ROLE OF CELLULAR THIOL STATUS IN TOCOPHERYL HEMISUCCINATE CYTOPROTECTION AGAINST ETHYL METHANESULFONATE-INDUCED TOXICITY

Suspensions of mt hepatocytes treated with the alkylating agent ethyl methanesulfonate (EMS) exhibited extensive lipid peroxidation as well as rapid and near complete depletion of cellular reduced glutathione ( GSH) levels prior to cell death. Pretreatment of hepatocytes with medi um deficient in sulfur amino acids accelerated cell death induced by E MS, confirming the previously reported cytoprotective role for GSH in this toxic event. Nearly all of the cellular GSH lost following 50 mM EMS treatment was accounted for as S-ethyl glutathione (GS-Et). No sig nificant formation of glutathione disulfide was observed. The GS-Et fo rmed was not exported from the cell but remained at high intracellular concentrations throughout the course of the experiment. In addition, EMS treatment inhibited the efflux of intracellular GSH and inhibited the cellular accumulation of glutamate (Glu). Supplementation of hepat ocytes with 25 mu M d-alpha-tocopheryl hemisuccinate (TS) protected th ese cells against EMS-induced lipid peroxidation and cell death. Cytop rotection with TS had no effect on EMS-induced depletion of intracellu lar GSH or intracellular levels of GS-Et or Glu. However, TS supplemen tation did prevent EMS-induced depletion of cellular protein thiols. I nterestingly, the pretreatment of hepatocytes with 1 mM dithiothreitol promoted EMS toxicity. The results of this study suggest that the cyt oprotective abilities of TS are related to the prevention of both EMS- induced lipid peroxidation and protein thiol depletion. Thus, the onse t of lipid peroxidation and the loss of protein thiols in hepatocytes appear to be critical cellular events leading to EMS-induced cell deat h. (C) 1997 Elsevier Science Inc.