Oxidation of glutathione during hydroperoxide metabolism

Abstract

In the present study freshly isolated rat hepatocytes treated with the glutathione reductase inhibitor BCNU (1,3-bis(2-chloroethyl)-1-nitrosourea) were used to investigate the metabolism of tert-butyl hydroperoxide and of hydrogen peroxide formed in different intracellular compartments. Glycolate, benzylamine and hexobarbital were used to stimulate H₂O₂ production in the peroxisomal, mitochondrial and endoplasmic reticular/cytosolic compartments, respectively. Our results support previous findings that catabolism of H₂O₂ formed in the mitochondrial and cytosolic compartments occurs predominantly by the glutathione peroxidase system, whereas H₂O₂ generated within the peroxisomes is metabolized by catalase. They further reveal that the capacity of uninhibited glutathione reductase to reduce glutathione disulfide, formed during hydroperoxide metabolism by glutathione peroxidase, is high and that a decreased NADPH/NADP⁺ redox level, rather than insufficient reductase activity, is responsible for the accumulation and subsequent excretion of cellular glutathione disulfide observed during hydroperoxide metabolism. Finally, our results demonstrate that H₂O₂ generated during cytochrome P-450-mediated drug oxidation is metabolized primarily by the glutathione peroxidase system.