Properties of blood cells and their interaction determine their distribution in flow. It is observed experimentally that erythrocytes migrate to the flow axis, platelets to the vessel wall, and leucocytes roll along the vessel wall. In this work, a three-dimensional model based on Dissipative Particle Dynamics method and a new hybrid (discrete-continuous) model for blood cells is used to study the interaction of erythrocytes with platelets and leucocytes in flow. Erythrocytes are modelled as elastic highly deformable membranes, while platelets and leucocytes as elastic membranes with their shape close to a sphere. Separation of erythrocytes and platelets in flow is shown for different values of hematocrit. Erythrocyte and platelet distributions are in a good qualitative agreement with the existing experimental results. Migration of leucocyte to the vessel wall and its rolling along the wall is observed.

No abstract

Curcumin is a natural bioactive component derived from the turmeric plant Curcuma longa, which exhibits a range of beneficial activities on human cells. Previously, an inhibitory effect of curcumin on platelets was demonstrated. However, it is unknown whether this inhibitory effect is due to platelet apoptosis or procoagulant platelet formation. In this study, curcumin did not activate caspase 3-dependent apoptosis of human platelets, but rather induced the formation of procoagulant platelets. Interestingly, curcumin at low concentration (5 µM) potentiated, and at high concentration (50 µM) inhibited ABT-737-induced platelet apoptosis, which was accompanied by inhibition of ABT-737-mediated thrombin generation. Platelet viability was not affected by curcumin at low concentration and was reduced by 17% at high concentration. Furthermore, curcumin-induced autophagy in human platelets via increased translocation of LC3I to LC3II, which was associated with activation of adenosine monophosphate (AMP) kinase and inhibition of protein kinase B activity. Because curcumin inhibits P-glycoprotein (P-gp) in cancer cells and contributes to overcoming multidrug resistance, we showed that curcumin similarly inhibited platelet P-gp activity. Our results revealed that the platelet inhibitory effect of curcumin is mediated by complex processes, including procoagulant platelet formation. Thus, curcumin may protect against or enhance caspase-dependent apoptosis in platelets under certain conditions.

Platelet activating receptor CLEC-2 has been identified on platelet surface a decade ago. The only confirmed endogenous CLEC-2 agonist is podoplanin. Podoplanin is a transmembrane protein expressed by lymphatic endothelial cells, reticular fibroblastic cells in lymph nodes, kidney podocytes and by cells of certain tumors. Association of CLEC-2 with podoplanin is involved in processes of embryonic development (blood-lymph vessel separation and angiogenesis), maintaining of vascular integrity of small vessels during inflammation and prevention of blood-lymphatic mixing in high endothelial venules. However, CLEC-2 and podoplanin are contributing to tumor metastasis progression, Salmonella sepsis and deep-vein thrombosis. This makes CLEC-2 and podoplanin a perspective target for pharmacological treatment. Aspirin and Ibrutinib are considered to be perspective for abrogation of podoplanin-induced platelet activation via CLEC-2. The present review discusses already known pathological and physiological roles of CLEC-2 and possibilities of a targeted therapy for CLEC-2 associated diseases.

Platelets are anucleate blood cells circulating in the bloodstream for up to 9 days in quiescent state. Upon vessel wall injury, platelets become activated, change their shape and adhere to the vessel wall and each other, thus forming a thrombus and preventing the blood loss. To get energy for these processes, they can use oxidative phosphorylation and glycolysis utilizing blood glucose, stored glycogen or fatty acids as fuel. Yet, there is no agreement in experimental data on platelet functioning in quiescent and activated states. This study is a systematic analysis of the energy abilities of quiescent platelets through mathematical modeling of their energy metabolism by Flux Balance Analysis (FBA). As a result of the FBA analysis we concluded that a platelet T.O. Shepelyuk et al. PBPK/PD and FBA of blood platelet __________________________________________ even in quiescent state utilizes blood glucose at high rate (0.1 mM/s), producing lactate from 99% of it and about 0.2 mM/s ATP from glycolysis and respiration. Such high fluxes of glucose are not always available due to platelet's glucose transporter (GLUT3) kinetic limitations. We positioned a "FBA" platelet in human glucose/insulin/glucagon PBPK/PD model to theoretically investigate platelet metabolism in close-to-real conditions. The main result of our study is that the stored glycogen could be daily used and resynthesized during platelet lifetime.

Platelet participation in hemostatic plug formation requires transition into an activated state (or, rather, variety of states) upon action of agonists like ADP, thromboxane A , collagen, thrombin, and others. The mechanisms of action for different agonists, their receptors and signaling pathways associated with them, as well as the mechanisms of platelet response inhibition are the subject of the present review. Collagen exposed upon vessel wall damage induced initial platelet attachment and start of thrombus formation, which involves numerous processes such as aggregation, activation of integrins, granule secretion and increase of intracellular Ca2+. Thrombin, ADP, thromboxane A , and ATP activated platelets that were not initially in contact with the wall and induce additional secretion of activating substances. Vascular endothelium and secretory organs also affect platelet activation, producing both positive (adrenaline) and negative (prostacyclin, nitric oxide) regulators, thereby determining the relation of activation and inhibition signals, which plays a significant role in the formation of platelet aggregate under normal and pathological conditions. The pathways of platelet signaling are still incompletely understood, and their exploration presents an important objective both for basic cell biology and for the development of new drugs, the methods of diagnostics and of treatment of hemostasis disorders.

No abstract

Patients with oncohematological diseases, both children and adults, face high risks of thrombotic and hemorrhagic complications.About 40 % of pediatric patients with acute lymphoblastic leukemia develop bleedings, and the incidence of thrombosis in this disease ranges from 1 to 36 %. Most thromboses are associated with the use of central venous catheters and the use of L-asparaginase, which leads to a significant reduction in the synthesis of coagulation proteins.Massive hemorrhages account for two-thirds of all causes of early death in pediatric patients with acute myelogenous leukemia (AML). Absolute risks of death due to bleeding and leukostasis range from 1.8 % in the total population of children with AML to 14.3 % in a population with hyperleukocytosis more than 200 × 109 /l. The risk of thrombotic complications in children with AML varies between 3.4–11 %. In patients with AML, complex systemic coagulopathies may occur, such as disseminated intravascular coagulation (DIC), excessive fibrinolysis, or nonspecific proteolysis. This scale is not yet applicable due to the lack of research on its effectiveness in the pediatric population. The laboratory diagnostics of hemostasis is difficult due to the combined nature of thrombotic and hemorrhagic complications: bleeding, thrombosis and even DIC syndrome (combining both hyper- and hypocoagulation phases) can be expected in each specific patient with hemoblastosis. Because of the long-term nature of the treatment and the varying intensity of the various treatment units, the patient’s hemostasis during disease manifestation does not allow one to predict with any certainty the complications on induction or consolidation therapy. Involving all the components of the hemostasis system – vascular, platelet and plasma – into the pathological process makes prediction and diagnosis of thrombohemorrhagic complications impossible with the help of standard hemostatic tests and a general blood test, since these tests are designed to assess the concentrations of individual proteins and the functioning of individual components of the hemostatic system, and does not assess the balance between its procoagulant and anticoagulant components. Global hemostatic tests such as thromboelastography, thrombodynamics and thrombin generation test adequately reflect hypercoagulable conditions and can serve as a basis for the development of a new set of laboratory hemostasis tests.Conflict of interest. F.I. Ataullakhanov is co-founder of HemaCore LLC, which holds several patents and patent applications that are related to the diagnostic use of Thrombodynamics® (Ataullakhanov F.I., international patent applications: PCT/CH2007/000543 filing date 02.11.2007 and РСТ/RU2012/000570 filing date 16.07.2012). None of the other authors has any competing interests to declare.