Psoralen ameliorates sepsis-induced acute lung injury by regulating microbiota-dependent tryptophan metabolism

BACKGROUND: Sepsis frequently leads to acute lung injury (ALI). Despite the documented anti-inflammatory effects of Psoralen (PSO), the exact mechanism by which it confers protection against septic ALI remains poorly understood. PURPOSE: This research explored the protective efficacy and mechanistic aspects of PSO in sepsis-induced ALI. METHODS: Lipopolysaccharide (LPS) was employed to create a murine ALI model. Pathological and inflammatory responses were evaluated. The dependency on gut microbiota was assessed through intestinal flora ablation and fecal microbiota transplantation. The aryl hydrocarbon receptor (AhR) engagement was demonstrated by its agonist FICZ and antagonist CH-223191. RESULTS: In a septic ALI model, PSO ameliorated the histopathological damage and attenuated the inflammatory response. Evidence for this included a lower lung neutrophil percentage and decreased amounts of the proinflammatory mediators tumor necrosis factor-α, interleukin-6, interleukin-1β, as well as MPO-DNA complexes. Additionally, PSO downregulated the abundance of key markers in pulmonary tissue, including peptidylarginine deiminase 4, colony-stimulating factor 2, citrullinated histone H3, and MPO, thereby suppressing neutrophil extracellular trap formation. Furthermore, PSO altered gut microbial diversity, an effect that relied on tryptophan metabolism originating from the gut microbiota. The treatment raised the relative abundance of indole-3-propionic acid (IPA) in serum, which subsequently triggered the AhR/CYP1A1 pathway and thereby alleviated ALI. Moreover, PSO enhanced intestinal tight junction protein expression. Nonetheless, these protective effects were abolished by the AhR inhibitor CH-223191.