Mustard vesicant-induced lung injury: Advances in therapy

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.

Overlapping Science in Radiation and Sulfur Mustard Exposures of Skin and Lung: Consideration of Models, Mechanisms, Organ Systems, and Medical Countermeasures: Overlapping science in radiation and sulfur mustard injuries to lung and skin

PURPOSE

To summarize presentations and discussions from the 2022 trans-agency workshop titled "Overlapping science in radiation and sulfur mustard (SM) exposures of skin and lung: Consideration of models, mechanisms, organ systems, and medical countermeasures."

METHODS

Summary on topics includes: (1) an overview of the radiation and chemical countermeasure development programs and missions; (2) regulatory and industry perspectives for drugs and devices; 3) pathophysiology of skin and lung following radiation or SM exposure; 4) mechanisms of action/targets, biomarkers of injury; and 5) animal models that simulate anticipated clinical responses.

RESULTS

There are striking similarities between injuries caused by radiation and SM exposures. Primary outcomes from both types of exposure include acute injuries, while late complications comprise chronic inflammation, oxidative stress, and vascular dysfunction, which can culminate in fibrosis in both skin and lung organ systems. This workshop brought together academic and industrial researchers, medical practitioners, US Government program officials, and regulators to discuss lung-, and skin- specific animal models and biomarkers, novel pathways of injury and recovery, and paths to licensure for products to address radiation or SM injuries.

CONCLUSIONS

Regular communications between the radiological and chemical injury research communities can enhance the state-of-the-science, provide a unique perspective on novel therapeutic strategies, and improve overall US Government emergency preparedness.

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.

MG53 Mitigates Nitrogen Mustard-Induced Skin Injury

Sulfur mustard (SM) and nitrogen mustard (NM) are vesicant agents that cause skin injury and blistering through complicated cellular events, involving DNA damage, free radical formation, and lipid peroxidation. The development of therapeutic approaches targeting the multi-cellular process of tissue injury repair can potentially provide effective countermeasures to combat vesicant-induced dermal lesions. MG53 is a vital component of cell membrane repair. Previous studies have demonstrated that topical application of recombinant human MG53 (rhMG53) protein has the potential to promote wound healing. In this study, we further investigate the role of MG53 in NM-induced skin injury. Compared with wild-type mice, mg53^-/- mice are more susceptible to NM-induced dermal injuries, whereas mice with sustained elevation of MG53 in circulation are resistant to dermal exposure of NM. Exposure of keratinocytes and human follicle stem cells to NM causes elevation of oxidative stress and intracellular aggregation of MG53, thus compromising MG53's intrinsic cell membrane repair function. Topical rhMG53 application mitigates NM-induced dermal injury in mice. Histologic examination reveals the therapeutic benefits of rhMG53 are associated with the preservation of epidermal integrity and hair follicle structure in mice with dermal NM exposure. Overall, these findings identify MG53 as a potential therapeutic agent to mitigate vesicant-induced skin injuries.

Evaluation of the effects of dexamethasone in modulating breathing pattern decomplexification in rats with 2-chloroethyl ethyl sulfide-induced lung injury

"Background and Objectives: Sulfur mustard is a functional alkylating chemical warfare agent that gives rise to appalling lung injury. In people with pulmonary diseases, including asthma, the complication of respirational dynamics is reduced. However, the complexity of breathing patterns in lung injury caused by chemical agents is not clear. In the current study, the outcome of 2-chloroethyl ethyl sulfide (CEES), and mustard analogue, upon breathing pattern of rats without or with treatment were reviewed. Methods: The interbeat interval (IBI) and respiratory volume (RV) data have been acquired from spontaneous respiration rats with lung injury by CEES using a whole-body plethysmograph. We calculated mean and coefficient of variation, alpha exponent derived from detrended fluctuation analysis (DFA), and sample entropy of IBI and RV. Finding: Entropy examination of respiratory variation displayed reduced inconsistency (less complication) in the breathing pattern of this rat model of lung injury. The mustard analogue also led to increased lung inflammation in damaged rats. However, treatment by NAC and dexamethasone had a compelling impact on the complication of the breathing rhythm and lung inflammation of rats with lung injury. Conclusion: Our findings show that inflammation could be the possible origin of respiratory dynamics shifting apart from the normal variation in CEES-induced lung injury"

Impaired energy metabolism and altered functional activity of alveolar type II epithelial cells following exposure of rats to nitrogen mustard

Nitrogen mustard (NM) is a cytotoxic vesicant known to cause acute lung injury which progresses to fibrosis. Alveolar Type II cells are primarily responsible for surfactant production; they also play a key role in lung repair following injury. Herein, we assessed the effects of NM on Type II cell activity. Male Wistar rats were administered NM (0.125 mg/kg) or PBS control intratracheally. Type II cells, lung tissue and BAL were collected 3 d later. NM exposure resulted in double strand DNA breaks in Type II cells, as assessed by expression of γH2AX; this was associated with decreased expression of the DNA repair protein, PARP1. Expression of HO-1 was upregulated and nitrotyrosine residues were noted in Type II cells after NM exposure indicating oxidative stress. NM also caused alterations in Type II cell energy metabolism; thus, both glycolysis and oxidative phosphorylation were reduced; there was also a shift from a reliance on oxidative phosphorylation to glycolysis for ATP production. This was associated with increased expression of pro-apoptotic proteins activated caspase-3 and -9, and decreases in survival proteins, β-catenin, Nur77, HMGB1 and SOCS2. Intracellular signaling molecules important in Type II cell activity including PI3K, Akt2, phospho-p38 MAPK and phospho-ERK were reduced after NM exposure. This was correlated with dysregulation of surfactant protein production and impaired pulmonary functioning. These data demonstrate that Type II cells are targets of NM-induced DNA damage and oxidative stress. Impaired functioning of these cells may contribute to pulmonary toxicity caused by mustards.

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.

BMSC-derived exosomes ameliorate sulfur mustard-induced acute lung injury by regulating the GPRC5A-YAP axis

Sulfur mustard (SM) is a highly toxic chemical warfare agent that causes acute lung injury (ALI) and/or acute respiratory distress syndrome (ARDS). There are no effective therapeutic treatments or antidotes available currently to counteract its toxic effects. Our previous study shows that bone marrow-derived mesenchymal stromal cells (BMSCs) could exert therapeutic effects against SM-induced lung injury. In this study, we explored the therapeutic potential of BMSC-derived exosomes (BMSC-Exs) against ALI and the underlying mechanisms. ALI was induced in mice by injection of SM (30 mg/kg, sc) at their medial and dorsal surfaces. BMSC-Exs (20 μg/kg in 200 μL PBS, iv) were injected for a 5-day period after SM exposure. We showed that BMSC-Exs administration caused a protective effect against pulmonary edema. Using a lung epithelial cell barrier model, BMSC-Exs (10, 20, 40 μg) dose-dependently inhibited SM-induced cell apoptosis and promoted the recovery of epithelial barrier function by facilitating the expression and relocalization of junction proteins (E-cadherin, claudin-1, occludin, and ZO-1). We further demonstrated that BMSC-Exs protected against apoptosis and promoted the restoration of barrier function against SM through upregulating G protein-coupled receptor family C group 5 type A (GPRC5A), a retinoic acid target gene predominately expressed in the epithelial cells of the lung. Knockdown of GPRC5A reduced the antiapoptotic and barrier regeneration abilities of BMSC-Exs and diminished their therapeutic effects in vitro and in vivo. BMSC-Exs-caused upregulation of GPRC5A promoted the expression of Bcl-2 and junction proteins via regulating the YAP pathway. In summary, BMSC-Exs treatment exerts protective effects against SM-induced ALI by promoting alveolar epithelial barrier repair and may be an alternative approach to stem cell-based therapy.

Ultrasensitive surface-enhanced Raman spectroscopy detection of gaseous sulfur-mustard simulant based on thin oxide-coated gold nanocone arrays

Surface Enhanced Raman Spectroscopy (SERS) could be a powerful technique for detecting trace gaseous sulfur-mustard, but it is still challenging due to the difficulty in efficiently capturing sulfur-mustard molecules by normal SERS substrates. Here, a chemically trapping strategy is presented for such detection via coating an ultrathin metal-oxide sensing layer on a SERS substrate. In the strategy, a SERS substrate Au-wrapped Si nanocone array is designed and fabricated by Si wafer-based organic template-etching and appropriate Au deposition, and coated with an ultrathin CuO for chemically capturing sulfur-mustard molecules. The validity of such strategy has been demonstrated via taking the gaseous 2-chloroethyl ethyl sulfide (a simulant of sulfur-mustard, or 2-CEES for short) as the target molecules. The response of the CuO-coated SERS substrate to the gaseous 2-CEES is detectable within 10 min, and the lowest detectable concentration is 10 ppb or less. Further experiments have shown that there exists an optimal CuO coating thickness which is about 6 nm. The CuO coating-based capture of 2-CEES molecules is attributed to the surface hydroxyl-induced specific adsorption, which is subject to the pseudo-second-order kinetics and Freundlich-typed model. This study presents the practical SERS chips and new route for the trace detection of gaseous sulfur-mustard.

Advice on assistance and protection provided by the Scientific Advisory Board of the Organisation for the Prohibition of Chemical Weapons: Part 3. On medical care and treatment of injuries from sulfur mustard

Blister agents damage the skin, eyes, mucous membranes and subcutaneous tissues. Other toxic effects may occur after absorption. The response of the Scientific Advisory Board (SAB) of the Organisation for the Prohibition of Chemical Weapons (OPCW) to a request from the OPCW Director-General in 2013 on the status of medical countermeasures and treatments to blister agents is updated through the incorporation of the latest information. The physical and toxicological properties of sulfur mustard and clinical effects and treatments are summarised. The information should assist medics and emergency responders who may be unfamiliar with the toxidrome of sulfur mustard and its treatment.

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.

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.

Deciphering the role of microRNAs in mustard gas-induced toxicity

Mustard gas (sulfur mustard, SM), a highly vesicating chemical warfare agent, was first deployed in warfare in 1917 and recently during the Iraq-Iran war (1980s) and Syrian conflicts (2000s); however, the threat of exposure from stockpiles and old artillery shells still looms large. Whereas research has been long ongoing on SM-induced toxicity, delineating the precise molecular pathways is still an ongoing area of investigation; thus, it is important to attempt novel approaches to decipher these mechanisms and develop a detailed network of pathways associated with SM-induced toxicity. One such avenue is exploring the role of microRNAs (miRNAs) in SM-induced toxicity. Recent research on the regulatory role of miRNAs provides important results to fill in the gaps in SM toxicity-associated mechanisms. In addition, differentially expressed miRNAs can also be used as diagnostic markers to determine the extent of toxicity in exposed individuals. Thus, in our review, we have summarized the studies conducted so far in cellular and animal models, including human subjects, on the expression profiles and roles of miRNAs in SM- and/or SM analog-induced toxicity. Further detailed research in this area will guide us in devising preventive strategies, diagnostic tools, and therapeutic interventions against SM-induced toxicity.

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.

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.

The HSP90 Inhibitor, AUY-922, Ameliorates the Development of Nitrogen Mustard-Induced Pulmonary Fibrosis and Lung Dysfunction in Mice

Increased levels of heat shock protein 90 (HSP90) have been recently implicated in the pathogenesis of pulmonary fibrosis and the use of HSP90 inhibitors constitutes a potential therapeutic approach. Similarly, acute exposure to nitrogen mustard (NM) is related to the development of chronic lung injury driven by TNF-α, TGF-β, ERK and HSP90. Thus, we developed a murine model of NM-induced pulmonary fibrosis by instilling C57BI/6J mice with 0.625 mg/kg mechlorethamine hydrochloride. After 24 h, mice began receiving AUY-922, a second generation HSP90 inhibitor, at 1 mg/kg 2 times per week or 2 mg/kg 3 times per week, for either 10 or 30 days. AUY-922 suppressed the NM-induced sustained inflammation, as reflected in the reduction of leukocyte and protein concentrations in bronchoalveolar lavage fluid (BALF), and inhibited the activation of pro-fibrotic biomarkers, ERK and HSP90. Furthermore, AUY-922 maintained normal lung function, decreased the overexpression and accumulation of extracellular matrix proteins, and dramatically reduced histologic evidence of fibrosis in the lungs of mice exposed to NM. The HSP90 inhibitor, AUY-922, successfully blocked the adverse effects associated with acute exposures to NM, representing a promising approach against NM-induced pulmonary fibrosis.

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.

NAD+ in sulfur mustard toxicity

Sulfur mustard (SM) is a toxicant and chemical warfare agent with strong vesicant properties. The mechanisms behind SM-induced toxicity are not fully understood and no antidote or effective therapy against SM exists. Both, the risk of SM release in asymmetric conflicts or terrorist attacks and the usage of SM-derived nitrogen mustards as cancer chemotherapeutics, render the mechanisms of mustard-induced toxicity a highly relevant research subject. Herein, we review a central role of the abundant cellular molecule nicotinamide adenine dinucleotide (NAD⁺) in molecular mechanisms underlying SM toxicity. We also discuss the potential beneficial effects of NAD⁺ precursors in counteracting SM-induced damage.

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.

Chemical warfare agents. Classes and targets

Synthetic toxic chemicals (toxicants) and biological poisons (toxins) have been developed as chemical warfare agents in the last century. At the time of their initial consideration as chemical weapon, only restricted knowledge existed about their mechanisms of action. There exist two different types of acute toxic action: nonspecific cytotoxic mechanisms with multiple chemo-biological interactions versus specific mechanisms that tend to have just a single or a few target biomolecules. TRPV1- and TRPA-receptors are often involved as chemosensors that induce neurogenic inflammation. The present work briefly surveys classes and toxicologically relevant features of chemical warfare agents and describes mechanisms of toxic action.

Phosgene oxime: Injury and associated mechanisms compared to vesicating agents sulfur mustard and lewisite

Phosgene Oxime (CX, Cl₂CNOH), a halogenated oxime, is a potent chemical weapon that causes immediate acute injury and systemic effects. CX, grouped together with vesicating agents, is an urticant or nettle agent with highly volatile, reactive, corrosive, and irritating vapor, and has considerably different chemical properties and toxicity compared to other vesicants. CX is absorbed quickly through clothing with faster cutaneous penetration compared to other vesicating agents causing instantaneous and severe damage. For this reason, it could be produced as a weaponized mixture with other chemical warfare agents to enhance their deleterious effects. The immediate devastating effects of CX and easy synthesis makes it a dangerous chemical with both military and terrorist potentials. Although CX is the most potent vesicating agent, it is one of the least studied chemical warfare agents and the pathophysiology as well as long term effects are largely unknown. CX exposure results in immediate pain and inflammation, and it mainly affects skin, eye and respiratory system. There are no antidotes available against CX-induced injury and the treatment is only supportive. This review summarizes existing knowledge regarding exposure, toxicity and the probable underlying mechanisms of CX compared to other important vesicants' exposure.

Th17/Treg immunoregulation and implications in treatment of sulfur mustard gas-induced lung diseases

INTRODUCTION

Sulfur mustard (SM) is an extremely toxic gas used in chemical warfare to cause massive lung injury and death. Victims exposed to SM gas acutely present with inhalational lung injury, but among those who survive, some develop obstructive airway diseases referred to as SM-lung syndrome. Pathophysiologically, SM-lung shares many characteristics with smoking-induced chronic obstructive pulmonary disease (COPD), including airway remodeling, goblet cell metaplasia, and obstructive ventilation defect. Some of the hallmarks of COPD pathogenesis, which include dysregulated lung inflammation, neutrophilia, recruitment of interleukin 17A (IL -17A) expressing CD4⁺T cells (Th17), and the paucity of lung regulatory T cells (Tregs), have also been described in SM-lung. Areas covered: A literature search was performed using the MEDLINE, EMBASE, and Web of Science databases inclusive of all literature prior to and including May 2017. Expert commentary: Here we review some of the recent findings that suggest a role for Th17 cell-mediated inflammatory changes associated with pulmonary complications in SM-lung and suggest new therapeutic approaches that could potentially alter disease progression with immune modulating biologics that can restore the lung Th17/Treg balance.

An Official American Thoracic Society Workshop Report: Chemical Inhalational Disasters. Biology of Lung Injury, Development of Novel Therapeutics, and Medical Preparedness

This report is based on the proceedings from the Inhalational Lung Injury Workshop jointly sponsored by the American Thoracic Society (ATS) and the National Institutes of Health (NIH) Countermeasures Against Chemical Threats (CounterACT) program on May 21, 2013, in Philadelphia, Pennsylvania. The CounterACT program facilitates research leading to the development of new and improved medical countermeasures for chemical threat agents. The workshop was initiated by the Terrorism and Inhalational Disasters Section of the Environmental, Occupational, and Population Health Assembly of the ATS. Participants included both domestic and international experts in the field, as well as representatives from U.S. governmental funding agencies. The meeting objectives were to (1) provide a forum to review the evidence supporting current standard medical therapies, (2) present updates on our understanding of the epidemiology and underlying pathophysiology of inhalational lung injuries, (3) discuss innovative investigative approaches to further delineating mechanisms of lung injury and identifying new specific therapeutic targets, (4) present promising novel medical countermeasures, (5) facilitate collaborative research efforts, and (6) identify challenges and future directions in the ongoing development, manufacture, and distribution of effective and specific medical countermeasures. Specific inhalational toxins discussed included irritants/pulmonary toxicants (chlorine gas, bromine, and phosgene), vesicants (sulfur mustard), chemical asphyxiants (cyanide), particulates (World Trade Center dust), and respirable nerve agents.

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.

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.