Characterization of an Anti-Factor VIII Monoclonal Antibody with A1 and A3 Epitopes Which Increases Factor VIII Activity.

Abstract Epitopes of anti-factor VIII (FVIII) neutralizing antibodies distribute all of the FVIII domains. They inhibit FVIII for instance by blocking the FVIII interaction with factor IXa, factor X/factor Xa (FX/FXa), phospholipid, von Willebrand factor, or thrombin. Therefore, localization of such FVIII inhibitory effect gives us useful information for understanding of FVIII structure and function. We expect FVIII enhancing antibody also may be a useful tool. In this study, we found an anti-FVIII monoclonal antibody (named by moAb216) that increased the FVIII cofactor activity. The addition of moAb216 increased FVIII activity by ~1.6-fold dose-dependently in one-stage clotting assay. The increase of FVIII activity in the presence of moAb216 correlated with that of generated thrombin or factor Xa in thrombin or FXa generation based-assay. Blotting analysis revealed that this antibody reacted with only intact FVIII molecule, whilst failed to react with either SDS-treated FVIII, FVIIIa (active-form), or isolated each A1, A2, and A3-C1-C2 subunit. Individual monoclonal antibody, with an epitope of the A1 or A3 acidic region in FVIII, competitively inhibited FVIII binding to moAb216 as well as the increase of FVIII activity by its antibody. However, anti-A2 or anti-C2 monoclonal antibody did not affect. These results supported that this unique antibody, with a discontinuous epitope spanning both acidic regions in the A1 and A3 domains, recognized the native conformation of FVIII. To examine the mechanism(s) of increasing effect by moAb216, we focused on the activation and/or inactivation of FVIII. Rate constants on thrombin- and FXa-catalyzed activation of FVIII in the presence of moAb216 were ~2 and 3-fold greater, respectively, in dose-dependent manners compared with that of FVIII in its absence. On the other hand, the antibody inhibited the activated protein C (APC)-catalyzed FVIII inactivation with ~10-fold lower of inactivation rate constant. SDS-PAGE analysis revealed that moAb216 accelerated the cleavage at Arg372 in the A1-A2 junction by thrombin and FXa, whilst decelerated the cleavage at Arg336 within the A1 domain by APC. In addition, FVIII activity in the presence of moAb216 was more stable following heat denaturation analysis than that in its absence. We demonstrated that the increasing effect of FVIII activity by moAb216 was attributed to the change of cleavage at Arg372 and/or Arg336 in the heavy chain caused by interaction with the A1/A3 domains. Furthermore, moAb216 would be useful as a new replacement therapy for hemophilia A patients, since this increases and stabilizes FVIII activity, and can function even in the presence of anti-FVIII (A2 and C2) inhibitors.

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The Anticoagulant Properties of a Modified Form of Protein S

Thrombosis and Haemostasis ◽

10.1055/s-0038-1647048 ◽

1988 ◽

Vol 60 (02) ◽

pp. 298-304 ◽

Cited By ~ 17

Author(s):

C A Mitchell ◽

S M Kelemen ◽

H H Salem

Keyword(s):

Monoclonal Antibody ◽

Anticoagulant Activity ◽

Activated Protein C ◽

Factor Xa ◽

Protein S ◽

Human Neutrophil Elastase ◽

Factor X ◽

Sds Page

SummaryProtein S (PS) is a vitamin K-dependent anticoagulant that acts as a cofactor to activated protein C (APC). To date PS has not been shown to possess anticoagulant activity in the absence of APC.In this study, we have developed monoclonal antibody to protein S and used to purify the protein to homogeneity from plasma. Affinity purified protein S (PSM), although identical to the conventionally purified protein as judged by SDS-PAGE, had significant anticoagulant activity in the absence of APC when measured in a factor Xa recalcification time. Using SDS-PAGE we have demonstrated that prothrombin cleavage by factor X awas inhibited in the presence of PSM. Kinetic analysis of the reaction revealed that PSM competitively inhibited factor X amediated cleavage of prothrombin. PS preincubated with the monoclonal antibody, acquired similar anticoagulant properties. These results suggest that the interaction of the monoclonal antibody with PS results in an alteration in the protein exposing sites that mediate the observed anticoagulant effect. Support that the protein was altered was derived from the observation that PSM was eight fold more sensitive to cleavage by thrombin and human neutrophil elastase than conventionally purified protein S.These observations suggest that PS can be modified in vitro to a protein with APC-independent anticoagulant activity and raise the possibility that a similar alteration could occur in vivo through the binding protein S to a cellular or plasma protein.

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Mechanisms of Plasmin-Catalyzed Inactivation of the Factor VIII.

Blood ◽

10.1182/blood.v106.11.1017.1017 ◽

2005 ◽

Vol 106 (11) ◽

pp. 1017-1017

Author(s):

Keiji Nogami ◽

Midori Shima ◽

Tomoko Matsumoto ◽

Katsumi Nishiya ◽

Masahiro Takeyama ◽

...

Keyword(s):

Factor Viii ◽

Heavy Chain ◽

Activated Protein C ◽

Factor Xa ◽

Protein S ◽

Fold Increase ◽

Clotting Factors ◽

Fviii Activity ◽

A1 Domain ◽

Von Willebrand

Abstract Factor VIII (FVIII) functions as a cofactor for factor IXa in the intrinsic tenase complex. This tenase activity is down-regulated by activated protein C (APC) or factor Xa (FXa). Plasmin, the most potent fibrinolytic protease, inactivates FVIII as well as other clotting factors. However, the mechanism of FVIII inactivation by plasmin is poorly understood. FVIII activity reached to the peak value of ~2-fold increase at 3 min after the addition of plasmin in a one-stage clotting assay. Then, the activity was decreased rapidly and was undetectable within 30 min. This time-dependent reaction was not affected in the presence of von Willebrand factor and phospholipid. The activation of FVIII by plasmin was an ~50% level of that by FXa. The rate constant (min-1) of inactivation of FVIIIa by plasmin possessed ~11.3- and ~2.5-folds greater than those by FXa and APC in the presence of protein S, respectively. SDS-PAGE analysis showed that plasmin cleaved the 90~210-kDa heavy chain of FVIII to 50, 48,45, 40, and 38-kDa fragments via 90-kDa fragment. Using western blot and N-terminal sequence analyses, these fragments derived from the heavy chain were identified as A11-372, A1337-372-A2, A11-336, A2, and A137-336, respectively, by cleavages at Arg372, Arg740, Lys36 and Arg336 in the A1 domain. On the other hand, the 80-kDa light chain was cleaved to 67-kDa fragment via 70-kDa fragment by cleavages at Arg1721 and Arg1689, respectively, consistent with the pattern of cleavage by FXa. However, the cleavage at Arg336 by plasmin was much quicker than that at Arg372, contrast with that by FXa. Furthermore, this cleavage was faster than that by APC, consistent with rapid inactivation of FVIII. In addition, the cleavage at Arg336 of FVIIIa by plasmin was faster than that of isolated A1 or A1/A3-C1–C2 dimer, different with that by FXa. These results demonstrate the importance of cleavage at Arg336 for the mechanism of plasmin-catalyzed FVIII inactivation. Furthermore, this cleavage appears to be selectively modulated by the A2 domain that may interact with plasmin.

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Inhibition of the intrinsic factor X activating complex by protein S: evidence for a specific binding of protein S to factor VIII

Blood ◽

10.1182/blood.v86.3.1062.bloodjournal8631062 ◽

1995 ◽

Vol 86 (3) ◽

pp. 1062-1071 ◽

Cited By ~ 2

Author(s):

SJ Koppelman ◽

TM Hackeng ◽

JJ Sixma ◽

BN Bouma

Keyword(s):

Factor Viii ◽

Protein C ◽

Intrinsic Factor ◽

Activated Protein C ◽

Protein S ◽

Inhibitory Effect ◽

Factor X ◽

Ic50 Values ◽

Factor X Activation ◽

Factor X Activating Complex

Protein S is a vitamin K-dependent nonenzymatic anticoagulant protein that acts as a cofactor to activated protein C. Recently it was shown that protein S inhibits the prothrombinase reaction independent of activated protein C. In this study, we show that protein S can also inhibit the intrinsic factor X activation via a specific interaction with factor VIII. In the presence of endothelial cells, the intrinsic activation of factor X was inhibited by protein S with an IC50 value of 0.28 +/- 0.04 mumol/L corresponding to the plasma concentration of protein S. This inhibitory effect was even more pronounced when the intrinsic factor X activation was studied in the presence of activated platelets (IC50 = 0.15 +/- 0.02 mumol/L). When a nonlimiting concentration of phospholipid vesicles was used, the plasma concentration of protein S (300 nmol/L) inhibited the intrinsic factor X activation by 40%. Thrombin-cleaved protein S inhibited the endothelial cell-mediated factor X activation with an IC50 similar to that of native protein S (0.26 +/- 0.02 mumol/L). Protein S in complex with C4b-binding protein inhibited the endothelial cell-mediated factor X activation more potently than protein S alone (IC50 = 0.19 +/- 0.03 mumol/L). Using thrombin activated factor VIII, IC50 values of 0.53 +/- 0.09 mumol/L and 0.46 +/- 0.10 mumol/L were found for native protein S and thrombin-cleaved protein S, respectively. The possible interactions of protein S with factor IXa, phospholipids, and factor VIII were investigated. The enzymatic activity of factor IXa was not affected by protein S, and interaction of protein S with the phospholipid surface could not fully explain the inhibitory effect of protein S on the factor X activation. Using a solid-phase binding assay, we showed a specific, saturable, and reversible binding of protein S to factor VIII with a high affinity. The concentration of protein S where half-maximal binding was reached (B1/2max) was 0.41 +/- 0.06 mumol/L. A similar affinity was found for the interaction of thrombin-cleaved protein S with factor VIII (B1/2max = 0.40 +/- 0.04 mumol/L). The affinity of the complex protein S with C4B-binding protein appeared to be five times higher (B1/2max = 0.07 +/- 0.03 mumol/L). Because the affinities of the interaction of the different forms of protein S with factor VIII correspond to the IC50 values observed for the intrinsic factor X activating complex, the interaction of protein S with factor VIII may explain the inhibitory effect of protein S on the intrinsic factor X activating complex.(ABSTRACT TRUNCATED AT 400 WORDS)

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Inhibition of the intrinsic factor X activating complex by protein S: evidence for a specific binding of protein S to factor VIII

Blood ◽

10.1182/blood.v86.3.1062.1062 ◽

1995 ◽

Vol 86 (3) ◽

pp. 1062-1071 ◽

Cited By ~ 45

Author(s):

SJ Koppelman ◽

TM Hackeng ◽

JJ Sixma ◽

BN Bouma

Keyword(s):

Factor Viii ◽

Protein C ◽

Intrinsic Factor ◽

Activated Protein C ◽

Protein S ◽

Inhibitory Effect ◽

Factor X ◽

Ic50 Values ◽

Factor X Activation ◽

Factor X Activating Complex

Abstract Protein S is a vitamin K-dependent nonenzymatic anticoagulant protein that acts as a cofactor to activated protein C. Recently it was shown that protein S inhibits the prothrombinase reaction independent of activated protein C. In this study, we show that protein S can also inhibit the intrinsic factor X activation via a specific interaction with factor VIII. In the presence of endothelial cells, the intrinsic activation of factor X was inhibited by protein S with an IC50 value of 0.28 +/- 0.04 mumol/L corresponding to the plasma concentration of protein S. This inhibitory effect was even more pronounced when the intrinsic factor X activation was studied in the presence of activated platelets (IC50 = 0.15 +/- 0.02 mumol/L). When a nonlimiting concentration of phospholipid vesicles was used, the plasma concentration of protein S (300 nmol/L) inhibited the intrinsic factor X activation by 40%. Thrombin-cleaved protein S inhibited the endothelial cell-mediated factor X activation with an IC50 similar to that of native protein S (0.26 +/- 0.02 mumol/L). Protein S in complex with C4b-binding protein inhibited the endothelial cell-mediated factor X activation more potently than protein S alone (IC50 = 0.19 +/- 0.03 mumol/L). Using thrombin activated factor VIII, IC50 values of 0.53 +/- 0.09 mumol/L and 0.46 +/- 0.10 mumol/L were found for native protein S and thrombin-cleaved protein S, respectively. The possible interactions of protein S with factor IXa, phospholipids, and factor VIII were investigated. The enzymatic activity of factor IXa was not affected by protein S, and interaction of protein S with the phospholipid surface could not fully explain the inhibitory effect of protein S on the factor X activation. Using a solid-phase binding assay, we showed a specific, saturable, and reversible binding of protein S to factor VIII with a high affinity. The concentration of protein S where half-maximal binding was reached (B1/2max) was 0.41 +/- 0.06 mumol/L. A similar affinity was found for the interaction of thrombin-cleaved protein S with factor VIII (B1/2max = 0.40 +/- 0.04 mumol/L). The affinity of the complex protein S with C4B-binding protein appeared to be five times higher (B1/2max = 0.07 +/- 0.03 mumol/L). Because the affinities of the interaction of the different forms of protein S with factor VIII correspond to the IC50 values observed for the intrinsic factor X activating complex, the interaction of protein S with factor VIII may explain the inhibitory effect of protein S on the intrinsic factor X activating complex.(ABSTRACT TRUNCATED AT 400 WORDS)

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Activation of Human Coagulation Factor VIII by Activated Factor X, the Common Product of the Intrinsic and the Extrinsic Pathway of Blood Coagulation

Thrombosis and Haemostasis ◽

10.1055/s-0038-1657137 ◽

1982 ◽

Vol 47 (02) ◽

pp. 096-100 ◽

Cited By ~ 22

Author(s):

K Mertens ◽

R M Bertina

Keyword(s):

Factor Viii ◽

Human Factor ◽

Intrinsic Factor ◽

Factor Xa ◽

Coagulation Factor ◽

Factor X ◽

Extrinsic Factor ◽

Extrinsic Pathway ◽

Factor Ixa ◽

The Common

SummaryThe intrinsic activation of human factor X has been studied in a system consisting of purified factors and in plasma. In both these systems factor Xa stimulated the activation of factor X by factor IXa plus factor VIII This is due to the activation of factor VIII by factor Xa. When this factor Xa is formed via the extrinsic pathway, the extrinsic factor X activator functions as a stimulator of the intrinsic factor X activator.

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Human Factor VIII Inhibitor Alloantibodies with a C2 Epitope Inhibit Factor Xa-catalyzed Factor VIII Activation: A new Anti-factor VIII Inhibitory Mechanism

Thrombosis and Haemostasis ◽

10.1055/s-0037-1613026 ◽

2002 ◽

Vol 87 (03) ◽

pp. 459-465 ◽

Cited By ~ 14

Author(s):

Keiji Nogami ◽

Katsumi Nishiya ◽

Yoshihiko Sakurai ◽

Ichiro Tanaka ◽

John Giddings ◽

...

Keyword(s):

Factor Viii ◽

Factor Xa ◽

Factor Viii Inhibitor ◽

Inhibitory Mechanism ◽

Fviii Inhibitor ◽

Fviii Activity ◽

Human Factor Viii ◽

Sds Page ◽

Viii Inhibitor ◽

C1 Domains

SummaryFactor VIII (FVIII) inhibitor alloantibodies react with the A2, C2, or A3-C1 domains of FVIII and inactivate FVIII activity. We recently demonstrated that an anti-C2 monoclonal antibody with a Val2248Gly2285 epitope, inhibited factor Xa (FXa)-catalyzed FVIII activation, and that a FXa binding site for FVIII was located within residues Thr2253-Gln2270. In this study, we investigated whether anti-C2 alloantibodies inhibit FXa-catalyzed FVIII activation. Anti-C2 alloantibodies from four patients inhibited FVIII activation by FXa in onestage clotting assay. Furthermore, analysis by SDS-PAGE showed that all alloantibodies inhibited FVIII proteolytic cleavage by FXa independently of phospholipid. To confirm direct inhibition of FVIII and FXa interaction, we examined the effect of alloantibodies on FVIII binding to anhydro-FXa, a catalytically inactive FXa, in ELISA. All alloantibodies and C2-affinity purified F(ab)’2 preparations inhibited FVIII binding to anhydro-FXa dose-dependently. Our results revealed a new inhibitory mechanism of FVIII, mediated by inhibition of FXa in the presence of anti-C2 alloantibodies.

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Active site-specific immunoassays

Blood ◽

10.1182/blood.v76.4.755.755 ◽

1990 ◽

Vol 76 (4) ◽

pp. 755-766 ◽

Cited By ~ 15

Author(s):

KG Mann ◽

EB Williams ◽

S Krishnaswamy ◽

W Church ◽

A Giles ◽

...

Keyword(s):

Active Site ◽

Serine Proteases ◽

Solid Phase ◽

Activated Protein C ◽

Factor Xa ◽

Immune Recognition ◽

Factor X ◽

Zymogen Activation ◽

Prothrombinase Complex ◽

Active Site Histidine

Abstract This study describes a process by which serine proteases that contain an S-1 arginine subsite and active site histidine may be inactivated and subsequently quantitated using a combination of peptidyl chloromethylketone chemistry and immune recognition technology. Active site labeling and inactivation of proteases is attained by modification of the active site histidine with a peptidyl chloromethylketone. In the specific illustrations demonstrated, we used the compound biotinyl- epsilon-aminocaproyl-phenylalanylprolylarginyl chloromethylketone. This reagent reacts quantitatively and specifically with the active site histidine of a wide variety of proteases that are elaborated in the coagulation and fibrinolytic system. The inactivated enzyme(s) may be quantitated by combinations of antiprotein antibodies and avidin binding technology using the biotin moiety on the peptide inhibitor. We have demonstrated the capability of capture of inactivated enzyme products directly on to solid-phase avidin with subsequent quantitation of bound protein using specific antibodies. In the converse system we have captured specific proteases using antiprotein antibodies in the solid phase and have quantitated bound enzyme by using avidin. Subsequent detection and quantitation has been achieved using the enzymatic activity of horseradish peroxidase conjugated either to the antibody or to avidin. Both types of assays are feasible, with avidin capture being the preferred mode when enzyme is evaluated in the presence of excess zymogen, as would be common in the evaluation of most blood-clotting enzymes. Assays are illustrated for tissue plasminogen activator, plasmin, thrombin, factor Xa, and activated protein C, which can measure protease concentrations as low as 50 pmol/L. Specific applications of the assays are provided in studies of the activation of prothrombin by the prothrombinase complex and of factor X with Russell's viper venom factor X activator. These assays measure the mass of active site present in the reaction mixture and are relatively independent of subspecies of enzyme or the environment in which the activity is generated. These assay systems provide powerful tools for elucidating product-precursor relationships in multienzyme feedback reactions involving zymogen activation.

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DEVELOPMENT OF A SIMPLE FACTOR VIII-ASSAY FOR CLINICAL USE

10.1055/s-0038-1644034 ◽

1987 ◽

Author(s):

R Wagenvoord ◽

H Hendrix ◽

H C Hemker

Keyword(s):

Factor Viii ◽

Room Temperature ◽

Plasma Sample ◽

Factor Xa ◽

Factor X ◽

Activation Time ◽

Simple Factor ◽

Working Day ◽

Working Procedure

We have developed an assay for the determination of factor VIII in human plasma. The criteria that such an assay must fulfil are: the method should be simple, the reagents should be stable for several hours at room temperature, the method should be sensitive and linear in the amount of factor VIII. The assay we have developed fulfils all these criteria.The working procedure is simple. Both a lyophilized factor VIII assay (containing factor IXa, thrombin, phospholipids and Ca++) and lyophilized factor X are reconstituted with water. A reaction tube is filled with 100 pi factor VIII assay, prewarmed at 25° or 37 °C, then 100 pi of a diluted (10-20 times) plasma sample is added (t = 0) and after 30 seconds activation time the reaction is started with 100 pi factor X. After 1-2 minutes a sample is taken and diluted in an EDTA-containing buffer to stop the reaction. The formed factor Xa is meausured with a FXa-substrate from which p-nitroaniline will be split, causing an increase of the A405nm. The lyophilized reagents are stable for several months (at least) and after reconstitution they do not loose activity during a whole working day. The sensitivity of the method Is high. A plasma containing 1% factor VIII gives an increase in absorption of three to four times of a fully factor VIII deficient plasma. Extensive studies have shown that a complete linearity excists between 0 - 200% factor VIII in the plasma and the increase of the A405nm

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HEPARIN IS NOT AN EFFICIENT INHIBITOR OF THE FACTOR Xa-DEPENDENT ACTIVATION OF FACTOR V AND FACTOR VIII

10.1055/s-0038-1642931 ◽

1987 ◽

Author(s):

F A Ofosu ◽

G J Modi ◽

M R Buchanan ◽

J Hirsh ◽

M A Blajchman

Keyword(s):

Factor Viii ◽

Antithrombin Iii ◽

Specific Inhibitor ◽

Factor Xa ◽

Factor V ◽

Factor X ◽

Inhibitory Effects ◽

Efficient Inhibitor ◽

System 1 ◽

Prothrombin Activation

We have previously proposed that the steps in coagulation most sensitive to inhibition by heparin are the thrombin-dependent activation of factor V and factor VIII. This observation was based on the demonstration that therapeutic concentrations of heparin or 1μM of the thrombin specific inhibitor, phe-pro-arg CH2Cl (PPACK) completely inhibited the activation of prothrombin when contact-activated plasma (CAP) was recalcified for up to 1 min. Under similar conditions, heparin and PPACK only partially inhibited the activation of factor X. Moreover, the addition of thrombin (lOnM) to CAP 1 min before that of heparin or PPACK reversed their inhibitory effects. We now provide further support for our hypothesis by showing that when the activity of thrombin is suppressed by heparin or PPACK, efficient activation of radiolabelled prothrombin occurs only when the factor Xa then present activates factor V and factor VIII. We compared the effects of HEP of PPACK on the following four systems for initiating the activation of prothrombin: (1) CAP; (2) CAP + lOnM thrombin; (3) CAP + InM Xa and (4) unactivated plasma + InM Xa + InM Va + coagulant phospholipids. In each system, the enzymes were added 1 min before the heparin or PPACK. In the absence of heparin or PPACK, all four systems generated the same amount of thrombin activity in 45s. Complete inhibition of prothrombin activation by heparin and PPACK was observed only in system 1 which did not contain exogenous thrombin or factor Xa. No inhibition by heparin or PPACK was observed when thrombin or factor Xa was added to CAP in systems (2) and (3). Only partial inhibition was observed in system (4) which contained exogenous prothrombi-nase complex. Factor Xa thus provides an effective by-pass mechanism for the activation of factor VIII and factor V in plasma containing therapeutic concentrations of heparin. Our data provide further evidence that the heparin-antithrombin III system is not effective in inactivating factor Xa. These results support the hypothesis that in unactivated normal plasma, the primary anticoagulant effect of heparin is the inhibition of the thrombin-dependent activation of factor V and factor VIII.

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Feiba Immuno: A Preparation with Factor Eight Inhibitor Bypassing Activity

10.1055/s-0039-1682501 ◽

1977 ◽

Author(s):

F. Elsinger

Keyword(s):

Factor Viii ◽

Factor Xa ◽

Coagulation Factors ◽

Active Principle ◽

Factor Viii Inhibitor ◽

Factor V ◽

In Vitro Experiments ◽

Factor X ◽

Viii Inhibitor

FEIBA IMMUNO is a preparation in which a new activity is generated capable of bypassing factor VIII. The preparation which is used to treat patients with inhibitors (especially inhibitors to factor VIII) is standardized in FEIBA units, i.e. in terms of its in vitro capacity to shorten the activated PTT of a factor VIII inhibitor plasma.It could be concluded from different in vitro experiments that none of the classic’ activated coagulation factors is responsible for the factor VIII bypassing reaction; FEIB-activity seems to be correlated to a new complex of coagulation factors.To get an answer to the question which coagulation factors are essential for FEIB-activity, we tried to generate this activity from different deficient plasmas; from these experiments the following conclusions could be drawn:, the presence of at least factors VII, IX, and X is essential for the generation of the molecular species responsible for factor VIII as well as factor X bypassing activity, but factor V is not bypassed. This activity is not factor Xa itself. Factors VIII and V are not necessary for the generation of this active principle, but factor V is finally needed for its bypassing action.

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