Search PubMed⌕ Search

Biomedical subjects

U Hedner

Publications and source records attributed to U Hedner.

At least 19 recordsLinked to original sources
PubMed2006

Activity and regulation of factor VIIa analogs with increased potency at the endothelial cell surface.

BACKGROUND: Variants of recombinant factor VIIa (rFVIIa) with increased intrinsic activity have been developed to improve efficacy in the treatment of bleeding disorders in the future. The increased potency of FVIIa variants was demonstrated in limited in vitro and in vivo studies. However, further characterization of FVIIa variants is needed to evaluate their potential clinical use. METHODS: In the present study, we investigated the interactions of two FVIIa variants, FVIIa(Q) and FVIIa(DVQ), with plasma inhibitors, tissue factor pathway inhibitor (TFPI) and antithrombin (AT), and vascular endothelium. TF-FVIIa activity or its inhibition was measured directly in an amidolytic activity assay or for its ability to activate factor X. RESULTS: Both TFPI and AT/heparin inhibited the FVIIa variants more rapidly than the wild-type (WT) FVIIa in the absence of tissue factor (TF). In the presence of TF, TFPI, TFPI-Xa, and AT/heparin inhibited FVIIa and FVIIa variants at similar rates. Although the WT FVIIa failed to generate significant amounts of FXa on unperturbed endothelial cells, FVIIa variants, particularly FVIIa(DVQ), generated a substantial amount of FXa on unperturbed endothelium. Annexin V fully attenuated the FVIIa-mediated activation of FX on unperturbed endothelial cells. On stimulated human umbilical vein endothelial cells, FVIIa and FVIIa variants activated FX at similar rates, and annexin V blocked the activation only partly. AT/heparin and TFPI-Xa inhibited the activity of FVIIa and FVIIa variants bound to endothelial cell TF in a similar fashion. Interestingly, despite significant differences observed in FXa generation on unperturbed endothelium exposed to FVIIa and FVIIa analogs, no differences were found in thrombin generation when cells were exposed to FVIIa or FVIIa analogs under plasma mimicking conditions. CONCLUSION: Overall, the present data suggest that although FVIIa variants generate substantial amounts of FXa, they do not generate excessive thrombin on the surface of endothelium.

Annexin A5↗
PubMed2005

Differential expression of tissue factor (TF) in calcineurin inhibitor-induced nephrotoxicity and rejection--implications for development of a possible diagnostic marker.

Deposition of fibrin in the form of fibrinoid necrosis is a common feature of severe acute renal allograft rejection. The role of the coagulation system and its initiator tissue factor (TF) during this process is, however, still poorly understood. In this study, we analyzed the expression of TF in 88 renal transplants afflicted with different forms of rejection and calcineurin inhibitor-induced nephrotoxicity, to see whether there was differential expression of this protein. TF immunoreactivity was evaluated semiquantitatively in six different renal structures: the podocytes, Bowman epithelium, the endothelium of the glomeruli, the brush border of tubular cells, the thin ascending loop of Henle, and small arteries/arterioles. The TF expression of normal renal tissue (n=6) was restricted to the glomerular podocytes and Bowman epithelium, and to some extent the ascending loop of Henle. Renal allografts undergoing acute rejection (AR) of grades I-III, (n=13, n=17 and n=12, respectively) did not show any altered TF expression in the glomeruli or vascular endothelium. In the ascending loop of Henle, a reduced expression could be seen (ARI, p=0.015; and ARII, p=0.043). TF staining of the brush border of renal transplants undergoing acute cyclosporin A (CsA) nephrotoxicity (n=18) was significantly higher than in normal kidneys (p=0.0003), as well as in transplants undergoing various degrees of acute rejection (ARI, p=0.027; ARII, p=0.0012; and ARIII, p=0.0001). Tubular brush border-expressed TF was also evident in 10 of 15 allografts suffering from chronic CsA nephrotoxicity, compared to 4 out of 13 cases with chronic allograft vasculopathy (CAV), but the increase was not statistically significant relative to normal kidneys. The majority of the grafts afflicted with either of the two chronic conditions displayed a TF-positive arterial endothelium (CAV, p=0.0034; and chronic CsA nephrotoxicity, p=0.0026) relative to controls. In conclusion, these results indicate that vascular TF expression is not altered during acute rejection, but may be of importance in chronic allograft nephropathy. Furthermore, TF immunoreactivity in the tubular brush border may be specific to acute CsA nephrotoxicity and might be used as a biomarker for this condition. Further studies are required to evaluate the possible role of brush border-expressed TF in the pathogenesis of CsA nephrotoxicity.

Acute Disease↗
PubMed2005

The effect of platelets on fibrin gel structure formed in the presence of recombinant factor VIIa in hemophilia plasma and in plasma from a patient with Glanzmann thrombasthenia.

Fibrin gel structure has been shown to be dependent on the thrombin concentration as well as the rate of thrombin generation. Accordingly, factor VIII (FVIII)- and FIX-deficient plasma (hemophilia A and B) form loose fibrin clots with high permeability constants. By adding rFVIIa in vitro to FVIII-deficient plasma containing platelets (frozen and thawed), the fibrin gel permeability constant normalized, indicating that extra rFVIIa (1.2 microg mL(-1) or higher) induced a tight fibrin structure. Thrombin generation is highly dependent on the number of platelets, and in this study it was demonstrated that the addition of rFVIIa (5 microg mL(-1)) normalizes the fibrin gel permeability in samples containing platelets (frozen-thawed) in numbers of at least down to 20 x 10(6) mL(-1). The effect of rFVIIa was not observed when unfrozen platelets instead of frozen-thawed platelets were added. Neither was any effect on the fibrin permeability seen, in the presence of annexin V, known to block the effect of phospholipids on the platelet surface. This indicates an important role of platelet phospholipids for the effect of rFVIIa. A similar effect on the fibrin permeability of rFVIIa was observed when added to platelet-rich plasma from a patient with Glanzmann thrombasthenia. Recombinant FVIIa has been found to induce hemostasis in patients with hemophilia and inhibitors against FVIII/FIX as well as in patients with Glanzmann thrombasthenia, indicating the importance of the formation of a tight fibrin gel structure, more resistant against premature proteolysis, for maintaining hemostasis. In conclusion, the addition of rFVIIa (5 microg mL(-1)) also substantially decreased the permeability constant of fibrin gels formed in FVIII-deficient plasma in the presence of low numbers of frozen-thawed platelets (down to 20 x 10(6) mL(-1)). A similar pattern was obtained in plasma from a Glanzmann patient. No effect was found in the presence of unfrozen instead of frozen-thawed platelets. Annexin V blocked any effect of rFVIIa. A normalization of the overall fibrinolysis potential (OFP) during the same condition supports the effect of rFVIIa on the fibrin permeability in the presence of a limited number of platelets.

Adult↗
PubMed2003

Assessment of recombinant factor VIIa as an antidote for bleeding induced in the rabbit by low molecular weight heparin.

While protamine sulfate reverses the anticoagulant effect of standard heparin, there currently is no effective antidote for low molecular weight heparin (LMWH)-induced bleeding. Recently, recombinant activated factor VII (rFVIIa) was approved by the FDA for use in hemophilia patients with factor (F)VIII or FIX inhibitors. However, this new pro-hemostatic agent has potential utility in other clinical scenarios. In this study, we utilized a well-characterized rabbit ear puncture model to test the efficacy of rFVIIa to reverse LMWH-induced prolonged bleeding. Animals were first treated with bolus intravenous LMWH (1800 anti-FXa U kg(-1)) which increased the primary bleeding time approximately fourfold and raised the plasma anti-FXa activity immediately and continuously throughout the 90-min experiment. In a randomized and blinded fashion, animals then received either rFVIIa (400 microg kg(-1)) or placebo by bolus intravenous injection, following which the ear puncture bleeding times were measured, along with blood levels of heparin (anti-FXa activity) and FVII. FVII activity increased 5.3-fold over baseline in treated animals, decreasing by only 24% over the full observation period. The rFVIIa-treated animals showed a slight decrease in bleeding time immediately after injection, but there was no statistically significant difference in bleeding after rFVIIa or placebo administration. In this study using a rabbit ear bleeding model, rFVIIa was not an effective antidote to LMWH-induced bleeding. However, the bolus injection of LMWH produced a very high blood anti-FXa level, which may have precluded rFVIIa effectiveness.

Animals↗
PubMed2003

The role of recombinant factor VIIa (FVIIa) in fibrin structure in the absence of FVIII/FIX.

Patients with hemophilia have an impaired thrombin generation and therefore form loose fibrin hemostatic plugs that are easily dissolved by fibrinolysis. This prevents maintained hemostasis in these patients, resulting in a severe bleeding disorder. Recombinant (F)VIIa has been shown to enhance thrombin generation on already thrombin-activated platelets in the absence of FVIII and FIX. An efficacy rate of 80-90% has been found in hemophilia patients with inhibitors against FVIII or FIX both in association with major surgery and in the treatment of serious bleedings. In a model measuring fibrin clot permeability in a platelet-containing system described by Blombäck et al. (1994) this was demonstrated to be dependent on the concentration of FVIII and FIX. The addition of rFVIIa in concentrations of 1.9, 4.8 and 9.6 microg mL(-1) normalized fibrin clot permeability. The concentration of 1.9 microg mL(-1) of rFVIIa normalized clot permeability in this system and the higher concentrations of rFVIIa added only slightly to the effect. No further decrease in clot permeability was found when rFVIIa in a concentration of 1.9 microg mL(-1) was added to a sample with a normal concentration (100%) of FVIII or FIX. Higher concentrations of rFVIIa added to the plasma containing 100% of FVIII or FIX induced only a slight further decrease of fibrin permeability constant, arguing against any unwanted effect of extra rFVIIa on clot permeability in the case of a normal hemostasis. Furthermore, the fibrin network was studied with 3D microscopy and the loose network found in the absence of FVIII or FIX increased in density with increasing FVIII or FIX concentrations. The addition of rFVIIa to FVIII- or FIX-deficient systems altered the network structure, making the fibers thinner and more tightly packed.

Blood Coagulation↗
PubMed2002

Acquired factor VII deficiency in hematopoietic stem cell transplant recipients.

Acquired factor VII (FVII) deficiency in the absence of vitamin K deficiency, oral anticoagulant therapy, synthetic liver dysfunction, or DIC is rare, with only a handful of cases thus far reported. In the period from 1990 to 1996 we identified eight patients with acquired FVII deficiency, all of whom presented with prolongation of the prothrombin time (PT) in the first 2 weeks following stem cell transplantation (SCT). The mean plasma FVII clotting activity (FVII:c) was 22% (range 8-35%) with an approximately equivalent reduction in FVII antigen (FVII:Ag) level. Mean plasma levels of fibrinogen and factors II, V, IX, and X were normal. Protein C activity was significantly depressed in only one of the three patients in whom it was measured. Several patients experienced bleeding complications, and hemorrhage directly accounted for death in two cases. Veno-occlusive disease of the liver developed in three patients. We conclude that FVII deficiency should be considered in the differential diagnosis of prolonged PT in patients who have recently undergone SCT. The mechanism of this acquired deficiency state remains to be defined.

Adult↗
PubMed2001

Anti- and procoagulant activities in factor VII-deficient subjects.

The clinical feature in patients with congenital factor VII deficiency is in part dependent on the underlying genetic defect, but the mechanisms influencing the genotype-phenotype correlation remain to be fully elucidated. In addition, thromboembolic events have been reported. Compensatory mechanisms involving vitamin K-dependent factors have been suggested. We have measured anticoagulant activities in 25 factor VII-deficient subjects (factor VII activity < or =36%) and 23 age-matched controls and correlated these to the vitamin K-dependent procoagulant activities. Two of the patients had a history of thromboembolism. The factor VII-deficient patients were found to have a significantly lower protein C activity than the controls [0.84 U/ml (95% CI 0.78; 0.89) vs. 0.98 U/ml (95% CI 0.91; 1.05), P=.004]. In addition, the protein C activity was correlated to that of factor VII (r=.36; P=.014), factor IX (r=.45; P=.002) and factor X (r=.50; P=.0006), respectively. The level of prothrombin fragment 1+2 was correlated to the protein C (r=.40; P=.012) and to the factor VII activity (r=.42; P=.011). No differences between patients and controls were seen regarding total and free protein S, antithrombin, plasminogen activator inhibitor-1 (PAI-1) and tissue factor pathway inhibitor (TFPI). Seven of the patients were found to have the Factor V Leiden mutation, but none of them had experienced any thromboembolic event. The present data support the notion that compensatory hemostatic mechanisms might exist in that the protein C activity was found to be decreased in the factor VII-deficient subjects. Whether this could influence the clinical feature, including the risk of thromboembolic events in association with replacement therapy, remains to be evaluated.

Activated Protein C Resistance↗
PubMed2001

Effect of recombinant factor VIIa (Novoseven) on thrombocytopenia-like conditions in vitro.

Recombinant factor VIIa (rFVIIa; NovoSeven, Novo Nordisk, Copenhagen, Denmark) may help to promote hemostasis in patients with thrombocytopenia. We used two in vitro models of thrombin generation to evaluate this effect. The reconstituted model contained tissue factor (TF)-expressing monocytes, unactivated platelets, isolated plasma coagulation proteins, and calcium. Platelet activation and thrombin generation were measured in timed aliquots. In the plasma-based model, thrombin generation was measured continuously after the addition of lipidated TF and calcium to platelet-rich plasma using a slowly cleaved fluorescent substrate. Thrombocytopenic conditions were mimicked by decreasing the platelet density. In both systems, a platelet density-dependent lowering of the thrombin-generation peak was observed. Addition of rFVIIa to samples with low platelet density (6700 to 10000/microL) increased the initial thrombin generation in both systems without normalizing thrombin-generation curves. The magnitude of the rFVIIa effect was most pronounced in the plasma-based model. Platelet activation was not significantly delayed at low platelet density in the reconstituted model. Addition of rFVIIa to samples with low platelet density caused faster platelet activation, most likely as a consequence of the increased initial thrombin generation. The data suggest that rFVIIa may help to achieve hemostasis at low platelet densities by increasing the initial thrombin generation, thereby compensating for low platelet number.

Blood Platelets↗
PubMed2001

Recombinant factor VIIa (Novoseven) as a hemostatic agent.

Recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Denmark) induces hemostasis in life- and limb-threatening bleeds and in major surgery of hemophilia A and B patients, regardless of inhibitor titer. A total of more than 6,500 patients have been treated, and NovoSeven has been administered in more than 180,000 standard doses. Experience gained from these clinical situations suggests that NovoSeven should be administered as a 90- to 110-microg/kg bolus dose every second hour. Hemophilia patients with mild to moderate bleeding episodes require two to three doses to achieve complete hemostasis, whereas patients with severe bleeding episodes may require more doses. For major surgery and in cases of life-threatening bleeding, dosing every second hour for the first 24 hours may be required. Thereafter, the same dose, but with longer intervals between doses, is recommended. Recent in vitro experiments indicate that even higher doses of NovoSeven may be needed to achieve full thrombin generation in the absence of factor VIII (FVIII), factor IX (FIX), and factor XI (FXI).

Blood Protein Disorders↗
PubMed2001

Initial inhibition of tissue factor signalling reduces chronic vascular changes in isogenic rat aortic transplants.

Vascular changes are considered the major histopathological indicator of chronic allograft dysfunction. These changes are characterized by intimal thickening caused by accumulation of primarily smooth muscle cells. Contributing factors may be of both immunological and nonimmunological origin. Cold ischemia has been shown to trigger intimal proliferation in the absence of alloantigen in an isogenic rat aortic transplant model. We have used this model to investigate the impact of inhibition of tissue factor (TF) signalling on the progression of intimal thickening. Group 1 was treated with recombinant FVIIa inhibited in its active site (rFVIIai), and group 2 served as untreated controls. At 8 weeks the intimal area was measured with image analysis. Medial areas and the proportion of medial necrosis were determined. Animals treated with rFVIIai showed significantly less intimal thickening compared with controls: median 0.147 vs. 0.256 mm2, respectively (p = 0.008). A positive correlation between intimal hyperplasia and medial necrosis (r(s) = 0.79, p = 0.01), as well as adventitial inflammation (r(s) = 0.83, p = 0.009), was found. TF mRNA was not detected in the neointima at 8 weeks, as determined by in situ hybridization. We conclude that active site inhibited FVIIa (rFVIIai) given prior to and directly after implantation of aortic transplants significantly reduces intimal hyperplasia caused by nonimmunological factors in this model.

Animals↗
PubMed2001

High-dose factor VIIa increases initial thrombin generation and mediates faster platelet activation in thrombocytopenia-like conditions in a cell-based model system.

Clinical experience has shown that high doses of recombinant factor VIIa (rFVIIa) may ensure haemostasis in thrombocytopenic patients. We have used a cell-based model system to mimic thrombocytopenia and analyse the effect of rFVIIa. Lowering the platelet density from 200 x 10(9)/l (reflecting normal conditions) to 100, 50, 20 and 10 x 10(9)/l revealed a platelet density-dependent decrease in the maximal rate of thrombin generation, a prolongation in the time to maximal thrombin activity and a lower maximal level of thrombin formed. The platelet activation, measured as the time to half-maximal P-selectin (CD62) exposure, was not significantly dependent on the platelet density in the range of 200 x 10(9)/l to 10 x 10(9)/l, although there was a tendency for slower platelet activation at 20 x 10(9) and 10 x 10(9) platelets/l than at the higher platelet densities. Addition of 50--500 nmol/l rFVIIa to samples with 20 x 10(9) or 10 x 10(9) platelets/l shortened the lag phase of thrombin generation as well as the time to half-maximal platelet activation. Our data indicate that high doses of rFVIIa may help to provide haemostasis in thrombocytopenic patients by increasing the initial thrombin generation, resulting in faster platelet activation and thereby compensating for the lower number of platelets present.

Cells, Cultured↗
PubMed2001

Rationale for the use of high dose rFVIIa in a high-titre inhibitor patient with haemophilia B during major orthopaedic procedures.

Inhibitor development is a serious complication in patients with haemophilia A and B. Historically, a lack of optimal therapies and factor products for treating inhibitor patients resulted in many patients developing chronic haemophilic arthropathies and flexion contractures of the involved joints. The introduction of immune-tolerance protocols to eradicate high-titre inhibitors has greatly diminished the incidence of these types of complications but as in the case reported here, immune tolerance is not always successful. Various elective surgical procedures were often delayed or not even considered in patients with inhibitor because of the variability in achieving adequate haemostasis and the thrombotic risks involved with the use of activated prothrombin-complex concentrates (APCCs) over extended periods of time. The development of recombinant factor VIIa (rFVIIa; NovoSeven) and its demonstrated safety and efficacy in treating inhibitor patients has opened new possibilities for addressing severe arthropathy with flexion contracture. This case report demonstrates that the use of rFVIIa in such a situation must include dosing flexibility that is both patient-specific and related to the potential for bleeding; the ability to maintain clinical haemostasis with a prophylactic dose of rFVIIa given as little as once daily; and the capacity for higher doses of rFVIIa, particularly in children because their kinetic profiles differ from adults.

Adolescent↗
PubMed2001

Active site-inactivated factor VIIa prevents thrombosis without increased surgical bleeding: topical and intravenous administration in a rat model of deep arterial injury.

PURPOSE: The primary event in the procoagulant response after vascular interventions is the tissue factor (TF)-factor VIIa complex formation, which occurs when TF is exposed to the circulating blood by the inflicted trauma. Human recombinant active site-inhibited coagulation factor VIIa (FFR-rFVIIa) binds well to TF but cannot initiate blood coagulation, and should thereby block thrombus formation. This hypothesis was tested with a rat model of arterial thrombosis. METHODS: In a blinded randomized study, the antithrombotic and antihemostatic effects of FFR-rFVIIa and heparin were evaluated in a rat model of mechanical deep arterial injury. In one arm of the study, FFR-rFVIIa (0.2 mg in 150 microL) or vehicle alone was applied topically at the site of vascular injury. In the other arm, FFR-rFVIIa (4 mg/kg), heparin (1 mg/kg), or vehicle alone was injected intravenously. RESULTS: FFR-rFVIIa produced a powerful antithrombotic effect after both topical and intravenous administrations (P =.02 and P =.005, respectively) without increasing the surgical bleeding. Heparin prevented thrombosis equally well as FFR-rFVIIa (P =.0007), but doubled the surgical bleeding compared with FFR-rFVIIa (P =.03) and controls (P =.008). In the topical study, the antithrombotic effect was achieved without altering parameters of plasma anticoagulation (prothrombin time and activated partial thromboplastin time) or producing detectable levels of FFR-rFVIIa in plasma. CONCLUSION: In this model FFR-rFVIIa effectively inhibits thrombus formation without the expense of increased surgical bleeding, which indicates the potential of FFR-rFVIIa as an effective and safe strategy for prevention of thrombosis in reconstructive vascular surgery and various forms of percutaneous revascularization.

Administration, Topical↗
PubMed2001

Expression of factor VII in the liver of patients with liver disease: correlations with the disease severity and impairment in the hemostasis.

Factor VII (FVII) plasma levels in patients with liver disease may be below the normal range. However, no data are available on FVII expression in liver biopsies from patients with liver diseases other than cirrhosis. We have analyzed the expression of FVII by in situ hybridization in liver biopsies from 50 patients in comparison with the procoagulant activity of FVII, and with the plasma levels as activated FVII (FVIIa) and FVII antigen. The level of FVIIa was significantly lower in stage 4 liver fibrosis patients than in the remaining ones (P < 0.05). The percentage of hepatocytes expressing FVII was significantly lower in stage 4 liver fibrosis patients (4.1+/-1.3%) than in stage 3 (22.7+/-6.1%), stage 2 (31.5+/-6.1%), stage 1 (43.7+/-8.2%) and stage 0 patients (63.8+/-4.4%) (P < 0.001). These percentages correlated inversely in a statistically significant way with the histological activity index and the liver function tests. We have demonstrated that the FVIIa plasma levels in patients with chronic liver disease other than cirrhosis may be below the normal range in the absence of blood coagulation impairment. The percentage of hepatocytes expressing FVII decreases as the severity of liver damage increases.

Adult↗
PubMed2001

Intravenous rFVIIa administered for hemorrhage control in hypothermic coagulopathic swine with grade V liver injuries.

BACKGROUND: Intravenous administration of recombinant activated human clotting factor VII (rFVIIa) has been used successfully to prevent bleeding in hemophilia patients undergoing elective surgery, but not in previously normal trauma patients. This study was conducted to determine whether rFVIIa was a useful adjunct to gauze packing for decreasing blood loss from grade V liver injuries in hypothermic and coagulopathic swine. METHODS: All animals (n = 10, 35 +/- 2 kg) underwent a 60% isovolemic exchange transfusion with 6% hydroxyethyl starch and were cooled to 33 degrees C core temperature. The swine then received a grade V liver injury and 30 seconds later, either 180 microg/kg rFVIIa, or saline control. All animals were gauze packed 30 seconds after injury and resuscitated 5.5 minutes after injury with lactated Ringer's solution to their preinjury mean arterial pressure. Posttreatment blood loss, mean arterial pressure, resuscitation volume, and clotting studies were monitored for 1 hour. Histology of lung, kidney, and small bowel were obtained to evaluate for the presence of microvascular thrombi. RESULTS: At the time of injury, core temperature was 33.3 degrees +/- 0.4 degrees C, hemoglobin was 6 +/- 0.7 g/dL, prothrombin time was 19.1 +/- 1.0 seconds, activated partial thromboplastin time was 29.0 +/- 4.8 seconds, fibrinogen was 91 +/- 20 mg/dL, and platelets were 221 +/- 57 x 105/mL, with no differences between groups (p > 0.05). Clotting factor levels confirmed a coagulopathy at the preinjury point. The posttreatment blood loss was less (p < 0.05) in group 1 (527 +/- 323 mL), than in group 2 (976 +/- 573 mL). The resuscitation volume was not different (p > 0.05). One-hour survival in both groups was 100%. Compared with the control group, rFVIIa increased the circulating levels of VIIa and, despite hypothermia, shortened the prothrombin time 5 minutes after injection (p < 0.05). Laboratory evaluation revealed no systemic activation of the clotting cascade. Postmortem evaluation revealed no evidence of large clots in the hepatic veins or inferior vena cava, or microscopic thrombi in lung, kidney, or small intestine. CONCLUSION: rFVIIa reduced blood loss and restored abnormal coagulation function when used in conjunction with liver packing in hypothermic and coagulopathic swine. No adverse effects were identified.

Animals↗