DPP4 and diabetes mellitus: Enzyme inhibition reduced the risk of NCD occurrence including Alzheimer’s disease (β-secretase (BACE-1), butyrylcholinesterase (BChE) and acetylcholinesterase (AChE)), obesity (lipase), hypertension (angiotensin-converting enzyme (ACE)) and diabetes mellitus (dipeptidyl peptidase-IV (DPP-IV), α-glucosidase and α-amylase).