2-Bromohydroquinone-induced toxicity to rabbit renal proximal tubules: the role of biotransformation, glutathione, and covalent binding.
2-Bromohydroquinone (BHQ) is a model toxic hydroquinone and plays an important role in bromobenzene-induced nephrotoxicity. Proximal tubules isolated to contain decreased glutathione (GSH) levels were at least twice as sensitive to the GSH depleting effects of BHQ and BHQ-induced mitochondrial dysfunction as were tubules with "normal" (i.e., in vivo) GSH content. The decrease in tubular GSH content resulted from BHQ-GSH conjugate formation. A mono-GSH conjugate (2-bromo-3-(glutathion-S-yl)hydroquinone) and a di-GSH conjugate (2-bromo-3,5- or 6-(diglutathion-S-yl)hydroquinone) were identified. In addition, a glucuronide conjugate was identified (2-bromo-1- or 4-O-glucuronylhydroquinone). BHQ-GSH conjugates were not responsible for BHQ-induced toxicity since (1) tubules with normal levels of GSH were more resistant to BHQ-induced toxicity even though they formed more BHQ-GSH conjugates than tubules with decreased GSH levels and (2) inhibition of gamma-glutamyltranspeptidase did not prevent BHQ-induced toxicity. BHQ-equivalents bound covalently to tubular protein in a concentration-, time-, and temperature-dependent manner with the majority of the binding (61%) occurring during the first 15 min after exposure to 0.2 mM BHQ. Tubules pretreated with GSH underwent less BHQ-protein alkylation and mitochondrial dysfunction, and the amount of BHQ recovered and BHQ-di-GSH conjugate formed increased. These data suggest that BHQ is biotransformed to a reactive intermediate (2-bromoquinone and/or 2-bromosemiquinone) and that this intermediate can react with GSH to form BHQ-GSH conjugates and/or bind covalently to tubular protein which may result in mitochondrial dysfunction and tubular death.
Schnellmann
R G
RG
Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens 30602.
Monks
T J
TJ
Mandel
L J
LJ
Lau
S S
SS
D000818:Animals; D001711:Biotransformation; D005978:Glutathione / Q000378:metabolism*; D006873:Hydroquinones / Q000378:metabolism / Q000493:pharmacokinetics / Q000633:toxicity*; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009761:Nystatin / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D011817:Rabbits; D005723:gamma-Glutamyltransferase / Q000037:antagonists & inhibitors
D006873:Hydroquinones; D009761:Nystatin; C042377:2-bromohydroquinone; D005723:gamma-Glutamyltransferase; D005978:Glutathione