Bakuchicin alleviates ovalbumin-induced allergic asthma by regulating M2 macrophage polarization

Objective: Asthma is an airway inflammatory disease caused by activation of numerous immune cells including macrophages. Bakuchicin (BKC) is known to exhibit anti-inflammatory effects and type 2 T helper (Th2) regulation, but has not been investigated for airway inflammation. This study aimed to evaluate the effects of BKC on airway inflammation and demonstrate the mechanisms of macrophage polarization. Methods: The anti-inflammatory effects were determined using lipopolysaccharide (LPS)-stimulated macrophages. The ovalbumin (OVA)-induced asthma mouse model was used to evaluate the effects of BKC on airway inflammation and Th2 responses. Moreover, the effect of BKC on macrophage polarization was confirmed in bone marrow-derived macrophages (BMDMs) differentiation. Results: BKC suppressed nitric oxide production and expression of pro-inflammatory cytokines by inhibiting signaling pathway in LPS-stimulated macrophages. In an OVA-induced asthma model, BKC treatment alleviated histological changes and mast cell infiltration and reduced the levels of eosinophil peroxidase, β-hexosaminidase, and immunoglobulin levels. In addition, BKC alleviated Th2 responses and M2 macrophage populations in bronchoalveolar fluid. In BMDMs, BKC suppressed IL-4-induced M2 macrophage polarization and the expression of M2 markers such as arginase-1 and Fizz-1 through inhibiting sirtuin 2 levels. Conclusion: BKC could be a drug candidate for the treatment of allergic asthma.