Inhibitory effects of flavonoids isolated from Fragaria ananassa Duch on IgE-mediated degranulation in rat basophilic leukemia RBL-2H3 Original Research Article

We isolated the 4 kinds of flavonoids from strawberry ‘Nohime’ and examined the effect of these flavonoids on the degranulation in RBL-2H3 cells. The flavonoids were found to suppress the degranulation from Ag-stimulated RBL-2H3 cells to different extents. To disclose the inhibitory mechanism of degranulation by flavonoids, we examined their effects on the intracellular free Ca2+ concentration ([Ca2+]i) and the intracellular signaling pathway such as Lyn, Syk, and PLCγs. The intracellular free Ca2+ concentration ([Ca2+]i) was elevated by FcεRI activation, but these flavonoid treatments reduced the elevation of [Ca2+]i by suppressing Ca2+ influx. Kaempferol strongly suppressed the activation of Syk and PLCγs. It was thus suggested that suppression of Ag-stimulated degranulation by the flavonoids is mainly due to suppression of [Ca2+]i elevation and Syk activation. These results suggested that strawberry would be of some ameliorative benefit for the allergic symptoms.