DPP4 and diabetes mellitus: As the main core etiological factors, data from recent studies confirmed that blockade of the positive feedback loop between AGE-receptor for advanced glycation end products (RAGE) axis by dipeptidyl peptidase-4 inhibitors might be a novel therapeutic target for vascular injury in diabetes [46], and furthermore exendin-4 could exert cardioprotective effect against diabetic cardiomyopathy, which may be associated with the inhibition of RAGE expression [47].