In vitro model of nicotine penetration through non-keratinized oral mucosa

Objectives: Nicotine replacement therapy (NRT), an important adjunct for smoking cessation, involves cutaneous and oral mucosal nicotine delivery. Our previous research shows that nicotine concentration (C_n) affects its flux (J_n) directly in skin but indirectly in non-keratinized oral mucosa (NK-OM). This paradox suggests the tissues have structural and compositional differences which may influence penetration pathway. In particular, we propose that nicotine permeation across NK-OM is transcellular and is influenced by the presence of intracellular amino acids. To test this hypothesis, we created a model cell to examine the effect of pH, C_n, and poly-lysine concentration (C_l) on J_n.

Methods: The model cell, consisting of two dialysis membranes (MWCO = 1000D) separated by a rubber gasket containing phosphate-buffered poly-lysine solution (MW>15,000, C_l = 25ug/mL or 75ug/mL, pH 7.5 or 9.5), was mounted in perfusion chambers with 1mL nicotine donor solution (1uCi 3H-nicotine, C_n = 0.5%wt/vol, 0.05%wt/vol; pH 9.5). Perfusate samples were collected, dpm counted, flux (dpm/sq cm/min) and K_p (cm/min) calculated, and data statistically analyzed (ANOVA, Tukey, p<0.05). Results: Increasing intracellular poly-lysine solution pH significantly increased K_p (p<0.001), but increasing donor C_n significantly decreased K_p (p<0.001). Increasing C_l had no effect on K_p. A significant interaction effect existed between C_n and pH.

Conclusions: Results from the in vitro model are consistent with previous observations made on NK-OM. Cationic poly-lysine, perhaps like intracellular protein and amino acids, repels nicotine from the cell. Increasing intracellular pH decreases the proportion of cationic lysine, resultantly decreasing electrostatic repulsion between nicotine and poly-lysine. The result would be to increase partitioning, and thus K_p, of nicotine. Similarly, low donor C_n decreases poly-lysine-nicotine interaction, resulting in more favorable partition of 3H-nicotine. Overall, the findings suggest that maintaining low surface C_n and high pH would benefit clinical NK-OM nicotine delivery in NRT.

Supported by an AADR Student Fellowship.