A dipeptidyl peptidase-4 inhibitor, sitagliptin, exerts anti-inflammatory effects in type 2 diabetic patients.

AIMS/HYPOTHESIS: Glucagon-like peptide-1 (GLP-1) exerts beneficial effects on the cardiovascular system. Here, we examined the effect of sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, on systemic inflammation and pro-inflammatory (M1)/anti-inflammatory (M2)-like phenotypes of peripheral blood monocytes in diabetic patients. METHODS: Forty-eight type 2 diabetic patients were divided into the following two groups: sitagliptin-treatment (50mg daily for 3months) (n=24) and untreated control (n=24) groups. Measurements were undertaken to assess changes in glucose-lipid metabolism, serum levels of inflammatory cytokines such as serum amyloid A-LDL (SAA-LDL), C-reactive protein (CRP), interleukin-6 (IL-6), IL-10 and tumor necrosis factor-α (TNF-α). Furthermore, the effects of sitagliptin treatment on M1/M2-like phenotypes in peripheral blood monocytes were examined. RESULTS: Treatment with sitagliptin significantly decreased fasting plasma glucose, hemoglobin A1c (HbA1c), serum levels of inflammatory markers, such as SAA-LDL, CRP, and TNF-α. In contrast, sitagliptin increased serum IL-10, an anti-inflammatory cytokine, as well as plasma GLP-1. In addition, sitagliptin increased monocyte IL-10 expression and decreased monocyte TNF-α expression. Multivariate regression analysis revealed that the sitagliptin treatment was the only factor independently associated with an increase in monocyte IL-10 (ß=0.499; R(2)=0.293, P<0.05). However, other factors including the improvement of glucose metabolism were not associated with the increase. CONCLUSIONS/INTERPRETATION: This study is the first to show that a DPP-4 inhibitor, sitagliptin, reduces inflammatory cytokines and improves the unfavorable M1/M2-like phenotypes of peripheral blood monocytes in Japanese type 2 diabetic patients.