title: Modulation by glutathione of DNA strand breaks induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and its aldehyde metabolites in rat hepatocytes.
abstract: Activation of the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) produced methylating species and two aldehydes: formaldehyde and 4-oxo-4-(3-pyridyl)-butanal (OPB). We investigated the modulation by glutathione of single-strand breaks (SSB) generated by N-methyl-N-nitrosourea (MNU) and the two aldehydes. Hepatocytes were simultaneously exposed to 0.2 mM MNU and to 0-2.00 mM formaldehyde or OPB for 4 h. Both aldehydes induced SSB in a dose-dependent manner. Formaldehyde and OPB exerted a synergistic effect on the formation of DNA SSB by MNU. It is postulated that both aldehydes interfere with DNA repair processes and thus increase the genotoxic effect of DNA methylating species. We investigated whether glutathione (GSH) could protect DNA from NNK-derived intermediates. Formaldehyde (2 mM) and OPB (2 mM) decreased intracellular GSH contents to 60 and 86% of control respectively. DL-Buthionine-[S,R]-sulfoximine (BSO) treatment reduced the GSH contents of hepatocytes to 19% of control but did not reduce the content of cytochrome P450 nor the metabolism of NNK. The frequency of DNA SSB induced by NNK, formaldehyde or OPB was significantly higher in GSH-depleted hepatocytes. GSH repletion with GSH monoethyl ester returned NNK-induced SSB to its initial frequency. OPB but not NNK nor formaldehyde induced double-strand breaks. We conclude that OPB and formaldehyde inhibit the repair of DNA damage induced by methylating species and that GSH reduces the level of DNA damage induced by NNK-derived reactive metabolites.
authors.affiliation: Laboratory of Cancer Etiology and Chemoprevention, School of Pharmacy, Laval University, Quebec City, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Demkowicz-Dobrzanski
authors.forename: A
authors.initials: A
authors.lastname: Castonguay
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D019328:Buthionine Sulfoximine; D002273:Carcinogens / Q000633:toxicity*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis; D004247:DNA / Q000187:drug effects; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair; D004305:Dose-Response Relationship, Drug; D005557:Formaldehyde / Q000633:toxicity*; D005978:Glutathione / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D008297:Male; D008717:Methionine Sulfoximine / Q000031:analogs & derivatives / Q000494:pharmacology; D009602:Nitrosamines / Q000633:toxicity*; D011725:Pyridines / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D000964:Antimetabolites, Antineoplastic; D002273:Carcinogens; D009602:Nitrosamines; D011725:Pyridines; D008717:Methionine Sulfoximine; D005557:Formaldehyde; D019328:Buthionine Sulfoximine; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; C062145:4-oxo-4-(3-pyridinebutanal); D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D005978:Glutathione