[Comparative studies of the adsorption behavior of plasma proteins to heparin-coated surfaces]

Over the past 10 years, investigations have shown that heparin coating optimizes haemocompatibility in extracorporeal circulation systems. To date, however, the mechanisms involved have not been identified. 20 ml of fresh human 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-III complex (TAT), PMN-elastase, beta-thromboglobulin (beta-TG) and terminal complement-complex (TCC). In uncoated tubing, high concentrations of fibrinogen, fibronectin, prothrombin, vitronectin, alpha 2-macroglobulin, von Willebrand factor and complement factor C3 were found. Large amounts of antithrombin-III, HMWK and C1-esterase inhibitor were found on the heparinized surfaces. In addition, the concentrations of the soluble plasma protein markers F1 + 2, FPA, PMN-elastase, TCC and beta-TG were significantly lower (p < 0.05) in the presence of heparin coating. The haemocompatibility of "foreign" surfaces depends largely on the extent to which the processes of activation and inhibition of humoral and cellular mediators permanently occurring at the natural endothelium can be simulated. Owing to the low adsorption of procoagulatory and proinflammatory enzymes, heparin-coated surfaces demonstrate significantly improved haemocompatibility.