DPP4 and Parkinson disease: We previously demonstrated in the rat that human clinically equivalent doses of the approved DPP-4 inhibitors sitagliptin and PF-00734,200 (gosogliptin) that induced in excess of 60% and 20% inhibition of plasma and brain DPP-4 activity, respectively, mitigated the loss of dopaminergic neurons and dopamine levels, as well as methamphetamine-mediated rotation, in rats challenged with a unilateral medial forebrain bundle 6-hydroxydopamine (6-OHDA) lesion [42]—a classical rodent model of PD.