Correlation between von Willebrand factor antigen,von Willebrand factor ristocetin cofactor activity and factor VIII activity in plasma

Background The laboratory diagnosis of von Willebrand Factor (VWF) deficiencies includes qualitative and quantitative measurements of VWF and clotting factor VIII (FVIII). Since the FVIII activity is frequently normal in patients with mild type 1 or 2 von Willebrand disease (VWD), there is controversy whether FVIII testing should accompany VWF Antigen (VWF:Ag) assay. Methods The aim of this study was to explore the correlation between VWF:Ag, VWF ristocetin cofactor activity (VWF:RCo) and FVIII in 213 consecutive patients undergoing screening for VWD. Results Forty-six patients were identified with VWF:Ag levels lower than the diagnostic threshold (54 IU/dl). A significant correlation was observed between VWF:Ag and VWF:RCo (r = 0.892; p < 0.001), VWF:Ag and FVIII (r = 0.834; p < 0.001), VWF:RCo and FVIII (r = 0.758; p < 0.001). Receiver operating characteristic curve analysis of the VWF:Ag assay revealed an area under the curve of 0.978 and 0.957 for detecting life-threatening values of FVIII (<30 IU/dl) and VWF:RCo (<40 IU/dl), respectively. The negative and positive predictive values at the VWF:Ag threshold value of 54 IU/dl were 100% and 33% for detecting life-threatening FVIII deficiencies, 94% and 80% for identifying abnormal values of VWF:RCo. Conclusions Due to the excellent correlation between VWF:Ag and FVIII and to the diagnostic efficiency of VWF:Ag for identifying abnormal FVIII levels in patients with VWF deficiency, routine measurement of FVIII may not be necessary in the initial screening of patients with suspected VWD. However, the limited negative predictive value of VWF:Ag for identifying type 2 VWD does not allow to eliminate VWF:RCo or VWF:FVIIIB assays from the diagnostic workout.     

A comparative in vitro evaluation of six von Willebrand factor concentrates

The efficacy of von Willebrand factor (VWF) concentrates for treatment of von Willebrand disease (VWD) is dependent on their content of VWF and factor VIII (FVIII). STUDY OBJECTIVES: To measure the content and quality of VWF and FVIII in six VWF concentrates: Haemate-P (Aventis Behring), Immunate (Baxter Bioscience), Koate (Bayer Corp.), 8Y (BPL), Innobrand (LFB) and Facteur Willebrand (LFB). METHODS: The VWF antigen content (VWF:Ag), ristocetin cofactor activity (VWF:RCo), collagen-binding activity (VWF:CB), VWF multimers with electrophoresis and densitometry, FVIII activity and total protein content. RESULTS: Specific activity (VWF:RCo/total protein) varied considerably (4.7-129.5 IU mg(-1)). Activity measures, VWF:RCo and VWF:CB, correlated well, but we found no correlation between any of these and VWF:Ag. The content of high-molecular weight multimer (HMWM) was normal or close to normal in Haemate-P, Innobrand and Facteur Willebrand, moderately reduced in Koate and 8Y, and significantly reduced in Immunate. The HMWM content correlated significantly with the VWF:RCo/VWF:Ag ratio. Only Haemate-P, Innobrand and Facteur Willebrand had VWF:RCo/VWF:Ag ratios >0.7. We found large differences in the content of FVIII and in the FVIII/VWF:RCo ratio. Facteur Willebrand had the lowest (0.02) and Immunate the highest (6.00) ratio. CONCLUSION: Treating physicians must be aware of the large differences between different VWF concentrates and the potential clinical implications. Concentrates lacking HMWM are probably less efficient for mucosal bleedings. FVIII is most important for surgical bleedings, but concentrates with high FVIII/VWF-ratio may induce very high FVIII levels with increased risk of thrombosis. A low FVIII content may be preferable except in case of acute surgery.     

Biological and genetic factors influencing plasma factor VIII levels in a healthy family population: results from the Stanislas cohort

The mechanisms underlying the variability of factor VIII (FVIII) levels are still poorly understood. The only receptor of FVIII identified so far is the lipoprotein receptor-related protein (LRP), which is thought to be involved in FVIII degradation. We aimed to characterize biological and genetic factors related to FVIII variability, focusing on coding polymorphisms of the LRP gene and polymorphisms potentially detected by molecular screening of the LRP-binding domains of the FVIII gene. Plasma FVIII coagulant activity (FVIII:C) and von Willebrand factor (VWF:Ag) antigen levels were measured in a sample of 100 healthy nuclear families (200 parents and 224 offspring). The ABO blood group and the three coding polymorphisms of the LRP gene (A217V, D2080N and C766T) were genotyped. Lipids and anthropometric factors poorly contributed to the variability of FVIII:C (<5%). A strong effect of ABO blood groups on FVIII:C levels was observed that remained significant after adjustment for VWF:Ag levels (P = 0.02). These two factors explained more than 50% of FVIII:C variability. After adjustment for VWF:Ag and ABO blood groups, a residual resemblance for FVIII:C persisted between biological relatives (rho = 0.13 +/- 0.06 between parents and offspring, rho = 0.24 +/- 0.09 between siblings) compatible with an additional genetic influence. The N allele of the LRP/D2080N polymorphism was associated with decreased levels of FVIII:C (90.4 +/- 8.7 vs. 102.2 +/- 3.5 IU/dl, P = 0.03) and VWF:Ag levels (109.1 +/- 11.2 vs. 125.4 +/- 4.4 IU/dl, P = 0.02). No polymorphism was detected in the LRP-binding domains of the FVIII gene. This study reinforces the hypothesis of a genetic influence of FVIII levels beyond the influence of VWF:Ag and ABO blood groups. The D2080N polymorphism of the LRP gene weakly contributed to the variability of FVIII:C levels in this healthy population.     

Relationships between factor VIII:Ag and factor VIII in recombinant and plasma-derived factor VIII concentrates

A variety of plasma-derived (pd) and recombinant (r) factor VIII (FVIII) concentrates are used to prevent and treat bleeding in severe hemophilia A patients. A significant side effect of FVIII replacement is the development of FVIII neutralizing antibodies (inhibitors) in up to 30% of patients receiving FVIII concentrates. The FVIII protein content (FVIII:Ag) per unit of FVIII:C in FVIII concentrates, and how effectively the FVIII:Ag in FVIII concentrates binds to von Willebrand factor (VWF) may provide information relevant for the survival of FVIII:C in vivo and for estimating the risk for inhibitor development. The FVIII:Ag content of nine r-FVIII and nine pd-FVIII concentrates were quantified in this study using two enzyme-linked immunosorbent assay (ELISA) platforms. The two ELISA platforms were based on the use of a monoclonal anti-(FVIII light chain)-IgG and polyclonal anti-FVIII antibodies as capture antibodies and both ELISAs were equally able to detect > or =0.005 IU of FVIII:Ag. Measured in international units, the r-FVIII concentrates contained significantly higher FVIII:Ag per unit of FVIII:C than the pd-FVIII concentrates. The VWF-binding profiles of the r-FVIII and pd-FVIII concentrates were also determined by gel filtration chromatography. Unlike the plasma-derived products, the r-FVIII concentrates invariably contained a fraction of FVIII:Ag molecules (approximately 20%) which was unable to associate with VWF. Given that VWF regulates both factor VIII proteolysis and survival of FVIII:Ag in vivo, the fraction of FVIII:Ag unable to bind to VWF may have a reduced survival and be more susceptible to proteolytic degradation in vivo. The extent to which the fractions of FVIII:Ag in concentrates able and unable to bind to VWF contribute to inhibitor development in severe FVIII-deficient patients is unknown.     

Genotype at the secretor blood group locus is a determinant of plasma von Willebrand factor level

Previous reports on the effect of Secretor and Lewis blood groups on plasma factor VIII-von Willebrand factor (FVIII-VWF) levels have produced conflicting findings. To determine whether either or both loci can influence plasma FVIII-VWF complex levels, we studied the relationship between Secretor and Lewis genotypes, determined definitively using polymerase chain reaction-restriction fragment length polymorphism analysis, and plasma FVIII coagulant activity (FVIII:C) and VWF antigen (VWF:Ag) levels in 136 healthy volunteers. Overall, significantly higher VWF:Ag levels were found in those individuals homozygous for the Se allele (genotype SeSe) than in those heterozygous for the Se allele (P < 0.001). To minimize any confounding influence of ABO genotype/phenotype, we investigated the relationship between Secretor genotype and plasma FVIII-VWF levels within individuals of the same ABO blood group genotype. In the subgroup analysis of group O1O1 individuals alone, VWF:Ag levels were again significantly higher in those individuals with Secretor genotype SeSe than in those either heterozygous or homozygous for the se null allele. Among A1O1 subjects, homozygous Secretors also had significantly higher VWF:Ag levels. In contrast, we found no relationship between Lewis genotype and either VWF:Ag or FVIII:C levels. This study is the first based on genotypic rather than serological analysis, and resolves the previously confounding effects of the Lewis and Secretor loci on plasma FVIII-VWF complex levels.     

Postpartum von Willebrand factor levels in women with and without von Willebrand disease and implications for prophylaxis

The aim of this study was to elucidate the fall in von Willebrand factor (VWF) and factor VIII activity (FVIII) after childbirth in women with and without von Willebrand disease (VWD). VWF:RCo, VWF:Ag, and FVIII were obtained in the third trimester of pregnancy, on admission for childbirth, and 10 times postpartum. Specimens were processed within 4 h and analysed centrally. Means were calculated at each time point. Forty women (40 pregnancies) without VWD and 32 women (35 pregnancies) with VWD were enrolled. 15/32 with VWD were treated (30% of those with type 1 and all of those with type 2) in 17 pregnancies. Treatments prior to delivery consisted of desmopressin (2/17), VWF concentrate (15/17) and after delivery VWF concentrate (16/17). Duration of treatment was 0–21 days (median 6). VWF levels peaked at 250% of baseline – 4 h postpartum in women with VWD and 12 h postpartum in women without VWD. Thereafter, VWF levels fell rapidly, approached baseline at 1 week and reached baseline at 3 weeks. Except immediately postpartum, when the levels among treated cases were higher, levels among women with VWD appeared to parallel, but were lower than those among women without VWD. Levels were lowest among those who received treatment. VWF levels fall rapidly after childbirth. Except immediately postpartum, current treatment strategies do not raise VWF levels to the levels of women without VWD or even to the levels of women with milder, untreated VWD. Consequently, women with VWD may be at risk of postpartum haemorrhage despite treatment.     

Determinants of factor VIII plasma levels in carriers of haemophilia A and in control women

Summary.  Factor VIII (FVIII) levels show a considerable variability in female carriers of haemophilia A. Presently, the reasons for this are poorly understood. The aim of the study was to elucidate the influence of genetic and non-genetic parameters on FVIII plasma levels in carriers ( n  = 42). Results were compared with age-matched healthy women without carriership of haemophilia A ( n  = 42). Each carrier was tested for the family-specific mutation, ABO blood group, FVIII level, von Willebrand factor (VWF) antigen and activity and C-reactive protein (CRP). FVIII levels were lower in carriers compared to non-carriers [74% (51–103) vs. 142% (109–169), P  < 0.001]. No statistically significant differences were observed between the two groups with respect to VWF activity, prothrombin–time, hs-CRP, fibrinogen, body mass index (BMI), age and smoking status as well as the distribution of ABO blood groups. In non-carriers, FVIII was statistically significantly correlated with BMI, activated partial thromboplastin time (APTT), VWF antigen, hs-CRP and fibrinogen. In carriers, significant correlations between FVIII and APTT, VWF antigen and activity were found, whereas BMI, hs-CRP or fibrinogen did not correlate with FVIII. In non-carriers, the association of FVIII with ABO blood groups was statistically significant ( P  = 0.006), but not in carriers of haemophilia A ( P  = 0.234). The type of FVIII gene mutation did not influence FVIII levels. Carrier status is the major determinant of a carrier`s FVIII plasma level. Factors known to influence FVIII levels in the general population do not significantly affect FVIII activity in carriers, neither does the type of mutation influence FVIII levels.     

Outgrowing the laboratory diagnosis of type 1 von Willebrand disease: A two decade study

Von Willebrand Factor (VWF) levels are known to increase with age in the general population, but that effect is unclear in von Willebrand disease (VWD) patients. Thus, it is important to assess the trends of VWF levels with age, and the extent and rate of their normalization in patients with VWD. In a retrospective cohort study, we reviewed the medical records of 126 patients between 1996 and 2016 who met the NHLBI diagnostic criteria for type 1 VWD or “Low VWF” (LVWF). We followed all their historically documented VWF antigen (VWF:Ag), VWF activity (VWF:RCo), and Factor VIII (FVIII) levels longitudinally over time, correlating data with clinical setting at time of testing. The average duration of follow‐up was 10.5 ± 3.7 years (SD). Out of the total study population, 27.8% achieved the primary outcome of complete normalization (CN) of both VWF:Ag and VWF:RCo levels, including 19.6% and 32.5% of those with VWD and LVWF, respectively. Linear regression demonstrated statistically significant positive trends of VWF:Ag, VWF:RCo, FVIII with time, calculated at 2.4, 1.4, and 1.4 U dL‐1/year, respectively (P < .001 each). In the largest study population of VWD patients to date whose levels were followed longitudinally, there is a statistically significant rise in VWF:Ag, VWF:RCo, and FVIII levels observed with time. CN of both VWF:Ag and VWF:RCo levels was observed in almost a third of patients with VWD or LVWF, over an average of 10 years. Whether the bleeding phenotype also improves is unclear and requires further study.     

Intravenous DDAVP and factor VIII-von Willebrand factor concentrate for the treatment and prophylaxis of bleedings in patients With von Willebrand disease type 1, 2 and 3.

The current standard set of von Willebrand factor (VWF) parameters used to differentiate type 1 from type 2 VWD include bleeding times (BTs), factor VIII coagulant activity (FVIII:C), VWF antigen (VWF:Ag), VWF ristocetine cofactor activity (VWF:RCo), VWF collagen binding activity (VWF:CB), ristocetine induced platelet aggregation (RIPA), and analysis of VWF multimers in low and high resolution agarose gels and the response to DDAVP. The BTs and RIPA are normal in asymptomatic carriers of a mutant VWF allele, in dominant type 1, and in recessive type 2N VWD, and this category has a normal response of VWF parameters to DDAVP. The response of FVIII:C is compromised in type 2N VWD. The BTs and RIPA are usually normal in type Vicenza and mild type 2A VWD, and these two VWD variants show a transiently good response of BT and VWF parameters followed by short in vivo half life times of VWF parameters. The BTS are strongly prolonged and RIPA typically absent in recessive severe type 1 and 3 VWD, in dominant type 2A and in recessive type 2C (very likely also 2D) VWD and consequently associated with low or absent platelet VWF, and no or poor response of VWF parameters to DDAVP. The BTs are prolonged and RIPA increased in dominant type 2B VWD, that is featured by normal platelet VWF and a poor response of BT and functional VWF to DDAVP. The BTs are prolonged and RIPA decreased in dominant type 2A and 2U, that all have low VWF platelet, very low VWF:RCo values as compared to VWF:Ag, and a poor response of functional VWF to DDAVP. VWD type 2M is featured by the presence of all VWF multimers in a low resolution agarose gel, normal or slightly prolonged BT, decreased RIPA, a poor response of VWF:RCo and a good response of FVIII and VWF:CB to DDAVP and therefore clearly in between dominant type 1 and 2U. The existing recommendations for prophylaxis and treatment of bleedings in type 2 VWD patients with FVIII/VWF concentrates are mainly derived from pharmocokinetic studies in type 3 VWD patients. FVIII/VWF concentrates should be characterised by labelling with FVIII:C, VWF:RCo, VWF:CB and VWF multimeric pattern to determine their safety and efficacy in prospective management studies. As the bleeding tendency is moderate in type 2 and severe in type 3 VWD and the FVIII:C levels are near normal in type 2 and very low in type 3 VWD patients. Proper recommendations of FVIII/VWF concentrates using VWF:RCo unit dosing for the prophylaxis and treatment of bleeding episodes are proposed and has to be stratified for the severity of bleeding, the type of surgery either minor or major and for type 2 and type 3 VWD as well.     

The relationship between ABO groups and subgroups, factor VIII and von Willebrand factor

The aim of this study was to correlate ABO groups with plasma levels of factor VIII (FVIII), von Willebrand factor (VWF:Ag), and ristocetin cofactor (VWF:RCo). Serological and molecular tests defined blood groups from 114 donors (10 AA, 10 BB, 10 AB, 10 AO1, 10 BO1,16 O1O1, 20 A2O1, 20 A2B, 4 A3O1, 3 AxO1, and 1 BelO1). The levels of VWF:Ag, FVIII and VWF:RCo observed in rare subgroups (A3O1, AxO1, BelO1) were similar to the values found in the O1O1 group. However, levels of these factors were significantly higher in A2O1 donors than in O1O1 donors (VWF:Ag p=0.01; FVIII p=0.04; VWF:RCo p<0.001). Strong correlations were demonstrated between plasma levels of VWF:Ag and FVIII (R=0.77; p=0.001) and between VWF:Ag and VWF:RCo (R=0.75; p=0.001).     

Correlation between endogenous VWF:Ag and PK parameters and bleeding frequency in severe haemophilia A subjects during three‐times‐weekly prophylaxis with rFVIII‐FS

Patients with severe haemophilia A experience frequent and spontaneous bleeding, causing debilitating damage to joints and decreasing quality of life. Prophylaxis with factor VIII (FVIII) reduces joint damage if initiated early. Circulating FVIII levels may be influenced by endogenous von Willebrand factor (VWF), a chaperone protein that binds and stabilizes FVIII. The aim of this study was to determine whether endogenous VWF antigen (VWF:Ag) levels are correlated with FVIII pharmacokinetic (PK) parameters and clinical outcomes in patients with severe haemophilia A. Previously treated, non‐inhibitor patients in a multinational, randomized, double‐blind, Ph II study received prophylaxis with once‐weekly BAY 79‐4980 (35 IU kg^?1) or thrice‐weekly recombinant sucrose‐formulated FVIII (rFVIII‐FS; 25 IU kg^?1). PK parameters were evaluated at weeks 1 and 26. The number of bleeds per patient during the study was captured as part of the core efficacy endpoint. Spearman rank correlations assessed relationships of VWF:Ag levels with patient age, PK and annualized bleeding rate. Of 131 study patients (aged 13?64 years; BAY 79‐4980, n = 63; rFVIII‐FS, n = 68), 27 (21%; n = 15 and 12 respectively) were evaluable for PK assessment. Baseline VWF:Ag levels correlated with patient age (P < 0.0001). There was no significant difference in PK results between treatments; thus, PK parameters and VWF levels of all patients were analysed together. AUC_norm and T_1/2 significantly increased with increased VWF:Ag (P < 0.001); clearance significantly decreased with increased VWF:Ag (P = 0.002). Annualized bleeding rate in patients treated with 3× per week rFVIII‐FS significantly correlated with VWF:Ag and age (P = 0.038 and 0.021 respectively). PK parameters as well as the clinical outcome significantly correlated with endogenous VWF:Ag. The improved clinical outcome in subjects with high VWF:Ag levels may be explained by VWF:Ag influence on FVIII PK.     

Comorbidities associated with higher von Willebrand factor (VWF) levels may explain the age‐related increase of VWF in von Willebrand disease

Some comorbidities, such as hypertension, are associated with higher von Willebrand factor (VWF) levels in the general population. No studies have been conducted to assess this association in patients with von Willebrand disease (VWD). Therefore, we studied this association in patients with type 1 (n = 333) and type 2 (n = 203) VWD from the ‘WiN” study. VWF antigen (VWF:Ag) was higher in type 1 VWD patients with hypertension [difference: 0·23 iu/ml, 95% confidence interval (CI): 0·11–0·35], diabetes mellitus (0·11 iu/ml, 95% CI: −0·02 to 0·23), cancer (0·14 iu/ml, 95% CI: 0·03–0·25) and thyroid dysfunction (0·14 iu/ml, 95% CI: 0·03–0·26) than in patients without these comorbidities (all corrected for age, sex and blood group). Similar results were observed for VWF collagen binding capacity (VWF:CB), VWF activity as measured by the VWF monoclonal antibody assay (VWF:Ab) and factor VIII (FVIII) coagulant activity (FVIII:C). In type 1 VWD, age was associated with higher VWF:Ag (0·03 iu/ml; 95% CI: 0·01–0·04), VWF:CB (0·02 iu/ml; 95% CI: 0·00–0·04), VWF:Ab (0·04 iu/ml; 95% CI: 0·02–0·06) and FVIII:C (0·03 iu/ml; 95% CI: 0·01–0·06) per decade increase. After adjustment for relevant comorbidities, these associations were no longer significant. Despite the higher VWF and FVIII levels, type 1 VWD patients with comorbidities had more bleeding episodes, particularly during surgery. There was no association between comorbidities and VWF/FVIII levels or bleeding phenotype in type 2 VWD patients. In conclusion, comorbidities are associated with higher VWF and FVIII levels in type 1 VWD and may explain the age‐related increase of VWF and FVIII levels.     

Analysis of current perioperative management with Haemate® P/Humate P® in von Willebrand disease: Identifying the need for personalized treatment

Introduction

Patients with Von Willebrand disease (VWD) are regularly treated with VWF‐containing concentrates in case of acute bleeding, trauma and dental or surgical procedures.

Aim

In this multicentre retrospective study, current perioperative management with a von Willebrand factor (VWF)/Factor VIII (FVIII) concentrate (Haemate^® P) in patients with VWD was evaluated.

Patients/Methods

Patients with VWD undergoing minor or major surgery between 2000 and 2015, requiring treatment with a VWF/FVIII concentrate (Haemate^® P), were included. Achieved VWF activity (VWF:Act) and FVIII during FVIII‐based treatment regimens were compared to predefined target levels in national guidelines.

Results

In total, 103 patients with VWD (148 surgeries) were included: 54 type 1 (73 surgeries), 43 type 2 (67 surgeries) and 6 type 3 (8 surgeries). Overall, treatment resulted in high VWF:Act and FVIII levels, defined as ≥0.20 IU/mL above predefined levels. In patients with type 1 VWD, respectively, 65% and 91% of trough VWF:Act and FVIII levels were higher than target levels. In patients with type 2 and type 3 VWD, respectively, 53% and 57% of trough VWF:Act and 72% and 73% of trough FVIII levels were higher than target level. Furthermore, FVIII accumulation over time was observed, while VWF:Act showed a declining trend, leading to significantly higher levels of FVIII than VWF:Act.

Conclusion

High VWF:Act and accumulation of FVIII were observed after perioperative FVIII‐based replacement therapy in patients with VWD, both underlining the necessity of personalization of dosing regimens to optimize perioperative treatment.     

Haemostatic changes and acquired activated protein C resistance in normal pregnancy.

Influence of changes in levels of coagulation factors and anticoagulants on acquired activated protein C (APC) resistance were studied in 40 healthy women during normal pregnancy. Factor VIII (FVIII), von Willebrand factor antigen (VWF:Ag), free protein S (FPS) and protein C were determined at 5-13, 14-26 and 27-40 weeks gestation and more than 6 weeks postpartum. APC anticoagulant activity was determined by measuring the activated partial thromboplastin time before and after adding human APC, expressed as the APC-sensitivity ratio (APC-SR). During the second and third gestation trimesters a significant increase (P < 0.05) in FVIII and VWF:Ag levels and a decrease in FPS levels were seen compared with the first trimester. Postpartum FVIII and VWF:Ag levels significantly decreased and FPS levels increased compared with the third trimester. Protein C levels remained unchanged during pregnancy and postpartum. Between increased FVIII and lowered APC-SR a trend of inverse correlation (r = -0.329; P = 0.076) occurred in the second trimester. No correlation was found between APC-SR and FPS or VWF:Ag levels. A remarkable finding is the strong inverse relationship between APC-SR and protein C levels (r 相似文献   

A shorter von Willebrand factor survival in O blood group subjects explains how ABO determinants influence plasma von Willebrand factor

ABO blood groups greatly influence circulating von Willebrand factor (VWF) levels, and O group subjects have lower VWF values. In this study, we investigated whether ABO groups affect VWF survival by monitoring the post-DDAVP (1-desamino-8-d arginine vasopressin) time courses of VWF antigen (VWF:Ag), VWF collagen binding (VWF:CB), and factor VIII (FVIII) in 47 healthy subjects (28 O and 19 non-O blood groups). The elimination half-life (T1/2el) of VWF was found significantly shorter in O than in non-O subjects (10.0+/-0.8 hours vs 25.5+/-5.3 hours, respectively; P<.01), as was the T1/2el of VWF:CB (7.9+/-0.5 hours vs 20.9+/-4.5 hours; P<.01). A direct linear correlation was found between basal VWF:Ag and T1/2el, subjects with higher VWF levels having longer-surviving VWF. ABO blood groups appeared to strongly influence VWF clearance, but not its synthesis or release from endothelial cells. The VWF propeptide to VWF:Ag ratio, useful for predicting an increased VWF clearance, was found significantly higher in O than in non-O individuals (1.6+/-0.1 vs 1.2+/-0.5, P<.001), with values that correlated inversely with T1/2el (P<.001). Based on these findings, we conclude that the lower VWF values in O group individuals is attributable to a shorter VWF survival and circulating VWF values are strongly influenced by its half-life.     

Relationship between ABO and Secretor genotype with plasma levels of factor VIII and von Willebrand factor in thrombosis patients and control individuals

In contrast to earlier reports, this study examined the relationship between plasma levels of factor VIII (FVIII) and von Willebrand factor (VWF) and ABO blood group and secretor status at the genetic level in 355 patients with venous thrombosis as well as in 236 controls. ABO glycosyl transferase alleles A(1) and B were more frequent in the thrombosis collective and alleles O(1), O(2) and A(2) were more frequent in the controls. A low-risk group for venous thrombosis of individuals with genotypes O(1)O(1), O(1)O(2) and O(1)A(2) (H-antigen rich) could be distinguished from a high-risk group with genotypes A(1)A(1), A(1)B, O(1)A(1) and O(1)B (H-antigen poor). In both the thrombosis and control groups, the H-antigen rich group showed significantly lower levels of FVIII coagulant activity (FVIII:C) and VWF antigen (VWF:Ag) than the H-antigen poor group. The frequency of the different secretor genotypes in the thrombosis group was not different from that in the control group. No significant differences of FVIII:C and VWF:Ag levels were seen between SeSe, Sese and sese individuals in the thrombosis and in the control group. Thus the risk of venous thrombosis is associated with the ABO blood group genotype but not with secretor status.     

Content and functional activity of von Willebrand factor in apheresis plasma

BACKGROUND AND OBJECTIVES: Von Willebrand Factor (VWF) is a complex high-molecular-weight (HMW) plasma glycoprotein playing a critical role in primary and secondary haemostasis. Owing to its multimeric structure and sensitivity to proteolysis, VWF can be used as a marker of the impact of collection procedures on the characteristics of plasma for transfusion and for fractionation. We studied VWF content, functional activity and HMW multimers in plasmas collected by five different automated apheresis collection procedures. MATERIALS AND METHODS: Five series of 30 plasma units were obtained from volunteer donors at two collection sites using Haemonetics PCS2 machines with Revision (Rev) F, Rev G, high-separation core (HSC), or filter core (FC) procedures, or Baxter-Fenwall Autopheresis-C (Auto-C). VWF antigen (VWF:Ag), ristocetin cofactor (VWF:RCo) activity and HMW multimers were first determined in 10 randomly selected plasma donations collected with Rev G, HSC, FC and Auto-C procedures. Then, the same analyses and the collagen binding (VWF:CB) activity were determined in the pools of 30 donations from each of the five procedures and compared with two normal plasma pools (NPP1 and NPP2). A reference plasma (RP) was used to calibrate each assay. RESULTS: There were a greater number of group O individuals in the Rev F, Rev G and FC donors than in the HSC and Auto-C donors. The mean VWF:Ag level was > 100 IU/dl, VWF:RCo activity was > 90 U/dl, the VWF:RCo/Ag ratio was close to 1, and the percentage of 11-15 mers was above 100% of RP in the 10 individual plasma units from Rev G, HSC, FC, and Auto-C and in their respective pools. The mean percentage of multimers > 15 mers, relative to RP, was significantly less in Rev G plasmas (48 +/- 17%; range 32-91%), compared with Auto-C, HSC and FC plasmas (P = 0.0211; 0.0257; and 0.0376, respectively). The VWF:CB activity of the 30-donation pools was 61 and 60 U/dl in Auto C and HSC, 50 U/dl in Rev F and FC, and 43 U/dl in the Rev G pool. The VWF:CB/Ag ratio was 0.54 (Auto-C), 0.49 (HSC), 0.46 (Rev F), 0.45 (FC) and 0.37 (Rev G), compared with 0.81and 0.92 in NPPs. The percentage of VWF multimers of 11-15 mers in apheresis plasma and NPP was normal. VWF multimers > 15 mers ranged from 38 to 64% of that of RP plasma, and was 111 and 112% in NPPs. CONCLUSIONS: The VWF:Ag, VWF:RCo activity and 11-15 mer VWF multimers were well preserved in all plasma units from each of the five apheresis procedures. The VWF:CB activity and the percentage of multimers > 15 mers in apheresis plasma was less than in normal plasma pools and differed slightly among procedures.     

The fraction of recombinant factor VIII:Ag unable to bind von Willebrand factor has no FVIII coagulant activity: studies in vitro

A fraction of FVIII:Ag in commercial recombinant FVIII (rFVIII) cannot bind VWF whereas all the FVIII:Ag in plasma‐derived FVIII (pd‐FVIII) concentrates does. To compare the FVIII:C activities of the fractions of rFVIII:Ag that can and cannot bind VWF. The FVIII:Ag contents of the rFVIII Kogenate, and Advate and a pd‐FVIII‐pd‐VWF (Fanhdi) were measured by ELISA. The FX activation was initiated by adding 1.0 IU of FVIII:C of each FVIII‐containing product to a coagulant phospholipids suspension containing 1.0 nm FIXa, 100 nm FX, 1 μm hirudin and 2 mm calcium chloride and measured after 1, 5 and 10 min. The same approach was followed after adding 2.0 IU of pd‐VWF to1.0 IU of FVIII:C of Kogenate or Advate. The FVIII:Ag content/IU of FVIII:C of Kogenate, Advate and Fanhdi were 1.80 ± 0.05, 1.31 ± 0.9 and 0.84 ± 1.5 IU respectively. Only Kogenate and Advate effectively enhanced FX activation 1 min after adding each FVIII:C to the coagulant suspension containing FIXa and FX. Thus, the FXa initially generated by FIXa readily activated FVIII:C in control Kogenate and Advate to thereby effectively enhance FX activation while the VWF in Fanhdi continued to suppress FX activation for up to 10 min. Addition of pd‐VWF to Kogenate or Advate effectively decreased their enhancements of FX activation to the same level as Fanhdi over 10 min. The FVIII:Ag fraction in Kogenate and Advate that cannot bind VWF appears to be inactive as it has no measureable FVIII:C activity in the presence of added VWF in vitro.     

Presurgical pharmacokinetic analysis of a von Willebrand factor/factor VIII (VWF/FVIII) concentrate in patients with von Willebrand’s disease (VWD) has limited value in dosing for surgery

Summary. Optimal doses of von Willebrand Factor/Factor VIII (VWF/FVIII) concentrates for surgical procedures in patients with VWD need to be determined. A prospective, multicenter study was performed that included an initial pharmacokinetic (PK) assessment following a standard dose of VWF/FVIII concentrate (Humate‐P^®) to determine individual PK parameters and guide therapeutic dosing during surgery. Forty one subjects received 60 IU kg^?1 VWF: RCo. Median plasma levels, half‐life, mean change from baseline and in vivo recovery (IVR) values were determined for VWF:RCo, VWF:Ag, and FVIII: C, and area under the plasma time‐concentration curve (AUC), mean residence time (MRT), clearance, volume of distribution and dose linearity were also assessed for VWF:RCo at various time points. Median baseline VWF:RCo level was 13 IU dL^?1 (range, 6–124); with a mean change from baseline >100 IU dL^?1 immediately after the infusion, decreasing to 10 IU dL^?1 at 48 h postinfusion. The group median incremental in vivo recovery (IVR) for VWF:RCo was 2.4 IU dL^?1 per IU kg^?1, for VWF:Ag 2.3 IU dL^?1 kg^?1 and for FVIII:C was 2.7 IU dL^?1 per IU kg^?1. When analysing individual recovery values on repeated infusions, a very weak correlation was observed between presurgery IVR and IVR for both VWF:RCo and FVIII, measured at various times just prior to and after the surgical procedure. Although group median values were fairly consistent among repeated IVR measurements, the intra‐individual IVR values for FVIII and VWF:RCo with repeated infusions showed a large degree of variability. IVR values obtained from pharmacokinetic analyses performed in advance of anticipated surgery do not reliably predict postinfusion circulating levels of VWF:RCo or FVIII attained preoperatively or with subsequent peri‐operative infusions.     

Pharmacokinetics of recombinant factor VIII (Kogenate-FS®) in children and causes of inter-patient pharmacokinetic variability

Summary.  Understanding the pharmacokinetics (PK) of factor VIII (FVIII) is important in the management of patients with haemophilia A. We studied the PK of FVIII in order to determine aetiological factors contributing to PK variability of FVIII in children.
Twenty children with haemophilia A (mean age 12.8 years) were administered a single bolus of 50 U kg⁻¹ of recombinant FVIII (rFVIII; Kogenate-FS^®, Bayer).
The mean incremental FVIII recovery was 1.87 (U mL⁻¹)/(U kg⁻¹) (range: 1.25–2.76) and the mean FVIII half-life was 10.7 h (range: 7.8–15.3). FVIII recovery was positively correlated with body surface area (BSA; P  = 0.04). FVIII half-life was positively correlated with preinfusion levels of von Willebrand factor antigen (VWF:Ag) ( P  = 0.0001) and was reduced in patients ( n  = 6) with very low FVIII inhibitor titres (<0.5 BU) vs. those ( n  = 14) with negative inhibitor titres ( P  = 0.06).
These observations suggest that (i) young children with haemophilia in comparison with adults have a low recovery of FVIII and that this might be explained by differences in body composition (BSA, plasma volume), (ii) levels of VWF:Ag may explain some of the differences in the half-life and clearance of FVIII and (iii) very low inhibitor titres, previously regarded as clinically insignificant, may actually be significant and should be evaluated in the context of PK studies.