Molecular mechanism of metabolic syndrome X: contribution of adipocytokines adipocyte-derived bioactive substances

Increased oxidative stress in obesity and its impact on metabolic syndrome

Obesity is a principal causative factor in the development of metabolic syndrome. Here we report that increased oxidative stress in accumulated fat is an important pathogenic mechanism of obesity-associated metabolic syndrome. Fat accumulation correlated with systemic oxidative stress in humans and mice. Production of ROS increased selectively in adipose tissue of obese mice, accompanied by augmented expression of NADPH oxidase and decreased expression of antioxidative enzymes. In cultured adipocytes, elevated levels of fatty acids increased oxidative stress via NADPH oxidase activation, and oxidative stress caused dysregulated production of adipocytokines (fat-derived hormones), including adiponectin, plasminogen activator inhibitor-1, IL-6, and monocyte chemotactic protein-1. Finally, in obese mice, treatment with NADPH oxidase inhibitor reduced ROS production in adipose tissue, attenuated the dysregulation of adipocytokines, and improved diabetes, hyperlipidemia, and hepatic steatosis. Collectively, our results suggest that increased oxidative stress in accumulated fat is an early instigator of metabolic syndrome and that the redox state in adipose tissue is a potentially useful therapeutic target for obesity-associated metabolic syndrome.

Increased oxidative stress in obesity and its impact on metabolic syndrome

Obesity is a principal causative factor in the development of metabolic syndrome. Here we report that increased oxidative stress in accumulated fat is an important pathogenic mechanism of obesity-associated metabolic syndrome. Fat accumulation correlated with systemic oxidative stress in humans and mice. Production of ROS increased selectively in adipose tissue of obese mice, accompanied by augmented expression of NADPH oxidase and decreased expression of antioxidative enzymes. In cultured adipocytes, elevated levels of fatty acids increased oxidative stress via NADPH oxidase activation, and oxidative stress caused dysregulated production of adipocytokines (fat-derived hormones), including adiponectin, plasminogen activator inhibitor-1, IL-6, and monocyte chemotactic protein-1. Finally, in obese mice, treatment with NADPH oxidase inhibitor reduced ROS production in adipose tissue, attenuated the dysregulation of adipocytokines, and improved diabetes, hyperlipidemia, and hepatic steatosis. Collectively, our results suggest that increased oxidative stress in accumulated fat is an early instigator of metabolic syndrome and that the redox state in adipose tissue is a potentially useful therapeutic target for obesity-associated metabolic syndrome.

Increased oxidative stress in obesity and its impact on metabolic syndrome

Obesity is a principal causative factor in the development of metabolic syndrome. Here we report that increased oxidative stress in accumulated fat is an important pathogenic mechanism of obesity-associated metabolic syndrome. Fat accumulation correlated with systemic oxidative stress in humans and mice. Production of ROS increased selectively in adipose tissue of obese mice, accompanied by augmented expression of NADPH oxidase and decreased expression of antioxidative enzymes. In cultured adipocytes, elevated levels of fatty acids increased oxidative stress via NADPH oxidase activation, and oxidative stress caused dysregulated production of adipocytokines (fat-derived hormones), including adiponectin, plasminogen activator inhibitor-1, IL-6, and monocyte chemotactic protein-1. Finally, in obese mice, treatment with NADPH oxidase inhibitor reduced ROS production in adipose tissue, attenuated the dysregulation of adipocytokines, and improved diabetes, hyperlipidemia, and hepatic steatosis. Collectively, our results suggest that increased oxidative stress in accumulated fat is an early instigator of metabolic syndrome and that the redox state in adipose tissue is a potentially useful therapeutic target for obesity-associated metabolic syndrome.

Increased oxidative stress in obesity and its impact on metabolic syndrome

Obesity is a principal causative factor in the development of metabolic syndrome. Here we report that increased oxidative stress in accumulated fat is an important pathogenic mechanism of obesity-associated metabolic syndrome. Fat accumulation correlated with systemic oxidative stress in humans and mice. Production of ROS increased selectively in adipose tissue of obese mice, accompanied by augmented expression of NADPH oxidase and decreased expression of antioxidative enzymes. In cultured adipocytes, elevated levels of fatty acids increased oxidative stress via NADPH oxidase activation, and oxidative stress caused dysregulated production of adipocytokines (fat-derived hormones), including adiponectin, plasminogen activator inhibitor-1, IL-6, and monocyte chemotactic protein-1. Finally, in obese mice, treatment with NADPH oxidase inhibitor reduced ROS production in adipose tissue, attenuated the dysregulation of adipocytokines, and improved diabetes, hyperlipidemia, and hepatic steatosis. Collectively, our results suggest that increased oxidative stress in accumulated fat is an early instigator of metabolic syndrome and that the redox state in adipose tissue is a potentially useful therapeutic target for obesity-associated metabolic syndrome.

Decrease in adiponectin levels in women with polycystic ovary syndrome after an oral glucose tolerance test

Adiponectin levels are decreased after an oral glucose tolerance test. At t = 2 hours, they are increased in obese and overweight women with polycystic ovary syndrome, compared with controls matched for body mass index.

Nuclear Receptors as Targets for Drug Development: Molecular Mechanisms for Regulation of Obesity and Insulin Resistance by Peroxisome Proliferator-Activated Receptor γ, CREB-Binding Protein, and Adiponectin

Obesity is defined as increased mass of adipose tissue, conferring a higher risk of cardiovascular and metabolic disorders such as diabetes, hyperlipidemia, and coronary heart disease. To investigate the role of transcriptional factors, which are involved in adipocytes differentiation and adiposity, we have generated peroxisome proliferator-activated receptor (PPAR) gamma or CREB-binding protein (CBP)-deficient mice by gene targeting. Heterozygous PPARgamma-deficient mice were protected from the development of insulin resistance due to adipocyte hypertrophy under a high-fat diet. Heterozygous CBP-deficient mice showed increased insulin sensitivity and were completely protected from body weight gain induced by a high-fat diet. PPARgamma or CBP deficiency results in increased effects of hormones such as adiponectin and leptin. Adiponectin was decreased in obesity and lipoatrophy, and replenishment of adiponectin ameliorated insulin resistance. Moreover, adiponectin-deficient mice showed insulin resistance and atherogenic phenotype. Finally, cDNA encoding adiponectin receptors (AdipoR1/R2) have been identified by expression cloning. The expression of AdipoR1/R2 appears to be inversely regulated by insulin in physiological and pathophysiological states such as fasting/refeeding, insulin deficiency, and hyperinsulinemia models, and it is correlated with adiponectin sensitivity. These results facilitate the understanding of molecular mechanisms of adiponectin actions and obesity-linked diseases such as diabetes and atherosclerosis and propose the molecular targets for anti-diabetic and anti-atherogenic drugs.

Resistin promotes smooth muscle cell proliferation through activation of extracellular signal-regulated kinase 1/2 and phosphatidylinositol 3-kinase pathways

BACKGROUND

Resistin, a novel adipokine, is elevated in patients with type 2 diabetes and may play a role in the vascular complications of this disorder. One recent study has shown that resistin has a proinflammatory effect on endothelial cells. However, there is no information on whether resistin could also affect vascular smooth muscle cells (SMCs). Thus, the purpose of this study was to assess whether resistin could induce SMC proliferation and to study the mechanisms whereby resistin signals in SMCs.

METHODS AND RESULTS

Human aortic smooth muscle cells (HASMCs) were stimulated with increasing concentrations of resistin for 48 hours. Cell proliferation was induced by resistin in a dose-dependent manner as assessed by direct cell counting. To gain more insights into the mechanism of action of resistin, we investigated the extracellular signal-regulated kinase (ERK) and/or phosphatidylinositol 3-kinase (PI3K) signaling pathways. Transient phosphorylation of the p42/44 mitogen-activated protein kinase (ERK 1/2) occurred after addition of resistin to HASMCs. U0126, a specific inhibitor of ERK phosphorylation, significantly inhibited ERK 1/2 phosphorylation and reduced resistin-simulated proliferation of HASMCs. LY294002, a specific PI3K inhibitor, also significantly inhibited HASMC proliferation after resistin stimulation.

CONCLUSIONS

Our results demonstrate that resistin induces HASMC proliferation through both ERK 1/2 and Akt signaling pathways. The proliferative action exerted by resistin on HASMCs may account in part for the increased incidence of restenosis in diabetes patients.

Dual action of adiponectin on insulin secretion in insulin-resistant mice

Adiponectin is secreted by adipocytes and has been implicated as a mediator of insulin sensitivity. In this study, the acute effects of adiponectin on islets isolated from normal or diet-induced insulin resistant mice were examined. In normal islets, adiponectin (5 microg/ml) had no significant effect on insulin secretion. In contrast, in islets from mice rendered insulin resistant by high-fat feeding, adiponectin inhibited insulin secretion at 2.8 mM (P < 0.01) but augmented insulin secretion at 16.7 mM glucose (P < 0.05). The augmentation of glucose-stimulated insulin secretion by adiponectin was accompanied by increased glucose oxidation (P < 0.005), but without any significant effect on palmitate oxidation or the islet ATP/ADP ratio. Furthermore, RT-PCR revealed the expression of the adiponectin receptor AdipoR1 mRNA in mouse islets, however, with no difference in the degree of expression level between the two feeding groups. The results thus uncover a potential dual role for adiponectin to modify insulin secretion in insulin resistance.

Adiponectin, insulin resistance, and C-reactive protein in postpubertal Asian Indian adolescents

High-sensitivity C-reactive protein (hs-CRP) levels are closely associated with adiposity and predict coronary heart disease and type 2 diabetes mellitus. However, relationships of CRP to adiponectin and other markers of insulin resistance have been inadequately researched in children. We measured fasting serum levels of adiponectin, insulin, hs-CRP, and lipoproteins, and recorded the anthropometric profile and percentage of body fat (%BF; bioimpedance method) in 62 (36 normal weight, 26 overweight) healthy, urban, postpubertal Asian Indian males (aged 14 to 18 years). Serum levels of adiponectin were lower (P = not significant [NS]), whereas those of fasting insulin (P = .01) and hs-CRP (P = .02) were higher in overweight subjects. Adiponectin levels inversely correlated with body mass index (BMI; r = -0.26, P < .05), %BF (r = -0.24, P < .05), fasting insulin (r = -0.32, P < .05) and insulin resistance measured by the homeostasis model of assessment (HOMA-IR; r = -0.31, P < .05), but not with hs-CRP levels. Fasting insulin and hs-CRP levels correlated significantly with BMI, %BF, waist circumference (WC), waist-to-hip circumference ratio (W-HR), and triceps and subscapular skinfold thickness. The correlation of adiponectin with insulin sensitivity was independent of abdominal obesity, but became nonsignificant after controlling for BMI and %BF. Further, BMI was an independent predictor of adiponectin levels and the ratio of adiponectin and %BF was an independent predictor of fasting insulin levels. Although adiponectin levels did not correlate with hs-CRP levels, we observed dichotomous relationships of adiponectin and hs-CRP levels with generalized and abdominal obesity, respectively. We conclude that generalized obesity affects the adiponectin-insulin relationship in postpubertal Asian Indian males; however, the relationship of adiponectin with hs-CRP needs further evaluation.

Prevalence and trends of a metabolic syndrome phenotype among u.s. Adolescents, 1999-2000

OBJECTIVE

To determine the prevalence of a metabolic syndrome phenotype among U.S. adolescents using the most recent national data and to examine trends in metabolic syndrome prevalence.

RESEARCH DESIGN AND METHODS

Analysis of data on 991 adolescents (aged 12-19 years) who had fasted for at least 6 h, from the National Health and Nutrition Examination Survey (NHANES 1999-2000). The metabolic syndrome was determined using the National Cholesterol Education Program (Adult Treatment Panel III) definition modified for age.

RESULTS

The overall prevalence of a metabolic syndrome phenotype among U.S. adolescents increased from 4.2% in NHANES III (1988-1992) to 6.4% in NHANES 1999-2000 (P < 0.001). The syndrome was more prevalent (P < 0.01) in male than female adolescents (9.1 vs. 3.7%) and was found in 32.1% of overweight adolescents (BMI > or = 95th percentile for age and sex), compared with 7.1% of adolescents at risk for overweight (BMI between 85th and 95th percentiles) (P < 0.001). Based on population-weighted estimates, > 2 million U.S. adolescents currently have a metabolic syndrome phenotype.

CONCLUSIONS

The prevalence of a metabolic syndrome phenotype has increased significantly over the past decade among U.S. adolescents and is particularly prevalent (> 30%) in overweight adolescents. These findings have important implications for public health because of the well-known health risks associated with the metabolic syndrome in adults.

An essential role of the JIP1 scaffold protein for JNK activation in adipose tissue

The c-Jun NH2-terminal kinase (JNK) is activated during obesity. One consequence of obesity is that JNK phosphorylates the adapter protein insulin receptor substrate 1 (IRS-1) on Ser 307 and inhibits signaling by the insulin receptor. JNK can therefore cause peripheral insulin resistance during obesity and may contribute to the development of type 2 diabetes. Here we report that the JNK-interacting protein 1 (JIP1) scaffold protein, which binds components of the JNK signaling module, is essential for JNK activation in the adipose tissue of obese mice. These data identify JIP1 as a novel molecular target for therapeutic intervention in the development of obesity.

Leptin stimulates ischemia-induced retinal neovascularization: possible role of vascular endothelial growth factor expressed in retinal endothelial cells

Diabetic retinopathy is the leading cause of new blindness in adults in developed countries. Leptin, an adipocyte-derived hormone, stimulates endothelial proliferation and angiogenesis. This study was designed to elucidate the pathophysiologic role of leptin in the progression of retinal neovascularization. Using the retinopathy of prematurity model, a mouse model of ischemia-induced retinal neovascularization, we have demonstrated more pronounced retinal neovascularization in 17-day-old transgenic mice overexpressing leptin than in age-matched wild-type littermates. Ischemia-induced retinal neovascularization was markedly suppressed in 17-day-old leptin-deficient ob/ob mice. Western blot analysis revealed that a biologically active leptin receptor isoform is expressed in mouse retinal endothelial cells. Leptin receptor expression was also detected in primary cultures of porcine retinal endothelial cells, where it upregulated vascular endothelial growth factor (VEGF) mRNA expression. This effect was thought to be mediated at least partly through the activation of signal transducers and activators of transcription (STAT)3, because adenoviral transfection of the dominant-negative form of STAT3 abolished the leptin-induced upregulation of VEGF mRNA expression in retinal endothelial cells. This study provides evidence that leptin stimulates the ischemia-induced retinal neovasucularization possibly through the upregulation of endothelial VEGF, thereby suggesting that leptin antagonism may offer a novel therapeutic strategy to prevent or treat diabetic retinopathy.

Oolong tea increases plasma adiponectin levels and low-density lipoprotein particle size in patients with coronary artery disease

BACKGROUND

Oolong tea has been studied for its effect on cardiovascular disease and obesity. Plasma adiponectin levels are reduced in obesity, in patients with type 2 diabetes mellitus and in coronary artery disease (CAD).

OBJECTIVE

To investigate prospectively, whether intake of Oolong tea influences plasma adiponectin levels, low-density lipoprotein (LDL) particle size, total cholesterol, high-density lipoprotein (HDL) cholesterol, LDL cholesterol, serum triglyceride and plasma glucose levels in patients with CAD.

METHODS

Twenty two patients in our study consumed Oolong tea (1000 ml) or water for 1 month in our randomized cross-over study design.

RESULTS

There was a significant difference in plasma adiponectin levels before and after 1 month intake of Oolong tea (6.26 +/- 3.26 microg/ml versus 6.88 +/- 3.28 microg/ml, P < 0.05), and in plasma level LDL particle size (25.02+/-0.67 nm versus 25.31+/-0.60 nm, P < 0.01). The water-consuming control group showed no changes (6.28+/-3.28 microg/ml versus 6.23+/-3.21 microg/ml) in adiponectin levels or LDL particle sizes (25.03+/-0.70 nm versus 25.02+/-0.72 nm). We also observed a significant difference in hemoglobin A1c levels (7.23 +/- 4.45% versus 6.99 +/- 4.30%, P < 0.05) before and after intake of Oolong tea.

CONCLUSION

Oolong tea may have beneficial effects on the progression of atherosclerosis in patients with CAD.

Insulin resistance syndrome (metabolic syndrome) and obesity in Asian Indians: evidence and implications

OBJECTIVES

This review describes prevalence, determinants, and possible pathophysiologic mechanisms and suggests management and research directions for insulin resistance syndrome (metabolic syndrome) in Asian Indians.

METHOD

We reviewed the topic using the terms Asian Indians, Asians, South Asians, and Indians coupled with the terms insulin resistance, hyperinsulinemia, metabolic syndrome, and obesity from the databases Pubmed (National Library of Medicine, Bethesda, MD, USA) and Current Contents (Institute for Scientific Information, Thomson Scientific, Philadelphia, PA, USA) and from non-indexed publications of the medical research and governmental institutions in India.

RESULTS

Asian Indians have a high prevalence of insulin resistance syndrome that may underlie their greater than normal tendency to develop diabetes mellitus and early atherosclerosis. Important reasons could be their excess body fat and adverse body fat patterning including abdominal adiposity even when the body mass index is within the currently defined normal limits. Some of these features have been reported at birth and childhood. Whether Asian Indians also have tendency to develop insulin resistance de novo, independent of total or regional adiposity, needs further investigation. Underlying genetic tendency or early-life adverse events may contribute to such a phenotype, but lifestyle factors alone or modulated by inherited factors appear to play an important role because obesity and dyslipidemia become worse with urbanization and migration. Systemic stress may contribute to insulin resistance syndrome in the intra-country and inter-country migrant Asian Indians.

CONCLUSIONS

High prevalences of excess body fat, adverse body fat patterning, hypertriglyceridemia, and insulin resistance beginning at a young age have been consistently recorded in Asian Indians irrespective of their geographic locations. These data suggest that primary prevention strategies should be initiated early in this ethnic group.

Impact of adiposity and plasma adipocytokines on diabetic angiopathies in Japanese Type 2 diabetic subjects

AIMS

Adipocytokines, products from adipose tissue, have biological activities on the vascular system, and may affect diabetic angiopathy. In this study, we assessed the relationship between adiposity and plasma adipocytokine levels, and investigated the clinical significance of adiposity and plasma adipocytokine levels on diabetic micro- and macroangiopathy in Type 2 diabetic subjects.

METHODS

We studied 231 Japanese Type 2 diabetic subjects (135 men and 96 women, aged 60.4 +/- 12.3 years, body mass index 24.8 +/- 5.2 kg/m2). We measured adipocytokine [adiponectin, leptin, resistin, and tumour necrosis factor (TNF)-alpha] levels, lipid profiles and urine albumin excretion. We also performed optic fundus examination and measured carotid intramedia thickness (IMT) using B-mode ultrasonography, and the localization of fat with abdominal computed tomography. A group of 93 subjects with microalbuminuria or overt proteinuria was compared with the other 148 to assess the effect on nephropathy. A group of 191 eyes with simple retinopathy or more advanced changes was compared with 263 eyes without retinal changes to assess the effect on retinopathy.

RESULTS

Plasma adiponectin level was negatively correlated with both visceral (r = -0.37, P < 0.01) and subcutaneous (r = -0.25, P < 0.01) fat areas. Resistin concentration was positively related with visceral fat area (r = 0.15, P < 0.05). Adiponectin concentration was positively correlated with age (r = 0.26, P < 0.01). TNF-alpha was correlated with IMT (r = 0.16, P < 0.05) after correction for age. Logistic regression analysis indicates a 4085 times greater chance of having retinopathy with a one unit increase in TNF-alpha (pmol/l) and a 30.64 times greater chance of having nephropathy with one unit increase in leptin (nmol/l).

CONCLUSIONS

The present observations suggest that visceral and subcutaneous fat has an impact on microangiopathy as well as macroangiopathy, possibly through different adipocytokines.

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.

Gender differences of adiponectin levels develop during the progression of puberty and are related to serum androgen levels

Adiponectin is an adipocytokine with profound antidiabetic and antiatherogenic effects that is decreased in obesity. With the increasing prevalence of obesity and the emergence of related disorders, including type 2 diabetes in children, the regulation of adiponectin and its relationship to childhood obesity is of great interest. In this study we aimed to elucidate the impact of gender, pubertal development, and obesity on adiponectin levels in children. We investigated two phenotypically characterized cohorts of 200 normal weight and 135 obese children and adolescents covering a wide range of age (3.4-17.9 yr) and body mass index (-2.1 to +4.8 sd score). In healthy lean boys, adiponectin levels significantly declined in parallel with physical and pubertal development, subsequently leading to significantly reduced adiponectin levels in adolescent boys compared with girls (5.6 +/- 0.5 vs. 7.1 +/- 0.5 mg/liter; P = 0.03). This decline was inversely related to testosterone (r = -0.42; P < 0.0001) and dehydroepiandrosterone sulfate (r = -0.20; P = 0.0068) serum concentrations and may account for the gender differences seen in adults. Using a stepwise forward multiple regression model, pubertal stage was the strongest independent predictor of adiponectin (r(2) = 0.206; P < 0.0001), with additional influences of body mass index sd score and testosterone. Adiponectin levels were decreased in obese children and adolescents compared with lean peers of corresponding age and pubertal stage (5.18 vs. 7.13 mg/liter; P = 0.015). In obese children, adiponectin levels were closely associated with parameters related to the metabolic syndrome, such as insulin resistance, hyperinsulinemia, blood pressure, and uric acid, in univariate and multivariate analyses, with the insulin sensitivity index being the strongest independent parameter identified by stepwise forward multiple regression (r(2) = 0.226; P < 0.0001). Hence, there is a strong association of adiponectin serum concentrations with obesity, pubertal development, and metabolic parameters in children indicating epidemiological and pathophysiological relevance already in childhood.

Visceral fat in hypertension: influence on insulin resistance and beta-cell function

Preferential visceral adipose tissue (VAT) deposition has been associated with the presence of insulin resistance in obese and diabetic subjects. The independent association of VAT accumulation with hypertension and its impact on insulin sensitivity and beta-cell function have not been assessed. We measured VAT and subcutaneous fat depots by multiscan MRI in 13 nondiabetic men with newly detected, untreated essential hypertension (blood pressure=151+/-2/94+/-2 mm Hg, age=47+/-2 years, body mass index [BMI]=28.4+/-0.7 kg x m(-2)) and 26 age-matched and BMI-matched normotensive men (blood pressure=123+/-1/69+/-2 mm Hg). Insulin secretion was measured by deconvolution of C-peptide data obtained during an oral glucose tolerance test, and dynamic indices of beta-cell function were calculated by mathematical modeling. For a similar fat mass in the scanned abdominal region (4.8+/-0.3 versus 3.9+/-0.3 kg, hypertensive subjects versus controls, P=0.06), hypertensive subjects had 60% more VAT than controls (1.6+/-0.2 versus 1.0+/-0.1 kg, P=0.003). Intrathoracic fat also was expanded in patients versus controls (45+/-5 versus 28+/-3 cm2, P=0.005). Insulin sensitivity was reduced (10.7+/-0.7 versus 12.9+/-0.4 mL x min(-1) x kg(ffm)(-1), P=0.006), and total insulin output was proportionally increased (64 [21] versus 45 [24] nmol x m(-2). h, median [interquartile range], P=0.01), but dynamic indices of beta-cell function (glucose sensitivity, rate sensitivity, and potentiation) were similar in the 2 groups. Abdominal VAT, insulin resistance, and blood pressure were quantitatively interrelated (rho's of 0.39 to 0.47, P<0.02 or less). In newly found, untreated men with essential hypertension, fat is preferentially accumulated intraabdominally and intrathoracically. Such visceral adiposity is quantitatively related to both height of blood pressure and severity of insulin resistance, but has no impact on the dynamics of beta-cell function.

The expression and functional role of nicotinic acetylcholine receptors in rat adipocytes

To clarify whether nicotine has a direct effect on the function of adipocytes, we evaluated nicotinic acetylcholine receptor (nAChR) expression in adipocytes by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry and the direct effects of nicotine on the production of adipocytokines by enzyme-linked immunosorbent assay and Western blot analysis. Receptor binding assays were performed using [3H]nicotine. RT-PCR studies revealed that alpha1-7, 9, 10, beta1-4, delta, and epsilon subunit mRNAs are expressed in adipocytes. Immunocytochemical experiments also suggested the presence of alpha7 and beta2 subunits. The receptor binding assay revealed a binding site for nicotine (Kd = 39.2 x 10(-9) M) on adipocytes. Adipocytes incubated with nicotine for 12 and 36 h released tumor necrosis factor-alpha (TNF-alpha), adiponectin, and free fatty acid (FFA) into the medium in a dose-dependent manner with increasing nicotine concentration from 6 x 10(-8) to 6 x 10(-4) M. However, TNF-alpha protein levels in adipocytes incubated for 12 and 36 h decreased in a dose-dependent manner with increasing nicotine concentration from 6 x 10(-8) to 6 x 10(-4) M. These results show that adipocytes have functional nAChRs and suggest that nicotine reduces TNF-alpha protein production in adipocytes through the activation of nAChRs. Nicotine may temporarily lower insulin sensitivity by stimulating the secretion of TNF-alpha and FFA, whereas long-term direct stimulation of nAChRs by nicotine in addition to autonomic nervous system stimulation may contribute to better insulin sensitivity in vivo through a modulated secretion of adipocytokines.

Circulating adiponectin levels increase in rats on caloric restriction: the potential for insulin sensitization

Caloric restriction (CR) has a well-known insulin sensitizing effect in vivo. Although this effect has been confirmed in rodents and primates for many years, its precise molecular mechanisms remain unknown. Here we show a significant increase in plasma adiponectin and a decrease in blood glucose, plasma triglyceride and insulin levels in rats maintained on CR diet for 2, 10, 15, and 20 months. Long-term CR rats exhibited significantly higher insulin-stimulated insulin receptor tyrosine phosphorylation and lower PTP-1B activity both in liver and skeletal muscle than those observed in rats fed ad libitum (AL). In addition, the triglyceride levels in these tissues were significantly lower in long-term CR animals. Interestingly, concentrations of plasma adiponectin in long-term CR rats were associated with increased expression of the transcription factor mRNAs for the peroxisome proliferator-activated receptor (PPAR)alpha, gamma and delta, but decreased expression for SREBP-1c, resulting in a concerted modulation in the expression of key transcription target genes involved in fatty acid oxidation and energy combustion in liver. Taken together, our findings suggest an important role for adiponectin in the beneficial effects of long-term CR.

Adipocytokines attenuate the association between visceral adiposity and diabetes in older adults

OBJECTIVE

To examine whether adiponectin is independently associated with diabetes and whether adiponectin and other adipocytokines account for the relationship between fat and diabetes.

RESEARCH DESIGN AND METHODS

A nested case-control study from the Health, Aging, and Body Composition (Health ABC) study. We measured four adipocytokines: adiponectin, interleukin (IL)-6, tumor necrosis factor-alpha, and plasminogen activator inhibitor 1 (PAI-1). Regional fat area was determined by computed tomography scan. The 519 case subjects had diabetes defined by fasting plasma glucose level > or =126 mg/dl or by use of diabetes medications. The 519 control subjects had normal glucose tolerance and were matched by sex, race, and study site. Sex-specific logistic models were adjusted for age, race, site, total adiposity, smoking, and physical activity.

RESULTS

Higher adiponectin levels were associated with lower risk of diabetes (P < 0.001). Visceral fat was the only adiposity measure associated with diabetes after adjusting for BMI (odds ratio 3.0 [2.1-4.3] in women and 1.3 [1.0-1.6] in men, P < 0.001 between-sex comparison). Adipocytokines attenuated the association between visceral fat and diabetes for both sexes but more strongly in men (women 2.3 [1.5-3.3], men 1.1 [0.9-1.4]). In men, adiponectin, IL-6, and PAI-1 remained independently associated with diabetes after adjusting for fat depots; in women, adiponectin was the only independently associated adipocytokine. Controlling for insulin, HDL, triglycerides, and blood pressure did not change these results.

CONCLUSIONS

Adiponectin is associated with lower odds of diabetes in older men and women. Whereas several adipocytokines explained the relationship between visceral adiposity and diabetes in men, only adiponectin partially mediated this association among women.

ANGPTL3 is increased in both insulin-deficient and -resistant diabetic states

Angiopoietin-like protein 3 (ANGPTL3) is secreted by the liver and was recently postulated to be an important hormone regulating serum triglyceride levels. In the present study, in order to clarify the regulation of ANGPTL3 gene expression in diabetic states, we examined mRNA and protein levels of ANGPTL3 in the livers of diabetic animals. The level of ANGPTL3 mRNA was increased approximately 2.2-fold in the livers of streptozotocin (STZ) diabetic mice, and this effect was reversed by administration of insulin. Furthermore, the level of ANGPTL3 mRNA was increased more than 3.0-fold in type 2 diabetic obese mice, db/db mice, as compared with age matched lean littermates. The hepatic level of ANGPTL3 protein was also increased in these diabetic mice to an extent similar to that of ANGPTL3 mRNA. Thus, the expression of ANGPTL3 was enhanced in both insulin-deficient and -resistant diabetic states. These results strongly suggest ANGPTL3 to play an important role in hyperlipidemia in diabetes.

Adiponutrin: A new gene regulated by energy balance in human adipose tissue

Adiponutrin is a newly identified nonsecreted adipocyte protein regulated by changes in energy balance in rodents. We documented the influence of energy balance modification on adiponutrin gene expression in humans. We investigated the mRNA expression in sc adipose tissue of nonobese women and in obese women during 2-d very low-calorie diet (VLCD) and subsequent refeeding as well as before and after a VLCD of 3 wk (21-d VLCD). The adiponutrin mRNA levels of the nonobese and obese women were not different (P > 0.05). Two-day VLCD reduced the average level of adiponutrin mRNA expression by 36% (P = 0.0016), whereas refeeding elevated the mRNA level by 31% (P = 0.004). The 3-wk VLCD caused a dramatic 58% fall of the adiponutrin mRNA expression level (P = 0.001). The mRNA level was negatively correlated with fasting glucose (Rho = -0.62; P < 0.0001), and subjects with high adiponutrin mRNA level had an increased insulin sensitivity. Compared with other adipocyte proteins such as leptin and adiponectin, adiponutrin mRNA did not show correlation with either adiposity indexes or with leptin or adiponectin mRNAs. These results indicate that adiponutrin gene expression in humans is highly regulated by changes in energy balance.

Metabolic syndrome and effects of conjugated linoleic acid in obesity and lipoprotein disorders: the Québec experience

The health hazards of obesity are well established. However, the fact that all obese individuals are not at equal risk of developing a disease is being increasingly recognized. The regional distribution of body fat has been identified as an important component of the obesity-related health hazards. Among obese individuals, those who accumulate fat predominantly in the abdominal area are more likely to present several metabolic perturbations of the metabolic syndrome, such as increased plasma triacylglycerol and apolipoprotein B concentrations, an elevated ratio of total cholesterol to HDL cholesterol, reduced plasma HDL-cholesterol concentrations, and small, dense LDL particles. This short review focuses on the risk associated with specific features of metabolic syndrome with use of data from the Québec Cardiovascular Study, an ongoing prospective study of traditional and nontraditional risk factors for ischemic heart disease in men. Recent data on the effect of conjugated linoleic acid on risk factors associated with metabolic syndrome are briefly reviewed. Data available to date suggest that conjugated linoleic acid might not be an appropriate dietary alternative for the treatment of metabolic syndrome and its complications.

Implications of plasma concentrations of adiponectin in patients with coronary artery disease

OBJECTIVE

To investigate whether concentrations of plasma adiponectin constitute a significant coronary risk factor, with particular focus on the relation between plasma concentrations of adiponectin and the development of acute coronary syndrome (ACS).

SUBJECTS AND METHODS

Plasma concentrations of adiponectin were measured in 123 patients with coronary artery disease (CAD) and in 17 control participants. Patients were divided into three groups according to condition type: acute myocardial infarction (AMI) group (n = 59), unstable angina pectoris (UAP) group (n = 28), and stable angina pectoris (SAP) group (n = 36).

RESULTS

Plasma concentrations of adiponectin correlated negatively with body mass index (r = -0.18, p < 0.05), serum triglyceride (r = -0.25, p < 0.01), and fasting glucose concentrations (r = -0.21, p < 0.05), but correlated positively with age (r = 0.26, p < 0.01), high density lipoprotein cholesterol concentrations (r = 0.35, p < 0.01), and low density lipoprotein particle size (r = 0.37, p < 0.01). Plasma concentrations of adiponectin in patients with ACS, in both the AMI and UAP groups, were significantly lower than those in patients with SAP and in the control group (ACS, 6.5 (3.0) microg/ml; SAP, 11.3 (5.9) micro g/ml; control 12.8 (4.3) microg/ml; p < 0.01). Additionally, plasma concentrations of adiponectin in patients with CAD (7.9 (4.6) microg/ml, p < 0.01) were significantly lower than in the control group. There were, however, no significant differences between patients with SAP and the control group (p = 0.36). Multiple logistic regression analysis showed that smoking, fasting glucose concentration, and low log adiponectin concentration correlated independently with the development of an ACS.

CONCLUSIONS

The findings suggest that measurement of plasma concentrations of adiponectin may be of use for assessing the risk of CAD and may be related to the development of ACS.

Serum adiponectin is associated with high-density lipoprotein cholesterol, triglycerides, and low-density lipoprotein particle size in young healthy men

The chromosomal localization of adiponectin has been found to be mapped to human chromosome 1q21.4-1q23, a region that was identified as a susceptibility locus for familial combined hyperlipidemia and polygenic type 2 diabetes. As these 2 disorders are associated with low high-density lipoprotein (HDL)-cholesterol, high triglycerides, and insulin resistance (IR), we examined the relation of serum adiponectin concentrations to serum lipid and lipoprotein profiles as well as IR in young healthy men. Serum adiponectin levels were positively associated with HDL-cholesterol, apolipoprotein (apo) A1, and low-density lipoprotein (LDL) particle size, and negatively associated with triglycerides and apo B. Negative associations were also found between adiponectin and body mass index (BMI), percent body fat, and IR,as determined by homeostasis model assessment (HOMA). However, after adjustment for BMI, no significant associations were found between adiponectin and LDL particle size and apo B. In a multiple regression analysis including all variables that showed significant univariate associations with adiponectin, associations of adiponectin with HDL-cholesterol (beta = 0.079, P =.0009), percent body fat (beta = -0.165, P =.002), and serum leptin (beta = -0.291, P =.01) were statistically significant. HDL-cholesterol (beta = 0.077, P =.001), percent body fat (beta = -0.078, P =.03), and LDL size (beta = 0.092, P =.03) emerged as significant and independent determinants of adiponectin after HOMA IR, fasting glucose, triglycerides, and systolic blood pressure (BP) were taken into account. Together, these variables explained 19% of adiponectin variability in the 2 models. HOMA IR did not emerge as a determinant of adiponectin in both models. These findings suggest that in young healthy men hypoadiponectinemia is more closely related to adiposity and dyslipidemia than IR.

Lower expression of adiponectin mRNA in visceral adipose tissue in lean and obese subjects

Adiponectin is an adipocyte-specific protein suggested to play a role in mediating the metabolic effects of obesity. In the present study, we investigated adiponectin mRNA levels in both visceral and subcutaneous abdominal adipose tissue (AT) from lean and obese subjects. Investigations on both "fresh" fat biopsies and incubations of AT fragments were performed. Regional differences in the effects of the cytokine interleukin-1beta (IL-1beta) were investigated. Adiponectin gene expression was 33% lower in visceral AT than in subcutaneous AT of lean subjects (P < 0.05), and 28% lower in obese subjects, albeit non-significant (P = 0.3). In both lean and obese subjects adiponectin mRNA expression in incubated AT fragments was significantly lower in visceral AT than in subcutaneous AT (lean: P < 0.01; obese: P < 0.05). No difference was found in adiponectin mRNA levels in gluteal compared to abdominal subcutaneous AT. IL-1beta suppressed adiponectin mRNA levels substantially in both subcutaneous and visceral AT. In conclusion, adiponectin gene expression is lower in visceral AT than in subcutaneous abdominal AT, suggesting subcutaneous AT to be more important for circulating adiponectin levels.

Modest weight loss and reduction in waist circumference after medical treatment are associated with favorable changes in serum adipocytokines

Modest weight loss if maintained is associated with significant metabolic benefits and reduction in cardiovascular risk. Adipose tissue secretes cytokines believed to contribute to the pathogenesis of insulin resistance and cardiovascular risk. We therefore observed the effect of modest weight loss on serum adipocytokines and their relationship with changes in anthropometric and metabolic parameters within a period of 6 months in the setting of a routine obesity hospital clinic after various medical treatments. In this prospective, nonrandomized, nonblinded observational study, patients were first given treatment (sibutramine or orlistat) as decided by the treating clinician and then allocated into 1 of 2 groups according to the treatment prescribed. The first group included 21 Caucasian nondiabetic female subjects, with a mean (+/-SD) age of 43 +/- 11 years and a mean body mass index (BMI) of 46 +/- 8.6 kg/m(2); subjects were treated with sibutramine 10 or 15 mg/d for weight loss. The second group included 20 Caucasian nondiabetic female subjects, mean age 42 +/- 9 years and mean BMI 45.2 +/- 5.2 kg/m(2); orlistat was introduced after 1 month on a low-fat (</=30%) diet in this group. Blood pressure and anthropometric measurements were performed before and after weight loss by a single observer. Serum glucose, insulin, lipid profile, C-reactive protein (CRP), resistin, leptin, and adiponectin were measured before and after weight loss on a fasting sample. After 6 months, the sibutramine group had a modest mean weight loss of 5.4% (P =.0001), and waist circumference was reduced by 4.5 +/- 1.4 cm. There was a decrease in serum resistin, leptin, and CRP levels, and a rise in serum adiponectin (P <.05). Change (%) (Delta) in BMI (DeltaBMI%) was associated with Deltainsulin(%) (P =.02, r = 0.53) and Deltaleptin(%) (P =.01, r = 0.58). Change in waist was associated with Deltainsulin(%) (P =.005, r = 0.75) and Deltaresistin(%) (P =.03, r = -0.55). The orlistat-treated group had a mean weight loss of 2.5%. Although this group did not show significant change in metabolic parameters, surprisingly there was a greater decrease of resistin (P =.02) associated with comparable (%) increase in adiponectin and (%) reduction of waist circumference and CRP. We conclude that modest weight loss (>5%) after medical treatment in a routine obesity hospital clinic is associated with improvements in insulin sensitivity and lipid profile. Modest weight loss is also associated with potentially favourably changes in serum adipocytokines, particularly in a rise of serum adiponectin. Reduction of waist circumference is associated with a change in serum resistin.

Decreased plasma adiponectin levels in young obese males

Plasma adiponectin levels are reduced in middle-aged obesity and in patients with type 2 diabetes and coronary artery disease. The purpose of this study was to investigate the effects of early-aged obesity on plasma adiponectin level. Twenty-six male college students (19.2 +/- 1.1 years, obese group: n = 15, [body mass index > 25, percent body fat > 25%], non-obese group: n = 11) participated in the present study. We measured anthropometric parameters and plasma adiponectin and leptin level. Plasma adiponectin levels in the obese group were significantly lower than those in the non-obese group (obese: 4.7 +/- 2.0 micro g/ml, non-obese: 6.8 +/- 2.2 micro g/ml, p < 0.05). On the other hand, plasma leptin levels in the obese group were significantly higher than those in the non-obese group (obese: 8.4 +/- 3.2 ng/ml, non-obese: 2.6 +/- 2.1 ng/ml, p < 0.001). Plasma adiponectin levels were significantly correlated with body weight (r = -0.415, p < 0.05) and percent body fat (r = -0.412, p < 0.05). Stepwise multiple regression analysis revealed that percent body fat was a significant independent predictor of plasma adiponectin level (r = 0.406, p < 0.05). These results show that obesity is associated with reduced plasma adiponectin even in young subjects.

Adiponectin, a fat cell product, influences the earliest lymphocyte precursors in bone marrow cultures by activation of the cyclooxygenase-prostaglandin pathway in stromal cells

Adiponectin, an adipocyte-derived hormone, is attracting considerable interest as a potential drug for diabetes and obesity. Originally cloned from human s.c. fat, the protein is also found in bone marrow fat cells and has an inhibitory effect on adipocyte differentiation. The aim of the present study is to explore possible influences on lymphohematopoiesis. Recombinant adiponectin strongly inhibited B lymphopoiesis in long-term bone marrow cultures, but only when stromal cells were present and only when cultures were initiated with the earliest category of lymphocyte precursors. Cyclooxygenase inhibitors abrogated the response of early lymphoid progenitors to adiponectin in stromal cell-containing cultures. Furthermore, PGE(2), a major product of cyclooxygenase-2 activity, had a direct inhibitory influence on purified hematopoietic cells, suggesting a possible mechanism of adiponectin action in culture. In contrast to lymphopoiesis, myelopoiesis was slightly enhanced in adiponectin-treated bone marrow cultures, and even when cultures were initiated with single lymphomyeloid progenitors. Finally, human B lymphopoiesis was also sensitive to adiponectin in stromal cell cocultures. These results suggest that adiponectin can negatively and selectively influence lymphopoiesis through induction of PG synthesis. They also indicate ways that adipocytes in bone marrow can contribute to regulation of blood cell formation.

Update on adipocyte hormones: regulation of energy balance and carbohydrate/lipid metabolism

Hormones produced by adipose tissue play a critical role in the regulation of energy intake, energy expenditure, and lipid and carbohydrate metabolism. This review will address the biology, actions, and regulation of three adipocyte hormones-leptin, acylation stimulating protein (ASP), and adiponectin-with an emphasis on the most recent literature. The main biological role of leptin appears to be adaptation to reduced energy availability rather than prevention of obesity. In addition to the well-known consequences of absolute leptin deficiency, subjects with heterozygous leptin gene mutations have low circulating leptin levels and increased body adiposity. Leptin treatment dramatically improves metabolic abnormalities (insulin resistance and hyperlipidemia) in patients with relative leptin deficiency due to lipoatrophy. Leptin production is primarily regulated by insulin-induced changes of adipocyte metabolism. Dietary fat and fructose, which do not increase insulin secretion, lead to reduced leptin production, suggesting a mechanism for high-fat/high-sugar diets to increase energy intake and weight gain. ASP increases the efficiency of triacylglycerol synthesis in adipocytes leading to enhanced postprandial lipid clearance. In mice, ASP deficiency results in reduced body fat, obesity resistance, and improved insulin sensitivity. Adiponectin production is stimulated by thiazolidinedione agonists of peroxisome proliferator-activated receptor-gamma and may contribute to increased insulin sensitivity. Adiponectin and leptin cotreatment normalizes insulin action in lipoatrophic insulin-resistant animals. These effects may be mediated by AMP kinase-induced fat oxidation, leading to reduced intramyocellular and liver triglyceride content. The production of all three hormones is influenced by nutritional status. These hormones, the pathways controlling their production, and their receptors are promising targets for managing obesity, hyperlipidemia, and insulin resistance.

Relationship between serum adiponectin and leptin concentrations and body fat distribution

The aim of this study was to investigate the relationship between adiponectin and leptin and body fat distribution. One hundred and ninety-seven women participated in this study. Subjects were grouped based on their visceral adipose tissue area (VAT). Body fat distribution was determined by computed tomography. The numbers in the subcutaneous fat dominant group (SFDG) and visceral fat dominant group (VFDG) were 79 and 118, respectively. The VFDG showed lower adiponectin levels than the SFDG (8.9+/-0.4 microg/ml versus 11.4+/-0.7 microg/ml, P=0.006), but leptin levels did not differ significantly between groups (18.8+/-1.1 ng/ml versus 17.7+/-1.8 ng/ml, P=0.111). Adiponectin levels were inversely correlated with fasting insulin, HOMA-IR, triglyceride, SBP and DBP, subcutaneous adipose tissue area (SAT) and VAT, and waist-to-hip ratio (WHR). Leptin levels were positively correlated with fasting glucose and insulin, HOMA-IR, triglyceride, SBP and DBP, VAT and SAT, and WHR (all values of P<0.05). VAT and HDL-cholesterol were independent variables of adiponectin concentrations (R(2)=0.207, P<0.0001), and SAT, fasting insulin, and HOMA-IR were independent variables of leptin concentrations (R(2)=0.498, P<0.0001) In conclusion, adiponectin and leptin concentrations, although associated with metabolic parameters, were more strongly influenced by VAT in the case of adiponectin, and by SAT in the case of leptin.

Neurotrophin presence in human coronary atherosclerosis and metabolic syndrome: a role for NGF and BDNF in cardiovascular disease?

The development of atherosclerotic cardiovascular disease is a common comorbidity in patients with the metabolic syndrome, a concurrence of cardiovascular risk factors in one individual. While multiple growth factors and adipokines are identified in atherosclerotic lesions, as well as neurotrophins implicated in both cardiac ischemia and lipid and glucose metabolism, the potential role of neurotrophins in human coronary atherosclerosis and in the metabolic syndrome still remains to be elucidated. Here we describe and discuss our results that represent a novel attempt to study the cardiovascular and metabolic biology of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and mast cells (MC). The local amount of NGF, the immunolocalization of p75 neurotrophin receptor (p75NTR) and the number of MC were correlatively examined in coronary vascular wall and in the surrounding subepicardial adipose tissue, obtained from autopsy cases in humans with advanced coronary atherosclerosis. We also analyzed the plasma levels of NGF, BDNF and leptin and the number of MC in biopsies from abdominal subcutaneous adipose tissue in patients with a severe form of the metabolic syndrome. The results demonstrate that NGF levels are decreased in atherosclerotic coronary vascular tissue but increased in the subepicardial adipose tissue, whereas both tissues express a greater number of MC and a stronger p75NTR immunoreactivity, compared to controls. Metabolic syndrome patients display a significant hyponeurotrophinemia and an increased number of adipose MC; the later correlates with elevated plasma leptin levels. In effect, we provide the first evidence for (i) an altered presence of NGF, p75NTR and MC in both coronary vascular and subepicardial adipose tissue in human coronary atherosclerosis, and (ii) a significant decrease in plasma NGF and BDNF levels and an elevated amount of plasma leptin and adipose MC in metabolic syndrome patients. Together our findings suggest that neuroimmune mediators such as NGF, BDNF, leptin and MC may be involved in the development of cardiovascular disease and related disorders.

Adiponectin, an adipocyte-derived protein, predicts future insulin resistance: two-year follow-up study in Japanese population

It has been reported that the serum adiponectin level was negatively correlated with body mass index (BMI), insulin resistance index, and triglycerides and was positively correlated with high-density lipoprotein cholesterol in several cross-sectional studies. However, the causal relationship has not been elucidated. We investigated whether the baseline adiponectin level could predict subsequent changes in insulin resistance, lipid profile, or body weight in a 2-yr longitudinal study. This study included 590 male Japanese subjects, aged 30-65 yr, who received annual health checkups in both 2000 and 2002. Blood pressure, heart rate, and anthropometric and metabolic parameters, including serum insulin and adiponectin levels, were determined. The insulin resistance index was calculated based on homeostasis model assessment. Baseline adiponectin level was not correlated with the subsequent change in lipid profile or BMI in 2 yr after adjustment for each baseline value. However, the baseline adiponectin level was negatively correlated with subsequent changes in insulin and insulin resistance index based on homeostasis model assessment, even after adjustment for change in BMI (r = -0.162 and r = -0.140, respectively). These findings suggest that the serum adiponectin concentration predicts subsequent changes in insulin resistance, but not in lipid profile or body weight.

Obesity as a cardiovascular risk factor

The prevalence of overweight and obesity continues to increase rapidly in the United States, with more than half of all adults currently overweight or obese. In general, people become obese because of a combination of inherited genes and a lifestyle consisting of low levels of physical activity and consumption of excess calories. Obesity, especially the central or visceral type, is a predisposing factor for the development of type 2 diabetes mellitus, hypertension, and cardiovascular disease (CVD). Obesity and type 2 diabetes are associated with insulin resistance. The relation among obesity, insulin resistance, and CVD appears to develop at a relatively young age. Central obesity is linked with hyperinsulinemia, insulin resistance, dyslipidemia, and proinflammatory and prothrombotic clinical states. Adipose tissue synthesizes and secretes biologically active molecules that may affect CVD risk factors. These chemical messengers include adiponectin, resistin, leptin, plasminogen activator inhibitor-1, tumor necrosis factor-alpha, and interleukin-6. In overweight and obese individuals, weight loss may improve insulin sensitivity, leading to reduction in risk factors for CVD and, consequently, the potential for cardiovascular events. Agents that improve insulin sensitivity, such as the thiazolidinediones, have been shown to reduce visceral obesity. Decreases in visceral adipose tissue contribute to improvements in insulin sensitivity and blood pressure, and weight loss reduces serum levels of triglycerides and low-density lipoprotein cholesterol while increasing serum levels of high-density lipoprotein cholesterol. Reduction of risk factors suggests that the development of cardiovascular disease will be reduced by the improvement of insulin sensitivity and weight loss.

The effect of leptin, tumor necrosis factor-alpha (TNF-alpha), and nitric oxide (NO) production on insulin resistance in Otsuka Long-Evans fatty rats

Adipocytokines and nitric oxide (NO) play important roles in type 2 diabetes; however, the regulatory mechanism has not been fully clarified. To investigate the role of adipocytokines and NO production on insulin resistance in type 2 diabetes, the LETO rats and the OLETF rats were fed a control diet or a high-fat diet for 4 weeks. After 4 weeks the blood levels of leptin, tumor necrosis factor-alpha (TNF-alpha), and NO were measured. As an indicator of insulin resistance, the homeostasis model assessment for insulin resistance (HOMA-R) was applied. Food intake in high-fat diet group rats was lower than in control diet group rats. The high fat diet increased body weight (BW), but did not significantly affect the HOMA-R and blood pressure (BP). Leptin and TNF-alpha levels were significantly higher in the OLETF rats than in the LETO rats, while NO levels did not change between the two groups. The high-fat diet elevated blood leptin levels, but not TNF-alpha and NO levels. The HOMA-R in the OLETF rats was correlated with leptin, but not with BP, BW, TNF-alpha or NO. NO showed an inverse correlation with BP. In conclusion, leptin, TNF-alpha, and NO may each regulate insulin sensitivity through their own unique pathways. The elucidation of the regulatory mechanism of adipocytokines and NO may give a clue to clarify the pathophysiology of insulin resistance.

Resistance to high-fat diet-induced obesity and altered expression of adipose-specific genes in HSL-deficient mice

To elucidate the role of hormone-sensitive lipase (HSL) in diet-induced obesity, HSL-deficient (HSL-/-) and wild-type mice were fed normal chow or high-fat diets. HSL-/- mice were resistant to diet-induced obesity showing higher core body temperatures. Weight and triacylglycerol contents were decreased in white adipose tissue (WAT) but increased in both brown adipose tissue (BAT) and liver of HSL-/- mice. Serum insulin levels in the fed state and tumor necrosis factor-alpha mRNA levels in adipose tissues were higher, whereas serum levels of adipocyte complement-related protein of 30 kDa (ACRP30)/adiponectin and leptin, as well as mRNA levels of ACRP30/adiponectin, leptin, resistin, and adipsin in WAT, were lower in HSL-/- mice than in controls. Expression of transcription factors associated with adipogenesis (peroxisome proliferator-activated receptor-gamma, CAAT/enhancer-binding protein-alpha) and lipogenesis (carbohydrate response element-binding protein, adipocyte determination- and differentiation-dependent factor-1/sterol regulatory element-binding protein-1c), as well as of adipose differentiation markers (adipocyte lipid-binding protein, perilipin, lipoprotein lipase), lipogenic enzymes (glycerol-3-phosphate acyltransferase, acyl-CoA:diacylglycerol acyltransferase-1 and -2, fatty acid synthase, ATP citrate lyase) and insulin signaling proteins (insulin receptor, insulin receptor substrate-1, GLUT4), was suppressed in WAT but not in BAT of HSL-/- mice. In contrast, expression of genes associated with cholesterol metabolism (sterol-regulatory element-binding protein-2, 3-hydroxy-3-methylglutaryl-CoA reductase, acyl-CoA:cholesterol acyltransferase-1) and thermogenesis (uncoupling protein-2) was upregulated in both WAT and BAT of HSL-/- mice. Our results suggest that impaired lipolysis in HSL deficiency affects lipid metabolism through alterations of adipose differentiation and adipose-derived hormone levels.

Increased expression of TNF-alpha, IL-6, and IL-8 in HALS: implications for reduced adiponectin expression and plasma levels

Human immunodeficiency virus (HIV)-associated lipodystrophy syndrome (HALS) is a side effect of highly active antiretroviral therapy of HIV-infected patients; however, the mechanism of the lipodystrophy and insulin resistance seen in this syndrome remains elusive. Adiponectin, an adipocyte-specific protein, is thought to play an important role in regulating insulin sensitivity. We investigated circulating levels and gene expression of adiponectin in subcutaneous abdominal adipose tissue (AT) from 18 HIV-infected patients with HALS compared with 18 HIV-infected patients without HALS. Implications of cytokines for adiponectin levels were investigated by determining circulating levels of TNF-alpha, IL-6, and IL-8 as well as gene expression of these cytokines in AT. HALS patients exhibited 40% reduced plasma adiponectin levels (P < 0.05) compared with non-HALS subjects. Correspondingly, adiponectin mRNA levels in AT were reduced by >50% (P = 0.06). HALS patients were insulin resistant, and a positive correlation was found between plasma adiponectin and insulin sensitivity (r = 0.55, P < 0.01) and percent limb fat (r = 0.61, P < 0.01). AT mRNA of TNF-alpha, IL-6, and IL-8 was increased in AT of HALS subjects (P < 0.05), and both AT TNF-alpha mRNA and plasma TNF-alpha were negatively correlated to plasma adiponectin (P < 0.05). Finally, TNF-alpha was found in vitro to inhibit human AT adiponectin mRNA by 80% (P < 0.05). In conclusion, HALS patients have reduced levels of plasma adiponectin and adiponectin mRNA in AT. Increased cytokine mRNA in AT is hypothesized to exert an inhibitory effect on adiponectin gene expression and, consequently, to play a role in the reduced plasma adiponectin levels found in HALS patients.

Conjugated linoleic acid enhances plasma adiponectin level and alleviates hyperinsulinemia and hypertension in Zucker diabetic fatty (fa/fa) rats

Adiponectin is a recently discovered hormone secreted by adipocytes that has been reported to enhance insulin sensitivity. Although insulin resistance and/or compensatory hyperinsulinemia are considered to be involved with hypertension in obese humans, the relationship between plasma adiponectin level and obesity-related hypertension has not been fully clarified. In this study, we investigated the effect of dietary conjugated linoleic acid (CLA), reported as an insulin sensitizer, on plasma adiponectin, plasma insulin, and blood pressure in Zucker diabetic fatty (ZDF) rats. During the onset of obesity, blood pressure increased in ZDF rats. The increase, however, was prevented by dietary CLA. After 8 weeks, accumulated plasma insulin and glucose were also attenuated by CLA feeding. Dietary CLA increased plasma adiponectin levels in ZDF rats and the increase was attributed to the enhanced mRNA expression in white adipose tissue. This study provides the first evidence that dietary CLA increases plasma adiponectin level through the enhancement of mRNA expression. We speculate that the increase alleviates hyperinsulinemia and prevents the onset of hypertension in CLA-fed ZDF rats.

Antiatherogenic effect of pioglitazone in type 2 diabetic patients irrespective of the responsiveness to its antidiabetic effect

OBJECTIVE

Thiazolidinediones (TZDs), a class of insulin-sensitizing agents used clinically to treat type 2 diabetes, are also antiatherogenic. This study was designed to elucidate the relationship between the antiatherogenic and antidiabetic effects of pioglitazone, a TZD, in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

A total of 136 Japanese type 2 diabetic patients were included and divided into two groups: the pioglitazone-treated group (30 mg daily for 3 months) (n = 70) and the untreated control group (n = 66). The changes in glycolipid metabolism as well as plasma high-sensitivity C-reactive protein (CRP), leptin, adiponectin, and pulse wave velocity (PWV) were monitored to analyze the relationship between the antiatherogenic and antidiabetic effects of pioglitazone.

RESULTS

The pioglitazone treatment significantly reduced hyperglycemia, hyperinsulinemia, and HbA(1c) levels and increased plasma adiponectin concentrations relative to the control group (P < 0.01). It also significantly decreased CRP and PWV (P < 0.01). The antiatherogenic effect was observed in both the nonresponders showing <1% of reduction in HbA(1c) (n = 30) and responders showing >1% of reduction (n = 40). ANCOVA revealed that treatment with pioglitazone was associated with a low CRP and PWV, independent of the changes in parameters related to glucose metabolism.

CONCLUSIONS

This study represents the first demonstration of the antiatherogenic effect of pioglitazone in both nonresponders and responders with respect to its antidiabetic effect and suggests that pioglitazone can exert its antiatherogenic effect independently of its antidiabetic effect.

Decrease in serum adiponectin level due to obesity and visceral fat accumulation in children

OBJECTIVE

To determine whether serum adiponectin is decreased in obesity and is restored toward normal level after treatment in children.

RESEARCH METHODS AND PROCEDURES

Subjects were 53 Japanese obese children, 33 boys and 20 girls (6 to 14 years old), and 30 age-matched nonobese controls for measuring adiponectin (16 boys and 14 girls). Blood was drawn after an overnight fast, and the obese children were subjected to anthropometric measurements including waist and hip circumferences and skinfold thicknesses. Paired samples were obtained from 21 obese children who underwent psychoeducational therapy. Visceral adipose tissue area was measured by computed tomography. Adiponectin was assayed by an enzyme-linked immunosorbent assay.

RESULTS

The serum levels of alanine aminotransferase, uric acid, triglyceride, total cholesterol, low-density lipoprotein-cholesterol, total cholesterol/high-density lipoprotein-cholesterol, apo B, apo B/apo A(1), and insulin in obese children were higher than the reference values. Serum adiponectin level was lower in the obese children than in the controls (6.4 +/- 0.6 vs. 10.2 +/- 0.8 mg/L, means +/- SEM, p < 0.001). In 21 obese children whose percent overweight declined during therapy, the adiponectin level increased (p = 0.002). The adiponectin level was correlated inversely with visceral adipose tissue area in obese children (r = -0.531, p < 0.001). The inverse correlations of adiponectin with alanine aminotransferase, uric acid, and insulin were significant after being adjusted for percentage overweight, percentage body fat, or sex.

DISCUSSION

Serum adiponectin level is decreased in obese children depending on the accumulation of visceral fat and is restored toward normal level by slimming.

Effect of lifestyle modification on adipokine levels in obese subjects with insulin resistance

OBJECTIVE

To study the effect of weight loss in response to a lifestyle modification program on the circulating levels of adipose tissue derived cytokines (adipokines) in obese individuals with insulin resistance.

RESEARCH METHODS AND PROCEDURES

Twenty-four insulin-resistant obese subjects with varying degrees of glucose tolerance completed a 6-month program consisting of combined hypocaloric diet and moderate physical activity. Adipokines [leptin, adiponectin, resistin, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6)] and highly sensitive C-reactive protein were measured before and after the intervention. Insulin sensitivity index was evaluated by the frequently sampled intravenous glucose tolerance test.

RESULTS

Participants had a 6.9 +/- 0.1 kg average weight loss, with a significant improvement in sensitivity index and reduction in plasma leptin (27.8 +/- 3 vs. 23.6 +/- 3 ng/mL, p = 0.01) and IL-6 (2.75 +/- 1.51 vs. 2.3 +/- 0.91 pg/mL, p = 0.012). TNF-alpha levels tended to decrease (2.3 +/- 0.2 vs. 1.9 +/- 0.1 pg/mL, p = 0.059). Adiponectin increased significantly only among diabetic subjects. The reductions in leptin were correlated with the decreases in BMI (r = 0.464, p < 0.05) and with changes in highly sensitive C-reactive protein (r = 0.466, p < 0.05).

DISCUSSION

Weight reduction in obese individuals with insulin resistance was associated with a significant decrease in leptin and IL-6 and a tendency toward a decrease in circulating TNF-alpha, whereas adiponectin was increased only in diabetic subjects. Further studies are needed to elucidate the relationship between changes of adipokines and the health benefits of weight loss.

Low resistin levels in adipose tissues and serum in high-fat fed mice and genetically obese mice: development of an ELISA system for quantification of resistin

Obesity is a major risk factor for insulin resistance. Resistin, an adipocyte-derived hormone-like molecule, is considered to serve as an important link between obesity and insulin resistance. However, the physiological role of resistin and the mechanism by which it neutralizes insulin action are still unclear. There are also conflicting reports that cast doubt on the cause of insulin resistance. In this study, we developed an enzyme-linked immunosorbent assay (ELISA) system for quantification of mouse resistin levels, analyzed in relation to insulin resistance. C57BL/6J mice fed high-fat diet compared with normal diet had low resistin levels (by 70%, P<0.01) in epididymal adipose tissues. Genetically obese mice, db/db and KK-A(y), had hyperinsulinemia and hyperglycemia but low resistin levels (decreases by 83 and 90%, both P<0.01) compared with C57/BL6J mice in epididymal adipose tissues. Serum resistin levels determined by Western blotting showed a similar pattern to those in adipose tissues. Resistin levels in adipose tissues correlated with serum adiponectin concentrations positively (r=0.49). Our results indicate that the novel ELISA system is suitable for measurement of resistin levels in adipose tissues. The results do not support a role for resistin in insulin resistance.

Transgenic amplification of glucocorticoid action in adipose tissue causes high blood pressure in mice

Obesity is closely associated with the metabolic syndrome, a combination of disorders including insulin resistance, diabetes, dyslipidemia, and hypertension. A role for local glucocorticoid reamplification in obesity and the metabolic syndrome has been suggested. The enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) regenerates active cortisol from inactive 11-keto forms, and aP2-HSD1 mice with relative transgenic overexpression of this enzyme in fat cells develop visceral obesity with insulin resistance and dyslipidemia. Here we report that aP2-HSD1 mice also have high arterial blood pressure (BP). The mice have increased sensitivity to dietary salt and increased plasma levels of angiotensinogen, angiotensin II, and aldosterone. This hypertension is abolished by selective angiotensin II receptor AT-1 antagonist at a low dose that does not affect BP in non-Tg littermates. These findings suggest that activation of the circulating renin-angiotensin system (RAS) develops in aP2-HSD1 mice. The long-term hypertension is further reflected by an appreciable hypertrophy and hyperplasia of the distal tubule epithelium of the nephron, resembling salt-sensitive or angiotensin II-mediated hypertension. Taken together, our findings suggest that overexpression of 11beta-HSD1 in fat is sufficient to cause salt-sensitive hypertension mediated by an activated RAS. The potential role of adipose 11beta-HSD1 in mediating critical features of the metabolic syndrome extends beyond obesity and metabolic complications to include the most central cardiovascular feature of this disorder.