Binetti Bianca M, Rotunno Crescenza, Tripodi Armando, Asti Daniela, Semeraro Fabrizio, Semeraro Nicola, Colucci Mario
Department of Biomedical Sciences, Section of General Pathology, University of Bari, Italy.
Thromb Haemost. 2006 Apr;95(4):606-11.
The prothrombin gene mutation G20210A is a common risk factor for thrombosis and has been reported to cause APC resistance. However, the inhibition of thrombin formation by APC not only limits fibrin formation but also stimulates fibrinolysis by reducing TAFI activation. We evaluated the influence of prothrombin G20210A mutation on the anticoagulant and fibrinolytic activities of APC (1 microg/ml). Thirty-two heterozygous carriers and 32 non carriers were studied. APC anticoagulant activity was assessed by aPTT prolongation whereas APC fibrinolytic activity was determined by a microplate clot lysis assay. APC-induced aPTT prolongation was markedly less pronounced in carriers than in non carriers. On the contrary, fibrinolysis time was shortened by APC to a comparable extent in both groups. Accordingly, prothrombin levels were strongly correlated with APC-induced aPTT prolongation but not with APC-induced shortening of lysis time. The addition of purified prothrombin to normal plasma (final concentration 150%) caused APC resistance in the clotting assay over the whole range of tested APC concentrations (0.125-1.5 microg/ml). In the fibrinolytic assay, instead, prothrombin supplementation made the sample resistant to low but not to high concentrations of APC (>0.5 microg/ml). Thrombin and TAFIa determination in the presence of 1 microg/ml APC revealed that hyperprothrombinemia, although capable of enhancing thrombin generation, was unable to induce detectable TAFIa formation. It is suggested that APC resistance caused by hyperprothrombinaemia does not translate in impaired fibrinolysis, at least in the presence of high APC levels, because the increase in thrombin formation is insufficient to activate the amount of TAFI required to inhibit plasminogen conversion. These data might help to better understand the relationship between thrombin formation and fibrinolysis down-regulation.
凝血酶原基因突变G20210A是血栓形成的常见危险因素，据报道可导致活化蛋白C（APC）抵抗。然而，APC对凝血酶形成的抑制作用不仅限制了纤维蛋白的形成，还通过减少凝血酶激活的纤溶抑制物（TAFI）的活化来刺激纤维蛋白溶解。我们评估了凝血酶原G20210A突变对APC（1微克/毫升）抗凝和纤溶活性的影响。研究了32名杂合子携带者和32名非携带者。通过活化部分凝血活酶时间（aPTT）延长来评估APC的抗凝活性，而通过微孔板凝块溶解试验来测定APC的纤溶活性。在携带者中，APC诱导的aPTT延长明显不如非携带者明显。相反，两组中APC使纤维蛋白溶解时间缩短的程度相当。因此，凝血酶原水平与APC诱导的aPTT延长密切相关，但与APC诱导的溶解时间缩短无关。向正常血浆中添加纯化的凝血酶原（终浓度150%）在整个测试的APC浓度范围（0.125 - 1.5微克/毫升）内的凝血试验中导致了APC抵抗。然而，在纤溶试验中，补充凝血酶原使样品对低浓度但不是高浓度的APC（>0.5微克/毫升）产生抵抗。在存在1微克/毫升APC的情况下测定凝血酶和凝血酶激活的纤溶抑制物a（TAFIa）发现，高凝血酶原血症虽然能够增强凝血酶的生成，但无法诱导可检测到的TAFIa形成。提示高凝血酶原血症引起的APC抵抗不会转化为纤维蛋白溶解受损，至少在高APC水平存在时如此，因为凝血酶生成的增加不足以激活抑制纤溶酶原转化所需的TAFI量。这些数据可能有助于更好地理解凝血酶形成与纤维蛋白溶解下调之间的关系。
