DPP4 and diabetes mellitus: The first-line treatment for diabetes is glucose-lowering therapy targeting different aspects of glucose metabolism, including insulin sensitivity (e.g., metformin and thiazolidinediones), insulin secretion and bioactivity (e.g., sulfonylureas, glucagon-like peptide 1 [GLP-1] analogues, dipeptidyl peptidase 4 [DPP-4] inhibitors, and insulin analogues), and modulation of blood glucose levels either by increased excretion (e.g., sodium–glucose cotransporter 2 inhibitors, SGLT2i) or by delaying onset following nutrient digestion (e.g., α-glucosidase inhibitors and amylin) [6].