Proposed mechanisms underlying the positive therapeutic effects of sitagliptin and exendin-4 on kidney ischemia-reperfusion (IR) injury. GLP-1R, glycogen-like peptide-1 receptor; TNF, tumor necrotic factor; MMP, matrix metalloproteinase; NF, nuclear factor; HO, heme oxygenase; NQO, NAD(P)H quinone oxidoreductase; GR, glutathione reductase; GPx, glutathione peroxidase; NOX, ADPH oxidase; SOD, superoxide dismutase; PARP, poly(ADP-ribose) polymerase; BUN, blood urine nitrogen.