nystatin-a1 and 2-bromohydroquinone

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.

Topics: Animals; Biotransformation; gamma-Glutamyltransferase; Glutathione; Hydroquinones; In Vitro Techniques; Kidney Tubules, Proximal; Mitochondria; Nystatin; Oxygen Consumption; Rabbits

An in vitro model using a suspension of rabbit renal proximal tubules was developed to investigate the mechanism of nephrotoxicity of bromobenzene. Using oxygen consumption, glutathione concentrations and retention of lactate dehydrogenase activity as markers of toxicity, the rank order of potency was bromobenzene (5 mM) less than 2-bromophenol (2 mM) less than 3-, 4-bromophenol (1 mM) less than 2-bromohydroquinone (0.1 mM). These data support in vivo results and are consistent with the hypothesis that 2-bromohydroquinone or a metabolite thereof is responsible for bromobenzene-induced nephrotoxicity. Inhibitors of cytochrome P-450 and the cyclooxygenase and peroxidase components of prostaglandin H synthase did not protect the proximal tubules from 2-bromohydroquinone-induced toxicity, suggesting that these enzymes do not play a role in 2-bromohydroquinone bioactivation. There is a specific sequence of events in 2-bromohydroquinone-induced toxicity. Early events include decreased glutathione levels and inhibited mitochondrial respiration, whereas an increase in plasma membrane permeability is a late event.

Topics: Animals; Biotransformation; Bromobenzenes; Cytochrome P-450 Enzyme System; Female; Glutathione; Hydroquinones; In Vitro Techniques; Indomethacin; Kidney Tubules, Proximal; L-Lactate Dehydrogenase; Nystatin; Ouabain; Oxygen Consumption; Phenols; Prostaglandin-Endoperoxide Synthases; Rabbits; Sodium-Potassium-Exchanging ATPase; Time Factors