Sepsis-induced acute lung injury in young rats is relieved by calycosin through inactivating the HMGB1/MyD88/NF-κB pathway and NLRP3 inflammasome

Sepsis is the primary cause for children's death worldwide. Calycosin (CAL) is an astragalus extract with anti-inflammatory, antioxidant and anti-tumor functions. This study aims to probe the role of CAL in alleviating sepsis-induced acute lung injury (ALI). Cecal ligation and puncture (CLP) was carried out in young rats to induce sepsis model, which were then treated with CAL. The histopathological changes of the lung were observed, and the dry/wet (W/D) weight ratio of the lung was calculated to analyze pulmonary edema. Apoptosis was determined by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay, and the contents of PaO2, PaCO2 and PaO2/FiO2 in the aortic blood of the rats were monitored by blood-gas analysis. In addition, lipopolysaccharide (LPS) was applied to treat Type II alveolar epithelial cells (AEC-II) to establish an in-vitro sepsis model. Cell viability was detected by the (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and apoptosis was examined by flow cytometry. The expression of apoptosis-related proteins Bax, Bcl2 and Caspase3, as well as the HMGB1/MyD88/NF-κB axis and NLRP3 inflammasome were measured by Western Blot. The profiles of inflammatory factors (TNF-α, IL-1β, and MCP-1) and oxidative stress markers (MDA, SOD, and CAT) in rat serum and AEC-II cells were also detected. CLP induced remarkable lung injury in the young rats. The administration of CAL significantly mitigated pathological injuries of rat lung, reduced lung edema and the apoptosis (labeled by TUNEL). In vitro, CAL treatment improved the damage of LPS-treated AEC-II cells. In addition, CAL dampened inflammation and oxidative stress both in vitro and in vivo, repressed the HMGB1/MyD88/NF-κB pathway and NLRP inflammasome activation induced by CLP or LPS. Interestingly, inhibiting HMGB1 (by ethyl pyruvate, EP) enhanced CAL-mediated protective effects against LPS in AEC-II cells. CAL alleviates sepsis-induced ALI in young rats by inhibiting the HMGB1/MyD88/NF-κB pathway and NLRP3 inflammasome activation.