The association of factor VIII with von Willebrand factor

Factor VIII (FVIII) and von Willebrand factor (vWF) are plasma glycoproteins that circulate as a tightly associated complex. Because they tend to copurify during procedures designed to isolate the biologic activities associated with them, their identity as distinct entities became unequivocally established only during the past 10 years. Improved procedures for the isolation of FVIII, the deduction of the amino acid sequences of FVIII and vWF by using molecular cloning techniques and by direct sequencing, and the use of a variety of biophysical and immunochemical techniques have enhanced the understanding of the FVIII-vWF association. Each subunit of multimeric vWF potentially can bind a single heterodimeric FVIII molecule, although in vivo most of these binding sites are empty. The binding of FVIII to vWF is primarily, if not exclusively, mediated by the light chain of FVIII to the amino-terminal region of the vWF subunit. Cleavage of a fragment from the amino-terminal region of the FVIII light chain by thrombin results in rapid dissociation of the FVIII-vWF complex, a process that apparently is necessary for development of procoagulant activity. Whether this cleavage is needed for the activation of FVIII in the absence of vWF is controversial. The extracellular association of FVIII with vWF may be necessary for efficient secretion of FVIII from its cell of origin. The thermodynamics, kinetics, and nature of the molecular contacts involved in the interaction have not been studied. The association of FVIII with vWF prolongs the lifetime of FVIII in plasma. Whether the FVIII-vWF interaction has other functional roles, such as restricting the location of procoagulant activity, remains unknown.     

Linkage analysis of factor VIII and von Willebrand factor loci as quantitative trait loci

Summary.   Elevated factor (F)VIII levels contribute to venous thrombotic risk. FVIII levels are determined to a large extent by levels of von Willebrand factor (VWF), its carrier protein which protects FVIII against proteolysis. VWF levels are largely dependent on ABO blood group. Subjects with blood group non-O have higher VWF and FVIII levels than individuals with blood group O. Apart from ABO blood group no genetic determinants of high FVIII levels have been identified, whereas clustering of FVIII levels has been reported within families even after adjustment for ABO blood group and VWF levels. We investigated the FVIII and VWF loci as possible quantitative trait loci (QTL) influencing FVIII and VWF levels. Two sequence repeats in the FVIII gene and three repeats in the VWF gene were typed in 52 FV Leiden families. Multipoint sib-pair linkage analysis was performed with the MAPMAKER/SIBS program. FVIII levels adjusted for VWF levels and age, and VWF levels adjusted for ABO blood group and age, were used for this linkage analysis. No linkage of FVIII levels to the FVIII locus was found, whereas we found evidence that the VWF locus contains a QTL for VWF levels [maximum likelihood no dominance variance lod score = 0.70 ( P  = 0.04) and non-parametric Z-score = 1.92 ( P  = 0.03)]. About 20% of the total variation in VWF levels may be attributed to this VWF locus.     

ABO blood group, hypercoagulability, and cardiovascular and cancer risk

The antigens of the ABO system (A, B, and H determinants, respectively) consist of complex carbohydrate molecules. It has been known for nearly half a century that the ABO blood group exerts a major influence on plasma levels of the von Willebrand factor (VWF)-factor VIII (FVIII) complex and that normal group O individuals have significantly lower levels of VWF and FVIII than do non-O individuals. As a consequence, several investigators have studied the association between ABO blood group and the risk of developing bleeding or thrombotic events. A number of epidemiological studies have also analyzed the biologic relevance of this interaction by assessing whether the ABO blood group could influence human longevity through the regulation of VWF-FVIII plasma levels. In this review, the molecular mechanisms by which the ABO blood group determines plasma VWF and consequently, FVIII levels, the possible clinical implications, and the current knowledge on the association between the ABO blood group and the risk of developing certain cancers will be reviewed.     

Factor VIII/von Willebrand factor complex in methylene blue-treated fresh plasma

BACKGROUND: The effect of virus inactivation of fresh plasma with methylene blue has been studied on the factor VIII/von Willebrand factor molecular complex (FVIII/vWF), factor XIII, and fibrinogen. STUDY DESIGN AND METHODS: FVIII function or activity, vWF activity, vWF antigen, vWF:Ag, vWF multimeric structure, fibrinogen, and factor XIII were analyzed in paired samples of control fresh plasma (untreated) and the same fresh plasma treated with methylene blue. Treated plasma was filtered (0.8-1.2 microm), mixed with a methylene blue solution (300 microg/L), and illuminated at 50,000 lux for 30 minutes on both sides. RESULTS: Average loss of biologic activity of coagulation factors studied was 25 percent (FVIII function, 29%; fibrinogen, 39%; factor XIII, 16%; and vWF activity, 18%). Reduction in vWF activity was significantly lower than that in FVIII function (p<0.05), and the vWF multimeric structure did not show alterations. CONCLUSION: Methylene blue-treated plasma and the cryoprecipitates obtained from it may be effective for replacement therapy in cases of von Willebrand disease and deficiencies of factor XIII and fibrinogen, but the clinical studies are needed to verify that possibility.     

Association of ABO(H) and I blood group system development with von Willebrand factor and Factor VIII plasma levels in children and adolescents

BACKGROUND: The modulation of Factor (F)VIII activity (FVIII : C), von Willebrand factor antigen (VWF : Ag), and von Willebrand factor ristocetin cofactor (VWF : RCo) by the ABO(H) blood group is well established in adults. Expression of ABH antigens on N‐linked glycans of VWF protects plasma VWF from proteolysis and clearance. Protection by H antigens is less effective than by AB antigens, resulting in approximately 25% lower VWF plasma levels in adults with blood group O compared to non‐O. Given the reduced branching of ABO(H) bearing structures (I blood group system) with lower numbers of H, A, and B antigen sites during the first 18 months of life, we reasoned that if the relationship between ABO(H) blood group and VWF levels were causal, the difference of ABO(H) blood group–dependent VWF levels should be marginal or not be observed in the first months of life. STUDY DESIGN AND METHODS: We undertook quantification of FVIII : C and VWF in 574 presumably healthy children aged 1 to 210 months and correlated the values with ABO(H) blood type. Moreover, we establish reference intervals for common coagulation variables for several pediatric age groups. RESULTS: Significant differences between blood group O versus non‐O values of FVIII : C, VWF : Ag, and VWF : RCo were not observed in the first months of life, started to develop during childhood, and in adolescence reached adult values. CONCLUSION: In comparison to the levels for adults and adolescents, we report fundamental differences of VWF levels in the first year of life, which may be associated with the physiologic development of the ABO(H) and I blood group system.     

血管性血友病因子在ABO血型个体中质和量差异的实验研究

目的比较血管性血友病因子在ABO血型中质和量的差异。方法运用ELISA法同时测定A血型、B血型、AB血型及O血型四组正常人的vWF抗原水平(vWF:Ag)、VWF瑞斯托霉素辅因子活性(vWF:Rcof)及vWF胶原结合试验(vWF:CBA),并应用统计方法比较不同血型之间结果的差异。结果O型血个体其vWF:Ag、vWF:Rcof及vWF:CBA均低于非O型血,差异有显著统计学意义(P<0.001);同时,vWF:CBA下降水平大于vWF:Rcof,使得vWF:CBA/Ag(P<0.001)小于vWF:Rcof/Ag(P值为0.84)。结论O型血较非O型血个体有更高的出血危险,在临床诊断vWD的过程中要充分考虑ABO血型系统对血浆vWF水平的影响。     

Low-density lipoprotein receptor-related protein 1 polymorphism 663 C > T affects clotting factor VIII activity and increases the risk of venous thromboembolism

BACKGROUND: Clotting factor (F) VIII is an independent risk factor for primary and recurrent venous thromboembolism (VTE). The causes for high plasma FVIII levels are not fully understood, but an involvement of genetic factors has been demonstrated. A multifunctional endocytic receptor, low-density lipoprotein receptor-related protein 1 (LRP1), mediates cellular uptake and subsequent degradation of FVIII and may contribute to variations in FVIII levels. OBJECTIVE: We assessed the association of a genetic variation of LRP1 (663C > T) with basal FVIII levels and the risk of venous thrombosis in a group of high-risk patients and in healthy controls. PATIENTS AND METHODS: One hundred and fifty-two patients with a history of recurrent VTE (median age 56 years, 47% women) were compared with 198 age- and sex-matched controls (median age 53 years, 50% women). The LRP1 663C > T genotype was analyzed by mutagenic separated polymerase chain reaction assay and heterozygosity was confirmed by sequence analysis. RESULTS: LRP1 663C > T genotype distribution differed significantly between patients (663CC n = 138, 663CT n = 14) and controls (663CC n = 190, 663CT n = 8; P = 0.048). In multivariable linear regression analysis including LRP1 663C > T, ABO blood group, von Willebrand factor antigen, C-reactive protein and age, LRP1 663CT was independently associated with FVIII activity (P = 0.02). LRP1 663CT was also associated with increased odds for VTE following adjustment for blood group O, FV Leiden and the prothrombin variation 20210G > A in multivariate analysis (odds ratio 3.3, 95% CI 1.3-8.5). CONCLUSIONS: According to our data the LRP1 663C > T polymorphism influences plasma FVIII levels independently of blood group, C-reactive protein and von Willebrand factor and is significantly associated with the risk of VTE.     

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.     

von Willebrand factor and its propeptide: the influence of secretion and clearance on protein levels and the risk of venous thrombosis

BACKGROUND AND OBJECTIVES: Elevated levels of factor (F)VIII are associated with an increased risk of thrombosis. FVIII levels are determined mainly by von Willebrand factor (VWF). We have investigated the contribution of secretion and clearance rates to the elevated VWF antigen (VWF:Ag) and to the risk of thrombosis. VWF is secreted in equimolar amounts with its propeptide, which has a shorter half-life. VWF propeptide can be used as a measure of VWF secretion and allows estimation of the VWF half-life. METHODS AND RESULTS: We have measured VWF propeptide, VWF:Ag, FVIII:Ag and FVIII activity (FVIII:C) in the Leiden Thrombophilia Study. In controls, high VWF propeptide was associated with high VWF:Ag, FVIII:Ag and FVIII:C. In contrast to mature VWF:Ag, VWF propeptide was not influenced by blood groups. Using an ELISA-based assay we have shown that VWF propeptide lacks ABO antigens. Levels were higher in men and increased with age. A long VWF half-life was also associated with high VWF:Ag, FVIII:Ag and FVIII:C. The VWF half-life was influenced by blood group (10 h in O vs. 12 h in non-O individuals), but not by sex, and only slightly by age. VWF propeptide was higher in thrombosis patients than in controls. The VWF half-life was similar in patients and controls (11.4 and 11.1 h, respectively). CONCLUSIONS: Both secretion and clearance rates are important determinants of VWF and FVIII levels. However, mainly high VWF and FVIII levels caused by increased secretion seem to be associated with thrombosis. ABO blood group influences the clearance rates of VWF rather than VWF secretion rates.     

von Willebrand factor variant p.Arg924Gln marks an allele associated with reduced von Willebrand factor and factor VIII levels

Summary. Background: von Willebrand factor (VWF) variant c.2771G>A; p.R924Q has been described as a benign polymorphism or a possible marker for a null allele and been associated with mild bleeding phenotypes. It was identified in several patients in recent type 1 von Willebrand disease (VWD) studies. Objectives: To determine whether the p.R924Q allele contributes to reduced VWF levels and type 1 VWD. Methods: One thousand one hundred and fifteen healthy controls and 148 index cases from the MCMDM‐1VWD study were genotyped for c.2771G>A; VWF and FVIII levels were analyzed in ABO blood group stratified individuals and the p.R924Q variant was expressed in 293 EBNA cells. Results: c.2771G>A was present in six index cases, five of whom had a second VWF variant which probably contributed to the phenotype. A common core haplotype identified in families, which included the rare G allele of c.5843‐8C>G, was present in the majority of 35 c.2771G>A heterozygous controls. c.2771G>A contributed about 10% variance in VWF and FVIII levels in controls and 35% variance when co‐inherited with blood group O. Recombinant p.R924Q VWF had no effect on in vitro expression and heterozygous family members had normal VWF‐FVIII binding and normal clearance of VWF and FVIII. Conclusions: The allele bearing c.2771A leads to reductions in VWF and FVIII levels particularly in combination with blood group O. Its inheritance alone may be insufficient for VWD diagnosis, but it appears to be associated with a further VWF level reduction in individuals with a second VWF mutation and it contributes to population variance in VWF and FVIII levels.     

ABO blood group determines plasma von Willebrand factor levels: a biologic function after all?

For many years, an association between ABO histo-blood group and risk of thrombosis has been recognized. Blood group non-O (A, B, and AB) individuals have consistently been found to demonstrate increased incidence of both arterial and venous thrombotic disease, compared to group O individuals. This increased risk is attributable to the fact that ABO blood group influences plasma levels of a coagulation glycoprotein named von Willebrand factor (VWF). VWF levels are 25 percent higher in non-O compared to group O individuals. The mechanism by which ABO group determines plasma VWF levels has not been determined. ABO(H) carbohydrate antigenic determinants, however, are expressed on the N-linked glycan chains of circulating plasma VWF. This review will focus on the carbohydrate structures of VWF and recent studies suggesting that subtle variations in these structures (particularly differences in ABO blood group antigen expression) may have clinically significant effects on VWF proteolysis and clearance.     

von Willebrand factor: evidence for variable clearance in vivo according to Y/C1584 phenotype and ABO blood group.

BACKGROUND: The plasma von Willebrand factor (VWF) level (VWF:Ag) is known to correlate with the VWF Y/C1584 variation and with ABO blood group. The ratio of the VWF propeptide (VWFpp) to VWF:Ag and the ratio of coagulation factor VIII (FVIII:C) to VWF:Ag have previously been used as indicators of VWF clearance and/or secretion. OBJECTIVES AND METHODS: To investigate the mechanism underlying the relationship between VWF phenotype and VWF:Ag, the VWFpp/VWF:Ag ratio and FVIII:C/VWF:Ag ratio were determined for plasmas of phenotype Y/C1584, Y/Y1584, blood group O and blood group A (n = 50 for each set). The blood group O plasmas comprised two sets of 25 with low and high mean VWF levels (Low-O and High-O), respectively; similarly for group A (Low-A and High-A). RESULTS AND CONCLUSIONS: The VWFpp/VWF:Ag ratio was greater than 1 (unity) for Y/C1584 plasmas and significantly higher than for Y/Y1584 plasmas; however, the FVIII:C/VWF:Ag ratio was near unity for both and was not significantly different. These results are consistent with increased clearance for Y/C1584 VWF. Similarly, the VWFpp/VWF:Ag ratio and FVIII:C/VWF:Ag ratio in combination were consistent with increased VWF clearance in blood group O compared with blood group A, and in Low-O and Low-A, respectively, compared with High-O and High-A. The data indicate that in vivo C1584 and blood group O are associated with increased VWF clearance, and that clearance contributes to differing VWF level within a given blood group.     

Elevated plasma factor VIII levels--a novel risk factor for venous thromboembolism

An association between elevated plasma levels of FVIII:C and arterial thrombosis was first described 20 years ago. More recently a growing literature has centered on the potential role for elevated FVIII:C in venous thromboembolic disease. 25% of patients have plasma FVIII:C levels greater than 1500 IU/l six months following venous thrombosis. This increased FVIII:C appears unrelated to any ongoing acute phase reaction, and reflects a true increase in circulating FVIII protein. Furthermore the increase in FVIII:C is sustained in the vast majority of subjects for years following the thrombotic episode. Multivariate analysis of the Leiden thrombophilia study has demonstrated that increased FVIII is an independent risk factor for venous thromboembolism. Individuals with FVIII:C exceeding 1500 IU/l had a six-fold increased risk, compared to those with FVIII:C levels less than 1000 IU/l. Also, prospective follow-up has shown that patients with high FVIII:C levels are at increased risk for episodes of recurrent venous thrombosis. These findings support the theory that increased plasma levels of FVIII:C represent a constitutional prothrombotic tendency. However the mechanism underlying the elevation in FVIII remains unknown.     

Elevated plasma levels of factor VIII in women with early recurrent miscarriage

Summary.  Aims : Inherited and acquired thrombophilia have been found to be associated with recurrent pregnancy loss. This paper examines whether or not elevated factor (F)VIII:C plasma levels, which have been demonstrated to be an independent risk factor for venous thromboembolism, are a risk factor for early recurrent miscarriages also. Patients and methods : Consecutive women referred to our clinic with a history of early recurrent abortion (at least three pregnancy losses before week 13 of gestation) were eligible for the study. Exclusion criteria were endocrine, immunological, anatomical and genetic causes of embryo demise, as well as any thrombophilic abnormality, either congenital or acquired, or a personal or familial history of venous thromboembolism. FVIII:C plasma levels were determined in 51 cases and in 51 controls matched for age, ethnicity and blood group. Results : The mean FVIII:C level in the control subjects was 106.8 IU dL⁻¹, compared with 128.2 IU dL⁻¹ in the patients group ( P  = 0.0002). Thirteen (25.5%) of the 51 patients had FVIII:C values exceeding the 90th centile of the control population (145 IU dL⁻¹), compared with four subjects in the control group (χ² = 4.52; P  = 0.033; odds ratio = 4.02, 95% confidence interval 1.09, 16.05). No cases with increase in FVIII:C levels attributable to an acute-phase reaction, as assessed by C-reactive protein plasma concentration, were found. Conclusions : We found FVIII:C levels significantly higher in women with early recurrent miscarriage compared with controls. This finding suggests a possible association between this thrombophilic condition and early reproductive failures.     

vWF基因A1381T多态性和ABO血型对血浆vWF水平的影响

本研究旨在探讨VWF基因A1381T多态性和ABO血型对血浆VWF水平的影响。采用酶联免疫吸附法测定120名（男女各60例）19—33岁健康志愿者血浆vWF：Ag水平,采用PCR限制性酶切片段长度分析vWF基因A1381T单核苷酸多态性,测序验证。实验数据根据志愿者性别、血型或／和基因型进行分组,采用t检验、方差分析等统计学处理。结果表明：志愿者0血型与非0血型相比,血浆vWF水平明显降低（P〈0．001）;vWF基因A1381 T多态性AA基因型与AG、GG型相比,血浆vWF水平明显降低（P=0．003和0．019）;而在男性、女性之间血浆vWF水平没有统计学意义（t=1．039,P=0．301）;在O血型中,A1381T的AG基因型血浆vWF水平与AA、GG基因型有显著性差异（t=2．321,P=0．028）;而在非O血型中,A1381T的AG基因型血浆vWF水平与AA基因型有显著性差异（p=0．032）。结论：血浆vWF的表达水平随ABO血型和vWF基因多态性不同而有明显的不同。O血型和vWF基因A1381T多态性的AA型血浆vWF水平明显低于其他血型或基因型,这些结果对了解出血性及血栓性疾病易感性具有明确的参考意义。     

Genetic determinants of von Willebrand factor levels and activity in relation to the risk of cardiovascular disease: a review

Summary. It is well established that high plasma von Willebrand factor (VWF) levels are associated with an increased risk of arterial thrombosis, including myocardial infarction and ischemic stroke. As plasma VWF levels are, to a large extent, genetically determined, numerous association studies have been performed to assess the effect of genetic variability in the VWF gene (VWF) on VWF antigen and activity levels, and on the risk of arterial thrombosis. Genetic variations in other regulators of VWF, including the ABO blood group, ADAMTS‐13, thrombospondin‐1 and the recently identified SNARE protein genes, have also been investigated. In this article, we review the current literature as exploring the associations between genetic variations and the risk of arterial thrombosis may help elucidate the role of VWF in the pathogenesis of arterial thrombosis. However, as studies frequently differ in design, population and endpoint, and are often underpowered, it remains unclear whether VWF is causally related to the occurrence of arterial thrombosis or primarily mirrors endothelial dysfunction, which predisposes to atherosclerosis and subsequent arterial thrombosis. Nevertheless, current studies provide interesting results that do not exclude the possibility of VWF as causal mediator and justify further research into the relationship between VWF and arterial thrombosis. Large prospective studies are required to further establish the role of VWF in the occurrence of arterial thrombosis.     

Expression patterns of plasma von Willebrand factor and serum interleukin-8 in patients with early-stage severe pulmonary contusion

BACKGROUND: von Willebrand factor (vWF) is only released from endothelial cells and platelets and is an in vivo and in vitro marker of endothelial injury in septic patients with acute lung injury (ALI). Interleukin-8 (IL-8), as a proinflammatory mediator causing recruitment of inflammatory cells, induces an increase in oxidant stress mediators and makes it as a key parameter for localized inflammation. However, it has not been well established whether the level of serum IL-8 is associated with the severity of lung injury and whether it is a prognosis marker for severe lung contusion. This study was to investigate the expression of plasma vWF and IL-8 and their association with the severity and outcomes of severe pulmonary contusion.METHODS: A total of 63 patients were divided into a severe pulmonary contusion with acute respiratory distress syndrome (ARDS) group and a non-ARDS group, or a survivor group and a non-survivor group, or an injury severity score (ISS) <20 group and an ISS ≥20 group. Another 20 healthy volunteers served as controls. The levels of plasma vWF and serum IL-8 were measured by enzyme-linked immunosorbent assay (ELISA) at 1, 3, 5 and 7 days after injury. The expression patterns of the plasma vWF and serum IL-8 were compared between different groups.RESULTS: The concentrations of plasma vWF and serum IL-8 were significantly increased in all severe pulmonary contusion patients at all time points in comparison with the control group. The concentrations of plasma vWF in patients with ARDS increased during the whole study period, but vWF in patients with non-ARDS increased gradually until day 5 and then decreased at day 7. The concentration of serum IL-8 showed a similar expression pattern in both groups, but the expression increased more significantly in the ARDS group than in the non-ARDS group. Interestingly, both plasma vWF and serum IL-8 levels steadily increased in the non-survivor group. Furthermore, the level of plasma vWF was higher in the ISS≥20 group than in the ISS<20 group. The level of serum IL-8 in the ISS≥20 group was consistently high, while that in the ISS<20 group peaked at day 3 and decreased at day 5. In addition, the level of plasma vWF was positively correlated with platelet count, but negatively correlated with oxygen index. The level of serum IL-8 was positively correlated with white blood cell count and ISS score, and inversely correlated with oxygen index.CONCLUSION: The elevated levels of plasma vWF and serum IL-8 in severe pulmonary contusion patients reflect the severity of pulmonary injury and patients outcomes, suggesting that the plasma vWF and serum IL-8 are sensitive markers for clinical evaluation of the severity of pulmonary injury and predication of patient prognosis.     

vWF基因单核苷酸多态性与血栓性疾病发病的关系

最近发现,不仅血管性血友病因子(vWF)减少会造成血管性血友病,而且vWF水平增加也会造成各种血栓性疾病。vWF水平受遗传因素的影响,不同单核苷酸多态性(SNP)基因型的人群对疾病的易感性不尽相同;不同血型的个体vWF表达水平也不同。环境因素也可影响血浆vWF水平。了解vWF基因的启动子、外显子和内含子区域多态性与血栓性疾病的关系有助于临床疾病的预防与治疗。本综述讨论vWF基因的启动子、外显子和内合子区域SNP与血栓性疾病关系的研究进展。     

Extra-hepatic factor VIII expression in porcine fulminant hepatic failure

In humans, fulminant hepatic failure (FHF) is frequently associated with increased factor VIII (FVIII) levels, despite widespread liver cell death. The mechanisms leading to increased FVIII levels and cellular sites of this enhanced FVIII production are poorly understood. We studied the effect of total hepatectomy in pigs, a large-animal model of FHF, on the expression of plasma and tissue FVIII during 24-hour follow-up. Tissue FVIII expression was determined before and 24 h after hepatectomy, both at the mRNA level and immunohistochemically. The expression of plasma and tissue von Willebrand factor (VWF), the natural stabilizing carrier protein of FVIII, was also measured. Total hepatectomy elicited a gradual and sustained twofold elevation of circulating FVIII, whereas FVIII mRNA levels in various organs did not increase after hepatectomy. The half-life of FVIII increased from 7.7 to 10.3 h and VWF levels were also elevated in anhepatic pigs. The increase in the half-life of FVIII and increased levels of VWF were not sufficient to explain the rise in plasma FVIII levels. At the protein level, prominent changes in the cellular distribution of FVIII were seen in spleen and kidney. These observations suggest that in this model of FHF the lack of hepatic FVIII synthesis is adequately compensated by other organs, notably spleen and kidneys.     

Rituximab and intermediate‐purity plasma‐derived factor VIII concentrate (Koate®) as adjuncts to therapeutic plasma exchange for thrombotic thrombocytopenic purpura in patients with an ADAMTS13 inhibitor

Thrombotic thrombocytopenic purpura (TTP) results from a congenital or acquired deficiency of the von Willebrand factor (vWF)‐cleaving protease ADAMTS13. The disease can be fatal and hence treatment should be initiated promptly. Therapeutic plasma exchange (TPE) remains the standard treatment along with adjunct therapies including steroids and immunosuppressive drugs. Addition of rituximab to TPE has been shown to be beneficial in refractory/relapsing TTP; however, TPE results in removal of rituximab from the circulation requiring more frequent dosing of rituximab to achieve a favorable outcome. The intermediate‐purity plasma‐derived Factor VIII concentrate (FVIII) Koate® contains the highest amount of ADAMTS13 activity yet reported and has been used successfully in treating congenital TTP. Here we report our experience with addition of this FVIII concentrate to rituximab, corticosteroids and TPE in three TTP patients with an ADAMTS13 inhibitor to permit withholding TPE for 48 h after rituximab infusion. J. Clin. Apheresis 30:50–54, 2015. © 2014 Wiley Periodicals, Inc.