Global haemostasis assays, from bench to bedside

Utility of Global Hemostatic Assays in Patients with Bleeding Disorders of Unknown Cause

Bleeding disorder of unknown cause (BDUC) is a diagnosis of exclusion after exhaustive evaluation of plasmatic coagulation and platelet function. This review explores the utility of global hemostatic assays as confirmatory tests and in elucidating the pathophysiology of BDUC. Unlike traditional hemostatic tests that focus on coagulation factors, global assays are conducted both in plasma and also whole blood. These assays provide a more comprehensive understanding of the cell-based model of coagulation, aid in the identification of plasmatic factor abnormalities that may reduce hemostatic capacity, and allow for the assessment of impaired platelet-endothelial interactions under shear stress, as well as hyperfibrinolytic states. While clinical tests such as skin bleeding time and global assays such as PFA-100 exhibit limited diagnostic capacity, the role of viscoelastic testing in identifying hemostatic dysfunction in patients with BDUC remains unclear. Thrombin generation assays have shown variable results in BDUC patients; some studies demonstrate differences compared with healthy controls or reference values, whereas others question its clinical utility. Fibrinolysis assessment in vitro remains challenging, with studies employing euglobulin clot lysis time, plasma clot lysis time, and fluorogenic plasmin generation yielding inconclusive or conflicting results. Notably, recent studies suggest that microfluidic analysis unveils shear-dependent platelet function defects in BDUC patients, undetected by conventional platelet function assays. Overall, global assays might be helpful for exploring underlying hemostatic impairments, when conventional hemostatic laboratory tests yield no results. However, due to limited data and/or discrepant results, further research is needed to evaluate the utility of global assays as screening tools.

Pharmacokinetic-Pharmacodynamic Modelling in Hemophilia A: Relating Thrombin and Plasmin Generation to Factor VIII Activity After Administration of a VWF/FVIII Concentrate

BACKGROUND

Hemophilia A patients are treated with factor (F) VIII prophylactically to prevent bleeding. In general, dosage and frequency are based on pharmacokinetic measurements. Ideally, an alternative dose adjustment can be based on the hemostatic potential, measured with a thrombin generation assay (TGA), like the Nijmegen hemostasis assay.

OBJECTIVE

The objective of this study was to investigate the predicted performance of a previously developed pharmacokinetic-pharmacodynamic model for FVIII replacement therapy, relating FVIII dose and FVIII activity levels with thrombin and plasmin generation parameters.

METHODS

Pharmacokinetic and pharmacodynamic measurements were obtained from 29 severe hemophilia A patients treated with pdVWF/FVIII concentrate (Haemate P®). The predictive performance of the previously developed pharmacokinetic-pharmacodynamic model was evaluated using nonlinear mixed-effects modeling (NONMEM). When predictions of FVIII activity or TGA parameters were inadequate [median prediction error (MPE) > 20%], a new model was developed.

RESULTS

The original pharmacokinetic model underestimated clearance and was refined based on a two-compartment model. The pharmacodynamic model displays no bias in the observed normalized thrombin peak height and normalized thrombin potential (MPE of 6.83% and 7.46%). After re-estimating pharmacodynamic parameters, EC50 and Emax values were relatively comparable between the original model and this group. Prediction of normalized plasmin peak height was inaccurate (MPE 58.9%).

CONCLUSION

Our predictive performance displayed adequate thrombin pharmacodynamic predictions of the original model, but a new pharmacokinetic model was required. The pharmacodynamic model is not factor specific and applicable to multiple factor concentrates. A prospective study is needed to validate the impact of the FVIII dosing pharmacodynamic model on bleeding reduction in patients.

A microfluidic hemostatic diagnostics platform: Harnessing coagulation-induced adaptive-bubble behavioral perception

Clinical viscoelastic hemostatic assays, which have been used for decades, rely on measuring biomechanical responses to physical stimuli but face challenges related to high device and test cost, limited portability, and limited scalability.. Here, we report a differential pattern using self-induced adaptive-bubble behavioral perception to refresh it. The adaptive behaviors of bubble deformation during coagulation precisely describe the transformation of viscoelastic hemostatic properties, being free of the precise and complex physical devices. And the integrated bubble array chip allows microassays and enables multi-bubble tests with good reproducibility. Recognition of the developed bubble behaviors empowers automated and user-friendly diagnosis. In a prospective clinical study (clinical model development [n = 273]; clinical assay [n = 44]), we show that the diagnostic accuracies were 99.1% for key viscoelastic hemostatic assay indicators (reaction time [R], kinetics time [K], alpha angle [Angle], maximum amplitude [MA], lysis at 30 min [LY30]; n = 220) and 100% (n = 44) for hypercoagulation, healthy, and hypocoagulation diagnoses. This should provide fresh insight into existing paradigms and help more clinical needs.

Thrombin generation assays to personalize treatment in bleeding and thrombotic diseases

Treatment of bleeding and thrombotic disorders is highly standardized and based on evidence-based medicine guidelines. These evidence-based treatment schemes are well accepted but may lead to either insufficient treatment or over-dosing, because the individuals' hemostatic properties are not taken into account. This can potentially introduce bleeding or thrombotic complications in individual patients. With the incorporation of pharmacokinetic (PK) and pharmacodynamic (PK-PD) parameters, based on global assays such as thrombin generation assays (TGAs), a more personalized approach can be applied to treat either bleeding or thrombotic disorders. In this review, we will discuss the recent literature about the technical aspects of TGAs and the relation to diagnosis and management of bleeding and thrombotic disorders. In patients with bleeding disorders, such as hemophilia A or factor VII deficiency, TGAs can be used to identify patients with a more severe bleeding phenotype and also in the management with non-replacement therapy and/or bypassing therapy. These assays have also a role in patients with venous thrombo-embolism, but the usage of TGAs in patients with arterial thrombosis is less clear. However, there is a potential role for TGAs in the monitoring of (long-term) antithrombotic therapy, for example with the use of direct oral anticoagulants. Finally this review will discuss controversies, limitations and knowledge gaps in relation to the introduction of TGAs to personalize medicine in daily medical practice.

Investigation of Blood Coagulation Using Impedance Spectroscopy: Toward Innovative Biomarkers to Assess Fibrinogenesis and Clot Retraction

This study focused on a coagulation assessment based on the novel technique of blood-impedance-magnitude measurement. With the impedance characterization of recalcified human blood, it was possible to identify two significative biomarkers (i.e., measurable indicators) related to fibrin formation (1st marker) and clot retraction (2nd marker). The confocal microscopy of clotting blood provided a complete visual analysis of all the events occurring during coagulation, validating the significance of the impedance biomarkers. By analyzing the impedance phase angle (Φ) of blood during coagulation, as well as those of the clot and serum expelled after retraction, it was possible to further clarify the origin of the 2nd marker. Finally, an impedance-magnitude analysis and a rotational thromboelastometry test (ROTEM®) were simultaneously performed on blood sampled from the same donor; the results pointed out that the 1st marker was related to clotting time. The developed technique gives rise to a comprehensive and evolutive insight into coagulation, making it possible to progressively follow the whole process in real time. Moreover, this approach allows coagulation to be tested on any materials' surface, laying the ground for new studies related to contact coagulation, meaning, thrombosis occurring on artificial implants. In a near future, impedance spectroscopy could be employed in the material characterization of cardiovascular prostheses whose properties could be monitored in situ and/or online using effective biomarkers.

Reference intervals for coagulation tests in adults with different ABO blood types

INTRODUCTION

Coagulation tests are affected by many factors, such as age, race, and gestation. Although coagulation test results vary by ABO blood type, reference intervals of different ABO blood groups remain to be determined. This study aims to investigate the reference ranges of coagulation tests for different ABO blood groups in the Han population in South China.

METHODS

A retrospective study was conducted in the First Affiliated Hospital of Shantou University Medical College. In all, 9600 individuals aged between 20 and 79 years were included. Coagulation tests, including prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (aPTT), thrombin time, and fibrinogen, were performed.

RESULTS

There was a significant difference in PT, INR, and aPTT among ABO blood groups. PT and INR varied slightly between ABO blood groups. There was a higher aPTT value in individuals in the O blood group than in those in non-O blood groups, in both males and females across the included age range. No differences were found in thrombin time and fibrinogen between the ABO blood groups.

CONCLUSION

The study provides reference data on coagulation tests from ABO blood groups in South China. The established reference intervals specific to ABO blood type, sex, and age may improve clinical decisions based on coagulation tests.

Fibrinolytic assays in bleeding of unknown cause: Improvement in diagnostic yield

Introduction

Analysis of fibrinolytic disorders is challenging and may potentially lead to underdiagnosis of patients with an increased bleeding tendency.

Aim

To compare clinical characteristics, laboratory measurements, and treatment modalities in a monocenter cohort of patients in whom fibrinolytic studies were performed.

Methods

Retrospective study of patients in whom fibrinolytic studies were performed between January 2016 and February 2020 in the Hemophilia Treatment Center, Nijmegen-Eindhoven-Maastricht, the Netherlands. Plasminogen activator inhibitor type 1 (PAI-1) antigen and activity level, α2-antiplasmin activity, tissue plasminogen activator, and euglobulin clot lysis time (ECLT) before and after venous compression were determined in all patients. Data of bleeding assessment tool (BAT) score, clinical characteristics, results of primary and secondary hemostasis assays, and general treatment plans were collected.

Results

In total, 160 patients were included: 97 (61%) without and 63 (39%) with a laboratory-based fibrinolytic disorder. Mean BAT score did not differ between the groups (9.3 vs 9.8, respectively). The presumptive fibrinolytic disorders were distributed as follows: 34 patients had an increased ECLT ratio or low baseline ECLT, 25 patients had low PAI-1 antigen and activity level, and four patients had both. The majority of these patients were treated with tranexamic acid monotherapy (60%) with only 40% additional treatment options, whereas 80% of patients without a presumptive fibrinolytic disorder had multiple treatment modalities.

Discussion

Analysis of fibrinolytic disorders in selected patients has a high diagnostic yield. General incorporation of fibrinolytic analysis in the diagnostic workup of patients with bleeding of unknown cause can improve diagnosis and management of their bleeding episodes.

Measuring Fibrinolysis

Physiological fibrinolysis under normal conditions progresses slowly, in contrast to coagulation which is triggered rapidly to stop bleeding and defend against microbial invasion. Methods to detect fibrinolysis abnormalities are less simple and poorly standardized compared with common coagulation tests. Fibrinolysis can be accelerated by preparing euglobulin from plasma to reduce endogenous inhibitors, or by adding plasminogen activators to normal plasma. However, these manipulations complicate interpretation of results and diagnosis of a "fibrinolysis deficit." Many observational studies on antigen levels of fibrinolysis inhibitors, plasminogen activator inhibitor 1 or thrombin-activatable fibrinolysis inhibitor, zymogen or active enzyme have been published. However, conclusions are mixed and there are clear problems with harmonization of results. Viscoelastic methods have the advantage of being rapid and are used as point-of-care tests. They also work with whole blood, allowing the contribution of platelets to be explored. However, there are no agreed protocols for applying viscoelastic methods in acute care for the diagnosis of hyperfibrinolysis or to direct therapy. The emergence of SARS-CoV-2 and the dangers of associated coagulopathy provide new challenges. A common finding in hospitalized patients is high levels of D-dimer fibrin breakdown products, indicative of ongoing fibrinolysis. Well-established problems with D-dimer testing standardization signal that we should be cautious in using results from such tests as prognostic indicators or to target therapies.

Diagnostic work up of patients with increased bleeding tendency

Introduction

The diagnostic trajectory of patients with increased bleeding tendency can be very costly and time‐consuming. In addition, previous studies have shown that half of these patients remain without final diagnosis despite all efforts.

Aim

This study aimed to improve insight into the current diagnostic process of these patients.

Methods

A total of 117 adult patients, referred to an academic hospital because of being suspected to have an increased bleeding tendency, were included. Different parameters were compared between patients receiving final diagnosis, patients without final diagnosis but a high Tosetto bleeding assessment tool (BAT) score (classified as bleeding of unknown cause, or BUC) and a control group consisting of patients without final diagnosis and a low BAT score.

Results

The BAT score was significantly higher in patients in the BUC group as compared to patients reaching final diagnosis (8.1 vs 4.9). Interestingly, the two subcategories most prevalently increased were surgery and post‐partum haemorrhage‐associated bleeding (surgery: 2.1 vs 1.1; post‐partum haemorrhage: 0.7 vs 0.0). Laboratory screening results were more often abnormal in patients reaching final diagnosis compared to patients remaining without diagnosis and a high BAT score (n = 32 (78%) vs n = 14 (46%), 95% CI 1.5‐12), especially concerning the PFA (=27 (66%) vs n = 10 (33%), 95% CI 1.4‐10) and von Willebrand factor activity levels (n = 11 (27%) vs n = 1 (3%), 95% CI 1.3‐91).

Conclusion

Isolated high bleeding score on surgical or post‐partum bleeding correlates with a lower chance of receiving final diagnosis. Withholding extensive haemostatic testing should be considered. Better screening and confirmative haemostatic assays are still needed.

Therapeutic Implications of Inherited Thrombophilia in Pregnancy

BACKGROUND

Inherited (hereditary) thrombophilia is a genetic disorder that affects coagulation, being responsible for more than 60% of idiopathic (spontaneous or unprovoked) thromboembolic events. Association of inherited thrombophilia with pregnancy increases the risk of thromboembolic disease, and it may be related to many complications, such as preeclampsia, recurrent miscarriage intrauterine growth restriction, early detachment of placenta, and prematurity.

AREAS OF UNCERTAINTY

Interpretation of a positive test for thrombophilia in pregnant women is difficult because they have many natural changes in the coagulation system. Genetic diagnosis of thrombophilia, after a thrombotic event or during a pregnancy complication, has a major importance, not only to define its etiology but also to determine the duration of anticoagulant treatment and risk stratification for prophylaxis treatment.

DATA SOURCES

Literature search was performed using electronic database (PubMed) between April 1981 and November 2018. We used different keywords and MeSH terms to generate the most relevant results related to the inherited thrombophilia and its impact on pregnancy.

RESULTS

Screening for inherited thrombophilia in young women is recommended in case of personal history of venous thromboembolism, first-degree relatives with a history of high-risk thrombophilia, or personal history of second-trimester miscarriage. Decision to recommend thromboprophylaxis with anticoagulant treatment in pregnant women with inherited thrombophilia is determined by history of venous thromboembolism, type and associated risk of inherited thrombophilia, and presence of additional risk factors. Low-molecular-weight heparins are the preferred agents for prophylaxis in pregnancy, while the doses vary depending on thrombophilia type, personal history, and associated risk factors.

CONCLUSIONS

Association between 2 procoagulant conditions, inherited thrombophilia and pregnancy, has an important impact for the mother and fetus. This review will summarize the impact of each inherited prothrombotic factor on cardiovascular and pregnancy outcomes and will discuss the role of anticoagulation treatment for women diagnosed with inherited thrombophilia.

Hemorrhagic disorders of fibrinolysis: a clinical review

Hyperfibrinolytic bleeding can be caused by a deficiency of one of the inhibitors of fibrinolysis (plasminogen activator inhibitor type 1 [PAI-1] or α2-antiplasmin [α2-AP]), or an excess of one of the activators of fibrinolysis: tissue-type plasminogen activator or urokinase-type plasminogen activator. This review focuses on the clinical implications of these disorders. The bleeding phenotype of fibrinolytic disorders is characterized by delayed bleeding after trauma, surgery and dental procedures. Bleeding in areas of high fibrinolytic activity is also common, such as menorrhagia and epistaxis. Patients with α2-AP deficiency present with the most severe bleeding episodes. Recently, it was discovered that hyperfibrinolytic disorders are associated with a high rate of obstetric complications such as miscarriage and preterm birth, especially in PAI-1 deficient patients. Hyperfibrinolytic disorders are probably underdiagnosed because of lack of knowledge and lack of accurate diagnostic tests. A substantial part of the large group of patients diagnosed as 'bleeding of unknown origin' could actually have a hyperfibrinolytic disorder. In the case of a high index of suspicion (i.e. because of a positive family history, recurrent bleeding or uncommon type of bleeding such as an intramedullary hematoma), further testing should not be withheld because of normal results of standard hemostatic screening assays. Timely diagnosis is important because these disorders can generally be treated well with antifibrinolytic agents.

Development of a fibrinolysis assay for canine plasma

Unbalanced coagulation and fibrinolysis leads to hemorrhage or thrombosis. Thromboelastography has been used to characterize hypo- and hyper-fibrinolysis in dogs, however the technique requires specialized instrumentation and proprietary reagents that limit its availability. The aim of this study was to develop a simple microplate method for assessment of fibrinolysis in canine plasma. Plasma from healthy dogs was mixed in a microwell plate with tissue factor, calcium, phospholipid and tissue plasminogen activator. Light absorbance was measured at regular intervals until return to baseline. Peak optical density (milli-absorption units, mAU), formation velocity (mAU/s), lysis velocity (mAU/s) and area under the curve (mAU.s) were calculated. The influence of potential interferents, variation in fibrinogen and ex vivo addition of heparin and aminocaproic acid on assay performance was determined. Inter-day coefficients of variation were ≤15% for all variables. Bilirubin≤1.88mg/dL and hemoglobin≤0.09mg/dL did not interfere with assay variables. Aminocaproic acid (40μg/mL) and heparin (0.125U/mL) caused almost complete inhibition of fibrinolysis and coagulation, respectively. All variables except lysis velocity (R²=0.08) were associated with fibrinogen concentration (R²>0.8). This assay showed acceptable performance characteristics for measurement of fibrinolysis in normal canine plasma. The assay utilizes small volume citrate plasma samples and readily available instrumentation and reagents, is not influenced by mild to moderate hemolysis or icterus and detects the presence of fibrinolysis inhibitors.

Plasma carboxypeptidase U (CPU, CPB2, TAFIa) generation during in vitro clot lysis and its interplay between coagulation and fibrinolysis

Carboxypeptidase U (CPU, CPB2, TAFIa) is a basic carboxypeptidase that is able to attenuate fibrinolysis. The inactive precursor procarboxypeptidase U is converted to its active form by thrombin, the thrombin-thrombomodulin complex or plasmin. The aim of this study was to investigate and characterise the time course of CPU generation in healthy individuals. In plasma of 29 healthy volunteers, CPU generation was monitored during in vitro clot lysis. CPU activity was measured by means of an enzymatic assay that uses the specific substrate Bz-o-cyano-Phe-Arg. An algorithm was written to plot the CPU generation curve and calculate the parameters that define it. In all individuals, CPU generation was biphasic. Marked inter-individual differences were present and a reference range was determined. The endogenous CPU generation potential is the composite effect of multiple factors. With respect to the first CPU activity peak characteristics, we found correlations with baseline proCPU concentration, proCPU Thr325Ile polymorphism, time to clot initiation and the clot lysis time. The second CPU peak related with baseline proCPU levels and with the maximum turbidity of the clot lysis profile. In conclusion, our method offers a technique to determine the endogenous CPU generation potential of an individual. The parameters obtained by the method quantitatively describe the different mechanisms that influence CPU generation during the complex interplay between coagulation and fibrinolysis, which are in line with the threshold hypothesis.

Thrombin generation assays for global evaluation of the hemostatic system: perspectives and limitations

The existing techniques to evaluate hemostasis in clinical laboratories are not sensitive enough to detect hypercoagulable and mild hypocoagulable states. Under different experimental conditions, the thrombin generation test may meet these requirements. This technique evaluates the overall balance between procoagulant and anticoagulant forces and has provided new insights in our understanding of the coagulation cascade, as well as of the diagnosis of hypocoagulability and hypercoagulability conditions. Thrombin generated in the thrombin generation test can be quantified as platelet-rich or platelet-poor plasma using the calibrated automated thrombogram method, which monitors the cleavage of a fluorogenic substrate that is simultaneously compared to the known thrombin activity in a non-clotting plasma sample. The calibrated automated thrombogram method is an open system, in which different antibodies, proteins, enzymes and peptides can be introduced to answer specific questions regarding hemostatic processes. The thrombin generation test has great clinical potential, such as in monitoring patients taking anticoagulants and antiplatelet drugs, screening for genetic or acquired thrombotic disorders, and evaluating bleeding risk control in patients with hemophilia using bypass agents or replacement therapy. Different to conventional coagulation tests, the thrombin generation test can be used for an overall evaluation of hemostasis, the results of which can then be used to evaluate specific characteristics of hemostasis, such as prothrombin time, activated partial thromboplastin time, and levels of fibrinogen and other coagulation factors. The introduction of this method will contribute to a better understanding and evaluation of overall hemostatic processes; however, this method still requires standardization and clinical validation.

Tissue factor-dependent coagulation activation by heme: A thromboelastometry study

Heme has been characterized as potent trigger of inflammation. In hemostasis, although heme has been shown to both induce and inhibit different compartments of hemostasis, its net effect on the hemostatic balance, and the biological relevance of these effects remain to be determined. Herein we evaluated the effect of heme on hemostasis using a global assay able to generate clinically relevant data in several other complex hemostatic diseases. Citrated whole blood samples from healthy participants were stimulated by heme or vehicle and incubated for 4h at 37°C. Rotational thromboelastometry was immediately performed. The participation of tissue factor in coagulation activation was evaluated using inhibitory antibody. Heme was able of inducing ex vivo coagulation activation in whole blood, affecting predominantly parameters associated with the initial phases of clot formation. This activation effect was at least partially dependent on hematopoietic tissue factor, since the effects of heme were partially abrogated by the inhibition of human tissue factor. In conclusion, using a global hemostasis assay, our study confirmed that heme is able to activate coagulation in whole blood, in a tissue factor-dependent way. These findings could explain the disturbance in hemostatic balance observed in conditions associated with the release of heme such as sickle cell disease.

Bleeding related to disturbed fibrinolysis

The components and reactions of the fibrinolysis system are well understood. The pathway has fewer reactants and interactions than coagulation, but the generation of a complete quantitative model is complicated by the need to work at the solid‐liquid interface of fibrin. Diagnostic tools to detect disease states due to malfunctions in the fibrinolysis pathway are also not so well developed as is the case with coagulation. However, there are clearly a number of inherited or acquired pathologies where hyperfibrinolysis is a serious, potentially life‐threatening problem and a number of antifibrinolytc drugs are available to treat hyperfibrinolysis. These topics will be covered in the following review.

Can the phenotype of inherited fibrinogen disorders be predicted?

Congenital fibrinogen disorders are rare diseases affecting either the quantity (afibrinogenaemia and hypofibrinogenaemia) or the quality (dysfibrinogenaemia) or both (hypodysfibrinogenaemia) of fibrinogen. In addition to bleeding, unexpected thrombosis, spontaneous spleen ruptures, painful bone cysts and intrahepatic inclusions can complicate the clinical course of patients with quantitative fibrinogen disorders. Clinical manifestations of dysfibrinogenaemia include absence of symptoms, major bleeding or thrombosis as well as systemic amyloidosis. Although the diagnosis of any type of congenital fibrinogen disorders is usually not too difficult with the help of conventional laboratory tests completed by genetic studies, the correlation between all available tests and the clinical manifestations is more problematic in many cases. Improving accuracy of diagnosis, performing genotype, analysing function of fibrinogen variants and carefully investigating the personal and familial histories may lead to a better assessment of patients' phenotype and therefore help in identifying patients at increased risk of adverse clinical outcomes. This review provides an update of various tests (conventional and global assays, molecular testing, fibrin clot analysis) and clinical features, which may help to better predict the phenotype of the different types of congenital fibrinogen disorders.

Purification and characterization of tenerplasminin-1, a serine peptidase inhibitor with antiplasmin activity from the coral snake (Micrurus tener tener) venom

A plasmin inhibitor, named tenerplasminin-1 (TP1), was isolated from Micrurus tener tener (Mtt) venom. It showed a molecular mass of 6542Da, similarly to Kunitz-type serine peptidase inhibitors. The amidolytic activity of plasmin (0.5nM) on synthetic substrate S-2251 was inhibited by 91% following the incubation with TP1 (1nM). Aprotinin (2nM) used as the positive control of inhibition, reduced the plasmin amidolytic activity by 71%. Plasmin fibrinolytic activity (0.05nM) was inhibited by 67% following incubation with TP1 (0.1nM). The degradation of fibrinogen chains induced by plasmin, trypsin or elastase was inhibited by TP1 at a 1:2, 1:4 and 1:20 enzyme:inhibitor ratio, respectively. On the other hand, the proteolytic activity of crude Mtt venom on fibrinogen chains, previously attributed to metallopeptidases, was not abolished by TP1. The tPA-clot lysis assay showed that TP1 (0.2nM) acts like aprotinin (0.4nM) inducing a delay in lysis time and lysis rate which may be associated with the inhibition of plasmin generated from the endogenous plasminogen activation. TP1 is the first serine protease plasmin-like inhibitor isolated from Mtt snake venom which has been characterized in relation to its mechanism of action, formation of a plasmin:TP1 complex and therapeutic potential as anti-fibrinolytic agent, a biological characteristic of great interest in the field of biomedical research. They could be used to regulate the fibrinolytic system in pathologies such as metastatic cancer, parasitic infections, hemophilia and other hemorrhagic syndromes, in which an intense fibrinolytic activity is observed.

Management of venous thrombosis in the pediatric patient

The incidence of venous thromboembolism in children has increased significantly over the past decade. The evaluation and management of the child with venous thromboembolism, while based on the adult experience, has its own particularities dictated by the differences in the hemostatic system of the newborn and child. The current review addresses the evaluation of pediatric patient with thrombosis as well as the established and emerging treatment interventions.

Disease Severity Correlates with Thrombotic Capacity in Experimental Nephrotic Syndrome

Thrombotic disease, a major life-threatening complication of nephrotic syndrome, has been associated with proteinuria and hypoalbuminemia severity. However, it is not fully understood how disease severity correlates with severity of the acquired hypercoagulopathy of nephrotic syndrome. Without this knowledge, the utility of proteinuria and/or hypoalbuminemia as biomarkers of thrombotic risk remains limited. Here, we show that two well established ex vivo hypercoagulopathy assays, thrombin generation and rotational thromboelastometry, are highly correlated with proteinuria and hypoalbuminemia in the puromycin aminonucleoside and adriamycin rat models of nephrotic syndrome. Notably, in the puromycin aminonucleoside model, hyperfibrinogenemia and antithrombin deficiency were also correlated with proteinuria severity, consistent with reports in human nephrotic syndrome. Importantly, although coagulation was not spontaneously activated in vivo with increasing proteinuria, vascular injury induced a more robust thrombotic response in nephrotic animals. In conclusion, hypercoagulopathy is highly correlated with nephrotic disease severity, but overt thrombosis may require an initiating insult, such as vascular injury. Our results suggest that proteinuria and/or hypoalbuminemia could be developed as clinically meaningful surrogate biomarkers of hypercoagulopathy to identify patients with nephrotic syndrome at highest risk for thrombotic disease and potentially target them for anticoagulant pharmacoprophylaxis.

Global assays of hemostasis

PURPOSE OF REVIEW

There exists an imbalance between our understanding of the physiology of the blood coagulation process and the translation of this understanding into useful assays for clinical application. As technology advances, the capabilities for merging the two areas have become more attainable. Global assays have advanced our understanding of the dynamics of the blood coagulation process beyond end point assays and are at the forefront of implementation in the clinic.

RECENT FINDINGS

We will review recent advances in the main global assays with a focus on thrombin generation that have potential for clinical utility. These assays include direct (thrombogram, whole blood, purified systems) and indirect empirical measures of thrombin generation (thromboelastography) and mechanism-based computational models that use plasma composition data from individuals to generate thrombin generation profiles.

SUMMARY

Empirical thrombin generation assays (direct and indirect) and computational modeling of thrombin generation have greatly advanced our understanding of the hemostatic balance. Implementation of these types of assays and visualization approaches in the clinic will potentially provide a basis for the development of individualized patient care. Advances in both empirical and computational global assays have made the goal of predicting precrisis changes in an individual's hemostatic state one step closer.

Global assays of hemostasis in the diagnostics of hypercoagulation and evaluation of thrombosis risk

Thrombosis is a deadly malfunctioning of the hemostatic system occurring in numerous conditions and states, from surgery and pregnancy to cancer, sepsis and infarction. Despite availability of antithrombotic agents and vast clinical experience justifying their use, thrombosis is still responsible for a lion’s share of mortality and morbidity in the modern world. One of the key reasons behind this is notorious insensitivity of traditional coagulation assays to hypercoagulation and their inability to evaluate thrombotic risks; specific molecular markers are more successful but suffer from numerous disadvantages. A possible solution is proposed by use of global, or integral, assays that aim to mimic and reflect the major physiological aspects of hemostasis process in vitro. Here we review the existing evidence regarding the ability of both established and novel global assays (thrombin generation, thrombelastography, thrombodynamics, flow perfusion chambers) to evaluate thrombotic risk in specific disorders. The biochemical nature of this risk and its detectability by analysis of blood state in principle are also discussed. We conclude that existing global assays have a potential to be an important tool of hypercoagulation diagnostics. However, their lack of standardization currently impedes their application: different assays and different modifications of each assay vary in their sensitivity and specificity for each specific pathology. In addition, it remains to be seen how their sensitivity to hypercoagulation (even when they can reliably detect groups with different risk of thrombosis) can be used for clinical decisions: the risk difference between such groups is statistically significant, but not large.

Modeling thrombin generation: plasma composition based approach

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

Correction of microplate location effects improves performance of the thrombin generation test

Background

Microplate-based thrombin generation test (TGT) is widely used as clinical measure of global hemostatic potential and it becomes a useful tool for control of drug potency and quality by drug manufactures. However, the convenience of the microtiter plate technology can be deceiving: microplate assays are prone to location-based variability in different parts of the microtiter plate.

Methods

In this report, we evaluated the well-to-well consistency of the TGT variant specifically applied to the quantitative detection of the thrombogenic substances in the immune globulin product. We also studied the utility of previously described microplate layout designs in the TGT experiment.

Results

Location of the sample on the microplate (location effect) contributes to the variability of TGT measurements. Use of manual pipetting techniques and applications of the TGT to the evaluation of procoagulant enzymatic substances are especially sensitive. The effects were not sensitive to temperature or choice of microplate reader. Smallest location effects were observed with automated dispenser-based calibrated thrombogram instrument. Even for an automated instrument, the use of calibration curve resulted in up to 30% bias in thrombogenic potency assignment.

Conclusions

Use of symmetrical version of the strip-plot layout was demonstrated to help to minimize location artifacts even under the worst-case conditions. Strip-plot layouts are required for quantitative thrombin-generation based bioassays used in the biotechnological field.

Improved neurocognitive functions correlate with reduced inflammatory burden in atrial fibrillation patients treated with intensive cholesterol lowering therapy

Background

Atrial fibrillation (AF) is associated with increased mortality and morbidity, including risk for cerebral macro- and microinfarctions and cognitive decline, even in the presence of adequate oral anticoagulation. AF is strongly related to increased inflammatory activity whereby anti-inflammatory agents can reduce the risk of new or recurrent AF. However, it is not known whether anti-inflammatory therapy can also modify the deterioration of neurocognitive function in older patients with AF. In the present study, older patients with AF were treated with intensive lipid-lowering therapy with atorvastatin 40 mg and ezetimibe 10 mg, or placebo. We examined the relationship between neurocognitive functions and inflammatory burden.

Findings

Analysis of inflammatory markers revealed significant reductions in high sensitivity C-reactive protein (hs-CRP), fibroblast growth factor (FGF), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-1 receptor antagonist (IL-1RA), interleukin (IL)-9, IL-13 and IL-17, and interferon-γ (IFNγ) in the treatment group compared to placebo. Reduction in plasma concentration of IL-1RA, IL-2, IL-9 and IL-12, and macrophage inflammatory protein-1β (MIP-1β) correlated significantly with improvement in the neurocognitive functions memory and speed. Loss of volume in amygdala and hippocampus, as determined by magnetic resonance imaging (MRI), was reduced in the treatment arm, statistically significant for left amygdala.

Conclusions

Anti-inflammatory therapy through intensive lipid-lowering treatment with atorvastatin 40 mg and ezetimibe 10 mg can modify the deterioration of neurocognitive function, and the loss of volume in certain cerebral areas in older patients with AF.

Trial registration Clinical Trials.gov

NCT00449410

Models for thrombin generation and risk of disease

Computational models can offer an integrated view of blood clotting dynamics and may ultimately be instructive regarding an individual's risk of bleeding or clotting. Appropriately, developed and validated models could allow clinicians to simulate the outcomes of therapeutics and estimate risk of disease. Computational models that describe the dynamics of thrombin generation have been developed and have been used in combination with empirical studies to understand thrombin dynamics on a mechanistic basis. The translation of an individual's specific coagulation factor composition data using these models into an integrated assessment of hemostatic status may provide a route for advancing the long-term goal of individualized medicine. This review details the integrated approaches to understanding: (i) What is normal thrombin generation in individuals? (ii) What is the effect of normal range plasma composition variation on thrombin generation in pathologic states? (iii) Can disease progression or anticoagulation be followed by understanding the boundaries of normal thrombin generation defined by plasma composition? (iv) What are the controversies and limitations of current computational approaches? Progress in these areas can bring us closer to developing models that can be used to aid in identifying hemostatic risk.

Biochemical and pharmacological properties of a new thrombin-like serine protease (Russelobin) from the venom of Russell's Viper (Daboia russelii russelii) and assessment of its therapeutic potential

BACKGROUND

Snake venoms are rich sources of bioactive molecules, and several venom-derived proteins have entered clinical trials for use in ischemic disorders; however, late-stage failure of a recent drug candidate due to low in vivo efficacy demonstrated the need for new sources of fibrinogenolytic drug candidates.

METHODS

A 51.3kDa thrombin-like serine protease (Russelobin) purified from the venom of Russell's Viper (Daboia russelii russelii) was subjected to extensive biochemical characterization, including N-terminal sequencing, substrate specificity, kinetic and inhibitor assays, glycosylation analysis and stability assays. Toxicity and pathology analyses were conducted in NSA mice.

RESULTS

Russelobin has extensive N-terminus identity with a beta-fibrinogenase-like serine proteinase precursor from Daboia russelii siamensis venom, a mass of 51.3kDa and contains extensive N-linked oligosaccharides. Serine protease inhibitors and heparin significantly decreased activity, with much lower inhibition by DTT, antithrombin-III and α2-macroglobulin. Russelobin preferentially released FPA and slowly released FPB from human fibrinogen, forming a labile fibrin clot readily hydrolyzed by plasmin. The partially deglycosylated enzyme showed significantly lower activity toward fibrinogen and less resistance against neutralization by plasma α2MG and antithrombin-III. Russelobin was non-cytotoxic, non-lethal and produced no histopathologies in mice, and it demonstrated in vivo dose-dependent defibrinogenating activity.

CONCLUSIONS

Russelobin is an A/B fibrinogenase with high specificity toward fibrinogen, both in vitro and in vivo. Extensive glycosylation appears to protect the molecule against endogenous protease inhibitors, prolonging its in vivo efficacy.

GENERAL SIGNIFICANCE

Due to its low toxicity, stability and activity as a defibrinogenating agent, Russelobin shows high potential for cardiovascular drug development.

Use of global assays to understand clinical phenotype in congenital factor VII deficiency

Congenital factor VII (FVII) deficiency is characterized by genotypic variability and phenotypic heterogeneity. Traditional screening and factor assays are unable to reliably predict clinical bleeding phenotype and guide haemorrhage prevention strategy. Global assays of coagulation and fibrinolysis may better characterize overall haemostatic balance and aid in haemorrhagic risk assessment. We evaluated the ability of novel global assays to better understand clinical bleeding severity in congenital FVII deficiency. Subjects underwent central determination of factor VII activity (FVII:C) as well as clot formation and lysis (CloFAL) and simultaneous thrombin and plasmin generation (STP) global assay analysis. A bleeding score was assigned to each subject through medical chart review. Global assay parameters were analysed with respect to bleeding score and FVII:C. Subgroup analyses were performed on paediatric subjects and subjects with FVII ≥ 1 IU dL(-1). CloFAL fibrinolytic index (FI2 ) inversely correlated with FVII:C while CloFAL maximum amplitude (MA) and STP maximum velocity of thrombin generation (VT max) varied directly with FVII:C. CloFAL FI2 directly correlated with bleeding score among subjects in both the total cohort and paediatric subcohort, but not among subjects with FVII ≥ 1 IU dL(-1) . Among subjects with FVII ≥ 1 IU dL(-1), STP time to maximum velocity of thrombin generation and time to maximum velocity of plasmin generation inversely correlated with bleeding score. These preliminary findings suggest a novel potential link between a hyperfibrinolytic state in bleeding severity and congenital FVII deficiency, an observation that should be further explored.

A novel μ-fluidic whole blood coagulation assay based on Rayleigh surface-acoustic waves as a point-of-care method to detect anticoagulants

A universal coagulation test that reliably detects prolonged coagulation time in patients, irrespective of the anticoagulant administered, has not been available to date. An easily miniaturised, novel μ-fluidic universal coagulation test employing surface acoustic waves (SAW) is presented here. SAW was employed to instantly mix and recalcify 6 μl citrated whole blood and image correlation analysis was used to quantify clot formation kinetics. The detection of clinically relevant anticoagulant dosing with old anticoagulants (unfractionated heparin, argatroban) and new anticoagulants (dabigatran, rivaroxaban) has been tested and compared to standard plasma coagulation assays. The applicability of this novel method has been confirmed in a small patient population. Coagulation was dose-proportionally prolonged with heparin, argatroban, dabigatran, and rivaroxaban, comparable to standard tests. Aspirin and clopidogrel did not interfere with the SAW-induced clotting time (SAW-CT), whereas the strong GPIIb/IIIa-inhibitor abciximab did interfere. Preliminary clinical data prove the suitability of the SAW-CT in patients being treated with warfarin, rivaroxaban, or dabigatran. The system principally allows assessment of whole blood coagulation in humans in a point-of-care setting. This method could be used in stroke units, emergency vehicles, general and intensive care wards, as well as for laboratory and home testing of coagulation.

Rare factor deficiencies

PURPOSE OF REVIEW

By definition, rare factor deficiencies have a prevalence of less than 200,000 in the US population, or an incidence of less than one in 2000 in Europe. The very small numbers of patients with rare disorders present challenges in diagnosis, evaluation of bleeding risk and treatment. Use of new assays, full genome sequencing, and global clotting assays will significantly improve diagnosis of patients with rare bleeding disorders.

RECENT FINDINGS

In addition to new assays available for monitoring patients, new therapy, both recombinant and plasma derived, is now available. Registries and clinical trials have demonstrated decreased bleeding and improved outcomes when patients are treated with these agents. Expanding international registries have been initiated to correlate genotype and bleeding phenotype in conjunction with global assays.

SUMMARY

Ongoing research continues to expand our understanding of the pathophysiology of rare factor deficiencies. This work complements medical practice to incorporate early diagnosis and new treatment options for patients, resulting in safer and less sensitizing regimens and much improved clinical outcomes.

The C-terminal fragment of axon guidance molecule Slit3 binds heparin and neutralizes heparin's anticoagulant activity

Slit3 is a large molecule with multiple domains and belongs to axon guidance families. To date, the biological functions of Slit3 are still largely unknown. Our recent study demonstrated that the N-terminal fragment of Slit3 is a novel angiogenic factor. In this study, we examined the biological function of the C-terminal fragment of human Slit3 (HSCF). The HSCF showed a high-affinity binding to heparin. The binding appeared to be heparin/heparan sulfate-specific and depends on the size, the degree of sulfation, the presence of N- and 6-O-sulfates and carboxyl moiety of the polysaccharide. Functional studies observed that HSCF inhibited antithrombin binding to heparin and neutralized the antifactor IIa and Xa activities of heparin and the antifactor IIa activity of low-molecular-weight heparin (LMWH). Thromboelastography analysis observed that HSCF reversed heparin's anticoagulation in global plasma coagulation. Taken together, these observations demonstrate that HSCF is a novel heparin-binding protein that potently neutralizes heparin's anticoagulation activity. This study reveals a potential for HSCF to be developed as a new antidote to treat overdosing of both heparin and LMWH in clinical applications.

Retrospective evaluation of bleeding tendency and simultaneous thrombin and plasmin generation in patients with rare bleeding disorders

Rare bleeding disorders (RBDs) are a heterogeneous group of diseases with varying bleeding tendency, only partially explained by their laboratory phenotype. We analysed the separate groups of RBD abnormalities, and we investigated retrospectively whether the novel haemostasis assay (NHA) was able to differentiate between bleeding tendency. We have performed simultaneous thrombin generation (TG) and plasmin generation (PG) measurements in 41 patients affected with deficiencies in prothrombin, factor (F) V, FVII, FX, FXIII and fibrinogen. Parameters of the NHA were classified based on (major or minor) bleeding tendency. Patients with deficiencies in coagulation propagation (FII, FV and FX) and major type of bleedings had diminished TG (expressed as AUC) below 20% of control. FVII deficient patients only had prolonged thrombin lag-time ratio of 1.6 ± 0.2 (P < 0.05) and normal AUC (92-125%). Afibrinogenemic patients demonstrated PG of 2-29% of normal and appeared to correlate with the type of mutation. Thrombin peak-height (57 ± 16%) was reduced (not significant) in these patients and AUC was comparable to the reference (102 ± 27%). FXIII-deficient plasmas resulted in a reduced thrombin peak-height of 59 ± 13% (P < 0.05) and normal AUC (90 ± 14%). Thrombin peak-height (P < 0.01) and plasmin potential (P < 0.05) were lower in the major bleeders compared with the minor bleeders. These results provided distinct TG and PG curves for each individual abnormality and differentiation of bleeding tendency was observed for thrombin and PG parameters. Prospective studies are warranted to confirm these retrospective results.