Low protein Z levels in patients with peripheral arterial disease

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.

Protein z exerts pro-angiogenic effects and upregulates CXCR4

Objective

Protein Z (PZ) is a vitamin K-dependent coagulation factor without catalytic activity. Evidence points towards PZ as an independent risk factor for the occurrence of human peripheral arterial disease. However, the role of PZ in ischemia-driven angiogenesis and vascular healing processes has not been elucidated so far.

Approach

Angiogenic potency of PZ was assessed in established in vitro assays using endothelial cells. PZ-deficient (PZ^−/−) mice and their wild-type littermates (PZ^+/+) were subjected to hindlimb ischemia. Furthermore, PZ^−/− mice were exposed to PZ expressing adenovirus (AdV-PZ) or control adenovirus (AdV-GFP). In an additional set of animals, PZ^−/− mice were exposed to AdV-PZ and AdV-GFP, each in combination with the CXCR4 antagonist AMD3100.

Results

In vitro, PZ stimulated migratory activity and capillary-like tube formation of endothelial cells comparable to SDF-1. PZ^−/− mice exhibited diminished hypoxia-driven neovascularization and reperfusion in post-ischemic hindlimbs, which was restored by adenoviral gene transfer up to levels seen in PZ^+/+ mice. The stimulatory impact of PZ on endothelial cells in vitro was abolished by siRNA targeting against PZ and PZ was not able to restore reduced migration after knock-down of CXCR4. The increased surface expression of CXCR4 on PZ-stimulated endothelial cells and the abrogated restoration of PZ^−/− mice via AdV-PZ after concomitant treatment with the CXCR4 antagonist AMD3100 supports the idea that PZ mediates angiogenesis via a G-protein coupled pathway and involves the SDF-1/CXCR4 axis. This is underlined by the fact that addition of the G-protein inhibitor PTX to PZ-stimulated endothelial cells abolished the effect of PZ on capillary-like tube formation.

Conclusions

The results of the current study reveal a role of PZ in ischemia-induced angiogenesis, which involves a G-protein coupled pathway and a raised surface expression of CXCR4. Our findings thereby extend the involvement of PZ from the coagulation cascade to a beneficial modulation of vascular homeostasis.

[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-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.