Analysis of N- and O-glucuronides of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in human urine

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a tobacco-specific lung carcinogen which may play an important role as a cause of lung cancer in smokers. NNK is extensively metabolized to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which like NNK is a potent pulmonary carcinogen. NNAL in turn is glucuronidated, and both NNAL and its glucuronides are excreted in human urine. Previous studies have clearly demonstrated the presence in human urine of 4-(methylnitrosamino)-1-(3-pyridyl)-1-(O-β-D-glucopyranuronosyl)-butane (NNAL-O-Gluc), but did not exclude the presence of 4-(methylnitrosamino)-1-(3-pyridyl-N-β-D-glucopyranuronosyl)- 1-butanolonium inner salt (NNAL-N-Gluc). In this study, we quantified NNAL, NNAL-N-Gluc, and NNAL-O-Gluc in the urine of smokers, snuff-dippers, and people who used the oral tobacco product "toombak". The presence of NNAL-N-Gluc in the urine of toombak users was confirmed by LC-ESI-MS/MS. In smokers' urine, NNAL-N-Gluc, NNAL-O-Gluc, and NNAL comprised (mean ± SD) 26.5 ± 6.2, 32.1 ± 17.6, and 41.4 ± 16.6%, respectively, of total NNAL. In snuff-dippers' urine, the corresponding figures were 13.6 ± 5.1, 46.6 ± 11.7, and 36.6 ± 9.3%. NNAL-N-Gluc comprised 50 ± 25% of total glucuronidated NNAL in smokers and 24 ± 12% in snuff-dippers. This difference was significant (P = 0.01), suggesting that smoking induces glucuronidation of NNAL. The results of this study demonstrate that NNAL-N-Gluc contributes substantially to NNAL-glucuronides in human urine. These results are important for a clearer understanding of mechanisms of detoxification of NNK in humans.