Bezafibrate on lipids and glucose metabolism in obese diabetic otsuka Long-Evans Tokushima fatty rats

Type 2 diabetes is caused by insulin resistance and β-cell dysfunction. The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an established animal model of human type 2 diabetes that exhibits chronic and slowly progressive hyperglycemia and hyperlipidemia and is accompanied by progressive fibrosis in the islets. The aim of the present study was to examine whether worsening of hyperglycemia, insulin resistance, and histologic alterations of the islets in OLETF rats is related to hyperlipidemia by treating these animals with a lipid-lowering drug, bezafibrate. The bezafibrate-treated groups of OLETF and their control counterpart Long-Evans Tokushima Otsuka (LETO) rats received a bezafibrate-rich diet (150 mg/100 g normal chow) for 16 weeks, from 12 to 28 weeks of age, while the other groups of rats received standard rat chow. Bezafibrate treatment significantly reduced serum triglyceride (TG) and free fatty acid (FFA) levels, suppressed the increase in islet size, and inhibited the expression of α-smooth muscle actin, a marker for activated pancreatic stellate cells that are involved in the fibrosis of the pancreas, in the islets in OLETF rats, but had no influences on food intake, body weight gain, abdominal adipose depots, and pancreatic insulin content in both strains of rats. Although bezafibrate significantly reduced circulating lipid levels and suppressed the increase in insulin secretion evaluated by area under the curve (AUC) analysis in response to an intravenous glucose tolerance test (IVGTT) until the end of the experiment, improvement of insulin resistance was observed only for the first 8 weeks after the onset of bezafibrate treatment. These results suggest that dyslipidemia is not responsible for the reduced insulin sensitivity, but the impairment of glucose tolerance is the primary defect in the OLETF rats, although improvement of dyslipidemia suppressed histologic alterations in the islets and temporally improved insulin resistance.