161 results on '"H.C. Hemker"'
Search Results
2. The balance of pro‐ and anticoagulant processes underlying thrombin generation
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Tessa Peters, Rob Wagenvoord, H.C. Hemker, Romy Kremers, Promovendi CD, Biochemie, Bedrijfsbureau CD, and RS: CARIM - R1 - Thrombosis and haemostasis
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Time Factors ,medicine.drug_class ,antithrombins ,Fibrinogen ,Models, Biological ,Thrombin generation ,computational biology ,Thrombin ,Rivaroxaban ,Prothrombinase ,medicine ,Humans ,Computer Simulation ,alpha-Macroglobulins ,Enoxaparin ,Blood Coagulation ,Antithrombins ,prothrombin ,Chromatography ,Chemistry ,Anticoagulant ,Antithrombin ,Healthy subjects ,Reproducibility of Results ,Thrombosis ,Hematology ,prothrombinase ,thrombin ,Biochemistry ,Blood Coagulation Tests ,Factor Xa Inhibitors ,circulatory and respiratory physiology ,medicine.drug - Abstract
Summary Background The generation of thrombin in time is the combined effect of the processes of prothrombin conversion and thrombin inactivation. Measurement of prothrombin consumption used to provide valuable information on hemostatic disorders, but is no longer used, due to its elaborate nature. Objectives Because thrombin generation (TG) curves are easily obtained with modern techniques, we developed a method to extract the prothrombin conversion curve from the TG curve, using a computational model for thrombin inactivation. Methods Thrombin inactivation was modelled computationally by a reaction scheme with antithrombin, α2Macroglobulin and fibrinogen, taking into account the presence of the thrombin substrate ZGGR-AMC used to obtain the experimental data. The model was validated by comparison with data obtained from plasma as well as from a reaction mixture containing the same reactants as plasma. Results The computational model fitted experimental data within the limits of experimental error. Thrombin inactivation curves were predicted within 2 SD in 96% of healthy subjects. Prothrombin conversion was calculated in 24 healthy subjects and validated by comparison with the experimental consumption of prothrombin during TG. The endogenous thrombin potential (ETP) mainly depends on the total amount of prothrombin converted and the thrombin decay capacity, and the peak height is determined by the maximum prothrombin conversion rate and the thrombin decay capacity. Conclusions Thrombin inactivation can be accurately predicted by the proposed computational model and prothrombin conversion can be extracted from a TG curve using this computational prediction. This additional computational analysis of TG facilitates the analysis of the process of disturbed TG.
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- 2015
3. Computational modelling of clot development in patient-specific cerebral aneurysm cases
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Romy Kremers, Rob Wagenvoord, B. de Laat, H.C. Hemker, RS: CARIM - R1.01 - Blood proteins & engineering, Promovendi CD, and Biochemie
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0301 basic medicine ,medicine.medical_specialty ,PLASMA ,business.industry ,Hematology ,030204 cardiovascular system & hematology ,medicine.disease ,Thrombin generation ,Surgery ,03 medical and health sciences ,030104 developmental biology ,0302 clinical medicine ,Aneurysm ,Text mining ,medicine ,In patient ,THROMBIN GENERATION ,business - Published
- 2017
4. Thrombin generation assay using factor IXa as a trigger to quantify accurately factor VIII levels in haemophilia A
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Theo Lindhout, B. De Laat, H.C. Hemker, R. van Oerle, Yesim Dargaud, Marisa Ninivaggi, Biochemie, Interne Geneeskunde, and RS: CARIM School for Cardiovascular Diseases
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Adult ,congenital, hereditary, and neonatal diseases and abnormalities ,animal diseases ,Coefficient of variation ,Haemophilia A ,Sensitivity and Specificity ,Severity of Illness Index ,Thrombin generation ,Thromboplastin ,Factor IXa ,Young Adult ,Thrombin ,Predictive Value of Tests ,hemic and lymphatic diseases ,Clinical heterogeneity ,medicine ,Humans ,In patient ,Aged ,Netherlands ,Blood coagulation test ,Factor VIII ,business.industry ,Reproducibility of Results ,Hematology ,Middle Aged ,medicine.disease ,factor IXa-driven thrombin generation ,Kinetics ,Phenotype ,Factor Xa ,Immunology ,hemophilia A ,Blood Coagulation Tests ,France ,business ,Biomarkers ,FVIII-assay ,medicine.drug - Abstract
Background: The available methods for measuring factor VIII (FVIII) activity suffer reportedly from lack of sensitivity and precision in the
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- 2011
5. The paradoxical stimulation by a reversible thrombin inhibitor of thrombin generation in plasma measured with thrombinography is caused by alpha(2)-macroglobulin-thrombin
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H.C. Hemker, Rob Wagenvoord, Johanna Deinum, M. Elg, Biochemie, Bedrijfsbureau CD, and RS: CARIM School for Cardiovascular Diseases
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Chemistry ,Area under the curve ,Substrate (chemistry) ,Stimulation ,Hematology ,sub-sampling technique ,Thrombin generation ,calibrated automated thrombinography ,Thrombin ,Endogenous Thrombin Potential ,Biochemistry ,Alpha macroglobulins ,Direct thrombin inhibitor ,thrombin generation ,medicine ,Biophysics ,reversible direct thrombin inhibitors ,circulatory and respiratory physiology ,medicine.drug - Abstract
Background. Thrombin generation (TG) in plasma can be monitored continuously with a fluorogenic thrombin substrate using calibrated automated thrombinography ( CAT). In the presence of low concentrations of a reversible direct thrombin inhibitor (DTI), CAT shows an unexpected effect: the endogenous thrombin potential (ETP) increases at low concentrations of the inhibitor to subsequently decrease concentration dependently at higher concentrations (> approximately 100 nM). Objectives. To find an explanation for this phenomenon, we measured the concentrations of free thrombin and alpha(2)-macroglobulin- thrombin complex (alpha 2MT) with a sub-sampling technique in the presence of AR-H067637, a selective DTI. Results. At all concentrations of the DTI there was a gradual dose-dependent decrease in the concentration of free, not-inhibited thrombin but a transient increase in free alpha 2MT due to competition of thrombin and alpha 2MT for the inhibitor. Because the CAT technique uses an algorithm to subtract alpha 2MT activity from the total amidolytic activity, this transient increase in alpha 2MT activity is not subtracted and erroneously attributed to thrombin itself. Conclusions. This study explains the spurious increase in ETP observed at low DTI concentrations. The results obtained in plasma were corroborated by observations in a thrombin generating system reconstituted with purified factors. In practise, the effect of DTIs on TG can be reliably evaluated from the area under the curve till time-to-peak.
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- 2010
6. The Synthesis of Prothrombin from Its Precursor Protein
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Cees Vermeer, H.C. Hemker, and Berry A.M. Soute
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Biochemistry ,business.industry ,Medicine ,business - Published
- 2015
7. The application of thrombin generation in real life clinical situations
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H.C. Hemker, Bedrijfsbureau CD, and RS: CARIM - R1 - Thrombosis and haemostasis
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medicine.medical_specialty ,business.industry ,Thrombin ,Hematology ,medicine.disease ,Thrombin generation ,Plasma ,Internal medicine ,Cardiology ,Medicine ,In real life ,Humans ,Medical emergency ,Blood Coagulation Tests ,business ,medicine.drug ,Blood coagulation test - Published
- 2015
8. Fixed dosage of low-molecular-weight heparins causes large individual variation in coagulability, only partly correlated to body weight
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H.C. Hemker, R. Al Dieri, Suzette Beguin, Susanne Alban, and Biochemie
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Adult ,Male ,medicine.medical_specialty ,Adolescent ,Coefficient of variation ,Antithrombin III ,Pharmacology ,Body weight ,Fixed dose ,Antifactor xa ,medicine ,Humans ,Thrombophilia ,Distribution (pharmacology) ,Blood Coagulation ,Dose-Response Relationship, Drug ,business.industry ,Body Weight ,Reproducibility of Results ,Hematology ,Heparin ,Heparin, Low-Molecular-Weight ,Surgery ,Molecular Weight ,Normal volunteers ,Coagulation ,Factor Xa ,Drug Evaluation ,Blood Coagulation Tests ,business ,medicine.drug - Abstract
Summary. Backgrounds: Low-molecular-weight heparins (LMWHs) are routinely given without the control of their effect on coagulation. The endogenous thrombin potential (ETP) is a sensitive detector of the heparin effect. Question: What is the interindividual variation in TG after a fixed dose of LMWH in normal volunteers, is it explained by variation in weight? Methods: Subcutaneous (s.c.) injection, in 12 healthy volunteers, of 9000 aXa-units of unfractionated heparin (UFH) and of three heparins with narrow MW distribution around 10.5, 6.0 and 4.5 kD. Measurement of anti-thrombin (aIIa) and antifactor Xa (aXa)-activities and ETP at 11 time points over 24 h. Results: The coefficient of variation (CV) of the AUCs of aXa- and aIIa-activities is 50% for UFH and 22–37% for LMWHs. Because of the hyperbolic form of the dose–response curve, the CV of the inhibition of the ETP is lower: 32% for UFH and 13–21% for the LMWHs. Fixed dosage of LMWH caused under-dosage in 10–13% of the samples and over-dosage in 5–11%. High or low response is an individual property independent of the type of heparin injected and only partially explained by variation in body weight. Conclusion: Optimized individual dosage of LMWH is possible through recognition of high and low responders, which requires one measurement of the heparin concentration or, preferably, the heparin effect on the ETP, 2–5 h after a first injection.
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- 2006
9. Initiating and potentiating role of platelets in tissue factor-induced thrombin generation in the presence of plasma
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Marion A.H. Feijge, H.C. Hemker, Peter Giesen, R. J. W. Van Kampen, H. Kenis, Kristof Vanschoonbeek, Johan W. M. Heemskerk, Biochemie, and Humane Biologie
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Blood Platelets ,Male ,Thrombin ,Hematology ,Phosphatidylserine ,Thrombomodulin ,Thromboplastin ,Kinetics ,chemistry.chemical_compound ,Tissue factor ,Coagulation ,chemistry ,Biochemistry ,Reference Values ,Biophysics ,medicine ,Humans ,Female ,Platelet ,Platelet activation ,Annexin A5 ,Phospholipids ,medicine.drug - Abstract
The hemostatic activity of plasma is determined by platelet activation and coagulation, which processes are mutually stimulatory. We studied this interaction by measuring the cleavage of fluorescent thrombin substrate in platelet-rich plasma (PRP), using the calibrated thrombogram method. In freshly isolated human plasma, thrombin formation triggered by tissue factor was fully dependent on the presence of platelets. It was abolished by annexin A5. indicating dependence on phosphatidylserine (PS) exposure at activated platelets. Comparison of plasmas from various subjects showed considerable interindividual variation in total amount of thrombin generation, regardless of whether platelets or PS-containing phospholipids were present. Integrin alpha(IIb)beta(3) antagonists and ADP receptor blockage, but not aspirin, decreased the rate of thrombin generation (thrombin peak level) and extended the time of onset. Platelet inhibition with cAMP-elevating agents decreased the thrombin-forming rate, but surprisingly shortened the onset time. Stimulation of platelets with agonists of Gi/q-coupled receptors and, to a larger extent, with collagen or Ca2+ -ionophore increased the rate of thrombin generation and shortened its onset. In PRP from donors with low and high generation, platelet inhibitors and activators were similarly effective. Taken together, these results indicate that, in tissue factor-triggered PRP, PS exposure on activated platelets regulates both onset and rate of thrombin generation. However, coagulant activity rather than platelet activation determines the total amount of thrombin formed, i.e. the endogenous thrombin potential. Thus, kinetics of thrombin generation in PRP are controlled by platelet inhibitors and agonists, but the process is restricted in amount by the subject-dependent variation in coagulation.
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- 2004
10. Title Page / Table of Contents / Preface
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Benvindo Justiça, E. Segalés, Gloria Saccani, Evy Bashardi, Andrew N. Nicolaides, Armando Tripodi, T. Fenyvesi, G. Origliani, J. Vermylen, R. Rossi, A. Nemmar, Alexander Koshkaryev, Silvia Navarro, S. Béguin, Francesco Violi, Tiziana Garofano, Antonella Tufano, Uri Seligsohn, Fabrizio Fabris, H.C. Hemker, G. Vilahur, Franco Semprini, R. Abbate, S. Fedi, Saul Yedgar, Sara Morais, C. Fatini, Licia Iacoviello, Irène Juhan-Vague, F. Gensini, Helga Grafenhofer, P. Giesen, S. Coccheri, B. Nemery, P. Carrasco, T. Grimaldi, Jacqueline Conard, G. Fantini, Ida Martinelli, Chiara Melloni, F.R. Rosendaal, Francesco Fallani, Gordon D.O. Lowe, E. Sticchi, Mónica Pereira, Joseph Loscalzo, J.I. Abad, V. Regnault, Juan Carlos Souto, T. Lecompte, Gregory Barshtein, Giovanni Romeo, V.V. Kakkar, Ingrid Pabinger, Ebrahim Shah, Giovanni Di Minno, A. De Fabritiis, F. Sofi, Pilar Medina, Alexandra Estevinho, Matteo Nicola Dario Di Minno, Justo Aznar, E. Conti, Grigoris T. Gerotziafas, George Geroulakos, E. de Smed, Maria Assunta Silvestri, Giuseppe G. Nenci, Fabio M. Pulcinelli, Luisa Lenti, Ismail Elalamy, B. Cosmi, Pierre Morange, Amparo Estellés, Angelo Branzi, Marie-Christine Alessi, Andrew H. Baker, Roberto Catasca, Raymond Verhaeghe, Samuele Nanni, V. Llorente, Francisco España, Andrea Ghiselli, F. Coppi, Domenico Prisco, Manuel Campos, M.F. Hoylaerts, P. Poredoš, Meyer Michel Samama, Stavros K. Kakkos, Giovanni Melandri, José Miguel P. Ferreira de Oliveira, Maura Griffin, David A. Lane, R. AlDieri, Augusto Di Castelnuovo, Serenella Rotondo, L. Badimon, J.J. Badimon, Giovanna Marchetti, Antonella Marcoccia, M.G. Modena, Henrik Sillesen, Joseph Emmerich, Daniela Turchetti, Luigina R. Mollica, Giovanni de Gaetano, Rossella Marcucci, Maria Benedetta Donati, José Manuel Cabeda, Pasquale Pignatelli, Giuseppe Germanò, Pierluigi Tricoci, J. Harenberg, Marie Hélène Horellou, Gianni Belcaro, Antonio Girolami, Bruno Girolami, R. Wagenvoord, Francesco Bernardi, M. Verstraete, P.M. Mannucci, Jean-Noël Fiessinger, I. Jörg, and Irene Pereira
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medicine.medical_specialty ,business.industry ,Physiology (medical) ,medicine ,Table of contents ,Hematology ,Title page ,business ,Classics ,Surgery - Published
- 2003
11. von Willebrand factor stimulates thrombin-induced exposure of procoagulant phospholipids on the surface of fibrin-adherent platelets
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Dominique Baruch, Jacob J. Briedé, Simone J.H. Wielders, Johan W. M. Heemskerk, H.C. Hemker, Theo Lindhout, Gezondheidsrisico Analyse en Toxicologie, Biochemie, Humane Biologie, and RS: NUTRIM School of Nutrition and Translational Research in Metabolism
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Blood Platelets ,Phosphatidylserines ,Fibrin ,chemistry.chemical_compound ,Thrombin ,Platelet Adhesiveness ,Von Willebrand factor ,Platelet adhesiveness ,Mole ,Crotalid Venoms ,von Willebrand Factor ,medicine ,Humans ,Platelet ,Blood Coagulation ,Calcium metabolism ,biology ,Chemistry ,Hematology ,Phosphatidylserine ,Perfusion ,Biochemistry ,biology.protein ,Biophysics ,Calcium ,Stress, Mechanical ,medicine.drug ,circulatory and respiratory physiology - Abstract
von Willebrand factor stimulates thrombin-induced exposure of procoagulant phospholipids on the surface of fibrin-adherent platelets.Briede JJ, Wielders SJ, Heemskerk JW, Baruch D, Hemker HC, Lindhout T.Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands.Studies from our laboratory have demonstrated that von Willebrand factor (VWF) stimulates thrombin generation in platelet-rich plasma. The precise role of VWF and fibrin in this reaction, however, remained to be clarified. In the present study we utilized thrombin-free planar fibrin layers and washed platelets to examine the relationship between platelet-fibrin interaction and exposure of coagulation-stimulating phosphatidylserine (PS) under conditions of low and high shear stress. Our study confirms that platelet adhesion to fibrin at a shear rate of 1000 s(-1) requires fibrin-bound VWF. The cytosolic calcium concentration ([Ca(2+)]i) of stationary platelets was not elevated and PS exposing platelets were virtually absent (2 +/- 2%). However, thrombin activation resulted in a marked increase in the number of PS exposing platelets (up to 85 +/- 14%) along with a transient elevation in [Ca(2+)]i from 0.05 micro mol L(-1) up to 1.1 +/- 0.2 micro mol L(-1). Platelet adhesion to fibrin at a shear rate of 50 s(-1) is mediated by thrombin but not by fibrin-bound VWF. The [Ca(2+)]i of these thrombin-activated platelets was elevated (0.2 +/- 0.1 micro mol L(-1)), but only a minority of the platelets (11 +/- 8%) exposed PS. The essential role of VWF in this thrombin-induced procoagulant response became apparent from low shear rate perfusion studies over fibrin that was incubated with VWF and botrocetin. After treatment with thrombin, the majority of the adherent platelets (57 +/- 23%) exposed PS and had peak values of [Ca(2+)]i of about 0.6 micro mol L(-1). Taken together, these results demonstrate that thrombin-induced exposure of PS and high calcium response on fibrin-adherent platelets depends on shear- or botrocetin-induced VWF-platelet interaction
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- 2003
12. Thrombin-induced Hyperactivity of Platelets of Young Stroke Patients
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E. C. M. van Pampus, H.C. Hemker, J. Lodder, Marion A.H. Feijge, Karly Hamulyák, Kristof Vanschoonbeek, Jeffrey F.W. Keuren, Johan W. M. Heemskerk, Humane Biologie, Biochemie, Klinische Neurowetenschappen, Interne Geneeskunde, and RS: NUTRIM School of Nutrition and Translational Research in Metabolism
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Agonist ,medicine.medical_specialty ,Aspirin ,business.industry ,medicine.drug_class ,Hematology ,medicine.disease ,Endocrinology ,Thrombin ,Prothrombinase ,Internal medicine ,medicine ,Platelet ,Platelet activation ,business ,Receptor ,Stroke ,medicine.drug - Abstract
Thrombin-induced Hyperactivity of Platelets of Young Stroke Patients.Vanschoonbeek K, Feijge MA, Keuren JF, Coenraad Hemker H, Lodder JJ, Hamulyak K, Van Pampus EC, Heemskerk JW.Dept. of Biochemistry, CARIM, University of Maastricht, P.O. Box 616, 6200 MD Maastricht, The Netherlands.Activated platelets are implicated in the development of premature arterial vascular diseases, in particular ischemic stroke. Since elevated cytosolic [Ca(2+)](i) is an integrative marker of platelet activation, we determined the generation of Ca(2+) signal in stimulated platelets from 26 young patients recuperating from stroke, 20 patients with symptomatic peripheral arterial disease, and 56 healthy volunteers. Even in the presence of aspirin, the platelets from various individuals showed highly different thrombin-induced Ca(2+) responses. On average, the thrombin-induced Ca(2+) response was increased for platelets from either patient group in comparison to the controls (P
- Published
- 2002
13. The effect of fibrin(ogen) on thrombin generation and decay
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Rob Wagenvoord, Romy Kremers, H.C. Hemker, RS: CARIM - R1 - Thrombosis and haemostasis, Biochemie, and Bedrijfsbureau CD
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0301 basic medicine ,030204 cardiovascular system & hematology ,Fibrinogen ,Thrombin generation ,Fibrin ,Antithrombins ,03 medical and health sciences ,Tissue factor ,Plasma ,0302 clinical medicine ,Thrombin ,gamma chain ,thrombin decay ,medicine ,Humans ,alpha-Macroglobulins ,Blood Coagulation ,biology ,Chemistry ,Fibrinogens, Abnormal ,prothrombin conversion ,Antithrombin ,Hematology ,030104 developmental biology ,Biochemistry ,thrombin generation ,Proteolysis ,biology.protein ,Biophysics ,circulatory and respiratory physiology ,medicine.drug ,Protein Binding - Abstract
SummaryDefibrination causes a ~30% decrease of thrombin generation (TG) which can be restored by adding native fibrinogen in its original concentration (3 mg/ml). The fibrinogen variant γA/γ′, which binds thrombin with high affinity, is over four times more efficient in this respect than the more common γA/γA form. By using high tissue factor concentrations we accelerated prothrombin conversion so as to obtain a descending part of the TG curve that was governed by thrombin decay only. From that part we calculated the antithrombin (AT)- and α2-macroglobulin- dependent decay constants at a series of concentrations of native, γA/γA and γA/γ′ fibrinogen. We found that the increase of TG in the presence of fibrinogen is primarily due to a dose-dependent decrease of thrombin inactivation by α2-macroglobulin, where the γA/γ′ form is much more active than the γA/γA form. AT-dependent decay is somewhat decreased by γA/γ′ fibrinogen but hardly by the γA/γA form. We assume that binding of thrombin to fibrin(ogen) interferes with its binding to inhibitors. Attenuation of decay only in part explains the stimulating effect of fibrinogen on TG, as fibrinogen stimulates prothrombin conversion, regardless of the fibrinogen variant.Note: Part of this work was presented at the ISTH meeting in 2013.
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- 2014
14. Regulation of platelet factor Va-dependent thrombin generation by activated protein C at the surface of collagen-adherent platelets
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Jacob J. Briedé, G.M.H. Tans, George M. Willems, Theo Lindhout, H.C. Hemker, Gezondheidsrisico Analyse en Toxicologie, Biochemie, RS: NUTRIM School of Nutrition and Translational Research in Metabolism, and RS: CARIM School for Cardiovascular Diseases
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Blood Platelets ,Time Factors ,Phospholipid ,Phosphatidylserines ,Biochemistry ,Thromboplastin ,chemistry.chemical_compound ,Platelet Adhesiveness ,Prothrombinase ,Phosphatidylcholine ,Platelet adhesiveness ,medicine ,Humans ,Platelet ,Platelet activation ,Molecular Biology ,Chemistry ,Thrombin ,Anticoagulants ,Biological Transport ,Cell Biology ,Phosphatidylserine ,Enzyme Activation ,Kinetics ,Gene Expression Regulation ,Factor Va ,Factor Xa ,Phosphatidylcholines ,Biophysics ,Prothrombin ,Collagen ,Protein C ,medicine.drug - Abstract
J Biol Chem 2001 Mar 9;276(10):7164-8 Related Articles, Books, LinkOut Regulation of platelet factor Va-dependent thrombin generation by activated protein C at the surface of collagen-adherent platelets.Briede JJ, Tans G, Willems GM, Hemker HC, Lindhout T.Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, 6200 MD Maastricht, The Netherlands.Recent studies have indicated that factor Va bound to activated platelets is partially protected from inactivation by activated protein C (APC). To explore whether this sustained factor Va activity could maintain ongoing thrombin generation, the kinetics of platelet factor Va-dependent prothrombinase activity and its inhibition by APC were studied. In an attempt to mimic physiologically relevant conditions, platelets were adhered to collagen type I-coated discs. These discs were then spun in solutions containing prothrombin and factor Xa either in the absence or presence of APC. The experiments were performed in the absence of platelet-derived microparticles, with thrombin generation and inhibition confined to the surface of the adherent platelets. APC completely inactivated platelet-associated prothrombinase activity with an overall second order rate constant of 3.3 x 10(6) m(-)1 s(-)1, which was independent of the prothrombin concentration over a wide range around the apparent K(m) for prothrombin. Kinetic studies on prothrombinase assembled at a planar phospholipid membrane composed of 25 mol % phosphatidylserine and 75 mol % phosphatidylcholine revealed a similar second order rate constant of inhibition (2.5 x 10(6) m(-1) s(-1)). Collectively, these data demonstrate that ongoing platelet factor Va-dependent thrombin generation at the surface of collagen-adherent platelets is effectively inhibited by APC. No differences were observed between the kinetics of APC inactivation of plasma-derived factor Va or platelet factor Va as part of the prothrombinase associated with, respectively, a planar membrane of synthetic phospholipids or collagen-adherent platelets.
- Published
- 2001
15. Contribution of platelet-derived factor Va to thrombin generation on immobilized collagen- and fibrinogen-adherent platelets
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Jacob J. Briedé, Johan W. M. Heemskerk, C. van 't Veer, H.C. Hemker, Theo Lindhout, RS: NUTRIM School of Nutrition and Translational Research in Metabolism, RS: CARIM School for Cardiovascular Diseases, Gezondheidsrisico Analyse en Toxicologie, Biochemie, Algemene Heelkunde, and Other departments
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Blood Platelets ,Phosphatidylserines ,Fibrinogen ,Hemostatics ,chemistry.chemical_compound ,Platelet Adhesiveness ,Thrombin ,Annexin ,medicine ,Humans ,Platelet ,biology ,business.industry ,Factor V ,Hematology ,Adhesion ,Phosphatidylserine ,Perfusion ,Kinetics ,chemistry ,Factor Va ,Factor Xa ,Immunology ,biology.protein ,Biophysics ,Calcium ,Prothrombin ,Collagen ,business ,medicine.drug - Abstract
Thromb Haemost 2001 Mar;85(3):509-13 Related Articles, Books, LinkOut Contribution of platelet-derived factor Va to thrombin generation on immobilized collagen- and fibrinogen-adherent platelets.Briede JJ, Heemskerk JW, van't Veer C, Hemker HC, Lindhout T.Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, The Netherlands.Adhesion of platelets to immobilized collagen induces the expression of anionic phospholipids, e.g. phosphatidylserine (PS), in the outer leaflet of the plasma membrane of these platelets. In contrast, of the platelets that adhere to immobilized fibrinogen only a small sub-population representing 10 +/- 3% of the total population of the fibrinogen-adherent platelets has exposed PS as probed by annexin V binding. Although the presence of PS is thought to be critical for thrombin generation at the platelet surface, no information is available about the effect of this differential PS exposure on the ability of adherent platelets to support thrombin generation. Perfusion of the fibrinogen- or collagen-adherent platelets with solutions containing factor Xa and prothrombin resulted in thrombin generation that i) increased linear during the first perfusion minutes, ii) was about two-fold faster at collagen-adherent than at fibrinogen-adherent platelets and iii) was for more than 98% restricted to the surface of the adherent platelets. It appeared that the lower thrombin generating capacity of fibrinogen-adherent platelets is not due to a lower overall surface density of PS, but is caused by lower amounts of platelet-bound factor Va. Firstly, in both cases thrombin generation could be completely attenuated with antibodies against human factor Va, and secondly, in the presence of an excess of exogenous plasma-derived factor Va similar initial rates of thrombin formation were measured for collagen- and fibrinogen-adherent platelets. Our findings suggest a unique role for immobilized collagen in maintaining haemostasis.
- Published
- 2001
16. Monitoring new oral antithrombotics: what we should know before we can decide
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H.C. Hemker and R. Al Dieri
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business.industry ,Medicine ,Hematology ,business - Published
- 2010
17. Human Blood Coagulation : Biochemistry, Clinical Investigation and Therapy
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H.C. Hemker, E.A. Loelinger, J.J. Veltkamp, H.C. Hemker, E.A. Loelinger, and J.J. Veltkamp
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- Hematology
- Abstract
Since 1952, postgraduate courses for practising physicians and speci alists have been given by the Medical Faculty of the University of Leiden in the Boerhaave Quarter, in which most of its clinics and laboratories are located. During these years, recent advances in a wide variety of m~dical fields and subjects have been discussed by distin guished speakers from many countries. The steadily increasing atten dance has shown that, as could be expected from the rapid progress of modern medicine, there is a widely felt need for this form of postgra duate study. In 1957, therefore, the Leiden Medical Faculty appointed a permanent committee for the organization of postgraduate medical education. Of the courses given since then, certain material proved to have sufficient immediate scientific value to justify publication, and it now gives the Committee great pleasure to announce that in collaboration with the Leiden University Press it will publish the Boerhaave Series for Postgraduate Medical Education. The first volume of this new series is the product of the course on Human Blood Coagulation given in Novem ber 1968. It is our hope that this book will prove valuable not only to those who participated in the course but also to many others working in this and associated fields.
- Published
- 2012
18. Ischaemic Heart Disease
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J.H. de Haas, H.C. Hemker, H.A. Snellen, J.H. de Haas, H.C. Hemker, and H.A. Snellen
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- Coronary heart disease--Congresses, Coronary disease--Congresses
- Abstract
The Boerhaave Courses in Cardiology have been held once or twice a year since 1955. For the greater part they were meant for specialists in Cardiology, Pediatrics, and Internal Medicine, who wished to hear about recent advances in Cardiology and in its anatomical and physical basis. For some time the courses reflected mostly the work in Leiden, especially on congenital heart disease, but soon the highly valuable cooperation of other centres was obtained on subjects in which they had more experience. In later years speakers from abroad were also invited and they con tributed greatly to the wider scope of the courses. It was thus possible to organize detailed discussions on special subjects by panels of experts for an audience of interested clinical specialists. General reviews were also given for widely varying groups including general practioners and health officers. The special courses were usually given in English and were international in character, while the general courses were given in Dutch. This book reports on a course that united both trends. It was held entirely in English mainly because it was combined with a meeting organized by the Dutch Heart Association and because of the support given by the Secretary of Health who opened this meeting personally and by the European branch of the World Health Organization which was represented by Dr. Pisa.
- Published
- 2012
19. Handbook of Synthetic Substrates
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H.C. Hemker and H.C. Hemker
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- Blood--Coagulation, Fibrinolysis, Chromogenic compounds--Analysis
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The need for a handbook on the use of synthetic substrates for assay of proteases of the coagulation and fibrinolytic systems became evident several years ago during the activities of the Subcommittee on Synthetic Substrates of the International Committee on Thrombosis and Haemo stasis (lCTH). Production of such a handbook, which was recommended during discussions of the ICTH at its meeting in London in 1979 was made possible by the generous efforts of Professor HC Hemker with the aid of several contributors with particular interests in the use of synthetic substrates in coagulation and fibrinolysis. As current Chairman and Secretary General of the ICTH we would like to express our sincere thanks to Professor Hemker for producing this handbook and look for ward to seeing the benefits of this tremendous effort reflected in the advancement of our understanding of thrombosis and hemostasis and the transfer of such knowledge into improved diagnosis and treatment of thrombotic and hemorrhagic disorders. Craig M Jackson Professor of Biological Chemistry Washington University School of Medicine, St. Louis, MO Chairman, ICTH Harold R Roberts Professor of Internal Medicine University of North Carolina, Chapel Hill, NC Secretary General, ICTH ix Foreword The advent of synthetic substrates for the study of blood coagulation and fibrinolysis was a significant step forward in the investigation of these systems. Both basic research and clinical laboratory investigations can profit from these advanced tools.
- Published
- 2012
20. Quantitation in Cardiology
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H.A. Snellen, H.C. Hemker, P.G. Hugenholtz, J.H. van Bemmel, H.A. Snellen, H.C. Hemker, P.G. Hugenholtz, and J.H. van Bemmel
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- Cardiology--Congresses, Hemodynamics--Congresses
- Abstract
This book comprises the essential records from a Boerhaave course given in June 1971 for specialists in cardiology and other fields of internal medicine interested in the subject of quantitation in cardiology. It is evident that in the wide field of medicine, and particularly in cardiology, there is a growing need for exact and detailed information in conjunction with existing diag nostic methods. This is apparent in the greater precision in anatomical and haemodynamic details required by the thoracic surgeon as the number of available heart operations gradually increases. In retrospect it is hardly surprising that the high initial mortality after the introduction of each operation depended to a large extent upon the degree of accuracy with which the diagnosis was made. Another urgent need for precise and quantitative information became apparent when monitoring of high-risk patients, in order to forestall compli cations and/or death, became routine. The same applies for the diagnostic procedures used to estimate the patient's chances of surviving an operation and/or rehabilitation after a serious incident, such as myocardial infarction. In these fields there is a vast amount of data to be handled and - in modern diagnostic procedures - it must be processed so rapidly that the human mind cannot suffice and computer equipment has becomeindispensable.
- Published
- 2012
21. Caution in the interpretation of continuous thrombin generation assays: a rebuttal
- Author
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H.C. Hemker, E. De Smedt, and Biochemie
- Subjects
business.industry ,Interpretation (philosophy) ,Rebuttal ,Medicine ,Hematology ,business ,Thrombin generation ,Epistemology - Published
- 2007
22. The Ca2+-mobilizing potency of alpha-thrombin and thrombin-receptor-activating peptide on human platelets -- concentration and time effects of thrombin-induced Ca2+ signaling
- Author
-
L. Henneman, Marion A.H. Feijge, Johan W. M. Heemskerk, H.C. Hemker, Jan Rosing, Humane Biologie, Biochemie, and RS: NUTRIM School of Nutrition and Translational Research in Metabolism
- Subjects
Blood Platelets ,Agonist ,Time Factors ,Thromboxane ,medicine.drug_class ,In Vitro Techniques ,Biochemistry ,Thromboxane A2 ,chemistry.chemical_compound ,Cytosol ,Thrombin ,Prothrombinase ,Homologous desensitization ,medicine ,Humans ,Platelet ,Protease-activated receptor ,Egtazic Acid ,Aspirin ,Chemistry ,Apyrase ,Platelet Activation ,Peptide Fragments ,Adenosine Diphosphate ,Kinetics ,15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid ,Biophysics ,Calcium ,Receptors, Thrombin ,Signal Transduction ,medicine.drug - Abstract
Department of Biochemistry, Maastricht University, The Netherlands. jwm.heemskerk@bioch.unimaas.nlIn single platelets and in suspensions of platelets, alpha-thrombin evokes dose-dependent, transient increases in cytosolic Ca2+ concentration, [Ca2+]i, which are more prolonged than the [Ca2+]i transients evoked by other platelet agonists such as the thrombin-receptor-activating hexapeptide SFLLRN, thromboxane A2 analog U46619, and ADP. As a quantity taking into account both the magnitude and length of the Ca2+ response, we defined the Ca2+-mobilizing potency (CMP) of an agonist as the integrated rise in [Ca2+]i during the time of the Ca2+ signal. It was observed that: (a) the CMP increased with the agonist concentration in a saturating way, its maximal value being about four-times higher with alpha-thrombin than with SFLLRN; (b) the high CMP of alpha-thrombin was for only a small part due to endogenous production of ADP or thromboxane, and was mainly a consequence of prolonged influx of external Ca2+; (c) the CMP declined when alpha-thrombin was inactivated during the course of the Ca2+ signal; (d) CMP values increased with the agonist concentration upon sequential addition of increasing amounts of alpha-thrombin or SFLLRN; (e) when alpha-thrombin was gradually added to the platelets or formed by an in situ reconstituted prothrombinase system (with factor Xa, factor Va, and prothrombin), integrated Ca2+ responses were a function of the product of the alpha-thrombin concentration and the time of its presence. However, in these cases, the final CMP values were independent of the rate of alpha-thrombin addition or formation. We conclude that alpha-thrombin-induced Ca2+ signals in platelets rely largely upon Ca2+ influx, are not, or only slightly, subjected to homologous desensitization, and reflect the enzymatic capacity of alpha-thrombin to cleave protease-activated receptors. Thus, the high and prolonged Ca2+ signal induced by alpha-thrombin is due to continuous receptor cleavage without desensitizing effects of previously cleaved receptors.
- Published
- 1997
23. The Activity of Unfractionated Heparin and Low Molecular Weight Heparins in Rabbit Plasma – The Need for Using Absolute Anti-factor Xa and Antithrombin Activities
- Author
-
S. Beguin, B. Boneu, V. Peyrou, H.C. Hemker, and Biochemie
- Subjects
chemistry.chemical_classification ,medicine.drug_class ,Antithrombin ,Anticoagulant ,Low molecular weight heparin ,Biological activity ,Hematology ,Heparin ,Enzyme ,Thrombin ,chemistry ,Biochemistry ,Antithrombotic ,medicine ,medicine.drug - Abstract
SummaryRabbit being a common animal model to evaluate the antithrombotic effect of heparins, our purpose was to apply the heparin Standard Independent Unit (SIU) approach to rabbit plasma. To take into account the specificities of the enzymes we have measured the decay constants of factor Xa and of thrombin from autologous and heterologous origins, in presence and in absence of heparin. Different heparins or heparin fractions with a mean molecular weight from 1.7 to 10.5 kDa were used.We found that: a) the decay constants varied strongly between species and between enzymes; b) the decay constants of thrombin were always higher than those of factor Xa; c) the specific anti-factor Xa activity of heparins increased with the molecular weight and was 1.33 times higher when determined with bovine factor Xa than with rabbit factor Xa; d) the specific antithrombin activity of heparins also increased with the molecular weight but was similar when determined with rabbit and human thrombin; e) the specific anti-factor Xa activity was always lower than the specific antithrombin activity; f) the calibration of the heparins and heparin fractions against the 4th International Standard of Heparin expressed in International Units (IU) lead to a systematic overestimation of the anti-factor Xa activity and to an underestimation of the antithrombin activity.These observations indicate that it may be very important to use the SIU approach and to know the accurate activities to better understand the mechanism of the antithrombotic activity of heparins in experimental models.
- Published
- 1997
24. Good mathematical practice: simulation of the hemostatic-thrombotic mechanism, a powerful tool but one that must be used with circumspection
- Author
-
H.C. Hemker, Fazoil I. Ataullakhanov, Biochemie, and RS: CARIM School for Cardiovascular Diseases
- Subjects
Value (ethics) ,Hemostasis ,Whole Blood Coagulation Time ,Mathematical model ,Mechanism (biology) ,business.industry ,Computers ,Hematology ,Models, Biological ,Mathematical practice ,Risk analysis (engineering) ,Physiology (medical) ,Medicine ,Computer Simulation ,business ,Blood Coagulation ,Biochemical mechanism ,Oral anticoagulation ,Scope (computer science) ,Diffi cult ,Mathematics - Abstract
Modeling means replacing a complicated mechanism by a simpler one that is more easy to understand and/or to manipulate. The complexity of the hemostatic and thrombotic system (H&TS) is such that it is impossible to understand without modeling. The Quick-time is a model of the downregulation of the H&TS by oral anticoagulation or liver disease. The bleeding time is another model of another subsystem of the H&TS, with another scope. This illustrates that models never are complete and that they do not need to be complete to be useful. Actually, the most complete models are usually also complex, time-consuming, expensive, and extremely diffi cult to interprete. Mathematical models are of a special kind (for a review of mathematical and computer research in coagulation, see [1] ). In the fi rst place they are impressive and impenetrable to the noninitiated – and the initiated are few. The biological scientist as a rule is not familiar with this approach. As soon as a biochemical mechanism is more complicated than the Michaelis-Menten model of enzyme action, many life-scientists and clinicians tend to be turned off, which is a pity because mathematical modeling is not an aim in itself, but should prove its value in the confrontation with actual laboratory data and needs the biologists for its verifi cation. This is one reason to broach mathematical modeling in a journal on patho
- Published
- 2005
25. Inhibition of platelet-mediated, tissue factor-induced thrombin generation by the mouse/human chimeric 7E3 antibody
- Author
-
H.C. Hemker, S Béguin, H Kessels, R. Kumar, Barry S. Coller, J C Reverter, and Biochemie
- Subjects
Blood Platelets ,Alpha-v beta-3 ,Recombinant Fusion Proteins ,Platelet Glycoprotein GPIIb-IIIa Complex ,Thromboplastin ,chemistry.chemical_compound ,Tissue factor ,Immunoglobulin Fab Fragments ,Mice ,Thrombin ,medicine ,Animals ,Humans ,Platelet ,Platelet activation ,Calcimycin ,business.industry ,Antibodies, Monoclonal ,Thrombosis ,General Medicine ,Molecular biology ,chemistry ,Immunology ,Acute Disease ,Chromatography, Gel ,business ,Platelet factor 4 ,medicine.drug ,circulatory and respiratory physiology ,Research Article - Abstract
The murine/human chimeric monoclonal antibody fragment (c7E3 Fab) blocks GPIIb/IIIa and alpha(v) beta(3) receptors, inhibits platelet aggregation, and decreases the frequency of ischemic events after coronary artery angioplasty in patients at high risk of suffering such events. Although inhibition of platelet aggregation is likely to be the major mechanism of c7E3 Fab's effects, since activated platelets facilitate thrombin generation, it is possible that c7E3 Fab also decreases thrombin generation. To test this hypothesis, the effects of c7E3 Fab and other antiplatelet agents were tested in a thrombin generation assay triggered by tissue factor. c7E3 Fab produced dose-dependent inhibition of thrombin generation, reaching a plateau of 45-50% inhibition at concentrations greater than or equal to 15 mu g/ml. It also inhibited thrombin-antithrombin complex formation, prothrombin fragment F-1+2 generation, platelet-derived growth factor and platelet factor 4 release, incorporation of thrombin into clots, and microparticle formation. Antibody 6D1, which blocks platelet GPIb binding of von Willebrand factor, had no effect on thrombin generation, whereas antibody 10E5, which blocks GPIIb/IIIa but not alpha(v) beta(3), receptors decreased thrombin generation by similar to 25%. Combining antibody LM609, which blocks alpha(v) beta(3) receptors, with 10E5 increased the inhibition of thrombin generation to similar to 32-41% The platelets from three patients with Glanzmann thrombasthenia, who lacked GPIIb/IIIa receptors but had normal or increased alpha(v) beta(3) receptors, supported similar to 25%. less thrombin generation than normal platelets. We conclude that thrombin generation initiated by tissue factor in the presence of platelets is significantly inhibited by c7E3 Fab, most likely in part through both GPIIb/IIIa and alpha(v) beta(3) blockade, and that this effect may contribute to its antithrombotic properties.
- Published
- 1996
26. A new regulatory function of activated factor V: inhibition of the activation by tissue factor/factor VII(a) of factor X
- Author
-
Rob Wagenvoord, R. Al Dieri, Hilde Kelchtermans, H.C. Hemker, Saartje Bloemen, Promovendi CD, Biochemie, and RS: CARIM School for Cardiovascular Diseases
- Subjects
medicine.drug_mechanism_of_action ,Lipoproteins ,Factor Xa Inhibitor ,Factor VIIa ,Thromboplastin ,chemistry.chemical_compound ,Tissue factor ,Tissue factor pathway inhibitor ,Thrombin ,Prothrombinase ,medicine ,Humans ,Blood Coagulation ,Factor VII ,biology ,Factor X ,anticoagulant ,Serine Endopeptidases ,Factor V ,Hematology ,tissue factor ,Molecular biology ,Antibodies, Neutralizing ,Recombinant Proteins ,Kinetics ,Protein Subunits ,chemistry ,Biochemistry ,Factor Va ,thrombin generation ,Factor Xa ,biology.protein ,factor VII ,Blood Coagulation Tests ,medicine.drug ,Factor Xa Inhibitors ,Protein Binding - Abstract
Summary Background We observed that minute amounts of thrombin or the enzyme Russell's viper venom activating factor V (RVV-V) added to plasma strongly diminish the potential of that plasma to generate thrombin after being triggered by tissue factor. Objective To find the mechanism behind this phenomenon. Methods and Results Thrombin generation (TG) initiated by tissue factor (TF) is strongly and dose-dependently inhibited by addition of activated factor V (FVa) or by addition of a factor V activator (thrombin or RVV-V). No inhibition is seen when TG is triggered via the intrinsic pathway or by direct activation of factor X. The effect is independent of proteins C and S and tissue factor pathway inhibitor (TFPI). In factor VII-deficient plasma the effect is seen when it is spiked with recombinant factor VII (FVII) and to a much lesser extent when spiked with recombinant FVIIa. In a purified system, FVa also dose-dependently inhibits the activation of FX by TF/FVII(a). The inhibitory effect is neutralized by antibodies against the light chain of FVa but not by antibodies against the heavy chain. Conclusions Our observations can be explained by assuming that FVa, via its light chain, binds to the complex TF/FVII(a) and prevents it from activating FX. We assume that this mechanism reduces the possibility that thrombin and factor Xa escaping from a wound area into the circulation, together with blood-borne tissue factor, would trigger intravascular coagulation.
- Published
- 2012
27. Is there value in kinetic modeling of thrombin generation? No (unless…)
- Author
-
S. Kerdelo, H.C. Hemker, Romy Kremers, Bedrijfsbureau CD, Promovendi CD, Biochemie, and RS: CARIM School for Cardiovascular Diseases
- Subjects
medicine.medical_specialty ,biology ,Chemistry ,medicine.medical_treatment ,Thrombin ,Hematology ,Thrombin generation ,Fibrin ,Article ,Endocrinology ,Internal medicine ,Fibrinolysis ,medicine ,biology.protein ,Animals ,Humans ,Partial Thromboplastin Time ,Blood Coagulation - Abstract
See also Stuijver DJF, Hooper JMW, Orme SM, van Zaane B, Squizzato A, Piantanida E, Hess K, Alzahrani S, Ajjan RA. Fibrin clot structure and fibrinolysis in hypothyroid individuals: the effects of normalising thyroid hormone levels. This issue, pp 1708–10.
- Published
- 2012
28. Functional properties of human factor Va lacking the Asp683-Arg709 domain of the heavy chain
- Author
-
L. Y. Yukelson, M. C. L. G. D. Thomassen, Jan Rosing, Guido Tans, H. M. Bakker, R. Ebberink, and H.C. Hemker
- Subjects
chemistry.chemical_classification ,Protease ,biology ,Stereochemistry ,medicine.medical_treatment ,Factor V ,Peptide ,Cell Biology ,Biochemistry ,Amino acid ,chemistry ,Prothrombinase ,biology.protein ,medicine ,Peptide bond ,Molecular Biology ,Polyacrylamide gel electrophoresis ,Peptide sequence - Abstract
A protease purified from the venom of the elapid snake Naja naja oxiana converts human blood coagulation factor Va into a molecule (factor VaNO) with greatly reduced cofactor activity. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed that the venom protease cleaved a small peptide from the heavy chain of factor Va and reduced the apparent M(r) from 105,000 to 101,000. This peptide was isolated by high performance liquid chromatography on a reversed-phase column. Amino acid sequence analysis of the peptide indicated that the venom enzyme cleaved the peptide bond between His682 and Asp683, thus removing 27 amino acids from the carboxyl-terminal part of the heavy chain. The cofactor activities of factors Va and VaNO were compared by measuring their abilities to support factor Xa-catalyzed prothrombin activation in the presence of phospholipids and calcium ions. Both factor Va molecules stimulated the binding of factor Xa to negatively charged phospholipids. However, the amounts of factor Va required for half-maximal incorporation of factor Xa into the membrane-bound factor Xa-Va complex were much lower for native factor Va (0.25 nM) than for factor VaNO (2.01 nM). At saturating concentrations of factor Va or factor VaNO the kcat values for prothrombin activation were 114 s-1 for factor Va and 128 s-1 for factor VaNO. The Km values for prothrombin determined under these conditions were 0.24 and 0.83 microM for prothrombinase complexes with native factor Va and factor VaNO, respectively. Direct binding studies revealed that factors Va and VaNO bind with equal affinity to phospholipids. These data indicate that factor VaNO is impaired in its ability to interact with factor Xa and prothrombin. Together with the structural data this implies that the carboxyl-terminal Asp683-Arg709 domain of the heavy chain is required for optimal interaction of factor Va with factor Xa and prothrombin.
- Published
- 1994
29. Kinetics of the inhibition of human factor Xa by full-length and truncated recombinant tissue factor pathway inhibitor
- Author
-
Ron Blezer, Theo Lindhout, George M. Willems, H.C. Hemker, and Biochemie
- Subjects
Stereochemistry ,Lipoproteins ,Kinetics ,Binding, Competitive ,Biochemistry ,Dissociation (chemistry) ,Structure-Activity Relationship ,Tissue factor ,Reaction rate constant ,Tissue factor pathway inhibitor ,Humans ,Binding site ,Molecular Biology ,Binding Sites ,biology ,Chemistry ,Osmolar Concentration ,Cell Biology ,Recombinant Proteins ,Enzyme inhibitor ,Factor Xa ,biology.protein ,Kunitz domain ,Factor Xa Inhibitors ,Research Article - Abstract
The inhibition equilibrium and kinetics of association and dissociation of the binding of three types of recombinant tissue factor pathway inhibitor (TFPI), namely full-length TFPI, C-terminal-truncated TFPI, and TFPI without the third Kunitz domain (TFPI1-161), to factor Xa have been measured. Formation and dissociation of the complexes were monitored by continuous measurement of the changes in the rate of hydrolysis of a peptidyl-p-nitroanilide substrate. Progress curves of product formation were fitted to a set of equations describing a one-step bimolecular inhibitory reaction in the presence of a competing substrate. For full-length TFPI the rate constants of association (kon) and dissociation (koff) were (5.1 +/- 0.7) x 10(6) M-1.s-1 and (2.6 +/- 0.9) x 10(-4)s-1 respectively. Thus, although the inhibition constant (50 pM) is far below the plasma concentration (2.5 nM) of TFPI, the half-time for transition to equilibrium in plasma is rather long (66s). The truncated forms of TFPI differ in that they have a 4-fold lower kon value but a similar dissociation rate constant. Therefore the inhibition constant, Ki, is 4-fold higher (0.2 nM) and the half-time to achieve equilibrium is prolonged to 250 s. The kon values of full-length and C-terminal-truncated TFPI, but not that of TFPI1-161, were found to decrease with increasing ionic strength.
- Published
- 1994
30. The Effect of Subcutaneous Injection of Unfractionated and Low Molecular Weight Heparin on Thrombin Generation in Platelet Rich Plasma - A Study in Human Volunteers
- Author
-
Kai H, A.V. Bendetowicz, R. W. C. Knebel, H Caplain, Theo Lindhout, Suzette Beguin, and H.C. Hemker
- Subjects
Subcutaneous injection ,Chemistry ,medicine.drug_class ,Platelet-rich plasma ,Healthy volunteers ,medicine ,Low molecular weight heparin ,Hematology ,Heparin ,Pharmacology ,Thrombin generation ,Critical length ,medicine.drug - Abstract
SummaryWe administered a dose of unfractionated heparin (UFH) and two doses of a low molecular weight heparin (LMWH) to healthy volunteers by SC injection. The doses given were: a) UFH, 5000IU, which represents 8.7 mg of >5,400 MW active heparin (ACLM) and no Excess amounts of platelet factor 4 (PF4) were able to neutralize completely the anti-thrombin activity in normal plasma spiked with enoxaparin as well as in plasma samples obtained after SC enoxaparin injection. With a large excess of PF4 the anti-factor Xa activity could be inhibited to a maximum of 50%. This indicates that ACLM (above critical length material, MW >5400) is neutralized completely by PF4 whereas BCLM (below critical length material, MW We conclude that in PRP the activity of the BCLM fraction of injected LMWH remains after platelet activation. The possible role of this activity in thrombin inhibition and in the antithrombotic action of low molecular weight heparins is discussed.
- Published
- 1994
31. An investigation of the coagulogical potential of the venoms of some Central Asian snakes
- Author
-
H.C. Hemker, L. Ya. Yukel'son, Guido Tans, É. S. Sadykov, N. A. Barabanshchikova, Jan Rosing, and Biochemie
- Subjects
chemistry.chemical_classification ,Viperid venom ,biology ,Chemistry ,Agkistrodon halys ,Venom ,Plant Science ,General Chemistry ,biology.organism_classification ,complex mixtures ,General Biochemistry, Genetics and Molecular Biology ,Enzyme ,Biochemistry ,Echis ,Chemical engineering - Abstract
The compositions of the proteolytic complexes of the venoms of the crotalid agkistrodon halys halysand the viperid echis multisquamatushave been investigated with the aid of a large number of specific natural and model substrates. A comparative analysis of the results obtained has revealed a predominance in the crotalid venom of fibrinogen-hydrolyzing enzymes, while the viperid venom is characterized as a procoagulant of the prothrombin-activating type. Among the fibrinogenases of the crotalid venom, a thrombin-like enzyme and a plasmin-like proteinase have been revealed and obtained in a purified state. A prothrombin-activating enzyme from the viperid venom has been isolated in the purified state and characterized with the aid of specific substrates.
- Published
- 1993
32. Protein C activation by an activator purified from the venom of Agkistrodon halys halys
- Author
-
L. Y. Yukelson, R M Bertina, Guido Tans, Truus Janssen-Claessen, H. M. Bakker, H.C. Hemker, Jan Rosing, and Biochemie
- Subjects
medicine.medical_treatment ,Trypsin inhibitor ,Molecular Sequence Data ,Sodium Chloride ,Benzamidine ,chemistry.chemical_compound ,Calcium Chloride ,Affinity chromatography ,Crotalid Venoms ,medicine ,Animals ,Humans ,Amino Acid Sequence ,Serine protease ,chemistry.chemical_classification ,Protease ,biology ,Activator (genetics) ,Fast protein liquid chromatography ,Hematology ,General Medicine ,Kinetics ,Enzyme ,chemistry ,Biochemistry ,Chromogenic Compounds ,biology.protein ,Cattle ,Protein C - Abstract
The protein C activator from Agkistrodon halys halys venom was purified 533-fold by ion-exchange chromatography on QAE-Sephadex A-50, affinity chromatography on aprotinin-Sepharose and Mono-Q fast protein liquid chromatography. The purified enzyme is a single chain protein with an apparent molecular weight of 36 000 that activates protein C by proteolytic removal of a small fragment from the heavy chain. The protein C activator exhibited a high amidolytic activity towards the tripeptide substrates D-Pro-Phe-Arg-pNA (S2302) and D-Phe-(pipecolyl)-Arg-pNA (S2238). The activity of the activator was not affected by thiolprotease or metalloprotease inhibitors. The activator was inhibited, however, by benzamidine, Phe-Pro-Arg chloromethyl ketone,p-nitrophenyl p-guanidinobenzoate and soy bean trypsin inhibitor, which classifies the enzyme as a serine protease. The purified protease was capable of activating both human and bovine protein C. Activation of human protein C only occurred at an appreciable rate in a calcium-free reaction medium at low ionic strength. Ca2+ ions inhibited the activation of human protein C with an apparent K(i) of 0.8 mM. Addition of NaCl to the reaction medium also strongly inhibited human protein C activation (50% inhibition at 20 mM NaCl). Kinetic analysis of human protein C activation by the venom activator (in a calcium-free medium) revealed an apparent K(m) for protein C of 0.52 muM and a k(cat) of 0.17 s-1 at 1 = 0.05 (k(cat)/K(m) = 3.3 X 10(5) M-1 s-1). At I = 0.15 rates of human protein C activation became linear with protein C indicating a strong increase in K(m) with increasing ionic strength. Activation of bovine protein C was hardly affected by variation of Ca2+ and NaCl concentrations in the reaction medium. The apparent K(i)s for calcium ion and NaCl inhibition of bovine protein C activation were > 10 mM and 220 mM, respectively. At I = 0.1 and in the absence of Ca2+ ions bovine protein C was activated with a K(m) of 0.056 muM and a k(cat) of 0.24 s-1 (k(cat)/K(m) = 4.3 x 10(6) M-1 s-1). Our data are indicative for a rather large conformational and/or structural difference between human and bovine protein C at physiological ionic strength.
- Published
- 1993
33. Thrombin generation is extremely sensitive to preheating conditions
- Author
-
E. De Smedt and H.C. Hemker
- Subjects
Chromatography ,Chemistry ,Kinetics ,Temperature ,Thrombin ,Reproducibility of Results ,Hematology ,Thrombin generation ,Calibration ,Humans ,Fluorometry ,Blood Coagulation Tests ,Blood Coagulation - Published
- 2010
34. Demonstration of three anomalous plasma proteins induced by a vitamin K antagonist
- Author
-
P.P.M. Reekers, B.H.M. Kop-Klaassen, H.C. Hemker, M.J. Lindhout, and Biochemie
- Subjects
medicine.medical_specialty ,Vitamin K ,medicine.drug_class ,Biochemistry, Genetics and Molecular Biology (miscellaneous) ,Antibodies ,Phenprocoumon ,Factor IX ,Internal medicine ,medicine ,Electrochemistry ,Animals ,Humans ,Cellulose ,Electrodes ,Electrophoresis, Agar Gel ,Chemistry ,Biological activity ,Blood Proteins ,Vitamin K antagonist ,Blood proteins ,Precipitating antibodies ,Endocrinology ,Coagulation ,Ethanolamines ,Factor X ,Cattle ,Prothrombin ,medicine.drug ,Subcellular Fractions - Abstract
With the aid of precipitating antibodies against the bovine coagulation factors II, IX, and X three immunologically non-identical proteins can be demonstrated that are induced by the administration of a vitamin K antagonist (phenprocoumon). Each of these proteins is immunologically identical to one of three coagulation factors mentioned. The proteins differ from normal coagulation factors (a) by a lack of biological activity; (b) by a faster anodic migration rate in the presence of Ca2+. The proteins appear in the plasma concomitantly with the decrease of the normal factor.
- Published
- 2009
35. Meizothrombin formation during factor Xa-catalyzed prothrombin activation. Formation in a purified system and in plasma
- Author
-
Robert F. A. Zwaal, Truus Janssen-Claessen, Guido Tans, Jan Rosing, H.C. Hemker, and Biochemie
- Subjects
Phospholipid ,Phosphatidylserines ,Biochemistry ,chemistry.chemical_compound ,Thrombin ,Prothrombinase ,medicine ,Humans ,Thromboplastin ,Platelet ,Molecular Biology ,Phospholipids ,Enzyme Precursors ,Factor X ,Factor V ,Cell Biology ,Phosphatidylserine ,Enzyme Activation ,Kinetics ,Coagulation ,chemistry ,Factor Xa ,Liposomes ,Prothrombin ,circulatory and respiratory physiology ,medicine.drug - Abstract
Meizothrombin and thrombin formation were quantitated during factor Xa-catalyzed activation of human prothrombin in reaction systems containing purified proteins and in plasma. In the purified system considerable amounts of meizothrombin accumulated when prothrombin was activated by factor Xa (with or without accessory components) under initial steady state conditions. The ratio of the rates of meizothrombin and thrombin formation was not influenced by variation of the pH, temperature, or ionic strength of the reaction medium. When 2 microM prothrombin was activated by the complete prothrombinase complex (factor Xa, factor Va, Ca2+, and phospholipid) 80-90% of the initially formed reaction product was meizothrombin. Lowering the prothrombin concentration from 2 to 0.03 microM caused a gradual decrease in the ratio of meizothrombin/thrombin formation from 5 to 0.6. When the phosphatidylserine content of the phospholipid vesicles was varied between 20 and 1 mol % and prothrombin activation was analyzed at 2 microM prothrombin the relative amount of meizothrombin formed decreased from 85 to 55%. With platelets, cephalin, or thromboplastin as procoagulant lipid, thrombin was the major reaction product and only 30-40% of the activation product was meizothrombin. We also analyzed complete time courses of prothrombin activation both with purified proteins and in plasma. In reaction systems with purified proteins substantial amounts of meizothrombin accumulated under a wide variety of experimental conditions. However, little or no meizothrombin was detected in plasma in which coagulation was initiated via the extrinsic pathway with thromboplastin or via the intrinsic pathway with kaolin plus phospholipid (cephalin, platelets, or phosphatidylserine-containing vesicles). Thus, thrombin was the only active prothrombin activation product that accumulated during ex vivo coagulation experiments in plasma.
- Published
- 1991
36. Membrane-mediated assembly of the prothrombinase complex
- Author
-
Peter L.A. Giesen, H.C. Hemker, George M. Willems, W. T. Hermens, and Biochemie
- Subjects
Chemistry ,Vesicle ,Bilayer ,Synthetic membrane ,Nanotechnology ,Cell Biology ,Biochemistry ,Dissociation constant ,Reaction rate constant ,Thrombin ,Membrane ,Prothrombinase ,medicine ,Biophysics ,Molecular Biology ,medicine.drug - Abstract
Prothrombinase assembly was studied on macroscopic planar bilayers consisting of 20% dioleoyl-phosphatidylserine (DOPS) and 80% dioleoyl-phosphatidylcholine (DOPC). The dissociation constant for the binding of factor Xa to the bilayer, measured by ellipsometry, was K(d) = 47 +/- 8 nM (mean +/- S.D.) and this value was lowered to K(d) = 2.2 +/- 0.3 pM by preadsorption of factor Va. This latter value was determined from direct measurement of steady-state thrombin production. A comparable value of K(d) = 1.0 +/- 0.1 pM was found by repeating these experiments in suspensions of phospholipid vesicles, and it was verified that prothrombinase assembly was not influenced by the addition of prothrombin.Using a minute amount (0.094 fmol cm-2) of preadsorbed factor Va, it was found that the rate of prothrombinase assembly exceeds the rate of collisions between Xa molecules from the buffer and the sparse Va molecules on the bilayer. Apparently, factor Xa adsorbs first to the membrane and then associates rapidly with factor Va by lateral diffusion. The data indicate almost instantaneous equilibrium of this complex formation on the surface with a lower limit for the bimolecular rate constant of k(on) = 2.8 x 10(13) (mol/cm2)-1 s-1.In suspensions of small phospholipid vesicles, prothrombinase assembly is collisionally limited and the value of k(on) should be proportional to vesicle diameter. This was verified with a method for estimation of k(on) values from thrombin generation curves. Values of 0.36 x 10(9) and 1.6 x 10(9) M-1 s-1 were found for vesicles of 20-30- and 60-80-nm diameter, respectively.
- Published
- 1991
37. Simulation model for thrombin generation in plasma
- Author
-
George M. Willems, Theo Lindhout, Hermens Wt, H.C. Hemker, and Biochemie
- Subjects
Hirudin ,Models, Biological ,Feedback ,Thromboplastin ,Reaction rate ,Thrombin ,Prothrombinase ,Physiology (medical) ,medicine ,Humans ,Computer Simulation ,biology ,Chemistry ,Antithrombin ,Factor V ,Hematology ,Heparin ,Plasma ,Hirudins ,Enzyme Activation ,Kinetics ,Factor Va ,Factor Xa ,biology.protein ,Biophysics ,Prothrombin ,medicine.drug ,Protein C - Abstract
A simulation model for the production of thrombin in plasma is presented. Values of the reaction rate constants as determined in purified systems are used and the model is tested by comparison of simulations of factor Xa, factor Va and thrombin generation curves with experimental data obtained in thromboplastin-activated plasma. Simulations of the effect of hirudin indicate that factor V is predominantly activated by thrombin and not by factor Xa. The model predicts a threshold value for the factor Xa production which, if exceeded, results in explosive and complete activation of prothrombinase. The dependence of this threshold value on different negative feedback reactions, e.g. the inactivation of thrombin and factor Xa by antithrombin III (+ heparin), is investigated. The threshold value, for control plasma in the range of 1–10 pM total factor Xa production, can be raised two orders of magnitude by accelerated inactivation of factor Xa and prothrombinase but is hardly affected by a tenfold increase in the rate of thrombin inactivation or by increased production of activated protein C. This latter effect, however, results in a more gradual input-response relation between factor Xa input and the extent of prothrombinase activation.
- Published
- 1991
38. Anwendung der Ellipsometrie zur Untersuchung von Biomaterialien
- Author
-
P.L.A. Giesen, H.A.M. Andree, H.C. Hemker, and Biochemie
- Subjects
Political science ,Hematology ,Humanities - Abstract
ZusammenfassungIm folgenden wird ein Überblick über die dynamische Ellipsometrie gegeben. Diese Meßtechnik wurde in unserem Labor entwickelt und ermöglicht es, die an eine Oberfläche adsorbierte Masse einer dünnen Schicht aus organischem Material kontinuierlich zu messen. Voraussetzung für die Anwendung dieser optischen Technik ist eine reflektierende Oberfläche. Auf dieser Fläche können mehrere Schichten übereinander »gestapelt« werden. Die Methode ist so sensitiv, daß einschichtige Lagen von Proteinen und Fetten leicht gemessen werden können. Genaue Messungen innerhalb kurzer Zeitfolgen (5-10 s) sind möglich.
- Published
- 1990
39. Binding of vascular anticoagulant alpha (VAC alpha) to planar phospholipid bilayers
- Author
-
Rudolf Hauptmann, George M. Willems, W. T. Hermens, H.C. Hemker, Chris P. M. Reutelingsperger, and Harry A. M. Andree
- Subjects
chemistry.chemical_classification ,Chromatography ,technology, industry, and agriculture ,Phospholipid ,chemistry.chemical_element ,Cell Biology ,Phosphatidic acid ,Calcium ,Biochemistry ,Divalent ,Dissociation constant ,Crystallography ,chemistry.chemical_compound ,chemistry ,Phospholipid Binding ,lipids (amino acids, peptides, and proteins) ,Lipid bilayer ,Sphingomyelin ,Molecular Biology - Abstract
Vascular anticoagulant alpha (VAC alpha, annexin V) is a member of the family of calcium and phospholipid binding proteins, the annexins. The binding properties of VAC alpha to phospholipid bilayers were studied by ellipsometry. Adsorption was calcium-dependent and completely reversible upon calcium depletion. Half-maximal adsorptions to phospholipid bilayers consisting of 100, 20, 5, and 1% dioleoyl-phosphatidylserine (DOPS) supplemented with dioleoyl-phosphatidylcholine (DOPC) were reached at Ca2+ concentrations of 0.04, 0.22, 1.5, and 8.6 mM. These surfaces all showed the same maximal adsorption of 0.22 +/- 0.01 micrograms of VAC alpha/cm2 (mean +/- S.D.). The adsorption to bilayers containing more than 10% DOPS was independent of VAC alpha concentrations in the range of 0.5-100 nM. Dissociation constants for VAC alpha binding to these surfaces were estimated to be below 2 x 10(-10) M. No adsorption was observed on pure DOPC bilayers at a Ca2+ concentration of 3 mM. The ability to mediate VAC alpha binding to 20% DOPS/80% DOPC bilayers was highly specific for Ca2+. The use of other divalent cations resulted in decreased binding in the order Cd2+ greater than Zn2+ greater than Mn2+ greater than Co2+ greater than Ba2+ greater than Mg2+. Zinc ions had a synergistic effect on Ca2(+)-dependent VAC alpha binding. The Ca2+ concentration needed for half-maximal binding to cardiolipin, dioleoyl-phosphatidylglycerol, DOPS, phosphatidylinositol, phosphatidic acid, dioleoyl-phosphatidylethanolamine, and sphingomyelin increased in that order. Adsorption was independent of the overall surface charge of the phospholipid membrane.
- Published
- 1990
40. Title Page / Table of Contents, Vol. 20, Supplement 1, 1990
- Author
-
P.G. Settembrini, I. Caramazza, Rosanna Abbate, Anna Maria Gori, K.-H. Usadel, G. Coggi, Sergio Coccheri, Valentin Fuster, R. Codemo, Domenico Prisco, Colin R. M. Prentice, Pietro Amedeo Modesti, H.C. Hemker, J. Harenberg, G. Zoppetti, Rita Paniccia, Monica Attanasio, G.G. Neri Semen, M. Lettino, K. Mall, A.L. Bloom, S. Roveri, G. Talarico, G. Galli, P. Prandoni, D.L. Heene, H. Bratsch, G. Stehle, F.A. Ofosu, Marc Verstraete, Ira M. Herman, E. Ambrosioni, M. Vigo, M. Bossi, N. Olivari, R. Lamberti, Ulf Lindahl, K.T. Preissner, G. Pezzuoli, Francesca Martini, Domenico Inzitari, Ilaria Cecioni, G. Andriuoli, E. Strocchi, K. Huck, Francesco Bonechi, A. Lotto, G.G. Neri Serneri, Luigi Amaducci, Alberto Fortini, S. Béguin, A.M. Cattelan, Luigi Tavazzi, B. Casu, G.F. Gensini, A. Ruol, G. Fratianni, G. Negri, Marc Cohen, Andrea Colella, A. Colombo, Betti Giusti, M. Blauth, Patricia A. D’Amore, and Ce. Dempfle
- Subjects
business.industry ,Physiology (medical) ,Library science ,Medicine ,Table of contents ,Hematology ,business ,Title page - Published
- 1990
41. New approaches for measuring coagulation
- Author
-
Marco Cattaneo, Gian Marco Podda, S. Béguin, C. H. Toh, J. Ingerslev, Trevor W. Barrowcliffe, Federico Lussana, Paolo Bucciarelli, Benny Sørensen, Anna Lecchi, H.C. Hemker, and Biochemie
- Subjects
Male ,medicine.medical_specialty ,Hemostasis ,business.industry ,Thrombin ,Hematology ,General Medicine ,Blood Coagulation Disorders ,Haemophilia ,medicine.disease ,Hemophilia A ,Thrombin generation ,Waveform analysis ,Coagulation ,Von willebrand ,medicine ,Thrombelastography ,Humans ,Blood Coagulation Tests ,Intensive care medicine ,business ,Thrombin generation test ,Genetics (clinical) - Abstract
Summary. Although specific assays of coagulation factors are essential for diagnostic purposes they only give partial information about an individual's haemostatic state. This can be better assessed by various global tests, and recent developments and evaluations of five such tests are described in this symposium: the PFA-100; waveform analysis; thrombin generation; overall haemostasis potential; thrombelastography. Each test has advantages in various applications, but the thrombin generation test and waveform analysis have been found most useful in haemophilia, whilst the PFA-100 is helpful in von Willebrand's disease.
- Published
- 2006
42. The limits of simulation of the clotting system
- Author
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Piet Hemker, R. Wagenvoord, H.C. Hemker, Biochemie, Analysis (KDV, FNWI), and Scientific Computing
- Subjects
Factor VIII ,Estimation theory ,Thrombomodulin ,Reaction scheme ,Thrombin ,Factor V ,Hematology ,Function (mathematics) ,Bioinformatics ,Hemophilia A ,Thrombin generation ,Models, Biological ,Exponential growth ,Factor X ,Humans ,Computer Simulation ,Prothrombin ,Biological system ,Blood Coagulation ,Mathematics ,Free parameter ,Mathematical simulation ,Protein C - Abstract
Objective: To investigate in how far successful simulation of a thrombin generation (TG) curve gives information about the underlying biochemical reaction mechanism.Results: The large majority of TG curves do not contain more information than can be expressed by four parameters. A limited kinetic mechanism of six reactions, comprising proteolytic activation of factor (F) X and FII, feedback activation of FV, a cofactor function of FVa and thrombin inactivation by antithrombin can simulate any TG curve in a number of different ways. The information content of a TG curve is thus much smaller than the information required to describe a physiologically realistic reaction scheme of TG. Consequently, much of the input information is irrelevant for the output. FVIII deficiency or activation of protein C can, for example, be simulated by a reaction mechanism in which these factors do not occur.Conclusion: A model that comprises not more than six reactions can simulate the same TG curve in a number of possible ways. The possibilities increase exponentially as the model grows more realistic. Successful simulation of experimental data therefore does not validate the underlying assumptions. A fortiori, simulation that is not checked against experimental data lacks any probative force. Simulation can be of use, however, to detect mistaken hypotheses and for parameter estimation in systems with fewer than five free parameters.
- Published
- 2006
43. Laboratory monitoring of low-molecular-weight heparin therapy: Part II
- Author
-
Suzette Beguin, H.C. Hemker, R. Al Dieri, and Biochemie
- Subjects
Low molecular weight heparin therapy ,medicine.diagnostic_test ,business.industry ,Laboratory monitoring ,medicine ,MEDLINE ,Hematology ,Heparin ,Bioinformatics ,business ,medicine.drug ,Partial thromboplastin time - Published
- 2005
44. Calibrated automated thrombinography (CAT)
- Author
-
H.C. Hemker and Biochemie
- Subjects
Chromatography ,business.industry ,Calibration (statistics) ,Medicine ,Hematology ,Chromogenic Compounds ,business ,Blood coagulation test - Published
- 2005
45. The ionic contrast medium ioxaglate interferes with thrombin-mediated feedback activation of factor V, factor VIII and platelets
- Author
-
H.C. Hemker, R. Al Dieri, Suzette Beguin, and Biochemie
- Subjects
Radiographic contrast media ,Abciximab ,Contrast Media ,In Vitro Techniques ,Fibrinogen ,Feedback ,Immunoglobulin Fab Fragments ,Thrombin ,Fibrinolytic Agents ,medicine ,Ioxaglic Acid ,Humans ,Platelet ,Drug Interactions ,Platelet activation ,Factor VIII ,biology ,Chemistry ,Heparin ,Antithrombin ,Factor V ,Angiography ,Antibodies, Monoclonal ,Thrombosis ,Hematology ,Platelet Activation ,Immunology ,biology.protein ,Biophysics ,Fibrinolytic agent ,circulatory and respiratory physiology ,medicine.drug - Abstract
Clinical observation shows that radiographic contrast media (CM) may influence thrombus formation. In the search for the underlying mechanism, we have shown that the ionic CM ioxaglate is a potent inhibitor of thrombin generation in platelet-poor and platelet-rich plasma, whereas the influence of the non-ionic contrast medium iodixanol is minimal. Ioxaglate boosts the inhibitory effect of the platelet GPIIb/IIIa antagonist abciximab and the effects of ioxaglate and heparin are additive. Ioxaglate inhibits the clotting of fibrinogen and the activation of factors V and VIII, and of platelets by thrombin. It does not inhibit hydrolysis of small chromogenic thrombin substrates, nor does it influence the heparin-catalyzed inactivation of thrombin by antithrombin. We assume therefore that ioxaglate interferes with the binding of macromolecular substrates to the anionic exosite I of thrombin. The biological correlation to the observed antithrombotic effect of ioxaglate is then to be found in the inhibition of thrombin generation via inhibition of thrombin-mediated feedback activations.
- Published
- 2003
46. Fundamental Mechanisms Implicated in Thrombosis: New Aspects
- Author
-
S. Lvy-Toledano and H.C. Hemker
- Subjects
medicine.medical_specialty ,business.industry ,Family medicine ,International congress ,medicine ,medicine.disease ,business ,Thrombosis ,Surgery - Published
- 1999
47. Venous and Arterial Thrombosis: Pathophysiological and Clinical Aspects
- Author
-
H.C. Hemker and S. Lvy-Toledano
- Subjects
medicine.medical_specialty ,business.industry ,International congress ,General surgery ,Medicine ,business ,medicine.disease ,Thrombosis ,Pathophysiology ,Surgery - Published
- 1999
48. Endogenous thrombin potential
- Author
-
H.C. Hemker and S. Béguin
- Subjects
medicine.medical_specialty ,Chemistry ,medicine.drug_class ,Anticoagulant ,Thrombin generation ,Tissue factor ,Thrombin ,Endocrinology ,Endogenous Thrombin Potential ,Internal medicine ,medicine ,Peak value ,circulatory and respiratory physiology ,medicine.drug - Abstract
The one and only function of the clotting system is to generate thrombin in the amounts and at the site required for haemostasis. The endogenous thrombin potential (ETP), is a parameter that reflects this function quantitatively1,2. The combined action of the procoagulant and anticoagulant systems in the blood is reflected in the course of thrombin concentration in a sample of blood after the clotting system is triggered, i.e. in the thrombin-generation curve (TGC; Figure 7.1). Such curves are characterized by an optional lag phase, a rise to a peak value and a decline to zero in the course of approximately 10 min.
- Published
- 1999
49. Heterogeneity in microparticle formation and exposure of anionic phospholipids at the plasma membrane of single adherent platelets
- Author
-
Johan W. M. Heemskerk, Theo Lindhout, Jacob J. Briedé, H.C. Hemker, Gezondheidsrisico Analyse en Toxicologie, Humane Biologie, Biochemie, and RS: NUTRIM School of Nutrition and Translational Research in Metabolism
- Subjects
Anions ,Blood Platelets ,Platelet morphology ,Calcium Chloride ,chemistry.chemical_compound ,Thrombin ,Anionic phospholipid exposure ,Annexin ,Cell Adhesion ,Image Processing, Computer-Assisted ,Extracellular ,medicine ,Humans ,Microscopy, Phase-Contrast ,Platelet ,Annexin A5 ,Particle Size ,Cytoskeleton ,Molecular Biology ,Phospholipids ,Cell Size ,Fluorescent Dyes ,Binding Sites ,Microscopy, Confocal ,Calpain ,Chemistry ,Platelet adhesion ,Microvesicle ,Cell Membrane ,Fibrinogen ,Dipeptides ,Cell Biology ,Phosphatidylserine ,Membrane vesiculation ,Microvesicles ,Calcium response ,Biochemistry ,Biophysics ,Calcium ,Fura-2 ,medicine.drug - Abstract
Adherent platelets were examined for their ability to form microvesicles and procoagulant sites for thrombin formation. Epifluorescence and phase-contrast microscopy were employed to visualize shape changes, changes in intracellular Ca(2+) levels ([Ca(2+)](i)), vesiculation of the plasma membrane and appearance of anionic phospholipids in the outer leaflet of the plasma membrane, as probed by annexin V binding. In the absence of extracellular Ca(2+) two stable populations of adherent platelets were observed. The majority of the adherent platelets were fully spread and about 10% remained in a non-spread dendritic state. In the presence of extracellular Ca(2+) vesiculation at the surface of spread platelets occurred at a rather slow rate (10% of the platelets after 20 min) concomitantly with an increase in [Ca(2+)](i) and binding of annexin V. However, a small fraction of the adherent platelets ( approximately 1%) responded much faster. Ionomycin-enhanced influx of Ca(2+) in dendritic platelets resulted in a rapid transformation of these platelets into inflated, balloon-shaped, platelets having a diameter of 2.0+/-0.7 microm without notable microvesicle formation. In contrast, fully spread platelets retained their shape but obtained frayed edges as a result of microvesicle formation. Confocal scanning fluorescence microscopy indicated that annexin V bound to very distinct sites at the outer plasma membrane of spread as well as balloon-shaped platelets. Inhibition of platelet calpain activity suppressed ionomycin-enhanced microvesicle formation and ballooning of platelets, but not annexin V binding. These findings indicate that vesiculation and ballooning, but not the exposure of phosphatidylserine at the outer leaflet of the adherent platelet membrane, are associated with cytoskeleton destruction. Altogether, the data suggest a similar relationship between [Ca(2+)](i) and the formation of platelet procoagulant sites as reported for platelets in suspension. However, the present investigations on single adherent platelets reveal for the first time that adhesion and spreading of platelets is not necessarily associated with the appearance of procoagulant sites. Secondly, an unexpected diversity was observed among adherent platelets with respect to sensitivity to Ca(2+)-induced generation of procoagulant sites and Ca(2+)-induced vesiculation of plasma membrane. It is tempting to speculate that this diversity is of importance for the procoagulant response of platelets to a hemostatic challenge elicited by an injured vessel wall.
- Published
- 1999
50. Mathematical and biological models of blood coagulation. A rebuttal
- Author
-
H.C. Hemker, Piet Hemker, de E. Smedt, Analysis (KDV, FNWI), Biochemie, and Scientific Computing
- Subjects
medicine.medical_specialty ,business.industry ,Rebuttal ,medicine ,Coagulation (water treatment) ,Hematology ,Intensive care medicine ,business - Published
- 2006
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