Protective effects of 15-deoxy-Δ12,14-prostaglandin J2against glutamate-induced cell death in primary cortical neuron cultures: induction of adaptive response and enhancement of cell tolerance primarily through up-regulation of cellular glutathione

An overview of hyperbaric oxygen preconditioning against ischemic stroke

Ischemic stroke (IS) has become the second leading cause of morbidity and mortality worldwide, and the prevention of IS should be given high priority. Recent studies have indicated that hyperbaric oxygen preconditioning (HBO-PC) may be a protective nonpharmacological method, but its underlying mechanisms remain poorly defined. This study comprehensively reviewed the pathophysiology of IS and revealed the underlying mechanism of HBO-PC in protection against IS. The preventive effects of HBO-PC against IS may include inducing antioxidant, anti-inflammation, and anti-apoptosis capacity; activating autophagy and immune responses; upregulating heat shock proteins, hypoxia-inducible factor-1, and erythropoietin; and exerting protective effects upon the blood-brain barrier. In addition, HBO-PC may be considered a safe and effective method to prevent IS in combination with stem cell therapy. Although the benefits of HBO-PC on IS have been widely observed in recent research, the implementation of this technique is still controversial due to regimen differences. Transferring the results to clinical application needs to be taken carefully, and screening for the optimal regimen would be a daunting task. In addition, whether we should prescribe an individualized preconditioning regimen to each stroke patient needs further exploration.

Lipid peroxidation products as a mediator of toxicity and adaptive response - The regulatory role of selenoprotein and vitamin E

Lipid peroxidation and its products have been investigated extensively and their biological importance, particularly in relation to physiological and pathophysiological conditions, has received considerable attention. Lipids are oxidized by three distinct mechanisms, i.e., enzymatic oxidation, nonenzymatic, free radical-mediated oxidation, and nonenzymatic, nonradical-mediated oxidation, which respectively yield specific products. Lipid hydroperoxides are the major primary products formed and are reduced to the corresponding hydroxides by antioxidative enzymes such as selenoproteins, and/or undergo secondary oxidation, generating various products with electrophilic properties, such as 4-hydroxy-2-nonenal. Lipid peroxidation induces a loss of fine structure and natural function of lipids, and can produce cytotoxicity and/or novel biological activity. This review broadly discusses the mechanisms of lipid peroxidation and its products, its utility as a biomarker for oxidative stress, the biological effects of lipid peroxidation products, including their action as a mediator of the adaptive response, and the role of the antioxidant system, particularly selenoproteins and vitamin E, in preventing lipid peroxidation and ferroptosis.

DJ-1 as a Biomarker of Parkinson's Disease

Parkinson's disease is a progressive, age-related, neurodegenerative disorder, and oxidative stress is an important mediator in its pathogenesis. DJ-1 has been identified as a causative gene of a familial form of Parkinson's disease, PARK7, and plays a significant role in antioxidative defense, protecting cells from oxidative stress. A cysteine residue of DJ-1 at position 106 (Cys-106) is preferentially oxidized under oxidative stress. This reactive Cys-106 plays a critical role in the biological function of DJ-1, which could act as a sensor of oxidative stress by regulating antioxidative defense depending on Cys-106 oxidation. Thus, the levels of Cys-106-oxidized DJ-1 (oxDJ-1) could be a possible biomarker of oxidative stress. This chapter focuses on the properties of DJ-1 and oxDJ-1 levels as a biomarker of Parkinson's disease. In particular, the usability of these biomarkers to prevent and treat this neurodegenerative disease is discussed. Further, this section deals with the importance of identifying a biomarker of early-phase Parkinson's disease. Finally, this chapter summarizes the features of oxDJ-1 levels in the brain and blood as a biomarker candidate for early-phase Parkinson's disease based on our results using oxDJ-1-specific antibodies.

The Modulation of NMDA and AMPA/Kainate Receptors by Tocotrienol-Rich Fraction and Α-Tocopherol in Glutamate-Induced Injury of Primary Astrocytes

Astrocytes are known as structural and supporting cells in the central nervous system (CNS). Glutamate, as a main excitatory amino acid neurotransmitter in the mammalian central nervous system, can be excitotoxic, playing a key role in many chronic neurodegenerative diseases. The aim of the current study was to elucidate the potential of vitamin E in protecting glutamate-injured primary astrocytes. Hence, primary astrocytes were isolated from mixed glial cells of C57BL/6 mice by applying the EasySep^® Mouse CD11b Positive Selection Kit, cultured in Dulbecco's modified Eagle medium (DMEM) and supplemented with special nutrients. The IC₂₀ and IC₅₀ values of glutamate, as well as the cell viability of primary astrocytes, were assessed with 100 ng/mL, 200 ng/mL, and 300 ng/mL of tocotrienol-rich fraction (TRF) and alpha-tocopherol (α-TCP), as determined by an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The mitochondrial membrane potential (MMP) detected in primary astrocytes was assessed with the same concentrations of TRF and α-TCP. The expression levels of the ionotropic glutamate receptor genes (Gria2, Grin2A, GRIK1) were independently determined using RT-PCR. The purification rate of astrocytes was measured by a flow-cytometer as circa 79.4%. The IC₂₀ and IC₅₀ values of glutamate were determined as 10 mM and 100 mM, respectively. Exposure to 100 mM of glutamate in primary astrocytes caused the inhibition of cell viability of approximately 64.75% and 61.10% in pre- and post-study, respectively (p < 0.05). Both TRF and α-TCP (at the lowest and highest concentrations, respectively) were able to increase the MMP to 88.46% and 93.31% pre-treatment, and 78.43% and 81.22% post-treatment, respectively. Additionally, the findings showed a similar pattern for the expression level of the ionotropic glutamate receptor genes. Increased extracellular calcium concentrations were also observed, indicating that the presence of vitamin E altered the polarization of astrocytes. In conclusion, α-TCP showed better recovery and prophylactic effects as compared to TRF in the pre-treatment of glutamate-injured primary astrocytes.

Discovery and identification of potential biomarkers for alcohol-induced oxidative stress based on cellular metabolomics

Biomarkers involved in alcohol-induced oxidative stress play an important role in alcoholic liver disease prevention and diagnosis. Alcohol-induced oxidative stress in human liver L-02 cells was used to discover the potential biomarkers. Metabolites from L-02 cells induced by alcohol were measured by high-performance liquid chromatography and mass spectrometry. Fourteen metabolites that allowed discrimination between control and model groups were discovered by multivariate statistical data analysis (i.e. principal components analysis, orthogonal partial least-squares discriminate analysis). Based on the retention time, UV spectrum and LC-MS findings of the samples and compared with the authentic standards, eight biomarkers involved in alcohol-induced oxidative stress, namely, malic acid, oxidized glutathione, γ-glutamyl-cysteinyl-glycine, adenosine triphosphate, phenylalanine, adenosine monophosphate, nitrotyrosine and tryptophan, were identified. These biomarkers offered important targets for disease diagnosis and other researches.

Oxidative stress and antioxidants: Distress or eustress?

There is a growing consensus that reactive oxygen species (ROS) are not just associated with various pathologies, but that they act as physiological redox signaling messenger with important regulatory functions. It is sometimes stated that "if ROS is a physiological signaling messenger, then removal of ROS by antioxidants such as vitamins E and C may not be good for human health." However, it should be noted that ROS acting as physiological signaling messenger and ROS removed by antioxidants are not the same. The lipid peroxidation products of polyunsaturated fatty acids and cholesterol induce adaptive response and enhance defense capacity against subsequent oxidative insults, but it is unlikely that these lipid peroxidation products are physiological signaling messenger produced on purpose. The removal of ROS and inhibition of lipid peroxidation by antioxidants should be beneficial for human health, although it has to be noted also that they may not be an effective inhibitor of oxidative damage mediated by non-radical oxidants. The term ROS is vague and, as there are many ROS and antioxidants which are different in chemistry, it is imperative to explicitly specify ROS and antioxidant to understand the effects and role of oxidative stress and antioxidants properly.

New aspects of 24(S)-hydroxycholesterol in modulating neuronal cell death

24(S)-Hydroxycholesterol (24S-OHC), which is enzymatically produced in the brain, has been known to play an important role in maintaining cholesterol homeostasis in the brain and has been proposed as a possible biomarker of neurodegenerative disease. Recent studies have revealed diverse functions of 24S-OHC and gained increased attention. For example, 24S-OHC at sublethal concentrations has been found to induce an adaptive response via activation of the liver X receptor signaling pathway, thereby protecting neuronal cells against subsequent oxidative stress. It has also been found that physiological concentrations of 24S-OHC suppress amyloid-β production via downregulation of amyloid precursor protein trafficking in neuronal cells. On the other hand, high concentrations of 24S-OHC have been found to induce a type of nonapoptotic programmed cell death in neuronal cells expressing little caspase-8. Because neuronal cell death induced by 24S-OHC has been found to proceed by a unique mechanism, which is different from but in some ways similar to necroptosis-necroptosis being a type of programmed necrosis induced by tumor necrosis factor α-neuronal cell death induced by 24S-OHC has been called "necroptosis-like" cell death. 24S-OHC-induced cell death is dependent on the formation of 24S-OHC esters but not on oxidative stress. This review article discusses newly reported aspects of 24S-OHC in neuronal cell death and sheds light on the possible importance of controlling 24S-OHC levels in the brain for preventing neurodegenerative disease.

Adaptive responses induced by 24S-hydroxycholesterol through liver X receptor pathway reduce 7-ketocholesterol-caused neuronal cell death

Lipid peroxidation products have been known to induce cellular adaptive responses and enhance tolerance against subsequent oxidative stress through up-regulation of antioxidant compounds and enzymes. 24S-hydroxycholesterol (24SOHC) which is endogenously produced oxysterol in the brain plays an important role in maintaining brain cholesterol homeostasis. In this study, we evaluated adaptive responses induced by brain-specific oxysterol 24SOHC in human neuroblastoma SH-SY5Y cells. Cells treated with 24SOHC at sub-lethal concentrations showed significant reduction in cell death induced by subsequent treatment with 7-ketocholesterol (7KC) in both undifferentiated and retinoic acid-differentiated SH-SY5Y cells. These adaptive responses were also induced by other oxysterols such as 25-hydroxycholesterol and 27-hydroxycholesterol which are known to be ligands of liver X receptor (LXR). Co-treatment of 24SOHC with 9-cis retinoic acid, a retinoid X receptor ligand, enhanced the adaptive responses. Knockdown of LXRβ by siRNA diminished the adaptive responses induced by 24SOHC almost completely. The treatment with 24SOHC induced the expression of LXR target genes, such as ATP-binding cassette transporter A1 (ABCA1) and G1 (ABCG1). The 24SOHC-induced adaptive responses were significantly attenuated by siRNA for ABCG1 but not by siRNA for ABCA1. Taken together, these results strongly suggest that 24SOHC at sub-lethal concentrations induces adaptive responses via transcriptional activation of LXR signaling pathway, thereby protecting neuronal cells from subsequent 7KC-induced cytotoxicity.

•

24SOHC induces adaptive responses against 7KC-induced cell death in neuronal cells.

•

Co-treatment of 24SOHC with 9cRA, an RXR ligand enhances adaptive responses.

•

Knockdown of LXRβ suppresses 24SOHC-induced adaptive responses.

•

ABCG1 is involved in LXR-mediated adaptive responses by 24SOHC.

Simultaneous inhibition of COX-2 and activation of PPAR-γ resulted in the same level and pattern of neuroprotection as they were targeted separately

The inflammatory response is an immune response of the body when exposed to internal and external stimuli. Cyclooxygenases (COX) are major inflammatory mediators implicated in inflammation. COX-2 is reported to be involved in neuroinflammation. Moreover, 15-Deoxy-D (12,14)-prostaglandin J2 (15d-PGJ2), an endogenous ligand of peroxisome proliferator-activated receptor gamma (PPAR-γ), has been demonstrated to have anti-inflammatory actions. In this study, we investigated whether co-therapy of a selective COX-2 inhibitor NS-398 and 15d-PGJ2 as a PPAR-γ ligand could exert additional neuroprotective effects in rat pheochromocytoma (PC12) cells. Our findings showed that 15d-PGJ2 and NS-398 suppress the apoptotic pathway in PC12 cells exposed to H(2)O(2) by attenuation of the Bax/Bcl-2 ratio. This effect was mediated through PPAR-γ, as it was reversed by GW9662 (a PPAR-γ inhibitor). Also, 15d-PGJ2 and NS-398 induced the Nrf2 signaling pathway and decreased NF-κB level in a PPAR-γ-dependent manner. We found that coadministration of a selective COX-2 inhibitor and a PPAR-γ ligand in PC12 cells has equal neuroprotective effect compared to their effects when used separately. Considering the higher affinity of 15d-PGJ2 for PPAR-γ than NS-398, it seems that the observed neuroprotection of this combination therapy was from 15d-PGJ2.

Neuroprotective cyclopentenone prostaglandins up-regulate neurotrophic factors in C6 glioma cells

In a previous study, we developed newly synthesized arylthio derivatives of cyclopentenone prostaglandins (GIF-0642, GIF-0643, GIF-0644, GIF-0745 and GIF-0747), which are neuroprotective against both manganese toxicity in PC12 cells and glutamate toxicity in HT22 cells. In the present study, we showed that these compounds and their lead compound, NEPP11, are potent inducers of glial cell line-derived neurotrophic factor (GDNF) expression in C6 glioma cells and primary astrocytes. These neuroprotective cyclopentenone prostaglandins also induced the gene expression of nerve growth factor and, to a lesser extent, brain-derived neurotrophic factor. The induction of GDNF mRNA was transcription-dependent, and the overexpression of dominant-negative Nrf2 attenuated the ability of the (arylthio)cyclopentenone prostaglandins to stimulate GDNF gene expression. These results suggest that (arylthio)cyclopentenone prostaglandins increase GDNF gene expression partly via the Keap1/Nrf2 pathway. A growing number of reports demonstrate the importance of increasing the amounts of neurotrophic factors, especially GDNF, in neuropathological states. Although the precise mechanisms by which the GIF compounds inhibit cell death are under investigation, an increase in neurotrophic factors may contribute to the diverse pharmacological properties of (arylthio)cyclopentenone prostaglandins in vivo and will make them potentially valuable in the treatment of neurodegenerative disorders.

Hyperbaric oxygen preconditioning protects cortical neurons against oxygen-glucose deprivation injury: role of peroxisome proliferator-activated receptor-gamma

Ischemic stroke is one of the leading causes of mortality and disability worldwide. Our previous studies have shown that hyperbaric oxygen (HBO) preconditioning can afford significant neuroprotection against cerebral ischemia-reperfusion (I/R) injury in rats. However, it is still unknown whether HBO preconditioning can directly protect primary cultured cortical neurons against oxygen-glucose deprivation (OGD). Peroxisome proliferator-activated receptor-gamma (PPAR γ) plays a central role in the regulation of apoptosis, oxidative stress and inflammation as well as affords significant neuroprotection against cerebral I/R injury. 15-deoxy-∆(12,14)-prostaglandin J(2) (15d-PGJ(2)) is an endogenous ligand with a high affinity for PPAR γ. Recently, some studies demonstrate that activation of PPAR γ mediates lipopolysaccharide and anesthetic preconditioning. In the present study, we firstly found that OGD exposure caused the significant damage of cultured cortical neurons evaluated by cell viability, lactate dehydrogenase (LDH) release and caspase-3 activity, which were significantly ameliorated by HBO preconditioning. Furthermore, HBO preconditioning significantly increased the levels of PPAR γ mRNA and protein, PPAR γ DNA binding activity, 15d-PGJ(2) and antioxidant enzymatic activities in primary cultured cortical neurons with OGD exposure. Moreover, PPAR γ antagonist GW9662 dose-dependently abolished the protection of HBO preconditioning in OGD-exposed neurons. GW9662 blocked the increase of PPAR γ DNA binding activity and antioxidant enzymatic activities, but did not influence the 15d-PGJ(2) level in OGD-exposed neurons with HBO preconditioning. However, the cyclooxygenase (COX)-2 inhibitor NS-398 blocked the production of 15d-PGJ(2) in OGD-exposed neurons with HBO preconditioning. In addition, 15d-PGJ(2) preconditioning could also protect cultured neurons against OGD injury. These results demonstrate that HBO preconditioning has directly beneficial effects on ODG-exposed cortical neurons by the activation of PPAR γ subsequent to the production of 15d-PGJ(2), which in turn increases the downstream antioxidant enzymatic activities.

Prevention of Oxidative Stress-Induced Retinal Pigment Epithelial Cell Death by the PPARgamma Agonists, 15-Deoxy-Delta 12, 14-Prostaglandin J(2)

Cellular oxidative stress plays an important role in retinal pigment epithelial (RPE) cell death during aging and the development of age-related macular degeneration. Early reports indicate that during phagocytosis of rod outer segments, there is an increase of RPE oxidative stress and an upregulation of PPARγ mRNA in these cells. These studies suggest that activation of PPARγ may modulate cellular oxidative stress. This paper presents a brief review of recent studies that investigate RPE oxidative stress under various experimental conditions. This is followed by a detailed review on those reports that examine the protective effect of the natural PPARγ ligand, 15d-PGJ₂, against RPE oxidative stress. This agent can upregulate glutathione and prevent oxidant-induced intracellular reactive oxygen species accumulation, mitochondrial depolarization, and apoptosis. The cytoprotective effect of this agent, however, is not shared by other PPARγ agonists. Nonetheless, this property of 15d-PGJ₂ may be useful in future development of pharmacological tools against retinal diseases caused by oxidative stress.

α-Tocopheryl phosphate: uptake, hydrolysis, and antioxidant action in cultured cells and mouse

α-Tocopheryl phosphate (α-TP), a water-soluble analogue of α-tocopherol, is found in humans, animals, and plants. α-TP is resistant to both acid and alkaline hydrolysis and may exert its own function in this form in vivo. In this study, the uptake, hydrolysis, and antioxidant action of α-TP were measured using α-TP with a deuterated methyl group, CD(3), at position 5 of the chroman ring (α-TP(CD3)). The hydrolysis of α-TP(CD3) was followed by measuring α-tocopherol containing the CD(3) group, α-T(CD3), in comparison to unlabeled α-tocopherol, α-T(CH3). α-TP(CD3) was incubated with cultured cells, and the intracellular α-T(CD3) formed was measured with HPLC-ECD and GC-MS. α-TP(CD3) was also administered to mice for 4 weeks by mixing in the diet, and α-T(CD3) was measured in plasma, liver, brain, heart, and testis to compare with endogenous unlabeled α-T(CH3). It was found that α-TP(CD3) was taken in and hydrolyzed readily to α-T(CD3) in cultured cells and in mice. The hydrolysis of α-TP(CD3) in cell culture medium was not observed. α-TP protected primary cortical neuronal cells from glutamate-induced cytotoxicity, and α-TP given to mice reduced the levels of lipid peroxidation products in plasma and liver. These results suggest that α-TP is readily hydrolyzed in vivo to α-T, which acts as an antioxidant, and that α-TP may be used as a water-soluble α-T precursor in intravenous fluids, in eye drops, or as a dietary supplement.

24(S)-hydroxycholesterol induces neuronal cell death through necroptosis, a form of programmed necrosis

24(S)-Hydroxycholesterol (24S-OHC) produced by cholesterol 24-hydroxylase expressed mainly in neurons plays an important physiological role in the brain. Conversely, it has been reported that 24S-OHC possesses potent cytotoxicity. The molecular mechanisms of 24S-OHC-induced cell death have not yet been fully elucidated. In this study, using human neuroblastoma SH-SY5Y cells and primary cortical neuronal cells derived from rat embryo, we characterized the form of cell death induced by 24S-OHC. SH-SY5Y cells treated with 24S-OHC exhibited neither fragmentation of the nucleus nor caspase activation, which are the typical characteristics of apoptosis. 24S-OHC-treated cells showed necrosis-like morphological changes but did not induce ATP depletion, one of the features of necrosis. When cells were treated with necrostatin-1, an inhibitor of receptor-interacting serine/threonine kinase 1 (RIPK1) required for necroptosis, 24S-OHC-induced cell death was significantly suppressed. The knockdown of RIPK1 by transfection of small interfering RNA of RIPK1 effectively attenuated 24S-OHC-induced cell death. It was found that neither SH-SY5Y cells nor primary cortical neuronal cells expressed caspase-8, which was regulated for RIPK1-dependent apoptosis. Collectively, these results suggest that 24S-OHC induces neuronal cell death by necroptosis, a form of programmed necrosis.

Cytoprotective effects of vitamin E homologues against glutamate-induced cell death in immature primary cortical neuron cultures: Tocopherols and tocotrienols exert similar effects by antioxidant function

Glutamate plays a critical role in pathological cell death within the nervous system. Vitamin E is known to protect cells from glutamate cytotoxicity, either by direct antioxidant action or by indirect nonantioxidant action. Further, α-tocotrienol (α-T3) has been reported to be more effective against glutamate-induced cytotoxicity than α-tocopherol (α-T). To shed more light on the function of vitamin E against glutamate toxicity, the protective effects of eight vitamin E homologues and related compounds, 2,2,5,7,8-pentamethyl-6-chromanol (PMC) and 2-carboxy-2,5,7,8-pentamethyl-6-chromanol (Trolox), against glutamate-induced cytotoxicity on immature primary cortical neurons were examined using different protocols. Glutamate induced the depletion of glutathione and generation of reactive oxygen species and lipid hydroperoxides, leading to cell death. α-, β-, γ-, and δ-T and -T3; PMC; and Trolox all exerted cytoprotective effects against glutamate-induced cytotoxicity, and a longer preincubation time increased both the cellular content and the cytoprotective effects of T more significantly than those of T3, the effect of preincubation being relatively small for T3 and PMC. The protective effect of Trolox was less potent than that of PMC. The cytoprotective effects of α-T and α-T3 corresponded to their intracellular content. Further, lipid peroxidation products were measured after reduction with triphenylphosphine followed by saponification with potassium hydroxide. It was found that glutamate treatment increased the formation of hydroxyeicosatetraenoic acid, hydroxyoctadecadienoic acid, and 8-F(2)-isoprostane 2α, which was suppressed by α-T. This study shows that vitamin E protects cells from glutamate-induced toxicity primarily by direct antioxidant action and that the apparent higher capacity of T3 compared to T is ascribed to the faster uptake of T3 compared to T into the cells. It is suggested that, considering the bioavailability, α-T should be more effective than α-T3 against glutamate toxicity in vivo.

Functional aspects of redox control during neuroinflammation

Neuroinflammation is a CNS reaction to injury in which some severe pathologies, regardless of their origin, converge. The phenomenon emphasizes crosstalk between neurons and glia and reveals a complex interaction with oxidizing agents through redox sensors localized in enzymes, receptors, and transcription factors. When oxidizing pressures cause reversible molecular changes, such as minimal or transitory proinflammatory cytokine overproduction, redox couples provide a means of translating the presence of reactive oxygen or nitrogen species into useful signals in the cell. Additionally, thiol-based redox sensors convey information about localized changes in redox potential induced by physiologic or pathologic situations. They are susceptible to oxidative changes and become key events during neuroinflammation, altering the course of a signaling response or the behavior of specific transcription factors. When oxidative stress augments the pressure on the intracellular environment, the effective reduction potential of redox pairs diminishes, and cell signaling shifts toward proinflammatory and proapoptotic signals, creating a vicious cycle between oxidative stress and neuroinflammation. In addition, electrophilic compounds derived from the oxidative cascade react with key protein thiols and interfere with redox signaling. This article reviews the relevant functional aspects of redox control during the neuroinflammatory process.

Neurotoxic lipid peroxidation species formed by ischemic stroke increase injury

Stroke is the third leading cause of death in the United States, yet no neuroprotective agents for treatment are clinically available. There is a pressing need to understand the signaling molecules that mediate ischemic cell death and identify novel neuroprotective targets. Cyclopentenone isoprostanes (IsoPs), formed after free radical-mediated peroxidation of arachidonic acid, are used as markers of stress, but their bioactivity is poorly understood. We have recently shown that 15-A(2t)-IsoP is a potent neurotoxin in vitro and increases the free radical burden in neurons. In this work, we demonstrate that 15-A(2t)-IsoP is abundantly produced in stroke-infarcted human cortical tissue. Using primary neuronal cultures we found that minimally toxic exposure to 15-A(2t)-IsoP does not alter ATP content, but in combination with oxygen glucose deprivation resulted in a significant hyperpolarization of the mitochondrial membrane and dramatically increased neuronal cell death. In the presence of Ca(2+), 15-A(2t)-IsoP led to a rapid induction of the permeability transition pore and release of cytochrome c. Taken with our previous work, these data support a model in which ischemia causes generation of reactive oxygen species, calcium influx, lipid peroxidation, and 15-A(2t)-IsoP formation. These factors combine to enhance opening of the permeability transition pore leading to cell death subsequent to mitochondrial cytochrome c release. These data are the first documentation of significant 15-A(2t)-IsoP formation after acute ischemic stroke and suggest that the addition of 15-A(2t)-IsoP to in vitro models of ischemia may help to more fully recapitulate stroke injury.

Select cyclopentenone prostaglandins trigger glutathione efflux and the role of ABCG2 transport

Electrophilic cyclopentenone prostaglandins (cyPGs), such as 15-deoxy-Delta(12,14)-prostaglandin J(2) (15dPGJ(2)), initiate redox-based cell signaling responses including increased intracellular glutathione (GSH) synthesis. We investigated whether cyPGs facilitated GSH efflux and if members of the ATP-binding cassette (ABC) protein family mediated the efflux. Four human cell lines were treated with 1-6 microM cyPGs for 48 h. Media and cells were harvested for GSH measurements using HPLC-EC. CyPG treatment increased extracellular GSH levels two- to threefold over controls in HN4 and C38 cells and five- to sixfold in SAEC and MDA 1586 cells and was dependent on increased GSH synthesis. Our studies show that prostaglandin D(2) and its metabolites, prostaglandin J(2) and 15dPGJ(2), specifically induce GSH efflux compared to other eicosanoids. These higher extracellular GSH levels were associated with protection from tert-butylhydroperoxide. Superarray analysis of ABC transporters suggested only ABCG2 expression had a positive relationship in the four cell types compared with extracellular GSH increases after cyPG treatment. The ABCG2 substrate Hoechst 33342 inhibited extracellular GSH increase after 15dPGJ(2) treatment. We report for the first time that ABCG2 may play a role in GSH efflux in response to cyPG treatment and may link inflammatory signaling with antioxidant adaptive responses.

Induction of adaptive response and enhancement of PC12 cell tolerance by lipopolysaccharide primarily through the upregulation of glutathione S-transferase A3 via Nrf2 activation

Increasing evidence indicates that reactive oxygen species and other physiologically existing oxidative stimuli upregulate the antioxidant system, thereby triggering the adaptive response. In this study, we focused on adaptive cytoprotection induced by lipopolysaccharide (LPS), which induces oxidative stress and inflammatory cytokines, in PC12 cells, a model of the neuronal cell. After treating PC12 cells with LPS at sublethal concentrations, we found that they developed resistance to subsequent oxidative stress induced by 13S-hydroperoxy-9Z,11E-octadecadienoic acid and 5-amino-3-(4-morpholinyl)-1,2,3-oxadiazolium. To determine the underlying molecular mechanisms responsible for an adaptive response induced by LPS, we studied the changes in the antioxidant system. LPS treatment resulted in an increase in the gene expression of glutathione S-transferase A3 (GST-A3) by up to 60-fold as well as in GST enzyme activity. A GST inhibitor and GST A3 small interfering RNA effectively attenuated the adaptive response. The nuclear factor erythroid 2 p45-related factor 2 (Nrf2) was transcriptionally activated by LPS. Nrf2 small interfering RNA effectively attenuated the increase in GST A3 mRNA level as well as the adaptive response induced by LPS. In addition, peripheral injection of LPS at sublethal concentrations increased GST enzyme activity in mouse brain. These findings, taken together, indicate that stimulation with LPS at sublethal concentrations induces an adaptive response and enhances PC12 cell tolerance, primarily through the induction of GST A3 via the transcriptional activation of the Nrf2 signaling pathway.

Gamma-tocopheryl quinone, not alpha-tocopheryl quinone, induces adaptive response through up-regulation of cellular glutathione and cysteine availability via activation of ATF4

alpha-Tocopheryl quinone (alpha-TQ) and gamma-TQ are oxidized metabolites of the corresponding tocopherol (T) isoforms, which are vitamin E homologues. Unlike alpha-TQ, gamma-TQ functions as an arylating agent that reacts with nucleophiles such as reduced sulphydryl groups and it has unique biological properties such as high toxicity. Increasing evidence indicates that reactive oxygen species and other physiologically existing oxidative stimuli upregulate the antioxidant system, thereby triggering the adaptive response. The present study used PC12 cells and immature primary cortical cells to examine the possible adaptive cytoprotective effects of gamma-TQ against oxidative stress. Pre-treatment with gamma-TQ at sub-lethal concentrations resulted in cytoprotective effects against oxidative stress. gamma-TQ induced a significant increase in the cellular glutathione (GSH) levels while alpha-TQ did not. gamma-TQ did not induce any considerable change in the activity of glutamate-cysteine ligase (GCL), the rate-limiting enzyme in GSH synthesis, whereas it increased the cellular GSH levels by facilitating the availability of cysteine through the induction of xCT, which is the core sub-unit of the x(c)(-) high-affinity cystine transporter system. An activating transcription factor 4 (ATF4)-small interfering RNA effectively attenuated the xCT mRNA level as well as the increase in cellular cysteine levels induced by gamma-TQ, while the NF-E2-related factor (Nrf2)-small interfering RNA treatment did not. Collectively, these findings indicate that gamma-TQ acts as a signal messenger to induce adaptive response through the upregulation of intracellular GSH synthesis via transcriptional activation of ATF4 in order to cope with the forthcoming oxidative insult.

Prevention of methylmercury-induced mitochondrial depolarization, glutathione depletion and cell death by 15-deoxy-delta-12,14-prostaglandin J(2)

Methylmercury (MeHg) is an environmental toxin that causes severe neurological complications in humans and experimental animals. In addition to neurons, glia in the central nervous system are very susceptible to MeHg toxicity. Pretreatment of glia with the prostaglandin derivative, 15-deoxy-delta-12,14-prostaglandin J(2) (15d-PGJ(2)), caused a significant protection against MeHg cytotoxicity. Results with the C6 glioma cells demonstrated that the protection was dependent on the duration of pretreatment, suggesting that time was required for the up-regulation of cellular defenses. Subsequent experiments indicated that 15d-PGJ(2) prevented MeHg induced mitochondrial depolarization. Similar protection against MeHg cytotoxicity was observed in primary cultures of mouse glia. Analysis of cellular glutathione (GSH) levels indicated that 15d-PGJ(2) caused an up-regulation of GSH and prevented MeHg-induced GSH depletion. Buthionine sulfoximine (BSO), a GSH synthesis inhibitor, completely inhibited the GSH induction by 15d-PGJ(2). However, BSO did not prevent the stabilization of mitochondrial potential and only partially prevented the protection caused by 15d-PGJ(2). While induction of heme oxygenase-1 was implicated in the cytoprotection by 15d-PGJ(2) under some experimental conditions, additional experiments indicated that this enzyme was not involved in the cytoprotection observed in this system. Together, these results suggested that while up-regulation of GSH by 15d-PGJ(2) might help cells to defend against MeHg toxicity, there may be other yet unidentified mechanism(s) initiated by 15d-PGJ(2) treatment that contributed to its protection against MeHg cytotoxicity.

Chemical reactivities and physical effects in comparison between tocopherols and tocotrienols: physiological significance and prospects as antioxidants

Vitamin E is a generic term for all tocopherol and tocotrienol derivatives. The most abundant and active form of vitamin E isoforms in vivo is alpha-tocopherol, but recently the roles of other forms of vitamin E have received renewed attention. In this review, we summarize the differences among alpha-, beta-, gamma-, delta-tocopherols and tocotrienols specifically regarding the following points; (i) their radical-scavenging efficacies and chemical reactivity with metal ions in solution, (ii) their physical effects at the liposomal membrane interior, and (iii) their protective effects against cell toxicity. Moreover, the physiological significance and future prospects for using vitamin E, especially tocotrienols, for the prevention and treatment of disease are discussed.

Assessment of antioxidative activity of extract from fermented grain food mixture using chemical and cellular systems

Fermented food is a rich source of antioxidants and micronutrients with the potential to prevent various human diseases. The increasing evidence indicates that in addition to its direct action, radical-scavenging antioxidants may modulate the cellular antioxidant system such as glutathione. In the present study, we investigated the antioxidant activity of Antioxidant Biofactor (AOB) extracts, a mixture of commercially available fermented grain food by using chemical and cellular experimental systems. In the former system, the total radical scavenging capacity was assessed from the bleaching of pyranine and pyrogallol red that is induced by free radicals generated from an azo initiator. In this assay system, the radical scavenging capacity per gram of AOB was estimated to be 95 micromol. On the other hand, the cytoprotective effect of AOB was also investigated on the basis of PC12 cell death induced by 6-hydroxydopamine. In this cellular system, AOB extract exhibited a cytoprotective effect only when the cells were pretreated with AOB. This pretreatment resulted in a significant increase in the levels of cellular glutathione as well as regulator of glutathione synthesis, such as the cystine/glutamate exchange transport system (xCT). This evidence suggests that AOB possesses both direct and indirect antioxidant activities to cope with oxidative insults.