High Von Willebrand Factor Levels Research Articles

Plasma levels of active Von Willebrand factor are increased in patients with first ST-segment elevation myocardial infarction: a multicenter and multiethnic study.

Von Willebrand factor (VWF), a key player in hemostasis and thrombosis, is released from endothelial cells during inflammation. Upon release, VWF is processed by ADAMTS13 into an inactive conformation. The aim of our study was to investigate whether plasma levels of active VWF, total VWF, ADAMTS13, osteoprotegerin (OPG) and the ratios between VWF and ADAMTS13 are risk factors for first ST-segment elevation myocardial infarction (STEMI). We assessed 1026 patients with confirmed first STEMI and 652 control subjects from China, Italy and Scotland, within six hours after their cardiovascular event. Median plasma levels of total VWF, active VWF, OPG and ratios VWF/ADAMTS13 were increased, while plasma levels of ADAMTS13 were decreased in patients compared to controls. The odds ratio (OR) of STEMI in patients with high plasma levels of active VWF was 2.3 (interquartile range (IQR): 1.8-2.9), total VWF was 1.8 (1.4-2.3), ADAMTS13 was 0.6 (05-0.8), OPG was 1.6 (1.2-2.0) and high VWF/ADAMTS13 ratios was 1.5 (1.2-2.0). The OR for total VWF, active VWF and ratios VWF/ADAMTS13 remained significant after adjustment for established risk factors, medical treatment, C-reactive protein, total VWF, ADAMTS13 and OPG. When we adjusted for levels of active VWF, the significance of the OR for VWF and ratios VWF/ADAMTS13 disappeared while the OR for active VWF remained significant. We found evidence that plasma levels of active VWF are an independent risk factor for first STEMI in patients from three different ethnic groups. Our findings confirm the presence of VWF abnormalities in patients with STEMI and may be used to develop new therapeutic approaches.

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.

Low paraoxonase 1 arylesterase activity and high von Willebrand factor levels are associated with severe coronary atherosclerosis in patients with non-diabetic stable coronary artery disease.

BackgroundParaoxonase 1 (PON1) activity and von Willebrand factor (VWF) release are associated with lesion initiation in atherosclerosis. Diabetes can complicate coronary artery disease (CAD) due to the production of advanced glycation end products. This study evaluated PON1 activity and VWF levels in non-post-acute coronary syndrome, stable CAD (SCAD) patients without diabetes.Material/MethodsNon-diabetic SCAD patients and patients experiencing acute stress periods were selected (n=130). Forty-seven cases with normal coronary angiography and 50 healthy individuals served as controls. The non-diabetic SCAD group was then stratified into single-vessel lesions, multiple-vessel lesions, and mild or severe luminal stenosis according to the number and the degree of luminal stenoses. Serum PON1 paraoxonase and arylesterase activities, and plasma VWF levels were measured, as well as serum total cholesterol, total triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and apolipoprotein A1. PON1 arylesterase activity was detected with an ordinary chemistry system using a novel phenylacetate derivative.ResultsBoth PON1 paraoxonase and arylesterase were lower in the non-diabetic SCAD group, but VWF levels were higher (versus controls, all P<0.001). PON1 paraoxonase activity (OR=0.991), PON1 arylesterase activity (OR=0.981), and VWF (OR 2.854) influenced SCAD in multiple logistic regression. Decreased PON1 arylesterase activity and increased VWF levels were associated with severe atherosclerosis in non-diabetic SCAD patients. We also observed a slight negative correlation between VWF and PON1 paraoxonase/arylesterase.ConclusionsPON1 and VWF are detectable markers that may predict the severity of stenoses, ideally facilitating a non-diabetic SCAD diagnosis before the sudden onset of life-threatening symptoms.

The Role Of High Von Willebrand Factor and Low ADAMTS13 Levels In The Risk Of Venous Thromboembolism

BackgroundVenous thromboembolism (VTE) is a common multicausal disease in the general population. von Willebrand factor (VWF) has been associated with VTE in epidemiological studies and recently VWF-mediated platelet adhesion has been shown to be critical for deep vein thrombosis (DVT) in mouse models. The large VWF multimers are cleaved by ADAMTS13 into smaller, less active multimers. Because of the key role of ADAMTS13, VWF and factor VIII (FVIII) in hemostasis and their close biological relationship, we aimed at investigating in the same population the effect of these proteins on VTE risk. Materials and MethodsWe included consecutive patients admitted to our anticoagulation clinic with a first objectively confirmed VTE event between January 2007 and July 2011. The study included only patients with DVT of the lower limbs and/or pulmonary embolism aged between 18-70 years, and without medical history of overt malignancy, arterial thrombosis, liver cirrhosis, renal failure on hemodialysis, connective tissue disease and other conditions characterized by chronic inflammation. Blood was collected at least 1 month after stopping anticoagulation and ≥ 6 months after VTE. Controls were recruited from friends or partners of patients, had no personal history of VTE and were matched to patients by gender and age. The other exclusion criteria for controls were the same as for patients, and in both groups pregnant or postpartum women at blood collection were excluded. ADAMTS13 and VWF antigens were determined by commercial ELISA and FVIII activity was measured using FVIII deficient plasma. High VWF (>150%) and FVIII (>150%) were defined by plasma levels of these proteins exceeding the 88th and 94th percentiles of the control group, respectively. To define low ADAMTS13 levels we used the 10th percentile of the controls (≤0.64 μg/ml). Odds ratios (OR) and 95% confidence intervals (CI) were presented adjusted for gender and age and medians with interquartile variation (25th-75th percentiles). Results358 patients with a first objectively confirmed VTE event were admitted to our clinic, of whom 282 did not participate in the study due to the exclusion criteria (n= 249) and loss of follow-up or refusal (n= 33). Therefore, we included 76 patients (53 women, 70%) with a median age of 43 years (33-55 years) and 96 controls (66 women, 69%), with a median age of 42 years (31-52 years). In controls, there was a negative albeit weak correlation between ADAMTS13 levels and VWF (rs= -0.213 by Spearman coefficient, p= 0.037) and FVIII (rs= -0.251, p= 0.014). As expected, VTE was associated with high levels of VWF (OR 2.80, 95% CI 1.20-6.54) and FVIII (OR 3.02, 95% CI 1.08-8.43). Low ADAMTS13 levels were detected in 12 patients and 9 controls (OR 1.76, 95% CI 0.70-4.46). The population was dichotomized according to the 88th percentile of VWF of the controls. Median ADAMTS13 was lower in the group with VWF >p88 compared to the group with VWF ≤p88 in controls (0.80μg/ml, 0.63-0.94μg/ml vs. 0.98μg/ml, 0.81-1.23μg/ml, p= 0.051) and in patients (0.75μg/ml, 0.53-0.95μg/ml vs. 0.95μg/ml, 0.81-1.14μg/ml, p= 0.001). Next the population was categorized into subjects with VWF ≤p88 and ADAMTS13 >p10 (reference category: 52 patients, 79 controls), VWF ≤p88 and ADAMTS13 ≤p10 (4 patients, 6 controls), VWF >p88 and ADAMTS13 >p10 (12 patients, 8 controls) and VWF >p88 and ADAMTS13 ≤p10 (8 patients, 3 controls). The combination of high VWF and low ADAMTS13 increased VTE risk when compared to the reference category (OR 4.14; 95% CI 1.03-16.71). The risk did not substantially change with adjustment for acute phase proteins and ABO group, and it was attenuated when further adjusted for high FVIII (OR 3.41, 95% CI 0.80-14.70). No correlation was found between the time since the VTE event and levels of VWF, FVIII and ADAMTS13 (p>0.05). Conclusionsour data suggest a potential effect of high VWF and low ADAMTS13 on VTE risk. An unbalance between these two interconnected proteins might have a role in the pathophysiology of VTE. Results should be interpreted with caution due to the wide 95% CI and to the attenuation of VTE risk with further adjustment for FVIII. In order to better explain our results studies with larger sample size are warranted. Disclosures:No relevant conflicts of interest to declare.

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.

Relationship of Von Willebrand Factor with carotid artery and aortic arch calcification in ischemic stroke patients

BackgroundLarge population studies have revealed that increased von Willebrand Factor (VWF) levels are associated with an increased risk of ischemic stroke. In previous studies VWF was associated with atherosclerosis in healthy individuals. However, it is yet unknown what the association is between atherosclerosis and VWF levels in patients with ischemic stroke. ObjectivesThe aim of our study was to determine the association of atherosclerosis, measured with recent developed techniques, and VWF levels in a large, well characterized, cohort of ischemic stroke patients and to determine the prognostic value. MethodsWe included 925 consecutive patients with transient ischemic attack (TIA) or ischemic stroke. Calcification volumes (mm3) were scored in the aortic arch and both carotid arteries using multidetector computed tomography (CT) angiography. VWF antigen (VWF:Ag) levels were measured using ELISA. ResultsMean VWF:Ag levels were significantly higher in the presence of calcification in either the aortic arch (1.47 vs. 1.37 IU/ml [P = 0.039]) or the carotid arteries (1.49 vs. 1.34 IU/ml [P = 0.001]). Patients with a large artery atherosclerosis ischemic stroke had significantly higher VWF:Ag levels then the other TOAST subtypes (P < 0.0001). High VWF:Ag levels were associated with an unfavorable outcome (modified Rankin Scale >2 vs. ≤2; 1.64 vs. 1.41 IU/ml, [P < 0.0001]). ConclusionOur study showed a strong association between the extent of atherosclerosis in both the aortic arch and the carotid arteries and VWF levels in patients with TIA or ischemic stroke. Higher VWF levels are found in large artery atherosclerosis and are associated with a poor outcome.

Common and rare von Willebrand factor (VWF) coding variants, VWF levels, and factor VIII levels in African Americans: the NHLBI Exome Sequencing Project

AbstractSeveral rare European von Willebrand disease missense variants of VWF (including p.Arg2185Gln and p.His817Gln) were recently reported to be common in apparently healthy African Americans (AAs). Using data from the NHLBI Exome Sequencing Project, we assessed the association of these and other VWF coding variants with von Willebrand factor (VWF) and factor VIII (FVIII) levels in 4468 AAs. Of 30 nonsynonymous VWF variants, 6 were significantly and independently associated (P < .001) with levels of VWF and/or FVIII. Each additional copy of the common VWF variants encoding p.Thr789Ala or p.Asp1472His was associated with 6 to 8 IU/dL higher VWF levels. The VWF variant encoding p.Arg2185Gln was associated with 7 to 13 IU/dL lower VWF and FVIII levels. The type 2N-related VWF variant encoding p.His817Gln was associated with 17 IU/dL lower FVIII level but normal VWF level. A novel, rare missense VWF variant that predicts disruption of an O-glycosylation site (p.Ser1486Leu) and a rare variant encoding p.Arg2287Trp were each associated with 30 to 40 IU/dL lower VWF level (P < .001). In summary, several common and rare VWF missense variants contribute to phenotypic differences in VWF and FVIII among AAs.

The Oxidative Modification of Von Willebrand Factor Is Associated with Thrombotic Angiopathies in Diabetes Mellitus

The thrombogenic activity of Von Willebrand factor (VWF) is proportional to its molecular size and inversely related to its proteolysis by ADAMTS-13. Oxidation of VWF severely impairs its proteolysis by the metalloprotease. This study was aimed at assessing in patients with type 1 and type 2 diabetes whether protein carbonyls, marker of oxidative stress, are associated with both the level and oxidation status of VWF as well as with micro- and macroangiopathic complications. Eighty-three diabetic patients (41 type 1 and 42 type 2 diabetic subjects) and their respective eighty-three healthy controls were studied after verifying the availability, through institutional databases, of clinical biochemistry records spanning at least 3 years. VWF and protein carbonyls were measured by immunoassays, whereas VWF multimers were studied by SDS-agarose gel electrophoresis. Type 2 diabetic subjects had higher levels of VWF antigen (VWF:ag), VWF activity (VWF:act) and plasma proteins’ carbonyls compared to both their controls and type 1 diabetic subjects. Moreover, high molecular weight VWF multimers and specific VWF-bound carbonyls were significantly increased in subjects with micro- and macro-angiopathic complications. In both type 1 and type 2 diabetic subjects, ADAMTS-13 activity was in the normal range. In a multivariable analysis, only VWF-bound carbonyls were significantly associated with any form of thrombotic angiopathy in the entire group of T1- and T2 diabetic patients. These data provide first evidence that not only high VWF levels but also its oxidation status and the presence of high molecular weight VWF multimers that are not observed in SDS-agarose gel electrophoresis of normal subjects are associated with thrombotic angiopathies in diabetes mellitus. These findings may help identify diabetic patients particularly at risk for these complications and elucidate a new pathophysiological mechanism of thrombotic angiopathies in this clinical setting.

Variation of Both Blood Group H and ABO Glycans Is Associated with VWF Levels

Abstract 3314ABO(H) is a carbohydrate blood group system primarily expressed on red cells, blood vessels, and mucosal surfaces. ABO blood group is known to influence von Willebrand Factor (VWF) levels, with low VWF associated with blood group O and increased diagnosis of von Willebrand Disease. Conversely, non-O blood group is associated with high VWF levels, and both non-O blood group and high VWF are associated with thrombotic vascular disease. We sought to characterize VWF levels relative to ABH glycan phenotypes in 1129 individuals from a healthy sibling cohort, the Genes and Blood Clotting Cohort (GABC). VWF:Ag levels were determined by AlphaLISA (Perkin Elmer) in platelet poor plasma. ABH forensic techniques were adapted to samples of RBC-rich, frozen buffy coat in the study repository. In brief, buffy coat fractions were diluted in TBS, applied to nitrocellulose, and A and B glycans detected using murine monoclonal anti-A (Immucor) or murine monoclonal anti-B (Immucor) followed by and streptavidin-conjugated donkey anti-mouse IgG HRP (Jackson ImmunoResearch). A biotinylated Ulex europaeus agglutinin (UEA lectin, Vector Labs) was used to detect H, followed by streptavidin-HRP. Blots were imaged using ImageQuant (GE) and scored semi-quantitatively for glycan density by two blinded independent observers using reference buffy coats from normal blood donors.ABO blood group frequencies were similar to that of the U.S. population (O=40%, A=42%, B=12%, AB=6%). Also consistent with previous reports, VWF:Ag levels varied significantly between ABO blood groups (O<A<B=AB, see Table 1). Within blood group A, we observed variation in A glycan density (scored 1+ to 3+). Lower A glycan density (similar to the A2 reference) correlated significantly (p<0.01) with lower VWF:Ag levels (see Table 1), and also appeared to have higher detectable H antigen. We also observed wide variation in H glycan density (scored 1+ to 5+). Overall, detection of A and B glycan density patterns were inversely related to H glycan, consistent with glycosylation of H by the ABO enzyme. Interestingly, higher H density correlated significantly (p<0.01) with lower VWF:Ag levels, even within blood group O (see Table 2).In summary, ABH glycan variation may impact VWF in a more complex fashion than previously suspected. Although these data are limited to semi-quantitative analyses by the heterogeneous nature of RBC-rich buffy coat, our findings are consistent with expectations for major ABO blood group frequencies and show that variation of RBC rich-buffy coat ABH glycan density within and between ABO blood groups correlates with VWF:Ag level. This work also suggests a previously unsuspected association between VWF and variation in H antigen, which we hypothesize may be due to variation in the FUT genes or other loci affecting H glcosylation patterns. Further work to characterize the complexity of the ABH carbohydrate system and its genetic determinants is warranted to better understand the impact of ABH subtypes on VWF and vascular phenotypes.Table 1ABO Blood Groups, Buffy Coat A Glycan Density, and VWF:Ag LevelNumber of SubjectsABO Blood GroupVWF:Ag (+/−1SD)VWF Difference (Ovs.Avs.Bvs.AB)*Difference from Group O*454O90+/−35473A119+/−45p<0.01p<0.01138B130+/−50p<0.01p<0.0164AB128+/−52NSp<0.01Number of SubjectsA Glycan DensityAvg H Glycan DensityVWF:Ag (+/−1SD)VWF Difference (A1+vs.2+vs.3+)*Difference from A 1+*681+3.598+/−401952+2.4123+/−44p<0.01p<0.012103+2.0123+/−45NSp<0.01*Each section above: One-way ANOVA; post-hoc Tukey's Least Significant Difference.Table 2Buffy Coat H Glycan Density and VWF:Ag LevelH Glycan Density in All SubjectsNumber of SubjectsH Glycan DensityVWF:Ag (+/−1SD)VWF Difference (H1vs.2vs.3vs.4vs.5)*Difference from H 1+*521+135+/−462572+130+/−53NSNS2603+117+/−44p<0.01p<0.013074+99+/−37p<0.01p<0.012525+88+/−32p<0.05p<0.01H Glycan Density in Blood Group O SubjectsNumber of SubjectsH Glycan Density**VWF:Ag (+/−1SD)VWF Difference (H3+vs.4+vs.5+)*Difference from H 3+*293+115+/−572074+92+/−33p<0.01p<0.012145+85+/−30NSp<0.01*One-way ANOVA; post-hoc: Tukey's Least Significant Difference.**No blood group O individuals scored <3+ H glycan density. Disclosures:No relevant conflicts of interest to declare.

Evaluation of Primary Haemostasis in Patients Undergoing Cardiac Surgery Using a Novel Automated Microchip Flow-Chamber System (T-TAS).

AbstractAbstract 2171Post operative bleeding is a common complication of cardiac surgery; its aetiology may be multifactorial but is often attributed to platelet dysfunction. However, at present no reliable point of care test (POCT) is available for this and patients are often managed empirically; approximately 40% receive pooled platelet transfusions but many require re-sternotomy. An automated microchip flow chamber system that directly measures platelet-collagen interaction under shear (1500s−1) has recently been developed (T-TAS; Total Thrombus-formation system; Zakros, Fujmori Kogyto, Japan). We hypothesized that this could be developed as a POCT to assess platelet function under shear, allowing targeted and more rational use of blood products. We used this system to study 20 patients aged 19–72 years, before and after cardiac surgery. The T-TAS was used to determine the onset of occlusion (time to 10kPa, T10) and primary haemostatic potential (AUCend-area under pressure curve). Haematocrit (Hct), platelet count and von Willebrand factor (VWF) levels and thromboelastography (TEG) were measured at the corresponding time points.Surgery resulted in a significant increase in time to occlusion onset (T10) (p=0.006; n=20, Figure 1A). Similarly, the AUCend significantly decreased after surgery (p=0.001, n=19; Figure 1B) with the majority of cases (12 out of 20) failing to occlude within 30 minutes. The change in T10 inversely correlated with change in AUCend(r=-0.5, p=0.02).VWF is essential for platelet adhesion to collagen under high shear stress. Higher VWF levels appeared to be associated with lower T10, but this was not significant and only observed prior to surgery. Moreover, no significant correlation between the change in T10 or AUCend and changes in VWF pre- and post-surgery was observed.Surprisingly, pre and post-operative hematocrit were both negatively correlated with AUCend (r=-0.5, p=0.03, n=11 and r=-0.5, p=0.02,n=11 respectively).No correlation was observed between platelet count and the T-TAS parameters. However, the change in AUCend (but not T10) was shown to correlate with the change in platelet count before and after surgery (r = 0.58, p = 0.01).Finally, T10 and AUCend values were not significantly altered in patients given anti-platelet drugs: aspirin and/or clopidrogel. This implies that the T-TAS is sensitive to the initial adhesion of platelets to VWF-collagen rather than to platelet activation and aggregation.These data demonstrate that cardiac bypass surgery affects VWF mediated platelet adhesion to collagen under flow and this can be detected using a microchip flow chamber system. The lack of correlation with VWF levels and apparently paradoxical effect of haematocrit suggest that the dominant mechanism for the impaired postoperative haemostasis is a decline in platelet function and in particular a decrease in adhesive function. This is likely to result from altered exposure and/or function of GPIb resulting from surgery and cardio-pulmonary bypass.Current POCTs are largely insensitive to primary haemostatic mechanisms, while conventional laboratory measures of primary haemostasis are non-physiological, and require a considerable expertise and time. As expected, TEG gave similar values pre and post-surgery for all subjects, indicating that a flow system is required to adequately evaluate primary haemostasis. The advantages of this novel automated microchip flow chamber system are the small blood volume required and the rapidity of results. Our data suggest a place for this system in a point-of care setting, providing useful assessment of haemostatic status following surgery and with the potential to improve patient management. Further studies are warranted. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Clinical and prognostic implications of low or high level of von Willebrand factor in patients with Waldenström macroglobulinemia

AbstractAcquired von Willebrand syndrome is described in patients with Waldenström macroglobulinemia (WM). Assessment of ristocetin cofactor activity (VWF:RCo) and von Willebrand factor (VWF) antigen (VWF:Ag) in 72 consecutive patients with WM showed a negative relation between VWF levels < 130 U/dL and both monoclonal immunoglobulin M concentration (mIgMC) and viscosity. Ten patients with VWF:RCo < 50 U/dL (< 40 for patients with blood group O) fulfilled the acquired von Willebrand syndrome criteria. They had higher mIgMC and viscosity. Reduction in mIgMC was associated with increase in VWF levels. The low VWF:RCo/VWF:Ag ratio suggested that high viscosity might be associated with increased shear force and cleavage of multimers. Surprisingly, 43 patients (59%) presented with high VWF:Ag (> 110 U/dL). They had higher bone marrow microvessel density and vascular endothelial growth factor expression on bone marrow mast cells. Five-year survival rates of patients with VWF:Ag < 110, between 110 and 250, and more than 250 U/dL were 96%, 71%, and 44%, respectively (P < .0001). High VWF:Ag was also a significant adverse prognostic factor for survival after first-line therapy (P < .0001), independently of the international scoring system. These results support systematic assessment of VWF in patients with WM. The adverse prognostic value of high VWF levels raises issues on interactions between lymphoplasmacytic cells, mast cells, and endothelial cells in WM.

Use of Haemate® P as immune tolerance induction in patients with severe haemophilia A who failed previous induction attempts: a multicentre observational study

Immune tolerance induction (ITI) can eliminate factor VIII (FVIII) inhibitory antibodies that appear during FVIII replacement therapy. If first-line ITI fails, switching to a different FVIII concentrate, especially one containing von Willebrand factor (VWF), has been advocated. The objective of the study was to assess the efficacy and safety of Haemate(®) P, a plasma-derived FVIII concentrate containing high levels of VWF, as ITI in severe haemophilia A patients who had failed at least one prior ITI attempt with a different FVIII concentrate. In this multicentre, observational study, Haemate(®) P was administered at a starting dose of 83-308 IU kg(-1) day(-1) (1500-6000 IU day(-1)). Efficacy was assessed by standard criteria (e.g. Bethesda titre, FVIII recovery and half-life), and bleeding characteristics. Nine patients from six haemophilia centres were treated with Haemate(®) P after failing one (n = 2), two (n = 5) or three (n = 2) prior ITI courses. The median time from inhibitor detection to Haemate(®) P treatment was 5.4 years. The median Haemate(®) P dose was 134 IU kg(-1), and the median treatment duration 32 months. During median of 47 months of follow-up, complete response, partial response and treatment failure were observed in one, three and five patients respectively. Five patients experienced seven adverse events (AEs), including two serious AEs (sepsis). Haemate(®) P was discontinued due to an AE in one patient with a partial response. Haemate(®) P salvage ITI resulted in complete or partial tolerization in four of nine patients (44%) who had failed previous ITI attempts using different FVIII concentrates.

Light Chain of Factor VIII Is Sufficient for Accelerating Cleavage of von Willebrand Factor by ADAMTS13 Metalloprotease

We previously demonstrated that coagulation factor VIII (FVIII) accelerates proteolytic cleavage of von Willebrand factor (VWF) by A disintegrin and metalloprotease with thrombospondin type 1 repeats (ADAMTS13) under fluid shear stress. In this study, the structural elements of FVIII required for the rate-enhancing effect and the biological relevance of this cofactor activity are determined using a murine model. An isolated light chain of human FVIII (hFVIII-LC) increases proteolytic cleavage of VWF by ADAMTS13 under shear in a concentration-dependent manner. The maximal rate-enhancing effect of hFVIII-LC is ∼8-fold, which is comparable with human full-length FVIII and B-domain deleted FVIII (hFVIII-BDD). The heavy chain (hFVIII-HC) and the light chain lacking the acidic (a3) region (hFVIII-LCΔa3) have no effect in accelerating VWF proteolysis by ADAMTS13 under the same conditions. Although recombinant hFVIII-HC and hFVIII-LCΔa3 do not detectably bind immobilized VWF, recombinant hFVIII-LC binds VWF with high affinity (K(D), ∼15 nM). Moreover, ultra-large VWF multimers accumulate in the plasma of fVIII(-/-) mice after hydrodynamic challenge but not in those reconstituted with either hFVIII-BDD or hFVIII-LC. These results suggest that the light chain of FVIII, which is not biologically active for clot formation, is sufficient for accelerating proteolytic cleavage of VWF by ADAMTS13 under fluid shear stress and (patho) physiological conditions. Our findings provide novel insight into the molecular mechanism of how FVIII regulates VWF homeostasis.

ABO Blood Group and von Willebrand Factor Levels Partially Explained the Incomplete Penetrance of Congenital Thrombophilia

We aimed to study the association among ABO blood group, von Willebrand factor, factor VIII plasma levels, and the risk of venous thrombosis (VT) in a cohort of 1774 relatives from 500 families with inherited thrombophilia. One hundred sixty-one of the 1774 relatives had a VT. Different risk groups were formed: no, low-(factor V Leiden or F2G20210A heterozygous carriers), and high-risk thrombophilia (antithrombin, protein C, protein S, factor V Leiden, or F2G20210A homozygous carriers and combined defects). Compared with group O, AB blood group was associated with increased risk of VT: hazard ratio (HR)=3.8 (2.0-7.2). The effect of blood group A and B was milder (HR=1.6 [1.1-2.5] and 1.8 [1.0-3.3], respectively). An increased risk of VT was observed with increasing levels of von Willebrand factor and factor VIII plasma levels (HR=2.96 [1.92-4.56] and HR=2.60 [1.92-4.56] for third versus first tertile of von Willebrand factor and factor VIII plasma levels, respectively). In multivariate analysis, AB group (HR=2.3 [1.1-4.8]), high-risk thrombophilia (HR=2.8 [1.6-4.6]), and high von Willebrand factor levels (HR=2.3 [1.3-4.0]) were significantly associated with increased risk of VT. The risk of VT in individuals with high-risk thrombophilia and AB group was 14.4× higher than in those without thrombophilia and O group (5.0-41.4). ABO blood group modifies the risk of VT in families with hereditary thrombophilia. Phenotyping of the ABO blood group should be performed to better assess the risk of VT in asymptomatic individuals from thrombophilic families.

Von Willebrand factor predicts major bleeding and mortality during oral anticoagulant treatment

Oral anticoagulation (OAC), predominantly with warfarin, is an effective treatment to prevent thromboembolic events. Serious bleeding is a frequent and feared treatment complication. In this longitudinal cohort study of OAC-treated patients, we aimed to evaluate the relationship between von Willebrand factor (VWF) levels and risk of bleeding complications, cardiovascular mortality and all-cause mortality. A total of 719 patients receiving warfarin treatment were observed for a mean duration of 4.2 years. All bleeding complications causing hospitalization were registered and classified into clinically relevant bleeding (CRB) and major bleeding. Ischaemic stroke, peripheral arterial embolism, myocardial infarction, and death were also recorded. We identified 113 cases of CRB and 73 of major bleeding. In total, 161 deaths occurred during follow-up with cardiovascular disease identified as the cause of death in 110 patients. Patients in the highest tertile of VWF had a significantly increased risk of bleeding complications: hazard ratio (HR) 2.53 (95% CI 1.41-4.56) for major bleeding and HR 2.19 (95% CI 1.38-3.48) for CRB. VWF, expressed either in tertiles or as a continuous variable, showed a significant association with cardiovascular mortality (HR 1.68, 95% CI 1.40-2.01) and all-cause mortality (HR 1.77, 95% CI 1.52-2.05). In multivariate Cox regression analysis, the findings remained significant after adjusting for age, high-sensitivity C-reactive protein and creatinine. Patients with high levels of VWF had an increased risk of bleeding complications, cardiovascular mortality and all-cause mortality during OAC treatment. Our findings imply that the use of VWF as a risk marker for thromboembolic events is complicated by the association of VWF with bleeding complications.

New Insight into the Hypercoagulability of Cushing’s Syndrome

Background: Hypercoagulability and a tendency for thromboembolic complications are reported in Cushing’s syndrome (CS). The hypercoagulability is due mainly to the cortisol-induced increase in von Willebrand factor (VWF) and factor VIII. This is not a constant feature of CS, however; it depends on particular single nucleotide polymorphism (SNP) haplotypes in the VWF gene promoter: haplotype 1 (–3268G/–2709C/–2661A/–2527G) confers a greater risk of VWF upregulation by cortisol than haplotype 2 (–3268C/ –2709T/–2661G/–2527A). In healthy individuals these SNPs are in linkage disequilibrium with the –2144 (GT)_n of the VWF promoter: haplotype 1 mainly segregates with short GT repeats (15–19, GTs), haplotype 2 with long repeats (GT ≧ 20, GT_L). Methods: We analyzed the (GT)_n locus, the SNP haplotypes and their association with VWF levels in 80 CS patients in order to precisely define the cortisol-sensitive VWF promoter pattern. CS patients were divided into groups A (increased VWF) and B (normal VWF). Results: Haplotype 1 and (GT)_S were more frequent in group A patients, and conferred a 9- and 7.5-fold risk of developing high VWF levels, respectively. Haplotype 2 and (GT)_L were more represented in group B. There was also an unexpected higher prevalence of recombinant SNP haplotypes in CS patients (6.2%) than in normals (0.9%), p = 0.002. Conclusions: Our results indicate that the cortisol-induced increase in VWF may be predicted by VWF promoter polymorphisms, haplotype 1 and (GT)_S being the sensitive pattern. These represent new markers for defining the prothrombotic risk of CS. The clinical significance, if any, of the increased recombination rate in SNP haplotypes in the VWF promoter warrants further study.

Letter by De Meyer et al Regarding Article “High von Willebrand Factor Levels Increase the Risk of Stroke: The Rotterdam Study”

HomeStrokeVol. 42, No. 3Letter by De Meyer et al Regarding Article “High von Willebrand Factor Levels Increase the Risk of Stroke: The Rotterdam Study” Free AccessLetterPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissionsDownload Articles + Supplements ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toSupplemental MaterialFree AccessLetterPDF/EPUBLetter by De Meyer et al Regarding Article “High von Willebrand Factor Levels Increase the Risk of Stroke: The Rotterdam Study” Simon F. De Meyer, Guido Stoll and Christoph Kleinschnitz Simon F. De MeyerSimon F. De Meyer Search for more papers by this author , Guido StollGuido Stoll Search for more papers by this author and Christoph KleinschnitzChristoph Kleinschnitz Search for more papers by this author Originally published3 Feb 2011https://doi.org/10.1161/STROKEAHA.110.604777Stroke. 2011;42:e41Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: January 1, 2011: Previous Version 1 To the Editor:With great interest, we read the article by Wieberdink et al, published in the October 2010 issue of Stroke.1 In this relevant study (as part of the Rotterdam Study), the authors investigated the association between plasma levels of von Willebrand factor (VWF) and the overall risk of stroke. To this end, a large population-based cohort of 6250 participants (age ≥55 years) who were free of stroke at baseline was followed for 5 years. Interestingly, the authors found that the risk of stroke increased with increasing VWF levels, independent from conventional cardiovascular risk factors and ABO blood group status; this clearly indicates an association between the amount of circulating VWF and the risk of stroke in this elderly population.While not discussed by the authors, their findings further confirm a critical role for VWF in stroke development, as shown in several recent studies of experimental stroke. Indeed, we recently demonstrated that VWF-deficient mice are protected from ischemic brain injury, evidenced by a dramatic reduction of infarct volume (approximately 60% of the infarct volumes in wild-type controls) and better functional outcome.2 Similar results were obtained in an independent study by Zhao et al.3 Reconstitution of plasma VWF in VWF-deficient mice by hydrodynamic gene transfer fully restored the susceptibility to cerebral ischemia.2 Furthermore, in a study aimed at the identification of crucial VWF interactions in stroke, we demonstrated that in VWF-deficient mice reconstituted with VWF mutants defective in binding to collagen or platelet glycoprotein (GP) Ibα, protection against stroke was sustained; however, VWF lacking the GPIIb/IIIa binding site restored full susceptibility to stroke similar to normal VWF.4 Thus, binding of VWF to both collagen and GPIb (but not to GPIIb/IIIa) are mandatory steps in stroke development. In addition, the central role of VWF in stroke development has recently been underlined by observations that VWF-cleaving protease a disintegrin and metalloprotease with thrombospondin type 1 repeats, 13 (referred to simply as ADAMTS13), which decreases the thrombogenicity of VWF by cleaving ultralarge VWF multimers into smaller ones, also plays a protective role in cerebral ischemia.3,5Taken together, we are excited to see that the findings of Wieberdink et al in humans nicely fit into the general concept of VWF as an important mediator of experimental stroke. The growing amount of data all point toward VWF as an attractive target for stroke prevention and treatment.Simon F. De Meyer, PhDGuido Stoll, MDChristoph Kleinschnitz, MD Immune Disease Institute Program in Cellular and Molecular Medicine, Children's Hospital Boston, and Department of Pathology Harvard Medical School Boston, MA Department of Neurology University of Wuerzburg Wuerzburg, GermanyFootnotesStroke welcomes Letters to the Editor and will publish them, if suitable, as space permits. Letters must reference a Stroke published-ahead-of-print article or an article printed within the past 3 weeks. The maximum length is 750 words including no more than 5 references and 3 authors. Please submit letters typed double-spaced. Letters may be shortened or edited. Include a completed copyright transfer agreement form (available online at http://stroke.ahajournals.org and http://submit-stroke.ahajournals.org).

Association of Quantitative and Qualitative Abnormalities of Von Willebrand Factor and Risk of Death In Hemodialysis Patients

AbstractAbstract 2217In order to evaluate the possible role of abnormalities of von Willebrand factor in the hemostatic defects seen in indivdiuals with chronic kidney disease (CKD), a cohort study was performed evaluating pre- and post-dialysis levels of von Willebrand factor (VWF), VWF multimer profiles and levels of its cleaving protease, ADAMTS-13. There were 57 subjects (31 males, 26 females) enrolled with CKD with a mean age of 75 years (range 60 – 90). Subjects with known vascular disease were recruited; 49 (86%) had documented ischemic heart disease, 16 (29%) had cerebrovascular disease and 17 (31%) had peripheral vascular disease. A little over half had diabetes mellitus (30 subjects or 54%), 37 (67%) were on antiplatelet therapy and 7 (13%) were chronically anticoagulated with warfarin. Blood samples were drawn immediately pre- and again post-dialysis and all results were compared with a group of age-matched normal controls (Table 1). As has been previously reported, VWF antigen levels (VWF:Ag) and VWF functional activity as measured by the ristocetin cofactor assay (VWF:RCo) were higher in the pre-dialysis samples compared with controls, and both levels were increased even further following dialysis. Additionally, the percentage of high molecular weight VWF multimers (% HMWM) were significantly increased in the pre-dialysis samples compared with controls. This is a novel finding, and the level of % HMWM seen in the subjects is similar to what has been reported in individuals with Thrombotic Thrombocytopenic Purpura (TTP). This difference decreased following dialysis, potentially due to the effect of shear stress on VWF and the resultant proteolytic processing, however still remained significantly higher when compared with controls. ADAMTS-13 functional activity was lower in the subjects compared with controls, providing a possibly explanation for the increase in % HMWM. IL-6 levels are higher in subjects compared with controls. IL-6, which is an inflammatory cytokine known to be increased in patients with CKD, has been previously reported as a marker of inactivation of ADAMTS-13. Two years after enrollment, follow up of the subjects revealed that 22 had died, 17 from documented cardiovascular events. Higher VWF levels at the time of enrollment significantly correlated with risk of death (p=0.041) during the study period. The increase in % HMWM suggests that a “TTP-like phenotype” may also be playing a role. Taken together, these data suggest that both quantitative and qualitative abnormalities of VWF contribute to the risk of thrombotic death in chronic kidney disease.Table 1Controls n=30Pre-Dialysis n=56Post-Dialysis n=56P value (ANOVA)Mean VWF:Ag IU/mL (range)1.39 (0.55–2.72)2.26 (0.64–4.71)2.70 (0.90–5.28)<0.001Mean VWF:RCo IU/mL (range)1.00 (0.59–1.43)2.03 (0.53–4.22)2.16 (0.59–3.98)<0.001Mean HMWM (%) (range)12 (4–20)18 (6–30)16 (4–29)<0.001Mean ADAMTS-13 IU/mL (range)1.10 (0.60–1.51)0.84 (0.44–1.29)0.91 (0.49–1.45)0.001Mean IL-6 pg/mL (range)2.43 (0.10–10)19 (0.24–371)20 (0.81–286)<0.001 Disclosures:No relevant conflicts of interest to declare.

High von Willebrand Factor Levels Increase the Risk of Stroke

Many studies have investigated the role of plasma von Willebrand factor level in coronary heart disease, but few have investigated its role in stroke. The aim of this study was to determine if von Willebrand factor levels are associated with the risk of stroke. The study was part of the Rotterdam Study, a large population-based cohort study among subjects aged ≥55 years. We included 6 250 participants who were free from stroke at baseline (1997 to 2001) and for whom blood samples were available. Follow-up for incident stroke was complete up to January 1, 2005. Data were analyzed with Cox proportional hazards models adjusted for age and sex and additionally with models adjusted for other potential confounders including ABO blood group. A subgroup analysis was performed in participants without atrial fibrillation. Effect modification by sex was tested on a multiplicative and on an additive scale. During an average follow-up time of 5.0 years, 290 first-ever strokes occurred, of which 197 were classified as ischemic. The risk of stroke increased with increasing von Willebrand factor levels (age- and sex-adjusted hazard ratios per SD increase in von Willebrand factor level: 1.12 [95% CI, 1.01 to 1.25] for stroke, 1.13 [95% CI, 0.99 to 1.29] for ischemic stroke). Adjustments for additional confounders slightly attenuated the association. The association was also present in subjects without atrial fibrillation and did not differ between sexes. High von Willebrand factor levels are associated with stroke risk in the general population.

Microsatellite (GT) n is part of the von Willebrand factor (VWF) promoter region that influences the glucocorticoid-induced increase in VWF in Cushing's syndrome

Introduction The cortisol-induced increase in von Willebrand factor (VWF) in Cushing's syndrome (CS) seems to depend on single nucleotide polymorphisms (SNPs) of the VWF promoter, haplotype 1 (-3268G/-2709C/-2661A/-2527G) being the susceptible pattern. Materials and Methods This study focused on a new variable region of the VWF promoter, the -2144(GT) n locus, to establish whether different GT-repeat lengths are also involved in modulating the cortisol-induced increase in VWF. Sixty-nine CS patients were investigated, divided into groups A (high VWF) and B (normal VWF). Results Analysing the (GT) n locus revealed a similar allele distribution in CS patients and normal subjects, (GT) n variants ranging from 15 to 24 repeats and (GT) 19 and (GT) 21 being the two most represented. However, when groups A and B were analysed separately, a different allele distribution was observed: short GT-repeats (15-19, GT S) were more frequent in group A, long GT-repeats (20-24, GT L) in group B (p = 0.01). About genotype distributions, (GT) S/(GT) S was higher in group A and rare in group B (22.5% and 3.4%, respectively), whereas (GT) L/(GT) L was higher in group B than in group A (55.2%, 27.5%) (p = 0.021). Odds-ratio analysis revealed a risk of a cortisol-dependent increase in VWF three times higher for alleles (GT) S than for (GT) L, and 13-fold for genotype (GT) S/(GT) S respect to (GT) L/(GT) L. Conclusions In conclusion, not only the SNPs haplotypes in the VWF gene promoter, but also the variable-length (GT) n locus predict the risk of developing high VWF levels under conditions of glucocorticoid excess; the combination of (GT) S and haplotype 1 represents the susceptible pattern.