Neutrophil abundance determines microvascular obstruction in endotoxemia

Background Excessive inflammation is associated with incident and recurrent cardiovascular events. Endotoxin induces stronger systemic inflammation in humans than mice, reflecting granulocyte predominance. We hypothesized that neutrophil abundance and neutrophil extracellular trap (NET) formation determine susceptibility to cardiovascular injury by disrupting extracellular DNA homeostasis. Methods Neutrophil expansion was induced via CSF3 overexpression prior to sublethal lipopolysaccharide (LPS) challenge in mice. Circulating cell-free DNA (cfDNA), systemic nuclease activity, hematologic parameters, and survival were assessed. Serial plasma samples from healthy volunteers (n=13) undergoing controlled endotoxin challenge (2 ng kg⁻¹ LPS) were analyzed for NET markers, elongated cfDNA, and circulating nuclease activity. Statistical analyses were performed using mixed-effects models and Kaplan–Meier survival analysis. Results Neutrophil expansion (38-71% vs 8-18% in controls) converted sublethal LPS exposure into lethal vascular injury, characterized by a marked rise in elongated cfDNA, microvascular DNA-rich occlusions, thrombocytopenia, erythrocyte loss, hypothermia, and 100% mortality within 6 hours (log-rank χ² = 12.4, P < 0.001; HR 23.9, 95% CI 4.1-139.1). In humans, endotoxin induced a coordinated rise in NET markers and elongated cfDNA (peak at 4 hours, P < 0.001) together with suppression of nuclease activity (P < 0.05), consistent with disruption of extracellular DNA homeostasis. Conclusions We show that endotoxemia impairs extracellular DNA clearance in humans and neutrophil expansion overwhelms this system and drives microvascular obstruction in mice. The balance between NET formation and extracellular DNA clearance is a regulator of inflammatory susceptibility. Our data suggests targeting extracellular DNA clearance to prevent cardiovascular injury and sepsis.