Low protein Z levels and risk of ischemic stroke: differences by diabetic status and gender

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.

Association of Protein Z with Prediabetes and Type 2 Diabetes

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a progressive metabolic disease. Early detection of prediabetes is important to reduce the risk of T2DM. Some cytokines are known to be associated with T2DM. Therefore, we aimed to identify cytokines as novel biomarkers of glucose dysmetabolism.

METHODS

The first stage of the study included 43 subjects (13 subjects with newly diagnosed T2DM, 13 with prediabetes, and 16 with normoglycemia) for cytokine microarray analysis. Blood samples of the subjects were assessed for 310 cytokines to identify potential indicators of prediabetes. The second stage included 142 subjects (36 subjects with T2DM, 35 with prediabetes, and 71 with normoglycemia) to validate the potential cytokines associated with prediabetes.

RESULTS

We identified 41 cytokines that differed by 1.5-fold or more in at least one out of the three comparisons (normoglycemia vs. prediabetes, normoglycemia vs. T2DM, and prediabetes vs. T2DM) among 310 cytokines. Finally, we selected protein Z (PROZ) and validated this finding to determine its association with prediabetes. Plasma PROZ levels were found to be decreased in patients with prediabetes (1,490.32±367.19 pg/mL) and T2DM (1,583.34±465.43 pg/mL) compared to those in subjects with normoglycemia (1,864.07±450.83 pg/mL) (P<0.001). There were significantly negative correlations between PROZ and fasting plasma glucose (P=0.001) and hemoglobin A1c (P=0.010).

CONCLUSION

PROZ levels were associated with prediabetes and T2DM. We suggest that PROZ may be a promising biomarker for the early detection of prediabetes. Further large-scale studies are needed to evaluate the relationship and mechanism between PROZ and prediabetes and T2DM.

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.

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.

Decreased Protein Z Concentrations Complicating the Hypercoagulable State of Behqet's Disease

Protein Z is a vitamin-K-dependent plasma protein that serves as a cofactor for the inhibition of factor Xa. Although the precise physiologic function of protein Z is still unknown, abnornal plasma protein Z concentrations have been associated with a number of thrombotic disease states. There is the evidence of universal activation of the hemostatic system in Behqet's disease (BD), which represents a hypercoagulable/prothrombotic state. Circulating protein Z levels in patients with BD were evaluated. Plasma protein Z concentrations were assayed in 24 patients with BD (male/female: 13/11, mean age 35.4 years) and in 24 healthy controls (males/females: 14/10, mean age 59.8 years). The disease duration was 10.6 years (range, 1-30 years). None of the subjects in either group had received anticoagulants within 3 weeks before the study, and none of them had liver dysfunction. Patients complicated with vascular disease were also excluded from the study. Mean plasma concentrations of protein Z were 141 ng/mL (range, 56.8-257) in healthy controls and 107.8 ng/mL (range, 21.2-202) in BD patients (p<0.05). There was a positive correlation between the disease duration and protein Z levels in the study group (p<0.05, r=0.448). Alterations of protein Z concentrations could complicate the pathobiology of the prothrombotic state of BD. Furthermore, the tendency of increment in the protein Z with the passage of time may reflect the diminution of the disease activity.

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.

Protein Z levels in pregnant Omani women: correlation with pregnancy outcome

Placental insufficiency resulting in fetal loss has been recognized in women with thrombophilic predisposition. Recent studies indicate that there is a high prevalence of protein Z (PZ) deficiency in patients with unexplained fetal loss. The objective of this study was to measure the PZ levels in pregnant Omani women in the first, second and third trimesters and correlate with the pregnancy outcome. The study enrolled 126 consecutive pregnant women after an informed consent prospectively. PZ was estimated in the first, second and third trimester in 15, 97 and 66 pregnant women respectively and they were followed for pregnancy outcomes including live birth, still birth, spontaneous abortion/induced abortion, maternal complications, fetal complications and health risks/complications in the newborn. The median PZ level (Mean ± SD) in the first, second and third trimester were 0.98 (1.07 ± 0.46), 1.3 (1.36 ± 0.61) and 1.44 (1.43 ± 0.69) (P < 0.05, Student's t-test, between first vs. second and first vs. third trimester). PZ deficiency defined as PZ level below 0.54 μg/ml (below 10th centile in the Omani population) was observed in 4 (4.7%) women, but interestingly all had a normal pregnancy outcome. Amongst the 43 subjects in whom paired PZ estimations were available, reducing PZ levels were observed from baseline values in 8 (33%) with normal pregnancy outcome; 5 (55%), with diabetes; 3 (50%) with hypertension and 2 (50%) with low birth weight respectively (P < 0.05, chi square test). PZ values increased progressively during the three trimesters of pregnancy. However, this increase is blunted in patients with abnormal pregnancy outcome like low birth weight babies or pregnancies associated hypertension or diabetes. Isolated PZ deficiency alone did not result in an abnormal outcome in this cohort of subjects.

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

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

[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.

Role of protein Z and protein C in neonates with respiratory distress syndrome in Egypt (experience of one centre)

The aim of this study is to evaluate Protein Z (PTZ) and protein C (PTC) levels in newborns suffering from RDS, healthy preterm and full term newborns and to compare PTZ serum levels in RDS preterm infants with healthy preterm before and after recovery. Sixty newborn infants, recruited from the neonatal unit, were enrolled in the study and divided into 3 groups: Group (I): 20 preterm with RDS, Group (II): 20 healthy preterm control newborns (CPT) and Group (III): 20 healthy full term control newborns (CFT). Protein Z and C were measured using ELISA kits. The results of the study showed lower levels of protein Z were obtained in RDS group compared to preterm controls whose levels were significantly lower than in full-term controls. A significant increase in PTZ levels in RDS' group after recovery, when compared to preterm controls. In RDS, no significant correlations existed between PTZ levels (before and after recovery) and routine investigations except for a significant negative correlation with platelets count. No significant differences were found in PTC levels between the 3 studied groups. To conclude: premature newborns suffering from RDS showed decreased serum protein Z levels than normal preterm control newborns with further increase in its pattern after recovery. Further studies are recommended to evaluate the role of PTZ on outcome in premature newborns with RDS and to evaluate the relationship between protein PTZ and PTC and other coagulation factors incriminated in the development of RDS.

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.

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).

A computational modeling and molecular dynamics study of the Michaelis complex of human protein Z-dependent protease inhibitor (ZPI) and factor Xa (FXa)

Protein Z-dependent protease inhibitor (ZPI) and antithrombin III (AT3) are members of the serpin superfamily of protease inhibitors that inhibit factor Xa (FXa) and other proteases in the coagulation pathway. While experimental structural information is available for the interaction of AT3 with FXa, at present there is no structural data regarding the interaction of ZPI with FXa, and the precise role of this interaction in the blood coagulation pathway is poorly understood. In an effort to gain a structural understanding of this system, we have built a solvent equilibrated three-dimensional structural model of the Michaelis complex of human ZPI/FXa using homology modeling, protein-protein docking and molecular dynamics simulation methods. Preliminary analysis of interactions at the complex interface from our simulations suggests that the interactions of the reactive center loop (RCL) and the exosite surface of ZPI with FXa are similar to those observed from X-ray crystal structure-based simulations of AT3/FXa. However, detailed comparison of our modeled structure of ZPI/FXa with that of AT3/FXa points to differences in interaction specificity at the reactive center and in the stability of the inhibitory complex, due to the presence of a tyrosine residue at the P1 position in ZPI, instead of the P1 arginine residue in AT3. The modeled structure also shows specific structural differences between AT3 and ZPI in the heparin-binding and flexible N-terminal tail regions. Our structural model of ZPI/FXa is also compatible with available experimental information regarding the importance for the inhibitory action of certain basic residues in FXa.

The G79A polymorphism of protein Z gene is an independent risk factor for cerebral venous thrombosis

BACKGROUND AND PURPOSE

Protein Z (PZ), a vitamin Kdependent protein, plays a role in inhibiting coagulation. Its plasma level or PZ gene polymorphisms have been discussed as risk factors for stroke with conflicting results reported between various studies. Only one of these polymorphisms was studied in a cohort of patients suffering from cerebral venous thrombosis (CVT).

METHODS

We performed a retrospective genetic study comparing 100 healthy controls to 54 patients referred to our hemostasis unit after CVT occurrence. We compared the distribution of three PZ gene polymorphisms that may influence PZ plasma levels: A-13G in the promoter and G79A in intron F were tested using previously described techniques, and we developed a technique to evaluate the G-103A in intron A.

RESULTS

The G79A polymorphism was significantly more frequent in patients than in controls (p = 0.012): the presence of at least one A allele led to an odds ratio of 2.57 with a 95 % confidence interval of 1.23-5.34. The A-13G polymorphism also showed a nonsignificant trend towards a higher prevalence in patients.

CONCLUSION

The G79A polymorphism of the PZ gene was shown to be a new independent risk factor for cerebral venous thrombosis. Nevertheless, these results have to be confirmed by a prospective study including plasma PZ evaluation.

Low protein Z levels but not the protein Z gene G79A polymorphism are a risk factor for ischemic stroke

BACKGROUND

Protein Z (PZ) is a vitamin K-dependent plasma protein that plays a role in both pro-and anticoagulant pathways, but its exact physiological function remains unclear. The aim of this study was to determine the association between the G79A PZ gene polymorphism in intron F, PZ levels and the occurrence of ischemic stroke.

METHODS

We performed a case-control study in 118 Caucasian patients with first ever ischemic stroke or TIA confirmed by CT, and 113 age-and sex-matched population controls. Venous blood samples for PZ levels were collected 7 to 14 days and 3 months after stroke onset. Estimates of relative risk (odds ratios) were adjusted for vascular risk factors.

RESULTS

The adjusted relative risk of ischemic stroke associated with PZ levels in the lowest quartile versus the highest quartile was 3.0 (95% CI: 1.1-8.7) at 7-14 days, and 5.1 (95% CI: 1.2-21.9) at 3 months after the stroke. PZ levels in the convalescent sample were significantly lower than in the acute sample. In the convalescent sample, odds ratios increased with lower quartiles of protein Z level (test for trend p=0.02). Thirty-nine patients (33%) and 32 (28%) controls were heterozygous for the G79A PZ gene polymorphism and 4 (3%) patients and 4 (4%) controls had the AA-genotype. The PZ levels were significantly lower in subjects with the AA-genotype and intermediate in heterozygote subjects. The odds ratio of ischemic stroke associated with A-allele carriers versus GG-homozygotes was 1.2 (95% CI: 0.7-2.1).

CONCLUSION

No association between the G79A PZ gene polymorphism and the occurrence of stroke was observed. However, low PZ levels are independently associated with an increased risk of ischemic stroke.

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.

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.

Role of protein Z in stroke

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

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.

Protein Z levels and central retinal vein or artery occlusion

OBJECTIVES

Central retinal vein occlusion (CRVO) and central retinal artery occlusion (CRAO) are common disorders associated with risk factors for atherosclerosis. Protein Z is a cofactor for the inactivation of activated factor X (Xa) by the protein Z dependent protease inhibitor. Protein Z deficiency was recently linked to increased risk of arterial thrombosis. We investigated whether CRVO and CRAO are associated with low protein Z levels.

PATIENTS AND METHODS

Patients with CRVO, CRAO or recurrent branch retinal vein occlusion were recruited to the study. Protein Z level, lupus anticoagulant (LAC), anticardiolipin antibodies (ACA) and activated protein C resistance (APCR) were determined in plasma from patients (n = 36) and healthy controls (n = 42).

RESULTS

Thirty patients in the study group had traditional risk factors for retinal vessel occlusion and six patients had none. There was no significant difference in protein Z levels between the whole study group patients and controls (1995 +/- 810 vs. 2010 +/- 603 ng/mL, P = 0.922). However, patients with no risk factors for retinal vessel occlusion had significantly lower protein Z levels than controls (1379 +/- 682 vs. 2010 +/- 603 ng/mL, P = 0.022). Positive LAC was found in six patients and one control subject (P = 0.04). There were three patients and one control subject with abnormal APCR (P = 0.3) and none with positive ACA. Low protein Z level (lower than fifth percentile of control) was not associated with the presence of LAC or APCR.

CONCLUSION

Low protein Z level may be another risk factor for retinal vessel occlusion in patients without traditional risk factors for these disorders.

Down-regulation of Factor IXa in the Factor Xase Complex by Protein Z-dependent Protease Inhibitor

Protein Z-dependent protease inhibitor (ZPI) is a serpin inhibitor of coagulation factor (F) Xa dependent on protein Z, Ca2+, and phospholipids. In new studies, ZPI inhibited FIXa in the FXase complex. Since this observation could merely represent inhibition of the FXa product whose activity was measured, inhibition of FIXa was investigated five ways. 1) FXase incubation mixtures with/without ZPI/protein Z were diluted in EDTA; FXa activity was measured after reversal of its inhibition. 2) FXase incubation mixtures were immunoblotted for FXa product. 3) FX activation peptide region was 3H-labeled; release of 3H was used to measure FXase activity. 4) Activity was monitored in a FIXa-based clotting assay. 5) FIXa amidolytic activity was measured. In all cases, FIXa was inhibited by subphysiologic levels of ZPI. Unlike inhibition of FXa, inhibition of FIXa did not strictly require protein Z. Low concentrations of FVIIIa increased the efficiency of ZPI inhibition of FIXa; FVIIIa in molar excess was not protective of FIXa unless FIXa/FVIIIa interacted prior to ZPI exposure. Unusual time courses were observed for inhibition of both FIXa in the FXase complex and FXa in the prothrombinase complex. Activity loss stabilized in <100 s at a level dependent on ZPI concentration, suggesting equilibrium interactions rather than typical covalent serpin-protease interactions. Surface plasmon resonance binding experiments revealed binding and dissociation of ZPI/FIXa with Kd (app) of 9-12 nm, similar to the concentration of ZPI needed for 50% inhibition. ZPI may be an unusual physiologic regulator of both the intrinsic FXase and the prothrombinase complexes.

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.

[Thrombophilia and thrombosis]

INTRODUCTION

Generally speaking, thrombophilia includes all congenital and acquired conditions associated with increased susceptibility to thrombosis. An impaired balance between stimulating and inhibitory components of the hemostasis system may result in thrombosis or hemorrhage (extreme disorders), while moderately impaired hemostasis induces thrombophilia.

THROMBOPHILIA, PRETHROMBOTIC STATE AND THROMBOSIS

A prethrombotic state is a condition of stimulated hemostasis system with tolerable intensity. When the activation level exceeds the capacity of inhibitory components, prethrombotic state advances to thrombosis.

CLASSIFICATION OF THROMBOPHILIA

Thrombophilia is classified as primary or hereditary and secondary or acquired. Hereditary or congenital thrombophilia is a condition of congenital mutation of one or more antithrombotic components. Acquired or secondary thrombophilia accompanies a variety of pathologic conditions and diseases.

LABORATORY DIAGNOSIS OF THROMBOPHILIA

Specific laboratory tests for congenital thrombophilia include assessment of the antigen component related to the activity of AT III, protein C, and protein S, evaluation of the resistance to the activated C protein, assessment of t-Pa and PAl-1 activity, as well as tests for hyperhomocysteinemia and prothrombin 20210 mutation.

MANAGEMENT OF THROMBOPHILIA

Treatment of patients with congenital AT III deficiency includes intravenous heparin and AT III concentrate (dosage 50 U/ kgbw). Patients with heterozygous protein C and S deficiency are treated by intravenous heparin and oral anticoagulant therapy. Regarding arterial thrombosis due to confirmed congenital hyperhomocysteinemia, it is treated the same as venous thrombosis.

Protein Z Gene Polymorphisms, Protein Z Concentrations, and Ischemic Stroke

Background and Purpose— We aimed to determine whether A-13G or G79A polymorphisms of the protein Z gene that have been reported to be an important determinant of blood concentrations of protein Z are associated with risk of ischemic stroke in a broad range of stroke patients and controls.

Methods— We conducted a case control study of 151 hospital cases of first-ever ischemic stroke and 164 randomly selected community controls. Protein Z genotype was determined for the A-13G promoter polymorphism and the G79A intron F polymorphism, and plasma protein Z concentrations were measured during the first 7 days and at 3 to 6 months after the acute stroke event.

Results— Geometric mean concentrations of protein Z measured within 7 days of acute stroke were significantly higher in cases compared with controls (1.51 μg/mL versus 1.13 μg/mL; P <0·0001). Protein Z concentrations were highest among subjects with the A-13G AA genotype, intermediate among those with the AG genotype, and lowest among those with the GG genotype (1.39 μg/mL versus 1.05 μg/mL versus 0.76 μg/mL; P <0.0001); and highest among those with the G79A GG genotype, intermediate among those with the GA genotype, and lowest among those with the AA genotype (1.47 μg/mL versus 1.13 μg/mL versus 0.66 μg/mL; P <0.0001). The prevalence of A-13G and G79A genotypes was not significantly different between cases of ischemic stroke and controls. However, compared with the G79A GG genotype (reference), the odds of ischemic stroke was progressively lower for the heterozygote GA (odds ratio [OR], 0.83; 95% CI, 0.52 to 1.33) and the homozygote AA genotype (OR, 0.63; 95% CI, 0.20 to 1.98). A pooled analysis showed that compared with the G79A GG genotype (reference), the odds of ischemic stroke was progressively lower for the heterozygote GA (OR, 0.78; 95% CI, 0.57 to 1.07) and the homozygote AA genotype (OR, 0.31; 95% CI, 0.14 to 0.69).

Conclusion— The consistency of the association between protein Z genotypes, blood concentrations of protein Z, and ischemic stroke, determined using 2 different methods that have different sources of bias strengthens the evidence that increased blood concentrations of protein Z concentrations are associated causally with an increased risk of ischemic stroke.

Screening and management of inherited thrombophilias in the setting of adverse pregnancy outcome

Inherited thrombophilic conditions are associated with adverse pregnancy outcomes, including severe pre-eclampsia, fetal loss, abruptio placentae, and intauterine growth restriction. Although the prevalence of these complications is approximately 8% in the general population, their presence is associated with a significantly increased recurrence risk. Thrombophilic conditions most strongly associated with adverse pregnancy outcome include factor V Leiden, prothrombin gene mutation, and deficiencies of protein S, protein C, and antithrombin. Other thrombophilic conditions, such as protein Z deficiency, also appear to be associated with an increased risk of pregnancy complications. Antenatal administration of heparin to prevent pregnancy complications has shown promise in small studies, but a randomized, placebo-controlled trial is necessary to determine whether heparin administration is beneficial in preventing adverse pregnancy outcome.

Mutations within the protein Z-dependent protease inhibitor gene are associated with venous thromboembolic disease: a new form of thrombophilia

Protein Z-dependent protease inhibitor (ZPI) is a serpin that inhibits the activated coagulation factors X and XI. The precise physiological significance of ZPI in the control of haemostasis is unknown although a deficiency of ZPI may be predicted to alter this balance. The coding region of the ZPI gene was screened for mutations using denaturing high-performance liquid chromatography. 16 mutations/polymorphisms within the coding region of ZPI were identified including two mutations, which generated stop codons at residues R67 and W303. We observed nonsense mutations within the ZPI gene in 4.4% of thrombosis patients (n = 250) compared with 0.8% of controls (n = 250). The difference in distribution of stop codon mutations between thrombosis patients and controls was significant (P = 0.02) with an odds ratio of 5.7 (95% confidence interval, 1.25-26.0). Our results suggest an association between ZPI deficiency and venous thrombosis and we propose that ZPI deficiency is potentially a new form of thrombophilia.

[Protein Z: a new regulator of coagulation in arterial vessels?]

Protein Z (PZ) is a vitamin K dependent factor identified in human plasma in 1984 whose physiological function was poorly understood. It was recently shown that protein Z is implicated in the down-regulation of coagulation by forming a complex with a plasma proteinase inhibitor called protein Z-dependent protease inhibitor (ZPI) which inhibits activated factor Xa on phospholipid surfaces. In the absence of an additional challenge, the disruption of PZ gene in mice is asymptomatic, but the association with the factor VLeiden mutation leads to a near complete mortality during the neonatal period with microvascular thrombosis. Unexpectedly, in humans, a relationship between protein Z deficiency and ischemic strokes, was firstly evidenced, but not confirmed by all the epidemiological study. Additional studies suggest that protein Z deficiency could be also a risk factor for acute coronary syndromes, early fetal losses, and increased the arterial risk in antiphospholipid syndrome. This review analyzes the different studies so far published and discusses the different results obtained in order to understand whether or not protein Z deficiency could be considered as an arterial ischemic risk factor.

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.

A Common Polymorphism of the Protein Z Gene Is Associated With Protein Z Plasma Levels and With Risk of Cerebral Ischemia in the Young

BACKGROUND AND PURPOSE

The vitamin K-dependent protein Z (PZ) has been shown to possess anticoagulant as well as procoagulant properties. Plasma levels of PZ show a broad interindividual variation, but it is unknown to which extent this variation is under genetic control. Recent clinical studies revealed contradictory results on the association of PZ plasma levels and the risk of ischemic stroke.

METHODS

We performed a case-control study including 200 patients with cerebral ischemia aged < or =50 years and 199 control subjects from the same South German region. We investigated a possible association of 2 common single nucleotide mutations in the PZ gene with the risk of cerebral ischemia. Furthermore, enzyme-linked immunosorbent assay measurements were done in control subjects without vascular disease to detect a potential association of different genotypes with PZ plasma (antigen) levels.

RESULTS

In patients, the frequency of the A allele of the intron F polymorphism G79A was significantly lower than in controls (15.7% versus 24.4%; odds ratio, 0.58; 95% CI, 0.39 to 0.86; P=0.007; adjusted for age, sex, and conventional risk factors). The G allele of the promoter polymorphism A-13G tended to be less common in patients (4.2% versus 7.0%; adjusted odds ratio, 0.56; 95% CI, 0.28 to 1.13; P=0.105). In 42 control subjects, the A allele of the intron F polymorphism was associated with lower PZ antigen levels (P=0.0032; Spearman correlation coefficient rs=-0.48).

CONCLUSIONS

The A allele of an intron F polymorphism of the PZ gene appears to be a novel protective genetic marker for the risk of cerebral ischemia in young adults. In the context of juvenile stroke, high PZ plasma levels may represent a prothrombotic condition.

Protein Z in ischemic stroke and its etiologic subtypes

BACKGROUND AND PURPOSE

Protein Z is a vitamin K-dependent plasma protein whose significance in arterial thrombosis remains uncertain. The objectives of this study were to determine the association between protein Z, ischemic stroke, and etiologic subtypes of ischemic stroke.

METHODS

We conducted a case-control study of 173 hospital cases of first-ever ischemic stroke and 186 randomly selected community controls. Using established criteria, we classified cases of stroke by etiologic subtype. Protein Z concentrations were measured during the first 7 days and at 3 to 6 months after the acute stroke event.

RESULTS

Blood levels of protein Z measured within 7 days of acute stroke were significantly higher in cases than in controls (geometric mean, 1.46 versus 1.16 microg/mL; P<0.0001). Compared with the lowest tertile, the upper 2 tertiles of protein Z were associated with an adjusted odds ratio (OR) of ischemic stroke of 1.75 (95% CI, 1.00 to 3.07) for the second tertile and 3.07 (95% CI, 1.73 to 5.45) for the upper tertile. The adjusted odds of ischemic stroke caused by large-artery atherothrombosis was nearly 8-fold greater for those with protein Z concentrations in the upper tertile compared with the lower tertile (OR, 7.91; 95% CI, 3.11 to 20.14). The adjusted odds of ischemic stroke due to small-artery disease (OR, 1.79; 95% CI, 0.83 to 3.87) and cardioembolism (OR, 1.80; 95% CI, 0.58 to 5.64) was also increased among individuals with protein Z concentrations in the upper tertile compared with the lower tertile, but not significantly so. There was no significant difference between mean protein Z concentrations among cases in the convalescent phase (3 months) after stroke and age- and sex-matched controls.

CONCLUSIONS

There is a strong, independent relationship between elevated blood levels of protein Z and ischemic stroke during the acute phase, particularly ischemic stroke due to large-artery atherothromboembolism, which is no longer evident during the convalescent phase. These results are consistent with the notion that protein Z is either an important factor in the pathogenesis of ischemic stroke due to large-artery atherothromboembolism or an acute phase reactant. Further studies are required to elucidate whether protein Z has a causative or prognostic role in acute arterial thrombosis.

Autoimmune antiphospholipid antibodies impair the inhibition of activated factor X by protein Z/protein Z-dependent protease inhibitor

The hemostatic process is tightly regulated by several antithrombotic mechanisms. Among them, protein Z (PZ)-dependent protease inhibitor (ZPI) potently inhibits factor (F)Xa in a manner dependent on calcium ions, phospholipids and PZ. Autoimmune antiphospholipid antibodies (aPL) are mainly directed against phospholipid-binding plasma proteins such as beta2-glycoprotein I (beta2GPI) and prothrombin, and are known to interfere with phospholipid-dependent hemostatic pathways. In this study, we investigated whether purified aPL are able to interfere with inhibition of FXa by PZ/ZPI. beta2GPI modestly delayed the FXa inactivation by PZ/ZPI and most isolated aPL-IgGs were found to further increase the inhibitory potential of beta2GPI on PZ/ZPI activity. Without beta2GPI, the PZ/ZPI activity was unaffected by the addition of aPL-IgG. As PZ deficiency is hypothesized to lead to a prothrombotic state, we performed a case-control study to measure plasma levels of PZ and ZPI in 66 patients with autoimmune aPL and 152 normal controls. The prevalence of low PZ levels (below the 5th percentile of controls) was significantly greater in the 37 patients with definite antiphospholipid syndrome (APS) (24.3%) but not in the 29 aPL patients not fulfilling the criteria for APS (10.3%) compared with the normal group (4.6%, P < 0.001 vs. APS). ZPI antigen levels were similar in patients with aPL and normal controls. Concomitant PZ deficiency increased by approximately sevenfold the risk of arterial thrombosis in aPL patients. Taken together, these data suggest that the PZ/ZPI system is commonly impaired in aPL patients thus probably increasing the thrombotic risk.