AN INHIBITOR OF PLATELET ADHESION TO ARTIFICIAL SURFACE

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Thrombosis and consumption of coagulation factors or formed elements of blood is often a consequence when blood comes in contact with a prosthetic device. Heparin and other pharmacologic agents are used to minimize these adverse reactions. In the absence of an ideal polymer that neither attracts blood cells nor activates clotting, several approaches have been taken to reduce adverse reactions when blood contacts a material. The applicants have demonstrated the presence of a unique albumin-immunoglobulin G complex (alb-IgG complex) in normal human serum. In an isolated state in vitro, this alb-IgG complex significantly inhibits the adhesion of platelets and adsorption of certain plasma proteins. Since surfaces coated with alb-IgG complex are less attractive to platelets, the applicants have proposed to carefully examine the effect of this protein complex on blood-material interaction. The specific aims include: attempts to develop better methods for purification of alb-IgG complex, and explore if this complex could be synthesized in vitro from albumin and IgG; develop a method for quantitation of alb-IgG complex and examine the concentration of this complex in normal serum and in patients whose blood is exposed to a large surface area of materials; and study the mechanism by which alb-IgG complex inhibits platelet adhesion. Affinity chromatographic techniques will be applied to evolve an efficient method for isolation and purification of alb-IgG complex from serum. Since albumin and IgG appear to be complexed via disulfide bond(s), thiol reagents will be used to explore possible synthesis of this complex. A synthetic alb-IgG complex with adhesion inhibitory property will be useful because investigators then do not have to depend on isolation and purification of this complex from serum in which it is present in small quantities (greater than 1 mg/ml). For quantitation of this complex in serum, an enzyme linked immunosorption assay (ELISA) will be developed; it is known that both albumin and IgG moieties in this complex react with their respective antibodies. Polymer surfaces coated with alb-IgG complex will be examined for their ability to attract platelets and leukocytes and their ability to initiate clotting at the blood-material interface; these experiments will be carried out in vitro with the help of a flow chamber and in ex vivo carotid-jugular Arterio-Venous shunt model in sheep. If surfaces coated with alb-IgG complex are found to be less thrombogenic, it may be possible to use this protein complex to improve the blood compatibility of prosthetic devices that contact blood.