DPP4 and type 2 diabetes mellitus: To overcome many shortcomings of the classic anti-diabetic drugs (ADDs) such as hypoglycemia and weight gain etc., incretin-based drugs including GLP-1 analogues and dipeptidyl peptidase-4 (DPP4) inhibitors have been progressively developed and been regarded as a recommended drug for glycemic control in patients with T2DM [8].