DPP4 and type 2 diabetes mellitus: Exogenous administration of GLP-1 to regulate blood glucose is a possible therapeutic solution for T2DM; however, once subcutaneously injected, the N-terminal of the naturally occurring GLP-1 molecule is rapidly cleaved by the DPP-4 enzyme, thus generating an inactive GLP-1-(9-36) amide [14,15], resulting in a very short half-life of approximately 1.5 min [16].