l-thiocitrulline: A potent protective agent against the toxicity of sulphur mustard in vitro

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.

Treatment for sulfur mustard lung injuries; new therapeutic approaches from acute to chronic phase

Objective

Sulfur mustard (SM) is one of the major potent chemical warfare and attractive weapons for terrorists. It has caused deaths to hundreds of thousands of victims in World War I and more recently during the Iran-Iraq war (1980–1988). It has ability to develop severe acute and chronic damage to the respiratory tract, eyes and skin. Understanding the acute and chronic biologic consequences of SM exposure may be quite essential for developing efficient prophylactic/therapeutic measures. One of the systems majorly affected by SM is the respiratory tract that numerous clinical studies have detailed processes of injury, diagnosis and treatments of lung. The low mortality rate has been contributed to high prevalence of victims and high lifetime morbidity burden. However, there are no curative modalities available in such patients. In this review, we collected and discussed the related articles on the preventive and therapeutic approaches to SM-induced respiratory injury and summarized what is currently known about the management and therapeutic strategies of acute and long-term consequences of SM lung injuries.

Method

This review was done by reviewing all papers found by searching following key words sulfur mustard; lung; chronic; acute; COPD; treatment.

Results

Mustard lung has an ongoing pathological process and is active disorder even years after exposure to SM. Different drug classes have been studied, nevertheless there are no curative modalities for mustard lung.

Conclusion

Complementary studies on one hand regarding pharmacokinetic of drugs and molecular investigations are mandatory to obtain more effective treatments.

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.

Melatonin alleviates lung damage induced by the chemical warfare agent nitrogen mustard

The cytotoxic mechanism of mustards has not been fully elucidated; recently, we reported that reactive oxygen species, nitric oxide [produced by inducible nitric oxide synthase (iNOS)] and peroxynitrite are involved in the pathogenesis and responsible for mustard-induced toxicity. Melatonin, a potent antioxidant molecule, acts as an iNOS inhibitor and a peroxynitrite scavenger. Using the prototypic nitrogen mustard (mechlorethamine/HN2) as a model and based on its known cytotoxic mechanisms, the present study was performed to test melatonin for its capability in protecting the lungs of injured male Wistar rats. Lung mustard toxicity was induced via an intratracheally injection of HN2 (0.5mg/kg) dissolved in saline (100microl). Control animals were injected the same amount of saline only. Melatonin was administered intraperitoneally with two different doses (20mg/kg or 40mg/kg) beginning 1h before HN2 application and continued every 12h for six replications. Forty-eight hours after the last melatonin injection, the animals were sacrificed and their lungs were taken for further assay, i.e., malondialdehyde (MDA) levels, and superoxide dismutase (SOD), glutathione peroxidase (GPx) and iNOS activity. Additionally their urine was collected for nitrite-nitrate (NO(x)) analysis. HN2 injection caused increased iNOS activity and MDA levels in lung tissue and NO(x) values in urine; lung GPx activity was significantly depressed. Melatonin restored all of these oxidative and nitrosative stress markers in a dose-dependent manner. In conclusion, the results of study provide evidence that melatonin may have the ability to reduce mustard-induced toxicity in the lungs.

pH-dependent toxicity of sulphur mustard in vitro

The dependence of sulphur mustard (HD) toxicity on intracellular (pH(i)) and extracellular pH was examined in CHO-K1 cells. HD produced an immediate and significant concentration-dependent decline in cytosolic pH, and also inhibited the mechanisms responsible for restoring pH(i) to physiological values. The concentration-response of HD-induced cytosolic acidification, closely paralleled the acidification of the extracellular buffer through HD hydrolysis. A viability study was carried out in order to assess the importance of HD-induced cytosolic acidification. Cultures were exposed to HD for 1 h in media that were adjusted through a pH range (pH 5.0-10), and the 24 h LC(50) values were assessed using the viability indicator dye alamarBlue. The toxicity of HD was found to be dependent on extracellular pH, with a greater than eight-fold increase in LD(50) obtained in cultures treated with HD at pH 9.5, compared to those treated at pH 5.0. Assays of apoptotic cell death, including morphology, soluble DNA, caspase-3 activity and TUNEL also showed that as pH was increased, much greater HD concentrations were required to cause cell death. The modest decline in HD half-life measured in buffers of increasing pH, did not account for the protective effects of basic pH. The early event(s) that HD initiates to eventually culminate in cell death are not known. However, based on the data obtained in this study, we propose that HD causes an extracellular acidification through chemical hydrolysis and that this, in both a concentration and temporally related fashion, results in cytosolic acidification. Furthermore, HD also acts to poison the antiporter systems responsible for maintaining physiological pH(i), so that the cells are unable to recover from this insult. It is this irreversible decline in pH(i) that initiates the cascade of events that results in HD-induced cell death.

Novel S-Substituted Aminoalkylamino Ethanethiols as Potential Antidotes against Sulfur Mustard Toxicity

Sulfur mustard (SM) is a highly toxic chemical warfare agent. A satisfactory treatment regimen is not yet available for this toxicant. In a search for an effective antidote against SM, a series of novel S-2(omega-aminoalkylamino)ethyl alkyl/aryl thioethers [H(2)N(CH(2))(n)()NHCH(2)CH(2)SR], where R = alky, alicyclic, aryl, and heterocyclic substituents, have been designed and synthesized as candidate antidotes against SM toxicity. These compounds were screened for their protective efficacy through the oral route against dermally applied sulfur mustard in female mice measured on the basis of percent survival following percutaneous administration of SM. A number of compounds demonstrated significant protection.

The Role of the Clinical Laboratory in Managing Chemical or Biological Terrorism

Background: Domestic and international acts of terrorism using chemicals and pathogens as weapons have recently attracted much attention because of several hoaxes and real incidents. Clinical laboratories, especially those affiliated with major trauma centers, should be prepared to respond rapidly by providing diagnostic tests for the detection and identification of specific agents, so that specific therapy and victim management can be initiated in a timely manner. As first-line responders, clinical laboratory personnel should become familiar with the various chemical or biological agents and be active participants in their local defense programs.

Approach: We review the selected agents previously considered or used in chemical and biological warfare, outline their poisonous and pathogenic effects, describe techniques used in their identification, address some of the logistical and technical difficulties in maintaining such tests in clinical laboratories, and comment on some of the analytical issues, such as specimen handling and personal protective equipment.

Content: The chemical agents discussed include nerve, blistering, and pulmonary agents and cyanides. Biological agents, including anthrax and smallpox, are also discussed as examples for organisms with potential use in bioterrorism. Available therapies for each agent are outlined to assist clinical laboratory personnel in making intelligent decisions regarding implementation of diagnostic tests as a part of a comprehensive defense program.

Summary: As the civilian medical community prepares for biological and chemical terrorist attacks, improvement in the capabilities of clinical laboratories is essential in supporting counterterrorism programs designed to respond to such attacks. Accurate assessment of resources in clinical laboratories is important because it will provide local authorities with an alternative resource for immediate diagnostic analysis. It is, therefore, recommended that clinical laboratories identify their current resources and the extent of support they can provide, and inform the authorities of their state of readiness.

DNA fragmentation pattern induced in thymocytes by sulphur mustard

Sulphur mustard (HD) is a blister agent for which no specific therapy exists. The mechanism of cell injury caused by HD is not well understood. This study examined DNA damage in thymocytes exposed to a range of HD concentrations over a time course of 1-24 h. Thymocytes incubated with HD showed an increase in the production of DNA fragments of the type frequently associated with apoptosis, namely, initial formation of large fragments of 30-50, 200-300 and > 700 kilobase pairs (kbp), followed by further degradation to produce an internucleosomal 'ladder' of oligomers of approximately 180 base pairs (bp). Pulsed field electrophoresis analysis of thymocytes incubated with HD detected breakdown of the chromatin up to 3 h before a corresponding increase in the low molecular weight (MW) oligonucleosomal fragments could be seen on conventional agarose gels. These results suggest that cells damaged by HD poisoning may be irretrievably committed to cell death sooner after exposure than previous studies suggested. The nature of the DNA fragments produced suggested that apoptosis may represent a component of the pathway of cell death induced by HD. These aspects may have implications for the search for specific therapeutic reagents effective in the prevention or treatment of HD poisoning.

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.