Hypochlorous acid damages histone proteins forming 3-chlorotyrosine and 3,5-dichlorotyrosine

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.

Role of innate immunity and systemic inflammation in cystic fibrosis disease progression

Pathophysiological manifestations of cystic fibrosis (CF) result from a functional defect in the cystic fibrosis transmembrane conductance regulator (CFTR) paving way for mucus obstruction and pathogen colonization. The role of CFTR in modulating immune cell function and vascular integrity, irrespective of mucus thickening, in determining the host cell response to pathogens/allergens and causing systemic inflammation is least appreciated. Since CFTR plays a key role in the conductance of anions like Cl^-, loss of CFTR function could affect various basic cellular processes, such as cellular homeostasis, lysosome acidification, and redox balance. CFTR aids in endotoxin tolerance by regulating Toll-like receptor-mediated signaling resulting in uncontrolled activation of innate immune cells. Although leukocytes of CF patients are hyperactivated, they exhibit compromised phagosome activity thus favouring the orchestration of sepsis from defective pathogen clearance. This review will emphasize the importance of innate immunity and systemic inflammatory response in the development of CF and other CFTR-associated pathologies.

Mapping the modification of histones by the myeloperoxidase-derived oxidant hypochlorous acid (HOCl)

Histones are critical for the packaging of nuclear DNA and chromatin assembly, which is facilitated by the high abundance of Lys and Arg residues within these proteins. These residues are also the site of a range of post-translational modifications, which influence the regulatory function of histones. Histones are also present in the extracellular environment, following release by various pathways, particularly neutrophil extracellular traps (NETs). NETs contain myeloperoxidase, which retains its enzymatic activity and produces hypochlorous acid (HOCl). This suggests that histones could be targets for HOCl under conditions where aberrant NET release is prevalent, such as chronic inflammation. In this study, we examine the reactivity of HOCl with a mixture of linker (H1) and core (H2A, H2B, H3 and H4) histones. HOCl modified the histones in a dose- and time-dependent manner, resulting in structural changes to the proteins and the formation of a range of post-translational modification products. N-Chloramines are major products following exposure of the histones to HOCl and decompose over 24 h forming Lys nitriles and carbonyls (aminoadipic semialdehydes). Chlorination and dichlorination of Tyr, but not Trp residues, is also observed. Met sulfoxide and Met sulfones are formed, though these oxidation products are also detected albeit at a lower extent, in the non-treated histones. Evidence for histone fragmentation and aggregation was also obtained. These results could have implications for the development of chronic inflammatory diseases, given the key role of Lys residues in regulating histone function.

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.

Hypochlorous Acid: From Innate Immune Factor and Environmental Toxicant to Chemopreventive Agent Targeting Solar UV-Induced Skin Cancer

A multitude of extrinsic environmental factors (referred to in their entirety as the 'skin exposome') impact structure and function of skin and its corresponding cellular components. The complex (i.e. additive, antagonistic, or synergistic) interactions between multiple extrinsic (exposome) and intrinsic (biological) factors are important determinants of skin health outcomes. Here, we review the role of hypochlorous acid (HOCl) as an emerging component of the skin exposome serving molecular functions as an innate immune factor, environmental toxicant, and topical chemopreventive agent targeting solar UV-induced skin cancer. HOCl [and its corresponding anion (OCl-; hypochlorite)], a weak halogen-based acid and powerful oxidant, serves two seemingly unrelated molecular roles: (i) as an innate immune factor [acting as a myeloperoxidase (MPO)-derived microbicidal factor] and (ii) as a chemical disinfectant used in freshwater processing on a global scale, both in the context of drinking water safety and recreational freshwater use. Physicochemical properties (including redox potential and photon absorptivity) determine chemical reactivity of HOCl towards select biochemical targets [i.e. proteins (e.g. IKK, GRP78, HSA, Keap1/NRF2), lipids, and nucleic acids], essential to its role in innate immunity, antimicrobial disinfection, and therapeutic anti-inflammatory use. Recent studies have explored the interaction between solar UV and HOCl-related environmental co-exposures identifying a heretofore unrecognized photo-chemopreventive activity of topical HOCl and chlorination stress that blocks tumorigenic inflammatory progression in UV-induced high-risk SKH-1 mouse skin, a finding with potential implications for the prevention of human nonmelanoma skin photocarcinogenesis.

Topical hypochlorous acid (HOCl) blocks inflammatory gene expression and tumorigenic progression in UV-exposed SKH-1 high risk mouse skin

Hypochlorous acid (HOCl) is the active oxidizing principle underlying drinking water disinfection, also delivered by numerous skin disinfectants and released by standard swimming pool chemicals used on a global scale, a topic of particular relevance in the context of the ongoing COVID-19 pandemic. However, the cutaneous consequences of human exposure to HOCl remain largely unknown, posing a major public health concern. Here, for the first time, we have profiled the HOCl-induced stress response in reconstructed human epidermis and SKH-1 hairless mouse skin. In addition, we have investigated the molecular consequences of solar simulated ultraviolet (UV) radiation and HOCl combinations, a procedure mimicking co-exposure experienced for example by recreational swimmers exposed to both HOCl (pool disinfectant) and UV (solar radiation). First, gene expression elicited by acute topical HOCl exposure was profiled in organotypic human reconstructed epidermis. Next, co-exposure studies (combining topical HOCl and UV) performed in SKH-1 hairless mouse skin revealed that the HOCl-induced cutaneous stress response blocks redox and inflammatory gene expression elicited by subsequent acute UV exposure (Nos2, Ptgs2, Hmox1, Srxn1), a finding consistent with emerging clinical evidence in support of a therapeutic role of topical HOCl formulations for the suppression of inflammatory skin conditions (e.g. atopic dermatitis, psoriasis). Likewise, in AP-1 transgenic SKH-1 luciferase-reporter mice, topical HOCl suppressed UV-induced inflammatory signaling assessed by bioluminescent imaging and gene expression analysis. In the SKH-1 high-risk mouse model of UV-induced human keratinocytic skin cancer, topical HOCl blocked tumorigenic progression and inflammatory gene expression (Ptgs2, Il19, Tlr4), confirmed by immunohistochemical analysis including 3-chloro-tyrosine-epitopes. These data illuminate the molecular consequences of HOCl-exposure in cutaneous organotypic and murine models assessing inflammatory gene expression and modulation of UV-induced carcinogenesis. If translatable to human skin these observations provide novel insights on molecular consequences of chlorination stress relevant to environmental exposure and therapeutic intervention.

MiR-1696/GPx3 axis is involved in oxidative stress mediated neutrophil extracellular traps inhibition in chicken neutrophils

As an important immune mechanism of neutrophils, the release of Web-like chromatin structures known as neutrophil extracellular traps (NETs) can rapidly locate and capture invading pathogens, which has received sustained attention. There are still some fundamental questions surrounding established studies on the mechanism of balance between reactive oxygen species (ROS) dependent release and neutrophil antioxidant response. Glutathione peroxidase 3 (GPx3) is an important antioxidant protein and has been identified can regulate the immune response. However, the effect of GPx3 on the NETs formation and microRNA in this process remain poorly understood. In the present study, we used chicken peripheral blood neutrophils treated with Phorbol-12-myristate-13-acetate (PMA) for 3 h as NETs formation model. The result of morphological observation showed that GPx3 inactivation compromised the release of NETs. Further analysis revealed that knockdown of GPx3 significantly disturbed oxidative balance by inhibiting antioxidant enzymes activity and increasing H₂ O₂ content. Quantitative analysis of NETs-related genes found that the phosphorylation level of mitogen-activated protein kinase (MAPK) pathway genes (ERK, JNK, and p38) and expression of phosphoinositide-3-kinase (PI3K)/AKT pathway genes (PI3K and AKT) were suppressed with the downregulation of GPx3. Meanwhile, we identified that miR-1696 can target GPx3 expression by using dual luciferase reporter system. Additionally, overexpression of miR-1696 can not only inhibit the formation of NETs by restraining the expression of GPx3, interfering with the generation of ROS and activation of the MAPK and PI3K/AKT pathways, but also reducing the release of PMA-induced NETs promoted by overexpression of GPx3. These results provide evidence that miR-1696 targeted GPx3 activities in neutrophils could be used to regulate the NETs formation stimulated by PMA.

Behçet's Syndrome as a Model of Thrombo-Inflammation: The Role of Neutrophils

Behçet's syndrome (BS) is a systemic vasculitis, clinically characterized by different organ involvement and often complicated by thrombosis which occurs in vessels of all sizes. Thrombosis is more frequent in male patients with active disease and represents an important cause of morbidity and mortality. Neutrophil involvement in BS has been repeatedly suggested in the last few years. Indeed, neutrophils have been shown to be hyperactivated in BS patients, probably with a HLAB51 related contribution, and represent the main cells infiltrating not only oral and genital ulcers or erythema nodosum, but also other sites. Besides being deputed to host defense against micro-organisms, neutrophils display fundamental roles both in inflammation and tissue damage becoming inappropriately activated by cytokines, chemokines and autoantibodies and subsequently producing large amounts of superoxide anion (O2.) via NADPH oxidase (NOX2). The strict relationship between inflammation and hemostasis has been already demonstrated. Indeed, inflammation and immune-mediated disorders increase the risk of thrombosis, but the pathways that link these processes have not been completely elucidated. In this regard, we recently demonstrated, in a large population of BS patients, a new neutrophil-dependent pathogenetic mechanism of thrombosis. In particular, it was shown that neutrophils, mainly through NADPH oxidase, produce excessive amounts of reactive oxygen species (ROS), which are able to markedly modify the secondary structure of fibrinogen and hence the overall architecture of the fibrin clot that becomes less susceptible to plasmin-induced lysis. These data point out that BS represents “per se” a model of inflammation-induced thrombosis and suggest that neutrophils specifically contribute to thrombo-inflammation in this rare disease. In particular, it is suggested that an alteration in fibrinogen structure and function are associated with enhanced ROS production via neutrophil NADPH oxidase. Altogether, these findings improve our understanding of the intricate pathogenetic mechanisms of thrombo-inflammation and may indicate potential new therapeutic targets.

Neutrophils and redox stress in the pathogenesis of autoimmune disease

Polymorphonuclear leukocytes, or neutrophils, are specialist phagocytic cells of the innate immune system. Their primary role is host defence against micro-organisms, which they kill via phagocytosis, followed by release of reactive oxygen species (ROS) and proteolytic enzymes within the phagosome. ROS are generated via the action of the NADPH oxidase (also known as NOX2), in a process termed the 'Respiratory Burst'. This process consumes large amounts of oxygen, which is converted into the highly-reactive superoxide radical O₂^- and H₂O₂. Subsequent activation of myeloperoxidase (MPO) generates secondary oxidants and chloroamines that are highly microbiocidal in nature, which together with proteases such as elastase and gelatinase provide a toxic intra-phagosomal environment able to kill a broad range of micro-organisms. However, under certain circumstances such as during an auto-immune response, neutrophils can be triggered to release ROS and proteases extracellularly causing damage to host tissues, modification of host proteins, lipids and DNA and dysregulation of oxidative homeostasis. This review describes the range of ROS species produced by human neutrophils with a focus on the implications of neutrophil redox products in autoimmune inflammation.

Chloramine T induced oxidative stress and the response of antioxidant system in Phanerochaete chrysosporium

In this study, the effect of chloramine T (Chl-T) on the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and glutathione S-transferase (GST); the levels of reduced (GSH) and oxidised glutathione (GSSG) and their ratios; and also membrane lipid peroxidation (LPO) levels in Phanerochaete chrysosporium were investigated in a dose- (0.25-1 mmol/L) and time-dependent (1.5-9 h) manner. The highest SOD activity was observed in 0.5 mmol/L Chl-T at 6th hour as 1.48-fold of its control. The observed highest level in CAT activities was 4.6-fold of control in 0.5 and 0.75 mmol/L at the 6th hour. The GSH levels that were over the control showed decreasing tendency from the beginning of incubation, except 0.25 mmol/L. In contrast with GSH level variations, GSSG levels reached 10.0-fold of its control by showing increasing tendency with the increases in concentration and time. While the GSH/GSSG ratios were over the control at 0.25 mmol/L during all incubation, they fell under the control values at the earlier hours of incubation with the increasing concentrations of Chl-T. Glutathione-related enzymes GSH-Px, GR and GST were also induced with Chl-T treatment, and the highest activities were 3.29-, 7.5- and 6.56-fold of their controls, respectively. On the other hand, the increases in LPO levels with increasing concentration and time up to 5.27-fold of its control showed that the inductions observed in antioxidant system could not prevent the Chl-T-based oxidative stress.

Kinetic studies on the reaction of cob(II)alamin with hypochlorous acid: Evidence for one electron oxidation of the metal center and corrin ring destruction

Kinetic and mechanistic studies on the reaction of a major intracellular vitamin B₁₂ form, cob(II)alamin (Cbl(II)), with hypochlorous acid/hypochlorite (HOCl/OCl^-) have been carried out. Cbl(II) (Co(II)) is rapidly oxidized by HOCl to predominately aquacobalamin/hydroxycobalamin (Cbl(III), Co(III)) with a second-order rate constant of 2.4×10⁷M^-1s^-1 (25.0°C). The stoichiometry of the reaction is 1:1. UHPLC/HRMS analysis of the product mixture of the reaction of Cbl(II) with 0.9mol equiv. HOCl provides support for HOCl being initially reduced to Cl and subsequent H atom abstraction from the corrin macrocycle occurring, resulting in small amounts of corrinoid species with two or four H atoms fewer than the parent cobalamin. Upon the addition of excess (H)OCl further slower reactions are observed. Finally, SDS-PAGE experiments show that HOCl-induced damage to bovine serum albumin does not occur in the presence of Cbl(II), providing support for Cbl(II) being an efficient HOCl trapping agent.

Degradation of Amino Acids and Structure in Model Proteins and Bacteriophage MS2 by Chlorine, Bromine, and Ozone

Proteins are important targets of chemical disinfectants. To improve the understanding of disinfectant-protein reactions, this study characterized the disinfectant:protein molar ratios at which 50% degradation of oxidizable amino acids (i.e., Met, Tyr, Trp, His, Lys) and structure were observed during HOCl, HOBr, and O3 treatment of three well-characterized model proteins and bacteriophage MS2. A critical question is the extent to which the targeting of amino acids is driven by their disinfectant rate constants rather than their geometrical arrangement. Across the model proteins and bacteriophage MS2 (coat protein), differing widely in structure, methionine was preferentially targeted, forming predominantly methionine sulfoxide. This targeting concurs with its high disinfectant rate constants and supports its hypothesized role as a sacrificial antioxidant. Despite higher HOCl and HOBr rate constants with histidine and lysine than for tyrosine, tyrosine generally was degraded in preference to histidine, and to a lesser extent, lysine. These results concur with the prevalence of geometrical motifs featuring histidines or lysines near tyrosines, facilitating histidine and lysine regeneration upon Cl[+1] transfer from their chloramines to tyrosines. Lysine nitrile formation occurred at or above oxidant doses where 3,5-dihalotyrosine products began to degrade. For O3, which lacks a similar oxidant transfer pathway, histidine, tyrosine, and lysine degradation followed their relative O3 rate constants. Except for its low reactivity with lysine, the O3 doses required to degrade amino acids were as low as or lower than for HOCl or HOBr, indicating its oxidative efficiency. Loss of structure did not correlate with loss of particular amino acids, suggesting the need to characterize the oxidation of specific geometric motifs to understand structural degradation.

Leveraging the Mechanism of Oxidative Decay for Adenylate Kinase to Design Structural and Functional Resistances

Characterization of the mechanisms underlying hypohalous acid (i.e., hypochlorous acid or hypobromous acid) degradation of proteins is important for understanding how the immune system deactivates pathogens during infections and damages human tissues during inflammatory diseases. Proteins are particularly important hypohalous acid reaction targets in pathogens and in host tissues, as evidenced by the detection of chlorinated and brominated oxidizable residues. While a significant amount of work has been conducted for reactions of hypohalous acids with a range of individual amino acids and small peptides, the assessment of oxidative decay in full-length proteins has lagged in comparison. The most rigorous test of our understanding of oxidative decay of proteins is the rational redesign of proteins with conferred resistances to the decay of structure and function. Toward this end, in this study, we experimentally determined a putative mechanism of oxidative decay using adenylate kinase as the model system. In turn, we leveraged this mechanism to rationally design new proteins and experimentally test each system for oxidative resistance to loss of structure and function. From our extensive assessment of secondary structure, protein hydrodynamics, and enzyme activity upon hypochlorous acid or hypobromous acid challenge, we have identified two key strategies for conferring structural and functional resistance, namely, the design of proteins (adenylate kinase enzymes) that are resistant to oxidation requires complementary consideration of protein stability and the modification (elimination) of certain oxidizable residues proximal to catalytic sites.

Kinetics of 3-nitrotyrosine modification on exposure to hypochlorous acid

The markers 3-nitrotyrosine and 3-chlorotyrosine are measured as surrogates for reactive nitrogen species and hypochlorous acid respectively, which are both elevated in inflamed human tissues. Previous studies reported a loss of 3-nitrotyrosine when exposed to hypochlorous acid, suggesting that observations of 3-nitrotyrosine underestimate the presence of reactive nitrogen species in diseased tissue (Whiteman and Halliwell, Biochemical and Biophysical Research Communications, 258, 168-172 (1999)). This report evaluates the significance of 3-nitrotyrosine loss by measuring the kinetics of the reaction between 3-nitrotyrosine and hypochlorous acid. The results demonstrate that 3-nitrotyrosine is chlorinated by hypochlorous acid or chloramines to form 3-chloro-5-nitrotyrosine. As 3-nitrotyrosine from in vivo samples is usually found within proteins rather than as free amino acid, we also examined the reaction of 3-nitrotyrosine modification in the context of peptides. The chlorination of 3-nitrotyrosine in peptides was observed to occur up to 700-fold faster than control reactions using equivalent amino acid mixtures. These results further advance our understanding of tyrosine chlorination and the use of 3-nitrotyrosine formed in vivo as a biomarker of reactive nitrogen species.

Chemical and cytokine features of innate immunity characterize serum and tissue profiles in inflammatory bowel disease

Inflammatory bowel disease (IBD) arises from inappropriate activation of the mucosal immune system resulting in a state of chronic inflammation with causal links to colon cancer. Helicobacter hepaticus-infected Rag2(-/-) mice emulate many aspects of human IBD, and our recent work using this experimental model highlights the importance of neutrophils in the pathology of colitis. To define molecular mechanisms linking colitis to the identity of disease biomarkers, we performed a translational comparison of protein expression and protein damage products in tissues of mice and human IBD patients. Analysis in inflamed mouse colons identified the neutrophil- and macrophage-derived damage products 3-chlorotyrosine (Cl-Tyr) and 3-nitrotyrosine, both of which increased with disease duration. Analysis also revealed higher Cl-Tyr levels in colon relative to serum in patients with ulcerative colitis and Crohn disease. The DNA chlorination damage product, 5-chloro-2'-deoxycytidine, was quantified in diseased human colon samples and found to be present at levels similar to those in inflamed mouse colons. Multivariate analysis of these markers, together with serum proteins and cytokines, revealed a general signature of activated innate immunity in human IBD. Signatures in ulcerative colitis sera were strongly suggestive of neutrophil activity, and those in Crohn disease and mouse sera were suggestive of both macrophage and neutrophil activity. These data point to innate immunity as a major determinant of serum and tissue profiles and provide insight into IBD disease processes.

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

SIGNIFICANCE

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

FUTURE DIRECTIONS

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

Role of lysine during protein modification by HOCl and HOBr: halogen-transfer agent or sacrificial antioxidant?

Although protein degradation by neutrophil-derived hypochlorous acid (HOCl) and eosinophil-derived hypobromous acid (HOBr) can contribute to the inactivation of pathogens, collateral damage to host proteins can also occur and has been associated with inflammatory diseases ranging from arthritis to atherosclerosis. Though previous research suggested halotyrosines as biomarkers of protein damage and lysine as a mediator of the transfer of a halogen to tyrosine, these reactions within whole proteins are poorly understood. Herein, reactions of HOCl and HOBr with three well-characterized proteins [adenylate kinase (ADK), ribose binding protein, and bovine serum albumin] were characterized. Three assessments of oxidative modifications were evaluated for each of the proteins: (1) covalent modification of electron-rich amino acids (assessed via liquid chromatography and tandem mass spectrometry), (2) attenuation of secondary structure (via circular dichroism), and (3) fragmentation of protein backbones (via sodium dodecyl sulfate-polyacrylamide gel electrophoresis). In addition to forming halotyrosines, HOCl and HOBr converted lysine into lysine nitrile (2-amino-5-cyanopentanoic acid), a relatively stable and largely overlooked product, in yields of up to 80%. At uniform oxidant levels, fragmentation and loss of secondary structure correlated with protein size. To further examine the role of lysine, a lysine-free ADK variant was rationally designed. The absence of lysine increased yields of chlorinated tyrosines and decreased yields of brominated tyrosines following treatments with HOCl and HOBr, respectively, without influencing the susceptibility of ADK to HOX-mediated losses of secondary structure. These findings suggest that lysine serves predominantly as a sacrificial antioxidant (via formation of lysine nitrile) toward HOCl and as a halogen-transfer mediator [via reactions involving ε-N-(di)haloamines] with HOBr.

Miscoding properties of 8-chloro-2'-deoxyguanosine, a hypochlorous acid-induced DNA adduct, catalysed by human DNA polymerases

Many chronic inflammatory conditions are associated with an increased risk of cancer development. At the site of inflammation, cellular DNA is damaged by hypochlorous acid (HOCl), a potent oxidant generated by myeloperoxidase. 8-Chloro-2'-deoxyguanosine (8-Cl-dG) is a major DNA adduct formed by HOCl and has been detected from the liver DNA and urine of rats administered lipopolysaccharide in an inflammation model. Thus, the 8-Cl-dG lesion may be associated with the carcinogenesis of inflamed tissues. In this study, we explored the miscoding properties of the 8-Cl-dG adduct generated by human DNA polymerases (pols). Site-specifically modified oligodeoxynucleotide containing a single 8-Cl-dG was prepared and used as a template in primer extension reactions catalysed by human pol α, ĸ or η. Primer extension reactions catalysed by pol α and ĸ in the presence of all four dNTPs were slightly retarded at the 8-Cl-dG site, while pol η readily bypassed the lesion. The fully extended products were analysed to quantify the miscoding frequency and specificity of 8-Cl-dG using two-phased polyacrylamide gel electrophoresis (PAGE). During the primer extension reaction in the presence of four dNTPs, pol ĸ promoted one-base deletion (6.4%), accompanied by the misincorporation of 2'-deoxyguanosine monophosphate (5.5%), dAMP (3.7%), and dTMP (3.5%) opposite the lesion. Pol α and η, on the other hand, exclusively incorporated dCMP opposite the lesion. The steady-state kinetic studies supported the results obtained from the two-phased PAGE assay. These results indicate that 8-Cl-dG is a mutagenic lesion; the miscoding frequency and specificity varies depending on the DNA polymerase used. Thus, HOCl-induced 8-Cl-dG adduct may be involved in inflammation-driven carcinogenesis.

Influences of chloride and hypochlorite on neutrophil extracellular trap formation

Background

The release by neutrophils of DNA-based extracellular traps (NETs) is a recently recognized innate immune phenomenon that contributes significantly to control of bacterial pathogens at tissue foci of infection. NETs have also been implicated in the pathogenesis of non-infectious diseases such as small vessel vasculitis, lupus and cystic fibrosis lung disease. Reactive oxygen species (ROS) are important mediators of NET generation (NETosis). Neutrophils with reduced ROS production, such as those from patients with chronic granulomatous disease or myeloperoxidase (MPO) deficiency, produce fewer NETs in response to inflammatory stimuli. To better understand the roles of various ROS in NETosis, we explore the role of MPO, its substrates chloride ion (Cl⁻) and hydrogen peroxide (H₂O₂), and its product hypochlorite (HOCl) in NETosis.

Findings

In human peripheral blood neutrophils, pharmacologic inhibition of MPO decreased NETosis. Absence of extracellular Cl⁻, a substrate for MPO, also reduced NETosis. While exogenous addition of H₂O₂ and HOCl stimulated NETosis, only exogenous HOCl could rescue NETosis in the setting of MPO inhibition. Neither pharmacological inhibition nor genetic deletion of MPO in murine neutrophils blocked NETosis, in contrast to findings in human neutrophils.

Conclusions

Our results pinpoint HOCl as the key ROS involved in human NETosis. This finding has implications for understanding innate immune function in diseases in which Cl⁻ homeostasis is disturbed, such as cystic fibrosis. Our results also reveal an example of significant species-specific differences in NET phenotypes, and the need for caution in extrapolation to humans from studies of murine NETosis.

Structure and biodegradation mechanism of milled Bombyx mori silk particles

The aim of this study was to understand the structure and biodegradation relationships of silk particles intended for targeted biomedical applications. Such a study is also useful in understanding structural remodelling of silk debris that may be generated from silk-based implants. Ultrafine silk particles were prepared using a combination of efficient wet-milling and spray-drying processes with no addition of chemicals other than those used in degumming. Milling reduced the intermolecular stacking forces within the β-sheet crystallites without changing the intramolecular binding energy. Because of the rough morphology and the ultrafine size of the particles, degradation of silk particles by protease XIV was increased by about 3-fold compared to silk fibers. Upon biodegradation, the thermal degradation temperature of silk increased, which was attributed to the formation of tight aggregates by the hydrolyzed residual macromolecules. A model of the biodegradation mechanism of silk particles was developed based on the experimental data. The model explains the process of disintegration of β-sheets, supported by quantitative secondary structural analysis and microscopic images.

Sporicidal/bactericidal textiles via the chlorination of silk

Bacterial spores, such as those of the Bacillus genus, are extremely resilient, being able to germinate into metabolically active cells after withstanding harsh environmental conditions or aggressive chemical treatments. The toughness of the bacterial spore in combination with the use of spores, such as those of Bacillus anthracis, as a biological warfare agent necessitates the development of new antimicrobial textiles. In this work, a route to the production of fabrics that kill bacterial spores and cells within minutes of exposure is described. Utilizing this facile process, unmodified silk cloth is reacted with a diluted bleach solution, rinsed with water, and dried. The chlorination of silk was explored under basic (pH 11) and slightly acidic (pH 5) conditions. Chloramine-silk textiles prepared in acidified bleach solutions were found to have superior breaking strength and higher oxidative Cl contents than those prepared under caustic conditions. Silk cloth chlorinated for ≥1 h at pH 5 was determined to induce >99.99996% reduction in the colony forming units of Escherichia coli, as well as Bacillus thuringiensis Al Hakam (B. anthracis simulant) spores and cells within 10 min of contact. The processing conditions presented for silk fabric in this study are highly expeditionary, allowing for the on-site production of protein-based antimicrobial materials from a variety of agriculturally produced feed-stocks.

AEOL10150: a novel therapeutic for rescue treatment after toxic gas lung injury

New therapeutics designed as rescue treatments after toxic gas injury such as from chlorine (Cl(2)) are an emerging area of interest. We tested the effects of the metalloporphyrin catalytic antioxidant AEOL10150, a compound that scavenges peroxynitrite, inhibits lipid peroxidation, and has SOD and catalase-like activities, on Cl(2)-induced airway injury. Balb/C mice received 100ppm Cl(2) gas for 5 min. Four groups were studied: Cl(2) only, Cl(2) followed by AEOL10150 1 and 9 h after exposure, AEOL10150 only, and control. Twenty-four hours after Cl(2) gas exposure airway responsiveness to aerosolized methacholine (6.25-50mg/ml) was measured using a small-animal ventilator. Bronchoalveolar lavage (BAL) was performed to assess airway inflammation and protein. Whole lung tissue was assayed for 4-hydroxynonenal. In separate groups, lungs were collected at 72 h after Cl(2) injury to evaluate epithelial cell proliferation. Mice exposed to Cl(2) showed a significantly higher airway resistance compared to control, Cl(2)/AEOL10150, or AEOL10150-only treated animals in response to methacholine challenge. Eosinophils, neutrophils, and macrophages were elevated in BAL of Cl(2)-exposed mice. AEOL10150 attenuated the increases in neutrophils and macrophages. AEOL10150 prevented Cl(2)-induced increase in BAL fluid protein. Chlorine induced an increase in the number of proliferating airway epithelial cells, an effect AEOL10150 attenuated. 4-Hydroxynonenal levels in the lung were increased after Cl(2) and this effect was prevented with AEOL10150. AEOL10150 is an effective rescue treatment for Cl(2)-induced airway hyperresponsiveness, airway inflammation, injury-induced airway epithelial cell regeneration, and oxidative stress.

Kinetics of 3-chlorotyrosine formation and loss due to hypochlorous acid and chloramines

The persistent activation of innate immune cells in chronic inflammation is gaining recognition as a contributing factor in a number of human diseases. A distinguishing feature of activated leukocytes at sites of inflammation is their production of reactive species such as hypochlorous acid (HOCl). Investigating the role of reactive molecules such as HOCl in inflammation and human disease requires appropriate biomarkers. The preferred biomarker for HOCl, and by extension its synthesizing enzyme myeloperoxidase, is 3-chlorotyrosine. 3-Chlorotyrosine is a chemically stable product formed when HOCl, or an HOCl-generated chloramine, reacts with the tyrosine side chain and is readily measured by sensitive mass spectrometry methods. However, Whiteman and Spencer ((2008) Biochem. Biophys. Res. Commun., 371, 50 - 53.) noted that 3-chlorotyrosine is degraded by HOCl, calling into question its use as a biomarker. The kinetic rate constants for the reaction of 3-chlorotyrosine with HOCl, histidine chloramine, or lysine chloramine to form 3,5-dichlorotyrosine are reported. The kinetics of tyrosine chlorination in the context of a peptide with a nearby lysine residue was also determined and further supports the role of chloramines in the chlorination of protein-bound tyrosine residues. The likelihood of free and protein-bound 3,5-dichlorotyrosine occurring in vivo, given the reported rate constants, is discussed.

Dose-dependent transitions in Nrf2-mediated adaptive response and related stress responses to hypochlorous acid in mouse macrophages

Hypochlorous acid (HOCl) is potentially an important source of cellular oxidative stress. Human HOCl exposure can occur from chlorine gas inhalation or from endogenous sources of HOCl, such as respiratory burst by phagocytes. Transcription factor Nrf2 is a key regulator of cellular redox status and serves as a primary source of defense against oxidative stress. We recently demonstrated that HOCl activates Nrf2-mediated antioxidant response in cultured mouse macrophages in a biphasic manner. In an effort to determine whether Nrf2 pathways overlap with other stress pathways, gene expression profiling was performed in RAW 264.7 macrophages exposed to HOCl using whole genome mouse microarrays. Benchmark dose (BMD) analysis on gene expression data revealed that Nrf2-mediated antioxidant response and protein ubiquitination were the most sensitive biological pathways that were activated in response to low concentrations of HOCl (<0.35 mM). Genes involved in chromatin architecture maintenance and DNA-dependent transcription were also sensitive to very low doses. Moderate concentrations of HOCl (0.35 to 1.4 mM) caused maximal activation of the Nrf2 pathway and innate immune response genes, such as IL-1beta, IL-6, IL-10 and chemokines. At even higher concentrations of HOCl (2.8 to 3.5 mM) there was a loss of Nrf2-target gene expression with increased expression of numerous heat shock and histone cluster genes, AP-1-family genes, cFos and Fra1 and DNA damage-inducible Gadd45 genes. These findings confirm an Nrf2-centric mechanism of action of HOCl in mouse macrophages and provide evidence of interactions between Nrf2, inflammatory, and other stress pathways.