Metabolism of rabbit plasma-derived factor VII in relation to prothrombin in rabbits

A novel compound heterozygous variant linked to hematuria in a family with hereditary factor VII deficiency

BACKGROUND

Hereditary Factor VII Deficiency (FVIID) is a rare congenital autosomal recessive bleeding disorder. In clinical manifestations, its onset is caused by variant of the F7 gene (NM_019616) with strong heterogeneity. We identified a family with hematuria caused by a novel F7 compound heterozygous variant and studied the FVIID-dependent mechanism impacted by these variants.

METHODS

Coagulation factors in the proband were functionally verified. We located pathogenic variants in relevant genes using next-generation sequencing after target enrichment and verified them by Sanger sequencing. We examined the coagulation activity and secretion pattern of recombinant FVII variants expressed in cells and observed their location and stability by immunofluorescence.

RESULTS

We found a missense variant c.1207G>A (p.Gly403Ser) and a frameshift variant c.154_155del (p.Arg53fs) in the F7 gene of the proband. FVII activity tests showed that the variants significantly decreased its presence in the cell culture supernatant. Moreover, the R53fs mutant lacked the FVII functional domain and had no detectable activity. Immunofluorescence indicated that the p.Gly403Ser variant was distributed to the cell membrane and cytoplasm, while the FVII R53fs variant was not detected. Deficient FVII protein function and severe coagulation disorder are the likely causes of hematuria and other bleeding symptoms in the proband.

CONCLUSION

The newly discovered F7 gene variants enrich the spectrum of hereditary FVII deficiency and provide a new foundation for the diagnosis and treatment of this type of coagulation disorder.

In vivo models of haemophilia - status on current knowledge of clinical phenotypes and therapeutic interventions

Animal models have contributed immensely to the understanding of and the improvement in treatment of haemophilia A and B. First, establishment of haemophilic dog colonies provided an invaluable opportunity to investigate the diseases and later, the advances in gene technologies resulting in small haemophilic animal models were a milestone in the preclinical research making it possible to address some of the many unanswered questions. This review provides an overview of animal models used in the study of haemophilia as well as a short overview of the contributions resulting from studies in these models.

Randomized, prospective clinical trial of recombinant factor VIIa for secondary prophylaxis in hemophilia patients with inhibitors

BACKGROUND

Hemophilic patients with factor VIII (FVIII) and FIX inhibitors suffer from frequent bleeding episodes and reduced quality of life.

OBJECTIVES

To evaluate whether secondary prophylaxis with activated recombinant factor VII (rFVIIa) can safely and effectively reduce bleeding frequency as compared to conventional on-demand therapy.

METHODS

Thirty-eight male patients entered a 3-month preprophylaxis period to confirm high baseline bleeding frequency (mean > or = 4 bleeds per month). Twenty-two patients were randomized 1:1 to receive daily rFVIIa prophylaxis with either 90 or 270 microg kg(-1) for 3 months, followed by a 3-month postprophylaxis period.

RESULTS

Bleeding frequency was reduced by 45% and 59% during prophylaxis with 90 and 270 microg kg(-1), respectively (P < 0.0001); however, there was no significant difference detected between doses. The majority of this reduction was maintained during the postprophylaxis period. Although all types of bleed were similarly reduced, the effect was most pronounced for spontaneous joint bleeds. Patients reported significantly fewer hospital admissions and days absent from work/school during prophylaxis as compared to the preprophylaxis period. No thromboembolic events were reported during prophylaxis.

CONCLUSION

Clinically relevant reductions in bleeding frequency during prophylaxis as compared to conventional on-demand therapy were achieved without raising safety concerns. These results provide evidence for the concept of secondary rFVIIa prophylaxis in inhibitor patients with frequent bleeds.

Tissue factor around dermal vessels has bound factor VII in the absence of injury

BACKGROUND

'Idling' or ongoing low-level activity of the tissue factor (TF) pathway is a postulated mechanism by which the coagulation process can become active without a lag period at sites of injury.

OBJECTIVE

To determine whether TF around cutaneous vessels has bound factor VIIa in the absence of injury, and thus could participate in the idling process.

METHODS

Immunostaining of mouse skin with antibodies against a 15-residue peptide from the sequence of mouse TF, and against the whole extracellular portion of TF.

RESULTS

The whole TF antibody recognized TF in squamous epithelium and around vessels in the dermis. By contrast, the monospecific antibody only recognized TF in the squamous epithelium, but not around vessels. We also found that biotinylated, active site-inhibited FVIIa (FVIIai) bound to tissue sections in the same areas in which TF was recognized by the monospecific antibody (squamous epithelium), but did not bind around vessels. Molecular modeling revealed that FVIIa and FX binding to TF masked a significant part of the surface of the target peptide.

CONCLUSIONS

In the aggregate, these data are most consistent with the interpretation that TF in perivascular sites has bound FVIIa, even in the absence of any injury. The presence of endogenously bound FVIIa prevents the subsequent binding of the monospecific antibody or exogenous FVIIai to perivascular TF.

Consumption of plasma factor VII in a rabbit model of non-overt disseminated intravascular coagulation

INTRODUCTION

We have recently described an experimental animal model of non-overt disseminated intravascular coagulation (DIC) in the rabbit in which the induction of tissue factor (TF) mRNA and TF antigen expression in peripheral blood leukocytes (PBL) was demonstrated to occur within 2 h of administration of low-dose endotoxin [Hematol. J. 2 (2001) 188]. In the present study, we demonstrate that the leukocyte TF expressed has procoagulant activity leading to a rapid decline in the concentration of factor VII (FVII) in rabbit plasma.

METHODS

Total plasma FVII antigen and FVIIa were quantitated by rabbit FVII-specific immunoassay and FVIIa-specific clotting assays, respectively. Plasma samples from either saline-injected rabbits or rabbits administered a single bolus of 10 microg/kg Salmonella lipopolysaccharide were compared over a 24-h period.

RESULTS

Total plasma FVII antigen decreased progressively post-endotoxin injection, reaching 71% of the baseline concentration at 8 h (p<0.001, n=18), and remained low (78%) at 24 h post-injection (p<0.01, n=16), returning to normal by 48 h. Plasma FVIIa levels increased to 120% within 2 h of endotoxin injection, fell to 73% of the baseline concentration at 8 h (p<0.05, n=18) and returned to normal by 24 h post-endotoxin administration. Procoagulant activity of rabbit peripheral blood leukocytes was enhanced at 2 h (p<0.01, n=6) and 4 h (p<0.05, n=6) post-endotoxin injection. The prothrombin time (PT) was increased by <3 s, and thrombin-antithrombin (TAT) complex formation was not significantly increased in the plasma of endotoxin-treated rabbits. No significant changes in total plasma FVII antigen, FVIIa or leukocyte procoagulant activity were observed in rabbits treated with saline.

CONCLUSIONS

We conclude that the activation of FVII to FVIIa and rapid consumption of total FVII/FVIIa occur very early and likely are integral events linked to the initiation and propagation of non-overt DIC induced by endotoxin.