Factor V Leiden improves in vivo hemostasis in murine hemophilia models

The role of factor V Leiden (FVL) as a modifier of the severe hemophilia phenotype is still unclear. We used mice with hemophilia A or B crossed with FVL to elucidate in vivo parameters of hemostasis. Real-time thrombus formation in the microcirculation was monitored by deposition of labeled platelets upon laser-induced endothelial injury using widefield microscopy in living animals. No thrombi formed in hemophilic A or B mice following vascular injuries. However, hemophilic mice, either heterozygous or homozygous for FVL, formed clots at all injured sites. Injection of purified activated FV into hemophilic A or B mice could mimic the in vivo effect of FVL. In contrast to these responses to a laser injury in a microvascular bed, FVL did not provide sustained hemostasis following damage of large vessels in a ferric chloride carotid artery injury model, despite of the improvement of clotting times and high circulating thrombin levels. Together these data provide evidence that FVL has the ability to improve the hemophilia A or B phenotype, but this effect is principally evident at the microcirculation level following a particular vascular injury. Our observations may partly explain the heterogeneous clinical evidence of the beneficial role of FVL in hemophilia.

Specific detection of human coagulation factor IX in cynomolgus macaques

After screening for species-specific antihuman factor (F)IX monoclonal antibodies, we found that antibody 3A6 did not bind to cynomolgus FIX. The 3A6 epitope was found to include Ala262 of human FIX. The 3A6 antibody was used as a catching antibody in an enzyme immunoassay (EIA) for specific detection of human FIX in cynomolgus macaque plasma. No significant increase of substrate hydrolysis was observed when EIA buffer containing cynomolgus macaque plasma was subjected to the 3A6-based EIA. Addition of up to 30% cynomolgus macaque plasma or canine plasma to the assay did not alter detection of human FIX. Three cynomolgus macaques were injected with human FIX (10 U kg-1; i.v.) and the circulating human FIX was quantified in the macaque plasma. The FIX level in the circulation increased to 470 +/- 37.6 ng mL-1 at 1 h after the injection and gradually decreased to 1.79 +/- 1.1 ng mL-1 by day 5, which is approximately 0.06% of the normal human plasma FIX concentration. These data suggest that the cynomolgus macaque can be used as a primate model for studying hemophilia B gene therapy by transduction of macaque organs with vectors to express human FIX in vivo and detection of human FIX using the 3A6 monoclonal antibody.

A protocol for the dental management of von Willebrand's disease, haemophilia A and haemophilia B

A guide for the dental management of the three inherited bleeding disorders, von Willebrand's disease, haemophilia A and haemophilia B, was established jointly by the Institute of Medical and Veterinary Science Transfusion and Haemostasis Unit in conjunction with the Medically Compromised Dental Unit at the Adelaide Dental Hospital. This protocol was subjected to a successful trial for 24 months.

Polycythaemia vera and Christmas disease with slightly prolonged prothrombin time

A family is reported in which Christmas disease in one member and polycythaemia in another were associated with prolongations of the one-stage prothrombin time of the factor-VII deficiency type. Changes in the prothrombin time were present in the siblings of the case of Christmas disease and in a number of unrelated cases of polycythaemia vera. The use of "mixing procedures" did not reveal any significant mutual correction of the changes in prothrombin time.

Diagnostic difficulties in mild haemophilia and Christmas disease

Two cases of haemorrhagic diathesis are described, where the laboratory diagnosis was confused owing to previous blood transfusions. Without the help of investigating the relatives, the nephew of Case 1, the haemophiliac, and the uncle of Case 2, with Christmas disease, there would have been considerable delay in reaching the diagnosis and so instituting the correct treatment.

Covalent fixation of soluble derivatized dextrans to model proteins in low-concentration medium: application to factor IX and protein C

Factor IX and protein C are zymogens implicated in blood clotting, and an increase in their plasmatic residence time would be of interest for the treatment of the disorders caused by their deficiency. In this context, the conjugation of these proteins to polymers such as modified dextrans could be used to approach the problem. Conjugate formation in concentrated medium ([protein] >50 g/L) is well documented, whereas drastic dilution ([protein] <1 g/L) is quite unfavorable. Before studying the binding of factor IX and protein C to polymers, the coupling of model proteins (human hemoglobin, Hb; human serum albumin, HSA) in low-concentration medium to benzenetetracarboxylate dextran (BTC-dextran) and dialdehyde dextran was investigated. To obtain soluble benzenetetracarboxylate dextran-based conjugates, the conditions of coupling were optimized; the use of sulfo-NHS was necessary to form a conjugate with benzenetetracarboxylate dextran. In fact, the O-acylurea intermediate formed between coupling agent [1-ethyl-3(3-dimethylaminopropyl) carbodiimide, EDC] and BTC-dextran must be stabilized. Concerning dialdehyde dextran, a more oxidized polymer and a higher pH of the buffer of coupling than for highly concentrated solution must be used to obtain a conjugate. Whatever polymer is used, HSA appeared clearly less reactive than Hb, which can be attributed to the better reactivity of N-terminal amino groups in this latter protein and to the marked affinity of benzenetetracarboxylate dextran for it. No soluble conjugate was formed between the same dextran derivatives and factor IX or protein C. Moreover, the activity of both coagulation factors was dramatically decreased by contact with EDC and glutaraldehyde, a small molecule. Thus, bad accessibility of protein amino groups is probably responsible for this lack of reactivity. Nevertheless, it could be shown that carboxylate and amino groups were essential to the activity of factor IX and protein C.

A coagulation factor IX-deficient mouse model for human hemophilia B

Coagulation factor IX deficiency causes hemophilia B in humans. We have used gene targeting to develop a coagulation factor IX-deficient (factor IX-knockout) mouse strain. Mouse embryonic stem (ES) cells were targeted by a socket-containing vector that replaces the promoter through exon 3 of the factor IX gene by neoDeltaHPRT, which is a functional neo gene plus a partially deleted hypoxanthine phosphoribosyl transferase minigene. Chimeric mice generated using these socket-containing ES cells transmitted the targeted factor IX gene to their female offspring. Male offspring from these females were characterized and shown to exhibit a phenotype similar to hemophilia B. This factor IX-deficient mouse strain will be useful for studying gene therapy methods and structure-function relationships of recombinant factor IX proteins in vivo.

PARTIAL THROMBOPLASTIN TIME TEST WITH KAOLIN. NORMAL RANGE AND MODIFICATIONS FOR THE DIAGNOSIS OF HAEMOPHILIA AND CHRISTMAS DISEASE

The partial thromboplastin time test provides a convenient and sensitive screening procedure for deficiencies of thromboplastic factors, especially factors VIII and IX. The test is carried out after preincubating the plasma for 10 minutes with kaolin, and Inosithin is used as a platelet substitute. The ;normal range' of the test has been estimated in terms of the differences encountered between random normal plasmas tested in pairs, because individual patients are usually tested against single control subjects. A patient's partial thromboplastin time should be regarded as abnormal if it is more than six seconds longer than the control time. In the diagnosis of haemophilia, patients' plasmas with concentrations of factor VIII as low as about 20% might be regarded as being within the range of normal, if the selected control subject's factor VIII happened to lie near the lower end of the normal range. When mild haemophilia is suspected, discrimination may be improved by diluting both the patient's and the control plasmas 1 in 20 in haemophilic plasma. With the test modified in this way the clotting time is prolonged, though the range of differences among normal subjects is unaltered, and plasmas with factor VIII concentrations below about 30%, i.e., in undiluted plasma, would be unlikely to be regarded as normal. The partial thromboplastin time may be similarly modified as a screening test for factor IX deficiency.Some clinical examples are reported.

The factor IX gene as a model for analysis of human germline mutations: an update

The variation generated by germline mutation is essential for evolution, but individuals pay a steep price in the form of Mendelian disease and genetic predisposition to complex disease. Indeed, the health of a species is determined ultimately by the rate of germline mutation. Analysis of the factor IX gene in patients with hemophilia B has provided insights into the human germline mutational process. Herein, seven topics will be reviewed with emphasis on recent advances: (i) proposed mechanisms of deletions, inversions, and insertions; (ii) discordant sex ratios of mutation and associated age effects; (iii) somatic mosaicism; (iv) founder effects; (v) mutation rates; (vi) the factor IX gene as a germline mutagen test; and (vii) cancer as a possible mechanism for maintaining a constant rate of germline mutation.

X-ray structure of clotting factor IXa: active site and module structure related to Xase activity and hemophilia B

Hereditary deficiency of factor IXa (fIXa), a key enzyme in blood coagulation, causes hemophilia B, a severe X chromosome-linked bleeding disorder afflicting 1 in 30,000 males; clinical studies have identified nearly 500 deleterious variants. The x-ray structure of porcine fIXa described here shows the atomic origins of the disease, while the spatial distribution of mutation sites suggests a structural model for factor X activation by phospholipid-bound fIXa and cofactor VIIIa. The 3.0-A-resolution diffraction data clearly show the structures of the serine proteinase module and the two preceding epidermal growth factor (EGF)-like modules; the N-terminal Gla module is partially disordered. The catalytic module, with covalent inhibitor D-Phe-1I-Pro-2I-Arg-3I chloromethyl ketone, most closely resembles fXa but differs significantly at several positions. Particularly noteworthy is the strained conformation of Glu-388, a residue strictly conserved in known fIXa sequences but conserved as Gly among other trypsin-like serine proteinases. Flexibility apparent in electron density together with modeling studies suggests that this may cause incomplete active site formation, even after zymogen, and hence the low catalytic activity of fIXa. The principal axes of the oblong EGF-like domains define an angle of 110 degrees, stabilized by a strictly conserved and fIX-specific interdomain salt bridge. The disorder of the Gla module, whose hydrophobic helix is apparent in electron density, can be attributed to the absence of calcium in the crystals; we have modeled the Gla module in its calcium form by using prothrombin fragment 1. The arched module arrangement agrees with fluorescence energy transfer experiments. Most hemophilic mutation sites of surface fIX residues occur on the concave surface of the bent molecule and suggest a plausible model for the membrane-bound ternary fIXa-FVIIIa-fX complex structure: fIXa and an equivalently arranged fX arch across an underlying fVIIIa subdomain from opposite sides; the stabilizing fVIIIa interactions force the catalytic modules together, completing fIXa active site formation and catalytic enhancement.

Recent advances in the management of patients with haemophilia and other bleeding disorders

Much attention has been focused recently on barriers to dental care, particularly for patients with disabilities, from the perspective of the patient and the dental team. Treatment of patients with haemorrhagic disorders may cause a certain amount of anxiety in dental staff. The authors of this paper aim to reduce this anxiety by clarifying confusion between the haemorrhagic disorders and making recommendations concerning the dental care of such patients.

Protein engineering of the propeptide of human factor IX

Vitamin-K-dependent plasma proteins contain a highly conserved propeptide sequence located between the classical hydrophobic leader sequence and the N-terminus of the mature protein. This acts as a recognition sequence for the vitamin-K-dependent carboxylase which catalyses the conversion of specific glutamate residues to gamma-carboxyglutamate (Gla) residues in the adjacent Gla domain. Protein engineering of the 18 residue propeptide from human factor IX has highlighted the importance of residues -16Phe and -10Ala with respect to carboxylase recognition. In addition, studies of haemophilia B patients have shown that C-terminal propeptide residues -4Arg and -1Arg are required for proteolysis of the propeptide from the mature protein. To extend these previous studies we have introduced two novel mutations into the propeptide of human factor IX at positions -17(Val----Asp) and -6(Leu----AsP), and studied the effect of these changes on gamma-carboxylation and proteolytic processing. Both mutations reduce the expression of a calcium-dependent epitope in the Gla domain; however, only -6Leu----Asp shows reduced binding to barium sulphate. In addition, this latter mutation prevents proteolytic processing of the propeptide. These data support the current hypothesis that the propeptide contains two recognition elements: one for carboxylase recognition located towards the N-terminus, and one for propeptidase recognition located near the C-terminus.