(-)Schisandrin B ameliorates paraquat-induced oxidative stress by suppressing glutathione depletion and enhancing glutathione recovery in differentiated PC12 cells.

Exposure to paraquat (PQ; N,N'-dimethyl-4-4'-bipyridium), a potent herbicide, can lead to neuronal cell death and increased risk of Parkinson's disease because of oxidative stress. In this study, we investigated the effect of (-)schisandrin B [(-)Sch B, a potent enantiomer of schisandrin B] on PQ-induced cell injury in differentiated pheochromocytoma cells (PC12). PQ treatment caused cell injury in PC12 cells, as indicated by the significant increase in lactate dehydrogenase (LDH) leakage. Pretreatment with (-)Sch B (5 μM) protected against PQ-induced toxicity in PC12 cells, as evidenced by the significant decrease in LDH leakage. (-)Sch B induced the cytochrome P-450-mediated reactive oxygen species generation in differentiated PC12 cells. The cytoprotection afforded by (-)Sch B pretreatment was associated with an increase in cellular reduced glutathione (GSH) level as well as the enhancement of γ-glutamylcysteine ligase (GCL) and glutathione reductase (GR) activity in PQ-challenged cells. Both GCL and GR inhibitors abrogated the cytoprotective effect of (-)Sch B in PQ-challenged cells. The biochemical mechanism underlying the GSH-enhancing effect of (-)Sch B was further investigated in PC12 cells subjected to an acute peroxide challenge. Although the initial GSH depletion induced by peroxide was reduced through GR-catalyzed regeneration of GSH in (-)Sch B-pretreated cells, the later enhanced GSH recovery was mainly mediated by GCL-catalyzed GSH synthesis. The results suggest that (-)Sch B treatment may increase the resistance of dopaminergic cells against PQ-induced oxidative stress through reducing the extent of oxidant-induced GSH depletion and enhancing the subsequent GSH recovery.