Formation and metabolism of a glutathione-S-conjugate in isolated rat liver and kidney cells

Abstract

The reaction sequence involved in drug metabolism, which includes initial oxidation by cytochrome P-450, conjugation with GSH, conversion of the glutathione-S-conjugate to the cysteine-S-conjugate, and N-acetylation of the cysteine-S-conjugate to form the mercapturic acid derivative, was reconstituted in vitro using isolated rat liver and kidney cells with paracetamol as substrate. Oxidation and GSH conjugation were catalyzed primarily by the liver cells, while conversion of the GSH conjugate to the mercapturic acid derivative was catalyzed primarily by the kidney cells. With kidney cells, but not with liver cells, added GSH was oxidized to GSSG. Subsequently, GSSG concentration decreased with stoichiometric increase in glutamate concentration. Addition of GSSG to kidney cells inhibited metabolism of the GSH conjugate of paracetamol to the mercapturic acid derivative. These data indicate a relationship between metabolism of GSH conjugates and of GSSG by kidney cells and demonstrate the overall conversion in vitro of a drug to urinary products.