In vitro bioactivation of N-hydroxy-2-amino-alpha-carboline.
2-Amino-alpha-carboline (A alpha C) is a mutagenic and carcinogenic heterocyclic amine present in foods cooked at high temperature and in cigarette smoke. The mutagenic activity of A alpha C is dependent upon metabolic activation to N-hydroxy-A alpha C (N-OH-A alpha C); however, the metabolism of N-OH-A alpha C has not been studied. We have synthesized 2-nitro-alpha-carboline and N-OH-A alpha C and have examined in vitro bioactivation of N-OH-A alpha C by human and rodent liver cytosolic sulfotransferase(s) and acetyltransferase(s) and by recombinant human N-acetyltransferases, NAT1 and NAT2. The sulfotransferase-dependent bioactivation of N-OH-A alpha C by human liver cytosol exhibited large inter-individual variation (0.5-75, n = 14) and was significantly higher than bioactivation of N-hydroxy-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP). Correlation and inhibition studies suggested that the isoform of sulfotransferase primarily responsible for bioactivation of N-OH-A alpha C in human liver cytosol is SULT1A1. O-Acetyltransferase-dependent bioactivation of N-OH-A alpha C by human liver cytosol also exhibited large inter-individual variation (16-192, n = 18). In contrast to other N-hydroxy heterocyclic amines, which are primarily substrates only for NAT2, both NAT1 and NAT2 catalyzed bioactivation of N-OH-A alpha C. The rate of bioactivation of N-OH-A alpha C by both NAT1 and NAT2 was significantly higher than that for N-OH-PhIP. In rat and mouse liver cytosols, the level of sulfotransferase-dependent bioactivation of N-OH-A alpha C was similar to the level in the high sulfotransferase activity human liver cytosol. The level of O-acetyltransferase-dependent bioactivation of N-OH-A alpha C in rat liver cytosol was also comparable with that in the high acetyltransferase activity human liver cytosol. However, the level of O-acetyltransferase-dependent bioactivation of N-OH-A alpha C in mouse liver cytosol was comparable with that in the low acetyltransferase activity human liver cytosol. In contrast to N-OH-PhIP, bioactivation of N-OH-A alpha C was not inhibited by glutathione S-transferase activity; however, DNA binding of N-acetoxy-A alpha C was inhibited 20% in the presence of GSH. These results suggest that bioactivation of N-OH-A alpha C may be a significant source of DNA damage in human tissues after dietary exposure to AalphaC and that the relative contribution of each pathway to bioactivation or detoxification of N-OH-A alpha C differs significantly from other N-hydroxy heterocyclic or aromatic amines.
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Division of Molecular Epidemiology, National Center for Toxicological Research, 3900 NCTR Road, Jefferson, AR 72079-9502, USA.
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D000107:Acetylation; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D015239:Arylsulfotransferase / Q000378:metabolism; D001711:Biotransformation; D002243:Carbolines / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D002273:Carcinogens / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D002417:Cattle; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D051381:Rats; D011916:Rats, Inbred F344; D011994:Recombinant Proteins / Q000378:metabolism
D002243:Carbolines; D002273:Carcinogens; D007527:Isoenzymes; C412014:N-hydroxy-2-aminocarboline; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D001191:Arylamine N-Acetyltransferase; C089384:N-acetyltransferase 1; C478900:NAT2 protein, human; D005982:Glutathione Transferase; D015239:Arylsulfotransferase