Chemical depletion of glutathione in vivo

A chloroplast sulphate transporter modulates glutathione-mediated redox cycling to regulate cell division

Glutathione redox cycling is important for cell cycle regulation, but its mechanisms are not well understood. We previously identified a small-sized mutant, suppressor of mat3 15-1 (smt15-1) that has elevated cellular glutathione. Here, we demonstrated that SMT15 is a chloroplast sulphate transporter. Reducing expression of γ-GLUTAMYLCYSTEINE SYNTHETASE, encoding the rate-limiting enzyme required for glutathione biosynthesis, corrected the size defect of smt15-1 cells. Overexpressing GLUTATHIONE SYNTHETASE (GSH2) recapitulated the small-size phenotype of smt15-1 mutant, confirming the role of glutathione in cell division. Hence, SMT15 may regulate chloroplast sulphate concentration to modulate cellular glutathione levels. In wild-type cells, glutathione and/or thiol-containing molecules (GSH/thiol) accumulated in the cytosol at the G1 phase and decreased as cells entered the S/M phase. While the cytosolic GSH/thiol levels in the small-sized mutants, smt15-1 and GSH2 overexpressors, mirrored those of wild-type cells (accumulating during G1 and declining at early S/M phase), GSH/thiol was specifically accumulated in the basal bodies at early S/M phase in the small-sized mutants. Therefore, we propose that GSH/thiol-mediated redox signalling in the basal bodies may regulate mitotic division number in Chlamydomonas reinhardtii. Our findings suggest a new mechanism by which glutathione regulates the multiple fission cell cycle in C. reinhardtii.

Nanomaterial-based regulation of redox metabolism for enhancing cancer therapy

Altered redox metabolism is one of the hallmarks of tumor cells, which not only contributes to tumor proliferation, metastasis, and immune evasion, but also has great relevance to therapeutic resistance. Therefore, regulation of redox metabolism of tumor cells has been proposed as an attractive therapeutic strategy to inhibit tumor growth and reverse therapeutic resistance. In this respect, nanomedicines have exhibited significant therapeutic advantages as intensively reported in recent studies. In this review, we would like to summarize the latest advances in nanomaterial-assisted strategies for redox metabolic regulation therapy, with a focus on the regulation of redox metabolism-related metabolite levels, enzyme activity, and signaling pathways. In the end, future expectations and challenges of such emerging strategies have been discussed, hoping to enlighten and promote their further development for meeting the various demands of advanced cancer therapies. It is highly expected that these therapeutic strategies based on redox metabolism regulation will play a more important role in the field of nanomedicine.

Validation of biomarkers for neonicotinoid exposure in Folsomia candida under mutual exposure to diethyl maleate

Neonicotinoid insecticides are harmful to non-target soil invertebrates, which are crucial for sustainable agriculture. Gene expression biomarkers could provide economic and high-throughput metrics of neonicotinoid exposure and toxicity to non-target invertebrates. Thereby, biomarkers can help guide remediation efforts or policy enforcement. Gene expression of Glutathione S-Transferase 3 (GST3) has previously been proposed as a biomarker for the neonicotinoid imidacloprid in the soil ecotoxicological model species Folsomia candida (Collembola). However, it remains unclear how reliably gene expression of neonicotinoid biomarkers, such as GST3, can indicate the exposure to the broader neonicotinoid family under putative GST enzymatic inhibition. In this work, we exposed springtails to two neonicotinoids, thiacloprid and imidacloprid, alongside diethyl maleate (DEM), a known GST metabolic inhibitor that imposes oxidative stress. First, we determined the influence of DEM on neonicotinoid toxicity to springtail fecundity. Second, we surveyed the gene expression of four biomarkers, including GST3, under mutual exposure to neonicotinoids and DEM. We observed no effect of DEM on springtail fecundity. Moreover, the expression of GST3 was only influenced by DEM under mutual exposure with thiacloprid but not with imidacloprid. The results indicate that GST3 is not a robust indicator of neonicotinoid exposure and that probable GST enzymatic inhibition mediates the toxicity of imidacloprid and thiacloprid differentially. Future research should investigate biomarker reliability under shifting metabolic conditions such as provided by DEM exposure.

Glutathione-Depleting Nanomedicines for Synergistic Cancer Therapy

Cancer cells frequently exhibit resistance to various molecular and nanoscale drugs, which inevitably affects the drugs' therapeutic outcomes. Overexpression of glutathione (GSH) has been observed in many cancer cells, and solid evidence has corroborated the resulting tumor resistance to a variety of anticancer therapies, suggesting that this biochemical characteristic of cancer cells can be developed as a potential target for cancer treatments. The single treatment of GSH-depleting agents can potentiate the responses of the cancer cells to different cell death stimuli; therefore, as an adjunctive strategy, GSH depletion is usually combined with mainstream cancer therapies for enhancing the therapeutic outcomes. Propelled by the rapid development of nanotechnology, GSH-depleting agents can be readily constructed into anticancer nanomedicines, which have shown a steep rise over the past decade. Here, we review the common GSH-depleting nanomedicines which have been widely applied in synergistic cancer treatments in recent years. Some current challenges and future perspectives for GSH depletion-based cancer therapies are also presented. With the understanding of the structure-property relationship and action mechanisms of these biomaterials, we hope that the GSH-depleting nanotechnology will be further developed to realize more effective disease treatments and even achieve successful clinical translations.

Noninvasive monitoring of hepatic glutathione depletion through fluorescence imaging and blood testing

Hepatic glutathione plays a key role in regulating redox potential of the entire body, and its depletion is known to increase susceptibility to oxidative stress involved in many diseases. However, this crucial pathophysiological event can only be detected noninvasively with high-end instrumentation or invasively with surgical biopsy, limiting both preclinical research and clinical prevention of oxidative stress-related diseases. Here, we report that both in vivo fluorescence imaging and blood testing (the first-line detection in the clinics) can be used for noninvasive and consecutive monitoring of hepatic glutathione depletion at high specificity and accuracy with assistance of a body-clearable nanoprobe, of which emission and surface chemistries are selectively activated and transformed by hepatic glutathione in the liver sinusoids. These findings open a new avenue to designing exogenous blood markers that can carry information of local disease through specific nanobiochemical interactions back to the bloodstream for facile and rapid disease detection.

New Insights into the Role of Glutathione in the Mechanism of Fever

Glutathione is one of the most important and potent antioxidants. The development of pharmacological compounds that can either increase or decrease glutathione concentrations has allowed investigation into the role of glutathione in various biological processes, including immune responses. Recent findings have shown that glutathione not only affects certain factors involved in immunological processes but also modifies complex immune reactions such as fever. Until recently, it was not known why some patients do not develop fever during infection. Data suggest that fever induction is associated with oxidative stress; therefore, antioxidants such as glutathione can reduce pyrexia. Surprisingly, new studies have shown that low glutathione levels can also inhibit fever. In this review, we focus on recent advances in this area, with an emphasis on the role of glutathione in immune responses accompanied by fever. We describe evidence showing that disturbed glutathione homeostasis may be responsible for the lack of fever during infections. We also discuss the biological significance of the antipyretic effects produced by pharmacological glutathione modulators.

Glutathione-mediated biotransformation in the liver modulates nanoparticle transport

Glutathione-mediated biotransformation in the liver is a well-known detoxification process to eliminate small xenobiotics, but its impacts on nanoparticle retention, targeting and clearance are much less understood than liver macrophage uptake, even though both processes are involved in liver detoxification. By designing a thiol-activatable fluorescent gold nanoprobe that can bind to serum protein and be transported to the liver, we non-invasively imaged the biotransformation kinetics in vivo at high specificity and examined this process at the chemical level. Our results show that glutathione efflux from hepatocytes results in high local concentrations of both glutathione and cysteine in liver sinusoids, which transforms the nanoparticle surface chemistry, reduces its affinity to serum protein and significantly alters its blood retention, targeting and clearance. With this biotransformation, liver detoxification, a long-standing barrier in nanomedicine translation, can be turned into a bridge toward maximizing targeting and minimizing nanotoxicity.

A Simple Glutathione-Responsive Turn-On Theranostic Nanoparticle for Dual-Modal Imaging and Chemo-Photothermal Combination Therapy

Constructing a tumor microenvironment stimuli activatable theranostic nanoparticle with simple components and preparation procedures for multimodality imaging and therapy remains a major challenge for current theranostic systems. Here we report a novel and simple glutathione (GSH)-responsive turn-on theranostic nanoparticle for dual-modal imaging and combination therapy. The theranostic nanoparticle, DHP, consisting of a disulfide-bond-linked hydroxyethyl starch paclitaxel conjugate (HES-SS-PTX) and a near-infrared (NIR) cyanine fluorophore DiR, is prepared with a simple one-step dialysis method. As DiR is encapsulated within the hydrophobic core formed by HES-SS-PTX, the fluorescence of DiR is quenched by the aggregation-caused quenching (ACQ) effect. Nonetheless, once DHP is internalized by cancer cells, the disulfide bond of HES-SS-PTX can be cleaved by intracellular GSH, leading to the synchronized release of conjugated PTX and loaded DiR. The released PTX could exert its therapeutic effect, while DiR could adsorb onto nearby endosome/lysosome membranes and regain its fluorescence. Thus, DHP could monitor the release and therapeutic effect of PTX through the fluorescence recovery of DiR. Remarkably, DHP can also be used as an in vivo probe for both fluorescent and photoacoustic imaging and at the same time achieves potent antitumor efficacy through chemo-photothermal combination therapy. This study provides novel insights into designing clinically translatable turn-on theranostic systems.

Synthesis and preliminary radiopharmacological characterisation of an 11 C-labelled azadipeptide nitrile as potential PET tracer for imaging of cysteine cathepsins

An O-methyltyrosine-containing azadipeptide nitrile was synthesised and investigated for its inhibitory activity towards cathepsins L, S, K, and B. Labelling with carbon-11 was accomplished by reaction of the corresponding phenolic precursor with [¹¹ C]methyl iodide starting from cyclotron-produced [¹¹ C]methane. Radiopharmacological evaluation of the resulting radiotracer in a mouse xenograft model derived from a mammary tumour cell line by small animal PET imaging indicates tumour targeting with complex pharmacokinetics. Radiotracer uptake in the tumour region was considerably lower under treatment with the nonradioactive reference compound and the epoxide-based irreversible cysteine cathepsin inhibitor E64. The in vivo behaviour observed for this radiotracer largely confirms that of the corresponding ¹⁸ F-fluoroethylated analogue and suggests the limited suitability of azadipeptide nitriles for the imaging of tumour-associated cysteine cathepsins despite target-mediated uptake is evidenced.

Role of glutathione in the regulation of epigenetic mechanisms in disease

Epigenetics is a rapidly growing field that studies gene expression modifications not involving changes in the DNA sequence. Histone H3, one of the basic proteins in the nucleosomes that make up chromatin, is S-glutathionylated in mammalian cells and tissues, making Gamma-L-glutamyl-L-cysteinylglycine, glutathione (GSH), a physiological antioxidant and second messenger in cells, a new post-translational modifier of the histone code that alters the structure of the nucleosome. However, the role of GSH in the epigenetic mechanisms likely goes beyond a mere structural function. Evidence supports the hypothesis that there is a link between GSH metabolism and the control of epigenetic mechanisms at different levels (i.e., substrate availability, enzymatic activity for DNA methylation, changes in the expression of microRNAs, and participation in the histone code). However, little is known about the molecular pathways by which GSH can control epigenetic events. Studying mutations in enzymes involved in GSH metabolism and the alterations of the levels of cofactors affecting epigenetic mechanisms appears challenging. However, the number of diseases induced by aberrant epigenetic regulation is growing, so elucidating the intricate network between GSH metabolism, oxidative stress and epigenetics could shed light on how their deregulation contributes to the development of neurodegeneration, cancer, metabolic pathologies and many other types of diseases.

Potentiation of Methylmercury-Induced Death in Rat Cerebellar Granular Neurons Occurs by Further Decrease of Total Intracellular GSH with BDNF via TrkB in Vitro

Brain-derived neurotrophic factor (BDNF) is a principal factor for neurogenesis, neurodevelopment and neural survival through a BDNF receptor, tropomyosin-related kinase (Trk) B, while BDNF can also cause a decrease in the intracellular glutathione (GSH) level. We investigated the exacerbation of methylmercury-induced death of rat cerebellar granular neurons (CGNs) by BDNF in vitro. Since methylmercury can decrease intracellular GSH levels, we hypothesized that a further decrease of the intracellular GSH level is involved in the process of the exacerbation of neuronal cell death. In the present study, we established that in CGN culture, a decrease of the intracellular GSH level was further potentiated with BDNF in the process of the methylmercury-induced neuronal death and also in GSH reducer-induced neuronal death. BDNF treatment promoted the decrease in GSH levels induced by methylmercury and also by L-buthionine sulfoximine (BSO) and diethyl maleate (DEM). The promoting effect of BDNF was observed in a TrkB-vector transformant of the rat neuroblastoma B35 cell line but not in the mock-vector transformant. These results indicate that the exacerbating effect of BDNF on methylmercury-induced neuronal death in cultures of CGNs includes a further decrease of intracellular GSH levels, for which TrkB is essential.

Non-linear impact of glutathione depletion on C. elegans life span and stress resistance

The redox environment in cells and organisms is set by low-molecular mass and protein-bound thiols, with glutathione (GSH) representing a major intracellular redox buffer. Subtle thiol oxidation elicits signal transduction processes and adaptive responses to cope with stressors, whereas highly oxidizing conditions may provoke cell death. We here tested how thiol depletion affects life span, stress resistance and stress signaling in the model organism Caenorhabditis elegans. Diethyl maleate (DEM), an α,β-unsaturated carbonyl compound that conjugates to GSH and other thiols, decreased C. elegans life span at a concentration of 1mM. In contrast, low and moderate doses of DEM (10-100µM) increased mean and maximum life span and improved resistance against oxidative stress. DEM-induced life span extension was not detectable in worms deficient in either the FoxO orthologue, DAF-16, or the Nrf2 orthologue, SKN-1, pointing to a collaborative role of the two transcription factors in life span extension induced by thiol depletion. Cytoprotective target genes of DAF-16 and SKN-1 were upregulated after at least 3 days of exposure to 100µM DEM, but not 1mM DEM, whereas only 1mM DEM caused upregulation of egl-1, a gene controlled by a p53-orthologue, CEP-1. In order to test whether depletion of GSH may elicit effects similar to DEM, we suppressed GSH biosynthesis in worms by attenuating γ-glutamylcysteine synthetase (gcs-1) expression through RNAi. The decline in GSH levels elicited by gcs-1 knockdown starting at young adult stage did not impair viability, but increased both stress resistance and life expectancy of the worms. In contrast, gcs-1 knockdown commencing right after hatching impaired nematode stress resistance and rendered young adult worms prone to vulval ruptures during egg-laying. Thus, modest decrease in GSH levels in young adult worms may promote stress resistance and life span, whereas depletion of GSH is detrimental to freshly hatched and developing worms.

Buthionine sulfoximine, a glutathione depletor, attenuates endotoxic fever and reduces IL-1β and IL-6 level in rats

PURPOSE

The aim of our study was to investigate the effect of buthionine sulfoximine (BSO) - a glutathione depletor - on a course of endotoxic fever and IL-1β and IL-6 production.

MATERIAL AND METHODS

Male Wistar rats were subjected to intraperitoneal injection of lipopolysaccharide (LPS) from E. coli (50μg/kg, ip) to provoke fever. The level of spleen glutathione, plasma interleukin (IL)-1β, IL-6, and deep body temperature (Tb) were measured.

RESULTS

The LPS administration provoked fever (the average Tb was 38.14±0.05°C in NaCl/LPS-treated rats vs 37.10±0.03°C in control, not-treated rats; p<0.001). We observed that LPS injection induced a decrease in spleen glutathione level (7.67±0.92nM/g vs 13.27±0.47nM/g in not-treated rats; p<0.001). Furthermore, the injection of LPS provoked an elevation of plasma IL-1β and IL-6 concentration (from values below the lowest detectable standard in not-treated animals to 199.99±34.89pg/mL and 7500±542.21pg/mL, respectively; p<0.001). Pretreatment with BSO enhanced glutathione decrease in LPS-treated rats (5.05±0.49nM/g), and significantly affected fever (maximal Tb was 37.81±0.07°C in BSO/LPS-treated rats vs 38.76±0.11°C in NaCl/LPS-treated rats). BSO 4h after LPS injection decreased IL-1β and IL-6 gene expression (about 1.5 fold, and 2 fold, respectively). In a consequence we observed a decrease in plasma IL-6 concentration (4h after LPS injection plasma IL-6 was 4167.17±956.54pg/mL in BSO/LPS-treated rats vs 7500±542.21pg/mL in NaCl/LPS-treated rats; p<0.001), and later IL-1β (7h after LPS injection the IL-1β concentration was not detected).

CONCLUSION

Based on these data, we conclude that BSO, in addition to well-known application as an inhibitor of glutathione synthesis, is an antipyretic agent which reduces both IL-1β and IL-6 concentration.

Aging is associated with dimerization and inactivation of the brain-enriched tyrosine phosphatase STEP

The STriatal-Enriched tyrosine Phosphatase (STEP) is involved in the etiology of several age-associated neurologic disorders linked to oxidative stress and is also known to play a role in neuroprotection by modulating glutamatergic transmission. However, the possible effect of aging on STEP level and activity in the brain is still unclear. In this study, using young (1 month), adult (4 months), and aged (18 months) rats, we show that aging is associated with increase in dimerization and loss of activity of STEP. Increased dimerization of STEP is primarily observed in the cortex and hippocampus and is associated with depletion of both reduced and total glutathione levels, suggesting an increase in oxidative stress. Consistent with this interpretation, studies in cell culture models of glutathione depletion and oxidative stress also demonstrate formation of dimers and higher order oligomers of STEP that involve intermolecular disulfide bond formation between multiple cysteine residues. Conversely, administration of N-acetyl cysteine, a major antioxidant that enhances glutathione biosynthesis, attenuates STEP dimerization both in the cortex and hippocampus. The findings indicate that loss of this intrinsic protective response pathway with age-dependent increase in oxidative stress may be a contributing factor for the susceptibility of the brain to age-associated neurologic disorders.

Toxicogenomic Screening of Replacements for Di(2-Ethylhexyl) Phthalate (DEHP) Using the Immortalized TM4 Sertoli Cell Line

Phthalate plasticizers such as di(2-ethylhexyl) phthalate (DEHP) are being phased out of many consumer products because of their endocrine disrupting properties and their ubiquitous presence in the environment. The concerns raised from the use of phthalates have prompted consumers, government, and industry to find alternative plasticizers that are safe, biodegradable, and have the versatility for multiple commercial applications. We examined the toxicogenomic profile of mono(2-ethylhexyl) phthalate (MEHP, the active metabolite of DEHP), the commercial plasticizer diisononyl cyclohexane-1,2-dicarboxylate (DINCH), and three recently proposed plasticizers: 1,4-butanediol dibenzoate (BDB), dioctyl succinate (DOS), and dioctyl maleate (DOM), using the immortalized TM4 Sertoli cell line. Results of gene expression studies revealed that DOS and BDB clustered with control samples while MEHP, DINCH and DOM were distributed far away from the control-DOS-BDB cluster, as determined by principle component analysis. While no significant changes in gene expression were found after treatment with BDB and DOS, treatment with MEHP, DINCH and DOM resulted in many differentially expressed genes. MEHP upregulated genes downstream of PPAR and targeted pathways of cholesterol biosynthesis without modulating the expression of PPAR’s themselves. DOM upregulated genes involved in glutathione stress response, DNA repair, and cholesterol biosynthesis. Treatment with DINCH resulted in altered expression of a large number of genes involved in major signal transduction pathways including ERK/MAPK and Rho signalling. These data suggest DOS and BDB may be safer alternatives to DEHP/MEHP than DOM or the commercial alternative DINCH.

Phenobarbital induction and chemical synergism demonstrate the role of UDP-glucuronosyltransferases in detoxification of naphthalophos by Haemonchus contortus larvae

We used an enzyme induction approach to study the role of detoxification enzymes in the interaction of the anthelmintic compound naphthalophos with Haemonchus contortus larvae. Larvae were treated with the barbiturate phenobarbital, which is known to induce the activity of a number of detoxification enzymes in mammals and insects, including cytochromes P450 (CYPs), UDP-glucuronosyltransferases (UDPGTs), and glutathione (GSH) S-transferases (GSTs). Cotreatment of larvae with phenobarbital and naphthalophos resulted in a significant increase in the naphthalophos 50% inhibitory concentration (IC50) compared to treatment of larvae with the anthelmintic alone (up to a 28-fold increase). The phenobarbital-induced drug tolerance was reversed by cotreatment with the UDPGT inhibitors 5-nitrouracil, 4,6-dihydroxy-5-nitropyrimidine, probenecid, and sulfinpyrazone. Isobologram analysis of the interaction of 5-nitrouracil with naphthalophos in phenobarbital-treated larvae clearly showed the presence of strong synergism. The UDPGT inhibitors 5-nitrouracil, 4,6-dihydroxy-5-nitropyrimidine, and probenecid also showed synergistic effects with non-phenobarbital-treated worms (synergism ratio up to 3.2-fold). This study indicates that H. contortus larvae possess one or more UDPGT enzymes able to detoxify naphthalophos. In highlighting the protective role of this enzyme group, this study reveals the potential for UDPGT enzymes to act as a resistance mechanism that may develop under drug selection pressure in field isolates of this species. In addition, the data indicate the potential for a chemotherapeutic approach utilizing inhibitors of UDPGT enzymes as synergists to increase the activity of naphthalophos against parasitic worms and to combat detoxification-mediated drug resistance if it arises in the field.

Unraveling the mechanisms involved in zearalenone-mediated toxicity in permanent fish cell cultures

The world-wide occurrence of zearalenone (ZEN) as a contaminant in feed for farm animals and fish requires the evaluation of toxicity mechanisms of action of ZEN. The present study investigates possible metabolization of ZEN in fish cell lines suggesting that mainly glucuronidation takes place. It demonstrates that concentrations up to 20,000 ng ml(-1) ZEN are capable of influencing cell viability in permanent fish cell cultures in a dose-response manner with different response patterns between the five tested cell lines, whereby lysosomes appeared to be the main target of ZEN. ZEN toxicity is often discussed in the context of oxidative stress. Our study shows a biphasic response of the cell lines when reactive oxygen species (ROS) production is monitored. Damage in cells was observed by measuring lipid peroxidation, DNA strand breaks, and alterations of intracellular glutathione levels. Metabolization of ZEN, especially at concentrations above 7500 ng ml(-1) ZEN, does not prevent cytotoxicity. ZEN as an estrogenic compound may involve processes mediated by binding to estrogen receptors (ER). Since one cell line showed no detectable expression of ER, an ER-mediated pathway seems to be unlikely in these cells. This confirms a lysosomal pathway as a main target of ZEN in fish cells.

Differences in the redox status of human visceral and subcutaneous adipose tissues--relationships to obesity and metabolic risk

OBJECTIVE

Metabolic homeostasis depends on adipocyte metabolic responses/processes, most of which are redox-regulated. Besides, visceral and subcutaneous adipose tissues (VAT and SAT, respectively) differ metabolically and in their contribution to metabolic complications, but their redox characteristics in humans are still unknown. To understand the molecular mechanisms of metabolic syndrome development, we analysed the redox characteristics of VAT and SAT in groups with various body weights and metabolic risks.

MATERIAL AND METHODS

Fifty premenopausal women were classified according to body mass index into normal-weight and obese groups, and these groups were further sub-classified into metabolically healthy and metabolically obese ("at risk") based on the homeostasis model assessment of insulin resistance (HOMA-IR) index and the triglyceride, total-, LDL- and HDL-cholesterol levels. Antioxidant components, NADPH oxidase protein and 4-hydroxynonenal (4-HNE) levels were analysed in VAT and SAT.

RESULTS

Compared with the SAT, the VAT showed a higher basal level of glutathione (GSH) and GSH-dependent enzyme activities. Compared with the metabolically healthy normal-weight controls, the obese groups of women showed lower GSH levels in both depots. However, in these groups, additional prooxidative changes (increased NADPH oxidase and 4-HNE and decreased levels of SOD and/or CAT) were observed only in VAT.

CONCLUSIONS

Because of the critical role of thiol-redox homeostasis in lipogenesis, interdepot-differences in the GSH-dependent antioxidant part may be connected to the higher metabolic activity found in VAT. Analogously, the lower GSH levels that occur during obesity and the corresponding additional redox imbalance may be signs of VAT metabolic dysfunction that underlie the subsequent metabolic impairment.

GSH protects against oxidative stress and toxicity in VL-17A cells exposed to high glucose

PURPOSE

The deficiency of glutathione (GSH) has been linked to several diseases. The study investigated the role of GSH as a protective factor against hyperglycemia-mediated injury in VL-17A cells treated with 50 mM glucose.

METHODS

The cell viability and different oxidative stress parameters including glyoxalase I activity were measured.

RESULTS

GSH supplementation with 2 mM N-acetyl cysteine (NAC) or 0.1 mM ursodeoxycholic acid (UDCA) increased the viability, GSH level and the GSH-dependent glyoxalase I activity in 50 mM glucose-treated VL-17A cells. Further, pretreatment of 50 mM glucose-treated VL-17A cells with NAC or UDCA decreased oxidative stress (levels of reactive oxygen species and protein carbonylation), apoptosis (caspase 3 activity and annexin V-propidium iodide positive cells) and glutathionylated protein formation, a measure of oxidative stress. GSH depletion with 0.4 mM buthionine sulfoximine (BSO) or 1 mM diethyl maleate (DEM) potentiated the decrease in viability, glyoxalase I activity and increase in oxidative stress and apoptosis, with decreased GSH levels in 50 mM glucose-treated VL-17A cells.

CONCLUSION

Thus, changes in GSH levels with exogenous agents such as NAC, UDCA, BSO or DEM modulate hyperglycemia-mediated injury in a cell model of VL-17A liver cells.

A novel small molecule that induces oxidative stress and selectively kills malignant cells

We have synthesized a novel molecule named XB05 (1-bromo-1,1-difluoro-non-2-yn-4-ol) and evaluated its effects in a variety of human cell lines. XB05 displayed potent antiproliferative activity against cell lines derived from leukemia or solid tumors, but had less effect on nonmalignant cells. To identify factors that contribute to the cancer selectivity of XB05, we chose three cell lines that had high sensitivity to XB05 (U937 leukemia), moderate sensitivity (A549 lung cancer), or low sensitivity (Hs27 nonmalignant skin fibroblasts), and proceeded to assess cell death and oxidative stress in these cells. XB05 was found to induce cell death via both apoptotic and nonapoptotic mechanisms in U937 and A549 cells, whereas it had no cytotoxicity against Hs27 cells at comparable concentrations. Treatment with XB05 caused an increase in reactive oxygen species in all cell lines tested, but levels were higher in malignant compared to nonmalignant cells. XB05 treatment also induced DNA damage exclusively in the malignant cells. Differences in antioxidant responses were observed between cell lines. For example, XB05 caused a decrease in levels of glutathione and nuclear Nrf2 in the most sensitive cells (U937), whereas the least sensitive cells (Hs27) displayed increased glutathione levels and no change in nuclear Nrf2. XB05 could react in vitro with cysteine and glutathione, but had much lower reactivity compared to typical thiol-reactive electrophiles, diethyl maleate and maleimide. In summary, XB05 is a novel compound that selectively kills malignant cells, most likely by disrupting cellular redox homeostasis, making it a promising candidate for development as a chemotherapeutic agent.

Impairments in hippocampal synaptic plasticity following prenatal ethanol exposure are dependent on glutathione levels

Previous studies from our laboratory have shown that prenatal ethanol exposure (PNEE) causes a significant deficit in synaptic plasticity, namely long-term potentiation (LTP), in the dentate gyrus (DG) region of the hippocampus of male rats. PNEE has also been shown to induce an increase in oxidative stress and a reduction in antioxidant capacity in the brains of both male and female animals. In this study the interaction between LTP and the major antioxidant in the brain, glutathione (GSH), is examined. We show that depletion of the intracellular reserves of GSH with diethyl maleate (DEM) reduces LTP in control male, but not female animals, mirroring the effects of PNEE. Furthermore, treatment of PNEE animals with N-acetyl cysteine (NAC), a cysteine donor for the synthesis of GSH, increases GSH levels in the hippocampus and completely restores the deficits in LTP in PNEE males. These results indicate that in males GSH plays a major role in regulating LTP, and that PNEE may cause reductions in LTP by reducing the intracellular pool of this endogenous antioxidant.

ATF2 knockdown reinforces oxidative stress-induced apoptosis in TE7 cancer cells

Cancer cells showing low apoptotic effects following oxidative stress-induced DNA damage are mainly affected by growth arrest. Thus, recent studies focus on improving anti-cancer therapies by increasing apoptosis sensitivity. We aimed at identifying a universal molecule as potential target to enhance oxidative stress-based anti-cancer therapy through a switch from cell cycle arrest to apoptosis. A cDNA microarray was performed with hydrogen peroxide-treated oesophageal squamous epithelial cancer cells TE7. This cell line showed checkpoint activation via p21^WAF1, but low apoptotic response following DNA damage. The potential target molecule was chosen depended on the following demands: it should regulate DNA damage response, cell cycle and apoptosis. As the transcription factor ATF2 is implicated in all these processes, we focused on this protein. We investigated checkpoint activation via ATF2. Indeed, ATF2 knockdown revealed ATF2-triggered p21^WAF1 protein expression, suggesting p21^WAF1 transactivation through ATF2. Using chromatin immunoprecipitation (ChIP), we identified a hitherto unknown ATF2-binding sequence in the p21^WAF1 promoter. p-ATF2 was found to interact with p-c-Jun, creating the AP-1 complex. Moreover, ATF2 knockdown led to c-Jun downregulation. This suggests ATF2-driven induction of c-Jun expression, thereby enhancing ATF2 transcriptional activity via c-Jun-ATF2 heterodimerization. Notably, downregulation of ATF2 caused a switch from cell cycle arrest to reinforced apoptosis, presumably via p21^WAF1 downregulation, confirming the importance of ATF2 in the establishment of cell cycle arrest. 1-Chloro-2,4-dinitrobenzene also led to ATF2-dependent G2/M arrest, suggesting that this is a general feature induced by oxidative stress. As ATF2 knockdown also increased apoptosis, we propose ATF2 as a target for combined oxidative stress-based anti-cancer therapies.

Significance of alterations in the metabolomics of sulfur-containing amino acids during liver regeneration

It has been known that liver regeneration is accompanied with a profound change in the metabolomics of sulfur-containing substances in liver. However, its physiological significance in the liver regenerative process is still unclear. Our previous work showed that buthioninesulfoximine and phorone, both widely used to deplete intracellular glutathione (GSH) in biological experiments, induced contrasting changes in the sulfur-containing amino acid metabolism in liver. In this study we employed these GSH-depleting agents to evaluate the role of sulfur-containing substances in the early phase of liver regeneration. Male rats treated with buthioninesulfoximine or phorone were subjected to two-thirds partial hepatectomy (PHx). At the doses used, the magnitude of GSH depletion after PHx was comparable, but buthioninesulfoximine administration inhibited the progression of liver regeneration as determined by liver weight increase, elevation of serum alanine aminotransferase activity, and cyclin D1 and proliferating cell nuclear antigen (PCNA) protein expressions, whereas liver recovery was significantly accelerated in the phorone-treated rats, suggesting that the role of GSH in this process is minimal. Hepatic concentrations of methionine, S-adenosylmethionine, cysteine, taurine and GSH were all elevated by PHx. Methionine adenosyltransferase activity was also induced in the remnant liver. Buthioninesulfoximine administration depressed the elevation of S-adenosylmethionine, but increased the catabolism of cysteine to taurine. In contrast, S-adenosylmethionine elevation was augmented whereas cysteine, hypotaurine and taurine were decreased in the phorone-treated rats. PHx elevated hepatic putrescine and spermidine, but lowered spermine concentrations. Buthioninesulfoximine administration increased putrescine further, but decreased spermidine and spermine concentrations. On the contrary, both spermidine and spermine concentrations were elevated in the rats treated with phorone. The results suggest that the availability of S-adenosylmethionine plays a critical role in the progression of liver regeneration via enhancement of polyamine synthesis. These findings raise the possibility that regulating hepatic transsulfuration reactions may be capable of modifying the recovery process after liver injury.

The AMPK family member Snf1 protects Saccharomyces cerevisiae cells upon glutathione oxidation

The AMPK/Snf1 kinase has a central role in carbon metabolism homeostasis in Saccharomyces cerevisiae. In this study, we show that Snf1 activity, which requires phosphorylation of the Thr210 residue, is needed for protection against selenite toxicity. Such protection involves the Elm1 kinase, which acts upstream of Snf1 to activate it. Basal Snf1 activity is sufficient for the defense against selenite, although Snf1 Thr210 phosphorylation levels become increased at advanced treatment times, probably by inhibition of the Snf1 dephosphorylation function of the Reg1 phosphatase. Contrary to glucose deprivation, Snf1 remains cytosolic during selenite treatment, and the protective function of the kinase does not require its known nuclear effectors. Upon selenite treatment, a null snf1 mutant displays higher levels of oxidized versus reduced glutathione compared to wild type cells, and its hypersensitivity to the agent is rescued by overexpression of the glutathione reductase gene GLR1. In the presence of agents such as diethyl maleate or diamide, which cause alterations in glutathione redox homeostasis by increasing the levels of oxidized glutathione, yeast cells also require Snf1 in an Elm1-dependent manner for growth. These observations demonstrate a role of Snf1 to protect yeast cells in situations where glutathione-dependent redox homeostasis is altered to a more oxidant intracellular environment and associates AMPK to responses against oxidative stress.

Transient glutathione depletion determines terminal differentiation in HL-60 cells

To better define the role of glutathione (GSH) in cell differentiation, the present study measured GSH concentrations during terminal HL-60 cell differentiation, in the presence and absence of differentiation-inducing agents, and in the presence and absence of GSH altering agents. Interestingly, there was a small transient increase in intracellular GSH levels during dimethyl sulfoxide (DMSO) or 1α,25-dihydroxyvitamin D3 (VD3) induced differentiation. This increase coincided with an increase in nitroblue tetrazolium (NBT) reduction capacity, a measure of superoxide anion production, but there was no apparent change in the GSH/glutathione disulfide (GSSG) ratio. Surprisingly, treatment of cells with low doses of 1-chloro-2,4-dinitrobenzene (CDNB; 5 µM) or diethylmaleate (DEM; 0.5 mM), which transiently deplete GSH levels to about 40% of control levels, resulted in enhanced differentiation of HL-60 cells exposed to VD3 or all-trans-retinoic acid (ATRA), as well as under un-induced conditions (i.e., spontaneous differentiation). Enhanced differentiation occurred when cells were treated with the GSH-depleting agents 4 hours after treatment with differentiation inducers. These findings indicate that intracellular GSH levels are regulated in a complex fashion during HL-60 cell differentiation, and that transient GSH depletion using low doses of CDNB and DEM enhances the differentiation process.

Plumbagin inhibits proliferative and inflammatory responses of T cells independent of ROS generation but by modulating intracellular thiols

Plumbagin inhibited activation, proliferation, cytokine production, and graft-versus-host disease in lymphocytes and inhibited growth of tumor cells by suppressing nuclear factor-kappaB (NF-kappaB). Plumbagin was also shown to induce reactive oxygen species (ROS) generation in tumor cells via an unknown mechanism. Present report describes a novel role of cellular redox in modulation of immune responses in normal lymphocytes by plumbagin. Plumbagin depleted glutathione (GSH) levels that led to increase in ROS generation. The decrease in GSH levels was due to direct reaction of plumbagin with GSH as evinced by mass spectrometric and HPLC analysis. Further, addition of plumbagin to cells resulted in decrease in free thiol groups on proteins and increase in glutathionylation of proteins. The suppression of mitogen-induced T-cell proliferation and cytokine (IL-2/IL-4/IL-6/IFN-gamma) production by plumbagin was abrogated by thiol antioxidants but not by non-thiol antioxidants confirming that thiols but not ROS play an important role in biological activity of plumbagin. Plumbagin also abrogated mitogen-induced phosphorylation of ERK, IKK, and degradation of IkappaB-alpha. However, it did not affect phosphorylation of P38, JNK, and AKT. Our results for the first time show that antiproliferative effects of plumbagin are mediated by modulation of cellular redox. These results provide a rationale for application of thiol-depleting agents as anti-inflammatory drugs.

Rat brain endothelial cells are a target of manganese toxicity

Manganese (Mn) is an essential trace metal; however, exposure to high Mn levels can result in neurodegenerative changes resembling Parkinson's disease (PD). Information on Mn's effects on endothelial cells of the blood-brain barrier (BBB) is lacking. Accordingly, we tested the hypothesis that BBB endothelial cells are a primary target for Mn-induced neurotoxicity. The studies were conducted in an in vitro BBB model of immortalized rat brain endothelial (RBE4) cells. ROS production was determined by F(2)-isoprostane (F(2)-IsoPs) measurement. The relationship between Mn toxicity and redox status was investigated upon intracellular glutathione (GSH) depletion with diethylmaleate (DEM) or L-buthionine sulfoximine (BSO). Mn exposure (200 or 800 microM MnCl(2) or MnSO(4)) for 4 or 24h led to significant decrease in cell viability vs. controls. DEM or BSO pre-treatment led to further enhancement in cytotoxicity vs. exposure to Mn alone, with more pronounced cell death after 24-h DEM pre-treatment. F(2)-IsoPs levels in cells exposed to MnCl(2) (200 or 800 microM) were significantly increased after 4h and remained elevated 24h after exposure compared with controls. Consistent with the effects on cell viability and F(2)-IsoPs, treatment with MnCl(2) (200 or 800 microM) was also associated with a significant decrease in membrane potential. This effect was more pronounced in cells exposed to DEM plus MnCl(2) vs. cells exposed to Mn alone. We conclude that Mn induces direct injury to mitochondria in RBE4 cells. The ensuing impairment in energy metabolism and redox status may modify the restrictive properties of the BBB compromising its function.

An adult tissue-specific stem cell in its niche: a gene profiling analysis of in vivo quiescent and activated muscle satellite cells

The satellite cell of skeletal muscle provides a paradigm for quiescent and activated tissue stem cell states. We have carried out transcriptome analyses on satellite cells purified by flow cytometry from Pax3(GFP/+) mice. We compared samples from adult skeletal muscles where satellite cells are mainly quiescent, with samples from growing muscles or regenerating (mdx) muscles, where they are activated. Analysis of regulation that is shared by both activated states avoids other effects due to immature or pathological conditions. This in vivo profile differs from that of previously analyzed satellite cells activated after cell culture. It reveals how the satellite cell protects itself from damage and maintains quiescence, while being primed for activation on receipt of the appropriate signal. This is illustrated by manipulation of the corepressor Dach1, and by the demonstration that quiescent satellite cells are better protected from oxidative stress than those from mdx or 1-week-old muscles. The quiescent versus in vivo activated comparison also gives new insights into how the satellite cell controls its niche on the muscle fiber through cell adhesion and matrix remodeling. The latter also potentiates growth factor activity through proteoglycan modification. Dismantling the extracellular matrix is important for satellite cell activation when the expression of proteinases is up-regulated, whereas transcripts for their inhibitors are high in quiescent cells. In keeping with this, we demonstrate that metalloproteinase function is required for efficient regeneration in vivo.

Mitochondrial glutathione uptake: characterization in isolated brain mitochondria and astrocytes in culture

Glutathione in the mitochondria is an important determinant of cellular responses to oxidative stress. Mitochondrial glutathione is maintained by uptake from the cytosol, a process that has been little studied in brain cells. In the present study, measurements using isolated rat brain mitochondria showed a rapid uptake of [3H]-glutathione that was strongly influenced by the mitochondrial glutathione content. [3H]-glutathione incorporated into the mitochondria was not rapidly released. Uptake was inhibited by substrates and inhibitors for several known mitochondrial anion transporters. Citrate, isocitrate and benzene-1,2,3-tricarboxylate were particularly effective inhibitors, suggesting a possible role for a tricarboxylate carrier in the glutathione transport. The properties of uptake differed greatly from those reported previously for mitochondria from kidney and liver. In astrocytes in primary culture, diethylmaleate or hydrogen peroxide treatment resulted in depletion of cytosolic and mitochondrial glutathione. The pattern of restoration of glutathione content in the presence of glutathione precursors following treatment with diethylmaleate was consistent with uptake into mitochondria being controlled primarily by the glutathione gradient between the cytosol and mitochondria. However, following hydrogen peroxide treatment, recovery of glutathione in the mitochondria initially preceded comparable proportional restoration in the cytosol, suggesting the possibility of additional controls on glutathione uptake in some conditions.

Is propylene oxide induced cell proliferation in rat nasal respiratory epithelium mediated by a severe depletion of water-soluble non-protein thiol?

Propylene oxide (PO) concentrations >or=300 ppm induced cell proliferation and tumors in rat nasal respiratory epithelium (NRE). Cell proliferation was suggested to result from depletion of glutathione (GSH) in NRE. In order to substantiate this hypothesis, cell proliferation - measured by bromodeoxyuridine incorporation into DNA of the epithelium lining middle septum, dorsal medial meatus, and medial and lateral surfaces of the nasoturbinate in transverse nasal sections taken immediately posterior to the upper incisor teeth - and water-soluble non-protein thiol (NPSH) in NRE were determined after exposing male Fischer 344 rats to 50 ppm, 100 ppm, 200 ppm, or 300 ppm PO (6 h/day, 3 days). Both parameters were also investigated after treating rats for 3 days with diethylmaleate (DEM; 2 x 250 mg/kg/day or 500 + 150 mg/kg/day) or buthionine sulfoximine (BSO; 500 mg/kg/day). Exposure to 50 ppm PO and treatment with 2 x2 50 mg/kg/day DEM resulted in NPSH levels approximating 50% and 80% of the level in untreated controls, respectively. Cell proliferation did not increase. After exposures to >or= 100 ppm PO or treatment with BSO or 500 + 150 mg/kg/day DEM, NPSH was depleted to <or=1/3 of the control level and cell proliferation increased 2.0-3.7-fold the control value. In conclusion, profound perturbation of the GSH status may represent a crucial step in PO induced rat nasal tumorigenicity.

Antioxidant levels represent a major determinant in the regenerative capacity of muscle stem cells

Stem cells are classically defined by their multipotent, long-term proliferation, and self-renewal capabilities. Here, we show that increased antioxidant capacity represents an additional functional characteristic of muscle-derived stem cells (MDSCs). Seeking to understand the superior regenerative capacity of MDSCs compared with myoblasts in cardiac and skeletal muscle transplantation, our group hypothesized that survival of the oxidative and inflammatory stress inherent to transplantation may play an important role. Evidence of increased enzymatic and nonenzymatic antioxidant capacity of MDSCs were observed in terms of higher levels of superoxide dismutase and glutathione, which appears to confer a differentiation and survival advantage. Further when glutathione levels of the MDSCs are lowered to that of myoblasts, the transplantation advantage of MDSCs over myoblasts is lost when transplanted into both skeletal and cardiac muscles. These findings elucidate an important cause for the superior regenerative capacity of MDSCs, and provide functional evidence for the emerging role of antioxidant capacity as a critical property for MDSC survival post-transplantation.

Oxidative Stress as a Mechanism of Valproic Acid-Associated Hepatotoxicity

Valproic acid (2-n-propylpentanoic acid; VPA) has several therapeutic indications, but it is used primarily as an anticonvulsant. VPA is a relatively safe drug, but its use is associated with idiosyncratic hepatotoxicity, which in some cases may lead to fatality. The underlying mechanism responsible for the hepatotoxicity is still not well understood, but various hypotheses have been proposed, including oxidative stress. This article discusses the experimental evidence on the effect of VPA on the various indices of oxidative stress and on the potential role of oxidative stress in VPA-associated hepatotoxicity.

Biochemical composition and metabolic pathways of filarial worms Setaria cervi: search for new antifilarial agents

The main problem regarding the chemotherapy of filariasis is that no safe and effective drug is available yet to combat the adult human filarial worms. Setaria cervi, the causal organism of setariasis and lumbar paralysis in cattle, is routinely employed as a model organism for conducting biochemical and enzymatic studies on filarial parasites. In view of the practical difficulties in procuring human strains of Wuchereria bancrofti and Brugia malayi for drug screening, the bovine filarial parasite S. cervi, resembling the human species in having microfilarial periodicity and chemotherapeutic response to known antifilarial agents, is widely used as a model in such studies. For a rational approach to antifilarial chemotherapy, knowledge of the biochemical composition and metabolic pathways of this helminth parasite may be of paramount importance, so that more potent antifilarial agents based on specific drug targets can be identified in drug discovery programmes. The present review provides an update on the biochemistry of the important metabolic pathways functioning within this potentially important bovine parasite, that have so far been studied, and on those that need to be investigated further so as to identify novel drug targets that can be exploited for designing new antifilarial drugs.

Potential Benefits of Peroxynitrite

Peroxynitrite (PN) is generated by the reaction of nitric oxide (NO) and superoxide in one of the most rapid reactions in biology. Studies have reported that PN is a cytotoxic molecule that contributes to vascular injury in a number of disease states. However, it has become apparent that PN has beneficial effects including vasodilation, inhibition of platelet aggregation, inhibition of inflammatory cell adhesion, and protection against ischemia/reperfusion injury in the heart. It is our hypothesis that PN may serve to inactivate superoxide and prolong the actions of NO in the circulation. This manuscript reviews the beneficial effects of PN in the cardiovascular system.

Analyses of (1-chloroethenyl)oxirane headspace and hemoglobin N-valine adducts in erythrocytes indicate selective detoxification of (1-chloroethenyl)oxirane enantiomers

Chloroprene (2-chloro-1,3-butadiene, CAS 126-99-8, CP) is a colorless volatile liquid used in manufacture of polychloroprene, a synthetic rubber polymer. National Toxicology Program inhalation studies of CP in rats and mice gave clear evidence of carcinogenic activity. CP is metabolized by CYP2E1 to electrophilic epoxides, including R- and S-(1-chloroethenyl)oxirane (CEO), which form adducts with nucleic acids and other nucleophiles including glutathione and hemoglobin. As detection of these epoxide metabolites in vivo is technically challenging, measurements of CEO-Hb adducts may provide biomarkers of exposure to bioactivated metabolites of CP. The present studies involved exposure of C57BL/6 mouse erythrocytes (RBC) in vitro to pure enantiomers of CEO. Headspace analysis of CEO using Cyclodex-B capillary GC/MS with selected ion monitoring enabled separation, specific detection, and quantification of CEO enantiomers as reactions proceeded in vitro with RBC. These analyses indicated that R-CEO was much more persistent when incubated in vitro with RBC, while S-CEO disappeared rapidly. After periods of exposure of RBC to various concentrations of R- or S-CEO, erythrocytes were lysed and globin isolated. Covalent adducts, formed by reaction of CEO with N-terminal valine in Hb, were analyzed following Edman cleavage and trimethylsilylation. SIM-GC/MS analyses using a 5%-phenyl-dimethylsiloxane capillary column enabled quantification of CEO-Hb adducts. These analyses produced two chromatographic peaks of CEO-valine adduct derivatives, which were tentatively identified from mass spectra, reaction, and abundance data to be 1-(3-chloro-2-trimethylsilyloxybut-3-en-1-yl)-5-isopropyl-3-phenyl-2-thiohydantoin and 1-[2-chloro-1-(trimethylsilyloxymethyl)prop-2-en-1-yl]-5-isopropyl-3-phenyl-2-thiohydantoin. Analyses quantified significantly greater levels of adducts formed from R-CEO than from S-CEO. Studies involving pretreatment of RBC with glutathione-depleting diethyl maleate diminished the selective detoxification of S-CEO, and suggest enantiomeric selectivity of mouse glutathione-S-transferase as a mechanism of differential detoxification of CEO enantiomers. These results indicate more rapid detoxification of S-CEO by mouse RBC in vitro, while R-CEO may persist to react with cellular nucleophiles.

Assessment of oxidative stress in chronic pancreatitis patients

AIM: To assess the levels of antioxidant capacity and oxidative damage in blood of chronic pancreatitis (CP) patients in comparison with those in healthy control subjects, by using several different analytical techniques.

METHODS: Thirty-five CP patients and 35 healthy control subjects were investigated prospectively with respect to plasma levels of thiols, ferric reducing ability of plasma (FRAP, i.e. antioxidant capacity), levels of protein carbonyls and thiobarbituric acid reactive substances (TBARS). Additionally, we evaluated the production of reactive oxygen species (ROS) in whole blood.

RESULTS: The antioxidative thiols including cysteine, cysteinylglycine and glutathione were significantly lower in CP patients. In addition, the non-enzymatic antioxidant capacity was significantly lower in CP patients, which correlated with the amount of oxidative protein (protein carbonyls) and the extent of lipid damage (TBARS), both were significantly higher in CP patients. The ROS production in whole blood after stimulation with phorbol 12-myritate 13-acetaat, demonstrated a strong tendency to produce more ROS in CP patients.

CONCLUSION: Oxidative stress may contribute to the pathogenesis of chronic pancreatitis by decreasing antioxidant capacity and increasing oxidative damage in CP patients may be a rationale for intervention with antioxidant therapy.

Styrene-7,8-Oxide Burden in Ventilated, Perfused Lungs of Mice and Rats Exposed to Vaporous Styrene

Styrene (ST) is an important industrial chemical. In long-term inhalation studies, ST-induced lung tumors in mice but not in rats. To test the hypothesis that the lung burden by the reactive metabolite styrene-7,8-oxide (SO) would be most relevant for the species-specific tumorigenicity, we investigated the SO burden in isolated lungs of male Sprague-Dawley rats and in-situ prepared lungs of male B6C3F1 mice ventilated with air containing vaporous ST and perfused with a modified Krebs-Henseleit buffer (37 degrees C). Styrene vapor concentrations were determined in air samples collected in the immediate vicinity of the trachea. They were almost constant during each experiment. Styrene exposures ranged from 50 to 980 ppm (rats) and from 40 to 410 ppm (mice). SO was quantified from the effluent perfusate. Lungs of both species metabolized ST to SO. After a mathematical translation of the ex-vivo data to ventilation and perfusion conditions as they are occurring in vivo, a species comparison was carried out. At ST concentrations of up to 410 ppm, mean SO levels in mouse lungs ranged up to 0.45 nmol/g lung, about 2 times higher than in rat lungs at equal conditions of ST exposure. We conclude that the species difference in the SO lung burden is too small to consider the genotoxicity of SO as sufficient for explaining the fact that only mice developed lung tumors when exposed to ST. Another cause is considered as driving force for lung tumor development in the mouse.

Cardiomyocyte apoptosis induced by short-term diabetes requires mitochondrial GSH depletion

Oxidative stress due to excessive reactive oxygen species (ROS) and depleted antioxidants such as glutathione (GSH) can give rise to apoptotic cell death in acutely diabetic hearts and lead to heart disease. At present, the source of these cardiac ROS or the subcellular site of cardiac GSH loss [i.e., cytosolic (cGSH) or mitochondrial (mGSH) GSH] has not been completely elucidated. With the use of rotenone (an inhibitor of the electron transport chain) to decrease the excessive ROS in acute streptozotocin (STZ)-induced diabetic rat heart, the mitochondrial origin of ROS was established. Furthermore, mitochondrial damage, as evidenced by loss of membrane potential, increases in oxidative stress, and reduction in mGSH was associated with increased apoptosis via increases in caspase-9 and -3 activities in acutely diabetic hearts. To validate the role of mGSH in regulating cardiac apoptosis, l-buthionine-sulfoximine (BSO; 10 mmol/kg ip), which blocks GSH synthesis, or diethyl maleate (DEM; 4 mmol/kg ip), which inactivates preformed GSH, was administered in diabetic rats for 4 days after STZ administration. Although both BSO and DEM lowered cGSH, they were ineffective in reducing mGSH or augmenting cardiomyocyte apoptosis. To circumvent the lack of mGSH depletion, BSO and DEM were coadministered in diabetic rats. In this setting, mGSH was undetectable and cardiac apoptosis was further aggravated compared with the untreated diabetic group. In a separate group, GSH supplementation induced a robust amplification of mGSH in diabetic rat hearts and prevented apoptosis. Our data suggest for the first time that mGSH is crucial for modulating the cell suicide program in short-term diabetic rat hearts.

Glutathione depletion inhibits lipopolysaccharide-induced intercellular adhesion molecule 1 synthesis

Cellular redox status is known to regulate a number of biological processes, including the activation of inflammatory genes. Our previous studies demonstrated that thiol depletion using diethyl maleate (DEM) reduced neutrophil sequestration in animal models of inflammation, an effect primarily mediated by impaired upregulation of the adhesion molecule, ICAM-1. The present studies were performed to discern the mechanism whereby DEM prevents LPS-induced ICAM-1 expression in human umbilical vein endothelial cells. DEM caused a time- and concentration-dependent inhibition of ICAM-1 expression in LPS-stimulated HUVEC by blocking induction of gene transcription. Interestingly, DEM had little effect on the degradation of the inhibitory protein IkappaB-alpha, but rather appeared to prevent translocation of the transcription factor NF-kappaB into the nucleus. Readdition of glutathione following DEM treatment restored the ability of LPS to induce NF-kappaB translocation and ICAM-1 synthesis. DEM plus LPS caused synergistic induction of heme oxygenase-1 (HO-1), suggesting its role in the inhibitory effects of DEM. However, HO-1 was shown to be neither sufficient nor necessary for the anti-inflammatory effects of glutathione depletion. These studies illustrate that thiol depletion may represent a potential therapy for inflammation, exerting its effects via a distinct mechanism on cell signaling pathways.

Valproic acid II: effects on oxidative stress, mitochondrial membrane potential, and cytotoxicity in glutathione-depleted rat hepatocytes

Oxidative stress has been associated with valproic acid (VPA) treatment, and mitochondrial dysfunction has been implicated in the pathogenesis of VPA-idiosyncratic hepatotoxicity. The present study investigated the effect of VPA and the role of GSH on oxidative stress, mitochondrial membrane potential, and toxicity in freshly isolated rat hepatocytes. Hepatocytes were isolated from Sprague-Dawley rats, and total levels of glutathione (GSH) reduced by pretreatment with a combination of L-buthionine sulfoximine (2 mM) and diethylmaleate (0.5 mM) prior to VPA (0-1000 microg/ml) treatment. Oxidative stress was determined by measuring the levels of 15-F(2t)-isoprostane (15-F(2t)-IsoP) and 2',7'-dichlorofluorescein (DCF). Mitochondrial membrane potential (Deltapsi(m)) was determined by using the dual-fluorescent dye JC-1, and cell viability was evaluated by the water-soluble tetrazolium salt WST-1 assay. Exposure of rat hepatocytes to VPA (0-1000 mug/ml) resulted in a time- and dose-dependent increase in 15-F(2t)-IsoP and DCF fluorescence, and these levels were further elevated in GSH-reduced hepatocytes. In control hepatocytes, VPA had no effect on cell viability; however, significant cytotoxicity was observed in the glutathione-depleted hepatocytes treated with 1000 mug/ml VPA. The Deltapsi(m) was only reduced in glutathione-reduced hepatocytes at 500 and 1000 microg/ml VPA. Our novel findings indicate that acute treatment of freshly isolated rat hepatocytes with VPA resulted in oxidative stress, which occurred in the absence of cytotoxicity, and that glutathione confers protection to hepatocytes against mitochondrial damage by VPA.

Consequences of abrupt glutathione depletion in murine Clara cells: ultrastructural and biochemical investigations into the role of glutathione loss in naphthalene cytotoxicity

Glutathione plays many critical roles within the cell, including offering protection from reactive chemicals. The bioactivated toxicant naphthalene forms chemically reactive intermediates that can deplete glutathione and covalently bind to cellular proteins. Naphthalene selectively injures the nonciliated epithelial cells of the intrapulmonary airways (i.e., Clara cells). This study attempted to define what role glutathione loss plays in naphthalene cytotoxicity by comparing Swiss-Webster mice treated with naphthalene with those treated with the glutathione depletor diethylmaleate. High-resolution imaging techniques were used to evaluate acute changes in Clara cell ultrastructure, membrane permeability, and cytoskeleton structure. A single dose of either diethylmaleate (1000 mg/kg) or naphthalene (200 mg/kg) caused similar glutathione losses in intrapulmonary airways (< 20% of control). Diethylmaleate did not increase membrane permeability, disrupt mitochondria, or lead to cell death--hallmark features of naphthalene cytotoxicity. However, diethylmaleate treatment did cause Clara cell swelling, plasma membrane blebs, and actin cytoskeleton disruptions similar to naphthalene treatment. Structural changes in mitochondria and Golgi bodies also were noted. Changes in ATP levels were measured as an indication of overall cell function, in isolated airway explants incubated with diethylmaleate, naphthalene, or naphthalene metabolites in vitro. Only the reactive metabolites of naphthalene caused significant ATP losses. Unlike the lethal injury caused by naphthalene, the disruptive cellular changes associated with glutathione loss from diethylmaleate seemed to be reversible after recovery of glutathione levels. This suggests that glutathione depletion may be responsible for some aspects of naphthalene cytotoxicity, but it is not sufficient to cause cell death without further stresses.