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Biomedical subjects

Mikhail A Panteleev

Publications and source records attributed to Mikhail A Panteleev.

7 recordsLinked to original sources
PubMed2006

Factor VIIIa regulates substrate delivery to the intrinsic factor X-activating complex.

Activation of coagulation factor X (fX) by activated factors IX (fIXa) and VIII (fVIIIa) requires the assembly of the enzyme-cofactor-substrate fIXa-fVIIIa-fX complex on negatively charged phospholipid membranes. Using flow cytometry, we explored formation of the intermediate membrane-bound binary complexes of fIXa, fVIIIa, and fX. Studies of the coordinate binding of coagulation factors to 0.8-microm phospholipid vesicles (25/75 phosphatidylserine/phosphatidylcholine) showed that fVIII (fVIIIa), fIXa, and fX bind to 32 700 +/- 5000 (33 200 +/- 14 100), 20 000 +/- 4500, and 30 500 +/- 1300 binding sites per vesicle with apparent K(d) values of 76 +/- 23 (71 +/- 5), 1510 +/- 430, and 223 +/- 79 nm, respectively. FVIII at 10 nm induced the appearance of additional high-affinity sites for fIXa (1810 +/- 370, 20 +/- 5 nm) and fX (12 630 +/- 690, 14 +/- 4 nm), whereas fX at 100 nm induced high-affinity sites for fIXa (541 +/- 67, 23 +/- 5 nm). The effects of fVIII and fVIIIa on the binding of fIXa or fX were similar. The apparent Michaelis constant of the fX activation by fIXa was a linear function of the fVIIIa concentration with a slope of 1.00 +/- 0.12 and an intrinsic K(m) value of 8.0 +/- 1.5 nm, in agreement with the hypothesis that the reaction rate is limited by the fVIIIa-fX complex formation. In addition, direct correlation was observed between the fX activation rate and formation of the fVIIIa-fX complex. Titration of fX, fVIIIa, phospholipid concentration and phosphatidylserine content suggested that at high fVIIIa concentration the reaction rate is regulated by the concentration of free fX rather than of membrane-bound fX. The obtained results reveal formation of high-affinity fVIIIa-fX complexes on phospholipid membranes and suggest their role in regulating fX activation by anchoring and delivering fX to the enzymatic complex.

Enzyme Activation↗
PubMed2005

Spatial propagation and localization of blood coagulation are regulated by intrinsic and protein C pathways, respectively.

Blood coagulation in vivo is a spatially nonuniform, multistage process: coagulation factors from plasma bind to tissue factor (TF)-expressing cells, become activated, dissociate, and diffuse into plasma to form enzymatic complexes on the membranes of activated platelets. We studied spatial regulation of coagulation using two approaches: 1), an in vitro experimental model of clot formation in a thin layer of plasma activated by a monolayer of TF-expressing cells; and 2), a computer simulation model. Clotting in factor VIII- and factor XI-deficient plasmas was initiated normally, but further clot elongation was impaired in factor VIII- and, at later stages, in factor XI-deficient plasma. The data indicated that clot elongation was regulated by factor Xa formation by intrinsic tenase, whereas factor IXa was formed by extrinsic tenase on activating cells and diffused into plasma, thus sustaining clot growth. Far from the activating cells, additional factor IXa was produced by factor XIa. Exogenously added TF had no effect on the clot growth rate, suggesting that plasma TF does not contribute significantly to the clot propagation process in a reaction-diffusion system without flow. Addition of thrombomodulin at 3-100 nM caused dose-dependent termination of clot elongation with a final clot size of 2-0.2 mm. These results identify roles of specific coagulation pathways at different stages of spatial clot formation (initiation, elongation, and termination) and provide a possible basis for their therapeutic targeting.

Blood Coagulation↗
PubMed2005

Mathematical modeling and computer simulation in blood coagulation.

Over the last two decades, mathematical modeling has become a popular tool in study of blood coagulation. The in silico methods were able to yield interesting and significant results in the understanding of both individual reaction mechanisms and regulation of large sections of the coagulation cascade. The objective of this paper is to review the development of theoretical research in hemostasis and thrombosis, to summarize the main findings, and outline problems and possible prospects in the use of mathematical modeling and computer simulation approaches. This review is primarily focused on the studies dealing with: (1) the membrane-dependent reactions of coagulation; (2) regulation of the coagulation cascade, including effects of positive and negative feedback loops, diffusion of coagulation factors, and blood flow.

Blood Coagulation↗
PubMed2005

Blood coagulation and propagation of autowaves in flow.

This study analyses the effect of flow and boundary reactions on spatial propagation of waves of blood coagulation. A simple model of coagulation in plasma consisting of three differential reaction-diffusion equations was used for numerical simulations. The vessel was simulated as a two-dimensional channel of constant width, and the anticoagulant influence of thrombomodulin present on the undamaged vessel wall was taken into account. The results of the simulations showed that this inhibition could stop the coagulation process in the absence of flow in narrow channels. For the used mathematical model of coagulation this was the case if the width was below 0.2 mm. In wider vessels, the process could be stopped by the rapid blood flow. The required flow rate increased with the increase of the damage region size. For example, in a 0.5-mm wide channel with 1-mm long damage region, the propagation of coagulation may be terminated at the flow rate of more than 20 mm/min.

Blood Coagulation↗
PubMed2004

Kinetics of Factor X activation by the membrane-bound complex of Factor IXa and Factor VIIIa.

Intrinsic tenase consists of activated Factors IX (IXa) and VIII (VIIIa) assembled on a negatively charged phospholipid surface. In vivo, this surface is mainly provided by activated platelets. In vitro, phosphatidylcholine/phosphatidylserine vesicles are often used to mimic natural pro-coagulant membranes. In the present study, we developed a quantitative mathematical model of Factor X activation by intrinsic tenase. We considered two situations, when complex assembly occurs on either the membrane of phospholipid vesicles or the surface of activated platelets. On the basis of existing experimental evidence, the following mechanism for the complex assembly on activated platelets was suggested: (i) Factors IXa, VIIIa and X bind to their specific platelet receptors; (ii) bound factors form complexes on the membrane: platelet-bound Factor VIIIa provides a high-affinity site for Factor X and platelet-bound Factor IXa provides a high-affinity site for Factor VIIIa; (iii) the enzyme-cofactor-substrate complex is assembled. This mechanism allowed the explanation of co-operative effects in the binding of Factors IXa, VIIIa and X to platelets. The model was reduced to obtain a single equation for the Factor X activation rate as a function of concentrations of Factors IXa, VIIIa, X and phospholipids (or platelets). The equation had a Michaelis-Menten form, where apparent V(max) and K(m) were functions of the factors' concentrations and the internal kinetic constants of the system. The equation obtained can be used in both experimental studies of intrinsic tenase and mathematical modelling of the coagulation cascade. The approach of the present study can be applied to research of other membrane-dependent enzymic reactions.

Blood Platelets↗
PubMed2002

Tissue factor pathway inhibitor: a possible mechanism of action.

We have analyzed several mathematical models that describe inhibition of the factor VIIa-tissue factor complex (VIIa-TF) by tissue factor pathway inhibitor (TFPI). At the core of these models is a common mechanism of TFPI action suggesting that only the Xa-TFPI complex is the inhibitor of the extrinsic tenase activity. However, the model based on this hypothesis could not explain well all the available experimental data. Here, we show that a good quantitative description of all experimental data could be achieved in a model that contains two more assumptions. The first assumption is based on the hypothesis originally proposed by Baugh et al. [Baugh, R.J., Broze, G.J. Jr & Krishnaswamy, S. (1998) J. Biol. Chem. 273, 4378-4386], which suggests that TFPI could inhibit the enzyme-product complex Xa-VIIa-TF. The second assumption proposes an interaction between the X-VIIa-TF complex and the factor Xa-TFPI complex. Experiments to test these hypotheses are suggested.

Blood Coagulation↗