The role of naturally-occurring antibodies against man-made materials in biocompatibility

In vitro evaluation of heparinized Cuprophan hemodialysis membranes

Cuprophan hemodialysis membranes can be heparinized using N,N'-carbonyldiimidazole (CDI) as a coupling agent. In this study, the characteristics of heparinized Cuprophan membranes have been evaluated. After immobilization, heparin partially retained its biologic activity. An anticoagulant activity of 12.4 +/- 4.2 mU/cm2 was measured using a thrombin inactivation assay. Immobilized heparin also displayed an anti-complement activity. After contact with human serum; heparinized Cuprophan induced no generation of significant amounts of fluid phase terminal complement complex (TCC), whereas untreated Cuprophan induced the generation of substantial amounts of TCC. Heparinization did not affect the permeability of Cuprophan for model solutes with molecular weights up to 12,000 g/mol except for sulfobromophthalein sodium salt. The permeability of Cuprophan for sulfobromophthalein sodium salt was slightly decreased after heparinization. The ultrafiltration rate of Cuprophan increased by about 30% after heparinization, probably owing to an increased swelling of the membrane in water. Heparinized Cuprophan incubated in phosphate-buffered saline at 37 degrees C showed some release of heparin. These amounts of released heparin, however, were very low as compared to the amounts of heparin which are systemically administered during clinical hemodialysis treatment. It is concluded that Cuprophan membranes heparinized by means of the CDI-activation procedure are highly promising for application in hemodialyzers to be used for the treatment of patients with reduced or without systemic administration of heparin.

Apheresis and Biocompatibility: Complement Activation

When blood comes into contact with plastic surfaces of extracorporeal circuits activation of different biological systems occurs, among them the complement. This will be activated mainly through the alternative pathway but also through the classical one. The activation through the latter pathway occurs when antibodies directed against polymeric materials used for the production of extracorporeal circuits or substances utilized for their sterilization are produced by the patient's immunosystem. Even if complement activation occurs almost constantly during apheretic procedures the natural inhibitory mechanisms of this system attenuate and disguise this phenomenon. Important and clinical manifestations occur in particular patients or in case of technologically more complex techniques. In apheresis the complement activation may be implicated in the relatively frequent complications such as fever and chills, hypotension, as well as in the rare but severe cases of ARDS.

Modification of the complement binding properties of polystyrene: effects of end-point heparin attachment

In recent years, conjugation of heparin to biomaterials has been shown to improve its biocompatibility. The purpose of the present work was to compare complement activation and binding of C3 to unmodified and heparin-treated polystyrene surfaces of microtitre plates. When polystyrene was incubated with human serum, C3 was deposited on the surface by both adsorption and binding dependent on activation of the classical (CPW) and alternative (APW) pathways. After end-point attachment of heparin, significant C3 deposition, although at reduced levels, occurred only by CPW-mediated mechanisms, while adsorption and APW-mediated binding were strongly reduced. Generally, the modified surface bound lower amounts of protein, e.g. serum albumin and IgG, than the unmodified. By contrast, it had increased affinity for C1q which leads to binding of C1 and activation of complement via the CPW. Nevertheless, the net effect of the surface modification on the complement reaction was an overall reduction of C3 binding due to obliteration of APW. This can be related to an enhanced factor H/I-dependent down-regulation of C3b and to the lowered protein-adsorbing property of the surface, both of which have inhibitory effects on APW and on the C3 shunt-dependent activation of the complement system.