Platelets provide robustness of spatial blood coagulation to the variation of initial conditions

Activated platelets provide phospholipid surface and secrete coagulation factors, enhancing blood clotting. We investigated the role of platelets in the regulation of blood coagulation spatial dynamics. We activated blood clotting with tissue factor-bearing (TF) surface in platelet-rich plasma (PRP) or platelet-free plasma (PFP). When blood coagulation was initiated by high TF density, clot growth rate (V) in PRP (2 × 105/μL platelets) was only 15 % greater than in PFP. Spatial distribution of thrombin in PRP had a peak-like shape in the area of the fibrin clot edge, while in PFP thrombin was distributed in the shape of descending plateau. Platelet inhibition with prostaglandin E1 or cytochalasin D made spatial thrombin distribution look like in the case of PFP. Inhibition of blood coagulation by natural endogenous inhibitor heparin was diminished in PRP, while the effect of the exogenous or artificial inhibitors (rivaroxaban, nitrophorin, hirudin) remained undisturbed in the presence of platelets. Ten times decrease of the TF surface density greatly depressed blood coagulation in PFP. In PRP only clotting initiation phase was, while the propagation phase remained intact. Coagulation factor deficiency greatly reduced amount of thrombin and decreased V in PFP rather than in PPR. Thus, platelets were redundant for clotting in normal plasma under physiological conditions but provided robustness of the coagulation system to the changes in initial conditions.

Hypercoagulation detected by routine and global laboratory hemostasis assays in patients with infective endocarditis

Background

Coagulation system is heavily involved into the process of infective endocarditis (IE) vegetation formation and can facilitate further embolization. In this study we aimed to assess the coagulation and platelet state in IE implementing a wide range of standard and global laboratory assays. We also aim to determine whether prothrombotic genetic polymorphisms play any role in embolization and mortality in IE patients.

Methods

37 patients with IE were enrolled into the study. Coagulation was assessed using standard coagulation assays (activated partial thromboplastin time (APTT), prothrombin, fibrinogen, D-dimer concentrations) and integral assays (thromboelastography (TEG) and thrombodynamics (TD)). Platelet functional activity was estimated by flow cytometry. Single nuclear polymorphisms of coagulation system genes were studied.

Results

Fibrinogen concentration and fibrinogen-dependent parameters of TEG and TD were increased in patients indicating systemic inflammation. In majority of patients clot growth rate in thrombodynamics was significantly shifted towards hypercoagulation in consistency with D-dimers elevation. However, in some patients prothrombin, thromboelastography and thrombodynamics were shifted towards hypocoagulation. Resting platelets were characterized by glycoprotein IIb-IIIa activation and degranulation. In patients with fatal IE, we observed a significant decrease in fibrinogen and thrombodynamics. In patients with embolism, we observed a significant decrease in the TEG R parameter. No association of embolism or mortality with genetic polymorphisms was found in our cohort.

Conclusions

Our findings suggest that coagulation in patients with infective endocarditis is characterized by general hypercoagulability and platelet pre-activation. Some patients, however, have hypocoagulant coagulation profile, which presumably can indicate progressing of hypercoagulation into consumption coagulopathy.

Determination of fibrin clot growth and spatial thrombin propagation in the presence of different types of phospholipid surfaces

In this work, we present a new method-Thrombodynamics-4D-for the assessment of both plasma and platelet contributions to clotting. Thrombodynamics-4D potentially allows for the determination of plasma or platelet disorders and the effects of various drugs on plasma clotting or on platelet procoagulant function. In this assay, clot formation in platelet-rich plasma or platelet-free plasma supplemented with phospholipids is activated with tissue factor immobilized on a surface. Spatial fibrin clot growth and thrombin concentration dynamics are registered by measuring light scattering of the fibrin clot and fluorescence of the product formed by cleavage of the synthetic fluorogenic substrate by thrombin, respectively. Here, we describe the preanalytical requirements, measurement methodology and calculation principles of assay parameters. Preanalytical and analytical variability and reference ranges of the assay are given. Additionally, we show some clinical examples, which determine the effect of anticoagulants, measure clotting dysfunction in patients with platelet or coagulation disorders and evaluate the effect of surgery.

Sensitivity and Robustness of Spatially Dependent Thrombin Generation and Fibrin Clot Propagation

Blood coagulation is a delicately regulated space- and time-dependent process that leads to the formation of fibrin clots preventing blood loss upon vascular injury. The sensitivity of the coagulation network was previously investigated without accounting for transport processes. To investigate its sensitivity to coagulation factor deficiencies in a spatial reaction-diffusion system, we combined an in vitro experimental design with a computational systems biology model. Clot formation in platelet-free plasma supplemented with phospholipids was activated with identical amounts of tissue factor (TF) either homogeneously distributed (concentration 5 pM, homogeneous model) or immobilized on the surface (surface density 100 pmole/m², spatially heterogeneous model). Fibrin clot growth and thrombin concentration dynamic in space were observed using video microscopy in plasma of healthy donors or patients with deficiencies in factors (F) II, FV, FVII, FVIII, FIX, FX, or FXI. In the spatially heterogeneous model, near-activator thrombin generation was decreased in FV-, FVII-, and FX-deficient plasma. In the homogeneous model, clotting was not registered in these samples. The simulation and experiment data showed that the coagulation threshold depended on the TF concentration. Our data indicate that the velocity of spatial clot propagation correlates linearly with the concentration of thrombin at the clot wave front but not with the overall thrombin wave amplitude. Spatial clot growth in normal plasma at early stages was neither reaction nor diffusion limited but became diffusion limited later. In contrast, clot growth was always diffusion limited in FV-, FVII-, and FX-deficient plasma and reaction limited in FVIII-, FIX-, and FXI-deficient plasma. We conclude that robustness of the spatially heterogeneous coagulation system was achieved because of the combination of 1) a local high TF surface density that overcomes activation thresholds, 2) diffusion control being shared between different active factors, and 3) an early saturated stimulus-response dependence of fibrin clot formation by thrombin.

Thrombodynamics-A new global hemostasis assay for heparin monitoring in patients under the anticoagulant treatment

BACKGROUND

Heparin therapy and prophylaxis may be accompanied by bleeding and thrombotic complications due to individual responses to treatment. Dosage control based on standard laboratory assays poorly reflects the effect of the therapy. The aim of our work was to compare the heparin sensitivity of new thrombodynamics (TD) assay with sensitivity of other standard and global coagulation tests available to date.

STUDY POPULATION AND METHODS

A total of 296 patients with high risk of venous thromboembolism (deep vein thrombosis (DVT), early postoperative period, hemoblastosis) were enrolled in the study. We used a case-crossover design to evaluate the sensitivity of new thrombodynamics assay (TD) to the hemostatic state before and after unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) therapy/prophylaxis and to compare it with the activated partial thromboplastin time (APTT), anti-Xa activity test, thrombin generation test (TGT) and thromboelastography (TEG). A receiver operating characteristic (ROC) curve analysis was used to evaluate changes before and after heparin prophylaxis and therapy. Blood was sampled before heparin injection, at the time of maximal blood heparin concentration and before the next injection.

RESULTS

Hypercoagulation before the start of heparin treatment was detected by TD, TGT and TEG but not by APTT. The area under the ROC curve (AUC) was maximal for TD and anti-Xa, intermediate for TGT and TEG and minimal for APTT.

CONCLUSIONS

These results indicate that TD has a high sensitivity to the effects of UFH and LMWH after both prophylactic and therapeutic regimes and may be used for heparin monitoring.

The laboratory control of anticoagulant thromboprophylaxis during the early postpartum period after cesarean delivery

INTRODUCTION

The incidence of venous thromboembolism (VTE) after cesarean section is up to 0.6%, and the widespread use of cesarean section draws attention to this group. The dosage and duration of low-molecular-weight heparin (LMWH) prophylaxis after delivery is estimated by anamnestic risk-scales; however, the predictive potency for an individual patient's risk can be low. Laboratory hemostasis assays are expected to solve this problem. The aim of this study was to estimate the potency of tests to reflect the coagulation state of patients receiving LMWH in the early postpartum period.

MATERIALS AND METHODS

We conducted an observational study on 97 women undergoing cesarean section. Standard coagulation tests (Fg, APTT, prothrombin, D-dimer), an anti-Xa assay, rotation thromboelastometry and thrombodynamics/thrombodynamics-4D were performed. Coagulation assay parameters were compared in groups formed in the presence or absence of LMWH to estimate the laboratory assays' sensitivity to anticoagulation.

RESULTS

Coagulation assays revealed hypercoagulation after delivery and a tendency toward normalization of coagulation during early postpartum. The thromboprophylaxis results revealed a higher percentage of coagulation parameters within the normal range in the LMWH group.

CONCLUSION

This research is potentially beneficial for the application of thrombodynamics and thrombodynamics-4D in monitoring coagulation among patients with high VTE risk who receive thromboprophylaxis with heparin.

Classic and Global Hemostasis Testing in Pregnancy and during Pregnancy Complications

Pregnancy is associated with a significant procoagulant shift in the hemostatic system balance as well as other metabolic changes. Pregnancy can thereby provoke manifestation of otherwise dormant disorders of hemostasis (e.g., thrombophilia), or even cause new, pregnancy-specific disorders (e.g., HELLP syndrome). Application and interpretation of laboratory assays of hemostasis in pregnancy is particularly challenging, because normal physiological ranges are no longer applicable, and because the most dangerous and complex changes are not detected by classic routine coagulation/platelet assays. New global assays of coagulation and of platelet-dependent hemostasis appear to be promising in this respect, but are still far from clinical practice and rarely appear in current patient management guidelines. These global assays require a high level of research to identify their relationship to clinically significant outcomes. Here, we review the state-of-the-art knowledge of the molecular changes in the hemostatic system in normal pregnancy and during pregnancy-related complications (preeclampsia, thrombotic microangiopathies, antiphospholipid syndrome, etc.). We also discuss the sensitivity of various classic and innovative assays to these pregnancy-associated changes, and describe current and potential future applications of these assays in meeting specific clinical needs.

Eculizumab effect on the hemostatic state in patients with paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by a hypercoagulable state associated with acute hemolysis. Eculizumab is used to reduce the intensity of intravascular hemolysis in PNH patients. The hemostatic status of three patients with PNH was assessed during eculizumab treatment by D-dimer assay and the global assays: thromboelastography (TEG), thrombin generation test (TGТ), and thrombodynamics (TD). In the state of hemolytic crisis before the therapy D-dimer concentration was increased in two patients accompanied by hypercoagulation changes in TEG parameter angle (α). TD parameter the clot growth velocity (V) revealed hypercoagulability while TGT parameter ETP was within the normal range in all patients. The lactate dehydrogenase (LDH) activity decreased during the 8months of eculizumab therapy. The physical health was improved, the frequency of hemolytic crisis decreased. Patients periodically exhibited hypercoagulable state: the mean values α=38±11° (with normal range 20-40°), ETP=1311±442nM·min (with normal range 800-1560nM·min), V=31±4μm/min (with normal range 20-29μm/min). During the eculizumab therapy two patients had the repeated clinical manifestation of acute hemolytic crisis, the parameters of the global tests were increased compared to the previous measurement. The global hemostasis tests TEG, TGT and TD revealed hypercoagulability in patients with PNH during eculizumab therapy.

[Influence of temperature on spatial fibrin clot formation process in thrombodynamics]

In this study we have investigated the process of spatial fibrin clot formation in non-steered platelet-free plasma at the temperatures from 20°C to 43°C using thrombodynamics - the novel in vitro hemostasis assay, which imitates the process of hemostatic clot growth in vivo. During data processing the following parameters were calculated: initial (V i ) and stationary (V st ) rates of clot growth which characterize initiation and propagation phases of clotting process, and clot size on the 30 th minute. The temperature dependence of extrinsic and intrinsic tenase activities, which determine values of the initial and stationary clot growth rates, respectively, have been also measured. It was established that the temperature lowering from 37°C to 24°C extends mainly on the initiation phase of clot growth, while the stationary rate of clot growth changes insignificantly. Meanwhile none of the thrombodynamics parameters shows the dramatic change of plasma coagulation system condition at the temperature of 24°C (acute hypothermia). Using the thrombodynamics assay an assumption, that the temperature lowering does not change the state of plasma hemostasis system significantly has been confirmed.

Drug-drug interaction of the anti-TFPI aptamer BAX499 and factor VIII: studies of spatial dynamics of fibrin clot formation in hemophilia A

BACKGROUND

In recent years, a number of tissue factor pathway inhibitor (TFPI) antagonists have been developed to serve as bypassing agents to improve hemostasis in hemophilia A. Since TFPI antagonists and FVIII concentrates are procoagulants, their combined effect on spatial clot formation could be potentially pro-thrombotic.

OBJECTIVE

To investigate the cooperative effect of TFPI inhibition and supplementation of FVIII in hemophilia A in a spatial, reaction-diffusion experiment in vitro.

METHODS

Plasma was collected at different time points from hemophilia A patients undergoing prophylaxis and was supplemented in vitro with TFPI inhibitor BAX499 (formerly ARC19499) at concentrations from 0 up to 600nM. Clotting propagation in recalcified plasma activated by a surface with immobilized tissue factor (TF) was monitored by videomicroscopy.

RESULTS

Increasing concentration of BAX499 improved coagulation for all hemophilia A plasma samples activated with TF at 1.6pmole/m(2) by shortening lag time and increasing initial clot growth velocity and clot size. In contrast, plasma concentration of FVIII had little effect on lag time, but increased spatial clot growth velocity. There was a decrease in the BAX499 efficiency as FVIII concentration increased (lag time shortened by 50% if FVIII:C<5%, but the effect was only 25% if FVIII:C>30%).

CONCLUSIONS

The results indicate that BAX499 has an effect on clotting in hemophilia A plasma at low FVIII concentrations, however has little effect at high FVIII concentrations.

Improvement of spatial fibrin formation by the anti-TFPI aptamer BAX499: changing clot size by targeting extrinsic pathway initiation

BACKGROUND

Tissue factor pathway inhibitor (TFPI) is a major regulator of clotting initiation and a promising target for pro- and anticoagulation therapy. The aptamer BAX499 (formerly ARC19499) is a high-affinity specific TFPI antagonist designed to improve hemostasis. However, it is not clear how stimulation of coagulation onset by inactivating TFPI will affect spatial and temporal clot propagation.

OBJECTIVE

To examine the BAX499 effect on clotting in a spatial, reaction-diffusion experimental system in comparison with that of recombinant activated factor VII (rVIIa).

METHODS

Clotting in plasma activated by immobilized tissue factor (TF) was monitored by videomicroscopy.

RESULTS

BAX499 dose-dependently improved coagulation in normal and hemophilia A plasma activated with TF at 2 pmole m(-2) by shortening lag time and increasing clot size by up to ~2-fold. The effect was TFPI specific as confirmed by experiments in TFPI-depleted plasma with or without TFPI supplementation. Clotting improvement was half-maximal at 0.7 nm of BAX499 and reached a plateau at 10 nm, remaining there at concentrations up to 1000 nm. The BAX499 effect decreased with TF surface density increase. RVIIa improved clotting in hemophilia A plasma activated with TF at 2 or 20 pmole m(-2) , both by shortening lag time and increasing spatial velocity of clot propagation; its effects were strongly concentration dependent.

CONCLUSIONS

BAX499 significantly improves spatial coagulation by inhibiting TFPI in a spatially localized manner that is different to that observed with rVIIa.

Task-oriented modular decomposition of biological networks: trigger mechanism in blood coagulation

Analysis of complex time-dependent biological networks is an important challenge in the current postgenomic era. We propose a middle-out approach for decomposition and analysis of complex time-dependent biological networks based on: 1), creation of a detailed mechanism-driven mathematical model of the network; 2), network response decomposition into several physiologically relevant subtasks; and 3), subsequent decomposition of the model, with the help of task-oriented necessity and sensitivity analysis into several modules that each control a single specific subtask, which is followed by further simplification employing temporal hierarchy reduction. The technique is tested and illustrated by studying blood coagulation. Five subtasks (threshold, triggering, control by blood flow velocity, spatial propagation, and localization), together with responsible modules, can be identified for the coagulation network. We show that the task of coagulation triggering is completely regulated by a two-step pathway containing a single positive feedback of factor V activation by thrombin. These theoretical predictions are experimentally confirmed by studies of fibrin generation in normal, factor V-, and factor VIII-deficient plasmas. The function of the factor V-dependent feedback is to minimize temporal and parametrical intervals of fibrin clot instability. We speculate that this pathway serves to lessen possibility of fibrin clot disruption by flow and subsequent thromboembolism.