Metabolism of para-aminophenol by rat hepatocytes

Autoxidation of para-aminophenol (PAP) has been proposed to account for the selective nephrotoxicity of this compound. However, other studies suggest that hepatic metabolites of PAP rather than the parent compound may be resp onsible for renal damage. These studies were designed to investigate PAP me tabolism in isolated hepatocytes. We synthesized several proposed metabolit es for analysis by HPLC/mass spectrometry and compared those results with H PLC/mass spectrometric analyses of metabolites found after incubating hepat ocytes with PAP. Hepatocytes prepared from male Sprague-Dawley rats were in cubated in Krebs-Henseleit buffer at 37 degrees C for 5 h with 2.3 mM PAP u nder an atmosphere of 5% CO2/95% O-2. Aliquots were withdrawn at 0.1 h of i ncubation and then hourly through 5 h of incubation. Reactions were termina ted by the addition of acetonitrile. Hepatocyte viability was unaltered wit h PAP present in the incubation medium. We found that hepatocytes converted PAP to two major metabolites (PAP-GSH conjugates and PAP-N-acetylcysteine conjugates) and several minor metabolites [PAP-O-glucuronide, acetaminophen (APAP), APAP-O-glucuronide, APAP-GSH conjugates, and 4-hydroxyformanilide] . Preincubating hepatocytes with 1-aminobenzotriazole, an inhibitor of cyto chromes P450, did not alter the pattern of PAP metabolism. In conclusion, w e found that PAP was metabolized in hepatocytes predominantly to PAP-GSH co njugates and PAP-N-acetylcysteine conjugates in sufficient quantities to ac count for the nephrotoxicity of PAP.