Studies on the Thrombogenic Activities in Two Prothrombin Complex Concentrates

The effect on the coagulation and fibrinolytic systems of various factor IX concentrates after addition of heparin, antithrombin III or Trasylol to the concentrate before infusion into dogs was studied in an attempt to characterize the clot-promoting activity or activities in these concentrates. After infusion of Preconativ (AB Kabi; 100 u factor IX/kg bodyweight) only small decreases of fibrinogen and platelet count in the samples taken 1 and 4 hrs after infusion were found. Addition of heparin (10 u/ml; 5 dogs) or Trasylol (40 u/u factor IX initially followed by 10,000 u/h; 3 dogs) had no effect but addition of antithrombin III (100 u/kg; 3 dogs) prevented all changes. Infusion of Konyne (Cutter Laboratories; 100 u/kg bodyweight) induced marked decreases of both fibrinogen and the platelet count at 1, 4 and 24 hrs after infusion and the ethanol gelation test became positive. Addition of heparin (10 u/ml; 5 dogs) diminished the changes but did not completely counteract them. Antithrombin III (100 u/kg; 3 dogs) added to the concentrate before infusion also reduced the induced changes to about the same extent as heparin. Trasylol (40 u/u factor IX initially followed by 10,000 u/h; 3 dogs) did not seem to have any effect. Addition of both antithrombin III and Trasylol (4 dogs) did, however, prevent almost all changes.

It is thus obvious that the two commercial factor IX concentrates used may contain clot promoting activities and that these activities may differ between various concentrates.

Inhibition of Extrinsic Pathway Inhibitor Shortens the Coagulation Time of Normal Plasma and of Hemophilia Plasma

An increasing amount of evidence suggests that coagulation factors VIII and IX play a role not only in the intrinsic but also in the extrinsic pathway of coagulation. In this context the influence of the Extrinsic Pathway Inhibitor (EPI) on the coagulation time of hemophilia plasma lacking FVIII or FIX has been investigated. The coagulation time was measured in a dilute thromboplastin assay. Addition of recombinant EPI (rEPI) prolonged the coagulation time of normal plasma while the addition of an inhibitory antibody against EPI shortened the coagulation time. At low concentrations of thromboplastin the coagulation time of hemophilia plasma was prolonged and at all dilutions of thromboplastin, addition of anti-EPI IgG normalized the coagulation time of a hemophilia plasma. Analysis of 10 individual donor plasma samples and 8 individual hemophilia samples showed that addition of anti-EPI IgG shortened the coagulation time more in hemophilia plasma than in normal plasma. This illustrates the importance of a powerful extrinsic FVII dependent pathway to achieve hemostasis in the case of FVIII or FIX deficiency (hemophilia A and B).

Determination of Plasminogen in Human Plasma by a Casein Method*

A modification of the casein method for determination of plasminogen in plasma has been devised.

1. Urokinase instead of streptokinase was used for activation of plasminogen in order to eliminate the effect of any antistreptokinase antibodies in the plasma.

2. A purified and stable plasmin preparation according to Wallén was used for preparing reference curves.

3. The plasminogen activity of plasma was converted into arbitrary casein - olytic units (ACU) defined in such a way that 10 caseinolytic units gave an extinction of 0.300.

4. Removal of the plasmin inhibitors by acidification of plasma to pH 2.0 was found to be better than using euglobulin precipitation.

5. The plasma should be tested immediately after thawing and not allowed to stand after acidification for obtaining optimal conditions.

6. The method can be used for determination of plasminogen in plasma in patients treated with ssss-ACA and AMCA.

7. The error of the method was found to be small ssss0.4.

The mean plasminogen level in a normal group of 72 was found to be 9.5 ssss 1.7 ACU/ml plasma. No variation with sex and age was found.

The method proved clinically useful. During the latter half of pregnancy the plasminogen level was found to be clearly elevated. In patients with liver cirrhosis the plasminogen level was low. It was a sensitive method for following the plasminogen content during streptokinase treatment.

Comparison between a Direct and an Indirect Method for Determining Plasminogen

A caseinolytic method for plasminogen determination using 30% ammonium sulphate to remove the inhibitors was compared with an immunochemical method in 44 apparently healthy individuals, 25 pregnant women in the third trimester, 24 patients with different liver diseases, 20 patients receiving thrombolytic therapy, 7 patients with septicemia and 9 foetuses obtained by induced legal abortion. The correlation found was strong and the regression line was found to pass near origo, indicating that the two methods measured, the same substance.

Both methods gave high plasminogen values in pregnant women and low values in patients receiving thrombolytic therapy and in foetuses.

Effects of Low Molecular Weight Heparin and Unfragmented Heparin on Induction of Osteoporosis in Rats

A comparison between the effect of low molecular weight heparin (LMWH) and unfragmented heparin (UH) on induction of osteoporosis was made in 60 rats treated with either UH (2 IU/ g b w), LMWH in 2 doses (2 Xal U/g or 0.4 Xal U/g) or placebo (saline) for 34 days. Studied variables were: bone mineral mass in femora; fragility of humera; zinc and calcium levels in serum and bone ash and albumin in plasma. A significant reduction in bone mineral mass was found in all heparin-treated rats. There was no difference between UH and LMWH in this respect. The effect was dose-dependent in LMWH-treated animals. The zinc contents in bone ash were decreased in all heparin-treated rats as compared with controls. No recognizable pattern was seen in alterations of zinc or calcium in serum. The fragility of the humera, tested as breaking strength did not differ between treatment groups and controls. In conclusion, if dosed according to similar factor Xa inhibitory activities, LMWH induces osteoporosis to the same extent as UH and in a dose-dependent manner. The zinc content in bone ash was decreased after heparin treatment, irrespective of type of heparin given.

Management of Haemophilia A with Antibodies - The Effect of Combined Treatment with Factor VIII, Hydrocortisone and Cyclophosphamide

Immune tolerance has by several methods been induced in haemophiliacs with antibodies. A conversion of “high responders” into “low responders” was previously reported after repeated moderate factor IX doses over periods of 7-10 days in combination with cyclophosphamide and steroids in two patients with haemophilia B and inhibitors. This paper reports similar results in a heamophilia A patient by giving factor VIII, cyclophosphamide, and steroids during relatively short periods of time (7-8 days). The anamnestic response markedly decreased already following the first treatment and never exceeded a level of 1 u/ml (˜ 3 BU/ml) even when boosted with ordinary factor VIII doses for only 3 days. It is concluded that the markedly decreased secondary antibody response is most probably the result of factor VIII given at short intervals (twice a day) for periods of up to about one week when given in combination with cyclophosphamide and steroids. The same effect may be achieved by other methods. The treatment schedule suggested in the present paper is, however, simple and avoids long periods of high antibody levels. Furthermore, the total factor VIII dose used is lower than suggested in most other treatment schedules, which makes the treatment substantially less expensive.

Heparin-Induced Osteoporosis in Rats

In order to study the effect of heparin in inducing osteoporosis, 30 female rats were divided in two groups and treated with daily injections of 2 IU heparin/g body weight for 33 and 65 days and compared with the same number of rats acting as controls. The mineral bone mass in the femora of the animals was measured quantitatively. A significant (p <0.001) reduction in bone mineral mass was found in the heparin-treated animals. This effect was present to the same degree after 33 days as after 65 days of treatment. It is concluded that heparin in this dose causes osteoporosis in rats after 33 days and that the described method can be used as an experimental model for further studies on this topic.

The Effect of Active Site-inhibited Factor VIIa on Tissue Factor-initiated Coagulation Using Platelets before and after Aspirin Administration

Active site-inactivated factor VIIa has potential as an antithrombotic agent. The effects of D-Phe-L-Phe-L-Arg-chloromethyl ketone-treated factor VIla (FFR-FVIIa) were evaluated in a cell-based system mimicking in vivo initiation of coagulation. FFR-FVIIa inhibited platelet activation (as measured by expression of P-selectin) and subsequent large-scale thrombin generation in a dose-dependent manner with IC50 values of 1.4 ± 0.8 nM (n = 8) and 0.9 ± 0.7 nM (n = 7), respectively. Kd for factor VIIa binding to monocytes ki for FFR-FVIIa competing with factor VIIa were similar (11.4 ± 0.8 pM and 10.6 ± 1.1 pM, respectively), showing that FFR-FVIIa binds to tissue factor in the tenase complex with the same affinity as factor VIIa. Using platelets from volunteers before and after ingestion of aspirin (1.3 g), there were no significant differences in the IC50 values of FFR-FVIIa [after aspirin ingestion, the IC50 values were 1.7 ± 0.9 nM (n = 8) for P-selectin expression, p = 0.37, and 1.4 ± 1.3 nM (n = 7) for thrombin generation, p = 0.38]. This shows that aspirin treatment of platelets does not influence the inhibition of tissue factor-initiated coagulation by FFR-FVIIa, probably because thrombin activation of platelets is not entirely dependent upon expression of thromboxane A2.

Immunological Aspects of Recombinant Factor Vila (rFVIIa) in Clinical Use

Patients, receiving rFVIIa for treatment of bleeding disorders, have been followed for specific antibody formation. No antibodies against FVII were demonstrated in 170 patients, with hemophilia, or with acquired inhibitors to clotting factors. Of 6 FVII-deficient patients, one overdosed patient developed antibodies to human FVII. There was no indication of de novo formation of antibodies to potential contaminating foreign protein, which could be correlated to the rFVIIa treatment. Except for the FVII-deficient population, which may represent a risk group, rFVIIa appears to be immunologically safe for use in patient groups with bleeding disorders, including hemophilia A and B patients.

Experimental Haemorrhagic Effect of Two-Domain Non-Glycosylated Tissue Factor Pathway Inhibitor Compared to Low Molecular Weight Heparin

The glycosylated multivalent three-domain Kunitz inhibitor TFPI is a natural inhibitor of tissue factor-FVIIa complex in the presence of FXa. TFPI has an experimental antithrombotic capacity indistinguishable from LMWH in a prophylactic dose, regardless of glycosylation and of the third domain. An inherited equilibrium between antithrombosis and haemorrhage exists. The aim of the study was to evaluate whether a two-domain non-glycosylated TFPI (117QTFPI1−161) has a bleeding potential in a rat gastric mucosa model. Groups; placebo, LMWH (tinzaparin) 60 and 250 anti-Xa IU/kg and 117QTFPIM61−161 1.0 and 10.0 mg/kg, given i.v. (bolus injection), randomised double dummy design.

All actively treated groups significantly prolonged both the bleeding volume (493-984 Μl) and the bleeding time (10-20 min) compared to placebo (41 Μl, 2 min). It was not possible to distinguish a difference between the lower dose of LMWH and 117QTFPI1−161 in either parameter (p = 0.23-0.71). The two doses of 117QTFPI1−161 caused elevation of plasma-TFPI, 18 and 150 times baseline value. Both LMWH doses (0.6-3.2 anti-Xa IU/ml) and both 117QTFPI1−161 doses (0.2-2.7 anti-Xa IU/ml), caused significant effect in the anti-Xa assay, however 117QTFPI1−161 significantly less. Only the largest dose of 117QTFPI1−161 caused significant prolongation in the APTT assay (34 s). Both doses of LMWH caused significant prolongation (60-300 s). LMWH was the only substance to prolong the dilute-PT assay.

Non-glycosylated two-domain 1.0 mg/kg TFPI, yielding supra-physiological plasma concentration, has an experimental haemorrhagic potential indistinguishable from LMWH in a prophylactic dose. The effect mediated by this type of TFPI could primarily be due to an inhibition of FXa.

Effects of an Enzymatically Depolymerized Heparin as Compared with Conventional Heparin in Healthy Volunteers

A low molecular weight heparin (LMW-heparin) with a mean molecular weight of 4900 dalton was prepared by controlled enzymatic depolymerization of conventional porcine mucosal heparin. The effects of 2,500, 5,000 and 10,000 U (Xal; 29,58 and 116 mg) on factor Xa inhibition (Xal), factor Ila inhibition (Hal), APTT, AT III and platelet count were compared to those of 5,000 U (Xal; 26 mg) of conventional heparin given s. c. to 6 healthy volunteers. 5,000 U (Xal; 58 mg) of LMW-heparin was given i. v. A dose related response with regard to the Xal and the Ila-inhibitory activities with peak values at 4 hours after the s. c. injections was obtained. An increase of the Xal/IIal ratio over the time after injection was seen only after i. v. administration of the LMW-heparin. The APTT was only slightly prolonged and remained within normal range after s. c. injection. AT III and platelet counts were unaffected. The biological half life of the LMW-heparin was 111 minutes if assayed by Xa inhibition, 76 minutes if assayed by Ila inhibition and 40 minutes if assayed by APTT. A strong correlation between the Xal activities obtained and body weight was seen, indicating that LMW-heparin should be administered individually according to body weight.

Pharmacokinetics of Full Length and Two-Domain Tissue Factor Pathway Inhibitor in Combination with Heparin in Rabbits

Tissue factor pathway inhibitor (TFPI) is a feed back inhibitor of the initial activation of the extrinsic pathway of coagulation. In humans, injection of heparin results in a 2-6 fold increase in plasma TFPI and recent studies suggest that TFPI may be important for the anticoagulant activity of heparin. Full length (FL) TFPI, but not recombinant two-domain (2D) TFPI, has a poly cationic C-terminus showing very strong heparin binding. Therefore, we have investigated if heparin affects the pharmacokinetics of TFPI with and without this C-terminus.

FL-TFPI (608 U/kg) and 2D-TFPI (337 U/kg) were injected intravenously in rabbits with and without simultaneous intravenous injections of low molecular weight heparin (450 anti-XaU/kg).

Heparin decreased the volume of distribution and the clearance of FL-TFPI by a factor 10-15, whereas the pharmacokinetics of 2D-TFPI were unaffected by heparin. When heparin was administered 2 h following TFPI the recovery of FL-TFPI was similar to that found in the group receiving the two compounds simultaneously, suggesting that the releasable pool of FL-TFPI is removed very slowly in the absence of circulating heparin.

Pharmacokinetics of Recombinant Factor VIIa in the Rat – A Comparison of Bio-, Immuno- and Isotope Assays

Recombinant human factor VII a (rFVIIa) is an activated coagulation factor for intravenous use as a haemostatic agent in haemophiliacs who generate antibodies against factor VIII or IX. Plasma kinetic studies are important for the understanding of the action of rFVIIa which is exerted in the vascular compartment of the body, more specifically on the vessel walls at the site of injury. In the present study, rats were dosed 100 or 500 μg/kg 125I-rFVIIa i. V., without any side effects being observed, and the plasma profile of rFVIIa was studied by 3 different assays that were shown to correlate well at early times post-dose: trichloroacetic acid (TCA)-precipitable drug-related radioactivity, rFVIIa antigen determination by ELISA technique, and the assay of clot activity which is the only clinically applicable assay. The plasma concentration curve could be resolved into 1-3 exponentials, depending on the FVIIa detection principle that was employed. Initially, there was a short (ca. 10 min) phase of increasing concentrations before the attainment of C max. This was followed by a plasma recovery (C max × plasma volume/dose) in the vicinity of one half of the administered dose. The initial volume of distribution (V 1) corresponded to the vascular compartment whereas the volume of distribution at steady state (V ss) was somewhat larger. Whole body clearance (CL-B) of rFVIIa was approx. 1 ml/min per kg, and mean residence time (MRT) and the half-life assumed to be associated with the loss of biological activity was approx. 1 h and 20-45 min, respectively. From these plasma data, rFVIIa appears to be a low clearance compound with limited tissue distribution and a short half-life. Tissue distribution studies showed that high 125I levels, assumed to be rFVIIa-related, included mineralised bone and well-perfused organs such as the liver which suggested that this organ was responsible for a major proportion of CL-B. Finally, mass balance studies showed that almost 90% of the administered radioactivity could be accounted for following an i. v. dose, predominantly as non drug-related radioactivity, even though a small amount of TCA-precipitable radioactivity was excreted via the biliary route. In conclusion, dose- or sex-dependent plasma kinetics and tissue distribution within a dose range of 100 to 500 μg/kg of rFVIIa was not observed. In the early and pharmacologically relevant phase after rFVIIa administration there appears to be good agreement between the various plasma assays employed in the study, indicating that the clot assay yields useful information in studies of rFVIIa plasma pharmacokinetics.

Various Prothrombin Complex Concentrates and their Effect on Coagulation and Fibrinolysis In Vivo

Thromboembolic complications occurring in patients treated with factor IX concentrates have been reported. To study the thrombogenicity various types of factor IX concentrates (50 or 100 units F. IX/kg bodyweight) have been infused in dogs. As control albumin was given. The various components of the coagulation and fibrinolytic system have been assayed before the infusion and at various intervals after the end of infusion (0, 1,4 and 24 hrs). Konyne resulted in marked activation of the coagulation process with decrease of platelets, fibrinogen, F. VIII and appearance of FDP and positive ethanol gelation test. Pro thro mplex and Pre-conativ gave no significant changes. Preconativ is prepared without addition of heparin during the procedure.

Gastric Fibrinolysis

Gastric juice from 15 normals, 20 patients with gastric ulcer and 4 patients with erosive haemorrhagic gastroduodenitis was investigated in respect of its activity on unheated and heated fibrin plates and its content of FDP and plasminogen or plasmin with immunochemical methods. Gastric juice from normals showed no activity on unheated and heated fibrin plates, and no FDP or plasminogen could be demonstrated. In the patients with gastric ulcer the gastric juice showed little or no fibrinolytic activity on fibrin plates except in 2, who had regurgitation of duodenal juice and neutral pH of the juice. These patients had equally high activity on heated as on unheated plates and no plasmin could be demonstrated. It was shown that this activity was not due to fibrinolysis, but to non-specific proteolytic activity (probably trypsin). The patients with erosive haemorrhagic gastroduodenitis exhibited quite a different picture. The gastric juice from these patients showed extremely high activity on fibrin plates, the activity was higher on unheated than on heated plates. The activity was inhibited in vitro by addition of EACA and in vivo after administration of AMCA. The occurrence of plasmin could be demonstrated directly immunologically in the gastric juice. By comparison of plasmin and trypsin in various assays it could further be proved that the gastric juice in these cases contained plasminogen activator and plasmin. The patients with erosive haemorrhagic gastroduodenitis showed no increase in fibrinolysis in the blood, but low values for plasminogen and α2M, and the serum contained FDP. These findings in the blood and gastric juice were interpreted as signs of local fibrinolysis in the stomach and duodenum. There is reason to assume that this gastric fibrinolysis contributes substantially to the bleeding tendency. The effect of administration of AMCA on fibrinolytic activity and the haemorrhage lends support to the assumption of such a mechanism.

Studies on an Inhibitor of Plasminogen Activation in Human Serum

A procedure is described for partial purification of an inhibitor of the activation of plasminogen by urokinase and streptokinase. The method involves specific adsorption of contammants, ion-exchange chromatography on DEAE-Sephadex, gel filtration on Sephadex G-200 and preparative electrophoresis. The inhibitor fraction contained no antiplasmin, no plasminogen, no α1-antitrypsin, no antithrombin-III and was shown not to be α2 M or inter-α-inhibitor. It contained traces of prothrombin and cerulo-plasmin. An antiserum against the inhibitor fraction capable of neutralising the inhibitor in serum was raised in rabbits.

Parallel Determinations of FDP and Fibrin Monomers with Various Methods

The following tests were performed in 305 persons with one or other of the following conditions: malignant disease, postoperative complications, sepsis or multiple fractures, liver disease, pregnancy, the puerperium, renal disease, dysproteinaemia and different blood disorders : 1. fibrinogen degradation products (FDP) with Niléhn’s immunochemical method; 2. the thrombin time; 3. the Reptilase time; 4. the ethanol gelation test; 5. the protamine sulphate precipitation test. It was found that a prolonged thrombin time or Reptilase time in a given case was not necessarily a sign of the presence of FDP. Thus, neither determination of the thrombin time nor of the Reptilase time can substitute for specific determination of FDP. A positive ethanol gelation test was found in only 5 out of 17 patients with a low platelet count, low P & P test, low factor V, low fibrinogen and clinical signs of disseminated intravascular coagulation such as shock, disturbance of the periphery circulation, oliguria or anuria. No association was found between a positive ethanol gelation test and the presence of FDP. The protamine sulphate precipitation test was positive in only one of the 305 patients.

Determination of Plasminogen in Clots and Thrombi

The plasminogen content was determined by a casein method in plasma and serum from 20 normal volunteers. The mean plasminogen content was found to be 10.1 ACU (the arbitrary caseinolytic unit defined in such a way that using a 3% casein solution and a digestion time of 20 min. at 37°C, 10 ACU gave an extinction of 0.300). No difference between serum and plasma regarding the plasminogen content was found.

Plasminogen was determined in drained and drained plus washed clots prepared from 2 ml plasma. The highest values found in the drained clots were 0.9 ACU/clot and 0.2 ACU/clot in the drained plus washed clots.

Plasminogen was also determined in drained and drained plus washed clots prepared from plasma with added purified plasminogen. The plasminogen was recovered in the washing fluid. According to these tests, then, purified added plasminogen is washed out of the clots.

The plasminogen content of 20 thrombi obtained post mortem was also determined. The mean value was found to be 0.7 ACU/cm thrombus. Judging from our results, the “intrinsic clot lysis theory” is not the main mechanism of clot dissolution.

Evaluation of Potential Antigenicity of Active-Site-Inhibited Recombinant Human FVIIa (FFR-rFVIIa) in an Immune-Tolerant Rat Model

Recombinant human FVIIa (rFVIIa) was inactivated by coupling Phe-Phe-Arg-CO- (FFR) covalently to the active site of the enzyme. To test the chemically-modified human protein for potential antigenicity prior to clinical trial an immune-tolerant rat model was established. Intraperitoneal injection of the parent compound, human rFVIIa, within 30 h after birth, followed by repeated subcutaneous challenge with rFVIIa in Freunds incomplete adjuvant resulted in 79% non-responding rats at day 32. Monthly subcutaneous challenge showed that the induced tolerance was stable over the 3 months study period in 80% of the rats. The clinically relevant route, intravenous administration, was used for evaluating the potential antigenicity of FFR-rFVIIa. Repeated intravenous administration of different dosages of FFR-rFVIIa did not break tolerance, indicating that FFR-rFVIIa might not be antigenic, for a limited number of intravenous administrations in a clinical setting.

Treatment of Patients with Factor VIII and Factor IX Inhibitors with Special Focus on the Use of Recombinant Factor VIIa

In caring for patients with hemophilia, the development of inhibitors against the missing coagulation protein remains a significant problem. Such inhibitors occur in about 15% of patients with severe hemophilia1 and are directed against the procoagulant part of the factor VIII or factor IX molecules. The goal in the treatment of patients with hemophilia is to achieve high enough levels of the missing factor to induce hemostasis in case of bleeding or to prevent bleeding during surgery. Patients with a low inhibitor titer, and especially those with a low anamnestic response, can be given high doses of the coagulation factor concentrate to induce hemostasis. However, for patients with high inhibitor levels, or high-responders, other treatments must be used, including procedures to decrease the antibody titers. To minimize the booster effect of high doses of antigen, immunosuppressive treatment may be added. Because such treatment procedures are complicated and associated with a number of potential side effects, they are not often used to treat mild-to-moderate bleeding episodes or to cover elective, less urgent surgery for inhibitor patients. As a result, a great deal of effort has been devoted to finding more convenient treatment modalities and to inducing immunologic tolerance to permanently eradicate the inhibitors.

Factor VIIa and its potential therapeutic use in bleeding-associated pathologies

Recombinant FVIIa (rFVIIa) was developed for treatment of haemophilia patients with inhibitors against FVIII/FIX. The haemostatic efficacy rate of 80–90% including major orthopaedic surgery (dosing of 90–120 µg/kg every other hour [h] for at least the first 24 h) was achieved in these patients. In a home-treatment setting the efficacy rate of haemostasis in mild-moderate bleedings was 92% (average number of 90 µg/kg doses was 2.2). A wide individual variation regarding recovery of rFVIIa (46 ± 12%; median 43%) as well as of clearance rate (36 ± 8 ml/kg/h; median 32 ml/kg/h in adults;children 2–3 times higher) has been observed. Thus children may require higher doses than adults. Accordingly the use of a dose of 270 µg/kg in one single injection was approved in the EU. Recent experience indicates that repeated doses of rFVIIa may decrease the number of bleeds in “target joints”, and thus may be useful as prophylaxis in severe hemophilia with inhibitors. Pharmacological concentrations of rFVIIa have been shown to enhance the thrombin generation on thrombin activated platelets in a cell-based model. By doing so a tight structured fibrin haemostatic plug resistant against premature lysis is formed. rFVIIa has been shown to induce haemostasis not only in haemophilia but also in other situations characterized by an impaired thrombin generation such as platelet defects, dilution coagulopathy developed as a result of trauma and extensive surgery. A special form of profuse bleeding, that may cause extensive problems is postpartum haemorrhage.

Δ4-Ethyloestrenol in Recurrent Deep Venous Thrombosis

Twenty-one patients with recurrent deep venous thrombosis were treated with an anabolic steroid (Δ4-ethyloestrenol) for up to 56 months. All had been shown to have a deficient fibrinolytic response to vascular occlusion and/or low vessel wall plasminogen activator content.

Therapy resulted in improvement in clinical and fibrinolytic parameters and no significant side effects were seen.

Validity of Tests of Fibrinolysis

In this paper the conventional tests of fibrinolysis are compared and contrasted. Tests of fibrinolytic potential by venous occlusion and injection of DDAVP are then described and the results of these tests shown in a population of patients at risk from venous thrombosis.

Advances in bypassing agent therapy for hemophilia patients with inhibitors to close care gaps and improve outcomes

In the past, patients with hemophilia and inhibitors have had less-than-optimal treatment and have experienced more orthopedic complications than patients without inhibitors. Bypassing agents offer the potential to close treatment gaps between inhibitor and noninhibitor patients by helping the former better attain key treatment goals, including: facilitating early initiation of treatment and hemostatic control in hemarthroses; providing effective treatment in serious hemorrhagic episodes; and performance of major surgery. Effective treatment with a bypassing agent minimizes joint and/or muscle damage and potentially can serve as an effective prophylactic agent to minimize the number of hemarthroses experienced per year, thereby mitigating the development of arthropathy. The reported efficacy of the currently available bypassing agents ranges from approximately 50-80% (50-64% in controlled studies) for plasma-derived activated prothrombin complex concentrate (pd-aPCC) and 81-91% (in controlled studies) for recombinant activated factor VII (rFVIIa), including use in major orthopedic surgery. Both bypassing agents have undergone key improvements in their formulation and/or properties in recent years. The nanofiltered, vapor-heated formulation of pd-aPCC has diminished the risk of acquiring blood-borne viral infections and the room temperature stable formulation of rFVIIa allows more convenient storage, increased ease to dissolve and inject, and smaller volumes, thereby increasing overall ease of administration. Use of recommended dosing has been demonstrated to provide effective hemostasis with a minimal number of injections for both agents. In this paper, we review the individual characteristics of pd-aPCC and rFVIIa and discuss clinical data from studies conducted in inhibitor patients that demonstrate the potential benefits of these bypassing agents in this difficult-to-treat population, and underscore the potential opportunities to close the gap in care between inhibitor and noninhibitor hemophilic patients.

Joint disease, the hallmark of haemophilia: what issues and challenges remain despite the development of effective therapies?

Although effective therapies for haemophilia have been available for decades, the prevention and treatment of joint disease remain major clinical concerns for all haemophilia patients. Early identification of joint disease is vital to initiate or modify treatment, and prevent arthropathy. However, there remains a need for more sensitive and accurate methods, which may also detect improvement in patient outcome with new therapies or different prophylaxis regimens. These topics were explored at the Ninth Zürich Haemophilia Forum. A summary of our shared views on the limitations of current assessment methods, and the potential advantages of more recently developed tools, is provided. Ultrasonography enables more frequent routine monitoring and the early detection of joint disease. In addition, serological markers may provide suitable biomarkers of early arthropathy. To prevent arthropathy, in our opinion, prophylaxis is key to prevent joint bleeds and subsequent initiation of the 'vicious circle of joint disease'. However, issues remain, including when prophylaxis should be started, stopped, and if it is efficacious for inhibitor patients. Once joint bleeding has occurred, enhanced on-demand treatment should be considered. For more advanced stages of joint disease, the issues regarding the treatment options available are explored. Radiosynovectomy should be performed to treat chronic synovitis, and may prevent the need for elective orthopaedic surgery (EOS). Ultimately, however, EOS can be considered once all other treatment options have been explored. While, bypassing agents have facilitated the use of EOS in inhibitor patients, a multidisciplinary approach and careful surveillance is required for good patient outcome.

Progressive improvement in wound healing with increased therapy in haemophilia B mice

Previous work has shown that normalized haemostasis only at the time of an injury is not sufficient to promote optimal wound healing in haemophilia B (HB) mice. However, the duration of treatment required for optimal healing has not been established. The goal of these studies was to determine the effect of different durations of replacement or bypassing therapy [factor IX(FIX) or factor VIIa (FVIIa)] on wound healing parameters in a mouse model of HB. A dermal wound was placed on the back of HB mice. Animals were either untreated or pretreated and then subsequently treated for 3 days, 5 days, or 7 days with FIX or FVIIa. Wound area, time to wound healing, haematoma formation and iron deposition were measured. All treated animals showed shortened time to healing relative to untreated animals. Haematoma formation was prevented by treatment and bleeding into the wounds, measured by iron scores, was reduced by treatment. In addition, there was a progressive improvement in healing with 7 days of treatment more effective than 5 days which was more effective than 3 days. Replacement therapy with FIX had slightly shorter healing times than bypassing therapy with FVIIa. HB mice treated with FIX had slightly smaller wound area than untreated animals; by contrast, FVIIa-treated animals had much smaller wound areas that were close to the wound areas seen in wild-type animals. The data suggest that sustained therapy is required for normal wound healing.

Endothelial cell protein C receptor-mediated redistribution and tissue-level accumulation of factor VIIa

BACKGROUND

Recent studies show that activated factor VII (FVIIa) binds to the endothelial cell protein C receptor (EPCR) on the vascular endothelium; however, the importance of this interaction in hemostasis or pathophysiology is unknown.

OBJECTIVE

The aim of the present study was to investigate the role of the FVIIa interaction with EPCR on the endothelium in mediating FVIIa transport from the circulation to extravascular tissues.

METHODS

Wild-type, EPCR-deficient or ECPR-over-expressing mice were injected with human recombinant (r)FVIIa (120 μg kg(-1) body weight) via the tail vein. At varying time intervals after rFVIIa administration, blood and various tissues were collected to measure FVIIa antigen and activity levels. Tissue sections were analyzed by immunohistochemistry for FVIIa and EPCR.

RESULTS

The data reveal that, after intravenous (i.v.) injection, rFVIIa rapidly disappears from the blood and associates with the endothelium in an EPCR-dependent manner. Immunohistochemical analyses revealed that the association of FVIIa with the endothelium was maximal at 30 min and thereafter progressively declined. The FVIIa association with the endothelium was undetectable at time points exceeding 24 h post-FVIIa administration. The levels of rFVIIa accumulated in tissue correlate with expression levels of EPCR in mice and FVIIa associated with tissues remained functionally active for periods of at least 7 days.

CONCLUSIONS

The observation that an EPCR-dependent association of FVIIa with the endothelium is most pronounced soon after rFVIIa administration and subsequently declines temporally, combined with the retention of functionally active FVIIa in tissue homogenates for extended periods, indicates that FVIIa binding to EPCR on the endothelium facilitates the transport of FVIIa from circulation to extravascular tissues where TF resides.

Factor VIIa binding to endothelial cell protein C receptor: differences between mouse and human systems

Recent in vitro studies have shown that the zymogen and activated form of factor (F)VII bind to endothelial cell protein C receptor (EPCR). At present, there is no evidence that FVIIa binds to EPCR on vascular endothelium in vivo in the presence of circulating protein C, a primary ligand for EPCR. The present study was carried out to investigate the interaction of murine and human ligands with murine EPCR both in vivo and in vitro . Measurement of endogenous plasma levels of FVII in wild-type, EPCR-deficient and EPCR-over expressing mice showed slightly lower levels of FVII in EPCR-over expressing mice. However, infusion of high concentrations of competing ligands, either human APCi or FVIIai, to EPCR-over expressing mice failed to increase plasma levels of mouse FVII whereas they increased the plasma levels of protein C by two- to three-fold. Examining the association of exogenously administered mouse FVIIa or human FVIIa by immunohistochemistry revealed that human, but not murine FVIIa, binds to the murine endothelium in an EPCR-dependent manner. In vitro binding studies performed using surface plasmon resonance and endothelial cells revealed that murine FVIIa binds murine EPCR negligibly. Human FVIIa binding to EPCR, particularly to mouse EPCR, is markedly enhanced by availability of Mg2+ ions. In summary, our data show that murine FVIIa binds poorly to murine EPCR, whereas human FVIIa binds efficiently to both murine and human EPCR. Our data suggest that one should consider the use of human FVIIa in mouse models to investigate the significance of FVIIa and EPCR interaction.

FVIIa as therapeutic agent in hemophilia and beyond

Around 20 % of the patients with severe hemophilia develop inhibitory antibodies against the factor they lack. In these patients the administration of FVIII/FIX-concentrates are not hemostatically effective. Since FVIIa is not enzymatically active unless complexed with tissue factor (TF) exposed following an injury to the vessel wall, it was considered an attractive candidate for improved treatment of patients with inhibitors. Plasma-derived FVIIa was purified and shown to induce hemostasis in two hemophilia A patients with inhibitors. Later recombinant FVIIa (rFVIIa) was developed and pharmacological doses have an efficacy rate of around 90 % in serious bleedings and permit major orthopaedic surgery. These findings were a breakthrough in understanding the FVII-TF pathway in hemostasis. The initially formed FVIIa-TF complexes provide a limited amount of thrombin, activating FVIII, FV, FXI as well as platelets. On the activated platelet surface the full burst of thrombin necessary for generating a firm fibrin hemostatic plug occurs. In case of impaired thrombin generation, loose fibrin plugs easily dissolved are formed. Extra rFVIIa enhances thrombin generation and generates tight fibrin plugs.

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.

Redistribution and hemostatic action of recombinant activated factor VII associated with platelets

Clinical evidence accumulated from hemophilic patients during prophylaxis with recombinant activated factor VII (rFVIIa) suggests that the duration of the hemostatic action of rFVIIa exceeds its predicted plasma half-life. Mechanisms involved in this outcome have not been elucidated. We have investigated in vitro the redistribution of rFVIIa in platelets from healthy donors, patients with FVII deficiency, and one patient with Bernard-Soulier syndrome. Platelet-rich plasma was exposed to rFVIIa (3 to 60 μg/mL). Flow cytometry, immunocytochemistry, and coagulation tests were applied to detect and quantify rFVIIa. The hemostatic effect of rFVIIa associated to platelets was evaluated using perfusion models. Our studies revealed a dose-dependent association of rFVIIa to the platelet cytoplasm with redistribution into the open canalicular system, and α granules. Mechanisms implicated in the internalization are multiple, involve GPIb and GPIV, and require phospholipids and cytoskeletal assembly. After platelet activation with thrombin, platelets exposed rFVIIa on their membrane. Perfusion studies revealed that the presence of 30% of platelets containing FVIIa improved platelet aggregate formation and enhanced fibrin generation (P < 0.01 versus control). Our results indicate that, at therapeutic concentrations, rFVIIa can be internalized into platelets, where it is protected from physiological clearance mechanisms and can still promote hemostatic activity. Redistribution of rFVIIa into platelets may explain the prolonged prophylactic effectiveness of rFVIIa in hemophilia.

First 20 years with recombinant FVIIa (NovoSeven)

This review describes the background for the development of recombinant FVIIa (rFVIIa; NovoSeven) for use in haemophilic patients with inhibitors. The first proof of principle for using pharmacological doses of FVIIa as a haemostatic agent was obtained by producing small amounts of pure plasma-derived FVIIa, which showed encouraging effect in two patients with haemophilia A and inhibitors. To make pure FVIIa available for use in a larger number of patients, rFVIIa was produced that was approved for use in patients with inhibitors against coagulation factors (congenital haemophilia and acquired haemophilia) in 1996 (EU), 1999 (USA) and 2000 (Japan). The efficacy rate in severe bleedings and in major surgery including major orthopaedic surgery has been found to be around 90% in controlled studies, and no serious safety concerns have been demonstrated. The availability of rFVIIa has facilitated the performance of elective major surgery in haemophilia patients with inhibitors. Further steps along the vision of providing a treatment for inhibitor patients similar to non-inhibitor patients have been the efficacy of rFVIIa in home-treatment and recently the encouraging experience in prophylaxis. The concept of using pharmacological doses of rFVIIa as a haemostatic agent is a new one, which has caused difficulties in finding the correct dose. A step forward has been the demonstration that similar efficacy can be achieved after one single dose of 270 μg kg(-1) instead of three injections of a dose of 90 μg kg(-1). The higher clearance rate in children suggests that higher doses may be beneficial in children. The availability of rFVIIa has made advances in the understanding of coagulation processes possible. In a cell-based in vitro model, it has been shown that rFVIIa binds to preactivated platelets if present in concentrations of 30 nm or higher. By doing so, it activates FX into FXa and enhances the thrombin generation on the activated platelet surface in the absence of FVIII/FIX. Through the increased thrombin generation, a firm, well-structured fibrin haemostatic plug, which is resistant to premature lysis, is formed. By exploiting this mechanism of action, rFVIIa may also be effective in situations other than haemophilia, characterized by an impaired thrombin generation.

Monitoring rFVIIa 90 μg kg⁻¹ dosing in haemophiliacs: comparing laboratory response using various whole blood assays over 6 h

Recombinant FVIIa is a haemostatic agent administered to patients with severe FVIII or FIX deficiency with inhibitors. Although rFVIIa is effective at stopping bleeding, a reliable assay to monitor its effect is lacking. To characterize the pharmacokinetics and global coagulation effects of rFVIIa for 6 h following a IV dose of 90 μg kg⁻¹. Ten non-bleeding subjects with severe FVIII or FIX deficiency were infused with a single-dose of rFVIIa 90 μg k⁻¹ body weight and blood was collected before and at 0.5, 1, 2, 4 and 6 h postdose. Global haemostasis was characterized throughout the study utilizing whole blood analyses (Hemodyne HAS, TEG, ROTEM). The clearance and half-life of factor FVII:C was estimated as 39.0 ± 8.8 mL h⁻¹ kg⁻¹ and 2.1 ± 0.2 h respectively. There was good inter-assay agreement with respect to clot initiation parameters (R, CT and FOT) and these parameters all fell to a mean of approximately 9 min following rFVIIa dosing. The platelet contractile force (PCF) and clot elastic modulus (CEM) were positively correlated to FVII:C (P < 0.0001), and these parameters were dynamic throughout the 6-h period. The MA and MCF did not correlate to FVII:C nor did they significantly change during the study. Prothrombin F1 + 2 significantly increased following rFVIIa dosing (P < 0.001), but remained steady throughout the study. There was no change in D-dimer concentrations over time. The FOT, R and CT characterized clot initiation following rFVIIa dosing. The PCF and CEM were correlated to FVII:C and characterized the dynamics of platelet function and clot strength over the rFVIIa dosing interval. The clinical significance of these findings needs additional study.

Recombinant human factor VIIa (rFVIIa) cleared principally by antithrombin following intravenous administration in hemophilia patients

OBJECTIVE

The objective of the present study was to evaluate the pharmacokinetics and the clearance pathways of rFVIIa after intravenous administration to hemophilia patients.

METHODS

Ten severe hemophilia patients were included in the study; all patients were intravenously administered a clinically relevant dose of 90 μg kg(-1) (1.8 nmol kg(-1)) rFVIIa. Blood samples were collected consecutively to describe the pharmacokinetics of rFVIIa. All samples were analyzed using three different assays: a clot assay to measure the activity (FVIIa:C), an enzyme immunoassay (EIA) to measure the antigen levels (FVII:Ag), and an EIA (FVIIa-AT) to measure the FVIIa antithrombin III (AT) complex. Pharmacokinetic parameters were evaluated both by use of standard non-compartmental methods and by use of mixed effects methods. A population pharmacokinetic model was used to simultaneously model all three datasets. The total body clearance of rFVIIa:C was estimated to be 38 mL h(-1) kg(-1). The rFVII-AT complex formation was responsible for 65% of the total rFVIIa:C clearance. The initial and the terminal half-life of rFVIIa:C was estimated to be 0.6 and 2.6 h, respectively. The formation of rFVII-AT complex was able to explain the difference observed between the rFVIIa:C and the rFVII:Ag concentration. The non-compartmental analysis resulted in almost identical parameters.

Bio-distribution of pharmacologically administered recombinant factor VIIa (rFVIIa)

BACKGROUND

Recent clinical studies suggest that the prophylactic use of recombinant factor VIIa (rFVIIa) markedly reduces the number of bleeding episodes in hemophilic patients with inhibitors. Given the short biological half-life of rFVIIa, it is unclear how rFVIIa could be effective in prophylactic treatment.

OBJECTIVES

To examine the extravascular distribution of pharmacologically administered rFVIIa to obtain clues on how rFVIIa could work in prophylaxis.

METHODS

Recombinant mouse FVIIa tagged with AF488 fluorophore (AF488-FVIIa) was administered into mice via the tail vein. At different time intervals following the administration, mice were exsanguinated and various tissues were collected. The tissue sections were processed for immunohistochemistry to evaluate distribution of rFVIIa.

RESULTS

rFVIIa, immediately following the administration, associated with the endothelium lining of large blood vessels. Within 1 h, rFVIIa bound to endothelial cells was transferred to the perivascular tissue surrounding the blood vessels and thereafter diffused throughout the tissue. In the liver, rFVIIa was localized to sinusoidal capillaries and accumulated in hepatocytes. In bone, rFVIIa was accumulated in the zone of calcified cartilage and some of it was retained there for a week. The common finding of the present study is that rFVIIa in extravascular spaces was mostly localized to regions that contain TF expressing cells.

CONCLUSIONS

The present study demonstrates that pharmacologically administered rFVIIa readily associates with the vascular endothelium and subsequently enters into extravascular spaces where it is likely to bind to TF and is retained for extended time periods. This may explain the prolonged pharmacological effect of rFVIIa.

Thrombin generation and platelet activation induced by rFVIIa (NovoSeven) and NN1731 in a reconstituted cell-based model mimicking haemophilia conditions

Replacement therapy with factor VIII (FVIII) and factor IX (FIX) is routinely used in haemophilia patients with haemophilia A and B, respectively, while recombinant activated FVII (rFVIIa) has proven to induce haemostasis in haemophilia patients with inhibitors. To evaluate the effect of therapeutic intervention in patients with residual factor activities, the effects of increasing concentrations of rFVIIa or NN1731 on thrombin generation and platelet activation were measured in a cell-based model system mimicking severe, moderate and mild haemophilia A or B. Purified monocytes stimulated to express tissue factor and non-activated platelets from peripheral blood of healthy donors were incubated with a mixture of purified human coagulation factors in the absence or presence of increasing concentrations of FVIII or FIX. Sub-samples were analysed for thrombin activity and platelet activation measured as exposure of P-selectin by flow cytometry. Dose-dependent increases in thrombin generation and platelet activation were observed following increasing concentrations of rFVIIa or NN1731 in both haemophilia A- and B-like conditions. At 25 nm rFVIIa, which nears the peak levels in patient plasma after 90 microg kg(-1) intravenous dosing, the effects on maximum thrombin generation rate (maxTG) at 1-10% FVIII were comparable to those at 100% and 200% FVIII in the absence of rFVIIa. Normalization of maxTG required 500 nm rFVIIa and 25 nm NN1731 or 25-100 nm rFVIIa and 5 nm NN1731 in severe or moderate/mild haemophilia A and haemophilia B, respectively. This suggests that NN1731 holds its promise as a future bypassing agent for haemophilia patients with and without inhibitors.