Constituents from oak bark (Quercus robur L.) inhibit degranulation and allergic mediator release from basophils and mast cells in vitro

Oak bark has been used since ancient times in Europaen ethnomedicine because of its adstringent, antimicrobial and hemostatic features, e.g. as a remedy for the treatment of wounds and skin diseases. Oak bark tannins are considered as bioactive natural products, interacting with surface proteins of mucous membranes and might be beneficial for the treatment of allergic diseases. This study investigated the effect of an oak bark decoction (OBD) and isolated tannin fractions on the degranulation capacity and cytokine/chemokine release from rat basophilic cells and human mast cells in vitro, which are essential for the initiation of early- and late-phase allergic reactions. By chromatographic separation on Sephadex® LH-20 high- and low-molecular weight tannins were separated from OBD and the tannin composition analyzed by HPLC(DAD)-MSn. Then, the OBD and its fractions were tested in degranulation (β-hexosaminidase activity) of allergen-specific-activated basophilic cells in a photometric assay. The OBD and the high-molecular tannin fraction showed a dose-dependent inhibition of cell degranulation. Furthermore, the OBD and particularly its high molecular weight tannin fraction exhibited an inhibitory activity on the IL-8-, IL-6- and TNF-α-secretion from stimulated human mast cells, detected and quantified by ELISA. The OBD and its high-molecular weight tannins revealed an impact on allergic mediator release of basophilic cells and human mast cells and thereby provide a rationale for the topical treatment with OBD preparations. [Display omitted]