蛋白Z和蛋白Z依赖的蛋白酶抑制剂在血栓性疾病中的作用

蛋白Z是一种维生素K依赖性蛋白,作为蛋白Z依赖的蛋白酶抑制剂(ZPI)的辅因子,在磷脂和钙离子存在的条件下,能够抑制因子Xa,ZPI也能抑制因子Ⅺa.蛋白Z,ZPI与血栓性疾病中的关系已有初步研究.     

蛋白Z和蛋白Z依赖的蛋白酶抑制剂研究进展

蛋白Z是一种维生素K依赖性蛋白,作为蛋白Z依赖的蛋白酶抑制剂(ZPI)的辅因子,在磷脂和钙离子存在的条件下,能够抑制因子Xa,ZPI也能抑制因子Xla。蛋白Z和 ZPI与血栓性疾病如心脑血管疾病、静脉血栓形成及不明原因流产等疾病的关系已有初步研究。     

脑梗死患者蛋白质Z检测的临床意义

目的方法采用双抗体夹心ELISA法检测75例急性脑梗死患者不同时间点血浆蛋白质Z水平,依据梗死灶面积大小分为轻度、中度及重度梗死组,另择50例健康体检者作为对照组,比较各组的血浆蛋白质Z水平。结果梗死组血浆蛋白质Z水平明显低于对照组（P〈0．01）;人院时、治疗7d及14d梗死组与对照组比较均有统计学差异（P均〈0．01）;重度梗死组明显低于中度及轻度梗死组,中度梗死组明显低于轻度梗死组（P均〈0．01）。结论血浆蛋白质Z参与了脑梗死的发病过程,并与梗死严重程度密切相关,可能是急性脑梗死早期预警因子之一。     

肝硬化患者血浆凝血酶激活的纤维蛋白溶解抑制物和蛋白Z的变化及意义

凝血酶激活的纤维蛋白溶解抑制物(thrombin activatable fibrinolysis inhibitor,TAFI)具有羧肽酶活性,当血液凝固时,TAFI可被凝血酶激活,特异性裂解纤维蛋白C末端赖氨酸残基,下调纤溶系统[1].蛋白Z(protein Z)是由肝脏合成的一种维生素K依赖性蛋白,在磷脂和钙离子存在的条件下,蛋白Z依赖的蛋白酶抑制剂(protein Z-dependent protease inhibitor,ZPI)抑制活化的凝血因子X(因子Xa),蛋白Z可使其作用增强1000倍.有研究发现,蛋白Z与血栓性疾病如脑梗死、深静脉血栓形成等关系密切[2].肝硬化患者存在血液凝血与纤维蛋白溶解异常,是由多种原因造成[3],而该类患者血浆TAFI和蛋白Z的变化如何,少见报道.     

蛋白质Z在急性缺血性脑卒中患者早期诊断中的价值

目的与同型半胱氨酸和B型脑钠肽比较,探讨蛋白质Z在急性缺血性脑卒中患者早期诊断中的价值。方法采用ELISA法检测32例急性缺血性脑卒中患者血浆蛋白质Z和同型半胱氨酸,同时采用快速荧光免疫法检测血浆B型脑钠肽,并与50例健康体检者（对照组）进行比较。结果急性缺血性脑卒患者发病早期（6 h）血浆中蛋白质Z、同型半胱氨酸和B型脑钠肽均明显高于对照组（P〈0.01）,发病6 h内蛋白质Z的敏感性显著高于同型半胱氨酸和B型脑钠肽（P均〈0.01）,三者特异性相比无统计学差异;梗死灶越大,神经功能缺损评分越高,血浆蛋白质Z水平越低（P均〈0.05）。结论血浆蛋白质Z可作为早期诊断急性缺血性脑卒中的生物学指标。     

重症病毒性肝炎的凝血障碍及其治疗

凝血因子主要在肝内合成，人体凝血系统共有12种凝血因子，其中有10种(即凝血因子Ⅰ、Ⅱ、Ⅴ、Ⅶ、Ⅷ、Ⅸ、Ⅹ、Ⅺ、Ⅻ及13)在肝内或主要在肝内合成，此外还有如激肽释放酶原(PK)、高分子量激肽酶原(HMWK)及抗凝血酶Ⅲ(ATⅢ)等，也是在肝内合成(见附表)，其中Ⅱ、Ⅶ、Ⅸ及Ⅹ因子在肝内合成，并需维生素K参与，所以又称维生素K依赖性因子。     

蛋白Z与卒中

蛋白Z是一种由肝脏合成的维生素K依赖性糖蛋白,在凝血过程中起重要的调节作用,它可能是卒中的一种独立危险因素。通过对蛋白Z进行研究,有助于我们深入了解蛋白Z在卒中早期诊断、预防和治疗中的作用。     

维生素K依赖性凝血因子的临床意义

维生素K(VK)是维持正常凝血过程必不可少的维生素。凝血因子Ⅱ、Ⅶ、Ⅸ和Ⅹ均是VK依赖性凝血因子。VK缺乏引起相关凝血因子活性下降,导致维生素K依赖性凝血因子缺乏症(VKCFD),临床上患者表现为各种出血症状,补充VK后出血症状可被纠正。我们现对VK的凝血作用、VKCFD的诊治及VK拮抗剂的应用进行综述。     

蛋白Z与出血及血栓性疾病

血液凝血 抗凝、纤溶系统的失衡是引起出血和血栓性疾病的主要机制。抗凝蛋白在凝血过程中发挥着重要的调节作用 ,其中蛋白C(PC)、蛋白S(PS)、抗凝血酶等的作用机制已基本明确 ,蛋白Z(PZ)是近年来新发现的维生素K(VK)依赖性糖蛋白 ,对PZ的研究使我们对凝血机制有了新的深入了解。PZ有多种生物学作用 ,主要是介导了凝血酶与内皮细胞表面磷脂的结合 ,发挥抗凝活性。一、PZ概况Prowse及Esnouf[1] 首次从牛血浆中提取出一种新的VK依赖性蛋白的糖蛋白 ,属于丝氨酸蛋白酶抑制物超家族成员。在无Ca2 + 、PZ及磷脂存在时 ,PZ不依赖性蛋…     

急性冠脉综合征患者冠脉介入术前后血浆TF和TFPI的变化及临床意义

血栓形成是急性冠状动脉综合征(ACS)以及冠脉介入术后再狭窄发生的主要病理生理基础[1,2].组织因子(TF)是凝血过程中主要的启动因子,其与凝血因子VⅡ(FVⅡ)形成TF-FVⅡa复合物后,即可启动下游凝血瀑布反应[3].组织因子途径抑制物(TFPI)则可反馈性抑制TF-FVⅡa复合物,并有活化凝血因子Ⅹ(FⅩa)的作用,从而对凝血的始动环节进行负性调节[4].因此,TF/TFPI平衡的破坏是冠脉内血栓形成的关键.本研究通过比较急性心肌梗死(AMI)和不稳定型心绞痛(UAP)患者在冠脉介入术前后血浆中TF和TFPI水平变化,探讨血浆TF和TFPI对ACS诊断和预后的临床价值.     

Protein Z/protein Z-dependent protease inhibitor system in loco in human gastric cancer

In gastric cancer, hemostatic system components contribute to cancer progression, as activation of factor X (FX) was observed. The protein Z (PZ)/protein Z-dependent protease inhibitor (ZPI) complex inhibits factor Xa proteolytic activity. The purpose of this study was to determine the distribution of ZPI and PZ in relation to FX, and prothrombin fragment (F1?+?2), a standard marker for blood coagulation activation, in human gastric cancer tissue. ABC procedures and a double staining method employed polyclonal antibodies against PZ, FX, and F1?+?2 and a monoclonal antibody against ZPI. In situ hybridization (ISH) methods employed biotin-labeled 25-nucleotide single-stranded DNA probes directed to either PZ or ZPI mRNAs. FX and components of PZ/ZPI coagulation inhibitory system were observed in cancer cells. F1?+?2 was observed in gastric cancer cells as well. Double staining studies revealed FX/PZ, FX/ZPI, and PZ/ZPI co-localization on gastric cancer cells. ISH studies demonstrated the presence of PZ mRNA and ZPI mRNA in gastric cancer cells indicating induced synthesis of these proteins. The co-localization of PZ/ZPI and FX in gastric cancer cells indicates in loco that these proteins may play a role in anticoagulant events at the tumor tissue.     

Characterization of the protein Z-dependent protease inhibitor

Protein Z-dependent protease inhibitor (ZPI) is a 72-kd member of the serpin superfamily of proteinase inhibitors that produces rapid inhibition of factor Xa in the presence of protein Z (PZ), procoagulant phospholipids, and Ca(++) (t(1/2) less than 10 seconds). The rate of factor Xa inhibition by ZPI is reduced more than 1000-fold in the absence of PZ. The factor Xa-ZPI complex is not stable to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but is detectable by alkaline-polyacrylamide gel electrophoresis. The combination of PZ and ZPI dramatically delays the initiation and reduces the ultimate rate of thrombin generation in mixtures containing prothrombin, factor V, phospholipids, and Ca(++). In similar mixtures containing factor Va, however, PZ and ZPI do not inhibit thrombin generation. Thus, the major effect of PZ and ZPI is to dampen the coagulation response prior to the formation of the prothrombinase complex. Besides factor Xa, ZPI also inhibits factor XIa in the absence of PZ, phospholipids, and Ca(++). Heparin (0.2 U/mL) enhances the rate (t(1/2) = 25 seconds vs 50 seconds) and the extent (99% vs 93% at 30 minutes) of factor XIa inhibition by ZPI. During its inhibitory interaction with factor Xa and factor XIa, ZPI is proteolytically cleaved with the release of a 4.2-kd peptide. The N-terminal amino acid sequence of this peptide (SMPPVIKVDRPF) establishes Y387 as the P(1) residue at the reactive center of ZPI. ZPI activity is consumed during the in vitro coagulation of plasma through a proteolytic process that involves the actions of factor Xa with PZ and factor XIa.     

Protein Z-dependent protease inhibitor deficiency produces a more severe murine phenotype than protein Z deficiency

Protein Z (PZ) is a plasma vitamin K–dependent protein that functions as a cofactor to dramatically enhance the inhibition of coagulation factor Xa by the serpin, protein Z–dependent protease inhibitor (ZPI). In vitro, ZPI not only inhibits factor Xa in a calcium ion–, phospholipid-, and PZ-dependent fashion, but also directly inhibits coagulation factor XIa. In murine gene-deletion models, PZ and ZPI deficiency enhances thrombosis following arterial injury and increases mortality from pulmonary thromboembolism following collagen/epinephrine infusion. On a factor V_Leiden genetic background, ZPI deficiency produces a significantly more severe phenotype than PZ deficiency, implying that factor XIa inhibition by ZPI is physiologically relevant. The studies in mice suggest that human PZ and ZPI deficiency would be associated with a modest thrombotic risk with ZPI deficiency producing a more severe phenotype.      

Isolation of a protein Z-dependent plasma protease inhibitor

Human protein Z (PZ) is a 62,000-M_r, vitamin K-dependent plasma protein whose structure is similar to coagulation factors VII, IX, X, protein C, and protein S, but whose function is not known. The procoagulant activity of factor Xa in a one-stage plasma coagulation assay is reduced when factor Xa is first incubated with PZ. This apparent inhibitory effect is time dependent, requires the presence of calcium ions and procoagulant phospholipids (rabbit brain cephalin), and appears predominantly related to the incubation period of PZ with cephalin. In serum the initial rate of inhibition of factor Xa with calcium ions and cephalin also is enhanced in the presence PZ. A PZ-dependent protease inhibitor (ZPI) has been isolated from plasma. ZPI is a 72,000-M_r single-chain protein with an N-terminal amino acid sequence of LAPSPQSPEXXA (X = indeterminate) and an estimated concentration in citrate-treated plasma of 1.0–1.6 μg/ml. In systems using purified components, the factor Xa inhibition produced by ZPI is rapid (>95% within 1 min by coagulation assay) and requires the presence of PZ, calcium ions, and cephalin. The inhibitory process appears to involve the formation of a factor Xa–PZ–ZPI complex at the phospholipid surface.     

Structural basis for catalytic activation of protein Z-dependent protease inhibitor (ZPI) by protein Z

The anticoagulant serpin, protein Z-dependent protease inhibitor (ZPI), is catalytically activated by its cofactor, protein Z (PZ), to regulate the function of blood coagulation factor Xa on membrane surfaces. The X-ray structure of the ZPI-PZ complex has shown that PZ binds to a unique site on ZPI centered on helix G. In the present study, we show by Ala-scanning mutagenesis of the ZPI-binding interface, together with native PAGE and kinetic analyses of PZ binding to ZPI, that Tyr240 and Asp293 of ZPI are crucial hot spots for PZ binding. Complementary studies with protein Z-protein C chimeras show the importance of both pseudocatalytic and EGF2 domains of PZ for the critical ZPI interactions. To understand how PZ acts catalytically, we analyzed the interaction of reactive loop-cleaved ZPI (cZPI) with PZ and determined the cZPI X-ray structure. The cZPI structure revealed changes in helices A and G of the PZ-binding site relative to native ZPI that rationalized an observed 6-fold loss in PZ affinity and PZ catalytic action. These findings identify the key determinants of catalytic activation of ZPI by PZ and suggest novel strategies for ameliorating hemophilic states through drugs that disrupt the ZPI-PZ interaction.     

Protein Z/Z-dependent protease inhibitor (PZ/ZPI) anticoagulant system and thrombosis

A new anticoagulant system involving a serpin has been recently characterised. The protein Z/Z-dependent protease inhibitor (PZ/ZPI) system inhibits activated factors X, XI and IX by different mechanisms. By homology with other anticoagulant systems (antithrombin or the protein C/protein S), deficiency of the serpin (ZPI) or its cofactor (PZ) might imbalance the haemostatic system with thrombotic consequences. Evidence supports the in vivo anticoagulant role of this complex and the thrombotic consequences of its deficiency. Non-sense variations of the ZPI (W303X and R67X) have been associated with increased risk of venous thrombosis. Moreover, PZ deficient mice carrying the FV Leiden have a thrombotic phenotype. Finally, some reports suggest that PZ deficiency might increase the risk of thrombosis. However, other studies question the thrombotic relevance of both ZPI and PZ deficiencies. This system could play a redundant role in haemostasis that explains the conflicting results on its thrombotic potential, which might be exacerbated in combination with other prothrombotic factors.     

Protéine Z,polymorphismes du gène de la protéine Z et thromboses

Protein Z (PZ) is a vitamin K dependent protein acting as the cofactor of the protein Z dependent inhibitor (ZPI), in the inhibition of activated factor X bound on the phospholipids. Normal plasma protein Z concentrations have wide variations among individuals, partly explained by a genetic control. Several protein Z gene polymorphisms influence plasma concentration, separately and in combination. The role of PZ in blood coagulation regulation has been demonstrated in vitro. The responsibility of low PZ level in the occurrence of thrombosis has been questioned. However, the roles of PZ plasma level and PZ gene polymorphisms remain debated with conflicting results in arterial, venous, or placental thrombosis. These discrepancies can be explained by the heterogeneity of populations chosen as control, by the PZ interindividual variability, by the small size of the cohorts in mainly retrospective studies and perhaps by the lack of real important influence of this protein on coagulation. PZ measurement is not actually considered as a biological marker of thrombophilia. Large prospective studies remain to be done to investigate its possible role in thrombosis.     

Prothrombotic phenotype of protein Z deficiency

Protein Z (PZ) is a vitamin K-dependent plasma protein whose function has been uncertain. The structure of PZ is very similar to that of the coagulation-related factors VII, IX, and X and PC, but PZ differs from these other proteins in that it is not the zymogen of a serine protease. We have shown recently that PZ forms a calcium ion-dependent complex with activated factor X at phospholipid surfaces and that this interaction leads to the inhibition of activated factor X activity through, in part, the action of a previously unidentified plasma protein named PZ-dependent protease inhibitor. Herein, we report that the presence of PZ dampens the coagulation response in human plasma and that concomitant PZ deficiency dramatically increases the severity of the prothrombotic phenotype of factor V(Leiden) mice. The results indicate that PZ plays a physiologically important role in the regulation of coagulation.     

Role of protein Z in stroke

Opinion statement Protein Z (PZ) is a vitamin K-dependent plasma glycoprotein that acts as a cofactor for PZ-dependent protease inhibitor to inhibit coagulation factor X_a. Studies in mice suggest that that decreased blood PZ levels lead to reduced inhibition of blood coagulation, thereby predisposing to thrombosis; however, clinical studies in humans have yielded conflicting results. Among patients with stroke, some epidemiologic studies have reported that reduced PZ levels increase the risk of stroke, whereas others have reported no association between PZ levels and stroke, or that elevated PZ levels increase stroke risk. Polymorphisms involving the gene for PZ can influence the PZ concentration and some polymorphisms (eg, intron G79A AA allele) may be protective against stroke, particularly among younger individuals. Although the association between PZ levels and stroke appears to be stronger in younger patients and in patients who do not have conventional vascular risk factors, it remains unclear whether the link between PZ levels and stroke is confounded or causal or whether blood levels of PZ are altered as a consequence of the acute stroke event.