Carcinogenesis Advance Access published online on January 16, 2004
Carcinogenesis, doi:10.1093/carcin/bgh077
© 2004 by Oxford University Press
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CARCINOGENESIS
1 German Institute of Human Nutrition (DIfE), Department of Toxicology, Arthur-Scheunert-Allee 114-116, 14558 Potsdam-Rehbrücke, Germany
* Corresponding author. E-mail: glatt{at}mail.dife.de.
Received 16 May 2003
; revised 20 December 2003
; accepted 30 December 2003
2-Amino-3-methyl-9H-pyrido[2,3-b]indole (MeA
acetyltransferase, heterocyclic amines, MeABioactivation of the heterocyclic aromatic amine 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeA
C) in recombinant test systems expressing human xenobiotic-metabolising enzymes
2 Danish Institute for Food and Veterinary Research, Mørkhøj Bygade 19, 2860 Søborg, Denmark
C) and some metabolites were investigated for mutagenicity in mammalian cell lines and bacterial strains engineered for the expression of human enzymes. MeAC induced gene mutations (studied at the hprt locus) in Chinese hamster V79-derived cells co-expressing cytochrome (CYP) 1A2 and sulphotransferase (SULT) 1A1 even at a concentration of 30 nM, but was inactive in cells co-expressing CYP1A2 and N-acetyltransferase (NAT) 1 or 2. MeAC, tested in the presence of rat liver postmitochondrial fraction, showed strongly enhanced mutagenicity in a Salmonella typhimurium strain expressing human SULT1A1 compared to the control (recipient) strain TA1538/1,8-DNP (deficient in endogenous acetyltransferase). Mutagenicity was also enhanced, although to a lesser extent, when NAT2 was expressed in the latter strain. The metabolite, 2-hydroylamino-3-methyl-9H-pyrido[2,3-b]indole (N-OH-MeAC) was a direct mutagen to strains TA1538 and TA1538/1,8-DNP. This mutagenicity was strongly enhanced in corresponding strains expressing SULT1A1. A moderate enhancement was observed when SULT1A2, SULT1B1, SULT1C2 or NAT2 were expressed in strain TA1538. The remaining enzymes studied (SULT1A3, 1C1, 1E1, 2A1, 2B1a, 2B1b, 4A1 and NAT1) did not indicate any activation of N-OH-MeAC. Preliminary mutagenicity experiments in SULT-expressing S. typhimurium strains were conducted with other hydroxylated metabolites of MeAC. The phenols, 6- and 7-hydroxy-MeAC, were inactive under the conditions studied. The benzylic alcohol, 2-amino-3-hydroxymethyl-9H-pyrido[2,3-b]indole, was mutagenic in a strain expressing SULT1A1, but its activity was much weaker than that of N-OH-MeAC. Thus, N-hydroxylation (e.g. mediated by CYP1A2) and sulpho conjugation (primarily mediated by SULT1A1) was the dominating activation pathway of MeAC in model systems engineered for human enzymes. Some other SULT forms as well as NAT2 were also capable of activating N-OH-MeAC, although with much lower efficiency than SULT1A1. Another minor activation pathway involved benzylic hydroxylation followed by sulpho conjugation by SULT1A1.C, mutagenicity, sulphotransferase
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