Fibrin clot characteristics and anticoagulant response in a SARS-CoV-2 infected endothelial cell model

ABSTRACT

Background: SARS-CoV-2 infection is associated with risk of thrombosis however not all SARS-CoV-2 positive patients have equal risk of developing thrombi. Evidence of COVID-19 associated coagulation has not been demonstrated in children, whilst adults with a known vasculopathy, have been identified as high-risk. Currently the mechanism through which SARS-Cov-2 infection promotes thrombosis is unknown. Aims: We hypothesise that plasma factors interact with SARS-CoV-2 infected endothelium and play a significant role in this process. Methods: We developed a novel tool for modelling coagulation in vitro . Human Umbilical Vein Endothelial Cells (HUVECs) were infected with SARS-CoV-2;Uninfected cells and cells infected with Influenza A/Singapore/6/86 were used as controls. Wells were incubated with recalcified plasma from healthy children, healthy adults or vasculopathic adults (previous stroke) for 2 h. This experiment was repeated in the presence of anticoagulants Bivalirudin (0.005 μg/μL), Defibrotide (0.02 μg/μL) and therapeutic and prophylactic doses of Low Molecular Weight Heparin (1 U/mL, 0.5 U/mL) and Unfractionated Heparin (0.7 U/mL, 0.4 U/mL). Fibrin clots were studied using scanning electron microscopy and fibrin characteristics were quantified manually using ImageJ software by two blinded reviewers. Results: Fibrin strands from child plasma had the largest thickness (0.32 μm), followed by adult plasma (0.30 μm) and finally vasculopath plasma (0.27 μm). Defibrotide and Bivalirudin had no effect, whilst Low Molecular Weight Heparin and Unfractionated Heparin completely eliminated clot formation at therapeutic and prophylactic doses. Conclusions: We demonstrate that SARS-CoV-2 infection of endothelial cells promotes thrombosis differently in plasma samples from children, adults and vasculopaths. Thinner fibrin strands in vasculopathy suggests formation of clots that are more resistant to lysis. Our results support that children are resistant to COVID-19 associated coagulation, and that adults with vasculopathies are an at-risk population. This novel cell-culture model for visualising coagulation is a valuable step towards incorporating the endothelium into haemostatic research.