Production of reactive persulfide species in chronic obstructive pulmonary disease

Supersulfide formation in the sinus mucosa of chronic rhinosinusitis

Objectives

Disruption of the oxidative stress defense system is involved in developing various diseases. Sulfur compounds such as glutathione (GSH) and cysteine (CysSH) are representative antioxidants in the body. Recently, supersulfides, including reactive persulfide and polysulfide species, have gained attention as potent antioxidants regulating oxidative stress and redox signaling. However, their involvement in the pathogenesis of chronic rhinosinusitis (CRS) remains unclear.

Methods

To clarify the changes in sulfur compounds within the sinus mucosa of each CRS subtype, we measured sulfur compound levels in the sinus mucosa of control individuals (n = 9), patients with eosinophilic CRS (ECRS) (n = 13), and those with non-ECRS (nECRS) (n = 11) who underwent sinus surgery using mass spectrometry.

Results

GSH and CysSH levels were significantly reduced, and the glutathione disulfide (GSSG)/GSH ratio, an oxidative stress indicator, was increased in patients with ECRS. Despite the absence of notable variations in supersulfides, patients with ECRS and nECRS exhibited a significant reduction in glutathione trisulfide (GSSSG), which serves as the precursor for supersulfides.

Conclusions

This study is the first quantitative assessment of supersulfides in normal and inflamed sinus mucosa, suggesting that sulfur compounds contribute to the pathogenesis of CRS.

Level of Evidence

N/A.

Characteristic volatile components analysis of Camelina sativa (L.) Crantz by GC-MS and their antibacterial and antioxidant activities

Camelina sativa (L.) Crantz is an oilseed plant common in Europe and Asia. This study used the gas chromatography-mass spectrometry (GC-MS) to examine the differences in the aroma on the basis of extraction method such as water distillation extraction (CSPW), Solid-phase microextraction (CSPM) and subcritical extraction (CSPS). Antibacterial test was evaluated by the microdilution method against Salmonella typhimurium, Streptococcus pneumoniae, Escherichia coli, Strepococcus pyogenens, Staphylococcus aureus, and antioxidant activity was determined through DPPH free radical, hydroxyl free radical, and superoxide anion radical scavenging capacity activity. The result revealed that three extraction methods were distinct from each other based on their volatile compounds. Sixty-one volatiles of diverse chemical nature were identified and quantified. The volatile components contain thioether, aldehydes, alcohols, ketones, acids, esters, alkene, alkanes, amide, and furan compounds. The volatile components of Camelina sativa (L.) Crantz have good antibacterial and antioxidant activities. Furthermore, this work provides reference methods for detecting novel volatile organic compounds in plants and products.

Redox Regulation of Xenobiotics by Reactive Sulfur and Supersulfide Species

Significance: Routine exposure to xenobiotics is unavoidable during our lifetimes. Certain xenobiotics are hazardous to human health, and are metabolized in the body to render them less toxic. During this process, several detoxification enzymes cooperatively metabolize xenobiotics. Glutathione (GSH) conjugation plays an important role in the metabolism of electrophilic xenobiotics. Recent Advances: Recent advances in reactive sulfur and supersulfide (RSS) analyses showed that persulfides and polysulfides bound to low-molecular-weight thiols, such as GSH, and to protein thiols are abundant in both eukaryotes and prokaryotes. The highly nucleophilic nature of hydropersulfides and hydropolysulfides contributes to cell protection against oxidative stress and electrophilic stress. Critical Issues: In contrast to GSH conjugation to electrophiles that is aided by glutathione S-transferase (GST), persulfides and polysulfides can directly form conjugates with electrophiles without the catalytic actions of GST. The polysulfur bonds in the conjugates are further reduced by perthioanions and polythioanions derived from RSS to form sulfhydrated metabolites that are no longer electrophilic but rather nucleophilic, and differ from metabolites that are formed via GSH conjugation. Future Directions: In view of the abundance of RSS in cells and tissues, metabolism of xenobiotics that is mediated by RSS warrants additional investigations, such as studies of the impact of microbiota-derived RSS on xenobiotic metabolism. Metabolites formed from reactions between electrophiles and RSS may be potential biomarkers for monitoring exposure to electrophiles and for studying their metabolism by RSS. Antioxid. Redox Signal. 40, 679-690.

Longevity control by supersulfide-mediated mitochondrial respiration and regulation of protein quality

Supersulfides, which are defined as sulfur species with catenated sulfur atoms, are increasingly being investigated in biology. We recently identified pyridoxal phosphate (PLP)-dependent biosynthesis of cysteine persulfide (CysSSH) and related supersulfides by cysteinyl-tRNA synthetase (CARS). Here, we investigated the physiological role of CysSSH in budding yeast (Saccharomyces cerevisiae) by generating a PLP-binding site mutation K109A in CRS1 (the yeast ortholog of CARS), which decreased the synthesis of CysSSH and related supersulfides and also led to reduced chronological aging, effects that were associated with an increased endoplasmic reticulum stress response and impaired mitochondrial bioenergetics. Reduced chronological aging in the K109A mutant could be rescued by using exogenous supersulfide donors. Our findings indicate important roles for CARS in the production and metabolism of supersulfides-to mediate mitochondrial function and to regulate longevity.

CYP27A1-27-hydroxycholesterol axis in the respiratory system contributes to house dust mite-induced allergic airway inflammation

BACKGROUND

27-Hydroxycholesterol (27-HC) derived from sterol 27-hydroxylase (CYP27A1) has pro-inflammatory biological activity and is associated with oxidative stress and chronic inflammation in COPD. However, the role of regulation of CYP27A1- 27-HC axis in asthma is unclear. This study aimed to elucidate the contribution of the axis to the pathophysiology of asthma.

METHODS

House dust mite (HDM) extract was intranasally administered to C57BL/6 mice and the expression of CYP27A1 in the airways was analyzed by immunostaining. The effect of pre-treatment with PBS or CYP27A1 inhibitors on the cell fraction in the bronchoalveolar lavage fluid (BALF) was analyzed in the murine model. In vitro, BEAS-2B cells were treated with HDM and the levels of CYP27A1 expression were examined. Furthermore, the effect of 27-HC on the expressions of E-cadherin and ZO-1 in the cells was analyzed. The amounts of RANTES and eotaxin from the 27-HC-treated cells were analyzed by ELISA.

RESULTS

The administration of HDM increased the expression of CYP27A1 in the airways of mice as well as the number of eosinophils in the BALF. CYP27A1 inhibitors ameliorated the HDM-induced increase in the number of eosinophils in the BALF. Treatment with HDM increased the expression of CYP27A1 in BEAS-2B cells. The administration of 27-HC to BEAS-2B cells suppressed the expression of E-cadherin and ZO-1, and augmented the production of RANTES and eotaxin.

CONCLUSIONS

The results of this study suggest that aeroallergen could enhance the induction of CYP27A1, leading to allergic airway inflammation and disruption of the airway epithelial tight junction through 27-HC production.

Untargeted polysulfide omics analysis of alternations in polysulfide production during the germination of broccoli sprouts

Higher consumption of broccoli (Brassica oleracea var. italica) is associated with a reduced risk of cardiometabolic diseases, neurological disorders, diabetes, and cancer. Broccoli is rich in various phytochemicals, including glucosinolates, and isothiocyanates. Moreover, it has recently reported the endogenous production of polysulfides, such as cysteine hydropersulfide (CysS2H) and glutathione hydropersulfide (GS2H), in mammals including humans, and that these bioactive substances function as potent antioxidants and important regulators of redox signaling in vivo. However, few studies have focused on the endogenous polysulfide content of broccoli and the impact of germination on the polysulfide content and composition in broccoli. In this study, we investigated the alternations in polysulfide biosynthesis in broccoli during germination by performing untargeted polysulfide omics analysis and quantitative targeted polysulfide metabolomics through liquid chromatography-electrospray ionization-tandem mass spectrometry. We also performed 2,2-diphenyl-1-picrylhydrazyl radical-scavenging assay to determine the antioxidant properties of the polysulfides. The results revealed that the total polysulfide content of broccoli sprouts significantly increased during germination and growth; CysS2H and cysteine hydrotrisulfide were the predominant organic polysulfide metabolites. Furthermore, we determined that novel sulforaphane (SFN) derivatives conjugated with CysS2H and GS2H were endogenously produced in the broccoli sprouts, and the novel SFN conjugated with CysS2H exhibited a greater radical scavenging capacity than SFN and cysteine. These results suggest that the abundance of polysulfides in broccoli sprouts contribute to their health-promoting properties. Our findings have important biological implications for the development of novel pharmacological targets for the health-promoting effects of broccoli sprouts in humans.

Reactive Sulfur Species in Human Diseases

Significance: Reactive sulfur species (RSS) have been recently recognized as redox molecules no less important than reactive oxygen species or reactive nitrogen species. They possess regulatory and protective properties and are involved in various metabolic processes, thereby contributing to the maintenance of human health. It has been documented that many disorders, including neurological, cardiovascular, and respiratory diseases, diabetes mellitus (DM), and cancer, are related to the disruption of RSS homeostasis. Recent Advances: There is still a growing interest in the role of RSS in human diseases. Since a decrease in hydrogen sulfide or other RSS has been reported in many disorders, safe and efficient RSS donors have been developed and tested under in vitro conditions or on animal models. Critical Issues: Cardiovascular diseases and DM are currently the most common chronic diseases worldwide due to stressful and unhealthy lifestyles. In addition, because of high prevalence and aging of the population, neurological disorders including Parkinson's disease and Alzheimer's disease as well as respiratory diseases are a formidable challenge for health care systems. From this point of view, the knowledge of the role of RSS in these disorders and RSS modulation options are important and could be useful in therapeutic strategies. Future Directions: Improvement and standardization of analytical methods used for RSS estimation are crucial for the use of RSS as diagnostic biomarkers. Finding good, safe RSS donors applicable for therapeutic purposes could be useful as primary or adjunctive therapy in many common diseases. Antioxid. Redox Signal. 39, 1000-1023.

Persulfide Biosynthesis Conserved Evolutionarily in All Organisms

Significance: Persulfides/polysulfides are sulfur-catenated molecular species (i.e., R-Sn-R', n > 2; R-Sn-H, n > 1, with R = cysteine, glutathione, and proteins), such as cysteine persulfide (CysSSH). These species are abundantly formed as endogenous metabolites in mammalian and human cells and tissues. However, the persulfide synthesis mechanism has yet to be thoroughly discussed. Recent Advances: We used β-(4-hydroxyphenyl)ethyl iodoacetamide and mass spectrometry to develop sulfur metabolomics, a highly precise, quantitative analytical method for sulfur metabolites. Critical Issues: With this method, we detected appreciable amounts of different persulfide species in biological specimens from various organisms, from the domains Bacteria, Archaea, and Eukarya. By using our rigorously quantitative approach, we identified cysteinyl-tRNA synthetase (CARS) as a novel persulfide synthase, and we found that the CysSSH synthase activity of CARS is highly conserved from the domains Bacteria to Eukarya. Because persulfide synthesis is found not only with CARS but also with other sulfotransferase enzymes in many organisms, persulfides/polysulfides are expected to contribute as fundamental elements to substantially diverse biological phenomena. In fact, persulfide generation in higher organisms-that is, plants and animals-demonstrated various physiological functions that are mediated by redox signaling, such as regulation of energy metabolism, infection, inflammation, and cell death, including ferroptosis. Future Directions: Investigating CARS-dependent persulfide production may clarify various pathways of redox signaling in physiological and pathophysiological conditions and may thereby promote the development of preventive and therapeutic measures for oxidative stress as well as different inflammatory, metabolic, and neurodegenerative diseases. Antioxid. Redox Signal. 39, 983-999.

Sulfur metabolic response in macrophage limits excessive inflammatory response by creating a negative feedback loop

The excessive inflammatory response of macrophages plays a vital role in the pathogenesis of various diseases. The dynamic metabolic alterations in macrophages, including amino acid metabolism, are known to orchestrate their inflammatory phenotype. To explore a new metabolic pathway that regulates the inflammatory response, we examined metabolome changes in mouse peritoneal macrophages (PMs) in response to lipopolysaccharide (LPS) and found a coordinated increase of cysteine and its related metabolites, suggesting an enhanced demand for cysteine during the inflammatory response. Because Slc7a11, which encodes a cystine transporter xCT, was remarkably upregulated upon the pro-inflammatory challenge and found to serve as a major channel of cysteine supply, we examined the inflammatory behavior of Slc7a11 knockout PMs (xCT-KO PMs) to clarify an impact of the increased cysteine demand on inflammation. The xCT-KO PMs exhibited a prolonged upregulation of pro-inflammatory genes, which was recapitulated by cystine depletion in the culture media of wild-type PMs, suggesting that cysteine facilitates the resolution of inflammation. Detailed analysis of the sulfur metabolome revealed that supersulfides, such as cysteine persulfide, were increased in PMs in response to LPS, which was abolished in xCT-KO PMs. Supplementation of N-acetylcysteine tetrasulfide (NAC-S2), a supersulfide donor, attenuated the pro-inflammatory gene expression in xCT-KO PMs. Thus, activated macrophages increase cystine uptake via xCT and produce supersulfides, creating a negative feedback loop to limit excessive inflammation. Our study highlights the finely tuned regulation of macrophage inflammatory response by sulfur metabolism.

Supersulphides provide airway protection in viral and chronic lung diseases

Supersulphides are inorganic and organic sulphides with sulphur catenation with diverse physiological functions. Their synthesis is mainly mediated by mitochondrial cysteinyl-tRNA synthetase (CARS2) that functions as a principal cysteine persulphide synthase (CPERS). Here, we identify protective functions of supersulphides in viral airway infections (influenza and COVID-19), in aged lungs and in chronic lung diseases, including chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF). We develop a method for breath supersulphur-omics and demonstrate that levels of exhaled supersulphides increase in people with COVID-19 infection and in a hamster model of SARS-CoV-2 infection. Lung damage and subsequent lethality that result from oxidative stress and inflammation in mouse models of COPD, IPF, and ageing were mitigated by endogenous supersulphides production by CARS2/CPERS or exogenous administration of the supersulphide donor glutathione trisulphide. We revealed a protective role of supersulphides in airways with various viral or chronic insults and demonstrated the potential of targeting supersulphides in lung disease.

Synthesis of Sulfides and Persulfides Is Not Impeded by Disruption of Three Canonical Enzymes in Sulfur Metabolism

Reactive sulfur species, or persulfides and polysulfides, such as cysteine hydropersulfide and glutathione persulfide, are endogenously produced in abundance in both prokaryotes and eukaryotes, including mammals. Various forms of reactive persulfides occur in both low-molecular-weight and protein-bound thiols. The chemical properties and great supply of these molecular species suggest a pivotal role for reactive persulfides/polysulfides in different cellular regulatory processes (e.g., energy metabolism and redox signaling). We demonstrated earlier that cysteinyl-tRNA synthetase (CARS) is a new cysteine persulfide synthase (CPERS) and is responsible for the in vivo production of most reactive persulfides (polysulfides). Some researchers continue to suggest that 3-mercaptopyruvate sulfurtransferase (3-MST), cystathionine β-synthase (CBS), and cystathionine γ-lyase (CSE) may also produce hydrogen sulfide and persulfides that may be generated during the transfer of sulfur from 3-mercaptopyruvate to the cysteine residues of 3-MST or direct synthesis from cysteine by CBS/CSE, respectively. We thus used integrated sulfur metabolome analysis, which we recently developed, with 3-MST knockout (KO) mice and CBS/CSE/3-MST triple-KO mice, to elucidate the possible contribution of 3-MST, CBS, and CSE to the production of reactive persulfides in vivo. We therefore quantified various sulfide metabolites in organs derived from these mutant mice and their wild-type littermates via this sulfur metabolome, which clearly revealed no significant difference between mutant mice and wild-type mice in terms of reactive persulfide production. This result indicates that 3-MST, CBS, and CSE are not major sources of endogenous reactive persulfide production; rather, CARS/CPERS is the principal enzyme that is actually involved in and even primarily responsible for the biosynthesis of reactive persulfides and polysulfides in vivo in mammals.

Intranasal administration of polysulfide prevents neurodegeneration in spinal cord and rescues mice from delayed paraplegia after spinal cord ischemia

BACKGROUND

Delayed paraplegia is a devastating complication of thoracoabdominal aortic surgery. Hydrogen sulfide (H₂S) was reported to be protective in a mouse model of spinal cord ischemia and the beneficial effect of H₂S has been attributed to polysulfides. The objective of this study was to investigate the effects of polysulfides on delayed paraplegia after spinal cord ischemia.

METHODS AND RESULTS

Spinal cord ischemia was induced in male and female C57BL/6J mice by clamping the aortic arch and the left subclavian artery. Glutathione trisulfide (GSSSG), glutathione (GSH), glutathione disulfide (GSSG), or vehicle alone was administered intranasally at 0, 8, 23, and 32 h after surgery. All mice treated with vehicle alone developed paraplegia within 48 h after surgery. GSSSG, but not GSH or GSSG, prevented paraplegia in 8 of 11 male mice (73%) and 6 of 8 female mice (75%). Intranasal administration of ³⁴S-labeled GSSSG rapidly increased ³⁴S-labeled sulfane sulfur species in the lumbar spinal cord. In mice treated with intranasal GSSSG, there were increased sulfane sulfur levels, and decreased neurodegeneration, microglia activation, and caspase-3 activation in the lumbar spinal cord. In vitro studies using murine primary cortical neurons showed that GSSSG increased intracellular levels of sulfane sulfur. GSSSG, but not GSH or GSSG, dose-dependently improved cell viability after oxygen and glucose deprivation/reoxygenation (OGD/R). Pantethine trisulfide (PTN-SSS) also increased intracellular sulfane sulfur and improved cell viability after OGD/R. Intranasal administration of PTN-SSS, but not pantethine, prevented paraplegia in 6 of 9 male mice (66%).

CONCLUSIONS

Intranasal administration of polysulfides rescued mice from delayed paraplegia after transient spinal cord ischemia. The neuroprotective effects of GSSSG were associated with increased levels of polysulfides and sulfane sulfur in the lumbar spinal cord. Targeted delivery of sulfane sulfur by polysulfides may prove to be a novel approach to the treatment of neurodegenerative diseases.

Dysregulated Polycomb Repressive Complex 2 contributes to chronic obstructive pulmonary disease by rewiring stem cell fate

Aberrant lung cell differentiation is a hallmark of many lung diseases including chronic obstructive pulmonary disease (COPD). The EZH2-containing Polycomb Repressive Complex 2 (PRC2) regulates embryonic lung stem cell fate, but its role in adult lung is obscure. Histological analysis of patient tissues revealed that loss of PRC2 activity was correlated with aberrant bronchiolar cell differentiation in COPD lung. Histological and single-cell RNA-sequencing analyses showed that loss of EZH2 in mouse lung organoids led to lowered self-renewal capability, increased squamous morphological development, and marked shifts in progenitor cell populations. Evaluation of in vivo models revealed that heterozygosity of Ezh2 in mice with ovalbumin-induced lung inflammation led to epithelial cell differentiation patterns similar to those in COPD lung. We also identified cystathionine-β-synthase as a possible upstream factor for PRC2 destabilization. Our findings suggest that PRC2 is integral to facilitating proper lung stem cell differentiation in humans and mice.

Hydrogen Sulfide: A Gaseous Mediator and Its Key Role in Programmed Cell Death, Oxidative Stress, Inflammation and Pulmonary Disease

Hydrogen sulfide (H₂S) has been acknowledged as a novel gaseous mediator. The metabolism of H₂S in mammals is tightly controlled and is mainly achieved by many physiological reactions catalyzed by a suite of enzymes. Although the precise actions of H₂S in regulating programmed cell death, oxidative stress and inflammation are yet to be fully understood, it is becoming increasingly clear that H₂S is extensively involved in these crucial processes. Since programmed cell death, oxidative stress and inflammation have been demonstrated as three important mechanisms participating in the pathogenesis of various pulmonary diseases, it can be inferred that aberrant H₂S metabolism also functions as a critical contributor to pulmonary diseases, which has also been extensively investigated. In the meantime, substantial attention has been paid to developing therapeutic approaches targeting H₂S for pulmonary diseases. In this review, we summarize the cutting-edge knowledge on the metabolism of H₂S and the relevance of H₂S to programmed cell death, oxidative stress and inflammation. We also provide an update on the crucial roles played by H₂S in the pathogenesis of several pulmonary diseases. Finally, we discuss the perspective on targeting H₂S metabolism in the treatment of pulmonary diseases.

The role of sulfur compounds in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease that brings about great social and economic burden, with oxidative stress and inflammation affecting the whole disease progress. Sulfur compounds such as hydrogen sulfide (H₂S), thiols, and persulfides/polysulfides have intrinsic antioxidant and anti-inflammatory ability, which is engaged in the pathophysiological process of COPD. Hydrogen sulfide mainly exhibits its function by S-sulfidation of the cysteine residue of the targeted proteins. It also interacts with nitric oxide and acts as a potential biomarker for the COPD phenotype. Thiols’ redox buffer such as the glutathione redox couple is a major non-enzymatic redox buffer reflecting the oxidative stress in the organism. The disturbance of redox buffers was often detected in patients with COPD, and redressing the balance could delay COPD exacerbation. Sulfane sulfur refers to a divalent sulfur atom bonded with another sulfur atom. Among them, persulfides and polysulfides have an evolutionarily conserved modification with antiaging effects. Sulfur compounds and their relative signaling pathways are also associated with the development of comorbidities in COPD. Synthetic compounds which can release H₂S and persulfides in the organism have gradually been developed. Naturally extracted sulfur compounds with pharmacological effects also aroused great interest. This study discussed the biological functions and mechanisms of sulfur compounds in regulating COPD and its comorbidities.

Reactive sulfur species and their significance in health and disease

Reactive sulfur species (RSS) have been recognized in the last two decades as very important molecules in redox regulation. They are involved in metabolic processes and, in this way, they are responsible for maintenance of health. This review summarizes current information about the essential biological RSS, including H₂S, low molecular weight persulfides, protein persulfides as well as organic and inorganic polysulfides, their synthesis, catabolism and chemical reactivity. Moreover, the role of RSS disturbances in various pathologies including vascular diseases, chronic kidney diseases, diabetes mellitus Type 2, neurological diseases, obesity, chronic obstructive pulmonary disease and in the most current problem of COVID-19 is presented. The significance of RSS in aging is also mentioned. Finally, the possibilities of using the precursors of various forms of RSS for therapeutic purposes are discussed.

Nutrition Interventions of Herbal Compounds on Cellular Senescence

When cells undergo large-scale senescence, organ aging ensues, resulting in irreversible organ pathology and organismal aging. The study of senescence in cells provides an important avenue to understand the factors that influence aging and can be used as one of the useful tools for examining age-related human diseases. At present, many herbal compounds have shown effects on delaying cell senescence. This review summarizes the main characteristics and mechanisms of cell senescence, age-related diseases, and the recent progress on the natural products targeting cellular senescence, with the aim of providing insights to aid the clinical management of age-related diseases.

Decreased expression of airway epithelial Axl is associated with eosinophilic inflammation in severe asthma

BACKGROUND

Airway epithelium-derived cytokines are critical to provoke and perpetuate type 2 inflammation in asthma. Yet it is poorly understood how this epithelial cell-driven inflammatory response is negatively regulated. We previously reported that Axl receptor tyrosine kinase was expressed by basal cells in the airway epithelium and had a role in defining their stem cell identity. However, whether and how Axl regulates airway type 2 inflammation remains unknown.

METHODS

We performed immunofluorescence staining to compare Axl expression in airway epithelium between non-asthmatic subjects, mild-moderate asthma and severe asthma. We confirmed this result by interrogating public databases of global gene expression in endobronchial biopsies. We then quantified eosinophil numbers infiltrating into the trachea of wild-type or Axl-knockout mice that were intranasally treated with house dust mite extracts (HDM). Cell-based assays using siRNA targeting Axl were further performed to identify molecules involved in Axl-mediated regulation of inflammation.

RESULTS

Histological assessments and transcriptome analyses revealed decreases in protein and mRNA of Axl in airway basal cells of severe asthmatics. This reduction of Axl expression was correlated with infiltration of eosinophils and mast cells in severe asthmatics. Eosinophil infiltration was more evident in the trachea of Axl-knockout mice in response to repetitive HDM administration. siRNA-mediated knockdown of Axl increased mRNA and protein expression of granulocyte macrophage-colony stimulating factor (GM-CSF) in human bronchial epithelial cells.

CONCLUSIONS

Axl kinase expressed by basal cells may suppress excessive eosinophilic inflammation via inhibition of GM-CSF in the airway. Axl reduction has clinical implications for the pathogenesis of severe asthma.

Enhancing cellular sulfane sulfur through β-glycosidase-activated persulfide donors: mechanistic insights and oxidative stress mitigation

Sulfane sulfur species such as persulfides and polysulfides along with hydrogen sulfide protect cells from oxidative stress and are key members of the cellular antioxidant pool. Here, we report perthiocarbamate-based prodrugs that are cleaved by β-glycosidases to produce persulfide and relatively innocuous byproducts. The β-glucosidase-activated persulfide donor enhances cellular sulfane sulfur and protects cells against lethality induced by elevated reactive oxygen species (ROS).

Development of Hydropersulfide Donors to Study Their Chemical Biology

Significance: Hydropersulfides (RSSH) are ubiquitous in prokaryotes, eukaryotic cells, and mammalian tissues. The unique chemical properties and prevalent nature of these species suggest a crucial role of RSSH in cell regulatory processes, yet little is known about their physiological functions. Recent Advances: Examining the biological roles of RSSH species is challenging because of their inherent instability. In recent years, researchers have developed a number of small-molecule donors that efficiently release RSSH in response to various stimuli, including pH, thiols, reactive oxygen species, enzymes, and light. These RSSH donors have provided researchers with chemical tools to uncover the potential function and role of RSSH as physiological signaling and/or protecting agents. Critical Issues: Because RSSH, hydrogen sulfide (H₂S), and higher order polysulfides are related to each other and can be present simultaneously in biological systems, distinguishing among the activities due to each of these species is difficult. Discerning this activity is critical to elucidate the chemical biology and physiology of RSSH. Moreover, although RSSH donors have been shown to confer cytoprotection against oxidative and electrophilic stress, their biological targets remain to be elucidated. Future Directions: The development of RSSH donors with optimal drug-like properties and selectivity toward specific tissues/pathologies represents a promising approach. Further investigation of releasing efficiencies in vivo and a clear understanding of RSSH biological responses remain targets for future investigation. Antioxid. Redox Signal. 36, 309-326.

Chemical Biology of Reactive Sulfur Species: Hydrolysis-Driven Equilibrium of Polysulfides as a Determinant of Physiological Functions

Significance: Polysulfide species (i.e., R-S_n-R', n > 2; and R-S_n-H, n > 1) exist in many organisms. The highly nucleophilic nature of hydropersulfides and hydropolysulfides contributes to the potent antioxidant activities of polysulfide species that protect organisms against oxidative and electrophilic stresses. Recent Advances: Accumulating evidence suggests that organic polysulfides (R-S_n-R') readily undergo alkaline hydrolysis, which results in formation of both nucleophilic hydrosulfide/polysulfide (R-S_n-1H) and electrophilic sulfenic acid (R'SOH) species. Polysulfides maintain a steady-state equilibrium that is driven by hydrolysis even in aqueous physiological milieus. This unique property makes polysulfide chemistry and biology more complex than previously believed. Critical Issues: The hydrolysis equilibrium of polysulfides shifts to the right when electrophiles are present. Strong electrophilic alkylating agents (e.g., monobromobimane) greatly enhance polysulfide hydrolysis, which leads to increased polysulfide degradation and artifactual formation of bis-S-bimane adducts in the absence of free hydrogen sulfide. The finding that hydroxyl group-containing substances such as tyrosine efficiently protected polysulfides from hydrolysis led to development of the new alkylating agent, N-iodoacetyl l-tyrosine methyl ester (TME-IAM). TME-IAM efficiently and specifically traps and stabilizes hydropolysulfides and protects polysulfide chains from hydrolysis, and, when used with mass spectrometry, TME-IAM allows speciation of the reactive sulfur metabolome. In addition, the polyethylene glycol-conjugated maleimide-labeling gel shift assay, which relies on unique hydrolysis equilibrium of polysulfides, will be a reliable technique for proteomics of polysulfide-containing proteins. Future Directions: Using precise methodologies to achieve a better understanding of the occurrence and metabolism of polysulfide species is necessary to gain insights into the undefined biology of polysulfide species. Antioxid. Redox Signal. 36, 327-336.

Sulphur metabolism in colon cancer tissues: a case report and literature review

Sulphur-containing compounds have been linked to colorectal cancer by factors such as the presence of methyl mercaptan in intestinal gas and long-term dietary intake associated with sulphur-metabolizing microbiota. Therefore, this current case report hypothesized that active sulphur metabolism in colorectal cancer results in the formation of sulphur compounds in the intestine and, thus, examined sulphur metabolites possibly associated with sulphur respiration in colon cancer tissues. The patient was a 73-year-old female that underwent laparoscopic right hemicolectomy for ascending colon cancer. During the surgery, colon cancer tissues and normal intestinal mucosa samples were collected. After optimizing the sample concentrations for homogenization (pre-treatment), the samples were stabilized using a hydroxyphenyl-containing derivative and the relevant metabolites were quantified using liquid chromatography with tandem mass spectrometry. The results showed that cysteine persulfide and cysteine trisulfide levels were higher in colon cancer tissues than in normal mucosal tissues. Thus, sulphur metabolism, possibly sulphur respiration, is enhanced in colon cancer tissues.

Redox Dysregulation in Aging and COPD: Role of NOX Enzymes and Implications for Antioxidant Strategies

With a rapidly growing elderly human population, the incidence of age-related lung diseases such as chronic obstructive pulmonary disease (COPD) continues to rise. It is widely believed that reactive oxygen species (ROS) play an important role in ageing and in age-related disease, and approaches of antioxidant supplementation have been touted as useful strategies to mitigate age-related disease progression, although success of such strategies has been very limited to date. Involvement of ROS in ageing is largely attributed to mitochondrial dysfunction and impaired adaptive antioxidant responses. NADPH oxidase (NOX) enzymes represent an important enzyme family that generates ROS in a regulated fashion for purposes of oxidative host defense and redox-based signalling, however, the associations of NOX enzymes with lung ageing or age-related lung disease have to date only been minimally addressed. The present review will focus on our current understanding of the impact of ageing on NOX biology and its consequences for age-related lung disease, particularly COPD, and will also discuss the implications of altered NOX biology for current and future antioxidant-based strategies aimed at treating these diseases.

Recent Advances in Detection, Isolation, and Imaging Techniques for Sulfane Sulfur-Containing Biomolecules

Hydrogen sulfide and its oxidation products are involved in many biological processes, and sulfane sulfur compounds, which contain sulfur atoms bonded to other sulfur atom(s), as found in hydropersulfides (R-S-SH), polysulfides (R-S-Sn-S-R), hydrogen polysulfides (H2Sn), etc., have attracted increasing interest. To characterize their physiological and pathophysiological roles, selective detection techniques are required. Classically, sulfane sulfur compounds can be detected by cyanolysis, involving nucleophilic attack by cyanide ion to cleave the sulfur-sulfur bonds. The generated thiocyanate reacts with ferric ion, and the resulting ferric thiocyanate complex can be easily detected by absorption spectroscopy. Recent exploration of the properties of sulfane sulfur compounds as both nucleophiles and electrophiles has led to the development of various chemical techniques for detection, isolation, and bioimaging of sulfane sulfur compounds in biological samples. These include tag-switch techniques, LC-MS/MS, Raman spectroscopy, and fluorescent probes. Herein, we present an overview of the techniques available for specific detection of sulfane sulfur species in biological contexts.

Upregulation of leukocyte immunoglobulin-like receptor B4 on interstitial macrophages in COPD; their possible protective role against emphysema formation

Background

Leukocyte immunoglobulin-like receptor B4 (LILRB4) is one of the inhibitory receptors in various types of immune cells including macrophages. Previous reports suggested that LILRB4 could be involved in a negative feedback system to prevent excessive inflammatory responses. However, its role has been unclear in chronic obstructive pulmonary disease (COPD), in which macrophages play a crucial role in the pathogenesis. In this study, we aimed to examine the changes of LILRB4 on macrophages both in the lung specimens of COPD patients and the lungs of a mouse emphysema model. We then tried to compare the differences in both inflammation and emphysematous changes of the model between wild-type and LILRB4-deficient mice in order to elucidate the role of LILRB4 in the pathogenesis of COPD.

Methods

We prepared single-cell suspensions of resected lung specimens of never-smokers (n = 21), non-COPD smokers (n = 16), and COPD patients (n = 14). The identification of LILRB4-expressing cells and the level of LILRB4 expression were evaluated by flow cytometry. We analyzed the relationships between the LILRB4 expression and clinical characteristics including respiratory function. In the experiments using an elastase-induced mouse model of emphysema, we also analyzed the LILRB4 expression on lung macrophages. We compared inflammatory cell accumulation and emphysematous changes induced by elastase instillation between wild-type and LILRB4-deficient mice.

Results

The levels of surface expression of LILRB4 are relatively high on monocyte linage cells including macrophages in the human lungs. The percentage of LILRB4⁺ cells in lung interstitial macrophages was increased in COPD patients compared to non-COPD smokers (p = 0.018) and correlated with the severity of emphysematous lesions detected by CT scan (r_s = 0.559, p < 0.001), whereas the amount of smoking showed no correlation with LILRB4 expression. Increased LILRB4 on interstitial macrophages was also observed in elastase-treated mice (p = 0.008). LILRB4-deficient mice showed severer emphysematous lesions with increased MMP-12 expression in the model.

Conclusions

LILRB4 on interstitial macrophages was upregulated both in human COPD lungs and in a mouse model of emphysema. This upregulated LILRB4 may have a protective effect against emphysema formation, possibly through decreasing MMP-12 expression in the lungs.

High-Precision Sulfur Metabolomics Innovated by a New Specific Probe for Trapping Reactive Sulfur Species

Aims: Persulfides and other reactive sulfur species are endogenously produced in large amounts in vivo and participate in multiple cellular functions underlying physiological and pathological conditions. In the current study, we aimed to develop an ideal alkylating agent for use in sulfur metabolomics, particularly targeting persulfides and other reactive sulfur species, with minimal artifactual decomposition. Results: We synthesized a tyrosine-based iodoacetamide derivative, N-iodoacetyl l-tyrosine methyl ester (TME-IAM), which reacts with the thiol residue of cysteine identically to that of β-(4-hydroxyphenyl)ethyl iodoacetamide (HPE-IAM), a commercially available reagent. Our previous study revealed that although various electrophilic alkylating agents readily decomposed polysulfides, HPE-IAM exceptionally stabilized the polysulfides by inhibiting their alkaline hydrolysis. The newly synthesized TME-IAM stabilizes oxidized glutathione tetrasulfide more efficiently than other alkylating agents, including HPE-IAM, iodoacetamide, and monobromobimane. In fact, our quantitative sulfur-related metabolome analysis showed that TME-IAM is a more efficient trapping agent for endogenous persulfides/polysulfides containing a larger number of sulfur atoms in mouse liver and brain tissues compared with HPE-IAM. Innovation and Conclusions: We developed a novel iodoacetamide derivative, which is the most ideal reagent developed to date for detecting endogenous persulfides/polysulfides formed in biological samples, such as cultured cells, tissues, and plasma. This new probe may be useful for investigating the unique chemical properties of reactive persulfides, thereby enabling identification of novel reactive sulfur metabolites that remain unidentified because of their instability, and thus can be applied in high-precision sulfur metabolomics in redox biology and medicine. We did not perform any clinical experiments in this study. Antioxid. Redox Signal. 34, 1407-1419.

Extracellular vesicles: Their emerging roles in the pathogenesis of respiratory diseases

Alveoli are the basic structure of the lungs, consisting of various types of parenchymal and bone marrow-derived cells including alveolar macrophages. These various types of cells have several important functions; thus, communication between these cells plays an important role in homeostasis as well as in the pathophysiology of diseases in the lungs. For a better understanding of the pathophysiology of lung diseases, researchers have isolated each type of lung cell to investigate the changes in their gene expressions, including their humoral factor or adhesion molecules, to reveal the intercellular communication among these cells. In particular, investigations during the past decade have focused on extracellular vesicles, which are lipid bilayer delimited vesicles released from a cell that can move among various cells and transfer substances, including microRNAs, mRNAs and proteins, thus, functioning as intercellular messengers. Extracellular vesicles can be classified into three general groups: apoptotic bodies, exosomes, and microparticles. Extracellular vesicles, especially exosomes and microparticles, are attracting increasing attention from pulmonologists as tools for understanding pathogenesis and disease diagnosis. Here, we review studies, including our own, on exosomes and microparticles and their roles in both lung homeostasis and the pathogenesis of lung diseases such as idiopathic pulmonary fibrosis, chronic obstructive lung diseases, and acute respiratory distress syndrome. This review also addresses the roles of extracellular vesicles in COVID-19, the current global public health crisis.

Hydrogen sulfide as a novel biomarker of asthma and chronic obstructive pulmonary disease

Hydrogen sulfide (H₂S) has recently been recognised as the third important gas-signalling molecule, besides nitric oxide and carbon monoxide. H₂S has been reported to be produced by many cell types in mammalian tissues and organs throughout the actions of H₂S-generating enzymes or redox reactions between the oxidation of glucose and element of sulfur. Although the pathological role of H₂S has not yet been fully elucidated, accumulative data suggest that H₂S may have biphasic effects. Briefly, it mainly has anti-inflammatory and antioxidant roles, although it can also have pro-inflammatory effects under certain conditions where rapid release of H₂S in tissues occur, such as sepsis. To date, there have been several clinical studies published on H₂S in respiratory disorders, including asthma and chronic obstructive pulmonary disease (COPD). According to previous studies, H₂S is detectable in serum, sputum, and exhaled breath, although a gold standard method for detection has not yet been established. In asthma and COPD, H₂S levels in serum and sputum can vary depending on the underlying conditions such as an acute exacerbation. Furthermore, sputum H₂S in particular correlates with sputum neutrophils and the degree of airflow limitation, indicating that H₂S has potential as a novel promising biomarker for neutrophilic airway inflammation for predicting current control state as well as future risks of asthma. In the future, concurrent measures of H₂S with conventional inflammatory biomarkers (fractional exhaled nitric oxide, eosinophils etc) may provide more useful information regarding the identification of inflammatory phenotypes of asthma and COPD for personalised treatment.

NOX4-Derived ROS Promotes Collagen I Deposition in Bronchial Smooth Muscle Cells by Activating Noncanonical p38MAPK/Akt-Mediated TGF-β Signaling

Background

Airway smooth muscle (ASM) remodeling is a hallmark in chronic obstructive pulmonary disease (COPD). NADPH oxidase 4- (NOX4-) mediated reactive oxygen species (ROS) production plays a crucial role in cell differentiation and extracellular matrix (ECM) synthesis in ASM remodeling. However, the precise mechanisms underpinning its pathogenic roles remain elusive.

Methods

The expression of NOX4 and TGF-β₁ in the airway of the lung was measured in COPD patients and the control group. Cigarette smoke- (CS-) induced emphysema mice were generated, and the alteration of α-SMA, NOX4, TGF-β₁, and collagen I was accessed. The changes of the expression of ECM markers, NOX4, components of TGF-β/Smad, and MAPK/Akt signaling in human bronchial smooth muscle cells (HBSMCs) were ascertained for delineating mechanisms of NOX4-mediated ROS production on cell differentiation and remodeling in human ASM cells.

Results

An increased abundance of NOX4 and TGF-β₁ proteins in the epithelial cells and ASM of lung was observed in COPD patients compared with the control group. Additionally, an increased abundance expression of NOX4 and α-SMA was observed in the lungs of the CS-induced emphysema mouse model. TGF-β₁ displayed abilities to increase the oxidative burden and collagen I production, along with enhanced phosphorylation of ERK, p38MAPK, and p-Akt473 in HBSMCs. These effects of TGF-β₁ could be inhibited by the ROS scavenger N-acetylcysteine (NAC), siRNA-mediated knockdown of Smad3 and NOX4, and pharmacological inhibitors SB203580 (p38MAPK inhibitor) and LY294002 (Akt inhibitor).

Conclusions

NOX4-mediated ROS production alters TGF-β₁-induced cell differentiation and collagen I protein synthesis in HBSMCs in part through the p38MAPK/Akt signaling pathway in a Smad-dependent manner.

Redox Regulation, Oxidative Stress, and Inflammation in Group 3 Pulmonary Hypertension

Group 3 pulmonary hypertension (PH), which occurs secondary to hypoxia lung diseases, is one of the most common causes of PH worldwide and has a high unmet clinical need. A deeper understanding of the integrative pathological and adaptive molecular mechanisms within this group is required to inform the development of novel drug targets and effective treatments. The production of oxidants is increased in PH Group 3, and their pleiotropic roles include contributing to disease progression by promoting prolonged hypoxic pulmonary vasoconstriction and pathological pulmonary vascular remodeling, but also stimulating adaptation to pathological stress that limits the severity of this disease. Inflammation, which is increasingly being viewed as a key pathological feature of Group 3 PH, is subject to complex regulation by redox mechanisms and is exacerbated by, but also augments oxidative stress. In this review, we investigate aspects of this complex crosstalk between inflammation and oxidative stress in Group 3 PH, focusing on the redox-regulated transcription factor NF-κB and its upstream regulators toll-like receptor 4 and high mobility group box protein 1. Ultimately, we propose that the development of specific therapeutic interventions targeting redox-regulated signaling pathways related to inflammation could be explored as novel treatments for Group 3 PH.

Glutathione Trisulfide Prevents Lipopolysaccharide-induced Inflammatory Gene Expression in Retinal Pigment Epithelial Cells

We investigated the effects of glutathione trisulfide (GSSSG) on lipopolysaccharide (LPS)-induced inflammatory gene expression in immortalized ARPE-19, and primary human and mouse retinal pigment epithelial (RPE) cells. Sulfane sulfur molecules were significantly increased in GSSSG-treated ARPE-19 cells. GSSSG prevented the LPS-induced upregulation of interleukin (IL)-1β, IL-6, and C-C motif chemokine ligand 2 (CCL2) in ARPE-19/primary RPE cells. Moreover, GSSSG prevented the activation of the nuclear factor-kappa B p65 subunit, and promoted the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in LPS-treated ARPE-19 cells. ERK1/2 inhibition prevented the GSSSG-mediated inhibition of LPS-induced IL-6 and CCL2 upregulation. Additionally, ERK1/2 activation prevented the upregulation of these genes in the absence of GSSSG. Knockdown of HMOX1 or NRF2, known as anti-oxidative genes, did not affect the activity of GSSSG in the context of LPS stimulation. These findings suggest that GSSSG attenuates LPS-induced inflammatory gene expression via ERK signaling hyperactivation, independently of the NRF2/HMOX1 pathway.

S-Persulfidation: Chemistry, Chemical Biology, and Significance in Health and Disease

Significance: S-Persulfidation generates persulfide adducts (RSSH) on both small molecules and proteins. This process is believed to be critical in the regulation of biological functions of reactive sulfur species such as H₂S, as well as in signal transduction. S-Persulfidation also plays regulatory roles in human health and diseases. Recent Advances: Some mechanisms underlying the generation of low-molecular-weight persulfides and protein S-persulfidation in living organisms have been uncovered. Some methods for the specific delivery of persulfides and the detection of persulfides in biological systems have been developed. These advances help to pave the road to better understand the functions of S-persulfidation. Critical Issues: Persulfides are highly reactive and unstable. Currently, their identification relies on trapping them by S-alkylation, but this is not always reliable due to rapid sulfur exchange reactions. Therefore, the presence, identity, and fates of persulfides in biological environments are sometimes difficult to track. Future Directions: Further understanding the fundamental chemistry/biochemistry of persulfides and development of more reliable detection methods are needed. S-Persulfidation in specific protein targets is essential in organismal physiological health and human disease states. Besides cardiovascular and neuronal systems, the roles of persulfidation in other systems need to be further explored. Contradictory results of persulfidation in biology, especially in cancer, need to be clarified.

Enzymatic Regulation and Biological Functions of Reactive Cysteine Persulfides and Polysulfides

Cysteine persulfide (CysSSH) and cysteine polysulfides (CysSS_nH, n > 1) are cysteine derivatives that have sulfane sulfur atoms bound to cysteine thiol. Advances in analytical methods that detect and quantify persulfides and polysulfides have shown that CysSSH and related species such as glutathione persulfide occur physiologically and are prevalent in prokaryotes, eukaryotes, and mammals in vivo. The chemical properties and abundance of these compounds suggest a central role for reactive persulfides in cell-regulatory processes. CysSSH and related species have been suggested to act as powerful antioxidants and cellular protectants and may serve as redox signaling intermediates. It was recently shown that cysteinyl-tRNA synthetase (CARS) is a new cysteine persulfide synthase. In addition, we discovered that CARS is involved in protein polysulfidation that is coupled with translation. Mitochondrial activity in biogenesis and bioenergetics is supported and upregulated by CysSSH derived from mitochondrial CARS. In this review article, we discuss the mechanisms of the biosynthesis of CysSSH and related persulfide species, with a particular focus on the roles of CARS. We also review the antioxidative and anti-inflammatory actions of persulfides.

Antioxidative and anti-inflammatory actions of reactive cysteine persulfides

Cysteine persulfide (CysSSH) and polysulfides (CysS[S]_nH, n>1) are cysteine derivatives having sulfane sulfur atoms bound to cysteine thiol. Recent advances in the development of analytical methods for detection and quantification of persulfides and polysulfides have revealed the biological presence, in both prokaryotes and eukaryotes, of persulfide/polysulfide in diverse forms such as CysSSH, glutathione persulfide and protein persulfides. Accumulating evidence has suggested that persulfide/polysulfide species may involve in a variety of biological events such as biosyntheses of sulfur-containing molecules, tRNA modification, regulation of redox-dependent signal transduction, mitochondrial energy metabolism via sulfur respiration, cytoprotection from oxidative stress via their antioxidant activities, and anti-inflammation against Toll-like receptor-mediated inflammatory responses. Development of chemical sulfur donors may facilitate further understanding of physiological and pathophysiological roles of persulfide/polysulfide species, including regulatory roles of these species in immune responses.

Oxidation of PKGIα mediates an endogenous adaptation to pulmonary hypertension

Chronic hypoxia causes pulmonary hypertension (PH), vascular remodeling, right ventricular (RV) hypertrophy, and cardiac failure. Protein kinase G Iα (PKGIα) is susceptible to oxidation, forming an interprotein disulfide homodimer associated with kinase targeting involved in vasodilation. Here we report increased disulfide PKGIα in pulmonary arteries from mice with hypoxic PH or lungs from patients with pulmonary arterial hypertension. This oxidation is likely caused by oxidants derived from NADPH oxidase-4, superoxide dismutase 3, and cystathionine γ-lyase, enzymes that were concomitantly increased in these samples. Indeed, products that may arise from these enzymes, including hydrogen peroxide, glutathione disulfide, and protein-bound persulfides, were increased in the plasma of hypoxic mice. Furthermore, low-molecular-weight hydropersulfides, which can serve as "superreductants" were attenuated in hypoxic tissues, consistent with systemic oxidative stress and the oxidation of PKGIα observed. Inhibiting cystathionine γ-lyase resulted in decreased hypoxia-induced disulfide PKGIα and more severe PH phenotype in wild-type mice, but not in Cys42Ser PKGIα knock-in (KI) mice that are resistant to oxidation. In addition, KI mice also developed potentiated PH during hypoxia alone. Thus, oxidation of PKGIα is an adaptive mechanism that limits PH, a concept further supported by polysulfide treatment abrogating hypoxia-induced RV hypertrophy in wild-type, but not in the KI, mice. Unbiased transcriptomic analysis of hypoxic lungs before structural remodeling identified up-regulation of endothelial-to-mesenchymal transition pathways in the KI compared with wild-type mice. Thus, disulfide PKGIα is an intrinsic adaptive mechanism that attenuates PH progression not only by promoting vasodilation but also by limiting maladaptive growth and fibrosis signaling.

Nitrosative stress in patients with asthma-chronic obstructive pulmonary disease overlap

BACKGROUND

Asthma-chronic obstructive pulmonary disease overlap (ACO) has frequent exacerbations and a poor quality of life and prognosis compared with those of chronic obstructive pulmonary disease alone. However, the pathogenesis of ACO has not been fully elucidated yet.

OBJECTIVES

The aim of this study was to investigate nitrosative stress, which causes a redox imbalance and tissue inflammation in the airways of patients with ACO, and to evaluate the relationship between nitrosative stress and the clinical course in study subjects.

METHODS

Thirty healthy subjects and 56 asthmatic patients participated in this study. The asthmatic patients were divided into 33 asthmatic patients and 23 patients with ACO. The study subjects had been followed prospectively for 2 years to evaluate the clinical course. Nitrosative stress was evaluated based on the production of 3-nitrotyrosine (3-NT) in sputum cells.

RESULTS

Production of 3-NT was significantly enhanced in patients with ACO compared with that in asthmatic patients. Amounts of reactive persulfides and polysulfides, newly identified powerful antioxidants, were significantly decreased in the ACO group. Baseline levels of 3-NT were significantly correlated with the frequency of exacerbations and decrease in FEV₁ adjusted by age, smoking history, and blood eosinophil count. The 3-NT-positive cells were also significantly correlated with amounts of proinflammatory chemokines and cytokines.

CONCLUSIONS

These findings suggested that greater nitrosative stress occurred in the airways of patients with ACO, and the degree of nitrosative stress was correlated with an impairment in the clinical course. Nitrosative stress might be related to the pathogenesis of ACO.

Polysulfide stabilization by tyrosine and hydroxyphenyl-containing derivatives that is important for a reactive sulfur metabolomics analysis

The physiological importance of reactive sulfur species (RSS) such as cysteine hydropersulfide (CysSSH) has been increasingly recognized in recent years. We have established a reactive sulfur metabolomics analysis by using RSS metabolic profiling, which revealed appreciable amounts of RSS generated endogenously and ubiquitously in both prokaryotic and eukaryotic organisms. The chemical nature of these polysulfides is not fully understood, however, because of their reactive or complicated redox-active properties. In our study here, we determined that tyrosine and a hydroxyphenyl-containing derivative, β-(4-hydroxyphenyl)ethyl iodoacetamide (HPE-IAM), had potent stabilizing effects on diverse polysulfide residues formed in CysSSH-related low-molecular-weight species, e.g., glutathione polysulfides (oxidized glutathione trisulfide and oxidized glutathione tetrasulfide). The protective effect against degradation was likely caused by the inhibitory activity of hydroxyphenyl residues of tyrosine and HPE-IAM against alkaline hydrolysis of polysulfides. This hydrolysis occurred via heterolytic scission triggered by the hydroxyl anion acting on polysulfides that are cleaved into thiolates and sulfenic acids, with the hydrolysis being enhanced by alkylating reagents (e.g. IAM) and dimedone. Moreover, tyrosine prevented electrophilic degradation occurring in alkaline pH. The polysulfide stabilization induced by tyrosine or the hydroxyphenyl moiety of HPE-IAM will greatly improve our understanding of the chemical properties of polysulfides and may benefit the sulfur metabolomics analysis if it can be applied successfully to any kind of biological samples, including clinical specimens.

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Polysulfides undergo hydrolysis under alkaline pH conditions.

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Alkylating reagents and dimedone enhance polysulfide decomposition.

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Tyr and hydroxyphenyl derivatives inhibit alkaline-induced polysulfide hydrolysis.

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Tyr protects polysulfides from electrophile- and dimedone-enhanced hydrolysis.

TLR7 agonist attenuates acetylcholine-induced, Ca2+ -dependent ionic currents in swine tracheal submucosal gland cells

NEW FINDINGS

What is the central question of this study? Does Toll-like receptor 7 (TLR7) have any direct effects on Ca²⁺ -dependent physiological function of tracheal submucosal gland cells? What is the main finding and its importance? TLR7 is co-localized with SERCA2 in tracheal submucosal gland cells and causes a rapid attenuation of acetylcholine (ACh)-induced, Ca²⁺ -dependent ionic currents through the activation of SERCA2-dependent Ca²⁺ clearance. TLR7 is abundantly expressed in the airways of both swine and healthy human subjects, but is significantly downregulated in chronic obstructive pulmonary disease (COPD) airways. These findings suggest that a dysfunction of TLR7 in COPD removes the brake on ACh-induced serous secretion during viral infections, resulting in prolonged airway hypersecretion, and that it is one of the triggers of COPD exacerbations.

ABSTRACT

Airway surface fluids are mainly secreted from submucosal glands (SMGs) and play important roles in the defence of airways via the activation of mucociliary transport. Toll-like receptor 7 (TLR7) recognizes and eliminates single stranded RNA (ssRNA) viruses through the induction of innate immunity. However, there is no obvious connection between TLR7 and mucus secretion, aside from TLR7 recognizing ssRNA viruses, which are often associated with airway hypersecretion in chronic obstructive pulmonary disease (COPD). Here, we investigated whether TLR7 has any direct effects on the Ca²⁺ -dependent physiological function of tracheal SMG cells. Patch-clamp analyses revealed that TLR7 ligand inhibited the acetylcholine (ACh)-induced ionic currents in isolated tracheal SMG cells. Intracellular calcium assays and pharmacological analyses revealed that TLR7 attenuated the transient rises in the intracellular calcium concentration evoked by ACh by activating sarco/endoplasmic reticulum Ca²⁺ -ATPase 2 (SERCA2). Immunofluorescence staining and immunohistochemical staining revealed that TLR7 was co-localized with SERCA2. These findings suggest that the activation of TLR7 during viral infections contributes to the rapid attenuation of ACh-induced ionic currents through an increase in SERCA2-dependent Ca²⁺ clearance in healthy airway SMG cells. Our study also revealed that TLR7 expression was significantly downregulated in COPD airways. Based on these findings, we speculate that a dysfunction of TLR7 may not only have an adverse effect on the elimination of these viruses but also remove the brake on ACh-induced serous secretion, resulting in prolonged hypersecretion and acting as one of the triggers of COPD exacerbations.

The reaction of hydrogen sulfide with disulfides: formation of a stable trisulfide and implications for biological systems

BACKGROUND AND PURPOSE

The signalling associated with hydrogen sulfide (H₂ S) remains to be established, and recent studies have alluded to the possibility that H₂ S-derived species play important roles. Of particular interest are hydropersulfides (RSSH) and related polysulfides (RSS_n R, n > 1). This work elucidates the fundamental chemical relationship between these sulfur species as well as examines their biological effects.

EXPERIMENTAL APPROACH

Using standard analytical techniques (¹ H-NMR and MS), the equilibrium reactions between H₂ S, disulfides (RSSR), RSSH, dialkyltrisulfides (RSSSR) and thiols (RSH) were examined. Their ability to protect cells from electrophilic and/or oxidative stress was also examined using cell culture.

KEY RESULTS

H₂ S, RSSR, RSSH, RSSSR and RSH are all in a dynamic equilibrium. In a biological system, these species can exist simultaneously, and thus, it is difficult to discern which species is (are) the biological effector(s). Treatment of cells with the dialkyl trisulfide cysteine trisulfide (Cys-SSS-Cys) resulted in high intracellular levels of hydropersulfides and protection from electrophilic stress.

CONCLUSIONS AND IMPLICATIONS

In aqueous systems, the reaction between H₂ S and RSSR results in the formation of equilibria whereby H₂ S, RSH, RSSR, RSSH and RSSSR are present. In a biological system, any of these species can be responsible for the observed biological activity. These equilibrium species can also be generated via the reaction of RSH with RSSSR. Due to these equilibria, Cys-SSS-Cys can be a method for generating any of the other species. Importantly, HEK293T cells treated with Cys-SSS-Cys results in increased levels of hydropersulfides, allowing examination of the biological effects of RSSH.

LINKED ARTICLES

This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc.

Systemic concentrations of asymmetric dimethylarginine (ADMA) in chronic obstructive pulmonary disease (COPD): state of the art

Experimental evidence suggests that oxidative stress (OS) may increase the activity of arginine methylating enzymes that produce the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA). In addition, it is well documented that OS can significantly decrease the synthesis and/or activity of ADMA degrading enzymes, thus causing ADMA accumulation in biological fluids. Recent reports have focused on circulating methylated arginine concentrations in chronic obstructive pulmonary disease, a disease characterized by a significant increase in OS. This review discusses the results of these studies and the opportunities for further research in this area.

Persulfide synthases that are functionally coupled with translation mediate sulfur respiration in mammalian cells

Cysteine persulfide and polysulfide are produced in cells and exist in abundance in both low MW and protein fractions. However, the mechanism of regulation of the formation of cellular cysteine polysulfides and the physiological functions of cysteine persulfides/polysulfides produced in cells are not fully understood. We recently demonstrated that cysteinyl-tRNA synthetase (CARS) is a novel cysteine persulfide synthase. CARS is involved in protein polysulfidation that is coupled with translation. In particular, mitochondria function in biogenesis and bioenergetics is also supported and up-regulated by cysteine persulfide derived from mitochondrial CARS (also known as CARS2). Here, we provide an overview of recent advances in reactive persulfide research and our understanding of the mechanisms underlying the formation and the physiological roles of reactive persufides, with a primary focus on the formation of cysteine persulfide by CARS and the most fundamental mitochondrial bioenergetics mediated by persulfides, that is, sulfur respiration. LINKED ARTICLES: This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc.

Oxidative stress enhances the expression of IL-33 in human airway epithelial cells

BACKGROUND

Interleukin-33 (IL-33) is a cytokine belonging to the IL-1 family, and its possible involvement in the pathophysiology of COPD and viral-induced exacerbations has been demonstrated. IL-33 has been shown to be increased in the airway epithelial cells from COPD patients, but the regulating mechanism of IL-33 expression in airway epithelial cells remains largely unknown. In the current study, we examined whether oxidative stress, which participates in the pathogenesis of COPD, affects the expression of IL-33 in airway epithelial cells and also evaluated the effect during viral infection.

METHODS

The involvement of oxidative stress in the expression of IL-33, and its signal pathway was examined after stimulation with hydrogen peroxide (H2O2), with or without stimulation by polyinosinic-polycytidylic acid [poly (I:C)], a synthetic analogue of dsRNA that mimics viral infection, or rhinovirus infection in NCI-H292 cells and primary human bronchial epithelial cells (HBECs). In addition, the effect of antioxidant, N-acetylcysteine (NAC) in the expression of IL-33 was compared between HBECs from healthy subjects and those from COPD patients.

RESULTS

Treatment with H2O2 significantly potentiated IL-33 expression in NCI-H292 cells, and the potentiation was reversed by NAC treatment. Mitogen-activated protein kinase (MAPK) inhibitors, but not nuclear factor-kappa B inhibitors, also significantly decreased the H2O2-potentiated IL-33 expression. In addition, H2O2 significantly potentiated the poly (I:C)- or rhinovirus-stimulated IL-33 expression. In HBECs from healthy subjects, H2O2-potentiated IL-33 expression and its reversal by NAC was also confirmed. Under the condition without H2O2-stimulation, treatment with NAC significantly decreased the expression of IL-33 in HBECs from COPD patients, but not in those from healthy subjects.

CONCLUSIONS

These results demonstrate that oxidative stress involves in the expression of IL-33 in airway epithelial cells via MAPK signal pathway and it augments IL-33 expression during viral infection. This mechanism may participate in the regulation of IL-33 expression in airway epithelial cells in COPD and the viral-induced exacerbations. Modulation of this pathway could become a therapeutic target for viral-induced exacerbations of COPD.

Role of Transient Receptor Potential Ankyrin 1 Ion Channel and Somatostatin sst4 Receptor in the Antinociceptive and Anti-inflammatory Effects of Sodium Polysulfide and Dimethyl Trisulfide

Transient receptor potential ankyrin 1 (TRPA1) non-selective ligand-gated cation channels are mostly expressed in primary sensory neurons. Polysulfides (POLYs) are Janus-faced substances interacting with numerous target proteins and associated with both protective and detrimental processes. Activation of TRPA1 in sensory neurons, consequent somatostatin (SOM) liberation and action on sst4 receptors have recently emerged as mediators of the antinociceptive effect of organic trisulfide dimethyl trisulfide (DMTS). In the frame of the present study, we set out to compare the participation of this mechanism in antinociceptive and anti-inflammatory effects of inorganic sodium POLY and DMTS in carrageenan-evoked hind-paw inflammation. Inflammation of murine hind paws was induced by intraplantar injection of carrageenan (3% in 30 µL saline). Animals were treated intraperitoneally with POLY (17 µmol/kg) or DMTS (250 µmol/kg) or their respective vehicles 30 min prior paw challenge and six times afterward every 60 min. Mechanical pain threshold and swelling of the paws were measured by dynamic plantar aesthesiometry and plethysmometry at 2, 4, and 6 h after initiation of inflammation. Myeloperoxidase (MPO) activity in the hind paws were detected 6 h after challenge by luminescent imaging. Mice genetically lacking TRPA1 ion channels, sst4 receptors and their wild-type counterparts were used to examine the participation of these proteins in POLY and DMTS effects. POLY counteracted carrageenan-evoked mechanical hyperalgesia in a TRPA1 and sst4 receptor-dependent manner. POLY did not influence paw swelling and MPO activity. DMTS ameliorated all examined inflammatory parameters. Mitigation of mechanical hyperalgesia and paw swelling by DMTS were mediated through sst4 receptors. These effects were present in TRPA1 knockout animals, too. DMTS inhibited MPO activity with no participation of the sensory neuron-SOM axis. While antinociceptive effects of POLY are transmitted by activation of peptidergic nerves via TRPA1, release of SOM and its effect on sst4 receptors, those of DMTS partially rely on SOM release triggered by other routes. SOM is responsible for the inhibition of paw swelling by DMTS, but TRPA1 does not contribute to its release. Modulation of MPO activity by DMTS is independent of TRPA1 and sst4.

Reactive Cysteine Persulphides: Occurrence, Biosynthesis, Antioxidant Activity, Methodologies, and Bacterial Persulphide Signalling

Cysteine hydropersulphide (CysSSH) is a cysteine derivative having one additional sulphur atom bound to a cysteinyl thiol group. Recent advances in the development of analytical methods for detection and quantification of persulphides and polysulphides have revealed the biological presence, in both prokaryotes and eukaryotes, of hydropersulphides in diverse forms such as CysSSH, homocysteine hydropersulphide, glutathione hydropersulphide, bacillithiol hydropersulphide, coenzyme A hydropersulphide, and protein hydropersulphides. Owing to the chemical reactivity of the persulphide moiety, biological systems utilize persulphides as important intermediates in the synthesis of various sulphur-containing biomolecules. Accumulating evidence has revealed another important feature of persulphides: their potent reducing activity, which implies that they are implicated in the regulation of redox signalling and antioxidant functions. In this chapter, we discuss the biological occurrence and possible biosynthetic mechanisms of CysSSH and related persulphides, and we include descriptions of recent advances in the analytical methods that have been used to detect and quantitate persulphide species. We also discuss the antioxidant activity of persulphide species that contributes to protecting cells from reactive oxygen species-associated damage, and we examine the signalling roles of CysSSH in bacteria.

Cysteinyl-tRNA synthetase governs cysteine polysulfidation and mitochondrial bioenergetics

Cysteine hydropersulfide (CysSSH) occurs in abundant quantities in various organisms, yet little is known about its biosynthesis and physiological functions. Extensive persulfide formation is apparent in cysteine-containing proteins in Escherichia coli and mammalian cells and is believed to result from post-translational processes involving hydrogen sulfide-related chemistry. Here we demonstrate effective CysSSH synthesis from the substrate l-cysteine, a reaction catalyzed by prokaryotic and mammalian cysteinyl-tRNA synthetases (CARSs). Targeted disruption of the genes encoding mitochondrial CARSs in mice and human cells shows that CARSs have a crucial role in endogenous CysSSH production and suggests that these enzymes serve as the principal cysteine persulfide synthases in vivo. CARSs also catalyze co-translational cysteine polysulfidation and are involved in the regulation of mitochondrial biogenesis and bioenergetics. Investigating CARS-dependent persulfide production may thus clarify aberrant redox signaling in physiological and pathophysiological conditions, and suggest therapeutic targets based on oxidative stress and mitochondrial dysfunction.

Cysteine hydropersulfides (CysSSH) are believed to have a cellular redox protective role. Here the authors show that these species can be produced from L-cysteine by cysteinyl-tRNA synthetases and that these enzymes are also involved in mitochondrial biogenesis and bioenergetics regulation.

Cysteine perthiosulfenic acid (Cys-SSOH): A novel intermediate in thiol-based redox signaling?

The reversible oxidation of protein cysteine residues (Cys-SH) is a key reaction in cellular redox signaling involving initial formation of sulfenic acids (Cys-SOH), which are commonly detected using selective dimedone-based probes. Here, we report that significant portions of dimedone-tagged proteins are susceptible to cleavage by DTT reflecting the presence of perthiosulfenic acid species (Cys-SSOH) due to similar oxidation of hydropersulfides (Cys-SSH), since Cys-S-dimedone adducts are stable toward DTT. Combined studies using molecular modeling, mass spectrometry, and cell-based experiments indicate that Cys-SSH are readily oxidized to Cys-SSOH, which forms stable adducts with dimedone-based probes. We additionally confirm the presence of Cys-SSH within protein tyrosine kinases such as EGFR, and their apparent oxidation to Cys-SSOH in response NADPH oxidase activation, suggesting that such Cys-SSH oxidation may represent a novel, as yet uncharacterized, event in redox-based signaling.

Exposure to Electrophiles Impairs Reactive Persulfide-Dependent Redox Signaling in Neuronal Cells

Electrophiles such as methylmercury (MeHg) affect cellular functions by covalent modification with endogenous thiols. Reactive persulfide species were recently reported to mediate antioxidant responses and redox signaling because of their strong nucleophilicity. In this study, we used MeHg as an environmental electrophile and found that exposure of cells to the exogenous electrophile elevated intracellular concentrations of the endogenous electrophilic molecule 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), accompanied by depletion of reactive persulfide species and 8-SH-cGMP which is a metabolite of 8-nitro-cGMP. Exposure to MeHg also induced S-guanylation and activation of H-Ras followed by injury to cerebellar granule neurons. The electrophile-induced activation of redox signaling and the consequent cell damage were attenuated by pretreatment with a reactive persulfide species donor. In conclusion, exogenous electrophiles such as MeHg with strong electrophilicity impair the redox signaling regulatory mechanism, particularly of intracellular reactive persulfide species and therefore lead to cellular pathogenesis. Our results suggest that reactive persulfide species may be potential therapeutic targets for attenuating cell injury by electrophiles.