The role of glutathione in chronic adaptation to oxidative stress: Studiesin a normal rat kidney epithelial (NRK52E) cell model of sustained upregulation of glutathione biosynthesis

Reduced glutathione (GSH) is considered to play a central role in protectio n of cells from oxidant injury. However, the question remains as to whether sustained elevation of intracellular GSH levels, as compared with the abil ity to rapidly upregulate GSH synthesis, is more important with respect to protection of cell constituents from oxidative stress. To address this ques tion, we conducted studies to evaluate the direct influence of chronically increased endogenous GSH content on chemically induced intracellular free r adical formation and oxidative stress using a kidney epithelial cell model adapted to sustain intracellular GSH concentrations in excess of eightfold that observed in unadapted parent kidney cells. Elevated GSH levels in adap ted cells were found to be attributable, at least in part, to coordinately increased amounts of both the regulatory and catalytic subunits of gamma-gl utamylcysteine synthetase (GCS), the rate-limiting enzyme in GSH synthesis. Studies using electron spin resonance (ESR) spectroscopy and scanning lase r cytometry demonstrated that cells having sustained elevation of GSH level s did not attenuate free radical formation and associated oxidative stress compared with parent cells when treated with the prooxidant chemicals, mena dione or potassium dichromate. In contrast, nonadapted kidney parent cells treated 18 h after initial prooxidant challenge displayed significantly att enuated free radical signals. Additionally, cells adapted to sustain excess GSH were somewhat more sensitive than parent cells in terms of resistance to prooxidant (chromate) toxicity, as determined by cell viability assays. These findings suggest that the capacity of cells to rapidly upregulate GSH synthesis, rather the ability to chronically sustain elevated intracellula r GSH levels, may play a more important role in terms of protection from cy totoxicity associated with prooxidant chemical exposures. (C) 1999 Academic Press.