Nicotine-enhanced epithelial differentiation in reconstructed human oral mucosa in vitro

Oral mucosal keratinocytes represent the cells that first encounter tobacco components. Therefore, tobacco-induced abnormal alteration of the mucosal keratinocytes may contribute to the development of oral white lesions. Nico tine is an ingredient of all tobacco products and pharmacologically the mos t active component of tobacco smoke. To clarify the effects of nicotine on the keratinization of oral mucosal and epidermal keratinocytes, we reconstr ucted artificial buccal mucosal and skin equivalents using keratinocytes an d fibroblasts from noncornifying buccal mucosa and adult foreskin, respecti vely. The effect of nicotine on keratinization was assessed with morphology , immunohistochemistry and immunoblotting. Long-term treatment with nicotin e for 2 weeks enhanced in a dose-dependent manner the expression of differe ntiation-specific proteins of oral mucosal keratinocytes on living oral muc osal equivalent and epidermal keratinocytes on living skin equivalent, resp ectively. The effect of nicotine on the cell viability was measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Oral m ucosal keratinocytes showed a higher resistance to nicotine toxicity than e pidermal keratinocytes. Our results suggest that nicotine stimulates differ entiation of both mucosal and epidermal keratinocytes, and this nicotine-in duced abnormal differentiation may be associated with the development of or al white lesions.