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

Decreased ADAMTS13 levels in patients after living donor liver transplantation

INTRODUCTION

Thrombotic microangiopathy (TMA) is a complication occurring after liver transplantation (LT), and an unusually large multimer (ULM) of Von Willebrand factor (VWF) and ADAMTS13 may play an important role in the onset of TMA during LT.

MATERIAL AND METHODS

Eight-one patients underwent living donor LT (LDLT). Seventeen of those patients had both severe thrombocytopenia and hemolytic anemia with fragmented red cells and were diagnosed as TMA- like syndrome (TMALS).

RESULTS AND CONCLUSIONS

A significant reduction of ADAMTS13 and an increase of VWF were observed in the patients with TMALS. The ADAMTS13 activity in patients after LDLT was significantly reduced from day 1 to day 21, and it was significantly low in those with TMALS at day 14 and 28. The VWF levels in patients with LDLT were significantly high, and the VWF/ADAMTS13 ratio was significantly increased in patients at 7, 14 and 28 days after LDLT, especially in patients with TMALS at day 14 and 28 after LDLT. High molecular weight multimers of VWF were observed to have increased in patients with LDLT, and the high molecular weight multimers of VWF were further increased in those with mild TMALS but they decreased in those with severe TMA. These findings suggest that ULM- VWF and ADAMTS13 might be associated with the onset of TMA after LT.

Diagnostic workup of patients with acquired von Willebrand syndrome: a retrospective single-centre cohort study

BACKGROUND

Diagnosis of acquired von Willebrand syndrome (AVWS) remains challenging. Diagnostic algorithms suggest the use of factor VIII (FVIII:C), von Willebrand factor antigen (VWF:Ag), ristocetin cofactor (VWF:RCo), and collagen-binding capacity (VWF:CB), but the sensitivity of these and other laboratory tests for the diagnosis of AVWS is unknown.

OBJECTIVES

To analyze the capacity of laboratory tests, including point-of-care testing (POCT), for the identification of patients with AVWS.

PATIENTS/METHODS

Thirty-five consecutive patients were enrolled with AVWS diagnosed because of a history of recent onset of bleeding, a negative family history of von Willebrand disease, and abnormal plasma VWF multimers.

RESULTS

According to our inclusion criteria, all patients had bleeding symptoms, and the VWF high molecular weight multimers were either decreased or absent. Regarding POCT, PFA-100 was inconclusive, due to anemia or thrombocytopenia, in 29%; the sensitivity was 80% in the remaining patients. The sensitivity of VWF:Ag (23%), VWF:RCo/Ag ratio < 0.7 (26%), VWF:CB/Ag ratio < 0.7 (46%), anti-VWF antibodies (15%) and VWF propeptide/Ag ratio (22%) was too low to rule out the disease. A combination of VWF:Ag < 50 IU dL(-1), VWF:RCo/Ag ratio < 0.7 and VWF:CB/Ag ratio < 0.8 yielded a sensitivity of 86%. Patients diagnosed only because of abnormal VWF multimers showed similar clinical characteristics as other patients.

CONCLUSIONS

Early diagnosis of AVWS is difficult, due to lack of sensitivity of the tests used. A substantial number of patients present with normal or increased test results, emphasizing the importance of multimer analysis in all patients with suspected AVWS.

Increased von Willebrand factor antigen and high molecular weight multimers in sickle cell disease associated with nocturnal hypoxemia

We evaluated vWF profiles in children and adolescents with SCD and sleep hypoxemia. Mean vWF:Ag levels were significantly elevated in the SCD-hypoxemia group when compared with SCD-normoxia and control groups (p=0.007); and correlated inversely with pulse oximetry (r=-0.54, p=0.01). Densitographic analyses of vWF multimer distribution also showed an inverse correlation between %HMW-multimers and oxygen saturation (r=-0.62, p=0.03). The previously reported association between nocturnal desaturation and SCD vascular complications, including stroke, may be influenced by hypoxemic modulation of vWF as noted in this study.

Platelet dysfunction and a high bone mass phenotype in a murine model of platelet-type von Willebrand disease

The platelet glycoprotein Ib-IX receptor binds surface-bound von Willebrand factor and supports platelet adhesion to damaged vascular surfaces. A limited number of mutations within the glycoprotein Ib-IX complex have been described that permit a structurally altered receptor to interact with soluble von Willebrand factor, and this is the molecular basis of platelet-type von Willebrand disease. We have developed and characterized a mouse model of platelet-type von Willebrand disease (G233V) and have confirmed a platelet phenotype mimicking the human disorder. The mice have a dramatic increase in splenic megakaryocytes and splenomegaly. Recent studies have demonstrated that hematopoetic cells can influence the differentiation of osteogenic cells. Thus, we examined the skeletal phenotype of mice expressing the G233V variant complex. At 6 months of age, G233V mice exhibit a high bone mass phenotype with an approximate doubling of trabecular bone volume in both the tibia and femur. Serum measures of bone resorption were significantly decreased in G233V animals. With decreased bone resorption, cortical thickness was increased, medullary area decreased, and consequently, the mechanical strength of the femur was significantly increased. Using ex vivo bone marrow cultures, osteoclast-specific staining in the G233V mutant marrow was diminished, whereas osteoblastogenesis was unaffected. These studies provide new insights into the relationship between the regulation of megakaryocytopoiesis and bone mass.

The effect of exercise on von Willebrand factor and ADAMTS-13 in individuals with type 1 and type 2B von Willebrand disease

BACKGROUND

The effect of exercise on von Willebrand factor (VWF) and ADAMTS-13 levels in individuals with von Willebrand disease (VWD) has never been reported.

OBJECTIVES

The aim was to quantify the effect of a standardized exercise protocol on individuals with type 1 and type 2B VWD.

PATIENTS/METHODS

Thirty individuals from three groups (10 controls, 11 with type 1 VWD and 9 with type 2B VWD) completed the Standard Bruce Protocol Treadmill Test. A bleeding questionnaire was administered and blood tests were performed pre- and immediately postexercise. The groups were well matched for age, gender and body mass index (BMI).

RESULTS

There was a correlation in all groups between the metabolic equivalents (METS) achieved and the degree of change of VWF and FVIII:C levels (P < 0.002, Pearson's correlation). There was a significant postexercise increase in VWF:Ag, VWF:RCo, FVIII:C and activated VWF levels in both the control group and in the type 2B VWD group, but not in the type 1 VWD group. Specific to the type 2B VWD group was an increase in the percentage of high molecular weight multimers (P = 0.022), a decrease in the mean platelet count compared with the other groups (P < 0.001) and an increase in the ADAMTS-13 level (P = 0.001).

CONCLUSIONS

There are significant differences in the effects of exercise on individuals with type 1 and type 2B VWD compared with controls. Further clinical studies are necessary to evaluate exercise as a therapeutic option in VWD.

Challenges in defining type 2M von Willebrand disease: results from a Canadian cohort study

BACKGROUND/METHODS

In order to better characterize the genotype-phenotype correlation in type 2M von Willebrand disease (VWD), we sequenced the coding region for the mature subunit of the von Willebrand factor (VWF) gene (exons 18-52, including exon/intron boundaries) in 16 index cases originally submitted to the Canadian Type 1 VWD Study as type 1 VWD, but reclassified as type 2M VWD on the basis of phenotype (excessive mucocutaneous bleeding and von Willebrand factor: antigen (VWF:Ag) and/or von Willebrand factor: ristocetin cofactor (VWF:RCo) between 0.05 and 0.50 IU mL(-1) on at least two occasions and RCo/Ag ratio < 0.6 and no loss of high molecular weight multimers). Available family members (16 affected, 23 unaffected and six unknown) were sequenced for identified mutations.

RESULTS

We identified eight different missense mutations (R854Q, T1054M, R1315C, R1374C, R1374H, L1382P, S2179F, and T2647M) within these 16 families. We were significantly more likely to identify a VWF mutation in cases with RCo/Ag ratios < 0.50 (P < 0.05, chi-squared test). Importantly, every index case with an RCo/Ag ratio < 0.40 (4/4 index cases) had a mutation identified within the A1 domain, in contrast to 1/12 cases with an RCo/Ag ratio > 0.40. Difficulties with the standardization of the VWF:RCo may be responsible for the heterogeneity in cases with RCo/Ag ratios between 0.40 and 0.60.

CONCLUSIONS

The genotype-phenotype correlation for cases with RCo/Ag ratios < 0.40 is clear. On the basis of our results, the phenotypic definition of type 2M VWD may need to be more stringent, and should be the subject of an international standardization initiative.

von Willebrand factor/factor VIII concentrate (Haemate P) dosing based on pharmacokinetics: a prospective multicenter trial in elective surgery

BACKGROUND

While plasma-derived concentrates containing large amounts of von Willebrand factor (VWF) are effective in treating von Willebrand disease (VWD), optimal dosing remains to be fully characterized.

OBJECTIVES

To determine the feasibility of dosing Haemate P VWF/factor VIII (FVIII) concentrate based on pharmacokinetics (PK) in the management of surgical subjects with VWD.

METHODS

VWD subjects scheduled for elective surgery were enrolled in a prospective multicenter open-label cohort study. A pre-operative loading dose of VWF/FVIII concentrate based upon prior individual subject PK analysis was administered followed by postoperative therapeutic/maintenance infusions.

RESULTS

Twenty-eight subjects with types 1, 2A or 3 VWD and one with type 2 M were enrolled. Median in vivo recovery of VWF ristocetin cofactor (VWF:RCo) was 1.9 IU dL(-1) (IU kg(-1))(-1) with an interquartile range (IQR) of 1.6-2.5 IU dL(-1) (IU kg(-1))(-1). Median response, half-life and clearance were 74.0% (IQR, 55.5-100%), 15.6 h (IQR, 9.0-28.4 h) and 3.26 mL kg(-1) h(-1) (IQR, 2.29-5.21 mL kg(-1) h(-1)), respectively. A PK-guided median VWF:RCo loading dose of 62.4 IU kg(-1) (IQR, 50.1-87.0 IU kg(-1)) was administered. Postoperative mean trough VWF:RCo levels of 62-73 IU dL(-1) were sufficient to prevent bleeding. Investigators rated hemostasis excellent or good in 96.3% of subjects on the day of surgery and 100% on the next day and on day 14. A subject with multiple risk factors developed pulmonary embolism, which resolved without sequelae.

CONCLUSIONS

Haemate P provided effective and safe hemostasis in VWD subjects undergoing elective surgery. Selection of Haemate P loading dose on the basis of VWF PK proved feasible.

Prophylactic fresh frozen plasma may prevent development of hepatic VOD after stem cell transplantation via ADAMTS13-mediated restoration of von Willebrand factor plasma levels

We initially conducted a multicenter, randomized trial (n=43), and subsequently a questionnaire study (n=209) of participating hospitals, to evaluate whether infused fresh frozen plasma (FFP) could prevent the occurrence of hepatic veno-occlusive disease (VOD) after stem cell transplantation (SCT). Forty-three patients were divided into two groups: 23 receiving FFP infusions and 20 not receiving it. VOD developed in three patients not receiving FFP. Plasma von Willebrand factor (VWF) antigen levels were lower at days 0, 7 and 28 after SCT in patients receiving FFP than in those not receiving it, whereas plasma ADAMTS13 activity (ADAMTS13:AC) did not differ between them. Plasma VWF multimer (VWFM) was demonstrated to be defective in the high approximately intermediate VWFM during the early post-SCT phase, but there was a significant increase in high VWFM just before VOD onset. This suggests that a relative enzyme-to-substrate (ADAMTS13/high-VWFM) imbalance is involved in the pathogenesis of VOD. To strengthen this hypothesis, the incidence of VOD was apparently lower in patients receiving FFP infusions than in those not receiving it (0/23 vs 3/20) in the randomized trial. Further, the results combined with the subsequent questionnaire study (0/36 vs 11/173) clearly showed the incidence to be statistically significant (0/59 vs 14/193, P=0.033).

The mutational spectrum of type 1 von Willebrand disease: Results from a Canadian cohort study

In order to evaluate the changes within the VWF gene that might contribute to the pathogenesis of type 1 von Willebrand disease (VWD), a large multicenter Canadian study was undertaken. We present data from the sequence analysis of the VWF gene in 123 type 1 VWD index cases and their families. We have identified putative mutations within the VWF gene in 63% (n = 78) of index cases, leaving 37% (n = 45) with no identified changes. These changes comprise 50 different putative mutations: 31 (62%) missense mutations, 8 (16%) changes involving the VWF transcriptional regulatory region, 5 (10%) small deletions/insertions, 5 (10%) splicing consensus sequence mutations, and 1 nonsense mutation. Twenty-one of the index cases had more than one putative VWF mutation identified. We were somewhat more likely to identify putative mutations in cases with lower VWF levels, and the contribution of other factors, such as ABO blood group, seems more important in milder cases. Taken as a whole, our data support a complex spectrum of molecular pathology resulting in type 1 VWD. In more severe cases, genetic changes are common within the VWF gene and are highly penetrant. In milder cases, the genetic determinants are more complex and involve factors outside of the VWF gene.

Genetic linkage and association analysis in type 1 von Willebrand disease: results from the Canadian type 1 VWD study

BACKGROUND

von Willebrand disease (VWD) is the most common bleeding disorder known in humans, with type 1 VWD representing the majority of cases. Unlike the other variant forms of VWD, type 1 disease represents a complex genetic trait, influenced by both genetic and environmental factors.

AIM

To evaluate the contribution of the von Willebrand factor (VWF) and ABO blood group loci to the type 1 VWD phenotype, and to assess the potential for locus heterogeneity in this condition, we have performed genetic linkage and association studies on a large, unselected type 1 VWD population.

METHOD

We initially collected samples from 194 Canadian type 1 VWD families for analysis. After the exclusion of families found to have either type 2 or type 3 VWD, and pedigrees with samples from single generations, linkage and association analysis was performed on 155 type 1 VWD families.

RESULTS AND CONCLUSION

The linkage study has shown a low heterogeneity LOD score of 2.13 with the proportion of families linked to the VWF gene estimated to be 0.41. Linkage was not detected to the ABO locus in this type 1 VWD population. In the family-based association test, significant association was found between the type 1 VWD phenotype, the quantitative traits, VWF:Ag, VWF:RCo, and FVIII:C and the ABO 'O' and 'A' alleles and the VWF codon 1584 variant. There was also weak association with the -1185 promoter polymorphism and VWF:Ag, VWF:RCo, and FVIII:C plasma levels. These studies provide further evidence to support the role for genetic loci other than VWF and ABO in the pathogenesis of type 1 VWD.

Platelets treated with ticlopidine are less reactive to unusually large von Willebrand factor multimers than are those treated with aspirin under high shear stress

Much attention has recently been focused on the interaction between unusually large von Willebrand factor multimers (UL-VWFM) and platelets under high shear stress in pathological thrombus formation. The antiplatelet drugs acetylsalicylic acid (aspirin) and a thienopyridine derivative (ticlopidine) are commonly used to treat cerebral ischemia but exert different effects on high-shear-stress-induced platelet aggregation (H-SIPA) in the plasma. To examine the effects of these drugs in the absence of plasma factors, we studied H-SIPA using washed platelets (WPs) and purified UL-VWFM. WPs were prepared from the blood of 9 aspirin-treated and 11 ticlopidine-treated patients with cerebral ischemia, and H-SIPA in the presence of UL-VWFM was measured using a cone plate aggregometer. Plasma levels of VWF antigen with its multimer analysis, ristocetin cofactor and VWF-cleaving protease (ADAMTS13) activity were also measured. Forty-six healthy volunteers from 2 age groups, 20-40 years (n=20) and 41-60 years old (n=26), were also tested as controls. H-SIPA was significantly inhibited for ticlopidine-treated platelets, but it was observed to a lesser extent for aspirin-treated platelets. For both groups, no difference in the plasma levels of VWF antigen, ristocetin cofactor and ADAMTS13 activity was noted. All patients possessed UL-VWFM, and it was detected in healthy volunteers with increasing frequency with increasing age. Under plasma-free conditions, platelets from aspirin-treated patients exhibit marginal but significant inhibition of H-SIPA. Furthermore, the presence of UL-VWFM in the plasma of patients and normal volunteers is directly related to their age rather than being a consequence of underlying disease.

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.

A practical concept for preoperative management of patients with impaired primary hemostasis

In a prospective study, 254 of 5649 unselected patients scheduled for surgery at our hospital were identified preoperatively as having either acquired (n=182) or inherited (n=72) impaired primary hemostasis (platelet dysfunction including von Willebrand disease). All patients were initially pretreated with desmopressin (DDAVP). Response to DDAVP or subsequent treatment(s) was defined as correction of any one of the abnormal PFA-100 platelet function tests. The non-responders were additionally treated with tranexamic acid or aprotinin; those with von Willebrand disease (vWD) received factor VIII concentrates with von Willebrand factor (vWF). Those still unresponsive to therapy received conjugated estrogens and, as a last attempt, a platelet transfusion. The administration of DDAVP led to a correction of platelet dysfunction in 229 of the 254 patients treated (90.2%). Tranexamic acid was effective in 12 of 16, aprotinin in 3 of 5, and factor VIII concentrates with vWF in all 4 patients with unresponsive to DDAVP. The remaining 6 patients were pretreated with conjugated estrogens, and 2 of these patients were additionally treated with platelet transfusion. The frequency of blood transfusion was lower, but not statistically significant (9.4% vs. 12.2%: p = 0.202) in preoperatively treated patients with impaired hemostasis than in patients without impaired hemostasis. In a retrospective group, the frequency of blood transfusion was statistically significant higher (89.3% vs. 11.3%: p < 0.001) in patients without preoperative correction of impaired hemostasis than in patients without impaired hemostasis. Preoperative correction of impaired primary hemostasis is possible in nearly all patients affected, and results in a reduction of homologous blood transfusions.

A novel type 2A (Group II) von Willebrand disease mutation (L1503Q) associated with loss of the highest molecular weight von Willebrand factor multimers

Type 2A von Willebrand disease (VWD) is characterized by decreased platelet-dependent function of von Willebrand factor (VWF) associated with an absence of high-molecular-weight multimers. In this study, sequence analysis of the VWF gene from a Type 2A VWD patient showed a novel, heterozygous T-->A transversion at nucleotide 4510, resulting in the non-conservative substitution of L1503Q in the mature VWF subunit. This substitution, which was not found in 55 unrelated normal individuals, was reproduced by in vitro site directed mutagenesis of a full-length VWF cDNA and was subsequently expressed in COS-7 cells. The corresponding recombinant mutant VWF protein was partially retained in COS-7 cells yet the full spectrum of multimers was observed, suggesting that the absence of the highest molecular weight multimers results from increased proteolysis. The recombinant mutant VWF protein was digested with the ADAMTS13 protease from VWF-depleted plasma and the aberrant VWF multimer pattern was observed. These results suggest that the L1503Q substitution induces a conformational change in the VWF protein, which increases the protein's susceptibility to proteolysis. A three-dimensional model of the A2 domain demonstrates that the L1503Q mutation and the physiological proteolytic cleavage site for ADAMTS13 (Y(1605)-M(1606)) are localized close together in two adjacent parallel beta-sheets. The mutation L1503Q does not significantly disrupt the conformation of the protein; thus the subtle loss of multimers in this patient may be due to altered interactions with the ADAMTS13 protease.

Template bleeding time and PFA-100 have low sensitivity to screen patients with hereditary mucocutaneous hemorrhages: comparative study in 148 patients

OBJECTIVES AND PATIENTS

We compared the template bleeding time (BT) and closure time (CT) in the PFA-100 as screening tests in 148 consecutive patients with unequivocal mucocutaneous bleeding and positive family history.

EXCLUSION CRITERIA

drug intake, concomitant diseases including minor infections, low platelet count, diseases of secondary hemostasis.

RESULTS

Type 1 von Willebrand disease (VWD-1) was diagnosed in 26 patients, primary platelet secretion defect (PSD) in 33, VWD-1 + PSD in nine, whereas 80 patients did not comply with the criteria for known hemostatic disorders (UD, unknown diagnosis). BT and CT were prolonged in 35.8% and 29.7% of all the patients, respectively (P = 0.23). Sensitivity increased to 48% if an abnormality of BT and/or CT was considered. Same comparisons for BT and CT in each diagnostic category were, respectively: 42 vs. 61.5% in VWD-1 (P = 0.18), 42 vs. 24% in platelet secretion defects (P = 0.11), 67 vs. 89% in VWD-1 + PSD (P = 0.50), and 27.5 vs. 15% in UD (P = 0.06).

CONCLUSION

Both tests were relatively insensitive and not significantly different in detecting incoming patients with mucocutaneous hemorrhages. In patients with VWD-1, the PFA-100 performed slightly better, whereas the opposite occurred in those patients with platelet secretion defects. In the UD group, both tests lost sensitivity, but the BT detected 1.8 times more patients than the PFA-100. Given the large proportion of undiagnosed bleeders and the overall low sensitivity of these tests, clinical decisions still rely on the medical history and etiological diagnosis of the bleeding disorder.

Founder von Willebrand factor haplotype associated with type 1 von Willebrand disease

To date, no dominant mutation has been identified in a significant proportion of patients with type 1 von Willebrand disease (VWD). In this study, we examined 70 families as part of the Canadian Type 1 VWD Study. The entire VWF gene was sequenced for 1 index case, revealing 2 sequence variations: intron 30 (5312-19A>C) and exon 28 at Tyr1584Cys (4751A>G). The Tyr1584Cys variation was identified in 14.3% (10 of 70) of the families and was in phase with the 5312-19A>C variation in 7 (10.0%) families. Both variants were observed in 2 of 10 UK families with type 1 VWD, but neither variant was found in 200 and 100 healthy, unrelated persons, respectively. Mean von Willebrand factor antigen (VWF:Ag), VWF ristocetin cofactor (VWF:RCo), and factor VIII coagulant activity (FVIII:C) for the index cases in these families are 0.4 U/mL, 0.36 U/mL, and 0.54 U/mL, respectively, and VWF multimer patterns show no qualitative abnormalities. Aberrant VWF splicing was not observed in these patients, and both alleles of the VWF gene are expressed as RNA. Molecular dynamic simulation was performed on a homology model of the VWF-A2 domain containing the Tyr1584Cys mutation. This showed that no significant structural changes occur as a result of the substitution but that a new solvent-exposed reactive thiol group is apparent. Expression studies revealed that the Tyr1584Cys mutation results in increased intracellular retention of the VWF protein. We demonstrate that all the families with the Tyr1584Cys mutation share a common, evolved VWF haplotype, suggesting that this mutation is ancient. This is the first report of a mutation that segregates in a significant proportion of patients with type 1 VWD.

Case series of thrombotic thrombocytopenic purpura in children and adolescents

Thrombotic thrombocytopenic purpura (TTP) is a well-described entity in adults but is rarely observed in children. The authors describe a series of seven children with suspected acquired TTP. Clinical findings included petechiae, purpura, or jaundice ( 6), central nervous system events ( 5), fever ( 3), diarrhea ( 3), renal insufficiency ( 2), and hematuria ( 2). Significant central nervous system events included cerebral vascular accidents ( 2), altered mental status ( 2), seizures ( 1), and hemiparesis ( 1). Patients were treated with daily plasma infusions (1/7) or plasma exchange (5/7). Response was prompt, although relapses were frequent. Decreased vWF-protease activity was found in four of five cases and vWF-protease inhibitors were found in three of five cases. Although rare, TTP is a life-threatening illness that does occur in children and should be considered in the differential diagnosis of thrombocytopenia with hemolytic anemia.

A mathematical framework for group analysis of von Willebrand factor multimeric composition following luminography

The objective of the present study was to establish a method for quantitative analysis of von Willebrand factor (vWF) multimeric composition using a mathematical framework based on curve fitting. Plasma vWF multimers from 15 healthy subjects and 13 patients with advanced pulmonary vascular disease were analyzed by Western immunoblotting followed by luminography. Quantitative analysis of luminographs was carried out by calculating the relative densities of low, intermediate and high molecular weight fractions using laser densitometry. For each densitometric peak (representing a given fraction of vWF multimers) a mean area value was obtained using data from all group subjects (patients and normal individuals) and plotted against the distance between the peak and IgM (950 kDa). Curves were constructed for each group using nonlinear fitting. Results indicated that highly accurate curves could be obtained for healthy controls and patients, with respective coefficients of determination (r2) of 0.9898 and 0.9778. Differences were observed between patients and normal subjects regarding curve shape, coefficients and the region of highest protein concentration. We conclude that the method provides accurate quantitative information on the composition of vWF multimers and may be useful for comparisons between groups and possibly treatments.

Acquired von Willebrand disease--hemostatic management of major orthopedic surgery with high-dose immunoglobulin, desmopressin, and continuous factor concentrate infusion

Acquired von Willebrand disease (aVWD) is a rare bleeding disorder that mimics congenital VWD in previously healthy individuals; it is most frequently associated with monoclonal gammopathy. Hemostatic therapy of aVWD is challenging due to the extremely shortened half-life of endogenous and exogenous VWF. High-dose intravenous immunoglobulin (ivIG) is recommended as the treatment of choice, usually rapidly normalizing coagulation; but in case of failure, alternative treatment options are not well explored. We report successful major orthopedic surgery in a 61-year-old woman with multiple myeloma IgG lambda and aVWD. IvIG alone failed to correct hemostasis. However, ivIG pretreatment improved the VWF ristocetin cofactor (VWF:RCo) half-life from only 1.5 hr to more than 4 hr, allowing desmopressin infusions twice daily to maintain sufficient VWF:RCo levels. Because of diminishing desmopressin effect, we attempted for the first time in aVWD a continuous VWF/FVIII infusion (Haemate HS), 2.1-2.7 FVIII U/kg/hr or 51-64 U/kg/day, respectively 4.6-6.0 VWF:RCo U/kg/hr or 110-145 U/kg/day) to reach constant factor levels. The steady-state clearance was 2.4 mL/kg/hr for FVIII:C and 13.5 mL/kg/hr for VWF:RCo. During surgery, VWF:RCo, FVIII:C, and PFA-100 closure time were normalized. Until day 5, VWF:RCo was kept above 50%, from day 6 to 10 at least 30% activity were attained. FVIII:C levels were always >70%. The clinical course was uneventful without bleeding. Two weeks after hip surgery the patient was discharged from the hospital without complaints. The therapy described can be recommended as safe and feasible for further evaluation in aVWD patients who are hyporesponsive to ivIG treatment alone. Continuous VWF/FVIII infusion can improve substitution therapy in aVWD.

Predicting response to plasma exchange in patients with thrombotic thrombocytopenic purpura with measurement of vWF-cleaving protease activity

BACKGROUND

Severe deficiency of vWF-cleaving protease (vWF-CPase) activity was recently found in patients with thrombotic thrombocytopenic purpura (TTP). Although the survival of patients with TTP has been dramatically improved with plasma exchange (PE), there are still many patients who are refractory to PE and immunosuppressive therapy.

STUDY DESIGN AND METHODS

The activities of vWF-CPase and its inhibitor were measured in 27 patients with nonfamilial TTP and hemolytic-uremic syndrome (HUS) to examine the relationship between the clinical variables and vWF-CPase activity.

RESULTS

Eight of nine patients with HUS had more than 40 percent of vWF-CPase activity, whereas one had 28 percent of the normal level at the acute phase. Ten of 12 TTP patients with a good outcome had a severe deficiency of vWF-CPase activity and its inhibitor, whereas four of six patients with a poor outcome had a moderate deficiency of vWF-CPase activity along with a lack of the inhibitor. PE produced normalization of the vWF-CPase activity and neutralization of the inhibitor in TTP patients with a good outcome; however, some TTP patients with vWF-CPase inhibitor had relapsed and required an immunosuppressive therapy. The response to the combination therapy with PE and immunosuppressive treatment was poor in TTP patients without a severe deficiency of vWF-CPase activity.

CONCLUSION

Assays of vWF-CPase activity and its inhibitor may be useful for predicting the response to therapy and the outcome of patients with TTP. In some patients, nonfamilial TTP with a poor prognosis may not be caused by a constitutional or acquired deficiency of vWF-CPase with its inhibitor. Although PE and immunosuppressive therapy are effective in patients with nonfamilial TTP and a vWF-CPase inhibitor, other therapeutic modalities may be needed for nonfamilial TTP with unknown etiology.

Impaired activity of plasma von Willebrand factor-cleaving protease may predict the occurrence of hepatic veno-occlusive disease after stem cell transplantation

Hepatic veno-occlusive disease (VOD) is a life-threatening complication after stem cell transplantation (SCT), characterized by thrombus formation in hepatic venules leading to a symptom triad of hyperbilirubinemia, hepatomegaly, and ascites. Multifactorial defects in the hemostatic system may contribute to its pathogenesis, but its remains to be investigated. Unusually large VWF multimers (UL-VWFMs), produced in and released from vascular endothelial cells, are most biologically active in the interaction with platelets under a high shear stress. UL-VWFMs are cleaved and degraded into smaller VWFMs by a specific liver producing plasma protease, termed VWF-cleaving protease (VWF-CPase), which has recently been identified as a metalloprotease solely produced in liver, termed ADAMTS13. Herein, we studied the correlation between plasma VWF-CPase activity and UL-VWFMs in 21 patients who received SCT, seven patients with VOD and 14 patients without VOD. In non-VOD patients, activities (mean +/- 1s.d.) of VWF-CPase were 78 +/- 17% of the control before the conditioning regimen, 76 +/- 18% on day 0, 64 +/- 19% on day 7, 57 +/- 23% on day 14, 68 +/- 13% on day 21 and 79 +/- 19% on day 28 after SCT. The respective values in VOD patients were 32 +/- 19%, 27 +/- 15%, 18 +/- 11%, 22 +/- 18%, 26 +/- 22% and 12 +/- 4%. Thus, VWF-CPase activity was significantly reduced in VOD patients, even before the conditioning regimen, and such a difference was not found in other laboratory tests. However, despite such a clear difference, UL-VWFMs were present in plasmas of both patient groups, together with the increase of VWF antigen and ristocetin cofactor activity. These results indicate that the measurement of this enzyme activity is extremely useful in predicting the occurrence of VOD prior to a demonstration of its direct involvement in its pathogenesis.

Plasma of patients with Upshaw-Schulman syndrome, a congenital deficiency of von Willebrand factor-cleaving protease activity, enhances the aggregation of normal platelets under high shear stress

Upshaw-Schulman syndrome (USS) is an autosomal recessive disorder characterized by repeated episodes of chronic thrombocytopenia and microangiopathic haemolytic anaemia (MAHA) that responds dramatically to infusions of fresh frozen plasma (FFP). Recent studies have provided consistent evidence that USS is a congenital deficiency of plasma von Willebrand factor-cleaving protease (VWF-CPase) activity and, therefore, unusually large VWF multimers (UL-VWFMs) are present in the plasma. However, the molecular mechanism of the clinical symptoms of USS is not well understood. We studied the relationship between UL-VWFMs and thrombocytopenia in two USS patients by analysing platelet aggregation using a mixture of the patient's plasma and normal washed platelets under high shear stress. Our results clearly showed a remarkably enhanced high shear stress-induced platelet aggregation (H-SIPA) by the patient's plasma. At 24 h after FFP infusion (approximately equal to 10 ml/kg body weight), the enhanced H-SIPA became almost completely normalized but, 2 d later, it began to return to the preinfusion level. These results were in accordance with the change in VWFM patterns. The specific effects of enhanced H-SIPA on VWF, platelet glycoprotein Ib and endogenous ADP released from platelets upon stimulation were confirmed using reagents that specifically inhibit their respective functions. Our present results clearly indicate that thrombocytopenia in USS patients is caused by a combination of the presence of UL-VWFMs, platelets and high shear stress generated in the microcirculation.

Von Willebrand factor and von Willebrand disease

von Willebrand disease (vWD) is caused by quantitative and/or qualitative defects of the von Willebrand factor (vWF), a multimeric high molecular weight glycoprotein. Typically, it affects the primary hemostatic system, which results in a mucocutaneous bleeding tendency simulating a platelet function defect. The vWF promotes its function in two ways: (i) by initiating platelet adhesion to the injured vessel wall under conditions of high shear forces, and (ii) by its carrier function for factor VIII in plasma. Accumulating knowledge of the different clinical phenotypes and the pathophysiological basis of the disease translated into a classification that differentiated between quantitative and qualitative defects by means of quantitative and functional parameters, and by analyzing the electrophoretic pattern of vWF multimers. The advent of molecular techniques provided the opportunity for conducting genotype-phenotype studies which have recently helped, not only to elucidate or confirm important functions of vWF and its steps in post-translational processing, but also many disease causing defects. Acquired von Willebrand syndrome (avWS) has gained more attention during the recent years. An international registry was published and recommendation by the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis in 2000. It concluded that avWS, although not a frequent disease, is nevertheless probably underdiagnosed. This should be addressed in future prospective studies. The aim of treatment is the correction of the impaired hemostatic system of the patient, ideally including the defects of both primary and secondary hemostasis. Desmopressin is the treatment of choice in about 70% of patients, mostly with type 1, while the others merit treatment with concentrates containing vWF.

Upshaw-Schulman syndrome revisited: a concept of congenital thrombotic thrombocytopenic purpura

Upshaw-Schulman syndrome (USS) is a congenital bleeding disorder characterized by repeated episodes of thrombocytopenia and microangiopathic hemolytic anemia that respond to infusions of fresh frozen plasma. Inheritance of USS has been thought to be autosomal recessive, because 2 siblings in the same family are often affected but their parents are asymptomatic. Recently, chronic relapsing thrombotic thrombocytopenic purpura (CR-TTP), reported almost exclusively in adults, was shown to be caused by inherited or acquired deficiency in the activity of a plasma von Willebrand factor-cleaving protease (vWF-CPase). The pathogenesis of USS is unknown, and a relationship between CR-YEP and USS has not been reported. We studied 3 unrelated USS patients (ST, SY, and KI) who presented with severe indirect neonatal hyperbilirubinemia. All 3 patients had undetectable vWF-CPase activity, and the inhibitors to vWF-CPase were all negative. In their parents with no clinical symptoms, vWF-CPase activities as a percentage of control samples (mother/father) were 17/20 for ST, 60/45 for SY, and 36/5.6 for KI. Thus, USS and vWF-CPase activity appear to be coinherited as autosomal recessive traits. Transfusion of fresh frozen plasma in 2 patients (ST and SY) resulted in the expected maximal increment of approximately 7% to 8% in vWF-CPase activity at 1 to 4 hours, but the levels became less than 3% within 2 days. After this decrease, platelet counts increased, plateaued in the normal range at 10 to 12 days, and declined thereafter. Thus, the 2 to 3 weeks of therapeutic benefit from plasma infusions will be discussed in relation to the intravascular lifetime of vWF-CPase.

Influence of ABO blood groups on primary hemostasis

BACKGROUND

Recently, the in vitro bleeding time test (IVBT) was proved to be a very sensitive screening method for the detection of vWD, showing rather good correlation between the closure time and the level of vWF. The vWF levels have been found to be significantly lower in healthy humans who are group O than in those who belong to the other ABO blood groups (non-group O). The aim of this study was to detect whether these differences in vWF levels in normal persons correspond to differences in nonvascular primary hemostasis when investigated by the IVBT.

MATERIAL AND METHODS

Healthy blood donors (n = 162) without evidence of hemostatic disorders, without ingestion of drugs for at least 2 weeks, and with normal in vivo bleeding time endpoints, normal factor VIII clotting activity levels, normal structure of vWF multimers, and normal ristocetin-induced platelet aggregation were examined by IVBT. IVBT was performed with two automated systems (Thrombostat 4000, VDG [TST]; and a platelet function analyzer (PFA-100, Dade Behring [PFA]). CaCl2 and ADP were used as aggregants for the two TST tests (TST-CaCl2 and TST-ADP), and ADP- or epinephrine (Epi)-coated membranes were used with the two PFA tests (PFA-ADP and PFA-Epi).

RESULTS

Closure time in the IVBT significantly correlated with the blood groups, but in reverse order (as did blood volume; data not shown): TST-ADP (mean +/- SD): group O, 89 +/- 14.6 seconds versus non-group O, 82 +/- 13 seconds (p<0.01); TST-CaCl(2): group O, 154 +/- 28.9 seconds versus non-group O, 140 +/- 31.3 seconds (p<0.01); PFA-ADP: group O, 91 +/- 13.4 seconds versus non-group O, 86 +/- 11.9 seconds (p<0.05); PFA-Epi: group O, 112 +/- 15.4 seconds versus non-group O, 104 +/- 16.7 seconds (p<0.05). Donors with vWF < or =77.5 % had longer closure time than those with vWF >77.5 % (p<0.05).

CONCLUSION

Significant ABO-group-specific differences in nonvascular primary hemostasis could be found by IVBT. The differences are small, however, and lie within the normal range. Whether these differences have any biologic relevance can only be speculated.

A rapid method to visualize von willebrand factor multimers by using agarose gel electrophoresis, immunolocalization and luminographic detection

A highly sensitive and rapid clinical method for the visualization of the multimeric structure of von Willebrand Factor in plasma and platelets is described. The method utilizes submerged horizontal agarose gel electrophoresis, followed by transfer of the von Willebrand Factor onto a polyvinylidine fluoride membrane, and immunolocalization and luminographic visualization of the von Willebrand Factor multimeric pattern. This method distinguishes type 1 from types 2A and 2B von Willebrand disease, allowing timely evaluation and classification of von Willebrand Factor in patient plasma. It also allows visualization of the unusually high molecular weight multimers present in platelets. There are several major advantages to this method including rapid processing, simplicity of gel preparation, high sensitivity to low concentrations of von Willebrand Factor, and elimination of radioactivity.

Increased von Willebrand factor binding to platelets in single episode and recurrent types of thrombotic thrombocytopenic purpura

Extensive microvascular platelet aggregation is characteristic of thrombotic thrombocytopenic purpura (TTP). Previous studies have indicated that abnormalities of von Willebrand factor (vWf) are often present in TTP patient plasma. There has not been previously any direct evidence linking these abnormalities to the process of intravascular platelet aggregation in TTP. We used flow cytometry to analyze the binding of vWf to single platelets, and the presence of platelet aggregates, in the blood of 4 children with chronic relapsing (CR) TTP and 5 adults with single episode or recurrent TTP. vWf on the single platelets of CRTTP patients at all time points studied was significantly increased compared to controls, and was increased further as platelet counts decreased to levels below 40,000/microl. The single episode and recurrent adult TTP patients had platelet aggregates in the blood, as well as increased vWf on single platelets, before therapy commenced and thereafter until recovery was in process. In the one unresponsive single episode TTP patient, vWf on single platelets remained elevated, and platelet aggregates persisted, until her death. The platelet alpha-granular protein, P-selectin, was not increased on the single platelets of most TTP blood samples, suggesting that it is vWf from plasma (rather than from alpha-granules) that attaches to platelet surfaces in association with platelet aggregation. These results suggest that vWf-platelet interactions are involved in the platelet clumping process that characterizes TTP.

New families with von Willebrand disease type 2M (Vicenza)

The variant von Willebrand disease (vWd) variant type 2M (Vicenza) was identified in 13 patients of 7 unrelated families. 11 patients were from different parts of germany and 2 patients from Turkey. Hitherto this variant of vWd has been described only in two families originating from the province of Vicenza in Northern Italy. Characteristically this type of vWd shows the supranormal multimers of von Willebrand factor (vWf) in plasma similar to those seen in normal plasma after desmopressin infusion. Clinically, the patients present with bleeding symptoms. Other laboratory abnormalities include reduced values for vWf antigen (vWf: Ag), factor VIII coagulant activity (VII:C), ristocetin cofactor activity (RiCof) and collagen binding activity (vWf: CBA). The hereditary transmission of this variant is consistent with an autosomal dominant mode of inheritance. The patients with vWd type 2M (Vicenza) could be allocated into two subgroups: type "platelet normal" with normal vWf properties in platelets and type "platelet low" with reduced vWf: Ag levels in platelets.

The generation of thrombin in vivo induces the selective loss of high molecular weight multimers of von Willebrand factor and the reversible sequestration of platelets

Various levels of thrombin generation were induced by the infusion of a combination of factor Xa (F.Xa) and phosphatidylcholine/phosphatidylserine (PCPS) vesicles into normal dogs and non-human primates. In the dog, an immediate loss of von Willebrand factor antigen (vWF:Ag) with a progressive recovery to normal levels by 45 min was observed. Multimeric assay demonstrated a selective loss of high molecular weight multimers (HMWM) with subsequent replacement. At low doses, in non-human primates (chimpanzees), identical changes to those seen in the dog were observed and this was associated with an equivalent loss of ristocetin co-factor activity (vWF:RCoF). At high dose a reversal of the wWF response occurred with levels increasing to twice that of baseline values by 2 min and multimeric analysis demonstrated the presence of abnormally large multimers and increased vWF:RCoF specific activity, suggesting that the response at each dosage reflected a net balance of consumption over release. This was supported by in vitro simulation where increasing thrombin generation was associated with a selective loss of HMWM without replacement. In both species, an immediate fall in platelet count occurred and this was directly correlated with the amount of thrombin generated. Full recovery occurred within 45 min and isotopic labelling studies demonstrated that platelet sequestration rather than consumption was occurring. These studies demonstrate that thrombin generation in vivo is associated with a selective loss of the multimeric forms of vWF known to interact with platelets and this may provide an in vivo model to characterize the physiology/pathophysiology of this primary event in haemostasis.

Inactivation of viruses in fresh-frozen plasma

Methylene blue (MB) or solvent/detergent (SD) treatment is used for the inactivation of lipid-enveloped viruses in plasma. One important characteristic of the SD treatment is the necessity to pool plasma from different donors, thus inducing the risk of spreading infectious particles. MB treatment can be applied to single-donor plasma, causing no greater infectious risk than conventional fresh-frozen plasma (FFP). However, the virucidal efficacy of the SD method regarding HIV, HBV and HCV has been significantly better examined and proven than the MB treatment. Most of the therapeutic constituents of both plasma products are well maintained; coagulation factors decrease by roughly 5-20%. SD treatment reduces protein S and alpha 2-antiplasmin by approximately 40%, whereas MB treatment leads to a significant photooxidative alteration of fibrinogen with a disturbance of fibrin polymerization. As current studies show, the use of either plasma product is obviously not limited by acute or chronic toxicity. Several studies are in progress to evaluate the relevance of alterations in FFP quality which may affect the clinical efficacy of virus-inactivated plasma.

Analysis of von Willebrand factor multimers using a commercially available enhanced chemiluminescence kit

AIMS

To develop a rapid, sensitive, and safe method for the analysis of von Willebrand factor (vWf) multimers in plasma or platelet lysates.

METHOD

Analysis of vWf multimers was carried out by sodium dodecyl sulphate-agarose discontinuous gel electrophoresis followed by protein transfer to nitrocellulose membranes by western blotting. Blots were probed using horseradish peroxidase (HRP) conjugated rabbit anti-vWf; visualisation of vWf multimers was achieved using a commercially available enhanced chemi-Luminescence (ECL) kit for detecting HRP labelled antibodies on western blots.

RESULTS

Electrophoretic transfer of vWf multimers to nitrocellulose membranes, including the higher molecular weight forms, was achieved satisfactorily and there was good resolution of individual multimer bands and of the triplet sub-band structure. Type II vWD variants were readily identifiable. The use of ECL conferred a high degree of sensitivity to the method and the end result on autoradiography film provided a permanent record which did not fade and which was suitable for scanning densitometry.

CONCLUSION

The method for vWf multimer analysis described here is sensitive, simple to carry out, uses minimal amounts of reagents, produces results within 48 hours, and does not require the use of potentially hazardous radioactive materials or carcinogenic enzyme substrates.

Chemiluminographic detection of von Willebrand factor multimeric composition

Diagnosis of von Willebrand's disease (vWD) requires quantitation of von Willebrand factor (vWF) in plasma plus qualitative assessment of the vWF multimers according to molecular size ranges. Characterization of vWF multimeric size distributions is typically done using sodium dodecyl sulfate-agarose gel electrophoresis (SDS-AGE) followed by immunoblotting in the gel with radiolabeled antibody against vWF and autoradiographic exposure. We applied a western blot technique to vWF multimeric analysis. It included SDS-AGE, electroblotting onto a membrane, and chemiluminescent detection using rabbit anti-human vWF as primary antibody and goat anti-rabbit IgG as secondary antibody conjugated with horseradish peroxidase. Using this method, 18 to 20 vWF multimers were regularly resolved in normal plasma with exposure times of 2 to 4 sec compared to 4 hr or longer by autoradiography. Sensitivity of detection was at least 4-fold enhanced by chemiluminescence compared to radiolabel. Specificity of the assay was confirmed by analysis of plasma samples known to be deficient to different degrees in the larger vWF multimers. The chemiluminographic assay for vWF multimers is superior to the autoradiographic one because it is more sensitive, avoids use of radioactivity, and has shorter total assay time (under 2 days versus five radiolabel).

Multimeric analysis of von Willebrand factor by vertical sodium dodecyl sulphate agarose gel electrophoresis, vacuum blotting technology and sensitive visualization by alkaline phosphatase anti-alkaline phosphatase complex

To detect von Willebrand factor multimers in plasma samples and factor VIII concentrates, a vertical discontinuous SDS electrophoresis was developed. A vacuum blotting system allowed to improve the transfer to the nitrocellulose membrane. The visualization of the separated multimers was sensitized by applying an alkaline phosphatase anti-alkaline phosphatase staining technique. The reported method clearly shows structural abnormalities of von Willebrand factor and deficiency of high multimers, the vacuum transfer is efficient and the sensitivity of the staining system is very high.