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

Life-Cycle-Dependent Toxicities of Mono- and Bifunctional Alkylating Agents in the 3R-Compliant Model Organism C. elegans

Caenorhabditis elegans (C. elegans) is gaining recognition and importance as an organismic model for toxicity testing in line with the 3Rs principle (replace, reduce, refine). In this study, we explored the use of C. elegans to examine the toxicities of alkylating sulphur mustard analogues, specifically the monofunctional agent 2-chloroethyl-ethyl sulphide (CEES) and the bifunctional, crosslinking agent mechlorethamine (HN2). We exposed wild-type worms at different life cycle stages (from larvae L1 to adulthood day 10) to CEES or HN2 and scored their viability 24 h later. The susceptibility of C. elegans to CEES and HN2 paralleled that of human cells, with HN2 exhibiting higher toxicity than CEES, reflected in LC50 values in the high µM to low mM range. Importantly, the effects were dependent on the worms' developmental stage as well as organismic age: the highest susceptibility was observed in L1, whereas the lowest was observed in L4 worms. In adult worms, susceptibility to alkylating agents increased with advanced age, especially to HN2. To examine reproductive effects, L4 worms were exposed to CEES and HN2, and both the offspring and the percentage of unhatched eggs were assessed. Moreover, germline apoptosis was assessed by using ced-1p::GFP (MD701) worms. In contrast to concentrations that elicited low toxicities to L4 worms, CEES and HN2 were highly toxic to germline cells, manifesting as increased germline apoptosis as well as reduced offspring number and percentage of eggs hatched. Again, HN2 exhibited stronger effects than CEES. Compound specificity was also evident in toxicities to dopaminergic neurons-HN2 exposure affected expression of dopamine transporter DAT-1 (strain BY200) at lower concentrations than CEES, suggesting a higher neurotoxic effect. Mechanistically, nicotinamide adenine dinucleotide (NAD+) has been linked to mustard agent toxicities. Therefore, the NAD+-dependent system was investigated in the response to CEES and HN2 treatment. Overall NAD+ levels in worm extracts were revealed to be largely resistant to mustard exposure except for high concentrations, which lowered the NAD+ levels in L4 worms 24 h post-treatment. Interestingly, however, mutant worms lacking components of NAD+-dependent pathways involved in genome maintenance, namely pme-2, parg-2, and sirt-2.1 showed a higher and compound-specific susceptibility, indicating an active role of NAD+ in genotoxic stress response. In conclusion, the present results demonstrate that C. elegans represents an attractive model to study the toxicology of alkylating agents, which supports its use in mechanistic as well as intervention studies with major strength in the possibility to analyze toxicities at different life cycle stages.

NAD+ Acts as a Protective Factor in Cellular Stress Response to DNA Alkylating Agents

Sulfur mustard (SM) and its derivatives are potent genotoxic agents, which have been shown to trigger the activation of poly (ADP-ribose) polymerases (PARPs) and the depletion of their substrate, nicotinamide adenine dinucleotide (NAD+). NAD+ is an essential molecule involved in numerous cellular pathways, including genome integrity and DNA repair, and thus, NAD+ supplementation might be beneficial for mitigating mustard-induced (geno)toxicity. In this study, the role of NAD+ depletion and elevation in the genotoxic stress response to SM derivatives, i.e., the monofunctional agent 2-chloroethyl-ethyl sulfide (CEES) and the crosslinking agent mechlorethamine (HN2), was investigated with the use of NAD+ booster nicotinamide riboside (NR) and NAD+ synthesis inhibitor FK866. The effects were analyzed in immortalized human keratinocytes (HaCaT) or monocyte-like cell line THP-1. In HaCaT cells, NR supplementation, increased NAD+ levels, and elevated PAR response, however, did not affect ATP levels or DNA damage repair, nor did it attenuate long- and short-term cytotoxicities. On the other hand, the depletion of cellular NAD+ via FK866 sensitized HaCaT cells to genotoxic stress, particularly CEES exposure, whereas NR supplementation, by increasing cellular NAD+ levels, rescued the sensitizing FK866 effect. Intriguingly, in THP-1 cells, the NR-induced elevation of cellular NAD+ levels did attenuate toxicity of the mustard compounds, especially upon CEES exposure. Together, our results reveal that NAD+ is an important molecule in the pathomechanism of SM derivatives, exhibiting compound-specificity. Moreover, the cell line-dependent protective effects of NR are indicative of system-specificity of the application of this NAD+ booster.

Advances in treatment of acute sulfur mustard poisoning - a critical review

Sulfur mustard (SM) is a blistering chemical warfare agent that was used during the World War I and in the Iraq-Iran conflict. The aim of this paper is to discuss and critically review the published results of experiments on the treatment of SM poisoning based on our clinical and research experience. The victims must remove from the contaminated zone immediately. The best solution for decontamination is large amounts of water, using neutral soap and 0.5% sodium hypochlorite. Severely intoxicated patients should be treated according to advanced life support protocols and intensive care therapy for respiratory disorders and the chemical burn. Sodium thiosulfate infusion (100-500 mg/kg/min) should be started up to 60 min after SM exposure. However, N-acetyle cysteine (NAC) is recommended, none of them acts as specific or effective antidote. The important protective and conservative treatment of SM-induced pulmonary injuries include humidified oxygen, bronchodilators, NAC as muculytic, rehydration, mechanical ventilation, appropriate antibiotics and respiratory physiotherapy as clinically indicated. Treatment of acute SM ocular lesions start with topical antibiotics; preferably sulfacetamide eye drop, continue with lubricants, and artificial tears. Treatment for cutaneous injuries include: moist dressing; preferably with silver sulfadiazine cream, analgesic, anti-pruritic, physically debridement, debridase, Laser debridement, followed by skin autologous split-thickness therapy as clinically indicated. The new suggested medications and therapeutic approaches include: anti-inflammatory agents, Niacinamide, Silibinin, Calmodulin antagonists, Clobetasol, full-thickness skin grafting for skin injuries; Doxycycline; Bevacizumab, and Colchicine for ocular injuries. Recommended compounds based on animal studies include Niacinamide, Aprotinin, des-aspartate-angiotensin-I, Gamma-glutamyltransferase, vitamin E, and vitamin D. In vitro studies revealed that Dimethylthiourea, L-nitroarginine, Methyl-ester, Sodium pyruvate, Butylated hydroxyanisole, ethacrynic acid, and macrolide antibiotics are effective. However, none of them, except macrolide antibiotics have been proved clinically. Avoidance of inappropriate polypharmacy is advisable.

NAD+ in sulfur mustard toxicity

Sulfur mustard (SM) is a toxicant and chemical warfare agent with strong vesicant properties. The mechanisms behind SM-induced toxicity are not fully understood and no antidote or effective therapy against SM exists. Both, the risk of SM release in asymmetric conflicts or terrorist attacks and the usage of SM-derived nitrogen mustards as cancer chemotherapeutics, render the mechanisms of mustard-induced toxicity a highly relevant research subject. Herein, we review a central role of the abundant cellular molecule nicotinamide adenine dinucleotide (NAD⁺) in molecular mechanisms underlying SM toxicity. We also discuss the potential beneficial effects of NAD⁺ precursors in counteracting SM-induced damage.

Immunochemical analysis of poly(ADP-ribosyl)ation in HaCaT keratinocytes induced by the mono-alkylating agent 2-chloroethyl ethyl sulfide (CEES): Impact of experimental conditions

Sulfur mustard (SM) is a bifunctional alkylating agent with a long history of use as a chemical weapon. Although its last military use is dated for the eighties of the last century, a potential use in terroristic attacks against civilians remains a significant threat. Thus, improving medical therapy of mustard exposed individuals is still of particular interest. PARP inhibitors were recently brought into the focus as a potential countermeasure for mustard-induced pathologies, supported by the availability of efficient compounds successfully tested in cancer therapy. PARP activation after SM treatment was reported in several cell types and tissues under various conditions; however, a detailed characterization of this phenomenon is still missing. This study provides the basis for such studies by developing and optimizing experimental conditions to investigate poly(ADP-ribosyl)ation (PARylation) in HaCaT keratinocytes upon treatment with the monofunctional alkylating agent 2-chloroethyl ethyl sulfide ("half mustard", CEES). By using an immunofluorescence-based approach, we show that optimization of experimental conditions with regards to the type of solvent, dilution factors and treatment procedure is essential to obtain a homogenous PAR staining in HaCaT cell cultures. Furthermore, we demonstrate that different CEES treatment protocols significantly influence the cytotoxicity profiles of treated cells. Using an optimized treatment protocol, our data reveals that CEES induces a dose- and time-dependent dynamic PARylation response in HaCaT cells that could be completely blocked by treating cells with the clinically relevant pharmacological PARP inhibitor ABT888 (also known as veliparib). Finally, siRNA experiments show that CEES-induced PAR formation is predominantly due to the activation of PARP1. In conclusion, this study provides a detailed analysis of the CEES-induced PARylation response in HaCaT keratinocytes, which forms an experimental basis to study the molecular mechanism of PARP1 activation and its functional consequences after mustard treatment in general. Such a study is presented in an accompanying article (Mangerich et al., 2016).

Sulfur and nitrogen mustards induce characteristic poly(ADP-ribosyl)ation responses in HaCaT keratinocytes with distinctive cellular consequences

Mustard agents are potent DNA alkylating agents with mutagenic, cytotoxic and vesicant properties. They include bi-functional agents, such as sulfur mustard (SM) or nitrogen mustard (mustine, HN2), as well as mono-functional agents, such as "half mustard" (CEES). Whereas SM has been used as a chemical warfare agent, several nitrogen mustard derivatives, such as chlorambucil and cyclophosphamide, are being used as established chemotherapeutics. Upon induction of specific forms of genotoxic stimuli, several poly(ADP-ribose) polymerases (PARPs) synthesize the nucleic acid-like biopolymer poly(ADP-ribose) (PAR) by using NAD(+) as a substrate. Previously, it was shown that SM triggers cellular poly(ADP-ribosyl) ation (PARylation), but so far this phenomenon is poorly characterized. In view of the protective effects of PARP inhibitors, the latter have been proposed as a treatment option of SM-exposed victims. In an accompanying article (Debiak et al., 2016), we have provided an optimized protocol for the analysis of the CEES-induced PARylation response in HaCaT keratinocytes, which forms an experimental basis to further analyze mustard-induced PARylation and its functional consequences, in general. Thus, in the present study, we performed a comprehensive characterization of the PARylation response in HaCaT cells after treatment with four different mustard agents, i.e., SM, CEES, HN2, and chlorambucil, on a qualitative, quantitative and functional level. In particular, we recorded substance-specific as well as dose- and time-dependent PARylation responses using independent bioanalytical methods based on single-cell immuno-fluorescence microscopy and quantitative isotope dilution mass spectrometry. Furthermore, we analyzed if and how PARylation contributes to mustard-induced toxicity by treating HaCaT cells with CEES, SM, and HN2 in combination with the clinically relevant PARP inhibitor ABT888. As evaluated by a novel immunofluorescence-based protocol for the detection of N7-ETE-guanine DNA adducts, the excision rate of CEES-induced DNA adducts was not affected by PARP inhibition. Furthermore, while CEES induced moderate changes in cellular NAD(+) levels, annexin V/PI flow cytometry analysis revealed that these changes did not affect CEES-induced short-term cytotoxicity 24h after treatment. In contrast, PARP inhibition impaired cell proliferation and clonogenic survival, and potentiated micronuclei formation of HaCaT cells upon CEES treatment. Similarly, PARP inhibition affected clonogenic survival of cells treated with bi-functional mustards such as SM and HN2. In conclusion, we demonstrate that PARylation plays a functional role in mustard-induced cellular stress response with substance-specific differences. Since PARP inhibitors exhibit therapeutic potential to treat SM-related pathologies and to sensitize cancer cells for mustard-based chemotherapy, potential long-term effects of PARP inhibition on genomic stability and carcinogenesis should be carefully considered when pursuing such a strategy.

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

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

Involvement of caspases and transmembrane metalloproteases in sulphur mustard-induced microvesication in adult human skin in organ culture: directions for therapy

While skin is a major target for sulphur mustard (HD), a therapy to limit HD-induced vesication is currently not available. Since it is supposed that apoptotic cell death and proteolytic digestion of extracellular matrix proteins by metalloproteases are initiating factors for blister formation, we have explored whether inhibition of these processes could prevent HD-induced epidermal-dermal separation using adult human skin in organ culture. Involvement of the caspase and the metalloprotease families was confirmed by the observation that their respective broad spectrum inhibitors, Z-VAD-fmk and GM6001, each suppressed HD-induced microvesication. The lowest effective concentrations were 10 and 100microM, respectively. Using specific inhibitors for caspase-8 (> or =10microM) and caspase-9 (> or =10microM) we learned that HD-induced apoptosis is initiated by the death receptor pathway as well as by the mitochondrial pathway. Remarkably, blocking caspase-8 activity resulted in morphologically better conserved cells than blocking caspase-9 activity. We zoomed in on the role of metalloproteases in HD-induced microvesication by testing the effects of two inhibitors: dec-RVKR-cmk and TAPI-2. Dec-RVKR-cmk is an inhibitor of furin, which activates transmembrane enzymes of the 'a disintegrin and metalloproteinase' (ADAM)-family as well as the membrane-type metalloproteases (MTx-MMP). TAPI-2 specifically inhibits TNFalpha-converting enzyme (TACE/ADAM17), which is involved in pericellular proteolysis. Both inhibitors prevented microvesication at concentrations of > or =500 and > or =20microM, respectively. This confirms that ADAMs and MT-MMPs play a role in HD-induced epidermal-dermal separation, with a particular role for TACE/ADAM17. Since TACE is involved not only in degradation of cell-matrix adhesion structures, but also in ectodomain shedding of ligands for epidermal growth factor receptor (EGFR) and in release of TNFalpha, these results imply TACE-mediated pathways as a new concept in HD toxicity. In conclusion, transmembrane metalloproteases probably form a main target for treatment of blisters in HD casualties. The observation that microvesication in the ex vivo human skin model still could be prevented when the metalloprotease inhibitor GM6001 was applied up to 8h after exposure to HD opens perspectives for non-urgent cure of HD casualties.

The role of NAD+ depletion in the mechanism of sulfur mustard-induced metabolic injury

Results of our previous studies on the chemical warfare agent sulfur mustard (2,2'-dichlorodiethyl sulfide) suggested that mustard-induced inhibition of glycolysis is not solely a function of NAD+ depletion. To define the role of NAD+ in mustard-induced metabolic injury, we examined the effects of mustard+/-niacinamide on energy metabolism in cultured human keratinocytes. Sulfur mustard caused concentration-dependent decreases in viable cell number and ATP content at 24 hours, but not earlier, and time- and concentration-dependent glycolytic inhibition and NAD+ depletion as early as 4 hours. Niacinamide partially protected NAD+ levels at all time points, but did not prevent adverse effects on glycolysis, intracellular ATP, or viable cell number. These results support our earlier conclusions and suggest that sulfur mustard may inhibit glycolysis directly.

Biochemical changes in mouse lung after subcutaneous injection of the sulfur mustard 2-chloroethyl 4-chlorobutyl sulfide

Sulfur mustard (HD) is a vesicant-type chemical warfare agent (CWA) introduced in World War I which continues to be produced, stockpiled, and occasionally deployed by some countries, and could be used potentially by terrorists. Exposure to HD can cause erythema, blisters, corneal opacity, and airway damage. We have reported previously that subcutaneous (SC) injection of immunodeficient athymic nude mice with the half mustard butyl 2-chloroethyl sulfide (BCS) causes systemic biochemical changes in several organs distal to the exposure site. In the present study, we examined the response of non-immunodeficient Swiss Webster mice to the mustard, 2-chloroethyl 4-chlorobutyl sulfide (CECBS). In a pilot study, we found that a single SC injection of 20-25 microl/mouse causes death within 24h. Consequently, we used 5 microl/mouse (approx. 0.017 mg/kg body weight) of neat CECBS or an equal volume of saline as control. We examined the lungs after 1, 24, and 48 h for biochemical changes including total and oxidized glutathione, protein, DNA, and lipid peroxidation contents in tissue homogenate, and superoxide dismutase, catalase, glucose-6-phosphate dehydrogenase, and glutathione S-transferases activities in the cytosol. After 1h and/or 24h, we found statistically significant changes that were resolved by 48 h. These changes mimicked those of HD and BCS and were generally consistent with free radical-mediated oxidative stress. The implications of these observations are two-fold. First, dermal exposure to low-dose mustard gas could elicit systemic changes impacting distal organs such as the lungs. It also suggests that antioxidants could potentially modulate the response and reduce the damage. Second, although the use of known CWAs such as HD is prohibited, analogs that are not recognized as agents are as toxic and could be dangerous if acquired and used by potential terrorists.

Sulfur mustard-induced apoptosis in hairless guinea pig skin

The present study was aimed to examine whether apoptosis is involved in the pathogenesis of sulfur mustard (SM)-induced basal cell death. Skin sites of the hairless guinea pig exposed to SM vapor for 8 minutes were harvested at 3, 6, 12, 24, and 48 hours postexposure. Immunohistochemical detection of basal cell apoptosis was performed using the ApopTag in situ apoptosis labeling kit. Only occasional apoptotic basal cells (BC)were observed in nonexposed and perilesional control sites. At lesional sites, apoptosis of BC was not detected at 3 hours postexposure. However, at 6 hours and 12 hours postexposure, 18% and 59% of BC were apoptotic, respectively. At 24 and 48 hours postexposure, individual apoptotic basal cells were not clearly recognizable due to necrosis. At the ultrastructural level, degenerating BC exhibited typical apoptotic morphology including nuclear condensation and chromatin margination. The results suggest that apoptotic cell death is a cytotoxic mechanism with the number of BC undergoing apoptosis significantly increasing from 6 to 12 hours postexposure. In addition, because necrosis is preferential at 24 hours postexposure, we believe that SM-induced cell death involves early apoptosis and late necrosis, which temporally overlap to produce a single cell death pathway along an apoptotic-necrotic continuum.

Sensitivity of HaCat keratinocytes to diabetogenic toxins

Metabolic, genetic and environmental factors very likely play an important role in the development of skin lesions in diabetes mellitus. While these lesions are involved in secondary diabetes complications, various diabetogenic genotoxic agents may induce direct skin damage. In the present study we examined the potential of known diabetogenic agents (streptozotocin (STZ) and alloxan (AL)), with different mechanisms of action, for induction of direct injury in an immortal human keratinocyte HaCat cell line. In contrast to STZ, which induces alkylation of DNA, a genotoxic effect of AL is achieved through reactive oxygen species. We found that HaCat cells are highly sensitive to STZ, but not to AL. At a concentration of 10mM STZ, cell viability decreased to 32 +/-13% of control (P<0.05), as compared to 82 +/-14% with 10mM of AL. Cells treated with 10 and 20mM STZ showed a significant increase in apoptosis (3.9- and 6.7-fold), but not in necrosis, compared to naive cells (P<0.05). In contrast to STZ, no increase in apoptotic and necrotic cell death was observed after AL treatment. Pretreatment with non-metabolizable 3-O-methyl glucose (3-OMG), which can blockade glucose transporter, or with poly(ADP-ribose) polymerase inhibitors (nicotinamide or 3-aminobenzamide), did not protect keratinocytes from STZ injury. Our results show that STZ, but not AL, is highly toxic to the HaCat cell line. Unlike insulin-producing cells, STZ-induced injury of immortal human keratinocyte HaCat cells is independent of the glucose transporters as well as of the activation of poly(ADP-ribose) polymerase.

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

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

Automated assay for nicotinamide adenine dinucleotide (NAD+)

Sulfur mustard (HD), a vesicating chemical warfare compound, has been shown to deplete the nicotinamide adenine dinucleotide (NAD+) content in several cell systems and tissues. This NAD+ depletion has been proposed as an indicator of HD exposure and can be used to evaluate potential antivesicant compounds. To examine NAD+ levels, an automated method based on the alcohol dehydrogenase cycling assay of Jacobson and Jacobson and utilizing a Cobas FARA clinical analyzer has been developed. Automation of this assay led to smaller sample volumes and more efficient use of personnel and resources. The usefulness of this automated method was tested by evaluating the protection, if any, by the topical application of vitamin D or betamethasone against HD-induced NAD+ depletion in skin punches from the hairless guinea pig. The results showed that the samples exposed to HD exhibited significant decreases in NAD+ levels when compared with controls. However, neither vitamin D nor betamethasone demonstrated protection against HD-induced NAD+ depletion. In fact, betamethasone exacerbated the NAD+ depletion when compared with the HD exposed group. This assay appears to be useful for testing potential antivesicant compounds using both in vivo and in vitro exposure systems.

Novel living skin replacement biotherapy approach for wounded skin tissues

A novel living skin replacement (LSR) biotherapy concept, addressing the challenging problems related to tissue regeneration and wound healing, is presented for the treatment of skin burns, traumatic injuries and ulcerations. LSR combines elements of cell therapy along with those of tissue engineering to allow for the regeneration of wounded skin. It takes advantage of biodegradable microspheres onto which donor skin epidermal and dermal cells can be attached and expanded in vitro for subsequent direct application down to the deepest recesses of the wound bed. The key element of the biotherapy is the ability of the skin cells to migrate freely from the microspheres into the wound for regeneration of the tissues. The large surface to volume ratio of the microspheres allows for the delivery of appropriate cell numbers while minimizing the amount of biomaterial to be resorbed. This novel approach presents a number of advantages over existing therapies including facilitated cell manipulations, ease of storage and transportation, rapid clinical intervention due to the elimination of any surgical suturing or stapling, and a more natural three-dimensional tissue remodeling and anatomical compliance. Preliminary in vitro and in vivo evidence of the LSR functionality and its potential benefits is presented.

Early nonsurgical removal of chemically injured tissue enhances wound healing in partial thickness burns

Chemical burns are slow healing injuries and their depth is difficult to assess. Tissue destruction continues as long as active material is present in the wound site. The routine therapy for treatment of full thickness chemical burns is early excision; it shortens hospitalization and reduces morbidity. However, presently there is no specific treatment for chemical burns of partial thickness. This study examined several treatment modalities for partial thickness chemical burns: surgical excision; laser ablation and chemical debridement with Debridase or trypsin-linked to gauze. Chemical burns were inflicted with nitrogen mustard (NM -- a nitrogen analog to sulfur mustard -- mustard gas) in an experimental guinea pig model. Debridase was most effective and reduced significantly lesion area of burns after 'humid' exposure to 2 mg NM. The healing action of Debridase was also evident in the significantly higher histopathological score of biopsies from local tissue obtained on day 5. Laser ablation was most effective and accelerated healing of burn lesions after 'dry' exposure to 5 mg NM. The histopathology score of the laser treated burns was higher on day 4 compared to untreated controls. It is concluded that for partial thickness chemical burns early nonsurgical removal of the damaged tissues accelerates wound healing.

Ex vivo application of delta-aminolevulinic acid induces high and specific porphyrin levels in human skin tumors: possible basis for selective photodynamic therapy

In photodynamic therapy with topically applied delta-aminolevulinic acid porphyrins are acting as photosensitizers. The profile of porphyrin metabolites in normal or in neoplastic skin after administration of delta-aminolevulinic acid has not been determined in detail yet. Thus, to study porphyrin biosynthesis in human skin an organ culture model was developed. Explant pieces of normal skin, keratoacanthoma, and basal cell carcinoma were incubated with 1 mM delta-aminolevulinic acid for 36 h. Levels of delta-aminolevulinic acid, porphyrins and porphyrin metabolites were measured in tissues and supernatants. After incubation with delta-aminolevulinic acid, higher porphyrin levels were demonstrated in tumors as compared to normal skin. In supernatants, most of formed porphyrins, preferentially highly carboxylated porphyrin metabolites, were measured. The pattern of synthesized porphyrins differed between normal and neoplastic skin explants. In tissues of basal cell carcinomas protoporphyrin was preferentially shown and tissues of keratoacanthomas were characterized by a predominance of coproporphyrin as compared to normal skin. The results show that explant cultures offer an easy approach to examine the porphyrin biosynthesis of various tissues. The tumor-specific delta-aminolevulinic acid metabolism indicates additional porphyrin metabolites such as coproporphyrin apart from protoporphyrin as effective photosensitizers and may offer a novel approach to tumor-selective photodynamic damage.

Cutaneous exposure to bis-(2-chloroethyl)sulfide results in neutrophil infiltration and increased solubility of 180,000 Mr subepidermal collagens

Exposure to bis-(2-chloroethyl)sulfide (BCES; "sulfur mustard") causes delayed formation of slowly healing skin blisters. Although the histopathology of BCES injury is well characterized [reviewed in Smith et al., J Am Acad Dermatol 32: 767-776, 1995], little is known of the cutaneous toxicity at the molecular level. To identify biological markers of exposure, epidermal and subepidermal extracts were prepared from 48 individual hairless guinea pigs (HGP) at successive 3-hr intervals following exposure to BCES vapor, and compared using gel electrophoresis, and lectin- and antisera-binding. Inflammation was assessed by measuring edema and myeloperoxidase activity. Edema reached peak levels at 15-18 hr and remained elevated above controls at 24 hr. Recruitment of neutrophils, deduced from increased myeloperoxidase, occurred as early as 3 hr after BCES exposure with maximum infiltration at 6-12 hr. Binding of concanavalin-A lectin revealed increased amounts, relative to contralateral control sites, of two approximately 180,000 Mr polypeptides in subepidermal protein extracts from the BCES-exposed skin obtained > or = 12 hr after exposure. This alteration was not found in epidermal protein extracts prepared from the same animals. Based upon the determined amino acid compositions, both polypeptides had significant collagenous triple helical content (>75%). They could be distinguished immunologically from collagen types I, III, and IV by using polyclonal antisera. We conclude that exposure of HGP skin to BCES results in an early neutrophil infiltration that precedes epidermal-dermal separation and selective alterations of the subepidermal extracellular matrix.

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

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

Effects of calmodulin antagonists and anesthetics on the skin lesions induced by 2-chloroethylethyl sulfide

The effects of calmodulin antagonists and anesthetics on the skin lesions induced by an alkylating vesicant, 2-chloroethylethyl sulfide, were investigated using female hairless mice. 2-Chloroethylethyl sulfide, topically applied (0.6 microliter/5 mm in diameter) on the back skin of hairless mice, induced mild to moderate petechiae on the 1st day, and ulcers with a thick scab after 3 days. The healing process started after 6 days, resulting in shedding of scabs on 9.52 days. Water-soluble ointment bases showed some beneficial effects, whereas oily bases made the skin lesions worse. Trifluoperazine (0.5-1%) and thioridazine (2%), potent calmodulin antagonists, in Pluronic F-127 base substantially prevented the development of 2-chloroethylethyl sulfide-induced skin lesions. A similar effect was achieved with pentamidine (10%), another type of calmodulin antagonist, but not with ketoconazole, a weak calmodulin antagonist. In addition, anesthetics, such as lidocaine and pentobarbital, showed some protection, although at high concentrations (> 5%). As judged by the microscopic appearance, trifluoperazine successfully reduced the hemorrhage and the infiltration of inflammatory cells in early skin lesions, and the formation of thick scabs, which leads to granulomatous scar tissue in late lesions. These results suggest that some calmodulin antagonists and anesthetics in water-soluble bases might be a choice for the treatment of 2-chloroethylethyl sulfide-induced skin burns.

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.

Toxicity of sulphur mustard in adult rat lung organ culture

The toxicity of the chemical warfare agent sulphur mustard, (bis-(2-chloroethyl)sulphide, HD), was examined in adult rat lung organ cultures. Assessment of HD-induced damage by the MTT cytotoxicity assay indicated that the median lethal concentration (LC50) of HD in these cultures was reproducible, and in the microM range. Damage to the lung slices was expressed only after a latent period of 48 h and did not increase significantly with longer expression times. Histopathological examination of HD-treated lung cultures showed that the structural changes in the lung tissue paralleled the toxicity measured biochemically, and were also similar to the damage found in animals and man exposed to HD in vivo. This in vitro model offers a useful tool with which to study the toxicity and mechanism of action of sulphur mustard.

Evaluation of protective effects of sodium thiosulfate, cysteine, niacinamide and indomethacin on sulfur mustard-treated isolated perfused porcine skin

Sulfur mustard (bis(2-chloroethyl)sulfide, HD), a bifunctional alkylating agent, causes severe cutaneous injury, including cell death, edema and vesication. However, the mechanisms underlying HD-induced cutaneous toxicity remain undefined. The isolated perfused porcine skin flap (IPPSF) has been utilized to investigate dermal toxic compounds and pharmacological intervention. In this study, 4 compounds with different pharmacological mechanisms were tested for their ability to prevent the dark basal cell formation, vesication and vascular response charcteristic of exposure to HD in the IPPSF. Reduction of HD-induced dark basal cells was observed in IPPSFs perfused with sodium thiosulfate and cysteine, which are HD scavengers; niacinamide, a possible NAD+ stabilizer and an inhibitor of poly (ADP-ribose) polymerase; or indomethacin, a cyclooxygenase inhibitor, respectively. Treatments with niacinamide and indomethacin, but not sodium thiosulfate or cysteine, resulted in an inhibition of the vascular response in IPPSF exposed to HD. Microvesicles caused by HD were only partially prevented in the indomethacin-perfused IPPSFs. These data suggest that none of these agents alone would be successful antivesicant agents and different mechanisms are involved in production of HD-induced dark basal cells, microvesicles and the vascular response; unfortunately, blocking of the cellular toxicity as evidenced by dark basal cell formation did not prevent vesication, suggesting that other mechanisms must be operative and that there is a multistep, biochemical process that leads to a final lesion.

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

Sulfur mustard (SM), a chemical warfare agent first used early in the 20th century, has re-emerged in the past decade as a major threat around the world. At present, there are no effective therapeutic measures for SM exposure. Because the skin as well as other interface epithelial surfaces are the first tissues effected as this agent is absorbed, reactions within the skin are an area of active research into the mechanism of action of this alkylating agent. The euthymic hairless guinea pig has been used as the animal model for the study of SM induced injuries because of morphologic similarity of its skin to human skin, with a multiple layer epidermis, and because this animal has a normal immune system. We reviewed 102 biopsy specimens from 51 animals exposed to three different dose times of saturated SM vapor. Histopathologic evidence exists for increased programmed cell death as well as cellular necrosis, subepidermal blister formation, and delayed re-epithelialization secondary to problems with adhesion. Information obtained from this study adds to the body of information important in the investigation of the mechanisms of action of SM.

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

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

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

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

Reduction of erythema in hairless guinea pigs after cutaneous sulfur mustard vapor exposure by pretreatment with niacinamide, promethazine and indomethacin

Erythema is the initial symptom that occurs after sulfur mustard (HD) cutaneous exposure. The time course of HD-induced erythema is similar to that observed after UV irradiation, which can be reduced by indomethacin. Sulfur mustard lethality is decreased by using promethazine, which is an antihistamine. Niacinamide can reduce microvesication after HD vapor exposure in hairless guinea pig (HGP) skin. The present study examines the effect of the combined administration of niacinamide, indomethacin and promethazine used alone or in all possible combinations on the degree of erythema and histopathologic skin damage after HD exposure in HGP. Niacinamide (750 mg kg-1, i.p.), promethazine (12.5 mg kg-1, i.m.) or indomethacin (4 mg kg-1, p.o.) used singly or in combination was given as a 30-min pretreatment before an 8-min HD vapor cup skin exposure. Using a combination pretreatment of niacinamide, promethazine and indomethacin, erythema was reduced at 4 (91%) and 6 (55%) h, but not 24 h after HD. The incidence of histopathological skin changes (microvesicles, follicular involvement, epidermal necrosis, intracellular edema and pustular epidermatitis) 24 h after HD was not reduced. This study indicates that HD-induced erythema may result from several different mechanisms, including inflammation, histamine release and DNA damage. It is suggested that two phases of inflammation may occur: an early phase sensitive to antihistamines and non-steroidal antiinflammatory drugs and a late phase of extensive cell damage that was not sensitive to these drug pretreatments.

Failure to observe a relationship between bis-(beta-chloroethyl)sulfide-induced NAD depletion and cytotoxicity in the rat keratinocyte culture

It has been proposed that the activation of poly(ADP-ribose) polymerase (Papirmeister et al., 1985), which results from the presence of strand breaks in bis-(beta-chloroethyl)sulfide (BCES) damaged DNA, causes depletion in the level of nicotinamide adenine dinucleotide (NAD) leading to cell death. This hypothesis has now been evaluated in the primary submerged culture of rat keratinocytes. The DNA content, the viable cell number, and the proliferative capability (measured by thymidine incorporation) of the culture were all reduced 48 h after exposure to 10 microM BCES. However, the total NAD level, that is, NAD+ plus NADH, was not changed at a dose of BCES lower than 50 microM. This observation was the same in both proliferating and early differentiating cultures. To further test this hypothesis, the modifying effect of inhibiting poly(ADP-ribose) polymerase on cytotoxicity in BCES-exposed cells was investigated. After exposure to 250 microM BCES, the NAD level was reduced to approximately 26 pmol/micrograms DNA. This value was increased to 34-49 pmol/micrograms DNA at both 24 and 48 h postexposure when the cultures were incubated in medium supplemented with 1-10 mM nicotinamide. Nevertheless, the decrease in the DNA content of the culture was not reversed. These results suggest that in the rat keratinocyte culture exposed to BCES, depletion of NAD is not a prerequisite for cell death.

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

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

Early cytotoxic effects induced by bis-chloroethyl sulphide (sulphur mustard): [Ca2+]i rise and time-dependent inhibition of B77 fibroblast serum response

Early cytotoxic events were studied on B77 fibroblasts. Cells were treated with sulphur mustard (SM) in short-term experiments in which cell viability was unchanged, as evaluated by the neutral red cytotoxicity test. This treatment was correlated to two early signs of cytotoxicity. The intracellular Ca2+ concentration [Ca2+]i level in SM-treated Fura-2-loaded fibroblasts showed a significant dose-dependent increase. This observed rise was sustained, in contrast to the Ca2+ signal induced by serum, and was already visible 5-10 min after the addition of SM to cell suspensions in vitro. Modification of the extracellular Ca2+ concentration in the medium had no effect on the cytosolic calcium rise caused by SM, suggesting release from intracellular Ca2+ pools. Furthermore, a time-dependent inhibition of the [Ca2+]i transient increase induced by growth-factors (as evaluated by the fetal calf serum (FCS) response) was observed within the first hour of exposure. These latter results suggest that early alterations of calcium distribution induced by SM could be one of the earliest markers of SM intoxication.

Effects of specific inhibitors of cellular functions on sulfur mustard-induced cell death

This study was conducted to determine whether inhibitors of normal cellular functions can reduce cytotoxicity induced by sulfur mustard (HD). The compounds examined include inhibitors of poly(ADP-ribose) polymerase (PADPRP), inhibitors of mono(ADP-ribose) transferase (MADPRT), inhibitors of lipid peroxidation, and an inhibitor of protein synthesis. To determine the effects of these compounds on HD-induced cell death, human lymphocyte preparations were treated with known concentrations (0.1 microM to 1000 microM) of an inhibitor and exposed to an estimated 87% effect concentration (EC87) of HD (170 microM) for loss in cell viability. Cell viability was determined at 24-26 hr post-exposure to HD using a dye (propidium iodide) exclusion assay and a flow cytometer. All of the selected PADPRP inhibitors were found to be effective at reducing the cytotoxic effects of HD. These inhibitors were rank-ordered based on the concentration that gives 50% (EC50) reduction of HD-induced cell death. A significant correlation (r = 0.94) was observed between the compounds' ability to inhibit PADPRP and the compounds' ability to reduce HD- induced cell death, suggesting that PADPRP plays a role in HD-induced cell death. Inhibitors of MADPRT, lipid peroxidation, and protein synthesis were not effective at reducing HD-induced cell death.

Sulfur mustard-induced microvesication in hairless guinea pigs: effect of short-term niacinamide administration

It has been postulated that sulfur mustard (HD) damage may activate poly(ADP-ribose) polymerase (PADPRP), resulting in depletion of cellular NAD+. This biochemical alteration is postulated to result in blister (vesicle) formation. It has been previously demonstrated that niacinamide (NAM), an inhibitor of PADPRP and a precursor for NAD+ synthesis, may be useful as a pretreatment compound to reduce HD-induced microvesication. The present study was undertaken to determine whether niacinamide's protective action could be extended beyond 24 hr and if the degree of microvesication is related to changes in skin NAD+ content. HD exposures were made by vapor cup to hairless guinea pigs. Niacinamide (750 mg/kg, ip) given as a 30-min pretreatment did not reduce the degree of microvesication 72 hr after HD compared to saline controls. However, niacinamide given as a 30-min pretreatment and at 6-, 24-, and 48-hr after HD, exhibited a 28% reduction in microvesication 72 hr after HD. Skin NAD+ content at 72 hr after HD was depleted by approximately 53% in the saline and NAM-treated groups. Skin NAD+ content was depleted despite NAM administration. Niacinamide did not reduce the degree of erythema at 48 or 72 hr. These results suggest that niacinamide's protective effect against HD-induced microvesication may be extended for at least 72 hr, but NAM levels must be sustained during the post-HD period. The link between maintenance of skin NAD+ and reductions in microvesication is still uncertain.

Mediators, initiating the inflammatory response, released in organ culture by full-thickness human skin explants exposed to the irritant, sulfur mustard

Mediators released from injured human skin that initiate the inflammatory response have not been adequately identified. Organ culture of full-thickness skin explants enables us to do so, because injury to the skin can be made in vitro, eliminating the rapid leakage of serum and infiltration of leukocytes that occur in vivo. In our studies, the military vesicant sulfur mustard (SM) (10 microliters of a 0.01 to 1.0% dilution) was topically applied to injure the epidermis of the explant. Then, the explants were cultured in small Petri dishes, usually for 18 h at 36 degrees C, and the organ-culture fluids were assayed for various inflammatory mediators. We found that the culture fluids from SM-exposed and control explants contained similar amounts of angiotensin-converting enzyme, trypsin-like and chymotrypsin-like proteases, acid phosphatase, beta-glucuronidase, beta-galactosidase, lysozyme, deoxyribonuclease, ribonuclease, interleukin 1, and lactic dehydrogenase. However, the culture fluids from SM-exposed explants contained increased amounts of histamine and plasminogen-activating activity, and often prostaglandin E2, when compared to culture fluids from control explants. After 3 to 4 d in culture, full-thickness human skin explants, when exposed to 0.2% SM (but not when exposed to 1.0% SM), sometimes showed separation of the epidermis and increased collagenase activity (i.e., hydroxyproline release). Thus, histamine (from local mast cells), and prostaglandin E2 and plasminogen-activating activity (probably from both mast cells and epidermal cells) are apparently involved in early mediation of the inflammatory response.