Influence of factor VIII on overall coagulability and fibrinolytic potential of haemophilic plasma as measured by global assay: monitoring in haemophilia A

Clot formation and fibrinolysis assays reveal functional differences among hemostatic agents in hemophilia A plasma

Background

Measuring the activity of hemostatic agents used to treat hemophilia A often requires drug-specific assays. In vitro assays show hemophilic clots have abnormal characteristics, including prolonged clotting time and decreased resistance to fibrinolysis. The ability of certain agents to correct these parameters in vitro is associated with hemostatic efficacy in vivo.

Objectives

To compare effects of established and emerging hemostatic agents on clot formation and fibrinolysis in hemophilia A plasma.

Methods

Pooled and individual hemophilia A platelet-poor plasmas were spiked with replacement (recombinant factor VIII [rFVIII], PEGylated rFVIII, polysialylated rFVIII, and porcine rFVIII) or bypassing (emicizumab, rFVIIa, and activated prothrombin complex concentrate) products. Effects on tissue factor-initiated clot formation and fibrinolysis were measured by turbidity.

Results

Compared to normal pooled plasma, hemophilia-pooled plasma showed reduced clot formation and increased fibrinolysis, and all replacement agents improved these characteristics. rFVIII and PEGylated rFVIII produced similar effects at similar concentrations, whereas polysialylated rFVIII produced slightly higher and porcine rFVIII slightly lower effects at these concentrations. Bypassing agents enhanced clot formation and stability, but patterns differed from replacement agents. The clotting rate showed a concentration-response relationship for all agents. High concentrations of all products produced effects that exceeded the normal range in at least some parameters. Responses of individual donors varied, but all agents improved clot formation and stability in all donors tested.

Conclusion

Clotting and fibrinolysis assays reveal hemostatic effects of replacement and bypassing therapies at clinically relevant concentrations. These assays may help characterize hemostatic agents and optimize dosing.

Thrombin generation and implications for hemophilia therapies: A narrative review

Thrombin plays an essential role in achieving and maintaining effective hemostasis and stable clot formation. In people with hemophilia, deficiency of procoagulant factor (F)VIII or FIX results in insufficient thrombin generation, leading to reduced clot stability and various bleeding manifestations. A correlation has been found between the bleeding phenotype of people with hemophilia and the extent of thrombin generation, with individuals with increased thrombin generation being protected from bleeding and those with lower thrombin generation having increased bleeding tendency. The amount, location, and timing of thrombin generation have been found to affect the formation and stability of the resulting clot. The goal of all therapies for hemophilia is to enhance the generation of thrombin with the aim of restoring effective hemostasis and preventing or controlling bleeding; current treatment approaches rely on either replacing or mimicking the missing procoagulant (ie, FVIII or FIX) or rebalancing hemostasis through lowering natural anticoagulants, such as antithrombin. Global coagulation assays, such as the thrombin generation assay, may help guide the overall management of hemostasis by measuring and monitoring the hemostatic potential of patients and, thus, assessing the efficacy of treatment in people with hemophilia. Nevertheless, standardization of the thrombin generation assay is needed before it can be adopted in routine clinical practice.

Plasma fibrinolysis, inflammatory markers, and postthrombotic syndrome: preliminary findings from the Kids-DOTT Biobank

Plasma levels of markers of coagulation and inflammation have been identified as prognostic factors for adult postthrombotic syndrome (PTS). We aimed to determine whether plasma fibrinolytic capacity and cytokine levels during the first 3 months after provoked deep venous thrombosis (DVT) are associated with risk of PTS in young patients. We analyzed plasma biospecimens (6 weeks and 3 months after provoked DVT) and clinical data from a National Heart, Lung, and Blood Institute-sponsored multinational trial of anticoagulation for provoked venous thromboembolism in patients younger than age 21 years (Kids-DOTT). Patients with a provoked extremity DVT who had plasma samples available at both 6-week and 3-month post-DVT time points and PTS assessment at 1 year were included. We measured plasma fibrinolytic capacity using the Clot Formation and Lysis (CloFAL) assay and plasma cytokine levels by multiplex immunoassay. Logistic regression analyses evaluated prognostic associations with PTS. Seventy-nine patients were included (median age, 12.8 years; range, 0.04-20.8 years). PTS developed in 34%. Complete veno-occlusion at 6 weeks after diagnosis of DVT (odds ratio [OR], 3.12; 95% confidence interval [CI], 0.81-11.94; P = .097), low fibrinolytic capacity in plasma at 3 months post-DVT (OR, 2.71; 95% CI, 0.92-7.97; P = .07), and elevated serum amyloid A at 3 months post-DVT (OR, 2.85; 95% CI, 0.98-8.34; P = .055) were identified as putative prognostic factors for development of PTS. In multivariable logistic regression analysis, these factors did not retain a statistically significant independent association with PTS, but these preliminary results warrant further investigation in an independent data set to definitively evaluate these findings and identify additional potential prognostic factors for the development of PTS after a provoked DVT in young patients.

In Children with Provoked Venous Thromboembolism, Increasing Plasma Coagulability during the First 3 Months Postdiagnosis is Prognostic of Recurrence

Prognostic factors for venous thromboembolism (VTE) recurrence following provoked VTE are largely unknown. Using the Clot Formation and Lysis (CloFAL) assay, single institutional research has shown overall improvement in acute hypercoagulability during the first 3 months postpediatric VTE, yet a rise in plasma coagulability in a subgroup of patients. We sought to define the incidence of rise in coagulability during the first 3 months post-provoked VTE, to investigate its relationship with elevated D-dimer, and to test the hypothesis that a marked rise in coagulability is independently prognostic of VTE recurrence. CloFAL and D-dimer assays were performed on plasma at 4 to 6 weeks and 3 months post-VTE in the Johns Hopkins pediatric VTE cohort and National Institutes of Health-sponsored Kids-DOTT trial. Associations of VTE recurrence with D-dimer and CloFAL assay measures were evaluated via logistic regression. Eighty-seven patients were included. Median follow-up was 1 year. Complete veno-occlusion was determined in 12% at 6 weeks. During the first 3 months post-VTE, a marked rise in coagulability was observed by CloFAL assay in 17% of patients, while D-dimer was elevated in 21%. Recurrent VTE occurred in 10% of patients. CloFAL assay, but not D-dimer, was associated with recurrence (odds ratio [OR] 5.87, 95% confidence interval [95% CI], 1.34-25.8]). After adjustment for veno-occlusion, patients with a marked rise in coagulability by CloFAL assay had a 10-fold increased risk of recurrent VTE (OR 10.33 [95% CI, 1.83-58.19]). Future work should seek to elucidate the mechanisms underlying a rise in plasma coagulability following provoked VTE and to substantiate its prognostic utility for recurrent VTE.

Coagulative function assessed preoperatively via the clot formation and lysis assay as a prognostic factor for blood loss in adolescents undergoing posterior spinal fusion for idiopathic scoliosis

BACKGROUND

Posterior spinal fusion for adolescent idiopathic scoliosis is a complex surgery often associated with clinically significant blood loss leading to perioperative blood transfusion. Knowledge of risk factors for blood loss and transfusion stems mostly from retrospective studies.

AIM

We sought to prospectively investigate putative prognostic factors for intraoperative blood loss and perioperative blood transfusion in adolescent idiopathic scoliosis patients undergoing posterior spine fusion, including clinical characteristics, surgical factors, and preoperative assessment of overall coagulative and fibrinolytic functions in plasma using the clot formation and lysis (CloFAL) assay.

METHODS

Following Internal Review Board approval, adolescents 10 to <21 years old with idiopathic scoliosis undergoing posterior spine fusion were enrolled preoperatively in a single-institutional prospective cohort and biobanking study. Clinical data were collected on patient characteristics, surgical approach, perioperative management, intraoperative estimated blood loss, and blood transfusion through hospital discharge. Coagulative and fibrinolytic functions in plasma were measured on preoperative samples by CloFAL assay (Coagulation Index and modified Fibrinolytic Index). Univariate linear regression and multivariable linear regression were performed to identify predictors of weight-indexed intraoperative estimated blood loss EBL (EBL/kg).

RESULTS

The final study population included 74 patients. Median age was 14.8 years (SD = 2.2). After adjustment for other putative prognostic factors via multivariable linear regression, coagulative function as determined preoperatively by CloFAL Coagulation Index was an independent predictor of intraoperative (EBL)/kg. Specifically, each 10% increase in CloFAL CI was associated with 3% decrease in the geometric mean of EBL/kg (OR 0.97, 95%CI 0.94-0.99, P = .01).

CONCLUSION

In adolescents undergoing posterior spinal fusion for idiopathic scoliosis, increased coagulative function measured preoperatively using the CloFAL assay is independently associated with decreased intraoperative blood loss. Future studies should expand upon these investigations of plasma coagulative and fibrinolytic capacities in combination with clinical factors, to guide precise preventive strategies against blood loss and blood transfusion in this patient population.

Factor VIII prophylaxis effects outweigh other hemostasis contributors in predicting severe haemophilia A joint outcomes

INTRODUCTION

The Joint Outcome Study (JOS) demonstrated that previously untreated children with severe haemophilia A treated with prophylactic factor VIII (FVIII) concentrate had superior joint outcomes at age 6 years compared to those children treated episodically for bleeding. However, variation in joint outcome within each treatment arm was not well explained.

AIM

In this study, we sought to better understand variation in joint outcomes at age 6 years in participants of the JOS.

METHODS

We evaluated the influence of FVIII half-life, treatment adherence, constitutional coagulant and anticoagulant proteins, and global assays on joint outcomes (number of joint bleeds, total number of bleeds, total MRI score and joint physical exam score). Logistic regression was used to evaluate the association of variables with joint failure status on MRI, defined as presence of subchondral cyst, surface erosion or joint-space narrowing. Each parameter was also correlated with each joint outcome using Spearman correlations.

RESULTS

Prophylaxis treatment arm and FVIII trough were each found to reduce risk of joint failure on univariate logistic regression analysis. When controlling for treatment arm, FVIII trough was no longer significant, likely because of the high level of covariation between these variables. We found no consistent correlation between any laboratory assay performed and any joint outcome parameter measured.

CONCLUSION

In the JOS, the effect of prescribed prophylactic FVIII infusions on joint outcome overshadowed the contribution of treatment adherence, FVIII half-life, global assays of coagulation and constitutional coagulation proteins. (ClinicalTrials.gov number, NCT00207597).

Measuring fibrinolysis: from research to routine diagnostic assays

Development and standardization of fibrinolysis methods have progressed more slowly than coagulation testing and routine high-throughput screening tests for fibrinolysis are still lacking. In laboratory research, a variety of approaches are available and are applied to understand the regulation of fibrinolysis and its contribution to the hemostatic balance. Fibrinolysis in normal blood is slow to develop. For practical purposes plasminogen activators can be added to clotting plasma, or euglobulin prepared to reduce endogenous inhibitors, but results are complicated by these manipulations. Observational studies to identify a 'fibrinolysis deficit' have concluded that excess fibrinolysis inhibitors, plasminogen activator inhibitor 1 (PAI-1) or thrombin-activatable fibrinolysis inhibitor (TAFI), zymogen or active enzyme, may be associated with an increased risk of thrombosis. However, results are not always consistent and problems of adequate standardization are evident with these inhibitors and also for measurement of fibrin degradation products (D-dimer). Few methods are available to investigate fibrinolysis under flow, or in whole blood, but viscoelastic methods (VMs) such as ROTEM and TEG do permit the contribution of cells, and importantly platelets, to be explored. VMs are used to diagnose clinical hyperfibrinolysis, which is associated with high mortality. There is a debate on the usefulness of VMs as a point-of-care test method, particularly in trauma. Despite the difficulties of many fibrinolysis methods, research on the fibrinolysis system, taking in wider interactions with hemostasis proteins, is progressing so that in future we may have more complete models and better diagnostic methods and therapeutics.

Two global haemostatic assays as additional tools to monitor treatment in cases of haemophilia A

Haemophilia A patients with similar levels of factor VIII (FVIII) may have different bleeding phenotypes and responses to treatment with FVIII concentrate. Therefore, a test which determines overall haemostasis may be appropriate for treatment monitoring in some patients. We studied two global haemostatic methods: endogenous thrombin potential (ETP) and overall haemostatic potential (OHP) before and after injection of FVIII concentrate in patients with haemophilia A treated prophylactically and on-demand. A significant correlation between FVIII and both ETP and OHP was observed, while ETP and OHP differed between patients with severe and mild clinical phenotypes. Both ETP and OHP differed significantly between severe, moderate and mild haemophilia A and controls. ETP and OHP increased after intravenous injection of FVIII concentrate in both groups of patients, but in spite of higher pre-treatment values of both ETP and OHP in patients treated prophylactically, and much higher post-treatment FVIII levels in comparison with the values in patients treated on-demand, no difference after treatment was observed for either ETP or OHP. ETP and OHP may be additional alternatives for monitoring (and even for individual tailoring) treatment in patients with haemophilia A.

Modern endovascular treatments of occlusive pediatric acute ischemic strokes: case series and review of the literature

PURPOSE

Literature on the endovascular treatment of occlusive acute ischemic stroke (AIS) in the pediatric population remains nebulous. Clinical trials evaluating the role of systemic and intra-arterial thrombolysis, and mechanical thrombectomy have been strictly isolated to the adult population and largely unknown in their safety and efficacy in the pediatric group.

METHODS

The authors present a review of the literature and their own two cases of occlusive acute ischemic stroke in children younger than the age of 10 years who were treated with modern endovascular devices, specifically with stent retrievers, and discuss their clinical and technical considerations as well as their limitations.

RESULTS

In both pediatric patients, a combination of stent retriever and Penumbra aspiration were used to achieve Thrombolysis In Cerebral Infarction (TICI) 2a or greater with reduction of overall stroke burden. A reduction of National Institutes of Health Stroke Scale (NIHSS) of 8 or greater was achieved at discharge. At 3-month follow-up, the patients had a NIHSS of 6 and 2, respectively. One patient continued to improve from NIHSS of 6 to 3 at 6 months.

CONCLUSION

In carefully, selected pediatric patients, modern endovascular techniques may be used to treat occlusive pediatric AIS. However, larger clinical trials are needed to evaluate the overall safety and effectiveness.

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.

Elevated lipoprotein (a), small apolipoprotein (a), and the risk of arterial ischemic stroke in North American children

Lipoprotein (a) is a risk factor for adult cardiovascular events, in which the apolipoprotein (a) component is thought to promote atherogenesis and impair fibrinolysis. We investigated whether elevated plasma lipoprotein (a) concentration and small predominant apolipoprotein (a) isoform size (number of kringle-4 domains) are risk factors for childhood arterial ischemic stroke and correlate with plasma fibrinolytic function. Patients who had had an arterial ischemic stroke in childhood (29 days - <21 years at onset; n=43) and healthy controls (n=127) were recruited for plasma sampling and laboratory determinations. Cases were followed for recurrence in a prospective cohort study. The median lipoprotein (a) concentration did not differ between groups [cases: median 18.0 nmol/L (7.5 mg/dL) and observed range 0.9-259 nmol/L (0.38-108.0 mg/dL), controls: 20.4 nmol/L (8.5 mg/dL) and 0.2-282 nmol/L (0.08-117.5 mg/dL); P=0.62]. While odds of incident stroke were not significantly increased, risks of recurrent arterial ischemic stroke were each more than ten-times increased for lipoprotein(a) >90(th) percentile of race-specific reference values and apolipoprotein (a) <10(th) percentiles [odds ratio=14.0 (95% confidence interval: 1.0-184), P=0.05 and odds ratio=12.8 (1.61-101), P=0.02]. Statistically significant but weak correlations were observed between euglobulin lysis time and both lipoprotein (a) level (r=0.18, P=0.03) and apolipoprotein (a) size (r= -0.26, P=0.002). In conclusion, elevated lipoprotein (a) and small apolipoprotein (a) potently increase the risk of recurrent arterial ischemic stroke in children, with a mechanism only partially attributable to impaired fibrinolysis. Collaborative studies are warranted to investigate these findings further and, more broadly, to establish key risk factors for incident and recurrent arterial ischemic stroke in children.

Monitoring hypercoagulability and hypofibrinolysis following acute venous Thromboembolism in children: application of the CloFAL assay in a prospective inception cohort study

Although individual thrombophilia tests are frequently performed in children with venous thromboembolism (VTE), global assays provide the opportunity to fill the gap in knowledge regarding their net impact on overall coagulative (and in some cases fibrinolytic) function. We first evaluated analytic sensitivity of the Clot Formation and Lysis (CloFAL) global assay to hypercoagulability and alterations in fibrinolysis, and then characterized changes in plasma coagulative and fibrinolytic capacities over time in children with acute VTE. In plasma ex vivo and in vitro experiments, the CloFAL assay area-under-the-curve (AUC) was analytically sensitive to hypercoagulable states, and its modified fibrinolytic index (FI2) was sensitive to both hyper- and hypofibrinolytic conditions. Clinical data and plasma samples for assay were collected during follow-up of 50 children enrolled in a prospective inception cohort study of VTE from May 2006 to June 2010. Follow-up periods were designated as follows: acute (<1 month post-event), sub-acute (1-3 months), early chronic (3-12 months), and late chronic (>12 months). Since most children were sampled at fewer than three pre-defined follow-up periods, study population findings were grouped by timepoint. AUC was significantly increased, and FI(2) significantly decreased, in the acute period of VTE when compared to healthy controls, indicating hypercoagulability and hypofibrinolysis, respectively. One-third of patients were hypercoagulable, and 23% were hypofibrinolytic, in the late chronic phase. AUC and FI(2) were strongly correlated with functional fibrinogen levels. These findings indicate the utility of the CloFAL assay in monitoring plasma coagulative and fibrinolytic capacities in children with VTE. Studies of its potential role in outcome prediction are ongoing.

Simultaneous thrombin and plasmin generation capacities in normal and abnormal states of coagulation and fibrinolysis in children and adults

INTRODUCTION

Thrombin and plasmin are the key enzymes involved in coagulation and fibrinolysis, respectively. Plasma coagulative and fibrinolytic potentials in normal children and adults, and in representative pathologically altered hemostatic states, were evaluated via simultaneous assessment of thrombin and plasmin generation.

MATERIALS AND METHODS

An assay of Simultaneous Thrombin and Plasmin generation (STP) was developed to measure thrombin and plasmin in plasma using individual fluorometric substrates. Coagulation is initiated with dilute tissue factor, phospholipid, and calcium in platelet-poor plasma; fibrinolysis is accelerated via tissue plasminogen activator (tPA). Abnormal states of hemostasis were investigated.

RESULTS

STP assay reproducibility and normal adult and pediatric values for measured and calculated parameters have been established. Onset of both thrombin and plasmin generation was significantly delayed in children relative to adults (p<0.001) and the maximum amplitudes of thrombin and plasmin generation were less in children than adults (p<0.01). No significant differences were measured among pediatric age groups. The most profound impairments in thrombin generation were observed for extrinsic and common pathway factor deficiencies, with the exception of afibrinogenemia. Plasmin generation was severely impaired in deficiencies of fibrinogen and plasminogen as well as with decreased tPA reagent concentration and addition of aminocaproic acid. Plasmin generation was greatly enhanced by alpha-2-antiplasmin deficiency and excess tPA reagent.

CONCLUSION

Simultaneous assessment of thrombin and plasmin generation in plasma shows promise for affording an enhanced understanding of overall coagulative and fibrinolytic functions in physiological and pathologically altered states of hemostasis in children and adults.

Hyperacute therapies for childhood stroke: a case report and review of the literature

Objective. The optimal management of pediatric patients with arterial ischemic stroke (AIS) is not known. Despite this, goal-oriented, time-sensitive therapies geared to rapid reestablishment of arterial blood flow are occasionally applied with beneficial effects. The inconsistent approach to AIS is in part due to a lack of knowledge and preparedness. Methods. Case report of a 12-year-old male with right middle cerebral artery (MCA) occlusion resulting in dense left hemiplegia and mutism and review of the literature. Intervention(s). Mechanical thrombectomy, intra-arterial administration of rt-PA, vasodilators, and platelet inhibitors, and systemic anticoagulation and subsequent critical care support. Results. Restoration of right MCA blood flow and complete resolution of neurologic deficits. Conclusion. We report the gratifying outcome of treatment of a case of AIS in a pediatric patient treated with hyperacute therapies geared to arterial recanalization and subsequent neurologic critical care and review the pertinent literature. Guidelines for the emergency room management of pediatric AIS from prospective, randomized trials are needed.

Treatment of congenital fibrinogen disorders

BACKGROUND

The goal of the coagulation pathway is the conversion of fibrinogen to fibrin and formation of an insoluble clot. Although relatively rare, congenital fibrinogen disorders are interesting and pose several challenges that can serve as paradigms for many diseases. An impressive body of knowledge has accumulated recently, particularly thanks to international collaborative clinical and genetic studies allowing the molecular characterization of these disorders. However, apart from the possibility of developing safer fibrinogen concentrates and the availability of prenatal diagnosis, the basic therapeutic approach has changed little.

OBJECTIVE

We need to better understand the clinical phenotype of patients in order to administer fibrinogen preparations or other treatments more appropriately.

METHODS

We discuss current therapeutic options and others that could be available in the near future.

RESULTS/CONCLUSION

Patients with congenital fibrinogen deficiencies require better predictive tests for clinical complications and more efficient and available fibrinogen concentrates. Global hemostasis tests in combination with routine assays could help to individually tailor therapeutic protocols.

Influence of factor IX on overall plasma coagulability and fibrinolytic potential as measured by global assay: monitoring in haemophilia B

We sought to determine the influence of factor IX (FIX) deficiency upon overall coagulative and fibrinolytic capacities in plasma using the clot formation and lysis (CloFAL) assay, and to investigate the role of this global assay as an adjunctive monitoring tool in haemophilia B. CloFAL assay parameters were measured in vitro in platelet-poor plasma in relation to FIX activity and antigen (FIX:Ag), and were determined ex vivo among FIX-deficient patients (n = 41) in comparison to healthy individuals (n = 48). Supplementation of FIX-deficient plasma with FIX in vitro demonstrated a non-linear concentration dependence of FIX upon overall plasma coagulability. Ex vivo, coagulability was significantly decreased in FIX-deficient vs. healthy subjects among adults [median coagulation index (CI): 4% vs. 104% respectively; P < 0.001] and children (median CI: 9% vs. 63%; P < 0.001). Fibrinolytic capacity was increased in adult FIX-deficient vs. healthy subjects (median fibrinolytic index: 216% vs. 125%, respectively, P < 0.001), and was supported by a trend in shortened euglobulin lysis time (ELT). Severe haemophilia B patients showed heterogeneity in aberrant CloFAL assay waveforms, influenced partly by FIX:Ag levels. Patients with relatively preserved FIX:Ag (i.e. dysfunctional FIX) exhibited a shorter time to maximal amplitude in clot formation than those with type I deficiency. During patient treatment monitoring, markedly hypocoagulable CloFAL assay waveforms normalized following 100% correction with infused FIX. The CloFAL global assay detects FIX deficiency, demonstrates differences in coagulability between dysfunctional FIX and type I deficiency, and appears useful as an adjunctive test to routine FIX measurement in monitoring haemophilia B treatment.