scholarly journals Inhibition of tissue factor/factor VIIa activity in plasma requires factor X and an additional plasma component

Blood ◽  
1985 ◽  
Vol 66 (1) ◽  
pp. 204-212 ◽  
Author(s):  
NL Sanders ◽  
SP Bajaj ◽  
A Zivelin ◽  
SI Rapaport
Keyword(s):  
Tissue Factor ◽  
Factor Viia ◽  
Factor Ix ◽  
Factor Vii ◽  
Factor X ◽  
Additional Material ◽  
Plasma Reaction ◽  
Progress Curve ◽  
Peptide Release ◽  
Release Data

Abstract A study was carried out to explore requirements for the inhibition of tissue factor-factor VIIa enzymatic activity in plasma. Reaction mixtures contained plasma, 3H-factor IX or 3H-factor X, tissue factor (vol/vol 2.4% to 24%), and calcium. Tissue factor-factor VIIa activity was evaluated from progress curves of activation of factor IX or factor X, plotted from tritiated activation peptide release data. With normal plasma, progress curves exhibited initial limited activation followed by a plateau indicative of loss of tissue factor-factor VIIa activity. With hereditary factor X-deficient plasma treated with factor X antibodies, progress curves revealed full factor IX activation. Adding only 0.4 micrograms/mL factor X (final concentration) could restore inhibition. Inhibition was not observed in purified systems containing 6% to 24% tissue factor, factor VII, 0.5 micrograms/mL, factor IX, 13 micrograms/mL, and factor X up to 0.8 micrograms/mL, but could be induced by adding barium-absorbed plasma to the reaction mixture. Thus, both factor X and an additional material in plasma were required for inhibition. The amount of factor X needed appeared related to the concentration of tissue factor; adding more tissue factor at the plateau of a progress curve induced further activation. These results also indicate that inhibited reaction mixtures contained active free factor VII(a). Preliminary data suggest that inhibition may stem from loss of activity of the tissue factor component of the tissue factor- factor VII(a) complex.

scholarly journals Inhibition of tissue factor/factor VIIa activity in plasma requires factor X and an additional plasma component

Blood ◽  
1985 ◽  
Vol 66 (1) ◽  
pp. 204-212
Author(s):  
NL Sanders ◽  
SP Bajaj ◽  
A Zivelin ◽  
SI Rapaport
Keyword(s):  
Tissue Factor ◽  
Factor Viia ◽  
Factor Ix ◽  
Factor Vii ◽  
Factor X ◽  
Additional Material ◽  
Plasma Reaction ◽  
Progress Curve ◽  
Peptide Release ◽  
Release Data

A study was carried out to explore requirements for the inhibition of tissue factor-factor VIIa enzymatic activity in plasma. Reaction mixtures contained plasma, 3H-factor IX or 3H-factor X, tissue factor (vol/vol 2.4% to 24%), and calcium. Tissue factor-factor VIIa activity was evaluated from progress curves of activation of factor IX or factor X, plotted from tritiated activation peptide release data. With normal plasma, progress curves exhibited initial limited activation followed by a plateau indicative of loss of tissue factor-factor VIIa activity. With hereditary factor X-deficient plasma treated with factor X antibodies, progress curves revealed full factor IX activation. Adding only 0.4 micrograms/mL factor X (final concentration) could restore inhibition. Inhibition was not observed in purified systems containing 6% to 24% tissue factor, factor VII, 0.5 micrograms/mL, factor IX, 13 micrograms/mL, and factor X up to 0.8 micrograms/mL, but could be induced by adding barium-absorbed plasma to the reaction mixture. Thus, both factor X and an additional material in plasma were required for inhibition. The amount of factor X needed appeared related to the concentration of tissue factor; adding more tissue factor at the plateau of a progress curve induced further activation. These results also indicate that inhibited reaction mixtures contained active free factor VII(a). Preliminary data suggest that inhibition may stem from loss of activity of the tissue factor component of the tissue factor- factor VII(a) complex.

scholarly journals Studies of a mechanism inhibiting the initiation of the extrinsic pathway of coagulation

Blood ◽  
1987 ◽  
Vol 69 (2) ◽  
pp. 645-651 ◽  
Author(s):  
LV Rao ◽  
SI Rapaport
Keyword(s):  
Tissue Factor ◽  
Factor Viia ◽  
Factor Xa ◽  
Factor Ix ◽  
Factor Vii ◽  
Factor X ◽  
Extrinsic Pathway ◽  
Mechanism Of Inhibition ◽  
Peptide Release ◽  
Release Assay

Abstract We have extended earlier studies (Blood 66:204, 1985) of a mechanism of inhibition of factor VIIa/tissue factor activity that requires a plasma component (called herein extrinsic pathway inhibitor or EPI) and factor Xa. An activated peptide release assay using 3H-factor IX as a substrate was used to evaluate inhibition. Increasing the tissue factor concentration from 20% to 40% (vol/vol) overcame the inhibitory mechanism in normal plasma but not in factor VII-deficient plasma supplemented with a low concentration of factor VII. A second wave of factor IX activation obtained by a second addition of tissue factor to plasma with a normal factor VII concentration was almost abolished by supplementing the reaction mixture with additional EPI and factor X. Factor Xa's active site was necessary for factor Xa's contribution to inhibition, but preliminary incubation of factor Xa with EPI in the absence of factor VIIa/tissue factor complex or of factor VIIa/tissue factor complex in the absence of EPI did not replace the need for the simultaneous presence of factor Xa, factor VIIa/tissue factor, calcium, and EPI in an inhibitory reaction mixture. Inhibition of factor VIIa/tissue factor was reversible; both tissue factor and factor VIIa activity could be recovered from a dissociated, inhibited factor VIIa/tissue factor complex. EPI appeared to bind to a factor VIIa/tissue factor complex formed in the presence of factor Xa but not to a factor VIIa/tissue factor complex formed in the absence of factor Xa.

scholarly journals Studies of a mechanism inhibiting the initiation of the extrinsic pathway of coagulation

Blood ◽  
1987 ◽  
Vol 69 (2) ◽  
pp. 645-651 ◽  
Author(s):  
LV Rao ◽  
SI Rapaport
Keyword(s):  
Tissue Factor ◽  
Factor Viia ◽  
Factor Xa ◽  
Factor Ix ◽  
Factor Vii ◽  
Factor X ◽  
Extrinsic Pathway ◽  
Mechanism Of Inhibition ◽  
Peptide Release ◽  
Release Assay

We have extended earlier studies (Blood 66:204, 1985) of a mechanism of inhibition of factor VIIa/tissue factor activity that requires a plasma component (called herein extrinsic pathway inhibitor or EPI) and factor Xa. An activated peptide release assay using 3H-factor IX as a substrate was used to evaluate inhibition. Increasing the tissue factor concentration from 20% to 40% (vol/vol) overcame the inhibitory mechanism in normal plasma but not in factor VII-deficient plasma supplemented with a low concentration of factor VII. A second wave of factor IX activation obtained by a second addition of tissue factor to plasma with a normal factor VII concentration was almost abolished by supplementing the reaction mixture with additional EPI and factor X. Factor Xa's active site was necessary for factor Xa's contribution to inhibition, but preliminary incubation of factor Xa with EPI in the absence of factor VIIa/tissue factor complex or of factor VIIa/tissue factor complex in the absence of EPI did not replace the need for the simultaneous presence of factor Xa, factor VIIa/tissue factor, calcium, and EPI in an inhibitory reaction mixture. Inhibition of factor VIIa/tissue factor was reversible; both tissue factor and factor VIIa activity could be recovered from a dissociated, inhibited factor VIIa/tissue factor complex. EPI appeared to bind to a factor VIIa/tissue factor complex formed in the presence of factor Xa but not to a factor VIIa/tissue factor complex formed in the absence of factor Xa.

scholarly journals A candidate activation pathway for coagulation factor VII

2019 ◽  
Vol 476 (19) ◽  
pp. 2909-2926
Author(s):  
Tina M. Misenheimer ◽  
Kraig T. Kumfer ◽  
Barbara E. Bates ◽  
Emily R. Nettesheim ◽  
Bradford S. Schwartz
Keyword(s):  
Tissue Factor ◽  
Blood Coagulation ◽  
Factor Viia ◽  
Coagulation Factor ◽  
Factor Ix ◽  
Factor Vii ◽  
Factor X ◽  
Contact Activation ◽  
Coagulation Factor Vii ◽  
Factor Viiia

Abstract The mechanism of generation of factor VIIa, considered the initiating protease in the tissue factor-initiated extrinsic limb of blood coagulation, is obscure. Decreased levels of plasma VIIa in individuals with congenital factor IX deficiency suggest that generation of VIIa is dependent on an activation product of factor IX. Factor VIIa activates IX to IXa by a two-step removal of the activation peptide with cleavages occurring after R191 and R226. Factor IXaα, however, is IX cleaved only after R226, and not after R191. We tested the hypothesis that IXaα activates VII with mutant IX that could be cleaved only at R226 and thus generate only IXaα upon activation. Factor IXaα demonstrated 1.6% the coagulant activity of IXa in a contact activation-based assay of the intrinsic activation limb and was less efficient than IXa at activating factor X in the presence of factor VIIIa. However, IXaα and IXa had indistinguishable amidolytic activity, and, strikingly, both catalyzed the cleavage required to convert VII to VIIa with indistinguishable kinetic parameters that were augmented by phospholipids, but not by factor VIIIa or tissue factor. We propose that IXa and IXaα participate in a pathway of reciprocal activation of VII and IX that does not require a protein cofactor. Since both VIIa and activated IX are equally plausible as the initiating protease for the extrinsic limb of blood coagulation, it might be appropriate to illustrate this key step of hemostasis as currently being unknown.

scholarly journals Studies of the activation of factor VII bound to tissue factor [see comments]

Blood ◽  
1996 ◽  
Vol 87 (9) ◽  
pp. 3738-3748 ◽  
Author(s):  
LV Rao ◽  
T Williams ◽  
SI Rapaport
Keyword(s):  
Tissue Factor ◽  
Factor Viia ◽  
Tissue Injury ◽  
Factor Xa ◽  
Inhibitory Effect ◽  
Factor Ix ◽  
Factor Vii ◽  
Activate Factor ◽  
Factor X ◽  
Ovarian Carcinoma Cell Line

Experiments were performed to evaluate activation of factor VII bound to relipidated tissue factor (TF) in suspension and to TF constitutively expressed on the surface of an ovarian carcinoma cell line (OC-2008). Activation was assessed by measuring cleavage of 125I- factor VII and by the ability of unlabeled factor VII to catalyze activation of a variant factor IX molecule that, after activation, cannot back-activate factor VII. Factor Xa was found to effectively activate factor VII bound to TF relipidated in either acidic or neutral phospholipid vesicles. Autoactivation of factor VII bound to TF in suspension was dependent on the preparation of TF apoprotein used and the technique of its relipidation. This highlights the need for caution in extrapolating data from TF in suspension to the activation of factor VII bound to cell surfaces during hemostasis. A relatively slow activation of factor VII bound to OC-2008 monolayers in the absence of added protease was observed consistently. Antithrombin in the presence or absence of heparin prevented this basal activation, whereas TF pathway inhibitor (TFPI/factor Xa complexes had only a limited inhibitory effect. Adding a substrate concentration of factor X markedly enhanced basal activation of factor VII, but both TFPI/factor Xa and antithrombin/heparin abolished this enhancement. Overall, our data are compatible with the hypothesis that not all factor VII/TF complexes formed at a site of tissue injury are readily activated to factor VIIa (VIIa)/TF complexes during hemostasis. The clinical significance of this is discussed.

scholarly journals Tissue factor-dependent activation of tritium-labeled factor IX and factor X in human plasma

Blood ◽  
1984 ◽  
Vol 63 (6) ◽  
pp. 1338-1347 ◽  
Author(s):  
SA Morrison ◽  
J Jesty
Keyword(s):  
Human Plasma ◽  
Tissue Factor ◽  
Factor Viia ◽  
Stimulate Factor ◽  
Specific Inhibitor ◽  
Factor Xa ◽  
Factor Ix ◽  
Factor Vii ◽  
Factor X ◽  
Bovine Plasma

Recent investigations have suggested that the activation of factor IX by factor VII/tissue factor may be an important alternative route to the generation of factor Xa. Accordingly, we have compared the tissue factor-dependent activation of tritium-labeled factor IX and factor X in a human plasma system and have studied the role of proteases known to stimulate factor VII activity. Plasma was defibrinated by heating and depleted of its factors IX and X by passing it through antibody columns. Addition of human brain thromboplastin, Ca2+, and purified 3H- labeled factor X to the plasma resulted, after a short lag, in burst- like activation of the factor X, measured as the release of radiolabeled activation peptide. The progress of activation was slowed by both heparin and a specific inhibitor of factor Xa, suggesting a feedback role for this enzyme, but factor X activation could not be completely abolished by such inhibitors. In the case of 3H-factor IX activation, the rate also increased for approximately 3 min after addition of thromboplastin, but was not subsequently curtailed. A survey of proteases implicated as activators of factor VII in other settings showed that both factor Xa and (to a much smaller extent) factor IXa could accelerate the activation of factor IX. However, factor Xa was unique in obliterating activation when present at concentrations greater than approximately 1 nM. Heparin inhibited the tissue factor-dependent activation of factor IX almost completely, apparently through the effect of antithrombin on the feedback reactions of factors Xa and IXa on factor VII. These results suggest that a very tight, biphasic control of factor VII activity exists in human plasma, which is modulated mainly by factor Xa. Variation of the factor IX or factor X concentrations permitted kinetic parameters for each activation to be derived. At saturation of factor VIIa/tissue factor, factor IX activation was significantly more rapid than was previously found in bovine plasma under similar conditions. The activation of factor X at saturation was slightly more rapid than in bovine plasma, despite the presence of heparin.

scholarly journals Activation of human factor VII in the initiation of tissue factor- dependent coagulation

Blood ◽  
1986 ◽  
Vol 68 (3) ◽  
pp. 685-691 ◽  
Author(s):  
LV Rao ◽  
SI Rapaport ◽  
SP Bajaj
Keyword(s):  
Tissue Factor ◽  
Factor Ix ◽  
Factor Vii ◽  
Activate Factor ◽  
Factor Xii ◽  
Factor X ◽  
Clotting Time ◽  
Activated Factor Vii ◽  
Peptide Release ◽  
Minimal Generation

Abstract We have used activation peptide release assays to compare factor VII and activated factor VII (VIIa) activation of factor X, normal factor IX (IXN), and a variant factor IX (IXBmLE), which, after activation, is unable to back-activate factor VII. In purified systems, factor VII and VIIa each rapidly activated factor X, but after a one minute lag for factor VII. VIIa also readily activated both IXN and IXBmLE. Factor VII initially failed to activate substantial amounts of either IXN or IXBmLE; on further incubation factor VII activated IXN but not IXBmLE. Activation of IXN began when approximately 10% of factor VII had been converted to VIIa, as measured by 125I-factor VII radioactivity profiles. Adding factor VII to VIIa slowed its activation of IXBmLE. However, in the presence of factor X, factor VII alone rapidly activated IXBmLE. Unlike purified systems, 1 nmol/L VIIa added to factor VII-deficient plasma failed to activate factor IX. Increasing factor VII to 10 nmol/L (plasma concentration) either as native VII or VIIa yielded similar activation curves for factor IX and similar activation curves for factor X. Adding 5% VIIa to factor X-deficient plasma and to factor XII-deficient plasma substantially shortened the dilute tissue factor clotting time of only the former. These data support the hypothesis that factor VII/tissue factor complex initiates tissue factor-dependent clotting through a minimal generation of Xa. This Xa then rapidly back-activates a small amount of factor VII, following which the rates of activation of both factors IX and X increase dramatically.

scholarly journals Tissue factor-dependent activation of tritium-labeled factor IX and factor X in human plasma

Blood ◽  
1984 ◽  
Vol 63 (6) ◽  
pp. 1338-1347 ◽  
Author(s):  
SA Morrison ◽  
J Jesty
Keyword(s):  
Human Plasma ◽  
Tissue Factor ◽  
Factor Viia ◽  
Stimulate Factor ◽  
Specific Inhibitor ◽  
Factor Xa ◽  
Factor Ix ◽  
Factor Vii ◽  
Factor X ◽  
Bovine Plasma

Abstract Recent investigations have suggested that the activation of factor IX by factor VII/tissue factor may be an important alternative route to the generation of factor Xa. Accordingly, we have compared the tissue factor-dependent activation of tritium-labeled factor IX and factor X in a human plasma system and have studied the role of proteases known to stimulate factor VII activity. Plasma was defibrinated by heating and depleted of its factors IX and X by passing it through antibody columns. Addition of human brain thromboplastin, Ca2+, and purified 3H- labeled factor X to the plasma resulted, after a short lag, in burst- like activation of the factor X, measured as the release of radiolabeled activation peptide. The progress of activation was slowed by both heparin and a specific inhibitor of factor Xa, suggesting a feedback role for this enzyme, but factor X activation could not be completely abolished by such inhibitors. In the case of 3H-factor IX activation, the rate also increased for approximately 3 min after addition of thromboplastin, but was not subsequently curtailed. A survey of proteases implicated as activators of factor VII in other settings showed that both factor Xa and (to a much smaller extent) factor IXa could accelerate the activation of factor IX. However, factor Xa was unique in obliterating activation when present at concentrations greater than approximately 1 nM. Heparin inhibited the tissue factor-dependent activation of factor IX almost completely, apparently through the effect of antithrombin on the feedback reactions of factors Xa and IXa on factor VII. These results suggest that a very tight, biphasic control of factor VII activity exists in human plasma, which is modulated mainly by factor Xa. Variation of the factor IX or factor X concentrations permitted kinetic parameters for each activation to be derived. At saturation of factor VIIa/tissue factor, factor IX activation was significantly more rapid than was previously found in bovine plasma under similar conditions. The activation of factor X at saturation was slightly more rapid than in bovine plasma, despite the presence of heparin.

scholarly journals Activation of human factor VII in the initiation of tissue factor- dependent coagulation

Blood ◽  
1986 ◽  
Vol 68 (3) ◽  
pp. 685-691 ◽  
Author(s):  
LV Rao ◽  
SI Rapaport ◽  
SP Bajaj
Keyword(s):  
Tissue Factor ◽  
Factor Ix ◽  
Factor Vii ◽  
Activate Factor ◽  
Factor Xii ◽  
Factor X ◽  
Clotting Time ◽  
Activated Factor Vii ◽  
Peptide Release ◽  
Minimal Generation

We have used activation peptide release assays to compare factor VII and activated factor VII (VIIa) activation of factor X, normal factor IX (IXN), and a variant factor IX (IXBmLE), which, after activation, is unable to back-activate factor VII. In purified systems, factor VII and VIIa each rapidly activated factor X, but after a one minute lag for factor VII. VIIa also readily activated both IXN and IXBmLE. Factor VII initially failed to activate substantial amounts of either IXN or IXBmLE; on further incubation factor VII activated IXN but not IXBmLE. Activation of IXN began when approximately 10% of factor VII had been converted to VIIa, as measured by 125I-factor VII radioactivity profiles. Adding factor VII to VIIa slowed its activation of IXBmLE. However, in the presence of factor X, factor VII alone rapidly activated IXBmLE. Unlike purified systems, 1 nmol/L VIIa added to factor VII-deficient plasma failed to activate factor IX. Increasing factor VII to 10 nmol/L (plasma concentration) either as native VII or VIIa yielded similar activation curves for factor IX and similar activation curves for factor X. Adding 5% VIIa to factor X-deficient plasma and to factor XII-deficient plasma substantially shortened the dilute tissue factor clotting time of only the former. These data support the hypothesis that factor VII/tissue factor complex initiates tissue factor-dependent clotting through a minimal generation of Xa. This Xa then rapidly back-activates a small amount of factor VII, following which the rates of activation of both factors IX and X increase dramatically.

Extrinsic Activation of Human Coagulation Factors IX and X on the Endothelial Surface

1991 ◽  
Vol 66 (03) ◽  
pp. 283-291 ◽  
Author(s):  
Victor J J Bom ◽  
Victor W M van Hinsbergh ◽  
Hanneke H Reinalda-Poot ◽  
Ramon W Mohanlal ◽  
Rogier M Bertina
Keyword(s):  
Tissue Factor ◽  
Factor Viia ◽  
Factor Xa ◽  
Coagulation Factors ◽  
Factor Ix ◽  
Factor Vii ◽  
Lag Phase ◽  
Factor X ◽  
Free System ◽  
Endothelial Surface

SummaryIn previous kinetic studies, the catalytic efficiency of the activation of human coagulation factors IX and X by factor VIIa in the presence of purified tissue factor apoprotein was found to be essentially equal. These activation reactions were now studied on the surface of human umbilical vein endothelial cells. The cells were stimulated with endotoxin to express tissue factor. This tissue factor activity was saturable with factor VIIa and could be inhibited by rabbit antibodies against human tissue factor apoprotein. Only stimulated cells supported factor VIIa activity. No difference in the reactivity of factor VII and VIIa was observed in the presence of factor X, due to rapid feedback activation of factor VII by factor Xa. However, the activation of factor IX by factor VII shows a 10 min lag-phase, which reflects that the activation of factor VII by factor IXa is a less efficient process. The kinetic parameters for the factor VIIa dependent activation of factor IX and factor X on the endothelial surface were: Km 0.09 εM, Vmax 0.13 pmol/min, and Km 0.071 εM, Vmax 0.41 pmol/min, respectively. The same ratio between the Vmax for factor X and factor IX activation was observed as in a cell free system. However, the Km of factor IX was 4-fold higher on the endothelial surface than in the cell free system. Together, these kinetic parameters will favour factor X activation 5-fold over factor IX activation at physiological concentrations of these proteins.The activation of factor X by factor VIIa on the endothelial surface was characterized by a short lag-phase, which was absent in factor IX activation. Further, both the activation of factor X and factor IX were down regulated by factor Xa.

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