Spirodela polyrhiza and its Chemical Constituent Vitexin Exert Anti-Allergic Effect via ORAI1 Channel Inhibition

Intracellular calcium signaling cascades are integral to early and late allergic responses involving mast cell degranulation and type 2 helper T cell activation, respectively. Both the responses are accompanied by the movement of calcium through the calcium release-activated calcium (CRAC) channel, encoded by the ORAI1 gene. Spirodela polyrhiza (L.) Schleid (SP) has anti-inflammatory and anti-allergic effects, but its effect on calcium signaling has not been reported. This study investigated whether a 30% ethanolic SP extract (SPEtOH) and its constituents can reduce CRAC currents (ICRAC), and thus inhibit mast cell degranulation and T cell activation. In Jurkat T lymphocytes, we found that 3mg/mL SPEtOH inhibited the ICRAC by 81.0±11.1%, whereas one of its constituents vitexin (100μM) inhibited the ICRAC by 48.9±8.71%. Furthermore, in the RBL-2H3 mast cell, the ICRAC was inhibited by 3mg/mL SPEtOH (86.7±5.83%) and 100μM vitexin (47.5±5.67%). Investigation of human primary T cell proliferation induced by co-stimulation with antibodies to cluster of differentiation 3 and 28, and of RBL-2H3 mast cell degranulation following IgE-antigen complex stimulation revealed that 100μM vitexin inhibited both T-cell proliferation (by 34.8±6.08%) and mast cell degranulation (by 36.7±0.07%). These effects were concentration-dependent, and no cytotoxicity was observed. Our findings suggest that vitexin is a promising candidate compound for the development of therapeutic agents to prevent and treat allergic diseases.