Thrombin generation in hemorrhage control and vascular occlusion

A retrospective study of the management and outcomes of pregnancies with inherited antithrombin deficiency

INTRODUCTION

Antithrombin (AT) deficiency is a rare but highly thrombogenic inherited thrombophilia. Its association with adverse pregnancy outcomes (APO) is undefined. There is limited guidance on managing AT deficiency in pregnancy. Some significant issues remain controversial, including risk assessment for prophylactic anticoagulation, anticoagulant therapy, and monitoring. Our goal was to examine if the antepartum management of patients with AT deficiency affected their pregnancy outcomes.

MATERIALS AND METHODS

This retrospective, single-center observational study included pregnant women with inherited AT deficiency in Peking Union Medical College Hospital between 2013 and 2024.

RESULTS

Seventeen pregnancies in 6 women with AT deficiency were identified. A total of 7 pregnancies received adjusted-dose low-molecular-weight heparin (LMWH) and were monitored by anti-Xa level, AT activity, and D-dimer. There were 5 live births (all received LMWH), 7 second-trimester abortions (1 received LMWH), and 5 early pregnancy losses (1 received LMWH). There were 5 abruptio placentae events (3 received LMWH) and 7 thrombotic events (2 received LMWH).

CONCLUSIONS

AT deficiency is at least an important partial factor contributing to APO. It is suggested to make a full assessment of AT patients both for venous thrombus embolism and APO risk. We observed a high prevalence of heparin resistance and a positive correlation between adequate anticoagulation and pregnancy outcome based on tight monitoring with anti-Xa level and timely adjustment of the LMWH dosage.

An intelligent DNA nanodevice for precision thrombolysis

Thrombosis is a leading global cause of death, in part due to the low efficacy of thrombolytic therapy. Here, we describe a method for precise delivery and accurate dosing of tissue plasminogen activator (tPA) using an intelligent DNA nanodevice. We use DNA origami to integrate DNA nanosheets with predesigned tPA binding sites and thrombin-responsive DNA fasteners. The fastener is an interlocking DNA triplex structure that acts as a thrombin recognizer, threshold controller and opening switch. When loaded with tPA and intravenously administrated in vivo, these DNA nanodevices rapidly target the site of thrombosis, track the circulating microemboli and expose the active tPA only when the concentration of thrombin exceeds a threshold. We demonstrate their improved therapeutic efficacy in ischaemic stroke and pulmonary embolism models, supporting the potential of these nanodevices to provide accurate tPA dosing for the treatment of different thromboses.

Fibrinolysis biomarker, thrombin, and activated protein C level alterations after coagulation activation depend on type of thrombophilia and clinical phenotype

Background

Recently, we have shown alterations in the anticoagulant response to recombinant activated factor VII (rFVIIa)-induced coagulation activation in patients with thrombophilia.

Objectives

This study aimed to extend this in vivo model to fibrinolysis biomarkers.

Methods

This interventional in vivo study included 56 patients with thrombophilia and previous venous thromboembolism (VTE+), 38 without VTE (VTE-), and 35 healthy controls. Plasma levels of D-dimer, plasmin-α2-antiplasmin (PAP) complex, and plasminogen activator inhibitor-1 (PAI-1) were monitored for over 8 hours after rFVIIa infusion (15 μg/kg) along with thrombin markers and activated protein C (APC).

Results

Throughout cohorts, median PAP increased by 40% to 52% (P < 3.9 × 10-10) and PAI-1 decreased by 59% to 79% (P < 3.5 × 10-8). In contrast to thrombin-antithrombin (TAT) complex, which also increased temporarily (44% to 115%, P < 3.6 × 10-6), changes in PAP and PAI-1 did not reverse during the observation period. The area under the measurement-time curves (AUCs) of PAP and TAT, which are measures of plasmin and thrombin formation, respectively, were each greater in the VTE+ cohort than in healthy controls (median PAP-AUC = 0.48 vs 0.27 ng·h/L [P = .003], TAT-AUC = 0.12 vs 0.03 nmol·h/L [P = 2.5 × 10-4]) and were correlated with one another (r = 0.554). As evidenced by the respective AUCs, asymptomatic factor (F)V Leiden carriers showed less PAP formation (0.22 vs 0.41 ng·h/L, P = 9 × 10-4), more pronounced PAI-1 decline (0.10 vs 0.18 ng·h/L, P = .01), and increased APC formation (28.7 vs 15.4 pmol·h/L, P = .02) than those within the VTE+ group (n = 19 each).

Conclusion

rFVIIa-induced thrombin formation is associated with fibrinolysis parameter changes outlasting the concomitant anticoagulant response. Both correlate with thrombosis history in FV Leiden and might help explain its variable clinical expressivity.

Statins Effects on Blood Clotting: A Review

Statins are powerful lipid-lowering drugs that inhibit cholesterol biosynthesis via downregulation of hydroxymethylglutaryl coenzyme-A reductase, which are largely used in patients with or at risk of cardiovascular disease. Available data on thromboembolic disease include primary and secondary prevention as well as bleeding and mortality rates in statin users during anticoagulation for VTE. Experimental studies indicate that statins alter blood clotting at various levels. Statins produce anticoagulant effects via downregulation of tissue factor expression and enhanced endothelial thrombomodulin expression resulting in reduced thrombin generation. Statins impair fibrinogen cleavage and reduce thrombin generation. A reduction of factor V and factor XIII activation has been observed in patients treated with statins. It is postulated that the mechanisms involved are downregulation of factor V and activated factor V, modulation of the protein C pathway and alteration of the tissue factor pathway inhibitor. Clinical and experimental studies have shown that statins exert antiplatelet effects through early and delayed inhibition of platelet activation, adhesion and aggregation. It has been postulated that statin-induced anticoagulant effects can explain, at least partially, a reduction in primary and secondary VTE and death. Evidence supporting the use of statins for prevention of arterial thrombosis-related cardiovascular events is robust, but their role in VTE remains to be further elucidated. In this review, we present biological evidence and experimental data supporting the ability of statins to directly interfere with the clotting system.

P2Y12 Inhibition Suppresses Proinflammatory Platelet-Monocyte Interactions

BACKGROUND

 Monocyte-platelet aggregates (MPAs) represent the crossroads between thrombosis and inflammation, and targeting this axis may suppress thromboinflammation. While antiplatelet therapy (APT) reduces platelet-platelet aggregation and thrombosis, its effects on MPA and platelet effector properties on monocytes are uncertain.

OBJECTIVES

 To analyze the effect of platelets on monocyte activation and APT on MPA and platelet-induced monocyte activation.

METHODS

 Agonist-stimulated whole blood was incubated in the presence of P-selectin, PSGL1, PAR1, P2Y12, GP IIb/IIIa, and COX-1 inhibitors and assessed for platelet and monocyte activity via flow cytometry. RNA-Seq of monocytes incubated with platelets was used to identify platelet-induced monocyte transcripts and was validated by RT-qPCR in monocyte-PR co-incubation ± APT.

RESULTS

 Consistent with a proinflammatory platelet effector role, MPAs were increased in patients with COVID-19. RNA-Seq revealed a thromboinflammatory monocyte transcriptome upon incubation with platelets. Monocytes aggregated to platelets expressed higher CD40 and tissue factor than monocytes without platelets (p < 0.05 for each). Inhibition with P-selectin (85% reduction) and PSGL1 (87% reduction) led to a robust decrease in MPA. P2Y12 and PAR1 inhibition lowered MPA formation (30 and 21% reduction, p < 0.05, respectively) and decreased monocyte CD40 and TF expression, while GP IIb/IIIa and COX1 inhibition had no effect. Pretreatment of platelets with P2Y12 inhibitors reduced the expression of platelet-mediated monocyte transcription of proinflammatory SOCS3 and OSM. CONCLUSIONS:  Platelets skew monocytes toward a proinflammatory phenotype. Among traditional APTs, P2Y12 inhibition attenuates platelet-induced monocyte activation.

Comparative sequence analysis of vitamin K-dependent coagulation factors

BACKGROUND

Prothrombin, protein C, and factors VII, IX, and X are vitamin K (VK)-dependent coagulation proteins that play an important role in the initiation, amplification, and subsequent attenuation of the coagulation response. Blood coagulation evolved in the common vertebrate ancestor as a specialization of the complement system and immune response, which in turn bear close evolutionary ties with developmental enzyme cascades. There is currently no comprehensive analysis of the evolutionary changes experienced by these coagulation proteins during the radiation of vertebrates and little is known about conservation of residues that are important for zymogen activation and catalysis.

OBJECTIVES

To characterize the conservation level of functionally important residues among VK-dependent coagulation proteins from different vertebrate lineages.

METHODS

The conservation level of residues important for zymogen activation and catalysis was analyzed in >1600 primary sequences of VK-dependent proteins.

RESULTS

Functionally important residues are most conserved in prothrombin and least conserved in protein C. Some of the most profound functional modifications in protein C occurred in the ancestor of bony fish when the basic residue in the activation site was replaced by an aromatic residue. Furthermore, during the radiation of placental mammals from marsupials, protein C acquired a cysteine-rich insert that introduced an additional disulfide in the EGF1 domain and evolved a proprotein convertase cleavage site in the activation peptide linker that also became significantly elongated.

CONCLUSIONS

Sequence variabilities at functionally important residues may lead to interspecies differences in the zymogen activation and catalytic properties of orthologous VK-dependent proteins.

To Clot or Not to Clot: Deepening Our Understanding of Alterations in the Hemostatic System

The session on the hemostatic system focused on new developments in coagulation and platelet biology as well as how therapeutic agents may affect hemostasis. The classic cascade model of coagulation was compared with the more recent models of cell-based and vascular-based coagulation, which may provide better insight on how the coagulation cascade works in vivo. A review of platelet biology highlighted that, as platelets age, desialylated platelets form and are recognized by Ashwell-Morell receptor (AMR), leading to hepatic uptake and subsequent increase in thrombopoietin (TPO) production. Administration of therapeutics that induce thrombocytopenia was also discussed, including Mylotarg, which is an antibody-drug conjugate that was shown to decrease human megakaryocyte development but had no effect on platelet aggregation. An acetyl co-A carboxylase inhibitor was shown to cause thrombocytopenia by inhibiting de novo lipogenesis, which is critical for the formation of the megakaryocyte demarcation membrane system responsible for platelet production. It was also illustrated how preclinical translation models have been very helpful in the development of adeno-associated virus (AAV) hemophilia B gene therapy and what old and new preclinical tools we have that can predict the risk of a prothrombotic state in people.

Femtomolar Detection of Thrombin in Serum and Cerebrospinal Fluid via Direct Electrocatalysis of Oxygen Reduction by the Covalent G4-Hemin-Aptamer Complex

Thrombin, a serine protease playing a central role in the coagulation cascade reactions and a potent neurotoxin produced by injured brain endothelial cells, is a recognized cardiac biomarker and a critical biomarker for Alzheimer's disease development. Both in vivo and in vitro, its low physiological concentrations and nonspecific binding of other components of physiological fluids complicate electroanalysis of thrombin. Here, femtomolar levels of thrombin in serum and an artificial cerebrospinal fluid (CSF) were detected by the indicator-free electrochemical methodology exploiting the O₂ reduction reaction directly, with no electron transfer mediators, electrocatalyzed by the covalent G4-hemin DNAzyme complex naturally self-assembling upon thrombin binding to the hemin-modified 29-mer DNA aptamer sequence tethered to gold via an alkanethiol linker. Coadsorbed PEG inhibited nonspecific protein binding and allowed the sought signal resolution. The proposed assay exploiting the "oxidase" activity of G4-hemin DNAzyme does not require any coreactants necessary for the traditional peroxidase activity-based assays with this DNAzyme, such as H₂O₂ and redox mediators, or solution deaeration and allows fast, overall 30 min analysis of thrombin in aerated buffer, CSF, and 1% human serum solutions. This pioneer approach exploiting the oxidase activity G4-hemin DNAzyme is simple, sensitive, and selective and represents a new tool for ultrasensitive electrocatalytic assays based on simple and efficient O₂-dependent DNAzyme labels.

Circulating Syndecan-1 and Tissue Factor Pathway Inhibitor, Biomarkers of Endothelial Dysfunction, Predict Mortality in Burn Patients

OBJECTIVE

The aim of this study is to evaluate the association between burn injury and admission plasma levels of Syndecan-1 (SDC-1) and Tissue Factor Pathway Inhibitor (TFPI), and their ability to predict 30-day mortality.

BACKGROUND

SDC-1 and TFPI are expressed by vascular endothelium and shed into the plasma as biomarkers of endothelial damage. Admission plasma biomarker levels have been associated with morbidity and mortality in trauma patients, but this has not been well characterized in burn patients.Methods: This cohort study enrolled burn patients admitted to a regional burn center between 2013 and 2017. Blood samples were collected within 4 h of admission and plasma SDC-1 and TFPI were quantified by ELISA. Demographics and injury characteristics were collected prospectively. The primary outcome was 30-day in-hospital mortality.

RESULTS

Of 158 patients, 74 met inclusion criteria. Most patients were male with median age of 41.5 years and burn TBSA of 20.5%. The overall mortality rate was 20.3%. Admission SDC-1 and TFPI were significantly higher among deceased patients. Plasma SDC-1 >34 ng/mL was associated with a 32-times higher likelihood of mortality [OR: 32.65 (95% CI, 2.67-399.78); P = 0.006] and a strong predictor of mortality (area under the ROC [AUROC] 0.92). TFPI was associated with a nine-times higher likelihood of mortality [OR: 9.59 (95% CI, 1.02-89.75); P = 0.002] and a fair predictor of mortality (AUROC 0.68).

CONCLUSIONS

SDC-1 and TFPI are associated with a higher risk of 30-day mortality. We propose the measurement of SDC-1 on admission to identify burn patients at high risk of mortality. However, further investigation with a larger sample size is warranted.

Burn-Induced Coagulopathies: a Comprehensive Review

Burn-induced coagulopathy is not well understood, and consensus on diagnosis, prevention, and treatments are lacking. In this review, literature on burn-induced (and associated) coagulopathy is presented along with the current understanding of the effects of burn injury on the interactions among coagulation, fibrinolysis, and inflammation in the acute resuscitative phase and reconstructive phase of care. The role of conventional tests of coagulopathy and functional assays like thromboelastography or thromboelastometry will also be discussed. Finally, reported methods for the prevention and treatment of complications related to burn-induced coagulopathy will be reviewed.

Functional Characterization of Antithrombin Mutations by Monitoring of Thrombin Inhibition Kinetics

Inactivation of thrombin by the endogenous inhibitor antithrombin (AT) is a central mechanism in the regulation of hemostasis. This makes hereditary AT deficiency, which is caused by SERPINC1 gene mutations, a major thrombophilic risk factor. Aim of this study was to assess to what extent AT mutations impair thrombin inhibition kinetics. The study population included 36 thrombophilic patients with 19 different mutations and mean AT levels of 65% in a thrombin-based functional assay, and 26 healthy controls. To assess thrombin inhibition kinetics, thrombin (3.94 mU/mL final concentration) was added to citrated plasma. Subsequently, endogenous thrombin inhibition was stopped by addition of the reversible thrombin inhibitor argatroban and the amount of argatroban-complexed thrombin quantified using an oligonucleotide-based enzyme capture assay. The plasma half-life of human thrombin was significantly longer in patients with AT mutations than in the controls (119.9 versus 55.9 s). Moreover, it was disproportionately prolonged when compared with preparations of wild type AT in plasma, in whom a comparable thrombin half-life of 120.8 s was reached at a distinctly lower AT level of 20%. These findings may help to better understand the increased thrombotic risk of SERPINC1 mutations with near normal AT plasma levels in functional assays.

Effects of antithrombotic drugs on the prothrombotic state in patients with atrial fibrillation: The west Birmingham atrial fibrillation project

BACKGROUND

Direct oral anticoagulants (DOACs) are known to prevent thrombosis but there is limited information about their activity on the clot formation and lysis cascade.

OBJECTIVES

This study assesses the role of apixaban, one of the four licenced DOACs, on clot dynamics in patients with atrial fibrillation (AF).

METHODS

We compared haemostatic and clot lysis characteristics between a group of patients with AF (n = 47) and a "disease control" group with ischaemic heart disease but in sinus rhythm (n = 39). Subsequently, we conducted clot structure studies in 3 groups of patients with AF on different antithrombotic drugs: warfarin (n = 60), apixaban (n = 60) or antiplatelets (n = 62) and in patients with AF naïve to oral anticoagulants before and after 3-months treatment with apixaban (n = 32). Haemostasis was investigated by a viscoelastic, whole blood technique (Thromboelastography/TEG), a "microplate-reader based", citrated plasma technique (microplate assay), immunoassays to determine plasma concentrations of plasminogen activator inhibitor-1 (PAI-1), tissue-Plasminogen Activator (t-PA), D-dimer and finally platelet derived and apoptotic microparticles.

RESULTS

Patients with AF have more potent thrombogenesis based on microplate assay indices [Rate of clot formation (p = 0.03, ƞ² = 0.06), Maximum optical density (p < 0.001, ƞ² = 0.05)] and delayed fibrinolysis [Rate of clot dissolution (p = 0.005, ƞ² = 0.17)] with increased levels of apoptotic microparticles (p = 0.02, ƞ² = 0.06) compared with the 'disease control' group. Apixaban was more effective in attenuating prothrombotic characteristics assessed by TEG {R (ε² = 0.21), K (ε² = 0.16) and angle [mean difference (MD), 95% Confidence Intervals (CI), vs warfarin 5, 0.96-8.6 and 8, 3.8-11.4 vs antiplatelets], (p < 0.001 for all indices)} compared with the other treatment groups. Patients on apixaban had lower D-dimer (p < 0.001, ε² = 0.17) and tPA (p = 0.03, MD 90, 95%CI 6-150 vs warfarin and MD 90, 95% CI 4-150 vs antiplatelets) levels. From the microplate assay analysis, warfarin and apixaban demonstrated comparable activity based on multiple indices, both superior to antiplatelets. However, warfarin was associated with reduced fibrin network robustness (Max. optical density p < 0.001, ε² = 0.1). Apixaban inhibited thrombosis, amplified fibrinolysis and decreased D-dimer (p = 0.001, r = 0.4) levels in the follow up study.

CONCLUSIONS

Patients with AF have impaired haemostasis and elevated levels of apoptotic microparticles. Apixaban appears to affect plasma prothrombotic characteristics in a distinctive manner compared with warfarin and to reduce biomarkers associated with adverse cardiovascular events.

Increased Platelet Aggregation in Children and Adolescents with Sleep-disordered Breathing

Rationale: Sleep-disordered breathing (SDB) is associated with increased vascular resistance in children and adults. Persistent increased vascular resistance damages vascular endothelial cells-a marker of which is increased platelet activation.Objectives: This study compared whole-blood impedance platelet aggregation in children with clinically diagnosed SDB warranting adenotonsillectomy and healthy control subjects.Methods: Thirty children who had SDB warranting intervention clinically diagnosed by experienced pediatric otolaryngologists were recruited from adenotonsillectomy waitlists, and 20 healthy children from the community underwent overnight polysomnography to determine SDB severity (obstructive apnea-hypopnea index). Snoring frequency was collected from parents. In the morning, a fasting blood sample was taken, and whole-blood platelet aggregation was measured.Measurements and Main Results: Children with SDB exhibited increased platelet aggregation to TRAP (thrombin receptor-activating peptide) (children with SDB = 114.8 aggregation units [AU] vs. control subjects = 98.0 AU; P < 0.05) and COL antibody (96.7 vs. 82.2 AU; P < 0.05) and an increased trend in ADP antibody (82.3 vs. 69.2 AU; P < 0.07) but not aspirin dialuminate (82.1 vs. 79.5 AU; P > 0.05). No significant association was observed between either the obstructive apnea-hypopnea index and any aggregation parameter, but parental report of snoring was positively associated with TRAP aggregation (Kendall's τ-c = 0.23; P < 0.05).Conclusions: The finding of increased platelet aggregation is consistent with endothelial damage. This suggests that the profile of cardiovascular changes noted in adults with SDB may also occur in children with SDB.

Self-regulated hirudin delivery for anticoagulant therapy

Pathological coagulation, a disorder of blood clotting regulation, induces a number of cardiovascular diseases. A safe and efficient system for the delivery of anticoagulants to mimic the physiological negative feedback mechanism by responding to the coagulation signal changes holds the promise and potential for anticoagulant therapy. Here, we exploit a "closed-loop" controlled release strategy for the delivery of recombinant hirudin, an anticoagulant agent that uses a self-regulated nanoscale polymeric gel. The cross-linked nanogel network increases the stability and bioavailability of hirudin and reduces its clearance in vivo. Equipped with the clot-targeted ligand, the engineered nanogels promote the accumulation of hirudin in the fibrous clots and adaptively release the encapsulated hirudin upon the thrombin variation during the pathological proceeding of thrombus for potentiating anticoagulant activity and alleviating adverse effects. We show that this formulation efficiently prevents and inhibits the clot formation on the mouse models of pulmonary embolism and thrombosis.

Intelligent classification of platelet aggregates by agonist type

Platelets are anucleate cells in blood whose principal function is to stop bleeding by forming aggregates for hemostatic reactions. In addition to their participation in physiological hemostasis, platelet aggregates are also involved in pathological thrombosis and play an important role in inflammation, atherosclerosis, and cancer metastasis. The aggregation of platelets is elicited by various agonists, but these platelet aggregates have long been considered indistinguishable and impossible to classify. Here we present an intelligent method for classifying them by agonist type. It is based on a convolutional neural network trained by high-throughput imaging flow cytometry of blood cells to identify and differentiate subtle yet appreciable morphological features of platelet aggregates activated by different types of agonists. The method is a powerful tool for studying the underlying mechanism of platelet aggregation and is expected to open a window on an entirely new class of clinical diagnostics, pharmacometrics, and therapeutics.

Platelets are small cells in the blood that primarily help stop bleeding after an injury by sticking together with other blood cells to form a clot that seals the broken blood vessel. Blood clots, however, can sometimes cause harm. For example, if a clot blocks the blood flow to the heart or the brain, it can result in a heart attack or stroke, respectively. Blood clots have also been linked to harmful inflammation and the spread of cancer, and there are now preliminary reports of remarkably high rates of clotting in COVID-19 patients in intensive care units.

A variety of chemicals can cause platelets to stick together. It has long been assumed that it would be impossible to tell apart the clots formed by different chemicals (which are also known as agonists). This is largely because these aggregates all look very similar under a microscope, making it incredibly time consuming for someone to look at enough microscopy images to reliably identify the subtle differences between them. However, finding a way to distinguish the different types of platelet aggregates could lead to better ways to diagnose or treat blood vessel-clogging diseases.

To make this possible, Zhou, Yasumoto et al. have developed a method called the “intelligent platelet aggregate classifier” or iPAC for short. First, numerous clot-causing chemicals were added to separate samples of platelets taken from healthy human blood. The method then involved using high-throughput techniques to take thousands of images of these samples. Then, a sophisticated computer algorithm called a deep learning model analyzed the resulting image dataset and “learned” to distinguish the chemical causes of the platelet aggregates based on subtle differences in their shapes. Finally, Zhou, Yasumoto et al. verified iPAC method’s accuracy using a new set of human platelet samples.

The iPAC method may help scientists studying the steps that lead to clot formation. It may also help clinicians distinguish which clot-causing chemical led to a patient’s heart attack or stroke. This could help them choose whether aspirin or another anti-platelet drug would be the best treatment. But first more studies are needed to confirm whether this method is a useful tool for drug selection or diagnosis.

The central role of thrombin in bleeding disorders

Maintaining normal hemostasis relies on a regulated system of procoagulant and anticoagulant pathways, and disruption of these processes leads to the loss of hemostatic control, with the potential for excessive bleeding or thrombosis. Evaluation of bleeding disorders has conventionally been achieved by laboratory assays that measure the activity of individual coagulation factors. While such assays have proven effective for detecting abnormalities of the coagulation system and aiding diagnosis, inherent limitations prevent them from capturing a complete picture of hemostatic function. An improved understanding of thrombin activity and its central role in hemostasis and bleeding disorders has led to the clinical development of global assays that are more physiologically relevant than traditional assays; furthermore, these global assays are able to monitor responses to therapy. In this review, we provide an overview of the role of thrombin in hemostasis, and describe the clinical benefits of thrombin monitoring in patients with bleeding disorders. Moreover, we discuss recent advances in thrombin-targeting therapeutic strategies that aim to correct thrombin deficiency and prevent bleeding in patients with hemophilia and other rare bleeding disorders.

Why patients with THBD c.1611C>A (p.Cys537X) nonsense mutation have high levels of soluble thrombomodulin?

Background

Recently our group has described a new autosomal dominant bleeding disorder characterized by very high plasma levels of soluble thrombomodulin (TM). The THBD c.1611C>A (p.Cys537X) mutation in heterozygous state was found in the propositus. This mutation leads to the synthesis of a truncated TM which has lost the last three amino-acids of the transmembrane domain and the cytoplasmic tail.

Objective

We investigated the mechanism responsible for TM shedding in endothelial cells with THBD c.1611C>A mutation.

Methods

Complementary DNA of TM wild type (TM-WT) was incorporated into a pcDNA3.1 vector for transient transfection in COS-1 cells. Mutagenesis was performed to create the c.1611C<A (TM_1-536) mutant and 4 other TM mutants (TM_1-515, TM_1-525, TM_1-533 and TM_1-537) with a transmembrane domain having different lengths. The effect of shear stress, metalloprotease inhibitor, certain proteases and reducing agents were tested on TM shedding.

Results

Western blot and immunofluorescent analysis showed that TM_1-536 was produced and a certain amount of TM_1-536 was anchored on the cell membrane. A significantly higher levels of soluble TM was observed in the TM_1-536 cell medium in comparison with TM-WT (56.3 +/- 5.2 vs 8.8 +/- 1.6 ng/mL, respectively, p = 0.001). The shedding of TM_1-536 was 75% decreased in cells cultured in the presence of a metalloprotease inhibitor. No difference was observed between TM_1-536 and TM-WT shedding after cell exposure to cathepsin G, elastase, several reducing agents and high shear stress (5000 s^-1). Significantly higher levels of soluble TM were observed in the cell media of TM_1-533, TM_1-525, TM_1-515 in comparison with TM-WT (p < 0.05).

Conclusion

The mechanism responsible for TM shedding is complex and is not completely understood: higher sensitivity of the TM_1-536 to the proteolysis by metalloproteases and a defect of synthesis due to the decreased size of the transmembrane domain might explain the high levels of soluble TM in plasma of the carriers.

Selective factor VIII activation by the tissue factor-factor VIIa-factor Xa complex

Safe and effective antithrombotic therapy requires understanding of mechanisms that contribute to pathological thrombosis but have a lesser impact on hemostasis. We found that the extrinsic tissue factor (TF) coagulation initiation complex can selectively activate the antihemophilic cofactor, FVIII, triggering the hemostatic intrinsic coagulation pathway independently of thrombin feedback loops. In a mouse model with a relatively mild thrombogenic lesion, TF-dependent FVIII activation sets the threshold for thrombus formation through contact phase-generated FIXa. In vitro, FXa stably associated with TF-FVIIa activates FVIII, but not FV. Moreover, nascent FXa product of TF-FVIIa can transiently escape the slow kinetics of Kunitz-type inhibition by TF pathway inhibitor and preferentially activates FVIII over FV. Thus, TF synergistically primes FIXa-dependent thrombin generation independently of cofactor activation by thrombin. Accordingly, FVIIa mutants deficient in direct TF-dependent thrombin generation, but preserving FVIIIa generation by nascent FXa, can support intrinsic pathway coagulation. In ex vivo flowing blood, a TF-FVIIa mutant complex with impaired free FXa generation but activating both FVIII and FIX supports efficient FVIII-dependent thrombus formation. Thus, a previously unrecognized TF-initiated pathway directly yielding FVIIIa-FIXa intrinsic tenase complex may be prohemostatic before further coagulation amplification by thrombin-dependent feedback loops enhances the risk of thrombosis.

The effects of nanomaterials on blood coagulation in hemostasis and thrombosis

The blood coagulation balance in the organism is achieved by the interaction of the blood platelets (PLTs) with the plasma coagulation system (PCS) and the vascular endothelial cells. In healthy organism, these systems prevent thrombosis and, in events of vascular damage, enable blood clotting to stop bleeding. The dysregulation of hemostasis may cause serious thrombotic and/or hemorrhagic pathologies. Numerous engineered nanomaterials are being investigated for biomedical purposes and are unavoidably exposed to the blood. Also, nanomaterials may access vascular system after occupational, environmental, or other types of exposure. Thus, it is essential to evaluate the effects of engineered nanomaterials on hemostasis. This review focuses on investigations of nanomaterial interactions with the blood components involved in blood coagulation: the PCS and PLTs. Particular emphases include the pathophysiology of effects of nanomaterials on the PCS, including the kallikrein-kinin system, and on PLTs. Methods for investigating these interactions are briefly described, and a review of the most important studies on the interactions of nanomaterials with plasma coagulation and platelets is provided. WIREs Nanomed Nanobiotechnol 2017, 9:e1448. doi: 10.1002/wnan.1448 For further resources related to this article, please visit the WIREs website.

Emerging roles for vascular smooth muscle cell exosomes in calcification and coagulation

Vascular smooth muscle cell (VSMC) phenotypic conversion from a contractile to 'synthetic' state contributes to vascular pathologies including restenosis, atherosclerosis and vascular calcification. We have recently found that the secretion of exosomes is a feature of 'synthetic' VSMCs and that exosomes are novel players in vascular repair processes as well as pathological vascular thrombosis and calcification. Pro-inflammatory cytokines and growth factors as well as mineral imbalance stimulate exosome secretion by VSMCs, most likely by the activation of sphingomyelin phosphodiesterase 3 (SMPD3) and cytoskeletal remodelling. Calcium stress induces dramatic changes in VSMC exosome composition and accumulation of phosphatidylserine (PS), annexin A6 and matrix metalloproteinase-2, which converts exosomes into a nidus for calcification. In addition, by presenting PS, VSMC exosomes can also provide the catalytic surface for the activation of coagulation factors. Recent data showing that VSMC exosomes are loaded with proteins and miRNA regulating cell adhesion and migration highlight VSMC exosomes as potentially important communication messengers in vascular repair. Thus, the identification of signalling pathways regulating VSMC exosome secretion, including activation of SMPD3 and cytoskeletal rearrangements, opens up novel avenues for a deeper understanding of vascular remodelling processes.

The assessment of thrombotic markers utilizing ionic versus non-ionic contrast during coronary angiography and intervention trial

OBJECTIVE

To determine how two different types of iodinated contrast media (CM), low-osmolar ionic dimer ioxaglate (Hexabrix) and iso-osmolar non-ionic dimer iodixanol (Visipaque), affect multiple indices of hemostasis.

BACKGROUND

In vitro models demonstrate differential effects of ionic and non-ionic CM on markers of hemostasis.

METHODS

This blinded endpoint trial randomized 100 patients to ioxaglate or iodixanol. The primary endpoint was change in endogenous thrombin potential (ETP) following diagnostic angiography. Secondary endpoints included change in markers of fibrinolysis [tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1 (PAI-1)] and platelet aggregation following diagnostic angiography and percutaneous coronary intervention (PCI) with bivalirudin. Data are presented as median [interquartile range].

RESULTS

ETP significantly decreased after diagnostic angiography in both ioxaglate (baseline 1810 nM*minute [1540-2089] to post-angiography 649 nM*minute [314-1347], p < 0.001) and iodixanol groups (baseline 1682 nM*minute [1534-2147] to post-angiography 681 nM*minute [229-1237], p < 0.001), but the decrease was not different between CM (p = 0.70). There was a significant increase in ETP during PCI (n = 45), despite the use of bivalirudin, suggesting a prothrombotic effect of PCI (post-angiography 764 nM*minute [286-1283] to post-PCI 1081 nM*minute [668-1552], p = 0.02). There were no significant differential effects on tPA, PAI-1, and markers of platelet activity.

CONCLUSION

There were no significant differential effects between ioxaglate and iodixanol. Both CM led to significant reductions in thrombin generation and no significant effects on fibrinolytic activity or platelet activity, thereby contributing to a favorable antithrombotic milieu. © 2016 Wiley Periodicals, Inc.

Evaluating the Atrial Myopathy Underlying Atrial Fibrillation: Identifying the Arrhythmogenic and Thrombogenic Substrate

Atrial disease or myopathy forms the substrate for atrial fibrillation (AF) and underlies the potential for atrial thrombus formation and subsequent stroke. Current diagnostic approaches in patients with AF focus on identifying clinical predictors with the evaluation of left atrial size by echocardiography serving as the sole measure specifically evaluating the atrium. Although the atrial substrate underlying AF is likely developing for years before the onset of AF, there is no current evaluation to identify the preclinical atrial myopathy. Atrial fibrosis is 1 component of the atrial substrate that has garnered recent attention based on newer MRI techniques that have been applied to visualize atrial fibrosis in humans with prognostic implications regarding the success of treatment. Advanced ECG signal processing, echocardiographic techniques, and MRI imaging of fibrosis and flow provide up-to-date approaches to evaluate the atrial myopathy underlying AF. Although thromboembolic risk is currently defined by clinical scores, their predictive value is mediocre. Evaluation of stasis via imaging and biomarkers associated with thrombogenesis may provide enhanced approaches to assess risk for stroke in patients with AF. Better delineation of the atrial myopathy that serves as the substrate for AF and thromboembolic complications might improve treatment outcomes. Furthermore, better delineation of the pathophysiologic mechanisms underlying the development of the atrial substrate for AF, particularly in its earlier stages, could help identify blood and imaging biomarkers that could be useful to assess risk for developing new-onset AF and suggest specific pathways that could be targeted for prevention.

Acute traumatic coagulopathy: Whole blood thrombelastography measures the tip of the iceberg

BACKGROUND

Thrombelastography (TEG) is suggested as an optimal instrument for the identification of acute traumatic coagulopathy-induced alterations in coagulation status. Patient whole blood (WB) used in TEG analysis is generally collected from a large blood vessel containing representative systemic blood, often close to 40% hematocrit (Hct). Trauma patients often exhibit bleeding from the microvasculature. This study examines early coagulation function changes at the simulated microvascular level based on altered Hct and pH in vitro through TEG analyses of normal donor blood.

METHODS

Anticoagulated normophysiologic fresh human blood was centrifuged. Individual component effects on coagulation were investigated through variable recombination groups: platelet-rich plasma (PRP), platelet-poor plasma (PPP), and red blood cells (RBCs), which were compared with WB. Acute traumatic coagulopathy-induced acidic microvascular environment was simulated and investigated using tissue factor-activated TEG analysis of variable Hct (40%, 30%, 20%, and 0%) samples and variable [H]. Incremental replacement of RBC with either PPP or normal saline (NS) simulated resuscitation in vitro was also conducted under similar conditions.

RESULTS

Only acidified PRP reflected loss of clot strength. Acidified PRP and PPP were delayed equally in clot time. In all groups, inclusion of RBCs normalized clot time. RBC replacement with PPP significantly delayed clot time when samples were acid-challenged, signifying greater acid effect in low Hct microvascular beds. NS simulated resuscitation incurred even greater clotting delays.

CONCLUSION

Acidemia-induced coagulopathy at the level of the capillary Hct (1) is more severe than at higher Hct levels (larger blood vessels), (2) shows that simulated resuscitation with NS causes greater increases in clot time and decreases in clot strength beyond that which occurs with plasma replacement, and (3) may not accurately be portrayed through common TEG practice of testing systemic WB of greater than 30% Hct.

Using a Systems Pharmacology Model of the Blood Coagulation Network to Predict the Effects of Various Therapies on Biomarkers

A number of therapeutics have been developed or are under development aiming to modulate the coagulation network to treat various diseases. We used a systems model to better understand the effect of modulating various components on blood coagulation. A computational model of the coagulation network was built to match in-house in vitro thrombin generation and activated Partial Thromboplastin Time (aPTT) data with various concentrations of recombinant factor VIIa (FVIIa) or factor Xa added to normal human plasma or factor VIII-deficient plasma. Sensitivity analysis applied to the model revealed that lag time, peak thrombin concentration, area under the curve (AUC) of the thrombin generation profile, and aPTT show different sensitivity to changes in coagulation factors' concentrations and type of plasma used (normal or factor VIII-deficient). We also used the model to explore how variability in concentrations of the proteins in coagulation network can impact the response to FVIIa treatment.

Development and validation of a new assay for assessing clot integrity

INTRODUCTION

Research and routine laboratory assessment of clot integrity can be time consuming, expensive, and cannot be batched as it is generally performed in real time. To address these issues, we developed and validated a micro-titre based assay to quantify thrombogenesis and fibrinolysis, the purpose being to assess patients at risk of cardiovascular events by virtue of hypercoagulability. In further validation, thrombogenesis results were compared to similar indices from the thrombelastograph (TEG).

METHODS

Our assay determines three indices of thrombogenesis (lag time to the start of thrombus formation (LT), rate of clot formation (RCF), and maximum clot density (MCD)) and two of fibrinolysis (rate of clot dissolution (RCD) and time for 50% of the clot to lyse (T50)). Plasma was tested fresh and again after being frozen at -70°C. Some samples were tested immediately, others after being left at room temperature for up to 24h.

RESULTS

The intra-assay coefficients of variation (CVs) of the three thrombogenesis measures (LT, RCF, MCD) and two fibrinolysis measures (RCD, T50) varied between 2.7 and 12.0% in fresh plasma and between 1.3% and 10.8% in frozen plasma respectively. Similarly, the inter-assay coefficients of variation of the thrombogenesis and fibrinolysis measures were 4.9-10.8% in fresh plasma and 2.2-6.5% in frozen plasma respectively. TEG assays intra- and inter assay CVs were around 25%. There were no significant differences in all plate assay indices up to 6h at room temperature. Certain plate assay thrombogenesis data were comparable to TEG indices after analysis by Pearson's correlation. The reagent processing cost per sample is £15 for TEG and £2 for the plate assays.

CONCLUSION

Our micro-titre based assay assessing plasma thrombogenesis and fibrinolysis has good intra- and inter-assay CVs, can assess plasma up to 6h after venepuncture, is more efficient (in terms of throughput) and is more economical than that of the TEG.

Modeling thrombin generation: plasma composition based approach

Thrombin has multiple functions in blood coagulation and its regulation is central to maintaining the balance between hemorrhage and thrombosis. Empirical and computational methods that capture thrombin generation can provide advancements to current clinical screening of the hemostatic balance at the level of the individual. In any individual, procoagulant and anticoagulant factor levels together act to generate a unique coagulation phenotype (net balance) that is reflective of the sum of its developmental, environmental, genetic, nutritional and pharmacological influences. Defining such thrombin phenotypes may provide a means to track disease progression pre-crisis. In this review we briefly describe thrombin function, methods for assessing thrombin dynamics as a phenotypic marker, computationally derived thrombin phenotypes versus determined clinical phenotypes, the boundaries of normal range thrombin generation using plasma composition based approaches and the feasibility of these approaches for predicting risk.

Kinetic model facilitates analysis of fibrin generation and its modulation by clotting factors: implications for hemostasis-enhancing therapies

Current mechanistic knowledge of protein interactions driving blood coagulation has come largely from experiments with simple synthetic systems, which only partially represent the molecular composition of human blood plasma. Here, we investigate the ability of the suggested molecular mechanisms to account for fibrin generation and degradation kinetics in diverse, physiologically relevant in vitro systems. We represented the protein interaction network responsible for thrombin generation, fibrin formation, and fibrinolysis as a computational kinetic model and benchmarked it against published and newly generated data reflecting diverse experimental conditions. We then applied the model to investigate the ability of fibrinogen and a recently proposed prothrombin complex concentrate composition, PCC-AT (a combination of the clotting factors II, IX, X, and antithrombin), to restore normal thrombin and fibrin generation in diluted plasma. The kinetic model captured essential features of empirically detected effects of prothrombin, fibrinogen, and thrombin-activatable fibrinolysis inhibitor titrations on fibrin formation and degradation kinetics. Moreover, the model qualitatively predicted the impact of tissue factor and tPA/tenecteplase level variations on the fibrin output. In the majority of considered cases, PCC-AT combined with fibrinogen accurately approximated both normal thrombin and fibrin generation in diluted plasma, which could not be accomplished by fibrinogen or PCC-AT acting alone. We conclude that a common network of protein interactions can account for key kinetic features characterizing fibrin accumulation and degradation in human blood plasma under diverse experimental conditions. Combined PCC-AT/fibrinogen supplementation is a promising strategy to reverse the deleterious effects of dilution-induced coagulopathy associated with traumatic bleeding.

Management of hemorrhage in trauma

Hemorrhage remains one of the leading causes of trauma-related deaths. Uncontrolled diffuse microvascular bleeding in the course of initial care is common, potentially resulting in exsanguination. Early and aggressive hemostatic intervention increases survival and reduces the incidence of massive transfusion. Thus, timely diagnosis of the underlying coagulation disorders is mandatory. It has been shown that standard coagulation tests do not sufficiently characterize trauma-induced coagulopathy (TIC). This has led to increasing interest in alternatives, such as the viscoelastic test, to diagnose TIC and to provide the basis for a goal-directed hemostatic therapy. The concept of damage control resuscitation (DCR) has been introduced widely in trauma patients with severe bleeding. This strategy addresses important confounders of the coagulation process such as hemodilution, hypothermia, and acidosis; DCR is based on a damage control surgical approach, permissive hypotension, and improvement of hemostatic competence. Many studies have shown benefit in mortality when using high ratios of fresh frozen plasma (FFP) to red blood cells (RBC) as early treatment. However, there is increased awareness that coagulation factor concentrate could be beneficial in the treatment of trauma-induced coagulopathy.

Bio-responsive polymer hydrogels homeostatically regulate blood coagulation

Bio-responsive polymer architectures can empower medical therapies by engaging molecular feedback-response mechanisms resembling the homeostatic adaptation of living tissues to varying environmental constraints. Here we show that a blood coagulation-responsive hydrogel system can deliver heparin in amounts triggered by the environmental levels of thrombin, the key enzyme of the coagulation cascade, which—in turn—becomes inactivated due to released heparin. The bio-responsive hydrogel quantitatively quenches blood coagulation over several hours in the presence of pro-coagulant stimuli and during repeated incubation with fresh, non-anticoagulated blood. These features enable the introduced material to provide sustainable, autoregulated anticoagulation, addressing a key challenge of many medical therapies. Beyond that, the explored concept may facilitate the development of materials that allow the effective and controlled application of drugs and biomolecules.

Implementing biomolecular recognition mechanisms in synthetic materials may enable a wealth of biomedical and related applications. Here Maitz et al. present a bio-responsive hydrogel that releases the anticoagulant heparin in amounts proportional to the environmental levels of the procoagulatory protein thrombin.

Anticoagulant effects of statins and their clinical implications

There is evidence indicating that statins (3-hydroxy-methylglutaryl coenzyme A reductase inhibitors) may produce several cholesterol-independent antithrombotic effects. In this review, we provide an update on the current understanding of the interactions between statins and blood coagulation and their potential relevance to the prevention of venous thromboembolism (VTE). Anticoagulant properties of statins reported in experimental and clinical studies involve decreased tissue factor expression resulting in reduced thrombin generation and attenuation of pro-coagulant reactions catalysed by thrombin, such as fibrinogen cleavage, factor V and factor XIII activation, as well as enhanced endothelial thrombomodulin expression, resulting in increased protein C activation and factor Va inactivation. Observational studies and one randomized trial have shown reduced VTE risk in subjects receiving statins, although their findings still generate much controversy and suggest that the most potent statin rosuvastatin exerts the largest effect.

Augmentation of thrombin generation in neonates undergoing cardiopulmonary bypass

INTRODUCTION

Factor concentrates are currently available and becoming increasingly used off-label for treatment of bleeding. We compared recombinant activated factor VII (rFVIIa) with three-factor prothrombin complex concentrate (3F-PCC) for the ability to augment thrombin generation (TG) in neonatal plasma after cardiopulmonary bypass (CPB). First, we used a computer-simulated coagulation model to assess the impact of rFVIIa and 3F-PCC, and then performed similar measurements ex vivo using plasma from neonates undergoing CPB.

METHODS

Simulated TG was computed according to the coagulation factor levels from umbilical cord plasma and the therapeutic levels of rFVIIa, 3F-PCC, or both. Subsequently, 11 neonates undergoing cardiac surgery were enrolled. Two blood samples were obtained from each neonate: pre-CPB and post-CPB after platelet and cryoprecipitate transfusion. The post-CPB products sample was divided into control (no treatment), control plus rFVIIa (60 nM), and control plus 3F-PCC (0.3 IU ml(-1)) aliquots. Three parameters of TG were measured ex vivo.

RESULTS

The computer-simulated post-CPB model demonstrated that rFVIIa failed to substantially improve lag time, TG rate and peak thrombin without supplementing prothrombin. Ex vivo data showed that addition of rFVIIa post-CPB significantly shortened lag time; however, rate and peak were not statistically significantly improved. Conversely, 3F-PCC improved all TG parameters in parallel with increased prothrombin levels in both simulated and ex vivo post-CPB samples.

CONCLUSIONS

Our data highlight the importance of prothrombin replacement in restoring TG. Despite a low content of FVII, 3F-PCC exerts potent procoagulant activity compared with rFVIIa ex vivo. Further clinical evaluation regarding the efficacy and safety of 3F-PCC is warranted.

From principle to practice: bridging the gap in patient profiling

The standard clinical coagulation assays, activated partial thromboplastin time (aPTT) and prothrombin time (PT) cannot predict thrombotic or bleeding risk. Since thrombin generation is central to haemorrhage control and when unregulated, is the likely cause of thrombosis, thrombin generation assays (TGA) have gained acceptance as "global assays" of haemostasis. These assays generate an enormous amount of data including four key thrombin parameters (lag time, maximum rate, peak and total thrombin) that may change to varying degrees over time in longitudinal studies. Currently, each thrombin parameter is averaged and presented individually in a table, bar graph or box plot; no method exists to visualize comprehensive thrombin generation data over time. To address this need, we have created a method that visualizes all four thrombin parameters simultaneously and can be animated to evaluate how thrombin generation changes over time. This method uses all thrombin parameters to intrinsically rank individuals based on their haemostatic status. The thrombin generation parameters can be derived empirically using TGA or simulated using computational models (CM). To establish the utility and diverse applicability of our method we demonstrate how warfarin therapy (CM), factor VIII prophylaxis for haemophilia A (CM), and pregnancy (TGA) affects thrombin generation over time. The method is especially suited to evaluate an individual's thrombotic and bleeding risk during "normal" processes (e.g pregnancy or aging) or during therapeutic challenges to the haemostatic system. Ultimately, our method is designed to visualize individualized patient profiles which are becoming evermore important as personalized medicine strategies become routine clinical practice.

Follow-up of thrombin generation after prostate cancer surgery: global test for increased hypercoagulability

Recent studies provided evidence that evaluation of thrombin generation identifies patients at thrombotic risk. Thrombin generation has a central role in hemorrhage control and vascular occlusion and its measurement provides new metrics of these processes providing sufficient evaluation of an individual's hemostatic competence and response to anticoagulant therapy. The objective of the study is to assess a new measure of hypercoagulability that predisposes to venous thromboembolism in the postoperative period after radical prostatectomy. Pre- (day-1) and postoperative (hour 1, day 6, month 1 and 10) blood samples of 24 patients were tested for plasma thrombin generation (peak thrombin), routine hematology and hemostasis. Patients received low molecular weight heparin for thromboprophylaxis. Peak thrombin levels were higher in patients compared to controls at baseline (p<0.001), and elevated further in the early postoperative period (p<0.001). Longer general anesthesia and high body mass index were associated with increased thrombin generation after surgery (p = 0.024 and p = 0.040). D dimer and fibrinogen levels were higher after radical prostatectomy (p = 0.001 and p<0.001). Conventional clotting tests remained within the reference range. Our study contributed to the cognition of the hypercoagulable state in cancer patients undergoing pelvic surgery and revealed the course of thrombin generation after radical prostatectomy. Whilst it is unsurprising that thrombin generation increases after tissue trauma, further evaluation of this condition during the postoperative period would lead urologists to an international and well-supported consensus regarding thromboprophylaxis in order to provide better clinical outcome. Considering the routine evaluation of procoagulant activity and extending prophylactic anticoagulant therapy accordingly may potentially prevent late thrombotic events.

The prothrombotic phenotypes in familial protein C deficiency are differentiated by computational modeling of thrombin generation

The underlying cause of thrombosis in a large protein C (PC) deficient Vermont kindred appears to be multicausal and not explained by PC deficiency alone. We evaluated the contribution of coagulation factors to thrombin generation in this population utilizing a mathematical model that incorporates a mechanistic description of the PC pathway. Thrombin generation profiles for each individual were generated with and without the contribution of the PC pathway. Parameters that describe thrombin generation: maximum level (MaxL) and rate (MaxR), their respective times (TMaxL, TMaxR), area under the curve (AUC) and clotting time (CT) were examined in individuals ± PC mutation, ± prothrombin G20210A polymorphism and ± thrombosis history (DVT or PE). This family (n = 364) is shifted towards greater thrombin generation relative to the mean physiologic control. When this family was analyzed with the PC pathway, our results showed that: carriers of the PC mutation (n = 81) had higher MaxL and MaxR and greater AUC (all p<0.001) than non-carriers (n = 283); and individuals with a DVT and/or PE history (n = 13) had higher MaxL (p = 0.005) and greater AUC (p<0.001) than individuals without a thrombosis history (n = 351). These differences were further stratified by gender, with women in all categories generating more thrombin than males. These results show that all individuals within this family with or without PC deficiency have an increased baseline procoagulant potential reflective of increased thrombin generation. In addition, variations within the plasma composition of each individual can further segregate out increased procoagulant phenotypes, with gender-associated plasma compositional differences playing a large role.

Prothrombin activation in blood coagulation: the erythrocyte contribution to thrombin generation

Prothrombin activation can proceed through the intermediates meizothrombin or prethrombin-2. To assess the contributions that these 2 intermediates make to prothrombin activation in tissue factor (Tf)-activated blood, immunoassays were developed that measure the meizothrombin antithrombin (mTAT) and α-thrombin antithrombin (αTAT) complexes. We determined that Tf-activated blood produced both αTAT and mTAT. The presence of mTAT suggested that nonplatelet surfaces were contributing to approximately 35% of prothrombin activation. Corn trypsin inhibitor-treated blood was fractionated to yield red blood cells (RBCs), platelet-rich plasma (PRP), platelet-poor plasma (PPP), and buffy coat. Compared with blood, PRP reconstituted with PPP to a physiologic platelet concentration showed a 2-fold prolongation in the initiation phase and a marked decrease in the rate and extent of αTAT formation. Only the addition of RBCs to PRP was capable of normalizing αTAT generation. FACS on glycophorin A-positive cells showed that approximately 0.6% of the RBC population expresses phosphatidylserine and binds prothrombinase (FITC Xa·factor Va). These data indicate that RBCs participate in thrombin generation in Tf-activated blood, producing a membrane that supports prothrombin activation through the meizothrombin pathway.

An integrated fluid-chemical model toward modeling the formation of intra-luminal thrombus in abdominal aortic aneurysms

Abdominal Aortic Aneurysms (AAAs) are frequently characterized by the presence of an Intra-Luminal Thrombus (ILT) known to influence their evolution biochemically and biomechanically. The ILT progression mechanism is still unclear and little is known regarding the impact of the chemical species transported by blood flow on this mechanism. Chemical agonists and antagonists of platelets activation, aggregation, and adhesion and the proteins involved in the coagulation cascade (CC) may play an important role in ILT development. Starting from this assumption, the evolution of chemical species involved in the CC, their relation to coherent vortical structures (VSs) and their possible effect on ILT evolution have been studied. To this end a fluid-chemical model that simulates the CC through a series of convection-diffusion-reaction (CDR) equations has been developed. The model involves plasma-phase and surface-bound enzymes and zymogens, and includes both plasma-phase and membrane-phase reactions. Blood is modeled as a non-Newtonian incompressible fluid. VSs convect thrombin in the domain and lead to the high concentration observed in the distal portion of the AAA. This finding is in line with the clinical observations showing that the thickest ILT is usually seen in the distal AAA region. The proposed model, due to its ability to couple the fluid and chemical domains, provides an integrated mechanochemical picture that potentially could help unveil mechanisms of ILT formation and development.