Equol, a Metabolite of Daidzein, Inhibits IgE-Dependent Basophil Activation by Modulating Intracellular Signaling

BACKGROUND: Currently, the health-promoting effects of equol, an active metabolite of the naturally occurring isoflavone daidzein, in human digestive organs are attracting attention. Although the anti-inflammatory properties of equol have been elucidated and reported, the effect of equol on basophil activation associated with allergy induction has not been clarified. OBJECTIVE: In this study, we investigated the inhibitory effects of equol on basophil degranulation, which is responsible for anaphylaxis and allergic symptoms. METHODS: ) was examined following various stimulations including anti-IgE stimulation. RESULTS: Pretreatment of equol for 15 min significantly inhibited β-hexosaminidase at 20 min and interleukin-4 release at 4 h after stimulation without affecting cell viability. The inhibitory effect of equol on cell degranulation was comparable to that of genistein and daidzein. Treatment with equol also diminished the IgE-dependent increase in the phosphorylation levels of Akt, ERK, JNK and p38. Moreover, equol attenuated IgE-dependent mouse primary basophil degranulation, as indicated by increased CD63 expression. Ionomycin- or thapsigargin-induced CD63 expression was also inhibited by the compound. CONCLUSIONS: These results suggest that equol might be a potential candidate as an anti-allergic agent as well as related isoflavones.