Microblister Formation in Vesicant-Exposed Pig Skin

Action of bis(betachloroethyl)sulphide (BCES) on human epidermis reconstituted in culture: Morphological alterations and biochemical depletion of glutathione

Human keratinocyte cultures were treated with bis(betachloroethyl)sulphide (BCES), an alkylating and vesicant agent. At concentrations of 5 x 10(-4) to 5 x 10(-3)m, spontaneous detachment of the epithelium from the culture plate was observed, reproducing in vitro the cutaneous vesication observed in vivo. Progressive cellular alterations were shown with increasing concentrations of BCES (5 x 10(-5) to 5 x 10(-3)m). At low concentrations (5 x 10(-5)m), lesions of the nucleus, a significant target for BCES, were observed, along with lesions in the cytoplasmic organelles. An acute, dose-dependent depletion of cellular glutathione was observed, which occurred within 1 hr of treatment. Mechlorethamine, an analogue of BCES, induced at equivalent doses the same glutathione depletion and similar spontaneous detachment in vitro. We suggest that BCES, in addition to its genetic effects, acts by direct metabolic toxicity and induces glutathione depletion by direct conjugation. The lesions obtained in vitro reproduced those observed in vivo. Human keratinocyte cultures can be proposed as a good model for the study of the mechanisms of action of BCES.

A vapor exposure model for neonatal mice

Sulfur mustard (HD) is a vesicant compound that was first used as a chemical warfare agent in World War I. (Papirmeister et al. 1991). Numerous animal models have been used to study HD-induced vesication. In this article, we describe modifications of the vapor cup model of Mershon and colleagues (1990) to establish a new vapor cup model for use in neonatal mice. The need to develop this model resulted from the development of gene-targeted knockout mice that can be used to evaluate the function of specific genes and their contribution to HD-induced pathology. However, the knockouts are haired mice; therefore, it is necessary to perform vapor exposures on the pups prior to their growing hair. Neonatal mice were anesthetized with isofluorane inhalation and placed in sternal recumbency on a 37 degrees C isothermal pad to maintain body heat during exposure. The vapor cup consisted of a 1.5-mL microfuge tube cap (8 mm inside diameter) modified using a Dremel tool to contour its rim to better fit the curve of a mouse pups back. The inside of the cap was fitted with an 8-mm disk of Whatman #2 filter paper, and the rim of the cap was coated with a thin bead of Thomas Lubriseal grease. Ten muL of neat HD was placed on the filter paper disk, and the cup was immediately inverted and placed onto the back of an anesthetized mouse pup. Exposure times varied from 10 to 30 min. At 24 h postexposure, the mice were euthanized; the HD-exposed skin was removed and fixed in 10% neutral buffered formalin. Following a minimum of 24 h of formalin fixation, the skin sections were bisected across the exposed area. The sections were embedded in paraffin with the central straight-cut surfaces being the focus of histological evaluation. The amount of damage associated with the HD vapor cup exposure varied with time in a dose response fashion. Typical damage consisted of varying amounts of epidermal necrosis at the basal cell level, with occasional separation of epidermis from dermis (microvesication). In severe cases there was complete coagulation of the epidermis and no microvesication. This model should prove useful in identifying the biochemical mechanism of action of HD and ultimately aid in the evaluation of treatment compounds. It may also provide a relevant exposure model for other compounds for which the assessment of vapor-induced damage is necessitated.

Mustard gas toxicity: the acute and chronic pathological effects

Ever since it was first used in armed conflict, mustard gas (sulfur mustard, MG) has been known to cause a wide range of acute and chronic injuries to exposure victims. The earliest descriptions of these injuries were published during and in the immediate aftermath of the First World War, and a further series of accounts followed the Second World War. More recently, MG has been deployed in warfare in the Middle East and this resulted in large numbers of victims, whose conditions have been studied in detail at hospitals in the region. In this review, we bring together the older and more recent clinical studies on MG toxicity and summarize what is now known about the acute and chronic effects of the agent on the eyes, skin, respiratory tract and other physiological systems. In the majority of patients, the most clinically serious long-term consequences of MG poisoning are on the respiratory system, but the effects on the skin and other systems also have a significant impact on quality of life. Aspects of the management of these patients are discussed.

Ameliorative effect of DRDE 07 and its analogues on the systemic toxicity of sulphur mustard and nitrogen mustard in rabbit

Despite extensive research efforts, there is no unanimous approval of any animal model to evaluate the toxicity of sulphur mustard [SM; bis (2-chloroethyl) sulphide] or nitrogen mustard [HN-3; tris-(2-chloroethyl) amine] and screening of various prophylactic and therapeutic agents against them. In this study, differential toxicity of mustard agents in higher animal model that is male rabbit was determined. Protective efficacy of DRDE 07 [S-2(2-aminoethylamino) ethyl phenyl sulphide] and its analogues were also evaluated against SM and HN-3 toxicity. Differential toxicity study of SM and HN-3 reveals that both the compounds were more toxic by percutaneous route as compared to subcutaneous route. Till date, there is no recommended drug to counteract SM induced toxicity or mortality in vivo. However, DRDE 07 (an amifostine analogue) and its analogues are found to be very effective protective agents against percutaneously exposed SM in rabbits. The present experiments also showed that SM does not cause skin injury alone but also can cause systemic toxicity as well. DRDE 07 and many of its analogues may prove as prototype compounds for the development of better prophylactic and therapeutic drugs to counter the toxicity of SM or HN-3. In conclusion, rodents and rabbits can be used for the screening of drugs against the blistering agents.

Microarray analysis of gene expression in murine skin exposed to sulfur mustard

The chemical warfare agent sulfur mustard [bis-(2-chloroethyl)-sulfide; SM] produces a delayed inflammatory response followed by blister formation in skin of exposed individuals. Studies are underway evaluating the efficacy of pharmacological compounds to protect against SM skin injury. Microarray analysis provides the opportunity to identify multiple transcriptional biomarkers associated with SM exposure. This study examined SM-induced changes in gene expression in skin from mice cutaneously exposed to SM using cDNA microarrays. Ear skin from five mice, paired as SM-exposed right ear and dichloromethane vehicle-exposed left ear at six dose levels (0.005, 0.01, 0.02, 0.04, 0.08, and 0.16 mg; 6 mM to 195 mM range), was harvested at 24 h post-exposure. SM-induced gene expression was analyzed using cDNA microarrays that included 1,176 genes. Genes were selected on the basis of all mice (N=5) in the same dose group demonstrating a > or =2-fold increase or decrease in gene expression for the SM-exposed tissue compared to the dichloromethane vehicle control ear tissue at all six SM doses. When skin exposed to all six concentrations of SM was compared to controls, a total of 19 genes within apoptosis, transcription factors, cell cycle, inflammation, and oncogenes and tumor suppressors categories were found to be upregulated; no genes were observed to be downregulated. Differences in the number and category of genes that were up- or down-regulated in skin exposed to low (0.005-0.01 mg) and high (0.08-0.16 mg) doses of SM were also observed. The results of this study provide a further understanding of the molecular responses to cutaneous SM exposure, and enable the identification of potential diagnostic markers and therapeutic targets for treating SM injury.

Time- and dose-dependent analysis of gene expression using microarrays in sulfur mustard-exposed mice

The chemical warfare agent sulfur mustard (SM) produces blister formation with a severe inflammatory reaction in skin of exposed individuals. The development of efficacious countermeasures against SM vesication requires an understanding of the cellular and molecular mechanism of SM-induced tissue injury. This study examined SM-induced alterations in gene expression using Atlas Mouse 5K DNA microarrays (5002 genes) to identify transcriptional events associated with SM skin injury. Mice (N=3) were exposed topically to SM (0.04, 0.08, and 0.16 mg; 48.8, 97.5, and 195 mM) on the inner surface of the right ear and skin tissues were harvested at 1.5, 3, 6, and 12 h. Genes were selected based on the three mice in the same dose group demonstrating a > or =2-fold increase or decrease in gene expression for the SM-exposed tissue when compared to the dichloromethane vehicle control ear at all three doses and four time points. At the 0.04 mg SM dose, the genes observed were primarily involved in inflammation, apoptosis, and cell cycle regulation. Exposure to 0.08 mg SM increased the expression of genes related to inflammation and cell cycle regulation. Exposure to 0.16 mg SM led to a total of six genes that were changed at all observed time periods; however, these genes do not appear to be directly influential in biological mechanisms such as inflammation, apoptosis, and cell cycle regulation as was observed at the lower SM doses of 0.04 and 0.08 mg. These functional categories have been observed in previous studies utilizing both in vivo and in vitro model systems of SM-induced dermal injury, suggesting that molecular mechanisms associated with inflammation, apoptosis, and cell cycle regulation may be appropriate targets for developing prophylactic/therapeutic treatments for SM skin injury.

Localization of substance P gene expression for evaluating protective countermeasures against sulfur mustard

Sulfur mustard [bis(2-chloroethyl)sulfide; SM] is a chemical warfare agent that produces edema and blister formation with a severe inflammatory reaction. The mouse ear vesicant model for SM injury has been used to evaluate pharmacological agents for countering SM dermal injury. The vanilloid olvanil reduces SM-induced edema and mRNA expression of cytokines and chemokines, suggesting that blocking the inflammatory effects of neuropeptides, such as substance P (SP), may provide protection against SM-induced dermal injury. This study examined SP expression in mice exposed to SM (0.16 mg) on the inner surface of the right ear, with or without olvanil pretreatment at 1, 10, 30, 60, and 360 min following exposure. In naïve skin, SP mRNA localization was associated with blood vessels and sebaceous glands. In SM-exposed skin, SP mRNA was also detected in perivascular dermal cells. Immunohistochemical localization of SP protein was observed in the ear skin of naïve, SM-, olvanil/SM-, and vehicle-treated mice. Quantification of SP+ perivascular dermal cells revealed that SM exposure led to a significant increase (P < or = 0.05) in SP+ cells over the observed time period. Olvanil pretreatment significantly reduced (P < or = 0.05) the mean number of SP+ cells at 60 and 360 min. This study demonstrates that SP expression could provide an additional endpoint for evaluating the effectiveness of vanilloid drugs on SM-induced skin inflammation.

Sulphur mustard injuries of the skin. Pathophysiology and management

Sulphur mustard is a vesicant (blistering agent), which produces chemical burns with widespread blistering. It was used extensively as a chemical warfare agent in the First World War, and has allegedly been employed in a number of conflicts since then, most recently by Iraq against Iran (1984-1987). The potential further use of mustard in military conflicts and by terrorists remains a significant threat that if realised in practice would result in a large number of casualties with severely incapacitating, partial thickness burns. Such injuries clearly present a huge potential wound care problem. The development and healing of mustard-induced cutaneous injuries has not only been observed in human casualties, but has been studied recently at the microscopic and ultrastructural levels in several animal models. Vesication generally begins on the second day after exposure, and may progress for up to 2 weeks. Wound healing is considerably slower than for a comparable thermal burn, and patients often require extended hospital treatment. The current management strategy is essentially symptomatic and supportive. Recently, two techniques for removing damaged tissue and improving wound healing have been investigated. Mechanical dermabrasion and laser debridement ('lasablation') both produced an increased rate of wound healing in animal models, and may be of benefit in a clinical context.

Cytokine, chemokine, and matrix metalloproteinase response after sulfur mustard injury to weanling pig skin

Cutaneous exposure to sulfur mustard [bis(2-chloroethyl) sulfide; SM] produces a delayed inflammatory skin response and severe tissue injury. Pig skin has organ similarities to human skin that is characterized by the content and types of epidermal lipids, the density of hair follicles and presence of sweat glands, which together afford penetration of topically applied compounds, complex inflammatory responses, and subsequent wound healing. The goal of this study was to identify in vivo proinflammatory biomarkers of the SM porcine skin injury within 72 h after SM challenge, using the weanling pig model. Changes in gene expression of inflammatory mediators were examined at 3, 6, 24, 48, and 72 h, using subtraction library analyses and by quantitation of selected transcripts by reverse transcription-polymerase chain reaction (RT-PCR). Sequence analysis of subtraction libraries identified up-regulation of IL-8 at 24, 48, and 72 h. No other specific proinflammatory gene transcripts were isolated from the libraries. Specific transcript RT-PCR analysis showed increased production of interleukin-1beta (IL-1beta), interleukin-6 (IL-6), interleukin-8 (IL-8), and matrix metalloproteinase-9 (MMP-9, gelatinase B) mRNA levels in response to SM exposure. Tumor necrosis factor-alpha (TNF-alpha) expression was only slightly increased and no change in the levels of expression was observed for monocyte chemoattractant protein-1 and MMP-2. This study identifies the main proinflammatory mediators involved in SM-induced skin injury in a weanling pig model. The results suggest transcriptional activity in the inflammatory response proteins IL-8, IL-6, IL-1beta, and MMP-9 and modest changes in TNF-alpha that together produce inflammation and contribute to the pathogenesis of SM dermatotoxicity. Therefore, drugs preventing SM-induced inflammation should be prime candidates for medical intervention to lessen collateral inflammation associated with tissue destruction.

Alterations in inflammatory cytokine gene expression in sulfur mustard-exposed mouse skin

Cutaneous exposure to sulfur mustard (bis(2-chloroethyl) sulfide, HD), a chemical warfare agent, produces a delayed inflammatory skin response and severe tissue injury. Despite defined roles of inflammatory cytokines produced or released in response to skin-damaging chemicals, in vivo cytokine responses associated with HD-induced skin pathogenesis are not well understood. Additionally, there is little information on the in vivo temporal sequence of gene expression of cytokines postexposure to HD. The goal of these studies was to identify in vivo molecular biomarkers of HD skin injury within 24 hours after HD challenge. Gene expression of interleukin 1beta (IL-1beta), granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin 6 (IL-6), and interleukin 1alpha (IL-1alpha) in the mouse ear vesicant model was examined by quantitative reverse transcription-polymerase chain reaction (RT-PCR). An increase in IL-1beta mRNA levels was first observed at 3 hours. IL-1beta, GM-CSF, and IL-6 mRNA levels were dramatically increased at 6-24 hours postexposure. IL-1alpha mRNA levels were not increased following HD exposure. Immunohistochemical studies demonstrated that IL-1beta and IL-6 protein was produced at multiple sites within the ear, including epithelial cells, inflammatory cells, hair follicles, sebaceous glands, the dermal microvasculature, smooth muscle, and the dermal connective tissue. An increase in the intensity of staining for IL-1beta, and IL-6 was observed in localized areas at 6 hours and was evident in multiple areas at 24 hours. Positive staining for GM-CSF immunoreactive protein was localized to the inflammatory cells within the dermis. The number of immunostaining cells was increased as early as 1 hour following HD exposure. These studies document an early increase in the in vivo expression of inflammatory cytokines following cutaneous HD exposure. An understanding of the in vivo cytokine patterns following HD skin exposure may lead to defining the pathogenic mechanisms of HD injury and the development of pharmacological countermeasures.

Sulfur mustard-induced skin burns in weanling swine evaluated clinically and histopathologically

Histopathological indicators and clinical observations were used to evaluate wound severity, depth and degree of healing on days 2 and 8 for full-skin-thickness sulfur-mustard (HD)-induced burns in weanling swine. Six female weanling swine were exposed for 2 h to 400 microl of HD at each of six dose sites on the hairless abdominal skin. Biopsy samples (8 mm) were taken from the periphery and from the center of the wound on day 2, and the wound was excised on day 8. Histopathological indicators evaluated were epidermal necrosis, follicular necrosis, dermal necrosis, vascular necrosis, depth of injury, ulceration (loss of epidermis), granulation tissue response, neovascularization, re-epithelialization (hyperplasia) and completeness of healing. Wounds were more severe from anterior to posterior. Histopathological assessment of epidermal ulceration and necrosis of epidermis, dermis, basal epithelium, adnexal structures and subcutaneous tissue were useful indicators of wound development on day 2. Granulation tissue response (observed as early as day 8) and re-epithelialization were good indicators of wound healing. Clinical evaluations were performed on day 2 prior to and after debriding, and on study day 8. Clinical observations on study day 2 were for wound size and for exudation, erythema, edema, necrosis and eschar. Clinical observations on study day 8 were for the previous parameters and for re-epithelialization, granulation and infection. Wound size and severity increased from anterior to posterior position. Size, exudation and edema were useful indicators of wound development. These histological and clinical observation parameters will be used in future experiments to compare various treatments for HD-induced burns.

A cutaneous full-thickness liquid sulfur mustard burn model in weanling swine: clinical pathology and urinary excretion of thiodiglycol

Sulfur mustard (bis(2-chloroethyl)sulfide, HD) is a well-known blistering chemical warfare agent. We have developed a cutaneous full-thickness HD burn model in weanling pigs for efficacy testing of candidate treatment regimens. This report addresses clinical pathology findings and the urinary excretion profile of a major HD metabolite (thiodiglycol, TDG) in this model. Six female Yorkshire pigs were exposed to HD liquid on the ventral surface for 2 h, generating six 3-cm diameter full-thickness dermal lesions per pig. Blood samples were collected throughout a 7-day observation period for hematology and serum chemistry examinations. Urine was collected in metabolism cages. Routine urinalysis was performed and the urine analyzed for TDG using gas chromatography/mass spectrometry. Examination of clinical pathology parameters revealed subtle HD-related changes that are suggestive of a mild hemolytic episode. No other signs of clinically significant systemic toxicities were noted, including bone marrow suppression. Thiodiglycol was detected at the earliest time point tested (6-8 h post-exposure) at levels ranging from 0.66 to 4.98 microg ml(-1) with a mean of 2.14 microg ml(-1). Thiodiglycol concentrations were the highest for half of the animals at this earliest time point and at 24-48 h for the others. By the evening of day 3, the mean level had reached 50 ng ml(-1). Mean levels remained 10-40 ng ml(-1) for the remainder of the 7-day observation period, with the highest individual concentration noted during this period of 132 ng ml(-1). Our results are in general agreement with the TDG excretion profiles previously described for rodent models and humans. Urinary excretion of absorbed HD in our weanling pig wound healing model appears to follow the same pattern as is seen in other laboratory animals models. In general, urinary excretion of TDG appears to peak within the first 1-4 days following exposure, with detectable levels after 1 week. Relatively high urinary TDG levels may thus indicate agent exposure within the previous 96 h. Low levels significantly above natural background levels may indicate either exposure to low levels of agent or exposure that occurred more than 4 days prior to collection of the sample.

Therapeutic approaches to dermatotoxicity by sulfur mustard. I. Modulaton of sulfur mustard-induced cutaneous injury in the mouse ear vesicant model

The mouse ear edema model is recognized for its usefulness in studying skin responses and damage following exposure to chemical irritants, and for evaluating pharmacological agents against chemically induced skin injury. We recently modified the mouse ear edema model for use with sulfur mustard (HD) and used this model to study the protective effect of 33 topically applied compounds comprising five pharmaceutical strategies (anti-inflammatories, protease inhibitors, scavengers/chelators, poly(ADP-ribose) polymerase (PARP) inhibitors, calcium modulators/chelators) against HD-induced dermatotoxicity. Pharmacological modulation of HD injury in mouse ears was established by a reduction in edema or histopathology (epidermal necrosis and epidermal-dermal separation) at 24 h following topical liquid HD exposure. Ten of the 33 compounds administered as single topical pretreatments up to 2 h prior to HD challenge produced significant reductions in edema. Five of these ten also produced significant reductions in histological endpoints. Three candidates (olvanil, indomethacin, hydrocortisone) showing protection at 24 h were evaluated further for 'extended protection' at 48 and 72 h after HD challenge and showed significant modulation of edema at 48 h but not at 72 h. Olvanil also showed significant reductions in histology at 48 and 72 h. Olvanil and indomethacin were shown to reduce significantly the edema at 24 h post-exposure when administered topically 10 min after HD challenge, with olvanil additionally protecting against epidermal necrosis. These results demonstrate prophylactic and treatment effects of pharmacological agents against HD-induced skin injury in an in vivo model and support the continued use of the mouse ear vesicant model (MEVM) for evaluating medical countermeasures against HD.

Dermabrasion--a novel concept in the surgical management of sulphur mustard injuries

Since its first use on the battlefields of Northern France during the First World War (1914-1918), sulphur mustard has remained a significant chemical threat to military forces around the world. Progress towards an effective treatment for these injuries has been slow due to the lack of suitable animal models upon which to study the toxicology and pathology. However, porcine and human skin are similar in structure and exposures to sulphur mustard vapour have been performed on porcine models to define the development and subsequent resolution of mustard-induced skin injuries. Yucatan miniature (n = 12) and large white (n = 6) pig models were used to assess the usefulness of mechanical dermabrasion in accelerating the naturally slow rate of healing of sulphur mustard vapour-induced injuries to the skin. Burn injuries underwent debridement at 4 days post-exposure and the resulting lesions were assessed at various time points up to 8 weeks post-abrasion. Rates of re-epithelialisation were accelerated in the dermabrasion (treated) vs the control (untreated) group by up to a factor of three (ANOVA: p = .0196, Yucatan; p = 0.165, large white pig). It was concluded that dermabrasion of sulphur mustard burns is a valuable procedure in the surgical management of these injuries.

Immunohistochemical characterization of the basement membrane epitopes in bis(2-chloroethyl) sulfide-induced toxicity in mouse ear skin

Sulfur mustard (bis(2-chloroethyl) sulfide (HD)), a potent cutaneous vesicant and bifunctional alkylating agent, produces significant time-dependent histopathological changes in the skin of the mouse. The right ears of male CD1 mice were exposed topically to 5.0 microl of 195 mM (0.16 mg) HD in dichloromethane and harvested at 6, 12, 18 and 24 h. The left ear control was dosed with 5.0 microl of dichloromethane. In all controls and HD-treated mouse ear, moderate immunofluorescence staining was seen at the epidermal-dermal junction with bullous pemphigoid (BP), epidermolysis bullosa acquisita (EBA) and laminin (Lam), and light staining was observed with bullous pemphigoid 180 (BP180), fibronectin (Fn) and type IV collagen (Coll IV). Mouse anti-human monoclonal antibodies for GB3, L3d and 19-DEJ-1 (Uncein) did not cross-react. In microvesicles, BP, BP180 and Fn showed areas of light focal epidermal staining and homogeneous dermal staining, and EBA, Lam and Coll IV showed moderate dermal staining. Both BP and Fn exhibited weak, inconsistent staining with time. Immunoelectron microscopy (IEM) revealed similar results, with an increase in cell damage from 6 to 24 h, which corresponded to a decrease in staining intensity. Cell proliferation, expressed as the growth fraction of proliferating cell nuclear antigen (PCNA), showed an increase in cell damage. The growth fraction was lower in the inner ear and showed time-dependent differences. The immunofluorescence and IEM results indicate that HD causes an undulating inconsistent separation in the uppermost lamina lucida with focal cleavage into the lower portion of the basal keratinocytes just above the plasma membrane. Although this pattern of separation differs from other in vivo models in which the split occurs exclusively within the lamina lucida, this should not preclude its role as a screening model to study the effects and development of specific prophylactic and therapeutic strategies.

Airway epithelial damage and release of inflammatory mediators in human lung parenchyma after sulfur mustard exposure

This study was performed to evaluate the morphological effects of sulfur mustard on human lung parenchyma in vitro and to measure the metabolites of arachidonic acid which are released during acute exposure to the alkylating agent. Histological analysis of the tissue following exposure to sulfur mustard for a period of 45 min at 10 mM revealed the presence of paranuclear vacuoles in the epithelium, specifically, in the ciliated cells. The release of metabolites of arachidonic acid were determined in the bath fluids by an enzymo-immunoassay. The basal release of prostaglandin E2 (PGE2: 1.36 +/- 0.33 ng/g tissue) and 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha: 8.83 +/- 1.17 ng/g tissue) were not modified during tissue exposure to sulfur mustard (45 min, 0.1 mM). In addition, the basal release of cysteinyl-leukotriene E4 (LTE4: 1.55 +/- 0.44 ng/g tissue) was also not altered by challenge of the tissues with sulfur mustard. In contrast, when the human lung parenchyma was stimulated with anti human IgE (anti-IgE) only the basal release of the metabolite of the 5-lipoxygenase pathway was significantly increased (LTE4: 6.84 +/- 1.57 ng/g tissue). These data suggest that sulfur mustard may produce morphological alterations in epithelial cells and at the time point studied (45 min exposure), this effect is not associated with a release of arachidonic acid metabolites. However, the increased release of LTE4 by anti-IgE suggests that the target cells for sulfur mustard and anti-IgE in the human lung may be different.

A model for quantitative measurement of sulfur mustard skin lesions in the rabbit ear

The search for treatment and protection against the vesicant and inflammatory skin lesions induced by sulfur mustard suffers from the lack of a good in vivo reproducible model. We applied sulfur mustard (25-500 microg/cm2) to the outer surface of the ears of 10 rabbits and measured the edema formation 12, 24 and 48 h post-application with a caliper especially designed for soft matter. There was a dose-dependent linear increase in edema magnitude in the range from 25 to 150 microg/cm2. Maximal edema was observed after 12 h. There was a 12% reduction in edema size 24 h after application and a further decrease after 48 h. Skin thickness, inflammatory cell infiltrate, necrosis and vesiculation were evaluated in biopsies taken after 24 h. We found the same dose-related increase both in skin thickness and in degree of blister formation. This simple dose-response in vivo model can be used for evaluation of the dermal inflammation induced by topical application of sulfur mustard. This model has the additional advantage of a built-in control, namely the untreated contralateral ear. Consequently, this model can serve as a useful tool for future screening of potential compounds for prevention and treatment of sulfur mustard-induced skin lesions.

Ultrastructural characterization of sulfur mustard-induced vesication in isolated perfused porcine skin

The isolated perfused porcine skin flap (IPPSF) is a novel alternative, humane in vitro model consisting of a viable epidermis and dermis with a functional microvasculature. For this study, 200 microliters of either 10.0, 5.0, 2.5, 1.25, 0.50, or 0.20 mg/ml of bis (2-chloroethyl) sulfide (HD) in ethanol or ethanol control was topically applied to a 5.0 cm2 dosing area of the IPPSF and perfused for 8 h with recirculating media. HD dermatotoxicity was assessed in the flap by cumulative glucose utilization (CGU), vascular resistance (VR), light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). HD produced a statistically significant dose relationship for gross blisters and microvesicles. The HD-treated IPPSFs were also characterized by a decrease in CGU and an increase in VR. Light microscopic changes included mild intracellular and slight intracellular epidermal edema, multifocal epidermal-dermal separation, and dark basal cells. Ultrastructural alterations consisted of cytoplasmic vacuoles, pyknotic basal cells, nucleolar segregation, and epidermal-dermal separation occurring between the lamina lucida and lamina densa of the basement membrane. The severity of these changes increased in a dose-dependent manner. Morphologically, the IPPSF appeared similar to human skin exposed to HD with the formation of macroscopic blisters and microscopic vesicles. In conclusion, the IPPSF appears to be an appropriate in vitro model with which to study the pathogenesis of vesicant-induced toxicity.

Cutaneous histopathologic features in weanling pigs after exposure to three different doses of liquid sulfur mustard

Sulfur mustard (2,2' dichlorodiethyl sulfide, HD) is a chemical warfare agent that is easily produced, and may be used against civilian populations as well as against military troops. However, good therapeutic and prophylactic measures await a better understanding of the pathophysiology of lesions produced by this agent. Because the skin remains is one of the principal routes for HD exposure and damage, the study of HD-induced skin lesions is of major interest. Blister formation is a characteristic of HD-induced skin lesions in humans. Attempts have been made to find an animal model that produces cutaneous microblisters after exposure to the naturally occurring liquid as well as vaporized HD. Weanling pigs were exposed to three different doses of liquid HD. Histopathologic findings showed microblister formation as well as variable apoptosis and/or necrosis of epidermal keratinocytes and vascular endothelium. Pig skin is morphologically similar to human skin. In the pig, the epidermal lipids, the density of hair follicles, the presence of sweat glands, the proliferation kinetics, and the antigenicity are all closer to human skin than are rodent models. All these features may be important in lesions induced by HD, and may mean that the pig is a superior model for studying the pathophysiology of HD-induced cutaneous lesions.

Assessment of the biochemical effects of percutaneous exposure of sulphur mustard in an in vitro human skin system

1. Sulphur mustard (HD) is a potent chemical warfare agent which causes incapacitating blisters on human skin. There is no specific pretreatment nor therapy against this agent and the mechanism of dermo-epidermal cleavage is unclear. The aim of this study was to use a human skin explant system to determine the consequences of percutaneous exposure to HD. 2. Increased activities of serine proteases associated with blistering disorders in humans were detected from human skin explants after exposure to HD. The most consistent response and the highest protease activities measured were found for trypsin. This class of enzyme is therefore implicated in the dermo-epidermal separation which is associated with blistering in humans following exposure to HD. 3. An inflammatory response was observed in the skin explants exposed to HD. At low doses of HD it was characterised by the presence of neutrophils in the papillary dermis, culminating in the infiltration of the epidermis by these inflammatory cells at higher concentrations of HD. A variety of other histopathological changes in the explants was found such as focal dermo-epidermal separation, nuclear pyknosis and perinuclear vacuolation. 4. The study indicates that full thickness human skin explants can be used to investigate various aspects of the possible pathogenesis of HD-induced skin damage, including the associated inflammatory response.

Indirect immunohistochemistry and immunoelectron microscopy distribution of eight epidermal-dermal junction epitopes in the pig and in isolated perfused skin treated with bis (2-chloroethyl) sulfide

Sulfur mustard (bis [2-chloroethyl] sulfide, HD) is a potent cutaneous vesicant that causes gross blisters by separation of the epidermal-dermal junction (EDJ). The EDJ of the skin is a highly specialized and complex structure composed of several components and plays a major role in the integrity of the skin. The isolated perfused porcine skin flap (IPPSF) was dosed with 0.2 mg/ml (n = 4), 5.0 mg/ml (n = 4), and 10.0 mg/ml (n = 5) HD or ethanol (n = 4) for 8 hr (dose-response study) and 10.0 mg/ml HD or ethanol for 1, 3, 5, and 8 hr (n = 4/treatment) (time-response study). Successful EDJ mapping was carried out in normal pig skin (NPS), ethanol-treated IPPSFs, and HD-treated IPPSFs using the following antibodies: laminin, type IV collagen, fibronectin, GB3 (Nicein), bullous pemphigoid (BP), and epidermolysis bullosa acquisita (EBA). Two mouse anti-human monoclonal antibodies, L3d and 19-DEJ-1 (Uncein), did not cross-react with the EDJ of the pig. Antibody staining in NPS, ranging from very intense for laminin and type IV collagen to weak for fibronectin, was generally more discrete than in the IPPSF. No differences in staining were noted between the ethanol and nonblistered areas of the HD-treated IPPSFs. In HD-blistered areas, BP stained only the epidermal hemidesmosomes, and laminin, fibronectin, and GB3 stained primarily the dermis with fragments attached to the basal pole of the stratum base cells, while type IV collagen and EBA stained only the dermis. Mapping of these epitopes determined that the precise plane of EDJ separation in the HD-treated skin occurred beneath the hemidesmosomes within the upper portion of the lamina lucida. The conservation of human epitopes in the EDJ of the pig further emphasizes the similarities between human skin and pig skin. Therefore, pig skin and the IPPSF may be used to study HD-induced vesication and blistering diseases.

Sulfur mustard: its continuing threat as a chemical warfare agent, the cutaneous lesions induced, progress in understanding its mechanism of action, its long-term health effects, and new developments for protection and therapy

Although sulfur mustard (SM) has been used as a chemical warfare agent since the early twentieth century, it has reemerged in the past decade as a major threat around the world. SM is an agent that is easily produced even in underdeveloped countries and for which there is no effective therapy. This agent is a potential threat not only on the battlefield but also to civilian populations. The skin and other epithelial surfaces are the first targets as this agent is absorbed, and reactions within the skin are the subject of active research into the mechanism of action of this alkylating agent. The depletion of glutathione, generation of reactive oxygen species, and the formation of stable DNA adducts remain theoretic and demonstrated by-products of SM exposure implicated in the disease produced. However, new findings related to the effects of SM on the basement membrane zone; interest in delayed healing of the lesions induced; the inflammatory mediators, enzymes, and cytokines that result; and cellular typing of the inflammatory infiltrate will increase our understanding of the pathophysiology of the lesions caused by SM. In addition, the recent development of a topical skin protectant for SM and for other chemical warfare agents may have broad applications within dermatology.

Changes in connective tissue macromolecular components of Yucatan mini-pig skin following application of sulphur mustard vapour

1. The aim of this study was to determine the nature of the macromolecular alterations in Yucatan mini-pig skin which occur following application of sulphur mustard vapour, with particular reference to laminin and type IV collagen. 2. The immunostaining of transfer blots from skin extracts run on SDS-PAGE gels revealed no evidence of cross-linking of type IV collagen or laminin. Laminin was, however, found to be partially degraded as determined by the resolution of 132 and 143 kDa fragments, possibly by the activation of proteases, following the application of sulphur mustard to pig skin. Type IV collagen was not subject to this form of degradation in the skin samples exposed to sulphur mustard. 3. Yucatan mini-pig skin was found to develop microblisters after exposure to sulphur mustard vapour. The immunohistochemical studies of sulphur mustard exposed skin revealed that separation of the epidermis from the dermis was found to occur within the lamina lucida of the subepidermal basement membrane, supporting the contention that cleavage of laminin networks occurs following mustard challenge. Immunohistochemical staining with anti-type IV collagen antibodies was restricted to the floor of the micro-blister lesions. 4. The results suggest that laminin may be a target for protease activation at the dermo-epidermal junction. This may account for the tendency of certain skin models to develop sulphur mustard-induced blistering. The Yucatan mini-pig may be valuable as a model to determine the efficacy of prophylactic and therapeutic regimes.

Pathogenesis of 2,2'-dichlorodiethyl sulfide in hairless guinea pigs

Developing skin lesions on hairless guinea pigs due to 2,2'-dichlorodiethyl sulfide (sulfur mustard, HD) exposure were examined to determine the time course for the appearance of histopathologic markers in relationship to skin NAD+ and NADP+ content after HD exposure. Hairless guinea pig skin was exposed to HD for 8 min by means of a vapor cup. Skin punches were taken at 1, 2, 4, 8, 12, 16, 20 and 24 h after HD exposure. Intracellular edema (IE) appeared at 2 h and increased steadily over 24 h. Epidermal necrosis (EN) and pustular epidermatitis (PE) developed at 8 h and reached a maximum at 16 h. Follicular necrosis (FN) appeared at 8 h and increased up to 24 h. Microvesicles (MV) developed between 12-16 h reaching a maximum at 24 h. Niacinamide (750 mg/kg, ip) pretreatment (30-min) reduced the incidence of MV (40%) and FN (45%) at 24 h, but did not reduce IE, EN, or PE. In all animals, skin NAD+ content decreased to a minimum (20% of control) at 16 h, but NAD+ decreases did not precede microvesicle formation. Skin NADP+ content increased (260%) between 1-2 h and returned to control at 4 h. Skin cell NADP+ increases may be indicative of an early phase of cellular oxidative stress that may contribute to HD-induced dermal pathogenesis. Since NAD+ reductions did not precede microvesication and NAM-induced increases in NAD+ content did not delay or reduce early cellular alterations, the contributory role of NAD+ to microvesicle formation may be limited and other biochemical changes should be investigated.

Characterization of lewisite toxicity in isolated perfused skin

Lewisite (L) is a potent organic arsenical that causes rapid onset of pain and severe vesication on contact with epithelial tissues. The isolated perfused porcine skin flap (IPPSF) is an in vitro model that has shown potential as a model for cutaneous vesicant research. The objective of this study was to characterize IPPSF responses after topical exposure to six concentrations of L ranging from 0.07 to 5.0 mg/ml (n = 4/treatment plus controls). Biochemical markers of viability (glucose utilization (CGU) and lactate dehydrogenase (LDH) release), vascular resistance (VR), venous arsenic flux, and morphological parameters (light and electron microscopy) were evaluated. In addition, lewisite lesions were characterized at 1, 3, 5, and 8 hr after exposure (n = 4/time plus controls) using these morphological parameters, as well as enzyme histochemistry. Macroscopic and microscopic lesions caused by L exposure were dose related. Mild decreases in CGU were noted with the higher concentrations of L, while generally increased responses in LDH release and VR were seen. Marked increases in LDH activity were noted in the blister fluid of IPPSFs treated with 5.0 mg/ml of L. Also, significant cutaneous arsenic flux was noted at the 5.0 mg/ml dose of L. The formation of gross blisters, the location and characterization of epidermal-dermal junction separation, and the time course of lesion production paralleled the description of L-induced lesions in humans. The sensitivity of the IPPSF to L exposure and the similarity of lesions to those described for humans suggests that this model provides a relevant in vitro model with which to study mechanisms of chemical vesication and arsenic toxicity, as well as protective and therapeutic intervention for vesicant exposure.

Effects of nicotinamide on biochemical changes and microblistering induced by sulfur mustard in human skin organ cultures

Blister formation due to sulfur mustard (HD) exposure was studied in an ex vivo human skin model. Pieces of fresh human skin were exposed to HD vapor and subsequently incubated in medium for 48 hr. During this culture period cellular NAD+ levels and uptake of glucose from the medium decreased relative to the duration of the exposure to HD. In light microscopic sections of skin that were exposed to HD for 6 min. clefts of variable size could be clearly observed between the epidermis and the dermis after a 48-hr culture period. Immunohistochemical staining of collagen type IV demonstrated that separation occurred between the basal membrane and the basal keratinocytes. The described ex vivo human skin model mimicked the in vivo process quite well. Since it was reported that nicotinamide could protect cellular NAD+ levels after HD exposure, HD-treated skin pieces were incubated in medium containing 10 mM nicotinamide. Although this incubation caused an elevation of cellular NAD+ levels and of glucose uptake from the medium compared to control values, it did not result in a substantial reduction of cell death or microblister formation as observed by light microscopy in tissue sections. It was concluded that depletion of cellular NAD+ levels is not the only cause of HD-induced cell death.

Cutaneous toxicity of 2-chloroethyl methyl sulfide in isolated perfused porcine skin

Previous research has shown the isolated perfused porcine skin flap (IPPSF) to be a novel in vitro experimental model for investigating xenobiotic percutaneous absorption. In this study, the IPPSF was used to biochemically and morphologically assess the dermatotoxicity of 2-chloroethyl methyl sulfide (CEMS), a monofunctional analog of the vesicant, sulfur mustard. IPPSFs were perfused in a recirculating perfusion system and were treated with 97% CEMS (n = 4) or served as controls (n = 4). Additional IPPSFs were perfused in a nonrecirculating perfusion system and were treated with CEMS (n = 4) or were controls (n = 4). After dosing, each IPPSF was perfused for 8 hr. Cumulative glucose utilization (GU) and lactate production/glucose utilization ratio (L/GU ratio) were used as viability parameters. The average rate of GU for CEMS was significantly lower than control (p less than 0.05) in the recirculating and nonrecirculating IPPSFs. The L/GU ratio for CEMS was not significantly different (p greater than 0.05) from control for either perfusion system. CEMS resulted in a marked increase in vascular resistance versus control in both perfusion systems. Gross vesicles and bullae formation occurred in six of the CEMS-treated IPPSFs. Light microscopy revealed subepidermal vesicle formation above the basement membrane and extensive basal cell pyknosis in all IPPSFs treated with CEMS. No macroscopic or microscopic lesions were noted in the control flaps. Transmission electron microscopy revealed separation between the lamina lucida and the lamina densa of the basal lamina, with intracellular vacuolization and mitochondrial swelling occurring in the stratum basale and stratum spinosum cells of IPPSFs treated with CEMS. These lesions are similar to those described after human exposure to sulfur mustard. Full characterization of the morphological and biochemical changes seen after topical exposure of the IPPSF to vesicants may shed light on the pathogenesis of cutaneous toxicity of these compounds in vivo and serve as a relevant model to assess protective strategies against vesicant exposure.