RM Liu, H Hu, TW Robison and HJ Forman
Department of Molecular Pharmacology and Toxicology, University of Southern California, Los Angeles 90033, USA.

Tert-butylhydroquinone (TBHQ) is a monofunctional Phase II enzyme inducer, which produces reactive oxygen species. Incubation with a sublethal concentration of TBHQ increased the activities of both gamma- glutamyl transpeptidase (GGT) and gamma-glutamylcysteine synthetase (GCS), although the mechanisms are different (Liu and colleagues, accompanying manuscript). In this study, we found that TBHQ increased intracellular glutathione (GSH) content in rat lung epithelial L2 cells. L2 cells pretreated with a nontoxic concentration of TBHQ (50 microM) acquired resistance to a subsequent challenge with a normally lethal concentration of TBHQ (200 microM). Pretreatment with L- buthionine S,R-sulfoximine (BSO), an inhibitor of GCS, prevented the TBHQ-induced increase in GSH and markedly diminished resistance to 200 microM TBHQ. Similarly, pretreatment with acivicin, an inhibitor of GGT, also prevented the TBHQ-induced increase in GSH and markedly diminished resistance to 200 microM TBHQ. Nevertheless, blockage of GGT by acivicin could be bypassed using 2-oxothiazolidine-4-carboxylate (procysteine) to provide the cell with a source of cysteine. This allowed an increase in GSH and restored resistance in the TBHQ- pretreated cells. The results suggest that elevation of GCS and GGT activities participated in acquired resistance to quinone toxicity.

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