Demkowicz-Dobrzanski K, Castonguay A
Laboratory of Cancer Etiology and Chemoprevention, School of Pharmacy, Laval University, Quebec City, Canada.
Carcinogenesis. 1992 Aug;13(8):1447-54. doi: 10.1093/carcin/13.8.1447.
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.
烟草致癌物4-（甲基亚硝胺基）-1-（3-吡啶基）-1-丁酮（NNK）的活化产生了甲基化物质以及两种醛：甲醛和4-氧代-4-（3-吡啶基）丁醛（OPB）。我们研究了谷胱甘肽对N-甲基-N-亚硝基脲（MNU）以及这两种醛所产生的单链断裂（SSB）的调节作用。肝细胞同时暴露于0.2 mM MNU以及0 - 2.00 mM甲醛或OPB中4小时。两种醛均以剂量依赖性方式诱导SSB。甲醛和OPB对MNU诱导的DNA SSB形成具有协同作用。据推测，这两种醛均干扰DNA修复过程，从而增加DNA甲基化物质的遗传毒性作用。我们研究了谷胱甘肽（GSH）是否能够保护DNA免受NNK衍生中间体的损伤。甲醛（2 mM）和OPB（2 mM）分别将细胞内GSH含量降低至对照的60%和86%。DL-丁硫氨酸-[S,R]-亚砜亚胺（BSO）处理将肝细胞的GSH含量降低至对照的19%，但未降低细胞色素P450的含量以及NNK的代谢。在GSH耗竭的肝细胞中，由NNK、甲醛或OPB诱导的DNA SSB频率显著更高。用谷胱甘肽单乙酯补充GSH可使NNK诱导的SSB恢复至初始频率。OPB可诱导双链断裂，而NNK和甲醛则不能。我们得出结论，OPB和甲醛抑制甲基化物质诱导的DNA损伤修复，并且GSH可降低NNK衍生的活性代谢物诱导的DNA损伤水平。
