Impact of topical application of sulfur mustard on mice skin and distant organs DNA repair enzyme signature

Skin Models Used to Define Mechanisms of Action of Sulfur Mustard

Sulfur mustard (SM) is a threat to both civilian and military populations. Human skin is highly sensitive to SM, causing delayed erythema, edema, and inflammatory cell infiltration, followed by the appearance of large fluid-filled blisters. Skin wound repair is prolonged following blistering, which can result in impaired barrier function. Key to understanding the action of SM in the skin is the development of animal models that have a pathophysiology comparable to humans such that quantitative assessments of therapeutic drugs efficacy can be assessed. Two animal models, hairless guinea pigs and swine, are preferred to evaluate dermal products because their skin is morphologically similar to human skin. In these animal models, SM induces degradation of epidermal and dermal tissues but does not induce overt blistering, only microblistering. Mechanisms of wound healing are distinct in these animal models. Whereas a guinea pig heals by contraction, swine skin, like humans, heals by re-epithelialization. Mice, rats, and rabbits are also used for SM mechanistic studies. However, healing is also mediated by contraction; moreover, only microblistering is observed. Improvements in animal models are essential for the development of therapeutics to mitigate toxicity resulting from dermal exposure to SM.

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.

Evaluation of DNA double-strand break repair capacity in human cells: Critical overview of current functional methods

DNA double-strand breaks (DSBs) are highly deleterious lesions, responsible for mutagenesis, chromosomal translocation or cell death. DSB repair (DSBR) is therefore a critical part of the DNA damage response (DDR) to restore molecular and genomic integrity. In humans, this process is achieved through different pathways with various outcomes. The balance between DSB repair activities varies depending on cell types, tissues or individuals. Over the years, several methods have been developed to study variations in DSBR capacity. Here, we mainly focus on functional techniques, which provide dynamic information regarding global DSB repair proficiency or the activity of specific pathways. These methods rely on two kinds of approaches. Indirect techniques, such as pulse field gel electrophoresis (PFGE), the comet assay and immunofluorescence (IF), measure DSB repair capacity by quantifying the time-dependent decrease in DSB levels after exposure to a DNA-damaging agent. On the other hand, cell-free assays and reporter-based methods directly track the repair of an artificial DNA substrate. Each approach has intrinsic advantages and limitations and despite considerable efforts, there is currently no ideal method to quantify DSBR capacity. All techniques provide different information and can be regarded as complementary, but some studies report conflicting results. Parameters such as the type of biological material, the required equipment or the cost of analysis may also limit available options. Improving currently available methods measuring DSBR capacity would be a major step forward and we present direct applications in mechanistic studies, drug development, human biomonitoring and personalized medicine, where DSBR analysis may improve the identification of patients eligible for chemo- and radiotherapy.

Sulphur mustard induces progressive toxicity and demyelination in brain cell aggregate culture

Sulphur mustard (H; bis(2-chloroethyl) sulphide) is a vesicant chemical warfare (CW) agent that has been well documented as causing acute injury to the skin, eyes and respiratory system. Although a great deal of research effort has been expended to understand how H exerts these effects, its mechanism of action is still poorly understood. At high exposures, H also causes systemic toxicity with chronic and long-term effects to the immune, cardiovascular and central nervous systems, and these aspects of H poisoning are much less studied and comprehended. Rat aggregate cultures comprised of multiple brain cell types were exposed to H and followed for four weeks post-exposure to assess neurotoxicity. Toxicity (LDH, caspase-3 and aggregate diameter) was progressive with time post-exposure. In addition, statistically significant changes in neurofilament heavy chain (NFH), glial fibrillary acidic protein (GFAP), Akt phosphorylation, IL-6, GRO-KC and TNF-α were noted that were time- and concentration-dependent. Myelin basic protein, CNPase and vascular endothelial growth factor (VEGF) were found to be especially sensitive to H exposure in a time- and concentration-dependent fashion, with levels falling to ∼50 % of control values at ∼10 μM H by 8 days post-exposure. Demyelination and VEGF inhibition may be causal in the long-term neuropsychological illnesses that have been documented in casualties exposed to high concentrations of H, and may also play a role in the peripheral neuropathy that has been observed in some of these individuals.

Early oxidative stress, DNA damage and inflammation resulting from subcutaneous injection of sulfur mustard into mice

Oxidative stress, DNA damage repair, and inflammation are three important reactions of sulfur mustard (SM) exposure. But molecular related chronological events in the earlier stage of SM exposure model are still unclear. In the research, reactive oxygen species (ROS) was measured by using flow cytometry. Cytokines were tested in Luminex method. Myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS), 8-hydroxy-2-deoxyguanosine (8-OHdG) and glutathione (GSH) activity or levels in serum were determined by commercially available kits. Western blot was used to determination of phosphorylated histone 2A.X (γ-H2A.X). Results showed that the oxidative stress biomarker of ROS and 8-OHdG were significantly increased early at 0.5h of SM exposure, but GSH level was decreased at 0.5h. Similarly, SM increased γ-H2A.X level early at 2h, which reached to peak at 8h and recovered to normal at 24h. MPO and iNOS activity were also increased early at 2h and 0.5h respectively. However, all selected inflammation biomarkers, including IL-6, TNF-α, IL-1β, MCP-1, GM-CSF and IL-10 concentrations are all unchangeable in 2h. The results indicated that oxidative stress and DNA damage had happened more quickly than inflammation reaction. These chronological events may be due to uncovered generation of reactive oxygen species, DNA alkylation and oxidative DNA damage. In conclusion, this research showed that both oxidative stress and DNA damage are earlier events than inflammation in sulfur mustard toxic mouse model.

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.

Tissue injury and repair following cutaneous exposure of mice to sulfur mustard

In mouse skin, sulfur mustard (SM) is a potent vesicant, damaging both the epidermis and the dermis. The extent of wounding is dependent on the dose of SM and the duration of exposure. Initial responses include erythema, pruritus, edema, and xerosis; this is followed by an accumulation of inflammatory leukocytes in the tissue, activation of mast cells, and the release of mediators, including proinflammatory cytokines and bioactive lipids. These proinflammatory mediators contribute to damaging the epidermis, hair follicles, and sebaceous glands and to disruption of the epidermal basement membrane. This can lead to separation of the epidermis from the dermis, resulting in a blister, which ruptures, leading to the formation of an eschar. The eschar stimulates the formation of a neoepidermis and wound repair and may result in persistent epidermal hyperplasia. Epidermal damage and repair is associated with upregulation of enzymes generating proinflammatory and pro-growth/pro-wound healing mediators, including cyclooxygenase-2, which generates prostanoids, inducible nitric oxide synthase, which generates nitric oxide, fibroblast growth factor receptor 2, and galectin-3. Characterization of the mediators regulating structural changes in the skin during SM-induced tissue damage and wound healing will aid in the development of therapeutic modalities to mitigate toxicity and stimulate tissue repair processes.