Treatment of Sulfur Mustard Corneal Injury by Augmenting the DNA Damage Response (DDR): A Novel Approach

Sulfur mustard (SM) is a highly reactive organic chemical has been used as a chemical warfare agent and terrorist threat since World War I. The cornea is highly sensitive to SM toxicity and exposure to low vapor doses can cause incapacitating acute injuries. Exposure to higher doses can elicit persistent secondary keratopathies that cause reduced quality of life and impaired or lost vision. Despite a century of research, there are no specific treatments for acute or persistent ocular SM injuries. SM cytotoxicity emerges, in part, through DNA alkylation and double-strand breaks (DSBs). Because DSBs can naturally be repaired by DNA damage response pathways with low efficiency, we hypothesized that enhancing the homologous recombination pathway could pose a novel approach to mitigate SM injury. Here, we demonstrate that a dilithium salt of adenosine diphosphoribose (INV-102) increases protein levels of p53 and Sirtuin 6, upregulates transcription of BRCA1/2, enhances γH2AX focus formation, and promotes assembly of repair complexes at DSBs. Based on in vitro evidence showing INV-102 enhancement of DNA damage response through both p53-dependent and p53-independent pathways, we next tested INV-102 in a rabbit preclinical model of corneal injury. In vivo studies demonstrate a marked reduction in the incidence and severity of secondary keratopathies in INV-102-treated eyes compared with vehicle-treated eyes when treatment was started 24 hours after SM vapor exposure. These results suggest DNA repair mechanisms are a viable therapeutic target for SM injury and suggest topical treatment with INV-102 is a promising approach for SM as well as other conditions associated with DSBs. SIGNIFICANCE STATEMENT: Sulfur mustard gas corneal injury currently has no therapeutic treatment. This study aims to show the therapeutic potential of activating the body's natural DNA damage response to activate tissue repair.

Mustard gas exposure instigates retinal Müller cell gliosis

Sulfur mustard (SM) is a chemical warfare agent (CWA) that causes severe eye pain, photophobia, excessive lacrimation, corneal and ocular surface defects, and blindness. However, SM's effects on retinal cells are relatively meager. This study investigated the role of SM toxicity on Müller glial cells responsible for cellular architecture, inner blood-retinal barrier maintenance, neurotransmitter recycling, neuronal survival, and retinal homeostasis. Müller glial cells (MIO-M1) were exposed to SM analog, nitrogen mustard (NM), at varying concentrations (50-500 μM) for 3 h, 24 h, and 72 h. Müller cell gliosis was evaluated using morphological, cellular, and biochemical methods. Real-time cellular integrity and morphological evaluation were performed using the xCELLigence real-time monitoring system. Cellular viability and toxicity were measured using TUNEL and PrestoBlue assays. Müller glia hyperactivity was calculated based on glial fibrillary acidic protein (GFAP) and vimentin immunostaining. Intracellular oxidative stress was measured using DCFDA and DHE cell-based assays. Inflammatory markers and antioxidant enzyme levels were determined by quantitative real-time PCR (qRT-PCR). AO/Br and DAPI staining further evaluated DNA damage, apoptosis, necrosis, and cell death. Inflammasome-associated Caspase-1, ASC, and NLRP3 were studied to identify mechanistic insights into NM toxicity in Müller glial cells. The cellular and morphological evaluation revealed the Müller glia hyperactivity after NM exposure in a dose- and time-dependent manner. NM exposure caused significant oxidative stress and enhanced cell death at 72 h. A significant increase in antioxidant indices was observed at the lower concentrations of NM. Mechanistically, we found that NM-treated MIO-M1 cells increased caspase-1 levels that activated NLRP3 inflammasome-induced production of IL-1β and IL-18, and elevated Gasdermin D (GSDMD) expression, a crucial component actuating pyroptosis. In conclusion, NM-induced Müller cell gliosis via increased oxidative stress results in caspase-1-dependent activation of the NLRP3 inflammasome and cell death driven primarily by pyroptosis.

Considerations for the optimization of in vitro models of chloropicrin toxicity

Chloropicrin (CP) is a common agricultural fumigant historically used as a chemical warfare agent and is a concern for potential use in warfare and terrorist applications. Our inability to effectively treat CP-induced injuries makes it essential to better understand CP toxicity. We set out to elucidate variables that must be understood to achieve optimal exposure conditions for in vitro investigations given that such models are important for the study of CP injury and potential therapeutics. To this end, we evaluated the effects of volatility, cell seeding density, and serum concentration of cell culture medium on CP toxicity in an immortalized human corneal epithelial cell line. We found that even with very dilute solutions, CP remained highly volatile, so much so that a 0.0019% CP solution resulted in 90% cell death at time 0, but was nearly nontoxic 45 min later. Not surprisingly, the CP-induced IL-8 response was shown to vary with cell viability in this experiment. After exposure with 0.00115% CP, cells that were 12% confluent experienced over 40% more cell death than cells exposed at 87% confluency. Exposure with the same CP dose in medium containing concentrations of fetal bovine serum (FBS) ranging from 0.1% to 15% exhibited a 17% difference in cell viability. Given that chemical toxicity can be significantly influenced by volatility, cell density, and serum content of cell culture medium, these phenomena should be explored during the development and optimization of toxicant exposure models.

A Systematic Review of Keratinocyte Secretions: A Regenerative Perspective

Cell regenerative therapy is a modern solution for difficult-to-heal wounds. Keratinocytes, the most common cell type in the skin, are difficult to obtain without the creation of another wound. Stem cell differentiation towards keratinocytes is a challenging process, and it is difficult to reproduce in chemically defined media. Nevertheless, a co-culture of keratinocytes with stem cells usually achieves efficient differentiation. This systematic review aims to identify the secretions of normal human keratinocytes reported in the literature and correlate them with the differentiation process. An online search revealed 338 references, of which 100 met the selection criteria. A total of 80 different keratinocyte secretions were reported, which can be grouped mainly into cytokines, growth factors, and antimicrobial peptides. The growth-factor group mostly affects stem cell differentiation into keratinocytes, especially epidermal growth factor and members of the transforming growth factor family. Nevertheless, the reported secretions reflected the nature of the involved studies, as most of them focused on keratinocyte interaction with inflammation. This review highlights the secretory function of keratinocytes, as well as the need for intense investigation to characterize these secretions and evaluate their regenerative capacities.

miR-584 and miR-146 are candidate biomarkers for acute respiratory distress syndrome

MicroRNAs (miRNAs/miRs) have important roles in inflammation and infections, which are common manifestations of acute respiratory distress syndrome (ARDS). The present study aimed to assess whether serum miRNAs are potential diagnostic biomarkers for human ARDS. For this, two sets of serum samples from healthy individuals and patients with ARDS were analysed by high-throughput sequencing to identify differentially expressed genes in ARDS. A total of 679 valid sequences were identified as differentially expressed (P<0.05). Of these, five differentially expressed miRNAs were subjected to reverse transcription-quantitative PCR validation. Finally, two miRNAs (miR-584 and miR-146a) were successfully verified. These two miRNAs were significantly downregulated in the serum of patients with ARDS. Gene Ontology annotations and Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that their target transcripts were implicated in a broad range of biological processes and various metabolic pathways, including involvement in the regulation of various inflammatory factors. The present study provided a framework for understanding the molecular mechanisms of ARDS and suggested that miR-584 and miR-146a are associated with ARDS and may be potential therapeutic targets.

High Throughput SiRNA Screening for Chloropicrin and Hydrogen Fluoride-Induced Cornea Epithelial Cell Injury

Toxicant-induced ocular injury is a true ocular emergency because chemicals have the potential to rapidly inflict significant tissue damage. Treatments for toxicant-induced corneal injury are generally supportive as no specific therapeutics exist to treat these injuries. In the efforts to develop treatments and therapeutics to care for exposure, it can be important to understand the molecular and cellular mechanisms of these injuries. We propose that utilization of high throughput small inhibitory RNA (siRNA) screening can be an important tool that could help to more rapidly elucidate the molecular mechanisms of chemical cornea epithelial injury. siRNA are double stranded RNA molecules that are 19-25 nucleotides long and utilize the post-transcriptional gene silencing pathway to degrade mRNA which have homology to the siRNA. The resulting reduction of expression of the specific gene can then be studied in toxicant exposed cells to ascertain the function of that gene in the cellular response to the toxicant. The development and validation of in vitro exposure models and methods for the high throughput screening (HTS) of hydrogen fluoride- (HF) and chloropicrin- (CP) induced ocular injury are presented in this article. Although we selected these two toxicants, our methods are applicable to the study of other toxicants with minor modifications to the toxicant exposure protocol. The SV40 large T antigen immortalized human corneal epithelial cell line SV40-HCEC was selected for study. Cell viability and IL-8 production were selected as endpoints in the screening protocol. Several challenges associated with the development of toxicant exposure and cell culture methods suitable for HTS studies are presented. The establishment of HTS models for these toxicants allows for further studies to better understand the mechanism of injury and to screen for potential therapeutics for chemical ocular injury.

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.

Nitrogen mustard-induced corneal injury involves the sphingomyelin-ceramide pathway

PURPOSE

Nitrogen mustard (NM), which simulates the effects of sulfur mustard (SM), is a potent vesicant known to cause irreversible corneal damage. This study investigates the mechanisms by which NM induces corneal damage by examining the impact of NM exposure on the morphology and lipidome of the cornea.

METHODS

Intact ex vivo rabbit eyes were placed in serum-free DMEM organ culture. NM (0, 1, 2.5, 5 or 10 mg/ml) was applied to the central cornea for 5, 10 or 15 min using a 5 mm filter disk and subsequently rinsed with DMEM. Corneas were then cultured for 3, 24, or 48 h before being fixed for morphological analysis or for 24 h before being snap frozen for lipidomic analysis.

RESULTS

No morphological changes were detected 3 h after NM exposure. Twenty-four h after exposure, 1 mg/ml NM caused erosion of the corneal epithelium, but no damage to the underlying stroma. Damage caused by 2.5 mg/ml NM extended almost two thirds through the corneal stroma, while 5 mg/ml completely penetrated the corneal stroma. An altered lipid profile occurred 24 h after corneas were exposed to NM. Specific sphingomyelins, ceramides, and diacylglycerols were increased up to 9-, 60- and 10-fold, respectively.

CONCLUSIONS

NM induces concentration- and exposure time-dependent damage to the cornea that increases in severity over time. Alterations in the sphingomyelin-ceramide pathway may contribute to the damaging effects of NM exposure.

An evidence-based review of the genotoxic and reproductive effects of sulfur mustard

Sulfur mustard (SM) is a chemical warfare agent which is cytotoxic in nature, and at the molecular level, SM acts as DNA alkylating agent leading to genotoxic and reproductive effects. Mostly, the exposed areas of the body are the main targets for SM; however, it also adversely affects various tissues of the body and ultimately exhibits long-term complications including genotoxic and reproductive effects, even in the next generations. The effect of SM on reproductive system is the reason behind male infertility. The chronic genotoxic and reproductive complications of SM have been observed in the next generation, such as reproductive hormones disturbances, testicular atrophy, deficiency of sperm cells, retarded growth of sperm and male infertility. SM exerts toxic effects through various mechanisms causing reproductive dysfunction. The key mechanisms include DNA alkylation, production of reactive oxygen species (ROS) and nicotinamide adenine dinucleotide (NAD) depletion. However, the exact molecular mechanism of such long-term effects of SM is still unclear. In general, DNA damage, cell death and defects in the cell membrane are frequently observed in SM-exposed individuals. SM can activate various cellular and molecular mechanisms related to oxidative stress (OS) and inflammatory responses throughout the reproductive system, which can cause decreased spermatogenesis and impaired sperm quality via damage to tissue function and structure. Moreover, the toxic effects of SM on the reproductive system as well as the occurrence of male infertility among exposed war troopers in the late exposure phase is still uncertain. The chronic effects of SM exposure in parents can cause congenital defects in their children. In this review, we aimed to investigate chronic genotoxic and reproductive effects of SM and their molecular mechanisms in the next generations.

Oleanolic acid rejuvenates testicular function through attenuating germ cell DNA damage and apoptosis via deactivation of NF-κB, p53 and p38 signalling pathways

OBJECTIVES

Inflammation can cause degenerative changes of reproductive function. Oleanolic acid (OA), the effective component from Ligustrum lucidum Ait., exhibits significantly anti-inflammation and antiageing activity. However, whether OA restores testicular dysfunction via inhibition of inflammation with ageing is unclear. Here, in a natural ageing rat model, we investigated the protection effects of OA and its mechanism of action.

METHODS

Eighteen-month-old Sprague Dawley (SD) rats were randomly divided into ageing control group and two OA-treated groups (5 and 25 mg/kg). Nine-month-old SD rats were used as adult controls. All rats were received either vehicle or OA for 6 months. Then, histomorphology, weight and index of testis, protein expression and immunohistochemistry were examined.

KEY FINDINGS

Oleanolic acid significantly restored testicular morphology and improved testicular weight and index. Moreover, OA significantly inhibited phospho-NF-κB p65 and its downstream proinflammatory cytokines' expressions, including IL-1β, COX-2 and TNF-α in testis tissues. Similarly, OA remarkably inhibited IL-1β and TNF-α production. OA significantly attenuated germ cells' DNA damage and apoptosis. Such changes were accompanied by downregulation of γH2AX, p-P53 and Bax expressions, and upregulation of Bcl-2 and Bcl-2/Bax ratio. In addition, OA remarkably inhibited p38 signalling.

CONCLUSIONS

Oleanolic acid effectively rejuvenates testicular function via attenuating germ cell DNA damage and apoptosis through deactivation of NF-κB, p53 and p38 signalling pathways.

Evaluation of miR-9 and miR-143 expression in urine specimens of sulfur mustard exposed patients

Sulfur mustard (SM) or mustard gas is a chemical alkylating agent that causes blisters in the skin (blister gas), burns the eyes and causes lung injury. Some major cellular pathways are involved in the damage caused by mustard gas such as NF-κb signaling, TGF-β signaling, WNT pathway, inflammation, DNA repair and apoptosis. MicroRNAs are non-coding small RNAs (19–25 nucleotides) that are involved in the regulation of gene expression and are found in two forms, extracellular and intracellular. Changes in the levels of extracellular microRNAs are directly associated with many diseases, it is thus common to study the level of extracellular microRNAs as a biomarker to determine the pathophysiologic status. In this study, 32 mustard gas injured patients and 32healthy subjects participated. Comparative evaluation of miR-9 and miR-143 expression in urine samples was performed by Real Time PCR and Graph Pad software. The Mann Whitney t-test analysis of data showed that the expression level of miR-143 and miR-9 had a significant decrease in sulfur mustard individuals with the respective p-value of 0.0480 and 0.0272 compared to normal samples, with an imbalance of several above mentioned pathways. It seems that reducing the expression level of these genes has a very important role in the pathogenicity of mustard gas injured patients.

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.

Inflammatory mechanisms of pulmonary injury induced by mustards

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

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.

Identification and validation of vesicant therapeutic targets using a high-throughput siRNA screening approach

Sulfur mustard [SM, bis-(2-chloroethyl) sulfide] is a highly reactive bifunctional alkylating agent that has been used as a vesicating agent in warfare scenarios to induce severe lung, skin, and eye injury. SM cutaneous lesions are characterized by both vesication and severe inflammation, but the molecular mechanisms that lead to these signs and symptoms are not well understood. There is a pressing need for effective therapeutics to treat this injury. An understanding of the molecular mechanisms of injury and identification of potential therapeutic targets is necessary for rational therapeutic development. We have applied a high-throughput small interfering RNA (siRNA) screening approach to the problem of SM cutaneous injury in an effort to meet these needs. Our siRNA screening efforts have initially focused on SM-induced inflammation in cutaneous injury since chronic inflammation after exposure appears to play a role in progressive clinical pathology, and intervention may improve clinical outcome. Also, targets that mitigate cellular injury should reduce the inflammatory response. Historical microarray data on this injury were mined for targets and pathways implicated in inflammation, and a siRNA library of 2,017 targets was assembled for screening. Primary screening and library deconvolution were performed using human HaCaT keratinocytes and focused on cell death and inflammatory markers as end points. Using this in vitro approach, we have identified and validated novel targets for the potential treatment of SM-induced cutaneous injury.

Time course of skin features and inflammatory biomarkers after liquid sulfur mustard exposure in SKH-1 hairless mice

Sulfur mustard (SM) is a strong bifunctional alkylating agent that produces severe tissue injuries characterized by erythema, edema, subepidermal blisters and a delayed inflammatory response after cutaneous exposure. However, despite its long history, SM remains a threat because of the lack of effective medical countermeasures as the molecular mechanisms of these events remain unclear. This limited number of therapeutic options results in part of an absence of appropriate animal models. We propose here to use SKH-1 hairless mouse as the appropriate model for the design of therapeutic strategies against SM-induced skin toxicity. In the present study particular emphasis was placed on histopathological changes associated with inflammatory responses after topical exposure of dorsal skin to three different doses of SM (0.6, 6 and 60mg/kg) corresponding to a superficial, a second-degree and a third-degree burn. Firstly, clinical evaluation of SM-induced skin lesions using non invasive bioengineering methods showed that erythema and impairment of skin barrier increased in a dose-dependent manner. Histological evaluation of skin sections exposed to SM revealed that the time to onset and the severity of symptoms including disorganization of epidermal basal cells, number of pyknotic nuclei, activation of mast cells and neutrophils dermal invasion were dose-dependent. These histopathological changes were associated with a dose- and time-dependent increase in expression of specific mRNA for inflammatory mediators such as interleukins (IL1β and IL6), tumor necrosis factor (TNF)-α, cycloxygenase-2 (COX-2), macrophage inflammatory proteins (MIP-1α, MIP-2 and MIP-1αR) and keratinocyte chemoattractant (KC also called CXCL1) as well as adhesion molecules (L-selectin and vascular cell adhesion molecule (VCAM)) and growth factor (granulocyte colony-stimulating factor (Csf3)). A dose-dependent increase was also noted after SM exposure for mRNA of matrix metalloproteinases (MMP9) and laminin-γ2 which are associated with SM-induced blisters formation. Taken together, our results show that SM-induced skin histopathological changes related to inflammation is similar in SKH-1 hairless mice and humans. SKH-1 mouse is thus a reliable animal model for investigating the SM-induced skin toxicity and to develop efficient treatment against SM-induced inflammatory skin lesions.

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.

The injury progression of T lymphocytes in a mouse model with subcutaneous injection of a high dose of sulfur mustard

BACKGROUND

In clinical studies, the findings on sulfur mustard (SM) toxicity for CD3(+)CD4(+) and CD3(+)CD8(+) T lymphocyte subsets are contradictory. In animal experiments, the effect of SM on the T cell number and proliferation is incompatible and is even the opposite of the results in human studies. In this study, we observed the dynamic changes of T lymphocytes in the first week in a high-dose SM-induced model.

METHODS

Mice were exposed to SM by subcutaneous injection (20 mg/kg) and were sacrificed 4 h, 24 h, 72 h and 168 h later. Spleen T lymphocyte proliferation was evaluated by (3)H-TdR. Flow cytometric analysis was used to observe the percentage of CD3(+)CD4(+) and CD3(+)CD8(+) T lymphocyte subsets. The IL-1β, IL-6, IL-10 and TNF-α levels in plasma were assayed using the Luminex method. DNA damage in bone marrow cells was observed with the single cell gel electrophoresis technique (SCGE).

RESULTS

SM continuously inhibited the proliferation of lymphocytes for 7 days, and there was a significant rebound of Con A-induced T lymphocyte proliferation only at 24 h. The percentage of CD3(+)CD4(+) and CD3(+)CD8(+) lymphocytes was upregulated, which was accompanied by increased IL-1β and TNF-α and decreased IL-10. The IL-6 level was gradually decreased in the PG group at 4 h. The peak of lymphocytic apoptosis and DNA damage occurred at 24 h and 72 h, respectively.

CONCLUSION

Our results show that SM significantly inhibited T lymphocyte proliferation as well as induced CD3(+)CD4(+) and CD3(+)CD8(+) upregulation. SM intoxication also significantly increased the levels of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α) and inhibited the level of anti-inflammatory cytokine IL-10. Our results may partly be due to the significant SM induced significant apoptosis and necrosis of lymphocytes as well as DNA damage of bone marrow cells. The results provided a favorable evaluation of SM immune toxicity in an animal model.

Cytokine regulation by MAPK activated kinase 2 in keratinocytes exposed to sulfur mustard

Uncontrolled inflammation contributes to cutaneous damage following exposure to the warfare agent bis(2-chloroethyl) sulfide (sulfur mustard, SM). Activation of the p38 mitogen activated protein kinase (MAPK) precedes SM-induced cytokine secretion in normal human epidermal keratinocytes (NHEKs). This study examined the role of p38-regulated MAPK activated kinase 2 (MK2) during this process. Time course analysis studies using NHEK cells exposed to 200μM SM demonstrated rapid MK2 activation via phosphorylation that occurred within 15 min. p38 activation was necessary for MK2 phosphorylation as determined by studies using the p38 inhibitor SB203580. To compare the role of p38 and MK2 during SM-induced cytokine secretion, small interfering RNA (siRNA) targeting these proteins was utilized. TNF-α, IL-1β, IL-6 and IL-8 secretion was evaluated 24h postexposure, while mRNA changes were quantified after 8h. TNF-α, IL-6 and IL-8 up regulation at the protein and mRNA level was observed following SM exposure. IL-1β secretion was also elevated despite unchanged mRNA levels. p38 knockdown reduced SM-induced secretion of all the cytokines examined, whereas significant reduction in SM-induced cytokine secretion was only observed with TNF-α and IL-6 following MK2 knockdown. Our observations demonstrate potential activation of other p38 targets in addition to MK2 during SM-induced cytokine secretion.

Absence of a p53 allele delays nitrogen mustard-induced early apoptosis and inflammation of murine skin

Bifunctional alkylating agent sulfur mustard (SM) and its analog nitrogen mustard (NM) cause DNA damage leading to cell death, and potentially activating inflammation. Transcription factor p53 plays a critical role in DNA damage by regulating cell cycle progression and apoptosis. Earlier studies by our laboratory demonstrated phosphorylation of p53 at Ser15 and an increase in total p53 in epidermal cells both in vitro and in vivo following NM exposure. To elucidate the role of p53 in NM-induced skin toxicity, we employed SKH-1 hairless mice harboring wild type (WT) or heterozygous p53 (p53+/-). Exposure to NM (3.2mg) caused a more profound increase in epidermal thickness and apoptotic cell death in WT relative to p53+/- mice at 24h. However, by 72h after exposure, there was a comparable increase in NM-induced epidermal cell death in both WT and p53+/- mice. Myeloperoxidase activity data showed that neutrophil infiltration was strongly enhanced in NM-exposed WT mice at 24h persisting through 72h of exposure. Conversely, robust NM-induced neutrophil infiltration (comparable to WT mice) was seen only at 72h after exposure in p53+/- mice. Similarly, NM-exposure strongly induced macrophage and mast cell infiltration in WT, but not p53+/- mice. Together, these data indicate that early apoptosis and inflammation induced by NM in mouse skin are p53-dependent. Thus, targeting this pathway could be a novel strategy for developing countermeasures against vesicants-induced skin injury.

Development of a mouse model for sulfur mustard-induced ocular injury and long-term clinical analysis of injury progression

CONTEXT

Sulfur mustard (SM) is a highly reactive vesicating agent that can induce severe ocular injury. The clinical features of this injury have been well documented, but the molecular basis for this pathology is not well understood. Identification and validation of specific targets is necessary in the effort to develop effective therapeutics for this injury. Currently used rabbit models are not well suited for many molecular studies because the necessary reagents are not widely available. However, these reagents are widely available for the mouse model.

OBJECTIVE

Our objective is to develop a mouse model of SM-induced ocular injury suitable for the study of the molecular mechanisms of injury and the evaluation of therapeutics.

MATERIALS AND METHODS

Ocular exposure to sulfur mustard vapor was accomplished by using a vapor cup method. Dose response studies were conducted in female BALB/c mice. An exposure dose which produced moderate injury was selected for further study as moderate injury was determined to be amenable to studying the beneficial effects of potential therapeutics. Histopathology and inflammatory markers were evaluated for up to 28 days after exposure, while clinical injury progression was evaluated for 1 year post-exposure.

RESULTS

A biphasic ocular injury was observed in mice exposed to SM. Acute phase SM ocular injury in mice was characterized by significant corneal epithelium loss, corneal edema, limbal engorgement, and ocular inflammation. This was followed by a brief recovery phase. A delayed injury phase then ensued in the following weeks to months and was characterized by keratitis, stromal edema, infiltrates, neovascularization, and eventual corneal scarring.

DISCUSSION AND CONCLUSIONS

SM-induced ocular injury in mice is consistent with observations of SM-induced ocular injury in humans and rabbit models. However, in the mouse model, the SM ocular injury, a more rapid onset of the delayed injury phase was observed. We have developed an animal model of SM injury that is suitable for studies to elucidate molecular mechanisms of injury and identify potential therapeutic targets.

Mechanisms of sulfur mustard analog 2-chloroethyl ethyl sulfide-induced DNA damage in skin epidermal cells and fibroblasts

Employing mouse skin epidermal JB6 cells and dermal fibroblasts, here we examined the mechanisms of DNA damage by 2-chloroethyl ethyl sulfide (CEES), a monofunctional analog of sulfur mustard (SM). CEES exposure caused H2A.X and p53 phosphorylation as well as p53 accumulation in both cell types, starting at 1h, that was sustained for 24h, indicating a DNA-damaging effect of CEES, which was also confirmed and quantified by alkaline comet assay. CEES exposure also induced oxidative stress and oxidative DNA damage in both cell types, measured by an increase in mitochondrial and cellular reactive oxygen species and 8-hydroxydeoxyguanosine levels, respectively. In the studies distinguishing between oxidative and direct DNA damage, 1h pretreatment with glutathione (GSH) or the antioxidant Trolox showed a decrease in CEES-induced oxidative stress and oxidative DNA damage. However, only GSH pretreatment decreased CEES-induced total DNA damage measured by comet assay, H2A.X and p53 phosphorylation, and total p53 levels. This was possibly due to the formation of GSH-CEES conjugates detected by LC-MS analysis. Together, our results show that CEES causes both direct and oxidative DNA damage, suggesting that to rescue SM-caused skin injuries, pleiotropic agents (or cocktails) are needed that could target multiple pathways of mustard skin toxicities.

Sulfur mustard primes human neutrophils for increased degranulation and stimulates cytokine release via TRPM2/p38 MAPK signaling

Sulfur mustard (2,2'-bis-chloroethyl-sulfide; SM) has been a military threat since the World War I. The emerging threat of bioterrorism makes SM a major threat not only to military but also to civilian world. SM injury elicits an inflammatory response characterized by infiltration of neutrophils. Although SM was reported to prime neutrophils, the mechanism has not been identified yet. In the present study, we investigated the mechanism of SM-induced priming in human neutrophils. SM increased [Ca(2+)](i) in human neutrophils in a concentration-dependent fashion. Transient receptor potential melastatin (TRPM) 2 inhibitors (clotrimazole, econazole and flufenamic acid) and silencing of TRPM2 by shRNA attenuated SM-induced [Ca(2+)](i) increase. SM primed degranulation of azurophil and specific granules in response to activation by fMLP as previously reported. SB203580, an inhibitor of p38 MAPK, inhibited SM-induced priming. Neither PD98057, an ERK inhibitor, nor SP600215, a JNK inhibitor, inhibited SM-induced priming. In addition, SM enhanced phosphorylation of NF-kB p65 and release of TNF-α, interleukin (IL)-6 and IL-8. SB203580 inhibited SM-induced NF-kB phosphorylation and cytokine release. These results suggest the involvement of TRPM2/p38 MAPK pathway in SM-induced priming and cytokines release in neutrophils.

Sulfur mustard induces differentiation in human primary keratinocytes: opposite roles of p38 and ERK1/2 MAPK

The chemical warfare agent sulfur mustard (SM) severely affects the regeneration capacity of skin. The underlying molecular and cellular mechanisms, however, are far from clear. Here, we demonstrate that normal human epidermal keratinocytes (NHEK) after exposure to SM strongly upregulated expression of keratin-1, involucrin, and loricrin, thus indicating premature epidermal differentiation. Furthermore, proliferation was repressed after treatment with SM. Analysis of intracellular signaling in NHEK revealed that SM enhances phosphorylation, nuclear translocation, and activity of the mitogen-activated protein kinases (MAPK) p38 and ERK1/2. Inhibition of p38 activity downregulated expression of keratin-1 and loricrin, whereas blockage of ERK1/2 significantly stimulated biosynthesis of these markers, pointing to opposite roles of p38 and ERK1/2 in the differentiation process. Simultaneous interruption of p38 and ERK1/2 activity led to a decreased expression of keratin-1 and loricrin. This suggests that NHEK differentiation is essentially controlled by p38 activity which may be negatively influenced by ERK1/2 activity. Functional analysis demonstrated that SM affects NHEK in their ability to migrate through extracellular matrix which can be rescued upon application of an inhibitor of p38 activity. Thus, our findings indicate that SM triggers premature differentiation in keratinocytes via p38 activity which may contribute to impaired regeneration of SM-injured skin.

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.

Capsaicinoids, chloropicrin and sulfur mustard: possibilities for exposure biomarkers

Incapacitating and irritating agents produce temporary disability persisting for hours to days after the exposure. One can be exposed to these agents occupationally in industrial or other working environments. Also general public can be exposed in special circumstances, like industrial accidents or riots. Incapacitating and irritating agents discussed in this review are chloropicrin and capsaicinoids. In addition, we include sulfur mustard, which is an old chemical warfare agent and known to cause severe long-lasting injuries or even death. Chloropicrin that was used as a warfare agent in the World War I is currently used mainly as a pesticide. Capsaicinoids, components of hot pepper plants, are used by police and other law enforcement personnel as riot control agents. Toxicity of these chemicals is associated particularly with the respiratory tract, eyes, and skin. Their acute effects are relatively well known but the knowledge of putative long-term effects is almost non-existent. Also, mechanisms of effects at cellular level are not fully understood. There is a need for further research to get better idea of health risks, particularly of long-term and low-level exposures to these chemicals. For this, exposure biomarkers are essential. Validated exposure biomarkers for capsaicinoids, chloropicrin, and sulfur mustard do not exist so far. Metabolites and macromolecular adducts have been suggested biomarkers for sulfur mustard and these can already be measured qualitatively, but quantitative biomarkers await further development and validation. The purpose of this review is, based on the existing mechanistic and toxicokinetic information, to shed light on the possibilities for developing biomarkers for exposure biomonitoring of these compounds. It is also of interest to find ideas for early effect biomarkers considering the need for studies on subchronic and chronic toxicity.