Search

Endogenous hypochlorous acid (HOCl) is one of the most important reactive oxygen species (ROS) and acts as a distinct biomarker that is involved in various inflammatory responses including rheumatoid arthritis (RA). Therefore, it's crucial to develop an efficient method for the tracking and analysis of HOCl levels in vivo. Natural products continue to be compounds of interest, because they not only offer diverse and specific molecular scaffolds but also provide invaluable sources for new drug discovery. Herein, we firstly demonstrated harmaline (HML), a natural alkaloid mainly found in Peganum harmala L, could be acted as a novel fluorescent probe for HOCl with exceptional precision and responsiveness. Remarkably, this probe not only specifically tracked HOCl levels in cells and inflammatory RA mouse models, but also exhibited effective anti-inflammatory effects on RAW264.7 cells and anti-proliferative effects on fibroblast-like synoviocytes. Furthermore, HML has the potential to alleviate LPS-induced inflammation by inhibiting the NF-κB signaling pathway. This study represents the first example of a natural product that can simultaneously act as a fluorescent probe for specific ROS and a promising therapeutic candidate for a specific disease, which will undoubtedly extend the application of fluorophore-rich natural products., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Acute liver injury (ALI) is a frequent and devastating liver disease that has been made more prevalent by the excessive use of chemicals, drugs, and alcohol in modern life. Hypochlorous acid (HClO), an important biomarker of oxidative stress originating mainly from the mitochondria, has been shown to be intimately connected to the development and course of ALI. Herein, a novel BODIPY-based NIR ratiometric fluorescent probe Mito-BS was constructed for the specific recognition of mitochondrial HClO. The probe Mito-BS can rapidly respond to HClO within 20 s with a ratiometric fluorescence response (from 680 nm to 645 nm), 24-fold fluorescence intensity ratio enhancement (I 645 /I 680 ), a wide pH adaptation range (5-9) and the low detection limit (31 nM). The probe Mito-BS has been effectively applied to visualize endogenous and exogenous HClO fluctuations in living zebrafish and cells based on its low cytotoxicity and prominent mitochondria-targeting ability. Furthermore, the fluorescent probe Mito-BS makes it possible to achieve the non-invasive in-situ diagnosis of ALI through in mice, and provides a feasible strategy for early diagnosis and drug therapy of ALI and its complications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Ferroptosis is a way of cell death mainly due to the imbalance between the production and degradation of lipid reactive oxygen species, which is closely associated with various diseases. Endogenous hypochlorous acid (HOCl) mainly produced in mitochondria is regarded as an important signal molecule of ferroptosis. Therefore, monitoring the fluctuation of endogenous HOCl is beneficial to better understand and treat ferroptosis-related diseases. Inspired by the promising aggregation-induced emission (AIE) properties of tetraphenylethene (TPE), herein, we rationally constructed a novel AIE-based fluorescent probe, namely QTrPEP, for HOCl with nice mitochondria-targeting ability and high sensitivity and selectivity. Probe QTrPEP consisted of phenylborate ester and the AIE fluorophore of quinoline-conjugated triphenylethylene (QTrPE). HOCl can brighten the strong fluorescence through a specific HOCl-triggered cleavage of the phenylborate ester bond and release of QTrPE, which has been demonstrated by MS, HPLC, and DLS experiments. In addition, combining QTrPE-doped test strips with a smartphone-based measurement demonstrated the excellent performance of the probe to sense HOCl. The obtained favorable optical properties and negligible cytotoxicity allowed the use of this probe for tracking of HOCl in three different cells. In particular, this work represents the first AIE-based mitochondria-targeting fluorescent probe for monitoring the fluctuation of HOCl in ferroptosis., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

Background: Photodynamic therapy (PDT) is a pioneering and effective anticancer modality with low adverse effects and high selectivity. Hypochlorous acid or hypochlorite (HClO/ClO - ) is a type of inflammatory cytokine. The abnormal increase of ClO - in tumor cells is related to tumor pathogenesis and may be a "friend" for the design and synthesis of responsive phototherapy agents. However, preparing responsive phototherapy agents for all-in-one noninvasive diagnosis and simultaneous in situ therapy in a complex tumor environment is highly desirable but still remains an enormously demanding task., Results: An acceptor-π bridge-donor-π bridge-acceptor (A-π-D-π-A) type photosensitizer TPTPy was designed and synthesized based on the phenothiazine structure which was used as the donor moiety as well as a ClO - responsive group. TPTPy was a multifunctional mitochondria targeted aggregation-induced emission (AIE) photosensitizer which could quickly and sensitively respond to ClO - with fluorescence "turn on" performance (19-fold fluorescence enhancement) and enhanced type I reactive oxygen species (ROS) generation to effectively ablate hypoxic tumor cells. The detection limit of TPTPy to ClO - was calculated to be 185.38 nM. The well-tailored TPTPy anchoring to mitochondria and producing ROS in situ could disrupt mitochondria and promote cell apoptosis. TPTPy was able to image inflammatory cells and tumor cells through ClO - response. In vivo results revealed that TPTPy was successfully utilized for PDT in tumor bearing nude mice and exhibited excellent biological safety for major organs., Significance and Novelty: A win-win integration strategy was proposed to design a tumor intracellular ClO - responsive photosensitizer TPTPy capable of both type I and type II ROS production to achieve photodynamic therapy of tumor. This work sheds light on the win-win integration design by taking full advantage of the characteristics of tumor microenvironment to build up responsive photosensitizer for in situ PDT of tumor., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Lysosomes, as crucial acidic organelles in cells, play a significant role in cellular functions. The levels and distribution of hypochlorous acid (HOCl) within lysosomes can profoundly impact their biological functionality. Hence, real-time monitoring of the concentration of HOCl in lysosomes holds paramount importance for further understanding various physiological and pathological processes associated with lysosomes. In this study, we developed a bodipy-based fluorescent probe derived from pyridine and phenyl selenide for the specific detection of HOCl in aqueous solutions. Leveraging the probe's sensitive photoinduced electron transfer effect from phenyl selenide to the fluorophore, the probe exhibited satisfactory high sensitivity (with a limit of detection of 5.2 nM and a response time of 15 s) to hypochlorous acid. Further biological experiments confirmed that the introduction of the pyridine moiety enabled the probe molecule to selectively target lysosomes. Moreover, the probe successfully facilitated real-time monitoring of HOCl in cell models stimulated by N-acetylcysteine (NAC) and lipopolysaccharide (LPS), as well as in a normal zebrafish model. This provides a universal method for dynamically sensing HOCl in lysosomes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

At inflammatory sites, immune cells generate oxidants including H₂O₂. Myeloperoxidase (MPO), released by activated leukocytes employs H₂O₂ and halide/pseudohalides to form hypohalous acids that mediate pathogen killing. Hypochlorous acid (HOCl) is a major species formed. Excessive or misplaced HOCl formation damages host tissues with this linked to multiple inflammatory diseases. Previously (Redox Biology, 2020, 28, 101331) we reported that iodide (I⁻) modulates MPO-mediated protein damage by decreasing HOCl generation with concomitant hypoiodous acid (HOI) formation. HOI may however impact on protein structure, so in this study we examined whether and how HOI, from peroxidase/H₂O₂/I⁻ systems ± Cl⁻, modifies proteins. Experiments employed MPO and lactoperoxidase (LPO) and multiple proteins (serum albumins, anastellin), with both chemical (intact protein and peptide mass mapping, LC-MS) and structural (SDS-PAGE) changes assessed. LC-MS analyses revealed dose-dependent iodination of anastellin and albumins by LPO/H 2 O 2 with increasing I⁻. Incubation of BSA with MPO/H 2 O 2 /Cl⁻ revealed modest chlorination (Tyr286, Tyr475, ∼4 %) and Met modification. Lower levels of these species, and extensive iodination at specific Tyr and His residues (>20 % modification with ≥10 μM I⁻) were detected with increasing I⁻. Anastellin dimerization was inhibited by increasing I⁻, but less marked changes were observed with albumins. These data confirm that I⁻ competes with Cl⁻ for MPO and is an efficient HOCl scavenger. These processes decrease protein chlorination and oxidation, but result in extensive iodination. This is consistent with published data on the presence of iodinated Tyr on neutrophil proteins. The biological implications of protein iodination relative to chlorination require further clarification., Competing Interests: Declaration of competing interest MJD declares consultancy contracts with Novo Nordisk A/S, and is a Director and major shareholder in the start-up company Seleno Therapeutics plc. These funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. Prof. Michael Davies is also an Editorial Board Member for Free Radical Biology and Medicine but was not involved in the editorial review or the decision to publish this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Aging represents a significant risk factor for compromised tissue function and the development of chronic diseases in the human body. This process is intricately linked to oxidative stress, with HClO serving as a vital reactive oxygen species (ROS) within biological systems due to its strong oxidative properties. Hence, conducting a thorough examination of HClO in the context of aging is crucial for advancing the field of aging biology. In this work, we successfully developed a fluorescent probe, OPD , tailored specifically for detecting HClO in senescent cells and in vivo. Impressively, OPD exhibited a robust reaction with HClO, showcasing outstanding selectivity, sensitivity, and photostability. Notably, OPD effectively identified HClO in senescent cells for the first time, confirming that DOX- and ROS-induced senescent cells exhibited higher HClO levels compared to uninduced normal cells. Additionally, in vivo imaging of zebrafish demonstrated that d-galactose- and ROS-stimulated senescent zebrafish displayed elevated HClO levels compared to normal zebrafish. Furthermore, when applied to mouse tissues and organs, OPD revealed increased fluorescence in the organs of senescent mice compared to their nonsenescent counterparts. Our findings also illustrated the probe's potential for detecting changes in HClO content pre- and post-aging in living mice. Overall, this probe holds immense promise as a valuable tool for in vivo detection of HClO and for studying aging biology in live organisms.

Inflammatory bowel disease (IBD) is an idiopathic intestinal inflammatory disease, whose etiology is intimately related to the overproduction of hypochlorous acid (HClO). Optical monitoring of HClO in the living body favors real-time diagnosis of inflammatory diseases. However, HClO-activated near-infrared (NIR) fluorescent probes with rapid response and high inflammatory cell uptake are still lacking. Herein, we report an activatable acceptor-π-acceptor (A-π-A)-type NIR fluorescent probe ( Cy-DM ) bearing two d-mannosamine groups for the sensitive detection of HClO in early IBD and stool testing. Once reacted with HClO, nonfluorescent Cy-DM could be turned on within 2 s by generating a donor-π-acceptor (D-π-A) structure due to the enhanced intramolecular charge transfer mechanism, showing intense NIR fluorescence emission at 700 nm and a large Stokes shift of 115 nm. Moreover, it was able to sensitively and selectively image exogenous and endogenous HClO in the lysosomes of living cells with a detection limit of 0.84 μM. More importantly, because of the d-mannosamine modification, Cy-DM was efficiently taken up by inflammatory cells in the intestine after intravenous administration, allowing noninvasive visualization of endogenous HClO in a lipopolysaccharide-induced IBD mouse model with a high fluorescence contrast of 6.8/1. In addition, water-soluble Cy-DM has also been successfully applied in ex vivo optical fecal analysis, exhibiting a 3.4-fold higher fluorescence intensity in the feces excreted by IBD mice. We believe that Cy-DM is promising as an invaluable tool for rapid diagnosis of HClO-related diseases as well as stool testing.

Ferroptosis is an iron-dependent programmed cell death that is characterized by the dysregulation of lipid reactive oxygen species (ROS) production, causing abnormal changes in hypochlorous acid (HClO) levels in lysosomes. Super-resolution imaging can observe the fine structure of the lysosome at the nanometer level; therefore, it can be used to detect lysosome HClO levels during ferroptosis at the suborganelle level. Herein, we utilize a ratiometric fluorescent probe, SRF-HClO , for super-resolution imaging of lysosome HClO. Structured-illumination microscopy (SIM) improves the accuracy of lysosome targeting and enables the probe SRF-HClO to be successfully applied to rapidly monitor the up-regulated lysosome HClO at the nanoscale during inflammation and ferroptosis. Importantly, the probe SRF-HClO can also detect HClO changes in inflammatory and ferroptosis mice and evaluate the inhibitory effect of ferroptosis on mice tumors.

Posttranslational modifications in fibrinogen resulting from induced oxidation or oxidative stress in the organism can have deleterious influence on optimal functioning of fibrinogen, causing a disturbance in assembly and properties of fibrin. The protective mechanism supporting the ability of fibrinogen to function in ROS-generating environment remains completely unexplored. The effects of very low and moderately low HOCl/ - OCl concentrations on fibrinogen oxidative modifications, the fibrin network structure as well as the kinetics of both fibrinogen-to-fibrin conversion and fibrin hydrolysis have been explored in the current study. As opposed to 25 Μm, HOCl/ - OCl, 10 μM HOCl/ - OCl did not affect the functional activity of fibrinogen. It is shown for the first time that a number of Met residues, AαMet476, AαMet517, AαMet584, BβMet367, γMet264, and γMet94, identified in 10 μM HOCl/-OCl fibrinogen by the HPLC-MS/MS method, operate as ROS scavengers, performing an important antioxidant function. In turn, this indicates that the fibrinogen structure is adapted to the detrimental action of ROS. The results obtained in our study provide evidence for a protective mechanism responsible for maintaining the structure and functioning of fibrinogen molecules in the bloodstream under conditions of mild and moderate oxidative stress., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Hypothiocyanous acid (HOSCN) is an endogenous oxidant produced by peroxidase oxidation of thiocyanate (SCN - ), an ubiquitous sulfur-containing pseudohalide synthesized from cyanide. HOSCN serves as a potent microbicidal agent against pathogenic bacteria, viruses, and fungi, functioning through thiol-targeting mechanisms, independent of currently approved antimicrobials. Additionally, SCN - reacts with hypochlorous acid (HOCl), a highly reactive oxidant produced by myeloperoxidase (MPO) at sites of inflammation, also producing HOSCN. This imparts both antioxidant and antimicrobial potential to SCN - . In this review, we discuss roles of HOSCN/SCN - in immunity and potential therapeutic implications for combating infections., Competing Interests: Declaration of competing interest The authors declare that they have no conflicts of interest., (Copyright © 2024 Elsevier Inc. All rights reserved.)

As a type of reactive oxygen species, hypochlorous acid (ClO - ) plays an important role in sterilization, disinfection and protection in organisms. However, excessive production of ClO - is closely related to various diseases. In this work, we have designed a robust ratiometric fluorescent probe, RDB-ClO, using the excited-state intramolecular proton transfer (ESIPT) strategy. RDB-ClO was achieved by modifying 2-(2-(benzo[d]thiazol-2-yl)-6-(diethylamino)-3-oxo-3H-xanthen-9-yl) benzoic acid (RDB-OH) with a 1-naphthoyl chloride group, specifically for the sensitive detection of ClO - . In the presence of ClO - , RDB-ClO demonstrated relatively good performance, showing swift response time (35 s), low detection limit of 5.1 nM and high selectivity towards ClO - . Notably, the convenience and accessibility detection of ClO - has been implemented using test strip and agarose probe. RDB-ClO effectively tracked both endogenous and exogenous ClO - in HeLa cells, HepG2 cells and zebrafish. Additionally, it is successfully applied to detect changes of exogenous ClO - content in E. coli. and acetaminophen (APAP)-induced liver injury in mice. The development of RDB-ClO represents a promising molecular tool for studying the pathogenesis of DILI and biotransformation of ClO - in bacteria., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Heightened oxidative stress is the principal driver behind the altered metabolism of neurotransmitters within the brains of Parkinson's disease (PD). Hypochlorous acid (HClO), a variant of reactive oxygen species (ROS), plays a crucial role in several lysosomal activities. An irregular concentration of HClO may result in significant molecular damage and contribute to the onset of neurodegenerative disorders. Despite this, the precise role of lysosomal HClO in PD remains unclear, due to its fast reactivity and low levels. This is further complicated by the lack of effective in situ imaging techniques for accurately tracking its dynamics. Therefore, it is of great significance to use effective tools to map the lysosomal HClO during the pathological process of PD. In this study, we propose a fluorogenic probe named Lys-PTZ-HClO for the specific and sensitive detection of HClO. Lys-PTZ-HClO exhibits features like a fast response time (10 s) and a low detection limit (0.72 μM). Benefiting from its superior properties, the probe was used to visualize the basal HClO levels, and the variation of HClO levels in lysosomal of living cells. More importantly, this probe was successfully applied for the first time to reveal increased lysosomal HClO in a cellular model of PD., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

It is crucial to identify aberrant HClO levels in living things since they pose a major health risk and are a frequent reactive oxygen species (ROS) in living organisms. In order to detect HClO in various biological systems, we created and synthesized a near-infrared fluorescent probe with an oxime group (-C = N-OH) as a recognition unit. The probe DCMP1 has the advantages of fast response (10 min), near-infrared emission (660 nm), large Stokes shift (170 nm) and high selectivity. This probe DCMP1 not only detects endogenous HClO in living cells, but also enables further fluorescence detection of HClO in living zebrafish. More importantly, it can also be used for fluorescence imaging of HClO in an rheumatoid arthritis mouse model. This fluorescent probe DCMP1 is anticipated to be an effective tool for researching HClO., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

There is a pressing medical need for improved treatments in skin fibrosis including keloids and hypertrophic scars (HTS). This study aimed to characterize the role of phosphodiesterase 4 (PDE4), specifically PDE4B in fibrotic skin remodeling in vitro and in vivo. In vitro, effects of PDE4A-D (Roflumilast) or PDE4B (siRNA) inhibition on TGFβ1-induced myofibroblast differentiation and dedifferentiation were studied in normal (NHDF) and keloid (KF) human dermal fibroblasts. In vivo, the role of PDE4 on HOCl-induced skin fibrosis in mice was addressed in preventive and therapeutic protocols. PDE4B (mRNA, protein) was increased in Keloid > HTS compared to healthy skin and in TGFβ-stimulated NHDF and KF. In Keloid > HTS, collagen Iα1, αSMA, TGFβ1 and NOX4 mRNA were all elevated compared to healthy skin confirming skin fibrosis. In vitro, inhibition of PDE4A-D and PDE4B similarly prevented TGFβ1-induced Smad3 and ERK1/2 phosphorylation and myofibroblast differentiation, elevated NOX4 protein and proliferation in NHDF. PDE4A-D inhibition enabled myofibroblast dedifferentiation and curbed TGFβ1-induced reactive oxygen species and fibroblast senescence. In KF PDE4A-D inhibition restrained TGFβ1-induced Smad3 and ERK1/2 phosphorylation, myofibroblast differentiation and senescence. Mechanistically, PDE4A-D inhibition rescued from TGFβ1-induced loss in PPM1A, a Smad3 phosphatase. In vivo, PDE4 inhibition mitigated HOCl-induced skin fibrosis in mice in preventive and therapeutic protocols. The current study provides novel evidence evolving rationale for PDE4 inhibitors in skin fibrosis (including keloids and HTS) and delivered evidence for a functional role of PDE4B in this fibrotic condition., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:JAVIER MILARA reports equipment, drugs, or supplies was provided by General University Hospital Consortium of Valencia. JAVIER MILARA reports a relationship with General University Hospital Consortium of Valencia that includes: employment. JAVIER MILARA has patent NO PATENT pending to NO LICENSE. JM, PR, SM, PM, IR, JC have no conflicts of interests to declare. HT is a full-time employee of TOPADUR Pharma AG and owns shares of this company. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Reactive oxygen species play a pivotal role in liver disease, contributing to severe liver damage and chronic inflammation. In liver injury driven by inflammation, adenosine-5'-triphosphate (ATP) and hypochlorite ion (ClO - ) emerge as novel biomarkers, reflecting mitochondrial dysfunction and amplified oxidative stress, respectively. However, the dynamic fluctuations of ATP and ClO - in hepatocytes and mouse livers remain unclear, and multidetection techniques for these biomarkers are yet to be developed. This study presents RATP-NClO , a dual-channel fluorescent bioprobe capable of synchronously detecting ATP and ClO - ions. RATP-NClO exhibits excellent selectivity and sensitivity for ATP and ClO - ions, demonstrating a dual-channel fluorescence response in a murine hepatocyte cell line. Upon intravenous administration, RATP-NClO reveals synchronized ATP depletion and ClO - amplification in the livers of mice with experimental metabolic dysfunction-associated steatohepatitis (MASH). Through a comprehensive analysis of the principal mechanism of the developed bioprobe and the verification of its reliable detection ability in both in vitro and in vivo settings, we propose it as a unique tool for monitoring changes in intracellular ATP and ClO - level. These findings underscore its potential for practical image-based monitoring and functional phenotyping of MASH pathogenesis.

Ulcerative colitis is a persistent inflammatory bowel disease characterized by inflammation and ulceration in the colon and gastrointestinal tract. It was indicated that the generation of hypochlorous acid (HClO) through the enzymatic activity of myeloperoxidase is significantly linked to ulcerative colitis. In this study, by assembling two hairpins (Hpa and Hpb) onto a quadrivalent cruciform DNA nanostructure, a novel HClO-activatable fluorescent probe was developed based on DNA nanomaterials (denoted MHDNA), which is sensitive, economic, simple, and stable. In the presence of HClO, the Trigger (T) was liberated from the MHDNA probe through a hydrolysis reaction between HClO and phosphorothioate (PS), which is modified on the MHDNA probe and has proved to exhibit particular susceptibility to the HClO. The liberated T subsequently initiated the opening of Hpa and Hpb to facilitate the catalyzed hairpin assembly (CHA) reaction, resulting in the changes of fluorescence and releasing T for recycled signal amplification to achieve sensitive detection of HClO (with a limit of detection 9.83 nM). Additionally, the MHDNA-based spatial-confinement effect shortens the physical distance between Hpa and Hpb and yields a high local concentration of the two reactive hairpins, achieving more rapid reaction kinetics in comparison to conventional CHA methods. Inspirationally, the MHDNA probe was effectively utilized for imaging HClO in ulcerative colitis mice, yielding valuable diagnostic insights for ulcerative colitis.

Type 2 diabetes mellitus (T2DM) is accompanied by halogenative stress resulting from the excessive activation of neutrophils and neutrophilic myeloperoxidase (MPO) generating highly reactive hypochlorous acid (HOCl). HOCl in blood plasma modifies serum albumin (Cl-HSA). We studied the formation of neutrophil extracellular traps (NETs) in the whole blood and by isolated neutrophils under the action of Cl-HSA. It was found that Cl-HSA induces neutrophil priming and NETosis. MPO-containing as well as MPO-free NETs were found. These NETs with different composition can be a product of NETosis of one and the same neutrophil. NET formation in neutrophils with vacuolated cytoplasm was detected. In the presence of Cl-HSA, acceleration of NET degradation was observed. Accelerated NET degradation and neutrophil priming can be the factors contributing to the development of complications in T2DM., (© 2024. Springer Science+Business Media, LLC, part of Springer Nature.)

Hypochlorous acid (HClO) is used in food preservation. However, excessive HClO can deteriorate nutritional composition of food, compromise its quality, and potentially induce various diseases. Consequently, the development of multifunctional fluorescent probes for the sensitive and selective detection of HClO is highly anticipated for food safety. In this work, we designed a nanoprobe using N-aminomorpholine (AM)-functionalized bromine-doped carbon dots (Br-CDs-AM) for sensing HClO. This nanoprobe exhibits pH stability, strong resistance to photobleaching, superior long-term photostability (12 weeks), high sensitivity (19.3 nM), and an ultrarapid response (8 s) for detecting HClO residues in food matrices with percentage recovery (96.5 %-108 %) and RSDs less than 5.34 %. In addition, extremely low cytotoxicity and outstanding biocompatibility enable the nanoprobe to be used primarily for lysosome tracking and rapidly visualizing HClO in live cells. Thus, this study provides a new pathway to design unconventional nanoprobes for food safety assessment and subcellular organelle-specific imaging HClO., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Ferroptosis is a burgeoning iron-dependent cell death form, and has close relation with hypochlorous acid (HClO). Exploring the fluctuation of the HClO level in living cells during ferroptosis could contribute to the profound study of the biological functions of HClO during ferroptosis. Here, we present a turn-on probe (RH-C) for the imaging of intracellular HClO during ferroptosis. The probe RH-C utilized the N,N-dimethylthiocarbamate group as a selective recognition site for HClO, and displayed desirable sensitivity and selectivity to HClO. The probe RH-C could detect the exogenous and endogenous HClO in living cells. Furthermore, RH-C was competent in monitoring the changes of endogenous HClO level during the process of ferroptosis. Biological imaging results suggested that erastin-induced ferroptosis can result in the excessive production of the endogenous HClO, and ferrostatin-1 (Fer-1) and vitamin E (VE) could block the massive accumulation of HClO in living cells., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Drug-induced liver injury (DILI) is a common liver disease with a high rate of morbidity, and its pathogenesis is closely associated with the overproduction of highly reactive hypochlorite (ClO - ) in the liver. However, bioluminescence imaging of endogenous hypochlorite in nontransgenic natural mice remains challenging. Herein, to address this issue, we report a strategy for imaging ClO - in living cells and DILI mice by harnessing a bioluminescent probe formylhydrazine luciferin ( ClO-Luc ) combined with firefly luciferase (fLuc) mRNA-loaded lipid nanoparticles (LNPs). LNPs could efficiently deliver fLuc mRNA into living cells and in vivo, expressing abundant luciferase in the cytoplasm in situ. In the presence of ClO - , probe ClO-Luc locked by formylhydrazine could release cage-free d-luciferin through oxidation and follow-up hydrolysis reactions, further allowing for bioluminescence imaging. Moreover, based on the luciferase-luciferin system, it was able to sensitively and selectively detect ClO - in vitro with a limit of detection of 0.59 μM and successfully monitor the endogenous hypochlorite generation in the DILI mouse model for the first time. We postulate that this work provides a new method to elucidate the roles of ClO - in related diseases via bioluminescence imaging.

Acute kidney injury (AKI) has become an increasing concern for patients due to the widespread clinical use of nephrotoxic drugs. Currently, the early diagnosis of AKI is still challenging and the available therapeutic drugs cannot meet the clinical demand. Herein, this work has investigated the key redox couple involved in AKI and develops a tailored photoacoustic (PA) imaging probe (AB-DiOH) which can reversibly respond to hypochlorite (ClO-)/glutathione (GSH) with high specificity and sensitivity. This probe enables the real-time monitoring of AKI by noninvasive PA imaging, with better detection sensitivity than the blood test. Furthermore, this probe is utilized for screening nephroprotective drugs among natural products. For the first time, astragalin is discovered to be a potential new drug for the treatment of AKI. After oral administration, astragalin can be efficiently absorbed by the animal body, alleviate kidney injury, and meanwhile induce no damage to other normal tissues. The treatment mechanism of astragalin has also been revealed to be the simultaneous inhibition of oxidative stress, ferroptosis, and cuproposis. The developed PA imaging probe and the discovered drug candidate provide a promising new tool and strategy for the early diagnosis and effective treatment of AKI., (© 2024 Wiley‐VCH GmbH.)

To establish infections in human hosts, Pseudomonas aeruginosa must overcome innate immune-generated oxidative stress, such as the hypochlorous acid (HOCl) produced by neutrophils. We set out to find specific biomarkers of oxidative stress through the development of a protocol for the metabolic profiling of P. aeruginosa cultures grown in the presence of different oxidants using a novel ionization technique for mass spectrometry, laser desorption rapid evaporative ionization mass spectrometry (LD-REIMS). We demonstrated the ability of LD-REIMS to classify samples as untreated or treated with a specific oxidant with 100% accuracy and identified a panel of 54 metabolites with significantly altered concentrations after exposure to one or more of the oxidants. Key metabolic changes were conserved in P. aeruginosa clinical strains isolated from patients with cystic fibrosis lung infections. These data demonstrated that HOCl stress impacted the Pseudomonas quinolone signal (PQS) quorum sensing system. Ten 2-alkyl-4-quinolones (AHQs) associated with the PQS system were significantly lower in concentration in HOCl-stressed P. aeruginosa cultures, including 2-heptyl-3-hydroxy-4(1H)-quinolone (PQS), the most active signal molecule of the PQS system. The PQS system regulates the production of virulence factors, including pyocyanin and elastase, and their levels were markedly affected by HOCl stress. No pyocyanin was detectable and elastase concentrations were reduced by more than 75% in cultures grown with sub-lethal concentrations of HOCl, suggesting that this neutrophil-derived oxidant may disrupt the ability of P. aeruginosa to establish infections through interference with production of PQS-associated virulence factors., Importance: This work demonstrates that a high-throughput ambient ionization mass spectrometry method can be used successfully to study a bacterial stress response. Its application to the opportunistic pathogen Pseudomonas aeruginosa led to the identification of specific oxidative stress biomarkers, and demonstrated that hypochlorous acid, an oxidant specifically produced by human neutrophils during infection, affects quorum sensing and reduces production of the virulence factors pyocyanin and elastase. No pyocyanin was detectable and elastase levels were reduced by more than 75% in bacteria grown in the presence of hypochlorous acid. This approach has the potential to be widely applicable to the characterization of the stress responses of bacteria., Competing Interests: The authors declare no conflict of interest.

Fluoride anions (F - ) play a crucial role in human physiological processes. However, excessive intake of F - would affect oxygen metabolism and promote the generation of oxygen-free radicals. Hence, it is essential to develop a precise and efficient fluorescent probe for visualizing F - -induced oxidative stress. In this work, we developed the first bifunctional BODIPY-based fluorescent probe dfBDP with p - tert -butyldimethylsilanolate benzyl thioether as the sensing site for the detection of F - and HClO via two distinct reactions, the self-immolative removal and the thioether oxidation, which generate the sensing products with two nonoverlap fluorescence bands: 800-1200 and 500-750 nm, respectively. The probe dfBDP displays rapid response, high specificity, and sensitivity for the detection of F - (LOD, 316.2 nM) and HClO (LOD, 33.9 nM) in vitro. Cellular imaging reveals a correlation between F - -induced oxidative stress and the upregulation of HClO. Finally, probe dfBDP was employed to detect F - and HClO in mice under the stimulation of F - . The experimental results display that the level of HClO elevates in the liver of mice.

Mitochondrial fission is a highly regulated process that can affect metabolism, proliferation, and apoptosis. Division at the periphery enables damaged material to be shed into smaller mitochondria destined for mitophagy, which is found preceded by increased Ca 2+ and reactive oxygen species, as well as reduced membrane potential and pH. However, the variation of hypochlorous acid (HOCl) during the peripheral fission has not been well studied, and the existing fluorescent probes are unsuitable for detecting mitochondrial HOCl because of the 0.8-fold decreased pH during this process. Herein, we design a novel CCS (changeable π-conjugation system)-based probe (ON-mito) with a dibenzo[1,4]oxazepine core, which can selectively react with HOCl at pH 6.4, generating an oxazine-containing product that emits at 660 nm. The capability of ON-mito for imaging the HOCl generation in HeLa cells during mitophagy is demonstrated under weakly acidic condition. Further, with ON-mito, we find for the first time a burst increase of the mitochondrial HOCl in COS-7 cells during peripheral fission, which may serve as an important indicator of this process. Probe ON-mito may be useful for studying mitochondrial damage under diverse conditions.

Duchenne muscular dystrophy (DMD) is a fatal X-linked disease characterised by severe muscle wasting. The mechanisms underlying the DMD pathology likely involve the interaction between inflammation, oxidative stress and impaired Ca 2+ signalling. Hypochlorous acid (HOCl) is a highly reactive oxidant produced endogenously via myeloperoxidase; an enzyme secreted by neutrophils that is significantly elevated in dystrophic muscle. Oxidation of Ca 2+ -handling proteins by HOCl may impair Ca 2+ signalling. This study aimed to determine the effects of HOCl on skeletal muscle function and its potential contribution to the dystrophic pathology. Extensor digitorum longus (EDL), soleus and interosseous muscles were surgically isolated from anaesthetised C57 (wild-type) and mdx (dystrophic) mice for measurement of ex vivo force production and intracellular Ca 2+ concentration. In whole EDL muscle, HOCl (200 μM) significantly decreased maximal force and increased resting muscle tension which was only partially reversible by dithiothreitol. The effects of HOCl (200 μM) on maximal force in slow-twitch soleus were lower than found in the fast-twitch EDL muscle. In single interosseous myofibres, HOCl (10 μM) significantly increased resting intracellular Ca 2+ concentration and decreased Ca 2+ transient amplitude. These effects of HOCl were reduced by the application of tetracaine, Gd 3+ or streptomycin, implicating involvement of ryanodine receptors and transient receptor potential channels. These results demonstrate the potent effects of HOCl on skeletal muscle function potentially mediated by HOCl-induced oxidation to Ca 2+ signalling proteins. Hence, HOCl may provide a link between chronic inflammation, oxidative stress and impaired Ca 2+ handling that is characteristic of DMD and presents a potential therapeutic target for DMD. KEY POINTS: Duchenne muscular dystrophy is a fatal genetic disease with pathological mechanisms which involve the complex interaction of chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca 2+ concentrations. Hypochlorous acid can be endogenously produced by neutrophils via the enzyme myeloperoxidase. Both neutrophil and myeloperoxidase activity are increased in dystrophic mice. This study found that hypochlorous acid decreased muscle force production and increased cytosolic Ca 2+ concentrations in isolated muscles from wild-type and dystrophic mice at relatively low concentrations of hypochlorous acid. These results indicate that hypochlorous acid may be key in the Duchenne muscular dystrophy disease pathology and may provide a unifying link between the chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca 2+ concentrations observed in Duchenne muscular dystrophy. Hypochlorous acid production may be a potential target for therapeutic treatments of Duchenne muscular dystrophy., (© 2023 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Systemic sclerosis (SSc) is an autoimmune disease characterized by vasculopathy, immune dysregulation, and multi-organ fibrosis. Interstitial lung disease (ILD) is a complication of SSc and a leading cause of SSc-death. The administration of hypochlorous acid (HOCl) intradermally in the mouse (HOCl-SSc) purportedly shows several features typical of SSc. We studied the model by injecting BALB/c mice daily intradermally with HOCl for 6-weeks, an exposure reported to induce lung fibrosis. On day 42, the skinfold thickness and the dermal thickness were two and three times larger respectively in the HOCl group compared to controls. HOCl treatment did not result in histological features of pulmonary fibrosis nor significant changes in lung compliance. Automated image analysis of HOCl mice lungs stained with picrosirius red did not show increased collagen deposition. HOCl injections did not increase pulmonary mRNA expression of pro-fibrotic genes nor induced the production of serum advanced oxidation protein products and anti-topoisomerase 1 antibodies. Immune cells in bronchoalveolar lavage fluid (BALF) and whole lung digests were not increased in HOCl-treated animals. Since lung fibrosis is proposed to be triggered by oxidative stress, we injected HOCl to Nrf2 -/- mice, a mouse deficient in many antioxidant proteins. Lung compliance, histology, and BALF leukocyte numbers were comparable between Nrf2 -/- mice and wild-type controls. We conclude that the HOCl-SSc model does not manifest SSc-lung disease., (© 2023. The Author(s).)

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., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Cystic fibrosis is a life-threatening genetic disorder caused by mutations in the CFTR chloride channel. Clinically, over 90% of patients with cystic fibrosis succumb to pulmonary complications precipitated by chronic bacterial infections, predominantly by Pseudomonas aeruginosa and Staphylococcus aureus. Despite the well-characterized gene defect and clearly defined clinical sequelae of cystic fibrosis, the critical link between the chloride channel defect and the host defense failure against these specific pathogens has not been established. Previous research from us and others has uncovered that neutrophils from patients with cystic fibrosis are defective in phagosomal production of hypochlorous acid, a potent microbicidal oxidant. Here we report our studies to investigate if this defect in hypochlorous acid production provides P. aeruginosa and S. aureus with a selective advantage in cystic fibrosis lungs. A polymicrobial mixture of cystic fibrosis pathogens (P. aeruginosa and S. aureus) and non-cystic fibrosis pathogens (Streptococcus pneumoniae, Klebsiella pneumoniae, and Escherichia coli) was exposed to varied concentrations of hypochlorous acid. The cystic fibrosis pathogens withstood higher concentrations of hypochlorous acid than did the non-cystic fibrosis pathogens. Neutrophils derived from F508del-CFTR HL-60 cells killed P. aeruginosa less efficiently than did the wild-type counterparts in the polymicrobial setting. After intratracheal challenge in wild-type and cystic fibrosis mice, the cystic fibrosis pathogens outcompeted the non-cystic fibrosis pathogens and exhibited greater survival in the cystic fibrosis lungs. Taken together, these data indicate that reduced hypochlorous acid production due to the absence of CFTR function creates an environment in cystic fibrosis neutrophils that provides a survival advantage to specific microbes-namely, S. aureus and P. aeruginosa-in the cystic fibrosis lungs., Competing Interests: Conflict of interest disclosure S.J. and G.W. receive royalties from F508del-CF HL-60 cell line licensed to EMD Millipore. All other authors declare no conflict of interest in related to this work., (© The Author(s) 2023. Published by Oxford University Press on behalf of Society for Leukocyte Biology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Aims: The MarR/DUF24-family QsrR and YodB repressors control quinone detoxification pathways in Staphylococcus aureus and Bacillus subtilis . In S. aureus , the QsrR regulon also confers resistance to antimicrobial compounds with quinone-like elements, such as rifampicin, ciprofloxacin, and pyocyanin. Although QsrR was shown to be inhibited by thiol- S -alkylation of its conserved Cys4 residue by 1,4-benzoquinone, YodB senses quinones and diamide by the formation of reversible intermolecular disulfides. In this study, we aimed at further investigating the redox-regulation of QsrR and the role of its Cys4, Cys29, and Cys32 residues under quinone and oxidative stress in S. aureus . Results: The QsrR regulon was strongly induced by quinones and oxidants, such as diamide, allicin, hypochlorous acid (HOCl), and AGXX ® in S. aureus . Transcriptional induction of catE2 by quinones and oxidants required Cys4 and either Cys29' or Cys32' of QsrR for redox sensing in vivo . DNA-binding assays revealed that QsrR is reversibly inactivated by quinones and oxidants, depending on Cys4. Using mass spectrometry, QsrR was shown to sense diamide by an intermolecular thiol-disulfide switch, involving Cys4 and Cys29' of opposing subunits in vitro . In contrast, allicin caused S -thioallylation of all three Cys residues in QsrR, leading to its dissociation from the operator sequence. Further, the QsrR regulon confers resistance against quinones and oxidants, depending on Cys4 and either Cys29' or Cys32'. Conclusion and Innovation: QsrR was characterized as a two-Cys-type redox-sensing regulator, which senses the oxidative mode of quinones and strong oxidants, such as diamide, HOCl, and the antimicrobial compound allicin via different thiol switch mechanisms.

Hepatocellular carcinoma (HCC) is one of the most common malignancies in the liver with poor prognosis. In order to improve the prognosis and overall survival of patients with HCC, it is important to identify it at early stage and resect it precisely. Cell microenvironment, active compounds, and enzymes may change during the cancerization of hepatocytes. Hypochlorous acid (HClO), one of the most significant signal molecules in the cellular signaling pathway, plays an important role in many cellular processes. To detect and treat liver cancers, it is imperative to study how HClO levels change in hepatocytes. However, developing fluorescent probes specific to liver cells to detect HClO still challenging. Herein, we designed and synthesized a NIR hepatocyte-specific fluorescent probe (MBH-MT) that displayed excellent optical properties for detecting HClO in biological samples. Cell imaging experiment conducted with the unique probe MBH-MT, showed that the biocompatible sensor is capable of monitoring HClO and distinguishing normal cells from cancer cells (e.g., HepG2, HUVEC, RAW264.7, L02 and HK-2 cells). An organ imaging experiment with the probe MBH-MT demonstrated its effectiveness in diagnosing and imaging hepatocellular carcinoma in vivo. MBH-MT's in situ imaging also demonstrated that it can target and image mouse hepatocellular carcinomas. Furthermore, MBH-MT has also successfully been used to diagnose and guide liver cancer surgery early. In the future, we expect that this powerful tool may be help in the detection and imaging of hepatocellular carcinoma, which may affect a large number of people., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

One challenge for invading pathogens represents the exposure to highly microbicidal hypohalous acids (HOX), such as hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN). Generated at high concentrations by innate immune cells during phagocytosis, HOX kills the engulfed microbes through extensive macromolecular damage. However, microorganisms have evolved strategies to detoxify the oxidants and/or alleviate HOX-mediated damage, which improves their survival during HOX exposure. Many of these defense systems are bacteria-specific and therefore considered potential drug targets. Our minireview highlights recent (July 2021 to November 2022) advances in the field of microbial HOX defense systems and how these systems are regulated. We report recent progress on redox-sensing transcriptional regulators, two-component systems, and σ/anti-σ factors and review how oxidative modifications in these regulatory proteins affect the expression of their target genes. Moreover, we discuss novel studies that describe how HOCl affects the activity of redox-regulated enzymes and highlight mechanisms that bacteria employ to reduce HOSCN., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

The cell envelope of gram-negative bacteria constitutes the first protective barrier between a cell and its environment. During host infection, the bacterial envelope is subjected to several stresses, including those induced by reactive oxygen species (ROS) and reactive chlorine species (RCS) produced by immune cells. Among RCS, N- chlorotaurine ( N- ChT), which results from the reaction between hypochlorous acid and taurine, is a powerful and less diffusible oxidant. Here, using a genetic approach, we demonstrate that Salmonella Typhimurium uses the CpxRA two-component system to detect N -ChT oxidative stress. Moreover, we show that periplasmic methionine sulfoxide reductase (MsrP) is part of the Cpx regulon. Our findings demonstrate that MsrP is required to cope with N -ChT stress by repairing N -ChT-oxidized proteins in the bacterial envelope. By characterizing the molecular signal that induces Cpx when S. Typhimurium is exposed to N -ChT, we show that N -ChT triggers Cpx in an NlpE-dependent manner. Thus, our work establishes a direct link between N -ChT oxidative stress and the envelope stress response.

Myeloperoxidase (MPO) exhibits a unique property to use H 2 O 2 to oxidize chloride and lead to the generation of a strong oxidant, hypochlorous acid (HOCl), which plays important roles in atherosclerosis. A lot of evidence indicates that quercetin, a natural polyphenol derived from human diet, effectively contributes to cardiovascular health. Herein, we found that dietary quercetin significantly inhibited vascular endothelial dysfunction and atherosclerosis in apolipoprotein E-deficient (ApoE -/- ) mice. Mechanistic studies revealed that dietary quercetin effectively suppressed the MPO level and activity in the vessels of ApoE -/- animals, and p47phox expression and NADPH oxidase activity were simultaneously attenuated after quercetin treatment. In vascular endothelial cells, NADPH oxidase was demonstrated to be the major source of H 2 O 2 formation. Moreover, quercetin effectively attenuated MPO/H 2 O 2 -mediated HOCl production and toxicity to human vascular endothelial cells, and this compound was not toxic. The inhibitory effect on MPO activity was likely attributed to that quercetin significantly inhibited NADPH oxidase-derived H 2 O 2 formation in human endothelial cells and could act as an effective mediator for MPO intermediates, subsequently preventing HOCl production by the MPO/H 2 O 2 system. Collectively, it was suggested that quercetin effectively suppressed endothelial dysfunction in atherosclerotic vasculature through the reduction of MPO/NADPH oxidase-mediated HOCl production.

Hypochlorite (ClO - ) plays an important role in the human immune defense system, but high concentrations of ClO - in the endoplasmic reticulum (ER) damage cellular proteins, causing ER stress, cell death, and various diseases. Herein, we developed a simple hydrazone probe (1) featuring aggregation-induced ratiometric emission, which would quickly (within 20 s) and sensitively (detection limit of 15.4 μM) respond to ClO - in an almost pure aqueous solution via a fluorescent ratiometric output. Furthermore, the probe was employed to track the level of ClO - in the ER of HeLa cells and zebrafish., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Neutrophil and airway epithelial cell interactions are critical in the inflammatory response to viral infections including respiratory syncytial virus, Sendai virus, and SARS-CoV-2. Airway epithelial cell dysfunction during viral infections is likely mediated by the interaction of virus and recruited neutrophils at the airway epithelial barrier. Neutrophils are key early responders to viral infection. Neutrophil myeloperoxidase catalyzes the conversion of hydrogen peroxide to hypochlorous acid (HOCl). Previous studies have shown HOCl targets host neutrophil and endothelial cell plasmalogen lipids, resulting in the production of the chlorinated lipid, 2-chlorofatty aldehyde (2-ClFALD). We have previously shown that the oxidation product of 2-ClFALD, 2-chlorofatty acid (2-ClFA) is present in bronchoalveolar lavage fluid of Sendai virus-infected mice, which likely results from the attack of the epithelial plasmalogen by neutrophil-derived HOCl. Herein, we demonstrate small airway epithelial cells contain plasmalogens enriched with oleic acid at the sn-2 position unlike endothelial cells which contain arachidonic acid enrichment at the sn-2 position of plasmalogen. We also show neutrophil-derived HOCl targets epithelial cell plasmalogens to produce 2-ClFALD. Further, proteomics and over-representation analysis using the ω-alkyne analog of the 2-ClFALD molecular species, 2-chlorohexadecanal (2-ClHDyA) showed cell adhesion molecule binding and cell-cell junction enriched categories similar to that observed previously in endothelial cells. However, in contrast to endothelial cells, proteins in distinct metabolic pathways were enriched with 2-ClFALD modification, particularly pyruvate metabolism was enriched in epithelial cells and mitochondrial pyruvate respiration was reduced. Collectively, these studies demonstrate, for the first time, a novel plasmalogen molecular species distribution in airway epithelial cells that are targeted by myeloperoxidase-derived hypochlorous acid resulting in electrophilic 2-ClFALD, which potentially modifies epithelial physiology by modifying proteins., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Foam cell formation and further accumulation in the subendothelial space of the vascular wall is a hallmark of early atherosclerosis (AS). Targeting foam cell formation can be a promising approach for the early detection and prevention of AS. However, only a few studies have actually examined foam cells in vivo , and most methods combined nanotechnology with angiography, which is complex and could cause further damage to the endothelium. Herein, based on methylene blue, a biosafe NIR dye approved by the FDA, an interventional probe (HMB-NA@Mp) triggered by hypochlorous acid (HClO) was designed for imaging foam cells easily, safely, and effectively in the early stage of AS. Here, encapsulation of the probe by foam cells targeted platelet membrane (Mp) increased probe targeting and reduced toxicity. Cell and animal experimental results showed that the probe could accumulate at the lesion site and significantly enhance fluorescence in the early AS model group. Remarkably, at the same time, it could also release the metabolite niacin, which played a role in inhibiting atherosclerosis. Thus, HMB-NA@Mp is expected to be a powerful means for the early detection and timely intervention of early AS in the absence of clinical symptoms.

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., Competing Interests: Declaration of competing interest None., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Aims: Vascular peroxidase 1 (VPO1) plays an important role in mediation of vascular remodeling with pulmonary arterial hypertension (PAH). This study aims to determine whether VPO1 can promote phenotypic transformation of pulmonary artery smooth muscle cells (PASMCs) and the underlying mechanisms., Main Methods: Sprague-Dawley (SD) rats were exposed to 10 % O 2 for 21 days to establish the model of vascular remodeling in pulmonary arterial hypertension. PASMCs were incubated with 3 % O 2 for 48 h to induce phenotypic transformation. Western blot was performed to detect the expressions of target proteins. The 5-ethynyl-2'-deoxyuridine (EdU) assay was conducted to measure the proliferation of PASMCs., Key Findings: In the rats exposed to hypoxia, there were increases in right ventricular systolic pressure, pulmonary vascular remodeling and phenotypic transformation of PASMCs (the down-regulated contractile proteins of α-smooth muscle actin, smooth muscle 22α while the up-regulated synthetic proteins of osteopontin, cyclinD1), accompanied by up-regulation of VPO1, increase of hypochlorous acid (HOCl) production and elevation of the phosphorylation of ERK. In the cultured PASMCs exposed to hypoxia, similar results were achieved but they were reversed by VPO1 small interfering RNA (VPO1 siRNA) or HOCl inhibitor. Replacement of hypoxia with NaOCl could induce PASMCs phenotypic transformation and activate the ERK signaling. Furthermore, ERK inhibitor (PD98059) could also attenuate hypoxia-induced PASMCs phenotypic transformation., Significance: VPO1 play a pivotal role in promotion of phenotypic transformation of PASMCs under hypoxic condition through activation of VPO1/HOCl/ERK pathway. It might serve as a potential target for prevention of pulmonary vascular remodeling., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2022. Published by Elsevier Inc.)

Targeting immune evasion tactics of pathogenic bacteria may hold the key to treating recalcitrant bacterial infections. Staphylococcus aureus produces bacillithiol (BSH), its major low-molecular-weight thiol, which is thought to protect this opportunistic human pathogen against the bombardment of oxidants inside neutrophil phagosomes. Here, we show that BSH was oxidized when human neutrophils phagocytosed S. aureus, but provided limited protection to the bacteria. We used mass spectrometry to measure the oxidation of BSH upon exposure of S. aureus USA300 to either a bolus of hypochlorous acid (HOCl) or a flux generated by the neutrophil enzyme myeloperoxidase. Oxidation of BSH and loss of bacterial viability were strongly correlated (r = 0.99, p < 0.001). BSH was fully oxidized after exposure of S. aureus to lethal doses of HOCl. However, there was no relationship between the initial BSH levels and the dose of HOCl required for bacterial killing. In contrast to the HOCl systems, only 50% of total BSH was oxidized when neutrophils killed the majority of phagocytosed bacteria. Oxidation of BSH was decreased upon inhibition of myeloperoxidase, implicating HOCl in phagosomal BSH oxidation. A BSH-deficient S. aureus USA300 mutant was slightly more susceptible to treatment with either HOCl or ammonia chloramine, or to killing within neutrophil phagosomes. Collectively, our data show that myeloperoxidase-derived oxidants react with S. aureus inside neutrophil phagosomes, leading to partial BSH oxidation, and contribute to bacterial killing. However, BSH offers only limited protection against the neutrophil's multifaceted killing mechanisms., (© 2022 The Authors. Journal of Leukocyte Biology published by Wiley Periodicals LLC on behalf of Society for Leukocyte Biology.)

Elevated levels of ruminal lipopolysaccharides (LPS) have been linked to ruminal acidosis; however, they result in reduced endotoxicity compared to LPS derived from species like Escherichia coli. Additionally, there is a knowledge gap on the potential effect of LPS derived from ruminal microbiome on ruminal bacteria species whose abundance is associated with ruminal acidosis. The objective of this study was to evaluate the effects of LPS-free anaerobic water (CTRL), E. coli-LPS (E. COLI), ruminal-LPS (RUM), and a 1:1 mixture of E. coli and ruminal-LPS (MIX) on the growth characteristics and fermentation end products of lactate-producing bacteria (Streptococcus bovis JB1, Selenomonas ruminantium HD4) and lactate-utilizing bacterium (Megasphaera elsdenii T81). The growth characteristics were predicted based on the logistic growth model, the ammonia concentration was determined by the phenolic acid/hypochlorite method and organic acids were analyzed with high performance liquid chromatography. Results indicate that, compared to the CTRL, the maximum specific growth rate of S. bovis JB1 decreased by approximately 19% and 23% when RUM and MIX were dosed, respectively. In addition, acetate and lactate concentrations in Se. ruminantium HD4 were reduced by approximately 30% and 18%; respectively, in response to MIX dosing. Compared to CTRL, lactate concentration from S. bovis JB1 was reduced approximately by 31% and 22% in response to RUM and MIX dosing; respectively. In summary, RUM decreased the growth and lactate production of some lactate-producing bacteria, potentially mitigating the development of subacute ruminal acidosis by restricting lactate availability to some lactate-utilizing bacteria that metabolize lactate into VFAs thus further contributing to the development of acidosis. Also, RUM did not affect Megasphaera elsdenii T81 growth., (© 2022. The Author(s).)

Oxidative stress-mediated formation of protein hydroperoxides can induce irreversible fragmentation of the peptide backbone and accumulation of cross-linked protein aggregates, leading to cellular toxicity, dysfunction, and death. However, how bacteria protect themselves from damages caused by protein hydroperoxidation is unknown. Here, we show that YjbI, a group II truncated haemoglobin from Bacillus subtilis , prevents oxidative aggregation of cell-surface proteins by its protein hydroperoxide peroxidase-like activity, which removes hydroperoxide groups from oxidised proteins. Disruption of the yjbI gene in B. subtilis lowered biofilm water repellence, which associated with the cross-linked aggregation of the biofilm matrix protein TasA. YjbI was localised to the cell surface or the biofilm matrix, and the sensitivity of planktonically grown cells to generators of reactive oxygen species was significantly increased upon yjbI disruption, suggesting that YjbI pleiotropically protects labile cell-surface proteins from oxidative damage. YjbI removed hydroperoxide residues from the model oxidised protein substrate bovine serum albumin and biofilm component TasA, preventing oxidative aggregation in vitro. Furthermore, the replacement of Tyr 63 near the haem of YjbI with phenylalanine resulted in the loss of its protein peroxidase-like activity, and the mutant gene failed to rescue biofilm water repellency and resistance to oxidative stress induced by hypochlorous acid in the yjbI -deficient strain. These findings provide new insights into the role of truncated haemoglobin and the importance of hydroperoxide removal from proteins in the survival of aerobic bacteria., Competing Interests: TI, RT, KH, MT, JK, HM No competing interests declared, (© 2022, Imai et al.)

The outbreak and spread of Corona Virus Disease 2019 (COVID-19) has led to a significant increase in the consumption of sodium hypochlorite (NaOCl) disinfectants. NaOCl hydrolyzes to produce hypochlorous acid (HOCl) to kill viruses, which is a relatively efficient chlorine-based disinfectant commonly used in public disinfection. While people enjoy the convenience of NaOCl disinfection, excessive and indiscriminate use of it will affect the water environment and threaten human health. Importantly, HOCl is an indispensable reactive oxygen species (ROS) in human body. Whether its concentration is normal or not is closely related to human health. Excessive production of HOCl in the body contributes to some inflammatory diseases and even cancer. Also, we noticed that the concentration of ROS in cancer cells is about 10 times higher than that in normal cells. Herein, we developed a HOCl-activatable biotinylated dual-function fluorescent probe BTH. For this probe, we introduced biotin on the naphthalimide fluorophore, which increased the water solubility and enabled the probe to aggregate in cancer cells by targeting specific receptor overexpressed on the surface of cancer cell membrane. After reacting to HOCl, the p-aminophenylether moiety of this probe was oxidatively removed and the fluorescence of the probe was recovered. As expected, in the PBS solution with pH of 7.4, BTH could give full play to the performance of detecting HOCl, and it has made achievements in detecting the concentration of HOCl in actual water samples. Besides that, BTH had effectively distinguished between cancer cells and normal cells through a dual-function discrimination strategy, which used biotin to enrich the probe in cancer cells and reacted with overexpressed HOCl in cancer cells. Importantly, this dual-function discrimination strategy could obtain the precision detection of cancer cells, thereby offering assistance for improving the accuracy of early cancer diagnosis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

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.

Pyroptosis is a newly identified form of cell death that is closely correlated with many diseases. Recent studies have indicated that the inflammation in pyroptosis would accelerate the generation of reactive oxygen species (ROS). In addition, intracellular viscosity is another key microenvironmental parameter that reflects many physiological and pathological states in the early stage, hypochlorous acid (HOCl), as an important ROS, also plays significant roles in a variety of pathologies. However, the fluctuation of viscosity and HOCl in the process of pyroptosis is still unknown. Herein, we present a dual-responsive fluorescent probe ( Lyso-VH ) for simultaneously detecting viscosity and HOCl. Lyso-VH was successfully used to image the fluctuation of HOCl and viscosity in the lysosome of three kinds of cells with dependent and independent channels. Moreover, Lyso-VH can be employed to investigate the changes of HOCl and viscosity during the process of pyroptosis in living cells and acute lung injury (ALI). Thus, this work can not only serve as a powerful tool to simultaneously visualize the fluctuation of HOCl and viscosity in lysosomes, but also provide a new insight into drug-induced pyroptosis in living cells and acute lung injury.

Liver and kidney injury caused by drug toxicity is a serious threat to human health. Acetaminophenol (APAP), as a common antipyretic and analgesic drug, inevitably causes injury. When it is overused, hypochlorous acid (HClO) is excessively generated due to metabolic abnormalities, resulting in the accumulation of HClO in the mitochondria of liver and kidney tissues and causing damage. In this study, we designed a series of HClO responsive ratiometric chemdosimeter NRH-X (NRH-O, NRH-S, and NRH-C) to evaluate liver and kidney injury, and found that NRH-O has a specific sensitive response to HClO. NRH-O can not only monitor the variations of endogenous HClO content of living cells by fluorescence ratio changes in the mitochondria but also detect the upregulation of HClO induced by APAP. In addition, NRH-O can also be used for anatomic diagnosis of liver and kidney injury by fluorescence ratio imaging of HClO in the tissues of inflammatory mice.

The ambiguous molecular mechanism remains a leading cause for the high mortality rate of liver cancer. An evident iron overload has been unveiled in liver cancer cell proliferation, which is closely related to oxidative stress. However oxidative stress-regulated chloride intracellular channel protein 1 (CLIC1) obviously increases in liver cancer cells. Cl - is also involved in cell proliferation, and its downstream product, HClO, can induce cell carcinoma when over-generated. However, whether iron overload could mediate the variation of intracellular Cl - and HClO is still uncharted. Herein, we present a dual-responsive fluorescence reporter MQFL-NH 2 for simultaneously visualizing the fluctuation of Cl - /HClO at the same spot in living cells. Electrostatic binding to Cl - effectively gave an attenuated signal with blue fluorescence, and HClO induced a sharp green fluorescence. In HL-7702 cells stimulated with iron, the blue/green dual fluorescence of MQFL-NH 2 displayed that Cl - and HClO were elevated. In contrast, they were both reduced in iron-removed SMMC-7721 cells. Further results revealed that iron overload could promote the levels of Cl - and HClO by up-regulating CLIC1 and myeloperoxidase. Altogether, the work will energetically contribute to grasp the molecular mechanism in iron overload-mediated pathogenesis of liver cancer.

Myeloperoxidase (MPO) mediates pathogen destruction by generating the bactericidal oxidant hypochlorous acid (HOCl). Formation of this oxidant is however associated with host tissue damage and disease. MPO also utilizes H 2 O 2 to oxidize other substrates, and we hypothesized that mixtures of other plasma anions, including bromide (Br - ), iodide (I - ), thiocyanate (SCN - ) and nitrite (NO 2 - ), at normal or supplemented concentrations, might modulate MPO-mediated HOCl damage. For the (pseudo)halide anions, only SCN - significantly modulated HOCl formation (IC 50 ∼33 μM), which is within the normal physiological range, as judged by damage to human plasma fibronectin or extracellular matrix preparations detected by ELISA and LC-MS. NO 2 - modulated HOCl-mediated damage, in a dose-dependent manner, at physiologically-attainable anion concentrations. However, this was accompanied by increased tyrosine and tryptophan nitration (detected by ELISA and LC-MS), and the overall extent of damage remained approximately constant. Increasing NO 2 - concentrations (0.5-20 μM) diminished HOCl-mediated modification of tyrosine and methionine, whereas tryptophan loss was enhanced. At higher NO 2 - concentrations, enhanced tyrosine and methionine loss was detected. These analytical data were confirmed in studies of cell adhesion and metabolic activity. Together, these data indicate that endogenous plasma levels of SCN - (but not Br - or I - ) can modulate protein modification induced by MPO, including the extent of chlorination. In contrast, NO 2 - alters the type of modification, but does not markedly decrease its extent, with chlorination replaced by nitration. These data also indicate that MPO could be a major source of nitration in vivo, and particularly at inflammatory sites where NO 2 - levels are often elevated., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Right ventricular (RV) remodeling is a major feature of pulmonary arterial hypertension (PAH). Vascular peroxidase 1 (VPO1) is reported to participate in the process of PAH. This study aims to explore whether VPO1 contributes to hypoxia-induced cardiac hypertrophy and the underlying mechanisms. SD rats were exposure to continuous hypoxia (10% O 2 ) for 3 weeks, which showed RV hypertrophy (increases in the ratio of RV weight to tibia length, cardiac cell size and hypertrophic markers), concomitant with upregulation of VPO1, elevation in hypochlorous acid (HOCl) production and ERK phosphorylation. In hypoxia (3% O 2 )-induced hypertrophic H9c2 cells, similar characteristics of cardiac hypertrophy to that of hypoxia-treated rats were observed. Administration of VPO1 siRNA or NaHS (the HOCl inhibitor) suppressed HOCl production, ERK phosphorylation, and cardiac hypertrophy. Replacement of hypoxia with NaClO (exogenous HOCl) could also induce cardiac cell hypertrophy and activate ERK signaling pathway. In addition, hypoxia-induced cardiac hypertrophy could be blocked by PD98059 (the ERK-specific inhibitor). Based on these observations, we conclude that VPO1 promotes RV remodeling in PAH rats through catalyzing HOCl production, leading to the activation of ERK signaling. Thus, VPO1 may have the potential as a therapeutic target for PAH., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Psoriasis is a common skin disease with complex pathogenesis that lacks diagnostic methods. Typically, psoriasis is an inflammation-related disease accompanied by high expression of reactive oxygen species (ROS) in the infected part. However, due to the lack of suitable tools, it is difficult to identify the ROS, especially certain types of ROS ( e.g. , HOCl) in the psoriasis model. Here, two HOCl-specific fluorescent probes, G1 and G2, were designed and synthesized based on oxazine 1. Both probes could react with HOCl with high selectivity among other ROS under physiological conditions. The selected probe G2 could detect HOCl in HL-60 cells without special stimulation and detect endogenously produced HOCl in the mouse model of arthritis. Thus, G2 was used to identify and image HOCl in situ in the imiquimod induced psoriasis model. The result showed that HOCl was a potential pathological marker of psoriasis.