Reactivity Of Human Fibrinogen Adsorbed On Two Different types Of Hemodialysis Membranes

Cuprophane and polyacrylonitrile are two common materials used as hemodialysis membranes. Examination by both phase contrast and electron microscopy of both types of material after clinical ex vivo use with uremic patients indicated that cellular deposition was extensive on Cuprophane but not on polyacrylonitrile. In vitro studies with ¹²⁵I-labeled human fibrinogen or immunpglobulin G (IgG) showed that the adsorption of fibrinogen and IgG was greater on polyacrylonitrile than on Cuprophane. These results appear to be in conflict with the general concept that materials that adsorb large quantities of protein, especially fibrinogen and IgG, will promote greater adhesion of platelets and leukocytes. Further studies of fibrinogen adsorbed on polyacrylonitrile surfaces indicated that the adsorbed fibrinogen: (a) was not readily accessible for reaction with ¹²⁵I-labeled antifibrinogen IgG, (b) was not desorbed readily from the surface, (c) was not appreciably displaced by other plasma proteins such as albumin, IgG, except fibrinogen, and (d) did not promote the adhesion of ⁵¹Cr-labeled platelets or polymorphonuclear leukocytes. These data indicate that fibrinogen, though present in high concentration on polyacrylonitrile, may adsorb in a biologically inactive form. This could be due to either the direct involvement of fibrinogen active sites in the interaction of the protein molecule with polyacrylonitrile or a conformational change in the fibrinogen molecule upon adsorption. Our observations suggest that the thrombogenicity of an artificial surface may not be assessed by the type and amount of various protein adsorbed but is likely determined by the reactivity of specific adsorbed protein species.