GCG and type 2 diabetes mellitus: Because GLP-1 is cleaved in vivo by dipeptidyl peptidase-4 (DPP-4) (EC number: 3.4.14.5) and the circulating half-life of GLP-1 in diabetic patients is only 1.5 to 2 min [29], GLP-1 receptor agonists (GLP-1RAs) for the treatment of T2DM are widely developed and used.