Elevated Levels of Interleukin 6 Are Reduced in Serum and Subcutaneous Adipose Tissue of Obese Women after Weight Loss*

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Abstract
The aim of this study was to investigate the potential role of adipose cytokines in the obesity-associated insulin resistance. To that end, we compared: 1) serum concentrations of interleukin 6 (IL-6), tumor necrosis factor α (TNFα), and leptin in eight healthy lean control females and in android obese female without (n = 14) and with (n = 7) type 2 diabetes; and 2) the levels of these cytokines both in serum and in sc adipose tissue in the 14 obese nondiabetic women before and after 3 weeks of a very low-calorie diet (VLCD). As compared with lean controls, obese nondiabetic and diabetic patients were more insulin resistant and presented increased values for leptin, IL-6, TNFα, and C-reactive protein. In the whole group, IL-6 values were more closely related to the parameters evaluating insulin resistance than leptin or TNFα values. VLCD resulted in weight loss and decreased body fat mass (∼3 kg). Insulin sensitivity was improved with no significant change in both serum and adipose tissue TNFα levels. In contrast, VLCD induced significant decreases in IL-6 and leptin levels in both adipose tissue and serum. These results suggest that, as for leptin, circulating IL-6 concentrations reflect, at least in part, adipose tissue production. The reduced production and serum concentrations after weight loss could play a role in the improved sensitivity to insulin observed in these patients.