Prognostic value of secretory autophagosomes in patients with acute respiratory distress syndrome

Background Growing evidence supports that extracellular vesicles (EVs) in blood plasma and other body fluids may function as biomarkers for disease. We previously found that secretory autophagosomes (SAPs), a kind of EV, could exacerbate lung injury in mice. However, the clinical value of SAPs in acute respiratory distress syndrome (ARDS), the most severe form of lung injury, remains unknown. Our study investigated the prognostic value of secretory autophagosomes in ARDS. Methods ARDS patients (n = 46) and controls (n = 8) were included in a prospective monocentric study. Bronchoalveolar lavage fluid (BALF) samples were collected from ARDS patients on the first day (Day 1) or the third day (Day 3) of enrollment and were collected from controls on Day 1. Gradient centrifugation was performed to isolate EVs. The size and concentration of EVs were characterized by nanoparticle tracking analysis (NTA). SAPs in EVs were characterized by flow cytometry, transmission electron microscopy, and western blot analysis, and the proportion of SAPs in EVs (PSV) was measured by flow cytometry. The association of SAPs with 28-day mortality was assessed. Results On Days 1 and 3, the proportion of SAPs (SAPs%) in BALF was higher in patients with ARDS than in controls. On Day 3, the SAPs% was significantly higher in nonsurvivors than in survivors. In particular, a high SAPs% was associated with poor overall survival in ARDS patients. Furthermore, the combination of SAPs% and SOFA obtained a higher predictive value of ARDS outcome than PSV or SOFA alone. Conclusion SAPs% in BALF is elevated in patients with ARDS and is associated with the risk of death in ARDS, suggesting that SAPs% may be a novel prognostic biomarker in ARDS.