Nonhuman primate pharmacokinetic/pharmacodynamic studies were undertaken to evaluate whether elevations in plasma and, more importantly, CNS levels of GIP and GLP-1 could be achieved with clinically translatable doses of the widely used DPP-4 inhibitor, sitagliptin, that were associated with neuroprotective, neuroregenerative, and anti-inflammatory actions that we demonstrated in a prior study involving a medial forebrain bundle 6-OHDA rat lesion model of PD [42]. This evidence concerns the gene GLP1R and Parkinson disease.