Effects of ethanol and various alcoholic beverages on the formation of O6-methyldeoxyguanosine from concurrently administered N-nitrosomethylbenzylamine in rats: a dose-response study.

Consumption of alcoholic beverages has been identified as a major cause of oesophageal cancer in industrialized countries, with an exceptionally high risk associated with apple-based liquors (calvados). In the present study, we have determined the dose--activity relationship of the effects of coincident ethanol on the formation of O6-methyldeoxyguanosine (O6-MEdG) by the oesophageal carcinogen N-nitrosomethylbenzylamine (NMBzA). Male Fischer 344 rats received a single intragastric dose of NMBzA (2.5 mg/kg body wt; 7.4 ml/kg body wt) in tap water containing 0-20% ethanol (v/v). Survival time was 3 h. In controls, concentrations of O6-MEdG were similar in oesophagus, lung and liver (11-14.9 mumol/mol dG). In oesophagus, coincident ethanol increased levels of O6-MEdG from 15.2 mumol/mol (0.1% ethanol) to 46.0 mumol/mol (20%). This increase was dose dependent for 1-20% ethanol; however, low doses produced a larger effect per gram of ethanol than higher doses. In lung, concentrations of O6-MEdG increased from 11 mumol/mol (0.1%) to a plateau value of 24 mumol/mol (greater than or equal to 5%). In nasal mucosa, an increase in O6-MEdG from 3.9 mumol/mol (controls) to 30.7 mumol/mol was observed with 4% ethanol. Effects of ethanol on hepatic DNA methylation were statistically non-significant. Modulation of NMBzA bioactivation by various alcoholic beverages (adjusted to 4% ethanol) was also investigated. Increases in oesophageal O6-MEdG were similar (+50% to +116%) with pear brandy, rice wine (sake), farm-made calvados, gin, Scotch whisky, white wine, Pilsner beer and aqueous ethanol. Significantly higher increases were elicited by commercially distilled calvados (+125%) and red burgundy (+162%). In contrast to its effects at an ethanol content of 4%, farm-made calvados diluted to 20% ethanol produced significantly higher (+200%) increases in oesophageal DNA methylation than aqueous ethanol (+148%). Our results show that ethanol is an effective modulator of nitrosamine bioactivation in vivo at intake levels equivalent to moderate social drinking, and that some alcoholic beverages contain congeners that amplify the effects of ethanol, suggesting that modulation of nitrosamine metabolism by acute ethanol may play a role in the etiology of human cancer.