Synthetic sorbents for removal of factor VIII inhibitors from haemophilic A plasma

Polystyrene derivatives as candidates for extracorporeal adsorption of Factor VIII antibodies in the management of haemophiliac patients

BACKGROUND AND OBJECTIVES

This article presents a new approach for removing the Factor VIII inhibitors (anti-FVIII) in haemophiliac patients by immunoadsorption using an affinity matrix.

MATERIALS AND METHODS

Ten blood samples from haemophiliac patients with anti-FVIII were assayed for antibodies, total immunoglobulins, procoagulant proteins and complement C3 protein after circulation over one or two columns filled with the polymers under investigation.

RESULTS

These new synthetic sorbents are able to remove in vitro 90% of anti-FVIII from haemophiliac plasma with inhibitors (up to 540 Bethesda Units/ml). Neither coagulation factor adsorption nor effects on complement system activation were observed.

CONCLUSIONS

The data presented clearly show that these polymers allow a rapid and efficient reduction of inhibitor titre. In view of the parameters studied, these polymers fulfil the requirements for use in a blood purification process to decrease high inhibitor titres without losing essential proteins.

Selective surface adhesion of the toxic microalga Alexandrium minutum induced by contact with substituted polystyrene derivatives

On the basis of observations that biospecific random copolymers (RACS) could induce phenotypic changes on contact with selected eukaryotic or prokaryotic cell lines, polystyrene derivatives of known compositions and obtained by random substitutions of sodium sulfonate and of sulfamides of aspartic acid dimethyl ester, phenylalanine and leucine, were placed in contact with swimming dinophytes of the PSP toxin producing species Alexandrium minutum and of the non-toxic species Heterocapsa triquetra. A. minutum cells exhibited higher adhesion for the random copolymer made up of polystyrene (29%), polystyrene aspartic acid dimethyl ester sulfamide (47%) and polystyrene sodium sulfonate (24%), than for samples of this series with different compositions. In contrast to this, A. minutum adhesion remained very low throughout the phenylalanine and leucine copolymer series. These results indicate that the cell-substrate adhesion phenomenon is dependent upon the final composition of the copolymer, i.e. that it is composition-specific. Taxonomic specificity was then demonstrated by presenting the PSAspOMe copolymer series with cells of the non toxic species H. triquetra (Peridinialia) related to A. minutum (Gonyaulacacea), and by observing no specific association, i.e. no signal above background levels at any composition. Specific ligand-cell adhesion is evidenced for the first time between biospecific RACS and phytoplankton, which may inspire a new generation of structures to be used in aquaculture as protective nets over shellfish clusters, or as selective filtering devices to assist in shellfish depuration from toxic microalgae.

Immune response to enzyme replacement therapy: clinical signs of hypersensitivity reactions and altered enzyme distribution in a high titre rat model

Immune responses to enzyme replacement therapy (ERT) have been reported and can result in a hypersensitivity/anaphylactic reaction during or immediately after enzyme infusion. We have investigated the infusion of the lysosomal enzyme N-acetylgalactosamine 4-sulphatase (4-sulphatase) into immunized, high titre rats as a model of immune response to ERT. To simulate ERT, high and low titre rats were infused with different doses of radiolabelled recombinant human 4-sulphatase (3H-rh4S). There was evidence of altered targeting, inactivation and degradation of 4-sulphatase in high titre (titre 1024000) compared to low titre (titre 64) rats. There was more 4-sulphatase enzyme activity detected in 5 mg/kg high titre rats when compared to 1 mg/kg high titre rats, suggesting that the antibodies could be saturable in vivo. However, the rats treated with 5 mg/kg 3H-rh4S all had clinical signs of hypersensitivity reactions to 4-sulphatase infusion. There were no apparent signs of adverse reactions in either the high titre 1 mg/kg rats or the low titre rats (1, 5 mg/kg). The high titre 5 mg/kg rats also had changes in 3H-rh4S distribution, with lower levels delivered to the liver and a marked increase in the level remaining in plasma, when compared to either 1 mg/kg high titre rats or low titre rats (1, 5 mg/kg).

Adsorption of immunoglobulin G and anti-factor VIII inhibitory antibody from haemophiliac plasma to derivatized polystyrenes

Modified polystyrene resins containing sulphonate groups and tyrosyl sulphamide or tyrosyl methyl ester sulphamide groups have been investigated with respect to their potential for selective binding of anti-Factor VIII inhibitory antibodies from plasma. Adsorption of total immunoglobulin G and of a monoclonal antibody to Factor VIII was measured following addition of the radioiodinated proteins to normal plasma, plasma depleted of Factor VIII by adsorption on a resin coupled to anti-Factor VIII antibody, and haemophiliac plasma containing various levels of inhibitory anti-Factor VIII antibody. Depletion of anti-Factor VIII antibody from the haemophiliac plasmas by incubation with the resins was also measured by Bethesda assay. The modified resins and their corresponding unmodified "controls' showed similar binding of total immunoglobulin G. However, only resins containing either sulphonate or a combination of sulphonate and tyrosyl sulphamide groups showed evidence of selective adsorption of anti-Factor VIII antibody from plasma.

Affinity of human anti-factor VIII antibodies for functional polystyrene supports

Human anti-factor VIII antibodies (anti-FVIII) neutralize Factor VIII (FVIII) procoagulant activity. These antibodies appear in about 5-15 per cent of severely affected patients with haemophilia A treated with FVIII concentrates (Mannucci, 1993). In order to obtain non-thrombogenic materials able to interact specifically with anti-FVIII, amino acids residues that mimic part of the FVIII molecule recognized by anti-FVIII have been grafted. Several cross-linked polystyrenes were functionalized with sulphonate and tyrosine sulphamide groups or tyrosine derivatives sulphamide groups such as methyl ester tyrosine, or the peptides aspartic acid methyl amide tyrosine, tyrosine aspatic acid methyl amide or aspartic acid aspatic acid methyl amide tyrosine. The in vitro removal of anti-FVIII from haemophilic A plasma was performed on different supports. These polymers exhibit strong and selective affinity for the anti-FVIII. The amount of adsorbed anti-FVIII varies with the composition of the polymer and a maximum is achieved for 15-35 per cent of amino acid sulphamide groups. The influence of different chemical groups on the surface of the polymeric solid supports on the adsorption of anti-FVIII was also studied.

Inhibitors in congenital haemophilia

Inhibitor formation is a serious complication, occurring in 24-52% of patients with haemophilia A and in 1.5-3% of patients with haemophilia B. Low-titre inhibitors can easily be overcome and do not represent a treatment challenge. They are treated with increased doses of factor concentrate. However, high-titre inhibitors may still cause death from haemorrhage in this population. Optimal treatment of acute, life-threatening haemorrhage in patients with factor VIII inhibitors includes either porcine factor VIII or human factor VIII in high doses since, with both modalities, circulating factor levels are achievable. If the inhibitor titres are too high, plasmapheresis may be warranted. For routine joint bleeds, PCC or aPCC can be administered at home with variable success. For patients with factor IX inhibitors treatment options are more limited. If the haemorrhage is life-threatening, plasmapheresis should be done to decrease the inhibitor and high doses of pure factor IX administered either by continuous infusion or bolus. Attainment of levels of > 20% should be attempted. New clinical options, such as rFVIIa, may emerge. For both groups of patients, IT should be started as soon as the inhibitor is discovered and its behaviour characterized. Unfortunately, no standard regimen for IT exists and the treater will have to choose whichever schedule he/she feels is the most appropriate.