Prager N A, Abendschein D R, McKenzie C R, Eisenberg P R
Cardiovascular Division, Washington University School of Medicine, St Louis, MO 63110, USA.
Circulation. 1995 Aug 15;92(4):962-7. doi: 10.1161/01.cir.92.4.962.
Thrombi are known to induce activation of the coagulation system, which may be a mechanism for progression of thrombosis and its recurrence after thrombolysis. This study was designed to characterize the relative role of thrombin and activated factor X (factor Xa) as mediators of procoagulant activity of whole blood clots in blood and plasma.
Clots formed from human blood were incubated in recalcified (25 mmol/L CaCl2) citrated plasma or nonanticoagulated blood with increasing concentrations of recombinant desulfatohirudin (hirudin) to inhibit thrombin activity, recombinant tick anticoagulant peptide (TAP) or recombinant tissue factor pathway inhibitor (TFPI) to inhibit factor Xa, or heparin. Fibrinopeptide A (FPA) was assayed serially as an index of procoagulant (thrombin) activity. FPA generation was greatly accelerated by addition of clots to recalcified plasma (from 1251 +/- 211 ng/mL after 15 minutes without clot to 5916 +/- 1412 ng/mL with clot, n = 7, P < .01) or whole blood (4803 +/- 761 ng/mL with clot compared with 546 +/- 233 without clot, n = 5, P < .05) and was attenuated by inhibitors of thrombin (> 90% inhibition of FPA with 0.05 mumol/L hirudin and 1.0 U/mL heparin) and factor Xa (> 90% inhibition of FPA with 1.0 mumol/L TAP and 0.15 mumol/L TFPI) in a concentration-dependent manner. Preincubation of clots with tissue-type plasminogen activator sufficient to induce partial clot lysis increased the rate of thrombin-induced FPA generation by increasing the surface area of clot exposed to plasma. However, procoagulant activity induced by partially lysed clots was attenuated by lower concentrations of both thrombin and Xa inhibitors, presumably because access of the inhibitors to bound procoagulant molecules was facilitated. Comparable results were obtained with incubations in nonanticoagulated blood.
These results indicate that factor Xa is primarily responsible for the procoagulant activity of clots in vitro and suggest a potential molecular mechanism for the observed efficacy of inhibitors of factor Xa in preventing recurrent thrombosis after coronary thrombolysis.
已知血栓会诱导凝血系统激活，这可能是血栓形成及其溶栓后复发的一种机制。本研究旨在确定凝血酶和活化的X因子（Xa因子）作为全血凝块在血液和血浆中促凝活性介质的相对作用。
将人血形成的凝块在添加了不同浓度重组去硫酸水蛭素（水蛭素）以抑制凝血酶活性、重组蜱抗凝肽（TAP）或重组组织因子途径抑制剂（TFPI）以抑制Xa因子或肝素的重新钙化（25 mmol/L氯化钙）枸橼酸盐血浆或未抗凝血液中孵育。连续检测纤维蛋白肽A（FPA）作为促凝（凝血酶）活性指标。向重新钙化的血浆（从无凝块时15分钟后的1251±211 ng/mL增加到有凝块时的5916±1412 ng/mL，n = 7，P <.01）或全血（有凝块时为4803±761 ng/mL，无凝块时为546±233 ng/mL，n = 5，P <.05）中添加凝块可大大加速FPA生成，并且凝血酶抑制剂（0.05 μmol/L水蛭素和1.0 U/mL肝素可使FPA抑制> 90%）和Xa因子抑制剂（1.0 μmol/L TAP和0.15 μmol/L TFPI可使FPA抑制> 90%）以浓度依赖方式减弱FPA生成。用足以诱导部分凝块溶解的组织型纤溶酶原激活剂对凝块进行预孵育，通过增加凝块暴露于血浆的表面积来提高凝血酶诱导的FPA生成速率。然而，部分溶解的凝块诱导的促凝活性被较低浓度的凝血酶和Xa因子抑制剂减弱，推测是因为抑制剂更容易接触到结合的促凝分子。在未抗凝血液中孵育也得到了类似结果。
这些结果表明Xa因子主要负责体外凝块的促凝活性，并提示了Xa因子抑制剂在预防冠状动脉溶栓后复发性血栓形成中观察到的疗效的潜在分子机制。
