NNN, present in all tobacco products, may be a cause of cancer in tobacco users. In this study, pyridyloxobutyl (POB)-DNA adducts were quantified during a chronic carcinogenicity study of NNN enantiomers in male F-344 rats. Few studies in the literature have quantified carcinogen-DNA adducts during long term chronic treatment. Some DNA adducts decrease during chronic treatment due to repair and related phenomena, while others remain at a steady state. The persistence of DNA adducts during treatment is important for their potential use as biomarkers and for mechanistic evaluations. A total of 108 male F344 rats, 7 weeks old, were randomly divided into three groups of 36: control, (S)-NNN and (R)-NNN. Rats in the treatment groups received 15 ppm of NNN in drinking water; control rats were given tap water. Nine rats per group were sacrificed at 10, 30, 50 and 70 weeks. DNA was isolated from normal liver, lung, esophagus, oral, and nasal olfactory and respiratory tissues, and analyzed by LC-ESI-MS/MS with selected reaction monitoring for POB-DNA adducts, including 7-POB-Gua and O2-POB-dThd. Adduct levels were high in nasal, esophageal, and oral tissue DNA. Total adduct levels in all six tissues were relatively stable during the long period of treatment. Adducts from (S)-NNN treatment were higher than those from (R)-NNN in oral, esophagus, liver, and nasal respiratory tissues. Definitely, there was no decreasing trend of total adduct levels in any tissue throughout the time course. Other groups of rats treated with (S)-NNN in this study and allowed to live for up to 75 weeks had high incidences of tumors in the oral cavity and esophagus, while (R)-NNN was weakly active. The results of this study demonstrate that POB-DNA adducts of NNN are not efficiently repaired, persist through exposure, and thus might be novel biomarker candidates for susceptibility to tobacco-related cancer.

Liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) quantitation of pyridyloxobutyl-DNA adducts in tissues of rats treated chronically with (R)- or (S)-N'-nitrosonornicotine (NNN)

246th National Meeting (2013)

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