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

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.

Skin remodeling and wound healing in the Gottingen minipig following exposure to sulfur mustard

Sulfur mustard (SM), a dermal vesicant that has been used in chemical warfare, causes inflammation, edema and epidermal erosions depending on the dose and time following exposure. Herein, a minipig model was used to characterize wound healing following dermal exposure to SM. Saturated SM vapor caps were placed on the dorsal flanks of 3-month-old male Gottingen minipigs for 30 min. After 48 h the control and SM wounded sites were debrided daily for 7 days with wet to wet saline gauze soaks. Animals were then euthanized, and full thickness skin biopsies prepared for histology and immunohistochemistry. Control skin contained a well differentiated epidermis with a prominent stratum corneum. A well-developed eschar covered the skin of SM treated animals, however, the epidermis beneath the eschar displayed significant wound healing with a hyperplastic epidermis. Stratum corneum shedding and a multilayered basal epithelium consisting of cuboidal and columnar cells were also evident in the neoepidermis. Nuclear expression of proliferating cell nuclear antigen (PCNA) was contiguous in cells along the basal epidermal layer of control and SM exposed skin; SM caused a significant increase in PCNA expression in basal and suprabasal cells. SM exposure was also associated with marked changes in expression of markers of wound healing including increases in keratin 10, keratin 17 and loricrin and decreases in E-cadherin. Trichrome staining of control skin showed a well-developed collagen network with no delineation between the papillary and reticular dermis. Conversely, a major delineation was observed in SM-exposed skin including a web-like papillary dermis composed of filamentous extracellular matrix, and compact collagen fibrils in the lower reticular dermis. Although the dermis below the wound site was disrupted, there was substantive epidermal regeneration following SM-induced injury. Further studies analyzing the wound healing process in minipig skin will be important to provide a model to evaluate potential vesicant countermeasures.

TRPA1 and issues relating to animal model selection for extrapolating toxicity data to humans

The transient receptor potential ankyrin 1 (TRPA1) ion channel is a sensor for irritant chemicals, has ancient lineage, and is distributed across animal species including humans, where it features in many organs. Its activation by a diverse panel of electrophilic molecules (TRPA1 agonists) through electrostatic binding and/or covalent attachment to the protein causes the sensation of pain. This article reviews the species differences between TRPA1 channels and their responses, to assess the suitability of different animals to model the effects of TRPA1-activating electrophiles in humans, referring to common TRPA1 activators (exogenous and endogenous) and possible mechanisms of action relating to their toxicology. It concludes that close matching of in vitro and in vivo models will help optimise the identification of relevant biochemical and physiological responses to benchmark the efficacy of potential therapeutic drugs, including TRPA1 antagonists, to counter the toxic effects of those electrophiles capable of harming humans. The analysis of the species issue provided should aid the development of medical treatments to counter poisoning by such chemicals.

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.

Designing of mouse model: a new approach for studying sulphur mustard-induced skin lesions

This study was planned to design a mouse model for studying sulphur mustard (SM)-induced skin injury. SM was applied dermally at dose of 5 or 10 mg kg(-1) in polyethyleneglycol-300 (PEG-300) or dimethylsulphoxide (DMSO) or acetone once. The changes in body weight, organ body weight indices (OBWI) and haematological and oxidative stress parameters were investigated over a period of 3-7 days and supported by histopathological observations. Exposure to SM in PEG-300 or DMSO resulted in a significant depletion in body weight, OBWI, hepatic glutathione (GSH) and elevation in hepatic lipid peroxidation, without affecting the blood GSH and hepatic oxidised glutathione (GSSG) levels. Interestingly, no aforesaid change was observed after dermal application of SM diluted in acetone. These biochemical changes were supported by the histological observations, which revealed pronounced toxic effect and damage to liver, kidney and spleen after dermal application of SM diluted in PEG-300 or DMSO. The skin showed similar microscopic changes after dermal application of SM in all the three diluents, however; the severity of lesions was found to be time and dose dependent. It can be concluded that dermal exposure of SM diluted in acetone can be used to mimic SM-induced skin toxicity without systemic toxicity in a mouse model.

Mechanisms mediating the vesicant actions of sulfur mustard after cutaneous exposure

Sulfur mustard (SM), a chemical weapon first employed during World War I, targets the skin, eyes, and lung. It remains a significant military and civilian threat. The characteristic response of human skin to SM involves erythema of delayed onset, followed by edema with inflammatory cell infiltration, the appearance of large blisters in the affected area, and a prolonged healing period. Several in vivo and in vitro models have been established to understand the pathology and investigate the mechanism of action of this vesicating agent in the skin. SM is a bifunctional alkylating agent which reacts with many targets including lipids, proteins, and DNA, forming both intra- and intermolecular cross-links. Despite the relatively nonselective chemical reactivity of this agent, basal keratinocytes are more sensitive, and blistering involves detachment of these cells from their basement membrane adherence zones. The sequence and manner in which these cells die and detach is still unresolved. Much has been discovered over the past two decades with respect to the mechanisms of SM-induced cytotoxicity and the intracellular and extracellular targets of this vesicant. In this review, the effects of SM exposure on the skin are described, as well as potential mechanisms mediating its actions. Successful therapy for SM poisoning will depend on following new mechanistic leads to develop drugs that target one or more of its sites of action.

The use of doxycycline as a protectant against sulphur mustard in HaCaT cells

As part of an ongoing programme on medical countermeasures against the chemical warfare agent sulphur mustard (HD) and set against the background of the involvement of matrix metalloproteinases (MMPs) in the pathology of HD-induced vesication processes, the potentially beneficial effects of doxycycline on cell attachment was determined in confluent HaCaT cell cultures exposed to HD. Doxycycline was found to inhibit to a significant extent the tendency of HD-exposed cells to detach from the growth substrate, however, analysis of the metabolic activity of the adherent cells indicated that doxycycline treatment did not maintain cell viability. It was confirmed that apoptosis was the predominant mode of HD-induced cell death. The results suggested that doxycycline and other MMP inhibitors may have a role to play in therapeutic intervention against HD exposure, but only as part of a combination therapy. The specific value of protease inhibitors in this capacity remains to be determined.

Molecular determination of laminin-5 degradation: a biomarker for mustard gas exposure diagnosis and its mechanism of action

Laminin-5, a heterotrimer of laminin alpha3, beta3 and gamma2 subunits, is a component of epithelial cell basement membranes. Laminin-5 functions as a ligand of the alpha3beta1 and alpha6beta4 integrins to regulate cell adhesion, migration and morphogenesis. In the skin, laminin-5 facilitates the assembly of basement membranes; thus it is essential for a stable attachment of the epidermis to the dermis and recovery of damaged skin. Sulphur mustard (SM), also known as mustard gas, is a vesicant that has been employed as a chemical weapon in various conflicts during the twentieth century. Skin exposure to SM results in fluid-filled blisters; proposed mechanisms are inflammation, protease stimulation, basal cell death and separation of the epidermis from the dermis apparently because of the degradation of attachment proteins like laminin-5. Therefore, we investigated the effects of SM exposure on the degradation of laminin-5 and its three subunits, alpha3, beta3 and gamma2 by exposing normal human epidermal keratinocytes (NHEK) to SM (0-300 microM, 1-24 h). We found that SM degraded laminin-5 and its two subunits beta3 and gamma2, but not alpha3. Preincubation of cells with a serine protease inhibitor (PMSF), or a metalloprotease inhibitor (1,10-phenanthroline) prior to SM exposure partially prevented SM-induced degradation of laminin-5 subunits, beta3 and gamma2. Specificity studies showed that the degradation of laminin-5 gamma2 was due to a bifunctional mustard compound such as SM, but not due to the other alkylating agents tested. Our results support that laminin-5 degradation is an important mechanism of SM injury as well as a useful biomarker of SM exposure. The knowledge of the mechanisms of laminin-5 degradation in SM-exposed NHEK has potential application in developing cutaneous therapeutics against SM.

Swine models in the design of more effective medical countermeasures against organophosphorus poisoning

Although the three most commonly used large mammal species in the safety assessment of drugs remain the dog, the macaque and the marmoset, swine, especially minipigs, have also been widely used over the years in many toxicological studies. Swine present a number of interesting biological and physiological characteristics. Similarities in skin properties with humans have led to extensive in vitro and in vivo studies. There is a specific interest in cardiovascular research, as well as in anaesthesiology and critical care medicine due to common features of swine and human physiology. Although knowledge of swine brain structure and functions remains incomplete, data does exist. The multiple blood sampling that is necessary in pharmacokinetic and toxicokinetic studies are possible, as well as multiparametric monitoring and interventions with equipment used in human clinical settings. Practicality (handling), scientific (stress reduction) and ethical (invasive monitoring) reasons have led research teams to incorporate anaesthesia into their paradigms which makes the analysis of data increasingly difficult. Although not substantiated by scientific data, the swine appears to have an intermediate position in the scale of public perception between non-human primates and animals commonly referred to as pets (i.e. dogs and cats) and rodents. The benefits of the swine model justify the use of these animals in the design of more effective medical countermeasures against known chemical warfare agents (nerve agents, vesicants and lung damaging agents). Exposure to organophosphorus (OP) pesticides represents a severe health issue in developing countries, while OP intoxication with the more lethal military nerve agents is not only of military concern but also a terrorist threat. Tailoring therapeutic regimens to the reality of OP poisoning is of the utmost importance when little experimental data and sparse human clinical data are available in the decision making process. We will present some of the advantages and disadvantages of the swine model in OP countermeasures elaborating on two examples. First, we will present the issues related to the use of anaesthesia during experimental OP poisoning and second we will show how results from experiments with swine can be integrated into a kinetic-based dynamic model to evaluate oxime efficacy. A better knowledge of OP poisoning in swine (comparative toxicokinetics, pharmacokinetics and biochemistry) is definitely necessary before accepting it as a first choice non-rodent model. However, there exists a large amount of data in the model on anaesthesia and different types of shock favouring their use for evaluation of complex situations such as the anaesthesia of OP poisoned patients and combined injuries.

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.

Efficacy of laser debridement with autologous split-thickness skin grafting in promoting improved healing of deep cutaneous sulfur mustard burns

The consequences of receiving a cutaneous sulfur mustard (SM) burn are prolonged wound healing and secondary infection. This study was undertaken to find a treatment that promotes quick healing with few complications and minimal disfigurement. Multiple deep SM burns (4 cm diameter) were generated on the ventrum of weanling pigs and treated at 48 h. Four treatments were compared: (1) full-thickness CO(2) laser debridement followed by skin grafting; (2) full-thickness sharp surgical tangential excision followed by skin grafting, the "Gold Standard" used in deep thermal burns management; (3) partial-thickness laser ablation with no grafting; and (4) partial-thickness sharp excision with no grafting. A computer controlled, raster scanned, high-powered continuous wave (cw) CO(2) laser was utilized. Ulceration, wound geometry, and wound contraction were evaluated during a 36-day healing period. Histopathological evaluations were conducted at the end of the healing period. Engraftment rates were similar between both methods of debridement. Laser debridement followed by skin grafting was as efficacious in improving the wound healing of deep SM burns as the "Gold Standard." Full-thickness laser debridement of these small total body surface area (TBSA) burns was time efficient and provided adequate beds for split-thickness skin grafting. Laser debridement offered additional benefits that included hemostatic control during surgery and minimal debridement of normal perilesional skin. Mid-dermal debridement by sharp excision or laser ablation without grafting produced less desirable results but was better than no treatment.

The treatment of Lewisite burns with laser debridement---'lasablation'

Lewisite (dichloro (2-chlorovinyl) arsine) was first synthesised in 1918 and its potential for use in military confrontations as a vesicant agent has been widely recognised. These agents cause blistering skin reactions with resultant full thickness burns. Effective treatments to date have been delayed by the lack of suitable animal models. Porcine skin has recently been used successfully to model the development and natural history of these burn injuries. A large white pig model (n=6) was employed to investigate the effectiveness of CO(2) and Erbium-YAG lasers (EYL) in laser dermabrasion of established Lewisite burns. Burns underwent treatment at 4 days post-exposure and were assessed at 1, 2 and 3 weeks, thereafter, for the rate of epithelial healing. The re-epithelialisation rates in the laser dermabraded groups were accelerated by a factor of four compared to untreated controls by the first week (analysis of vartiance, ANOVA, P=0.006 for pulsed CO(2) and P=0.011 for Erbium-YAG). Ablation of the burn eschar was thought to accelerate the rate of healing by causing partial debridement. This method has been termed 'lasablation' and represents a significant advance in the clinical management of this type of injury.

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.

The development of Lewisite vapour induced lesions in the domestic, white pig

Studies performed in the past in our laboratory have detailed the development of sulphur mustard lesions in the domestic, white pig using small glass chambers to achieve saturated vapour exposure under occluded conditions. We have now used this experimental model to produce cutaneous lesions for detailed histopathological studies following challenge with lewisite. Histological examination of resulting lesions have revealed that although the overall pattern of lesion development is similar to that seen following mustard challenge, the time-course of cellular events is very much compressed. The epidermis showed focal basal cell vacuolation with associated acute inflammation as early as one hour postexposure. Coagulative necrosis of the epidermis and papillary dermis was complete by 24 hours and followed the appearance of multiple coalescent blisters between six and 12 hours post-exposure. At 48 hours, the lesions were full thickness burns with necrosis extending into the deep subcutaneous connective and adipose tissues. The study of lesions beyond 24 hours revealed early epithelial regeneration at the wound edge. The overall spontaneous healing rate of these biologically severe lesions was significantly faster than comparable sulphur mustard injuries and probably reflected a lack of alkylation of DNA and RNA.

Diisopropylglutathione ester protects A549 cells from the cytotoxic effects of sulphur mustard

The A549 cell line was used to assess the ability of diisopropylglutathione (DIPE) to protect against a 100 microM challenge dose of sulphur mustard (HD) using gentian violet (GV), thiazolyl blue (MTT) and neutral red (NR) assays as indicators of cell culture viability. As part of a continuing study of the efficacy of protective nucleophiles as candidate treatments for HD poisoning, several different combinations of protectant and HD were used to determine the optimal means of protecting A549 cells from the effects of HD. It was found that DIPE (4 mM) could protect cells against the effects of HD though for optimal effect, DIPE had to be present at the time of HD challenge. Cultures protected with DIPE were up to 2.9-fold more viable than HD exposed cells 48 h after HD challenge when using the GV, MTT and NR assays to assess viability. Observations by phase contrast microscopy of GV stained cultures confirmed these findings. Pretreating A549 cultures with DIPE for 1 h followed by its removal prior to HD challenge did maintain cell viability, though at a relatively low level (only up to 1.4-fold more viable than HD only exposed cells). DIPE was also able to protect HD exposed A549 cultures when added to cell cultures at intervals of up to 12 to 15 min after the initial HD exposure, though viability tended to decrease over this period, so that at 1 h, addition of DIPE did not maintain the viability of the cultures. This is the first such report of the anti-HD protectant properties of DIPE in A549 cells. It is concluded that the protection observed against HD is probably largely due to extracellular inactivation of HD by DIPE.

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.