Ratio Of Von Willebrand Factor Research Articles

ADAMTS13 related markers and von Willebrand factor in plasma from patients with thrombotic microangiopathy (TMA)

The ADAMTS13 (a disintegrin and metalloprotease with a thrombospondin type I domain 13) related markers were measured in the plasma of healthy volunteers and thrombotic microangiopathy (TMA) patients including thrombotic thrombocytopenic purpura (TTP) to examine their efficacy in the diagnosis of TTP. The plasma levels of the ADAMTS13 antigen and ADAMTS13-factor XI complex were significantly lower in TMA patients with a significant decreased ADAMTS13 activity (and these patients were considered to have TTP) than in the healthy volunteers. The plasma levels of ADAMTS13 antigens closely correlated with those of ADAMTS13-factor XI complex. Autoantibody for ADAMTS 13 was also positive in almost all TTP patients. In addition, the ratio of von Willebrand factor (VWF)/ADAMTS13 activity was significantly high in TTP suggesting that this ratio might be more useful for the differential diagnosis of TTP than the ADAMTS13 assay alone. These findings suggest that ADAMTS13 related markers are useful for the diagnosis and analysis of TTP.

Effect of oral anticoagulant therapy on thrombospondin-1 and von Willebrand factor in patients with stable heart failure

IntroductionHeart failure (HF) is associated with coagulation activation, abnormal inflammation and endothelial dysfunction. High levels of von Willebrand factor (VWF) may manifest endothelial dysfunction and hypercoagulable state. The haemostatic activity of VWF is a function of multimers size; only large multimers of VWF are haemostatically active. Thrombospondin-1 (TSP-1) reduces the average multimer size of VWF. Patients with HF are in risk of thromboembolic events and oral anticoagulation therapy (OAT) has been shown to prevent it. This study was designed to evaluate whether VWF and TSP-1 levels are modified by OAT in stable HF patients. The effect of OAT on markers of inflammation and coagulation was also investigated. Materials and methodsFifty-nine patients with stable HF were studied and 33 of them received OAT. VWF, TSP-1, fibrinogen, prothrombin fragment 1+2 (F1+2), tissue factor (TF), D-dimer, endogenous thrombin generation (ETG), C reactive protein (CRP), tumour necrosis factor α (TNFα) and interleukin 6 (IL-6) were measured. ResultsStable HF patients receiving OAT had higher VWF (p=0.02) and lower TSP-1 (p=0.02), ETG and F1+2 (p=0.003) than patients without OAT. However, there were no significant differences in the levels of fibrinogen, TF, D-dimer, CRP, IL6 and TNFα. The TSP-1/VWF ratio in patients receiving AOT was significantly lower than in patients without OAT (p=0.005). ConclusionOAT may have a dual effect on the haemostatic profile in stable HF by reducing thrombin generation and increasing the VWF. The decrease of TSP-1 induced by OAT may be clinically effective in neoangiogenesis. The increase of VWF in patients receiving anticoagulant treatment may also reflect an effect of OAT on endothelial dysfunction.

Clearance mechanisms of von Willebrand factor and factor VIII.

Clearance mechanisms of von Willebrand factor and factor VIII.

Impact of plasma von Willebrand factor levels in the diagnosis of type 1 von Willebrand disease: results from a multicenter European study (MCMDM-1VWD).

Presence of bleeding symptoms, inheritance and reduced von Willebrand factor (VWF) contribute to the diagnosis of type 1 von Willebrand disease (VWD). However, quantitative analysis of the importance of VWF antigen (VWF:Ag) and ristocetin cofactor activity (VWF:RCo) levels in the diagnosis is lacking. To evaluate the relative contribution of VWF measurement to the diagnosis of VWD. From the MCMDM-1VWD study cohort, 204 subjects (considered as affected by VWD based on the enrolling Center diagnoses and the presence of linkage with the VWF locus) were compared with 1155 normal individuals. Sensitivity, specificity and diagnostic positive likelihood ratios (LR) of VWF:Ag and VWF:RCo were computed. ABO blood group was the variable most influencing VWF levels, but adjustment of the lower reference limit for the ABO group did not improve sensitivity and specificity of VWF:Ag or VWF:RCo. The lower reference limit (2.5th percentile) was 47 IU dL(-1) for both VWF:Ag and VWF:RCo and showed similar diagnostic performance [receiver-operator curve area: 0.962 and 0.961 for VWF:Ag and VWF:RCo, respectively; P = 0.81]. The probability of VWD was markedly increased only for values below 40 IU dL(-1) (positive LR: 95.1 for VWF:Ag), whereas intermediate values (40 to 60 IU dL(-1)) of VWF only marginally indicated the probability of VWD. Although the conventional 2.5 lower percentile has good sensitivity and specificity, only VWF:Ag or VWF:RCo values below 40 IU dL(-1) appear to significantly indicate the likelihood of type 1 VWD. The LR profile of VWF level could be used in a diagnostic algorithm.

Efficacy and safety of a high purity, double virus inactivated factor VIII/von Willebrand factor concentrate (Biostate®) in patients with von Willebrand disorder requiring invasive or surgical procedures

Biostate is a double virally inactivated, plasma derived coagulation factor VIII (FVIII)/von Willebrand factor (VWF) concentrate registered and used in Australia, New Zealand and Asia for the treatment of patients with haemophilia A. Although Biostate has been well characterized for FVIII and VWF (ratio 1:2 respectively) and shows a similar VWF multimeric pattern to normal plasma, limited published data is available on its clinical efficacy and safety in patients with von Willebrand disorder (VWD) who require surgical procedures. We retrospectively assessed the efficacy and safety of Biostate in all VWD patients treated at three Australian haemophilia treatment centres undergoing invasive procedures or surgery over a 29-month period between April 2003 and September 2005. A chart review of 43 VWD patients (26 VWD type 1, 12 VWD type 2, 5 VWD type 3; 21 male, 22 female; mean age 52 years, range 19-80 years) undergoing 58 surgical procedures (24 major, 34 minor) was performed. For each procedure, data were collected on Biostate dosage and administration, adverse reactions, haemostatic efficacy and bleeding events. Haemostatic efficacy of Biostate was assessed as excellent in 78% or good in 22% of procedures. There were no bleeding events attributable to lack of efficacy in any patients. No adverse reactions related to the administration of Biostate were observed. These results suggest that Biostate is both safe and efficacious for the prevention of excessive bleeding in VWD patients undergoing surgery or invasive procedures.

Comparison of the pharmacokinetics of two von Willebrand factor concentrates [Biostate and AHF (High Purity)] in people with von Willebrand disorder

Plasma-derived factor concentrates are important in the management of von Willebrand disorder (VWD). In our geographic locality, a single viral inactivation step concentrate (AHF [High Purity]), has been replaced with one using a double viral inactivation step (Biostate). The aim of this study was to compare the pharmacokinetics of von Willebrand factor (VWF) and factor VIII (FVIII) after administration of AHF (High Purity) and Biostate. This study was a single-blind, randomised cross-over, multi-centre investigation in twelve people with VWD, comprising four type 3, two type 2B, one type 2M and five type 1 VWD. The subjects received a single infusion of 60 IU/kg ristocetin cofactor activity (VWF:RCo) of either AHF (High Purity) or Biostate, and after a minimum 15-day wash-out period they received the alternative product. Blood samples were collected for up to 48 hours after each dose for assay of FVIII coagulant activity (FVIII:C) and VWF by VWF:RCo, collagen binding capacity (VWF:CB) and antigen (VWF:Ag). As a measure of delivered VWF 'functionality' we calculated the area-under-the-concentration-time-curve (AUC) ratios of VWF:RCo to VWF:Ag and VWF:CB to VWF:Ag. The effect on platelet adhesiveness by PFA-100 closure times (CTs) was measured prior to and 30 minutes post infusion. VWF multimers were also assessed pre and post infusion. Pharmacokinetic parameters after AHF (High Purity) and Biostate were in close agreement for VWF:RCo (confirming dosing equivalence). Parameters for other study markers were also similar, although Biostate tended to yield relatively lower VWF:Ag and higher VWF:CB levels. Although AHF (High Purity) and Biostate resulted in similar levels of high-molecular-weight (HMW) multimers post-infusion, the relative level of HMW to low-molecular-weight (LMW) multimers were determined to be higher following Biostate. The relative levels of functional VWF (i.e. VWF:CB and VWF:RCo) to VWF:Ag were also higher in Biostate compared to AHF (High Purity). With both study products, PFA-100 CTs 30 minutes post infusion showed minor improvement for only some subjects. In conclusion, the pharmacokinetics of FVIII:C and VWF are not significantly different after administration of AHF (High Purity) and Biostate. Study parameters considered as 'in-vitro' markers of VWF 'functionality' or potential clinical efficacy (i.e. VWF:CB and VWF:RCo relative to VWF:Ag, level of HMW VWF relative to LMW-VWF) were determined to be higher for Biostate than AHF (High Purity). PFA-100 CTs did not adequately reflect changes in these VWF parameters. Based on these results, one would expect Biostate to be at least as effective, if not superior to AHF (High Purity) for the treatment of VWD.

Characterization of Recessive Severe Type 1 and 3 von Willebrand Disease (VWD), Asymptomatic Heterozygous Carriers Versus Bloodgroup O-Related von Willebrand Factor Deficiency, and Dominant Type 1 VWD

Recessive type 3 von Willebrand disease (VWD) is caused by homozygosity or double heterozygosity for two non-sense mutations (null alleles). Type 3 VWD is easy to diagnose by the combination of a strongly prolonged bleeding time (BT), absence of ristocetine-induced platelet aggregation (RIPA), absence of von Willebrand factor (VWF) protein, and prolonged activated partial thromboplastin time (aPTT) due to factor VIII:coagulant (FVIII:C) deficiency. VWD type 3 is associated with a pronounced tendency to mucocutaneous and musculoskeletal bleedings since early childhood. Carriers of one null allele are usually asymptomatic at VWF levels of 50% of normal. Recessive severe type 1 VWD is caused by homozygosity or double heterozygosity for a missense mutation. Recessive type 1 VWD differs from type 3 VWD by the presence of detectable von Willebrand factor: antigen VWF:Ag and FVIII:C levels between 0.09 and 0.40 U/mL. Patients with recessive type 1 VWD show an abnormal VWF multimeric pattern in plasma and/or platelets consistent with severe type 2 VWD. Carriers of a missense mutation may have mild bleeding and mild VWF deficiency and can be diagnosed by a double VWF peak on cross immunoelectrophoresis (CIE). There will be cases of mild and moderate recessive type 1 VWD due to double heterozygosity of two missense mutations, or with the combination of one missense mutation with a non-sense or bloodgroup O. Mild deficiency of VWF in the range of 0.20 to 0.60 U/mL, with normal ratios of von Willebrand factor: ristocetine cofactor/antigen VWF:RCo/Ag and VWF:collagen binding/antigen (VWF:CB/Ag), normal VWF multimers, and a completely normal response to desmopressin acetate (DDAVP) with VWF level rising from below to above 1.00 U/mL are very likely cases of so-called pseudo-VWF deficiency in individuals with normal VWF protein and gene. Autosomal dominant type 1 VWD variants are in fact type 2 variants caused by a heterozygous missense mutation in the VWF gene that produces a mutant VWF protein that has a dominant effect on normal VWF protein produced by the normal VWF allele with regard to the synthesis, processing, storage, secretion, and/or proteolysis of VWF in endothelial cells. A DDAVP challenge test clearly differentiates between dominant type 1 VWD phenotype and dominant type 2 M VWD.

Von Willebrand Factor Propeptide: Response to 1-Deamino-8-D-Arginine Vasopressin and Investigation of Relationship with Plasma Clearance of Von Willebrand Factor Antigen in Type 1 Von Willebrand Disease.

The propeptide of von Willebrand factor (VWFpp) has been demonstrated to be critical for multimerization and intracellular storage of the mature von Willebrand factor (VWF) protein. Although VWFpp and VWF have been shown to circulate at a distinct ratio in plasma, they are stored in endothelial cells in equimolar amounts and stimulation of the endothelium results in acute simultaneous release of these polypeptides in equimolar concentrations. This includes following DDAVP administration to healthy individuals. An increased ratio of plasma VWFpp to VWF antigen (VWF:Ag) may reflect increased clearance of VWF:Ag or reduced clearance of VWFpp. We have quantitated plasma VWFpp levels and the VWFpp to VWF:Ag ratio in patients with type 1 VWD and examined their relationship with the plasma clearance of VWF:Ag and VWFpp. We have also examined the endothelial release of VWFpp and VWF:Ag following DDAVP stimulation in these patients. Plasma molar VWF:Ag and VWFpp concentrations were determined by immunosorbent assay1 in 27 patients with type 1 VWD and 21 normal controls. In the VWD patients VWF:Ag and VWFpp levels were quantitated over 6 hours following the administration of intravenous DDAVP. The half-lives of VWF:Ag (VWF:Ag t1/2) and VWFpp (VWFpp t1/2) were calculated by determining the first-order rate constant for the elimination phase of the respective proteins.2 To determine the molar ratio of VWFpp and VWF:Ag released following DDAVP, values at 30 mins were extrapolated from semi-log plots of VWFpp and VWF:Ag against time. Median concentrations of VWFpp and VWF:Ag were 2.9nmol/L (range, 1.4–10.9) and 24.5nmol/L (2.5–42) pre-DDAVP in VWD group and 9.7nmol/L (5.8–18.1) and 51.5nmol/L (32–98.5) at baseline in normal subjects. The median VWFpp/VWF:Ag ratio was 0.13 (0.06–1.5) in the VWD group as compared to 0.23 (0.08–0.34) in the normals. Median VWF:Ag t1/2 and VWFpp t1/2 values in the VWD patients were 4 hours (0.9–8.7) and 2.5 hours (1.7–8) respectively. VWF:Ag normally has a half-life of 8–12 hours in plasma,3 while that of VWFpp is 2–3 hours.1 In the patient group, inverse correlation was found between VWFpp/VWF:Ag ratio and VWF:Ag t1/2, r=−0.48, p=0.01. There was also significant inverse correlation between VWFpp and VWF:Ag t1/2, r=−0.53, p<0.005. In contrast, there was no correlation between VWFpp/VWF:Ag ratio and VWFpp t1/2, r=−0.29, p>0.1. The values for VWFpp and VWF:Ag extrapolated 30 mins post DDAVP were corrected for baseline values and plotted to give a slope of 0.48, representing release of two moles of VWF per mole VWFpp in the patient group. The range of the plasma VWFpp/VWF:Ag ratio is wide in type 1 VWD patients and this may reflect heterogeneity in the pathophysiological processes, including post secretion events such as increased clearance of VWF:Ag, that contribute towards disease phenotype. The finding of inverse correlation between VWF:Ag t1/2 and the ratio of VWFpp to VWF:Ag indicates that increased plasma clearance of VWF:Ag is not associated with an increased VWFpp clearance in some patients with type 1 VWD. In addition, we have not demonstrated equimolar release of VWFpp and mature VWF in patients with type 1 VWD.

Cysteine-mutations in von Willebrand factor associated with increased clearance

von Willebrand disease (VWD) is a bleeding disorder caused by the decrease of functional von Willebrand factor (VWF). Low levels of VWF can result from decreased synthesis, impaired secretion, increased clearance or combinations thereof. Several mutations lead to impaired synthesis or secretion of VWF, however, little is known about the survival of VWF in the circulation. To evaluate the effect of several VWF mutations on VWF clearance. The effect of three cysteine-mutations (C1130F, C1149R or C2671Y) on the in vivo survival of VWF was studied in patients carrying these mutations and in a VWF-deficient mice model. In patients carrying these mutations, we observed increased propeptide/mature VWF ratios and rapid disappearance of VWF from the circulation after desmopressin treatment. Detailed analysis of in vivo clearance of recombinant VWF in a VWF-deficient mice model revealed a fourfold increased clearance rate of the mutants. The mutations C1130F, C1149R and C2671Y are each associated with reduced survival of VWF in the circulation. Detailed analysis of the recombinant mutant VWF demonstrated that increased clearance was not due to increased proteolysis by ADAMTS-13. We did not identify functional or structural characteristics that the mutant proteins have in common and could be associated with the phenomenon of increased clearance. Cysteine-mutations in VWF may result in reduced in vivo survival. The observation that various mutations are associated with increased in vivo clearance may have major implications for the therapeutic strategies that rely on the rise of endogenous VWF after desmopressin administration.

Reassessment of von Willebrand factor (VWF), VWF propeptide, factor VIII:C and plasminogen activator inhibitors 1 and 2 during normal pregnancy.

The use of von Willebrand factor [VWF antigen (WF:Ag)] measurement as a marker of endothelial cell activation for monitoring hypertensive pregnancies is limited by the poor definition of reference values. We reassessed these reference values using different assays, and those of the propeptide (VWF:Ag II) and factor VIII coagulant activity (factor VIII:C), in a large population of normal pregnancies, at 3-week intervals of gestational age. Plasminogen activator inhibitors (PAI-1 and PAI-2) were measured in parallel. Blood was collected at single time points between 12 weeks and delivery in 306 women undergoing normal singleton pregnancy. For clinical purposes, the VWF:Ag reference values were assay independent and the influence of ABO blood group on VWF:Ag or factor VIII:c was found to be limited during the third trimester. VWF:Ag II was not influenced by the ABO blood group. The ratio, VWF:Ag/factor VIII:C was close to 1.0 throughout pregnancy. In contrast, VWF:Ag II increased more slowly than VWF:Ag and the ratio of VWF:Ag II to VWF:Ag in plasma decreased from 1.00 to 0.5 at term. PAI-1 and PAI-2 increased with gestational age, but PAI-2 decreased during the last 2 weeks, indicating physiological placental regression at the very end of pregnancy.

Arterial flow conditions downregulate thrombomodulin on saphenous vein endothelium.

The antithrombogenic properties of venous endothelium may be attenuated when vein is implanted in the arterial circulation. Such changes may facilitate thrombosis, which is the final common pathway for saphenous vein arterial bypass graft occlusion. Using human saphenous vein in a validated ex vivo flow circuit, we investigated (1) the possibility that arterial flow conditions (mean pressure, 100 mm Hg, 90 cpm, approximately 200 mL/min) alter the concentration of proteins involved in regulating thrombosis at the vessel wall and (2) the influence of ion channel blockade on such effects. Concentrations of thrombomodulin and tissue factor were quantified by Western blotting (ratio of von Willebrand factor staining) and immunohistochemistry (as a percentage of CD31-staining area). Thrombomodulin concentrations after 90 minutes of venous and arterial flow conditions were quantified by immunostaining (68.9+/-4.8% and 41.0+/-3.0% CD31, respectively; P<0.01) and by Western blotting (1.35+/-0.20 and 0. 15+/-0.03 ratio of von Willebrand factor, respectively; P<0.01). The ability of endothelial cells to generate activated protein C also decreased from 62+/-14 to 19+/-10 ng. min-1. 1000 cells-1 (P=0.01). The significant reduction in thrombomodulin was attenuated if calcium was removed from the perfusate but not by external vein stenting. Inclusion in the vein perfusate of drugs that reduce calcium entry (including Gd3+, to block stretch-activated ion channels, and nifedipine) abolished the reduction in thrombomodulin concentration observed after arterial flow conditions. In freshly excised vein, negligible concentrations of tissue factor were detected on the endothelium and concentrations did not increase after 90 minutes of arterial flow conditions, although the inclusion of nifedipine caused the immunostaining to increase from 3.0+/-0.4% to 8.5+/-0.7% CD31 (P<0.02). In saphenous vein endothelium exposed to arterial flow conditions, there is rapid downregulation of thrombomodulin, sufficient to limit protein C activation, by a calcium-dependent mechanism.

Coagulation Parameters in Maternal and Cord Blood at Delivery

A wide range of hemostatic variables were studied in 300 maternal/neonatal pairs at the time of delivery and also in 375 healthy nonpregnant women who served as controls. There was significant prol...