凝血酶激活的纤溶抑制物

凝血酶激活的纤溶抑制物（Thrombin－activatablefibrinolysisinhibitor,TAFI）是近年来发现的存在于血浆中的一种蛋白酶原,经凝血酶-血栓调节蛋白复合物激活后,具有抑制纤溶系统活性的作用。本文就TAFI的基因及其蛋白质、TAFI抑制纤溶活性的机制以及凝血因子XI、V和活化的蛋白C对TAFI的作用作一综述。     

凝血酶激活的纤溶抑制物的研究进展

凝血酶激活的纤溶抑制物(TAFI)属于羧肽酶家族成员。血液凝固时,TAFI可以被凝血酶激活,特异性裂解纤维蛋白C末端赖氨酸残基,下调纤溶系统。在动物实验中,抑制TAFI可以缩短血凝块溶解时间,增强溶栓药物的作用,TAFI抑制物有可能成为血栓性疾病治疗的一类新的药物。     

凝血酶激活的纤溶抑制物

凝血酶激活的纤溶抑制物（Ｔｈｒｏｍｂｉｎ－ａｃｔｉｖａｔａｂｌｅｆｉｂｒｉｎｏｌｙｓｉｓｉｎｈｉｂｉｔｏｒ，ＴＡＦＩ）是近年来发现的存在于血浆中的一种蛋白酶原，经凝血酶－血栓调节蛋白复合物激活后，具有抑制纤溶系统活性的作用，本文就ＴＡＦＩ的基因及其蛋白质，ＴＡＦＩ抑制纤溶活性的机制以及凝血因子ＸＩ，Ｖ和活化的蛋白Ｃ对ＴＡＦＩ的作用作一综述。     

凝血酶激活的纤溶抑制物

凝血酶激活的纤溶抑制物 (ＴＡＦＩ)是近年来发现存在于血浆中的一种蛋白酶原 ,经凝血酶 凝血酶调节蛋白 (ＴＭ)复合物激活后 ,具有抑制纤溶系统活性的作用。现就其研究进展作一综述。1　基因及其蛋白质　 1995年Ｂａｊｚａｒ等[1 ] 发现血凝块中凝血酶原的激活可使血凝块的溶解时间延长 ,推测血浆中可能存在依赖于凝血酶原激活的纤溶抑制物 ,于是他们利用纤溶酶原 (Ｐｌｇ) Ｓｅｐｈａｒｏｓｅ柱层析的方法从血浆中分离到相对分子质量为 6 0 0 0 0的单链蛋白质 ,这种蛋白质经凝血酶作用后可使血浆凝块的纤溶时间延长 ,因此将其命名为ＴＡ…     

肝硬化患者血浆凝血酶激活的纤溶抑制物变化观察

血浆凝血酶激活的纤溶抑制物（thrombin activated fibrinolysis inhibitor，ATFI）作为新的凝血与纤溶调控因子，越来越受到人们的关注，本文旨在探讨肝硬化患者发病过程中TAFI、组织纤溶酶原激活物（t—PA）、纤溶酶原激活物抑制物（PAI-1）的变化，以评价TAFI变化在肝硬化患者中的临床意义及与Child—Pugh分级的关系。     

凝血酶激活的纤溶抑制物的研究进展

凝血酶激活的纤溶抑制物（TAFI）属于羧肽酶家族成员。血液凝固时，TAFI可以被凝血酶激活，特异性裂解纤维蛋白C末端赖氨酸残基，下调纤溶系统。在动物实验中，抑制TAFI可以缩短血凝块溶解时间，增强溶栓药物的作用，TAFI抑制物有可能成为血栓性疾病治疗的一类新的药物。     

冠心病患者血浆凝血酶激活的纤溶抑制物的检测及其临床意义

目的　检测正常人群血浆中 TAFI:Ag和 TAFI:A的水平 ,确立正常人血浆中 TAFI:Ag和TAFI:A的参考值范围及其在冠心病患者血浆中的变化。方法　应用 ELISA方法测定 34名正常人、1 9例冠心病患者及 1 5例 DIC患者血浆中 TAFI:Ag的含量 ,应用发色底物法检测血浆中 TAFI:A的水平。对正常人、冠心病患者血浆中 TAFI:Ag和 TAFI:A的含量进行对照分析。结果　正常人 TAFI:Ag平均值为 ( 77± 2 8) % ,参考值范围为 2 1 %～ 1 33% ,TAFI:A平均值为 ( 2 4± 5 ) μg/ml,参考值为 1 4～ 34μg/ml。冠心病患者血浆中 TAFI:Ag为 ( 1 5 6± 32 ) % ,TAFI:A为 ( 4 3± 7) μg/ml。结论　正常人血浆中的TAFI:Ag含量具有很大变异性 ,正常人 TAFI的活性与 TAFI抗原含量呈剂量相关性 ,冠心病患者血浆中 TAFI:Ag和 TAFI:A显著增高 ,表明 TAFI在冠心病发病中起一定作用。     

凝血酶激活的纤溶抑制物与血栓性疾病关系的研究进展

目前,血栓性疾病严重威胁着患者的生命与健康,用特异性溶栓药物进行治疗是防治血栓性疾病的重要措施,为此人们仍不断探索新的治疗方法。凝血酶激活的纤溶抑制物（thrombin activatabie fibrinolysis nhibitor,TAFI）是存在于血浆中的一种蛋白酶原,是体内纤溶系统的重要成分,它被激活后具有抑制纤维蛋白溶解的作用。由于它与血栓性疾病的发生、发展有关,已成为医学界研究如何防治血栓性疾病的热点之一,其作用日益受到重视。     

凝血酶激活的纤溶抑制物编码区基因单核苷酸多态性与静脉血栓栓塞症的相关性分析

本研究探讨凝血酶激活的纤溶抑制物(TAFI)及其基因编码区2个位点(505a/g,1040c/t)单核苷酸多态性与静脉血栓栓塞症(VTE)的相关性。应用等位基因特异性-聚合酶链反应(AS-PCR)分析技术,检测80例VTE患者和80例正常对照的TAFI基因型分布。结果表明:1040c/t点VTE组t等位基因的频率较对照组明显下降(40%vs 53.75%,P<0.05),这主要由于病例组tt纯合子型比例显著下降所致(P<0.05,风险比1.74,95%CI 1.2-2.70),但505a/g多态性位点在VTE及对照组中各基因型及基因频率的差异无统计学意义。结论:TAFI 1040c/t基因多态性与VTE患者存在相关性;t等位基因可能在VTE患者起保护作用;TAFI 505a/g基因多态性可能与VTE无关。     

凝血酶激活的纤溶抑制物及其抑制物的研究进展

凝血酶激活的纤溶抑制物(TAFI)是一种含锌的金属羧肽酶原。TAFI通过消除部分降解的纤维蛋白上的赖氨酸残基，从而抑制纤维蛋白的进一步溶解。这一机理表明TAFI在纤维蛋白溶解及血栓溶解过程中具有重要的调节作用。对TAFI及其抑制物的深入研究可以为辅助溶栓药物的开发提供新的思路。     

A new functional assay of thrombin activatable fibrinolysis inhibitor

New thrombin activatable fibrinolysis inhibitor (TAFI) assays are necessary for studying the role of this fibrinolysis inhibitor in cardiovascular disease. The identification of a functional single nucleotide polymorphism (SNP) (1040C/T) leading to a TAFI-variant with increased stability but lower antigen levels has made the determination of functional activity even more essential. Therefore, we developed a new assay for the functional activity of TAFI in citrated plasma samples. This assay is based on the retardation of plasma clot lysis by TAFIa. TAFI activation was induced simultaneously with fibrin formation and lysis was mediated by rt-PA. The variability of other plasma components was minimized by a 20-fold dilution of the samples in TAFI-depleted plasma. Lysis times (-/+ potato carboxypeptidase inhibitor) and the TAFI-related retardation of clot lysis, the functional parameter of the assay, were determined in a group of 92 healthy volunteers, as well as TAFI antigen levels (electroimmunoassay) and two TAFI SNPs (-438A/G and 1040C/T). TAFI-related retardation was 19.8 +/- 5.6 min (mean +/- SD) and was correlated with the antigen level. The specific antifibrinolytic activity of TAFI was associated with the -438A/G and 1040C/T genotypes. Individuals with the 325Ile-variant had on average a 34% higher TAFI-specific antifibrinolytic activity than individuals with the 325Thr-isoform. The TAFI-related retardation in the two groups of individuals did not differ, as a lower level compensated for the higher specific antifibrinolytic activity of the 325Ile-isoform. This assay provides valuable information about the performance of different TAFI isoforms and constitutes a new method for studying the role of TAFI in cardiovascular disease.     

脑卒中患者血浆凝血酶激活的纤溶抑制物的临床研究

目的研究总凝血酶激活的纤溶抑制物(TAFI)抗原(TAFI∶Ag)和活化的TAFI∶Ag(TAFIa∶Ag)与脑卒中的相关性,探讨二者在缺血性脑卒中(IS)和出血性脑卒中(ICH)的临床意义。方法采用酶联免疫吸附试验(ELISA)对228例脑卒中患者血浆TAFI水平变化进行研究分析,并将IS和ICH分别与对照组比较。结果与对照组[TAFI∶Ag(100.63±25.28)μg/mL;TAFIa∶Ag(126.43±31.88)ng/mL]相比,卒中发作时,2指标在IS[(118.72±31.41)μg/mL,(168.79±55.36)ng/mL]和ICH[(127.51±37.59)μg/mL,(207.99±73.71)ng/mL]均明显升高(P<0.01),并有较高发生率;TAFI评估脑卒中发病风险时,TAFIa∶Ag在IS是对照组的3倍,在ICH是对照组的7倍。结论血浆TAFI与脑卒中存在密切关系,TAFI升高大大地增加了脑卒中的发病风险。     

Increased zymogen activity of thrombin‐activatable fibrinolysis inhibitor prolongs clot lysis

Summary. Background and objectives: Thrombin‐activatable fibrinolysis inhibitor (TAFI) is a zymogen that can be activated by proteolytic cleavage into the active enzyme TAFIa. Hydrolysis of the C‐terminal lysines on fibrin by TAFIa results in a down‐regulation of fibrinolysis. Recent studies demonstrated that the zymogen also exerts an intrinsic enzymatic activity. Our objective was to identify and characterize zymogen‐stimulatory nanobodies. Methods and results: The screening of 24 nanobodies against TAFI revealed that two nanobodies (i.e. Vhh‐TAFI‐a51 and Vhh‐TAFI‐i103) were able to stimulate the zymogen activity 10‐ to 21‐fold compared with the baseline zymogen activity of TAFI. The increase in catalytic efficiency can be attributed mainly to an increased catalytic rate, as no change in the K_M‐value was observed. The stability, the susceptibility towards PTCI and GEMSA and the kinetics of the stimulated zymogen activity differ significantly from those of TAFIa activity. Epitope mapping revealed that both Asp⁷⁵ and Thr³⁰¹ are major determinants in the binding of these nanobodies to TAFI. Localization of the epitope strongly suggests that this instability is as a result of a disruption of the stabilizing interactions between the activation peptide and the dynamic flap region (residues 296–350). In TAFI‐depleted plasma reconstituted with a non‐activatable variant of TAFI (TAFI‐R92A), clot lysis could be prolonged by nanobody‐induced stimulation of its zymogen activity as well as by increasing its concentration. Conclusions: Increasing the zymogen activity of TAFI results in an antifibrinolytic effect.     

Thrombin‐activatable fibrinolysis inhibitor is degraded by Salmonella enterica and Yersinia pestis

Summary. Background: Pathogenic bacteria modulate the host coagulation system to evade immune responses or to facilitate dissemination through extravascular tissues. In particular, the important bacterial pathogens Salmonella enterica and Yersinia pestis intervene with the plasminogen/fibrinolytic system. Thrombin‐activatable fibrinolysis inhibitor (TAFI) has anti‐fibrinolytic properties as the active enzyme (TAFIa) removes C‐terminal lysine residues from fibrin, thereby attenuating accelerated plasmin formation. Results: Here, we demonstrate inactivation and cleavage of TAFI by homologous surface proteases, the omptins Pla of Y. pestis and PgtE of S. enterica. We show that omptin‐expressing bacteria decrease TAFI activatability by thrombin‐thrombomodulin and that the anti‐fibrinolytic potential of TAFIa was reduced by recombinant Escherichia coli expressing Pla or PgtE. The functional impairment resulted from C‐terminal cleavage of TAFI by the omptins. Conclusions: Our results indicate that TAFI is degraded directly by the omptins PgtE of S. enterica and Pla of Y. pestis. This may contribute to the ability of PgtE and Pla to damage tissue barriers, such as fibrin, and thereby to enhance spread of S. enterica and Y. pestis during infection.     

2型糖尿病患者血浆凝血酶激活的纤溶抑制物变化观察

目的评价血浆凝血酶激活的纤溶抑制物(TAFI)在2型糖尿病患者凝血及纤溶功能变化中的作用。方法检测90例2型糖尿病患者和30例与患者年龄相匹配的健康者血浆中TAFI、组织纤溶酶原激活物(t-PA)、纤溶酶原激活物抑制物(PAI-1)。结果TAFI的活性在2型糖尿病各组患者血浆中高于对照组(P<0.05),高蛋白尿组较尿蛋白正常组和低蛋白尿组升高(P<0.05)。t-PA在无并发症组低于对照组,但无统计学意义(P>0.05),高蛋白尿约较尿蛋白正常组和低蛋白尿组低(P<0.05)。PAI-1在2型糖尿病各组患者高于对照组(P<0.05),高蛋白尿组较尿蛋白正常组利低蛋白尿组升高(P<0.05)。TAFI的活性与t-PA和PAI-1含量有较好的相关性。结论检测2型糖尿病患者血浆中TAFI活性水平,对于预测2型糖尿病患者的微血管病变程度,防治2型糖尿病并发症有着重要意义。     

The role of thrombin activatable fibrinolysis inhibitor and factor XI in platelet‐mediated fibrinolysis resistance: a thromboelastographic study in whole blood

Summary. Background: The resistance of platelet‐rich thrombi to fibrinolysis is generally attributed to clot retraction and platelet PAI‐1 release. The role of TAFI in platelet‐mediated resistance to lysis is unclear. Objective: We investigated the contribution of TAFI to the antifibrinolytic effect of platelets in whole blood by thromboelastography. Methods: Platelet‐poor (PP‐WB, < 40 × 10³ μL^?1) and platelet‐rich (PR‐WB, > 400 × 10³ μL^?1) blood samples were obtained from normal human blood (N‐WB, 150–220 × 10³ μL^?1). Clot lysis time was measured by thromboelastography in recalcified blood supplemented with t‐PA (100 ng mL^?1) and tissue factor (1:1000 Recombiplastin). Results: t‐PA‐induced lysis time increased in parallel with platelet concentration (up to 3‐fold). Neutralization of TAFI, but not of PAI‐1, shortened the lysis time by ～ 50% in PR‐WB and by < 10% in PP‐WB. Accordingly, prothrombin F1+2 and TAFIa accumulation was greater in PR‐WB than in PP‐WB. A similar TAFI‐dependent inhibition of fibrinolysis was observed when clot retraction was prevented by cytochalasin D or abciximab, or when platelet membranes were tested. Moreover, in blood with an intact contact system, platelet‐mediated fibrinolysis resistance was attenuated by an anti‐FXI but not by an anti F‐XII antibody. Finally, platelets made the clots resistant to the profibrinolytic effect of heparin concentrations displaying a strong anticoagulant activity. Conclusions: Our data indicate that TAFI activation is one major mechanism whereby platelets make clots resistant to fibrinolysis and underscore the importance of TAFI inhibitors as new antithrombotic agents.     

The role of thrombin activatable fibrinolysis inhibitor in arterial thrombosis at a young age: the ATTAC study1

Summary. Background and objectives: Thrombin activatable fibrinolysis inhibitor (TAFI) attenuates fibrinolysis and may therefore contribute to the pathophysiology of arterial thrombosis. The aim of the present study was to elucidate the pathogenetic role of TAFI levels and genotypes in young patients with arterial thrombosis. Patients and methods: In a case–control study, 327 young patients with a recent first‐ever event of coronary heart disease (CHD subgroup) or cerebrovascular disease (ischemic stroke subgroup) and 332 healthy young controls were included. TAFI levels [intact TAFI, activation peptide (TAFI‐AP) and (in)activated TAFI (TAFIa(i)] and TAFI activity were measured and genetic variations in the TAFI gene (?438G/A, 505G/A and 1040C/T) were determined. Results: In the total group of patients, TAFIa(i) levels were higher (145.1 ± 37.5%) than in controls (137.5 ± 31.3%, P = 0.02). Plasma levels of intact TAFI, TAFI‐AP and TAFI activity were similar in patients and controls. In the CHD subgroup (n = 218), intact TAFI levels were higher (109.4 ± 23.0%) than in controls (102.8 ± 20.7%, P = 0.02). In 325Ile/Ile homozygotes, lower TAFI levels and a decreased risk of arterial thrombosis were observed (OR 0.58, 95% CI 0.34–0.99) compared with patients with the common 325Thr/Thr genotype. This association was most evident in CHD patients (OR 0.48, 95% CI 0.26–0.90). Haplotype analyses supported a role for the Thr325Ile polymorphism. Conclusions: TAFIa(i) levels were higher in patients with cardiovascular disease. Furthermore, the TAFI 325Thr/Ile polymorphism was associated with lower TAFI levels and with the risk of cardiovascular disease in young patients, especially in CHD.