Inhibitory effects of an ellagic acid glucoside, okicamelliaside, on antigen-mediated degranulation in rat basophilic leukemia RBL-2H3 cells and passive cutaneous anaphylaxis reaction in mice

Abstract

Degranulation inhibitors in plants are widely used for prevention and treatment of immediate-type allergy. We previously isolated a new ellagic acid glucoside, okicamelliaside (OCS), from Camellia japonica leaves for use as a potent degranulation inhibitor. Crude extracts from leaves also suppressed allergic conjunctivitis in rats. In this study, we evaluated the in vivo effect of OCS using a pure sample and performed in vitro experiments to elucidate the mechanism underlying the extraordinary high potency of OCS and its aglycon. The IC50 values for degranulation of rat basophilic leukemia cells (RBL-2H3) were 14nM for OCS and 3μM for aglycon, indicating that the two compounds were approximately 2 to 3 orders of magnitude more potent than the anti-allergic drugs ketotifen fumarate, DSCG, and tranilast (0.17, 3, and >0.3mM, respectively). Antigen-induced calcium ion (Ca2+) elevation was significantly inhibited by OCS and aglycon at all concentrations tested (p<0.05). Upstream of the Ca2+ elevation in the principle signaling pathway, phosphorylation of Syk (Tyr525/526) and PLCγ-1 (Tyr783 and Ser1248) were inhibited by OCS and aglycon. In DNA microarray-screening test, OCS inhibited expression of proinflammatory cytokines [interleukin (IL)-4 and IL-13], cytokine-producing signaling factors, and prostaglandin-endoperoxidase 2, indicating that OCS broadly inhibits allergic inflammation. During passive cutaneous anaphylaxis in mice, OCS significantly inhibited vascular hyperpermeability by two administration routes: a single intraperitoneal injection at 10mg/kg and per os at 5mg/kg for 7days (p<0.05). These results suggest the potential for OCS to alleviate symptoms of immediate-type allergy.