Rasmus Rojkjaer

Recombinant factor VIIa reduces bleeding in severely thrombocytopenic rabbits.

Severe thrombocytopenia is a common complication to intensive chemotherapeutic regimens. For bleeding episodes associated with severe thrombocytopenia, the current standard treatment is platelet transfusion. However, due to several transfusion complications such as transfusion-transmitted diseases, platelet refractoriness and immunomodulation, as well as increasing problems with sufficient supply of platelet products, it is imperative to search for alternatives to platelet transfusion. To test the efficacy of recombinant activated human coagulation factor VII (rFVIIa, NovoSeven) in thrombocytopenia, a preclinical study was conducted in thrombocytopenic rabbits. Thrombocytopenia was induced by a combination of gamma-irradiation and the use of platelet antibodies, and the effect of rFVIIa on nail cuticle bleeding was determined. Administration of rFVIIa at 2 mg/kg significantly shortened the prolonged bleeding time in thrombocytopenic animals (rFVIIa vs. control, median 23 min 41 s vs. 60 min, p=0.016) as well as significantly reducing the blood loss (rFVIIa vs. control, median: 8.8 vs. 12.2 nmol hemoglobin/ml, p=0.016). This effect was also reflected by a significant reduction of the prothrombin time, activated partial thromboplastin time, as well as improvement in clotting parameters in an in vitro thromboelastography thrombocytopenia model. Histopathological evaluation of kidney biopsies for the presence of micro thrombi did not reveal evidence of prothrombotic effects of rFVIIa in this model. These data demonstrate the haemostatic efficacy of rFVIIa in a rabbit model of severe thrombocytopenia. Clinical trials will be needed to further explore the potential of NovoSeven as a haemostatic agent in thrombocytopenic patients.

Effect of haemodilution, acidosis, and hypothermia on the activity of recombinant factor VIIa (NovoSeven®)

Background A range of plasma volume expanders is used clinically, often in settings where haemostasis may already be impaired. The haemostatic agent, recombinant activated factor VII (rFVIIa, NovoSeven®), may be used to improve haemostasis but potential interactions with different volume expanders are poorly understood. Methods Clot formation was measured by thromboelastography (TEG) using blood from healthy volunteers. In vitro effects of rFVIIa with haemodilution, acidosis, and hypothermia were examined. Conditions were induced by dilution with NaCl (0.9%), lactated Ringers solution, albumin 5%, or hydroxyethyl starch (HES) solutions [MW (molecular weight) 130–670 kDa]; by adjusting pH to 6.8 with 1 M HEPES (N-2-hydroxyethylpiperazine-N′-2-ethanesulphonic acid) buffer; or by reducing temperature to 32°C. We also studied the effect of low vs high MW HES (MW 200 vs 600 kDa) and rFVIIa on in vivo bleeding time (BT) in rabbits. Results Haemodilution progressively altered TEG parameters. rFVIIa improved TEG parameters in the presence of acidosis, hypothermia or 20% haemodilution (P<0.05). At 40% haemodilution, the rFVIIa effect was diminished particularly with high MW HES. In vivo, rFVIIa shortened the BT (P<0.05) with low but not high MW HES. Conclusions Efficacy of rFVIIa was affected by the degree of haemodilution and type of volume expander, but not by acidosis or hypothermia.

Impairment of the hemostatic potential of platelets during storage as evaluated by flow cytometry, thrombin generation, and thrombelastography under conditions promoting formation of coated platelets

BACKGROUND: The increasing demand for platelet (PLT) transfusions has focused attention on appropriate use. Coated PLTs are a subpopulation of highly procoagulant PLTs formed by simultaneous stimulation by the agonists collagen and thrombin hypothesized to drive clot formation at the site of vascular injury. Prolonged storage of PLTs may reduce their ability to support optimal hemostasis upon transfusion.

Hemostatic and neuroprotective effects of human recombinant activated factor VII therapy after traumatic brain injury in pigs

Human recombinant activated factor-VII (rFVIIa) has been used successfully in the treatment of spontaneous intracerebral hemorrhage. In addition, there is increasing interest in its use to treat uncontrolled bleeding of other origins, including trauma. The aim of this study was to evaluate the safety and potential effectiveness of rFVIIa to mitigate bleeding using a clinically relevant model of traumatic brain injury (TBI) in the pig. A double injury model was chosen consisting of (1) an expanding cerebral contusion induced by the application of negative pressure to the exposed cortical surface and (2) a rapid rotational acceleration of the head to induce diffuse axonal injury (DAI). Injuries were performed on 10 anesthetized pigs. Five minutes after injury, 720 microg/kg rFVIIa (n=5) or vehicle control (n=5) was administered intravenously. Magnetic resonance imaging (MRI) studies were performed within 30 min and at 3 days post-TBI to determine the temporal expansion of the cerebral contusion. Euthanasia and histopathologic analysis were performed at day 3. This included observations for hippocampal neuronal degeneration, axonal pathology and microclot formation. The expansion of contusion volume over the 3 days post-injury period was reduced significantly in animals treated with rFVIIa compared to vehicle controls. Surprisingly, immunohistochemical analysis demonstrated that the number of dead/dying hippocampal neurons and axonal pathology was reduced substantially by rFVIIa treatment compared to vehicle. In addition, there was no difference in the extent of microthrombi between groups. rFVIIa treatment after TBI in the pig reduced expansion of hemorrhagic cerebral contusion volume without exacerbating the severity of microclot formation. Finally, rFVIIa treatment provided a surprising neuroprotective effect by reducing hippocampal neuron degeneration as well as the extent of DAI.

Differential clot stabilising effects of rFVIIa and rFXIII‐A2 in whole blood from thrombocytopenic patients and healthy volunteers

The haemostatic effect of recombinant activated factor VII (rFVIIa; NovoSeven®) in thrombocytopenic patients has been a matter of controversy. Haemostasis by rFVIIa occurs via FVIIa‐mediated thrombin generation in a platelet‐dependent manner and may therefore be suboptimal in patients without functional platelets. Under such conditions, a clot‐stabilizing agent, such as factor XIII (FXIII), may supplement the effect of rFVIIa and improve haemostasis. Recombinant factor XIII (rFXIII‐A2) is produced as an A2 homodimer of the FXIII A subunit and is equivalent to cellular FXIII normally found in platelets. The combined effects of rFVIIa and rFXIII‐A2 were evaluated in clot lysis assays using factor XIII‐deficient plasma and by whole blood thrombelastography (TEG) analysis from normal donors and thrombocytopenic stem cell transplantation patients. Clotting time was shortened by rFVIIa (0·6–10 μg/ml). rFVIIa only modestly improved anti‐fibrinolysis, whereas rFXIII‐A2 (0–20 μg/ml) enhanced anti‐fibrinolysis without effect on clotting time. TEG analysis showed rFVIIa shortened the clotting time, and enhanced clot development, maximal mechanical strength and resistance to fibrinolysis, whereas, rFXIII‐A2 enhanced clot development, maximal mechanical strength and markedly enhanced resistance to fibrinolysis. These data illustrate that rFVIIa and rFXIII‐A2 contribute to clot formation and stability by different mechanisms suggesting enhanced haemostatic efficacy by combining these agents.

Preclinical trauma studies of recombinant factor VIIa.

Preclinical studies in animals and ex vivo human blood have provided a solid rationale for conducting prospective randomized trials in trauma patients. Small animal models have been utilized to study the efficacy of recombinant activated factor VII (rFVIIa; NovoSeven®) in treating thrombocytopenic rabbits and for the reversal of anticoagulation. Safety models in the rabbit also exist to test for systemic activation of clotting and pathologic thrombosis. Animal models simulating traumatic injuries in humans have primarily been performed in pigs because of species similarities in terms of coagulation characteristics and the larger internal organs. The pig studies, utilizing human rFVIIa, have shown increased strength of clot formation, decreased bleeding, and improved survival. However, these findings are not uniform and are dependant on the model chosen. All of the animal models described have provided good safety data and suggest that the use of rFVIIa is not associated with systemic activation of coagulation or microthrombosis of end organs.