Amelioration of diet-induced diabetes mellitus by removal of visceral fat

Abstract

The effect of visceral fat removal upon glucose homeostasis, insulin signal transduction, and serum adipokine levels in an animal model of diet-induced obesity and diabetes mellitus (DIO) was evaluated. Swiss mice were initially divided into two groups fed with regular rodent chow or with chow containing 24 g% saturated fat (DIO). DIO mice became obese and overtly diabetic after 8 weeks. DIO mice were then divided into three groups: control, sham, and visceral (epididymal and perinephric) fat removal. All groups were submitted to evaluation of basal glucose and insulin levels and i.p. insulin tolerance test. Insulin signal transduction in muscle was evaluated by immunoprecipitation and immunoblot, and serum adipokine levels were determined by ELISA. DIO mice became diabetic (228 versus 115 mg/dl), hyperinulinemic (7.59 versus 3.15 ng/ml) and insulin resistant (Kitt 2.88 versus 4.97%/min) as compared with control. Visceral fat removal partially reverted all parameters (147 mg/dl glucose; 3.82 ng/ml insulin; and 4.20%/min Kitt). In addition, visceral fat removal completely reversed the impairment of insulin signal transduction through insulin receptor, insulin receptor substrate (IRS)-1, IRS-2 and Akt in muscle. Finally, serum levels of the pro-inflammatory cytokines tumour necrosis factor-α, interleukin (IL)-1β and IL-6 were significantly increased, while adiponectin levels were significantly reduced in DIO mice. After visceral fat removal the levels of adipokines returned to near control levels. The present study shows that removal of visceral fat improves insulin signal transduction and glucose homeostasis in an animal model of diet-induced obesity and diabetes mellitus and these metabolic and molecular outcomes are accompanied by the restoration of adipokine levels.