Topical efficacy of dimercapto-chelating agents against lewisite-induced skin lesions in SKH-1 hairless mice

Development of 4-phenylbutyric acid microsponge gel formulations for the treatment of lewisite-mediated skin injury

Lewisite, a chemical warfare agent, causes skin blisters, erythema, edema, and inflammation, requiring mitigation strategies in case of accidental or deliberate exposure. 4-phenyl butyric acid (4-PBA), a chemical chaperone, reduces endoplasmic reticulum stress and skin inflammation. The study aimed to encapsulate 4-PBA in microsponges for effective, sustained delivery against lewisite injury. Porous microsponges in a topical gel would potentially sustain delivery and improve residence time on the skin. Microsponges were developed using the quasi-emulsion solvent diffusion method with Eudragit RS100. Optimized formulation showed 10.58%w/w drug loading was incorporated in a carboxymethylcellulose (CMC) and Carbopol gel for in vitro release and permeation testing using dermatomed human skin. A sustained release was obtained from all vehicles in the release study, and IVPT results showed that compared to the control (41.52 ± 2.54 µg/sq.cm), a sustained permeation profile with a reduced delivery was observed for microsponges in PBS (14.16 ± 1.23 µg/sq.cm) along with Carbopol 980 gel (12.55 ± 1.41 µg/sq.cm), and CMC gel (10.09 ± 1.23 µg/sq.cm) at 24 h. Optimized formulation showed significant protection against lewisite surrogate phenyl arsine oxide (PAO) challenged skin injury in Ptch1+/-/SKH-1 hairless mice at gross and molecular levels. A reduction in Draize score by 29%, a reduction in skin bifold thickness by 8%, a significant reduction in levels of IL-1β, IL6, and GM-CSF by 54%, 30%, and 55%, respectively, and a reduction in apoptosis by 31% was observed. Thus, the translational feasibility of 4-PBA microsponges for effective, sustained delivery against lewisite skin injury is demonstrated.

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.

Microneedle-mediated transdermal delivery of N-acetyl cysteine as a potential antidote for lewisite injury

Lewisite is a chemical warfare agent intended for use in World War and a potential threat to the civilian population due to presence in stockpiles or accidental exposure. Lewisite-mediated skin injury is characterized by acute erythema, pain, and blister formation. N-acetyl cysteine (NAC) is an FDA-approved drug for acetaminophen toxicity, identified as a potential antidote against lewisite. In the present study, we have explored the feasibility of rapid NAC delivery through transdermal route for potentially treating chemical warfare toxicity. NAC is a small, hydrophilic molecule with limited passive delivery through the skin. Using skin microporation with dissolving microneedles significantly enhanced the delivery of NAC into and across dermatomed human skin in our studies. Microporation followed by application of solution (poke-and-solution) resulted in the highest in vitro delivery (509.84 ± 155.04 µg/sq·cm) as compared to poke-and-gel approach (474.91 ± 70.09 µg/sq·cm) and drug-loaded microneedles (226.89 ± 33.41 µg/sq·cm). The lag time for NAC delivery through poke-and-solution approach (0.23 ± 0.04 h) was close to gel application (0.25 ± 0.02 h), with the highest for drug-loaded microneedles (1.27 ± 1.16 h). Thus, we successfully demonstrated the feasibility of rapid NAC delivery using various skin microporation approaches for potential treatment against lewisite-mediated skin toxicity.

Metabolomics for identifying pathways involved in vesicating agent lewisite-induced corneal injury

Lewisite (LEW) is an arsenical vesicant that can be a potentially dangerous chemical warfare agent (CWA). Eyes are particularly susceptible to vesicant induced injuries and ocular LEW exposure can act swiftly, causing burning of eyes, edema, inflammation, cell death and even blindness. In our previous studies, we developed a LEW exposure-induced corneal injury model in rabbit and showed increased inflammation, neovascularization, cell death, and structural damage to rabbit corneas upon LEW exposure. In the present study, we further assessed the metabolomic changes to delineate the possible mechanisms underlying the LEW-induced corneal injuries. This information is vital and could help in the development of effective targeted therapies against ocular LEW injuries. Thus, the metabolomic changes associated with LEW exposures in rabbit corneas were assessed as a function of time, to delineate pathways from molecular perturbations at the genomic and proteomic levels. New Zealand white rabbit corneas (n = 3-6) were exposed to LEW vapor (0.2 mg/L; flow rate: 300 ml/min) for 2.5 min (short exposure; low dose) or 7.5 min (long-exposure; high dose) and then collected at 1, 3, 7, or 14 days post LEW exposure. Samples were prepared using the automated MicroLab STAR® system, and proteins precipitated to recover the chemically diverse metabolites. Metabolomic analysis was carried out by reverse phase UPLC-MS/MS and gas chromatography (GC)-MS. The data obtained were analyzed using Metabolon's software. The results showed that LEW exposures at high doses were more toxic, particularly at the day 7 post exposure time point. LEW exposure was shown to dysregulate metabolites associated with all the integral functions of the cornea and cause increased inflammation and immune response, as well as generate oxidative stress. Additionally, all important metabolic functions of the cells were also affected: lipid and nucleotide metabolism, and energetics. The high dose LEW exposures were more toxic, particularly at day 7 post LEW exposure (>10-fold increased levels of histamine, quinolinate, N-acetyl-β-alanine, GMP, and UPM). LEW exposure dysregulated integral functions of the cornea, caused inflammation and heightened immune response, and generated oxidative stress. Lipid and nucleotide metabolism, and energetics were also affected. The novel information about altered metabolic profile of rabbit cornea following LEW exposure could assist in delineating complex molecular events; thus, aid in identifying therapeutic targets to effectively ameliorate ocular trauma.

Role of hair follicles in the pathogenesis of arsenical-induced cutaneous damage

Arsenical vesicants cause skin inflammation, blistering, and pain. The lack of appropriate animal models causes difficulty in defining their molecular pathogenesis. Here, Ptch1+/- /C57BL/6 mice were employed to investigate the pathobiology of the arsenicals lewisite and phenylarsine oxide (PAO). Following lewisite or PAO challenge (24 h), the skin of animals becomes grayish-white, thick, leathery, and wrinkled with increased bi-fold thickness, Draize score, and necrotic patches. In histopathology, infiltrating leukocytes (macrophages and neutrophils), epidermal-dermal separation, edema, apoptotic cells, and disruption of tight and adherens junction proteins can be visualized. PCR arrays and nanoString analyses showed significant increases in cytokines/chemokines and other proinflammatory mediators. As hair follicles (HFs), which provide an immune-privileged environment, may affect immune cell trafficking and consequent inflammatory responses, we compared the pathogenesis of these chemicals in this model to that in Ptch1+/- /SKH-1 hairless mice. Ptch1+/- /SKH-1 mice have rudimentary, whereas Ptch1+/- /C57BL/6 mice have well-developed HFs. Although no significant differences were observed in qualitative inflammatory responses between the two strains, levels of cytokines/chemokines differed. Importantly, the mechanism of inflammation was identical; both reactive oxygen species induction and consequent activation of unfolded protein response signaling were similar. These data reveal that the acute molecular pathogenesis of arsenicals in these two murine models is similar.

Dynamic Regulation of the Nexus Between Stress Granules, Roquin, and Regnase-1 Underlies the Molecular Pathogenesis of Warfare Vesicants

The use of chemical warfare agents is prohibited but they have been used in recent Middle Eastern conflicts. Their accidental exposure (e.g. arsenical lewisite) is also known and causes extensive painful cutaneous injury. However, their molecular pathogenesis is not understood. Here, we demonstrate that a nexus of stress granules (SGs), integrated stress, and RNA binding proteins (RBPs) Roquin and Reganse-1 play a key role. Lewisite and its prototype phenylarsine oxide (PAO) induce SG assembly in skin keratinocytes soon after exposure, which associate with various RBPs and translation-related proteins. SG disassembly was detected several hours after exposure. The dynamics of SG assembly-disassembly associates with the chemical insult and cell damage. Enhanced Roquin and Regnase-1 expression occurs when Roquin was recruited to SGs and Regnase-1 to the ribosome while in the disassembling SGs their expression is decreased with consequent induction of inflammatory mediators. SG-targeted protein translational control is regulated by the phosphorylation-dependent activation of eukaryotic initiation factors 2α (eIF2α). Treatment with integrated stress response inhibitor (ISRIB), which blocks eIF2α phosphorylation, impacted SG assembly dynamics. Topical application of ISRIB attenuated the inflammation and tissue disruption in PAO-challenged mice. Thus, the dynamic regulation of these pathways provides underpinning to cutaneous injury and identify translational therapeutic approach for these and similar debilitating chemicals.

Toxic blister agents: Chemistry, mode of their action and effective treatment strategies

Since their use during the First World War, Blister agents have posed a major threat to the individuals and have caused around two million casualties. Major incidents occurred not only due to their use as chemical warfare agents but also because of occupational hazards. Therefore, a clear understanding of these agents and their mode of action is essential to develop effective decontamination and therapeutic strategies. The blister agents have been categorised on the basis of their chemistry and the biological interactions that entail post contamination. These compounds have been known to majorly cause blisters/bullae along with alkylation of the contaminated DNA. However, due to the high toxicity and restricted use, very little research has been conducted and a lot remains to be clearly understood about these compounds. Various decontamination solutions and detection technologies have been developed, which have proven to be effective for their timely mitigation. But a major hurdle seems to be the lack of proper understanding of the toxicological mechanism of action of these compounds. Current review is about the detailed and updated information on physical, chemical and biological aspects of various blister agents. It also illustrates the mechanism of their action, toxicological effects, detection technologies and possible decontamination strategies.

Cutaneous exposure to lewisite causes acute kidney injury by invoking DNA damage and autophagic response

Lewisite (2-chlorovinyldichloroarsine) is an organic arsenical chemical warfare agent that was developed and weaponized during World Wars I/II. Stockpiles of lewisite still exist in many parts of the world and pose potential environmental and human health threat. Exposure to lewisite and similar chemicals causes intense cutaneous inflammatory response. However, morbidity and mortality in the exposed population is not only the result of cutaneous damage but is also a result of systemic injury. Here, we provide data delineating the pathogenesis of acute kidney injury (AKI) following cutaneous exposure to lewisite and its analog phenylarsine oxide (PAO) in a murine model. Both agents caused renal tubular injury, characterized by loss of brush border in proximal tubules and tubular cell apoptosis accompanied by increases in serum creatinine, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1. Interestingly, lewisite exposure enhanced production of reactive oxygen species (ROS) in the kidney and resulted in the activation of autophagic and DNA damage response (DDR) signaling pathways with increased expression of beclin-1, autophagy-related gene 7, and LC-3A/B-II and increased phosphorylation of γ-H2A.X and checkpoint kinase 1/2, respectively. Terminal deoxyribonucleotide-transferase-mediated dUTP nick-end labeling-positive cells were detected in renal tubules along with enhanced proapoptotic BAX/cleaved caspase-3 and reduced antiapoptotic BCL2. Scavenging ROS by cutaneous postexposure application of the antioxidant N-acetyl-l-cysteine reduced lewisite-induced autophagy and DNA damage. In summary, we provide evidence that topical exposure to lewisite causes AKI. The molecular mechanism underlying these changes involves ROS-dependent activation of autophagy and DDR pathway associated with the induction of apoptosis.

Histopathological and Molecular Changes in the Rabbit Cornea From Arsenical Vesicant Lewisite Exposure

Lewisite (LEW), a potent arsenical vesicating chemical warfare agent, poses a continuous risk of accidental exposure in addition to its feared use as a terrorist weapon. Ocular tissue is exquisitely sensitive to LEW and exposure can cause devastating corneal lesions. However, detailed pathogenesis of corneal injury and related mechanisms from LEW exposure that could help identify targeted therapies are not available. Using an established consistent and efficient exposure system, we evaluated the pathophysiology of the corneal injury in New Zealand white rabbits following LEW vapor exposure (at 0.2 mg/L dose) for 2.5 and 7.5 min, for up to 28 day post-exposure. LEW led to an increase in total corneal thickness starting at day 1 post-exposure and epithelial degradation starting at day 3 post-exposure, with maximal effect at day 7 postexposure followed by recovery at later time points. LEW also led to an increase in the number of blood vessels and inflammatory cells but a decrease in keratocytes with optimal effects at day 7 postexposure. A significant increase in epithelial-stromal separation was observed at days 7 and 14 post 7.5 min LEW exposure. LEW also caused an increase in the expression levels of cyclooxygenase-2, IL-8, vascular endothelial growth factor, and matrix metalloproteinase-9 at all the study time points indicating their involvement in LEW-induced inflammation, vesication, and neovascularization. The outcomes here provide valuable LEW-induced corneal injury endpoints at both lower and higher exposure durations in a relevant model system, which will be helpful to identify and screen therapies against LEW-induced corneal injury.

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.

Defining cutaneous molecular pathobiology of arsenicals using phenylarsine oxide as a prototype

Arsenicals are painful, inflammatory and blistering causing agents developed as chemical weapons in World War I/II. However, their large stockpiles still exist posing threat to public health. Phenylarsine oxide (PAO), a strong oxidant and a prototype arsenical is tested for its suitability to defining molecular mechanisms underlying arsenicals-mediated tissue injury. Topically applied PAO induces cutaneous erythema, edema and micro-blisters. These gross inflammatory responses were accompanied by the enhanced production of pro-inflammatory cytokines, ROS and unfolded protein response (UPR) signaling activation. To demonstrate the involvement of UPR in the pathobiology of these lesions, we employed chemical chaperone, 4-phenylbutyric acid (4-PBA) which attenuates UPR. 4-PBA significantly reduced PAO-induced inflammation and blistering. Similar to its effects in murine epidermis, a dose- and time-dependent upregulation of ROS, cytokines, UPR proteins (GRP78, p-PERK, p-eIF2α, ATF4 and CHOP) and apoptosis were observed in PAO-treated human skin keratinocytes NHEK and HaCaT. In addition, 4-PBA significantly restored these molecular alterations in these cells. Employing RNA interference (RNAi)-based approaches, CHOP was found to be a key regulator of these responses. These effects are similar to those manifested by lewisite suggesting that PAO could be used as a prototype of arsenicals to define the molecular pathogenesis of chemical injury.

Biological and environmental hazards associated with exposure to chemical warfare agents: arsenicals

Arsenicals are highly reactive inorganic and organic derivatives of arsenic. These chemicals are very toxic and produce both acute and chronic tissue damage. On the basis of these observations, and considering the low cost and simple methods of their bulk syntheses, these agents were thought to be appropriate for chemical warfare. Among these, the best-known agent that was synthesized and weaponized during World War I (WWI) is Lewisite. Exposure to Lewisite causes painful inflammatory and blistering responses in the skin, lung, and eye. These chemicals also manifest systemic tissue injury following their cutaneous exposure. Although largely discontinued after WWI, stockpiles are still known to exist in the former Soviet Union, Germany, Italy, the United States, and Asia. Thus, access by terrorists or accidental exposure could be highly dangerous for humans and the environment. This review summarizes studies that describe the biological, pathophysiological, toxicological, and environmental effects of exposure to arsenicals, with a major focus on cutaneous injury. Studies related to the development of novel molecular pathobiology-based antidotes against these agents are also described.

Molecular Mechanism Underlying Pathogenesis of Lewisite-Induced Cutaneous Blistering and Inflammation: Chemical Chaperones as Potential Novel Antidotes

Lewisite is a potent arsenic-based chemical warfare agent known to induce painful cutaneous inflammation and blistering. Only a few modestly effective antidotes have so far been described in the literature. However, the discovery of effective antidotes for lewisite was hampered by the paucity of the exact molecular mechanism underlying its cutaneous pathogenesis. We investigated the molecular mechanism underlying lewisite-induced cutaneous blistering and inflammation and describe its novel antidotes. On the basis of our initial screening, we used a highly sensitive murine model that recapitulates the known human pathogenesis of arsenicals-induced cutaneous inflammation and blistering. Topically administered lewisite induced potent acute inflammation and microvesication in the skin of Ptch1(+/-)/SKH-1 mice. Even at a very low dose, lewisite up-regulates unfolded protein response signaling, inflammatory response, and apoptosis. These cutaneous lesions were associated with production of reactive oxygen species and extensive apoptosis of the epidermal keratinocytes. We confirmed that activation of reactive oxygen species-dependent unfolded protein response signaling is the underlying molecular mechanism of skin damage. Similar alterations were noticed in lewisite-treated cultured human skin keratinocytes. We discovered that chemical chaperone 4-phenyl butyric acid and antioxidant N-acetylcysteine, which significantly attenuate lewisite-mediated skin injury, can serve as potent antidotes. These data reveal a novel molecular mechanism underlying the cutaneous pathogenesis of lewisite-induced lesions. We also identified novel potential therapeutic targets for lewisite-mediated cutaneous injury.

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.

Clinical progression of ocular injury following arsenical vesicant lewisite exposure

Ocular injury by lewisite (LEW), a potential chemical warfare and terrorist agent, results in edema of eyelids, inflammation, massive corneal necrosis and blindness. To enable screening of effective therapeutics to treat ocular injury from LEW, useful clinically-relevant endpoints are essential. Hence, we designed an efficient exposure system capable of exposing up to six New-Zealand white rabbits at one time, and assessed LEW vapor-induced progression of clinical ocular lesions mainly in the cornea. The right eye of each rabbit was exposed to LEW (0.2 mg/L) vapor for 2.5, 5.0, 7.5 and 10.0 min and clinical progression of injury was observed for 28 days post-exposure (dose-response study), or exposed to same LEW dose for 2.5 and 7.5 min and clinical progression of injury was observed for up to 56 days post-exposure (time-response study); left eye served as an unexposed control. Increasing LEW exposure caused corneal opacity within 6 h post-exposure, which increased up to 3 days, slightly reduced thereafter till 3 weeks, and again increased thereafter. LEW-induced corneal ulceration peaked at 1 day post-exposure and its increase thereafter was observed in phases. LEW exposure induced neovascularization starting at 7 days which peaked at 22-35 days post-exposure, and remained persistent thereafter. In addition, LEW exposure caused corneal thickness, iris redness, and redness and swelling of the conjunctiva. Together, these findings provide clinical sequelae of ocular injury following LEW exposure and for the first time establish clinically-relevant quantitative endpoints, to enable the further identification of histopathological and molecular events involved in LEW-induced ocular injury.

Time course of skin features and inflammatory biomarkers after liquid sulfur mustard exposure in SKH-1 hairless mice

Sulfur mustard (SM) is a strong bifunctional alkylating agent that produces severe tissue injuries characterized by erythema, edema, subepidermal blisters and a delayed inflammatory response after cutaneous exposure. However, despite its long history, SM remains a threat because of the lack of effective medical countermeasures as the molecular mechanisms of these events remain unclear. This limited number of therapeutic options results in part of an absence of appropriate animal models. We propose here to use SKH-1 hairless mouse as the appropriate model for the design of therapeutic strategies against SM-induced skin toxicity. In the present study particular emphasis was placed on histopathological changes associated with inflammatory responses after topical exposure of dorsal skin to three different doses of SM (0.6, 6 and 60mg/kg) corresponding to a superficial, a second-degree and a third-degree burn. Firstly, clinical evaluation of SM-induced skin lesions using non invasive bioengineering methods showed that erythema and impairment of skin barrier increased in a dose-dependent manner. Histological evaluation of skin sections exposed to SM revealed that the time to onset and the severity of symptoms including disorganization of epidermal basal cells, number of pyknotic nuclei, activation of mast cells and neutrophils dermal invasion were dose-dependent. These histopathological changes were associated with a dose- and time-dependent increase in expression of specific mRNA for inflammatory mediators such as interleukins (IL1β and IL6), tumor necrosis factor (TNF)-α, cycloxygenase-2 (COX-2), macrophage inflammatory proteins (MIP-1α, MIP-2 and MIP-1αR) and keratinocyte chemoattractant (KC also called CXCL1) as well as adhesion molecules (L-selectin and vascular cell adhesion molecule (VCAM)) and growth factor (granulocyte colony-stimulating factor (Csf3)). A dose-dependent increase was also noted after SM exposure for mRNA of matrix metalloproteinases (MMP9) and laminin-γ2 which are associated with SM-induced blisters formation. Taken together, our results show that SM-induced skin histopathological changes related to inflammation is similar in SKH-1 hairless mice and humans. SKH-1 mouse is thus a reliable animal model for investigating the SM-induced skin toxicity and to develop efficient treatment against SM-induced inflammatory skin lesions.