The Activity of von Willebrand Factor in Hospitalized Patients with COVID‐19

Bray, Monica; Lam, Fong; Yee, Andrew; Rumbaut, Rolando; Cruz, Miguel

Infection with the SARS‐CoV‐2 virus, or COVID‐19, is associated with an increased risk of thrombosis at all levels of the vascular tree including the microvasculature, arteries and veins. However, the mechanisms involved in the heterogenic thrombotic presentations in COVID‐19 are poorly understood. One potential contributor to the prothrombotic state in COVID‐19 is von Willebrand Factor (vWF), a multimeric glycoprotein produced by endothelial cells and platelets that is unfolded and activated by shear stress or artificially with ristocetin. vWF has been implicated in pathogenesis of arterial clots including stroke, consistent with its activation by shear. vWF has also been implicated in thrombotic thrombocytopenic purpura, a subtype of microvascular thrombosis. Elevated vWF has even been associated with increased risk of venous thrombosis, a classically low shear environment. The purpose of this study was to determine whether vWF had a higher propensity to become activated in COVID‐19, suggestive of an altered configuration. We hypothesized that vWF from patients with COVID‐19 would be more active than healthy controls. Discarded whole blood samples were collected from hospitalized patients diagnosed with COVID‐19; blood from healthy donors was collected via venipuncture. Patient and control plasma were rapidly thawed at 37 ℃ then transferred to de‐identified containers to blind performing scientist. Samples were processed in a duplicate manner adding 30 μL of plasma to a solution containing 200 x10(3)/μL lyophilized platelets. We measured vWF activation using two methods: the first involved agglutination with an intermediate concentration of ristocetin (between 0.6 ‐ 0.7 mg/mL) to achieve less than 40% of normal agglutination. The second method involved detection of A1‐12 antibody binding with ELISA. The A1‐12 antibody binds to the N‐terminus of the A1 subunit, a location that is typically obscured by the A2 domain and thus is only accessible with vWF is unfolded. All measured values were compared to normal pooled plasma (NPP) processed in the same experiment. Notably all measures of activation of vWF were significantly higher in COVID‐19 patients compared to healthy controls. The primary slope of the agglutination was the most significantly elevated when compared to controls (162 verses 106 % of NPP, p = 0.002). The absolute amount of vWF was also significantly increased in patients compared to controls (148 verses 100% of NPP, p < 0.001). These preliminary data are suggestive of increased activity of vWF in COVID‐19 infectionin addition to an increased absolute level. vWF may be a significant pathway that becomes dysregulated during the immune response to SARS‐CoV‐2. This study is limited by its use of discarded blood that has undergone one freeze‐thaw cycle. Further work is needed to correlate these results to clinical outcomes.