THROMB HAEMOSTASIS

Endothelial dysfunction is central to COVID-19 pathophysiology, contributing to vascular complications and disease progression. However, the mechanisms driving disease evolution and response to endothelial-targeted therapies remain unclear. This study characterizes endothelial activation throughout the course of acute COVID-19 and evaluates the response to potential therapeutic agents.Serum samples from patients admitted due to moderate to severe COVID-19 pneumonia were prospectively collected on three study time points (+1 day, +4 days and +10 days). Human microvascular endothelial cells were cultured in medium supplemented with pooled serum within the same disease stage, with or without defibrotide, apixaban, or tocilizumab. Endothelial activation was assessed by immunofluorescence and quantitative mRNA expression of adhesion molecules, extracellular matrix (ECM) proteins, and innate immunity receptors. ECM reactivity was evaluated using a platelet adhesion assay. Intracellular signaling pathways were analyzed by immunoblotting.One-hundred and two patients were included. Compared to healthy donor plasma, patient plasma induced upregulation of Vascular cell adhesion molecule-1, Toll-like receptor 4, and von Willebrand factor in endothelial cells. This effect decreased over admission days and in response to drugs. Similarly, ECM reactivity was highest at admission and declined as the disease progressed. Vascular-endothelial cadherin was mildly downregulated, but its expression was unaffected by drug treatment in vitro. Defibrotide mitigated COVID-19 serum induced p38MAPK and Erk activation but enhanced Akt phosphorylation.Serum from severe COVID-19 patients induces a proinflammatory and prothrombotic endothelial phenotype, which can be modulated by endothelial-targeted therapies. These findings support the potential clinical value of endothelial-directed treatments.