Anti-allergic activity of emodin on IgE-mediated activation in RBL-2H3 cells

Background: Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is a Chinese herbal anthraquinone derivative from the rhizome of rhubarb (Rheum palmatum L.) that exhibits numerous biological activities, such as antitumor, antibacterial, antiinflammatory, and immunosuppressive. In the present studies, the anti-allergic activities of emodin were investigated to elucidate the underlying active mechanisms. Methods: The inhibitory effects of emodin on the IgE-mediated allergic response in rat basophilic leukemia (RBL-2H3) cells were evaluated by measuring the release of granules and cytokines. The Ca2+ mobilization in RBL-2H3 cells loaded with the Ca2+-reactive fluorescent probe Fluo-4 AM was also measured by laser scanning confocal microscope. Results: Emodin inhibited the release of beta-hexosaminidase (beta-HEX; IC50 = 5.5 mu M) and tumor necrosis factor (TNF)-alpha (IC50 = 11.5 mu M) from RBL-2H3 cells induced by 2,4-dinitrophenylated bovine serum albumin (DNP-BSA) and displayed stronger inhibition of beta-HEX release than ketotifen fumarate salt (IC50 = 63.8 mu M). Emodin at a concentration of 12.5 mu M also inhibited the DNP-BSA-induced influx of extracellular Ca2+ in RBL-2H3 cells. Conclusions: These results suggested that emodin likely exhibits anti-allergic activities via increasing the stability of the cell membrane and inhibiting extracellular Ca2+ influx.