Numerous studies have reported significant associations between ABO blood group and risk of cardiovascular disease. These studies have consistently demonstrated that thrombotic risk is significantly ...reduced in individuals in blood group O. Nevertheless, the biological mechanisms through which ABO influences hemostasis have remained poorly understood. Exciting recent data have provided novel insights into how these ABO effects are modulated and have highlighted that ABO group significantly influences platelet plug formation at sites of vascular injury (primary hemostasis). In particular, ABO affects multiple aspects of von Willebrand factor (VWF) biology. In keeping with their reduced thrombotic risk, plasma VWF levels are ∼25% lower in healthy group O compared with healthy group non-O individuals. In addition, blood group O VWF demonstrates enhanced susceptibility to ADAMTS13 proteolysis. Finally, preliminary findings suggest that the interaction of group O VWF with platelets may also be reduced. Although the molecular mechanisms underlying these ABO effects on VWF have not been fully elucidated, it seems likely that they are mediated in large part by the ABO(H) carbohydrate structures that are carried on both the N- and O-linked glycans of VWF. Interestingly, ABO(H) determinants are also expressed on several different platelet surface glycoprotein receptors. Recent studies support the hypothesis that ABO group not only exerts major quantitative and qualitative effects on VWF, but also affect specific aspects of platelet function. Given the severe morbidity and the mortality associated with thrombotic disorders, defining the mechanisms underlying these ABO effects is not only of scientific interest, but also of direct clinical importance.
Background
Persistent symptoms including breathlessness, fatigue, and decreased exercise tolerance have been reported in patients after acute SARS‐CoV‐2 infection. The biological mechanisms ...underlying this “long COVID” syndrome remain unknown. However, autopsy studies have highlighted the key roles played by pulmonary endotheliopathy and microvascular immunothrombosis in acute COVID‐19.
Objectives
To assess whether endothelial cell activation may be sustained in convalescent COVID‐19 patients and contribute to long COVID pathogenesis.
Patients and Methods
Fifty patients were reviewed at a median of 68 days following SARS‐CoV‐2 infection. In addition to clinical workup, acute phase markers, endothelial cell (EC) activation and NETosis parameters and thrombin generation were assessed.
Results
Thrombin generation assays revealed significantly shorter lag times (p < .0001, 95% CI −2.57 to −1.02 min), increased endogenous thrombin potential (p = .04, 95% CI 15–416 nM/min), and peak thrombin (p < .0001, 95% CI 39–93 nM) in convalescent COVID‐19 patients. These prothrombotic changes were independent of ongoing acute phase response or active NETosis. Importantly, EC biomarkers including von Willebrand factor antigen (VWF:Ag), VWF propeptide (VWFpp), and factor VIII were significantly elevated in convalescent COVID‐19 compared with controls (p = .004, 95% CI 0.09–0.57 IU/ml; p = .009, 95% CI 0.06–0.5 IU/ml; p = .04, 95% CI 0.03–0.44 IU/ml, respectively). In addition, plasma soluble thrombomodulin levels were significantly elevated in convalescent COVID‐19 (p = .02, 95% CI 0.01–2.7 ng/ml). Sustained endotheliopathy was more frequent in older, comorbid patients, and those requiring hospitalization. Finally, both plasma VWF:Ag and VWFpp levels correlated inversely with 6‐min walk tests.
Conclusions
Collectively, our findings demonstrate that sustained endotheliopathy is common in convalescent COVID‐19 and raise the intriguing possibility that this may contribute to long COVID pathogenesis.
Summary
Endothelial cell (EC) activation plays a key role in the pathogenesis of pulmonary microvascular occlusion, which is a hallmark of severe coronavirus disease 2019 (COVID‐19). Consistent with ...EC activation, increased plasma von Willebrand factor antigen (VWF:Ag) levels have been reported in COVID‐19. Importantly however, studies in other microangiopathies have shown that plasma VWF propeptide (VWFpp) is a more sensitive and specific measure of acute EC activation. In the present study, we further investigated the nature of EC activation in severe COVID‐19. Markedly increased plasma VWF:Ag median (interquatile range, IQR) 608·8 (531–830)iu/dl and pro‐coagulant factor VIII (FVIII) levels median (IQR) 261·9 (170–315) iu/dl were seen in patients with severe severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) infection. Sequential testing showed that these elevated VWF–FVIII complex levels remained high for up to 3 weeks. Similarly, plasma VWFpp levels were also markedly elevated median (IQR) 324·6 (267–524) iu/dl. Interestingly however, the VWFpp/VWF:Ag ratio was reduced, demonstrating that decreased VWF clearance contributes to the elevated plasma VWF:Ag levels in severe COVID‐19. Importantly, plasma VWFpp levels also correlated with clinical severity indices including the Sequential Organ Failure Assessment (SOFA) score, Sepsis‐Induced Coagulopathy (SIC) score and the ratio of arterial oxygen partial pressure to fractional inspired oxygen (P/F ratio). Collectively, these findings support the hypothesis that sustained fulminant EC activation is occurring in severe COVID‐19, and further suggest that VWFpp may have a role as a biomarker in this setting.
Background
Consistent with fulminant endothelial cell activation, elevated plasma von Willebrand factor (VWF) antigen levels have been reported in patients with COVID‐19. The multimeric size and ...function of VWF are normally regulated through A Disintegrin And Metalloprotease with ThrombSpondin Motif type 1 motif, member 13 (ADAMTS‐13)‐‐mediated proteolysis.
Objectives
This study investigated the hypothesis that ADAMTS‐13 regulation of VWF multimer distribution may be impaired in severe acute respiratory syndrome‐coronavirus‐2 (SARS‐CoV‐2) infection contributing to the observed microvascular thrombosis.
Patients and Methods
Patients with COVID‐19 (n = 23) were recruited from the Beaumont Hospital Intensive Care Unit (ICU) in Dublin. Plasma VWF antigen, multimer distribution, ADAMTS‐13 activity, and known inhibitors thereof were assessed.
Results
We observed markedly increased VWF collagen‐binding activity in patients with severe COVID‐19 compared to controls (median 509.1 versus 94.3 IU/dl). Conversely, plasma ADAMTS‐13 activity was significantly reduced (median 68.2 IU/dl). In keeping with an increase in VWF:ADAMTS‐13 ratio, abnormalities in VWF multimer distribution were common in patients with COVID‐19, with reductions in high molecular weight VWF multimers. Terminal sialylation regulates VWF susceptibility to proteolysis by ADAMTS‐13 and other proteases. We observed that both N‐ and O‐linked sialylation were altered in severe COVID‐19. Furthermore, plasma levels of the ADAMTS‐13 inhibitors interleukin‐6, thrombospondin‐1, and platelet factor 4 were significantly elevated.
Conclusions
These findings support the hypothesis that SARS‐CoV‐2 is associated with profound quantitative and qualitative increases in plasma VWF levels, and a multifactorial down‐regulation in ADAMTS‐13 function. Further studies will be required to determine whether therapeutic interventions to correct ADAMTS‐13‐VWF multimer dysfunction may be useful in COVID‐microvascular thrombosis and angiopathy.
Background
Persistent fatigue, breathlessness, and reduced exercise tolerance have been reported following acute COVID‐19 infection. Although immuno‐thrombosis has been implicated in acute COVID‐19 ...pathogenesis, the biological mechanisms underpinning long COVID remain unknown. We hypothesized that pulmonary microvascular immuno‐thrombosis may be important in this context.
Methods
One hundred fifty COVID‐19 patients were reviewed at St James's Hospital Dublin between May and September 2020 at a median of 80.5 (range 44–155) days after initial diagnosis. These included patients hospitalized during initial illness (n = 69) and others managed entirely as out‐patients (n = 81). Clinical examination, chest x‐ray, and 6‐min walk tests were performed. In addition, a range of coagulation and inflammatory markers were assessed.
Results
Increased D‐dimer levels (>500 ng/ml) were observed in 25.3% patients up to 4 months post‐SARS‐CoV‐2 infection. On univariate analysis, elevated convalescent D‐dimers were more common in COVID‐19 patients who had required hospital admission and in patients aged more than 50 years (p < .001). Interestingly, we observed that 29% (n = 11) of patients with elevated convalescent D‐dimers had been managed exclusively as out‐patients during their illness. In contrast, other coagulation (prothrombin time, activated partial thromboplastin time, fibrinogen, platelet count) and inflammation (C‐reactive protein, interleukin‐6, and sCD25) markers had returned to normal in >90% of convalescent patients.
Conclusions
Elucidating the biological mechanisms responsible for sustained D‐dimer increases may be of relevance in long COVID pathogenesis and has implications for clinical management of these patients.
Prolonged recovery is common after acute SARS-CoV-2 infection; however, the pathophysiological mechanisms underpinning Long COVID syndrome remain unknown. VWF/ADAMTS-13 imbalance, dysregulated ...angiogenesis, and immunothrombosis are hallmarks of acute COVID-19. We hypothesized that VWF/ADAMTS-13 imbalance persists in convalescence together with endothelial cell (EC) activation and angiogenic disturbance. Additionally, we postulate that ongoing immune cell dysfunction may be linked to sustained EC and coagulation activation.
Fifty patients were reviewed at a minimum of 6 weeks following acute COVID-19. ADAMTS-13, Weibel Palade Body (WPB) proteins, and angiogenesis-related proteins were assessed and clinical evaluation and immunophenotyping performed. Comparisons were made with healthy controls (n = 20) and acute COVID-19 patients (n = 36).
ADAMTS-13 levels were reduced (p = 0.009) and the VWF-ADAMTS-13 ratio was increased in convalescence (p = 0.0004). Levels of platelet factor 4 (PF4), a putative protector of VWF, were also elevated (p = 0.0001). A non-significant increase in WPB proteins Angiopoietin-2 (Ang-2) and Osteoprotegerin (OPG) was observed in convalescent patients and WPB markers correlated with EC parameters. Enhanced expression of 21 angiogenesis-related proteins was observed in convalescent COVID-19. Finally, immunophenotyping revealed significantly elevated intermediate monocytes and activated CD4+ and CD8+ T cells in convalescence, which correlated with thrombin generation and endotheliopathy markers, respectively.
Our data provide insights into sustained EC activation, dysregulated angiogenesis, and VWF/ADAMTS-13 axis imbalance in convalescent COVID-19. In keeping with the pivotal role of immunothrombosis in acute COVID-19, our findings support the hypothesis that abnormal T cell and monocyte populations may be important in the context of persistent EC activation and hemostatic dysfunction during convalescence.
Previous studies have shown that loss of terminal sialic acid causes enhanced von Willebrand factor (VWF) clearance through the Ashwell-Morrell receptor (AMR). In this study, we investigated (1) the ...specific importance of N- vs O-linked sialic acid in protecting against VWF clearance and (2) whether additional receptors contribute to the reduced half-life of hyposialylated VWF. α2-3-linked sialic acid accounts for <20% of total sialic acid and is predominantly expressed on VWF O-glycans. Nevertheless, specific digestion with α2-3 neuraminidase (α2-3Neu-VWF) was sufficient to cause markedly enhanced VWF clearance. Interestingly, in vivo clearance experiments in dual VWF−/−/Asgr1−/− mice demonstrated enhanced clearance of α2-3Neu-VWF even in the absence of the AMR. The macrophage galactose-type lectin (MGL) is a C-type lectin that binds to glycoproteins expressing terminal N-acetylgalactosamine or galactose residues. Importantly, the markedly enhanced clearance of hyposialylated VWF in VWF−/−/Asgr1−/− mice was significantly attenuated in the presence of an anti-MGL inhibitory antibody. Furthermore, dose-dependent binding of human VWF to purified recombinant human MGL was confirmed using surface plasmon resonance. Additionally, plasma VWF:Ag levels were significantly elevated in MGL1−/− mice compared with controls. Collectively, these findings identify MGL as a novel macrophage receptor for VWF that significantly contributes to the clearance of both wild-type and hyposialylated VWF.
•VWF sialylation modulates in vivo clearance through Ashwell-Morrell independent pathways.•VWF binding to MGL plays a novel role in facilitating VWF clearance.
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Terminal sialylation determines the plasma half-life of von Willebrand factor (VWF). A role for macrophage galactose lectin (MGL) in regulating hyposialylated VWF clearance has recently been ...proposed. In this study, we showed that MGL influences physiological plasma VWF clearance. MGL inhibition was associated with a significantly extended mean residence time and 3-fold increase in endogenous plasma VWF antigen levels (P<0.05). Using a series of VWF truncations, we further demonstrated that the A1 domain of VWF is predominantly responsible for enabling the MGL interaction. Binding of both full-length and VWF-A1-A2-A3 to MGL was significantly enhanced in the presence of ristocetin (P<0.05), suggesting that the MGL-binding site in A1 is not fully accessible in globular VWF. Additional studies using different VWF glycoforms demonstrated that VWF O-linked glycans, clustered at either end of the A1 domain, play a key role in protecting VWF against MGLmediated clearance. Reduced sialylation has been associated with pathological, increased clearance of VWF in patients with von Willebrand disease. Herein, we demonstrate that specific loss of α2-3 linked sialylation from O-glycans results in markedly increased MGL-binding in vitro, and markedly enhanced MGL-mediated clearance of VWF in vivo. Our data further show that the asialoglycoprotein receptor (ASGPR) does not have a significant role in mediating the increased clearance of VWF following loss of O-sialylation. Conversely however, we observed that loss of N-linked sialylation from VWF drives enhanced circulatory clearance predominantly via the ASGPR. Collectively, our data support the hypothesis that in addition to regulating physiological VWF clearance, the MGL receptor works in tandem with ASGPR to modulate enhanced clearance of aberrantly sialylated VWF in the pathogenesis of von Willebrand disease.
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