Regulating adiponectin: of flax and flux

Role of adipokines in complications related to obesity: a review

Worldwide, the prevalence of overweight and obesity and associated complications is increasing. Cardiovascular complications are the most important factor determining survival and influencing clinical management. However, obesity is also associated with an increased risk of metabolic syndrome, type 2 diabetes, cancer and other diseases. The development of complications depends on the amount of body fat and its endocrine function. The hormones (leptin, adiponectin, resistin) and cytokines (TNF alpha, IL-6, PAI-1) produced by the adipose tissue are the link between obesity and obesity-related complications. The present article discusses the structure, function and clinical significance of adipokines.

The sympathetic nervous system and the metabolic syndrome

Studies performed in the past two decades have unequivocally shown that several of the components of the metabolic syndrome are associated with indirect and direct markers of adrenergic overdrive. This is the case for hypertension and obesity, in which resting tachycardia, elevated plasma norepinephrine values, increased sympathetic nerve traffic, as well as augmented levels of total and regional norepinephrine spillover have been reported. This is also the case for insulin resistance, i.e. a metabolic condition frequently complicating the various components of the pathological condition identified as the 'metabolic syndrome'. After briefly describing the epidemiological and the cardiovascular risk profile of the disease, this paper will examine the behaviour of the sympathetic nervous system in the metabolic syndrome as well as the mechanisms potentially responsible for this neurogenic abnormality. This will be followed by an analysis of the role played by neuroadrenergic factors in disease progression as well as in the pathogenesis of its complications. Finally, the therapeutic implications of these findings will be highlighted.

Adiponectin gene expression and adipocyte NF-kappaB transcriptional activity in elderly overweight and obese women: inter-relationships with fat distribution, hs-CRP, leptin and insulin resistance

OBJECTIVE

The regulatory processes that modulate adiponectin production and the mechanisms involved in nuclear factor kB (NF-kB) transcriptional activity in human adipocytes are not yet fully known. The aim of our study was to evaluate the inter-relationships between body fat, fat distribution, systemic inflammation, insulin resistance, leptin and the serum and subcutaneous adipose tissue gene expression levels of tumor necrosis factor-alpha (TNF-alpha), adiponectin and the inhibitor kappa B-alpha (IkB-alpha), in subjects with a wide range of body mass index (BMI). We also wanted to determine which of these variables was most closely related to adiponectin gene expression and adipocyte NF-kB transcriptional power.

METHODS

A total of 27 women aged between 50 and 80 years, with BMI ranging from 22.1 to 53.3 kg/m(2), were studied. In all subjects BMI, waist circumference, body composition by dual X-ray absorptometry, triglycerides, cholesterol, high-density lipoprotein cholesterol (HDL-Ch), glucose, insulin, homeostasis model assessment of insulin resistance (HOMA), high-sensitive C-reactive protein (hs-CRP), serum adiponectin, leptin and TNF-alpha were evaluated. Subcutaneous adipose tissue biopsies were taken from the abdomen of all subjects and the mRNA levels of adiponectin, TNF-alpha and IkB-alpha were determined.

RESULTS

BMI and waist circumference were associated positively with leptin, HOMA, and hs-CRP, and negatively with HDL-Ch; waist was also associated with adiponectin and IkB-alpha mRNA. HOMA was negatively associated with serum adiponectin and adiponectin mRNA. Hs-CRP was negatively associated with IkB-alpha mRNA, and was positively associated with HOMA. Step-down multiple regression analysis was performed to determine the joint effects of BMI, waist circumference, triglycerides, HDL-Ch, HOMA, hs-CRP, leptin, serum and TNF-alpha mRNA on adiponectin gene expression: waist circumference and leptin were both included in the best fitting regression equation for predicting adiponectin gene expression (R(2)=0.403, P=0.006). Stepwise multiple regression analysis was performed, considering IkB-alpha mRNA as a dependent variable and BMI, waist, HDL-Ch, HOMA, hs-CRP and adiponectin mRNA as independent variables. Adiponectin mRNA was the only variable to enter the regression (R(2)=0.406, P<0.001).

CONCLUSION

Our results suggest that abdominal adiposity and leptin are independent predictors of adiponectin gene expression and that in human adipocytes, adiponectin gene expression is strongly related to IkB-alpha mRNA.

Neel revisited: the adipocyte, seasonality and type 2 diabetes

The modern epidemic of obesity and insulin resistance with cardiovascular risk factor clustering is related to the development of type 2 diabetes and cardiovascular disease. Over 40 years ago, Neel postulated that insulin resistance should confer survival benefit. Extrapolating Neel's hypothesis, we propose that the cluster of associated abnormalities also confers survival benefit and is related to metabolic responses seen in seasonally responsive animals. Weight gain in preparation for winter is accompanied by a range of acute metabolic changes virtually identical to the long-term changes seen in type 2 diabetes. In seasonal animals the responses are acute, physiological and protective. In man, similar responses that would once have conferred survival benefit have become chronic, pathological and harmful in modern life. We hypothesise that type 2 diabetes and cardiovascular disease in man are the result of chronic and inappropriate pineal-hypothalamic-adipocyte interactions biologically related to seasonal change.