Low-density lipoprotein receptor-related protein polymorphisms in patients with elevated factor VIII coagulant activity and venous thrombosis.

Elevated factor VIII coagulant activity (FVIII:C) levels (>150 IU/dl) represent a prevalent independent risk factor for venous thromboembolism (VTE). Low-density lipoprotein receptor-related protein (LRP) is involved in factor VIII clearance in vivo, and elevated FVIII:C was a feature of the LRP knockout mouse model. Three coding polymorphisms of LRP1 (exon 3, C766T; exon 14, A217V; and exon 39, D2080N), together with an insertion/deletion polymorphism within the first intron of lipoprotein receptor-associated protein (LRPAP1), have been identified. In addition, LRP1 2080D was recently reported to be associated with increased plasma FVIII:C levels in normal individuals. In this study, we investigated the role of these four polymorphisms in patients with objectively confirmed VTE and elevated FVIII:C levels. In our control group, genotype distributions were consistent with previous reports. Neither the allele frequencies nor genotype distributions at LRP1 A217V, LRP1 D2080N and LRPAP1 intron 1 were significantly different between the elevated FVIII:C and control groups. In contrast to previous reports, we found no effect of LRP1 D2080N genotype on plasma FVIII:C levels in normal individuals. More importantly, prevalence of the LRP1 2080D allele was not increased in the group of patients with high FVIII:C and VTE. We conclude that LRP1 and LRPAP1 polymorphisms are not responsible for high FVIII:C levels in patients with VTE.     

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.     

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).     

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.     

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.     

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.     

Gene‐centric approach identifies new and known loci for FVIII activity and VWF antigen levels in European Americans and African Americans

Coagulation factor VIII and von Willebrand factor (VWF) are key proteins in procoagulant activation. Higher FVIII coagulant activity (FVIII:C) and VWF antigen (VWF:Ag) are risk factors for cardiovascular disease and venous thromboembolism. Beyond associations with ABO blood group, genetic determinants of FVIII and VWF are not well understood, especially in non European‐American populations. We performed a genetic association study of FVIII:C and VWF:Ag that assessed 50,000 gene‐centric single nucleotide polymorphisms (SNPs) in 18,556 European Americans (EAs) and 5,047 African Americans (AAs) from five population‐based cohorts. Previously unreported associations for FVIII:C were identified in both AAs and EAs with KNG1 (most significantly associated SNP rs710446, Ile581Thr, P = 5.10 × 10^?7 in EAs and P = 3.88 × 10^?3 in AAs) and VWF rs7962217 (Gly2705Arg, P = 6.30 × 10^?9 in EAs and P = 2.98 × 10^?2 in AAs). Significant associations for FVIII:C were also observed with F8/TMLHE region SNP rs12557310 in EAs (P = 8.02 × 10^?10), with VWF rs1800380 in AAs (P = 5.62 × 10^?11), and with MAT1A rs2236568 in AAs (P = 1.69 × 10^?6). We replicated previously reported associations of FVIII:C and VWF:Ag with the ABO blood group, VWF rs1063856 (Thr789Ala), rs216321 (Ala852Gln), and VWF rs2229446 (Arg2185Gln). Findings from this study expand our understanding of genetic influences for FVIII:C and VWF:Ag in both EAs and AAs. Am. J. Hematol. 90:534–540, 2015. © 2015 Wiley Periodicals, Inc.     

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.     

Contribution of low density lipoprotein receptor-related protein genotypes to coagulation factor VIII levels in thrombotic women

The contribution of low density lipoprotein (LDL) receptor-related protein (LRP) to variance of factor VIII (FVIII) levels in plasma was investigated in thrombotic women through analysis of frequent LRP genotypes. The G allele of the LRP -25C/G polymorphism, predicting increased LRP expression, was associated with 15% and 18% mean reductions of FVIII activity and protein levels, respectively. The combination of -25C/G LRP polymorphism with FVIII D1241E and ABO polymorphisms produced a gradient of FVIII levels, thus supporting the notion that several factors, acting in FVIII biosynthesis, post-translational modification and removal from circulation, have additive effects on the variance of FVIII levels in plasma.     

Effect of von Willebrand factor Y/C1584 on in vivo protein level and function and interaction with ABO blood group

Blood group O and the cysteine allele of the Y/C1584 change in von Willebrand factor (VWF) are enriched in type 1 VWD, but neither causes disease. We investigated the effect of C1584, alone and in combination with the ABO blood group, on the level and properties of plasma VWF. A cohort of 5052 blood donors was recruited: 50 donors were heterozygous for Y/C1584 and 5002 were homozygous for Y/Y1584. Mean VWF antigen (VWF:Ag) for heterozygotes (82 +/- 35 IUdL(-1)) was significantly lower than for homozygotes (111 +/- 37 IUdL(-1)) (P < .001). Foreach ABO blood group, VWF:Ag was decreased among Y/C1584 heterozygotes compared with Y/Y1584 homozygotes; a larger decrease was observed for group O. Among donors with VWF:Ag levels of 50 IUdL(-1) or lower, Y/C1584 heterozygosity was markedly enriched (18%) compared with the entire cohort (1.5%). Blood group O was enriched to a lesser extent (2.4%), but Y/C1584 in conjunction with group O was strikingly enriched (34.8%). VWF collagen binding activity (VWF:CB) and ristocetin cofactor activity (VWF:RCo) were significantly lower for Y/C1584 heterozygotes than for Y/Y1584 homozygotes, and a qualitative difference in Y/C1584 plasma VWF multimer profile was observed compared with that for Y/Y1584 VWF. The data support a multifactorial basis for low VWF levels in some individuals.     

Bombay phenotype is associated with reduced plasma-VWF levels and an increased susceptibility to ADAMTS13 proteolysis

ABO blood group is an important determinant of plasma von Willebrand factor antigen (VWF:Ag) levels, with lower levels in group O. Previous reports have suggested that ABO(H) sugars affect the susceptibility of VWF to ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type-1 repeats-13) cleavage. To further test this hypothesis, we collected plasma from individuals with the rare Bombay blood group. VWF:Ag levels were significantly lower in Bombay patients (median, 0.69 IU/mL) than in groups AB, A, or B (P < .05) and lower than in group O individuals (median, 0.82 IU/mL). Susceptibility of purified VWF fractions to recombinant ADAMTS13 cleavage, assessed using VWF collagen-binding assay (VWF:CB), was increased in Bombays compared with either group O or AB. Increasing urea concentration (0.5 to 2 M) increased the cleavage rate for each blood group but eliminated the differences between groups. We conclude that reduction in the number of terminal sugars on N-linked glycan increases susceptibility of globular VWF to ADAMTS13 proteolysis and is associated with reduced plasma VWF:Ag and VWF:CB levels.     

Identifying carriers of type 2N von Willebrand disease: procedures and significance.

The defective FVIII carrier function of von Willebrand factor (VWF) identifies type 2N von Willebrand disease (VWD), a variant with a pattern resembling hemophilia A. Type 2N characterization is based on the evaluation of the capacity of VWF to bind exogenous FVIII (VWF:FVIIIB). Here we report on a retrospective evaluation of hemostatic laboratory parameters most useful in detecting type 2N carriers. The diagnostic capacity of aPTT, FVIII, VWF:Ag, FVIII/VWF:Ag ratio, VWF:FVIIIB and VWF:FVIIIB/VWF:Ag ratio was evaluated in 21 type 2N VWD carriers. Twenty subjects were heterozygous for the R854Q mutation, one was heterozygous for the R760C missense mutation, which interferes with cleavage of the VWF propeptide. We found that prolongation of aPTT and decrease in FVIII and FVIII/VWF:Ag ratio were not frequent findings in type 2N carriers. The same was true for VWF:FVIIIB which was not always abnormal. On the contrary, VWF:FVIIIB/VWF:Ag ratio was always defective and its values were not related with FVIII and FVIII/VWF:Ag ratio or influenced by plasma VWF concentration. Given these results, we attribute the greatest significance to VWF:FVIIIB/VWF:Ag ratio in the diagnosis of type 2N defects, and only search for type 2N mutations, to validate the diagnosis, if the ratio proves abnormal.     

Influence of single nucleotide polymorphisms in factor VIII and von Willebrand factor genes on plasma factor VIII activity: the ARIC Study

Factor VIII (FVIII) functions as a cofactor for factor IXa in the contact coagulation pathway and circulates in a protective complex with von Willebrand factor (VWF). Plasma FVIII activity is strongly influenced by environmental and genetic factors through VWF-dependent and -independent mechanisms. Single nucleotide polymorphisms (SNPs) of the coding and promoter sequence in the FVIII gene have been extensively studied for effects on FVIII synthesis, secretion, and activity, but impacts of non-disease-causing intronic SNPs remain largely unknown. We analyzed FVIII SNPs and FVIII activity in 10,434 healthy Americans of European (EA) or African (AA) descent in the Atherosclerosis Risk in Communities (ARIC) study. Among covariates, age, race, diabetes, and ABO contributed 2.2%, 3.5%, 4%, and 10.7% to FVIII intersubject variation, respectively. Four intronic FVIII SNPs associated with FVIII activity and 8 with FVIII-VWF ratio in a sex- and race-dependent manner. The FVIII haplotypes AT and GCTTTT also associated with FVIII activity. Seven VWF SNPs were associated with FVIII activity in EA subjects, but no FVIII SNPs were associated with VWF Ag. These data demonstrate that intronic SNPs could directly or indirectly influence intersubject variation of FVIII activity. Further investigation may reveal novel mechanisms of regulating FVIII expression and activity.     

Laboratory diagnostic approach of the parents-children relationship in differentiating low-level von Willebrand factor from mild type 1 von Willebrand disease

The present study aimed to evaluate the parent-child relationship in differentiating between unaffected healthy individuals and those with von Willebrand disease (VWD). This study was performed on 15 children between the ages of 5 and 15 years and parents with personal and familial evidence of bleeding. Diagnosis of VWD as considered 'low von Willebrand factor (VWF) level or mild type 1 VWD' in the following children: those with low VWF levels (VWF:RCo and VWF:Ag between 30 and 50 U/dl), at least one bleeding symptom and a family member with at least one bleeding symptom. Laboratory values in the parents of families 1-7 were VWF:Ag 65-90, VWF:RCo 54-87, and FVIII:C 74-110, versus VWF:Ag 33-47, VWF:RCo 30-42, and FVIII:C 36-67 in their children. The normal laboratory values in the parents of families 1-7 suggested that their children would probably have low VWF levels. Our findings are that VWF levels are increasing with age. Laboratory values in the parents of families 8-15 were VWF:Ag 30-59, VWF:RCo 32-55, and FVIII:C 44-66, versus VWF:Ag 32-48, VWF:RCo 30-54, and FVIII:C 38-55 in their children. The laboratory values in the children from families 8-15 were close to the minimum range of normal or below normal, which suggested that it was possible that the parents and children in families 8-15 could be diagnosed as having mild type 1 VWD. The present study's findings show that comparison of the VWF levels in parents and their children may be helpful in differentiating children with low VWF levels and mild type 1 VWD from children that only have low VWF levels.     

Parameters influencing FVIII pharmacokinetics in patients with severe and moderate haemophilia A

In haemophilia A patients factor VIII (FVIII) recovery and half‐life can vary substantially. There are parameters known to modulate FVIII pharmacokinetics (PK), but they explain only about 34% of the variability. The aim of this study was to identify new parameters that influence FVIII PK and thus to expand the current knowledge. FVIII PK were determined in 42 haemophilia A patients (37 severe, 5 moderate) without inhibitor. Patients' characteristics and laboratory parameters were evaluated for an association with FVIII PK. We analysed plasma levels of low‐density lipoprotein receptor‐related protein 1 (LRP1) and protein C (PC) activity, which had been hypothesized to influence FVIII activity. Furthermore, four variations in intron 6 of the LRP1 gene, which had been shown to influence LRP1, were investigated. FVIII half‐life differed widely from 6.2 to 20.7 h, with a median of 10.0 h. Patients with blood group O had shorter FVIII half‐life compared to patients with non‐O blood group (median FVIII half‐life 9.0 h vs. 10.4 h, P = 0.018). Age was significantly associated with FVIII half‐life (r = 0.32, P = 0.035). Besides age, also VWF antigen (r = 0.52, P < 0.001) and blood group (r = ?0.37, P = 0.015) was associated with FVIII half‐life. No correlation was found with FVIII‐ or LRP1‐genotype, LRP1 or PC concentrations. Our data showed large differences in FVIII PK between individual patients and revealed age, blood group and VWF levels as important determining factors for FVIII half‐life. FVIII genotype or levels of LRP1 or PC had no influence on FVIII PK.     

Relationship between ABO blood groups and von Willebrand factor,ADAMTS13 and factor VIII in patients undergoing hemodialysis

Several studies have demonstrated that non-O blood groups subjects present an increased VTE risk as compared to those carrying O blood group. The aim of this study was to investigate the ABO blood groups influence on factor VIII (FVIII) activity, von Willebrand factor (VWF), and ADAMTS13 plasma levels in patients undergoing hemodialysis (HD). Patients undergoing HD (N=195) and 80 healthy subjects (control group) were eligible for this cross-sectional study. The ABO blood group phenotyping was performed by the reverse technique. FVIII activity was measured through coagulometric method, and VWF and ADAMTS13 antigens were assessed by ELISA. FVIII activity and VWF levels were significantly higher and ADAMTS13 levels was decreased in HD patients, as compared to healthy subjects (P < 0.001, in three cases). HD patients carrying non-O blood groups showed a significant increase in FVIII activity (P = 0.001) and VWF levels (P < 0.001) when compared to carriers of O blood group. However, no significant difference was observed in ADAMTS13 levels (P = 0.767). In the control group, increased in FVIII activity (P = 0.001) and VWF levels (P = 0.002) and decreased in ADAMTS13 levels (P = 0.005) were observed in subjects carrying non-O blood groups as compared to carriers of O blood group.Our data confirmed that ABO blood group is an important risk factor for increased procoagulant factors in plasma, as FVIII and VWF. Admitting the possible role of kidneys in ADAMTS13 synthesis or on its metabolism, HD patients were not able to increase ADAMTS13 levels in order to compensate the increase of VWF levels mediated by ABO blood groups. Considering that non-O blood groups constitute a risk factor for thrombosis, it is reasonable to admit that A, B and AB HD patients need a careful and continuous follow-up in order to minimize thrombotic events.     

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   

Elevated plasma factor VIII in a mouse model of low-density lipoprotein receptor-related protein deficiency

It has been established that low-density lipoprotein receptor-related protein (LRP) is involved in the cellular uptake and degradation of coagulation factor VIII (FVIII) in vitro. To address the physiologic role of LRP in regulating plasma FVIII in vivo, we used cre/loxP-mediated conditional LRP- deficient mice (MX1cre(+)LRP(flox/flox)). Upon inactivation of the LRP gene, MX1cre(+)LRP(flox/flox) mice had significantly higher plasma FVIII as compared with control LRP(flox/flox) mice (3.4 and 2.0 U/mL, respectively; P <.001). Elevated plasma FVIII levels in MX1cre(+)LRP(flox/flox) mice coincided with increased plasma von Willebrand factor (VWF) (2.0 and 1.6 U/mL for MX1cre(+)LRP(flox/flox) and control LRP(flox/flox) mice, respectively; P <.05). Elevation of plasma FVIII and VWF persisted for at least 6 weeks after inactivation of the LRP gene. Upon comparing plasma FVIII and VWF in individual mice, we observed an increase of the FVIII/VWF ratio in MX1cre(+)LRP(flox/flox) mice as compared with control LRP(flox/flox) mice. Administration of either a vasopressin analog or an endotoxin resulted in increased plasma VWF, but not FVIII. In clearance experiments, MX1cre(+)LRP(flox/flox) mice displayed a 1.5-fold prolongation of FVIII mean residence time. Adenovirus-mediated overexpression of the 39-kDa receptor-associated protein (RAP) in normal mice resulted in a 3.5-fold increase of plasma FVIII. These data confirm that the regulation of plasma FVIII in vivo involves a RAP-sensitive mechanism. Surprisingly, plasma FVIII in MX1cre(+)LRP(flox/flox) mice increased 2-fold after RAP gene transfer. We propose that RAP-sensitive determinants other than hepatic LRP contribute to the regulation of plasma FVIII in vivo.     

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.