Procyanidin C1 from apple extracts inhibits FcεRI-mediated mast cell activation

Background: Polyphenol-enriched fractions, which are extracted from unripe apples (Rosaceae, Malus spp.), consisting of procyanidins (polymers of catechins) are known to have an anti-allergenic effect on patients with various allergic diseases. Although it has been reported that apple extracts inhibit histamine release from mast cells, the molecular mechanisms for this anti-allergenic effect are not well understood. To elucidate the molecular mechanisms by which apple extracts induce their anti-allergenic effects, the effects of purified apple extract components on high-affinity receptors for IgE (FcεRI)-mediated mast cell activation were investigated. Methods: The anti-allergic effect of oral administration of apple procyanidin extracts on passive cutaneous anaphylactic responses of BALB/c mice was assessed. We evaluated the effects of procyanidin C1 (PC1) [epicatechin-(4β→8)- epicatechin-(4β→8)-epicatechin], a component of the procyanidin fraction, on mouse bone-marrow-derived mast cell degranulation, cytokine production, protein tyrosine phosphorylation and on the generation of intracellular reactive oxygen species (ROS) of cells stimulated by FcεRI cross-linking in vitro. Results: In an in vivo study, oral administration of the procyanidin fraction suppressed the mast-cell-dependent allergic reaction. In in vitro studies, PC1 dose-dependently decreased FcεRI-mediated degranulation and cytokine production of mast cells. Furthermore, PC1 inhibited tyrosine phosphorylation of Syk and linker for activation of T cells, and the ROS generation in stimulated mast cells. Conclusions: PC1 suppresses FcεRI-mediated mast cell activation by inhibiting intracellular signaling pathways. These observations provide evidence for the anti-allergenic effects of the procyanidin-enriched apple extract.