Myeloperoxidase attracts neutrophils by physical forces

Advancements in rheumatoid arthritis therapy: a journey from conventional therapy to precision medicine via nanoparticles targeting immune cells

Rheumatoid arthritis (RA) is a progressive autoimmune disease that mainly affects the inner lining of the synovial joints and leads to chronic inflammation. While RA is not known as lethal, recent research indicates that it may be a silent killer because of its strong association with an increased risk of chronic lung and heart diseases. Patients develop these systemic consequences due to the regular uptake of heavy drugs such as disease-modifying antirheumatic medications (DMARDs), glucocorticoids (GCs), nonsteroidal anti-inflammatory medicines (NSAIDs), etc. Nevertheless, a number of these medications have off-target effects, which might cause adverse toxicity, and have started to become resistant in patients as well. Therefore, alternative and promising therapeutic techniques must be explored and adopted, such as post-translational modification inhibitors (like protein arginine deiminase inhibitors), RNA interference by siRNA, epigenetic drugs, peptide therapy, etc., specifically in macrophages, neutrophils, Treg cells and dendritic cells (DCs). As the target cells are specific, ensuring targeted delivery is also equally important, which can be achieved with the advent of nanotechnology. Furthermore, these nanocarriers have fewer off-site side effects, enable drug combinations, and allow for lower drug dosages. Among the nanoparticles that can be used for targeting, there are both inorganic and organic nanomaterials such as solid-lipid nanoparticles, liposomes, hydrogels, dendrimers, and biomimetics that have been discussed. This review highlights contemporary therapy options targeting macrophages, neutrophils, Treg cells, and DCs and explores the application of diverse nanotechnological techniques to enhance precision RA therapies.

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.

Myeloperoxidase induces monocyte migration and activation after acute myocardial infarction

Introduction

Myocardial infarction (MI) is a significant contributor to morbidity and mortality worldwide. Many individuals who survive the acute event continue to experience heart failure (HF), with inflammatory and healing processes post-MI playing a pivotal role. Polymorphonuclear neutrophils (PMN) and monocytes infiltrate the infarcted area, where PMN release high amounts of the heme enzyme myeloperoxidase (MPO). MPO has numerous inflammatory properties and MPO plasma levels are correlated with prognosis and severity of MI. While studies have focused on MPO inhibition and controlling PMN infiltration into the infarcted tissue, less is known on MPO's role in monocyte function.

Methods and results

Here, we combined human data with mouse and cell studies to examine the role of MPO on monocyte activation and migration. We revealed a correlation between plasma MPO levels and monocyte activation in a patient study. Using a mouse model of MI, we demonstrated that MPO deficiency led to an increase in splenic monocytes and a decrease in cardiac monocytes compared to wildtype mice (WT). In vitro studies further showed that MPO induces monocyte migration, with upregulation of the chemokine receptor CCR2 and upregulation of inflammatory pathways identified as underlying mechanisms.

Conclusion

Taken together, we identify MPO as a pro-inflammatory mediator of splenic monocyte recruitment and activation post-MI and provide mechanistic insight for novel therapeutic strategies after ischemic injury.

Beyond host defense and tissue injury: the emerging role of neutrophils in tissue repair

Neutrophils, the most abundant immune cells in human blood, play a fundamental role in host defense against invading pathogens and tissue injury. Neutrophils carry potentially lethal weaponry to the affected site. Inadvertent and perpetual neutrophil activation could lead to nonresolving inflammation and tissue damage, a unifying mechanism of many common diseases. The prevailing view emphasizes the dichotomy of their function, host defense versus tissue damage. However, tissue injury may also persist during neutropenia, which is associated with disease severity and poor outcome. Numerous studies highlight neutrophil phenotypic heterogeneity and functional versatility, indicating that neutrophils play more complex roles than previously thought. Emerging evidence indicates that neutrophils actively orchestrate resolution of inflammation and tissue repair and facilitate return to homeostasis. Thus, neutrophils mobilize multiple mechanisms to limit the inflammatory reaction, assure debris removal, matrix remodeling, cytokine scavenging, macrophage reprogramming, and angiogenesis. In this review, we will summarize the homeostatic and tissue-reparative functions and mechanisms of neutrophils across organs. We will also discuss how the healing power of neutrophils might be harnessed to develop novel resolution and repair-promoting therapies while maintaining their defense functions.

Targeting myeloperoxidase limits myeloid cell immunosuppression enhancing immune checkpoint therapy for pancreatic cancer

Pancreatic ductal adenocarcinoma is a devastating disease characterized by an extreme resistance to current therapies, including immune checkpoint therapy. The limited success of immunotherapies can be attributed to a highly immunosuppressive pancreatic cancer microenvironment characterized by an extensive infiltration of immune suppressing myeloid cells. While there are several pathways through which myeloid cells contribute to immunosuppression, one important mechanism is the increased production of reactive oxygen species. Here, we evaluated the contribution of myeloperoxidase, a myeloid-lineage restricted enzyme and primary source of reactive oxygen species, to regulate immune checkpoint therapy response in preclinical pancreatic cancer models. We compared treatment outcome, immune composition and characterized myeloid cells using wild-type, myeloperoxidase-deficient, and myeloperoxidase inhibitor treated wild-type mice using established subcutaneous pancreatic cancer models. Loss of host myeloperoxidase and pharmacological inhibition of myeloperoxidase in combination with immune checkpoint therapy significantly delayed tumor growth. The tumor microenvironment and systemic immune landscape demonstrated significant decreases in myeloid cells, exhausted T cells and T regulatory cell subsets when myeloperoxidase was deficient. Loss of myeloperoxidase in isolated myeloid cell subsets from tumor-bearing mice resulted in decreased reactive oxygen species production and T cell suppression. These data suggest that myeloperoxidase contributes to an immunosuppressive microenvironment and immune checkpoint therapy resistance where myeloperoxidase inhibitors have the potential to enhance immunotherapy response. Repurposing myeloperoxidase specific inhibitors may provide a promising therapeutic strategy to expand therapeutic options for pancreatic cancer patients to include immunotherapies.

The Roles of Neutrophil-Derived Myeloperoxidase (MPO) in Diseases: The New Progress

Myeloperoxidase (MPO) is a heme-containing peroxidase, mainly expressed in neutrophils and, to a lesser extent, in monocytes. MPO is known to have a broad bactericidal ability via catalyzing the reaction of Cl- with H2O2 to produce a strong oxidant, hypochlorous acid (HOCl). However, the overproduction of MPO-derived oxidants has drawn attention to its detrimental role, especially in diseases characterized by acute or chronic inflammation. Broadly speaking, MPO and its derived oxidants are involved in the pathological processes of diseases mainly through the oxidation of biomolecules, which promotes inflammation and oxidative stress. Meanwhile, some researchers found that MPO deficiency or using MPO inhibitors could attenuate inflammation and tissue injuries. Taken together, MPO might be a promising target for both prognostic and therapeutic interventions. Therefore, understanding the role of MPO in the progress of various diseases is of great value. This review provides a comprehensive analysis of the diverse roles of MPO in the progression of several diseases, including cardiovascular diseases (CVDs), neurodegenerative diseases, cancers, renal diseases, and lung diseases (including COVID-19). This information serves as a valuable reference for subsequent mechanistic research and drug development.

Infection and inflammation stimulate expansion of a CD74+ Paneth cell subset to regulate disease progression

Paneth cells (PCs), a specialized secretory cell type in the small intestine, are increasingly recognized as having an essential role in host responses to microbiome and environmental stresses. Whether and how commensal and pathogenic microbes modify PC composition to modulate inflammation remain unclear. Using newly developed PC-reporter mice under conventional and gnotobiotic conditions, we determined PC transcriptomic heterogeneity in response to commensal and invasive microbes at single cell level. Infection expands the pool of CD74+ PCs, whose number correlates with auto or allogeneic inflammatory disease progressions in mice. Similar correlation was found in human inflammatory disease tissues. Infection-stimulated cytokines increase production of reactive oxygen species (ROS) and expression of a PC-specific mucosal pentraxin (Mptx2) in activated PCs. A PC-specific ablation of MyD88 reduced CD74+ PC population, thus ameliorating pathogen-induced systemic disease. A similar phenotype was also observed in mice lacking Mptx2. Thus, infection stimulates expansion of a PC subset that influences disease progression.

Myeloperoxidase is a critical mediator of anthracycline-induced cardiomyopathy

Cardiotoxicity is a major complication of anthracycline therapy that negatively impacts prognosis. Effective pharmacotherapies for prevention of anthracycline-induced cardiomyopathy (AICM) are currently lacking. Increased plasma levels of the neutrophil-derived enzyme myeloperoxidase (MPO) predict occurrence of AICM in humans. We hypothesized that MPO release causally contributes to AICM. Mice intravenously injected with the anthracycline doxorubicin (DOX) exhibited higher neutrophil counts and MPO levels in the circulation and cardiac tissue compared to saline (NaCl)-treated controls. Neutrophil-like HL-60 cells exhibited increased MPO release upon exposition to DOX. DOX induced extensive nitrosative stress in cardiac tissue alongside with increased carbonylation of sarcomeric proteins in wildtype but not in Mpo-/- mice. Accordingly, co-treatment of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with DOX and MPO aggravated loss of hiPSC-CM-contractility compared to DOX treatment alone. DOX-treated animals exhibited pronounced cardiac apoptosis and inflammation, which was attenuated in MPO-deficient animals. Finally, genetic MPO deficiency and pharmacological MPO inhibition protected mice from the development of AICM. The anticancer efficacy of DOX was unaffected by MPO deficiency. Herein we identify MPO as a critical mediator of AICM. We demonstrate that DOX induces cardiac neutrophil infiltration and release of MPO, which directly impairs cardiac contractility through promoting oxidation of sarcomeric proteins, cardiac inflammation and cardiomyocyte apoptosis. MPO thus emerges as a promising pharmacological target for prevention of AICM.

Cardiac Biomarkers and Their Role in Identifying Increased Risk of Cardiovascular Complications in COVID-19 Patients

Cardiovascular disease (CVD) is a global health concern, causing significant morbidity and mortality. Both lifestyle and genetics influence the development of CVD. It is often diagnosed late, when the treatment options are limited. Early diagnosis of CVD with help of biomarkers is necessary to prevent adverse outcomes. SARS-CoV-2 infection can cause cardiovascular complications even in patients with no prior history of CVD. This review highlights cardiovascular biomarkers, including novel ones, and their applications as diagnostic and prognostic markers of cardiovascular complications related to SARS-CoV-2 infection. Patients with severe SARS-CoV-2 infection were shown to have elevated levels of cardiac biomarkers, namely N-terminal pro-brain natriuretic peptide (NT-pro-BNP), creatine kinase-myocardial band (CK-MB), and troponins, indicating acute myocardial damage. These biomarkers were also associated with higher mortality rates and therefore should be used throughout COVID-19 patient care to identify high-risk patients promptly to optimize their outcomes. Additionally, microRNAs (miRNAs) are also considered as potential biomarkers and predictors of cardiac and vascular damage in SARS-CoV-2 infection. Identifying molecular pathways contributing to cardiovascular manifestations in COVID-19 is essential for development of early biomarkers, identification of new therapeutic targets, and better prediction and management of cardiovascular outcomes.

Mechanisms of neutrophil extracellular trap in chronic inflammation of endothelium in atherosclerosis

Cardiovascular diseases are a primary cause of morbidity and mortality around the world. In addition, atherosclerosis (AS)-caused cardiovascular disease is the primary cause of death in human diseases, and almost two billion people suffer from carotid AS worldwide. AS is caused by chronic inflammation of the arterial vessel and is initiated by dysfunction of vascular endothelial cells. Neutrophils protect against pathogen invasion because they function as a component of the innate immune system. However, the contribution of neutrophils to cardiovascular disease has not yet been clarified. Neutrophil extracellular traps (NETs) represent an immune defense mechanism that is different from direct pathogen phagocytosis. NETs are extracellular web-like structures activated by neutrophils, and they play important roles in promoting endothelial inflammation via direct or indirect pathways. NETs consist of DNA, histones, myeloperoxidase, matrix metalloproteinases, proteinase 3, etc. Most of the components of NETs have no direct toxic effect on endothelial cells, such as DNA, but they can damage endothelial cells indirectly. In addition, NETs play a critical role in the process of AS; therefore, it is important to clarify the mechanisms of NETs in AS because NETs are a new potential therapeutic target AS. This review summarizes the possible mechanisms of NETs in AS.

Alterations in Circulating miRNA Levels after Infection with SARS-CoV-2 Could Contribute to the Development of Cardiovascular Diseases: What We Know So Far

The novel coronavirus disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and poses significant complications for cardiovascular disease (CVD) patients. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression and influence several physiological and pathological processes, including CVD. This critical review aims to expand upon the current literature concerning miRNA deregulation during the SARS-CoV-2 infection, focusing on cardio-specific miRNAs and their association with various CVDs, including cardiac remodeling, arrhythmias, and atherosclerosis after SARS-CoV-2 infection. Despite the scarcity of research in this area, our findings suggest that changes in the expression levels of particular COVID-19-related miRNAs, including miR-146a, miR-27/miR-27a-5p, miR-451, miR-486-5p, miR-21, miR-155, and miR-133a, may be linked to CVDs. While our analysis did not conclusively determine the impact of SARS-CoV-2 infection on the profile and/or expression levels of cardiac-specific miRNAs, we proposed a potential mechanism by which the miRNAs mentioned above may contribute to the development of these two pathologies. Further research on the relationship between SARS-CoV-2, CVDs, and microRNAs will significantly enhance our understanding of this connection and may lead to the use of these miRNAs as biomarkers or therapeutic targets for both pathologies.

Characterization of Myeloperoxidase in the Healthy Equine Endometrium

Myeloperoxidase (MPO), as a marker of neutrophil activation, has been associated with equine endometritis. However, in absence of inflammation, MPO is constantly detected in the uterine lumen of estrous mares. The aim of this study was to characterize MPO in the uterus of mares under physiological conditions as a first step to better understand the role of this enzyme in equine reproduction. Total and active MPO concentrations were determined, by ELISA and SIEFED assay, respectively, in low-volume lavages from mares in estrus (n = 26), diestrus (n = 18) and anestrus (n = 8) in absence of endometritis. Immunohistochemical analysis was performed on 21 endometrial biopsies randomly selected: estrus (n = 11), diestrus (n = 6) and anestrus (n = 4). MPO, although mostly enzymatically inactive, was present in highly variable concentrations in uterine lavages in all studied phases, with elevated concentrations in estrus and anestrus, while in diestrus, concentrations were much lower. Intracytoplasmic immunoexpression of MPO was detected in the endometrial epithelial cells, neutrophils and glandular secretions. Maximal expression was observed during estrus in mid and basal glands with a predominant intracytoplasmic apical reinforcement. In diestrus, immunopositive glands were sporadic. In anestrus, only the luminal epithelium showed residual MPO immunostaining. These results confirm a constant presence of MPO in the uterine lumen of mares in absence of inflammation, probably as part of the uterine mucosal immune system, and suggest that endometrial cells are a source of uterine MPO under physiological cyclic conditions.

Myeloperoxidase: Regulation of Neutrophil Function and Target for Therapy

Neutrophils, the most abundant white blood cells in humans, are critical for host defense against invading pathogens. Equipped with an array of antimicrobial molecules, neutrophils can eradicate bacteria and clear debris. Among the microbicide proteins is the heme protein myeloperoxidase (MPO), stored in the azurophilic granules, and catalyzes the formation of the chlorinating oxidant HOCl and other oxidants (HOSCN and HOBr). MPO is generally associated with killing trapped bacteria and inflicting collateral tissue damage to the host. However, the characterization of non-enzymatic functions of MPO suggests additional roles for this protein. Indeed, evolving evidence indicates that MPO can directly modulate the function and fate of neutrophils, thereby shaping immunity. These actions include MPO orchestration of neutrophil trafficking, activation, phagocytosis, lifespan, formation of extracellular traps, and MPO-triggered autoimmunity. This review scrutinizes the multifaceted roles of MPO in immunity, focusing on neutrophil-mediated host defense, tissue damage, repair, and autoimmunity. We also discuss novel therapeutic approaches to target MPO activity, expression, or MPO signaling for the treatment of inflammatory and autoimmune diseases.

Non-Canonical Functions of Myeloperoxidase in Immune Regulation, Tissue Inflammation and Cancer

Myeloperoxidase (MPO) is one of the most abundantly expressed proteins in neutrophils. It serves as a critical component of the antimicrobial defense system, facilitating microbial killing via generation of reactive oxygen species (ROS). Interestingly, emerging evidence indicates that in addition to the well-recognized canonical antimicrobial function of MPO, it can directly or indirectly impact immune cells and tissue responses in homeostatic and disease states. Here, we highlight the emerging non-canonical functions of MPO, including its impact on neutrophil longevity, activation and trafficking in inflammation, its interactions with other immune cells, and how these interactions shape disease outcomes. We further discuss MPO interactions with barrier forming endothelial and epithelial cells, specialized cells of the central nervous system (CNS) and its involvement in cancer progression. Such diverse function and the MPO association with numerous inflammatory disorders make it an attractive target for therapies aimed at resolving inflammation and limiting inflammation-associated tissue damage. However, while considering MPO inhibition as a potential therapy, one must account for the diverse impact of MPO activity on various cellular compartments both in health and disease.

Hypochlorous Acid Chemistry in Mammalian Cells—Influence on Infection and Role in Various Pathologies

This review discusses the formation of hypochlorous acid HOCl and the role of reactive chlorinated species (RCS), which are catalysed by the enzyme myeloperoxidase MPO, mainly located in leukocytes and which in turn contribute to cellular oxidative stress. The reactions of RCS with various organic molecules such as amines, amino acids, proteins, lipids, carbohydrates, nucleic acids, and DNA are described, and an attempt is made to explain the chemical mechanisms of the formation of the various chlorinated derivatives and the data available so far on the effects of MPO, RCS and halogenative stress. Their presence in numerous pathologies such as atherosclerosis, arthritis, neurological and renal diseases, diabetes, and obesity is reviewed and were found to be a feature of debilitating diseases.

Unexpected Role of MPO-Oxidized LDLs in Atherosclerosis: In between Inflammation and Its Resolution

Inflammation and its resolution are the result of the balance between pro-inflammatory and pro-resolving factors, such as specialized pro-resolving mediators (SPMs). This balance is crucial for plaque evolution in atherosclerosis, a chronic inflammatory disease. Myeloperoxidase (MPO) has been related to oxidative stress and atherosclerosis, and MPO-oxidized low-density lipoproteins (Mox-LDLs) have specific characteristics and effects. They participate in foam cell formation and cause specific reactions when interacting with macrophages and endothelial cells. They also increase the production of intracellular reactive oxygen species (ROS) in macrophages and the resulting antioxidant response. Mox-LDLs also drive macrophage polarization. Mox-LDLs are known to be pro-inflammatory particles. However, in the presence of Mox-LDLs, endothelial cells produce resolvin D1 (RvD1), a SPM. SPMs are involved in the resolution of inflammation by stimulating efferocytosis and by reducing the adhesion and recruitment of neutrophils and monocytes. RvD1 also induces the synthesis of other SPMs. In vitro, Mox-LDLs have a dual effect by promoting RvD1 release and inducing a more anti-inflammatory phenotype macrophage, thereby having a mixed effect on inflammation. In this review, we discuss the interrelationship between MPO, Mox-LDLs, and resolvins, highlighting a new perception of the role of Mox-LDLs in atherosclerosis.

The effects of dietary immunostimulants on the innate immune response of Indian major carp: A review

Immunostimulants, as feed additives, play an important role in maintaining fish health and enhancing their overall growth by providing resistance against diseases in cultured fish. At the initial stages of life of fish, innate immunity is the essential mechanism in their survival. Later, innate immunity has an instructive role in adapting acquired immune response and homeostasis through different receptor proteins. Several studies have been conducted to analyze the effect of dietary immunostimulants like algae, plant extracts, vitamins, herbs, probiotics, and prebiotics-containing diets in Indian major carps. Many bacterial, fungal and viral pathogens are responsible for high death rates in both wild and cultured fish. It's a major limiting factor for world aquaculture industries. Recognition of invading pathogens by different pathogen recognition receptor plays an important role for the activation of different pathways to initiate protective immune responses. Hence, there is a growing need to control the devastating effects of diseases without recourse to toxic chemicals or antibiotics. Keeping with alternative approaches without using toxic chemicals to control fish diseases in mind, many immunostimulants are used, which enhance immune responses along with their gene expression level through different signaling pathway. The objective of this review is to summarize and evaluate the current knowledge of various immunostimulants and their immune responses in three Indian major carps namely Catla catla, Labeo rohita and Cirrhinus mrigala, which are preferred by the people.

Myeloperoxidase Deficiency Alters the Process of the Regulated Cell Death of Polymorphonuclear Neutrophils

Polymorphonuclear neutrophils (PMNs) play a key role in host defense. However, their massive accumulation at the site of inflammation can delay regenerative healing processes and can initiate pathological inflammatory processes. Thus, the efficient clearance of PMNs mediated by the induction of regulated cell death is a key process preventing the development of these pathological conditions. Myeloperoxidase (MPO), a highly abundant enzyme in PMN granules, primarily connected with PMN defense machinery, is suggested to play a role in PMN-regulated cell death. However, the contribution of MPO to the mechanisms of PMN cell death remains incompletely characterized. Herein, the process of the cell death of mouse PMNs induced by three different stimuli – phorbol 12-myristate 13-acetate (PMA), opsonized streptococcus (OST), and N-formyl-met-leu-phe (fMLP) – was investigated. MPO-deficient PMNs revealed a significantly decreased rate of cell death characterized by phosphatidylserine surface exposure and cell membrane permeabilization. An inhibitor of MPO activity, 4-aminobenzoic acid hydrazide, did not exhibit a significant effect on PMA-induced cell death compared to MPO deficiency. Interestingly, only the limited activation of markers related to apoptotic cell death was observed (e.g. caspase 8 activation, Bax expression) and they mostly did not correspond to phosphatidylserine surface exposure. Furthermore, a marker characterizing autophagy, cleavage of LC3 protein, as well as histone H3 citrullination and its surface expression was observed. Collectively, the data show the ability of MPO to modulate the life span of PMNs primarily through the potentiation of cell membrane permeabilization and phosphatidylserine surface exposure.

Ex vivo observation of granulocyte activity during thrombus formation

Background

The process of thrombus formation is thought to involve interactions between platelets and leukocytes. Leukocyte incorporation into growing thrombi has been well established in vivo, and a number of properties of platelet-leukocyte interactions critical for thrombus formation have been characterized in vitro in thromboinflammatory settings and have clinical relevance. Leukocyte activity can be impaired in distinct hereditary and acquired disorders of immunological nature, among which is Wiskott-Aldrich Syndrome (WAS). However, a more quantitative characterization of leukocyte behavior in thromboinflammatory conditions has been hampered by lack of approaches for its study ex vivo. Here, we aimed to develop an ex vivo model of thromboinflammation, and compared granulocyte behavior of WAS patients and healthy donors.

Results

Thrombus formation in anticoagulated whole blood from healthy volunteers and patients was visualized by fluorescent microscopy in parallel-plate flow chambers with fibrillar collagen type I coverslips. Moving granulocytes were observed in hirudinated or sodium citrate-recalcified blood under low wall shear rate conditions (100 s⁻¹). These cells crawled around thrombi in a step-wise manner with an average velocity of 90–120 nm/s. Pre-incubation of blood with granulocyte priming agents lead to a significant decrease in mean-velocity of the cells and increase in the number of adherent cells. The leukocytes from patients with WAS demonstrated a 1.5-fold lower mean velocity, in line with their impaired actin polymerization. It is noteworthy that in an experimental setting where patients’ platelets were replaced with healthy donor’s platelets the granulocytes’ crawling velocity did not change, thus proving that WASP (WAS protein) deficiency causes disruption of granulocytes’ behavior. Thereby, the observed features of granulocytes crawling are consistent with the neutrophil chemotaxis phenomenon. As most of the crawling granulocytes carried procoagulant platelets teared from thrombi, we propose that the role of granulocytes in thrombus formation is that of platelet scavengers.

Conclusions

We have developed an ex vivo experimental model applicable for observation of granulocyte activity in thrombus formation. Using the proposed setting, we observed a reduction of motility of granulocytes of patients with WAS. We suggest that our ex vivo approach should be useful both for basic and for clinical research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01238-x.

Association of cardiometabolic microRNAs with COVID-19 severity and mortality

AIMS

Coronavirus disease 2019 (COVID-19) can lead to multiorgan damage. MicroRNAs (miRNAs) in blood reflect cell activation and tissue injury. We aimed to determine the association of circulating miRNAs with COVID-19 severity and 28 day intensive care unit (ICU) mortality.

METHODS AND RESULTS

We performed RNA-Seq in plasma of healthy controls (n = 11), non-severe (n = 18), and severe (n = 18) COVID-19 patients and selected 14 miRNAs according to cell- and tissue origin for measurement by reverse transcription quantitative polymerase chain reaction (RT-qPCR) in a separate cohort of mild (n = 6), moderate (n = 39), and severe (n = 16) patients. Candidates were then measured by RT-qPCR in longitudinal samples of ICU COVID-19 patients (n = 240 samples from n = 65 patients). A total of 60 miRNAs, including platelet-, endothelial-, hepatocyte-, and cardiomyocyte-derived miRNAs, were differentially expressed depending on severity, with increased miR-133a and reduced miR-122 also being associated with 28 day mortality. We leveraged mass spectrometry-based proteomics data for corresponding protein trajectories. Myocyte-derived (myomiR) miR-133a was inversely associated with neutrophil counts and positively with proteins related to neutrophil degranulation, such as myeloperoxidase. In contrast, levels of hepatocyte-derived miR-122 correlated to liver parameters and to liver-derived positive (inverse association) and negative acute phase proteins (positive association). Finally, we compared miRNAs to established markers of COVID-19 severity and outcome, i.e. SARS-CoV-2 RNAemia, age, BMI, D-dimer, and troponin. Whilst RNAemia, age and troponin were better predictors of mortality, miR-133a and miR-122 showed superior classification performance for severity. In binary and triplet combinations, miRNAs improved classification performance of established markers for severity and mortality.

CONCLUSION

Circulating miRNAs of different tissue origin, including several known cardiometabolic biomarkers, rise with COVID-19 severity. MyomiR miR-133a and liver-derived miR-122 also relate to 28 day mortality. MiR-133a reflects inflammation-induced myocyte damage, whilst miR-122 reflects the hepatic acute phase response.

Isolation, Characterization and In Silico Studies of Secondary Metabolites from the Whole Plant of Polygala inexpectata Peşmen & Erik

Polygala species are frequently used worldwide in the treatment of various diseases, such as inflammatory and autoimmune disorders as well as metabolic and neurodegenerative diseases, due to the large number of secondary metabolites they contain. The present study was performed on Polygala inexpectata, which is a narrow endemic species for the flora of Turkey, and resulted in the isolation of nine known compounds, 6,3'-disinapoyl-sucrose (1), 6-O-sinapoyl,3'-O-trimethoxy-cinnamoyl-sucrose (tenuifoliside C) (2), 3'-O-(O-methyl-feruloyl)-sucrose (3), 3'-O-(sinapoyl)-sucrose (4), 3'-O-trimethoxy-cinnamoyl-sucrose (glomeratose) (5), 3'-O-feruloyl-sucrose (sibiricose A5) (6), sinapyl alcohol 4-O-glucoside (syringin or eleutheroside B) (7), liriodendrin (8), and 7,4'-di-O-methylquercetin-3-O-β-rutinoside (ombuin 3-O-rutinoside or ombuoside) (9). The structures of the compounds were determined by the spectroscopic methods including 1D-NMR (1H NMR, 13C NMR, DEPT-135), 2D-NMR (COSY, NOESY, HSQC, HMBC), and HRMS. The isolated compounds were shown in an in silico setting to be accommodated well within the inhibitor-binding pockets of myeloperoxidase and inducible nitric oxide synthase and anchored mainly through hydrogen-bonding interactions and π-effects. It is therefore plausible to suggest that the previously established anti-inflammatory properties of some Polygala-derived phytochemicals may be due, in part, to the modulation of pro-inflammatory enzyme activities.

Myeloperoxidase: a new target for the treatment of stroke?

Myeloperoxidase is an important inflammatory factor in the myeloid system, primarily expressed in neutrophils and microglia. Myeloperoxidase and its active products participate in the occurrence and development of hemorrhagic and ischemic stroke, including damage to the blood-brain barrier and brain. As a specific inflammatory marker, myeloperoxidase can be used in the evaluation of vascular disease occurrence and development in stroke, and a large amount of experimental and clinical data has indicated that the inhibition or lack of myeloperoxidase has positive impacts on stroke prognosis. Many studies have also shown that there is a correlation between the overexpression of myeloperoxidase and the risk of stroke. The occurrence of stroke not only refers to the first occurrence but also includes recurrence. Therefore, myeloperoxidase is significant for the clinical evaluation and prognosis of stroke. This paper reviews the potential role played by myeloperoxidase in the development of vascular injury and secondary brain injury after stroke and explores the effects of inhibiting myeloperoxidase on stroke prognosis. This paper also analyzes the significance of myeloperoxidase etiology in the occurrence and development of stroke and discusses whether myeloperoxidase can be used as a target for the treatment and prediction of stroke.

[Patterns of immunological reactions in the pathogenesis of chronic heart failure: review]

The immune system is essential for maintaining the homeostasis. At present, there is convincing evidence for participation of the immune system in the pathogenesis of cardiovascular pathology, including the final step of cardiovascular continuum, heart failure. Objective difficulties in understanding subtle processes of loss of the normal cardiac structure and function are based on the diversity of pathogenetic factors of development and progression of chronic heart failure (CHF) and the involvement of most organs and body systems. Russian and international scientists actively study issues of immune homeostasis, including the efficacy of current immune therapy. At the same time, available reports are largely uncompiled and reflect isolated parts of the immunopathogenesis of cardiovascular diseases. This review focuses on comprehensive elucidation of major patterns of immune processes in the CHF pathogenesis to form an integral view of the problem under study.

Astrocyte-derived microparticles initiate a neuroinflammatory cycle due to carbon monoxide poisoning

We hypothesized that carbon monoxide (CO) establishes an inflammatory cycle mediated by microparticles (MPs). Mice exposed to a CO protocol (1000 ​ppm for 40 ​min and then 3000 ​ppm for 20 ​min) that causes neuroinflammation exhibit NF-κB activation in astrocytes leading to generation of MPs expressing thrombospondin-1(TSP-1) that collect in deep cervical lymph nodes draining the brain glymphatic system. TSP-1 bearing MPs gain access to the blood stream where they activate neutrophils to generate a new family of MPs, and also stimulate endothelial cells as documented by leakage of intravenous 2000 ​kDa dextran. At the brain microvasculature, neutrophil and MPs sequestration, and myeloperoxidase activity result in elevations of the p65 subunit of NF-κB, serine 536 phosphorylated p65, CD36, and loss of astrocyte aquaporin-4 that persist for at least 7 days. Knock-out mice lacking the CD36 membrane receptor are resistant to all CO inflammatory changes. Events triggered by CO are recapitulated in naïve wild type mice injected with cervical node MPs from CO-exposed mice, but not control mice. All MPs-mediated events are inhibited with a NF-κB inhibitor, a myeloperoxidase inhibitor, or anti-TSP-1 antibodies. We conclude that astrocyte-derived MPs expressing TSP-1 establish a feed-forward neuroinflammatory cycle involving endothelial CD36-to-astrocyte NF-κB crosstalk. As there is currently no treatment for CO-induced neurological sequelae, these findings pose several possible sites for therapeutic interventions.

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Carbon monoxide (CO) causes neurological injuries poorly correlated to hypoxic stress.

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Astrocyte NF-κB triggers thrombospondin-1(TSP-1) microparticle (MP) production.

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TSP-1 MPs enter the blood stream, stimulating neutrophils and endothelium.

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Circulating MPs linkage to endothelial cell CD36 causes vascular damage.

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Endothelial CD36-to-astrocyte NF-κB crosstalk establishes a neuroinflammatory cycle.

ZnO-loaded DNA nanogels as neutrophil extracellular trap-like structures in the treatment of mouse peritonitis

Neutrophil extracellular traps (NETs) are chromatin-based structures that are released from neutrophils during infections and prevent microbes from spreading in the body through efficient degradation of their composition. Based on this chromatin-driven strategy of capturing and killing bacteria, we designed NET-like structures using DNA and ZnO nanoparticles (NPs). DNA was first purified from kiwifruit and treated with HCl to increase hydroxyl groups in the opened-deoxylribose form. The carboxyl groups of citric acid were then thermally crosslinked with said hydroxyl and primary amine groups in DNA, forming DNA-HCl nanogels (NGs). ZnO NPs were then used as positively charged granule enzymes, adsorbed onto the DNA-HCl NG, obtaining ZnO/DNA-HCl NGs (with NET biomimicry). In an anti-inflammatory assay, ZnO/DNA-HCl NGs significantly inhibited TNF-α, IL-6, iNOS and COX-2 expression in LPS-stimulated Raw264.7 cells. Moreover, the ZnO/DNA-HCl NGs markedly alleviated clinical symptoms in LPS-induced mouse peritonitis. Finally, ZnO/DNA-HCl NGs suppressed E. coli from entering circulation in septic mice while prolonging their survival. Our results suggest that the ZnO/DNA-HCl NGs, which mimic NET-like structures in the blocking of bacteria-inducted inflammation, may be a potential therapeutic strategy for bacterial infections.

Ureaplasma diversum clearance in lung mice infection is mediated by neutrophils

Pneumonia in cattle is one of the causes of morbidity rates and economic loss. The host response to lung infections caused by Ureaplasma diversum in bovines is virtually unknown. Here in the immune response was evaluated in a murine model for an experimental pulmonary infection by U. diversum. Therefore, AJ, BALB/C and C57BL/6 mice received intratracheal inoculation of U. diversum and were evaluated after 1, 2, 3, 7 and 14 days and the clinical specimens were collected. In bronchoalveolar lavages (BAL) an increase of inflammatory cells was observed. Neutrophils were the main cells recruited to the site of infection and the infiltration was coincided with the production of pro-inflammatory cytokines. We found a large amount of neutrophil in this initial period, followed by a decrease 7 and 14 days post infection, accompanied by bacterial clearance. Our results evidenced the presence of U. diversum within the neutrophil that suggests a phagocytic role of this cell in the elimination of the infection. The immune response features reported here are the initial evidence that healthy immune systems may control these microorganisms. This may be the first step to design new strategies immune based to control the infections in naturally infected hosts.

Role of myeloperoxidase and oxidant formation in the extracellular environment in inflammation-induced tissue damage

The heme peroxidase family generates a battery of oxidants both for synthetic purposes, and in the innate immune defence against pathogens. Myeloperoxidase (MPO) is the most promiscuous family member, generating powerful oxidizing species including hypochlorous acid (HOCl). Whilst HOCl formation is important in pathogen removal, this species is also implicated in host tissue damage and multiple inflammatory diseases. Significant oxidant formation and damage occurs extracellularly as a result of MPO release via phagolysosomal leakage, cell lysis, extracellular trap formation, and inappropriate trafficking. MPO binds strongly to extracellular biomolecules including polyanionic glycosaminoglycans, proteoglycans, proteins, and DNA. This localizes MPO and subsequent damage, at least partly, to specific sites and species, including extracellular matrix (ECM) components and plasma proteins/lipoproteins. Biopolymer-bound MPO retains, or has enhanced, catalytic activity, though evidence is also available for non-catalytic effects. These interactions, particularly at cell surfaces and with the ECM/glycocalyx induce cellular dysfunction and altered gene expression. MPO binds with higher affinity to some damaged ECM components, rationalizing its accumulation at sites of inflammation. MPO-damaged biomolecules and fragments act as chemo-attractants and cell activators, and can modulate gene and protein expression in naïve cells, consistent with an increasing cycle of MPO adhesion, activity, damage, and altered cell function at sites of leukocyte infiltration and activation, with subsequent tissue damage and dysfunction. MPO levels are used clinically both diagnostically and prognostically, and there is increasing interest in strategies to prevent MPO-mediated damage; therapeutic aspects are not discussed as these have been reviewed elsewhere.

Expression profile analysis reveals hub genes that are associated with immune system dysregulation in primary myelofibrosis

OBJECTION

Primary myelofibrosis (PMF) is a familiar chronic myeloproliferative disease with an unfavorable prognosis. The effect of infection on the prognosis of patients with PMF is crucial. Immune system dysregulation plays a central role in the pathophysiology of PMF. To date, very little research has been conducted on the molecular mechanism of immune compromise in patients with PMF.

METHODS

To explore potential candidate genes, microarray datasets GSE61629 and 26049 were obtained from the Gene Expression Omnibus (GEO) database. The differentially expressed genes (DEGs) between PMF patients and normal individuals were evaluated, gene function was measured and a series of hub genes were identified. Several significant immune cells were selected via cell type enrichment analysis. The correlation between hub genes and significant immune cells was determined.

RESULTS

A total of 282 DEGs were found, involving 217 upregulated genes and 65 downregulated genes. Several immune cells were found to be reduced in PMF, such as CD4⁺ T cells, CD4⁺ Tems, CD4⁺ memory T cells. Gene Ontology (GO) enrichment analysis of DEGs reflected that most biological processes were associated with immune processes. Six hub genes, namely, HP, MPO, MMP9, EPB42, SLC4A1, and ALAS2, were identified, and correlation analysis revealed that these hub genes have a negative correlation with immune cell abundance.

CONCLUSIONS

Taken together, the gene expression profile of whole blood cells in PMF patients indicated a battery of immune events, and the DEGs and hub genes might contribute to immune system dysregulation.

A Proteomics-Based Assessment of Inflammation Signatures in Endotoxemia

We have previously shown that multimers of plasma pentraxin-3 (PTX3) were predictive of survival in patients with sepsis. To characterize the release kinetics and cellular source of plasma protein changes in sepsis, serial samples were obtained from healthy volunteers (n = 10; three time points) injected with low-dose endotoxin (lipopolysaccharide [LPS]) and analyzed using data-independent acquisition MS. The human plasma proteome response was compared with an LPS-induced endotoxemia model in mice. Proteomic analysis of human plasma revealed a rapid neutrophil degranulation signature, followed by a rise in acute phase proteins. Changes in circulating PTX3 correlated with increases in neutrophil-derived proteins following LPS injection. Time course analysis of the plasma proteome in mice showed a time-dependent increase in multimeric PTX3, alongside increases in neutrophil-derived myeloperoxidase (MPO) upon LPS treatment. The mechanisms of oxidation-induced multimerization of PTX3 were explored in two genetic mouse models: MPO global knock-out (KO) mice and LysM Cre Nox2 KO mice, in which NADPH oxidase 2 (Nox2) is only deficient in myeloid cells. Nox2 is the enzyme responsible for the oxidative burst in neutrophils. Increases in plasma multimeric PTX3 were not significantly different between wildtype and MPO or LysM Cre Nox2 KO mice. Thus, PTX3 may already be stored and released in a multimeric form. Through in vivo neutrophil depletion and multiplexed vascular proteomics, PTX3 multimer deposition within the aorta was confirmed to be neutrophil dependent. Proteomic analysis of aortas from LPS-injected mice returned PTX3 as the most upregulated protein, where multimeric PTX3 was deposited as early as 2 h post-LPS along with other neutrophil-derived proteins. In conclusion, the rise in multimeric PTX3 upon LPS injection correlates with neutrophil-related protein changes in plasma and aortas. MPO and myeloid Nox2 are not required for the multimerization of PTX3; instead, neutrophil extravasation is responsible for the LPS-induced deposition of multimeric PTX3 in the aorta.

Extracellular vesicles mediate cellular interactions in renal diseases-Novel views of intercellular communications in the kidney

The kidney is a complicated and important internal organ receiving approximately 20% of the cardiac output and mediates numerous pathophysiologic actions. These include selectively filtering macromolecules of the blood, exquisite reclaimation of electrolyctes, urine concentration via an elegant osmotic mechanism, and excretion of an acid load. In addition, the renal tubules carry out secretory functions and produce hormones and cytokines. The kidney receives innervation and hormonal regulation. Therefore, dysfunction of the kidney leads to retention of metabolic waste products, and/or significant proteinuria and hematuria. In the past several decades, the role of extracellular vesicles (EVs) in intercellular communications, and the uptake of EVs by recipient cells through phagocytosis and endocytosis have been elucidated. The new knowledge on EVs expands over the classical mechanisms of cellular interaction, and may change our way of thinking of renal pathophysiology in the subcellular scale. Based on some ultrastructural discoveries in the kidney, this review will focus on the role of EVs in intercellular communications, their internalization by recipient cells, and their relationship to renal pathology.

The effects of neutrophil-generated hypochlorous acid and other hypohalous acids on host and pathogens

Neutrophils are predominant immune cells that protect the human body against infections by deploying sophisticated antimicrobial strategies including phagocytosis of bacteria and neutrophil extracellular trap (NET) formation. Here, we provide an overview of the mechanisms by which neutrophils kill exogenous pathogens before we focus on one particular weapon in their arsenal: the generation of the oxidizing hypohalous acids HOCl, HOBr and HOSCN during the so-called oxidative burst by the enzyme myeloperoxidase. We look at the effects of these hypohalous acids on biological systems in general and proteins in particular and turn our attention to bacterial strategies to survive HOCl stress. HOCl is a strong inducer of protein aggregation, which bacteria can counteract by chaperone-like holdases that bind unfolding proteins without the need for energy in the form of ATP. These chaperones are activated by HOCl through thiol oxidation (Hsp33) or N-chlorination of basic amino acid side-chains (RidA and CnoX) and contribute to bacterial survival during HOCl stress. However, neutrophil-generated hypohalous acids also affect the host system. Recent studies have shown that plasma proteins act not only as sinks for HOCl, but get actively transformed into modulators of the cellular immune response through N-chlorination. N-chlorinated serum albumin can prevent aggregation of proteins, stimulate immune cells, and act as a pro-survival factor for immune cells in the presence of cytotoxic antigens. Finally, we take a look at the emerging role of HOCl as a potential signaling molecule, particularly its role in neutrophil extracellular trap formation.

Myeloperoxidase mediated alteration of endothelial function is dependent on its cationic charge

Endothelial cell (EC) glycocalyx (GLX) comprise a multicomponent layer of proteoglycans and glycoproteins. Alteration of its integrity contributes to chronic vascular inflammation and leads to the development of cardiovascular diseases. Myeloperoxidase (MPO), a highly abundant enzyme released by polymorphonuclear neutrophils, binds to the GLX and deleteriously affects vascular EC functions. The focus of this study was to elucidate the mechanisms of MPO-mediated alteration of GLX molecules, and to unravel subsequent changes in endothelial integrity and function. MPO binding to GLX of human ECs and subsequent internalization was mediated by cell surface heparan sulfate chains. Moreover, interaction of MPO, which is carrying a cationic charge, with anionic glycosaminoglycans (GAGs) resulted in reduction of their relative charge. By means of micro-viscometry and atomic force microscopy, we disclosed that MPO can crosslink GAG chains. MPO-dependent modulation of GLX structure was further supported by alteration of wheat germ agglutinin staining. Increased expression of ICAM-1 documented endothelial cell activation by both catalytically active and also inactive MPO. Furthermore, MPO increased vascular permeability connected with reorganization of intracellular junctions, however, this was dependent on MPO's catalytic activity. Novel proteins interacting with MPO during transcytosis were identified by proteomic analysis. Altogether, these findings provide evidence that MPO through interaction with GAGs modulates overall charge of the GLX, causing modification of its structure and thus affecting EC function. Importantly, our results also suggest a number of proteins interacting with MPO that possess a variety of cellular localizations and functions.

Systemic Inflammatory Response Syndrome After Surgery: Mechanisms and Protection

The immune system is an evolutionary hallmark of higher organisms that defends the host against invading pathogens and exogenous infections. This defense includes the recruitment of immune cells to the site of infection and the initiation of an inflammatory response to contain and eliminate pathogens. However, an inflammatory response may also be triggered by noninfectious stimuli such as major surgery, and, in case of an overshooting, still not comprehensively understood reaction, lead to tissue destruction and organ dysfunction. Unfortunately, in some cases, the immune system may not effectively distinguish between stimuli elicited by major surgery, which ideally should only require a modest inflammatory response, and those elicited by trauma or pathogenic infection. Surgical procedures thus represent a potential trigger for systemic inflammation that causes the secretion of proinflammatory cytokines, endothelial dysfunction, glycocalyx damage, activation of neutrophils, and ultimately tissue and multisystem organ destruction. In this review, we discuss and summarize currently available mechanistic knowledge on surgery-associated systemic inflammation, demarcation toward other inflammatory complications, and possible therapeutic options. These options depend on uncovering the underlying mechanisms and could include pharmacologic agents, remote ischemic preconditioning protocols, cytokine blockade or clearance, and optimization of surgical procedures, anesthetic regimens, and perioperative inflammatory diagnostic assessment. Currently, a large gap between basic science and clinically confirmed data exists due to a limited evidence base of translational studies. We thus summarize important steps toward the understanding of the precise time- and space-regulated processes in systemic perioperative inflammation.

Myeloperoxidase Modulates Hydrogen Peroxide Mediated Cellular Damage in Murine Macrophages

Myeloperoxidase (MPO) is involved in the development of many chronic inflammatory diseases, in addition to its key role in innate immune defenses. This is attributed to the excessive production of hypochlorous acid (HOCl) by MPO at inflammatory sites, which causes tissue damage. This has sparked wide interest in the development of therapeutic approaches to prevent HOCl-induced cellular damage including supplementation with thiocyanate (SCN^-) as an alternative substrate for MPO. In this study, we used an enzymatic system composed of glucose oxidase (GO), glucose, and MPO in the absence and presence of SCN^-, to investigate the effects of generating a continuous flux of oxidants on macrophage cell function. Our studies show the generation of hydrogen peroxide (H₂O₂) by glucose and GO results in a dose- and time-dependent decrease in metabolic activity and cell viability, and the activation of stress-related signaling pathways. Interestingly, these damaging effects were attenuated by the addition of MPO to form HOCl. Supplementation with SCN^-, which favors the formation of hypothiocyanous acid, could reverse this effect. Addition of MPO also resulted in upregulation of the antioxidant gene, NAD(P)H:quinone acceptor oxidoreductase 1. This study provides new insights into the role of MPO in the modulation of macrophage function, which may be relevant to inflammatory pathologies.

High Plasma Myeloperoxidase Is Associated with Plaque Erosion in Patients with ST-Segment Elevation Myocardial Infarction

We aimed to investigate the association between plasma myeloperoxidase (MPO) and plaque erosion in patients presenting with ST-segment elevation myocardial infarction (STEMI). Two hundred and fifty-two patients with STEMI who underwent optical coherence tomography (OCT) evaluation of culprit lesion were prospectively enrolled. Of them, 92 and 80 patients were identified with plaque rupture and plaque erosion, respectively. Plasma MPO levels, measured using enzyme-linked immunoassay, were significantly higher in patients with plaque erosion versus plaque rupture (median (interquartile range), 96.3 ng/mL [44.2-173.3] vs. 41.7 ng/mL (29.2-66.3); p < 0.001). Multivariable logistic regression analysis indicated that plasma MPO was independently associated with plaque erosion (odds ratio, 3.25; 95% confidence interval, 1.37-7.76; p = 0.008). The area under the receiver-operating characteristic curve was 0.75 for MPO to discriminate between plaque erosion and plaque rupture. Plasma MPO level significantly correlated with plaque erosion in patients with STEMI.

Role of mechanical stress and neutrophils in the pathogenesis of plaque erosion

Mechanical stress is a well-recognized driver of plaque rupture. Likewise, investigating the role of mechanical forces in plaque erosion has recently begun to provide some important insights, yet the knowledge is by far less advanced. The most significant example is that of shear stress, which has early been proposed as a possible driver for focal endothelial death and denudation. Recent findings using optical coherence tomography, computational sciences and mechanical models show that plaque erosion occurs most likely around atheromatous plaque throats with specific stress pattern. In parallel, we have recently shown that neutrophil-dependent inflammation promotes plaque erosion, possibly through a noxious action on ECs. Most importantly, spontaneous thrombosis - associated or not with EC denudation - can be impacted by hemodynamics, and it is now established that neutrophils promote thrombosis and platelet activation, highlighting a potential relationship between, mechanical stress, inflammation, and EC loss in the setting of coronary plaque erosion. Here, we review our current knowledge regarding the implication of both mechanical stress and neutrophils, and we discuss their implication in the promotion of plaque erosion via EC loss and thrombosis.

Myeloperoxidase: A versatile mediator of endothelial dysfunction and therapeutic target during cardiovascular disease

Myeloperoxidase (MPO) is a prominent mammalian heme peroxidase and a fundamental component of the innate immune response against microbial pathogens. In recent times, MPO has received considerable attention as a key oxidative enzyme capable of impairing the bioactivity of nitric oxide (NO) and promoting endothelial dysfunction; a clinically relevant event that manifests throughout the development of inflammatory cardiovascular disease. Increasing evidence indicates that during cardiovascular disease, MPO is released intravascularly by activated leukocytes resulting in its transport and sequestration within the vascular endothelium. At this site, MPO catalyzes various oxidative reactions that are capable of promoting vascular inflammation and impairing NO bioactivity and endothelial function. In particular, MPO catalyzes the production of the potent oxidant hypochlorous acid (HOCl) and the catalytic consumption of NO via the enzyme's NO oxidase activity. An emerging paradigm is the ability of MPO to also influence endothelial function via non-catalytic, cytokine-like activities. In this review article we discuss the implications of our increasing knowledge of the versatility of MPO's actions as a mediator of cardiovascular disease and endothelial dysfunction for the development of new pharmacological agents capable of effectively combating MPO's pathogenic activities. More specifically, we will (i) discuss the various transport mechanisms by which MPO accumulates into the endothelium of inflamed or diseased arteries, (ii) detail the clinical and basic scientific evidence identifying MPO as a significant cause of endothelial dysfunction and cardiovascular disease, (iii) provide an up-to-date coverage on the different oxidative mechanisms by which MPO can impair endothelial function during cardiovascular disease including an evaluation of the contributions of MPO-catalyzed HOCl production and NO oxidation, and (iv) outline the novel non-enzymatic mechanisms of MPO and their potential contribution to endothelial dysfunction. Finally, we deliver a detailed appraisal of the different pharmacological strategies available for targeting the catalytic and non-catalytic modes-of-action of MPO in order to protect against endothelial dysfunction in cardiovascular disease.

Therapeutic Targeting of Myeloperoxidase Attenuates NASH in Mice

Myeloperoxidase (MPO) activity has been associated with the metabolic syndrome, cardiovascular and liver disease. Here, we evaluate the therapeutic potential of MPO inhibition on nonalcoholic steatohepatitis (NASH) and NASH-induced fibrosis, the main determinant of outcomes. MPO plasma levels were elevated in patients with nonalcoholic fatty liver disease (NAFLD) compared with healthy controls. In a second cohort, hepatic MPO messenger RNA expression correlated with higher body mass index and hemoglobin A1c, both being risk factors for NAFLD. We could establish by immunohistochemistry that MPO-positive cells were recruited to the liver in various mouse models of fibrogenic liver injury, including bile duct ligation, carbon tetrachloride (CCl₄) treatment, spontaneous liver fibrogenesis in multidrug resistance 2 knockout (MDR2 KO) mice, and NASH-inducing diet. Comparison of MPO-deficient mice and their wild-type littermates exposed to a high-caloric diet revealed that MPO deficiency protects against NASH-related liver injury and fibrosis. In line with this, hepatic gene expression analysis demonstrated a MPO-dependent activation of pathways relevant for wound healing, inflammation, and cell death in NASH. MPO deficiency did not affect NAFLD-independent liver injury and fibrosis in MDR2 KO or CCl₄-treated mice. Finally, we treated wild-type mice exposed to NASH-inducing diet with an oral MPO inhibitor. Pharmacological MPO inhibition not only reduced markers of MPO-mediated liver damage, serum alanine aminotransferase levels, and hepatic steatosis, but also significantly decreased NASH-induced liver fibrosis. MPO inhibitor treatment, but not MPO deficiency, significantly altered gut microbiota including a significant expansion of Akkermansia muciniphila. Conclusions: MPO specifically promotes NASH-induced liver fibrosis. Pharmacological MPO inhibition attenuates NASH progression and NASH-induced liver fibrosis in mice and is associated with beneficial changes of intestinal microbiota.

Effect of Roux-en-Y Bariatric Bypass Surgery on Subclinical Atherosclerosis and Oxidative Stress Markers in Leukocytes of Obese Patients: A One-Year Follow-Up Study

Little is known about the mechanisms underlying the cardioprotective effect of Roux en-Y gastric bypass (RYGB) surgery. Therefore, the aim of the present study was to investigate whether weight loss associated with RYGB improves the oxidative status of leukocytes and ameliorates subclinical atherosclerotic markers. This is an interventional study of 57 obese subjects who underwent RYGB surgery. We determined biochemical parameters and qualitative analysis of cholesterol, leukocyte and systemic oxidative stress markers —superoxide production, glutathione peroxidase 1 (GPX1), superoxide dismutase (SOD) activity and protein carbonylation—, soluble cellular adhesion molecules —sICAM-1 and sP-selectin—, myeloperoxidase (MPO) and leukocyte-endothelium cell interactions—rolling flux, velocity and adhesion. RYGB induced an improvement in metabolic parameters, including hsCRP and leukocyte count (p < 0.001, for both). This was associated with an amelioration in oxidative stress, since superoxide production and protein carbonylation were reduced (p < 0.05 and p < 0.01, respectively) and antioxidant systems were enhanced (GPX1; p < 0.05 and SOD; p < 0.01). In addition, a significant reduction of the following parameters was observed one year after RYGB: MPO and sICAM (p < 0.05, for both), sPselectin and pattern B of LDL particles (p < 0.001, for both), and rolling flux and adhesion of leukocytes (p < 0.05 and p < 0.01, respectively). Our results suggest that patients undergoing RYGB benefit from an amelioration of the prooxidant status of leukocytes, metabolic outcomes, and subclinical markers of atherosclerosis.

Inflammatory state of lymphatic vessels and miRNA profiles associated with relapse in ovarian cancer patients

Lymphogenic spread is associated with poor prognosis in epithelial ovarian cancer (EOC), yet little is known regarding roles of non-peri-tumoural lymphatic vessels (LVs) outside the tumour microenvironment that may impact relapse. The aim of this feasibility study was to assess whether inflammatory status of the LVs and/or changes in the miRNA profile of the LVs have potential prognostic and predictive value for overall outcome and risk of relapse. Samples of macroscopically normal human lymph LVs (n = 10) were isolated from the external iliac vessels draining the pelvic region of patients undergoing debulking surgery. This was followed by quantification of the inflammatory state (low, medium and high) and presence of cancer-infiltration of each LV using immunohistochemistry. LV miRNA expression profiling was also performed, and analysed in the context of high versus low inflammation, and cancer-infiltrated versus non-cancer-infiltrated. Results were correlated with clinical outcome data including relapse with an average follow-up time of 13.3 months. The presence of a high degree of inflammation correlated significantly with patient relapse (p = 0.033). Cancer-infiltrated LVs showed a moderate but non-significant association with relapse (p = 0.07). Differential miRNA profiles were identified in cancer-infiltrated LVs and those with high versus low inflammation. In particular, several members of the let-7 family were consistently down-regulated in highly inflamed LVs (>1.8-fold, p<0.05) compared to the less inflamed ones. Down-regulation of the let-7 family appears to be associated with inflammation, but whether inflammation contributes to or is an effect of cancer-infiltration requires further investigation.

Endothelial signaling by neutrophil-released oncostatin M enhances P-selectin-dependent inflammation and thrombosis

In the earliest phase of inflammation, histamine and other agonists rapidly mobilize P-selectin to the apical membranes of endothelial cells, where it initiates rolling adhesion of flowing neutrophils. Clustering of P-selectin in clathrin-coated pits facilitates rolling. Inflammatory cytokines typically signal by regulating gene transcription over a period of hours. We found that neutrophils rolling on P-selectin secreted the cytokine oncostatin M (OSM). The released OSM triggered signals through glycoprotein 130 (gp130)-containing receptors on endothelial cells that, within minutes, further clustered P-selectin and markedly enhanced its adhesive function. Antibodies to OSM or gp130, deletion of the gene encoding OSM in hematopoietic cells, or conditional deletion of the gene encoding gp130 in endothelial cells inhibited neutrophil rolling on P-selectin in trauma-stimulated venules of the mouse cremaster muscle. In a mouse model of P-selectin-dependent deep vein thrombosis, deletion of OSM in hematopoietic cells or of gp130 in endothelial cells markedly inhibited adhesion of neutrophils and monocytes and the rate and extent of thrombus formation. Our results reveal a paracrine-signaling mechanism by which neutrophil-released OSM rapidly influences endothelial cell function during physiological and pathological inflammation.

Contribution of neutrophils in the pathogenesis of rheumatoid arthritis

Neutrophils are major innate immune effector cells for host defense and have been a topic of active research for their participation in the pathogenesis of autoimmune inflammatory diseases including rheumatoid arthritis (RA) due to recently discovered neutrophil extracellular trap (NET) formation. NET formation and other mechanisms leading to the release of neutrophil nuclear and cytoplasmic contents are implicated as a source of citrullinated antigens in RA. Further investigations are required to delineate what factors diverge neutrophils from host defense to autoimmune response in RA.

The effect of myeloperoxidase isoforms on biophysical properties of red blood cells

Myeloperoxidase (MPO), an oxidant-producing enzyme, stored in azurophilic granules of neutrophils has been recently shown to influence red blood cell (RBC) deformability leading to abnormalities in blood microcirculation. Native MPO is a homodimer, consisting of two identical protomers (monomeric MPO) connected by a single disulfide bond but in inflammatory foci as a result of disulfide cleavage monomeric MPO (hemi-MPO) can also be produced. This study investigated if two MPO isoforms have distinct effects on biophysical properties of RBCs. We have found that hemi-MPO, as well as the dimeric form, bind to the glycophorins A/B and band 3 protein on RBC's plasma membrane, that lead to reduced cell resistance to osmotic and acidic hemolysis, reduction in cell elasticity, significant changes in cell volume, morphology, and the conductance of RBC plasma membrane ion channels. Furthermore, we have shown for the first time that both dimeric and hemi-MPO lead to phosphatidylserine (PS) exposure on the outer leaflet of RBC membrane. However, the effects of hemi-MPO on the structural and functional properties of RBCs were lower compared to those of dimeric MPO. These findings suggest that the ability of MPO protein to influence RBC's biophysical properties depends on its conformation (dimeric or monomeric isoform). It is intriguing to speculate that hemi-MPO appearance in blood during inflammation can serve as a regulatory mechanism addressed to reduce abnormalities on RBC response, induced by dimeric MPO.

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.

Proteomic atlas of organ vasculopathies triggered by Staphylococcus aureus sepsis

Sepsis is a life-threatening condition triggered by a dysregulated host response to microbial infection resulting in vascular dysfunction, organ failure and death. Here we provide a semi-quantitative atlas of the murine vascular cell-surface proteome at the organ level, and how it changes during sepsis. Using in vivo chemical labeling and high-resolution mass spectrometry, we demonstrate the presence of a vascular proteome that is perfusable and shared across multiple organs. This proteome is enriched in membrane-anchored proteins, including multiple regulators of endothelial barrier functions and innate immunity. Further, we automated our workflows and applied them to a murine model of methicillin-resistant Staphylococcus aureus (MRSA) sepsis to unravel changes during systemic inflammatory responses. We provide an organ-specific atlas of both systemic and local changes of the vascular proteome triggered by sepsis. Collectively, the data indicates that MRSA-sepsis triggers extensive proteome remodeling of the vascular cell surfaces, in a tissue-specific manner.

Vascular surfaces are rapidly remodeled during systemic inflammatory responses and sepsis. Here, the authors combine in vivo biotinylation and high-resolution mass spectrometry to characterize organ-level changes of the murine vascular cell surface proteome induced by MRSA sepsis.

Myeloperoxidase Deficiency Inhibits Cognitive Decline in the 5XFAD Mouse Model of Alzheimer's Disease

Myeloperoxidase (MPO) is an enzyme expressed mostly by neutrophils and is a primary mediator of neutrophils oxidative stress response. While a profound body of evidence associates neutrophil-derived MPO in the pathogenesis of Alzheimer’s disease (AD), this role has not been assessed in an animal model of AD. Here, we produced hematologic chimerism in the 5XFAD mouse model of AD, with MPO deficient mice, resulting in 5XFAD with hematologic MPO deficiency (5XFAD-MPO KO). Behavioral examinations of 5XFAD-MPO KO showed significant superior performance in spatial learning and memory, associative learning, and anxiety/risk assessment behavior, as compared to 5XFAD mice transplanted with WT cells (5XFAD-WT). Hippocampal immunohistochemical and mRNA expression analyses showed significantly reduced levels of inflammatory mediators in 5XFAD-MPO KO mice with no apparent differences in the numbers of amyloid-β plaques. In addition, immunoblotting and mRNA analyses showed significantly reduced levels of APOE in 5XFAD-MPO KO. Together, these results indicate a substantial involvement of neutrophil-derived MPO in the pathology of 5XFAD model of AD and suggest MPO as a potential therapeutic target in AD.

4-Methylbenzenecarbothioamide, a hydrogen sulfide donor, inhibits tumor necrosis factor-α and CXCL1 production and exhibits activity in models of pain and inflammation

The gasotransmitter hydrogen sulfide (H₂S) is known to regulate many pathophysiological processes. Preclinical assays have demonstrated that H₂S donors exhibit anti-inflammatory and antinociceptive activities, characterized by reduction of inflammatory mediators production, leukocytes recruitment, edema and mechanical allodynia. In the present study, the effects induced by 4-methylbenzenecarbothioamide (4-MBC) in models of pain and inflammation in mice, the mechanisms mediating such effects and the H₂S-releasing property of this compound were evaluated. 4-MBC spontaneously released H₂S in vitro in the absence of organic thiols. Intraperitoneal (i.p.) administration of 4-MBC (100 or 150 mg/kg) reduced the second phase of the nociceptive response induced by formaldehyde and induced a long lasting inhibitory effect on carrageenan mechanical allodynia. 4-MBC antiallodynic effect was not affected by previous administration of naltrexone or glibenclamide. 4-MBC (50, 100 or 150 mg/kg, i.p.) induced a long lasting inhibitory effect on paw edema induced by carrageenan. The highest dose (150 mg/kg, i.p.) of 4-MBC inhibited tumor necrosis factor-α and CXCL1 production and myeloperoxidase activity induced by carrageenan. Mechanical allodynia and paw edema induced by carrageenan were not inhibited by the 4-MBC oxo analogue (p-toluamide). In summary, 4-MBC, an H₂S releasing thiobenzamide, exhibits antinociceptive and anti-inflammatory activities. These activities may be due to reduced cytokine and chemokine production and neutrophil recruitment. The H₂S releasing property is likely essential for 4-MBC activity. Our results indicate that 4-MBC may represent a useful pharmacological tool to investigate the biological roles of H₂S.