Elution and identification of proteins adsorbed onto dialysis membranes during clinical use

Protein adsorption onto dialysis membranes plays a key role not only in biocompatibility but also for the elimination of certain kinds of uremic toxins. We eluted and analyzed protein that had been adsorbed onto clinically used hemodialyzer membranes, including cellulosic membranes (cuprophane, vitamin E-coated cellulose, cellulose acetate and hemophane) and synthetic membranes (polyamide, polysulfone, polymethylmethacrylate and acrylonitrile-sodium methallyl sulfonate (AN69)). After the dialysis session, protein was eluted by diffusion of blood compartments, filtration, overnight elution and diffusion of dialysate compartments, respectively. The amounts of eluted protein were measured by Lowry's method. The molecular weight of each eluted protein was analyzed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The eluted protein was identified by Western blotting. The total amount of eluted protein tended to be higher with synthetic membranes than with cellulosic membranes. The elution characteristics varied according to the membrane material. Abundant protein was eluted by filtration with AN69 and polymethylmethacrylate, although few proteins were eluted by filtration with cellulosic membranes. SDS-PAGE and Western blotting demonstrated that various kinds of proteins such as albumin, IgG, complement, and β2-microglobulin were adsorbed irrespective of the plasma concentration. Protein adsorption onto dialysis membranes depends on their particular characteristics including structure and pore size, which may regulate biocompatibility.