2-3-5-(triglutathion-s-yl)hydroquinone and acivicin

Hydroquinone, an intermediate used in the chemical industry and a metabolite of benzene, is a nephrocarcinogen in the 2-year National Toxicology Program bioassay in male Fischer 344 rats. Current evidence suggests that certain chemicals may induce carcinogenesis by a mechanism involving cytotoxicity, followed by sustained regenerative hyperplasia and ultimately tumor formation. Glutathione (GSH) conjugates of a variety of hydroquinones are potent nephrotoxicants, and we now report on the effect of hydroquinone and 2,3,5-(tris-glutathion-S-yl)hydroquinone, on site-selective cytotoxicity and cell proliferation in rat kidney. Male Fischer 344 rats (160-200 g) were treated with hydroquinone (1.8 mmol/kg or 4.5 mmol/kg, p.o.) or 2,3,5-(tris-glutathion-S-yl)hydroquinone (7.5 micromol/kg; 1.2-1.5 micromol/rat, i.v.), and blood urea nitrogen (BUN), urinary gamma-glutamyl transpeptidase (gamma-GT), alkaline phosphatase (ALP), glutathione-S-transferase (GST) and glucose were measured as indices of nephrotoxicity. Hydroquinone (1.8 mmol/kg, p.o.) is nephrotoxic in some rats, but not others, but cell proliferation (BrDU incorporation) in proximal tubular cells of the S3M region correlates with the degree of toxicity in individual rats. At 4.5 mmol/kg, hydroquinone causes significant increases in the urinary excretion of gamma-GT, ALP and GST. Pretreatment of rats with acivicin prevents hydroquinone-mediated nephrotoxicity, indicating that toxicity is dependent on the formation of metabolites that require processing by gamma-GT. Consistent with this view, 2,3,5-(tris-glutathion-S-yl)hydroquinone, a metabolite of hydroquinone, causes increases in BUN, urinary gamma-GT and ALP, all of which are maximal 12 h after administration of 2,3,5-(tris-glutathion-S-yl)hydroquinone. In contrast, the maximal excretion of GST and glucose occurs after 24 h. By 72 h, BUN and glucose concentrations return to control levels, while gamma-GT, ALP and GST remain slightly elevated. Examination of kidney slices by light microscopy revealed the presence of tubular necrosis in the S3M segment of the proximal tubule, extending into the medullary rays. Cell proliferation rates in this region were 2.4, 6.9, 15.3 and 14.3% after 12, 24, 48 and 72 h, respectively, compared to 0.8-2.4% in vehicle controls. Together with the metabolic data, the results indicate a role for hydroquinone-thioether metabolites in hydroquinone toxicity and carcinogenicity.

Topics: Animals; Carcinogens; Cell Division; Cell Survival; gamma-Glutamyltransferase; Glutathione; Hydroquinones; Isoxazoles; Kidney; Kidney Diseases; Kidney Neoplasms; Male; Rats; Rats, Inbred F344

2,3,5-(Triglutathion-S-yl)hydroquinone [2,3,5-(triGSyl)HQ] is a potent nephrotoxicant when administered to male rats. We now report that significant species differences exist in susceptibility to 2,3,5-(triGSyl)HQ-mediated nephrotoxicity. Metabolism of glutathione conjugates involves cleavage of teh glutamate and glycine moieties by gamma-glutamyltranspeptidase (gamma-GT) and dipeptidases, respectively, and the nephrotoxicity of 2,3,5-(triGSyl)HQ can be prevented by the inhibition of renal gamma-GT. The resulting cysteine conjugate exhibits a balance between N-acetylation, and N-deacetylation of the mercapturic acid biosynthesis in various species contribute to species susceptibility to 2,3,5-(triGSyl)HQ. Renal gamma-GT activity toward 2,3,5-(triGSyl)HQ was highest in the rat (Fischer 344 and Sprague-Dawley) and consistent with the sensitivity of this species to 2,3,5-(triGSyl)HQ (20 micromol/kg iv)-mediated nephrotoxicity. The gamma-GT-mediated hydrolysis of 2,3,5-(triGSyl)HQ was similar in B6C3F1 and BALB/c mice and guinea pigs. In these species, the gamma-GT activity ranged between 30-45% of the activity measured in rats. Although, the activity of gamma-GT was similar in mice and guinea pigs, only guinea pigs were susceptible to 2,3,5-(triGSyl)HQ (200 micromol/kg iv)-induced renal necrosis. The gamma-GT-mediated hydrolysis of 2,3,5-(triGSyl)HQ was lowest in the hamster, and this species were not susceptible to the renal toxicity of this conjugate. Thus, factors in addition to gamma-GT activity probably contribute to species susceptibility to 2,3,5-(triGSyl)HQ nephrotoxicity. The kinetics of the AT-125-mediated inhibition of gamma-GT differed between species, indicative of potential differences in the regulation of gamma-GT. Consistent with this view, the ratio between the hydrolysis and transpeptidation of 2,3,5-(triGSyl)HQ varied 10-fold between the species examined, and was highest in the guinea pig (0.48) and lowest in the hamster (0.05). Guinea pigs also exhibited the highest renal cytosolic N-deacetylase activity and the lowest N-acetylase activity. The ratios of N-deacetylation to N-acetylation in guinea pigs, BALB/c mice, B6C3F1 mice, hamsters, Fischer 344 rats, and Sprague-Dawley rats were 4.57, 0.16, 0.14, 0.04, 0.03, and 0.02, respectively. Because quinol-cysteine conjugates seem to undergo oxidation more readily than the corresponding mercapturates, the balance of N-deacetylase and N-acetylase in the guinea pig may contribute to the suscepti

Topics: Acetylation; Animals; Cricetinae; gamma-Glutamyltransferase; Glutathione; Guinea Pigs; Hydroquinones; Isoxazoles; Kidney; Male; Mesocricetus; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Rabbits; Rats; Rats, Inbred F344; Rats, Sprague-Dawley; Species Specificity