Astragaloside IV alleviates lung inflammation in Klebsiella pneumonia rats by suppressing TGF-β1/Smad pathway

Astragaloside IV is a biologically active substance derived from the traditional Chinese medicine Astragalus mambranaceus Bunge, and has antioxidant, anti-inflammatory, and anti-apoptotic properties. In this study, we aimed to investigate the effects of astragaloside IV on Klebsiella pneumonia rats and the underlying mechanisms. Klebsiella pneumoniae (K. pneumoniae) rats were treated with different dosages of astragaloside IV (5, 10, and 20 mg/kg) by intragastric administration. The levels of pro-inflammatory cytokines interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α in bronchoalveolar lavage fluid (BALF) were determined. Pathological changes of lung tissue were inspected by HE staining. The expression of transforming growth factor (TGF)-β1 in lung tissue was determined with immunohistochemistry, and the expression levels of TGF-β1, p-Smad2/SMAD2, p-Smad3/SMAD3, IκBα/p-IκBα, and p65/p-p65 in lung tissue were determined by western blot. The mechanism was further investigated with TGF-β1 inhibitor SB-431542. Astragaloside IV reduced the elevated levels of pro-inflammatory cytokines caused by K. pneumoniae and improved lung tissue damage in a dose-dependent manner. Astragaloside IV also decreased the expression of TGF-β1/Smad signaling pathway-related proteins and decreased the protein levels of inflammation-related p-IκBα and p65 in lung tissues induced by K. pneumoniae. Additionally, it was found that the effects of 20 mg/kg astragaloside IV were similar to SB-431542, which could improve pulmonary fibrosis induced by K. pneumoniae, decrease the levels of TGF-β1/Smad signaling pathway-related proteins in lung, and reduce inflammation at the same time. Astragaloside IV could alleviate the inflammation of rat pneumonia induced by K. pneumoniae through suppressing the TGF-β1/Smad pathway.