Enteroinsular axis of db/db mice and efficacy of dipeptidyl peptidase IV inhibition.

In type 2 diabetic patients, the administration of glucagon-like peptide-1 (GLP-1), known as an incretin, exerts antidiabetic effects. However, GLP-1 is rapidly degraded by dipeptidyl peptidase IV (DPPIV) after its release. DPPIV inhibition is thought to be a rational strategy to treat type 2 diabetes. In this study, using C57BLKS/J-db/db (db/db) mice as a model of type 2 diabetes, we examined the effect of acute DPPIV inhibition on glucose tolerance at the early and later stages of diabetes, determining plasma active GLP-1 and insulin levels. In addition, we investigated changes of plasma DPPIV activity. Compared with normal C57BL6/J (B6) and db/+ mice, significantly increased plasma DPPIV activities were observed in db/db mice. Expression of the proglucagon gene encoding GLP-1 was significantly upregulated in the colon of db/db mice. The administration of valine-pyrrolidide, a DPPIV inhibitor, resulted in potentiated insulin secretion mediated by increased endogenous GLP-1 action, leading to improved glucose tolerance in db/db mice at 6 weeks of age. However, although acute DPPIV inhibition with valine-pyrrolidide resulted in higher plasma active GLP-1 and insulin levels in db/db mice at 23 weeks of age, it did not improve glucose tolerance. The function of the enteroinsular axis is preserved in both stage of diabetes and the DPPIV inhibitor potentiated it, but the progression of insulin resistance appeared to block the improvement of glucose tolerance through DPPIV inhibition. Our results suggest that DPPIV inhibition is a suitable approach for treatment of impaired glucose tolerance (IGT), and type 2 diabetes in the early stage.