Background Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening diseases and could occur in severe COVID-19 patients. Re-Du-Ning injection (RDN) is a tradition Chinese medicine preparation which has been clinically used for treatment of respiratory diseases including COVID-19. Purpose To elucidate the potential mechanisms of RDN for the treatment of ALI. Methods Female C57BL/6J mice were used to establish ALI model by intraperitoneal injection 10 mg/kg LPS, and RDN injection was intraperitoneally administered with the dose of 5 and 10 mL/kg. The cytokines were measured by ELISA and qPCR. The data related to NETs were analyzed by ELISA, immunofluorescence, Western blotting and network pharmacological approach. Results RDN robustly alleviated LPS-induced ALI. Meanwhile, RDN downregulated the expression of pro-inflammatory cytokines, such as IL-1β, IL-6 and TNF-α. Specifically, RDN treatment inhibited the formation of neutrophil extracellular traps (NETs) and remarkably suppressed the protein of PAD4. The active compound from RDN decreased the phosphorylation of ERK1/2. Conclusion These findings demonstrate that RDN ameliorates LPS-induced ALI through suppressing MAPK pathway to inhibit the formation of NETs.

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