DPP4 and diabetes mellitus: There are many treatments for DM, and all of them are classified according to their mechanism of action into seven principal groups: insulin sensitizers (thiazolidinediones and biguanides), secretagogues (meglitinides and sulfonylureas), dipeptidyl peptidase-4 (DPP-4) inhibitors, incretin mimetics, glucagon-like peptide-1 (GLP-1) inhibitors, α-glucosidase inhibitors and sodium-glucose cotransporter (SGLT) inhibitors [34,35].