DPP4 and diabetes mellitus: Insulin, metformin, sodium-glucose cotransporter 2 (SGLT-2) inhibitors, incretin-based agent-like glucagon-like peptide-1 (GLP-1) receptor agonists (RAs), α-glucosidase inhibitors, sulfonylureas (SUF), dipeptidyl peptidase-4 (DPP-4) inhibitors, glinides, and thiazolidinediones (TZDs) are the currently available drugs for the treatment of diabetes [4].