Low levels of protein Z and the risk of venous thromboembolism

Markers of Hereditary Thrombophilia with Unclear Significance

Thrombophilia leads to an increased risk of venous thromboembolism. Widely accepted risk factors for thrombophilia comprise deficiencies of protein C, protein S, and antithrombin, as well as the factor V "Leiden" mutation, the prothrombin G20210A mutation, dysfibrinogenemia, and, albeit less conclusive, increased levels of factor VIII. Besides these established markers of thrombophilia, risk factors of unclear significance have been described in the literature. These inherited risk factors include deficiencies or loss-of-activity of the activity of ADAMTS13, heparin cofactor II, plasminogen, tissue factor pathway inhibitor (TFPI), thrombomodulin, protein Z (PZ), as well as PZ-dependent protease inhibitor. On the other hand, thrombophilia has been linked to the gain-of-activity, or elevated levels, of α2-antiplasmin, angiotensin-converting enzyme, coagulation factors IX (FIX) and XI (FXI), fibrinogen, homocysteine, lipoprotein(a), plasminogen activator inhibitor-1 (PAI-1), and thrombin-activatable fibrinolysis inhibitor (TAFI). With respect to the molecular interactions that may influence the thrombotic risk, more complex mechanisms have been described for endothelial protein C receptor (EPCR) and factor XIII (FXIII) Val34Leu. With focus on the risk for venous thrombosis, the present review aims to give an overview on the current knowledge on the significance of the aforementioned markers for thrombophilia screening. According to the current knowledge, there appears to be weak evidence for a potential impact of EPCR, FIX, FXI, FXIII Val34Leu, fibrinogen, homocysteine, PAI-1, PZ, TAFI, and TFPI on the thrombotic risk.

Anticoagulant SERPINs: Endogenous Regulators of Hemostasis and Thrombosis

Appropriate activation of coagulation requires a balance between procoagulant and anticoagulant proteins in blood. Loss in this balance leads to hemorrhage and thrombosis. A number of endogenous anticoagulant proteins, such as antithrombin and heparin cofactor II, are members of the serine protease inhibitor (SERPIN) family. These SERPIN anticoagulants function by forming irreversible inhibitory complexes with target coagulation proteases. Mutations in SERPIN family members, such as antithrombin, can cause hereditary thrombophilias. In addition, low plasma levels of SERPINs have been associated with an increased risk of thrombosis. Here, we review the biological activities of the different anticoagulant SERPINs. We further consider the clinical consequences of SERPIN deficiencies and insights gained from preclinical disease models. Finally, we discuss the potential utility of engineered SERPINs as novel therapies for the treatment of thrombotic pathologies.

The Proteolytic Inactivation of Protein Z-Dependent Protease Inhibitor by Neutrophil Elastase Might Promote the Procoagulant Activity of Neutrophil Extracellular Traps in Sepsis

Septic shock is the archetypal clinical setting in which extensive crosstalk between inflammation and coagulation dysregulates the latter. The main anticoagulant systems are systematically impaired, depleted, and/or downregulated. Protein Z-dependent protease inhibitor (ZPI) is an anticoagulant serpin that not only targets coagulation factors Xa and XIa but also acts as an acute phase reactant whose plasma concentration rises in inflammatory settings. The objective of the present study was to assess the plasma ZPI antigen level in a cohort of patients suffering from septic shock with or without overt-disseminated intravascular coagulation (DIC). The plasma ZPI antigen level was approximately 2.5-fold higher in the patient group (n = 100; 38 with DIC and 62 without) than in healthy controls (n = 31). The elevation's magnitude did not appear to depend on the presence/absence of DIC. Furthermore, Western blots revealed the presence of cleaved ZPI in plasma from patients with severe sepsis, independently of the DIC status. In vitro, ZPI was proteolytically inactivated by purified neutrophil elastase (NE) and by NE on the surface of neutrophil extracellular traps (NETs). The electrophoretic pattern of ZPI after NE-catalyzed proteolysis was very similar to that resulting from the clotting process-suggesting that the cleaved ZPI observed in severe sepsis plasma is devoid of anticoagulant activity. Taken as a whole, our results (1) suggest that NE is involved in ZPI inactivation during sepsis, and (2) reveal a novel putative mechanism for the procoagulant activity of NETs in immunothrombosis.

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.

Uncertain thrombophilia markers

The development of venous thromboembolism (VTE), which includes deep-vein thrombosis and pulmonary embolism, may be associated with inherited or acquired risk factors that can be measured in plasma or DNA testing. The main inherited thrombophilias include the plasma deficiencies of the natural anticoagulants antithrombin, protein C and S; the gain-of-function mutations factor V Leiden and prothrombin G20210A; some dysfibrinogenaemias and high plasma levels of coagulation factor VIII. Besides these established biomarkers, which usually represent the first-level laboratory tests for thrombophilia screening, a number of additional abnormalities have been less consistently associated with an increased VTE risk. These uncertain causes of thrombophilias will be discussed in this narrative review, focusing on their clinical impact and the underlying pathogenetic mechanisms. Currently, there is insufficient ground to recommend their inclusion within the framework of conventional thrombophilia testing.

Circulating protein Z concentration, PROZ variants, and unexplained cerebral infarction in young and middle-aged adults

Protein Z (PZ) is a vitamin K-dependent plasma protein that exhibits both pro- and anticoagulant properties. Both low and high PZ levels have been linked to ischaemic stroke. Although PZ-lowering gene variants have been found to be less common in ischaemic stroke, the relationship remains unclear. We investigated PZ levels and PROZ variants in a multi-ethnic case-control study of unexplained stroke in participants aged 18 to 64. Plasma PZ was measured in cases (≥2 months post-stroke) and controls. PZ polymorphisms G79A (rs3024735) and A13G (2273971) were genotyped. A combined genetic score (0-4 minor alleles) was created assuming additive effects. A total of 715 individuals (1:1.4 cases:controls) was included. Analyses revealed evidence of a non-linear association. After adjusting for demographic and clinical covariates, PZ levels >2.5 µg/ml (90^th %ile) were significantly associated with cryptogenic stroke (OR 2.41 [95 % CI 1.34, 4.34]) as compared with lower levels. Higher genetic score was related to progressively lower levels of PZ, and the presence of four minor alleles was associated with lower odds of stroke (adjusted OR 0.26 [95 % CI 0.07, 0.96]) versus 0 minor alleles. In this multi-ethnic study of young and middle-aged adults, there was evidence of a non-linear positive association between PZ level and unexplained stroke, with a directionally consistent association for genetic variants related to PZ levels and cryptogenic stroke. These findings support elevated PZ levels as a risk factor for cryptogenic stroke.

Plasma Concentrations of Protein Z and Protein Z-Dependent Protease Inhibitor in Patients With Essential Thrombocythemia

The pathological consequences of decreased protein Z (PZ) and/or Z-dependent protease inhibitor (ZPI) levels remain as yet unclear, despite a growing body of evidence which supports their involvement in an increased thrombotic risk. The purpose of the present study was 2-fold: to evaluate plasma concentrations of protein Z and ZPI in patients with essential thrombocythemia (ET) and to determine their significance in thrombotic complications. The median (range) plasma concentrations of PZ in our patients with ET were lower, but not significantly, than in healthy individuals: PZ (1.42 µg/mL, 0.36-3.14 µg/mL vs 1.6 µg/mL, 0.75-2.56 µg/mL, P = .08). On the other hand, the median (range) plasma concentrations of ZPI in the said patients with ET were meaningfully lower than in the reference group: ZPI (3.22 µg/mL, 0.85-6.97 µg/mL vs 4.41 µg/mL, 1.63-7.83 µg/mL, P = .0004). More importantly, the study revealed a statistically significant lower concentration of PZ and ZPI in patients with the presence of the JAK2V617F mutation relative to patients without the mutation, for PZ: 1.38 µg/mL, 0.36-2.6 µg/mL versus 1.63 µg/mL, 0.88-3.14 µg/mL, P = .03, and ZPI 2.89 µg/mL, 0.85-5.91 µg/mL versus 3.61 µg/mL, 1.53-6.97 µg/mL, P = .002. Additionally, significant differences between the concentrations of PZ and ZPI were found in patients with venous thrombotic episodes compared to healthy individuals, for PZ: 1.23 µg/mL, 0.82-1.99 µg/mL versus 1.6 µg/mL, 0.75-2.56 µg/mL, P = .043, and ZPI: 2.42 µg/mL, 0.85-4.21 µg/mL versus 4.41 µg/mL, 1.63-7.83 µg/mL, P < .0001. To recapitulate, our results suggest that the deficiency of PZ may increase tendency to thrombosis in patients with ET.

Protein Z G79A polymorphism and puerperal cerebral venous thrombosis

Protein Z (PZ), a cofactor for PZ-dependent protease inhibitor, is known to play an important role in inhibiting the coagulation cascade. The aim of the study was to investigate whether PZ G79A polymorphism is a risk factor for puerperal cerebral venous thrombosis (CVT). A total of 71 patients with puerperal CVT and 98 healthy controls were genotyped for PZ 79GA polymorphism by polymerase chain reaction-restriction fragment length polymorphism method. In patients, the genotype distribution for GG, GA, and AA genotypes was 22.5%, 43.7%, and 33.8%, and in controls, 25.5%, 40.8%, and 33.7%, respectively. The risk associated with carrying the mutant genotype (GA and AA) versus the wild GG genotype was found to be 1.11 (95% confidence interval: 0.52-2.35; P = .909). There was no significant difference in the clinical features of the patients with and without the polymorphism. We therefore conclude that PZ G79A polymorphism is not a risk factor for puerperal CVT in Indian women.

Protein Z, an anticoagulant protein with expanding role in reproductive biology

Protein Z (PZ) is a vitamin K-dependent factor characterized by its homology to other vitamin K-dependent factors (factors VII, IX, and X, protein C and protein S), but lacks any enzymatic activity. Instead, PZ acts as a cofactor for the inhibition of factor Xa through the serpin PZ-dependent protease inhibitor (ZPI). PZ deficiency is associated with a procoagulant state, highlighted by excessive FXa secretion and thrombin production, and is linked with several thrombotic disorders, including arterial vascular and venous thromboembolic diseases. A role for the PZ-ZPI complex in the regulation of physiological pregnancy has been demonstrated, highlighted by the progressive elevation in PZ levels in the first trimester of gestation, which then steadily decline toward delivery. An association between altered plasma PZ concentrations and adverse pregnancy outcomes (recurrent miscarriage, stillbirth, preeclampsia, intrauterine growth restriction, and placental abruption) has been reported. The mechanism by which PZ deficiency leads to adverse pregnancy outcomes is not clear, but it is multifactorial. It may be attributed to the anti-PZ IgG and IgM autoantibodies, which apparently act independently of classical antiphospholipid antibodies (lupus anticoagulant, anticardiolipin, and anti-β2-glycoprotein I antibodies). PZ deficiency has also been reported to be constitutional, and a number of variants in the PROZ (PZ) gene and SERPINA10 (ZPI) gene are linked with specific adverse pregnancy complications. This review summarizes the relationship between adverse pregnancy outcomes and acquired and constitutional PZ-ZPI deficiency, in order to understand whether or not PZ deficiency could be considered as a risk factor for poor pregnancy outcomes.

The evaluation of protein Z levels of children with acute lymphoblastic leukaemia during induction therapy

The objective of this study was to evaluate the protein Z levels of children with acute lymphoblastic leukaemia (ALL) during induction therapy. Although several studies investigated the association between steroid and L-asparaginase (L-ASP) administration and levels of coagulation proteins such as protein C, protein S and antithrombin in children with ALL, protein Z levels have not been examined in any study yet. Peripheral blood was drawn from the study group before chemotherapy (PZ0) at diagnosis, at 12th day (PZ1), 15th day (PZ2), 18th day (PZ3) and 21st day (PZ4) of treatment wherein L-ASP treatment is given along with steroid administration according to ALL BFM-1995 chemotherapy protocol. Plasma protein Z levels were measured by enzyme immunoassay method. Mean protein Z level at PZ0 was 1.628 ± 0.485 μg/ml in the study group and 1.672 ± 0.662 μg/ml in the control group. No statistical difference was observed. In the study group, there was a slight increase in protein Z levels between the PZ0 and PZ1 periods in which only steroid therapy was administered. Statistically significant decrease was observed between protein Z levels in PZ0-PZ4, PZ1-PZ2, PZ1-PZ3, PZ1-PZ4 and PZ3-PZ4 periods. During the induction treatment, symptomatic haemorrhage or thrombosis was not followed up in any patients. We demonstrated that children with ALL have similar protein Z values to those of the control group at diagnosis. A significant decrease occurs at the end of the induction treatment with steroid and L-ASP administration. However, this deficiency does not result in development of symptomatic thrombosis or bleeding in these patients.

Participation of protein Z-dependent protease inhibitor and protein Z system in the pathomechanism of thrombotic complications

Thrombotic complications of unknown etiology remain a serious diagnostic and therapeutic problem. Occurrence of the inherited polymorphisms of genes encoding proteins involved in the coagulation cascade is one of the possible causes of these complications. In recent years, protein Z (PZ) and PZ-dependent protease inhibitor (ZPI) have been added to the list of prothrombotic factors. PZ is a glycoprotein serving as a cofactor of ZPI, which is responsible for the inhibition of prothrombinase. Expression of the PZ gene is under the control of many transcriptional factors; several polymorphisms alternate the rate of gene expression. The present article describes the significance of the ZPI-PZ system in venous and arterial thrombosis, adverse pregnancy outcomes and antiphospholipid syndrome complications.

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.

[Protein Z, polymorphisms in the protein Z gene and thrombosis]

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

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.

Protein Z-dependent protease inhibitor and protein Z in peripheral arterial disease patients

SUMMARY INTRODUCTION

Protein Z is a vitamin K-dependent protein that serves as a cofactor for the inhibition of activated factor X by the serpin protein Z-dependent protease inhibitor (ZPI). Protein Z plasma levels have been shown to be reduced in patients with peripheral arterial disease (PAD), but ZPI levels have not yet been reported. The aim of this study was to more fully assess the protein Z-ZPI system in individuals with atherosclerosis selected by the presence of symptomatic PAD.

MATERIALS AND METHODS

Protein Z and ZPI levels were determined in 95 PAD patients (73 males; 22 females) [median age: 73 years (range, 50-86 years)] and in 190 controls comparable for age and gender. Protein Z was measured using a commercial immunoassay, and ZPI was measured with a homemade immunoassay and a functional assay.

RESULTS

Protein Z antigen, ZPI antigen and ZPI function were found to be significantly lower in PAD patients with respect to controls [protein Z, median 72.5% (range: 3.4-123.7%) vs. 90.7% (range: 32.1-203.2%), P < 0.0001; ZPI antigen, 86.1% (range: 25.1-149.5%) vs. 93.2% (range: 48.9-171.3%), P = 0.004; ZPI function, 83.5% (range: 21.1-135.2%) vs. 97.2% (range: 50.5-175.5%), P < 0.0001]. The lowest tertiles of protein Z antigen [odds ratio (OR) 5.4, 95% confidence interval (CI) 2.2-13.5, P < 0.0001] and ZPI function (OR 2.4, 95% CI 1.1-5.5, P = 0.03) were associated with PAD on multivariate analysis after adjustment for age, gender, and traditional cardiovascular risk factors. A significant inverse relationship was also observed between protein Z and ZPI levels and the number of traditional cardiovascular risk factors and the clinical severity of disease (Fontaine stage).

CONCLUSIONS

Low levels of protein Z antigen and protein Z activity are significantly associated with the occurrence and severity of atherosclerotic PAD.

Pregnancy-associated changes in the hemostatic system in wild-type and factor V Leiden mice

BACKGROUND

Pregnancy, oral contraceptive (OC)use and hormone replacement therapy (HRT) are established risk factors for venous thrombosis. Acquired resistance to activated protein C (APC) has been proposed to contribute to the increased thrombosis risk. Mouse models are often used for preclinical testing of newly developed hormone preparations. However, it is not known whether hormone-induced APC resistance is also observed in laboratory animals.

OBJECTIVES

To investigate whether hormonal changes modulate APC resistance in mice, we used pregnant mice as a model of hormone-induced APC resistance. The effect of pregnancy on APC resistance was studied in wild-type and factor (F)V Leiden mice.

METHODS

APC resistance was determined in mouse plasma using a thrombin generation-based APC resistance test. APC resistance determinants,i.e. prothrombin, FV, FX, antithrombin and protein S levels,and of tissue factor pathway inhibitor (TFPI) activity were evaluated in plasma from non-pregnant and pregnant mice.

RESULTS

In contrast to humans, pregnancy induced a decrease in APC resistance in wild-type and in FV Leiden mice.Pregnant mice had higher levels of prothrombin, FV, FX,protein S and TFPI activity as compared with non-pregnant mice.

CONCLUSIONS

Pregnancy causes a decrease in APC resistance in mice, which can be explained by the elevation of protein S levels and increased TFPI activity in plasma. Our findings show species specificity in the effects of pregnancy on the major determinants of the protein C system and suggest that protein S and TFPI play an important role in the development of pregnancy-induced APC resistance in humans.

Pyelonephritis during pregnancy: a cause for an acquired deficiency of protein Z

OBJECTIVE

Pyelonephritis has a more severe course during pregnancy than in the non-pregnant state. This has been attributed to the increased susceptibility of pregnant women to microbial products. An acquired protein Z deficiency has been reported when there is excessive thrombin activity. The aim of this study was to determine whether pyelonephritis during pregnancy is associated with changes in maternal plasma protein Z concentrations.

STUDY DESIGN

A cross-sectional study was conducted to compare plasma protein Z concentrations between normal pregnant women (N = 71) and pregnant women with pyelonephritis (N = 42). Protein Z concentrations were measured by enzyme-linked immunosorbent assay. Parametric and non-parametric statistics were used for analysis.

RESULTS

Patients with pyelonephritis had a significantly lower median plasma concentration of protein Z than did patients with normal pregnancies (median 2.14 microg/mL (0.4-3.4) vs. median 2.36 microg/mL (1.09-3.36); p = 0.03). There was no difference in the median plasma concentration of anti-protein Z antibodies between patients with pyelonephritis and those with normal pregnancies.

CONCLUSION

The median maternal plasma protein Z concentration was significantly lower in patients with pyelonephritis during pregnancy than in patients with normal pregnancies.

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.

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.

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.

Low protein Z levels and risk of occurrence of deep vein thrombosis

BACKGROUND

Protein Z (PZ) serves as a cofactor for activated factor X inhibition by the PZ-dependent protease inhibitor. In vivo and in vitro studies aimed at investigating the role of PZ levels in venous thombosis have produced conflicting results.

OBJECTIVES

We investigated whether reduced PZ levels and PZ gene common variants are associated deep vein thrombosis (DVT).

PATIENTS AND METHODS

In 197 patients with DVT and in 197 age-matched and sex-matched controls, PZ plasma levels and gene polymorphisms were evaluated by means of an enzyme-linked immunosorbent assay and direct cycle sequence analysis.

RESULTS

Similar PZ levels were found in controls (1.44; SD 0.63 microg mL-1) and in patients (1.44; SD 0.96 microg mL-1). The incidence of PZ levels below the 5.0 (0.52 microg mL-1) or the 2.5 percentile of controls (0.47 microg mL-1) was higher in patients (10.2% and 8.7%, respectively) than in controls {4.1% [odds ratio (OR) 2.7, 95% confidence interval (CI) 1.2-7.3], and 2.0% (OR 4.6, 95% CI 1.5-13.9), respectively}. This relationship was independent of the effect of age, sex, and factor V Leiden and FII A(20210) alleles [OR 2.8 (95% CI 1.1-7.3), and OR 4.9 (95% CI 1.4-17.3)]. PZ levels were associated with the intron C G-42A and the intron F G79A polymorphisms in cases (r2=0.129) and in controls (r2=0.140). However, frequencies of the PZ gene polymorphisms were similar in the two groups and were not associated with very low PZ levels.

CONCLUSIONS

The present data suggest an association between very low PZ plasma levels and the occurrence of DVT, with PZ gene polymorphisms contributing little to this relationship.