Biological and molecular mechanisms of sulfur mustard analogue-induced toxicity in JB6 and HaCaT cells: possible role of ataxia telangiectasia-mutated/ataxia telangiectasia-Rad3-related cell cycle checkpoint pathway

Insights into the Cytotoxicity and Irritant Potential of Chlorhexidine Digluconate: An In Vitro and In Ovo Safety Screening

Chlorhexidine (CHX) represents one of the most commonly used antiseptics in dentistry and other medical-pharmaceutical fields due to its broad-spectrum antimicrobial activity. However, the potential toxic events arising from its common use in practice has become a subject of increasing concern. Thus, the present study was designed to investigate the potential toxicity of CHX digluconate at concentrations covering its antibacterial properties (0.0002-0.2%) in HGF primary gingival fibroblasts, HaCaT immortalized human keratinocytes, and JB6 Cl 41-5a epidermal cells, as well as its irritant action in ovo. Our results indicate that CHX exerted a concentration- and time-dependent cytotoxicity in all cell lines, which was evidenced by the reduction in cell viability, number, and confluence, damaged cell membrane integrity, impaired cell morphology, and specific apoptotic nuclear shape. The highest cytotoxicity was caused by CHX digluconate 0.02% and 0.2%, concentrations, at which an irritant effect on the chorioallantoic membrane was also observed. The novel findings revealed in this research contribute to the overall safety profile of CHX and stand as a basis for further investigations in this regard.

Mitigation of Nitrogen Mustard-Induced Skin Injury by the β-Blocker Carvedilol and Its Enantiomers

The chemical warfare agent sulfur mustard and its structural analog nitrogen mustard (NM) cause severe vesicating skin injuries. The pathologic mechanisms for the skin injury following mustard exposure are poorly understood; therefore, no effective countermeasure is available. Previous reports demonstrated the protective activity of carvedilol, a US Food and Drug Administration (FDA)-approved β-blocker, against UV radiation-induced skin damage. Thus, the current study evaluated the effects of carvedilol on NM-induced skin injuries in vitro and in vivo. In the murine epidermal cell line JB6 Cl 41-5a, β-blockers with different receptor subtype selectivity were examined. Carvedilol and both of its enantiomers, R- and S-carvedilol, were the only tested ligands statistically reducing NM-induced cytotoxicity. Carvedilol also reduced NM-induced apoptosis and p53 expression. In SKH-1 mice, NM increased epidermal thickness, damaged skin architecture, and induced nuclear factor κB (NF-κB)-related proinflammatory genes as assessed by RT2 Profiler PCR (polymerase chain reaction) Arrays. To model chemical warfare scenario, 30 minutes after exposure to NM, 10 μM carvedilol was applied topically. Twenty-four hours after NM exposure, carvedilol attenuated NM-induced epidermal thickening, Ki-67 expression, a marker of cellular proliferation, and multiple proinflammatory genes. Supporting the in vitro data, the non-β-blocking R-enantiomer of carvedilol had similar effects as racemic carvedilol, and there was no difference between carvedilol and R-carvedilol in the PCR array data, suggesting that the skin protective effects are independent of the β-adrenergic receptors. These data suggest that the β-blocker carvedilol and its enantiomers can be repurposed as countermeasures against mustard-induced skin injuries. SIGNIFICANCE STATEMENT: The chemical warfare agent sulfur mustard and its structural analog nitrogen mustard cause severe vesicating skin injuries for which no effective countermeasure is available. This study evaluated the effects of US Food and Drug Administration (FDA)-approved β-blocker carvedilol on nitrogen mustard-induced skin injuries to repurpose this cardiovascular drug as a medical countermeasure.

NAD+ Acts as a Protective Factor in Cellular Stress Response to DNA Alkylating Agents

Sulfur mustard (SM) and its derivatives are potent genotoxic agents, which have been shown to trigger the activation of poly (ADP-ribose) polymerases (PARPs) and the depletion of their substrate, nicotinamide adenine dinucleotide (NAD+). NAD+ is an essential molecule involved in numerous cellular pathways, including genome integrity and DNA repair, and thus, NAD+ supplementation might be beneficial for mitigating mustard-induced (geno)toxicity. In this study, the role of NAD+ depletion and elevation in the genotoxic stress response to SM derivatives, i.e., the monofunctional agent 2-chloroethyl-ethyl sulfide (CEES) and the crosslinking agent mechlorethamine (HN2), was investigated with the use of NAD+ booster nicotinamide riboside (NR) and NAD+ synthesis inhibitor FK866. The effects were analyzed in immortalized human keratinocytes (HaCaT) or monocyte-like cell line THP-1. In HaCaT cells, NR supplementation, increased NAD+ levels, and elevated PAR response, however, did not affect ATP levels or DNA damage repair, nor did it attenuate long- and short-term cytotoxicities. On the other hand, the depletion of cellular NAD+ via FK866 sensitized HaCaT cells to genotoxic stress, particularly CEES exposure, whereas NR supplementation, by increasing cellular NAD+ levels, rescued the sensitizing FK866 effect. Intriguingly, in THP-1 cells, the NR-induced elevation of cellular NAD+ levels did attenuate toxicity of the mustard compounds, especially upon CEES exposure. Together, our results reveal that NAD+ is an important molecule in the pathomechanism of SM derivatives, exhibiting compound-specificity. Moreover, the cell line-dependent protective effects of NR are indicative of system-specificity of the application of this NAD+ booster.

HSP90/CDC37 inactivation promotes degradation of LKB1 protein to suppress AMPK signaling in bronchial epithelial cells exposed to sulfur mustard analog, 2-chloroethyl ethyl sulfide

To investigate the role of the liver kinase (LK) B1 protein, an activator of AMP-activated protein kinase (AMPK), in AMPK signaling suppression when exposed to vesicant, a kind of chemical warfare agent. Cultured human bronchial epithelial cells were inflicted with sulfur mustard (SM) analog, 2-chloroethyl ethyl sulfide (CEES) of 0.2-1.0 mM concentration, and cell proliferation, apoptosis, autophagy, and cellular ATP level were analyzed up to 24 h after the exposure. Focusing on LKB1, heat shock protein (HSP) 90, and cell division cycle (CDC) 37 proteins, the protein expression, phosphorylation, and interaction were examined with western blot, immunofluorescence staining, and/or immunoprecipitation. AMPK signaling was found to be inhibited 24 h after being exposed to either sub-cytotoxic (0.5 mM) or cytotoxic (1.0 mM) concentration of CEES based on MTS assay. Consistently, the degradation of the LKB1 protein and its less interaction with the HSP90/CDC37 complex was confirmed. It was found that 1.0, not 0.5 mM CEES also decreased the CDC37 protein, proteasome activity, and cellular ATP content that modulates HSP90 protein conformation. Inhibiting proteasome activity could alternatively activate autophagy. Finally, either 0.5 or 1.0 mM CEES activated HSP70 and autophagy, and the application of an HSP70 inhibitor blocked autophagy and autophagic degradation of the LKB1 protein. In conclusion, we reported here that AMPK signaling inactivation by CEES was a result of LKB1 protein loss via less protein complex formation and enhanced degradation.

MG53 Mitigates Nitrogen Mustard-Induced Skin Injury

Sulfur mustard (SM) and nitrogen mustard (NM) are vesicant agents that cause skin injury and blistering through complicated cellular events, involving DNA damage, free radical formation, and lipid peroxidation. The development of therapeutic approaches targeting the multi-cellular process of tissue injury repair can potentially provide effective countermeasures to combat vesicant-induced dermal lesions. MG53 is a vital component of cell membrane repair. Previous studies have demonstrated that topical application of recombinant human MG53 (rhMG53) protein has the potential to promote wound healing. In this study, we further investigate the role of MG53 in NM-induced skin injury. Compared with wild-type mice, mg53^-/- mice are more susceptible to NM-induced dermal injuries, whereas mice with sustained elevation of MG53 in circulation are resistant to dermal exposure of NM. Exposure of keratinocytes and human follicle stem cells to NM causes elevation of oxidative stress and intracellular aggregation of MG53, thus compromising MG53's intrinsic cell membrane repair function. Topical rhMG53 application mitigates NM-induced dermal injury in mice. Histologic examination reveals the therapeutic benefits of rhMG53 are associated with the preservation of epidermal integrity and hair follicle structure in mice with dermal NM exposure. Overall, these findings identify MG53 as a potential therapeutic agent to mitigate vesicant-induced skin injuries.

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.

Sulfur mustard analog 2-chloroethyl ethyl sulfide increases triglycerides by activating DGAT1-dependent biogenesis and inhibiting PGC1ɑ-dependent fat catabolism in immortalized human bronchial epithelial cells

Using sulfur mustard analog 2-chloroethyl ethyl sulfide (CEES), we established an in vitro model by poisoning cultured immortalized human bronchial epithelial cells. Nile Red staining revealed lipids accumulated 24 h after a toxic dose of CEES (0.9 mM). Lipidomics analysis showed most of the increased lipids were triglycerides (TGs), and the increase in TGs was further confirmed using a Triglyceride-Glo™ Assay kit. Protein and mRNA levels of DGAT1, an important TG biogenesis enzyme, were increased following 0.4 mM CEES exposure. Under higher dose CEES (0.9 mM) exposure, protein and mRNA levels of PPARγ coactivator-1ɑ (PGC-1ɑ), a well-known transcription factor that regulates fatty acid oxidation, were decreased. Finally, application with DGAT1 inhibitor A 922500 or PGC1ɑ agonist ZLN005 was able to block the CEES-induced TGs increase. Overall, our dissection of CEES-induced TGs accumulation provides new insight into energy metabolism dysfunction upon vesicant exposure.HIGHLIGHTSIn CEES (0.9 mM)-injured cells:Triglycerides (TGs) were abundant in the accumulated lipids.Expression of DGAT1, not DGAT2, was increased.Expression of PGC1ɑ, not PGC1β, was reduced.DGAT1 inhibitor or PGC1ɑ agonist blocked the CEES-mediated increase in TGs.

A Supersaturated Oxygen Emulsion for the Topical Treatment of Ocular Trauma

INTRODUCTION

Roughly 13% of all battlefield injuries include some form of ocular trauma. Ocular tissue preservation is critical for wound healing for warfighters with ocular injuries. Our team hypothesized that oxygen plays a vital role in ocular tissue preservation and wound healing and has developed a supersaturated oxygen emulsion (SOE) for the topical treatment of ocular trauma.

MATERIALS AND METHODS

The partial pressure of oxygen (PO2) was measured in the SOE. Safety and efficacy studies were carried out in primary human corneal epithelial (HCE) cells, as the outermost layer is the first barrier to chemical and mechanical injury. Western blot, scratch assay, and MTT assays were conducted to determine the effect of the SOE on various molecular markers, the rate of scratch closure, and cellular viability, respectively.

RESULTS

Data indicate that the SOE releases oxygen in a time-dependent manner, reaching a partial pressure within the emulsion over four times atmospheric levels. Studies in HCE cells indicate that application of the SOE does not lead to DNA damage, promote cell death, or hinder the rate of scratch closure and enhances cellular viability. Preliminary studies were carried out with chloropicrin (CP; developed as a chemical warfare agent and now a commonly used pesticide) as a chemical agent to induce ocular injury in HCE cells. CP exposures showed that SOE treatment reverses CP-induced DNA damage, apoptotic cell death, and oxidative stress markers.

CONCLUSIONS

Maintaining adequate tissue oxygenation is critical for tissue preservation and wound repair, especially in avascular tissues like the cornea. Further studies examining the application of the SOE in corneal injury models are warranted.

Evaluation of decontamination efficacy of electrolytically generated hypochlorous acid for vesicating agent: A multimodel Study

BACKGROUND

Sulfur Mustard is a strong vesicant and chemical warfare agent that imposes toxicity to the lungs, eyes, and skin after accidental or intended exposure.

OBJECTIVES

The current study was intended to explore in vitro and in vivo decontamination properties of electrolytically generated HOCl (hypochlorous acid) against CEES (2-chloroethyle ethyle sulphide), a known sulfur mustard simulant & vesicating agent.

METHODS

In vitro studies were carried out using UV spectroscopy and GC-MS methods. In vivo studies were perfomred in Strain A and immune compromised mice by subcutaneous as well as prophylactic topical administrion of HOCl pretreated CEES. The blister formation and mortality were considered as end-point. Histopathological study was conducted on skin samples by H & E method. DNA damage studies measuring γ-H2AX and ATM has been carried out in human blood using flow cytometry. Anti-bacterial action was tested by employing broth micro dilution methods. Comparative study was also carried out with known oxidizing agents.

RESULTS

The topical application of pre-treated CEES at 5, 30 min and 1 h time points showed significant (p<0.001) inhibition of blister formation. DNA damage study showed reduced mean flourences intensity of DSBs nearly 17-20 times, suggesting that HOCl plays a protective role against DNA damage. Histopathology showed no sign of necrosis in the epidermis upto 5 min although moderate changes were observed at 30 min. Pretreated samples were analyzed for detection of reaction products with m/z value of 75.04, 69.08, 83.93, 85.95, 123.99, 126.00, and 108.97. HOCl showed strong bactericidal effect at 40 ppm. The absorbance spectra of HOCl treated CEES showed lowered peaks in comparison to CEES alone and other oxidizing agents Conclusion: In a nutshell, our results signify the decontamination role of HOCl for biological surface application.

miR-34a in extracellular vesicles from bone marrow mesenchymal stem cells reduces rheumatoid arthritis inflammation via the cyclin I/ATM/ATR/p53 axis

Extracellular vesicles (Evs) participate in the development of rheumatoid arthritis (RA), but the mechanisms remain unclear. This study aimed to determine the mechanism by which microRNA‐34a (miR‐34a) contained in bone marrow mesenchymal stem cell (BM‐MSC)‐derived Evs functions in RA fibroblast‐like synoviocytes (RA‐FLSs). BM‐MSC‐derived Evs and an Evs inhibitor were extracted. A rat model of RA was established. miR‐34a gain‐ and loss‐of‐function experiments were performed, and the inflammation in rat synovial fluid and tissues was detected. The role of miR‐34a in RA‐FLSs was also measured in vitro. The target gene of miR‐34a was predicted using the online software TargetScan and identified using a dual‐luciferase reporter gene assay, and the activation of the ATM/ATR/p53 signalling pathway was assessed. BM‐MSC‐derived Evs mainly elevated miR‐34a expression, which reduced RA inflammation in vivo and inhibited RA‐FLS proliferation and resistance to apoptosis in vitro, while inhibited miR‐34a expression enhanced RA development. In addition, miR‐34a could target cyclin I to activate the ATM/ATR/p53 signalling pathway, thus inhibiting abnormal RA‐FLS growth and RA inflammation. Our study showed that miR‐34a contained in BM‐MSC‐derived Evs could reduce RA inflammation by inhibiting the cyclin I/ATM/ATR/p53 signalling pathway.

Deciphering the role of microRNAs in mustard gas-induced toxicity

Mustard gas (sulfur mustard, SM), a highly vesicating chemical warfare agent, was first deployed in warfare in 1917 and recently during the Iraq-Iran war (1980s) and Syrian conflicts (2000s); however, the threat of exposure from stockpiles and old artillery shells still looms large. Whereas research has been long ongoing on SM-induced toxicity, delineating the precise molecular pathways is still an ongoing area of investigation; thus, it is important to attempt novel approaches to decipher these mechanisms and develop a detailed network of pathways associated with SM-induced toxicity. One such avenue is exploring the role of microRNAs (miRNAs) in SM-induced toxicity. Recent research on the regulatory role of miRNAs provides important results to fill in the gaps in SM toxicity-associated mechanisms. In addition, differentially expressed miRNAs can also be used as diagnostic markers to determine the extent of toxicity in exposed individuals. Thus, in our review, we have summarized the studies conducted so far in cellular and animal models, including human subjects, on the expression profiles and roles of miRNAs in SM- and/or SM analog-induced toxicity. Further detailed research in this area will guide us in devising preventive strategies, diagnostic tools, and therapeutic interventions against SM-induced toxicity.

Identification of creatine kinase and alpha-1 antitrypsin as protein targets of alkylation by sulfur mustard

Sulfur mustard (SM) is a toxic chemical warfare agent deployed in several conflicts within the last 100 years and still represents a threat in terroristic attacks and warfare. SM research focuses on understanding the pathophysiology of SM and identifying novel biomarkers of exposure. SM is known to alkylate nucleophilic moieties of endogenous proteins, for example, free thiol groups of cysteine residues. The two-dimensional-thiol-differences in gel electrophoresis (2D-thiol-DIGE) technique is an initial proteomics approach to detect proteins with free cysteine residues. These amino acids are selectively labeled with infrared-maleimide dyes visualized after GE. Cysteine residues derivatized by alkylating agents are no longer accessible for the maleimide-thiol coupling resulting in the loss of the fluorescent signal of the corresponding protein. To prove the applicability of 2D-thiol-DIGE, this technology was exemplarily applied to neat human serum albumin treated with SM, to lysates from human cell culture exposed to SM as well as to human plasma exposed to CEES (chloroethyl ethyl sulfide, an SM analogue). Exemplarily, the most prominent proteins modified by SM were identified by matrix-assisted laser desorption/ionization time-of-flight (tandem) mass spectrometry, MALDI-TOF MS(/MS), as creatine kinase (CK) from human cells and as alpha-1 antitrypsin (A1AT) from plasma samples. Peptides containing the residue Cys²⁸² of CK and Cys²³² of A1AT were unambiguously identified by micro liquid chromatography-electrospray ionization high-resolution tandem-mass spectrometry (μLC-ESI MS/HR MS) as being alkylated by SM bearing the specific hydroxyethylthioethyl-(HETE)-moiety. Both peptides might represent potential biomarkers of SM exposure. This is the first report introducing these endogenous proteins as targets of SM alkylation.

A review of Sulfur Mustard-induced pulmonary immunopathology: An Alveolar Macrophage Approach

Despite many studies investigating the mechanism of Sulfur Mustard (SM) induced lung injury, the underlying mechanism is still unclear. Inflammatory and subsequent fibroproliferative stages of SM-toxicity are based upon several highly-related series of events controlled by the immune system. The inhalation of SM gas variably affects different cell populations within the lungs. Various studies have shown the critical role of macrophages in triggering a pulmonary inflammatory response as well as its maintenance, resolution, and repair. Importantly, macrophages can serve as either pro-inflammatory or anti-inflammatory populations depending on the present conditions at any pathological stage. Different characteristics of macrophages, including their differentiation, phenotypic, and functional properties, as well as interactions with other cell populations determine the outcomes of lung diseases and the extent of long- or short-term pulmonary damage induced by SM. In this paper, we summarize the current state of knowledge regarding the role of alveolar macrophages and their mediators in the pathogenesis of SM in pulmonary injury. Investigating the specific cells and mechanisms involved in SM-lung injury may be useful in finding new target opportunities for treatment of this injury.

In vitro stress response induced by sulfur mustard in lung fibroblasts NHLF and human pulmonary epithelial cells A-549

Sulfur mustard [bis(2-chloroethyl) sulfide; SM] is a highly poisonous chemical warfare agent. The mechanism of its cytotoxicity affects several pathways, which cause cell damage or death. The main organ affected in case of exposure to both aerosol and vapor is lungs. The present study focuses on time- and concentration-dependent changes in human lung fibroblasts NHLF and lung epithelial cell line A-549. The cells were treated with SM at the concentrations of 5, 10 and 100 µM and signs of stress response were evaluated during 1-72 h post-treatment. Parameters for testing included cell viability and morphology, loss of transmembrane mitochondrial potential, apoptosis, oxidative stress, changes in the cell cycle, and ATM kinase activation. The cytotoxic effect of SM resulted in a time-dependent decrease in viability of A-459 associated with apoptosis more markedly than in NHLF. We did not observe any generation of reactive oxygen species by SM. SM at concentrations of 5 and 10 µM induced the S-phase cell cycle arrest at both cell lines. On the other hand, 100 µM caused nonspecific cell cycle arrest. ATM kinase was activated transiently. The results indicate that NHLF cells are less prone to toxic damage by SM in case of cell viability, apoptosis and loss of transmembrane mitochondrial potential. The analysis provides a time-related cytotoxic profile of A-549 and NHLF cells for further investigation into the prevention of SM toxic effects and their potential treatment.

Toxic consequences and oxidative protein carbonylation from chloropicrin exposure in human corneal epithelial cells

Chloropicrin (CP), a warfare agent now majorly used as a soil pesticide, is a strong irritating and lacrimating compound with devastating toxic effects. To elucidate the mechanism of its ocular toxicity, toxic effects of CP (0-100 μM) were studied in primary human corneal epithelial (HCE) cells. CP exposure resulted in reduced HCE cell viability and increased apoptotic cell death with an up-regulation of cleaved caspase-3 and poly ADP ribose polymerase indicating their contribution in CP-induced apoptotic cell death. Following CP exposure, cells exhibited increased expression of heme oxygenase-1, and phosphorylation of H2A.X and p53 as well as 4-hydroxynonenal adduct formation, suggesting oxidative stress, DNA damage and lipid peroxidation. CP also caused increases in mitogen activated protein kinase-c-Jun N-terminal kinase and inflammatory mediator cyclooxygenase-2. Proteomic analysis revealed an increase in the carbonylation of 179 proteins and enrichment of pathways (including proteasome pathway and catabolic process) in HCE cells following CP exposure. CP-induced oxidative stress and lipid peroxidation can enhance protein carbonylation, prompting alterations in corneal epithelial proteins as well as perturbing signaling pathways resulting in toxic effects. Pathways and major processes identified following CP exposure could be lead-hit targets for further biochemical and molecular characterization as well as therapeutic intervention.

DNA damage signaling in the cellular responses to mustard vesicants

Mustard vesicants, including sulfur mustard (2,2'-dichlorodiethyl sulfide, SM) and nitrogen mustard (bis(2-chloroethyl)methylamine, HN2) are cytotoxic blistering agents synthesized for chemical warfare. Because they contain highly reactive electrophilic chloroethyl side chains, they readily react with cellular macromolecules like DNA forming monofunctional and bifunctional adducts. By targeting DNA, mustards can compromise genomic integrity, disrupt the cell cycle, and cause mutations and cytotoxicity. To protect against genotoxicity following exposure to mustards, cells initiate a DNA damage response (DDR). This involves activation of signaling cascades including ATM (ataxia telangiectasia mutated), ATR (ataxia telangiectasia and Rad3-related) and DNA-PKcs (DNA-dependent protein kinase, catalytic unit). Signaling induced by the DDR leads to the recruitment and activation of repair related proteins such as phospho H2AX and phospho p53 to sites of DNA lesions. Excessive DNA modifications by mustards can overwhelm DNA repair leading to single and double strand DNA breaks, cytotoxicity and tissue damage, sometimes leading to cancer. Herein we summarize DDR signaling pathways induced by SM, HN2 and the half mustard, 2-chloroethyl ethyl sulfide (CEES). At the present time, little is known about how mustard-induced DNA damage leads to the activation of DDR signaling. A better understanding of mechanisms by which mustard vesicants induce the DDR may lead to the development of countermeasures effective in mitigating tissue injury.

Validation of automated pipetting systems for cell culture seeding, exposure and bio-analytical assays in sulfur mustard toxicology

In vitro cell culture experiments are highly important techniques to accelerate drug discovery, conduct safety testing and reduce the need for animal studies. Therefore, automatization may help to enhance the technical precision, reduce external (including operator's) influence on the data and thus improve reliability. Prior to application in scientific studies, validation of automated systems is absolutely necessary. In this study we present the validation of two combined automated pipetting systems to conduct toxicity studies in HaCaT cells consisting of cell seeding, noxious agent exposure and several assays to assess cell survival, apoptosis and interleukin production. After initial validation of pipetting accuracy, we compared homogeneity after automated seeding to plates seeded by expert laboratory technicians. Moreover, automated dispensing of a potentially unstable noxious agent was analyzed in terms of speed and consistency. We found a 2 % technical imprecision for the cell survival assay and 4.5-6 % for the other assays, bioluminescent and ELISA techniques. Thus, we could demonstrate the excellent technical precision of our assays. In a final step, we found that intraday variations, though acceptable, were much larger than technical variations and had to assume an intraday biological variability between different wells of the same experimental group.

Sulfur Mustard Analog Mechlorethamine (Bis(2-chloroethyl)methylamine) Modulates Cell Cycle Progression via the DNA Damage Response in Human Lung Epithelial A549 Cells

Nitrogen mustard, mechlorethamine (bis(2-chloroethyl)methylamine; HN2), and sulfur mustard are potent vesicants that modify and disrupt cellular macromolecules including DNA leading to cytotoxicity and tissue injury. In many cell types, HN2 upregulates DNA damage signaling pathways including ataxia telangiectasia mutated (ATM), ataxia telangiectasia mutated- and Rad3-related (ATR) as well as DNA-dependent protein kinase (DNA-PK). In the present studies, we investigated crosstalk between the HN2-induced DNA damage response and cell cycle progression using human A549 lung epithelial cells. HN2 (1-20 μM; 24 h) caused a concentration-dependent arrest of cells in the S and G2/M phases of the cell cycle. This was associated with inhibition of DNA synthesis, as measured by incorporation of 5-ethynyl-2'-deoxyuridine (EdU) into S phase cells. Cell cycle arrest was correlated with activation of DNA damage and cell cycle checkpoint signaling. Thus, HN2 treatment resulted in time- and concentration-dependent increases in expression of phosphorylated ATM (Ser1981), Chk2 (Thr68), H2AX (Ser139), and p53 (Ser15). Activation of DNA damage signaling was most pronounced in S-phase cells followed by G2/M-phase cells. HN2-induced cell cycle arrest was suppressed by the ATM and DNA-PK inhibitors, KU55933 and NU7441, respectively, and to a lesser extent by VE821, an ATR inhibitor. This was correlated with abrogation of DNA damage checkpoints signaling. These data indicate that activation of ATM, ATR, and DNA-PK signaling pathways by HN2 are important in the mechanism of vesicant-induced cell cycle arrest and cytotoxicity. Drugs that inhibit activation of DNA damage signaling may be effective countermeasures for vesicant-induced tissue injury.

DNA repair mechanisms in response to genotoxicity of warfare agent sulfur mustard

Sulfur mustard (SM) is an alkylating agent that causes severe damages to the skin, eyes, and the respiratory system. DNA alkylation is one of the most critical lesions that could lead to monoadducts and cross-links, as well as DNA strand breaks. In response to these adducts, cells initiate a series of reactions to recruit specific DNA repair pathways. The main DNA repair pathways in human cells, which could be involved in the DNA SM-induced DNA damages, are base excision repair (BER), nucleotide excision repair (NER), homologous recombination (HR) and non-homologous end joining (NHEJ). There is, thus, a need for a short review to clarify which damage caused by SM is repaired by which repair pathway. Increasing our knowledge about different DNA repair mechanisms following SM exposure would lay the first step for developing new therapeutic agents to treat people exposed to SM. In this review, we describe the major DNA repair pathways, according to the DNA adducts that can be caused by SM.

Modulation of antioxidative defense expression and osmolyte content by co-application of 24-epibrassinolide and salicylic acid in Pb exposed Indian mustard plants

The study focuses on potential of combined pre-soaking treatment of 24-Epibrassinolide (EBL) and Salicylic acid (SA) in alleviating Pb phytotoxicity in Brassica juncea L. plants. The seeds after treatment with combination of both the hormones were sown in mixture of soil, sand and manure (3:1:1) and were exposed to Pb concentrations (0.25mM, 0.50mM and 0.75mM). After 30 days of growth, the plants were harvested and processed, for quantification of various metabolites. It was found that pre-sowing of seeds in combination of EBL and SA, mitigated the adverse effects of metal stress by modulating antioxidative defense response and enhanced osmolyte contents. Dry matter content and heavy metal tolerance index were enhanced in response to co-application of EBL and SA. The levels of superoxide anions, hydrogen peroxide and malondialdehyde were lowered by the combined treatment of hormones. Enhancement in activities of guaiacol peroxidase, catalase, glutathione reductase and glutathione-s-transferase were recorded. Contents of glutathione, tocopherol and ascorbic acid were also enhanced in response to co-application of both hormones. Expression of POD, CAT, GR and GST1 genes were up-regulated whereas SOD gene was observed to be down-regulated. Contents of proline, trehalose and glycine betaine were also reported to be elevated as a result of treatment with EBL+SA. The results suggest that co-application of EBL+SA may play an imperative role in improving the antioxidative defense expression of B. juncea plants to combat the oxidative stress generated by Pb toxicity.

Sulfur mustard skin lesions: A systematic review on pathomechanisms, treatment options and future research directions

Sulfur mustard (SM) is a chemical warfare, which has been used for one hundred years. However, its exact pathomechanisms are still incompletely understood and there is no specific therapy available so far. In this systematic review, studies published between January 2000 and July 2017 involving pathomechanisms and experimental treatments of SM-induced skin lesions were analyzed to summarize current knowledge on SM pathology, to provide an overview on novel treatment options, and to identify promising targets for future research to more effectively counter SM effects. We suggest that future studies should focus on (I) systemic effects of SM intoxication due to its distribution throughout the body, (II) removal of SM depots that continuously release active compound contributing to chronic skin damage, and (III) therapeutic options that counteract the pleiotropic effects of SM.

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

Phosgene Oxime (CX, Cl₂CNOH), a halogenated oxime, is a potent chemical weapon that causes immediate acute injury and systemic effects. CX, grouped together with vesicating agents, is an urticant or nettle agent with highly volatile, reactive, corrosive, and irritating vapor, and has considerably different chemical properties and toxicity compared to other vesicants. CX is absorbed quickly through clothing with faster cutaneous penetration compared to other vesicating agents causing instantaneous and severe damage. For this reason, it could be produced as a weaponized mixture with other chemical warfare agents to enhance their deleterious effects. The immediate devastating effects of CX and easy synthesis makes it a dangerous chemical with both military and terrorist potentials. Although CX is the most potent vesicating agent, it is one of the least studied chemical warfare agents and the pathophysiology as well as long term effects are largely unknown. CX exposure results in immediate pain and inflammation, and it mainly affects skin, eye and respiratory system. There are no antidotes available against CX-induced injury and the treatment is only supportive. This review summarizes existing knowledge regarding exposure, toxicity and the probable underlying mechanisms of CX compared to other important vesicants' exposure.

Effects of sulfur mustard on mesenchymal stem cells

Chronic wound healing disorders that occur as a result of a sulfur mustard (SM) exposure present a particular challenge. These chronic wounds are similar to other chronic wounds. In the past, it has been shown that mesenchymal stem cells (MSC) play an important role in the healing of chronic wounds. An important property to support wound healing is their ability to migrate. However, we were able to show that SM leads to a reduction in MSC migration even at low concentrations. Currently, exposed MSCs are still able to differentiate. Further alterations are not known. The current investigation therefore focused onto the question how SM affects MSC.

MATERIAL & METHODS

The effect of SM on MSC was investigated. Here, the alkylation of DNA was considered, and DNA adducts were quantified over a period of 48h. The modification of the nuclei under the influence of SM was analyzed as well as proliferation of the cells by immunohistochemical staining with Ki-67 and quantification. For the quantification of the apoptosis rate, antibodies against cleaved Caspase-3, 8, and apoptosis inducing factor (AIF) were used. The senescence analysis was performed after histological staining against β-galactosidase. Quantifications were carried out by using the TissueQuest System and the software TissueFAX.

RESULTS

SM exposure of MSC results in a dose dependent formation of nuclear DNA adducts. 4h after exposure the cells display a decreasing concentration of DNA adducts. This process is accompanied by a change of nuclei shape but without an increase of apoptosis induction. In parallel the number of cells undergoing senescence increases as a function of the SM concentration.

DISCUSSION

SM exposure of MSC leads to adduct formation on chromosomal DNA. These DNA adducts can be reduced without MSC are undergoing apoptosis. This indicates an active DNA damage response (DDR) pathway in combination with the formation of persistent nuclear DNA damage foci. This process is accompanied by a reduced capability of proliferation and a transition into the senescent state.

Breviscapine (BVP) inhibits prostate cancer progression through damaging DNA by minichromosome maintenance protein-7 (MCM-7) modulation

Naturally occurring compounds are reported as effective candidates for prevention and treatment of various cancers. Breviscapine (BVP) is a mixture of flavonoid glycosides, derived from the Chinese herbs. Previous researches have indicated that BVP has comprehensive pharmacological functions. However, little is known about whether BVP has preventive effects on human prostate cancer. Here, we attempted to explore if BVP inhibits human prostate cancer in vitro and in vivo in a comprehensive manner. We found that BVP triggered cytotoxicity in prostate cancer cell lines dose-dependently. BVP-induced DNA damage caused the cell cycle arrest and apoptosis and further induced cell death. High expression of MCM-7 was reduced in BVP-treated cancer cells and tumor tissues, and also the DNA damage response marker of γH2AX is down-regulated by BVP, associated with MCM-7 expression through regulating retinoblastoma protein (Rb) and checkpoint control proteins expression. Additionally, BVP induced apoptotic response in prostate cancer cells and tumors via activating Caspase-3 and PARP. In vivo studies indicated that BVP impeded tumor growth in xenograft animal models. In conclusion, our data indicates that breviscapine (BVP) can be further explored for its potential, which might be used in human prostate cancer therapeutics.

Nitrogen Mustard-Induced Corneal Injury Involves DNA Damage and Pathways Related to Inflammation, Epithelial-Stromal Separation, and Neovascularization

PURPOSE

To evaluate the toxic effects and associated mechanisms in corneal tissue exposed to the vesicating agent, nitrogen mustard (NM), a bifunctional alkylating analog of the chemical warfare agent sulfur mustard.

METHODS

Toxic effects and associated mechanisms were examined in maximally affected corneal tissue using corneal cultures and human corneal epithelial (HCE) cells exposed to NM.

RESULTS

Analysis of ex vivo rabbit corneas showed that NM exposure increased apoptotic cell death, epithelial thickness, epithelial-stromal separation, and levels of vascular endothelial growth factor, cyclooxygenase 2, and matrix metalloproteinase-9. In HCE cells, NM exposure resulted in a dose-dependent decrease in cell viability and proliferation, which was associated with DNA damage in terms of an increase in p53 ser15, total p53, and H2A.X ser139 levels. NM exposure also induced caspase-3 and poly ADP ribose polymerase cleavage, suggesting their involvement in NM-induced apoptotic death in the rabbit cornea and HCE cells. Similar to rabbit cornea, NM exposure caused an increase in cyclooxygenase 2, matrix metalloproteinase-9, and vascular endothelial growth factor levels in HCE cells, indicating a role of these molecules and related pathways in NM-induced corneal inflammation, epithelial-stromal separation, and neovascularization. NM exposure also induced activation of activator protein 1 transcription factor proteins and upstream signaling pathways including mitogen-activated protein kinases and Akt protein kinase, suggesting that these could be key factors involved in NM-induced corneal injury.

CONCLUSIONS

Results from this study provide insight into the molecular targets and pathways that could be involved in NM-induced corneal injuries laying the background for further investigation of these pathways in vesicant-induced ocular injuries, which could be helpful in the development of targeted therapies.

Sulfur mustard inhalation: mechanisms of injury, alteration of coagulation, and fibrinolytic therapy

Acute lung injury due to sulfur mustard (SM) inhalation causes the formation of airway fibrin casts that obstruct airways at multiple levels, leading to acute respiratory failure and death. These pathophysiological effects are seen in rodent models of acute SM vapor inhalation, as well as in human victims of acute SM inhalation. In rat models, the initial steps in activation of the coagulation system at extravascular sites depend on tissue factor (TF) expression by airway cells, especially in the microparticle fraction, and these effects can be inhibited by TF pathway inhibitor protein. Not only does the procoagulant environment of the acutely injured lung contribute to airway cast formation, but these lesions persist in airways because of the activation of multiple antifibrinolytic pathways, including plasminogen activator inhibitor-1, thrombin-activatable fibrinolysis inhibitor, and α2-antiplasmin. Airway administration of tissue plasminogen activator can overwhelm these effects and save lives by preventing fibrin-dependent airway obstruction, gas-exchange abnormalities, and respiratory failure. In human survivors of SM inhalation, fibrotic processes, including bronchiolitis obliterans and interstitial fibrosis of the lung, are among the most disabling chronic lesions. Antifibrotic therapies may prove useful in preventing either or both of these forms of chronic lung damage.

Mustard vesicating agent-induced toxicity in the skin tissue and silibinin as a potential countermeasure

Exposure to the vesicating agents sulfur mustard (SM) and nitrogen mustard (NM) causes severe skin injury with delayed blistering. Depending upon the dose and time of their exposure, edema and erythema develop into blisters, ulceration, necrosis, desquamation, and pigmentation changes, which persist weeks and even years after exposure. Research advances have generated data that have started to explain the probable mechanism of action of vesicant-induced skin toxicity; however, despite these advances, effective and targeted therapies are still deficient. This review highlights studies on two SM analogs, 2-chloroethyl ethyl sulfide (CEES) and NM, and CEES- and NM-induced skin injury mouse models that have substantially added to the knowledge on the complex pathways involved in mustard vesicating agent-induced skin injury. Furthermore, employing these mouse models, studies under the National Institutes of Health Countermeasures Against Chemical Threats program have identified the flavanone silibinin as a novel therapeutic intervention with the potential to be developed as an effective countermeasure against skin injury following exposure to mustard vesicating agents.

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.

Dynamic cytotoxic profiles of sulfur mustard in human dermal cells determined by multiparametric high-content analysis

Sulfur mustard (SM) is a well known chemical warfare agent that poses a major threat to military personnel and also populace. It targets multiple macromolecules, and its toxic effects are mediated by complex mechanisms. However, the sequence and manner of SM-induced cellular and molecular events underpinning the pathological processes are not fully elucidated. Effective therapeutic agents against SM poisoning are also lacking. The present study aimed to determine the dynamic cytotoxic profiles of SM in primary cultured human epidermal keratinocytes-fetal (HEK-f) and human dermal fibroblasts-adult (HDF-a) by establishing a high content analysis (HCA)-based multiparametric toxicity assay panel. SM was found to produce multiple, concentration-dependent cellular responses, including abnormal cellular morphology, cycle arrest, apoptosis, necrosis, mitochondrial membrane potential imbalance, increased membrane permeability, oxidative stress, DNA damage, and lysosome impairment. Time-course analysis indicated that the cellular and molecular responses related to the highly reactive targets of SM, such as glutathione depletion, reactive oxygen species release, DNA and lysosomal damage, and actin microfilament architecture modification, were congenerous initial events for SM injury. Moreover, this study demonstrated a novel finding that SM induced autophagy, and it was closely related to lysosome alterations in both cell types. Higher susceptibility of HEK-f cells to SM was associated with early lysosomal damage and decreased autophagy activity. Multiparametric HCA also revealed the concentration-dependent cytoprotective effect of hydroxychloroquine in HDF-a cells. The above results provided overall and objective evidence for elucidating the cytotoxic mechanism of SM, and also a good scientific base for further research on countermeasures against SM injury.

Immunochemical analysis of poly(ADP-ribosyl)ation in HaCaT keratinocytes induced by the mono-alkylating agent 2-chloroethyl ethyl sulfide (CEES): Impact of experimental conditions

Sulfur mustard (SM) is a bifunctional alkylating agent with a long history of use as a chemical weapon. Although its last military use is dated for the eighties of the last century, a potential use in terroristic attacks against civilians remains a significant threat. Thus, improving medical therapy of mustard exposed individuals is still of particular interest. PARP inhibitors were recently brought into the focus as a potential countermeasure for mustard-induced pathologies, supported by the availability of efficient compounds successfully tested in cancer therapy. PARP activation after SM treatment was reported in several cell types and tissues under various conditions; however, a detailed characterization of this phenomenon is still missing. This study provides the basis for such studies by developing and optimizing experimental conditions to investigate poly(ADP-ribosyl)ation (PARylation) in HaCaT keratinocytes upon treatment with the monofunctional alkylating agent 2-chloroethyl ethyl sulfide ("half mustard", CEES). By using an immunofluorescence-based approach, we show that optimization of experimental conditions with regards to the type of solvent, dilution factors and treatment procedure is essential to obtain a homogenous PAR staining in HaCaT cell cultures. Furthermore, we demonstrate that different CEES treatment protocols significantly influence the cytotoxicity profiles of treated cells. Using an optimized treatment protocol, our data reveals that CEES induces a dose- and time-dependent dynamic PARylation response in HaCaT cells that could be completely blocked by treating cells with the clinically relevant pharmacological PARP inhibitor ABT888 (also known as veliparib). Finally, siRNA experiments show that CEES-induced PAR formation is predominantly due to the activation of PARP1. In conclusion, this study provides a detailed analysis of the CEES-induced PARylation response in HaCaT keratinocytes, which forms an experimental basis to study the molecular mechanism of PARP1 activation and its functional consequences after mustard treatment in general. Such a study is presented in an accompanying article (Mangerich et al., 2016).

Sulfur and nitrogen mustards induce characteristic poly(ADP-ribosyl)ation responses in HaCaT keratinocytes with distinctive cellular consequences

Mustard agents are potent DNA alkylating agents with mutagenic, cytotoxic and vesicant properties. They include bi-functional agents, such as sulfur mustard (SM) or nitrogen mustard (mustine, HN2), as well as mono-functional agents, such as "half mustard" (CEES). Whereas SM has been used as a chemical warfare agent, several nitrogen mustard derivatives, such as chlorambucil and cyclophosphamide, are being used as established chemotherapeutics. Upon induction of specific forms of genotoxic stimuli, several poly(ADP-ribose) polymerases (PARPs) synthesize the nucleic acid-like biopolymer poly(ADP-ribose) (PAR) by using NAD(+) as a substrate. Previously, it was shown that SM triggers cellular poly(ADP-ribosyl) ation (PARylation), but so far this phenomenon is poorly characterized. In view of the protective effects of PARP inhibitors, the latter have been proposed as a treatment option of SM-exposed victims. In an accompanying article (Debiak et al., 2016), we have provided an optimized protocol for the analysis of the CEES-induced PARylation response in HaCaT keratinocytes, which forms an experimental basis to further analyze mustard-induced PARylation and its functional consequences, in general. Thus, in the present study, we performed a comprehensive characterization of the PARylation response in HaCaT cells after treatment with four different mustard agents, i.e., SM, CEES, HN2, and chlorambucil, on a qualitative, quantitative and functional level. In particular, we recorded substance-specific as well as dose- and time-dependent PARylation responses using independent bioanalytical methods based on single-cell immuno-fluorescence microscopy and quantitative isotope dilution mass spectrometry. Furthermore, we analyzed if and how PARylation contributes to mustard-induced toxicity by treating HaCaT cells with CEES, SM, and HN2 in combination with the clinically relevant PARP inhibitor ABT888. As evaluated by a novel immunofluorescence-based protocol for the detection of N7-ETE-guanine DNA adducts, the excision rate of CEES-induced DNA adducts was not affected by PARP inhibition. Furthermore, while CEES induced moderate changes in cellular NAD(+) levels, annexin V/PI flow cytometry analysis revealed that these changes did not affect CEES-induced short-term cytotoxicity 24h after treatment. In contrast, PARP inhibition impaired cell proliferation and clonogenic survival, and potentiated micronuclei formation of HaCaT cells upon CEES treatment. Similarly, PARP inhibition affected clonogenic survival of cells treated with bi-functional mustards such as SM and HN2. In conclusion, we demonstrate that PARylation plays a functional role in mustard-induced cellular stress response with substance-specific differences. Since PARP inhibitors exhibit therapeutic potential to treat SM-related pathologies and to sensitize cancer cells for mustard-based chemotherapy, potential long-term effects of PARP inhibition on genomic stability and carcinogenesis should be carefully considered when pursuing such a strategy.

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.

Flavanone silibinin treatment attenuates nitrogen mustard-induced toxic effects in mouse skin

Currently, there is no effective antidote to prevent skin injuries by sulfur mustard (SM) and nitrogen mustard (NM), which are vesicating agents with potential relevance to chemical warfare, terrorist attacks, or industrial/laboratory accidents. Our earlier report has demonstrated the therapeutic efficacy of silibinin, a natural flavanone, in reversing monofunctional alkylating SM analog 2-chloroethyl ethyl sulfide-induced toxic effects in mouse skin. To translate this effect to a bifunctional alkylating vesicant, herein, efficacy studies were carried out with NM. Topical application of silibinin (1 or 2mg) 30 min after NM exposure on the dorsal skin of male SKH-1 hairless mice significantly decreased NM-induced toxic lesions at 24, 72 or 120 h post-exposure. Specifically, silibinin treatment resulted in dose-dependent reduction of NM-induced increase in epidermal thickness, dead and denuded epidermis, parakeratosis and microvesication. Higher silibinin dose also caused a 79% and 51%reversal in NM-induced increases in myeloperoxidase activity and COX-2 levels, respectively. Furthermore, silibinin completely prevented NM-induced H2A.X phosphorylation, indicating reversal of DNA damage which could be an oxidative DNA damage as evidenced by high levels of 8-oxodG in NM-exposed mouse skin that was significantly reversed by silibinin. Together, these findings suggest that attenuation of NM-induced skin injury by silibinin is due to its effects on the pathways associated with DNA damage, inflammation, vesication and oxidative stress. In conclusion, results presented here support the optimization of silibinin as an effective treatment of skin injury by vesicants.

Water stress proteins from Nostoc commune Vauch. exhibit anti-colon cancer activities in vitro and in vivo

Nostoc commune has been traditionally used in China as a health food and medicine. The water stress proteins (WSP) of Nostoc commune are the major component of the extracellular matrix. This study purified and identified the water stress proteins (WSP1) from Nostoc commune Vauch., which could inhibit the proliferation of human colon cancer cell lines. The IC50 values of WSP1 against DLD1, HCT116, HT29, and SW480 cells were 0.19 ± 0.02, 0.21 ± 0.03, 0.39 ± 0.05, and 0.41 ± 0.01 μg/μL, respectively. Notably, it displayed very little effect on the normal human intestinal epithelial FHC cell line. The IC50 value of WSP1 against FHC cells was 0.67 ± 0.05 μg/μL. Moreover, the growth of DLD1 xenografted tumors in nude mice were significantly suppressed in the WSP1 treated group. Mechanistically, the cell-cycle analysis revealed that WSP1 induced growth inhibition by G1/S arrest. Meanwhile, Western blotting and immunohistochemistry assays showed WSP1 could activate caspase-8, -9, and -3, along with subsequent PARP cleavage. Furthermore, the pan-caspase inhibitor, z-VAD-FMK, partly reversed the effect caused by WSP1, confirming that WSP1 induced cell apoptosis through caspase-dependent pathway. Collectively, WSP1 has targeted inhibition for colon cancer proliferation both in vitro and in vivo and it is valuable for future exploitation and utilization as an antitumor agent.

Whole genome expression analysis in primary bronchial epithelial cells after exposure to sulphur mustard

Sulphur mustard (SM) is a highly toxic chemical agent and poses a current threat to both civilians and military personnel in the event of a deliberate malicious release. Acute SM toxicity develops over the course of several hours and mainly affects the skin and mucosal surfaces of the eyes and respiratory system. In cases of acute severe exposure, significant lung injury can result in respiratory failure and death. Systemic levels of SM can also be fatal, frequently due to immunodepletion and the subsequent development of secondary infections. Whilst the physical effects associated with SM exposure are well documented, the molecular mechanisms mediating these changes are poorly understood, hindering the development of an effective therapeutic strategy. To gain a better understanding of the mechanism of SM toxicity, this study investigated whole genome transcriptional changes after SM in primary human bronchial epithelial cells, as a model for inhalation exposure. The analysis revealed >400 transcriptional changes associated with SM exposure. Pathways analysis confirmed the findings of previous studies suggesting that DNA damage, cell cycle arrest, cell death and inflammation were important components of SM toxicity. In addition, several other interesting observations were made, suggesting that protein oxidation as well as effects on the mitotic apparatus may contribute to SM toxicity.

Catalytic antioxidant AEOL 10150 treatment ameliorates sulfur mustard analog 2-chloroethyl ethyl sulfide-associated cutaneous toxic effects

Our previous studies and other published reports on the chemical warfare agent sulfur mustard (SM) and its analog 2-chloroethyl ethyl sulfide (CEES) have indicated a role of oxidative stress in skin injuries caused by these vesicating agents. We examined the effects of the catalytic antioxidant AEOL 10150 in the attenuation of CEES-induced toxicity using our established skin injury models (skin epidermal cells and SKH-1 hairless mice) to validate the role of oxidative stress in the pathophysiology of mustard vesicating agents. Treatment of mouse epidermal JB6 and human HaCaT cells with AEOL 10150 (50μM) 1h post-CEES exposure resulted in significant (p < 0.05) reversal of CEES-induced decreases in both cell viability and DNA synthesis. Similarly, AEOL 10150 treatment 1h after CEES exposure attenuated CEES-induced DNA damage in these cells. Similar AEOL 10150 treatments also caused significant (p < 0.05) reversal of CEES-induced decreases in cell viability in normal human epidermal keratinocytes. Cytoplasmic and mitochondrial reactive oxygen species measurements showed that AEOL 10150 treatment drastically ameliorated the CEES-induced oxidative stress in both JB6 and HaCaT cells. Based on AEOL 10150 pharmacokinetic studies in SKH-1 mouse skin, mice were treated with a topical formulation plus subcutaneous injection (5mg/kg) of AEOL 10150 1h after CEES (4mg/mouse) exposure and every 4h thereafter for 12h. This AEOL 10150 treatment regimen resulted in over 50% (p < 0.05) reversal of CEES-induced skin bi-fold and epidermal thickness, myeloperoxidase activity, and DNA oxidation in mouse skin. Results from this study demonstrate the potential therapeutic efficacy of AEOL 10150 against CEES-mediated cutaneous lesions, supporting AEOL 10150 as a medical countermeasure against SM-induced skin injuries.

Activation of DNA damage repair pathways in response to nitrogen mustard-induced DNA damage and toxicity in skin keratinocytes

Nitrogen mustard (NM), a structural analog of chemical warfare agent sulfur mustard (SM), forms adducts and crosslinks with DNA, RNA and proteins. Here we studied the mechanism of NM-induced skin toxicity in response to double strand breaks (DSBs) resulting in cell cycle arrest to facilitate DNA repair, as a model for developing countermeasures against vesicant-induced skin injuries. NM exposure of mouse epidermal JB6 cells decreased cell growth and caused S-phase arrest. Consistent with these biological outcomes, NM exposure also increased comet tail extent moment and the levels of DNA DSB repair molecules phospho H2A.X Ser139 and p53 Ser15 indicating NM-induced DNA DSBs. Since DNA DSB repair occurs via non homologous end joining pathway (NHEJ) or homologous recombination repair (HRR) pathways, next we studied these two pathways and noted their activation as defined by an increase in phospho- and total DNA-PK levels, and the formation of Rad51 foci, respectively. To further analyze the role of these pathways in the cellular response to NM-induced cytotoxicity, NHEJ and HRR were inhibited by DNA-PK inhibitor NU7026 and Rad51 inhibitor BO2, respectively. Inhibition of NHEJ did not sensitize cells to NM-induced decrease in cell growth and cell cycle arrest. However, inhibition of the HRR pathway caused a significant increase in cell death, and prolonged G2M arrest following NM exposure. Together, our findings, indicating that HRR is the key pathway involved in the repair of NM-induced DNA DSBs, could be useful in developing new therapeutic strategies against vesicant-induced skin injury.

Myeloperoxidase deficiency attenuates nitrogen mustard-induced skin injuries

The pathologic mechanisms of skin injuries, following the acute inflammatory response induced by vesicating agents sulfur mustard (SM) and nitrogen mustard (NM) exposure, are poorly understood. Neutrophils which accumulate at the site of injury, abundantly express myeloperoxidase (MPO), a heme protein that is implicated in oxidant-related antimicrobial and cytotoxic responses. Our previous studies have shown that exposure to SM analog 2-chloroethyl ethyl sulfide (CEES) or NM results in an inflammatory response including increased neutrophilic infiltration and MPO activity. To further define the role of neutrophil-derived MPO in NM-induced skin injury, here we used a genetic approach and examined the effect of NM exposure (12h and 24h) on previously established injury endpoints in C57BL/6J wild type (WT) and B6.129X1-MPOtm1Lus/J mice (MPO KO), homozygous null for MPO gene. NM exposure caused a significant increase in skin bi-fold thickness, epidermal thickness, microvesication, DNA damage and apoptosis in WT mice compared to MPO KO mice. MPO KO mice showed relatively insignificant effect. Similarly, NM induced increases in the expression of inflammatory and proteolytic mediators, including COX-2, iNOS and MMP-9 in WT mice, while having a significantly lower effect in MPO KO mice. Collectively, these results show that MPO, which generates microbicidal oxidants, plays an important role in NM-induced skin injuries. This suggests the development of mechanism-based treatments against NM- and SM-induced skin injuries that inhibit MPO activity and attenuate MPO-derived oxidants.

Histopathological and immunohistochemical evaluation of nitrogen mustard-induced cutaneous effects in SKH-1 hairless and C57BL/6 mice

Sulfur mustard (SM) is a vesicant warfare agent which causes severe skin injuries. Currently, we lack effective antidotes against SM-induced skin injuries, in part due to lack of appropriate animal model(s) that can be used for efficacy studies in laboratory settings to identify effective therapies. Therefore, to develop a relevant mouse skin injury model, we examined the effects of nitrogen mustard (NM), a primary vesicant and a bifunctional alkylating agent that induces toxic effects comparable to SM. Specifically, we conducted histopathological and immunohistochemical evaluation of several applicable cutaneous pathological lesions following skin NM (3.2mg) exposure for 12-120h in SKH-1 and C57BL/6 mice. NM caused a significant increase in epidermal thickness, incidence of microvesication, cell proliferation, apoptotic cell death, inflammatory cells (neutrophils, macrophages and mast cells) and myleoperoxidase activity in the skin of both mouse strains. However, there was a more prominent NM-induced increase in epidermal thickness, and macrophages and mast cell infiltration, in SKH-1 mice relative to what was seen in C57BL/6 mice. NM also caused collagen degradation and edema at early time points (12-24h); however, at later time points (72 and 120h), dense collagen staining was observed, indicating either water loss or start of integument repair in both the mouse strains. This study provides quantitative measurement of NM-induced histopathological and immunohistochemical cutaneous lesions in both hairless and haired mouse strains that could serve as useful tools for screening and identification of effective therapies for treatment of skin injuries due to NM and SM.

Temporal and spatial features of the formation of DNA adducts in sulfur mustard-exposed skin

Sulfur mustard (SM) is a chemical warfare agent that targets skin where it induces large blisters. DNA alkylation is a critical step to explain SM-induced cutaneous symptoms. We determined the kinetics of formation of main SM-DNA adducts and compare it with the development of the SM-induced pathogenesis in skin. SKH-1 mice were exposed to 2, 6 and 60 mg/kg of SM and treated skin was biopsied between 6h and 21 days. Formation of SM DNA adducts was dose-dependent with a maximum immediately after exposure. However, adducts were persistent and still detectable 21 days post-exposure. The time-dependent formation of DNA adducts was also found to be correlated with the appearance of apoptotic cells. This temporal correlation suggests that these two early events are responsible for the severity of the damage to the skin. Besides, SM-DNA adducts were also detected in areas located next to contaminated zone, thus suggesting that SM diffuses in skin. Altogether, this work provides for the first time a clear picture of SM-induced genotoxicity using DNA adducts as a marker.

Mesenchymal stem cells are highly resistant to sulfur mustard

The effect of sulfur mustard (SM) to the direct injured tissues of the skin, eyes and airways is well investigated. Little is known about the effect of SM to mesenchymal stem cells (MSC). However, this is an interesting aspect. Comparing the clinical picture of SM it is known today that MSC play an important role e.g. in chronic impaired wound healing. Therefore we wanted to get an understanding about how SM affects MSC and if these findings might become useful to get a better understanding of the effect of sulfur mustard gas with respect to skin wounds. We used mesenchymal stem cells, isolated from femoral heads from healthy donors and treated them with a wide range of SM to ascertain the dose-response-curve. With the determined inhibitory concentrations IC1 (1μM), IC5 (10μM), IC10 (20μM) and IC25 (40μM) we did further investigations. We analyzed the migratory ability and the differentiation capacity under influence of SM. Already very low concentrations of SM demonstrated a strong effect to the migratory activity whereas the differentiation capacity seemed not to be affected. Putting these findings together it seems to be likely that a link between MSC and the impaired wound healing after SM exposure might exist. Same as in patients with chronic impaired wound healing MSC had shown a reduced migratory activity. The fact that MSC are able to tolerate very high concentrations of SM and still do not lose their differentiation capacity may reveal new ways of treating wounds caused by sulfur mustard.

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.

Silibinin attenuates sulfur mustard analog-induced skin injury by targeting multiple pathways connecting oxidative stress and inflammation

Chemical warfare agent sulfur mustard (HD) inflicts delayed blistering and incapacitating skin injuries. To identify effective countermeasures against HD-induced skin injuries, efficacy studies were carried out employing HD analog 2-chloroethyl ethyl sulfide (CEES)-induced injury biomarkers in skin cells and SKH-1 hairless mouse skin. The data demonstrate strong therapeutic efficacy of silibinin, a natural flavanone, in attenuating CEES-induced skin injury and oxidative stress. In skin cells, silibinin (10 µM) treatment 30 min after 0.35/0.5 mM CEES exposure caused a significant (p<0.05) reversal in CEES-induced decrease in cell viability, apoptotic and necrotic cell death, DNA damage, and an increase in oxidative stress. Silibinin (1 mg) applied topically to mouse skin 30 min post-CEES exposure (2 mg), was effective in reversing CEES-induced increases in skin bi-fold (62%) and epidermal thickness (85%), apoptotic cell death (70%), myeloperoxidase activity (complete reversal), induction of iNOS, COX-2, and MMP-9 protein levels (>90%), and activation of transcription factors NF-κB and AP-1 (complete reversal). Similarly, silibinin treatment was also effective in attenuating CEES-induced oxidative stress measured by 4-hydroxynonenal and 5,5-dimethyl-2-(8-octanoic acid)-1-pyrolline N-oxide protein adduct formation, and 8-oxo-2-deoxyguanosine levels. Since our previous studies implicated oxidative stress, in part, in CEES-induced toxic responses, the reversal of CEES-induced oxidative stress and other toxic effects by silibinin in this study indicate its pleiotropic therapeutic efficacy. Together, these findings support further optimization of silibinin in HD skin toxicity model to develop a novel effective therapy for skin injuries by vesicants.