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

Dermal Exposure to Vesicating Nettle Agent Phosgene Oxime: Clinically Relevant Biomarkers and Skin Injury Progression in Murine Models

Phosgene oxime (CX), categorized as a vesicating chemical threat agent, causes effects that resemble an urticant or nettle agent. CX is an emerging potential threat agent that can be deployed alone or with other chemical threat agents to enhance their toxic effects. Studies on CX-induced skin toxicity, injury progression, and related biomarkers are largely unknown. To study the physiologic changes, skin clinical lesions and their progression, skin exposure of SKH-1 and C57BL/6 mice was carried out with vapor from 10 μl CX for 0.5-minute or 1.0-minute durations using a designed exposure system for consistent CX vapor exposure. One-minute exposure caused sharp (SKH-1) or sustained (C57BL/6) decrease in respiratory and heart rate, leading to mortality in both mouse strains. Both exposures caused immediate blanching, erythema with erythematous ring (wheel) and edema, and an increase in skin bifold thickness. Necrosis was also observed in the 0.5-minute CX exposure group. Both mouse strains showed comparative skin clinical lesions upon CX exposure; however, skin bifold thickness and erythema remained elevated up to 14 days postexposure in SKH-1 mice but not in C57BL/6 mice. Our data suggest that CX causes immediate changes in the physiologic parameters and gross skin lesions resembling urticaria, which could involve mast cell activation and intense systemic toxicity. This novel study recorded and compared the progression of skin injury to establish clinical biomarkers of CX dermal exposure in both the sexes of two murine strains relevant for skin and systemic injury studies and therapeutic target identification. SIGNIFICANCE STATEMENT: Phosgene oxime (CX), categorized as a vesicating agent, is considered as a potent chemical weapon and is of high military and terrorist threat interest since it produces rapid onset of severe injury as an urticant. However, biomarkers of clinical relevance related to its toxicity and injury progression are not studied. Data from this study provide useful clinical markers of CX skin toxicity in mouse models using a reliable CX exposure system for future mechanistic and efficacy studies.

HSP90, a Common Therapeutic Target for Suppressing Skin Injury Caused by Exposure to Chemically Diverse Classes of Blistering Agents

Vesicants such as arsenicals and mustards produce highly painful cutaneous inflammatory and blistering responses, hence developed as chemical weapons during World War I/II. Here, using lewisite and sulfur mustard surrogates, namely phenylarsine oxide (PAO) and 2-chloroethyl ethyl sulfide (CEES), respectively, we defined a common underlying mechanism of toxic action by these two distinct classes of vesicants. Murine skin exposure to these chemicals causes tissue destruction characterized by increase in skin bifold thickness, Draize score, infiltration of inflammatory cells, and apoptosis of epidermal and dermal cells. RNA sequencing analysis identified ∼346 inflammatory genes that were commonly altered by both PAO and CEES, along with the identification of cytokine signaling activation as the top canonical pathway. Activation of several proinflammatory genes and pathways is associated with phosphorylation-dependent activation of heat shock protein 90α (p-HSP90α). Topical treatment with known HSP90 inhibitors SNX-5422 and IPI-504 post PAO or CEES skin challenge significantly attenuated skin damage including reduction in overall skin injury and clinical scores. In addition, highly upregulated inflammatory genes Saa3, Cxcl1, Ccl7, IL-6, Nlrp3, Csf3, Chil3, etc. by both PAO and CEES were significantly diminished by treatment with HSP90 inhibitors. These drugs not only reduced PAO- or CEES-induced p-HSP90α expression but also its client proteins NLRP3 and pP38 and the expression of their target inflammatory genes. Our data confirm a critical role of HSP90 as a shared underlying molecular target of toxicity by these two distinct vesicants and provide an effective and novel medical countermeasure to suppress vesicant-induced skin injury. SIGNIFICANCE STATEMENT: Development of effective and novel mechanism-based antidotes that can simultaneously block cutaneous toxic manifestations of distinct vesicants is important and urgently needed. Due to difficulties in determining the exact nature of onsite chemical exposure, a potent drug that can suppress widespread cutaneous damage may find great utility. Thus, this study identified HSP90 as a common molecular regulator of cutaneous inflammation and injury by two distinct warfare vesicants, arsenicals and mustards, and HSP90 inhibitors afford significant protection against skin damage.

Metabolomics for identifying pathways involved in vesicating agent lewisite-induced corneal injury

Lewisite (LEW) is an arsenical vesicant that can be a potentially dangerous chemical warfare agent (CWA). Eyes are particularly susceptible to vesicant induced injuries and ocular LEW exposure can act swiftly, causing burning of eyes, edema, inflammation, cell death and even blindness. In our previous studies, we developed a LEW exposure-induced corneal injury model in rabbit and showed increased inflammation, neovascularization, cell death, and structural damage to rabbit corneas upon LEW exposure. In the present study, we further assessed the metabolomic changes to delineate the possible mechanisms underlying the LEW-induced corneal injuries. This information is vital and could help in the development of effective targeted therapies against ocular LEW injuries. Thus, the metabolomic changes associated with LEW exposures in rabbit corneas were assessed as a function of time, to delineate pathways from molecular perturbations at the genomic and proteomic levels. New Zealand white rabbit corneas (n = 3-6) were exposed to LEW vapor (0.2 mg/L; flow rate: 300 ml/min) for 2.5 min (short exposure; low dose) or 7.5 min (long-exposure; high dose) and then collected at 1, 3, 7, or 14 days post LEW exposure. Samples were prepared using the automated MicroLab STAR® system, and proteins precipitated to recover the chemically diverse metabolites. Metabolomic analysis was carried out by reverse phase UPLC-MS/MS and gas chromatography (GC)-MS. The data obtained were analyzed using Metabolon's software. The results showed that LEW exposures at high doses were more toxic, particularly at the day 7 post exposure time point. LEW exposure was shown to dysregulate metabolites associated with all the integral functions of the cornea and cause increased inflammation and immune response, as well as generate oxidative stress. Additionally, all important metabolic functions of the cells were also affected: lipid and nucleotide metabolism, and energetics. The high dose LEW exposures were more toxic, particularly at day 7 post LEW exposure (>10-fold increased levels of histamine, quinolinate, N-acetyl-β-alanine, GMP, and UPM). LEW exposure dysregulated integral functions of the cornea, caused inflammation and heightened immune response, and generated oxidative stress. Lipid and nucleotide metabolism, and energetics were also affected. The novel information about altered metabolic profile of rabbit cornea following LEW exposure could assist in delineating complex molecular events; thus, aid in identifying therapeutic targets to effectively ameliorate ocular trauma.

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.

Toxic blister agents: Chemistry, mode of their action and effective treatment strategies

Since their use during the First World War, Blister agents have posed a major threat to the individuals and have caused around two million casualties. Major incidents occurred not only due to their use as chemical warfare agents but also because of occupational hazards. Therefore, a clear understanding of these agents and their mode of action is essential to develop effective decontamination and therapeutic strategies. The blister agents have been categorised on the basis of their chemistry and the biological interactions that entail post contamination. These compounds have been known to majorly cause blisters/bullae along with alkylation of the contaminated DNA. However, due to the high toxicity and restricted use, very little research has been conducted and a lot remains to be clearly understood about these compounds. Various decontamination solutions and detection technologies have been developed, which have proven to be effective for their timely mitigation. But a major hurdle seems to be the lack of proper understanding of the toxicological mechanism of action of these compounds. Current review is about the detailed and updated information on physical, chemical and biological aspects of various blister agents. It also illustrates the mechanism of their action, toxicological effects, detection technologies and possible decontamination strategies.

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.

Effect of supersaturated oxygen emulsion treatment on chloropicrin-induced chemical injury in ex vivo rabbit cornea

With a possibility for the use of chemical weapons in battlefield or in terrorist activities, effective therapies against the devastating ocular injuries, from their exposure, are needed. Oxygen plays a vital role in ocular tissue preservation and wound repair. We tested the efficacy of supersaturated oxygen emulsion (SSOE) in reducing ex vivo corneal and keratocyte injury from chloropicrin (CP). CP, currently used as a pesticide, is a chemical threat agent like the vesicating mustard agents and causes severe corneal injury. Since our previous study in human corneal epithelial cells showed the treatment potential of SSOE (55 %), we further tested its efficacy in an ex vivo CP-induced rabbit corneal injury model. Corneas were exposed to CP (700 nmol) for 2 h, washed and cultured with or without SSOE for 24 h or 96 h. At 96 h post CP exposure, SSOE treatment presented a healing tendency of the corneal epithelial layer, and abrogated the CP-induced epithelial apoptotic cell death. SSOE treatment also reduced the CP induced DNA damage (H2A.X phosphorylation) and inflammatory markers (e.g. MMP9, IL-21, MIP-1β, TNFα). Further examination of the treatment efficacy of SSOE alone or in combination with other therapies in in vivo cornea injury models for CP and vesicants, is warranted.

Phosgene oxime: a highly toxic urticant and emerging chemical threat

Highly toxic industrial chemicals that are widely accessible, and hazardous chemicals like phosgene oxime (CX) that can be easily synthesized, pose a serious threat as potential chemical weapons. In addition, their accidental release can lead to chemical emergencies and mass casualties. CX, an urticant, or nettle agent, grouped with vesicating agents, causes instant pain, injury and systemic effects, which can lead to mortality. With faster cutaneous penetration, corrosive properties, and more potent toxicity compared to other vesicating agents, CX causes instantaneous and severe tissue damage. CX, a potential chemical terrorism threat agent, could therefore be weaponized with other chemical warfare agents to enhance their harmful effects. CX is the least studied vesicant and its acute and long-term toxic effects as well as its mechanism of action are largely unknown. This has hampered the identification of therapeutic targets and the development of effective medical countermeasures. There are only protective measures, decontamination, and supportive treatments available for reducing the toxic effects from CX exposure. This review summarizes CX toxicity, its known mechanism of action, and our current studies exploring the role of mast cell activation and associated signaling pathways in CX cutaneous exposure under the National Institutes of Health Countermeasures Against Chemical Threats program. Potential treatment options and the development of effective targeted countermeasures against CX-induced morbidity and mortality is also discussed.

Protective role of mesenchymal stem cells transfected with miRNA-378a-5p in phosgene inhalation lung injury

Phosgene-induced lung injury is an important type of acute lung injury (ALI). Currently, no effective clinical treatment has been developed yet. Our previous study revealed that expressions of 6 miRNAs were significantly increased in phosgene-induced lung injury. The screened miRNA with the most significant effect on hepatocyte growth factor (HGF) expression by mesenchymal stem cells (MSCs) was transfected into MSCs. This study aimed to investigate whether the transfected MSCs had better therapeutic effects than MSCs alone. MSCs were co-cultured with miRNA mimics for 24h and 48h. HGF expression in culture supernatant was detected by ELISA. HGF expression in MSCs was detected by Western blot after being co-cultured with the selected miRNA inhibitor. The transfected MSCs were given to rats suffering from phosgene-induced lung injury. Expressions of TNF-α, IL-6, IL-1β and IL-10, were assayed by ELISA. SP-C mRNA level was tested by RT-PCR. VE-CAD expression was tested by Western blot. We found that miRNA-378a-5p most increased HGF expression among the six miRNAs. After transfection of MSCs with miRNA-378a-5p inhibitor, HGF expression was decreased. Compared with untreated MSCs, MSCs transfected with miRNA-378a-5p exhibited more significant decreases in lung injury score, white blood cell count and protein content while restoring respiratory indexes. Meanwhile, expressions of TNF-α, IL-6, IL-1β were decreased while those of IL-10, SP-C and VE-cadherin were increased. In conclusion, MSCs transfected with miRNA-378a-5p were more effective in treating phosgene-induced lung injury by repairing the secretion of alveolar epithelial cells and improving the permeability of vascular endothelial cells compared with MSCs alone.

Cutaneous lewisite exposure causes acute lung injury

Lewisite is a strong vesicating and chemical warfare agent. Because of the rapid transdermal absorption, cutaneous exposure to lewisite can also elicit severe systemic injury. Lewisite (2.5, 5.0, and 7.5 mg/kg) was applied to the skin of Ptch1^+/- /SKH-1 mice and acute lung injury (ALI) was assessed after 24 hours. Arterial blood gas measurements showed hypercapnia and hypoxemia in the lewisite-exposed group. Histological evaluation of lung tissue revealed increased levels of proinflammatory neutrophils and a dose-dependent increase in structural changes indicative of injury. Increased inflammation was also confirmed by altered expression of cytokines, including increased IL-33, and a dose-dependent elevation of CXCL1, CXCL5, and GCSF was observed in the lung tissue. In the bronchoalveolar lavage fluid of lewisite-exposed animals, there was a significant increase in HMGB1, a damage-associated molecular pattern molecule, as well as elevated CXCL1 and CXCL5, which coincided with an influx of neutrophils to the lungs. Complete blood cell analysis revealed eosinophilia and altered neutrophil-lymphocyte ratios as a consequence of lewisite exposure. Mean platelet volume and RBC distribution width, which are predictors of lung injury, were also increased in the lewisite group. These data demonstrate that cutaneous lewisite exposure causes ALI and may contribute to mortality in exposed populations.