HEPATIC MICROSOMAL N-GLUCURONIDATION AND NUCLEIC-ACID BINDING OF N-HYDROXY ARYLAMINES IN RELATION TO URINARY-BLADDER CARCINOGENESIS

Abstract

Uridine 5''-diphosphoglucuronic acid-fortified hepatic microsomes from dogs, rats or humans rapidly metabolized [3H]-N-hydroxy-2-naphthylamine (N-HO-2-NA) to a water soluble product that yielded 98% of the parent N-hydroxy amine on treatment with .beta.-glucuronidase. The metabolite was identified as N-(.beta.-1-glucosiduronyl)-N-hydroxy-2-naphthylamine from UV, IR and mass spectral analyses of the glucuronide and its nitrone derivative. Incubation of N-hydroxy-1-naphthylamine (N-HO-1-NA), N-hydroxy-4-aminobiphenyl (N-HO-ABP) or the N-hydroxy derivatives of 2-aminofluorene, 4-aminoazobenzene or N-acetyl-2-aminofluorene with uridine 5''-diphosphoglucuronic acid fortified hepatic microsomes also yielded water soluble products. .beta.-Glucuronidase treatment released 80-90% of the [3H]-N-HO-1-NA and [3H]-N-HO-ABP conjugates as 3H ether extractable derivatives. N-HO-1-Na, N-HO-2-NA and N-HO-ABP and the glucuronides of these N-hydroxy arylamines were relatively stable and nonreactive near neutral pH. At pH 5, the N-glucuronide of N-HO-2-NA and the presumed N-glucuronides of N-HO-1-NA and N-HO-ABP were rapidly hydrolyzed to the N-hydroxy arylamines that were then converted to reactive derivatives capable of binding covalently to nucleic acids. These data support the concept that arylamine bladder carcinogens are N-oxidized and N-glucuronidated in the liver and the N-glucuronides are transported to the urinary bladder. Hydrolysis of the glucuronides to N-hydroxy arylamines and the conversion of the latter derivatives to highly reactive electrophilic arylnitrenium ions in the normally acidic urine of dogs and humans may be critical reactions for tumor induction in the urinary bladder.