N-acetyl-meta-aminophenol, the alleged nontoxic isomer of acetaminophen, is toxic in both rat and human precision-cut liver slices

Abstract

N-acetyl-meta-aminophenol (AMAP) is generally considered as a non-toxic regioisomer of the well-known hepatotoxicant acetaminophen (APAP). However, so far AMAP has only been shown to be non-toxic in mice and hamsters. To investigate whether AMAP could also be used as non-toxic analog of APAP in studies in rat and human, the toxicity of APAP and AMAP was tested ex vivo in precision-cut liver slices (PCLS) of mouse, rat and human. Based on ATP content and histomorphology, APAP was most toxic in mouse and least toxic in human PCLS. Surprisingly, although AMAP showed a much lower toxicity than APAP in mouse PCLS, AMAP was more toxic than APAP at all concentrations tested in both rat and human PCLS. In HepG2 cells, AMAP caused similar apoptosis and induced a higher Nrf2-mediated oxidative stress signal than APAP. The protein profile in the medium of AMAP-treated rat PCLS was similar to that of APAP, whereas in the medium of mouse PCLS it was similar to the control. Metabolite profiling indicated that mouse PCLS produced the highest amount of glutathione conjugate of APAP, while no glutathione conjugate of AMAP was detected in all three species. Mouse also produced ten times more hydroquinone metabolites of AMAP, the assumed proximate reactive metabolites, than rat or human. In conclusion, AMAP can be used as non-toxic isomer of APAP in mouse but not in rat and human. The marked species differences in APAP and AMAP toxicity and metabolism underline the importance of using human tissues for better prediction of toxicity in man