Glucuronidation of carcinogenic arylamines and their N-hydroxy derivatives by rat and human phenol UDP-glucuronosyltransferase of the UGT1 gene complex.
Since carcinogenic arylamines are sequentially oxidized and conjugated with glucuronic acid, differences in glucuronidation may critically determine the toxic potential of these compounds. Therefore, N-glucuronidation of 1- and 2-naphthylamine (1-NA and 2-NA),4-aminobiphenyl(4-ABP) and their N-hydroxy derivatives was investigated using rat and human liver microsomes and V79 cell-expressed phenol UDP-glucuronosyltransferases (UGT) of the UGT1 gene complex. Cell-expressed UGTs included rat and human UGT1.6, which are known to conjugate planar phenols, and human UGT1.7, conjugating both planar and bulky phenol. (i) N-Glucuronidation of 1- and 2-NA and of N-hydroxy-2-NA was inducible by 3-methylcholanthrene in rat liver microsomes whereas N-glucuronidation of the bulky arylamines 4-ABP and N-hydroxy-4-ABP was not. In support of these findings mutagenicity of N-hydroxy-2-NA in the Ames test was markedly reduced upon addition of UDP-glucuronic acid using liver homogenates from 3-methylcholanthrene-treated rats. (ii) With cell-expressed rat UGT1.6, non-carcinogenic 1-NA was conjugated with the highest rate and with higher affinity than 2-NA. UGT1.6 showed poor activity towards N-hydroxy-4-ABP and 4-ABP. (iii) Substrate specificity of human UGT1.6 also appeared to be limited to planar 1-NA, 2-NA and its N-hydroxy derivative, whereas UGT1.7 showed broader substrate specificity, including the bulky arylamine 4-ABP and its N-hydroxy derivative. The results suggest marked differences in substrate specificity of different UGT isozymes for arylamines and their N-hyroxy derivatives.
Orzechowski
A
A
Institute of Toxicology, University of Tübingen, Germany.
Schrenk
D
D
Bock-Hennig
B S
BS
Bock
K W
KW
D015057:1-Naphthylamine / Q000378:metabolism*; D015081:2-Naphthylamine / Q000378:metabolism*; D000368:Aged; D000611:Aminobiphenyl Compounds / Q000378:metabolism*; D000818:Animals; D002273:Carcinogens / Q000378:metabolism*; D002675:Child, Preschool; D005965:Glucuronates / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013379:Substrate Specificity
D000611:Aminobiphenyl Compounds; D002273:Carcinogens; D005965:Glucuronates; D007527:Isoenzymes; C006757:4-biphenylamine; D015057:1-Naphthylamine; D015081:2-Naphthylamine; D014453:Glucuronosyltransferase