Regulation of Immunoglobulin E-Mediated Signal Transduction in Mast Cells by 5, 7, 3′, 4′-Tetrahydroxy-6,8-Diprenylisoflavone from Cudrania tricuspidata and Magnolialide from Laurus nobilis

Abstract

Allergic diseases such as atopic dermatitis (AD), asthma, and rhinitis have been characteristically associated with immunoglobulin E (IgE) hyper-production, and mast cells play a crucial role in the development of allergic and inflammatory disorders. Many drugs are based on improvements in existing therapies or on an understanding of the molecular mechanisms involved in allergic diseases. New therapies in development are aimed at inhibiting signals of the allergic inflammatory responses. In this study, we investigated the effects of natural products on IgE-mediated signaling in mast cells in order to discover new lead compounds for the treatment of allergic disorders. Cudrania tricuspidata fruit extracts are rich sources of prenylated flavonoids with potential anti-atherosclerotic, hepatoprotective, and anti-inflammatory properties. However, the effect of Cudrania tricuspidata fruits extracts and its active compounds on the high affinity IgE receptor (FcεRI)-mediated signaling remains unknown. In this study, the effect of methanol extract from the fruits of Cudrania tricuspidata (MFC) and its active compound, 5,7,3′,4′-tetrahydroxy-6,8-diprenylisoflavone (THDPI), on FcεRI-mediated signaling in mast cells were investigated. MFC and THDPI suppressed mast cell degranulation and Ca2+ influx. MFC also interfered with IgE-FcεRI interaction and decreased FcεRIβ mRNA expression in mast cells. Furthermore, MFC and THDPI inhibited the phosphorylation of Syk, LAT, and PLCγ, and F-actin redistribution. THDPI also up-regulated Src-like adaptor protein (SLAP) regulating phosphorylated Syk kinase via c-Cbl-dependent ubiquitin-proteasome pathway. These results indicate that MFC and its active compound, THDPI, inhibit mast cell activation through the inhibition of FcεRI-mediated Syk activation, suggesting a therapeutic potential for controlling mast cell activation in inflammatory and/or allergic processes. This study also investigated the effect of several isolated compounds from Laurus nobilis on the inhibition of antigen-induced IgE-mediated mast cell degranulation by measuring the amount of β-hexosaminidase released, and the extent of interleukin (IL)-4 production using a rat basophilic leukemia mast cells (RBL-2H3) in comparison with anti-allergic drug, cromoglycate and ketotifen. Among the seven isolated compounds from Laurus nobilis, magnolialide attenuated the beta-hexosaminidase release by antigen-induced IgE-activated RBL-3H3 cells, while the other compounds revealed no effects at concentrations tested. Furthermore, magnolialide significantly decreased the IL-4 release in RBL-2H3 cells, and IL-4 mRNA was inhibited. In addition, the inhibition of IL-5-dependent proliferation of early B cells (Y16 cells) by magnolialide was demonstrated. These results suggest that the magnolialide may have beneficial effects for IgE-mediated allergic responses by inhibiting mast cell degranulation, an effector phase of allergic hypersensitivity, and by suppressing IL-4 production and IL-5-dependent early B cell proliferation, key factors in the development and amplification of allergic responses.