Metabolic complicationsassociated with obesity —anadipose tissue problemPETER ARNER

Department of Medicine. Karolinska Institutet. Stockholm.Sweden.

Correspondence: Dr. P. Arner.E-mail: [email protected]

There is almost an epidemic increase in the occurrence of obesity inmost countries. This is creating a grooving health economy problem,mainly because of the metabolic complications that are associated withobesity and which, ultimately, leads to atherosclerotic disorders that pro-mote disability and early death. Although a number of factors may ex-plain the association between obesity and abnormal metabolism, the adi-pose tissue itself may be the worst culprit because the tissue produces anumber of signalling molecules that influence other tissues. This reviewwill focus on the role of adipose tissue for the metabolic complications toobesity paying particular interest to free fatty acids (FFAs), derived th-rough adipocyte lipolysis, because those molecules are best characterizedas regards a cause-effect relationship. Because of clinical concerns the re-view will predominantly deal with human adipose tissue. In the interestof space, review articles rather than original publications will be citedwhenever possible.

ADIPOSE TISSUE AS A SECRETORY FACTOR

Previously, adipose tissue was just looked upon as a storage organ forFFAs, thus playing a role solely in energy homeostasis. This picture hasmarkedly changed during the last 15 years or so because it has becameincreasingly apparent that adipose tissue produces and secretes a largenumber of proteins1. Some of these proteins are signalling molecules ha-ving various effects in other organs. Others have above all autocrine/pa-racrine roles within the adipose tissue. Some proteins (mainly inflamma-tory ones) are not only produced by the fat cells but also by the stromacells in adipose tissue and participate in a low grade inflammatory reac-tion of adipose tissue that is observed in the obese state2. Among the in-flammatory proteins only interleukin-6 is proven to be secreted from adi-pose tissue into the circulation and it is possible, but not proven, that theincreased release of interleukin-6, which is observed among the obese,could play a role for insulin resistance in liver and muscle2,3.

Adiponectin is a protein that almost solely is produced by adipocytes4.It has insulin-like effects and seems to protect against adverse effect ofobesity, in particular in the liver. Although the adipose production of adi-ponectin is decreased in the obese state and in other insulin resistant di-sorders there is no proof yet in humans that adiponectin has a role in anymetabolic complication associated with obesity. However, the putativereceptors for adiponectin are isolated so it is possible that we in the nearfuture will have a better knowledge about the pathophysiological role ofadiponectin in obesity.

Leptin was the first discovered adipocyte specific hormone. This pro-tein has major roles in energy homeostasis, appetite regulation and repro-duction5. It is, however, less clear whether leptin causes metabolic com-

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plication to obesity or not. Indeed leptin production and cir-culating leptin are increased among the obese but the meta-bolic effect of this change is not known in man. Studies ofanimals have suggested that hyperleptinemia may cause in-creased lipid accumulation (i.e. lipotoxicity) in tissue outsi-de of adipose tissue such the heart, skeletal muscle and theliver6. Whether this also occurs in man remains to be pro-ven. Recently other adipose specific proteins have been de-tected; as regard about metabolic complication to obesity,some of them are proven to be a false trait. For example, re-sistin is produced by rodent adipocytes and in an increasedrate in obesity. In rodents this molecule causes insulin resis-tance. In man however, it is not produced by fat cells andseems to be of no or little concern for metabolic changesand/or insulin resistance among the obese3. FFAs were dis-covered some 50 years ago and rapidly a relationship bet-ween obesity and circulating FFAs was established. FFA isstill the strongest causative link between metabolic compli-cations and obesity, which is discussed in some detail be-low.

FFA LEVELS IN OBESITY

It is well established that circulating FFA levels are in-creased in obesity and that this is associated with decreasedoverall insulin sensitivity. The relationship is particularlystrong among upper body obese. A recent example from myown laboratory is shown in figures 1 and 2 examining therelationship between upper body obesity, in vivo insulinsensitivity (measured as HOMA-index) and fasting serumFFA levels. Among about 2,500 healthy subjects the serum-FFA level is positively correlated with the waist and withthe level of insulin resistance (p < 0.0001).

Several factors are causing elevation of FFA among theobese7. Firstly, there is an increase in the basal (spontane-ous) lipolytic activity of fat cells in all adipose regions sothat more FFA are delivered into the blood stream. Recentdata suggest that this might be due to increased adipose tis-sue production of the cytokine tumour necrosis factor alpha,which is a potent stimulator of basal lipolytic activity3.

As regards hormone induced lipolysis the situation ismore complex because the major lipolysis regulating hor-

mones in man, catecholamines and insulin, are subject tomarked regional variations7-9. In obesity the lipolytic effectof catecholamines is increased in visceral fat cells but de-creased in subcutaneous adipocytes. As regards the antili-polytic effect of insulin in obesity it is much more impairedin visceral adipose tissue than in the subcutaneous adiposetissue. Thus, during hormone excess such as in connectionwith physical activity (catecholamines) or after meal inges-tion (insulin) relatively more FFAs are produced by the vis-ceral depot than by the subcutaneous depot due to the regio-nal variations in hormone induced lipolysis. Only visceralfat is drained by the portal vein so that visceral fat is di-rectly connected to the liver. Thus, malfunctions of hormo-ne induced lipolysis is more important for the liver than ot-her organs in the obese subjects because of elevatedcirculating levels of “portal” FFAs.

A normalization of the metabolism of FFAs in adipocy-tes, which occurs after antidiabetic therapy with glitazones,has marked effects on metabolic abnormalities in type 2diabetes. This strongly suggests that FFAs indeed are of im-portance for the metabolic complications in the obese type 2diabetics.

HOW ARE FFAs CAUSING METABOLICCOMPLICATIONS IN OBESITY?

As reviewed, elevated circulating levels of FFA lead to anumber of abnormalities in non-adipose tissues10. In skeletalmuscle FFAs are competing with glucose as substrate foroxidation according to the so called Randle’s cycle. Highavailability of FFAs impairs glucose handling of the skele-tal muscle and results in hyperglycaemia. A high uptake ofFFAs by the muscle may lead to intracellular accumulationof triglycerides which causes insulin resistance. FFAs mayalso directly interfere with insulin signalling in musclecells.

As regards the liver, FFAs have several effects. They im-pair insulin metabolism and may cause hyperinsulinemia.They inhibit insulin action and may cause hepatic insulinresistance. They stimulate gluconeogenesis and may causeincreased glucose output from the liver and, finally, they aresubstrates for VLDL triglyceride synthesis by the liver and

Arner P. Metabolic complications associated with obesity —an adipose tissue problem


2

1.5

1

0.5

050 70 90 110 130 150 170

Waist, cm

r = 0.32; p < 0.0001

s-F

FA, m

mol

/l

1.75

1.25

0.75

0.25

–0.25

–0.750 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

s-FFA, mmol/l

r = 0.26; p < 0.0001

log

HO

MA

inde

x

Fig. 1. Relationship between upper body fat (measured as waist)and fasting levels of serum free fatty acids (s-FFA) in 2,527 he-althy subjects. Results of linear regression analysis.

Fig. 2. Relationship between fasting s-FFA and insulin resistance(measured as log HOMA index) in 2,438 healthy subjects. See le-gend to figure 1 for further details.

therefore may cause dyslipidemia. Finally, FFAs regulateinsulin production by the pancreas and a high FFA levelsmay induce impaired insulin secretion and, thus, cause dia-betes.

CONCLUSIONS

There is strong evidence suggesting that molecules pro-duced by adipose tissue are major factors behind the meta-bolic alterations among the obese. Although the release ofseveral adipose tissue-derived proteins such as adiponectin,interleukin-6 and (maybe) leptin is influenced by obesityand such changes may alter insulin action and metabolicevents in liver and muscle, there is not yet enough humandata available to suggest a cause effect relationship. Eleva-ted FFAs, which is a hallmark in obesity, seems, however,to be a causative link between metabolic complications andobesity. In the resting fasting state, there is increased deli-very of FFAs from fat cells to the blood stream due to en-hanced rate of basal lipolysis in all adipose regions amongthe obese, which at least in part is caused by local overpro-duction of tumour necrosis factor alpha within the adiposedepots. During hormone stimulation, such as after exercise(catecholamines) and after meal ingestion (insulin) moreFFAs are released from visceral fat than from subcutaneousfat due to regional differences in hormone action on lipoly-sis. This elevates “portal” FFAs and has selective effects onthe liver. Since the regional variations in lipolysis are mostprominent among upper body obese subjects, the depot va-

riations might link between central obesity stronger to meta-bolic complications than peripheral obesity. It could be pos-sible in the future to develop new therapeutic agents thatmodify lipolysis by adipose tissue and thereby improve themetabolic status among the obese.

REFERENCES

1. Trayhurn P. Endocrine and signalling role of adipose tissue: new pers-pectives on fat. Acta Physiol Scand. 2005;184:285-93.

2. Berg AH, Scherer PE. Adipose tissue, inflammation, and cardiovascu-lar disease. Circ Res. 2005;96:939-49.

3. Arner P. Insulin resistance in type 2 diabetes —role of the adipokines.Curr Mol Med. 2005;5:333-9.

4. Haluzik M. Adiponectin and its potential in the treatment of obesity,diabetes and insulin resistance. Curr Opin Investig Drugs. 2005;6:988-93.

5. Zhang F, Chen Y, Heiman M, Dimarchi R. Leptin: structure, functionand biology. Vitam Horm. 2005;71:345-72.

6. Unger RH. Minireview: weapons of lean body mass destruction: therole of ectopic lipids in the metabolic syndrome. Endocrinology.2003;144:5159-65.

7. Large V, Arner P. Regulation of lipolysis in humans. Pathophysiologi-cal modulation in obesity, diabetes, and hyperlipidaemia. Diabetes Me-tab. 1998;24:409-18.

8. Giorgino F, Laviola L, Eriksson JW. Regional differences of insulin ac-tion in adipose tissue: insights from in vivo and in vitro studies. ActaPhysiol Scand. 2005;183:13-30.

9. Wajchenberg BL, Giannella-Neto D, Da Silva ME, Santos RF. Depot-specific hormonal characteristics of subcutaneous and visceral adiposetissue and their relation to the metabolic syndrome. Horm Metab Res.2002;34:616-21.

10. Arner P. The adipocyte in insulin resistance: key molecules and the im-pact of the thiazolidinediones. Trends Endocrinol Metab. 2003;14:137-45.

Arner P. Metabolic complications associated with obesity —an adipose tissue problem




Experiencia DRECEMIGUEL A. RUBIO, EN REPRESENTACIÓN DEL GRUPO DRECE

Unidad de Nutrición Clínica y Dietética. Servicio deEndocrinología y Nutrición. Hospital Clínico Universitario SanCarlos. Madrid. España.

Correspondencia: Dr. M.A. Rubio.Correo electrónico: [email protected]

El estudio Dieta y Riesgo de Enfermedades Cardiovasculares en Espa-ña (DRECE) se inició en 1991 con la finalidad de conocer la prevalenciade los principales factores de riesgo cardiovascular y los hábitos alimen-tarios en una muestra de 4.787 personas entre 5 y 59 años de edad, repre-sentativa de la población española. Como objetivos a largo plazo, sucesi-vos análisis de esta cohorte (1991-1992, 1996-1997 y 2005-2006) nospermitirán conocer la evolución temporal de estos factores de riesgo, asícomo analizar la mortalidad cardiovascular en España.

En el estudio DRECE participan 52 centros de salud distribuidos ho-mogéneamente por áreas rurales y urbanas de todo el territorio nacional,de acuerdo con un modelo sectorial de 8 grandes áreas propuesto por elMinisterio de Agricultura, Pesca y Alimentación.

RESULTADOS DEL DRECE-1

Realizado entre 1991 y 1992, se pudo conocer los diferentes factoresde riesgo cardiovascular de la población objeto del estudio, así como loshábitos alimentarios en ese momento. En la tabla 1 se pueden ver algunosde los resultados en los que ya se apreciaban prevalencias elevadas de losprincipales factores de riesgo.

En cuanto a los hábitos alimentarios, se ponía de manifiesto una dismi-nución del aporte de hidratos de carbono (un 40% de la energía) a favorde un mayor consumo de grasas (un 40-43% de la energía), sobre todo aexpensas de las grasas saturadas (un 13-15%) procedentes del consumode derivados lácteos y cárnicos, bollería y aperitivos. Se demostró que laingestión de grasa saturada y colesterol se correlacionaba con las concen-traciones de lípidos (positivamente para el colesterol de las lipoproteínasde baja densidad [cLDL] y los triglicéridos y negativamente para el co-lesterol de las lipoproteínas de alta densidad [cHDL]) en las regiones conmayor consumo de estos ácidos grasos (Levante, Andalucía, Canarias),áreas poblacionales que, por otro lado, se corresponden con las de mayortasa de enfermedades cardiovasculares en España.

RESULTADOS DEL DRECE-2

Este segundo análisis de la cohorte DRECE se realizó 5 años despuésde la primera observación (1996-1997). En esta ocasión se seleccionó atodos los sujetos con factores de riesgo cardiovascular y a una muestrarepresentativa de 600 individuos, apareados por edad y sexo, sin eviden-cia de factores de riesgo cardiovascular. Los resultados encontrados nomostraron apenas cambios respecto a 1992, entre otros motivos porque se

tuvo especial esmero en no intervenir en la población objetodel estudio. Sólo los sujetos con factores de riesgo cardio-vasculares habían mejorado ligeramente sus hábitos alimen-tarios reduciendo significativamente el porcentaje de grasasaturada y colesterol. En este segundo estudio se analizó laprevalencia de síndrome metabólico y de obesidad abdomi-nal en relación con los factores de riesgo cardiovascular. Laprevalencia general de síndrome metabólico fue del 23,7%de la población, muy similar a otros resultados obtenidos enCanarias o Estados Unidos (un 22-26%). La obesidad abdo-minal y el síndrome metabólico tienen relación con un in-cremento significativo de la proteína C reactiva, lo que indi-ca un mayor riesgo cardiovascular en este colectivo desujetos.

Por último, se analizó la incidencia de eventos cardiovas-culares incluyendo mortalidad por esa causa, y se observóque los sujetos tipificados como en riesgo cardiovascularpresentaban una odds ratio de 3,96 de tener un episodio car-diovascular respecto a los individuos sin riesgo. El análisisde regresión permitió deducir que las concentraciones detriglicéridos, pero no otras variables clásicas, tienen rela-

ción muy significativa con el riesgo de contraer una enfer-medad cardiovascular.

PERSPECTIVAS FUTURAS

Se ha comenzado a realizar un tercer corte transversal de lamisma cohorte (DRECE-3), con un seguimiento de 14 años,lo que nos permitirá analizar con más detenimiento no sólo laevolución de los principales factores de riesgo y los hábitosalimentarios de la muestra sino, sobre todo, disponer de infor-mación relativa a morbilidad y mortalidad en esta población;sin duda, nos ayudará a explicar mejor las tendencias en estaenfermedad en un área geográfica como la nuestra.

BIBLIOGRAFÍA GENERAL

Ballesteros MD, Rubio MA, Gutiérrez-Fuentes JA, Gómez-Gerique JA, Gó-mez de la Cámara A, Pascual O, et al; DRECE-II group. Dietary habitsand cardiovascular risk in the spanish population: the DRECE study (I).Ann Nutr Metab. 2000;44:108-14.

Ballesteros MD, Rubio MA, Gutiérrez-Fuentes JA, Gómez-Gerique JA, Gó-mez de la Cámara A, Pascual O, et al; DRECE-II group. Dietary habitsand cardiovascular risk in the spanish population: the DRECE study (II).Micronutrients intake. Ann Nutr Metabol. 2000;44:177-82.

Ballesteros MD, Rubio MA, Gutiérrez-Fuentes JA, Gómez-Gerique JA.Evaluación de la calidad de la dieta española en el estudio DRECE: ade-cuación a las recomendaciones de la Sociedad Española de Arterioscle-rosis. Clin Invest Arterioscl. 2001;13:97-102.

Gómez Gerique JA, Gutiérrez-Fuentes JA, Montoya MT, Porres A, RuedaA, Avellaneda A, et al; en representación del grupo de estudio DRECE.Perfil lipídico de la población española: estudio DRECE (Dieta y Riesgode Enfermedad Cardiovascular en España). Med Clin (Barc). 1999;113:730-6.

Gutiérrez-Fuentes JA, Gómez-Gerique JA, Gómez de la Cámara A, RubioMA, García-Hernández A, Arístegui I, por el grupo DRECE. Dieta yriesgo cardiovascular en España (DRECE II): descripción de la evolu-ción del perfil cardiovascular. Med Clin (Barc). 2000;115:726-9.

Rubio MA, Gutiérrez Fuentes JA, Gómez Gerique JA, Ballesteros MD,Montoya MT, por el grupo DRECE. Estudio DRECE: Dieta y riesgo deenfermedades cardiovasculares en España. Hábitos nutricionales en lapoblación española. Endocrinol Nutr. 2000;47:294-300.

Rubio MA. Experiencia DRECE


Varones (%) Mujeres (%)

Fumadores 54 34Hipertensión arterial 24 21Colesterol total > 240 mg/dl 21 20Triglicéridos > 150 mg/dl 39 19cHDL < 40 mg/dl 23 6Diabetes 5,1 4,9Obesidad (IMC > 30) 19,6 15,1

TABLA 1. Prevalencia de los diferentes factores de riesgo cardiovasculares

cHDL: colesterol de las lipoproteínas de baja densidad; IMC: índice demasa corporal.



On the trail to arrest theprogression of the metabolicsyndromeJOSÉ F. CARO

Lilly Research Laboratories. Lilly Corporate Center. Indianapolis.Indiana. United States of America.

Correpondence: J.E. Caro.E-mail: [email protected]

The metabolic syndrome is a cluster of metabolic anomalies that repre-sent one of the major unmet medical needs. The metabolic anomalies in-clude among others, diabetes, obesity, hypertension and atherosclerosis.They represent the phenotype of survival genes in an environment of ple-nitude.

There are two major goals for treatment: a) secondary prevention — inthose patients identified with the metabolic syndrome, reductions of therisks for atherosclerotic disease is the primary goal, and b) primary pre-vention — in those populations at risk for the development of the meta-bolic syndrome lifestyle interventions, dietary changes, physical activityand possibly pharmacotherapy are the primary goals.

SECONDARY PREVENTION

The current recommendations of the American Heart Association/Na-tional Heart, Lung, and Blood Institute are summarized in table 11. Thereis general agreement on those recommendations by the American Diabe-tes Association, the European Association of the Study of Diabetes2, theInternational Diabetes Federation3, and the practicing physicians at large.

The role of statins targeting LDL cholesterol in the reduction of CVDrisk, morbidity and mortality is now well established. These studies wererecently reviewed4. The role of fenofibrate targeting HDL cholesterolwas recently published5. The Fenofibrate Intervention and Event Lowe-ring in Diabetes (FIELD) study assess the effect of fenofibrate on cardio-vascular events in patients with diabetes. Fenofibrate did not significantlyreduce the risk of the primary outcome of coronary events5, but it did re-duce secondary outcomes. The role of pioglitazone on the secondary pre-vention of macrovascular events in patients with type 2 diabetes in thePROactive Study was recently reported6. Pioglitazone did not reduce theprimary composite endpoint but it did reduce secondary outcomes6. Insummary, the results from these well-executed trials5,6 do not warrant yeta general recommendation different from that in table 1.

PRIMARY PREVENTION

There are not primary prevention studies on the metabolic syndrome.However, there are many prevention studies on diabetes. A significantpercent of subjects with pre-diabetes, impaired glucose tolerance or im-paired fasting glucose have a phenotype consistent with that of the meta-bolic syndrome. Therefore learning from these studies could be appliedto the larger and more heterogeneous population of patients with the me-

Caro JF. On the trail to arrest the progression of the metabolic syndrome


Therapeutic target and goals of therapy Therapeutic recommendations

Lifestyle risk factorsAbdominal obesityReduce body weight by 7% to 10% during year 1 of therapy. Continue weight loss thereafter to extent possible with goal to ultimately achieve desirable weight (BMI < 25)Physical inactivity

Regular moderate-intensity physical activity;at least 30 min of continuous or intermittent(and preferably ≥ 60 min) 5 days/week, butpreferably daily

Atherogenic dietReduced intake of saturated fat, trans fat,cholesterol

Metabolic risk factorsAtherogenic dyslipidemia Primary target: elevated LDL-C. Secondarytarget: elevated non-HDL-CHigh-risk patientsa: < 130 mg/dl (3.4 mmol/l)(optional: < 100 mg/dl [2.6 mmol/l] for veryhigh-risk patientsb. Moderately high-riskpatientsc: < 160 mg/dl (4.1 mmol/l);therapeutic option: < 130 mg/dl (3.4 mmol/l).Moderate-risk patientsd: < 160 mg/dl (4.1mmol/l). Lower-risk patientse: < 190 mg/dl(4.9 mmol/l)Tertiary target: reduced HDL-CNo specific goal: Raise HDL-C to extentpossible with standard therapies foratherogenic dyslipidemiaElevated BPReduce BP to at least achieve BP of < 140/90mmHg (or < 130/80 mmHg if diabetespresent). Reduce BP further to extent possiblethrough lifestyle changes.

Elevated glucoseFor IFG, delay progression to type 2 diabetesmellitus. For diabetes, hemoglobin A1C < 7%

Prothrombotic stateReduce thrombotic and fibrinolytic risk factors

Proinflammatory state

TABLE 1. Therapeutic goals and recommendations for clinical management of metabolic syndrome

Long-term prevention of CVD and prevention (or treatment) of type 2 diabetes mellitus

Consistently encourage weight maintenance/reduction through appropriate balance ofphysical activity, caloric intake, and formal behavior-modification programs whenindicated to maintain/achieve waist circumference of < 40 inches in men and < 35inches in women. Aim initially at slow reduction of 7% to 10% from baseline weight.Even small amounts of weight loss are associated with significant health benefits

In patients with established CVD, assess risk with detailed physical activity historyand/or an exercise test, to guide prescription. Encourage 30 to 60 min of moderate-intensity aerobic activity: brisk walking, preferably daily, supplemented by increase indaily lifestyle activities (e.g., pedometer step tracking, walking breaks at work,gardening, housework). Longer exercise times can be achieved by accumulatingexercise throughout day. Encourage resistance training 2 days/week. Advise medicallysupervised programs for high-risk patients (e.g., recent acute coronary syndrome orrevascularization, CHF)

Recommendations: saturated fat < 7% of total calories; reduce trans fat; dietarycholesterol < 200 mg/dl; total fat 25% to 35% of total calories. Most dietary fat shouldbe unsaturated; simple sugars should be limitedShorter-term prevention of CVD or treatment of type 2 diabetes mellitus

Elevated LDL-C. Elevated non-HDL-C

First option to achieve non-HDL-C goal: Intensify LDL-lowering therapy. Secondoption to achieve non-HDL-C goal: Add fibrate (preferably fenofibrate) or nicotinicacid if non-HDL-C remains relatively high after LDL-lowering drug therapy. Givepreference to adding fibrate or nicotinic acid in high-risk patients. Give preference toavoiding addition of fibrate or nicotinic acid in moderately high-risk or moderate-riskpatients All patients: If TG is 500 mg/dl, initiate fibrate or nicotinic acid (before LDL-lowering therapy; treat non-HDL-C to goal after TG-lowering therapy)Reduced HDL-CMaximize lifestyle therapies: weight reduction and increased physical activity.Consider adding fibrate or nicotinic acid after LDL-C-lowering drug therapy as outlinedfor elevated non-HDL-C

For BP ≥ 120/80 mmHg: Initiate or maintain lifestyle modification in all patients withmetabolic syndrome: weight control, increased physical activity, alcohol moderation,sodium reduction, and emphasis on increased consumption of fresh fruits, vegetables,and low-fat dairy products. For BP ≥ 140/90 mmHg (or ≥ 130/80 mmHg for individualswith chronic kidney disease or diabetes): As tolerated, add BP medication as needed toachieve goal BP

For IFG, encourage weight reduction and increased physical activity. For type 2diabetes mellitus, lifestyle therapy, and pharmacotherapy, if necessary, should be usedto achieve near-normal HbA1C (< 7%). Modify other risk factors and behaviors (e.g.,abdominal obesity, physical inactivity, elevated BP, lipid abnormalities)

High-risk patients: Initiate and continue low-dose aspirin therapy; in patients withASCVD, consider clopidogrel if aspirin is contraindicated. Moderately high-riskpatients: Consider low-dose aspirin prophylaxisRecommendations: no specific therapies beyond lifestyle therapies

ASCVD: atherosclerotic cardiovascular disease; BMI: body mass index; BP: blood pressure; CHF: congestive heart failure; CVD: cardiovascular disease;IFG: impaired fasting glucose; TG: triglycerides.aHigh-risk patients are those with established ASCVD, diabetes, or 10-year risk for coronary heart disease > 20%. For cerebrovascular disease, high-risk con-dition includes TIA or stroke of carotid origin or > 50% carotid stenosis.bVery high-risk patients are those who are likely to have major CVD events in next few years, and diagnosis depends on clinical assessment. Factors that mayconfer very high risk include recent acute coronary syndromes, and established coronary heart disease + any of following: multiple major risk factors (espe-cially diabetes), severe and poorly controlled risk factors (especially continued cigarette smoking), and metabolic syndrome.cModerately high-risk patients are those with 10-year risk for coronary heart disease 10% to 20%. Factors that favor therapeutic option of non-HDL-C < 100mg/dl are those that can raise individuals to upper range of moderately high risk: multiple major risk factors, severe and poorly controlled risk factors (espe-cially continued cigarette smoking), metabolic syndrome, and documented advanced subclinical atherosclerotic disease (e.g., coronary calcium or carotid inti-mal-medial thickness > 75th percentile for age and sex).dModerate-risk patients are those with 2+ major risk factors and 10-year risk < 10%.eLower-risk patients are those with 0 or 1 major risk factor and 10-year risk < 10%.From: Grundy et al1.

tabolic syndrome. Several studies have demonstrated thatweight loss and lifestyle interventions reduced the incidenceof type 2 diabetes in patients at risk. One of the first pilotstudies demonstrating this benefit used bariatric surgery as away to achieve long lasting and significant weight loss7.

About 60% loss of excess body weight in patients withclinically severe obesity (> 45 kg excess body weight) pre-vented the progression of impaired glucose tolerance to dia-betes by > 30-fold. The incidence of type 2 diabetes (pa-tients/years) was 1/682 in the experimental group(incidence rate = 0.15) and 6/127 in the control group (inci-dence rate = 4.75). The incidence rate (100 person-years) ofthe control group was similar to other observation studieson pre-diabetes7. This study conducted from 1980 to 1991used a patient population and a method of weight loss thatwas neither representative of the majority of obese subjectsnor of the optimal treatment modality7. Therefore, it had tobe established that less obese individuals with pre-diabeteswere able to prevent or delay their conversion to type 2 dia-betes by weight loss using less invasive therapeutic proce-dures. More recently, evidence from three large randomizedcontrolled and longer-term trials examining the impact of li-festyle changes on the progression of pre-diabetes to type 2diabetes has been reported. These trials have been recentlyreviewed4 and they are summarized in table 2.

Thus, lifestyle interventions are the recommended appro-aches for the prevention of type 2 diabetes and thereforealso the metabolic syndrome. Pharmacotherapy with met-formin, thiazolidinediones, alpha-glycosidase inhibitors,and others, recently reviewed4, also prevent type 2 diabetes,but in general to a lesser extent than lifestyle interventions.Thus, pharmacotherapy may well become part of the secon-dary approach for prevention of the metabolic syndromejust as it may be for type 2 diabetes.

CONCLUSIONS

It is clear that the continuing globalization and the adop-tion of the “western” lifestyle across the world will mostcertainly cause more widespread conflict between these “thrifty genes” and the environment8. Thus, effective pre-vention will only be achieved by a multi-factorial approach,

including lifestyle interventions, socio-economical inter-ventions, and pharmacological interventions. For the pre-sent, it is essential that research effort is directed to unders-tand the etiology and mechanism(s) of the metabolic syn-drome. This information will be used to refine the currentworking diagnostics criteria of the syndrome and targetedtherapy for the myriad of diseases that will prove to includethe metabolic syndrome8.

REFERENCES

1. Grundy SM, Cleeman JI, Daniels SR, Donato KA, Eckel RH, FranklinBA, et al; American Heart Association; National Heart, Lung, and BloodInstitute. Diagnosis and management of the metabolic syndrome: anAmerican Heart Association/National Heart, Lung, and Blood InstituteScientific Statement. Circulation. 2005;112:2735-52.

2. Kahn R, Buse J, Ferrannini E, Stern M; American Diabetes Association;European Association for the Study of Diabetes. The metabolic syndro-me: time for a critical appraisal: joint statement from the American Dia-betes Association and the European Association for the Study of Diabe-tes. Diabetes Care. 2005;28:2289-304.

3. Alberti KG, Zimmet P, Shaw J; IDF Epidemiology Task Force Consen-sus Group. The metabolic syndrome—a new worldwide definition. Lan-cet. 2005;366:1059-62.

4. Cameron A, Shaw J, Zimmet P. The metabolic syndrome: lifestyle,drugs, or both? En: Serrano Ríos M, Caro JF, Carraro R, Gutiérrez Fuen-tes JA, editors. The metabolic syndrome at the beginning of the XXIstCentury. Barcelona: Elsevier; 2005.

5. Keech A, Simes RJ, Barter P, et al, for the FIELD Study Investigators.Effects of long-term fenofibrate therapy on cardiovascular events in9795 people with type 2 diabetes mellitus (the FIELD study): Randomi-sed controlled trial. Lancet. 2005;366:1849-61.

6. Dormandy JA, Charbonnel B, Eckland DJ, Erdmann E, Massi-BenedettiM, Moules IK, et al; the PROactive study investigators. Secondary pre-vention of macrovascular events in patients with type 2 diabetes in thePROactive Study (PROspective pioglitAzone Clinical Trial In macro-Vascular Events): a randomised controlled trial. Lancet. 2005;366:1279-89.

7. Long SD, O’Brien K, MacDonald KG Jr, Leggett-Frazier N, SwansonMS, Pories WJ, et al. Weight loss in severely obese subjects prevents theprogression of impaired glucose tolerance to type II diabetes. A longitu-dinal interventional study. Diabetes Care. 1994;17:372-5.

8. Karathanasis SK, Schiebinger RJ. Drug treatment in the metabolic syn-drome. En: Serrano Ríos M, Caro JF, Carraro R, Gutiérrez Fuentes JA,editores. The metabolic syndrome at the beginning of the XXIst Century.Barcelona: Elsevier; 2005.

Caro JF. On the trail to arrest the progression of the metabolic syndrome


n Characteristics Mean duration Intervention Indicence Incidence reduction of subjects (years) of DM(% p.a.) (%)

Diabetes Prevention 3,234 IGT; 2.8 Control 11.0Program (USA) mean age, 51; Lifestylea 4.8 58%

mean BMI, 34 Metformin 7.8 31%Diabetes Prevention 522 IGT; 3.2 Control 7.8Study (Finland) mean age, 55; Lifestyleb 3.2 58%

mean BMI, 31Da Qing IGT and Diabetes 577 IGT; 6 Control 15.7Study (China) mean age, 45; Dietc 10.0 33%

mean BMI, 26 Exercised 8.3 47%Diet and exercise 9.6 38%

TABLE 2. Intervention studies to reduce incidence of type 2 diabetes mellitus

DM: diabetes mellitus; IGT: impared glucose tolerance.aAt least 7% weight loss and 150 min of physical activity per week.bAt least 5% weight loss and 210 min physical activity per week.cTarget: BMI = 23.dIncrease exercise by at least 1 unit per day (e.g. extra 30 min slow walking or 5 min swimming).From: Cameron A et al4.



Síndrome metabólico y riesgocardiovascularRAFAEL CARMENA

Servicio de Endocrinología y Nutrición. Hospital ClínicoUniversitario. Valencia. España.

Trabajo realizado con una Beca del Instituto de Salud Carlos III, Red de Centros Meta-bolismo y Nutrición (C03/08), Madrid.

Correspondencia: Dr. R. Carmena.Correo electrónico: [email protected]

CONCEPTO Y DEFINICIÓN

La combinación de factores de riesgo cardiovascular de origen endóge-no en un mismo individuo fue descrita por Marañón y Kylin a comienzosdel pasado siglo y alcanzó especial relieve con la publicación porReaven1 en 1988 del llamado síndrome X. Desde esa fecha aumentó ex-ponencialmente el número de publicaciones dedicadas a ese síndrome co-nocido como síndrome X, síndrome de resistencia a la insulina o cuartetode la muerte, hasta la más utilizada denominación actual de síndrome me-tabólico (SM).

El SM se define como la agrupación en un mismo individuo de facto-res de riesgo cardiovascular de origen endógeno y confiere un riesgo ele-vado de contraer diabetes tipo 2 y enfermedades cardiovasculares, nota-blemente cardiopatía isquémica (CHD). Su prevalencia es alta en lassociedades industriales y su utilidad para identificar fácilmente en unapoblación a sujetos de alto riesgo está bien demostrada.

Los principales alteraciones o factores de riesgo habitualmente inclui-dos en el SM son: obesidad abdominal (expresada por el perímetro de lacintura), hipertensión arterial, alteraciones del metabolismo de los hidra-tos de carbono, anomalías lipoproteínicas (hipertrigliceridemia, colesterolde las lipoproteínas de alta densidad [cHDL] bajo y aumento de los áci-dos grasos libres, las partículas de lipoproteínas de baja densidad [LDL]pequeñas y densas y de las lipoproteínas portadoras de apolipoproteínaB) y microalbuminuria. Más recientemente se han ido añadiendo otroscomponentes, relacionados con la inflamación, la disfunción endotelial,el estado protrombótico, la esteatosis hepática, etc., que describiremos enotro apartado. Conviene aclarar que el perímetro de la cintura puede utili-zarse como un marcador indirecto pero fiable del contenido de grasa in-traabdominal, ya que se correlaciona significativamente con dicho depó-sito cuantificado por tomografía computarizada (TC)2.

Se piensa que las alteraciones descritas tienen una base fisiopatológicacomún, la resistencia periférica a la insulina (RI), acompañada general-mente de hiperinsulinismo compensador3. La RI y el hiperinsulinismo enayunas tienen relación independiente con la dislipemia, la hipertensiónarterial, la disfunción endotelial y otras manifestaciones del síndrome. LaRI está condicionada por factores genéticos y ambientales, como una die-ta hipercalórica rica en grasa saturada, obesidad, tabaquismo y sedenta-rismo. La relación entre RI y SM no es la de una simple agrupación, sinoque se trata de una verdadera conexión causa-efecto y explica, entreotras, la dislipemia, la disglucemia y la hipertensión. La elevación de losácidos grasos libres en sangre es una de las consecuencias fisiopatológi-cas más importantes de la RI, a la que a su vez potencian. La elevación

de citocinas, como el factor de necrosis tumoral alfa(TNFα) y otras, contribuye también a potenciar la RI y quese desarrolle un estado inflamatorio crónico, objeto de otraspresentaciones. Otros componentes del SM, como la estea-tosis hepática no alcohólica, el estado protrombótico, la dis-función endotelial, las elevaciones de leptina y ferritina,etc., son también objeto de otras presentaciones.

CRITERIOS DIAGNÓSTICOS

Un problema persistente al abordar el estudio del SM esel de los criterios para diagnosticarlo, y hay cerca de unadecena de ellos propuestos por grupos de expertos o socie-dades científicas. En las tablas 1 a 3 resumimos los 3 crite-rios más aceptados en la actualidad.

La Organización Mundial de la Salud (OMS) publicóen 19994 unos criterios para definir el SM y considera laIR como factor sine qua non. Estos criterios exigen quehaya una tolerancia anormal a la glucosa o diabetes melli-tus o IR (valorada con el modelo HOMA). Como es ob-vio, esta definición tiende a identificar a sujetos que yatienen una alteración de la regulación del metabolismo dela glucosa y alto riesgo de contraer diabetes tipo 2. Escierto que aproximadamente el 80% de los diabéticos tipo2 cumplen criterios diagnósticos de SM, pero al menos untercio de los sujetos con SM conservan una tolerancianormal a la glucosa5. Por ello, las normas del Grupo Eu-ropeo para el estudio de la Resistencia a la Insulina(EGIR)6 para el diagnóstico del SM incluyen la IR y ex-cluyen la diabetes, con la razonable justificación de queuna posible complicación del síndrome no debe formarparte de sus criterios diagnósticos.

El National Cholesterol Educational Program Adult Tre-atment Program III (NCEP ATP-III)7, en Estados Unidos,publicó otras normas que dan prioridad a la presencia deobesidad abdominal y requirien que concurran 3 de los si-guientes 5 determinantes: aumento de la circunferencia dela cintura, triglicéridos elevados, cHDL bajo, presión arte-rial elevada y glucemia en ayunas alterada. Por su pragma-tismo y fácil aplicación, han recibido la aceptación mayori-taria y han sido actualizados recientemente8. Finalmente, en2005, la International Diabetes Federation (IDF) ha introdu-cido modificaciones a los criterios ATP-III para dar especialimportancia a la obesidad abdominal y cambiar los puntosde corte del perímetro de la cintura según las diferentes et-nias (tabla 2)9.

El criterio diagnóstico utilizado influye en las estimacio-nes de prevalencia del SM en una población10. En España,la prevalencia de SM en población adulta oscila entre el 18y el 30%, dependiendo de la edad de la población y los cri-terios usados para su diagnóstico11-14. En todos los estudiosepidemiológicos se observa una clara tendencia al aumentode la prevalencia con la edad de la población.

Los criterios NCEP ATP-III e IDF identifican sobretodo a sujetos con alto riesgo cardiovascular, mientrasque los de la OMS identifican a sujetos con riesgo de dia-betes mellitus tipo 2. Usando los criterios ATP-III, quetienen un umbral diagnóstico más bajo, se identifica a unnúmero más alto de sujetos con SM que con los criteriosde la OMS. Con los criterios de IDF de 2005, con puntosde corte para perímetro de cintura más bajos, se puedeidentificar a más sujetos en algunas poblaciones. Sin em-bargo, en Estados Unidos, la mayoría de los varones concintura > 94 cm y las mujeres con cintura > 80 cm cum-plen también los criterios del ATP-III e igualmente se losdiagnosticaría12. Por ahora no disponemos de datos com-parativos sobre la asociación del SM con el riesgo cardio-vascular usando cada una de las definiciones15.

SÍNDROME METABÓLICO Y RIESGOCARDIOVASCULAR

El SM y sus distintos componentes confieren un elevadoriesgo cardiovascular, y se estima que éste duplica el halla-do en sujetos sin SM de iguales edad y sexo. Debe quedarclaro, sin embargo, que el SM no es un predictor de riesgoabsoluto y que la estimación de éste exige el empleo de ta-blas o algoritmos que incluyan otros factores de riesgo car-diovascular (edad, sexo, tabaquismo, cLDL, antecedentesfamiliares, etc.). Por lo tanto, una vez establecido el diag-nóstico de SM, procede calcular el riesgo absoluto o riesgogeneral, y en función de ello decidir si, además de la im-prescindible intervención con cambios del estilo de vida,hay que añadir fármacos. Las tablas y ecuaciones más utili-zadas para el cálculo del riesgo absoluto son las de Fra-mingham, PROCAM16 y otras mencionadas más adelante.Aunque los estadísticos que trabajan con datos epidemioló-gicos continúan discutiendo si el riesgo cardiovascular atri-buido al SM supera al aportado por la suma de los de cadacomponente17, la mayoría se inclina por lo primero. Es de-cir, el riesgo que acompaña al SM es fruto de un efectomultiplicativo, más que de una mera adición4.

En apoyo de esta postura, los resultados de estudios pros-pectivos llevados a cabo en Europa, como el Estudio Bru-neck, el Kuopio Ischemic Heart Disease Risk Study y el Es-

Carmena R. Síndrome metabólico y riesgo cardiovascular


TABLA 1. Criterios diagnósticos del síndromemetabólico

ATP-III 2001-2005

De los siguientes, 3 o másObesidad abdominal: perímetro de la cintura > 102 cm(varones) o > 88 cm (mujeres)Hipertrigliceridemia ≥ 150 mg/dl (1,6 mmol/l)cHDL bajo

Varones, < 40 mg/dl (1,04 mmol/l)Mujeres, < 50 mg/dl (1,29 mmol/l)

Presión arterial ≥ 130/85 mmHgGlucemia basal ≥ 100 mg/dl (≥ 5,6 mmol/l)

OMS 1999

Al menos 1 de los siguientesDiabetes mellitus tipo 2Tolerancia anormal a la glucosaResistencia a la insulina (HOMA Q4)

Más al menos 2 de los siguientesHipertensión ≥ 140/90 mmHgObesidad (IMC ≥ 30)Hipertrigliceridemia ≥ 150 mg/dl o cHDL bajo (< 35 mg/dl

en varones y < 40 mg/dl en mujeres)Microalbuminuria ≥ 20 µg/min

cHDL: colesterol de las lipoproteínas de alta densidad; cLDL: colesterol delas lipoproteínas de baja densidad; IMC: índice de masa corporal.

TABLA 2. Consenso de la IDF 2005. Definición de obesidad central

Más de 2 de los siguientesTriglicéridos ≥ 1,7 mmol/l (150 mg/dl)*cHDL

Varones < 1 mmol/l (40 mg/dl)*Mujeres < 1,1 mmol/l (50 mg/dl)*

Presión arterial sistólica ≥ 130 mmHg* oPresión arterial diastólica ≥ 85 mmHg*Glucemia en ayunas ≥ 5,6 mmol/l (100 mg/dl)*

*O estar recibiendo tratamiento específico. Tomado de Alberti et al9.

tudio Botnia, han demostrado que los sujetos con SM tienenhasta 3 veces más riesgo de morbilidad y mortalidad porCHD18,19 aunque no tengan diabetes y enfermedad coronariaal inicio de la observación20.

Además, los análisis estadísticos post-hoc de grandes es-tudios prospectivos, como el West Of Scotland COronaryPrevention Study (WOSCOPS) y el Multiple Risk FactorIntervention Trial (MRFIT), han demostrado una relaciónsignificativa entre el riesgo coronario y el número de com-ponentes del SM identificados en los sujetos21,22.

En un subgrupo de sujetos incluidos en el estudioWOSCOPS, el riesgo de CHD calculado fue 2,3, 3,2 y 3,7veces mayor en los que presentaban 2, 3 y 4 o más com-ponentes del síndrome, respectivamente. Aunque la rela-ción entre los valores elevados de cLDL y CHD está bienestablecida en la literatura, la contribución relativa al ries-go coronario de la hipertrigliceridemia y de los valoresbajos de cHDL está definida con menos precisión. Sinembargo, algunos datos disponibles indican que la asocia-ción de hipertrigliceridemia y cHDL bajo en sujetos conun cLDL elevado aumenta considerablemente el riesgocoronario. En un análisis post-hoc del Scandinavian Sim-vastatin Survival Study (4S), el subgrupo de pacientescon la llamada “tríada lipídica” (hipertrigliceridemia,cHDL bajo y cLDL elevado) mostró mayor número deotros componentes del SM y mayor riesgo coronario en elgrupo placebo que entre los sujetos con sólo elevación delcLDL. Además, los sujetos con la tríada lipídica tratadoscon simvastatina fueron los que alcanzaron las mayoresreducciones en la tasa de accidentes coronarios23.

Las recomendaciones clínicas para valorar y orientarsesobre el riesgo cardiovascular en sujetos con SM están dis-ponibles en varias pautas y guías de consenso. Los docu-mentos más significativos son las recomendaciones delThird Joint Task Force of European and other Societies onCardiovascular Disease Prevention in Clinical Practice (dis-

ponible en: http://www.escardio.org/scinfo/Guidelines/cvd-prevention.pdf) y los ya mencionados del NCEP ATP-III(disponible en: http://www.nhlbi.nih.gov/guidelines/choles-terol/atp3full.pdf) y el Consenso 2005 de la IDF10. Además,la International Atherosclerosis Society Harmonized Guide-lines on Prevention of Atherosclerotic Cardiovascular Dise-ases ha elaborado un documento para integrar y armonizarlas diversas recomendaciones y guías que se encuentra dis-ponible en: http://www.athero.org/download/fullreport.pdf

Las recomendaciones más aceptadas indican que si elriesgo cardiovascular estimado a 10 años es bajo, se debecomenzar con cambios en el estilo de vida; en cambio, si seconsidera elevado el riesgo (> 20%), se iniciará al mismotiempo un tratamiento farmacológico de los diferentes com-ponentes del síndrome4.

TRATAMIENTO DEL SÍNDROME METABÓLICO

Dado que el SM es una constelación de distintas altera-ciones interrelacionadas, su tratamiento exige un enfoquemultifactorial de todos los factores de riesgo existentes, co-menzando por los cambios de estilo de vida. Quede claroque no hay, por ahora, un tratamiento específico del SM,aparte del tratamiento intensivo de todos sus componentes.Además, la estrategia terapéutica estará precedida por unavaloración del riesgo cardiovascular de cada sujeto. En latabla 4 se recogen los objetivos terapéuticos según las reco-mendaciones publicadas recientemente12,13.

Cambios de estilo de vida

La obesidad y el sedentarismo son los determinantes bá-sicos de la mayoría de los componentes del SM y se debetratarlos inicialmente y con intensidad. Una pérdida signifi-cativa de peso mejora todos los factores de riesgo relaciona-dos con el SM y reduce también el riesgo de diabetes tipo224. Se recomienda pautar una dieta hipocalórica (1.000-1.200 kcal/día) y baja (< 8%) en grasas saturadas y un pro-grama personalizado de ejercicio aeróbico (idealmente, de30 min al día) con el objetivo de una pérdida ponderal de un7-10% en 1 año. La cirugía bariátrica puede ser una opciónválida en casos de obesidad mórbida y SM, que llega a de-saparecer en el 95% de los casos al año de la intervención25.

La abstención absoluta del hábito tabáquico y el consumomoderado de bebidas alcohólicas, sal, azúcares simples ohidratos de carbono con alto índice glucémico forman parteimportante de este apartado.

Dos estudios prospectivos recientemente publicados res-paldan la importancia de los cambios en el estilo de vidapara la prevención del SM y de su evolución hacia la diabe-tes tipo 2. El 53% de los participantes en el Diabetes Pre-vention Program (DPP) fueron diagnosticados de SM al ini-cio del estudio26. Respecto al grupo control, el tratamientocon un programa intensivo de ejercicio aeróbico y dieta hi-pocalórica pobre en grasa saturada durante 3 años redujo elSM en un 41%, mientras que el tratamiento con metforminaconsiguió hacerlo en un 17% de los sujetos. Estos resulta-dos coinciden con los obtenidos por Tuomilehto et al27 enun grupo más reducido de sujetos con tolerancia anormal ala glucosa y SM. Una pérdida de peso de aproximadamente4,5 kg y la práctica habitual de ejercicio aeróbico proporcio-naron una significativa reducción de SM y de la progresióna diabetes tipo 2 respecto a los resultados del tratamientocon metformina o placebo.

Por lo tanto, la combinación de dieta hipocalórica pobreen grasa saturada y ejercicio aeróbico permite prevenir laaparición del SM en un porcentaje significativo de los suje-tos.



TABLA 3. Criterios de la IDF para el perímetro de la cintura (cm)

Varones Mujeres

Caucásicos ≥ 94 ≥ 80China y sudeste asiático ≥ 90 ≥ 80Japón ≥ 85 ≥ 90

Tomado de Alberti et al9.

TABLA 4. Objetivos terapéuticos en el síndromemetabólico

Obesidad abdominal Pérdida de un 7-10% del peso en 1 año; continuar con más pérdida de peso o mantenerlo

Sedentarisno 30-60 min/día de ejercicio aeróbicoPresión arterial < 135/85 mmHg; en diabéticos,

< 130/80 mmHgGlucemia en ayunas < 100 mg/dl (5,5 mmol/l)Glucohemoglobina < 7%cLDL Muy alto riesgo, < 70 mg/dl

(1,8 mmol/l)Alto riesgo, < 100 mg/dl (2,6 mmol/l)Riesgo moderado, < 130 mg/dl (3,4 mmol/l)

cHDL Varones, > 40 mg/dlMujeres, > 50 mg/dl

Triglicéridos < 150 mg/dl (1,7 mmol/l)

Tratamiento farmacológico de los factores de riesgo

Si las medidas expuestas no bastan para alcanzar los ob-jetivos terapéuticos, como ocurre a menudo en sujetos deriesgo alto o muy alto, se añadirá fármacos. La prioridadpara su empleo son las elevaciones del cLDL, presión arte-rial y glucemia.

El tratamiento coadyuvante de la obesidad con fármacospuede ser necesario en algunos casos. El empleo de orlistat,sibutramina o antagonistas de los receptores endocanabinoi-des tipo 1, como rimonabant, ha mostrado utilidad, si bienson necesarios estudios de confirmación más prolongados28.

El tratamiento de la dislipidemia con estatinas en sujetoscon SM se ha demostrado beneficioso reduciendo significa-tivamente la cantidad de cLDL y apolipoproteína B y elriesgo cardiovascular29,30. Los fibratos también se han mos-trado capaces de reducir el riesgo en este grupo de sujetos31

y la combinación de estatinas con fenofibrato puede resultarespecialmente eficaz en algunos casos. No se debe utilizar,en cambio, combinada con gemfibrozilo, por el mayor ries-go de miopatía.

Se recomienda que el tratamiento de la hipertensión arte-rial en sujetos con SM se inicie indistintamente con inhibi-dores de la enzima de conversión de angiotensina o antago-nistas de los receptores de angiotensina II. Un aspecto quedestacar en el contexto del SM con tolerancia anormal a laglucosa es la aparente protección contra la aparición de dia-betes ofrecida por estos fármacos, como han puesto de ma-nifiesto recientes estudios32. Como en el caso de la diabetes,una proporción importante de los hipertensos con SM re-querirá el empleo de al menos 3 fármacos hipotensores paraalcanzar los objetivos.

El tratamiento farmacológico de la tolerancia anormal a laglucosa o de la diabetes se ha de llevar a cabo con agentesorales (inhibidores de la alfaglucosilasa intestinal, insulinose-cretagogos, metformina o glitazonas) o, en su caso, insulina.El recientemente publicado estudio PROACTIVE ha mostra-do una reducción de las complicaciones cardiovasculares enlos diabéticos tipo 2 de alto riesgo que, además de su trata-miento habitual, recibieron pioglitazona durante 3 años33.

En fase todavía experimental se encuentran los nuevosfármacos tipo incretinas, como la exenatida y otros análo-gos del glucagon-like-peptide (GLP) 1, interesantes en elcontexto que nos ocupa ya que facilitan la pérdida de peso.En fase también preclínica se hallan los agonistas dualesPPARα/PPARγ, como tesaglitazar, naveglitazar y otros,que mejoran la dislipidemia y la IR.

COMENTARIOS FINALES

El SM se ha convertido recientemente en el centro de unacontroversia34,35, más semántica que científica, sobre susverdaderas utilidad y fisiopatología36. Aun cuando algunasde las críticas vertidas no carecen de fundamento, pensamosque el concepto del SM ha funcionado como un paradigmaútil en la práctica clínica para identificar a sujetos en riesgode diabetes o complicaciones cardiovasculares por arterios-clerosis, y por ello se debe conservarlo. Además, el concep-to integrador de SM sirve como testimonio de que el riesgode enfermedad coronaria isquémica (CHD) es multifactorialy existe más allá de los valores de cLDL. Ciertamente, esimprescindible investigar más en sus mecanismos fisiopato-lógicos y valorar mejor el riesgo cardiovascular aportadopor los distintos componentes del síndrome. Pero, en cual-quier caso, hay más argumentos a favor de conservar elconcepto de SM que en contra, y el interés por su detecciónprecoz para la prevención de las complicaciones antes alu-didas está más que justificado.

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ENDOCRINOLOGÍA YNUTRICIÓN · María de Molina 3, 1.º – 28006 Madrid – Tel.: 91 781 50 70 Fax...

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