Effects of selected arginine analogues on sulphur mustard toxicity in human and hairless guinea pig skin keratinocytes

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.

Ophthalmic Complications and Managements of Sulfur Mustard Exposure: A Narrative Review

Sulfur mustard (SM) is a lethal chemical agent that affects many organs, particularly the eyes, respiratory system and skin. Even asymptomatic patients with documented SM vapor exposure may develop organ disorder many years later. Patients with even minor signs in the acute stage may experience late complications that necessitate surgery. Early decontamination and conservative measures could help the patients and decrease the complications. Despite decades of research, there is still no effective treatment for either acute or long-term SM-induced ocular complications. Even after multiple medications and surgical procedures, the majority of patients continue to have symptoms. For dry eye, punctual occlusion, autologous eye drops, and aggressive lubrication are used; for persistent epithelial defects (PED), tarsorrhaphy, amniotic membrane transplant, and stem cell transplantation are used; for total limbal stem cell deficiency (LSCD), living-related conjunctivolimbal allograft and keratolimbal allograft are used; for corneal vascularization, steroids, non-steroidal anti-inflammatory drugs, and anti-vascular endothelial growth factor prescribed; and for corneal opacities, corneal transplantation is done. Platelet rich plasma and topical drops containing stem cell transplantation for LSCD, photodynamic therapy paired with subconjunctival or topical anti-vascular endothelial growth factors for corneal vascularization, topical curcumin and topical ciclosporin-A for dry eye, and orbital fat-derived stem cells for PED are all alternative treatments that can be suggested. Despite the experimental and clinical research on the complications of SM exposure over the past decades, there is still no effective treatment for eye complications. However, supportive medical and surgical management has been applied with relatively good outcome.

Lack of a role for creatine phosphate kinase in sulphur mustard-induced cytotoxicity

Several compounds involved in the creatine phosphate kinase (CPK) pathway were evaluated for their protective effects against the chemical warfare (CW) agent sulphur mustard (HD), in primary chick embryo neuron and first passage human skin keratinocyte cultures. High concentrations of both creatine and creatine phosphate were found to be protective under all culture conditions and increased the LC50 of HD in both culture systems up to ~250%. Little difference was observed in the protective activity of these compounds in undifferentiated versus differentiated neuronal culture, or in proliferating versus differentiating cultures of keratinocytes. The protective effect of these compounds was found to be strictly prophylactic in nature. Although a modest decline in HD half-life was measured in buffer containing creatine phosphate, this did not account for the protective effects of this compound. In contrast to historical literature reporting 90—100% HD-induced CPK inhibition of purified enzyme, less than 30% of CPK activity was found to be inhibited by HD in both human keratinocytes and in swine blood plasma. Incubation of keratinocyte cultures with creatine or creatine phosphate prior to HD exposure did not alter CPK activity, compared with HD-only treated cultures. Although high mM concentrations of both creatine and creatine phosphate exert significant protective effects against HD, these results do not support a role for CPK in its toxicity or in the development of medical countermeasures against this CW agent. Human & Experimental Toxicology (2007) 26, 891—897.

Attenuation of sulfur mustard toxicity by S-2(2-aminoethylamino)ethyl phenyl sulfide (DRDE-07) in mouse liver

Sulfur mustard (SM) (bis-(2-chloroethyl) sulfide) is a chemical warfare agent. Evaluation of toxicity and protective effect of DRDE-07 (S-2(2-aminoethylamino)ethyl phenyl sulfide) was studied in mouse liver after SM challenging. Female mice were given orally 0.2 LD(50) of DRDE-07 (249 mg/kg body weight) and exposed percutaneously with 1.0 LD(50) of SM (8.1 mg/kg body weight). Gene expression profiles were determined using global genome microarray analysis at 3 days post-exposure. DRDE-07 alone treated animal showed significant upregulation to metabolism of xenobiotics by cytochrome P450 pathways. Genes related to cell adhesion molecules (CAMs), were downregulated. DRDE-07 pretreated SM exposed animals showed upregulation of xenobiotic cytochrome P450 pathway genes. Antigen presenting, cell adhesion molecules, cytokine, cytokine receptor metabolism, fatty acid metabolism, glutathione metabolism, cell cycle signaling pathway genes showed downregulation. The present study showed that SM-induced toxicity in mouse liver was attenuated by the pretreatment with DRDE-07.

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.

Lipopolysaccharide induced protection against sulfur mustard cytotoxicity in RAW264.7 cells through generation of TNF-alpha

Sulfur mustard (HD), a very potent alkylating agent and lipopolysacchride (LPS), are both well characterized inflammatory factors. We have found that concomitant exposure of murine macrophage cells (RAW264.7) to LPS and HD induced protection against HD induced cytotoxicity. Both HD and LPS induce release of inflammatory markers in RAW264.7 cells. However, there are marked differences in the repertoire of inflammatory factors released by the two toxins: While exposure to HD, induced a dose-dependant death of these cells, no significant change in survival rate was observed following LPS (1-100 ng/ml) exposure. Additionally, LPS elicited a robust nitric oxide (NO) and TNF-alpha secretion whereas HD was practically ineffective. Both toxins increased PGE(2) secretion in a concentration dependent manner. Treatment of HD-exposed RAW264.7 cells with anti-inflammatory drugs such as dexamethazone (5 muM), voltaren (diclofenac) (8 muM) or doxycycline (5 muM), decreased the release of cytokines but had no effect on cell viability. Simultaneous application of LPS (100 ng/ml) and HD (20-100 muM) resulted in an amelioration of HD cytotoxicity. Adding the NO generator S-nitrosoglutathione (GSNO) or inhibiting NO production using L-N(G)-monomethyl Arginine, had no effect on cell viability. Moreover, addition of PGE(2) (20 ng/ml) failed to induce any changes in cell viability under basal or HD-induced toxicity. In contrast, TNF-alpha (20 ng/ml) provided remarkable protection against HD-induced cell death. These findings strongly suggest that LPS exerts its protective action against HD toxicity through the generation of TNF-alpha and may provide better understanding of the mechanism of cytoprotection.

Oxidants and antioxidants in sulfur mustard-induced injury

Sulfur mustard (SM) is a chemical weapon that targets the skin, eyes, and lung. It was first employed during World War I and it remains a significant military and civilian threat. As a bifunctional alkylating agent, SM reacts with a variety of macromolecules in target tissues including nucleic acids, proteins and lipids, as well as small molecular weight metabolites such as glutathione. By alkylating subcellular components, SM disrupts metabolism, a process that can lead to oxidative stress. Evidence for oxidative stress in tissues exposed to SM or its analogs include increased formation of reactive oxygen species, the presence of lipid peroxidation products and oxidized proteins, and increases in antioxidant enzymes such as superoxide dismutase, catalase, and glutathione-S-transferase. Inhibition of antioxidant enzymes including thioredoxin reductase by SM can also disrupt cellular redox homeostasis. Consistent with these findings, SM-induced toxicity has been shown to be reduced by antioxidants in both in vitro and in vivo models. These data indicate that drugs that target oxidative stress pathways may represent important candidates for reducing SM-induced tissue injury.

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

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

Comparative evaluation of some flavonoids and tocopherol acetate against the systemic toxicity induced by sulphur mustard

OBJECTIVE

To evaluate the protective value of quercetin, gossypin, Hippophae rhamnoides (HR) flavone and tocopherol acetate against the systemic toxicity of percutaneously administered sulphur mustard (SM) in mice.

MATERIALS AND METHODS

Quercetin, gossypin, HR flavone or tocopherol acetate (200 mg/kg, i.p.) were administered just before percutaneous administration of SM and protection against the SM lethality was evaluated. In another experiment quercetin, gossypin, HR flavone or tocopherol acetate were administered against 2 LD(50) SM. The animals were sacrificed seven days post SM administration and various biochemical parameters were estimated.

RESULTS

The protection against the lethality of SM was very good with the flavonoids (quercetin = 4.7 folds; gossypin = 6.7 folds and HR flavone = 5.6 folds), compared to no protection with tocopherol acetate (0.7 fold). SM (2 LD(50)) showed decrease in reduced and oxidised glutathione (GSH and GSSG) levels, and an increase in malondialdehyde level (MDA). Oxidative stress enzymes like glutathione peroxidase, glutathione reductase and superoxide dismutase were significantly decreased. The total antioxidant status was also significantly decreased. Additionally, there was a significant increase in red blood corpuscles and hemoglobin content. All the flavonoids significantly protected the GSH, GSSG and MDA, and also the hematological variables. Tocopherol acetate failed to offer any protection in those parameters. Gossypin protected glutathione peroxidase, while HR flavone protected both glutathione reductase and glutathione peroxidase significantly. The decrease in body weight induced by SM and the histological lesions in liver and spleen were also significantly protected by the flavonoids but not by tocopherol acetate.

CONCLUSION

The present study supports that SM induces oxidative stress and flavonoids are promising cytoprotectants against this toxic effect.

Evaluation of analogues of DRDE-07 as prophylactic agents against the lethality and toxicity of sulfur mustard administered through percutaneous route

Sulfur mustard (SM), chemically bis (2-chloroethyl) sulfide is a bifunctional alkylating agent that causes serious blisters on contact with human skin. Although several antidotes have been reported for the systemic toxicity of SM in experimental animals none of them are approved so far and decontamination of SM immediately by physical or chemical means is recommended as the best protection. Two compounds amifostine [S-2(3-aminopropylamino) ethyl phosphorothioate] and DRDE-07 [S-2(2-aminoethylamino) ethyl phenyl sulfide] gave very good protection as an oral prophylactic agent against SM the in mouse model, but in the rat model the protection was only moderate. In the search for more effective and less toxic compounds, a number of analogues of DRDE-07 were synthesised and their protective efficacy was evaluated in mouse and rat models. The LD50 of S-aryl substitution was between 1 and 2 g kg(-1) and S-alkyl substitution was more than 2 g kg(-1). In the mouse model, DRDE-07, DRDE-10, DRDE-21, DRDE-30 and DRDE-35 gave about 20 fold protection, and DRDE-23 and DRDE-38 gave less protection of 4.8 and 9.0 fold respectively, against percutaneously administered SM. In the rat model, DRDE-07, DRDE-09, DRDE-10 and DRDE-21 gave about two fold protection. Percutaneously administered SM (19.33 mg kg(-1)) significantly depleted the hepatic GSH content in mice. Pretreatment with DRDE-21 significantly elevated the levels. A 4.4 fold increase in % DNA fragmentation was observed 7 days after SM administration (19.33 mg kg(-1)) in mice. Pretreatment with DRDE-07, DRDE-09, DRDE-10, DRDE-21, DRDE-30 and DRDE-35 significantly protected the mice from SM induced DNA damage. The histopathological lesions in liver and spleen induced by percutaneously administered SM was reduced by pretreatment with DRDE-07, DRDE-09, DRDE-10 and DRDE-21. These analogues may prove as prototypes for the designing of more effective prophylactic drug for SM.

Therapeutic effects of hypothermia on Lewisite toxicity

The cytotoxicity of the arsenical vesicant Lewisite was assessed in first passage cultures of proliferating neonatal human skin keratinocytes. Both munitions grade and distilled Lewisite were extremely toxic with LC(50) values in the low ng/ml range, with no significant differences between them. This similarity in toxicity was also mirrored with respect to their toxic effects on hairless guinea pig skin. Two-, 4- and 6-min vapour exposures of these agents resulted in similar and severe skin injury that was obvious by 3-5h post-exposure and almost maximal at 24h. The toxicity of Lewisite in culture was temperature dependent, with a >10-fold reduction in 24h LC(50) values as the incubation temperature was reduced from 37 to 25 degrees C. However, this cooling induced protection was not persistent. In contrast, cooling of Lewisite exposed hairless guinea pig skin at approximately 10 degrees C for as little as 30 min post-exposure resulted in dramatic and permanent protection, with 4h of cooling almost completely eliminating Lewisite induced skin injury. Further, significant protection was also evident even when cooling was delayed for as long as 2h post-Lewisite exposure. In an effort to investigate whether cooling might also increase the window in which chelation therapy against this vesicant agent would be useful, we examined the protective effects of the heavy metal chelator dimercaptosuccinic acid (DMSA). Topical application to Lewisite exposed skin was extremely protective, even when delayed for 2h after Lewisite. Cooling of Lewisite exposed skin for 2h, followed by DMSA topical application resulted in decreased skin injury compared to either treatment in isolation. It appears that the simple and non-invasive application of cooling measures may provide not only significant therapeutic relief to Lewisite exposed skin, but that it may also increase the therapeutic window in which medical countermeasures against this vesicant agent are useful.

Hypothermia reduces sulphur mustard toxicity

The effect of temperature on the development of sulphur mustard (HD)-induced toxicity was investigated in first passage cultures of human skin keratinocytes and on hairless guinea pig skin. When cells exposed to HD were incubated at 37 degrees C, a concentration-dependent decline in viability was observed that was maximal by 2 days. In contrast, no significant HD-induced toxicity was evident up to 4 days posttreatment when the cells were incubated at 25 degrees C. However, these protective effects were lost by 24 h when the cells were switched back to 37 degrees C. The protective effects of hypothermia were also demonstrated when apoptotic endpoints were examined. The HD concentration-dependent induction of fragmented DNA (as quantitated using soluble DNA and the TUNEL reaction), morphology, and p53 expression were all significantly depressed when cell cultures were incubated at 25 degrees C compared to 37 degrees C. When animals were exposed to HD vapour for 2, 4, and 6 min and left at room temperature, lesions were produced whose severity was dependent on exposure time and that were maximal by 72 h posttreatment. Moderate cooling (5-10 degrees C) of HD exposure sites posttreatment (4-6 h) significantly reduced the severity of the resultant lesions. However, in contrast to the in vitro results, these effects were permanent. It appears that the early and noninvasive act of cooling HD-exposed skin may provide a facile means of reducing the severity of HD-induced cutaneous lesions.

Protective effect of topical iodine preparations upon heat-induced and hydrofluoric acid-induced skin lesions

In this study, the protective prophylactic and post-exposure effects of novel topical iodine preparations were demonstrated upon heat- and hydrofluoric acid-induced skin lesions in the haired guinea pig. Prophylactic treatment of thermal bums with a liquid iodine preparation resulted in statistically significant reductions of 39% and 30%, respectively, in acute inflammation and hemorrhage-microscopic dermal parameters indicative of acute tissue damage. A clear trend of iodine-induced reduction in dermal necrosis occurred, and the epidermal healing markers, acanthosis and hyperkeratosis, were increased. Postexposure treatment of thermal burns with an iodine ointment preparation immediately after occurrence also conferred significant therapeutic reduction in parameters of tissue damage such as epidermal ulceration (87%), acute inflammation (58%), and hemorrhage (30%). Gross pathological evaluation showed that prophylactic and postexposure treatments with the liquid iodine preparation significantly reduced the heat-induced ulceration area by 97% and 65%, respectively. In addition, immediate treatment with an ointment iodine formulation significantly decreased the ulceration area by 98%; its tetraglycol vehicle also had a beneficial effect. Postexposure treatment with the iodine ointment proved efficacious upon hydrofluoric acid-induced skin burns. We observed statistically significant reductions of 76% and 68% in ulceration areas at intervals of 5 and 10 minutes between exposure and treatment, whereas a weaker effect was observed at a longer time interval of 15 minutes. Our findings suggest the therapeutic usage of these newly developed iodine preparations for thermally induced and hydrofluoric acid-induced skin burns.

Protective effects of amifostine and its analogues on sulfur mustard toxicity in vitro and in vivo

Sulfur mustard (bis(2-chloroethyl)sulfide, SM) is a highly reactive bifunctional alkylating agent that forms sulfonium ions in the body. SM alkylates DNA, leading to DNA strand breaks and cell death in a variety of cell types and tissues. Although several approaches have been proposed to challenge the toxic action(s) of SM, no satisfactory treatment regimen has evolved. The synthetic aminothiol amifostine, earlier known as WR-2721 (S-2-(3-aminopropylamino)ethyl phosphorothioate), has been extensively used as a chemical radioprotector for the normal tissues in cancer radiotherapy and chemotherapy. SM is known as a radiomimetic agent and this prompted us to evaluate the protective efficacy of amifostine (2.5 mM) and three of its analogues, DRDE-06 (S-2 (3-aminopropylamino) ethyl phenyl sulfide), DRDE-07 (S-2 (2-aminoethylamino) ethyl phenyl sulfide), and DRDE-08 (S-2 (4-aminobutylamino) ethyl phenyl sulfide), against SM toxicity in rat liver slices. Of the four agents tested, a 30-min pretreatment of amifostine and DRDE-07 enhanced the LC50 (a concentration producing 50% leakage of lactate dehydrogenase (LDH) or alanine aminotransferase (ALT)) of SM by 5.9- and 3.3-fold for LDH and 10.2- and 5.5-fold for ALT, respectively. Except DNA fragmentation, both these agents significantly attenuated the loss of intracellular K(+) and mitochondrial integrity (MTT assay), depletion of GSH levels, and histopathology produced by a toxic concentration (80 microM) of SM. However, when amifostine and DRDE-07 were introduced 2 h after SM, no significant protection was observed. SM (77.5 or 155 mg/kg) was also applied dermally on female albino mice and challenged by 0.20 LD50 (po) of amifostine, DRDE-06, DRDE-07, or DRDE-08 at -30 min, 0 min, or +6 h. Protection was observed only when the agents were administered at -30 min or 0 min; posttreatment (+6 h) did not offer any protection. The magnitude of in vivo protection was in the following order: DRDE-07 >or= amifostine > DRDE-08 > DRDE-06. Gas chromatographic analysis showed that there was no direct chemical interaction between SM and the antidotes. The po LD50s of amifostine, DRDE-06, DRDE-07, and DRDE-08 were 1049, 1345, 1248, and 951 mg/kg, respectively. Both in vitro and in vivo data indicate promising roles of amifostine and DRDE-07 as prophylactic agents against SM poisoning.

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.