Influence of the charge of low molecular weight proteins on their efficacy of filtration and/or adsorption on dialysis membranes with different intrinsic properties

Hemodialysis membranes eliminate by filtration low-molecular-weight toxic metabolites (urea and creatinine) with minimum interactions between blood components and the membrane itself. However. the ability of a membrane to adsorb specific proteins could be beneficial if the accumulation of these same proteins is implicated in the genesis of a pathological condition. P-amyloidosis which accompanies the elevation Of beta (2)-microglobulin (11.8 kDa) in the plasma of dialysed patients is one such condition (Biochem. Biophys. Res. Commun. 129 (3) (1985) 701-706 Lancet I (1986) 1240-1311). To determine whether increases in plasma beta (2)-microglobulin levels were due to differences in filtration efficacy of the membrane used and/or to certain characteristics of this protein, e.g. its charge (pI 5.7) the adsorption and filtration of [H-3] beta (2)-microglobulin and [H-3] lysozyme of similar MW 14.5 kDa, but pI: 10.8 were compared on different membranes. It was found that. neither [H-3] beta (2)-microglobulin nor [H-3] lysozyme are removed by cuprophan, whereas over 75% of beta (2)-microglobulin is removed by filtration on polyacrylonitrile, pol,acrylonitrile-polyethyleneimine, polysulfone and >95% by adsorption to polymethylmethacrylate-BK, For lysozyme, removal by adsorption is >95% on polyacrylonitrile and polyacrylonitrile-polyethyleneimine. 72% on polymethylmethacrylate-BK and by filtration is 95% on polysulfone. Hemodialysis membranes must therefore not simply be considered as filters of low-molecular-weight metabolites but should be equally assessed for their capacity to eliminate potentially deleterious low-molecular-weight plasma proteins. (C) 2001 Elsevier Science Ltd. All rights reserved.