Tag Archives: platelets

Clot formation and lysis in platelet rich plasma of healthy donors and patients with resistant hypertension

I. I. Patalakh1, O. V. Revka1, O. B. Kuchmenko2, O. O. Matova2, T. F. Drobotko2, T. V. Grinenko1

1Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: sedrickedel@gmail.com
2National Scientific Center “Strazhesko Institute of Cardiology” NAMS of Ukraine, Kyiv

Hemostatic balance in blood is affected by numerous factors, including coagulation and fibrinolytic proteins, the wide spectrum of their inhibitors, and blood cells. Since platelets can participate in contradictory processes, they significantly complicate the whole picture. Therefore, nowadays the development of global assays of hemostasis, which can reflect the physiological process of hemostasis and can be used for point-of-care diagnosis of thrombosis, is crucial. This paper outlines a new approach we used to analyze the capabilities of clot waveform analysis tools to distinguish the response of platelet-rich plasma from healthy donors and patients with arterial hypertension caused by stimulation of coagulation and lysis (with exogenous thrombin and recombinant tissue-type plasminogen activator, respectively). In donor plasma, when the clot degradation was accompanied by 40 IU/ml of recombinant tissue-type plasminogen activator, platelets potentiated fibrinolysis more than coagulation, which ultimately shifts the overall balance to a profibrinolytic state. At the same time, for patients with hypertension, platelets, embedded in clot obtained from platelet-rich plasma, showed a weaker ability to stimulate fibrinolysis. The obtained data gives the evidence that platelets can act not only as procoagulants but also as profibrinolytics. By simultaneously amplifying coagulation and fibrinolysis, making their rates comparable, platelets would control plasma procoagulant activity, thereby regulating local hemostatic balance, the size and lifetime of the clot. Moreover, clot waveform analysis may be used to distinguish the effects of platelet-rich plasma on clotting or lysis of fibrin clots in healthy donors and patients with essential hypertension.

Glu- and Lys-forms of plasminogen differentially affect phosphatidylserine exposure on the platelet surface

D. D. Zhernossekov, Y. M. Roka-Moiia, A. O. Tykhomyrov,
M. M. Guzyk, T. V. Grinenko

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: chemikdd@mail.ru

Plasminogen/plasmin system is known for its ability to support hemostatic balance of blood. However, plasminogen may be considered as an adhesive ligand and in this way could affect the functioning of blood cells. We showed that exogenous Lys-plasminogen, but not its Glu-form, inhibited platelet aggregation and suppressed platelet α-granule secretion. The aim of this work was to investigate the influence of Glu- and Lys-form of plasminogen on the formation of platelet procoagulant surface using phosphatidylserine exposure as a marker. Human platelets were obtained from human platelet-rich plasma (donors were healthy volunteers, men aged 30-40 years) by gel-filtration on Sepharose 2B. Phosphatidylserine exposure on the platelet surface was evaluated by flow cytometry with FITC-conjugated annexin A5. Glu- and Lys-plasminogen have different impact on the platelet functioning. Exogenous Lys-plasminogen has no significant effect on phosphatidylserine exposure, while Glu-plasminogen increases phosphatidylserine exposure on the surface of thrombin- and collagen-activated human platelets. Glu-plasminogen can be considered as a co-stimulator of agonist-induced platelet secretion and procoagulant surface formation. Meanwhile effects of Lys-plasminogen are probably directed at platelet-platelet interactions and not related to agonist-stimulated pro-apoptotic changes. The observed different effects of Glu- and Lys-plasminogen on phosphatidylserine exposure can be explained by their structural peculiarities.

The search of compounds with antiaggregation activity among S-esters of thiosulfonic acids

T. I. Halenova1, I. V. Nikolaeva1, A. V. Nakonechna2,
K. B. Bolibrukh2, N. Y. Monka2, V. I. Lubenets2,
O. M. Savchuk1, V. P. Novikov2, L. I. Ostapchenko1

1Educational and Scientific Centre “Institute of Biology”,
Taras Shevchenko National University of Kyiv, Ukraine;
2Lviv Polytechnic National University, Ukraine;
е-mail: galenovatanya@rambler.ru

According to the current understanding, the hyperactivation of platelets may lead to increased intravascular coagulation and thrombosis. Today a relevant issue is the search for new anti-thrombotic agents that are able to modulate the activity of platelet receptors, thus, influence the processes of activation and aggregation of platelets. The aim of this study was to investigate the effects of newly synthesized thiosulfonate derivatives on platelet aggregation. The activity of the compounds was tested in vitro using platelet-rich plasma. As a result of the screening test, structural formulas of four agents with high antiaggregative activity were established. These compounds inhibited ADP- and collagen-induced platelet aggregation in a dose-dependent manner. Two of these compounds were shown to be more effective inhibitors of aggregation induced by ADP (IC50 ~ 8-10 µM), as well as collagen (IC50 ~ 1.5-2.0 µM).

Dynamics of thrombin-induced exposition of actin on the platelet surface

A. A. Tykhomyrov

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: artem_tykhomyrov@ukr.net

Platelets play the key role in thrombosis and are also involved in angiogenesis as well as immune and reparative responses. In the function cascade, platelets undergo a complex cell processing, and subcellular fragments, not detectable in the resting state, are exposed on platelet surface after stimulation with agonists. This study has been performed to evaluate dynamic characteristics of actin exposition on the surface of plasma membrane of thrombin-activated platelets. Using flow-cytometric assay, it has been observed that the level of actin presented on activated platelets directly depends on agonist concentration. In the case of platelet stimulation with thrombin in the highest concentration (1.0 U/ml) taken for this study, the level of actin exposed on activated platelets was up to 4.4 times higher as compared with resting cells. Confirmation of the flow cytometry data for cell-surface actin on thrombin-activated platelets was achieved by direct visualization using a confocal laser scanning microscopy. Period of actin exposition appeared to be longer than the time phase corresponding to platelet secretion stage. Functional role of platelet surface actin has required further detailed studying, however, it is thought that superficial actin could interact with various blood plasma proteins, including plasminogen and its activators, serving as a binding site and/or center for their pericellular processing.