What is all that thrombin for?

New Frontiers in Skin Rejuvenation, Including Stem Cells and Autologous Therapies

One of the greatest challenges in the progression of aesthetic medicine lies in providing treatments with long-term results that are also minimally invasive and safe. Keeping up with this demand are developments in autologous therapies such as adipose-derived stem cells, stromal vascular fraction, microfat, nanofat, and platelet therapies, which are being shown to deliver satisfactory results. Innovations in more traditional cosmetic therapies, such as botulinum toxin, fillers, and thread lifts, are even more at the forefront of the advancement in aesthetics. Combining autologous therapies with traditional noninvasive methods can ultimately provide patients with more effective rejuvenation options.

Elevated thrombin generation in patients with congenital disorder of glycosylation and combined coagulation factor deficiencies

BACKGROUND

Congenital disorders of glycosylation are rare inherited diseases affecting many different proteins. The lack of glycosylation notably affects the hemostatic system and leads to deficiencies of both procoagulant and anticoagulant factors.

OBJECTIVE

To assess the hemostatic balance in patients with multiple coagulation disorders by using a thrombin generation assay.

METHOD

We performed conventional coagulation assays and a thrombin generation assay on samples from patients with congenital disorder of glycosylation. The thrombin generation assay was performed before and after activation of the protein C system by the addition of soluble thrombomodulin.

RESULTS

A total of 35 patients were included: 71% and 57% had low antithrombin and factor XI levels, respectively. Protein C and protein S levels were abnormally low in 29% and 26% of the patients, respectively, whereas only 11% displayed low factor IX levels. Under baseline conditions, the thrombin generation assay revealed a significantly higher endogenous thrombin potential and thrombin peak in patients, relative to controls. After spiking with thrombomodulin, we observed impaired involvement of the protein C system. Hence, 54% of patients displayed a hypercoagulant phenotype in vitro. All the patients with a history of stroke-like episodes or thrombosis displayed this hypercoagulant phenotype.

CONCLUSION

A thrombin generation assay revealed a hypercoagulant in vitro phenotype under baseline condition; this was accentuated by impaired involvement of the protein C system. This procoagulant phenotype may thus reflect the risk of severe vascular complications. Further research will have to determine whether the thrombin generation assay is predictive of vascular events.

Green fluorescent carbon quantum dots functionalized with polyethyleneimine, and their application to aptamer-based determination of thrombin and ATP

Brightly fluorescent carbon quantum dots coated with polyethylenimine (PEI-CDs) were prepared using malic acid and PEI as the precursors. The PEI-CDs have a high quantum yield (41%) and green emission (peaking at 502 nm under 430 nm excitation), both of which are not affected by high ionic strength. The PEI-CDs have a positive charge at physiological pH values and can electrostatically bind aptamers with their negative charge. This is shown for aptamers binding thrombin or ATP. Binding of aptamers results in quenching of fluorescence. If thrombin or ATP are introduced, the respective aptamer will bind them, and the complex is then released from the PEI-CDs. Fluorescence increases in proportion to the analyte concentration. Under optimized conditions, thrombin and ATP can be sensitively and selectively detected by fluorometry with lower detection limits of 1.2 and 13 nM, respectively. The assay was successfully applied to the determination of thrombin and of ATP in spiked serum samples. Graphical abstract Green fluorescent carbon quantum dots were functionalized with polyethyleneimine. They were applied to aptamer-based determination of thrombin and ATP. The PEI-functionalized carbon quantum dots (PEI-CDs) have bright green fluorescence are were synthesized by one-step hydrothermal treatment of malic acid and PEI. Employing the PEI-CDs, a fluorometric aptamer-based assay was developed for the determination of thrombin and ATP.

Surfing the Blood Coagulation Cascade: Insight into the Vital Factor Xa

Factor Xa (FXa) plays a key role in haemostasis, it is a central part of the blood coagulation cascade which catalyzes the production of thrombin and leads to clot formation and wound closure. Therefore, FXa is an attractive target for the development of new anticoagulant agents. In this review, we will first describe the molecular features of this fundamental protein in order to understand its mechanism of action, an essential background for the design of novel inhibitors by means of synthetic organic chemistry or using peptides obtained from recombinant methodologies. Then, we will review the current state of the synthesis of novel direct FXa inhibitors along with their mechanisms of action. Finally, approved reversal agents that aid in maintaining blood haemostasis by using these commercial drugs will also be discussed.

Clotting factors: Clinical biochemistry and their roles as plasma enzymes

The purpose of this review is to describe structure and function of the multiple proteins of the coagulation system and their subcomponent domains. Coagulation is the process by which flowing liquid blood plasma is converted to a soft, viscous gel entrapping the cellular components of blood including red cells and platelets and thereby preventing extravasation of blood. This process is triggered by the minimal proteolysis of plasma fibrinogen. This transforms the latter to sticky fibrin monomers which polymerize into a network. The proteolysis of fibrinogen is a function of the trypsin-like enzyme termed thrombin. Thrombin in turn is activated by a cascade of trypsin-like enzymes that we term coagulation factors. In this review we examine the mechanics of the coagulation cascade with a view to the structure-function relationships of the proteins. We also note that two of the factors have no trypsin like protease domain but are essential cofactors or catalysts for the proteases. This review does not discuss the major role of platelets except to highlight their membrane function with respect to the factors. Coagulation testing is a major part of routine diagnostic clinical pathology. Testing is performed on specimens from individuals either with bleeding or with thrombotic disorders and those on anticoagulant medications. We examine the basic in-vitro laboratory coagulation tests and review the literature comparing the in vitro and in vivo processes. In vitro clinical testing typically utilizes plasma specimens and non-physiological or supraphysiological activators. Because the review focuses on coagulation factor structure, a brief overview of the evolutionary origins of the coagulation system is included.

Epicatechin influences primary hemostasis, coagulation and fibrinolysis

The different stages of hemostasis (i.e., primary hemostasis, coagulation and fibrinolysis) are involved in the early atherothrombosis steps. The aim of this study was to investigate the effect of epicatechin, a major flavonoid compound, on the hemostasis phenotype using clinically relevant in vitro global assays that mimic the complexity of the in vivo hemostasis systems. Plasma samples from 10 healthy volunteers were spiked with increasing concentrations of epicatechin (1 to 100 μM). Epicatechin effect on primary hemostasis, coagulation and fibrinolysis was assessed by measuring platelet aggregation using light transmission aggregometry, thrombin generation and clot lysis time (CLT), respectively. Epicatechin (100 μM) significantly decreased the maximal platelet aggregation induced by adenosine diphosphate (-39%), thrombin receptor activating peptide (-48%), epinephrine (-30%), and collagen (-30%). The endogenous thrombin potential was significantly reduced starting from 1 μM epicatechin (1332 ± 230 versus 1548 ± 241 nM min for control) (p < 0.01). Fibrinolysis was promoted by epicatechin, as indicated by CLT decrease by 16 and 33% with 10 and 100 μM epicatechin respectively, compared with control (1271 ± 775 s). These findings show that epicatechin reduces platelet function and leads to an anticoagulant and pro-fibrinolytic profile, providing new evidence of its interest for cardiovascular disease prevention.

Comparison of two point of care whole blood coagulation analysis devices and conventional coagulation tests as a predicting tool of perioperative bleeding in adult cardiac surgery-a pilot prospective observational study in Japan

BACKGROUND

It is widely accepted that Point-of Care Test (PoCT) devices are useful in the detection of coagulopathies in situations of massive bleeding such as major cardiac surgery. These devices contribute to the reduction of blood transfusion. However, their implementation remains limited in Japan because of their cost and lack of health insurance support.

STUDY DESIGN AND METHODS

Conventional coagulation tests and thromboelastography (TEG)/Sonoclot values were measured in 50 consecutive cardiac surgery cases. Clinical background information such as operative procedures was obtained from electronic medical records, and the theoretical perioperative total blood loss was calculated by measuring the hemoglobin content and total red blood cell transfusion volume. The correlation between perioperative total blood loss and the measured laboratory values or clinical parameters was evaluated by a multivariate linear regression analysis. The risk factors of the total amount of platelet transfusion and postoperative drain bleeding volume were similarly evaluated.

RESULTS

No significant association between the estimated perioperative total blood loss (eTBL) and the laboratory measurements including conventional coagulation tests, TEG and Sonoclot was observed. On the other hand, postoperative drain bleeding volume was significantly associated with postoperative Sonoclot CR (p = 0.039) as well as preoperative use of oral anticoagulants and cell saver treated blood volume. Platelet transfusion amount was significantly associated with post-CBP PF and time to peak value of Sonoclot (p = 0.014 and 0.001, respectively).

CONCLUSION

Sonoclot measurements may be useful to estimate the risks of postoperative bleeding and platelet transfusion in cardiac surgeries in Japan.

Thrombin Induces Angiotensin II-Mediated Senescence in Atrial Endothelial Cells: Impact on Pro-Remodeling Patterns

BACKGROUND

Besides its well-known functions in hemostasis, thrombin plays a role in various non-hemostatic biological and pathophysiologic processes. We examined the potential of thrombin to promote premature atrial endothelial cells (ECs) senescence.

METHODS AND RESULTS

Primary ECs were isolated from porcine atrial tissue. Endothelial senescence was assessed by measuring beta-galactosidase (SA-β-gal) activity using flow cytometry, oxidative stress using the redox-sensitive probe dihydroethidium, protein level by Western blot, and matrix metalloproteinases (MMPs) activity using zymography. Atrial endothelial senescence was induced by thrombin at clinically relevant concentrations. Thrombin induced the up-regulation of p53, a key regulator in cellular senescence and of p21 and p16, two cyclin-dependent kinase inhibitors. Nicotinamide adenine dinucleotide phosphate NADPH oxidase, cyclooxygenases and the mitochondrial respiration complex contributed to oxidative stress and senescence. Enhanced expression levels of vascular cell adhesion molecule (VCAM)-1, tissue factor, transforming growth factor (TGF)-β and MMP-2 and 9 characterized the senescence-associated secretory phenotype of atrial ECs. In addition, the pro-senescence endothelial response to thrombin was associated with an overexpression of both angiotensin converting enzyme and AT1 receptors and was inhibited by perindoprilat and losartan.

CONCLUSIONS

Thrombin promotes premature ageing and senescence of atrial ECs and may pave the way to deleterious remodeling of atrial tissue by a local up-regulation of the angiotensin system and by promoting pro-inflammatory, pro-thrombotic, pro-fibrotic and pro-remodeling responses. Hence, targeting thrombin and/or angiotensin systems may efficiently prevent atrial endothelial senescence.

Phylovenomics of Daboia russelii across the Indian subcontinent. Bioactivities and comparative in vivo neutralization and in vitro third-generation antivenomics of antivenoms against venoms from India, Bangladesh and Sri Lanka

Russell's viper (Daboia russelii) is, together with Naja naja, Bungarus caeruleus and Echis carinatus, a member of the medically important 'Big Four' species responsible for causing a large number of morbidity and mortality cases across the Indian subcontinent. Despite the wide distribution of Russell's viper and the well-documented ubiquity of the phenomenon of geographic variability of intraspecific snake venom composition, Indian polyvalent antivenoms against the "Big Four" venoms are raised against venoms sourced mainly from Chennai in the southeastern Indian state of Tamil Nadu. Biochemical and venomics investigations have consistently revealed notable compositional, functional, and immunological differences among geographic variants of Russell's viper venoms across the Indian subcontinent. However, these studies, carried out by different laboratories using different protocols and involving venoms from a single geographical region, make the comparison of the different venoms difficult. To bridge this gap, we have conducted bioactivities and proteomic analyses of D. russelii venoms from the three corners of the Indian subcontinent, Pakistan, Bangladesh, and Tamil Nandu (India) and Sri Lanka, along with comparative in vivo neutralization and in vitro third-generation antivenomics of antivenoms used in India, Bangladesh and Sri Lanka. These analyses let us to propose two alternative routes of radiation for Russell's viper in the Indian subcontinent. Both radiations, towards the northeast of India and Bangladesh and towards south India and Sri Lanka, have a common origin in Pakistan, and provide a phylovenomics ground for rationalizing the geographic variability in venom composition and their distinct immunoreactivity against available antivenoms. BIOLOGICAL SIGNIFICANCE: Russell's viper (Daboia russelii), the Indian cobra (Naja naja), the common krait (Bungarus caeruleus), and the saw-scaled viper (Echis carinatus) constitute the 'Big Four' snake species responsible for most snakebite envenomings and deaths in the Indian subcontinent. Despite the medical relevance of Daboia russelii, and the well documented variations in the clinical manifestations of envenomings by this wide distributed species, which are doubtless functionally related to differences in venom composition of its geographic variants, antivenoms for the clinical treatment of envenomings by D. russelii across the Indian subcontinent are invariably raised using venom sourced mainly from the southeastern Indian state of Tamil Nadu. We have applied a phylovenomics approach to compare the venom proteomes of Russell's vipers from the three corners of the Indian subcontinent, Pakistan, Bangladesh, and South India/Sri Lanka, and have assessed the in vitro (third-generation antivenomics) and in vivo preclinical efficacy of a panel of homologous antivenoms. The identification of two dispersal routes of ancestral D. russelii into the Indian subcontinent provides the ground for rationalizing the variability in composition and immunoreactivity of the venoms of extant geographic variants of Russell's viper. Such knowledge is relevant for envisioning strategies to improve the clinical coverage of anti- D. russelii antivenoms.

Reactive microglia and astrocytes in neonatal intraventricular hemorrhage model are blocked by mesenchymal stem cells

Severe intraventricular hemorrhage (IVH) in premature infants triggers reactive gliosis, causing acute neuronal death and glial scar formation. Transplantation of mesenchymal stem cells (MSCs) has often showed improved CNS recovery in an IVH model, but whether this response is related to reactive glial cells is still unclear. Herein, we suggest that MSCs impede the response of reactive microglia rather than astrocytes, thereby blocking neuronal damage. Astrocytes alone showed mild reactiveness under hemorrhagic conditions mimicked by thrombin treatment, and this was not blocked by MSC-conditioned medium (MSC-CM) in vitro. In contrast, thrombin-induced microglial activation and release of proinflammatory cytokines were inhibited by MSC-CM. Interestingly, astrocytes showed greater reactive response when co-cultured with microglia, and this was abolished in the presence of MSC-CM. Gene expression profiles in microglia revealed that transcript levels of genes for immune response and proinflammatory cytokines were altered by thrombin treatment. This result coincided with the robust phosphorylation of STAT1 and p38 MAPK, which might be responsible for the production and release of proinflammatory cytokines. Furthermore, application of MSC-CM diminished thrombin-mediated phosphorylation of STAT1 and p38 MAPK, supporting the acute anti-inflammatory role of MSCs under hemorrhagic conditions. In line with this, activation of microglia and consequent cytokine release were impaired in Stat1-null mice. However, reactive response in Stat1-deficient astrocytes was maintained. Taken together, our results demonstrate that MSCs mainly block the activation of microglia involving STAT1-mediated cytokine release and subsequent reduction of reactive astrocytes.

Compact Grating-Coupled Biosensor for the Analysis of Thrombin

A compact optical biosensor for direct detection of thrombin in human blood plasma (HBP) is reported. This biosensor platform is based on wavelength spectroscopy of diffraction-coupled surface plasmons on a chip with a periodically corrugated gold film that carries an antifouling thin polymer layer consisting of poly[(N-(2-hydroxypropyl)methacrylamide)-co-(carboxybetaine methacrylamide)] (poly(HPMA-co-CBMAA)) brushes. This surface architecture provides superior resistance to nonspecific and irreversible adsorption of abundant compounds in the analyzed HBP samples in comparison to standard surface modifications. The carboxylate groups along the polymer brushes were exploited for the covalent immobilization of aptamer ligands. These ligands were selected to specifically capture the target thrombin analyte from the analyzed HBP sample in a way that does not activate the coagulatory process at the biosensor surface with poly(HPMA-co-CBMAA) brushes. Direct label-free analysis of thrombin in the medically relevant concentration range (1-20 nM) is demonstrated without the need for diluting the HBP samples or using additional steps for signal enhancement. The reported platform constitutes the first step toward a portable and sensitive point-of-care device for direct detection of thrombin in human blood.

Active thrombin produced by the intestinal epithelium controls mucosal biofilms

Proteolytic homeostasis is important at mucosal surfaces, but its actors and their precise role in physiology are poorly understood. Here we report that healthy human and mouse colon epithelia are a major source of active thrombin. We show that mucosal thrombin is directly regulated by the presence of commensal microbiota. Specific inhibition of luminal thrombin activity causes macroscopic and microscopic damage as well as transcriptomic alterations of genes involved in host-microbiota interactions. Further, luminal thrombin inhibition impairs the spatial segregation of microbiota biofilms, allowing bacteria to invade the mucus layer and to translocate across the epithelium. Thrombin cleaves the biofilm matrix of reconstituted mucosa-associated human microbiota. Our results indicate that thrombin constrains biofilms at the intestinal mucosa. Further work is needed to test whether thrombin plays similar roles in other mucosal surfaces, given that lung, bladder and skin epithelia also express thrombin.

The roles played by thrombin in the human intestinal mucosa are unclear. Here, the authors show that the commensal microbiota modulates epithelial production of active thrombin, which controls biofilm growth and contributes to protection of the mucosa from bacterial invasion.

Antithrombotic and Antiplatelet Activities of New Isohopane Triterpene From the Roots of Rubia akane

A new isohopane triterpenoid (1) and two known triterpenoids (2-3) were isolated from the roots of Rubia akane (Rubiaceae). The molecular formula C30H46O4 of 1 was determined by HRESIMS. Detailed NMR spectroscopic data analysis suggested that compound 1 is a new isohopane triterpenoid with a ketone moiety at C-16. Based on the key NOE correlations of H-3/H-5 and H-21/H3-28, compound 1 was determined as 3β-hydroxy-16-oxo-21β-isohop-22(29)-en-24-oic acid. The anticoagulant activities of new isohopane 1 were evaluated by monitoring activated partial thromboplastin time (aPTT), prothrombin time (PT), and the activities of thrombin (Factor IIa, FIIa) and activated factor X (FXa). The effects of 1 on expression of plasminogen activator inhibitor type 1 (PAI-1) and tissue-type plasminogen activator (t-PA) were evaluated in tumor necrosis factor-α activated human umbilical vein endothelial cells. Treatment with 1 (200 μM) resulted in the prolongation of aPTT and PT and the inhibition of relative thrombin (28%) and FXa (29%) activities. In addition, 1 inhibited thrombin-catalyzed fibrin polymerization (18% inhibition at 100 μM) and platelet aggregation (21.8% inhibition at 100 μM). Compound 1 also elicited anticoagulant effects in mice in a dose-dependent manner ranging from 18.8 to 94.0 μg/mouse. In addition, treatment with 1 resulted in significant reduction of the PAI-1 to t-PA ratio (25% decreased). Collectively, the new isohopane triterpenoid 1 possesses antithrombotic activities and offers a basis for the development of a new anticoagulant agent.

Tumor microenvironment and clonal monocytes from chronic myelomonocytic leukemia induce a procoagulant climate

Chronic myelomonocytic leukemia (CMML) is a myeloid hematological malignancy with overlapping features of myelodysplastic syndromes (MDSs) and myeloproliferative neoplasms (MPNs). The knowledge of the role of the tumor microenvironment (TME), particularly mesenchymal stromal cells (MSCs), in MDS pathogenesis is increasing. Generally, cancer is associated with a procoagulant state participating in tumor development. Monocytes release procoagulant, tissue factor (TF)-bearing microparticles. We hypothesized that MSCs and clonal monocytes release procoagulant extracellular vesicles (EVs) within the CMML TME, inducing a procoagulant state that could modify hematopoietic stem cell (HSC) homeostasis. We isolated and cultured MSCs and monocytes from CMML patients and MSCs from healthy donors (HDs). Their medium EVs and small EVs (sEVs) were collected after iterative ultracentrifugations and characterized by nanoparticle tracking analysis. Their impact on hemostasis was studied with a thrombin generation assay and fibrinography. CMML or HD HSCs were exposed to sEVs from either CMML or HD MSCs. CMML MSC sEVs increased HD HSC procoagulant activity, suggesting a transfer of TF from the CMML TME to HD HSCs. The presence of TF on sEVs was shown by electron microscopy and western blot. Moreover, CMML monocyte EVs conferred a procoagulant activity to HD MSCs, which was reversed by an anti-TF antibody, suggesting the presence of TF on the EVs. Our findings revealed a procoagulant "climate" within the CMML environment related to TF-bearing sEVs secreted by CMML MSCs and monocytes.

Oxygenation impairment in patients with acute aortic dissection is associated with disorders of coagulation and fibrinolysis: a prospective observational study

Background

Stanford type-A acute aortic dissection (AAD) is typically accompanied by oxygenation impairment before surgery. In addition, inflammation, coagulation and fibrinolysis also impair blood oxygenation. However, our understanding of the concentration of these factors in bronchoalveolar lavage fluid (BALF) has not been reported. The objective of the study was to investigate the impact of preoperative acute lung injury (ALI) on postoperative oxygenation impairment and to explore the effect of coagulation and fibrinolysis in blood and BALF.

Methods

This investigation utilized a prospective observational study design, which was registered at www.clinicaltrials.gov (identifier NCT01894334). The study included 53 patients undergoing surgery for Stanford type-A AAD at an academic hospital in China between October 2013 and July 2014. Preoperative ALI was identified according to the oxygenation index calculated by the PaO₂/FiO₂ ratio. The subjects were divided into the ALI group (oxygenation index ≤300 mmHg) or the control group (oxygenation index >300 mmHg). The primary outcome was patient oxygenation index, while secondary outcomes were concentrations of tissue factor (TF), tissue factor pathway inhibitor (TFPI), and plasminogen activator inhibitor-1 (PAI-1) in serum and BALF.

Results

The incidence of preoperative ALI for Stanford type-A AAD patients was 41.5%. Stanford type-A AAD patients with preoperative ALI had a lower postoperative oxygenation index (104.6±31.7 vs. 248.7±48.0 mmHg, P<0.001), higher concentrations of TF in serum and BALF (F=133.67, P<0.001; F=68.14, P<0.001), higher concentrations of TFPI in serum and BALF (F=31.98, P<0.001; F=45.58, P<0.001), and higher concentrations of PAI-1 in serum and BALF (F=213.88, P<0.001; F=107.95, P<0.001) when compared with those without preoperative ALI. Type-A AAD patients also showed a greater loss of blood (1,524±458 vs. 1,175±327 mL, P=0.040), longer mechanical ventilation time in the ICU (27.24±8.37 vs. 17.33±7.36 h, P<0.001), longer total stay in the ICU (42.27±10.85 vs. 33.45±9.05 h, P=0.002), and longer total hospital stay (17.77±5.00 vs. 13.48±3.97 days, P=0.001). Multivariate linear regression analysis indicated that preoperative PAI-1 in BALF, and TF in both serum and BALF were significantly associated with preoperative oxygenation impairment in patients with Stanford type-A AAD.

Conclusions

Preoperative ALI caused more serious postoperative oxygenation impairment for Stanford type-A AAD, and coagulation and fibrinolysis appear to play critical roles in this process. Preoperative PAI-1 in BALF and TF in both serum and BALF were significant factors related to the occurrence of preoperative oxygenation impairment for Stanford type-A AAD.

The direct oral anticoagulants rivaroxaban and dabigatran do not inhibit orthotopic growth and metastasis of human breast cancer in mice

Essentials Factor Xa (FXa)-targeting direct oral anticoagulants (DOACs) reduce venous thromboembolism (VTE) The effects of FXa-targeting DOACs on cancer progression remain to be studied In xenograft models, a FXa-targeting DOAC did not inhibit breast cancer growth and metastasis A thrombin-targeting DOAC, dabigatran, also did not inhibit breast cancer growth and metastasis ABSTRACT: Background Factor Xa-targeting DOACs were recently found to reduce recurrent VTE efficiently in cancer patients when compared to the standard treatment with low-molecular-weight heparins (LMWHs). While the anticancer effects of LMWHs have been extensively studied in preclinical cancer models, the effects of FXa-targeting DOACs on cancer progression remain to be studied. Objective We investigated whether the FXa-targeting DOAC rivaroxaban and the thrombin-targeting DOAC dabigatran etexilate (DE) affected human breast cancer growth and metastasis in orthotopic xenograft models. Methods/results Mice that were put on a custom-made chow diet supplemented with rivaroxaban (0.4 or 1.0 mg/g diet) or dabigatran etexilate (DE) (10 mg/g diet) showed prolonged ex vivo coagulation times (prothrombin time [PT] and activated partial thromboplastin time [aPTT] assay, respectively). However, rivaroxaban and DE did not inhibit MDA-MB-231 tumor growth and metastasis formation in lungs or livers of 7-week-old fully immunodeficient NOD/SCID/ƴC-/- (NSG) mice. Comparable data were obtained for rivaroxaban-treated mice when using NOD-SCID mice. Rivaroxaban and DE treatment also did not significantly inhibit tumor growth and metastasis formation when using another human triple negative breast cancer (TNBC) cell line (HCC1806) in NOD-SCID mice. The FXa and thrombin-induced gene expression of the downstream target CXCL8 in both cell lines, but FXa and thrombin, did not significantly stimulate migration, proliferation, or stemness in vitro. Conclusion Although effectively inhibiting coagulation, the DOACs rivaroxaban and DE did not inhibit orthotopic growth and metastasis of human TNBC. It remains to be investigated whether DOACs exert antitumorigenic effects in other types of cancer.

Pharmacokinetics and pharmacodynamics of oral anticoagulants used in atrial fibrillation

INTRODUCTION

The availability of non-vitamin K antagonist oral anti-coagulants alongside vitamin K antagonists has offered a variety of options for anti-coagulation, but has also necessitated a good understanding of the pharmacological properties of each of these drugs prior to their use, to maximise the therapeutic benefit and minimise patient harm Areas covered: This review article outlines the pharmacokinetic and pharmacodynamic profiles of the currently licensed VKAs and NOACs that are most commonly used in clinical practice, with the aim of demonstrating how variations in these characteristics influence their use in clinical practice. A literature search was conducted on PubMed using keywords and relevant articles published by the 31^st of December 2018 were included. Expert opinion: The effect of a drug is determined by a combination of elements which include patient characteristics and external factors, in addition to its pharmacokinetic and pharmacodynamic properties. A good understanding of these is essential. Despite the wealth of information available, particularly on VKAs, our knowledge on the pharmacology responsible for certain drug effects and inter-individual variations is still limited. Increasing efforts are being made to understand these and include focus on pharmacogenomics and drug transporter proteins.

Critical Evaluation of Strategies for the Production of Blood Coagulation Factors in Plant-Based Systems

The use of plants as production platforms for pharmaceutical proteins has been on the rise for the past two decades. The first marketed plant-made pharmaceutical, taliglucerase alfa against Gaucher's disease produced in carrot cells by Pfizer/Protalix Biotherapeutics, was approved by the US Food and Drug Administration (FDA) in 2012. The advantages of plant systems are low cost and highly scalable biomass production compared to the fermentation systems, safety compared with other expression systems, as plant-based systems do not produce endotoxins, and the ability to perform complex eukaryotic post-translational modifications, e.g., N-glycosylation that can be further engineered to achieve humanized N-glycan structures. Although bleeding disorders affect only a small portion of the world population, costs of clotting factor concentrates impose a high financial burden on patients and healthcare systems. The majority of patients, ∼75% in the case of hemophilia, have no access to an adequate treatment. The necessity of large-scale and less expensive production of human blood coagulation factors, particularly factors associated with rare bleeding disorders, may be an important area for plant-based systems, as coagulation factors do not fit into the industry-favored production models. In this review, we explore previous studies on recombinant production of coagulation Factor II, VIII, IX, and XIII in different plant species. Production of bioactive FII and FIX in plants was not achieved yet due to complex post-translational modifications, including vitamin K-dependent γ-carboxylation and propeptide removal. Although plant-made FVIII and FXIII showed specific activities, there are no follow-up studies like pre-clinical/clinical trials. Significant progress has been achieved in oral delivery of bioencapsulated FVIII and FIX to induce immune tolerance in murine models of hemophilia A and B, resp. Potential strategies to overcome bottlenecks in the production systems are also addressed in this review.

Rivaroxaban for prevention and treatment of venous thromboembolism

Until recently, heparins and vitamin K antagonists (VKAs) were the cornerstones for prevention and treatment of venous thromboembolism (VTE). This situation changed with the introduction of the direct oral anticoagulants, which are now replacing low-molecular-weight heparin for thromboprophylaxis after elective hip or knee arthroplasty and VKAs for VTE treatment. Rivaroxaban, an oral factor Xa inhibitor, was the first direct oral anticoagulant licensed for VTE prevention and treatment. This paper provides the rationale for factor Xa as a target for anticoagulants, describes the development of rivaroxaban, reviews its pharmacological profile, discusses the clinical trials with rivaroxaban for VTE prevention and treatment and highlights areas of uncertainty.

Impaired platelet activity and hypercoagulation in healthy term and moderately preterm newborns during the early neonatal period

BACKGROUND

Preterm newborns are at thrombohemorrhagic risk during the early neonatal period. Taking into account the lack of informative tools for the laboratory diagnosis of hemostasis disorders in newborns, our goal was to determine the baseline values of thrombodynamics and platelet functional activity in healthy term and moderately preterm newborns during the early neonatal period future potential clinical use of these tests.

METHODS

Coagulation was assessed using an integral assay of thrombodynamics and standard coagulation assays, and platelet functional activity was estimated by flow cytometry.

RESULTS

Hypercoagulation of newborns, represented by a significantly higher clot growth velocity and the presence of spontaneous clots in the thrombodynamics, was combined with platelet hypoactivity. Granule release, phosphatidylserine exposure, and the ability to change shape upon activation were decreased in the platelets of moderately preterm newborns. The platelet function remained at the same level over the first four days of life, whereas the hypercoagulation became less pronounced.

CONCLUSIONS

The hemostasis of newborns is characterized by hypercoagulation combined with reduced platelet functional activity. Moderately preterm and term newborns do not differ in the parameters of coagulation, while some of the functional responses of platelets are lower in moderately preterm newborns than in term.

Correlation of plasma coagulation tests and fibrinogenClauss with rotational thromboelastometry parameters and prediction of bleeding in dogs

Background

Correlation of plasma fibrinogen concentration (fibrinogen_Clauss) with rotational thromboelastometry (ROTEM) parameters has not been investigated in dogs.

Objectives

To determine the correlation between plasma coagulation tests and fibrinogen_Clauss with ROTEM parameters and to evaluate their ability to predict bleeding in dogs.

Animals

Ninety‐seven dogs with concurrent determination of fibrinogen_Clauss and fibrin polymerization test (FIBTEM) analysis.

Methods

Signalment, pretreatment, clinical signs of bleeding, fibrinogen_Clauss, plasma coagulation test results, hematocrit, platelet count, FIBTEM, extrinsic (EXTEM) and intrinsic (INTEM) activated ROTEM assays were retrieved retrospectively. Correlations between fibrinogen_Clauss and FIBTEM maximum clot firmness (MCF_FIBTEM) and between prothrombin time (PT) or activated partial thromboplastin time (aPTT) and ROTEM parameters were determined. Dogs were further assigned to groups with or without clinical signs of bleeding. The prognostic significance of significantly different parameters to predict bleeding was evaluated.

Results

Fibrinogen_Clauss showed strong correlation with MCF_FIBTEM (r = 0.860, n = 97, P < .001). PT showed strong correlation with EXTEM clotting time (CT_EXTEM) (r = 0.839, n = 53, P < .001), and aPTT was strongly correlated with INTEM CT (CT_INTEM) (r = 0.664, n = 31, P < .001). Platelet count, PT/aPTT, EXTEM clot formation time (CFT_EXTEM), MCF_EXTEM, EXTEM maximum clot elasticity (MCE_EXTEM), and CT_INTEM were significantly different between groups. A CT_INTEM >149 seconds was 100% sensitive to detect bleeding.

Conclusions and Clinical Importance

The MCF_FIBTEM can be used to evaluate the effect of fibrinogen on hemostasis as an alternative to determination of fibrinogen_Clauss. In addition, CT_EXTEM and CT_INTEM are strongly correlated with PT and aPTT, respectively.

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

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

Dynamic Optimization with Particle Swarms (DOPS): a meta-heuristic for parameter estimation in biochemical models

BACKGROUND

Mathematical modeling is a powerful tool to analyze, and ultimately design biochemical networks. However, the estimation of the parameters that appear in biochemical models is a significant challenge. Parameter estimation typically involves expensive function evaluations and noisy data, making it difficult to quickly obtain optimal solutions. Further, biochemical models often have many local extrema which further complicates parameter estimation. Toward these challenges, we developed Dynamic Optimization with Particle Swarms (DOPS), a novel hybrid meta-heuristic that combined multi-swarm particle swarm optimization with dynamically dimensioned search (DDS). DOPS uses a multi-swarm particle swarm optimization technique to generate candidate solution vectors, the best of which is then greedily updated using dynamically dimensioned search.

RESULTS

We tested DOPS using classic optimization test functions, biochemical benchmark problems and real-world biochemical models. We performed [Formula: see text] = 25 trials with [Formula: see text] = 4000 function evaluations per trial, and compared the performance of DOPS with other commonly used meta-heuristics such as differential evolution (DE), simulated annealing (SA) and dynamically dimensioned search (DDS). On average, DOPS outperformed other common meta-heuristics on the optimization test functions, benchmark problems and a real-world model of the human coagulation cascade.

CONCLUSIONS

DOPS is a promising meta-heuristic approach for the estimation of biochemical model parameters in relatively few function evaluations. DOPS source code is available for download under a MIT license at http://www.varnerlab.org .

A novel fibrinogen variant in a Chinese pedigree with congenital dysfibrinogenemia caused by FGA P. Arg38Thr mutation: A case report

RATIONALE

Congenital dysfibrinogenemia (CD) is characterized by altered functional properties of the fibrinogen; people who suffer from CD often have a low activity of fibrinogen and the mutation in the genomic DNA.

PATIENT CONCERNS

A 6-year-old child was examined with a low activity of fibrinogen measured by Von Clauss method and PT-derived method which indicated a normal level of fibrinogen; this abnormality was also detected in her mother. The genomic DNA of all the family members was extracted, and all exons of 3 fibrinogen genes which encode fibrinogen alpha chain (FGA), fibrinogen beta chain (FGB), and fibrinogen gamma chain (FGG) were amplified by polymerase chain reaction (PCR), in addition, sanger sequencing, homologous sequence alignment and bioinformatics software were performed for the further analysis.

DIAGNOSES

CD in this pedigree is associated with c.113G>C in the exon 2 of FGA which caused Arg38Thr mutation.

OUTCOMES

The child and her mother showed a low plasma concentration of fibrinogen measured by Von Clauss method, whereas a normal result measured by PT-derived method; finally, c.113G>C in the exon 2 of FGA was detected in the pedigree which caused Arg38Thr mutation and it is the first report on a pedigree with CD caused by AαArg38Thr.

LESSONS

This case gives us the lesson that not all patients with CD showed typical symptoms and laboratory test results; the result of fibrinogen concentration and antigen which is tested by Von Clauss method and immunoturbidimetric assay is various according to the condition of each CD patient.

Comparison of antithrombin-dependent and direct inhibitors of factor Xa or thrombin on the kinetics and qualitative characteristics of blood clots

BACKGROUND

Venous thromboembolism (VTE) is associated with significant morbidity and mortality.

OBJECTIVES

We investigated the impact of direct and AT-dependent FXa or thrombin inhibitors on thrombus formation.

METHODS

Whole blood thromboelastometry and thrombin generation were assessed after triggering the TF pathway. Clinically relevant concentrations of rivaroxaban, fondaparinux, dabigatran or tinzaparin and an association of rivaroxaban and dabigatran were examined.

RESULTS

All agents delayed thrombus formation in a concentration-dependent manner, as documented by the prolongation of the clotting time (CT) and clot formation time (CFT). Rivaroxaban did not significantly alter the α-angle or maximum clot firmness (MCF). In contrast, dabigatran and fondaparinux altered the process of clot structure by decreasing the α-angle, but did not modify clot firmness. The later property was significantly affected only by tinzaparin that also reduced the MCF. The association of rivaroxaban and dabigatran did not affect the MCF, although it amplified the effect on CFT and α-angle.

CONCLUSIONS

All agents delayed thrombus formation. However, the compounds differed substantially with respect to fibrin polymerization rate and clot firmness. Comparison of the data obtained by thrombin generation assessment with those obtained by the thromboelastometric study shows that the delay in clot formation is principally associated with prolongation of the initiation phase of thrombin formation as well as a reduction of the propagation phase. Tinzaparin was much more potent than the other agents both with regard to suppression of thrombin generation and by delay in clot formation.

Coated platelets introduce significant delay in onset of peak thrombin production: Theoretical predictions

Platelets play a crucial role in the initiation, progress, termination as well as regulation of blood coagulation. Recent studies have confirmed that not all but only a small percentage of thrombin-activated platelets ("coated" platelets) exhibit procoagulant properties (namely the expression of phosphatidylserine binding sites) required for the acceleration and progress of coagulation. A mechanistic model is developed for in vitro coagulation whose key features are distinct equations for coated platelets, thrombin dose-dependence for coated platelets, and competitive binding of coagulation factors to platelet membrane. Model predictions show significant delay in the onset of peak Va production, and peak thrombin production when dose-dependence is incorporated instead of a fixed theoretical maximum percentage of coated platelets. Further, peak thrombin concentration is significantly overestimated when either fractional presence of coated platelets is ignored (by 299.4%) or when dose-dependence on thrombin is ignored (by 24.7%).

Effects of malignancy on blood coagulation in septic intensive care patients

: The objectives of the study are to examine the effect of sepsis on the coagulation profile of patients having solid cancer and to test the hypothesis that septic patients with cancer have normal or increased hemostatic capacity despite prolonged standard coagulation tests (SCTs) compared with noninfected cancer patients. Patients with solid cancer were included in the study forming two groups: study group included patients with sepsis with minimum two organ dysfunctions and control group formed by noninfected cancer patients. SCTs, platelet count, plasma levels of coagulation factors and rotation thromboelastometry (TEM International GmbH, Munich, Germany) were determined in both groups. Study group patients (n = 35) showed prolonged SCTs, thrombocytopenia, decreased coagulation factor levels and increased D-dimer compared with control group (n = 35). However, fibrinogen levels and clot firmness assessed by rotation thromboelastometry were not different between groups and clot lysis indexes at 45 and 60 min were increased in study group compared with control group. The first derivative of the clot firmness curve revealed an increased time to the maximum velocity of clot formation for study group, without differences in the maximum velocity of clot formation, or in total thrombus formation. Sepsis with organ dysfunction in cancer patients is associated with delayed initiation of coagulation and reduced fibrinolysis compared with control patients, but overall clot formation and stabilization is not different. For septic cancer patients, SCTs and plasmatic indicators of fibrinolysis do not translate well to whole blood clot formation and may be misleading indicators of thrombotic or bleeding risk.

Abnormal coagulation and enhanced fibrinolysis due to lysinuric protein intolerance associates with bleeds and renal impairment

INTRODUCTION

Lysinuric protein intolerance (LPI), a rare autosomal recessive transport disorder of cationic amino acids lysine, arginine and ornithine, affects intestines, lungs, liver and kidneys. LPI patients may display potentially life-threatening bleeding events, which are poorly understood.

AIMS

To characterize alterations in haemostatic and fibrinolytic variables associated with LPI.

METHODS

We enrolled 15 adult patients (8 female) and assessed the clinical ISTH/SSC-BAT bleeding score (BS). A variety of metabolic and coagulation assays, including fibrin generation test derivatives, clotting time (CT) and clot lysis time (CLT), thromboelastometry (ROTEM), and PFA-100 and Calibrated Automated Thrombogram (CAT), were used.

RESULTS

All patients had mild-to-moderate renal insufficiency, and moderate bleeding tendency (BS 4) without spontaneous bleeds. Mild anaemia and thrombocytopenia occurred. Traditional clotting times were normal, but in contrast, CT in fibrin generation test, and especially ROTEM FIBTEM was abnormal. The patients showed impaired primary haemostasis in PFA, irrespective of normal von Willebrand factor activity, but together with lowered fibrinogen and FXIII. Thrombin generation (TG) was reduced in vitro, according to CAT-derived endogenous thrombin potential, but in vivo TG was enhanced in the form of circulating prothrombin fragment 1 and 2 values. Very high D-dimer and plasmin-α2-antiplasmin (PAP) complex levels coincided with shortened CLT in vitro.

CONCLUSIONS

Defective primary haemostasis, coagulopathy, fibrin abnormality (FIBTEM, CT and CLT), low TG in vitro and clearly augmented fibrinolysis (PAP and D-dimer) in vivo were all detected in LPI. Altered fibrin generation and hyperfibrinolysis were associated with the metabolic and renal defect, suggesting a pathogenetic link in LPI.

Reversible covalent direct thrombin inhibitors

INTRODUCTION

In recent years, the traditional treatments for thrombotic diseases, heparin and warfarin, are increasingly being replaced by novel oral anticoagulants offering convenient dosing regimens, more predictable anticoagulant responses, and less frequent monitoring. However, these drugs can be contraindicated for some patients and, in particular, their bleeding liability remains high.

METHODS

We have developed a new class of direct thrombin inhibitors (VE-DTIs) and have utilized kinetics, biochemical, and X-ray structural studies to characterize the mechanism of action and in vitro pharmacology of an exemplary compound from this class, Compound 1.

RESULTS

We demonstrate that Compound 1, an exemplary VE-DTI, acts through reversible covalent inhibition. Compound 1 inhibits thrombin by transiently acylating the active site S195 with high potency and significant selectivity over other trypsin-like serine proteases. The compound inhibits the binding of a peptide substrate with both clot-bound and free thrombin with nanomolar potency. Compound 1 is a low micromolar inhibitor of thrombin activity against endogenous substrates such as fibrinogen and a nanomolar inhibitor of the activation of protein C and thrombin-activatable fibrinolysis inhibitor. In the thrombin generation assay, Compound 1 inhibits thrombin generation with low micromolar potency but does not increase the lag time for thrombin formation. In addition, Compound 1 showed weak inhibition of clotting in PT and aPTT assays consistent with its distinctive profile in the thrombin generation assay.

CONCLUSION

Compound 1, while maintaining strong potency comparable to the current DTIs, has a distinct mechanism of action which produces a differentiating pharmacological profile. Acting through reversible covalent inhibition, these direct thrombin inhibitors could lead to new anticoagulants with better combined efficacy and bleeding profiles.

Carboxypeptidase B2 and carboxypeptidase N in the crosstalk between coagulation, thrombosis, inflammation, and innate immunity

Two basic carboxypeptidases, carboxypeptidase B2 (CPB2) and carboxypeptidase N (CPN) are present in plasma. CPN is constitutively active, whereas CPB2 circulates as a precursor, procarboxypeptidase B2 (proCPB2), that needs to be activated by the thrombin-thrombomodulin complex or plasmin bound to glycosaminoglycans. The substrate specificities of CPB2 and CPN are similar; they both remove C-terminal basic amino acids from bioactive peptides and proteins, thereby inactivating them. The complement cascade is a cascade of proteases and cofactors activated by pathogens or dead cells, divided into two phases, with the second phase only being triggered if sufficient C3b is present. Complement activation generates anaphylatoxins: C3a, which stimulates macrophages; and C5a, which is an activator and attractant for neutrophils. Pharmacological intervention with inhibitors has shown that CPB2 delays fibrinolysis, whereas CPN is responsible for systemic inactivation of C3a and C5a. Among mice genetically deficient in either CPB2 or CPN, in a model of hemolytic-uremic syndrome, Cpb2-/- mice had the worst disease, followed by Cpn-/- mice, with wild-type (WT) mice being the most protected. This model is driven by C5a, and shows that CPB2 is important in inactivating C5a. In contrast, when mice were challenged acutely with cobra venom factor, the reverse phenotype was observed; Cpn-/- mice had markedly worse disease than Cpb2-/- mice, and WT mice were resistant. These observations need to be confirmed in humans. Therefore, CPB2 and CPN have different roles. CPN inactivates C3a and C5a generated spontaneously, whereas proCPB2 is activated at specific sites, where it inactivates bioactive peptides that would overwhelm CPN.

Thrombin and factor Xa link the coagulation system with liver fibrosis

Background

Thrombin activates hepatic stellate cells via protease-activated receptor-1. The role of Factor Xa (FXa) in hepatic fibrosis has not been elucidated. We aimed to evaluate the impact of FXa and thrombin in vitro on stellate cells and their respective inhibition in vivo using a rodent model of hepatic fibrosis.

Methods

HSC-LX2 cells were incubated with FXa and/or thrombin in cell culture, stained for αSMA and relative gene expression and gel contraction calculated. C57BL/6 J mice were administered thioacetamide (TAA) for 8 weeks with Rivaroxaban (n = 15) or Dabigatran (n = 15). Control animals received TAA alone (n = 15). Fibrosis was scored and quantified using digital image analysis and hepatic tissue hydroxyproline estimated.

Results

Stellate cells treated with FXa and thrombin demonstrated upregulation of procollagen, TGF-beta, αSMA and significant cell contraction (43.48%+/− 4.12) compared to culturing with FXa or thrombin alone (26.90%+/− 8.90, p = 0.02; 13.1%+/− 9.84, p < 0.001). Mean fibrosis score, percentage area of fibrosis and hepatic hydroxyproline content (2.46 vs 4.08, p = 0.008; 2.02% vs 3.76%, p = 0.012; 276.0 vs 651.3, p = 0.0001) were significantly reduced in mice treated with the FXa inhibitor compared to control mice. FXa inhibition was significantly more effective than thrombin inhibition in reducing percentage area of fibrosis and hepatic hydroxyproline content (2.02% vs 3.70%,p = 0.031; 276.0 vs 413.1,p = 0.001).

Conclusions

FXa promotes stellate cell contractility and activation. Early inhibition of coagulation using a FXa inhibitor significantly reduces TAA induced murine liver fibrosis and may be a viable treatment for liver fibrosis in patients.

Continuous thrombin generation in whole blood: New applications for assessing activators and inhibitors of coagulation

Hemostatic tests have been utilized to clarify the blood coagulation potential. The novel thrombin generation (TG) assay of this study provides explicit information and is the most physiologically-relevant hemostatic test ex vivo. We describe how this assay allows for TG under a number of relevant circumstances. First, whole blood (WB) from healthy individuals was analyzed ± 5 pM tissue factor (TF) and ± contact pathway inhibition. Without an exogenous initiator TG was decreased and delayed, but addition of 5 pM TF shortened the lag phase and increased peak thrombin. Additional experiments included fresh WB from a trauma patient analyzed for endogenous activity and TG from healthy donors subjected to TG antagonists which prolonged the lag phase whereas TG agonists consistently shortened the lag phase in a dose dependent manner. Lastly, platelet-poor plasma was reconstituted with packed red blood cells and TG was monitored in the presence and absence of both TF as an activator and PCPS as a phospholipid surface. Our data illustrate the potential that this continuous TG assay has in the evaluation of disorders relevant to blood coagulation and in the monitoring of treatments administered in response to these disorders.

Thrombosis in Cerebral Aneurysms and the Computational Modeling Thereof: A Review

Thrombosis is a condition closely related to cerebral aneurysms and controlled thrombosis is the main purpose of endovascular embolization treatment. The mechanisms governing thrombus initiation and evolution in cerebral aneurysms have not been fully elucidated and this presents challenges for interventional planning. Significant effort has been directed towards developing computational methods aimed at streamlining the interventional planning process for unruptured cerebral aneurysm treatment. Included in these methods are computational models of thrombus development following endovascular device placement. The main challenge with developing computational models for thrombosis in disease cases is that there exists a wide body of literature that addresses various aspects of the clotting process, but it may not be obvious what information is of direct consequence for what modeling purpose (e.g., for understanding the effect of endovascular therapies). The aim of this review is to present the information so it will be of benefit to the community attempting to model cerebral aneurysm thrombosis for interventional planning purposes, in a simplified yet appropriate manner. The paper begins by explaining current understanding of physiological coagulation and highlights the documented distinctions between the physiological process and cerebral aneurysm thrombosis. Clinical observations of thrombosis following endovascular device placement are then presented. This is followed by a section detailing the demands placed on computational models developed for interventional planning. Finally, existing computational models of thrombosis are presented. This last section begins with description and discussion of physiological computational clotting models, as they are of immense value in understanding how to construct a general computational model of clotting. This is then followed by a review of computational models of clotting in cerebral aneurysms, specifically. Even though some progress has been made towards computational predictions of thrombosis following device placement in cerebral aneurysms, many gaps still remain. Answering the key questions will require the combined efforts of the clinical, experimental and computational communities.

Thrombin generation test: A reliable tool to evaluate the pharmacodynamics of vitamin K antagonist rodenticides in rats

Vitamin K antagonist rodenticide pharmacodynamics (PD) is studied in rodents with traditional laboratory tests. We wondered if thrombin generation test (TGT) could add value. Difethialone (10 mg/kg) was administered per os to 97 OFA-Sprague Dawley rats. PD was studied over a 72 h-period using the Calibrated Automated Thrombogram on platelet poor plasma before and after intoxication (3 female and 3 male rats for each 13 time points) and TGT parameters were compared with the prothrombin time (PT) and vitamin K dependent factor activities previously reported. Following intoxication, preliminary tests evidenced rapid and full inhibition of thrombin generation triggered with 5 or 20 pM human recombinant tissue factor. To study the evolution of TGT parameters following difethialone intake, we adapted the test by complementing intoxicated rat samples with pooled normal rat plasma (3/1, v/v). Adapted TGT confirmed the known higher procoagulant basal level in females compared to males through higher endogenous thrombin potential (ETP) and peak height (PH) (p < 0.0001 and p = 0.0003, respectively). An exponential model fitted well the PH and ETP decay after intoxication. In contrast to PT, the decreases were observed immediately following VKA intake and had comparable time to halving values: 10.5 h (95% CI [8.2; 13.6]) for ETP and 10.4 h (95% CI [7.8; 14.1]) for PH. The decrease of FVII and FX preceded that of PH, ETP and FII while FIX decreased later on, contributing to the severe hypo-coagulability. We demonstrated that TGT performed in samples of intoxicated rats complemented with normal plasma is a reliable tool for evaluation of VKA rodenticide PD in rats.

The roles of cellular and molecular components of a hematoma at early stage of bone healing

Bone healing is a complex repair process that commences with the formation of a blood clot at the injured bone, termed hematoma. It has evidenced that a lack of a stable hematoma causes delayed bone healing or non-union. The hematoma at the injured bone constitutes the early healing microenvironment. It appears to dictate healing pathways that ends in a regenerative bone. However, the hematoma is often clinically removed from the damaged site. Conversely, blood-derived products have been used in bone tissue engineering for treating critical sized defects, including fibrin gels and platelet-rich plasma. A second generation of platelet concentrate that is based on leukocyte and fibrin content has also been developed and introduced in market. Conflicting effect of these products in bone repair are reported. We propose that the bone healing response becomes dysregulated if the blood response and subsequent formation and properties of a hematoma are altered. This review focuses on the central structural, cellular, and molecular components of a fracture hematoma, with a major emphasis on their roles in regulating bone healing mechanism, and their interactions with mesenchymal stem cells. New angles towards a better understanding of these factors and relevant mechanisms involved at the beginning of bone healing may help to clarify limited or adverse effects of blood-derived products on bone repair. We emphasize that the recreation of an early hematoma niche with critical compositions might emerge as a viable therapeutic strategy for enhanced skeletal tissue engineering.

Anwendungen des endogenen Thrombinpotenzials

An overview is given on the method and the applications of thrombin generation assays. Thrombin generation assays provide a tool which can be used to trace the entire thrombin formation and inactivation of a plasma sample. Therefore they are principally different from traditional global assays like PT and aPTT and promise new opportunities for the assessment of bleeding or thrombotic risks.

The impact of frailty on coagulation and responses to warfarin in acute older hospitalised patients with atrial fibrillation: a pilot study

BACKGROUND

The evidence on coagulation changes with frailty is not consistent and clinical studies suggest that frail older people may be at an increased risk of bleeding complications with anticoagulant therapy.

AIMS

This study aims to assess the impact of frailty on coagulation function and on response to warfarin.

METHODS

Inpatients aged over 65 years with atrial fibrillation (AF) were recruited. Frailty was determined using the Reported Edmonton Frail Scale. The Overall Haemostatic Potential (OHP) and Calibrated Automated Thrombogram (CAT) were used to globally assess coagulation function.

RESULTS

Data of 95 participants were analysed, mean age 85.5 ± 6.2, 40% female, and 50.5% frail. Among participants not on anticoagulants (N = 36), there was an increased fibrin generation and decreased thrombin generation compared to the local established normal ranges in young healthy volunteers; the frail had significantly reduced fibrin generation compared to the non-frail. In the warfarin-treated group (N = 59), there was no difference on coagulation profiles between the frail and the non-frail from any of the coagulation tests.

CONCLUSION

In this cohort of acute hospitalised patients with AF, the observed decreased fibrin generation in the frail may reflect decreased acute phase response as suggested with the lower plasma fibrinogen in that group. There was no difference in coagulation profiles between the frail and the non-frail amongst those taking warfarin. Compared to young healthy volunteers, older inpatients had increased fibrin generation and decreased thrombin generation. The findings reflect the complex interaction between age, frailty, acute illness, and coagulation.

Coagulopathy in Children With Liver Disease

It was thought that a high international normalized ratio predicted bleeding in patients with chronic liver disease (CLD) and patients were "autoanticoagulated." Contrary to this belief, while patients with CLD experienced bleeding, they also developed thromboses. In the last decade, the prevailing literature challenged the idea that an elevated international normalized ratio increased bleeding risk. The global assays of coagulation such as thromboelastography (TEG)/rotational thromboelastometry and thrombin generation assays provide additional insight into coagulation processes. It has become apparent that a parallel reduction of procoagulant and anticoagulant factors leave patients in a new "balanced" state, albeit a fragile one, where the balance can be easily disrupted. The inherent differences in coagulation between children and adults such as differences in levels of procoagulant and anticoagulant factors, underlying liver disease, and the paucity of studies in children make extrapolation of these findings to the pediatric population problematic. Ultimately, this is an area that requires further investigation to avoid inappropriate use of blood products and medication.

Venous and arterial thrombosis – pathogenesis and the rationale for anticoagulation

Thromboembolic disorders are major causes of morbidity and mortality. It is well-recognised that the pathogenesis is different for arterial and venous thrombosis; however, both involve coagulation activation. Anticoagulants are used for the prevention and treatment of a wide variety of thromboembolic and related conditions. Agents with anti-inflammatory properties in addition to anticoagulation may be particularly beneficial. Traditional anticoagulants, although effective, are associated with certain limitations. Understanding the pathological processes associated with thrombosis and the rational target for anticoagulation is essential, not only for the development of safer and more effective agents, but also for better clinical management of patients who require anticoagulation therapy. In recent years, new oral agents that target single enzymes of the coagulation cascade have been developed – some of those are in advanced stages of clinical development. Based on scientific rationale, both factor Xa and thrombin are viable targets for effective anticoagulation.

General mechanisms of coagulation and targets of anticoagulants (Section I)

Contrary to previous models based on plasma, coagulation processes are currently believed to be mostly cell surface-based, including three overlapping phases: initiation, when tissue factor-expressing cells and microparticles are exposed to plasma; amplification, whereby small amounts of thrombin induce platelet activation and aggregation, and promote activation of factors (F)V, FVIII and FXI on platelet surfaces; and propagation, in which the Xase (tenase) and prothrombinase complexes are formed, producing a burst of thrombin and the cleavage of fibrinogen to fibrin. Thrombin exerts a number of additional biological actions, including platelet activation, amplification and self-inhibition of coagulation, clot stabilisation and anti-fibrinolysis, in processes occurring in the proximity of vessel injury, tightly regulated by a series of inhibitory mechanisms. ″Classical″ anticoagulants, including heparin and vitamin K antagonists, typically target multiple coagulation steps. A number of new anticoagulants, already developed or under development, target specific steps in the process, inhibiting a single coagulation factor or mimicking natural coagulation inhibitors.