DPP4 and diabetes mellitus: Alkaloids, in recent years, have received extra attention due to their potential role in the treatment of diabetes through inhibition of α-glucosidase, α-amylase [59, 61], dipeptidyl peptidase-4 (DPP-4), and AGEs and by possessing potent protein tyrosine phosphatase 1B (PTP1B) inhibitory effects [61].