Mechanism by which recombinant factor VIIa shortens the aPTT: activation of factor X in the absence of tissue factor

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.

A rapid, sensitive, and specific assay to measure TF activity based on chromogenic determination of thrombin generation

BACKGROUND

Most tissue factor (TF) activity assays are based on measurement of factor X (FX) activation by TF in the presence of factor VII (FVII)/FVIIa. This requires long incubation, which may result in TF-independent activity of FX and inaccurate measurement of TF activity.

AIM

To develop a sensitive and specific TF activity assay, which does not register a non-specific TF activity, using commercial coagulation factors.

METHODS

Tissue factor activity was measured based on the ability of TF to accelerate the activation of FX by FVIIa in the presence of factor V (FV)/Va, prothrombin, and phospholipids. Following 4 min incubation at 37°C, TF activity was quantified in test samples of different nature by thrombin generation using a chromogenic substrate.

RESULTS

The TF activity assay proved high sensitivity (low fM range) and specificity, assessed by neutralization of TF activity by anti-TF antibody and the use of FVIIai. TF activity was detected in extracellular vesicles (EVs) derived from HAP1-TF+cells, while no activity was measured in EVs from HAP1-TF/KO cells. The assay was applicable for measurement of TF activity on the surface of live endothelial cells and monocytes activated in vitro, and cell lysates. Infusion of low dose lipopolysaccharide (2 ng/kg bodyweight endotoxin) caused a transient 8-fold increase (peaked at 4 h) in TF activity in EVs isolated from plasma of healthy volunteers.

CONCLUSION

Our assay provides a fast, sensitive, and specific measurement of TF activity. It reliably quantifies TF activity on cell surface, cell lysate, and isolated EVs. The assay can be used for laboratory and clinical research.

Kaolin, used to trigger coagulation in thrombin generation test, increases sensitivity of the method in hemophilia patients

: Thrombin generation test (TGT) is well established tool to research blood coagulation in plasma of hemophilia patients. Traditionally coagulation in this test is triggered by a tissue factor (TF), an extrinsic coagulation pathway activator. However, it is known that disorders of the intrinsic pathway are most important for coagulation in hemophilia. In this study, we hypothesized that triggering coagulation via the intrinsic pathway could increase a sensitivity of the TGT to monitor hemophilia treatment. The aim of this study was to compare thrombin generation in hemophilia A patients with inhibitors to factor VIII before and after infusion of bypassing agent [recombinant-activated factor VIIa (rVIIa)] using standard activation of coagulation by TF or by kaolin, an activator of coagulation by intrinsic pathway. Endogenous thrombin potential (ETP) in nine patients was measured. ETP before (ETP0) and 60 min after rVIIa infusion (ETP60) were compared. It was shown that ETP0 and ETP60 were significantly different when using any coagulation activator (paired Student's t test, P = 0.017 and 3.7 × 10 for clotting activation by TF and kaolin, respectively). The ratios of ETP60/ETP0 were 1.2 ± 0.2 or 30.0 ± 22.4 (mean ± SD, n = 9) for coagulation activated by TF or kaolin, respectively, and were significantly different (paired Student's t test, P < 0.005). The TGT clearly distinguished between ETP0 and ETP60 in the case of any coagulation activator, but ETP increasing after rVIIa infusion was significantly higher when activated with kaolin. This provided increased sensitivity of this method for monitoring hemophilia therapy.

Darexaban: anticoagulant effects in mice and human plasma in vitro, antithrombotic effects in thrombosis and bleeding models in mice and effects of anti-inhibitor coagulant complex and recombinant factor VIIa

Here, we investigated the anticoagulant effects of darexaban in mice and human plasma in vitro, effects of darexaban in thrombosis and bleeding models in mice, and reversal effects of anti-inhibitor coagulant complex (ACC) and recombinant factor VIIa (rFVIIa) on anticoagulant effects of darexaban. In mice, darexaban inhibited FXa activity in plasma with an ED50 value of 24.8 mg/kg. Both darexaban and warfarin prolonged prothrombin time (PT) at 3 mg/kg and 0.3 mg/kg/day, respectively. PT and activated partial thromboplastin time (aPTT) prolonged by darexaban were dose-dependently reversed by intravenously-administered rFVIIa, significantly so at 1 mg/kg. In a pulmonary thromboembolism (PE) mouse model, both darexaban and warfarin dose-dependently reduced the mortality rate, significantly so at 10 mg/kg and 3 mg/kg/day, respectively. In a FeCl3-induced venous thrombosis (VT) mouse model, darexaban (0.3-10 mg/kg) dose-dependently decreased the thrombus protein content, significantly so at doses of 3 mg/kg or higher. In a tail-transection mouse model, darexaban had no significant effect on the amount of blood loss at doses up to 10 mg/kg, while warfarin showed a dose-dependent increase in blood loss, significantly so from 1 mg/kg/day. Darexaban and its metabolite darexaban glucuronide significantly prolonged PT and aPTT in human plasma in vitro, and while rFVIIa concentration-dependently reversed the prolonged PT in this plasma, ACC dose-dependently reversed both PT and aPTT changes prolonged by darexaban. Taken together, these results suggest that darexaban has a potential to be an oral anticoagulant with a better safety profile than warfarin, and that rFVIIa and ACC may be useful as antidotes to darexaban in cases of overdose.

Potent anticoagulant aptamer directed against factor IXa blocks macromolecular substrate interaction

An aptamer targeting factor IXa has been evaluated in animal models and several clinical studies as a potential antithombotic therapy. We elucidate the molecular mechanism by which this aptamer acts as an anticoagulant. The aptamer binds tightly to factor IXa and prolongs the clotting time of human plasma. The aptamer completely blocks factor IXa activation of factor X regardless of the presence of factor VIIIa. However, the aptamer does not completely block small synthetic substrate cleavage, although it does slow the rate of cleavage. These data are consistent with the aptamer binding to the catalytic domain of factor IXa in such a way as to block an extended substrate-binding site. Therefore, unlike small molecule inhibitors, aptamers appear to be able to bind surfaces surrounding an active site and thereby sterically interfere with enzyme activity. Thus, aptamers may be useful agents to probe and block substrate-binding sites outside of the active site of an enzyme.

Recombinant factor VIIa analog NN1731 (V158D/E296V/M298Q-FVIIa) enhances fibrin formation, structure and stability in lipidated hemophilic plasma

INTRODUCTION

The bypassing agent recombinant factor VIIa (rFVIIa) is efficacious in treating bleeding in hemophilia patients with inhibitors. Efforts have focused on the rational engineering of rFVIIa variants with increased hemostatic potential. One rFVIIa analog (V158D/E296V/M298Q-FVIIa, NN1731) improves thrombin generation and clotting in purified systems, whole blood from hemophilic patients and factor VIII-deficient mice.

METHODS

We used calibrated automated thrombography and plasma clotting assays to compare effects of bypassing agents (rFVIIa, NN1731) on hemophilic clot formation, structure, and ability to resist fibrinolysis.

RESULTS

Both rFVIIa and NN1731 shortened the clotting onset and increased the maximum rate of fibrin formation and fibrin network density in hemophilic plasma clots. In the presence of tissue plasminogen activator, both rFVIIa and NN1731 shortened the time to peak turbidity (TTPeak(tPA)) and increased the area under the clot formation curve (AUC(tPA)). Phospholipids increased both rFVIIa and NN1731 activity in a lipid concentration-dependent manner. Estimated geometric mean concentrations of rFVIIa and NN1731 producing similar onset, rate, TTPeak(tPA), and AUC(tPA) as seen with 100% factors VIII and IX were: 24.5, 74.3, 29.7, and 37.1 nM rFVIIa, and 8.6, 31.2, 9.0, and 11.3 nM NN1731, respectively. In each case, the NN1731 concentration was significantly lower than rFVIIa.

CONCLUSIONS

These findings suggest that like rFVIIa, NN1731 improves the formation, structure, and stability of hemophilic clots. Higher lipid concentrations may facilitate assessment of both rFVIIa and NN1731 activity. NN1731 appears likely to support rapid clot formation in tissues with high endogenous fibrinolytic activity.

Exploratory study on the reversal of warfarin with rFVIIa in healthy subjects

The use of warfarin has a well-known bleeding risk. Recombinant activated factor VII (rFVIIa) is a non–plasma-derived, rapid-acting, and rapidly infused potential treatment. This randomized, single-center, placebo-controlled, double-blinded, dose-escalation, exploratory phase 1 trial assessed safety and effects of rFVIIa in reversing warfarin-induced changes in bleeding and coagulation parameters, using a punch biopsy–induced bleeding model in healthy subjects. The effects of warfarin (experiment 1) and rFVIIa (5-80 μg/kg; experiment 2) were evaluated. Outcomes were bleeding duration, blood loss, coagulation parameters, and safety. Warfarin treatment significantly increased bleeding duration and blood loss from pretreatment (experiment 1, 12 subjects). However, these parameters after rFVIIa treatment were not significantly different from placebo (experiment 2, 85 subjects). Mean activated partial thromboplastin time, prothrombin time, and international normalized ratio were reduced from warfarin-elevated levels. rFVIIa (80 μg/kg) significantly reversed warfarin effects on all thromboelastography parameters, compared with placebo (P < .05), and returned the thrombin generation speed to baseline. There were no thromboembolic or serious adverse events. In this exploratory trial, the reversal of warfarin effects was observed in the thromboelastography, thrombin generation, and clotting assays. However, this reversal did not translate to improvements in the bleeding model parameters evaluated in the punch biopsy model. Trial registration is exempt (phase 1).

Failure of recombinant factor VIIa to correct the coagulopathy in a case of severe postpartum hemorrhage

BACKGROUND

Postpartum hemorrhage (PPH)remains an important cause of maternal morbidity and mortality. Several published reports suggest that recombinant factor VIIa (rFVIIa) is effective in controlling bleeding in PPH. This study reports a case of severe PPH complicated by disseminated intravascular coagulation(DIC), in which early rFVIIa (44 mg/kg) administration not only failed to control the bleeding in vivo but also, surprisingly, failed to correct the patient's international normalized ratio (INR) in vitro. It was hypothesized that the failure of rFVIIa to correct the INR indicated a deficiency in a downstream coagulation factor(s). To investigate this, coagulation factor levels were measured in blood samples that had been drawn periodically during resuscitation in the operating room.

STUDY DESIGN AND METHODS

Clinical and laboratory data were extracted from the medical record.Plasma samples that had been obtained during resuscitation were frozen, and activity levels of the following factors were subsequently measured: fibrinogen, FII, FV, FVII, F IX, and FX.

RESULTS

After rFVIIa administration, the patient's INR remained elevated at 1.9, and bleeding continued. It was determined that at the time rFVIIa was administered, the patient's fibrinogen level was very low(60 mg/dL). INR normalization and control of bleeding was achieved only after the patient's fibrinogen level was restored to normal. FII, F IX, and FX remained at hemostatic levels throughout resuscitation.

CONCLUSIONS

In this case of severe PPH complicated by DIC, fibrinogen appears to have been limiting at the time rFVIIa was administered. It is suggested that fibrinogen levels should be corrected during PPH resuscitation before rFVIIa use is considered.

Preclinical toxicity biomarkers for combination treatment with clotting factors rFXIII and rFVIIa

Combination treatment with the clotting factors recombinant activated factor VII (rFVIIa), serine protease, and recombinant factor XIII (rFXIII), protransglutaminase, is being explored for haemostatic therapy. We performed a single-dose toxicology study in the cynomolgus monkey, with four dose groups receiving 0.1 + 0.34 mg kg(-1) (group 1), 0.33 + 1.12 mg kg(-1) (group 2), 1.67 + 5.60 mg kg(-1) (group 3) and 5.00 + 16.80 mg kg(-1) (group 4) of a rFVIIa + rFXIII combination. In the three lower dose groups, no clinical, histopathological or blood chemistry changes were observed. In group 4, the animals died at 4 h post-dosing, with histopathology revealing a systemic coagulopathy resembling, but distinct from, disseminated intravascular coagulation. Due to the absence of toxicity warning signs, toxicity biomarkers were identified by a Western blot-based screening of approximately 20 plasma proteins known to be involved in the clotting cascade. Three of the examined proteins were specifically affected by rFVIIa + rFXIII treatment. Fibronectin and fibrinogen exhibited dose-dependent reductions from less than 10% reduction (group 2) to more than 90% reduction (group 4). These reductions were reversible, and specific. For vitronectin, a dose-dependent conversion to the 65-kDa form was found to occur in groups 3 and 4. Thus, fibrinogen, fibronectin and vitronectin represent the first biomarkers for clotting factor toxicity.

Successful management of intra-abdominal hemorrhage in the presence of severe alcoholic liver disease with activated recombinant factor VII (rFVIIa; NovoSeven): a case report and review of the literature on approved and off-label use of rFVIIa

A 37-year-old male with history of alcohol abuse presented to us with nausea, vomiting, and abdominal pain with ascites. He was diagnosed with alcoholic liver disease with coagulopathy and pancreatitis. During hospitalization, the patient developed intra-abdominal hemorrhage. He was treated with platelets, packed red blood cells and fresh frozen plasma without any improvement. Following this he was treated with activated recombinant factor VII (90 microg/kg), which resulted in normalization of the prothrombin time and the activated partial thromboplastin time and stabilization of hematocrit within a few hours. We review the current literature on the approved and off-label use of activated recombinant factor VII.

Effective Management of Refractory Postcardiotomy Bleeding With the Use of Recombinant Activated Factor VII

BACKGROUND

Severe coagulopathy after cardiovascular surgery may lead to intractable bleeding and is associated with increased mortality and morbidity. Recent studies have suggested that recombinant activated factor VII (rFVIIa) may play a role in decreasing postoperative bleeding. Herein we report our experience with the off-label use of rFVIIa in patients with refractory postcardiotomy bleeding.

METHODS

From June 2003 to December 2005, 17 patients (mean age, 65 +/- 18 years) received rFVIIa for refractory bleeding after cardiac surgery. Preoperative risk factors for bleeding included reoperation (n = 7), emergency surgery (n = 7), and renal or hepatic failure (n = 3). Surgical procedures were aortic surgery (n = 7), complex valve operations (n = 7), coronary artery bypass grafting (n = 2), and cardiac tumor resection (n = 1).

RESULTS

The average dose of rFVIIa was 103.1 +/- 30.2 microg/kg. After the administration of rFVIIa the blood loss was reduced and chest tube output decreased from an average of 300 mL/h to 60 mL/h (p = 0.024). Coagulation variables normalized (mean prothrombin time, 18 +/- 7 versus 14 +/- 3 seconds; p = 0.03; mean partial thromboplastin time, 94 +/- 50 versus 49 +/- 14 seconds; p = 0.02), and the need for blood products was significantly reduced. Only 1 patient required mediastinal reexploration. No thromboembolic complications occurred during hospitalization.

CONCLUSIONS

This study suggests that rFVIIa is safe and efficacious in the management of refractory postcardiotomy bleeding. The use of rFVIIa is associated with reduced blood loss, rapid improvement of coagulation variables, and decreased need for blood products. Further studies are necessary to determine the safety and efficacy of this new hemostatic agent and its precise role in the treatment of severe postoperative coagulopathy.

Use of recombinant factor VIIa prior to lumbar puncture in pediatric patients with acute leukemia

The persistence of abnormal coagulation test results after standard treatment with fresh frozen plasma (FFP) poses significant problems in children with acute leukemia requiring a diagnostic lumbar puncture and intrathecal chemotherapy. We report the prophylactic use of a single dose of 90 microg/kg recombinant activated factor VII (rFVIIa) in three children and the rapid correction of abnormal coagulation test results previously not corrected by FFP. Administration of rFVIIa was useful in avoiding a delay of diagnostic lumbar punctures and intrathecal chemotherapy. Hemorrhagic complications and adverse effects of rFVIIa were not observed. Prospective evaluation of this indication and dose appears warranted. (c) 2005 Wiley-Liss, Inc.

Plasma and plasma products in the treatment of massive haemorrhage

Massive haemorrhage requires the use of plasma products when it is accompanied by a coagulopathy or when the more than one blood volume has been lost and intractable bleeding continues. The coagulopathy results from haemorrhagic shock, hypothermia, and activation, consumption and dilution of coagulation factors. Plasma products have a critical role in maintaining sufficient levels of coagulation proteins to ensure haemostasis can occur. Fresh frozen plasma is a source of all coagulation proteins and is required when the prothrombin time and activated partial thromboplastin time exceed 1.5 times the normal control. Cryoprecipitate is the plasma product of choice if fibrinogen, the most critical coagulation protein, is required rapidly and to maintain levels at >1g/L. Prothrombin complex concentrates, monocomponent factor therapy and fibrin sealants each have a role in specific clinical settings. Recombinant factor VIIa has now been shown to have a role in massive haemorrhage. Randomised controlled trials are currently underway to determine the optimal dose and timing of its administration. The physiology and management of the coagulation disturbance using plasma products in the massive haemorrhage of specific clinical situations are described.

Prerequisites for recombinant factor VIIa-induced thrombin generation in plasmas deficient in factors VIII, IX or XI

BACKGROUND

Recombinant factor VIIa (rFVIIa) used for the treatment of hemophilia A or B patients with an inhibitor is hemostatically effective because it induces thrombin generation (TG), despite grossly impaired FVIII- and FIX-dependent amplification of FX activation. Tissue factor (TF) and or activated platelets were shown to be essential for the rFVIIa activity.

OBJECTIVE

To evaluate the relative effects of TF and phospholipids on rFVIIa-induced TG in FVIII-, FIX- and FXI-deficient plasmas.

METHODS

Phospholipids had an independent effect that was augmented by TF. The contribution of blood-borne TF in FVIII-, FIX- and FXI-deficient plasma to rFVIIa-induced TG was demonstrated by removing microparticles and use of anti-TF antibodies.

RESULTS

At increasing concentrations of rFVIIa, the dependence of rFVIIa-induced TG on TF declined, but the presence of phospholipids was essential. rFVIIa was also shown to activate purified FIX and FX in the presence of phospholipids and absence of TF. rFVIIa-induced TG was dramatically augmented in FVIII- or FIX-deficient plasma in which the level of FVIII or FIX was increased to 1 or 2 U dL(-1).

CONCLUSIONS

The data indicate that rFVIIa-induced TG is affected by TF, phospholipids, rFVIIa concentration, and the presence of FVIII and FIX.

Mechanistic implications for the use and monitoring of recombinant activated factor VII in trauma

As interest in the use of activated recombinant factor VII (rFVIIa) in trauma grows, questions arise regarding how best to monitor rFVIIa therapy and when rFVIIa may be expected to improve hemostasis. Knowledge of the mechanisms of action may be combined with available data on laboratory monitoring and efficacy in various coagulopathic states in coming to clinically relevant conclusions. This review addresses the physiology of hemostasis, placing emphasis on how rFVIIa influences the process by both tissue factor dependent and tissue factor independent mechanisms. This is extended to a mechanistic consideration of how rFVIIa may function under acidotic, hypothermic, and hemodilutional and/or consumptive conditions of trauma related coagulopathy. When these considerations are viewed alongside the available clinical data, it becomes apparent that rFVIIa has potential to improve hemostasis during trauma coagulopathy, within limitations. Common laboratory procedures are discussed with reference to mechanisms of action of rFVIIa and the available clinical data. Although there is no single assay that can predict rFVIIa efficacy in trauma, the prothrombin time (PT) is recommended as a minimum. Although a shortened PT does not predict success, correction of PT into the normal range may be a better indicator. A nonresponding PT appears to indicate that rFVIIa alone will not lead to hemostasis, and that additional blood products and other measures must be applied. Once the patient is more stable, PT and thromboelastography are recommended.

The safety and efficacy of the administration of recombinant activated factor VII in major surgery and trauma patients

Recombinant activated Factor VII (rFVIIa) has been successfully used in the treatment of haemophilia A and B with associated inhibitors for some years. Activated Factor VII binds to activated platelets independently of tissue factor. The resulting stimulation of an exaggerated early thrombin burst at sites of vascular injury makes it an attractive potential treatment for massive, uncontrolled bleeding associated with surgery and trauma. This article describes the evidence relating to surgery and trauma. The lack of large, controlled trials of rFVIIa means that a definitive recommendation regarding its use cannot be made at present. However, in the context of clearly defined protocols and balanced treatment strategies, rFVIIa may have a role in traumatic bleeding. Large scale, randomised controlled trials in trauma are required, as is further work on the safety profile of rFVIIa with an independent international safety monitoring committee.

Haemophilia and thrombophilia: an unexpected association!

In patients with haemophilia, a close correlation is usually observed between the clinical expression of the disease and plasmatic factor VIII/factor IX clotting activity. However, some patients experience milder bleeding phenotypes than others, although they exhibit a similar biological profile. The high prevalence of some inherited thrombophilia risk factors offers the possibility of a co-inheritance in haemophilic patients which could influence the phenotypic expression of the disease. Rare thrombotic complications occurring in haemophiliacs could also be facilitated by the co-inheritance of modifier genes. The majority of thrombotic events occurring in haemophiliacs are in relation to clotting factor infusions or central venous catheters. Concerning surgical situations, in the absence of therapeutic recommendations, postoperative thromboprophylaxis is not systematically performed in haemophiliacs. However, substitutive treatment more or less completely corrects the coagulation defect and makes the venous thrombosis risk closer to the control population. It should be emphasized that haemophilia does not fully protect against venous thromboembolic disease. Patients with haemophilia very infrequently experience thrombotic events. Thus, the management of thrombotic complications occurring in haemophilic patients should be discussed in each case according to the precipitating risk factors, the clinical context and the thrombo-haemorrhagic balance of the patient with respect to a particular clinical situation.

Comparative thrombotic event incidence after infusion of recombinant factor VIIa versus factor VIII inhibitor bypass activity

Thrombosis is a rare but well-recognized potential complication of Factor VIII Inhibitor Bypass Activity (FEIBA) infusion. Recombinant factor VIIa (rFVIIa) is increasingly used as an alternative to FEIBA; however, the thrombotic safety profile of rFVIIa remains incompletely characterized. To determine the incidence rates of thrombotic adverse events (AEs) after infusion of rFVIIa and FEIBA. Data from the MedWatch pharmacovigilance program of the US Food and Drug Administration, as supplemented by published case reports, were used in conjunction with estimated numbers of infusions available from manufacturers to assess comparative incidence of thrombotic AEs in patients receiving rFVIIa or FEIBA in the period from April 1999 through June 2002. Reported thrombotic AEs were rare, with incidence rates of 24.6 per 10(5) infusions (CI, 19.1-31.2 per 10(5) infusions) for rFVIIa and 8.24 per 10(5) infusions (CI, 4.71-13.4 per 10(5) infusions) for FEIBA. Thrombotic AEs were significantly more frequent in rFVIIa than FEIBA recipients (incidence rate ratio, 2.98; CI, 1.71-5.52). The most commonly documented single type of thrombotic AE after rFVIIa infusion was cerebrovascular thrombosis, while myocardial infarction was the most frequent type in patients receiving FEIBA. Contrasting AE reporting patterns between rFVIIa and FEIBA may have contributed to the observed difference in thrombotic event incidence. Nevertheless, this comprehensive pharmacovigilance assessment does not support superior thrombotic safety of rFVIIa and suggests that thrombotic AE risk may be higher in rFVIIa than FEIBA recipients.

The use of recombinant factor VIIa in the treatment of bleeding disorders

Recombinant factor VIIa was initially developed for the treatment of hemorrhagic episodes in hemophilic patients with inhibitors to factors VIII and IX. After its introduction, it has also been used "off-label" to enhance hemostasis in nonhemophilic patients who experience bleeding episodes not responsive to conventional therapy. Evidence so far indicates that the use of factor VIIa in hemophilic patients with inhibitors is both safe and effective. Anecdotal reports also suggest that the product is safe and effective in controlling bleeding in nonhemophilic patients. However, its use in these conditions has not been approved by the FDA, and conclusive evidence of its effectiveness from controlled clinical trials is not yet available. Several questions pertaining to the use of factor VIIa require further investigation, including the mechanism of action; the optimal dose; definitive indications; ultimate safety; and laboratory tests for monitoring therapy.

Dosing with recombinant factor viia based on current evidence

Recombinant factor VIIa (rFVIIa; NovoSeven(R), Novo Nordisk, Bagsvaerd, Denmark) induces hemostasis in patients with severe hemophilia and inhibitors, and has been found to control hemorrhage associated with severe trauma and surgery in patients with basically normal hemostatic mechanisms from the start. By enhancing the generation of thrombin on activated platelets, rFVIIa facilitates the formation of a tight, stable fibrin plug that is resistant to premature lysis. Clinical efficacy has been achieved with doses of rFVIIa much lower than originally proposed by in vitro models. Based on early clinical experiences, a dosing schedule of 90 to 120 microg/kg every 2 hours for the first 24 hours was recommended for serious bleeds and surgical cover. This schedule has been shown to induce and maintain hemostasis in 83% to 95% of serious bleeding episodes, and in 90% to 100% of major surgical cases. However, "mega" doses of rFVIIa may demonstrate greater efficacy in the treatment of joint bleeds, as they are more likely to evoke a full thrombin burst. Interpatient variation in recovery rates, clearance rates, and the ability to generate thrombin on the activated platelet surface may influence the efficacy of rFVIIa. Optimal doses may thus vary not only between hemophilia patients, but also between patients treated for other bleeding disorders.

Monitoring coagulation and the clinical effects of recombinant factor VIIa

Accurately monitoring hemostasis in patients with coagulation disorders is vital in order to allow physicians to optimize anticoagulant therapy and deliver effective patient management. Traditional assays, based on the measurement of the time to first evidence of clot formation, fail to describe the kinetics of clot production that ultimately define the quality of the final clot. This review describes the technologies that have been developed to accurately describe and monitor the kinetics of clot formation. Using clinical examples, the utility of these technologies is assessed and conclusions drawn about the most useful diagnostic measures for monitoring hemostasis.

Safety profile of recombinant factor VIIa

Recombinant factor VIIa (rFVIIa; NovoSeven(R), Novo Nordisk, Bagsvaerd, Denmark) has been used for many years in the successful management of bleeding episodes in patients with hemophilia and inhibitors. More recently, rFVIIa has also shown considerable success as a hemostatic agent in trauma and surgery patients without pre-existing coagulopathy. Despite extensive and varied usage of rFVIIa, the incidence of serious adverse events associated with its use is less than 1%; however, there remain concerns regarding the agent's potential to induce thrombosis. This paper will review the safety profile of rFVIIa by examining existing clinical evidence, and will demonstrate that the isolated thrombotic events reported following rFVIIa treatment are due primarily to an improvement in the coagulation mechanism rather than rFVIIa treatment per se. The demonstrated safety of rFVIIa is probably due to its localization to injured areas of the vascular tree by binding to tissue factor (TF) and activated platelets at the bleeding site, thus avoiding systemic activation of coagulation. Finally, those situations in which rFVIIa therapy may not be safe, such as disseminated intravascular coagulation (DIC) and sepsis, will also be discussed.

Recombinant factor VIIa in orthotopic liver transplantation: influence on parameters of coagulation and fibrinolysis

The effect of recombinant factor VIIa (rFVIIa) on blood loss was evaluated in cirrhotic patients undergoing orthotopic liver transplantation. In the present study, we explored the effect of rFVIIa on coagulation and fibrinolysis during orthotopic liver transplantation. Coagulation factors, parameters of thrombin generation and parameters of fibrinolysis were measured in six patients who had received a single dose of 80 micro g/kg rFVIIa and in ten controls, during and after orthotopic liver transplantation. Baseline concentrations and course of coagulation factors were similar in patients and controls. Thrombin generation did not rise after the administration of rFVIIa, but showed a sharp increase after reperfusion in patients, as compared with controls. No difference in fibrinolysis was apparent between patients and controls. No evidence of diffuse intravascular coagulation was seen. We conclude that the use of rFVIIa in orthotopic liver transplantation seems to enhance thrombin generation in a localized and time-limited matter, without causing systemic coagulation.

The interaction between platelets and factor VII/VIIa

Blood coagulation normally occurs when factor VII interacts with its specific cellular receptor, tissue factor, which is exposed when a blood vessel is severed. The factor VII/tissue factor complex then initiates a cascade of proteolytic reactions involving factors IX, X, prothrombin and fibrinogen, culminating in the formation of a fibrin clot. The role of platelets in the initiation phase of blood coagulation is still unclear. It has been postulated that platelets bind activated factor VIIa independently of tissue factor, and that this interaction forms the basis of the usefulness of high-dose recombinant factor VIIa in treating hemophiliacs with inhibitory antibodies, and other thrombocytopenia-like syndromes. In this review, we will examine the evidence for and against such an hypothesis, as well as discuss an alternative mechanism for the efficacy of high-dose factor VIIa in treating hemophilic patients with inhibitors.

Treatment of diffuse alveolar hemorrhage after allogeneic bone marrow transplant with recombinant factor VIIa

Diffuse alveolar hemorrhage (DAH) is a potentially life-threatening pulmonary toxicity that occurs in 1-21% of patients following bone marrow transplantation. The syndrome is associated with a high mortality rate; and current treatment options are limited. Recombinant factor VIIa (rFVIIa, Novoseven) has recently been approved for the treatment of bleeding in patients with hemophilia A/B with inhibitors. A greater understanding of the mechanism by which rFVIIa restores hemostasis has recently become available; with in vitro evidence supporting that the thrombin burst achieved by rFVIIa is independent of the presence or binding to tissue factor. This insight has suggested a range of other potential clinical uses for the drug; including the setting of pulmonary hemorrhage. We review our experience with using rFVIIa for treatment of DAH in a patient with acute myelogenous leukemia following a matched unrelated donor bone marrow transplant. Boluses of 90 microg/kg rFVIIa were given every 3 h x 4 doses/day, concurrently with high-dose corticosteroids and maintenance of a platelet count >50 000/mm(3). Rapid clinical and radiological improvement was noted within several doses of rFVIIa, with discontinuation of the drug after eight doses. However, the patient's clinical condition began to rapidly deteriorate following cessation of rVIIa, resulting in reinstitution of therapy 24 h later. The patient again exhibited rapid clinical improvement; and rFVIIa was continued for an additional 16 doses with no further evidence of pulmonary hemorrhage noted. No toxicity or adverse events were observed with rFVIIa treatment. Our experience indicates that rFVIIa may be an effective treatment option for DAH post bone marrow transplant; although further clinical studies are needed before recommendations can be made regarding off label use of rFVIIa in this clinical setting.

Effects of recombinant activated factor VII on coagulation measured by thromboelastography in liver transplantation

Besides the conventional laboratory tests, thromboelastography (TEG) is used to monitor hemostasis during liver transplantation. A previous pilot study suggested a beneficial effect of recombinant activated factor VII (rFVIIa) on transfusion requirements in liver transplantation. In the present study, we assess the effects of rFVIIa on coagulation variables and TEG. In six study patients, the prothrombin time (PT), the activated partial thromboplastin time (aPTT) and TEG variables [reaction time (r), kinetic time (k), or clot formation time, alpha angle (alpha), and maximal amplitude (MA)] were recorded before and after the administration of a bolus of 80 microg/kg rFVIIa. These patients were compared with six controls who did not receive rFVIIa. In contrast with the control group, a significant shortening of PT (P = 0.028) and aPTT (P = 0.028), r (P = 0.046) and k (P = 0.043) values, and a significant incline of the alpha angle (P = 0.028) were noticed after injection of rFVIIa, whereas MA increased not significantly (P = 0.075). rFVIIa rapidly improved coagulation variables in liver transplant patients including PT and aPTT. Of the TEG variables, r, k and alpha angle significantly improved, and MA showed a trend to increase. These data suggest that rFVIIa not only influences the speed of clot formation, but also the physical properties of the clot, which cannot be detected by routine coagulation tests.

The N-terminal epidermal growth factor-like domain in factor IX and factor X represents an important recognition motif for binding to tissue factor

Factors VII, IX, and X play key roles in blood coagulation. Each protein contains an N-terminal gamma-carboxyglutamic acid domain, followed by EGF1 and EGF2 domains, and the C-terminal serine protease domain. Protein C has similar domain structure and functions as an anticoagulant. During physiologic clotting, the factor VIIa-tissue factor (FVIIa*TF) complex activates both factor IX (FIX) and factor X (FX). FVIIa represents the enzyme, and TF represents the membrane-bound cofactor for this reaction. The substrates FIX and FX may utilize multiple domains in binding to the FVIIa*TF complex. To investigate the role of the EGF1 domain in this context, we expressed wild type FIX (FIX(WT)), FIX(Q50P), FIX(PCEGF1) (EGF1 domain replaced with that of protein C), FIX(DeltaEGF1) (EGF1 domain deleted), FX(WT), and FX(PCEGF1). Complexes of FVIIa with TF as well as with soluble TF (sTF) lacking the transmembrane region were prepared, and activations of WT and mutant proteins were monitored by SDS-PAGE and by enzyme assays. FVIIa*TF or FVIIa*sTF activated each mutant significantly more slowly than the FIX(WT) or FX(WT). Importantly, in ligand blot assays, FIX(WT) and FX(WT) bound to sTF, whereas mutants did not; however, all mutants and WT proteins bound to FVIIa. Further experiments revealed that the affinity of the mutants for sTF was reduced 3-10-fold and that the synthetic EGF1 domain (of FIX) inhibited FIX binding to sTF with K(i) of approximately 60 microm. Notably, each FIXa or FXa mutant activated FVII and bound to antithrombin, normally indicating correct folding of each protein. In additional experiments, FIXa with or without FVIIIa activated FX(WT) and FX(PCEGF1) normally, which is interpreted to mean that the EGF1 domain of FX does not play a significant role in its interaction with FVIIIa. Cumulatively, our data reveal that substrates FIX and FX in addition to interacting with FVIIa (enzyme) interact with TF (cofactor) using, in part, the EGF1 domain.

The use of recombinant factor VIIa (NovoSeven) in a patient with a factor XI deficiency and a circulating anticoagulant

A 75-year-old female known to have a chronic myelomonocytic leukaemia and an acquired FXI deficiency (FXI level, 5%) related to a FXI inhibitor (38 Bethesda units) was admitted to the hospital for acute pneumonia associated with a bulky pleural effusion. A therapeutic puncture was found to be essential for the patient. But, such a procedure is a haemostatic challenge which requires adequate preparation. A first treatment composed of intravenous immunoglobulins and immunosuppressive therapy failed to eradicate the inhibitor and to restore a normal FXI level. In this context, steroids or FXI concentrates were not recommended. Thus, small doses of recombinant activated factor VII were used to achieve haemostasis. The procedure was successful, the tolerance was good and no adverse events occurred.

Effects of agents, used to treat bleeding disorders, on bleeding time prolonged by a very high dose of a direct thrombin inhibitor in anesthesized rats and rabbits

Melagatran is the active form of the oral, direct thrombin inhibitor, H 376/95, that is under evaluation in clinical trials for the prevention and treatment of thromboembolism. In this study, a single dose, calculated on body weight basis, of antifibrinolytic treatment, factor VIIa, factor VIII with and without von Willebrand factor (vWF), factor IX, activated (APCC) or nonactivated (PCC) prothrombin complex concentrates was given intravenously to rats and rabbits, in an attempt to reverse the prolonged bleeding time during intensive anticoagulation with melagatran (2 micromol/kg/h). The doses used were at or above human therapeutic doses. The cutaneous tail bleeding time in the rat, as well as the ear incision bleeding time and cuticle bleeding time, and the blood loss in the rabbit were used for evaluation of the hemostatic effects of these agents. In vivo Feiba (APCC) and Prothromplex-T (PCC) shortened the prolonged cutaneous bleeding times in rats (P<.05); Feiba and Autoplex (APCC) shortened the cutaneous bleeding times in rabbits (P<.05). In contrast, Prothromplex-T prolonged bleeding times and blood loss in the rabbits (P<.05). Ex vivo Feiba, Autoplex and NovoSeven (rF VIIa) significantly (P<.05) shortened the prolonged whole blood clotting time (WBCT). Prothromplex-T significantly prolonged WBCT, activated clotting time (ACT) and activated partial thromboplastin time (APTT). Feiba, Autoplex, and Prothromplex-T increased thrombin generation measured as increased thrombin-antithrombin complex (TAT) formation. In conclusion, APCCs were found to be the most effective agents for reversing bleeding time induced by a very high plasma concentration of melagatran. APCC and recombinant activated factor FVII (rF VIIa) effectively shortened the prolonged WBCT. Thus, stimulating thrombin generation with the use of APCC may counteract the anticoagulant effect observed with a very high dose of a thrombin inhibitor.

In vivo bypass of hemophilia A coagulation defect by factor XIIa implant

Hemophilia A and B coagulation defects, which are caused by deficiencies of Factor VIII and Factor IX, respectively, can be bypassed by administration of recombinant Factor VIIa. However, the short half-life of recombinant Factor VIIa in vivo negates its routine clinical use. We report here an in vivo method for the continuous generation of Factor VIIa. The method depends on the implantation of a porous chamber that contains Factor Xa or XIIa, and continuously generates Factor VIIa bypass activity from the subject's own Factor VII, which enters the chamber by diffusion. Once inside, the Factor VII is cleaved to Factor VIIa by the immobilized Factor Xa or XIIa. The newly created Factor VIIa diffuses out of the chamber and back into the circulation, where it can bypass the deficient Factors VIII or IX, and enable coagulation to occur. In vitro, this method generates sufficient Factor VIIa to substantially correct Factor VIII-deficient plasma when assessed by the classical aPTT coagulation assay. In vivo, a Factor XIIa peritoneal implant generates bypass activity for up to one month when tested in rhesus monkeys. Implantation of such a chamber in a patient with hemophilia A or B could eventually provide a viable alternative to replacement therapies using exogenous coagulation factors.

[Recombinant activated factor VII: a new treatment for hemophilia]

Recombinant factor VIIa (NovoSeven, NovoNordisk) initiates coagulation in inhibitor patients who either develop alloantibodies to clotting factors or those with acquired haemophilia. The human gene for FVII was transfected into a baby hamster kidney (BHK) cell line which secretes FVII in a single-chain form. Recombinant FVII is purified from the medium by four chromatographic steps including immunoaffinity chromatography with a monoclonal anti-FVII. During this process rFVII undergoes autoactivation to rFVIIa. NovoSeven does not contain any stabilising protein including human albumin. The SA is 50 KU/mg, the concentration is 0.6 mg/mL. Recovery is 45%, clearance is 31 mL/h/kg, the half-life was estimated between 2 and 3 hours. Combined to tissue factor rFVIIa directly activates factor X without implication of FVIIIa and FIXa. There is no systemic coagulation activation. Efficacy was assessed from data derived largely from the Compassionate Use Programme and clinical studies using rFVIIa as first line therapy. Various situations were proven to be efficiently resolved with rFVIIa including surgeries. Usual dosages are 90-120 mcg/kg administered every 2-3 hours. There were no side effects even in cases of prolonged administration. Drawbacks are the short half-life and the cost of the product.

The activation of factor X and prothrombin by recombinant factor VIIa in vivo is mediated by tissue factor

The human coagulation system continuously generates very small quantities of Factor Xa and thrombin. Current evidence suggests that basal level activation of the hemostatic mechanism occurs via Factor VIIa-dependent activation of Factor X, but direct proof has not been available for the participation of tissue factor in this pathway. To examine this issue, we infused relatively high concentrations of recombinant Factor VIIa (approximately 50 micrograms/kg body wt) into normal chimpanzees and observed significant increases in the plasma levels of Factor IX activation peptide, Factor X activation peptide, and prothrombin activation fragment F1+2. Metabolic turnover studies with radiolabeled Factor IX activation peptide, Factor X activation peptide, and F1+2 indicate that elevated levels of the activation peptides are due to accelerated conversion of the three coagulation system zymogens into serine proteases. The administration of a potent monoclonal antibody to tissue factor, which immediately neutralizes function of the Factor VIIa-tissue factor complex in vitro, abolishes the activation of Factor X and prothrombin mediated by the infused recombinant protein, and also suppresses basal level activation of Factor IX and Factor X. The above results suggest that recombinant Factor VIIa functions as a prohemostatic agent by interacting with endogenous tissue factor sites, but definitive proof will require studies in hemophilic animals using relevant hemostatic endpoints.

Platelet activation in patients with thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a rare syndrome of unknown etiology. It is characterized by platelet microthrombi in small vessels, which results in tissue dysfunction and a microangiopathic hemolytic anemia. Activation of coagulation is not a prominent feature of TTP. It is not known whether the process which results in platelet aggregate formation might also activate platelets. Using GMP-140 as a marker of activation, we examined the activation state of circulating platelets in seven TTP patients and three normal controls, as well as the ability of purified platelets from three TTP patients and three controls to be activated in vitro. There was no statistically significant difference in the percentage of activated platelets circulating in patients and controls (4% vs. 2%). Both TTP and control platelets increased GMP-140 expression and procoagulant activity after stimulation with thrombin or the calcium ionophore A23187. Thus, we conclude that TTP patients do not have a significantly increased proportion of circulating activated platelets, and their platelets can be activated normally by thrombin or a calcium ionophore.

Recombinant human factor VIIa (rFVIIa) in a rabbit stasis model

The thrombogenicity of recombinant human FVIIa (rFVIIa) and FEIBA was studied in a rabbit stasis model. Only minor thrombus formation in isolated vein segments during 10 min. of stasis was seen following the administration of rFVIIa 100-1000 micrograms/kg or FEIBA 50-100 U/kg whereas both compounds caused clear thrombus formation during 30 min. of stasis. RFVIIa caused no change in platelet counts or plasma fibrinogen 3 hours after administration, whereas a small decrease of APTT was seen due to the direct effect of rFVIIa in this assay. In contrast, FEIBA caused a significant and dose-dependent decrease of platelet counts as well as of fibrinogen, and an increase of APTT which demonstrate a general consumption of coagulation factors. In conclusion the study demonstrated a local pharmacological effect of rFVIIa in the absence of a general activation of the coagulation cascade.