Eva H. N. Olsen

A novel B-domain O-glycoPEGylated FVIII (N8-GP) demonstrates full efficacy and prolonged effect in hemophilic mice models

Frequent infusions of intravenous factor VIII (FVIII) are required to prevent bleeding associated with hemophilia A. To reduce the treatment burden, recombinant FVIII with a longer half-life was developed without changing the protein structure. FVIII-polyethylene glycol (PEG) conjugates were prepared using an enzymatic process coupling PEG (ranging from 10 to 80 kDa) selectively to a unique O-linked glycan in the FVIII B-domain. Binding to von Willebrand factor (VWF) was maintained for all conjugates. Upon cleavage by thrombin, the B-domain and the associated PEG were released, generating activated FVIII (FVIIIa) with the same primary structure and specific activity as native FVIIIa. In both FVIII- and VWF-deficient mice, the half-life was found to increase with the size of PEG. In vivo potency and efficacy of FVIII conjugated with a 40-kDa PEG (N8-GP) and unmodified FVIII were not different. N8-GP had a longer duration of effect in FVIII-deficient mouse models, approximately a twofold prolonged half-life in mice, rabbits, and cynomolgus monkeys; however, the prolongation was less pronounced in rats. Binding capacity of N8-GP on human monocyte-derived dendritic cells was reduced compared with unmodified FVIII, resulting in several-fold reduced cellular uptake. In conclusion, N8-GP has the potential to offer efficacious prevention and treatment of bleeds in hemophilia A at reduced dosing frequency.

Plasma elimination kinetics for factor VII are independent of its activation to factor VIIa and complex formation with plasma inhibitors.

The mechanism for the elimination of factor VII (FVII) from the circulation is unknown, just as it is unclear how activation of FVII to FVIIa and subsequent complex formation with antithrombin III (AT) or alpha2-macroglobulin (alpha2M) affects clearance. The possibility that the clearance mechanism involves activation and inhibitor complex formation as obligatory intermediate reactions is examined in this study. Human and murine sera were spiked with human FVIIa in the absence and presence of heparin and analysed for complex formation. Complex formation in vivo was studied after intravenous injection of (125)I-VIIa in mice; and the pharmacokinetics (PK) of human and murine FVIIa was studied in normal mice. Furthermore, comparative PK studies were performed with FVII, FVIIa, active site blocked FVIIa and a preformed FVIIa-AT complex in normal and alpha2M-deficient mice. The data demonstrated that FVIIa-AT complexes and to a much lesser extent FVIIa-alpha2M-complexes accumulated in vivo after FVIIa administration. FVIIa-AT accounted for about 50% of total FVIIa antigen left in the circulation after 3 hours. All FVII derivatives studied including FVII, FVIIa and FVIIa-AT were cleared with similar rates suggesting an elimination kinetics which is unaffected by FVII activation and subsequent inactivation by plasma inhibitors.

RECOMBINANT FACTOR XIII DIMINISHES MULTIPLE ORGAN DYSFUNCTION IN RATS CAUSED BY GUT ISCHEMIA-REPERFUSION INJURY

Plasma factor XIII (FXIII) is responsible for stabilization of fibrin clot at the final stage of blood coagulation. Because FXIII has also been shown to modulate inflammation and endothelial permeability, we hypothesized that FXIII diminishes multiple organ dysfunction caused by gut I/R injury. A model of superior mesenteric artery occlusion (SMAO) was used to induce gut I/R injury. Rats were subjected to 45-min SMAO or sham SMAO and treated with recombinant human FXIII A2 subunit (rFXIII) or placebo at the beginning of the reperfusion period. Lung permeability, lung and gut myeloperoxidase activity, gut histology, neutrophil respiratory burst, and microvascular blood flow in the liver and muscles were measured after a 3-h reperfusion period. The effect of activated rFXIII on transendothelial resistance of human umbilical vein endothelial cells was tested in vitro. Superior mesenteric artery occlusion-induced lung permeability as well as lung and gut myeloperoxidase activity was significantly lower in rFXIII-treated versus untreated animals. Similarly, rFXIII-treated rats had lower neutrophil respiratory burst activity and ileal mucosal injury. Rats treated with rFXIII also had higher liver microvascular blood flow compared with the placebo group. Superior mesenteric artery occlusion did not cause FXIII consumption during the study period. In vitro, activated rFXIII caused a dose-dependent increase in human umbilical vein endothelial cell monolayer resistance to thrombin-induced injury. Thus, administration of rFXIII diminishes SMAO-induced multiple organ dysfunction in rats, presumably by preservation of endothelial barrier function and the limitation of polymorphonuclear leukocyte activation.

Recombinant Factor XIII Mitigates Hemorrhagic Shock-Induced Organ Dysfunction

BACKGROUND Plasma factor XIII (FXIII) is responsible for stabilization of fibrin clot at the final stage of blood coagulation. Since FXIII has also been shown to modulate inflammation, endothelial permeability, as well as diminish multiple organ dysfunction (MOD) after gut ischemia-reperfusion injury, we hypothesized that FXIII would reduce MOD caused by trauma-hemorrhagic shock (THS). MATERIALS AND METHODS Rats were subjected to a 90 min THS or trauma sham shock (TSS) and treated with either recombinant human FXIII A(2) subunit (rFXIII) or placebo immediately after resuscitation with shed blood or at the end of the TSS period. Lung permeability, lung and gut myeloperoxidase (MPO) activity, gut histology, neutrophil respiratory burst, microvascular blood flow in the liver and muscles, and cytokine levels were measured 3 h after the THS or TSS. FXIII levels were measured before THS or TSS and after the 3-h post-shock period. RESULTS THS-induced lung permeability as well as lung and gut MPO activity was significantly lower in rFXIII-treated than in placebo-treated animals. Similarly, rFXIII-treated rats had lower neutrophil respiratory burst activity and less ileal mucosal injury. rFXIII-treated rats also had a higher liver microvascular blood flow compared with the placebo group. Cytokine response was more favorable in rFXIII-treated animals. Trauma-hemorrhagic shock did not cause a drop in FXIII activity during the study period. CONCLUSIONS Administration of rFXIII diminishes THS-induced MOD in rats, presumably by preservation of the gut barrier function, limitation of polymorphonuclear leukocyte (PMN) activation, and modulation of the cytokine response.

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.

Does recombinant factor XIII eliminate early manifestations of multiple-organ injury after experimental burn similarly to gut ischemia-reperfusion injury or trauma-hemorrhagic shock?

The authors have previously shown that recombinant factor XIII (rFXIII) eliminates early manifestations of multiple-organ injury caused by experimental superior mesenteric artery occlusion or trauma-hemorrhagic shock. The aim of the present study was to test the hypothesis that rFXIII provides similar protective effect in experimental burn injury. Rats were randomly divided into five groups (eight animals per group): group 1: burn + placebo treatment; group 2: burn + rFXIII pretreatment; group 3: burn + rFXIII treatment; group 4: sham burn + placebo treatment, and group 5: sham burn + rFXIII treatment. Burn (40% of TBSA) was achieved by immersing the back and abdomen of a rat into 97°C water for 10 and 5 seconds, respectively. Infusion of rFXIII (1 mg/kg) or placebo was performed immediately after burn/sham burn in treatment groups or 24 hours before burn and repeated immediately after it in pretreatment group. Endpoint parameters measured 3 hours after burn/sham burn included muscle blood flow and PO2, lung permeability, gut histology, lung and gut myeloperoxidase activity, neutrophil respiratory burst, and FXIII activity. Both treatment and pretreatment with rFXIII partially preserved microvascular blood flow in the muscle. Muscle PO2 in pretreated rats did not differ from that in shams. Pretreatment but not treatment with rFXIII preserved lung permeability. rFXIII did not have any protective effect on other endpoint parameters. In contrast to superior mesenteric artery occlusion and trauma-hemorrhagic shock experimental models, rFXIII at the doses tested has a limited effect on preventing early manifestations of multiple-organ injury after experimental burn.