Harpagide alleviates sepsis-induced acute respiratory distress syndrome via gut microbiota modulation

Sepsis-associated acute respiratory distress syndrome (ARDS) remains a leading cause of mortality in critically ill patients, with limited therapeutic options beyond supportive care. The gut-lung axis is critical in sepsis pathogenesis, yet effective targeting strategies remain scarce. Harpagide (HPG), an iridoid glycoside from Scrophularia ningpoensis, exhibits anti-inflammatory properties, but whether it protects against sepsis-induced ARDS through gut microbiota modulation remains unexplored.

Sepsis-induced ARDS was established using the cecal ligation and puncture (CLP) model. Gut microbiota dependency was assessed via antibiotic depletion (ABX) and fecal microbiota transplantation (FMT). Ffar2^-/- mice were used to verify receptor necessity. Microbial composition and SCFAs were analyzed by 16S rRNA sequencing and GC-MS. Lung signaling was assessed by RNA-seq, Western blot, and RT-qPCR. Plasma SCFAs were quantified in sepsis-induced ARDS patients (n = 12) and healthy controls (n = 12) by LC-MS/MS.

HPG significantly improved survival, attenuated lung injury, and suppressed cytokine storm in septic mice. These effects were abolished by ABX but transferable via FMT, confirming microbiota dependency. HPG enriched acetate-producing taxa, elevating fecal and plasma acetate. Transcriptomic analysis revealed simultaneous suppression of NF-κB signaling and excessive IFN-γ/STAT1 activation. HPG-mediated protection was completely abrogated in Ffar2^-/- mice, and exogenous sodium acetate recapitulated these effects in a Ffar2-dependent manner. Clinically, plasma acetate was significantly depleted in ARDS patients and correlated with disease severity.

HPG alleviates sepsis-induced ARDS by reshaping gut microbiota to boost acetate production, which activates FFAR2 to orchestrate immune reprogramming via NF-κB and IFN-γ/STAT1 pathways, offering a novel microbial-metabolic therapeutic strategy.