[Purification of human fibronectin by precipitation and immunoadsorption]

Fibronectin purification from human plasma in a packed-bed column system with gelatin immobilized PHEMA microspheres

Bioaffinity chromatography has a unique and powerful role that is used as a purification tool in the production of therapeutic plasma protein derivatives. In this study, a bioaffinity-ligand, i.e. gelatin, was covalently immobilized with PHEMA microspheres (150-200 microm in diameter). The affinity sorbent carrying 7.5 mg gelatin g(-1) polymer was then used to separate fibronectin from human plasma in a packed-bed column system. Fibronectin separation from human plasma on unmodified PHEMA microspheres was 0.45 mg g(-1), while much higher adsorption values, up to 21.8 mg g(-1), were obtained with gelatin-immobilized microspheres. The fibronectin adsorption capacity of the microspheres decreased with an increase in the recirculation rate of plasma. Fibronectin adsorption increased with decreasing temperature, and the maximum adsorption achieved at 4 degrees C (26.3 mg fibronectin g(-1)). Up to 94.7% of the adsorbed fibronectin was desorbed by using 2 M urea in the presence of 1 M sodium chloride as elution agent. The adsorption-desorption cycle was repeated ten times using the same affinity column. There was no remarkable reduction in the adsorption capacity of the gelatin-immobilized PHEMA microspheres.

[Human plasma fibronectin. Comparison of methods for preparation of a concentrate for therapeutic use from different sources]

Three methods, successive precipitations, affinity chromatography on immobilized gelatin and immunoaffinity chromatography with monoclonal anti-fibronectin antibodies were optimized and compared in order to be used for large scale preparation of human plasma fibronectin (Fn). The functional properties of the various Fn preparations were investigated by means of two assays: quantitation of the gelatin-binding activity by ELISA and quantitation of the Fn-mediated attachment of fibroblasts on plastic. Functional alterations of the purified Fn were observed when it was isolated by successive precipitations. Both chromatographic methods provide a rapid and convenient way for isolation of pure and functional Fn. Mass production of monoclonal antibodies is too expensive and legislative requirements for the therapeutic use of monoclonal antibodies are limiting factors for the choice of immunopurification as large scale isolation procedure. Plasma Fn can be isolated from different sources: fresh frozen plasma, cryoprecipitate supernatant or by-products from factor VIII preparation. When gelatin-Sepharose chromatography is performed under optimized conditions, fibronectins isolated from these sources show similar properties. Large scale purifications of Fn from a by-product of factor VIII preparation were performed either by gelatin affinity chromatography or by successive precipitations. These two purification methods can be easily scaled-up since the data obtained closely correlate with analytical results. The chromatographic method supplies a higher purified (98 vs 75%) and functional (95 vs 50%) material when compared with successive precipitations. Yield is also higher (50 vs 26%). The starting material undergoes viral inactivation and the affinity purified Fn, sterile, atoxic, apyrogen, which can be freeze-dried without additives fulfils all requirements for an injectable product.

Affinity purification of human plasma fibronectin on immobilized gelatin

Several problems are associated with the biospecific affinity purification of plasma fibronectin on gelatin-Sepharose. Large-scale development of this purification procedure requires optimization of adsorption and elution conditions. The adsorption capacity depends on the amount of gelatin coupled to the Sepharose, the residence time, the temperature and the amount of fibronectin loaded on the adsorbent. Elution of adsorbed fibronectin with 3 M urea leads to incomplete recovery. The elution yield was found to vary with both the gelatin concentration and the amount of adsorbed fibronectin. Despite the incomplete elution, the adsorption capacity did not decrease after twelve consecutive isolation procedures. Under optimized conditions, the method described here provides a rapid, single-step and convenient way for the isolation of pure and functional fibronectin, either for analytical or large-scale preparative purposes.