Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.6 (thromboplastin)
13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The exposed Serpin reactive centre loop controls the specificity of the serpin proteinase interaction. Mutations within this region have been used to generate novel potentially therapeutic inhibitors. In this study we examine the effect of the serpin scaffold and reactive centre loop length upon the generation of such inhibitors. The reactive centre loop regions, P7-P3', of alpha1-antitrypsin and alpha1-antichymotrypsin were replaced by the corresponding residues of the viral serpin, Serp1, to form AT/Serp1 and ACT/Serp1, respectively. AT/Serp1 formed SDS stable complexes with a range of proteinases with association rate constants for plasmin, tissue plasminogen activator, urokinase, thrombin and factor Xa of approximately 10(4) M(-1)s(-1) and a stoichiometry of inhibition of approximately 1 for all of them. ACT/Serp1, however, formed SDS-stable complexes with only plasmin and thrombin with association rate constant 100-fold slower than AT/Serp1 and an increased stoichiometry of inhibition. The reactive centre loop of ACT/Serp1 is four amino acid residues longer than AT/Serp1. These four additional residues (VETR) were inserted into AT/Serp1 to form AT/Serp1(VETR). AT/Serp1(VETR) formed SDS stable complexes with plasmin, thrombin and tissue plasminogen activator similar to AT/Serp1, however, the association rate constants were 10-fold slower than those observed with AT/Serp1, while the stoichiometry of inhibition remained around 1. These results suggest that the additional reactive centre loop residues effect the rate of initial complex formation by placing the reactive centre loop in a non-ideal conformation. This study demonstrates that both reactive centre loop length and serpin scaffold are important in defining the inhibitory characteristics of a serpin.
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PMID:Protein engineering of chimeric Serpins: an investigation into effects of the serpin scaffold and reactive centre loop length. 993 Jun 74

Argatroban is the smallest anticoagulant molecule of direct thrombin inhibitors. The main attributes of this synthetic drug are its rapid onset of anti-thrombin action, the rapid reversibility of its anticoagulant effect, potent inhibition of clot-bound thrombin, the absence of antibody formation and no need for dosage adjustment in patients with renal impairment. It is eliminated by hepatic metabolism. These properties make argatroban a predictable anticoagulant with intravenous use in a routine clinical setting. Argatroban is approved in the US and Canada for both prophylaxis and treatment of thrombosis in patients with heparin-induced throm-bocytopenia (HIT) and in the US as an antithrombotic agent during percutaneous coronary interventions in patients with HIT or a history of HIT. Preliminary reports document the feasibility of using argatroban for anticoagulation during hemodialysis and as adjunct to thrombolysis for treatment of myocardial infarction. Current recommendations for argatroban monitoring are to use the aPTT (activated partial thromboplastin time) for low doses and the ACT (activated clotting time) for high doses. The specific inhibition of thrombin can be measured with the ECT (ecarin clotting time).
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PMID:[Experimental and clinical results with the thrombin inhibitor Argatroban]. 1221 62

Recently, we designed (-)-epicatechin sulfate (ECS), the first small nonsaccharide molecule, as an activator of antithrombin for the accelerated inhibition of factor Xa, a key proteinase of the coagulation cascade (Gunnarsson, G. T.; Desai, U. R. J. Med. Chem. 2002, 45, 1233-1243). Although sulfated flavanoid ECS was found to bind antithrombin with an affinity ( approximately 10.7 microM) comparable to the reference trisaccharide DEF ( approximately 4.5 microM), it accelerated the inhibition of factor Xa only 10-fold as compared to the approximately 300-fold observed with DEF. To determine whether this conformational activation of the inhibitor is dependent on the structure of the organic activator and to probe the basis for the deficiency in activation, we studied the interaction of similar sulfated flavanoids with antithrombin. (+)-Catechin sulfate (CS), a chiral stereoisomer of ECS, bound plasma antithrombin with a 3-fold higher affinity (K(D) = 3.5 microM) and a 2-fold higher second-order rate constant for factor Xa inhibition (k(ACT) = 6750 M(-1) s(-1)). On the contrary, the K(D) and k(ACT) were found to be lower approximately 7.4- and approximately 2.4-fold, respectively, for its racemic counterpart, (+/-)-catechin sulfate. Dependence of the equilibrium dissociation constant on the ionic strength of the medium at pH 6.0 and 7.4 suggests that nonionic interactions contribute a major proportion ( approximately 55-73%) of the total binding energy, and only 1-2 ion pairs, in comparison to the expected approximately 4 ion pairs for the reference trisaccharide, are formed in the interaction. Competitive binding experiments indicate that activator CS does not compete with a saccharide ligand that binds antithrombin in the pentasaccharide binding site, while it competes with full-length low-affinity heparin. A molecular docking study suggests plausible binding of CS in the extended heparin binding site, which is adjacent to the binding domain for the reference trisaccharide DEF. In combination, the results demonstrate that although conformational activation of antithrombin with small sulfated flavanoids is dependent on the structure of the activator, the designed activators do not bind in the pentasaccharide binding site in antithrombin resulting in weak activation. The mechanistic investigation highlights plausible directions to take in the rational design of specific high-affinity organic antithrombin activators.
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PMID:Interaction of designed sulfated flavanoids with antithrombin: lessons on the design of organic activators. 1223 25

Unfractionated heparin (UH) and low-molecular-weight heparins (LMWH) are antithrombotic drugs covering virtually all indications requiring immediately effective anticoagulation. For prevention and treatment of venous thromboembolism (VTE) UH have mainly been replaced by LMWH due to their practical usefulness (one or two subcutaneous daily doses without laboratory test for dose adjustment) and their more favourable risk-benefit profile. With respect to arterial occlusions this statement is also valid for unstable angina pectoris. The risk to develop heparin-induced thrombocytopenia (HIT) appears to be ten times lower with LMWH. In hospitals the use of UH is reserved for complex cases with high bleeding risk and the necessity to interrupt heparin effects rapidly. Therapeutic doses of UH are monitored by the classical coagulation assays, activated partial thromboplastin time (aPTT) and thrombin time (TT), but also by automated chromogenic tests of anti-factor Xa activity. There are no prospective studies directly comparing the efficiency of these three approaches. Disagreements between tests are not rare in individual cases. However, dosing recommendations for UH treatment of VTE (intravenous bolus of 80 IU/kg, followed by 18 IU/kg/h infusion) and average doses used are concordant. 0.30-0.70 anti-Xa IU/ml are considered as therapeutic range for UF infusion. Higher UH activities required during extracorporeal circulation in heart surgery or during coronary angioplasty are usually guided by bedside ACT (activated clotting time). For LMWH tests of anti-Xa activities may only be necessary during weight adjusted treatment of pregnant women, children, or cases with reduced kidney function (glomerular filtration rate < 30 ml/min.) or increased bleeding risk. Expected anti-Xa activities are 0.5-1.1 IU/ml and 1.0-2.0 IU/ml 4 hours after subcutaneous LMWH for dosing intervals of 12 hours and 24 hours respectively.
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PMID:[Heparins]. 1263 71

Heparin has been conventionally used as an anticoagulant for medical and surgical indications. Because factor Xa is an essential component of the prothrombinase complex and leads to the generation of thrombin, its inhibition has become a focus of newer antithrombotic drug development. The in vitro anticoagulant profile of DX-9065a, a synthetic direct factor Xa inhibitor, was studied using activated clotting time assay, thrombelastography, and global clotting tests, such as prothrombin time (PT), activated partial thromboplastin time (aPTT), diluted aPTT, Heptest, Heptest-HI, dilute Russell's viper venom time (dRVVT), thrombin time, ecarin clotting time, and amidolytic anti-Xa assay. In addition, the effect of DX-9065a on platelet aggregation and inhibition of thrombin generation markers (FPA, F1+2, and TAT) were studied. The pharmacokinetic and pharmacodynamic profiles of DX-9065a were also studied in a non-human primate (Macaca mulatta) model. DX-9065a produced a concentration-dependent increase in the Hemochron celite ACT and HemoTec ACT. Clotting times of 538 +/- 19 and 401 +/- 12, respectively, were reached at a concentration of 25 microg/mL signifying that DX-9065a may be useful in interventional cardiological procedures. DX-9065a prolonged the r-time on thrombelastography. DX-9065a did not show any effect on adenosine diphosphate (ADP)-, collagen-, epinephrine-, and arachidonic acid-induced platelet aggregation at concentrations up to 10 microgram/mL. DX-9065a exhibited a concentration-dependent prolongation of the PT, aPTT, diluted aPTT, Heptest, dRVVT, and reached the clotting times of 51.6, 132, 193, 47.9, 129.9 seconds, respectively, at a final concentration of 12.5 microgram/mL; compared to a control value of 10.6, 30.2, 41.9, 14, 32.2 seconds, respectively. DX-9065a did not affect the ecarin clotting time and thrombin time at concentrations up to 12.5 microgram/mL. Because DX-9065a prolonged the dRVVT, this may impact diagnostic screening of patients with systemic lupus erythematosus.
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PMID:Global anticoagulant effects of a synthetic anti-factor Xa inhibitor (DX-9065a): implications for interventional use. 1264 18

Preclinical studies and initial clinical trials have documented the feasibility of adenoassociated virus (AAV)-mediated gene therapy for hemophilia B. In an 8-year study, inhibitor-prone hemophilia B dogs (n = 2) treated with liver-directed AAV2 factor IX (FIX) gene therapy did not have a single bleed requiring FIX replacement, whereas dogs undergoing muscle-directed gene therapy (n = 3) had a bleed frequency similar to untreated FIX-deficient dogs. Coagulation tests (whole blood clotting time [WBCT], activated clotting time [ACT], and activated partial thromboplastin time [aPTT]) have remained at the upper limits of the normal ranges in the 2 dogs that received liver-directed gene therapy. The FIX activity has remained stable between 4% and 10% in both liver-treated dogs, but is undetectable in the dogs undergoing muscle-directed gene transfer. Integration site analysis by linear amplification-mediated polymerase chain reaction (LAM-PCR) suggested the vector sequences have persisted predominantly in extrachromosomal form. Complete blood count (CBC), serum chemistries, bile acid profile, hepatic magnetic resonance imaging (MRI) and computed tomography (CT) scans, and liver biopsy were normal with no evidence for tumor formation. AAV-mediated liver-directed gene therapy corrected the hemophilia phenotype without toxicity or inhibitor development in the inhibitor-prone null mutation dogs for more than 8 years.
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PMID:Long-term correction of inhibitor-prone hemophilia B dogs treated with liver-directed AAV2-mediated factor IX gene therapy. 1895 84

The purpose of this study was to validate a device designed to measure activated clotting time in low-range heparin plasma concentrations (ACT-LR) prospectively during the post-operative period of vascular surgery. Measurement of ACT-LR and activated partial thromboplastin time (APTT) were performed before heparinisation (T0) and at the end of surgery (T1). ACT-LR(T1) and DeltaACT-LR (defined as ACT-LR(T1) - ACT-LR(T0)) were evaluated as diagnostic tests for excessive anticoagulation, defined by APTT more than twice the laboratory's normal, by Bland-Altman method and receiver operating characteristic (ROC) curves. In 103 patients, mean (SD) ACT-LR was 137 (33) s at T0 and 176 (39) s at T1. Bland-Altman graph did not show a good agreement between APTT and ACT-LR. Areas under ROC curves were 0.82 (95% CI: 0.75-0.89) and 0.87 (95% CI: 0.80-0.93) for ACT-LR(T1) and DeltaACT-LR, respectively. Using a threshold of 32 s for DeltaACT-LR, test sensitivity was 87% (95% CI: 81-93%), specificity was 85% (95% CI: 78-92%), positive predictive value was 90% (95% CI: 84-96%) and negative predictive value was 81% (95% CI: 73-86%). While DeltaACT-LR may have some potential in evaluating excessive anticoagulation in vascular surgery, the poor correlation between ACT-LR and APTT does not support its routine use.
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PMID:Validation of a bedside activated clotting time test (Hemochron Jr II Signature) with low dose heparin therapy. 1931 10

The REG1 system consists of factor IXa inhibitor, RB006, an aptamer-based anticoagulant and its antidote, RB007. The optimal use of RB006 can be facilitated by understanding its effect on the formation of thrombin and fibrin, and other standard tests of coagulation. Blood from consented volunteers was drawn into 3.2% citrate (9:1 v/v) and either used immediately or centrifuged to obtain platelet-poor plasma. Increasing concentrations of aptamer (6-24 microg/ml) alone or in combination with heparin (0.1 U/ml) or lepirudin (0.2 microg/ml) were added to blood and plasma samples. Activated clotting times (ACT+, low range-ACT), thrombelastometry (ROTEM) or thrombelastography (TEG) were performed in recalcified whole blood samples. Thrombin generation, prothrombin time (PT) and activated partial thromboplastin time (aPTT) were performed in plasma samples. To some samples the antidote RB007 was added to neutralise the anticoagulation activity of RB006. In all experiment the ratio of RB006 to RB007 was kept 1:2. RB006 dose-dependently prolonged aPTT and low range-ACT, but, as expected, had no effect on PT. RB006 prolonged the lag time and decreased the peak of Actin-triggered thrombin generation. Thrombin-activated TEG demonstrated that RB006 decreases the rate of clot formation. These effects were potentiated when RB006 was combined with heparin or lepirudin. In all experiments RB007 reversed the effects of RB006 back to baseline. In conclusion, RB006 inhibits thrombin generation and clot formation in a concentration-dependent manner. It is feasible to monitor RB006 and its reversal with RB007 using aPTT, low range-ACT, and thrombin-activated TEG.
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PMID:In-vitro evaluation of anti-factor IXa aptamer on thrombin generation, clotting time, and viscoelastometry. 1940 34

Determine the effect of age and congenital heart disease (CHD) on whole blood tests for monitoring unfractionated heparin (UFH) in children. Determine correlation with anti-Xa levels in children undergoing cardiac catheterization or cardiac surgery. A prospective cross-sectional study of 211 healthy children about to have minor surgery (median age 3.5 years) and 110 CHD patients (median age 2.1 years) undergoing cardiac catheterization or cardiac surgery. Commonly used whole blood tests (two activated clotting times and an activated partial thromboplastin time; ACT+, ACT-LR, and APTT, respectively) were obtained before procedures and after UFH in CHD patients. Data were analyzed for effect of age and CHD and correlation with anti-Xa levels. In healthy subjects the ACT+ was lower in younger (<3 years) patients while the ACT-LR and APTT were unaffected. CHD patients exhibited an opposite trend with higher values in the younger patients. After bolus heparin the ACT+ exhibited the strongest correlation (r = 0.89) with anti-Xa levels in both locations (the APTT was too sensitive at post-bolus levels). When anti-Xa levels were below 1.0 IU/ml (range of thromboembolism therapy 0.35-0.7 IU/ml), the APTT correlation coefficient was 0.72. Some whole blood coagulation tests are affected by age in healthy children similar to laboratory tests and are variably influenced by the presence of CHD. ACT+ is the most reliable predictor of anti-Xa levels in both catheterization and surgery for pediatric patients. The APTT exhibited stronger correlation with anti-Xa than previous reports of laboratory APTT and warrants further evaluation for monitoring heparin thromboembolism therapy.
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PMID:Monitoring unfractionated heparin in pediatric patients with congenital heart disease having cardiac catheterization or cardiac surgery. 1971 46

Nitroglycerin (NTG) reduces the anticoagulant effects of heparin and may lead to heparin resistance. Fresh frozen plasma (FFP) and antithrombin III (ATIII) may be used for the treatment of heparin resistance. We aimed to compare the effects of FFP and ATIII on heparin requirement, coagulation parameters, and bleeding in patients undergoing coronary artery bypass graft surgery (CABGS) with moderate dose of intraoperative NTG infusion. Forty-eight patients undergoing CABGS with NTG infusion were randomly allocated to three groups. Group C served as control, whereas the patients in group P received FFP and those in group A received ATIII after anesthesia induction. ATIII activity and coagulation parameters were measured at five different times intraoperatively. Total heparin requirement, heparin consumption, and heparin sensitivity were calculated. ATIII activity and ACT were significantly higher and activated partial thromboplastin time and fibrinogen level were significantly lower during cardiopulmonary bypass in group A than in groups P and C. Heparin sensitivity was significantly higher and total heparin requirement and consumption were significantly lower in ATIII group than in other groups. ATIII administration increases heparin sensitivity and decreases heparin requirements compared with FFP in patients undergoing CABGS with peroperative NTG infusion. ATIII may be preferred to FFP in patients with heparin resistance due to NTG infusion undergoing CABGS.
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PMID:Peroperative effects of fresh frozen plasma and antithrombin III on heparin sensitivity and coagulation during nitroglycerine infusion in coronary artery bypass surgery. 2179 98


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