Metabolism and toxicity of 2-bromo-(diglutathion-s-yl)-hydroquinone and 2- bromo-3-(glutathion-S-yl)hydroquinone in the in situ perfused rat kidney

2-Br-(diglutathion-S-yl)hydroquinone (2-Br-(diGSyl)HQ) is a potent nephrotoxicant, causing glucosuria, enzymuria, proteinuria, elevations in blood urea nitrogen, and severe histological alterations to renal proximal tubules at doses of 10-15 μmol/kg. In contrast, 2-Br-3-(glutathion-S- yl)hydroquinone (2-Br-3-(GSyl)HQ) is substantially less nephrotoxic than 2- Br-(diGSyl)HQ and requires a dose of at least 50 μmol/kg to cause modest elevations in blood urea nitrogen concentrations. The reason or reasons for this difference in potency is unclear, but since inhibition of renal γ- glutamyl transpeptidase (γ-GT) prevents 2-Br-(diGSyl)HQ-mediated nephrotoxicity, metabolism of these conjugates by the kidney must play an important role. To address this question we have compared the metabolism and toxicity of 2-Br-(diGSyl)HQ and 2-Br-3-(GSyl)HQ in the in situ perfused rat kidney (ISPRK). Following infusion of 20 μmol 2-Br-3-(GSyl)HQ into the right renal artery of male Sprague Dawley rats, a total of 23.5 ± 1.9% (mean ± SE) of the dose was accounted for in urine and bile over a period of 180 min. 2-Bromo-3-(cystein-S-yl)hydroquinone and 2-bromo-3-(N-acetylcystein-S- yl)hydroquinone were identified in urine, and unchanged 2-Br-3-(GSyl)HQ was identified in urine and bile. The product arising from the oxidative cyclization of 2-bromo-3-(cystein-S-glycine)hydroquinone, 2H-(3-glycine)-7- hydroxy-8-bromo-1,4-benzothiazine, was also identified in urine. In contrast, no known metabolites of 2-Br-(diGSyl)HQ were found in the urine or bile following its infusion (20 μmol) into the ISPRK, and only minor amounts of several unidentified metabolites, in addition to unchanged 2-Br-(diGSyl)HQ, were detected. Toxicity was assessed by determining mitochondrial function and the urinary excretion of γ-GT. Neither conjugate altered mitochondrial respiratory function or the activity of succinate dehydrogenase. The kinetics of γ-GT excretion into urine produced from the perfused and contralateral kidneys differed substantially following perfusion with either 2-Br-3- (GSyl)HQ or 2-Br-(diGSyl)HQ. The susceptibility of individual ISPRK preparations to the toxicity of 2-Br-3-(GSyl)HQ correlated with differences in the overall metabolism of 2-Br-3-(GSyl)HQ in that preparations that excreted more conjugate in the unmetabolized form excreted less γ-GT. Substantial differences in the intrarenal metabolism and disposition of 2- Br-(diGSyl)HQ and 2-Br-3-(GSyl)HQ may contribute to their differences in nephrotoxicity.