Histopathologic features seen in sulfur mustard induced cutaneous lesions in hairless guinea pigs

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.

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.

Mustard vesicating agent-induced toxicity in the skin tissue and silibinin as a potential countermeasure

Exposure to the vesicating agents sulfur mustard (SM) and nitrogen mustard (NM) causes severe skin injury with delayed blistering. Depending upon the dose and time of their exposure, edema and erythema develop into blisters, ulceration, necrosis, desquamation, and pigmentation changes, which persist weeks and even years after exposure. Research advances have generated data that have started to explain the probable mechanism of action of vesicant-induced skin toxicity; however, despite these advances, effective and targeted therapies are still deficient. This review highlights studies on two SM analogs, 2-chloroethyl ethyl sulfide (CEES) and NM, and CEES- and NM-induced skin injury mouse models that have substantially added to the knowledge on the complex pathways involved in mustard vesicating agent-induced skin injury. Furthermore, employing these mouse models, studies under the National Institutes of Health Countermeasures Against Chemical Threats program have identified the flavanone silibinin as a novel therapeutic intervention with the potential to be developed as an effective countermeasure against skin injury following exposure to mustard vesicating agents.

Myeloperoxidase deficiency attenuates nitrogen mustard-induced skin injuries

The pathologic mechanisms of skin injuries, following the acute inflammatory response induced by vesicating agents sulfur mustard (SM) and nitrogen mustard (NM) exposure, are poorly understood. Neutrophils which accumulate at the site of injury, abundantly express myeloperoxidase (MPO), a heme protein that is implicated in oxidant-related antimicrobial and cytotoxic responses. Our previous studies have shown that exposure to SM analog 2-chloroethyl ethyl sulfide (CEES) or NM results in an inflammatory response including increased neutrophilic infiltration and MPO activity. To further define the role of neutrophil-derived MPO in NM-induced skin injury, here we used a genetic approach and examined the effect of NM exposure (12h and 24h) on previously established injury endpoints in C57BL/6J wild type (WT) and B6.129X1-MPOtm1Lus/J mice (MPO KO), homozygous null for MPO gene. NM exposure caused a significant increase in skin bi-fold thickness, epidermal thickness, microvesication, DNA damage and apoptosis in WT mice compared to MPO KO mice. MPO KO mice showed relatively insignificant effect. Similarly, NM induced increases in the expression of inflammatory and proteolytic mediators, including COX-2, iNOS and MMP-9 in WT mice, while having a significantly lower effect in MPO KO mice. Collectively, these results show that MPO, which generates microbicidal oxidants, plays an important role in NM-induced skin injuries. This suggests the development of mechanism-based treatments against NM- and SM-induced skin injuries that inhibit MPO activity and attenuate MPO-derived oxidants.

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.

Sulfur mustard analog, 2-chloroethyl ethyl sulfide-induced skin injury involves DNA damage and induction of inflammatory mediators, in part via oxidative stress, in SKH-1 hairless mouse skin

Bifunctional alkyalating agent, sulfur mustard (SM)-induced cutaneous injury is characterized by inflammation and delayed blistering. Our recent studies demonstrated that 2-chloroethyl ethyl sulfide (CEES), a monofunctional analog of SM that can be used in laboratory settings, induces oxidative stress. This could be the major cause of the activation of Akt/MAP kinase and AP1/NF-κB pathways that are linked to the inflammation and microvesication, and histopathological alterations in SKH-1 hairless mouse skin. To further establish a link between CEES-induced DNA damage and signaling pathways and inflammatory responses, skin samples from mice exposed to 2 mg or 4 mg CEES for 9-48 h were subjected to molecular analysis. Our results show a strong CEES-induced phosphorylation of H2A.X and an increase in cyclooxygenase-2 (COX-2), inducible NOS (iNOS), and matrix metalloproteinase-9 (MMP-9) levels, indicating the involvement of DNA damage and inflammation in CEES-induced skin injury in male and female mice. Since, our recent studies showed reduction in CEES-induced inflammatory responses by glutathione (GSH), we further assessed the role of oxidative stress in CEES-related DNA damage and the induction of inflammatory molecules. Oral GSH (300 mg/kg) administration 1h before CEES exposure attenuated the increase in both CEES-induced H2A.X phosphorylation (59%) as well as expression of COX-2 (68%), iNOS (53%) and MMP-9 (54%). Collectively, our results indicate that CEES-induced skin injury involves DNA damage and an induction of inflammatory mediators, at least in part via oxidative stress. This study could help in identifying countermeasures that alone or in combination, can target the unveiled pathways for reducing skin injury in humans by SM.

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.

2-Chloroethyl ethyl sulfide causes microvesication and inflammation-related histopathological changes in male hairless mouse skin

Sulfur mustard (HD) is a vesicating agent that has been used as a chemical warfare agent in a number of conflicts, posing a major threat in both military conflict and chemical terrorism situations. Currently, we lack effective therapies to rescue skin injuries by HD, in part, due to the lack of appropriate animal models, which are required for conducting laboratory studies to evaluate the therapeutic efficacy of promising agents that could potentially be translated in to real HD-caused skin injury. To address this challenge, the present study was designed to assess whether microvesication could be achieved in mouse skin by an HD analog 2-chloroethyl ethyl sulfide (CEES) exposure; notably, microvesication is a key component of HD skin injury in humans. We found that skin exposure of male SKH-1 hairless mice to CEES caused epidermal-dermal separation indicating microvesication. In other studies, CEES exposure also caused an increase in skin bi-fold thickness, wet/dry weight ratio, epidermal thickness, apoptotic cell death, cell proliferation, and infiltration of macrophages, mast cells and neutrophils in male SKH-1 hairless mouse skin. Taken together, these results establish CEES-induced microvesication and inflammation-related histopathological changes in mouse skin, providing a potentially relevant laboratory model for developing effective countermeasures against HD skin injury in humans.

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

BACKGROUND/PURPOSE

Skin exposure to sulfur mustard (HD) results in erythema, edema and severe injury, which take long time to heal and might impose a heavy burden on the health system. Despite many years of research, there is no treatment that prevents the development of the cytotoxic effects of HD causing acute and prolonged damage to the skin. Therefore, it is of great importance to develop treatments that will ameliorate the extent of injury and improve as well as shorten the healing process. The aim of the present study was to establish a small animal model for a long-term HD-induced skin injury using the hairless guinea-pig (HGP) and to further test the efficacy of anti-inflammatories in ameliorating the pathology.

METHODS

HGPs were exposed to HD vapor on four sites for various time durations (1, 5, 10, 15 and 30 min). Clinical evaluation was conducted using reflectance colorimetry, transepidermal water loss and wound-area measurements. Biochemical [prostaglandin (PGE) content and metalloproteinase-9 (MMP-9) activity] and histopathological evaluations were conducted up to 2 weeks post-exposure.

RESULTS

Typical symptoms of HD skin injury developed including erythema and edema and the extent of injury was closely related to the exposure duration. Histological evaluation revealed severe edema, infiltration of inflammatory cells, damage to basal cells and vesication. By 2 weeks, healing was not completed, impaired basement membrane and epithelial hyperplasia were observed. PGE content and MMP-9 activity increased at 2 h post-exposure; however, while PGE returned to baseline levels within 24 h, MMP-9 remained elevated at least up to 48 h. Furthermore, a short-term, topical, anti-inflammatory post-exposure treatment was effective in reducing the extent of the acute injury.

CONCLUSION

These results indicate that the effects of HD on HGP skin are similar to previously shown effects in the pig model and in humans and therefore support the use of the HGP as an animal model for long-term effects of HD on skin injury and for studying the efficacy of anti-inflammatory treatments.

Cutaneous challenge with chemical warfare agents in the SKH-1 hairless mouse. (I) Development of a model for screening studies in skin decontamination and protection

Exposure to lethal chemical warfare agents (CWAs) is no longer only a military issue due to the terrorist threat. Among the CWAs of concern are the organophosphorus nerve agent O-ethyl-S-(2[di-isopropylamino]ethyl)methyl-phosphonothioate (VX) and the vesicant sulfur mustard (SM). Although efficient means of decontamination are available, most of them lose their efficacy when decontamination is delayed after exposure of the bare skin. Alternatively, CWA skin penetration can be prevented by topical skin protectants. Active research in skin protection and decontamination is thus paramount. In vivo screening of decontaminants or skin protectants is usually time consuming and may be expensive depending on the animal species used. We were thus looking for a suitable, scientifically sound and cost-effective model, which is easy to handle. The euthymic hairless mouse Crl: SKH-1 (hr/hr) BR is widely used in some skin studies and has previously been described to be suitable for some experiments involving SM or SM analogs. To evaluate the response of this species, we studied the consequences of exposing male anaesthetized SKH-1 mice to either liquid VX or to SM, the latter being used in liquid form or as saturated vapours. Long-term effects of SM burn were also evaluated. The model was then used in the companion paper (Taysse et al.(1)).

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.

Inflammatory biomarkers of sulfur mustard analog 2-chloroethyl ethyl sulfide-induced skin injury in SKH-1 hairless mice

Sulfur mustard (HD) is an alkylating and cytotoxic chemical warfare agent, which inflicts severe skin toxicity and an inflammatory response. Effective medical countermeasures against HD-caused skin toxicity are lacking due to limited knowledge of related mechanisms, which is mainly attributed to the requirement of more applicable and efficient animal skin toxicity models. Using a less toxic analog of HD, chloroethyl ethyl sulfide (CEES), we identified quantifiable inflammatory biomarkers of CEES-induced skin injury in dose- (0.05-2 mg) and time- (3-168 h) response experiments, and developed a CEES-induced skin toxicity SKH-1 hairless mouse model. Topical CEES treatment at high doses caused a significant dose-dependent increase in skin bi-fold thickness indicating edema. Histopathological evaluation of CEES-treated skin sections revealed increases in epidermal and dermal thickness, number of pyknotic basal keratinocytes, dermal capillaries, neutrophils, macrophages, mast cells, and desquamation of epidermis. CEES-induced dose-dependent increases in epidermal cell apoptosis and basal cell proliferation were demonstrated by the terminal deoxynucleotidyl transferase (tdt)-mediated dUTP-biotin nick end labeling and proliferative cell nuclear antigen stainings, respectively. Following an increase in the mast cells, myeloperoxidase activity in the inflamed skin peaked at 24 h after CEES exposure coinciding with neutrophil infiltration. F4/80 staining of skin integuments revealed an increase in the number of macrophages after 24 h of CEES exposure. In conclusion, these results establish CEES-induced quantifiable inflammatory biomarkers in a more applicable and efficient SKH-1 hairless mouse model, which could be valuable for agent efficacy studies to develop potential prophylactic and therapeutic interventions for HD-induced skin toxicity.

A dorsal model for cutaneous vesicant injury by 2-chloroethyl ethyl sulfide using C57BL/6 mice

To evaluate stem cell-derived therapeutics for cutaneous vesicant injuries, we developed a dorsal exposure model using C57BL/6 black mice and half-mustard, 2-chloroethyl ethyl sulfide (CEES). The dorsal side of a mouse was exposed to 1-5 microl of CEES for 10 minutes and then decontaminated. The data demonstrate that 3 microl of CEES induced edema and erythema that peaked 24 h post exposure. Histopathology showed a central area of deep injury characterized by severe necrosis of epidermis and dermis. The C57BL/6 is a unique model that can be used to unravel the molecular mechanism of injury, identify the effects of black skin pigmentation, and evaluate the efficacy of stem cell therapeutics for cutaneous vesicant exposure.

Chemical Warfare Agents Chemical Warfare Agents: Their Past and Continuing Threat and Evolving Therapies Part II of II

Chemical warfare agents are ideal weapons for terrorists and for use in military operations against both civilian populations and troops. Thus, there have been efforts by the United States in cooperation with other concerned nations to develop animal models to understand the pathophysiology of the injuries induced by these agents, and to develop suitable animal models for testing of pre-and post-exposure protectants and therapies. Sulfur mustard remains the most significant chemical warfare agent that produces cutaneous injuries. Institution of standard recommendations prior to threatened exposure or after exposure are something that we need to be aware of in the world we live in. In addition, pre-and post-exposure therapies now being studied offer hope for moderating the mortality and morbidity that can result from chemical exposure.

Topical iodine preparation as therapy against sulfur mustard-induced skin lesions

Sulfur mustard (SM) is a powerful vesicant employed as an agent of chemical warfare. This study demonstrates the therapeutic effect of a novel topical iodine preparation as a postexposure treatment against SM-induced lesions in the fur-covered guinea-pig skin model. Iodine treatment 15 min after SM exposure resulted in statistically significant reductions of 48, 50, and 55% in dermal acute inflammation, hemorrhage, and necrosis, respectively, whereas, the epidermal healing markers, hyperkerathosis and acanthosis, were significantly elevated by 72 and 67%, respectively, 2 days after treatment. At the interval of 30 min between SM exposure and iodine treatment, there was a significant degree of healing or recovery, albeit to a lesser extent than that observed in the shorter interval. Although the epidermal healing markers were not elevated, the parameters indicative of active tissue damage, such as subepidermal microblisters, epidermal ulceration, dermal acute inflammation, hemorrhage, and necrosis, were significantly reduced by 35, 67, 43, 39, and 45%, respectively. At the 45-min interval between exposure and treatment, there was also a certain degree of healing or recovery expressed as significant reductions in dermal subacute inflammation, subepidermal microblister formation, and epidermal ulceration, whereas, acanthosis was statistically elevated, indicating an increased healing potential. At the 60-min interval, iodine was less efficacious; nevertheless, a significant reduction in the incidence of subepidermal microblisters and an expansion of the acanthotic area were observed. Gross ulceration was significantly decreased at intervals of 15 and 30 min between exposure and treatment. The local anesthetic, lidocaine, did not alter the therapeutic effect of iodine. SM was not affected chemically by iodine as measured by gas chromatography-mass spectrometry (GC-MS) analysis. These findings suggest that the iodine preparation functions as an antidote against skin lesions induced by SM.

Cutaneous uptake of 14C-HD vapor by the hairless guinea pig

The hairless guinea pig (HGP) is used by our laboratory to model the human cutaneous response to sulfur mustard (HD), bis(2-chloroethylsulfide), exposure. We determined the HD content in the skin of HGP after a 7-min exposure to vapors saturated with a mixture of HD and 14C-HD. Concentration/time (CT) values in the range of 2 micrograms/cm2/min were determined by counting skin 14C disintegrations per min (dpm) in animals euthanized immediately after exposure. These values are similar to human penetration rates obtained by other investigators. A rate curve monitoring the reduction in skin 14C dpm was developed for animals euthanized between 0 and 24 hr post- exposure. This curve showed the greatest change after 1 hr. The epidermal (62%) to dermal (38%) ratio of 14C at 24 hr was measured for two animals. We saw no site preference for HD penetration among the 8 sites used. The 14C content of template adhesive tape was determined to follow HD distribution. These results contribute to a better understanding of the cutaneous response to HD in the HGP model.

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.

The prevention and treatment of cutaneous injury secondary to chemical warfare agents. Application of these finding to other dermatologic conditions and wound healing

Chemical warfare agents are easily and inexpensively produced and are therefore potentially accessible to even underdeveloped nations and are a threat to civilian populations as well as advancing troops. Sulfur mustard is by far the most significant chemical warfare agent that produces cutaneous injury. Significant advances over the past few years have been made in understanding the pathophysiology of the lesions produced by sulfur mustard, as well as development of barrier creams and pre and post exposure therapies to moderate the damage and accelerate healing. Not only have these advances improved our understanding of the sulfur mustard injury and the care of the patients, these are potentially numerous applications for these findings in other dermatologic conditions including the treatment of chronic wounds.

Histopathologic and immunohistochemical features in human skin after exposure to nitrogen and sulfur mustard

N-methyl-2,2'-dichlorodiethylamine (HN2)is a topical chemotherapeutic agent used as therapy for cutaneous T-cell lymphomas (CTCL). Di(2-chloroethyl)sulfide (SM), and less often HN2, have been used as chemical weapons, with the skin being a principle target. The mechanisms by which these chemicals produce their therapeutic and toxic effects in skin, however, are not clearly defined. We exposed human skin explants to two doses of HN2 and SM. At 18 hours after exposure, histopathologic features were compared. In addition, immunohistochemical markers to basement membrane proteins were used to evaluate the effects of both chemicals on the basement membrane zone. Gross vesication was not seen. Pyknotic nuclei with or without dyskeratotic changes within epidermal keratinocytes were present at both doses. These changes varied more between skin specimens than they did between doses. Ballooning degeneration was more marked after SM exposures. Diffuse dermal-epidermal separation was present only at high-dose exposures and did not appear to correlate with the degree of changes locally in the overlying epidermis. Antibodies to laminin-5 showed decreased immunoreactivity after exposure to HN2 and SM. Immunoreactivity for laminin- was decreased to a lesser extent, and immunoreactivity for collagen IV and VII was unchanged. HN2 and SM produce similar histopathologic and immunohistochemical features after cutaneous exposure. These features suggest that part of mechanism of action of HN2 and SM is a direct effect on the basement membrane zone. Understanding the effects of HN2 and SM separate from their effect on DNA may be important in designing therapies and in advancing our understanding of the pathophysiologic changes induced by these chemicals when delivered topically.

Increased smooth muscle actin, factor XIIIa, and vimentin-positive cells in the papillary dermis of carbon dioxide laser-debrided porcine skin

BACKGROUND

Pulsed carbon dioxide (CO2) laser debridement is now being used as therapy for photodamaged skin. It has been proposed that the long duration of erythema and a tissue scaffold, which results from tightening of the collagen helix induced by the laser heat, may lead to tightening of sagging skin and skin creases of lesser magnitude.

METHODS

Weanling pigs exposed to mild and moderate erythema producing doses of sulfur mustard (bis-2-chloroethyl sulfide; HD) were treated with the CO2 laser (Tru-Pulse) at 6, 24, and 48 hours after exposure. In addition to histologic examination of laser-debrided and nondebrided biopsy specimens obtained at 14 days after exposure, immunohistochemical staining with antibodies to smooth muscle actin, Factor XIIIa, vimentin, and CD3 was performed.

RESULTS

CO2 laser debridement of the HD-exposed skin resulted in clearing of the cytologic atypia induced by this chemical carcinogen and reduced the inflammatory infiltrate. In addition laser debridement resulted in increased numbers of stromal cells within the papillary dermis, which showed immunohistochemical staining for smooth muscle actin, Factor XIIIa, and vimentin.

CONCLUSIONS

CO2 laser debridement is effective in clearing the epidermis of cytologically damage cells in HD as well as solar-damaged skin. In addition CO2 laser debridement may result in tightening of sagging skin and produce a decrease in skin creases initially, by inducing increased stromal cells within the papillary dermis, with prominent contractile actin filaments. The collagen produced by these stromal cells may subsequently maintain these improvements in the photoaged skin.

CO2 laser debridement of sulphur mustard (bis-2-chloroethyl sulphide) induced cutaneous lesions accelerates production of a normal epidermis with elimination of cytological atypia

Sulphur mustard (bis-2-chloroethyl sulphide; HD) exposure acutely produces lesions that vary from mild erythema, to blister formation, to necrosis. When blisters occur, with or without necrosis, healing of the lesions is delayed. Weanling pigs exposed to a mild erythema-producing dose of HD and to a moderate erythema-producing dose that consistently gave microblister formation were treated with CO2 laser (Tru-Pulse) debridement at 6, 24 or 48 h after exposure. The histopathological features observed at 14 days after exposure in control skin and skin exposed to both HD doses were compared with the features observed in CO2 laser-debrided skin in non-exposed and HD-exposed skin sites. The overlying epidermis in the non-laser treated lesions was thin, with cytological atypia and squamoid changes within the basal cell layer, as well as scattered apoptotic/necrotic keratinocytes. An increased inflammatory infiltrate and necrobiotic changes in the dermis were seen at the higher HD dose. All laser-treated lesions appeared identical, with a thick, differentiated epidermis and a well-formed basal cell layer. There was minimal inflammatory infiltrate. In the papillary dermis there were increased stromal cells. Laser debridement of mild clinical lesions induced by HD produced a more functional epidermis by 14 days as well as clearing the epidermis of damaged keratinocytes.

A double-label technique that monitors sulfur mustard damage to nuclei and mitochondria of normal human epidermal keratinocytes in vitro

Sulfur mustard and 2-chloro ethyl ethyl sulfide (CEES, a sulfur mustard analog) is known to have immediate (minutes), long-term (hours to days), and toxic effects on human skin. Research was directed toward developing a single in vitro assay that might reflect both these short-term and long-term effects of this vesicating agent on normal human epidermal keratinocytes (NHEK) in vitro. Such an assay system would be useful in identifying and developing sulfur mustard therapeutic agents. NHEK were exposed to the monofunctional sulfur mustard analog 2-chloro ethyl ethyl sulfide for a variety of times. The effects of CEES on NHEK nuclei were assessed using the membrane-permeable SYTO nuclear stains, whereas the effects of CEES on NHEK metabolism were determined by using the nontoxic mitochondria dye Alamar blue. CEES enhanced SYTO binding in a concentration-dependent manner to the nucleus immediately subsequent to a 2-hr exposure, whereas CEES had relatively little effect on metabolic activity at this time. Fifteen to 36 hr subsequent to CEES exposure, however, Alamar blue revealed a robust, sulfur mustard-dependent effect on mitochondrial activity. To determine if both these indicator dyes could be used simultaneously, NHEK were exposed to CEES and stained with the SYTO nuclear stain 2 hr subsequent to exposure. This procedure was followed by assay of the same cell cultures with Alamar blue at 36 hr subsequent to initial CEES exposure. The data indicate that this nuclear/mitochondrial double-label technique can be used to monitor the short- and long-term effects of sulfur mustard on the same culture of NHEK.

Immunohistochemical studies of basement membrane proteins and proliferation and apoptosis markers in sulfur mustard induced cutaneous lesions in weanling pigs

Sulfur mustard (2,2-dichlorodiethyl sulfide, HD) is a chemical warfare agent that is a threat to both troops and civilians. The focus of HD research has been on intracellular adduct formation leading to apoptosis and/or necrosis in cutaneous lesions. However, there is work which suggests that HD may have a more direct effect on the basement membrane zone. Immunohistochemical staining to desmosomal proteins, cellular fibronectin, laminin 1, laminin 5, collagen IV, collagen VII, p53, Bcl-2, and PCNA was performed on weanling pig skin exposed to vesicating doses of HD, GB3, an antibody to laminin 5, showed a progressive decrease with loss of expression during the time period of clinical vesiculation. The other basement membrane proteins showed no change or inconsistent changes. PCNA, and p53 staining increased in the overlying epidermis in areas of vesiculation without significant necrosis. Bcl-2 positive cells were decreased or absent after exposure. This study implicates laminin 5 as the main basement membrane protein affected acutely by HD exposure. The patterns of staining of PCNA, Bcl-2, and p53 within the epidermis suggest that apoptosis and cellular necrosis both may play a role in cell death secondary to HD.

Histopathologic features seen with different animal models following cutaneous sulfur mustard exposure

In an effort to understand the pathophysiology of sulfur mustard (2,2' dichlorodiethyl sulfide, HD)-induced cutaneous lesions, a number of animal models have been used. Animal models have been and will continue to be used in the development of therapeutic strategies to protect against and/or moderate lesions, and to potentiate wound healing after HD exposure. Upon reviewing the histopathologic features seen after HD-exposure, we propose roles for different animal models in HD-research. Hematoxylin and eosin slides from protocols done originally as dose response studies for either liquid or vapor HD-exposures were examined. The animal models reported include the hairless guinea pig (HGP), weanling pig (WP), mouse ear (ME) and hairless mouse (HM). In all these animal models. HD induces subepidermal blister formation as well as epidermal cell death. The HGP appears to be the most sensitive model for epidermal necrosis. The HGP and, to a lesser degree, the HM react with a marked neutrophilic infiltrate. The ME provides a quantitative measure for HD effects and a mild inflammatory infiltrate similar to what is seen in human skin. Doses necessary to produce microblister formation in the WP are usually associated with more significant stromal and vascular changes than in other animal models. In addition to a quantitative measure of the HD effect and a mild inflammatory response, the cost, as well as the availability of specific antibodies, and DNA and RNA probes and primers gives the ME advantages for both drug screening and for the study of the pathophysiology of HD-induced cutaneous lesions. The sensitivity of the HGP and the abundant experience with vapor exposures establishes a place for this animal model in barrier cream and drug screening. The similarity of WP skin to human skin is important in the study of wound healing after HD exposure, as well as in the study of the pathophysiology of the cutaneous lesion and in more definitive therapeutic studies.

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.