Omarigliptin Mitigates 6-Hydroxydopamine- or Rotenone-Induced Oxidative Toxicity in PC12 Cells by Antioxidant, Anti-Inflammatory, and Anti-Apoptotic Actions.

Dipeptidyl peptidase-4 (DPP-4) inhibitors are reported to exhibit promising effects on several pathological processes associated with Parkinson's disease (PD). To explore its repositioning potential as an antiparkinsonian agent, we evaluated the effects of omarigliptin (OMG), a DPP-4 inhibitor recently approved as a hypoglycemic drug, on neurotoxin-induced toxicity, using PC12 cells as a cellular model of PD. The molecular mechanism(s) underlying its protective activity was also investigated. OMG alleviated oxidative toxicity and the production of reactive oxygen species induced by 6-hydroxydopamine (6-OHDA) or rotenone. It also partially attenuated the formation of DPPH radicals and lipid peroxidation, demonstrating the antioxidant properties of OMG. OMG upregulated Nrf2 and heme oxygenase-1 (HO-1). Notably, treatment with a selective HO-1 inhibitor and Nrf2 knockdown by siRNA abolished the beneficial effects of OMG, indicating that the activated Nrf2/HO-1 signaling was responsible for the protective activity. Moreover, OMG exhibited anti-inflammatory activity, blocking inflammatory molecules, such as nitric oxide (NO) and inducible NO synthase, through inhibition of IκBα phosphorylation and NF-κB activation in an Akt-dependent fashion. Finally, OMG decreased the levels of cleaved caspase-3 and Bax and increased the level of Bcl-2, indicating its anti-apoptotic properties. Collectively, these results demonstrate that OMG alleviates the neurotoxin-induced oxidative toxicity through Nrf2/HO-1-mediated antioxidant, NF-κB-mediated anti-inflammatory, and anti-apoptotic mechanisms in PC12 cells. Our findings elucidating multiple mechanisms of antiparkinsonian activity strongly support the therapeutic potential of OMG in the treatment of PD.