Biomarkers for human uptake and metabolic activation of tobacco-specific nitrosamines

Tobacco-specific nitrosamines are a group of carcinogens formed from nicotine and related tobacco alkaloids. Two of these compounds, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine, are believed to be involved as causative agents for cancers of the lung, oral cavity, esophagus, and pancreas associated with the use of tobacco products. The goal of the studies described here is to develop biomarkers which will allow us to understand the uptake, metabolic activation, and detoxification of these carcinogens in humans. Two metabolites of NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronide, have been identified and quantified in human urine. These metabolites allow assessment of NNK uptake in smokers, tobacco chewers, and people exposed to environmental tobacco smoke. NNK and N'-nitrosonornicotine form hemoglobin and DNA adducts upon metabolic activation by alpha-hydroxylation. These adducts release 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) upon hydrolysis. The released 4-hydroxy-1-(3-pyridyl)-1-butanone can be quantified by gas chromatography-mass spectrometry. A subset of smokers and most tobacco chewers have hemoglobin adduct levels which are higher than detected in nonsmokers. 4-Hydroxy-1-(3-pyridyl)-1-butanone-releasing DNA adducts are higher in lung tissue from smokers than from nonsmokers. These data indicate that some smokers and tobacco chewers are capable of metabolically activating NNK or N'-nitrosonornicotine to intermediates which bind to cellular macromolecules and are, therefore, at potentially higher risk for cancer development. The application of these biomarkers to studies on cancer induction by tobacco products is discussed.