Identification of early events in nitrogen mustard pulmonary toxicity that are independent of infiltrating inflammatory cells using precision cut lung slices

Nitrogen mustard (NM; mechlorethamine) is a cytotoxic vesicant known to cause acute lung injury which can progress to chronic disease. Due to the complex nature of NM injury, it has been difficult to analyze early responses of resident lung cells that initiate inflammation and disease progression. To investigate this, we developed a model of acute NM toxicity using murine precision cut lung slices (PCLS), which contain all resident lung cell populations. PCLS were exposed to NM (1-100 μM) for 0.5-3 h and analyzed 1 and 3 d later. NM caused a dose-dependent increase in cytotoxicity and a reduction in metabolic activity, as measured by LDH release and WST-1 activity, respectively. Optimal responses were observed with 50 μM NM after 1 h incubation and these conditions were used in further experiments. Analysis of PCLS bioenergetics using an Agilent Seahorse showed that NM impaired both glycolytic activity and mitochondrial respiration. This was associated with injury to the bronchial epithelium and a reduction in methacholine-induced airway contraction. NM was also found to cause DNA damage in bronchial epithelial cells in PCLS, as measured by expression of γ-H2AX, and to induce oxidative stress, which was evident by a reduction in glutathione levels and upregulation of the antioxidant enzyme catalase. Cleaved caspase-3 was also upregulated in airway smooth muscle cells indicating apoptotic cell death. Characterizing early events in NM toxicity is key in identifying therapeutic targets for the development of efficacious countermeasures.

Role of macrophage bioenergetics in N-acetylcysteine-mediated mitigation of lung injury and oxidative stress induced by nitrogen mustard

Nitrogen mustard (NM) is a toxic vesicant that causes acute injury to the respiratory tract. This is accompanied by an accumulation of activated macrophages in the lung and oxidative stress which have been implicated in tissue injury. In these studies, we analyzed the effects of N-acetylcysteine (NAC), an inhibitor of oxidative stress and inflammation on NM-induced lung injury, macrophage activation and bioenergetics. Treatment of rats with NAC (150 mg/kg, i.p., daily) beginning 30 min after administration of NM (0.125 mg/kg, i.t.) reduced histopathologic alterations in the lung including alveolar interstitial thickening, blood vessel hemorrhage, fibrin deposition, alveolar inflammation, and bronchiolization of alveolar walls within 3 d of exposure; damage to the alveolar-epithelial barrier, measured by bronchoalveolar lavage fluid protein and cells, was also reduced by NAC, along with oxidative stress as measured by heme oxygenase (HO)-1 and Ym-1 expression in the lung. Treatment of rats with NAC attenuated the accumulation of macrophages in the lung expressing proinflammatory genes including Ptgs2, Nos2, Il-6 and Il-12; macrophages expressing inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2 and tumor necrosis factor (TNF)α protein were also reduced in histologic sections. Conversely, NAC had no effect on macrophages expressing the anti-inflammatory proteins arginase-1 or mannose receptor, or on NM-induced increases in matrix metalloproteinase (MMP)-9 or proliferating cell nuclear antigen (PCNA), markers of tissue repair. Following NM exposure, lung macrophage basal and maximal glycolytic activity increased, while basal respiration decreased indicating greater reliance on glycolysis to generate ATP. NAC increased both glycolysis and oxidative phosphorylation. Additionally, in macrophages from both control and NM treated animals, NAC treatment resulted in increased S-nitrosylation of ATP synthase, protecting the enzyme from oxidative damage. Taken together, these data suggest that alterations in NM-induced macrophage activation and bioenergetics contribute to the efficacy of NAC in mitigating lung injury.

Suppression of Lung Oxidative Stress, Inflammation, and Fibrosis following Nitrogen Mustard Exposure by the Selective Farnesoid X Receptor Agonist Obeticholic Acid

Nitrogen mustard (NM) is a cytotoxic vesicant known to cause pulmonary injury that can progress to fibrosis. NM toxicity is associated with an influx of inflammatory macrophages in the lung. Farnesoid X receptor (FXR) is a nuclear receptor involved in bile acid and lipid homeostasis that has anti-inflammatory activity. In these studies, we analyzed the effects of FXR activation on lung injury, oxidative stress, and fibrosis induced by NM. Male Wistar rats were exposed to phosphate-buffered saline (vehicle control) or NM (0.125 mg/kg) by intratracheal Penncentury-MicroSprayer aerosolization; this was followed by treatment with the FXR synthetic agonist, obeticholic acid (OCA, 15 mg/kg), or vehicle control (0.13-0.18 g peanut butter) 2 hours later and then once per day, 5 days per week thereafter for 28 days. NM caused histopathological changes in the lung, including epithelial thickening, alveolar circularization, and pulmonary edema. Picrosirius red staining and lung hydroxyproline content were increased, indicative of fibrosis; foamy lipid-laden macrophages were also identified in the lung. This was associated with aberrations in pulmonary function, including increases in resistance and hysteresis. Following NM exposure, lung expression of HO-1 and iNOS, and the ratio of nitrates/nitrites in bronchoalveolar lavage fluid (BAL), markers of oxidative stress increased, along with BAL levels of inflammatory proteins, fibrinogen, and sRAGE. Administration of OCA attenuated NM-induced histopathology, oxidative stress, inflammation, and altered lung function. These findings demonstrate that FXR plays a role in limiting NM-induced lung injury and chronic disease, suggesting that activating FXR may represent an effective approach to limiting NM-induced toxicity. SIGNIFICANCE STATEMENT: In this study, the role of farnesoid-X-receptor (FXR) in mustard vesicant-induced pulmonary toxicity was analyzed using nitrogen mustard (NM) as a model. This study's findings that administration of obeticholic acid, an FXR agonist, to rats reduces NM-induced pulmonary injury, oxidative stress, and fibrosis provide novel mechanistic insights into vesicant toxicity, which may be useful in the development of efficacious therapeutics.

Direct assessment of nitrative stress in lipid environments: Applications of a designer lipid-based biosensor for peroxynitrite

Lipid membranes and lipid-rich organelles are targets of peroxynitrite (ONOO-), a highly reactive species generated under nitrative stress. We report a membrane-localized phospholipid (DPPC-TC-ONOO-) that allows the detection of ONOO- in diverse lipid environments: biomimetic vesicles, mammalian cell compartments, and within the lung lining. DPPC-TC-ONOO- and POPC self-assemble to membrane vesicles that fluorogenically and selectively respond to ONOO-. DPPC-TC-ONOO-, delivered through lipid nanoparticles, allowed for ONOO- detection in the endoplasmic reticulum upon cytokine-induced nitrative stress in live mammalian cells. It also responded to ONOO- within lung tissue murine models upon acute lung injury. We observed nitrative stress around bronchioles in precision cut lung slices exposed to nitrogen mustard and in pulmonary macrophages following intratracheal bleomycin challenge. Results showed that DPPC-TC-ONOO- functions specifically toward iNOS, a key enzyme modulating nitrative stress, and offers significant advantages over its hydrophilic analog in terms of localization and signal generation.

Skin Models Used to Define Mechanisms of Action of Sulfur Mustard

Sulfur mustard (SM) is a threat to both civilian and military populations. Human skin is highly sensitive to SM, causing delayed erythema, edema, and inflammatory cell infiltration, followed by the appearance of large fluid-filled blisters. Skin wound repair is prolonged following blistering, which can result in impaired barrier function. Key to understanding the action of SM in the skin is the development of animal models that have a pathophysiology comparable to humans such that quantitative assessments of therapeutic drugs efficacy can be assessed. Two animal models, hairless guinea pigs and swine, are preferred to evaluate dermal products because their skin is morphologically similar to human skin. In these animal models, SM induces degradation of epidermal and dermal tissues but does not induce overt blistering, only microblistering. Mechanisms of wound healing are distinct in these animal models. Whereas a guinea pig heals by contraction, swine skin, like humans, heals by re-epithelialization. Mice, rats, and rabbits are also used for SM mechanistic studies. However, healing is also mediated by contraction; moreover, only microblistering is observed. Improvements in animal models are essential for the development of therapeutics to mitigate toxicity resulting from dermal exposure to SM.

Targeting Tumor Necrosis Factor Alpha to Mitigate Lung Injury Induced by Mustard Vesicants and Radiation

Pulmonary injury induced by mustard vesicants and radiation is characterized by DNA damage, oxidative stress, and inflammation. This is associated with increases in levels of inflammatory mediators, including tumor necrosis factor (TNF)α in the lung and upregulation of its receptor TNFR1. Dysregulated production of TNFα and TNFα signaling has been implicated in lung injury, oxidative and nitrosative stress, apoptosis, and necrosis, which contribute to tissue damage, chronic inflammation, airway hyperresponsiveness, and tissue remodeling. These findings suggest that targeting production of TNFα or TNFα activity may represent an efficacious approach to mitigating lung toxicity induced by both mustards and radiation. This review summarizes current knowledge on the role of TNFα in pathologies associated with exposure to mustard vesicants and radiation, with a focus on the therapeutic potential of TNFα-targeting agents in reducing acute injury and chronic disease pathogenesis.

Role of PPARγ in dyslipidemia and altered pulmonary functioning in mice following ozone exposure

Exposure to ozone causes decrements in pulmonary function, a response associated with alterations in lung lipids. Pulmonary lipid homeostasis is dependent on the activity of peroxisome proliferator activated receptor gamma (PPARγ), a nuclear receptor that regulates lipid uptake and catabolism by alveolar macrophages (AMs). Herein, we assessed the role of PPARγ in ozone-induced dyslipidemia and aberrant lung function in mice. Exposure of mice to ozone (0.8 ppm, 3 h) resulted in a significant reduction in lung hysteresivity at 72 h post exposure; this correlated with increases in levels of total phospholipids, specifically cholesteryl esters, ceramides, phosphatidylcholines, phosphorylethanolamines, sphingomyelins, and di- and triacylglycerols in lung lining fluid. This was accompanied by a reduction in relative surfactant protein-B (SP-B) content, consistent with surfactant dysfunction. Administration of the PPARγ agonist, rosiglitazone (5 mg/kg/day, i.p.) reduced total lung lipids, increased relative amounts of SP-B, and normalized pulmonary function in ozone-exposed mice. This was associated with increases in lung macrophage expression of CD36, a scavenger receptor important in lipid uptake and a transcriptional target of PPARγ. These findings highlight the role of alveolar lipids as regulators of surfactant activity and pulmonary function following ozone exposure and suggest that targeting lipid uptake by lung macrophages may be an efficacious approach for treating altered respiratory mechanics.

Single inhalation exposure to polyamide micro and nanoplastic particles impairs vascular dilation without generating pulmonary inflammation in virgin female Sprague Dawley rats

BACKGROUND

Exposure to micro- and nanoplastic particles (MNPs) in humans is being identified in both the indoor and outdoor environment. Detection of these materials in the air has made inhalation exposure to MNPs a major cause for concern. One type of plastic polymer found in indoor and outdoor settings is polyamide, often referred to as nylon. Inhalation of combustion-derived, metallic, and carbonaceous aerosols generate pulmonary inflammation, cardiovascular dysfunction, and systemic inflammation. Additionally, due to the additives present in plastics, MNPs may act as endocrine disruptors. Currently there is limited knowledge on potential health effects caused by polyamide or general MNP inhalation.

OBJECTIVE

The purpose of this study is to assess the toxicological consequences of a single inhalation exposure of female rats to polyamide MNP during estrus by means of aerosolization of MNP.

METHODS

Bulk polyamide powder (i.e., nylon) served as a representative MNP. Polyamide aerosolization was characterized using particle sizers, cascade impactors, and aerosol samplers. Multiple-Path Particle Dosimetry (MPPD) modeling was used to evaluate pulmonary deposition of MNPs. Pulmonary inflammation was assessed by bronchoalveolar lavage (BAL) cell content and H&E-stained tissue sections. Mean arterial pressure (MAP), wire myography of the aorta and uterine artery, and pressure myography of the radial artery was used to assess cardiovascular function. Systemic inflammation and endocrine disruption were quantified by measurement of proinflammatory cytokines and reproductive hormones.

RESULTS

Our aerosolization exposure platform was found to generate particles within the micro- and nano-size ranges (thereby constituting MNPs). Inhaled particles were predicted to deposit in all regions of the lung; no overt pulmonary inflammation was observed. Conversely, increased blood pressure and impaired dilation in the uterine vasculature was noted while aortic vascular reactivity was unaffected. Inhalation of MNPs resulted in systemic inflammation as measured by increased plasma levels of IL-6. Decreased levels of 17β-estradiol were also observed suggesting that MNPs have endocrine disrupting activity.

CONCLUSIONS

These data demonstrate aerosolization of MNPs in our inhalation exposure platform. Inhaled MNP aerosols were found to alter inflammatory, cardiovascular, and endocrine activity. These novel findings will contribute to a better understanding of inhaled plastic particle toxicity.

Resolution of inflammation in xenobiotic-induced mucosal injury and chronic disease

It has been appreciated for decades that exposure to toxicants can induce injury and inflammation leading to multiple pathologies in many organ systems. However, recently the field has begun to recognize that toxicants can cause chronic pathologies and diseases by impairing processes known to promote the resolution of inflammation. This process is comprised of dynamic and active responses including pro-inflammatory mediator catabolism, dampening of downstream signaling, production of pro-resolving mediators, apoptosis, and efferocytosis of inflammatory cells. These pathways promote the return to local tissue homeostasis and prevent chronic inflammation that can lead to disease. The aim of this special issue was to identify and report on the potential hazards of toxicant exposure on the resolution of inflammation responses. Papers included in the issue also provide insights into biological mechanisms by which toxicants perturb these resolution processes and identify potential therapeutic targets.

Menthol flavoring in e-cigarette condensate causes pulmonary dysfunction and cytotoxicity in precision cut lung slices

E-cigarette consumption is under scrutiny by regulatory authorities due to concerns about product toxicity, lack of manufacturing standards, and increasing reports of e-cigarette- or vaping-associated acute lung injury. In vitro studies have demonstrated cytotoxicity, mitochondrial dysfunction, and oxidative stress induced by unflavored e-cigarette aerosols and flavoring additives. However, e-cigarette effects on the complex lung parenchyma remain unclear. Herein, the impact of e-cigarette condensates with or without menthol flavoring on functional, structural, and cellular responses was investigated using mouse precision cut lung slices (PCLS). PCLS were exposed to e-cigarette condensates prepared from aerosolized vehicle, nicotine, nicotine + menthol, and menthol e-fluids at doses from 50 to 500 mM. Doses were normalized to the glycerin content of vehicle. Video-microscopy of PCLS revealed impaired contractile responsiveness of airways to methacholine and dampened ciliary beating following exposure to menthol-containing condensates at concentrations greater than 300 mM. Following 500 mM menthol-containing condensate exposure, epithelial exfoliation in intrabronchial airways was identified in histological sections of PCLS. Measurement of lactate dehydrogenase release, mitochondrial water-soluble-tetrazolium salt-1 conversion, and glutathione content supported earlier findings of nicotine or nicotine + menthol e-cigarette-induced dose-dependent cytotoxicity and oxidative stress responses. Evaluation of PCLS metabolic activity revealed dose-related impairment of mitochondrial oxidative phosphorylation and glycolysis after exposure to menthol-containing condensates. Taken together, these data demonstrate prominent menthol-induced pulmonary toxicity and impairment of essential physiological functions in the lung, which warrants concerns about e-cigarette consumer safety and emphasizes the need for further investigations of molecular mechanisms of toxicity and menthol effects in an experimental model of disease.

Lung injury and oxidative stress induced by inhaled chlorine in mice is associated with proinflammatory activation of macrophages and altered bioenergetics

Chlorine (Cl2) gas is a highly toxic and oxidizing irritant that causes life-threatening lung injuries. Herein, we investigated the impact of Cl2-induced injury and oxidative stress on lung macrophage phenotype and function. Spontaneously breathing male C57BL/6J mice were exposed to air or Cl2 (300 ppm, 25 min) in a whole-body exposure chamber. Bronchoalveolar lavage (BAL) fluid and cells, and lung tissue were collected 24 h later and analyzed for markers of injury, oxidative stress and macrophage activation. Exposure of mice to Cl2 resulted in increases in numbers of BAL cells and levels of IgM, total protein, and fibrinogen, indicating alveolar epithelial barrier dysfunction and inflammation. BAL levels of inflammatory proteins including surfactant protein (SP)-D, soluble receptor for glycation end product (sRAGE) and matrix metalloproteinase (MMP)-9 were also increased. Cl2 inhalation resulted in upregulation of phospho-histone H2A.X, a marker of double-strand DNA breaks in the bronchiolar epithelium and alveolar cells; oxidative stress proteins, heme oxygenase (HO)-1 and catalase were also upregulated. Flow cytometric analysis of BAL cells revealed increases in proinflammatory macrophages following Cl2 exposure, whereas numbers of resident and antiinflammatory macrophages were not altered. This was associated with increases in numbers of macrophages expressing cyclooxygenase (COX)-2 and inducible nitric oxide synthase (iNOS), markers of proinflammatory activation, with no effect on mannose receptor (MR) or Ym-1 expression, markers of antiinflammatory activation. Metabolic analysis of lung cells showed increases in glycolytic activity following Cl2 exposure in line with proinflammatory macrophage activation. Mechanistic understanding of Cl2-induced injury will be useful in the identification of efficacious countermeasures for mitigating morbidity and mortality of this highly toxic gas.

Novel method to assess resident alveolar macrophage efferocytosis of apoptotic neutrophils by flow cytometry

Macrophage efferocytosis of apoptotic neutrophils (PMNs) plays a key role in the resolution of inflammation. In these studies, we describe a novel flow cytometric method to assess efferocytosis of apoptotic PMNs. Resident alveolar macrophages and PMNs were collected from lungs of mice exposed to inhaled ozone (0.8 ppm, 3 h) followed by lipopolysaccharide (3 mg/kg, i.v.) to induce acute lung injury. PMNs were labeled with PKH26 or DilC18(5)-DS (D12730) cell membrane dye and then incubated with resident alveolar macrophages at a ratio of 5:1. After 90 min, macrophage efferocytosis was analyzed by flow cytometry and confirmed by confocal microscopy. Whereas alveolar macrophages incubated with D12730-labeled PMNs could readily be identified as efferocytotic or non-efferocytotic, this was not possible with PKH26 labeled PMNs due to confounding macrophage autofluorescence. Using D12730 labeled PMNs, subsets of resident alveolar macrophages were identified with varying capacities to perform efferocytosis, which may be linked to the activation state of these cells. Future applications of this method will be useful in assessing the role of efferocytosis in the resolution of inflammation in response to toxicant exposure.

Regulation of macrophage activation by S-Nitrosothiols following ozone-induced lung injury

Acute exposure to ozone causes oxidative stress, characterized by increases in nitric oxide (NO) and other reactive nitrogen species in the lung. NO has been shown to modify thiols generating S-nitrosothiols (SNOs); this results in altered protein function. In macrophages this can lead to changes in inflammatory activity which impact the resolution of inflammation. As SNO formation is dependent on the redox state of both the NO donor and the recipient thiol, the local microenvironment plays a key role in its regulation. This dictates not only the chemical feasibility of SNO formation but also mechanisms by which they may form. In these studies, we compared the ability of the SNO donors, ethyl nitrite (ENO), which targets both hydrophobic and hydrophilic thiols, SNO-propanamide (SNOPPM) which targets hydrophobic thiols, and S-nitroso-N-acetylcysteine. (SNAC) which targets hydrophilic thiols. to modify macrophage activation following ozone exposure. Mice were treated with air or ozone (0.8 ppm, 3 h) followed 1 h later by intranasal administration of ENO, SNOPPM or SNAC (1-500 μM) or appropriate controls. Mice were euthanized 48 h later. Each of the SNO donors reduced ozone-induced inflammation and modified the phenotype of macrophages both within the lung lining fluid and the tissue. ENO and SNOPPM were more effective than SNAC. These findings suggest that the hydrophobic SNO thiol pool targeted by SNOPPM and ENO plays a major role in regulating macrophage phenotype following ozone induced injury.

Farnesoid X receptor regulates lung macrophage activation and injury following nitrogen mustard exposure

Nitrogen mustard (NM) is a cytotoxic vesicant known to cause acute lung injury which progresses to fibrosis; this is associated with a sequential accumulation of pro- and anti-inflammatory macrophages in the lung which have been implicated in NM toxicity. Farnesoid X receptor (FXR) is a nuclear receptor involved in regulating lipid homeostasis and inflammation. In these studies, we analyzed the role of FXR in inflammatory macrophage activation, lung injury and oxidative stress following NM exposure. Wild-type (WT) and FXR-/- mice were treated intratracheally with PBS (control) or NM (0.08 mg/kg). Bronchoalveolar lavage fluid (BAL) and lung tissue were collected 3, 14 and 28 d later. NM caused progressive histopathologic alterations in the lung including inflammatory cell infiltration and alveolar wall thickening and increases in protein and cells in BAL; oxidative stress was also noted, as reflected by upregulation of heme oxygenase-1. These changes were more prominent in male FXR-/- mice. Flow cytometric analysis revealed that loss of FXR resulted in increases in proinflammatory macrophages at 3 d post NM; this correlated with upregulation of COX-2 and ARL11, markers of macrophage activation. Markers of anti-inflammatory macrophage activation, CD163 and STAT6, were also upregulated after NM; this response was exacerbated in FXR-/- mice at 14 d post-NM. These findings demonstrate that FXR plays a role in limiting macrophage inflammatory responses important in lung injury and oxidative stress. Maintaining or enhancing FXR function may represent a useful strategy in the development of countermeasures to treat mustard lung toxicity.

Sulfur mustard corneal injury is associated with alterations in the epithelial basement membrane and stromal extracellular matrix

Sulfur mustard (SM; bis(2-chloroethyl) sulfide) is a highly reactive bifunctional alkylating agent synthesized for chemical warfare. The eyes are particularly sensitive to SM where it causes irritation, pain, photophobia, and blepharitis, depending on the dose and duration of exposure. In these studies, we examined the effects of SM vapor on the corneas of New Zealand white male rabbits. Edema and hazing of the cornea, signs of acute injury, were observed within one day of exposure to SM, followed by neovascularization, a sign of chronic or late phase pathology, which persisted for at least 28 days. Significant epithelial-stromal separation ranging from ~8-17% of the epithelial surface was observed. In the stroma, there was a marked increase in CD45+ leukocytes and a decrease of keratocytes, along with areas of disorganization of collagen fibers. SM also disrupted the corneal basement membrane and altered the expression of perlecan, a heparan sulfate proteoglycan, and cellular fibronectin, an extracellular matrix glycoprotein. This was associated with an increase in basement membrane matrix metalloproteinases including ADAM17, which is important in remodeling of the basement membrane during wound healing. Tenascin-C, an extracellular matrix glycoprotein, was also upregulated in the stroma 14-28 d post SM, a finding consistent with its role in organizing structural components of the stroma necessary for corneal transparency. These data demonstrate that SM vapor causes persistent alterations in structural components of the cornea. Further characterization of SM-induced injury in rabbit cornea will be useful for the identification of targets for the development of ocular countermeasures.

Microvesicle-Derived miRNAs Regulate Proinflammatory Macrophage Activation in the Lung Following Ozone Exposure

Ozone is a ubiquitous air pollutant that causes lung damage and altered functioning. Evidence suggests that proinflammatory macrophages contribute to ozone toxicity. Herein, we analyzed the role of extracellular vesicles (EVs) and microRNA (miRNA) cargo in ozone-induced macrophage activation. Exposure of mice to ozone (0.8 ppm, 3 h) resulted in increases in bronchoalveolar lavage fluid EVs, which were comprised predominantly of microvesicles (MVs). NanoFACS analysis revealed that MVs generated following both air and ozone exposure was largely from CD45+ myeloid cells; these MVs were readily taken up by macrophages. Functionally, MVs from ozone, but not air treated mice, upregulated mRNA expression of inflammatory proteins in macrophages including inducible nitric oxide synthase (iNOS), CXCL-1, CXCL-2, and interleukin (IL)-1β. The miRNA profile of MVs in bronchoalveolar lavage fluid (BALF) was altered after ozone exposure; thus, increases in miR-21, miR-145, miR320a, miR-155, let-7b, miR744, miR181, miR-17, miR-92a, and miR-199a-3p were observed, whereas miR-24-3p and miR-20 were reduced. Ingenuity pathway analysis revealed that these miRNAs regulate pathways that promote inflammatory macrophage activation, and predicted that let-7a-5p/let-7b, miR-24-3p, miR-21-5p, miR-17, and miR-181a-5p are key upstream regulators of inflammatory proteins. After ozone exposure, miR-199a-3p, but not precursor miR-199a-3p, was increased in lung macrophages, indicating that it is derived from MV-mediated delivery. Furthermore, lung macrophage mRNA expression of IL-1β was upregulated after administration of MVs containing miR-199a-3p mimic but downregulated by miR-199a-3p inhibitor. Collectively, these data suggest that MVs generated following ozone exposure contribute to proinflammatory macrophage activation via MV-derived miRNAs including miR-199a-3p. These findings identify a novel pathway regulating macrophage inflammatory responses to inhaled ozone.

Nitrogen Mustard Alkylates and Cross-Links p53 in Human Keratinocytes

Cytotoxic blistering agents such as sulfur mustard and nitrogen mustard (HN2) were synthesized for chemical warfare. Toxicity is due to reactive chloroethyl side chains that modify and damage cellular macromolecules including DNA and proteins. In response to DNA damage, cells initiate a DNA damage response directed at the recruitment and activation of repair-related proteins. A central mediator of the DNA damage response is p53, a protein that plays a critical role in regulating DNA repair. We found that HN2 causes cytosolic and nuclear accumulation of p53 in HaCaT keratinocytes; HN2 also induced post-translational modifications on p53 including S15 phosphorylation and K382 acetylation, which enhance p53 stability, promote DNA repair, and mediate cellular metabolic responses to stress. HN2 also cross-linked p53, forming dimers and high-molecular-weight protein complexes in the cells. Cross-linked multimers were also modified by K48-linked ubiquitination indicating that they are targets for proteasome degradation. HN2-induced modifications transiently suppressed the transcriptional activity of p53. Using recombinant human p53, HN2 alkylation was found to be concentration- and redox status-dependent. Dithiothreitol-reduced protein was more efficiently cross-linked indicating that p53 cysteine residues play a key role in protein modification. LC-MS/MS analysis revealed that HN2 directly alkylated p53 at C124, C135, C141, C176, C182, C275, C277, H115, H178, K132, and K139, forming both monoadducts and cross-links. The formation of intermolecular complexes was a consequence of HN2 cross-linked cysteine residues between two molecules of p53. Together, these data demonstrate that p53 is a molecular target for mustard vesicants. Modification of p53 likely mediates cellular responses to HN2 including DNA repair and cell survival contributing to vesicant-induced cytotoxicity.

Regulation of Lung Macrophage Activation and Oxidative Stress Following Ozone Exposure by Farnesoid X Receptor

Inflammatory macrophages are known to contribute to ozone toxicity. Farnesoid X receptor (FXR) is a nuclear receptor involved in regulating bile acid and lipid homeostasis; it also exerts anti-inflammatory activity by suppressing macrophage NF-κB. Herein, we analyzed the role of FXR in regulating macrophage activation in the lung following ozone exposure. Treatment of wild-type (WT) mice with ozone (0.8 ppm, 3 h) resulted in increases in proinflammatory (F4/80+CD11c+CD11b+Ly6CHi) and anti-inflammatory (F4/80+CD11c+CD11b+Ly6CLo) macrophages in the lung. The accumulation of proinflammatory macrophages was increased in FXR-/- mice compared with WT mice; however, anti-inflammatory macrophage activation was blunted as reflected by reduced arginase and mannose receptor expression, a response correlated with decreased Nur77. This was associated with prolonged oxidative stress, as measured by 4-hydroxynonenal-modified proteins in the lung. Loss of FXR was accompanied by protracted increases in lung NF-κB activity and its target, inducible nitric oxide synthase in response to ozone. Levels of Tnf-α, Il-1β, Ccr2, Ccl2, Cx3cr1, and Cx3cl1 were also increased in lungs of FXR-/- relative to WT mice; conversely, genes regulating lipid homeostasis including Lxrα, Apoe, Vldlr, Abcg1, and Abca1 were downregulated, irrespective of ozone exposure. In FXR-/- mice, ozone caused an increase in total lung phospholipids, with no effect on SP-B or SP-D. Dyslipidemia was correlated with blunting of ozone-induced increases in positive end-expiratory pressure-dependent quasi-static pressure volume curves indicating a stiffer lung in FXR-/- mice. These findings identify FXR as a regulator of macrophage activation following ozone exposure suggesting that FXR ligands may be useful in mitigating inflammation and oxidative stress induced by pulmonary irritants.

Characterization of the rabbit conjunctiva: Effects of sulfur mustard

Sulfur mustard (SM; bis (2-chloroethyl) sulfide) is a potent vesicant which causes irritation of the conjunctiva and damage to the cornea. In the present studies, we characterized the ocular effects of SM in New Zealand white rabbits. Within one day of exposure to SM, edema and hazing of the cornea were observed, followed by neovascularization which persisted for at least 28 days. This was associated with upper and lower eyelid edema and conjunctival inflammation. The conjunctiva is composed of a proliferating epithelium largely consisting of stratified columnar epithelial cells overlying a well-defined dermis. Superficial layers of the conjunctival epithelium were found to express keratin 1, a marker of differentiating squamous epithelium, while in cells overlying the basement membrane expressed keratin 17, a marker of stratified squamous epithelium. SM exposure upregulated keratin 17 expression. Mucin 5 ac producing goblet cells were interspersed within the conjunctiva. These cells generated both acidic and neutral mucins. Increased numbers of goblet cells producing neutral mucins were evident after SM exposure; upregulation of expression of membrane-associated mucin 1 and mucin 4 in the superficial layers of the conjunctival epithelium were also noted. These data demonstrate that ocular exposure of rabbits to SM causes significant damage not only to the cornea, but to the eyelid and conjunctiva, suggesting multiple targets within the eye that should be assessed when evaluating the efficacy of potential countermeasures.

Macrophage activation in the lung during the progression of nitrogen mustard induced injury is associated with histone modifications and altered miRNA expression

Activated macrophages have been implicated in lung injury and fibrosis induced by the cytotoxic alkylating agent, nitrogen mustard (NM). Herein, we determined if macrophage activation is associated with histone modifications and altered miRNA expression. Treatment of rats with NM (0.125 mg/kg, i.t.) resulted in increases in phosphorylation of H2A.X in lung macrophages at 1 d and 3 d post-exposure. This DNA damage response was accompanied by methylation of histone (H) 3 lysine (K) 4 and acetylation of H3K9, marks of transcriptional activation, and methylation of H3K36 and H3K9, marks associated with transcriptional repression. Increases in histone acetyl transferase and histone deacetylase were also observed in macrophages 1 d and 28 d post-NM exposure. PCR array analysis of miRNAs (miR)s involved in inflammation and fibrosis revealed unique and overlapping expression profiles in macrophages isolated 1, 3, 7, and 28 d post-NM. An IPA Core Analysis of predicted mRNA targets of differentially expressed miRNAs identified significant enrichment of Diseases and Functions related to cell cycle arrest, apoptosis, cell movement, cell adhesion, lipid metabolism, and inflammation 1 d and 28 d post NM. miRNA-mRNA interaction network analysis revealed highly connected miRNAs representing key upstream regulators of mRNAs involved in significantly enriched pathways including miR-34c-5p and miR-27a-3p at 1 d post NM and miR-125b-5p, miR-16-5p, miR-30c-5p, miR-19b-3p and miR-148b-3p at 28 d post NM. Collectively, these data show that NM promotes histone remodeling and alterations in miRNA expression linked to lung macrophage responses during inflammatory injury and fibrosis.

Macrophage Activation in the Lung during the Progression of Nitrogen Mustard Induced Injury is Associated with Altered miRNA Expression

Activated macrophages have been implicated in lung injury and fibrosis induced by the cytotoxic alkylating agent, nitrogen mustard (NM). Accumulating evidence suggests that phenotypic activation of macrophages during initiation, progression, and resolution of inflammatory responses is regulated by groups of miRNAs that act in concert to coordinate cellular activity. Herein, we determined if macrophage activation after NM injury was associated with altered miRNA expression. Male rats were exposed to NM (0.125 mg/kg, i.t.) and PCR array analysis of miRNAs involved in inflammation and fibrosis was performed in alveolar macrophages recovered from bronchoalveolar lavage. Results revealed unique and overlapping miRNA expression profiles in macrophages isolated 1, 3, 7, and 28 d post-NM. Seven miRNAs were upregulated in macrophages throughout the time-course, while three miRNAs were uniquely expressed 1 d post-NM, six at 3 d, six at 7 d, and nineteen at 28 d. Linkage with macrophage RNA-seq data showed differentially expressed miRNAs regulated mRNAs involved in STAT3, IL-6 and iNOS inflammatory signaling pathways at 1 d, and IL-4, PPAR and Sirtuin signaling at 28 d post-NM. Ingenuity Pathway Analysis predicted miR-21-5p, miR-29, miR-26a, miR-34a and let-7a as key regulators of macrophage mobilization, activation, and lipid homeostasis after NM. Collectively, these data show that NM promotes alterations in miRNA expression linked to lung macrophage responses during inflammatory injury and fibrosis. These findings provide clues on pathways regulating macrophage activation and may help identify novel therapeutic targets. This work was supported by NIH grants AR055073, ES004738, HL086621, ES005022, ES030984, and ES007148.

Farnesoid X receptor regulates macrophage activation and recruitment to the lung following exposure of mice to nitrogen mustard

Nitrogen mustard (NM) is a toxic vesicant known to cause acute lung injury which progresses to fibrosis. This is accompanied by the accumulation of pro-inflammatory/cytotoxic M1 macrophages and anti-inflammatory/pro-fibrotic M2 macrophages in the lung. Farnesoid X receptor (FXR) is a bile-acid activated nuclear receptor involved in lipid homeostasis; it has also been shown to exert anti-inflammatory activity. In these studies, we analyzed the role of FXR in regulating macrophage accumulation and activation in the lung following NM exposure. Male and female wild type (WT) and FXR−/− mice were treated with PBS (control) or NM (0.08 mg/kg) via intratracheal instillation. Lung tissue and bronchoalveolar lavage (BAL) fluid were collected 3, 14, and 28 days later. NM caused histopathologic alterations in the lung including inflammatory cell infiltration, septal damage, and epithelial thickening, which were more prominent in FXR−/− mice relative to WT mice at all post exposure time points. This correlated with aggravated increases in BAL protein and cell content. Flow cytometric analysis revealed pro-inflammatory macrophages were most abundant in BAL 3 days post NM, a response more pronounced in FXR−/− mice. In male but not female mice, increases in proinflammatory macrophages persisted in the lung for at least 28 d post NM. In contrast, while anti-inflammatory macrophages also increased in the lung following NM administration, no differences were observed between WT and FXR−/− mice. These findings demonstrate that FXR modulates proinflammatory macrophage responses to NM in a sex-dependent manner and suggest a potential new target for the development of therapeutics to blunt mustard vesicant induced lung inflammation and injury.

Myeloid cell dynamics in bleomycin-induced pulmonary injury in mice; effects of anti-TNFα antibody

Bleomycin is a cancer therapeutic known to cause lung injury which progresses to fibrosis. Evidence suggests that macrophages contribute to this pathological response. Tumor necrosis factor (TNF)α is a macrophage-derived pro-inflammatory cytokine implicated in lung injury. Herein, we investigated the role of TNFα in macrophage responses to bleomycin. Treatment of mice with bleomycin (3 U/kg, i.t.) caused histopathological changes in the lung within 3 d which culminated in fibrosis at 21 d. This was accompanied by an early (3-7 d) influx of CD11b+ and iNOS+ macrophages into the lung, and Arg-1+ macrophages at 21 d. At this time, epithelial cell dysfunction, defined by increases in total phospholipids and SP-B was evident. Treatment of mice with anti-TNFα antibody (7.5 mg/kg, i.v.) beginning 15-30 min after bleomycin, and every 5 d thereafter reduced the number and size of fibrotic foci and restored epithelial cell function. Flow cytometric analysis of F4/80+ alveolar macrophages (AM) isolated by bronchoalveolar lavage and interstitial macrophages (IM) by tissue digestion identified resident (CD11b-CD11c+) and immature infiltrating (CD11b+CD11c-) AM, and mature (CD11b+CD11c+) and immature (CD11b+CD11c-) IM subsets in bleomycin treated mice. Greater numbers of mature (CD11c+) infiltrating (CD11b+) AM expressing the anti-inflammatory marker, mannose receptor (CD206) were observed at 21 d when compared to 7 d post bleomycin. Mature proinflammatory (Ly6C+) IM were greater at 7 d relative to 21 d. These cells transitioned into mature anti-inflammatory/pro-fibrotic (CD206+) IM between 7 and 21 d. Anti-TNFα antibody heightened the number of CD11b+ AM in the lung without altering their activation state. Conversely, it reduced the abundance of mature proinflammatory (Ly6C+) IM in the tissue at 7 d and immature pro-fibrotic IM at 21 d. Taken together, these data suggest that TNFα inhibition has beneficial effects in bleomycin induced injury, restoring epithelial function and reducing numbers of profibrotic IM and the extent of pulmonary fibrosis.

Assessment of mustard vesicant lung injury and anti-TNF-α efficacy in rodents using live-animal imaging

Nitrogen mustard (NM) causes acute lung injury, which progresses to fibrosis. This is associated with a macrophage-dominant inflammatory response and the production of proinflammatory/profibrotic mediators, including tumor necrosis factor alpha (TNF-α). Herein, we refined magnetic resonance imaging (MRI) and computed tomography (CT) imaging methodologies to track the progression of NM-induced lung injury in rodents and assess the efficacy of anti-TNF-α antibody in mitigating toxicity. Anti-TNF-α antibody was administered to rats (15 mg/kg, every 8 days, intravenously) beginning 30 min after treatment with phosphate-buffered saline control or NM (0.125 mg/kg, intratracheally). Animals were imaged by MRI and CT prior to exposure and 1-28 days postexposure. Using MRI, we characterized acute lung injury and fibrosis by quantifying high-signal lung volume, which represents edema, inflammation, and tissue consolidation; these pathologies were found to persist for 28 days following NM exposure. CT scans were used to assess structural components of the lung and to register changes in tissue radiodensities. CT scans showed that in control animals, total lung volume increased with time. Treatment of rats with NM caused loss of lung volume; anti-TNF-α antibody mitigated this decrease. These studies demonstrate that MRI and CT can be used to monitor lung disease and the impact of therapeutic intervention.

Chemical warfare agent research in precision-cut tissue slices-a useful alternative approach

The use of chemical warfare agents (CWAs) in military conflicts and against civilians is a recurrent problem. Despite ongoing CWA research using in vitro or in vivo models, progress to elucidate mechanisms of toxicity and to develop effective therapies, decontamination procedures, and general countermeasures is still limited. Novel scientific approaches to address these questions are needed to expand perspectives on existing knowledge and gain new insights. To achieve this, the use of ex vivo techniques like precision-cut tissue slices (PCTSs) can be a valuable approach. Existing studies employing this economical and relatively easy to implement method show model suitability and comparability with the use of in vitro and in vivo models. In this article, we review research on CWAs in PCTSs to illustrate the advantages of the approach and to promote future applications.

Disease-modifying treatment of chemical threat agent-induced acute lung injury

Acute respiratory distress syndrome (ARDS) is a highly morbid lung pathology induced by exposure to chemical warfare agents, including vesicants, phosgene, chlorine, and ricin. In this review, we describe the pathology associated with the development of ARDS in humans and experimental models of acute lung injury following animal exposure to these high-priority threat agents. Potential future approaches to disease-modifying treatment used in preclinical animal studies, including antioxidants, anti-inflammatories, biologics, and mesenchymal stem cells, are also described. As respiratory pathologies, including ARDS, are the major cause of morbidity and mortality following exposure to chemical threat agents, understanding mechanisms of disease pathogenesis is key to the development of efficacious therapeutics beyond the primary intervention principle, which remains mechanical ventilation.

Nutraceuticals as potential therapeutics for vesicant-induced pulmonary fibrosis

Exposure to vesicants, including sulfur mustard and nitrogen mustard, causes damage to the epithelia of the respiratory tract and the lung. With time, this progresses to chronic disease, most notably, pulmonary fibrosis. The pathogenic process involves persistent inflammation and the release of cytotoxic oxidants, cytokines, chemokines, and profibrotic growth factors, which leads to the collapse of lung architecture, with fibrotic involution of the lung parenchyma. At present, there are no effective treatments available to combat this pathological process. Recently, much interest has focused on nutraceuticals, substances derived from plants, herbs, and fruits, that exert pleiotropic effects on inflammatory cells and parenchymal cells that may be useful in reducing fibrogenesis. Some promising results have been obtained with nutraceuticals in experimental animal models of inflammation-driven fibrosis. This review summarizes the current knowledge on the putative preventive/therapeutic efficacy of nutraceuticals in progressive pulmonary fibrosis, with a focus on their activity against inflammatory reactions and profibrotic cell differentiation.

Progressive Lung Injury, Inflammation, and Fibrosis in Rats Following Inhalation of Sulfur Mustard

Sulfur mustard (SM) inhalation causes debilitating pulmonary injury in humans which progresses to fibrosis. Herein, we developed a rat model of SM toxicity which parallels pathological changes in the respiratory tract observed in humans. SM vapor inhalation caused dose (0.2-0.6 mg/kg)-related damage to the respiratory tract within 3 days of exposure. At 0.4-0.6 mg/kg, ulceration of the proximal bronchioles, edema and inflammation were observed, along with a proteinaceous exudate containing inflammatory cells in alveolar regions. Time course studies revealed that the pathologic response was biphasic. Thus, changes observed at 3 days post-SM were reduced at 7-16 days; this was followed by more robust aberrations at 28 days, including epithelial necrosis and hyperplasia in the distal bronchioles, thickened alveolar walls, enlarged vacuolated macrophages, and interstitial fibrosis. Histopathologic changes were correlated with biphasic increases in bronchoalveolar lavage (BAL) cell and protein content and proliferating cell nuclear antigen expression. Proinflammatory proteins receptor for advanced glycation end product (RAGE), high-mobility group box protein (HMGB)-1, and matrix metalloproteinase (MMP)-9 also increased in a biphasic manner following SM inhalation, along with surfactant protein-D (SP-D). Tumor necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS), inflammatory proteins implicated in mustard lung toxicity, and the proinflammatory/profibrotic protein, galectin (Gal)-3, were upregulated in alveolar macrophages and in bronchiolar regions at 3 and 28 days post-SM. Inflammatory changes in the lung were associated with oxidative stress, as reflected by increased expression of heme oxygenase (HO)-1. These data demonstrate a similar pathologic response to inhaled SM in rats and humans suggesting that this rodent model can be used for mechanistic studies and for the identification of efficacious therapeutics for mitigating toxicity.

The amplex red/horseradish peroxidase assay requires superoxide dismutase to measure hydrogen peroxide in the presence of NAD(P)H

A sensitive fluorescence assay based on Amplex Red (AR) oxidation by horseradish peroxidase (AR/HRP) is described which continuously monitor rates of H2O2 production by microsomal enzymes in the presence of relatively high concentrations of NADPH. NADPH and NADH are known to interact with HRP and generate significant quantities of superoxide anion, a radical that spontaneously dismutates to form H2O2 which interferes with the AR/HRP assay. Microsomal enzymes generate H2O2 as a consequence of electron transfer from NADPH to cytochrome P450 hemoproteins with subsequent oxygen activation. We found that superoxide anion formation via the interaction of NADPH with HRP was inhibited by superoxide dismutase (SOD) without affecting H2O2 generation by microsomal enzymes. Using SOD in enzyme assays, we consistently detected rates of H2O2 production using microgram quantities of microsomal proteins (2.62 ± 0.20 picomol/min/µg protein for liver microsomes from naïve female rats, 12.27 ± 1.29 for liver microsomes from dexamethasone induced male rats, and 2.17 ± 0.25 picomol/min/µg protein for human liver microsomes). This method can also be applied to quantify rates of H2O2 production by oxidases where superoxide anion generation by NADH or NADPH and HRP can interfere with enzyme assays.

Transcriptional profiling of lung macrophages during pulmonary injury induced by nitrogen mustard

Nitrogen mustard (NM) and sulfur mustard are cytotoxic alkylating agents that cause severe and progressive damage to the respiratory tract. Evidence indicates that macrophages play a key role in the acute inflammatory phase and the later resolution/profibrotic phase of the pathogenic response. These diverse roles are mediated by inflammatory macrophages broadly classified as M1 proinflammatory and M2 anti-inflammatory that sequentially accumulate in the lung in response to injury. The goal of the present study was to identify signaling mechanisms contributing to macrophage activation in response to mustards. To accomplish this, we used RNA sequencing to analyze the gene expression profiles of lung macrophages isolated 1 and 28 days after intratracheal exposure of rats to NM (0.125 mg/kg) or phosphate-buffered saline control. We identified 641 and 792 differentially expressed genes 1 and 28 days post-NM exposure, respectively. These genes are primarily involved in processes related to cell movement and are regulated by cytokines, including tumor necrosis factor-α, interferon-γ, and interleukin-1β. Some of the most significantly enriched canonical pathways included STAT3 and NF-κB signaling. These cytokines and pathways may represent potential targets for therapeutic intervention to mitigate mustard-induced lung toxicity.

Skin remodeling and wound healing in the Gottingen minipig following exposure to sulfur mustard

Sulfur mustard (SM), a dermal vesicant that has been used in chemical warfare, causes inflammation, edema and epidermal erosions depending on the dose and time following exposure. Herein, a minipig model was used to characterize wound healing following dermal exposure to SM. Saturated SM vapor caps were placed on the dorsal flanks of 3-month-old male Gottingen minipigs for 30 min. After 48 h the control and SM wounded sites were debrided daily for 7 days with wet to wet saline gauze soaks. Animals were then euthanized, and full thickness skin biopsies prepared for histology and immunohistochemistry. Control skin contained a well differentiated epidermis with a prominent stratum corneum. A well-developed eschar covered the skin of SM treated animals, however, the epidermis beneath the eschar displayed significant wound healing with a hyperplastic epidermis. Stratum corneum shedding and a multilayered basal epithelium consisting of cuboidal and columnar cells were also evident in the neoepidermis. Nuclear expression of proliferating cell nuclear antigen (PCNA) was contiguous in cells along the basal epidermal layer of control and SM exposed skin; SM caused a significant increase in PCNA expression in basal and suprabasal cells. SM exposure was also associated with marked changes in expression of markers of wound healing including increases in keratin 10, keratin 17 and loricrin and decreases in E-cadherin. Trichrome staining of control skin showed a well-developed collagen network with no delineation between the papillary and reticular dermis. Conversely, a major delineation was observed in SM-exposed skin including a web-like papillary dermis composed of filamentous extracellular matrix, and compact collagen fibrils in the lower reticular dermis. Although the dermis below the wound site was disrupted, there was substantive epidermal regeneration following SM-induced injury. Further studies analyzing the wound healing process in minipig skin will be important to provide a model to evaluate potential vesicant countermeasures.

A Novel Bivalent Mannosylated Targeting Ligand Displayed on Nanoparticles Selectively Targets Anti-Inflammatory M2 Macrophages

Persistent activation of macrophages (MP)s into a proinflammatory M1 or anti-inflammatory M2 phenotype plays a role in several pathological conditions, including autoimmune diseases, fibrosis, infections, atherosclerosis and tumor development. The mannose receptor (MR, CD206), expressed at low levels on resting MPs and absent on M1 MPs, is highly expressed on M2 MPs, making it a potential target and drug delivery portal. Recently, we developed a novel, highly selective MR targeting ligand (MRTL), consisting of two mannose molecules separated by a monodisperse 12 unit poly(ethylene glycol) linker, to enhance the cellular uptake of polymeric nanocarriers. The feasibility of using the MRTL ligand for selectively targeting M2 MPs for intracellular delivery of nanoparticles (NPs) was investigated. Rat peritoneal MPs were differentiated into an M1 or M2 phenotype using IFN-γ and IL-4/IL-13, respectively. Expression of the M1 marker, inducible nitric oxide synthase (iNOS), and the M2 markers arginase (Arg)-1 and MR (at both the mRNA and protein levels) confirmed MP phenotypic activation. Resting, M1 and M2 MPs were treated with fluorescein isothiocyanate (FITC)-labeled MRTL or NPs displaying FITC-labeled MRTL at two surface densities (1 and 10%) and examined by confocal microscopy. Intracellular fluorescence was also quantified. Uptake of the MRTL was 2.4- and 11.8-fold higher in M2 MPs when compared to resting or M1 MPs, respectively, consistent with marker expression levels. Mannan, a competitive inhibitor of the MR, abrogated MRTL uptake. MRTL also co-localized with a fluid-phase endocytosis marker, further suggesting that uptake was mediated by MR-mediated endocytosis. Intracellular NP fluorescence was confirmed by flow cytometry and by confocal microscopy. MRTL-NPs accumulated intracellularly with no significant cell surface binding, suggesting efficient translocation. NPs displaying a low surface density (1%) of the MRTL exhibited significantly higher (2.3-fold) uptake into M2 MPs, relative to resting and M1 MPs. The 10% MRTL-NPs displayed greater uptake by M2 MPs when compared to resting and M1 MPs, but less uptake than 1% MRTL-NPs into M2 MPs. Control FITC-labeled plain NPs did not exhibit selective MP uptake. These studies demonstrate that M2 MPs are selectively targeted by NPs displaying a novel bivalent ligand that utilizes the MR as a target/portal for cell entry. This study also establishes the feasibility of the approach allowing for further investigation in vivo.

Antioxidant/stress response in mouse epidermis following exposure to nitrogen mustard

Nitrogen mustard (NM) is a highly reactive bifunctional alkylating agent that induces inflammation, edema and blistering in skin. An important mechanism mediating the action of NM and related mustards is oxidative stress. In these studies a modified murine patch-test model was used to analyze DNA damage and the antioxidant/stress response following NM exposure in isolated epidermis. NM (20 μmol) was applied to glass microfiber filters affixed to a shaved dorsal region of skin of CD-1 mice. NM caused structural damage to the stratum corneum as reflected by increases in transepidermal water loss and skin hydration. This was coordinate with edema, mast cell degranulation and epidermal hyperplasia. Within 3 h of NM exposure, a 4-fold increase in phosphorylated histone H2AX, a marker of DNA double-stranded breaks, and a 25-fold increase in phosphorylated p53, a DNA damage marker, were observed in the epidermis. This was associated with a 40% increase in 8-oxo-2'-deoxyguanosine modified DNA in the epidermis and a 4-fold increase in 4-hydroxynonenal modified epidermal proteins. At 12 h post NM, there was a 3-75 fold increase in epidermal expression of antioxidant/stress proteins including heme oxygenase-1, thioredoxin reductase, superoxide dismutase, glutathione reductase, heat shock protein 27 and cyclooxygenase 2. These data indicate that NM induces early oxidative epidermal injury in mouse skin leading to an antioxidant/stress response. Agents that enhance this response may be useful in mitigating mustard-induced skin injury.

Role of extracellular vesicles in cell-cell communication and inflammation following exposure to pulmonary toxicants

Extracellular vesicles (EVs) have emerged as key regulators of cell-cell communication during inflammatory responses to lung injury induced by diverse pulmonary toxicants including cigarette smoke, air pollutants, hyperoxia, acids, and endotoxin. Many lung cell types, including epithelial cells and endothelial cells, as well as infiltrating macrophages generate EVs. EVs appear to function by transporting cargo to recipient cells that, in most instances, promote their inflammatory activity. Biologically active cargo transported by EVs include miRNAs, cytokines/chemokines, damage-associated molecular patterns (DAMPs), tissue factor (TF)s, and caspases. Findings that EVs are taken up by target cells such as macrophages, and that this leads to increased proinflammatory functioning provide support for their role in the development of pathologies associated with toxicant exposure. Understanding the nature of EVs responding to toxic exposures and their cargo may lead to the development of novel therapeutic approaches to mitigating lung injury.

Regulation of Macrophage Foam Cell Formation During Nitrogen Mustard (NM)-Induced Pulmonary Fibrosis by Lung Lipids

Nitrogen mustard (NM) is a vesicant known to target the lung, causing acute injury which progresses to fibrosis. Evidence suggests that activated macrophages contribute to the pathologic response to NM. In these studies, we analyzed the role of lung lipids generated following NM exposure on macrophage activation and phenotype. Treatment of rats with NM (0.125 mg/kg, i.t.) resulted in a time-related increase in enlarged vacuolated macrophages in the lung. At 28 days postexposure, macrophages stained positively for Oil Red O, a marker of neutral lipids. This was correlated with an accumulation of oxidized phospholipids in lung macrophages and epithelial cells and increases in bronchoalveolar lavage fluid (BAL) phospholipids and cholesterol. RNA-sequencing and immunohistochemical analysis revealed that lipid handling pathways under the control of the transcription factors liver-X receptor (LXR), farnesoid-X receptor (FXR), peroxisome proliferator-activated receptor (PPAR)-ɣ, and sterol regulatory element-binding protein (SREBP) were significantly altered following NM exposure. Whereas at 1-3 days post NM, FXR and the downstream oxidized low-density lipoprotein receptor, Cd36, were increased, Lxr and the lipid efflux transporters, Abca1 and Abcg1, were reduced. Treatment of naïve lung macrophages with phospholipid and cholesterol enriched large aggregate fractions of BAL prepared 3 days after NM exposure resulted in upregulation of Nos2 and Ptgs2, markers of proinflammatory activation, whereas large aggregate fractions prepared 28 days post NM upregulated expression of the anti-inflammatory markers, Il10, Cd163, and Cx3cr1, and induced the formation of lipid-laden foamy macrophages. These data suggest that NM-induced alterations in lipid handling and metabolism drive macrophage foam cell formation, potentially contributing to the development of pulmonary fibrosis.

Lung injury, oxidative stress and fibrosis in mice following exposure to nitrogen mustard

Nitrogen mustard (NM) is a cytotoxic vesicant known to cause acute lung injury which progresses to fibrosis. Herein, we developed a murine model of NM-induced pulmonary toxicity with the goal of assessing inflammatory mechanisms of injury. C57BL/6J mice were euthanized 1-28 d following intratracheal exposure to NM (0.08 mg/kg) or PBS control. NM caused progressive alveolar epithelial thickening, perivascular inflammation, bronchiolar epithelial hyperplasia, interstitial fibroplasia and fibrosis, peaking 14 d post exposure. Enlarged foamy macrophages were also observed in the lung 14 d post NM, along with increased numbers of microparticles in bronchoalveolar lavage fluid (BAL). Following NM exposure, rapid and prolonged increases in BAL cells, protein, total phospholipids and surfactant protein (SP)-D were also detected. Flow cytometric analysis showed that CD11b⁺Ly6G^-F4/80⁺Ly6C^hi proinflammatory macrophages accumulated in the lung after NM, peaking at 3 d. This was associated with macrophage expression of HMGB1 and TNFα in histologic sections. CD11b⁺Ly6G^-F4/80⁺Ly6C^lo anti-inflammatory/pro-fibrotic macrophages also increased in the lung after NM peaking at 14 d, a time coordinate with increases in TGFβ expression and fibrosis. NM exposure also resulted in alterations in pulmonary mechanics including increases in tissue elastance and decreases in compliance and static compliance, most prominently at 14 d. These findings demonstrate that NM induces structural and inflammatory changes in the lung that correlate with aberrations in pulmonary function. This mouse model will be useful for mechanistic studies of mustard lung injury and for assessing potential countermeasures.

Sulfur Mustard Analog Mechlorethamine (Bis(2-chloroethyl)methylamine) Modulates Cell Cycle Progression via the DNA Damage Response in Human Lung Epithelial A549 Cells

Nitrogen mustard, mechlorethamine (bis(2-chloroethyl)methylamine; HN2), and sulfur mustard are potent vesicants that modify and disrupt cellular macromolecules including DNA leading to cytotoxicity and tissue injury. In many cell types, HN2 upregulates DNA damage signaling pathways including ataxia telangiectasia mutated (ATM), ataxia telangiectasia mutated- and Rad3-related (ATR) as well as DNA-dependent protein kinase (DNA-PK). In the present studies, we investigated crosstalk between the HN2-induced DNA damage response and cell cycle progression using human A549 lung epithelial cells. HN2 (1-20 μM; 24 h) caused a concentration-dependent arrest of cells in the S and G2/M phases of the cell cycle. This was associated with inhibition of DNA synthesis, as measured by incorporation of 5-ethynyl-2'-deoxyuridine (EdU) into S phase cells. Cell cycle arrest was correlated with activation of DNA damage and cell cycle checkpoint signaling. Thus, HN2 treatment resulted in time- and concentration-dependent increases in expression of phosphorylated ATM (Ser1981), Chk2 (Thr68), H2AX (Ser139), and p53 (Ser15). Activation of DNA damage signaling was most pronounced in S-phase cells followed by G2/M-phase cells. HN2-induced cell cycle arrest was suppressed by the ATM and DNA-PK inhibitors, KU55933 and NU7441, respectively, and to a lesser extent by VE821, an ATR inhibitor. This was correlated with abrogation of DNA damage checkpoints signaling. These data indicate that activation of ATM, ATR, and DNA-PK signaling pathways by HN2 are important in the mechanism of vesicant-induced cell cycle arrest and cytotoxicity. Drugs that inhibit activation of DNA damage signaling may be effective countermeasures for vesicant-induced tissue injury.

Role of Macrophages in Acute Lung Injury and Chronic Fibrosis Induced by Pulmonary Toxicants

A diverse group of toxicants has been identified that cause injury to the lung including gases (eg, ozone, chlorine), particulates/aerosols (eg, diesel exhaust, fly ash, other combustion products, mustards, nanomaterials, silica, asbestos), chemotherapeutics (eg, bleomycin), and radiation. The pathologic response to these toxicants depends on the dose and duration of exposure and their physical/chemical properties. A common response to pulmonary toxicant exposure is an accumulation of proinflammatory/cytotoxic M1 macrophages at sites of tissue injury, followed by the appearance of anti-inflammatory/wound repair M2 macrophages. It is thought that the outcome of the pathogenic responses to toxicants depends on the balance in the activity of these macrophage subpopulations. Overactivation of either M1 or M2 macrophages leads to injury and disease pathogenesis. Thus, the very same macrophage-derived mediators, released in controlled amounts to destroy injurious materials and pathogens (eg, reactive oxygen species, reactive nitrogen species, proteases, tumor necrosis factor α) and initiate wound repair (eg, transforming growth factor β, connective tissue growth factor, vascular endothelial growth factor), can exacerbate acute lung injury and/or induce chronic disease such as fibrosis, chronic obstructive pulmonary disease, and asthma, when released in excess. This review focuses on the role of macrophage subsets in acute lung injury and chronic fibrosis. Understanding how these pathologies develop following exposure to toxicants, and the contribution of resident and inflammatory macrophages to disease pathogenesis may lead to the development of novel approaches for treating lung diseases.

Protective Role of Surfactant Protein-D Against Lung Injury and Oxidative Stress Induced by Nitrogen Mustard

Nitrogen mustard (NM) is a vesicant known to cause acute pulmonary injury which progresses to fibrosis. Macrophages contribute to both of these pathologies. Surfactant protein (SP)-D is a pulmonary collectin that suppresses lung macrophage activity. Herein, we analyzed the effects of loss of SP-D on NM-induced macrophage activation and lung toxicity. Wild-type (WT) and SP-D-/- mice were treated intratracheally with PBS or NM (0.08 mg/kg). Bronchoalveolar lavage (BAL) fluid and tissue were collected 14 days later. In WT mice, NM caused an increase in total SP-D levels in BAL; multiple lower molecular weight forms of SP-D were also identified, consistent with lung injury and oxidative stress. Flow cytometric analysis of BAL cells from NM treated WT mice revealed the presence of proinflammatory and anti-inflammatory macrophages. Whereas loss of SP-D had no effect on numbers of these cells, their activation state, as measured by proinflammatory (iNOS, MMP-9), and anti-inflammatory (MR-1, Ym-1) protein expression, was amplified. Loss of SP-D also exacerbated NM-induced oxidative stress and alveolar epithelial injury, as reflected by increases in heme oxygenase-1 expression, and BAL cell and protein content. This was correlated with alterations in pulmonary mechanics. In NM-treated SP-D-/-, but not WT mice, there was evidence of edema, epithelial hypertrophy and hyperplasia, bronchiectasis, and fibrosis, as well as increases in BAL phospholipid content. These data demonstrate that activated lung macrophages play a role in NM-induced lung injury and oxidative stress. Elucidating mechanisms regulating macrophage activity may be important in developing therapeutics to treat mustard-induced lung injury.

Functional Evidence of Pulmonary Extracellular Vesicles in Infectious and Noninfectious Lung Inflammation

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a highly complex process that can be triggered by both noninfectious (sterile) and infectious stimuli. Inflammatory lung responses are one of the key features in the pathogenesis of this devastating syndrome. How ALI/ARDS-associated inflammation develops remains incompletely understood, particularly after exposure to sterile stimuli. Emerging evidence suggests that extracellular vesicles (EVs) regulate intercellular communication and inflammatory responses in various diseases. In this study, we characterized the generation and function of pulmonary EVs in the setting of ALI/ARDS, induced by sterile stimuli (oxidative stress or acid aspiration) and infection (LPS/Gram-negative bacteria) in mice. EVs detected in bronchoalveolar lavage fluid (BALF) were markedly increased after exposure of animals to both types of stimuli. After sterile stimuli, alveolar type-І epithelial cells were the main source of the BALF EVs. In contrast, infectious stimuli-induced BALF EVs were mainly derived from alveolar macrophages (AMs). Functionally, BALF EVs generated in both the noninfectious and infectious ALI models promoted the recruitment of macrophages in in vivo mouse models. Furthermore, BALF EVs differentially regulated AM production of cytokines and inflammatory mediators, as well as TLR expression in AMs in vivo. Regardless of their origin, BALF EVs contributed significantly to the development of lung inflammation in both the sterile and infectious ALI. Collectively, our results provide novel insights into the mechanisms by which EVs regulate the development of lung inflammation in response to diverse stimuli, potentially providing novel therapeutic and diagnostic targets for ALI/ARDS.

Concerted action of IFN-α and IFN-λ induces local NK cell immunity and halts cancer growth

Hepatocellular carcinoma (HCC) is the most prevalent type of liver cancer. No significant improvement has been reported with currently available systemic therapies. IFN-α has been tested in both clinic and animal models and only moderate benefits have been observed. In animal models, similar modest antitumor efficacy has also been reported for IFN-λ, a new type of IFN that acts through its own receptor complex. In the present study, the antitumor efficacy of the combination of IFN-α and IFN-λ was tested in the BNL mouse hepatoma model. This study was accomplished by using either engineered tumor cells (IFN-α/IFN-λ gene therapy) or by directly injecting tumor-bearing mice with IFN-α/IFN-λ. Both approaches demonstrated that IFN-α/IFN-λ combination therapy was more efficacious than IFN monotherapy based on either IFN-α or IFN-λ. In complement to tumor surgery, IFN-α/IFN-λ combination induced complete tumor remission. Highest antitumor efficacy has been obtained following local administration of IFN-α/IFN-λ combination at the tumor site that was associated with strong NK cells tumor infiltration. This supports the use of IFN-α/IFN-λ combination as a new cancer immunotherapy for stimulating antitumor response after cancer surgery.

The effect of fibroblast growth factor 15 deficiency on the development of high fat diet induced non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a form of non-alcoholic fatty liver disease (NAFLD) characterized by steatosis, inflammation, and fibrosis often associated with metabolic syndrome. Fibroblast growth factor 15 (FGF15), an endocrine factor mainly produced in the distal part of small intestine, has emerged to be a critical factor in regulating bile acid homeostasis, energy metabolism, and liver regeneration. We hypothesized that FGF15 alters the development of each of the listed features of NASH. To test this hypothesis, four-week old male Fgf15^-/- and their corresponding wild-type (WT) mice were fed either a high fat diet (HFD) or a control chow diet for six months. The results confirmed that HFD feeding for six months in WT mice recapitulated human NASH phenotype, including macrovesicular steatosis, inflammation, and fibrosis. Whereas FGF15 deficiency had no effect on the severity of liver steatosis or inflammation, it was associated with decreased liver fibrosis. Furthermore, FGF15 deficiency resulted in abnormal bile acid homeostasis, increased insulin resistance, increased HFD-induced serum triglycerides, decreased inductions of hepatic cholesterol content by HFD, and altered gene expression of lipid metabolic enzymes. These data suggest that FGF15 improves lipid homeostasis and reduces bile acid synthesis, but promotes fibrosis during the development of NASH.

Diacetyl/l-Xylulose Reductase Mediates Chemical Redox Cycling in Lung Epithelial Cells

Reactive carbonyls such as diacetyl (2,3-butanedione) and 2,3-pentanedione in tobacco and many food and consumer products are known to cause severe respiratory diseases. Many of these chemicals are detoxified by carbonyl reductases in the lung, in particular, dicarbonyl/l-xylulose reductase (DCXR), a multifunctional enzyme important in glucose metabolism. DCXR is a member of the short-chain dehydrogenase/reductase (SDR) superfamily. Using recombinant human enzyme, we discovered that DCXR mediates redox cycling of a variety of quinones generating superoxide anion, hydrogen peroxide, and, in the presence of transition metals, hydroxyl radicals. Redox cycling activity preferentially utilized NADH as a cosubstrate and was greatest for 9,10-phenanthrenequinone and 1,2-naphthoquinone, followed by 1,4-naphthoquinone and 2-methyl-1,4-naphthoquinone (menadione). Using 9,10-phenanthrenequinone as the substrate, quinone redox cycling was found to inhibit DCXR reduction of l-xylulose and diacetyl. Competitive inhibition of enzyme activity by the quinone was observed with respect to diacetyl (K_i = 190 μM) and l-xylulose (K_i = 940 μM). Abundant DCXR activity was identified in A549 lung epithelial cells when diacetyl was used as a substrate. Quinones inhibited reduction of this dicarbonyl, causing an accumulation of diacetyl in the cells and culture medium and a decrease in acetoin, the reduced product of diacetyl. The identification of DCXR as an enzyme activity mediating chemical redox cycling suggests that it may be important in generating cytotoxic reactive oxygen species in the lung. These activities, together with the inhibition of dicarbonyl/l-xylulose metabolism by redox-active chemicals, as well as consequent deficiencies in pentose metabolism, are likely to contribute to lung injury following exposure to dicarbonyls and quinones.

Anti-TNFα therapy in inflammatory lung diseases

Increased levels of tumor necrosis factor (TNF) α have been linked to a number of pulmonary inflammatory diseases including asthma, chronic obstructive pulmonary disease (COPD), acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), sarcoidosis, and interstitial pulmonary fibrosis (IPF). TNFα plays multiple roles in disease pathology by inducing an accumulation of inflammatory cells, stimulating the generation of inflammatory mediators, and causing oxidative and nitrosative stress, airway hyperresponsiveness and tissue remodeling. TNFα-targeting biologics, therefore, present a potentially highly efficacious treatment option. This review summarizes current knowledge on the role of TNFα in pulmonary disease pathologies, with a focus on the therapeutic potential of TNFα-targeting agents in treating inflammatory lung diseases.

Regulation of Nitrogen Mustard-Induced Lung Macrophage Activation by Valproic Acid, a Histone Deacetylase Inhibitor

Nitrogen mustard (NM)-induced lung injury is associated with an accumulation of proinflammatory/cytotoxic M1 and antiinflammatory/wound repair M2 macrophages, which have been implicated in tissue injury and repair. Herein, we analyzed the effects of valproic acid (VPA), a histone deacetylase (HDAC) inhibitor with antiinflammatory and antioxidant activity, on lung macrophages responding to NM. Treatment of rats with NM (0.125 mg/kg, i.t.) resulted in structural alterations in the lung and a macrophage-rich inflammatory cell infiltrate, at 3 d and 7 d. This was accompanied by expression of PCNA, a marker of proliferation, and CYPb5, HO-1, and MnSOD, markers of oxidative stress. Administration of VPA (300 mg/kg/day; i.p.), beginning 30 min after NM, reduced increases in PCNA, CYPb5, HO-1, and MnSOD. This was associated with increases in immature CD11b+CD43+ M1 macrophages in the lung, and decreases in mature CD11b+CD43- M2 macrophages 3 d post NM, suggesting delayed maturation and phenotypic switching. VPA also attenuated NM-induced increases in lung iNOS+ and CCR2+ M1 macrophages, a response correlated with downregulation of NOS2, IL12B, PTGS2, MMP-9, and CCR2 expression. Conversely, numbers of CD68+, CD163+ , and ATR-1α+ M2 macrophages increased after VPA, along with the expression of IL10, ApoE, and ATR-1A. NM exposure resulted in increased HDAC activity and upregulation of HDAC2 and acetylated H3K9 in the lung. Whereas VPA blunted the effects of NM on HDAC2 expression, histone H3K9 acetylation increased. These data suggest that alterations in the balance between histone acetylases and deacetylases contribute to lung macrophage maturation and activation following NM exposure.