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

TLDR

The study investigates whether adipose cytokines contribute to insulin resistance in obesity. The authors compared serum and subcutaneous adipose levels of IL‑6, TNFα, and leptin among lean controls, obese non‑diabetic and diabetic women, and assessed changes after a 3‑week very low‑calorie diet. Obese women exhibited higher insulin resistance and elevated IL‑6, TNFα, leptin, and CRP, with IL‑6 most closely linked to insulin resistance; a 3‑week very low‑calorie diet reduced body fat, improved insulin sensitivity, and significantly lowered IL‑6 and leptin in serum and adipose tissue, suggesting that decreased adipose‑derived IL‑6 contributes to insulin sensitivity gains.

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 alpha (TNFalpha), 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, TNFalpha, and C-reactive protein. In the whole group, IL-6 values were more closely related to the parameters evaluating insulin resistance than leptin or TNFalpha values. VLCD resulted in weight loss and decreased body fat mass (approximately 3 kg). Insulin sensitivity was improved with no significant change in both serum and adipose tissue TNFalpha 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.