Effect of sitagliptin, a dipeptidyl peptidase-4 inhibitor, on beta-cell function in patients with type 2 diabetes: a model-based approach

Purpose:  The purpose of this exploratory analysis was to assess the effect of sitagliptin, a dipeptidyl peptidase-4 inhibitor, on pancreatic beta-cell function using a model-based analysis. Methods:  Data for this analysis were from three large, placebo-controlled clinical studies that examined sitagliptin 100 mg q.d. as add-on to metformin therapy or as monotherapy over 18 or 24 weeks. In these studies, subsets of patients consented to undergo extensive blood sampling as part of a nine-point meal tolerance test performed at baseline and study end-point. Blood samples were collected at −10, 0, 10, 20, 30, 60, 90, 120 and 180 min relative to the start of a meal and subsequently were assayed for plasma glucose and serum C-peptide concentrations. Parameters for beta-cell function were calculated using the C-peptide minimal model, which estimates insulin secretion rate (ISR) and partitions the ISR into basal (Φb; ISR at basal glucose concentrations), static (Φs; ISR at above basal glucose concentrations following a meal) and dynamic (Φd; ISR in response to the rate of increase in above basal glucose concentrations following a meal) components. The total responsivity index (Φtotal; average ISR over the average glucose concentration) is calculated as a function of Φs, Φd and Φb. Insulin sensitivity was assessed with a validated composite index (ISI). Disposition indices (DI), which assess insulin secretion in the context of changes in insulin sensitivity, were calculated as the product of Φand ISI. Results:  When administered in combination with ongoing metformin therapy or as monotherapy, sitagliptin was associated with substantial reductions in postprandial glycaemic excursion following a meal challenge relative to placebo. Sitagliptin produced significant (p < 0.05 vs. placebo) improvements in Φs and Φtotal, regardless of treatment regimen (add-on to metformin or as monotherapy). For Φd, there was a numerical, but not statistically significant, improvement with sitagliptin relative to placebo. Treatment with sitagliptin increased Φb, but the difference relative to placebo was only significant with monotherapy. ISI was not significantly different between sitagliptin and placebo. The DIs for the static, dynamic and total measures were significantly (p < 0.05) increased with sitagliptin treatment relative to placebo. Conclusions:  In this model-based analysis, sitagliptin improved beta-cell function relative to placebo in both fasting and postprandial states in patients with type 2 diabetes.