pH-dependent toxicity of sulphur mustard in vitro

N-Acetylcysteine as a treatment for sulphur mustard poisoning

In the long and intensive search for effective treatments to counteract the toxicity of the chemical warfare (CW) agent sulphur mustard (H; bis(2-chloroethyl) sulphide), the most auspicious and consistent results have been obtained with the drug N-acetylcysteine (NAC), particularly with respect to its therapeutic use against the effects of inhaled H. It is a synthetic cysteine derivative that has been used in a wide variety of clinical applications for decades and a wealth of information exists on its safety and protective properties against a broad range of toxicants and disease states. Its primary mechanism of action is as a pro-drug for the synthesis of the antioxidant glutathione (GSH), particularly in those circumstances where oxidative stress has exhausted intracellular GSH stores. It impacts a number of pathways either directly or through its GSH-related antioxidant and anti-inflammatory properties, which make it a prime candidate as a potential treatment for the wide range of deleterious cellular effects that H is acknowledged to cause in exposed individuals. This report reviews the available literature on the protection afforded by NAC against the toxicity of H in a variety of model systems, including its efficacy in treating the long-term chronic lung effects of H that have been demonstrated in Iranian veterans exposed during the Iran-Iraq War (1980-1988). Although there is overwhelming evidence supporting this drug as a potential medical countermeasure against this CW agent, there is a requirement for carefully controlled clinical trials to determine the safety, efficacy and optimal NAC dosage regimens for the treatment of inhaled H.

Effect of sulfur mustard on melanogenesis in vitro

The chemical warfare agent sulfur mustard (SM) affects all cells in the epidermis including melanocytes which are responsible for melanin synthesis. After exposure to SM, pigment abnormalities like hypo- and hyperpigmentation can occur. The underlying molecular pathomechanisms of SM exposure on human melanogenesis have not been elucidated so far. In our study, we investigated the effect of SM on human melanocytes and melanogenesis. Normal human epidermal melanocytes (NHEM) were used as in vitro model and they were exposed to different concentrations of SM (4.5 μM-100 μM). Melanin production was analyzed by absorption measurements at 405 nm. In addition, quantitative real-time PCR (qPCR) and Western blot experiments were performed to determine the expression of essential melanogenesis-related proteins including tyrosinase (TYR), tyrosinase-related protein (TRP) 1 and 2 and microphthalmia transcription factor (MITF). Our findings demonstrated that exposure to low SM concentrations increased melanin synthesis accompanied with an increase in protein expression. In contrast, high SM concentrations led to decreased melanin content and a downregulation in expression of all investigated melanogenesis-associated proteins. We concluded that low SM concentrations may cause hyperpigmentation while high SM concentrations decreased melanin content which may explain hypopigmented skin areas in SM exposed patients.

Sulfur mustard skin lesions: A systematic review on pathomechanisms, treatment options and future research directions

Sulfur mustard (SM) is a chemical warfare, which has been used for one hundred years. However, its exact pathomechanisms are still incompletely understood and there is no specific therapy available so far. In this systematic review, studies published between January 2000 and July 2017 involving pathomechanisms and experimental treatments of SM-induced skin lesions were analyzed to summarize current knowledge on SM pathology, to provide an overview on novel treatment options, and to identify promising targets for future research to more effectively counter SM effects. We suggest that future studies should focus on (I) systemic effects of SM intoxication due to its distribution throughout the body, (II) removal of SM depots that continuously release active compound contributing to chronic skin damage, and (III) therapeutic options that counteract the pleiotropic effects of SM.

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.

Biological and molecular mechanisms of sulfur mustard analogue-induced toxicity in JB6 and HaCaT cells: possible role of ataxia telangiectasia-mutated/ataxia telangiectasia-Rad3-related cell cycle checkpoint pathway

Effective medical treatment and preventive measures for chemical warfare agent sulfur mustard (HD)-caused incapacitating skin toxicity are lacking, because of limited knowledge of its mechanism of action. The proliferating basal epidermal cells are primary major sites of attack during HD-caused skin injury. Therefore, employing mouse JB6 and human HaCaT epidermal cells, here, we investigated the molecular mechanism of HD analogue 2-chloroethyl ethyl sulfide (CEES)-induced skin cytotoxicity. As compared to the control, up to 1 mM CEES treatment of these cells for 2, 4, and 24 h caused dose-dependent decreases in cell viability and proliferation as measured by DNA synthesis, together with S and G2-M phase arrest in cell cycle progression. Mechanistic studies showed phosphorylation of DNA damage sensors and checkpoint kinases, ataxia telangiectasia-mutated (ATM) at ser1981 and ataxia telangiectasia-Rad3-related (ATR) at ser428 within 30 min of CEES exposure, and modulation of S and G2-M phase-associated cell cycle regulatory proteins, which are downstream targets of ATM and ATR kinases. Hoechst-propidium iodide staining demonstrated that CEES-induced cell death was both necrotic and apoptotic in nature, and the latter was induced at 4 and 24 h of CEES treatment in HaCaT and JB6 cells, respectively. An increase in caspase-3 activity and both caspase-3 and poly(ADP-ribose)polymerase (PARP) cleavage coinciding with CEES-caused apoptosis in both cell lines suggested the involvement of the caspase pathway. Together, our findings suggest a DNA-damaging effect of CEES that activates ATM/ATR cell cycle checkpoint signaling as well as caspase-PARP pathways, leading to cell cycle arrest and apoptosis/necrosis in both JB6 and HaCaT cells. The identified molecular targets, quantitative biomarkers, and epidermal cell models in this study have the potential and usefulness in rapid development of effective prophylactic and therapeutic interventions against HD-induced skin toxicity.

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.

Ionic dependence of sulphur mustard cytotoxicity

The effect of ionic environment on sulphur mustard (bis 2-chloroethyl sulphide; HD) toxicity was examined in CHO-K1 cells. Cultures were treated with HD in different ionic environments at constant osmolar conditions (320 mOsM, pH 7.4). The cultures were refed with fresh culture medium 1h after HD exposure, and viability was assessed. Little toxicity was apparent when HD exposures were carried out in ion-free sucrose buffer compared to LC(50) values of approximately 100-150 microM when the cultures were treated with HD in culture medium. Addition of NaCl to the buffer increased HD toxicity in a salt concentration-dependent manner to values similar to those obtained in culture medium. HD toxicity was dependent on both cationic and anionic species with anionic environment playing a much larger role in determining toxicity. Substitution of NaI for NaCl in the treatment buffers increased HD toxicity by over 1000%. The activity of the sodium hydrogen exchanger (NHE) in recovering from cytosolic acidification in salt-free and in different chloride salts did not correlate with the HD-induced toxicity in these buffers. However, the inhibition by HD of intracellular pH regulation correlated with its toxicity in NaCl, NaI and sucrose buffers. Analytical chemical studies and the toxicity of the iodine mustard derivative ruled out the role of chemical reactions yielding differentially toxic species as being responsible for the differences in HD toxicity observed. This work demonstrates that the early events that HD sets into motion to cause toxicity are dependent on ionic environment, possibly due to intracellular pH deregulation.