Effects of <i>Astragalus membranaceus</i> Leaf Extract on Allergic Inflammation in Immune Cell Lines

<i>Astragalus membranaceus</i> is a perennial plant belonging to the Fabaceae family that is widely distributed across northern Asia. <i>A. membranaceus</i> roots have been used as a traditional medicinal herb because of their numerous health benefits. However, the physiological properties of <i>A. membranaceus</i> leaves remain unknown. During allergic reactions, chemical mediators are released from mast cells, which trigger immediate hypersensitivity and subsequent macrophage-mediated inflammation. In the present study, we investigated the inhibitory effects of <i>A. membranaceus</i> leaf extract (AMLE) on allergic and inflammatory responses in immune cell lines. The results showed that AMLE suppressed the release of histamine and leukotriene B₄ from stimulated mast cells during allergic response by inhibiting the influx of calcium ions and downregulating the expression of 5-lipoxygenase. Moreover, AMLE suppressed the release of nitric oxide, prostaglandin E₂, and cytokines from stimulated macrophages during inflammatory response. These effects were attributed to the suppression of mRNA and protein expressions of inducible nitric oxide synthase and microsomal prostaglandin E synthase-1 and the inhibition of the nuclear translocation of nuclear factor kappa-light-chain-enhancer of activated B cells. Compared with the <i>A. membranaceus</i> root extract, AMLE had more potent inhibitory effects. Quercetin and kaempferol, the predominant polyphenolic compounds present in AMLE, suppressed the release of chemical mediators during allergic and inflammatory responses in immune cells. These results suggest that <i>A. membranaceus</i> leaves have a therapeutic potential for alleviating allergic inflammation and that polyphenols are the primary bioactive constituents of <i>A. membranaceus</i> leaves.