Oxygen free radicals induce de novo synthesis of tissue factor (TF), the initiator of the extrinsic pathway of coagulation, within the coronary vasculature during postischemic reperfusion. In the present study we wanted to assess whether TF expression might cause myocardial injury during postischemic reperfusion. Anesthetized rabbits underwent 30 min of coronary occlusion followed by 5.5 h of reperfusion. At reperfusion the animals received 1) saline (n = 8), 2) human recombinant, active site-blocked activated factor VII (FVIIai, 1 mg/kg, n = 8), or 3) human recombinant activated FVII (FVIIa, 1 mg/kg, n = 8). FVIIai binds to TF as native FVII, but with the active site blocked it inhibits TF procoagulant activity. The area at risk of infarction (AR), the infarct size (IS), and the no-reflow area (NR) were determined at the end of the experiment. FVIIai resulted in a significant reduction in IS and NR with respect to control animals (28.1 +/- 11.3 and 11.1 +/- 6.1% of AR vs. 59.8 +/- 12.8 and 24.4 +/- 2.7% of AR, respectively, P < 0.01), whereas FVIIa resulted in a significant increase in IS and NR to 80.1 +/- 13. 1 and 61.9 +/- 13.8% of AR, respectively (P < 0.01). In conclusion, TF-mediated activation of the extrinsic coagulation pathway makes an important contribution to myocardial injury during postischemic reperfusion.

After surgery in haemophilia, haemostasis is difficult to maintain in the presence of an antifactor VIII antibody. This study assessed the pharmacokinetics of recombinant activated factor VII (rFVIIa) and its efficacy in securing post-operative haemostasis in haemophiliacs with inhibitors. Continuous infusion of rFVIIa was evaluated for elective major orthopaedic surgery in nine patients with neutralizing antibodies to FVIII and at high risk of bleeding. After an initial preoperative bolus of 90 micro g/kg, rFVIIa was infused at a fixed rate of 50 micro g/kg/h for a median of 20 d (range 7-20 d). The median plasma FVII coagulant activity (FVII:C) at 24 h, 72 h and 20 d after surgery was 38 IU/ml (range 22-169 IU/ml), 45 IU/ml (range 17-88 IU/ml) and 31 IU/ml (range 27-46 IU/ml) respectively. The median plasma FVIIa:C at the same time points was 51 (range 24-211), 63 (range 22-99) and 44 (range 28-76) IU/ml respectively. Median total rFVIIa clearance remained stable during the rFVIIa continuous infusion period and was 40 (range 9-70), 34 (range 17-86) and 48 (range 32-55)ml/kg/h at the end of 24 h, 72 h and 20 d infusion respectively. Post-operatively, there were bleeds in six patients, which settled readily after a single bolus of rFVIIa (60 micro g/kg). There was a good clinical outcome for all patients. These data indicate that rFVIIa infusion at 50 micro g/kg/h achieves continuous plasma FVII procoagulant activity in excess of 30 IU/ml (12-15 nmol/l) and provides adequate haemostatic control for inhibitor patients during major orthopaedic surgery.

A multicenter prospective study of recombinant activated factor VII (rFVIIa) given by continuous infusion (CI) to treat severe hemorrhages and to handle surgical procedures was carried out. Relations between clinical efficacy, dosages used and levels of FVII coagulant activity (FVII:C) achieved in plasma were also evaluated. Case material included 25 patients with hemophilia (9 children and 16 adults) with high-responding inhibitors and 3 patients with acquired factor VIII inhibitors. Overall, 35 CI courses were given for 10 spontaneous bleeding episodes, 11 major surgical procedures and 14 minor surgical procedures. Bolus doses of 90 to 150 microg/kg (median: 100) were followed by CI given at median rates of 20 microg/kg/h for major surgery and of 17 and 16 microg/kg/h for minor surgery and spontaneous hemorrhages. Satisfactory hemostasis was obtained in 30 of 35 courses (88%). rFVIIa CI was ineffective in 2 hemophiliacs undergoing surgical operations and in another hemophiliac with hemoperitoneum who had to be switched to other treatments (high doses of porcine or human factor VIII concentrates). rFVIIa CI was partially effective in 2 hemophiliacs who had mild local bleeding after minor surgery. The CI rates and the corresponding FVII:C levels in plasma were similar in effective, partially effective and ineffective courses (median rate: 17, 20 and 20 microg/kg/h, respectively; median FVII:C:14, 18 and 18 IU/ml, respectively). A single adverse event was observed, superficial thrombophlebitis. This study confirms that rFVIIa given by CI is effective in a high proportion of patients with factor VIII inhibitors. It also demonstrates that FVII:C levels attained in plasma do not always predict efficacy because similarly high levels were attained during successful treatments and in those that failed.

Factor VII (FVII) is a zymogen for a vitamin K-dependent serine protease essential for the initiation of blood coagulation. It is synthesized primarily in the liver and circulates in plasma at a concentration of approximately 0.5 microg/ml (10 nmol/L). The FVII gene (F7) is located on chromosome 13 (13q34), consists of 9 exons, and spans approximately 12kb. It encodes a mature protein of 406 amino acids, which has an N-terminal domain (Gla) post-translationally modified by gamma-carboxylation of glutamic acid residues, two domains with homology to epidermal growth factor (EGF1 and 2), and a C-terminal serine protease domain. The single chain zymogen is activated by proteolytic cleavage at Arg152-Ile153. There are 238 individuals described in the world literature with mutations in their F7 genes (FVII mutation database; europium.csc. mrc.ac.uk). Complete absence of FVII activity in plasma is usually incompatible with life, and individuals die shortly after birth due to severe hemorrhage. The majority of individuals with mutations in their F7 gene(s), however, are either asymptomatic or the clinical phenotype is unknown. In general, a severe bleeding phenotype is only observed in individuals homozygous for a mutation in their F7 genes with FVII activities (FVII:C) below 2% of normal, however, a considerable proportion of individuals with a mild-moderate bleeding phenotype have similar FVII:C by in vitro assay. The failure of in vitro tests to differentiate between these groups may be due to lack of sensitivity in the assays to the very low amounts of FVII:C, which are sufficient to initiate coagulation in vivo. A number of polymorphisms have been identified in the F7 gene and some have been shown to influence plasma FVII antigen levels.

For hemophilia patients with inhibitors against FVIII or FIX, the development of recombinant factor VIIa (rFVIIa) raises the possibility of a therapeutic alternative whose availability and convenience of treatment are comparable to those of FVIII or FIX. In support of this new concept for the treatment of bleeding episodes, pharmacological doses of FVIIa have been shown to induce hemostasis. Pharmacological doses of rFVIIa enhance thrombin generation on thrombin-activated platelets, thereby facilitating the formation of strong, well-structured fibrin plugs resistant to premature proteolysis. Modified rFVIIa molecules with a stronger hemostatic potential have been produced. Inhibition of the FVII-TF-dependent pathway (TFPI and rFVIIai) has been tried in attempts to prevent thrombosis, with promising results in animal models so far not confirmed in clinical trials.

The intensity of warfarin therapy for prevention of primary and secondary thromboembolic complications in paediatric patients, is extrapolated from guidelines for adults, which may not be optimal. Therefore, we assessed thrombin regulation ex vivo and in vitro in plasmas from 40 children (1 to 18 years old with a median age of 13 years) and 27 adults receiving warfarin with an international normalized ratio of 2 to 3 (child: 2.5 +/- 0.15; adult: 2.4 +/- 0.14). Ex vivo concentrations of prothrombin fragment 1.2 were significantly lower in children (0.30 +/- 0.03 nM) compared to adults (0.45 +/- 0.04 nM; p <0.01). Thrombin generation in defibrinated plasmas (Arvin) was decreased and delayed for children compared to adults when activated by either activated partial thromboplastin time (child = 32 +/- 1.7, adult = 45 +/- 1.9 microM x s) or prothrombin time (child = 35 +/- 0.7, adult = 46 +/- 1.0 microM x s) reagents (p <0.01 for both). Although plasma concentrations of factors (F) II, FVII, FIX, F X, protein C and protein S were similar, more of the thrombin generated was complexed to alpha2 macroglobulin (alpha2M) at times close to peak thrombin activity (60 s) in plasma from children (general linear analysis of variance; p <0.03). Thus, increased alpha2M levels may enhance thrombin regulation in paediatric compared to adult patients receiving warfarin, suggesting that clinical trials in children, using less intense warfarin treatment, may be required to determine optimum therapy.

The intake of long-chain n-3 PUFA, including DHA (22 : 6n-3), is associated with a reduced risk of CVD. Schizochytrium sp. are an important primary source of DHA in the marine food chain but they also provide substantial quantities of the n-6 PUFA docosapentaenoic acid (22 : 5n-6; DPA). The effect of this oil on cardiovascular risk factors was evaluated using a double-blind randomised placebo-controlled parallel-design trial in thirty-nine men and forty women. Subjects received 4 g oil/d for 4 weeks; the active treatment provided 1.5 g DHA and 0.6 g DPA. Active treatment increased plasma concentrations of arachidonic acid, adrenic acid, DPA and DHA by 21, 11, 11 and 88 mg/l respectively and the proportions of DPA and DHA in erythrocyte phospholipids by 78 and 27 % respectively. Serum total, LDL- and HDL-cholesterol increased by 0.33 mmol/l (7.3 %), 0.26 mmol/l (10.4 %) and 0.14 mmol/l (9.0 %) compared with placebo (all P < or =0.001). Factor VII (FVII) coagulant activity increased by 12 % following active treatment (P = 0.006). There were no significant differences between treatments in LDL size, blood pressure, plasma glucose, serum C-reactive protein, plasma FVII antigen, FVII activated, fibrinogen, von Willebrand factor, tocopherol or carotenoid concentrations, plasminogen activator inhibitor-1, creatine kinase or troponin-I activities, haematology or liver function tests or self-reported adverse effects. Overall, the oil was well tolerated and did not adversely affect cardiovascular risk.

Congenital factor VII (FVII) deficiency is a rare bleeding disorder with high phenotypic variability, and optimal management has yet to be determined. Treatment has traditionally involved FVII replacement therapy using fresh frozen plasma, prothrombin complex concentrates or plasma-derived FVII concentrates. Recombinant activated FVII (rFVIIa, NovoSeven(R)), the first recombinant treatment option, has recently been approved in the European Union for use in congenital FVII deficiency, but has been available on an emergency and compassionate use basis since 1988. In FVII deficiency, rFVIIa serves as substitution therapy as it provides the physiological ligand (FVIIa) for tissue factor, its receptor exposed at the site of vascular injury. This paper provides an overview of published and unpublished experience with rFVIIa in patients with congenital FVII deficiency from the NovoSeven compassionate and emergency use programmes (1988-99) and of independent reports in the literature. Recombinant FVIIa has been reported to provide effective haemostasis in patients of all ages and in a range of bleeding situations, including acute central nervous system/life-threatening bleeding episodes (15 episodes in 12 patients), non-life-threatening bleeding episodes (>32 episodes in 17 patients), surgery (>40 interventions in 25 patients) and childbirth (three women). Preliminary reports suggest that it may also be effective prophylactically. The risk of thrombosis in FVII-deficient patients treated with rFVIIa is unknown, as is the occurrence of inhibiting antibodies. A postlicensure pharmacovigilance registry (Seven Treatment Evaluation Registry) has been set up to continue to monitor the efficacy and safety (including alloantibody development) of rFVIIa in patients with FVII deficiency.

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.

BACKGROUND

Plaque disruption and exposure of subendothelial procoagulants such as tissue factor (TF) to circulating factor VII/VIIa (FVII/VIIa) lead to intravascular thrombosis. Tissue factor pathway inhibitor (TFPI) is an endogenous inhibitor of TF-induced coagulation that binds to factor Xa and the TF-FVIIa catalytic complex in a two-step process. The aim of this study was to determine the expression of TFPI within human atherosclerotic plaque and its role in modulation of TF activity.

RESULTS

We measured the level of TFPI antigen in human carotid plaque and determined the relationship between TFPI and TF activity within plaque. Furthermore, we examined the biological activity and immunolocalization patterns of TFPI within carotid plaque. TFPI was detectable (TFPI+ group) in 22 of 34 specimens (mean+/-SEM, 404. 4+/-91.8 pg/mg) and undetectable (TFPI- group) in 12 of 34 specimens. In the TFPI- group, normalized TF activity was significantly greater than that in the TFPI+ group (0.28+/-0.04 vs 0.14+/-0.02 U/pg, P=0.002). Furthermore, neutralization of TFPI activity using a polyclonal antibody resulted in an 8-fold increase in TF activity in the TFPI+ group (P=0.001) but had no effect in the TFPI- group. Immunostaining for TFPI showed localization to endothelial cells, vascular smooth muscle cells within the fibrous cap region of the plaque, and macrophages within the shoulder region of the plaque.

CONCLUSIONS

Taken together, these data suggest that biologically active TFPI is present within human atherosclerotic plaque and is associated with attenuated TF activity.

Haemostasis is initiated by the complex formed by TF and FVIIa present in the blood (1% of the FVII protein). Recombinant FVIIa, which is active only after having formed complex with TF exposed following tissue damage, has been demonstrated to induce haemostasis in haemophilia patients with life- and limb-threatening bleedings with an efficacy rate of 76-84% in patients having failed on other treatment. Several had proven septicaemia but only one patient developed consumption coagulaopathy during extensive surgical manipulation and removal of myonecrotic tissue. No antibody formation against FVII has been seen in haemophilia patients. In 13 major surgical episodes complete intra- and post-operative haemostasis was achieved. rFVIIa has been used successfully in FVII-deficient patients and has been found to normalise the PT in patients with liver disease and in warfarin treated individuals. Single patients with platelet defects and with vWillebrand's disease type 3 achieved haemostasis with rFVIIa.

BACKGROUND

There is increasing international interest in producing components from blood that has been stored at room temperature for 24 hours. The lack of comprehensive data on the quality of plasma produced from blood stored in this way led to this international study.

METHODS

A total of 128 units of whole blood were pooled in groups of four and split to produce 32 sets of four identical blood units that were processed either within 8 hours of blood collection or after 24-hour storage at 18 to 25°C.

RESULTS

Storage of whole blood for 24 hours resulted in a 23% decrease in the activity of Factor (F)VIII, but not significant loss of activity of coagulation factors FV, FVII, FXI, FXII, fibrinogen, antithrombin, or von Willebrand factor. There was a small, but significant decrease in levels of FII, FIX, and FX (all <5%) as well as protein C (6%) and free protein S activity (14%). The ability of plasma to generate thrombin after 24-hour storage as whole blood was unaltered, as assessed by real-time thrombin generation tests as was the rate and strength of clot formation by rotational thombelastometry. Levels of all coagulation factors measured were above 0.50 U/mL in plasma produced from whole blood stored for 24 hours.

CONCLUSIONS

These data show that there is minimal effect of storing whole blood at ambient temperature for 24 hours on the coagulation activity of plasma and that this is an acceptable alternative to producing plasma on the day of blood collection.

Factor VII (FVII) deficiency is a rare haemorrhagic condition, normally inherited as an autosomal recessive trait, in which clinical presentation is highly variable and correlates poorly with laboratory phenotype. The FVII (F7) gene was sequenced in 48 unrelated individuals with FVII deficiency, yielding a total of 23 novel lesions including 15 missense mutations, 2 micro-deletions, 5 splice junction mutations and a single base-pair substitution in the 5' untranslated region. Family studies were performed in order to distinguish the contributions of individual mutant F7 alleles to the clinical and laboratory phenotypes. Specific missense mutations were evaluated by molecular modelling in the context of the FVIIa-tissue factor crystal structure. Single base-pair substitutions in splice sites and the 5' untranslated region were studied by in vitro splicing assay and luciferase reporter gene assay, respectively. All probands were also typed for four previously reported F7 polymorphisms. In the majority of cases of FVII deficiency studied here, consideration of both mutational and polymorphism data permitted the derivation of plausible explanations for the FVII activity and antigen levels measured in the laboratory. Inter-familial variation in FVII activity and the antigen levels of heterozygous relatives of probands was found to be significantly higher than intra-familial variation, consistent with the view that the nature of the F7 gene lesion(s) segregating in a given family is a prime determinant of laboratory phenotype. Although no relationship could be discerned between laboratory phenotype and polymorphism genotype, the frequencies of the A2 and M2 polymorphic alleles were significantly higher in the FVII-deficient individuals tested than in controls. This suggests that the presence of these alleles may have served to increase the likelihood of pathological F7 gene lesions coming to clinical attention.

Localization of human quantitative trait loci (QTLs) is now routine. However, identifying their functional DNA variants is still a formidable challenge. We present a complete dissection of a human QTL using novel statistical techniques to infer the most likely functional polymorphisms of a QTL that influence plasma levels of clotting factor VII (FVII), a risk factor for cardiovascular disease. Resequencing of 15 kb in and around the F7 gene identified 49 polymorphisms, which were then genotyped in 398 people. Using a Bayesian quantitative trait nucleotide (BQTN) method, we identified four to seven functional variants that completely account for this QTL. These variants include both rare coding variants and more common, potentially regulatory polymorphisms in intronic and promoter regions.

A series of coagulation parameters and lipoprotein(a) (Lp(a)) were explored in plasma from 40 patients with central retinal vein occlusion (CRVO, non-ischemic type n = 12; ischemic type n = 28) free of local and systemic predisposing factors, 1 to 12 months after the acute event. Forty age- and sex-matched patients with cataract served as controls. Prothrombin fragment 1.2 (F1.2), D-dimer, FVII:C--but not FVII:Ag--were higher and fibrinogen was lower in CRVO patients than in controls. Patients with non-ischemic CRVO had higher F1.2 and FVII:C and lower heparin cofactor II than patients with ischemic CRVO. Lp(a) levels greater than 300 mg/l were observed in 12 patients with CRVO and in 4 controls (30% vs 10%, p < 0.025). Patients with high Lp(a)--consistently associated with the S2 phenotype--had higher FVII:C, FVII:C/Ag ratio, and fibrinogen than the remaining CRVO patients. Plasma F1.2 and D-dimer correlated fairly in controls (r = 0.41) and patients with normal Lp(a) levels (r = 0.55), but they did not in the group of patients with high Lp(a) (r = 0.19), where the latter parameter was negatively related to D-dimer (r = -0.55). There was no dependence of the abnormalities observed on the time elapsed from vein occlusion. The findings of activated FVII and high F1.2, D-dimer, and Lp(a) are not uncommon in patients with CRVO. Increased thrombin formation with fibrin deposition and impaired fibrinolysis may play a role in the pathophysiology of CRVO and require specific treatment.

To assess the role of genetic variation in determining factor VII (FVII) activity and antigen levels we studied a polymorphism located in the 5' region of the gene (5'F7), an intronic mutation (IVS7), and the 353Arg-Gln polymorphism. All the polymorphisms, which showed strong allelic association, analyzed separately or in combination by the one-way analysis of variance, were associated with significantly different FVII levels. The 5'F7 and 353Arg-Gln polymorphic systems, which have very similar allele frequencies, contributed to a similar extent to the total phenotypic variance, whereas the contribution of the IVS7 polymorphism was lower. Genetic variation at the FVII locus, evaluated on combined genotypes, accounted for up to 40% of the phenotype FVII variance. As also shown by the two-way analysis of variance, the use of two out of three markers is advisable, and since the 5'F7 polymorphism can be screened by a simple immunoassay, it should be preferred for population-based studies. No substantial differences between FVII activity and FVII antigen levels were found, thus suggesting that the variation was due to biosynthesis- or stability-mediated mechanisms. The genetic control of FVII levels described in this study plays an important role in determining plasma FVII level variability, which may influence the hemostatic balance.

After the first observations about blood coagulation by Hippocrates, it took until the early 1900s before the classic theory of blood coagulation was presented. As more and more other coagulation factors were discovered, the four-factor coagulation scheme became more complex, but better understood, leading to the current coagulation cascade. As during the last decade it turned out that coagulation factors might do more than just promoting (or inhibiting) blood coagulation, new scientific avenues were pursued focusing on coagulation-independent properties of individual coagulation factors. This led to the current understanding that coagulation factors, like tissue factor (TF), FVII, FX, and thrombin, are important players in inflammation, vascular development, angiogenesis, and tumorigenesis. However, the molecular mechanism by which coagulation factors exert their pleiotropic effects in pathophysiology remains one of the major challenges in the field. This overview presents current insight in how the main coagulation factors might induce inflammation.

Factor (F)VII deficiency is an autosomal recessive disorder for which a replacement therapy is not universally available; recombinant FVIIa has been utilized as a therapeutic substitute. As FVII competes with FVIIa for binding to tissue factor in initiating the extrinsic pathway of blood coagulation, a lower dose of FVIIa replacement in cross-reacting material-negative (CRM-) individuals can achieve hemostasis. Three coagulation models (computational, synthetic and in vitro whole blood) were used to predict the FVIIa levels needed to provide apparent hemostasis in a non-bleeding state. Our whole blood results show that a 'normalized' coagulation profile for FVII-deficient individuals has an initiation phase that ends at 5.8 +/- 0.5 min (clot time) and the propagation phase of thrombin generation (thrombin-antithrombin III) yields a maximum concentration of 380 +/- 29 nmol L(-1). When CRM- FVII-deficient subjects were infused with a prophylactic dose of 23 micro g kg(-1) of recombinant FVIIa, 6-8 h postinfusion resulted in a comparable normalized whole blood profile. This FVIIa concentration (0.3-0.7 nmol L(-1)/equivalent dose: 0.8-1.8 micro g kg(-1)) is approximately 1/10 that currently used in treating FVII-deficient individuals and suggests that therapies should be altered relative to the concentration of the FVII zymogen.

BACKGROUND

Inherited factor (F)VII deficiency is the commonest of the rare bleeding disorders, with a wide set of hemorrhagic features. Other than for the severe clinical forms (for which treatment guidelines are well defined), consistent recommendations regarding perioperative replacement management do not exist for mild and asymptomatic FVII-deficient patients.

OBJECTIVE

The present study aimed to evaluate the influence of bleeding history, FVII procoagulant activity levels (FVII:C) and the type of surgical procedure on the management of inherited FVII-deficient patients before surgery.

METHODS

One hundred and fifty-seven surgical procedures, performed without replacement therapy, in 83 unrelated FVII-deficient patients (median FVII:C=5%, range 0.6%-35%) were analyzed.

RESULTS

The overall bleeding rate was 15.3%. We found a significant relationship between previous deep traumatic hematomas and bleeding at surgery, although relationships with previous common epistaxis, easy bruising and menorrhagia were not significant. The receiver-operating characteristic (ROC) curve analysis performed on the first 83 procedures allowed us to define a cut-off value of 7% with a sensitivity of 87% (negative predictive value: 94%). To enhance the sensitivity, and to take into account the potential variation resulting from non-standardized FVII:C measurements, we would suggest applying a threshold of 10%.

CONCLUSIONS

We have proposed recommendations for the perioperative management of FVII-deficient patients based on FVII:C levels, a thorough bleeding history and the type of surgery involved. By applying these recommendations, minor procedures that risk only external or controlled hemorrhage can be performed in asymptomatic or mildly affected adults, even those with FVII:C levels below 10%.

An activity detected in a prothrombin complex concentrate, termed 'thrombin-like' due to its amidolytic properties, was recently reported by another working group. This serine-protease revealed partial structural homology with a 'hepatocyte growth factor activator'. An impact of this protease on coagulation has not yet been described. The protease was isolated from plasma fractions by ion exchange chromatography and adsorption to immobilized heparin and/or aprotinin. Clotting tests including the FVIIa-rTF assay were performed employing coagulometry. A monoclonal antibody-derived F(ab')2 to FVIII was used to investigate the FVIII bypassing activity (FEIBA). The identity of the-protease with the so-called 'thrombin-like' protease was supported by sequencing of the amino-termini. Its amidolytic activity was significantly enhanced in the presence of calcium and/or heparin. Incubation with purified FVII revealed the generation of FVIIa, but was prevented by pre-incubation of the protease with aprotinin. In contrast, purified FV and FVIII were inactivated. Studying coagulation parameters, clotting times like plasma recalcification times and the prothrombin times were found to be shortened by addition of the protease. Employing a FVIII-inhibitory F(ab')2 and enhancing clotting times significantly, FEIBA of the protease was found. We demonstrated that the isolated protease activates FVII independent of tissue factor. Net acceleration of coagulation was found in several global clotting assays resulting in an in vitro FEIBA. The physiological relevance of these findings deserves further investigation.

Tissue factor (TF), an integral membrane protein, is the cofactor for the serine protease, coagulation factor VIIa (FVIIa). Previous studies of the isolated extracellular domain of TF (sTF) reported a kcat for factor X (FX) activation by the sTF.VIIa complex only 4% that of wild-type TF.VIIa and furthermore, a complete inability of sTF to support FVII autoactivation. We now report that in the presence of poly(L-lysine), sTF promoted both FX activation and FVII autoactivation, the latter with an apparent second-order rate constant higher than reported previously for wild-type TF in phospholipid vesicles. This led us to reexamine the cofactor ability of sTF, using high concentrations of phospholipid to promote nearly quantitative binding of sTF.VII(a) complexes to the phospholipid surface. Rate constants for the activation of FX or FVII by sTF.VIIa were similar to those of wild-type TF.VIIa, indicating that the apparent deficiency of sTF is largely attributable to kinetic consequences of relatively weak affinity of FVIIa (and sTF.VIIa) for phospholipid surfaces in these surface-dependent reactions, compared with TF being embedded in the membrane. This supports the notion that sTF recapitulates the protein-protein interactions of wild-type TF with high, and possibly full, catalytic activity. It also provides a biochemical explanation for the specificity of our recently described, sTF-based clotting assay for plasma FVIIa.

In the last decade, the endothelial cell protein C/activated protein C receptor (EPCR) has received considerable attention. The role initially attributed to EPCR, i.e. the enhancement of protein C (PC) activation by the thrombin-thrombomodulin complex on the surface of the large vessels, although important, did not go beyond the haemostasis scenario. However, the discovery of the cytoprotective, anti-inflammatory and anti-apoptotic features of the activated PC (APC) and the required involvement of EPCR for APC to exert such actions did place the receptor in a privileged position in the crosstalk between coagulation and inflammation. The last five years have shown that PC/APC are not the only molecules able to interact with EPCR. Factor VII/VIIa (FVII/VIIa) and factor Xa (FXa), two other serine proteases that play a central role in haemostasis and are also involved in signalling processes influencing wound healing, tissue remodelling, inflammation or metastasis, have been reported to bind to EPCR. These observations have paved the way for an exploration of unsuspected new roles for the receptor. This review aims to offer a new image of EPCR in the light of its extended panel of ligands. A brief update of what is known about the APC-evoked EPCR-dependent cell signalling mechanisms is provided, but special care has been taken to assemble all the information available about the interaction of EPCR with FVII/VIIa and FXa.

Rare bleeding disorders (RBDs) are autosomal recessive diseases including the inherited deficiencies of coagulation factors such as fibrinogen, factor (F) II, FV, FV + FVIII, FVII, FX, FXI, FXIII, and multiple deficiency of vitamin K-dependent factors, with clinical manifestations ranging from mild to severe. They represent 3 to 5% of all the inherited coagulation deficiencies with a prevalence in the general population varying between 1 in 500,000 and 1 in 2 million, being higher in areas where consanguineous marriages are diffuse. Despite the progress made in past years, as a consequence of the rarity of these deficiencies, the type and severity of bleeding symptoms, the underlying molecular defects, the actual management of bleeding episodes and particularly the prophylactic treatment in patients affected with RBDs are not well established. In this introductory article, the main features, diagnosis, available treatment options, and treatment complications of RBDs will be discussed.

The blood coagulation cascade is initiated when vessel injury allows factor VII (FVII) to form a complex with tissue factor (TF). Complete deficiency of FVII causes a lethal bleeding diathesis, but individuals with moderately reduced FVII levels are often asymptomatic. Some of these individuals have circulating partially functional FVII, as a result of point missense mutations in critical parts of the molecule. One such mutation has been reported at position 79 in the first epidermal growth factor-like (EGF) domain of FVII, where an arginine residue has been replaced by glutamine. There is controversy as to whether or not this mutation reduces the affinity of the FVII/TF interaction compared to wild-type FVII. To address this problem, we have expressed recombinant FVII-R79Q and subjected it to detailed biochemical analysis. One-stage FVII:C assays show the variant FVII to have reduced activity with respect to the wild type. Rates of autoactivation and activation by FXa to the two-chain molecule were identical for wild-type and variant FVII. The Vmax for FX activation was lower for the mutant as measured using an amidolytic assay for FX activity. In contrast, the Km for FX was lower for the variant than the wild-type molecule. Peptidyl substrate hydrolysis was virtually identical for both variant and normal FVIIa in the presence and absence of TF. The variant has reduced affinity for TF as measured by surface plasmon resonance. FVII-R79Q has an association rate constant (kassoc) one-fifth of that of normal FVII, but a similar kdiss, resulting in a decrease in the affinity of the enzyme for its cofactor.(ABSTRACT TRUNCATED AT 250 WORDS)