The Structure and Function of von Willebrand Factor

von Willebrand disease

von Willebrand disease (VWD) is the most common inherited bleeding disorder. The disorder is characterized by excessive mucocutaneous bleeding. The most common bleeding manifestations of this condition include nosebleeds, bruising, bleeding from minor wounds, menorrhagia or postpartum bleeding in women as well as bleeding after surgery. Other less frequent symptoms include gastrointestinal bleeding, haematomas or haemarthroses. VWD pathophysiology is complex and results from defects in von Willebrand factor (VWF) glycoprotein. Quantitative deficiencies are responsible for type 1 VWD with a partial decrease of VWF and type 3 with the complete absence of VWF. Qualitative abnormalities cause type 2 VWD, being further divided into types 2A, 2B, 2M and 2N. Although common, VWD is at risk of misdiagnosis, overdiagnosis and underdiagnosis owing to several factors, including complex diagnosis, variability of bleeding symptoms, presence of external variables (blood groups and other physiological modifiers such as exercise, thyroid hormones, oestrogens, and ageing), and lack of disease awareness among non-specialist health-care providers. Establishing the correct VWD diagnosis requires an array of specialized phenotypic assays and/or molecular genetic testing of the VWF gene. The management of bleeding includes increasing endogenous VWF levels with desmopressin or infusion of exogenous VWF concentrates (plasma-derived or recombinant). Fibrinolytic inhibitors, topical haemostatic agents and hormonal therapies are used as effective adjunctive measures.

A novel mouse model of type 2N VWD was developed by CRISPR/Cas9 gene editing and recapitulates human type 2N VWD

A novel type 2N VWD mouse model was established in which VWF is incapable of binding FVIII but is otherwise fully functional.

VWF^2N/2N mice exhibited a severe bleeding phenotype after tail tip amputation but not in lateral tail vein or ventral artery injury models.

Type 2N von Willebrand disease is caused by mutations in the factor VIII (FVIII) binding site of von Willebrand factor (VWF), resulting in dysfunctional VWF with defective binding capacity for FVIII. We developed a novel type 2N mouse model using CRISPR/Cas9 technology. In homozygous VWF^2N/2N mice, plasma VWF levels were normal (1167 ± 257 mU/mL), but the VWF was completely incapable of binding FVIII, resulting in 53 ± 23 mU/mL of plasma FVIII levels that were similar to those in VWF-deficient (VWF^−/−) mice. When wild-type human or mouse VWF was infused into VWF^2N/2N mice, endogenous plasma FVIII was restored, peaking at 4 to 6 hours post-infusion, demonstrating that FVIII expressed in VWF^2N mice is viable but short-lived unprotected in plasma due to dysfunctional 2N VWF. The whole blood clotting time and thrombin generation were impaired in VWF^2N/2N but not in VWF^−/− mice. Bleeding time and blood loss in VWF^2N/2N mice were similar to wild-type mice in the lateral tail vein or ventral artery injury model. However, VWF^2N/2N mice, but not VWF^−/− mice, lost a significant amount of blood during the primary bleeding phase after a tail tip amputation injury model, indicating that alternative pathways can at least partially restore hemostasis when VWF is absent. In summary, we have developed a novel mouse model by gene editing with both the pathophysiology and clinical phenotype found in severe type 2N patients. This unique model can be used to investigate the biological properties of VWF/FVIII association in hemostasis and beyond.

von Willebrand Factor Gene Polymorphism in Preeclampsia Pregnant at Medan, Indonesia

BACKGROUND: von Willebrand Factor (vWF) is a large glycoprotein mediating hemostasis and thrombosis. The roles of vWF are platelets adhesion to sites of vascular damage and stabilization of coagulation factor VIII. AIM: This study aimed to analyze the polymorphism of the vWF gene on preeclampsia (PE) in pregnancy in Medan, Indonesia. MATERIALS AND METHODS: DNA was amplified using the polymerase chain reaction and was electrophoresed in agarose 2%. Electrophoresis results were detected using Gel Doc 1000 (Biorad, USA). The sequencing method was used to identify polymorphism from vWF gene. RESULTS: From 50 samples of PE patients, the g.93308C>T vWF gene polymorphism was found with the percentage of TT, CT, and CC genotypes as 50%, 42%, and 8%, respectively. CONCLUSION: The c.93308C>T vWF gene polymorphism was found in the genotype percentage of homozygous TT, and heterozygote CT was greater than wild-type CC.

Von Willebrand factor, ADAMTS13 and mortality in dialysis patients

BACKGROUND

Von Willebrand Factor (VWF) multimers are cleaved into smaller and less coagulant forms by the metalloprotease ADAMTS13. The aim of this study was to investigate the association between VWF and ADAMTS13 and mortality in dialysis patients.

METHODS

We prospectively followed 956 dialysis patients. VWF levels and ADAMTS13 activity were measured. Cox proportional hazard analyses were used to calculate hazard ratios (HRs) with 95 % confidence intervals (CIs) to investigate the association between quartiles of VWF levels and ADAMTS13 activity and all-cause mortality. HRs were adjusted for age, sex, body mass index, cardiovascular disease, dialysis modality, primary kidney disease, use of antithrombotic medication, systolic blood pressure, albumin, C-reactive protein and residual GFR.

RESULTS

Of the 956 dialysis patients, 288 dialysis patients died within three years (mortality rate 151 per 1000 person-years). The highest quartile of VWF as compared with lower levels of VWF was associated with a 1.4-fold (95 %CI 1.1-1.8) increased mortality risk after adjustment. The lowest quartile of ADAMTS13 activity as compared with other quartiles was associated with a 1.3-fold (95 %CI 1.0-1.7) increased mortality risk after adjustment. The combination of the highest VWF quartile and lowest ADAMTS13 quartile was associated with a 2.0-fold (95 %CI 1.3-3.0) increased mortality risk as compared with the combination of the lowest VWF quartile and highest ADAMTS13 quartile.

CONCLUSIONS

High VWF levels and low ADAMTS13 activity were associated with increased mortality risks in dialysis patients.

Endothelial Dysfunction, Fibrinolytic Activity, and Coagulation Activity in Patients With Atrial Fibrillation According to Type II Diabetes Mellitus Status

Recent findings in atrial fibrillation (AF) patients receiving oral anticoagulation showed that diabetes without insulin therapy has a thromboembolic risk comparable to nondiabetic patients, whereas only diabetic patients on insulin have a heightened thromboembolic risk. We explored possible pathophysiological correlates of such finding on 90 AF patients on oral anticoagulation, divided according to diabetes status (n = 30 without diabetes; n = 29 with diabetes on oral antidiabetic drugs; n = 31 with insulin-requiring diabetes). We assessed von Willebrand Factor (VWF) concentration (VWF:Ag) and activity (VWF R:Co) as measures of endothelial dysfunction; and thrombin-activatable fibrinolysis inhibitor (TAFI) and prothrombin fragment 1 + 2 (F1+2) levels as markers of fibrinolytic activity and thrombin generation. Values of VWF:Ag, VWF:RCo, and TAFI were similar in the 3 groups. Patients with diabetes requiring insulin had significantly higher levels of F1+2 (median 23.1 pg/ml [interquartile range 17.6; 33.5]) than those without diabetes (16.3 pg/ml [11.5; 22.5], p = 0.036) and diabetic patients on oral antidiabetic drugs (20.6 pg/ml [13.3; 29], p = 0.046). Thus, in AF patients receiving oral anticoagulation, those with diabetes, regardless of the diabetes type (with or without insulin therapy), and those without diabetes have comparable indices of the explored parameters of endothelial dysfunction and fibrinolytic activity. Despite anticoagulant therapy, thrombin generation is selectively higher in diabetic patients' on insulin than in those without diabetes or with diabetes on oral antidiabetic drugs, with no differences between these latter 2 conditions. Thrombin generation might thus be a predominant contributor to the excess of thromboembolic risk in AF patients on insulin-requiring diabetes.

Increased von Willebrand factor over decreased ADAMTS-13 activity is associated with poor prognosis in patients with advanced non-small-cell lung cancer

BACKGROUND

Hypercoagulability induced by the imbalance between von Willebrand factor (VWF) secretion and its cleaving protease (ADAMTS-13) has been correlated with cancer metastasis. The aim of this study was to explore the prognostic significance of the VWF/ADAMTS-13 ratio in advanced non-small-cell lung cancer (NSCLC).

METHODS

Pre-treatment sera/plasma levels of VWF, ADAMTS-13, VWF/ADAMTS-13 ratio, factor (F) VIII, and other clinical/laboratory parameters were measured in 119 patients with advanced NSCLC and 102 healthy controls. All patients were followed up to determine the predictive value of these parameters for prognosis of advanced NSCLC.

RESULTS

Elevated VWF, VWF/ADAMTS-13 ratio, and reduced ADAMTS-13 were significantly correlated with the stage and grade of advanced NSCLC and the final status of disease (P<.05). VWF levels and the VWF/ADAMTS-13 ratio were also associated with response to chemotherapy (P<.05). Multivariate analysis identified the VWF/ADAMTS-13 ratio and D-dimer as significant independent predictors of patient mortality. The area under the curve showed that the VWF/ADAMTS-13 ratio was more useful than VWF, ADAMTS-13, and D-dimer to predict mortality. Kaplan-Meier analysis showed that a low VWF/ADAMTS-13 ratio was significantly predictive of improved survival (P=.004).

CONCLUSION

These results suggest that the imbalance between VWF secretion and ADAMTS-13 may play a critical role in the hypercoagulability state in advanced NSCLC. Moreover, elevation of the plasma VWF/ADAMTS-13 ratio may serve as an independent predictive factor for mortality in patients with advanced NSCLC.

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.

The Association between Fibrinogen, von Willebrand Factor, Antithrombin III, and D-dimer Levels and Survival Outcome by 36 Months from Ovarian Cancer

Thirty-five patients diagnosed to have ovarian cancer (early FIGO stage I/II n = 11, advanced FIGO stage III/IV, n = 24) were evaluated for hemostatic parameters relating to survival outcome by 36 months of disease. Systemic plasminogen activators and inhibitors were evaluated and we found no significant association with survival outcome and eventually only fibrinogen, von Willebrand Factor (vWF), antithrombin III (ATIII), and D-dimer levels were determined for their association with disease outcome by 12 months, 24 months, and 36 months. Twenty-four patients succumbed to the disease by 36 months (early n = 2, advanced n = 22). The 11 surviving patients (advanced n = 3, including one deceased at 52 months) is still living past 36 months and 82 months at the time of analysis. Elevated fibrinogen, vWF, and D-dimer together with reduced ATIII levels were found to be associated with poor survival outcome by 12 months of disease. Moreover, elevated vWF and D-dimer with reduced ATIII levels was strongly implicated with poor survival outcome by 36 months from ovarian cancer. The overall survival rate at 36 months from ovarian cancer was 31.4%. It is therefore suggested that fibrinogen, vWF, ATIII, and D-dimer levels be used together as prognostic markers for disease outcome especially in patients with advanced ovarian cancer within 36 months of disease. An expanded study is required to confirm these findings.

Shear-induced Filter Blockage. A Population Based Appraisal of a Method for the Assessment of Platelet, White Cell and von Willebrand Factor Interactions

Blood behaviour under shear-stress is assessed by a filter method in the Caerphilly Prospective Heart Study. Associations with haemostatic and lifestyle factors in 941 men aged 55 to 69 years are reported. The importance of platelets in filter blockage is confirmed, and roles for white cells and plasma viscosity in determining flow prior to blockage are identified. The aspect of platelet activity involved in blockage appears to be independent of mechanisms mediated by cyclo-oxygenase and adenosine diphosphate. von Willebrand factor however is associated with filter blockage, probably as an inter-platelet ligand. Fibrinogen is not required for blockage. Men regularly consuming alcohol or garlic supplements show reduced blockage, and biochemical mechanisms are suggested which might explain these associations. No effects of aspirin, smoking or consumption of fish oil supplements were noted. Shear-induced filter blockage is a simple method for measuring complex flow-dependent interactions of haemostatic factors. Its application in a wide range of investigations, including epidemiological studies, would appear to be appropriate.

A common VWF exon 28 haplotype in the Turkish population

An increasing number of mutations and polymorphisms have been identified in the von Willebrand factor (VWF) gene of patients with von Willebrand disease (VWD). Most of the sequence alterations are within exon 28, duplicated in the VWF pseudogene on chromosome 22. Genetic recombination causing the gene conversion between the VWF gene and its pseudogene is associated with multiple substitutions in the VWF gene and with VWD. In the present study, VWF gene exon 28 was analyzed in 33 patients with VWD by DNA sequencing. A total of 73% of the patients were heterozygous for p.D1472H, p.V1485L, p.1500A, p.1501F, p.L1503P, and p.S1506L single-nucleotide polymorphisms. Family analysis revealed that the gene conversion occurred between the VWF gene and its pseudogene in 3 patients. Case-control association analysis by Haploview 4.2 did not show an association between the haplotype and VWD. In conclusion, a common exon 28 haplotype in the Turkish population, which might have arisen from the gene conversion events in the founder population, was identified.

Genetic determinants of von Willebrand factor plasma levels and the risk of stroke: the Rotterdam Study

BACKGROUND

High von Willebrand factor (VWF) plasma levels are associated with an increased risk of stroke. VWF levels are strongly heritable. A previous meta-analysis of five large genome-wide association studies identified single-nucleotide polymorphisms (SNPs) within eight genetic loci as determinants of VWF levels. Whether these SNPs are associated with stroke risk is not known. The aim of our study was to investigate the association between genetic determinants of VWF levels and stroke risk.

METHODS

The study was part of the Rotterdam Study, a large population-based cohort study among subjects aged ≥ 55 years. A total of 5763 participants for whom DNA was available, and who were free of stroke at baseline, were eligible for analysis. VWF antigen (VWF:Ag) levels were measured in 3379 eligible participants. Within each of the eight loci, one top SNP was defined. The association between the eight SNPs and the risk of stroke was analyzed. Then, a genetic score, based on these eight SNPs, was constructed, and its total contribution to VWF plasma levels and stroke risk was investigated.

RESULTS

None of the eight SNPs was individually associated with stroke risk. A higher genetic score was significantly associated with a higher VWF:Ag level, but was not associated with an increased risk of stroke.

CONCLUSION

Eight SNPs that strongly determine VWF levels are not associated with stroke risk, either individually, or combined in a genetic score.

Intravascular recovery of VWF and FVIII following intraperitoneal injection and differences from intravenous and subcutaneous injection in mice

Intravenous infusion studies in humans suggest that both von Willebrand factor (VWF) and factor VIII (FVIII) remain intravascular in contrast to other coagulation proteins. We explored whether infusion of VWF and FVIII by either intraperitoneal (i.p.) or subcutaneous (s.c.) injection would result in efficient absorption of these large proteins into the vascular circulation. FVIII(null) or VWF(null) mice were infused with plasma-derived or recombinant VWF and/or FVIII by i.p., s.c., or intravenous (i.v.) injection. Both VWF and FVIII were absorbed into the blood circulation after i.p. injection with a peak between 2 and 4 h at levels similar to those observed in mice infused intravenously. In contrast, neither VWF nor FVIII was detected in the plasma following s.c. injection. Although i.v. injection achieved peak plasma levels quickly, both human VWF and FVIII rapidly decreased during the first 2 h following i.v. injection. Following both i.v. and i.p. infusion of VWF, the multimeric structure of circulating VWF was similar to that observed in the infusate. These results demonstrate that both VWF and FVIII can be efficiently absorbed into the blood circulation following i.p., but not s.c. injection, indicating that i.p. administration could be an alternative route for VWF or FVIII infusion.

Modulation of the von Willebrand factor-dependent platelet adhesion through alternative proteolytic pathways

Introduction

Platelet adhesion to collagen under high shear rates depends on the optimal size of the von Willebrand factor (VWF) multimers, which is determined by their limited proteolysis. The present study attempts to identify the role of hemostatic-fibrinolytic enzymes (thrombin, plasmin) and leukocyte-derived proteases (matrix metalloproteinase (MMP)-8, MMP-9, neutrophil elastase) in the cleavage of VWF and to characterize the effect of flow and platelets on this proteolysis and its functional consequences on platelet adhesion.

Methods and results

According to VWF immunoblots, plasmin, neutrophil elastase and thrombin at concentrations of in vivo relevance resulted in extensive degradation of VWF within several minutes. Platelets protected VWF against this proteolysis under static conditions, whereas perfusion of the proteases at 3350 s^-1 shear rate over VWF immobilized on artery cross sections enhanced its degradation and blocked the protective effect of platelets. In parallel with VWF digestion, the examined proteases impaired the VWF-dependent platelet adhesion as reflected in the decreased surface-bound GpIIb/IIIa immunoreactivity following perfusion of collagen-coated surfaces or artery sections with blood and plasmin, neutrophil elastase or thrombin. Within the time frame of minutes no VWF cleavage could be detected under static or flow conditions after exposure to MMP-8 and MMP-9 at concentrations relevant to physiological neutrophil counts.

Conclusion

Our results indicate a shear- and platelet-dependent role for several proteases in the local modulation of the VWF function.

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

BACKGROUND AND PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

High von Willebrand factor levels are associated with stroke risk in the general population.

Neutrophil granulocyte-dependent proteolysis enhances platelet adhesion to the arterial wall under high-shear flow

SUMMARY BACKGROUND

Under high shear stress platelets adhere preferentially to the adventitia layer of the arterial vessel wall in a von Willebrand factor (VWF)-dependent manner.

OBJECTIVE

The present study was undertaken in an attempt to characterize the structural background of the relative thromboresistance of the media and the impact of neutrophil leukocyte-derived proteases (matrix metalloproteinases, neutrophil elastase) on platelet adhesion in this layer of the arteries.

METHODS AND RESULTS

Platelet adhesion to cross-sections of the human iliac artery was monitored by indirect immunofluorescent detection of GpIIb/IIIa antigen. Exposure of the vessel wall to activated neutrophils or neutrophil-derived proteases increased platelet adhesion to the media about tenfold over the control level at 3350 s(-1) surface shear rate. In parallel with this enhanced thrombogenicity morphological changes in the media were evidenced by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The fine proteoglycan meshwork seen with Cupromeronic Blue enhancement of the SEM images was removed by the proteolytic treatment and the typical collagen fiber structure was exposed on the AFM images of the media.

CONCLUSION

Through their proteases activated neutrophils degrade proteoglycans, unmask VWF binding sites and thus abolish the thromboresistance of the media in human arteries.

Relation of endothelial function to residual platelet reactivity after clopidogrel in patients with stable angina pectoris undergoing percutaneous coronary intervention

Platelet reactivity is greater in patients with stable angina and with more extensive peripheral vascular atherosclerosis. We sought to evaluate whether impaired peripheral microcirculatory endothelial function might correlate with platelet reactivity after clopidogrel and therefore predispose to an unfavorable outcome after percutaneous coronary intervention (PCI). In 52 consecutive patients with stable angina undergoing elective PCI, endothelial function was assessed by (1) endothelial peripheral arterial tonometry (measuring the "Endoscore"); (2) the von Willebrandt factor antigen level and ristocetin co-factor activity. Basal platelet reactivity was assessed by soluble P-selectin. Patients then received a 600-mg clopidogrel loading dose > or = 12 hours before PCI. A blood sample was withdrawn 12 hours later, but before PCI, to assess platelet reactivity using the P2Y12 reaction unit and percentage of P2Y12 inhibition with the point-of-care VerifyNow P2Y12 assay. Troponin T was assessed 24 hours after PCI. The Endoscore inversely correlated with von Willebrandt factor antigen activity (r = -0.52, p = 0.0001) and soluble P-selectin concentration (r = -0.36, p = 0.021), suggesting greater platelet reactivity with increased impaired endothelial function. After clopidogrel, the Endoscore correlated directly with the percentage of P2Y12 inhibition (r = 0.36, p = 0.009) and inversely with the P2Y12 reaction unit (r = -0.41, p = 0.002), suggesting greater residual platelet reactivity with more impaired endothelial function. The average Endoscore was significantly lower in patients with troponin T elevation (troponin positive group 0.267 + or - 0.091) than in patients without troponin T elevation (troponin negative group 0.508 + or - 0.041, p = 0.015 vs troponin positive). In conclusion, an impaired endothelial response before clopidogrel was associated with greater platelet reactivity after clopidogrel. This link might explain the unfavorable PCI outcomes in patients with more severe endothelial impairment.

Association between von Willebrand factor gene polymorphism and preeclampsia

AIMS

The aims of this study were to assess whether the Msp I polymorphism of von Willebrand factor (vWF)(intron 19) gene differs between patients with preeclampsia and normal pregnancies in Chinese Han population, and to study the relationship between the Msp I polymorphism in the vWF(intron 19) gene and severity of preeclampsia symptoms within the preeclampsia group.

METHODS

In this case-control study, peripheral blood samples of 70 patients with preeclampsia and 82 normal pregnancies were genotyped for the Msp I polymorphism in vWF(intron 19) gene on the basis of a hospital-based study. The genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and direct sequencing techniques.

RESULTS

The genotype frequencies for M+/M+, M+/M- and M-/M- were 22.9, 45.7 and 31.4% in patients with preeclampsia, and 1.2, 36.6 and 62.2% in normal pregnancies, respectively. The frequency of the M+ allele in patients with preeclampsia was significantly higher than in normal pregnancies (45.7 vs. 19.5%).

CONCLUSIONS

The Msp I polymorphism in intron 19 (M+ allele) of vWF gene is associated with the development and the severity of preeclampsia, and may be a susceptibility factor for preeclampsia.

Elevation of serum von Willebrand factor and anti-endothelial cell antibodies in patients with immunoglobulin A nephropathy are associated with intrarenal arterial lesions

AIM

Recent studies suggest that intrarenal arterial lesions are frequently observed in patients with immunoglobulin A nephropathy (IgAN). However, the mechanisms of the injury have not been elucidated. The level of serum von Willebrand factor (vWF) and the prevalence of anti-endothelial cell antibodies (AECA) were investigated in patients with IgAN with different intrarenal arterial lesions.

METHODS

Sera from 28 patients with mild intrarenal arterial lesions (group 1) and 36 patients with severe intrarenal arterial lesions (group 2) were collected. Sera from 20 patients with idiopathic membranous nephropathy (group 3) and 50 healthy volunteers were also obtained as disease and normal controls, respectively. Serum vWF and AECA of both IgG and IgA isotype were detected.

RESULTS

In comparison with normal controls, serum vWF was significantly higher in group 2 and group 3. Serum vWF was also significantly higher in group 2 than in group 1. Both IgG-AECA and IgA-AECA could be detected in three groups of patients. The prevalence of anti-87 kD IgG-AECA was greatest in patients in group 2. IgAN patients, especially those in group 2 with IgG-AECA or anti-87 kD IgG-AECA, had significantly higher serum creatinine and lower creatinine clearance than those without. No significant difference could be found for IgA-AECA. The level of serum vWF was higher in IgAN patients with IgG-AECA than that in patients without.

CONCLUSION

Intrarenal arterial lesions are associated with endothelial cell damage in IgAN, and vWF is a useful serological biomarker of severe intrarenal arterial lesions. AECA, especially IgG-AECA, may play an important role in the pathogenesis of intrarenal arterial damage in IgAN.

A systematic overview of the first pasteurised VWF/FVIII medicinal product, Haemate P/ Humate -P: history and clinical performance

Patients with von Willebrand disease (VWD) and haemophilia A (HA) lack, to varying degrees, the von Willebrand factor (VWF) and coagulation factor VIII (FVIII) that are critical for normal haemostasis. These conditions in turn make patients prone to uncontrolled bleeding. Historically, patients with severe forms of VWD or HA were crippled before adulthood and their life expectancy was significantly reduced. Over the past decades, specific coagulation factor replacement therapies including Haemate P, have been developed to help patients achieve and maintain normal haemostasis. Haemate P is a human, plasma-derived VWF/FVIII medicinal product, which was first licensed in Germany in 1981 for the treatment of HA-associated bleeding. It has since then come to be accepted as the gold standard for both the treatment and prophylaxis of bleeding in VWD, especially in cases where desmopressin [1-deamino-8-D-arginine vasopressin (DDAVP)] has been ineffective. Haemate P was the first effectively virus-inactivated (pasteurisation: 60 degrees C for 10 h in aqueous solution) FVIII product, whereby the risk of potentially threatening infective complications of plasma-derived products was reduced. Haemate P was also shown to have a VWF multimer profile remarkably close to that of normal plasma. This bibliographic review presents previously unpublished clinical data of Haemate P, based upon internal clinical study reports of the proprietor, CSL Behring, in addition to data already presented in other publications. The data demonstrate a predictable and well-characterised pharmacokinetic profile, and a proven record of short- and long-term safety, while effectively correcting the haemostatic defects in VWD and HA. Recently available data have also shown Haemate P to be of haemostatic value in exceptional clinical circumstances including surgical interventions. By virtue of its plasma-derived combination of VWF and FVIII, in addition to its high VWF:FVIII content ratio (2.4:1), Haemate P is also associated with successful immune tolerance induction in those patients developing inhibitor antibodies. Although the theoretical risk of thromboembolic complications does exist while receiving Haemate P, as it does with any FVIII replacement therapy, the incidence of such complications has remained notably low. Given the robust data that have accumulated for the use of Haemate P, dosing recommendations are also described in this review; the recommendations are tailored to patient-specific contexts including baseline VWF and FVIII levels in plasma and the type of surgical intervention being undertaken. A wide variety of studies have also provided data on paediatric and geriatric populations, all of which have suggested that Haemate P can be safely and effectively used in a wide variety of clinical circumstances.

Platelet adhesive dynamics. Part II: high shear-induced transient aggregation via GPIbalpha-vWF-GPIbalpha bridging

A three-dimensional multiscale computational model, platelet adhesive dynamics (PAD), is developed and applied in Part I and Part II articles to characterize and quantify key biophysical aspects of GPIbalpha-von-Willebrand-factor (vWF)-mediated interplatelet binding at high shear rates, a necessary and enabling step that initiates shear-induced platelet aggregation. In this article, an adhesive dynamics model of the transient aggregation of two unactivated platelets via GPIbalpha-vWF-GPIbalpha bridging is developed and integrated with the three-dimensional hydrodynamic flow model discussed in Part I. Platelet binding efficiencies predicted by PAD are in good agreement with platelet aggregation behavior observed experimentally, as documented in the literature. Deviations from average vWF ligand size or healthy GPIbalpha-vWF-A1 binding kinetics are observed in simulations to have significant effects on the dynamics of transient platelet aggregation, i.e., the efficiency of platelet aggregation and characteristics of bond failure, in ways that typify diseased conditions. The GPIbalpha-vWF-A1 bond formation rate is predicted to have piecewise linear dependence on the prevailing fluid shear rate, with a sharp transition in fluid shear dependency at 7200 s(-1). Interplatelet bond force-loading is found to be complex and highly nonlinear. These results demonstrate PAD as a powerful predictive modeling tool for elucidating platelet adhesive phenomena under flow.

[Von Willebrand factor, endothelial lesion, and ischemic heart disease]

OBJECTIVE

To analyze if the levels of von Willebrand factor (FvW) are higher in patients with ischemic heart disease than in healthy subjects and evaluate the relationship of these levels with clinical recurrence and coronary interventionism.

DESIGN

Observational prospective study.

PATIENTS

We analyzed the levels of FvW in 75 patients with ischemic heart disease who underwent coronary interventionism (Group I) and compared them with those of 30 healthy subjects with no cardiovascular risk factors and who, theoretically, had no coronary injuries (Group II).

MAIN VARIABLES

Levels of FvW before coronary interventionism (sample 0), 24 hours after (sample 1), and at three months of out-patient follow-up (sample 2). A single measurement was made of the FvW levels in Group II.

RESULTS

Subjects with ischemic heart disease had higher levels of FvW than healthy subjects (162+/-74% versus 95+/-33%; p=0.0001). FvW levels were significantly increased after coronary interventionism (162.4+/-74.9% in sample 0 versus 213+/-90% in sample 1; p=0.0001). Patients with clinical symptoms at three months have no significant difference regarding those with no symptoms in the FvW levels (125+/-63% versus 133+/-60%; p=0.57).

CONCLUSIONS

FvW levels reflect an endothelial alteration in patients with ischemic heart disease. The increase of the levels after coronary interventionism could be due to the endothelial aggression itself of the intervention. It was not possible to demonstrate higher levels of FvW in patients with symptoms in the three month follow-up.

Sustained FVIII expression and phenotypic correction of hemophilia A in neonatal mice using an endothelial-targeted sleeping beauty transposon

Hemophilia A, deficiency of coagulation factor VIII (FVIII), is an attractive candidate for gene therapy as expression of modest amounts of FVIII can provide therapeutic benefit. Most gene transfer approaches for hemophilia have focused on the liver, as this is the major source of endogenous FVIII; however, increasing evidence suggests that endothelial cells are capable of synthesis and release of FVIII. Here the Sleeping Beauty (SB) transposon is employed to target long-term expression of the human B-domain-depleted FVIII gene (approved gene symbol F8) within lung endothelia of hemophilic mice. As the formation of inhibitory antibodies to FVIII has been a significant impediment toward achieving therapeutic plasma levels after gene or protein therapy, we chose to perform gene transfer in neonatal mice, which are more likely to be immune tolerant. Using this approach, low therapeutic levels of FVIII ( approximately 10%), as well as phenotypic correction of the bleeding disorder, were achieved in all animals that received the FVIII transposon and functional transposase throughout the duration of the study (24 weeks). Rechallenge of these animals with additional gene transfer did not result in significant increases in FVIII levels, due mainly to increases in inhibitory antibodies. These studies demonstrate the feasibility of using endothelial-targeted SB transposons for the treatment of hemophilia A.

Impact of mutations in the von Willebrand factor A2 domain on ADAMTS13-dependent proteolysis

Classical von Willebrand disease (VWD) type 2A, the most common qualitative defect of VWD, is caused by loss of high-molecular-weight multimers (HMWMs) of von Willebrand factor (VWF). Underlying mutations cluster in the A2 domain of VWF around its cleavage site for ADAMTS13. We investigated the impact of mutations commonly found in patients with VWD type 2A on ADAMTS13-dependent proteolysis of VWF. We used recombinant human ADAMTS13 (rhuADAMTS13) to digest recombinant full-length VWF and a VWF fragment spanning the VWF A1 through A3 domains, harboring 13 different VWD type 2A mutations (C1272S, G1505E, G1505R, S1506L, M1528V, R1569del, R1597W, V1607D, G1609R, I1628T, G1629E, G1631D, and E1638K). With the exception of G1505E and I1628T, all mutations in the VWF A2 domain increased specific proteolysis of VWF independent of the expression level. Proteolytic susceptibility of mutant VWF in vitro closely correlated with the in vivo phenotype in patients. The results imply that increased VWF susceptibility for ADAMTS13 is a constitutive property of classical VWD type 2A, thus explaining the pronounced proteolytic fragments and loss of HMWM seen in multimer analysis in patients.

Comparison of sea turtle thrombocyte aggregation to human platelet aggregation in whole blood

The endangered sea turtles are living "fossils" that afford us an opportunity to study the hemostatic process as it likely existed millions of years ago. There are essentially no data about turtle thrombocyte aggregation prior to our studies. Thrombocytes are nucleated cells that serve the same hemostatic functions as the anucleated mammalian platelet. Sea turtle thrombocytes aggregate in response to collagen and beta-thrombin. Ristocetin induces an agglutination/aggregation response indicating the presence of a von Willebrand-like receptor, GPIb, found in all mammalian platelets. Samples treated with alpha-thrombin plus gamma-thrombin followed by ristocetin results in a rapid, stronger response than ristocetin alone. These responses are inhibited by the RGDS peptide that blocks fibrinogen cross-linking of mammalian platelets via the fibrinogen receptor, GPIIb/IIIa. Three platelet-like proteins, GPIb, GPIIb/IIIa and P-selection are detected in sea turtle thrombocytes by fluorescence activated cell sorting. Turtle thrombocytes do not respond to ADP, epinephrine, serotonin, thromboxane A2 mimetic, U46619, trypsin, or alpha-thrombin and gamma-thrombin added alone. Comparison of hemostasis in sea turtles to other vertebrates could provide a framework for understanding the structure/function and evolution of these pathways and their individual components.

A novel nanobody that detects the gain-of-function phenotype of von Willebrand factor in ADAMTS13 deficiency and von Willebrand disease type 2B

Von Willebrand factor (VWF) is unable to interact spontaneously with platelets because this interaction requires a conversion of the VWF A1 domain into a glycoprotein Ibalpha (GpIbalpha) binding conformation. Here, we discuss a llama-derived antibody fragment (AU/VWFa-11) that specifically recognizes the GpIbalpha-binding conformation. AU/VWFa-11 is unable to bind VWF in solution, but efficiently interacts with ristocetin- or botrocetin-activated VWF, VWF comprising type 2B mutation R1306Q, or immobilized VWF. These unique properties allowed us to use AU/VWFa-11 for the detection of activated VWF in plasma of patients characterized by spontaneous VWF-platelet interactions: von Willebrand disease (VWD) type 2B and thrombotic thrombocytopenic purpura (TTP). For VWD type 2B, levels of activated VWF were increased 12-fold (P < .001) compared to levels in healthy volunteers. An inverse correlation between activated VWF levels and platelet count was observed (R2 = 0.74; P < .003). With regard to TTP, a 2-fold (P < .001) increase in activated VWF levels was found in plasma of patients with acquired TTP, whereas an 8-fold increase (P < .003) was found in congenital TTP. No overlap in levels of activated VWF could be detected between acquired and congenital TTP, suggesting that AU/VWFa-11 could be used to distinguish between both disorders. Furthermore, it could provide a tool to investigate the role of VWF in the development of thrombocytopenia in various diseases.

Independent association of von Willebrand factor with surrogate markers of atherosclerosis in middle-aged asymptomatic subjects

Von Willebrand factor (VWF) is considered a reliable marker of endothelial damage. Plasma levels of VWF were measured in 857 middle-aged subjects (80.4% men) free of clinically overt atherosclerotic disease, in relation to cardiovascular risk factors, carotid intima-media thickness (IMT) and microalbuminuria, two established surrogate markers of atherosclerosis. There was linear trend for the increase of VWF, carotid IMT (p < 0.001) and microalbuminuria (p = 0.018). The association between VEF and both markers remained statistically significant after adjusting for cardiovascular risk factors and inflammatory markers (p < 0.01). In conclusion, VWF was independently associated with both structural and functional surrogates of atherosclerosis in asymptomatic subjects, thus representing a systemic biomarker of subclinical atherosclerosis.

A part le fibrinogène, les facteurs/marqueurs d’hémostase ont-ils aussi une place pour évaluer le risque d’accident cardiovasculaire ischémique ?

Most cardiovascular events result from a thrombotic complication of atherosclerotic lesions. In arterial vessels such as the coronary bed, an interrelationship of haemostatic, coagulation and fibrinolytic factors is implicated. While it can be demonstrated that fibrinogen is a risk factor/marker, the role of other factors is not well established. Under arterial flow conditions, platelets are predominantly involved in the thrombotic reaction. Yet, apart from a large increase in the platelet count, the involvement of platelet parameters in cardiovascular risk is not clearly evident. The lack of definitive platelet markers is at least partly due to the difficulty of studying platelet function ex vivo. Several polymorphisms of platelet glycoproteins carrying a moderate increase in risk have been reported, but only in younger patients. One potentially important factor for coagulation is the fibrin structure, which is dependent on fibrinogen, the rate of thrombin generation, the activity of factor XIII and the interrelationship of the cells concerned, all of which act on its sensitivity to thrombosis. Coagulation factors largely affect the rate of thrombin generation. The activity of the fibrinolytic system (and principally any deficiency) has a role in the cardiovascular risk. General markers of cardiovascular risk such as D-dimers are potentially useful, but they increase with thrombin generation and are decreased by a deficiency in fibrinolysis. Furthermore, possibly because they are not indicative of the fibrin structure, they are poorly correlated with clinical events. The poor significance of the available haemostatic, coagulation and/or fibrinolytic parameters is probably due to their lack of representativeness, since haemostatic, coagulation and fibrinolytic systems are all involved in the thrombotic response (and some in atherogenesis itself). Atherogenesis is a multifactorial process and numerous moderate risk factors act in association. Better predictability of the haemostatic tests would probably result from both the design of more representative tests and the evaluation of multiple parameters, and would lead to the definition of a risk score. Technological advances will make this possible.

Clinical significance of von Willebrand factor in patients with adult dermatomyositis

Because the clinical significance of von Willebrand factor (vWF), a marker of endothelial injury, has not been well studied in adult patients with dermatomyositis (DM), we evaluated whether plasma vWF levels are useful as an index of disease activity in these patients. We measured plasma vWF antigen levels in 11 patients with active adult DM, 13 patients with inactive DM, and 18 healthy subjects using an enzyme-linked immunosorbent assay. The association of vWF level with clinical condition and muscle-derived enzyme leakage among DM patients was examined using analysis of covariance and logistic regression analysis. Furthermore, we studied the effects of treatment on the vWF antigen level. The mean vWF antigen level was significantly higher in active DM patients than in inactive DM patients and healthy subjects. Higher vWF levels were associated with clinical symptoms, such as general fatigue, fever, and muscle weakness. They were also associated with the levels of aspartate aminotransferase, alanine aminotransferase, and aldolase, but not with those of lactate dehydrogenase and creatine kinase (CK). vWF antigen was correlated with muscle enzymes except for CK. The plasma vWF levels in six patients with active DM significantly decreased after successful corticosteroid treatment. Plasma vWF level may be considered a useful marker of disease activity in adult DM patients.

Presence and functional activity of the aryl hydrocarbon receptor in isolated murine cerebral vascular endothelial cells and astrocytes

Numerous functions regulated by the central nervous system (CNS) are targeted by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD); however, the cell specific targets and mechanisms of toxicity are unknown. Outside of the brain, the peripheral vascular endothelium has been identified as a significant cellular target of TCDD toxicity resulting in apoptosis, edema, hemorrhaging and vascular dysfunction. Possible effects of TCDD in the vascular endothelium of the CNS have not been examined. Cellular dysfunction in this endothelium may disrupt function of the blood-brain barrier (BBB), which could severely compromise neuronal homeostasis and potentiate neurotoxicity. TCDD toxicity is mediated primarily by the aryl hydrocarbon receptor (AhR), a ligand activated transcription factor that modulates the expression of a large battery of genes. This study examined the presence and functional activity of the AhR in response to TCDD in endothelial cells and astrocytes, the two primary components of the BBB. Primary mouse cortical endothelial cells and astrocytes express the AhR, as shown by immunocytochemical and western blot analyses. AhR activity was assessed by time- and concentration-dependent analyses of CYP1A1 and CYP1B1 protein expression following TCDD treatment. Both CYP1A1 and CYP1B1 proteins were induced in endothelial cells after 4 and 8h, respectively, while only CYP1B1 protein induction was detected in astrocytes after 16h. The CYP450 protein induction was sustained for greater than 72h in both cell types. These changes in protein expression were dependent on AhR activity as indicated by the inhibition of these responses by a receptor antagonist. Together these data indicate endothelial cells and astrocytes are responsive to TCDD through the AhR-mediated pathway and therefore could be targets of toxicity.

Molecular modeling of the von Willebrand factor A2 Domain and the effects of associated type 2A von Willebrand disease mutations

A homology model for the A2 domain of von Willebrand factor (VWF) is presented. A large number of target-template alignments were combined into a consensus alignment and used for constructing the model from the structures of six template proteins. Molecular dynamics simulation was used to study the structural and dynamic effects of eight mutations introduced into the model, all associated with type 2A von Willebrand disease. It was found that the group I mutations G1505R, L1540P and S1506L cause significant deviations over multiple regions of the protein, coupled to significant thermal fluctuations for G1505R and L1540P. This suggests that protein instability may be responsible for their intracellular retention. The group II mutations R1597W, E1638K and G1505E caused single loop displacements near the physiologic VWF proteolysis site between Y1605-M1606. These modest structural changes may affect interactions between VWF and the ADAMTS13 protease. The group II mutations I1628T and L1503Q caused no significant structural change in the protein, suggesting that inclusion of the protease in this model is necessary for understanding their effect. [Figure: see text]. Homology model of the von Willebrand factor A2 domain

Effects of inflammatory cytokines on the release and cleavage of the endothelial cell-derived ultralarge von Willebrand factor multimers under flow

ADAMTS13 cleaves ultralarge and hyperreactive von Willebrand factor (ULVWF) freshly released from activated endothelial cells to smaller and less active forms. This process may be affected by the amount of ULVWF released and the processing capacity of ADAMTS13, contributing to the development of thrombotic diseases. We examined the effects of inflammatory cytokines on the release and cleavage of ULVWF to evaluate potential links between inflammation and thrombosis. Human umbilical vein endothelial cells were treated with interleukin 6 (IL-6), IL-8, or tumor necrosis factor alpha (TNF-alpha), and the formation of platelet-decorated ULVWF strings was quantitated. IL-8 and TNF-alpha significantly stimulated the release of ULVWF in a dose-dependent manner. IL-6 induced ULVWF release only when it was in complex with the soluble IL-6 receptor. IL-6, but not IL-8 nor TNF-alpha, inhibited the cleavage of ULVWF strings by ADAMTS13 under flowing, but not static, conditions. These results suggest that inflammatory cytokines may stimulate the ULVWF release (IL-8 and TNF-alpha) and inhibit the ULVWF cleavage (IL-6), resulting in the accumulation of hyperreactive ULVWF in plasma and on the surface of endothelial cells to induce platelet aggregation and adhesion on the vascular endothelium. The findings describe a potential linkage between inflammation and thrombosis that may be of therapeutic importance.

P-selectin anchors newly released ultralarge von Willebrand factor multimers to the endothelial cell surface

von Willebrand factor (VWF) released from endothelium is ultralarge (UL) and hyperreactive. If released directly into plasma, it can spontaneously aggregate platelets, resulting in systemic thrombosis. This disastrous consequence is prevented by the ADAMTS13 (ADisintegrin and Metalloprotease with ThromboSpondin motif) cleavage of ULVWF into smaller, less active forms. We previously showed that ULVWF, on release, forms extremely long stringlike structures. ADAMTS13 cleaves these strings under flow significantly faster than it does under static conditions. As ULVWF tethering to endothelium is important for its rapid proteolysis, we investigated 2 molecules for their potential to anchor the ULVWF strings: P-selectin and integrin alpha v beta 3. We demonstrated that P-selectin anchors ULVWF to endothelium by several means. First, Chinese hamster ovary (CHO) cells expressing P-selectin specifically adhered to immobilized ULVWF and ULVWF-coated beads to immobilized P-selectin. Second, an anti-VWF antibody coimmunoprecipitates P-selectin from the histamine-activated endothelial cells. Third, P-selectin antibody or soluble P-selectin, but not a alpha v beta 3 antibody, RGDS peptide, or heparin, blocked the formation of ULVWF strings. Fourth, P-selectin expression was in clusters predominantly along the ULVWF strings. Finally, the strength of the minimal ULVWF-P-selectin bond was measured to be 7.2 pN. We, therefore, conclude that P-selectin may anchor ULVWF strings to endothelial cells and facilitate their cleavage by ADAMTS13.

ADAMTS-13 metalloprotease interacts with the endothelial cell-derived ultra-large von Willebrand factor

Thrombotic thrombocytopenic purpura is caused by congenital or acquired deficiency of ADAMTS-13, a metalloprotease that cleaves the endothelium-derived ultra-large multimers of von Willebrand factor (ULVWF). The proteolysis converts hyper-reactive and thrombogenic ULVWF into smaller and less adhesive plasma forms. Activity of ADAMTS-13 is usually measured in a static system under non-physiological conditions that require protein denaturation and prolonged incubation. We have demonstrated previously that ULVWF multimers, upon release from endothelial cells, form platelet-decorated string-like structures that are rapidly cleaved by ADAMTS-13. Here we report the direct interaction between ADAMTS-13 and VWF under both static and flowing conditions. ADAMTS-13-coated beads adhered to both immobilized VWF and ULVWF strings presented by stimulated endothelial cells. These beads adhered to VWF under both venous (2.5 dynes/cm2) and arterial (30 dynes/cm2) shear stresses. We then demonstrated that ADAMTS-13 beads adhered to immobilized recombinant VWF-A1 and -A3 domains, but soluble metalloprotease bound preferentially to the A3 domain, suggesting that the VWF A3 domain may be the primary docking site for the metalloprotease. We suggest that tensile stresses imposed by fluid shear stretch endothelial bound ULVWF multimers to expose binding sites within the A domains for circulating ADAMTS-13. The bound enzyme then cleaves within the A2 domain that lies in close proximity and releases smaller VWF multimers into the plasma. Once released, these cleaved VWF fragments become inaccessible for the metalloprotease to prevent further cleavage.

Type 2B vWD: the varied clinical manifestations in two kindreds

Type 2B von Willebrand's disease (vWD) is associated with spontaneous binding of large von Willebrand factor (vWF) multimers to platelets in vivo, followed by clearance of both the large multimers and platelets resulting in thrombocytopenia, which may be intermittent, mild to severe, and may be exacerbated by stress such as infection or pregnancy. We report our experience in two kindreds (49 caucasian individuals) with type 2B vWD and discuss their varied clinical manifestations. The largest kindred (45 patients) was traced back five generations to a presumed index case. The genetic defect in this kindred was identified as a missense mutation, with a C to T transition at a CpG dinucleotide (nucleotide 3916) resulting in an amino acid substitution (Arg 543 to Trp) within the glycoprotein Ib binding domain of vWF. Ristocetin cofactor activity varied from < 10 to 28%, and factor VIII activity from 7 to 69%. Analysis of von Willebrand multimers consistently revealed loss of large molecular weight forms. Platelet counts in those with thrombocytopenia varied from 10 x 10(9) L(-1) to 120 x 10(9) L(-1). The severity of thrombocytopenia has also varied within the same individual during the period of follow-up. The clinical manifestations were varied and ranged from mild to moderate spontaneous bleeding episodes, including epistaxis, menorrhagia and gastro-intestinal haemorrhage. Severe bleeding episodes were observed in those undergoing surgery (both elective and non-elective), and in a few patients despite aggressive replacement with exogenous source of intact vWF, antifibrinolytics when indicated, and a near normal platelet count. Thrombotic disease may be a rare and unusual sequela of this disorder as was noted in one of our patients. Obtaining a platelet count at birth in infants of mothers with type 2B vWD who exhibit thrombocytopenia, may help in the earlier detection of infants at risk for thrombocytopenia.

The Sma I polymorphism in the von Willebrand factor gene associated with acute ischemic stroke

The von Willebrand factor (vWF) is a highly multimerized glycoprotein that promotes platelet adhesion and aggregation at a high shear rate, and also acts as a carrier of coagulation factor VIII. vWF has been identified as a risk factor for recurrent myocardial infarction in the general population. It has been reported that two polymorphisms of vWF gene promoter and the Thr789Ala polymorphism in vWF gene are associated with arterial thrombosis. The Sma I polymorphism is located in intron 2 of vWF gene. The relevance of this polymorphism to thrombotic disease was investigated by genotypic identification in two case-control studies: 107 patients with acute ischemic stroke, 49 patients with acute myocardial infarction (AMI), and 113 health controls age- and race-matched for each patient. Twenty-eight (26.2%) of the 107 patients with acute ischemic stroke, 8 (16.3%) of 49 patients with AMI, and 11 (9.7%) of 113 controls were found to be homozygous for CC genotype, respectively. The prevalence of the CC genotype in acute ischemic stroke was significantly higher than that of the normal controls (odds ratio [OR]=3.29, 95% confidence interval [CI]=1.54-7.01,.01>P>.001). However, the prevalence of the CC genotype in AMI was not significantly different from that of the normal controls (OR=1.81, 95% CI=0.68-4.82,.30>P>.20). Plasma vWF:Ag was also determined by enzyme-linked immunosorbent assay (ELISA) on the frozen plasma of 122 subjects. The mean plasma vWF:Ag levels of the controls, patients with acute ischemic stroke, and AMI were 0.468, 0.584, and 0.783 U/ml, respectively. The mean level of plasma vWF:Ag did not differ significantly between controls and patients with acute ischemic stroke (P=.195), but had significantly difference between controls and patients with AMI (P=.001). No association was found between the Sma I polymorphism and vWF plasma levels in controls, patients with acute ischemic stroke, or the AMI group (one-way ANOVA, P=.323, P=.315, P=.96). Results show that the Sma I polymorphism is strongly associated with increased risk of acute ischemic stroke, however, no association was observed between this polymorphism and AMI. This polymorphism of vWF may represent a newly identified risk factor for acute ischemic stroke in Chinese. Whether it is the real functional variant associated with acute ischemic stroke remains to be elucidated.

Purification of human von Willebrand factor-cleaving protease and its identification as a new member of the metalloproteinase family

von Willebrand factor (vWF) is synthesized in megakaryocytes and endothelial cells as a very large multimer, but circulates in plasma as a group of multimers ranging from 500 to 10 000 kd. An important mechanism for depolymerization of the large multimers is the limited proteolysis by a vWF-cleaving protease present in plasma. The absence or inactivation of the vWF-cleaving protease results in the accumulation of large multimers, which may cause thrombotic thrombocytopenic purpura. The vWF-cleaving protease was first described as a Ca(++)-dependent proteinase with an apparent molecular weight of approximately 300 kd. Thus far, however, it has not been isolated and characterized. In this study, the purification of human vWF-cleaving protease from a commercial preparation of factor VIII/vWF concentrate by means of several column chromatographic steps, including 2 steps of heparin-Sepharose column, is reported. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the anion exchange and gel filtration column fractions showed that the vWF-cleaving protease activity corresponded to a protein band of 150 kd. After reduction, it migrated with an apparent weight of 190 kd. The amino terminal sequence of the 150-kd band was AAGGIL(H)LE(L)L(D)AXG(P)X(V)XQ (single-letter amino acid codes), with the tentative residues shown in parentheses. A search of the human genome sequence identified the vWF-cleaving protease as a new member of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin type I motif) family of metalloproteinase. An active site sequence of HEIGHSFGLEHE (single-letter amino acid codes) was located at 150 residues from the N terminus of the protein.

Adherence properties of Staphylococcus aureus under static and flow conditions: roles of agr and sar loci, platelets, and plasma ligands

Global regulatory genes in Staphylococcus aureus, including agr and sar, are known to regulate the expression of multiple virulence factors, including cell wall adhesins. In the present study, the adherence of S. aureus RN6390 (wild type), RN6911 (agr), ALC136 (sar), and ALC135 (agr sar) to immobilized fibrinogen, fibronectin, von Willebrand factor (vWF), extracellular matrix (ECM), and human endothelial cells (EC) EAhy.926 was studied. Bacteria grown to postexponential phase were subjected to light oscillation (static condition) or to shear stress at 200 s(-1) (flow condition) on tissue culture polystyrene plates coated with either protein ligands, ECM, or EC. Adherence of nonlabeled bacteria to immobilized ligands was measured by an image analysis system, while adherence of [(3)H]thymidine-labeled S. aureus to ECM and EC was measured by a beta-scintillation counter. The results showed increased adherence of agr and agr sar mutants to immobilized fibrinogen and higher potential of these mutants to induce platelet aggregation in suspension, decreased adherence of sar and agr sar mutants to immobilized fibronectin and vWF as well as to ECM and EC, increased adherence of both S. aureus wild type and sar mutant to EC treated with platelet-rich plasma (PRP) compared to platelet-poor plasma (PPP) and to EC treated with PPP compared to the control, and increased adherence of S. aureus wild type to EC coated with PRP in which platelets were activated with phorbol 12-myristate 13-acetate compared to intact PRP. This finding paralleled the increased adherence to EC of activated compared to intact platelets. It is suggested that platelet-mediated S. aureus adherence to EC depends on platelet activation and the number of adherent platelets and available receptors on the platelet membrane. In conclusion, the agr locus downregulates S. aureus adherence to fibrinogen, while the sar locus upregulates S. aureus adherence to fibronectin, vWF, ECM, and EC. The effect of both agr and sar on S. aureus adherence properties develops primarily under flow conditions, which suggests different adhesion mechanisms in static and flow conditions.

Adrenaline potentiates type 2B von Willebrand factor-induced activation of human platelets by enhancing both the formation and action of thromboxanes

Von Willebrand factor (vWF) is a large plasma glycoprotein that mediates platelet adhesion at sites of vascular injury. We have previously reported that the pathological type 2B (formerly named type IIB) variant of vWF promotes platelet activation through phospholipase A(2)-mediated release of arachidonic acid. The present report shows that adrenaline (1 microM) potentiates type 2B vWF-induced platelet aggregation, serotonin secretion, rise in cytosolic Ca(2+) concentration, and pleckstrin phosphorylation, as well as thromboxane B(2) production. The hormone also increases the partially inhibited release of serotonin observed in platelets pretreated with the anti-GPIIb-IIIa antibody LJCP8 but does remove the total inhibition on the secretion caused by the anti-GPIb antibody LJIB1. Adrenaline also increases type 2B vWF-elicited tyrosine phosphorylation of proteins with apparent molecular masses of 60 and 80 kDa. Furthermore, adrenaline potentiates the rise in cytosolic Ca(2+) and the release of thromboxane B(2) in platelets stimulated with arachidonic acid (2 microM) as well as the increase in Ca(2+) induced by the thromboxane mimetic U46619 (0.3 microM). Platelet pretreatment with yohimbine or 13-azaprostanoic acid, which are antagonists of the alpha(2)-adrenergic and thromboxane receptors, respectively, or with acetylsalicylate and indomethacin, both of which act as inhibitors of thromboxane formation, abolishes the potentiating effect of adrenaline. These observations lead to the conclusion that the potentiating action of adrenaline on type 2B vWF-promoted platelet responses is due to an increase in both the formation and activating action of thromboxanes.

Increased glomerular deposits of von Willebrand factor in chronic, but not acute, rejection of primate renal allografts

BACKGROUND

In our previously described primate renal allograft model, T cell ablation leads to long-term graft survival. The role of endothelial cell alteration in chronic rejection was examined in our model.

METHODS

Renal transplants were performed in rhesus monkeys using a T cell- depleting immunotoxin, FN18-CRM9. Sections from 10 rejected kidneys (5 acute and 7 chronic rejection) were examined after immunohistochemical staining for expression of endothelium-related proteins [von Willebrand factor (vWF), CD62P, and CD31], fibrinogen, and a macrophage marker (CD68). Glomerular staining for each antigen was graded on a semiquantitative scale.

RESULTS

Intense staining for vWF was consistently observed in glomerular endothelium, subendothelium, and mesangium in all kidneys removed due to chronic rejection. vWF staining was weak in kidneys showing acute rejection. The difference in glomerular staining was statistically significant. Staining for vWF in extraglomerular vessels was nearly identical in kidneys showing acute and chronic rejection. Expression of CD62P was increased in extraglomerular vessels in allografts with chronic rejection, but the glomeruli showed little or no staining. There was no significant difference in the glomerular staining for CD62P or CD31 in organs showing acute and chronic rejection. Fibrinogen staining of glomerular mesangium was seen in kidneys with chronic rejection. Macrophages (CD68+) infiltrating glomeruli were more numerous in kidneys showing chronic rejection.

CONCLUSION

Increased glomerular deposition of vWF in renal allografts showing chronic rejection, without increased staining for CD62P or CD31, suggests increased constitutive secretion of vWF from endothelial cells as a component of the mechanism of chronic rejection in our model.

Aortic endothelial cell von Willebrand factor content, and circulating plasminogen activator inhibitor-1 are increased, but expression of endothelial leukocyte adhesion molecules is unchanged in insulin-dependent diabetic BB rats

Endothelial cell injury has been implicated in the increased incidence of vascular disease associated with diabetes mellitus. In diabetic humans, elevated plasma von Willebrand Factor (vWF) has been interpreted as an indication of endothelial damage. In contrast, in an animal model of inherited insulin-dependent diabetes, the bio-breeding (BB) rat, plasma vWF levels did not differ from those in age-matched control rats during the first 7 months of diabetes although morphological evidence of mild aortic endothelial alteration or injury was observed. In the present study efforts have been made to define the endothelial alterations in BB diabetic rats compared to controls more precisely over this time period. Thus, adhesion molecules: intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1(VCAM-1) were evaluated by in situ immunohistochemistry, vWF content was determined by biochemical analysis of aortic extracts and by quantitative immunohistochemistry, plasma vWF levels were measured by ELISA and vWF mRNA by RNAse protection assay. Neither age nor diabetic state significantly affected either the expression of adhesion molecules, or the levels of circulating vWF. Endothelial vWF content was significantly increased in the diabetic vessels, as observed by both approaches but the vWF mRNA content was not different from that in control vessels. Plasma plasminogen activator inhibitor (PAI-1) activity was significantly increased in diabetic animals. In conclusion, endothelial alterations in BB rats associated with diabetes, together with the raised plasma PAI-1 levels, promote the thrombogenic potential of the vessel wall, and are consistent with an increased risk for vascular disease.

Association between high von willebrand factor levels and the Thr789Ala vWF gene polymorphism but not with nephropathy in type I diabetes. The GENEDIAB Study Group and the DESIR Study Group

BACKGROUND

A genetic susceptibility for diabetic kidney disease is suspected since diabetic nephropathy occurs in only 30 to 40% of type I diabetic patients. As elevated von Willebrand factor (vWF) plasma concentrations have been reported to precede the development of microalbuminuria in type I diabetes, we addressed a possible implication of vWF as a genetic determinant for diabetic nephropathy.

METHODS

Three known vWF gene polymorphisms were genotyped in a group of 493 type I diabetic subjects, all showing proliferative retinopathy, but with various stages of renal involvement, which ranged from no microalbuminuria, despite a mean duration of diabetes of 31 years, to advanced nephropathy (GENEDIAB Study): Thr789Ala (Rsa I), M-/M+ (Msp I) (intron 19), and Ala1381Thr (Hph I). Plasma vWF and factor VIII (F VIII) levels were also measured in this population.

RESULTS

Plasma vWF and F VIII levels were increased in diabetic subjects with nephropathy (P < 0.001) or with coronary heart disease (CHD; P < 0.001), but there was no interaction of both conditions on plasma levels. The Msp I polymorphism (M-/M+) was weakly associated with nephropathy (P = 0. 04), but this association was not more significant when other risk factors were used in a logistic regression analysis. The vWF Thr789Ala polymorphism was associated with CHD (P = 0.002) and with plasma vWF levels. Logistic regression analysis indicated an independent and codominant effect of the Thr789Ala polymorphism on CHD, but not on nephropathy, with a maximal risk for Ala/Ala homozygotes (OR = 4.2, 95% CI, 1.8 to 9.9, P = 0.0008).

CONCLUSION

It is unlikely that polymorphisms in the vWF gene contribute to the risk for nephropathy in type I diabetic patients. However, the Thr789Ala polymorphism might affect the risk for CHD in this population through modulation of plasma vWF levels.

Evaluation of the von Willebrand factor antigen (vWF-Ag) assay using an immuno-turbidimetric method (STA Liatest vWF) automated on the MDA 180 coagulometer

The standard enzyme-linked immunosorbent assay (ELISA) test for von Willebrand factor antigen (vWF-Ag), though sensitive and specific, does not deliver the flexibility to handle single sample assessments economically or provide rapid, emergency testing capability. The present study examined the performance characteristics of an immuno-turbidimetric assay kit (STA Liatest) modified for automation on the MDA(R)180 coagulation analyser using a supplied protocol. One hundred and sixteen patient samples were assessed by both the standard and the modified method. The correlation coefficient was 0.98 across the range of values 1-487 IU/dl. Above 200 IU/dl, where specimen dilution was indicated, there was greater diversity (r = 0.86) between the techniques. Plotting the difference between methods against the mean of both showed excellent agreement between methods below 100 IU/dl vWF. The intra-assay and interassay coefficients of variation were less than 3% at both low and normal range levels. The MDA(R)180 automated vWF assay merits consideration as an alternative to ELISA testing that provides random access and result availability within 30 min.

Evidence for Extracellular Processing of Pro-von Willebrand Factor After Infusion in Animals With and Without Severe von Willebrand Disease

Although proteolytic processing of pro-von Willebrand factor (pro-vWF) resulting in free propeptide and mature vWF is known to be initiated intracellularly, vWF released from endothelial cells may contain a high proportion of incompletely processed pro-vWF. Because pro-vWF is only rarely detectable in normal human plasma, we investigated whether extracellular processing of pro-vWF is possible. A recombinant preparation (rpvWF) containing both pro-vWF and mature vWF subunits was infused into 2 pigs and 1 dog with severe von Willebrand disease, 2 mice with a targeted disruption of the vWF gene, and 2 healthy baboons. Total vWF antigen (vWF:Ag), free propeptide, and pro-vWF were measured using enzyme-linked immunosorbent assay techniques in blood samples drawn before and after infusion. vWF:Ag increased promptly. No pro-vWF could be detected when the first postinfusion sample was drawn after 30 minutes (pigs) or 60 minutes (mice), but pro-vWF was detectable for short periods when postinfusion samples were drawn after 15 minutes (dog) or 5 minutes (baboons). In contrast, free propeptide was increased at the first timepoint measured, suggesting that it was generated from the pro-vWF in the rpvWF preparation. vWF multimers were analyzed in the rpvWF preparation and in plasma samples drawn before and after infusion of rpvWF using ultra-high resolution 3% agarose gels to allow separation of homo- and hetero-forms of the vWF polymers. Within 30 minutes after infusion in the pigs, 1 hour in the dog and the mice, and within 2 hours in the baboons, the multimer pattern had changed to that typically seen in mature vWF. These data indicate that propeptide cleavage from unprocessed vWF can occur extracellularly in the circulation. The enzyme or enzymes responsible for this cleavage in plasma remain to be identified.

Evidence for Extracellular Processing of Pro-von Willebrand Factor After Infusion in Animals With and Without Severe von Willebrand Disease

Although proteolytic processing of pro-von Willebrand factor (pro-vWF) resulting in free propeptide and mature vWF is known to be initiated intracellularly, vWF released from endothelial cells may contain a high proportion of incompletely processed pro-vWF. Because pro-vWF is only rarely detectable in normal human plasma, we investigated whether extracellular processing of pro-vWF is possible. A recombinant preparation (rpvWF) containing both pro-vWF and mature vWF subunits was infused into 2 pigs and 1 dog with severe von Willebrand disease, 2 mice with a targeted disruption of the vWF gene, and 2 healthy baboons. Total vWF antigen (vWF:Ag), free propeptide, and pro-vWF were measured using enzyme-linked immunosorbent assay techniques in blood samples drawn before and after infusion. vWF:Ag increased promptly. No pro-vWF could be detected when the first postinfusion sample was drawn after 30 minutes (pigs) or 60 minutes (mice), but pro-vWF was detectable for short periods when postinfusion samples were drawn after 15 minutes (dog) or 5 minutes (baboons). In contrast, free propeptide was increased at the first timepoint measured, suggesting that it was generated from the pro-vWF in the rpvWF preparation. vWF multimers were analyzed in the rpvWF preparation and in plasma samples drawn before and after infusion of rpvWF using ultra-high resolution 3% agarose gels to allow separation of homo- and hetero-forms of the vWF polymers. Within 30 minutes after infusion in the pigs, 1 hour in the dog and the mice, and within 2 hours in the baboons, the multimer pattern had changed to that typically seen in mature vWF. These data indicate that propeptide cleavage from unprocessed vWF can occur extracellularly in the circulation. The enzyme or enzymes responsible for this cleavage in plasma remain to be identified.