Epidemiologic studies have associated higher dietary consumption of soy isoflavones with decreased self-report of cough and allergic respiratory symptoms, but the pharmacodynamic effects of soy isoflavone on asthmatic model have not been well-described. Here, we hypothesized that soy isoflavone may have potential effects on airway hyperresponsiveness, inflammation and airway remodeling in a murine of asthma. Mice sensitized and challenged with ovalbumin developed airway inflammation. Bronchoalveolar lavage fluid was assessed for inflammatory cell counts, and for cytokine levels. Lung tissues were examined for cell infiltration, mucus hypersecretion and airway remodeling, and for the expression of inflammatory biomarkers. Airway hyperresponsiveness was monitored by direct airway resistance analysis. Oral administration of soy isoflavone significantly reduced ovalbumin-induced airway hyperresponsiveness to intravenous methacholine, and inhibited ovalbumin-induced increases in eosinophil counts. RT-PCR analysis of whole lung lysates revealed that soy isoflavone markedly suppressed ovalbumin-induced mRNA expression of eotaxin, interleukin(IL)-5, IL-4 and matrix metalloproteinase-9, and increased mRNA expression of interferon (IFN)-γ and tissue inhibitor of metalloproteinase-1 in a dose-dependent manner. Soy isoflavone also substantially recovered IFN-γ/IL-4 (Th1/Th2) levels in bronchoalveolar lavage fluid. In addition, histologic studies showed that soy isoflavone dramatically inhibited ovalbumin-induced lung tissue eosinophil infiltration, airway mucus production and collagen deposition in lung tissues. Our findings suggest that soy isoflavone as nutritional supplement may provide a novel means for the treatment of airway inflammatory disease.
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