Metabolism of 2-(glutathione-s-yl)hydroquinone and 2,3,5-(triglutathion-s-yl)hydroquinone in the in situ perfused rat kidney: Relationship to nephrotoxicity

2,3,5-(Triglutathion-S-yl)hydroquinone [2,3,5-(triGSyl)HQ] (20 μmol/kg) and 2-(glutathion-S-yl)hydroquinone [2-(GSyl)HQ] (250 μmol/kg) both cause nephrotoxicity when administered to male rats, although the former is considerably more potent than the latter. To address the issue of the differential potency of these conjugates we investigated the metabolism and toxicity of 2,3,5-(triGSyl)HQ and 2-(GSyl)HQ in the in situ perfused rat kidney. Infusion of 5 and 10 μmol 2,3,5-(triGSyl)HQ into the right renal artery caused a time-dependent elevation in γ-glutamyl transpeptidase (γ-GT) excretion into urine produced by both the perfused and the contralateral kidneys. At the lower concentration, γ-GT excretion was greater from the perfused kidney, whereas γ-GT excretion from the perfused and contralateral kidneys was the same at the higher concentration. Using HPLC-EC to analyze urine and bile, metabolites of 2,3,5-(triGSyl)HQ (10 μmol) were observed only within the first 30 min of perfusion. At the lower dose (5 μmol) neither parent compound nor metabolites were found in urine or bile. Infusion of 40 μmol 2-(GSyl)HQ into the right renal artery also caused a time-dependent excretion of γ-GT into urine: Excretion being greater from the perfused kidney. HPLC-EC analysis of urine and bile from 2-(GSyl)HQ perfused kidneys demonstrated the formation of three known metabolites; 2-(N-acetyl-cystein-S-yl)HQ (9.2 ± 0.5 μmol), 2-(cystein-S-ylglycine)HQ (0.8 ± 0.3 μmol), and 2-(cystein-S-yl)HQ (1.3 ± 0.3 μmol). Unchanged 2-(GSyl)HQ was detected in the urine and bile (0.8 ± 0.1 μmol). A greater fraction of the dose (74%) was recovered in urine following infusion of 40 μmol 2-(GSyl)[¹⁴C]HQ than of 10 μmol 2,3,5-(triGSyl)[¹⁴C]HQ (29%). In contrast, a greater fraction of the dose was retained by the kidney following treatment with 10 μmol 2,3,5-(triGSyl)[¹⁴C]HQ than following treatment with 40 μmol 2-(GSyl)[¹⁴C]HQ (36 and 11%, respectively). This result suggests that metabolites derived from 2,3,5-(triGSyl)[¹⁴C]HQ are more reactive than those derived from 2(GSyl)[¹⁴C]HQ, which is consistent with the finding that 2,3,5-(tricystein-S-yl)hydro quinone exhibits a lower oxidation potential than 2-(cystein-S-yl)hydroquinone. Differences in the reactivity of the metabolites derived from 2,3,5-(triGSyl)[¹⁴C]HQ and 2-(GSyl)[¹⁴C]HQ probably account for the more potent nephrotoxicity of 2,3,5-(triGSyl)HQ.