Plasma levels of myeloperoxidase are not elevated in patients with stable coronary artery disease

Myeloperoxidase as a Promising Therapeutic Target after Myocardial Infarction

Coronary artery disease (CAD) and myocardial infarction (MI) remain leading causes of death and disability worldwide. CAD begins with the formation of atherosclerotic plaques within the intimal layer of the coronary arteries, a process driven by persistent arterial inflammation and oxidation. Myeloperoxidase (MPO), a mammalian haem peroxidase enzyme primarily expressed within neutrophils and monocytes, has been increasingly recognised as a key pro-inflammatory and oxidative enzyme promoting the development of vulnerable coronary atherosclerotic plaques that are prone to rupture, and can precipitate a MI. Mounting evidence also implicates a pathogenic role for MPO in the inflammatory process that follows a MI, which is characterised by the rapid infiltration of activated neutrophils into the damaged myocardium and the release of MPO. Excessive and persistent cardiac inflammation impairs normal cardiac healing post-MI, resulting in adverse cardiac outcomes and poorer long-term cardiac function, and eventually heart failure. This review summarises the evidence for MPO as a significant oxidative enzyme contributing to the inappropriate inflammatory responses driving the progression of CAD and poor cardiac healing after a MI. It also details the proposed mechanisms underlying MPO's pathogenic actions and explores MPO as a novel therapeutic target for the treatment of unstable CAD and cardiac damage post-MI.

Genetic and clinical study of myeloperoxidase's association with coronary artery disease

BACKGROUND

Unraveling myeloperoxidase's (MPO) correlation with coronary artery disease (CAD) and genetic variations, this study seeks to enhance diagnostic precision and therapeutic strategies.

RESULTS

CAD patients were found to be older and more male than controls. Several clinical parameters, including glucose, total bilirubin, alkaline phosphatase, creatinine, and troponin levels, showed significant variations. Moreover, CAD patients had lower red cell distribution width (RDW%) and mean platelet volume (MPV) than controls. Serum MPO levels did not differ significantly between CAD patients and controls, and no correlation was found with other clinical parameters except for glucose, creatinine, and total bilirubin.

CONCLUSIONS

The data suggest that serum MPO levels are not substantially related to CAD patients, as indicated by lower MPO levels in CAD patients compared to controls. While highlighting the potential of MPV and RDW% as predictors of severe atherosclerosis in CAD. Further research is needed to validate the diagnostic and prognostic value of RDW%, MPV, and MPO levels in CAD.

TRIAL REGISTRATION

15092021-9-12. Registered 15 September 2021.

Regulation of coagulation activation in newly diagnosed AML by the heme enzyme myeloperoxidase

INTRODUCTION

Patients with acute myeloid leukemia (AML) are at increased risk of thrombohemorrhagic complications. Overexpressed tissue factor (TF) on AML blasts contributes to systemic coagulation activation. We have recently shown that the heme enzyme myeloperoxidase (MPO) negatively regulates TF procoagulant activity (PCA) on myelomonocytic cells in vitro. We now aimed to further characterize the functional interaction of MPO and TF in AML in vivo.

METHODS

We prospectively recruited 66 patients with newly diagnosed AML. TF PCA of isolated peripheral blood mononuclear cells (PBMC) was assessed by single-stage clotting assay in the presence or absence of inhibitors against MPO catalytic activity (ABAH) or against MPO-binding integrins (anti-CD18). MPO in plasma and in AML blasts was measured by ELISA, and plasma D-dimers and prothrombin fragment F1+2 were quantified by automated immunoturbidimetric and chemiluminescence assays, respectively.

RESULTS

Patients with AML had significantly higher MPO plasma levels compared to healthy controls and exhibited increased levels of D-dimers and F1+2. In vivo thrombin generation was mediated by TF PCA on circulating PBMC. Ex vivo incubation of isolated PBMC with ABAH or anti-CD18 antibody resulted in either increased or decreased TF PCA. The strong and robust correlation of F1+2 with TF PCA of circulating PBMC was abrogated at MPO plasma levels higher than 150 ng/mL, indicating a modulatory role for MPO on TF-mediated in vivo thrombin generation above this threshold.

CONCLUSION

Our study indicates that catalytically active MPO released by circulating myeloblasts regulates TF-dependent coagulation in patients with newly diagnosed AML in a CD18-dependent manner.

Effects of ω-3 PUFA-Rich Oil Supplementation on Cardiovascular Morphology and Aortic Vascular Reactivity of Adult Male Rats Submitted to an Hypercholesterolemic Diet

Simple Summary

Currently, processed and ultraprocessed foods represent a significant component of the diet of modern societies, increasing the risk of developing obesity, diabetes and atherosclerosis. Therefore, replacing saturated fats with mono- and polyunsaturated fats, such as omega-3 polyunsaturated fatty acids (ω-3 PUFAs), has been considered as a dietary strategy to reduce clinical events related to atherosclerosis. In the present study, the effects of 56-day ω-3 PUFA-rich oil supplementation on liver function, lipid profile, and oxidative stress in hypercholesterolemic rats were investigated, as well as its impact on cardiovascular health. Interestingly, we observed a positive effect in reducing hepatic markers, preserving cardiovascular morphology, and increasing vasodilator responsiveness. These findings contribute to the generation of consistent recommendations for the therapeutic use of ω-3 PUFAs in the treatment of atherosclerosis, leading to a consequent reduction in related morbidity and mortality.

Abstract

Atherosclerosis is a cardiovascular disease associated with abnormalities of vascular functions. The consumption of mono- and polyunsaturated fatty acids can be considered a strategy to reduce clinical events related to atherosclerosis. In the present study, we investigated the effects of supplementation with 310 mg of ω-3 PUFAs (2:1 eicosapentaenoic/docosahexaenoic acids) for 56 days on rats with hypercholesterolemia induced by a diet containing cholesterol (0.1%), cholic acid (0.5%), and egg yolk. Serum biochemical parameters were determined by the enzymatic colorimetric method. Assessment of vascular effects was performed by analysis of histological sections of the heart and aortic arch stained with hematoxylin and eosin and vascular reactivity of the aorta artery. We observed that treatment with ω-3 PUFAs did not promote alterations in lipid profile. On the other hand, we documented a favorable reduction in liver biomarkers, as well as contributions to the preservation of heart and aortic arch morphologies. Interestingly, the vascular reactivity of rat thoracic aortic preparations was improved after treatment with ω-3 PUFAs, with a decrease in hyperreactivity to phenylephrine and increased vasorelaxation promoted by acetylcholine. Our findings suggest that the supplementation of hypercholesterolemic rats with ω-3 PUFAs promoted improvement in liver and vascular endothelial function as well as preserving heart and aortic tissue, reinforcing the early health benefits of ω-3 PUFAs in the development of atherosclerotic plaque and further related events.

Serum Myeloperoxidase, C-reactive Protein and α1-acid Glycoprotein: Insights about Cardiovascular Risk in End-stage Renal Disease

Background Cardiovascular disease (CVD) is the leading cause of death in patients with end-stage renal disease (ESRD). Elevated serum concentrations of myeloperoxidase (MPO) are associated with an increased risk of developing CVD. The objective of this study was to evaluate serum MPO levels, as well as other laboratory parameters, in individuals with ESRD, with and without CVD, undergoing hemodialysis.

Methods 80 volunteers were admitted, divided into the following groups: control group (CON): 20 individuals without chronic kidney disease (CKD); ESRD group: 45 individuals with CKD stage V and ESRD/CVD group: 15 individuals with CKD stage V and with CVD. The following biomarkers were evaluated: MPO, High sensitivity C-reactive protein (hs-CRP) and α1-acid glycoprotein, following the manufacturer's guidelines in the package inserts. The data were processed through the statistical software SPSS 20.0®.

Results The level of MPO for the CON group was 84 ng/mL (73–87 ng/mL), for the ESRD group 77 ng/mL (11–89 ng/mL) and for the ESRD/CVD group 21 ng/mL (8–47 ng/mL), with a significant statistical difference of the ESRD/CVD group from the CON and ESRD groups (p<0.001). For the parameters hs-CRP and α1-acid glycoprotein a statistical difference between the ESRD and ESRD/CVD groups from the CON group (p<0.0001) was observed, but not between the ESRD and ESRD/CVD groups.

Conclusion It is suggested that further studies should be performed to define the potential role of MPO as a cardiovascular risk marker for patients with ESRD on hemodialysis.

Joint Measurements of Leukocyte Elastase and Myeloperoxidase Promote Identification of the State of Neutrophils in Diabetic Patients

The clinic of diabetes mellitus (DM) offers a number of hypotheses about the leading role of polymorphonuclear neutrophils (PMNs) in both oxidative stress and diabetic complications. However, the results of numerous studies are extremely controversial. Why is it so? We appreciated the clinical significance of simultaneous measurement data of several PMN parameters, which must complement each other. For this purpose, myeloperoxidase (MPO) and elastase (EL) were jointly analyzed in the blood plasma from 160 type 2 diabetes mellitus patients with high levels of HbA_1c. A weakly positive correlation (r ∼ 0.56) was observed between MPO and EL analytical data, and any correlation between the concentrations of MPO/EL and HbA_1c was absent. Medians of 160 measurements of MPO/EL concentrations were ∼103/190 ng/mL, and 95% of all results were in the range below 320/1016 ng/mL, respectively. The share of DM patients whose concentrations of MPO, EL, or either of two parameters exceeded the corresponding reference values was 65%, 80%, and 82.5%, respectively. These findings—a high intensity of neutrophil degranulation process—indicated that some diabetic conditions promote the transfer of PMNs to an “arousal” or “subactivation” state, which is identical or similar to their activation, providing in vivo an almost inexhaustible source of extremely “aggressive” MPO and EL. Thus, the conjoint MPO/EL measurements confirm the leading role of PMNs in the development of various complications of diabetes. The paradox is that the diagnostic significance of MPO/EL as independent parameters in diabetic patients is unambiguous for a number of reasons.

Myeloperoxidase - A bridge linking inflammation and oxidative stress with cardiovascular disease

Myeloperoxidase (MPO) is a member of the superfamily of heme peroxidases that is mainly expressed in neutrophils and monocytes. MPO-derived reactive species play a key role in neutrophil antimicrobial activity and human defense against various pathogens primarily by participating in phagocytosis. Elevated MPO levels in circulation are associated with inflammation and increased oxidative stress. Multiple lines of evidence suggest an association between MPO and cardiovascular disease (CVD) including coronary artery disease, congestive heart failure, arterial hypertension, pulmonary arterial hypertension, peripheral arterial disease, myocardial ischemia/reperfusion-related injury, stroke, cardiac arrhythmia and venous thrombosis. Elevated MPO levels are associated with a poor prognosis including increased risk for overall and CVD-related mortality. Elevated MPO may signify an increased risk for CVD for at least 2 reasons. First, low-grade inflammation and increased oxidative stress coexist with many metabolic abnormalities and comorbidities and consequently an elevated MPO level may represent an increased cardiometabolic risk in general. Second, MPO produces a large number of highly reactive species which can attack, destroy or modify the function of every known cellular component. The most common MPO actions relevant to CVD are generation of dysfunctional lipoproteins with an increased atherogenicity potential, reduced NO availability, endothelial dysfunction, impaired vasoreactivity and atherosclerotic plaque instability. These actions strongly suggest that MPO is directly involved in the pathophysiology of CVD. In this regard MPO may be seen as a mediator or an instrument through which inflammation promotes CVD at molecular and cellular level. Clinical value of MPO therapeutic inhibition remains to be tested.

Myeloperoxidase activity and acute coronary syndrome survival: long-term evaluation in the ERICO study

AIM

We aimed to analyze the influence of myeloperoxidase (MPO) activity on mortality in the Acute Coronary Syndrome Registry Strategy (ERICO) study.

METHODS

MPO activity levels were evaluated in 342 patients. We performed survival analyses using Kaplan-Meier curves and Cox regression with respective hazard ratios, 95% CI, according to MPO tertiles distribution up to 7 years of follow-up.

RESULTS

Higher MPO activity levels were seen in men, smokers, diabetics and those who were taking aspirin. MPO activity levels were neither significant in relation to mortality nor to survival rates up to seven years.

CONCLUSION

We found no relationship between elevated levels of MPO activity post-acute coronary syndrome and mortality up to 7-years of follow-up in the ERICO study.

Review of biomarkers to assess the effects of switching from cigarettes to modified risk tobacco products

Context: One approach to reducing the harm caused by cigarette smoking, at both individual and population level, is to develop, assess and commercialize modified risk alternatives that adult smokers can switch to. Studies to demonstrate the exposure and risk reduction potential of such products generally involve the measuring of biomarkers, of both exposure and effect, sampled in various biological matrices.Objective: In this review, we detail the pros and cons for using several biomarkers as indicators of effects of changing from conventional cigarettes to modified risk products.Materials and methods: English language publications between 2008 and 2017 were retrieved from PubMed using the same search criteria for each of the 25 assessed biomarkers. Nine exclusion criteria were applied to exclude non-relevant publications.Results: A total of 8876 articles were retrieved (of which 7476 were excluded according to the exclusion criteria). The literature indicates that not all assessed biomarkers return to baseline levels following smoking cessation during the study periods but that nine had potential for use in medium to long-term studies.Discussion and conclusion: In clinical studies, it is important to choose biomarkers that show the biological effect of cessation within the duration of the study.

Unraveling mechanisms of toxicant-induced oxidative stress in cardiovascular disease

To date, numerous clinical studies examining correlations between oxidative stress biomarkers and cardiovascular diseases (CVD) have repeatedly suggested a role for oxidant injury in the pathogenesis of diseases such as atherosclerosis. Despite this, antioxidant supplementation trials have not demonstrated a reduction in disease progression. Nevertheless, small animal and epidemiological studies have linked exposures to certain toxicants with increased CVD risk involving putative oxidative stress mechanisms. A few prototypical vascular toxicants will be discussed as examples of toxicants that likely act via oxidative stress mechanisms. For discussion, we will classify these toxicants as those that induce direct (e.g., arsenic, nucleoside reverse transcriptase inhibitors) versus indirect (particulate matter, ozone) oxidative stress mechanisms, and those that likely induce CVD through both direct and indirect mechanisms (cigarette smoke). Finally, new findings in oxidative stress research, including the emerging importance of reactive sulfur species, hydrogen peroxide as a presumed endothelium-derived hyperpolarizing factors, etc., will be discussed, as well as the need to determine the role of toxicants in modulating these newly identified pathways. Moreover, given the lack of success in conclusively demonstrating the roles of oxidative stress in CVD risk stratification, research probing the roles of toxicant exposures in propagating CVD pathogenesis may be a novel approach for more conclusively delineating the causal role of oxidative stress in CVD initiation and progression.

Myeloperoxidase Levels and Its Product 3-Chlorotyrosine Predict Chronic Kidney Disease Severity and Associated Coronary Artery Disease

BACKGROUND

The role of myeloperoxidase in chronic kidney disease (CKD) and its association with coronary artery disease (CAD) is controversial. In this study, we compared myeloperoxidase and protein-bound 3-chlorotyrosine (ClY) levels in subjects with varying degrees of CKD and tested their associations with CAD.

METHODS

From Clinical Phenotyping Resource and Biobank Core, 111 patients were selected from CKD stages 1 to 5. Plasma myeloperoxidase level was measured using enzyme-linked-immunosorbent assay. Plasma protein-bound 3-ClY, a specific product of hypochlorous acid generated by myeloperoxidase was measured by liquid chromatography mass spectrometry.

RESULTS

We selected 29, 20, 24, 22, and 16 patients from stages 1 to 5 CKD, respectively. In a sex-adjusted general linear model, mean ± SD of myeloperoxidase levels decreased from 18.1 ± 12.3 pmol in stage 1 to 10.9 ± 4.7 pmol in stage 5 (p = 0.011). In patients with and without CAD, the levels were 19.1 ± 10.1 and 14.8 ± 8.7 pmol (p = 0.036). There was an increase in 3-ClY mean from 0.81 ± 0.36 mmol/mol-tyrosine in stage 1 to 1.42 ± 0.41 mmol/mol-tyrosine in stage 5 (p < 0.001). The mean 3-ClY levels in patients with and without CAD were 1.25 ± 0.44 and 1.04 ± 0.42 mmol/mol-tyrosine (p = 0.023), respectively. C-statistic of ClY when added to myeloperoxidase level to predict CKD stage 5 was 0.86, compared to 0.79 for the myeloperoxidase level alone (p = 0.0097).

CONCLUSION

The myeloperoxidase levels decrease from stages 1 to 5, whereas activity increases. In contrast, both myeloperoxidase and ClY levels rise in the presence of CAD at various stages of CKD. Measuring both plasma myeloperoxidase and 3-CLY levels provide added value to determine the burden of myeloperoxidase-mediated oxidative stress.

Association of the serum myeloperoxidase/high-density lipoprotein particle ratio and incident cardiovascular events in a multi-ethnic population: Observations from the Dallas Heart Study

BACKGROUND AND AIMS

Myeloperoxidase (MPO), a product of systemic inflammation, promotes oxidation of lipoproteins; whereas, high-density lipoprotein (HDL) exerts anti-oxidative effects in part via paraoxonase-1 (PON1). MPO induces dysfunctional HDL particles; however, the interaction of circulating levels of these measures in cardiovascular disease (CVD) has not been studied in humans. We tested whether serum levels of MPO indexed to HDL particle concentration (MPO/HDLp) are associated with increased CVD risk in a large multiethnic population sample, free of CVD at baseline.

METHODS

Levels of MPO, HDL-C, and HDL particle concentration (HDLp) by NMR were measured at baseline in 2924 adults free of CVD. The associations of MPO/HDLp with incident ASCVD (first non-fatal myocardial infarction, non-fatal stroke, coronary revascularization, or CVD death) and total CVD were assessed in Cox proportional-hazards models adjusted for traditional risk factors. The median follow-up period was 9.4 years.

RESULTS

Adjusted for sex and race/ethnicity, MPO/HDLp was associated directly with body mass index, smoking status, high-sensitivity C-reactive protein, and interleukin 18, and inversely with age, HDL-C levels, HDL size, and PON1 arylesterase activity, but not with cholesterol efflux. In fully adjusted models, the highest versus lowest quartile of MPO/HDLp was associated with a 74% increase in incident ASCVD (aHR, 1.74, 95% CI 1.12-2.70) and a 91% increase in total incident CVD (aHR, 1.91, 95% CI 1.27-2.85).

CONCLUSIONS

Increased MPO indexed to HDL particle concentration (MPO/HDLp) at baseline is associated with increased risk of incident CVD events in a population initially free of CVD over the 9.4 year period.

The roles of myeloperoxidase in coronary artery disease and its potential implication in plaque rupture

Atherosclerosis is the main pathophysiological process underlying coronary artery disease (CAD). Acute complications of atherosclerosis, such as myocardial infarction, are caused by the rupture of vulnerable atherosclerotic plaques, which are characterized by thin, highly inflamed, and collagen-poor fibrous caps. Several lines of evidence mechanistically link the heme peroxidase myeloperoxidase (MPO), inflammation as well as acute and chronic manifestations of atherosclerosis. MPO and MPO-derived oxidants have been shown to contribute to the formation of foam cells, endothelial dysfunction and apoptosis, the activation of latent matrix metalloproteinases, and the expression of tissue factor that can promote the development of vulnerable plaque. As such, detection, quantification and imaging of MPO mass and activity have become useful in cardiac risk stratification, both for disease assessment and in the identification of patients at risk of plaque rupture. This review summarizes the current knowledge about the role of MPO in CAD with a focus on its possible roles in plaque rupture and recent advances to quantify and image MPO in plasma and atherosclerotic plaques.

Myeloperoxidase-Related Chlorination Activity Is Positively Associated with Circulating Ceruloplasmin in Chronic Heart Failure Patients: Relationship with Neurohormonal, Inflammatory, and Nutritional Parameters

Rationale. Heart failure (HF) is accompanied by the development of an imbalance between oxygen- and nitric oxide-derived free radical production leading to protein nitration. Both chlorinating and peroxidase cycle of Myeloperoxidase (MPO) contribute to oxidative and nitrosative stress and are involved in tyrosine nitration of protein. Ceruloplasmin (Cp) has antioxidant function through its ferroxidase I (FeO_xI) activity and has recently been proposed as a physiological defense mechanism against MPO inappropriate actions. Objective. We investigated the relationship between plasma MPO-related chlorinating activity, Cp and FeO_xI, and nitrosative stress, inflammatory, neurohormonal, and nutritional biomarkers in HF patients. Methods and Results. In chronic HF patients (n = 81, 76 ± 9 years, NYHA Class II (26); Class III (29); Class IV (26)) and age-matched controls (n = 17, 75 ± 11 years, CTR), plasma MPO chlorinating activity, Cp, FeO_xI, nitrated protein, free Malondialdehyde, BNP, norepinephrine, hsCRP, albumin, and prealbumin were measured. Plasma MPO chlorinating activity, Cp, BNP, norepinephrine, and hsCRP were increased in HF versus CTR. FeO_xI, albumin, and prealbumin were decreased in HF. MPO-related chlorinating activity was positively related to Cp (r = 0.363, P < 0.001), nitrated protein, hsCRP, and BNP and inversely to albumin. Conclusions. Plasma MPO chlorinated activity is increased in elderly chronic HF patients and positively associated with Cp, inflammatory, neurohormonal, and nitrosative parameters suggesting a role in HF progression.

Clinical Application of NOX Activity and Other Oxidative Biomarkers in Cardiovascular Disease: A Critical Review

SIGNIFICANCE

The oxidative stress theory of atherosclerosis is based on the assumption that the production of reactive oxidant species (ROS) by blood, as well as resident cells of the artery wall, elicits the formation of oxidized low-density lipoproteins (ox-LDL), which, in turn, promotes a series of inflammatory responses, ultimately leading to atherosclerotic plaque. This theory prompted the development of new laboratory methodologies that aimed at assessing the relationship between oxidative stress and clinical progression of human atherosclerosis.

CRITICAL ISSUES

Markers assessing the oxidation of phospholipid and protein components of LDL were among the first to be developed. Clinical trials included cross-sectional as well as retrospective and prospective studies that, however, provided equivocal results. Thus, clear evidence that oxidative biomarkers add more to the risk stratification by common atherosclerotic risk factors is still lacking.

RECENT ADVANCES

More recently, the analysis of oxidative stress focused on enzymatic pathways generating ROS, such as NADPH oxidase and myeloperoxidase (MPO). Experimental and clinical studies suggest that both enzymes may be implicated in promoting atherosclerotic disease. Novel laboratory methodologies have been, therefore, developed to study NADPH oxidase and MPO in patients with stable atherosclerosis as well as in patients with acute coronary and cerebro-vascular syndromes.

FUTURE DIRECTIONS

This review will analyze the strengths and weaknesses of the current methodology to study these enzymes in human atherosclerosis with particular regard to their clinical application in several settings of cardiovascular disease. Clinical methodology and results of previous studies with regard to markers of LDL oxidation have also been reviewed as a useful background for the future development of clinical trials.

Neutrophil extracellular trap-derived enzymes oxidize high-density lipoprotein: an additional proatherogenic mechanism in systemic lupus erythematosus

OBJECTIVE

Oxidative stress and oxidized high-density lipoprotein (HDL) are implicated as risk factors for cardiovascular disease (CVD) in systemic lupus erythematosus (SLE). Yet, how HDL is oxidized and rendered dysfunctional in SLE remains unclear. Neutrophil extracellular traps (NETs), the levels of which are elevated in lupus, possess oxidant-generating enzymes, including myeloperoxidase (MPO), NADPH oxidase (NOX), and nitric oxide synthase (NOS). We hypothesized that NETs mediate HDL oxidation, impairing cholesterol efflux capacity (CEC).

METHODS

Plasma MPO levels and CEC activity were examined in controls and lupus patients, and 3-chlorotyrosine (MPO specific) and 3-nitrotyrosine (derived from reactive nitrogen species) were quantified in human HDL. Multivariable linear models were used to estimate and test differences between groups. HDL was exposed to NETs from control and lupus neutrophils in the presence or absence of MPO, NOX, NOS inhibitors, and chloroquine (CQ). Murine HDL oxidation was quantified after NET inhibition in vivo.

RESULTS

SLE patients displayed higher MPO levels and diminished CEC compared to controls. SLE HDL had higher 3-nitrotyrosine and 3-chlorotyrosine content than control HDL, with site-specific oxidation signatures on apolipoprotein A-I. Experiments with human and murine NETs confirmed that chlorination was mediated by MPO and NOX, and nitration by NOS and NOX. Mice with lupus treated with the NET inhibitor Cl-amidine displayed significantly decreased HDL oxidation. CQ inhibited NET formation in vitro.

CONCLUSION

Active NOS, NOX, and MPO within NETs significantly modify HDL, rendering the lipoprotein proatherogenic. Since NET formation is enhanced in SLE, these findings support a novel role for NET-derived lipoprotein oxidation in SLE-associated CVD and identify additional proatherogenic roles of neutrophils and putative protective roles of antimalarials in autoimmunity.

Myeloperoxidase levels predicts angiographic severity of coronary artery disease in patients with chronic stable angina

BACKGROUND

Myeloperoxidase (MPO) has an important role in the both processes of inflammation and oxidative stress. It plays proatherogenic role via low-density lipoprotein oxidation, functional inactivation of the high-density lipoprotein and endothelial dysfunction, and seems to be involved in the atherogenesis of coronary arteries. This study designed to evaluate the association between the plasma MPO levels and angiographic severity of coronary artery disease (CAD) in patients with the stable CAD.

MATERIALS AND METHODS

Sixty-eight patients who had documented CAD with angiography and 66 subjects who had normal angiography were selected as case and the control groups for this study, respectively. Gensini scoring system was used for evaluation of severity of coronary artery stenosis. Plasma MPO and C-reactiveprotein (CRP) levels of both case and control groups were determined.

RESULTS

Plasma MPO levels and CRP levels were significantly higher in CAD patients (P < 0.001), and plasma levels of MPO and CRP were correlated with Genssini scores.

CONCLUSIONS

Our findings indicated that the plasma MPO levels increase in patients with stable CAD and hence that, it can be used as adiagnostic factor to predict the coronary artery atherosclerosis severity in stable CAD patients; However, it needs further widespread investigations to achieve an accurate cut point.

Association of myeloperoxidase with total and cardiovascular mortality in individuals undergoing coronary angiography--the LURIC study

Background

The phagocytic enzyme myeloperoxidase (MPO) acts as a front-line defender against microorganisms. However, increased MPO levels have been found to be associated with complex and calcified atherosclerotic lesions and incident cardiovascular disease. Therefore, this study aimed to investigate a predictive role of MPO, a biomarker of inflammation and oxidative stress, for total and cardiovascular mortality in patients referred to coronary angiography.

Methods and results

MPO plasma concentrations along with eight MPO polymorphisms were determined in 3036 participants of the Ludwigshafen Risk and Cardiovascular Health study (median follow-up 7.75 years). MPO concentrations were positively associated with age, diabetes, smoking, markers of systemic inflammation (interleukin-6, fibrinogen, C-reactive protein, serum amyloid A) and vascular damage (vascular cellular adhesion molecule-1 and intercellular adhesion molecule-1) but negatively associated with HDL-cholesterol and apolipoprotein A-I. After adjustment for cardiovascular risk factors MPO concentrations in the highest versus the lowest quartile were associated with a 1.34-fold risk (95% CI: 1.09–1.67) for total mortality. In the adjusted model the hazard ratio for cardiovascular mortality in the highest MPO quartile was 1.42 (95% CI: 1.07–1.88). Five MPO polymorphisms were positively associated with MPO concentrations but not with mortality. Using Mendelian randomization, we did not obtain evidence for a causal association of MPO with either total or cardiovascular mortality.

Conclusions

MPO concentrations but not genetic variants at the MPO locus are independently associated with risk for total and cardiovascular mortality in coronary artery disease patients.

Is there a clinical role for oxidative stress biomarkers in atherosclerotic diseases?

Growing evidences suggest that reactive oxidant species (ROS) are involved in the pathogenesis and progression of the atherosclerotic diseases. Markers assessing the oxidation of LDL and formation of eicosanoids, such as isoprostanes, were among the first that were analyzed. More recently, new biomarkers, such as endogenous secretory receptor for AGEs have been suggested to play an oxidative role in specific atherosclerotic settings, such as diabetes. Unfortunately, clinical trials included cross-sectional as well as retrospective and prospective studies which provide inconclusive results. Thus, clear evidence that oxidative biomarkers can improve risk stratification in addition to the common used atherosclerotic risk factors is still lacking. The analysis of oxidative stress focused on enzymatic systems generating ROS. The most studied enzymes were NADPH oxidase and myeloperoxidase (MPO). Experimental and clinical studies suggest that both enzymes may be implicated in promoting atherosclerotic disease. Novel laboratory methodologies have been, therefore, developed to study NADPH oxidase and MPO in patients with stable atherosclerosis as well in patients with acute coronary syndrome and cerebrovascular accident. This review will report on the more relevant studies in which the clinical application of the oxidative biomarkers was evaluated.

The potentiation of myeloperoxidase activity by the glycosaminoglycan-dependent binding of myeloperoxidase to proteins of the extracellular matrix

BACKGROUND

Myeloperoxidase (MPO) is an abundant hemoprotein expressed by neutrophil granulocytes that is recognized to play an important role in the development of vascular diseases. Upon degranulation from circulating neutrophil granulocytes, MPO binds to the surface of endothelial cells in an electrostatic-dependent manner and undergoes transcytotic migration to the underlying extracellular matrix (ECM). However, the mechanisms governing the binding of MPO to subendothelial ECM proteins, and whether this binding modulates its enzymatic functions are not well understood.

METHODS

We investigated MPO binding to ECM derived from aortic endothelial cells, aortic smooth muscle cells, and fibroblasts, and to purified ECM proteins, and the modulation of these associations by glycosaminoglycans. The oxidizing and chlorinating potential of MPO upon binding to ECM proteins was tested.

RESULTS

MPO binds to the ECM proteins collagen IV and fibronectin, and this association is enhanced by the pre-incubation of these proteins with glycosaminoglycans. Correspondingly, an excess of glycosaminoglycans in solution during incubation inhibits the binding of MPO to collagen IV and fibronectin. These observations were confirmed with cell-derived ECM. The oxidizing and chlorinating potential of MPO was preserved upon binding to collagen IV and fibronectin; even the potentiation of MPO activity in the presence of collagen IV and fibronectin was observed.

CONCLUSIONS

Collectively, the data reveal that MPO binds to ECM proteins on the basis of electrostatic interactions, and MPO chlorinating and oxidizing activity is potentiated upon association with these proteins.

GENERAL SIGNIFICANCE

Our findings provide new insights into the molecular mechanisms underlying the interaction of MPO with ECM proteins.

Myeloperoxidase: a leukocyte-derived protagonist of inflammation and cardiovascular disease

SIGNIFICANCE

The heme-enzyme myeloperoxidase (MPO) is one of the major neutrophil bactericidal proteins and is stored in large amounts inside azurophilic granules of neutrophils. Upon cell activation, MPO is released and extracellular MPO has been detected in a wide range of acute and chronic inflammatory conditions. Recent ADVANCES AND CRITICAL ISSUES: Apart from its role during infection, MPO has emerged as a critical modulator of inflammation throughout the last decade and is currently discussed in the initiation and propagation of cardiovascular diseases. MPO-derived oxidants (e.g., hypochlorous acid) interfere with various cell functions and contribute to tissue injury. Recent data also suggest that MPO itself exerts proinflammatory properties independent of its catalytic activity. Despite advances in unraveling the complex action of MPO and MPO-derived oxidants, further research is warranted to determine the precise nature and biological role of MPO in inflammation.

FUTURE DIRECTIONS

The identification of MPO as a central player in inflammation renders this enzyme an attractive prognostic biomarker and a potential target for therapeutic interventions. A better understanding of the (patho-) physiology of MPO is essential for the development of successful treatment strategies in acute and chronic inflammatory diseases.

High density lipoprotein is targeted for oxidation by myeloperoxidase in rheumatoid arthritis

OBJECTIVE

Phagocyte-derived myeloperoxidase (MPO) and pro-inflammatory high density lipoprotein (HDL) associate with rheumatoid arthritis (RA), but the link between MPO and HDL has not been systematically examined. In this study, we investigated whether MPO can oxidise HDL and determined MPO-specific oxidative signature by apoA-1 by peptide mapping in RA subjects with and without known cardiovascular disease (CVD).

METHODS

Two MPO oxidation products, 3-chlorotyrosine and 3-nitrotyrosine, were quantified by tandem mass spectrometry (MS/MS) in in vitro model system studies and in plasma and HDL derived from healthy controls and RA subjects. MPO levels and cholesterol efflux were determined. Site-specific nitration and chlorination of apoA-1 peptides were quantified by MS/MS.

RESULTS

RA subjects demonstrated higher levels of MPO, MPO-oxidised HDL and diminished cholesterol efflux. There was marked increase in MPO-specific 3-chlorotyrosine and 3-nitrotyrosine content in HDL in RA subjects consistent with specific targeting of HDL, with increased nitration in RA subjects with CVD. Cholesterol efflux capacity was diminished in RA subjects and correlated inversely with HDL 3-chlorotyrosine suggesting a mechanistic role for MPO. Nitrated HDL was elevated in RACVD subjects compared with RA subjects without CVD. Oxidative peptide mapping revealed site-specific unique oxidation signatures on apoA-1 for RA subjects with and without CVD.

CONCLUSIONS

We report an increase in MPO-mediated HDL oxidation that is regiospecific in RA and accentuated in those with CVD. Decreased cholesterol efflux capacity due to MPO-mediated chlorination is a potential mechanism for atherosclerosis in RA and raises the possibility that oxidant resistant forms of HDL may attenuate this increased risk.

Myeloperoxidase: New Roles for an Old Molecule

Myeloperoxidase (MPO) is a member of the heme peroxidase-cyclooxygenase superfamily. It is abundantly expressed in neutrophils and monocytes. During inflammation MPO is released from leukocytes and catalyzes the formation of several reactive species and tissue damage. In this article we present state of the art knowledge on the general properties, biosynthesis and processing and trafficking of MPO. The basic functions of MPO in inflammation and oxidative stress are discussed in detail. This article also summarizes the studies that investigated the relationship between MPO and cardiovascular disease. An overview of the assays for determination of MPO, the sample type and preanalytical procedures is given. Future studies are needed before this marker is introduced into routine clinical practice.

Oxidative stress biomarkers as predictors of cardiovascular disease

Evidence for the role of oxidative stress in the pathogenesis of cardiovascular disease (CVD) is primarily based on experimental and observational human studies. The aim of this review is to examine the observational longitudinal studies that have investigated the relationship between oxidative stress biomarkers and CVD. Fifty-one studies were identified with twenty-six of these measuring oxidized (Ox)-LDL, fifteen assessing myeloperoxidase, seven using lipid peroxidation measures and three quantifying protein oxidation. Results of studies using Ox-LDL have been equivocal with sixteen of the twenty-six studies reporting that this measure is predictive of cardiovascular events. These inconsistent results are not explained by differences in the study populations (primary or secondary CVD) or the type of assay used (auto or monoclonal antibodies). Six of the seven lipid peroxidation, and two of three protein oxidation studies found associations. Twelve of fifteen studies assessing the role of myeloperoxidase reported it to be predictive of CVD. However, issues surrounding the specificity of myeloperoxidase as a marker of oxidative stress and the small number of research groups reporting these results, limit this finding. In summary, the ability of oxidative stress biomarkers to predict CVD has yet to be established. Furthermore, it is important to note that the methods used to assess oxidative stress in these studies are indirect, and the evidence that the various methods actually reflect oxidative stress in vivo is limited.

Current role of myeloperoxidase in routine clinical practice

Recognition of inflammation as a critical contributor to atherothrombosis has led to the pursuit of new approaches for the diagnosis and treatment of patients with coronary heart disease. As the intricate relationships between cellular and noncellular participants in the inflammatory aspects of atherogenesis, plaque destabilization and thrombosis have been defined, specific constituents have emerged as potential noninvasive indicators of these processes. Myeloperoxidase is a protein released during degranulation of neutrophils and monocytes. The available experimental and epidemiologic data provide compelling evidence to sustain strong interest in myeloperoxidase as a candidate for clinical application. Nevertheless, additional investigation will be important to fully evaluate myeloperoxidase as a sensitive predictor for myocardial infarction in patients with chest pain.

Diagnostic efficacy of myeloperoxidase for the detection of acute coronary syndromes

BACKGROUND

Early diagnosis of acute coronary syndrome (ACS) is frequently a challenging task, while immediate risk stratification remains crucial for the prompt implementation of appropriate therapy in this setting. Employing markers that increase rapidly after the symptom onset may enhance triage and therapeutic decision-making in patients suspected for ACS. Myeloperoxidase (MPO) exerting proinflammatory and pro-oxidative properties is suggested as a reliable early marker for ACS associated with unfavourable clinical outcome. We assessed the diagnostic efficacy of plasma MPO alone or in combination with cardiac troponin I (cTnI) for detecting ACS in patients presenting with chest pain initiating within 6h before the hospital admission.

MATERIAL AND METHODS

A study group consisted of 253 patients diagnosed with ACS and 47 subjects having other heart disease or unspecified chest pain. Clinically healthy volunteers (n=124) served as controls. MPO concentration was measured in plasma (Abbott Diagnostics, USA), while serum was assayed for cTnI, creatine-kinase MB, lipids, glucose, creatinine, brain natriuretic peptide type B and C-reactive protein.

RESULTS

Both MPO and cTnI values were significantly lower in non-ACS subjects than in patients with ACS. At 97·5th percentile as cut-off, the superiority of MPO over cTnI was observed in patients with unstable angina and non-ACS subjects. Considerably higher MPO concentrations were demonstrated in the troponin-negative ACS patients on admission who became troponin-positive after 6h. Combined evaluation of MPO and cTnI possessed remarkably higher sensitivity than assessment of cTnI alone in all patients with ACS.

CONCLUSIONS

Myeloperoxidase substantially facilitates the early diagnosis of ACS.

Elevated plasma myeloperoxidase levels in relation to circulating inflammatory markers in coronary artery disease

Aims: Elevation of the leukocyte enzyme myeloperoxidase (MPO) in stable coronary artery disease (CAD) is controversial and its relationship with oxidized low-density lipoprotein (ox-LDL) and nitrite/nitrate (NOx) levels in CAD patients has not been evaluated. Therefore, we sought to evaluate these relationships. Materials & methods: This study included 50 stable CAD patients, 50 unstable CAD patients and 50 control subjects. Plasma MPO and ox-LDL levels were determined using enzyme immunoassay. Plasma NOx and other risk factors were also measured in the patients. Results: Plasma MPO levels were higher in unstable CAD patients (71.2 ± 19.6 ng/ml) than in stable CAD patients (34.5 ± 6.8 ng/ml) and control subjects (23.0 ± 3.6 ng/ml) (p < 0.001). Furthermore, plasma MPO was positively correlated with ox-LDL and negatively correlated with NOx levels (p < 0.05). Conclusion: Plasma MPO levels were elevated in CAD patients and its relation to CAD may be through the oxidation of LDL and reduction of NO levels.

Myeloperoxidase improves risk stratification in patients with ischemia and normal cardiac troponin I concentrations

BACKGROUND

We assessed the ability of myeloperoxidase (MPO) to identify the risk for major adverse cardiac events (MACE) in patients who present with ischemic symptoms suggestive of acute coronary syndrome and have a normal cardiac troponin I (cTnI) value.

METHODS

We used Siemens (n = 400) and Abbott (n = 350) assays to measure MPO and cTnI in plasma samples from 400 patients. Event rates (myocardial infarction, cardiac death, percutaneous coronary intervention, coronary artery bypass grafting) were estimated by the Kaplan-Meier method and compared with the log-rank statistic.

RESULTS

At the 30-day follow-up, the adjusted hazard ratios for MACE were 3.9 (P < 0.001) for increased cTnI and 2.7 (P = 0.006) for increased MPO for the Siemens assays and were 5.5 (P < 0.001) for increased cTnI and 2.9 (P = 0.001) for increased MPO for the Abbott assays. Similar findings were observed with 6 months of follow-up. Patients who initially had a normal cTnI value and an increased Siemens MPO value demonstrated a higher rate of MACE at 30 days than those in whom both values were normal (16.1% vs 3.6%, P = 0.002) and 6 months (18.1% vs 5.0%, P = 0.002). Similarly, patients who had an increased Abbott MPO result demonstrated a higher MACE rate at 30 days (12.3% vs 3.9%, P = 0.03) and at 6 months (16.2% vs 5.1%, P = 0.01) than those with normal values.

CONCLUSIONS

A combination of MPO and cTnI allowed the identification of a greater proportion of patients at risk for MACE than the use of cTnI alone. Increased MPO values remained predictive of future cardiac events even when the cTnI value was normal.

Plasma myeloperoxidase predicts incident cardiovascular risks in stable patients undergoing medical management for coronary artery disease

BACKGROUND

Myeloperoxidase (MPO) concentrations predict adverse clinical outcomes in the setting of acute coronary syndromes and heart failure, but the prognostic role of MPO in stable patients with known atherosclerotic burden is unclear.

METHODS

We examined plasma MPO concentrations and their relationship with prevalent significant coronary artery disease (defined as >50% stenosis in any coronary vessel) and incident major adverse cardiovascular events (MACEs), including death, myocardial infarction, and stroke, in a 3-year prospective follow-up study of 1895 patients undergoing elective coronary angiography.

RESULTS

The median plasma MPO concentration was 101 pmol/L (interquartile range 68-187 pmol/L). Patients with plasma MPO concentrations >322 pmol/L (14.6% of population) had increased risk of developing future MACEs [hazard ratio (HR) 1.78, 95% CI 1.33-2.37, P < 0.001], and MPO as a single variable predictor of MACE showed an area under the ROC curve of 0.67. After adjusting for traditional cardiac risk factors, creatinine clearance, B-type natriuretic peptide, and high-sensitivity C-reactive protein (hsCRP), increased MPO concentrations remained significantly associated with incident MACEs over the ensuing 3-year period (HR 1.71; 95% CI 1.27-2.30, P < 0.001). In patients with increased hsCRP, MPO ≤322 pmol/L was associated with lower event rates than observed with MPO >322 pmol/L.

CONCLUSIONS

Plasma MPO concentrations provide independent prognostic value for the prediction of long-term incident MACEs in a stable, medically managed patient population with coronary artery disease. In individuals with increased hsCRP concentrations, we observed lower risk of incident MACEs when concomitant MPO concentrations were low vs when MPO concentrations were high.

Lack of association between plasma myeloperoxidase levels and angiographic severity of coronary artery disease in patients with acute coronary syndrome

OBJECTIVE

To evaluate the association between plasma myeloperoxidase (MPO) levels and angiographic severity of coronary atherosclerotic lesions in patients with non-ST elevation acute coronary syndrome (ACS).

DESIGN AND METHODS

This cross-sectional study examined high-risk ACS patients who underwent coronary angiography within 72 h of the onset of symptoms by measuring their plasma MPO levels after sheath insertion. Gensini score was used to evaluate angiographic severity of coronary artery disease.

RESULTS

A total of 48 patients were included in the study. Median MPO levels and Gensini scores were 6.9 ng/mL (4.4-73.5 ng/mL) and 10 (0-87.5), respectively. Spearman's correlation coefficient did not show a significant association between MPO levels and Gensini scores (r (s) = 0.2; p = 0.177). There was no correlation between MPO and age, hypertension, diabetes, leukocyte count, troponin I, CK-MB ≥ 2 × ULN (upper limit of normal), TIMI risk score ≥ 4 and Gensini score in the multivariate analysis.

CONCLUSION

Our findings indicate that MPO expression is not associated with anatomical severity of coronary lesions in ACS.

Myeloperoxidase and C-reactive protein have combined utility for long-term prediction of cardiovascular mortality after coronary angiography

OBJECTIVES

We evaluated the relative and combined value of oxidative stress biomarkers for predicting cardiovascular mortality in patients undergoing selective coronary angiography.

BACKGROUND

Oxidative stress participates in all stages of cardiovascular disease, from lipoprotein modification to plaque rupture, and biomarkers of oxidative stress predict development of coronary artery disease (CAD). Oxidative stress biomarkers merit investigation for the value they may offer for long-term cardiovascular risk prediction.

METHODS

Myeloperoxidase (MPO), nitrotyrosine, oxidized low-density lipoprotein, and antioxidant capacity were measured in a prospective cohort of 885 selective coronary angiography patients followed up for >13 years for cardiovascular mortality.

RESULTS

MPO independently predicted CAD, and top tertile MPO levels predicted a 2.4-fold risk of cardiovascular mortality (95% confidence interval [CI]: 1.47 to 2.98), compared with patients with lowest tertile MPO levels. MPO also improved risk model discrimination and patient risk category classification. Elevations in multiple oxidative stress biomarkers predicted increased mortality risk; however, the strongest risk prediction was achieved by assessing MPO and C-reactive protein (CRP) together. Patients with either MPO or CRP elevated had 5.3-fold higher cardiovascular mortality risk (95% CI: 1.86 to 14.9), and patients with high levels of both MPO and CRP had a 4.3-fold risk compared with patients with only elevated marker (95% CI: 2.26 to 8.31). These results remained significant with adjustment for cardiovascular risk factors and baseline disease burden.

CONCLUSIONS

MPO accurately predicted cardiovascular mortality risk in coronary angiography patients. Considering MPO and CRP together may improve long-term risk assessment and CAD patient outcomes.

Myeloperoxidase: a useful biomarker for cardiovascular disease risk stratification?

BACKGROUND

Inflammation and oxidative stress are associated with atherosclerosis. Myeloperoxidase (MPO) is linked to both inflammation and oxidative stress by its location in leukocytes and its role in catalyzing the formation of oxidizing agents. Recent evidence suggests that MPO activity precipitates atherogenesis. Measurement of MPO in plasma may therefore contribute to cardiovascular disease (CVD) risk stratification.

CONTENT

Cross-sectional studies, case-control studies, and prospective-cohort studies investigating the relation between MPO and CVD have been evaluated. Differences in study populations, sample materials, sample handling, and assays were ascertained. Potential causal mechanisms linking MPO to accelerated atherosclerosis are discussed here. A majority of studies indicate that measurement of MPO in plasma was associated with improved CVD risk stratification above and beyond risk stratification results obtained with markers used in routine clinical practice. However, comparison of these epidemiological studies with regard to MPO and outcome is hampered because the reported MPO concentration depends on the assay method, sampling material, and preanalytical and analytical procedures. The link between MPO and CVD can, at least partly, be explained by MPO-dependent oxidation of LDL and HDL, subsequently leading to cholesterol accumulation in the arterial wall. Furthermore, MPO may reduce the bioavailability of nitric oxide, resulting in endothelial dysfunction. Finally, MPO destabilizes atherosclerotic plaques.

SUMMARY

Increasing evidence suggests that MPO is causally linked to atherosclerosis and its measurement may improve CVD risk estimation. Before MPO can be used in routine clinical practice, however, standardization of sampling and laboratory procedures is needed.