PubMed Health⌕ Search

Biomedical subjects

H Kessels

Publications and source records attributed to H Kessels.

8 recordsLinked to original sources
PubMed1996

Inhibition of platelet-mediated, tissue factor-induced thrombin generation by the mouse/human chimeric 7E3 antibody. Potential implications for the effect of c7E3 Fab treatment on acute thrombosis and "clinical restenosis".

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 > or = 15 micrograms/ml. It also inhibited thrombin-antithrombin complex formation, prothrombin fragment F1-2 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 approximately 25%. Combining antibody LM609, which blocks alpha v beta 3 receptors, with 10E5 increased the inhibition of thrombin generation to approximately 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 approximately 21% 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.

Acute Disease↗
PubMed1994

Analysis of thrombin generation in plasma.

Thrombin is the central enzyme of haemostasis. Information on the production and inhibition of thrombin in plasma is important for evaluating the state of the coagulation system. Measurement of thrombin generation in plasma using small oligopeptide chromogenic substrates gives rise to a signal that not only reflects the enzymatic activity of free thrombin, but also contains a contribution of the complex of thrombin with one of its inhibitors, alpha 2-macroglobulin. This paper describes a mathematical procedure to extract from the measured curves the signal due to free thrombin only. The time integral of this free thrombin curve, which we call the thrombin potential, is a parameter which condenses much of the information present in such a curve. Thrombin production from prothrombin can be calculated from the concentration of free thrombin, when the rate constants governing the decay of thrombin are known. It is described how this calculation can be performed, accounting for the consumption of some of the inhibitors of thrombin during coagulation. Measurement of the time integral of the thrombin concentration promises clinical applicability of thrombin generation tests. It is based on the continuous registration of conversion of chromogenic substrate by thrombin during coagulation in plasma. It is shown how the curves obtained by this test can be analysed by a procedure which is analogous to the analysis of curves measured by subsampling from clotting plasma.

Blood Coagulation↗
PubMed1994

Measurement of thrombin generation in whole blood--the effect of heparin and aspirin.

A technique has been developed to monitor the development of thrombin in freshly collected whole blood in the absence of anticoagulants. It is based on the centrifugal separation of the cellular components from subsamples of blood drawn from non-anticoagulated clotting whole blood which are diluted in buffer containing a chromogenic substrate. It is shown that the burst of thrombin generation after triggering coagulation with trace amounts of tissue thromboplastin occurs sooner in non-anticoagulated whole blood than in citrated whole blood. Heparin is shown to prolong the lag-time of thrombin generation more in native blood than in recalcified citrated blood. It is also demonstrated that intake of 500 mg of aspirin significantly delays and inhibits thrombin generation in non-anticoagulated, thromboplastin triggered whole blood, whereas it has no effect on the coagulation in citrated plasma. The effect of aspirin intake on thrombin generation in blood is roughly equal to that of 0.03 U/ml of unfractionated heparin. This demonstrates that platelet reactions and the coagulation system are closely linked processes. It further lends support to the hypothesis that inhibition of thrombin generation is a common denominator of antithrombotic therapy.

Aspirin↗
PubMed1993

Continuous registration of thrombin generation in plasma, its use for the determination of the thrombin potential.

A method is described by which the time-course of thrombin generation in plasma can be obtained from a continuous optical density recording of p-nitroaniline (pNA) production in a 2:3 diluted plasma. A chromogenic substrate, methylmalonyl-methylanalyl-arginyl-pNA (SQ 68), is used that is specifically split by thrombin but at a low rate. The thrombin that appears and disappears in the plasma does not split more than 5% of the substrate added, so the rate of substrate conversion is in good approximation proportional to the amidolytic activity in the plasma over the entire period of thrombin generation. The course of the enzyme concentration can be calculated from the amidolytic activity curve. It is shown that the thrombin generation curves obtained in this way are essentially identical to those obtained via the classical subsampling method. The presence of SQ 68 influences the amount of free thrombin that appears in plasma because it competitively inhibits the inactivation of thrombin by AT III and alpha 2 macroglobulin. The inhibition of the thrombin peak by heparin, relative to an uninhibited control, remains unaltered by the presence of the substrate. From the course of thrombin activity and the prevailing decay constants, the course of prothrombin conversion velocity can be calculated. Prothrombin conversion was seen to be inhibited at high (> 500 microM) substrate concentrations only, and experimental conditions are found under which the inhibition of the clotting process by the substrate is negligible. The amidolytic activity is the sum of the activities of free thrombin and of the alpha 2 macroglobulin-thrombin complex formed.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromogenic Compounds↗
PubMed1992

The consumption of antithrombin III during coagulation, its consequences for the calculation of prothrombinase activity and the standardisation of heparin activity.

The decay rate of thrombin in plasma is shown to be linearly proportional to the concentration of antithrombin III (AT III), not only in the absence but also in the presence of heparin. This is a consequence of partitioning of heparin between AT III and other plasma proteins. In previous articles were calculated the prothrombin converting activity assuming a fixed concentration of AT III. Since AT III is consumed during the clotting process, prothrombinase activity is more accurately approximated using an algorithm that counts with the decrease of the AT III concentration. It is shown this leads to higher prothrombinase activities. The (absence of) inhibition of prothrombin conversion by prothrombinase in the presence of heparins found with the previous method is also found using the new algorithm. From the results presented it is evident that characteristic parameters of heparin action have to be normalised to the AT III concentration. On this basis we define a Standard Independent Unit of the antithrombin activity of heparin.

Antithrombin III↗
PubMed1991

A method for measuring activated factor VIII in plasma.

A method is described which enables a quantitative measurement of the concentration of activated factor VIII (VIIIa) in plasma. Based on the ability of factor VIIIa to accelerate the activation of factor X by factor IXa, phospholipid and calcium ions, the course of factor X activation in time is measured using a chromogenic substrate. Free factor Xa is able to activate nonactivated factor VIII present in a plasma sample, which increases the factor X activation velocity, and thus disturbs the measurement of factor VIIIa. Furthermore, factor Xa was found to be inactivated by serine protease inhibitors from the plasma sample. By adding surplus chromogenic substrate these reactions of factor Xa are inhibited and at the same time the rate of substrate conversion is a measure of the amount of factor Xa present. Factor X activation and amidolysis of chromogenic substrate then take place simultaneously. It is shown that under proper conditions the factor X activation velocity is linearly proportional to the factor VIIIa concentration. This causes the optical density to increase as a parabolic function of time. The concentration of factor VIIIa can be obtained from the quadratic coefficient of the equation describing the parabola. The method is specific for factor VIIIa in that the extrinsic factor X activator is shown to have no influence on the measurement of factor VIIIa in thromboplastin activated plasma. We conclude that a sensitive and reliable method for assessing factor VIIIa concentrations in plasma has been developed on the basis of simultaneous inhibition and measurement of factor Xa by a high concentration of chromogenic substrate.

Chromogenic Compounds↗