Hyperleptinemia as a component of a metabolic syndrome of cardiovascular risk

Cardiovascular death and the metabolic syndrome: role of adiposity-signaling hormones and inflammatory markers

OBJECTIVE

Levels of adiposity-signaling hormones and inflammatory markers are less favorable in individuals with the metabolic syndrome; their role in the association between the metabolic syndrome and cardiovascular mortality remains unclear.

RESEARCH DESIGN AND METHODS

We conducted a prospective study of 977 men and 1,141 women aged 40-94 years in 1984-1987, followed for mortality for a maximum of 20 years. Adiponectin, leptin, ghrelin, interleukin-6 (IL-6), C-reactive protein (CRP), and Adult Treatment Panel III-defined metabolic syndrome components were measured in fasting blood samples obtained in 1984-1987. Cox-proportional hazards models were used in survival analyses.

RESULTS

The age- and sex-adjusted hazard ratio (HR) (95% CI) for coronary heart disease (CHD) mortality associated with the metabolic syndrome was 1.65 (1.25-2.18) (P < 0.001); this association did not differ significantly by sex, age, or diabetic status (P > 0.2 for each interaction). The association between the metabolic syndrome and CHD mortality was not materially changed after adjustment for adiponectin, leptin, and ghrelin; it was attenuated by 25% after adjustment for IL-6 and 35% after adjustment for CRP. CHD mortality increased linearly with greater levels of IL-6 and CRP (P(trend) < 0.001 for each); the age- and sex-adjusted HRs comparing highest versus lowest quarter were 3.0 (1.87-4.89) for IL-6 and 2.1 (1.41-3.21) for CRP. IL-6, but not CRP, remained a significant predictor of CHD mortality in models including both inflammatory markers and the metabolic syndrome.

CONCLUSIONS

Adiposity-signaling hormones and inflammatory markers explain little to some of the association between the metabolic syndrome and CHD mortality. IL-6 levels predict CHD mortality independently of CRP.

Plasma leptin: associations with metabolic, inflammatory and haemostatic risk factors for cardiovascular disease

BACKGROUND AND AIM

Leptin, an adipocyte-derived protein, regulating food intake and metabolism has been implicated in the development of coronary heart disease. We have examined the relationship between leptin and vascular risk factors including insulin resistance, metabolic, inflammatory and haemostatic risk factors.

METHODS AND RESULTS

The study was carried out in 3640 non-diabetic men aged 60-79 years drawn from general practices in 24 British towns and who were not on warfarin. Leptin was strongly positively correlated with waist circumference (r=0.58; p<0.0001). Leptin concentrations decreased significantly with increasing physical activity and were lowered in cigarette smokers and elevated in men with pre-existing coronary heart disease and stroke; alcohol intake showed no association with leptin concentration. After adjustment for waist circumference and these lifestyle factors, increased leptin was independently associated with significant increases in insulin resistance, triglycerides, inflammatory markers (interleukin-6, C-reactive protein, fibrinogen, plasma viscosity), coagulation factor VIII, endothelial markers von Willebrand factor, tissue plasminogen activator, and fibrin D-dimer levels; and a decrease in HDL-cholesterol. No association was seen between leptin and blood pressure, total cholesterol, glucose or white cell count after adjusting for waist circumference. Further adjustment for insulin resistance abolished the relationships between leptin and triglycerides and HDL-cholesterol, weakened the associations with the haemostatic factors although they remained significant, but made minor differences to the associations with inflammatory markers.

CONCLUSION

Plasma leptin is associated with insulin resistance, inflammation and disturbances in haemostasis independent of waist circumference, suggesting possible pathways by which leptin may influence risk of cardiovascular disease.

Gingival Crevicular Fluid Leptin Levels in Periodontitis Patients With Long-Term and Heavy Smoking

BACKGROUND

The aim of the present study was to evaluate gingival crevicular fluid (GCF) leptin levels and the influence of long-term and heavy smoking on GCF leptin levels in patients with chronic periodontitis.

METHODS

In this study, 143 individuals were divided into three groups: non-smokers (NS), smokers (S), and control (C). Three subgroups of NS and S were grouped as follows: a) probing depth (PD) <or=3 mm; b) PD = 4 to 5 mm; and c) PD >5 mm. For each patient, PD, gingival index (GI), plaque index (PI), gingival bleeding time index (GBTI), and clinical attachment level (CAL) values were recorded. The GCF leptin levels obtained from sampling sites were determined by using enzyme-linked immunosorbent assay kits.

RESULTS

The GCF leptin levels were found significantly lower in the a and b subgroups in the S group than those in the NS group (P <0.05). The inflammatory markers GI and GBTI showed significant correlations with leptin in NS (P <0.05).

CONCLUSIONS

Our results suggest that higher leptin GCF levels in healthy sites in periodontitis patients may play a protective role in periodontal disease. Further studies are needed to determine the cellular origin of the leptin in the gingiva and the effect of plasma leptin levels on GCF leptin concentrations.

Lifestyle variables, non-traditional cardiovascular risk factors, and the metabolic syndrome in an Aboriginal Canadian population

OBJECTIVE

To examine lifestyle factors associated with metabolic syndrome (MetS) and to explore the relationships between MetS and non-traditional cardiovascular disease risk factors [adiponectin, leptin, C-reactive protein (CRP), interleukin-6 (IL-6), and serum amyloid A (SAA)] in an isolated Aboriginal Canadian community.

RESEARCH METHODS AND PROCEDURES

Data were obtained from 360 non-diabetic adults participating in a population-based study of Aboriginal Canadians. Fasting samples were drawn for glucose, insulin, lipids, adiponectin, leptin, CRP, IL-6, and SAA. Percentage body fat was measured using bioelectrical impedance analysis. Past year physical activity and fitness level were assessed. MetS was diagnosed according to the criteria of the National Cholesterol Education Program, the World Health Organization, and the International Diabetes Federation.

RESULTS

The results showed that older age, higher percentage body fat, and lower fitness levels were associated with increased odds of MetS regardless of MetS definition and subject gender. Past year physical activity was independently related with the World Health Organization-MetS in male subjects. Subjects with MetS had significantly higher leptin, CRP, IL-6, and SAA levels and lower adiponectin levels; however, only adiponectin remained significantly low after adjustment for age and percentage body fat.

DISCUSSION

The study showed that higher percentage body fat and lower physical activity and fitness were associated with a higher prevalence of MetS in this Aboriginal community and that hypoadiponectinemia was independently associated with MetS.

Leptin down-regulates peroxisome proliferator-activated receptor gamma (PPAR-gamma) mRNA levels in primary human monocyte-derived macrophages

Increased leptin levels are associated with cardiovascular disease in obesity although the mechanism is unknown. Peroxisome proliferator-activated receptor gamma (PPARgamma) is a key regulator of macrophage lipid metabolism and its activation by thiazolidinediones protects against atherosclerosis. The aim of this study was to assess the effects of human recombinant leptin on PPARgamma mRNA levels in primary human macrophages and macrophage-derived foam cells. Leptin treatment (100 ng/ml) for 24 h caused a 41% reduction (p < 0.01) in PPARgamma transcript levels in human-derived macrophages. This fall was accompanied by a reduction in the mRNA expression of carnitine palmitoyltransferase (CPT-I) (36%, p < 0.05) and ABCA1 (62%, p < 0.05), whereas CD36 mRNA reduction (34%) was not significant. In macrophage-derived foam cells, leptin at 20 ng/ml reduced PPARgamma mRNA levels by 33% (p < 0.01) and CPT-I by 27% (p < 0.05). At this concentration, leptin did not modify the expression of either ABCA1 or CD36. In agreement with these results, intracellular cholesterol ester accumulation was not altered in macrophage-derived foam cells by leptin at 20 ng/ml. We propose that the reduction in PPARgamma expression in both macrophages and foam cells may be one of the factors linking high leptin levels and cardiovascular disease.

O papel dos hormônios leptina e grelina na gênese da obesidade

A prevalência da obesidade está aumentando e estudos prospectivos mostram que, em 2025, o Brasil será o quinto país do mundo a apresentar problemas de obesidade em sua população. A etiologia da obesidade não é de fácil identificação, uma vez que a mesma é caracterizada como uma doença multifatorial, ou seja, diversos fatores estão envolvidos em sua gênese, incluindo fatores genéticos, psicológicos, metabólicos e ambientais. Pesquisas recentes na área de metabolismo mostram que o adipócito é capaz de sintetizar várias substâncias e, diferentemente do que se supunha anteriormente, o tecido adiposo não é apenas um sítio de armazenamento de triglicérides, é hoje considerado um órgão endócrino. Dentre as diversas substâncias sintetizadas pelo adipócito, destacam-se a adiponectina, a angiotensina e a leptina. A leptina é um petídeo que desempenha importante papel na regulação da ingestão alimentar e no gasto energético, gerando um aumento na queima de energia e diminuindo a ingestão alimentar. Além dos avanços no estudo da célula adiposa, um novo hormôrnio relacionado ao metabolismo foi descoberto recentemente, a grelina. A grelina é um peptídeo produzido nas células do estômago, e está diretamente envolvida na regulação do balanço energético a curto prazo. Assim, este artigo abordará o papel da leptina e da grelina no controle do peso corporal e as limitações que ainda existem para tratar a obesidade em humanos.

Is the factor structure of the metabolic syndrome comparable between men and women and across three ethnic groups: the Miami Community Health Study

PURPOSE

The metabolic syndrome (MS) is conceived as a cluster of disorders that increase risk for coronary heart disease and type 2 diabetes. Studies examining its structure primarily have used an exploratory factor analytic technique, but yielded discrepant results. There also is a lack of research that investigates whether the clustering pattern is similar across sex and ethnic groups. This study uses confirmatory factor analysis to evaluate the factor structure of the MS and examines its similarity between men and women and across three ethnic groups (Caucasian, African, and Cuban Americans).

METHOD

A hierarchical four-factor model with an overarching MS factor uniting insulin resistance, obesity, lipid, and blood pressure factors was tested with 517 individuals from the Miami Community Health Study.

RESULTS

Findings show that the proposed structure was well supported (comparative fit index=0.97) and similar between men and women and across ethnic groups. The MS was represented strongly by insulin resistance, followed by obesity, lipid factors, and, to a lesser extent, a blood pressure factor.

CONCLUSIONS

This study provides empirical support for identifying and diagnosing the MS by its component factors in a diverse population.

Plasma leptin response to oral glucose tolerance and fasting/re-feeding tests in rats with fructose-induced metabolic derangements

The aim of this study was to compare the postprandial leptin response in rats with and without metabolic syndrome induced by a fructose-enriched diet. The effect of aging and the association between variations in metabolic substrates was also evaluated. Oral glucose tolerance test (OGTT) and fasting/re-feeding test were used to evaluate the responses of leptin and to explore the dynamic relationship between endogenous leptin and metabolic substrates, including glucose, insulin and triglycerides (TG). At the 7th week, plasma leptin was unchanged in control rats after oral glucose loading. However, plasma leptin levels increased in fructose-fed rats with insulin resistant OGTT curves. At the 11th month, plasma leptin level was reduced during starvation and returned to the level prior to starvation during re-feeding in control rats. In contrast, the starvation-induced reduction in leptin showed a potentially larger rebound effect during re-feeding in fructose-fed rats. Analysis of covariance demonstrated that there alone was no interactive effect of dietary manipulation between leptin and TG, suggesting that fructose diet-induced insulin resistance-related metabolic syndrome may concomitantly elevate leptin and TG. Furthermore, multiple regression analysis suggests TG was the primary correlative determinant of endogenous leptin concentration. Our data showed that there are different patterns of leptin response to OGTT and fasting/re-feeding tests in rats with and without metabolic syndrome. The results suggest that these effects may be related to a TG-mediated impairment of leptin function and a protective mechanism to reduce lipid-induced tissue damage in patients with metabolic syndrome.

The metabolic syndrome and cardiovascular disease

The metabolic syndrome, which is very common in the general population, is defined by the clustering of several classic cardiovascular risk factors, such as type 2 diabetes, hypertension, high triglycerides and low high-density lipoprotein cholesterol (HDL). Central obesity and insulin resistance, which are the two underlying disorders of the syndrome, are further risk factors for cardiovascular disease. Moreover, a panel of novel (non-traditional) risk factors are ancillary features of the metabolic syndrome. They include biomarkers of chronic mild inflammation (e.g. C-reactive protein, CRP), increased oxidant stress (e.g. oxidized low density lipoprotein, LDL), thrombophilia (e.g. plasminogen activator inhibitor-1, PAI-1) and endothelial dysfunction (e.g. E-selectin). Therefore, subjects with the metabolic syndrome are potentially at high risk of developing atherosclerosis and clinical cardiovascular events.In recent years several longitudinal studies have confirmed that subjects with the metabolic syndrome present with atherosclerosis and suffer from myocardial infarction and stroke at rates higher than subjects without the syndrome. The risk of cardiovascular disease (CVD) is particularly high in women with the syndrome and in subjects with pre-existing diabetes, CVD and/or high CRP. However, an increased risk is already present in subjects with a cluster of multiple mild abnormalities. The risk related to the metabolic syndrome is definitely higher when subjects affected are compared to subjects free of any metabolic abnormality.

Influence of the metabolic syndrome on aortic stiffness in never treated hypertensive patients

BACKGROUND AND AIM

Metabolic syndrome (MS) carries an increased risk for cardiovascular events and there is a growing awareness that large artery stiffening is a powerful predictor of cardiovascular morbidity and mortality. Little is known about the relationship of MS with aortic stiffness. The aim of our study was to analyze, in patients with essential hypertension, the influence of MS, defined according to the criteria proposed by the Third Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (NCEP-ATP III), on carotid-femoral pulse wave velocity (PWV), a measure of aortic stiffness.

METHODS

Ninety-three untreated essential hypertensives, aged between 23 and 61 years, without diabetes mellitus, were studied. All subjects underwent routine blood chemistry, oral glucose tolerance test with glucose and insulin determinations, albumin excretion rate (AER) measurement, 24-h ambulatory blood pressure monitoring, and measurement of carotid-femoral PWV, by means of a computerized method.

RESULTS

Patients with MS (n = 28) showed higher age-adjusted carotid-femoral PWV (10.1 +/- 1.4 vs 9.3 +/- 1.4 m/s; p = 0.01) when compared to subjects without MS. This difference held after controlling for gender and for 24-h mean blood pressure (MBP) (p = 0.02) and lost its statistical significance after further adjustment for AER. In a multiple regression model, excluding the individual components of MS, in which metabolic syndrome was added along with age, gender, smoking habit, LDL cholesterol, HOMA index, 24-h MBP and 24-h heart rate, MS remained independently associated with carotid-femoral PWV (beta = 0.29; p = 0.002). The statistical significance of this association disappeared after the inclusion into this model of AER.

CONCLUSIONS

Metabolic syndrome is associated with an increased aortic stiffness. Main explanatory factors of this association are age, systolic blood pressure and albumin excretion rate.

Homeostatic model assessment (HOMA) index cut-off values to identify the metabolic syndrome in children

The aim of the study was to establish the best cut-off value for the homeostatic model assessment (HOMA) index in identifying children and adolescents with the metabolic syndrome. The study included 72 non-obese and 68 obese children aged 7 to 16 years. Obesity is defined using the criteria proposed by Cole et al., being included as metabolic syndrome variables waist circumference, systolic blood pressure, diastolic blood pressure and seric values of glucose, uric acid, fasting insulin, leptin, triglycerides and HDL-cholesterol. Children were considered as having the metabolic syndrome when four or more characteristics showed abnormal values. The HOMA index was calculated as the product of the fasting plasma insulin level (microU/mL) and the fasting plasma glucose level (mmol/L), divided by 22.5. HOMA index cut-offs from the 5th to the 95th percentile were used. A receiver operating characteristic (ROC) curve was generated using the different HOMA cut-offs for the screening of the metabolic syndrome. The areas under the ROC curve, 95% confidence intervals, and the point to the ROC curve closest to 1, were calculated. The area under the ROC curve was 0.863 (95% C.I.: 0.797, 0.930). The point closest to 1 corresponds to the 60th percentile of the HOMA index distribution in our sample. HOMA index value at the 60th percentile was 2.28. Cut-off values corresponding to a range of HOMA index from the 50 to the 75 percentile, showed similar distances to 1. HOMA index values for percentiles 50 to 75 ranged from 2.07 to 2.83. In conclusion, HOMA index could be a useful tool to detect children and adolescents with the metabolic syndrome. HOMA cut-off values need to be defined in the paediatric population; however, values near to 3 seem to be adequate.

Atorvastatin reduces serum leptin concentration in hypercholesterolemic rabbits

BACKGROUND

Leptin may play an important role in the development of atherosclerosis. We evaluated the effect of atorvastatin on leptin secretion in vivo and in vitro.

METHODS

Sixteen rabbits fed with high-cholesterol diet for 8 weeks were randomly divided into 2 groups: (1) high cholesterol diet for 6 weeks (n=8), and (2) the same cholesterol diet plus atorvastatin (2.5 mg/kg/day) for 6 weeks (n=8). A control group (n=5) was fed with normal diet for 14 weeks. Subcutaneous adipose was collected for RNA analysis. The direct effect of atorvastatin on leptin release was assayed in primary rabbit adipocytes. Leptin levels in serum and adipocytes culture supernatant were measured by ELISA. RT-PCR was used to evaluate leptin mRNA expressions in adipose and adipocytes.

RESULTS

Compared with control group, rabbits fed with high cholesterol diet showed higher levels of serum total cholesterol, LDL cholesterol and leptin, all of which were significantly reduced by atorvastatin treatment. Leptin mRNA expression of adipose was significant lower in rabbits treated with atorvastatin than those fed with high cholesterol diet continuously (0.81+/-0.31 vs. 1.23+/-0.36, P<0.05). Atorvastatin dose-dependently inhibited leptin secretion and mRNA expression in cultured adipocytes.

CONCLUSION

Atorvastatin can inhibit leptin release and mRNA expression, and reduces serum leptin level in hypercholesterolemic rabbits.

Leptin resistance extends to the coronary vasculature in prediabetic dogs and provides a protective adaptation against endothelial dysfunction

Hyperleptinemia, associated with prediabetes, is an independent risk factor for coronary artery disease and a mediator of coronary endothelial dysfunction. We previously demonstrated that acutely raising the leptin concentration to levels comparable with those observed in human obesity significantly attenuates coronary dilation/relaxation to acetylcholine (ACh) both in vivo in anesthetized dogs and in vitro in isolated canine coronary rings. Accordingly, the purpose of this investigation was to extend these studies to a model of prediabetes with chronic hyperleptinemia. In the present investigation, experiments were conducted on control and high-fat-fed dogs. High-fat feeding caused a significant increase (131%) in plasma leptin concentration. Furthermore, in high-fat-fed dogs, exogenous leptin did not significantly alter vascular responses to ACh in vivo or in vitro. Coronary vasodilator responses to ACh (0.3–30.0 μg/min) and sodium nitroprusside (1.0–100.0 μg/min) were not significantly different from those observed in control dogs. Also, high-fat feeding did not induce a switch to an endothelium-derived hyperpolarizing factor as a major mediator of muscarinic coronary vasodilation, because dilation to ACh was abolished by combined pretreatment with Nω-nitro-l-arginine methyl ester (150 μg/min ic) and indomethacin (10 mg/kg iv). Quantitative, real-time PCR revealed no significant difference in coronary artery leptin receptor gene expression between control and high-fat-fed dogs. In conclusion, high-fat feeding induces resistance to the coronary vascular effects of leptin, and this represents an early protective adaptation against endothelial dysfunction. The resistance is not due to altered endothelium-dependent or -independent coronary dilation, increased endothelium-derived hyperpolarizing factor, or changes in coronary leptin receptor mRNA levels.

Effects of exercise on metabolic risk variables in overweight postmenopausal women: a randomized clinical trial

OBJECTIVE

This study examined the effects of exercise on metabolic risk variables insulin, leptin, glucose, and triglycerides in overweight/obese postmenopausal women.

RESEARCH METHODS AND PROCEDURES

Sedentary women (n = 173) who were overweight or obese (BMI > or = 25 kg/m(2) or > or =24 kg/m(2) with > or =33% body fat), 50 to 75 years of age, were randomized to 12 months of exercise (> or =45 minutes of moderate-intensity aerobic activity 5 d/wk) or to a stretching control group. Body composition (DXA) and visceral adiposity (computed tomography) were measured at baseline and 12 months. Insulin, glucose, triglycerides, and leptin were measured at baseline and 3 and 12 months. Insulin resistance was evaluated by the homeostasis model assessment formula. Differences from baseline to follow-up were calculated and compared across groups.

RESULTS

Exercisers had a 4% decrease and controls had a 12% increase in insulin concentrations from baseline to 12 months (p = 0.0002). Over the same 12-month period, leptin concentrations decreased by 7% among exercisers compared with remaining constant among controls (p = 0.03). Homeostasis model assessment scores decreased by 2% among exercisers and increased 14% among controls from baseline to 12 months (p = 0.0005). The exercise effect on insulin was modified by changes in total fat mass (trend, p = 0.03), such that the exercise intervention abolished increases in insulin concentrations associated with gains in total fat mass.

DISCUSSION

Regular moderate-intensity exercise can be used to improve metabolic risk variables such as insulin and leptin in overweight/obese postmenopausal women. These results are promising for health care providers providing advice to postmenopausal women for lifestyle changes to reduce risk of insulin resistance, coronary heart disease, and diabetes.

Lifestyle modification improves risk factors in type 2 diabetes relatives

AIMS

To investigate the short-term (16 weeks) effect of lifestyle intervention on insulin sensitivity, anthropometric and metabolic variables in non-diabetic first-degree relatives of type 2 diabetic patients (FDR).

METHODS

Seventy-seven (49 male, 28 female) FDR were allocated to one of three groups, diet (D-group; n = 25), diet and exercise (DE-group; n = 30) or control group (C-group; n = 22). Lifestyle counselling was based on current nutrition recommendations, including increased intake of fatty fish and low glycaemic index foods. Group counselling was given on two occasions with follow-up through telephone interviews every 10 days. Assessments included insulin sensitivity index (Si), anthropometry, lipid parameters, circulating leptin and adiponectin levels.

RESULTS

The D-group reduced total cholesterol (-0.31 mmol/l, P = 0.024), LDL cholesterol (-0.22 mmol/l, P = 0.021) and apolipoprotein B (-9.5 mg/dl, P = 0.009) levels, whereas the DE-group decreased body weight (-2.1%, P = 0.030) and waist circumference (-3.0 cm, P < 0.001) versus controls. A 13% reduction in fasting insulin was observed in the DE-group, but no significant improvement in Si in D-group or DE-group was observed. A subgroup, adherent to diet and who increased exercise, significantly improved Si and lipid profile.

CONCLUSIONS

The improved metabolic risk profile in FDR suggests that lifestyle changes can be effective in individuals at high risk to develop type 2 diabetes and cardiovascular disease.

Serum leptin and myocardial infarction in hypertension

The adipose tissue-derived hormone leptin is among the physiologic processes involved in cardiovascular regulation. The aim of the present study was to elucidate if serum leptin may predict cardiovascular risk, particularly myocardial infarction (MI), in hypertensive men and women. In a prospective study cohort of hypertensive men and women, serum leptin was compared in 171 patients with MI and in 342 matched controls. The mean serum concentration of leptin was 25.1 +/- 20.0 ng/ml in the MI patients and 20.0 +/- 16.6 ng/ml in the controls (p = 0.007). The association between serum leptin and MI was independent of traditional risk factors. Leptin concentrations were higher in women than in men. In women, serum leptin was the most important predictor of MI. The present study indicates that serum leptin is associated with MI in a hypertensive population. Leptin concentrations may be of practical importance when estimating the risk of MI, especially in women, where leptin was found to be the most important predictor for MI.

Leptin and the metabolic syndrome in Korean adolescents: factor analysis

BACKGROUND

The objectives of this study were to evaluate the relationships of leptin with the metabolic syndrome and to examine leptin's role in clustering of the metabolic components among Korean adolescents.

METHODS

A cross sectional study was carried out in 68 male and 80 female adolescents aged 13-18 years in an urban area of South Korea. Anthropometric variables were measured and blood pressure, fasting plasma glucose, low-density lipoprotein cholesterol, triglyceride, high-density lipoprotein cholesterol, and serum leptin were obtained.

RESULTS

As more metabolic components were clustered, body mass index, body fat, waist circumference, and serum leptin levels were significantly increased. Principal components factor analysis revealed three factors in males and females that explained 70% and 65%, respectively, of the observed variance of the 10 measured variables. These were obesity-leptin-lipid factor, blood pressure factor, and glucose-cholesterol factor in males and obesity-leptin-glucose factor, blood pressure factor, and cholesterol factor in females. Leptin loaded on only one factor in both genders.

CONCLUSION

Leptin did not appear to have a major role linking various components of the metabolic syndrome, even though it was strongly associated with obesity indices. Gender difference of linking of leptin with glucose or lipid was observed. There seems to be more than one pathophysiological mechanism which might underlie full expression of the metabolic syndrome among Korean adolescents.

The association of coronary calcium score and conventional cardiovascular risk factors in Type 2 diabetic subjects asymptomatic for coronary heart disease (The PREDICT Study)

AIM

To determine the association between coronary calcification score (CACS) obtained by electron beam computed tomography (EBCT) and cardiovascular risk factors in Type 2 diabetic subjects entered into a prospective cohort study.

METHODS

Type 2 diabetic subjects attending routine hospital diabetic clinics without known coronary heart disease (CHD) underwent EBCT to measure CACS. Demographic data were obtained and conventional cardiovascular risk factors were measured at baseline.

RESULTS

Four hundred and ninety-five subjects were assessed of whom 67.7% were male. They had a mean (SD) age of 62.9 (7.1) years, with median (inter-quartile range) duration of diabetes of 8 (4-13) years. None had a history of coronary artery disease. Forty-five per cent were receiving lipid-lowering agents (including 36% statins). In a univariate analysis, there were significant associations between increased CACS and age, duration of diabetes, male gender, waist-hip ratio (WHR), systolic blood pressure, and the use of statins. In a multivariate model adjusting for the possible interaction of these and other factors, the significant association between CACS and WHR, systolic blood pressure, male gender and statin use remained.

CONCLUSIONS

The close association between CACS and WHR and the association with systolic blood pressure suggest that coronary calcification may be particularly linked to the metabolic syndrome in Type 2 diabetes.

Relation of serum leptin and insulin-like growth factor-1 levels to intima-media thickness and functions of common carotid artery in children and adolescents with type 1 diabetes

BACKGROUND AND AIM

Leptin and insulin-like growth factor-1 (IGF-1) have been suggested to be involved in the pathogenesis of atherosclerosis. The aim of this study was to evaluate the relationship between serum leptin, IGF-1 and intima-media thickness (IMT) and functions of common carotid artery (CCA) in children and adolescent patients with type 1 diabetes.

MATERIAL AND METHODS

Serum leptin and IGF-1 levels were measured in 45 diabetic patients (23 girls and 22 boys). Age, diabetes duration as well as major cardiovascular risk factors, including anthropometric and metabolic parameters, were matched between girls and boys. The relation of serum leptin and IGF-1 levels to CCA structure and functions were measured by ultrasonography as IMT, cross-sectional compliance (CSC), cross-sectional distensibility (CSD), diastolic wall stress (DWS) and incremental elastic modulus (IEM).

RESULTS

Serum leptin levels of diabetic girls were higher than those in the boys (21.8 +/- 14.5 microg/l vs 8.9 +/- 10.6 micro/l, p = 0.002). However, the difference for serum IGF-I levels was not significant between diabetic girls and boys (240.7 +/- 96.8 ng/ml vs 234.7 +/- 93.2 ng/ml; p > 0.05). In all subjects, leptin levels were correlated with CSC (p = 0.04), CSD (p = 0.04) and IEM (p = 0.01), and IGF-1 levels were only correlated with CSC (p = 0.01). Leptin did not show any correlation with ultrasonographic measurements in both girls and boys separately. IGF-1 was correlated with CSC (p = 0.001), CSD (p = 0.002) and IEM (p < 0.001) in boys but not in girls. In a multivariate regression model, IGF-1 emerged as independent correlates for mean CSD and IEM in boys but not in girls.

CONCLUSION

Serum leptin and IGF-1 levels in children and adolescent patients with type 1 diabetes are associated with functions of common carotid artery, and the association of IGF-1 levels is influenced by sex.

Obesity, adipocytokines, and insulin resistance in breast cancer

The adipocytokines are biologically active polypeptides that are produced either exclusively or substantially by the adipocytes, and act by endocrine, paracrine, and autocrine mechanisms. Most have been associated with obesity, hyperinsulinaemia, type 2 diabetes, and chronic vascular disease; in addition, six adipocytokines--vascular endothelial growth factor, hepatocyte growth factor, leptin, tumour necrosis factor-alpha, heparin-binding epidermal growth factor-like growth factor, and interleukin-6--promote angiogenesis while one, adiponectin, is inhibitory. Obesity and insulin resistance have both been identified as risk factors for breast cancer and are associated with late-stage disease and poor prognosis. Angiogenesis is essential for breast cancer development and progression, and so it is plausible that obesity-related increases in adipocytokine production and a reduction in adiponectin may adversely affect breast cancer outcome by their angiogenesis-related activities. There is also experimental evidence that some adipocytokines can act directly on breast cancer cells to stimulate their proliferation and invasive capacity. Thus, adipocytokines may provide a biological mechanism by which obesity and insulin resistance are causally associated with breast cancer risk and poor prognosis. Both experimental and clinical studies are needed to develop this concept, and particularly in oestrogen-independent breast cancers where preventive and therapeutic options are limited.

Leptin, obesity and cardiovascular disease

PURPOSE OF REVIEW

Obesity is a risk factor for cardiovascular diseases. Leptin levels are increased in obesity and leptin exhibits cardiovascular actions that may contribute to increased cardiovascular risk. We review the sympathetic, renal and vascular actions of leptin and their relevance to cardiovascular disease.

RECENT FINDINGS

Leptin possesses cardio-renal actions potentially contributing to obesity-related hypertension including generalized sympathoactivation. However, given that leptin resistance occurs in obesity, it has been difficult to link hyperleptinemia with hypertension. One possibility is that leptin resistance is confined to the metabolic effects of leptin, with preservation of its sympathoexcitatory actions. Other mechanisms may contribute to the pressor effects of leptin. For instance, angiotensin II induces leptin generation. Leptin also potentiates the pressor effect of insulin. Therefore, interactions between angiotensin II and insulin with leptin could have deleterious cardiovascular effects in obesity. Additionally, leptin appears to stimulate vascular inflammation, oxidative stress and hypertophy. These actions may contribute to the pathogenesis of hypertension, atherosclerosis, and left ventricular hypertrophy.

SUMMARY

The potential actions of leptin in the pathophysiology of cardiovascular complications of obesity are diverse, despite evidence of leptin resistance to its metabolic actions. However, most information about cardiovascular actions of leptin derives from in-vitro and animal studies. Future research in humans is widely awaited.

Plasma leptin is associated with insulin resistance independent of age, body mass index, fat mass, lipids, and pubertal development in nondiabetic adolescents

OBJECTIVE

The rising epidemic worldwide in overweight and obese children requires urgent attention. Leptin has been found to be associated with body weight control and possibly affects insulin sensitivity. Since insulin resistance is associated with obesity in adults and possibly in adolescents, we set out to investigate the association of plasma leptin level with various anthropometric indices, body fat mass (FM), lipids, and insulin resistance (IR) index in nondiabetic adolescents.

DESIGN

A cross-sectional study from three high schools in Taipei City in Taiwan.

SUBJECTS

A total of 402 nondiabetic subjects (162 boys and 240 girls; age range, 10-19 y; mean age, 15.8+/-1.9 y, and mean body mass index (BMI), 24.8+/-4.6 kg/m(2)) were recruited.

MEASUREMENTS

The fasting plasma leptin, plasma glucose, insulin, lipids, and anthropometric indices including height, weight, waist (WC) and hip circumferences, and waist-to-hip ratio (WHR) were examined. Total body FM and percentage body fat (FM%) were obtained from dual-energy X-ray absorptiometry. The homeostasis model was applied to estimate the degree of IR.

RESULTS

The plasma leptin levels were significantly higher in girls (17.45+/-10.13 ng/ml) than boys (8.81+/-6.71 ng/ml, P<0.001). The plasma leptin levels were positively correlated to BMI, WC, WHR, FM, FM%, and triglycerides (TG). The IR index was positively correlated to BMI, WC, WHR, FM, FM%, TG, and leptin. Using the multivariate linear regression models, we found that plasma leptin remains significantly associated with IR index even after adjusting for age, gender, BMI, FM, WC, Tanner stage, and TG.

CONCLUSION

Plasma leptin was associated with IR index independent of age, gender, BMI, FM, WC, Tanner stage, and TG. Plasma leptin levels in adolescents could be a predictor for the development of the metabolic syndrome disorders and cardiovascular diseases.

Circulating leptin is associated with oxidized LDL in postmenopausal women

Recently, leptin has been suggested as a possible cause of atherosclerotic disease. In the present study, we have investigated in postmenopausal women (n = 60; age: 52 +/- 13) the relationship between circulating levels of leptin, oxidized LDL (Ox-LDL) and other biochemical and anthropometric variables of atherosclerotic risk. In addition, we have evaluated soluble thrombomodulin (sTM) as a marker of endothelial damage. An additional study was conducted in a subgroup of obese subjects to determine the short-term effects of weight loss on selected variables. Ox-LDL showed a positive correlation with leptin circulating levels (r = 0.65, P < 0.0001). A significant association was also found between Ox-LDL and body mass index (r = 0.69, P < 0.0001), waist-to-hip ratio (r = 0.50, P < 0.0001), insulin levels (r = 0.65, P < 0.0001), HOMA index (r = 0.55, p < 0.0001) and sTM (r = 0.74, P < 0.0001) levels. After multivariate regression analysis leptin was still related to Ox-LDL levels (P = 0.007). In obese women who completed the program of weight reduction, leptin changes persisted as a significant predictor of plasma changes in Ox-LDL levels. These findings suggested a novel link between leptin and Ox-LDL, possibly involved in atherosclerotic disease.

Metabolic and inflammation variable clusters and prediction of type 2 diabetes: factor analysis using directly measured insulin sensitivity

Factor analysis, a multivariate correlation technique, has been used to provide insight into the underlying structure of the metabolic syndrome. The majority of previous factor analyses, however, have used only surrogate measures of insulin sensitivity; very few have included nontraditional cardiovascular disease (CVD) risk factors such as plasminogen activator inhibitor (PAI)-1, fibrinogen, and C-reactive protein (CRP); and only a limited number have assessed the ability of factors to predict type 2 diabetes. The objective of this study was to investigate, using factor analysis, the clustering of metabolic and inflammation variables using data from 1,087 nondiabetic participants in the Insulin Resistance Atherosclerosis Study (IRAS) and to determine the association of these clusters with risk of type 2 diabetes at follow-up. This study includes information on directly measured insulin sensitivity (S(i)) from the frequently sampled intravenous glucose tolerance test among African-American, Hispanic, and non-Hispanic white subjects aged 40-69 years. Principal factor analysis of data from nondiabetic subjects at baseline (1992-1994) identified three factors, which explained 28.4, 7.4, and 6% of the total variance in the dataset, respectively. Based on factor loadings of >or= 0.40, these factors were interpreted as 1) a "metabolic" factor, with positive loadings of BMI, waist circumference, 2-h glucose, log triglyceride, and log PAI-1 and inverse loadings of log S(i) + 1 and HDL; 2) an "inflammation" factor, with positive loadings of BMI, waist circumference, fibrinogen, and log CRP and an inverse loading of log S(i) + 1; and 3) a "blood pressure" factor, with positive loadings of systolic and diastolic blood pressure. The results were similar within strata of ethnicity, and there were only subtle differences in sex-specific analyses. In a prospective analysis, each of the factors was a significant predictor of diabetes after a median follow-up period of 5.2 years, and each factor remained significant in a multivariate model that included all three factors, although this three-factor model was not significantly more predictive than models using either impaired glucose tolerance or conventional CVD risk factors. Factor analysis identified three underlying factors among a group of inflammation and metabolic syndrome variables, with insulin sensitivity loading on both the metabolic and inflammation variable clusters. Each factor significantly predicted diabetes in multivariate analysis. The findings support the emerging hypothesis that chronic subclinical inflammation is associated with insulin resistance and comprises a component of the metabolic syndrome.

Relation Between Leptin and the Metabolic Syndrome in Elderly Women

BACKGROUND

Leptin has been shown to be linked to adiposity and insulin resistance in middle-aged participants. However, the association between leptin and metabolic syndrome independently of body fat and body fat distribution has not been evaluated in healthy elderly people.

METHODS

We studied the independent relation between leptin and the components of the metabolic syndrome in 107 women aged 67-78 years with body mass index (BMI) ranging from 18.19 to 36.16 kg/m2. In all participants, we evaluated BMI, waist and hip circumferences, body composition by dual energy X-ray absorptiometry, fasting, and 2-hour glucose, lipids, insulin, homeostasis model assessment of insulin resistance (HOMA), systolic (SBP), diastolic blood pressure (DBP), and leptin.

RESULTS

Significant correlation was found between leptin, BMI, waist circumference, fat mass, DBP, SBP, cholesterol, triglycerides, insulin, and HOMA. After adjusting for age and waist circumference, as well for age and fat mass, leptin was significantly related to insulin levels, HOMA, and cholesterol. In a stepwise multiple regression analysis using insulin levels or HOMA as dependent variables and age, waist circumference, fat mass, leptin, SBP, DBP, cholesterol, and triglycerides as independent variables, leptin entered the regression first, waist circumference second, and age third.

CONCLUSION

Our study shows that leptin is significantly related to indices of adiposity in elderly women, and leptin is significantly associated with insulin levels, HOMA, and cholesterol independent of age, body fat, and fat distribution. Leptin, waist circumference, and age together explained 31% and 33% of insulin levels and HOMA variance, respectively, in healthy elderly women.

Breast cancer and obesity: an update

Obesity has a complicated relationship to both breast cancer risk and the clinical behavior of the established disease. In postmenopausal women, particularly the elderly, various measures of obesity have been positively associated with risk. However, before menopause increased body weight is inversely related to breast cancer risk. In both premenopausal and postmenopausal breast cancer, the mechanisms by which body weight and obesity affect risk have been related to estrogenic activity. Obesity has also been related to advanced disease at diagnosis and with a poor prognosis in both premenopausal and postmenopausal breast cancer. Breast cancer in African-American women, considering its relationship to obesity, exhibits some important differences from those described in white women, although the high prevalence of obesity in African-American women may contribute to the relatively poor prognosis compared with white American women. Despite the emphasis on estrogens to explain the effects of obesity on breast cancer, other factors may prove to be equally or more important, particularly as they relate to expression of an aggressive tumor phenotype. Among these, this review serves to stress insulin, insulin-like growth factor-I, and leptin, and their relationship to angiogenesis, and transcriptional factors.

Leptin increase is associated with markers of the hemostatic system in obese healthy women

BACKGROUND

Leptin, a hormone secreted by the adipose tissue, might be a link between obesity and increased morbidity for cardiovascular disease. Leptin exerts proinflammatory, pro-angiogenic actions by activating a specific receptor (Ob-Rb) which is expressed in human endothelial cells. Thus, a link may exist between leptin expression and endothelial dysfunction.

OBJECTIVES

We sought to determine whether in obese women there is a correlation between leptin levels, endothelial perturbation and coagulative activation.

METHODS

Circulating levels of leptin, von Willebrand Factor (VWF), factor (F)VIIa, prothrombin fragment 1 + 2 (F1+2), were measured in 51 non-diabetic, obese women and in 51 normal-weight subjects, using immunoenzymatic assays.

RESULTS

Obese women had significantly higher levels of leptin, VWF, FVIIa, F1+2 compared with healthy women. Simple correlation coefficients showed significant correlation between leptin and either VWF, FVIIa, or F1+2 concentrations. A multiple linear regression analysis, performed to quantify further the relationship between leptin levels and the above-mentioned variables as well as the inflammatory marker C-reactive protein (CRP) and including age, body mass index (BMI), waist-hip ratio (WHR) and lipid parameters as potential confounders, revealed that only FVIIa and VWF were independently related to leptin levels. Reduction in adipose tissue after weight loss resulted in a decrease in both circulating leptin and endothelial and coagulative activation markers.

CONCLUSIONS

We suggest that leptin might have pro-atherogenic effects in vivo, with a mechanism involving endothelial cell activation.

Serum leptin is elevated in Saudi Arabian patients with metabolic syndrome and coronary artery disease

AIMS

To compare plasma leptin in Saudi subjects with Type 2 diabetes and coronary heart disease (CHD) with non-diabetic control subjects and to examine the relationship of plasma leptin to other CHD risk factors.

RESEARCH DESIGN AND METHOD

Serum leptin concentrations were measured in 144 Saudi men. Subjects studied included 59 with Type 2 diabetes mellitus [BMI 27.5 (3.7) kg/m2 mean (sd)], 34 with coronary heart disease [BMI 29.6 (1.8) kg/m2], and 51 non-diabetic controls [BMI 28.0 (3.5) kg/m2]. There was no significant difference in BMI between the groups. Fasting serum leptin, lipids, insulin, apolipoproteins and glucose were measured. BMI, blood pressure; smoking habit and age were also recorded. Insulin resistance was assessed using the HOMA model.

RESULTS

Leptin concentrations were significantly higher in diabetic and CHD patients than in controls (P = 0.024 and 0.016, respectively). Multiple regression analysis showed that body weight (P < 0.0006), serum triglyceride concentration (P = 0.046) and systolic blood pressure (P = 0.013) were all significantly related to the logarithm of the serum leptin concentration (R2 = 0.549) in CHD patients. A subgroup analysis, comparing those patients who had the metabolic syndrome, as defined by WHO, with controls, showed higher serum leptin in those with metabolic syndrome (P = 0.05).

CONCLUSIONS

Serum leptin is increased in Saudi subjects with diabetes mellitus, metabolic syndrome and CHD. Leptin may be a marker of risk of CHD, at least in men, and contribute to the CHD risk profile in subjects with insulin resistance. Further studies are needed to evaluate this relationship prospectively.

Insulin resistance induces hyperleptinemia, cardiac contractile dysfunction but not cardiac leptin resistance in ventricular myocytes

Insulin resistance is a metabolic syndrome commonly seen in obesity. Leptin, the obese gene product, plays a role in the regulation of cardiac function. Elevated leptin levels have been demonstrated under insulin-resistant states such as obesity and hypertension, although their role in cardiac dysfunction is unknown. This study was designed to determine the impact of prediabetic insulin resistance on leptin levels and leptin-induced cardiac contractile response. Whole-body insulin resistance was generated with a 10-week dietary sucrose feeding. Contractile and intracellular Ca(2+) properties were evaluated in ventricular myocytes using an IonOptix system. The contractile indices analyzed included peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90)), maximal velocity of shortening/relengthening (+/-dL/dt), fura-fluorescence intensity change (deltaFFI) and decay rate (tau). Sucrose-fed rats displayed significantly elevated body weight and plasma leptin levels, depressed PS, +/-dL/dt, shortened TPS, prolonged TR(90) and tau, as well as reduced deltaFFI compared to the starch-fed control group. Leptin (1-1000 nM) elicited a concentration-dependent depression of PS and deltaFFI in myocytes from both starch and sucrose groups. Leptin-induced contractile depression was abolished by the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyle ester, elevation of the extracellular Ca(2+) concentration, the Janus activated kinase 2 inhibitor AG-490 or the mitogen activated protein kinase inhibitor SB203580 in myocytes from both sucrose and starch groups. Moreover, AG-490 and SB203580 unmasked a positive response of PS in myocytes from both groups. These data indicate that insulin resistance directly induces hyperleptinemia and cardiac contractile dysfunction, without affecting leptin-mediated cardiac contractile function at the myocyte level.

Metabolic Syndrome: epidemiology and more extensive phenotypic description. Cross-sectional data from the Bruneck Study

OBJECTIVES

The present study aimed at evaluating the prevalence of the Metabolic Syndrome and at identifying its additional clinical features.

RESEARCH DESIGN AND METHODS

Within a prospective population-based survey examining 888 subjects aged 40-79 y, subjects were identified fulfilling the WHO and the National Cholesterol Education Program-Adult Treatment Panel III (NCEP-ATPIII) criteria for diagnosing the Metabolic Syndrome. In these subjects and in the rest of the sample (controls), several metabolic and nonmetabolic biochemical parameters were compared.

RESULTS

The prevalence of the Metabolic Syndrome by WHO criteria was 34.1% (95% CI 31.0-37.2) and by NCEP-ATPIII criteria 17.8% (15.5-20.3). The prevalence was significantly higher in older subjects and in those less physically active. Subjects with the Metabolic Syndrome either by WHO or by NCEP-ATPIII criteria showed higher levels of oxidized low-density lipoprotein, apolipoprotein B, urate, leptin, fibrinogen, leukocytes, erythrocyte sedimentation rate, GOT, gamma-GT and soluble endothelial adhesion molecules (E-selectin, vascular adhesion molecule-1 and intercellular adhesion molecule-1) and lower apolipoprotein A concentrations. Insulin resistance, as assessed by the Homeostasis Model Assessment, increased with the increase in the number of traits composing the syndrome found within the single individual. Subjects with insulin resistance had more pronounced abnormalities in several parameters, including the additional features of the syndrome (eg fibrinogen and soluble adhesion molecules).

CONCLUSIONS

The Metabolic Syndrome occurs very frequently in the general population aged 40-79 y, and is associated with several additional metabolic and nonmetabolic abnormalities that likely contribute to an increased cardiovascular risk. Insulin resistance seems to play a major role in classic and additional abnormalities featuring the Metabolic Syndrome.

The association between leptin and left ventricular hypertrophy: a population-based cross-sectional study

BACKGROUND AND OBJECTIVES

Plasma leptin levels have been shown to be an independent risk factor for cardiovascular disease. Leptin has been shown to have sympathetic and vascular effects, and may increase cardiovascular risk through increased blood pressure, left ventricular hypertrophy, or atherosclerotic mechanisms. This study examines whether leptin levels, independent of body mass and insulin resistance, are a risk factor for hypertension and left ventricular hypertrophy.

METHODS AND PARTICIPANTS

A population-based, cross-sectional sample of 410 adults from rural Spain was studied. The correlations between plasma leptin levels and left ventricular mass index, sum of wall thicknesses, and blood pressure were calculated. Multiple linear regression analysis was used to adjust for other cardiovascular risk factors.

RESULTS

After adjusting for age, body mass index, systolic blood pressure, sex, and insulin resistance, leptin was inversely associated with left ventricular mass index (beta = -0.20, P < 0.01). Leptin was also inversely related to the sum of wall thicknesses; however, this association did not reach statistical significance (beta = -0.12, P = 0.063). Leptin was not statistically associated with blood pressure after adjusting for body mass index.

CONCLUSIONS

The results do not support the hypothesis that leptin increases cardiovascular risk by increasing left ventricular mass index or blood pressure. Other mechanisms, related to atherosclerosis, could explain the increased risk of cardiovascular diseases observed with high leptin levels.

Lean, nondiabetic Asian Indians have decreased insulin sensitivity and insulin clearance, and raised leptin compared to Caucasians and Chinese subjects

OBJECTIVE

To study and compare the insulin sensitivity of healthy, nondiabetic Asian Indians with that of two other ethnic groups (Caucasian and Chinese) living in Singapore.

DESIGN

Study of insulin sensitivity using euglycaemic hyperinsulinaemic glucose clamp.

SUBJECTS

A total of 10 healthy, lean, young male subjects of each ethnic group, matched for age, body mass index (BMI) and physical activity. They all had normal glucose tolerance and had no family history of diabetes.

MEASUREMENTS

Anthropometric parameters (BMI, waist-hip ratio (WHR) and percentage body fat (PBF)), fasting lipid profile and leptin concentration, insulin sensitivity index, and insulin clearance.

RESULTS

Healthy lean (BMI 22.1+/-1.5 kg/m(2) (mean+/-s.d.)) Indians had significantly higher fasting serum leptin (5.1+/-2.5 vs Chinese 1.0+/-0.9 vs Caucasian 2.3+/-1.2 ng/ml; P<0.001), lower insulin sensitivity index (9.9+/-3.3 vs Chinese 14.1+/-3.5 vs Caucasian 18.8+/-9.2 mg/min kg fat-free mass/microU/ml; P<0.002), and lower insulin clearance (461.4+/-54.8 vs Chinese 621.0+/-99.3 vs Caucasian 646.9+/-49.2 ml/min m(2); P<0.001). Indians also had a higher PBF (26.5+/-5.2 vs Chinese 19.5+/-2.2 vs Caucasians 22.9+/-1.4%; P<0.001), diastolic blood pressure (P=0.036), fasting insulin (P<0.006) and fasting triglyceride (P=0.022). Stepwise regression analysis showed that ethnicity was the only significant independent determinant variable for the differences in insulin sensitivity index (P=0.008).

CONCLUSION

Healthy lean nondiabetic Indians were more insulin resistant compared to other ethnic groups despite the similarity in living environment. These findings may warrant preventive health-care strategies for type II diabetes and coronary artery disease to target Indians at an earlier stage compared to other ethnic groups.

Soluble leptin receptor and soluble receptor-bound fraction of leptin in the metabolic syndrome

OBJECTIVE

In obesity, plasma leptin is high and soluble leptin receptor (sOb-R) levels are low, resulting in a low fraction of bound leptin. The aim of this study was to investigate the influence of insulin resistance (IR) and the metabolic syndrome (MS) on sOb-R concentration and the bound-free ratio of leptin.

RESEARCH METHODS AND PROCEDURES

sOb-R, leptin levels, and homeostasis model assessment (HOMA) index for IR were determined in 76 middle-aged obese or overweight men.

RESULTS

Concentration of sOb-R and soluble receptor-bound fraction of leptin were lowest in the highest tertile of HOMA-IR. sOb-R and the bound-free ratio of leptin correlated with HOMA-IR, leptin concentration, and waist-to-hip ratio independently of age, BMI, and fat mass. Leptin and waist-to-hip ratio were the sole independent determinants of sOb-R concentration, and BMI, HOMA-IR, and visceral adipose tissue were independent determinants of the bound fractin of leptin. sOb-R concentration and the bound fraction of leptin decreased with increasing numbers of components of the MS, resulting in lower sOb-R concentration and a lower fraction of bound leptin in men with the MS.

DISCUSSION

IR and abdominal obesity are associated with low sOb-R concentration and low bound-free ratio of leptin independent of fat mass. Low sOb-R concentration and low bound-free ratio of leptin segregate with components of the MS. We suggest that low sOb-R levels and a low fraction of specifically bound leptin are markers of leptin resistance, which is independently associated with IR and abdominal obesity and may constitute an additional component of the MS.

Depressive symptoms and metabolic risk in adult male twins enrolled in the National Heart, Lung, and Blood Institute twin study

OBJECTIVE

To determine the extent to which depressive symptoms are associated with metabolic risk factors and whether genetic or environmental factors account for this association.

METHOD

Twin structural equation modeling was employed to estimate genetic and environmental contributions to the covariation of depressive symptoms, as indexed by the Centers for Epidemiological Studies-Depression Scale, and common variance among blood pressure, body mass index, waist-to-hip ratio, and serum triglycerides and glucose among 87 monozygotic and 86 dizygotic male twin pairs who participated in the NHLBI twin study.

RESULTS

Depressive symptoms were associated with individual components of the metabolic syndrome and common variance among the risk factors. Twin structural equation modeling indicated that the associations were attributable to environmental (nongenetic) factors.

CONCLUSIONS

These results support the hypothesis that depressive symptoms may increase risk for a pattern of physiological risk consistent with the metabolic syndrome.

Plasma leptin, fatty acids, and tumor necrosis factor-receptor and insulin resistance in children

OBJECTIVE

To evaluate the effect of plasma leptin, nonsterified fatty acids (NEFAs), and tumor necrosis factor-receptor 1 (TNFR1) on plasma insulin and insulin-resistance status in children.

RESEARCH METHODS AND PROCEDURES

One thousand thirty-two children (521 boys and 511 girls) were included in this study. We measured plasma insulin and leptin levels by radioimmunoassay, plasma NEFA levels by enzymatic acyl-coenzyme A synthase-acyl-coenzyme A oxidase spectrophotometric methods, and TNFR1 levels by enzyme-linked immunosorbent assay. We calculated insulin resistance index (IRI) using homeostasis model assessment and calculated insulin-resistance syndrome summary score (IRS) by adding the quartile ranks from the distribution of systolic blood pressure (BP), serum triglyceride, high-density lipoprotein-cholesterol (inverse), and insulin levels.

RESULTS

Overweight children had higher BP, plasma leptin, and insulin levels and higher IRI and IRS than normal-weight children. Plasma leptin and TNFR1 were positively correlated with insulin levels, IRI, and IRS. The correlation coefficients of leptin and TNFR1 in IRI were 0.53 and 0.12, respectively, for boys and 0.25 and 0.18, respectively, for girls. In multivariate regression analyses, TNFR1 was positively associated with insulin level and IRI in girls; NEFA was positively associated only with IRS. Plasma leptin levels were significantly positively associated with insulin levels, IRI, and IRS, even after adjusting for BMI and other potential confounders.

DISCUSSION

Overweight children had higher BP, plasma insulin, and leptin levels and adverse insulin-resistance status than normal-weight children. Plasma leptin levels, rather than NEFA and TNFR1, may play a significant role in the development of hyperinsulinemia and insulin resistance in children.

Risk factor clustering in the insulin resistance syndrome and its relationship to cardiovascular disease in postmenopausal white, black, hispanic, and Asian/Pacific Islander women

The aim of this study was to examine how major components of the insulin resistance (IR) syndrome relate to each other and to cardiovascular disease (CVD) in postmenopausal women in 4 ethnic groups. Baseline data from the Women's Health Initiative (WHI) on 3,083 50- to 79-year-old women (1,635 white, 802 black, 390 Hispanic, and 256 Asian/Pacific Islander) were examined. Participants underwent a personal interview and a physical examination, blood samples were drawn, and a detailed cardiovascular history was ascertained. Factor analysis was used to assess the clustering and interdependence of groups of CVD-related IR syndrome variables. Four factors were identified. An obesity factor included IR in all groups and had a significant association with CVD in white (P =.0001) and Hispanic (P =.0024) women. A dyslipidemia factor (high-density lipoprotein [HDL], triglycerides, and HDL2: total HDL ratio) also included insulin and IR and was significantly correlated with CVD in black (P=.0006) and Hispanic (P =.0217) women and had a borderline association in white women (P =.068). Total and low-density lipoprotein (LDL) cholesterol did not relate to CVD in any group. Blood pressure was related weakly to CVD in white women (P =.0434) and strongly in black women (P =.0095). Components of the IR syndrome appear to be associated with CVD in postmenopausal women, although the magnitude of these relationships differed by ethnicity.

Factor analysis of the metabolic syndrome among elderly Koreans--the South-west Seoul Study

AIMS

To examine the relationship between the components of the metabolic syndrome and to explore whether insulin resistance unifies the clustering of components of the metabolic syndrome among urban elderly Koreans using exploratory factor analysis.

METHODS

We included 1314 non-diabetic subjects over the age of 60 years, selected from a cross-sectional study, which was conducted in 1999 in Seoul, Korea. Factor analysis was carried out using the principle components analysis with Varimax orthogonal rotation of the components of the metabolic syndrome.

RESULTS

We found four major factors of cardiovascular disease risk variables in our study subjects. Impaired glucose tolerance, dyslipidaemia, hypertension and obesity aggregated as the major domain. Obesity and dyslipidaemia variables were closely related and loaded on the same factor. However, hypertension was not linked closely with other factors of the metabolic syndrome.

CONCLUSIONS

Insulin resistance is not the only contributor to the metabolic syndrome among urban elderly Koreans. Although the components of the metabolic syndrome were closely related, the finding of more than one factor suggests that more than one pathophysiological mechanism underlies full expression of the metabolic syndrome among elderly Koreans.

Relationship between high plasma leptin concentrations and metabolic syndrome in obese pre-pubertal children

OBJECTIVE

To evaluate the relationship between serum leptin levels and metabolic syndrome, fasting insulin level and anthropometric index in obese pre-pubertal children.

DESIGN

A cross-sectional study was carried out on obese children.

SUBJECTS

A study was made of 41 obese children (aged 6-9 y) and the same number of non-obese children (control group), matched by age and sex.

METHODS

Body mass index (BMI), waist/hip ratio (WHR) and blood pressure were determined in each child. Serum leptin, glucose, insulin, lipid profile, sex hormone binding globulin (SHBG), plasminogen activator inhibitor-1 (PAI-1), tissue-plasminogen activator (t-PA) and fibrinogen were all measured.

RESULTS

The serum leptin level was significantly higher in obese children (15.47 vs 4.73 ng/ml). In the obese group, leptin showed a positive correlation with BMI (P<0.001), insulin (P<0.001), triglycerides (P<0.05), PAI-1 (P<0.05) and t-PA (P<0.05), and correlated negatively with SHBG (P<0.01), apolipoprotein A-I (P<0.05) and high-density lipoproteins cholesterol (HDL-C) (P<0.05). Corrected for BMI and WHR, leptin (P partial=0.002) is only an independent predictive factor for basal insulin. Using multivariant regression analysis, only insulin (P partial=0.003) and BMI (P partial=0.018) were independent predictive factors for leptin.

CONCLUSION

For this age group, high leptin resistance may be another component of metabolic syndrome, and may be involved in its etiopathogenesis. The involvement of leptin in this syndrome may be indirect, modulating the insulin's action.

Relationships between left ventricular mass and the renin-angiotensin system, catecholamines, insulin and leptin

OBJECTIVES

Several neurohormonal systems have been suggested to stimulate myocardial cell growth, and thus take part in the development of left ventricular (LV) hypertrophy. We studied associations between LV mass and markers of the renin-angiotensin-aldosterone system (RAAS), the sympathetic nervous system, glucose homeostasis and leptin.

DESIGN

A total of 115 hypertensive patients with LV hypertrophy and two age- and gender-matched control groups consisting of 38 hypertensive patients without LV hypertrophy and 38 normotensive subjects were included. We examined determinants of the RAAS, plasma levels and 24-h urinary excretions of noradrenaline and adrenaline, plasma proinsulin, insulin, glucose, leptin and LV mass by echocardiography.

RESULTS

Plasma renin activity (PRA) and serum aldosterone were higher (both P < 0.001) in the LV hypertrophy group than in patients without LV hypertrophy and normotensive subjects (1.0 +/- 0.8, 0.2 +/- 0.2 and 0.2 +/- 0.2 ng mL(-1) h(-1), and 327 +/- 126, 269 +/- 146 and 221 +/- 80 pmol L(-1), respectively). PRA and aldosterone both related (P < 0.001) to LV mass index (r = 0.44 and 0.27, respectively). Catecholamine levels and excretions were similar in all three groups and did not relate to LV mass index. Proinsulin, insulin and leptin levels were all elevated in the hypertensive patients (P < 0.01), but proinsulin, insulin, insulin sensitivity (by the homeostasis model assessment) and leptin did not relate to LV geometry, when indexed for body size.

CONCLUSIONS

Plasma renin activity and serum aldosterone levels are elevated in hypertensive LV hypertrophy and relate to LV mass index. In addition to blood pressure, activation of the RAAS may be an important nonhaemodynamic mechanism in the control of LV hypertrophy.

Relationship between plasma leptin levels and lipid profiles among school children in Taiwan--the Taipei Children Heart Study

Leptin, an adipose tissue-derived of gene product, is important in energy metabolism. However, the role of leptin in the metabolism of lipids is still not clear in humans. The purpose of this study was to evaluate the association of plasma leptin concentrations and lipid profiles among school children in Taiwan. After multistage sampling of 85 junior high schools in Taipei, we randomly selected 1264 children (617 boys and 647 girls) aged 12-16 years for this study. We measured the anthropometric variables, lifestyle factors and biochemical parameters among these children. Anthropometric measurements included body height (BH) and weight (BW) and we calculated body mass index (BMI) as the ratio of the BW to the square of the BH, expressed in kg/m2. Plasma leptin levels were measured by radioimmunoassay. We also measured lipid profiles including serum total cholesterol (CHOL), triglyceride (TG), high density lipoprotein-cholesterol (HDL-C), apolipoprotein-A1 (Apo-A1), apolipoprotein-B (Apo-B), and lipoprotein(a) (Lp(a)) levels, and calculated low density lipoprotein-cholesterol (LDL-C) levels and CHOL to HDL-C ratio (TCHR). Girls had higher leptin, CHOL, TG, HDL-C, (LDL-C), Apo-A1, Apo-B, and Lp(a) levels and lower BMI than boys did. Plasma leptin concentrations were significantly positively correlated with TG, LDL-C, and Apo-B, but negatively with HDL-C and Apo-A1 in both the genders. Children with higher plasma leptin levels (>75th percentiles) have significantly higher TG, HDL-C, LDL-C, TCHR, and Apo-B than those with relatively lower leptin levels. In multivariate regression analyses, the association between plasma leptin level and lipid profiles (such as CHOL, TG, and Apo-B) were still significant (p < 0.05) even after adjusting for BMI among boys. However, this association became attenuated and insignificant among girls. Finally, in the model that included the standard covariates, plasma leptin was the most predictive of CHOL, TG and Apo-B levels among those school children in Taiwan. Our results suggest that plasma leptin and BMI were independently associated with the lipids and lipoprotein profiles among Taiwanese Children. In both genders, children in the top 25% of the leptin distribution have more adverse lipid and lipoprotein profiles.

Components of the "metabolic syndrome" and incidence of type 2 diabetes

The combination of insulin resistance, dyslipidemia, hypertension, and obesity has been described as a "metabolic syndrome" that is a strong determinant of type 2 diabetes. Factor analysis was used to identify components of this syndrome in 1,918 Pima Indians. Prospective analyses were conducted to evaluate associations of identified factors with incidence of diabetes. Factor analysis identified 4 factors that accounted for 79% of the variance in the original 10 variables. Each of these factors reflected a proposed component of the metabolic syndrome: insulinemia, body size, blood pressure, and lipid metabolism. Among 890 originally nondiabetic participants with follow-up data, 144 developed diabetes in a median follow-up of 4.1 years. The insulinemia factor was strongly associated with diabetes incidence (incidence rate ratio [IRR] for a 1-SD difference in factor scores = 1.81, P < 0.01). The body size and lipids factors also significantly predicted diabetes (IRR 1.52 and 1.37, respectively, P < 0.01 for both), whereas the blood pressure factor did not (IRR 1.11, P = 0.20). Identification of four unique factors with different associations with incidence of diabetes suggests that the correlations among these variables reflect distinct metabolic processes, about which substantial information may be lost in the attempt to combine them into a single entity.

Leptin activates cardiac fatty acid oxidation independent of changes in the AMP-activated protein kinase-acetyl-CoA carboxylase-malonyl-CoA axis

Leptin regulates fatty acid metabolism in liver, skeletal muscle, and pancreas by partitioning fatty acids into oxidation rather than triacylglycerol (TG) storage. Although leptin receptors are present in the heart, it is not known whether leptin also regulates cardiac fatty acid metabolism. To determine whether leptin directly regulates cardiac fatty acid metabolism, isolated working rat hearts were perfused with 0.8 mm [9,10-(3)H]palmitate and 5 mm [1-(14)C]glucose to measure palmitate and glucose oxidation rates. Leptin (60 ng/ml) significantly increased palmitate oxidation rates 60% above control hearts (p < 0.05) and decreased TG content by 33% (p < 0.05) over the 60-min perfusion period. In contrast, there was no difference in glucose oxidation rates between leptin-treated and control hearts. Although leptin did not affect cardiac work, oxygen consumption increased by 30% (p < 0.05) and cardiac efficiency was decreased by 42% (p < 0.05). AMP-activated protein kinase (AMPK) plays a major role in the regulation of cardiac fatty acid oxidation by inhibiting acetyl-CoA carboxylase (ACC) and reducing malonyl-CoA levels. Leptin has also been shown to increase fatty acid oxidation in skeletal muscle through the activation of AMPK. However, we demonstrate that leptin had no significant effect on AMPK activity, AMPK phosphorylation state, ACC activity, or malonyl-CoA levels. AMPK activity and its phosphorylation state were also unaffected after 5 and 10 min of perfusion in the presence of leptin. The addition of insulin (100 microunits/ml) to the perfusate reduced the ability of leptin to increase fatty acid oxidation and decrease cardiac TG content. These data demonstrate for the first time that leptin activates fatty acid oxidation and decreases TG content in the heart. We also show that the effects of leptin in the heart are independent of changes in the AMPK-ACC-malonyl-CoA axis.

Factor analysis of metabolic syndrome using directly measured insulin sensitivity: The Insulin Resistance Atherosclerosis Study

Factor analysis, a multivariate correlation technique, has been used to provide insight into the underlying structure of metabolic syndrome, which is characterized by physiological complexity and strong statistical intercorrelation among its key variables. The majority of previous factor analyses, however, have used only surrogate measures of insulin sensitivity. In addition, few have included members of multiple ethnic groups, and only one has presented results separately for subjects with impaired glucose tolerance. The objective of this study was to investigate, using factor analysis, the clustering of physiologic variables using data from 1,087 nondiabetic participants in the Insulin Resistance Atherosclerosis Study (IRAS). This study includes information on the directly measured insulin sensitivity index (S(I)) from intravenous glucose tolerance testing among African-American, Hispanic, and non-Hispanic white subjects aged 40-69 years at various stages of glucose tolerance. Principal factor analysis identified two factors that explained 28 and 9% of the variance in the dataset, respectively. These factors were interpreted as 1) a " metabolic" factor, with positive loadings of BMI, waist, fasting and 2-h glucose, and triglyceride and inverse loadings of log(S(I)+1) and HDL; and 2) a "blood pressure" factor, with positive loadings of systolic and diastolic blood pressure. The results were unchanged when surrogate measures of insulin resistance were used in place of log(S(I)+1). In addition, the results were similar within strata of sex, glucose tolerance status, and ethnicity. In conclusion, factor analysis identified two underlying factors among a group of metabolic syndrome variables in this dataset. Analyses using surrogate measures of insulin resistance suggested that these variables provide adequate information to explore the underlying intercorrelational structure of metabolic syndrome. Additional clarification of the physiologic characteristics of metabolic syndrome is required as individuals with this condition are increasingly being considered candidates for behavioral and pharmacologic intervention.

Involvement of leptin in the association between percentage of body fat and cardiovascular risk factors

OBJECTIVES

Recent epidemiologic studies have shown that obesity is associated with elevated blood concentrations of prothrombotic-proinflammatory factors and markers of endothelial dysfunction such as fibrinogen, C-reactive protein (CRP), von Willebrand factor (vWF), and homocysteine. We have assessed whether these markers are associated with percentage of body fat (BF), insulin sensitivity as well as with leptin concentrations.

DESIGN AND METHODS

Twenty-five men aged 49.6 +/- 12.7 yr (mean +/- SD) underwent whole-body air displacement plethysmography (Bod-Pod(R)) for estimating BF. Blood analyses for leptin and several other metabolic and cardiovascular markers were carried out.

RESULTS

Obese subjects had higher levels as compared to controls of BF (37.5 +/- 5.1 vs. 26.0 +/- 6.6, p < 0.01), fibrinogen (3.30 +/- 0.43 vs. 2.67 +/- 0.11, p < 0.01), vWF (136.4 +/- 50.4% vs. 81.6 +/- 12.6%, p < 0.05), and leptin (17.6 +/- 8.7 vs. 6.2 +/- 3.3, p < 0.01), lower concentrations of HDL-cholesterol (1.09 +/- 0.20 vs. 1.51 +/- 0.10, p < 0.001) and lower QUICKI (1/[log(Ins(0)) + log(Glu(0))]) (0.31 +/- 0.03 vs. 0.34 +/- 0.02, p < 0.05). No significant changes were observed in CRP (5.7 +/- 3.4 vs. 3.8 +/- 1.6, p = 0.327) and homocysteine (9.4 +/- 4.2 vs. 8.3 +/- 0.9, p = 0.749). A positive correlation was observed between BF and fibrinogen (r = 0.67, p = 0.0003). Plasma leptin concentrations were correlated with fibrinogen (r = 0.71, p = 0.0001) and CRP (r = 0.43, p = 0.044). After adjustment for BF leptin emerged as a significant predictor of fibrinogen (beta = 0.47, p = 0.023; R(2) = 0.59, p < 0.001). QUICKI was positively correlated with HDL-cholesterol (r = 0.59, p = 0.010) and negatively with fibrinogen (r = -0.53, p = 0.025), CRP (r = -0.52, p = 0.028) and vWF (r = -0.56, p = 0.013).

CONCLUSIONS

Increased BF and impaired insulin sensitivity are associated with increased concentrations of cardiovascular risk factors. Leptin seems to be involved in this elevation and emerges as a predictor of circulating fibrinogen concentrations.