Effects of 6-Month Sitagliptin Treatment on Insulin and Glucagon Responses in Korean Patients with Type 2 Diabetes Mellitus

A genetic variant in GLP1R is associated with response to DPP-4 inhibitors in patients with type 2 diabetes

Incretin hormone-based therapy in type 2 diabetes has been widely used, and dipepdityl peptidase-4 (DPP-4) inhibitors, which prevent incretin degradation, have become popular oral hypoglycemic agents. The efficacy of DPP-4 inhibitors varies from individuals, and factors determining responses to DPP-4 inhibitors have not been fully established. We aimed to investigate whether genetic variations in glucagon-like peptide (GLP-1) receptor are associated with responses to DPP-4 inhibitors in patients with type 2 diabetes.Genetic variations of rs3765467 in GLP-1 receptor were explored in 246 patients with type 2 diabetes who received DPP-4 inhibitors treatment for 24 weeks in addition to previous medication. Patients with glycated hemoglobin (HbA1c) > 7% and who were naive to any DPP-4 inhibitors were enrolled. Responders were defined as those who showed a > 10% reduction in HbA1c after DPP-4 inhibitor treatment.DPP-4 inhibitors improved glycemic parameters and lipid profiles. Compared to the major genotype (GG), a larger proportion of patients with the minor allele genotype (GA/AA) were responders (P = 0.018), and also showing greater HbA1c reductions (1.3 ± 1.1 vs 0.9 ± 1.2%; P = 0.022). This genetic effect remained significant even after adjustment for other confounding factors (OR = 2.00, 95% CI = 1.03-3.89).Polymorphism in the GLP-1 receptor may influence DPP-4 inhibitor response. Further studies in larger population will help determine the association between genetic variation and interindividual differences in DPP-4 inhibitor therapy.

Effects of sitagliptin on circulating zinc-α2-glycoprotein levels in newly diagnosed type 2 diabetes patients: a randomized trial

OBJECTIVE

Zinc-α2-glycoprotein (ZAG) has recently been characterized as a potent metabolic regulator. However, the effects of anti-diabetic agents on circulating ZAG levels in humans remain largely unknown. To explore the possible mechanisms by which the dipeptidyl peptidase-IV (DPP-IV) inhibitor improves insulin resistance, we investigated the effect of sitagliptin, a DPP-IV inhibitor, on circulating cytokine levels in newly diagnosed type 2 diabetes (nT2DM) patients.

DESIGN AND METHODS

A subset of 141 subjects with nT2DM were assigned to receive placebo (n=47) or sitagliptin (n=94) for 3 months. Before and after treatment, subjects received a 75 g oral glucose tolerance test, euglycemic-hyperinsulinemic clamp (EHC), and measurement of ZAG and adiponectin (ADI) concentrations.

RESULTS

Circulating ZAG levels were lower in nT2DM than in control individuals (P<0.01). After 3 months of sitagliptin treatment, HbA1c, fasting plasma glucose, postprandial glucose, 2-h insulin after glucose overload, triglycerides, and homeostasis model assessment of insulin resistance (HOMA-IR) were decreased significantly compared with pre-treatment (P<0.05 or P<0.01), whereas the glucose infusion rate during the stable period of the clamp (M values) during EHC were significantly increased (P<0.01). In addition, circulating ZAG and ADI concentrations were significantly increased along with improved glucose metabolism and insulin sensitivity compared with pre-treatment (both P<0.01) and the change of ZAG (ΔZAG) was positively associated with ΔADI, ΔHOMA-IR, ΔBMI, Δfasting insulin and negatively associated with Δ tumor necrosis factor-α (TNF-α). Furthermore, sitagliptin treatment resulted in significantly lowered plasma TNF-α level (P<0.05).

CONCLUSION

A low level of circulating ZAG is associated with insulin resistance and sitagliptin treatment significantly increases circulating ZAG levels. These observations have implications in relation to the mode of action of the DPP-IV inhibitor as an insulin sensitizing agent.