COVALENT BINDING OF ACETAMINOPHEN TO N-10-FORMYL-TETRAHYDROFOLATE DEHYDROGENASE IN MICE

The analgesic acetaminophen is frequently used as a model chemical to study hepatotoxicity; however, the critical mechanisms by which it pro duces toxicity within the cell are unknown. It has been postulated tha t covalent binding of a toxic metabolite to crucial proteins may inhib it vital cellular functions and may be responsible for, or contribute to, the hepatotoxicity. To further understand the importance of covale nt binding in the toxicity, a major cytosolic acetaminophen-protein ad duct of 100 kDa has been purified by a combination of anion exchange c hromatography and preparative electrophoresis. N-Terminal and internal amino acid sequences of peptides from the purified 100-kDa acetaminop hen-protein adduct were found to be homologous with the deduced amino acid sequence from the cDNA of N-10-formyltetrahydrofolate dehydrogena se. Anti-serum specific for N-10-formyltetrahydrofolate dehydrogenase and acetaminophen react in a Western blot with the purified 100-kDa ac etaminophen-protein adduct. Administration of a toxic dose of acetamin ophen (400 mg/kg) to mice resulted in a 25% decrease in cytosolic N-10 -formyltetrahydrofolate dehydrogenase activity at 2 hr. The covalent b inding of acetaminophen to proteins such as N-10-formyltetrahydrofolat e dehydrogenase and the subsequent decreases in their enzyme activity may play a role in acetaminophen hepatotoxicity.