Clinical and experimental research progress on neurotoxicity of sulfur mustard and its possible mechanisms

The immune cells profiles of individuals with sulfur mustard-induced serious long-term respiratory complications

Sulfur mustard (SM) induced pulmonary disorder is a heterogeneous disease characterized by uncontrolled inflammatory immune responses. In this cross-sectional study carried out in Isfahan-Iran, our objective was to thoroughly evaluate the clinical health and peripheral blood leukocyte profiles of adult veterans exposed to SM 25-30 years. In total, 361 people were studied in two groups, 287 chemical veterans with pulmonary complications and 64 healthy individuals as a control group. The participants underwent a comprehensive lung evaluation, including physical examination, Pulmonary Assessment, and Spirometry Assessment. Blood samples were collected in EDTA-treated tubes and flow cytometry analysis was employed to study different population of leukocytes including lymphocytes, monocytes, and natural killer cells. In our results, SM-exposed patients showed a significant increase in mean WBC and lymphocyte absolute count. However, the frequency of CD14+ monocytes and CD3+ CD4+ CD25+Hi as regulatory T cell subsets significantly decreased in SM-exposed patients. In addition, there was a negative correlation between CD45+ CD14+ cells and residual volume (RV). The population of NK cells showed a negative correlation with forced expiratory volume in the first one second to the forced vital capacity (FEV1/FVC). On the other hand, the percentage of CD19+ B cells positively correlated with Mid-maximum expiratory flow (MMEF) rate, ppm Reading, Carboxyhemoglobin (CoHb), and FEV1, and it was negatively correlated with airway resistance (RAW). Evaluation of CD3+ CD8+ cytotoxic T cells frequency negatively correlated with CoHb, ppm Reading, total lung capacity (TLC), and RV. Furthermore, the count of CD3+ CD4+ T cells demonstrated a negative correlation with TLC. The percentage of CD3+ CD4+ CD25+ cells was positively correlated with ppm reading and CoHb. Overall, our findings revealed modifications in total lymphocyte dynamics and a decrease in the percentage and absolute number of regulatory T cells, compromising the regulatory arm of the immune system to modulate SM-induced inflammatory damages.

Life-Cycle-Dependent Toxicities of Mono- and Bifunctional Alkylating Agents in the 3R-Compliant Model Organism C. elegans

Caenorhabditis elegans (C. elegans) is gaining recognition and importance as an organismic model for toxicity testing in line with the 3Rs principle (replace, reduce, refine). In this study, we explored the use of C. elegans to examine the toxicities of alkylating sulphur mustard analogues, specifically the monofunctional agent 2-chloroethyl-ethyl sulphide (CEES) and the bifunctional, crosslinking agent mechlorethamine (HN2). We exposed wild-type worms at different life cycle stages (from larvae L1 to adulthood day 10) to CEES or HN2 and scored their viability 24 h later. The susceptibility of C. elegans to CEES and HN2 paralleled that of human cells, with HN2 exhibiting higher toxicity than CEES, reflected in LC50 values in the high µM to low mM range. Importantly, the effects were dependent on the worms' developmental stage as well as organismic age: the highest susceptibility was observed in L1, whereas the lowest was observed in L4 worms. In adult worms, susceptibility to alkylating agents increased with advanced age, especially to HN2. To examine reproductive effects, L4 worms were exposed to CEES and HN2, and both the offspring and the percentage of unhatched eggs were assessed. Moreover, germline apoptosis was assessed by using ced-1p::GFP (MD701) worms. In contrast to concentrations that elicited low toxicities to L4 worms, CEES and HN2 were highly toxic to germline cells, manifesting as increased germline apoptosis as well as reduced offspring number and percentage of eggs hatched. Again, HN2 exhibited stronger effects than CEES. Compound specificity was also evident in toxicities to dopaminergic neurons-HN2 exposure affected expression of dopamine transporter DAT-1 (strain BY200) at lower concentrations than CEES, suggesting a higher neurotoxic effect. Mechanistically, nicotinamide adenine dinucleotide (NAD+) has been linked to mustard agent toxicities. Therefore, the NAD+-dependent system was investigated in the response to CEES and HN2 treatment. Overall NAD+ levels in worm extracts were revealed to be largely resistant to mustard exposure except for high concentrations, which lowered the NAD+ levels in L4 worms 24 h post-treatment. Interestingly, however, mutant worms lacking components of NAD+-dependent pathways involved in genome maintenance, namely pme-2, parg-2, and sirt-2.1 showed a higher and compound-specific susceptibility, indicating an active role of NAD+ in genotoxic stress response. In conclusion, the present results demonstrate that C. elegans represents an attractive model to study the toxicology of alkylating agents, which supports its use in mechanistic as well as intervention studies with major strength in the possibility to analyze toxicities at different life cycle stages.

Melatonin as Modulator for Sulfur and Nitrogen Mustard-Induced Inflammation, Oxidative Stress and DNA Damage: Molecular Therapeutics

Sulfur and nitrogen mustards, bis(2-chloroethyl)sulfide and tertiary bis(2-chloroethyl) amines, respectively, are vesicant warfare agents with alkylating activity. Moreover, oxidative/nitrosative stress, inflammatory response induction, metalloproteinases activation, DNA damage or calcium disruption are some of the toxicological mechanisms of sulfur and nitrogen mustard-induced injury that affects the cell integrity and function. In this review, we not only propose melatonin as a therapeutic option in order to counteract and modulate several pathways involved in physiopathological mechanisms activated after exposure to mustards, but also for the first time, we predict whether metabolites of melatonin, cyclic-3-hydroxymelatonin, N1-acetyl-N2-formyl-5-methoxykynuramine, and N1-acetyl-5-methoxykynuramine could be capable of exerting a scavenger action and neutralize the toxic damage induced by these blister agents. NLRP3 inflammasome is activated in response to a wide variety of infectious stimuli or cellular stressors, however, although the precise mechanisms leading to activation are not known, mustards are postulated as activators. In this regard, melatonin, through its anti-inflammatory action and NLRP3 inflammasome modulation could exert a protective effect in the pathophysiology and management of sulfur and nitrogen mustard-induced injury. The ability of melatonin to attenuate sulfur and nitrogen mustard-induced toxicity and its high safety profile make melatonin a suitable molecule to be a part of medical countermeasures against blister agents poisoning in the near future.