Adsorption of plasma proteins at heparin-coated surfaces - Comparative investigations

Over the past 10 years, investigations have shown that heparin coating opti mizes haemocompatibility in extracorporeal circulation systems. To date, ho wever, the mechanisms involved have not been identified. 20 mi of fresh hum an blood were circulated in an in vitro closed-loop model with and without heparin coating. Using a newly developed ELISA, a quantitative analysis of the adsorbed plasma proteins was done. In addition, changes in coagulation, complement and blood cell releasing factors were measured by ELISA methods : prothrombin fragment 1+2 (F1+2), thrombin-antithrombin-LU: complex (TAT), PMN-elastase, beta -thromboglobulin (beta -TG) and terminal complement-com plex (TCC). In uncoated tubing, high concentrations of fibrinogen, fibronec tin, prothrombin, vitronectin, alpha (2)-macroglobulin, von Willebrand fact or and complement factor C-3 were found. Large amounts of antithrombin-III, HMWK and C-1-esterase inhibitor were found on the heparinized surfaces. In addition, the concentrations of the soluble plasma protein markers F1+2, F PA, PMN-elastase, TCC and beta -TG were significantly lower (p < 0.05) in t he presence of heparin coating. The haemocompatibility of "foreign" surface s depends largely on the extent to which the processes of activation and in hibition of humoral and cellular mediators permanently occurring at the nat ural endothelium can be simulated. Owing to the low adsorption of procoagul atory and proinflammatory enzymes, heparin-coated surfaces demonstrate sign ificantly improved haemocompatibility.