Effects of Schisandrin B Enantiomers on Cellular Glutathione and Menadione Toxicity in AML12 Hepatocytes

Abstract

Effects of schisandrin B enantiomer ((+)Sch B and (–)Sch B) treatment on the reduced cellular glutathione (GSH) level and susceptibility to menadione-induced toxicity were investigated and compared in AML12 hepatocytes. (+)Sch B or (–)Sch B treatment at 6.25 µmol/l produced a time-dependent change in cellular GSH level, with the maximal stimulation occurring 16 h after dosing. (+)Sch B/(–)Sch B pretreatment for 16 h dose-dependently protected against menadione toxicity, with the maximum degree of protection observable at 6.25 µmol/l and the extent of protection afforded by (–)Sch B being larger than that of (+)Sch B. The cytoprotection was associated with a parallel enhancement in cellular GSH level in both non-menadione (control) and menadione-intoxicated cells. While the GSH depletion produced by buthionine sulfoximine/phorone treatment largely abrogated the cytoprotective action of (+)Sch B/(–)Sch B, it almost completely abolished the GSH-enhancing effect of (+)Sch B and (–)Sch B in both control and menadione-treated cells. Both (+)Sch B and (–)Sch B treatments increased the GSH reductase activity in control and menadione-treated cells, with the stimulatory action of (–)Sch B being more potent than that of (+)Sch B in the control condition. (+)Sch B and (–)Sch B also enhanced the γ-glutamate cysteine ligase activity in menadione-intoxicated cells. The results indicate that (–)Sch B is more effective than (+)Sch B in enhancing cellular GSH and protecting against oxidant injury in hepatocytes.