Saikosaponin D ameliorates sepsis-induced acute lung injury by maintaining alveolar epithelial barrier integrity and inhibiting ferroptosis via Nrf2/HO-1 pathway

Background Saikosaponin D (SSD), a triterpenoid saponin extracted from Bupleurum chinensis, has many pharmacological properties. The goal of our study is to assess the roles and mechanisms of SSD in septic acute lung injury (ALI).Methods ALI in mice was induced by cecal ligation and puncture (CLP). After CLP surgery, mice were intragastrically administered with SSD (4 mg/kg) or vehicle for five consecutive days. Alveolar epithelial barrier function was detected by measuring total protein in BALF and tight junction proteins in lung tissues. Morphological changes of lung tissues were examined by hematoxylin-eosin staining. ROS content in lung tissues was measured by DHE staining. GSH and MDA levels were estimated to evaluate oxidative stress. Western blotting was used to evaluate protein levels. An in vitro model of septic lung injury was established in MLE-12 cells via LPS stimulation. Cytotoxicity, TEER values, and FITC-dextran flux were detected. Intracellular ROS content was evaluated by DCFH-DA staining.Results SSD improved alveolar epithelial barrier function and suppressed ferroptosis in CLP-induced septic mice. SSD activated Nrf2/HO-1 signaling in CLP mice and LPS-exposed MLE-12 cells. ML385 (an Nrf2 inhibitor) attenuated SSD-mediated protective effects against ferroptosis and alveolar epithelial cell barrier dysfunction in vitro.Conclusion SSD ameliorates septic ALI by maintaining alveolar epithelial barrier integrity and suppressing ferroptosis via the activation of Nrf2 signaling.