Metabolic activation of sulfur mustard leads to oxygen free radical formation

Dienediamine: A safe surrogate for the herbicide paraquat

Paraquat (PQ) has been used as an herbicide worldwide because of its potent activity against weeds. However, it is highly toxic to humans. The very high fatality of PQ poisoning is due to its inherent toxicity and the lack of any effective treatment. Consequently, developing a non-toxic herbicide with comparable efficacy to PQ will contribute to global food security and help prevent PQ-related fatalities. Herein, we report a new herbicide called dienediamine, which was discovered from how to intervene the redox cycle of PQ, an inherent toxicity nature. Dienediamine, the "reduced" form of PQ with no function as an electron transfer agent, was shown to be non-toxic through comprehensive in vivo and in vitro experiments at molar concentrations equivalent to PQ's absolute lethal dose. Remarkably, dienediamine can undergo conversion to PQ under natural sunlight and ambient air conditions, exhibiting herbicidal activities that are comparable to those of PQ. The conversion of dienediamine to PQ, which is toxic to chloroplasts, is the key mechanism underlying its potent herbicidal activity. Our study discovers that dienediamine is a safe and superior alternative to PQ, possessing significant potential for application in sustainable agriculture globally.

Melatonin as Modulator for Sulfur and Nitrogen Mustard-Induced Inflammation, Oxidative Stress and DNA Damage: Molecular Therapeutics

Sulfur and nitrogen mustards, bis(2-chloroethyl)sulfide and tertiary bis(2-chloroethyl) amines, respectively, are vesicant warfare agents with alkylating activity. Moreover, oxidative/nitrosative stress, inflammatory response induction, metalloproteinases activation, DNA damage or calcium disruption are some of the toxicological mechanisms of sulfur and nitrogen mustard-induced injury that affects the cell integrity and function. In this review, we not only propose melatonin as a therapeutic option in order to counteract and modulate several pathways involved in physiopathological mechanisms activated after exposure to mustards, but also for the first time, we predict whether metabolites of melatonin, cyclic-3-hydroxymelatonin, N1-acetyl-N2-formyl-5-methoxykynuramine, and N1-acetyl-5-methoxykynuramine could be capable of exerting a scavenger action and neutralize the toxic damage induced by these blister agents. NLRP3 inflammasome is activated in response to a wide variety of infectious stimuli or cellular stressors, however, although the precise mechanisms leading to activation are not known, mustards are postulated as activators. In this regard, melatonin, through its anti-inflammatory action and NLRP3 inflammasome modulation could exert a protective effect in the pathophysiology and management of sulfur and nitrogen mustard-induced injury. The ability of melatonin to attenuate sulfur and nitrogen mustard-induced toxicity and its high safety profile make melatonin a suitable molecule to be a part of medical countermeasures against blister agents poisoning in the near future.

Chronic senescent human mesenchymal stem cells as possible contributor to the wound healing disorder after exposure to the alkylating agent sulfur mustard

Wound healing is a complex process, and disturbance of even a single mechanism can result in chronic ulcers developing after exposure to the alkylating agent sulfur mustard (SM). A possible contributor may be SM-induced chronic senescent mesenchymal stem cells (MSCs), unable to fulfil their regenerative role, by persisting over long time periods and creating a proinflammatory microenvironment. Here we show that senescence induction in human bone marrow derived MSCs was time- and concentration-dependent, and chronic senescence could be verified 3 weeks after exposure to between 10 and 40 µM SM. Morphological changes, reduced clonogenic and migration potential, longer scratch closure times, differences in senescence, motility and DNA damage response associated genes as well as increased levels of proinflammatory cytokines were revealed. Selective removal of these cells by senolytic drugs, in which ABT-263 showed initial potential in vitro, opens the possibility for an innovative treatment strategy for chronic wounds, but also tumors and age-related diseases.

Development of a Series of Fluorescent Probes for the Early Diagnostic Imaging of Sulfur Mustard Poisoning

Sulfur mustard is one of the most harmful chemical warfare agents and can induce skin, eye, and lung injuries. However, it is hard for medical stuff to diagnose sulfur mustard poisoning early because of the incubation period after sulfur mustard exposure. Detecting intact sulfur mustard in vivo might be an effective approach for the early diagnosis of sulfur mustard poisoning. A series of fluorescent probes for intact sulfur mustard detection were developed in this study. All of the developed probes could react with sulfur mustard selectivity. Among these probes, SiNIR-SM exhibited an extremely good response rate and a high off/on contrast. To the best of our knowledge, SiNIR-SM is the first near-infrared fluorescent probe for the sulfur mustard detection. Both SiNIR-SM and OxSM-1 were successfully applied to image sulfur mustard in living cells. Using SiNIR-SM, we found that sulfur mustard accumulates in the mitochondria of living cells. This result could provide a new insight for the treatment of sulfur mustard injuries. We also found that SiNIR-SM is suitable for the early diagnostic imaging of sulfur mustard poisoning in SKH-1 mice via the detection of intact sulfur mustard.

Disturbance of photosystem II-oxygen evolution complex induced the oxidative damage in Chlorella vulgaris under the stress of cetyltrimethylammonium chloride

Oxygen evolution complex (OEC) in photosystem II (PSII) is sensitive to environmental stressors. However, oxidative damage mechanism in PSII-OEC is still unclear. Here, we investigated photosynthetic performance of PSII, oxidative stress and antioxidant reaction induced by reactive oxygen species (ROS) in a unicellular green alga Chlorella vulgaris (C. vulgaris) under the stress of cetyltrimethylammonium chloride (CTAC). From the changes of chlorophyll fluorescence parameters and PSII activity, it was proved that the electron transport, which occurred initially at the electron donor side of OEC, was disturbed by CTAC. Moreover, a significant decrease of the oxygen evolution rate in OEC (40.95%) while an increase of ROS (50.50%) was obtained after the exposure to 0.6 mg/L CTAC compared to the control (without CTAC), confirming that more oxygen transferred to ROS under the stress. Furthermore, the increased ROS in chloroplast and the structural destruction in thylakoid membrane were observed, respectively. These results proved that oxidative damage mechanism in PSII-OEC is mainly through the reduction of oxygen evolution and the production of excessive ROS, thus leading to the destruction of OEC performance and chloroplast structure.

Cellular and molecular mechanisms of sulfur mustard toxicity on spermatozoa and male fertility

Sulfur mustard (SM) is a toxic compound that can target human spermatozoa. SM induces a wide variety of pathological effects in human reproductive organs, including sexual hormone disturbance, testicular atrophy, impaired spermatogenesis, poor sperm quality, defects in embryo development, childhood physical abnormalities, and severe fertility problems. However, the molecular and cellular mechanisms of SM action on male reproductive health and human sperm function are unclear. Excessive production of reactive oxygen species and the resulting oxidative stress is likely a significant mechanism of SM action, and could be associated with sperm DNA damage, membrane lipid peroxidation, reduced membrane fluidity, mitochondrial deficiency, apoptosis, and poor sperm quality. In this review, we aim to discuss the cellular and molecular mechanisms of SM action on sperm and reproductive health, the significance of OS, and the mechanisms through which SM enhances the infertility rate among SM-exposed individuals.

Mechanisms of diazinon effects on impaired spermatogenesis and male infertility

Diazinon (DZN) is an organophosphate insecticide that has cytotoxic and pathological effects on the reproductive system. It causes a wide variety of pathological effects on the reproductive system such as testicular atrophy, disturbance in sex hormones, impaired spermatogenesis, low quality of sperm, and fertility problems. However, molecular and cellular mechanisms of its adverse effects are not well understood. General events such as testicular damage, inflammation, mitochondrial deficiency, DNA fragmentation, disintegration of sperm plasma membrane, apoptosis, and cell death are observed in DZN-exposed animals. Oxidative stress (OS) induced by reactive oxygen species may be a main mechanism, which can be associated with sperm DNA fragmentation, reduced integrity of sperm cell membrane, apoptosis, depletion of antioxidants, and subsequently poor sperm quality and male infertility. Therefore, identification of these pathways may provide valuable information regarding the mechanisms of DZN action on the male reproductive system. In this review, we aim to discuss the proposed cellular and molecular mechanisms of DZN action on male reproductive system, the importance of OS and mechanisms by which DZN induces OS and depletion of other antioxidants.

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.

Neglected role of hydrogen sulfide in sulfur mustard poisoning: Keap1 S-sulfhydration and subsequent Nrf2 pathway activation

Sulfur mustard (SM) is a chemical warfare agent and a terrorism choice that targets various organs and tissues, especially lung tissues. Its toxic effects are tightly associated with oxidative stress. The signaling molecule hydrogen sulfide (H₂S) protects the lungs against oxidative stress and activates the NF-E2 p45-related factor 2 (Nrf2) pathway. Here, we sought to establish whether endogenous H₂S plays a role in SM induced lesion in mouse lungs and lung cells and whether endogenous H₂S plays the role through Nrf2 pathway to protect against SM-induced oxidative damage. Furthermore, we also explored whether activation of Nrf2 by H₂S involves sulfhydration of Kelch-like ECH-associated protein-1 (Keap1). Using a mouse model of SM-induced lung injury, we demonstrated that SM-induced attenuation of the sulfide concentration was prevented by NaHS. Concomitantly, NaHS attenuates SM-induced oxidative stress. We also found that H₂S enhanced Nrf2 nuclear translocation, and stimulated expression of Nrf2-targeted downstream protein and mRNA levels. Incubation of the lung cells with NaHS decreased SM-induced ROS production. Furthermore, we also found that H₂S S-sulfhydrated Keap1, which induced Nrf2 dissociation from Keap1, and enhanced Nrf2 nuclear translocation. Our data indicate that H₂S is a critical, however, being long neglected signal molecule in SM-induced lung injury.

Alteration of miRNA expression in a sulfur mustard resistant cell line

BACKGROUND

MicroRNAs (miRNAs) are responsible for post-transcriptional control of protein expression. Numerous miRNAs have been identified to be responsible for the resistance of tumor cells to cytostatic drugs. Possibly, the same miRNAs also play a role in the sulfur mustard (SM)-resistance of the keratinocyte cell line HaCaT/SM as alkylating cytostatics exhibit similar cytotoxic effects as SM.

METHODS

Basal expression levels of 1920 miRNAs in total were analyzed in HaCaT/SM compared to the origin human keratinocyte cell line HaCaT. The effect for selected miRNAs on cell survival was analyzed using antagomirs for ectopic miRNA level decrease or miRNA mimics for increase. Cell survival was calculated as SM dose-dependent-curves.

RESULTS

Out of 1920 miRNAs analyzed, 49 were significantly up- and 29 were significantly downregulated in HaCaT/SM when compared to HaCaT controls. Out of these, 36 could be grouped in miRNA families. Most of the 15 miRNA family members showed either a common increase or decrease. Only the members of miR-10, miR-154, miR-430 and miR-548 family showed an inconsistent picture. The ectopic increase of miR-181 in HaCaT/SM had a positive effect on cell survival in the presence of SM.

CONCLUSION

In summary, the extensive differences in miRNA expression pattern between these cell lines indicate that specific miRNAs may play a role in the resistance mechanism against sulfur mustard. The miR-125b-2 and miR-181b alone are not responsible for the resistance development against SM, but an ectopic increase of miR-181 even enhances the SM resistance of HaCaT/SM. Improving the resistance in normal keratinocytes by treatment with either both miRNAs together or a different combination might be used as an initial step in development of an innovative new drug or prophylactic agent against SM.

From the Cover: Catalytic Antioxidant Rescue of Inhaled Sulfur Mustard Toxicity

Sulfur mustard (bis 2-chloroethyl ethyl sulfide, SM) is a powerful bi-functional vesicating chemical warfare agent. SM tissue injury is partially mediated by the overproduction of reactive oxygen species resulting in oxidative stress. We hypothesized that using a catalytic antioxidant (AEOL 10150) to alleviate oxidative stress and secondary inflammation following exposure to SM would attenuate the toxic effects of SM inhalation. Adult male rats were intubated and exposed to SM (1.4 mg/kg), a dose that produces an LD₅₀ at approximately 24 h. Rats were randomized and treated via subcutaneous injection with either sterile PBS or AEOL 10150 (5 mg/kg, sc, every 4 h) beginning 1 h post-SM exposure. Rats were euthanized between 6 and 48 h after exposure to SM and survival and markers of injury were determined. Catalytic antioxidant treatment improved survival after SM inhalation in a dose-dependent manner, up to 52% over SM PBS at 48 h post-exposure. This improvement was sustained for at least 72 h after SM exposure when treatments were stopped after 48 h. Non-invasive monitoring throughout the duration of the studies also revealed blood oxygen saturations were improved by 10% and clinical scores were reduced by 57% after SM exposure in the catalytic antioxidant treatment group. Tissue analysis showed catalytic antioxidant therapy was able to decrease airway cast formation by 69% at 48 h post-exposure. To investigate antioxidant induced changes at the peak of injury, several biomarkers of oxidative stress and inflammation were evaluated at 24 h post-exposure. AEOL 10150 attenuated SM-mediated lung lipid oxidation, nitrosative stress and many proinflammatory cytokines. The findings indicate that catalytic antioxidants may be useful medical countermeasure against inhaled SM exposure.

Mustard vesicant-induced lung injury: Advances in therapy

Most mortality and morbidity following exposure to vesicants such as sulfur mustard is due to pulmonary toxicity. Acute injury is characterized by epithelial detachment and necrosis in the pharynx, trachea and bronchioles, while long-term consequences include fibrosis and, in some instances, cancer. Current therapies to treat mustard poisoning are primarily palliative and do not target underlying pathophysiologic mechanisms. New knowledge about vesicant-induced pulmonary disease pathogenesis has led to the identification of potentially efficacious strategies to reduce injury by targeting inflammatory cells and mediators including reactive oxygen and nitrogen species, proteases and proinflammatory/cytotoxic cytokines. Therapeutics under investigation include corticosteroids, N-acetyl cysteine, which has both mucolytic and antioxidant properties, inducible nitric oxide synthase inhibitors, liposomes containing superoxide dismutase, catalase, and/or tocopherols, protease inhibitors, and cytokine antagonists such as anti-tumor necrosis factor (TNF)-α antibody and pentoxifylline. Antifibrotic and fibrinolytic treatments may also prove beneficial in ameliorating airway obstruction and lung remodeling. More speculative approaches include inhibitors of transient receptor potential channels, which regulate pulmonary epithelial cell membrane permeability, non-coding RNAs and mesenchymal stem cells. As mustards represent high priority chemical threat agents, identification of effective therapeutics for mitigating toxicity is highly significant.

Antioxidants as potential medical countermeasures for chemical warfare agents and toxic industrial chemicals

The continuing horrors of military conflicts and terrorism often involve the use of chemical warfare agents (CWAs) and toxic industrial chemicals (TICs). Many CWA and TIC exposures are difficult to treat due to the danger they pose to first responders and their rapid onset that can produce death shortly after exposure. While the specific mechanism(s) of toxicity of these agents are diverse, many are associated either directly or indirectly with increased oxidative stress in affected tissues. This has led to the exploration of various antioxidants as potential medical countermeasures for CWA/TIC exposures. Studies have been performed across a wide array of agents, model organisms, exposure systems, and antioxidants, looking at an almost equally diverse set of endpoints. Attempts at treating CWAs/TICs with antioxidants have met with mixed results, ranging from no effect to nearly complete protection. The aim of this commentary is to summarize the literature in each category for evidence of oxidative stress and antioxidant efficacy against CWAs and TICs. While there is great disparity in the data concerning methods, models, and remedies, the outlook on antioxidants as medical countermeasures for CWA/TIC management appears promising.

The transient but not resident (TBNR) microbiome: a Yin Yang model for lung immune system

The concept of microbial content of the lung is still controversial. What make this more complicated are controversial results obtaining from different methodologies about lung microbiome and the definition of "lung sterility". Lungs may have very low bacteria but are not completely germ-free. Bacteria are constantly entering from the upper respiratory tract, but are then quickly being cleared. We can find bacterial DNA in the lungs, but it is much harder to ask about living bacteria. Here, we propose that if there is any trafficking of the microorganisms in the lung, it should be a "Transient But Not Resident (TBNR)" model. So, we speculate a "Yin Yang model" for the lung immune system and TBNR. Despite beneficial roles of microbiome on the development of lung immune system, any disruption and alteration in the microbiota composition of upper and lower airways may trigger or lead to several diseases such as asthma, chronic obstructive pulmonary disease and mustard lung disease.

Bipyridine (2,2'-dipyridyl) potentiates Escherichia coli lethality induced by nitrogen mustard mechlorethamine

Alkylating agents are used in anti-tumor chemotherapy because they bind covalently to DNA and generate adducts that may lead to cell death. Bifunctional (HN2) and monofunctional (HN1) nitrogen are two such agents, and HN2 was the first drug successfully employed in anti-leukemia chemotherapy. Currently, HN2 is used either alone or combined with other drugs to treat Hodgkin's disease. It is well known that several crosslinking agents require metabolic activation via reactive oxygen species (ROS) to exert their lethal effects. The objective of this work was therefore to determine whether the abovementioned mustards would also require metabolic activation to exert lethal action against Escherichia coli. For this purpose, we measured survival following exposure to HN2 in E. coli strains that were deficient in nucleotide excision repair (uvrA NER mutant), base excision repair (xthA nfo nth fpg BER mutant) or superoxide dismutase (sodAB mutant) activity. We also performed the same experiments in cells pretreated with an iron chelator (2,2'-dipyridyl, DIP). The NER and BER mutants were only sensitive to HN2 treatment (survival rates similar to those of the wild-type were achieved with 5-fold lower HN2 doses). However, wild-type and sodAB strains were not sensitive to treatment with HN2. In all tested strains, survival dropped by 2.5-fold following pretreatment with DIP compared to treatment with HN2 alone. Furthermore, DIP treatment increased ROS generation in both wild type and sodAB-deficient strains. Based on these data and on the survival of the SOD-deficient strain, we suggest that the increased production of ROS caused by Fe(2+) chelation may potentiate the lethal effects of HN2 but not HN1. This potentiation may arise as a consequence of enhancement in the number of or modification of the type of lesions formed. No sensitization was observed for the non-crosslinkable HN2 analog, HN1.