scholarly journals Kinetics of factor VIII-von Willebrand factor association

Blood ◽  
1996 ◽  
Vol 87 (5) ◽  
pp. 1809-1816 ◽  
Author(s):  
AJ Vlot ◽  
SJ Koppelman ◽  
JC Meijers ◽  
C Dama ◽  
HM van den Berg ◽  
...  
Keyword(s):  
Factor Viii ◽  
Rate Constant ◽  
Von Willebrand Factor ◽  
Hemophilia A ◽  
Dissociation Kinetics ◽  
Human Factor Viii ◽  
Von Willebrand ◽  
Willebrand Factor ◽  
Kinetics Of

Abstract The binding of factor VIII to von Willebrand factor (vWF) is essential for the protection of factor VIII against proteolytic degradation in plasma. We have characterized the binding kinetics of human factor VIII with vWF using a centrifugation binding assay. Purified or plasma vWF was immobilized with a monoclonal antibody (MoAb RU1) covalently linked to Sepharose (Pharmacia LKB Biotechnology, Uppsala, Sweden). Factor VIII was incubated with vWF-RU1-Sepharose and unbound factor VIII was separated from bound factor VIII by centrifugation. The amount of bound factor VIII was determined from the decrease of factor VIII activity in the supernatant. Factor VIII binding to vWF-RU1-Sepharose conformed to the Langmuir model for independent binding sites with a Kd of 0.46 +/- 0.12 nmol/L, and a stoichiometry of 1.3 factor VIII molecules per vWF monomer at saturation, suggesting that each vWF subunit contains a binding site for factor VIII. Competition experiments were performed with a recombinant vWF (deltaA2-rvWF), lacking residues 730 to 910 which contain the epitope for MoAB RU1. DeltaA2-rvWF effectively displaced previously bound factor VIII, confirming that factor VIII binding to vWF-RU1-Sepharose was reversible. To determine the association rate constant (k(on)) and the dissociation rate constant (k(off)), factor VIII was incubated with vWF-RU1-Sepharose for various time intervals. The observed association kinetics conformed to a simple bimolecular association reaction with k(on) = 5.9 +/- 1.9 x 10(6) M(-1) s(-1) and k(off) = 1.6 +/- 1.2 x 10(-3) s(-1) (mean +/- SD). Similar values were obtained from the dissociation kinetics measured after dilution of preformed factor VIII-vWF-RU1-Sepharose complexes. Identical rate constants were obtained for factor VIII binding to vWF from normal pooled plasma and to vWF from plasma of patients with hemophilia A. The kinetic parameters in this report allow estimation of the time needed for complex formation in vivo in healthy individuals and in patients with hemophilia A, in which monoclonally purified or recombinant factor VIII associates with endogenous vWF. Using the plasma concentration of vWF (50 nmol/L in monomers) and the obtained values for K(on) and K(off), the time needed to bind 50% of factor VIII is approximately 2 seconds.

scholarly journals Kinetics of factor VIII-von Willebrand factor association

Blood ◽  
1996 ◽  
Vol 87 (5) ◽  
pp. 1809-1816 ◽  
Author(s):  
AJ Vlot ◽  
SJ Koppelman ◽  
JC Meijers ◽  
C Dama ◽  
HM van den Berg ◽  
...  
Keyword(s):  
Factor Viii ◽  
Rate Constant ◽  
Von Willebrand Factor ◽  
Hemophilia A ◽  
Dissociation Kinetics ◽  
Human Factor Viii ◽  
Von Willebrand ◽  
Willebrand Factor ◽  
Kinetics Of

The binding of factor VIII to von Willebrand factor (vWF) is essential for the protection of factor VIII against proteolytic degradation in plasma. We have characterized the binding kinetics of human factor VIII with vWF using a centrifugation binding assay. Purified or plasma vWF was immobilized with a monoclonal antibody (MoAb RU1) covalently linked to Sepharose (Pharmacia LKB Biotechnology, Uppsala, Sweden). Factor VIII was incubated with vWF-RU1-Sepharose and unbound factor VIII was separated from bound factor VIII by centrifugation. The amount of bound factor VIII was determined from the decrease of factor VIII activity in the supernatant. Factor VIII binding to vWF-RU1-Sepharose conformed to the Langmuir model for independent binding sites with a Kd of 0.46 +/- 0.12 nmol/L, and a stoichiometry of 1.3 factor VIII molecules per vWF monomer at saturation, suggesting that each vWF subunit contains a binding site for factor VIII. Competition experiments were performed with a recombinant vWF (deltaA2-rvWF), lacking residues 730 to 910 which contain the epitope for MoAB RU1. DeltaA2-rvWF effectively displaced previously bound factor VIII, confirming that factor VIII binding to vWF-RU1-Sepharose was reversible. To determine the association rate constant (k(on)) and the dissociation rate constant (k(off)), factor VIII was incubated with vWF-RU1-Sepharose for various time intervals. The observed association kinetics conformed to a simple bimolecular association reaction with k(on) = 5.9 +/- 1.9 x 10(6) M(-1) s(-1) and k(off) = 1.6 +/- 1.2 x 10(-3) s(-1) (mean +/- SD). Similar values were obtained from the dissociation kinetics measured after dilution of preformed factor VIII-vWF-RU1-Sepharose complexes. Identical rate constants were obtained for factor VIII binding to vWF from normal pooled plasma and to vWF from plasma of patients with hemophilia A. The kinetic parameters in this report allow estimation of the time needed for complex formation in vivo in healthy individuals and in patients with hemophilia A, in which monoclonally purified or recombinant factor VIII associates with endogenous vWF. Using the plasma concentration of vWF (50 nmol/L in monomers) and the obtained values for K(on) and K(off), the time needed to bind 50% of factor VIII is approximately 2 seconds.

Intracellular Co-Localization of Factor VIII and Von Willebrand Factor Is Necessary for In Vivo FVIII Secretion.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 41-41 ◽  
Author(s):  
Patricia A. Lamont ◽  
Margaret V. Ragni
Keyword(s):  
Liver Transplantation ◽  
Factor Viii ◽  
Von Willebrand Factor ◽  
Hemophilia A ◽  
Liver Function Tests ◽  
Von Willebrand Disease ◽  
Von Willebrand ◽  
Willebrand Factor

Abstract Although the extracellular association of Factor VIII (FVIII) and Von Willebrand Factor (VWF) is well established, the intracellular interaction of FVIII and VWF is not well understood. Recently, the importance of intracellular co-localization of FVIII and VWF for in vitro FVIII secretion was demonstrated in endothelial cell lines. Whether intracellular co-localization of FVIII and VWF is required for in vivo FVIII secretion, however, is not known. We previously showed that liver transplantation leads to phenotypic cure of hemophilia A, by virtue of FVIII production in the allograft liver. Because FVIII is synthesized only in the allograft liver but not in endothelial cells of transplant recipients, and VWF is synthesized in extrahepatic tissue, this is an ideal model to study whether co-localization of FVIII and VWF is required for in vivo FVIII secretion. We, therefore, studied FVIII and VWF response after desmopression (DDAVP) infusion, administered at 0.3 mcg/kg by intravenous infusion over 30 minutes, in each of two men with severe hemophilia A (FVIII:C <0.01 U/ml) who had undergone orthotopic liver transplantation for endstage liver disease six months earlier. Both men had HIV and hepatitis C co-infection and were clinically well, with mildly elevated liver function tests, and FVIII:C levels >30% following transplantation. Coagulation studies, drawn before and after DDAVP, revealed that VWF:RCoF and VWF:Ag, but not FVIII:C, increased after DDAVP administration (see Table). The prolonged aPTT and correction in a 1:1 aPTT mix confirmed the absence of an inhibitor in these subjects. The lack of FVIII response to DDAVP supports previous in vitro work, and demonstrates for the first time that intracellular co-localization of FVIII and VWF is essential for in vivo FVIII secretion. These data also suggest that extrahepatic FVIII synthesis is necessary for in vivo response of the DDAVP releasable pool of FVIII. By contrast, co-localization does not appear to be necessary for VWF secretion. Although it is not possible to exclude that a chronic, exhaustive post-transplant increase in VWF may have limited VWF response to DDAVP, it is clear that FVIII did not increase following DDAVP. These findings have important implications for the design of gene therapies for hemophilia A and Von Willebrand Disease. Subject Demographic Sample aPTT aPTT mix FVIII:C VWF:RCoF VWF:Ag 01-BW 32yoM Hem A Pre-DDAVP 44.4 sec 37.7 sec 0.50 U/ml 2.17 U/ml 2.42 U/ml HIV+/HCV+ Post-DDAVP 44.8 sec 37.4 sec 0.48 U/ml 2.91 U/ml 2.91 U/ml 02-PB 36yoM Hem A Pre-DDAVP 49.5 sec 38.0 sec 0.32 U/ml 1.61 U/ml 2.16 U/ml HIV+/HCV+ Post-DDAVP 50.8 sec 38.5 sec 0.30 U/ml 2.20 U/ml 2.50 U/ml

Non-Classical Anti-Factor VIII C2 Domain Antibodies Are Pathogenic in a Murine in Vivo Bleeding Model.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2027-2027
Author(s):  
Shannon Meeks ◽  
John F. Healey ◽  
Ernest T. Parker ◽  
Rachel T. Barrow ◽  
John (Pete) Lollar
Keyword(s):  
Blood Loss ◽  
Factor Viii ◽  
Von Willebrand Factor ◽  
Hemophilia A ◽  
Classical Type ◽  
Type I ◽  
Acquired Hemophilia ◽  
Von Willebrand ◽  
Willebrand Factor

Abstract Approximately 30% of patients with severe hemophilia A will develop inhibitory antibodies to factor VIII (fVIII inhibitors). In addition, autoimmune antibodies to fVIII can develop in non-hemophiliacs, producing acquired hemophilia A, which frequently produces life- or limb-threatening bleeding. Patients with congenital hemophilia who develop inhibitors usually have a polyclonal antibody response directed against the A2 and C2 domains of fVIII. Patients with acquired hemophilia typically have a more limited B-cell epitope response with antibodies directed against the A2 or C2 domain not both. Classical anti-C2 antibodies inhibit the binding of fVIII to phospholipid membranes and to von Willebrand factor. We recently have identified anti-C2 antibodies that inhibit the activation of fVIII, but do not inhibit the binding of fVIII to phospholipid membranes or to von Willebrand factor. These non-classical inhibitors are found in the plasmas of most inhibitor patients (Meeks, S.L. et al. Blood112, 1151-1153, 2008). The pathogenicity of classical and non-classical murine anti-human fVIII monoclonal antibodies (MAbs) was tested in a murine in vivo bleeding model. MAbs were injected into the tail veins of –hemophilia A mice to a peak plasma concentration of 60 nM followed by an injection human B domain-deleted fVIII to a concentration of 2 nM. At 2 hours the mice were anesthetized and a 4 mm tail snip was made. The amount of blood lost into a collection tube of normal saline over 40 minutes was measured. 4A4 is a type I anti-A2 inhibitor with an inhibitory titer of 40,000 Bethesda units (BU)/mg IgG. I54 and 1B5 are classical type I anti-C2 inhibitors with inhibitory titers of 1300 and 930 BU/mg IgG, respectively. 2-77 is a non-classical type II anti-C2 inhibitor that produces a residual fVIII level of 40% at saturating concentrations and whose titer is 21,000 BU/mg IgG. 2-117 is a non-classical anti-C2 MAb with inhibitory activity less than 0.4 BU/mg IgG. All of these MAbs except 2-117 significantly increased blood loss over control mice injected with fVIII alone (p= 0.01-0.02, Mann-Whitney Test) (Fig .1). The amount of blood loss was similar at these saturating concentrations of antibody despite inhibitory titers ranging from 930-40,000 BU/mg IgG. Increasing the dose of fVIII to 4 nM could overcome the bleeding diathesis produced by the non-classical MAb 2-77, but not the type I antibodies, 4A4 and I54. Similar results were seen in the in vitro Bethesda assay where 4A4 completely inhibited both 1 U/ml and 3 U/ml fVIII at saturating concentrations, while 2-77 had 40% residual activity with either 1 or 3 U/ml fVIII (0.4 U and 1.2 U respectively) (Fig. 2). These results suggest that high-dose fVIII rather than bypassing agents may be warranted in patients with an inhibitor response dominated by non-classical anti-C2 antibodies. FIGURE 1. FIGURE 1. FIGURE 2. FIGURE 2.

scholarly journals Factor VIII/von Willebrand factor in subendothelium mediates platelet adhesion

Blood ◽  
1985 ◽  
Vol 65 (4) ◽  
pp. 823-831 ◽  
Author(s):  
VT Turitto ◽  
HJ Weiss ◽  
TS Zimmerman ◽  
II Sussman
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Vessel Wall ◽  
Platelet Adhesion ◽  
Human Factor ◽  
Rabbit Aorta ◽  
Human Factor Viii ◽  
Plasma Factor ◽  
Von Willebrand ◽  
Willebrand Factor

The present studies were undertaken to determine whether factor VIII/von Willebrand factor (vWF) present in the vessel wall (in addition to that in plasma) may mediate the attachment of platelets to subendothelium. Subendothelium from everted rabbit aorta was exposed to human citrated blood flowing through an annular perfusion chamber at 40 mL/min (wall shear rate of 2,600 s-1 for five minutes). The vessel segments were incubated at 37 degrees C for one hour with various dilutions of either goat-anti-rabbit factor VIII/vWF serum or an IgG fraction prepared from the serum. Control segments were incubated with serum or IgG from a nonimmunized goat. Values of platelet contact (C), platelet adhesion (C + S), and thrombus formation (T) on the subendothelium were evaluated by a morphometric technique. Compared with vessels incubated with fractions prepared from a normal goat, a significant decrease in platelet adhesion (C + S), ranging from 45% to 65%, was observed on vessels incubated with various dilutions (1:5 to 1:50) of either serum or IgG fractions of goat-anti-rabbit factor VIII/vWF. A similar decrease in platelet adhesion was observed with vessels incubated with an F(ab')2 fragment against rabbit factor VIII/vWF prepared in the goat. When goat-anti-rabbit factor VIII/vWF IgG was added to rabbit blood (1:75 dilution), platelet adhesion was reduced to the same extent (65%) on normal rabbit vessels and on vessels pre-incubated with goat-anti-rabbit factor VIII/vWF. Immunofluorescence studies revealed the presence of rabbit factor VIII/vWF in the subendothelium of rabbit aorta and the continued binding of the goat-anti-factor VIII/vWF antibodies on subendothelium during the perfusion studies. No uptake of human factor VIII/vWF on the rabbit subendothelium was observed by this immunologic technique; human factor VIII/vWF was found to be entirely associated with the attached human platelets. Thus, factor VIII/vWF in the vessel wall may mediate platelet attachment to subendothelium in a manner similar to that of plasma factor VIII/vWF.

A novel cause of mild/moderate hemophilia A: mutations scattered in the factor VIII C1 domain reduce factor VIII binding to von Willebrand factor

Blood ◽  
2000 ◽  
Vol 96 (3) ◽  
pp. 958-965 ◽  
Author(s):  
Marc Jacquemin ◽  
Renaud Lavend'homme ◽  
Abdellah Benhida ◽  
Beatrijs Vanzieleghem ◽  
Roseline d'Oiron ◽  
...  
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Cho Cells ◽  
Hemophilia A ◽  
Chinese Hamster ◽  
Expression Vectors ◽  
Scatchard Analysis ◽  
C1 Domain ◽  
Von Willebrand ◽  
Willebrand Factor

Abstract The mechanisms responsible for the low factor VIII (fVIII) activity in the plasma of patients with mild/moderate hemophilia A are poorly understood. In such patients, we have identified a series of fVIII mutations (Ile2098Ser, Ser2119Tyr, Asn2129Ser, Arg2150His, and Pro2153Gln) clustered in the C1 domain and associated with reduced binding of fVIII to von Willebrand factor (vWf). For each patient plasma, the specific activity of mutated fVIII was close to that of normal fVIII. Scatchard analysis showed that the affinity for vWf of recombinant Ile2098Ser, Ser2119Tyr, and Arg2150His fVIII mutants was reduced 8-fold, 80-fold, and 3-fold, respectively, when compared with normal fVIII. Given the importance of vWf for the stability of fVIII in plasma, these findings suggested that the reduction of fVIII binding to vWf resulting from the above-mentioned mutations could contribute to patients' low fVIII plasma levels. We, therefore, analyzed the effect of vWf on fVIII production by Chinese hamster ovary (CHO) cells transfected with expression vectors for recombinant B domain-deleted normal, Ile2098Ser, Ser2119Tyr, and Arg2150His fVIII. These 3 mutations impaired the vWf-dependent accumulation of functional fVIII in culture medium. Analysis of fVIII production by transiently transfected CHO cells indicated that, in addition to the impaired stabilization by vWf, the secretion of functional Ile2098Ser and Arg2150His fVIII was reduced about 2-fold and 6-fold, respectively, by comparison to Ser2119Tyr and normal fVIII. These findings indicate that C1-domain mutations resulting in reduced fVIII binding to vWf are an important cause of mild/moderate hemophilia A.

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