Toxicity of sulfur mustard in primary neuron culture

Evidence for the systemic diffusion of (2-chloroethyl)-ethyl-sulfide, a sulfur mustard analog, and its deleterious effects in brain

Sulfur mustard, a chemical warfare agent known to be a vesicant of skin, readily diffuses in the blood stream and reaches internal organs. In the present study, we used the analog (2-chloroethyl)-ethyl-sulfide (CEES) to provide novel data on the systemic diffusion of vesicants and on their ability to induce brain damage, which result in neurological disorders. SKH-1 hairless mice were topically exposed to CEES and sacrificed at different time until 14 days after exposure. A plasma metabolomics study showed a strong systemic impact following a self-protection mechanism to alleviate the injury of CEES exposure. This result was confirmed by the quantification of specific biomarkers in plasma. Those were the conjugates of CEES with glutathione (GSH-CEES), cysteine (Cys-CEES) and N-acetyl-cysteine (NAC-CEES), as well as the guanine adduct (N7Gua-CEES). In brain, N7Gua-CEES could be detected both in DNA and in organ extracts. Similarly, GSH-CEES, Cys-CEES and NAC-CEES were present in the extracts until day14. Altogether, these results, based on novel exposure markers, confirm the ability of vesicants to induce internal damage following dermal exposure. The observation of alkylation damage to glutathione and DNA in brain provides an additional mechanism to the neurological insult 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.

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

The toxicity of sulphur mustard (HD) was characterized in first passage cultures of human neonatal foreskin keratinocytes and then several arginine analogues were investigated to ascertain their efficacies in protecting against HD toxicity in this system. d- and l-nitroarginine methyl ester (d/l-NAME), l-phosphoarginine, and l-nitroarginine were all found to confer concentration-related protective effects against HD in confluent cultures. l-NAME was used to further characterize this protection and was only effective in cultures that were not actively proliferating. This compound was also found to be efficacious when added to the cultures up to several hours after HD exposure, although its continued presence was required in order for protection to be effective. The protective effects of l-thiocitrulline (l-TC) against HD toxicity were also assessed. This arginine analogue was extremely potent in preventing HD toxicity in actively proliferating, just-confluent, and postconfluent cultures in a concentration-dependent fashion (0.1-15 mM), with little HD toxicity apparent at high l-TC concentrations. Protection was prophylactic in nature, with l-TC having almost maximal effect when added to the cultures only 1 min prior to HD culture exposure. Efficacy then declined rapidly so that no protection was evident when l-TC was added 30 min post-HD. The effects of this drug were persistent, with no decrease in protective efficacy up to 4 days after HD exposure, even when l-TC was removed from the cultures. l-TC did not protect against the antimitotic effects of HD; while l-TC-protected cells were subcultured successfully, they displayed no clonogenic activity. Although l-TC is closely related structurally to protective nitroarginine derivatives, the characteristics of l-TC protection against HD were markedly different and suggest that they exert their protective activities at different sites. Administration of l-NAME and l-TC by a variety of routes did not result in consistent protection against topical vapor challenges of HD in hairless guinea pigs. However, both compounds were effective in preventing the toxicity of HD in primary cultures of hairless guinea pig skin keratinocytes, indicating that species differences were not likely to be responsible for the poor efficacy of these compounds in vivo.

Effect of lowered temperature on the toxicity of sulphur mustard in vitro and in vivo

Primary cultures of chick embryo neurons were exposed to sulphur mustard (HD) and L-nitroarginine methyl ester (L-NAME) and then incubated at either 25 or 37 degrees C. Lowering the temperature of the cultures decreased the 24-h toxicity of HD, but did not increase the efficacy of L-NAME protection. However, the length of time post-HD treatment in which L-NAME was maximally effective in protecting against HD toxicity was dramatically enhanced, out to 12 h after HD exposure. In addition, the persistence of L-NAME protection of the cells against HD was significantly lengthened. Tests conducted in human skin keratinocytes also showed that lowering the incubation temperature of actively proliferating, just-confluent or post-confluent cultures significantly and persistently decreased the cytotoxicity of HD. The persistence of L-NAME protection was increased in non-proliferating cells. Finally, cooling of HD-vapour exposed sites on hairless guinea pigs for 4.5 h decreased the severity of the resultant lesions out to 72 h post-exposure.

Synergistic protective effects of selected arginine analogues against sulphur mustard toxicity in neuron culture

Previous studies in this laboratory have shown that the arginine analogues L-thiocitrulline (L-TC) and L-nitroarginine methyl ester (L-NAME) have potent protective activity against sulphur mustard (HD) toxicity that was not related to their nitric oxide synthase inhibiting activities. Furthermore, their characteristics of action suggested that they act at different sites to exert their protection. L-TC acted rapidly (minutes of preincubation) and was equipotent in protecting either immature or mature cultures of chick embryo neurons against the toxicity of HD while L-NAME was only effective in mature cultures. Maximal protection occurred at mM drug concentrations and increased the LC50 of HD by approximately 200% (L-NAME) to approximately 800% (L-TC). L-NAME did not alter the efficacy of L-TC in immature cultures but increased the LC50 up to 1500% in mature cultures. Removal of L-NAME eliminated this synergism, leaving only the persistent protection of L-TC. L-Nitroarginine and d-NAME also increased the protective efficacy of L-TC in a concentration-related manner in mature cultures. The timing of drug administration before or after HD culture exposure was critical. Drug coadministration resulted in synergistic protection only when L-TC was added to the cultures prior to HD treatment. Thus, synergistic protective effects were also achieved when L-NAME was added up to 8 h after HD exposure, if they were pretreated with L-TC. Based on these findings, it is proposed that HD initiates its toxicity extremely rapidly through a cell surface-mediated event that can be blocked by L-TC. A signal is transduced into the cell that results in an additional event or lesion that manifests itself several hours downstream. This event/lesion progresses to cell death unless blocked reversibly by L-NAME.