Arsenic alters ATP-dependent Ca²+ signaling in human airway epithelial cell wound response

Assessment of disease burden in the arsenic exposed population of Chapar village of Samastipur district, Bihar, India, and related mitigation initiative

Fast growing arsenic menace is causing serious health hazards in Bihar, India, with an estimated 10 million people at risk. The exposed population is often unaware of the problem, which only amplifies the burden of arsenic health effects. In the present study, we have assessed the current situation of arsenic exposure in Chapar village of Samastipur district, Bihar. The health of the inhabitants was assessed and correlated with (1) arsenic concentrations in the groundwater of individual wells and (2) arsenic concentration found in their hair and urine. Altogether, 113 inhabitants were assessed, and 113 hair, urine and groundwater samples were collected. The health study reveals that the exposure to arsenic has caused serious health hazard amongst the exposed population with pronounced skin manifestations, loss of appetite, anaemia, constipation, diarrhoea, general body weakness, raised blood pressure, breathlessness, diabetes, mental disabilities, diabetes, lumps in the body and few cancer incidences. It was found that 52% of the total collected groundwater samples had arsenic levels higher than the WHO limit of 10 µg/l (with a maximum arsenic concentration of 1212 µg/l) and the reduced arsenite was the predominant form in samples tested for speciation (N = 19). In the case of hair samples, 29% of the samples had arsenic concentrations higher than the permissible limit of 0.2 mg/kg, with a maximum arsenic concentration of 46 µg/l, while in 20% exposed population, there was significant arsenic contamination in urine samples > 50 µg/l. In Chapar village, the probability of carcinogenic-related risk in the exposed population consuming arsenic contaminated water is 100% for children, 99.1% for females and 97.3% for male subjects. The assessment report shared to the government enabled the village population to receive two arsenic filter units. These units are currently operational and catering 250 households providing arsenic-free water through piped water scheme. This study therefore identified a significant solution for this arsenic-exposed population.

Hydrogen peroxide in neutrophil inflammation: Lesson from the zebrafish

The zebrafish has become an excellent model for the study of inflammation and immunity. Its unique advantages for in vivo imaging and gene and drug screening have allowed the visualization of dual oxidase 1 (Duox1)-derived hydrogen peroxide (H₂O₂) tissue gradients and its crosstalk with neutrophil infiltration to inflamed tissue. Thus, it has been shown that H₂O₂ directly recruits neutrophils via the Src-family tyrosine kinase Lyn and indirectly by the activation of several signaling pathways involved in inflammation, such as nuclear factor κB (NF-κB), mitogen activated kinases and the transcription factor AP1. In addition, this model has also unmasked the unexpected ability of H₂O₂ to induce the expression of the gene encoding the key neutrophil chemoattractant CXC chemokine ligand 8 by facilitating the accessibility of transcription factors to its promoter through histone covalent modifications. Finally, zebrafish models of psoriasis have shown that a H₂O₂/NF-κB/Duox1 positive feedback inflammatory loop operates in this chronic inflammatory disorder and that pharmacological inhibition of Duox1, but not of downstream mediators, inhibits inflammation and restores epithelial homeostasis. Therefore, these results have pointed out DUOX1 and H₂O₂ as therapeutic targets for the treatment of skin inflammatory disorders, such as psoriasis.

Cytotoxicity Assessment of Gallium- and Indium-Based Nanoparticles Toward Human Bronchial Epithelial Cells Using an Impedance-Based Real-Time Cell Analyzer

The semiconductor manufacturing sector plans to introduce III/V film structures (eg, gallium arsenide (GaAs), indium arsenide (InAs) onto silicon wafers due to their high electron mobility and low power consumption. Aqueous solutions generated during chemical and mechanical planarization of silicon wafers can contain a mixture of metal oxide nanoparticles (NPs) and soluble indium, gallium, and arsenic. In this work, the cytotoxicity induced by Ga- and In-based NPs (GaAs, InAs, Ga₂O₃, In₂O₃) and soluble III-V salts on human bronchial epithelial cells (16HBE14o-) was evaluated using a cell impedance real-time cell analysis (RTCA) system. The RTCA system provided inhibition data at different concentrations for multiple time points, for example, GaAs (25 mg/L) caused 60% inhibition after 8 hours of exposure and 100% growth inhibition after 24 hours. Direct testing of As(III) and As(V) demonstrated significant cytotoxicity with 50% growth inhibition concentrations after 16-hour exposure (IC₅₀) of 2.4 and 4.5 mg/L, respectively. Cell signaling with rapid rise and decrease in signal was unique to arsenic cytotoxicity, a precursor of strong cytotoxicity over the longer term. In contrast with arsenic, soluble gallium(III) and indium(III) were less toxic. Whereas the oxide NPs caused low cytotoxicity, the arsenide compounds were highly inhibitory (IC₅₀ of GaAs and InAs = 6.2 and 68 mg/L, respectively). Dissolution experiments over 7 days revealed that arsenic was fully leached from GaAs NPs, whereas only 10% of the arsenic was leached out of InAs NPs. These results indicate that the cytotoxicity of GaAs and InAs NPs is largely due to the dissolution of toxic arsenic species.

Mucociliary transport as a link between chronic rhinosinusitis and trace element dysbalance

Chronis rhinosinusitis is considered as a widespread public health issue with a prevalence of 10%. The disease significantly reduces quality of life and increases the risk of cardiovascular diseases as well as certain forms of cancer. Alteration of mucociliary clearance frequently observed in the patients and plays a significant role in disease pathogenesis. Certain studies have demonstrated that patients with chronic rhinosinusitis are characterized by significant reduction of essential trace elements and toxic metal overload. However, the particular mechanisms of the role of trace element dysbalance in chronic rhinosinusitis are unclear. We hypothesize that exposure to toxic trace elements (arsenic, nickel, cadmium) damages ciliary mucosal epithelium thus affecting mucociliary transport. In turn, altered mucociliary transport results in reduced removal of the inhaled metal-containing particles from nasal mucosa leading to their absorption and further aggravation of toxicity. Essential trace elements (zinc, selenium) play a significant role in regulation of mucociliary transport and immunity, thus their deficiency (either dietary or due to antagonism with toxic metals) may be associated with impaired functions and increased toxic metal toxicity. Therefore, a vicious circle involving metal accumulation and toxicity, essential element deficiency, impairment of mucociliary transport and metal particle removal, resulting in further accumulation of metals and aggravation of toxic effects is formed. The present hypothesis is supported by the findings on the impact of trace elements especially zinc and arsenic on mucociliary clearance, the role of mucociliary transport in heavy metal particles elimination from the airways, trace element dysbalance in chronic rhinosinusitis, as well as toxic and essential metal antagonism. The data from hypothesis testing and its verification may be used for development of therapeutic approach for management of chronic rhinosinusitis. Particularly, the use of essential elements (zinc, selenium) may reduce toxic metal toxicity thus destroying the vicious circle of heavy metal exposure, toxicity, alteration of mucociliary clearance, and aggravation of chronic rhinosinusitis. Essential element supplementation may be considered as a tool for management of chronic refractory rhinosinusitis. In addition, analysis of essential and toxic trace element status may provide an additional diagnostic approach to risk assessment of chronic rhinosinusitis in highly polluted environments.

State of the science review of the health effects of inorganic arsenic: Perspectives for future research

Human exposure to inorganic arsenic (iAs) is a global health issue. Although there is strong evidence for iAs-induced toxicity at higher levels of exposure, many epidemiological studies evaluating its effects at low exposure levels have reported mixed results. We comprehensively reviewed the literature and evaluated the scientific knowledge on human exposure to arsenic, mechanisms of action, systemic and carcinogenic effects, risk characterization, and regulatory guidelines. We identified areas where additional research is needed. These priority areas include: (1) further development of animal models of iAs carcinogenicity to identify molecular events involved in iAs carcinogenicity; (2) characterization of underlying mechanisms of iAs toxicity; (3) assessment of gender-specific susceptibilities and other factors that modulate arsenic metabolism; (4) sufficiently powered epidemiological studies to ascertain relationship between iAs exposure and reproductive/developmental effects; (5) evaluation of genetic/epigenetic determinants of iAs effects in children; and (6) epidemiological studies of people chronically exposed to low iAs concentrations.

Cerium dioxide (CeO2) nanoparticles decrease arsenite (As(III)) cytotoxicity to 16HBE14o- human bronchial epithelial cells

The production and application of engineered nanoparticles (NPs) are increasing in demand with the rapid development of nanotechnology. However, there are concerns that some of these novel materials could lead to emerging environmental and health problems. Some NPs are able to facilitate the transport of contaminants into cells/organisms via a "Trojan Horse" effect which enhances the toxicity of the adsorbed materials. In this work, we evaluated the toxicity of arsenite (As(III)) adsorbed onto cerium dioxide (CeO2) NPs to human bronchial epithelial cells (16HBE14o-) using the xCELLigence real time cell analyzing system (RTCA). Application of 0.5 mg/L As(III) resulted in 81.3% reduction of cell index (CI, an RTCA measure of cell toxicity) over 48 h when compared to control cells exposed to medium lacking As(III). However, when the cells were exposed to 0.5 mg/L As(III) in the presence of CeO2 NPs (250 mg/L), the CI was only reduced by 12.9% compared to the control. The CeO2 NPs had a high capacity for As(III) adsorption (20.2 mg/g CeO2) in the bioassay medium, effectively reducing dissolved As(III) in the aqueous solution and resulting in reduced toxicity. Transmission electron microscopy was used to study the transport of CeO2 NPs into 16HBE14o- cells. NP uptake via engulfment was observed and the internalized NPs accumulated in vesicles. The results demonstrate that dissolved As(III) in the aqueous solution was the decisive factor controlling As(III) toxicity of 16HBE14o- cells, and that CeO2 NPs effectively reduced available As(III) through adsorption. These data emphasize the evaluation of mixtures when assaying toxicity.

In vitro assessment of arsenic mobility in historical mine waste dust using simulated lung fluid

Exposure studies have linked arsenic (As) ingestion with disease in mining-affected populations; however, inhalation of mine waste dust as a pathway for pulmonary toxicity and systemic absorption has received limited attention. A biologically relevant extractant was used to assess the 24-h lung bioaccessibility of As in dust isolated from four distinct types of historical gold mine wastes common to regional Victoria, Australia. Mine waste particles less than 20 µm in size (PM₂₀) were incubated in a simulated lung fluid containing a major surface-active component found in mammalian lungs, dipalmitoylphosphatidylcholine. The supernatants were extracted, and their As contents measured after 1, 2, 4, 8 and 24 h. The resultant As solubility profiles show rapid dissolution followed by a more modest increasing trend, with between 75 and 82% of the total 24-h bioaccessible As released within the first 8 h. These profiles are consistent with the solubility profile of scorodite, a secondary As-bearing phase detected by X-ray diffraction in one of the investigated waste materials. Compared with similar studies, the cumulative As concentrations released at the 24-h time point were extremely low (range 297 ± 6-3983 ± 396 µg L^-1), representing between 0.020 ± 0.002 and 0.036 ± 0.003% of the total As in the PM₂₀.

In vivo and in vitro methods for evaluating soil arsenic bioavailability: relevant to human health risk assessment

Arsenic (As) is the most frequently occurring contaminant on the priority list of hazardous substances, which lists substances of greatest public health concern to people living at or near U.S. National Priorities List site. Accurate assessment of human health risks from exposure to As-contaminated soils depends on estimating its bioavailability, defined as the fraction of ingested As absorbed across the gastrointestinal barrier and available for systemic distribution and metabolism. Arsenic bioavailability varies among soils and is influenced by site-specific soil physical and chemical characteristics and internal biological factors. This review describes the state-of-the science that supports our understanding of oral bioavailability of soil As, the methods that are currently being explored for estimating soil As relative bioavailability (RBA), and future research areas that could improve our prediction of the oral RBA of soil As in humans. The following topics are addressed: (1) As soil geochemistry; (2) As toxicology; (3) in vivo models for estimating As RBA; (4) in vitro bioaccessibility methods; and (5) conclusions and research needs.

Effects of Orally Ingested Arsenic on Respiratory Epithelial Permeability to Bacteria and Small Molecules in Mice

BACKGROUND

Arsenic exposure via drinking water impacts millions of people worldwide. Although arsenic has been associated epidemiologically with increased lung infections, the identity of the lung cell types targeted by peroral arsenic and the associated immune mechanisms remain poorly defined.

OBJECTIVES

We aimed to determine the impact of peroral arsenic on pulmonary antibacterial host defense.

METHODS

Female C57BL/6 mice were administered drinking water with 0, 250 ppb, or 25 ppm sodium arsenite for 5 wk and then challenged intratracheally with Klebsiella pneumoniae, Streptococcus pneumoniae, or lipopolysaccharide. Bacterial clearance and immune responses were profiled.

RESULTS

Arsenic had no effect on bacterial clearance in the lung or on the intrapulmonary innate immune response to bacteria or lipopolysaccharide, as assessed by neutrophil recruitment to, and cytokine induction in, the airspace. Alveolar macrophage TNFα production was unaltered. By contrast, arsenic-exposed mice had significantly reduced plasma TNFα in response to systemic lipopolysaccharide challenge, together suggesting that the local airway innate immune response may be relatively preserved from arsenic intoxication. Despite intact intrapulmonary bacterial clearance during pneumonia, arsenic-exposed mice suffered dramatically increased bacterial dissemination to the bloodstream. Mechanistically, this was linked to increased respiratory epithelial permeability, as revealed by intratracheal FITC-dextran tracking, serum Club Cell protein 16 measurement, and other approaches. Consistent with barrier disruption at the alveolar level, arsenic-exposed mice had evidence for alveolar epithelial type 1 cell injury.

CONCLUSIONS

Peroral arsenic has little effect on local airway immune responses to bacteria but compromises respiratory epithelial barrier integrity, increasing systemic translocation of inhaled pathogens and small molecules. https://doi.org/10.1289/EHP1878.

Plasma membrane wounding and repair in pulmonary diseases

Various pathophysiological conditions such as surfactant dysfunction, mechanical ventilation, inflammation, pathogen products, environmental exposures, and gastric acid aspiration stress lung cells, and the compromise of plasma membranes occurs as a result. The mechanisms necessary for cells to repair plasma membrane defects have been extensively investigated in the last two decades, and some of these key repair mechanisms are also shown to occur following lung cell injury. Because it was theorized that lung wounding and repair are involved in the pathogenesis of acute respiratory distress syndrome (ARDS) and idiopathic pulmonary fibrosis (IPF), in this review, we summarized the experimental evidence of lung cell injury in these two devastating syndromes and discuss relevant genetic, physical, and biological injury mechanisms, as well as mechanisms used by lung cells for cell survival and membrane repair. Finally, we discuss relevant signaling pathways that may be activated by chronic or repeated lung cell injury as an extension of our cell injury and repair focus in this review. We hope that a holistic view of injurious stimuli relevant for ARDS and IPF could lead to updated experimental models. In addition, parallel discussion of membrane repair mechanisms in lung cells and injury-activated signaling pathways would encourage research to bridge gaps in current knowledge. Indeed, deep understanding of lung cell wounding and repair, and discovery of relevant repair moieties for lung cells, should inspire the development of new therapies that are likely preventive and broadly effective for targeting injurious pulmonary diseases.

Engineering an FMN-based iLOV protein for the detection of arsenic ions

Over the past few decades, genetically encoded fluorescent proteins have been widely used as efficient probes to explore and investigate the roles of metal ions in biological processes. The discovery of small FMN-based fluorescent proteins, such as iLOV and FbFP, has enabled researchers to exploit these fluorescent reporter proteins for metal-sensing applications. In this study, we report the inherent binding properties of iLOV towards arsenic ions. The fluorescence quenching of iLOV was linearly related to the concentration of arsenic ions, and engineered proteins showed better sensitivity than the wild-type protein. Engineering key residues around the chromophore converted the iLOV protein into a highly sensitive sensor for As³⁺ ions. iLOV_N468S exhibited an improved binding affinity with a dissociation constant of 1.5 μM. Furthermore, the circular dichroism spectra indicated that the fluorescence quenching mechanism might be related to arsenic-protein complex formation. Thus, the reagentless sensing of arsenic can potentially be exploited to determine intracellular or environmental arsenic using a genetically encoded biosensing approach.

The Epithelial Sodium Channel and the Processes of Wound Healing

The epithelial sodium channel (ENaC) mediates passive sodium transport across the apical membranes of sodium absorbing epithelia, like the distal nephron, the intestine, and the lung airways. Additionally, the channel has been involved in the transduction of mechanical stimuli, such as hydrostatic pressure, membrane stretch, and shear stress from fluid flow. Thus, in vascular endothelium, it participates in the control of the vascular tone via its activity both as a sodium channel and as a shear stress transducer. Rather recently, ENaC has been shown to participate in the processes of wound healing, a role that may also involve its activities as sodium transporter and as mechanotransducer. Its presence as the sole channel mediating sodium transport in many tissues and the diversity of its functions probably underlie the complexity of its regulation. This brief review describes some aspects of ENaC regulation, comments on evidence about ENaC participation in wound healing, and suggests possible regulatory mechanisms involved in this participation.

Airway epithelial cell exposure to distinct e-cigarette liquid flavorings reveals toxicity thresholds and activation of CFTR by the chocolate flavoring 2,5-dimethypyrazine

BACKGROUND

The potential for adverse respiratory effects following exposure to electronic (e-) cigarette liquid (e-liquid) flavorings remains largely unexplored. Given the multitude of flavor permutations on the market, identification of those flavor constituents that negatively impact the respiratory tract is a daunting task. In this study we examined the impact of common e-liquid flavoring chemicals on the airway epithelium, the cellular monolayer that provides the first line of defense against inhaled particulates, pathogens, and toxicants.

METHODS

We used the xCELLigence real-time cell analyzer (RTCA) as a primary high-capacity screening tool to assess cytotoxicity thresholds and physiological effects of common e-liquid flavoring chemicals on immortalized human bronchial epithelial cells (16HBE14o-). The RTCA was used secondarily to assess the capability of 16HBE14o- cells to respond to cellular signaling agonists following a 24 h exposure to select flavoring chemicals. Finally, we conducted biophysical measurements of well-differentiated primary mouse tracheal epithelial (MTE) cells with an Ussing chamber to measure the effects of e-cigarette flavoring constituents on barrier function and ion conductance.

RESULTS

In our high-capacity screens five of the seven flavoring chemicals displayed changes in cellular impedance consistent with cell death at concentrations found in e-liquid. Vanillin and the chocolate flavoring 2,5-dimethylpyrazine caused alterations in cellular physiology indicative of a cellular signaling event. At subcytotoxic levels, 24 h exposure to 2,5-dimethylpyrazine compromised the ability of airway epithelial cells to respond to signaling agonists important in salt and water balance at the airway surface. Biophysical measurements of 2,5-dimethylpyrazine on primary MTE cells revealed alterations in ion conductance consistent with an efflux at the apical airway surface that was accompanied by a transient loss in transepithelial resistance. Mechanistic studies confirmed that the increases in ion conductance evoked by 2,5-dimethylpyrazine were largely attributed to a protein kinase A-dependent (PKA) activation of the cystic fibrosis transmembrane conductance regulator (CFTR) ion channel.

CONCLUSIONS

Data from our high-capacity screening assays demonstrates that individual e-cigarette liquid flavoring chemicals vary in their cytotoxicity profiles and that some constituents evoke a cellular physiological response on their own independent of cell death. The activation of CFTR by 2,5-dimethylpyrazine may have detrimental consequences for airway surface liquid homeostasis in individuals that use e-cigarettes habitually.

Airway epithelial cell exposure to distinct e-cigarette liquid flavorings reveals toxicity thresholds and activation of CFTR by the chocolate flavoring 2,5-dimethypyrazine

Background

The potential for adverse respiratory effects following exposure to electronic (e-) cigarette liquid (e-liquid) flavorings remains largely unexplored. Given the multitude of flavor permutations on the market, identification of those flavor constituents that negatively impact the respiratory tract is a daunting task. In this study we examined the impact of common e-liquid flavoring chemicals on the airway epithelium, the cellular monolayer that provides the first line of defense against inhaled particulates, pathogens, and toxicants.

Methods

We used the xCELLigence real-time cell analyzer (RTCA) as a primary high-capacity screening tool to assess cytotoxicity thresholds and physiological effects of common e-liquid flavoring chemicals on immortalized human bronchial epithelial cells (16HBE14o-). The RTCA was used secondarily to assess the capability of 16HBE14o- cells to respond to cellular signaling agonists following a 24 h exposure to select flavoring chemicals. Finally, we conducted biophysical measurements of well-differentiated primary mouse tracheal epithelial (MTE) cells with an Ussing chamber to measure the effects of e-cigarette flavoring constituents on barrier function and ion conductance.

Results

In our high-capacity screens five of the seven flavoring chemicals displayed changes in cellular impedance consistent with cell death at concentrations found in e-liquid. Vanillin and the chocolate flavoring 2,5-dimethylpyrazine caused alterations in cellular physiology indicative of a cellular signaling event. At subcytotoxic levels, 24 h exposure to 2,5-dimethylpyrazine compromised the ability of airway epithelial cells to respond to signaling agonists important in salt and water balance at the airway surface. Biophysical measurements of 2,5-dimethylpyrazine on primary MTE cells revealed alterations in ion conductance consistent with an efflux at the apical airway surface that was accompanied by a transient loss in transepithelial resistance. Mechanistic studies confirmed that the increases in ion conductance evoked by 2,5-dimethylpyrazine were largely attributed to a protein kinase A-dependent (PKA) activation of the cystic fibrosis transmembrane conductance regulator (CFTR) ion channel.

Conclusions

Data from our high-capacity screening assays demonstrates that individual e-cigarette liquid flavoring chemicals vary in their cytotoxicity profiles and that some constituents evoke a cellular physiological response on their own independent of cell death. The activation of CFTR by 2,5-dimethylpyrazine may have detrimental consequences for airway surface liquid homeostasis in individuals that use e-cigarettes habitually.

Inorganic arsenic and respiratory health, from early life exposure to sex-specific effects: A systematic review

This systematic review synthesizes the diverse body of epidemiologic research accrued on inorganic arsenic exposure and respiratory health effects. Twenty-nine articles were identified that examined the relationship between inorganic arsenic exposure and respiratory outcomes (i.e. lung function, symptoms, acute respiratory infections, chronic non-malignant lung diseases, and non-malignant lung disease mortality). There was strong evidence of a general association between arsenic and non-malignant respiratory illness, including consistent evidence on lung function impairment, acute respiratory tract infections, respiratory symptoms, and non-malignant lung disease mortality. Overall, early life exposure (i.e. in utero and/or early-childhood) had a marked effect throughout the lifespan. This review also identified some research gaps, including limited evidence at lower levels of exposure (water arsenic <100μg/L), mixed evidence of sex differences, and some uncertainty on arsenic and any single non-malignant respiratory disease or pathological process. Common limitations, including potential publication bias; non-comparability of outcome measures across included articles; incomplete exposure histories; and limited confounder control attenuated the cumulative strength of the evidence as it relates to US populations. This systematic review provides a comprehensive assessment of the epidemiologic evidence and should be used to guide future research on arsenic's detrimental effects on respiratory health.

Fast calcium wave inhibits excessive apoptosis during epithelial wound healing

Successful wound closure is mainly the result of two cellular processes: migration and proliferation. Apoptosis has also been suggested to play a role in the mechanisms of wound healing. The fast calcium wave (FCW), triggered immediately after a wound is produced, has been proposed to be involved in determining healing responses in epithelia. We have explored the effects of the reversible inhibition of FCW on the apoptotic and proliferative responses of healing bovine corneal endothelial (BCE) cells in culture. The most important findings of this study are that caspase-dependent apoptosis occurs during the healing process, that the amount of apoptosis has a linear dependence on the migrated distance, and that FCW inhibition greatly increases the apoptotic index. We have further been able to establish that FCW plays a role in the control of cell proliferation during BCE wound healing. These results indicate that one of the main roles of the wave is to inhibit an excessive apoptotic response of the healing migrating cells. This property might represent a basic mechanism to allow sufficient migration and proliferation of the healing cells to assure proper restitution of the injured tissue.

Physiological impact of abnormal lipoxin A₄ production on cystic fibrosis airway epithelium and therapeutic potential

Lipoxin A4 has been described as a major signal for the resolution of inflammation and is abnormally produced in the lungs of patients with cystic fibrosis (CF). In CF, the loss of chloride transport caused by the mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel gene results in dehydration, mucus plugging, and reduction of the airway surface liquid layer (ASL) height which favour chronic lung infection and neutrophil based inflammation leading to progressive lung destruction and early death of people with CF. This review highlights the unique ability of LXA4 to restore airway surface hydration, to stimulate airway epithelial repair, and to antagonise the proinflammatory program of the CF airway, circumventing some of the most difficult aspects of CF pathophysiology. The report points out novel aspects of the cellular mechanism involved in the physiological response to LXA4, including release of ATP from airway epithelial cell via pannexin channel and subsequent activation of and P2Y11 purinoreceptor. Therefore, inadequate endogenous LXA4 biosynthesis reported in CF exacerbates the ion transport abnormality and defective mucociliary clearance, in addition to impairing the resolution of inflammation, thus amplifying the vicious circle of airway dehydration, chronic infection, and inflammation.

Damage response involves mechanisms conserved across plants, animals and fungi

All organisms are constantly exposed to adverse environmental conditions including mechanical damage, which may alter various physiological aspects of growth, development and reproduction. In plant and animal systems, the damage response mechanism has been widely studied. Both systems posses a conserved and sophisticated mechanism that in general is aimed at repairing and preventing future damage, and causes dramatic changes in their transcriptomes, proteomes, and metabolomes. These damage-induced changes are mediated by elaborate signaling networks, which include receptors/sensors, calcium (Ca(2+)) influx, ATP release, kinase cascades, reactive oxygen species (ROS), and oxylipin signaling pathways. In contrast, our current knowledge of how fungi respond to injury is limited, even though various reports indicate that mechanical damage triggers reproductive processes. In fungi, the damage response mechanism has been studied more in depth in Trichoderma atroviride. Interestingly, these studies indicate that the mechanical damage response involves ROS, Ca(2+), kinase cascades, and lipid signaling pathways. Here we compare the response to mechanical damage in plants, animals and fungi and provide evidence that they appear to share signaling molecules and pathways, suggesting evolutionary conservation across the three kingdoms.

Activation of P2RY11 and ATP release by lipoxin A4 restores the airway surface liquid layer and epithelial repair in cystic fibrosis

In cystic fibrosis (CF), the airway surface liquid (ASL) height is reduced as a result of impaired ion transport, which favors bacterial colonization and inflammation of the airway and leads to progressive lung destruction. Lipoxin (LX)A4, which promotes resolution of inflammation, is inadequately produced in the airways of patients with CF. We previously demonstrated that LXA4 stimulates an ASL height increase and epithelial repair. Here we report the molecular mechanisms involved in these processes. We found that LXA4 (1 nM) induced an apical ATP release from non-CF (NuLi-1) and CF (CuFi-1) airway epithelial cell lines and CF primary cultures. The ATP release induced by LXA4 was completely inhibited by antagonists of the ALX/FPR2 receptor and Pannexin-1 channels. LXA4 induced an increase in intracellular cAMP and calcium, which were abolished by the selective inhibition of the P2RY11 purinoreceptor. Pannexin-1 and ATP hydrolysis inhibition and P2RY11 purinoreceptor knockdown all abolished the increase of ASL height induced by LXA4. Inhibition of the A2b adenosine receptor did not affect the ASL height increase induced by LXA4, whereas the PKA inhibitor partially inhibited this response. The stimulation of NuLi-1 and CuFi-1 cell proliferation, migration, and wound repair by LXA4 was inhibited by the antagonists of Pannexin-1 channel and P2RY11 purinoreceptor. Taken together, our results provide evidence for a novel role of LXA4 in stimulating apical ATP secretion via Pannexin-1 channels and P2RY11 purinoreceptors activation leading to an ASL height increase and epithelial repair.

ATP modulates acute inflammation in vivo through dual oxidase 1-derived H2O2 production and NF-κB activation

Dual oxidase 1 (Duox1) is the NADPH oxidase responsible for the H2O2 gradient formed in tissues after injury to trigger the early recruitment of leukocytes. Little is known about the signals that modulate H2O2 release from DUOX1 and whether the H2O2 gradient can orchestrate the inflammatory response in vivo. In this study, we report on a dominant-negative form of zebrafish Duox1 that is able to inhibit endogenous Duox1 activity, H2O2 release and leukocyte recruitment after tissue injury, with none of the side effects associated with morpholino-mediated Duox1 knockdown. Using this specific tool, we found that ATP release following tissue injury activates purinergic P2Y receptors, and modulates Duox1 activity through phospholipase C (PLC) and intracellular calcium signaling in vivo. Furthermore, Duox1-derived H2O2 is able to trigger the NF-κB inflammatory signaling pathway. These data reveal that extracellular ATP acting as an early danger signal is responsible for the activation of Duox1 via a P2YR/PLC/Ca(2+) signaling pathway and the production of H2O2, which, in turn, is able to modulate in vivo not only the early recruitment of leukocytes to the wound but also the inflammatory response through activation of the NF-κB signaling pathway.

Arsenic trioxide inhibits transforming growth factor-β1-induced fibroblast to myofibroblast differentiation in vitro and bleomycin induced lung fibrosis in vivo

Background

Idiopathic pulmonary fibrosis (IPF) is a progressive disease of insidious onset, and is responsible for up to 30,000 deaths per year in the U.S. Excessive production of extracellular matrix by myofibroblasts has been shown to be an important pathological feature in IPF. TGF-β1 is expressed in fibrotic lung and promotes fibroblast to myofibroblast differentiation (FMD) as well as matrix deposition.

Methods

To identify the mechanism of Arsenic trioxide’s (ATO)’s anti-fibrotic effect in vitro, normal human lung fibroblasts (NHLFs) were treated with ATO for 24 hours and were then exposed to TGF-β1 (1 ng/ml) before harvesting at multiple time points. To investigate whether ATO is able to alleviate lung fibrosis in vivo, C57BL/6 mice were administered bleomycin by oropharyngeal aspiration and ATO was injected intraperitoneally daily for 14 days. Quantitative real-time PCR, western blotting, and immunofluorescent staining were used to assess the expression of fibrotic markers such as α-smooth muscle actin (α-SMA) and α-1 type I collagen.

Results

Treatment of NHLFs with ATO at very low concentrations (10-20nM) inhibits TGF-β1-induced α-smooth muscle actin (α-SMA) and α-1 type I collagen mRNA and protein expression. ATO also diminishes the TGF-β1-mediated contractile response in NHLFs. ATO’s down-regulation of profibrotic molecules is associated with inhibition of Akt, as well as Smad2/Smad3 phosphorylation. TGF-β1-induced H₂O₂ and NOX-4 mRNA expression are also blocked by ATO. ATO-mediated reduction in Smad3 phosphorylation correlated with a reduction of promyelocytic leukemia (PML) nuclear bodies and PML protein expression. PML-/- mouse embryonic fibroblasts (MEFs) showed decreased fibronectin and PAI-1 expression in response to TGF-β1. Daily intraperitoneal injection of ATO (1 mg/kg) in C57BL/6 mice inhibits bleomycin induced lung α-1 type I collagen mRNA and protein expression.

Conclusions

In summary, these data indicate that low concentrations of ATO inhibit TGF-β1-induced fibroblast to myofibroblast differentiation and decreases bleomycin induced pulmonary fibrosis.

Extracellular ATP activates MAPK and ROS signaling during injury response in the fungus Trichoderma atroviride

The response to mechanical damage is crucial for the survival of multicellular organisms, enabling their adaptation to hostile environments. Trichoderma atroviride, a filamentous fungus of great importance in the biological control of plant diseases, responds to mechanical damage by activating regenerative processes and asexual reproduction (conidiation). During this response, reactive oxygen species (ROS) are produced by the NADPH oxidase complex. To understand the underlying early signaling events, we evaluated molecules such as extracellular ATP (eATP) and Ca(2+) that are known to trigger wound-induced responses in plants and animals. Concretely, we investigated the activation of mitogen-activated protein kinase (MAPK) pathways by eATP, Ca(2+), and ROS. Indeed, application of exogenous ATP and Ca(2+) triggered conidiation. Furthermore, eATP promoted the Nox1-dependent production of ROS and activated a MAPK pathway. Mutants in the MAPK-encoding genes tmk1 and tmk3 were affected in wound-induced conidiation, and phosphorylation of both Tmk1 and Tmk3 was triggered by eATP. We conclude that in this fungus, eATP acts as a damage-associated molecular pattern (DAMP). Our data indicate the existence of an eATP receptor and suggest that in fungi, eATP triggers pathways that converge to regulate asexual reproduction genes that are required for injury-induced conidiation. By contrast, Ca(2+) is more likely to act as a downstream second messenger. The early steps of mechanical damage response in T. atroviride share conserved elements with those known from plants and animals.

Arsenic compromises conducting airway epithelial barrier properties in primary mouse and immortalized human cell cultures

Arsenic is a lung toxicant that can lead to respiratory illness through inhalation and ingestion, although the most common exposure is through contaminated drinking water. Lung effects reported from arsenic exposure include lung cancer and obstructive lung disease, as well as reductions in lung function and immune response. As part of their role in innate immune function, airway epithelial cells provide a barrier that protects underlying tissue from inhaled particulates, pathogens, and toxicants frequently found in inspired air. We evaluated the effects of a five-day exposure to environmentally relevant levels of arsenic {<4μM [~300 μg/L (ppb)] as NaAsO2} on airway epithelial barrier function and structure. In a primary mouse tracheal epithelial (MTE) cell model we found that both micromolar (3.9 μM) and submicromolar (0.8 μM) arsenic concentrations reduced transepithelial resistance, a measure of barrier function. Immunofluorescent staining of arsenic-treated MTE cells showed altered patterns of localization of the transmembrane tight junction proteins claudin (Cl) Cl-1, Cl-4, Cl-7 and occludin at cell-cell contacts when compared with untreated controls. To better quantify arsenic-induced changes in tight junction transmembrane proteins we conducted arsenic exposure experiments with an immortalized human bronchial epithelial cell line (16HBE14o-). We found that arsenic exposure significantly increased the protein expression of Cl-4 and occludin as well as the mRNA levels of Cl-4 and Cl-7 in these cells. Additionally, arsenic exposure resulted in altered phosphorylation of occludin. In summary, exposure to environmentally relevant levels of arsenic can alter both the function and structure of airway epithelial barrier constituents. These changes likely contribute to the observed arsenic-induced loss in basic innate immune defense and increased infection in the airway.

Arsenic immunotoxicity: a review

Exposure to arsenic (As) is a global public health problem because of its association with various cancers and numerous other pathological effects, and millions of people worldwide are exposed to As on a regular basis. Increasing lines of evidence indicate that As may adversely affect the immune system, but its specific effects on immune function are poorly understood. Therefore, we conducted a literature search of non-cancer immune-related effects associated with As exposure and summarized the known immunotoxicological effects of As in humans, animals and in vitro models. Overall, the data show that chronic exposure to As has the potential to impair vital immune responses which could lead to increased risk of infections and chronic diseases, including various cancers. Although animal and in vitro models provide some insight into potential mechanisms of the As-related immunotoxicity observed in human populations, further investigation, particularly in humans, is needed to better understand the relationship between As exposure and the development of disease.

Chronic arsenic exposure in nanomolar concentrations compromises wound response and intercellular signaling in airway epithelial cells

Paracrine ATP signaling in the lung epithelium participates in a variety of innate immune functions, including mucociliary clearance, bactericide production, and as an initiating signal in wound repair. We evaluated the effects of chronic low-dose arsenic relevant to U.S. drinking water standards (i.e., 10 ppb [130nM]) on airway epithelial cells. Immortalized human bronchial epithelial cells (16HBE14o-) were exposed to 0, 130, or 330nM arsenic (as Na-arsenite) for 4-5 weeks and examined for wound repair efficiency and ATP-mediated Ca(2+) signaling. We found that chronic arsenic exposure at these low doses slows wound repair and reduces ATP-mediated Ca(2+) signaling. We further show that arsenic compromises ATP-mediated Ca(2+) signaling by altering both Ca(2+) release from intracellular stores (via metabotropic P2Y receptors) and Ca(2+) influx mechanisms (via ionotropic P2X receptors). To better model the effects of arsenic on ATP-mediated Ca(2+) signaling under conditions of natural exposure, we cultured tracheal epithelial cells obtained from mice exposed to control or 50 ppb Na-arsenite supplemented drinking water for 4 weeks. Tracheal epithelial cells from arsenic-exposed mice displayed reduced ATP-mediated Ca(2+) signaling dynamics similar to our in vitro chronic exposure. Our findings demonstrate that chronic arsenic exposure at levels that are commonly found in drinking water (i.e., 10-50 ppb) alters cellular mechanisms critical to airway innate immunity.

Purinergic signaling in the airways

Evidence for a significant role and impact of purinergic signaling in normal and diseased airways is now beyond dispute. The present review intends to provide the current state of knowledge of the involvement of purinergic pathways in the upper and lower airways and lungs, thereby differentiating the involvement of different tissues, such as the epithelial lining, immune cells, airway smooth muscle, vasculature, peripheral and central innervation, and neuroendocrine system. In addition to the vast number of well illustrated functions for purinergic signaling in the healthy respiratory tract, increasing data pointing to enhanced levels of ATP and/or adenosine in airway secretions of patients with airway damage and respiratory diseases corroborates the emerging view that purines act as clinically important mediators resulting in either proinflammatory or protective responses. Purinergic signaling has been implicated in lung injury and in the pathogenesis of a wide range of respiratory disorders and diseases, including asthma, chronic obstructive pulmonary disease, inflammation, cystic fibrosis, lung cancer, and pulmonary hypertension. These ostensibly enigmatic actions are based on widely different mechanisms, which are influenced by the cellular microenvironment, but especially the subtypes of purine receptors involved and the activity of distinct members of the ectonucleotidase family, the latter being potential protein targets for therapeutic implementation.

Differential effects of arsenic on calcium signaling in primary keratinocytes and malignant (HSC-1) cells

Arsenic is highly toxic to living cells, especially skin, and skin cancer is induced by drinking water containing arsenic. The molecular mechanisms of arsenic-induced cancer, however, are not well understood. To examine the initial processes in the development of arsenic-induced cancer, we analyzed calcium signaling at an early stage of arsenic treatment of human primary cells and compared the effects with those observed with arsenic treatment in carcinoma-derived cells. We found that arsenic inhibited inositol trisphosphate receptor (IP3R) function in the endoplasmic reticulum by inducing phosphorylation, which led to decreased intracellular calcium levels. Blockade of IP3R phosphorylation by the serine/threonine protein kinase Akt inhibitor wortmannin rescued calcium signaling. In contrast, arsenic treatment of cells derived from a carcinoma (human squamous carcinoma; HSC-1) for 1h had no obvious effect. Taken together, these results suggest that arsenic-induced reduction in calcium signaling is one of the initial mechanisms underlying the malignant transformation in the development of skin cancer.