| The biochemical mechanism leading to para-aminophenol (PAP) nephrotoxicity is unknown. PAP can undergo auto-oxidation and/or enzymatic oxidation to quinoneimine intermediates, which in turn have the ability to nonenzymatically react with glutathione or undergo redox cycling to ultimately form superoxide anion. By inhibition of several different enzyme systems, this study investigated the metabolic pathway leading to bioactivation of PAP in LLC-PK1 cells. Four enzyme systems were chosen based on their wide substrate specificity and their tissue distribution. No significant protection was observed from PAP when cells were treated with 1-aminobenzotriazole (a cytochrome P450 inhibitor), methimazole (a flavin monooxygenase (FMO) inhibitor), caffeic acid (a lipoxygenase (LO) inhibitor), and acetylsalicylic acid (a prostaglandin H synthase (PHS) inhibitor). These data suggest that the observed cytotoxicity in LLC-PK1 cells may be due to auto-oxidation of PAP. In addition, activity and expression of each enzyme were determined in LLC-PK 1 S9. Cytochrome P450, FMO and PHS activity and expression were virtually undetectable in LLC-PK1 S9. These data suggest that the drug metabolizing capability of LLC-PK1 cells is very low. For toxicants that require metabolic bioactivation, LLC-PK1 cells may not represent a suitable model. |
