This view is substantiated by the known role of DPP-4 in inflammation [89–91], the involvement of inflammation in PD progression and aging [19, 92–96], the maintenance of the drug targets GLP-1R and GIPR across age and in PD brain, and the efficacy of the GLP-1R agonist exenatide in phase 2 clinical trials in moderate PD [28–30]. Here, GIPR is linked to Parkinson disease.