What is all that thrombin for?

Pharmacological Difference Between Platelet Aggregations in Cardioembolic Stroke Patients with Direct Oral Anticoagulants: A Pilot Study

Background Selecting the appropriate direct oral anticoagulants (DOACs) for embolic ischemic stroke patients, especially on concurrent antiplatelet therapy, is important. However, a limited number of studies have reported on the pharmacological differences in platelet aggregation of each DOAC. We aimed to evaluate the antiplatelet effects of selected DOACs, by comparing dabigatran (a direct oral thrombin inhibitor) and factor Xa (FXa) inhibitors (apixaban and rivaroxaban) in patients who had suffered a cardioembolic stroke. Methods We retrospectively evaluated 12 patients diagnosed with a cardioembolic stroke who took any DOAC without an antiplatelet drug and underwent platelet aggregation tests within 60 days from the onset of symptoms. The platelet aggregation tests were analyzed by both light transmission aggregometry and VerifyNow®. Results Six patients (50%) took dabigatran, while the other six (50%) took an FXa inhibitor (n = 4 for apixaban and n = 2 for rivaroxaban). From the light transmission aggregometry analysis, it was found that the maximal extent of aggregation for adenosine diphosphate (ADP) was significantly higher with dabigatran than with FXa inhibitors, and the ED₅₀ value of ADP on platelet aggregation was significantly lower with dabigatran than with FXa inhibitors. Moreover, the VerifyNow® analyses revealed that P2Y₁₂ reaction units were significantly higher with dabigatran than with FXa inhibitors. Conclusions Dabigatran had little impact on platelet aggregation compared to FXa inhibitors in patients who had suffered a cardioembolic stroke with atrial fibrillation, and who took DOACs for secondary prevention within 60 days from the onset.

The role of procoagulant phospholipids on the surface of circulating blood cells in thrombosis and haemostasis

Phospholipids (PLs) are found in all cell types and are required for structural support and cell activation signalling pathways. In resting cells, PLs are asymmetrically distributed throughout the plasma membrane with native procoagulant aminophospholipids (aPLs) being actively maintained in the inner leaflet of the membrane. Upon platelet activation, aPLs rapidly externalize to the outer leaflet and are essential for supporting the coagulation cascade by providing binding sites for factors in the cell-based model. More recent work has uncovered a role for enzymatically oxidized PLs (eoxPLs) in facilitating coagulation, working in concert with native aPLs. Despite this, the role of aPLs and eoxPLs in thrombo-inflammatory conditions, such as arterial and venous thrombosis, has not been fully elucidated. In this review, we describe the biochemical structures, distribution and regulation of aPL externalization and summarize the literature on eoxPL generation in circulating blood cells. We focus on the currently understood role of these lipids in mediating coagulation reactions in vitro, in vivo and in human thrombotic disease. Finally, we highlight gaps in our understanding in how these lipids vary in health and disease, which may place them as future therapeutic targets for the management of thrombo-inflammatory conditions.

Persistent hypercoagulability in dogs envenomated by the European adder (Vipera berus berus)

Background

Envenomation by the European adder, Vipera berus berus (Vbb), is a medical emergency. The overall in vivo haemostatic effects of pro- and anticoagulant components in Vbb venom, and the downstream effects of cellular injury and systemic inflammation, are unclear.

Objectives

To longitudinally describe the global coagulation status of dogs after Vbb envenomation and compare to healthy controls. A secondary aim was to investigate differences between dogs treated with and without antivenom.

Methods

Citrated plasma was collected at presentation, 12 hours (h), 24 h, 36 h and 15 days after bite from 28 dogs envenomated by Vbb, and from 28 healthy controls at a single timepoint. Thrombin generation (initiated with and without exogenous phospholipids and tissue factor), thrombin-antithrombin (TAT)-complexes and the procoagulant activity of phosphatidylserine (PS)-expressing extracellular vesicles (EVs), expressed as PS-equivalents, were measured.

Results

At presentation the envenomated dogs were hypercoagulable compared to controls, measured as increased thrombin generation, TAT-complexes and PS-equivalents. The hypercoagulability decreased gradually but compared to controls thrombin generation and PS-equivalents were still increased at day 15. The discrepancy in peak thrombin between envenomated dogs and controls was greater when the measurement was phospholipid-dependent, indicating that PS-positive EVs contribute to hypercoagulability. Lag time was shorter in non-antivenom treated dogs, compared to antivenom treated dogs <24 h after envenomation.

Conclusions

Hypercoagulability was measured in dogs up to 15 days after Vbb envenomation. Dogs treated with antivenom may be less hypercoagulable than their non-antivenom treated counterparts. Thrombin generation is a promising diagnostic and monitoring tool for Vbb envenomation.

Mapping the Prothrombin Binding Site of Pseutarin C by Site-directed PEGylation

Results support our previously published model and reveal the surprising role of the a1-loop in presenting Arg320 for initial cleavage.

Using pseutarin C as model prothrombinase, the interaction site for prothrombin was probed by site-directed PEGylation and other mutations.

The prothrombinase complex processes prothrombin to thrombin through sequential cleavage at Arg320 followed by Arg271 when cofactor, factor (f) Va, protease, fXa, and substrate, prothrombin, are all bound to the same membrane surface. In the absence of the membrane or cofactor, cleavage occurs in the opposite order. For the less favorable cleavage site at Arg320 to be cleaved first, it is thought that prothrombin docks on fVa in a way that presents Arg320 and hides Arg271 from the active site of fXa. Based on the crystal structure of the prothrombinase complex from the venom of the Australian eastern brown snake, pseutarin C, we modeled an initial prothrombin docking mode, which involved an interaction with discrete portions of the A1 and A2 domains of fV and the loop connecting the 2 domains, known as the a1-loop. We interrogated the proposed interface by site-directed PEGylation and by swapping the a1-loop in pseutarin C with that of human fV and fVIII and measuring the effect on rate and pathway of thrombin generation. PEGylation of residues within our proposed binding site greatly reduced the rate of thrombin generation, without affecting the pathway, whereas those outside the proposed interface had no effect. PEGylation of residues within the a1-loop also reduced the rate of thrombin generation. The sequence of the a1-loop was found to play a critical role in prothrombin binding and in the presentation of Arg320 for initial cleavage.

Development of an Innovative Quantification Assay Based on Aptamer Sandwich and Isothermal Dumbbell Exponential Amplification

Detecting blood biomarkers such as proteins with high sensitivity and specificity is of the utmost importance for early and reliable disease diagnosis. As molecular probes, aptamers are raising increasing interest for biosensor applications as an alternative to antibodies, which are used in classical enzyme-linked immuno-sorbent assays (ELISA). We have developed a sensitive and antibody-free molecular quantification assay that combines the specificity of aptamers and the sensitivity of the loop-mediated isothermal amplification (LAMP). For the proof-of-concept, we consider two types of biomarkers: (i) a model of oligonucleotide mimicking nucleic acid targets and (ii) the thrombin involved in the complex coagulation cascade as a model protein for which two relevant aptamers form a stable sandwich. The assay protocol is based on a few successive steps, similar to sandwich ELISA. First, aptamer-coated magnetic beads are added to the sample to specifically capture the targets. Then, the sandwich complex is formed by adding the second aptamer. This secondary aptamer is integrated in a larger oligonucleotide dumbbell sequence designed for LAMP detection using only two primers. After a proper rinsing step, the isothermal dumbbell exponential amplification is performed to detect and quantify a low amount of targets (limit of detection ∼ 1 pM for the oligonucleotide and ∼100 pM for thrombin). This study demonstrates that our innovative aptamero-LAMP assay could be relevant for the detection of different types of biomarkers and their quantification at physiological levels. This may also pave the way for antibody-free molecular assays.

Major bleeding during oral anticoagulant therapy associated with factor V activation by factor Xa

OBJECTIVE

Plasma thrombin generation (TG) provides important information on coagulation status; however, current TG output parameters do not predict major bleeding of patients on anticoagulants. We recently reported that factor V (FV) activation by factor X (FX)a contributes importantly to the initiation phase of TG. Here we investigated how this pathway varies in the normal population and whether FXa-mediated activation of FV is associated with major bleeding in patients on anticoagulant therapy.

APPROACH

We employed TIX-5, a specific inhibitor of FV activation by FXa, to estimate the contribution of FXa-mediated FV activation to tissue factor (TF)-initiated TG.

RESULTS

We show that the contribution of this pathway to plasma TG varies considerably in the normal population, as measured by the time needed to form the first traces of thrombin (TG lag time; mean prolongation by TIX-5 40%, range 0%-116%). Comparing patients on vitamin K antagonists (VKA) of the BLEED study (263 patients with and 538 patients without major bleeding), showed a marked prolongation in the median TG lag time in the presence of TIX-5 in cases (12.83 versus 11.00 minutes, P = 0.0030), while the TG lag time without TIX-5 only showed a minor although significant difference (5.83 vs. 5.67 minutes, P = 0.0198). The TIX-5 sensitivity (lag time + TIX-5/lag time + vehicle) in the upper quartile was associated with a 1.62-fold (95% confidence interval 1.04-2.52) increased risk of major bleeding compared to the lowest quartile.

CONCLUSION

A greater dependence on FXa-mediated activation of FV of TG is associated with increased risk of major bleeding during VKA therapy.

Bioresponsive Polyphenol-Based Nanoparticles as Thrombolytic Drug Carriers

Thrombolytic (clot-busting) therapies with plasminogen activators (PAs) are first-line treatments against acute thrombosis and ischemic stroke. However, limitations such as narrow therapeutic windows, low success rates, and bleeding complications hinder their clinical use. Drug-loaded polyphenol-based nanoparticles (NPs) could address these shortfalls by delivering a more targeted and safer thrombolysis, coupled with advantages such as improved biocompatibility and higher stability in vivo. Herein, a template-mediated polyphenol-based supramolecular assembly strategy is used to prepare nanocarriers of thrombolytic drugs. A thrombin-dependent drug release mechanism is integrated using tannic acid (TA) to cross-link urokinase-type PA (uPA) and a thrombin-cleavable peptide on a sacrificial mesoporous silica template via noncovalent interactions. Following drug loading and template removal, the resulting NPs retain active uPA and demonstrate enhanced plasminogen activation in the presence of thrombin (1.14-fold; p < 0.05). Additionally, they display lower association with macrophage (RAW 264.7) and monocytic (THP-1) cell lines (43 and 7% reduction, respectively), reduced hepatic accumulation, and delayed blood clearance in vivo (90% clearance at 60 min vs 5 min) compared with the template-containing NPs. Our thrombin-responsive, polyphenol-based NPs represent a promising platform for advanced drug delivery applications, with potential to improve thrombolytic therapies.

Correlations between rotational thromboelastometry (ROTEM) and standard coagulation tests following viper snakebites

BACKGROUND

A high prevalence of venom-induced consumption coagulopathy has been reported in individuals with viper snakebites. Rotational thromboelastometry (ROTEM) is a rapid technique that could be advantageous in assessing and monitoring coagulation disorders.

PURPOSE

To explore correlations between ROTEM and standard coagulation tests.

PATIENTS AND METHODS

This prospective observational study was performed among 41 patients with viper envenomation admitted to the Vietnam Poison Control Center from April 2016 to October 2017. Standard coagulation measurements [platelet count, prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen level] and ROTEM indicators [clotting time (CT), amplitude (at set time: 5 and 10 minutes), clot information time (CFT) and maximum clot firmness (MCF) for extrinsic (EXTEM), intrinsic (INTEM), and fibrin based (FIBTEM) ROTEM] were obtained.

RESULTS

For INTEM, EXTEM, the FIBTEM, proportions of patients with prolonged CT were 34.1%, 63.4%, and 61.0% respectively and the proportions of patients with decreased MCF were 62.2%, 62.2%, and 35.5%, respectively. Moderate correlations were observed between PT and EXTEM CT (r = 0.627), aPTT and INTEM CT (r = 0.626), fibrinogen and FIBTEM MCF (r = 0.723), and platelet count and EXTEM MCF (0.60).

CONCLUSION

ROTEM indicated a hypocoagulation state in patients with viper snakebite and was moderately correlated with standard coagulation parameters.

Factor Xa Inhibitors for Patients after Mechanical Heart Valve Replacement?

Patients with a mechanical heart valve need a lifelong anticoagulation due to the increased risk of valve thrombosis and thrombo-embolism. Currently, vitamin K antagonists (VKA) are the only approved class of oral anticoagulants, but relevant interactions and side effects lead to a large number of patients not achieving the optimal therapeutic target international normalized ration (INR). Therefore, steady measurements of the INR are imperative to ensure potent anticoagulation within a distinctive range. Direct oral anticoagulants (DOACs) with newer agents could serve as a possible alternative to VKAs in this patient cohort. DOACs are approved for several indications, e.g., atrial fibrillation (AF). They only have a minor interaction potential, which is why monitoring is not needed. Thereby, DOACs improve the livability of patients in need of chronical anticoagulation compared with VKAs. In contrast to dual platelet inhibition using aspirin in combination with an ADP receptor antagonist and the direct thrombin inhibitor dabigatran, the oral factor Xa inhibitors apixaban and rivaroxaban show promising results according to current evidence. In small-scale studies, factor Xa inhibitors were able to prevent thrombosis and thrombo-embolic events in patients with mechanical heart valves. Finally, DOACs seem to represent a feasible treatment option in patients with mechanical heart valves, but further studies are needed to evaluate clinical safety. In addition to the ongoing PROACT Xa trial with apixaban in patients after aortic On-X valve implantation, studies in an all-comer collective with rivaroxaban could be promising.

The Role of TEG and ROTEM in Damage Control Resuscitation

ABSTRACT

Trauma-induced coagulopathy is associated with very high mortality, and hemorrhage remains the leading preventable cause of death after injury. Directed methods to combat coagulopathy and attain hemostasis are needed. The available literature regarding viscoelastic testing, including thrombelastography (TEG) and rotational thromboelastometry (ROTEM), was reviewed to provide clinically relevant guidance for emergency resuscitation. These tests predict massive transfusion and developing coagulopathy earlier than conventional coagulation testing, within 15 min using rapid testing. They can guide resuscitation after trauma, as well. TEG and ROTEM direct early transfusion of fresh frozen plasma when clinical gestalt has not activated a massive transfusion protocol. Reaction time and clotting time via these tests can also detect clinically significant levels of direct oral anticoagulants. Slowed clot kinetics suggest the need for transfusion of fibrinogen via concentrates or cryoprecipitate. Lowered clot strength can be corrected with platelets and fibrinogen. Finally, viscoelastic tests identify fibrinolysis, a finding associated with significantly increased mortality yet one that no conventional coagulation test can reliably detect. Using these parameters, guided resuscitation begins within minutes of a patient's arrival. A growing body of evidence suggests this approach may improve survival while reducing volumes of blood products transfused.

Thrombin generation assays are versatile tools in blood coagulation analysis: A review of technical features, and applications from research to laboratory routine

Thrombin is the pivotal enzyme in the biochemistry of secondary hemostasis crucial to maintaining homeostasis of hemostasis. In contrast to routine coagulation tests (PT or aPTT) or procoagulant or anticoagulant factor assays (e.g. fibrinogen, factor VIII, antithrombin or protein C), the thrombin generation assay (TGA), also named thrombin generation test (TGT) is a so-called "global assay" that provides a picture of the hemostasis balance though a continuous and simultaneous measurement of thrombin formation and inhibition. First described in the early 1950s, as a manual assay, efforts have been made in order to standardize and automate the assay to offer researchers, clinical laboratories and the pharmaceutical industry a versatile tool covering a wide range of clinical and non-clinical applications. This review describes technical options offered to properly run TGA, including a review of preanalytical and analytical items, performance, interpretation, and applications in physiology research and pharmacy.

Role of Direct Oral Anticoagulation Agents as Thromboprophylaxis in Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is an autoimmune disorder that causes venous, arterial and small-vessel thrombosis, pregnancy loss, and premature birth. Cardiac valvular disease, renal thrombotic microangiopathy, thrombocytopenia, hemolytic anemia, and cognitive impairment are some of its other clinical symptoms. Antiphospholipid antibodies cause endothelial cells, monocytes, and platelets to become activated, as well as an increase in tissue factor and thromboxane A2. Complement activation might play a key function in pathogenesis. Long-term oral anticoagulation is used to treat thrombosis, and individuals having arterial episodes should be treated quickly. Patients with systemic lupus erythematosus (SLE), as well as those with solely obstetric antiphospholipid syndrome, should get primary thromboprophylaxis. Obstetric care is based on a combination of medical and obstetric high-risk management, as well as aspirin and heparin therapy. Possible supplementary therapy for this condition is hydroxychloroquine. Statins, rituximab, and novel anticoagulant medicines are all potential future treatments for non-pregnant individuals with antiphospholipid syndrome. We aim to review the role of direct-acting oral anticoagulants (DOACs) as thromboprophylactic drugs in the treatment of APS in this article. The treatment of venous thromboembolism has been transformed by a new class of DOACs. These drugs, such as rivaroxaban, function by inhibiting factor Xa directly. Not only do they have known anticoagulant actions, but they also obviate the need for dosage monitoring and modification, in contrast to warfarin. We conducted an exhaustive literature search of PubMed/MEDLINE and Google Scholar Indexes using the keywords "Antiphospholipid syndrome," "thromboprophylaxis," and "oral anticoagulants" up to September 2021. We found that DOACs have been shown to be non-inferior to warfarin in a variety of anticoagulation situations in a number of high-powered clinical studies. In many hypercoagulable conditions such as APS, DOACs are quickly establishing themselves as first-line therapy. This article is focused on comprehensively reviewing the mechanism of action of DOACs, their role as thromboprophylactic drugs, risks and complications of DOACs, and comparing their efficacy with the standard treatment protocol and warfarin.

Ratiometric Bioluminescent Indicator for a Simple and Rapid Measurement of Thrombin Activity Using a Smartphone

Hemostasis is an essential function that repairs tissues and maintains the survival of living organisms. To prevent diseases caused by the abnormality of the blood coagulation mechanism, it is important to carry out a blood test periodically by a method that is convenient and less burdensome for examiners. Thrombin is a protease that catalyzes the conversion of fibrinogen, and its cleavage activity can be an index of coagulation activity. Here, we developed a ratiometric bioluminescent indicator, Thrombastor (thrombin activity sensing indicator), which reflects the thrombin cleavage activity in blood by changing the emission color from green to blue. Compared to the current thrombin activity indicator, the rapid color change of the emission indicated a 2.5-fold decrease in the K_m for thrombin, and the cleavage rate was more than two times faster. By improving the absolute bioluminescence intensity, detection from a small amount of plasma could be achieved with a smartphone camera. Using Thrombastor and a versatile device, an effective diagnosis for preventing coagulation disorders can be provided.

Pathophysiology of Trauma-Induced Coagulopathy

There is no standard definition for trauma-induced coagulopathy (TIC). However, it could be defined as an abnormal hemostatic response secondary to trauma. The terms "early TIC" and "late TIC" have been recently suggested. "Early TIC" would refer to the inability to achieve effective hemostasis exacerbating an uncontrolled bleeding in a shocked patient with ischemia-reperfusion damage (bleeding phenotype) and takes place usually early after injury, whereas "late TIC" would represent a hypercoagulable state after surviving a severe tissue injury, that would contribute to thromboembolic events and multiorgan failure (MOF), (thrombotic phenotype), occurring typically hours after the trauma insult though it could be delayed for days. In addition, severe tissue injury when there is no associated shock could be followed by an early hypercoagulable state, representing an evolutionary maladaptive response of a physiologic mechanism created to increase clot formation and prevent bleeding. Therefore, TIC is not a uniform phenotype, ranging from bleeding to pro-thrombotic profiles. This current concept of TIC is mainly based on the recognition of TIC as a unique clotting disorder following trauma in which alterations in the endothelial function, fibrinolysis regulation and platelet behavior after major trauma are the main cornerstones.

Thrombin Generation Assay and Hemostatic Profile for Elucidating Hypercoagulability in Endogenous Canine Hyperadrenocorticism

Canine hyperadrenocorticism is a common endocrine disorder caused by chronic secretion of glucocorticoid, often associated with hypercoagulability and secondary thrombosis. The thrombin generation assay (TGA) evaluates hemostasis globally by measuring endogenous thrombin potential. We aimed to determine whether TGA is suitable for assessing hypercoagulability in dogs with endogenous hyperadrenocorticism (HAC), and to correlate TGA with coagulation markers including fibrinogen, antithrombin (AT), D-dimer, prothrombin time (PT) and activated partial thromboplastin time (aPTT), and with routine laboratory tests for elucidating prothrombotic mechanisms and evaluating their utility as hypercoagulability screening tests. Thrombin generation performed with high activator concentration showed significantly higher endogenous thrombin potential (ETP) (P = .0239) and peak thrombin (P = .0281) in Cushing patients. Fibrinogen (P = <.0001) and AT (P = .0444) activities were significantly higher in the HAC group, while those of PT (P = .0046) and aPTT (P = .0002) were lower. Basal cortisol levels correlated positively with fibrinogen (r = 0.4503; P = .0355) and negatively with AT activity (r = -0.4580; P = .0280). Fibrinogen and hematocrit values were inversely correlated (r = -0.4853; P = .0076). Our study confirmed the presence of higher thrombin generation in dogs with HAC. However, TGA performed with lower activator concentrations was unsuitable for detecting hypercoagulability. Higher AT and fibrinogen levels and lower aPTT activity were identified in dogs with HAC relative to controls suggesting a potential role for the combined use of these assays when assessing hypercoagulability in canine hyperadrenocorticism.

Thrombin generation test based on a 96-channel pipettor for evaluation of FXIa procoagulant activity in pharmaceuticals

Thrombin generation (TG) assays are used widely to investigate both diseases and drugs that impact thrombosis and bleeding. TG assays were also instrumental in the identification of thrombogenic impurities in immune globulin products, which were associated with thrombotic adverse events in patients. TG assays are therefore now used by quality control laboratories of plasma derivative drug manufacturers and regulatory agencies responsible for the safety testing and release of immune globulin products. In this protocol, we describe a robust and sensitive version of the TG assay for quantitative measurement of thrombogenic activity in immune globulin products. Compared with the version of the assay commonly used in clinical laboratories that compares individual patient plasma samples with normal donor samples, our TG assay is suitable for quick (170-260 min) semiautomated analysis of multiple drug samples against the World Health Organization international standard for factor XIa. Commercially available reagents can be used for the assay, and it does not require specialized equipment. The protocol can be easily adapted for the measurement of the procoagulant activity of other biopharmaceuticals, e.g., coagulation factors.

Burn-Induced Coagulopathies: a Comprehensive Review

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

Fibrin Clot Properties in Atherosclerotic Vascular Disease: From Pathophysiology to Clinical Outcomes

Fibrin is a major component of thrombi formed on the surface of atherosclerotic plaques. Fibrin accumulation as a consequence of local blood coagulation activation takes place inside atherosclerotic lesions and contributes to their growth. The imbalance between thrombin-mediated fibrin formation and fibrin degradation might enhance atherosclerosis in relation to inflammatory states reflected by increased fibrinogen concentrations, the key determinant of fibrin characteristics. There are large interindividual differences in fibrin clot structure and function measured in plasma-based assays and in purified fibrinogen-based systems. Several observational studies have demonstrated that subjects who tend to generate denser fibrin networks displaying impaired clot lysis are at an increased risk of developing advanced atherosclerosis and arterial thromboembolic events. Moreover, the majority of cardiovascular risk factors are also associated with unfavorably altered fibrin clot properties, with their improvement following effective therapy, in particular with aspirin, statins, and anticoagulant agents. The prothrombotic fibrin clot phenotype has been reported to have a predictive value in terms of myocardial infarction, ischemic stroke, and acute limb ischemia. This review article summarizes available data on the association of fibrin clot characteristics with atherosclerotic vascular disease and its potential practical implications.

Altered fibrin clot properties and fibrinolysis in patients with atrial fibrillation: practical implications

Compelling evidence indicates that a hypercoagulable state occurs in patients with atrial fibrillation (AF) including those in sinus rhythm following paroxysmal and persistent AF. Activation of blood coagulation in AF reflects heightened thrombin generation with the subsequent increased formation of fibrin as evidenced by elevated soluble fibrin monomers and D-dimer. Formation of denser fibrin meshworks, relatively resistant to plasmin-mediated lysis has been demonstrated in patients with AF. The presence of stroke risk factors in AF, such as diabetes, heart failure, hypertension, previous myocardial infarction, or stroke, advanced age have been shown to be linked to the prothrombotic clot characteristics, including reduced clot permeability and lysability. Importantly, biomarkers, including cardiac troponins and N-terminal pro-brain natriuretic peptide, are associated with thrombin generation and fibrin-related markers in AF patients. Recently, increased fibrin clot density (low clot permeability measured in plasma-based assays) and impaired fibrinolysis measured off anticoagulation have been demonstrated to predict ischaemic cerebrovascular events in patients with AF receiving vitamin K antagonists and those on rivaroxaban. The current review summarizes evidence for a role of altered fibrin clot properties and hypofibrinolysis in AF and their prognostic value in terms of adverse events.

When the Blood Hits Your Brain: The Neurotoxicity of Extravasated Blood

Hemorrhage in the central nervous system (CNS), including intracerebral hemorrhage (ICH), intraventricular hemorrhage (IVH), and aneurysmal subarachnoid hemorrhage (aSAH), remains highly morbid. Trials of medical management for these conditions over recent decades have been largely unsuccessful in improving outcome and reducing mortality. Beyond its role in creating mass effect, the presence of extravasated blood in patients with CNS hemorrhage is generally overlooked. Since trials of surgical intervention to remove CNS hemorrhage have been generally unsuccessful, the potent neurotoxicity of blood is generally viewed as a basic scientific curiosity rather than a clinically meaningful factor. In this review, we evaluate the direct role of blood as a neurotoxin and its subsequent clinical relevance. We first describe the molecular mechanisms of blood neurotoxicity. We then evaluate the clinical literature that directly relates to the evacuation of CNS hemorrhage. We posit that the efficacy of clot removal is a critical factor in outcome following surgical intervention. Future interventions for CNS hemorrhage should be guided by the principle that blood is exquisitely toxic to the brain.

Role of Thrombin in Central Nervous System Injury and Disease

Thrombin is a Na+-activated allosteric serine protease of the chymotrypsin family involved in coagulation, inflammation, cell protection, and apoptosis. Increasingly, the role of thrombin in the brain has been explored. Low concentrations of thrombin are neuroprotective, while high concentrations exert pathological effects. However, greater attention regarding the involvement of thrombin in normal and pathological processes in the central nervous system is warranted. In this review, we explore the mechanisms of thrombin action, localization, and functions in the central nervous system and describe the involvement of thrombin in stroke and intracerebral hemorrhage, neurodegenerative diseases, epilepsy, traumatic brain injury, and primary central nervous system tumors. We aim to comprehensively characterize the role of thrombin in neurological disease and injury.

Added Value of Blood Cells in Thrombin Generation Testing

The capacity of blood to form thrombin is a critical determinant of coagulability. Plasma thrombin generation (TG), a test that probes the capacity of plasma to form thrombin, has improved our knowledge of the coagulation system and shows promising utility in coagulation management. Although plasma TG gives comprehensive insights into the function of pro- and anticoagulation drivers, it does not measure the role of blood cells in TG. In this literature review, we discuss currently available continuous TG tests that can reflect the involvement of blood cells in coagulation, in particular the fluorogenic assays that allow continuous measurement in platelet-rich plasma and whole blood. We also provide an overview about the influence of blood cells on blood coagulation, with emphasis on the direct influence of blood cells on TG. Platelets accelerate the initiation and velocity of TG by phosphatidylserine exposure, granule content release and surface receptor interaction with coagulation proteins. Erythrocytes are also major providers of phosphatidylserine, and erythrocyte membranes trigger contact activation. Furthermore, leukocytes and cancer cells may be important players in cell-mediated coagulation because, under certain conditions, they express tissue factor, release procoagulant components and can induce platelet activation. We argue that testing TG in the presence of blood cells may be useful to distinguish blood cell-related coagulation disorders. However, it should also be noted that these blood cell-dependent TG assays are not clinically validated. Further standardization and validation studies are needed to explore their clinical usefulness.

Fluorescence artifact correction in the thrombin generation assay: Necessity for correction algorithms in procoagulant samples

INTRODUCTION

The thrombin generation (TG) test is a global hemostasis assay sensitive to procoagulant conditions. However, some TG assays may underestimate elevated TG when the thrombin fluorogenic substrate is depleted or fluorescence is attenuated by the inner filter effect (IFE).

OBJECTIVES

We sought to elucidate the extent to which procoagulant conditions require correcting for fluorogenic substrate depletion and/or IFE.

METHODS

We analyzed corrections for substrate depletion and IFE and their effect on TG parameters in plasma samples with elevated blood coagulation factors in the presence or absence of thrombomodulin via commercial calibrated automated thrombogram (CAT) platform and in-house software capable of internal thrombin calibration with or without CAT-like artifact correction.

RESULTS

Elevated thrombin peak height (TPH) and endogenous thrombin potential (ETP) were detected with 2× and 4× increases in blood coagulation factors I, V, VIII, IX, X, and XI, or prothrombin in the presence or absence of artifact correction. The effect of the CAT algorithm was evident in TG curves from both low procoagulant (thrombomodulin-supplemented) and procoagulant (factor-supplemented) plasma samples. However, in all samples, with the exception of elevated prothrombin, CAT's correction was small (<10%) and did not affect detection of procoagulant samples versus normal plasma. For elevated prothrombin samples, uncorrected TPH or ETP values were underestimated, and CAT correction produced drastically elevated TG curves.

CONCLUSIONS

Our data suggest that correction for substrate consumption and IFE, as offered by the CAT algorithm, is critical for detecting a subset of extremely procoagulant samples, such as elevated prothrombin, but is not necessary for all other conditions, including elevated factors XI and VIII.

Whole Blood, Fixed Ratio, or Goal-Directed Blood Component Therapy for the Initial Resuscitation of Severely Hemorrhaging Trauma Patients: A Narrative Review

This narrative review explores the pathophysiology, geographic variation, and historical developments underlying the selection of fixed ratio versus whole blood resuscitation for hemorrhaging trauma patients. We also detail a physiologically driven and goal-directed alternative to fixed ratio and whole blood, whereby viscoelastic testing guides the administration of blood components and factor concentrates to the severely bleeding trauma patient. The major studies of each resuscitation method are highlighted, and upcoming comparative trials are detailed.

Efficacy of resuscitation with fibrinogen concentrate and platelets in traumatic hemorrhage swine model

BACKGROUND

This study compared the resuscitation effects of platelets and fibrinogen concentrate (FC) on coagulation and hemodynamics in pigs with traumatic hemorrhage and reduced platelet counts.

METHODS

Thirty pigs (40 ± 3 kg) were anesthetized and catheterized with an apheresis catheter to remove platelets using the Haemonetics 9000 (Haemonetics, Braintree, MA). Afterward, a femur fracture was induced, followed by hemorrhage of 35% the estimated blood volume. Pigs were then randomized to be resuscitated with 5% human albumin (12.5 mL/kg), FC (250 mg/kg, 12.5 mL/kg), or platelets collected from apheresis (11.0 ± 0.5 mL/kg). Animals were monitored for 2 hours or until death. Blood samples were collected before (baseline [BL]) and after apheresis, after hemorrhage, and after resuscitation to assess changes in hemodynamics and coagulation using Rotem.

RESULTS

No change in mean arterial pressure (MAP) or heart rate (HR) was observed by platelet apheresis. Hemorrhage reduced MAP to 57% ± 5% and elevated HR to 212% ± 20% of BL (both p < 0.05). Resuscitation with albumin, FC, or platelets did not revert MAP or HR to BL. Platelet counts were reduced by apheresis from BL 383 ± 20 × 10/μL to 141 ± 14 × 10/μL and were reduced further after resuscitation with albumin (88 ± 18 × 10/μL) or FC (97 ± 13 × 10/μL, all p < 0.05), but improved with platelet resuscitation (307 ± 24 × 10/μL). Fibrinogen concentration was reduced by apheresis from BL 225 ± 9 mg/dL to 194 ± 8 mg/dL, fell after albumin infusion (134 ± 11 mg/dL), increased to 269 ± 10 mg/dL after FC resuscitation (all p < 0.05), and was not affected by platelet resuscitation. Rotem α-angle decreased from 79 ± 2 degrees to 69 ± 1 degrees by apheresis and hemorrhage (p < 0.05), and recovered similarly by resuscitation with FC (87 ± 1 degrees) or platelets (78 ± 2 degrees), but not by albumin (63 ± 3 degrees). Similar responses were observed in Rotem maximum clot firmness.

CONCLUSION

In this traumatic hemorrhage swine model, low-volume resuscitation with FC or platelets was similarly effective in restoring coagulation.

Changing of haemostatic system in a pig model during different types of hypothermic circulatory arrest

BACKGROUND

Hypothermic circulatory arrest is usually used in aortic surgery, congenital heart defect repairs and other complex surgeries. It is frequently associated with excessive postoperative bleeding and the transfusion of allogeneic blood products. The physiopathology of hypothermic circulatory arrest-induced coagulopathy has never been systematically studied. The aim of the study was to investigate this phenomenon in a pig model.

METHODS

Ten pigs were randomly assigned to 30 min of hypothermic circulatory arrest at either 15 °C (n = 5) or 25 °C (n = 5). Detection of apoptosis and haemostatic system assays were performed in this experiment. Enzyme-linked immunosorbent assays were performed at ten time points in each group to study the changes in the coagulation system in hypothermic circulatory arrest. All of the statistical analyses were performed in SPSS software, version 18.0, and as bilateral tests, and p < 0.05 was considered statistically significant.

RESULTS

There was no significant difference in the effect of different types of hypothermic circulatory arrest on routine laboratory tests and tissue sample analysis (p > 0.05, for all). Our results demonstrated that more severe systemic activation of the coagulation system (TAT and F1+2) was applied in the deep hypothermic circulatory arrest group but not in the moderate hypothermic circulatory arrest group (TAT/p = 0.01, F1+2/p = 0.03). However, this activation of the coagulation system (AT III and PC) was not associated with changes in the anticoagulation pathway (AT III/p = 0.24, PC/p = 0.33). In addition, analysis of biomarkers of the haemostatic system revealed that the consumption of coagulation is more concentrated on extrinsic coagulation factors (FVII/p = 0.01).

CONCLUSIONS

Moderate hypothermic circulatory arrest is more suitable for patients with coagulation dysfunction. We believe the application of deep hypothermic circulatory arrest should pay more attention to changes in coagulation rather than the anticoagulation pathway. Extrinsic coagulation factor supplementation is more effective after deep hypothermic circulatory arrest.

Extensive characterization of the composition and functional activities of five preparations of human platelet lysates for dedicated clinical uses

Human platelet lysates (HPLs), rich in various growth factors and cell growth-promoting molecules, encompass a new range of blood products that are being used for regenerative medicine, cell therapies, and tissue engineering. Well-characterized dedicated preparations, tailor-made to best fit specific therapeutic applications, are needed for optimal clinical efficacy and safety. Here, five types of HPL were prepared from the same platelet concentrates and extensively characterized to determine and compare their proteins, growth factors, cytokines, biochemical profiles, thrombin-generating capacities, thrombin-associated proteolytic activities, phospholipid-associated procoagulant potential, contents of extracellular vesicles expressing phosphatidylserine and tissue factor, and antioxidative properties. Our results revealed that all five HPL preparations contained detectable supraphysiological levels, in the ca. 0.1 ~ 350-ng/ml range, of all growth factors assessed, except insulin-like growth factor-1 detected only in HPL containing plasma. There were significant differences observed among these HPLs in total protein content, fibrinogen, complement components C3 and C4, albumin, and immunoglobulin G, and, most importantly, in their functional coagulant and procoagulant activities and antioxidative capacities. Our data revealed that the biochemical and functional properties of HPL preparations greatly vary depending upon their mode of production, with potential impacts on the safety and efficacy for certain clinical indications. Modes of preparation of HPLs should be carefully designed, and the product properties carefully evaluated based on the intended therapeutic use to ensure optimal clinical outcomes.

Risk of bleeding during oral surgery in patients with liver cirrhosis: A systematic review

BACKGROUND

The liver is responsible for the production of almost all coagulation factors, but does this indicate a risk of developing unusual bleeding in patients with liver cirrhosis during dental surgery?

TYPES OF STUDIES REVIEWED

In this systemic review, the authors followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist and performed a search of PubMed, Latin American and Caribbean Health Sciences Literature, Web of Science, Scopus, and Cochrane databases.

RESULTS

Seven studies met the inclusion criteria. The sample sizes ranged from 23 through 318 participants, number of extracted teeth ranged from 62 through 1,183, platelet count ranged from 16,000 through 216,000 per cubic milimeter, and the international normalized ratio was less than 4. The prevalence of hemorrhagic events in the studies ranged from 0% through 8.9%, and almost all were controlled with local hemostatic measures.

CONCLUSIONS AND PRACTICAL IMPLICATIONS

During dental treatment, patients with liver cirrhosis have a low bleeding risk in spite of the decreased number of platelets and increased international normalized ratio.

Computationally Driven Discovery in Coagulation

Bleeding frequency and severity within clinical categories of hemophilia A are highly variable and the origin of this variation is unknown. Solving this mystery in coagulation requires the generation and analysis of large data sets comprised of experimental outputs or patient samples, both of which are subject to limited availability. In this review, we describe how a computationally driven approach bypasses such limitations by generating large synthetic patient data sets. These data sets were created with a mechanistic mathematical model, by varying the model inputs, clotting factor, and inhibitor concentrations, within normal physiological ranges. Specific mathematical metrics were chosen from the model output, used as a surrogate measure for bleeding severity, and statistically analyzed for further exploration and hypothesis generation. We highlight results from our recent study that employed this computationally driven approach to identify FV (factor V) as a key modifier of thrombin generation in mild to moderate hemophilia A, which was confirmed with complementary experimental assays. The mathematical model was used further to propose a potential mechanism for these observations whereby thrombin generation is rescued in FVIII-deficient plasma due to reduced substrate competition between FV and FVIII for FXa (activated factor X).

How to Capture the Bleeding Phenotype in FXI-Deficient Patients

Factor XI (FXI) is a serine protease involved in the propagation phase of coagulation and in providing clot stability. Several mutations in the F11 gene lead to FXI deficiency, a rare mild bleeding disorder. Current laboratory methods are unable to assess bleeding risk in FXI-deficient patients, because the degree of bleeding tendency does not correlate with plasma FXI activity as measured by routine coagulometric aPTT–based assays. Bleeding manifestations are highly variable among FXI-deficient patients and FXI replacement therapy can be associated with an increased thrombotic risk. A correct evaluation of the patient hemostatic potential is crucial to prevent under- or overtreatment. In recent years, different research groups have investigated the use of global coagulation assays as alternative for studying the role of FXI in hemostasis and identifying the clinical phenotype of FXI deficiency. This brief review article summarizes the main features of coagulation factor XI and its deficiency and resumes the principle axes of research and methods used to investigate FXI functions.

Tissue Factor-Independent Coagulation Correlates with Clinical Phenotype in Factor XI Deficiency and Replacement Therapy

BACKGROUND

 In factor XI (FXI) deficiency, bleeding cannot be predicted by routine analyses. Since FXI is involved in tissue factor (TF)-independent propagation loop of coagulation, we hypothesized that investigating the spatiotemporal separated phases of coagulation (TF-dependent and -independent) could improve diagnostics.

OBJECTIVES

 This article investigates the correlation of parameters describing TF-dependent and -independent coagulation with the clinical phenotype of FXI deficiency and their ability to assess hemostasis after FXI replacement.

METHODS

 We analyzed: (1) plasma from healthy controls (n = 53); (2) normal plasma (n = 4) spiked with increasing concentrations of a specific FXI inhibitor (C7P); (3) plasma from FXI-deficient patients (n = 24) with different clinical phenotypes (13 bleeders, 8 non-bleeders, 3 prothrombotics); (4) FXI-deficient plasma spiked with FXI concentrate (n = 6); and (5) plasma from FXI-deficient patients after FXI replacement (n = 7). Thrombin generation was measured with the reference method calibrated automated thrombogram and with Thrombodynamics (TD), a novel global assay differentiating TF-dependent and -independent coagulation.

RESULTS

 C7P dose-dependently decreased FXI activity, prolonged activated partial thromboplastin time, and hampered TF-independent coagulation. In FXI-deficient bleeders, TD parameters describing TF-independent propagation of coagulation and fibrin clot formation were reduced compared with controls and FXI-deficient nonbleeders and increased in FXI-deficient patients with prothrombotic phenotype. Receiver operating characteristic analysis indicated that TF-independent parameters were useful for discriminating FXI-deficient bleeders from non-bleeders. In FXI-deficient plasma spiked with FXI concentrate and in patients receiving FXI replacement, TD parameters were shifted toward hypercoagulation already at plasma FXI levels around 20%.

CONCLUSION

 TF-independent coagulation parameters assessed by TD have the potential to identify the clinical phenotype in FXI-deficient patients and to monitor FXI replacement therapy.

Trauma-Induced Coagulopathy and Massive Bleeding: Current Hemostatic Concepts and Treatment Strategies

Hemorrhage after trauma remains a significant cause of preventable death. Trauma-induced coagulopathy (TIC) at the time of hospital admission is associated with an impaired outcome. Rather than a universal phenotype, TIC represents a complex hemostatic disorder, and standard coagulation tests are not designed to adequately reflect the complexity of TIC. Viscoelastic testing (VET) has gained increasing interest for the characterization of TIC because it provides a more comprehensive depiction of the coagulation process. Thus, VET has been established as a point-of-care-available hemostatic monitoring tool in many trauma centers. Damage-control resuscitation and early administration of tranexamic acid provide the basis for treating TIC. To improve survival, ratio-driven massive transfusion protocols favoring early and high-dose plasma transfusion have been implemented in many trauma centers around the world. Although plasma contains all coagulation factors and inhibitors, only high-volume plasma transfusion allows for adequate substitution of lacking coagulation proteins. However, high-volume plasma transfusion has been associated with several relevant risks. In some European trauma facilities, a more individualized hemostatic therapy concept has been implemented. The hemostatic profile of the bleeding patient is evaluated by VET. Subsequently, goal-directed hemostatic therapy is primarily based on coagulation factor concentrates such as fibrinogen concentrate or prothrombin complex concentrate. However, a clear difference in survival benefit between these two treatment strategies has not yet been shown. This concise review aims to summarize current evidence for different diagnostic and therapeutic strategies in patients with TIC.

Rivaroxaban for the prevention of major adverse cardiovascular events in patients with coronary or peripheral artery disease

In the COMPASS trial, the combination of rivaroxaban 2.5 mg twice daily and low-dose aspirin 75-100 mg daily produced a net clinical benefit of 20% in patients with chronic atherosclerotic vascular disease because it reduced major adverse events by 24% and overall mortality by 18% despite an initial increase in major bleeding. In this paper, we examine the rationale for targeting coagulation factor Xa in patients with atherosclerosis, summarize the pharmacology of the 2.5-mg dose, review the trials that led to the approval of the combination of rivaroxaban and aspirin for the long-term management of patients with chronic coronary artery disease or peripheral artery disease and discuss who would benefit the most. We also address the unresolved issues and challenges in the implementation of this therapy.

Global Coagulation Assays in Transgender Women on Oral and Transdermal Estradiol Therapy

CONTEXT

The thrombotic effects of estradiol therapy in transgender women are unclear. Global coagulation assays (GCA) may be better measures of hemostatic function compared with standard coagulation tests.

OBJECTIVE

To assess the GCA profiles of transgender women in comparison to cisgender controls and to compare how GCA differ between routes of estradiol therapy in transgender women.

DESIGN

Cross-sectional case-control study.

SETTING

General community.

PARTICIPANTS

Transgender women, cisgender male and cisgender female controls.

MAIN OUTCOME MEASURES

Citrated blood samples were analyzed for (i) whole blood thromboelastography (TEG®5000), (ii) platelet-poor plasma thrombin generation (calibrated automated thrombogram); and (iii) platelet-poor plasma fibrin generation (overall hemostatic potential assay). Mean difference (95% confidence intervals) between groups are presented.

RESULTS

Twenty-six transgender women (16 oral estradiol, 10 transdermal estradiol) were compared with 98 cisgender women and 55 cisgender men. There were no differences in serum estradiol concentration (P = 0.929) and duration of therapy (P = 0.496) between formulations. Transgender women demonstrated hypercoagulable parameters on both thromboelastography (maximum amplitude + 6.94 mm (3.55, 10.33); P < 0.001) and thrombin generation (endogenous thrombin potential + 192.62 nM.min (38.33, 326.91); P = 0.009; peak thrombin + 38.10 nM (2.27, 73.94); P = 0.034) but had increased overall fibrinolytic potential (+4.89% (0.52, 9.25); P = 0.024) compared with cisgender men. No significant changes were observed relative to cisgender women. Route of estradiol delivery or duration of use did not influence the GCA parameters.

CONCLUSION

Transgender women on estradiol therapy demonstrated hypercoagulable GCA parameters compared with cisgender men with a shift towards cisgender female parameters. Route of estradiol delivery did not influence the GCA parameters.

Coagulation status of critically ill patients with and without liver disease assessed using a novel thrombin generation analyzer

The liver synthesizes the majority of pro- and anti-coagulant and fibrinolytic proteins, and during liver dysfunction synthesis of these proteins is reduced. The end point of conventional hemostatic tests, such as the prothrombin time (PT), occurs when only 5% of thrombin generation (TG) has taken place and is not sensitive to the effects of natural anti-coagulants. The aim of this study was to determine whether TG in the presence of thrombomodulin (TM) provides more useful information about coagulation potential, in comparison to the PT. Analysis was performed on ST Genesia, a novel TG analyzer from Diagnostica Stago. TG was measured using STG-Thromboscreen, a reagent containing an intermediate concentration of human tissue factor (TF) ± rabbit TM to account for anti-coagulant protein C (PC) activity. Platelet-poor plasma (PPP) samples were from the Intensive Care Study of Coagulopathy-2 (ISOC-2), which recruited patients admitted to critical care with a prolonged PT (3 seconds above the reference range). Despite a prolonged PT, 48.0% and 60.7% of patients in the liver and non-liver groups had TG parameters within the normal range. Addition of TM reduced TG by 34.5% and 41.8% in the liver and non-liver groups, respectively. Interestingly, fresh frozen plasma (FFP) transfusion had no impact on TG. Measurement of TG with addition of TM provides a more informative assessment of coagulation capacity and indicates that hemostasis is balanced in patients with liver disease during critical illness, despite conventional tests suggesting that bleeding risk is increased.

How Good is Jarzynski's Equality for Computer-Aided Drug Design?

Accurate determination of the binding affinity of the ligand to the receptor remains a difficult problem in computer-aided drug design. Here, we study and compare the efficiency of Jarzynski’s equality (JE) combined with steered molecular dynamics and the linear interaction energy (LIE) method by assessing the binding affinity of 23 small compounds to six receptors, including β-lactamase, thrombin, factor Xa, HIV-1 protease (HIV), myeloid cell leukemia-1, and cyclin-dependent kinase 2 proteins. It was shown that Jarzynski’s nonequilibrium binding free energy ΔG_neq^Jar correlates with the available experimental data with the correlation levels R = 0.89, 0.86, 0.83, 0.80, 0.83, and 0.81 for six data sets, while for the binding free energy ΔG_LIE obtained by the LIE method, we have R = 0.73, 0.80, 0.42, 0.23, 0.85, and 0.01. Therefore, JE is recommended to be used for ranking binding affinities as it provides accurate and robust results. In contrast, LIE is not as reliable as JE, and it should be used with caution, especially when it comes to new systems.

Hemostatic Alterations in Patients With Cirrhosis: From Primary Hemostasis to Fibrinolysis

In the setting of liver cirrhosis (LC), profound hemostatic changes occur, which affect primary hemostasis, coagulation, and fibrinolysis. They involve prohemorrhagic and prothrombotic alterations at each of these steps. Patients with cirrhosis exhibit multifactorial thrombocytopenia and in vitro thrombocytopathy, counterbalanced by increased von Willebrand factor. The resultant shift is difficult to assess, but overall these changes probably result in a rebalanced primary hemostasis. Concerning coagulation, the reduced activity of coagulation factors is counterbalanced by an increase in factor VIII (produced by liver sinusoidal endothelial cells), a decrease of the natural anticoagulants, and complex changes, including changes in circulating microparticles, cell-free DNA, and neutrophil extracellular traps. Overall, these alterations result in a procoagulant state. As for fibrinolysis, increased tissue-type and urokinase-type plasminogen activators, a relatively decreased plasminogen activator inhibitor 1, and decreased levels of thrombin-activatable fibrinolysis inhibitor and α2-antiplasmin are counterbalanced by decreased plasminogen and a decreased fibrin clot permeability. Whether and how these changes shift fibrinolysis remains to be determined. Overall, the current consensus is that in patients with cirrhosis, the hemostasis is shifted toward a procoagulant state. We review the published evidence for the concept of LC as a prothrombotic state, discuss discordant data, and highlight the impact of the underlying cause of LC on the resultant imbalance.

Continuous Detection of Increasing Concentrations of Thrombin Employing a Label-Free Photonic Crystal Aptasensor

Thrombin generation is a complex and finely regulated pathway that provokes dynamical changes of thrombin concentration in blood when a vascular injury occurs. In order to characterize the initiation phase of such process, when thrombin concentration is in the nM range, a label-free optical aptasensor is proposed here. This aptasensor combines a 1D photonic crystal structure consisting of a silicon corrugated waveguide with thrombin binding aptamers on its surface as bioreceptors. As a result, this aptasensor has been demonstrated to specifically detect thrombin concentrations ranging from 270 pM to 27 nM with an estimated detection limit of 33.5 pM and a response time of ~2 min. Furthermore, it has also been demonstrated that this aptasensor is able to continuously respond to consecutive increasing concentrations of thrombin and to detect binding events as they occur. All these features make this aptasensor a good candidate to continuously study how thrombin concentration progressively increases during the initiation phase of the coagulation cascade.

Liquid chromatography-tandem mass spectrometry method for determination of rivaroxaban in human plasma and its application to a pharmacokinetic study

A high-performance liquid chromatography tandem mass spectrometric method for the determination of Rivaroxaban in human plasma has been developed and validated using Rivaroxaban D₄ as an internal standard. The extraction of analyte and internal standard was accomplished by solid phase extraction technique. The method has been validated over a concentration range of 5.96-801 ng/mL. Chromatographic separations were achieved using Gemini C18, 150 mm × 4.6 mm, 5 µm, column eluted at flow rate of 1.5 mL/min with mobile phase (acetonitrile: ammonium acetate buffer (80:20 v/v)). The overall run time of method was about 1.8 min with elution times of Rivaroxaban and its internal standard Rivaroxaban D₄ at around 1.18 min. The multiple reaction monitoring transitions were set at 436/145 (m/z) and 440/145 (m/z) for Rivaroxaban and Rivaroxaban D₄, respectively. The calibration curves were linear (r²≥ 0.99) over the range of 5.96-801 ng/mL with lower limit of quantitation validated at 5.96 ng/mL. Extraction recoveries were >88% for both rivaroxaban and its stable labeled internal standard rivaroxaban D₄. The inter-day/between run precisions were ranged from 1.08% to 3.75%, while accuracy ranged from 96.3% to 102%. The presented method was used in pharmacokinetic study in healthy volunteers. Results of incurred sample reanalysis were within the acceptance range of ±20% of original value, for 98.3% of samples reanalyzed. This indicated good assay precision of target analytes in their real matrix at the employed experimental conditions. The applicability of the assay for the determination of the pharmacokinetic parameters was demonstrated.

Thrombin generation and bleeding in cardiac surgery: a clinical narrative review

This narrative review discusses the role of thrombin generation in coagulation and bleeding in cardiac surgery, the laboratory methods for clinical detection of impaired thrombin generation, and the available hemostatic interventions that can be used to improve thrombin generation. Coagulopathy after cardiopulmonary bypass (CPB) is associated with excessive blood loss and adverse patient outcomes. Thrombin plays a crucial role in primary hemostasis, and impaired thrombin generation can be an important cause of post-CPB coagulopathy. Existing coagulation assays have significant limitations in assessing thrombin generation, but whole-blood assays designed to measure thrombin generation at the bed-side are under development. Until then, clinicians may need to institute therapy empirically for non-surgical bleeding in the setting of normal coagulation measures. Available therapies for impaired thrombin generation include administration of plasma, prothrombin complex concentrate, and bypassing agents (recombinant activated factor VII and factor eight inhibitor bypassing activity). In vitro experiments have explored the relative potency of these therapies, but clinical studies are lacking. The potential incorporation of thrombin generation assays into clinical practice and treatment algorithms for impaired thrombin generation must await further clinical development.

Combination Antiplatelet and Oral Anticoagulant Therapy in Patients With Coronary and Peripheral Artery Disease

Antiplatelet therapy is the mainstay for the treatment of acute and chronic arterial disease involving the coronary and peripheral beds. However, questions remain about optimal antithrombotic therapy for long-term treatment of chronic vascular disease. The observation that dual antiplatelet therapy with acetylsalicylic acid and clopidogrel was associated with lower thrombotic event rates than acetylsalicylic acid monotherapy in patients with acute coronary syndromes and those undergoing percutaneous coronary intervention changed the treatment paradigm. Moreover, the demonstration that more pharmacodynamically potent P2Y₁₂ inhibitors than clopidogrel were associated with fewer thrombotic event occurrences further solidified the dual antiplatelet therapy approach. However, recurrent thrombotic events occur in ≈1 in 10 patients in the first year following an acute coronary syndrome event, despite treatment with the most potent P2Y₁₂ inhibitors, a limitation that has stimulated interest in exploring the efficacy and safety of approaches using anticoagulants on top of antiplatelet therapy. These investigations have included treatment with very-low-dose oral anticoagulation, and even its replacement of acetylsalicylic acid in the presence of a P2Y₁₂ inhibitor, in patients stabilized after an acute coronary syndrome event. Recent basic and translational studies have suggested noncanonical effects of coagulation factor inhibition that may further modulate clinical benefits. This in-depth review will discuss developments in our understanding of the roles that platelets and coagulation factors play in atherothrombosis and review the rationale and clinical evidence for combining antiplatelet and oral anticoagulant therapy in patients with coronary and peripheral artery disease.

Global coagulation assays in hemophilia A: A comparison to conventional assays

BACKGROUND

Global assays measure the interactions of coagulants, anticoagulants, and platelets on thrombin generation and may reflect the comprehensive coagulation potential in patients with hemophilia better than conventional assays.

OBJECTIVES

The objectives of the current study were to investigate the value of global assays for measuring and monitoring the coagulation potential of patients with hemophilia A (HA).

PATIENTS/METHODS

Rotational thromboelastometry, thrombin generation assay (TGA), and activated partial thromboplastin time (APTT) clot waveform analysis were investigated in a cohort of patients with severe, moderate, and mild HA and compared with conventional assays.

RESULTS

The maximum velocity (MaxVel) parameter of modified thromboelastometry analysis, initiated by tissue factor and in the presence of corn trypsin inhibitor (CTI), had 92% sensitivity and 95% specificity for hemophilia diagnosis. The MaxVel also strongly correlated with factor VIII (FVIII) levels of patients with HA (r = .805, P < .0001). CTI improved the sensitivity of TGA, providing more accurate results. In particular, peak height parameter of platelet-rich plasma samples with CTI had a sensitivity and specificity of 100% and 94%, respectively, in all patients with HA. APTT clot waveform analysis minimum value of first derivative (Min1) and minimum value of second derivative (Min2) parameters (representing speed and acceleration of clot formation, respectively) were sensitive and correlated more strongly with FVIII levels than APTT clotting times did (Min1: r = 0.786, P < 0.0001; Min2: r = 0.759, P < 0.0001; APTT: r = -0.513, P = 0.001).

CONCLUSIONS

The sensitivity and specificity of the global assays was method dependent. Correlation between clinical end points and thrombin generation might also be valuable in the era of non-factor replacement therapy.

Cardiac Expression of Factor X Mediates Cardiac Hypertrophy and Fibrosis in Pressure Overload

•

Factor X expression was increased in the heart following pressure overload and in isolated cardiac myocytes and fibroblasts.

•

Rivaroxaban treatment at doses that do not affect thrombin generation, blood coagulation or cardiac hemostasis attenuated cardiac inflammation, hypertrophy, and fibrosis caused by pressure overload and improved cardiac diastolic function.

•

Activated coagulation factor X induced PAR-1/-2–mediated elongated cardiomyocyte hypertrophy and PAR1-mediated cardiac fibroblast proliferation, migration and differentiation.

•

Activated coagulation factor X derived from a cardiac source may represent an important physiologic and pathophysiologic activator of PAR-1/PAR-2.

•

Non-anticoagulation dosage of rivaroxaban could provide an effective therapy to attenuate early phases of heart failure development.

Activated factor X is a key component of the coagulation cascade, but whether it directly regulates pathological cardiac remodeling is unclear. In mice subjected to pressure overload stress, cardiac factor X mRNA expression and activity increased concurrently with cardiac hypertrophy, fibrosis, inflammation and diastolic dysfunction, and responses blocked with a low coagulation-independent dose of rivaroxaban. In vitro, neurohormone stressors increased activated factor X expression in both cardiac myocytes and fibroblasts, resulting in activated factor X-mediated activation of protease-activated receptors and pro-hypertrophic and -fibrotic responses, respectively. Thus, inhibition of cardiac-expressed activated factor X could provide an effective therapy for the prevention of adverse cardiac remodeling in hypertensive patients.

CYP2C19*17 May Increase the Risk of Death Among Patients with an Acute Coronary Syndrome and Non-Valvular Atrial Fibrillation Who Receive Clopidogrel and Rivaroxaban

INTRODUCTION

The aim of this study is to assess the influence of gene CYP2C19, CYP3A4, CYP3A5 and ABCB1 polymorphisms on clopidogrel antiplatelet activity, rivaroxaban concentration equilibrium, and clinical outcomes among patients with acute coronary syndrome and non-valvular atrial fibrillation.

METHODS

In the multicenter prospective registry study of the efficacy and safety of a combined antithrombotic therapy 103 patients with non-valvular atrial fibrillation both undergoing or not a percutaneous coronary intervention were enrolled. The trial assessed the primary outcomes (major bleeding, in-hospital death, cardiovascular death, stroke\transient ischaemic attack, death/renal insufficiency) and secondary outcomes (platelet reactivity units (PRU), rivaroxaban concentration).

RESULTS

For none of the clinical outcomes when combined with other covariates, the carriership of polymorphisms CYP3A5*3 rs776746, CYP2C19*2 rs4244285;*17 rs12248560, ABCB1 3435 C>T, ABCB1 rs4148738 was significant. None of the markers under study (CYP3A5*3 rs776746, CYP2C19*2 rs4244285, *17 rs12248560, ABCB1 3435 C>T, ABCB1 rs4148738) has proven to affect rivaroxaban equilibrium concentration in blood plasma among patients with atrial fibrillation and acute coronary syndrome.

CONCLUSION

In situations of double or triple antithrombotic rivaroxaban and clopidogrel therapy among patients with atrial fibrillation and acute coronary syndrome, the genetic factors associated with bleeding complications risk (CYP2C19*17) may prove to be clinically relevant.

Platelet Apoptosis Can Be Triggered Bypassing the Death Receptors

In nucleated cells, the extrinsic pathway of the programmed cell death (apoptosis) is triggered by interaction of death ligands of the tumor necrosis factor superfamily with the death receptors on external cell surface membrane. In this review, we present evidence that, in contrast to nucleated cells, apoptosis in anucleate platelets can be induced through bypassing the death receptors, using instead specific receptors on the platelet surface mediating platelet activation, aggregation, and blood coagulation. These platelet surface receptors include the protease-activated receptor 1 of thrombin and glycoproteins IIbIIIa and Ibα, receptors of fibrinogen, and von Willebrand factor. The pro-apoptotic BH3 mimetic ABT-737 and calcium ionophore A23187 also trigger platelet apoptosis without using death receptors. These agents induce the intrinsic pathway of platelet apoptosis by direct targeting mitochondrial and extra-mitochondrial apoptotic responses.

N-methyl mesoporphyrin IX as a highly selective light-up probe for G-quadruplex DNA

N-methyl mesoporphyrin IX (NMM) is a water-soluble, non-symmetric porphyrin with excellent optical properties and unparalleled selectivity for G-quadruplex (GQ) DNA. G-quadruplexes are non-canonical DNA structures formed by guanine-rich sequences. They are implicated in genomic stability, longevity, and cancer. The ability of NMM to selectively recognize GQ structures makes it a valuable scaffold for designing novel GQ binders. In this review, we survey the literature describing the GQ-binding properties of NMM as well as its wide utility in chemistry and biology. We start with the discovery of the GQ-binding properties of NMM and the development of NMM-binding aptamers. We then discuss the optical properties of NMM, focusing on the light-switch effect - high fluorescence of NMM induced upon its binding to GQ DNA. Additionally, we examine the affinity and selectivity of NMM for GQs, as well as its ability to stabilize GQ structures and favor parallel GQ conformations. Furthermore, a portion of the review is dedicated to the applications of NMM-GQ complexes as biosensors for heavy metals, small molecules (e.g. ATP and pesticides), DNA, and proteins. Finally and importantly, we discuss the utility of NMM as a probe to investigate the roles of GQs in biological processes.