Suppressive Effect of Antioxidants on Intercellular Adhesion Molecule-1 (ICAM-1) Expression in Human Epidermal Keratinocytes

Intercellular adhesion molecule-1 (ICAM-1) is strongly expressed by human epidermal keratinocytes during the course of inflammatory skin diseases. To test the possibility that reactive oxygen species produced in the skin during an inflammatory response affect ICAM-1 expression, cultured human epidermal keratinocytes were treated with H2O2 at concentrations that did not damage the cells, and cell-surface ICAM-1 expression was analyzed. Expression of ICAM-1 was induced on keratinocytes by treatment with 300 microM H2O2 for 1 h. The antioxidant N-acetyl-L-cysteine strongly inhibited H2O2-induced ICAM-1 expression, whereas the antioxidants pyrrolidine dithiocarbamate and alpha-tocopherol were less inhibitory. N-acetyl-L-cysteine also suppressed keratinocyte surface expression of ICAM-1 induced by the cytokines interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha), whereas pyrrolidine dithiocarbamate and alpha-tocopherol suppressed IFN-gamma-induced surface expression but not TNF-alpha-induced expression. We found that N-acetyl-L-cysteine treatment reduced ICAM-1 mRNA levels when keratinocytes were stimulated with either IFN-gamma or TNF-alpha; however, pyrrolidine dithiocarbamate and alpha-tocopherol had no effect on either IFN-gamma- or TNF-alpha-induced ICAM-1 mRNA levels. Our results indicate that reactive oxygen species may be involved in the skin inflammatory process by increasing epidermal ICAM-1 expression and that some antioxidants may be effective in suppressing the epidermal ICAM-1 expression induced by reactive oxygen species and cytokines in inflammatory skin diseases.