High von Willebrand factor levels increase the risk of stroke: the Rotterdam study

Von Willebrand factor contribution to pathophysiology outside of von Willebrand disease

VWF is a procoagulant protein that plays a central role in the initiation of platelets aggregate formation and thrombosis. While von Willebrand disease has long been known to result from qualitative and quantitative deficiencies of VWF, it is recently that contribution of elevated levels of VWF to various pathological conditions including thrombosis, inflammation, angiogenesis, and cancer metastasis has been appreciated. Here, we discuss contribution of elevated levels of VWF to various thrombotic and nonthrombotic pathological conditions.

Tuning the endothelial response: differential release of exocytic cargos from Weibel-Palade bodies

Essentials Endothelial activation initiates multiple processes, including hemostasis and inflammation. The molecules that contribute to these processes are co-stored in secretory granules. How can the cells control release of granule content to allow differentiated responses? Selected agonists recruit an exocytosis-linked actin ring to boost release of a subset of cargo.

SUMMARY

Background Endothelial cells harbor specialized storage organelles, Weibel-Palade bodies (WPBs). Exocytosis of WPB content into the vascular lumen initiates primary hemostasis, mediated by von Willebrand factor (VWF), and inflammation, mediated by several proteins including P-selectin. During full fusion, secretion of this large hemostatic protein and smaller pro-inflammatory proteins are thought to be inextricably linked. Objective To determine if secretagogue-dependent differential release of WPB cargo occurs, and whether this is mediated by the formation of an actomyosin ring during exocytosis. Methods We used VWF string analysis, leukocyte rolling assays, ELISA, spinning disk confocal microscopy, high-throughput confocal microscopy and inhibitor and siRNA treatments to demonstrate the existence of cellular machinery that allows differential release of WPB cargo proteins. Results Inhibition of the actomyosin ring differentially effects two processes regulated by WPB exocytosis; it perturbs VWF string formation but has no effect on leukocyte rolling. The efficiency of ring recruitment correlates with VWF release; the ratio of release of VWF to small cargoes decreases when ring recruitment is inhibited. The recruitment of the actin ring is time dependent (fusion events occurring directly after stimulation are less likely to initiate hemostasis than later events) and is activated by protein kinase C (PKC) isoforms. Conclusions Secretagogues differentially recruit the actomyosin ring, thus demonstrating one mechanism by which the prothrombotic effect of endothelial activation can be modulated. This potentially limits thrombosis whilst permitting a normal inflammatory response. These results have implications for the assessment of WPB fusion, cargo-content release and the treatment of patients with von Willebrand disease.

Ischemic stroke across sexes: What is the status quo?

Stroke prevalence is expected to increase in the next decades due to the aging of the Western population. Ischemic stroke (IS) shows an age- and sex-dependent distribution in which men represent the most affected population within 65 years of age, being passed by post-menopausal women in older age groups. Furthermore, a sexual dimorphism concerning risk factors, presentation and treatment of IS has been widely recognized. In order to address these phenomena, a number of issue have been raised involving both socio-economical and biological factors. The latter can be either dependent on sex hormones or due to intrinsic factors. Although women have poorer outcomes and are more likely to die after a cerebrovascular event, they are still underrepresented in clinical trials and this is mirrored by the lack of sex-tailored therapies. A greater effort is needed in the future to ensure improved treatment and quality of life to both sexes.

Targeting von Willebrand Factor in Ischaemic Stroke: Focus on Clinical Evidence

Despite great efforts in stroke research, disability and recurrence rates in ischaemic stroke remain unacceptably high. To address this issue, one potential target for novel therapeutics is the glycoprotein von Willebrand factor (vWF), which increases in thrombogenicity especially under high shear rates as it bridges between vascular sub-endothelial collagen and platelets. The rationale for vWF as a potential target in stroke comes from four bodies of evidence. (1) Animal models which recapitulate the pathogenesis of stroke and validate the concept of targeting vWF for stroke prevention and the use of the vWF cleavage enzyme ADAMTS13 in acute stroke treatment. (2) Extensive epidemiologic data establishing the prognostic role of vWF in the clinical setting showing that high vWF levels are associated with an increased risk of first stroke, stroke recurrence or stroke-associated mortality. As such, vWF levels may be a suitable marker for further risk stratification to potentially fine-tune current risk prediction models which are mainly based on clinical and imaging data. (3) Genetic studies showing an association between vWF levels and stroke risk on genomic levels. Finally, (4) studies of patients with primary disorders of excess or deficiency of function in the vWF axis (e.g. thrombotic thrombocytopenic purpura and von Willebrand disease, respectively) which demonstrate the crucial role of vWF in atherothrombosis. Therapeutic inhibition of VWF by novel agents appears particularly promising for secondary prevention of stroke recurrence in specific sub-groups of patients such as those suffering from large artery atherosclerosis, as designated according to the TOAST classification.

Ischemic stroke across sexes: what is the status quo?

Stroke prevalence is expected to increase in the next decades due to the aging of the Western population. Ischemic stroke (IS) shows an age- and sex-dependent distribution in which men represent the most affected population within 65 years of age, being passed by post-menopausal women in older age groups. Furthermore, a sexual dimorphism concerning risk factors, presentation and treatment of IS has been widely recognized. In order to address these phenomena, a number of issue have been raised involving both socio-economical and biological factors. The latter can be either dependent on sex hormones or due to intrinsic factors. Although women have poorer outcomes and are more likely to die after a cerebrovascular event, they are still underrepresented in clinical trials and this is mirrored by the lack of sex-tailored therapies. A greater effort is needed in the future to ensure improved treatment and quality of life to both sexes.

Von Willebrand factor and ADAMTS13 activity in relation to risk of dementia: a population-based study

Low ADAMTS13 activity is associated with an increased risk of cardiovascular disease, which is generally attributed to its proteolytic effects on Von Willebrand factor (VWF). Cardiovascular health is an important determinant of cognitive decline, but the association of either VWF or ADAMTS13 with risk of dementia is unknown. Between 1997–2002, we measured VWF antigen and ADAMTS13 activity in 6055 participants of the population-based Rotterdam Study (mean age 69.3 years, 57.2% women). At baseline, 85 participants had dementia, and during 15 years of follow-up 821 developed dementia. Higher VWF was associated with prevalence and risk of dementia, unaffected by concurrent ADAMTS13 activity, but estimates strongly attenuated over time and were no longer statistically significant at 4 years of follow-up (relative risks [95% CI] per standard deviation increase– cross-sectional: 1.37 [1.06–1.77], and longitudinal: 1.05 [0.97–1.14]). In contrast, low ADAMTS13 was associated with increased risk of dementia throughout follow-up (hazard ratio per SD decrease– 1.16 [1.06–1.28]), which alike for ischaemic stroke, was modified by the presence of diabetes (P-interaction = 0.003). In conclusion, higher VWF and low ADAMTS13 activity are associated with increased risk of dementia, but differences in time-course and lack of synergistic effects may indicate in part independent underlying mechanisms.

Verification of a proteomic biomarker panel to diagnose minor stroke and transient ischaemic attack: phase 1 of SpecTRA, a large scale translational study

OBJECTIVE

To derive a plasma biomarker protein panel from a list of 141 candidate proteins which can differentiate transient ischaemic attack (TIA)/minor stroke from non-cerebrovascular (mimic) conditions in emergency department (ED) settings.

DESIGN

Prospective clinical study (#NCT03050099) with up to three timed blood draws no more than 36 h following symptom onset. Plasma samples analysed by multiple reaction monitoring-mass spectrometry (MRM-MS).

PARTICIPANTS

Totally 545 participants suspected of TIA enrolled in the EDs of two urban medical centres.

OUTCOMES

90-day, neurologist-adjudicated diagnosis of TIA informed by clinical and radiological investigations.

RESULTS

The final protein panel consists of 16 proteins whose patterns show differential abundance between TIA and mimic patients. Nine of the proteins were significant univariate predictors of TIA [odds ratio (95% confidence interval)]: L-selectin [0.726 (0.596-0.883)]; Insulin-like growth factor-binding protein 3 [0.727 (0.594-0.889)]; Coagulation factor X [0.740 (0.603-0.908)]; Serum paraoxonase/lactonase 3 [0.763 (0.630-0.924)]; Thrombospondin-1 [1.313 (1.081-1.595)]; Hyaluronan-binding protein 2 [0.776 (0.637-0.945)]; Heparin cofactor 2 [0.775 (0.634-0.947)]; Apolipoprotein B-100 [1.249 (1.037-1.503)]; and von Willebrand factor [1.256 (1.034-1.527)]. The scientific plausibility of the panel proteins is discussed.

CONCLUSIONS

Our panel has the potential to assist ED physicians in distinguishing TIA from mimic patients.

Discovery and Longitudinal Evaluation of Candidate Biomarkers for Ischaemic Stroke by Mass Spectrometry-Based Proteomics

Application of acute therapies such as thrombolysis for ischaemic stroke (IS) is constrained because of diagnostic uncertainty and the dynamic nature of stroke biology. To investigate changes in blood proteins after stroke and as a result of thrombolysis treatment we performed label-free quantitative proteomics on serum samples using high-resolution mass spectrometry and long high-performance liquid chromatography gradient (5 hours) combined with a 50-cm column to optimise the peptide separation. We identified (false discovery rate [FDR]: 1%) and quantified a total of 574 protein groups from a total of 92 samples from 30 patients. Ten patients were treated by thrombolysis as part of a randomised placebo-controlled trial and up to 5 samples were collected from each individual at different time points after stroke. We identified 26 proteins differently expressed by treatment group (FDR: 5%) and significant changes of expression over time for 23 proteins (FDR: 10%). Molecules such as fibrinogen and C-reactive protein showed expression profiles with a high-potential clinical utility in the acute stroke setting. Protein expression profiles vary acutely in the blood after stroke and have the potential to allow the construction of a stroke clock and to have an impact on IS treatment decision making.

Fibrin Clot Architecture in Acute Ischemic Stroke Treated With Mechanical Thrombectomy With Stent-Retrievers - Cohort Study

BACKGROUND

The composition of intra-arterial clots might influence the efficacy of mechanical thrombectomy (MT) in ischemic stroke (IS) due to the acute occlusions within large cerebral arteries. The aims were to assess the factors associated with blood clot structure and the impact of thromboembolus structure on MT using stent-retrievers in patients with acute large artery IS in the anterior circulation.Methods and Results:In an observational cohort study, we studied the components of intra-arterial clots retrieved from large cerebral arteries in 80 patients with acute IS treated with MT with or without i.v. thrombolysis (IVT). Histology of the clots was carried out without knowledge of the clinical findings, including the treatment methods. The components of the clots, their age, origin and semi-quantitative graded changes in the architecture of the fibrin components (e.g., "thinning") were compared via neuro-interventional, clinical and laboratory data. The most prominent changes in the architecture of the fibrin components in the thromboemboli were associated with IVT (applied in 44 patients; OR, 3.50; 95% CI: 1.21-10.10, P=0.02) and platelet count (OR, 2.94; 95% CI: 1.06-8.12, P=0.04).

CONCLUSIONS

In patients with large artery IS treated with the MT using stent-retrievers, bridging therapy with IVT preceding MT and higher platelet count were associated with significant changes of the histological structure of blood clots.

Carotid Plaque Morphology and Ischemic Vascular Brain Disease on MRI

BACKGROUND AND PURPOSE

Vulnerable carotid plaque components are reported to increase the risk of cerebrovascular events. Yet, the relation between plaque composition and subclinical ischemic brain disease is not known. We studied, in the general population, the association between carotid atherosclerotic plaque characteristics and ischemic brain disease on MR imaging.

MATERIALS AND METHODS

From the population-based Rotterdam Study, 951 participants underwent both carotid MR imaging and brain MR imaging. The presence of intraplaque hemorrhage, lipid core, and calcification and measures of plaque size was assessed in both carotid arteries. The presence of plaque characteristics in relation to lacunar and cortical infarcts and white matter lesion volume was investigated and adjusted for cardiovascular risk factors. Stratified analyses were conducted to explore effect modification by sex. Additional analyses were conducted per carotid artery in relation to vascular brain disease in the ipsilateral hemisphere.

RESULTS

Carotid intraplaque hemorrhage was significantly associated with the presence of cortical infarcts (OR, 1.9; 95% confidence interval, 1.1-3.3). None of the plaque characteristics were related to the presence of lacunar infarcts. Calcification was the only characteristic that was associated with higher white matter lesion volume. There was no significant interaction by sex.

CONCLUSIONS

The presence of carotid intraplaque hemorrhage on MR imaging is independently associated with MR imaging-defined cortical infarcts, but not with lacunar infarcts. Plaque calcification, but not vulnerable plaque components, is related to white matter lesion volume.

Von Willebrand Factor: Multimeric Structure and Functional Activity in Patients With Atrial Fibrillation With and Without Oral Anticoagulation

von Willebrand factor (vWF) is a multimeric glycoprotein present in blood plasma. It is synthesized in megakaryocytes and endothelial cells, secreted into circulation in the form of high-molecular-weight multimers (HMWMs), and cleaved into shorter, less active multimers by ADAMTS13. It is essential for platelet adhesion and aggregation. Previous studies have investigated the relationship between vWF levels and thromboembolic events with little regard to vWF multimeric structure. Patients with atrial fibrillation (AF) exhibit higher plasma vWF and lower ADAMTS13 levels. One hundred seven patients with AF, 51 anticoagulated and 56 nonanticoagulated, were eligible for the study. Plasma samples were analyzed for vWF antigen, vWF activity, and ADAMTS13; vWF multimers were analyzed by Western blot in 1% to 1.3% sodium dodecyl sulfate agarose gel electrophoresis. Patients with AF without oral anticoagulation (OAC) had significantly higher vWF plasma levels (154.00 [75-201] UI/dL) and vWF activity (60.00% [20%-210%]) compared to patients with OAC (133.50 [90-192] UI/dL, P = <.001; 50.00% [20%-160%], P = .02). Both were specially decreased in patients treated with acenocumarin. Patients without OAC also showed lower ADAMTS13 levels and presence of vWF HMWMs. Patients with AF show higher plasma levels and vWF activity. Moreover, treatment with traditional OAC (acenocumarin) significantly reduced vWF levels. Patients without OAC might have an increased risk of thrombotic events showing lower ADAMTS13 and higher vWF levels. Patients with stroke had higher plasma levels, vWF activity, and HMWMs. Our study suggests that increased vWF levels and presence of HMWMs could be related to cerebrovascular disease and may represent useful biomarkers for stroke in AF.

vWF correlates with visceral and pericardial adipose tissue in patients with a recent stroke of suspected cardiogenic etiology

Aims

A chronically elevated level of von Willebrand factor (vWF) is a common finding in patients with cardiovascular diseases. Obesity is a well-recognized risk factor for thrombotic cardiovascular complications including ischemic stroke, and it has been linked with increased plasma vWF. We evaluated whether elevated plasma levels of vWF associate with areas of visceral (VAT), pericardial (PAT), and subcutaneous adipose tissue (SAT) compartments in patients with acute/subacute stroke.

Methods and results

A total of 69 patients with stroke of suspected cardiogenic etiology were examined. The plasma level of vWF antigen (vWF-ag) was measured both in the acute phase and in the chronic phase three months after stroke. The areas of VAT and/or PAT were assessed with computed tomography. As expected, in stroke patients, the levels of plasma vWF-ag were significantly higher than in the national reference population both in the acute and in the chronic phase. The level of vWF-ag in the chronic phase correlated with the amounts of VAT and PAT, but not with subcutaneous adipose tissue.

Conclusions

These results agree with previous observations of the chronic inflammation/prothrombotic tendency in patients with cerebrovascular disease. Future studies should seek to clarify the role of visceral type adipose tissue in the pathophysiology of ischemic stroke.

Gut microbiota regulate hepatic von Willebrand factor synthesis and arterial thrombus formation via Toll-like receptor-2

The symbiotic gut microbiota play pivotal roles in host physiology and the development of cardiovascular diseases, but the microbiota-triggered pattern recognition signaling mechanisms that impact thrombosis are poorly defined. In this article, we show that germ-free (GF) and Toll-like receptor-2 (Tlr2)-deficient mice have reduced thrombus growth after carotid artery injury relative to conventionally raised controls. GF Tlr2^-/- and wild-type (WT) mice were indistinguishable, but colonization with microbiota restored a significant difference in thrombus growth between the genotypes. We identify reduced plasma levels of von Willebrand factor (VWF) and reduced VWF synthesis, specifically in hepatic endothelial cells, as a critical factor that is regulated by gut microbiota and determines thrombus growth in Tlr2^-/- mice. Static platelet aggregate formation on extracellular matrix was similarly reduced in GF WT, Tlr2^-/- , and heterozygous Vwf^+/- mice that are all characterized by a modest reduction in plasma VWF levels. Defective platelet matrix interaction can be restored by exposure to WT plasma or to purified VWF depending on the VWF integrin binding site. Moreover, administration of VWF rescues defective thrombus growth in Tlr2^-/- mice in vivo. These experiments delineate an unexpected pathway in which microbiota-triggered TLR2 signaling alters the synthesis of proadhesive VWF by the liver endothelium and favors platelet integrin-dependent thrombus growth.

The Role of von Willebrand Factor in Vascular Inflammation: From Pathogenesis to Targeted Therapy

Beyond its role in hemostasis, von Willebrand factor (VWF) is an emerging mediator of vascular inflammation. Recent studies highlight the involvement of VWF and its regulator, ADAMTS13, in mechanisms that underlie vascular inflammation and immunothrombosis, like leukocyte rolling, adhesion, and extravasation; vascular permeability; ischemia/reperfusion injury; complements activation; and NETosis. The VWF/ADAMTS13 axis is implicated in the pathogenesis of atherosclerosis, promoting plaque formation and inflammation through macrophage and neutrophil recruitment in inflamed lesions. Moreover, VWF and ADAMTS13 have been recently proposed as prognostic biomarkers in cardiovascular, metabolic, and inflammatory diseases, such as diabetes, stroke, myocardial infarction, and sepsis. All these features make VWF an attractive therapeutic target in thromboinflammation. Several lines of research have recently investigated “tailor-made” inhibitors of VWF. Results from animal models and clinical studies support the potent anti-inflammatory and antithrombotic effect of VWF antagonism, providing reassuring data on its safety profile. This review describes the role of VWF in vascular inflammation “from bench to bedside” and provides an updated overview of the drugs that can directly interfere with the VWF/ADAMTS13 axis.

Clinical role of von Willebrand factor in acute ischemic stroke

BACKGROUND

An elevated level of von Willebrand factor (VWF) is associated with an increased risk for coronary heart disease and ischemic stroke. The objective of the study was to determine whether the level of VWF is associated with the cardioembolic subtype of ischemic stroke, stroke severity, and clinical outcome.

PATIENTS AND METHODS

In this study 108 patients suffering from acute ischemic stroke (AIS) were included. According to the etiology of the stroke, patients were classified into the subtype of cardioembolic (CE) stroke and the group with non-CE stroke. Patients with non-CE stroke were further classified into subtype of large vessel disease, subtype of small vessel disease and subtype of cryptogenic stroke. Laboratory tests were performed in the acute phase and VWF was determined for all patients. The National Institutes of Health Stroke Scale (NIHSS) was applied on admission and the modified Rankin scale (MRS) at discharge.

RESULTS

The only significant factor which predicted CE stroke was age (B = 0.077; standard error, SE = 0.026; P = 0.003). The level of VWF was not significantly higher in the group with the cardioembolic stroke compared to the group with non-CE stroke. Patients assessed by NIHSS on admission as the most disabled had significantly higher levels of VWF (B = 0.006; SE = 0.003; P = 0.045). Those with higher scores of MRS at discharge also had significantly increased levels of VWF (B = 0.006; SE = 0.003; P = 0.028).

CONCLUSION

Among the patients with ischemic stroke, levels of VWF were not increased in those with CE stroke. High levels of VWF were associated with greater severity of stroke as well as with poor clinical outcome.

Endothelial cell markers from clinician's perspective

Endothelial cell markers are membrane-bound or cytoplasmic molecules expressed by endothelial cells, which help their easier identification and discrimination from other cell types. During vasculogenesis, endothelial cells differentiate from hemangioblasts to form new blood vessels. With the discovery of endothelial progenitor cells (EPC) and their ability to form new blood vessels, the term vasculogenesis is not only reserved for the embryonic development. Possibility of de novo blood vessel formation from EPC is now widely explored in different ischemic conditions, especially in cardiovascular medicine. Numerous clinical trials have tested enhancing tissue vascularization by delivering hematopoietic cells that expressed endothelial markers. This therapeutic approach proved to be challenging and promising, particularly for patients who have exhausted all conventional therapeutic modalities. Angiogenesis, which refers to the formation of new blood vessels from existing vasculature, is indispensable process during tumor progression and metastasis. Blockage of tumor angiogenesis by targeting and inhibiting endothelial cell has emerged as novel safe and efficacious method to control many advanced malignant diseases. Numerous clinical studies are currently testing new antiangiogenic drugs which target and inhibit endothelial cell markers, receptors or molecules which transmit receptor-mediated signals, therefore inhibiting endothelial cell proliferation, migration and vascular tube formation. Many of these drugs are now widely used in clinical settings as first- or second-line chemotherapy in advanced malignant conditions. So far, these therapeutic approaches gave modest, yet encouraging clinical improvements, prolonging survival and improving functional capacity and quality of life for many terminally ill patients. Here we present the most commonly used endothelial cell markers along with their applicability in contemporary clinical practice.

ADAMTS13 activity as a novel risk factor for incident type 2 diabetes mellitus: a population-based cohort study

AIMS/HYPOTHESIS

ADAMTS13 is a protease that breaks down von Willebrand factor (VWF) multimers into smaller, less active particles. VWF has been associated with an increased risk of incident type 2 diabetes mellitus. Here, we determine whether ADAMTS13 activity and VWF antigen are associated with incident diabetes.

METHODS

This study included 5176 participants from the Rotterdam Study, a prospective population-based cohort study. Participants were free of diabetes at baseline and followed up for more than 20 years. Cox proportional hazards models were used to examine the association of ADAMTS13 activity and VWF antigen with incident diabetes.

RESULTS

ADAMTS13 activity was associated with an increased risk of incident diabetes (HR 1.17 [95% CI 1.08, 1.27]) after adjustment for known risk factors and VWF antigen levels. Although ADAMTS13 activity was positively associated with fasting glucose and insulin, the association with incident diabetes did not change when we adjusted for these covariates. ADAMTS13 activity was also associated with incident prediabetes (defined on the basis of both fasting and non-fasting blood glucose) after adjustment for known risk factors (HR 1.11 [95% CI 1.03, 1.19]), while the VWF antigen level was not. VWF antigen was associated with incident diabetes, but this association was attenuated after adjustment for known risk factors.

CONCLUSIONS/INTERPRETATION

ADAMTS13 activity appears to be an independent risk factor for incident prediabetes and type 2 diabetes. As the association between ADAMTS13 and diabetes did not appear to be explained by its cleavage of VWF, ADAMTS13 may have an independent role in the development of diabetes.

Does von Willebrand factor improve the predictive ability of current risk stratification scores in patients with atrial fibrillation?

Von Willebrand factor (vWF) is a biomarker of endothelial dysfunction. We investigated its role on prognosis in anticoagulated atrial fibrillation (AF) patients and determined whether its addition to clinical risk stratification schemes improved event-risk prediction. Consecutive outpatients with non-valvular AF were recruited and rates of thrombotic/cardiovascular events, major bleeding and mortality were recorded. The effect of vWF on prognosis was calculated using a Cox regression model. Improvements in predictive accuracy over current scores were determined by calculating the integrated discrimination improvement (IDI), net reclassification improvement (NRI), comparison of receiver-operator characteristic (ROC) curves and Decision Curve Analysis (DCA). 1215 patients (49% males, age 76 (71–81) years) were included. Follow-up was almost 7 years. Significant associations were found between vWF and cardiovascular events, stroke, mortality and bleeding. Based on IDI and NRI, addition of vWF to CHA₂DS₂-VASc statistically improved its predictive value, but c-indexes were not significantly different. For major bleeding, the addition of vWF to HAS-BLED improved the c-index but not IDI or NRI. DCA showed minimal net benefit. vWF acts as a simple prognostic biomarker in AF and, whilst its addition to current scores statistically improves prediction for some endpoints, absolute changes and impact on clinical decision-making are marginal.

Plasma ADAMTS13 activity and von Willebrand factor antigen and activity in patients with subarachnoid haemorrhage

Increased von Willebrand factor (VWF) and reduced ADAMTS13 activity are associated with arterial thrombosis. This may also be the culprit mechanism implicated in delayed cerebral ischaemia after aneurysmal subarachnoid haemorrhage (SAH). It was our objective to determine plasma VWF and ADAMTS13 in patients with SAH and healthy subjects; and to explore the levels of those markers and outcome after SAH. Forty consecutive patients were enrolled between September 2007 and April 2014 in a pilot study. Plasma samples were collected from SAH patients on post-bleed day (PBD) 0, 1, 3, 5, 7 and 10 and healthy controls. VWF antigen (VWFAg) and VWF activity (VWFAc) were determined by enzyme-linked immunoassay and collagen binding assay, respectively. ADAMTS13 activity was determined by the cleavage of a fluorescent substrate. Univariate descriptive statistics and cluster analyses were performed based on outcomes in the group with SAH only. Mean age of SAH patients was 52.4 years (26-84 years) and 30 (75 %) were women. 12/40 (30 %) had a high Hunt and Hess grade (IV-V) and 25 (62.5 %) were treated with coil embolisation. Plasma VWFAg and VWFAc were significantly higher in SAH patients than those in healthy subjects on each PBD (p<0.0001). Concurrently, plasma ADAMTS13 activity in SAH patients was significantly lower than that in healthy subjects (p<0.0001). Among those with SAH, cluster analysis demonstrated that patients with higher VWFAg and VWFAc and/or lower ADAMTS13 activity might be at risk of increased mortality. In conclusion, the relative deficiency of plasma ADAMTS13 activity in SAH patients may associate with worse outcome.

Biological Variation of Hemostasis Variables in Thrombosis and Bleeding: Consequences for Performance Specifications

BACKGROUND

Levels of hemostasis factors vary between and within individuals as a result of genetic and environmental factors and analytical variation of the assays. The current state of the art for defining analytical precision requirements for analytical testing is based on this between- and within-individual (biological) variation. However, information on biological variation in hemostasis variables is still limited.

The aim of this study was to determine the biological variation of coagulation variables involved in thrombosis and bleeding to provide a recommendation for performance specifications and to assess whether hemostasis assays fulfill the recommendation.

METHODS

We performed a longitudinal study by repeated blood sampling (in total 13 times over a 1-year period) in 40 healthy individuals and measured prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen, antithrombin, factor VIII, factor IX, von Willebrand factor (VWF), protein C, and protein S. We evaluated the effect of the biological variation on parameters of analytical variation and propose required performance specifications.

RESULTS

Biological variation was highly different for various hemostasis variables: the within-subject variation ranged from 2.6% (PT) to 25.6% [VWF collagen binding (CB) activity], the between-subject variation varied from 4.1% (PT) to 31.2% (VWF:ristocetin cofactor acitivity), and the assay variation from 1.3% (PT) to 12.9% (VWF:CB).

CONCLUSIONS

With the reagents and analyzers used in this study, most of the hemostasis tests variables fulfill the current quality criteria for diagnosis and monitoring of routine hemostasis assays.

Von Willebrand Factor, ADAMTS13, and the Risk of Mortality

Objective—

Von Willebrand Factor (VWF) is a plasma protein that plays a major role in platelet adhesion and aggregation. Large VWF multimers are cleaved into smaller, less coagulant forms by the metalloprotease ADAMTS13 (A Disintegrin And Metalloprotease with ThromboSpondin motif repeats 13). Previous studies have shown that high VWF and low ADAMTS13 levels are associated with cardiovascular disease, but whether these factors are associated with mortality is unclear. Our aim is to establish the association between VWF antigen (VWF:Ag) levels, ADAMTS13 activity, and mortality.

Approach and Results—

We included 6130 participants of the Rotterdam study, a population-based cohort study among individuals aged ≥55 years. We determined the association between ADAMTS13 activity, VWF:Ag levels, and all-cause and cardiovascular mortality by Cox proportional hazard regression analysis. During a median follow-up time of 11.3 years and a total of 90 635 person years, 1868 of the 6130 individuals died (30.5%), of whom 442 (23.7%) died because of cardiovascular disease. In individuals with low ADAMTS13 activity, the risk of cardiovascular mortality (hazard ratio, 1.46; 95% confidence interval, 1.09–1.96) was higher than that in individuals with high ADAMTS13 activity. The risk of cardiovascular mortality (hazard ratio, 1.29; 95% confidence interval 0.98–1.70) was higher in individuals with the highest VWF:Ag levels than in those with the lowest levels. In individuals with both low ADAMTS13 activity and high VWF:Ag levels, the risk of cardiovascular mortality was even higher (hazard ratio, 1.73 95% confidence interval, 1.28–2.35).

Conclusions—

In this large prospective cohort study, ADAMTS13 activity and VWF:Ag levels are both associated with an increased risk of all-cause and cardiovascular mortality.

Von Willebrand factor and coagulation factor VIII in Moyamoya disease associated with Graves' disease: A case report

The present study reported the case of a Chinese boy who was diagnosed with Moyamoya disease (MMD) associated with Graves' disease (GD). An overactivation of von Willebrand factor (vWF) and coagulation factor VIII (FVIII) was identified in the plasma of the patient. Thiamazole and metoprolol treatment was thus administrated. After 2 months of treatment, the patient's thyroid function returned to normal and the neurological symptoms improved gradually. At the same time, the activities of vWF and FVIII were depressed. During the 20-month follow-up, information regarding the neurological symptoms, cerebrovascular imaging, thyroid function, thyroid autoantibodies and coagulation parameters was collected. High levels of thyroid autoantibodies persisted throughout the follow-up period, while other coagulation parameters remained in the normal range. In conclusion, considering the vital role of vWF and FVIII in vascular diseases, it is hypothesized that these two factors may serve an important role in the occurrence of GD associated with MMD.

Update on ADAMTS13 and VWF in cardiovascular and hematological disorders

Endothelial cells (EC) respond to injury by releasing numerous factors, including von Willebrand factor (VWF). High circulating levels of unusually large VWF multimers (UL-VWFM) have strong procoagulant activity and facilitate platelet adhesion and aggregation by interacting with platelets after an acute event superimposed on peripheral arterial disease and coronary artery disease. ADAMTS13-a disintegrin-like metalloproteinase with thrombospondin motif type 1 member 13-regulates a key physiological process of coagulation in the circulation by cleaving VWF multimers into small, inactive fragments. Low levels of ADAMTS13 in the blood may play a role in cardiovascular and hematological disorders, and clarifying its role may help improve disease management. The genetic, pharmacological, physiological, and pathological aspects related to ADAMTS13/VWF have been extensively investigated. Here, we provide an update on recent findings of the relationship between ADAMTS13 and hematological/cardiovascular disorders, including thrombotic thrombocytopenic purpura, arterial thrombosis, thrombotic microangiopathy, myocardial infarction, ischemic stroke, heart failure, and hypertension.

Consumption of nattokinase is associated with reduced blood pressure and von Willebrand factor, a cardiovascular risk marker: results from a randomized, double-blind, placebo-controlled, multicenter North American clinical trial

OBJECTIVE

The objective of this study is to evaluate the effects of consumption of nattokinase on hypertension in a North American hypertensive population with associated genetic, dietary, and lifestyle factors. This is in extension of, and contrast to, previous studies on Asian populations.

MATERIALS AND METHODS

A randomized, double-blind, placebo-controlled, parallel-arm clinical study was performed to evaluate nattokinase (NSK-SD), a fermented soy extract nattō from which vitamin K2 has been removed. Based on the results from previous studies on Asian populations, 79 subjects were enrolled upon screening for elevated blood pressure (BP; systolic BP ≥130 or diastolic BP ≥90 mmHg) who consumed placebo or 100 mg nattokinase/d for the 8-week study duration. Blood collections were performed at baseline and 8 weeks for testing plasma renin activity, von Willebrand factor (vWF), and platelet factor-4. Seventy-four people completed the study with good compliance.

RESULTS

Consumption of nattokinase was associated with a reduction in both systolic and diastolic BP. The reduction in systolic BP was seen for both sexes but was more robust in males consuming nattokinase. The average reduction in diastolic BP in the nattokinase group from 87 mmHg to 84 mmHg was statistically significant when compared to that in the group consuming placebo, where the average diastolic BP remained constant at 87 mmHg (P<0.05), and reached a high level of significance for males consuming nattokinase, where the average diastolic BP dropped from 86 mmHg to 81 mmHg (P<0.006). A decrease in vWF was seen in the female population consuming nattokinase (P<0.1). In the subpopulation with low plasma renin activity levels at baseline (<0.29 ng/mL/h), an increase was seen for 66% of the people after 8-week consumption of nattokinase (P<0.1), in contrast to only 8% in the placebo group.

CONCLUSION

The data suggest that nattokinase consumption in a North American population is associated with beneficial changes to BP in a hypertensive population, indicating sex-specific mechanisms of action of nattokinase's effect on vWF and hypertension.

Prevalence and Risk Factors Associated With Hypertension in von Willebrand Disease

BACKGROUND

von Willebrand factor (VWF) is a biomarker for endothelial damage. Increased VWF levels are observed in hypertension (HTN) and disorders of endothelial dysfunction, for example, atherosclerotic heart disease (ASHD) and diabetes. Whether low VWF protects against HTN is unknown.

METHODS

To determine prevalence and risk factors for HTN in patients with von Willebrand disease (VWD), we conducted a cross-sectional analysis of discharge data from the National Inpatient Sample, 2009 to 2011. Group comparisons were performed by Rao-Scott χ² test. Odds of HTN and HTN outcomes in VWD were estimated by weighted multivariable logistic regression.

RESULTS

The prevalence of hypertension in patients with VWD (N = 7556), 37.35%, was significantly lower than that in non-VWD patients (N = 19 918 970), 49.40%, P < .0001. Hypertension risk factors (hyperlipidemia, diabetes, smoking, hepatitis C, and HIV) and HTN outcomes (ASHD, myocardial infarction [MI], ischemic stroke, and renal failure) were less common in patients with VWD than in non-VWD patients, all P ≤ .0001. Patients with VWD were younger, 49.67 versus 57.30 years, Caucasian, 82.23% versus 68.35%, and female, 75.44% versus 59.61%, P < .0001. Patients with HTN were older, 67.55 versus 47.29 years, male, 45.99% versus 34.90%, and had more HTN risk factors and HTN outcomes than those without HTN, all P < .0001, including male and female subgroups, each P < .0001. The unadjusted odds of HTN in patients with VWD (odds ratio [OR] = 0.611, P < .0001) and of HTN outcomes in patients with VWD (ASHD, OR = 0.509; MI, OR = 0.422; ischemic stroke, OR = 0.521; renal failure, OR = 0.420, all P < .0001) became insignificant after adjustment for HTN risk factors plus demographics (age/race/gender), OR = 1.035, P = .260.

CONCLUSION

The risk of HTN is reduced in patients with VWD, but not after adjustment for HTN risk factors plus demographics, as patients with VWD not having HTN are also typically young, Caucasian, and female.

von Willebrand Factor, ADAMTS13 Activity, and Decline in Kidney Function: A Population-Based Cohort Study

BACKGROUND

Altered levels of von Willebrand factor (vWF) and ADAMTS13 can promote thrombosis and disturb blood flow in kidney microcirculations. We investigated the association of serum vWF:ADAMTS13 ratio in relation to decline in kidney function.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

2,479 individuals (mean age, 65.1±5.9 [SD] years; 43% men) from the population-based Rotterdam Study.

PREDICTORS

vWF, ADAMTS13, and vWF:ADAMTS13 ratio.

OUTCOMES & MEASUREMENTS

Annual decline in estimated glomerular filtration rate (eGFR), halving of eGFR, and new-onset eGFR<60mL/min/1.73m² were assessed.

RESULTS

During a median follow-up of 11 (range, 7.81-13.57) years, 500 cases of new-onset eGFR<60mL/min/1.73m² occurred. The population had a mean eGFR decline of 0.96±0.92mL/min/1.73m² per year. Higher vWF:ADAMTS13 ratio was associated with steeper annual decline in eGFR (difference, -0.06 [95% CI, -0.09 to -0.02] mL/min/1.73m² per year) and higher risk for new-onset eGFR<60mL/min/1.73m² (OR, 1.13; 95% CI, 1.01-1.27). Likewise, higher vWF:ADAMTS13 ratio was associated with higher risk for halving of eGFR (OR, 1.40; 95% CI, 1.02-1.93). After adjustment for cardiovascular risk factors and blood group, effect estimates remained the same.

LIMITATIONS

No data available for albuminuria. Participants were classified based on a single measurement of vWF and ADAMTS13.

CONCLUSIONS

In this population-based study, we showed that higher vWF:ADAMTS13 ratio is associated with decline in kidney function, suggesting a role of elevated prothrombotic factors in the development and progression of kidney disease.

The VWF-GPIb axis in ischaemic stroke: lessons from animal models

Stroke is a leading cause of death and long-term disability worldwide. Ischaemic stroke is caused by a blood clot that obstructs cerebral blood flow. Current treatment mainly consists of achieving fast reperfusion, either via pharmacological thrombolysis using tissue plasminogen activator or via endovascular thrombectomy. Unfortunately, reperfusion therapy is only available to a limited group of patients and reperfusion injury can further aggravate brain damage. Hence, there is an urgent need for better understanding of ischaemic stroke pathophysiology in order to develop novel therapeutic strategies. In recent years, the pathophysiological importance of von Willebrand factor (VWF) in ischaemic stroke has become clear from both clinical and experimental studies. In particular, binding of VWF to platelet glycoprotein Ib (GPIb) has become an interesting target for ischaemic stroke therapy. Recent insights show that inhibting the VWF-GPIb interaction could result in a pro-thrombolytic activity improving cerebral reperfusion rates and concurrently reducing cerebral ischaemia/reperfusion damage. This review gives an overview of the experimental evidence that illustrates the crucial role of the VWF-GPIb axis in ischaemic stroke.

Gender Differences of Thromboembolic Events in Atrial Fibrillation

Atrial fibrillation (AF) is the most common clinically relevant arrhythmia and increases the risk of thromboembolism and stroke; however, these risks are not the same for women and men. This review examines the evidence and clinical significance of increased thromboembolic risk in women with AF. The balance of results from over 30 recent studies suggests that female gender is an independent stroke risk factor in AF, and the inclusion of female gender in stroke risk stratification models, such as CHA2DS2-VASc, has improved risk assessment. Reasons for the increased thrombogenicity in women remain incompletely elucidated, but biological factors including increased hypertension, renal dysfunction, and hyperthyroidism in female patients with AF; cardiovascular remodeling; increased hypercoagulability, and estrogen hormone replacement therapy in women have been proposed. More importantly, gender differences exist in medical management of patients with AF, and compared with men, women have been found to have greater thromboembolic risk when not on anticoagulants, but may benefit from greater risk reduction when systemically anticoagulated. In conclusion, increased clinician awareness of these gender differences may help to improve the management of patients with AF.

ADAMTS13-mediated thrombolysis of t-PA-resistant occlusions in ischemic stroke in mice

Rapid vascular recanalization forms the basis for successful treatment of cerebral ischemia. Currently, tissue plasminogen activator (t-PA) is the only approved thrombolytic drug for ischemic stroke. However, t-PA does not always result in efficient thrombus dissolution and subsequent blood vessel recanalization. To better understand thrombus composition, we analyzed thrombi retrieved from ischemic stroke patients and found a distinct presence of von Willebrand factor (VWF) in various samples. Thrombi contained on average 20.3% ± 10.1% VWF, and this was inversely correlated with thrombus red blood cell content. We hypothesized that ADAMTS13 can exert a thrombolytic effect in VWF-containing thrombi in the setting of stroke. To test this, we generated occlusive VWF-rich thrombi in the middle cerebral artery (MCA) of mice. Infusion of t-PA did not dissolve these MCA occlusions. Interestingly, administration of ADAMTS13 5 minutes after occlusion dose-dependently dissolved these t-PA-resistant thrombi resulting in fast restoration of MCA patency and consequently reduced cerebral infarct sizes (P < .005). Delayed ADAMTS13 administration 60 minutes after occlusion was still effective but to a lesser extent (P < .05). These data show for the first time a potent thrombolytic activity of ADAMTS13 in the setting of stroke, which might become useful in treatment of acute ischemic stroke.

Low ADAMTS13 activity is associated with an increased risk of ischemic stroke

ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin motif repeats 13) has antithrombotic properties because it cleaves von Willebrand factor (VWF) in smaller, less active multimers. The aim of our study was to investigate prospectively the association between ADAMTS13 activity and ischemic stroke. We included 5941 individuals ≥55 years without a history of stroke or transient ischemic attack (TIA) of the Rotterdam Study, a population-based cohort study. ADAMTS13 activity was measured at inclusion with the FRETS-VWF73 assay and VWF antigen (VWF:Ag) levels by enzyme-linked immunosorbent assay. We assessed the association among ADAMTS13 activity, VWF:Ag levels, and ischemic stroke by Cox proportional hazard analysis. The added value of ADAMTS13 activity above the traditional risk factors for ischemic stroke risk prediction was examined by the C-statistic and the net reclassification improvement index (NRI). All individuals were followed for incident stroke or TIA. Over a median follow-up time of 10.7 years (56,403 total person-years), 461 participants had a stroke, 306 of which were ischemic. After adjustment for cardiovascular risk factors, individuals with ADAMTS13 activity in the lowest quartile had a higher risk of ischemic stroke (absolute risk, 7.3%) than did those in the reference highest quartile (absolute risk, 3.8%; hazard ratio, 1.65; 95% confidence interval [CI], 1.16-2.32). Adding ADAMTS13 to the model in prediction of ischemic stroke, increased the C-statistic by 0.013 (P = .003) and provided 0.058 (95% CI, -0.002 to 0.119) NRI. Low ADAMTS13 activity is associated with the risk of ischemic stroke and improves the accuracy of risk predictions for ischemic stroke beyond traditional risk factors.

Role of inflammation in atrial fibrillation pathophysiology and management

Atrial fibrillation (AF) is the most common clinically relevant arrhythmia, but the methods available for treating AF and its complications (of which the most important is thrombogenesis), as well as for assessing AF risk and underlying pathophysiology, are largely limited. Emerging evidence suggests a significant role of inflammation in the pathogenesis of AF. That evidence includes elevated serum levels of inflammatory biomarkers in AF subjects, the expression of inflammatory markers in cardiac tissues of AF patients and animal models of AF, and beneficial effects of anti-inflammatory drugs in experimental AF paradigms. Inflammation is suggested to be linked to various pathological processes, such as oxidative stress, apoptosis, and fibrosis, that promote AF substrate formation. Inflammation has also been associated with endothelial dysfunction, platelet activation, and coagulation cascade activation, leading to thrombogenesis. Thus, inflammation may contribute to both the occurrence/maintenance of AF and its thromboembolic complications. Here, we review the evidence for a role of inflammation and inflammatory biomarkers in the risk management and treatment of AF. We also summarize the current knowledge of inflammation-dependent cellular and molecular mechanisms in AF pathophysiology and their potential as therapeutic targets.

Conventional rapid latex agglutination in estimation of von Willebrand factor: method revisited and potential clinical applications

Measurement of von Willebrand factor antigen (VWF : Ag) levels is usually performed in a specialised laboratory which limits its application in routine clinical practice. So far, no commercial rapid test kit is available for VWF : Ag estimation. This paper discusses the technical aspect of latex agglutination method which was established to suit the purpose of estimating von Willebrand factor (VWF) levels in the plasma sample. The latex agglutination test can be performed qualitatively and semiquantitatively. Reproducibility, stability, linearity, limit of detection, interference, and method comparison studies were conducted to evaluate the performance of this test. Semiquantitative latex agglutination test was strongly correlated with the reference immunoturbidimetric assay (Spearman's rho = 0.946, P < 0.001, n = 132). A substantial agreement (κ = 0.77) was found between qualitative latex agglutination test and the reference assay. Using the scoring system for the rapid latex test, no agglutination is with 0% VWF : Ag (control negative), 1+ reaction is equivalent to <20% VWF : Ag, and 4+ reaction indicates >150% VWF : Ag (when comparing with immunoturbidimetric assay). The findings from evaluation studies suggest that latex agglutination method is suitable to be used as a rapid test kit for the estimation of VWF : Ag levels in various clinical conditions associated with high levels and low levels of VWF : Ag.

Is female sex a risk factor for stroke and thromboembolism in patients with atrial fibrillation? A systematic review and meta-analysis

BACKGROUND

Atrial fibrillation (AF) increases the risk of stroke, but this risk is not homogenous. Many risk factors contribute to stroke risk however, the evidence for female sex as a risk factor is less well-established.

AIM

To perform a systematic review and meta-analysis of the available evidence to establish if female sex is a risk factor for stroke/thromboembolism among patients with AF.

METHODS

A systematic literature search was conducted using Medline. The search term 'atrial fibrillation' was used in combination with 'stroke risk', 'thromboembolism', 'female' and 'gender differences' and returned 735 articles, of which 17 were appraised and included. Females with AF were compared with males with AF for the outcome of stroke/thromboembolism.

RESULTS

Seventeen studies, 5 randomized-controlled trials and 12 prospective observational studies were included; 10 demonstrated an increased risk of stroke in women. Meta-analysis of the 17 studies revealed a 1.31-fold (95% confidence intervals (CIs) 1.18-1.46) elevated risk of stroke in women with AF; the risk appearing greatest for women aged ≥75 years. Only three studies compared entirely anticoagulated populations; stroke rates among these patients varied from 1.2-1.44% per-patient year for men and 2.08-2.43% per-patient year for women. Risk of stroke in women appeared similar regardless of oral anticoagulation therapy [risk ratio (95% CI 1.29 (1.09-1.52) and 1.49 (1.17-1.90) in non-anticogulated vs. anticoagulated/mixed cohorts, respectively).

CONCLUSIONS

Women with AF are at increased risk of stroke, particularly elderly women. Comprehensive stroke risk assessment, including sex as a risk factor, should be undertaken in all AF patients.

Von Willebrand factor regulation in patients with acute and chronic cerebrovascular disease: a pilot, case-control study

BACKGROUND AND PURPOSE

In animal models, von Willebrand factor (VWF) is involved in thrombus formation and propagation of ischemic stroke. However, the pathophysiological relevance of this molecule in humans, and its potential use as a biomarker for the risk and severity of ischemic stroke remains unclear. This study had two aims: to identify predictors of altered VWF levels and to examine whether VWF levels differ between acute cerebrovascular events and chronic cerebrovascular disease (CCD).

METHODS

A case-control study was undertaken between 2010 and 2013 at our University clinic. In total, 116 patients with acute ischemic stroke (AIS) or transitory ischemic attack (TIA), 117 patients with CCD, and 104 healthy volunteers (HV) were included. Blood was taken at days 0, 1, and 3 in patients with AIS or TIA, and once in CCD patients and HV. VWF serum levels were measured and correlated with demographic and clinical parameters by multivariate linear regression and ANOVA.

RESULTS

Patients with CCD (158 ± 46%) had significantly higher VWF levels than HV (113 ± 36%, P<0.001), but lower levels than AIS/TIA patients (200 ± 95%, P<0.001). Age, sex, and stroke severity influenced VWF levels (P<0.05).

CONCLUSIONS

VWF levels differed across disease subtypes and patient characteristics. Our study confirms increased VWF levels as a risk factor for cerebrovascular disease and, moreover, suggests that it may represent a potential biomarker for stroke severity, warranting further investigation.

Von Willebrand factor and ADAMTS13 in arterial thrombosis: a systematic review and meta-analysis

Von Willebrand Factor (VWF) plays an important role in hemostasis by mediating platelet adhesion and aggregation. Ultralarge VWF multimers are cleaved by ADAMTS13 in smaller, less procoagulant forms. An association between high VWF levels and cardiovascular disease has frequently been reported, and more recently also an association has been observed between low ADAMTS13 levels and arterial thrombosis. We reviewed the current literature and performed meta-analyses on the relationship between both VWF and ADAMTS13 with arterial thrombosis. Most studies showed an association between high VWF levels and arterial thrombosis. It remains unclear whether ADAMTS13 is a causal independent risk factor because the association between low ADAMTS13 and arterial thrombosis is so far only shown in case-control studies. Prospective studies are awaited. A causal role for ADAMTS13 is supported by mice studies of cerebral infarction where the infusion of recombinant human ADAMTS13 reduced the infarct size.

Stroke and Bleeding Risks in Patients with Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia and is associated with a substantial risk of stroke and mortality. Strokes in patients with AF are associated with a greater disability and poorer outcomes than strokes in patients in sinus rhythm. Patients with AF are at increased risk of bleeding, especially if they use anticoagulant therapy. Recent research in the field of anticoagulation has led to development of new anticoagulants for stroke prevention in addition to antiplatelet agents and warfarin. This review discusses the role of AF as a risk factor for stroke and evaluates the role of various schemes for predicting the risk of stroke and bleeding in patients with AF.

Performance related factors are the main determinants of the von Willebrand factor response to exhaustive physical exercise

Background

Physical stress triggers the endothelium to release von Willebrand Factor (VWF) from the Weibel Palade bodies. Since VWF is a risk factor for arterial thrombosis, it is of great interest to discover determinants of VWF response to physical stress. We aimed to determine the main mediators of the VWF increase by exhaustive physical exercise.

Methods

105 healthy individuals (18–35 years) were included in this study. Each participant performed an incremental exhaustive exercise test on a cycle ergometer. Respiratory gas exchange measurements were obtained while cardiac function was continuously monitored. Blood was collected at baseline and directly after exhaustion. VWF antigen (VWF:Ag) levels, VWF collagen binding (VWF:CB) levels, ADAMTS13 activity and common variations in Syntaxin Binding Protein-5 (STXBP5, rs1039084 and rs9399599), Syntaxin-2 (STX2, rs7978987) and VWF (promoter, rs7965413) were determined.

Results

The median VWF:Ag level at baseline was 0.94 IU/mL [IQR 0.8–1.1] and increased with 47% [IQR 25–73] after exhaustive exercise to a median maximum VWF:Ag of 1.38 IU/mL [IQR 1.1–1.8] (p<0.0001). VWF:CB levels and ADAMTS13 activity both also increased after exhaustive exercise (median increase 43% and 12%, both p<0.0001). The strongest determinants of the VWF:Ag level increase are performance related (p<0.0001). We observed a gender difference in VWF:Ag response to exercise (females 1.2 IU/mL; males 1.7 IU/mL, p = 0.001), which was associated by a difference in performance. Genetic variations in STXBP5, STX2 and the VWF promoter were not associated with VWF:Ag levels at baseline nor with the VWF:Ag increase.

Conclusions

VWF:Ag levels strongly increase upon exhaustive exercise and this increase is strongly determined by physical fitness level and the intensity of the exercise, while there is no clear effect of genetic variation in STXBP5, STX2 and the VWF promoter.

Markers of endothelial dysfunction and cerebral blood flow in older adults

We investigated the association of 2 markers of endothelial dysfunction, tissue plasminogen activator (t-PA) and Von Willebrand factor (VWF), with cerebral blood flow (CBF) in 541 older participants at high risk for cardiovascular disease. Serum levels of t-PA and VWF were measured at baseline. Participants underwent 2 successive brain magnetic resonance imaging scans, first at baseline and the then after a mean follow-up of 33 months. Total CBF was determined in each scan and also standardized for brain parenchymal volume. At baseline, higher t-PA was associated with lower CBF (p = 0.034). In the longitudinal analysis, higher levels of VWF were associated with a steeper decline in CBF (p = 0.043). There was no association between t-PA and decrease in CBF. These associations were independent of sociodemographic and cardiovascular factors. In conclusion, elevated markers of endothelial dysfunction are associated with lower CBF in older adults at risk for cardiovascular disease.

Proteolytic processing of von Willebrand factor by adamts13 and leukocyte proteases

ADAMTS13 is a 190 kDa zinc protease encoded by a gene located on chromosome 9q34. This protease specifically hydrolyzes von Willebrand factor (VWF) multimers, thus causing VWF size reduction. ADAMTS13 belongs to the A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats (ADAMTS) family, involved in proteolytic processing of many matrix proteins. ADAMTS13 consists of numerous domains including a metalloprotease domain, a disintegrin domain, several thrombospondin type 1 (TSP1) repeats, a cysteine-rich domain, a spacer domain and 2 CUB (Complement c1r/c1s, sea Urchin epidermal growth factor, and Bone morphogenetic protein) domains. ADAMTS13 cleaves a single peptide bond (Tyr1605-Met1606) in the central A2 domain of the VWF molecule. This proteolytic cleavage is essential to reduce the size of ultra-large VWF polymers, which, when exposed to high shear stress in the microcirculation, are prone to form with platelets clumps, which cause severe syndromes called thrombotic microangiopathies (TMAs). In this review, we a) discuss the current knowledge of structure-function aspects of ADAMTS13 and its involvement in the pathogenesis of TMAs, b) address the recent findings concerning proteolytic processing of VWF multimers by different proteases, such as the leukocyte-derived serine and metallo-proteases and c) indicate the direction of future investigations.

On the versatility of von Willebrand factor

Von Willebrand factor (VWF) is a large multimeric protein, the function of which has been demonstrated to be pivotal to the haemostatic system. Indeed, quantitative and/or qualitative abnormalities of VWF are associated with the bleeding disorder Von Willebrand disease (VWD). Moreover, increased plasma concentrations of VWF have been linked to an increased risk for thrombotic complications. In the previous decades, many studies have contributed to our understanding of how VWF is connected to the haemostatic system, particularly with regard to structure-function relationships. Interactive sites for important ligands of VWF (such as factor VIII, collagen, glycoprotein Ibα, integrin αIIbβ3 and protease ADAMTS13) have been identified, and mutagenesis studies have confirmed the physiological relevance of the interactions between VWF and these ligands. However, we have also become aware that VWF has a more versatile character than previously thought, given its potential role in various non-hemostatic processes, like intimal thickening, tumor cell apoptosis and inflammatory processes. In the presence review, a summary of our knowledge on VWF structure-function relationships is provided in the context of the “classical” haemostatic task of VWF and in perspective of pathological processes beyond haemostasis.