Von Willebrand factor and von Willebrand disease

Von Willebrand factor in diagnostics and treatment of cardiovascular disease: Recent advances and prospects

Von Willebrand factor (VWF) is a large multimeric glycoprotein involved in hemostasis. It is essential for platelet adhesion to the subendothelium of the damaged endothelial layer at high shear rates. Such shear rates occur in small-diameter arteries, especially at stenotic sites. Moreover, VWF carries coagulation factor VIII and protects it from proteolysis in the bloodstream. Deficiency or dysfunction of VWF predisposes to bleeding. In contrast, an increase in the concentration of high molecular weight multimers (HMWM) of VWF is closely associated with arterial thrombotic events. Severe aortic stenosis (AS) or hypertrophic obstructive cardiomyopathy (HOCM) can deplete HMWM of VWF and lead to cryptogenic, gastrointestinal, subcutaneous, and mucosal bleeding. Considering that VWF facilitates primary hemostasis and a local inflammatory response at high shear rates, its dysfunction may contribute to the development of coronary artery disease (CAD) and its complications. However, current diagnostic methods do not allow for an in-depth analysis of this contribution. The development of novel diagnostic techniques, primarily microfluidic, is underway. Such methods can provide physiologically relevant assessments of VWF function at high shear rates; however, they have not been introduced into clinical practice. The development and use of agents targeting VWF interaction with the vessel wall and/or platelets may be reasonable in prevention of CAD and its complications, given the prominent role of VWF in arterial thrombosis.

Integrated Bioinformatics Analysis Reveals Novel miRNA as Biomarkers Associated with Preeclampsia

Preeclampsia is a leading cause of perinatal maternal-foetal mortality and morbidity. This study aims to identify the key microRNAs (miRNA) in preeclampsia and uncover their potential functions. We downloaded the miRNA expression profile of GSE119799 for plasma and GSE177049 for the placenta. Each dataset consisted of five patients (PE) and five controls (N). From a technical point of view, we analysed the counts per million (CPM) for both datasets, highlighting 358 miRNAs in common, 78 unique for plasma and 298 unique for placenta. At the same time, we performed an expression differential analysis (|logFC| ≥ 1|and FDR ≤ 0.05) to evaluate the biological impact of the miRNAs. This approach allowed us to highlight 321 miRNAs in common between plasma and placenta, within which four were upregulated in plasma. Furthermore, the same analysis revealed five miRNAs expressed exclusively in plasma; these were also upregulated. In conclusion, the in-depth bioinformatics analysis conducted during our study will allow us, on the one hand, to verify the targets of each of the nine identified miRNAs; on the other hand, to use them both as new non-invasive biomarkers and as therapeutic targets for the development of personalised treatments.

Towards novel treatment options in von Willebrand disease

Deficiency or dysfunction of von Willebrand factor (VWF) is associated with a bleeding disorder known as von Willebrand disease (VWD). The clinical manifestations of VWD are heterogeneous, and are in part dictated by the structural or functional defects of VWF. The tools to control bleeding in VWD are dominated by VWF concentrates, desmopressin and antifibrinolytic therapy. In view of these treatments being considered as effective, it is surprising that quality-of-life studies consistently demonstrate a significant mental and physical burden in VWD patients, particularly in women. Apparently, the current weaponry to support the management of VWD is insufficient to fully address the needs of the patients. It is important therefore to continue to search for innovative treatment options which could better serve the VWD patients. In this short review, two of such options are discussed in more detail: emicizumab to correct for the deficiency of factor VIII (FVIII), and the pegylated aptamer BT200 to increase endogenous levels of the VWF/FVIII complex.

Shear Stress-Induced Activation of von Willebrand Factor and Cardiovascular Pathology

The von Willebrand factor (vWF) is a plasma protein that mediates platelet adhesion and leukocyte recruitment to vascular injury sites and carries coagulation factor VIII, a building block of the intrinsic pathway of coagulation. The presence of ultra-large multimers of vWF in the bloodstream is associated with spontaneous thrombosis, whereas its deficiency leads to bleeding. In cardiovascular pathology, the progression of the heart valve disease results in vWF deficiency and cryptogenic gastrointestinal bleeding. The association between higher plasma levels of vWF and thrombotic complications of coronary artery disease was described. Of note, it is not the plasma levels that are crucial for vWF hemostatic activity, but vWF activation, triggered by a rise in shear rates. vWF becomes highly reactive with platelets upon unfolding into a stretched conformation, at shear rates above the critical value (more than 5000 s⁻¹), which might occur at sites of arterial stenosis and injury. The activation of vWF and its counterbalance by ADAMTS-13, the vWF-cleaving protease, might contribute to complications of cardiovascular diseases. In this review, we discuss vWF involvement in complications of cardiovascular diseases and possible diagnostic and treatment approaches.

Characterization of a Porcine Model for Von Willebrand Disease Type 1 and 3 Regarding Expression of Angiogenic Mediators in the Nonpregnant Female Reproductive Tract

Von Willebrand disease (VWD), a blood coagulation disorder, is also known to cause angiodysplasia. Hitherto, no animal model has been found with angiodysplasia that can be studied in vivo. In addition, VWD patients tend to have a higher incidence of miscarriages for reasons unknown. Thus, we aimed to examine the influence of von Willebrand factor (VWF) on the female reproductive tract histology and the expression and distribution of angiogenic factors in a porcine model for VWD types 1 and 3. The disease-causing tandem duplication within the VWF gene occurred naturally in these pigs, making them a rare and valuable model. Reproductive organs of 6 animals (2 of each mutant genotype and 2 wildtype (WT) animals) were harvested. Genotype plus phenotype were confirmed. Several angiogenic factors were chosen for possible connections to VWF and analyzed alongside VWF by immunohistochemistry and quantitative gene expression studies. VWD type 3 animals showed angiodysplasia in the uterus and shifting of integrin α_Vβ₃ from the apical membrane of uterine epithelium to the cytoplasm accompanied by increased vascular endothelial growth factor (VEGF) expression. Varying staining patterns for angiopoietin (Ang)-2 were observed among the genotypes. As compared with WT, the ovaries of the VWD type 3 animals showed decreased gene expression of ANG2 and increased gene expression of TIE (tyrosine kinase with immunoglobulin and epidermal growth factor homology domains) 2, with some differences in the ANG/TIE-system among the mutant genotypes. In conclusion, severely reduced VWF seems to evoke angiodysplasia in the porcine uterus. Varying distribution and expression of angiogenic factors suggest that this large animal model is promising for investigation of influence of VWF on angiogenesis in larger groups.

Enhanced processing of von Willebrand factor reflects disease severity and discriminates severe portal hypertension in cirrhosis

OBJECTIVES

Portal hypertension in cirrhosis is associated with endothelial dysfunction, impaired wound healing, and decreased platelet count. Increased von Willebrand factor (VWF) formation has been suggested as a compensatory mechanism, but the role of VWF processing has not been directly assessed. The aim was to measure the processing of activated VWF (VWF-A) in addition to VWF release (VWF-N) to investigate the association of primary hemostasis with disease activity and portal hypertension in liver cirrhosis.

PARTICIPANTS AND METHODS

Plasma samples from 105 participants undergoing liver vein catheterization and with liver cirrhosis of varying severity were included in the study together with 20 controls without liver disease. Competitive enzyme-linked immunosorbent assay format was used to estimate biomarkers of VWF turnover using neo-epitope-specific monoclonal antibodies.

RESULTS

VWF-N levels and VWF-A levels were significantly elevated in cirrhotic patients compared with controls (P<0.0001), and both markers could discriminate mild from severe cirrhosis (VWF-N, P<0.0001; VWF-A, P<0.05). Both markers correlated well with increasing portal hypertension and could identify patients with clinically significant portal hypertension (VWF-N, area under the curve: 0.78; VWF-A, area under the curve: 0.67). Only VWF-A significantly separated compensated from decompensated patients (P<0.05).

CONCLUSION

The data indicate that both VWF release and processing of active VWF are increased in cirrhosis, reflecting ongoing wound healing initiation. VWF-N and VWF-A may specifically contain information to assess the presence and severity of PHT as an early indicator of cirrhosis, and for acute damage in decompensated cirrhosis. Whether the increased wound healing affects long-term outcome needs to be addressed in future studies.

Evaluation of a modified thromboelastography assay for the screening of von Willebrand disease

Thromboelastography (TEG) has been shown to be a valuable point-of-care device for the rapid diagnosis of various bleeding disorders. However, TEG has thus far not been used for the screening for von Willebrand disease (VWD). We evaluated the performance of a modified TEG assay for the laboratory screening of VWD. Three hundred twenty-eight patients (148 male, 180 female, median age 8.4 years, range 0.1 – 72.7 years) were included in the study. The diagnosis and classification of patients was based on personal and familial case history, von Willebrand factor antigen, ristocetin cofactor levels, collagen binding assay, factor VIII coagulant activity and multimer analysis. The ratio of clot strength after preincubation with ristocetin, and without ristocetin, represents the component of clot strength that is formed by cross-linked fibrin fibres and is dependent on the agglutinated platelet fraction. The decrease of the maximum amplitude is a function of the ristocetin concentration and provides a diagnostic parameter able to differentiate between healthy individuals and patients having VWD. Based on a preliminary cut-off value of 25% for the area under the curve (AUC) ratio, the sensitivity varied from 53% to 100% for the different VWD patient groups. The test is suitable for use as a screening test using whole blood and has the additional benefit of being suitable as a point of care test. It appears also useful for monitoring responses to desmopressin (DDAVP) and infusion therapy.

Characterization of aberrant splicing of von Willebrand factor in von Willebrand disease: an underrecognized mechanism

Approximately 10% of von Willebrand factor (VWF) gene mutations are thought to alter messenger RNA (mRNA) splicing through disruption of consensus splice sites. This mechanism is likely underrecognized and affected by mutations outside consensus splice sites. During VWF synthesis, splicing abnormalities lead to qualitative defects or quantitative deficiencies in VWF. This study investigated the pathologic mechanism acting in 3 von Willebrand disease (VWD) families with putative splicing mutations using patient-derived blood outgrowth endothelial cells (BOECs) and a heterologous human embryonic kidney (HEK 293(T)) cell model. The exonic mutation c.3538G>A causes 3 in-frame splicing variants (23del, 26del, and 23/26del) which cannot bind platelets, blood coagulation factor VIII, or collagen, causing VWD through dominant-negative intracellular retention of coexpressed wild-type (WT) VWF, and increased trafficking to lysosomes. Individuals heterozygous for the c.5842+1G>C mutation produce exon 33 skipping, exons 33-34 skipping, and WT VWF transcripts. Pathogenic intracellular retention of VWF lacking exons 33-34 causes their VWD. The branch site mutation c.6599-20A>T causes type 1 VWD through mRNA degradation of exon 38 skipping transcripts. Splicing ratios of aberrant transcripts and coexpressed WT were altered in the BOECs with exposure to shear stress. This study provides evidence of mutations outside consensus splice sites disrupting splicing and introduces the concept that VWF splicing is affected by shear stress on endothelial cells.

Persimmon leaf flavonoid promotes brain ischemic tolerance

Persimmon leaf flavonoid has been shown to enhance brain ischemic tolerance in mice, but its mechanism of action remains unclear. The bilateral common carotid arteries were occluded using a micro clip to block blood flow for 10 minutes. After 10 minutes of ischemic preconditioning, 200, 100, and 50 mg/kg persimmon leaf flavonoid or 20 mg/kg ginaton was intragastrically administered per day for 5 days. At 1 hour after the final administration, ischemia/reperfusion models were estab-lished by blocking the middle cerebral artery for 2 hours. At 24 hours after model establishment, compared with cerebral ischemic rats without ischemic preconditioning or drug intervention, plasma endothelin, thrombomodulin and von Willebrand factor levels significantly decreased and intercel-lular adhesion molecule-1 expression markedly reduced in brain tissue from rats with ischemic pre-conditioning. Simultaneously, brain tissue injury reduced. Ischemic preconditioning combined with drug exposure noticeably improved the effects of the above-mentioned indices, and the effects of 200 mg/kg persimmon leaf flavonoid were similar to 20 mg/kg ginaton treatment. These results indicate that ischemic preconditioning produces tolerance to recurrent severe cerebral ischemia. However, persimmon leaf flavonoid can elevate ischemic tolerance by reducing inflammatory reactions and vascular endothelial injury. High-dose persimmon leaf flavonoid showed an identical effect to ginaton.

An update on type 2B von Willebrand disease

Type 2B von Willebrand disease (VWD) accounts for fewer than 5% of all VWD patients. In this disease, mutations in the A1 domain result in increased von Willebrand factor (VWF) binding to platelet GPIbα receptors, causing increased platelet clearance and preferential loss of high molecular weight VWF multimers. Diagnosis is complicated because of significant clinical variations even among patients with identical mutations. Platelet transfusion often provides suboptimal results since transfused platelets may be aggregated by the patients' abnormal VWF. Desmopressin may cause a transient decrease in platelet count that could lead to an increased risk of bleeding. Replacement therapy with factor VIII/VWF concentrates is the most effective approach to prevention and treatment of bleeding in type 2B VWD.

ADAMTS13 content in plasma-derived factor VIII/von Willebrand factor concentrates

Thrombotic thrombocytopenic purpura (TTP) is a microangiopathy syndrome caused by a congenital or acquired deficiency of ADAMTS13, a plasma metalloprotease that cleaves von Willebrand factor (VWF) and thus prevents the formation of platelet-rich thrombi in the microcirculation. TTP can be fatal if not appropriately and timely treated with the infusion of fresh frozen plasma (FFP) or exchange plasmapheresis, that reverse the process of microangiopathy by removing anti-ADAMTS13 autoantibodies and replacing functional ADAMTS13. The treatment of TTP with FFP is not free from risks and must be administered in hospitals or clinics, owing to the substantial amount of plasma volume infused or exchanged and the frequent need of catheter application. Moreover, most FFPs are not subjected to treatments to remove or inactivate blood-borne infectious agents. A number of recent reports indicate that certain plasma-derived VWF-factor VIII (FVIII) concentrates are clinically effective in the treatment of congenital TTP. In this study, we measured ADAMTS13 levels in various plasma-derived VWF-FVIII concentrates, showing that Koate(®) -DVI (Grifols), contained relatively high amounts of ADAMTS13 and that Alphanate(®) (Grifols) was the closest other product in terms of protease content. Koate(®) -DVI contains, on average (five lots tested), 0.091 ± 0.007 Units of ADAMTS13 activity per IU of FVIII. On the basis of this analysis and other reports of VWF-FVIII concentrate utilization in congenital TTP, potential dosing, and future clinical developments are discussed.

Antigenic Peptides Capable of Inducing Specific Antibodies for Detection of the Major Alterations Found in Type 2B Von Willebrand Disease

Von Willebrand disease (VWD) is an inherited hemorrhagic disorder promoted by either quantitative or qualitative defects of the von Willebrand factor (VWF). The disease represents the most common human coagulopathy afflicting 1.3% of the population. Qualitative defects are subdivided into four subtypes and classified according to the molecular dysfunction of the VWF. The differential diagnosis of the VWD is a difficult task, relying on a panel of tests aimed to assess the plasma levels and function of the VWF. Here, we propose biochemical approaches for the identification of structural variants of the VWF. A bioinformatic analysis was conducted to design seven peptides among which three were representatives of specific amino acid sequences belonging to normal VWF and four encompassed sequences found in the most common VWD subtype 2B. These peptides were used to immunize mice, after which, peptide-specific immunoglobulins were purified. This resulted in four Ig preparations capable of detecting alterations in the subtype 2B VWD plus additional three antibody fractions targeting the normal VWF. The panel of antibodies could serve many applications among them (1) assessment of VWF: antigen interaction, (2) VWF multimer analysis, and (3) production of monoclonal antibodies against VWF for therapeutic purposes as in thrombotic thrombocytopenic purpura.

[Management of bleeding disorders in intensive care medicine]

Bleeding disorders are frequent in intensive care medicine, the most common form being acquired. Trauma, gastrointestinal bleeding, liver failure, hematologic malignancies, and adverse drug reactions play an important role. Moderate to severe hereditary bleeding disorders are usually known prior to the acute disease state, while mild hereditary forms may manifest for the first time in association with the acute stress condition. Generally, proper history taking and structured observation are decisive in order to conduct an appropriate diagnostic workup and initiate logical hemostatic management. One cannot always wait for laboratory results during continuous blood loss or conditions such as hypothermia and acidosis. In such cases, pathophysiological extrapolation of expected hemostatic disturbances is essential for timely hemostatic management.

Platelet reactive conformation and multimeric pattern of von Willebrand factor in acquired thrombotic thrombocytopenic purpura during acute disease and remission

BACKGROUND

Binding of von Willebrand factor (VWF) multimers of ultra-large size to platelets is considered the triggering mechanism of microvascular thrombosis in thrombotic thrombocytopenic purpura (TTP).

OBJECTIVE

To assess the potential of VWF-related measurements as markers of disease activity and severity in TTP.

METHODS

VWF antigen (VWF:Ag), platelet glycoprotein-Ib-α binding-conformation (GPIb-α/BC) and multimeric pattern were investigated in 74 patients with acquired TTP during acute disease, remission or both and 73 healthy controls. In patients with both acute and remission samples available, VWF ristocetin co-factor activity (VWF:RCo) and collagen binding (VWF:CB) were also measured. The relationships of study measurements with the presence of acute disease and remission and with markers of disease severity were assessed.

RESULTS

VWF:Ag and VWF-GPIb-α/BC were higher in TTP patients than controls (P < 0.001 and 0.004). However, there was no statistically significant difference in VWF-GPIb-α/BC between samples obtained during acute TTP and remission. Larger VWF multimers were frequently lacking in acute TTP patients, who displayed ultra-large multimers at remission. The degree of loss of larger VWF multimers correlated with the degree of abnormality of hemoglobin, platelet counts and serum lactate dehydrogenase (LDH) and was associated with low levels of both VWF:RCo/Ag and VWF:CB/Ag ratios.

CONCLUSIONS

In TTP the platelet-binding conformation of VWF is not exclusively present in acute disease, nor is it associated with its clinical and laboratory severity. The loss of larger VWF multimers, accompanied by low VWF:RCo/Ag and VWF:CB/Ag ratio values, represents an index of disease activity and severity of acute TTP in patients with severe ADAMTS-13 deficiency.

A cluster of mutations in the D3 domain of von Willebrand factor correlates with a distinct subgroup of von Willebrand disease: type 2A/IIE

Among the different phenotypes of von Willebrand disease (VWD) type 2A, we identified a particular subgroup with a high frequency of 29%, characterized by a relative decrease of large von Willebrand factor (VWF) multimers and decreased A Disintegrin And Metalloproteinase with ThromboSpondin type 1 motifs, member 13 (ADAMTS13)-mediated proteolysis previously described in a single family as VWD type IIE (VWD2A/IIE). Phenotype and genotype of 57 patients from 38 unrelated families displaying a particular multimer pattern resembling the original VWD2A/IIE were studied. Pathogenicity of candidate mutations was confirmed by expression studies and phenotypic characterization of recombinant mutants. Specific mutations were identified in all patients. Twenty-two different mutations, most of them affecting cysteine residues, 17 of them being novel, are clustering mainly in the VWF D3 domain and correlate with the VWD2A/IIE phenotype. An intracellular retention of most mutants and/or a defect of multimerization seem to be the main pathogenic molecular mechanisms. ADAMTS13 proteolysis of mutant VWF was not different from wild-type VWF in a static assay, suggesting that reduced in vivo proteolysis is not an intrinsic property of mutant VWF. Our study identified a distinct VWD subtype with a common molecular background which contributes significantly to the heterogeneous spectrum of VWD.

A comparison of nano-electrospray gas-phase electrophoretic mobility macromolecular analysis and matrix-assisted laser desorption/ionization linear time-of-flight mass spectrometry for the characterization of the recombinant coagulation glycoprotein von Willebrand factor

Von Willebrand factor (VWF), an adhesive glycoprotein with an approximate molecular weight (MW) of the monomer of 260 kDa, circulates in human blood plasma as a series of multimers ranging in size up to 20.000 kDa; thus the determination of the accurate MW of the monomer is of great importance and due to its high MW quite challenging. In this study accurate MW determination of intact recombinant VWF monomer (rVWF) was performed with GEMMA (gas-phase electrophoretic mobility macromolecular analysis) and MALDI TOF MS (matrix-assisted laser desorption/ionization linear time-of-flight mass spectrometry). Three rVWF preparations with differing buffer systems and glycoprotein concentrations were analyzed. First investigations directed towards heterogeneity determination by means of capillary gel electrophoresis (CGE)-on-the-chip with a laser-induced fluorescence detector revealed two compounds (MW of 277 kDa (migration time 44.3 s) and 341 kDa (migration time 49.5 s)) present in each sample to varying extents, namely mature and pro-rVWF. MALDI MS analysis in the linear positive ion mode allowed the detection of mature rVWF with an exact MW of 256.1 kDa (+/-0.8%) and pro-rVWF with a MW of 349.8 kDa (+/-0.8%). Two samples containing pro-rVWF in very minor concentration resulted in GEMMA detection of the mature rVWF with a MW of 227.4 kDa (+/-2.5%), derived from the measured globular size of 10.9 nm. For one sample containing both rVWF species in almost equal concentrations no differentiation of the two species was possible with GEMMA. Due to its lower resolution only a peak representing a mixture of both species at 11.8 nm could be observed, yielding a MW of 298.8 kDa (+/-1.6%).

Prevalence of Von Willebrand Disease in Dogs from São Paulo State, Brazil

The aims of the current study were to assess the prevalence of von Willebrand disease (vWD) in dogs from the region of Botucatu, São Paulo State, Brazil, and to evaluate laboratory tests to diagnose this disease. The study included 350 dogs of various ages, different breeds, and both sexes. Dogs included in the study had no historical or clinical evidence of abnormal bleeding. von Willebrand factor antigen (vWF: Ag), buccal mucosal bleeding time, activated partial thromboplastin time, and factor VIII activity were evaluated in their ability to diagnose vWD. The prevalence of vWD in dogs was 1.43% in the Botucatu region of Brazil. Determination of vWF: Ag was the best laboratory test to diagnose vWD.

Endothelial cell confluence regulates Weibel-Palade body formation

Secretory granules called Weibel-Palade bodies (WPBs) containing Von Willebrand factor (VWF) are characteristic of the mammalian endothelium. We hypothesized that vascular-specific antigens such as VWF are linked to endothelial identity and proliferation in vitro. To test this idea, the cellular accumulation of VWF in WPBs was monitored as a function of cell proliferation, confluence and passage number in human umbilical vein endothelial cells (HUVECs). We found that as passage number increased the percentage of cells containing VWF in WPBs was reduced significantly, whilst the protein was still detected within the secretory pathway at all times. However, the endothelial-specific marker protein, PECAM-1, is present on all cells even when WPBs are absent, indicating partial maintenance of endothelial identity. Biochemical studies show that a significant pool of immature pro-VWF can be detected in sub-confluent HUVECs; however, a larger pool of mature, processed VWF is detected in confluent cells. Newly synthesized VWF must thus be differentially sorted and packaged along the secretory pathway in semi-confluent versus confluent endothelial cells. Our studies thus show that WPB formation is linked to the formation of a confluent endothelial monolayer.

Bleeding complications after oral surgery in outpatients with compromised haemostasis: incidence and management

PURPOSE AND RESULTS: The aim of this prospective study was to determine the incidence of postoperative bleeding after oral surgery under local anaesthesia performed in outpatients with haemostatic disorders within a 5-year period (2003-2007). One hundred twenty one (70 males, 51 females) out of 2,056 outpatients with different haemostatic disorders (acquired or hereditary) were included in this study. The following data were recorded: medical history and general condition; medications; indication for the surgical procedure; specification of local anaesthesia; applied surgical techniques, considering the kind of haemostatic disorder; and peri- or postoperative bleeding complications. Postoperative bleeding was observed in 12 patients (9.9%). In three cases, inpatient treatment became necessary. The management of two patients with a haemostatic disorder (von Willebrand s disease and haemophilia A) is presented in short case reports.

CONCLUSION

In a heterogeneous group of 121 outpatients with known haemostatic disorders, a combination of a few haemostatic agents with appropriate operative technique enables an effective wound management. In cases of failed local interventions after postoperative bleeding, further diagnostic investigations are required.

A highly-sensitive plasma von Willebrand factor ristocetin cofactor (VWF:RCo) activity assay by flow cytometry

BACKGROUND

Assays of plasma von Willebrand factor (VWF) ristocetin cofactor activity (VWF:RCo) are essential for the laboratory diagnosis of von Willebrand disease (VWD) and for monitoring therapy. However, current manual or automated VWF:RCo assay methods have relatively poor operating characteristics. Our goal was to develop and validate a simple, accurate, specific and sensitive platelet-based VWF:RCo assay.

METHODS

Using green or red fluorochrome-labeled, fixed normal platelets and normal or patient plasma, ristocetin-dependent and VWF-mediated platelet aggregation was detected by flow cytometry. VWF:RCo activity was assayed as the number of double-positive events (green and red) among all green or red events, relative to the calibrator plasma signal (6-150% or IU dL(-1)), and reported as percent or IU dL(-1). We tested plasma samples from normal donors (n = 51) and known VWD patients (type 1, n = 16; type 2, n = 17) based on clinical history, levels of plasma VWF antigen (VWF:Ag), VWF:RCo activity (manual platelet aggregometry/agglutination assay), factor (F) VIII activity and VWF multimer analysis.

RESULTS

For normal donors and type 1 VWD patients, VWF:RCo activity by flow cytometry vs. manual platelet aggregation correlated closely (R2 = 0.74), and VWF:RCo/VWF:Ag ratios did not differ significantly. In contrast, VWF:RCo/VWF:Ag ratios for type 2 VWD subtypes were significantly lower using VWF:RCo by flow cytometry vs. manual platelet aggregation assay (P < 0.01), especially for type 2A VWD patients.

CONCLUSIONS

This new flow cytometry-based VWF:RCo assay is simple, accurate, specific and sensitive, particularly for type 2 VWD.

Genetics of von Willebrand disease type 1

The most common form of von Willebrand disease (VWD) is reported to be type 1, accounting for as much as 80% of reported cases. With prevalence estimates as high as 1.6% in the general population, upwards of 4.5 million Americans may be affected. Unfortunately, VWD type 1 is also the most difficult type to diagnose. Despite the continuing progress in defining the genetic lesions responsible for VWD types 2 and 3, identification of the genetic determinants of VWD type 1 remains elusive. Herein the phenomenon known as VWD is summarized, the challenges associated with the diagnosis of type 1 VWD are described, and the role of genetic research in meeting these challenges is explored. The authors identify key gaps in the current genetics literature and suggest new avenues for future research. Lastly, they explore the role of nurses in this research and clinical endeavor. To the authors'knowledge, this review is the first to address these complex issues in nursing research.

Comparison of a new automated von Willebrand factor activity assay with an aggregation von Willebrand ristocetin cofactor activity assay for the diagnosis of von Willebrand disease

von Willebrand disease (VWD) is caused by quantitative and/or qualitative defects of von Willebrand factor (VWF). The HemosIL von Willebrand Factor Activity assay, a new automated immunological test to measure VWF activity, was implemented on STAC and compared with the von Willebrand ristocetin cofactor activity (VWF:RCo) aggregation method. Imprecision and dilution studies were also performed. Within-run imprecision was 17.2% and between-run imprecision was 8.3% (coefficients of variation). Dilution studies showed a linearity between 12.5 and 100%. Passing and Bablok regression comparing the HemosIL von Willebrand Factor Activity assay and the aggregation method yielded a slope of 1.25 (95% confidence interval: 1.11-1.38) and intercept of -1.40 (95% confidence interval: -8.07 to 0.00). The correlation coefficient was 0.84 (95% confidence interval: 0.78-0.89). With a cut-off value of 50% for VWF activity, the assay has a sensitivity of 94.1% and a specificity of 92.8%, compared with the VWF:RCo aggregation assay with a cut-off value of 60% producing a sensitivity of 100.0% (specificity 87.6%). With a cut-off value of 60%, the HemosIL von Willebrand Factor Activity assay on STAC is a reliable assay for VWD. VWF:RCo or other functional testing is still required to confirm the diagnosis and for further classification of VWD.

von Willebrand disease R1374C: type 2A or 2M? A challenge to the revised classification. High frequency in the northwest of Spain (Galicia)

Patients initially diagnosed with type 1 von Willebrand disease (VWD) have been reclassified as type 2 after a more exhaustive analysis in several studies. Our study's objectives were (1) to reanalyze patients that were previously diagnosed as type 1 to achieve a more accurate diagnosis and (2) to compare the von Willebrand factor (VWF) ristocetin cofactor assay (VWF:RCo) and the VWF collagen binding assay (VWF:CB) in order to evaluate the possibility of replacing the former assay with the latter in the diagnosis of VWD. Twenty-one patients from two large unrelated families and 104 normal controls were studied. VWF:Ag, VWF:RCo, FVIII coagulant activity (FVIII:C), bleeding time (BT), PFA(100), and multimeric analysis of VWF were tested. Genetic analysis by sequencing exon 28 on the VWF gene was also carried out. Patients presented lower levels of VWF:Ag and VWF:RCo, a dissociation between VWF:RCo/VWF:Ag, and the presence of all sizes of multimers in plasma VWF. The results for VWF:CB varied depending on the type of collagen used. The genetic analysis showed that the mutation R1374C is responsible for type 2M VWD. A high frequency of the R1374C mutation is observed in northwestern Spain (Galicia). Some types of 2M VWD are misdiagnosed as type 1 VWD. The VWF:CB (with type I collagen) assay was unable to discriminate defective platelet binding of the R1374C VWF. This confirms that VWF:CB cannot substitute for VWF:RCo, and both should be tested when diagnosing VWD.

Regulation of osteoblastic phenotype and gene expression by hop-derived phytoestrogens

Certain plant-derived compounds show selective estrogen receptor modulator (SERM) activity and may therefore be an alternative to the conventional hormone replacement therapy, which prevents osteoporosis but is also associated with an increased risk of breast and endometrial cancers. In the current study, we tested the effects of the hop-derived compounds 8-prenylnaringenin, 6-prenylnaringenin, xanthohumol and isoxanthohumol (1) to modulate markers of differentiation and gene expression in osteoblasts and (2) to regulate proliferation in MCF-7 breast cancer cells. Additionally, we analyzed the ER-binding affinities of these hop compounds as well as the ER-mediation of their effects. Bone-forming activity and ER-subtype specificity were investigated by measuring alkaline phosphatase (AP) activity in hFOB/ERalpha cells and regulation of gene transcription for AP, interleukin-6, pS2 and von Willebrand factor (VWF) in U-2 OS/ERalpha and U-2 OS/ERbeta cells. Our results demonstrate that AP, pS2 and VWF mRNA levels are significantly increased by the compounds in an estrogen-like manner via both ERalpha and ERbeta, while IL-6 is down-regulated in U-2 OS/ERalpha cells. Consistently, AP enzymatic activity is up-regulated by all compounds in hFOB/ERalpha9 cells. Depending on their concentration, all compounds show proliferative effects in MCF-7 cells. Except for 8-PN the hop constituents display an ERbeta-preference. Reversal of estrogen-specific AP-induction in Ishikawa cells indicates an ER-regulated mechanism. Finally, the flavonoids display cytotoxic effects only at high concentrations (> or =10(-4)M). In summary, we have demonstrated for the first time that specific phytoestrogen compounds found in hop extracts exert estrogen-like activities on bone metabolism. Regarding a potential for use in osteoporosis-prevention therapy, the dosage of a phytoestrogen, which is taken, will play an important role concerning a desired in vivo profile.

New perspectives on von Willebrand factor functions in hemostasis and thrombosis

The adhesive protein, von Willebrand factor (VWF), mediates the initiation and progression of thrombus formation at sites of vascular injury by means of specific interactions with extracellular matrix components and platelet receptors. The essential biologic properties of VWF have been elucidated, with progress particularly in the areas of genetic regulation, biosynthesis, and specific bimolecular interactions. The three-dimensional structure of selected domains has been solved, but our understanding of detailed structure-function relationships is still fragmented, partly because of the complexity and size of the VWF molecule. The biomechanical properties of the interaction between the VWF A1 domain and the platelet receptor glycoprotein (GP) Ibalpha also are better known, but we can still only hypothesize how this adhesive bond can oppose the fluid dynamic effects of rapidly flowing blood to initiate thrombus formation and contribute to platelet activation. Elucidating the details of VWF and GPIbalpha function will lead to a more satisfactory definition of the role of platelets in atherothrombosis, since hemodynamic forces greatly influence responses to vascular injury in stenosed and partially occluded arteries. Progress in this direction is also aided by rapidly expanding novel information on the mechanisms that regulate VWF multimer size in the circulation, a topic of relevance to explain microvascular thrombosis and, perhaps, arterial thrombosis in general. Developments in these areas of research will refine our understanding of the role played by VWF in vascular biology and pathology.

The von Willebrand factor self-association is modulated by a multiple domain interaction

BACKGROUND

Platelet adhesion and aggregation at sites of vascular injury exposed to rapid blood flow require von Willebrand factor (VWF). VWF becomes immobilized by binding to subendothelial components or by a self-association at the interface of soluble and surface-bound VWF.

OBJECTIVES

As this self-association has been demonstrated only under shear conditions, our first goal was to determine whether the same interaction could be observed under static conditions. Furthermore, we wanted to identify VWF domain(s) important for this self-association.

RESULTS

Biotinylated VWF (b-VWF) interacted dose-dependently and specifically with immobilized VWF in an enzyme-linked immunosorbent assay (ELISA) assay, showing that shear is not necessary to induce the VWF self-association. Whereas anti-VWF monoclonal antibodies (mAbs) had no effect on the self-association, the proteolytic VWF-fragments SpII(1366-2050) and SpIII(1-1365) inhibited the b-VWF-VWF interaction by 70 and 80%, respectively. Moreover, a specific binding of b-VWF to immobilized Sp-fragments was demonstrated. Finally, both biotinylated SpII and SpIII were able to bind specifically to both immobilized SpII and SpIII. Similar results were observed under flow conditions, which confirmed the functional relevance of our ELISA system.

CONCLUSION

We have developed an ELISA binding assay in which a specific VWF self-association under static conditions can be demonstrated. Our results suggest a multiple domain interaction between immobilized and soluble VWF.

Platelet function analysis

Since the last guidelines for BCSH platelet function testing were written in the late 1980s, many new tests have become available. Previously most platelet function tests were traditionally utilized to aid in the diagnosis and management of patients with platelet and haemostatic disorders. Most traditional tests were also largely restricted to the specialized laboratory or centre. However, nowadays there is also much renewed interest in monitoring the efficacy of anti-platelet therapy and measuring platelet hyper-function. A number of dedicated platelet function instruments have now become available that are much simpler to use and are beginning to be utilized as point of care instruments. These can now provide measurement of platelet function within whole blood without the requirement of sample processing. Some are also beginning to be incorporated into routine clinical use and can be utilized as not only as general screening tests of platelet function but to monitor anti-platelet therapy and to potentially assess both risk of bleeding and/or thrombosis. Modern flow cytometric-based platelet function analysis now also provides a wide variety of specific tests that can assess different aspects of platelet biology that are useful for diagnostic purposes. This review will highlight some of these of new tests/instruments and discuss their potential utility both within the haemostasis laboratory but also as potential point of care instruments.

A monoclonal antibody directed against human von Willebrand factor induces type 2B-like alterations

We have previously described a monoclonal antibody (mAb), 1C1E7, against von Willebrand factor (VWF), that increases ristocetin-induced platelet aggregation (RIPA) and induces a preferential binding of the high-molecular-weight multimers of VWF to platelet GPIb. Further investigations using a rotational viscometer at a shear rate of 4000 s(-1) could now demonstrate that shear-induced platelet aggregation (SIPA) is significantly increased with 1C1E7 and that this could be completely inhibited by the anti-GPIb mAb 6D1. In contrast, platelet adhesion to a collagen surface at a shear rate of 2600 s(-1), using a rectangular perfusion chamber, was significantly inhibited in the presence of 1C1E7. When citrated whole blood was incubated with 1C1E7, a spontaneous binding of VWF to the platelet GPIb could be demonstrated by flow cytometric analysis. Parallel to this, a decrease of the highest molecular weight multimers of VWF in the plasma was found. Platelets with bound VWF on their surface were able to form macroaggregates but were no longer able to adhere. These phenomena are very similar to the alterations described in von Willebrand's disease type 2B. The epitope of this mAb could be localized to the N-terminal part of the subunit; therefore a distant conformational change in the A1 domain of VWF is suggested.

Crystal structure of the wild-type von Willebrand factor A1-glycoprotein Ibalpha complex reveals conformation differences with a complex bearing von Willebrand disease mutations

The adhesion of platelets to the subendothelium of blood vessels at sites of vascular injury under high shear conditions is mediated by a direct interaction between the platelet receptor glycoprotein Ibalpha (GpIbalpha) and the A1 domain of the von Willebrand factor (VWF). Here we report the 2.6-A crystal structure of a complex comprised of the extracellular domain of GpIbalpha and the wild-type A1 domain of VWF. A direct comparison of this structure to a GpIbalpha-A1 complex containing "gain-of-function" mutations, A1-R543Q and GpIbalpha-M239V, reveals specific structural differences between these complexes at sites near the two GpIbalpha-A1 binding interfaces. At the smaller interface, differences in interaction show that the alpha1-beta2 loop of A1 serves as a conformational switch, alternating between an open alpha1-beta2 isomer that allows faster dissociation of GpIbalpha-A1, as observed in the wild-type complex, and an extended isomer that favors tight association as seen in the complex containing A1 with a type 2B von Willebrand Disease (VWD) mutation associated with spontaneous binding to GpIbalpha. At the larger interface, differences in interaction associated with the GpIbalpha-M239V platelet-type VWD mutation are minor and localized but feature discrete gamma-turn conformers at the loop end of the beta-hairpin structure. The beta-hairpin, stabilized by a strong classic gamma-turn as seen in the mutant complex, relates to the increased affinity of A1 binding, and the beta-hairpin with a weak inverse gamma-turn observed in the wild-type complex corresponds to the lower affinity state of GpIbalpha. These findings provide important details that add to our understanding of how both type 2B and platelet-type VWD mutations affect GpIbalpha-A1 binding affinity.

An experimental model to study the in vivo survival of von Willebrand factor. Basic aspects and application to the R1205H mutation

To explore the molecular basis of von Willebrand factor (VWF) clearance, an experimental model employing VWF-deficient mice was developed. Biodistribution was examined by the injection of radiolabeled VWF, which was primarily directed to the liver with minor amounts in other organs. Disappearance of VWF from plasma was characterized by a rapid initial phase (t((1/2))alpha = 13 min) and a slow secondary phase (t((1/2))beta = 3 h), with a mean residence time (MRT) of 2.8 h. A similar clearance was observed for VWF consisting of only high or low molecular weight multimers, indicating that, in our experimental model, clearance is independent of multimeric distribution. This allowed us to compare the survival of full-length VWF to truncated variants. Deletion of both the amino-terminal D'-D3 and carboxyl-terminal D4-CK domains resulted in a fragment with a similar clearance to wild-type VWF. Deletion of only the D'-D3 region was associated with an almost 2-fold lower recovery and increased clearance (MRT = 1.6 h), whereas deletion of only the D4-CK region resulted in a significantly reduced clearance (MRT = 4.5 h, p < 0.02). These results point to a role of the D'-D3 region in preventing clearance of VWF. Furthermore, replacement of D3 domain residue Arg-1205 by His resulted in a markedly increased clearance (MRT = 0.3 h; p = 0.004). Therefore, this mutation seems to abrogate the protective effect of the D'-D3 region. In vitro analysis of this mutant also revealed a 2-fold reduced affinity for VWF propeptide at low pH, showing that mutation of Arg-1205 results not only in an increased clearance rate but is also associated with an impaired pH-dependent interaction with VWF propeptide.

Gastrointestinal bleeding, angiodysplasia, cardiovascular disease, and acquired von Willebrand syndrome

Recent evidence points to isolated deficiency of the largest multimers of von Willebrand factor (VWF)-known as von Willebrand syndrome type 2A (VWS-2A)-as a risk factor for bleeding from gastrointestinal (GI) angiodysplasia. This disorder is not widely recognized, perhaps because most patients do not exhibit generalized hemostatic impairment (bleeding is generally restricted to GI angiodysplasia) and because all but the largest multimers of VWF remain detectable in the plasma (thus, routine screening tests for VWS-2A are usually normal). The "Rosetta stone" for elucidating this syndrome was the enigma of Heyde's syndrome (aortic stenosis plus bleeding GI angiodysplasia), particularly the striking observation that aortic valve replacement generally cures GI bleeding and that preoperative deficiency of the largest VWF multimers undergoes long-term normalization after valve replacement. We critically review the evidence implicating VWS-2A as a risk factor for bleeding GI angiodysplasia. We hypothesize that VWS-2A secondary to cardiovascular disease other than severe aortic stenosis, such as peripheral arterial occlusive disease, could explain why elderly patients often develop recurrent GI bleeding or iron deficiency anemia from GI angiodysplasia.

Estrogen receptor isoform-specific regulation of endogenous gene expression in human osteoblastic cell lines expressing either ER? or ER?

Estrogen (17beta-estradiol, E2) plays pivotal roles in the function and maintenance of the skeleton, including the bone-forming osteoblasts (OBs). The functions of E2 are largely mediated through two distinct estrogen receptor isoforms, ERalpha and ERbeta, both of which are expressed in OBs. The level of each isoform dominates at early or late stages of OB differentiation. To date, only a limited comparison between the transcriptional targets of ERalpha and ERbeta on endogenous gene expression has been reported. We have developed new stable cell lines, which contain doxycycline (Dox)-inducible ERalpha and ERbeta, in the U2OS human osteosarcoma to determine the global transcriptional profile of ERalpha- and ERbeta-regulation of endogenous gene expression. The U2OS-ERalpha and U2OS-ERbeta cell lines were treated with Dox and either vehicle control or E2 for 24 h. Gene expression analysis was performed using a microarray containing approximately 6,800 full-length genes. We detected 63 genes that were regulated solely by ERalpha and 59 genes that were only regulated solely by ERbeta. Of the ERalpha-regulated genes, 81% were upregulated and 19% were inhibited. Similarly 76% of the ERbeta-regulated genes were upregulated whereas 24% were inhibited by E2. Surprisingly, only 17 genes were induced by both ERalpha and ERbeta. Real-time PCR was employed to confirm the expression of a selected number of genes. The regulation of a number of known E2-responsive genes in human OBs, as well as many interesting novel genes, is shown. The distinct patterns of E2-dependent gene regulation in the U2OS cells by ERalpha and ERbeta shown here suggest that during OB differentiation, when either isoform dominates, a unique pattern of gene responses will occur, partially due to the differentiation state and the ER isoform present.