Mechanical ventilation-induced neutrophil extracellular vesicles as mediators of postoperative pulmonary complications

RATIONALE: Postoperative pulmonary complications (PPC) remain a leading cause of perioperative morbidity and mortality, yet the underlying mechanisms are poorly understood. While alveolar stretch from mechanical ventilation is a known driver of lung inflammation, the role of extracellular vesicles (EVs) is unknown. OBJECTIVES: To characterise the biogenesis of alveolar stretch-induced EVs and determine their role in perioperative alveolar inflammation and PPC development. METHODS: Serial, bilateral bronchoalveolar lavage (BAL) samples were obtained from forty-two patients undergoing esophagectomy and requiring one- and two-lung ventilation. EV subtypes were identified using flow cytometry and correlated with inflammatory mediators and clinical data. Western blotting identified neutrophil-specific inflammatory matrix metalloproteinases (MMP-8/9) within patient-derived BAL neutrophil-EVs (NEV), and their bioactivity was assessed using a primary human alveolar epithelial cell-macrophage coculture. An in vitro alveolar stretch model, comprising epithelial cells and neutrophils, was used to explore mechanisms of NEV biogenesis. MEASUREMENTS AND MAIN RESULTS: Unphysiological one-lung ventilation, but not two-lung ventilation, induced a marked increase in NEVs (4.8-fold), which were associated with alveolar inflammation and a greater incidence of PPCs. BAL NEVs contained abundant MMP-8/9, generating pro-inflammatory responses in vitro, which were reduced by MMP inhibition. In vitro, NEV production was induced by injurious stretch of an epithelial-neutrophil co-culture through an ATP-dependent mechanism. CONCLUSIONS: We identify a novel mechanistic pathway whereby mechanical ventilation induces NEV release, propagating alveolar inflammation via their biologically active cargo, which may be associated with PPCs. This suggests NEVs could become a potential biomarker and therapeutic target for reducing ventilator-induced lung inflammation and PPCs.