Addition Of Tissue Factor Research Articles

Predictive parameters for spontaneous joint bleeding during emicizumab prophylaxis

AbstractEmicizumab is approved for prophylaxis of patients with hemophilia A (HA). Despite its efficacy in reducing bleeding, some patients on emicizumab still experience hemarthrosis, but no tool is yet available to identify those at a higher risk of spontaneous joint bleeding. This study aimed to evaluate whether laboratory measurements (global coagulation assays and emicizumab concentration) and/or arthropathy scores can distinguish patients at higher risk of spontaneous joint bleeding while on emicizumab prophylaxis. A thrombin generation assay was performed upon the addition of tissue factor and synthetic phospholipids. Nonactivated thromboelastography was performed on citrated whole blood. Emicizumab concentrations were measured using a modified 1-stage factor VIII assay. The degree of hemophilic arthropathy was assessed using the Hemophilia Joint Health Score and Hemophilia Early Arthropathy Detection with Ultrasound (HEAD-US) score. A Cox proportional hazards model was used to evaluate the association between variables and bleeding. The predictive power of these variables was investigated using receiver operating characteristic (ROC) analysis. Forty patients with severe HA, with or without inhibitors, on emicizumab prophylaxis were enrolled in an observational cohort study. Ten of 40 developed spontaneous joint bleeding. None of the laboratory parameters were able to distinguish patients with a higher risk of spontaneous joint bleeding. ROC analysis showed that during emicizumab prophylaxis, only the presence of synovitis and a higher HEAD-US score were associated with spontaneous joint bleeding (area under the curve, 0.84). A greater degree of arthropathy and the presence of synovitis could help predict the risk of spontaneous joint bleeding in patients with HA on emicizumab prophylaxis.

Exploring Coagulation and Fibrinolysis Activation As Mechanisms of Sepsis-Related Tissue Damage in Patients with Severe Neutropenia and Thrombocytopenia Secondary to Hematological Malignancies

Sepsis is a life-threatening end-organ dysfunction resulting from dysregulated host responses to infection with physiopathology not fully understood. Yet, it has been long recognized that platelets and neutrophil extracellular traps collaborate to promote secondary tissue damage. Interestingly, patients with hematological malignancies and febrile neutropenia (FN) secondary to chemotherapy, with neutrophils and platelet counts frequently around zero, develop sepsis and septic shock, raising questions about which mechanisms are involved. Here, we show that extracellular vesicles (EVs) and activation of the fibrinolytic system are two potential mediators of tissue damage in sepsis among patients with very low platelets and neutrophil counts. The study population consisted of patients with hematologic malignancies who underwent antineoplastic treatment and that presented neutrophil counts < 500/μl and temperature ≥ 37.5 °C. Sepsis was defined as an increase of at least 2 points in the Sequential Organ Failure Assessment (SOFA) score and septic shock was defined by the need for vasoactive drugs after adequate volume infusion. Samples were obtained after FN diagnosis, at sepsis onset, and 72 h thereafter. A control group of patients with hematological malignancies and chemotherapy-induced neutropenia without fever was also included. Forty-two subjects, both genders, aged from 21 to 71 years were included and categorized into 4 groups, referred to: FN (n=18), FN + sepsis (n=10), FN + sepsis 72h (n=9), and the control group (n=18). The clinical and laboratory characteristics of these groups are described in Table 1. We first evaluated whether the release of EVs could be associated with the development of sepsis in these patients. EVs were characterized and enumerated from platelet-poor plasma (PPP) obtained from all groups and then separated through high-speed centrifugation (30 min, 20,000 g, 4ºC). EVs were marked with CD146 and 144 for endothelial cells; CD66b for granulocytes; CD14 and CD68 for monocytes, CD41 for platelets, and CD142 for tissue factor (TF) expression. Lactadherin and calcein were used to identify EVs according to size and integrity. Samples were acquired in a flow cytometer, Cytoflex S, with 30 μL/min flow rate and calibration microbeads were used to identify EV of specific sizes (Rosetta). The main findings are shown in Table 2. The main results were an increase in monocyte-derived EVs in patients with FN after sepsis onset (FN + sepsis 72h), compared to all other groups (p=0.01). Moreover, the expression of TF + was higher in these EVs (FN + sepsis 72h) when compared to EVs obtained at sepsis onset (FN + sepsis): 0.50 (IQR 0.29 - 1.10) events/μL versus 0.28 (IQR 0.12 - 0.56) in FN + Sepsis (p=0.03). Additionally, an increase in endothelial (CD146 +) and granulocyte-derived EVs were observed at the same time-point compared to FN and the control group. Of note, monocyte-derived EVs counts were not correlated with monocyte cell counts (Rs= 0.03; p=0.94). Given that coagulation activation plays a role in the immunothrombotic cascade known to mediate tissue damage in sepsis, we also explored whether thrombin and plasmin generation were increased in these patients. Briefly, the assay used PPP and two independent fluorometric substrates for thrombin (Boc-Val-Pro-Arg-MCA) and plasmin (Boc-Glu-Lys-Lys-MCA) in a 96-well plate, lately initiated by the addition of TF (10 pM). The plate was read in a fluorometric spectrophotometer for 4 h. Results are shown in Table 2, and no differences were observed in thrombin generation. However, the area under the curve of plasmin generation, which could be interpreted as a proxy of the plasma fibrinolytic potential, was lower in both FN + sepsis and FN + sepsis 72 h when compared to FN and the control group. Our findings reveal that EVs might present a role in the pathogenesis of sepsis in a scenario where cells known to be critical to this process are virtually absent. The increase of TF + EVs from monocytes, which has been demonstrated in classical sepsis, seems to be relevant even in this context, warranting additional studies using functional assays to further explore this mechanism of tissue damage. Our results also demonstrate that hypofibrinolysis is a characteristic of FN-associated sepsis, suggesting that deregulation of the fibrinolytic system is at least in part independent of the participation of granulocytes and platelets in these patients.

Increased Activated Protein C Response Rates to Thrombin Formation in Asymptomatic Factor V Leiden Carriers Are Driven By the Endothelium

Background The thrombophilic factor V Leiden (FVL) mutation shows a highly variable clinical expressivity. We have shown in vivo that asymptomatic FVL carriers respond to extrinsic coagulation activation with higher activated protein C (APC) formation rates than those with a history of venous thromboembolism (VTE). Recently we have established an ex vivo model for personalized assessment of the protein C (PC) pathway combining endothelial colony forming cells (ECFCs) and autologous plasma. Aim of this study was to investigate potential modulating factors of the APC response in the endothelium unraveling the enigma of the variable expressivity of the FVL phenotype. Methods ECFCs were isolated from FVL carriers with (FVL VTE+) or without (FVL VTE-) a history of unprovoked VTE and healthy controls (non-FVL) (n=7 each). Quality control of cultured cells included cobblestone morphology as examined by light microscopy, positive staining for CD31, CD309, CD201, and CD141, CD34, and negative staining for CD45 analyzed by flow cytometry. We either added autologous or pooled normal defibrinated plasma to the confluent cell culture and inititated thrombin formation by addition of tissue factor (1 pmol/L) and CaCl 2 (16.6 mmol/L) ( Fig. 1A). Thrombin and APC formation were measured over time using oligonucleotide-based enzyme capture assays (OECAs) and the ratio between the area under the curve (AUC) of APC formation and the AUC of thrombin formation was calculated as measure for APC response to thrombin. Moreover, we quantified thrombomodulin (TM) and endothelial protein C receptor (EPCR) expression in cell-based enzyme-linked immunosorbent assays (cell-ELISAs) and measured activation of purified PC on ECFCs in the APC-OECA. Results ECFC morphology in light microscopy and characteristic surface marker expression in flow cytometry did not differ between non-FVL, FVL VTE-, and FVL VTE+ subgroups. In the ECFC-based ex vivo model, the APC response in plasma on autologous cells was significantly higher in asymptomatic FVL VTE- carriers compared to non-FVL carriers (P = .0072) and compared to the FVL VTE+ subgroup (P = .0292) whereas it did not differ significantly between non-FVL and FVL VTE+ carriers. EPCR expression on ECFCs measured by cell-ELISA was higher in non-FVL carriers compared to FVL VTE+ subjects (P = .0374) but did not differ significantly when comparing non-FVL versus FVL VTE-, and FVL VTE+ versus FVL VTE-. Similarly, we showed that TM expression as well as activation of purified PC on ECFCs did not differ between cohorts. However, when the APC response was assessed on FVL VTE- and FVL VTE+ ECFCs using non-FVL plasma, the difference in the APC response between asymptomatic FVL carriers and FVL carriers with a history of VTE persisted (P = .0111) ( Fig. 1B). Conclusion Consistent with previous in vivo experiments, APC response rates to thrombin formation were increased on ECFCs obtained from asymptomatic FVL carriers compared to those from FVL carriers with a history of VTE in autologous plasma. Although TM and EPCR expression did not differ between both groups, we showed that the endothelial APC response in asymptomatic FVL carriers remained increased when using plasma from healthy controls. Our observations suggest that the increased APC response to thrombin in asymptomatic FVL carriers is driven by the endothelium. Further studies are warranted to elucidate the underlying mechanism for a better understanding of endogenous protective factors in FVL carriers. These findings may pave the way towards personalized, precision medicine approaches for managing the thrombotic risk in FVL and other disorders related to the PC pathway.

Ex Vivo Modeling of the PC (Protein C) Pathway Using Endothelial Cells and Plasma: A Personalized Approach.

The endothelial cell-dependent PC (protein C) pathway is critically involved in the regulation of coagulation, anti-inflammatory, and cytoprotective signaling. Its reactivity shows high interindividual variability, and it contributes to prothrombotic disorders, such as the FVL (factor V Leiden) mutation. Endothelial colony-forming cells (ECFCs) were isolated from heparinized peripheral blood from healthy individuals and FVL carriers. Confluent monolayers of ECFCs were overlaid with plasma, and thrombin formation was initiated by addition of tissue factor (1 pmol/L). Subsequently, thrombin and APC (activated PC) formation rates were measured over time using oligonucleotide-based enzyme capture assays. To induce downregulation of TM (thrombomodulin) expression, ECFCs were stimulated with IL-1β (interleukin 1β). In vivo APC response rates were monitored in study participants after infusion of low-dose rFVIIa (recombinant activated factor VII). The median peak APC concentration was 1.12 nmol/L in experiments with IL-1β stimulated ECFCs and 3.66 nmol/L without IL-1β. Although thrombin formation rates were comparable, APC formation rates were significantly higher in FVL carriers (n=6) compared to noncarriers (n=5) as evidenced by a higher ratio between the area under the curve of APC generation to the area under the curve of thrombin generation (median 0.090 versus 0.031, P=0.017). These ex vivo results were correlated with an increased APC response to rFVIIa-induced thrombin formation in FVL carriers in vivo. Patient-specific ex vivo modeling of the PC pathway was achieved using blood-derived ECFCs. The correlation between in and ex vivo APC response rates confirms that the autologous PC model accurately depicts the in vivo situation.

Resonant Acoustic Rheometry to Measure Coagulation Kinetics in Hemophilia A and Healthy Plasma: A Novel Viscoelastic Method.

Compared with conventional coagulation tests and factor-specific assays, viscoelastic hemostatic assays (VHAs) can provide a more thorough evaluation of clot formation and lysis but have several limitations including clot deformation. In this proof-of-concept study, we test a noncontact technique, termed resonant acoustic rheometry (RAR), for measuring the kinetics of human plasma coagulation. Specifically, RAR utilizes a dual-mode ultrasound technique to induce and detect surface oscillation of blood samples without direct physical contact and measures the resonant frequency of the surface oscillation over time, which is reflective of the viscoelasticity of the sample. Analysis of RAR results of normal plasma allowed defining a set of parameters for quantifying coagulation. RAR detected a flat-line tracing of resonant frequency in hemophilia A plasma that was corrected with the addition of tissue factor. Our RAR results captured the kinetics of plasma coagulation and the newly defined RAR parameters correlated with increasing tissue factor concentration in both healthy and hemophilia A plasma. These findings demonstrate the feasibility of RAR as a novel approach for VHA, providing the foundation for future studies to compare RAR parameters to conventional coagulation tests, factor-specific assays, and VHA parameters.

Transcription Factor RUNX1 Regulates Factor FXIIIA Subunit (F13A1) Expression in Megakaryocytic Cells and Platelet F13A1 Expression is Downregulated in RUNX1 Haplodeficiency

Plasma Factor XIII, a transglutaminase, is a complex of two A (gene F13A1) chains with catalytic activity and two B chains (gene F13B). FXIII induces clot stabilization and retraction via cross-linking of fibrin monomers and other proteins. Factor XIII deficiency in plasma causes a major bleeding disorder with impaired clot retraction. FXIIIA is synthesized in megakaryocytes, and is abundant in platelets. It is expressed on activated platelets and cross-links proteins on platelet surface. Little is known regarding the regulation of F13A1 in megakaryocytes and platelets. RUNX1 is a major hematopoietic transcription factor and regulates expression of numerous genes in megakaryocytes and platelets. Patients with RUNX1 haplodeficiency (RHD) with heterozygous mutations have thrombocytopenia, platelet dysfunction with impaired responses to activation, and predisposition to myeloid malignancies. Platelet expression profiling using Affymetrix microarrays of a patient (P1) with a heterozygous RUNX1 mutation (c.969-323G>T) revealed decreased F13A expression, which encodes for subunit A of FXIII: fold-change 0.30; p=0.006; patient profiled twice 10 months apart and compared to 6 healthy subjects. These findings were confirmed by qPCR With RT-PCR platelet F13A mRNA expression was decreased to ~ 20% of mean expression in 4 subjects. Platelet F13A protein expression was decreased by ~50% as assessed by corrected total cellular fluorescence imaging. Platelet F13A mRNA expression was also decreased (to less than 20% of expression in 5 controls) in two siblings (P2 and P3 ages 8 and 3 years) from an unrelated family with a heterozygous RUNX1 mutation 508+1G>A). Plasma FXIII was normal in the patient P1. We studied the regulation of F13A by RUNX1 in human erythroleukemia (HEL) cells treated with phorbol myristate acetate (PMA) to induce megakaryocytic transformation. In silico analyses of the 5' upstream region of F13A showed 7 RUNX1 consensus sites within 545bp from ATG. Chromatin immunoprecipitation studies performed using HEL cells and RUNX1 antibody showed that that RUNX1 binds in the region encompassing site 4 and sites 5-7. In parallel, electrophoretic mobility shift assay (EMSA) studies showed binding of nuclear protein to labeled DNA probes with sites 1, 4, 5, 6, and 7. RUNX1 antibody produced a "supershift" with addition suggesting RUNX1 binding. Site-directed mutagenesis of the RUNX1 binding sites in F13A1 promoter decreased promoter activity in luciferase reporter studies in HEL cells, providing evidence that the binding sites are functional. Further, overexpression of RUNX1 in HEL cells increased F13A1 promoter activity and protein while siRNA RUNX1 knockdown reduced F13A1 protein. We assessed clot retraction over 90 min at 37oC in the patient P1 and his daughter (also with RUNX1 mutation) in citrated whole blood following addition of tissue factor (1 pM) and CaCl2 (1 mM), and in washed platelets resuspended in platelet poor plasma from a healthy subject supplemented with added fibrinogen (0.5 mg/mL) and stimulated with 0.5 U/mL thrombin in the presence of CaCl2. These preliminary studies suggested that clot retraction was slower in the patient P1 compared to the controls, particularly in studies with platelet suspensions. Conclusions: Overall, these studies provide the first evidence that hematopoietic transcription factor RUNX1 regulates expression of F13A1 in megakaryocytic cells and that platelet expression of F13A1 is decreased in platelets from patients with RUNX1 haplodeficiency. The decreased expression of F13A1 in RHD may contribute to the platelet dysfunction in RHD. These findings are particularly interesting because they reflect regulation of a coagulation protein (FXIIIA) by hematopoietic transcription factor RUNX1. Disclosures Lambert: Dova: Consultancy, Membership on an entity's Board of Directors or advisory committees; Principia: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Shionogi: Consultancy; Educational Concepts in Medicine: Consultancy; Octapharma: Consultancy, Research Funding; Bayer: Consultancy; Platelet Disorder Support Association (PDSA): Consultancy; 22qSociety: Consultancy; ITP Australia: Consultancy; CdLS Foundation: Consultancy; RDMD ITP study: Consultancy; Sysmex: Research Funding; AstraZeneca: Research Funding; Argenix: Consultancy; ClinGen: Honoraria.

Molecular Characterization of Two Homozygous Factor VII Variants Associated with Intracranial Bleeding

Introduction Congenital factor (F) VII deficiency is an inherited bleeding disorder with an autosomal recessive inheritance pattern. We report on two probands who had intracranial bleedings as toddlers. One of them had concomitant high titer FVII inhibitor that developed soon after initiation of treatment with recombinant FVII (eptacog alfa, NovoSeven). The underlying molecular mechanisms of these variants by recombinant overexpression in human cell lines were characterized. Methods All nine F7 exons, including exon/intron boundaries, were sequenced, and the sequences were aligned with the NCBI reference sequence for F7. Clotting factor activity, FVII antigen (FVII:Ag) and thrombin generation (TG) were measured in patient plasma. Structural analysis was based on the previously determined crystal structure of the complex of FVII with soluble tissue factor (TF) (PDB ID: 1DAN) and the molecular visualization system PyMOL. The mutations were created by site-directed mutagenesis and human embryonic kidney 293 or Chinese hamster ovary K1 cells were transiently transfected with lipofectamine. FVII:Ag was measured in cells and in supernatants. Endoplasmic reticulum (ER) stress was evaluated by a luciferase reporter assay, and by quantitative RT-PCR. Intracellular localization of FVII was assessed using confocal immunofluorescence microscopy. Results Proband 1 (P1) was homozygous for a deletion of two nucleotides in exon 1, c.27_28delCT, leading to a frame shift and a premature stop codon at amino acid 16 (p.C10Pfs*16), causing nonsense-mediated mRNA decay (NMD). Proband 2 (P2) was homozygous for a missense mutation in exon 8, c.718G>C, resulting in a glycine to arginine substitution at amino acid 240 (p.G240R). The latter variant has previously been described in the literature, but caused by a c.718G>A transition. Both probands had FVII activity < 1 IU/dL and FVII:Ag was concomitantly reduced, i.e. a type I deficiency. P1 developed a high-titer FVII inhibitor (>50 Bethesda Units/mL) shortly after initiation of treatment with NovoSeven. In such plasma with a high-titer of FVII inhibitor, thrombin was not generated within 90 min after the addition of TF and phospholipids to the re-calcified plasma. In P2, TG, especially the parameter lag time, was severely reduced. The amino acid G240 is located in the hydrophobic core within the catalytic domain. Our structure analysis suggests that a glycine to arginine substitution at this position likely will cause steric interactions and destabilization of the catalytic domain. The intracellular levels of FVII-c.27-28delCT were non-detectable and the levels of FVII-c.718 was reduced by 35%, relative to FVIIwt. FVII:Ag secreted to the conditioned medium of both variants was non-detectable. The ER stress luciferase assay and analysis of spliced (s) X-box binding protein (XBP) 1 mRNA demonstrated significantly increased ER stress levels in cells expressing FVII-c.718 compared to FVIIwt. Confocal immunofluorescence microscopy showed that the FVII-c.718 was localized in the ER and not in the Golgi, whereas FVIIwt could be found in both compartments. Conclusions The deficient secretion of the FVII-c.27_28delCT variant was caused by a lack of synthesis of the FVII protein, as a consequence of NMD. The inhibitor development in P1 was likely linked to the complete absence of circulating FVII. The molecular mechanism underlying the FVII-c.718 mutation could be reduced secretion caused by protein destabilization and misfolding. Disclosures No relevant conflicts of interest to declare.

P.849A five-year follow up study of a naturalistic cohort treated with long-acting injectable antipsychotics

Patients with schizophrenia are at increased risk of venous thromboembolism. The mechanisms underlying this association are poorly understood.We investigated whether there is a global hypercoagulable state in patients with schizophrenia utilising the overall haemostatic potential (OHP) assay which assesses overall coagulation potential (OCP), haemostatic potential (OHP) and fibrinolytic potential (OFP).Citrated plasma was collected for OHP assays from patients with schizophrenia on long-term antipsychotic treatment and compared with healthy age- and sex-matched controls. Time courses of fibrin formation and degradation were measured by spectrophotometry (absorption of 405 nm) after the addition of tissue factor and tissue plasminogen activator to plasma.Ninety patients with schizophrenia (antipsychotic treatment-15.9 ± 9.7 years) and 30 controls were recruited. Patients with schizophrenia had higher rates of smoking and levels of inflammatory markers (high-sensitivity C-reactive protein and neutrophil-to-lymphocyte ratio) than controls. Whilst D-dimer, fibrinogen and platelet count did not differ between patients with schizophrenia and controls, the OCP (54.0 ± 12.6 vs 45.9 ± 9.1, p = 0.002) and OHP (12.6 ± 5.8 vs 7.2 ± 3.7, p < 0.001) were higher, and OFP was lower (76.6 ± 9.8% vs 84.9 ± 6.4%, p < 0.001) in patients with schizophrenia, implying both a hypercoagulable and hypofibrinolytic state in these patients. Importantly, abnormalities in overall coagulation were independently predicted by levels of plasminogen-activator-inhibitor-1, fibrinogen, platelet count, inflammatory markers and plasma triglycerides, suggesting a multifactorial aetiology.Patients with schizophrenia have evidence of a global hypercoagulable and hypofibrinolytic state which may contribute to their increased risk of venous thromboembolism.

Анализ влияния транексамовой кислоты, фактора XIII и концентрата фибриногена на формирование и лизис кровяного сгустка при избыточном фибринолизе, индуцированном тканевым и урокиназным активатором плазминогена

Aim of the study. To compare the effects of tranexamic acid (TXA), factor XIII concentrate (FXIII) and fibrinogen concentrate on clot formation and fibrinolytic resistance in the in vitro model of hyperfibrinolysis induced by tissue- (tPA) vs urokinase-type (uPA) plasminogen activators. Materials and methods. Citrated whole blood from 28 adult healthy volunteers was supplemented with 10 μg/ mL TXA, 2 IU/mL FXIII, or 3 mg/mL fibrinogen concentrate. Hyperfibrinolysis was induced by spiking the blood with tPA or uPA at their half-maximal effective concentrations (90 and 33 IU/mL, respectively). Clotting was induced by recalcification and addition of tissue factor and monitored using rotation thromboelastometry. Results. The use of TXA increased maximal clot firmness in the presence of tPA and markedly inhibited clot lysis in the presence of any of the plasminogen activators. Supplementation of blood with FXIII significantly increased clot firmness and improved fibrinolytic resistance in the presence of either tPA or uPA. Supplementation with fibrinogen concentrate elicited a strikingly different effect on clot formation and lysis depending on the type of plasminogen activator. In the presence of tPA, fibrinogen concentrate significantly increased clot firmness and attenuated clot lysis. In contrast, in the presence of uPA, the use of fibrinogen markedly reduced clot firmness and promoted clot lysis. Similar effects of fibrinogen concentrate were observed in platelet-rich and microparticles-free plasma. Conclusion. In hyperfibrinolysis, effect of the hemostatic drugs significantly depends on the type of plasminogen activator used. Therefore, mechanisms of hyperfibrinolysis should be taken into consideration while administering hemostatic drugs.

Graft Product for Autologous Peripheral Blood Stem Cell Transplantation Enhances Thrombin Generation and Expresses Procoagulant Microparticles and Tissue Factor

The beneficial effect of autologous peripheral blood stem cell transplantation (APBSCT) may be compromised by acute vascular complications related to hypercoagulability. We studied the impact of graft product on thrombin generation of normal plasma and the expression of tissue factor (TF) and procoagulant platelet-derived procoagulant microparticles (Pd-MPs) in samples of graft products. Graft products from 10 patients eligible for APBSCT were mixed with platelet-poor plasma (PPP) or platelet-rich plasma (PRP) from healthy volunteers and assessed for in vitro thrombin generation. In control experiments, thrombin generation was assessed in (1) PPP and PRP without any exogenous TF and/or procoagulant phospholipids, (2) PPP with the addition of TF (5 pM) and procoagulant phospholipids (4 μM), (3) in PRP with the addition of TF (5 pM). Graft products were assessed with Western blot assay for TF expression, with a specific clotting assay for TF activity and with flow cytometry assay for Pd-MPs. The graft product enhanced thrombin generation and its procoagulant activity was related to the presence of Pd-MPs and TF. The concentration of Pd-MPs in the graft product was characterized by a significant interindividual variability. The present study reveals the need for a thorough quality control of the graft products regarding their procoagulant potential.

The evaluation of the relevance of thrombin generation and procoagulant activity in thrombotic risk assessment in BCR-ABL-negative myeloproliferative neoplasm patients.

It has been recently suggested that microparticles (MP) play a role in the pathogenesis of thrombotic complications. This study aimed to assess the contribution of procoagulant activity expressed by circulating MP in thrombotic events in MPN patients. Seventy-four MPN patients were enrolled in a trans-sectional study. The MP procoagulant activity was measured using two assays: (i) the thrombin generation (TG) assay used in different conditions with the addition of both tissue factor (TF) and phospholipids (PL) and with the addition of TF or PL alone and (ii) the PROCOAG-PPL assay. The mean age was 62 (26 men and 48 women). The prevalence of thrombotic events was 28%. When comparing patients with thrombosis to those without, age, sex, MPN type, cardiovascular risk factors, and history of thrombosis were not significantly associated with thrombosis. The JAK2 V617F mutation was significantly associated with thrombotic events (90% vs 67%; P=.04). Results from the TG assay and the PROCOAG-PPL assays did not demonstrate a significant association between the MP procoagulant activity and thrombotic events. The MP procoagulant activity did not predict thrombosis in MPN patients. The contribution of TG assay in the assessment of the thrombotic risk is still in debate.

A mathematical model for in vitro coagulation of blood: role of platelet count and inhibition

A mechanistic model including the role of platelets is proposed for clot formation and growth in plasma in vitro. Initiation of clot formation is by the addition of tissue factor, and initiation via the intrinsic pathway is neglected. Activation of zymogens follows the extrinsic pathway cascade and reactions on platelet membranes are included. Platelet activation occurs due to thrombin and also due to other activated platelets. Inhibition of the active clotting factors is by ATIII and TFPI, whereas inhibition due to APC is not relevant in the conditions modeled. The model predictions matched existing data for thrombin production in synthetic plasma. The model predicts that inhibition of platelet-driven activation of platelets has a major effect on concentration of activated platelets in PRP, normal plasma and PPP. Inhibition of platelet activation by (other activated) platelets significantly delays thrombin production in PRP and normal plasma as compared to that by thrombin. Further, sensitivity analysis shows that the model is most sensitive to the activation of platelet membrane-bound factor X by the intrinsic tenase complex.

Imaging analyses of coagulation-dependent initiation of fibrinolysis on activated platelets and its modification by thrombin-activatable fibrinolysis inhibitor.

Using intravital confocal microscopy, we observed previously that the process of platelet phosphatidylserine (PS) exposure, fibrin formation and lysine binding site-dependent plasminogen (plg) accumulation took place only in the centre of thrombi, not at their periphery. These findings prompted us to analyse the spatiotemporal regulatory mechanisms underlying coagulation and fibrinolysis. We analysed the fibrin network formation and the subsequent lysis in an in vitro experiment using diluted platelet-rich plasma supplemented with fluorescently labelled coagulation and fibrinolytic factors, using confocal laser scanning microscopy. The structure of the fibrin network formed by supplemented tissue factor was uneven and denser at the sites of coagulation initiation regions (CIRs) on PS-exposed platelets. When tissue-type plasminogen activator (tPA; 7.5 nM) was supplemented, labelled plg (50 nM) as well as tPA accumulated at CIRs, from where fibrinolysis started and gradually expanded to the peripheries. The lysis time at CIRs and their peripheries (50 µm from the CIR) were 27.9 ± 6.6 and 44.4 ± 9.7 minutes (mean ± SD, n=50 from five independent experiments) after the addition of tissue factor, respectively. Recombinant human soluble thrombomodulin (TMα; 2.0 nM) attenuated the CIR-dependent plg accumulation and strongly delayed fibrinolysis at CIRs. A carboxypeptidase inhibitor dose-dependently enhanced the CIR-dependent fibrinolysis initiation, and at 20 µM it completely abrogated the TMα-induced delay of fibrinolysis. Our findings are the first to directly present crosstalk between coagulation and fibrinolysis, which takes place on activated platelets' surface and is further controlled by thrombin-activatable fibrinolysis inhibitor (TAFI).

Principles of dielectric blood coagulometry as a comprehensive coagulation test.

Dielectric blood coagulometry (DBCM) is intended to support hemostasis management by providing comprehensive information on blood coagulation from automated, time-dependent measurements of whole blood dielectric spectra. We discuss the relationship between the series of blood coagulation reactions, especially the aggregation and deformation of erythrocytes, and the dielectric response with the help of clot structure electron microscope observations. Dielectric response to the spontaneous coagulation after recalcification presented three distinct phases that correspond to (P1) rouleau formation before the onset of clotting, (P2) erythrocyte aggregation and reconstitution of aggregates accompanying early fibrin formation, and (P3) erythrocyte shape transformation and/or structure changes within aggregates after the stable fibrin network is formed and platelet contraction occurs. Disappearance of the second phase was observed upon addition of tissue factor and ellagic acid for activation of extrinsic and intrinsic pathways, respectively, which is attributable to accelerated thrombin generation. A series of control experiments revealed that the amplitude and/or quickness of dielectric response reflect platelet function, fibrin polymerization, fibrinolysis activity, and heparin activity. Therefore, DBCM sensitively measures blood coagulation via erythrocytes aggregation and shape changes and their impact on the dielectric permittivity, making possible the development of the battery of assays needed for comprehensive coagulation testing.

Persistent global hypercoagulability in long-term survivors of acute pulmonary embolism.

Hypercoagulable and/or hypofibrinolytic states are risk factors for venous thromboembolism (VTE) including acute pulmonary embolism. Current screening for thrombophilia is targeted towards identifying a specific defect and guidelines recommend a population-based rather than individualized strategy for anticoagulation treatment. We investigated whether there is a global hypercoagulable state in long-term survivors of pulmonary embolism no longer receiving therapeutic anticoagulation utilizing the overall haemostatic potential (OHP) assay, which assesses overall coagulation potential (OCP), OHP and overall fibrinolytic potential (OFP). Long-term survivors of acute pulmonary embolism were identified from a local registry and OHP assays were performed and compared with age and sex-matched controls without pulmonary embolism. Time courses of fibrin formation and degradation were measured by spectrophotometry (absorption 405 nm) after addition of tissue factor and tissue plasminogen activator to plasma. OHP assays were performed in 67 long-term survivors of single pulmonary embolism (7.9 ± 1.4 years after pulmonary embolism) and 20 age (61.7 ± 11.2 vs 56.6 ± 6.4 years, P = 0.06) and sex (P = 0.45)-matched controls. Survivors of pulmonary embolism were more hypercoagulable as reflected by significantly higher OCP (56.4 ± 13.0 vs 49.9 ± 6.9, P = 0.03) and had impaired fibrinolysis with higher OHP (12.6 ± 7.0 vs 5.9 ± 2.0, P < 0.001) and lower OFP (78.1 ± 9.4 vs 88.2 ± 2.9, P < 0.001) compared with controls. Importantly, these abnormalities in overall coagulation were independently predicted by levels of fibrinogen, platelet count, shortened activated partial thromboplastin time and inflammatory markers suggesting a multifactorial cause. Long-term survivors of pulmonary embolism demonstrate enhanced global coagulation and reduced fibrinolytic potential. Assessment of global coagulation may provide new insights into the aggregate effects of multiple prothombotic factors and long-term risk of VTE recurrence.

The impact of thrombin generation and rotation thromboelastometry on assessment of severity of factor XI deficiency

The phenotype of bleeding in patients with severe FXI deficiency is unpredictable and unlike other bleeding disorders, it is not directly correlated with levels of FXI. In this study we analyzed whether the global coagulation assays can serve as a clinical tool in predicting bleeding tendency in patients with severe FXI deficiency undergoing surgery, taking into account the large inter-individual variability of FXI levels and genotypes. Thrombin generation (TG) was measured in 39 platelet-poor plasma with or without tissue factor (TF) and in the presence or absence of corn trypsin inhibitor (CTI). Rotation thromboelastometry (ROTEM) was performed with fresh whole blood of 26 patients applying NATEM and INTEM tests. TG induced by recalcification can distinguish between bleeding and non-bleeding patients with severe FXI deficiency particularly among those with FXI activity of 2–20IU/dl. The addition of TF or TF and CTI to the TG assay masked the ability to differentiate between XI activity, genotype as well as bleeding and non-bleeding patients. ROTEM assays failed to distinguish bleeding from non-bleeding patients but could do so between different FXI activity levels and genotypes. In conclusion, in the current study we found a sensitive tool to distinguish between bleeding and non-bleeding patients. In order to recommend TG as a predictive tool for treatment tailoring, a larger patient group is required.

Viscoelasticity and Ultrastructure in Coagulation and Inflammation: Two Diverse Techniques, One Conclusion.

The process of blood clotting has been studied for centuries. A synopsis of current knowledge pertaining to haemostasis and the blood components, including platelets and fibrin networks which are closely involved in coagulation, are discussed. Special emphasis is placed on tissue factor (TF), calcium and thrombin since these components have been implicated in both the coagulation process and inflammation. Analysis of platelets and fibrin morphology indicate that calcium, tissue factor and thrombin at concentrations used during viscoelastic analysis (with thromboelastography or TEG) bring about alterations in platelet and fibrin network ultrastructure, which is similar to that seen in inflammation. Scanning electron microscopy indicated that, when investigating platelet structure in disease, addition of TF, calcium or thrombin will mask disease-induced alterations associated with platelet activation. Therefore, washed platelets without any additives is preferred for morphological analysis. Furthermore, morphological and viscoelastic analysis confirmed that thrombin activation is the preferred method of fibrin activation when investigating fibrin network ultrastructure.

Global hypercoagulability in patients with schizophrenia receiving long-term antipsychotic therapy

BackgroundPatients with schizophrenia are at increased risk of venous thromboembolism. The mechanisms underlying this association are poorly understood. AimsWe investigated whether there is a global hypercoagulable state in patients with schizophrenia utilising the overall haemostatic potential (OHP) assay which assesses overall coagulation potential (OCP), haemostatic potential (OHP) and fibrinolytic potential (OFP). MethodCitrated plasma was collected for OHP assays from patients with schizophrenia on long-term antipsychotic treatment and compared with healthy age- and sex-matched controls. Time courses of fibrin formation and degradation were measured by spectrophotometry (absorption of 405nm) after the addition of tissue factor and tissue plasminogen activator to plasma. ResultsNinety patients with schizophrenia (antipsychotic treatment-15.9±9.7years) and 30 controls were recruited. Patients with schizophrenia had higher rates of smoking and levels of inflammatory markers (high-sensitivity C-reactive protein and neutrophil-to-lymphocyte ratio) than controls. Whilst D-dimer, fibrinogen and platelet count did not differ between patients with schizophrenia and controls, the OCP (54.0±12.6 vs 45.9±9.1, p=0.002) and OHP (12.6±5.8 vs 7.2±3.7, p<0.001) were higher, and OFP was lower (76.6±9.8% vs 84.9±6.4%, p<0.001) in patients with schizophrenia, implying both a hypercoagulable and hypofibrinolytic state in these patients. Importantly, abnormalities in overall coagulation were independently predicted by levels of plasminogen-activator-inhibitor-1, fibrinogen, platelet count, inflammatory markers and plasma triglycerides, suggesting a multifactorial aetiology. ConclusionPatients with schizophrenia have evidence of a global hypercoagulable and hypofibrinolytic state which may contribute to their increased risk of venous thromboembolism.

Abnormal plasma clot structure and stability distinguish bleeding risk in patients with severe factor XI deficiency

Factor XI (FXI) deficiency is a rare autosomal recessive disorder. Many patients with even very low FXI levels (<20IUdL(-1) ) are asymptomatic or exhibit only mild bleeding, whereas others experience severe bleeding, usually following trauma. Neither FXI antigen nor activity predicts the risk of bleeding in FXI-deficient patients. (i) Characterize the formation, structure and stability of plasma clots from patients with severe FXI deficiency and (ii) determine whether these assays can distinguish asymptomatic patients ('non-bleeders') from those with a history of bleeding ('bleeders'). Platelet-poor plasmas were prepared from 16 severe FXI-deficient patients who were divided into bleeders or non-bleeders, based on bleeding associated with at least two tooth extractions without prophylaxis. Clot formation was triggered by recalcification and addition of tissue factor and phospholipids in the absence or presence of tissue plasminogen activator and/or thrombomodulin. Clot formation and fibrinolysis were measured by turbidity and fibrin network structure by laser scanning confocal microscopy. Non-bleeders and bleeders had similarly low FXI levels, normal prothrombin times, normal levels of fibrinogen, factor VIII, von Willebrand factor and factor XIII, and normal platelet number and function. Compared with non-bleeders, bleeders exhibited lower fibrin network density and lower clot stability in the presence of tissue plasminogen activator. In the presence of thrombomodulin, seven of eight bleeders failed to form a clot, whereas only three of eight non-bleeders did not clot. Plasma clot structure and stability assays distinguished non-bleeders from bleeders. These assays may reveal hemostatic mechanisms in FXI-deficient patients and have clinical utility for assessing the risk of bleeding.

Natural history of hypercoagulability in patients undergoing coronary revascularization and effect of preoperative myocardial infarction

The balance between hyper- and hypocoagulable states is critical after coronary artery surgery both with (coronary artery bypass grafting [CABG]) and without (off-pump coronary artery bypass [OPCAB]) cardiopulmonary bypass to prevent thrombotic or bleeding complications. We aimed to quantify novel parameters of coagulation, fibrinolysis, and overall hemostasis ≤6 months after CABG and OPCAB and to determine the influences on these parameters. A total of 63 patients (30 CABG, 33 OPCAB) had blood collected before and at various points ≤6 months after surgery. Fibrin and fibrinolysis time curves were generated by measuring the absorption of 405 nm each minute for 100 minutes after the addition of tissue factor and tissue plasminogen activator to cell-free plasma. The parameters were compared with those from a group of healthy controls. The patients' preoperative prothrombotic assay parameters were compared with those from healthy controls. Both CABG and OPCAB patients were hypercoagulable until at least day 10 after surgery, with elevation of fibrin generation (CABG, peak day 3, +28.9%; OPCAB, peak day 1, +16.3% vs preoperative baseline) and impairment of fibrinolysis capacity (CABG, day 1, -58.4%; OPCAB, day 1, -22.6%). Surgical revascularization resulted in resolution of preoperative hypercoagulability by 6 months postoperatively. Patients with preoperative myocardial infarction (MI) had prolonged hypercoagulability after surgery that was most exaggerated after CABG (overall hemostatic potential day 5, no MI, +64.1% vs with MI, +128.9% compared with baseline; P=.013). Patients will be vulnerable to thrombotic events for ≤6 weeks after coronary surgery yet will have resolution of hypercoagulability by 6 months. Preoperative factors, such as MI, could require individualized management of thrombosis prophylaxis in the postoperative period.