Myeloperoxidase: a key regulator of neutrophil oxidant production

Analysis of protein chlorination by mass spectrometry

Chlorination of tyrosine is a commonly known effect/consequence of myeloperoxidase activity at sites of inflammation, and detection of 3-chlorotyrosine has been used as biomarker for inflammatory diseases. However, few studies have addressed site specific chlorination in proteins, and no methods for large scale chloroproteomics studies have yet been published.

In this study, we present an optimized mass spectrometry based protocol to identify and quantify chlorinated peptides from single proteins modified by HOCl (100 and 500 μM, within estimated pathophysiological levels), at a high level of sensitivity and accuracy. Particular emphasis was placed on 1) sensitive and precise detection of modification sites, 2) the avoidance of loss or artefactual creation of modifications, 3) accurate quantification of peptide abundance and reduction of missing values problem, 4) monitoring the dynamics of modification in samples exposed to different oxidant concentrations and 5) development of guidelines for verification of chlorination sites assignment.

A combination of an optimised sample preparation protocol, and improved data analysis approaches have allowed identification of 33 and 15 chlorination sites in laminin and fibronectin, respectively, reported in previous manuscripts [1,2]. The method was subsequently tested on murine basement membrane extract, which contains high levels of laminin in a complex mixture. Here, 10 of the major chlorination sites in laminin were recapitulated, highlighting the utility of the method in detecting damage in complex samples.

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An optimized mass spectrometry method is presented to detect protein chlorination.

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Reduction and alkylation leads to loss of chlorinated residues.

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Identification of modification sites in fibronectin and laminin induced by HOCl.

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Quantification of relative site occupancy (RSO) of chlorinated residues.

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Largest chloroproteomics dataset to date.

A highly specific and sensitive turn-on fluorescence probe for hypochlorite detection and its bioimaging applications

Development of high performance fluorescent chemosensors for the detection of ClO- in vitro and in vivo is very desirable, because many human diseases are caused by ClO-. In this paper, a highly selectivity and sensitive fluorescent probe, EDPC, based on 3-acetylcoumarin, was synthesized, which could respond to ClO- and exhibit an "off-on" mode in Tris-HCl buffer (pH = 7.2, 10 mM, 50% C2H5OH) solutions. The detection limit of the EDPC probe for ClO- was as low as 1.2 × 10-8 M. Moreover, the high selectivity and high sensitivity of EDPC towards ClO- are attributed to the oxidation reaction between the C-O of the coumarin lactone and the C[double bond, length as m-dash]C formed by aldol condensation and the mechanism was further verified using ESI-MS and DFT. Additionally, the concentrations of ClO- in real water were also calculated using the EDPC probe and showed good recovery. Finally, the distribution of intracellular endogenous ClO- was gained by confocal fluorescence microscopy in living HEK293T cells.

A transgenic zebrafish line for in vivo visualisation of neutrophil myeloperoxidase

The neutrophil enzyme myeloperoxidase (MPO) is a major enzyme made by neutrophils to generate antimicrobial and immunomodulatory compounds, notably hypochlorous acid (HOCl), amplifying their capacity for destroying pathogens and regulating inflammation. Despite its roles in innate immunity, the importance of MPO in preventing infection is unclear, as individuals with MPO deficiency are asymptomatic with the exception of an increased risk of candidiasis. Dysregulation of MPO activity is also linked with inflammatory conditions such as atherosclerosis, emphasising a need to understand the roles of the enzyme in greater detail. Consequently, new tools for investigating granular dynamics in vivo can provide useful insights into how MPO localises within neutrophils, aiding understanding of its role in preventing and exacerbating disease. The zebrafish is a powerful model for investigating the immune system in vivo, as it is genetically tractable, and optically transparent. To visualise MPO activity within zebrafish neutrophils, we created a genetic construct that expresses human MPO as a fusion protein with a C-terminal fluorescent tag, driven by the neutrophil-specific promoter lyz. After introducing the construct into the zebrafish genome by Tol2 transgenesis, we established the Tg(lyz:Hsa.MPO-mEmerald,cmlc2:EGFP)sh496 line, and confirmed transgene expression in zebrafish neutrophils. We observed localisation of MPO-mEmerald within a subcellular location resembling neutrophil granules, mirroring MPO in human neutrophils. In Spotless (mpxNL144) larvae-which express a non-functional zebrafish myeloperoxidase-the MPO-mEmerald transgene does not disrupt neutrophil migration to sites of infection or inflammation, suggesting that it is a suitable line for the study of neutrophil granule function. We present a new transgenic line that can be used to investigate neutrophil granule dynamics in vivo without disrupting neutrophil behaviour, with potential applications in studying processing and maturation of MPO during development.

Dietary Flavonoids Scavenge Hypochlorous Acid via Chlorination on A- and C-Rings as Primary Reaction Sites: Structure and Reactivity Relationship

Dietary flavonoids are known as scavengers of reactive oxygen species such as hypochlorous acid. In spite of the abundant scavenging capacity data reported, few reports have addressed the relationship between the scavenging capacity and structures of different flavonoids. We characterized the reaction products of five flavonoids (apigenin, quercetin, naringenin, ampelopsin, and epicatechin) with hypochlorous acid and found that primary chlorination reaction occurred on the A-ring (C6 or C8) and/or C-rings but not on B-rings. Correlation of the hypochlorous acid scavenging capacity (IC₅₀ values) and the structural features of flavonoids revealed that the hydroxyl groups in the A-ring and B-ring can enhance the scavenging capacity, whereas the C(2)C(3) double bond has a negative impact on the HClO scavenging capacity. Combining the SAR analysis and chemical study, we proposed that the reaction mechanism between flavonoids and HClO should be an electrophilic substitution reaction. Density functional theory (DFT) results are consistent with the selectivity of chlorination on the flavonoids. Our findings highlight the importance of considering specific reactive oxygen species when measuring radical scavenging capacity of dietary antioxidants.

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.

Looking for a partner: ceruloplasmin in protein-protein interactions

Ceruloplasmin (CP) is a mammalian blood plasma ferroxidase. More than 95% of the copper found in plasma is carried by this protein, which is a member of the multicopper oxidase family. Proteins from this group are able to oxidize substrates through the transfer of four electrons to oxygen. The essential role of CP in iron metabolism in humans is particularly evident in the case of loss-of-function mutations in the CP gene resulting in a neurodegenerative syndrome known as aceruloplasminaemia. However, the functions of CP are not limited to the oxidation of ferrous iron to ferric iron, which allows loading of the ferric iron into transferrin and prevents the deleterious reactions of Fenton chemistry. In recent years, a number of novel CP functions have been reported, and many of these functions depend on the ability of CP to form stable complexes with a number of proteins.

Bioluminescent probe for detecting endogenous hypochlorite in living mice

As a kind of biologically important reactive oxygen species (ROS), hypochlorite (ClO^-) plays a crucial role in many physiological processes. As such, endogenous ClO^- is a powerful antibacterial agent during pathogen invasion. Nonetheless, excessive endogenous ClO^- could pose a health threat to mammalian animals including humans. However, the detection of endogenous ClO^- by bioluminescence probes in vivo remains a considerable challenge. Herein, based on a caged strategy, we developed a turn-on bioluminescent probe 1 for the highly selective detection of ClO^-in vitro and imaging endogenous ClO^- in a mouse inflammation model. We anticipate that such a probe could help us understand the role of endogenous ClO^- in a variety of physiological and pathological processes.

Crude extract from Libidibia ferrea (Mart. ex. Tul.) L.P. Queiroz leaves decreased intra articular inflammation induced by zymosan in rats

Background

Libidibia ferrea (L. ferrea) has been used in folk medicine to treat several conditions and to prevent cancer. This study performed a chromatographic analysis of the crude aqueous extract of Libidibia ferrea (Mart. ex. Tul.) L.P. Queiroz (LfAE) leaves and evaluated its in vivo antioxidant and anti-inflammatory potential.

Methods

Polyphenols present in LfAE were characterized by high performance liquid chromatography (HPLC). Anti-inflammatory activity was studied in an experimental model of zymosan-induced intra-articular inflammation, conducted in Wistar rats treated with LfAE at the doses of 100, 200 and 300 mg/kg by gavage. Synovial fluid was collected for global leukocyte count, for spectrocopical UV/VIS analysis of myeloperoxidase (MPO) activity, total glutathione and malondialdehyde (MDA), and for quantification of inflammatory cytokines IL1-β and TNF-α by enzyme-linked immunosorbent assay. Synovial membrane was collected for histological analysis. The level of statistical significance was p < 0.05.

Results

HPLC detected concentrations of 1.56 (0.77) %m/m for ellagic acid and 1.20 (1.38) %m/m for gallic acid in LfAE leaves. Treatment with LfAE at all doses significantly decreased the leukocyte influx into the synovial fluid (p < 0.001) and myeloperoxidase activity (p < 0.001), an important marker of neutrophils. LfAE at doses of 100 (p < 0.05), 200 and 300 mg/kg (p < 0.001) also reduced the levels of MDA. LfAE at doses of 200 and 300 mg/kg significantly decreased the levels of IL-1β (p < 0.05) and TNF-α (p < 0.001). All doses of LfAE resulted in increased levels of total glutathione (p < 0.001). Histopathological findings confirmed a reduction of the inflammatory infiltrate in the rats treated with LfAE at a dose of 200 mg/kg (p < 0.05).

Conclusion

LfAE has an important anti-oxidant and anti-inflammatory effect on intra-articular inflammation.

pH controlled byproduct formation in aqueous decomposition of N-chloro-α-alanine

N-chloro-amino acids are readily formed in chlorination water treatment technologies. These reactions are also important in biological systems where HOCl plays an important role in the defense mechanism against invading pathogens. The intermediates and the products formed are of primary concern because they may have significant biological activities. In order to clarify intimate details and resolve discrepancies in the literature, the decomposition kinetics of N-chloro-α-alanine (MCA) was studied in the neutral - alkaline pH range by UV-vis spectrophotometry and ¹H-NMR method. In contrast to earlier reports, the decomposition reaction proceeds via two distinct reaction paths: k_obs1 = k_OH[OH^-] + k, where k_OH = (1.38 ± 0.02) × 10^-2 M^-1s^-1 and k = (2.95 ± 0.09) × 10^-4 s^-1. In slightly alkaline solution, the sole product is acetaldehyde. Under alkaline conditions, the main product is pyruvate ion, however, N-acetyl-α-alanine is also formed in a subsequent reaction sequence. A detailed kinetic model is postulated which involves the rate determining dissociation of MCA into Cl^- and ethanimine which produces acetaldehyde in further reaction steps. Via the OH^- assisted path, first a carbanion is formed which undergoes dechlorination and produces iminopropionate ion. This species is transformed into pyruvate ion through hydration and deamination steps.

A "reactive" turn-on fluorescence probe for hypochlorous acid and its bioimaging application

An aza-BODIPY-CNOH probe attached aldoxime group demonstrated the specific detection for hypochlorous acid by the turn-on red emission signal. NMR and HRMS experiments confirmed that the fluorescence originated from the oxidation degradation of the non-fluorescence, aldoxime-based aza-BODIPY-CNOH probe into the red-fluorescence, nitrile oxide-based aza-BODIPY compound aza-BODIPY-CNO. The aza-BODIPY-CNOH probe showed good biocompatibility and was low toxic to living cells as shown from MTT experiments. Living RAW264.7 cells imaging indicated the aza-BODIPY-CNOH probe had good permeability and either exogenous or endogenous HClO caused the intracellular bright-red fluorescence, showing its potential hypochlorous acid-specific sensing ability in biological systems.

An ultra-sensitive ratiometric fluorescent probe for hypochlorous acid detection by the synergistic effect of AIE and TBET and its application of detecting exogenous/endogenous HOCl in living cells

TR-OClexhibits ultra-high sensitivity towards HOCl with a 7000-fold enhancement in the fluorescence ratio (I₅₈₉/I₄₇₇) and a detection limit of 1.29 nM, which is one of the highest recorded so far.

Formation of 8-S-L-Cysteinyladenosine from 8-Bromoadenosine and Cysteine

When 8-bromoadenosine was incubated with cysteine at pH 7.2 and 37°C, an exclusive product was generated. This product was identified as a cysteine substitution derivative of adenosine at the 8 position, 8-S-L-cysteinyladenosine. The reaction accelerated as pH increased from mildly acidic to basic conditions. The isolated cysteine adduct of adenosine decreased with a half-life of 15 h at pH 7.2 and 37°C. Similar results were obtained for the incubation of 8-bromo-2'-deoxyadenosine and 8-bromoadenosine 3',5'-cyclic monophosphate with cysteine. These results suggest that 8-bromoadenine in nucleotides, RNA, and DNA can react with thiols, resulting in adducts under physiological conditions.

A novel isolongifolanone based fluorescent probe with super selectivity and sensitivity for hypochlorite and its application in bio-imaging

In this study, a novel biocompatible fluorescent probe (DN) capable of detecting ClO^- in physiological medium was rationally designed and synthesized from natural and renewable isolongifolanone. This probe underwent a highly specific and sensitive oxidation reaction with ClO^- and liberated an isolongifolanone derivative (PA) emitting intensive blue fluorescence. In response to ClO^-, the fluorescence emission of DN was obviously enhanced within a short time. The detection limit of DN toward ClO^- was found to be as low as 5.86 × 10^-9 M. IR, MS and DFT calculation were employed to further confirm the sensing mechanism. Moreover, the test strips coated with DN could easily recognize ClO^- from other relevant species through the changes of fluorescence color under 365 nm UV lamp. More importantly, we also successfully demonstrated the potential application of DN for the detection of intracellular hypochloritein living cells.

Conjugation of urate-derived electrophiles to proteins during normal metabolism and inflammation

Urate is often viewed as an antioxidant. Here, we present an alternative perspective by showing that, when oxidized, urate propagates oxidative stress. Oxidation converts urate to the urate radical and the electrophilic products dehydrourate, 5-hydroxyisourate, and urate hydroperoxide, which eventually break down to allantoin. We investigated whether urate-derived electrophiles are intercepted by nucleophilic amino acid residues to form stable adducts on proteins. When urate was oxidized in the presence of various peptides and proteins, two adducts derived from urate (M _r 167 Da) were detected and had mass additions of 140 and 166 Da, occurring mainly on lysine residues and N-terminal amines. The adduct with a 140-Da mass addition was detected more frequently and was stable. Dehydrourate (M _r 166 Da) also formed transient adducts with cysteine residues. Urate-derived adducts were detected on human serum albumin in plasma of healthy donors. Basal adduct levels increased when neutrophils were added to plasma and stimulated, and relied on the NADPH oxidase, myeloperoxidase, hydrogen peroxide, and superoxide. Adducts of oxidized urate on serum albumin were elevated in plasma and synovial fluid from individuals with gout and rheumatoid arthritis. We propose that rather than acting as an antioxidant, urate's conversion to electrophiles contributes to oxidative stress. The addition of urate-derived electrophiles to nucleophilic amino acid residues, a process we call oxidative uratylation, will leave a footprint on proteins that could alter their function when critical sites are modified.

Ginger (Zingiber officinale Roscoe) for the treatment and prevention of necrotizing enterocolitis

ETHNOPHARMACOLOGICAL RELEVANCE

Necrotizing enterocolitis (NEC) is the most important gastrointestinal emergency affecting especially preterm infants and causes severe morbidities and mortality. However, there is no cure. Oxidant stress, inflammation, apoptosis, as well as prematurity are believed to responsible in the pathogenesis of the disease. Ginger and its compounds have anti-inflammatory, antimicrobial, anti-oxidant properties and immunomodulatory, cytoprotective/regenerative actions.

AIM OF THE STUDY

This study aimed to evaluate the beneficial effects of ginger on the intestinal damage in an experimental rat model of NEC.

MATERIALS AND METHODS

Thirty newborn Wistar rats were divided into three groups: NEC, NEC + ginger and control in this experimental study. NEC was induced by injection of intraperitoneal lipopolysaccharide, feeding with enteral formula, hypoxia-hyperoxia and cold stress exposure. The pups in the NEC + ginger group were orally administered ginger at a dose of 1000 mg/kg/day. Proximal colon and ileum were excised. Histopathological, immunohistochemical (TUNEL for apoptosis, caspase 3 and 8) and biochemical assays including xanthine oxidase (XO), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), malonaldehyde (MDA) and myeloperoxidase (MPO), tumor necrosis factor-α (TNF-α), interleukin1β (IL-1β), and interleukin 6 (IL-6) activity were evaluated.

RESULTS

Compared with the NEC group, the rat pups in the NEC + ginger group had better clinical disease scores and weight gain (p < 0.05). Macroscopic evaluation, Histopathologic and apoptosis assessment (TUNEL, caspase 3 and 8) releaved that severity of intestinal damage were significantly lower in the NEC + ginger group (p < 0.05). The levels of TNF-α, IL-1β and IL-6 in the ginger treated group were significantly decreased (P < 0.05). The GSH-Px and SOD levels of the ginger treated group were significantly preserved in the NEC + ginger group (p < 0.05). The tissue XO, MDA and MPO levels of the NEC + ginger group were significantly lower than those in the NEC group (P < 0.05).

CONCLUSION

Ginger therapy efficiently ameliorated the severity of intestinal damage in NEC and may be a promising treatment option.

Selective Monitoring and Imaging of Eosinophil Peroxidase Activity with a J-Aggregating Probe

The specific detection of eosinophil peroxidase (EPO) activity requires the difficult distinction between hypobromous acid generated by EPO and hypochlorous acid generated by other haloperoxidases. Here we report a fluorogenic probe that is halogenated with high kinetic selectivity (≥1200:1) for HOBr over HOCl. Heavy-atom effects do not quench the dibrominated product because of its self-assembly into emissive J-aggregates that provide a turn-on signal. Applications of this fluorogen to EPO activity assays, dipstick sensors, fluorescence imaging of EPO activity, assays of oxidative stress in cancer cells, and immune response detection in live mice are reported.

Oxidative stress in autoimmune rheumatic diseases

The management of patients with autoimmune rheumatic diseases such as rheumatoid arthritis (RA) remains a significant challenge. Often the rheumatologist is restricted to treating and relieving the symptoms and consequences and not the underlying cause of the disease. Oxidative stress occurs in many autoimmune diseases, along with the excess production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). The sources of such reactive species include NADPH oxidases (NOXs), the mitochondrial electron transport chain, nitric oxide synthases, nitrite reductases, and the hydrogen sulfide producing enzymes cystathionine-β synthase and cystathionine-γ lyase. Superoxide undergoes a dismutation reaction to generate hydrogen peroxide which, in the presence of transition metal ions (e.g. ferrous ions), forms the hydroxyl radical. The enzyme myeloperoxidase, present in inflammatory cells, produces hypochlorous acid, and in healthy individuals ROS and RNS production by phagocytic cells is important in microbial killing. Both low molecular weight antioxidant molecules and antioxidant enzymes, such as superoxide dismutase, catalase, glutathione peroxidase, and peroxiredoxin remove ROS. However, when ROS production exceeds the antioxidant protection, oxidative stress occurs. Oxidative post-translational modifications of proteins then occur. Sometimes protein modifications may give rise to neoepitopes that are recognized by the immune system as 'non-self' and result in the formation of autoantibodies. The detection of autoantibodies against specific antigens, might improve both early diagnosis and monitoring of disease activity. Promising diagnostic autoantibodies include anti-carbamylated proteins and anti-oxidized type II collagen antibodies. Some of the most promising future strategies for redox-based therapeutic compounds are the activation of endogenous cellular antioxidant systems (e.g. Nrf2-dependent pathways), inhibition of disease-relevant sources of ROS/RNS (e.g. isoform-specific NOX inhibitors), or perhaps specifically scavenging disease-related ROS/RNS via site-specific antioxidants.

Detection of Hydrogen Peroxide with Fluorescent Dyes

SIGNIFICANCE

Hydrogen peroxide (H₂O₂) is a powerful effector of redox signaling. It is able to oxidize cysteine residues, metal ion centers, and lipids. Understanding H₂O₂-mediated signaling requires, to some extent, measurement of H₂O₂ level. Recent Advances: Chemically and genetically encoded fluorescent probes for the detection of H₂O₂ are currently the most sensitive and popular. Novel probes are constantly being developed, with the latest progress particular with boronates and genetically encoded probes.

CRITICAL ISSUES

All currently available probes display limitations in terms of sensitivity, local and temporal resolution, and specificity in the detection of low H₂O₂ concentrations. In this review, we discuss the power of fluorescent probes and the systems in which they have been successfully employed. Moreover, we recommend approaches for overcoming probe limitations and for the avoidance of artifacts.

FUTURE DIRECTIONS

Constant improvements will lead to the generation of probes that are not only more sensitive but also specifically tailored to individual cellular compartments. Antioxid. Redox Signal. 29, 585-602.

Neopterin, Inflammation, and Oxidative Stress: What Could We Be Missing?

Neopterin has been extensively used as a clinical marker of immune activation during inflammation in a wide range of conditions and stresses. However, the analysis of neopterin alone neglects the cellular reactions that generate it in response to interferon-γ. Neopterin is the oxidation product of 7,8-dihydroneopterin, which is a potent antioxidant generated by interferon-γ-activated macrophages. 7,8-Dihydroneopterin can protect macrophage cells from a range of oxidants through a scavenging reaction that generates either neopterin or dihydroxanthopterin, depending on the oxidant. Therefore, plasma and urinary neopterin levels are dependent on both macrophage activation to generate 7,8-dihydroneopterin and subsequent oxidation to neopterin. This relationship is clearly shown in studies of exercise and impact-induced injury during intense contact sport. Here, we argue that neopterin and total neopterin, which is the combined value of 7,8-dihydroneopterin and neopterin, could provide a more comprehensive analysis of clinical inflammation than neopterin alone.

Myeloperoxidase in the inflamed colon: A novel target for treating inflammatory bowel disease

Inflammatory bowel disease (IBD) is a debilitating disorder involving inflammation of the gastrointestinal tract. The incidence of IBD is increasing worldwide. Immunological responses in the gastrointestinal (GI) tract to altered gut microbiota, mucosal injury and loss of intestinal epithelial cell function all contribute to a complex mechanism underlying IBD pathogenesis. Immune cell infiltration, particularly neutrophils, is a histological feature of IBD. This innate immune response is aimed at resolving intestinal damage however, neutrophils and monocytes that are recruited and accumulate in the GI wall, participate in IBD pathogenesis by producing inflammatory cytokines and soluble mediators such as reactive oxygen species (ROS; one- and two-electron oxidants). Unregulated ROS production in host tissue is linked to oxidative damage and inflammation and may potentiate mucosal injury. Neutrophil-myeloperoxidase (MPO) is an abundant granule enzyme that catalyses production of potent ROS; biomarkers of oxidative damage (and MPO protein) are increased in the mucosa of patients with IBD. Targeting MPO may mitigate oxidative damage to host tissue and ensuing inflammation. Here we identify mechanisms by which MPO activity perpetuates inflammation and contributes to host-tissue injury in patients with IBD and discuss MPO as a potential therapeutic target to protect the colon from inflammatory injury.

Myeloperoxidase as an Active Disease Biomarker: Recent Biochemical and Pathological Perspectives

Myeloperoxidase (MPO) belongs to the family of heme-containing peroxidases, produced mostly from polymorphonuclear neutrophils. The active enzyme (150 kDa) is the product of the MPO gene located on long arm of chromosome 17. The primary gene product undergoes several modifications, such as the removal of introns and signal peptides, and leads to the formation of enzymatically inactive glycosylated apoproMPO which complexes with chaperons, producing inactive proMPO by the insertion of a heme moiety. The active enzyme is a homodimer of heavy and light chain protomers. This enzyme is released into the extracellular fluid after oxidative stress and different inflammatory responses. Myeloperoxidase is the only type of peroxidase that uses H₂O₂ to oxidize several halides and pseudohalides to form different hypohalous acids. So, the antibacterial activities of MPO involve the production of reactive oxygen and reactive nitrogen species. Controlled MPO release at the site of infection is of prime importance for its efficient activities. Any uncontrolled degranulation exaggerates the inflammation and can also lead to tissue damage even in absence of inflammation. Several types of tissue injuries and the pathogenesis of several other major chronic diseases such as rheumatoid arthritis, cardiovascular diseases, liver diseases, diabetes, and cancer have been reported to be linked with MPO-derived oxidants. Thus, the enhanced level of MPO activity is one of the best diagnostic tools of inflammatory and oxidative stress biomarkers among these commonly-occurring diseases.

Integrated transcriptomic and proteomic analyses reveal potential mechanisms linking thermal stress and depressed disease resistance in the turbot Scophthalmus maximus

A worldwide increase in the reports of diseases affecting marine organisms has paralleled the climate warming over the past few decades. In this study, we applied omics to explore the mechanisms underlying thermo-linked epizootics, by comparing both the transcriptome- and proteome-wide response of turbots to a mimic pathogen (poly I:C) between high temperature and low temperature using a time-course approach. Our results showed that myeloperoxidase (MPO) and insulin were differentially expressed transcripts shared by all five time-points post poly I:C-injection between high and low temperature and also had a consistent expression trend as differentially expressed proteins at 24 h post injection. Combined with other data, it was suggested that the elevated temperature enhanced neutrophil-mediated immunity and the resultant MPO-mediated oxidative stress, which lasted for at least 5 days. The contents of malondialdehyde and protein carbonyls, markers of oxidative damage for lipids and proteins, respectively, were compared between different temperature groups, and the results further implied the emergence of oxidative damage under high temperature. It was also suggested that metabolism disorder likely occur considering the sustained expression changes of insulin. Hence, prolonged MPO-mediated oxidative stress and metabolic disorder might be involved in the thermo-linked epizootic.

Pharmacological targeting of ROS reaction network in myeloid leukemia cells monitored by ultra-weak photon emission

Acute myeloid leukemia (AML) is a blood cancer that is caused by a disorder of the process that normally generates neutrophils. Function and dysfunction of neutrophils are key to physiologic defense against pathogens as well as pathologies including autoimmunity and cancer. A major mechanism through which neutrophils contribute to health and disease is oxidative burst, which involves rapid release of reactive oxygen species (ROS) generated by a chemical reaction network catalyzed by enzymes including NADPH oxidase and myeloperoxidase (MPO). Due to the involvement of neutrophil-derived reactive oxygen species in many diseases and importance of NADPH oxidase and MPO-mediated reactions in progression and treatment of myeloid leukemia, monitoring this process and modulating it by pharmacological interventions is of great interest. In this work, we have evaluated the potential of a label-free method using ultra-weak photon emission (UPE) to monitor ROS production in neutrophil-like HL60 myeloid leukemia cells. Suppression of ROS was achieved by several drug candidates that target different parts of the reaction pathway. Our results show that UPE can report on ROS production as well as suppression by pharmacological inhibitors. We find that UPE is primarily generated by MPO catalyzed reaction and thus will be affected when an upstream reaction is pharmacologically modulated.

A highly sensitive and selective fluorescent probe for fast sensing of endogenous HClO in living cells

A highly sensitive and fast-response fluorescent probe for HClO detection was developed and employed to reveal the H₂S-induced HClO biogenesis in living cells.

Ultra-sensitive fluorescent probes for hypochlorite acid detection and exogenous/endogenous imaging of living cells

Two fluorescent probes have been developed to detect HOCl with ultra-high sensitivity and employed to image exogenous/endogenous HOCl in living cells.

Selenium-containing indolyl compounds: Kinetics of reaction with inflammation-associated oxidants and protective effect against oxidation of extracellular matrix proteins

Activated white blood cells generate multiple oxidants in response to invading pathogens. Thus, hypochlorous acid (HOCl) is generated via the reaction of myeloperoxidase (from neutrophils and monocytes) with hydrogen peroxide, and peroxynitrous acid (ONOOH), a potent oxidizing and nitrating agent is formed from superoxide radicals and nitric oxide, generated by stimulated macrophages. Excessive or misplaced production of these oxidants has been linked to multiple human pathologies, including cardiovascular disease. Atherosclerosis is characterized by chronic inflammation and the presence of oxidized materials, including extracellular matrix (ECM) proteins, within the artery wall. Here we investigated the potential of selenium-containing indoles to afford protection against these oxidants, by determining rate constants (k) for their reaction, and quantifying the extent of damage on isolated ECM proteins and ECM generated by human coronary artery endothelial cells (HCAECs). The novel selenocompounds examined react with HOCl with k 0.2-1.0 × 10⁸M^-1s^-1, and ONOOH with k 4.5-8.6 - × 10⁵M^-1s^-1. Reaction with H₂O₂ is considerably slower (k < 0.25M^-1s^-1). The selenocompound 2-phenyl-3-(phenylselanyl)imidazo[1,2-a]pyridine provided protection to human serum albumin (HSA) against HOCl-mediated damage (as assessed by SDS-PAGE) and damage to isolated matrix proteins induced by ONOOH, with a concomitant decrease in the levels of the biomarker 3-nitrotyrosine. Structural damage and generation of 3-nitroTyr on HCAEC-ECM were also reduced. These data demonstrate that the novel selenium-containing compounds show high reactivity with oxidants and may modulate oxidative and nitrosative damage at sites of inflammation, contributing to a reduction in tissue dysfunction and atherogenesis.

Protective effect of hydrogen-saturated saline on acute lung injury induced by oleic acid in rats

Background

The purpose of the study is to investigate the role and mechanisms of hydrogen-saturated saline (HSS) in the acute lung injury (ALI) induced by oleic acid (OA) in rats.

Methods

Rats were treated with OA (0.1 mL/kg) to induce ALI and then administered with HSS (5 mL/kg) by intravenous (iv) and intraperitoneal (ip) injection, respectively. Three hours after the injection with OA, the arterial oxygen partial pressure (PaO₂), arterial oxygen saturation (SaO₂), carbon dioxide partial pressure (PaCO₂), and bicarbonate (HCO₃⁻) levels were analyzed using blood gas analyzer. In addition, the levels of malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), and interleukin 1β (IL-1β) and myeloperoxidase (MPO) activity were measured by commercial kits, and pathological changes of lung tissue were examined by HE staining. Finally, the correlations of MPO activity or MDA level with the levels of TNF-α or IL-1β were analyzed by Pearson’s correlation analysis.

Results

We found decreased PaO₂ levels and the pathological changes of lung tissue of ALI after OA injection. In addition, OA increased the levels of MDA, TNF-α, and IL-1β, as well as MPO activity in lung tissues (P < 0.05). However, after treatment with HSS, all of these changes were alleviated (P < 0.05), and these changes were mitigated when treated with HSS by ip then iv injection (P < 0.05). Furthermore, MDA level and MPO activity were positively correlated with TNF-α and IL-1β levels in the lung tissue, respectively (P < 0.01).

Conclusion

HSS attenuated ALI induced by OA in rats and might protect against ALI through selective resistance to oxidation and inhibiting inflammatory infiltration.

Mesna (2-mercaptoethane sodium sulfonate) functions as a regulator of myeloperoxidase

Myeloperoxidase (MPO), an abundant protein in neutrophils, monocytes, and macrophages, is thought to play a critical role in the pathogenesis of various disorders ranging from cardiovascular diseases to cancer. We show that mesna (2-mercaptoethanesulfonic acid sodium salt), a detoxifying agent, which inhibits side effects of oxazaphosphorine chemotherapy, functions as a potent inhibitor of MPO; modulating its catalytic activity and function. Using rapid kinetic methods, we examined the interactions of mesna with MPO compounds I and II and ferric forms in the presence and absence of chloride (Cl^-), the preferred substrate of MPO. Our results suggest that low mesna concentrations dramatically influenced the build-up, duration, and decay of steady-state levels of Compound I and Compound II, which is the rate-limiting intermediate in the classic peroxidase cycle. Whereas, higher mesna concentrations facilitate the porphyrin-to-adjacent amino acid electron transfer allowing the formation of an unstable transient intermediate, Compound I*, that displays a characteristic spectrum similar to Compound I. In the absence of plasma level of chloride, mesna not only accelerated the formation and decay of Compound II but also reduced its stability in a dose depend manner. Mesna competes with Cl^-, inhibiting MPO's chlorinating activity with an IC₅₀ of 5µM, and switches the reaction from a 2e^- to a 1e^- pathway allowing the enzyme to function only with catalase-like activity. A kinetic model which shows the dual regulation through which mesna interacts with MPO and regulates its downstream inflammatory pathways is presented further validating the repurposing of mesna as an anti-inflammatory drug.

Immune evasion by a staphylococcal inhibitor of myeloperoxidase

Staphylococcus aureus is highly adapted to its host and has evolved many strategies to resist opsonization and phagocytosis. Even after uptake by neutrophils, S. aureus shows resistance to killing, which suggests the presence of phagosomal immune evasion molecules. With the aid of secretome phage display, we identified a highly conserved protein that specifically binds and inhibits human myeloperoxidase (MPO), a major player in the oxidative defense of neutrophils. We have named this protein "staphylococcal peroxidase inhibitor" (SPIN). To gain insight into inhibition of MPO by SPIN, we solved the cocrystal structure of SPIN bound to a recombinant form of human MPO at 2.4-Å resolution. This structure reveals that SPIN acts as a molecular plug that prevents H2O2 substrate access to the MPO active site. In subsequent experiments, we observed that SPIN expression increases inside the neutrophil phagosome, where MPO is located, compared with outside the neutrophil. Moreover, bacteria with a deleted gene encoding SPIN showed decreased survival compared with WT bacteria after phagocytosis by neutrophils. Taken together, our results demonstrate that S. aureus secretes a unique proteinaceous MPO inhibitor to enhance survival by interfering with MPO-mediated killing.

Sex and tissue specific gene expression patterns identified following de novo transcriptomic analysis of the Norway lobster, Nephrops norvegicus

BACKGROUND

The Norway lobster, Nephrops norvegicus, is economically important in European fisheries and is a key organism in local marine ecosystems. Despite multi-faceted scientific interest in this species, our current knowledge of genetic resources in this species remains very limited. Here, we generated a reference de novo transcriptome for N. norvegicus from multiple tissues in both sexes. Bioinformatic analyses were conducted to detect transcripts that were expressed exclusively in either males or females. Patterns were validated via RT-PCR.

RESULTS

Sixteen N. norvegicus libraries were sequenced from immature and mature ovary, testis and vas deferens (including the masculinizing androgenic gland). In addition, eyestalk, brain, thoracic ganglia and hepatopancreas tissues were screened in males and both immature and mature females. RNA-Sequencing resulted in >600 million reads. De novo assembly that combined the current dataset with two previously published libraries from eyestalk tissue, yielded a reference transcriptome of 333,225 transcripts with an average size of 708 base pairs (bp), with an N50 of 1272 bp. Sex-specific transcripts were detected primarily in gonads followed by hepatopancreas, brain, thoracic ganglia, and eyestalk, respectively. Candidate transcripts that were expressed exclusively either in males or females were highlighted and the 10 most abundant ones were validated via RT-PCR. Among the most highly expressed genes were Serine threonine protein kinase in testis and Vitellogenin in female hepatopancreas. These results align closely with gene annotation results. Moreover, a differential expression heatmap showed that the majority of differentially expressed transcripts were identified in gonad and eyestalk tissues. Results indicate that sex-specific gene expression patterns in Norway lobster are controlled by differences in gene regulation pattern between males and females in somatic tissues.

CONCLUSIONS

The current study presents the first multi-tissue reference transcriptome for the Norway lobster that can be applied to future biological, wild restocking and fisheries studies. Sex-specific markers were mainly expressed in males implying that males may experience stronger selection than females. It is apparent that differential expression is due to sex-specific gene regulatory pathways that are present in somatic tissues and not from effects of genes located on heterogametic sex chromosomes. The N. norvegicus data provide a foundation for future gene-based reproductive studies.

The preventive and curative effects of melatonin against abdominal aortic aneurysm in rats

OBJECTIVE

Oxygen free radicals are important components involved in the histopathologic tissue alterations observed during abdominal aortic aneurysms (AAAs). This study examined whether melatonin has protective or therapeutic effects against AAAs.

METHODS

Sprague-Dawley rats were divided into four groups. A CaCl₂ model was used to induce AAA. Starting on the operation day (Mel+AAA+Mel group) or 4 weeks after the operation (AAA+Mel group), the rats received intraperitoneal melatonin (10 mg/kg/day) for 6 and 2 weeks, respectively. The control and AAA groups received vehicle for 2 weeks after the sham operation and AAA induction, respectively. Angiographic measurements were recorded at the beginning, week 4, and week 6 of the study. After decapitation, aorta tissues were taken for the measurement of malondialdehyde, 8-hydroxy-2'-deoxyguanosine, glutathione levels, and myeloperoxidase and caspase-3 activity. Matrix metalloproteinase (MMP)-2, MMP-9, tumor necrosis factor-α, and inducible nitric oxide synthase protein expressions were analyzed by Western blot technique. Aortic tissues were also examined by light microscopy.

RESULTS

CaCl₂ caused an inflammatory response and oxidative damage indicated by rises in malondialdehyde and 8-hydroxy-2'-deoxyguanosine levels. Myeloperoxidase and caspase-3 activities were increased, but glutathione levels were reduced. On the one hand, MMP-2, MMP-9, tumor necrosis factor-α, and inducible nitric oxide synthase protein expressions were increased in the vehicle-treated AAA group. On the other hand, melatonin treatment reversed all of these biochemical indices and histopathologic alterations.

CONCLUSIONS

According to the data, although melatonin tended to reverse the biochemical parameters given on week 4, the preventive effect is more pronounced when given concomitantly with AAA induction because values were closer to the control levels.

Reaction of Thymidine with Hypobromous Acid in Phosphate Buffer

When thymidine was treated with hypobromous acid (HOBr) in 100 mM phosphate buffer at pH 7.2, two major product peaks appeared in the HPLC chromatogram. The products in each peak were identified by NMR and MS as two isomers of 5-hydroxy-5,6-dihydrothymidine-6-phosphate (a novel compound) and two isomers of 5,6-dihydroxy-5,6-dihydrothymidine (thymidine glycol) with comparable yields. 5-Hydroxy-5,6-dihydrothymidine-6-phosphate was relatively stable, and decomposed with a half-life of 32 h at pH 7.2 and 37°C generating thymidine glycol. The results suggest that 5-hydroxy-5,6-dihydrothymidine-6-phosphate in addition to thymidine glycol may have importance for mutagenesis by the reaction of HOBr with thymine residues in nucleotides and DNA.

The presence of modified nucleosides in extracellular fluids leads to the specific incorporation of 5-chlorocytidine into RNA and modulates the transcription and translation

Myeloperoxidase (MPO) is able to promote several kinds of damage and is involved in mechanisms leading to various diseases such as atherosclerosis or cancers. An example of these damages is the chlorination of nucleic acids, which is considered as a specific marker of the MPO activity. Since 5-chlorocytidine has been recently shown in healthy donor plasmas, this study aimed at discovering if these circulating modified nucleosides could be incorporated into RNA and DNA and if their presence impacts the ability of enzymes involved in the incorporation, transcription, and translation processes. Experimentations, which were carried out in vitro with endothelial and prostatic cells, showed a large penetration of all chloronucleosides but an exclusive incorporation of 5-chlorocytidine into RNA. However, no incorporation into DNA was observed. This specific incorporation is accompanied by an important reduction of translation yield. Although, in vitro, DNA polymerase processed in the presence of chloronucleosides but more slowly than in control conditions, ribonucleotide reductase could not reduce chloronucleotides prior to the replication. This reduction seems to be a limiting step, protecting DNA from chloronucleoside incorporation. This study shows the capacity of transcription enzyme to specifically incorporate 5-chlorocytidine into RNA and the loss of capacity-complete or partial-of different enzymes, involved in replication, transcription or translation, in the presence of chloronucleosides. Questions remain about the long-term impact of such specific incorporation in the RNA and such decrease of protein production on the cell viability and function.

A fast-response fluorescent probe for hypochlorous acid detection and its application in exogenous and endogenous HOCl imaging of living cells

A facile fluorescent probe for exogenous and endogenous HOCl detection in living cells.