de Fouw N J, Haverkate F, Bertina R M
Gaubius Institute TNO, Leiden, The Netherlands.
Adv Exp Med Biol. 1990;281:235-43. doi: 10.1007/978-1-4615-3806-6_23.
The effect of purified human activated protein C (APC) on fibrinolysis was studied by using in vitro clot lysis techniques. Clots were formed from citrated blood or plasma (supplemented with 125I-labeled fibrinogen) by adding thrombin and Ca(2+)-ions; lysis of the clots was achieved by the addition of tissue-type plasminogen activator before clot formation. The gradual release of labeled fibrin degradation products from the clot into the supernatant was taken as a measure for the lysis rate. It was demonstrated that the acceleration of clot lysis by APC added before clot formation depends on the presence of Protein S, Ca(2+)-ions and phospholipids. These observations suggest a role of APC as anticoagulant in clot lysis, since the cofactors for the expression of its anticoagulant and profibrinolytic effect are very similar. Indeed, we could demonstrate that the profibrinolytic effect of APC in vitro is associated with reduction of thrombin generation through the coagulation cascade by inactivation of factor VIIIa and factor Va. For instance, APC did not accelerate the lysis of factor X deficient blood clots. More generally, thrombin generation was associated with retarded fibrinolysis in vitro. Consequently anticoagulants such as APC or Heparin are profibrinolytic, whereas pro-coagulants such as phospholipids (in cell-free plasma) inhibit fibrinolysis through the generation of thrombin. Thrombin thus plays a crucial role as a link between coagulation and fibrinolysis. As thrombin is able to inhibit the lysis of blood and plasma clots, and not of purified fibrin clots, we hypothesize that thrombin inhibits lysis through an as yet unidentified mediator in plasma.
采用体外凝块溶解技术研究了纯化的人活化蛋白C（APC）对纤维蛋白溶解的影响。通过添加凝血酶和钙离子，由枸橼酸盐血或血浆（补充有125I标记的纤维蛋白原）形成凝块；在凝块形成前添加组织型纤溶酶原激活剂实现凝块溶解。将标记的纤维蛋白降解产物从凝块中逐渐释放到上清液中作为溶解速率的指标。结果表明，在凝块形成前添加APC加速凝块溶解取决于蛋白S、钙离子和磷脂的存在。这些观察结果提示APC在凝块溶解中作为抗凝剂发挥作用，因为其抗凝和促纤维蛋白溶解作用的辅因子非常相似。实际上，我们能够证明APC在体外的促纤维蛋白溶解作用与通过灭活因子VIIIa和因子Va减少凝血级联反应中凝血酶的生成有关。例如，APC不会加速因子X缺乏的血凝块的溶解。更普遍地说，凝血酶生成与体外纤维蛋白溶解延迟有关。因此，诸如APC或肝素之类的抗凝剂具有促纤维蛋白溶解作用，而诸如磷脂（在无细胞血浆中）之类的促凝剂则通过凝血酶的生成抑制纤维蛋白溶解。因此，凝血酶作为凝血和纤维蛋白溶解之间的联系起着关键作用。由于凝血酶能够抑制血液和血浆凝块的溶解，而不能抑制纯化的纤维蛋白凝块的溶解，我们推测凝血酶通过血浆中一种尚未确定的介质抑制溶解。
