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

Previous studies from our laboratory have demonstrated that the admini stration of alpha-tocopheryl hemisuccinate (TS),but not unesterified a lpha-tocopherol (T), protects hepatocytes from a variety of toxic insu lts including chemicals, drugs, metals, and oxidative stress. One poss ible mechanism for this unique cytoprotection is that succinate releas ed from cellular TS is used as a supplemental energy source during a t oxic challenge. To test this hypothesis, we examined the effect of TS (25 mu M) administration on cell viability, lipid peroxidation, and se veral cellular energy-related processes such as mitochondrial membrane potential (MMP, Psi Delta), lactate formation, and ATP and K+ concent rations in isolated hepatocyte suspensions during a toxic challenge wi th the alkylating agent, ethyl methanesulfonate (EMS). Data from these studies demonstrate that EMS treatment results in rapid cell death an d lipid peroxidation following 2 h of incubation. Preceding EMS-induce d cell death was a rapid loss of MMP, intracellular ATP and K+ levels, and mitochondrial ultrastructure as well as a transient increase in c ellular lactate production. Pretreatment of hepatocytes with TS prior to EMS exposure prevented the loss of MMP and mitochondrial ultrastruc tural changes as well as lipid peroxidation and cell death. Cellular A TP levels and lactate production did not reflect the protection afford ed to TS-treated hepatocytes. Protection against EMS-induced toxicity was not observed when hepatocytes were: (i) pretreated with TS and est erase inhibitors (preventing T and succinate release from TS); (ii) pr etreated with other lipophilic succinate derivatives (cholesteryl hemi succinate, monomethyl and dimethyl succinate); or (iii) pretreated wit h T and sodium succinate. Unlike monomethyl succinate, cytoprotective TS pretreatment did not stimulate gluconeogenesis or glycolysis. Hepat ocytes isolated from rats pretreated for 24 h with T were not protecte d from the toxic effects of EMS, unlike TS-pretreated rats. In conclus ion, TS cytoprotection against the mitochondrial toxicant EMS appears to be related to the hepatocellular accumulation of TS and the mainten ance of mitochondrial function (MMP). Based on our earlier findings an d the present observations, we propose that a unique subcellular dispo sition for TS and the subsequent release of T and succinate at a criti cal mitochondrial site is responsible for the observed cytoprotection. (C) 1994 Academic Press, Inc.