These same NHP doses in our present study, notably, align with those selected in our previous rat 6-OHDA studies (10 and 30 mg/kg sitagliptin [42]) in which sitagliptin significantly elevated plasma and brain incretin levels, and mitigated neuroinflammation and, importantly, neurodegeneration of the dopaminergic system in a well characterized rodent PD model [42]. This evidence concerns the gene GCG and Parkinson disease.