Metabolism and cytotoxicity of acetaminophen in hepatocytes isolated from resistant and susceptible species.

Acetaminophen (APAP) disposition was studied in vitro using hepatocytes isolated from rats, hamsters, rabbits, and dogs, species that vary markedly in susceptibility to the hepatotoxicity of this drug. Metabolism was assessed by concurrent measurements of glutathione depletion and protein adduct formation (activation pathway) and of total aqueous metabolite production (detoxication pathways). Cytotoxicity was monitored by cell count and by lactate dehydrogenase (LDH) release to culture medium. In agreement with whole animal studies, hepatocytes from hamsters were very susceptible to APAP-induced toxicity whereas rat and rabbit hepatocytes were resistant. In vivo data were unavailable for the dog, but dog hepatocytes were also relatively resistant. Parameters of APAP metabolism generally correlated with the species susceptibility ranking; however, no single parameter was an ideal index of the sensitivity observed. As predicted by the cytotoxicity data, hamster hepatocytes produced more covalent adducts of APAP, were depleted of GSH more rapidly, and detoxified APAP by formation of polar metabolites at a slower rate than rat hepatocytes. On the other hand, rabbit hepatocytes had no detectable covalent adducts, retained higher amounts of GSH, and metabolized more APAP to polar conjugates than the other species. Dog hepatocytes formed low amounts of both covalent adducts and conjugates. These studies indicate that interspecies comparisons using isolated hepatocytes to study xenobiotic metabolism and the resulting cytotoxicity are feasible, but for a clear understanding of observed differences, it is necessary to study the interrelationships between the toxication and detoxication pathways of metabolism.