Inhibitory effects of mulberry fruit extract in combination with naringinase on the allergic response in IgE-activated RBL-2H3 cells

Abstract

In this study, we investigated the anti-allergic action of mulberry fruit extract (MFE) or MFE in combination with naringinase (MFEN) in IgE-activated RBL-2H3 cells, and investigated the mechanisms responsible for the anti-allergic effects of MFEN. β-hexosaminidase release assay was used to measure the amount of β-hexosaminidase released from the cells, and ELISA was used to measure the levels of tumor necrosis factor-α (TNF-α). We found that MFE significantly reduced the release of β-hexosaminidase (IC(50), 10.59 mg/ml) and TNF-α (IC(50), 4.87 mg/ml). Moreover, MFEN enhanced the inhibitory effects on the release of β-hexosaminidase (IC(50), 123.10 µg/ml) and TNF-α (IC(50), 65.01 µg/ml). Furthermore, MFEN had no cytotoxicity at the concentration range used to exert the anti-allergic effects. In addition, we evaluated the effects of MFEN on the formation of pro-inflammatory lipid mediators, such as prostaglandin D(2) (PGD(2)), leukotriene C(4) (LTC(4)) and leukotriene B(4) (LTB(4)) using enzyme immunoassay (EIA) kits. MFEN markedly reduced the formation of PGD(2) (IC(50), 6.47 µg/ml) and LTC(4) (IC(50), 0.31 µg/ml), but not LTB(4) (IC(50), 25.75 µg/ml). In mechanistic analyses, we measured the phosphorylation of Syk, Lyn and Fyn by immunoblot analysis. MFEN significantly inhibited the phosphorylation of Syk, but not that of Lyn or Fyn. MFEN also suppressed the phosphorylation of phospholipase C (PLC)γ1/2, protein kinase C (PKC)δ, linker for activation of T cells (LAT), extracellular signal-regulated protein kinase (ERK)1/2, JNK, GRB2-associated binding protein 2 (Gab2), phosphoinositide-3-kinase (PI3K), Akt, cytosolic phospholipase A2 and 5-lipoxygenase, as well as the expression of cyclooxygenase-2. In conclusion, these results suggest that MFEN exerts potent inhibitory effects on allergic response through the suppression of the activation of the FcεRI signaling cascade. Our data demonstrating the anti-allergic effects of MFEN may provide further insight into the therapeutic application of MFEN or its use as a functional food.