DPP4 and type 2 diabetes mellitus: Moreover, studies focusing on brain derived neurotrophic factor (BDNF), one of the most essential neurotrophic factors in the brain [27], and dipeptidyl peptidase-4 (DPP4), initially identified as a therapeutic target for type 2 diabetes [28], have demonstrated that both BDNF and DPP4 function as an antigenic enzyme involved in hyperglycemia, oxidative stress and inflammation-associated insulin resistance [29]).