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PubMed1985

Activation of porcine factor VIII:C by thrombin and factor Xa.

The activation of porcine factor VIII:C by thrombin and by factor Xa was studied by a chromogenic substrate assay and by sodium dodecyl sulfate-polyacrylamide gel radioelectrophoresis of 125I-labeled factor VIII:C activation products. In the chromogenic assay, the kinetics of factor VIII:C dependent activation of factor X by factor IXa in the presence of calcium and phosphatidylserine/phosphatidylcholine vesicles were measured with N-benzoyl-L-isoleucyl-L-glutamylglycyl-L-arginine p-nitroanilide (S2222) as substrate. Substrate dependence of initial rates of the reaction at fixed factor IXa, factor VIII:C, lipid, and calcium obeyed Michaelis-Menten kinetics. At fixed factor IXa, factor X, lipid, and calcium the initial rates of the reaction varied linearly with lower factor VIII:C concentrations and plateaued at higher concentrations. The linear initial rate dependence formed the basis of a rapid, plasma-free assay of activated factor VIII:C. The activation of factor VIII:C by thrombin or factor Xa and the enzyme-independent rate of spontaneous inactivation were studied under conditions of excess enzyme. A model of the activation kinetics was developed and fit to the data by a nonlinear least-squares technique. From the model, the catalytic efficiencies (kcat/Km) of factor VIII:C activation by thrombin and factor Xa were 5.0 X 10(6) M-1 s-1 and 1.1 X 10(6) M-1 s-1, respectively. By comparison with published values of the catalytic efficiencies of several other coagulation enzymes for various substrates, both thrombin and factor Xa are efficient enzymes toward factor VIII:C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

Involvement of low-density lipoprotein receptor-related protein (LRP) in the clearance of factor VIII in von Willebrand factor-deficient mice.

Factor VIII is tightly noncovalently linked to von Willebrand factor (vWF) in plasma with a stoichiometry of 1:50, and vWF deficiency results in secondary factor VIII deficiency, with accelerated clearance of factor VIII from the circulation. We used a murine model of severe von Willebrand disease (vWF knockout mice) to study the effect of a recombinant vWF/pro-vWF preparation (rpvWF) on factor VIII survival and to investigate whether low-density lipoprotein receptor-related protein (LRP) might be involved in the in vivo clearance of factor VIII in the absence of vWF. vWF-deficient mice received 70 U/kg rpvWF in the first series of experiments, and in a second series, 80 mg/kg receptor-associated protein (RAP) as a recombinant fusion protein to block the action of LRP. Factor VIII levels were measured at time 0, or 1 or 3 hours after administration of rpvWF or RAP. RAP induced a sustained rise in factor VIII levels comparable to that induced by rpvWF. In a third series, the preadministration of RAP resulted in a slower disappearance of factor VIII antigen (measured by an enzyme-linked immunosorbent assay specific for human factor VIII) after infusion of recombinant factor VIII. These findings suggest that the accelerated clearance of factor VIII seen in the absence of vWF may be a result of the involvement of LRP in factor VIII metabolism. (Blood. 2000;95:1703-1708)

Animals↗
PubMed1984

Use of porcine factor VIII in the management of seventeen patients with factor VIII antibodies.

A polyelectrolyte-fractionated porcine factor VIII concentrate was given to 16 hemophiliacs with anti-F VIII antibodies (Ab) and to a woman with post-partum-acquired Ab during 24 courses of treatment including three major surgical procedures. Before treatment, antiporcine F VIII Ab was always lower than anti-human F VIII Ab, with a median cross reactivity of 32%. After treatment, the mean rise in F VIII was 1.5 U/dl/Unit infused/Kg b.w. and in vivo recovery was 50% of the theoretical values. Anamnestic rises in anti-porcine F VIII Ab (3 X the baseline titer) were seen after 9 of 22 courses of treatment with porcine F VIII only; similar rises in anti-human F VIII Ab, after 6 courses of treatment; median cross reactivity did not change significantly. Lower than expected increases in plasma F VIII without marked changes in Ab titers and severe thrombocytopenia occurred during surgery in two patients. Porcine F VIII is a rational and effective therapeutic choice for patients who have anti-human Ab titers above 10 U/ml; it can solve clinical situations that would otherwise be very difficult to manage; anamnesis is perhaps less frequent than after human F VIII; however, the incidence of thrombocytopenia, resistance and other side-effects is still higher than desirable.

Adolescent↗
PubMed1984

Immunochemical characterization of factor VIII inhibitors.

Factor VIII inhibitors are antibodies, predominantly of the IgG class, that inactivate factor VIII procoagulant activity. They do not fix complement and cannot be detected by standard immunoprecipitin assays. Their immunochemical properties are unusual, for the alloantibodies have consistent light chain restriction (kappa) and most allo- and auto- anti-VIII:C are predominantly or exclusively IgG4. This property may be responsible for the lack of complement fixation and immunoprecipitation. Human anti-VIII:C react with several different VIII:C antigenic determinants, and recent studies have begun to characterize the major epitopes. In addition, anti-VIII:C idiotypes have been identified using both rabbit anti-idiotype serum and monoclonal antibodies. These reagents provide a new way to obtain more precise immunochemical characterization.

Antigen-Antibody Complex↗
PubMed1981

Alterations of factor VIII von Willebrand factor in clinical conditions associated with an increase in its plasma concentration.

Factor VIII-related antigen (VIIIR:Ag) was consistently higher than factor-VIII procoagulant activity (VIII:C) in 57 patients with clinical conditions characterized by acute-phase reactions. Two different methods for measuring VIII:C (one- and two-stage assays) and VIIIR:Ag (electroimmunodiffusion and immunoradiometric assay) gave concordant results in the majority of cases. In 43% of plasma samples, crossed immunoelectrophoresis in agarose gel was characterized by the appearance of an additional, fast-moving precipitin peak which was immunologically identical with the major, slower-moving VIIIR:Ag peak. The fast-moving peak was detected in all the patients with clinical conditions typically associated with increased plasma proteolysis (DIC, acute pancreatitis, during thrombolytic therapy). It was present in a smaller proportion of cases with liver and renal failure and malignancies and in the post-operative period. The additional VIIIR:Ag peak is thought to be the result of in vivo factor VIII/von Willebrand factor fragmentation by proteolytic enzymes.

Antigens↗
PubMed1999

Pharmacokinetics of recombinant factor VIII (recombinate) using one-stage clotting and chromogenic factor VIII assay.

In a study designed to demonstrate the safety and pharmacokinetics of a recombinant factor VIII (Recombinate) manufactured in Andover, MA and Thousand Oaks, CA, two different methods of factor VIII assay (one-stage clotting and Chromogenic substrate) were compared in vivo. The study was performed in four centres in the UK: London, Oxford, Cardiff and Manchester. Two pharmacokinetic studies, at least one week apart, were performed in 30 patients with severe haemophilia A (VIII:C < 2 IU/dl). A dose of 50 IU/kg was administered with sampling pre-infusion, and +0.25, 0.5, 1, 3, 6, 9, 12 and 24 h post-infusion. The aggregate 60 pharmacokinetic study showed a half-life of 12.7 and 13.0 h (p = 0.28) and recovery of 127 and 161 IU/dl (p = 0.0001) using one-stage clotting or chromogenic substrate respectively. In a supplementary experiment, 20 post-infusion samples were re-assayed by 1-stage and chromogenic assay using two plasma (20th British plasma standard and an "in-house" pooled normal plasma) and two concentrate standards, derived from the same type, but different batch of infused concentrate (Recombinate) and pre-diluted in either individual pre-infusion sample or in pooled commercial haemophilic plasma. The use of the Recombinate concentrate standard overcame the significant difference in FVIII levels between 1-stage and chromogenic assay methods when a plasma standard was used (p <0.0001). It is concluded that where potency dosing designation is carried out by an assay system different to that used in the clinical situation, the use of the recombinant concentrate as a standard in post-infusion plasma samples is likely to give more reliable and reproducible results.

Biological Assay↗
PubMed1979

A randomized study of factor VIII or prothrombin complex concentrate infusions in children with haemophilia and antibodies to factor VIII.

In four children with haemophilia A and antibodies to factor VIII, 18 bleeding episodes were randomized for treatment with factor VIII concentrate (30 units/kg) and 18 for treatment with a prothrombin-complex concentrate (prothrombinex) given in a dose of 30 units of factor IX/kg. Treatment with prothrombinex was associated with a better clinical response, a significantly greater shortening of the kaolin partial thromboplastin time and significantly lower incidence of post-infusion increase of levels of factor VIII antibodies. Although treatment with factor VIII concentrate was clinically successful in 15 episodes, treatment failures occurred in three instances leading to parental request for withdrawal from study in two families.

Antibodies↗
PubMed1996

[Combined treatment with factor VIII and immunosuppressive agents in a young woman with acquired factor VIII inhibitor].

A twenty seven year-old woman is reported with severe haemorrhagic symptoms caused by an acquired coagulant factor VIII inhibitor eleven months after delivery. The inhibitor was quantified as 77 units according to the Bethesda method. Steroids treatment and high-dose immunoglobulins failed to elicit any response. Combined chemotherapy will cyclophosphamide, vincristine and prednisone after intravenous factor VIII, every fourth week, succeeded in eradicating the acquired inhibitor and progressively restoring the rates of factor VIII in this patient with acquired haemophilia.

Adult↗
PubMed2001

[High factor VIII as a risk factor for venous thrombosis].

Several studies have shown that increased concentrations of factor VIII are associated with thrombophilia. It has been also shown that this is not an acute phase response pattern, and that these individuals have increased factor VIII concentrations due to genetic and environmental causes. Part of the thrombophilic pattern might be related to an acquired Activated Protein C resistance condition. Since individuals with venous thromboembolism and increased factor VIII concentrations present a high recurrence rate, the determination of factor VIII concentrations should be included in the laboratory thrombophilia screening work-up.

Biomarkers↗
PubMed1996

[Molecular biologic study and the factor VIII gene in hemophilia A].

Results of inversion in the intron 22 region of the VIII factor gene studied by Southern blot are presented. Inversion was found in 20 of 46 patients. In 14 cases (70%) distal and in 6 cases (30%) proximal type of inversion was detected. The significance of the positive result in genetic counseling and in presymptomatic diagnosis of Haemophilia A is emphasized.

Adult↗
PubMed1990

Hemophilia as a defect of the tissue factor pathway of blood coagulation: effect of factors VIII and IX on factor X activation in a continuous-flow reactor.

The effect of factors VIII and IX on the ability of the tissue factor-factor VIIa complex to activate factor X was studied in a continuous-flow tubular enzyme reactor. Tissue factor immobilized in a phospholipid bilayer on the inner surface of the tube was exposed to a perfusate containing factors VIIa, VIII, IX, and X flowing at a shear rate of 57, 300, or 1130 sec-1. Factor Xa in the effluent was determined by chromogenic assay. The flux of factor Xa (moles formed per unit surface area per unit time) was strongly dependent on wall shear rate, increasing about 3-fold as wall shear rate increased from 57 to 1130 sec-1. The addition of factors VIII and IX at their respective plasma concentrations resulted in a further 2- to 3-fold increase. The direct activation of factor X by tissue factor-factor VIIa could be virtually eliminated by the lipoprotein-associated coagulation inhibitor; however, when factors VIII and IX were present at their approximate plasma concentrations, factor Xa production rates were enhanced 15- to 20-fold. These results suggest that the tissue factor pathway, mediated through factors VIII and IX, produces significant levels of factor Xa even in the presence of an inhibitor of the tissue factor-factor VIIa complex; moreover, the activation is dependent on local shear conditions. These findings are consistent both with a model of blood coagulation in which initiation of the system results from tissue factor and with the bleeding observed in hemophilia.

Blood Coagulation↗
PubMed1996

Factor VIII inhibitor antibodies with C2 domain specificity are less inhibitory to factor VIII complexed with von Willebrand factor.

In order to clarify the potential role of von Willebrand factor (vWf) in attenuating the inactivation of factor VIII (fVIII) by those antibodies with C2 domain specificity, we investigated a panel of 14 human antibodies to fVIII. Immunoblotting analysis localized light chain (C2 domain) epitopes for four cases, heavy chain (A2 domain) epitopes in five cases, while the remaining five cases were both light and heavy chains. The inhibitor titer was considerably higher for Kogenate, a recombinant fVIII concentrate, than for Haemate P, a fVIII/vWf complex concentrate, in all inhibitor plasmas that had C2 domain specificity. In five inhibitor plasmas with A2 domain specificity and in five with both A2 and C2 domain specificities, Kogenate gave titers similar to or lower than those with Haemate P. The inhibitory effect of IgG of each inhibitor plasma was then compared with recombinant fVIII and its complex with vWf. When compared to the other 10 inhibitor IgGs, IgG concentration, which inhibited 50% of fVIII activity (IC50), was remarkably higher for the fVIII/vWf complex than for fVIII in all the inhibitor IgGs that had C2 domain reactivity. Competition of inhibitor IgG and vWf for fVIII binding was observed in an ELISA system. In 10 inhibitors that had C2 domain reactivity, the dose dependent inhibition of fVIII-vWf complex formation was observed, while, in the group of inhibitors with A2 domain specificity, there was no inhibition of the complex formation except one case. We conclude that a subset of fVIII inhibitors, those that bind to C2 domain determinants, are less inhibitory to fVIII when it is complexed with vWf that binds to overlapping region in the C2 domain.

Antibody Specificity↗
PubMed1984

Factor VIII procoagulant antigen recovery is a dose-related response to Factor VIII concentrate infusions.

The recovery and initial half-disappearance rate of factor VIII procoagulant activity (VIIIC) and procoagulant antigen (VIIICAg) were studied in 9 haemophilia A patients following infusion of factor VIII concentrates to varying plasma VIIIC levels. While VIIIC recovery was independent of dose, the VIIICAg recovery varied in a dose-dependent fashion. The excess of VIIICAg relative to VIIIC found in the factor VIII concentrates (VIIICAg/VIIIC ratios of 1.9-3.1) was not observed in plasma samples taken after low level infusions (plasma VIIIC less than 1 U/ml) but a significant excess of VIIICAg was observed in higher level infusions. The VIIICAg recovery of post-infusion plasma was not increased by treatment with phospholipase C.

Antigens↗
PubMed1989

Importance of a quality assurance scheme for factor VIII assays in quality monitoring of human plasma destined for fractionation into factor VIII concentrate.

A national quality assurance scheme has been established to monitor the validity of factor VIII assays performed by the various laboratories of the Scottish National Blood Transfusion Service engaged in collection and processing of donor plasma destined for fractionation. The results over the first 3-year period show that comparable assay values can be obtained by participating centres using a common standard, despite differences in equipment, methods or substrate chosen for the one-stage assay. The results also showed that chromogenic factor VIII assays correlated well with the one-stage method. Random factor VIII assays performed on plasma, harvested and frozen within 18 h from collection, were analysed to validate recently proposed Scottish specifications which stipulate that 70% of plasma donations destined for fractionation should contain at least 0.7 IU/ml. Plasma harvested and frozen between 8 and 18 h from collection did not meet the specified level in any of the regional centres. This nationally specified level was also not met by plasma harvested and frozen within 8 h from collection in spite of being achieved individually by three regional centres. Assays performed on large plasma pools at the Fractionation Centre suggested loss of some factor VIII during storage, transportation and thawing of plasma prior to bulk processing.

Blood Banks↗
PubMed1980

[Determination of coagulation factor VIII inhibitors].

Factor VIII inhibitors represent a severe complication of the haemophilia A. Different methodical approach in the diagnostics of the laboratory and various definitions of the inhibitor unit render difficult the comparability of the results of examination. Methods for the unitary performance of the qualitative proof of inhibitors and the quantitative estimation of inhibitors are described and their application in the examination of two patients with factor VIII inhibitors are shown.

Antibodies↗