N-acetyl-l-cysteine improves function of islet beta cell in hyperlipidemic rats and its mechanism

Abstract

To investigate the effect of N-acetyl-l-cysteine (NAC) on islet beta cell function in hyperlipidemic rats and its mechanism. Fifty-nine male SD rats of 8 week old were randomly divided into 3 groups: normal diet group(NC, n=20), high fat diet group (HF, n=20) and NAC treated group (NAC, n=19, NAC 300 mg x kg(-1) x d(-1) and high fat diet). At the end of 20 weeks, fasting serum insulin (Ins), glucose(Glu), malonaldehyde (MDA) and reduced glutathione (GSH) were determined in plasma and pancreas tissue. The glucose infusion rate (GIR) was measured by euglycemic hyperinsulinemia clamp to evaluate the peripheral insulin resistance.Pancreatic islets were isolated and subjected to a perifusion medium containing 3.3 mmol/L glucose for 15 min, followed by 16.7 mmol/L glucose for 30 min, insulin content of perifusion medium was measured by RIA. The expressions of IRS-1, IRS-2, Glut-2 gene in islets were detected by real time PCR. (1)The insulin, glucose and MDA concentration in HF group were higher than those in NC group, but GSH levels in plasma and pancreas were lower. NAC intervention could reverse these effects. (2)The GIR was decreased significantly in HF group compared with NC group [(5.25 +/-1.2) Compared with (13.56 +/-1.7) mg x min(-1) x kg(-1), P<0.01], NAC intervention reversed these effect: GIR[(9.28 +/-1.50) Compared with (5.25 +/-1.2)mg x min(-1) x kg(-1), P<0.01]. (3) 16.7 mmol/L glucose increased the insulin secretion in the islet cells of the three groups, but the peak was lower in HF group. NAC intervention reversed these effects. (4) The gene expression of IRS-1 was significantly decreased by 42.3 % in HF group (P<0.05), and the expressions of IRS-2 and Glut-2 were decreased by 28.1% and 22.9% (P<0.05) compared with NC group. In contrast, the expressions of IRS-1, IRS-2, Glut-2 in NAC group increased by 40.2%, 30.2% and 19.1%, respectively than those in HF group. NAC can reverse functional disorder of islet beta cells induced by high-fat-diet feeding. This antioxidant effect might be associated with upgrading gene expression of insulin signal transduction molecules in islet beta cells.