Bilirubin reduces mortality in sepsis models by inhibiting NOX2-mediated formation of neutrophil extracellular traps.

Abstract

OBJECTIVES: Sepsis is a life-threatening condition driven by a dysregulated immune response to infection, yet therapeutic options beyond antibiotics and vasopressors remain limited. Neutrophil extracellular traps (NETs) contribute significantly to sepsis-induced tissue injury, and NETosis inhibition has emerged as a potential therapeutic strategy. We hypothesized that the endogenous metabolite bilirubin mitigates inflammation in sepsis by inhibiting NETosis through targeting NOX2. METHODS: Two murine sepsis models were used to assess the effects of bilirubin on survival and systemic NETosis. Plasma NET biomarkers were quantified, and primary human neutrophils were used to validate the NETosis-inhibitory activity of bilirubin. Mechanistic studies included ROS measurements, NOX2 loop C mutational analysis, and inhibition of endocytosis and autophagy to examine how bilirubin modulates NOX2 stability. RESULTS: Bilirubin improved survival and reduced NET biomarkers in both models. It inhibited NETosis in human neutrophils by suppressing ROS-dependent NETosis and promoting the internalization and degradation of NOX2 via endocytosis and autophagy. DISCUSSION: These findings identify bilirubin as an endogenous inhibitor of NETosis. By targeting NOX2 and suppressing NETosis, bilirubin may represent a promising therapeutic candidate for sepsis management.