title: Lack of correlation between DNA methylation and hepatocarcinogenesis in rats and hamsters treated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.
abstract: Previous studies have demonstrated that the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induced liver tumors in F344 rats but not in Syrian golden hamsters. The aim of this study was to determine whether there was a correlation between the persistence of O6-methylguanine (O6-mGua) adducts and the rate of recovery of O6-methylguanine-DNA methyltransferase (O6-mGuaT) after depletion in the liver and susceptibility to NNK in F344 rat and Syrian golden hamster injected s.c. with NNK (80 mg/kg). The levels of both 7-methylguanine and O6-mGua reached a maximum 24 h after NNK treatment. O6-mGua in NNK-treated rat liver was undetectable after 48 h. In the rat, the depletion of O6-mGuaT activity occurred within 4 h following NNK treatment. A subsequent rapid recovery of enzyme activity was observed 36 h after NNK exposure. In contrast, high levels of O6-mGua persisted in hamster liver DNA and no O6-mGuaT activity was detected up to 336 h after NNK injection. Thus, the persistence of O6-mGua in hamster liver is most likely related to a lack of recovery of the O6-mGuaT. These results suggested that factors other than O6-mGua may be determining NNK-induced hepatocarcinogenesis in rats. An aldehyde generated by alpha-hydroxylation of NNK, 4-oxo-4-(3-pyridyl)butanal, inhibited O6-mGuaT activity in rat hepatocytes, suggesting that this aldehyde contributes to the carcinogenicity of NNK by inhibiting this repair enzyme.
authors.affiliation: Laboratory of Cancer Etiology and Chemoprevention, School of Pharmacy, Laval University, Quebec City, PQ, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.forename: A
authors.initials: A
authors.lastname: Castonguay
authors.forename: S L
authors.initials: SL
authors.lastname: Gerson
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000633:toxicity*; D002478:Cells, Cultured; D006224:Cricetinae; D004247:DNA / Q000737:chemistry / Q000187:drug effects*; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000201:enzymology; D008113:Liver Neoplasms / Q000139:chemically induced*; D008297:Male; D008647:Mesocricetus; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D009602:Nitrosamines / Q000633:toxicity*; D019853:O(6)-Methylguanine-DNA Methyltransferase; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D002273:Carcinogens; D009602:Nitrosamines; D006147:Guanine; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; D004247:DNA; C008449:O-(6)-methylguanine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase