Early Alveolar Epithelial Cell Necrosis is a Potential Driver of ARDS with COVID-19 (preprint)

Rationale: Acute respiratory distress syndrome (ARDS) with COVID-19 is aggravated by hyperinflammatory responses even after passing the peak of viral load. However, the underlying mechanisms remain unclear. Objectives : Here, we assess whether alveolar epithelial cell necrosis and subsequent releases of damage associated molecular patterns (DAMPs) at an early disease stage aggravate ARDS with COVID-19 Methods: In patients with COVID-19 with and without ARDS and healthy adults, serum levels of the following were quantified: an epithelial total cell death marker, cytokeratin18-M65; an epithelial apoptosis marker, CK18-M30; HMGB-1; and alveolar epithelial and endothelial injury markers, sRAGE, angiopoietin-2, and surfactant protein-D. Molecular mechanisms of alveolar epithelial cell death and effects of HMGB-1 neutralization on alveolar tissue injury were assessed using a mouse model of COVID-19-induced ARDS. Measurements and main results: The levels of CK18-M65, CK18-M30, and alveolar tissue injury markers were elevated in early stages of ARDS. The median M30/M65 ratio, an epithelial apoptosis indicator, was 31.50% in patients with ARDS, a value significantly lower than that of non-ARDS patients or healthy subjects. Serum levels of HMGB-1, one of DAMPs released from necrotic cells, were also significantly elevated in ARDS versus non-ARDS patients. In a COVID-19-induced ARDS mouse model, alveolar epithelial cell necrosis involved two forms of programmed necrosis, necroptosis and pyroptosis. Finally, neutralization of HMGB-1 attenuated alveolar tissue injury in the mouse model. Conclusions: Necrosis, including necroptosis and pyroptosis, seems to be the primary form of alveolar epithelial cell death, and subsequent release of DAMPs is a potential driver of COVID-19-induced ARDS.

Distinct Time Courses and Pathogenic Contributions of Alveolar Epithelial and Endothelial Injury in Acute Respiratory Distress Syndrome With COVID-19: Evidence From Circulating Biomarkers (preprint)

Background: In severe cases of coronavirus disease (COVID-19), acute respiratory distress syndrome (ARDS) with alveolar tissue injury occurs. However, the time course and specific contributions of alveolar epithelial and endothelial injury to the pathogenesis of COVID-19 ARDS remain unclear.Methods: We evaluated the levels of a circulating alveolar epithelial injury marker (soluble receptor for advanced glycation end-products: sRAGE) and an endothelial injury marker (angiopoietin-2: ANG-2), along with an alveolar permeability indicator (surfactant protein D: SP-D) in 107 serum samples from nine patients with ARDS and eight without ARDS, all with COVID-19, admitted to Yokohama City University Hospital from January to July 2020. We compared the initial levels of these markers between ARDS and non-ARDS patients, and analysed the temporal changes of these markers in ARDS patients. Results: All the initial levels of sRAGE (median: 2680 pg/mL, IQR:1522–5076 vs. median 701 pg/mL, IQR:344–1148.0, p=0.0152), ANG-2 (median: 699 pg/mL, IQR: 410-2501 vs. median: 231 pg/mL, IQR: 64-584, p=0.0464), and SP-D (median: 17542 pg/mL, IQR: 7423-22979 vs. 1771 pg/mL, IQR: 458-204, p=0.0274) were significantly higher in the ARDS patients than in the non-ARDS patients. The peak sRAGE level in the ARDS patients was observed at the very early phase of disease progression (median: day 1, IQR: day 1–3.5). However, the peaks of ANG-2 (median: day 4, IQR: day 2.5–6) and SPD (median: day 5, IQR: day 3–7.5) were observed at a later phase. Moreover, the ANG-2 level was significantly correlated with the arterial oxygenation (p=0.030) and the SPD level (p=0.002), but the sRAGE level was not. Conclusion: Evaluation of circulating markers confirms that COVID-19 ARDS is characterised by severe alveolar tissue injury. Our data indicate that the endothelial injury, which continues for a longer period than the epithelial injury, seems to be the main contributor to alveolar barrier disruption. Targeting the endothelial injury may, thus, be a promising approach to overcome ARDS with COVID-19.

Characteristics of changes in circulating markers of alveolar epithelial and endothelial injury in acute respiratory distress syndrome with COVID-19 (preprint)

The time course and specific contributions of alveolar epithelial and endothelial injury to the pathogenesis of acute respiratory distress syndrome (ARDS) with coronavirus disease (COVID-19) remain unclear. Here, we evaluated the characteristics of circulating markers of alveolar epithelial and endothelial injury in 107 serum samples from nine ARDS patients and eight non-ARDS patients, all with COVID-19. Although both the alveolar epithelial and endothelial injury markers were markedly elevated in the COVID-19 ARDS patients, our data indicate that the endothelial injury, which continues for a longer period than the epithelial injury, seems to be the main contributor to alveolar barrier disruption.