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.

The U-shaped association of serum iron level with disease severity in adult hospitalized patients with COVID-19 (preprint)

Coronavirus disease 2019 (COVID-19) is an emerging infectious disease that leads to severe respiratory failure (RF). It is known that host exposure to viral infection triggers an iron-lowering response to mitigate pathogenic load and tissue damage. However, the association between host iron-lowering response and COVID-19 severity is not clear. This two-center observational study of 136 adult hospitalized COVID-19 patients analyzed the association between disease severity and initial serum iron, total iron-binding capacity (TIBC), and transferrin saturation (TSAT) levels. Serum iron levels were significantly lower in patients with mild RF than in the non-RF group; however, there were no significant differences in iron levels between the non-RF and severe RF groups, depicting a U-shaped association between serum iron levels and disease severity. TIBC levels decreased significantly with increasing severity; consequently, TSAT was significantly higher in patients with severe RF than in other patients. Multivariate analysis including only patients with RF adjusted for age and sex demonstrated that higher serum iron and TSAT levels were independently associated with the development of severe RF, indicating that inadequate response to lower serum iron might be an exacerbating factor for COVID-19.

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.