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

Protective potential of different compounds and their combinations with MESNA against sulfur mustard-induced cytotoxicity and genotoxicity

The purpose of this study was to evaluate the efficacy of potential candidate molecules or their combinations against strong alkylation agent sulfur mustard (SM) on the human lung alveolar epithelial cell line A-549. Candidate molecules were chosen on the basis of their previously observed protective effects in vitro. The tested compounds, including antioxidants, sulfhydryl or other sulfur-containing molecules, nitrogen-containing molecules, PARP inhibitors and a NO synthase inhibitor, were applicated 30min before SM treatment. The efficiency of candidate molecules to protect cells against DNA damage and cell death induced by SM was determined using single-cell gel electrophoresis (comet assay) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction by viable cells. The damage of DNA was assessed 1 and 24h after dose 50μM SM. Cell survival was assessed 24 and 72h after the exposure. To achieve maximal cytoprotection, combinations of selected compounds with sodium 2-mercaptoethane sulphonate (MESNA) were tested. We found significant protective effects by several drugs used individually and also in combination with MESNA. High protection was achieved by sodium thiosulphate, which was further potentiated when combined with MESNA. Most of the selected compounds or mixture provided only moderate genoptotection without having any effect towards cell viability.

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.

Free radical production from the interaction of 2-chloroethyl vesicants (mustard gas) with pyridine nucleotide-driven flavoprotein electron transport systems

The biochemical sequelae to chloroethyl mustard exposure correspond very well to toxic processes initiated by free radicals. Additionally, mustard solutions contain spontaneously formed cyclic onium ions which produce carbon free radicals when reduced electrochemically. Therefore, we hypothesized that the onium ions of sulfur or nitrogen mustards might produce carbon free radicals upon being reduced enzymatically, and that these radicals might constitute a metabolic activation. We set out to document radical production using an in vitro metabolic system and electron paramagnetic resonance (EPR). Our system consisted of NADPH, one of several pyridine nucleotide-driven flavoprotein reductases, cytochrome c as a terminal electron acceptor, various sulfur or nitrogen mustards and the spin trap alpha-[4-pyridyl-1-oxide]-N-tert-butylnitrone in buffer. Reactions were started by adding the reductase to the other materials, vortexing and immediately transferring the mixture to a 10 mm EPR flat cell. Repeated scans on a Bruker ESP 300E EPR spectrometer produced a triplet of doublets with hyperfine splitting constants of a(N)=15.483 G and a(H)=2.512 G. The outcome supported our hypothesis that carbon-centered free radicals are produced when mustard-related onium ions are enzymatically reduced. The EPR results varied little with the chloroethyl compound used or with porcine or human cytochrome P450 reductase, the reductase domain of rat brain neuronal nitric oxide synthase or rat liver thioredoxin reductase. Our results offer new insight into the basis for mustard-induced vesication and the outcome of exposure to different mustards. The free radical model provides an explanation for similarities in the lesions arising from mustard exposure and energy-based lesions such as those from heat, ultraviolet and nuclear radiation as well as damage across tissue types such as skin, eyes or airway epithelium.

Molecular targets against mustard toxicity: implication of cell surface receptors, peroxynitrite production, and PARP activation

Despite many years of research into chemical warfare agents, cytotoxic mechanisms induced by mustards are not well understood. Reactive oxygen and nitrogen species (ROS and RNS) are likely to be involved in chemical warfare agents induced toxicity. These species lead to lipid peroxidation, protein oxidation, and DNA injury, and trigger many pathophysiological processes that harm the organism. In this article, several steps of pathophysiological mechanisms and possible ways of protection against chemical warfare agents have been discussed. In summary, pathogenesis of mustard toxicity is explained by three steps: (1) mustard binds target cell surface receptor, (2) activates intracellular ROS and RNS leading to peroxynitrite (ONOO(-)) production, and (3) the increased ONOO(-) level damages organic molecules (lipids, proteins, and DNA) leading to poly(adenosine diphosphate-ribose) polymerase (PARP) activation. Therefore, protection against mustard toxicity could also be performed in these ways: (1) blocking of cell surface receptor, (2) inhibiting the ONOO(-) production or scavenging the ONOO(-) produced, and (3) inhibiting the PARP, activated by ONOO(-) and hydroxyl radical (OH(*)) induced DNA damage. As conclusion, to be really effective, treatment against mustards must take all molecular mechanisms of cytotoxicity into account. Combination of several individual potent agents, each blocking one of the toxic mechanisms induced by mustards, would be interesting. Therefore, variations of combination of cell membrane receptor blockers, antioxidants, nitric oxide synthase inhibitors, ONOO(-) scavengers, and PARP inhibitors should be investigated.

Effect of doxycycline on sulfur mustard-induced respiratory lesions in guinea pigs

Respiratory tract lesions induced by the chemical warfare agent sulfur mustard (SM) are characterized by epithelial damages associated with inflammatory cell infiltration. Here we evaluated the imbalance between gelatinase and tissue inhibitors of metalloproteinases (TIMPs), and we tested pretreatment with the protease inhibitor doxycycline. Guinea pigs were intoxicated intratracheally with SM and evaluated 24 h after exposure. Matrix metalloproteinase (MMP) gelatinase activity of bronchial lavage (BL) fluid from SM-exposed guinea pigs was high compared with controls, as shown by both zymography and biotinylated substrate degradation, whereas TIMP-1 and -2 levels by immunoblotting were similar. Extensive areas of lysis were evidenced by in situ zymography, indicating imbalance between gelatinases and inhibitors towards net proteolytic activity. Doxycycline pretreatment resulted in 1) decreased gelatinase activity (zymography, free gelatinase activity assay, and in situ zymography); 2) decreased inflammation (BL fluid cellularity and protein level); and 3) dramatic decrease in histological epithelial lesions. Our results suggest inadequate levels of TIMP to counteract increased gelatinase activity and further support a role for MMP gelatinases in SM-induced respiratory lesions. They also suggest that doxycycline may hold promise as a therapeutic tool.

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.

Sulphur mustard induced DNA damage in mice after dermal and inhalation exposure

Sulphur mustard (SM) is a chemical warfare agent of the blistering agent category for which there is still no effective therapy. SM, being a strong electrophile, readily reacts with a wide range of cellular macromolecules including DNA, RNA and protein. Since the main intoxication routes for SM are inhalation and dermal penetration, in the present study we have exposed female mice to different concentrations of SM by dermal and inhalation exposures and estimated the DNA damage in different organs viz., liver, lung, spleen and thymus. SM was applied at 38.7, 77.4, 154.7 mg/kg body weight, on the hair-clipped skin (dermal exposure) equivalent to 0.25, 0.5 and 1.0 of the LD50. Inhalation exposure was carried out at 10.6, 21.2 and 42.3 mg/m3 for 1 h duration equivalent to 0.25, 0.5 and 1.0 LC50. SM induced a dose-dependent DNA damage in all the organs except the lung in dermal exposure. Similarly the inhalation exposure resulted in dose- and time-dependent effect in all the organs including lung. By both routes of exposure liver was the most affected organ followed by spleen, thymus and lung in decreasing order. The quantitative data were corroborated by qualitative analysis of DNA on agarose gel electrophoresis. The genomic DNA analysis of the organs had revealed random nuclear DNA fragmentation resulting in a 'smear' typical of necrotic form of cell death. Since DNA damage is not reversible especially in liver, this can be used as a marker for SM exposure through either the dermal or inhalation route.