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 meta bolite of nicotine, was detected, thus demonstrating the metabolism of nicotine in HaCaT cells. Low nicotine concentrations (0.1-200 mu g/ml ) did not influence the incorporation rate of thymidine into DNA or am ino acids into proteins. Inhibition of DNA and protein synthesis was o nly observed at concentrations > 200 mu g/ml. After application of 400 mu g/ml nicotine, the cells were vacuolated. This process was reverse d after nicotine withdrawal. At low nicotine concentrations, no change s in microtubules and actin filaments could be detected. However, in t he presence of nicotine (1-10 mu g/ml), keratin filaments showed a mor e orderly pattern that controls, and the expression of the suprabasal keratins 1 and 10/11 was induced and increased according to the concen tration of nicotine. The number of cornified envelopes also increased markedly. Nicotine concentrations > 100 mu g/ml led to a disarrangemen t of keratin filaments and to a decrease in keratin expression and cor nified envelope formation. Our results suggest that nicotine at concen trations up to 100 mu g/ml is not an irritant but may induce cornifica tion of the skin.