Icaritin protects against airway inflammation by inhibiting the TLR4/NF-κB pathway in vivo and in vitro

Icaritin, a bioactive phytomolecule derived from Epimedium flavonoids (EFs), has been shown to have anti-inflammatory, anti-proliferative, and pro-apoptotic properties. However, its potential mechanisms in asthma airway inflammation have not been elucidated. In this study, Ovalbumin (OVA)-induced asthma mouse model and human bronchial epithelial cells (BEAS-2B) were used to illustrate the effects and mechanisms of Icaritin on airway inflammation. Specific airway resistance (sRAW) was used to detect the airway hyperresponsiveness (AHR). Hematoxylin-eosin (H&E) and periodic acid schiff (PAS) were used to detect the pathological changes. Bronchoalveolar lavage fluid (BALF) was used to detect the airway inflammatory cells. Serum and supernatants were used to detect the cytokines. Immunohistochemistry (IHC) and western blotting were used to detect the expression of TLR4, p-65, p-p65, IκBα, and p-IκBα. Cell Counting Kit-8 (CCK-8) was used to detect the cell viability. Icaritin suppressed AHR, attenuated eosinophilic infiltration and mucus hypersecretion, and significantly reduced the levels of OVA-specific cytokines in asthmatic mice. Moreover, Icaritin inhibited TLR4 expression, decreased phosphorylation of IκBα, and reduced NF-κB p65 activation in lung tissue of asthmatic mice. Further mechanistic studies showed that Icaritin reduces TLR4-induced inflammatory factor expression and blocks TLR4-activated NF-κB pathway in BEAS-2B cells. These findings demonstrate for the first time that Icaritin suppresses airway inflammation in asthma by inhibiting the TLR4/NF-κB pathway, suggesting its potential as a therapeutic agent for asthma.