Sulfur Mustard Analog Research Articles

Time course study of oxidative stress in sulfur mustard analog 2‑chloroethyl ethyl sulfide-induced toxicity

Oxidative stress is the major mechanism impairing cell homeostasis, inducing cell death and tissue damage in sulfur mustard (SM)-exposed individuals. The aim of the present study was to evaluate time course changes of oxidative stress in the mice exposed with 2‑chloroethyl ethyl sulfide (CEES) as SM analog. For this purpose, male BALB/c mice were divided into control groups and experimental groups that received CEES (10 mg/kg) through intraperitoneal injection. In both groups, animals were euthanized at three periods: short (12, 24 h and 1 week), medium (1, 2 and 3 months) and long-term (5 and 6 months) after CEES exposure. Oxidative stress indices and the antioxidant defense systems were evaluated in lung and liver tissues. The time course findings in both tissues showed a significant increase in oxidative damage markers such as malondialdehyde (lung P < 0.001, liver P < 0.001), protein carbonyl (lung P < 0.0001), and 8-hydroxy-deoxyguanosine (lung P < 0.0001, Liver P < 0.0001) and also a significant reduction in the antioxidant defense system including reduced glutathione level (lung P < 0.001, Liver P < 0.001,), activities of catalase (lung P < 0.01 and liver P < 0.05), superoxide dismutase (lung P < 0.05), glutathione S‑transferase (lung P < 0.05, liver P < 0.01), glutathione peroxidase (lung, P < 0.05, Liver P < 0.05) and glutathione reductase (lung P < 0.001, liver P < 0.01) in the long-term. However, these changes occur with less intensity in the short-term and return to the normal status in the medium-term. Moreover, there was a positive time course correlation between oxidative damage indices and the percent of histopathological damage in both tissues (P < 0.05). This correlation finding confirms and supports the fact that time course oxidative-antioxidant imbalance plays an important role in the development of SM-induced acute and delayed injuries.

Phospholipid and Triglyceride keep vortex-dispersed sulfur mustard analog as undissolved droplets which induce necrosis from nearby cells via declining mitochondrial membrane potential

SM (Sulfur mustard) is an oily, hydrophobic, and lipophilic chemical agent that damages cells with intricate patterns. CEES (2-chloroethyl ethyl sulfide soluble) is a standard SM analog commonly employed in the toxicity mechanism study. To obtain ideal results in vitro, researchers should disperse CEES well in the medium, avoiding the presence of undissolved droplets. However, such a purpose is not easy to reach under the conventional solution preparation, and the information about droplet formation and function is little available. Here, we showed that phospholipid and triglyceride, two essential components of serum lipids, could prevent CEES from dissolving in water after vortex, which kept partial CEES as small droplets. By detecting CEES level, we proved that residual droplets slowed CEES hydrolysis and conversion. Under the microscope, CEES droplets were observed to degrade and diffuse with time to induce the necrosis and mitochondrial membrane potential decline from nearby cells. In conclusion, the damage pattern of CEES droplets is quite different from that of dissolved CEES, and a low level of phospholipid and triglyceride is beneficial for preventing droplets formation in preparing CEES solution.

A Mouse Model of Acute and Delayed Complications of Sulfur Mustard Analogue, 2-Chloroethyl Ethyl Sulfide

Background: Numerous studies have been conducted on humans, animals, and cell cultures exposed to Sulfur Mustard (SM). However, the precise mechanism and cause or long-term pattern of SM injuries are not well defined. There is no protocol available for treating people with severe eye, lung, and skin ailments. The current study aimed to develop an animal model of the acute and delayed complications of SM exposure.Materials and Methods: Two strains of mice (BALB/c and C57BL/6), 6-8 weeks old at the onset of the study, were exposed to 2-Chloroethyl Ethyl Sulfide (CEES) (1-200 mg/kg) and solvents (Tyrode’s solution, Polyethylene Glycol 300, herbal oil) for a duration of 12 hours to 7 months. The administration route was Intraperitoneal (IP) injection. The mortality rate, signs, and apparent side effects were explored. At the end of the study, the mice’s lung, liver, and spleen tissues were extracted and fixed for future histopathological assessments.Results: Tyrode’s solution and Polyethylene Glycol 300 solvents were not appropriate for the present research. Pathological features observed in BALB/c mice were better than the C57BL/6 mice. Overall, 10 mg/kg CEES was the most suitable dose, because it had the least mortality rate and demonstrated the most pathological findings, such as the infiltration of inflammatory cells and proliferation of fibroblasts and fibrotic tissue in the lung. Five months after the CEES administration, the delayed phase complications were studied. Conclusion: The IP injection of 10 mg/kg CEES to BALB/c mice imitates short- and long-term complications of SM exposure in humans. This model is useful for preventing and treating SM exposure.

TRPA1 and CGRP antagonists counteract vesicant-induced skin injury and inflammation

The skin is highly sensitive to the chemical warfare agent in mustard gas, sulfur mustard (SM) that initiates a delayed injury response characterized by erythema, inflammation and severe vesication (blistering). Although SM poses a continuing threat, used as recently as in the Syrian conflict, no mechanism-based antidotes against SM are available.Recent studies demonstrated that Transient Receptor Potential Ankyrin 1 (TRPA1), a chemosensory cation channel in sensory nerves innervating the skin, is activated by SM and 2‐chloroethyl ethyl sulfide (CEES), an SM analog, in vitro, suggesting it may promote vesicant injury.Here, we investigated the effects of TRPA1 inhibitors, and an inhibitor of Calcitonin Gene Related Peptide (CGRP), a neurogenic inflammatory peptide released upon TRPA1 activation, in a CEES-induced mouse ear vesicant model (CEES-MEVM). TRPA1 inhibitors (HC-030031 and A-967079) and a CGRP inhibitor (MK-8825) reduced skin edema, pro-inflammatory cytokines (IL-1β, CXCL1/KC), MMP-9, a protease implicated in skin damage, and improved histopathological outcomes.These findings suggest that TRPA1 and neurogenic inflammation contribute to the deleterious effects of vesicants in vivo, activated either directly by alkylation, or indirectly, by reactive intermediates or pro-inflammatory mediators. TRPA1 and CGRP inhibitors represent new leads that could be considered for validation and further development in other vesicant injury models.

Efficacy of anti-inflammatory, antibiotic and pleiotropic agents in reversing nitrogen mustard-induced injury in ex vivo cultured rabbit cornea

Vesicating agent, Sulfur mustard (SM), causes devastating eye injury; however, there are no effective antidotes available. Using nitrogen mustard (NM), a bi-functional analog of SM, we have earlier reported that NM-induced corneal injury in ex vivo rabbit cornea organ culture model parallels corneal injury reported with SM. Using this model, we have demonstrated the therapeutic efficacy of dexamethasone (DEX), doxycycline (DOX) and silibinin (SB) in reversing NM (2h exposure)-induced corneal injuries when added immediately after washing NM. In the present study, we further examined the efficacy of similar/higher doses of these agents when added immediately, 2, or 4h after washing NM following its 2h exposure. All three treatment agents caused a reversal in established NM-induced injury biomarkers when added immediately or 2h after washing NM following its 2h exposure; however, when treatments were carried out 4h after washing NM, there was no significant effect. Together, our results further show the beneficial effect of these agents in reversing NM-induced corneal injury and indicate the time window for effective treatment. This could be useful towards future development of targeted therapeutics against vesicant-induced ocular injury.

Cognitive and emotional impairments after cutaneous intoxication by CEES (a sulfur mustard analog) in mice

Cognitive and emotional disorders have been reported in veterans intoxicated with sulfur mustard (SM) a chemical weapon belonging to the category of vesicating agents. However, the intense stress associated with the SM intoxication may render difficult determining the exact role played by SM intoxication itself on the emergence and maintaining of cognitive disorders. Animal's model would allow overcoming this issue. So far, we presently investigated the cognitive and emotional impact of an acute cutaneous intoxication with CEES (2-chloroethyl ethyl sulfide), a SM analog in C57/Bl6 mice.Our study evidenced that up to 5days after a single acute neat CEES skin exposure, compared to controls, mice exhibited i) a significant increase in anxiety-like reactivity in an elevated plus-maze and in an open-field tasks and ii) an alteration of working memory in a sequential alternation task. In contrast, mice submitted to intoxication with a diluted CEES solution or hydrochloric acid (HCl) did not show any memory or emotional impairments. Given that, Our data shows that a single local cutaneous intoxication with neat CEES induced long-lasting cognitive and emotional pejorative effects, in accordance with the epidemiological observations in veterans. Thus, the single acute neat CEES cutaneous intoxication in mice could allow studying the sulfur mustard-induced cognitive and emotional disorders and their further counter-measures.

Interaction parameters for the uptake of sulfur mustard mimics into polyurethane films

• QCM methods interrogated sulfur mustard simulant uptake into polyurethane films. • Results predict high levels of sulfur mustard vapor uptake into polyurethane films. • Polymer swelling is influenced by a simulant’s dipole strength and polarizability. • Uptake measurements reveal how interaction parameters vary across classes of compounds. Chemical warfare agent (CWA) sorption into polymeric coatings is an important consideration for preventing human exposure to CWAs. The specific nature of CWA – polymer interactions greatly influences the degree of gas uptake into a polymeric coating. By uncovering the role the various functional groups in CWAs play during gas sorption, better films and coatings can be engineered. This study utilized a quartz crystal microbalance to measure sulfur mustard (HD) analog (simulant) and hexane vapor uptake into polyurethane films. Analysis of the uptake data with Flory–Huggins theory yielded interaction parameter values ( χ ) between 0.24 and 0.40 for each HD simulant-polyurethane system compared to 0.97 for hexane, revealing the importance of the chlorine and sulfur groups in gas uptake at the thin film interface. We predict similar uptake behavior for HD in polyurethane coatings due to structural similarities between HD and the simulants.

78 - LPS Infection Increasing ROS Level Regulates Stress Signaling Cascades, Inflammation and Apoptosis in Keratinocyte after 2-Chloroethyl Ethyl Sulphide Challenge

2-chloroethyl ethyl sulphide (CEES), a monofunctional analog of sulfur mustard (SM), is a well-known chemical warfare agent that induces vesicles or blisters on cutaneous toxicity in exposed individuals. CEES form highly reactive electrophilic sulphonium ions, which attack nucleophilic centers of biomolecules especially nucleic acid, caused damage in epithelial layers of skin, lungs and eye. Infection with the bacterial endotoxin lipopolysaccharides (LPS) are important immune system infection cues in epithelial layers of skin, but it remains unknown the molecular mechanisms to activate signaling cascades regulates inflammation and loss of cell-cell communication after CEES exposure. In the present study, we investigate the molecular mechanisms of inflammation and loss of cell-cell communication after LPS infection with CEES exposure on keratinocytes. Our results shows that LPS infection with CEES exposure enhanced accumulation of reactive oxygen species (ROS), resulting in the activation of nuclear factor κB (NF-κB) via ERK1/2MAPK/Akt/tuberin-mTOR pathways, which subsequently subdue the pro-inflammatory mediators, apoptosis and lose of cell-cell communication, leading to biomolecules damage. Protection against LPS infection with CEES toxicity could also be performed by blocking of ROS activation with antioxidant N-acetyl-L-cysteine (NAC), and ERK1/2MAPK (PD98059, U0126) and Akt inhibitors (LY294002, Wortmannin), which inhibit the intracellular redox-sensitive signaling pathways regulates inflammation and cell-cell communication. These results illustrate that accumulated ROS in mouse keratinocytes functions as a key NF-κB signaling cascade via ERK1/2MAPK/Akt/tuberin-mTOR regulatory pathways induced by CEES after LPS infection, leading to inflammation, apoptosis and loss of cell-cell communication, which is attenuated by antioxidant NAC, ERK1/2MAPK and Akt inhibitors. This work was supported by Indian Council of Medical Research (ICMR), Grant: 53/21/2010-CMB/BMS/ICMR, Government of India to Dr. Arttatrana Pal.

Corneal toxicity induced by vesicating agents and effective treatment options.

The vesicating agents sulfur mustard (SM) and lewisite (LEW) are potent chemical warfare agents that primarily cause damage to the ocular, skin, and respiratory systems. However, ocular tissue is the most sensitive organ, and vesicant exposure results in a biphasic injury response, including photophobia, corneal lesions, corneal edema, ulceration, and neovascularization, and may cause loss of vision. There are several reports on ocular injury from exposure to SM, which has been frequently used in warfare. However, there are very few reports on ocular injury by LEW, which indicate that injury symptoms appear instantly after exposure and faster than SM. In spite of extensive research efforts, effective therapies for vesicant-induced ocular injuries, mainly to the most affected corneal tissue, are not available. Hence, we have established primary human corneal epithelial cells and rabbit corneal organ culture models with the SM analog nitrogen mustard, which have helped to test the efficacy of potential therapeutic agents. These agents will then be further evaluated against in vivo SM- and LEW-induced corneal injury models, which will assist in the development of potential broad-spectrum therapies against vesicant-induced ocular injuries.

Nitrogen mustard exposure of murine skin induces DNA damage, oxidative stress and activation of MAPK/Akt-AP1 pathway leading to induction of inflammatory and proteolytic mediators

Our recent studies in SKH-1 hairless mice have demonstrated that topical exposure to nitrogen mustard (NM), an analog of sulfur mustard (SM), triggers the inflammatory response, microvesication and apoptotic cell death. Here, we sought to identify the mechanism/s involved in these NM-induced injury responses. Results obtained show that NM exposure of SKH-1 hairless mouse skin caused H2A.X and p53 phosphorylation and increased p53 accumulation, indicating DNA damage. In addition, NM also induced the activation of MAPKs/ERK1/2, JNK1/2 and p38 as well as that of Akt together with the activation of transcription factor AP1. Also, NM exposure induced robust expression of pro-inflammatory mediators namely cyclooxygenase 2 and inducible nitric oxide synthase and cytokine tumor necrosis factor alpha, and increased the levels of proteolytic mediator matrix metalloproteinase 9. NM exposure of skin also increased lipid peroxidation, 5,5-dimethyl-2-(8-octanoic acid)-1-pyrroline N-oxide protein adduct formation, protein and DNA oxidation indicating an elevated oxidative stress. We also found NM-induced increase in the homologous recombinant repair pathway, suggesting its involvement in the repair of NM-induced DNA damage. Collectively, these results indicate that NM induces oxidative stress, mainly a bi-phasic response in DNA damage and activation of MAPK and Akt pathways, which activate transcription factor AP1 and induce the expression of inflammatory and proteolytic mediators, contributing to the skin injury response by NM. In conclusion, this study for the first time links NM-induced mechanistic changes with our earlier reported murine skin injury lesions with NM, which could be valuable to identify potential therapeutic targets and rescue agents.

DNA Damage Initiated by the Sulfur Mustard Analog Mechlorethamine (methylbis(2‐chloroethyl)amine) in Mouse Keratinocytes is Associated with an Oxidative Stress Response

Sulfur mustard and nitrogen mustard (HN2, mechlorethamine) are bifunctional alkylating agent that cause dermal inflammation, edema and blistering. Skin keratinocytes are known to be important targets for mustards, which form both monofunctional DNA adducts and inter- and intrastrand DNA cross-links in the cells leading to cytotoxicity. In these studies, we used PAM212 mouse keratinocytes to analyze mechanisms underlying HN2 toxicity. Treatment of PAM212 cells with HN2 (3-30 μM) caused cytostasis; this was associated with a cell cycle block in late S phase and G2M phase. HN2 also caused DNA double strand breaks as shown by increased expression of phospho-H2A.X, a H2A histone variant that binds to double stranded DNA breaks creating a repair recognition domain. HN2-induced phosphorylation of H2A.X was both time- and concentration-dependent. Maximal increases were evident in cells at 24 h post HN2. HN2 induced double strand breaks were correlated with increases in the cellular antioxidants heme oxygenase-1 (HO-1) and heat shock protein27 (hsp27), which peaked 3 h and 6 h post HN2-treatment. These findings are consistent with the idea that HN2 initiates a DNA damage response in mouse keratinocytes that leads to induction of an adaptive stress response. Interfering with DNA strand breaks may be an effective strategy to mitigate mustard-induced damage in keratinocytes. Support: AR055073 and ES005022

Flavanone silibinin treatment attenuates nitrogen mustard-induced toxic effects in mouse skin

Currently, there is no effective antidote to prevent skin injuries by sulfur mustard (SM) and nitrogen mustard (NM), which are vesicating agents with potential relevance to chemical warfare, terrorist attacks, or industrial/laboratory accidents. Our earlier report has demonstrated the therapeutic efficacy of silibinin, a natural flavanone, in reversing monofunctional alkylating SM analog 2-chloroethyl ethyl sulfide-induced toxic effects in mouse skin. To translate this effect to a bifunctional alkylating vesicant, herein, efficacy studies were carried out with NM. Topical application of silibinin (1 or 2mg) 30min after NM exposure on the dorsal skin of male SKH-1 hairless mice significantly decreased NM-induced toxic lesions at 24, 72 or 120h post-exposure. Specifically, silibinin treatment resulted in dose-dependent reduction of NM-induced increase in epidermal thickness, dead and denuded epidermis, parakeratosis and microvesication. Higher silibinin dose also caused a 79% and 51%reversal in NM-induced increases in myeloperoxidase activity and COX-2 levels, respectively. Furthermore, silibinin completely prevented NM-induced H2A.X phosphorylation, indicating reversal of DNA damage which could be an oxidative DNA damage as evidenced by high levels of 8-oxodG in NM-exposed mouse skin that was significantly reversed by silibinin. Together, these findings suggest that attenuation of NM-induced skin injury by silibinin is due to its effects on the pathways associated with DNA damage, inflammation, vesication and oxidative stress. In conclusion, results presented here support the optimization of silibinin as an effective treatment of skin injury by vesicants.

Airway tissue plasminogen activator prevents acute mortality due to lethal sulfur mustard inhalation.

Sulfur mustard (SM) is a chemical weapon stockpiled today in volatile regions of the world. SM inhalation causes a life-threatening airway injury characterized by airway obstruction from fibrin casts, which can lead to respiratory failure and death. Mortality in those requiring intubation is more than 80%. No therapy exists to prevent mortality after SM exposure. Our previous work using the less toxic analog of SM, 2-chloroethyl ethyl sulfide, identified tissue plasminogen activator (tPA) an effective rescue therapy for airway cast obstruction (Veress, L. A., Hendry-Hofer, T. B., Loader, J. E., Rioux, J. S., Garlick, R. B., and White, C. W. (2013). Tissue plasminogen activator prevents mortality from sulfur mustard analog-induced airway obstruction. Am. J. Respir. Cell Mol. Biol. 48, 439-447). It is not known if exposure to neat SM vapor, the primary agent used in chemical warfare, will also cause death due to airway casts, and if tPA could be used to improve outcome. Adult rats were exposed to SM, and when oxygen saturation reached less than 85% (median: 6.5 h), intratracheal tPA or placebo was given under isoflurane anesthesia every 4 h for 48 h. Oxygen saturation, clinical distress, and arterial blood gases were assessed. Microdissection was done to assess airway obstruction by casts. Intratracheal tPA treatment eliminated mortality (0% at 48 h) and greatly improved morbidity after lethal SM inhalation (100% death in controls). tPA normalized SM-associated hypoxemia, hypercarbia, and lactic acidosis, and improved respiratory distress. Moreover, tPA treatment resulted in greatly diminished airway casts, preventing respiratory failure from airway obstruction. tPA given via airway more than 6 h after exposure prevented death from lethal SM inhalation, and normalized oxygenation and ventilation defects, thereby rescuing from respiratory distress and failure. Intra-airway tPA should be considered as a life-saving rescue therapy after a significant SM inhalation exposure incident.

Catalytic antioxidant AEOL 10150 treatment ameliorates sulfur mustard analog 2-chloroethyl ethyl sulfide-associated cutaneous toxic effects

Our previous studies and other published reports on the chemical warfare agent sulfur mustard (SM) and its analog 2-chloroethyl ethyl sulfide (CEES) have indicated a role of oxidative stress in skin injuries caused by these vesicating agents. We examined the effects of the catalytic antioxidant AEOL 10150 in the attenuation of CEES-induced toxicity using our established skin injury models (skin epidermal cells and SKH-1 hairless mice) to validate the role of oxidative stress in the pathophysiology of mustard vesicating agents. Treatment of mouse epidermal JB6 and human HaCaT cells with AEOL 10150 (50μM) 1h post-CEES exposure resulted in significant (p < 0.05) reversal of CEES-induced decreases in both cell viability and DNA synthesis. Similarly, AEOL 10150 treatment 1h after CEES exposure attenuated CEES-induced DNA damage in these cells. Similar AEOL 10150 treatments also caused significant (p < 0.05) reversal of CEES-induced decreases in cell viability in normal human epidermal keratinocytes. Cytoplasmic and mitochondrial reactive oxygen species measurements showed that AEOL 10150 treatment drastically ameliorated the CEES-induced oxidative stress in both JB6 and HaCaT cells. Based on AEOL 10150 pharmacokinetic studies in SKH-1 mouse skin, mice were treated with a topical formulation plus subcutaneous injection (5mg/kg) of AEOL 10150 1h after CEES (4mg/mouse) exposure and every 4h thereafter for 12h. This AEOL 10150 treatment regimen resulted in over 50% (p < 0.05) reversal of CEES-induced skin bi-fold and epidermal thickness, myeloperoxidase activity, and DNA oxidation in mouse skin. Results from this study demonstrate the potential therapeutic efficacy of AEOL 10150 against CEES-mediated cutaneous lesions, supporting AEOL 10150 as a medical countermeasure against SM-induced skin injuries.

Activation of DNA damage repair pathways in response to nitrogen mustard-induced DNA damage and toxicity in skin keratinocytes

Nitrogen mustard (NM), a structural analog of chemical warfare agent sulfur mustard (SM), forms adducts and crosslinks with DNA, RNA and proteins. Here we studied the mechanism of NM-induced skin toxicity in response to double strand breaks (DSBs) resulting in cell cycle arrest to facilitate DNA repair, as a model for developing countermeasures against vesicant-induced skin injuries. NM exposure of mouse epidermal JB6 cells decreased cell growth and caused S-phase arrest. Consistent with these biological outcomes, NM exposure also increased comet tail extent moment and the levels of DNA DSB repair molecules phospho H2A.X Ser139 and p53 Ser15 indicating NM-induced DNA DSBs. Since DNA DSB repair occurs via non homologous end joining pathway (NHEJ) or homologous recombination repair (HRR) pathways, next we studied these two pathways and noted their activation as defined by an increase in phospho- and total DNA-PK levels, and the formation of Rad51 foci, respectively. To further analyze the role of these pathways in the cellular response to NM-induced cytotoxicity, NHEJ and HRR were inhibited by DNA-PK inhibitor NU7026 and Rad51 inhibitor BO2, respectively. Inhibition of NHEJ did not sensitize cells to NM-induced decrease in cell growth and cell cycle arrest. However, inhibition of the HRR pathway caused a significant increase in cell death, and prolonged G2M arrest following NM exposure. Together, our findings, indicating that HRR is the key pathway involved in the repair of NM-induced DNA DSBs, could be useful in developing new therapeutic strategies against vesicant-induced skin injury.

Intratracheal heparin improves plastic bronchitis due to sulfur mustard analog

Inhalation of sulfur mustard (SM) and SM analog, 2-chloroethyl ethyl sulfide (CEES), cause fibrinous cast formation that occludes the conducting airways, similar to children with Fontan physiology-induced plastic bronchitis. These airway casts cause significant mortality and morbidity, including hypoxemia and respiratory distress. Our hypothesis was that intratracheal heparin, a highly cost effective and easily preserved rescue therapy, could reverse morbidity and mortality induced by bronchial cast formation. Sprague-Dawley rats were exposed to 7.5% CEES via nose-only aerosol inhalation to produce extensive cast formation and mortality. The rats were distributed into three groups: non-treated, phosphate-buffered saline (PBS)-treated, and heparin-treated groups. Morbidity was assessed with oxygen saturations and clinical distress. Blood and bronchoalveolar lavage fluid (BALF) were obtained for analysis, and lungs were fixed for airway microdissection to quantify the extent of airway cast formation. Heparin, given intratracheally, improved survival (100%) when compared to non-treated (75%) and PBS-treated (90%) controls. Heparin-treated rats also had improved oxygen saturations, clinical distress and airway cast scores. Heparin-treated rats had increased thrombin clotting times, factor Xa inhibition and activated partial thromboplastin times, indicating systemic absorption of heparin. There were also increased red blood cells (RBCs) in the BALF in 2/6 heparin-treated rats compared to PBS-treated control rats. Intratracheal heparin 1 hr after CEES inhalation improved survival, oxygenation, airway obstruction, and clinical distress. There was systemic absorption of heparin in rats treated intratracheally. Some rats had increased RBCs in BALF, suggesting a potential for intrapulmonary bleeding if used chronically after SM inhalation.

Myeloperoxidase deficiency attenuates nitrogen mustard-induced skin injuries

The pathologic mechanisms of skin injuries, following the acute inflammatory response induced by vesicating agents sulfur mustard (SM) and nitrogen mustard (NM) exposure, are poorly understood. Neutrophils which accumulate at the site of injury, abundantly express myeloperoxidase (MPO), a heme protein that is implicated in oxidant-related antimicrobial and cytotoxic responses. Our previous studies have shown that exposure to SM analog 2-chloroethyl ethyl sulfide (CEES) or NM results in an inflammatory response including increased neutrophilic infiltration and MPO activity. To further define the role of neutrophil-derived MPO in NM-induced skin injury, here we used a genetic approach and examined the effect of NM exposure (12h and 24h) on previously established injury endpoints in C57BL/6J wild type (WT) and B6.129X1-MPOtm1Lus/J mice (MPO KO), homozygous null for MPO gene. NM exposure caused a significant increase in skin bi-fold thickness, epidermal thickness, microvesication, DNA damage and apoptosis in WT mice compared to MPO KO mice. MPO KO mice showed relatively insignificant effect. Similarly, NM induced increases in the expression of inflammatory and proteolytic mediators, including COX-2, iNOS and MMP-9 in WT mice, while having a significantly lower effect in MPO KO mice. Collectively, these results show that MPO, which generates microbicidal oxidants, plays an important role in NM-induced skin injuries. This suggests the development of mechanism-based treatments against NM- and SM-induced skin injuries that inhibit MPO activity and attenuate MPO-derived oxidants.

Optical “Turn off” based selective detection and concomitant degradation of 2-chloroethyl ethyl sulfide (CEES) via Mg-porphyrazine complex immobilized on glass

Covalently assembled monolayers (CAMs) of Mg-porphyrazine complex on glass and silicon substrates were fabricated and employed as “Turn off” sensor for ppm level detection and degradation of a sulfur mustard analogue: 2-chloroethyl ethyl sulfide (CEES). The detection process was read-out optically via an off-the-shelf UV/Vis spectrophotometer in transmission mode. Monolayer based sensor system was shown to be quite robust and stable, sufficiently accurate and reversible under given experimental conditions. Notably, the sensor system exhibited marked selectivity for CEES when exposed exclusively or in mix to different potent analytes. Moreover, action of KMnO4 on monolayer-CEES complex lead to CEES degradation and resetting of the sensor to its native state for reuse.

Cutaneous Injury-Related Structural Changes and Their Progression following Topical Nitrogen Mustard Exposure in Hairless and Haired Mice

To identify effective therapies against sulfur mustard (SM)-induced skin injuries, various animals have been used to assess the cutaneous pathology and related histopathological changes of SM injuries. However, these efforts to establish relevant skin injury endpoints for efficacy studies have been limited mainly due to the restricted assess of SM. Therefore, we employed the SM analog nitrogen mustard (NM), a primary vesicating and bifunctional alkylating agent, to establish relevant endpoints for efficient efficacy studies. Our published studies show that NM (3.2 mg) exposure for 12–120 h in both the hairless SKH-1 and haired C57BL/6 mice caused clinical sequelae of toxicity similar to SM exposure in humans. The NM-induced cutaneous pathology-related structural changes were further analyzed in this study and quantified morphometrically (as percent length or area of epidermis or dermis) of skin sections in mice showing these lesions. H&E stained skin sections of both hairless and haired mice showed that NM (12–120 h) exposure caused epidermal histopathological effects such as increased epidermal thickness, epidermal-dermal separation, necrotic/dead epidermis, epidermal denuding, scab formation, parakeratosis (24–120 h), hyperkeratosis (12–120 h), and acanthosis with hyperplasia (72–120 h). Similar NM exposure in both mice caused dermal changes including necrosis, edema, increase in inflammatory cells, and red blood cell extravasation. These NM-induced cutaneous histopathological features are comparable to the reported lesions from SM exposure in humans and animal models. This study advocates the usefulness of these histopathological parameters observed due to NM exposure in screening and optimization of rescue therapies against NM and SM skin injuries.

Cross-Linking of Thioredoxin Reductase by the Sulfur Mustard Analogue Mechlorethamine (Methylbis(2-chloroethyl)amine) in Human Lung Epithelial Cells and Rat Lung: Selective Inhibition of Disulfide Reduction but Not Redox Cycling

Oxidative stress plays a key role in mechlorethamine (methylbis(2-chloroethyl)amine, HN2) toxicity. The thioredoxin system, consisting of thioredoxin reductase (TrxR), thioredoxin, and NADPH, is important in redox regulation and protection against oxidative stress. HN2 contains two electrophilic side chains that can react with nucleophilic sites in proteins, leading to changes in their structure and function. We report that HN2 inhibits the cytosolic (TrxR1) and mitochondrial (TrxR2) forms of TrxR in A549 lung epithelial cells. TrxR exists as homodimers under native conditions; monomers can be detected by denaturing and reducing SDS-PAGE followed by western blotting. HN2 treatment caused marked decreases in TrxR1 and TrxR2 monomers along with increases in dimers and oligomers under reducing conditions, indicating that HN2 cross-links TrxR. Cross-links were also observed in rat lung after HN2 treatment. Using purified TrxR1, NADPH reduced, but not oxidized, enzyme was inhibited and cross-linked by HN2. LC-MS/MS analysis of TrxR1 demonstrated that HN2 adducted cysteine- and selenocysteine-containing redox centers forming monoadducts, intramolecule and intermolecule cross-links, resulting in enzyme inhibition. HN2 cross-links two dimeric subunits through intermolecular binding to cysteine 59 in one subunit of the dimer and selenocysteine 498 in the other subunit, confirming the close proximity of the N- and C-terminal redox centers of adjacent subunits. Despite cross-linking and inhibition of TrxR activity by HN2, TrxR continued to mediate menadione redox cycling and generated reactive oxygen species. These data suggest that disruption of the thioredoxin system contributes to oxidative stress and tissue injury induced by HN2.