Mouse Ear Vesicant Model Research Articles

Dysregulation of the mTOR pathway by mechlorethamine

Mechlorethamine (HN2) is a derivative of the chemical warfare agent sulfur mustard (SM) and cutaneous exposure to HN2 is associated with dermal-epidermal junction (DEJ) disruption (vesication). The primary purpose of the present study was to investigate the effect of HN2 on the mammalian target of rapamycin (mTOR) signaling pathway using an in vivo mouse ear vesicant model (MEVM). To this end, the ears of male C57BL/ 6 J mice were exposed to a single topical dose of HN2 (100 mM) or vehicle control (DMSO). Mice were then euthanized 30 min, 1 h or 24 h following exposure. Mouse ear skin exposed to HN2 and biopsied 24 h thereafter exhibited increased tissue expression of Raptor, an important member of the mTORC1 complex, relative to vehicle treated samples. HN2 reduced the downstream effectors phospho S6 (Ser 240/244) ribosomal protein and phospho 4E-BP1 (Thr 37/46) of the mTOR pathway in the epidermis at 30 min, 1 h and 24 h following HN2 exposure but not in the dermis. These results support the hypothesis that HN2-mediated cutaneous toxicity involves dysregulation of the mTOR signaling pathway in the epidermis.

B-Raf inhibitor vemurafenib counteracts sulfur mustard-induced epidermal impairment through MAPK/ERK signaling

The chemical warfare agent sulfur mustard (SM) causes severe cutaneous lesions characterized by epidermal cell death, apoptosis, and inflammation. At present, the molecular mechanisms underlying SM-induced injury are not well understood, and there is no standard treatment protocol for SM-exposed patients. Here, we conducted a high-content screening of the Food and Drug Administration (FDA)-approved drug library of 1018 compounds against SM injury on an immortal human keratinocyte HaCaT cell line, focusing on cell survival. We found that the B-Raf inhibitor vemurafenib had an apparent therapeutic effect on HaCaT cells and resisted SM toxicity. Other tested B-Raf inhibitors, both type-I (dabrafenib and encorafenib) and type-II (RAF265 and AZ628), also exhibited potent therapeutic effects on SM-exposed HaCaT cells. Both SM and vemurafenib triggered extracellular signal-related kinase (ERK) activation. The therapeutic effect of vemurafenib in HaCaT cells during SM injury was ERK-dependent, indicating a specific role of ERK in keratinocyte regulatory mechanisms. Furthermore, vemurafenib partially improved cutaneous damage in a mouse ear vesicant model. Collectively, our results provide evidence that the B-Raf inhibitor vemurafenib is a potential therapeutic agent against SM injury, and oncogenic B-Raf might be an exciting new therapeutic target following exposure to mustard vesicating agents.

Combination of ebselen and hydrocortisone substantially reduces nitrogen mustard-induced cutaneous injury

The purpose of the present study was to investigate the vesicant countermeasure effects of hydrocortisone (HC) and ebselen (EB-1), administered as monotherapy or as a combination treatment. The mouse ear vesicant model (MEVM) was utilized and test doses of HC (0.016, 0.023, 0.031, 0.047, 0.063, 0.125 or 0.250 mg/ear), EB-1 (0.125, 0.187, 0.250, 0.375 or 0.500 mg/ear) or the combination of HC + EB-1 were topically applied at 15 min, 4 h and 8 h after nitrogen mustard exposure. Ear punch biopsies were obtained 24 h after mechlorethamine (HN2) exposure. Compared to control ears, ear tissues exposed topically to HN2 (0.500 µmol/ear) presented with an increase in ear thickness, vesication, TUNEL fluorescence and expression of matrix metalloproteinase 9 (MMP-9) and inducible nitric oxide synthase (iNOS). In contrast, HN2 exposed ears treated topically with EB-1 showed a significant decrease in morphometric thickness and vesication vs. HN2 alone. Ear tissues exposed to HN2 and then treated with HC also demonstrated reductions in morphometric thickness and vesication. Combination treatment of HC + EB-1 was found to be the most effective at reducing HN2-induced ear edema and vesication. The combination also dramatically decreased HN2-mediated cutaneous expression of iNOS and MMP-9 and decreased HN2-induced TUNEL staining. Taken together, our study demonstrates that the combination of HC + EB-1 is an efficacious countermeasure to HN2.

A type IV collagenase inhibitor, N-hydroxy-3-phenyl-2-(4-phenylbenzenesulfonamido) propanamide (BiPS), suppresses skin injury induced by sulfur mustard

Sulfur mustard (SM) is a highly toxic blistering agent thought to mediate its action, in part, by activating matrix metalloproteinases (MMPs) in the skin and disrupting components of the basement membrane zone (BMZ). Type IV collagenases (MMP-9) degrade type IV collagen in the skin, a major component of the BMZ at the dermal-epidermal junction. In the present studies, a type IV collagenase inhibitor, N-hydroxy-3-phenyl-2-(4-phenylbenzenesulfonamido) propanamide (BiPS), was tested for its ability to protect the skin against injury induced by SM in the mouse ear vesicant model. SM induced inflammation, epidermal hyperplasia and microblistering at the dermal/epidermal junction of mouse ears 24–168 h post-exposure. This was associated with upregulation of MMP-9 mRNA and protein in the skin. Dual immunofluorescence labeling showed increases in MMP-9 in the epidermis and in the adjacent dermal matrix of the SM injured skin, as well as breakdown of type IV collagen in the basement membrane. Pretreatment of the skin with BiPS reduced signs of SM-induced cutaneous toxicity; expression of MMP-9 mRNA and protein was also downregulated in the skin by BiPS. Following BiPS pretreatment, type IV collagen appeared intact and was similar to control skin. These results demonstrate that inhibiting type IV collagenases in the skin improves basement membrane integrity after exposure to SM. BiPS may hold promise as a potential protective agent to mitigate SM induced skin injury.

Expression of Laminin γ2 Proteolytic Fragments in Murine Skin Following Exposure to Sulfur Mustard.

Laminin-332 is a basement membrane protein composed of three genetically distinct polypeptide chains that actively promote both skin epidermal cell adhesion and migration. Proteolytic fragments of the laminin γ2 chain stimulate migration and scattering of keratinocytes and cancer cells. Sulfur mustard (SM) is a bifunctional alkylating agent that induces separation of basal keratinocytes from the dermal-epidermal junction and invokes a strong inflammatory response leading to delayed wound repair. In the present studies, the role of laminin γ2 in SM-induced skin injury and wound repair was investigated using the mouse ear vesicant model. We found that laminin γ2 chain mRNA was preferentially upregulated in mouse ear skin exposed to SM. In situ hybridization confirmed overexpression of laminin γ2 transcript. Western blot analysis showed increased protein expression of the full-length proform of laminin γ2 and smaller processed fragments of laminin γ2 in skin exposed to SM. Dual immunofluorescence labeling indicated that laminin γ2 fragments are prevalent in suprabasal keratinocytes behind the leading edge in areas of hyperplasia in injured skin. In addition, co-expression of laminin γ2 and the senescent marker, p16-INK4a was found to overlap with the hyperplastic migratory epithelial sheet. This observation is similar to hypermotile keratinocytes reported in invasive carcinoma cells. Overall, our studies indicate that laminin γ2 is preferentially expressed in skin post SM exposure and that protein expression appears to become progressively more fragmented. The laminin γ2 fragments may play a role in regulating SM-induced skin wound repair. Anat Rec, 2020. © 2020 American Association for Anatomy.

Matrix Metalloproteinase 9 (MMP9) Inhibitor Prevents Mustard Induced Microvesication and Promotes Cutaneous Wound Healing

Skin exposure to the chemical warfare agent, sulfur mustard (bis‐2‐chloroethylsulfide, SM), is characterized by severe blister formation and a prolonged inflammatory response. The mechanisms of these SM toxic effects are still poorly defined, and effective medical countermeasures against SM‐induced cutaneous injury have yet to be established. Animal models demonstrate disruption of the skin architecture at the dermal‐epidermal junction (DEJ) when exposed to the vesicant, SM; the damage may be further exacerbated by overexpression of MMP9. Studies show MMP9 degrades basement membrane (BM) components and regulates inflammation in tissue injuries; inhibition of MMP9 suppresses inflammation and promotes wound repairs in tumors and various wound models. In the present studies, ([N‐hydroxy‐3‐phenyl‐2‐(4‐phenylbenzenesulfonamido) propanamide], BiPS), a specific MMP9 inhibitor, was evaluated for its ability to prevent microvesication, suppress inflammation, and promote wound healing following SM exposure using the mouse ear vesicant model. Treatment of male CD1 mouse ear skin with SM (0.08 mg) caused a characteristic SM induced injury including edema, inflammatory cell infiltration, and the formation of microvesicles at the DEJ. Expression of MMP9 mRNA and protein in the skin progressively increased with time 24–168 h following SM exposure. Immunofluorescence studies showed disruption of the BM molecule type IV collagen (COL4), increased expression of inflammation marker, COX2, and upregulation of the skin wound marker keratin 6 (K6) in SM induced skin wounds. SM also caused macrophage (F4/80) accumulation in the tissue which persisted up to 168 h post exposure. Pretreatment of ear skin with BiPS significantly reduced SM‐induced dermal edema and maintained the integrity of the DEJ‐BM as evidenced by contiguous expression of COL4. At 168 h post SM exposure, mRNA and protein expression of MMP9 was significantly downregulated in BiPS treated mice. BiPS treatment also reduced the number of macrophages accumulating in the tissue, and suppressed expression of COX2, and downregulated expression of K6. Taken together, these data indicate that BiPS treatment was able to suppress both inflammation and degradation of BM zone in skin due to SM. This compound was effective in targeting MMP9 to protect against SM induced microvesication and promote wound repairs. MMP9 inhibitors may be useful as medical countermeasure against SM‐induced cutaneous injury.Support or Funding InformationSupported by NIH grants ES005022 and AR055073.

The Type IV Collagenase Inhibitor, BiPS, Alters Keratin Expression in Sulfur Mustard Exposed Mouse Skin

Sulfur mustard (SM) is a potent chemical vesicant targeting many tissues including skin. The SM induced cutaneous toxicity is associated with edema, epidermal erosions, inflammation, and prolonged wound repair. Earlier studies have shown that overexpression of matrix metalloproteinase 9 (MMP9) degrades extracellular matrix proteins and leads to the separation of epidermis from dermis in skin exposed to SM. We have found that MMP9, a type IV collagenase, disrupts collagen IV (Col IV) a major component of the basement membrane (BM) zone in SM induced blisters. Col IV in the BM network has recently been reported to be a regulator of epidermal differentiation and keratin expression during wound repair. The type IV collagen (Col IV) BM network may regulate epidermal differentiation and keratin expression during development and wound repair. In this present study, we evaluated the MMP9 inhibitor BiPS [N‐hydroxy‐3‐phenyl‐2‐(4‐phenylbenzenesulfonamido) propanamide] in an epidermal wound healing model following SM exposure. Time course (24, 72, and 168 hrs post‐SM exposure) and compound evaluation studies (BiPS as a single pretreatment) were performed in a mouse ear vesicant model (MEVM) using histopathological changes, degree of hyperplasia and edema, and expression of type IV collagen, MMP9, keratin 10 (K10, differentiation marker), and keratin 6 (K6, wound‐inducible marker) for comparison. MMP9 mRNA and protein expression increased with time. Dual immunofluorescence studies using Col IV α1 and MMP9 antibodies showed BM zone breakdown of Col IV and apparent MMP9 expression in the epidermis and the adjacent dermal matrix of the SM injured skin. Dual immunofluorescent studies using K6 and K10 showed strong K6 and weak K10 expression in the hyperplastic epidermis. In the compound evaluation study, the BiPS pretreatment group demonstrated significant reduction in edema with 25% reduction of epidermal thickness, and improvement in overall tissue structure by 72 hr post‐SM exposure. mRNA expression of MMP9 was significantly downregulated in the BiPS treated group by 168 hr post exposure. Immunofluorescent studies showed that significant reduction of MMP9 expression in the skin and a continuous expression pattern of Col IV; similar to the unexposed control skin. Dual immunofluorescent studies show reduced K6 and increased K10 expression in hyperplastic epidermis when compared to SM treated samples. These results suggest that BiPS treatment may effectively improve BM integrity by the inhibition of MMP9 in SM exposed skin. This may in turn modulate the epidermal keratin expression and promote keratinocyte differentiation for wound repair. Targeting MMP9 for the restoration of BM may be an effective strategy for countering SM‐induced cutaneous injury.Support or Funding InformationGrant funding supported by ES005022, T32ES007148, and NIAMS U54AR055073.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Assessment of the time-dependent dermatotoxicity of mechlorethamine using the mouse ear vesicant model.

Mechlorethamine (HN2) is an alkylating agent and sulfur mustard gas mimetic which is also used in anticancer therapy. HN2 is associated with skin inflammation and blistering which can lead to secondary infections. The purpose of the present study was to investigate the time-dependent dermatotoxicity of HN2 using the mouse ear vesicant model (MEVM). To this end, our operational definition of dermatotoxicity included tissue responses to HN2 consistent with an increase in the wet weights of mouse ear punch biopsies, an increase in the morphometric thickness of H&E stained ear sections and histopathologic observations including tissue edema, inflammatory cell infiltration and vesication. The ears of male Swiss Webster mice were topically exposed to a single dose of HN2 (0.5 μmol/ear) or DMSO vehicle (5 μl/ear) or left untreated (naive). Mice were then euthanized at 15 min, 1, 2, 4, 8 or 24 hr following HN2 exposure. Compared to control ears, mouse ears exposed to HN2 at all time points showed an increase in wet weights, morphometric thickness, edema, inflammatory cell infiltration and signs of vesication. The incidence in tissue vesication sharply increased between 4 and 8 hr after exposure, revealing that tissue vesication is well established by 8 hr and remains elevated at 24 hr after exposure. It is noteworthy that, compared to control ears, mouse ears treated with DMSO vehicle alone also exhibited an increase in wet weights and morphometric thickness at 15 min, 1, 2 and 4 hr following treatment; however, these vehicle effects begin to subside after 4 hr. The results obtained here using the MEVM provide a more holistic understanding of the kinetics of vesication, and indicate that time points earlier than 24 hr may prove useful not only for investigating the complex mechanisms involved in vesication but also for assessing the effects of vesicant countermeasures.

Ebselen oxide attenuates mechlorethamine dermatotoxicity in the mouse ear vesicant model

Mechlorethamine (HN2) is an alkylating agent and sulfur mustard mimetic. Topical exposure to HN2 is associated with tissue blistering. Previous work in our laboratory has shown that ebselen (EB-1) possesses anti-vesicant, anti-inflammatory, anti-bacterial, anti-fungal, and cytoprotective properties, both in vivo and in vitro. We recently reported that ebselen oxide (EB-2), an analog of EB-1 with a tetravalent selenium atom, also possesses anti-bacterial and anti-fungal activity and confers cytoprotection against HN2 in vitro. The purpose of the present study was to determine the vesicant countermeasure potential of EB-2 using the mouse ear vesicant model (MEVM). Compared to control ears, mouse ears exposed to a single dose of HN2 (0.500 µmol/ear) showed an increase in wet weights, ear thickness, hyperplasia, vesication, and inflammatory cell infiltration after 24 h. Fluorescence microscopy of terminal deoxynucleotidyl transferase (TdT) dUTP nick end labeling (TUNEL)-stained sections showed that the occurrence of apoptosis extended from the epidermis of the HN2-treated side, all the way to the contralateral epidermis. In contrast, HN2-exposed ears treated topically with EB-2 at a test dose of 0.250 mg/ear showed a significant decrease in wet weight (12% less vs. HN2 alone), morphometric thickness (13% less vs. HN2 alone), and vesication. In addition, TUNEL staining revealed that HN2 ears treated with EB-2 (0.250 mg/ear) showed a decrease in apoptosis as compared to the HN2 group. EB-2 also reduced the abundance of matrix metalloproteinase-9 (MMP-9) in ear tissues exposed to HN2. Taken together, our study demonstrates that EB-2 is an efficacious countermeasure to HN2.

TRPA1 and CGRP antagonists counteract vesicant-induced skin injury and inflammation

The skin is highly sensitive to the chemical warfare agent in mustard gas, sulfur mustard (SM) that initiates a delayed injury response characterized by erythema, inflammation and severe vesication (blistering). Although SM poses a continuing threat, used as recently as in the Syrian conflict, no mechanism-based antidotes against SM are available.Recent studies demonstrated that Transient Receptor Potential Ankyrin 1 (TRPA1), a chemosensory cation channel in sensory nerves innervating the skin, is activated by SM and 2‐chloroethyl ethyl sulfide (CEES), an SM analog, in vitro, suggesting it may promote vesicant injury.Here, we investigated the effects of TRPA1 inhibitors, and an inhibitor of Calcitonin Gene Related Peptide (CGRP), a neurogenic inflammatory peptide released upon TRPA1 activation, in a CEES-induced mouse ear vesicant model (CEES-MEVM). TRPA1 inhibitors (HC-030031 and A-967079) and a CGRP inhibitor (MK-8825) reduced skin edema, pro-inflammatory cytokines (IL-1β, CXCL1/KC), MMP-9, a protease implicated in skin damage, and improved histopathological outcomes.These findings suggest that TRPA1 and neurogenic inflammation contribute to the deleterious effects of vesicants in vivo, activated either directly by alkylation, or indirectly, by reactive intermediates or pro-inflammatory mediators. TRPA1 and CGRP inhibitors represent new leads that could be considered for validation and further development in other vesicant injury models.

Effects of poly (ADP-ribose) polymerase-1 (PARP-1) inhibition on sulfur mustard-induced cutaneous injuries in vitro and in vivo.

Early studies with first-generation poly (ADP-ribose) polymerase (PARP) inhibitors have already indicated some therapeutic potential for sulfur mustard (SM) injuries. The available novel and more potential PARP inhibitors, which are undergoing clinical trials as drugs for cancer treatment, bring it back to the centre of interest. However, the role of PARP-1 in SM-induced injury is not fully understood. In this study, we selected a high potent specific PARP inhibitor ABT-888 as an example to investigate the effect of PARP inhibitor in SM injury. The results showed that in both the mouse ear vesicant model (MEVM) and HaCaT cell model, PARP inhibitor ABT-888 can reduce cell damage induced by severe SM injury. ABT-888 significantly reduced SM induced edema and epidermal necrosis in MEVM. In the HaCaT cell model, ABT-888 can reduce SM-induced NAD+/ATP depletion and apoptosis/necrosis. Then, we studied the mechanism of PARP-1 in SM injury by knockdown of PARP-1 in HaCaT cells. Knockdown of PARP-1 protected cell viability and downregulated the apoptosis checkpoints, including p-JNK, p-p53, Caspase 9, Caspase 8, c-PARP and Caspase 3 following SM-induced injury. Furthermore, the activation of AKT can inhibit autophagy via the regulation of mTOR. Our results showed that SM exposure could significantly inhibit the activation of Akt/mTOR pathway. Knockdown of PARP-1 reversed the SM-induced suppression of the Akt/mTOR pathway. In summary, the results of our study indicated that the protective effects of downregulation of PARP-1 in SM injury may be due to the regulation of apoptosis, necrosis, energy crisis and autophagy. However, it should be noticed that PARP inhibitor ABT-888 further enhanced the phosphorylation of H2AX (S139) after SM exposure, which indicated that we should be very careful in the application of PARP inhibitors in SM injury treatment because of the enhancement of DNA damage.

Use of the mouse ear vesicant model to evaluate the effectiveness of ebselen as a countermeasure to the nitrogen mustard mechlorethamine

Previous studies in this and other laboratories have demonstrated that ebselen (EB-1), an organoselenium compound, spares cells from mechlorethamine (HN2) toxicity in vitro. In the present study, the hypothesis that EB-1 will reduce dermal toxicity of HN2 in vivo is put forward and found to have merit. Using the mouse ear vesicant model (MEVM), HN2, applied topically, showed a dose-dependent effect upon ear swelling and thickness 24 h after treatment; whereas tissue injury consistent with vesication was observed at the higher test doses of HN2 (≥ 0.250 µmol per ear). To examine HN2 countermeasure activity using the MEVM, either hydrocortisone (HC), as a positive control, or EB-1, the test countermeasure, was administered as three topical treatments 15 min, 4 and 8 h after HN2 exposure. Using this approach, both HC and EB-1 were found to reduce tissue swelling associated with HN2 toxicity 24 h after exposure to the vesicant. Taken together, these data demonstrate for the first time the effectiveness of EB-1 as a vesicant countermeasure in a relevant in vivo model.

The Endoplasmic Reticulum Stress and Unfolded Protein Responses in Sulfur Mustard induced Mouse Skin Wound Repair

The endoplasmic reticulum stress (ERS) pathways activate the unfolded protein response (UPR) to mediate cell survival against severe stress in an attempt to prevent ERS mediated apoptosis. Sulfur mustard (SM), a chemical warfare vesicating agent, causes significant delayed wound repair in skin. This study explored the contribution of UPR and ERS to SM cutaneous injury in mice. We performed time course studies using the mouse ear vesicant model and showed histopathology changes over time. RT‐PCR demonstrated at least a 2‐fold increased of the ER stress survival gene, GRP78; UPR gene, ATF6; and proapoptotic gene, CHOP as time progressed from 24h to 168h post‐SM exposure. Western blot analysis demonstrated increased GRP78, CHOP, and full length and cleaved (activated) forms of ATF6 as time progressed. This was confirmed by immunofluorescence which showed significant nuclear staining of cleaved ATF6 in the hyperplastic epidermis at 168h post exposure. Double immunofluorescent labeling for GRP78 and CHOP at 72h post exposure showed abundant cytoplasmic staining of GRP78 in the basal, proliferating epidermis. In contrast, the expression of CHOP was more numerous in the migrating keratinocytes. This suggests that the migrating cells are targeted for apoptosis while the basal, proliferating cells are targeted for survival. The continued proliferation of the basal cells and their subsequent conversion to migrating cells may in part explain the delayed wound repair frequently observed in SM skin injury.Grant Funding Source: NIH grants AR055073, EY09056, and ES005022.

Sulfur mustard induces an endoplasmic reticulum stress response in the mouse ear vesicant model

The endoplasmic reticulum (ER) stress response is a cell survival pathway upregulated when cells are under severe stress. Severely damaged mouse ear skin exposed to the vesicant, sulfur mustard (bis-2-chloroethyl sulfide, SM), resulted in increased expression of ER chaperone proteins that accompany misfolded and incorrectly made proteins targeted for degradation. Time course studies with SM using the mouse ear vesicant model (MEVM) showed progressive histopathologic changes including edema, separation of the epidermis from the dermis, persistent inflammation, upregulation of laminin γ2 (one of the chains of laminin-332, a heterotrimeric skin glycoprotein required for wound repair), and delayed wound healing from 24h to 168h post exposure. This was associated with time related increased expression of the cell survival ER stress marker, GRP78/BiP, and the ER stress apoptosis marker, GADD153/CHOP, suggesting simultaneous activation of both cell survival and non-mitochondrial apoptosis pathways. Dual immunofluorescence labeling of a keratinocyte migration promoting protein, laminin γ2 and GRP78/BIP, showed colocalization of the two molecules 72h post exposure indicating that the laminin γ2 was misfolded after SM exposure and trapped within the ER. Taken together, these data show that ER stress is induced in mouse skin within 24h of vesicant exposure in a defensive response to promote cell survival; however, it appears that this response is rapidly overwhelmed by the apoptotic pathway as a consequence of severe SM-induced injury.

Investigation of anticholinergic and non‐steroidal anti‐inflammatory prodrugs which reduce chemically induced skin inflammation

As part of a continuous effort to develop efficient counter measures against sulfur mustard injuries, several unique NSAID prodrugs have been developed and screened for anti-inflammatory properties. Presented herein are three classes of prodrugs which dually target inflammation and cholinergic dysfunction. Compounds 1-28 contain common NSAIDs linked either to choline bioisosteres or to structural analogs of acetylcholinesterase (AChE) inhibitors. These agents have shown utility as anti-vesicants and anti-inflammatory agents when screened in a mouse ear vesicant model (MEVM) against both 2-chloroethyl ethyl sulfide (CEES), a blistering agent, and 12-O-tetradecanoylphorbol-13-acetate (TPA), a common topical irritant. Many of the prodrugs have activity against CEES, with 5, 18, 22 and 27 reducing inflammation by more than 75% compared with a control. Compounds 12, 13, 15 and 22 show comparable activity against TPA. Promising activity in the MEVM is related to half-lives of NSAID release in plasma, moderate to high lipophilicity, and some degree of inhibition of AChE, a potential contributor to sulfur mustard-mediated tissue damage.

Upregulation of gamma‐2 laminin‐332 in the mouse ear vesicant wound model

Epithelial cell migration during wound healing is regulated in part by enzymatic processing of laminin-332 (formerly LN-5), a heterodimer formed from alpha, beta, and gamma polypeptide chains. Under static conditions, laminin-332 is secreted into the extracellular matrix as a proform and has two chains processed to smaller forms, allowing it to anchor epithelial cells to the basement membrane of the dermis. During incisional wounding, laminin gamma2 chains in particular are processed to smaller sizes and function to promote epithelial sheet migration over the wound bed. The present study examines whether this same function occurs following chemical injury. The mouse ear vesicant model (MEVM) was used to follow the pathology in the ear and test whether processed laminin-332 enhances epithelial cell migration. Skin biopsies of sulfur mustard (SM) exposed ears for several time points were analyzed by histology, immunohistochemistry, real-time PCR, and Western blot analysis. SM exposure greatly increased mRNA levels for laminin-gamma2 in comparison to the other two chains. Protein production of laminin-gamma2 was upregulated, and there was an increase in the processed forms. Protein production was in excess of the amount required to form heterotrimeric laminin-332 and was associated with the migrating epithelial sheet, suggesting a potential role in wound healing for monomeric laminin-gamma2.

Endoplasmic reticulum stress response is induced by sulfur mustard in the mouse ear vesicant model

Time‐related changes in the histopathology of mouse skin occur after topical exposure to the vesicant agent, bis(2‐chloroethyl) sulfide (SM) using the mouse ear vesicant model (MEVM). Some of these changes include increasing edema, detachment of the epidermis from the dermis, and upregulation of laminin‐332. Endoplasmic reticulum stress response (ESR) was observed by confocal microscopy. Microarray analysis and RT‐PCR experiments indicated there was upregulation of several heat shock proteins and folding chaperones such glucose‐regulated protein 78 and GRP94 in the ER. It confirmed the confocal observations and suggested that ER stress occurs very quickly in the MEVM. The accumulation of laminin γ2 protein, one of the chains of laminin‐332, in the ER was visualized by confocal microscopy and co localized with the ER chaperones. This accumulation appeared specifically in the migrating, but not proliferating cells. These observations are consistent with recent reports that laminin‐332 is found in migrating, transformed epithelial cells that have left the cell cycle, but not in proliferating cells. These results suggest that laminin γ2 is misfolded after SM treatment, resulting in decreased secretion and reduced overall amounts of laminin‐332 in the extracellular matrix. This would explain the observation that there is a delayed wound healing response evident in this wound model.Grant Funding SourceES005022, ES004738, EY09056, and the NIH CounterACT Program through NIAMS U54AR055073

Microarray Analysis of Mouse Ear Tissue Exposed to Bis-(2-chloroethyl) Sulfide: Gene Expression Profiles Correlate with Treatment Efficacy and An Established Clinical Endpoint

Bis-(2-chloroethyl) sulfide (sulfur mustard; SM) is a potent alkylating agent. Three treatment compounds have been shown to limit SM damage in the mouse ear vesicant model: dimercaprol, octyl homovanillamide, and indomethacin. Microarrays were used to determine gene expression profiles of biopsies taken from mouse ears after exposure to SM in the presence or absence of treatment compounds. Mouse ears were topically exposed to SM alone or were pretreated for 15 min with a treatment compound and then exposed to SM. Ear tissue was harvested 24 h after exposure for ear weight determination, the endpoint used to evaluate treatment compound efficacy. RNA extracted from the tissues was used to generate microarray probes for gene expression profiling of therapeutic responses. Principal component analysis of the gene expression data revealed partitioning of the samples based on treatment compound and SM exposure. Patterns of gene responses to the treatment compounds were indicative of exposure condition and were phenotypically anchored to ear weight. Pretreatment with indomethacin, the least effective treatment compound, produced ear weights close to those treated with SM alone. Ear weights from animals pretreated with dimercaprol or octyl homovanillamide were more closely associated with exposure to vehicle alone. Correlation coefficients between gene expression level and ear weight revealed genes involved in mediating responses to both SM exposure and treatment compounds. These data provide a basis for elucidating the mechanisms of response to SM and drug treatment and also provide a basis for developing strategies to accelerate development of effective SM medical countermeasures.

Amelioration of sulfur mustard skin injury following a topical treatment with a mixture of a steroid and a NSAID

The ability to ameliorate sulfur mustard (HD)-induced oedema by treatment with anti-inflammatory drugs was reported previously after screening four steroids and four non-steroidal anti-inflammatory drugs (NSAIDs) using the mouse ear vesicant model. Following the screening study, one steroid and one NSAID (Adexone and Voltaren) were selected as the most effective, and a mixture of the two was chosen for the present more extensive research. The effect of the combined treatment on clinical, biochemical and histopathological parameters following HD insult was studied. Mice ears were exposed to 0.2 micro l of HD for 10 min to produce a moderate skin injury. Oedema development peaked ca. 48 h following exposure, as determined by weighing ear biopsies. Histological observations at that time exhibited damage to the epidermis and dermis. An increase in prostaglandin E (PGE) was measured in skin homogenates, starting 8 h following exposure and lasting at least up to 48 h post-exposure. A topical treatment using the above anti-inflammatory mixture significantly reduced inflammatory parameters when applied up to 4 h following exposure. These parameters included extent of oedema, levels of PGE, area of clinical damage and extent of cytotoxic injury (vesications and damaged epithelial cells). Thus, a combination of a steroid and NSAID was found to be effective in reducing the intensity of HD skin injury and possibly shortening the time to full recovery. The treatment, however, did not prevent completely the ensuing cytotoxic processes in the epithelial layer.

Alterations of Gene Expression in Sulfur Mustard‐Exposed Skin Topically Treated with Vanilloids

Sulfur mustard [bis(2‐chloroethyl)sulfide, SM] is a chemical warfare agent that penetrates the skin rapidly and causes extensive blistering. Using the mouse ear vesicant model (MEVM), we evaluated the effect of topically applied anti‐inflammatory agents (octyl homovanillamide and heptyl isovanillamide) on ear edema formation and gene expression following SM exposure. Relative ear weight and real‐time reverse transcriptase polymerase chain reaction of GM‐CSF, IL‐1β, and IL‐6 were used to evaluate the effects of octyl homovanillamide and heptyl isovanillamide. Both vanilloids significantly reduced SM‐induced edema. At the single dose and number of animals/group tested, octyl homovanillamide produced a trend of reduced mRNA levels; however, the reduction was not significant for GM‐CSF, IL‐1β, or IL‐6. Heptyl isovanillamide significantly reduced (p ≤ 0.05) GM‐CSF, IL‐1β, and IL‐6 mRNA levels. These results show that octyl homovanillamide and heptyl isovanillamide reduce skin edema and heptyl isovanillamide significantly reduced cytokine mRNA expression following SM exposure. In addition to measuring edema formation, monitoring expression of biomarkers such as GM‐CSF, IL‐1β, and IL‐6 may also serve to evaluate therapeutic treatments against SM‐induced dermal injury.