Variation of platelet function in clinical phenotypes of acute venous thromboembolism - Results from the GMP-VTE project

BACKGROUND

The role of platelets in the pathogenesis of venous thromboembolism (VTE) is receiving increasing attention; however, limited information is available on platelet function in the acute phase of the disease.

OBJECTIVE

To characterize platelet function according to VTE phenotypes.

PATIENTS/METHODS

In total, 154 subjects (isolated pulmonary embolism [iPE], n = 28; isolated deep vein thrombosis [iDVT], n = 35; DVT+PE, n = 91) were included. In this study platelet function analyzer (PFA)-200, light transmission aggregometry (LTA), thrombin generation (TG) in presence (PRP) and absence (PFP) of platelets and platelet flow cytometry were investigated. LASSO regression was used to select clinical and platelet biomarkers that distinguish between VTE phenotypes.

RESULTS

PFA-200 results did not differ between VTE phenotypes. LTA from DVT+PE subjects showed lowest maximum aggregation after epinephrine and adenosine diphosphate compared to iPE and iDVT. Lower % of PAC-1-positive platelets after in-vitro trigger were present in DVT+PE and iPE compared to iDVT. TG in PRP had lower peak height and velocity in DVT+PE and iPE against iDVT. The results of LASSO regression for the distinction between DVT+PE vs iDVT identified 18 variables (AUC =0.93) of which 72% were platelet biomarkers. For distinction between iPE and iDVT, 10 variables were selected (AUC = 0.96) of which 50% were platelet-related. Obesity was the only variable weakly discriminating between DVT+PE vs iPE (AUC = 0.66).

CONCLUSION

This explorative study suggests an important distinction between PE-related phenotypes and iDVT when considering clinical and platelet function data. Lower platelet-dependent TG along with reduced platelet reactivity suggest higher platelet degranulation in PE-dependent phenotypes compared to iDVT.

Vitamin K antagonist use induces calcification and atherosclerotic plaque progression resulting in increased hypercoagulability

Aims

Vascular calcification is a hallmark of atherosclerotic burden and can predict the cardiovascular outcome. Vitamin K antagonists (VKA) are widely used anticoagulant drugs to treat patients at risk of arterial and venous thrombosis but are also associated with increase vascular calcification progression. We aim to unravel the paradox that VKA suppresses plasma coagulation but promotes vascular calcification and subsequent atherosclerosis-dependent coagulability of the vessel wall.

Methods and results

Apoe^−/− mice were placed on western-type diet enriched with the VKA warfarin for 18 weeks to measure atherosclerotic plaque burden, calcification, and coagulation. Patients (n = 54) displaying paroxysmal atrial fibrillation with a low cardiovascular risk, who were treated with VKA were included to measure pre-thrombotic state. Finally, primary vascular smooth muscle cells (VSMC) derived from human tissue explants were used for in vitro experiments. In Apoe^−/− mice, VKA increases both atherosclerotic plaque size and calcification. Higher plaque calcification was associated with increased plasma levels of thrombin-antithrombin and factor IXa-antithrombin complexes in mice and patients treated with VKA. Mechanistically, phenotypic switching of VSMC into synthetic VSMC promotes thrombin generation, which is enhanced in a tissue-factor (TF)-dependent manner by VSMC calcification. Moreover, calcified VSMC exposed to whole blood under flow significantly enhanced platelet deposition and TF-dependent fibrin formation.

Conclusions

Oral anticoagulation with VKA aggravates vascular calcification and atherosclerosis. VSMC phenotype differentiation impacts coagulation potential in a TF-dependent manner. VKA-induced vascular calcification increases hypercoagulability and could thereby potentially positively affect atherothrombosis.

The impact of platelet indices on clinical outcome in heart failure: results from the MyoVasc study

Aims

Platelet indices have been associated with traditional cardiovascular risk factors, cardiovascular diseases and all‐cause mortality. This study aimed to investigate the role of platelet count, mean platelet volume (MPV) and platelet‐to‐leukocyte ratio, including platelet‐to‐monocyte and platelet‐to‐lymphocyte ratio with cardiac function, heart failure (HF) phenotypes and clinical outcome, worsening of HF.

Methods and results

Univariate and multivariable linear and Cox regression analyses were used to investigate the associations between platelet indices, cardiac function and worsening of HF in 3250 subjects enrolled in the MyoVasc study. Higher MPV, lower platelet count, lower platelet‐to‐leukocyte and platelet‐to‐monocyte ratios have been associated with reduced left ventricular ejection fraction (beta estimate [β]_{MPV [fL]} = −0.05 [−0.09; −0.02], β_{platelet count (× 10/L)}⁹ = 3.4 [1.2; 5.6], β_{platelet‐to‐leukocyte ratio} = 1.4 [1.1; 1.8], β_{platelet‐to‐monocyte ratio} = 28 [20; 36]) and increased E/E' ratio (β _{MPV [fL]} = 0.04 [0.003; 0.07], β_{platelet count (× 10/L)}⁹ = −3.1 [−5.3; −0.92], β_{platelet‐to‐leukocyte ratio} = −0.83 [−1.2; −0.46], β_{platelet‐to‐monocyte ratio} = −20 [−28; −12]), independent of age and sex. Cox regression demonstrated an increased risk for worsening of HF in subjects with MPV > 75th percentile (hazard ratio [HR] = 1.47 [1.16; 1.87]), platelet count < 25th percentile (HR = 1.36 [1.07; 1.74]), platelet‐to‐leukocyte < 25th percentile (HR = 1.53 [1.20; 1.95]), platelet‐to‐monocyte < 25th percentile (HR = 1.38 [1.08; 1.77]) and platelet‐to‐lymphocyte > 75th percentile (HR = 1.50 [1.17; 1.93]) ratios, independent of potential confounders. MPV > 75th percentile and platelet count < 25th percentile were strongly related to outcome in HFpEF vs. HFrEF (P for difference = 0.040). Platelet‐to‐leukocyte ratios were associated with worse outcome in both HF phenotypes, without a significant difference between HFpEF and HFrEF.

Conclusions

Platelet indices are linked with worse cardiac function and adverse clinical outcome, independent of subjects' underlying cardiovascular profile. This study emphasizes their important value to provide additional information on pathophysiology and risk stratification in HF syndrome.

Vascular protective effect of aspirin and rivaroxaban upon endothelial denudation of the mouse carotid artery

While in recent trials the dual pathway inhibition with aspirin plus rivaroxaban has shown to be efficacious in patients with atherosclerotic cardiovascular disease, little is known about the effects of this combination treatment on thrombus formation and vascular remodelling upon vascular damage. The aim of this study was to examine the effects of aspirin and/or rivaroxaban on injury-induced murine arterial thrombus formation in vivo and in vitro, vessel-wall remodelling, and platelet-leukocyte aggregates. Temporary ligation of the carotid artery of C57BL/6 mice, fed a western type diet, led to endothelial denudation and sub-occlusive thrombus formation. At the site of ligation, the vessel wall stiffened and the intima-media thickened. Aspirin treatment antagonized vascular stiffening and rivaroxaban treatment led to a positive trend towards reduced stiffening. Local intima-media thickening was antagonized by both aspirin or rivaroxaban treatment. Platelet-leukocyte aggregates and the number of platelets per leukocyte were reduced in aspirin and/or rivaroxaban treatment groups. Furthermore, rivaroxaban restricted thrombus growth and height in vitro. In sum, this study shows vascular protective effects of aspirin and rivaroxaban, upon vascular injury of the mouse artery.

Comprehensive platelet phenotyping supports the role of platelets in the pathogenesis of acute venous thromboembolism - results from clinical observation studies

Background

The pathogenesis of arterial and venous thrombosis is in large part interlaced. How much platelet phenotype relates to acute venous thromboembolism (VTE) independent of the underlying cardiovascular profile is presently poorly investigated.

Methods

Platelet count and mean platelet volume (MPV), platelet aggregation in whole blood and platelet rich plasma (PRP), platelet-dependent thrombin generation (TG) and platelet surface activation markers were measured under standardized conditions. Machine learning was applied to identify the most relevant characteristics associated with VTE from a large array (N = 58) of clinical and platelet-related variables.

Findings

VTE cases (N = 159) presented with lower platelet count and MPV vs controls (N = 140). Whole blood aggregation showed shorter collagen/Epinephrine closure times in cases, particularly within acetylsalicylic acid (ASA) users. Within ASA users, higher PRP aggregation after adenosine diphosphate (ADP), epinephrine, collagen and arachidonic acid was observed in cases vs controls. Within non-ASA and/or subjects on anticoagulants, cases presented with lower aggregation after ADP and collagen vs controls. Lower platelet-dependent TG, higher CD63 on resting and lower PAC-1 expression after collagen/ADP in-vitro stimulated platelets further characterized VTE cases vs controls, independent of therapy. Lasso regression analysis identified 26 variables associated with VTE of which 69% were platelet-related.

Interpretation

Comprehensive phenotyping of platelet function identified a large proportion of low responders to ASA in VTE cases. Lower platelet-dependent TG and lower platelet reactivity after ex-vivo stimulation characterized the “platelet exhausted syndrome” in cases. Finally, from a large array of covariates including clinical risk factors, platelet biomarkers comprised 69% of all selected variables differentiating VTE cases vs controls.

Funding

German Federal Ministry of Education and Research, CTH-Mainz and Bayer AG.

Atrial fibrillation progression risk factors and associated cardiovascular outcome in well-phenotyped patients: data from the AF-RISK study

Aims

Atrial fibrillation (AF) is a progressive disease, but identifying patients at risk for AF progression is challenging. We aimed to identify factors associated with AF progression.

Methods and results

Atrial fibrillation progression was assessed in 392 patients with recent-onset paroxysmal or persistent AF included in the prospective, observational, multicentre identification of a risk profile to guide atrial fibrillation (AF-RISK) study. Progression of AF was assessed by Holter monitoring and 2-week event recorder at baseline and 1-year follow-up. AF progression was defined as: (i) doubling in AF burden at 1 year compared to baseline with a minimum AF burden of 10% in paroxysmal AF; or (ii) transition from paroxysmal to persistent or permanent AF; or (iii) persistent to permanent AF. Age was 60 ± 11 years, 62% were men, and 83% had paroxysmal AF. At 1 year, 52 (13%) had AF progression (11% in paroxysmal; 26% in persistent AF). Multivariable logistic regression showed that left atrial volume [odds ratio (OR) per 10 mL 1.251, 95% confidence interval (CI) 1.078–1.450; P &lt; 0.001], N-terminal pro-B-type natriuretic peptide (NT-proBNP; OR per standard deviation increase 1.583, 95% CI 1.099–2.281; P = 0.014), and plasminogen activator inhibitor-1 (PAI-1; OR per standard deviation increase 0.660, 95% CI 0.472–0.921; P = 0.015) were associated with AF progression. In an additional follow-up of 1.9 (0.9–3.3) years patients with AF progression developed more cardiovascular events and all-cause mortality (12.4%/year vs. 2.3%/year, P &lt; 0.001).

Conclusion

Atrial fibrillation progression occurred in 13% of patients with recent-onset AF during 1-year follow-up. Left atrial volume, NT-proBNP, and PAI-1 were associated with AF progression. Patients with AF progression had a higher event rate.

Trial registration number

Clinicaltrials.gov NCT01510210.

Roles of Coagulation Proteases and PARs (Protease-Activated Receptors) in Mouse Models of Inflammatory Diseases

Activation of the blood coagulation cascade leads to fibrin deposition and platelet activation that are required for hemostasis. However, aberrant activation of coagulation can lead to thrombosis. Thrombi can cause tissue ischemia, and fibrin degradation products and activated platelets can enhance inflammation. In addition, coagulation proteases activate cells by cleavage of PARs (protease-activated receptors), including PAR1 and PAR2. Direct oral anticoagulants have recently been developed to specifically inhibit the coagulation proteases FXa (factor Xa) and thrombin. Administration of these inhibitors to wild-type mice can be used to determine the roles of FXa and thrombin in different inflammatory diseases. These results can be compared with the phenotypes of mice with deficiencies of either Par1 (F2r) or Par2 (F2rl1). However, inhibition of coagulation proteases will have effects beyond reducing PAR signaling, and a deficiency of PARs will abolish signaling from all proteases that activate these receptors. We will summarize studies that examine the roles of coagulation proteases, particularly FXa and thrombin, and PARs in different mouse models of inflammatory disease. Targeting FXa and thrombin or PARs may reduce inflammatory diseases in humans.

Proteomic analysis reveals procoagulant properties of cigarette smoke-induced extracellular vesicles

Airway epithelial cells secrete extracellular vesicles (EVs) under basal conditions and when exposed to cigarette smoke extract (CSE). Getting insights into the composition of these EVs will help unravel their functions in homeostasis and smoking-induced pathology. Here, we characterized the proteomic composition of basal and CSE-induced airway epithelial EVs. BEAS-2B cells were left unexposed or exposed to 1% CSE for 24 h, followed by EV isolation using ultrafiltration and size exclusion chromatography. Isolated EVs were labelled with tandem mass tags and their proteomic composition was determined using nano-LC-MS/MS. Tissue factor (TF) activity was determined by a factor Xa generation assay, phosphatidylserine (PS) content by prothrombinase assay and thrombin generation using calibrated automated thrombogram (CAT). Nano-LC-MS/MS identified 585 EV-associated proteins with high confidence. Of these, 201 were differentially expressed in the CSE-EVs according to the moderated t-test, followed by false discovery rate (FDR) adjustment with the FDR threshold set to 0.1. Functional enrichment analysis revealed that 24 proteins of the pathway haemostasis were significantly up-regulated in CSE-EVs, including TF. Increased TF expression on CSE-EVs was confirmed by bead-based flow cytometry and was associated with increased TF activity. CSE-EVs caused faster and more thrombin generation in normal human plasma than control-EVs, which was partly TF-, but also PS-dependent. In conclusion, proteomic analysis allowed us to predict procoagulant properties of CSE-EVs which were confirmed in vitro. Cigarette smoke-induced EVs may contribute to the increased cardiovascular and respiratory risk observed in smokers.

Characterization of hemostasis in mice lacking the novel thrombosis susceptibility gene Slc44a2

INTRODUCTION

Recent genome wide association studies (GWAS) identified a novel susceptibility locus for thrombosis, harbouring the SLC44A2 gene which encodes the Solute Carrier Family 44 Member 2 protein (SLC44A2). Thus far, SLC44A2 has not been studied in the context of thrombosis, and may be a unique contributor to thrombotic disease. Here we utilize mice lacking SLC44A2 (Slc44a2^-/-) to evaluate a possible role of SLC44A2 in hemostasis.

METHODS

Slc44a2^-/- mice were evaluated in key aspects of normal hemostasis including a challenge of vascular damage by applying laser induced injury to the cremaster muscle arteriole.

RESULTS

Slc44a2^-/- mice had comparable levels of thrombin generation and gene expression of coagulation related genes, as compared to littermate wild type controls. Lower levels of circulating plasma Von Willebrand factor (VWF) were measured in Slc44a2^-/- mice, while no difference in VWF multimerization or vascular localization was detected. Upon in vivo laser injury of the cremaster arterioles, we detected an impairment of clot formation for Slc44a2^-/- mice.

CONCLUSIONS

Although mice lacking SLC44A2 are normal for several hemostasis parameters, we do observe a reduction of plasma VWF levels and an altered response upon vascular damage, which suggests that SLC44A2 contributes to hemostasis upon injury. These findings are in line with the reported GWAS data and support further research on SLC44A2 in thrombosis.

Intake of Vitamin K Antagonists and Worsening of Cardiac and Vascular Disease: Results From the Population-Based Gutenberg Health Study

Background Preclinical data have indicated a link between use of vitamin K antagonists ( VKA ) and detrimental effects on vascular structure and function. The objective of the present study was to determine the relationship between VKA intake and different phenotypes of subclinical cardiovascular disease in the population. Methods and Results Clinical and laboratory data, as well as medical-technical examinations were assessed from 15 010 individuals aged 35 to 74 years during a highly standardized 5-hour visit at the study center of the population-based Gutenberg Health Study. In total, the study sample comprised 287 VKA users and 14 564 VKA nonusers. Multivariable analysis revealed an independent association between VKA intake and stiffness index (β=+2.54 m/s; [0.41/4.66]; P=0.019), ankle-brachial index (β=-0.03; [-0.04/-0.01]; P<0.0001), intima-media thickness (β=+0.03 mm [0.01/0.05]; P=0.0098), left ventricular ejection fraction (β=-4.02% [-4.70/-3.33]; P<0.0001), E/E' (β=+0.04 [0.01/0.08]; P=0.014) left ventricular mass (β=+5.34 g/m2.7 [4.26/6.44]; P<0.0001), and humoral markers of cardiac function and inflammation (midregional pro-atrial natriuretic peptide: β=+0.58 pmol/L [0.50/0.65]; P<0.0001; midregional pro-adrenomedullin: β=+0.18 nmol/L [0.14/0.22]; P<0.0001; N-terminal pro B-type natriuretic peptide: β=+1.90 pg/mL [1.63/2.17]; P<0.0001; fibrinogen: β=+143 mg/dL [132/153]; P<0.0001; C-reactive protein: β=+0.31 mg/L [0.20/0.43]; P<0.0001). Sensitivity analysis in the subsample of participants with atrial fibrillation stratified by intake of VKA demonstrated consistent and robust results. Genetic variants in CYP 2C9, CYP 4F2, and VKORC 1 were modulating effects of VKA on subclinical markers of cardiovascular disease. Conclusions These data demonstrate negative effects of VKA on vascular and cardiac phenotypes of subclinical cardiovascular disease, indicating a possible influence on long-term disease development. These findings may be clinically relevant for the provision of individually tailored antithrombotic therapy.

Abstract 147: The Role of Thrombin Generation in Cardiovascular Disease and Mortality - Results from the Population-based Gutenberg Health Study

Background: Thrombin formation is one of the key enzymatic processes that direct the activity of the hemostatic system. Thrombin generation (TG), a method addressing the overall potential of a given plasma sample to form thrombin, may be a potential tool to improve risk stratification for cardiovascular diseases (CVD). This study aims to explore the relation between TG and cardiovascular risk factors (CVRFs), CVD, and total mortality.

Methods: For this study, N=5000 subjects from the population-based Gutenberg Health Study were analyzed in a highly standardized setting. TG was measured by the Calibrated Automated Thrombogram method at 1 and 5 pM tissue factor (TF) trigger in platelet poor plasma. Lag time, endogenous thrombin potential (ETP), and peak height were derived from the TG curve. Sex-specific multivariable linear regression analysis adjusted for age, CVRFs, CVD and therapy (vitamin K antagonists, oral contraceptives and hormonal replacement therapy), was used to analyze the determinants of TG. Cox regression models adjusted for age, sex, CVRFs and vitamin K antagonists investigated the association between TG parameters and total mortality.

Results: Lag time (at 1 and 5 pM TF) was positively associated with obesity and dyslipidemia for both sexes (p<0.0001). Additionally, obesity was a positive determinant of ETP (at 1pM and 5 pM TF) in both sexes (p<0.0001) and peak height in males (1 pM TF, p=0.0048) and females (1 pM TF and 5 pM TF, p<0.0001). Cox regression models showed an increased mortality in individuals with a lag time (1 pM TF, HR=1.46, [95% CI: 1.07; 2.00], p=0.018) and ETP (5 pM TF, HR = 1.50, [1.06; 2.13], p=0.023) above the 95th percentile of the reference group, independent of the cardiovascular risk profile. Kaplan Meier survival curves showed a decreased survival in individuals with a lag time above the 90th percentile of the reference (1 and 5 pM TF, p<0.0001) and ETP above the 97.5th percentile of the reference (1 pM TF, p=0.00097).

Conclusion: This large-scale study provides important insights in the effects of traditional CVRFs, particularly obesity, on TG in males and females. Lag time and ETP were found as potentially relevant predictors of increased mortality in the general population, which deserves further investigation.

Abstract 599: Exposure to Biodiesel Exhaust Triggers Atherosclerotic Plaque Destabilisation through Increased Apoptosis of Vascular Smooth Muscle Cells in the Arterial Vessel Wall

Introduction: Long-term exposure to air pollutants increases cardiovascular morbidity and mortality. Particulate matter (PM) derived from diesel exhaust has been documented to be pro-atherogenic in animal studies. Biodiesels are widely introduced as new fuels with improved emission characteristics. However, biodiesel contains relatively more polycyclic aromatic carbohydrates (PAH) compared to diesel. Therefore, we hypothesise that exposure to biodiesel as compared to diesel exhaust results in increased atherosclerosis.

Methods and Results: In a carotid cuff atherosclerosis model, the effects of exposure to exhaust PM of biodiesel vs. diesel PM vs. saline (control) on atherosclerosis were evaluated. Both common carotid arteries in LDLR -/- mice were cuffed at week 2 in the course of an 8-week high-fat diet regimen. All mice were intratracheally instilled with saline, PM biodiesel or biodiesel once-weekly for 5 times. Immunohistochemistry and primary human vascular smooth muscle cells (hVSMC) were used for evaluation.

Results: Exposure to both biodiesel and diesel didn’t exacerbate atherosclerosis development, however, biodiesel affected plaque composition towards a more vulnerable phenotype as compared to diesel with decreased total collagen content and hVSMC (respectively -100%, p=0.09 and -339%, p&lt;0.01 and tend to increase necrotic core volumes (37.5% vs 28.9 % p=0.2). Exposure to biodiesel PM triggered loss of hVSMC in tunica-media, strongly correlating with apoptosis in the vessel wall (Pearson r=0.7, p&lt;0.01). These findings were supported by dose-dependent apoptosis of hVSMCs upon 2-hour PAH treatment.

Conclusions: This study demonstrates that exposure to biodiesel exhaust PM dramatically modulates atherosclerotic plaque composition, resulting in an unstable plaque phenotype through enhanced pro-apoptotic mechanisms.

Clinical Determinants of Thrombin Generation Measured in Presence and Absence of Platelets-Results from the Gutenberg Health Study

The tendency of a plasma sample to generate thrombin, a central enzyme in blood coagulation, might be an important indicator of prothrombotic risk linked to cardiovascular disease (CVD), but the presence of platelets may be a critical determinant. Clinical data, laboratory markers and thrombin generation (TG), investigated in both platelet-rich plasma (PRP) and platelet-free plasma (PFP) at 1 pM TF, were available in 407 individuals from the Gutenberg Health Study. Given the well-known effect of anticoagulants on TG, subjects taking anticoagulants (n = 15) have been excluded resulting in 392 subjects for further analysis. Lag time, endogenous thrombin potential (ETP) and peak height were the investigated parameters of a TG curve. Multivariable linear regression analysis was used to identify TG determinants. Mean platelet volume (MPV) and platelet count were both negatively associated to lag time and positively to peak height (MPV, β:6.35 [2.66; 10.0]; platelet count, β:0.111 [0.054; 0.169]) in PRP only. C-reactive protein was positively associated with lag time and ETP in both PRP and PFP, with a stronger effect on ETP in PRP (PRP, β:76.7 [47.5; 106]; PFP, β:34.8 [10.3; 59.2]). After adjustment for fibrinogen, the relation between CRP and ETP was attenuated in PRP and PFP. Of the traditional cardiovascular risk factors (CVRFs), obesity was positively associated to TG in PRP only. Our findings support that TG, particularly in PRP, relates to traditional CVRFs in a representative sample from a population-based study. Assessment of procoagulant activity in a platelet-dependent manner by TG is a promising tool for assessing individual risk for CVD.

Coagulation and inflammation in long-term cancer survivors: results from the adult population

Essentials The increase of cancer survival remains curtailed by cardiovascular mortality. We studied a large range of inflammatory and coagulation biomarkers in long-term cancer survivors. Cancer history has an important impact on mortality independent of cardiovascular risk factors. Fibrinogen and von Willebrand factor are potential biomarkers in survivors of increased mortality.

SUMMARY

Background The advances in cancer treatment and detection of early cancer have resulted in a steady increase in the number of of cancer survivors over the years. However, because of the long-term toxic effects of chemotherapy and radiotherapy, the incidence of cardiovascular disease (CVD) is increasing in survivors. Objectives To investigate traditional cardiovascular risk factors (CVRFs), inflammation and the coagulation profile in long-term cancer survivors (cancer diagnosis ≥ 5 years) from a large adult population-based study sample. Methods The presence of cardiovascular risk factors (CVRFs) and laboratory markers were compared in individuals with (n = 723) and without (n = 13626) a long-term history of cancer from the Gutenberg Health Study. Data on coagulation factors, D-dimer and von Willebrand factor (VWF) activity were available for 4974 individuals (n = 244 cancer survivors). Results In multivariable regression models, a history of cancer was, independently of CVRFs and CVD, associated with higher fibrinogen levels (β 6.99, 95% confidence interval [CI] 1.16-12.8), VWF activity (β 5.08, 95% CI 0.02-10.1), and antithrombin activity (β 1.85, 95% CI 0.44-3.27). Cancer survivors with CVD showed notably higher VWF activity than individuals with CVD without a history of cancer, with a difference in the means of 23.0 (7.9-38.1). Multivariate Cox regression analysis, adjusted for CVRFs, confirmed that a long-term history of cancer is associated with a 72% higher mortality. Increased mortality in cancer survivors was dependent on fibrinogen level and VWF activity level. Conclusion Cancer survivors showed a worse inflammation and coagulation profile than individuals without a history of cancer. Overall mortality in long-term cancer survivors was increased independently of traditional CVRFs. These results underline the need to further investigate plasma biomarkers as complementary cardiovascular risk predictors in cancer survivors.

Dose requirements for idarucizumab reversal of dabigatran in a lethal porcine trauma model with continuous bleeding

Idarucizumab is licensed for emergency reversal of dabigatran. A single 5 g dose is usually sufficient, but higher doses may sometimes be required and optimum dosing has not been defined. It was the aim of this study to investigate the effect of idarucizumab, given once or as a split dose, after double trauma in pigs anticoagulated with dabigatran. Dabigatran etexilate (30 mg/kg bid) was given to 18 male pigs orally for 3 days. On day 4, animals were randomised 1:1:1 to receive idarucizumab 60+0, 60+60 or 120+0 mg/kg. Doses were administered 15 and 75 minutes after initial liver trauma. At 60 minutes, a second liver injury was undertaken. Animals were monitored for 5 hours after initial trauma or until death. Blood loss during the first hour was 990 ± 109 ml, 988 ± 84 ml and 964 ± 75 ml in the 60+0, 60+60 and 120+0 groups, respectively. In the 120+0 and 60+60 groups, total blood loss was 1659 ± 346 and 1426 ± 106 ml, respectively, and survival at 5 hours was 100 %. However, in the 60+0 group, total blood loss was 3561 ± 770 ml and survival was 50 %. Analysis of dabigatran plasma concentrations showed that equimolar concentrations of idarucizumab are necessary to bind all dabigatran and achieve sufficient thrombin generation. At sufficient doses, idarucizumab rapidly reduced blood loss and improved survival in this lethal porcine model of double trauma with dabigatran anticoagulation. In clinical practice, should bleeding continue after initial treatment with the approved 5 g dose of idarucizumab, a second dose may potentially be effective to control bleeding caused by redistribution of unbound dabigatran.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Abstract 328: Coagulation Proteases are Potential Regulators in the Development of Exercise-Related Endofibrosis

Background: High performance athletes can develop symptomatic arterial flow restriction during exercise, caused by endofibrosis. The disease is an poorly understood condition, characterized by fibrosis of the external iliac artery. Pathophysiological processes involved in the development of endofibrosis are unknown. However, evidence shows that coagulation enzymes such as thrombin and factor Xa (FXa) can influence pro-fibrotic processes, mainly mediated through activation of protease activated receptors (PAR).

Aim: We investigated the immunohistochemical characteristics of endofibrotic lesions to determine the potential role of coagulation proteases and their receptors in development of endofibrosis.

Methods: 19 arterial endofibrotic specimens were collected during endarterectomy. As controls 20 arterial segments of the external iliac artery were collected post mortem from individuals who donated their body to medical science, with no medical history of cardiovascular disease. Acquired arteries were paraffinized and cut in tissue sections for immunohistochemical staining. Data were analyzed using a Mann-Whitney U test. A 2-tailed p<0.05 was considered as statistically significant.

Results: Endofibrotic segments contained a neo-intima, resulting in an intraluminal stenosis (42±14%). Compared to the intima of controls, endofibrotic lesions were highly positive for collagen (47±16% vs 15±5%, p=0.0001) and elastin (38±9% vs 16±4%, p=0.0003). These findings were accompanied by significantly increased alpha smooth muscle actin expression (51±10% vs 36±11%, p=0.01), which morphologically appeared to be myofibroblasts in endofibrotic lesions; which were hardly present in controls. In addition, PAR1 (49±17% vs 22±10%, p=0.0003) and PAR4 (39±8% vs 10±4%, p<0.0001) were upregulated and proenzymes of their activators, prothrombin and factor X were abundantly present in endofibrosis.

Conclusion: This is the first study to show that myofibroblasts, and the subsequent collagen and elastin production, might be key factors in the development of endofibrosis. The special association suggests that these processes may be regulated through activation of PARs by coagulation proteases, which needs to be established in further studies.

Mean Platelet Volume and Arterial Stiffness - Clinical Relationship and Common Genetic Variability

Vessel wall stiffening is an important clinical parameter, but it is unknown whether platelets, key elements in the pathogenesis of arterial thrombosis, are associated with arterial stiffness. The present studies sought to determine whether mean platelet volume (MPV), a potential marker of platelet activation, is linked to vascular elasticity as assessed by the augmentation index (AIx), in 15,010 individuals from the population-based Gutenberg Health Study. Multivariable analysis showed that MPV in both males (β 0.776; 95^thCI [0.250;1.16]; p = 0.0024) and females (β 0.881[0.328;1.43]; p = 0.0018) is strongly associated with AIx. Individuals with MPV and AIx above the sex-specific medians had worse survival. Association analysis between MPV-related genetic variants and arterial stiffness identified four genetic variants in males and one in females related with AIx. Cox regression analysis for mortality identified one of these joint genetic variants close to ring finger protein 145 gene (RNF145, rs10076782) linked with increased mortality (hazard ratio 2.02; 95^thCI [1.35;3.02]; p = 0.00061). Thus, these population-based data demonstrate a close relation between platelet volume as a potential marker of platelet activation and arterial stiffness in both sexes. Further research is warranted to further elucidate the mechanisms underlying larger platelets‘ role in arterial stiffening including the role of shared common genetics.

PO-58 - Cardiovascular risk profile in survivors of adult cancer - results from the general population study

INTRODUCTION

The advancements in cancer treatment and detection of early cancer have resulted in steady increase of adult cancer survivors over the years. However, due to the long term toxic effects of chemotherapy and radiotherapy, the incidence of cardiovascular diseases (CVD) is increasing in survivors. Identifying risk factors and interventions to reduce the excess burden of CVD in this vulnerable population is urgently needed.

AIM

To investigate the cardiovascular risk factors (CVRFs), inflammation and coagulation profile in cancer survivors from a large population-based study.

MATERIALS AND METHODS

Presence of CVRFs and laboratory markers have been compared in individuals with (n=1,359) and without (n=13,626) history of cancer. Standard laboratory profile, including blood glucose and lipid profile, has been evaluated in 15,010 individuals from the Gutenberg Health Study (GHS). Coagulation factors, D-dimer and von Willebrand factor (vWF) activity were available in N=4,993.

RESULTS

The individuals with history of cancer were older compared to no history of cancer with mean age of 61,5years and 54.4years, respectively (p<0.001). Traditional CVRFs as diabetes (14% vs 8.8%), dyslipidemia (49.6% vs 43.7%) and hypertension (60.3 vs 48.7%) were more frequent whereas smoking was less frequent (14.5% vs 19.9%) in cancer survivors (p<0.001). The standard laboratory profile showed cancer survivors with lower erythrocyte, platelet and white blood cell counts and higher C-reactive protein (CRP), glucose, HbA1c and triglycerides levels (p<0.001). Multivariable logistic regression analysis adjusted for age, sex and CVRFs demonstrated an independent association with diabetes (odds ratio, OR: 1.24, 1.02-1.50; p=0.027) and higher CRP (OR: 1.01, 1.01-1.02; p=0.00071). Fibrinogen, FV, FVII, FVIII and FXI, D-dimer and vWF activity were higher in cancer survivors (p<0.001). Multivariable logistic regression confirmed an independent association with higher fibrinogen (OR: 1.002, 1.000-1.003) and vWF activity (OR: 1.005, 1.001-1.008).

CONCLUSIONS

This is the first study investigating CVRFs, inflammation and coagulation profile in individuals with history of cancer from a well characterized population-representative adult sample. It gives evidence for higher prevalence of CVRFs, particularly diabetes in this vulnerable population. Markers of inflammation as CRP and fibrinogen and vWF activity were higher in cancer survivors independent of the cardiovascular risk profile. These results underline the increased risk of CVD and need for development of cardio-oncology programs offering cardiovascular prevention.

Associations Between Thrombin Generation and the Risk of Cardiovascular Disease in Elderly Patients: Results From the PROSPER Study

BACKGROUND

Hypercoagulability may be an important contributor to the pathophysiology of atherosclerosis and atherothrombosis. As thrombin fulfills a central role in coagulation and links to several cellular mechanisms involved in arterial disease, we hypothesized that thrombin generation is associated with cardiovascular events in elderly patients.

METHODS

We studied the relationship between plasma thrombin generation and incident coronary heart disease (CHD) and stroke in the PROspective Study of Pravastatin in the Elderly at Risk (PROSPER). From this multicenter prospective cohort, 4,932 samples of subjects (70-82 years) with pre-existing vascular disease or risk factors were available for thrombin generation measurements.

RESULTS

Within the 3.2 years of follow-up incident stroke and CHD was observed in 227 and 545 subjects, respectively. Baseline thrombin generation was significantly decreased in subjects with incident stroke compared with subjects without: normalized peak height 71.1±40.8% versus 82.3±44.9%, p = .0002, and normalized endogenous thrombin potential 79.1±23.3% versus 87.0±24.8%, p < .0001 (mean and SDs). Thrombin generation was independently and inversely associated with stroke risk: hazard ratio 0.71 (95%CI: 0.60-0.85), 0.68 (95%CI: 0.58-0.79), for normalized peak height and normalized endogenous thrombin potential, respectively (all p < .001). In subjects with incident CHD, thrombin generation was comparable to subjects without a coronary event. Only an increased normalized peak height was significantly associated with incident CHD (hazard ratio 1.17 [95% CI: 1.06-1.28], p = .002).

CONCLUSIONS

We demonstrate that a delayed and decreased thrombin generation is a strong and independent predictor for stroke in elderly people at increased risk of vascular disease. However, no convincing consistent association could be demonstrated between thrombin generation and incident CHD.

Biomarkers for post thrombotic syndrome: a case-control study

INTRODUCTION

There is limited knowledge on the etiology of post thrombotic syndrome (PTS), although several mechanisms have been proposed. The objectives are to explore the role of different pathogenic mechanisms for PTS, through measurement of an elaborate panel of biomarkers in patients with and without PTS.

MATERIALS AND METHODS

Patients with a history of deep vein thrombosis (DVT) with PTS (cases) and without PTS after minimal 2years follow-up (controls), were selected from the outpatient clinic of two Dutch hospitals. As a reference to the normal population healthy individuals (HI) without a history of venous thromboembolism were invited to participate. The population consisted of: 26 cases, 27 controls, and 26 HI. A panel of predefined biomarkers was measured in venous blood.

RESULTS

D-dimer showed a decreasing trend from cases to controls to HI; p=0.010. Thrombin/antithrombin complex levels were significantly higher in cases than in controls; p=0.032, and HI; p=0.017. APC-ratio was significantly lower in cases compared to controls; p=0.032, and HI; p=0.011. A significant trend of increasing proTAFI from cases, to controls, and HI; p=0.002 was found. There were no differences in inflammatory markers (CRP, Interleukin-6, Interleukin-8). Thrombomodulin, tissue-plasminogen activator, and von Willebrand factor were higher in patients compared to HI. There was a significant trend of decreasing sVCAM, from cases, to controls, and HI; p=0.029.

CONCLUSIONS

Patients with PTS displayed increased coagulation activity, an altered pattern of fibrinolytic marker expression, and increased endothelial activation. We found no evidence of systemic inflammation in patients with PTS at 63months since the last DVT.

Phenotypic fitness of primary endothelial cells cultured from patients with high cardiovascular risk or chronic kidney disease for vascular tissue engineering

Vascular tissue engineering relies on the combination of patient-derived cells and biomaterials to create new vessels. For clinical application, data regarding the function and behavior of patient-derived cells are needed. We investigated cell growth and functional characteristics of human venous endothelial cells (HVECs) from coronary arterial bypass graft (CABG), chronic kidney disease (CKD), and control patients. HVECs were isolated from venous specimens that were obtained during elective surgical procedures by means of collagenase digestion. Gene expression, proliferation, migration, secretory functions, and thrombogenic characteristics were evaluated using high-throughput assays. A total of 48 cell batches (14 control, 19 CABG, and 15 CKD subjects) were assessed. Proliferation, population doubling times, and migration of HVECs derived from CABG and CKD patients did not differ from controls. Thrombomodulin expression was higher in CABG-HVECs compared with controls. HVEC-induced thrombin formation in plasma did not differ between groups, and the contact activation pathway was the major contributor to coagulation. Patient-derived HVECs were able to attach and survive on polycaprolactone scaffolds that were coated with fibrin. HVECs from cardiovascular-diseased and CKD patients showed comparable functional characteristics with HVECs derived from uncompromised patients. We, therefore, conclude that endothelial cells from aged patients with comorbidities can be safely used for isolation and in vitro expansion for vascular tissue engineering.

Accelerated in vivo thrombin formation independently predicts the presence and severity of CT angiographic coronary atherosclerosis

OBJECTIVES

This study sought to investigate the association between thrombin generation in plasma and the presence and severity of computed tomography angiographically defined coronary atherosclerosis in patients with suspected coronary artery disease (CAD).

BACKGROUND

Besides its pivotal role in thrombus formation, experimental data indicate that thrombin can induce an array of pro-atherogenic and plaque-destabilizing effects. Although thrombin plays a role in the pathophysiology of atherosclerosis progression and vascular calcification, the clinical evidence remains limited.

METHODS

Using 64-slice coronary computed tomographic angiography, we assessed the presence and characteristics of CAD in patients (n = 295; median age 58 years) with stable chest pain. Coronary artery calcification was graded as absent (Agatston score 0), mild (Agatston score 1 to 100), moderate (Agatston score 101 to 400), and severe (Agatston score >400). Calibrated automated thrombography was used to assess endogenous thrombin potential in plasma in vitro. Thrombin-antithrombin complex (TATc) levels were measured as a marker for thrombin formation in vivo.

RESULTS

TATc plasma levels were substantially higher in patients with CAD versus patients without CAD (p = 0.004). Significant positive correlations were observed between steadily increasing TATc levels and the severity of CAD (r = 0.225, p < 0.001). In multinomial logistic regression models, after adjusting for established risk factors, TATc levels predicted the degree of coronary artery calcification: mild (odds ratio: 1.56, p = 0.006), moderate (odds ratio: 1.56, p = 0.007), and severe (odds ratio: 1.67, p = 0.002). Trends were comparable between the groups when stratified according to the degree of coronary luminal stenosis.

CONCLUSIONS

This study provides novel clinical evidence indicating a positive independent association between enhanced in vivo thrombin generation and the presence and severity of coronary atherosclerosis, which may suggest that thrombin plays a role in the pathophysiology of vascular calcification and atherosclerosis progression.

Endothelial cells (ECs) for vascular tissue engineering: venous ECs are less thrombogenic than arterial ECs

Primary endothelial cells (ECs) are the preferred cellular source for luminal seeding of tissue-engineered (TE) vascular grafts. Research into the potential of ECs for vascular TE has focused particularly on venous rather than arterial ECs. In this study we evaluated the functional characteristics of arterial and venous ECs, relevant for vascular TE. Porcine ECs were isolated from femoral artery (PFAECs) and vein (PFVECs). The proliferation rate was comparable for both EC sources, whereas migration, determined through a wound-healing assay, was less profound for PFVECs. EC adhesion was lower for PFVECs on collagen I, measured after 10 min of arterial shear stress. Gene expression was analysed by qRT-PCR for ECs cultured under static conditions and after exposure to arterial shear stress and revealed differences in gene expression, with lower expression of EphrinB2 and VCAM-1 and higher levels of vWF and COUP-TFII in PFVECs than in PFAECs. PFVECs exhibited diminished platelet adhesion under flow and cell-based thrombin generation was delayed for PFVECs, indicating diminished tissue factor (TF) activity. After stimulation, prostacyclin secretion, but not nitric oxide (NO), was lower in PFVECs. Our data support the use of venous ECs for TE because of their beneficial antithrombogenic profile.

Do blood collection methods influence whole-blood platelet function analysis?

Pre-analytical variables interact with standard coagulation parameters. How these variables affect the platelet function analysis is not completely known. How collection site and puncture method affect multiple electrode aggregometry (MEA) and platelet function analyzer (PFA-100®) was compared regarding contact activation. First, volunteers scheduled for elective cardiac surgery had blood collected from four lines: venous, arterial, central venous and by venipuncture. MEA and PFA-100® were analysed blinded for site origin. Second, two samples (citrate, Corn Trypsin Inhibitor, CTI) were collected in syringe or vacuum tubes. Thrombin generation (TG) was determined. MEA was triggered by adenosine diphosphate (ADP, 6.4 µM), arachidonic acid (ASPI, 0.5 mM), collagen (Col, 3.2 µg/ml), ristocetin (Risto, 0.2 mg/ml) and thrombin receptor-activating peptide (TRAP, 32 µM). PFA-100® was triggered by collagen/epinephrine and collagen/ADP. TG was assessed in platelet-poor plasma with 1 pM tissue factor and 4 µM phospholipids and without trigger. Data were analysed using a two-way mixed-effects model for the intraclass correlation (ICC) and by the Mann-Whitney U-test. MEA and PFA-100® revealed good correlation (ICC) between the sites. CTI inhibited TG significantly more effective than citrate. Contact activation was independent of the collection method. Only the MEA ASPI test revealed significant differences between the two collection methods. Blood sampling from all lines for MEA and PFA-100® assays is justified. Contact activation is always present. Apparently this does not influence platelet function test results. Collection methods do not seem relevant, although, one should always consider using a standardized method.

Pulmonary and cardiovascular effects of traffic-related particulate matter: 4-week exposure of rats to roadside and diesel engine exhaust particles

Traffic-related particulate matter (PM) may play an important role in the development of adverse health effects, as documented extensively in acute toxicity studies. However, rather little is known about the impacts of prolonged exposure to PM. We hypothesized that long-term exposure to PM from traffic adversely affects the pulmonary and cardiovascular system through exacerbation of an inflammatory response. To examine this hypothesis, Fisher F344 rats, with a mild pulmonary inflammation at the onset of exposure, were exposed for 4 weeks, 5 days/week for 6 h a day to: (a) diluted diesel engine exhaust (PM(DEE)), or: (b) near roadside PM (PM(2.5)). Ultrafine particulates, which are largely present in diesel soot, may enter the systemic circulation and directly or indirectly trigger cardiovascular effects. Hence, we assessed the effects of traffic-related PM on pulmonary inflammation and activity of procoagulants, vascular function in arteries, and cytokine levels in the heart 24 h after termination of the exposures. No major adverse health effects of prolonged exposure to traffic-related PM were detected. However, some systemic effects due to PM(DEE) exposure occurred including decreased numbers of white blood cells and reduced von Willebrand factor protein in the circulation. In addition, lung tissue factor activity is reduced in conjunction with reduced lung tissue thrombin generation. To what extent these alterations contribute to thrombotic effects and vascular diseases remains to be established. In conclusion, prolonged exposure to traffic-related PM in healthy animals may not be detrimental due to various biological adaptive response mechanisms.

Platelet polyphosphates are proinflammatory and procoagulant mediators in vivo

Platelets play a central role in thrombosis, hemostasis, and inflammation. We show that activated platelets release inorganic polyphosphate (polyP), a polymer of 60-100 phosphate residues that directly bound to and activated the plasma protease factor XII. PolyP-driven factor XII activation triggered release of the inflammatory mediator bradykinin by plasma kallikrein-mediated kininogen processing. PolyP increased vascular permeability and induced fluid extravasation in skin microvessels of mice. Mice deficient in factor XII or bradykinin receptors were resistant to polyP-induced leakage. PolyP initiated clotting of plasma via the contact pathway. Ablation of intrinsic coagulation pathway proteases factor XII and factor XI protected mice from polyP-triggered lethal pulmonary embolism. Targeting polyP with phosphatases interfered with procoagulant activity of activated platelets and blocked platelet-induced thrombosis in mice. Addition of polyP restored defective plasma clotting of Hermansky-Pudlak Syndrome patients, who lack platelet polyP. The data identify polyP as a new class of mediator having fundamental roles in platelet-driven proinflammatory and procoagulant disorders.

Elevated procoagulant microparticles expressing endothelial and platelet markers in essential thrombocythemia

BACKGROUND

Most cell types, including blood--and vascular cells, produce microparticles upon activation. Since cellular microparticles are known to be elevated in thromboembolic diseases, we hypothesized a role for microparticles in the pathogenesis of thrombosis in essential thrombocythemia.

DESIGN AND METHODS

In plasma samples from 21 patients with essential thrombocythemia and ten healthy subjects, the levels and the cellular origin of microparticles were determined by flowcytometric analysis, while the microparticle-associated procoagulant activity was measured using a thrombin generation assay.

RESULTS

Patients with essential thrombocythemia had significantly higher numbers of circulating annexin V-positive microparticles than controls (median 4500 vs. 2500x10(6) events/L; p=0.039), including significantly higher numbers of microparticles positive for the platelet marker CD61 (p=0.043), the endothelial markers CD62E (p=0.009) and CD144 (p=0.021), and for tissue factor (p=0.036). CD62E was co-expressed with the platelet marker CD41 on microparticles, suggesting a bilineage origin of such microparticles, which were observed only in patients with risk factors for thrombosis. Patients with essential thrombocythemia had higher plasma levels of mature von Willebrand factor (p=0.045) but similar propeptide levels compared to controls. In thrombin generation analyses, microparticle-rich plasma from patients with essential thrombocythemia had a shorter lag time (p=0.001) and higher peak height (p=0.038) than plasma from controls. Peak height correlated significantly with the total number of microparticles (R=0.634, p<0.001).

CONCLUSIONS

Patients with essential thrombocythemia had higher number of circulating microparticles with platelet and endothelial markers, suggesting ongoing platelet and endothelial activation. This was confirmed by an increased level of mature von Willebrand factor, an abnormal mature von Willebrand factor/propeptide ratio, and a hypercoagulable state reflected in thrombin generation. These findings suggest a role for microparticles in thrombosis in essential thrombocythemia.

Differential expression of bone matrix regulatory proteins in human atherosclerotic plaques

In the present study, we examined the expression of regulators of bone formation and osteoclastogenesis in human atherosclerosis because accumulating evidence suggests that atherosclerotic calcification shares features with bone calcification. The most striking finding of this study was the constitutive immunoreactivity of matrix Gla protein, osteocalcin, and bone sialoprotein in nondiseased aortas and the absence of bone morphogenetic protein (BMP)-2, BMP-4, osteopontin, and osteonectin in nondiseased aortas and early atherosclerotic lesions. When atherosclerotic plaques demonstrated calcification or bone formation, BMP-2, BMP-4, osteopontin, and osteonectin were upregulated. Interestingly, this upregulation was associated with a sustained immunoreactivity of matrix Gla protein, osteocalcin, and bone sialoprotein. The 2 modulators of osteoclastogenesis (osteoprotegerin [OPG] and its ligand, OPGL) were present in the nondiseased vessel wall and in early atherosclerotic lesions. In advanced calcified lesions, OPG was present in bone structures, whereas OPGL was only present in the extracellular matrix surrounding calcium deposits. The observed expression patterns suggest a tight regulation of the expression of bone matrix regulatory proteins during human atherogenesis. The expression pattern of both OPG and OPGL during atherogenesis might suggest a regulatory role of these proteins not only in osteoclastogenesis but also in atherosclerotic calcification.

Matrix Gla protein accumulates at the border of regions of calcification and normal tissue in the media of the arterial vessel wall

Vitamin K-dependent matrix Gla protein (MGP) has been suggested to play a role in the inhibition of soft-tissue calcification. Here we report the expression of recombinant prokaryotic MGP as part of a fusion protein and the preparation of two antibodies that specifically recognize MGP. Monoclonal antibodies were raised against synthetic peptides homologous to the sequences 3-15 and 63-75 of human MGP. Both antibodies recognize recombinant and synthetic human MGP. Immunohistochemical analysis showed that MGP was associated with the extracellular matrix of noncalcified bone and with chondrocytes in cartilage. In the healthy human arterial vessel wall, MGP antigen was demonstrated in association with smooth muscle cells and elastic laminae of the tunica media and with the extracellular matrix of the adventitia. Colocalization with the elastic laminae was lost at sites of medial calcification; in both human and rat arteries, high amounts of MGP were found in the extracellular matrix at borders of intimal and medial calcification. Our data demonstrate the close association between MGP and calcification. It is suggested that undercarboxylated MGP is biologically inactive and that poor vascular vitamin K status may form a risk factor for vascular calcification.

A polymorphism of the human matrix gamma-carboxyglutamic acid protein promoter alters binding of an activating protein-1 complex and is associated with altered transcription and serum levels

Matrix gamma-carboxyglutamic acid protein (MGP) is a mineral-binding extracellular matrix protein synthesized by vascular smooth muscle cells (VSMCs) and chondrocytes that is thought to be a key regulator of tissue calcification. In this study, we identified four polymorphisms in the promoter region of the human MGP gene. Transfection studies showed that the G-7A and T-138C polymorphisms have an important impact on in vitro promoter activity when transiently transfected into VSMCs. We found that one of these polymorphisms (T-138C) is significantly correlated with serum MGP levels in human subjects. Promoter deletion analysis showed that this polymorphism lies in a region of the promoter critical for transcription in VSMCs. This region contains a potential activating protein-1 (AP-1) binding element located between -142 and -136. We have demonstrated that the T-138C polymorphism results in altered binding of an AP-1 complex to this region. The -138T allelic variant binds AP-1 complexes consisting primarily of c-Jun, JunB and its partners Fra-1 and Fra-2 in rat VSMC. Furthermore, the -138T variant form of the promoter was induced following phorbol 12-myristate 13-acetate treatment, while the -138C variant was refractive to phorbol 12-myristate 13-acetate treatment, confirming that AP-1 factors preferentially bind to the -138T variant. This study therefore suggests that a common polymorphism of the MGP promoter influences binding of the AP-1 complex, which may lead to altered transcription and serum levels. This could have important implications for diseases such as atherosclerosis and aortic valve stenosis, since it strongly suggests a genetic basis for regulation of tissue calcification.

Total chemical synthesis of human matrix Gla protein

Human matrix Gla protein (MGP) is a vitamin K-dependent extracellular matrix protein that binds Ca2+ ions and that is involved in the prevention of vascular calcification. MGP is a 10.6-kD protein (84 amino acids) containing five gamma-carboxyglutamic acid (Gla) residues and one disulfide bond. Studies of the mechanism by which MGP prevents calcification of the arterial media are hampered by the low solubility of the protein (<10 microg/mL). Because of solubility problems, processing of a recombinantly expressed MGP-fusion protein chimera to obtain MGP was unsuccessful. Here we describe the total chemical synthesis of MGP by tBoc solid-phase peptide synthesis (SPPS) and native chemical ligation. Peptide Tyr1-Ala53 was synthesized on a derivatized resin yielding a C-terminal thioester group. Peptide Cys54-Lys84 was synthesized on Lys-PAM resin yielding a C-terminal carboxylic acid. Subsequent native chemical ligation of the two peptides resulted in the formation of a native peptide bond between Ala53 and Cys54. Folding of the 1-84-polypeptide chain in 3 M guanidine (pH 8) resulted in a decrease of molecular mass from 10,605 to 10,603 (ESI-MS), representing the loss of two protons because of the formation of the Cys54-Cys60 internal disulfide bond. Like native MGP, synthetic MGP had the same low solubility when brought into aqueous buffer solutions with physiological salt concentrations, confirming its native like structure. However, the solubility of MGP markedly increased in borate buffer at pH 7.4 in the absence of sodium chloride. Ca2+-binding to MGP was confirmed by analytical HPLC, on which the retention time of MGP was reduced in the presence of CaCl2. Circular dichroism studies revealed a sharp increase in alpha-helicity at 0.2 mM CaCl2 that may explain the Ca2+-dependent shift in high-pressure liquid chromatography (HPLC)-retention time of MGP. In conclusion, facile and efficient chemical synthesis in combination with native chemical ligation yielded MGP preparations that can aid in unraveling the mechanism by which MGP prevents vascular calcification.

Role of vitamin K and vitamin K-dependent proteins in vascular calcification

OBJECTIVES

To provide a rational basis for recommended daily allowances (RDA) of dietary phylloquinone (vitamin K1) and menaquinone (vitamin K2) intake that adequately supply extrahepatic (notably vascular) tissue requirements.

BACKGROUND

Vitamin K has a key function in the synthesis of at least two proteins involved in calcium and bone metabolism, namely osteocalcin and matrix Gla-protein (MGP). MGP was shown to be a strong inhibitor of vascular calcification. Present RDA values for vitamin K are based on the hepatic phylloquinone requirement for coagulation factor synthesis. Accumulating data suggest that extrahepatic tissues such as bone and vessel wall require higher dietary intakes and have a preference for menaquinone rather than for phylloquinone.

METHODS

Tissue-specific vitamin K consumption under controlled intake was determined in warfarin-treated rats using the vitamin K-quinone/epoxide ratio as a measure for vitamin K consumption. Immunohistochemical analysis of human vascular material was performed using a monoclonal antibody against MGP. The same antibody was used for quantification of MGP levels in serum.

RESULTS

At least some extrahepatic tissues including the arterial vessel wall have a high preference for accumulating and using menaquinone rather than phylloquinone. Both intima and media sclerosis are associated with high tissue concentrations of MGP, with the most prominent accumulation at the interface between vascular tissue and calcified material. This was consistent with increased concentrations of circulating MGP in subjects with atherosclerosis and diabetes mellitus.

CONCLUSIONS

This is the first report demonstrating the association between MGP and vascular calcification. The hypothesis is put forward that undercarboxylation of MGP is a risk factor for vascular calcification and that the present RDA values are too low to ensure full carboxylation of MGP.

Novel mutation in the gamma-glutamyl carboxylase gene resulting in congenital combined deficiency of all vitamin K-dependent blood coagulation factors

A mutation in the gamma-glutamyl carboxylase gene leading to a combined congenital deficiency of all vitamin K-dependent coagulation factors was identified in a Lebanese boy. He is the first offspring of consanguineous parents and was homozygous for a unique point mutation in exon 11, resulting in the conversion of a tryptophan codon (TGG) to a serine codon (TCG) at amino acid residue 501. Oral vitamin K(1) administration resulted in resolution of the clinical symptoms. Screening of several family members on this mutation with an RFLP technique revealed 10 asymptomatic members who were heterozygous for the mutation, confirming the autosomal recessive pattern of inheritance of this disease. In 50 nonrelated normal subjects, the mutation was not found. This is the second time a missense mutation in the gamma-glutamyl carboxylase gene is described that has serious impact on normal hemostasis.

Assay for human matrix gla protein in serum: potential applications in the cardiovascular field

Matrix Gla protein (MGP) is synthesized in a vitamin K-dependent way in smooth muscle cells of the healthy vessel wall, and its mRNA transcription is substantially upregulated in atherosclerotic lesions. Here we report the preparation of a monoclonal antibody against human MGP and its use in an enzyme-linked immunosorbent assay. The intra-assay and interassay coefficients of variation in serum samples were 5.4% and 12.6%, respectively, and the lower detection limit was 8.5% of the normal serum value. Individual within-day variations were <11% and did not show a distinct circadian pattern. Day-to-day variations in fasting morning samples were <8%. In a first explorative survey, serum MGP concentrations were found to be significantly increased in patients with severe atherosclerosis, whereas these values were normal in those with low bone mass and osteoporosis. This finding is consistent with the high MGP mRNA expression observed in atherosclerotic vessels and plaques. More elaborate studies are required to assess the potential clinical utility of this newly developed assay.