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

Chronic kidney disease amplifies severe kidney injury and mortality in a mouse model of skin arsenical exposure

In previously published work, we elucidated the role of cutaneous arsenical exposure in promoting acute kidney injury (AKI) in adult healthy mice. Here, we determine whether preexisting chronic kidney disease (CKD) increases the severity of AKI. Following exposure to aristolochic acid (AA) (a nephrotoxic phytochemical in humans), mice manifested classical markers of CKD, including robust interstitial fibrosis and loss in kidney function. Skin challenge with phenylarsine oxide (PAO), a surrogate for warfare arsenicals, led to significantly worse kidney injury, as evidenced by tubulointerstitial fibrosis, glomerulosclerosis, a persistent loss of estimated glomerular filtration rate, and mortality in AA-induced CKD mice compared with mice without CKD. These PAO-challenged CKD mice exhibited enhanced production of serum/urine neutrophil gelatinase-associated lipocalin and a significant rise in serum creatinine along with histological markers of kidney injury, including brush border loss, tubular atrophy, cast formation, glomerular injury, and interstitial inflammatory cell infiltration. Serum cytokines IL-4, IL-6, IFN-γ, IL-12p70, TNF-α, and IL-18 significantly elevated in CKD mice following PAO exposure when compared with animals exposed to PAO alone. Furthermore, we found increased TUNEL-positive tubular cells in the kidneys of CKD mice following PAO exposure, suggesting enhanced PAO-mediated cell death in CKD mice. Mechanistically, we determined that DNA damage-regulated p53 signaling was a major mediator of cellular responses to PAO in CKD mice. In summary, our data demonstrate that CKD significantly increased the severity of AKI following exposure to arsenicals and suggest that human populations with preexisting CKD could be highly susceptible to arsenical-mediated kidney injury and associated morbidity and mortality.NEW & NOTEWORTHY Preexisting chronic kidney disease (CKD) predisposes experimental animals to augmented morbidity and mortality following cutaneous vesicant exposure. The mechanism underlying increased susceptibility to renal injury and associated morbidity involves the DNA damage-regulated p53 signaling pathway.

Overlapping Science in Radiation and Sulfur Mustard Exposures of Skin and Lung: Consideration of Models, Mechanisms, Organ Systems, and Medical Countermeasures: Overlapping science in radiation and sulfur mustard injuries to lung and skin

PURPOSE

To summarize presentations and discussions from the 2022 trans-agency workshop titled "Overlapping science in radiation and sulfur mustard (SM) exposures of skin and lung: Consideration of models, mechanisms, organ systems, and medical countermeasures."

METHODS

Summary on topics includes: (1) an overview of the radiation and chemical countermeasure development programs and missions; (2) regulatory and industry perspectives for drugs and devices; 3) pathophysiology of skin and lung following radiation or SM exposure; 4) mechanisms of action/targets, biomarkers of injury; and 5) animal models that simulate anticipated clinical responses.

RESULTS

There are striking similarities between injuries caused by radiation and SM exposures. Primary outcomes from both types of exposure include acute injuries, while late complications comprise chronic inflammation, oxidative stress, and vascular dysfunction, which can culminate in fibrosis in both skin and lung organ systems. This workshop brought together academic and industrial researchers, medical practitioners, US Government program officials, and regulators to discuss lung-, and skin- specific animal models and biomarkers, novel pathways of injury and recovery, and paths to licensure for products to address radiation or SM injuries.

CONCLUSIONS

Regular communications between the radiological and chemical injury research communities can enhance the state-of-the-science, provide a unique perspective on novel therapeutic strategies, and improve overall US Government emergency preparedness.

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.

Fluorescent probes for the detection of chemical warfare agents

Chemical warfare agents (CWAs) are toxic chemicals that have been intentionally developed for targeted and deadly use on humans. Although intended for military targets, the use of CWAs more often than not results in mass civilian casualties. To prevent further atrocities from occurring during conflicts, a global ban was implemented through the chemical weapons convention, with the aim of eliminating the development, stockpiling, and use of CWAs. Unfortunately, because of their relatively low cost, ease of manufacture and effectiveness on mass populations, CWAs still exist in today's world. CWAs have been used in several recent terrorist-related incidents and conflicts (e.g., Syria). Therefore, they continue to remain serious threats to public health and safety and to global peace and stability. Analytical methods that can accurately detect CWAs are essential to global security measures and for forensic analysis. Small molecule fluorescent probes have emerged as attractive chemical tools for CWA detection, due to their simplicity, ease of use, excellent selectivity and high sensitivity, as well as their ability to be translated into handheld devices. This includes the ability to non-invasively image CWA distribution within living systems (in vitro and in vivo) to permit in-depth evaluation of their biological interactions and allow potential identification of therapeutic countermeasures. In this review, we provide an overview of the various reported fluorescent probes that have been designed for the detection of CWAs. The mechanism for CWA detection, change in optical output and application for each fluorescent probe are described in detail. The limitations and challenges of currently developed fluorescent probes are discussed providing insight into the future development of this research area. We hope the information provided in this review will give readers a clear understanding of how to design a fluorescent probe for the detection of a specific CWA. We anticipate that this will advance our security systems and provide new tools for environmental and toxicology monitoring.

Comparative analysis of chlorambucil-induced DNA lesion formation and repair in a spectrum of different human cell systems

Chlorambucil (CLB) belongs to the class of nitrogen mustards (NMs), which are highly reactive bifunctional alkylating agents and were the first chemotherapeutic agents developed. They form DNA interstrand crosslinks (ICLs), which cause a blockage of DNA strand separation, inhibiting essential processes in DNA metabolism like replication and transcription. In fast replicating cells, e.g., tumor cells, this can induce cell death. The upregulation of ICL repair is thought to be a key factor for the resistance of tumor cells to ICL-inducing cytostatic agents including NMs. To monitor induction and repair of CLB-induced ICLs, we adjusted the automated reversed fluorometric analysis of alkaline DNA unwinding assay (rFADU) for the detection of ICLs in adherent cells. For the detection of monoalkylated DNA bases we established an LC-MS/MS method. We performed a comparative analysis of adduct formation and removal in five human cell lines and in peripheral blood mononuclear cells (PBMCs) after treatment with CLB. Dose-dependent increases in adduct formation were observed, and suitable treatment concentrations were identified for each cell line, which were then used for monitoring the kinetics of adduct formation. We observed significant differences in the repair kinetics of the cell lines tested. For example, in A2780 cells, hTERT immortalized VH10 cells, and in PBMCs a time-dependent repair of the two main monoalkylated DNA-adducts was confirmed. Regarding ICLs, repair was observed in all cell systems except for PBMCs. In conclusion, LC-MS/MS analyses combined with the rFADU technique are powerful tools to study the molecular mechanisms of NM-induced DNA damage and repair. By applying these methods to a spectrum of human cell systems of different origin and transformation status, we obtained insight into the cell-type specific repair of different CLB-induced DNA lesions, which may help identify novel resistance mechanisms of tumors and define molecular targets for therapeutic interventions.

A review of chemical warfare agents linked to respiratory and neurological effects experienced in Gulf War Illness

Over 40% of veterans from the Persian Gulf War (GW) (1990-1991) suffer from Gulf War Illness (GWI). Thirty years since the GW, the exposure and mechanism contributing to GWI remain unclear. One possible exposure that has been attributed to GWI are chemical warfare agents (CWAs). While there are treatments for isolated symptoms of GWI, the number of respiratory and cognitive/neurological issues continues to rise with minimum treatment options. This issue does not only affect veterans of the GW, importantly these chronic multisymptom illnesses (CMIs) are also growing amongst veterans who have served in the Afghanistan-Iraq war. What both wars have in common are their regions and inhaled exposures. In this review, we will describe the CWA exposures, such as sarin, cyclosarin, and mustard gas in both wars and discuss the various respiratory and neurocognitive issues experienced by veterans. We will bridge the respiratory and neurological symptoms experienced to the various potential mechanisms described for each CWA provided with the most up-to-date models and hypotheses.

Proliferating Stem Cells are Acutely Affected by DNA Damage Induced by Sulfur Mustard

Sulfur mustard (SM), a chemical warfare agent, can form adducts with DNA, RNA, and proteins. Reactions with DNA lead to the formation of both DNA monoadducts and interstrand cross-links, resulting in DNA damage, and is an important component of SM toxicity. Our previous in vivo studies indicated that dividing cells such as hematopoietic stem cells and intestinal villi stem cells seemed to have increased sensitivity to SM. Therefore, to compare the sensitivity of somatic and stem cells to SM and to investigate the mechanism of SM cytotoxicity, we isolated human foreskin fibroblasts, reprogrammed them into pluripotent stem cells, and then compared the DNA damage repair pathways involved upon SM treatment. Our results indicated that proliferating stem cells were more sensitive to SM-induced DNA damage, and the damage mainly comprised single-stranded breaks. Furthermore, the pathways involved in DNA repair in stem cells and somatic cells were different.

Nitrogen Mustard Alkylates and Cross-Links p53 in Human Keratinocytes

Cytotoxic blistering agents such as sulfur mustard and nitrogen mustard (HN2) were synthesized for chemical warfare. Toxicity is due to reactive chloroethyl side chains that modify and damage cellular macromolecules including DNA and proteins. In response to DNA damage, cells initiate a DNA damage response directed at the recruitment and activation of repair-related proteins. A central mediator of the DNA damage response is p53, a protein that plays a critical role in regulating DNA repair. We found that HN2 causes cytosolic and nuclear accumulation of p53 in HaCaT keratinocytes; HN2 also induced post-translational modifications on p53 including S15 phosphorylation and K382 acetylation, which enhance p53 stability, promote DNA repair, and mediate cellular metabolic responses to stress. HN2 also cross-linked p53, forming dimers and high-molecular-weight protein complexes in the cells. Cross-linked multimers were also modified by K48-linked ubiquitination indicating that they are targets for proteasome degradation. HN2-induced modifications transiently suppressed the transcriptional activity of p53. Using recombinant human p53, HN2 alkylation was found to be concentration- and redox status-dependent. Dithiothreitol-reduced protein was more efficiently cross-linked indicating that p53 cysteine residues play a key role in protein modification. LC-MS/MS analysis revealed that HN2 directly alkylated p53 at C124, C135, C141, C176, C182, C275, C277, H115, H178, K132, and K139, forming both monoadducts and cross-links. The formation of intermolecular complexes was a consequence of HN2 cross-linked cysteine residues between two molecules of p53. Together, these data demonstrate that p53 is a molecular target for mustard vesicants. Modification of p53 likely mediates cellular responses to HN2 including DNA repair and cell survival contributing to vesicant-induced cytotoxicity.

Phosgene oxime: a highly toxic urticant and emerging chemical threat

Highly toxic industrial chemicals that are widely accessible, and hazardous chemicals like phosgene oxime (CX) that can be easily synthesized, pose a serious threat as potential chemical weapons. In addition, their accidental release can lead to chemical emergencies and mass casualties. CX, an urticant, or nettle agent, grouped with vesicating agents, causes instant pain, injury and systemic effects, which can lead to mortality. With faster cutaneous penetration, corrosive properties, and more potent toxicity compared to other vesicating agents, CX causes instantaneous and severe tissue damage. CX, a potential chemical terrorism threat agent, could therefore be weaponized with other chemical warfare agents to enhance their harmful effects. CX is the least studied vesicant and its acute and long-term toxic effects as well as its mechanism of action are largely unknown. This has hampered the identification of therapeutic targets and the development of effective medical countermeasures. There are only protective measures, decontamination, and supportive treatments available for reducing the toxic effects from CX exposure. This review summarizes CX toxicity, its known mechanism of action, and our current studies exploring the role of mast cell activation and associated signaling pathways in CX cutaneous exposure under the National Institutes of Health Countermeasures Against Chemical Threats program. Potential treatment options and the development of effective targeted countermeasures against CX-induced morbidity and mortality is also discussed.

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.

Antioxidant/stress response in mouse epidermis following exposure to nitrogen mustard

Nitrogen mustard (NM) is a highly reactive bifunctional alkylating agent that induces inflammation, edema and blistering in skin. An important mechanism mediating the action of NM and related mustards is oxidative stress. In these studies a modified murine patch-test model was used to analyze DNA damage and the antioxidant/stress response following NM exposure in isolated epidermis. NM (20 μmol) was applied to glass microfiber filters affixed to a shaved dorsal region of skin of CD-1 mice. NM caused structural damage to the stratum corneum as reflected by increases in transepidermal water loss and skin hydration. This was coordinate with edema, mast cell degranulation and epidermal hyperplasia. Within 3 h of NM exposure, a 4-fold increase in phosphorylated histone H2AX, a marker of DNA double-stranded breaks, and a 25-fold increase in phosphorylated p53, a DNA damage marker, were observed in the epidermis. This was associated with a 40% increase in 8-oxo-2'-deoxyguanosine modified DNA in the epidermis and a 4-fold increase in 4-hydroxynonenal modified epidermal proteins. At 12 h post NM, there was a 3-75 fold increase in epidermal expression of antioxidant/stress proteins including heme oxygenase-1, thioredoxin reductase, superoxide dismutase, glutathione reductase, heat shock protein 27 and cyclooxygenase 2. These data indicate that NM induces early oxidative epidermal injury in mouse skin leading to an antioxidant/stress response. Agents that enhance this response may be useful in mitigating mustard-induced skin injury.

Inhibition of DNA Repair Protein Ku70 in High-Glucose Environment Aggravates the Neurotoxicity Induced by Bupivacaine in SH-SY5Y Cells

Bupivacaine, a common local anesthetic, causes serious nerve injury, especially in diabetic patients, as high glucose has been reported to enhance bupivacaine-induced neurotoxicity. However, the key regulator for synergism remains unknown. To our surprise, the expression of repair protein Ku70 is suppressed, while the high-glucose environment induces DNA oxidative damage in neurons. Here, we aim to investigate whether the inhibition of Ku70 by high-glucose conditions aggrandized bupivacaine-induced DNA damage. Consistent with previous results, bupivacaine induced reactive oxygen species production and upregulated Ku70 and cleaved caspase-3 expressions at both transcript and protein levels and ultimately caused nucleic acid damage and apoptosis in human neuroblastoma (SH-SY5Y) cells. High-glucose treatment inhibited the expression of Ku70 and enhanced bupivacaine-induced neurotoxicity. In contrast, the overexpression of Ku70 mitigated DNA damage and apoptosis triggered by bupivacaine and high glucose. In conclusion, our data indicated that local anesthetics may aggravate nerve toxicity in a high-glucose environment.

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.

Chemical warfare agents. Classes and targets

Synthetic toxic chemicals (toxicants) and biological poisons (toxins) have been developed as chemical warfare agents in the last century. At the time of their initial consideration as chemical weapon, only restricted knowledge existed about their mechanisms of action. There exist two different types of acute toxic action: nonspecific cytotoxic mechanisms with multiple chemo-biological interactions versus specific mechanisms that tend to have just a single or a few target biomolecules. TRPV1- and TRPA-receptors are often involved as chemosensors that induce neurogenic inflammation. The present work briefly surveys classes and toxicologically relevant features of chemical warfare agents and describes mechanisms of toxic action.

The relationship of REL proto-oncogene to pathobiology and chemoresistance in follicular and transformed follicular lymphoma

Follicular lymphoma (FL) is a common type of indolent lymphoma that occasionally transforms to more aggressive B-cell lymphomas. These transformed follicular lymphomas (tFL) are often associated with chemoresistance whose mechanisms are currently unknown. REL, a proto-oncogene located on frequently amplified 2p16.1-p15 locus, promotes tumorigenesis in many cancer types through deregulation of the NF-κB pathway; however, its role in FL pathobiology or chemoresistance has not been addressed. Here, we evaluated REL gene copy number by q-PCR on FFPE FL tumor samples, and observed REL amplification in 30.4% of FL cases that was associated with weak elevation of transcript levels. PCR-Sanger analysis did not show any somatic mutation in FL tumors. In support of a marginal oncogenic role, a REL-transduced FL cell line was positively selected under limiting serum conditions. Interestingly, reanalysis of previously reported gene expression profiles revealed significant enrichment of DNA damage-induced repair and cell cycle arrest pathways in tFL tumors with high REL expression compared to those with low REL expression consistent with the critical role of c-REL in genotoxicity-induced NF-κB signaling, which was reported to lead to drug resistance. In addition to DNA damage repair genes such as ATM and BRCA1, anti-apoptotic BCL2 was significantly elevated in REL-high FL and tFL tumors. Altogether these data suggest that other genes located in amplified 2p16.1-p15 locus may have more oncogenic role in FL etiology; however, high REL expression may be useful as a predictive biomarker of response to immunochemotherapy, and inhibition of c-REL may potentially sensitize resistant FL or tFL cells to chemotherapy.

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.

Mitigation of nitrogen mustard mediated skin injury by a novel indomethacin bifunctional prodrug

Nitrogen mustard (NM) is a bifunctional alkylating agent that is highly reactive in the skin causing extensive tissue damage and blistering. In the present studies, a modified cutaneous murine patch model was developed to characterize NM-induced injury and to evaluate the efficacy of an indomethacin pro-drug in mitigating toxicity. NM (20μmol) or vehicle control was applied onto 6mm glass microfiber filters affixed to the shaved dorsal skin of CD-1 mice for 6min. This resulted in absorption of approximately 4μmol of NM. NM caused localized skin damage within 1 d, progressing to an eschar within 2-3 d, followed by wound healing after 4-5 d. NM-induced injury was associated with increases in skin thickness, inflammatory cell infiltration, reduced numbers of sebocytes, basal keratinocyte double stranded DNA breaks, as measured by phospho-histone 2A.X expression, mast cell degranulation and increases in inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Wound healing was characterized by epidermal hyperplasia and marked increases in basal cells expressing proliferating cell nuclear antigen. A novel indomethacin-anticholinergic prodrug (4338) designed to target cyclooxygenases and acetylcholinesterase (AChE), was found to markedly suppress NM toxicity, decreasing wound thickness and eschar formation. The prodrug also inhibited mast cell degranulation, suppressed keratinocyte expression of iNOS and COX-2, as well as markers of epidermal proliferation. These findings indicate that a novel bifunctional pro-drug is effective in limiting NM mediated dermal injury. Moreover, our newly developed cutaneous patch model is a sensitive and reproducible method to assess the mechanism of action of countermeasures.

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.

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 hydrochloride-induced acute respiratory failure and myelosuppression: A case report

Nitrogen mustards are chemical agents that are similar to sulfur mustards, with similar toxicities. The present study describes a case of nitrogen mustard-induced acute respiratory failure and myelosuppression in a 33-year-old man. The patient, who was accidentally exposed to nitrogen mustard hydrochloride in a pharmaceutical factory, exhibited severe inhalation injury and respiratory symptoms. Laboratory tests revealed reduced white blood cell counts and lowered platelet levels during the first 6 days after the skin exposure to nitrogen mustard. Following treatment with mechanical ventilation, immunity-enhancing agents and nutritional supplements for 1 month, the patient successfully recovered and was released from hospital.

OGG1 Involvement in High Glucose-Mediated Enhancement of Bupivacaine-Induced Oxidative DNA Damage in SH-SY5Y Cells

Hyperglycemia can inhibit expression of the 8-oxoG-DNA glycosylase (OGG1) which is one of the key repair enzymes for DNA oxidative damage. The effect of hyperglycemia on OGG1 expression in response to local anesthetics-induced DNA damage is unknown. This study was designed to determine whether high glucose inhibits OGG1 expression and aggravates bupivacaine-induced DNA damage via reactive oxygen species (ROS). SH-SY5Y cells were cultured with or without 50 mM glucose for 8 days before they were treated with 1.5 mM bupivacaine for 24 h. OGG1 expression was measured by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot. ROS was estimated using the redox-sensitive fluorescent dye DCFH-DA. DNA damage was investigated with immunostaining for 8-oxodG and comet assays. OGG1 expression was inhibited in cells exposed to high glucose with concomitant increase in ROS production and more severe DNA damage as compared to control culture conditions, and these changes were further exacerbated by bupivacaine. Treatment with the antioxidant N-acetyl-L-cysteine (NAC) prevented high glucose and bupivacaine mediated increase in ROS production and restored functional expression of OGG1, which lead to attenuated high glucose-mediated exacerbation of bupivacaine neurotoxicity. Our findings indicate that subjects with diabetes may experience more detrimental effects following bupivacaine use.

Role of p53 in the progression from ochratoxin A-induced DNA damage to gene mutations in the kidneys of mice

Carcinogenic doses of ochratoxin A (OTA) cause increases of mutant frequencies (MFs) of the red/gam gene (Spi(-)) in the kidneys of p53-deficient gpt delta mice, but not in p53-proficient mice. Here, we investigated the role of p53 in the progression from OTA-induced DNA damage to gene mutations. To this end, p53-proficient and -deficient mice were administered 5 mg/kg OTA for 3 days or 4 weeks by gavage. After 3 days of administration, comet assays were performed and there were no differences in the degrees of OTA-induced DNA damage between p53-proficient and -deficient mice. However, the frequencies of γ-H2AX-positive tubular epithelial cells in p53-deficient mice were significantly higher than those in p53-proficient mice, implying that p53 inhibited the progression from DNA damage to DNA double-strand breaks (DSBs). Evaluation of global gene expression and relevant mRNA/protein expression levels demonstrated that OTA increased the expression of Cdkn1a, which encodes the p21 protein, in p53-proficient mice, but not in p53-deficient mice. Moreover, in p53-deficient mice, mRNA levels of cell cycle progression and DSB repair (homologous recombination repair [HR])-related genes were significantly increased. Thus, G1/S arrest due to activation of the p53/p21 pathway may contribute to the prevention of DSBs in p53-proficient mice. In addition, single base deletions/insertions/substitutions were predominant, possibly due to HR. Overall, these results suggested that OTA induced DSBs at the carcinogenic target site in mice and that p53/p21-mediated cell cycle control prevented an increase in the formation of DSBs, leading to gene mutations.

The importance of evaluating the physicochemical and toxicological properties of a contaminant for remediating environments affected by chemical incidents

In the event of a major chemical incident or accident, appropriate tools and technical guidance need to be available to ensure that a robust approach can be adopted for developing a remediation strategy. Remediation and restoration strategies implemented in the aftermath of a chemical incident are a particular concern for public health. As a result an innovative methodology has been developed to help design an effective recovery strategy in the aftermath of a chemical incident that has been developed; the UK Recovery Handbook for Chemical Incidents (UKRHCI). The handbook consists of a six-step decision framework and the use of decision trees specifically designed for three different environments: food production systems, inhabited areas and water environments. It also provides a compendium of evidence-based recovery options (techniques or methods for remediation) that should be selected in relation to their efficacy for removing contaminants from the environment. Selection of effective recovery options in this decision framework involves evaluating the physicochemical and toxicological properties of the chemical(s) involved. Thus, the chemical handbook includes a series of tables with relevant physicochemical and toxicological properties that should be assessed in function of the environment affected. It is essential that the physicochemical properties of a chemical are evaluated and interpreted correctly during the development of a remedial plan in the aftermath of a chemical incident to ensure an effective remedial response. This paper presents a general overview of the key physicochemical and toxicological properties of chemicals that should be evaluated when developing a recovery strategy. Information on how physicochemical properties have impacted on previous remedial responses reported in the literature is also discussed and a number of challenges for remediation are highlighted to include the need to develop novel approaches to remediate sites contaminated by mixtures of chemicals as well as methods for interpreting chemical reactions in different environmental matrices to include how climate change may affect the speciation and mobility of chemicals in the environment.