Pro‐ and anticoagulant factors facilitate thrombin generation and balance the haemostatic response to FEIBA ® in prophylactic therapy

Prethrombin-1 as a Drug Substance Promoting Hemostasis with Reduced Risk of Thrombosis

INTRODUCTION

 Prethrombin-1 is a Gla-domain lacking enzymatically inactive split product that results from the cleavage of fragment 1 from prothrombin by thrombin in a feedback reaction.

METHODS

 A prethrombin-1 preparation derived from human plasma was tested for its hemostatic and thrombogenic properties. Animal models of nail clipping (for rabbits) and tail clipping (for mice) were developed to measure blood loss in FVIII-inhibitor or rivaroxaban anticoagulated rabbits and mice, respectively. A modified Wessler test was used in rabbits to assess the thrombogenic potential by Wessler score and clot weight. Studies were performed in groups of three to six for prethrombin-1 dose escalation and comparison with prothrombin, Beriplex®, FEIBA®, and saline as a control. Data were analyzed using t-statistics or the Mann Whitney U test as applicable.

RESULTS

 Prethrombin-1 has excellent hemostatic properties in anticoagulated mouse and rabbit bleeding models. Wessler tests suggest that in contrast to activated and nonactivated prothrombin complexes, prethrombin-1 has negligible thrombogenic potential.

CONCLUSION

 The thrombin zymogen prethrombin-1 promotes hemostasis with reduced risk of thrombosis. Prethrombin-1 may have potential to become a life-saving treatment for patients who bleed or are at risk of bleeding.

Factor Eight Inhibitor Bypassing Activity as First-line Therapy for Coagulopathy in Cardiac Surgery

OBJECTIVES

To compare the outcomes of factor eight inhibitor bypassing activity (FEIBA) versus fresh frozen plasma (FFP) as the primary treatment for postoperative coagulopathy in patients undergoing cardiac surgery.

DESIGN

A retrospective, propensity-matched study.

SETTING

A single, tertiary hospital.

PARTICIPANTS

Patients who underwent noncoronary cardiac surgery with cardiopulmonary bypass between 2015 and 2023.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We stratified patients into 2 groups based on whether they received intraoperative FFP or FEIBA; cases using both were excluded. We analyzed 434 cases, with 197 receiving FFP and 237 receiving FEIBA. After propensity matching, there was no significant difference in the proportion of the patients who required packed red blood cell transfusions (p = 0.08). However, of those who required packed red blood cell transfusions, patients in the FEIBA group required significantly fewer units of packed red blood cells (p < 0.001). Significantly fewer patients in the FEIBA group required platelet (p < 0.001) and cryoprecipitate (p < 0.001) transfusions. The FEIBA group showed decreased prolonged postoperative intubation (p = 0.05), decreased intensive care unit length of stay (p = 0.04), and lower 30-day readmission rates (p = 0.03). There were no differences in the rates of thrombotic complications between the 2 cohorts.

CONCLUSIONS

In the initial treatment of postcardiopulmonary bypass coagulopathy, FEIBA may be more effective than FFP in decreasing blood product transfusions and readmission rates. Further studies are needed to explore the potential routine use of FEIBA as first-line agent in this patient population.

Emicizumab promotes factor Xa generation on endothelial cells

BACKGROUND

Until recently, the treatment of hemophilia A relied on factor (F)VIII replacement. However, up to one-third of patients with severe hemophilia A develop neutralizing alloantibodies that render replacement therapies ineffective. The development of emicizumab, a bispecific antibody that partially mimics FVIIIa, has revolutionized the treatment of these patients. However, the use of an activated prothrombin complex concentrate [FEIBA (Takeda)] to treat breakthrough bleeding in patients on emicizumab has been associated with thrombotic complications including a unique microangiopathy.

OBJECTIVES

We hypothesized that the thrombotic complications observed with the combination of emicizumab and FEIBA might be due to excessive expression of procoagulant activity on the surface of endothelial cells.

METHODS

We examined the ability of emicizumab to promote FX activation on endothelial cells using 2 cell culture models.

RESULTS

We found that endothelial cells readily support emicizumab-mediated activation of FX by FIXa. The level of FXa generation depends on the concentration of available FIXa. The addition of FEIBA to emicizumab increased FXa generation in a dose-dependent manner on endothelial cells in both models. The rate of FXa generation was further enhanced by endothelial cell activation. However, unlike emicizumab, we found limited FXa generation in the presence of FVIII(a), which followed a significant lag time and was not dependent on FIXa concentration under these conditions.

CONCLUSION

Emicizumab promotes FXa generation on the surface of endothelial cells, which is markedly enhanced in the presence of FEIBA. These findings demonstrate a potential mechanism for the thrombotic complications seen with the combined use of emicizumab and FEIBA.

Activated protein C resistance in the copresence of emicizumab and activated prothrombin complex concentrates

Background

Venous thromboembolic events have been reported in persons with hemophilia A who received emicizumab and activated prothrombin complex concentrate (APCC) concomitantly, but the relevant mechanism(s) remains unclear. We speculated that activated protein C (APC) and antithrombin (AT) resistance might be associated with these adverse events.

Objectives

To investigate APC and AT resistance in factor (F)VIII-deficient (FVIIIdef) plasma in the presence of emicizumab and APCC.

Methods

In pooled normal plasma or FVIIIdef plasma samples mixed with emicizumab (50 μg/mL) and FVIII-bypassing agents, including recombinant FVIIa (2.2 μg/mL), APCC (1.3 IU/mL), or plasma-derived FVIIa/FX (1.5 μg/mL), the suppression effect of AT (0-2.4 μM) and APC (0-16 nM) was assessed by tissue factor-triggered thrombin generation assay. The APC effects in FVIIIdef plasma with the copresence of emicizumab, FII (1.3 μM), and/or FIXa (280 pM) were also examined.

Results

The AT resistance in emicizumab and each bypassing agent was not observed. Moreover, APC dose-dependent suppression effect was observed in pooled normal plasma or FVIIIdef plasma mixed with emicizumab and recombinant FVIIa or plasma-derived FVIIa/FX. However, APC-catalyzed inactivation had little effect on thrombin generation assay potential in FVIIIdef plasma spiked with emicizumab and APCC. The addition of FIXa to emicizumab in FVIIIdef plasma could lead to partial APC resistance. Furthermore, FVIIIdef plasma spiked with emicizumab, FIXa, and FII was markedly resistant to APC-mediated inactivation.

Conclusion

FII and FIXa in APCCs were key clotting factors for APC resistance in FVIIIdef plasma supplemented with emicizumab and APCCs. The APC resistance in persons with hemophilia A receiving emicizumab and APCC may contribute to venous thromboembolic events.

The Use of Bypassing Treatment Strategies in Hemophilia and Their Effect on Laboratory Testing

Factor VIII and IX inhibitors in congenital hemophilia A and B, respectively, neutralize the infused coagulation factor concentrate rendering them ineffective. Bypassing agents (BPAs) that circumvent the block imposed by the inhibitors are used for the prevention and management of bleeding. Activated prothrombin complex concentrate was the original BPA, recombinant activated factor VII was then introduced, and more recently nonfactor agents that target the procoagulant and anticoagulant systems have been developed and are in clinical use (e.g., emicizumab, a bispecific antibody for hemophilia A). Other BPAs are in clinical trials (e.g., fitusiran targets antithrombin, concizumab and marstacimab target tissue factor pathway inhibitor, and SerpinPC targets activated protein C). The BPAs have a varied effect on coagulation assays, and as more patients are exposed to these agents, it is important to be aware of the effects. Herein, we present an overview of the effect of BPAs on routine and specialized coagulation assays including thrombin generation and viscoelastic assays.

Review of Potential Barriers to Effective Hemostatic Management of Acquired Hemophilia A by Non-Hemophilia Experts in the United States

Acquired hemophilia A (AHA) is an ultra-rare autoimmune disorder caused by autoantibodies against factor VIII. It often presents with life-threatening bleeding to non-hemophilia experts, who have limited awareness of this condition. This review evaluated hemostatic management and identified barriers to optimal management of AHA by non-hemophilia experts in the United States through a literature review. AHA case reports published by non-hemophilia experts from January 2016 through November 2021 in non-hematology journals were critically reviewed for a chronology of clinical course and management, consultation with a hemophilia expert, referencing of available AHA recommendations, discussion of all hemostatic options, and bleed control outcomes; 24 case reports representing 24 patients were identified. Twelve patients had an apparent delay in diagnosis, 17 cases did not seek expert consultation, and 15 did not reference the 2009 International AHA Recommendations, including six in whom hemostatic treatment was not consistent with the recommendations. Of the 17 articles published after the 2017 AHA Guidance, eight did not reference them. Of the five articles published after the 2020 International Recommendations for AHA, three did not reference them. Overall, 14 articles did not discuss all available hemostatic treatment options. Four patients died. Our findings reveal variability in hemostatic management of AHA by non-hemophilia experts in the United States. Lack of AHA awareness remains a primary barrier for optimal management of AHA among non-hemophilia experts. Increasing education about existing AHA guidelines, including available therapies and access to expert care at hemophilia treatment centers, may help improve the outcomes of patients with AHA.

The use of FEIBA for refractory bleeding in cardiac surgery - a systematic review

INTRODUCTION

Significant blood loss during cardiac surgery is associated with a significant increase in morbidity and mortality. Factor Eight Inhibitor Bypassing Activity (FEIBA), a hemostatic bypassing agent mainly used in hemophiliac patients, has also been used for intractable surgical bleeding during cardiac surgical procedures in non-hemophiliac patients. However, concerns exist that its use may be linked to increased incidence of perioperative adverse effects including thrombotic complications.

AREAS COVERED

A systematic literature search was performed on MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials databases for all studies that reported the administration of FEIBA for treatment of bleeding during adult cardiac surgery in non-hemophiliac patients. After selecting of title and abstracts, two authors assessed the methodological quality of the full-text articles prior to final inclusion in the manuscript.

EXPERT OPINION

The safety profile of FEIBA was determined through an aggregate count of adverse events. Major complications included renal failure, re-operation for unresolved bleeding, postoperative mortality, and thromboembolic events. Overall, there is insufficient robust evidence to make a definitive conclusion about the safety or efficacy of using of FEIBA as a hemostatic agent in the setting of cardiac surgery.

Hemostatic efficacy of marstacimab alone or in combination with bypassing agents in hemophilia plasmas and a mouse bleeding model

Background

Patients with hemophilia have deficiencies in intrinsic coagulation factors and can develop inhibitors that limit the effectiveness of replacement coagulation factors. Marstacimab, a human monoclonal antibody, binds and inhibits the human tissue factor pathway inhibitor. Marstacimab is currently under development as a potential prophylactic treatment to prevent bleeding episodes in patients with hemophilia A and B.

Objective

To assess the effects of marstacimab alone or in combination with the bypassing agent recombinant factor FVIIa (rFVIIa) or activated prothrombin complex concentrate (aPCC) on thrombin generation and bleeding.

Methods

Marstacimab and/or rFVIIa or aPCC were added to hemophilic A or B plasma or nonhemophilic plasma in vitro. Hemostatic activity was measured using the thrombin generation assay. In vivo effects were assessed using a mouse acute bleeding model. Male hemophilia A mice were dosed with marstacimab plus aPCC before tail clip; blood loss was quantified by measuring hemoglobin.

Results

Marstacimab plus rFVIIa or aPCC slightly increased peak thrombin levels compared with either agent alone. This increase was within the reported range for nonhemophilic plasma and did not exceed levels observed in nonhemophilic plasma treated with marstacimab alone. Hemophilia A mice that received 200 U/kg aPCC had significantly reduced bleeding (62%) compared with vehicle-treated mice (p < 0.05), and marstacimab plus aPCC reduced bleeding by 83.3% compared with vehicle (p= 0.0009).

Conclusions

Marstacimab alone or with bypassing agents increased hemostasis in hemophilia plasma without generating excessive thrombin. The hemostatic activity of marstacimab plus aPCC was confirmed in hemophilia A mice.

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

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

Clotting factor concentrates for preventing bleeding and bleeding-related complications in previously treated individuals with haemophilia A or B

BACKGROUND

The hallmark of severe hemophilia (A or B) is recurrent bleeding into joints and soft tissues with progressive joint damage, despite on-demand treatment. Prophylaxis has long been used, but not universally adopted, because of medical, psychosocial, and cost controversies.

OBJECTIVES

To determine the effectiveness of clotting factor concentrate prophylaxis in managing previously-treated individuals with hemophilia A or B.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. In addition, we searched MEDLINE and Embase and online trial registries. Most recent search of Group's Coagulopathies Trials Register: 24 February 2021.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs evaluating people with hemophilia A or hemophilia B, who were previously treated with clotting factor concentrates to manage their hemophilia.

DATA COLLECTION AND ANALYSIS

Two authors independently reviewed trials for eligibility, assessed risk of bias and extracted data. The authors used the GRADE criteria to assess the certainty of the evidence.

MAIN RESULTS

Ten trials (including 608 participants) were eligible for inclusion. Eight of the trials (477 participants) had arms comparing two or more prophylactic regimens to one another and four of the trials (n = 258) compared prophylaxis to on-demand treatment (two trials had multiple arms and were included in both comparisons). Comparison of two or more prophylactic regimens For trials comparing one prophylaxis regimen to another, given the heterogeneity of the data, none of the data were pooled for this comparison. Considering the individual trials, three trials reported the primary outcome of joint bleeding, and none showed a dfference between dosing regimens (low-certainty evidence). For the secondary outcome of total bleeding events, prophylaxis with a twice-weekly regimen of FIX likely results in reduced total bleeds compared to a once-a-week regimen of the same dose, mean difference (MD) 11.2 (5.81 to 16.59) (one trial, 10 participants, low-certainty evidence). Transient low-titer anti-FVIII inhibitors were reported in one of the trials. Blood-transmitted infections were not identified. Other adverse events reported include hypersensitivity, oedema, and weight gain. These were, however, rare and unrelated to study drugs (very low-certainty evidence). Comparison of prophylactic and on-demand regimens Four of the trials (258 participants) had arms that compared prophylaxis to on-demand treatment. Prophylaxis may result in a large decrease in the number of joint bleeds compared to on-demand treatment, MD -30.34 (95% CI -46.95 to -13.73) (two trials, 164 participants, low-certainty evidence). One of these trials (84 participants) also reported the long-term effects of prophylaxis versus on-demand therapy showing improved joint function, quality of life, and pain; but no differences between groups in joint structure when assessed by magnetic resonance imaging (MRI). In one trial (84 participants) validated measures for joint health and pain assessment showed that prophylaxis likely improves joint health compared to an on-demand regimen with an estimated change difference of 0.94 points (95% CI 0.23 to 1.65) and improves total pain scores, MD -17.20 (95% CI -27.48 to -6.92 (moderate-certainty evidence). Two trials (131 participants) reported that prophylaxis likely results in a slight increase in adverse events, risk ratio 1.71 (1.24 to 2.37) (moderate-certainty evidence). No inhibitor development and blood-transmitted infections were identified. Overall, the certainty of the body of evidence was judged to be low because of different types of bias that could have altered the effect.   AUTHORS' CONCLUSIONS: There is evidence from RCTs that prophylaxis, as compared to on-demand treatment, may reduce bleeding frequency in previously-treated people with hemophilia. Prophylaxis may also improve joint function, pain and quality of life, even though this does not translate into a detectable improvement of articular damage when assessed by MRI.  When comparing two different prophylaxis regimens, no significant differences in terms of protection from bleeding were found. Dose optimization could, however, result in improved efficacy. Given the heterogeneity of the data, pooled estimates were not obtained for most comparisons.  Well-designed RCTs and prospective observational controlled studies with standardised definitions and measurements are needed to establish the optimal and most cost-effective treatment regimens.

Factor VIII inhibitor bypass activity (FEIBA) for the reduction of transfusion in cardiac surgery: a randomized, double-blind, placebo-controlled, pilot trial

BACKGROUND

Uncontrolled bleeding after cardiac surgery can be life-threatening. Factor eight inhibitor bypassing activity (FEIBA) is a prothrombin complex concentrate empirically used as rescue therapy for correction of refractory bleeding diathesis post-cardiopulmonary bypass (CPB). FEIBA used as rescue therapy for bleeding diathesis after CPB has been associated with a low incidence of complications and a reduction in transfusion requirement and re-exploration. The feasibility and efficacy of early administration of FEIBA after the termination of CPB have not been studied in a prospective randomized trial.

METHODS

We designed a small randomized, double-blinded, placebo-controlled pilot trial to determine the feasibility of a larger trial testing the hypothesis that FEIBA decreases transfusion requirements after CPB. The study was designed to evaluate the feasibility of a larger pivotal trial to determine the effectiveness of FEIBA in reducing the total volume of blood products transfused perioperatively, and its safety profile. Study participants were adult patients undergoing elective major aortic cardiovascular surgery at a tertiary referral hospital, who were equally randomized to receive a single dose of either FEIBA or matched placebo intraoperatively at the end of CPB.

RESULTS

Twenty patients were screened and 12 were randomized and included in the analysis. Protocol adherence was high, and all patients received the study drug per intention-to-treat except one patient. There were no protocol deviations or events of unblinding, and adverse events were not different between groups. Patients in the FEIBA group were older and more likely to be female and had higher BMI, lower hematocrit, and longer hypothermic circulatory arrest. There were no differences in post-randomization blood product transfusions (difference FEIBA vs. placebo -899 mL; 95% CI -5206 to 3409) or in the administration of open-label FEIBA.

CONCLUSIONS

This pilot trial confirmed the adequacy of the trial design that involved the early, blinded administration of FEIBA, by demonstrating excellent protocol adherence. We conclude that a larger trial establishing the effectiveness of early prothrombin complex concentrate administration to reduce the use of blood products in the setting of high-risk cardiac surgery is feasible.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02577614 . Registered 16 October 2015.

Thrombin generation potential in the presence of concizumab and rFVIIa, APCC, rFVIII, or rFIX: In vitro and ex vivo analyses

BACKGROUND

The anti-tissue factor plasma inhibitor monoclonal antibody concizumab is under clinical investigation for subcutaneous prophylaxis of hemophilia A/B (HA/HB) with or without inhibitors. Breakthrough bleeds while on concizumab prophylaxis may be treated with bypassing agents (recombinant activated factor VIIa [rFVIIa] and activated prothrombin complex concentrate [APCC]), or with factor VIII (FVIII) or factor IX (FIX).

OBJECTIVES

To evaluate the effect of combining concizumab with rFVIIa, APCC, rFVIII, and rFIX on thrombin generation (TG) potential.

METHODS

Pooled HA plasma was spiked in vitro with concizumab alone or together with rFVIIa, APCC, or rFVIII. rFVIIa, APCC, and rFVIII were added ex vivo to plasma from HA patients receiving concizumab prophylaxis. Pooled HB plasma was spiked with concizumab alone or together with rFIX. TG potential was measured after initiation with tissue factor.

RESULTS

Concizumab increased thrombin peak in a concentration-dependent manner. Adding rFVIIa, APCC, rFVIII, or rFIX caused a further increase in thrombin peak. The effects of concizumab and rFVIIa, APCC, rFVIII, or rFIX were mainly additive, with no or up to maximally ~25% extra effect caused by drug--drug interaction. No strong synergistic effects were observed upon combining concizumab with rFVIIa, APCC, rFVIII, or rFIX. The thrombin peak obtained with 0.5 IU/ml rFVIII or rFIX in the presence of concizumab was on occasion slightly higher, but mostly comparable to the thrombin peak with 1 IU/ml rFVIII or rFIX in the absence of concizumab.

CONCLUSION

rFVIIa, APCC, rFVIII, and rFIX enhanced plasma TG potential in the presence of concizumab. Dose levels of concomitant use should be adjusted accordingly to balance potential safety concerns while maintaining the necessary hemostatic effect. Please see the video in the Supplementary Material for an animated summary of the data presented.

The Use of Factor Eight Inhibitor Bypass Activity (FEIBA) for the Treatment of Perioperative Hemorrhage in Left Ventricular Assist Device Implantation

OBJECTIVE

To test the hypothesis that factor eight inhibitor bypassing activity (FEIBA) can be used to control bleeding following left ventricular assist device (LVAD) implantation without increasing the 14-day composite thrombotic outcome of pump thrombus, ischemic cerebrovascular accidents, pulmonary embolism, and deep venous thrombosis.

DESIGN

Retrospective cohort study.

SETTING

Academic hospital.

PARTICIPANTS

Three hundred nineteen consecutive patients who underwent LVAD implantation (December 1, 2009 to December 30, 2018).

INTERVENTION

FEIBA administered to control perioperative hemorrhage.

MEASUREMENTS AND MAIN RESULTS

The 82 patients (25.7%) in the FEIBA cohort had more risk factors for perioperative hemorrhage, such as lower preoperative platelet count (169 ± 66 v 194 ± 68 × 10³/mL, p = 0.004), prior cardiac surgery (36.6% v 21.9%, p = 0.008), and longer cardiopulmonary bypass (CPB) time (100.3 v 75.2 minutes, p = 0.001) than the 237 controls. After 16.6 units (95% CI: 14.3-18.9) of blood products were given, 992 units (95% CI: 821-1163) of FEIBA were required to control bleeding in the FEIBA cohort. Compared to the controls, there were no differences in the 14-day composite thrombotic outcome (11.0% v 7.6%, p = 0.343) or mortality rate (3.7% v 1.3%, p = 0.179). Multivariate logistical regression identified preoperative international normalized ratio (odds ratio [OR]: 1.30, 95% CI: 1.04-1.62) and CPB time (OR: 1.11, 95% CI: 1.02-1.20) as risk factors for 14-day thrombotic events, but FEIBA usage was not associated with an increased risk.

CONCLUSIONS

In this retrospective cohort study, the use of FEIBA (∼1,000 units, ∼13 units/kg) to control perioperative hemorrhage following LVAD implantation was not associated with increases in mortality or composite thrombotic outcome.

Origins, Development, Current Challenges and Future Directions with Activated Prothrombin Complex Concentrate for the Treatment of Patients with Congenital Haemophilia with Inhibitors

Congenital haemophilia A (HA) is caused by deficiency of coagulation factor VIII (FVIII) activity, leading to spontaneous or traumatic bleeding events. While FVIII replacement therapy can treat and prevent bleeds, approximately 30% of patients with severe HA develop inhibitor antibodies that render FVIII replacement therapy ineffective. The bypassing agents (BPAs), activated prothrombin complex concentrate (aPCC) and recombinant activated FVII, first approved in 1977 and 1996, respectively, act to generate thrombin independent of pathways that involve factors IX and VIII. Both may be used in patients with congenital haemophilia and inhibitors (PwHIs) for the treatment and prevention of acute bleeds and quickly became standard of care. However, individual patients respond differently to different agents. While both agents are approved for on-demand treatment and perioperative management for patients with congenital haemophilia with inhibitors, aPCC is currently the only BPA approved worldwide for prophylaxis in PwHI. Non-factor therapies (NFTs) have a mechanism of action distinct from BPAs and have reported higher efficacy rates as prophylactic regimens. Nonetheless, treatment challenges remain with NFTs, particularly regarding the potential for synergistic action on thrombin generation with concomitant use of other haemostatic agents, such as BPAs, for the treatment of breakthrough bleeds and in perioperative management. Concomitant use of NFTs with other haemostatic agents could increase the risk of adverse events such as thromboembolic events or thrombotic microangiopathy. This review focuses on the origins, development and on-going role of aPCC in the evolving treatment landscape in the management of PwHI.

Differential response to FEIBA is strongly associated with the prothrombotic microparticles

BACKGROUND

Treatment of patients with hemophilia with an inhibitor is generally done using bypassing agents (BPA), wherein variability in response is observed. Due to lack of validated laboratory assays, monitoring is being carried out by clinical response only. Emerging biomarkers like procoagulant microparticles (MPs) may prove to be promising.

AIM

To analyze whether procoagulant MP levels correlate with clinical response to FEIBA therapy.

MATERIALS AND METHODS

Total phosphatidylserine (PS) expressing MPs along with different cell derived MPs were measured in blood samples obtained prior and 2 hour post-FEIBA infusion in 64 bleeding episodes associated with 43 severe hemophilia patients.

RESULTS AND DISCUSSION

Patients with excellent response showed statistically significant increase in %MP of PS-MPs (p < 0.0001; 95.0% CI Range: -64.33 to -24.42) when compared to those with moderate response; platelet %MP change was also found significantly associated (p < 0.05) with clinical response. In search of an assay for monitoring FEIBA, results though preliminary seem to be promising with increase in %PS-MP correlating well with the clinical response. Coagulation being multifactorial process involves multiple factors for balanced hemostasis, which needs to be accounted. Larger studies in this line may provide indications for usage of MPs as monitoring and dose adjustment tool of FEIBA therapy.

Reversal strategies in patients treated with direct oral anticoagulants

Administration of direct oral anticoagulants (DOACs) for the treatment of venous thrombotic events (VTE) or non-valvular atrial fibrillation (AF) is now standard of care and has demonstrated clinical efficacy and safety in numerous clinical studies. Usually these substances have lower overall mortality and less risk of cerebral hemorrhage, but depending on the substance and study, they are more likely to cause gastrointestinal bleeding than vitamin K antagonists (VKA), the medication that used to be standard for VTE and AF. Since DOACs have very short plasma elimination half-lives compared to VKA, for most bleeding events, expert opinions suggest that withdrawal of DOACs and supportive care will likely suffice to stop a bleeding episode. Because there is a bleeding risk associated with DOACs, reversal strategies may be needed if a patient receiving DOAC therapy bleeds during surgery or an invasive procedure. So far, idarucizumab has been the only available antidote that binds specifically to dabigatran and safely and quickly reverses its anticoagulant effects. Idarucizumab has no effects on anti Xa inhibitors or other anticoagulants. To date, treatment of serious, life-threatening bleeds in patients with anti-Xa-inhibitor has involved 4 factor prothrombin complex concentrates (PCC). PCC restores normal hemostasis laboratory values in most patients with major bleeding events after anti Xa inhibitor intake. Recently, the US Food and Drug Administration (FDA) approved andexanet alfa as the first specific antidote for the anti-Xa inhibitors apixaban and rivaroxaban. So far clinical experience with this substance and data comparing it with PCC are lacking. Currently ciraparantag is under investigation as a universal reversal agent for all DOACs and low molecular weight heparin as well. Because it is so broadly applicable, ciraparantag might be a good future option for the management of most bleeding complications under anticoagulant treatment. The aim of this review is to summarize recent study data and recommendations on nonspecific and specific DOAC reversal strategies and to present the current evidence.

Anti-tissue factor pathway inhibitor (TFPI) therapy: a novel approach to the treatment of haemophilia

Novel approaches to the treatment of haemophilia are needed due to the limitations of the current standard of care, factor replacement therapy. Aspirations include lessening the treatment burden and effectively preventing joint damage. Treating haemophilia by restoring thrombin generation may be an effective approach. A promising target for restoring thrombin generation is tissue factor pathway inhibitor (TFPI), a multivalent Kunitz-type serine protease inhibitor that regulates tissue factor-induced coagulation via factor Xa-dependent feedback inhibition of the tissue factor-factor VIIa complex. Inhibition of TFPI reverts the coagulation process to a more primitive state evolutionarily, whilst regulation by other natural inhibitors is preserved. An aptamer and three monoclonal antibodies directed against TFPI have been investigated in clinical trials. As well as improving thrombin generation in the range associated with mild haemophilia, anti-TFPI therapies have the advantage of subcutaneous administration. However, the therapeutic window needs to be defined along with the potential for complications due to the novel mechanism of action. This review provides an overview of TFPI, its role in normal coagulation, the rationale for TFPI inhibition, and a summary of anti-TFPI therapies, previously or currently in development.

In vitro studies show synergistic effects of a procoagulant bispecific antibody and bypassing agents

Essentials Patients with hemophilia A and inhibitors receiving emicizumab experience breakthrough bleeding. Safety concerns may exist when combining emicizumab with bypassing agents. Combined bypassing agent and bispecific antibody increased thrombin generation up to 17-fold. Thrombotic effects should be considered when combining emicizumab with plasma bypassing agent.

SUMMARY

Background Investigational non-factor products such as emicizumab offer a treatment option for patients with hemophilia and inhibitors. However, their mechanism of action raises questions regarding safety when they are combined with treatments for breakthrough bleeding. Objectives To evaluate in vitro thrombin generation (TG) and clot formation for combinations of activated prothrombin complex concentrate (aPCC), recombinant activated factor VII (rFVIIa), and a sequence-identical analog of emicizumab (SIA). Methods Therapeutic concentrations of SIA (20-600 nm) alone or with aPCC (0.05-1 U mL-1 ), isolated aPCC components or rFVIIa (0.88-5.25 μg mL-1 ) were tested for TG and compared with reference ranges for healthy donor plasma. Coagulation of FVIII-inhibited blood was determined with a widely established method, i.e. rotational thromboelastometry (ROTEM), and confirmed with the Total Thrombus-formation Analysis System. Results and conclusions SIA (600 nm) or aPCC (0.5 U mL-1 ) alone resulted in peak thrombin levels of 21.4 nm and 38.6 nm, respectively, both of which are lower than normal (83.7 ± 29.8 nm). SIA plus aPCC (0.5 U mL-1 ) increased the peak thrombin level 17-fold over SIA alone, exceeding the reference plasma value by 4.2-fold. This hypercoagulable effect occurred with 600 nmSIA combined with as little as 0.25 U mL-1 aPCC, confirmed by ROTEM. FIX was the main driver for enhanced TG. SIA plus rFVIIa (1.75 μg mL-1 ) induced a 1.8-fold increase in the peak thrombin level in platelet-rich plasma, but it did not reach the normal range. These in vitro experiments demonstrate excessive TG after administration of a combination of aPCC and SIA at clinically relevant doses. Careful judgement may be required when breakthrough bleeding is treated in patients receiving emicizumab.

Inhibition of Tissue Factor Pathway Inhibitor (TFPI) as a Treatment for Haemophilia: Rationale with Focus on Concizumab

Replacement therapy with missing factor (F) VIII or IX in haemophilia patients for bleed management and preventative treatment or prophylaxis is standard of care. Restoration of thrombin generation through novel mechanisms has become the focus of innovation to overcome limitations imposed by protein replacement therapy. Tissue factor pathway inhibitor (TFPI) is a multivalent Kunitz-type serine protease inhibitor that regulates tissue factor (TF)-induced coagulation through a FXa-dependent feedback inhibition of the TF.FVIIa complex in plasma and on endothelial surfaces. Concizumab is a monoclonal, humanised antibody, specific for the second Kunitz domain of TFPI that binds and inhibits FXa, abolishing the inhibitory effect of TFPI. Concizumab restored thrombin generation in FVIII and FIX deficient plasmas and decreased blood loss in a rabbit haemophilia model. Phase 1 single and multiple dose escalation studies in haemophilia patients demonstrated a dose dependent decrease in TFPI levels and a pro-coagulant effect with increasing d-dimers and prothrombin fragment 1 + 2. A dose dependent increase in peak thrombin and endogenous thrombin potential was observed with values in the normal range when plasma TFPI levels were nearly undetectable. A few haemophilia patients in the highest dose cohorts with complete inhibition of plasma TFPI showed a decreased fibrinogen concentration with normal levels of anti-thrombin and platelets and no evidence of thrombosis. Pharmacokinetic parameters were influenced by binding to the target (TFPI), demonstrating target mediated drug disposition. A trend towards decreasing bleeding tendency was observed and this preventative effect is being studied in Phase 2 studies with additional data gathered to improve our understanding of the therapeutic window and potential for thrombosis.

Modified clot waveform analysis to measure plasma coagulation potential in the presence of the anti-factor IXa/factor X bispecific antibody emicizumab

Essentials The activated partial prothrombin time (aPTT) cannot predict the activity of emicizumab (Emi). Adjusted clot waveform analyses using a prothrombin time (PT)/aPTT initiator were developed. Activity of Emi in the co-presence of factor VIII or bypassing agents was quantified. This assay is useful for assessing coagulation potential in Emi-treated hemophilia A.

SUMMARY

Background Emicizumab is an anti-activated factor IX/FX bispecific antibody that mimics activated FVIII cofactor function. Emicizumab does not require activation by thrombin, and its effect on shortening the activated partial thromboplastin time (APTT) is much greater than that of FVIII. Therefore, the APTT has limited utility in hemophilia A (HA) patients treated with emicizumab. Aim To evaluate the global coagulation potential of emicizumab. Methods Clot waveform analysis (CWA) with prothrombin time (PT)/APTT mixed reagents was used to define hemostatic monitoring protocols in HA patients. A modified parameter, adjusted-|min1| (Ad|min1|), was developed. Maximum and minimum percentage transmittance were defined as 100% and 0% in the precoagulation and postcoagulation phases, respectively. Ad|min1| was calculated as an index of the maximum velocity of the coagulation process. Results Ad|min1| obtained with mixed-trigger reagent (PT/APTT/buffer, 1 : 15 : 135) in the presence of emicizumab optimally corresponded to the conversion rate estimated in animals; 0.2-0.4 IU dL-1 equivalent FVIII per 1 μg mL-1 emicizumab). Ex vivo addition of emicizumab to HA plasma with or without inhibitors resulted in concentration-dependent increases in Ad|min1|, with some individual variations. The addition of various concentrations of FVIII to HA plasma mixed with emicizumab resulted in dose-dependent increases in Ad|min1|. Similarly, mixtures of activated prothrombin complex concentrate and emicizumab added to HA plasma resulted in dose-dependent increases in Ad|min1|. In contrast, enhanced coagulation potential appeared to be better defined by the clot time than by Ad|min1| in experiments using recombinant activated FVII. Conclusion The PT/APTT reagent-triggered adjusted CWA could provide a useful means of assessing global coagulation potential in emicizumab-treated HA patients, with enhanced activity neither masking nor being masked by FVIII or bypassing agents.

The Potential Close Future of Hemophilia Treatment - Gene Therapy, TFPI Inhibition, Antithrombin Silencing, and Mimicking Factor VIII with an Engineered Antibody

Summary Hemophilia is one of the best researched monogenic diseases. Hemophilia A will affect approximately 1:5,000 male live births. In recent decades, great progress has been made with the introduction of recombinant proteins in the 1990s for therapy and prophylaxis, securing adequate availability and, with the introduction of the prophylaxis concept, reducing the negative impact of hemophilia on morbidity (especially arthropathy). Despite this progress, there are still challenges to overcome to secure adequate prophylaxis and treatment: for the time being, causal pharmacological hemophilia prophylaxis and therapy requires repeated i.v. application on a regular basis. Although this approach leads to a reduced comorbidity, it does not yet represent an optimized approach with continuous reversal of the hemophilic defect, which would be the ideal solution. This review summarizes the very new treatment strategies for the treatment of hemophilia A and B.

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.

Thromboembolic event rate in patients exposed to anti-inhibitor coagulant complex: a meta-analysis of 40-year published data

Anti-inhibitor coagulant complex (AICC), an activated prothrombin complex concentrate, has been available for the treatment of patients with inhibitors since 1977, and thromboembolic events (TEEs) have been reported after infusion of AICC in patients with congenital or acquired hemophilia. With the aim of estimating the TEE incidence rate (IR) related to AICC exposure in these patients, a systematic review of the literature was carried out in Medline, according to PRISMA guidelines, from inception date to March 2017. The IR of TEEs was estimated through a meta-analytic approach by using a generalized linear mixed model based on a Poisson distribution. Thirty-nine studies were included (1980-2016). Overall, 46 TEEs were reported; of these, 13 were reported as disseminated intravascular coagulations, 11 as myocardial infarctions, and 3 as thrombotic cerebrovascular accidents. The pooled TEE IR was 2.87 (95% confidence interval [CI], 0.32-25.40) per 100 000 AICC infusions (5.42 in retrospective studies [95% CI, 0.92-31.82]; 1.09 in prospective studies [95% CI, 0.01-238.77]). The TEE rate was 5.09 (95% CI, 0.01-1795.60) per 100 000 AICC infusions administered on demand, whereas no TEEs were reported with prophylaxis. Interestingly, the estimated IR in patients with congenital hemophilia was <0.01 per 100 000 infusions. These findings provide robust evidence of safety of AICC over almost 40 years of published studies.

Bypassing agent prophylaxis in people with hemophilia A or B with inhibitors

BACKGROUND

People with hemophilia A or B with inhibitors are at high risk of bleeding complications. Infusion of bypassing agents, such as recombinant activated FVII (rFVIIa) and plasma-derived activated prothrombin complex concentrate, are suggested as alternative therapies to factor VIII (haemophilia A) or IX (haemophilia B) for individuals who no longer respond to these treatments because they develop inhibitory antibodies. The ultimate goal of treatment is to preserve the individual's joints, otherwise destroyed by recurrent bleeds.

OBJECTIVES

To assess the effects of bypassing agent prophylaxis to prevent bleeding in people with hemophilia A or B and inhibitors.

SEARCH METHODS

We searched for relevant studies from the Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register, comprising of references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings. We also searched trial registries (16 February 2017) and bibliographic references of retrieved studies were reviewed for potential articles to be included in the review.Date of the last search of the Cochrane Cystic Fibrosis and Genetic Disorders Coagulopathies Trials Register: 12 December 2016.

SELECTION CRITERIA

We included randomized and quasi-randomized controlled studies (cross-over or parallel design) evaluating the effect of prophylaxis treatment with bypassing agents compared with on-demand treatment, or studies evaluating the effects of high-dose compared with low-dose prophylaxis in males of any age with hemophilia with inhibitors.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies and extracted data and assessed the risk of bias according to standard Cochrane criteria. They assessed the quality of the evidence using the GRADE criteria.

MAIN RESULTS

We included four randomized studies (duration 7 to 15 months) involving 116 males. Risk of bias was judged to be high in two studies due to the open-label study design and in one study due to attrition bias.Two studies compared on-demand treatment to prophylaxis with bypassing agents. In one study (34 males) prophylaxis significantly reduced mean overall bleeding rates, MD - 7.27 (95% CI -9.92 to -4.62) (low quality evidence), mean number of overall bleeding events per month, MD -1.10 (95% CI -1.54 to -0.66), mean number of hemarthrosis, MD -6.60 (95% CI -9.32 to -3.88) (low quality evidence) and mean number of joints that had hemarthrosis, MD -0.90 (95% CI -1.36 to -0.44). The meta-analysis did not conclusively demonstrate significant benefit of prophylaxis on health-related quality of life as measured by Haem-A-QoL score, EQ-5D total score and utility score, EQ-5D VAS and SF-36 physical summary and mental summary score (low quality evidence for all health-related quality of life analyses).The remaining two studies compared dose regimens. The results from one study (22 males) did not conclusively demonstrate benefit or harm of high-dose versus low-dose recombinant activated factor VIIa (rFVIIa) as a prophylaxis for overall bleeding rate, MD -0.82 (95% CI -2.27 to 0.63) (moderate quality evidence), target joint bleeding rate, MD -3.20 (95% CI -7.23 to 0.83) (moderate quality evidence) and serious adverse events, RR 9.00 (95% CI, 0.54 to 149.50) (moderate quality evidence).The overall quality of evidence was moderate to low due to imprecision from limited information provided by studies with small sample sizes and incomplete outcome data in one study.

AUTHORS' CONCLUSIONS

The evidence suggests that prophylaxis with bypassing agents may be effective in reducing bleeding in males with hemophilia with inhibitors. However, there is a lack of evidence for the superiority of one agent over the other or for the optimum dosage regimen. Further studies are needed to evaluate the benefits and harms of prophylaxis treatment on health-related quality of life, as well as the effects of dose of bypassing agents on the outcomes.