Dipeptidyl peptidase-4 (DPP-4) inhibitors prevent the degradation of glucagon-like peptide-1 (GLP-1) and improve glycemic control. The GLP-1 insulinotropic effect involves a pathway through vagus nerve GLP-1 receptors in the gut, in addition to a direct effect on the pancreas. Therefore, this study verified whether DPP-4 inhibition in the gut contributed to the improvement of glycemic control. Anagliptin, a DPP-4 inhibitor, was administered orally or subcutaneously (with or without passing through the gastrointestinal tract, respectively) to mice. The association between blood glucose suppression following oral glucose challenge and DPP-4 inhibition in the small intestine and plasma was assessed. Oral administration of anagliptin (0.03-0.3 mg/kg) in normal mice significantly suppressed blood glucose, which was associated with an increase in insulin secretion at a dose of ≥0.1 mg/kg (P < 0.05). Subcutaneous administration of anagliptin (0.01-0.1 mg/kg) produced similar results. However, plasma DPP-4 inhibition following oral administration was weaker than that following subcutaneous administration; blood glucose suppression was significantly correlated with small intestinal DPP-4 inhibition (r = 0.949, P < 0.01), but not with plasma DPP-4 inhibition. Additionally, similar results were observed in a type 2 diabetes model (r = 0.975, P < 0.001). Thus, these results demonstrated that an improvement in glycemic control was dependent upon small intestinal DPP-4 inhibition. As these effects were accompanied by the elevation of intact GLP-1 in the portal, this suggests that improvement in glucose tolerance after anagliptin treatment might be related to an increase in GLP-1 receptor signaling in the small intestine and portal vein.
Keywords: Dipeptidyl peptidase-4; Dipeptidyl peptidase-4 inhibitor; Glucagon-like peptide-1; Hepatic portal; Intestine.
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