HEPARIN-LIKE FUNCTIONALIZED POLYMER SURFACES - DISCRIMINATION BETWEENCATALYTIC AND ADSORPTION PROCESSES DURING THE COURSE OF THROMBIN INHIBITION

Thrombus formation on blood-contacting artificial surfaces is a major problem. Antithrombogenic polymer surfaces have been obtained either b y heparin binding, or by grafting sulphonate and/or amino acid sulphon amide groups on insoluble polystyrene. In addition to their capacity t o adsorb thrombin, such surfaces were shown to be able to catalyse its inhibition by antithrombin III (AT), i.e. they are endowed with hepar in-like activity. The results were mainly obtained by using clotting a ssays. In many cases, delineating adsorption and catalytic processes b y such assays is not possible when evaluating anticoagulant polymer su rfaces. To overcome this problem, the kinetics of thrombin adsorption and inhibitions by AT and heparin cofactor II (HC) in the presence of such surfaces have been measured by using an assay performed with a th rombin-specific chromogenic substrate. A simple kinetic model of throm bin consumption is proposed. The relevant calculations, carried out wi th the help of a computer program, lead to determination of relative s econd order rate constants of thrombin adsorption and inhibitions by A T and HC in the presence of the polymers. In addition to thrombin adso rption, polystyrene surfaces bearing only sulphonate groups catalyse i nhibition by AT, whereas polystyrene surfaces bearing either aspartate , glycinate or isophthalate sulphonamide groups catalyse both inhibiti ons by AT and HC.