Selective and sustained inhibition of surface-bound thrombin activity by intimatan/heparin cofactor II and its relevance to assessing systemic anticoagulation in vivo, ex vivo and in vitro

We compare the relative activities of surface-bound and fluid-phase thrombi n and their inhibition by heparin and Intimatan, a novel heparin cofactor I I (HCII) agonist. In vitro, we compared the observed amidolytic activities of fluid-phase and surface-bound thrombin with the expected activities base d upon I-125-specific activity. In vivo, we compared the inhibitory effects of heparin and Intimatan on thrombin activity bound to injured vessel wall s. In vitro, the correlations between observed and expected activities of f luid-phase and surface-bound thrombin, were: r=0.9974, p <0.001 and r=0.967 8, p <0.001; respectively. In vivo, injured vessel wall surface-bound throm bin activity persisted for > 24 h. This activity was not inhibited by hepar in, but was inhibited by Intimatan, p <0.001. We conclude that surface-bound thrombin is as active as fluid-phase thrombi n and remains protected from inhibition by heparin, thereby contributing to vessel wall thrombogenicity following injury. In contrast, surface-bound t hrombin is inhibited by Intimatan, thereby effectively decreasing vessel wa ll thrombogenicity following injury in vivo.