Luminographic Detection of von Willebrand Factor Multimers in Agarose Gels and on Nitrocellulose Membranes

VWF-ADAMTS13 axis dysfunction in children with sickle cell disease treated with hydroxycarbamide vs blood transfusion

Previous studies have reported elevated von Willebrand factor (VWF) levels in patients with sickle cell disease (SCD) and demonstrated a key role for the VWF-ADAMTS13 axis in the pathobiology of SCD vaso-occlusion. Although blood transfusion is the gold standard for stroke prevention in SCD, the biological mechanisms underpinning its improved efficacy compared with hydroxycarbamide are not fully understood. We hypothesized that the improved efficacy of blood transfusion might relate to differences in VWF-ADAMTS13 axis dysfunction. In total, 180 children with a confirmed diagnosis of SCD (hemoglobin SS) on hydroxycarbamide (n = 96) or blood transfusion (n = 84) were included. Despite disease-modifying treatment, plasma VWF and VWF propeptide were elevated in a significant proportion of children with SCD (33% and 47%, respectively). Crucially, all VWF parameters were significantly higher in the hydroxycarbamide compared with the blood transfusion cohort (P < .05). Additionally, increased levels of other Weibel-Palade body-stored proteins, including factor VIII (FVIII), angiopoietin-2, and osteoprotegerin were observed, indicated ongoing endothelial cell activation. Children treated with hydroxycarbamide also had higher FVIII activity and enhanced thrombin generation compared with those in the blood transfusion cohort (P < .001). Finally, hemolysis markers strongly correlated with VWF levels (P < .001) and were significantly reduced in the blood transfusion cohort (P < .001). Cumulatively, to our knowledge, our findings demonstrate for the first time that despite treatment, ongoing dysfunction of the VWF-ADAMTS13 axis is present in a significant subgroup of pediatric patients with SCD, especially those treated with hydroxycarbamide.

Increased cleavage of von Willebrand factor by ADAMTS13 may contribute strongly to acquired von Willebrand syndrome development in patients with essential thrombocythemia

BACKGROUND

Patients with essential thrombocythemia (ET) often experience bleeding associated with acquired von Willebrand syndrome (AVWS) when the platelet count is markedly increased.

OBJECTIVE

We investigated whether von Willebrand factor (VWF) degradation is enhanced in patients with ET.

METHODS

Seventy patients with ET underwent VWF multimer (VWFM) analysis and measurement of VWF-related parameters. We calculated the VWFM index, defined as the ratio of intensities of a patient's molecular weight-categorized VWFMs, and those of a healthy subject's, using densitometric analysis. VWF degradation product (DP) was measured via ELISA using a monoclonal antibody that specifically recognizes Y1605 at the C-terminal boundary, which is exposed following ADAMTS13-mediated cleavage of the Y1605-M1606 bond of the VWF A2 domain.

RESULTS

Patients with higher platelet counts had a significantly reduced high molecular weight (HMW)-VWFM index and an increased VWF-DP:VWF antigen (Ag) ratio compared to those with lower platelet counts. On multivariate analysis, the VWF-DP/VWF:Ag ratio was an independent predictor of the HMW-VWFM index. Patients who underwent cytoreductive therapy had a significantly higher HMW-VWFM index and lower VWF-DP/VWF:Ag ratio than those who did not. Among individual patients, there was also a significant increase in the HMW-VWFM index and a decrease in the VWF-DP/VWF:Ag ratio after cytoreductive therapy compared to pre-therapy values.

CONCLUSION

In patients with ET, an increased platelet count is associated with enhanced cleavage of VWF at the Y1605-M1606 bond, primarily by ADAMTS13, leading to AVWS. Cytoreductive therapy reduces the platelet count, prevents excessive VWF cleavage, and improves VWFM distributions.

Analysis focusing on plasma von Willebrand factor in pachychoroid neovasculopathy and age-related macular degeneration

Pachychoroid neovasculopathy (PNV) is a new concept of macular disorder. Some cases diagnosed as age-related macular degeneration (AMD) have been re-diagnosed as PNV. However, the biological features of PNV are still uncertain. The purpose of this study was to compare PNV and AMD by analyses focusing on von Willebrand factor (VWF) and complement factor H (CFH). Ninety-seven patients who were previously diagnosed with treatment naïve AMD were enrolled in this study. They were re-classified as either PNV or AMD based on the clinical criteria and 33 patients were classified as PNV and 64 patients as AMD. We examined the clinical data, analyzed VWF multimer and two genetic polymorphisms (I62V and Y402H) in the CFH. PNV group was significantly younger than AMD group (P = 0.001). In both I62V and Y402H, there were no significant differences between PNV and AMD while the recessive homozygous (AA) was found only in PNV group in I62V. The presence of unusually large VWF multimers (UL-VWFMs) and subretinal hemorrhages were significantly higher in PNV than in AMD (P = 0.045, P = 0.020, respectively). Thus, the residual UL-VWFMs may result in platelet thrombosis and hemorrhages in the choriocapillaris of PNV. In conclusion, our results suggest the biological differences between PNV and AMD.

Dual preparation of plasma and platelet concentrates in platelet additive solution from platelet concentrates in plasma using a novel filtration system

BACKGROUND AND OBJECTIVES

Platelet concentrates suspended in a platelet additive solution (PAS-PC) are associated with a reduction in allergic response and are suitable for preparing pathogen-inactivated PC. We aimed to develop an efficient platform for the dual preparation of PAS-PC and platelet-poor plasma.

MATERIALS AND METHODS

PAS-PC was prepared in six steps by using a hollow-fibre system based on cross-flow filtration: priming, loading PC, loading PAS, collection of filtered liquid (flow-through) and collection of platelets by washing with PAS followed by washing with air. In this study, the efficacy of platelet and plasma protein recovery and characteristics of recovered PAS-PC and flow-through plasma were analysed in detail.

RESULTS

Recoveries of platelet in PAS-PC and plasma protein in the flow-through were 95.4% ± 3.7% and 61.6% ± 5.0%, respectively. The residual plasma protein in PAS-PC was 34.1% ± 2.8%. Although the expression level of CD62P, a platelet activation marker, in recovered platelets was approximately 1.2-fold of that in original platelets, swirling patterns were well retained, and aggregation in PAS-PC was not visible. Agonist-induced aggregabilities, platelet morphology and hypotonic shock recovery were conserved. The patterns of plasma protein and lipoprotein in the flow-through were comparable with those in the original PCs. The multimeric pattern analysis of VWF remained unaltered.

CONCLUSION

We propose a highly efficient preparation system that enables the simultaneous production of PAS-PC and platelet-poor plasma. It also achieves a high recovery of functionally well-retained platelets with very low activation.

Management of a COVID-19 Patient during ECMO: Paying Attention to Acquired von Willebrand Syndrome

Patients with severe COVID-19 often experience complications including coagulopathy and fatal thrombosis. COVID-19 pneumonia sometimes leads to acute respiratory distress syndrome, requiring extracorporeal membrane oxygenation (ECMO), during which thrombosis and bleeding are major causes of death. Anticoagulation such as heparin is essential for COVID-19 patients on ECMO; however, bleeding might be caused by not only heparin, but also acquired von Willebrand syndrome (AVWS). To date, no study has examined ECMO-related bleeding and AVWS in COVID-19 patients.

We report a COVID-19 patient who experienced bleeding from AVWS in addition to disseminated intravascular coagulation (DIC) during ECMO. The level of high–molecular weight VWF multimers decreased during ECMO therapy, and these findings promptly improved after discontinuation of ECMO. Plasma levels of VWF antigen were extremely high, probably due to endothelial cell damage caused by COVID-19. On the other hand, plasma levels of ADAMTS13 activity were moderately reduced, to 20–30% of normal. The patient was successfully treated with cryoprecipitate in bleeding during ECMO without a reduction in heparin, which might have induced thromboembolism. Bleeding found in this patient might be caused by AVWS and DIC.

Severe COVID-19 patients are in a thrombotic state and need to receive anticoagulant therapy. However, once they receive ECMO therapy, bleeding symptoms could be observed. In such cases, physicians should think of AVWS in addition to the side effect of heparin and DIC.

Improving diagnosis of von Willebrand disease: Reference ranges for von Willebrand factor multimer distribution

BACKGROUND

Phenotypic von Willebrand disease (VWD) classification requires multiple tests including analysis of multimeric distributions von Willebrand factor (VWF) and evaluation of its structure. VWF multimer analysis is labor intensive, nonstandardized, and limited to specialized laboratories. A commercial semiautomatic assay, HYDRAGEL VW multimer assay (H5/11VWM, Sebia), has become available.

OBJECTIVES

Establishment of reference ranges for H5/11VWM to improve VWD classification.

METHODS

Implementation validation, establishment and validation of normal and pathological reference intervals (NRIs/PRIs), comparison with in-house method using 40 healthy volunteers and 231 VWD patients.

RESULTS

Qualitative and quantitative validation of NRI obtained sensitivity of 88% and 79%, respectively, for type 2. Comparison of the two methods showed an overall concordance of 86% with major conflicting results in all atypical 2B (n = 7) and 50% 2M-GPIb (n = 41) showing quantitative and qualitative multimeric loss, that was not detected with in-house method. We were able to use established PRIs, with 73% validity in type 2 cases, to distinguish individual type 2A subtypes (IIA, IIC, IID, IIE) from 2M and 2B.

CONCLUSION

H5/11VWM could be used for all clinical purposes because its reliability and its rapid and accurate diagnostic ability and reduced observer bias. Although H5/11VWM cannot evaluate triplet structures, we were able to define 2A subtypes by stripping back to the percentage of intermediate/high-molecular-weight multimers. H5/11HWM could be an efficient and widely available alternative for the "gold standard" technique.

Ischaemia-reperfusion injury with Pringle's maneuver induces unusually large von Willebrand factor multimers after hepatectomy

INTRODUCTION

von Willebrand factor (VWF) is synthesised in vascular endothelial cells and released into the plasma as unusually large VWF multimers (UL-VWFMs). Sinusoidal endothelial cells are a major target of ischaemia-reperfusion injury due to liver surgery. This study aimed to clarify the effect of hepatectomy on UL-VWFMs.

MATERIALS AND METHODS

Thirty-five patients who underwent hepatectomy were eligible for the study. Plasma ADAMTS13 activity and VWF antigen levels were measured by enzyme-linked immunosorbent assay and multimer analysis of plasma VWF was performed according to Ruggeri and Zimmerman's method. For analyses, patients were categorised according to UL-VWFM positivity after hepatectomy.

RESULTS

Plasma ADAMTS13 activity significantly decreased from 61.0% (27.7%-126.2%) before operation to 37.4% (20.2%-71.4%) on postoperative day 7 (p < 0.001). Plasma VWF antigen levels significantly increased from 172.1% (80.5%-412.8%) before operation to 361.0% (154.7%-745.8%) on postoperative day 2, which remained high until postoperative day 7 (p < 0.001). Seven patients remained UL-VWFMs-negative and 22 patients became UL-VWFMs-positive after operation. Pringle's maneuver duration was significantly longer and blood loss volume was significantly higher in the UL-VWFMs-positive group (p = 0.001 and p = 0.003, respectively). By multivariable analysis, Pringle's maneuver duration [odds ratio 1.049, 95% confidence interval (CI) 1.001-1.098; p = 0.043] was significantly associated with increased UL-VWFMs level after hepatectomy. UL-VWFMs index was significantly correlated with Pringle's maneuver duration (r = 0.444, p = 0.017).

CONCLUSIONS

Plasma UL-VWFMs levels increased after hepatectomy due to ischaemia-reperfusion injury with Pringle's maneuver.

Blood group antigen A on von Willebrand factor is more protective against ADAMTS13 cleavage than antigens B and H

BACKGROUND

ADAMTS13 specifically cleaves the peptide bond between Y1605 and M1606 within the VWF-A2 domain.

OBJECTIVE

The VWF contains ABO(H) blood group antigens, which may influence the susceptibility of VWF to ADAMTS13.

METHODS

Using a unique monoclonal antibody recognizing the Y1605 residue, we have developed a sandwich ELISA to analyze the generation of a VWF-DP by ADAMTS13 quantitatively.

RESULTS

Production of VWF-DP after exposure to four different degrees of high shear stress was validated in comparison to the reduction in high-molecular-weight multimers using VWF multimer analysis. In analysis of plasma from 259 healthy individuals, plasma levels of VWF antigen (VWF:Ag) were significantly lower in blood group O than in the other groups and were significantly correlated with plasma VWF-DP levels. The ratio between VWF-DP and VWF:Ag was significantly higher in blood group O than in blood groups A and AB. The ratio in blood group B was also significantly higher than those in A and AB, but did not differ from blood group O. Finally, to examine whether ABO(H) blood group antigens contributed to VWF cleavage, 82 plasma samples were exposed to high shear stress using a cone-plate shear stress inducer. The difference in the VWF-DP/VWF:Ag ratio before and after high shear stress in blood group O was significantly greater than those in groups A and AB.

CONCLUSION

These results indicate that blood group antigen A on VWF was more protective against ADAMTS13 cleavage than antigens B and H.

Involvement of the ADAMTS13-VWF axis in acute Kawasaki disease and effects of intravenous immunoglobulin

INTRODUCTION

ADAMTS13 modulates shear-dependent platelet thrombus formation (PTF) by limited proteolysis of von Willebrand factor (VWF). A high-plasma-ratio of VWF antigen to ADAMTS13 activity (VWF:Ag/ADAMTS13:AC) promotes PTF and aggravates shear-induced inflammation mediated by VWF. A role of ADAMTS13 in Kawasaki disease (KD) remains unknown, however. We investigated the involvement of ADAMTS13-VWF axis in the acute-phase of KD (acute-KD).

METHODS

VWF:Ag and ADAMTS13:AC in 77 KD infants were measured at three time-points; immediately before (Pre), one-week (1 W) and one-month (1 M) after intravenous-immunoglobulin (IVIG) treatment. VWF multimer (VWFM) distribution and ADAMTS13-isoelectrofocusing (IEF) patterns were compared between the responders and non-responders to IVIG.

RESULTS

A high VWF:Ag (195.7 ± 85.6%, p < 0.05), low ADAMTS13:AC (60.3 ± 23.8%, p < 0.05) and high VWF:Ag/ADAMTS13:AC ratio (3.70 ± 2.12, p < 0.05) at Pre were seen compared to control plasmas. These parameters returned to normal levels time-dependently after IVIG treatment. Non-responders to IVIG demonstrated high VWF:Ag and low ADAMTS13:AC at Pre, and high VWF:Ag/ADAMTS13:AC ratio at 1 W compared to responders, but there were no significant differences in VWFM distribution between both groups. IEF analyses revealed the decreased free form of ADAMTS13 and increased complex form with ADAMTS13 and high-molecular-weight-VWFM at Pre in non-responders. A high VWF:Ag/ADAMTS13:AC ratio was associated with increased white blood cell counts, together with decreased serum albumin and sodium at Pre and 1 W.

CONCLUSIONS

A high VWF:Ag/ADAMTS13:AC ratio in acute-KD persisted after primary treatment in non-responders, and unbalanced substrate-to-enzyme ratio appeared to associate with vascular endothelial damage. Analysis of existing mode of ADAMTS13 may help to clarify pathogenesis of IVIG resistance in acute-KD.

Advancing multimer analysis of von Willebrand factor by single-molecule AFM imaging

The formation of hemostatic plugs at sites of vascular injury crucially involves the multimeric glycoprotein von Willebrand factor (VWF). VWF multimers are linear chains of N-terminally linked dimers. The latter are formed from monomers via formation of the C-terminal disulfide bonds Cys2771-Cys2773', Cys2773-Cys2771', and Cys2811-Cys2811'. Mutations in VWF that impair multimerization can lead to subtype 2A of the bleeding disorder von Willebrand Disease (VWD). Commonly, the multimer size distribution of VWF is assessed by electrophoretic multimer analysis. Here, we present atomic force microscopy (AFM) imaging as a method to determine the size distribution of VWF variants by direct visualization at the single-molecule level. We first validated our approach by investigating recombinant wildtype VWF and a previously studied mutant (p.Cys1099Tyr) that impairs N-terminal multimerization. We obtained excellent quantitative agreement with results from earlier studies and with electrophoretic multimer analysis. We then imaged specific mutants that are known to exhibit disturbed C-terminal dimerization. For the mutants p.Cys2771Arg and p.Cys2773Arg, we found the majority of monomers (87 ± 5% and 73 ± 4%, respectively) not to be C-terminally dimerized. While these results confirm that Cys2771 and Cys2773 are crucial for dimerization, they additionally provide quantitative information on the mutants' different abilities to form alternative C-terminal disulfides for residual dimerization. We further mutated Cys2811 to Ala and found that only 23 ± 3% of monomers are not C-terminally dimerized, indicating that Cys2811 is structurally less important for dimerization. Furthermore, for mutants p.Cys2771Arg, p.Cys2773Arg, and p.Cys2811Ala we found 'even-numbered' non-native multimers, i.e. multimers with monomers attached on both termini; a multimer species that cannot be distinguished from native multimers by conventional multimer analysis. Summarizing, we demonstrate that AFM imaging can provide unique insights into VWF processing defects at the single-molecule level that cannot be gained from established methods of multimer analysis.

Evaluation of a semi-automated von Willebrand factor multimer assay, the Hydragel 5 von Willebrand multimer, by two European Centers

BACKGROUND

The phenotypic diagnosis of von Willebrand disease (VWD) is a multistep process with classification dependent on the quantification of von Willebrand factor (VWF) multimeric structure. VWF multimer analysis is a technically challenging, lengthy and non-standardised assay, usually performed in specialist laboratories. Recently, a new semi-automated multimer assay, the Hydragel 5 von Willebrand multimers (H5VWM) has become available.

OBJECTIVES

This study, performed in two European centres, compared existing in-house multimer assays to the H5VWM in individuals with and without VWD.

RESULTS

Overall agreement of 91.1% was observed in 74 individuals with normal VWF levels, 57 patients grouped as type 1 VWD, 33 type 2A, 16 type 2B, 28 type 2M, 11 type 2N. Patients tested following Desmopressin or VWF concentrate, with thrombotic thrombocytopenic purpura and acquired von Willebrand syndrome were also evaluated. Many of the discrepancies between methods were in patients with genetic mutations linked to more than one type of VWD including p.R1374C/H and p.R1315C. Quantifiable multimer results were available within one working day. Densitometry improved the interpretation of the multimers with slight structural variations that were not apparent by visual inspection of the in-house method.

CONCLUSIONS

5VWM was a rapid, sensitive, standardised assay which used existing technology and could be included as an initial screen of VWF multimers in a VWD diagnostic algorithm in conjunction with traditional multimer analysis.

A comparative analysis of different automated von Willebrand factor glycoprotein Ib-binding activity assays in well typed von Willebrand disease patients

Essentials Von Willebrand ristocetin cofactor activity (VWF:RCo) is not a completely reliable assay. Three automated VWF activity assays were compared within a von Willebrand disease (VWD) cohort. Raw values for all three assays were virtually the same. An overall problem within type 2A/IIE VWD using VWF:GPIb-binding activity/VWF:Ag was observed.

SUMMARY

Background von Willebrand disease (VWD) is an inherited bleeding disorder caused by quantitative (type 1 and 3) or qualitative (type 2) von Willebrand factor (VWF) defect. VWD diagnosis and classification require numerous laboratory tests. VWF: glycoprotein Ib (GPIb)-binding activity assays are used to distinguish type 1 from type 2 VWD. Objectives Three different automated VWF:GPIb-binding activity assays were compared. Patients and methods BC-VWF:RCo (Siemens Healthcare Diagnostics), HemosIL® VWF:RCo (Instrumentation Laboratory) and INNOVANCE® VWF:Ac (Siemens Healthcare Diagnostics) were performed in a well typed VWD cohort (n = 142). Results Based on the three most used VWD parameters (FVIII:C, VWF:Ag and VWF:GPIb-binding activity) and using a cut-off of <0.70 for type 2 VWD revealed sensitivity and specificity of, respectively, 92% and 72.4% for VWF:RCo/VWF:Ag, 84% and 89.7% for VWF:GPIbR/VWF:Ag, and 92% and 85.1% for VWF:GPIbM/VWF:Ag, whereas a lowered cut-off of < 0.60 resulted in reduced sensitivity with increased specificity for all assays. Conclusion VWD classification based on FVIII:C, VWF:Ag and VWF:GPIb-binding activity revealed an overall problem with normal VWF:GPIb-binding activity/VWF:Ag within type 2, especially type 2A/IIE. Although all assays were practically identical, BC-VWF:RCo had higher %CV compared with both new assays but comparable lower limit of quantification (LLOQ) ~4 IU dL-1 . No clear improved distinction between type 1 and 2 VWD with new assays was seen.

BC-VWF

RCo and HemosIL® are ristocetin dependent, whereas INNOVANCE® does not rely upon ristocetin and is not influenced by VWF polymorphisms increasing VWF:GPIb-binding activity levels. INNOVANCE® seems to be the best choice as a first-line VWF:GPIb-binding activity assay, providing the best balance between sensitivity and specificity for type 2 VWD.

Intravitreal injection of aflibercept, an anti-VEGF antagonist, down-regulates plasma von Willebrand factor in patients with age-related macular degeneration

We investigated the association between von Willebrand factor (VWF) and exudative age-related macular degeneration (AMD) in 114 Japanese patients. Intravitreal injection of vascular endothelial growth factor (VEGF) inhibitor is the most effective therapy for AMD. Therefore, we analyzed changes of VWF antigen (VWF:Ag) and VWF multimers (VWFMs) after intravitreal injection of aflibercept, an anti-VEGF antagonist. The relationship between polymorphisms in complement factor H (p.Y402H and p.I62V) and AMD was previously reported. In our patients, p.I62V, but not p.Y402H, was significantly associated with an increased risk of AMD. Pre-treatment plasma levels of VWF:Ag in patients with AMD were significantly higher than those in controls. Unusually large VWFMs (UL-VWFMs) were detected in the majority of AMD patients with concurrent vitreous or subretinal hemorrhage. After intravitreal injection of aflibercept, plasma levels of VWF:Ag and VEGF-A were significantly decreased. UL-VWFMs disappeared after aflibercept injection in three cases, but persisted even 1 month after injection in the other five cases. In conclusion, plasma VWF:Ag levels were significantly elevated in patients with AMD, and decreased after intravitreal aflibercept injection. VWF may play an important role in the pathophysiology of AMD, and aflibercept might improve AMD by reducing plasma levels of VWF in addition to VEGF-A.

von Willebrand disease type 2A phenotypes IIC, IID and IIE: A day in the life of shear-stressed mutant von Willebrand factor

The bleeding disorder von Willebrand disease (VWD) is caused by mutations of von Willebrand factor (VWF), a multimeric glycoprotein essential for platelet-dependent primary haemostasis. VWD type 2A–associated mutations each disrupt VWF biosynthesis and function at different stages, depending on the VWF domain altered by the mutation. These effects cause considerable heterogeneity in phenotypes and symptoms. To characterise the molecular mechanisms underlying the specific VWF deficiencies in VWD 2A/IIC, IID and IIE, we investigated VWF variants with patient-derived mutations either in the VWF pro-peptide or in domains D3 or CK. Additionally to static assays and molecular dynamics (MD) simulations we used microfluidic approaches to perform a detailed investigation of the shear-dependent function of VWD 2A mutants. For each group, we found distinct characteristics in their intracellular localisation visualising specific defects in biosynthesis which are correlated to respective multimer patterns. Using microfluidic assays we further determined shear flow-dependent characteristics in polymer-platelet-aggregate formation, platelet binding and string formation for all mutants. The phenotypes observed under flow conditions were not related to the mutated VWF domain. By MD simulations we further investigated how VWD 2A/IID mutations might alter the ability of VWF to form carboxy-terminal dimers. In conclusion, our study offers a comprehensive picture of shear-dependent and shear-independent dysfunction of VWD type 2A mutants. Furthermore, our microfluidic assay might open new possibilities for diagnosis of new VWD phenotypes and treatment choice for VWD patients with shear-dependent VWF dysfunctions that are currently not detectable by static tests.

Changes in von Willebrand factor-cleaving protease (ADAMTS-13) in patients with aortic stenosis undergoing valve replacement or balloon valvuloplasty

It was the objective of this study to determine whether reduced cleavage of von Willebrand factor (VWF) multimers following aortic valve replacement (AVR) is a consequence of reduced shear stress or postoperative changes in VWF cleavage protease (ADAMTS-13) activity. Aortic stenosis (AS) may be complicated by acquired von Willebrand disease. Aortic valve replacement (AVR) corrects the associated haematologic abnormalities. We enrolled 114 patients with severe AS scheduled for either balloon aortic valvuloplasty (BAV; n=64) or AVR (n=50). Haematologic assessments of VWF levels and activity and ADAMTS-13 were performed before and 24 hours after valve intervention. The VWF:RCo to VWF:Ag ratio, a surrogate for large VWF multimer activity, increased by 37% (p < 0.0001) after AVR and by 10% (p = 0.0002) after BAV. ADAMTS-13 activity significantly decreased after AVR (579 ± 127 to 468 ± 135 ng/ml; p<0.0001), but not after BAV (484 ± 153 to 529 ± 185 ng/ml; p = 0.10). By multivariable analysis, the change in VWF:RCo ratio after AVR was more strongly associated with the fall in ADAMTS-13 than with reduction of valve gradient; whereas the change in gradient better predicted the rise in VWF:RCo after BAV. In conclusion, both BAV and AVR reverse the haematological abnormalities of the acquired von Willebrand syndrome of AS and ADAMTS-13 levels decrease after AVR. These findings suggest that a portion of the haematologic benefit of AVR may be due to a postoperative decline in ADAMTS-13 rather than solely to relief of AS as previously thought.

Discrepant platelet and plasma von Willebrand factor in von Willebrand disease patients with p.Pro2808Leufs*24

Essentials von Willebrand factor (VWF) is synthesized in endothelial cells and platelet precursors. Type 3 patients with Pro2808Leufs*24 have lower bleeding scores than other type 3s. The Pro2808Leufs*24 variant was examined in patient platelets and endothelial cells. Type 3s with this variant contain releaseable VWF, possibly reducing bleeding.

SUMMARY

Background A novel variant, p.Pro2808Leufs*24, in the von Willebrand factor (VWF) gene was previously identified in the Canadian von Willebrand disease (VWD) patient population. Clinical observations of type 3 VWD patients with this variant indicate a milder bleeding phenotype compared with other type 3 patients. Objective To assess the effect of the Pro2808Leufs*24 variant on the molecular pathogenesis of VWD and correlate this with the phenotype observed in patients. Patients/Methods Phenotypic data from individuals in the Canadian type 3 VWD study were analyzed. VWF expression in platelets and plasma was assessed via immunoblotting. Cellular expression of VWF in platelets and blood outgrowth endothelial cells (BOEC) was examined via immunofluorescence microscopy and biochemical analysis in a type 3 index case and family member with Pro2808Leufs*24. Results Twenty-six individuals with the Pro2808Leufs*24 variant (16 type 3 VWD homozygous or compound heterozygous and 10 heterozygous family members) were studied. Bleeding scores were lower in type 3 patients with Pro2808Leufs*24 compared with type 3 patients with other variants, confirming a milder bleeding phenotype. Immunoblotting of platelet lysates detected VWF in the platelets of type 3 patients with Pro2808Leufs*24. Examination of an index case detected VWF within platelets via immunofluorescence microscopy, and in vitro experiments showed that this VWF was released upon platelet activation. Patient BOECs showed decreased VWF synthesis and secretion, although some VWF-containing granules were observed. Conclusion Type 3 VWD patients with the Pro2808Leufs*24 have bioavailable platelet-derived VWF that may produce a milder bleeding phenotype than other type 3s.

Implementation of a rapid assay of ADAMTS13 activity was associated with improved 30-day survival rate in patients with acquired primary thrombotic thrombocytopenic purpura who received platelet transfusions

BACKGROUND

Platelet (PLT) transfusions are probably harmful in patients with acquired idiopathic thrombotic thrombocytopenic purpura (aTTP). Introduction of a rapid assay for ADAMTS13 activity should reduce the time to definite diagnosis of aTTP, reduce the amount of inappropriately transfused PLT concentrates, and improve mortality and morbidity.

STUDY DESIGN AND METHODS

We selected 265 aTTP patients with severe ADAMTS13 deficiency. Of these, 91 patients were diagnosed by March 2005 (Period 1), when ADAMTS13 activity was measured by von Willebrand factor multimer assay, which took 4 to 7 days until the result was reported. An additional 174 patients were diagnosed after April 2005 (Period 2), when the activity was measured by a chromogenic enzyme-linked immunosorbent assay, which took 1 to 2 days.

RESULTS

We found no significant differences in 30-day survival rate between the two periods. Overall, 48 patients received PLT transfusions. Mortality was slightly greater between patients with (22.9%) versus without PLT transfusion (17.7%), but not significant. In Period 1, Cox proportional hazards regression analysis showed that older age (≥60 years) and PLT transfusion administration were independent factors associated with higher risks of 30-day mortality. In contrast, in Period 2, lower Rose-Eldor TTP severity score and use of plasma exchange and corticosteroid therapy were independent factors associated with higher survival rates while nonadministration of PLT transfusions was not.

CONCLUSION

Our results indicate that PLT transfusions are harmful for aTTP patients when the definite diagnosis of severe ADAMTS13 deficiency is delayed. If it can be done as soon as possible, PLT transfusions for severe bleeding or surgical interventions might be allowed with subsequent plasmapheresis.

Severe Aortic Valve Stenosis

Aortic valve stenosis (AVS) is the most common valve disease in adults. Severe forms are associated with acquired von Willebrand syndrome (aVWS) with loss of the largest von Willebrand factor (VWF) multimers. Diagnostic gold standard is the VWF multimer analysis. Valve replacement rapidly restores the VWF structure. Uncertainty exists if this effect is permanent and how functional VWF assays perform compared with multimer analysis. We studied 21 consecutive patients with severe AVS before and 6 to 18 months after valve surgery and compared them with 14 controls without valve disease referred for coronary angiography. The VWF multimers, VWF antigen (VWF:Ag), VWF collagen binding capacity (VWF:CB), VWF:CB/VWF:Ag ratio, in vitro bleeding time (PFA-100), factor VIII coagulation activity (FVIII:C), and VWF ristocetin cofactor activity (VWF:RCo) were determined. In all patients with AVS, the large VWF multimers were strongly reduced (56 ± 13% of normal plasma); all controls had normal multimers. The PFA-100 collagen/ADP closure times (coll/ADP CT) were prolonged in patients with AVS compared with the controls (175 ± 56 seconds vs 86 ± 14 seconds, P < .001). The VWF:CB/VWF:Ag ratio was pathological in 20 of the 21 patients but normal in controls. After surgery, the multimers normalized in all patients and coll/ADP CT shortened (pre 184 ± 65 seconds vs post 102 ± 22 seconds; P < .001). The VWF:CB/VWF:Ag ratio strongly improved ( P < .001) and normalized in 14 of 17 patients. In conclusion, all consecutive patients with severe AVS had an aVWS. The combination of coll/ADP CT and VWF:CB/VWF:Ag ratio detected the aVWS in all patients. More than 6 months after valve replacement, the VWF multimers were still normalized in all patients indicating a permanent cure of the aVWS.

A Practical Concept for Preoperative Identification of Patients with Impaired Primary Hemostasis

The findings of a large prospective study designed to identify primary and/or secondary hemostatic disorders before surgical interventions are presented. A total of 5649 unselected adult patients were enrolled to identify impaired hemostasis before surgical interventions. Each patient was asked to answer a standardized questionnaire concerning bleeding history. Activated partial thromboplastin time (aPTT), prothrombin time (PT), and platelet counts (PC) including PFA-100 (platelet function analyzer): collagen-epinephrine (C/E), and collagen-ADP (C/ADP) were routinely done in all patients. Additional tests, bleeding time (BT), and von Willebrand factor (vWF: Ag) were performed only in patients with a positive bleeding history and/or evidence of impaired hemostasis; e.g., drug ingestion. The bleeding history was negative in 5021 patients (88.8%) but positive in the remaining 628 (11.2%). Impaired hemostasis could be verified only in 256 (40.8%) of these patients. The vast majority were identified with PFA-100: C/E (n=250; 97.7%). The other six patients with impaired hemostasis were identifiable solely based on the PT (n=2), PFA-100: C/ADP (n=2), and vWF: Ag (n=2). The PFA-100: C/ADP detected 199 patients (77.7%). The only abnormality found among patients with a negative bleeding history was a prolonged aPTT due to lupus anticoagulant in nine patients (0.2%). The sensitivity of the PFA-100: collagen-epinephrine was the highest (90.8%) in comparison to the other screening tests (BT, aPTT, PT, vWF: Ag). The positive predictive value of the PFA-100: collagen-epinephrine was high (81.8%), but the negative predictive value was higher (93.4%). The use of a standardized questionnaire and, if indicated, the PFA-100: C/E and/or other specific tests not only ensure the detection of impaired hemostasis in almost every case but also a significant reduction of the cost.

Evaluation of von Willebrand factor with a fully magnetically levitated centrifugal continuous-flow left ventricular assist device in advanced heart failure

BACKGROUND

Contemporary continuous-flow left ventricular assist devices (CF-LVADs) are associated with degradation of von Willebrand factor (vWF) high-molecular-weight multimers (HMWMs), a critical factor supporting platelet function. We hypothesized that the HeartMate 3 fully magnetically levitated LVAD, designed to reduce circulatory shear stress, favorably influences these hemostatic parameters.

METHODS

Fifteen consecutive HeartMate 3 LVAD patients were compared with 11 consecutive HeartMate II controls. Serial plasma samples were collected pre-implant and on Days 2, 7, 30 and 45 post-operatively. Changes in vWF HMWMs were evaluated by 2 independent, study-blind hematologists and confirmed using densitometry-based computerized software. Ristocetin cofactor (RiCO) and vWF antigen (vWF Ag) were measured using standard protocols with enzyme-linked immunosorbent assay.

RESULTS

HeartMate 3 patients and HeartMate II controls had a mean age of 67.3 ± 1.4 and 52.8 ± 2.5 years, respectively (INTERMACS Profiles 2 to 4 in 93.3% and 91%, respectively). HeartMate 3 group demonstrated a significantly greater preservation of HMWMs compared with the HeartMate II group, with the most prominent decrease occurring by Day 2 post-operatively and sustained through 45 days (71.94% vs 31.16%, p = 0.001). Laboratory values (normalized to baseline) for RiCO activity, vWF Ag and RiCO:vWF Ag ratio remained in the functional range with no statistically significant differences observed between groups.

CONCLUSION

The HeartMate 3 LVAD is associated with enhanced hemocompatibility compared with the HeartMate II LVAD, as demonstrated by the improved preservation of vWF HMWMs, In contrast, effects on HMWM degradation appeared to be dissociated from functional attributes. Further confirmation of these findings in randomized clinical trials is warranted.

Von Willebrand factor regulates complement on endothelial cells

Atypical hemolytic uremic syndrome and thrombotic thrombocytopenic purpura have traditionally been considered separate entities. Defects in the regulation of the complement alternative pathway occur in atypical hemolytic uremic syndrome, and defects in the cleavage of von Willebrand factor (VWF)-multimers arise in thrombotic thrombocytopenic purpura. However, recent studies suggest that both entities are related as defects in the disease-causing pathways overlap or show functional interactions. Here we investigate the possible functional link of VWF-multimers and the complement system on endothelial cells. Blood outgrowth endothelial cells (BOECs) were obtained from 3 healthy individuals and 2 patients with Type 3 von Willebrand disease lacking VWF. Cells were exposed to a standardized complement challenge via the combination of classical and alternative pathway activation and 50% normal human serum resulting in complement fixation to the endothelial surface. Under these conditions we found the expected release of VWF-multimers causing platelet adhesion onto BOECs from healthy individuals. Importantly, in BOECs derived from patients with von Willebrand disease complement C3c deposition and cytotoxicity were more pronounced than on BOECs derived from normal individuals. This is of particular importance as primary glomerular endothelial cells display a heterogeneous expression pattern of VWF with overall reduced VWF abundance. Thus, our results support a mechanistic link between VWF-multimers and the complement system. However, our findings also identify VWF as a new complement regulator on vascular endothelial cells and suggest that VWF has a protective effect on endothelial cells and complement-mediated injury.

Rapid Restoration of Thrombus Formation and High-Molecular-Weight von Willebrand Factor Multimers in Patients with Severe Aortic Stenosis After Valve Replacement

AIM

Patients with severe aortic stenosis (AS) may have bleeding episodes due to the loss of high-molecular-weight (HMW) von Willebrand factor multimers (VWFMs). The absence of HMW-VWFMs and bleeding tendency are usually corrected after aortic valve replacement (AVR). To investigate the process of VWFM recovery and symptoms in patients with severe AS, we analyzed changes in VWF antigen (VWF:Ag), ADAMTS13 activity (ADAMTS13:AC), and platelet thrombus formation under high shear stress conditions.

METHODS

Nine patients with severe AS undergoing AVR were analyzed.

RESULTS

Evident deficiency of HMW-VWFMs was observed in six patients before surgery, which was rapidly restored within 8 days after AVR. Median levels of VWF:Ag before surgery, on postoperative days (PODs) 1, 8, 15, and 22, and one year after AVR were 78.1%, 130%, 224%, 155%, 134%, and 142%, respectively. In contrast, ADAMTS13:AC was 50.5%, 35.5%, 25.5%, 25.1%, 30.3%, and 84.6%, respectively. Preoperative thrombus formation but not surface coverage was significantly lower than that on POD 22, which was considered as normal level in each patient. Compared with preoperative levels, thrombus volume was significantly lower on POD 1, but rapidly increased by POD 8.

CONCLUSION

Bleeding tendency and loss of HMW-VWFMs observed in patients with severe AS before surgery was rapidly corrected after AVR. Instead, patients were in a VWF-predominant state between POD 8 and 22.

von Willebrand Factor-Rich Platelet Thrombi in the Liver Cause Sinusoidal Obstruction Syndrome following Oxaliplatin-Based Chemotherapy

Oxaliplatin-based chemotherapy is widely used to treat advanced colorectal cancer (CRC). Sinusoidal obstruction syndrome (SOS) due to oxaliplatin is a serious type of chemotherapy-associated liver injury (CALI) in CRC patients. SOS is thought to be caused by the sinusoidal endothelial cell damage, which results in the release of unusually-large von Willebrand factor multimers (UL-VWFMs) from endothelial cells. To investigate the pathophysiology of CALI after oxaliplatin-based chemotherapy, we analyzed plasma concentration of von Willebrand factor (VWF) and the distribution of VWFMs in CRC patients. Twenty-three patients with advanced CRC who received oxaliplatin-based chemotherapy with (n = 6) and without (n = 17) bevacizumab were analyzed. CALI (n = 6) and splenomegaly (n = 9) were found only in patients who did not treated with bevacizumab. Plasma VWF antigen (VWF:Ag) and serum aspartate aminotransferase (AST) levels increased after chemotherapy only in patients without bevacizumab. VWFM analysis in patients who did not receive bevacizumab showed the presence of UL-VWFMs and absence of high molecular weight VWFMs during chemotherapy, especially in those with CALI. In addition, plasma VWF:Ag and AST levels increased after chemotherapy in patients with splenomegaly (n = 9), but not in patients without splenomegaly (n = 14). Histological findings in the liver tissue of patients who did not receive bevacizumab included sinusoidal dilatation and microthrombi in the sinusoids. Many microthrombi were positive for both anti-IIb/IIIa and anti-VWF antibodies. Plasma UL-VWFM levels might be increased by damage to endothelial cells as a result of oxaliplatin-based chemotherapy. Bevacizumab could prevent CALI and splenomegaly through inhibition of VWF-rich platelet thrombus formation.

Force-sensitive autoinhibition of the von Willebrand factor is mediated by interdomain interactions

Von Willebrand factor (VWF) plays a central role in hemostasis. Triggered by shear-stress, it adheres to platelets at sites of vascular injury. Inactivation of VWF has been associated to the shielding of its adhesion sites and proteolytic cleavage. However, the molecular nature of this shielding and its coupling to cleavage under shear-forces in flowing blood remain unknown. In this study, we describe, to our knowledge, a new force-sensory mechanism for VWF-platelet binding, which addresses these questions, based on a combination of molecular dynamics (MD) simulations, atomic force microscopy (AFM), and microfluidic experiments. Our MD simulations demonstrate that the VWF A2 domain targets a specific region at the VWF A1 domain, corresponding to the binding site of the platelet glycoprotein Ibα (GPIbα) receptor, thereby causing its blockage. This implies autoinhibition of the VWF for the binding of platelets mediated by the A1-A2 protein-protein interaction. During force-probe MD simulations, a stretching force dissociated the A1A2 complex, thereby unblocking the GPIbα binding site. Dissociation was found to be coupled to the unfolding of the A2 domain, with dissociation predominantly occurring before exposure of the cleavage site in A2, an observation that is supported by our AFM experiments. This suggests that the A2 domain prevents platelet binding in a force-dependent manner, ensuring that VWF initiates hemostasis before inactivation by proteolytic cleavage. Microfluidic experiments with an A2-deletion VWF mutant resulted in increased platelet binding, corroborating the key autoinhibitory role of the A2 domain within VWF multimers. Overall, autoinhibition of VWF mediated by force-dependent interdomain interactions offers the molecular basis for the shear-sensitive growth of VWF-platelet aggregates, and might be similarly involved in shear-induced VWF self-aggregation and other force-sensing functions in hemostasis.

Diagnosis of inherited von Willebrand disease: comparison of two methodologies and analysis of the discrepancies

Diagnostics of von Willebrand disease (VWD) includes assessment of factor VIII (FVIII) coagulant activity, von Willebrand factor (VWF) antigen (VWF:Ag) and VWF ristocetin cofactor activity (VWF:RCo), and more specific tests as multimeric and genetic analyses are necessary for the correct VWD classification. The ACL AcuStar analyzer introduces chemiluminescence (CL) technology in detection of VWD with automated VWF:Ag and VWF:RCo assays. Compare VWF:Ag-ELISA and VWF:RCo by aggregometry conventional assays with new CL VWF:Ag-IL and VWF:RCo-IL assays, investigate the ability to make accurate VWD diagnosis and concordance with multimeric and genetic analyses. 146 patients with congenital VWD (51 Type 1; 34 Type 2A; 16 Type 2B; 31 Type 2M; 5 Type 2N; 9 Type 3) and 30 healthy normal subjects were included. A comparison was made between CL and conventional methods. Diagnostic evaluation included: VWF:RCo/VWF:Ag ratio, multimeric distribution (sodium dodecyl sulfate [SDS]-agarose gel) of VWF and genetic analysis in 110 of 146 patients. CL and conventional methods revealed good correlation. Kappa test agreement diagnosis was >0.8. CL diagnostic sensitivity was 100% and specificity 97%. Multimeric and genetic analysis were of help in clarifying 13 discrepancies of diagnosis between methods, of which six discrepancies were explained by lack of conventional methods′ sensibility. CL methodology can detect VWD and discriminate between type 1, 3 and variant forms and offers an automated, faster, sensitive and less cumbersome method when compared to conventional assays, in particular VWF:RCo by aggregometry. In some cases, even with all phenotype and genetic analyses, discrepancies exist in the classification of VWD.

ADAMTS13 content and VWF multimer and triplet structure in commercially available VWF/FVIII concentrates

ADAMTS13 is a metalloproteinase that cleaves von Willebrand factor (VWF) into smaller multimers in vivo. This cleavage creates both the typical multimeric size distribution and the characteristic triplet band distribution of VWF. Here we analysed ADAMTS13 content, VWF multimeric size distribution and VWF triplet structure in five commercial VWF/factor VIII (FVIII) concentrates. The relative distribution of ADAMTS13 activity values corresponded well to the ADAMTS13 antigen values for all examined concentrates except Haemate HS®, which had markedly higher ADAMTS13 antigen/activity ratio, with Fanhdi® and Haemate HS® displaying the most intense ADAMTS13 signal. Interestingly, ADAMTS13 levels did not correlate with the high molecular weight multimer content of the concentrates, but did correlate with VWF triplet distribution. Densitometric quantification showed that Wilate®, Immunate® and Willfact® displayed human plasma-like VWF triplet distribution, whereas Fanhdi® and Haemate HS® showed enhanced content of the faster migrating triplet band, which corresponded well to their higher ADAMTS13 content. In summary, Immunate®, Willfact® and Wilate® had lower levels of ADAMTS13 antigen and activity and exhibited a plasma-like VWF triplet structure. Fanhdi® and Haemate HS® had higher ADAMTS13 content and an altered triplet structure. The possible impact of these observations on function and clinical efficacy of VWF/FVIII concentrates is discussed.

ATZ11 recognizes not only Z-α1-antitrypsin-polymers and complexed forms of non-Z-α1-antitrypsin but also the von Willebrand factor

AIMS

The ATZ11 antibody has been well established for the identification of α1-anti-trypsin (AAT) molecule type PiZ (Z-AAT) in blood samples and liver tissue. In this study, we systematically analyzed the antibody for additional binding sites in human tissue.

METHODS AND RESULTS

Ultrastructural ATZ11 binding was investigated immunoelectron microscopically in human umbilical vein endothelial cells (HUVECs) and in platelets of a healthy individual. Human embryonic kidney (HEK293) cells were transiently transfected with Von Willebrand factor (VWF) and analyzed immunocytochemically using confocal microscopy and SDS-PAGE electrophoresis followed by western blotting (WB). Platelets and serum samples of VWF-competent and VWF-deficient patients were investigated using native PAGE and SDS-PAGE electrophoresis followed by WB. The specificity of the ATZ11 reaction was tested immunohistochemically by extensive antibody-mediated blocking of AAT- and VWF-antigens. ATZ11-positive epitopes could be detected in Weibel-Palade bodies (WPBs) of HUVECs and α-granules of platelets. ATZ11 stains pseudo-WBP containing recombinant wild-type VWF (rVWF-WT) in HEK293 cells. In SDS-PAGE electrophoresis followed by WB, anti-VWF and ATZ11 both identified rVWF-WT. However, neither rVWF-WT-multimers, human VWF-multimers, nor serum proteins of VWF-deficient patients were detected using ATZ11 by WB, whereas anti-VWF antibody (anti-VWF) detected rVWF-WT-multimers as well as human VWF-multimers. In human tissue specimens, AAT-antigen blockade using anti-AAT antibody abolished ATZ11 staining of Z-AAT in a heterozygous AAT-deficient patient, whereas VWF-antigen blockade using anti-VWF abolished ATZ11 staining of endothelial cells and megakaryocytes.

CONCLUSIONS

ATZ11 reacts with cellular bound and denatured rVWF-WT and human VWF as shown using immunocytochemistry and subsequent confocal imaging, immunoelectron microscopy, SDS-PAGE and WB, and immunohistology. These immunoreactions are independent of the binding of Z-AAT-molecules and non-Z-AAT complexes.

Quantification of perioperative changes in von Willebrand factor and factor VIII during elective orthopaedic surgery in normal individuals

von Willebrand's disease (VWD) patients undergoing major surgery are prophylactically treated to promote haemostasis. There is variability in perioperative clinical practice; however, most guidelines suggest replacing the deficient factor to a level of 1.0 IU mL(-1) (or 100%). A review of the literature reveals a paucity of well constructed descriptive data quantifying the changes in coagulation that occur in response to surgical stress. The aim of this study was to quantify the changes in haemostatic variables occurring in response to elective orthopaedic surgery in normal individuals. Eligible subjects >18 years of age undergoing total hip or knee replacement were recruited. Blood samples were drawn at five time points: baseline, preoperatively, 30 min after surgical incision, 30 min postoperatively, postoperative day (POD) 1. Analyses included t-tests and repeated measures anova. Overall 30 patients, 21 women and 9 men, with a mean age of 65 were included in the final analysis. All von Willebrand factor (VWF) variables were seen to significantly decrease intraoperatively and increase postoperatively. VWF multimers showed a statistically significant decrease in high molecular weight multimers intraoperatively and an increase postoperatively. On subgroup analysis, age, gender and anaesthesia type were significantly correlated with changes in VWF parameters. Data presented in the current study establish a physiological baseline for VWF parameters in the normal population and demonstrate mean VWF/factor VIII levels greater than 1.0 IU mL(-1) intraoperatively. As such, current management in VWD patients does not appear to mimic the normal physiological response to surgery.

A comparative evaluation of a new automated assay for von Willebrand factor activity

The ristocetin cofactor assay (VWF:RCo) is the reference method for assessing von Willebrand factor (VWF) activity in the diagnosis of von Willebrand's Disease (VWD). However, the assay suffers from poor reproducibility and sensitivity at low levels of VWF and is labour intensive. We have undertaken an evaluation of a new immunoturbidimetric VWF activity (VWF:Ac) assay (INNOVANCE(®) VWF Ac. Siemens Healthcare Diagnostics, Marburg, Germany) relative to an established platelet-based VWF:RCo method. Samples from 50 healthy normal subjects, 80 patients with VWD and 50 samples that exhibited 'HIL' (i.e. Haemolysis, Icterus or Lipaemia) were studied. VWF:Ac, VWF:RCo and VWF:Ag were performed on a CS-analyser (Sysmex UK Ltd, Milton Keynes, UK), all reagents were from Siemens Healthcare Diagnostics. The VWF:Ac assay, gave low intra- and inter-assay imprecision (over a 31-day period, n = 200 replicate readings) using commercial normal (Mean 96.2 IU dL(-1), CV < 3.0%) and pathological (Mean 36.1 IU dL(-1), CV < 3.5%) control plasmas. The normal and clinical samples exhibited good correlation between VWF:RCo (range 3-753 IU dL(-1)) and VWF:Ac (rs = 0.97, P < 0.0001), with a mean bias of 5.6 IU dL(-1). Ratios of VWF:Ac and VWF:RCo to VWF:Ag in the VWD samples were comparable, although VWF:Ac had a superior lower level of detection to that of VWF:RCo (3% and 5% respectively). A subset (n = 97) of VWD and HIL samples were analysed for VWF:Ac at two different dilutions to assess the effect on relative potency, no significant difference was observed (P = 0.111). The INNOVANCE(®) VWF Ac assay was shown to be reliable and precise.

Native analysis of plasma-derived clotting factor VIII concentrates: "sponge effect" and contaminants

In the present study, we analysed two commercially available plasma-derived FVIII preparations, Beriate and Emoclot, through native gel-based approaches (CN-PAGE). The rationale behind this study was to assess whether protein complexes from plasma resisted the aggressive manufacturing processes. A preliminary analysis of plasma complexes was performed focusing on the molecular weight range between 45 kDa and 1 MDa. As a result, we could evidence in both preparations the presence of complexes, which resisted the cryoprecipitation, chromatographic and heat treatment processing steps. These complexes behaved in a "sponge-effect"-like fashion through the enrichment of otherwise less abundant contaminants. The use of an alternative electrophoretic approach such as CN-PAGE allowed us to confirm 2DE-based observations and expand the list of non-FVIII proteins which contaminate the preparations.

Impact of loss of high-molecular-weight von Willebrand factor multimers on blood loss after aortic valve replacement

BACKGROUND

Severe aortic stenosis is associated with loss of the largest von Willebrand factor (vWF) multimers, which could affect primary haemostasis. We hypothesized that the altered multimer structure with the loss of the largest multimers increases postoperative bleeding in patients undergoing aortic valve replacement.

METHODS

We prospectively included 60 subjects with severe aortic stenosis. Before and after aortic valve replacement, vWF antigen, activity, and multimer structure were determined and platelet function was measured by impedance aggregometry. Blood loss from mediastinal drainage and the use of blood and haemostatic products were evaluated perioperatively.

RESULTS

Before operation, the altered multimer structure was present in 48 subjects (80%). Baseline characteristics and laboratory data were similar in all subjects. The median blood loss after 6 h was 250 (105-400) and 145 (85-240) ml in the groups with the altered and normal multimer structures, respectively (P=0.182). After 24 h, the cumulative loss was 495 (270-650) and 375 (310-600) ml in the groups with the altered and normal multimer structures, respectively (P=0.713). Multivariable analysis revealed no significant influence of multimer structure and platelet function on bleeding volumes after 6 and 24 h. After 24 h, there was no obvious difference in vWF antigen, activity, and multimer structure in subjects with and without the altered multimer structure before operation or in subjects with and without perioperative plasma transfusion.

CONCLUSIONS

The altered vWF multimer structure before operation was not associated with increased bleeding after aortic valve replacement. Our findings might be explained by perioperative release of vWF and rapid recovery of the largest vWF multimers.

Acquired von Willebrand syndrome and mitral valve prosthesis leakage. A pilot study

BACKGROUND

Of patients with severe aortic stenosis, 15-25% present with bleeding episodes possibly attributable to acquired von Willebrand syndrome (AVWS). AVWS associated with mitral valve prosthesis leakage has not been reported.

METHODS AND RESULTS

Five patients receiving appropriate oral anticoagulation showed mitral valve prosthesis leakage and bleeding episodes; all of them required hospitalization and two blood transfusions, and a von Willebrand factor (VWF) analysis was performed. Two patients with normal functioning metallic prosthesis valves were included as controls. Before surgery, after cessation of acenocumarol, the patients had prolonged activated partial thromboplastin time; four had prolonged closure time (CT) from the platelet function analyzer. Factor VIII procoagulant activity (FVIII:C), VWF ristocetin cofactor activity (VWF:RCo), and VWF collagen binding (VWF:CB) were considerably elevated, while VWF antigen (VWF:Ag) was most elevated. Disproportionate VWF:RCo/VWF:Ag and VWF:CB/VWF:Ag ratios were seen with the loss of large VWF multimers. Following surgery, all parameters were markedly increased and the ratios, CT, and multimeric VWF profile became normal.

CONCLUSIONS

Acquired VWF qualitative alterations in mitral valve prosthesis leakage may be associated with or contribute to bleeding diathesis. AVWS should be taken into consideration in patients with mitral valve prosthesis leakage with bleeding diathesis not explained by excessive oral anticoagulation.

The pharmacokinetic diversity of two von Willebrand factor (VWF)/ factor VIII (FVIII) concentrates in subjects with congenital von Willebrand disease. Results from a prospective, randomised crossover study

The pharmacokinetic (PK) profiles of von Willebrand factor (VWF) /factor VIII (FVIII) concentrates are important for treatment efficacy and safety of von Willebrand disease (VWD) patients. This prospective, head-to-head, randomised crossover study compared the PK profile of a new, high purity, human plasma-derived (pd)VWF/FVIII concentrate, Wilate, with the PK profile of an intermediate purity (pd)VWF/FVIII concentrate, Humate-P, in VWD patients. Subjects with inherited VWD were randomised to a single intravenous dose (40 IU/kg VWF ristocetin cofactor activity [VWF:RCo]) of Wilate or Humate-P in Period 1, and switched to the other study drug in Period 2. Each period was preceded by a washout time of ≥ 7 days. Coagulation factor parameters were analysed at multiple time-points. Of 22 randomised subjects, 20 had evaluable PK profiles, which indicated comparability for VWF antigen and VWF:RCo between Wilate and Humate-P. The reported VWF:RCo average and terminal t1/2 of 10.4 and 15.8 hours (h), respectively, for Wilate and 9.3 h and 12.8 h for Humate-P, were not statistically different. Also, the mean VWF:RCo in vivo recoveries (Wilate 1.89, Humate-P 1.99 IU/dl per IU/kg) were similar between the two replacement therapies. Wilate showed parallel decay curves for VWF:RCo and FVIII clotting activity (FVIII:C) over time, while FVIII:C of Humate-P displayed a plateau between 0 and 12-24 h. This study demonstrated bioequivalent PK properties for VWF between Wilate and Humate-P. The PK profile of Wilate, combined with the 1:1 VWF/FVIII ratio, theoretically should facilitate dosing and laboratory monitoring of VWF replacement to prevent bleeding in individuals with VWD.

Native multimer analysis of plasma and platelet von Willebrand factor compared to denaturing separation: implication for the interpretation of satellite bands

Blue native electrophoresis (BNE) was applied to analyze the von Willebrand factor (vWF) multimers in their native state and to present a methodology to perform blue native electrophoresis on human plasma proteins, which has not been done before. The major difference between this method and the commonly used SDS-agarose gel electrophoresis is the lack of satellite bands in the high-resolution native gel. To further analyze this phenomenon, a second dimension was performed under denaturing conditions. Thereby, we obtained a pattern in which each protein sub-unit from the first dimension dissociates into three distinct sub-bands. These bands confirm the triplet structure, which consists of an intermediate band and two satellite bands. By introducing the second dimension, our novel method separates the triplet structure into a higher resolution than the commonly used SDS-agarose gel electrophoresis does. This helps considerably in the classification of ambiguous von Willebrand's disease subtypes. In addition, our method has the additional advantage of being able to resolve the triplet structure of platelet vWF multimers, which has not been identified previously through conventional SDS-agarose electrophoresis multimer analysis. This potential enables us to compare the triplet structure from platelet and plasmatic vWF, and may help to find out whether structural abnormalities concern the vWF molecule in the platelet itself, or whether they are due to the physiological processing of vWF shed into circulation. Owing to its resolution and sensitivity, this native separation technique offers a promising tool for the analysis and detection of von Willebrand disorder, and for the classification of von Willebrand's disease subtypes.

The effect of prion reduction in solvent/detergent-treated plasma on haemostatic variables

BACKGROUND

Octapharma PPGmbH has recently modified its manufacturing process for solvent/detergent-treated plasma to incorporate a prion reduction step, in which a 3 log reduction has been demonstrated. The current study was undertaken to assess the impact of this procedure on haemostatic variables in the new product OctaplasLG in comparison with standard Octaplas.

METHODS

Production batches of standard Octaplas (n=4) and OctaplasLG (n=16) were assessed for levels of coagulation factors, physiological protease inhibitors, markers of activation and procoagulant microparticles. Global haemostasis was assessed by a thrombin generation test (TGT) and rotational thromboelastometry (ROTEM).

RESULTS

Mean levels of factors: II, V, VII, IX, X, XI, XII and XIII, VWF:Ag, antithrombin, protein C and free protein S were all >75 u/dl. ADAMTS-13 activity levels were normal. Factor VIII and VWF:RCo were >55 u/dl. TGT and ROTEM were similar in both preparations, and microparticles were present at negligible levels. Two units of OctaplasLG had slightly elevated levels of Prothrombin Fragments 1+2, but D-Dimer and thrombin-antithrombin complexes were normal in all batches.

CONCLUSION

These studies indicate that the affinity chromatography procedure used in OctaplasLG does not appear to adversely affect the proven haemostatic quality of Octaplas, while offering a selective reduction in the concentration of pathological prion proteins.

Acquired von Willebrand syndrome in patients with an axial flow left ventricular assist device

BACKGROUND

Rotary blood pumps used as left ventricular assist devices (LVADs) allow for long-term support and may become suitable alternatives to heart transplantation. Effects of this technology on the coagulation system are not completely understood, leading to controversial anticoagulation protocols. Thus, we investigated the primary hemostasis in patients with chronic LVAD therapy.

METHODS AND RESULTS

Twenty-six outpatients received axial flow LVAD (HeartMate II; Thoratec) for a median support time of 4.5 months. In a cross-sectional protocol, platelet aggregation in response to ADP and epinephrine, von Willebrand antigen (vWF:AG), and collagen-binding capacity (vWF:CB) were obtained. Von Willebrand factor (vWF) multimer analyses were performed, and patients were screened for bleeding events. This analysis was repeated after removal of the device for transplantation or recovery (n=12) and after a median of 15.5 months in ongoing patients (n=11). In all patients on devices, severe impairment of platelet aggregation as well as a loss of large vWF multimers were found. In 10 patients, a decreased vWF:CB/vWF:AG ratio was observed. Bleeding episodes occurred with an incidence of 0.17 per patient-year. After removal of the device, normal patterns of platelet aggregation, multimer analysis, and vWF:CB/vWF:AG ratio were recorded. In the second analysis of ongoing patients, impairment of platelet aggregation and loss of large vWF multimers were verified.

CONCLUSIONS

A diagnosis of von Willebrand syndrome type 2 was established in all patients after LVAD implantation, and bleeding events confirmed this finding. Reversibility of this condition was found after removal of the device.

An Evaluation of the DDAVP Infusion Test With PFA-100 and vWF Activity Assays to Distinguish vWD Types in Children

von Willebrand disease (vWD) is classified into partial (type 1), qualitative (type 2), and total deficiency (type 3).The aims of the study were to evaluate prospectively the potency of the DDAVP infusion test together with von Willebrand factor (vWF) ristocetin cofactor (vWF:RCo), vWF antigen (vWF:Ag), factor VIII coagulant activity (FVIII:C), and platelet function analyzer (PFA)-100 to distinguish vWD types. Genetic analysis and multimeric analysis of vWF was not applied. We classified the 112 patients and 47 healthy children phenotypically according to the laboratory test results and bleeding severity score. PFA-100 closure times (CT), FVIII:C, vWF:RCo, vWF:Ag, ristocetin-induced platelet aggregation (RIPA), and the response of FVIII:C and vWF parameters to desmopressin (DDAVP) were used to define types 1, 2, and 3 vWD. Type 1 vWD is mild in 34 cases (vWF:RCo % 40-55), moderate in 29 (vWF:RCo %27-40), severe type 1 vWD or nonclassical type 2 vWD in 12 cases (vWF:RCo % 4-16), and type 2 vWD in 23 cases (vWF:RCo %4-38).The response to DDAVP of vWF parameters is normal in all patients with mild/moderate type 1 vWD, 6 patients with severe type 1 vWD or nonclassical type 2 vWD and 11 patients with type 2 vWD. In conclusion, this study showed that measurement of vWF:RCo, vWF:Ag, FVIII:C, and PFA-100 parameters can differentiate vWD types but not severe type 1 vWD or nonclassical type 2 vWD. In the differentiation of severe type 1 vWD and nonclassical type 2 vWD, DDAVP response may be used.

Analysis of von Willebrand factor multimers by simultaneous high- and low-resolution vertical SDS-agarose gel electrophoresis and Cy5-labeled antibody high-sensitivity fluorescence detection

Analysis of von Willebrand factor (vWF) multimers allows classification of the subtypes of von Willebrand disease (vWD) in human serum and platelet lysates. A novel method for multimer analysis of vWF by 2-chamber, vertical (sodium dodecyl sulfate), agarose gel electrophoresis, designed for comparing discontinuous high- and low-resolving gels for plasma and platelets, followed by Western blotting and high-sensitivity fluorescence detection (HSFD) of cyanine (Cy)5-labeled vWF multimers is presented. HSFD shows that this method has high discriminatory power for visualization and densitometric analysis of platelets and plasma vWF multimers in various types of vWD and allows rapid classification of vWD types, to separate types 2A and 2B. The described procedures of vWF multimer analysis with high-sensitivity Cy5 fluorescence detection and direct comparison of high- and low-resolving gels for screening and detection of the complete range of high- and low-molecular vWF multimers is efficient and useful for screening, detecting, and classifying vWD subtypes and makes this method diagnostically and clinically relevant.

Thromboelastography reflects global hemostatic variation among severe haemophilia A dogs at rest and following acute exercise

The heterogeneity among severe haemophilia A patients reflects on variable tendencies for bleeding and also variable responses to FVIII therapy. This variability cannot be detected or predicted by routine coagulation tests. Thromboelastography (TEG) has recently been evaluated for assessing hemostatic patterns in haemophiliacs and proved valuable in monitoring therapy and/or prophylaxis, however, usually only in limited small case series. Exercise is an important component of overall haemophilia care, however, in severe haemophiliacs there is an increased risk of bleeding. The availability of a validated hemostatic test to evaluate the influence of exercise would be advantageous. This study has used TEG analysis to evaluate the global hemostatic status of a group of severe haemophilia A dogs at rest and after a standardized period of exercise. The study demonstrated significant inter and intra-individual variations based on TEG patterns at rest and following acute exercise as well as significant improvement of global hemostasis after exercise in the majority of tested dogs. The study supports the utilization of TEG in assessment of the hemostatic pattern in severe haemophilia A and provides a potential for utilizing TEG evaluation in managing exercise regimens for haemophilia care.