Oxidation of calprotectin by hypochlorous acid prevents chelation of essential metal ions and allows bacterial growth: Relevance to infections in cystic fibrosis

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.

Significant alteration of protein profiles in a mouse model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is an endocrine disorder, affecting women of child-bearing age, and the incidence rate is growing and assuming epidemic proportions. The etiology of PCOS remains unknown and there is no cure. Some animal models for PCOS have been established which have enhanced our understanding of the underlying mechanisms, but omics data for revealing PCOS pathogenesis and for drug discovery are still lacking. In the present study, proteomics analysis was used to construct a protein profile of the ovaries in a PCOS mouse model. The result showed a clear difference in protein profile between the PCOS and control group, with 495 upregulated proteins and 404 downregulated proteins in the PCOS group. The GO term and KEGG pathway analyses of differentially expressed proteins mainly showed involvement in lipid metabolism, oxidative stress, and immune response, which are consistent with pathological characteristics of PCOS in terms of abnormal metabolism, endocrine disorders, chronic inflammation and imbalance between oxidant and antioxidant levels. Also, we found that inflammatory responses were activated in the PCOS ovarium, while lipid biosynthetic process peroxisome, and bile secretion were inhibited. In addition, we found some alteration in unexpected pathways, such as glyoxylate and dicarboxylate metabolism, which should be investigated. The present study makes an important contribution to the current lack of PCOS ovarian proteomic data and provides an important reference for research and development of effective drugs and treatments for PCOS.

Substrate-dependent metabolomic signatures of myeloperoxidase activity in airway epithelial cells: Implications for early cystic fibrosis lung disease

Myeloperoxidase (MPO) is released by neutrophils in inflamed tissues. MPO oxidizes chloride, bromide, and thiocyanate to produce hypochlorous acid (HOCl), hypobromous acid (HOBr), and hypothiocyanous acid (HOSCN), respectively. These oxidants are toxic to pathogens, but may also react with host cells to elicit biological activity and potential toxicity. In cystic fibrosis (CF) and related diseases, increased neutrophil inflammation leads to increased airway MPO and airway epithelial cell (AEC) exposure to its oxidants. In this study, we investigated how equal dose-rate exposures of MPO-derived oxidants differentially impact the metabolome of human AECs (BEAS-2B cells). We utilized enzymatic oxidant production with rate-limiting glucose oxidase (GOX) coupled to MPO, and chloride, bromide (Br-), or thiocyanate (SCN-) as substrates. AECs exposed to GOX/MPO/SCN- (favoring HOSCN) were viable after 24 h, while exposure to GOX/MPO (favoring HOCl) or GOX/MPO/Br- (favoring HOBr) developed cytotoxicity after 6 h. Cell glutathione and peroxiredoxin-3 oxidation were insufficient to explain these differences. However, untargeted metabolomics revealed GOX/MPO and GOX/MPO/Br- diverged significantly from GOX/MPO/SCN- for dozens of metabolites. We noted methionine sulfoxide and dehydromethionine were significantly increased in GOX/MPO- or GOX/MPO/Br--treated cells, and analyzed them as potential biomarkers of lung damage in bronchoalveolar lavage fluid from 5-year-olds with CF (n = 27). Both metabolites were associated with increasing bronchiectasis, neutrophils, and MPO activity. This suggests MPO production of HOCl and/or HOBr may contribute to inflammatory lung damage in early CF. In summary, our in vitro model enabled unbiased identification of exposure-specific metabolite products which may serve as biomarkers of lung damage in vivo. Continued research with this exposure model may yield additional oxidant-specific biomarkers and reveal explicit mechanisms of oxidant byproduct formation and cellular redox signaling.

Post-translational modifications on the metal-sequestering protein calprotectin

Human calprotectin (CP, S100A8/S100A9 oligomer) is an abundant neutrophil protein that contributes to innate immunity by sequestering nutrient metal ions in the extracellular space. This process starves invading microbial pathogens of essential metal nutrients, which can inhibit growth and colonization. Over the past decade, fundamental and clinical studies have revealed that the S100A8 and S100A9 subunits of CP exhibit a variety of post-translational modifications (PTMs). This review summarizes PTMs on the CP subunits that have been detected and highlights two recent studies that evaluated the structural and functional consequences of methionine and cysteine oxidation on CP. Collectively, these investigations indicate that the molecular speciation of extracellular CP is complex and composed of multiple proteoforms. Moreover, PTMs may impact biological function and the lifetime of the protein. It is therefore important that post-translationally modified CP species receive consideration and integration into the current working model for how CP functions in nutritional immunity.

Formation of Calprotectin-Derived Peptides in the Airways of Children with Cystic Fibrosis

Calprotectin is released by activated neutrophils along with myeloperoxidase (MPO) and proteases. It plays numerous roles in inflammation and infection, and is used as an inflammatory biomarker. However, calprotectin is readily oxidized by MPO-derived hypohalous acids to form covalent dimers of its S100A8 and S100A9 subunits. The dimers are susceptible to degradation by proteases. We show that detection of human calprotectin by ELISA declines markedly because of its oxidation by hypochlorous acid and subsequent degradation. Also, proteolysis liberates specific peptides from oxidized calprotectin that is present at inflammatory sites. We identified six calprotectin-derived peptides by mass spectrometry and detected them in the bronchoalveolar lavage fluid of children with cystic fibrosis (CF). We assessed the peptides as biomarkers of neutrophilic inflammation and infection. The content of the calprotectin peptide ILVI was related to calprotectin (r = 0.72, p = 0.01, n = 10). Four of the peptides were correlated with the concentration of MPO (r > 0.7, p ≤ 0.01, n = 21), while three were higher (p < 0.05) in neutrophil elastase-positive (n = 14) than -negative samples (n = 7). Also, five of the peptides were higher (p < 0.05) in the bronchoalveolar lavage fluid from children with CF with infections (n = 21) than from non-CF children without infections (n = 6). The specific peptides liberated from calprotectin will signal uncontrolled activity of proteases and MPO during inflammation. They may prove useful in tracking inflammation in respiratory diseases dominated by neutrophils, including coronavirus disease 2019.

Myeloperoxidase: Growing importance in cancer pathogenesis and potential drug target

Myeloperoxidase is a heme-peroxidase which makes up approximately 5% of the total dry cell weight of neutrophils where it is predominantly found in the primary (azurophilic) granules. Other cell types, such as monocytes and certain macrophage subpopulations also contain myeloperoxidase, but to a much lesser extent. Initially, the function of myeloperoxidase had been mainly associated with its ability as a catalyzer of reactive oxidants that help to clear pathogens. However, over the past years non-canonical functions of myeloperoxidase have been described both in health and disease. Attention has been specially focused on inflammatory diseases, in which an exacerbate infiltration of leukocytes can favor a poorly-controlled production and release of myeloperoxidase and its oxidants. There is compelling evidence that myeloperoxidase derived oxidants contribute to tissue damage and the development and propagation of acute and chronic vascular inflammation. Recently, neutrophils have attracted much attention within the large diversity of innate immune cells that are part of the tumor microenvironment. In particular, neutrophil-derived myeloperoxidase may play an important role in cancer development and progression. This review article aims to provide a comprehensive overview of the roles of myeloperoxidase in the development and progression of cancer. We propose future research approaches and explore prospects of inhibiting myeloperoxidase as a strategy to fight against cancer.

Role of inflammation and oxidative stress in tissue damage associated with cystic fibrosis: CAPE as a future therapeutic strategy

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, responsible for the synthesis of the CFTR protein, a chloride channel. The gene has approximately 2000 known mutations and all of them affect in some degree the protein function, which makes the pathophysiological manifestations to be multisystemic, mainly affecting the respiratory, gastrointestinal, endocrine, and reproductive tracts. Currently, the treatment of the disease is restricted to controlling symptoms and, more recently, a group of drugs that act directly on the defective protein, known as CFTR modulators, was developed. However, their high cost and difficult access mean that their use is still very restricted. It is important to search for safe and low-cost alternative therapies for CF and, in this context, natural compounds and, mainly, caffeic acid phenethyl ester (CAPE) appear as promising strategies to assist in the treatment of the disease. CAPE is a compound derived from propolis extracts that has antioxidant and anti-inflammatory activities, covering important aspects of the pathophysiology of CF, which points to the possible benefit of its use in the disease treatment. To date, no studies have effectively tested CAPE for CF and, therefore, we intend with this review to elucidate the role of inflammation and oxidative stress for tissue damage seen in CF, associating them with CAPE actions and its pharmacologically active derivatives. In this way, we offer a theoretical basis for conducting preclinical and clinical studies relating the use of this molecule to CF.

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.

Methionine sulfoxide and the methionine sulfoxide reductase system as modulators of signal transduction pathways: a review

Methionine oxidation and reduction is a common phenomenon occurring in biological systems under both physiological and oxidative-stress conditions. The levels of methionine sulfoxide (MetO) are dependent on the redox status in the cell or organ, and they are usually elevated under oxidative-stress conditions, aging, inflammation, and oxidative-stress related diseases. MetO modification of proteins may alter their function or cause the accumulation of toxic proteins in the cell/organ. Accordingly, the regulation of the level of MetO is mediated through the ubiquitous and evolutionary conserved methionine sulfoxide reductase (Msr) system and its associated redox molecules. Recent published research has provided new evidence for the involvement of free MetO or protein-bound MetO of specific proteins in several signal transduction pathways that are important for cellular function. In the current review, we will focus on the role of MetO in specific signal transduction pathways of various organisms, with relation to their physiological contexts, and discuss the contribution of the Msr system to the regulation of the observed MetO effect.

Divalent cations influence the dimerization mode of murine S100A9 protein by modulating its disulfide bond pattern

S100A9, with its congener S100A8, belongs to the S100 family of calcium-binding proteins found exclusively in vertebrates. These two proteins are major constituents of neutrophils. In response to a pathological condition, they can be released extracellularly and become alarmins that induce both pro- and anti-inflammatory signals, through specific cell surface receptors. They also act as antimicrobial agents, mainly as a S100A8/A9 heterocomplex, through metal sequestration. The mechanisms whereby divalent cations modulate the extracellular functions of S100A8 and S100A9 are still unclear. Importantly, it has been proposed that these ions may affect both the ternary and quaternary structure of these proteins, thereby influencing their physiological properties. In the present study, we report the crystal structures of WT and C80A murine S100A9 (mS100A9), determined at 1.45 and 2.35 Å resolution, respectively, in the presence of calcium and zinc. These structures reveal a canonical homodimeric form for the protein. They also unravel an intramolecular disulfide bridge that stabilizes the C-terminal tail in a rigid conformation, thus shaping a second Zn-binding site per S100A9 protomer. In solution, mS100A9 apparently binds only two zinc ions per homodimer, with an affinity in the micromolar range, and aggregates in the presence of excess zinc. Using mass spectrometry, we demonstrate that mS100A9 can form both non-covalent and covalent homodimers with distinct disulfide bond patterns. Interestingly, calcium and zinc seem to affect differentially the relative proportion of these forms. We discuss how the metal-dependent interconversion between mS100A9 homodimers may explain the versatility of physiological functions attributed to the protein.

Myeloperoxidase inhibition decreases morbidity and oxidative stress in mice with cystic fibrosis-like lung inflammation

BACKGROUND

Cystic fibrosis (CF) lung disease is characterized by severe bacterial infections, excessive neutrophilic inflammation and oxidative stress. The neutrophil enzyme myeloperoxidase (MPO), which produces hypochlorous acid, is associated with worse disease outcomes. Therefore, pharmacological inhibition of MPO in the airways has therapeutic potential. We investigated whether treating mice with an MPO inhibitor during pulmonary infection decreases oxidative stress and improves infection outcomes in mice with CF-like lung inflammation without impacting on bacterial clearance.

METHODS

Transgenic β-epithelial sodium channel (βENaC)-overexpressing mice (n = 10) were infected with Burkholderia multivorans and treated twice daily with the MPO inhibitor AZM198 (125 μmol/kg) or vehicle administered by oral gavage for two days. Bodyweight was recorded daily. MPO activity, markers of oxidative stress, inflammatory cytokines and leukocytes numbers were measured in bronchoalveolar lavage fluid (BALF). Bacterial burden was determined in lung tissue homogenates.

RESULTS

During the course of infection, mice treated with AZM198 lost less weight than vehicle-treated mice (p < 0.01). MPO activity and glutathione sulfonamide, a hypochlorous acid-specific glutathione oxidation product, were significantly lower in BALF from AZM198-treated mice (p < 0.05). The inflammatory cytokines CXCL1 and TNF-α in BALF and bacterial burden in the lung were not significantly different between treated and control mice.

CONCLUSIONS

Orally administered AZM198 inhibits MPO activity in epithelial lining fluid. Blocking hypochlorous acid production in epithelial lining fluid during pulmonary infections through inhibition of MPO improves morbidity in mice with CF-like lung inflammation without interfering with clearance of bacteria. Pharmacological inhibition of MPO is an approach to limit destructive oxidative stress in cystic fibrosis lung disease in humans.

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.

Hypochlorous acid-mediated modification of proteins and its consequences

Myeloperoxidase (MPO) is a mammalian heme peroxidase released by activated immune cells, which forms chemical oxidants, including hypochlorous acid (HOCl), to kill bacteria and other invading pathogens. In addition to this important role in the innate immune system, there is significant evidence from numerous chronic inflammatory pathologies for the elevated production of HOCl and associated oxidative modification of proteins and damage to host tissue. Proteins are major targets for HOCl in biological systems, owing to their abundance and the high reactivity of several amino acid side-chains with this oxidant. As such, there is significant interest in understanding the molecular mechanisms involved in HOCl-mediated protein damage and defining the consequences of these reactions. Exposure of proteins to HOCl results in a wide range of oxidative modifications and the formation of chlorinated products, which alter protein structure and enzyme activity, and impact the function of biological systems. This review describes the reactivity of HOCl with proteins, including the specific pathways involved in side-chain modification, backbone fragmentation and aggregation, and outlines examples of some of the biological consequences of these reactions, particularly in relation to the development of chronic inflammatory disease.

Oxidative cross-linking of calprotectin occurs in vivo, altering its structure and susceptibility to proteolysis

Calprotectin, the major neutrophil protein, is a critical alarmin that modulates inflammation and plays a role in host immunity by strongly binding trace metals essential for bacterial growth. It has two cysteine residues favourably positioned to act as a redox switch. Whether their oxidation occurs in vivo and affects the function of calprotectin has received little attention. Here we show that in saliva from healthy adults, and in lavage fluid from the lungs of patients with respiratory diseases, a substantial proportion of calprotectin was cross-linked via disulfide bonds between the cysteine residues on its S100A8 and S100A9 subunits. Stimulated human neutrophils released calprotectin and subsequently cross-linked it by myeloperoxidase-dependent production of hypochlorous acid. The myeloperoxidase-derived oxidants hypochlorous acid, taurine chloramine, hypobromous acid, and hypothiocyanous acid, all at 10 μM, cross-linked calprotectin (5 μM) via reversible disulfide bonds. Hypochlorous acid generated A9-A9 and A8-A9 cross links. Hydrogen peroxide (10 μM) did not cross-link the protein. Purified neutrophil calprotectin existed as a non-covalent heterodimer of A8/A9 which was converted to a heterotetramer - (A8/A9)₂ - with excess calcium ions. Low level oxidation of calprotectin with hypochlorous acid produced substantial proportions of high order oligomers, whether oxidation occurred before or after addition of calcium ions. At high levels of oxidation the heterodimer could not form tetramers with calcium ions, but prior addition of calcium ions afforded some protection for the heterotetramer. Oxidation and formation of the A8-A9 disulfide cross link enhanced calprotectin's susceptibility to proteolysis by neutrophil proteases. We propose that reversible disulfide cross-linking of calprotectin occurs during inflammation and affects its structure and function. Its increased susceptibility to proteolysis will ultimately result in a loss of function.

Oxidative Post-translational Modifications Accelerate Proteolytic Degradation of Calprotectin

Oxidative post-translational modifications affect the structure and function of many biomolecules. Herein we examine the biophysical and functional consequences of oxidative post-translational modifications to human calprotectin (CP, S100A8/S100A9 oligomer, MRP8/MRP14 oligomer, calgranulins A/B oligomer). This abundant metal-sequestering protein contributes to innate immunity by starving invading microbial pathogens of transition metal nutrients in the extracellular space. It also participates in the inflammatory response. Despite many decades of study, little is known about the fate of CP at sites of infection and inflammation. We present compelling evidence for methionine oxidation of CP in vivo, supported by using ¹⁵N-labeled CP-Ser (S100A8(C42S)/S100A9(C3S)) to monitor for adventitious oxidation following human sample collection. To elucidate the biochemical and functional consequences of oxidative post-translational modifications, we examine recombinant CP-Ser with methionine sulfoxide modifications generated by exposing the protein to hydrogen peroxide. These oxidized species coordinate transition metal ions and exert antibacterial activity. Nevertheless, oxidation of M81 in the S100A9 subunit disrupts Ca(II)-induced tetramerization and, in the absence of a transition metal ion bound at the His₆ site, accelerates proteolytic degradation of CP. We demonstrate that native CP, which contains one Cys residue in each full-length subunit, forms disulfide bonds within and between S100A8/S100A9 heterodimers when exposed to hydrogen peroxide. Remarkably, disulfide bond formation accelerates proteolytic degradation of CP. We propose a new extension to the working model for extracellular CP where post-translational oxidation by reactive oxygen species generated during the neutrophil oxidative burst modulates its lifetime in the extracellular space.

Oxidative stress in early cystic fibrosis lung disease is exacerbated by airway glutathione deficiency

Neutrophil-derived myeloperoxidase (MPO) is recognized as a major source of oxidative stress at the airway surface of a cystic fibrosis (CF) lung where, despite limited evidence, the antioxidant glutathione is widely considered to be low. The aims of this study were to establish whether oxidative stress or glutathione status are associated with bronchiectasis and whether glutathione deficiency is inherently linked to CF or a consequence of oxidative stress. MPO was measured by ELISA in 577 bronchoalveolar lavage samples from 205 clinically-phenotyped infants and children with CF and 58 children without CF (ages 0.2-6.92 years). Reduced glutathione (GSH), oxidized glutathione species (GSSG; glutathione attached to proteins, GSSP; glutathione sulfonamide, GSA) and allantoin, an oxidation product of uric acid, were measured by mass spectrometry. The odds of having bronchiectasis were associated with MPO and GSSP. GSH was low in children with CF irrespective of oxidation. Oxidized glutathione species were significantly elevated in CF children with pulmonary infections compared to uninfected CF children. In non-CF children, infections had no effect on glutathione levels. An inadequate antioxidant response to neutrophil-mediated oxidative stress during infections exists in CF due to an inherent glutathione deficiency. Effective delivery of glutathione and inhibition of MPO may slow the development of bronchiectasis.

Assessment of glutathione/glutathione disulphide ratio and S-glutathionylated proteins in human blood, solid tissues, and cultured cells

Glutathione (GSH) is the major non-protein thiol in humans and other mammals, which is present in millimolar concentrations within cells, but at much lower concentrations in the blood plasma. GSH and GSH-related enzymes act both to prevent oxidative damage and to detoxify electrophiles. Under oxidative stress, two GSH molecules become linked by a disulphide bridge to form glutathione disulphide (GSSG). Therefore, assessment of the GSH/GSSG ratio may provide an estimation of cellular redox metabolism. Current evidence resulting from studies in human blood, solid tissues, and cultured cells suggests that GSH also plays a prominent role in protein redox regulation via S -glutathionylation, i.e., the conjugation of GSH to reactive protein cysteine residues. A number of methodologies that enable quantitative analysis of GSH/GSSG ratio and S-glutathionylated proteins (PSSG), as well as identification and visualization of PSSG in tissue sections or cultured cells are currently available. Here, we have considered the main methodologies applied for GSH, GSSG and PSSG detection in biological samples. This review paper provides an up-to-date critical overview of the application of the most relevant analytical, morphological, and proteomics approaches to detect and analyse GSH, GSSG and PSSG in mammalian samples as well as discusses their current limitations.

S100A8/A9: From basic science to clinical application

Neutrophils and monocytes belong to the first line of immune defence cells and are recruited to sites of inflammation during infection or sterile injury. Both cells contain huge amounts of the heterodimeric protein S100A8/A9 in their cytoplasm. S100A8/A9 belongs to the Ca²⁺ binding S100 protein family and has recently gained a lot of interest as a critical alarmin modulating the inflammatory response after its release (extracellular S100A8/A9) from neutrophils and monocytes. Extracellular S100A8/A9 interacts with the pattern recognition receptors Toll-like receptor 4 (TLR4) and Receptor for Advanced Glycation Endproducts (RAGE) promoting cell activation and recruitment. Besides its biological function, S100A8/A9 (also known as myeloid related protein 8/14, MRP8/14) was identified as interesting biomarker to monitor disease activity in chronic inflammatory disorders including inflammatory bowel disease and rheumatoid arthritis. Furthermore, S100A8/A9 has been tested successfully in pre-clinical imaging studies to localize sites of infection or sterile injury. Finally, recent evidence using small molecule inhibitors for S100A8/A9 also suggests that blocking S100A8/A9 activity exerts beneficial effects on disease activity in animal models of autoimmune diseases including multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis and inflammatory bowel disease. This review will provide a comprehensive and detailed overview into the structure and biological function of S100A8/A9 and also will give an outlook in terms of diagnostic and therapeutic applications targeting S100A8/A9.

Diagnosis and early life risk factors for bronchiectasis in cystic fibrosis: a review

INTRODUCTION

Lung disease in cystic fibrosis begins in early life with neutrophil-dominated inflammation and infection, is progressive and results in structural lung damage characterised by bronchial dilation and bronchiectasis. Preventative strategies must be employed in early life but require a better understanding of how bronchiectasis develops.

AREAS COVERED

In this review we have addressed the diagnosis and early life risk factors for bronchiectasis in young children with cystic fibrosis. A systematic review was not performed and the literature reviewed was known to the authors. Expert commentary: Bronchiectasis represents a process of progressive dilatation and damage of airway walls and is traditionally considered to be irreversible. Diagnosis is primarily by detecting a bronchial:arterial ratio of >1 on chest CT scan. Lung volume has a greater influence on airway diameter than on arterial making control of lung volume during scanning critical. Early life risk factors for the onset and progression bronchiectasis include: severe cystic fibrosis genotype; neutrophilic inflammation with free neutrophil elastase activity in the lung; and pulmonary infection. Bronchiectasis develops in the majority of children before they reach school age despite the best current therapy. To prevent bronchiectasis novel therapies are going to have to be given to infants.

Reactive Oxygen Species and Neutrophil Function

Neutrophils are essential for killing bacteria and other microorganisms, and they also have a significant role in regulating the inflammatory response. Stimulated neutrophils activate their NADPH oxidase (NOX2) to generate large amounts of superoxide, which acts as a precursor of hydrogen peroxide and other reactive oxygen species that are generated by their heme enzyme myeloperoxidase. When neutrophils engulf bacteria they enclose them in small vesicles (phagosomes) into which superoxide is released by activated NOX2 on the internalized neutrophil membrane. The superoxide dismutates to hydrogen peroxide, which is used by myeloperoxidase to generate other oxidants, including the highly microbicidal species hypochlorous acid. NOX activation occurs at other sites in the cell, where it is considered to have a regulatory function. Neutrophils also release oxidants, which can modify extracellular targets and affect the function of neighboring cells. We discuss the identity and chemical properties of the specific oxidants produced by neutrophils in different situations, and what is known about oxidative mechanisms of microbial killing, inflammatory tissue damage, and signaling.