Abstract
Accumulating evidence suggests the anti-allergic effect of green tea extract. Although histamine is a major chemical mediator in the pathogenesis of allergic rhinitis, the effect of green tea extract on histamine signaling was unknown. In this study, we investigated the effect of tea extract on the toluene-2, 4-diisocyanate (TDI)-induced up-regulations of the histamine H1 receptor (H1R) and Th2 cytokines gene expressions in the nasal mucosa of TDI-sensitized allergy model rats. Pre-treatment with tea extract once daily for 3 weeks significantly suppressed the TDI-induced mRNA elevations of Th2 cytokines such as interleukin (IL)-4, IL-5, IL-9, and IL-13, and tended to suppress H1R mRNA elevation induced by TDI. Further investigations revealed that the 80% ethanol eluate from a TOYOPEARL HW40EC column, in which epigallocatechin-3-O-gallate (EGCG) was a major constituent, inhibited the IgE-stimulated mRNA elevations of Th2 cytokines in RBL-2H3 cells. EGCG suppressed the elevations of IgE-stimulated IL-4 mRNA and phorbol-12-myristate-13-acetate (PMA)-induced H1R mRNA in a dose-dependent manner. In TDI-sensitized rats, pre-treatment with EGCG once daily for 3 weeks decreased the number of sneezes and suppressed the TDI-induced elevations of H1R and IL-4 mRNAs in the nasal mucosa. These findings suggest that EGCG alleviates nasal symptoms by inhibiting histamine signaling as well as IL-4 signaling by suppressing TDI-induced H1R and IL-4 gene up-regulations in TDI-sensitized rats.
