Apoptosis as a mechanism of 2-chloroethylethyl sulfide-induced cytotoxicity

Tear proteomics analysis of patient suffered from delayed mustard gas keratopathy

Understanding the molecular and cellular mechanisms involved in the pathogenesis of ocular injured induced by mustard gas can help better identify complications and discover appropriate therapies. This study aimed to analyze the proteomics of tears of chemical warfare victims with mustard gas ocular injuries and compare it with healthy individuals. In this case-control research, 10 mustard gas victims with long-term ocular difficulties (Chronic) were included in the patient group, while 10 healthy persons who were age and sex matched to the patients were included in the control group. Schirmer strips were used to collect the tears of the participants. Proteomics experiments were performed using the high-efficiency TMT10X method to evaluate the tear protein profile, and statistical bioinformatics methods were used to identify the differently expressed proteins. 24 proteins had different expressions between the two groups. Among these 24 proteins, 8 proteins had increased expression in veterans' tears, while the remaining 16 proteins had decreased expression. Reactome pathways were used to look at proteins with various expressions, and 13 proteins were found to be engaged in the immune system, 9 of which were effective in the innate immune system, and 5 proteins were effective in the complement cascade. Ocular mustard gas exposure may cause a compromised immune system on the eye's surface, exposing the cornea to external and endogenous infections, and eventually causing corneal opacity and reduced vision.

Effects of CEES and LPS synergistically stimulate oxidative stress inactivates OGG1 signaling in macrophage cells

2-chloroethyl ethyl sulphide (CEES), a monofunctional analogue of sulfur mustard, is a strong vesicant and an alkylating chemical warfare agent. We studied the molecular mechanism of oxidative stress triggered signaling cascades in murine macrophages exposed to CEES with lipopolysaccharide (LPS). Exposure of CEES with specific dose of LPS stimulates oxidative stress caused increasing level of intracellular ROS and RNS, decreased antioxidant enzymes, increasing bimolecular damage, reduced cell viability, and cell cycle arrest. Synergistic exposure of CEES and LPS provoked significant increase in phosphorylation of MAPKs, Akt, tuberin, that down regulate OGG1 expression and 8-OHdG accumulations. Treatment with Akt and ERK1/2 inhibitors, the cells with constitutively active inhibiting activity of Akt and ERK1/2MAPK significant reduce CEES and LPS challenge tuberin but not the OGG1. In addition, the N-acetylcysteine inhibited ROS/RNS generation, elevation of antioxidants level, expression of ERK1/2, Akt, tuberin phosphorylation, resulted in deceased 8-OHdG accumulation and upregulation of OGG1 protein expression suggesting no involvement of Akt and ERK1/2MAPK pathways after CEES and LPS challenge. Collectively, our results indicate that exposure of CEES and LPS induces oxidative stress and the activation of tuberin, and 8-OHdG accumulation via upstream signaling pathways including Akt and ERK1/2MAPK pathway in macrophages but not the down regulation of OGG1.

Structural changes in the skin of hairless mice following exposure to sulfur mustard correlate with inflammation and DNA damage

Sulfur mustard (SM, bis(2-chloroethyl)sulfide) is a bifunctional alkylating agent that causes dermal inflammation, edema and blistering. To investigate the pathogenesis of SM-induced injury, we used a vapor cup model which provides an occlusive environment in which SM is in constant contact with the skin. The dorsal skin of SKH-1 hairless mice was exposed to saturated SM vapor or air control. Histopathological changes, inflammatory markers and DNA damage were analyzed 1-14 days later. After 1 day, SM caused epidermal thinning, stratum corneum shedding, basal cell karyolysis, hemorrhage and macrophage and neutrophil accumulation in the dermis. Cleaved caspase-3 and phosphorylated histone 2A.X (phospho-H2A.X), markers of apoptosis and DNA damage, respectively, were increased whereas proliferating cell nuclear antigen (PCNA) was down-regulated after SM exposure. By 3 days, epithelial cell hypertrophy, edema, parakeratosis and loss of epidermal structures were noted. Enzymes generating pro-inflammatory mediators including myeloperoxidase and cyclooxygenase-2 were upregulated. After 7 days, keratin-10, a differentiation marker, was evident in the stratum corneum. This was associated with an underlying eschar, as neoepidermis began to migrate at the wound edges. Trichrome staining revealed increased collagen deposition in the dermis. PCNA expression in the epidermis was correlated with hyperplasia, hyperkeratosis, and parakeratosis. By 14 days, there was epidermal regeneration with extensive hyperplasia, and reduced expression of cleaved caspase-3, cyclooxygenase-2 and phospho-H2A.X. These findings are consistent with the pathophysiology of SM-induced skin injury in humans suggesting that the hairless mouse can be used to investigate the dermatoxicity of vesicants and the potential efficacy of countermeasures.

Ocular effects of exposure to industrial chemicals: clinical management and proteomic approaches to damage assessment

Industrial chemicals in a variety of applications are often found in highly populated areas and their presence carries risks. The threat of serious consequences from inadvertent or intentional events involving hazardous chemicals is a possibility. Extremism and/or other illicit activities pose environmental threats from chemical exposures. We present here a review of the threat of ocular injury in small-and large-scale chemical releases and discuss mechanisms of damage and repair to the eyes. The emerging field of proteomics has been described in relation to its potential role in the assessment of ocular changes following chemical exposures and management of ocular trauma.

Genotoxicants target distinct molecular networks in neonatal neurons

BACKGROUND

Exposure of the brain to environmental agents during critical periods of neuronal development is considered a key factor underlying many neurologic disorders.

OBJECTIVES

In this study we examined the influence of genotoxicants on cerebellar function during early development by measuring global gene expression changes.

METHODS

We measured global gene expression in immature cerebellar neurons (i.e., granule cells) after treatment with two distinct alkylating agents, methylazoxymethanol (MAM) and nitrogen mustard (HN2). Granule cell cultures were treated for 24 hr with MAM (10-1,000 microM) or HN2 (0.1-20 microM) and examined for cell viability, DNA damage, and markers of apoptosis.

RESULTS

Neuronal viability was significantly reduced (p < 0.01) at concentrations > 500 microM for MAM and > 1.0 microM for HN2; this correlated with an increase in both DNA damage and markers of apoptosis. Neuronal cultures treated with sublethal concentrations of MAM (100 microM) or HN2 (1.0 microM) were then examined for gene expression using large-scale mouse cDNA microarrays (27,648). Gene expression results revealed that a) global gene expression was predominantly up-regulated by both genotoxicants; b) the number of down-regulated genes was approximately 3-fold greater for HN2 than for MAM; and c) distinct classes of molecules were influenced by MAM (i.e, neuronal differentiation, the stress and immune response, and signal transduction) and HN2 (i.e, protein synthesis and apoptosis).

CONCLUSIONS

These studies demonstrate that individual genotoxicants induce distinct gene expression signatures. Further study of these molecular networks may explain the variable response of the developing brain to different types of environmental genotoxicants.

Thymic atrophy via estrogen-induced apoptosis is related to Fas/FasL pathway

A convincing body of evidence indicates that estrogen has significant immunomodulatory properties, including induction of thymic involution. However, it is unclear whether or not estrogen induces thymic involution by triggering apoptosis depended on Fas-FasL interactions. In the present study, estradiol-17beta (E(2)) was used to treat rats by gavages at 10, 1, 0.1, 0.01, and 0 ng/kg/day, respectively. Atrophy of thymus was determined by in situ morphological examination. Apoptotic cells were identified by terminal deoxynucleotide transferase-mediated deoxy-UTP nick end labeling (TUNEL) assay. A semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method was used to analyze Fas and FasL mRNA levels. The results showed that E(2) induced thymic atrophy, increased the rates of apoptotic death, and enhanced the Fas/FasL mRNA levels. These findings suggested that Fas/FasL-mediated apoptosis involved in the induction of thymic atrophy by E(2).

Protection by antioxidants against toxicity and apoptosis induced by the sulphur mustard analog 2-chloroethylethyl sulphide (CEES) in Jurkat T cells and normal human lymphocytes

1. The mechanism of toxicity of sulphur mustard was investigated by examining the biochemical effects of the analog 2-chloroethylethyl sulphide (CEES) in both human Jurkat cells as well as normal human lymphocytes. 2. Exposure of both types of cells to CEES resulted in a marked decrease in the intracellular concentration of the reduced form of glutathione (GSH), and CEES-induced cell death was potentiated by l-buthionine sulphoximine, an inhibitor of GSH synthesis. 3. CEES increased the endogenous production of reactive oxygen species (ROS) in Jurkat cells, and CEES-induced cell death was potentiated by hydrogen peroxide. 4. CEES induced various hallmarks of apoptosis, including collapse of the mitochondrial membrane potential, proteolytic processing and activation of procaspase-3, and cleavage of poly (ADP-ribose) polymerase. 5. The effects of CEES on the accumulation of ROS, the intracellular concentration of GSH, the mitochondrial membrane potential, and caspase-3 activity were all inhibited by pretreatment of cells with the GSH precursor N-acetyl cysteine or with GSH-ethyl ester. Furthermore, CEES-induced cell death was also prevented by these antioxidants. 6. CEES toxicity appears to be mediated, at least in part, by the generation of ROS and consequent depletion of GSH. Given that sulphur mustard is still a potential biohazard, the protective effects of antioxidants against CEES toxicity demonstrated in Jurkat cells and normal human lymphocytes may provide the basis for the development of a therapeutic strategy to counteract exposure to this chemical weapon.

Low-dose sulfur mustard primes oxidative function and induces apoptosis in human polymorphonuclear leukocytes

Although considerable work has focused on understanding the processes of direct tissue injury mediated by the chemical warfare vesicant, sulfur mustard (2,2'-bis-chloroethyl sulfide; SM), relatively little is known regarding the mechanisms of secondary injury caused potentially by the acute inflammatory response that follows SM exposure. Polymorphonuclear leukocytes (PMNs) play a central role in the initiation and propagation of inflammatory responses that, in some cases, result in autoimmune tissue damage. The potential for PMN-derived tissue damage following SM exposure may, in part, account for the protracted progression of the injury before it resolves. The current study was undertaken to evaluate the priming, oxidative function, and viability of PMN following exposure to low doses of SM such as those that might remain in tissues as a result of topical exposure. Our results demonstrate that doses of SM ranging from 25 to 100 microM primed PMN for oxidative burst in response to activation by fMLP, and that doses of SM ranging from 50 to 100 microM induced PMN apoptosis. Understanding the mechanisms through which SM directly affects PMN activation and apoptosis will be of critical value in developing novel treatments for inflammatory tissue injury following SM exposure.

Lipopolysaccharide enhances the cytotoxicity of 2-chloroethyl ethyl sulfide

BACKGROUND

The bacterial endotoxin, lipopolysaccharide (LPS), is a well-characterized inflammatory factor found in the cell wall of Gram-negative bacteria. In this investigation, we studied the cytotoxic interaction between 2-chloroethyl ethyl sulfide (CEES or ClCH2CH2SCH2CH3) and LPS using murine RAW264.7 macrophages. CEES is a sulfur vesicating agent and is an analog of 2,2'-dichlorodiethyl sulfide (sulfur mustard). LPS is a ubiquitous natural agent found in the environment. The ability of LPS and other inflammatory agents (such as TNF-alpha and IL-1beta) to modulate the toxicity of CEES is likely to be an important factor in the design of effective treatments.

RESULTS

RAW 264.7 macrophages stimulated with LPS were found to be more susceptible to the cytotoxic effect of CEES than unstimulated macrophages. Very low levels of LPS (20 ng/ml) dramatically enhanced the toxicity of CEES at concentrations greater than 400 microM. The cytotoxic interaction between LPS and CEES reached a maximum 12 hours after exposure. In addition, we found that tumor necrosis factor-alpha (TNF-alpha) and interleukin-1-beta (IL-1-beta) as well as phorbol myristate acetate (PMA) also enhanced the cytotoxic effects of CEES but to a lesser extent than LPS.

CONCLUSION

Our in vitro results suggest the possibility that LPS and inflammatory cytokines could enhance the toxicity of sulfur mustard. Since LPS is a ubiquitous agent in the natural environment, its presence is likely to be an important variable influencing the cytotoxicity of sulfur mustard toxicity. We have initiated further experiments to determine the molecular mechanism whereby the inflammatory process influences sulfur mustard cytotoxicity.

Protective effect of topical iodine preparations upon heat-induced and hydrofluoric acid-induced skin lesions

In this study, the protective prophylactic and post-exposure effects of novel topical iodine preparations were demonstrated upon heat- and hydrofluoric acid-induced skin lesions in the haired guinea pig. Prophylactic treatment of thermal bums with a liquid iodine preparation resulted in statistically significant reductions of 39% and 30%, respectively, in acute inflammation and hemorrhage-microscopic dermal parameters indicative of acute tissue damage. A clear trend of iodine-induced reduction in dermal necrosis occurred, and the epidermal healing markers, acanthosis and hyperkeratosis, were increased. Postexposure treatment of thermal burns with an iodine ointment preparation immediately after occurrence also conferred significant therapeutic reduction in parameters of tissue damage such as epidermal ulceration (87%), acute inflammation (58%), and hemorrhage (30%). Gross pathological evaluation showed that prophylactic and postexposure treatments with the liquid iodine preparation significantly reduced the heat-induced ulceration area by 97% and 65%, respectively. In addition, immediate treatment with an ointment iodine formulation significantly decreased the ulceration area by 98%; its tetraglycol vehicle also had a beneficial effect. Postexposure treatment with the iodine ointment proved efficacious upon hydrofluoric acid-induced skin burns. We observed statistically significant reductions of 76% and 68% in ulceration areas at intervals of 5 and 10 minutes between exposure and treatment, whereas a weaker effect was observed at a longer time interval of 15 minutes. Our findings suggest the therapeutic usage of these newly developed iodine preparations for thermally induced and hydrofluoric acid-induced skin burns.

Gene expressions in Jurkat cells poisoned by a sulphur mustard vesicant and the induction of apoptosis

1. The sulphur mustard vesicant 2-chloroethylethyl sulphide (CEES) induced apoptosis in Jurkat cells. 2. Akt (PKB), a pivotal protein kinase which can block apoptosis and promotes cell survival, was identified to be chiefly down-regulated in a dose-dependent manner following CEES treatment. Functional analysis showed that the attendant Akt activity was simultaneously reduced. 3. PDK1, an upstream effector of Akt, was also down-regulated following CEES exposure, but two other upstream effectors of Akt, PI3-K and PDK2, remained unchanged. 4. The phosphorylation of Akt at Ser(473) and Thr(308) was significantly decreased following CEES treatment, reflecting the suppressed kinase activity of both PDK1 and PDK2. 5. Concurrently, the anti-apoptotic genes, Bcl family, were down-regulated, in sharp contrast to the striking up-regulation of some death executioner genes, caspase 3, 6, and 8. 6. Based on these findings, a model of CEES-induced apoptosis was established. These results suggest that CEES attacked the Akt pathway, directly or indirectly, by inhibiting Akt transcription, translation, and post-translation modification. 7. Taken together, upon exposure to CEES, apoptosis was induced in Jurkat cells via the down-regulation of the survival factors that normally prevent the activation of the death executioner genes, the caspases.

Mitochondrial and nuclear DNA damage induced by sulphur mustard in keratinocytes

The extent and role of mitochondrial DNA damage in the mechanism of action of sulphur mustard (SM) is poorly understood. In this study, a combination of quantitative polymerase chain reaction and Southern hybridization was used to determine the levels of both total DNA adducts and DNA interstrand crosslinks in genomic and mitochondrial DNA isolated from normal human epidermal keratinocytes exposed to SM. The formation of both types of lesions occurred simultaneously in nuclear and mitochondrial DNA, however, SM produced significantly higher levels of both total adducts and crosslinks in genomic DNA than mitochondrial DNA. The total lesion frequency was 0.45 lesions/kb per 100 microM SM in the DHFR gene and 0.12 lesions/kb per 100 microM SM in the mitochondrial segment. Interstrand crosslinks occurred at a frequency of 0.28 crosslinks/10 kb per 100 microM SM in the DHFR gene and 0.05 crosslinks/10 kb per 100 microM SM in the mitochondrial segment. DNA interstrand crosslinks are thought to be the critical lesion produced by similar bi-functional alkylating agents. However, the levels of DNA cross-linking revealed in this study show that even at vesicating doses of SM mitochondrial DNA is still largely free of cross-links and the predominant form of DNA damage contributing to cell death occurs in the nucleus.

Nuclear dependence of sulfur mustard-mediated cell death

Although sulfur mustard (SM) has been reported to be a DNA alkylating agent, it is not clear how much of the cytotoxicity of this agent is secondary to DNA damage. To test the hypothesis that the presence of a nucleus is required for the toxicity of sulfur mustard, enucleated endothelial cytoplasts were treated with SM. Using a combination of biochemical and microscopic assays, we demonstrate that some aspects of SM-induced cell death may be dependent on the presence of a nucleus, while others may not be. For example, it was found that cytoskeletal changes, such as loss of stress fibers and rounding, proceed in response to sulfur mustard treatment even in the absence of a nucleus. However, significant further increases in caspase activity and the associated phosphatidylserine translocation were not observed in cytoplasts treated with 500 microM SM for 6 h (following a 20-h recovery at the end of cytoplast preparation). In contrast, cytoplasts treated with chelerythrine, an agent previously reported to induce rapid apoptosis, demonstrated increases in caspase activity in cytoplasts comparable to that observed in the nucleated cells. This indicates that sulfur mustard-induced alkylation of nuclear DNA may be an important stimulus for activation of caspases in nucleated cells. Interestingly, the baseline caspase activity in cytoplasts was greater than in nucleated cells. Analysis of the time course of caspase activation in untreated adherent cytoplasts indicated that the activity increases initially and then stabilizes by 8 h to a low level that was comparable to the level observed at 26 h in untreated cytoplasts. This indicates that cytoplasts are able to tolerate stable low levels of caspase activity and not proceed immediately into the execution phase of apoptosis. The cytoplast model may be quite useful in the toxicological assessment of agents that are thought to exert their toxicity through DNA damage.

Topical iodine preparation as therapy against sulfur mustard-induced skin lesions

Sulfur mustard (SM) is a powerful vesicant employed as an agent of chemical warfare. This study demonstrates the therapeutic effect of a novel topical iodine preparation as a postexposure treatment against SM-induced lesions in the fur-covered guinea-pig skin model. Iodine treatment 15 min after SM exposure resulted in statistically significant reductions of 48, 50, and 55% in dermal acute inflammation, hemorrhage, and necrosis, respectively, whereas, the epidermal healing markers, hyperkerathosis and acanthosis, were significantly elevated by 72 and 67%, respectively, 2 days after treatment. At the interval of 30 min between SM exposure and iodine treatment, there was a significant degree of healing or recovery, albeit to a lesser extent than that observed in the shorter interval. Although the epidermal healing markers were not elevated, the parameters indicative of active tissue damage, such as subepidermal microblisters, epidermal ulceration, dermal acute inflammation, hemorrhage, and necrosis, were significantly reduced by 35, 67, 43, 39, and 45%, respectively. At the 45-min interval between exposure and treatment, there was also a certain degree of healing or recovery expressed as significant reductions in dermal subacute inflammation, subepidermal microblister formation, and epidermal ulceration, whereas, acanthosis was statistically elevated, indicating an increased healing potential. At the 60-min interval, iodine was less efficacious; nevertheless, a significant reduction in the incidence of subepidermal microblisters and an expansion of the acanthotic area were observed. Gross ulceration was significantly decreased at intervals of 15 and 30 min between exposure and treatment. The local anesthetic, lidocaine, did not alter the therapeutic effect of iodine. SM was not affected chemically by iodine as measured by gas chromatography-mass spectrometry (GC-MS) analysis. These findings suggest that the iodine preparation functions as an antidote against skin lesions induced by SM.

Sustained enhancement of Ca(2+) influx by glibenclamide induces apoptosis in RINm5F cells

Cytosolic Ca(2+) elevations are known to be involved in triggering apoptosis in many tissues, but the effect of sustained enhancement of Ca(2+) influx on apoptosis in beta cells remains unknown. We have found that the viability of RINm5F cells is decreased dose-dependently by continuous exposure to glibenclamide at concentrations from 10(-7) to 10(-4) M, and that this effect is partially ameliorated by pretreatment with cycloheximide. Electrophoresis of the cells exposed to glibenclamide revealed ladder-like fragmentation characteristic of apoptosis, and which also is suppressed by cycloheximide pretreatment. By using terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining, we detected increased DNA fragmentation in the nuclei of the cells exposed to glibenclamide, and staining with Hoechst 33342 and propidium iodide showed a dose-dependent increase in the number of cells with the chromatin condensation and fragmentation in their nuclei that is characteristic of apoptosis. The effects of glibenclamide on cell viability and apoptotic cell death were partially inhibited by treatment with Ca(2+) channel blocker, and by reducing the extracellular Ca(2+) concentration during glibenclamide exposure, suggesting that they may be derived from increased Ca(2+) influx. Furthermore, only the percentage of apoptotic cells, and not that of necrotic cells, increased with the increasing intracellular Ca(2+) concentration during glibenclamide exposure. In conclusion, we have demonstrated that the sustained enhancement of Ca(2+) influx caused by glibenclamide exposure can induce apoptotic cell death in a pure beta cell line.

DNA fragmentation pattern induced in thymocytes by sulphur mustard

Sulphur mustard (HD) is a blister agent for which no specific therapy exists. The mechanism of cell injury caused by HD is not well understood. This study examined DNA damage in thymocytes exposed to a range of HD concentrations over a time course of 1-24 h. Thymocytes incubated with HD showed an increase in the production of DNA fragments of the type frequently associated with apoptosis, namely, initial formation of large fragments of 30-50, 200-300 and > 700 kilobase pairs (kbp), followed by further degradation to produce an internucleosomal 'ladder' of oligomers of approximately 180 base pairs (bp). Pulsed field electrophoresis analysis of thymocytes incubated with HD detected breakdown of the chromatin up to 3 h before a corresponding increase in the low molecular weight (MW) oligonucleosomal fragments could be seen on conventional agarose gels. These results suggest that cells damaged by HD poisoning may be irretrievably committed to cell death sooner after exposure than previous studies suggested. The nature of the DNA fragments produced suggested that apoptosis may represent a component of the pathway of cell death induced by HD. These aspects may have implications for the search for specific therapeutic reagents effective in the prevention or treatment of HD poisoning.

Effects of selected arginine analogues on sulphur mustard toxicity in human and hairless guinea pig skin keratinocytes

The toxicity of sulphur mustard (HD) was characterized in first passage cultures of human neonatal foreskin keratinocytes and then several arginine analogues were investigated to ascertain their efficacies in protecting against HD toxicity in this system. d- and l-nitroarginine methyl ester (d/l-NAME), l-phosphoarginine, and l-nitroarginine were all found to confer concentration-related protective effects against HD in confluent cultures. l-NAME was used to further characterize this protection and was only effective in cultures that were not actively proliferating. This compound was also found to be efficacious when added to the cultures up to several hours after HD exposure, although its continued presence was required in order for protection to be effective. The protective effects of l-thiocitrulline (l-TC) against HD toxicity were also assessed. This arginine analogue was extremely potent in preventing HD toxicity in actively proliferating, just-confluent, and postconfluent cultures in a concentration-dependent fashion (0.1-15 mM), with little HD toxicity apparent at high l-TC concentrations. Protection was prophylactic in nature, with l-TC having almost maximal effect when added to the cultures only 1 min prior to HD culture exposure. Efficacy then declined rapidly so that no protection was evident when l-TC was added 30 min post-HD. The effects of this drug were persistent, with no decrease in protective efficacy up to 4 days after HD exposure, even when l-TC was removed from the cultures. l-TC did not protect against the antimitotic effects of HD; while l-TC-protected cells were subcultured successfully, they displayed no clonogenic activity. Although l-TC is closely related structurally to protective nitroarginine derivatives, the characteristics of l-TC protection against HD were markedly different and suggest that they exert their protective activities at different sites. Administration of l-NAME and l-TC by a variety of routes did not result in consistent protection against topical vapor challenges of HD in hairless guinea pigs. However, both compounds were effective in preventing the toxicity of HD in primary cultures of hairless guinea pig skin keratinocytes, indicating that species differences were not likely to be responsible for the poor efficacy of these compounds in vivo.