Inhibition of Thrombin Generation in Plasma by Fibrin Formation (Antithrombin I)

2002 ◽  
Vol 88 (08) ◽  
pp. 253-258 ◽  
Author(s):  
N. B. de Bosch ◽  
A. Ruiz-Sáez ◽  
M. Echenagucia ◽  
A. Rodriguez-Lemoin ◽  
M. W. Mosesson
Keyword(s):  
New York ◽  
Binding Sites ◽  
Thrombin Generation ◽  
High Affinity ◽  
Fibrin Formation ◽  
Normal Plasma ◽  
Carboxy Terminal Region ◽  
Carboxy Terminal ◽  
Inhibition Of Thrombin ◽  
Prothrombin Activation

SummaryThe adsorption of thrombin to fibrin during clotting defines “Antithrombin I” activity. We confirmed that thrombin generation in afibrinogenemic or in Reptilase defibrinated normal plasma was higher than in normal plasma. Repletion of these fibrinogen-deficient plasmas with fibrinogen 1 (‘γA/’γA), whose fibrin has two “low affinity” non-substrate thrombin binding sites, resulted in moderately reduced thrombin generation by 29-37%. Repletion with fibrinogen 2 (‘γ´/’γA), which in addition to low affinity thrombin-binding sites in fibrin, has a “high affinity” non-substrate thrombin binding site in the carboxy-terminal region of its ‘γ´ chain, was even more effective and reduced thrombin generation by 57-67%. Adding peptides that compete for thrombin binding to fibrin [S-Hir53-64 (hirugen) or ‘γ´ 414-427] caused a transient delay in the onset of otherwise robust thrombin generation, indicating that fibrin formation is necessary for full expression of Antithrombin I activity. Considered together, 1) the increased thrombin generation in afibrinogenemic or fibrinogen-depleted normal plasma that is mitigated by fibrinogen replacement; 2) evidence that prothrombin activation is increased in afibrinogenemia and normalized by fibrinogen replacement; 3) the severe thrombophilia that is associated with defective thrombin-binding in dysfibrinogenemias Naples I and New York I, and 4) the association of afibrinogenemia or hypofibrinogenemia with venous or arterial thromboembolism, indicate that Antithrombin I (fibrin) modulates thromboembolic potential by inhibiting thrombin generation in blood.Presented in part at the XVII Congress of the ISTH, Washington, D. C. (1)

Antithrombin - Mechanism Of Action And Binding Of Heparin

1981 ◽  
Author(s):  
I Björk ◽  
U Lindahl
Keyword(s):  
Binding Sites ◽  
Serine Proteases ◽  
Enzyme Inactivation ◽  
Substrate Complex ◽  
High Affinity ◽  
Enzyme Substrate ◽  
Rate Limiting Step ◽  
Carboxy Terminal Region ◽  
Carboxy Terminal ◽  
Rate Limiting

Antithrombin inhibits a variety of serine proteases by forming equimolar, inactive complexes with the enzymes. The anti thrombin-thrombin complex, extensively studied as a model for complexes with other coagulation proteases, dissociates with a half-life of several days to free enzyme and a proteolytically modified inhibitor. It thus behaves like a kinetically stable enzyme-substrate complex. Several observations indicate that deacylation is the rate-limiting step. The active site of antithrombin, i.e. the bond slowly cleaved by the target enzyme, is the Arg-385/Ser-386 bond in the carboxy-terminal region of the protein. The formation of most anti thrombin-protease complexes is greatly accelerated by certain forms of heparin. These active molecules comprise about 1/3 of normal heparin preparations and bind with high affinity (K∼108 M-1) to the inhibitor, regardless of the size of the polysaccharide. The stoichiometry of binding is 1:1 for most heparin molecules, although some high-molecular-weight chains have two antithrombin binding sites. Evidence from spectroscopic and kinetic analyses suggests that the binding of high-affinity heparin induces a conformational change in antithrombin that probably is involved in the mechanism of the increased rate of enzyme inactivation. Oligosaccharides with high-affinity for anti thrombin have been isolated by affinity chromatography following partial deaminative cleavage of heparin with nitrous acid. The smallest such oligosaccharide obtained is an octasaccharide, in which a pentasaccharide sequence appears to comprize the actual antithrombin-binding site. This active sequence contains a unique, 3-O-sulfated glucosamine residue that does not appear to occur in other portions of the heparin molecule. In addition, two N-sulfate groups and probably at least one O-sulfate group within the pentasaccharide sequence are essential for high-affinity binding of heparin to antithrombin.

Antithrombin I. Inhibition of thrombin generation in plasma by fibrin formation

2003 ◽  
Vol 89 (01) ◽  
pp. 9-12 ◽  
Author(s):  
Michael Mosesson
Keyword(s):  
Binding Sites ◽  
Thrombin Generation ◽  
Dominant Role ◽  
Substrate Binding ◽  
Proteolytic Processing ◽  
Binding Potential ◽  
High Affinity ◽  
Fibrin Formation ◽  
Platelet Binding ◽  
Modest Effect

SummaryThrombin substrate binding is mediated through fibrinogen recognition “exosite 1” in thrombin, resulting in fibrinopeptide cleavage to form fibrin. In addition, thrombin exhibits “non-substrate” binding to fibrin, an activity termed “Antithrombin I”. Antithrombin I (AT-I) is characterized by two classes of throm-bin binding sites, the first of “low affinity” in the fibrin E domain, and the other of high affinity, that is situated between C-terminal residues 414 and 427 of a variant γ chain termed γ’ 1-427L. Plasma fibrinogen molecules containing γ ’ chains (“fibrino-gen 2”) are virtually all heterodimers containing one γA chain (platelet-binding) and one γ’ chain. The remaining fibrinogen (~ 85%) is homodimeric, lacks high affinity thrombin-binding potential, and is termed “fibrinogen 1” (γA/γA). Thrombin generation in recalcified fibrinogen-depleted or congenital afibrinogenemic plasma is increased. Repletion with fibrino-gen 1 has a modest effect in normalizing thrombin generation, whereas repletion with fibrinogen 2 (γA/γ’) has a more marked effect. A post-translational γ’ chain derivative, γ’ 1-423P, accounts for 3%-34% of the γ’ chain population, lacks thrombin binding potential, and arises by proteolytic processing at the expense of γ’ 1-427L chains. Little is known about its effect on plasma AT-I activity under normal or pathological circumstances. In summary, fibrin formation (Antithrombin I) inhibits throm-bin generation in clotting blood by sequestering thrombin, and “high-affinity” thrombin-binding (i.e., via γ’ chains) plays a dominant role in this process. AT-1 should be considered when assessing the pathogenesis of thromboembolic disease.

Recombinant Thrombomodulin Inhibits Tissue Factor Mediated Thrombin Generation in Blood Plasma and Is Modulated By Prothrombin Complex Concentrates

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 2303-2303
Author(s):  
Jawed Fareed ◽  
Debra Hoppensteadt ◽  
Daneyal Syed ◽  
Daniel Kahn ◽  
Michael Mosier ◽  
...  
Keyword(s):  
Tissue Factor ◽  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
Anticoagulant Effect ◽  
Dependent Manner ◽  
Prothrombin Complex Concentrates ◽  
Complex Disorders ◽  
Fibrin Formation ◽  
Recombinant Thrombomodulin ◽  
Inhibition Of Thrombin

Abstract Introduction: Thrombomodulin plays an important role in the regulation of serine proteases and endothelial function. Because of its multiple modulatory action it has a central role in inhibiting thrombogenesis and inflammatory processes in such complex disorders as sepsis associated coagulopathies. A recombinant thrombomodulin (Recomodulin, Asahai Kasei, Tokyo, Japan) is currently used for the management of disseminated intravascular coagulation (DIC) and related disorders in Japan and is currently undergoing a global phase 3 trial in sepsis-induced coagulopathy. Recomodulin (RM) is capable of forming complexes with circulating thrombin generated in sepsis and not only inhibits its coagulant function but also inhibits thrombin generation. The purpose of this study is to determine the effect of RM on thrombin generation in plasma systems and its modulation by both activated and non-activated prothrombin complex concentrates (PCCs). PCCs may have the potential to overcome the anticoagulant effects of RM and may be useful as an antidote. Materials and Methods: RM 12,800 IU (2.02 mg) ampules were commercially obtained. Working solutions of buffered RM were prepared at 100 µg/ml. Tissue factor mediated generation of thrombin and its inhibition in normal human plasma (NHP) (n=50), platelet rich plasma (PRP) (n=50), plasma obtained from patients with DIC (n=25) and various PCCs such as Beriplex, Cofact, Feiba, Konyne, Octaplex, Preconativ, Profilnine, Prothromplex at 1 - 5 IU/ml were investigated. A fluorometric thrombokinetics method (Technoclone, Vienna, Austria) was used to determine thrombin generation and its modulation by RM. In addition such thrombin generation markers as prothrombin fragment (F1.2) and thrombin-antithrombin complex (TAT) were measured. The effect of RM on thrombin mediated fibrinokinetics was also measured using an optical method. Results: RM produced a concentration dependent inhibition of thrombin generation in the plasma based systems. In NHP the IC50 was 0.29±0.06 µg/ml in contrast to PRP where the IC50 was 1.99±0.31 µg/ml. The inhibition of thrombin generation in various PCCs was also concentration and product dependent and only four factor concentrates were found to generate thrombin.. At concentrations of 1 IU/ml marked inhibition of thrombin generation was noted in Preconativ, Prothromplex and Beriplex. RM decreased the generation of F1.2 and TAT in a concentration dependent manner. However, at concentrations >2.5 IU/ml the thrombin generated in such PCCs as Prothromplex and Beriplex, markedly higher thrombin was generated overcoming the anticoagulant effect of RM. Proportionately higher levels of thrombin generation markers were formed and were dependant on PCC concentrations. RM also inhibited the thrombin induced formation of fibrin in both PRP and PPP systems in a differential manner. However, at higher concentration of thrombin the inhibitory effects of RM on fibrin formation were overcome. Conclusions: These results suggest that in plasma based systems and in the PCCs at concentrations <1 IU/ml, RM is capable of inhibiting tissue factor mediated thrombin generation in addition to the direct inhibition of pre-formed thrombin. However, such PCCs as Beriplex and Prothromplex are capable of overcoming the thrombin generation inhibitory actions of RM in a concentration dependent fashion. Moreover, RM is also capable of modulating fibrin formation as evident by fibrinokinetic studies where increased thrombin levels may also overcome its effect on fibrin formation. These observations suggest that PCCs may have the potential to reverse the anticoagulant effect of RM and may be considered as a potential antidote for this agent. Disclosures Williams: Asahi Kasei Pharma America: Employment.

DEVELOPMENT OF HOMOLOGOUS IMMUNOLOGICAL ASSAYS FOR HUMAN PARATHYROID HORMONE

1980 ◽  
Vol 85 (1) ◽  
pp. 161-170 ◽  
Author(s):  
R. M. MANNING ◽  
G. N. HENDY ◽  
S. E. PAPAPOULOS ◽  
J. L. H. O'RIORDAN
Keyword(s):  
Parathyroid Hormone ◽  
Trichloroacetic Acid ◽  
Terminal Region ◽  
Human Parathyroid Hormone ◽  
Antibody Assay ◽  
Amino Terminal ◽  
High Affinity ◽  
Carboxy Terminal Region ◽  
Immunological Assays ◽  
Carboxy Terminal

SUMMARY Antisera to a trichloroacetic-acid precipitate of human parathyroid hormone (PTH) were produced in goats. Two of these antisera (G36 and G31) were of high affinity, and the bovine and porcine hormones were less reactive. Synthetic peptides containing the amino-terminal region of human PTH reacted with both antisera; the 1–34 peptide (PTH-(1–34)), with the sequence proposed by Niall, Sauer, Jacobs, Keutmann, Segre, O'Riordan, Aurbach & Potts in 1974, was more reactive than that having the sequence proposed by Brewer, Fairwell, Ronan, Sizemore & Arnaud in 1972. The antisera were further characterized with a number of other native and synthetic fragments of human PTH and reacted poorly with fragments from the carboxy-terminal region of the molecule. Since the amino-terminal fragments did not account for all the immunoreactivity, it is assumed that the antisera had some recognition sites for the central part of the molecule. Highly purified human PTH-(1–84) was labelled with 125I and radioimmunoassays were developed using this tracer and antiserum G36. To avoid the problems associated with labelling human PTH with 125I, a labelled antibody assay was developed with G36 and an immunoadsorbent consisting of human PTH-(1–34) (sequence of Niall et al.) coupled to cellulose. A sensitive homologous amino-terminal specific assay was developed in this way.

Location of major antibody binding domains on alpha-subunit of dog kidney Na+-K+-ATPase

1986 ◽  
Vol 250 (6) ◽  
pp. C896-C906 ◽  
Author(s):  
R. A. Farley ◽  
G. T. Ochoa ◽  
A. Kudrow
Keyword(s):  
Binding Sites ◽  
Alpha Subunit ◽  
Amino Terminus ◽  
Amino Terminal ◽  
Binding Domains ◽  
Dog Kidney ◽  
Carboxy Terminal Region ◽  
Polyclonal Antisera ◽  
Carboxy Terminal ◽  
A Site

The locations of binding sites on the alpha-subunit of dog kidney Na+-K+-ATPase for both monoclonal antibodies and antibodies from polyclonal antisera have been determined. Three distinct regions of the alpha-subunit, all located within the amino terminal half of the polypeptide, were recognized by the antibodies: a region near the amino terminus of the polypeptide and two regions that are separated by a site for trypsin cleavage of the ATPase in KCl. No significant binding of antibodies to the carboxy terminal region of the alpha-subunit was detected. The binding sites for the antibodies are located within regions of the polypeptide predicted to be exposed within the cytoplasm of the cell (P. L. Jorgensen, S. J. D. Karlish, and C. Gitler, J. Biol. Chem. 257: 7435-7442, 1982). This prediction was verified by the demonstration that the antibodies did not react with Na+-K+-ATPase in tight right-side-out vesicles but would bind to the protein after the vesicles had been disrupted with detergent. A model for the folding of the alpha-subunit through the membrane, based on these data, is presented.

Heparin and Low Molecular Weight Heparins Inhibit Prothrombinase Formation but not its Activity in Plasma

1994 ◽  
Vol 72 (06) ◽  
pp. 862-868 ◽  
Author(s):  
Frederick A Ofosu ◽  
J C Lormeau ◽  
Sharon Craven ◽  
Lori Dewar ◽  
Noorildan Anvari
Keyword(s):  
Factor Xa ◽  
Catalytic Efficiency ◽  
Thrombin Inhibitor ◽  
Lag Phase ◽  
Factor V ◽  
Factor X ◽  
Normal Plasma ◽  
Plasma Factor ◽  
Prothrombin Activation ◽  
Plasma Heparin

SummaryFactor V activation is a critical step preceding prothrombinase formation. This study determined the contributions of factor Xa and thrombin, which activate purified factor V with similar catalytic efficiency, to plasma factor V activation during coagulation. Prothrombin activation began without a lag phase after a suspension of coagulant phospholipids, CaCl2, and factor Xa was added to factor X-depleted plasma. Hirudin, a potent thrombin inhibitor, abrogated prothrombin activation initiated with 0.5 and 1.0 nM factor Xa, but not with 5 nM factor Xa. In contrast, hirudin did not abrogate prothrombin activation in plasmas pre-incubated with 0.5,1.0 or 5 nM α-thrombin for 10 s followed by the coagulant suspension containing 0.5 nM factor Xa. Thus, thrombin activates plasma factor V more efficiently than factor Xa. At concentrations which doubled the clotting time of contact-activated normal plasma, heparin and three low Mr heparins also abrogated prothrombin activation initiated with 0.5 nM factor Xa, but not with 5 nM factor Xa. If factor V in the factor X-depleted plasma was activated (by pre-incubation with 10 nM a-thrombin for 60 s) before adding 0.5,1.0, or 5 nM factor Xa, neither hirudin nor the heparins altered the rates of prothrombin activation. Thus, none of the five anticoagulants inactivates prothrombinase. When 5 or 10 pM relipidated r-human tissue factor and CaCl2 were added to normal plasma, heparin and the three low Mr heparins delayed the onset of prothrombin activation until the concentration of factor Xa generated exceeded 1 nM, and they subsequently inhibited prothrombin activation to the same extent. Thus, hirudin, heparin and low Mr heparins suppress prothrombin activation solely by inhibiting prothrombinase formation.

High Affinity Binding Sites for Activated Protein C and Protein C on Cultured Human Umbilical Vein Endothelial Cells

1994 ◽  
Vol 72 (03) ◽  
pp. 465-474 ◽  
Author(s):  
Neelesh Bangalore ◽  
William N Drohan ◽  
Carolyn L Orthner
Keyword(s):  
Binding Sites ◽  
Protein C ◽  
Umbilical Vein ◽  
Activated Protein C ◽  
Affinity Binding ◽  
Cell Binding ◽  
High Affinity Binding ◽  
High Affinity ◽  
Gla Domain ◽  
Umbilical Vein Endothelial Cells

SummaryActivated protein C (APC) is an antithrombotic serine proteinase having anticoagulant, profibrinolytic and anti-inflammatory activities. Despite its potential clinical utility, relatively little is known about its clearance mechanisms. In the present study we have characterized the interaction of APC and its active site blocked forms with human umbilical vein endothelial cells (HUVEC). At 4° C 125I-APC bound to HUVEC in a specific, time dependent, saturable and reversible manner. Scatchard analysis of the binding isotherm demonstrated a Kd value of 6.8 nM and total number of binding sites per cell of 359,000. Similar binding isotherms were obtained using radiolabeled protein C (PC) zymogen as well as D-phe-pro-arg-chloromethylketone (PPACK) inhibited APC indicating that a functional active site was not required. Competition studies showed that the binding of APC, PPACK-APC and PC were mutually exclusive suggesting that they bound to the same site(s). Proteolytic removal of the N-terminal γ-carboxyglutamic acid (gla) domain of PC abolished its ability to compete indicating that the gla-domain was essential for cell binding. Surprisingly, APC binding to these cells appeared to be independent of protein S, a cofactor of APC generally thought to be required for its high affinity binding to cell surfaces. The identity of the cell binding site(s), for the most part, appeared to be distinct from other known APC ligands which are associated with cell membranes or extracellular matrix including phospholipid, thrombomodulin, factor V, plasminogen activator inhibitor type 1 (PAI-1) and heparin. Pretreatment of HUVEC with antifactor VIII antibody caused partial inhibition of 125I-APC binding indicating that factor VIII or a homolog accounted for ∼30% of APC binding. Studies of the properties of surface bound 125I-APC or 125I-PC and their fate at 4°C compared to 37 °C were consistent with association of ∼25% of the initially bound radioligand with an endocytic receptor. However, most of the radioligand appeared not to be bound to an endocytic receptor and dissociated rapidly at 37° C in an intact and functional state. These data indicate the presence of specific, high affinity binding sites for APC and PC on the surface of HUVEC. While a minor proportion of binding sites may be involved in endocytosis, the identity and function of the major proportion is presently unknown. It is speculated that this putative receptor may be a further mechanisms of localizing the PC antithrombotic system to the vascular endothelium.

Inhibition of Thrombin Generation in Plasma by Inhibitors of Factor Xa

1997 ◽  
Vol 78 (04) ◽  
pp. 1215-1220 ◽  
Author(s):  
D Prasa ◽  
L Svendsen ◽  
J Stürzebecher
Keyword(s):  
Thrombin Generation ◽  
Factor Xa ◽  
Thrombin Inhibitors ◽  
Thrombin Inhibitor ◽  
Thrombin Generation Assay ◽  
Ic50 Values ◽  
Fxa Inhibitor ◽  
20 Nm ◽  
Tick Anticoagulant Peptide ◽  
Inhibition Of Thrombin

SummaryA series of inhibitors of factor Xa (FXa) were investigated using the thrombin generation assay to evaluate the potency and specificity needed to efficiently block thrombin generation in activated human plasma. By inhibiting FXa the generation of thrombin in plasma is delayed and decreased. Inhibitor concentrations which cause 50 percent inhibition of thrombin generation (IC50) correlate in principle with the Ki values for inhibition of free FXa. Recombinant tick anticoagulant peptide (r-TAP) is able to inhibit thrombin generation with considerably low IC50 values of 49 nM and 37 nM for extrinsic and intrinsic activation, respectively. However, the potent synthetic, low molecular weight inhibitors of FXa (Ki values of about 20 nM) are less effective in inhibiting the generation of thrombin with IC50 values at micromolar concentrations.The overall effect of inhibitors of FXa in the thrombin generation assay was compared to that of thrombin inhibitors. On the basis of similar Ki values for the inhibition of the respective enzyme, synthetic FXa inhibitors are less effective than thrombin inhibitors. In contrast, the highly potent FXa inhibitor r-TAP causes a stronger reduction of the thrombin activity in plasma than the most potent thrombin inhibitor hirudin.

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