GLP1R and type 2 diabetes mellitus: According to the pharmacodynamic studies of alogliptin, saxagliptin, sitagliptin, and linagliptin, the DPP4 inhibitors significantly increased native GLP-1 levels in patients with T2DM (compared with placebo), yielding an average level of ≤ 19.0 pmol/L (Table 2 and Figure S1) (20–23).