DPP4 and infectious disease: Medicinal properties through inhibition of enzymatic reactions related to non-communicable diseases including obesity (lipase), diabetes (α-amylase, α-glucosidase, and dipeptidyl peptidase-IV), Alzheimer’s disease (acetylcholinesterase, butyrylcholinesterase, and β-secretase), and hypertension (angiotensin-converting enzyme) of SO and CO were also investigated.