Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.69 (APC)
 16,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recent studies suggest that low-dose oral contraceptives may cause acquired resistance to activated protein C (APC). The aims of this study were to determine whether hormone replacement therapy (HRT) may also induce acquired APC resistance and to study the effects of APC resistance on the risk of recurrent thrombosis. The patients comprised 140 females with at least one previous venous thromboembolism (VTE), who were randomized to receive continuous treatment with 2 mg 17-beta-oestradiol and 1 mg norethisterone acetate (n = 71) or placebo (n = 69). Normalized APC sensitivity ratios (nAPCsr) were calculated by measurement of the effect of APC on thrombin generation in plasma collected at baseline and after 3 months of treatment. Of the 140 women, 121 had plasma samples collected both at baseline and after 3 months. The nAPCsr increased significantly (P < 0.001) on HRT (n = 62), both in females not carrying the factor V(Leiden) mutation [mean change 0.57 (95% CI 0.45-0.70), n = 50] and in females heterozygous for the factor V(Leiden) mutation [mean change 1.10 (0.71-1.49), n = 12], but remained unchanged on placebo (n = 59). The baseline nAPCsr as well as the increase in nAPCsr associated with HRT use was not higher in the five women who subsequently developed recurrent VTE. Free protein S and free TFPI were both important parameters for the acquired APC resistant phenotype. We conclude that HRT diminishes the efficacy by which APC downregulates in-vitro thrombin formation in a similar fashion to that observed with low-dose oral contraceptives, but the increase in nAPCsr alone is not sufficient to explain the increased risk of VTE associated with use of HRT.
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PMID:Hormone replacement therapy and acquired resistance to activated protein C: results of a randomized, double-blind, placebo-controlled trial. 1170 44

The process of tissue factor initiated blood coagulation is discussed. Reactions of the blood coagulation cascade are propagated by complex enzymes containing a vitamin K-dependent serine protease and an accessory cofactor protein that are assembled on a membrane surface in a calcium-dependent manner. These complexes are 105-109-fold more efficient in proteolyses of their natural substrates than enzymes alone. Based upon data acquired using several in vitro models of blood coagulation, tissue factor initiated thrombin generation can be divided into two phases: an initiation phase and a propagation phase. The initiation phase is characterized by the generation of nanomolar amounts of thrombin, femto- to picomolar amounts of factors VIIa, IXa, Xa, and XIa, partial activation of platelets, and almost quantitative activation of procofactors, factors V and VIII. The duration of this phase is primarily influenced by concentrations of tissue factor and TFPI. The characteristic features of the propagation phase are: almost quantitative prothrombin activation at a high rate, completion of platelet activation, and solid clot formation. This phase is primarily regulated by antithrombin III and the protein C system. Thrombin generation during the propagation phase is remarkably suppressed in the absence of factor VIII and IX (hemophilia A and B, respectively) and at platelet counts <5% of mean plasma concentration. The majority of data accumulated in in vitro models and discussed in this review are in good agreement with the results of in vivo observations.
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PMID:Blood coagulation. 1184 35

Gateways to clinical trials is a guide to the most recent clinical trials in current literature and congresses. The data in the following tables has been retrieved from the Clinical Studies knowledge area of Prous Science Integrity, the drug discovery and development portal, http://integrity.prous.com. This issue focuses on the following selection of drugs: 5A8; Agomelatine, alefacept, almotriptan, anakinra, APC-8015, atazanavir, atomoxetine hydrochloride, azimilide hydrochloride; Bicifadine; Cannabidiol, caspofungin acetate, CAT-213, CGP-51901, ciclesonide, cipamfylline; Darbepoetin alfa, desloratadine, dibotermin alfa, DX-9065a; Ecogramostim, efalizumab, eletriptan, eniluracil, EPI-KAL2, erlosamide, ertapenem sodium, etilevodopa, etoricoxib, ezetimibe; Fosamprenavir calcium, fosamprenavir sodium, fumagillin; Gadofosveset sodium, gefitinib, gemtuzumab ozogamicin; HSPPC-96, human papillomavirus vaccine; Icatibant Id-KLH, imatinib mesylate, INS-37217, iodine (I131) tositumomab; LAS-34475, levobupivacaine hydrochloride, levocetirizine, linezolid, 131I-lipiodol, lonafarnib, lopinavir, LY-450108; Magnetites, MBI-594AN, melagatran, melatonin, mepolizumab, mycophenolic acid sodium salt; NC-100100; 1-Octanol, omalizumab, omapatrilat, onercept; PEG-filgrastim, (PE)HRG21, peginterferon alfa-2a, peginterferon alfa-2b, pleconaril, pneumococcal 7-valent conjugate vaccine, prasterone; Ranelic acid distrontium salt, rasagiline mesilate, reslizumab, rFGF-2, rhOP-1, rosuvastatin calcium, roxifiban acetate; Sitaxsentan sodium, sodium lauryl sulfate; Tadalafil, telithromycin, tenofovir disoproxil fumarate, tipranavir, TMC-114, tucaresol; Valdecoxib, voriconazole; Ximelagatran; Zofenopril calcium, zosuquidar trihydrochloride.
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PMID:Gateways to clinical trials. 1274 28

The last few years have clarified the tight link between inflammation and coagulation. In addition to the identification of new regulatory mechanisms of the coagulation system and of an explosive number of mediators of inflammation, it is now clear that the existence of a positive feed-back between inflammation and coagulation leads to reciprocal activation of both pathways. Plasma levels of acute phase proteins involved in coagulation and fibrinolysis are elevated during inflammation, while natural anticoagulant mechanisms are depressed. Pro-inflammatory cytokines "activate" cell membranes exposed to flowing blood (endothelium, platelets, monocytes, neutrophils) which from physiologically inert or anticoagulant become procoagulant. Increased tissue factor expression results in increased thrombin formation within the microcirculation. Thrombin is central to fibrin deposition but it also plays a key role in cell-mediated mechanisms involving inflammation, cell proliferation and activation of the natural anticoagulant protein C. Depression of natural anticoagulant mechanisms, occurring in severe sepsis, results in uncontrolled thrombin formation, with pro-inflammatory activity prevailing, and the feed-back loop of inflammation and coagulation ultimately leading to multi-organ failure. However, both in the clinical setting and in animal experiments, heparin or direct anticoagulants have shown no effect on survival even if blocking fibrin deposition. Organ failure is only partially due to the thrombotic occlusion of the microcirculation, while other mechanisms of endothelial damage are probably more relevant in the development of ischemia. The endothelium is central to the maintenance of the natural anticoagulant mechanisms (TFPI, antithrombin, protein C). The protein C system, in addition to dumping thrombin formation, specifically modulates inflammation by cell signaling. This system is markedly depressed in severe sepsis. The infusion of activated protein C, or restoring normal levels of protein C within the circulation - depending on the individual bleeding risk are powerful tools to treat the endothelitis responsible for the clinical sequelae of severe sepsis.
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PMID:[Protein C and coagulation in sepsis]. 1518 14

In normal pregnancy, there is a marked increase in the procoagulant activity in maternal blood characterized by elevation of factors VII, X, VIII, fibrinogen and von Willebrand factor, which is maximal around term. This is associated with an increase in prothrombin fragments (PF1+2) and thrombin-antithrombin complexes. There is a decrease in physiological anticoagulants manifested by a significant reduction in protein S activity and by acquired activated protein C (APC) resistance. The overall fibrinolytic activity is impaired during pregnancy, but returns rapidly to normal following delivery. This is largely due to placental derived plasminogen activator inhibitor type 2 (PAI-2), which is present in substantial quantities during pregnancy. D-dimer, a specific marker of fibrinolysis resulting from breakdown of cross-linked fibrin polymer by plasmin, increases as pregnancy progresses. Overall, there is a 4- to 10-fold increased thrombotic risk throughout gestation and the postpartum period. Local haemostasis at the placental throphoblast level is characterized by increased tissue factor (TF) expression and low expression of the inhibitor TFPI. Microparticles derived from maternal endothelial cells and platelets, and from placental throphoblasts may contribute to the procoagulant effect. Local anticoagulant mechanisms on placental throphoblasts are important for counterbalance of the procoagulant milieu. Disruption of anticoagulant mechanisms, for example, autoantibodies, to annexin V may increase pregnancy complications in patients with antiphospholipid antibodies (APLA).
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PMID:Haemostatic changes in pregnancy. 1550 71

Recombinant human-activated protein C (rhAPC, Drotrecogin alpha (activated), Xigris) has been shown to reduce organ damage and decrease mortality in severe sepsis. Since protein S (PS) serves as a potentiating cofactor of activated protein C and since PS levels are low in neonatal plasma, we hypothesized that the anticoagulant effect of rhAPC would be decreased in cord plasma compared to adult plasma. We demonstrate that the anticoagulant action of 0.3 microg ml(-1) rhAPC (5 nmol l(-1)) was decreased in cord plasma compared to adult plasma, and dose dependently increased in cord plasma in the presence of increasing activities of PS. Correspondingly, the anticoagulant action of rhAPC decreased in adult plasma in the presence of decreasing activities of PS. The low anticoagulant action of rhAPC in cord compared to adult plasma is attributable to low neonatal levels of PS, and as previously shown, to low neonatal levels of TFPI and AT. Our laboratory experiments do not allow definite conclusions for clinical situations. However, we speculate that the anticoagulant efficacy of rhAPC is impaired in neonates and in clinical situations associated with consumption and/or inhibition of PS, AT, and TFPI, such as severe sepsis.
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PMID:Protein S modulates the anticoagulant action of recombinant human activated protein C: a comparison between neonates and adults. 1627 21

A mathematical model of intravascular coagulation is presented; it encompasses the biochemistry of the tissue factor pathway, platelet activation and deposition on the subendothelium, and flow- and diffusion-mediated transport of coagulation proteins and platelets. Simulation experiments carried out with the model indicate the predominant role played by the physical processes of platelet deposition and flow-mediated removal of enzymes in inhibiting coagulation in the vicinity of vascular injury. Sufficiently rapid production of factors IXa and Xa by the TF:VIIa complex can overcome this inhibition and lead to formation of significant amounts of the tenase complex on the surface of activated platelets and, as a consequence, to substantial thrombin production. Chemical inhibitors are seen to play almost no (TFPI) or little (AT-III and APC) role in determining whether substantial thrombin production will occur. The role of APC is limited by the necessity for diffusion of thrombin from the site of injury to nearby endothelial cells to form the thrombomodulin-thrombin complex and for diffusion in the reverse direction of the APC made by this complex. TFPI plays an insignificant part in inhibiting the TF:VIIa complex under the conditions studied whether its action involves sequential binding of TFPI to Xa and then TFPI:Xa to TF:VIIa, or direct binding of TFPI to Xa already bound to the TF:VIIa complex.
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PMID:Coagulation under flow: the influence of flow-mediated transport on the initiation and inhibition of coagulation. 1643 11

Our research aims to provide quantitatively transparent, biologically realistic descriptions of the processes involved in hemostasis which will permit predictions of the behavior of the coagulation system in normal and pathologic states. We use four models of coagulation: (1) numerical approximations of the tissue factor (Tf) pathway of thrombin generation based upon mechanism and dynamics; (2) Tf activation of the "blood coagulation proteome" from isolated cells and proteins; (3) Tf activated contact pathway inhibited whole blood in vitro; and (4) blood shed from standardized microvascular wounds in vivo. The results from these models are integrated in interactive assessments aimed at achieving convergence of biochemical rigor and biological authenticity. Microvascular injury is the most biologically secure but least accessible to mechanistic study. Numerical models while quantitatively transparent are biologically limited. By the integrated analyses of all four models, we establish observations which require inclusion or discovery of new parameters to achieve mechanistically interpretable biological reality. Discoveries made in this fashion have included thrombin's role in the initiation phase, TFPI/ATIII/APC synergy interactions, rfVIIa in fVII deficiency, the roles of fVIII and fIX in the Tf reaction, and the cleavage of fIX by fXa membrane. Ideally, our results will provide descriptions which predict the behavior of the biological blood coagulation system under normal and pathologic conditions.
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PMID:Models of blood coagulation. 1650 Jan 22

Protein S (PS) is a cofactor for activated protein C (APC), which inactivates coagulation factors (F) Va and VIIIa. Deficiency of protein C or PS is associated with risk of thrombosis. We found that PS also has APC-independent anticoagulant activity (PS-direct) and directly inhibits thrombin generated by FXa/FVa (prothrombinase complex). Here we report that PS contains Zn(2+) that is required for PS-direct and that is lost during certain purification procedures. Immunoaffinity-purified PS contained 1.4 +/- 0.6 Zn(2+)/mol, whereas MonoQ-purified and commercial PS contained 0.15 +/- 0.15 Zn(2+)/mol. This may explain the controversy regarding the validity of PS-direct. Zn(2+) content correlated positively with PS-direct in prothrombinase assays and clotting assays, but APC-cofactor activity of PS was independent of Zn(2+) content. PS-direct and Zn(2+) were restored to inactive PS under mildly denaturing conditions. Conversely, o-phenanthroline reversibly impaired the PS-direct of active PS. Zn(2+)-containing PS bound FXa more efficiently (K(d)(app)=9.3 nM) than Zn(2+)-deficient PS (K(d)(app)=110 nM). PS bound TFPI efficiently, independently of Zn(2+) content (K(d)(app)=21 nM). Antibodies that block PS-direct preferentially recognized Zn(2+)-containing PS, suggesting conformation differences at or near the interface of 2 laminin G-like domains near the PS C terminus. Thus, Zn(2+) is required for PS-direct and efficient FXa binding and may play a role in stabilizing PS conformation.
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PMID:Plasma protein S contains zinc essential for efficient activated protein C-independent anticoagulant activity and binding to factor Xa, but not for efficient binding to tissue factor pathway inhibitor. 1924 62

In vitro thrombin generation, which reflects an individual's plasma coagulation potential and has been shown to correlate with the risk of venous thromboembolism (VTE), might represent a useful intermediate phenotype for the genetic dissection of VTE. As a proof of principle, we have investigated whether the thrombin generation assay can detect changes in the haemostatic balance associated with common genetic variation affecting the level or function of coagulation factors and inhibitors. The study population consisted of 140 healthy individuals. Plasma levels of coagulation factors and inhibitors and thrombin generation parameters determined at low tissue factor (TF) + or - thrombomodulin (TM) and at high TF + or - activated protein C (APC) were available from a previous study. All individuals were genotyped for F5 Leiden, F2 G20210A and 19 additional single nucleotide polymorphisms (SNPs) in haemostasis-related genes. The association of each SNP with plasma levels of the corresponding proteins and with thrombin generation parameters (lag time, peak height and endogenous thrombin potential [ETP]) was evaluated by statistical analysis. Not only F5 Leiden and F2 G20210A, but also several other common SNPs, significantly affected thrombin generation parameters. In particular, FGA A1069G (Thr312Ala) decreased the ETP(-APC), F2 A19911G increased the ETP(-APC), F10 IVS2 C+517G decreased the ETP(+APC), F12 C-46T decreased peak height at low TF, and TFPI T-287C and TFPI IVS7 T-33C decreased the ETP(+APC). These results indicate that the thrombin generation assay is sensitive to genetic variation in haemostasis-related genes, which makes it a promising tool to identify novel genetic risk factors of VTE.
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PMID:Thrombin generation as an intermediate phenotype for venous thrombosis. 2006 24


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