Amino acid sequence of human protein Z, a vitamin K-dependent plasma glycoprotein

Plasma levels and urinary excretion of protein Z in patients with urolithiasis

OBJECTIVES

Protein Z (PZ) is a γ-carboxyglutamic acid protein present in plasma that is involved in blood coagulation. Detailed analysis of urinary stones from patients with urolithiasis has revealed that PZ is often found in urinary stones composed of calcium oxalate monohydrate. In this study, we compared blood and urinary PZ concentrations between healthy individuals and patients with urolithiasis.

METHODS

Plasma and urine were collected from healthy individuals and patients with urolithiasis who provided informed consent. PZ was detected as a urinary stone matrix protein in some of the patients. PZ was quantified by ELISA, creatinine was measured by the enzymatic method, and the total protein concentration was measured by the Bradford method.

RESULTS

The plasma PZ level was 2.54 ± 1.02 μg/mL in healthy individuals and that in urolithiasis patients classified by stone history were from 1.16 ± 0.77 to 3.73 ± 1.09 μg/mL, which was not significantly different. The urinary excretion of PZ (PZ/creatinine) was also not different in patients with urolithiasis and in healthy individuals (from 54.1 ± 40.9 to 95.4 ± 69.4 ng/mg vs. 73.3 ± 36.0 ng/mg). A positive correlation was found between the plasma PZ level and creatinine-corrected urinary PZ concentration (r = 0.46).

CONCLUSIONS

Both the plasma level and urinary excretion of PZ in urolithiasis patients were not significantly different with normal individuals. PZ detected in urinary stones as a matrix protein is thought to be incorporated into urinary stones regardless of blood and urine levels of PZ.

Identification of non-neutralizing anti-factor X autoantibodies in three Japanese cases of autoimmune acquired factor X deficiency

INTRODUCTION

Autoimmune factor X (FX or F10) deficiency (AiF10D) is an extremely rare acquired haemorrhagic disorder characterized by a severe reduction in FX activity due to autoantibodies against FX.

AIM

Anti-FX autoantibodies were investigated in four patients with suspected AiF10D, and their properties were analysed.

METHODS AND RESULTS

Anti-FX auto antibodies in plasma were detected by ELISA with three of four cases. One case of anti-FX autoantibody negativity was later diagnosed as AL-amyloidosis. IgG1 and IgG3 coexisted in all anti-FX autoantibodies of the three patients with AiF10D (cases X1, X2, and X3). Western blot analysis showed that the antibodies were bound to the FX light chain for cases X2 and X3, but the binding was weak for case X1. When the fusion proteins of a secretory luciferase with full-length FX or its γ-carboxylated glutamic acid (Gla) domain were added to the plasma of the three patients, both fusion proteins were immunoprecipitated as antigen-antibody complexes. Contrarily, the latter fusion protein produced in the presence of warfarin demonstrated a decrease in the collection rate, suggesting that their autoantibodies recognized the light chain and regions containing Gla residues. Since all three patients were essentially negative for FX inhibitors, it was concluded that the anti-FX autoantibodies for these cases were predominantly non-neutralizing. The concentration of the FX antigen also significantly reduced in these patients, suggesting that anti-FX autoantibodies promote the clearance of FX.

CONCLUSION

Immunological anti-FX autoantibody detection is highly recommended to ensure that AiF10D cases are not overlooked, and to start necessary immunosuppressive therapies.

Microfluidic device for single step measurement of protein C in plasma samples for sepsis prognosis

Protein C is a vitamin K dependant protein in plasma that plays an essential role in regulating the coagulation cascade and inflammatory response. As a result of its importance in these roles, it has been suggested as a biomarker for prognosis of patients affected by sepsis. Sepsis is a dysregulated host response to an infection that is the leading cause of mortality in U.S. hospitals and results in the highest cost of hospitalization. It was found that protein C concentration in non-surviving sepsis patients is significantly lower (1.8 μg mL^-1) than in survivors and healthy patients who have a protein C concentration of 3.9-5.9 μg mL^-1. Current methods for diagnosing sepsis rely on expensive immunoassays or functional assays that require multiple steps for isolation and activation of protein C. We demonstrate in this paper a low cost, single step assay for detection of protein C in blood plasma. This was done by combining isoelectric gates with barium-immobilized metal affinity trapping. The electric field was optimized for use with immobilized metal affinity using COMSOL simulation. The integrated device was tested with samples containing buffered protein C, protein C in the presence of high concentration bovine serum albumin and alpha 1-proteinase inhibitor, and in blood plasma with spiked protein C. The stability of the measured values was tested by monitoring the intensity of a mixture of protein C with BSA and A1PI every minute to determine that measurement after 40 minutes was optimal. The results showed that the device could be used to distinguish a reduction in protein C from 4.46 μg mL^-1 to 1.96 μg mL^-1 with greater than 98% confidence in plasma making it suitable for sepsis prognosis.

GGCX mutations show different responses to vitamin K thereby determining the severity of the hemorrhagic phenotype in VKCFD1 patients

BACKGROUND

Vitamin K dependent coagulation factor deficiency type 1 (VKCFD1) is a rare hereditary bleeding disorder caused by mutations in γ-glutamyl carboxylase (GGCX). VKCFD1 patients are treated life-long with high doses of vitamin K in order to correct the bleeding phenotype. However, normalization of clotting factor activities cannot be achieved for all VKCFD1 patients.

OBJECTIVE

The current study aims to investigate the responsiveness to vitamin K for all reported GGCX mutations with respect to clotting factors in order to optimize treatment.

METHODS

This study developed an assay using genetically engineered GGCX-/- cells, in which GGCX mutations were analyzed with respect to their ability to γ-carboxylate vitamin K dependent pro-coagulatory and anti-coagulatory clotting factors by ELISA. Additionally, factor VII activity was measured in order to proof protein functionality. For specific GGCX mutations immunofluorescent staining was performed to assess the intracellular localization of clotting factors with respect to GGCX wild-type and mutations.

RESULTS

All GGCX mutations were categorized into responder and low responder mutations, thereby determining the efficiency of vitamin K supplementation. Most VKCFD1 patients have at least one vitamin K responsive GGCX allele that is able to γ-carboxylate clotting factors. In few patients, the hemorrhagic phenotype cannot be reversed by vitamin K administration because GGCX mutations on both alleles affect either structural or catalytically important sites thereby resulting in residual ability to γ-carboxylate clotting factors.

CONCLUSION

With these new functional data we can predict the hemorrhagic outcome of each VKCFD1 genotype, thus recommending treatments with either vitamin K or prothrombin complex concentrate.

Thrombin: An Approach to Developing a Higher-Order Reference Material and Reference Measurement Procedure for Substance Identity, Amount, and Biological Activities

Thrombin, the proteolytic enzyme that catalyzes the transformation of soluble fibrinogen to the polymerized fibrin clot, participates in multiple reactions in blood coagulation in addition to the clotting reaction. Although reference materials have existed for many years, structural characterization and measurement of biological activity have never been sufficient to permit claims of clear metrological traceability for the thrombin preparations. Our current state-of-the-art methods for protein characterization and determination of the catalytic properties of thrombin now make it practical to develop and characterize a metrologically acceptable reference material and reference measurement procedure for thrombin. Specifically, α-thrombin, the biologically produced protease formed during prothrombin activation, is readily available and has been extensively characterized. Dependences of thrombin proteolytic and peptide hydrolytic activities on a variety of substrates, pH, specific ions, and temperature are established, although variability remains for the kinetic parameters that describe thrombin enzymatic action. The roles of specific areas on the surface of the thrombin molecule (exosites) in substrate recognition and catalytic efficiency are described and characterized. It is opportune to develop reference materials of high metrological order and technical feasibility. In this article, we review the properties of α-thrombin important for its preparation and suggest an approach suitable for producing a reference material and a reference measurement procedure that is sensitive to thrombin’s catalytic competency on a variety of substrates.

Co-localization of Coagulation Factor X and its Inhibitory System, PZ/ZPI, in Human Endometrial Cancer Tissue

BACKGROUND/AIM

Hemostatic system components contribute to cancer progression independently from their roles in hemostasis. It has been shown that protein Z (PZ)/protein Z-dependent protease inhibitor (ZPI) inhibit coagulation factor X (FX). The aim of the study was to analyze the expression of PZ/ZPI in relation to the main coagulation factor - FX in human endometrial cancer tissue.

MATERIALS AND METHODS

Immunohistochemical analysis was performed on 21 endometrial cancer specimens employing antibodies against ZPI, PZ and FX.

RESULTS

Endometrial cancer cells showed a strong expression of ZPI and PZ and medium expression of FX. Normal endometrial tissue showed no expression of ZPI, PZ or FX.

CONCLUSION

Strong expression of PZ and ZPI in endometrial cancer cells suggests a role of these proteins in endometrial cancer.

The protein Z/protein Z-dependent protease inhibitor complex

Protein Z (PZ) is a vitamin K-dependent factor identified in human plasma in 1984 but it has no enzymatic activity. It is a cofactor of a serpin, the protein Z-dependent protease inhibitor (ZPI), and the complex PZ/ZPI inhibits activated factor X on phospholipid surfaces. In mice, the disruption of PZ or ZPI gene is asymptomatic, but enhances the thrombotic phenotype and mortality of other thrombotic risk factors. Most of the clinical studies focused on PZ. Despite conflicting results, a recent meta-analysis indicated that PZ deficiency could be a risk for venous and arterial thrombosis and early fetal loss. However, these conclusions are drawn from case-control studies of small size, constituting an important limitation. Recently, it was shown that PZ and/or ZPI are synthesised by normal kidney and different cancer cells, suggesting that the complex PZ/ZPI could play a role in inhibiting the tissue deposition of fibrin. The physiopathological consequences of these observations remain to be established. At this time, the measurement of plasma PZ and ZPI or analysis of their gene polymorphisms should not be performed routinely for the exploration of thrombophilia.

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.

This work was presented at the 23rd International Society on Thrombosis and Haemostasis meetings in Kyoto, July 2011.

Low protein Z plasma level is a risk factor for acute myocardial infarction in coronary atherosclerosis disease patients

OBJECTIVES

To examine plasma protein Z (PZ) levels in acute myocardial infarction (AMI) and chronic coronary atherosclerosis disease (CCAD) patients without history of AMI and explore its potential clinical significance.

METHODS

Plasma PZ concentrations were measured in 90 AMI patients (Group A), 87 CCAD patients without AMI history who remained free of major clinical events at least one year (Group B), and 88 clinically healthy controls (Group C).

RESULTS

PZ was found to be significantly lower (P<0.001) in Group A (1508.5±486.2ng/mL) compared with Group B (1823.0±607.8ng/mL) and C (2001.7±733.0ng/mL) and in Group A+B compared with Group C (Group A+B 1663.1±570.0 ng/mL, P<0.001). No statistically significant difference was reached between Group B and C (P=0.081). PZ level was significantly correlated with concentration of creatine kinase MB, high sensitive-cardiac troponin T, high sensitive C reactive protein, D-dimer and coagulation factor II and may be a useful predictor for AMI (OR: 1.38, 95% CI: 1.13-1.77, P=0.03). Subgroup analysis showed PZ concentration below the lowest tertile (<1398ng/mL) had a significantly increased risk for AMI and CCAD (OR: 3.39; 95% CI: 1.12-10.31; P=0.03 and OR: 7.39; 95% CI: 2.62-20.79; P<0.001 respectively).

CONCLUSIONS

PZ deficiency is found in AMI patients and could potentially reflect the myocardium injury, local coagulation activation and inflammation response during the acute phase of coronary atherosclerosis disease.

Phosphatidylserine and Phosphatidylethanolamine Bind to Protein Z Cooperatively and with Equal Affinity

Protein Z (PZ) is an anticoagulant that binds with high affinity to Protein Z-dependent protease inhibitor (ZPI) and accelerates the rate of ZPI-mediated inhibition of factor Xa (fXa) by more than 1000-fold in the presence of Ca²⁺ and phospholipids. PZ promotion of the ZPI-fXa interaction results from the anchoring of the Gla domain of PZ onto phospholipid surfaces and positioning the bound ZPI in close proximity to the Gla-anchored fXa, forming a ternary complex of PZ/ZPI/fXa. Although interaction of PZ with phospholipid membrane appears to be absolutely crucial for its cofactor activity, little is known about the binding of different phospholipids to PZ. The present study was conceived to understand the interaction of different phospholipids with PZ. Experiments with both soluble lipids and model membranes revealed that PZ binds to phosphatidylserine (PS) and phosphatidylethanolamine (PE) with equal affinity (K_d~48 μM); further, PS and PE bound to PZ synergistically. Equilibrium dialysis experiments revealed two lipid-binding sites for both PS and PE. PZ binds with weaker affinity to other phospholipids, e.g., phosphatidic acid, phosphatidylglycerol, phosphatidylcholine and binding of these lipids is not synergistic with respect to PS. Both PS and PE -containing membranes supported the formation of a fXa-PZ complex. PZ protection of fXa from antithrombin inhibition were also shown to be comparable in presence of both PS: PC and PE: PC membranes. These findings are particularly important and intriguing since they suggest a special affinity of PZ, in vivo, towards activated platelets, the primary membrane involved in blood coagulation process.

Pseudoproteases: mechanisms and function

Catalytically inactive enzymes (also known as pseudoproteases, protease homologues or paralogues, non-peptidase homologues, non-enzymes and pseudoenzymes) have traditionally been hypothesized to act as regulators of their active homologues. However, those that have been characterized demonstrate that inactive enzymes have an extensive and expanding role in biological processes, including regulation, inhibition and immune modulation. With the emergence of each new genome, more inactive enzymes are being identified, and their abundance and potential as therapeutic targets has been realized. In the light of the growing interest in this emerging field the present review focuses on the classification, structure, function and mechanism of inactive enzymes. Examples of how inactivity is defined, how this is reflected in the structure, functions of inactive enzymes in biological processes and their mode of action are discussed.

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.

The role of Ca(2+) ions in the complex assembling of protein Z and Z-dependent protease inhibitor: A structure and dynamics investigation

We investigated the solution structure and dynamics of the human anti-coagulation protein Z (PZ) in the complex with protein Zdependent protease inhibitor (ZPI) to order to understand key structural changes in the presence and absence of Ca(2+). Structural features of the complete complex of PZ-ZPI are poorly understood due to lack of complete atomic model of the PZ-ZPI complex. We have constructed a model of the complete PZ-ZPI complex and molecular dynamics (MD) simulation of the solvated PZ-ZPI complex with and without Ca(2+) was achieved for 100ns. It is consider that the Ω-loop of GLA domains interacts with negatively charged biological membranes in the presence of Ca(2+) ions. The PZ exerts its role as cofactor in a similar way. However, we used solvent-equilibrated dynamics to show structural features of the PZ-ZPI complex in the presence and the absence of Ca(2+)ions. We observed that the distance between the interacting sites of the ZPI with the PZ and the GLA domain decreases in the presence of Ca(2+) ions. Further, we postulated that the calculated distance between the dominant plane of the Ca(2+) ions and Ser196 of the pseudo-catalytic triad of the PZ is similar to the equivalent distance of FXa. This suggests that the central role of the PZ in the blood coagulation may be to align the inhibitory site of the ZPI with the active site of the FXa, which is depends on the interaction of the calcium bound GLA domain of the PZ with the active membrane.

Mechanism of protein-z-mediated inhibition of coagulation factor xa by z-protein-dependent inhibitor: a molecular dynamic approach

Protein Z is a plasma protein functioning as a carrier for ZPI. Protein Z also accelerates inhibitory effect of ZPI on factor Xa by 1000-fold. Inhibition of coagulation cascade via FXa by ZPI and other serpins is very important safety factor for normal homeostasis protecting human life against unwanted thrombosis. In the present work using native structure of PZ, ZPI, FXa and in a dynamic simulation, using NAMD software, the ternary complex was studied in an up to 10 nanoseconds protocol. Rely on trajectory analyses, we postulated that PZ binds ZPI by using its SP-like domain and through noncovalent forces. PZ then transfers ZPI through-out the blood, and by using its GLA domain and a bivalent cation of calcium, PZ binds to phospholipid bilayers (e.g., platelet) where the FXa is preallocated. In case of PZ-ZPI binding to plasma membrane, a series of complementary interactions take place between FXa, and PZ-ZPI complex including interactions between RCL loop of ZPI and catalytic site of FXa and some take place between long arm of PZ (composed of GLA, EGF1, and EGF2 domains) and GLA domain of FXa. In our claim these complementary interactions lead PZ to bind correctly to prelocated FXa.

Protein Z concentrations in patients with acute leukemia

Protein Z (PZ) deficiency may induce bleeding as well as thrombosis. The aim of our study was to estimate the concentration of PZ in patients with acute leukemia. Plasma levels of PZ were determined in 76 patients with newly diagnosed acute leukemia ([AML], n = 50; acute lymphoblastic leukemia [ALL], n = 26) and 62 healthy participants. In the patients, mean plasma concentrations of PZ were statistically lower than in healthy individuals: AML (1.24 ± 0.11 μg/mL vs 1.58 ± 0.05 μg/mL P = .01) and ALL (1.19 ± 0.16 μg/mL vs 1.58 ± 0.05 μg/mL P = .01). Levels of PZ below the fifth percentile (0.873 μg/mL) of normal value distribution in control participants were found in 30% of patients with AML and ALL and in 3% of controls (P < .0001). In this AML subgroup, we found statistically significant correlation between episodes of bleeding and PZ level (P = .01). There was no such correlation in ALL group. The results suggest that PZ can be a cofactor associated with an increased bleeding tendency in patients with AML.

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.

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.

Basis for the specificity and activation of the serpin protein Z-dependent proteinase inhibitor (ZPI) as an inhibitor of membrane-associated factor Xa

The serpin ZPI is a protein Z (PZ)-dependent specific inhibitor of membrane-associated factor Xa (fXa) despite having an unfavorable P1 Tyr. PZ accelerates the inhibition reaction approximately 2000-fold in the presence of phospholipid and Ca(2+). To elucidate the role of PZ, we determined the x-ray structure of Gla-domainless PZ (PZ(DeltaGD)) complexed with protein Z-dependent proteinase inhibitor (ZPI). The PZ pseudocatalytic domain bound ZPI at a novel site through ionic and polar interactions. Mutation of four ZPI contact residues eliminated PZ binding and membrane-dependent PZ acceleration of fXa inhibition. Modeling of the ternary Michaelis complex implicated ZPI residues Glu-313 and Glu-383 in fXa binding. Mutagenesis established that only Glu-313 is important, contributing approximately 5-10-fold to rate acceleration of fXa and fXIa inhibition. Limited conformational change in ZPI resulted from PZ binding, which contributed only approximately 2-fold to rate enhancement. Instead, template bridging from membrane association, together with previously demonstrated interaction of the fXa and ZPI Gla domains, resulted in an additional approximately 1000-fold rate enhancement. To understand why ZPI has P1 tyrosine, we examined a P1 Arg variant. This reacted at a diffusion-limited rate with fXa, even without PZ, and predominantly as substrate, reflecting both rapid acylation and deacylation. P1 tyrosine thus ensures that reaction with fXa or most other arginine-specific proteinases is insignificant unless PZ binds and localizes ZPI and fXa on the membrane, where the combined effects of Gla-Gla interaction, template bridging, and interaction of fXa with Glu-313 overcome the unfavorability of P1 Tyr and ensure a high rate of reaction as an inhibitor.

Low levels of protein Z are associated with HELLP syndrome and its severity

Protein Z (PZ) was found to be associated with pregnancy complications. There are no data implying an association between hemolysis (H), elevated liver enzymes (EL), and low platelet counts (LP) (HELLP) syndrome and changes in plasma levels of PZ. The aim of this study is to investigate whether HELLP syndrome is associated with plasma concentrations of PZ. Protein Z levels in 29 women with HELLP syndrome were compared with 29 healthy, nulliparous and 25 normal pregnant women. The median PZ levels in patients with HELLP syndrome were found to be significantly lower than those of pregnant women. No significant difference was found between HELLP and healthy groups. Protein Z levels correlated with platelet counts, lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) levels in patients with HELLP syndrome. Median PZ level was higher in partial HELLP than in complete HELLP. We calculated 1330 ng/mL as a cutoff value for PZ level to discriminate HELLP syndrome from normal pregnancy. Low PZ levels are associated with the pathobiology of HELLP syndrome.

A meta-analysis of potential risks of low levels of protein Z for diseases related to vascular thrombosis

The relationship between protein Z levels and thrombosis is controversial. We performed a systematic review and meta-analysis of the available studies to assess the association between protein Z and vascular thrombotic diseases. We conducted an electronic literature search through MedLine, Embase, Google Scholar, Web of Science, The Cochrane Library, bibliographies of retrieved articles and abstracts of congresses up to October, 2009. Studies were included if they analysed protein Z levels in patients with vascular thrombotic diseases. After the review process, 28 case-control studies (33 patient cohorts), including 4,218 patients with thrombotic diseases and 4,778 controls, were selected for analysis. The overall analysis using a random-effects model showed that low protein Z levels were associated with an increased risk of thrombosis (odds ratio [OR] 2.90, 95% confidence interval [CI] 2.05-4.12; p<0.00001). On subgroup analysis, a significant association was found between low protein Z levels and arterial vascular diseases (OR 2.67, 95%CI 1.60-4.48; p=0.0002), pregnancy complications (OR 4.17, 95%CI 2.31-7.52; p<0.00001), and venous thromboembolic diseases (OR 2.18, 95%CI 1.19-4.00; p=0.01). The results of this meta-analysis are consistent with a role for protein Z deficiency in thrombotic diseases, including arterial thrombosis, pregnancy complications and venous thromboembolism.

Distinct C-terminus of the B subunit of factor XIII in a population-associated major phenotype: the first case of complete allele-specific alternative splicing products in the coagulation and fibrinolytic systems

OBJECTIVES

The purpose of this study was to elucidate the molecular bases of the heterogeneity of the B subunit of coagulation factor XIII (FXIII-B), classified by isoelectric focusing into its three population-associated major phenotypes.

METHODS AND RESULTS

By genetic sequencing and polymerase chain reaction (PCR)-restriction fragment length polymorphism analyses, a C-to-G change was identified in intron K for the Asian-associated major phenotype FXIII-B*3. A transcript containing the novel exon XII' was detected by reverse transcription PCR using hepatocyte cell lines with this allele. The exclusive existence of a novel C-terminal peptide in a homozygote of FXIII-B*3 was also detected by matrix-assisted laser-desorption ionization time of flight mass spectrometry. The FXIII-B*3 isoform had a C-terminus 15 residues longer than the other isoforms, containing two additional basic amino acids and one extra acidic amino acid. Accordingly, the C-to-G nucleotide substitution created an efficient splice acceptor AG dinucleotide, which resulted in allele-specific alternative splicing in intron K. When compared with FXIII-B*1, the third major phenotype, FXIII-B*2, had an A-to-G change in exon III, converting His95 to Arg, and a rare phenotype, FXIII-B*4, had an A-to-T change in exon VII, converting Glu368 to Val.

CONCLUSIONS

We found an extremely rare event of complete allele-specific alternative splicing for FXIII-B. The FXIII-B*3 isoform had a distinct C-terminal peptide, while the FXIII-B*2 and FXIII-B*4 isoforms had His95 to Arg and Glu368 to Val substitutions, respectively, which led to differential isoelectric points of these isoforms. Such variations in the amino acid sequence of FXIII-B may have profound effects on its structure-function relationship, plasma FXIII levels, and disease susceptibility.

Protein Z Plasma Levels are Not Elevated in Patients with Non-Arteritic Anterior Ischemic Optic Neuropathy

Background:

Protein Z is a glycoprotein that acts as a co-factor for the inhibition of activated coagulation factor X. Protein Z circulating in abnormal levels has been associated with increased risk for acute ischemic events. Non-arteritic Anterior Ischemic Optic Neuropathy (N-AION) is caused by acute ischemic infarction of the optic nerve head, supplied by the posterior ciliary arteries.

Objectives:

The aim was to investigate whether there is an association between N-AION and plasma protein Z levels.

Patients and Methods:

Twenty-six cases of confirmed N-AION and fifty-two controls were included in the study group. Protein Z was estimated in thawed citrate plasma on both N-AION cases and controls by an enzyme immunoassay. The imprecision of the estimation was satisfactory (CV = 4, 6%).

Results:

The controls’ protein Z values distributed within a range 340 to 4200 ng/ml (median = 1420, mean = 1673, SD = 1040 ng/ml). Patients’ protein Z values distributed within a range 420 to 3600 ng/ml (median = 1030, mean = 1520, SD = 939 ng/ml). There was no statistical difference between the two distributions (Independent t-test, p=0.529).

Conclusion:

In our study, protein Z levels are not implicated in the pathogenesis of non-arteritic anterior ischemic optic neuropathy (N-AION).

Unique secretion mode of human protein Z: its Gla domain is responsible for inefficient, vitamin K–dependent and warfarin-sensitive secretion

Protein Z is a vitamin K–dependent plasma glycoprotein that is involved in the regulation of blood coagulation. Plasma concentrations of protein Z vary widely between subjects and are greatly reduced during warfarin therapy. We developed a sensitive and quantitative assay for protein secretion using a secretory luciferase to explore the mode of secretion of protein Z compared with that of factor X. Protein Z secretion was much less efficient than factor X and was totally dependent upon added vitamin K, while factor X secretion was not. Protein Z secretion was highly sensitive to warfarin treatment of the synthesizing cells. In contrast, although factor X secretion was not precluded by warfarin, its γ-carboxylation was completely blocked. An exchange of the propeptide and/or γ-carboxyglutamic acid domain between protein Z and factor X reproduced the inefficient and warfarin-sensitive secretion pattern of protein Z, and vice versa. Joining of the propeptide and γ-carboxyglutamic acid domain to luciferase also demonstrated that the γ-carboxyglutamic acid domain of protein Z was responsible for its warfarin-sensitive secretion. Thus, it was concluded that the difference observed in secretion patterns of protein Z and factor X was mainly based on the structure of their γ-carboxyglutamic acid domains.

Association of the protein Z ATG haplotype with symptomatic nonvascular stroke or thromboembolism in white children: a family-based cohort study

To clarify the role of protein Z (PZ) in children with stroke/thromboembolism (TE), the present haplotype (HT)–based family study was performed. We genotyped 365 pediatric stroke/TE families (stroke n = 216; TE n = 149) for 4 single nucleotide polymorphisms (SNPs; rs3024718, rs3024731, rs3024772, and rs3024778) to assess the association between genetic variation within a conserved block of linkage disequilibrium harboring the PZ gene and pediatric TE. Association was assessed with use of the transmission disequilibrium test (TDT), corrected for multiple testing (permutation testing: HAPLOVIEW). In addition, PZ antigen was determined and correlated with carriership of PZ haplotypes and the FV G1691A mutation. Rs3024718, rs3024731, and rs3024772 are in tight linkage disequilibrium (LD) and define 4 haplotypes, capturing 97% of the genetic variation for this LD block. HT1 (ATG) was significantly overtransmitted from parents to affected offspring (HT frequency 73.5%, T:U 122:80, χ2 = 8.791, P = .003). The ATG risk haplotype was significantly correlated with greater PZ antigen levels. Multivariate analysis adjusted for age, sex, established thrombophilias, smoking, fibrinogen, and PZ levels revealed a significant association of the ATG haplotype and TE in children (odds ratio [OR] 1.4; 95% confidence interval [95% CI] 1.08-1.93). Our results suggest that the ATG haplotype of the PZ gene is a genetic marker for symptomatic TE in white German children.

Protein Z-dependent protease inhibitor binds to the C-terminal domain of protein Z

Protein Z (PZ) is a multidomain vitamin K-dependent plasma protein that functions as a cofactor to promote the inactivation of factor Xa (fXa) by PZ-dependent protease inhibitor (ZPI) by three orders of magnitude. To understand the mechanism by which PZ improves the reactivity of fXa with ZPI, we expressed wild-type PZ, PZ lacking the gamma-carboxyglutamic acid domain (GD-PZ), and a chimeric PZ mutant in which both Gla and EGF-like domains of the molecule were substituted with identical domains of fXa. The ZPI binding and the cofactor function of the PZ derivatives were characterized in both binding and kinetic assays. The binding assay indicated that all PZ derivatives interact with ZPI with a similar dissociation constant (K(D)) of approximately 7 nm. However, the apparent K(D) for the chimeric PZ-mediated ZPI inhibition of fXa was elevated 6-fold on PC/PS vesicles and its capacity to function as a cofactor to accelerate the ZPI inhibition of fXa was also decreased 6-fold. The cofactor activity of GD-PZ was dramatically impaired; however, the deletion mutant exhibited a normal cofactor function in solution. A chimeric activated protein C mutant containing the Gla domain of fXa was susceptible to inhibition by ZPI in the presence of PZ. These results suggest that: (i) the ZPI interactive site of PZ is located within the C-terminal domain of the cofactor and (ii) a specific interaction between the Gla domains of PZ and fXa contributes approximately 6-fold to the acceleration of the ZPI inhibition of fXa on phospholipid membranes.

A unique group of inactive serine protease homologues from snake venom

A number of inactive serine protease homologues (SPHs), which have poorly understood functions, have been identified in invertebrates and vertebrates. Recently, several SPH transcripts have been reported from snake venom glands, which provide potential new tools for the study of the functions of SPHs. Herein we report for the first time a snake venom serine protease homologue (svSPH) protein, designated as TjsvSPH, isolated from the venom of Trimeresurus jerdonii. Despite its high sequence similarity to snake venom serine proteases (SVSPs), TjsvSPH is devoid of arginine esterase and proteolytic activity. This is probably due to the replacement of Arg-43 by His-43 in the catalytic triad. TjsvSPH did not influence the coagulation time of human plasma, induce human platelet aggregation, inhibit adenosine diphosphate/thrombin-induced human platelet aggregation or increase capillary permeability. Phylogenetic analysis showed that svSPHs were separated from SVSPs and formed an independent group. Structural analysis revealed that the structures of svSPHs are quite different from those of SPHs previously reported. These results indicate that snake venoms contain a unique group of svSPH proteins.

Computational study of the putative active form of protein Z (PZa): sequence design and structural modeling

Although protein Z (PZ) has a domain arrangement similar to the essential coagulation proteins FVII, FIX, FX, and protein C, its serine protease (SP)-like domain is incomplete and does not exhibit proteolytic activity. We have generated a trial sequence of putative activated protein Z (PZa) by identifying amino acid mutations in the SP-like domain that might reasonably resurrect the serine protease catalytic activity of PZ. The structure of the activated form was then modeled based on the proposed sequence using homology modeling and solvent-equilibrated molecular dynamics simulations. In silico docking of inhibitors of FVIIa and FXa to the putative active site of equilibrated PZa, along with structural comparison with its homologous proteins, suggest that the designed PZa can possibly act as a serine protease.

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.

Genomic evidence for a simpler clotting scheme in jawless vertebrates

Mammalian blood clotting involves numerous components, most of which are the result of gene duplications that occurred early in vertebrate evolution and after the divergence of protochordates. As such, the genomes of the jawless fish (hagfish and lamprey) offer the best possibility for finding systems that might have a reduced set of the many clotting factors observed in higher vertebrates. The most straightforward way of inventorying these factors may be through whole genome sequencing. In this regard, the NCBI Trace database ( http://www.ncbi.nlm.nih.gov/Traces/trace.cgi ) for the lamprey (Petromyzon marinus) contains more than 18 million raw DNA sequences determined by whole-genome shotgun methodology. The data are estimated to be about sixfold redundant, indicating that coverage is sufficiently complete to permit judgments about the presence or absence of particular genes. A search for 20 proteins whose sequences were determined prior to the trace database study found all 20. A subsequent search for specified coagulation factors revealed a lamprey system with a smaller number of components than is found in other vertebrates in that factors V and VIII seem to be represented by a single gene, and factor IX, which is ordinarily a cofactor of factor VIII, is not present. Fortuitously, after the completion of the survey of the Trace database, a draft assembly based on the same database was posted. The draft assembly allowed many of the identified Trace fragments to be linked into longer sequences that fully support the conclusion that lampreys have a simpler clotting scheme compared with other vertebrates. The data are also consistent with the hypothesis that a whole-genome duplication or other large scale block duplication occurred after the divergence of jawless fish from other vertebrates and allowed the simultaneous appearance of a second set of two functionally paired proteins in the vertebrate clotting scheme.

Protein Z levels and anti-protein Z antibodies in patients with arterial and venous thrombosis

INTRODUCTION

The thrombotic risk associated with protein Z (PZ) deficiency is unclear. Anti-protein Z (anti-PZ) has been described as a risk factor in unexplained embryo demise. The aim of our study was to evaluate a possible PZ deficiency and presence of anti-PZ antibodies on thrombotic diseases.

MATERIAL AND METHODS

We performed a case-control study on 114 patients with preexisting arterial or venous thrombosis (50 and 64, respectively). Thrombosis was studied based on etiology (creating factor risk subgroups) and on specific thrombotic disease.

RESULTS

PZ levels of patients were significantly lower compared to controls (1709+-761.3 ng/mL vs. 2437+-964.7 ng/mL P=0.001). The high arterial risk factor subgroup showed the lowest PZ level (1267.5+-609 ng/mL) whereas the rest of arterial and venous etiological subgroups presented similar PZ levels. Patients with peripheral artery disease had the lowest PZ level (1022+-966 ng/mL). The rest of arterial and venous thrombotic diseases presented similar PZ levels. A significant increased risk for arterial and venous thrombosis for the lowest (<1685 ng/mL) quartile of PZ has been founded (OR:52, P=0.001 and OR:18, P=0.007, respectively). Anti-PZ antibodies were negative in the majority of patients, although mean anti-PZ IgG antibody levels in the arterial thrombosis group were significantly higher compared to venous thrombosis and control groups (P=0.05 and P=0.005, respectively).

CONCLUSIONS

The results suggest that both arterial and venous thrombotic events are related to low PZ levels and that low PZ concentrations are associated with thrombosis in our study. In arterial thrombosis our findings strengthen previous studies that related low PZ levels to atherosclerotic disease. Anti-PZ antibodies do not seem to play a potent role in thrombosis.

Regulation of human protein Z gene expression by liver-enriched transcription factor HNF-4alpha and ubiquitous factor Sp1

BACKGROUND AND OBJECTIVES

Protein Z (PZ), which regulates blood coagulation, is mainly synthesized in the liver. Its plasma level varies widely among individuals, and is highly sensitive to Warfarin. The mechanism for the basic transcription of the human PZ gene, however, has not been reported. The aim of this study was to elucidate the mechanism of gene regulation for PZ by characterizing its 5'-flanking region.

METHODS AND RESULTS

A reporter gene assay using the human hepatoma cell line, HepG2, identified a minimal promoter region (site A) and two enhancer regions (sites B and C) in the PZ gene. DNase I footprinting and electromobility shift assays revealed binding of the liver-enriched transcriptional factor hepatocyte nuclear factor (HNF)-4alpha to site A, the ubiquitous transcriptional factor Sp1 to sites A and C, and an unidentified factor to site B. The co-transfection of an HNF-4alpha expression vector with reporter gene constructs to the non-hepatic cell line HeLa resulted in a significant increase of PZ promoter activity.

CONCLUSIONS

HNF-4alpha plays a crucial role in human PZ gene expression in hepatocytic cells, and Sp1 is also important. These findings provide the first step toward understanding the mechanisms of the varying plasma PZ levels in individuals under physiological and pathological conditions.

Plasma protein Z and protein C inhibitors and their role in hypercoagulability of thalassemia

A hypercoagulable state has been described in thalassemia patients, partly due to a deficiency of inhibitors, protein C (PC) in particular. Since a potential role of a new hemostatic factor named protein Z (PZ) has been reported in hypercoagulability, we evaluated plasma PZ and PC levels in thalassemia and their possible relation to the hypercoagulable state. Sixty subjects with thalassemia major and 10 with thalassemia intermedia (TI) followed at our Department were enrolled in the study. An age-matched control group of healthy subjects was considered. PZ, thrombin-antithrombin complexes, PC concentration (PC:Ag) and activity (PC:Act) were measured. PZ, PC:Ag and PC:Act were significantly lower in thalassemia major and thalassemia intermedia subjects than in 30 healthy controls (p < 0.001), while thrombin-antithrombin complex levels were significantly increased (p < 0.001) and related to PC levels but not to PZ levels (p < 0.05). PZ and PC levels are reduced in thalassemia but only PC has an effect on the thalassemia hypercoagulable state.

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.

Plasma protein Z concentrations in pregnant women with idiopathic intrauterine bleeding and in women with spontaneous preterm labor

OBJECTIVES

Preterm parturition has been associated with decidual vascular disorders and excessive thrombin generation. The objective of this study was to examine maternal plasma concentrations of protein Z in normal pregnancies, as well as in those presenting with spontaneous preterm labor (PTL) and intrauterine bleeding during pregnancy.

STUDY DESIGN

A cross-sectional study was designed to include patients with preterm labor and intact membranes and those with idiopathic intrauterine bleeding during pregnancy. Protein Z plasma concentrations were measured in the following groups: (1) normal pregnant women (n = 71); (2) patients at term with (n = 67) and without labor (n = 88); (3) patients with spontaneous PTL before 34 weeks who were classified into: (a) PTL with intra-amniotic infection/inflammation (IAI; n = 35), (b) PTL without IAI (n = 54), and (c) patients with PTL who delivered at term (n = 49); and (4) patients with idiopathic intrauterine bleeding in the second and third trimester who were divided into: (a) subsequent spontaneous PTL and delivery, and (b) term delivery. Maternal plasma protein Z concentration was measured by a specific and sensitive immunoassay. Moreover, the amniotic fluid concentration of protein Z was determined in a subset of patients with preterm labor (n = 30).

RESULTS

(1) There was no correlation between maternal plasma protein Z concentration and gestational age in normal pregnant women. (2) The mean maternal plasma concentration of protein Z was significantly lower in women during spontaneous labor at term than in those not in labor (mean 2.15 microg/mL (95% CI 2.01-2.29) vs. mean 2.45+/-0.52 microg/mL (95% CI 2.34-2.56), respectively; p = 0.001). (3) Women with PTL without IAI who delivered preterm had a significantly lower mean protein Z concentration than normal pregnant women (mean 2.12 mug/mL (95% CI 1.98-2.26) vs. mean 2.39 microg/mL (95% CI 2.28-2.5); p = 0.008). (4) Of interest, PTL with IAI was not associated with lower plasma concentrations of protein Z, nor were those with PTL who delivered at term (p > 0.05 for each). (5) No differences were found in the maternal plasma concentrations of anti-protein Z antibodies between normal pregnancies and those with spontaneous PTL. (6) Patients with idiopathic intrauterine bleeding who had spontaneous PTL and delivery had a significantly lower mean plasma protein Z concentration than those who delivered at term (mean 1.24 microg/mL (95% CI 1.08-1.4) vs. mean 1.49+/-0.47 microg/mL (95% CI 1.33-1.65), respectively; p = 0.03). (7) Amniotic fluid was found to contain immunoreactive protein Z.

CONCLUSIONS

(1) Patients with PTL leading to preterm delivery in the absence of IAI had a significantly lower plasma concentration of protein Z than those with normal pregnancies. (2) Patients with idiopathic intrauterine bleeding and subsequently spontaneous PTL and delivery had a significantly lower plasma concentration of protein Z than those with idiopathic intrauterine bleeding who delivered at term. (3) Protein Z was present in the amniotic fluid of patients with PTL. Collectively, these observations suggest that a subgroup of patients with PTL have a hemostatic disorder that involves bleeding/thrombosis as a mechanism of disease.

Protein-Z-deficiency as a rare case of unexpected perioperative bleeding in a patient with spinal cord injury

STUDY DESIGN

Case report describing the management of repeated perioperative bleeding probably due to Protein-Z-deficiency in a post-traumatic paraplegic patient.

OBJECTIVES

To describe the difficulty in diagnosing this rare form of hypocoagulability and the monitoring and substitution concept during three elective surgical interventions.

SETTING

Spinal Cord Injury Center, Bergmannstrost, Halle, Germany.

CASE REPORT

A 19-year-old male suffering from a post-traumatic paraplegia sub Th8 (ASIA-A) since childhood had experienced two life-threatening intraoperative bleeding incidents before finally Protein-Z-deficiency as the underlying coagulation disorder was diagnosed. After substitution of 2000 IE PPSB (Beriplex P/N) a repeatedly postponed implantation of a sphincter-externus (Brindley-) stimulator could be performed without bleeding complications, and this was also true for two additional urological interventions 1 year later. Protein-Z levels were monitored before, during and after the operations. The preoperative application of between 1000 and 2000 IE PPSB was safe and sufficient to raise the patients' plasma Protein-Z level to almost normal and so prevent excessive intraoperative blood loss.

CONCLUSION

In case of repeated bleeding tendency of unknown origin it is mandatory to look for rare causes of hypocoagulability such as Protein-Z-deficiency. We developed a substitution concept using a plasma concentrate with guaranteed Protein-Z amount (PPSB) allowing the safe performance of elective surgical interventions.

Protein Z plasma levels in different phases of activity of coronary atherosclerosis

We previously reported that low protein Z plasma levels are associated with acute coronary syndromes (ACS). Aim of the present study was to evaluate protein Z levels in different phases of activity of coronary atherosclerosis. Protein Z plasma levels were measured in 166 (131 male and 35 female) patients consecutively admitted to the University of Florence with a diagnosis of ACS (group A), 166 (131 male and 35 female) patients selected by age and gender in relation to group A from those with a clinical history of ACS who remained symptom- and/or event-free over the last year before the investigation (group B); and 332 (262 male and 70 female) controls comparable for age and gender with the other two groups. None had liver or renal dysfunction nor showed a positivity for antiphospholipid antibodies or for factor V Leiden mutation. Patients under warfarin therapy were excluded. Mean protein Z plasma levels were found to be significantly (P < 0.0001) lower in group A (1475 +/- 684.1 ng mL(-1)) and group B (1327.6 +/- 690.7 ng mL(-1)) as compared with control group (1650.1 +/- 634.5 ng mL(-1)), while no significant differences existed between the two groups of patients (P = 0.06). A logistic regression analysis, performed after the division of the study population into quartiles of protein Z levels and adjusted for all possible confounders, showed a significant increased risk of ACS for the lowest (<1213 ng mL(-1)) as compared with the highest quartile of protein Z in both groups of patients [group A odds ratio (OR): 2.7, 95% CI 1.3-5.5, P = 0.007; group B OR: 3.2, 95% CI 1.1-8.9, P = 0.02). In conclusion, these results strengthen our previous data on low protein Z plasma levels in ACS and indicate a possible dose-response effect of decreasing protein Z plasma levels on the coronary atherosclerotic disease.

R255h Amino acid substitution of protein Z identified in patients with factor V Leiden mutation

The clinical significance of diminished protein Z in plasma is controversial. Studies in mice demonstrated that deficiency of protein Z dramatically increases the prothrombotic tendency of factor V Leiden mutation. This finding was confirmed by initial results in humans, indicating that thromboembolism in factor V Leiden patients with lowered protein Z level occurs earlier than in patients with normal protein Z levels. Consequently, the aim of our present study was to find out whether genetic alterations of protein Z were demonstrated in patients with factor V Leiden mutation and early onset of thromboembolic disease. DNA-sequencing of the protein Z gene was performed in two patients with factor V Leiden mutation, early onset of thromboembolism, and lowered protein Z levels. In both patients, R255H substitution of the protein Z gene was identified. Subsequently, the R255H substitution was also found in 12 of 132 additional patients. Patients presenting with the R255H substitution in addition to factor V Leiden mutation showed thromboembolic events more frequently than factor V Leiden patients without R255H substitution of the protein Z gene. In conclusion, R255H substitution of the protein Z gene seems to influence clinical symptoms of thromboembolism in factor V Leiden patients.

A naturally occurring E30Q mutation in the Gla domain of protein Z causes its impaired secretion and subsequent deficiency

Protein Z is a vitamin K-dependent glycoprotein that plays a role in the regulation of coagulation. A nucleotide substitution of G by C in exon II of the protein Z gene, resulting in the replacement of Glu-30 with Gln (E30Q), and a G to A transition at the 79th nucleotide in intron F (IntF79G/A) were heterozygously identified in a patient with a severe thrombotic tendency, whose plasma protein Z level was about 15% of normal. Other vitamin K-dependent coagulation factors were within normal ranges. Glu-30 is one of 13 gamma-carboxylation sites in protein Z and is well conserved among vitamin K-dependent proteins. Expression studies revealed that the E30Q mutant was not released from synthesizing cells, although wild-type protein Z was readily secreted in a vitamin K-dependent fashion. The E30Q mutant was N-glycosylated, gamma-carboxylated, and translocated from the endoplasmic reticulum (ER) to the Golgi in the presence of vitamin K, as was the wild type. Coexpression of E30Q with wild-type protein Z interfered with the secretion of the wild type, while only a minor or no effect was observed on the secretion of factor X and plasminogen. The IntF79A allele has been reported to be also associated with lowered protein Z levels.

The physiology of vitamin K nutriture and vitamin K-dependent protein function in atherosclerosis

Recent advances in the discovery of new functions for vitamin K-dependent (VKD) proteins and in defining vitamin K nutriture have led to a substantial revision in our understanding of vitamin K physiology. The only unequivocal function for vitamin K is as a cofactor for the carboxylation of VKD proteins which renders them active. While vitamin K was originally associated only with hepatic VKD proteins that participate in hemostasis, VKD proteins are now known to be present in virtually every tissue and to be important to bone mineralization, arterial calcification, apoptosis, phagocytosis, growth control, chemotaxis, and signal transduction. The development of improved methods for analyzing vitamin K has shed considerable insight into the relative importance of different vitamin K forms in the diet and their contribution to hepatic vs. non-hepatic tissue. New assays that measure the extent of carboxylation in VKD proteins have revealed that while the current recommended daily allowance for vitamin K is sufficient for maintaining functional hemostasis, the undercarboxylation of at least one non-hemostatic protein is frequently observed in the general population. The advances in defining VKD protein function and vitamin K nutriture are described, as is the potential impact of VKD proteins on atherosclerosis. Many of the VKD proteins contribute to atherogenesis. Recent studies suggest involvement in arterial calcification, which may be influenced by dietary levels of vitamin K and by anticoagulant drugs such as warfarin that antagonize vitamin K action.

Plasma protein Z levels in healthy and high-risk newborn infants

AIM

To evaluate plasma protein Z (PZ) levels in healthy and high-risk newborn infants.

METHODS

A longitudinal observational study was conducted. Inclusion criteria were: healthy term and preterm newborns normal for gestational age and newborns belonging to one of the following groups: newborns small for gestational age (SGA), newborns affected by respiratory distress syndrome (RDS), newborns from mothers with pre-eclampsia. Newborns with sepsis, congenital malformation or haemorrhagic disorders were excluded. Plasma PZ levels, protein C (PC) concentration, PC activity and protein-induced vitamin K absence levels were measured.

RESULTS

53 newborns were enrolled into the study. PZ and PC antigen levels varied significantly among analysed subgroups on day 1 (p < 0.01): lower levels of these inhibitors were found in RDS newborns (group C), newborns from mothers affected by pre-eclampsia (group D) and SGA newborns (group E) than in healthy term and preterm newborns (groups A and B).

CONCLUSION

PZ deficiency occurs in newborns affected by severe RDS, in newborns from pre-eclamptic mothers and in SGA newborns, probably owing to activated coagulation in the first two conditions and to reduced PZ synthesis in the last condition.

Echinococcus granulosus antigen 5 is closely related to proteases of the trypsin family

Antigen 5 (Ag5) is a dominant secreted component of the larval stage of Echinococcus granulosus, and is highly immunogenic in human infections. Although the diagnostic value of Ag5 has been thoroughly evaluated, there has been little progress in its molecular characterization and the understanding of its biological role. In the present study, the Ag5 gene was cloned by reverse transcription-PCR on the basis of the amino acid sequences of tryptic fragments. The nucleotide sequence indicates that Ag5 is synthesized as a single polypeptide chain that is afterwards processed into single disulphide-bridged 22 and 38 kDa subunits. Whereas the 22 kDa component contains a highly conserved glycosaminoglycan-binding motif that may help to confine Ag5 in the host tissue surrounding the parasite, the 38 kDa subunit is closely related to serine proteases of the trypsin family. The sequences in the vicinity of the active-site histidine, aspartic acid and serine residues, and critical cysteine residues involved in disulphide formation, are well conserved, but the catalytic serine residue is replaced by threonine. Since there are no significant chemical differences between the O gamma atoms of these residues, we performed a series of enzymic assays to find out whether Ag5 is a catalytic molecule. Neither proteolytic activity nor binding to protease inhibitors could be detected using the native purified antigen. Thus it may be possible that Ag5 possesses a highly specific physiological substrate or, more likely, that trypsin-like folding has been recruited to fulfil novel functions.

Factor X deficiency

Factor X is one of the vitamin K-dependent serine proteases. It plays a crucial role in the coagulation cascade, as the first enzyme in the common pathway of thrombus formation. The gene for factor X maps to the long arm of chromosome 13, approximately 2.8 kb downstream of the factor VII gene. The gene consists of eight exons, each of which encodes a specific functional domain within the protein. Both the gene structure and the amino acid sequence show homology to other vitamin K-dependent clotting factors, suggesting their origin in a common ancestral protein. Factor X deficiency is one of the rarest of the inherited coagulation disorders. Inheritance is in an autosomal recessive manner. The clinical phenotype is of a variable bleeding tendency. Homozygous factor X deficiency has an incidence of 1:1,000,000 in the general population. Heterozygotes are often clinically asymptomatic. Acquired factor X deficiency is rare, but when it occurs it is usually in association with amyloidosis. Treatment of factor X deficiency involves replacement of the protein with either fresh frozen plasma or prothrombin complex concentrates, although the latter should be used with caution as infusion may be associated with an increased risk of thrombosis.

Protein Z influences the prothrombotic phenotype in Factor V Leiden patients

Protein Z enhances the inhibition of factor Xa by protein Z-dependent protease inhibitor (ZPI). Thus, diminution of protein Z should induce prothrombotic tendency due to lowered cofactor activity for ZPI. In Factor V Leiden mice, prothrombotic tendency of severe diminution or lack of protein Z was demonstrated. We here present first studies in humans, indicating that diminution of protein Z in factor V Leiden patients aggravates thromboembolic risk.

Protein Z in ischaemic stroke

Many risk factors associated with ischaemic stroke are known, including high levels of fibrinogen or factor VII. Protein Z is a vitamin K-dependent coagulation factor, which was found to promote the assembly of thrombin with phospholipid vesicles that might promote coagulation. Indeed, a low protein Z level may be associated with a varying bleeding tendency. Therefore, we hypothesized that high protein Z levels could induce a hypercoagulable state and performed a case-control study to investigate a potential association between high protein Z plasma levels and ischaemic stroke. We measured protein Z in plasma samples from 157 patients with stroke of unknown aetiology and 192 control subjects. All patients had survived an ischaemic stroke or transient ischaemic attack (TIA) for at least 2 months. We found an increased relative risk of ischaemic stroke with increasing protein Z levels, with an odds ratio of 4.3 [95% confidence interval (CI): 1.7--11] for protein Z plasma levels > or = 160%. Excluding patients with a history of venous thromboembolism from the analysis, the same result was obtained (odds ratio 4.2; 95% CI: 1.6--11.2). Using a logistic regression model, this association also remained significant (P = 0.04) after adjustment for established risk factors. Our data indicated that a high plasma level of protein Z is an independent risk factor for ischaemic stroke.