Reactions of human keratinocytes in vitro after application of nicotine

Nicotine is rapidly taken up by human keratinocytes (HaCaT cells) and after 3 h the uptake is approximately 50% of maximum. Cotinine, a metabolite of nicotine, was detected, thus demonstrating the metabolism of nicotine in HaCaT cells. Low nicotine concentrations (0.1-200 micrograms/ml) did not influence the incorporation rate of thymidine into DNA or amino acids into proteins. Inhibition of DNA and protein synthesis was only observed at concentrations > 200 micrograms/ml. After application of 400 micrograms/ml nicotine, the cells were vacuolated. This process was reversed after nicotine withdrawal. At low nicotine concentrations, no changes in microtubules and actin filaments could be detected. However, in the presence of nicotine (1-10 micrograms/ml), keratin filaments showed a more orderly pattern that controls, and the expression of the suprabasal keratins 1 and 10/11 was induced and increased according to the concentration of nicotine. The number of cornified envelopes also increased markedly. Nicotine concentrations > 100 micrograms/ml led to a disarrangement of keratin filaments and to a decrease in keratin expression and cornified envelope formation. Our results suggest that nicotine at concentrations up to 100 micrograms/ml is not an irritant but may induce cornification of the skin.