Mechanistic Insights of Sulfur Mustard-Induced Acute Tracheal Injury in Rats

Sulfur mustard triggers oxidative stress through glutathione depletion and altered expression of glutathione-related enzymes in human airways

CONTEXT

Sulfur mustard (SM) is a lipophilic and reactive chemical compound that targets human airway system.

OBJECTIVE

Glutathione (GSH) depletion, oxidative stress (OS) status, and changes in expression of GSH-dependent antioxidant enzymes were considered in human mustard lungs.

MATERIALS AND METHODS

Lung biopsies and bronchoalveolar lavage (BAL) were collected from non-exposed (n = 10) individuals and SM-exposed patients (n = 12). Alterations in expression of GSH-dependent enzymes were studied using RT² Profiler™ PCR array. OS was evaluated by determining BAL fluid levels of total antioxidant capacity (TAC), malondialdehyde (MDA), and GSH.

RESULTS

Mean TAC (0.142 ± 0.027 µmol/l) and GSH (4.98 ± 1.02 nmol/l) in BAL fluids of control group was significantly higher (p < .05) than those in SM-exposed patients (TAC = 0.095 ± 0.018 µmol/l and GSH= 3.09 ± 1.02 nmol/l), while MDA level in BAL fluids of these patients (0.71 ± 0.06 nmol/l) was significantly (p = .001) higher than that in controls (0.49 ± 0.048 nmol/l). Glutathione peroxidases (GPXs), glutathione-s-transferases (GSTs), and glutathione synthetase (GSS) enzymes were overexpressed in mustard lung biopsies, while glutathione reductase (GSR) was significantly downregulated (14.95-fold).

CONCLUSIONS

GSH depletion induced by GSR downregulation may be a major mechanism of SM toxicity on human lung. Despite overexpression of GSTs and GPXs genes, GSH depletion may decline the productivity of these enzymes and total antioxidants capacity, which is associated with OS.

Free Radical Production and Oxidative Stress in Lung Tissue of Patients Exposed to Sulfur Mustard: An Overview of Cellular and Molecular Mechanisms

Sulfur mustard (SM) is a chemical alkylating compound that primary targets lung tissue. It causes a wide variety of pathological effects in respiratory system such as chronic bronchitis, bronchiolitis obliterans, necrosis of the mucosa and inflammation, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. However, molecular and cellular mechanisms for these pathologies are still unclear. Oxidative stress (OS) induced by reactive oxygen species (ROS) is likely a significant mechanism by which SM leads to cell death and tissues injury. SM can trigger various molecular and cellular pathways that are linked to ROS generation, OS, and inflammation. Hypoxia-induced oxidative stress, reduced activity of enzymatic antioxidants, depletion of intercellular glutathione (GSH), decreased productivity of GSH-dependent antioxidants, mitochondrial dysfunction, accumulation of leukocytes and proinflammatory cytokines, and increased expression of ROS producing-related enzymes and inflammatory mediators are the major events in which SM leads to massive production of ROS and OS in pulmonary system. Therefore, understanding of these molecules and signaling pathways gives us valuable information about toxicological effects of SM on injured tissues and the way for developing a suitable clinical treatment. In this review, we aim to discuss the possible mechanisms by which SM induces excessive production of ROS, OS, and antioxidants depletion in lung tissue of exposed patients.

From the Cover: Catalytic Antioxidant Rescue of Inhaled Sulfur Mustard Toxicity

Sulfur mustard (bis 2-chloroethyl ethyl sulfide, SM) is a powerful bi-functional vesicating chemical warfare agent. SM tissue injury is partially mediated by the overproduction of reactive oxygen species resulting in oxidative stress. We hypothesized that using a catalytic antioxidant (AEOL 10150) to alleviate oxidative stress and secondary inflammation following exposure to SM would attenuate the toxic effects of SM inhalation. Adult male rats were intubated and exposed to SM (1.4 mg/kg), a dose that produces an LD₅₀ at approximately 24 h. Rats were randomized and treated via subcutaneous injection with either sterile PBS or AEOL 10150 (5 mg/kg, sc, every 4 h) beginning 1 h post-SM exposure. Rats were euthanized between 6 and 48 h after exposure to SM and survival and markers of injury were determined. Catalytic antioxidant treatment improved survival after SM inhalation in a dose-dependent manner, up to 52% over SM PBS at 48 h post-exposure. This improvement was sustained for at least 72 h after SM exposure when treatments were stopped after 48 h. Non-invasive monitoring throughout the duration of the studies also revealed blood oxygen saturations were improved by 10% and clinical scores were reduced by 57% after SM exposure in the catalytic antioxidant treatment group. Tissue analysis showed catalytic antioxidant therapy was able to decrease airway cast formation by 69% at 48 h post-exposure. To investigate antioxidant induced changes at the peak of injury, several biomarkers of oxidative stress and inflammation were evaluated at 24 h post-exposure. AEOL 10150 attenuated SM-mediated lung lipid oxidation, nitrosative stress and many proinflammatory cytokines. The findings indicate that catalytic antioxidants may be useful medical countermeasure against inhaled SM exposure.

Antioxidants as potential medical countermeasures for chemical warfare agents and toxic industrial chemicals

The continuing horrors of military conflicts and terrorism often involve the use of chemical warfare agents (CWAs) and toxic industrial chemicals (TICs). Many CWA and TIC exposures are difficult to treat due to the danger they pose to first responders and their rapid onset that can produce death shortly after exposure. While the specific mechanism(s) of toxicity of these agents are diverse, many are associated either directly or indirectly with increased oxidative stress in affected tissues. This has led to the exploration of various antioxidants as potential medical countermeasures for CWA/TIC exposures. Studies have been performed across a wide array of agents, model organisms, exposure systems, and antioxidants, looking at an almost equally diverse set of endpoints. Attempts at treating CWAs/TICs with antioxidants have met with mixed results, ranging from no effect to nearly complete protection. The aim of this commentary is to summarize the literature in each category for evidence of oxidative stress and antioxidant efficacy against CWAs and TICs. While there is great disparity in the data concerning methods, models, and remedies, the outlook on antioxidants as medical countermeasures for CWA/TIC management appears promising.