L-Oxothiazolidine 4-carboxylate pretreatment of isolated human peripheral blood lymphocytes reduces sulfur mustard cytotoxicity

Sulfur mustard (HD, mustard gas) is a vesicant chemical warfare agent for which there is no specific medical countermeasure. A potential approach to combating the debilitating effects of this agent is the use of compounds that can react with this material before it interacts with critical macro-molecules. Glutathione (GSH), a tripeptide that exists in high concentrations in cells, reacts with HD and is involved in HD detoxification. Pretreatment of human peripheral blood lymphocytes (PBL) with 10 mmol/L L-oxothiazolidine-4-carboxylate (OTC), a "masked" cysteine precursor, increased intracellular glutathione levels 25-50% over control values. Pretreated PBL were harvested, washed, and exposed to 10, 50, or 100 µmol/L HD. Flow cytometry was used to measure cytotoxicity by propidium iodide uptake. Pretreatment of PBL with OTC led to small decreases in cytotoxicity after HD exposure. However, treatment of cells with OTC after HD exposure was not beneficial. Compounds that can modulate GSH levels within the cell may help to reduce the cytotoxicity of HD when used as a pretreatment.     

Effect of sulfur exposure on protease activity in human peripheral blood lymphocytes

Sulfur mustard is a waemical warfare blistering agent for which neither the mechanism of action nor an antidote is known. Papirmeister et al. (1985) have postulated a biochemical hypothesis for mustard-induced cutaneous injury involving a sequelae of DNA alkylation, metabolic disruption and activation of protease. Human peripheral blood lymphocytes in cell cultures were employed as an in vitro model for alkylating agent toxicity. A chromogenic peptide substrate assay was used for detection of protease in lymphocytes treated with sulfur mustard or chloroethyl ethyl sulfide. Exposure of human peripheral blood lymphocytes from normal donors to these alkylating agents resulted in an increase in cell associated protease activity. This increase in protease activity may contribute to the pathology or act as an indicator to predict methods of therapeutic intervention for sulfur mustard toxicity.Abbreviations PBL peripheral blood lymphocytes - CEES chloroethyl ethyl sulfide - DFP diisopropyl fluoro-phosphate - pNA p-nitroaniline - CPSPA Chromogenic Peptide Substrate Protease Assay The opinions or assertions herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.     

Inhibition of sulfur mustard-increased protease activity by niacinamide,N-acetyl-L-cysteine or dexamethasone

The pathologic mechanisms underlying sulfur mustard-induced skin vesication remain undefined. Papirmeister et al. (1985) have postulated a biochemical mechanism for sulfur mustard-induced cutaneous injury involving DNA alkylation, metabolic disruption, and enhanced proteolysic activity. We have previously utilized a chromogenic peptide substrate assay to establish that human peripheral blood lymphocytes exposed to sulfur mustard exhibited enhanced proteolytic activity. In this study, compounds known to alter the biochemical events associated with sulfur mustard exposure or to reduce protease activity were tested for their ability to block the sulfur mustard-increased proteolysis. Treatment of cells with niacinamide, N-acetyl-L-cysteine, or dexamethasone resulted in a decrease of sulfur mustard-increased protease activity. Complete inhibition of sulfur mustard-increased proteolysis was achieved by using protease inhibitors (antipain, leupeptin, and 4-(2-aminoethyl)-benzenesulfonylfluoride). These data suggest that therapeutic intervention in the biochemical pathways that culminate in protease activation or direct inhibition of proteolysis might serve as an approach to the treatment of sulfur mustard-induced pathology.Abbreviations APMSF 4-(2-aminoethyl)-benzenesulfonylfluoride, HCI - CPSPA Chromogenic Peptide Substrate Protease Assay - EDTA ethylenediaminetetraacetic acid - HD sulfur mustard - PBL human peripheral blood lymphocytes - pNA p-nitroaniline     

Putative roles of inflammation in the dermatopathology of sulfur mustard

The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.     

Atopic dermatitis-associated protein interaction network lead to new insights in chronic sulfur mustard skin lesion mechanisms

Chronic sulfur mustard skin lesions (CSMSLs) are the most common complications of sulfur mustard exposure; however, its mechanism is not completely understood.According to clinical signs, there are similarities between CSMSL and atopic dermatitis (AD). In this study, proteomic results of AD were reviewed and the AD-associated protein–protein interaction network (PIN) was analyzed. According to centrality measurements, 16 proteins were designated as pivotal elements in AD mechanisms. Interestingly, most of these proteins had been reported in some sulfur mustard-related studies in late and acute phases separately. Based on the gene enrichment analysis, aging, cell response to stress, cancer, Toll- and NOD-like receptor and apoptosis signaling pathways have the greatest impact on the disease. By the analysis of directed protein interaction networks, it is concluded that TNF, IL-6, AKT1, NOS3 and CDKN1A are the most important proteins. It is possible that these proteins play role in the shared complications of AD and CSMSL including xerosis and itching.     

Assessment of sulfur mustard interaction with basement membrane components

Bis-2-chloroethyl sulfide (sulfur mustard, HD) is a bifunctional alkylating agent which causes severe vesication characterized by slow wound healing. Our previous studies have shown that the vesicant HD disrupts the epidermal-dermal junction at the lamina lucida of the basement membrane. The purpose of this study was to examine whether HD directly modifies basement membrane components (BMCs), and to evaluate the effect of HD on the cell adhesive activity of BMCs. EHS laminin was incubated with [¹⁴C]HD, and extracted by gel filtration. Analysis of the [¹⁴C]HD-conjugated laminin fraction by a reduced sodium dodecyl sulfate-polyacrylaminde gel electrophoresis (SDS-PAGE) revealed the incorporation of radioactivity into both laminin subunits and a laminin trimer resistant to dissociation in reduced SDS-PAGE sample buffer, suggesting direct alkylation and cross-linking of EHS laminin by [¹⁴C]HD. Normal human foreskin epidermal keratinocytes were biosynthetically labeled with [³⁵S]cysteine.³⁵S-labeled laminin isoforms, Ae. B1e. B2e. laminin and K.B1e.B2e. laminin (using the nomenclature of Engel), fibronectin, and heparan sulfate proteoglycan were isolated by immunoprecipitation from the cell culture medium, treated with HD or ethanol as control, and then analyzed by SDS-PAGE. On reduced SDS gels, these three BMCs not treated with HD showed the typical profile of dissociated subunits. However, HD treatment caused the appearance of higher molecular weight bands indicative of cross-linking of subunits within these BMCs. The HD scavengers sodium thiosulfate and cysteine prevented the cross-linking of BMC subunits by HD. Finally, Tissue culture dishes coated with laminin or fibronectin were treated with HD or ethanol as a control, and human keratinocytes were plated on the BMC-coated surfaces. After 20 h of incubation, it was observed that cell adhesion was decreased significantly on the BMC-coated surfaces treated with HD. As expected, the preincubation of HD with cysteine diminished the HD inhibition of cell adhesion. Thus, HD alkylates adhesive macromolecules of the basement membrane zone and inhibits their cell adhesive activity. These findings support the hypothesis that the alkylation of basement membrane components by HD destabilizes the epidermal-dermal junction in the process of HD-induced vesication. The failure of the HD-alkylated BMCs to support the attachment of keratinocytes might also contribute to the slow reepithelialization of the wound site which is characteristic of HD-induced blistering.Abbreviations BMC basement membrane component - DEM Dulbecco's modified Eagle's medium - ECM extracellular matrix - EHS Englebreth-Holm-Swarm sarcoma - HD sulfur mustard - HSPG heparan sulfate proteoglycan - KGM keratinocyte growth medium - NHEK normal human keratinocytes - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Violacein cytotoxicity on human blood lymphocytes and effect on phosphatases

Given the importance of protein phosphorylation in the context of cellular functions, abnormal protein phosphatase activity has been implicated in several diseases, including cancer. These critical roles of protein phosphatases qualify them as potential targets for the development of medicinal compounds that possess distinct modes of action such as violacein. In this work, studies with this natural indolic pigment at a concentration of 10.0 μmol L^{? 1} demonstrated a 20% activation of total protein phosphatase extracted from human lymphocytes. Although no alteration was observed on protein tyrosine phosphatase (CD45), 30% of inhibition was achieved in cytoplasmatic protein phosphatase activity after incubation with 10.0 μmol L^{? 1} violacein. Additionally, 5.0 μmol L^{? 1} of violacein inhibited by 50% the serum tartrate-resistant acid phosphatase activity. Violacein presented toxic effect on lymphocytes with IC50 values of 3 and 10 μmol L^{? 1} for protein content and protein phosphatase activity, respectively. These findings suggest an important role for protein phosphatases in the mechanisms controlling proliferation and cell death.     

Detoxification of sulfur mustard by enzyme-catalyzed oxidation using chloroperoxidase

One of the most interesting methods for the detoxification of sulfur mustard is enzyme-catalyzed oxidation. This study examined the oxidative destruction of a sulfur mustard by the enzyme chloroperoxidase (EC 1.11.1.10). Chloroperoxidase (CPO) belongs to a group of enzymes that catalyze the oxidation of various organic compounds by peroxide in the presence of a halide ion. The enzymatic oxidation reaction is affected by several factors: pH, presence or absence of chloride ion, temperature, the concentrations of hydrogen peroxide and enzyme and aqueous solubility of the substrate. The optimum reaction conditions were determined by analyzing the effects of all factors, and the following conditions were selected: solvent, Britton–Robinson buffer (pH = 3) with tert-butanol (70:30 v/v); CPO concentration, 16 U/mL; hydrogen peroxide concentration, 40 mmol/L; sodium chloride concentration, 20 mmol/L. Under these reaction conditions, the rate constant for the reaction is 0.006 s⁻¹. The Michaelis constant, a measure of the affinity of an enzyme for a particular substrate, is 1.87 × 10⁻³ M for this system. The Michaelis constant for enzymes with a high affinity for their substrate is in the range of 10⁻⁵ to 10⁻⁴ M, so this value indicates that CPO does not have a very high affinity for sulfur mustard.     

The use of human epidermal keratinocytes in culture as a model for studying the biochemical mechanisms of sulfur mustard toxicity

Human epidermal keratinocytes in culture were studied to evaluate their usefulness in demonstrating toxic events following exposure to sulfur mustard. Exposure of keratinocytes to sulfur mustard over a concentration range of 1–1000 μM HD, reduced NAD+ levels from 96% to 32% of control levels. When keratinocytes were exposed to a concentration of 300 μM HD, NAD+ levels began to fall at 1 hour and reached a plateau of 47% of control levels at 4 hours. Niacinamide, an inhibitor of the enzyme poly(ADP-ribose) polymerase, partially protected mustard-exposed cells against NAD+ depletion. It also protected cellular viability as assessed by vital staining 24 hours after exposure. This protection was not seen in long-term (72 hr) cultures. These studies suggest that human epidermal keratinocytes in culture can serve as a usefulin vitro model for research into the biochemical mechanisms of sulfur mustard-induced cutaneous injury.     

Protection of intracellular dopamine cytotoxicity by dopamine disposition and metabolism factors

Dopamine has been hypothesized as a contributing factor for the selective degeneration of dopaminergic neurons in Parkinson's disease. However, the cytotoxic mechanisms of dopamine and its metabolites remain poorly understood. Using a stable aromatic amino acid decarboxylase (AADC) expressing a fibroblast cell line, we previously demonstrated a novel, non-oxidative cytotoxicity of intracellular dopamine. In this study, we further investigate the roles of dopamine metabolism and disposition proteins against intracellular dopamine cytotoxicity by co-expressing these factors in AADC-expressing cells. Our results indicate that overexpression of the vesicular monoamine transporter and monoamine oxidase A-induced protection against intracellular dopamine toxicity, and conversely that pharmacological inhibition of these pathways potentiated L-DOPA toxicity in catecholaminergic PC12 cells. Macrophage migration inhibitory factor and glutathione S-transferase (GST), factors that have recently been shown to be involved in dopamine metabolism, also exhibited a strong protective role against intracellular dopamine cytotoxicity. Our results support a potential role for non-oxidative cytoplasmic dopamine toxicity, and imply that disruption in dopamine disposition and/or metabolism could underlie the progressive degeneration of dopaminergic neurons in Parkinson's disease.     

Effect of cellular glutathione depletion on cadmium-induced cytotoxicity in human lung carcinoma cells

The effect of glutathione depletion on cellular toxicity of cadmium was investigated in a subpopulation (T27) of human lung carcinoma A549 cells with coordinately high glutathione levels and Cd⁺⁺-resistance. Cellular glutathione levels were depleted by exposing the cells to diethyl maleate or buthionine sulfoximine. Depletion was dose-dependent. Exposure of the cells to 0.5 mM diethyl maleate for 4 hours or to 10 mM buthionine sulfoximine for 8 hours eliminated the threshold for Cd⁺⁺ cytotoxic effect and deccreased the LD_50S. Cells that were pretreated with 0.5 mM diethyl maleate or 10 mM buthionine sulfoximine and then exposed to these same concentrations of diethyl maleate or buthionine sulfoximine during the subsequent assay for colony forming efficiency produced no colonies, reflecting an enhanced sensitivity to these agents at low cell density. Diethyl maleate was found to be more cytotoxic than buthionine sulfoximine. Synergistic cytotoxic effects were observed in the response of diethyl maleate pretreated cells exposed to Cd⁺⁺. Thus the results demostrated that depletion of most cellular glutathione in A549-T27 cells prior to Cd⁺⁺ exposure sensitizes them to the agent's cytotoxic effects. Glutathione thus may be involved in modulating the early cellular Cd⁺⁺ cytotoxic response. Comparison of reduced glutathione levels and of Cd⁺⁺ cytotoxic responses in buthionine sulfoximine-treated A549-T27 cells with those levels in other, untreated normal and tumor-derived cells suggests that the higher level of glutathione in A549-T27 is not the sole determinant of its higher level of Cd⁺⁺ resistance.Abbreviations BSO DL-buthionine-(R,S)-sulfoximine - DEM diethyl maleate - DMSO dimethyl sulfoxide - GSH reduced glutathione - MT metallothionein     

Modulation of sulfur mustard induced cell death in human epidermal keratinocytes using IL-10 and TNF-alpha

We compared the effects of overexpressing a tightly regulated anti-inflammatory cytokine, interleukin 10 (IL-10), and the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) on sulfur mustard induced cytotoxicity in human epidermal keratinocytes. Both cytokines were overexpressed when compared with the cells transfected with the empty vector as determined by quantitative ELISA. Cells overexpressing interleukin 10 suppressed the pro-inflammatory cytokines interleukin 8 and interleukin 6 following exposure to 50-300 microM sulfur mustard. These cells exhibited delayed onset of sulfur mustard induced cell death. On the other hand, cells overexpressing tumor necrosis factor alpha induced a sustained elevation in both interleukin 6 and 8 expression following exposure to 50-300 microM sulfur mustard. These cells were sensitized to the effects of sulfur mustard that resulted in an increased sulfur mustard induced cell death. Normal human epidermal keratinocytes treated with sulfur mustard exhibited elevated levels of tumor necrosis factor alpha expression and increased activity of nuclear factor kappa B. Gene array data indicated that cells overexpressing interleukin 10 induced several genes that are involved in growth promotion and cell-fate determination. We, therefore, identify IL-10 and TNF-alpha signal transduction pathways and their components as possible candidates for early therapeutic intervention against sulfur mustard induced cell injury.     

NMR- and GC/MS-based metabolomics of sulfur mustard exposed individuals: a pilot study

Sulfur mustard (SM) is a potent alkylating agent and its effects on cells and tissues are varied and complex. Due to limitations in the diagnostics of sulfur mustard exposed individuals (SMEIs) by noninvasive approaches, there is a great necessity to develop novel techniques and biomarkers for this condition. We present here the first nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC/MS) metabolic profiling of serum from and healthy controls to identify novel biomarkers in blood serum for better diagnostics. Of note, SMEIs were exposed to SM 30 years ago and that differences between two groups could still be found. Pathways in which differences between SMEIs and healthy controls are observed are related to lipid metabolism, ketogenesis, tricarboxylic acid (TCA) cycle and amino acid metabolism.     

Interference of plasmatic reduced glutathione and hemolysis on glutathione disulfide levels in human blood

The blood reduced glutathione (GSH)/GSH disulfide (GSSG) ratio is an index of the oxidant/antioxidant balance of the whole body. Nevertheless, data indicating GSH and GSSG physiological levels are still widely divergent, especially those on GSSG, probably due to its low concentration. Standardization in methodological protocols and sample manipulation could help to minimize these discrepancies. Therefore, we have investigated how plasma reduced GSH, which is rapidly oxidized after blood withdrawal, could alter the blood GSSG measurement if the sample is not suitably processed. We have observed that an increase in plasma GSH concentration, due to red blood cell hemolysis, is responsible for a significant overestimation of blood GSSG level. Our results show that, before performing blood GSSG determination, thiols have to be rapidly blocked, to avoid possible pitfalls in GSSG measurement, in particular when hemolysis is present.     

Evidence of a significant role of glutathione reductase in the sulfur assimilation pathway

With the objective of studying the role of glutathione reductase (GR) in the accumulation of cysteine and methionine, we generated transgenic tobacco and Arabidopsis lines overexpressing the cytosolic AtGR1 and the plastidic AtGR2 genes. The transgenic plants had higher contents of cysteine and glutathione. To understand why cysteine levels increased in these plants, we also used gr1 and gr2 mutants. The results showed that the transgenic plants have higher levels of sulfite, cysteine, glutathione and methionine, which are downstream to adenosine 5′ phosphosulfate reductase (APR) activity. However, the mutants had lower levels of these metabolites, while the sulfate content increased. A feeding experiment using ³⁴SO₄^2– also showed that the levels of APR downstream metabolites increased in the transgenic lines and decreased in gr1 compared with their controls. These findings, and the results obtained from the expression levels of several genes related to the sulfur pathway, suggest that GR plays an essential role in the sulfur assimilation pathway by supporting the activity of APR, the key enzyme in this pathway. GR recycles the oxidized form of glutathione (GSSG) back to reduce glutathione (GSH), which serves as an electron donor for APR activity. The phenotypes of the transgenic plants and the mutants are not significantly altered under non‐stress and oxidative stress conditions. However, when germinating on sulfur‐deficient medium, the transgenic plants grew better, while the mutants were more sensitive than the control plants. The results give substantial evidence of the yet unreported function of GR in the sulfur assimilation pathway.     

Role of glutathione in intracellular amyloid-alpha precursor protein/carboxy-terminal fragment aggregation and associated cytotoxicity

Abstract Alterations in glutathione (GSH) metabolism are associated with neurodegeneration in Alzheimer's disease (AD), and GSH depletion follows application of exogenous fibrillar amyloid beta (Abeta) peptides in experimental systems; these results are commonly cited as evidence of oxidative damage in AD. We used MC65 human neuroblastoma cells that conditionally express carboxy-terminal fragments of the Abeta precursor protein (Abeta/CTFs) to directly test the hypothesis that GSH is part of the cellular response to stressors associated with Abeta/CTF accumulation and not simply a marker of oxidative damage. Our data showed that Abeta/CTFs accumulated by post-translational processes and were associated with progressive increases in oxidative damage and cytotoxicity. Ethycrinic acid (EA) or diethyl maleate (DEM), reagents that deplete GSH through non-specific thiol adduction, gave rise to dose-dependent cytotoxicity that was independent of Abeta/CTF expression and minimally responsive to alpha-tocopherol (AT). In contrast, buthionine sulfoximine (BSO), a selective inhibitor of GSH synthase, not only augmented Abeta/CTF-associated cell death but unexpectedly potentiated Abeta/CTF accumulation; both outcomes were completely suppressed by AT. These data suggest that antioxidants may serve as 'Abeta targeting' therapies that suppress toxic protein aggregation rather than simply acting as downstream radical scavengers.     

Interleukin-6 protects PC12 cells from 4-hydroxynonenal-induced cytotoxicity by increasing intracellular glutathione levels

Oxidative stress plays an important role in neuronal cell death associated with many different neurodegenerative conditions, and it is reported that 4-hydroxynonenal (HNE), an aldehydic product of membrane lipid peroxidation, is a key mediator of neuronal cell death induced by oxidative stress. Previously, we have demonstrated that interleukin-6 (IL-6) protects PC12 cells from serum deprivation and 6-hydroxydopamine-induced toxicity. Therefore, in the present study, we examined the effects of interleukins on HNE toxicity in PC12 cells. Exposure of PC12 cells to HNE resulted in a decrease in levels of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction, which was due to necrotic and apoptotic cell death. Addition of IL-6 24 h before HNE treatment provided a concentration-dependent protection against HNE toxicity, whereas neither IL-1β nor IL-2 had any effect. Addition of glutathione (GSH)-ethyl ester, but not superoxide dismutase or catalase, before HNE treatment to the culture medium protected PC12 cells from HNE toxicity. We found that IL-6 increases intracellular GSH levels and the activity of γ-glutamylcysteine synthetase (γ-GCS) in PC12 cells. Buthionine sulfoximine (BSO), an inhibitor of γ-GCS, reversed the protective effect of IL-6 against HNE toxicity. These results suggest that IL-6 protects PC12 cells from HNE-induced cytotoxicity by increasing intracellular levels of GSH.     

Suppression of sulfur mustard-increased IL-8 in human keratinocyte cell cultures by serine protease inhibitors: implications for toxicity and medical countermeasures

The toxicity of the chemical warfare blistering agent sulfur mustard (2,2'-dichlorodiethyl sulfide; SM) has been investigated for nearly a century; however, the toxicological mechanisms of SM remain obscure and no antidote exists. The similarity of dermal-epidermal separation caused by SM exposure, proteolysis, and certain bullous diseases has fostered the hypothesis that SM vesication involves proteolysis and/or inflammation. Compound screening conducted by the US Army Medical Research Institute of Chemical Defense established that topical application of three tested serine protease inhibitors could reduce SM toxicity in the mouse ear vesicant model. Although most of the drugs with efficacy for SM toxicity in rodent models are anti-inflammatory compounds, no in vitro assay is in current use for screening of potential anti-inflammatory SM antidotes. IL-8 is a potent neutrophil chemotactic cytokine that is increased in human epidermal keratinocyte (HEK) cell cultures following exposure to SM and has been proposed as a marker for SM-induced inflammation. This study was conducted to establish in vitro screening of IL-8 in SM-exposed HEK as a possible model for evaluating candidate compounds prior to in vivo testing. We chose two protease inhibitors, one from those shown as successful in the MEVM (ethyl p-guanidinobenzoate hydrochloride, ICD 1579) and a prototypic inhibitor of trypsin, N-tosyl-L-lysine chloromethyl ketone (TLCK). TLCK (62.5 to 1000 μmol/L) or ICD 1579 (31.25 to 1000 μmol/L) was added to HEK cell cultures 1 h after SM exposure (200 μmol/L) and dose-dependently suppressed SM-increased IL-8. The suppression of SM-increased IL-8 by a class of drug candidate compounds such as protease inhibitors may provide a mechanistic marker that helps predict future medical countermeasures for SM toxicity and reduces the need for testing in animal models. This revised version was published online in July 2006 with corrections to the Cover Date.