Effect of ascorbic acid, acivicin and probenecid on the nephrotoxicity of 4-aminophenol in the Fischer 344 rat

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Abstract
4-Aminophenol (p-aminophenol, PAP) causes selective necrosis to the pars recta of the proximal tubule in Fischer 344 rats. The basis for this selective toxicity is not known but PAP can undergo oxidation in a variety of systems to form the 4-aminophenoxy free radical. Oxidation or disproportionation of this radical will form 1,4-benzoquinoneimine which can covalently bind to cellular macromolecules. We have recently reported that a glutathione conjugate of PAP, 4-amino-3-S-glutathionylphenol, is more toxic to the kidney than the parent compound itself. In this study we have examined the distribution and covalent binding of radiolabel from 4-[ring3H]-aminophenol in the plasma, kidney and liver of rats 24 h after dosing and related these findings to the extent of nephrotoxicity. In addition, we have examined the effect of ascorbic acid which will slow the oxidation of PAP; acivicin, an inhibitor of γ-glutamyltransferase and hence the processing of glutathione-derived conjugates; and probenecid, an inhibitor of organic anion transport on the nephrotoxicity produced by PAP. Administration of a single dose of PAP at 458 or 687 μmol kg−1 produced a dose-related alteration in renal function within 24 h which was associated with proximal tubular necrosis. The lesion at the lower dose was restricted to the S3 proximal tubules in the medullary rays, while at the higher dose it additionally affected the S3 tubules in the pars recta region of the cortex. Administration of ascorbic acid protected rats against the nephrotoxicity produced by PAP, markedly reducing the effect on renal function, and the extent of renal tubular necrosis. Associated with this protection was a reduction in the concentration of both total and covalently bound radiolabel from PAP in the kidney. In contrast, prior treatment with acivicin slightly potentiated the nephrotoxicity of PAP at the lower dose of 458 μmol kg−1, by increasing the extent of proximal tubular necrosis and azotemia. In association with this potentiation the concentration of both total and covalently bound radiolabel from PAP in the kidney was increased. Prior treatment with probenecid had little or no effect on the nephrotoxicity of PAP or on the distribution of radiolabel from PAP in the kidney. These studies indicate that oxidation of PAP to form a metabolite which can covalently bind to renal proteins may be an important step in the nephrotoxic process and that treatment with ascorbic acid reduces this and thereby affords protection.

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