Myeloperoxidase acts as a profibrotic mediator of atrial fibrillation

The Role of Myeloperoxidase in Biomolecule Modification, Chronic Inflammation, and Disease

Significance: The release of myeloperoxidase (MPO) by activated leukocytes is critical in innate immune responses. MPO produces hypochlorous acid (HOCl) and other strong oxidants, which kill bacteria and other invading pathogens. However, MPO also drives the development of numerous chronic inflammatory pathologies, including atherosclerosis, neurodegenerative disease, lung disease, arthritis, cancer, and kidney disease, which are globally responsible for significant patient mortality and morbidity. Recent Advances: The development of imaging approaches to precisely identify the localization of MPO and the molecular targets of HOCl in vivo is an important advance, as typically the involvement of MPO in inflammatory disease has been inferred by its presence, together with the detection of biomarkers of HOCl, in biological fluids or diseased tissues. This will provide valuable information in regard to the cell types responsible for releasing MPO in vivo, together with new insight into potential therapeutic opportunities. Critical Issues: Although there is little doubt as to the value of MPO inhibition as a protective strategy to mitigate tissue damage during chronic inflammation in experimental models, the impact of long-term inhibition of MPO as a therapeutic strategy for human disease remains uncertain, in light of the potential effects on innate immunity. Future Directions: The development of more targeted MPO inhibitors or a treatment regimen designed to reduce MPO-associated host tissue damage without compromising pathogen killing by the innate immune system is therefore an important future direction. Similarly, a partial MPO inhibition strategy may be sufficient to maintain adequate bacterial activity while decreasing the propagation of inflammatory pathologies.

Suppression of experimental atrial fibrillation in a canine model of rapid atrial pacing by the phosphodiesterase 3 inhibitor cilostazol

OBJECTIVE

Atrial fibrillation (AF) represents the most common arrhythmia encountered in cardiology department. The purpose of this study was designed to investigate whether cilostazol, an oral phosphodiesterase 3 inhibitor (PDE3) could have protective effects on atrial remodeling in a canine model of AF and explore the potential molecular mechanisms.

METHODS

Dogs were randomly assigned to Sham, Paced, Paced + cilostazol group, 7 dogs in each group. In Sham group, pacemaker was instrumented but without pacing. Rapid atrial pacing (RAP) at 600 or 500 bpm/min was maintained in Paced group and Paced + cilo group for 2 h or 2 weeks in acute or chronic experiment, respectively. The Paced + cilo group of dogs were pretreated with cilostazol orally (10 mg·kg^-1·d^-1, cilo) for 1 h or 2 days prior RAP induction and served as treatment group. Atrial effective refractory periods (AERP) at different basic cycle lengths (BCLs), inducibility, and duration time of AF were measured after pacing for 2 h. The blood sample, echocardiography, histopathology, inflammation and oxidative stress makers, protein and mRNA expression levels of matrix metalloproteinase-2 (MMP-2) and MMP-9 were detected after 2 weeks pacing in each group.

RESULTS

Significant changes in electrophysiological parameters were observed in the acute RAP canine model, the AERPs shortened with increased inducibility and duration of AF, which was attenuated by cilostazol (P < 0.05). The serum inflammation makers as interleukin-8 (IL-8) and toll like receptor 4 (TLR 4) levels and oxidative stress indicators like xanthine oxidative (XO) and reactive oxygen species (ROS) in the Paced group was significantly higher than that in Sham group (P < 0.01), and was significantly reduced by cilostazol treatment (P < 0.01). The level of mean platelet volume (MPV) which is one of the platelet indices was significantly elevated in Paced group (P < 0.01). While after cilostazol treated for 2 weeks, the level of MPV was obviously decreased than Paced group (P < 0.01). Pathology and echocardiography studies showed that cilostazol can also prevent RAP induced cardiac fibrosis and structural remodeling. The MPV level has close correlations with IL-8, TLR4, XO and ROS (all P < 0.01). MMP-2 and MMP-9 expression were significantly increased in Paced group (all P < 0.01), which can be attenuated by cilostazol.

CONCLUSIONS

Cilostazol may have protective effects on RAP-induced atrial remodeling by anti-inflammatory, anti-oxidative stress action and regulate the extracellular collagen matrix in a canine model. Moreover, MPV level is associated with inflammation and oxidative stress response of RAP, which might be an important predictors of new-onset and recurrent AF.

The Role of Halogenative Stress in Atherogenic Modification of Low-Density Lipoproteins

This review discusses formation of reactive halogen species (RHS) catalyzed by myeloperoxidase (MPO), an enzyme mostly present in leukocytes. An imbalance between the RHS production and body's ability to remove or neutralize them leads to the development of halogenative stress. RHS reactions with proteins, lipids, carbohydrates, and antioxidants in the content of low-density lipoproteins (LDLs) of the human blood are described. MPO binds site-specifically to the LDL surface and modifies LDL properties and structural organization, which leads to the LDL conversion into proatherogenic forms captured by monocytes/macrophages, which causes accumulation of cholesterol and its esters in these cells and their transformation into foam cells, the basis of atherosclerotic plaques. The review describes the biomarkers of MPO enzymatic activity and halogenative stress, as well as the involvement of the latter in the development of atherosclerosis.

MFGE8 attenuates Ang-II-induced atrial fibrosis and vulnerability to atrial fibrillation through inhibition of TGF-β1/Smad2/3 pathway

Atrial fibrillation (AF) is characterized by potentiated growth of atrial fibroblasts and excessive deposition of the extracellular matrix. Atrial fibrosis has emerged as a hallmark of atrial structural remodeling linked to AF. Nonetheless, the specific mechanism underlying the progression of atrial fibrosis to AF is still largely unknown. MFGE8 (milk fat globule-EGF factor 8) is a soluble glycoprotein associated with many human diseases. Recently, a number of studies revealed that MFGE8 plays a crucial role in heart disease. Yet, MFGE8 regulation and function in the process of atrial fibrosis and vulnerability to AF remain unexplored. In this study, we found that the expression of MFGE8 was downregulated in the atriums of patients with AF compared with individuals without AF. In addition, the expression of MFGE8 was lower in atriums of angiotensin II (Ang-II)-stimulated rats as compared with the sham group. In vitro, silencing of MFGE8 by small interfering RNA significantly increased Ang-II-induced atrial fibrosis, whereas administration of recombinant human MFGE8 (rhMFGE8) attenuated the atrial fibrosis. Moreover, we found that the activated TGF-β1/Smad2/3 pathway after Ang-II treatment was significantly potentiated by the MFGE8 knockdown but inhibited by rhMFGE8 in vitro. Inhibition of integrin β3 which is the receptor for MFGE8, suppressed the TGF-β1/Smad2/3 activating effects of the MFGE8 knockdown in Ang-II-treated rat atrial fibroblasts. Finally, we administered rhMFGE8 to rats; it attenuated atrial fibrosis and remodeling and further reduced AF vulnerability induced by Ang-II, indicating that MFGE8 might have the potential both as a novel biomarker and as a therapeutic target in atrial fibrosis and AF.

Neutrophils, monocytes and other immune components in the equine endometrium: Friends or foes?

The innate and adaptive immune mechanisms are key components of regulation of reproductive physiological function and uterine disorders in equine uterus. The predominant immunological response in equine endometrium, characterized by an innate immune response, occurs under estrogens influence, in the follicular phase. Although, the increase in immune-related genes in equine endometrium during estrus has been suggested to play a role in uterine clearance after mating, immune cells and their product, i.e. cytokines play also mandatory role in the luteal development and maintenance, regression of equine corpus luteum, as well as in early pregnancy. Innate immune response is nonspecific and acts as the first line of defense against pathogens, foreign stimuli that include constituents of seminal fluid and local infections (endometritis). It has been recently established that a phagocytosis-independent mechanism to restrain bacteria, by means of neutrophil extracellular traps (NETs) formation, is involved in pathogenesis of in mare endometrial fibrosis (endometrosis). Moreover, persistent macrophages and mast cell activation could also have pro-fibrotic roles by secreting great amounts of pro-fibrotic factors and lead to fibrosis. This review will highlight the involvement of immune key components of the innate and adaptive immune system and their products in equine uterus and their contribution to reproductive physiological function and uterine disorders.

Fibrosis independent atrial fibrillation in older patients is driven by substrate leukocyte infiltration: diagnostic and prognostic implications to patients undergoing cardiac surgery

Background

The objectives of the study were to characterize and quantify cellular inflammation and structural remodeling of human atria and correlate findings with molecular markers of inflammation and patient surrogate outcome.

Methods

Voluntary participants undergoing heart surgery were enrolled in the study and blood samples were collected prior to surgery, and right atrium samples were harvested intraoperatively. Blood samples were analyzed by flow cytometry and complete blood counts. Atrial samples were divided for fixed fibrosis analysis, homogenized for cytokine analysis and digested for single cell suspension flow cytometry.

Results

A total of 18 patients were enrolled and samples assessed. Isolated cells from the atria revealed a CD45+ population of ~ 20%, confirming a large number of leukocytes. Further characterization revealed this population as 57% lymphocytes and 26% monocyte/macrophages (MoΦ), with the majority of the latter cells being classical (CD14++/CD16−). Interstitial fibrosis was present in 87% of samples and correlated significantly with patient age. Older patients (> 65) had significantly more atrial fibrosis and cellular inflammation. AFib patients had no distinguishing feature of atrial fibrosis and had significantly greater CD45+ MoΦ, increased expression of MMP9 and presented with a significant correlation in length of stay to CCL-2/MCP-1 and NLR (neutrophil-to-lymphocyte ratio).

Conclusion

Atrial fibrosis is correlated with age and not determinate to AFib. However, severity of atrial leukocyte infiltration and markers of matrix degradation are determinant to AFib. This also correlated with CCL2 (or MCP-1) and NLR-indicative of marked inflammation. These data show the potential importance of diagnostic and prognostic assessments that could inform clinical decision making in regard to the intensity of AFib patient management.

Pharmacological myeloperoxidase (MPO) inhibition in an obese/hypertensive mouse model attenuates obesity and liver damage, but not cardiac remodeling

Lifestyle factors are important drivers of chronic diseases, including cardiovascular syndromes, with low grade inflammation as a central player. Attenuating myeloperoxidase (MPO) activity, an inflammatory enzyme associated with obesity, hypertension and heart failure, could have protective effects on multiple organs. Herein, the effects of the novel oral available MPO inhibitor AZM198 were studied in an obese/hypertensive mouse model which displays a cardiac phenotype. Eight week old male C57BL6/J mice received 16 weeks of high fat diet (HFD) combined with angiotensin II (AngII) infusion during the last 4 weeks, with low fat diet and saline infusion as control. Treated animals showed therapeutic AZM198 levels (2.1 µM), corresponding to 95% MPO inhibition. AZM198 reduced elevated circulating MPO levels in HFD/AngII mice to normal values. Independent of food intake, bodyweight increase and fat accumulation were attenuated by AZM198, alongside with reduced visceral adipose tissue (VAT) inflammation and attenuated severity of nonalcoholic steatohepatitis. The HFD/AngII perturbation caused impaired cardiac relaxation and contraction, and increased cardiac hypertrophy and fibrosis. AZM198 treatment did, however, not improve these cardiac parameters. Thus, AZM198 had positive effects on the main lipid controlling tissues in the body, namely adipose tissue and liver. This did, however, not directly result in improved cardiac function.

A versatile imaging platform with fluorescence and CT imaging capabilities that detects myeloperoxidase activity and inflammation at different scales

Aberrant innate immune response drives the pathophysiology of many diseases. Myeloperoxidase (MPO) is a highly oxidative enzyme secreted by activated myeloid pro-inflammatory immune cells such as neutrophils and macrophages, and is a key mediator of the damaging innate immune response. Current technologies for detecting MPO activity in living organisms are sparse and suffer from any combination of low specificity, low tissue penetration, or low spatial resolution. We describe a versatile imaging platform to detect MPO activity using an activatable construct conjugated to a biotin moiety (MPO-activatable biotinylated sensor, MABS) that allows monitoring the innate immune response and its modulation at different scales and settings.

Methods:We designed and synthesized MABS that contains MPO-specific and biotin moieties, and validated its specificity and sensitivity combining with streptavidin-labeled fluorescent agent and gold nanoparticles imaging in vitro and in vivo in multiple mouse models of inflammation and infection, including Matrigel implant, dermatitis, cellulitis, cerebritis and complete Fraud's adjuvant (CFA)-induced inflammation.

Results: MABS MPO imaging non-invasively detected varying MPO concentrations, MPO inhibition, and MPO deficiency in vivo with high sensitivity and specificity. MABS can be used to obtain not only a fluorescence imaging agent, but also a CT imaging agent, conferring molecular activity information to a structural imaging modality. Importantly, using this method on tissue-sections, we found that MPO enzymatic activity does not always co-localize with MPO protein detected with conventional techniques (e.g., immunohistochemistry), underscoring the importance of monitoring enzymatic activity.

Conclusion:By choosing from different available secondary probes, MABS can be used to create systems suitable to investigate and image MPO activity at different scales and settings.

Key inflammatory mechanisms underlying heart failure

Inflammation plays a central role in the development of heart failure, especially in heart failure with preserved ejection fraction (HFpEF). Furthermore, the inflammatory response enables the induction of regenerative processes following acute myocardial injury. Recent studies in humans and animals have greatly advanced our understanding of the underlying mechanisms behind these adaptations. Importantly, inflammation can have both beneficial and detrimental effects, dependent on its extent, localization, and duration. Therefore, modulation of cardiac inflammation has been suggested as an attractive target for the treatment of heart failure, which has been investigated in numerous clinical trials. This review discusses key inflammatory mechanisms contributing to the pathogenesis of heart failure and their potential impact as therapeutic targets.

Reducing myeloperoxidase activity decreases inflammation and increases cellular protection in ischemic stroke

Myeloperoxidase (MPO) is a pro-inflammatory enzyme abundantly secreted by activated myeloid cells after stroke. We show that when MPO activity is either blocked by the specific inhibitor 4-aminobenzoic acid hydrazide (ABAH) in wildtype (WT) mice or congenitally absent (MPO-/-), there was decreased cell loss, including degenerating neurons and oligodendrocytes, in the ischemic brains compared to vehicle-treated WT mice after stroke. MPO inhibition also reduced the number of activated myeloid cells after ischemia. MPO inhibition increased cytoprotective heat shock protein 70 (Hsp70) by 70% and p-Akt by 60%, while decreased the apoptotic marker p53 level by 62%, compared to vehicle-treated mice after ischemia. Similarly, MPO inhibition increased the number of Hsp70+/NeuN+ cells after stroke by 60%. Notably, MPO inhibition significantly improved neurological outcome compared with the vehicle-treated group after stroke. We further found longer treatment periods resulted in larger reduction of infarct size and greater neurobehavioral improvement from MPO inhibition, even when given days after stroke. Therefore, MPO inhibition with ABAH or MPO deficiency creates a protective environment that decreased inflammatory cell recruitment and increased expression of survival factors to improve functional outcome. MPO inhibition may represent a promising therapeutic target for stroke therapy, possibly even days after stroke has occurred.

Asymmetric and Symmetric Dimethylarginine Predict Outcomes in Patients With Atrial Fibrillation: An ARISTOTLE Substudy

BACKGROUND

There is little mechanistic information on factors predisposing atrial fibrillation (AF) patients to thromboembolism or bleeding, but generation of nitric oxide (NO) might theoretically contribute to both.

OBJECTIVES

The authors tested the hypothesis that plasma levels of the methylated arginine derivatives asymmetric and symmetric dimethylarginine (ADMA/SDMA), which inhibit NO generation, might be associated with outcomes in AF.

METHODS

Plasma samples were obtained from 5,004 patients with AF at randomization to warfarin or apixaban in the ARISTOTLE (Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation) trial. ADMA and SDMA concentrations were measured by high-performance liquid chromatography. Relationships to clinical characteristics were evaluated by multivariable analyses. Associations with major outcomes, during a median of 1.9 years follow-up, were evaluated by adjusted Cox proportional hazards models.

RESULTS

Both ADMA and SDMA plasma concentrations at study entry increased significantly with patients' age, female sex, renal impairment, permanent AF, or congestive heart failure. ADMA and SDMA increased (p < 0.001) with both increased CHA₂DS₂-VASc and HAS-BLED scores, but decreased in the presence of diabetes. On multivariable analysis adjusting for established risk factors and treatment, tertile groups of ADMA concentrations were significantly associated with stroke/systemic embolism (p = 0.034), and death (p < 0.0001), whereas tertile groups of SDMA were associated with major bleeding and death (p < 0.001 for both). Incorporating ADMA and SDMA into CHA₂DS₂-VASc or HAS-BLED predictive models improved C-indices for those outcomes. Neither ADMA nor SDMA predicted differential responses to warfarin or apixaban.

CONCLUSIONS

In anticoagulated patients with AF, elevated ADMA levels are weakly associated with thromboembolic events, elevated SDMA levels with bleeding events and both are strongly associated with increased mortality. These findings suggest that disturbances of NO function modulate both thrombotic and hemorrhagic risk in anticoagulated patients with AF. (Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation [ARISTOTLE]; NCT00412984).

Cardioimmunology: the immune system in cardiac homeostasis and disease

The past few decades have generated growing recognition that the immune system makes an important contribution to cardiac development, composition and function. Immune cells infiltrate the heart at gestation and remain in the myocardium, where they participate in essential housekeeping functions throughout life. After myocardial infarction or in response to infection, large numbers of immune cells are recruited to the heart to remove dying tissue, scavenge pathogens and promote healing. Under some circumstances, immune cells can cause irreversible damage, contributing to heart failure. This Review focuses on the role of the immune system in the heart under both homeostatic and perturbed conditions.

Effects of Myeloperoxidase on Methicillin-Resistant Staphylococcus aureus-Colonized Burn Wounds in Rats

Objective: To achieve better therapeutic results in burn wound infections and to examine alternatives to antibiotics, we designed this study to elaborate the role of myeloperoxidase (MPO) on infected burn wounds in rats. Approach: We compared chemical properties as well as bacteriostatic ability of MPO in different concentrations with NeutroPhase. Subsequently, we applied MPO (MPO group), NeutroPhase (NeutroPhase group), NaCl+H₂O₂ (NaCl+H₂O₂ group), or NaCl (control group) on rat dorsal burn wounds inoculated with methicillin-resistant Staphylococcus aureus (MRSA). Their effects on MRSA-colonized wounds were evaluated by microscopy, histologic section, and Western blot. Results: MPO produced more H⁺ and HClO^-, leading to a more acidic environment. Moreover, MPO inhibited the growth of MRSA more intensely after 6 h of inoculation ex vivo. In vivo the open wound rate in the MPO group was significantly lower, while the contraction rate and epithelialization rate of MPO group were higher than that of the control group, NaCl+H₂O₂ group, and NeutroPhase group on day 20. The hematoxylin and eosin staining of MPO group showed better wound healing than other groups. More vascular endothelial growth factor (VEGF) was expressed in wound tissue of MPO group by Western blot. Innovation: This is the first study to use MPO for MRSA-colonized burn wound therapy. Conclusion: MPO displayed more effective bacteriostatic ability, possibly beneficial for MRSA-colonized wound healing.

Myeloperoxidase in atrial fibrillation: association with progression, origin and influence of renin-angiotensin system antagonists

BACKGROUND

Myeloperoxidase (MPO), secreted by neutrophils under inflammatory conditions, is elevated in atrial fibrillation (AF). MPO may be involved in atrial remodeling that underpins AF progression characterized by a switch from paroxysmal to persistent AF and the formation of low-voltage areas (LVA). MPO levels are modulated by renin-angiotensin system antagonists (RAS-A), commonly used to treat AF comorbidities, and are associated with reduced AF incidence, implicating a potential link.

OBJECTIVE

We investigated MPO levels in progressing AF in peripheral and left atrial (LA) blood and analyzed a potential effect of RAS-A.

METHODS

Samples of AF patients were collected from the femoral vein and the LA during catheter ablation (n = 121) and at follow-up (n = 23). No-AF probands (n = 37) served as controls. MPO was determined using commercial ELISA.

RESULTS

MPO levels were significantly increased in AF patients compared to controls (median, 27.7 ng/ml (IQR 14.3-66.6) versus 12.6 (IQR 9.9-17.7), p < 0.001), without differences between clinical AF progression phenotypes. MPO concentration was tenfold higher in LA than periphery (279.2 ng/ml (IQR 202.2-342.9) versus 27.7 ng/ml (IQR 14.3-65.9), p < 0.001). MPO remained increased at midterm follow-up irrespective of rhythm outcome. RAS-A was associated with significantly lower peripheral (22.2 ng/ml (IQR 12.7-48.2) versus 37.1 ng/ml (IQR 18.2-85.2), p < 0.05) MPO levels in AF patients.

CONCLUSION

The pro-fibrotic enzyme MPO is generally elevated in AF patients irrespective of AF type, the presence of LVA or midterm rhythm outcome. Our data suggest that MPO may directly originate from the LA. RAS-A decrease peripheral MPO levels in AF patients.

An activatable PET imaging radioprobe is a dynamic reporter of myeloperoxidase activity in vivo

Myeloperoxidase (MPO) is a critical proinflammatory enzyme implicated in cardiovascular, neurological, and rheumatological diseases. Emerging therapies targeting inflammation have raised interest in tracking MPO activity in patients. We describe 18F-MAPP, an activatable MPO activity radioprobe for positron emission tomography (PET) imaging. The activated radioprobe binds to proteins and accumulates at sites of MPO activity. The radioprobe 18F-MAPP has a short blood half-life, remains stable in plasma, does not demonstrate cytotoxicity, and crosses the intact blood-brain barrier. The 18F-MAPP imaging detected sites of elevated MPO activity in living mice embedded with human MPO and in mice induced with chemical inflammation or myocardial infarction. The 18F-MAPP PET imaging noninvasively differentiated varying amounts of MPO activity, competitive inhibition, and MPO deficiency in living animals, confirming specificity and showing that the radioprobe can quantify changes in in vivo MPO activity. The radiosynthesis has been optimized and automated, an important step in translation. These data indicate that 18F-MAPP is a promising translational candidate to noninvasively monitor MPO activity and inflammation in patients.

B-type natriuretic peptide enhances fibrotic effects via matrix metalloproteinase-2 expression in the mouse atrium in vivo and in human atrial myofibroblasts in vitro

B-type natriuretic peptide (BNP) was approved by the US Food and Drug Administration in 2001 for the treatment of heart failure. However, the effects of BNP in clinical applications are controversial and uncertain. Recently, study indicated that high BNP levels are associated with an increased risk of developing atrial fibrillation. In this study, we investigated the direct effects of BNP on TNF-α-induced atrial fibrosis mice, as well as its effects on human atrial myofibroblasts. We found that injecting TNF-α-induced mice with recombinant human BNP enhanced atrial fibrosis via matrix metalloproteinase-2 (MMP-2) expression and collagen accumulation. Furthermore, we found that BNP stimulated MMP-2 expression in human atrial myofibroblasts. Treatment of human atrial myofibroblasts with cycloheximide had no effect on this outcome; however, treatment of cells with MG132 enhanced BNP-induced MMP-2 expression, indicating that protein stability and inhibition of proteasome-mediated protein degradation pathways are potentially involved. Inhibition of SIRT1 significantly decreased BNP-induced MMP-2 expression. Additionally, confocal and coimmunoprecipitation data indicated that BNP-regulated MMP-2 expression are likely to be mediated through direct interaction with SIRT1, which is thought to deacetylate MMP-2 and to increase its protein stability in human atrial myofibroblasts. Finally, we confirmed that SIRT1 is expressed and cytoplasmically redistributed as well as colocalized with MMP-2 in mouse fibrotic atrial tissue. We suggest a possible fibrosis-promoting role of BNP in the atrium, although the antifibrotic properties of BNP in the ventricle have been reported in previous studies, and that the coordination between MMP-2 and SIRT1 in BNP-induced atrial myofibroblasts participates in atrial fibrosis.

Heart Inflammation: Immune Cell Roles and Roads to the Heart

Heart failure (HF) has been traditionally viewed as a disease of the cardiac muscle associated with systemic inflammation. Burgeoning evidence implicates immune effector mechanisms that include immune cell activation and trafficking to the heart. Immune cell infiltration in the myocardium can have adverse effects in the heart and contribute to the pathogenesis of HF. Both innate and adaptive immunity operate sequentially, and the specificity of these responses depends on the initial trigger sensed by the heart. Although the role of the immune system in the initial inflammatory response to infection and injury is well studied, what sets the trajectory to HF from different etiologies and the role of immunity once HF has been established is less understood. Herein, we review experimental and clinical knowledge of cardiac inflammation induced by different triggers that often result in HF from different etiologies. We focus on the mechanisms of immune cell activation systemically and on the pathways immune cells use to traffic to the heart.

Biomarkers in Atrial Fibrillation and Heart Failure

Atrial fibrillation (AF) is the most common sustained arrhythmia encountered in clinical practice and an important contributor to cardiovascular morbidity and mortality. Although the exact mechanisms behind AF are not completely elucidated, the underlying pathophysiological changes have been well described. Predisposal factors for AF include the older age, the increased left atrial size, the decreased left atrial function, the presence of heart failure and left ventricular systolic dysfunction and the presence of coronary heart disease or pulmonary or mitral valve disease. In addition to these factors, emerging evidence demonstrate that myocardial strain, fibrosis and inflammation, are associated with AF as well as the pathogenesis of the arrhythmia. The natruretic peptide system including Atrial Natriuretic Peptide (ANP), Brain Natriuretic Peptide (BNP) and C-type Natriuretic Peptide (CNP) is indicative of the level of myocardial strain which may predispose to AF. As a result, the aforementioned peptides are increased in AF patients. The levels of myocardial fibrosis biomarkers, such as ST2 and Galectin-3, are elevated suggesting atrial structural abnormalities, while the increased levels of CRP and Interleukin-6 supplement the inflammatory profile of AF patients. Emerging data for the aforementioned biomarkers are discussed in the present review.

Integrative analysis of transcriptome-wide association study data and mRNA expression profiles identified candidate genes and pathways associated with atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia characterized by extensive structural, contractile and electrophysiological remodeling. The genetic basis of AF remained elusive until now. Transcriptome-wide association study (TWAS) was conducted by FUSION tool using gene expression weights of 7 tissues combined with a large-scale genome-wide association study (GWAS) dataset of AF, totally involving 8180 AF cases and 28,612 controls. Significant genes identified by TWAS were then subjected to gene ontology (GO) and pathway enrichment analysis. The genome-wide mRNA gene expression profiling of AF was compared with the results of TWAS to detect common genes shared by TWAS and mRNA expression profiling of AF. TWAS detected a group of candidate genes with P_TWAS values < 0.05 across the seven tissues for AF, such as CMAH (P_TWAS = 3.15 × 10^-25 for whole blood), INCENP (P_TWAS = 1.77 × 10^-22 for artery aorta), CMAHP (P_TWAS = 4.57 × 10^-20 for artery aorta). Pathway enrichment analysis identified multiple candidate pathways, such as protein K48-linked ubiquitination (P value = 0.0124), positive regulation of leukocyte chemotaxis (P value = 0.0046) and fatty acid degradation (P value = 0.0295). Further comparing the GO results of TWAS and mRNA expression profiling, 2 common GO terms were identified, including actin binding (P_TWAS = 0.0446, P_mRNA = 7.00 × 10^-4) and extracellular matrix (P_TWAS = 0.0037, P_mRNA = 3.00 × 10^-6). We detected multiple novel candidate genes, GO terms and pathways for AF, providing novel clues for understanding the genetic mechanism of AF.

Immunopathogenesis and biomarkers of recurrent atrial fibrillation following ablation therapy in patients with preexisting atrial fibrillation

INTRODUCTION

Recurrent atrial fibrillation (RAF) following ablation therapy occurs in about 50% of patients. The pathogenesis of RAF is unknown, but is believed to be driven by atrial remodeling in the setting of background inflammation. Structural, electrophysiological and mechanical remodeling has been associated with atrial fibrillation (AF). Inflammation and fibrotic remodeling are the major factors perpetuating AF, as mediators released from the atrial tissues and cardiomyocytes due to mechanical and surgical injury could initiate the inflammatory process. In this article, we have critically reviewed the key mediators that may serve as potential biomarkers to predict RAF. Areas covered: Damage associated molecular patterns, heat shock proteins, inflammatory cytokines, non-inflammatory markers, markers of inflammatory cell activity, and markers of collagen deposition and metabolism are evaluated as potential biomarkers with molecular treatment options in RAF. Expert commentary: Establishing biomarkers to predict RAF could be useful in reducing morbidity and mortality. Investigations into the role of DAMPs participating in a sterile immune response may provide greater insight into the pathogenesis of RAF. Markers evaluating immune cell activity, collagen deposition, and levels of heat shock proteins show the greatest promise as potential biomarkers to predict RAF and develop novel therapies.

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.

Safety, tolerability, pharmacokinetics and effect on serum uric acid of the myeloperoxidase inhibitor AZD4831 in a randomized, placebo-controlled, phase I study in healthy volunteers

Aims

Myeloperoxidase activity can contribute to impaired vascular endothelial function and fibrosis in chronic inflammation‐related cardiovascular disease. Here, we investigated the safety, tolerability and pharmacokinetics of the myeloperoxidase inhibitor, AZD4831.

Methods

In this randomized, single‐blind, placebo‐controlled, phase I, first‐in‐human study, healthy men in five sequential cohorts were randomized 3:1 to receive a single oral dose of AZD4831 (5, 15, 45, 135 or 405 mg) or placebo, after overnight fasting. After at least 7 days' washout, one cohort additionally received AZD4831 45 mg after a high‐calorie meal.

Results

Forty men participated in the study (eight per cohort: AZD4831, n = 6; placebo, n = 2). AZD4831 distributed rapidly into plasma, with a half‐life of 38.2–50.0 hours. The area under the plasma concentration–time curve (AUC) increased proportionally with dose (AUC_0–∝ slope estimate 1.060; 95% confidence interval [CI] 0.9943, 1.127). Increases in maximum plasma concentration were slightly more than dose proportional (slope estimate 1.201; 95% CI 1.071, 1.332). Food intake reduced AZD4831 absorption rate but did not substantially affect overall exposure or plasma half‐life (n = 4). Serum uric acid concentrations decreased by 71.77 (95% CI 29.15, 114.39) and 84.42 (58.90, 109.94) μmol L⁻¹ with AZD4831 135 mg and 405 mg, respectively. Maculopapular rash (moderate intensity) occurred in 4/30 participants receiving AZD4831 (13.3%). No other safety concerns were identified.

Conclusions

AZD4831 was generally well tolerated, rapidly absorbed, had a long plasma half‐life and lowered uric acid concentrations after single oral doses in healthy men. These findings support the further clinical development of AZD4831.

Treatment with mononuclear cell populations improves post-infarction cardiac function but does not reduce arrhythmia susceptibility

Background

Clinical and experimental data give evidence that transplantation of stem and progenitor cells in myocardial infarction could be beneficial, although the underlying mechanism has remained elusive. Ventricular tachyarrhythmia is the most frequent and potentially lethal complication of myocardial infarction, but the impact of mono nuclear cells on the incidence of ventricular arrhythmia is still not clear.

Objective

We aimed to characterize the influence of splenic mononuclear cell populations on ventricular arrhythmia after myocardial infarction.

Methods

We assessed electrical vulnerability in vivo in mice with left ventricular cryoinfarction 14 days after injury and intramyocardial injection of specific subpopulations of mononuclear cells (MNCs) (CD11b-positive cells, Sca-1-positive cells, early endothelial progenitor cells (eEPCs)). As positive control group we used embryonic cardiomyocytes (eCMs). Epicardial mapping was performed for analysing conduction velocities in the border zone. Left ventricular function was quantified by echocardiography and left heart catheterization.

Results

In vivo pacing protocols induced ventricular tachycardia (VT) in 30% of non-infarcted mice. In contrast, monomorphic or polymorphic VT could be evoked in 94% of infarcted and vehicle-injected mice (p<0.01). Only transplantation of eCMs prevented post-infarction VT and improved conduction velocities in the border zone in accordance to increased expression of connexin 43. Cryoinfarction resulted in a broad aggravation of left ventricular function. All transplanted cell types augmented left ventricular function to a similar extent.

Conclusions

Transplantation of different MNC populations after myocardial infarction improves left ventricular function similar to effects of eCMs. Prevention of inducible ventricular arrhythmia is only seen after transplantation of eCMs.

Increase in white blood cell count is associated with the development of atrial fibrillation after an acute coronary syndrome

BACKGROUND

Evidence linking an elevated white blood cell count (WBCC), a marker of inflammation, to the development of atrial fibrillation (AF) after an acute coronary syndrome (ACS) is limited. We examined the association between WBCC at hospital admission, and changes in WBCC during hospitalization, with the development of new-onset AF during hospitalization for an ACS.

METHODS

Development of AF was based on typical ECG changes in a systematic review of hospital medical records. Increase in WBCC was calculated as the difference between maximal WBCC during hospitalization and WBCC at hospital admission. Multiple logistic regression analysis was used to adjust for several potentially confounding demographic and clinical variables in examining the association between WBCC, and changes over time therein, with the occurrence of AF.

RESULTS

The median age of study patients (n = 1325) was 60 years, 31.8% were women, and 80.1% were non-Hispanic whites. AF developed in 7.3% of patients with an ACS. Patients who developed AF, as compared with those who did not, had a similar WBCC at admission, but a greater increase in WBCC during hospitalization (6.0 × 10⁹ cell/L vs. 2.7 × 10⁹ cell/L, p < 0.001). After adjusting for several potentially confounding factors, an increase in WBCC was associated with the development of AF. This association was observed in patients with different ACS subtypes, types of treatment received, and according to time of acute symptom onset.

CONCLUSION

Increase in the WBCC during hospitalization for an ACS should be further studied as a potentially simple predictor for new-onset AF in these patients.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Arrhythmogenic Substrates for Atrial Fibrillation in Obesity

Global obesity rates have nearly tripled since 1975. This obesity rate increase is mirrored by increases in atrial fibrillation (AF) that now impacts nearly 10% of Americans over the age of 65. Numerous epidemiologic studies have linked incidence of AF and obesity and other obesity-related diseases, including hypertension and diabetes. Due to the wealth of epidemiologic data linking AF with obesity-related disease, mechanisms of AF pathogenesis in the context of obesity are an area of ongoing investigation. However, progress has been somewhat slowed by the complex phenotype of obesity; separating the effects of obesity from those of related sequelae is problematic. While the initiation of pathogenic pathways leading to AF varies with disease (including increased glycosylation in diabetes, increased renin angiotensin aldosterone system activation in hypertension, atrial ischemia in coronary artery disease, and sleep apnea) the pathogenesis of AF is united by shared mediators of altered conduction in the atria. We suggest focusing on these downstream mediators of AF in obesity is likely to yield more broadly applicable data. In the context of obesity, AF is driven by the interrelated processes of inflammation, atrial remodeling, and oxidative stress. Obesity is characterized by a constant low-grade inflammation that leads to increased expression of pro-inflammatory cytokines. These cytokines contribute to changes in cardiomyocyte excitability. Atrial structural remodeling, including fibrosis, enlargement, and fatty infiltration is a prominent feature of AF and contributes to the altered conduction. Finally, obesity impacts oxidative stress. Within the cardiomyocyte, oxidative stress is increased through both increased production of reactive oxygen species and by downregulation of scavenging enzymes. This increased oxidative stress modulates of cardiomyocyte excitability, increasing susceptibility to AF. Although the initiating insults vary, inflammation, atrial remodeling, and oxidative stress are conserved mechanisms in the pathophysiology of AF in the obese patients. In this review, we highlight mechanisms that have been shown to be relevant in the pathogenesis of AF across obesity-related disease.

Risk of Malignant Cancer Among Women With New-Onset Atrial Fibrillation

IMPORTANCE

A substantial proportion of patients with atrial fibrillation (AF) die of noncardiovascular causes, and recent studies suggest a link between AF and cancer.

OBJECTIVE

To evaluate the associations between AF and cancer in a large, long-term prospective cohort study.

DESIGN, SETTING, AND PARTICIPANTS

In this cohort study, a total of 34 691 women 45 years or older and free of AF, cardiovascular disease, and cancer at baseline were prospectively followed up between 1993 and 2013, for incident AF and malignant cancer within the Women's Health Study, a randomized clinical trial of aspirin and vitamin E for the prevention of cardiovascular disease and cancer. Cox proportional hazards models using time-updated covariates were constructed to assess the association of new-onset AF with subsequent cancer and to adjust for potential confounders. Data analysis was performed from December 2014 to May 2015.

EXPOSURE

New-onset AF.

MAIN OUTCOMES AND MEASURES

Incident malignant cancer confirmed by an end point committee.

RESULTS

During a median follow-up of 19.1 years of 34 691 study participants (interquartile range [IQR], 17.6-19.7 years), new-onset AF and malignant cancer were confirmed among 1467 (4.2%) and 5130 (14.8%) participants, respectively. Median age at baseline among participants with new-onset AF and new-onset cancer during follow-up was 58 years (IQR, 52-64 years) and 55 years (IQR, 50-61 years), respectively. Atrial fibrillation was a significant risk factor for incident cancer in age-adjusted (hazard ratio [HR], 1.58; 95% CI, 1.34-1.87; P < .001) and multivariable-adjusted (HR, 1.48; 95% CI, 1.25-1.75; P < .001) models. The relative risk of cancer was highest in the first 3 months after new-onset AF (HR, 3.54; 95% CI, 2.05-6.10; P < .001) but remained significant beyond 1 year after new-onset AF (adjusted HR, 1.42; 95% CI, 1.18-1.71; P < .001), and a trend toward an increased cancer mortality was observed (adjusted HR, 1.32; 95% CI, 0.98-1.79; P = .07). In contrast, among women with new-onset cancer, the relative risk of AF was increased only within the first 3 months (HR, 4.67; 95% CI, 2.85-7.64; P < .001) but not thereafter (HR, 1.15; 95% CI, 0.95-1.39; P = .15).

CONCLUSIONS AND RELEVANCE

In this large, initially healthy cohort, women with new-onset AF had an elevated cancer risk beyond 1 year of AF diagnosis. Shared risk factors and/or common systemic disease processes might underlie this association.

Role of inflammatory signaling in atrial fibrillation

Atrial fibrillation (AF), the most prevalent arrhythmia, is often associated with enhanced inflammatory response. Emerging evidence points to a causal role of inflammatory signaling pathways in the evolution of atrial electrical, calcium handling and structural remodeling, which create the substrate of AF development. In this review, we discuss the clinical evidence supporting the association between inflammatory indices and AF development, the molecular and cellular mechanisms of AF, which appear to involve multiple canonical inflammatory pathways, and the potential of anti-inflammatory therapeutic approaches in AF prevention/treatment.

Cardiac magnetic resonance using late gadolinium enhancement and atrial T1 mapping predicts poor outcome in patients with atrial fibrillation after catheter ablation therapy

To determine the pre-procedural value of different fibrotic biomarkers and comprehensive cardiac magnetic resonance (CMR) for the prediction of poor response to ablation therapy in patients with atrial fibrillation (AF). Left atrial (LA) late gadolinium enhancement (LGE) and native LA T1 relaxation times were assessed using CMR. Plasma levels of relaxin, myeloperoxidase and serum levels of matrix metalloproteinase (MMP)-mediated cardiac specific titin fragmentation and MMP-mediated type IV collagen degradation were obtained. Poor outcome was defined by the recurrence of AF during 1-year follow-up. 61 patients were included in final analysis. Twenty (32.8%) patients had recurrence of AF. Patients with a recurrence of AF had a higher percentage of LA LGE (26.7 ± 12.5% vs. 17.0 ± 7.7%; P < 0.001), higher LA T1 relaxation times (856.7 ± 112.2 ms vs. 746.8 ± 91.0 ms; P < 0.001) and higher plasma levels of relaxin (0.69 ± 1.34 pg/ml vs. 0.37 ± 0.88 pg/ml; P = 0.035). In the multivariate Cox regression analysis, poor ablation outcome was best predicted by advanced LGE stage (hazard ratio (HR):5.487; P = 0.001) and T1 relaxation times (HR:1.007; P = 0.001). Pre-procedural CMR is a valuable tool for prediction of poor response to catheter ablation therapy in patients with AF. It offers various imaging techniques for outcome prediction and might be valuable for a better patient selection prior to ablation therapy.

Oxidative stress and atrial fibrillation: an update

Atrial remodelling involves electrophysiological and structural abnormalities that promote the development and perpetuation of atrial fibrillation. Experimental and clinical data indicate that oxidative stress is implicated in the pathophysiology of atrial remodelling. The mechanistic links between atrial remodelling and oxidative stress are complex with several underlying diseases and conditions may affect these pathways. Therefore, the development of antioxidant interventions in this setting remains difficult. Besides classical antioxidant compounds, several agents with pleiotropic effects, including anti-inflammatory and antioxidant, have been tested in experimental and clinical settings with variable results. Strategies applying conventional antioxidants in specific situations such as postoperative atrial fibrillation show beneficial effects, especially the two-step regimen of antioxidants combination. Of note, there are limited data on the development of strategies that target specific sources of reactive oxygen species implicated in atrial remodelling. Lifestyle, diet, and risk factors modification is a complementary promising approach. This updated review provides a concise and critical overview of all available data regarding oxidative stress and its modulation in atrial fibrillation. Future directions on this exciting field are also discussed.

Inflammation and atrial fibrillation: A comprehensive review

Atrial fibrillation (AF) has different underlying substrates. Atrial remodeling involves electrophysiological and structural abnormalities that promote the development and perpetuation of AF. Experimental and clinical data indicate that inflammation is implicated in the pathophysiology of atrial remodeling. The mechanistic links between atrial remodeling and inflammation are complex while diverse underlying diseases and conditions may affect these pathways. Inflammatory markers have also been associated with AF development, recurrence, perpetuation, total AF burden as well as with thromboembolic complications. The development of specific anti-inflammatory interventions in this setting seems to be challenging and complicated. Several agents with pleiotropic properties, including anti-inflammatory, have been tested in experimental and clinical settings with variable results. This updated review provides a concise overview of all available data regarding the role of inflammation in AF including the predictive role of inflammatory markers. Also, current knowledge and future directions on anti-inflammatory strategies are critically discussed.

Myeloperoxidase aggravates pulmonary arterial hypertension by activation of vascular Rho-kinase

Pulmonary arterial hypertension (PAH) remains a disease with limited therapeutic options and dismal prognosis. Despite its etiologic heterogeneity, the underlying unifying pathophysiology is characterized by increased vascular tone and adverse remodeling of the pulmonary circulation. Myeloperoxidase (MPO), an enzyme abundantly expressed in neutrophils, has potent vasoconstrictive and profibrotic properties, thus qualifying as a potential contributor to this disease. Here, we sought to investigate whether MPO is causally linked to the pathophysiology of PAH. Investigation of 2 independent clinical cohorts revealed that MPO plasma levels were elevated in subjects with PAH and predicted adverse outcome. Experimental analyses showed that, upon hypoxia, right ventricular pressure was less increased in Mpo-/- than in WT mice. The hypoxia-induced activation of the Rho-kinase pathway, a critical subcellular signaling pathway yielding vasoconstriction and structural vascular remodeling, was blunted in Mpo-/- mice. Mice subjected to i.v. infusion of MPO revealed activation of Rho-kinase and increased right ventricular pressure, which was prevented by coinfusion of the Rho-kinase inhibitor Y-27632. In the Sugen5416/hypoxia rat model, PAH was attenuated by the MPO inhibitor AZM198. The current data demonstrate a tight mechanistic link between MPO, the activation of Rho-kinase, and adverse pulmonary vascular function, thus pointing toward a potentially novel avenue of treatment.

Impact of Intracardiac Neurons on Cardiac Electrophysiology and Arrhythmogenesis in an Ex Vivo Langendorff System

Since its invention in the late 19^th century, the Langendorff ex vivo heart perfusion system continues to be a relevant tool for studying a broad spectrum of physiological, biochemical, morphological, and pharmacological parameters in centrally denervated hearts. Here, we describe a setup for the modulation of the intracardiac autonomic nervous system and the assessment of its influence on basic electrophysiology, arrhythmogenesis, and cyclic adenosine monophosphate (cAMP) dynamics. The intracardiac autonomic nervous system is modulated by the mechanical dissection of atrial fat pads-in which murine ganglia are located mainly-or by the usage of global as well as targeted pharmacological interventions. An octapolar electrophysiological catheter is introduced into the right atrium and the right ventricle, and epicardial-placed multi-electrode arrays (MEA) for high-resolution mapping are used to determine cardiac electrophysiology and arrhythmogenesis. Förster resonance energy transfer (FRET) imaging is performed for the real-time monitoring of cAMP levels in different cardiac regions. Neuromorphology is studied by means of antibody-based staining of whole hearts using neuronal markers to guide the identification and modulation of specific targets of the intracardiac autonomic nervous system in the performed studies. The ex vivo Langendorff setup allows for a high number of reproducible experiments in a short time. Nevertheless, the partly open nature of the setup (e.g., during MEA measurements) makes constant temperature control difficult and should be kept to a minimum. This described method makes it possible to analyze and modulate the intracardiac autonomic nervous system in decentralized hearts.

MiR-146a Regulates Neutrophil Extracellular Trap Formation That Predicts Adverse Cardiovascular Events in Patients With Atrial Fibrillation

OBJECTIVE

Atrial fibrillation (AF) patients experience adverse cardiovascular events (ACEs) despite anticoagulant therapy. We reported that rs2431697 of miR-146a, a negative regulator of inflammation, predicts ACEs in patients with AF. The relationship between neutrophil extracellular traps and thrombogenesis is known. Thus, our aim was to evaluate the role of neutrophil extracellular trap compounds as prognostic markers of ACEs in AF and to study whether miR-146a affects NETosis.

APPROACH AND RESULTS

We included 336 steadily anticoagulated AF patients with a median follow-up of 7.9 years (interquartile range, 7.3-8.1) and 127 healthy subjects. The reviewed ACEs included stroke (ischemic/embolic), acute coronary syndrome, acute heart failure, and global or vascular death. We quantified cell-free DNA and NE (neutrophil elastase) at diagnosis. Rs2431697 was genotyped. Neutrophils from human and mice were seeded to analyze shed cell-free DNA and H3cit (citrullinated histone 3) after activation. In human plasmas, higher NE levels (>55.29 ng/mL), but not cell-free DNA, were independently associated with higher risk of all-cause mortality (hazard ratio, 2.24; 95% CI, 1.36-3.68), cardiovascular mortality (hazard ratio, 4.77; 95% CI, 1.11-20.47), and composite cardiovascular events (hazard ratio, 1.84; 95% CI, 1.01-3.76). In patients, NE levels were associated with rs2431697 (TT: 51.82±2.73 versus CC: 40.01±3.05 ng/mL; P=0.040). In vitro, both human (TT for rs2431697) and miR-146a^-/- mice neutrophils yielded higher levels of cell-free DNA and H3cit than CC or wild-type cells, respectively.

CONCLUSIONS

NE activity can provide new ACE prognostic information in AF patients. These findings provide evidence of a potential role of miR-146a in neutrophil extracellular trap generation and cardiovascular risk in AF.

Constituents of neutrophil extracellular traps induce in vitro collagen formation in mare endometrium

Neutrophil extracellular traps (NETs) are DNA complexes carrying nuclear and cytoplasmic proteins, such as elastase (ELA), cathepsin-G (CAT) and myeloperoxidase (MPO). Mare endometrosis is a chronic degenerative process characterized by excessive collagen in endometrium. While NETs fight bacteria that cause endometritis, they may trigger endometrial fibrogenesis. The aim was to evaluate the in vitro effect of some NETs components on mare endometrial fibrogenesis and determine its relationship with histopathology or estrous cycle. Endometrial explants were incubated with NETs components (ELA, CAT, MPO or oxytocin). Collagen type I (COL1) protein and type I and III (COL3) gene transcription were evaluated in follicular and mid-luteal phases endometria (Kenney and Doig type I/IIA and IIB/III). Increased COL1 occurred with all NETs proteins, although endometrial response to each NETs protease depended on estrous cycle and/or endometrial category. Since ELA enhanced COL1 production, NETs persistence might be linked to endometrosis. Estrous cycle influenced COL1 protein concentration and COL3 transcripts, suggesting that follicular phase may favor endometrial collagen production. However, luteal phase endometria with moderate or severe lesions may be also susceptible to fibrotic effects of NETs constituents. These data propose that NETs involvement in chronic endometritis in mares may act as putative endometrial fibrogenic mediators.

Myeloperoxidase: Its role for host defense, inflammation, and neutrophil function

Myeloperoxidase (MPO) is a heme-containing peroxidase expressed mainly in neutrophils and to a lesser degree in monocytes. In the presence of hydrogen peroxide and halides, MPO catalyzes the formation of reactive oxygen intermediates, including hypochlorous acid (HOCl). The MPO/HOCl system plays an important role in microbial killing by neutrophils. In addition, MPO has been demonstrated to be a local mediator of tissue damage and the resulting inflammation in various inflammatory diseases. These findings have implicated MPO as an important therapeutic target in the treatment of inflammatory conditions. In contrast to its injurious effects at sites of inflammation, recent studies using animal models of various inflammatory diseases have demonstrated that MPO deficiency results in the exaggeration of inflammatory response, and that it affects neutrophil functions including cytokine production. Given these diverse effects, a growing interest has emerged in the role of this well-studied enzyme in health and disease.

A highly sensitive and rapidly responding fluorescent probe based on a rhodol fluorophore for imaging endogenous hypochlorite in living mice

Hypochlorous (HOCl) acid is generated as a defense tool in the immune system and plays a vital role in killing a wide range of pathogens. There is therefore great interest in developing fluorescent probes that can endogenously respond to the change in concentration of HOCl in vivo. To address this challenge, we here present a rapidly responding fluorescent probe RO610 to image endogenous HOCl in living mice. The development of RO610 was based on a novel water-soluble and pH-independent fluorescent xanthene dye, 2'-formylrhodol ROA, which exhibits highly selective and sensitive responses to HOCl/ClO^- over other reactive species. Moreover, adding a little more than 5 equiv. of ClO^- to the solution of RO610 resulted in a clearly observable fluorescence enhancement (48-fold) within 30 s. Based on these properties, RO610 was used to detect ClO^- in A549 cells without interference by other oxidants. It was applied for the imaging of endogenous HOCl in living nude mice with satisfactory results.

Development of nonfibrotic left ventricular hypertrophy in an ANG II-induced chronic ovine hypertension model

Hypertension is a major risk factor for many cardiovascular diseases and leads to subsequent concomitant pathologies such as left ventricular hypertrophy (LVH). Translational approaches using large animals get more important as they allow the use of standard clinical procedures in an experimental setting. Therefore, the aim of this study was to establish a minimally invasive ovine hypertension model using chronic angiotensin II (ANG II) treatment and to characterize its effects on cardiac remodeling after 8 weeks. Sheep were implanted with osmotic minipumps filled with either vehicle control (n = 7) or ANG II (n = 9) for 8 weeks. Mean arterial blood pressure in the ANG II‐treated group increased from 87.4 ± 5.3 to 111.8 ± 6.9 mmHg (P = 0.00013). Cardiovascular magnetic resonance imaging showed an increase in left ventricular mass from 112 ± 12.6 g to 131 ± 18.7 g after 7 weeks (P = 0.0017). This was confirmed by postmortem measurement of left ventricular wall thickness which was higher in ANG II‐treated animals compared to the control group (18 ± 4 mm vs. 13 ± 2 mm, respectively, P = 0.002). However, ANG II‐treated sheep did not reveal any signs of fibrosis or inflammatory infiltrates as defined by picrosirius red and H&E staining on myocardial full thickness paraffin sections of both atria and ventricles. Measurements of plasma high‐sensitivity C‐reactive protein and urinary 8‐iso‐prostaglandin F_2α were inconspicuous in all animals. Furthermore, multielectrode surface mapping of the heart did not show any differences in epicardial conduction velocity and heterogeneity. These data demonstrate that chronic ANG II treatment using osmotic minipumps presents a reliable, minimally invasive approach to establish hypertension and nonfibrotic LVH in sheep.

Increased Mobilization of CD45+CD34+VLA-4+ Cells in Acute Viral Myocarditis Induced by Coxsackievirus B3

OBJECTIVES

Bone marrow-derived cells (BMCs) have recently been identified to play a vital role in repairing damaged myocardium; however, it is not known whether or not mobilization of BMCs is involved in the pathogenesis of acute viral myocarditis (VMC). Thus, we analyzed the expression of CD45+CD34+VLA-4+ cells and vascular cell adhesion protein-1 (VCAM-1) in a murine model of acute VMC.

METHODS

Male BALB/c mice were intraperitoneally infected with coxsackievirus B3 to establish acute VMC. The frequency of CD45+CD34+VLA-4+ cells in the heart, peripheral blood, and bone marrow was examined by flow cytometry 3, 7, 14, and 28 days after injection. Cardiac VCAM-1 and pathology scores were determined by immunohistochemistry, and myocardial VCAM-1, IL-1β, and TNF-α were analyzed by RT-PCR and Western blot.

RESULTS

In mice with acute VMC, the CD45+CD34+VLA-4+ cell population in the heart was significantly increased by day 7 and then decreased; in contrast, the CD45+CD34+VLA-4+ cell population decreased in the bone marrow and peripheral blood by day 3 and then increased. High expression of VCAM-1 was detected in the heart in parallel with CD45+CD34+VLA-4+ cell expression.

CONCLUSIONS

In mice with acute VMC, VCAM-1-induced CD45+CD34+VLA-4+ cell mobilization into the injured heart is involved in the repair of injured myocardium.

Myeloperoxidase Mediates Postischemic Arrhythmogenic Ventricular Remodeling

RATIONALE

Ventricular arrhythmias remain the leading cause of death in patients suffering myocardial ischemia. Myeloperoxidase, a heme enzyme released by polymorphonuclear neutrophils, accumulates within ischemic myocardium and has been linked to adverse left ventricular remodeling.

OBJECTIVE

To reveal the role of myeloperoxidase for the development of ventricular arrhythmias.

METHODS AND RESULTS

In different murine models of myocardial ischemia, myeloperoxidase deficiency profoundly decreased vulnerability for ventricular tachycardia on programmed right ventricular and burst stimulation and spontaneously as assessed by ECG telemetry after isoproterenol injection. Experiments using CD11b/CD18 integrin-deficient (CD11b-/-) mice and intravenous myeloperoxidase infusion revealed that neutrophil infiltration is a prerequisite for myocardial myeloperoxidase accumulation. Ventricles from myeloperoxidase-deficient (Mpo-/-) mice showed less pronounced slowing and decreased heterogeneity of electric conduction in the peri-infarct zone than wild-type mice. Expression of the redox-sensitive gap junctional protein Cx43 (Connexin 43) was reduced in the peri-infarct area of wild-type compared with Mpo-/- mice. In isolated wild-type cardiomyocytes, Cx43 protein content decreased on myeloperoxidase/H2O2 incubation. Mapping of induced pluripotent stem cell-derived cardiomyocyte networks and in vivo investigations linked Cx43 breakdown to myeloperoxidase-dependent activation of matrix metalloproteinase 7. Moreover, Mpo-/- mice showed decreased ventricular postischemic fibrosis reflecting reduced accumulation of myofibroblasts. Ex vivo, myeloperoxidase was demonstrated to induce fibroblast-to-myofibroblast transdifferentiation by activation of p38 mitogen-activated protein kinases resulting in upregulated collagen generation. In support of our experimental findings, baseline myeloperoxidase plasma levels were independently associated with a history of ventricular arrhythmias, sudden cardiac death, or implantable cardioverter-defibrillator implantation in a cohort of 2622 stable patients with an ejection fraction >35% undergoing elective diagnostic cardiac evaluation.

CONCLUSIONS

Myeloperoxidase emerges as a crucial mediator of postischemic myocardial remodeling and may evolve as a novel pharmacological target for secondary disease prevention after myocardial ischemia.

The crucial role of activin A/ALK4 pathway in the pathogenesis of Ang-II-induced atrial fibrosis and vulnerability to atrial fibrillation

Atrial fibrosis, the hallmark of structural remodeling associated with atrial fibrillation (AF), is characterized by abnormal proliferation of atrial fibroblasts and excessive deposition of extracellular matrix. Transforming growth factor-β1 (TGF-β1)/activin receptor-like kinase 5 (ALK5)/Smad2/3/4 pathway has been reported to be involved in the process. Recent studies have implicated both activin A and its specific downstream component activin receptor-like kinase 4 (ALK4) in stimulating fibrosis in non-cardiac organs. We recently reported that ALK4 haplodeficiency attenuated the pressure overload- and myocardial infarction-induced ventricular fibrosis. However, the role of activin A/ALK4 in the pathogenesis of atrial fibrosis and vulnerability to AF remains unknown. Our study provided experimental and clinical evidence for the involvement of activin A and ALK4 in the pathophysiology of atrial fibrosis and AF. Patients with AF had higher activin A and ALK4 expression in atriums as compared to individuals devoid of AF. After angiotensin-II (Ang-II) stimulation which mimicked atrial fibrosis progression, ALK4-deficient mice showed lower expression of ALK4 in atriums, reduced activation of atrial fibroblasts, blunted atrial enlargement and atrial fibrosis, and further reduced AF vulnerability upon right atrial electrophysiological studies as compared to wild-type littermates. Moreover, we found that apart from the well-known TGF-β1/ALK5 pathway, the activation of activin A/ALK4/smad2/3 pathway played an important role in the pathogenesis of Ang-II-mediated atrial fibrosis and inducibility of AF, suggesting that targeting ALK4 might be a potential therapy for atrial fibrosis and AF.

Long noncoding RNAs and novel inflammatory genes determined by RNA sequencing in human lymphocytes are up-regulated in permanent atrial fibrillation

Atrial fibrillation (AF) is a common arrhythmia in clinical practice. Currently, approximately 33.5 million individuals are affected by AF globally. AF involves multiple complicated mechanisms which have not been fully investigated yet. RNA sequencing (RNAseq) is an outstanding method for investigation of diseases due to its high-throughput information. Here, RNAseq was applied to determine mRNA and long noncoding RNA (lncRNA) expression profiles in human lymphocytes from 6 permanent atrial fibrillation (pmAF) patients and 6 healthy controls. Quantitative real-time PCR (qRT-PCR) was applied to further validate 3 lncRNAs and 4 inflammatory mRNAs. It was discovered that there were numerous differentially-expressed mRNAs and lncRNAs between these two groups. GO analysis indicated that differentially-expressed mRNAs were mainly involved in native immunity, inflammation, signaling transduction and so forth, and they were also enriched in pathways like TNF signaling pathway, NF-kappa B signaling pathway, Toll-like receptor pathway and NOD-like receptor pathway. Moreover, co-expression network demonstrated that dysregulated mRNAs and lncRNAs in pmAF lymphocytes participated in inflammation, autophagy, mitochondrial functions, oxidative stress, etc. Further validation by qRT-PCR demonstrated mRNAs and lncRNAs were significantly higher in lymphocytes from pmAF patients compared with controls. In conclusion, mRNA and lncRNA expression profiles in lymphocytes are significantly different between pmAF and controls, differentially-expressed mRNAs and lncRNAs are involved in pathways closely associated with inflammation, oxidative stress, autophagy, cell apoptosis and collagen synthesis, suggesting lymphocytes might play indispensable roles in the development of pmAF.