Loganin alleviates sepsis-induced acute lung injury by regulating macrophage polarization and inhibiting NLRP3 inflammasome activation

Sepsis is a systemic inflammatory response syndrome resulted from severe infection. Excessive inflammation response plays an important role in sepsis-induced acute lung injury (ALI). Loganin is an iridoid glycoside isolated from Corni fructus and exerts an anti-inflammatory effect in multiple inflammatory diseases; however, the role of loganin in sepsis-induced ALI remains unknown. In the current study, the cecal ligation and puncture (CLP)-induced murine sepsis model was constructed to investigate the anti-inflammatory property of loganin in sepsis-induced ALI. Lipopolysaccharide (LPS)-treated Raw 264.7 cells and primary murine peritoneal macrophages were established to further explore underlying mechanism of loganin. Results showed that intragastrical administration of loganin significantly increased murine survival, reduced the alveolar structure damage and inflammatory cell infiltration. Loganin suppressed the release of the M1 macrophage-associated pro-inflammatory cytokines and induced the activation of M2-type anti-inflammatory cytokines. Besides, loganin dramatically inhibited NLRP3 inflammasome-mediated caspase-1 activation and subsequent IL-1β secretion. Further in vitro studies confirmed that loganin efficiently inhibited M1 macrophage polarization and NLRP3 inflammasome activation by blocking the extra-cellular signal-regulated kinase (ERK) and nuclear factor-kappa B (NF-κB) pathways. Taken together, the anti-inflammatory effect of loganin in sepsis-induced ALI was associated with the ERK and NF-κB pathway-mediated macrophage polarization and NLRP3 inflammasome activation. Our study offers a favorable mechanistic basis to support the therapeutic potential of loganin in anti-inflammatory diseases, such as sepsis-induced ALI.