Inhibition of DPP-4 with sitagliptin improves glycemic control and restores islet cell mass and function in a rodent model of type 2 diabetes

Inhibition of dipeptidyl peptidase-4 (DPP-4) activity has been shown to improve glycemic control in patients with type 2 diabetes by prolonging and potentiating the actions of incretin hormones. This study is designed to determine the effects of the DPP-4 inhibitor sitagliptin on improving islet function in a mouse model of insulin resistance and insulin secretion defects. ICR mice were pre-treated with high fat diet and a low dose of streptozotocin to induce insulin resistance and impaired insulin secretion, respectively. Diabetic mice were treated with sitagliptin or the sulfonylurea agent glipizide as admixture to high fat diet for ten weeks. Sustained reduction of blood glucose, HbA1c, circulating glucagon and improvement in oral glucose tolerance were observed in mice treated with sitagliptin. In contrast, glipizide improved glycemic control only during the early weeks and to a lesser degree compared to sitagliptin, and had no effect on circulating glucagon levels or glucose tolerance. The improvement in glycemic control in sitagliptin-treated mice was associated with a significant increase in glucose-dependent insulin secretion in both perfused pancreas and isolated islets. Importantly, in contrast to the lack of effect by glipizide, sitagliptin significantly restored β and α cell mass as well as α/β cell ratio. These data indicate that DPP-4 inhibition by sitagliptin provided better overall improvement of glycemic control compared to glipizide in the high fat diet/streptozotocin induced diabetic mouse model. The ability of sitagliptin to enhance islet cell function may offer insight into the potential for disease modification.