Glutathione protection against hydrogen peroxide, tert-butyl hydroperoxide and diamide cytotoxicity in rat hepatoma-derived Fa32 cells

Protective effects of tiopronin on oxidatively challenged human lung carcinoma cells (A549)

Tiopronin (MPG) is a thiol antioxidant drug that has been explored as a treatment for various oxidative stress-related disorders. However, many of its antioxidant capabilities remain untested in well-validated cell models. To more thoroughly understand the action of this promising pharmaceutical compound against acute oxidative challenge, A549 human lung carcinoma cells were exposed to tert-butyl hydroperoxide (tBHP) and treated with MPG. Analyses of cell viability, intracellular glutathione (GSH) levels, and the prevalence of reactive oxygen species (ROS) and mitochondrial superoxide were used to examine the effects of MPG on tBHP-challenged cells. MPG treatment suppressed intracellular ROS and mitochondrial superoxide and prevented tBHP-induced GSH depletion and apoptosis. These results indicate that MPG is effective at preserving redox homeostasis against acute oxidative insult in A549 cells if present at sufficient concentrations during exposure to oxidants such as tBHP. The effects of treatment gleaned from this study can inform experimental design for future in vivo work on the therapeutic potential of MPG.

Sedoheptulose-1,7-bisphospate Accumulation and Metabolic Anomalies in Hepatoma Cells Exposed to Oxidative Stress

We have previously shown that GSH depletion alters global metabolism of cells. In the present study, we applied a metabolomic approach for studying the early changes in metabolism in hydrogen peroxide- (H₂O₂-) treated hepatoma cells which were destined to die. Levels of fructose 1,6-bisphosphate and an unusual metabolite, sedoheptulose 1,7-bisphosphate (S-1,7-BP), were elevated in hepatoma Hep G2 cells. Deficiency in G6PD activity significantly reduced S-1,7-BP formation, suggesting that S-1,7-BP is formed in the pentose phosphate pathway as a response to oxidative stress. Additionally, H₂O₂ treatment significantly increased the level of nicotinamide adenine dinucleotide phosphate (NADP⁺) and reduced the levels of ATP and NAD⁺. Severe depletion of ATP and NAD⁺ in H₂O₂-treated Hep G2 cells was associated with cell death. Inhibition of PARP-mediated NAD⁺ depletion partially protected cells from death. Comparison of metabolite profiles of G6PD-deficient cells and their normal counterparts revealed that changes in GSH and GSSG per se do not cause cell death. These findings suggest that the failure of hepatoma cells to maintain energy metabolism in the midst of oxidative stress may cause cell death.

Effects of dietary yeast Saccaromyces cerevisiae on the antioxidant system in the liver of juvenile sea bass Dicentrarchus labrax

The main goal of this work was to determine the effect of dietary live yeast Saccharomyces cerevisiae on the oxidative status of sea bass Dicentrarchus labrax juveniles. Fishes were fed on three diets: the GM group were fed a diet containing lyophilized yeast grown on grape must, the CS group were fed a diet containing lyophilized yeast grown on cornstarch, and the control group were fed a diet without yeast. The activity of the main antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase, glutathione S-transferase (GST), and glutathione (GSH) content, as well as lipid peroxidation, was measured in the liver of sea bass juveniles 90 days after hatching. Supplementation of the diet with S. cerevisiae significantly reduced the SOD and CAT activity, increased the GST activity, decreased the GSH content, and had no effect on lipid peroxidation. The results support the already reported radical-scavenging properties of yeast and usefulness of its employment as antiperoxidative agent in fish.

OLA1, an Obg-like ATPase, suppresses antioxidant response via nontranscriptional mechanisms

Oxidative stress has been implicated in diverse disease states and aging. To date, induction of cellular responses to combat oxidative stress has been characterized largely at the transcriptional level, with emphasis on Nrf2-mediated activation of antioxidant response elements. In this study, we demonstrate that OLA1, a novel Obg-like ATPase, functions as a negative regulator of the cellular antioxidant response independent of transcriptional processes. Knockdown of OLA1 in human cells elicited an increased resistance to oxidizing agents including tert-butyl hydroperoxide (tBH) and diamide without affecting cell proliferation, baseline apoptosis, or sensitivity to other cytotoxic agents that target the mitochondria, cytoskeleton, or DNA. Conversely, overexpression of OLA1 increased cellular sensitivity to tBH and diamide. When challenged with oxidants, OLA1-knockdown cells had decreased production of intracellular reactive oxygen species and exhibited less depletion of reduced glutathione. Surprisingly, knockdown of OLA1 caused only minimal genomic response; no changes were found in the mRNA levels of genes encoding antioxidant enzymes, enzymes that produce antioxidants (including glutathione), or other genes known to respond to Nrf2. Moreover, when de novo protein synthesis was blocked by cycloheximide in OLA1-knockdown cells, they continued to demonstrate increased resistance to both tBH and diamide. These data demonstrate that OLA1 suppresses the antioxidant response through nontranscriptional mechanisms. The beneficial effects observed upon OLA1-knockdown suggest that this regulatory ATPase is a potential novel target for antioxidative therapy.

Glucocorticoid pretreatment increases toxicity due to peroxides in alveolar epithelial-like cell lines

In previous experiments an increase in zinc-mediated toxicity was found after pretreatment of alveolar epithelial type II-like cells with glucocorticoids. In this work toxicity of two peroxides (tertiary butyl hydroperoxide [tBHP], hydrogene peroxide [HP]) was assessed in L2 and A549 cells compared to dexamethasone (DEX) pretreated cells. Pretreatment of cells with 7.5micromol/l DEX for 72h decreased cellular glutathione content in both cell lines. Furthermore compared to not pretreated cells toxicity of both peroxides was increased in A549 cells, while in L2 cells only toxicity of tBHP was significantly increased by the glucocorticoid pretreatment. HP toxicity only showed a tendency to be increased in L2 cells after DEX pretreatment. The results point to a glucocorticoid-dependent increased oxidative stress of alveolar epithelial type II cells as antagonised by antioxidative enzymes such as catalase and/or preferentially by the glutathione system. This furthermore should be considered for all glucocorticoid applications in vivo as well.

Expression of the trxC gene of Rhodobacter capsulatus: response to cellular redox status is mediated by the transcriptional regulator OxyR

Despite the importance of thioredoxins in cellular functions, little is known about the regulation of trx genes. To understand the molecular mechanisms involved in the regulation of the Rhodobacter capsulatus trxC gene, the expression of this gene was investigated. We describe OxyR-dependent redox regulation of the trxC gene that adjusts the levels of thioredoxins in the cell.

Effect of Nutritional Status and Ozone Exposure on Some Biomarkers of Oxidative Stress in Rat Brain Regions

The aim of this study was to analyze the effect of nutritional condition and simulated exposure to ozone on Glutathione (GSH), the activity of Na+/K+ ATPase and lipid peroxidation in rat brain. Male Wistar rats were fed with 7% and 23% protein diets. Two groups were formed for each nutritional condition: one group was exposed for 15 successive days to 0.75 ppm of ozone and the other to air. Subsequently, the brain was dissected in cortex, hemispheres, cerebellum, and brainstem to measure the activity of thiobarbituric acid reactive substances (TBARS), ATPase, and levels of GSH. The activity of Na+/K+ ATPase increased in cerebellum of well-nourished rats exposed to ozone, while total ATPase and TBARS decreased in all studied areas in the malnourished groups. The levels of GSH decreased significantly (P < 0.05) in the brain of rats fed with 7% of protein diet and exposed to ozone but increased in rats fed with normal diet and exposed to ozone. These results suggest that malnutrition causes alterations in the values of Na+/K+ ATPase, total ATPase, GSH, and lipid peroxidation, while ozone contributes to these modifications. As a consequence, both variables are involved in oxidative stress in the rat brain.

Modification of endoplasmic reticulum Ca2+ stores by select oxidants produces changes reminiscent of those in cells from patients with Alzheimer disease

Abnormalities in calcium homeostasis and oxidative processes occur in fibroblasts from patients with Alzheimer disease (AD) and in fibroblasts and neurons from transgenic mice bearing a presenilin-1 (PS-1) mutation. Bombesin-releasable endoplasmic reticulum Ca2+ stores (BRCS) are exaggerated in all of these cells. Our previous studies show that H2O2 exaggerates BRCS. The goal of the present study was to determine whether select reactive species exaggerate BRCS in cultured human fibroblasts and to determine if the ability of fibroblasts to handle these specific oxidant species is altered in cells from AD patients. Two fluorescent indicators were used to distinguish different reactive oxygen species (ROS): 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate, di(acetoxymethyl ester) (c-DCF) and 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM). ROS were produced by a variety of oxidants, including tert-butyl-hydroxyperoxide (t-BHP), hypoxanthine/xanthine oxidase, S-nitroso-N-acetylpenicillamine, 3-morpholinosydnonimine, and sodium nitroprusside. Different oxidants selectively induced various ROS in distinct patterns. These oxidants also induced selective modification in [Ca2+]i and/or BRCS. Of the several oxidants tested, t-BHP was most specific for exaggerating BRCS without affecting basal [Ca2+]i and inducing only c-DCF-detectable ROS. On the other hand, the results show that NO that reacted with DAF-FM was not responsible for alterations in BRCS. Furthermore, the c-DCF-detectable ROS production induced by t-BHP was higher in fibroblasts from AD patients bearing a PS-1 mutation (n = 7) than in those from aged controls (n = 8). The higher production of c-DCF-detectable ROS may underlie the exaggeration of BRCS in fibroblasts from AD patients. Thus, these results are consistent with the hypothesis that abnormalities in selective cellular ROS cause AD-related changes in intracellular calcium regulation.

Effects of ozone oxidative preconditioning on TNF-alpha release and antioxidant-prooxidant intracellular balance in mice during endotoxic shock

Ozone oxidative preconditioning is a prophylactic approach, which favors the antioxidant-prooxidant balance for preservation of cell redox state by the increase of antioxidant endogenous systems in both in vivo and in vitro experimental models. Our aim is to analyze the effect of ozone oxidative preconditioning on serum TNF-α levels and as a modulator of oxidative stress on hepatic tissue in endotoxic shock model (mice treated with lipopolysaccharide (LPS)). Ozone/oxygen gaseous mixture which was administered intraperitoneally (0.2, 0.4, and 1.2 mg/kg) once daily for five days before LPS (0.1 mg/kg, intraperitoneal). TNF-α was measured by cytotoxicity on L-929 cells. Biochemical parameters such as thiobarbituric acid reactive substances (TBARS), enzymatic activity of catalase, glutathione peroxidase, and glutathione-S transferase were measured in hepatic tissue. One hour after LPS injection there was a significant increase in TNF-α levels in mouse serum. Ozone/oxygen gaseous mixture reduced serum TNF-α levels in a dose-dependent manner. Statistically significant decreases in TNF-α levels after LPS injection were observed in mice pretreated with ozone intraperitoneal applications at 0.2 (78%), 0.4 (98%), and 1.2 (99%). Also a significant increase in TBARS content was observed in the hepatic tissue of LPS-treated mice, whereas enzymatic activity of glutathion-S transferase and glutathione peroxidase was decreased. However in ozone-treated animals a significant decrease in TBARS content was appreciated as well as an increase in the activity of antioxidant enzymes. These results indicate that ozone oxidative preconditioning exerts inhibitory effects on TNF-α production and on the other hand it exerts influence on the antioxidant-prooxidant balance for preservation of cell redox state by the increase of endogenous antioxidant systems.

The role of glutathione in the neurotoxicity of artemisinin derivatives in vitro

The role of antioxidants in the neurotoxicity of the antimalarial endoperoxides artemether and dihydroartemisinin was studied in vitro by quantitative image analysis of neurite outgrowth in the neuroblastoma cell line NB2a. Intracellular glutathione concentrations were measured by high performance liquid chromatography with fluorescence detection. Both dihydroartemisinin (1 microM) and a combination of artemether (0.3 microM) plus haemin (2 microM) significantly inhibited neurite outgrowth from differentiating NB2a cells to 11.5 +/- 11.0% (SD) and 19.6 +/- 15.2% of controls, respectively. The inhibition by artemether/haemin was prevented by the antioxidants superoxide dismutase (109.7 +/- 47.8% of control), catalase (107.0 +/- 29.3%) glutathione (123.8 +/- 12.4%), L-cysteine (88.0 +/- 6.3%), N-acetyl-L-cysteine (107.8 +/- 14.9%), and ascorbic acid (104.3 +/- 12.7%). Dihydroartemisinin-induced neurotoxicity was completely or partially prevented by L-cysteine (99.5 +/- 17.7% of control), glutathione (57.9 +/- 23.4% of control), and N-acetyl-L-cysteine (57.3 +/- 9.5%), but was not prevented by superoxide dismutase, catalase, or ascorbic acid. Buthionine sulphoximine, an inhibitor of gamma-glutamylcysteine synthetase, significantly increased the neurotoxic effect of non-toxic concentrations of artemether/haemin (0.1 microM/2 microM) and dihydroartemisinin (0.2 microM), suggesting that endogenous glutathione participates in the prevention of the neurotoxicity of artemether/haemin and dihydroartemisinin. Artemether/haemin completely depleted intracellular glutathione levels, whereas dihydroartemisinin had no effect. We conclude that although glutathione status is an important determinant in the neurotoxicity of endoperoxides, depletion of glutathione is not a prerequisite for their toxicity. This is consistent with their mechanisms of toxicity being free radical-mediated damage to redox-sensitive proteins essential for neurite outgrowth, or alteration of a redox-sensitive signalling system which regulates neurite outgrowth.