Protein Z gene polymorphisms are associated with protein Z plasma levels

Low Protein Z Level: A Thrombophilic Risk Biomarker for Acute Coronary Syndrome

Acute coronary syndrome (ACS) encompasses a range of thrombotic coronary artery diseases. Protein Z (PZ)/PZ-dependent protease inhibitor complex is a natural anticoagulant system with a presumptive role for PZ deficiency in the pathogenesis of ACS. We aimed to evaluate plasma PZ level and role as a risk biomarker in Egyptian patients with ACS. Hundred patients with stable ACS and 60 matched controls were enrolled. ACS patients were divided into 3 clinical subgroups (ST-segment elevation myocardial infarction, non-ST-segment elevation myocardial infarction, and unstable angina), and 2 age subgroups (group A ≤ 55 years, and group B > 55 years). Plasma PZ levels were evaluated using enzyme linked immunosorbent assay. Lower PZ levels were found in ACS patients' group and clinical subgroups compared with controls. PZ levels showed a decrease with increasing age and were lower in females versus males. Lower PZ levels were found in hypertensive ACS patients in both age subgroups. Smokers and patients with family history of ACS in group A had lower PZ levels, while group B revealed lower PZ among diabetic patients. In group A, increased number of ACS conventional risk factors was associated with lower PZ levels. PZ level 3.7 μg/mL was the best cut-off value for prediction of ACS. Logistic regression analyses approved PZ as an independent risk biomarker for ACS. PZ levels are reduced in stable ACS and are significantly and independently associated with increased susceptibility for ACS, denoting PZ deficiency as a reliable thrombophilic risk biomarker in Egyptian patients with ACS.

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.

Structural analysis of protein Z gene variants in patients with foetal losses

The role of protein Z (PZ) in the etiology of human disorders is unclear. A number of PZ gene variants, sporadic or polymorphic and found exclusively in the serine protease domain, have been observed. Crystal structures of PZ in complex with the PZ-dependent inhibitor (PZI) have been recently obtained. The aim of this study was a structural investigation of the serine protease PZ domain, aiming at finding common traits across disease-linked mutations. We performed 10–20 ns molecular dynamics for each of the observed PZ mutants to investigate their structure in aqueous solution. Simulation data were processed by novel tools to analyse the residue-by-residue backbone flexibility. Results showed that sporadic mutations are associated with anomalous flexibility of residues belonging to specific regions. Among them, the most important is a loop region which is in contact with the longest helix of PZI. Other regions have been identified, which hold anomalous flexibility associated with potentially protective gene variants. In conclusion, a possible interpretation of effects associated with observed gene variants is provided. The exploration of PZ/PZI interactions seems essential in explaining these effects.

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.

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 variants associated with protein Z plasma levels and with risk of idiopathic recurrent miscarriage

Protein Z (PZ) deficiency due to anti-PZ autoantibodies and/or mutations in PZgene was linked with adverse pregnancy outcomes, including idiopathic recurrent miscarriage (IRM). We investigated the association of rs3024718, rs3024719, rs3024731, rs3024778, rs3024772, and rs3024735 (G79A) PZ variants and changes in PZ levels in 287 women with IRM, and 308 control women. Of the 6 single nucleotide polymorphisms (SNPs) analyzed, higher minor allele frequency of rs3024735 (G79A) and rs3024731 were seen in IRM cases than in control women. Significantly higher frequencies of rs3024735/G79A G/A and A/A (P< .001), rs3024719 G/A (P= .009), and rs3024731 A/A (P = .012), but not rs3024718 (P= .12), rs3024778 (P = .76), or rs3024772 (P= .27) genotype carriers were seen between IRM cases versus control women, respectively, and was linked with reduced PZ levels. Six-locus (rs3024718/rs3024719/rs3024778/rs3024731/rs3024735/rs3024772) PZhaplotypes analysis demonstrated increased frequency of GAGAAG and AGGTAG and reduced frequency of AGGTGC haplotypes in IRM cases, thereby conferring disease susceptibility and protective nature to these haplotypes, respectively. These results demonstrate that specific PZSNPs and haplotypes are significantly associated with IRM.

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.

A review of hereditary and acquired coagulation disorders in the aetiology of ischaemic stroke

The diagnostic workup in patients with ischaemic stroke often includes testing for prothrombotic conditions. However, the clinical relevance of coagulation abnormalities in ischaemic stroke is uncertain. Therefore, we reviewed what is presently known about the association between inherited and acquired coagulation disorders and ischaemic stroke, with a special emphasis on the methodological aspects. Good-quality data in this field are scarce, and most studies fall short on epidemiological criteria for causal inference. While inherited coagulation disorders are recognised risk factors for venous thrombosis, there is no substantial evidence for an association with arterial ischaemic stroke. Possible exceptions are the prothrombin G20210A mutation in adults and protein C deficiency in children. There is proof of an association between the antiphospholipid syndrome and ischaemic stroke, but the clinical significance of isolated mildly elevated antiphospholipid antibody titres is unclear. Evidence also suggests significant associations of increased homocysteine and fibrinogen concentrations with ischaemic stroke, but whether these associations are causal is still debated. Data on other acquired coagulation abnormalities are insufficient to allow conclusions regarding causality. For most coagulation disorders, a causal relation with ischaemic stroke has not been definitely established. Hence, at present, there is no valid indication for testing all patients with ischaemic stroke for these conditions. Large prospective population-based studies allowing the evaluation of interactive and subgroup effects are required to appreciate the role of coagulation disorders in the pathophysiology of arterial ischaemic stroke and to guide the management of individual patients.

[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.

Protein Z G79A polymorphism in patients with severe sepsis

The aim of the study is to investigate whether the presence of a protein Z polymorphism is a risk factor for the development and outcome of sepsis. Sepsis is a clinical syndrome characterized by the presence of systemic signs and symptoms of inflammation. When sepsis leads to organ failure, the term severe sepsis and septic shock is used. The genetic causes of severe sepsis are not fully explained. Protein Z is a vitamin K- dependent glycoprotein and a member of the coagulation cascade. The study included 53 patients with severe sepsis and 70 control healthy volunteers without a familial history of thrombosis. The G79A polymorphism of intron F of the protein Z gene was analyzed by the method of polymerase chain reaction-based DNA analysis. The protein Z intron F G79A polymorphism frequencies of the patients and controls were 43.4% and 40%, respectively. Carrying 79 AA genotype could be a risk factor for severe sepsis and septic shock (OR = 4.5, 95% CI: 0.45-46.1), but it could not find any difference between survivor and nonsurvivor groups. They concluded that the frequency of intron F G79A polymorphism of protein Z gene was higher in patients than controls, and carrying 79 AA genotype could be a risk factor for severe sepsis and septic shock.

Low protein Z levels, but not the intron F G79A polymorphism, are associated with unexplained pregnancy loss

INTRODUCTION

The present case-control study was designed in order to investigate the association between plasma protein Z (PZ) levels, the intron F G79A polymorphism and unexplained pregnancy loss.

MATERIALS AND METHODS

51 women with at least two consecutive or three non-consecutive fetal losses between the 8th and 12th week of gestation and 47 apparently healthy parous women of reproductive age with no history of pregnancy loss (controls) were enrolled. Allele frequencies of the PZ intron F G79A polymorphism and PZ levels were measured.

RESULTS

PZ levels (mg/L) were significantly lower in cases (mean +/- S.D. 1.28 +/- 0.56) than controls (1.97 +/- 0.76, p < 0.001) and in carriers of the A allele (1.46 +/- 0.62), compared to GG homozygous subjects (1.72 +/- 0.81, p = 0.044). A higher proportion of cases (41.2%) were PZ-deficient (<1 mg/L), compared to controls (10.6%, p = 0.001). No significant difference in the frequency of at least one A allele carriers was observed between cases (39.2%) and controls (40.4%).

CONCLUSION(S)

It is possible that low PZ levels are a novel risk factor for unexplained recurrent miscarriage or fetal death. The presence of the F 79A allele is associated with significantly lower PZ levels, but, in the present study, was unrelated to unexplained early pregnancy loss.

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.

Association of the protein Z intron F G79A gene polymorphism with recurrent pregnancy loss

OBJECTIVE

To investigate the association of the common protein Z (PZ) intron F G79A gene polymorphism with recurrent early pregnancy loss (RPL) and its gene-gene interaction with known thrombophilic risk factors for RPL.

DESIGN

Case control study.

SETTING

University clinic.

PATIENT(S)

We enrolled 49 women with a history of two consecutive or three to six nonconsecutive pregnancy losses between the 8th and 12th weeks of gestation and 48 age-matched parous controls without a history of pregnancy complications.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Allele frequencies of the PZ intron F G79A polymorphism and its gene-gene interaction with known risk factors for RPL.

RESULT(S)

Fourteen case subjects (28.6%) and 24 control subjects (50.0%) carried at least one A allele. This was associated with a significant reduction of the relative risk for recurrent pregnancy loss (odds ratio [OR] 0.4, 95% confidence interval [CI] 0.2-0.9; adjusted OR 0.3, 95% CI 0.1-0.8). Coexistence of any thrombophilic risk factor studied with the 79A allele resulted in a clear reduction of the primal relative risk for recurrent pregnancy loss.

CONCLUSION(S)

The isolated presence of the PZ intron F 79A allele as well as the combination with known thrombophilic risk factors was protective against RPL between the 8th and 12th weeks of gestation.

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.

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.

Risk of cerebral venous thrombosis and novel gene polymorphisms of the coagulation and fibrinolytic systems

BACKGROUND AND PURPOSE

Genetic thrombophilic conditions such as those associated with Factor V Leiden (FVL) and the prothrombin mutant (PT G20210A) have been identified as risk factors for cerebral venous thrombosis (CVT). Recently, a single nucleotide polymorphism (SNP) of the thrombin activatable fibrinolysis inhibitor (TAFI G-438A) has been shown to be associated with lower TAFI levels and to decrease the risk for peripheral venous thrombosis. Furthermore, a protective role in juvenile stroke was shown for a SNP of the vitamin K dependent protein Z (PZ Intron F G79A) which is linked with low PZ levels.

PATIENTS AND METHODS

In 77 consecutive patients with CVT and in 203 randomly selected population controls from the same region of Southern Germany, we investigated the following functional SNPs using PCR and restriction fragment analysis techniques: TAFI G-438A, PZ Intron F G79A, FVL and PT G20210A.

RESULTS

The prevalence of FVL tended to be higher (OR 2.08, 95 % CI 0.91-4.75, p = 0.06) and that of PT G20210A (OR 4.57, 95 % CI 1.45-14.44, p = 0.007) was significantly higher in patients with CVT than in controls. The A-allele frequency of the TAFI G-438A polymorphism did not significantly differ between patients (21.3 %) and controls (26.9%; OR 0.71, 95 % CI 0.45-1.12; p = 0.17). For the PZ G79A SNP, the frequency of the A-allele was 19.5% in CVT and 24.6% in controls (OR 0.77, 95 % CI 0.49-1.21; p = 0.31).

CONCLUSIONS

In this large series of CVT patients, a positive association with established thrombophilic risk factors FVL and especially the PT G20210A mutation was confirmed. In contrast, our study found no significant association of CVT with SNPs of the TAFI and the PZ genes. Other than testing for FVL and the PT G20210A mutation, exploration of these potential thrombophilic variants seems to be of limited value in the investigation of CVT.

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.