Replacement of isoleucine-397 by threonine in the clotting proteinase factor IXa (Los Angeles and Long Beach variants) affects macromolecular catalysis but not L-tosylarginine methyl ester hydrolysis. Lack of correlation between the ox brain prothrombin time and the mutation site in the variant proteins

Evaluation of Nonacog Beta Pegol Long-term Safety in the Immune-deficient Rowett Nude Rat (Crl:NIH-Foxn1rnu)

Nonacog beta pegol is a 40-kDa polyethylene glycosylated (PEGylated) human recombinant coagulation factor IX, intended for the treatment of hemophilia B. Human coagulation factors are immunogenic in animals; therefore, to evaluate the long-term toxicity of nonacog beta pegol, an immune-deficient, athymic rat (Rowett nude; Crl:NIH-Foxn1(rnu)) was used. Rats (n = 216) were given intravenous nonacog beta pegol 0, 40, 150, 600, or 1,200 IU/kg every 5th day for 26 weeks. To avoid infections, the animals were housed in a full-barrier environment with sterilized food and bedding. Standard toxicity end points were unaffected by treatment. All treated animals were exposed to nonacog beta pegol throughout the study, and no animals developed antidrug antibodies. Immunohistochemical staining revealed PEG in choroid plexus epithelial cells in a dose-dependent manner. Transmission electron microscopy showed that PEG was distributed in cytoplasmic vesicles of these cells, with no apparent effect on cellular organelle structures. Fourteen (6.5%) animals were euthanized or died prematurely due to nontreatment-related infections in the urogenital system and skin. In conclusion, the athymic rat is a suitable model for testing chronic toxicity of human proteins that are immunogenic in animals. Nonacog beta pegol was generally well tolerated, with no adverse effect of PEG on choroid plexus epithelial cells.

Detailed characterization of an anti-factor IX monoclonal antibody that neutralizes the prolonged ox brain prothrombin time of hemophilia B(M) by synthetic peptides

In a previous study, we prepared a monoclonal antibody (MoAb) to coagulation factor IX (FIX), designated 65-10, which interfered with the activation of FIX by the activated factor XI/Ca(2+) and neutralized the prolonged ox brain prothrombin time of hemophilia B(M) [11,12]. The location of the epitope on the FIX for 65-10 MoAb is (168) Ile-Thr-Gln-Ser-Thr-Gln-Ser-Phe-Asn-Asp-Phe-Thr-Arg-Val-Val(182) [21]. In this paper, we studied in more detail an epitope on FIX using the systematic substitution of different amino acids at each residue of the epitope peptides and the influence of the epitope peptide on the prolonged ox brain prothrombin time of the hemophilia B(M) plasma of 65-10 MoAb. In the replacement set of amino acids, peptides showing low or no reactivity to 65-10 were (175)Phe --> Asp, Glu, Gly, Lys, Arg, Thr, Val, (176)Asn --> Asp, Glu, Phe, Ile, Lys, Leu, Pro, Val, Tyr, (177)Asp --> Cys, Glu, Phe, Ile, Lys, Leu, Met, Pro, Gln, Arg, Ser, Thr, Val, Trp, Tyr, and (178) Phe --> Pro. These results imply that a hydrophobic molecule of (175) Phe, a hydrophilic molecule of (176)Asn, and a negative charge molecule of (177)Asp were important to the epitope. The 65-10 MoAb antibody neutralized the prolonged ox brain prothrombin time of hemophilia B(M) Nagoya 2 ((180)Arg -->Trp) and Kashihara ((181)Val --> Phe) as well as B(M) Kiryu ((313)Val --> Asp) and Niigata ((390)Ala --> Val). This reaction was inhibited by preincubation with a (168) Ile-Thr-Gln-Ser-Thr-Gln-Ser-Phe-Asn-Asp-Phe-Thr-Arg-Val-Val(182) peptide conjugated with bovine serum albumin (BSA). 65-10 MoAb that has been useful in detailing epitopes will be useful for qualitative analysis of hemophilia B(M).

Protease and EGF1 domains of factor IXa play distinct roles in binding to factor VIIIa. Importance of helix 330 (helix 162 in chymotrypsin) of protease domain of factor IXa in its interaction with factor VIIIa

Previous studies revealed that cleavage at Arg-318-Ser-319 in the protease domain autolysis loop of factor IXa results in its diminished binding to factor VIIIa. Now, we have investigated the importance of adjacent surface-exposed helix 330-338 (162-170 in chymotrypsin numbering) of IXa in its interaction with VIIIa. IXWT, eight point mutants mostly based on hemophilia B patients, and a replacement mutant (IXhelixVII in which helix 330-338 is replaced by that of factor VII) were expressed, purified, and characterized. Each mutant was activated normally by VIIa-tissue factor-Ca2+ or XIa-Ca2+. However, in both the presence and absence of phospholipid, interaction of each activated mutant with VIIIa was impaired. The role of IXa EGF1 domain in binding to VIIIa was also examined. Two mutants (IXQ50P and IXPCEGF1, in which EGF1 domain is replaced by that of protein C) were used. Strikingly, interactions of the activated EGF1 mutants with VIIIa were impaired only in the presence of phospholipid. We conclude that helix 330 in IXa provides a critical binding site for VIIIa and that the EGF1 domain in this context primarily serves to correctly position the protease domain above the phospholipid surface for optimal interaction with VIIIa.

Changing residue 338 in human factor IX from arginine to alanine causes an increase in catalytic activity

This study was designed to identify functionally important factor IX (FIX) residues. Using recombinant techniques and cell culture, we produced a mutant FIX with arginine at 338 changed to alanine (R338A-FIX). This molecule had approximately 3 times greater clotting activity than that of wild type FIX (wt-FIX) in the activated partial thromboplastin assay. R338A-FIX reacted normally with a panel of three FIX specific monoclonal antibodies and migrated on sodium dodecyl sulfate-polyacrylamide gels indistinguishably from wt-FIX. Using functional assays, we determined that R338A-FIXa's Kd for factor VIIIa (FVIIIa) was similar to that of wt-FIXa. Our kinetic analysis, using factor X as substrate, indicated that the mutation's major effects were a 3-fold increase in kcat and a 2-fold decrease in Km both manifested only in the presence of FVIIIa. R338A-FIXa's increased catalytic efficiency did not result from ablation of a thrombin sensitive site, reported to occur at arginine 338, since in our assays the thrombin inhibitor, hirudin, had no effect on activity of either wt-FIXa or R338A-FIXa. R338A-FIXa and wt-FIXa had equal activity, with or without FVIIIa, toward the synthetic substrate, methylsulfonyl-D-cyclohexylglycyl-arginine-p-nitroanilide. Interestingly, R338A-FIXa had reduced affinity for heparin. Therefore, we propose that R338A-FIXa's increased activity is not due to an allosteric effect on the active site, but that the Arg-338 residue is part of an exosite that binds both factor X and the mucopolysaccharide, heparin.

Haemophilia B (sixth edition): a database of point mutations and short additions and deletions

The sixth edition of the haemophilia B database lists in easily accessible form all known factor IX mutations due to small changes (base substitutions and short additions and/or deletions of <30 bp) identified in haemophilia B patients. The 1380 patient entries are ordered by the nucleotide number of their mutation. Where known, details are given on factor IX activity, factor IX antigen in circulation and origin of mutation. References to published mutations are given and the laboratories generating the data are indicated.

Haemophilia B: database of point mutations and short additions and deletions, fifth edition, 1994

The fifth edition of the haemophilia B database lists in easily accessible form all known factor IX mutations due to small changes (base substitutions and short additions and/or deletions of < 30bp) identified in haemophilia B patients. The 1,142 patient entries are ordered by the nucleotide number of their mutation. Where known, details are given on: factor IX activity, factor IX antigen in circulation, and origin of mutation. References to published mutations are given and the laboratories generating the data are indicated.

Comparison of the behavior of normal factor IX and the factor IX Bm variant Hilo in the prothrombin time test using tissue factors from bovine, human, and rabbit sources

A subset of hemophilia B patients have a prolonged bovine-brain prothrombin time. These CRM+ patients are classified as having hemophilia Bm. The prolongation of the prothrombin time has been reported only with bovine brain (referred to as ox brain in some literature) as the source of thromboplastin; prothrombin times determined with thromboplastin from rabbit brain or human brain are not reported to be prolonged. Factor IX from a hemophilia Bm patient (factor IX Hilo) was isolated. The activity of factor IX Hilo was compared to that of normal factor IX in prothrombin time assays when the thromboplastin source was of bovine, rabbit, or human origin. Factor IX, either normal or Hilo, prolonged a prothrombin time regardless of the tissue factor source. However, unless thromboplastin was from a bovine source, this prolongation required high concentrations of factor IX. Further, factor IX normal was as effective as factor IX Hilo in prolonging the prothrombin time when rabbit or human thromboplastin was used. With bovine thromboplastin, factor IX Hilo was significantly better than factor IX normal at prolonging the prothrombin time. The amount of prolongation was dependent on the amount of factor IX Hilo added. In addition, the prolongation was dependent on the concentration of factor X present in the sample. The prothrombin time changed as much as 20 seconds when the factor X concentration was varied from 50% to 150% to normal (fixed concentration of factor IX Hilo). These results demonstrate the difficulty of classifying the severity of a hemophilia Bm patient based on the bovine brain prothrombin time unless both the factor IX and factor X concentrations are known.

T296----M, a common mutation causing mild hemophilia B in the Amish and others: founder effect, variability in factor IX activity assays, and rapid carrier detection

By direct genomic sequencing, we have delineated the causative mutation in 64 families of European decent with hemophilia B. Six (9%) had a C----T transition at base 31008, which substitutes methionine for threonine 296 (T296----M) in the catalytic domain of factor IX. Five of the patients had the same haplotype (frequency of 16% in the northern European population). These individuals are of Amish/German descent and they are likely to share a common ancestor. The sixth patient had a different haplotype, which indicates that his mutation had an independent origin. The data highlight the importance of clinical criteria for the classification of hemophilia B. All six patients had clinically mild disease and their factor IX coagulant activities were in the range of 3%-6% when tested simultaneously in one laboratory, yet the factor IX activities provided with patient records varied 40-fold. Due to the high frequency of this mutation, we have utilized the technique of polymerase chain reaction amplification of specific alleles (PASA) to perform rapid and inexpensive carrier diagnoses in the families with this mutation. This is of particular importance for the Amish since the mutation should account for much of, if not all, the mild hemophilia B that is commonly found in this population.

Single nucleotide primer extension to detect genetic diseases: experimental application to hemophilia B (factor IX) and cystic fibrosis genes

In this report, we describe an approach to detect the presence of abnormal alleles in those genetic diseases in which frequency of occurrence of the same mutation is high (e.g., cystic fibrosis and sickle cell disease), and in others in which multiple mutations cause the disease and the sequence variation in an affected member of a given family is known (e.g., hemophilia B). Initially, from each subject, the DNA fragment containing the putative mutation site is amplified by the polymerase chain reaction. For each fragment two reaction mixtures are then prepared. Each contains the amplified fragment, a primer (18-mer or longer) whose sequence is identical to the coding sequence of the normal gene immediately flanking the 5' end of the mutation site, and either an alpha-32P-labeled nucleotide corresponding to the normal coding sequence at the mutation site or an alpha-32P-labeled nucleotide corresponding to the mutant sequence. Single nucleotide primer extensions are then carried out and analyzed by denaturing polyacrylamide gel electrophoresis and autoradiography. As predicted by the Watson-Crick base-pair rule, in the wild type only the normal base, in an affected member only the mutant base, and in carriers both the normal and the mutant base are incorporated into the primer. Thus, an essential feature of the present methodology is that the base immediately 3' to the template-bound primer is one of those altered in the mutant, since in this way an extension of the primer by a single base will give an extended molecule characteristic of either the mutant or the wild type. The method is rapid and should be useful in carrier detection and prenatal diagnosis of every genetic disease with a known sequence variation.