Stigmasterol alleviates airway inflammation in OVA-induced asthmatic mice via inhibiting the TGF-β1/Smad2 and IL-17A signaling pathways.

Stigmasterol is a common dietary phytosterol with high nutritional value and physiological activity. In this study, we evaluated the effects of stigmasterol on inflammatory cytokines and the TGF-β1/Smad2 and IL-17A signaling pathway in an ovalbumin (OVA)-induced asthma mouse model. Stigmasterol treatment improved airway remodeling. In addition, it significantly attenuated the symptoms of asthma attacks, reduced the number of macrophages, lymphocytes, neutrophils, and eosinophils in BALF and inflammatory cytokines, including IL-1β, IL-5, IL-6, and IL-13. It further decreased the level of IL-17A in BALF, serum and spleen. Spleen single-cell suspension analysis via flow cytometry showed that IL-17A level was consistent with the results obtained in BALF, serum and spleen. Stigmasterol decreased the protein expression levels of TGF-β, p-Smad2 and IL-17A in the spleen, by increasing the protein expression level of IL-10. After 24 h of co-culture of TGF-β, IL-6 and stigmasterol, the level of IL-17 in CD4 T cell supernatant was lower relative to levels in the group without stigmasterol. Meanwhile, stigmasterol treatment attenuated the expression level of TGF- β, p-Smad2 and IL-17A proteins in CD4 T cells and enhanced the expression levels of IL-10 protein. These data suggested that stigmasterol inhibited the TGF-β1/Smad2 and IL-17A signaling pathway to achieve anti-asthmatic effects in the OVA-induced asthma mouse model. Collectively, the results of this study are that stigmasterol has achieved preliminary efficacy in the non-clinical laboratory, further studies are needed to consider the clinical application of stigmasterol.