Sulfur Mustard Induces Apoptosis in Cultured Normal Human Airway Epithelial Cells: Evidence of a Dominant Caspase-8-mediated Pathway and Differential Cellular Responses

Divinyl sulfone, an oxidative metabolite of sulfur mustard, induces caspase-independent pyroptosis in hepatocytes

Sulfur mustard (SM) is a highly toxic blister agent which has been used many times in several wars and conflicts and caused heavy casualties. Ease of production and lack of effective therapies make SM a potential threat to public health. SM intoxication causes severe damage on various target organs, such as the skin, eyes, and lungs. In addition, SM exposure can also lead to hepatotoxicity and severe liver injuries. However, despite decades of research, the molecular mechanism underlying SM-induced liver damage remains obscure. SM can be converted into various products via complex hepatic metabolism in vivo. There are some pieces of evidence that one of the oxidation products of SM, divinyl sulfone (DVS), exhibits even more significant toxicity than SM. Nevertheless, the molecular toxicology of DVS is still hardly known. In the present study, we confirmed that DVS is even more toxic than SM in the human hepatocellular carcinoma cell line HepG2. Further mechanistic study revealed that DVS exposure (200 μM) promotes pyroptosis in HepG2 cells, while SM (400 μM) mainly induces apoptosis. DVS induces gasdermin D (GSDMD) mediated pyroptosis, which is independent of caspases activation but depends on the large amounts of reactive oxygen species (ROS) and severe oxidative stress produced during DVS exposure. Our findings may provide novel insights for understanding the mechanism of SM poisoning and may be helpful to discover promising therapeutic strategies for SM intoxication.

Small-interfering RNA for c-Jun attenuates cell death by preventing JNK-dependent PARP1 cleavage and DNA fragmentation in nitrogen mustard-injured immortalized human bronchial epithelial cells

Sulfur mustard (a type of vesicant) can directly damage lung bronchial epithelium via aerosol inhalation, and prevalent cell death is an early event that obstructs the respiratory tract. JNK/c-Jun is a stress response pathway, but its role in cell death of the injured cells is not clear. Here, we report that JNK/c-Jun was activated in immortalized human bronchial epithelial (HBE) cells exposed to a lethal dose (20 μM) of nitrogen mustard (NM, a sulfur mustard analog). c-Jun silencing using small-interfering RNA (siRNA) rendered the cells resistant to NM-mediated cell death by blocking poly(ADP-ribose) polymerase 1 (PARP1) cleavage and DNA fragmentation. In addition, the transduction of upstream extrinsic (Fasl-Fas-caspase-8) and intrinsic (loss of Bcl-2 and mitochondrial membrane potential, ΔΨm) apoptosis pathways, as well as phosphorylated (p)-H2AX (Ser139), an epigenetic marker contributing to DNA fragmentation and PARP1 activity, was partially suppressed. To mimic the detachment of cells by NM, HBE cells were trypsinized and seeded on culture plates that were pre-coated with poly-HEMA to prevent cell adhesion. The JNK/c-Jun pathway was found to be activated in the detached cells. In conclusion, our results indicate that JNK/c-Jun pathway activation is necessary for NM-caused HBE cell death and further suggest that c-Jun silencing may be a potential approach to protect HBE cells from vesicant damage.

Acute cytotoxicity and increased vascular endothelial growth factor after in vitro nitrogen mustard vapor exposure

Nitrogen mustard (NM) is a highly toxic alkylating agent. Inhalation exposure can cause acute and chronic lung injury. This study's aims were to develop an in vitro coculture model of mustard-induced airway injury and to identify growth factors contributing to airway pathology. Primary human bronchial epithelial cells cultured with pulmonary endothelial cells were exposed to NM (25, 50, 100, 250, or 500 μM) or PBS (control) for 1 hour. Lactate dehydrogenase (LDH) and transepithelial electrical resistance (TEER) were measured before and 24 h after NM exposure. Fixed cultures were stained for hematoxylin and eosin or live/dead staining. Culture media were analyzed for 11 growth factors. A 1-h vapor exposure to greater than or equal to 50 μM NM increased supernatant LDH, decreased TEER, and caused airway epithelial cell detachment. Endothelial cell death occurred at 500 μM NM. Vascular endothelial growth factor A (VEGF-A) and placental growth factor (PlGF) expression increased in 500 μM NM-exposed cultures compared with PBS-exposed control cultures. NM vapor exposure causes differential cytotoxicity to airway epithelial and endothelial injury in culture. Increased VEGF-A and PlGF expression occurred acutely in airway cocultures. Future studies are required to validate the role of VEGF signaling in mustard-induced airway pathology.

Advances in treatment of acute sulfur mustard poisoning - a critical review

Sulfur mustard (SM) is a blistering chemical warfare agent that was used during the World War I and in the Iraq-Iran conflict. The aim of this paper is to discuss and critically review the published results of experiments on the treatment of SM poisoning based on our clinical and research experience. The victims must remove from the contaminated zone immediately. The best solution for decontamination is large amounts of water, using neutral soap and 0.5% sodium hypochlorite. Severely intoxicated patients should be treated according to advanced life support protocols and intensive care therapy for respiratory disorders and the chemical burn. Sodium thiosulfate infusion (100-500 mg/kg/min) should be started up to 60 min after SM exposure. However, N-acetyle cysteine (NAC) is recommended, none of them acts as specific or effective antidote. The important protective and conservative treatment of SM-induced pulmonary injuries include humidified oxygen, bronchodilators, NAC as muculytic, rehydration, mechanical ventilation, appropriate antibiotics and respiratory physiotherapy as clinically indicated. Treatment of acute SM ocular lesions start with topical antibiotics; preferably sulfacetamide eye drop, continue with lubricants, and artificial tears. Treatment for cutaneous injuries include: moist dressing; preferably with silver sulfadiazine cream, analgesic, anti-pruritic, physically debridement, debridase, Laser debridement, followed by skin autologous split-thickness therapy as clinically indicated. The new suggested medications and therapeutic approaches include: anti-inflammatory agents, Niacinamide, Silibinin, Calmodulin antagonists, Clobetasol, full-thickness skin grafting for skin injuries; Doxycycline; Bevacizumab, and Colchicine for ocular injuries. Recommended compounds based on animal studies include Niacinamide, Aprotinin, des-aspartate-angiotensin-I, Gamma-glutamyltransferase, vitamin E, and vitamin D. In vitro studies revealed that Dimethylthiourea, L-nitroarginine, Methyl-ester, Sodium pyruvate, Butylated hydroxyanisole, ethacrynic acid, and macrolide antibiotics are effective. However, none of them, except macrolide antibiotics have been proved clinically. Avoidance of inappropriate polypharmacy is advisable.

Circulating mesenchymal stem cells in sulfur mustard-exposed patients with long-term pulmonary complications

Sulfur mustard (SM) is a toxic agent that causes acute and long-term pulmonary complications. Recent evidence has shown the impact of SM on mesenchymal stem cells (MSCs). These cells have a critical role in repairing the damaged tissues. In this study, we evaluated the mobilization of MSCs in SM-exposed patients with long-term pulmonary complications. Fifty-nine SM-injured patients with prolonged pulmonary complications and 20 healthy individuals were included. Patients were classified based on taking drugs, having comorbidities, and severity of respiratory consequence. MSCs with phenotype of CD45-CD44⁺CD29⁺CD105⁺ were evaluated in peripheral blood using flow cytometry. Circulating MSCs were lower in SM-exposed patients compared to the control group (0.93 vs. 2.72 respectively, P = 0.005). No significant difference was observed in the MSC count between patients taking corticosteroids or antibiotics and those patients not taking them. Comorbidities like liver and kidney diseases had changed the count of MSCs in SM-exposed subjects. In addition, the frequency of MSCs did not show any association with the severity of long-term pulmonary complications. In conclusion, SM-exposure causes a decline in the frequency of circulating MSCs in survivors. The lower number of the peripheral MSC population in SM-exposed patients was not affected by taking corticosteroids or antibiotics, but comorbidities are probably involved in MSC frequency. The decreases observed in the number of circulating MSCs was not associated with the severity of the pulmonary complications; however, further studies in mustard lung models are required to demonstrate the therapeutic or pathologic role of MSCs in SM injuries.

Free Radical Production and Oxidative Stress in Lung Tissue of Patients Exposed to Sulfur Mustard: An Overview of Cellular and Molecular Mechanisms

Sulfur mustard (SM) is a chemical alkylating compound that primary targets lung tissue. It causes a wide variety of pathological effects in respiratory system such as chronic bronchitis, bronchiolitis obliterans, necrosis of the mucosa and inflammation, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. However, molecular and cellular mechanisms for these pathologies are still unclear. Oxidative stress (OS) induced by reactive oxygen species (ROS) is likely a significant mechanism by which SM leads to cell death and tissues injury. SM can trigger various molecular and cellular pathways that are linked to ROS generation, OS, and inflammation. Hypoxia-induced oxidative stress, reduced activity of enzymatic antioxidants, depletion of intercellular glutathione (GSH), decreased productivity of GSH-dependent antioxidants, mitochondrial dysfunction, accumulation of leukocytes and proinflammatory cytokines, and increased expression of ROS producing-related enzymes and inflammatory mediators are the major events in which SM leads to massive production of ROS and OS in pulmonary system. Therefore, understanding of these molecules and signaling pathways gives us valuable information about toxicological effects of SM on injured tissues and the way for developing a suitable clinical treatment. In this review, we aim to discuss the possible mechanisms by which SM induces excessive production of ROS, OS, and antioxidants depletion in lung tissue of exposed patients.

Apoptotic cell death in rat lung following mustard gas inhalation

To investigate apoptosis as a mechanism of sulfur mustard (SM) inhalation injury in animals, we studied different caspases (caspase-8, -9, -3, and -6) in the lungs from a ventilated rat SM aerosol inhalation model. SM activated all four caspases in cells obtained from bronchoalveolar lavage fluid (BALF) as early as 6 h after exposure. Caspase-8, which is known to initiate the extrinsic Fas-mediated pathway of apoptosis, was increased fivefold between 6 and 24 h, decreasing to the unexposed-control level at 48 h. The initiator, caspase-9, in the intrinsic mitochondrial pathway of apoptosis as well as the executioner caspases, caspase-3 and -6, all peaked ( P < 0.01) at 24 h; caspase-3 and -6 remained elevated, but caspase-9 decreased to unexposed-control level at 48 h. To study further the Fas pathway, we examined soluble as well as membrane-bound Fas ligand (sFas-L and mFas-L, respectively) and Fas receptor (Fas-R) in both BALF cells and BALF. At 24 h after SM exposure, sFas-L increased significantly in both BALF cells ( P < 0.01) and BALF ( P < 0.05). However, mFas-L increased only in BALF cells between 24 and 48 h ( P < 0.1 and P < 0.001, respectively). Fas-R increased only in BALF cells by 6 h ( P < 0.01) after SM exposure. Apoptosis in SM-inhaled rat lung specimens was also confirmed by both immunohistochemical staining using cleaved caspase-3 and -9 antibodies and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining as early as 6 h in the proximal trachea and bronchi, but not before 48 h in distal airways. These findings suggest pathogenic mechanisms at the cellular and molecular levels and logical therapeutic target(s) for SM inhalation injury in animals.

Evaluation of an in vitro screening model to assess phosgene inhalation injury

Therapeutic development against exposure to toxic gases is hindered by the lack of appropriate models to evaluate candidate compounds prior to animal efficacy studies. In this study, an in vitro, air-liquid interface exposure model has been tested to examine its potential application for screening treatments for phosgene (carbonyl chloride)-induced pulmonary injury. Epithelial cultures on Transwell^® inserts, combined with a Vitrocell^® exposure apparatus, provided a physiologically relevant exposure environment. Differentiated human bronchial epithelial (16HBE) cultures were exposed for 8 min to phosgene ranging from 0 to 64 ppm and assessed for changes in transepithelial electrical resistance (TEER, epithelial barrier integrity), cellular viability (XTT) and post-exposure (PE) cellular metabolic energy status. Exposure to phosgene concentrations ≥8 ppm caused dose-dependent and significant decreases in TEER and XTT which did not recover within 24-h PE. In addition, at 64 ppm the rate of oxidative glutamine metabolism was significantly inhibited at 6 and 24 h after exposure. Glycolytic activities (glucose utilization and lactate production) were also inhibited, but to a lesser extent. Decreased glycolytic function can translate to insufficient energy sources to counteract barrier function failure. Consistent and sensitive markers of phosgene exposure were TEER, cell viability and decreased metabolism. As such, we have assessed an appropriate in vitro model of phosgene inhalation that produced quantifiable alterations in markers of lung cell metabolism and injury in human airway epithelial cells. Data indicate the suitability of this model for testing classes of anti-edemagenic compounds such as corticosteroids or phosphodiesterase inhibitors for evaluating phosgene therapeutics.

Characterization of Lung Fibroblasts More than Two Decades after Mustard Gas Exposure

Purpose

In patients with short-term exposure to the sulfur mustard gas, the delayed cellular effects on lungs have not been well understood yet. The lung pathology shows a dominant feature consistent with obliterative bronchiolitis, in which fibroblasts play a central role. This study aims to characterize alterations to lung fibroblasts, at the cellular level, in patients with delayed respiratory complications after short-term exposure to the sulfur mustard gas.

Methods

Fibroblasts were isolated from the transbronchial biopsies of patients with documented history of exposure to single high-dose sulfur mustard during 1985–7 and compared with the fibroblasts of control subjects.

Results

Compared with controls, patients’ fibroblasts were thinner and shorter, and showed a higher population doubling level, migration capacity and number of filopodia. Sulfur mustard decreased the in vitro viability of fibroblasts and increased their sensitivity to induction of apoptosis, but did not change the rate of spontaneous apoptosis. In addition, higher expression of alpha smooth muscle actin showed that the lung's microenvironment in these patients is permissive for myofibroblastic differentiation.

Conclusions

These findings suggest that in patients under the study, the delayed pulmonary complications of sulfur mustard should be considered as a unique pathology, which might need a specific management by manipulation of cellular components.

Respiratory effects of sulfur mustard exposure, similarities and differences with asthma and COPD

CONTEXT

Previous research has found relationships between sulfur mustard (SM) toxicity and its adverse effects.

OBJECTIVE

SM is highly toxic to the respiratory system, leading to hacking cough, rhinorrheachest tightness, acute pharyngitis and laryngitis, chronic bronchitis and lung fibrosis. In this review, based on the scientific literature, we provide an updated summary of information on SM exposures and their differences with asthma and COPD.

METHOD

Information of this review was obtained by searching Medline/PubMed, ScienceDirect, Scopus, Google Scholar, ISI Web of Knowledge and Chemical Abstracts.

RESULTS

SM exposure can decrease pulmonary function tests (PFTs) values. In addition, inflammatory cell accumulation in the respiratory tract and increased expression of some pro-inflammatory cytokines including tumor necrosis factor-α (TNFα), IL-1a, IL-1β, and reactive oxygen radicals due to SM exposure have been shown. Matrix metalloproteinase (MMP) which degrade extracellular matrix proteins, contributing to inflammatory cell recruitment, tissue injury and fibrosis are also up-regulated in the lung after SM exposure. In the lung, SM exposure also can cause serious pathological changes including airway inflammation, parenchymal tissue destruction and airway obstruction which can lead to asthma or chronic obstructive pulmonary disease (COPD). Following SM poisoning, DNA damage, apoptosis and autophagy are observed in the lung along with the increased expression of activated caspases and DNA repair enzymes.

CONCLUSION

In the present article, respiratory symptoms, changes in PFTs, lung pathology and lung inflammation due to SM exposure and the similarities and differences between them and those observed in asthma and COPD were reviewed.

Mechanism underlying acute lung injury due to sulfur mustard exposure in rats

Sulfur mustard (SM), a bifunctional alkylating agent that causes severe lung damage, is a significant threat to both military and civilian populations. The mechanisms mediating the cytotoxic effects of SM are unknown and were investigated in this study. The purpose of this study was to establish a rat model of SM-induced lung injury to observe the resulting changes in the lungs. Male rats (Sprague Dawley) were anesthetized, intratracheally intubated, and exposed to 2 mg/kg of SM by intratracheal instillation. Animals were euthanized 6, 24, 48, and 72 h post-exposure, and bronchoalveolar lavage fluid (BALF) and lung tissues were collected. Exposure of rats to SM resulted in rapid pulmonary toxicity, including partial bronchiolar epithelium cell shedding, focal ulceration, and an increased amount of inflammatory exudate and number of cells in the alveoli. There was also evidence that the protein content and cell count of BALF peaked at 48 h, and the alveolar septum was widened and filled with lymphocytes. SM exposure also resulted in partial loss of type I alveolar epithelial cell membranes, fuzzy mitochondrial cristae, detachment and dissociation of ribosomes attached to the surface of rough endoplasmic reticulum, cracked, missing, and disorganized microvilli of type II alveolar epithelial cells, and increased apoptotic cells in the alveolar septum. The propylene glycol control group, however, was the same as the normal group. These data demonstrate that the mechanism of a high concentration of SM (2 mg/kg) induced acute lung injury include histologic changes, inflammatory reactions, apoptosis, oxidative stress, and nuclear DNA damage; the degree of injury is time dependent.

Mechanistic Insights of Sulfur Mustard-Induced Acute Tracheal Injury in Rats

Sulfur mustard (SM) is believed to be a major threat to civilian populations because of the persistent asymmetric threat by nonstate actors, such as terrorist groups, the ease of synthesis and handling, and the risk of theft from stockpiles. The purpose of this study was to establish mechanisms of acute tracheal injury in rats induced by SM using histopathologic, immunohistochemical, and biochemical parameters. Male rats (Sprague-Dawley) were anesthetized, intratracheally intubated, and exposed to 2 mg/kg of SM. Animals were euthanized 6-, 24-, 48-, and 72-hour postexposure, and intracavitary blood samples from the heart and tracheal tissues were collected. Exposure of rats to SM resulted in rapid tracheal injury, including tracheal epithelial cell shedding, focal ulceration, and abundant lymphocyte invasion of the submucosa. There was also evidence of a large number of apoptotic cells in the epithelium and submucosa, the serum levels of tumor necrosis factor α, interleukin 1β (IL) 1β, IL-6, and γ-glutamyl transferase peaked at 24 hours, and the serum levels of lactate dehydrogenase, glutathione peroxidase, and thiobarbituric acid reactive substance peaked at 6 hours. The SM exposure also resulted in a loss of the cellular membrane, leakage of cytoplasm, fuzzy mitochondrial cristae, medullary changes in ciliated and goblet cells, and the nuclear chromatin appeared marginated in basal cells and fibroblasts. The results in the propylene glycol group were the same as the control group. These data demonstrated the histologic changes, inflammatory reactions, apoptosis, oxidative stress, and DNA damage following SM (2 mg/kg)-induced acute tracheal injury; the severity of changes was time dependent.

Mustard Gas Inhalation Injury

Mustard gas (sulfur mustard [SM], bis-[2-chloroethyl] sulfide) is a vesicating chemical warfare agent and a potential chemical terrorism agent. Exposure of SM causes debilitating skin blisters (vesication) and injury to the eyes and the respiratory tract; of these, the respiratory injury, if severe, may even be fatal. Therefore, developing an effective therapeutic strategy to protect against SM-induced respiratory injury is an urgent priority of not only the US military but also the civilian antiterrorism agencies, for example, the Homeland Security. Toward developing a respiratory medical countermeasure for SM, four different classes of therapeutic compounds have been evaluated in the past: anti-inflammatory compounds, antioxidants, protease inhibitors and antiapoptotic compounds. This review examines all of these different options; however, it suggests that preventing cell death by inhibiting apoptosis seems to be a compelling strategy but possibly dependent on adjunct therapies using the other drugs, that is, anti-inflammatory, antioxidant, and protease inhibitor compounds.

A clinicopathological approach to sulfur mustard-induced organ complications: a major review

CONTEXT

Sulfur mustard (SM), with an old manufacturing history still remains as potential threat due to easy production and extensive effects.

OBJECTIVES

Increasing studies on SM indicates the interest of researchers to this subject. Almost all human body organs are at risk for complications of SM. This study offers organ-by-organ information on the effects of SM in animals and humans.

METHODS

The data sources were literature reviews since 1919 as well as our studies during the Iraq-Iran war. The search items were SM and its all other nomenclatures in relation to, in vivo, in vitro, humans, animals, eye, ocular, ophthalmic, lungs, pulmonary, skin, cutaneous, organs and systemic. Amongst more than 1890 SM-related articles, 257 more relevant clinicopathologic papers were selected for this review.

RESULTS

SM induces a vast range of damages in nearly all organs. Acute SM intoxication warrants immediate approach. Among chronic lesions, delayed keratitis and blindness, bronchiolitis obliterans and respiratory distress, skin pruritus, dryness and cancers are the most commonly observed clinical sequelae.

CONCLUSION

Ocular involvements in a number of patients progress toward a severe, rapid onset form of keratitis. Progressive deterioration of respiratory tract leads to "mustard lung". Skin problems continue as chronic frustrating pruritus on old scars with susceptibility to skin cancers. Due to the multiple acute and chronic morbidities created by SM exposure, uses of multiple drugs by several routes of administrations are warranted.

Postexposure application of Fas receptor small-interfering RNA to suppress sulfur mustard-induced apoptosis in human airway epithelial cells: implication for a therapeutic approach

Sulfur mustard (SM) is a vesicant chemical warfare and terrorism agent. Besides skin and eye injury, respiratory damage has been mainly responsible for morbidity and mortality after SM exposure. Previously, it was shown that suppressing the death receptor (DR) response by the dominant-negative Fas-associated death domain protein prior to SM exposure blocked apoptosis and microvesication in skin. Here, we studied whether antagonizing the Fas receptor (FasR) pathway by small-interfering RNA (siRNA) applied after SM exposure would prevent apoptosis and, thus, airway injury. Normal human bronchial/tracheal epithelial (NHBE) cells were used as an in vitro model with FasR siRNA, FasR agonistic antibody CH11, and FasR antagonistic antibody ZB4 as investigative tools. In NHBE cells, both SM (300 µM) and CH11 (100 ng/ml) induced caspase-3 activation, which was inhibited by FasR siRNA and ZB4, indicating that SM-induced apoptosis was via the Fas response. FasR siRNA inhibited SM-induced caspase-3 activation when added to NHBE cultures up to 8 hours after SM. Results using annexin V/propidium iodide-stained cells showed that both apoptosis and necrosis were involved in cell death due to SM; FasR siRNA decreased both apoptotic and necrotic cell populations. Bronchoalveolar lavage fluid (BALF) of rats exposed to SM (1 mg/kg, 50 minutes) revealed a significant (P < 0.05) increase in soluble Fas ligand and active caspase-3 in BALF cells. These findings suggest an intervention of Fas-mediated apoptosis as a postexposure therapeutic strategy with a therapeutic window for SM inhalation injury and possibly other respiratory diseases involving the Fas response.

Molecular and cellular mechanism of lung injuries due to exposure to sulfur mustard: a review

Sulfur mustard (SM), a potent chemical weapon agent, was used by Iraqi forces against Iranian in the Iraq-Iran war (1981-1989). Chronic obstructive pulmonary disease (COPD) is a late toxic pulmonary consequence after SM exposure. The COPD observed in these patients is unique (described as Mustard Lung) and to some extent different from COPD resulted from other well-known causes. Several mechanisms have been hypothesized to contribute to the pathogenesis of COPD including oxidative stress, disruption of the balance between apoptosis and replenishment, proteinase-antiproteinase imbalance and inflammation. However, it is not obvious which of these pathways are relevant to the pathogenesis of mustard lung. In this paper, we reviewed studies addressing the pathogenicity of mustard lung, and reduced some recent ambiguities in this field. There is ample evidence in favor of crucial role of both oxidative stress and apoptosis as two known mechanisms that are more involved in pathogenesis of mustard lung comparing to COPD. However, according to available evidences there are no such considerable data supporting neither proteolytic activity nor inflammation mechanism as the main underlying pathogenesis in Mustard Lung.

Sulfur mustard vapor effects on differentiated human lung cells

CONTEXT

Sulfur mustard (SM) causes skin blistering and long-term pulmonary dysfunction. Its adverse effects have been studied in battlefield-exposed humans, but lack of knowledge regarding confounding factors makes interpretation challenging. Animal studies are critical to understanding mechanisms, but differences between animals and humans must be addressed. Studies of cultured human cells can bridge animal studies and humans.

OBJECTIVE

Evaluate effects of SM vapor on airway cells.

MATERIALS AND METHODS

We examined responses of differentiated human tracheal/bronchial epithelial cells, cultured at an air-liquid interface, to SM vapors. SM effects on metabolic activity (Water Soluble Tetrazolium (WST) assay), cytokine and metalloproteinase secretion, and cellular heme oxygenase 1 (HO-1), an oxidative stress indicator, were measured after 24 h.

RESULTS

At noncytotoxic levels of exposure, interleukin 8 and matrix metalloproteinase-13 were significantly increased in these cultures, but HO-1 was not significantly affected.

DISCUSSION AND CONCLUSION

Exposure of differentiated airway epithelial cells to sub-cytotoxic levels of SM vapor induced inflammatory and degradative responses that could contribute to the adverse health effects of inhaled SM.

Sulfur mustard toxicity: history, chemistry, pharmacokinetics, and pharmacodynamics

Sulfur mustard (SM) and similar bifunctional agents have been used as chemical weapons for almost 100 years. Victims of high-dose exposure, both combatants and civilians, may die within hours or weeks, but low-dose exposure causes both acute injury to the eyes, skin, respiratory tract and other parts of the body, and chronic sequelae in these organs are often debilitating and have a serious impact on quality of life. Ever since they were first used in warfare in 1917, SM and other mustard agents have been the subjects of intensive research, and their chemistry, pharmacokinetics and mechanisms of toxic action are now fairly well understood. In the present article we review this knowledge and relate the molecular-biological basis of SM toxicity, as far as it has been elucidated, to the pathological effects on exposure victims.

The Role of Fas-FasL Signaling Pathway in Induction of Apoptosis in Patients with Sulfur Mustard-Induced Chronic Bronchiolitis

Sulfur mustard (SM) is an alkylating agent that induces apoptosis and necrosis in cells. Fas-Fas ligand (FasL) interaction could induce apoptosis as well. In this study, it was hypothesized that apoptosis might play an important role in the pathogenesis of SM-induced lung injury via Fas-FasL signaling pathway. In a case-control study, Fas and FasL levels, caspase-3 activity and percent of apoptotic cells were measured in bronchoalveolar lavage (BAL) fluid of patients 20 years after exposure to sulfur mustard and compared with the control group. Results show that Fas and FasL levels were significantly higher in BAL fluid cells in patients group compared with the control (P = .001). No significant differences were observed between mild and moderate-severe groups. BAL fluid cells caspase-3 activity was not significantly different among the mild, moderate-severe, and control groups. The data suggest that Fas-FasL-induced apoptosis was impaired in BAL fluid cells of SM-exposed patients which might be one of the initiators of pathogenesis in SM-induced lung injury in these patients.

Sulfur mustard-induced pulmonary injury: therapeutic approaches to mitigating toxicity

Sulfur mustard (SM) is highly toxic to the lung inducing both acute and chronic effects including upper and lower obstructive disease, airway inflammation, and acute respiratory distress syndrome, and with time, tracheobronchial stenosis, bronchitis, and bronchiolitis obliterans. Thus it is essential to identify effective strategies to mitigate the toxicity of SM and related vesicants. Studies in animals and in cell culture models have identified key mechanistic pathways mediating their toxicity, which may be relevant targets for the development of countermeasures. For example, following SM poisoning, DNA damage, apoptosis, and autophagy are observed in the lung, along with increased expression of activated caspases and DNA repair enzymes, biochemical markers of these activities. This is associated with inflammatory cell accumulation in the respiratory tract and increased expression of tumor necrosis factor-α and other proinflammatory cytokines, as well as reactive oxygen and nitrogen species. Matrix metalloproteinases are also upregulated in the lung after SM exposure, which are thought to contribute to the detachment of epithelial cells from basement membranes and disruption of the pulmonary epithelial barrier. Findings that production of inflammatory mediators correlates directly with altered lung function suggests that they play a key role in toxicity. In this regard, specific therapeutic interventions currently under investigation include anti-inflammatory agents (e.g., steroids), antioxidants (e.g., tocopherols, melatonin, N-acetylcysteine, nitric oxide synthase inhibitors), protease inhibitors (e.g., doxycycline, aprotinin, ilomastat), surfactant replacement, and bronchodilators. Effective treatments may depend on the extent of lung injury and require a multi-faceted pharmacological approach.

Inflammatory effects of inhaled sulfur mustard in rat lung

Inhalation of sulfur mustard (SM), a bifunctional alkylating agent that causes severe lung damage, is a significant threat to both military and civilian populations. The mechanisms mediating its cytotoxic effects are unknown and were investigated in the present studies. Male rats Crl:CD(SD) were anesthetized, and then intratracheally intubated and exposed to 0.7-1.4mg/kg SM by vapor inhalation. Animals were euthanized 6, 24, 48h or 7days post-exposure and bronchoalveolar lavage fluid (BAL) and lung tissue collected. Exposure of rats to SM resulted in rapid pulmonary toxicity, including focal ulceration and detachment of the trachea and bronchial epithelia from underlying mucosa, thickening of alveolar septal walls and increased numbers of inflammatory cells in the tissue. There was also evidence of autophagy and apoptosis in the tissue. This was correlated with increased BAL protein content, a marker of injury to the alveolar epithelial lining. SM exposure also resulted in increased expression of markers of inflammation including cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNFα), inducible nitric oxide synthase (iNOS), and matrix metalloproteinase-9 (MMP-9), each of which has been implicated in pulmonary toxicity. Whereas COX-2, TNFα and iNOS were mainly localized in alveolar regions, MMP-9 was prominent in bronchial epithelium. In contrast, expression of the anti-oxidant hemeoxygenase, and the anti-inflammatory collectin, surfactant protein-D, decreased in the lung after SM exposure. These data demonstrate that SM-induced oxidative stress and injury are associated with the generation of cytotoxic inflammatory proteins which may contribute to the pathogenic response to this vesicant.

In Vitro Assessment of Apoptosis and Necrosis Following Cold Storage in a Human Airway Cell Model

As advances in medical technology improve the efficacy of cell and tissue transplantation, a void remains in our knowledge base as to the specific molecular responses of cells to low-temperature storage. While much focus has been given to solution formulation for tissue perfusion during storage, investigations into cold exposure-induced complex molecular changes remain limited. The intent of this study was to quantify the levels of cell death following hypothermic storage in a lung cell model, establishing a foundation for future in-depth molecular analysis. Normal human lung fibroblasts (IMR-90) were stored for 1 day or 2 days and small airway epithelial cells (SAEC) were stored for 5 days or 7 days at 4°C in complete media, ViaSpan, or ViaSpan + pan-caspase (VI) inhibitor. (Poststorage viability was assessed for 3 days using alamarBlue(™).) Sample analysis revealed that IMR-90 cells stored in ViaSpan remained 80% (±9) viable after 1 day of storage and 21% (±7) viable after 2 days of storage. SAEC cells stored in ViaSpan remained 81% (±5) viable after 5 days and 28% (±7) after 7 days. Microfluidic flow cytometry analysis of the apoptotic and necrotic populations in the ViaSpan-stored samples revealed that in the IMR-90 cells stored for 2 days, 7% of the population was apoptotic at 4-h poststorage, while ∼70% was identified as necrotic. Analysis of the SAEC cell system following 7 days of ViaSpan storage revealed an apoptotic peak of 19% at 4-h poststorage and a corresponding necrotic peak of 19%. Caspase inhibition during hypothermic storage increased viability 33% for IMR-90 and 25% for SAEC. Data revealed a similar pattern of cell death, through both apoptosis and necrosis, once the onset of cold storage failure began, implying a potential conserved mechanism of cold-induced cell death. These data highlight the critical need for a more in-depth understanding of the molecular changes that occur as a result of cold exposure in cells and tissues.

Involvement of caspases and transmembrane metalloproteases in sulphur mustard-induced microvesication in adult human skin in organ culture: directions for therapy

While skin is a major target for sulphur mustard (HD), a therapy to limit HD-induced vesication is currently not available. Since it is supposed that apoptotic cell death and proteolytic digestion of extracellular matrix proteins by metalloproteases are initiating factors for blister formation, we have explored whether inhibition of these processes could prevent HD-induced epidermal-dermal separation using adult human skin in organ culture. Involvement of the caspase and the metalloprotease families was confirmed by the observation that their respective broad spectrum inhibitors, Z-VAD-fmk and GM6001, each suppressed HD-induced microvesication. The lowest effective concentrations were 10 and 100microM, respectively. Using specific inhibitors for caspase-8 (> or =10microM) and caspase-9 (> or =10microM) we learned that HD-induced apoptosis is initiated by the death receptor pathway as well as by the mitochondrial pathway. Remarkably, blocking caspase-8 activity resulted in morphologically better conserved cells than blocking caspase-9 activity. We zoomed in on the role of metalloproteases in HD-induced microvesication by testing the effects of two inhibitors: dec-RVKR-cmk and TAPI-2. Dec-RVKR-cmk is an inhibitor of furin, which activates transmembrane enzymes of the 'a disintegrin and metalloproteinase' (ADAM)-family as well as the membrane-type metalloproteases (MTx-MMP). TAPI-2 specifically inhibits TNFalpha-converting enzyme (TACE/ADAM17), which is involved in pericellular proteolysis. Both inhibitors prevented microvesication at concentrations of > or =500 and > or =20microM, respectively. This confirms that ADAMs and MT-MMPs play a role in HD-induced epidermal-dermal separation, with a particular role for TACE/ADAM17. Since TACE is involved not only in degradation of cell-matrix adhesion structures, but also in ectodomain shedding of ligands for epidermal growth factor receptor (EGFR) and in release of TNFalpha, these results imply TACE-mediated pathways as a new concept in HD toxicity. In conclusion, transmembrane metalloproteases probably form a main target for treatment of blisters in HD casualties. The observation that microvesication in the ex vivo human skin model still could be prevented when the metalloprotease inhibitor GM6001 was applied up to 8h after exposure to HD opens perspectives for non-urgent cure of HD casualties.

A role for mitochondrial oxidative stress in sulfur mustard analog 2-chloroethyl ethyl sulfide-induced lung cell injury and antioxidant protection

Sulfur mustards (SMs) have been used as warfare agents since World War I and still pose a significant threat against civilian and military personnel. SM exposure can cause significant blistering of the skin, respiratory injury, and fibrosis. No antidote currently exists for SM exposure, but recent studies, using the SM analog 2-chloroethyl ethyl sulfide (CEES), have focused on the ability of antioxidants to prevent toxicity. Although antioxidants can prevent CEES-induced toxicity, the mechanisms by which these compounds are effective against SM agents are largely unknown. Using human bronchial epithelial (16HBE) cells and primary small airway epithelial cells, we show that CEES causes a significant increase in mitochondrial dysfunction as early as 4 h, which is followed by increases in mitochondrial reactive oxygen species (ROS), peaking 12 h after exposure. We also have identified a catalytic antioxidant metalloporphyrin that can rescue airway cells from CEES-induced toxicity when added 1 h after CEES exposure. In addition, the cytoprotective effects of the catalytic antioxidant are associated with correcting mitochondrial dysfunction ROS, DNA oxidation, and decreases in intracellular GSH. These findings suggest a role for oxidative stress in CEES toxicity and provide a rationale to investigate antioxidants as rescue agents in SM exposures.

A clinically relevant in vitro model for evaluating the effects of aerosolized vesicants

The chemical warfare vesicant sulfur mustard (HD) is a known toxic agent to the human respiratory tract and the major airways are considered to be a primary target of HD-induced injury. However, there is no consensus regarding which model systems are most appropriate for studying the effects of aerosolized vesicants on human airway epithelium. In this study, we evaluated the consequences of exposure of differentiated human respiratory epithelial cells in air-liquid interface to mechlorethamine (HN2), an HD functional analog. HN2 challenge was administered via the apical (air) interface over a wide dose range (20-400 microM) to differentiated HBE1 cells. Cultures were observed over 1-48 h for evidence of HN2-induced morphologic abnormalities as well as for possible cellular cytotoxicity, apoptotic changes, and induction of cytokine secretion. HN2 at concentrations of > or =200 microM caused disruption and denudation of the airway epithelial architecture within 24h of exposure. Moreover, HN2-induced cytotoxic and apoptotic changes in HBE1 cells in a dose- and time-dependent fashion. HN2 challenge also induced secretion of chemokines and proinflammatory cytokines including TNF-alpha, IL-1 alpha, IL-1 beta, IL-6, IL-8, RANTES, MCP-1, IP-10, G-CSF, GM-CSF and IL-15. These observations parallel those described in the lungs of HD-exposed victims and underscore the utility and potential applicability of this model to future mechanistic studies of vesicant-induced pulmonary injury.