Pine bark extract pycnogenol downregulates IFN-γ-induced adhesion of T cells to human keratinocytes by inhibiting inducible ICAM-1 expression

Abstract

Expression of intercellular adhesion molecule-1 (ICAM-1) is necessary for leukocyte/keratinocyte interactions. Upregulation of ICAM-1 expression in keratinocytes has been observed in several inflammatory dermatoses, such as psoriasis, atopic dermatitis, and lupus erythematosus. Inflammatory cytokines, such as interferon-γ (IFN-γ), upregulate ICAM-1 expression in keratinocytes. Because of potent antioxidant and anti-inflammatory properties of the French maritime pine bark extract, Pycnogenol (Horphag Research, Geneva, Switzerland), its effects were investigated on the interaction of T cells with keratinocytes after activation with IFN-γ and the molecular mechanisms involved in such interactions. Studies were performed using a human keratinocyte cell line, HaCaT. Cell adhesion in the presence of IFN-γ was studied using a coculture assay. Treatment of HaCaT cells with 20 U/ml IFN-γ for 24 h markedly induced adherence of Jurkat T cells to HaCaT cells. PYC pretreatment (50 μg/ml, 12 h) significantly inhibited IFN-γ induced adherence of T cells to HaCaT cells ( p < .01). ICAM-1 plays a major role in the IFN-γ-induced adherence of T cells to keratinocytes. Thus, the effect of PYC on IFN-γ-induced ICAM-1 expression was investigated as well. Pretreatment of HaCaT cells with PYC significantly inhibited IFN-γ-induced expression of ICAM-1 expression in HaCaT cells. The downregulation of inducible ICAM-1 expression by PYC was both dose and time dependent. A 50 μg/ml dose of PYC and a 12 h pretreatment time (i.e., before activation with IFN-γ) provided maximal (∼70%) inhibition of inducible ICAM-1 expression in HaCaT cells. Gamma-activated sequence present on the ICAM-1 gene confers IFN-γ responsiveness in selected cells of epithelial origin (e.g., keratinocytes) that are known to express ICAM-1 on activation with IFN-γ. Gel-shift assays revealed that PYC inhibits IFN-γ-mediated activation of Stat1, thus suggesting a transcriptional regulation of inducible ICAM-1 expression by PYC. These results indicate the therapeutic potential of PYC in patients with inflammatory skin disorders.