GIP and Parkinson disease: This efficacy associated with an inhibition of DPP-4 activity and a rise in GLP-1 and GIP levels in plasma and brain [42], and was achieved with a gliptin dose that provided a Cmax plasma concentration of 976 nmol/L [42] that matched those reported in humans administered a routine clinical sitagliptin dose [41, 43, 44], thereby supporting consideration of a gliptin as a treatment for human PD.