The role of recombinant factor VIIa (FVIIa) in fibrin structure in the absence of FVIII/FIX

Analysis of fibrin networks using topological data analysis - a feasibility study

Blood clot formation, a crucial process in hemostasis and thrombosis, has garnered substantial attention for its implications in various medical conditions. Microscopic examination of blood clots provides vital insights into their composition and structure, aiding in the understanding of clot pathophysiology and the development of targeted therapeutic strategies. This study explores the use of topological data analysis (TDA) to assess plasma clot characteristics microscopically, focusing on the identification of the elements components, holes and Wasserstein distances. This approach should enable researchers to objectively classify fibrin networks based on their topologic architecture. We tested this mathematical characterization approach on plasma clots formed in static conditions from porcine and human citrated plasma samples, where the effect of dilution and direct thrombin inhibition was explored. Confocal microscopy images showing fluorescence labeled fibrin networks were analyzed. Both treatments resulted in visual differences in plasma clot architecture, which could be quantified using TDA. Significant differences between baseline and diluted samples, as well as blood anticoagulated with argatroban, were detected mathematically. Therefore, TDA could be indicative of clots with compromised stability, providing a valuable tool for thrombosis risk assessment. In conclusion, microscopic examination of plasma clots, coupled with Topological Data Analysis, offers a promising avenue for comprehensive characterization of clot microstructure. This method could contribute to a deeper understanding of clot pathophysiology and thereby refine our ability to assess clot characteristics.

Lipid nanoparticles and siRNA targeting plasminogen provide lasting inhibition of fibrinolysis in mouse and dog models of hemophilia A

Antifibrinolytic drugs are used extensively for on-demand treatment of severe acute bleeding. Controlling fibrinolysis may also be an effective strategy to prevent or lessen chronic recurring bleeding in bleeding disorders such as hemophilia A (HA), but current antifibrinolytics have unfavorable pharmacokinetic profiles. Here, we developed a long-lasting antifibrinolytic using small interfering RNA (siRNA) targeting plasminogen packaged in clinically used lipid nanoparticles (LNPs) and tested it to determine whether reducing plasmin activity in animal models of HA could decrease bleeding frequency and severity. Treatment with the siRNA-carrying LNPs reduced circulating plasminogen and suppressed fibrinolysis in wild-type and HA mice and dogs. In HA mice, hemostatic efficacy depended on the injury model; plasminogen knockdown improved hemostasis after a saphenous vein injury but not tail vein transection injury, suggesting that saphenous vein injury is a murine bleeding model sensitive to the contribution of fibrinolysis. In dogs with HA, LNPs carrying siRNA targeting plasminogen were as effective at stabilizing clots as tranexamic acid, a clinical antifibrinolytic, and in a pilot study of two dogs with HA, the incidence of spontaneous or excess bleeding was reduced during 4 months of prolonged knockdown. Collectively, these data demonstrate that long-acting antifibrinolytic therapy can be achieved and that it provides hemostatic benefit in animal models of HA.

The effect of factor XIa on thrombin and plasmin generation, clot formation, lysis and density in coagulation factors deficiencies

INTRODUCTION

Growing evidence supports the importance of factor (F) XI activation for thrombosis and hemostasis as well as inflammation and complement systems. In this study, we evaluated the effect of activated FXI (FXIa) on the detection of factor deficiencies by global hemostasis assays of thrombin generation (TG), plasmin generation (PG), and clot formation and lysis (CFL).

MATERIALS AND METHODS

An absorbance and fluorescence microplate assay was used to simultaneously observe TG, PG, and CFL in FV-, FVII-, FVIII-, and FIX-deficient plasmas supplemented with purified factors. Coagulation was initiated with tissue factor with or without FXIa in the presence of tissue plasminogen activator. Thrombin and plasmin peak heights (TPH and PPH), maximal clot density (MCD), times to clotting (CT), thrombin and plasmin peaks (TPT and PPT) and clot lysis (LyT) and a new parameter, clot lifetime (LiT), were evaluated.

RESULTS

TG/CFL were elevated by the FXIa at low FV (below 0.1 IU/mL), and at FVIII and FIX above 0.01 IU/mL. FXIa affected PG only at low FV and FVII. At high factor concentrations, FXIa reduced MCD. Thrombin and plasmin substrates had effect on CT, LyT, LiT and MCD parameters.

CONCLUSIONS

FXIa reveals new relationships between TG, PG and CFL parameters in factor deficiencies suggesting potential benefits for discrimination of bleeding phenotypes.

Fibrin Network Porosity and Endo-/Exogenous Thrombin Cross-talk

The earliest assessment of fibrin network porosity used a liquid permeation system and confocal 3D microscopy, which was later replaced by scanning electron microscopy. Although the methods have extensively been applied in studies of health or disease, there remains debate on the choice of a proper clotting trigger. In this review, we assess published data and convey our opinions with regard to several issues. First, when the coagulation process is initiated by recombinant tissue factor (rTF) and phospholipids, the fibrin network porosity is regulated by the endogenous thrombin based on enzymatic activations of multiple coagulants. If purified thrombin (1.0 IU/mL) is employed as the clotting trigger, fibrin network porosity may be affected by exogenous thrombin, which directly polymerizes fibrinogen in plasma, and additionally by endogenous thrombin stemming from a "positive feedback loop" action of the added thrombin. Second, with use of either endogenous or exogenous thrombin, the concentration and clotting property of available fibrinogen both influence the fibrin network porosity. Third, in the assay systems in vitro, exogenous thrombin but not rTF-induced endogenous thrombin seems to be functional enough to activate factor XIII, which then contributes to a decrease in the fibrin network porosity. Fourth, fibrin network porosity determines the transport of fibrinolytic components into/through the clots and therefore serves as an indicator of the fibrinolysis potential in plasma.

Weekly low-dose recombinant factor VIIa prophylaxis in Glanzmann thrombasthenia

Glanzmann thrombasthenia is an inherited disease causing bleeding episodes due to platelet dysfunction. The standard treatment for moderate-severe bleeding is platelet transfusion. Recombinant factor VIIa (rFVIIa) is successfully used in bleeding episodes and invasive procedures. Here, we present a patient with Glanzmann thrombasthenia, whose bleeding episodes could only be controlled by rFVIIa. The patient is a 28 years old male, who has had frequent bleeding episodes unresponsive to local hemostatic agents and tranexamic acid and had an anaphylactoid reaction to platelet transfusion. We started the patient on a low-dose (20 μg/kg) rFVIIa once a week. The patient has no spontaneous bleeding since then. This is the first case report of a Glanzmann thrombasthenia patient on routine prophylaxis with low-dose rFVIIa.

Role, Laboratory Assessment and Clinical Relevance of Fibrin, Factor XIII and Endogenous Fibrinolysis in Arterial and Venous Thrombosis

Diseases such as myocardial infarction, ischaemic stroke, peripheral vascular disease and venous thromboembolism are major contributors to morbidity and mortality. Procoagulant, anticoagulant and fibrinolytic pathways are finely regulated in healthy individuals and dysregulated procoagulant, anticoagulant and fibrinolytic pathways lead to arterial and venous thrombosis. In this review article, we discuss the (patho)physiological role and laboratory assessment of fibrin, factor XIII and endogenous fibrinolysis, which are key players in the terminal phase of the coagulation cascade and fibrinolysis. Finally, we present the most up-to-date evidence for their involvement in various disease states and assessment of cardiovascular risk.

Fibrinogen and Fibrin

Fibrinogen is a large glycoprotein, synthesized primarily in the liver. With a normal plasma concentration of 1.5-3.5 g/L, fibrinogen is the most abundant blood coagulation factor. The final stage of blood clot formation is the conversion of soluble fibrinogen to insoluble fibrin, the polymeric scaffold for blood clots that stop bleeding (a protective reaction called hemostasis) or obstruct blood vessels (pathological thrombosis). Fibrin is a viscoelastic polymer and the structural and mechanical properties of the fibrin scaffold determine its effectiveness in hemostasis and the development and outcome of thrombotic complications. Fibrin polymerization comprises a number of consecutive reactions, each affecting the ultimate 3D porous network structure. The physical properties of fibrin clots are determined by structural features at the individual fibrin molecule, fibrin fiber, network, and whole clot levels and are among the most important functional characteristics, enabling the blood clot to withstand arterial blood flow, platelet-driven clot contraction, and other dynamic forces. This chapter describes the molecular structure of fibrinogen, the conversion of fibrinogen to fibrin, the mechanical properties of fibrin as well as its structural origins and lastly provides evidence for the role of altered fibrin clot properties in both thrombosis and bleeding.

The Clotting Trigger Is an Important Determinant for the Coagulation Pathway In Vivo or In Vitro-Inference from Data Review

Blood coagulation comprises a series of enzymatic reactions leading to thrombin generation and fibrin formation. This process is commonly illustrated in a waterfall-like manner, referred to as the coagulation cascade. In vivo, this "cascade" is initiated through the tissue factor (TF) pathway, once subendothelial TF is exposed and bound to coagulation factor VII (FVII) in blood. In vitro, a diminutive concentration of recombinant TF (rTF) is used as a clotting trigger in various global hemostasis assays such as the calibrated automated thrombogram, methods that assess fibrin turbidity and fibrin viscoelasticity tests such as rotational thromboelastometry. These assays aim to mimic in vivo global coagulation, and are useful in assessing hyper-/hypocoagulable disorders or monitoring therapies with hemostatic agents. An excess of rTF, a sufficient amount of negatively charged surfaces, various concentrations of exogenous thrombin, recombinant activated FVII, or recombinant activated FIXa are also used to initiate activation of specific sub-processes of the coagulation cascade in vitro. These approaches offer important information on certain specific coagulation pathways, while alterations in pro-/anticoagulants not participating in these pathways remain undetectable by these methods. Reviewing available data, we sought to enhance our knowledge of how choice of clotting trigger affects the outcome of hemostasis assays, and address the call for further investigations on this topic.

Platelet-like particles improve fibrin network properties in a hemophilic model of provisional matrix structural defects

Following injury, a fibrin-rich provisional matrix is formed to stem blood loss and provide a scaffold for infiltrating cells, which rebuild the damaged tissue. Defects in fibrin network formation contribute to impaired healing outcomes, as evidenced in hemophilia. Platelet-fibrin interactions greatly influence fibrin network structure via clot contraction, which increases fibrin density over time. Previously developed hemostatic platelet-like particles (PLPs) are capable of mimicking platelet functions including binding to fibrin fibers, augmenting clotting, and inducing clot retraction. In this study, we aimed to apply PLPs within a plasma-based in vitro hemophilia B model of deficient fibrin network structure to determine the ability of PLPs to improve fibrin structure and wound healing responses within hemophilia-like abnormal fibrin network formation. PLP impact on structurally deficient clot networks was assessed via confocal microscopy, a micropost deflection model, atomic force microscopy and an in vitro wound healing model of early cell migration within a provisional fibrin matrix. PLPs improved clot network density, force generation, and stiffness, and promoted fibroblast migration within an in vitro model of early wound healing under hemophilic conditions, indicating that PLPs could provide a biomimetic platform for improving wound healing events in disease conditions that cause deficient fibrin network formation.

Dense and dangerous: The tissue plasminogen activator-resistant fibrinolysis shutdown phenotype is due to abnormal fibrin polymerization

BACKGROUND

Both hyperfibrinolysis and fibrinolysis shutdown can occur after severe trauma. The subgroup of trauma patients with fibrinolysis shutdown resistant to tissue plasminogen activator (t-PA)-mediated fibrinolysis have increased mortality. Fibrin polymerization and structure may influence fibrinolysis subgroups in trauma, but fibrin architecture has not been characterized in acutely injured subjects. We hypothesized that fibrin polymerization measured in situ will correlate with fibrinolysis subgroups.

METHODS

Blood samples were collected from trauma patients and noninjured controls. We selected samples across a range of fibrinolysis phenotypes (shutdown, physiologic, hyperfibrinolysis) and t-PA sensitivities (sensitive, physiologic, resistant) determined by thrombelastography. Plasma clots were created in situ with fluorescent fibrinogen and imaged using confocal microscopy for analysis of clot architecture in three dimensions. For each clot, we quantified the fiber resolvability, a metric of fiber distinctness or clarity, by mapping the variance of fluorescence intensity relative to background fluorescence. We also determined clot porosity by measuring the size and distribution of the gaps between fibrin fibers in three-dimensional space. We compared these measures across fibrinolysis subgroups.

RESULTS

Fiber resolvability was significantly lower in all trauma subgroups compared with controls (n = 35 and 5, respectively; p < 0.05). We observed markedly different patterns of fibrin architecture among trauma patients stratified by fibrinolysis subgroup. Subjects with t-PA-resistant fibrinolysis shutdown exhibited abnormal, densely packed fibrin clots nearly devoid of pores. Individuals with t-PA-hypersensitive fibrinolysis shutdown had highly irregular clots with pores as large as 2500 μm to 20,000 μm, versus 78 μm to 1250 μm in noninjured controls.

CONCLUSION

Fiber resolvability was significantly lower in trauma patients than controls, and subgroups of fibrinolysis differ in the porosity of the fibrin clot structure. The dense fibrin network in the t-PA-resistant group may prevent access to plasmin, suggesting a mechanism for thrombotic morbidity after injury.

Synergistic Effect of Bypassing Agents and Sequence Identical Analogue of Emicizumab and Fibrin Clot Structure in the In Vitro Model of Hemophilia A

Development of inhibitors to factor VIII (FVIII) occurs in approximately 30% of severe hemophilia A (HA) patients. These patients are treated with bypassing agents (activated prothrombin complex concentrate [aPCC] and recombinant activated FVII-rFVIIa). Recently, a bispecific FIX/FIXa- and FX/FXa-directed antibody (emicizumab) has been approved for the treatment of HA patients with inhibitors. However, the data from clinical studies imply that coadministration of emicizumab and bypassing agents, especially aPCC, could have a thrombotic effect.

This study was aimed to address the question of potential hypercoagulability of emicizumab and bypassing agents' coadministration, we have investigated fibrin clot formation and structure in the in vitro model of severe HA after adding sequence-identical analogue (SIA) of emicizumab and bypassing agents.

Combined overall hemostasis potential (OHP) and fibrin clot turbidity assay was performed in FVIII-deficient plasma after addition of different concentrations of SIA, rFVIIa, and aPCC. Pooled normal plasma was used as control. The fibrin clots were analyzed by scanning electron microscopy (SEM).

OHP and turbidity parameters improved with the addition of aPCC, while therapeutic concentrations of rFVIIa did not show substantial improvement. SIA alone and in combination with rFVIIa or low aPCC concentration improved OHP and turbidity parameters and stabilized fibrin network, while in combination with higher concentrations of aPCC expressed hypercoagulable pattern and generated denser clots.

Our in vitro model suggests that combination of SIA and aPCC could potentially be prothrombotic, due to hypercoagulable changes in fibrin clot turbidity and morphology. Additionally, combination of SIA and rFVIIa leads to the formation of stable clots similar to normal fibrin clots.

Hemostatic effect of tranexamic acid combined with factor VIII concentrate in prophylactic setting in severe hemophilia A: A preclinical study

BACKGROUND

Hemophilia is characterized by a compromised hemostatic response with delayed development of a clot and the formation of clots that are vulnerable to fibrinolysis. We proposed to study, in vitro and in factor VIII knockout mice (FVIII-KO), whether hemostasis is improved with the addition of tranexamic acid (TXA) to low FVIII plasma concentrations.

METHODS

In vitro, blood samples from adults with severe hemophilia-A, spiked to final concentrations of 0-3-10 and 30IU.dL-1 of FVIII, were studied with and without TXA 0.1 mg/mL using thromboelastography in the presence of tPA (ROTEM-tPA), thrombin generation (TG) assay, and scanning electron microscopy. FVIII-KO mice received prophylaxis before trauma, to obtain circulating plasma FVIII at 3 IU.dL-1 or FVIII 3IU.dL-1  + TXA 0.1 mg/mL. After trauma-induced knee joint bleeding, magnetic resonance imaging, histological analysis, and tail clip assay were used to compare hemostastic efficacy of the two prophylactic strategies.

RESULTS

A dose-dependent improvement of TG was observed with recombinant FVIII (rFVIII) alone (P = .024). As expected, no effect of TXA on TG capacity was observed. Fibrin fiber diameters were significantly decreased with TXA + rFVIII compared to rFVIII, suggesting a stronger fibrin network. Surprisingly, ROTEM-tPA was normalized with TXA alone. In FVIII-KO mice, blood loss after tail clip was lower after prophylaxis with rFVIII + TXA compared to rFVIII, with no statistical significance (P = .15). However, MRI results and histological analysis of knee joints showed that the addition of TXA significantly decreased joint bleeding (P = .022).

CONCLUSION

Our results suggest a potential benefit of TXA when used in combination with FVIII in prophylactic settings.

Absence of functional compensation between coagulation factor VIII and plasminogen in double-knockout mice

Plasminogen deficiency is associated with severely compromised fibrinolysis and extravascular deposition of fibrin. In contrast, coagulation factor VIII (FVIII) deficiency leads to prolonged and excessive bleeding. Based on opposing biological functions of plasminogen and FVIII deficiencies, we hypothesized that genetic elimination of FVIII would alleviate the systemic formation of fibrin deposits associated with plasminogen deficiency and, in turn, elimination of plasminogen would limit bleeding symptoms associated with FVIII deficiency. Mice with single and combined deficiencies of FVIII (F8^-/-) and plasminogen (Plg^-/-) were evaluated for phenotypic characteristics of plasminogen deficiency, including wasting disease, shortened lifespan, rectal prolapse, and multiorgan fibrin deposition. Conversely, to specifically examine the role of plasmin-mediated fibrinolysis on bleeding caused by FVIII deficiency, F8^-/- and F8^-/-/Plg^-/- mice were subjected to a bleeding challenge. Mice with a combined deficiency in FVIII and plasminogen displayed no phenotypic differences relative to mice with single FVIII or plasminogen deficiency. Plg^-/- and F8^-/-/Plg^-/- mice exhibited the same penetrance and severity of wasting disease, rectal prolapse, extravascular fibrin deposits, and reduced viability. Furthermore, following a tail vein-bleeding challenge, no significant differences in bleeding times or total blood loss could be detected between F8^-/- and F8^-/-/Plg^-/- mice. Moreover, F8^-/- and F8^-/-/Plg^-/- mice responded similarly to recombinant FVIII (rFVIII) therapy. In summary, the pathological phenotype of Plg^-/- mice developed independently of FVIII-dependent coagulation, and elimination of plasmin-driven fibrinolysis did not play a significant role in a nonmucosal bleeding model in hemophilia A mice.

Thrombin-generating potential, plasma clot formation, and clot lysis are impaired in patients with bleeding of unknown cause

BACKGROUND

In a large proportion of patients with a mild to moderate bleeding tendency no diagnosis can be established (bleeding of unknown cause, BUC).

OBJECTIVES

To investigate possible dysfunctions in thrombin generation and plasma clot formation and lysis in patients with BUC from the Vienna Bleeding Biobank (VIBB).

PATIENTS AND METHODS

Thrombin generation and plasma clot properties of 382 BUC patients were compared to those of 100 healthy controls and 16 patients with factor VIII (FVIII) activity ≤50%.

RESULTS

Thrombin generation was significantly impaired in BUC patients compared to healthy controls, exhibiting a prolonged lag time and time to peak and decreased maximum thrombin generation, velocity index, and area under the curve (AUC). The assessment of clot formation and lysis in BUC patients revealed a lower clot formation rate (Vmax), resulting in a longer TTP, increased absorbance (ΔAbs), and a shorter clot lysis time (CLT) than in healthy controls. Comparing patients with FVIII activity ≤ 50% to those with BUC, parameters of thrombin generation and clot formation and lysis were either stronger or comparably impaired. Bleeding severity did not correlate with parameters of thrombin generation, clot formation, or clot lysis.

CONCLUSION

Patients with BUC have an impaired hemostatic capacity reflected by a lower thrombin-generation potential, a lower clot formation rate, increased clot turbidity, and shorter clot lysis time, which might contribute to their increased bleeding tendency. Assays monitoring these parameters can alert physicians of hemostatic impairment and should be considered in situations where traditional hemostatic lab tests fail to reveal the clinical bleeding tendency.

Fibrinolysis in patients with chemotherapy-induced thrombocytopenia and the effect of platelet transfusion

Essentials Bleeding in chemotherapy induced thrombocytopenia (CIT) might be influenced by hyperfibrinolysis. t-PA-thromboelastography is a fast and reliable assay for hyperfibrinolysis in CIT patients. Clots of CIT patients are more susceptible to t-PA induced lysis compared to healthy individuals. Besides platelets, other factors are likely to influence clot lysis in CIT patients.

BACKGROUND

Bleeding events in chemotherapy-induced thrombocytopenic (CIT) patients with similar platelet counts might be influenced by changes in clot lysis potential.

OBJECTIVES

To investigate, in an observational study, thromboelastographic lysis parameters, alterations in clot strength and susceptibility to clot lysis in CIT patients. To identify factors associated with fibrinolytic profiles, and to evaluate the effects of platelet transfusions.

METHODS

Independent determinants of tissue-type plasminogen activator (t-PA)-ROTEM lysis parameters were identified with multivariable linear regression. Clot formation, strength and lysis parameters were compared with the results of healthy individuals. Characteristics of CIT patients with and without hyperfibrinolytic profiles were compared. t-PA-ROTEM results before, 1 hour after and 24 hours after platelet transfusion were compared.

RESULTS

A total of 72 consecutive CIT patients were included. t-PA-ROTEM lysis parameters correlated with changes in fibrinolytic proteins. Clot formation time was longer, maximum clot firmness was weaker and lysis times were shorter than in healthy individuals. CIT patients had low plasminogen activator inhibitor-1 and thrombin-activatable fibrinolysis inhibitor levels, and 40% showed hyperfibrinolytic profiles. Platelet transfusions resulted in less hyperfibrinolytic profiles in many, but not all CIT patients. Patients without hyperfibrinolytic profiles had higher fibrinogen, factor VIII and α2 -antiplasmin levels.

CONCLUSIONS

t-PA-ROTEM can be used as a fast and reliable assay to detect hyperfibrinolytic profiles in CIT patients. CIT patients have weaker clots, which are more susceptible to clot lysis, than healthy individuals. Besides platelets, other factors are likely to influence clot susceptibility to fibrinolysis in CIT patients. The impact of a hyperfibrinolytic t-PA-ROTEM profile on bleeding remains to be investigated.

Efficacy and Safety of Recombinant Activated Factor VII Off-label Use in a Pediatric Hematology/Oncology Cohort

BACKGROUND

Recombinant activated factor VII (rFVIIa) has been used off-label to treat or prevent severe bleeding in patients for whom conventional treatments are unsuccessful. However, studies in children remain limited.

PROCEDURE

To examine the efficacy and safety of rFVIIa, we performed a retrospective analysis of rFVIIa off-label use in a pediatric hematology/oncology cohort at a single center from 2006 to 2014.

RESULTS

Of 58 patients identified, 46 (79.3%) received rFVIIa to treat bleeding and 12 (20.7%) to prevent bleeding. Thirty-three (71.7%) patients had life-threatening bleeding. In the treatment group, 63.0% patients were responders (ie, bleeding decreased or stopped) and 37.0% were nonresponders (ie, bleeding did not change). Blood products usage was similar between responders and nonresponders. After rFVIIa administration, prothrombin time, partial thromboplastin time and lactate were significantly lower, but fibrinogen was significantly higher in responders than nonresponders. Venous thromboembolism developed in 5.2% (3/58) patients, but its relation to rFVIIa remains unclear. Responders had significantly lower mortality than nonresponders (17.2% vs. 82.4%, P<0.0001).

CONCLUSIONS

rFVIIa controlled most bleeding events in this cohort, despite predominance of life-threatening bleeding, suggesting good efficacy. Venous thromboembolism rate was low. Further studies are warranted to identify predictors of favorable response to rFVIIa in similar patients.

Inherited platelet functional disorders: General principles and practical aspects of management

Platelets are a critical component for effecting hemostasis and wound healing. Disorders affecting any platelet pathway mediating adhesion, activation, aggregation and procoagulant surface exposure can result in a bleeding diathesis. Specific diagnosis even with advanced techniques which are unavailable to most centers is often difficult. Inherited platelet function disorders therefore represent a heterogeneous and complex collection of disorders with a spectrum of bleeding severity, from relatively mild (and easily missed or misdiagnosed) to severe bleeding phenotype with salient diagnostic features. We advocate the use of bleeding assessment tools to help identification of patients and more importantly for assessment of individual patient bleeding phenotype to guide management decisions for treating and preventing bleeding. The complex management of these patients is best coordinated in a multidisciplinary comprehensive care clinic setting expert in managing bleeding disorders and associated complications, with particular attention to the physical and psychosocial health of patients and their families. Depending on the bleeding phenotype, the location and severity of bleeding, and the nature of an invasive procedure, available treatment modalities range from conservative measures using local pressure, topical thrombin, fibrin sealant, antifibrinolytics etc. to the use of systemic haemostatics such as desmopressin (DDAVP), platelets and recombinant human activated factor VII (rFVIIa). This review will provide opinions on the practical aspects and general management of inherited platelet function disorders, with discussion on the mechanism of action, and the pros and cons of various hemostatic agents. Finally, the prospect of curative treatment for patients with severe bleeding phenotype refractory to available treatments and with poor quality of life will be briefly discussed.

Abrogating fibrinolysis does not improve bleeding or rFVIIa/rFVIII treatment in a non-mucosal venous injury model in haemophilic rodents

Essentials The efficacy of systemic antifibrinolytics for hemophilic non-mucosal bleeding is undetermined. The effect of systemically inhibiting fibrinolysis in hemophilic mice and rats was explored. Neither bleeding nor the response to factor treatment was improved after inhibiting fibrinolysis. The non-mucosal bleeding phenotype in hemophilia A appears largely unaffected by fibrinolysis.

SUMMARY

Background Fibrinolysis may exacerbate bleeding in patients with hemophilia A (HA). Accordingly, antifibrinolytics have been used to help maintain hemostatic control. Although antifibrinolytic drugs have been proven to be effective in the treatment of mucosal bleeds in the oral cavity, their efficacy in non-mucosal tissues remain an open question of significant clinical interest. Objective To determine whether inhibiting fibrinolysis improves the outcome in non-mucosal hemophilic tail vein transection (TVT) bleeding models, and to determine whether a standard ex vivo clotting/fibrinolysis assay can be used as a predictive surrogate for in vivo efficacy. Methods A highly sensitive TVT model was employed in hemophilic rodents with a suppressed fibrinolytic system to examine the effect of inhibiting fibrinolysis on bleeding in non-mucosal tissue. In mice, induced and congenital hemophilia models were combined with fibrinolytic attenuation achieved either genetically or pharmacologically (tranexamic acid [TXA]). In hemophilic rats, tail bleeding was followed by whole blood rotational thromboelastometry evaluation of the same animals to gauge the predictive value of such assays. Results The beneficial effect of systemic TXA therapy observed ex vivo could not be confirmed in vivo in hemophilic rats. Furthermore, neither intravenously administered TXA nor congenital knockout of the fibrinolytic genes encoding plasminogen or tissue-type plasminogen activator markedly improved the TVT bleeding phenotype or response to factor therapy in hemophilic mice. Conclusions The findings here suggest that inhibition of fibrinolysis is not effective in limiting the TVT bleeding phenotype of HA rodents in non-mucosal tissues.

Targeting anticoagulant protein S to improve hemostasis in hemophilia

Improved treatments are needed for hemophilia A and B, bleeding disorders affecting 400 000 people worldwide. We investigated whether targeting protein S could promote hemostasis in hemophilia by rebalancing coagulation. Protein S (PS) is an anticoagulant acting as cofactor for activated protein C and tissue factor pathway inhibitor (TFPI). This dual role makes PS a key regulator of thrombin generation. Here, we report that targeting PS rebalances coagulation in hemophilia. PS gene targeting in hemophilic mice protected them against bleeding, especially when intra-articular. Mechanistically, these mice displayed increased thrombin generation, resistance to activated protein C and TFPI, and improved fibrin network. Blocking PS in plasma of hemophilia patients normalized in vitro thrombin generation. Both PS and TFPIα were detected in hemophilic mice joints. PS and TFPI expression was stronger in the joints of hemophilia A patients than in those of hemophilia B patients when receiving on-demand therapy, for example, during a bleeding episode. In contrast, PS and TFPI expression was decreased in hemophilia A patients receiving prophylaxis with coagulation factor concentrates, comparable to osteoarthritis patients. These results establish PS inhibition as both controller of coagulation and potential therapeutic target in hemophilia. The murine PS silencing RNA approach that we successfully used in hemophilic mice might constitute a new therapeutic concept for hemophilic patients.

Factor XIII cotreatment with hemostatic agents in hemophilia A increases fibrin α-chain crosslinking

Essentials Factor XIII (FXIII)-mediated fibrin crosslinking is delayed in hemophilia. We determined effects of FXIII cotreatment with hemostatic agents on clot parameters. FXIII cotreatment accelerated FXIII activation and crosslinking of fibrin and α2 -antiplasmin. These data provide biochemical rationale for FXIII cotreatment in hemophilia.

SUMMARY

Background Hemophilia A results from the absence, deficiency or inhibition of factor VIII. Bleeding is treated with hemostatic agents (FVIII, recombinant activated FVII [rFVIIa], anti-inhibitor coagulation complex [FEIBA], or recombinant porcine FVIII [rpFVIII]). Despite treatment, some patients have prolonged bleeding. FXIII-A2 B2 (FXIII) is a protransglutaminase. During clot contraction, thrombin-activated FXIII (FXIIIa) crosslinks fibrin and α2 -antiplasmin, which promotes red blood cell retention and increases clot stability and weight. We hypothesized that FXIII cotreatment in hemophilia would accelerate FXIII activation, leading to increased fibrin crosslinking. Methods FVIII-deficient plasma and whole blood were clotted with or without hemostatic agents (FVIII, rFVIIa, FEIBA, or recombinant B-domain-deleted porcine FVIII [rpFVIII]) and/or FXIII. The effects on FXIII activation, thrombin generation, fibrin and α2 -antiplasmin crosslinking, clot formation and clot weight were measured by western blotting, calibrated automated thrombography, thromboelastography, and clot contraction assays. Results As compared with FVIII-treated hemophilic plasma, FVIII + FXIII cotreatment accelerated FXIIIa formation without increasing thrombin generation. As compared with buffer-treated or FXIII-treated hemophilic plasma, FVIII treatment and FVIII + FXIII cotreatment increased the generation and amount of crosslinked fibrin, including α-chain-rich high molecular weight species and crosslinked α2 -antiplasmin. In the presence of FVIII inhibitors, as compared with hemostatic treatments (rFVIIa, FEIBA, or rpFVIII) alone, FXIII cotreatment increased whole blood clot weight. Conclusion In hemophilia A plasma and whole blood, FXIII cotreatment with hemostatic agents accelerated FXIIIa formation, increased the generation and amount of fibrin α-chain crosslinked species, accelerated α2 -antiplasmin crosslinking, and increased clot weight. FXIII cotreatment with hemostatic therapy may augment hemostasis through increased crosslinking of fibrin and α2 -antiplasmin.

Diagnostic laboratory for bleeding disorders ensures efficient management of haemorrhagic disorders

Haemorrhagic disorders like Postpartum haemorrhage and Dengue haemorrhagic fever are life threatening and requires an active and efficient transfusion service that could provide the most appropriate blood product which could be effective in managing them. This would essentially require prompt identification of the coagulopathy so that the best available product can be given to the bleeding patient to correct the identified haemostatic defect which will help control the bleeding. This would only be possible if the transfusion service has a laboratory to correctly detect the haemostatic defect and that too with an accuracy and precision which is ensured by a good laboratory quality assurance practices. These same processes are necessary for the transfusion services to ensure the quality of the blood products manufactured by them and that it contains adequate amounts of haemostasis factors which will be good to be effective in the management of haemorrhagic disorders. These issues are discussed in detail individually in the management of postpartum haemorrhage and Dengue haemorrhagic fever including when these can help in the use of rFVIIa in Dengue haemorrhagic fever. The requirements to ensure good-quality blood products are made available for the management of these disorders and the same have also been described.

New Insights Into the Treatment of Glanzmann Thrombasthenia

Glanzmann thrombasthenia (GT) is a rare inherited autosomal recessive bleeding disorder of platelet function caused by a quantitative or qualitative defect of platelet membrane glycoprotein IIb/IIIa (integrin αIIbβ3), a fibrinogen receptor required for platelet aggregation. Bleeds in GT are variable and may be severe and unpredictable. Bleeding not responsive to local and adjunctive measures, as well as surgical procedures, is treated with platelets, recombinant activated factor VII (rFVIIa), or antifibrinolytics, alone or in combination. Although platelets are the standard treatment for GT, their use is associated with the risk of blood-borne infection transmission and may also cause the development of platelet antibodies (to human leukocyte antigens and/or αIIbβ3), potentially resulting in platelet refractoriness. Currently, where rFVIIa is approved for use in GT, this is mostly for patients with platelet antibodies and/or a history of platelet refractoriness. However, data from the prospective Glanzmann's Thrombasthenia Registry (829 bleeds and 206 procedures in 218 GT patients) show that rFVIIa was frequently used in nonsurgical and surgical bleeds, with high efficacy rates, irrespective of platelet antibodies/refractoriness status. The mechanisms underpinning rFVIIa effectiveness in GT have been studied. At therapeutic concentrations, rFVIIa binds to activated platelets and directly activates FX to FXa, resulting in a burst of thrombin generation. Thrombin converts fibrinogen to fibrin and also enhances GT platelet adhesion and aggregation mediated by the newly converted (polymeric) fibrin, leading to primary hemostasis at the wound site. In addition, thrombin improves the final clot structure and activates thrombin-activatable fibrinolysis inhibitor to decrease clot lysis.

Interconnectedness of global hemostasis assay parameters in simultaneously evaluated thrombin generation, fibrin generation and clot lysis in normal plasma

BACKGROUND

Fluorogenic thrombin generation (TG) assays and turbidity-based fibrin generation (FG)- and fibrinolysis (FL)-resistance assays have been sought to assess bleeding and clotting disorders. Theoretically, TG, FG and FL tests should provide overlapping information because thrombin is responsible for FG and induces protection from FL. The relationships between TG, FG and FL parameters remain poorly investigated, partly because existing experimental systems do not permit simultaneous detection of both TG and FG in the same sample of plasma, and are instead tested in separate experiments.

OBJECTIVES AND METHODS

We evaluated the potential benefits of a combined TG/FG/FL assay by testing responses of normal plasma to a wide range of tissue factor (TF) and tissue plasminogen activator (tPA) concentrations. Correlations between multiple parameters extracted from the TG and FG/FL curves were also compared.

RESULTS

Rate of FG correlated well with TG peak height at all TF concentrations, but correlations between TG and FL parameters depended on the TF concentration. Without thrombomodulin, all FG/FL parameters at high TF could be predicted from TG parameters and no FL protection was observed. With thrombomodulin and high TF, TF-dependent FL protection did not correlate with TF-dependent TG. The fluorogenic thrombin substrate did not interfere with optical density readings, and meaningful tPA concentrations did not interfere with TG readings.

CONCLUSIONS

In normal plasma, TG, FG and FL parameters may provide interchangeable information. Evaluation of FL-resistance may provide additional data under special assay conditions, but the value of this information should be studied under disease conditions.

Investigation into the effects of antioxidant-rich extract of Tamarindus indica leaf on antioxidant enzyme activities, oxidative stress and gene expression profiles in HepG2 cells

The leaf extract of Tamarindus indica L. (T. indica) had been reported to possess high phenolic content and showed high antioxidant activities. In this study, the effects of the antioxidant-rich leaf extract of the T. indica on lipid peroxidation, antioxidant enzyme activities, H₂O₂-induced ROS production and gene expression patterns were investigated in liver HepG2 cells. Lipid peroxidation and ROS production were inhibited and the activity of antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase was enhanced when the cells were treated with the antioxidant-rich leaf extract. cDNA microarray analysis revealed that 207 genes were significantly regulated by at least 1.5-fold (p < 0.05) in cells treated with the antioxidant-rich leaf extract. The expression of KNG1, SERPINC1, SERPIND1, SERPINE1, FGG, FGA, MVK, DHCR24, CYP24A1, ALDH6A1, EPHX1 and LEAP2 were amongst the highly regulated. When the significantly regulated genes were analyzed using Ingenuity Pathway Analysis software, “Lipid Metabolism, Small Molecule Biochemistry, Hematological Disease” was the top biological network affected by the leaf extract, with a score of 36. The top predicted canonical pathway affected by the leaf extract was the coagulation system (P < 2.80 × 10⁻⁶) followed by the superpathway of cholesterol biosynthesis (P < 2.17 × 10⁻⁴), intrinsic prothrombin pathway (P < 2.92 × 10⁻⁴), Immune Protection/Antimicrobial Response (P < 2.28 × 10⁻³) and xenobiotic metabolism signaling (P < 2.41 × 10⁻³). The antioxidant-rich leaf extract of T. indica also altered the expression of proteins that are involved in the Coagulation System and the Intrinsic Prothrombin Activation Pathway (KNG1, SERPINE1, FGG), Superpathway of Cholesterol Biosynthesis (MVK), Immune protection/antimicrobial response (IFNGR1, LEAP2, ANXA3 and MX1) and Xenobiotic Metabolism Signaling (ALDH6A1, ADH6). In conclusion, the antioxidant-rich leaf extract of T. indica inhibited lipid peroxidation and ROS production, enhanced antioxidant enzyme activities and significantly regulated the expression of genes and proteins involved with consequential impact on the coagulation system, cholesterol biosynthesis, xenobiotic metabolism signaling and antimicrobial response.

CVD risk factors are related to plasma fibrin clot properties independent of total and or γ' fibrinogen concentration

INTRODUCTION

Cardiovascular disease (CVD) risk factors are associated with total fibrinogen concentration and/or altered clot structure. It is however, unclear whether such associations with clot structure are ascribed to fibrinogen concentration or other independent mechanisms. We aimed to determine whether CVD risk factors associated with increased total and/or γ' fibrinogen concentration, were also associated with altered fibrin clot properties and secondly whether such associations were due to the fibrinogen concentration or through independent associations.

MATERIALS AND METHODS

In a plasma setting CVD risk factors (including total and γ' fibrinogen concentration) were cross-sectionally analysed in 2010 apparently healthy black South African participants. Kinetics of clot formation (lag time, slope and maximum absorbance) as well as clot lysis times were calculated from turbidity curves.

RESULTS

Of the measured CVD risk factors age, metabolic syndrome, C-reactive protein (CRP), high density lipoprotein (HDL)-cholesterol and homocysteine were significantly associated with altered fibrin clot properties after adjustment for total and or γ' fibrinogen concentration. Aging was associated with thicker fibres (p=0.004) while both metabolic syndrome and low HDL-cholesterol levels were associated with lower rates of lateral aggregation (slope), (p=0.0004 and p=0.0009), and the formation of thinner fibres (p=0.007 and p=0.0004). Elevated CRP was associated with increased rates of lateral aggregation (p=0.002) and consequently thicker fibres (p<0.0001). Hyperhomocysteinemia was associated with increased rates of lateral aggregation (p=0.0007) without affecting fibre thickness.

CONCLUSION

Final clot structure may contribute to increased CVD risk in vivo through associations with other CVD risk factors independent from total or γ' fibrinogen concentration.

Improvement of fibrin clot structure after factor VIII injection in haemophilia A patients treated on demand

Patients with haemophilia A have seriously impaired thrombin generation due to an inherited deficiency of factor (F)VIII, making them form unstable fibrin clots that are unable to maintain haemostasis. Data on fibrin structure in haemophilia patients remain limited. Fibrin permeability, assessed by a flow measurement technique, was investigated in plasma from 20 patients with severe haemophilia A treated on demand, before and 30 minutes after FVIII injection. The results were correlated with concentrations of fibrinogen, FVIII and thrombin-activatable fibrinolysis inhibitor (TAFI), and global haemostatic markers: endogenous thrombin potential (ETP) and overall haemostatic potential (OHP). Fibrin structure was visualised using scanning electron microscopy (SEM). The permeability coefficient Ks decreased significantly after FVIII treatment. Ks correlated significantly with FVIII levels and dosage, and with ETP, OHP and levels of TAFI. SEM images revealed irregular, porous fibrin clots composed of thick and short fibers before FVIII treatment. The clots had recovered after FVIII replacement almost to levels in control samples, revealing compact fibrin with smaller intrinsic pores. To the best of our knowledge, this is the first description of fibrin porosity and structure before and after FVIII treatment of selected haemophilia patients. It seems that thrombin generation is the main determinant of fibrin structure in haemophilic plasma.

Recombinant Activated Factor VII in Patients at High Risk of Bleeding

Currently, recombinant activated factor VII (rFVIIa) (NovoSeven) is indicated for the treatment of spontaneous and surgical bleeding in congenital haemophilia A and B patients with inhibitors to factors VIII (FVIII) and IX (FIX) >5 Bethesda units (BU) worldwide, and in patients with acquired haemophilia, congenital FVII deficiency and Glanzmann's thrombasthenia in Europe. Until April 2003, almost three-quarters of a milion doses of rFVIIa have been administered proving its efficacy and excellent safety record. According to results from initial clinical trials and a large number of case reports, the rFVIIa may be effective not only in treating haemophilia patients but also in treatment of bleeding in patients on oral anticoagulation or heparin, patients with liver diseases, von Willebrand disease (vWD), thrombocytopenia, various platelet defects, congenital or acquired deficiency of FVII, and in subjects without any pre-existing coagulopathy with diffuse life-threatening bleeding triggered by surgery or trauma. This review will briefly summarize rFVIIa mode of action in haemostasis, the current clinical experience with rFVIIa and focus on the alternative use of rFVIIa in patients at the high risk of bleeding in both spontaneous cases and clinical trials reports.

Permeability of three-dimensional fibrin constructs corresponds to fibrinogen and thrombin concentrations

Research in the last few years have focused on the use of three-dimensional (3D) fibrin construct to deliver growth factors and cells. Three-dimensional construct permeability and porosity are important aspects for proper nutrient uptake, gas exchange, and waste removal—factors that are critical for cell growth and survival. We have previously reported that the mechanical strength (stiffness) of 3D fibrin constructs is dependent on the fibrinogen and thrombin concentration. In this study, we established two new in vitro models to examine how fibrin composition affects the final 3D fibrin construct permeability and pore size; thereby, influencing the diffusivity of macromolecules throughout the network of fibrin fibrils. Flow measurements of both liquid and fluoresceinated-dextran microparticles are conducted to calculate the permeability and pore size of 3D fibrin constructs of different fibrinogen and thrombin concentrations. Similarly, the diffusivity of liquid and fluoresceinated-dextran microparticles through these 3D fibrin constructs are determined through diffusion models. Data from these studies show that the structural permeability and pore size of 3D fibrin constructs directly correlate to fibrinogen and thrombin concentration in the final 3D fibrin construct. More specifically, at a constant thrombin concentration of 2 or 5 μ/mL, pore size of the 3D fibrin constructs is dependent on fibrinogen if the concentration is 5 mg/mL and to a lesser extent if the concentration is 10–15 mg/mL. These findings suggest that fibrin's diffusive property can be manipulated to fabricate 3D constructs that are optimized for cellular growth, protein transport, and for the controlled delivery of bioactive molecules such as growth factors.

Recombinant factor VIIa treatment for asymptomatic factor VII deficient patients going through major surgery

Factor VII deficiency is the most common among the rare autosomal recessive coagulation disorders worldwide. In factor VII deficient patients, the severity and clinical manifestations cannot be reliably determined by factor VII levels. Severe bleeding tends to occur in individuals with factor VII activity levels of 2% or less of normal. Patients with 2-10% factor VII vary between asymptomatic to severe life threatening haemorrhages behaviour. Recombinant factor VIIa (rFVIIa) is the most common replacement therapy for congenital factor VII deficiency. However, unlike haemophilia patients for whom treatment protocols are straight forward, in asymptomatic factor VII deficiency patients it is still debatable. In this study, we demonstrate that a single and very low dose of recombinant factor VIIa enabled asymptomatic patients with factor VII deficiency to go through major surgery safely. This suggestion was also supported by thrombin generation, as well as by thromboelastometry.

Effect of BAX499 aptamer on tissue factor pathway inhibitor function and thrombin generation in models of hemophilia

INTRODUCTION

In hemophilia, thrombin generation is significantly suppressed due to decreased factor (F)X activation. Clinical studies and experiments with transgenic mice have suggested that the severity of hemophilia is substantially reduced by tissue factor pathway inhibitor (TFPI) deficiency.

METHODS

We evaluated the effect of TFPI antagonist aptamer BAX499 (formerly ARC19499) on TFPI function in purified systems and on thrombin generation and clot formation in plasma and blood.

RESULTS

BAX499 effectively neutralized TFPI inhibition of FXa and FXa dependent inhibition of TF/FVIIa by TFPI. BAX499 did not inhibit FXa or TF/FVIIa when used up to 500 nM. In the synthetic coagulation proteome with TFPI at its mean physiologic concentration, BAX499 at 1 - 10nM increased thrombin generation triggered with 5 pM relipidated TF in a concentration-dependent manner. In severe hemophilia A or B models using the synthetic coagulation proteome, the addition of BAX499 at 5 nM increased thrombin generation to the levels observed in normal control. Thrombin generation measured in induced hemophilia B plasma required ~100nM BAX499 to restore thrombin levels to those seen in untreated plasma. In induced hemophilia B whole blood, BAX499 repaired the clotting time but failed to appreciably impact the propagation phase of thrombin generation.

CONCLUSION

These data suggest that inhibition of TFPI by BAX499 may have potential for hemophilia treatment but requires further study in blood-based hemophilia systems.

Recombinant activated factor VII for hemorrhage after pediatric cardiac surgery

Postoperative bleeding is a common complication after pediatric cardiac surgery. Use of recombinant activated factor VII for intractable hemorrhage after cardiac, pediatric, and neurosurgery has been shown to decrease postoperative bleeding, but data in children are limited. This retrospective study analyzed 20 children <15 years-old who underwent cardiac surgery and received recombinant activated factor VII for refractory postoperative hemorrhage. All patients underwent mediastinal reexploration before recombinant activated factor VII was administered as a bolus dose over 2–3 min as rescue therapy. If no significant decrease in chest tube drainage was observed, the dose was repeated after an interval of at least 2 h. The median dose of recombinant activated factor VII administered per bleeding episode was 83.33 µg·kg−1 (range, 72.47–87.50 µg·kg−1), and the dose per patient was 154.16 µg·kg−1 (range, 93.06–180.52 µg·kg−1). The median number of doses found to be effective in these children was 1.76. There were significant decreases in mediastinal chest tube drainage and the volume of packed red blood cells, platelet concentrates, and cryoprecipitate administered after recombinant activated factor VII. No complications were observed during the therapy.