Induction of apoptosis in a human leukemic cell line via reactive oxygen species modulation by antioxidants

In the human acute myeloid leukemia cell line M07e, the growth factor interleukin-3 (IL-3) induces ROS formation, positively affecting Glut1-mediated glucose uptake and cell survival. The effect of IL-3 and exogenous hydrogen peroxide on cell viability seems to be mediated through inhibition of the cell death commitment, as shown by apoptotic markers such as caspase activities, apoptotic nuclei, and changes in the amount of proteins belonging to the Bcl-2 family. The pivotal role of ROS is confirmed using various antioxidants, such as EUK-134, ebselen, TEMPO, and hydroxylamine probe. In fact, these antioxidants, acting through different mechanisms, decrease glucose transport activity and cell proliferation activated by IL-3 or by low concentrations of hydrogen peroxide. Moreover, antioxidants foster programmed cell death commitment, as shown by the cited apoptotic parameters. EUK-134, a combined superoxide dismutase/catalase mimetic, opposes the effects of IL-3 and H₂O₂, decreasing phosphorylation levels of signaling enzymes such as Akt, Src tyrosine kinase, and ERK. Results show that ROS production induced by IL-3 can protect leukemic cells from apoptosis, the effect being counteracted by antioxidants. This mechanism may play an important role in supporting acute myeloid leukemia treatment, thus representing a novel therapeutic strategy.     

Comparison of the effects of the superoxide dismutase mimetics EUK-134 and tempol on paraquat-induced nephrotoxicity

Paraquat-induced nephrotoxicity involves severe renal cell damage caused by reactive oxygen species (ROS), specifically via increasing concentrations of superoxide anions in the kidney. Recently, superoxide dismutase (SOD) mimetics (SODm) have been developed that display safe SOD activities but which also possess additional antioxidant enzyme (e.g., catalase) or ROS-scavenging activities. The aim of this study was to compare the effects of two such SODm, specifically, EUK-134, a SODm with catalase activity, and tempol, a SODm with ROS-scavenging properties, on paraquat-induced nephrotoxicity of renal NRK-52E cells. Incubation with paraquat (1 mM) for 24 h reduced cell viability and increased necrosis significantly. Paraquat also generated significant quantities of superoxide anions and hydroxyl radicals. Both EUK-134 (10-300 microM) and tempol (0.3-1.0 mM) were able to improve cell viability and reduced paraquat-induced cell death significantly via dismutation or scavenging of superoxide anions and reduced hydroxyl radical generation. The data presented here suggest that SODm such as EUK-134 and tempol, which possess additional catalase and/or ROS-scavenging activities, can significantly reduce renal cell damage caused by paraquat. These effects were evident at concentrations which avoid the pro-oxidant activities associated with higher concentrations of SOD. Such SODm could therefore prove to be beneficial as therapies for paraquat nephrotoxicity.     

Molecular mechanisms of nitric oxide-induced growth arrest and apoptosis in fetal pulmonary arterial smooth muscle cells

Superoxide plays an important role in pulmonary arterial smooth muscle cell (SMC) proliferation and survival. The rapid reaction between superoxide and nitric oxide (NO) to form peroxynitrite suggests that endothelium-derived NO may influence adjacent SMC growth. To investigate this possibility, we determined the dose-dependent effects of NO on the proliferation and viability of pulmonary arterial SMC isolated from fetal lambs (FPASMC). Using fluorescence microscopy we found a dose-dependent decrease in superoxide levels in FPASMC treated with the NO donor spermine NONOate. This was associated with an increase in peroxynitrite-mediated protein nitration. At doses between 50 and 250 microM, spermine NONOate attenuated serum-induced FPASMC proliferation resulting in a G(0)/G(1) cell cycle arrest. This process involved a decrease in levels of cyclin A and an increase in the nuclear localization of p21 and p27. Furthermore, 500 microM spermine NONOate decreased viable cell number by inducing programmed cell death: FPASMC treated with 500 microM spermine NONOate displayed a loss of mitochondrial membrane potential, followed by caspase activation and DNA fragmentation. These data suggest that NO inhibits superoxide-induced proliferation of FPASMC and at higher doses induces apoptosis. NO donors may therefore prove to be useful therapeutic tools to treat diseases resulting from excessive proliferation of vascular smooth muscle.     

Role of mitochondrial electron transport chain complexes in capsaicin mediated oxidative stress leading to apoptosis in pancreatic cancer cells

We evaluated the mechanism of capsaicin-mediated ROS generation in pancreatic cancer cells. The generation of ROS was about 4-6 fold more as compared to control and as early as 1 h after capsaicin treatment in BxPC-3 and AsPC-1 cells but not in normal HPDE-6 cells. The generation of ROS was inhibited by catalase and EUK-134. To delineate the mechanism of ROS generation, enzymatic activities of mitochondrial complex-I and complex-III were determined in the pure mitochondria. Our results shows that capsaicin inhibits about 2.5-9% and 5-20% of complex-I activity and 8-75% of complex-III activity in BxPC-3 and AsPC-1 cells respectively, which was attenuable by SOD, catalase and EUK-134. On the other hand, capsaicin treatment failed to inhibit complex-I or complex-III activities in normal HPDE-6 cells. The ATP levels were drastically suppressed by capsaicin treatment in both BxPC-3 and AsPC-1 cells and attenuated by catalase or EUK-134. Oxidation of mitochondria-specific cardiolipin was substantially higher in capsaicin treated cells. BxPC-3 derived ρ(0) cells, which lack mitochondrial DNA, were completely resistant to capsaicin mediated ROS generation and apoptosis. Our results reveal that the release of cytochrome c and cleavage of both caspase-9 and caspase-3 due to disruption of mitochondrial membrane potential were significantly blocked by catalase and EUK-134 in BxPC-3 cells. Our results further demonstrate that capsaicin treatment not only inhibit the enzymatic activity and expression of SOD, catalase and glutathione peroxidase but also reduce glutathione level. Over-expression of catalase by transient transfection protected the cells from capsaicin-mediated ROS generation and apoptosis. Furthermore, tumors from mice orally fed with 2.5 mg/kg capsaicin show decreased SOD activity and an increase in GSSG/GSH levels as compared to controls. Taken together, our results suggest the involvement of mitochondrial complex-I and III in capsaicin-mediated ROS generation and decrease in antioxidant levels resulting in severe mitochondrial damage leading to apoptosis in pancreatic cancer cells.     

Response of the antioxidant defense system to tert-butyl hydroperoxide and hydrogen peroxide in a human hepatoma cell line (HepG2)

The aim of this work was to investigate the response of the antioxidant defense system to two oxidative stressors, hydrogen peroxide and tert-butyl hydroperoxide, in HepG2 cells in culture. The parameters evaluated included enzyme activity and gene expression of superoxide dismutase, catalase, glutathione peroxidase, and activity of glutathione reductase. Besides, markers of the cell damage and oxidative stress evoked by the stressors such as cell viability, intracellular reactive oxygen species generation, malondialdehyde levels, and reduced glutathione concentration were evaluated. Both stressors, hydrogen peroxide and tert-butyl hydroperoxide, enhanced cell damage and reactive oxygen species generation at doses above 50 microM. The concentration of reduced glutathione decreased, and levels of malondialdehyde and activity of the antioxidant enzymes consistently increased only when HepG2 cells were treated with tert-butyl hydroperoxide but not when hydrogen peroxide was used. A slight increase in the gene expression of Cu/Zn superoxide dismutase and catalase with 500 microM tert-butyl hydroperoxide and of catalase with 200 microM hydrogen peroxide was observed. The response of the components of the antioxidant defense system evaluated in this study indicates that tert-butyl hydroperoxide evokes a consistent cellular stress in HepG2.     

Endothelin-1 decreases endothelial NOS expression and activity through ETA receptor-mediated generation of hydrogen peroxide

Similar to infants born with persistent pulmonary hypertension of the newborn (PPHN), there is an increase in circulating endothelin-1 (ET-1) and decreased endothelial nitric oxide synthase (eNOS) gene expression in an ovine model of PPHN. These abnormalities lead to vasoconstriction and vascular remodeling. Our previous studies have demonstrated that reactive oxygen species (ROS) levels are elevated in the pulmonary arteries from PPHN lambs and that ET-1 increases ROS production in pulmonary arterial smooth muscle cells (PASMC) in culture. Thus the objective of this study was to determine whether there was a feedback mechanism between the ET-1-mediated increase in ROS in fetal PASMC (FPASMC) and a decrease in eNOS gene expression in fetal pulmonary arterial endothelial cells (FPAEC). Our results indicate that ET-1 increased H2O2 levels in FPASMC in an endothelin A receptor-dependent fashion. This was observed in both FPASMC monoculture and in cocultures of FPASMC and FPAEC. Conversely, ET-1 decreased H2O2 levels in FPAEC monoculture in an endothelin B receptor-dependent fashion. Furthermore, ET-1 decreased eNOS promoter activity by 40% in FPAEC in coculture with FPASMC. Promoter activity was restored in the presence of catalase. In FPAEC in monoculture treated with 0-100 microM H2O2, 12 microM had no effect on eNOS promoter activity, but it increased eNOS protein levels by 50%. However, at 100 microM, H2O2 decreased eNOS promoter activity and protein levels in FPAEC by 79 and 40%, respectively. These data suggest a role for smooth muscle cell-derived H2O2 in ET-1-mediated downregulation of eNOS expression in children born with PPHN.     

Contribution of reactive oxygen species to the regulation of Glut1 in two hemopoietic cell lines differing in cytokine sensitivity

Glucose transport activity and its possible regulation by reactive oxygen species in two Glut1-expressing megakaryocytic cell lines, MO7e and B1647, differing in cytokine sensitivity were compared. Results show that: (1) In MO7e cells, glucose transport rate increased in response to thrombopoietin, granulocyte-macrophage colony-stimulating factor, or stem cell factor, due to a decreased Km. (2) A higher Vmax value was determined in B1647 cells, owing to the relative higher abundance of Glut1 on the plasmalemma; in these cells no change in glucose transport rate was observed on cytokine treatment. (3) The basal level of intracellular ROS was higher in B1647 than in M07e cells, where ROS production was enhanced upon cytokine exposure. (4) Basal or stimulated ROS production and Glut1 activity were significantly reduced by pretreating both cell lines with EUK-134, a superoxide dismutase and catalase mimetic. (5) In MO7e cells, EUK-134 brought back to control levels the Km values obtained on cytokine treatment, whereas in B1647 cells the antioxidant drastically reduced Vmax by decreasing the Glut1 content of the plasma membrane. Our data suggest that differences in acute regulation of glucose transport activity in the two cell lines may be related to differences in amplitude and spatial organization of ROS production.     

Amplification of proinflammatory phenotype, damage, and weakness by oxidative stress in the diaphragm muscle of mdx mice

Duchenne muscular dystrophy (DMD) is a common and devastating type of childhood-onset muscular dystrophy, attributed to an X-linked defect in the gene that encodes dystrophin. Myopathy with DMD is most pronounced in the diaphragm muscle and fast-twitch limb muscles and is dependent upon susceptibility to damage, inflammatory cell infiltration, and proinflammatory signaling (nuclear factor-κB; NF-κB). Although recent papers have reawakened the notion that oxidative stress links inflammatory signaling with pathology in DMD in limb muscle, the importance of redox mechanisms had been clouded by inconsistent results from indirect scavenger approaches, including in the diaphragm muscle. Therefore, we used a novel catalytic mimetic of superoxide dismutase and catalase (EUK-134) as a direct scavenger of oxidative stress in myopathy in the diaphragm of the mdx mouse model. EUK-134 reduced 4-hydroxynonenal and total hydroperoxides, markers of oxidative stress in the mdx diaphragm. EUK-134 also attenuated positive staining of macrophages and T-cells as well as activation of NF-κB and p65 protein abundance. Moreover, EUK-134 ameliorated markers of muscle damage including internalized nuclei, variability of cross-sectional area, and type IIc fibers. Finally, impairment of contractile force was partially rescued by EUK-134 in the diaphragm of mdx mice. We conclude that oxidative stress amplifies DMD pathology in the diaphragm muscle.     

Superoxide dismutase mimetics elevate superoxide dismutase activity in vivo but do not retard aging in the nematode Caenorhabditis elegans

According to the oxidative damage theory a primary cause of aging is the accrual of molecular damage from reactive oxygen species (ROS), particularly superoxide and its derivatives. This predicts that treatments that reduce ROS levels should retard aging. Using the nematode Caenorhabditis elegans, we tested the effects on stress resistance and life span of treatment with EUK-8 and EUK-134, synthetic mimetics of the antioxidant enzyme superoxide dismutase (SOD), which neutralises superoxide. Treatment with SOD mimetics elevated in vivo SOD activity levels, particularly in mitochondria, where up to 5-fold increases in SOD activity were recorded. Treatment with exogenous SOD mimetics did not affect endogenous protein SOD levels. Where life span was reduced by the superoxide generators paraquat and plumbagin, EUK-8 treatment increased life span in a dose-dependent fashion. Yet in the absence of a superoxide generator, treatment with EUK-8 or EUK-134 did not increase life span, even at doses that were optimal for protection against pro-oxidants. Thus, an elevation of SOD activity levels sufficient to increase life span when it is limited by superoxide generators does not retard aging in the absence of superoxide generators. This suggests that C. elegans life span is not normally limited by levels of superoxide and its derivatives.     

Protection of insulin-producing cells against toxicity of dexamethasone by catalase overexpression

Pancreatic β cells are very sensitive to reactive oxygen species (ROS) and this might play an important role in β cell death in diabetes. Dexamethasone is a synthetic diabetogenic glucocorticoid, which impairs pancreatic β cell function. Therefore we investigated the toxicity of dexamethasone in RINm5F insulin-producing cells and its dependence on the expression level of the antioxidant enzyme catalase, which inactivates hydrogen peroxide. This was correlated with oxidative stress and cell death. An increased generation of ROS was observed in dexamethasone-treated cells together with an increase in caspase-3 activity and apoptosis rate. Interestingly, exposure to dexamethasone increased the cytosolic superoxide dismutase Cu/ZnSOD protein expression and activity, whereas the mitochondrial MnSOD isoform was not affected by the glucocorticoid. Catalase overexpression in insulin-producing cells prevented all the cytotoxic effects of dexamethasone. In conclusion, dexamethasone-induced cell death in insulin-producing cells is ROS mediated. Increased levels of expression and activity of the Cu/ZnSOD might favor the generation of hydrogen peroxide in dexamethasone-treated cells. Increased ROS scavenging capacity in insulin-producing cells, through overexpression of catalase, prevents a deleterious increase in hydrogen peroxide generation and thus prevents dexamethasone-induced apoptosis.     

Production of superoxide and hydrogen peroxide in medium used to culture Legionella pneumophila: catalytic decomposition by charcoal

The difficulties associated with the growth of Legionella species in common laboratory media may be due to the sensitivity of these organisms to low levels of hydrogen peroxide and superoxide radicals. Exposure of yeast extract (YE) broth to fluorescent light generated superoxide radicals (3 microM/h) and hydrogen peroxide (16 microM/h). Autoclaved YE medium was more prone to photochemical oxidation than YE medium sterilized by filtration. Activated charcoals and, to a lesser extent, graphite, but not starch, prevented photochemical oxidation of YE medium, decomposed hydrogen peroxide and superoxide radicals, and prevented light-accelerated autooxidation of cysteine. Also, suspensions of charcoal in phosphate buffer and in charcoal yeast extract medium readily decomposed exogenous peroxide (17 and 23 nmol/ml per min, respectively). Combinations of bovine superoxide dismutase and catalase also decreased the rate of photooxidation of YE medium. Medium protected from light did not accumulate appreciable levels of hydrogen peroxide, and autoclaved YE medium protected from light supported good growth of Legionella micdadei. Various species of Legionella (10(4) cells per ml) exhibited sensitivity to relatively low levels of hydrogen peroxide (26.5 microM) in challenge experiments. The level of hydrogen peroxide that accumulated in YE medium over a period of several hours (greater than 50 microM) was in excess of the level tolerated by Legionella pneumophila, which contained no measurable catalase activity. Strains of L. micdadei, Legionella dumoffi, and Legionella bozmanii contained this enzyme, but the presence of catalase did not appear to confer appreciable tolerance to exogenously generated hydrogen peroxide.     

Reactive oxygen species are required for hyperoxia-induced Bax activation and cell death in alveolar epithelial cells

Exposure of animals to hyperoxia results in respiratory failure and death within 72 h. Histologic evaluation of the lungs of these animals demonstrates epithelial apoptosis and necrosis. Although the generation of reactive oxygen species (ROS) is widely thought to be responsible for the cell death observed following exposure to hyperoxia, it is not clear whether they act upstream of activation of the cell death pathway or whether they are generated as a result of mitochondrial membrane permeabilization and caspase activation. We hypothesized that the generation of ROS was required for hyperoxia-induced cell death upstream of Bax activation. In primary rat alveolar epithelial cells, we found that exposure to hyperoxia resulted in the generation of ROS that was completely prevented by the administration of the combined superoxide dismutase/catalase mimetic EUK-134 (Eukarion, Inc., Bedford, MA). Exposure to hyperoxia resulted in the activation of Bax at the mitochondrial membrane, cytochrome c release, and cell death. The administration of EUK-134 prevented Bax activation, cytochrome c release, and cell death. In a mouse lung epithelial cell line (MLE-12), the overexpression of Bcl-XL protected cells against hyperoxia by preventing the activation of Bax at the mitochondrial membrane. We conclude that exposure to hyperoxia results in Bax activation at the mitochondrial membrane and subsequent cytochrome c release. Bax activation at the mitochondrial membrane requires the generation of ROS and can be prevented by the overexpression of Bcl-XL.     

Butyrate increases catalase activity and protects rat pulmonary artery smooth muscle cells against hyperoxia

A protective effect of butyrate against hyperoxia was found with adult rat pulmonary artery smooth muscle cells. Butyrate (5mM) when added just prior to the hyperoxic exposure (95%) markedly decreased lactate dehydrogenase release from cells during 68 hours of exposure (22% release with butyrate versus 98% without). The uptake and reduction of a tetrazolium compound as another index of cell viability also showed similar improvement with butyrate. Butyrate was associated with a striking increase of catalase to three times the control in the air exposed group while GSH content and the activities of superoxide dismutase and glutathione peroxidase were not significantly changed. In the groups exposed to hyperoxia alone, both enzyme activities were decreased compared to the air exposed controls. When butyrate was present with hyperoxia, the superoxide dismutase was maintained closer to the air exposed control values and the catalase activity remained nearly twice as high as the air exposed control cells. These results suggest that butyrate protects rat pulmonary artery smooth muscle cells from hyperoxia by increasing catalase activity which may help to preserve superoxide dismutase activity. This may be a good model to determine the biological significance of catalase and its interrelationships with other antioxidant systems within the cell.     

Reactive oxygen species released from granulocytes stimulate 5-lipoxygenase activity in a B-lymphocytic cell line.

B-lymphocytes express 5-lipoxygenase (5-LO) protein but cellular leukotriene production is suppressed by selenium-dependent peroxidases. Thus it was of interest to check whether reactive oxygen species (ROS) which are released under inflammatory conditions can stimulate B-lymphocyte 5-LO and counteract peroxidase-mediated suppression of cellular 5-LO activity. It was found that 5-LO in the Epstein-Barr virus-transformed B-lymphocytic cell line BL41-E95-A is activated by addition of hydrogen peroxide or xanthine/xanthine oxidase and after increasing the oxidative state of the cell by azodicarboxylic acid bis(dimethylamide). Generation of endogenous ROS from mitochondria by antimycin A also lead to a threefold upregulation of 5-LO activity in B-cells. There was almost no detectable endogenous superoxide formation in BL41-E95-A cells after stimulation with 4beta-phorbol 12-myristate 13-acetate. Co-incubation experiments with BL41-E95-A cells and granulocytes demonstrated that granulocyte-derived ROS can activate B-lymphocyte 5-LO. Addition of superoxide dismutase and/or catalase to the B-lymphocyte/granulocyte co-incubations and to B-lymphocyte homogenates revealed that the 5-LO activation is due to the superoxide-derived release of hydroperoxides or hydrogen peroxide from granulocytes. The data suggest that ROS formation plays an important role in the regulation of cellular 5-LO activity in B-lymphocytes. As leukotrienes affect B-cell functions like cell proliferation, activation and maturation, this finding provides a new link between the formation of ROS and the regulation of immune responses.     

Effects of Cr(VI) long-term and low-dose action on mammalian antioxidant enzymes (an in vitro study)

In order to investigate the low-dose long-term Cr(VI) action on antioxidant enzymes in cultured mammalian cells we estimated the activity of glutathione dependent antioxidant enzymes, catalase and superoxide dismutase (SOD) under various chromium concentrations in human epithelial-like L-41 cells. The long-term action of 20 microM causes the toxicity that results in losing of the cell viability by activating the apoptotic process, as identified by morphological analysis, the activation of caspase-3, and DNA fragmentation. The toxic chromium concentration totally destroys glutathione antioxidant system, and diminishes the activity of catalase and cytosolic Cu, ZnSOD. The non-toxic concentration (2 microM) causes the activation of the antioxidant defense systems, and they neutralize the oxidative impact.     

Evaluation of the oxidative burst in suspension cell culture of Phaseolus vulgaris

Plants respond to the attack of pathogens with the oxidative burst, a production of reactive oxygen species (ROS). In this work a cell culture suspension of Phaseolus vulgaris was used to investigate the oxidative burst triggered by a conidia suspension of different races of Colletotrichum lindemuthianum. As a defence response of the cells a two-phase peak was observed with all used races of Colletotrichum lindemuthianum, varying only in the produced amounts of hydrogen peroxide. Findings with additives such as superoxide dismutase (SOD), diphenyleneiodonium (DPI) and catalase gave rise to the conclusion that more superoxide radicals were produced than be detectable with Amplex Red as hydrogen peroxide. It is assumed that the conversion of the superoxide radical is spontaneous and not driven via a cell-derived superoxide dismutase. The addition of low-molecular cell wall components (ergosterol, glucosamine, galactosamine) showed clearly that compounds like this act as elicitors and thus are involved in triggering the burst. Furthermore, an evaluation of the metabolizing capacities of hydrogen peroxide of the suspension culture cells revealed the enormous capacity of the cells to detoxify this ROS.     

Direct current electrical fields induce apoptosis in oral mucosa cancer cells by NADPH oxidase-derived reactive oxygen species

The presence of more than one dental alloy in the oral cavity often causes pathological galvanic currents and voltage resulting in superficial erosions of the oral mucosa and eventually in the emergence of oral cancer. In the present study the mechanisms of apoptosis of oral mucosa cancer cells in response to electromagnetic fields was investigated. Direct current (DC) electrical fields with field strengths between 2 and 16 V/m, applied for 24 h to UM-SCC-14-C oral mucosa cancer cells, dose-dependently resulted in decreased cell proliferation as evaluated by Ki-67 immunohistochemistry and upregulation of the cyclin-dependent kinase (CDK) inhibitors p21(cip1/waf1) and p27(kip1), which are associated with cell cycle arrest. Electrical field treatment (4 V/m, 24 h) increased apoptosis as evaluated by immunohistochemical analysis of cleaved caspase-3 and poly-(ADP-ribose)-polymerase-1 (PARP-1). Furthermore, robust reactive oxygen species (ROS) generation, increased expression of NADPH oxidase subunits as well as Hsp70 was observed. Electrical field treatment (4 V/m, 24 h) resulted in increased expression of Cu/Zn superoxide dismutase and decreased intracellular concentration of reduced glutathione (GSH), whereas the expression of catalase remained unchanged. Pre-treatment with the free radical scavenger N-acetyl cysteine (NAC) and the superoxide dismutase mimetic EUK-8 abolished caspase-3 and PARP-1 induction, suggesting that apoptosis in oral mucosa cancer cells is initated by ROS generation in response to DC electrical field treatment.     

Fas-stimulated generation of reactive oxygen species or exogenous oxidative stress sensitize cells to Fas-mediated apoptosis

Inhibition of Fas-mediated apoptosis in B cell lymphomas by thiol antioxidants (glutathione and N-acetylcysteine) supported previous studies, suggesting that Fas-stimulated ROS generation may play a role in Fas-mediated apoptosis. Thus, the goal of the current study was to determine if Fas stimulation could induce ROS generation and what role, if any, it played in apoptosis. Fas crosslinking induced rapid generation of ROS (within 15 min) well before the appearance of characteristic apoptotic changes. Overexpression of catalase or superoxide dismutase suggested that Fas induced production of both superoxide anion and hydrogen peroxide. ROS generation was only observed, however, in cells that were sensitive to apoptosis and not in B cells inherently resistant to anti-Fas or in those in which resistance was induced by B cell receptor crosslinking. The exogenous addition of 250 microM hydrogen peroxide could reverse the resistant phenotype and sensitize cells to Fas-induced apoptosis. In Fas-sensitive cells, depletion of endogenous antioxidant defenses with buthionine sulfoximine increased the sensitivity to Fas-induced apoptosis, while overexpression of antioxidant enzymes and antiapoptotic proteins suggested a role for Fas-induced production of hydrogen peroxide in apoptosis. Further analysis suggested a redox-sensitive step early in Fas signaling at the level of initiator caspase (caspase-8) activation. Thus, the data suggest that the level of oxidative stress, either from exogenous sources or generated endogenously upon receptor stimulation, regulates the sensitivity to Fas-mediated apoptosis.     

Superoxide dismutase/catalase mimetics are neuroprotective against selective paraquat-mediated dopaminergic neuron death in the substantial nigra: implications for Parkinson disease

Exposure of mice to the herbicide paraquat has been demonstrated to result in the selective loss of dopaminergic neurons of the substantia nigra, pars compacta (SNpc) akin to what is observed in Parkinson disease (PD). In this study, we investigate the efficacy of two synthetic superoxide dismutase/catalase mimetics (EUK-134 and EUK-189) in protecting against paraquat-induced dopaminergic cell death in both the rat dopaminergic cell line 1RB3AN27 (N27) and primary mesencephalic cultures in vitro and in adult mice in vivo. Our data demonstrate that pretreatment with either EUK-134 or EUK-189 significantly attenuates paraquat-induced neurotoxicity in vitro in a concentration-dependent manner. Furthermore, systemic administration of EUK-189 decreases paraquat-mediated SNpc dopaminergic neuronal cell death in vivo. These findings support a role for oxidative stress in paraquat-induced neurotoxicity and suggest novel therapeutic approaches for neurodegenerative disorders associated with oxidative stress such as PD.