ANTITHROMBIN-III AFFINITY DEPENDENCE ON THE ANTICOAGULANT, ANTIPROTEASE, AND TISSUE FACTOR PATHWAY INHIBITOR ACTIONS OF HEPARINS

To investigate AT-III affinity dependence on heparin's actions, hepari n (UH) was fractionated on an AT-III-Sepharose column into a high (HAH ) and a Low affinity (LAH) fraction. Molecular profiling revealed a mo lecular weight of 11.8 kDa for (UH), 12.6 kDa for HAH, and 10.6 kDa fo r LAH. The USP anticoagulant potencies were found to be: UH = 160 U/mg , HAH = 198 U/mg, and LAH = 42 U/mg. The anticoagulant effects of each of these fractions were proportionate to the USP potencies. However, protease generation inhibitory activities did not follow the same orde r. All fractions were also tested for their interactions with tissue f actor pathway inhibitor (TFPI). No significant differences were noted on the anti-Xa effects of TFPI with these fractions. Administration of each fraction to primates resulted in equivalent release of TFPI. In a model of jugular vein clamping induced venous occlusion, all agents produced a dose-dependent antithrombotic action. HAH produced a 60 to 70% stronger antithrombotic effect than LAH or UH. Simultaneous admini stration of TFPI markedly augmented the antithrombotic actions of both UFH and LAH. The effect of TFPI on the antithrombotic activity of HAH was weaker than that on LAH. These observations suggest that AT-III a ffinity is not the sole determinant of the antithrombotic actions of h eparin. The endogenous release of TFPI may contribute to the antithrom botic actions of heparin and related glycosaminoglycans. Furthermore, TFPI is capable of AT-III independent amplification of the antithrombo tic actions of both UH and LAH, suggesting a crucial role of this poly valent inhibitor in the control of thrombogenesis.