Understanding FVIII/VWF complex--report from a symposium of XXIX WFH meeting 2010.

von Willebrand factor (VWF) has the capacity to form a complex with factor VIII (FVIII) which may modulate the immunogenicity of FVIII. It has been proposed that a significant fraction of recombinant FVIII (rFVIII) is unable to bind VWF. In an experimental model studied at the McMaster University in Canada, this VWF-unbound rFVIII fraction showed no coagulant function. Sulphation of FVIII tyrosine (Tyr) 1680 has been reported as essential for the interaction with VWF. In a study performed at the Grifols and CNS-CSIC in Spain, Tyr1680 sulphation was observed to be incomplete in rFVIII and complete in plasma-derived FVIII (pdFVIII). This could explain the incapability of some rFVIII molecules to bind VWF. Experience with immune tolerance induction (ITI) at the Bonn Haemophilia Centre indicates that only eradication of FVIII inhibitors allows safe haemostasis control and the option of prophylactic treatment. Various clinical trials were planned to evaluate the clinical role VWF-containing FVIII concentrates (FVIII/VWF). RES.I.ST (an acronym for REScue Immunotolerance STudy) is an international, prospective study aimed at assessing whether FVIII/VWF can induce ITI in high-risk haemophilia patients (RES.I.ST naïve) and whether patients who previously failed ITI with FVIII alone can be rescued with FVIII/VWF (RES.I.ST experienced). Enrolment started in November 2009. In the FAIReSt.Will (Fanhdi and Alphanate Italian Retrospective Study in Willebrand disease) study, 120 von Willebrand disease (VWD) patients treated with Fanhdi(®) or Alphanate(®) were retrospectively analysed. Efficacy was excellent and no side effects were reported. The ongoing PRO.Will study is a prospective, multicenter trial aimed at assessing the efficacy, safety and pharmacoeconomics of secondary long-term prophylaxis in patients with severe inherited VWD.

Transfusion of multiple units of Js(b+) red blood cells in the presence of anti-Jsb in a patient with sickle beta-thalassemia disease and a review of the literature.

Jsb is a high-frequency antigen. Anti-Jsb is a rare alloantibody, and its clinical significance is poorly documented. We report a case in which a 12-year-old boy of Nigerian descent with sickle beta- thalassemia presented with multiple alloantibodies, including a panagglutinin and acute chest syndrome, necessitating the emergent transfusion of five units of phenotype-similar, crossmatchincompatible RBCs, four of which were given during an exchange transfusion. The patient was later found to have anti-Jsb. In addition to routine serologic methods to study the patient's RBCs and plasma, a monocyte monolayer assay (MMA) was performed on the patient's samples obtained 2 and 9 days after transfusion of the Js(b+) RBCs to determine the potential clinical significance of the anti-Jsb. Various laboratory parameters including quantitative hemoglobin fraction analyses were used to monitor for increased RBC destruction. The MMA reactivity of the patient's anti-Jsb increased from 2.3 percent on day 2 after transfusion to strongly positive at 88 percent and 66.5 percent (with and without the addition of fresh serum) 1 week later. MMA reactivity of greater than 5 percent is associated with increased RBC destruction. There was no clinical or laboratory evidence of increased hemolysis above baseline. However, decreased RBC survival was suggested by the relatively brisk decrease of the HbA1 fraction after the transfusions. The current case and others reported in the literature suggest that anti-Jsb may have limited potential for causing overt hemolysis. However, in patients with underlying hematologic disease, even mildly increased RBC destruction may pose problems clinically,and thus transfusion of Js(b+) RBCs should be avoided. In emergent situations, the potential of adverse effects of transfusing incompatible units should be balanced against the risk of withholding transfusion. Family members, especially siblings, should be considered as potential designated donors for patients with antibodies directed against high-frequency antigens. Available reports on anti-Jsb in the literature are also reviewed.

Dissociation of multiply charged negative ions for hirudin (54-65), fibrinopeptide B, and insulin A (oxidized).

Collision-induced dissociation (CID) was performed on multiply deprotonated ions from three commercial peptides: hirudin (54-65), fibrinopeptide B, and oxidized insulin chain A. Ions were produced by electrospray ionization in a Fourier transform ion cyclotron resonance mass spectrometer. Each of these peptides contains multiple acidic residues, which makes them very difficult to ionize in the positive mode. However, the peptides deprotonate readily making negative ion studies a viable alternative. The CID spectra indicated that the likely deprotonation sites are acidic residues (aspartic, glutamic, and cysteic acids) and the C-terminus. The spectra are rife with c, y, and internal ions, although some a, b, x, and z ions form. Many of the fragment ions were formed from cleavage adjacent to acidic residues, both N- and C-terminal to the acidic site. In addition, neutral loss (e.g., NH3, CH3, H2O, and CO2) was prevalent from both the parent ions and from fragment ions. These neutral eliminations were often indicative of specific amino acid residues. The fragmentation patterns from several charge states of the parent ions, when combined, provide significant primary sequence information. These results suggest that negative mode CID of multiply deprotonated ions provides useful structural information and can be worthwhile for highly acidic peptides that do not form positive ions in abundance.

In vitro detection of mild inhibitors to factor VIII in hemophilia.

Plasma samples from patients with severe classic hemophilia, suspected of having mild inhibitors not detected in the standard Bethesda inhibitor test, were examined in modified Bethesda tests and in a screening test based on the activated partial thromboplastin time (APTT). The APTT test was more sensitive to mild inhibitors than any modification of the Bethesda method. Increasing the ratio of patient to normal plasma in either the APTT or the Bethesda test improved the sensitivity to mild inhibitors. If a patient's plasma is used as its own control in the APTT test, results are more consistent as minor fluctuations in the APTT occur over time.

Determination of the gas-phase basicities of proline and its di- and tripeptides with glycine: the enhanced basicity of prolylproline.

The gas-phase basicity (GB) of proline, which is the only imino acid and is reported to play a significant role in protein folding, was determined by deprotonation reactions in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Protonated peptide ions were generated by fast atom bombardment in an external ion source. The GB of proline was found to be 213.3 kcal/mol. Among the dipeptides studied, the GB of glycylproline (GlyPro) was determined to be 214.8 kcal/mol, while prolyglycine (ProGly) was 4.2 kcal/mol more basic (GB = 219.0 kcal/mol). The basicity of the tripeptide prolylglycylglycine (ProGlyGly, GB = 219.0 kcal/mol) is 2 kcal/mol higher than the basicities of glycylglycylproline (GlyGlyPro) and glycylprolylglycine (GlyProGly), both of which have GB = 217.0 kcal/mol. The enhanced basicity of ProGlyGly is consistent with the protonation site being the terminal amino nitrogen with enhanced stabilization of the charge by the nearby bulkier residue. Interestingly, prolyproline (ProPro), which has a GB of 223.3 kcal/mol, is more basic than the other di- and tripeptides studied. Consequently, semi-empirical AM1 calculations were employed to probe the structural characteristics and intramolecular hydrogen bonding interactions for ProPro, GlyPro, ProGly and glycylglycine (GlyGly). ProPro was found to have a unique structure with two potential hydrogen bonds between amino hydrogens and both carbonyl oxygens.

Gas-phase basicities for ions from bradykinin and its des-arginine analogues.

Apparent gas-phase basicities (GB(app)s) for [M + H]+ of bradykinin, des-Arg1-bradykinin and des-Arg9-bradykinin have been assigned by deprotonation reactions of [M + 2H]2+ in a Fourier transform ion cyclotron resonance mass spectrometer. With a GB(app) of 225.8 +/- 4.2 kcal x mol(-1), bradykinin [M + H]+ is the most basic of the ions studied. Ions from des-Arg1-bradykinin and des-Arg9-bradykinin have GB(app) values of 222.8 +/- 4.3 kcal x mol(-1) and 214.9 +/- 2.3 kcal x mol(-1), respectively. One purpose of this work was to determine a suitable reaction efficiency 'break point' for assigning GB(app) values to peptide ions using the bracketing method. An efficiency value of 0.1 (i.e. approximately 10% of all collisions resulting in a deprotonation reaction) was used to assign GB(app)s. Support for this criterion is provided by the fact that our GB(app) values for des-Arg1-bradykinin and des-Arg9-bradykinin are identical, within experimental error, to literature values obtained using a modified kinetic method. However, the GB(app)s for bradykinin ions from the two studies differ by 10.3 kcal x mol(-1). The reason for this is not clear, but may involve conformation differences produced by experimental conditions. The results may be influenced by salt-bridge conformers and/or by conformational changes caused by the use of a proton-bound heterodimer in the kinetic method. Factors affecting the basicities of these peptide ions are also discussed, and molecular modeling is used to provide information on protonation sites and conformations. The presence of two highly basic arginine residues on bradykinin results in its high GB(app), while the basicity of des-Arg1-bradykinin ions is increased by the presence of two proline residues at the N-terminus. The proline residue in the second position folds the peptide chain in a manner that increases intramolecular hydrogen bonding to the protonated N-terminal amino group of the proline at the first position.

Prophylactic treatment with activated prothrombin complex concentrate (FEIBA) reduces the frequency of bleeding episodes in paediatric patients with haemophilia A and inhibitors.

Orthopaedic complications are among the most disabling sequelae occurring in patients with haemophilia and inhibitors. Recurrent or refractory joint bleeds can lead to joint damage, limiting mobility and causing permanent disability. Activated prothrombin complex concentrates (aPCCs) are effective in controlling acute, intraoperative and postoperative bleeding in patients with haemophilia and inhibitors. The relatively long, dosing interval and safety profile distinguish aPCCs as a well-suited option for prophylaxis. Therefore, it is postulated that long-term routine aPCC administration will decrease the frequency of recurrent bleeds, prevent damage to normal joints, and slow the progression of existing joint disease in patients with inhibitors. To test this hypothesis, a retrospective chart audit was performed. In four treatment centres, five patients were identified who received aPCC [Factor Eight Inhibitor Bypassing Activity, Anti-Inhibitor Coagulant Complex (FEIBA); Baxter AG, Vienna, Austria] prophylactically for > or = 6 months to prevent or reduce further joint deterioration, reduce bleeding and prevent postsurgical bleeding. Median treatment duration was 15 months and included administration of >1300 doses of aPCC. Dosages ranged from 50 to 75 U kg(-1) three times per week in four patients; one patient received 100 U kg(-1) daily. Orthopaedic status was maintained in four patients and improved in one; the frequency of bleeding episodes was reduced in all patients. No adverse events or thrombotic complications were reported. This case series demonstrates that routine aPCC administration may be used safely and effectively to reduce the occurrence of bleeding episodes and to maintain or improve clinical joint status in some patients.

Induction of immune tolerance, the future of the Registry.

Factor VIII (FVIII) inhibitors are IgG antibodies that neutralize the procoagulant activity of FVIII, rendering hemorrhages difficult to manage. There may exist a genetic predisposition with consequent imbalance of T and B cell function. Efforts at inhibitor eradication in the last 20 years have produced a multitude of immune tolerance induction (IIT) protocols with variable outcome. Data derived from the International Registry indicate that inhibitor titer at outset of IIT and dose of FVIII concentrate used are important predictors of success. Future Registry activities should identify optimally standardized IIT regimens designed on the basis of patient likelihood to achieve tolerance and should provide further understanding of T and B cell interaction in the treatment process.

Comparative efficacy of nonheated and heat-treated factor IX complex concentrate in treatment of hemophiliacs with inhibitors.

To determine if heat-treated factor IX complex concentrate is as effective as nonheated factor IX complex concentrate for treatment of subjects with hemophilia A and antifactor VIII antibodies (inhibitor patients), we have retrospectively reviewed consecutive home treatment records of ten inhibitor patients who had been receiving nonheat-treated factor IX complex concentrate (NHT-Konyne) and subsequently converted to heat-treated factor complex concentrate (Konyne-HT) when it was licensed in late 1984. Overall, 162 of 284 (57%) separate bleeding episodes treated with NHT-Konyne and 53 of 80 (66.3%) separate bleeding episodes treated with Konyne-HT required only one treatment course of approximately 60-75 U/kg. The distribution of bleeding sites and the absolute factor IX unitage required per treatment episode were similar for both preparations. These data suggest that the percentage of hemophilic inhibitor patients responding to factor IX complex concentrate remains at least 50%, as was reported several years ago in a controlled study, and that inhibitor bypass activity has not altered by heat treatment.

Induction of immune tolerance to factor VIII in hemophiliacs with inhibitors.

Induction of immune tolerance in patients with severe hemophilia A and inhibitors to factor VIII was attempted by daily infusion of 50 U of factor VIII per kilogram of body weight without adjunctive immunosuppressive drugs. Modest initial anamnestic elevation of inhibitor levels occurred in six patients within the first month of therapy; inhibitor levels then fell sharply. The other six patients had no increase in inhibitor levels while on the study protocol. Inhibitors became undetectable within one to ten months in nine of the patients; they now receive smaller and less frequent infusions of factor VIII to maintain suppression. Inhibitors were not eradicated in three patients, who had the highest baseline and historic inhibitor levels. Ten patients gave consent for human immunodeficiency virus (HIV) testing; three had no antibody to HIV at the outset. Two of these patients seroconverted while on the protocol, one of whom had received only donor-screened, heat-treated factor VIII. Thus, the benefits of inhibitor suppression must be weighed against the risks of HIV seroconversion or transient elevation of inhibitor levels, as well as against the cost of the factor concentrate used.

Hematologic management of hemophilia A for surgery.

From mid-1967 to mid-1983, three hundred fifty surgical operations were performed on 163 patients with hemophilia A, without factor VIII inhibitor. One death occurred, in a patient with a serious head injury. Postoperative hemorrhages occurred after 23% of operations, but the incidence after surgery on the knee, 40%, was decidedly higher than the 15% incidence after operations at other sites. Concurrent plasma factor VIII levels were over 0.40 units/mL in 72% of instances and under 0.30 units/mL in only 15% of instances. The incidence of postoperative hemorrhage did not change over the study period despite a threefold increase in typical dosage of factor VIII (from 600 to 2,000 units/kg per operation) and doubling of typical trough factor VIII levels (from 0.37 units/mL to 0.70 units/mL). Circulating factor VIII levels apparently are not the sole determinants of postoperative bleeding in hemophilia A.

Therapeutic choices for patients with hemophilia and high-titer inhibitors.

Effective treatment of bleeding episodes in hemophilia with high titer inhibitors (HTI) remains a challenge, despite the fact that the therapeutic armamentarium has expanded considerably over the past few years. Treatment safety has improved with the availability of porcine factor VIII (FVIII) and bypassing products such as recombinant factor VIIa (rFVIIa), and plasma-derived activated Prothrombin Complex Concentrates (aPCCs) that are virally inactivated. The major drawbacks of rFVIIa and aPCCs are their unpredictable hemostatic effect, lack of laboratory assays to monitor efficacy and dosing frequency, and the risk of thrombosis. The proceedings of a one-day workshop of physicians who specialized in treating patients with hemophilia held in Vienna on May 13, 2000 have been summarized. In making a decision regarding the choice of product, physicians often consider the type of bleeding episode (life or limb threatening), age of the patient, volume of the reconstituted product, previous exposure to plasma derived products, cost, efficacy, and safety. For plasma naïve patients, to achieve rapid hemostasis a majority of the panelists used porcine FVIII (for patients who lack porcine inhibitory antibodies) or rFVIIa. For patients previously treated with plasma derived factors, in addition to the above concentrates, aPCCs were recommended. Although no data exists regarding safety and efficacy, switching products was routinely practiced either because of availability or cost. Furthermore, the panelists were uncertain about the efficacy of bypassing agents in the prevention of joint disease in inhibitor patients. The workshop participants felt that future research offers the best solution to resolve some of the dilemmas faced by clinicians and may help individualise treatment in a hemophilia patient with a high titer inhibitor.