Effect of menthol on the penetration of tobacco carcinogens and nicotine across porcine oral mucosa ex vivo

Menthol is a flavored tobacco additive claimed to mask the bitter taste and reduce the harshness of cigarette smoke. (Azzi, C., Zhang, J., Purdon, C. H., Chapman, J. M., Nitcheva, D., Hebert, J. R., et al., 2006, Permeation and reservoir function of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and benzo[a]pyrene (B[a]P) across porcine esophageal tissue in the presence of ethanol and menthol. Carcinogenesis, 27, 137-145). have shown that menthol increased the flux of tobacco carcinogens (TC) across porcine esophagus. As oral mucosa is exposed to both smoke and smokeless tobacco in tobacco users, the objective of this study was to determine whether menthol influenced the penetration of the TC nitrosonornicotine (NNN) across porcine buccal (BM) and floor of mouth (FM) mucosa. Porcine BM and FM were collected at slaughter, mounted in perfusion chambers (n = 7/group), and exposed to tritiated NNN ((3)H-NNN; Amersham, activity 1 mu Ci/ml) and tritiated nicotine ((3)H-nicotine; Sigma) in 3% nicotine/phosphate-buffered saline (0.01 M, pH 7.4) containing 0.01% unlabeled NNN (National Cancer Institute Chemical Carcinogen Repository) +/- 0.08% menthol for 0.5, 1, 2, or 12 hr. K(p) values (cm/min) were determined and statistically analyzed (analysis of variance, Tukey's, p < .05). FM and BM permeability to both (3)H-NNN and (3)H-nicotine was significantly increased (p < .05) with addition of menthol over that of nicotine alone regardless of exposure times. Even short 30-min menthol exposure significantly increased the flux of both compounds, and this was maintained throughout the experiment. Menthol enhances penetration of NNN and nicotine through FM and BM in vitro, even after short exposure. This may reflect loading of a superficial epithelial reservoir (Squier, C. A., Kremer, M. J., Bruskin, A., Rose, A., & Haley, J. D., 1999. Oral mucosal permeability and stability of transforming growth factor beta-3 in vitro. Pharmaceutical Research, 16, 1557-1563.), thus delivering menthol and enhancing flux for several hours. Practical implications are for a potentially increased oral exposure to carcinogens among users of menthol-flavored cigarettes and chewing tobacco.