THE ACETAMINOPHEN REGIOISOMER 3'-HYDROXYACETANILIDE INHIBITS AND COVALENTLY BINDS TO CYTOCHROME-P450 2E1

3'-Hydroxyacetanilide has been previously studied as a nontoxic regioi somer of the analgesic acetaminophen (4'-hydroxyacetanilide). The radi olabeled derivative has been shown to covalently bind to liver protein s at levels similar to that observed with hepatotoxic doses of radiola beled acetaminophen with no evidence of hepatic damage. Using an anti- arylacetamide antiserum the primary protein adduct detected following administration of 3'-hydroxyacetanilide (300 and 600 mg/kg) to mice wa s a 50 kDa microsomal protein that co-migrated with cytochrome P450 2E 1. Cytochrome P450 2E1 enzyme activity (p-nitrophenol hydroxylase) was decreased by 79% in the mice treated with 3'-hydroxyacetanilide (600 mg/kg). Incubation of 3'-hydroxyacetanilide with hepatic microsomes re sulted in a time dependent 47% decrease in cytochrome P450 2E1 activit y. Pre-incubation of acetaminophen with microsomes did not result in c ovalent binding to the cytochrome P450 nor was there a decrease in p-n itrophenol hydroxylase activity. These data suggest that 3'-hydroxyace tanilide covalently binds to cytochrome P450 2E1 with preferential los s of activity. (C) 1998 Elsevier Science Ireland Ltd. All rights reser ved.