Protein Z-dependent regulation of coagulation

Protein Z (PZ) is a 62 kDa vitamin K-dependent plasma protein that serves as a cofactor for the inhibition of factor Xa by protein Z-dependent protease inhibitor (ZPI). ZPI is a recently identified 72 kDa member of the serpin superfamily of proteinase inhibitors that contains a tyrosine at its reactive center. PZ circulates in plasma in a complex with ZPI. Inhibition of factor Xa by ZPI in the presence of phospholipids and Ca++ is enhanced 1000-fold by PZ, but ZPI also inhibits factor XIa in a process that does not require PZ, phospholipids or Ca++. ZPI activity is consumed during coagulation through proteolysis mediated by factor Xa with PZ and factor Xla. Concomitant PZ deficiency dramatically increases the severity of the prothrombotic phenotype of factor VLeiden mice. Studies to determine the potential roles of PZ and ZPI deficiency in human thrombosis are in progress.     

Protein Z, a protein seeking a pathology

Protein Z (PZ) is a vitamin K-dependent factor identified in human plasma in 1984 characterized by an homology with other vitamin K-dependent factors (factor VII, IX, X, protein C). In contrast to these factors, PZ does not possess any enzymatic activity but is involved as a cofactor in the down-regulation of coagulation by forming a complex with the protein Z-dependent protease inhibitor (ZPI). ZPI inhibits the activated factor X (FXa) on phospholipid surface. In mice, the disruption of PZ gene is asymptomatic, but the association with the factor V Leiden mutation leads to a quasi complete mortality during the neonatal period with microvascular thrombosis. In humans, PZ is characterized by an unusual wide distribution in plasma, and a major decrease induced by warfarin. Isolated PZ deficiency does not seem to constitute a risk for venous thrombosis, but a severe PZ deficiency could increase the risk of well recognized venous thrombotic risk factors such as factor V Leiden, G20210A mutation or hyperhomocysteinemia. Unexpectedly, a relationship between PZ deficiency and ischemic arterial diseases such as stroke, acute coronary syndromes or peripheral arterial disease was described but not confirmed by all studies. PZ deficiency could be also a risk factor for early fetal losses, and increases the arterial risk in antiphospholipid syndrome. This review analyzes the different studies so far published and discusses the various results obtained in order to understand whether or not protein Z deficiency could be considered as an arterial ischemic risk factor.     

Factor V Leiden and hemophilia

Several inherited prothrombotic risk factors have been identified so far. Among them, the factor V (FV) Leiden mutation causes a reduced ability of activated protein C to inactivate activated FV and is the most frequent genetic predisposing factor for venous thromboembolism. However, the high prevalence of FV Leiden (up to 15%) in the Caucasian population suggests that this mutation might confer an evolutionary survival advantage. Indeed, there is mounting evidence about the role of FV Leiden in modulating the clinical phenotype of some physiological and pathological conditions, including hemophilia. The existing literature on the interaction between FV Leiden and hemophilia-related factor VIII or IX mutations is analyzed in this review focusing on the clinical effects and possible pathogenic mechanisms. In summary, current evidence suggests that this prothrombotic mutation may compensate for the low factor VIII or IX levels, resulting in more efficient thrombin generation and ensuing attenuation of clinical symptoms. On the other hand, the association of this prothrombotic mutation with other acquired or inherited thrombophilic factors might overcome the congenital bleeding tendency in hemophiliacs, thereby increasing the risk of thrombotic complications.     

Protein Z and protein Z-dependent protease inhibitor. Determinants of levels and risk of venous thrombosis

To assess the potential roles of protein Z (PZ) and protein Z-dependent protease inhibitor (ZPI) in venous thrombosis, their plasma levels were measured in 426 individuals with venous thrombosis and 471 control individuals participating in the Leiden Thrombophilia Study. A relationship between the level of PZ or ZPI and venous thrombosis was not detected in the overall case-control study. PZ and ZPI circulate as a complex and their plasma levels are interdependent. Both PZ and ZPI are increased with oral contraceptive use and reduced with oral anticoagulant therapy.     

Thrombin generation in first-degree relatives of patients with venous thromboembolism who have factor V Leiden. A pilot study

The thrombin generation test appears to be a highly sensitive and specific test in the detection of thrombophilia in patients with venous thromboembolism. We aimed to determine the accuracy of the thrombin generation test to detect factor V Leiden and/or other prothrombotic states in first-degree relatives of patients with venous thromboembolism and factor V Leiden. Sixty-two first-degree relatives of 21 index cases were tested for factor V Leiden, the G20210A prothrombin gene mutation and thrombin generation. Information about oestrogen therapy and previous VTE was also collected. The normalized Thrombomodulin sensitivity ratio (n-TMsr) was defined as the ratio of endogenous thrombin potential determined in the presence and absence of thrombomodulin which was normalized against the same ratio determined in normal control plasma. The mean n-TMsr was 1.37 (+/- 0.33) in the 45 relatives with one or more prothrombotic state (factor V Leiden, G20210A prothrombin mutation, oestrogen therapy or hormonal therapy) and 1.02 (+/- 0.34) in the 17 relatives without prothrombotic state (p = 0.001). The positive predictive value was 90.3 (95%CI, 73.1-97.4). In relatives with an abnormal n-TMsr, the adjusted odds ratio for having a prothrombotic state was 8.3 (95%CI, 1.9-36.9) and the adjusted odds ratio for having the factor V Leiden was 14.3 (95%CI, 2.9-71.2). An abnormal thrombin generation test appears highly predictive for having factor V Leiden and/or other prothrombotic states in first-degree relatives of patients with venous thromboembolism and factor V Leiden.     

Basilar artery thrombosis in a child heterozygous for factor V Leiden mutation

Activated protein C resistance, usually because of factor V Leiden mutation, is considered to be the most common hereditary prothrombotic condition. A 9-year-old male with a basilar artery stroke and activated protein C resistance is described. The patient, found to be heterozygous for factor V Leiden mutation, is one of several recent reports that suggest that activated protein C resistance is an important risk factor for spontaneous arterial thrombosis in infancy and childhood.     

Etiological analysis of presumed perinatal stroke

This study aimed to investigate the maternal, pre- and perinatal, and prothrombotic factors with congenital hemiparesis due to presumed perinatal stroke (PPS). Prothrombotic risk factors including protein C and S, antithrombin III, lipoprotein (a), homocystein, factor VIII levels; anticardiolipin antibodies and lupus anticoagulant; methylenetetrahydrofolate reductase mutations, factor V Leiden, prothrombin G20210A mutations were investigated. Arterial ischemic stroke was detected in 60% and periventricular venous infarction in 40%. At least one prothrombotic risk factor was present in 69%, two in 17%, and three or more in 8.5% of cases. The most common combination was methylenetetrahydrofolate reductase C677T and factor V Leiden heterozygosity. The etiology and pathogenesis of PPS is still unclear. According to this study, most of the patients with PPS might have one or more prothrombotic risk factors and certain prenatal risk factors including intrauterine growth retardation, twin gestation and preeclampsia might be related to PPS.     

Protein Z circulates in plasma in a complex with protein Z-dependent protease inhibitor

Protein Z (PZ) is a vitamin K-dependent plasma protein that forms a Ca++-dependent complex with factor Xa at phospholipid surfaces. This interaction between PZ and factor Xa enhances by >1,000-fold the inhibition of factor Xa by the serpin called protein Z-dependent protease inhibitor (ZPI). These experiments show that PZ also binds ZPI in a process that does not require Ca++ or phospholipids. In pooled normal plasma, which contains excess ZPI relative to PZ, all the PZ appears to be bound in a complex with ZPI. The binding of PZ to ZPI reduces the rate and extent of factor XIa inhibition produced by ZPI. During the course of these studies, it was noted that a PZ purification procedure, that included NaSCN (2.0 M) elution of PZ from an immunoaffinity column, produced aggregated, inactive forms of PZ.     

Increase in the plasma levels of protein Z-dependent protease inhibitor in normal pregnancies but not in non-pregnant patients with unexplained recurrent miscarriage

Protein Z (PZ)-dependent protease inhibitor (ZPI) is a serine protease inhibitor which efficiently inactivates activated factor X, when ZPI is complexed with PZ in plasma. Reduced plasma levels of ZPI and PZ have been reported in association with thrombosis. It has also been reported that PZ increases during pregnancy and that its partial deficiency is related to early pregnancy loss or recurrent miscarriage (RM). However, until now there has been no report on ZPI in pregnancy. To explore the possible role(s) of ZPI in the maintenance of pregnancy, we studied 42 non-pregnant normal women, 32 women with normal pregnancies, and 134 cases of unexplained RM in Japan, as well as 64 non-pregnant normal German females. Plasma ZPI was measured by in-house ELISA. There were significantly higher concentrations of plasma ZPI in normal pregnancies compared to non-pregnant women. The present study also confirmed that both factor X, the major target of ZPI, and protein Z increased during normal pregnancies. This increased ZPI and PZ may counteract the increased activated factor X, which may in turn contribute to the maintenance of normal placental circulation. Plasma ZPI levels were unchanged in non-pregnant RM women, while the plasma PZ level was slightly reduced, a finding consistent with existing reports. The exact relationship between RM and this unaltered ZPI with mild PZ reduction relative to normal pregnancies warrants further investigation.     

Inherited prothrombotic states and ischaemic stroke in childhood

OBJECTIVE—To investigate the prevalence ofcurrently recognised inherited prothrombotic states in a population ofchildren with arterial stroke.
METHODS—Children with arterial stroke presentingto a tertiary level paediatric neurology centre between 1990 and 1996 were investigated for inherited prothrombotic states.
RESULTS—Sixty seven children with arterial strokewere investigated. Abnormalities were initially identified in 16 patients; however, only eight children (12%) had an inheritedprothrombotic state. This was type 1 protein S deficiency in onepatient, the factor V Leiden mutation in six, and activated protein Cresistance (without the factor V Leiden mutation) in one. Theprevalence of the factor V Leiden mutation was not significantly higherin children with arterial stroke (12%) than in a control population ofchildren without thrombosis attending the same institution (5.2%;Fisher's exact test, p=0.19; difference in prevalence between patients and controls (95% confidence interval)=6.8% (−2.78% to 16.8%)).
CONCLUSIONS—Currently recognised inheritedprothrombotic tendencies were rarely associated with stroke in thisgroup of children, although larger numbers of patients would be neededto confirm this. Age appropriate normal values should be used wheninterpreting the results of a prothrombotic screen. Prothromboticabnormalities seen acutely are as often transient as inherited.Longitudinal assessment and family studies are required before lowconcentrations of an anticoagulant protein found acutely can beattributed to an inherited abnormality.

     

The risk of occurrence of venous thrombosis: focus on protein Z

Protein Z (PZ) is a vitamin K-dependent factor identified in human plasma in 1984 characterized by an homology with other vitamin K-dependent factors. PZ acts as the cofactor of the PZ dependent inhibitor (ZPI), in the inhibition of activated factor X bound on phospholipid surface. In humans, PZ is characterized by an unusual wide distribution in plasma partly explained by a genetic control. Several PZ gene polymorphisms influencing plasma concentration have been described. In mice, the disruption of PZ gene is asymptomatic, but in association with homozygous FV Leiden produced a severe prothrombotic phenotype. This review analyzes the results obtained from different studies so far published in order to understand whether PZ deficiency could be considered as a risk factor for venous thrombosis.The roles of PZ plasma level and PZ gene polymorphisms remain debated with conflicting results. Many of these studies reported low PZ levels in association with an increased risk of venous thrombosis. On the other side, some studies did not observe an association between low levels of PZ and thrombotic events. A relationship between PZ deficiency and pregnancy complications was also described but not confirmed by all studies.These discrepancies can be explained by the heterogeneity of populations chosen as control, by the PZ interindividual variability and by the small size of the cohorts in mainly retrospective studies. Large prospective studies remain to be done to investigate its possible role in thrombosis.     

Inherited thrombophilia in pediatric ischemic stroke: an Egyptian study

Pediatric stroke is relatively uncommon, with often subtle clinical presentations. Numerous predisposing risk factors can be both inherited and acquired, including cardiac disease, vascular abnormalities, infectious diseases, collagen tissue diseases, inborn errors of metabolism, anticardiolipin antibody, lupus anticoagulant, deficiencies of protein C, protein S, antithrombin, or plasminogen, and prothrombotic mutations. We explored risk factors, clinical features, and neuroimaging among Egyptian children with ischemic stroke, and estimated the prevalence of inherited thrombophilia. We included 20 children with ischemic stroke, recruited from the Pediatric Neurology Outpatient Clinic (Ain Shams University). Basic clinical evaluations for stroke and genotyping for factor V 1691 G-A (factor V Leiden), prothrombin 20210 G-A mutations, and methylenetetrahydrofolate reductase 677 C-T polymorphisms were performed using real-time polymerase chain reaction, with fluorescent melting curve detection analysis. Ten patients (50%) manifested methylenetetrahydrofolate reductase polymorphisms (six homozygotes and four heterozygotes). Heterozygous factor V Leiden was present in five (25%), whereas prothrombin mutation was present in only one (5%). Five patients (25%) manifested combined prothrombotic abnormalities. Thirteen demonstrated evidence of inherited thrombophilic disorder; 25% manifested more than one mutation. For appropriate risk assessment, even in the presence of overt acquired thrombotic risk factors, physicians should request complete thrombophilia screening for patients with stroke.     

Cerebrovascular disorders in children with the factor V Leiden mutation.

Since 1995, at least 128 children with a cerebrovascular disorder, cerebral palsy, or both and the factor V Leiden mutation have been reported. The majority of these strokes were in the first year of life, many of them in the perinatal period. Two thirds had an additional exogenous risk factor for thrombosis, and 42% had another recognized endogenous prothrombotic risk factor in combination with the mutation. We review the association of the factor V Leiden mutation and a cerebrovascular disorder in children younger than 16 years of age and describe the clinical features of 8 children with cerebral palsy and the Leiden mutation. This mutation should be considered in the evaluation of children with a stroke or its sequelae, including infants with perinatal stroke.     

Minor events and the risk of deep venous thrombosis

BACKGROUND: Deep venous thrombosis is a common disease, with genetic and acquired risk factors. Many patients have a history of minor events (short periods of immobilisation such as prolonged travel, short illness, minor surgery or injuries) before onset of venous thrombosis. However, the role of these minor events has received little formal study. Also, we do not know how minor events might interact with the presence of genetic prothrombotic defects (factor V Leiden mutation, factor II mutation, protein C, S and antithrombin deficiency). PATIENTS AND METHODS: On the basis of case-control data from a thrombosis service in the Netherlands, we added a follow-up period for a case-cross-over analysis of minor events as risk factors, and a case-only analysis for the interaction with factor V Leiden. A total of 187 patients with first, objectively diagnosed venous thrombosis of the legs, aged 15-70, without underlying malignancies and without major acquired risk factors entered the study. For the analysis of minor events in the case-cross-over analysis, we used a matched odds ratio; in the case-only analysis, we used the multiplicative synergy index. RESULTS: In 32.6% of the 187 patients with deep venous thrombosis who did not have major acquired risk factors, minor events were the only external risk factors. Minor events increased the risk of thrombosis about 3-fold, as estimated in the case-cross-over analysis (odds ratio 2.9, 95% confidence interval 1.5-5.4). The synergy index between minor events and factor V Leiden mutation in the case-only analysis was 0.7 (95% confidence interval 0.3-1.5). Therefore, persons with factor V Leiden mutation who experience a minor event will have an estimated risk increase of about 17-fold, which exceeds the sum of the individual risk factors. CONCLUSIONS: Minor events are likely to play an important role in the development of deep venous thrombosis, especially in the presence of genetic prothrombotic conditions.     

Mouse protein Z-dependent protease inhibitor cDNA

Protein Z-dependent protease inhibitor (ZPI) is plasma proteinase inhibitor in the serpin superfamily that produces rapid inhibition of factor Xa in the presence of phospholipids, Ca++ and protein Z (PZ). Mouse ZPI cDNA was isolated and cloned from mouse liver RNA using RT-PCR. The cDNA contains 100 nucleotides 5' of a translation initiation codon and an open reading frame of 1344 nucleotides followed by a 163 nucleotide 3' untranslated sequence with a poly (A) tail. The cDNA predicts a signal peptide containing 21 amino acids and a mature protein of 427 residues with 8 potential sites for N-linked glycosylation. The oligonucleotide and predicted amino acid sequences of mouse ZPI are 72% and 81% homologous with those of human ZPI. Like human ZPI, mouse ZPI contains tyrosine-serine (P1-P1') at its reactive center in contrast to the rat molecule which contains tyrosine-cysteine. By Northern analysis, mouse ZPI mRNA is 1.6 kb in size and, similar to both human and rat, it is detectable in liver, but not in heart, brain, spleen, lung, kidney, skeletal muscle or testes.     

Prothrombotic states in retinal artery and vein occlusions

An increasing number of studies have examined the role of prothrombotic states in retinal vascular occlusions. Large case-controlled studies have revealed a cardiovascular risk profile for retinal venous occlusions. Considerable evidence implicates altered rheology, especially increased plasma viscosity and elevated hematocrit, in retinal venous thrombosis. The documented role of specific genetic thrombophilic factors in retinal vascular occlusions is limited. The majority of studies have assessed the role of factor V Leiden. These studies show that screening all patients with retinal venous occlusions for factor V Leiden is not indicated. Screening for factor V Leiden may be helpful in 2 uncommon situations: in patients with a retinal venous thrombosis and a personal or family history of thromboembolic disease, and in patients with recurrent retinal venous occlusions. The extent of the thrombophilic laboratory assessment is based on the age of the patient and the degree of vascular risk factors. Older patients with extensive vascular diseases require little investigation, whereas younger patients with no vascular risk factors require aggressive investigation.     

Co-localization of Protein Z, Protein Z-Dependent protease inhibitor and coagulation factor X in human colon cancer tissue: implications for coagulation regulation on tumor cells

Introduction

Several hemostatic system components, including factor X (FX), contribute to cancer progression. The Protein Z (PZ)/protein Z-dependent protease inhibitor (ZPI) complex directly inhibits factor Xa proteolytic activity. The aim of this study was to determine the antigenic distribution of ZPI and PZ, in relation to FX, as well as indicators of blood coagulation activation (F1+2 and fibrin) in human colon cancer tissue.

Materials & methods

Studies were performed on human colon cancer fragments. Immunohistochemical (IHC) ABC procedures and double staining method employed polyclonal antibodies against PZ, FX, F1+2 and monoclonal antibodies against ZPI and fibrin. In-situ hybridization (ISH) methods employed biotin-labeled 25-nucleotide single-stranded DNA probes directed to either FX, PZ or ZPI mRNAs.

Results

Expression of FX, PZ and ZPI in association with colon cancer cells was observed by IHC. Moreover, the presence of both F1+2 and fibrin in association with colon cancer cells was found, which indicates that blood coagulation activation proceeds extravascularly at the tumor site. Furthermore, expression of FX and PZ was visualized in association with endothelial cells. In turn, colon cancer-associated macrophages were characterized by FX , PZ and ZPI presence. The double staining studies revealed strong FX/PZ, FX/ZPI, as well as PZ/ZPI co-localization on colon cancer cells. ISH studies revealed the presence of FX mRNA, PZ mRNA and ZPI mRNA in colon cancer cells indicating induced synthesis of these proteins.

Conclusions

The localization of PZ/ZPI and FX in colon cancer cells indicates that PZ/ZPI may contribute to anticoagulant events at the tumor site. Strong co-localization of PZ/ZPI and FX in cancer cells, and the presence of the mRNAs encoding the proteins, suggests their role in the tumor's biology. However, the presence of F1+2 and fibrin at the colon cancer site also suggests that the regulation of FXa by the PZ/ZPI complex at this site is incomplete.     

An automated heteroduplex assay for the Pi(A) polymorphism of glycoprotein IIb/IIIa, multiplexed with two prothrombotic genetic markers

Screening for the PIA polymorphism has been made faster and simpler with the advent of heteroduplex technology. Simultaneous screening for three common prothrombotic polymorphisms pl(A), factor V Leiden, and MTHFR(C677T) has been achieved with multiplex heteroduplex analysis. We describe a quick and simple method for PlA heteroduplex probe production. The probe was multiplexed with heteroduplex probes for MTHFR(C677T) and factor V Leiden polymorphisms in a one tube assay, allowing rapid automated genotyping of all three. This automated multiplex assay was applied to a cohort of 165 patients and showed excellent correlation with gel-based assays, both PAGE and RFLP. This approach will facilitate the analysis of multiple polymorphisms in complex disease in large populations.     

Two missense mutations identified in venous thrombosis patients impair the inhibitory function of the protein Z dependent protease inhibitor

Protein Z-dependent protease inhibitor (ZPI) is a plasma inhibitor of factor (F)Xa and FXIa. In an earlier study, five mutations were identified within the ZPI gene of venous thrombosis patients and healthy controls. Two of these were nonsense mutations and three were missense mutations in important regions of the protein. Here we report that two of these latter three mutations, F145L and Q384R, impair the inhibitory function of ZPI in vitro. Recombinant wild-type and mutant proteins were prepared; stability in response to thermal challenge was similar. Inhibition of FXa in the presence of the cofactor protein Z was reduced 68-fold by the Q384R mutant; inhibition of FXIa by the F145L mutant was reduced two- to three-fold compared to the wild-type ZPI. An analysis of all five ZPI mutations was undertaken in a cohort of venous thrombosis patients (n=550) compared to healthy controls (n=600). Overall, there was a modest increase in incidence of these mutations in the thrombosis group (odds ratio 2.0, 1.05-3.7, p=0.044). However, in contrast to W324X (nonsense mutation), the Q384R missense mutation and R88X nonsense mutation were evenly distributed in patients and controls; F145L was rare. The final mutation (S143Y) was also rare and did not significantly alter ZPI function in laboratory studies. The F145L and particularly the Q384R mutation impaired the function of the coagulation inhibitor ZPI; however, there was no convincing association between these mutations and venous thrombosis risk. The functional role for ZPI in vivo has yet to be clarified.     

Prothrombotic factors and the risk of acute onset non-cardioembolic stroke in young Asian Indians

Introduction

Several prothrombotic factors - both hereditary and acquired - are known to cause stroke. Commonly investigated causes are activated protein C resistance, factor V Leiden mutation, factor VIII levels, prothrombin 20210 G-to-A mutation, coagulation inhibitors such as proteins C and S, and antiphospholipid antibodies such as β₂-glycoprotein.

Objective

The literature on the prevalence of hematological defects pertaining to these variables in the Asian Indian stroke population is limited to a few isolated reports. In the current study we investigate the above-mentioned variables in 120 stroke patients (non-cardioembolic acute-onset stroke) and compare their status with the hematological profile of an equal number of healthy age- and sex-matched controls.

Material and Methods

Plasma and blood leukocytes were collected from all patients and controls for performing hematological assays and molecular tests respectively. The mutations were detected using standard polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) procedures. Statistical analysis was done using SPSS version 12.0.

Results

Factor V Leiden (prevalence 8.3% in patients) and activated protein C resistance (prevalence 19.6% in patients) both showed a high degree of association (P < 0.01) with the disease condition. However, contrary to common expectations, factor V Leiden was observed much less frequently in patients showing activated protein C resistance (10 out of 23; 43.4%) than is commonly observed in the Caucasian population (almost 90%). Post-acute-phase factor VIII levels were also found to be significantly associated with stroke: 125.6 + 21.1% number of profitable positions (NPP) for controls and 136.2 + 28.8% NPP for patients (P = 0.001).

Conclusion

factor V mutations, such as factor V Leiden, may be important risk factors for stroke in an Asian Indian population. Activated protein C resistance has a stronger association with stroke than factor V Leiden and may be caused by other factors such as elevated factor VIII levels in the Asian Indian population apart from factor V Leiden itself.