Circulating Biomarkers of COVID-19-Triggered Endotheliopathy: From Conjecture to Certainty

Background: Clinical and analytical data on patients suffering from coronavirus disease-2019 (COVID-19) indicate that endothelial damage plays a key role in the pathophysiology of the disease and is responsible for the pulmonary complications and the thrombotic microangiopathy affecting multiple organs, which contribute directly to mortality (Ackerman et al. N Engl J Med 2020). Detection of biomarkers of endothelial injury in circulating blood may provide critical diagnostic and prognostic information on the disease course (Goshua et al. Lancet Haematology 2020). Endothelial injury is also a cornerstone of pathobiology in other septic and potentially life-threatening inflammatory syndromes. Objectives: To identify circulating markers of endothelial damage in COVID-19 patients, and compare their levels with those observed in other septic syndromes. Methods: Plasma samples from non-critically ill patients with confirmed COVID-19 pneumonia (positive nasopharyngeal swab and confirmatory radiological chest imaging) requiring admission (n=42) were collected during the first 36h of hospitalization. Endothelial damage was evaluated by measuring in plasma: i) markers of endothelial function and activation (sVCAM-1, VWF, ADAMTS-13 activity, Protein C and α2-antiplasmin as a marker of fibrinolysis); ii) heparan sulfate (HS) levels, as indicators of endothelial glycocalyx degradation and loss of endothelial barrier function; and iii) C5b9 deposits on endothelial cells in culture, and soluble C5b9 (sC5b9) levels, to measure complement activation. Circulating dsDNA was analyzed as an indicator of the presence of neutrophil extracellular traps (NETs). ELISA tests were used for sVCAM-1, Protein C, HS, and sC5b9 levels. ADAMTS-13 activity was evaluated by FRETS. VWF, Protein C, and α2-antiplasmin were measured at the Atellica COAG 360 (Siemens Healthineers). C5b9 deposits were assessed by immunofluorescence and dsDNA levels by Quant-iT PicoGreen assay kit. Results were compared with those obtained in healthy donors (controls, n=45), and patients with non-infectious systemic inflammatory response syndrome (NI-SIRS, n=8) and septic shock (SS, n=8). Results: Levels of sVCAM-1 were significantly higher in COVID-19 patients vs. controls, NI-SIRS and SS (159±12 vs. 79±4, 57±8 and 80±10 ng/mL, respectively, p