Studies on the effects of l-ascorbic acid on acetaminophen-induced hepatotoxicity : 1. Inhibition of the covalent binding of acetaminophen metabolites to hepatic microsomes in vitro

Abstract

The covalent binding of [ 14C]acetaminophen metabolites to male mouse hepatic microsomes was inhibited by the sulfhydryl compounds, reduced glutathione, cysteamine, and l-cysteine, and also by l-ascorbic acid (vitamin C, LAA). Although the sulfhydryl compounds were more effective inhibitors of macromolecular binding than LAA, the combination of LAA with any of the thiol agents resulted in additive inhibition of covalent binding of [ 14C]acetaminophen metabolites. Similar results were obtained in studies with hepatic microsomes from female mice and male hamsters. Investigations into the mechanism of inhibition of covalent binding of [ 14C]acetaminophen metabolites indicated that LAA probably acts by scavenging the reactive intermediates generated by the microsomal mixed-function oxidase enzymes rather than by the inhibition of their formation. The results suggest that LAA, at concentrations found in rodent and human liver, may supplement the endogenous protective mechanisms (such as reduced glutathione) which operate in vivo to prevent the covalent binding of reactive acetaminophen metabolites and hence hepatic necrosis. The possible application of this study to the use of LAA in the prevention and treatment of acetaminophen-induced hepatotoxicity in man is discussed.