Characterization of acute and long-term sulfur mustard-induced skin injuries in hairless guinea-pigs using non-invasive methods

Skin Models Used to Define Mechanisms of Action of Sulfur Mustard

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

Depilatory double-disc mouse model for evaluation of vesicant dermal injury pharmacotherapy countermeasures

BACKGROUND

Sulfur mustard (SM) is a chemical warfare vesicant that severely injures exposed eyes, lungs, and skin. Mechlorethamine hydrochloride (NM) is widely used as an SM surrogate. This study aimed to develop a depilatory double-disc (DDD) NM skin burn model for investigating vesicant pharmacotherapy countermeasures.

METHODS

Hair removal method (clipping only versus clipping followed by a depilatory), the effect of acetone in the vesicant administration vehicle, NM dose (0.5-20 μmol), vehicle volume (5-20 μl), and time course (0.5-21 days) were investigated using male and female CD-1 mice. Edema, an indicator of burn response, was assessed by biopsy skin weight. The ideal NM dose to induce partial-thickness burns was assessed by edema and histopathologic evaluation. The optimized DDD model was validated using an established reagent, NDH-4338, a cyclooxygenase, inducible nitric oxide synthase, and acetylcholinesterase inhibitor prodrug.

RESULTS

Clipping/depilatory resulted in a 5-fold higher skin edematous response and was highly reproducible (18-fold lower %CV) compared to clipping alone. Acetone did not affect edema formation. Peak edema occurred 24-48 h after NM administration using optimized dosing methods and volume. Ideal partial-thickness burns were achieved with 5 μmol of NM and responded to treatment with NDH-4338. No differences in burn edematous responses were observed between males and females.

CONCLUSION

A highly reproducible and sensitive partial-thickness skin burn model was developed for assessing vesicant pharmacotherapy countermeasures. This model provides clinically relevant wound severity and eliminates the need for organic solvents that induce changes to the skin barrier function.

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.

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.

Cutaneous injury-related structural changes and their progression following topical nitrogen mustard exposure in hairless and haired mice

To identify effective therapies against sulfur mustard (SM)-induced skin injuries, various animals have been used to assess the cutaneous pathology and related histopathological changes of SM injuries. However, these efforts to establish relevant skin injury endpoints for efficacy studies have been limited mainly due to the restricted assess of SM. Therefore, we employed the SM analog nitrogen mustard (NM), a primary vesicating and bifunctional alkylating agent, to establish relevant endpoints for efficient efficacy studies. Our published studies show that NM (3.2 mg) exposure for 12–120 h in both the hairless SKH-1 and haired C57BL/6 mice caused clinical sequelae of toxicity similar to SM exposure in humans. The NM-induced cutaneous pathology-related structural changes were further analyzed in this study and quantified morphometrically (as percent length or area of epidermis or dermis) of skin sections in mice showing these lesions. H&E stained skin sections of both hairless and haired mice showed that NM (12–120 h) exposure caused epidermal histopathological effects such as increased epidermal thickness, epidermal-dermal separation, necrotic/dead epidermis, epidermal denuding, scab formation, parakeratosis (24–120 h), hyperkeratosis (12–120 h), and acanthosis with hyperplasia (72–120 h). Similar NM exposure in both mice caused dermal changes including necrosis, edema, increase in inflammatory cells, and red blood cell extravasation. These NM-induced cutaneous histopathological features are comparable to the reported lesions from SM exposure in humans and animal models. This study advocates the usefulness of these histopathological parameters observed due to NM exposure in screening and optimization of rescue therapies against NM and SM skin injuries.

Clinically-relevant cutaneous lesions by nitrogen mustard: useful biomarkers of vesicants skin injury in SKH-1 hairless and C57BL/6 mice

A paucity of clinically applicable biomarkers to screen therapies in laboratory is a limitation in the development of countermeasures against cutaneous injuries by chemical weapon, sulfur mustard (SM), and its analog nitrogen mustard (NM). Consequently, we assessed NM-caused progression of clinical cutaneous lesions; notably, skin injury with NM is comparable to SM. Exposure of SKH-1 hairless and C57BL/6 (haired) mice to NM (3.2 mg) for 12-120 h caused clinical sequelae of toxicity, including microblister formation, edema, erythema, altered pigmentation, wounding, xerosis and scaly dry skin. These toxic effects of NM were similar in both mouse strains, except that wounding and altered pigmentation at 12-24 h and appearance of dry skin at 24 and 72 h post-NM exposure were more pronounced in C57BL/6 compared to SKH-1 mice. Conversely, edema, erythema and microblister formation were more prominent in SKH-1 than C57BL/6 mice at 24-72 h after NM exposure. In addition, 40-60% mortality was observed following 120 h of NM exposure in the both mouse strains. Overall, these toxic effects of NM are comparable to those reported in humans and other animal species with SM, and thus represent clinically-relevant cutaneous injury endpoints in screening and optimization of therapies for skin injuries by vesicating agents.

A clinicopathological approach to sulfur mustard-induced organ complications: a major review

CONTEXT

Sulfur mustard (SM), with an old manufacturing history still remains as potential threat due to easy production and extensive effects.

OBJECTIVES

Increasing studies on SM indicates the interest of researchers to this subject. Almost all human body organs are at risk for complications of SM. This study offers organ-by-organ information on the effects of SM in animals and humans.

METHODS

The data sources were literature reviews since 1919 as well as our studies during the Iraq-Iran war. The search items were SM and its all other nomenclatures in relation to, in vivo, in vitro, humans, animals, eye, ocular, ophthalmic, lungs, pulmonary, skin, cutaneous, organs and systemic. Amongst more than 1890 SM-related articles, 257 more relevant clinicopathologic papers were selected for this review.

RESULTS

SM induces a vast range of damages in nearly all organs. Acute SM intoxication warrants immediate approach. Among chronic lesions, delayed keratitis and blindness, bronchiolitis obliterans and respiratory distress, skin pruritus, dryness and cancers are the most commonly observed clinical sequelae.

CONCLUSION

Ocular involvements in a number of patients progress toward a severe, rapid onset form of keratitis. Progressive deterioration of respiratory tract leads to "mustard lung". Skin problems continue as chronic frustrating pruritus on old scars with susceptibility to skin cancers. Due to the multiple acute and chronic morbidities created by SM exposure, uses of multiple drugs by several routes of administrations are warranted.

Environmental hazard of yperite released at sea: sublethal toxic effects on fish

The aim of this study was to evaluate the potential toxicological effects on fish related to the leakage of yperite from rusted bomb shells dumped at sea. Both in vivo and field studies have been performed. As for the in vivo experiment, specimen of European eel were subcutaneously injected with 0.015, 0.15 and 1.5mg/kg of yperite and sacrificed after 24 and 48 h. In the field study, specimen of Conger eel were collected from a dumping site in the Southern Adriatic Sea. The presence/absence of yperite in tissues, genotoxicity, detoxification enzymes, histological alterations and gross abnormalities were investigated. Results of the in vivo experiment showed a significant increase of EROD activity at both 24h and 48 h. UGT activity increased significantly at 48 h post injection. An acute inflammatory response after 24h in skin layers and muscle was observed, associated to cell degeneration and necrosis after 48 h at the highest dose. On field, comet assay revealed genotoxicity in gills of fish from the dumping site. Specimen from the dumping site showed significantly higher EROD activities compared to controls, deep ulcers and papules on skin together with liver and spleen histopathological lesions.

Characterization of acute and long-term pathologies of superficial and deep dermal sulfur mustard skin lesions in the hairless guinea pig model

Sulfur mustard induces severe acute and prolonged damage to the skin and only partially effective treatments are available. We have previously validated the use of hairless guinea pigs as an experimental model for skin lesions. The present study aimed to characterize a model of a deep dermal lesion and to compare it with the previously described superficial lesion. Clinical evaluation of the lesions was conducted using reflectance colorimetry, trans-epidermal water loss and wound area measurements. Prostaglandin E(2) content, matrix metalloproteinase-2 and 9 activity, and histopathology were conducted up to 4 weeks post-exposure. Sulfur mustard skin injury, including erythema and edema, impairment of skin barrier and wounds developed in a dose-dependent manner. Prostaglandin E(2) content and matrix metalloproteinase-2 and 9 activities were elevated during the wound development and the healing process. Histological evaluation revealed severe damage to the epidermis and deep dermis and vesications. At 4 weeks postexposure, healing was not completed: significantly impaired stratum corneum, absence of hair follicles, and epidermal hyperplasia were observed. These results confirm the use of the superficial and deep dermal skin injuries in the hairless guinea pigs as suitable models that can be utilized for the investigation of the pathological processes of acute as well as long-term injuries. These models will be further used to develop treatments to improve the healing process and prevent skin damage and long-term effects.

Time course pathogenesis of sulphur mustard-induced skin lesions in mouse model

Sulphur mustard (SM) is a bifunctional alkylating agent that causes cutaneous blistering in humans and animals. In this study, we have presented closer views on pathogenesis of SM-induced skin injury in a mouse model. SM diluted in acetone was applied once dermally at a dose of 5 or 10 mg/kg to Swiss albino mice. Skin was dissected out at 0, 1, 3, 6, 12, 24, 48, 72 and 168 hours, post-SM exposure for studying histopathological changes and immunohistochemistry of inflammatory-reparative biomarkers, namely, transforming growth factor alpha (TGF-α), fibroblast growth factor (FGF), endothelial nitric oxide synthase (eNOS) and interlukin 6 (IL-6). Histopathological changes were similar to other mammalian species and basal cell damage resembled the histopathological signs observed with vesication in human skin. Inflammatory cell recruitment at the site of injury was supported by differential expressions of IL-6 at various stages. Time-dependent expressions of eNOS played pivotal roles in all the events of wound healing of SM-induced skin lesions. TGF-α and FGF were strongly associated with keratinocyte migration, re-epithelialisation, angiogenesis, fibroblast proliferation and cell differentiation. Furthermore, quantification of the tissue leukocytosis and DNA damage along with semiquantitative estimation of re-epithelialisation, fibroplasia and neovascularisation on histomorphologic scale could be efficiently used for screening the efficacy of orphan drugs against SM-induced skin injury.

Structural changes in the skin of hairless mice following exposure to sulfur mustard correlate with inflammation and DNA damage

Sulfur mustard (SM, bis(2-chloroethyl)sulfide) is a bifunctional alkylating agent that causes dermal inflammation, edema and blistering. To investigate the pathogenesis of SM-induced injury, we used a vapor cup model which provides an occlusive environment in which SM is in constant contact with the skin. The dorsal skin of SKH-1 hairless mice was exposed to saturated SM vapor or air control. Histopathological changes, inflammatory markers and DNA damage were analyzed 1-14 days later. After 1 day, SM caused epidermal thinning, stratum corneum shedding, basal cell karyolysis, hemorrhage and macrophage and neutrophil accumulation in the dermis. Cleaved caspase-3 and phosphorylated histone 2A.X (phospho-H2A.X), markers of apoptosis and DNA damage, respectively, were increased whereas proliferating cell nuclear antigen (PCNA) was down-regulated after SM exposure. By 3 days, epithelial cell hypertrophy, edema, parakeratosis and loss of epidermal structures were noted. Enzymes generating pro-inflammatory mediators including myeloperoxidase and cyclooxygenase-2 were upregulated. After 7 days, keratin-10, a differentiation marker, was evident in the stratum corneum. This was associated with an underlying eschar, as neoepidermis began to migrate at the wound edges. Trichrome staining revealed increased collagen deposition in the dermis. PCNA expression in the epidermis was correlated with hyperplasia, hyperkeratosis, and parakeratosis. By 14 days, there was epidermal regeneration with extensive hyperplasia, and reduced expression of cleaved caspase-3, cyclooxygenase-2 and phospho-H2A.X. These findings are consistent with the pathophysiology of SM-induced skin injury in humans suggesting that the hairless mouse can be used to investigate the dermatoxicity of vesicants and the potential efficacy of countermeasures.

Time course of lesion development in the hairless guinea-pig model of sulfur mustard-induced dermal injury

The objective of these studies was to provide detailed analyses of the time course of sulfur mustard (SM) vapor-induced clinical, histological, and biochemical changes following cutaneous exposure in hairless guinea-pigs. Three 6 cm(2) sites on the backs of each guinea-pig were exposed to SM vapor (314 mg(3) ) for 6 minutes (low dose) or 12 minutes (high dose). Animals were killed at 6, 24, and 48 hours, or 2 weeks postexposure. Erythema, edema, histopathology, and analysis of matrix metalloproteinase (MMP)-2 and -9 content were evaluated. Erythema was observed by 6 hours, and edema by 24 hours postexposure. Vapor exposure caused epidermal necrosis with varying degrees of dermatitis, ulceration, hemorrhage, and separation of the dermis from the epidermis. Later changes included epidermal regeneration with hyperplasia and formation of granulation tissue in the dermis with loss of hair follicles and glandular structures. Relative amounts of pro and active MMP-2 and MMP-9 were significantly increased in the high-dose SM group at 2 weeks. Erythema, edema, and histologic changes are consistent with findings among human victims of SM attack. This model, with observations to 2 weeks, will be useful in assessing the efficacy of countermeasures against SM.

Uptake, tissue distribution, and excretion of 14C-sulfur mustard vapor following inhalation in F344 rats and cutaneous exposure in hairless guinea pigs

Sulfur mustard (SM), a vessicating agent, has been used in chemical warfare since 1918. The purpose of this study was to quantitate SM vapor deposition, tissue distribution, and excretion following intratracheal inhalation in rats and cutaneous exposure in guinea pigs. 14C-SM vapors for inhalation studies were generated by metering liquid 14C-SM into a heated J tube. Vapors were transported via carrier air supplemented with oxygen and isoflurane to an exposure plenum. Anesthetized rats with transorally placed tracheal catheters were connected to the plenum port via the catheter hub for exposure (approximately 250 mg 14C-SM vapor/m(3); 10 min). For dermal exposure, 3 Teflon cups (6.6 cm(2) exposure area per cup) were applied to the backs of each animal and vapors (525 mg 14C-SM/m(3); 12 min) were generated by applying 6 μl 14C-SM to filter paper within each cup. Animals were euthanized at selected times up to 7 d postexposure. SM equivalents deposited in rats and guinea pigs were 18.1 ± 3 μg and 29.8 ± 5.31 μg, respectively. Inhaled SM equivalents rapidly distributed throughout the body within 2 h postexposure, with the majority (>70%) of material at that time located in carcass and pelt. In guinea pigs, >90% of deposited SM equivalents remained in skin, with minor distribution to blood and kidneys. Urine was the primary route of excretion for both species. Results indicate inhaled SM is rapidly absorbed from the lung and distributed throughout the body while there is limited systemic distribution following cutaneous exposure.

Anti-inflammatory effects of peptide fragments of H2A histone and Oryza Sativa Japonica protein

Anti-inflammatory drugs are often of limited use due to low efficacy and toxic effects. The present study describes the anti-inflammatory effects of a novel nonapeptide termed IIIM1, using the mouse hind paw edema as an experimental model of inflammation. Multiple prophylactic injections of IIIM1 resulted in a significant reduction in carrageenan-induced foot pad swelling, both in mice and rats. A single prophylactic treatment of the peptide caused the maximal effect at 7-9 days between the initial peptide treatment and the subsequent carrageenan injection. A reduced inflammatory reaction was observed in transgenic mice constitutively expressing the peptide. A marked decrease in oxidative burst was observed in activated peritoneal macrophages obtained from peptide-treated mice. Furthermore, the sera of IIIM1-treated mice caused a significant decrease in the oxidative burst of macrophages. In addition, the reduction of hind paw swelling in mice injected with the sera of IIIM1-treated mice strongly suggests the presence of a circulating inducible factor responsible for the anti-inflammatory effect of the peptide. Previous LC/MS/MS analysis revealed the presence of a new peptide, termed RA1, in the sera of IIIM1-treated mice. RA1 was identified as a fragment of the Oryza Sativa Japonica protein. The anti-inflammatory effect of RA1 as evidenced by the reduction in carrageenan-induced hind paw swelling corresponded with the decrease in the oxidative burst of macrophages treated in vitro with this peptide. In conclusion, both IIIM1 and RA1 represent potential agents for the efficient treatment of inflammatory diseases that are currently incurable using presently available drugs.

Expression of proliferative and inflammatory markers in a full-thickness human skin equivalent following exposure to the model sulfur mustard vesicant, 2-chloroethyl ethyl sulfide

Sulfur mustard is a potent vesicant that induces inflammation, edema and blistering following dermal exposure. To assess molecular mechanisms mediating these responses, we analyzed the effects of the model sulfur mustard vesicant, 2-chloroethyl ethyl sulfide, on EpiDerm-FT™, a commercially available full-thickness human skin equivalent. CEES (100-1000 μM) caused a concentration-dependent increase in pyknotic nuclei and vacuolization in basal keratinocytes; at high concentrations (300-1000 μM), CEES also disrupted keratin filament architecture in the stratum corneum. This was associated with time-dependent increases in expression of proliferating cell nuclear antigen, a marker of cell proliferation, and poly(ADP-ribose) polymerase (PARP) and phosphorylated histone H2AX, markers of DNA damage. Concentration- and time-dependent increases in mRNA and protein expression of eicosanoid biosynthetic enzymes including COX-2, 5-lipoxygenase, microsomal PGE₂ synthases, leukotriene (LT) A₄ hydrolase and LTC₄ synthase were observed in CEES-treated skin equivalents, as well as in antioxidant enzymes, glutathione S-transferases A1-2 (GSTA1-2), GSTA3 and GSTA4. These data demonstrate that CEES induces rapid cellular damage, cytotoxicity and inflammation in full-thickness skin equivalents. These effects are similar to human responses to vesicants in vivo and suggest that the full thickness skin equivalent is a useful in vitro model to characterize the biological effects of mustards and to develop potential therapeutics.