Attenuation of acute nitrogen mustard-induced lung injury, inflammation and fibrogenesis by a nitric oxide synthase inhibitor

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.

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.

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.

The effects of pentoxifylline and caffeic acid phenethyl ester on TNF-α and lung histopathology in D-galactosamine-induced pulmonary injury in rats

In this study, we aimed to investigate the effects of pentoxifylline [PTX] and caffeic acid phenethyl ester [CAPE] in D-galactosamine [D-GAL]-induced pulmonary injury in rats. The rats were randomly divided into six groups: control, D-GAL, D-GAL+PTX, D-GAL+CAPE, PTX and CAPE. Each group included eight animals. Lung sections from the control, PTX and CAPE groups had a normal histological appearance. The D-GAL group showed histopathological changes in lung tissue, including haemorrhage, oedema, inter-alveolar septal thickening and widespread infiltration of inflammatory lymphocytes and macrophages. Administration of PTX and CAPE significantly reduced histopathological damage scores in the D-GAL+PTX and D-GAL+CAPE groups compared with the D-GAL group. PTX and CAPE treatment also significantly decreased malondialdehyde levels, increased levels of reduced GSH and increased catalase and superoxide dismutase activity in lung tissue samples. These results indicate that the destructive effects of D-GAL-induced inflammation in the rat lung are significantly reduced following administration of PTX and CAPE.

MG53 attenuates nitrogen mustard-induced acute lung injury

Nitrogen mustard (NM) is an alkylating vesicant that causes severe pulmonary injury. Currently, there are no effective means to counteract vesicant‐induced lung injury. MG53 is a vital component of cell membrane repair and lung protection. Here, we show that mice with ablation of MG53 are more susceptible to NM‐induced lung injury than the wild‐type mice. Treatment of wild‐type mice with exogenous recombinant human MG53 (rhMG53) protein ameliorates NM‐induced lung injury by restoring arterial blood oxygen level, by improving dynamic lung compliance and by reducing airway resistance. Exposure of lung epithelial and endothelial cells to NM leads to intracellular oxidative stress that compromises the intrinsic cell membrane repair function of MG53. Exogenous rhMG53 protein applied to the culture medium protects lung epithelial and endothelial cells from NM‐induced membrane injury and oxidative stress, and enhances survival of the cells. Additionally, we show that loss of MG53 leads to increased vulnerability of macrophages to vesicant‐induced cell death. Overall, these findings support the therapeutic potential of rhMG53 to counteract vesicant‐induced lung injury.

Vitamin D3 protects against nitrogen mustard-induced apoptosis of the bronchial epithelial cells via activating the VDR/Nrf2/Sirt3 pathway

Respiratory system injury is the main cause of mortality for nitrogen mustard (NM)-induced damage. Previous studies indicate that reactive oxygen species (ROS) participates in NM-mediated respiratory injuries, but the detailed mechanism is not quite clear. Human bronchial epithelial cell lines 16HBE and BEAS-2B were treated with HN2, a type of NM. In detail, it was shown that HN2 treatment induced impaired cell viability, excessive mitochondrial ROS production and enhanced cellular apoptosis in bronchial epithelial cells. Moreover, impaired Sirt3/SOD2 axis was observed upon HN2 treatment, with decreased Sirt3 and increased acetylated SOD2 expression levels. Sirt3 overexpression partially ameliorated HN2-induced cell injury. Meanwhile, vitamin D3 treatment partially attenuated HN2-induced apoptosis and improved the mitochondrial functions upon HN2 intervention. In addition, HN2 exposure decreased VDR expression, thus inhibiting the Nrf2 phosphorylation and Sirt3 activation. Inhibition of Nrf2 or Sirt3 could decrease the protective effects of vitamin D3 and enhance mitochondrial ROS production via modulating mitochondrial redox balance. In conclusion, impaired VDR/Nrf2/Sirt3 axis contributed to NM-induced apoptosis, while vitamin D3 supplementation provides protective effects via the activation of VDR and the improvement of mitochondrial functions. This study provides novel mechanism and strategy for NM exposure-induced pulmonary injuries.

Pulmonary injury and oxidative stress in rats induced by inhaled sulfur mustard is ameliorated by anti-tumor necrosis factor-α antibody

Sulfur mustard (SM) is a bifunctional alkylating agent that causes severe injury to the respiratory tract. This is accompanied by an accumulation of macrophages in the lung and the release of the proinflammatory cytokine, tumor necrosis factor (TNF)α. In these studies, we analyzed the effects of blocking TNFα on lung injury, inflammation and oxidative stress induced by inhaled SM. Rats were treated with SM vapor (0.4 mg/kg) or air control by intratracheal inhalation. This was followed 15-30 min later by anti-TNFα antibody (15mg/kg, i.v.) or PBS control. Animals were euthanized 3 days later. Anti-TNFα antibody was found to blunt SM-induced peribronchial edema, perivascular inflammation and alveolar plasma protein and inflammatory cell accumulation in the lung; this was associated with reduced expression of PCNA in histologic sections and decreases in BAL levels of fibrinogen. SM-induced increases in inflammatory proteins including soluble receptor for glycation end products, its ligand, high mobility group box-1, and matrix metalloproteinase-9 were also reduced by anti-TNFα antibody administration, along with increases in numbers of lung macrophages expressing TNFα, cyclooxygenase-2 and inducible nitric oxide synthase. This was correlated with reduced oxidative stress as measured by expression of heme oxygenase-1 and Ym-1. Together, these data suggest that inhibiting TNFα may represent an efficacious approach to mitigating acute lung injury, inflammatory macrophage activation, and oxidative stress induced by inhaled sulfur mustard.

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.

Pulmonary toxicants and fibrosis: innate and adaptive immune mechanisms

Pulmonary fibrosis is characterized by destruction and remodeling of the lung due to an accumulation of collagen and other extracellular matrix components in the tissue. This results in progressive irreversible decreases in lung capacity, impaired gas exchange and eventually, hypoxemia. A number of inhaled and systemic toxicants including bleomycin, silica, asbestos, nanoparticles, mustard vesicants, nitrofurantoin, amiodarone, and ionizing radiation have been identified. In this article, we review the role of innate and adaptive immune cells and mediators they release in the pathogenesis of fibrotic pathologies induced by pulmonary toxicants. A better understanding of the pathogenic mechanisms underlying fibrogenesis may lead to the development of new therapeutic approaches for patients with these debilitating and largely irreversible chronic diseases.

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.

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.

Mannose-anchored N,N,N-trimethyl chitosan nanoparticles for pulmonary administration of etofylline

Drug delivery to lungs via pulmonary administration offers potential for the development of new drug delivery systems. Here we fabricated the etofylline (ETO) encapsulated mannose-anchored N,N,N-trimethyl chitosan nanoparticles (Mn-TMC NPs). The prominent characteristics like biocompatibility, controlled release, targeted delivery, high penetrability, enhanced physical stability, and scalability mark Mn-TMC NPs as a viable alternative to various nanoplatform technologies for effective drug delivery. Mannosylation of TMC NPs leads to the evolution of new drug delivery vehicle with gratifying characteristics, and potential benefits in efficient drug therapy. It is widely accepted that following pulmonary administration, the introduction of mannose to the surface of drug nanocarriers provide selective macrophage targeting via receptor-mediated endocytosis. The fabricated Mn-TMC NPs exhibited particle size of 223.3 nm, PDI 0.490, and ζ-potential -19.1 mV, drug-loading capacity 76.26 ± 1.2%, and encapsulation efficiency of 91.75 ± 0.88%. Sustained drug release, biodegradation studies, stability, safety, and aerodynamic behavior revealed the effectiveness of prepared nanoformulation for pulmonary administration. In addition, the in vivo pharmacokinetic studies in Wistar rat model revealed a significant improvement in therapeutic efficacy of ETO, illustrating mannosylation a promising approach for efficient therapy of airway diseases following pulmonary administration.

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.

A review of Sulfur Mustard-induced pulmonary immunopathology: An Alveolar Macrophage Approach

Despite many studies investigating the mechanism of Sulfur Mustard (SM) induced lung injury, the underlying mechanism is still unclear. Inflammatory and subsequent fibroproliferative stages of SM-toxicity are based upon several highly-related series of events controlled by the immune system. The inhalation of SM gas variably affects different cell populations within the lungs. Various studies have shown the critical role of macrophages in triggering a pulmonary inflammatory response as well as its maintenance, resolution, and repair. Importantly, macrophages can serve as either pro-inflammatory or anti-inflammatory populations depending on the present conditions at any pathological stage. Different characteristics of macrophages, including their differentiation, phenotypic, and functional properties, as well as interactions with other cell populations determine the outcomes of lung diseases and the extent of long- or short-term pulmonary damage induced by SM. In this paper, we summarize the current state of knowledge regarding the role of alveolar macrophages and their mediators in the pathogenesis of SM in pulmonary injury. Investigating the specific cells and mechanisms involved in SM-lung injury may be useful in finding new target opportunities for treatment of this injury.

Development of chronic lung injury and pulmonary fibrosis in mice following acute exposure to nitrogen mustard

Objective: Sulfur mustards are toxic agents used as a chemical warfare in the twentieth century. Exposure to nitrogen mustards (NM), their more water-soluble analogs, is associated with respiratory, dermatological, neurological, and systemic symptoms whose severity depends on dose and length of contact. Long-term effects of acute inhalation have been related to the development of chronic lung injury and pulmonary fibrosis whose precise mechanisms and potential antidotes are yet to be discovered.Materials and methods: We have developed a model of NM-induced pulmonary fibrosis by intratracheally instilling mechlorethamine hydrochloride into C57Bl/6J male mice.Results and Discussion: Following mechlorethamine exposure, strong early and milder late inflammatory responses were observed. Initially, the number of white blood cells and levels of protein and pro-inflammatory cytokines in the bronchoalveolar lavage fluid (BALF) increased, followed by increases in the number of macrophages and the levels of transforming growth factor-β (TGF-β), a pro-fibrotic mediator. Analysis of lung homogenates revealed increased phosphorylation of pro-fibrotic biomarkers, serine/threonine-selective protein kinases (p-ERK), and heat shock protein 90 (P-HSP90) at 10 and 30 days after exposure. Total collagen expression and deposition of extracellular matrix proteins also increased. Lung function measurements demonstrated the presence of both obstructive and restrictive disease in agreement with evidence of increased lower airway peribronchial collagen deposition and parenchymal fibrosis.Conclusions: We conclude that the mouse represents a useful model of NM-induced acute lung injury and chronic pulmonary fibrosis, the latter driven by the overexpression of TGF-β, p-ERK, and P-HSP90. This model may prove useful in the pre-clinical development of antidotes and other countermeasures.

Long-term Respiratory Effects of Mustard Vesicants

Sulfur mustard and related vesicants are cytotoxic alkylating agents that cause severe damage to the respiratory tract. Injury is progressive leading, over time, to asthma, bronchitis, bronchiectasis, airway stenosis, and pulmonary fibrosis. As there are no specific therapeutics available for victims of mustard gas poisoning, current clinical treatments mostly provide only symptomatic relief. In this article, the long-term effects of mustards on the respiratory tract are described in humans and experimental animal models in an effort to define cellular and molecular mechanisms contributing to lung injury and disease pathogenesis. A better understanding of mechanisms underlying pulmonary toxicity induced by mustards may help in identifying potential targets for the development of effective clinical therapeutics aimed at mitigating their adverse effects.

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.

Ameliorative effects of silymarin on HCl-induced acute lung injury in rats; role of the Nrf-2/HO-1 pathway

OBJECTIVES

Aspiration is a common cause of acute lung injury (ALI), which lacks an effective treatment. Inflammation and oxidative stress play key roles in ALI development. Silymarin is an active extract of Silybum marianum plant seeds (milk thistle). Silymarin has potent anti-inflammatory and antioxidant effects; however its role in aspiration induced ALI has not been investigated. The aim of this study is to investigate the role of silymarin in the treatment of hydrochloric acid (HCl) aspiration induced ALI and explores its mechanisms of action.

MATERIALS AND METHODS

The study included three groups of rats: Control non-treated group, ALI group (intra-tracheal HCl injected), and silymarin treated ALI group. White blood cells (WBCs) with differential count, oxidative stress parameters, B-cell lymphoma 2 (Bcl-2), transforming growth factor-beta (TGF-β), cyclooxygenase 2 (COX-2), nuclear factor erythroid 2-related factor-2 (Nrf-2), and heme oxygenase-1 (HO-1) were investigated. Lung tissue histopathology and immunohistochemical expression of survivin and proliferating cell nuclear antigen (PCNA) were also examined.

RESULTS

The results of the study showed that HCL caused histopathological changes in ALI with leukocytopenia and increased oxidative stress biomarkers. It increased TGF-β, up-regulated mRNA expression of COX-2, Nrf-2, and HO-1 and increased survivin and PCNA but decreased Bcl-2. Silymarin ameliorated the histopathological lung injury with further up-regulation of Nrf-2 and HO-1 mRNA and decreased the inflammatory and fibrotic parameters together with up-regulation of the anti-apoptotic and the proliferation parameters.

CONCLUSION

The protective effect of silymarin against ALI is mediated by Nrf-2/HO-1 pathway with subsequent antioxidant, anti-inflammatory, antiapoptotic, and proliferating activities.

The immunomodulatory effects of mesenchymal stem cells on long term pulmonary complications in an animal model exposed to a sulfur mustard analog

INTRODUCTION

Sulfur Mustard (SM) is one of the most lethal chemicals with major complications manifested in the lungs. Although the pathogenesis behind SM-induced lung injury still remains poorly understood, prolonged activation and the imbalance of two major macrophage populations (M1 and M2) have been suggested to be involved. Here, we tried to investigate the effectiveness of adipose-derived mesenchymal stem cells (AD-MSC) on long-term lesions induced by CEES, an SM analog. The modulation of pulmonary immune cells and alveolar macrophage phenotype alteration was studied in the animal model used.

METHODS

Histopathological changes were investigated in the lungs and analysis of surface markers of alveolar macrophages as well as their cytokine expression in the BAL fluid was carried out by flow cytometry and ELISA, respectively.

RESULTS

Treatment of mice with AD-MSC after intraperitoneal administration of CEES (10 mg/kg) reduces progressive histopathologic changes in the lung. Flow cytometric analysis of isolated alveolar macrophages in the bronchoalveolar lavage showed that the accumulation of both M1 and M2 macrophages in response to CEES was reduced by MSC administration. AD-MSCs caused a marked reduction in the CD86- and CD206-expressing macrophages compared to the untreated groups. The modulating effect of AD-MSCs in the M1-subset was much more significant compared to M2. These findings suggest that AD-MSCs understand their environment and restore the balance in disorders associated with Th1 or Th2 imbalance. Our results indicate that MSCs may represent an effective approach to repair lung injury induced by mustards.

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.

Effects of treatment with gold nanoparticles in a model of acute pulmonary inflammation induced by lipopolysaccharide

The bacterial lipopolysaccharide (LPS) is a highly toxic molecule derived from the outer membrane of gram-negative bacteria. LPS endotoxin affects the lungs and is used as a model of acute pulmonary inflammation affecting the cellular morphology of the organ. Previously, gold nanoparticles (GNPs) have been shown to demonstrate anti-inflammatory and antioxidative activity in muscle and epithelial injury models. The objective of this study was to investigate the effect of the intraperitoneal treatment using GNPs on the inflammatory response and pulmonary oxidative stress induced by LPS. Wistar rats were divided into four groups (N = 10): Sham; Sham + GNPs 2.5 mg/kg; LPS; and LPS + GNPs 2.5 mg/kg. Treatment with LPS upregulated the levels of markers of cellular and hepatic damage (CK, LDH, AST, and alanine aminotransferase); however, the group treated with only GNPs exhibited no toxicity. Treatment with GNPs reversed LPS-induced changes with respect to total peritoneal leukocyte count and the pulmonary levels of pro-inflammatory cytokines (IFN-γ and IL-6). Histological analysis revealed that treatment with GNPs reversed the increase in alveolar septum thickness due to LPS-induced fibrosis. In addition, treatment with GNPs decreased production of oxidants (nitrite and DCFH), reduced oxidative damage (carbonyl and sulfhydryl), and downregulated activities of superoxide dismutase and catalase. Treatment with GNPs did not showed toxicity; however, it exhibited anti-inflammatory and antioxidative activity that reversed morphological alterations induced by LPS.

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.

Xuebijing injection attenuates pulmonary injury by reducing oxidative stress and proinflammatory damage in rats with heat stroke

The present study aimed to investigate the protective effect of Xuebijing injection (XBJ) on lung injury in heat-stroke rats and the underlying mechanisms. In total, 54 rats were randomly assigned to non-thermal, saline vehicle and XBJ groups. The rectal temperature (Tc), mean arterial pressure (MAP) and respiratory rate (RR) of the rats were recorded. The time-point of heat stroke and the time of survival were assessed, and indicators of arterial blood gas were regularly measured from 0 to 60 min. The concentration of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-10 was also determined. At the end of the experiment, lung tissue was harvested for histopathological analysis. Inducible nitric oxide synthase (iNOS) and superoxide dismutase (SOD) expression was measured by immunohistochemistry. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling was used to measure apoptosis. XBJ pretreatment prolonged the decline of clinical characteristics, as demonstrated by increases in Tc, MAP, RR and indicators in arterial blood gas in rats under heat stress. The time until heat stroke and the survival time in the Saline group were shorter than in rats treated with XBJ. The expression of iNOS in lung tissue and the concentration of TNF-α, IL-1β and IL-10 in the bronchoalveolar lavage fluid of rats treated with saline was higher than in rats with XBJ pre-treatment. Contrarily, SOD expression in rats treated with saline was decreased compared with that in rats treated with XBJ. Moreover, the apoptotic rate in the lung tissues of rats with saline treatment was higher than that in rats treated with XBJ. In conclusion, XBJ delayed the development of heat stroke and increased the survival time in rats under heat-stress by ameliorating pulmonary failure and acute lung injury. The underlying mechanisms of this effect may be the reduction of inflammatory cytokines as well as attenuation of oxidative stress and apoptosis by XBJ.

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.

Extracellular matrix remodeling in idiopathic pulmonary fibrosis. It is the 'bed' that counts and not 'the sleepers'

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disease characterized by irreversible fibrosis. Current disease pathogenesis assumes an aberrant wound healing process in response to repetitive injurious stimuli leading to apoptosis of epithelial cells, activation of fibroblasts and accumulation of extracellular matrix (ECM). Particularly, lung ECM is a highly dynamic structure that lies at the core of several physiological and developmental pathways. The scope of this review article is to summarize current knowledge on the role of ECM in the pathogenesis of IPF, unravel novel mechanistic data and identify future more effective therapeutic targets. Areas covered: The exact mechanisms through which lung microenvironment activates fibroblasts and inflammatory cells, regulates profibrotic signaling cascades through growth factors, integrins and degradation enzymes ultimately leading to excessive matrix deposition are discussed. Furthermore, the potential therapeutic usefulness of specific inhibitors of matrix deposition or activators of matrix degradation pathways are also presented. Expert commentary: With a gradually increasing worldwide incidence IPF still present a major challenge in clinical research due to its unknown etiopathogenesis and current ineffective treatment approaches. Today, there is an amenable need for more effective therapeutic targets and ECM components may represent one.

Mustard vesicant-induced lung injury: Advances in therapy

Most mortality and morbidity following exposure to vesicants such as sulfur mustard is due to pulmonary toxicity. Acute injury is characterized by epithelial detachment and necrosis in the pharynx, trachea and bronchioles, while long-term consequences include fibrosis and, in some instances, cancer. Current therapies to treat mustard poisoning are primarily palliative and do not target underlying pathophysiologic mechanisms. New knowledge about vesicant-induced pulmonary disease pathogenesis has led to the identification of potentially efficacious strategies to reduce injury by targeting inflammatory cells and mediators including reactive oxygen and nitrogen species, proteases and proinflammatory/cytotoxic cytokines. Therapeutics under investigation include corticosteroids, N-acetyl cysteine, which has both mucolytic and antioxidant properties, inducible nitric oxide synthase inhibitors, liposomes containing superoxide dismutase, catalase, and/or tocopherols, protease inhibitors, and cytokine antagonists such as anti-tumor necrosis factor (TNF)-α antibody and pentoxifylline. Antifibrotic and fibrinolytic treatments may also prove beneficial in ameliorating airway obstruction and lung remodeling. More speculative approaches include inhibitors of transient receptor potential channels, which regulate pulmonary epithelial cell membrane permeability, non-coding RNAs and mesenchymal stem cells. As mustards represent high priority chemical threat agents, identification of effective therapeutics for mitigating toxicity is highly significant.

Macrophages and inflammatory mediators in pulmonary injury induced by mustard vesicants

Sulfur mustard (SM) and nitrogen mustard (NM) are cytotoxic alkylating agents that cause severe and progressive injury to the respiratory tract, resulting in significant morbidity and mortality. Evidence suggests that macrophages and the inflammatory mediators they release play roles in both acute and long-term pulmonary injuries caused by mustards. In this article, we review the pathogenic effects of SM and NM on the respiratory tract and potential inflammatory mechanisms contributing to this activity.

Emerging targets for treating sulfur mustard-induced injuries

Sulfur mustard (SM; bis-(2-chlororethyl) sulfide) is a highly reactive, potent warfare agent that has recently reemerged as a major threat to military and civilians. Exposure to SM is often fatal, primarily due to pulmonary injuries and complications caused by its inhalation. Profound inflammation, hypercoagulation, and oxidative stress are the hallmarks that define SM-induced pulmonary toxicities. Despite advances, effective therapies are still limited. This current review focuses on inflammatory and coagulation pathways that influence the airway pathophysiology of SM poisoning and highlights the complexity of developing an effective therapeutic target.

Early indicators of survival following exposure to mustard gas: Protective role of 25(OH)D

The use of sulfur mustard (SM) as a chemical weapon for warfare has once again assumed center stage, endangering civilian and the military safety. SM causes rapid local skin vesication and late-onset systemic toxicity. Most studies on SM rely on obtaining tissue and blood for characterizing burn pathogenesis and assessment of systemic pathology, respectively. However the present study focuses on developing a non-invasive method to predict mortality from high dose skin SM exposure. We demonstrate that exposure to SM leads to a dose dependent increase in wound area size on the dorsal surface of mice that is accompanied by a progressive loss in body weight loss, blood cytopenia, bone marrow destruction, and death. Thus our model utilizes local skin destruction and systemic outcome measures as variables to predict mortality in a novel skin-based model of tissue injury. Based on our recent work using vitamin D (25(OH)D) as an intervention to treat toxicity from SM-related compounds, we explored the use of 25 (OH)D in mitigating the toxic effects of SM. Here we show that 25(OH)D offers protection against SM and is the first known demonstration of an intervention that prevents SM-induced mortality. Furthermore, 25 (OH)D represents a safe, novel, and readily translatable potential countermeasure following mass toxic exposure.

Characterization of Distinct Macrophage Subpopulations during Nitrogen Mustard-Induced Lung Injury and Fibrosis

Nitrogen mustard (NM) is an alkylating agent known to cause extensive pulmonary injury progressing to fibrosis. This is accompanied by a persistent macrophage inflammatory response. In these studies, we characterized the phenotype of macrophages accumulating in the lung over time following NM exposure. Treatment of rats with NM (0.125 mg/kg, intratracheally) resulted in an increase in CD11b(+) macrophages in histologic sections. These cells consisted of inducible nitric oxide synthase(+) (iNOS) proinflammatory M1 macrophages, and CD68(+), CD163(+), CD206(+), YM-1(+), and arginase-II(+)antiinflammatory M2 macrophages. Although M1 macrophages were prominent 1-3 days after NM, M2 macrophages were most notable at 28 days. At this time, they were enlarged and vacuolated, consistent with a profibrotic phenotype. Flow cytometric analysis of isolated lung macrophages identified three phenotypically distinct subpopulations: mature CD11b(-), CD43(-), and CD68(+) resident macrophages, which decreased in numbers after NM; and two infiltrating (CD11b(+)) macrophage subsets: immature CD43(+) M1 macrophages and mature CD43(-) M2 macrophages, which increased sequentially. Time-related increases in M1 (iNOS, IL-12α, COX-2, TNF-α, matrix metalloproteinase-9, matrix metalloproteinase-10) and M2 (IL-10, pentraxin-2, connective tissue growth factor, ApoE) genes, as well as chemokines/chemokine receptors associated with trafficking of M1 (CCR2, CCR5, CCL2, CCL5) and M2 (CX3CR1, fractalkine) macrophages to sites of injury, were also noted in macrophages isolated from the lung after NM. The appearance of M1 and M2 macrophages in the lung correlated with NM-induced acute injury and the development of fibrosis, suggesting a potential role of these macrophage subpopulations in the pathogenic response to NM.

Suppression of Hyperactive Immune Responses Protects against Nitrogen Mustard Injury

DNA alkylating agents like nitrogen mustard (NM) are easily absorbed through the skin and exposure to such agents manifest not only in direct cellular death but also in triggering inflammation. We show that toxicity resulting from topical mustard exposure is mediated in part by initiating exaggerated host innate immune responses. Using an experimental model of skin exposure to NM we observe activation of inflammatory dermal macrophages that exacerbate local tissue damage in an inducible nitric oxide synthase (iNOS)-dependent manner. Subsequently these activated dermal macrophages reappear in the bone marrow to aid in disruption of hematopoiesis and contribute ultimately to mortality in an experimental mouse model of topical NM exposure. Intervention with a single dose of 25-hydroxyvitamin D3 (25(OH)D) is capable of suppressing macrophage-mediated iNOS production resulting in mitigation of local skin destruction, enhanced tissue repair, protection from marrow depletion, and rescue from severe precipitous wasting. These protective effects are recapitulated experimentally using pharmacological inhibitors of iNOS or by compounds that locally deplete skin macrophages. Taken together, these data highlight a critical unappreciated role of the host innate immune system in exacerbating injury following exposure to NM and support the translation of 25(OH)D in the therapeutic use against these chemical agents.

Inflammatory mechanisms of pulmonary injury induced by mustards

Exposure of humans and animals to vesicants, including sulfur mustard (SM) and nitrogen mustard (NM), causes severe and debilitating damage to the respiratory tract. Both acute and long term pathological consequences are observed in the lung following a single exposure to these vesicants. Evidence from our laboratories and others suggest that macrophages and the inflammatory mediators they release play an important role in mustard-induced lung injury. In this paper, the pathogenic effects of SM and NM on the lung are reviewed, along with the potential role of inflammatory macrophages and mediators they release in mustard-induced pulmonary toxicity.

Thioredoxin Cross-Linking by Nitrogen Mustard in Lung Epithelial Cells: Formation of Multimeric Thioredoxin/Thioredoxin Reductase Complexes and Inhibition of Disulfide Reduction

The thioredoxin (Trx) system, which consists of Trx and thioredoxin reductase (TrxR), is a major cellular disulfide reduction system important in antioxidant defense. TrxR is a target of mechlorethamine (methylbis(2-chloroethyl)amine; HN2), a bifunctional alkylating agent that covalently binds to selenocysteine/cysteine residues in the redox centers of the enzyme, leading to inactivation and toxicity. Mammalian Trx contains two catalytic cysteines; herein, we determined if HN2 also targets Trx. HN2 caused a time- and concentration-dependent inhibition of purified Trx and Trx in A549 lung epithelial cells. Three Trx cross-linked protein complexes were identified in both cytosolic and nuclear fractions of HN2-treated cells. LC-MS/MS of these complexes identified both Trx and TrxR, indicating that HN2 cross-linked TrxR and Trx. This is supported by our findings of a significant decrease of Trx/TrxR complexes in cytosolic TrxR knockdown cells after HN2 treatment. Using purified recombinant enzymes, the formation of protein cross-links and enzyme inhibition were found to be redox status-dependent; reduced Trx was more sensitive to HN2 inactivation than the oxidized enzyme, and Trx/TrxR cross-links were only observed using reduced enzyme. These data suggest that HN2 directly targets catalytic cysteine residues in Trx resulting in enzyme inactivation and protein complex formation. LC-MS/MS confirmed that HN2 directly alkylated cysteine residues on Trx, including Cys32 and Cys35 in the redox center of the enzyme. Inhibition of the Trx system by HN2 can disrupt cellular thiol-disulfide balance, contributing to vesicant-induced lung toxicity.

Protective role of spleen-derived macrophages in lung inflammation, injury, and fibrosis induced by nitrogen mustard

Nitrogen mustard (NM) is a vesicant that causes lung injury and fibrosis, accompanied by a persistent macrophage inflammatory response. In these studies we analyzed the spleen as a source of these cells. Splenectomized (SPX) and sham control rats were treated intratracheally with NM (0.125 mg/kg) or PBS control. Macrophage responses were analyzed 1-7 days later. Splenectomy resulted in an increase in lung macrophages expressing CCR2, but a decrease in ATR-1α(+) cells, receptors important in bone marrow and spleen monocyte trafficking, respectively. Splenectomy was also associated with an increase in proinflammatory M1 (iNOS(+), CD11b(+)CD43(+)) macrophages in lungs of NM-treated rats, as well as greater upregulation of iNOS and COX-2 mRNA expression. Conversely, a decrease in CD11b(+)CD43(-) M2 macrophages was observed in SPX rats, with no changes in CD68(+), CD163(+), CD206(+), or YM-1(+) M2 macrophages, suggesting distinct origins of M2 subpopulations responding to NM. Macrophage expression of M2 genes including IL-10, ApoE, PTX-2, PTX-3, 5-HT2α, and 5-HT7 was also reduced in NM-treated SPX rats compared with shams, indicating impaired M2 activity. Changes in lung macrophages responding to NM as a consequence of splenectomy were correlated with exacerbated tissue injury and more rapid fibrogenesis. These data demonstrate that the spleen is a source of a subset of M2 macrophages with anti-inflammatory activity; moreover, in their absence, proinflammatory/cytotoxic M1 macrophages predominate in the lung, resulting in heightened pathology. Understanding the origin of macrophages and characterizing their phenotype after vesicant exposure may lead to more targeted therapeutics aimed at reducing toxicity and disease pathogenesis.

Attenuation of Nitrogen Mustard-Induced Pulmonary Injury and Fibrosis by Anti-Tumor Necrosis Factor-α Antibody

Nitrogen mustard (NM) is a bifunctional alkylating agent that causes acute injury to the lung that progresses to fibrosis. This is accompanied by a prominent infiltration of macrophages into the lung and upregulation of proinflammatory/profibrotic cytokines including tumor necrosis factor (TNF)α. In these studies, we analyzed the ability of anti-TNFα antibody to mitigate NM-induced lung injury, inflammation, and fibrosis. Treatment of rats with anti-TNFα antibody (15 mg/kg, iv, every 9 days) beginning 30 min after intratracheal administration of NM (0.125 mg/kg) reduced progressive histopathologic alterations in the lung including perivascular and peribronchial edema, macrophage/monocyte infiltration, interstitial thickening, bronchiolization of alveolar walls, fibrin deposition, emphysema, and fibrosis. NM-induced damage to the alveolar-epithelial barrier, measured by bronchoalveolar lavage (BAL) protein and cell content, was also reduced by anti-TNFα antibody, along with expression of the oxidative stress marker, heme oxygenase-1. Whereas the accumulation of proinflammatory/cytotoxic M1 macrophages in the lung in response to NM was suppressed by anti-TNFα antibody, anti-inflammatory/profibrotic M2 macrophages were increased or unchanged. Treatment of rats with anti-TNFα antibody also reduced NM-induced increases in expression of the profibrotic mediator, transforming growth factor-β. This was associated with a reduction in NM-induced collagen deposition in the lung. These data suggest that inhibiting TNFα may represent an efficacious approach to mitigating lung injury induced by mustards.

Nitrogen mustard hydrochloride-induced acute respiratory failure and myelosuppression: A case report

Nitrogen mustards are chemical agents that are similar to sulfur mustards, with similar toxicities. The present study describes a case of nitrogen mustard-induced acute respiratory failure and myelosuppression in a 33-year-old man. The patient, who was accidentally exposed to nitrogen mustard hydrochloride in a pharmaceutical factory, exhibited severe inhalation injury and respiratory symptoms. Laboratory tests revealed reduced white blood cell counts and lowered platelet levels during the first 6 days after the skin exposure to nitrogen mustard. Following treatment with mechanical ventilation, immunity-enhancing agents and nutritional supplements for 1 month, the patient successfully recovered and was released from hospital.

Regulation of ozone-induced lung inflammation and injury by the β-galactoside-binding lectin galectin-3

Macrophages play a dual role in ozone toxicity, contributing to both pro- and anti-inflammatory processes. Galectin-3 (Gal-3) is a lectin known to regulate macrophage activity. Herein, we analyzed the role of Gal-3 in the response of lung macrophages to ozone. Bronchoalveolar lavage (BAL) and lung tissue were collected 24-72h after exposure (3h) of WT and Gal-3(-/-) mice to air or 0.8ppm ozone. In WT mice, ozone inhalation resulted in increased numbers of proinflammatory (Gal-3(+), iNOS(+)) and anti-inflammatory (MR-1(+)) macrophages in the lungs. While accumulation of iNOS(+) macrophages was attenuated in Gal-3(-/-) mice, increased numbers of enlarged MR-1(+) macrophages were noted. This correlated with increased numbers of macrophages in BAL. Flow cytometric analysis showed that these cells were CD11b(+) and consisted mainly (>97%) of mature (F4/80(+)CD11c(+)) proinflammatory (Ly6GLy6C(hi)) and anti-inflammatory (Ly6GLy6C(lo)) macrophages. Increases in both macrophage subpopulations were observed following ozone inhalation. Loss of Gal-3 resulted in a decrease in Ly6C(hi) macrophages, with no effect on Ly6C(lo) macrophages. CD11b(+)Ly6G(+)Ly6C(+) granulocytic (G) and monocytic (M) myeloid derived suppressor cells (MDSC) were also identified in the lung after ozone. In Gal-3(-/-) mice, the response of G-MDSC to ozone was attenuated, while the response of M-MDSC was heightened. Changes in inflammatory cell populations in the lung of ozone treated Gal-3(-/-) mice were correlated with reduced tissue injury as measured by cytochrome b5 expression. These data demonstrate that Gal-3 plays a role in promoting proinflammatory macrophage accumulation and toxicity in the lung following ozone exposure.

Nω-NITRO-Nω'-SUBSTITUTED GUANIDINES: A SIMPLE CLASS OF NITRIC OXIDE SYNTHASE INHIBITORS

A series of N^ω-nitro-N^ω'-substituted guanidines has been prepared as potential inhibitors of the human Nitric Oxide Synthase (NOS) isoforms. The reported utility of aminoguanidine and nitroarginine in iNOS inhibition points to a potential similar utility for analogs of nitro-guanidine. The compound library was tested against the three isoforms of Nitric Oxide Synthase (eNOS, iNOS and nNOS). Several candidates showed excellent activity and good selectivity for nNOS. One particular compound even demonstrated good selectivity for iNOS. The potential usefulness of such selective inhibitors is discussed.

Pentoxifylline attenuates nitrogen mustard-induced acute lung injury, oxidative stress and inflammation

Nitrogen mustard (NM) is a toxic alkylating agent that causes damage to the respiratory tract. Evidence suggests that macrophages and inflammatory mediators including tumor necrosis factor (TNF)α contribute to pulmonary injury. Pentoxifylline is a TNFα inhibitor known to suppress inflammation. In these studies, we analyzed the ability of pentoxifylline to mitigate NM-induced lung injury and inflammation. Exposure of male Wistar rats (150-174 g; 8-10 weeks) to NM (0.125 mg/kg, i.t.) resulted in severe histopathological changes in the lung within 3d of exposure, along with increases in bronchoalveolar lavage (BAL) cell number and protein, indicating inflammation and alveolar-epithelial barrier dysfunction. This was associated with increases in oxidative stress proteins including lipocalin (Lcn)2 and heme oxygenase (HO)-1 in the lung, along with pro-inflammatory/cytotoxic (COX-2(+) and MMP-9(+)), and anti-inflammatory/wound repair (CD163+ and Gal-3(+)) macrophages. Treatment of rats with pentoxifylline (46.7 mg/kg, i.p.) daily for 3d beginning 15 min after NM significantly reduced NM-induced lung injury, inflammation, and oxidative stress, as measured histologically and by decreases in BAL cell and protein content, and levels of HO-1 and Lcn2. Macrophages expressing COX-2 and MMP-9 also decreased after pentoxifylline, while CD163+ and Gal-3(+) macrophages increased. This was correlated with persistent upregulation of markers of wound repair including pro-surfactant protein-C and proliferating nuclear cell antigen by Type II cells. NM-induced lung injury and inflammation were associated with alterations in the elastic properties of the lung, however these were largely unaltered by pentoxifylline. These data suggest that pentoxifylline may be useful in treating acute lung injury, inflammation and oxidative stress induced by vesicants.

The protective effect of melatonin and S-methylisothiourea treatments in nitrogen mustard induced lung toxicity in rats

OBJECTIVES

Mustard is highly toxic to the lung. Its toxic effects are associated with inflammatory cell accumulation and increased pro-inflammatory cytokines as well as reactive oxygen and nitrogen species. In this study, we aimed to investigate the efficiency of melatonin (MEL) and S-methylisothiourea (SMT) on mechlorethamine (MEC) induced lung toxicity.

METHODS

Thirty-six male rats were randomly divided into four groups: control, MEC, MEC+MEL, and MEC+SMT. Control group was given saline only via transdermal route. Other groups were exposured to a single dose of MEC (3.5 mg/kg) via transdermal route. MEL (100 mg/kg) was administered intraperitoneally 30 min after the application of MEC, and after the same dose of MEL was given every 12 h for a total of six doses. SMT (50 mg/kg) was also given intraperitoneally 30 min after the application of MEC.

RESULTS

MEC injection resulted in alveolar epithelial injury, hemorrhage, inflammation, edema and interalveolar septal thickening in the lung tissues. The tissue TNF-α, IL-1β, and nitrate/nitrite (NOx) levels were found significantly different for all groups (p<0.001). TNF-α and IL-1β levels increased significantly with MEC exposure, and MEL and SMT ameliorated these increases in lung tissues. MEC also elevated NOx levels in lung tissue. Melatonin showed meaningful protection against lung injury. But protection of SMT was weaker.

CONCLUSION

Inflammation plays an important role in the MEC induced lung toxicity as well as oxidative and nitrosative stress. Melatonin has also anti-inflammatory properties similar to SMT, as well as anti-oxidant properties. But melatonin treatment was found more efficient than SMT treatment.

The generation of 4-hydroxynonenal, an electrophilic lipid peroxidation end product, in rabbit cornea organ cultures treated with UVB light and nitrogen mustard

The cornea is highly sensitive to oxidative stress, a process that can lead to lipid peroxidation. Ultraviolet light B (UVB) and nitrogen mustard (mechlorethamine) are corneal toxicants known to induce oxidative stress. Using a rabbit air-lifted corneal organ culture model, the oxidative stress responses to these toxicants in the corneal epithelium was characterized. Treatment of the cornea with UVB (0.5 J/cm(2)) or nitrogen mustard (100 nmol) resulted in the generation of 4-hydroxynonenal (4-HNE), a reactive lipid peroxidation end product. This was associated with increased expression of the antioxidant, heme oxygenase-1 (HO-1). In human corneal epithelial cells in culture, addition of 4-HNE or 9-nitrooleic acid, a reactive nitrolipid formed during nitrosative stress, caused a time-dependent induction of HO-1 mRNA and protein; maximal responses were evident after 10h with 30 μM 4-HNE or 6h with 10 μM 9-nitrooleic acid. 4-HNE and 9-nitrooleic acid were also found to activate Erk1/2, JNK and p38 MAP kinases, as well as phosphoinositide-3-kinase (PI3)/Akt. Inhibition of p38 blocked 4-HNE- and 9-nitrooleic acid-induced HO-1 expression. Inhibition of Erk1/2, and to a lesser extent, JNK and PI3K/Akt, suppressed only 4-HNE-induced HO-1, while inhibition of JNK and PI3K/Akt, but not Erk1/2, partly reduced 9-nitrooleic acid-induced HO-1. These data indicate that the actions of 4-HNE and 9-nitrooleic acid on corneal epithelial cells are distinct. The sensitivity of corneal epithelial cells to oxidative stress may be an important mechanism mediating tissue injury induced by UVB or nitrogen mustard.

Rat models of acute lung injury: exhaled nitric oxide as a sensitive, noninvasive real-time biomarker of prognosis and efficacy of intervention

Exhaled nitric oxide (eNO) has received increased attention in clinical settings because this technique is easy to use with instant readout. However, despite the simplicity of eNO in humans, this endpoint has not frequently been used in experimental rat models of septic (endotoxemia) or irritant acute lung injury (ALI). The focus of this study is to adapt this method to rats for studying ALI-related lung disease and whether it can serve as instant, non-invasive biomarker of ALI to study lung toxicity and pharmacological efficacy. Measurements were made in a dynamic flow of sheath air containing the exhaled breath from spontaneously breathing, conscious rats placed into a head-out volume plethysmograph. The quantity of eNO in exhaled breath was adjusted (normalized) to the physiological variables (breathing frequency, concentration of exhaled carbon dioxide) mirroring pulmonary perfusion and ventilation. eNO was examined on the instillation/inhalation exposure day and first post-exposure day in Wistar rats intratracheally instilled with lipopolysaccharide (LPS) or single inhalation exposure to chlorine or phosgene gas. eNO was also examined in a Brown Norway rat asthma model using the asthmagen toluene diisocyanate (TDI). The diagnostic sensitivity of adjusted eNO was superior to the measurements not accounting for the normalization of physiological variables. In all bioassays - whether septic, airway or alveolar irritant or allergic, the adjusted eNO was significantly increased when compared to the concurrent control. The maximum increase of the adjusted eNO occurred following exposure to the airway irritant chlorine. The specificity of adjustment was experimentally verified by decreased eNO following inhalation dosing of the non-selective nitric oxide synthase inhibitor amoniguanidine. In summary, the diagnostic sensitivity of eNO can readily be applied to spontaneously breathing, conscious rats without any intervention or anesthesia. Measurements are definitely improved by accounting for the disease-related changes in exhaled CO2 and breathing frequency. Accordingly, adjusted eNO appears to be a promising methodological improvement for utilizing eNO in inhalation toxicology and pharmacological disease models with fewer animals.