High molecular weight kininogen adsorption on hemodialysis membranes: influence of pH and relationship with contact phase activation of blood plasma. influence of pre-treatment with poly(ethyleneimine).

Protein adsorption is an essential parameter for the evaluation of the hemocompatibility of biomedical materials. In effect, protein adsorption often generates unfavorable, complex, biochemical reactions and precedes cell adhesion on artificial interfaces. It is therefore necessary to modify the surface in contact with blood in order to minimize the onset of undesirable, biochemical, cascade reactions. Adsorption of high molecular weight kininogen (HK), which participates in the contact phase activation of the endogenous blood coagulation cascade, was evaluated at 37 degrees C. This paper also presents the results of contact phase activation tests carried out in vitro with 1:20 diluted human plasma flowing through minidialyzers containing hollow fibers of synthetic hemodialysis membranes. These tests showed that contact phase activation is strongly dependent on pH around the physiological value (ranging from 7.35 to 7.80) for negatively-charged membranes. The same pH effect was observed on the AN69 membrane as regards HK adsorption from binary labeled solutions of 125I-HK and 131I-Fibrinogen at concentrations corresponding to 1% diluted plasma. It is suggested that the influence of pH could be related to imidazole pKa values in histidine residues of kininogen D5H domain. The same study was also conducted with hemodialysis membranes pre-treated with poly(ethyleneimine). Both HK adsorption and contact phase activation proved to be greatly reduced, irrespective of the pH value (between 7.0 and 7.8). Hence, positively-charged poly(ethyleneimine) adsorbed on the membrane through strong ionic interactions with sulfonate groups of the surface probably constitutes a repelling, water-swollen layer for the kininogen molecule. In addition, the advantages of the high levels of adsorbance of small molecules on the AN69 membrane leading to blood epuration, due to its high porosity and for some of them to its charge density, should not be lost by such a surface treatment.