Effect of diet-induced weight loss on plasma apelin and cytokine levels in individuals with the metabolic syndrome

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Background and aims Adipose tissue is an active endocrine organ that secretes signaling molecules involved in the regulation of insulin sensitivity, food intake and inflammation. Apelin is a peptide secreted by adipose tissue that has been shown to modulate cardiovascular tone in animals. The aim of this study was to measure abdominal fat, blood pressure and circulating apelin, adiponectin, leptin, ghrelin, TNF-α and IL-6 levels in patients with the metabolic syndrome after a diet-induced weight loss. Methods and results 35 obese individuals with the metabolic syndrome underwent an 8-week very-low-calorie diet (VLCD) and a 6-month weight maintenance period (WM) with 120 mg orlistat or placebo administered 3 times daily. VLCD and WM (−15.1 ± 1.0 kg) decreased mean arterial pressure (MAP), insulin, leptin, triglycerides and visceral and subcutaneous adipose tissue. Moreover, adiponectin increased in response to the weight loss. However, the overall changes in plasma apelin, TNF-α and IL-6 were non-significant. A correlation between plasma apelin and TNF-α was observed at baseline (0.41, p < 0.05), and the minor changes in plasma apelin levels were associated with changes in BMI during VLCD and MAP and TNF-α during VLCD and WM periods. Conclusion Despite reductions in BMI, body adiposity, MAP and enhancement of glucose metabolism and adiponectin in response to weight loss, no significant changes in plasma apelin, TNF-α and IL-6 were observed. However, apelin significantly correlated with TNF-α and MAP. These results suggest that apelin may not be that strongly correlated with the fat mass as an adipokine like the more abundant adipokines adiponectin or leptin and it might be involved in the regulation of inflammation and cardiovascular tone.