Oxidative stress in a clonal cell line of neuronal origin: effects of antioxidant enzyme modulation

New phenotypic cytotoxicity assay for ROS-inducing compounds using rat renal epithelial cells

An important mechanism of chemical toxicity is the induction of oxidative stress through the production of excess reactive oxygen species (ROS). In this study, we show that the level of drug-induced ROS production between NRK52E and HepG2 cells is significantly different for several marketed drugs and a number of Takeda's internal proprietary compounds. Nifedipine, a calcium channel blocker and the initial focus of the study, was demonstrated to promote in vitro ROS production and a decrease in cell viability in NRK52E cells but not HepG2 cells. ROS production after nifedipine treatment was inhibited by a NOX inhibitor (GKT136901) but not the mitochondrial NADH dehydrogenase inhibitor, rotenone, suggesting that nifedipine decreases NRK52E cell viability primarily through a NOX-mediated pathway. To understand the breadth of NOX-mediated ROS production, 12 commercially available compounds that are structurally and/or pharmacologically related to nifedipine as well as 172 internal Takeda candidate drugs, were also evaluated against these two cell types. Over 15 % of compounds not cytotoxic to HepG2 cells (below 50 μM) were cytotoxic to NRK52E cells. Our results suggest that a combination of cell viability data from both NRK52E and HepG2 cells was superior for the prediction of in vivo toxicity findings when compared to use of only one cell line. Further, the NRK52E cell viability assay is a good predictor of NOX-mediated ROS production and can be used as a follow up assay following a negative HepG2 response to aid in the selection of suitable compounds for in vivo toxicity studies.

A novel antiviral inhibits Zika virus infection while increasing intracellular glutathione biosynthesis in distinct cell culture models

We investigated the effects of a specific free-form amino acids formulation on Zika virus replication in two different cell culture model systems, one representative of humans and the other of Old World primates from whom Zika virus was first isolated. Here we present data demonstrating that the formulation of the specific free-form amino acid (FFAAP), comprising cystine, glycine, and a glutamate source, along with a minute concentration of selenium inhibited Zika virus replication by up to 90% with an ED₉₀ (effective dose at which 90% of a dose of Zika virus was inhibited) of 2.5 mM in human cells and 4 mM Vero cells. The ED₉₀ concentration of precursors was innocuous for uninfected cells, but resulted in reduced Zika virus replication by up to 90% at 2-5 mM concentrations in nonhuman primate cells and at 1-3 mM concentration in human placental cells. Two important observations were forthcoming: 1) Zika virus production was decreased by up to 90% in Vero and JEG-3 cells treated with FFAAP (ED₉₀ 4.0 mM, and 2.5 mM, respectively) throughout 48-72 h of post infection (hpi) compared to untreated infected cells and 2) Zika virus requires intracellular glutathione for replication in human placental cells, while showing enhanced replication in Vero cells with no glutathione. Relative increases in intracellular glutathione biosynthesis followed FFAAP treatment but blocking intracellular biosynthesis of glutathione in human cells resulted in virus inhibition in human placental cells. The blockade of biosynthesis actually increased Zika virus replication in Vero cells. These findings identify an efficacious inhibitor, FFAAP, of Zika virus replication in both human and nonhuman primate cells, while providing novel insight into the different roles of intracellular glutathione in Zika virus replication.

Altered cytotoxicity of ROS-inducing compounds by sodium pyruvate in cell culture medium depends on the location of ROS generation

Induction of oxidative stress by drugs and other xenobiotics is an important mechanism of cytotoxicity. However, in vitro studies on the relationship between oxidative stress and cytotoxicity in cultured cells is frequently complicated by the fact that cell culture medium components affect reactive oxygen species (ROS) exposures in ways that vary with the mode of ROS production. The objectives of this study were to first determine the mode of ROS induction by certain model compounds when they are applied to cultured cells, and then to determine how ROS induction and cytotoxicity were affected by the ROS-quenching medium component pyruvate. Three compounds, eseroline, benserazide, and pyrogallol induced H₂O₂ in cell culture media independent of cells. However, another compound, menadione, induced H₂O₂ in a manner largely dependent on the MDA-MB-231 breast cancer cells used in this study, which is consistent with its known mechanism of inducing ROS through intracellular redox cycling. 1 mM pyruvate, as well as catalase, reduced the H₂O₂ in culture wells with each ROS inducer tested but it only reduced the cytotoxicity of cell-independent inducers. It reduced the cytotoxicity of benserazide and pyrogallol >10-fold and of eseroline about 2.5-fold, but had no effect on menadione cytotoxicity. From this data, it was concluded that depending on the mechanism of ROS induction, whether intra- or extracellular, a ROS-quenching medium component such as pyruvate will differentially affect the net ROS-induction and cytotoxicity of a test compound.

Effects of resveratrol on hydrogen peroxide-induced oxidative stress in embryonic neural stem cells

Resveratrol, a natural phenolic compound, has been shown to prevent cardiovascular diseases and cancer and exhibit neuroprotective effects. In this study, we examined the neuroprotective and antioxidant effects of resveratrol against hydrogen peroxide in embryonic neural stem cells. Hydrogen peroxide treatment alone increased catalase and glutathione peroxidase activities but did not change superoxide dismutase levels compared with hydrogen peroxide + resveratrol treatment. Nitric oxide synthase activity and concomitant nitric oxide levels increased in response to hydrogen peroxide treatment. Conversely, resveratrol treatment decreased nitric oxide synthase activity and nitric oxide levels. Resveratrol also attenuated hydrogen peroxide-induced nuclear or mitochondrial DNA damage. We propose that resveratrol may be a promising agent for protecting embryonic neural stem cells because of its potential to decrease oxidative stress by inducing higher activity of antioxidant enzymes, decreasing nitric oxide production and nitric oxide synthase activity, and alleviating both nuclear and mitochondrial DNA damage.

Screening and functional analysis of glioma‑related genes induced by candoxin

This study aimed to identify time‑specific and common differential genes (CDGs) expressed in glioma cells following exposure to candoxin at three different time‑points. Gene expression data from candoxin‑treated human glioma (Hs 683) cells were downloaded from the Gene Expression Omnibus database (accession number, GSE1682), from a 12‑time‑point set of samples. Differentially expressed genes were screened between control and candoxin‑treated samples at different time‑points, and three time‑specific gene sets and CDGs were identified. All genes were subject to pathway enrichment analysis to gain further insight into gene function. CDGs were clustered based upon their original expression between 0 and 48 h, and, from this subset, feature genes were selected. Small molecules associated with candoxin were identified by comparing the expression pattern of the most valid candidate genes with that of differential genes exposed to small molecules in the Connectivity Map. From the 12‑, 24‑ and 48‑h time‑points, 746, 265 and 539 differentially expressed genes were identified, respectively. A total of 129 genes were differentially expressed and significantly enriched in focal adhesion and gap junction pathways. From these, 11 feature genes and one marker gene (EPS8L1) were identified. Four small molecules that were most relevant to candoxin action were identified. In conclusion, it is hypothesized that candoxin stimulation can cause glial inflammation through mutations in cell adhesion activity. The EPS8L1 gene may be a valid marker for glioma diagnosis, and the four small molecules identified may be relevant for future drug design.

Ameliorating reactive oxygen species-induced in vitro lipid peroxidation in brain, liver, mitochondria and DNA damage by Zingiber officinale Roscoe

Iron is an essential nutrient for a number of cellular activities. However, excess cellular iron can be toxic by producing reactive oxygen species (ROS) such as superoxide anion (O(2) (-)) and hydroxyl radical (HO(·)) that damage proteins, lipids and DNA. Mutagenic and genotoxic end products of lipid peroxidation can induce the decline of mitochondrial respiration and are associated with various human ailments including aging, neurodegenerative disorders, cancer etc. Zingiber officinale Roscoe (ginger) is a widely used spice around the world. The protective effect of aqueous ethanol extract of Z. officinale against ROS-induced in vitro lipid peroxidation and DNA damage was evaluated in this study. The lipid peroxidation was induced by hydroxyl radical generated from Fenton's reaction in rat liver and brain homogenates and mitochondrial fraction (isolated from rat liver). The DNA protection was evaluated using H(2)O(2)-induced changes in pBR-322 plasmid and Fenton reaction-induced DNA fragmentation in rat liver. The results indicated that Z. officinale significantly (P<0.001) protected the lipid peroxidation in all the tissue homogenate/mitochondria. The extract at 2 and 0.5 mg/ml could protect 92 % of the lipid peroxidation in brain homogenate and liver mitochondria respectively. The percent inhibition of lipid peroxidation at 1mg/ml of Z. officinale in the liver homogenate was 94 %. However, the extract could partially alleviate the DNA damage. The protective mechanism can be correlated to the radical scavenging property of Z. officinale. The results of the study suggest the possible nutraceutical role of Z. officinale against the oxidative stress induced human ailments.

Preferentially increased nitration of alpha-synuclein at tyrosine-39 in a cellular oxidative model of Parkinson's disease

Alpha-synuclein is a major component of Lewy bodies, proteinacious inclusions which are a major hallmark of Parkinson's disease (PD). Lewy bodies contain high levels of nitrated tyrosine residues as determined by antibodies specific for 3-nitrotyrosine (3NT) and via mass spectrometry (MS). We have developed a multiple reaction monitoring (MRM) mass spectrometry method to sensitively quantitate the 3NT levels of specific alpha-synuclein tyrosine residues. We found a 9-fold increase (relative to controls) in levels of 3NT at Tyr-39 of alpha-synuclein in an inducible transgenic cellular model of Parkinson's disease in which monoamine oxidase B (MAO-B) is overexpressed and which emulates several features of PD. Increased nitration of Tyr-39 on endogenous alpha-synuclein via elevations in MAO-B levels could be abrogated by the addition of deprenyl, a specific MAO-B inhibitor. The increased levels of 3NT was selective for Tyr-39 as no significant increases in 3NT levels were detected at other tyrosine residues present in the protein (Tyr-125, Tyr-133, and Tyr-136). This is the first report of increased 3NT levels of a specific tyrosine in a PD model and the first use of MRM mass spectrometry to quantify changes in 3NT modifications at specific sites within a target protein.

Semichronic Inhibition of Glutathione Reductase Promotes Oxidative Damage to Proteins and Induces both Transcription and Translation of Tyrosine Hydroxylase in the Nigrostriatal System

We have evaluated the effect of N,N-bis (2-chloroethyl)-N-nitrosourea (BCNU), an inhibitor of glutathione reductase (GR), on the oxidative status along with the integrity of the nigrostriatal dopaminergic system of the rat. The oxidative status was studied by the quantification of carbonyl groups coupled to protein homogenates. Moreover, the specific oxidations in glial fibrillary acidic protein (GFAP) and neurofilament-200 (NF-200) were also measured. The results show that oxidative damage in proteins in the nigrostriatal system is confined to the striatum. Specific carbonyl groups coupled to native NF-200 and GFAP were also increased. These changes were accompanied by reactive astrocytosis in striatum but not in substantia nigra. In substantia nigra, decreased levels of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were observed following BCNU treatment. In contrast, DA levels were increased in the striatum along with an overall decrease in the ratios of DA metabolites to DA. We also studied the mRNA levels for tyrosine hydroxylase (TH) and the dopamine transporter (DAT) by in situ hybridization. TH mRNA but not DAT mRNA was significantly induced in substantia nigra following BCNU treatment, which was consistent with significant elevations in TH enzyme amount and activity and unchanged DA uptake in striatum. All these results support the DA free radical hypothesis and the key role of the striatal glutathione system in protecting the striatal system against oxidative stress.

Effects of Some Antibiotics on Activity of Glucose-6-Phosphate Dehydrogenase from Human Erythrocytes In Vitro and Effect of Isepamicin Sulfate on Activities of Antioxidant Enzymes in Rat Erythrocytes

The purpose of this study was to investigate effects of some antibiotics on glucose-6-phosphate dehydrogenase (G6PD), antioxidant enzymes, and malondialdehyde (MDA). Initially, for in vitro studies, G6PD was purified from human erythrocyte, 9811-fold in a yield of 42.4% by using ammonium sulfate precipitation and 2',5' ADP-Sepharose 4B affinity gel. The purified enzyme showed a single band on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The effects of four different antibiotics (isepamicin sulfate, meropenem, chloramphenicol, and thiamphenicol glisinat hydrochloride) were investigated on the purified enzyme. K(i) value and type of inhibition were determined by means of Lineweaver-Burk graphs and regression analysis graphs. Isepamicin sulfate inhibited the enzyme activity (I(50) value, 2.1 mM; K(i) value, 1.7 mM), whereas thiamphenicol glisinat hydrochloride activated the G6PD dose dependently. Other drugs showed no inhibition and activation effect. In addition, the effects of isepamicin sulfate on the activities of G6PD, glutathione reductase (GR), superoxide dismutases (SOD), glutathione peroxidase (GPx), catalase (CAT), and glutathione S-transferase (GST) and MDA concentrations were examined in Sprague-Dawley rat erythrocytes in vivo. A marked alteration in the activities of these enzymes and MDA levels may be the result of oxidative stress in the rats receiving isepamicin sulfate.

MAO-B elevation in mouse brain astrocytes results in Parkinson's pathology

Age-related increases in monoamine oxidase B (MAO-B) may contribute to neurodegeneration associated with Parkinson's disease (PD). The MAO-B inhibitor deprenyl, a long-standing antiparkinsonian therapy, is currently used clinically in concert with the dopamine precursor L-DOPA. Clinical studies suggesting that deprenyl treatment alone is not protective against PD associated mortality were targeted to symptomatic patients. However, dopamine loss is at least 60% by the time PD is symptomatically detectable, therefore lack of effect of MAO-B inhibition in these patients does not negate a role for MAO-B in pre-symptomatic dopaminergic loss. In order to directly evaluate the role of age-related elevations in astroglial MAO-B in the early initiation or progression of PD, we created genetically engineered transgenic mice in which MAO-B levels could be specifically induced within astroglia in adult animals. Elevated astrocytic MAO-B mimicking age related increase resulted in specific, selective and progressive loss of dopaminergic neurons in the substantia nigra (SN), the same subset of neurons primarily impacted in the human condition. This was accompanied by other PD-related alterations including selective decreases in mitochondrial complex I activity and increased mitochondrial oxidative stress. Along with a global astrogliosis, we observed local microglial activation within the SN. These pathologies correlated with decreased locomotor activity. Importantly, these events occurred even in the absence of the PD-inducing neurotoxin MPTP. Our data demonstrates that elevation of murine astrocytic MAO-B by itself can induce several phenotypes of PD, signifying that MAO-B could be directly involved in multiple aspects of disease neuropathology. Mechanistically this may involve increases in membrane permeant H(2)O(2) which can oxidize dopamine within dopaminergic neurons to dopaminochrome which, via interaction with mitochondrial complex I, can result in increased mitochondrial superoxide. Our inducible astrocytic MAO-B transgenic provides a novel model for exploring pathways involved in initiation and progression of several key features associated with PD pathology and for therapeutic drug testing.

Redox-cycling compounds can cause the permeabilization of mitochondrial membranes by mechanisms other than ROS production

The participation of reactive oxygen species (ROS) in the regulation of mitochondrial permeability transition pore (mPTP) opening by the redox-cycling compounds menadione and lucigenin was explored. The level of ROS was modulated by antioxidants, anoxia, and switching the sites of the reduction of redox cyclers, the dehydrogenases of the inner and outer mitochondrial membranes. We found that the reduction of both lucigenin and menadione in the outer mitochondrial membrane caused a strong production of ROS. However, mPTP opening was accelerated only in the presence of the cationic acceptor lucigenin. The antioxidants and scavengers of ROS that considerably decreased the level of ROS in mitochondria did not prevent or delay the mPTP opening. If the transmembrane potential under anoxia was supported by exogenous ATP or ferricyanide, the permeabilization of mitochondrial membranes by menadione or lucigenin was the same as under normoxia or even more pronounced. Under anoxia, the lucigenin-dependent permeabilization of membranes was less sensitive to mPTP antagonists than under normoxia. We conclude that the opening of the mPTP by redox cyclers may be independent of ROS and is due to the direct oxidation of mitochondrial pyridine nucleotides by menadione and the modification of critical thiols of the mPTP by the cation radical of lucigenin.

Effects of antiemetic drugs on glucose 6-phosphate dehydrogenase and some antioxidant enzymes

The aim of this study was to investigate effect of antiemetics on G6PD and antioxidant enzymes. Antiemetics are currently being used to reduce or prevent nausea and vomiting in patients. This is the first study to show effect of antiemetics on glucose-6-phosphate dehydrogenase (G6PD) and antioxidant enzyme activities. For in vitro studies, G6PD was purified from human erythrocyte, 10, 26-fold in a yield of 51.3% by using ammonium sulphate precipitation and 2',5'-ADP-Sepharose 4B affinity gel. The purified enzyme showed a single band on sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS-PAGE). The effects of four different antiemetics (granisetron hydrochloride, ondansetron hydrochloride, metoclopramide hydrochloride, trimethobenzamide hydrochloride) were investigated on the purified enzyme. Granisetron hydrochloride and ondansetron hydrochloride inhibited the enzyme activity (Ki values; 5.05 mM and 0.034 mM, I50 values; 3.9 mM and 0.036 mM, respectively). Metoclopramide hydrochloride, trimethobenzamide hydrochloride showed no inhibition effects. In addition, in vivo studies, effects of ondansetron hydrochloride on the G6PD, glutathione reductase (GR), glutathione peroxidase (GPx) and catalase (CAT) were examined in the rat erythrocytes. G6PD (49% of control), GR (55% of control), CAT (60% of control) activities in erythrocytes were significantly decreased whereas GPx (183% of control) was significantly increased. A marked alteration in these enzymes may be result of oxidative stress in the rats receiving ondansetron hydrochloride.

Down's syndrome astrocytes have greater antioxidant capacity than euploid astrocytes

Down's syndrome (trisomy 21) brain tissue is considered to be susceptible to oxidative injury, mainly because its increased Cu/Zn-superoxide dismutase (SOD1) activity is not followed by an adaptive rise in hydrogen peroxide metabolizing enzymes. In vitro, trisomic neurons suffer oxidative stress and degenerate. We studied the response of trisomy 21 neuron and astrocyte cultures to hydrogen peroxide injury and found that they were, respectively, more and less vulnerable than their euploid counterparts. Differences were detected 24 h after exposures in the region of 50 microm and 500 microm hydrogen peroxide for neuron and astrocyte cultures, respectively. Cytotoxicity results were paralleled by a decrease in cellular glutathione. In addition, trisomic astrocytes showed a lower basal content of superoxide ion and a higher clearance of hydrogen peroxide from the culture medium. In the presence of hydrogen peroxide, trisomic astrocytes maintained their concentration of intracellular superoxide and hydroperoxides at a lower level than euploid astrocytes. Consistent with these results, trisomic astrocytes in neuron coculture were more neuroprotective than euploid astrocytes against hydrogen peroxide injury. We suggest that SOD1 overexpression has beneficial effects on astrocytes, as it does in other systems with similarly high disposal of hydroperoxides. In addition to a higher enzymatic activity of SOD1, cultures of trisomic astrocytes showed slightly higher glutathione reductase activity than euploid cultures. Thus, trisomy 21 astrocytes showed a greater antioxidant capacity against hydrogen peroxide than euploid astrocytes, and they partially counteracted the oxidative vulnerability of trisomic neurons in culture.

Perspectives on MAO-B in aging and neurological disease: where do we go from here?

The catecholamine-oxidizing enzyme monoamine oxidase-B (MAO-B) has been hypothesized to be an important determining factor in the etiology of both normal aging and age-related neurological disorders such as Parkinson's disease (PD). Catalysis of substrate by the enzyme produces H2O2 which is a primary originator of oxidative stress which in turn can lead to cellular damage. MAO-B increases with age as does predisposition towards PD which has also been linked to increased oxidative stress. Inhibition of MAO-B, along with supplementation of lost dopamine via L-DOPA, is one of the major antiparkinsonian therapies currently in use. In this review, we address several factors contributing to a possible role for MAO-B in normal brain aging and neurological disease and also discuss the use of MAO-B inhibitors as drug therapy for these conditions.

Oxidative alpha-ketoglutarate dehydrogenase inhibition via subtle elevations in monoamine oxidase B levels results in loss of spare respiratory capacity: implications for Parkinson's disease

Age-related increases in brain monoamine oxidase B (MAO-B) and its ability to produce reactive oxygen species as a by-product of catalysis could contribute to neurodegeneration associated with Parkinson's disease. This may be via increased oxidative stress and/or mitochondrial dysfunction either on its own or through its interaction with endogenous or exogenous neurotoxic species. We have created genetically engineered dopaminergic PC12 cell lines with subtly increased levels of MAO-B mimicking those observed during normal aging. In our cells, increased MAO-B activity was found to result in increased H2O2 production. This was found to correlate with a decrease in mitochondrial complex I activity which may involve both direct oxidative damage to the complex itself as well as oxidative effects on the tricarboxylic acid cycle enzyme alpha-ketoglutarate dehydrogenase (KGDH) which provides substrate for the complex. Both complex I and KGDH activities have been reported to be decreased in the Parkinsonian brain. These in vitro events are reversible by catalase addition. Importantly, MAO-B elevation was found to abolish the spare KGDH threshold capacity, which can normally be significantly inhibited before it affects maximal mitochondrial oxygen consumption rates. Our data suggest that H2O2 production via subtle elevations in MAO-B levels can result in oxidative effects on KGDH that can compromise the ability of dopaminergic neurons to cope with increased energetic stress.

Differential gene expression induced by insulin and insulin-like growth factor-II through the insulin receptor isoform A

The human insulin receptor (IR) exists in two isoforms (IR-A and IR-B). IR-A is a short isoform, generated by the skipping of exon 11, a small exon encoding for 12 amino acid residues at the carboxyl terminus of the IR alpha-subunit. Recently, we found that IR-A is the predominant isoform in fetal tissues and malignant cells and binds with a high affinity not only insulin but also insulin-like growth factor-II (IGF-II). To investigate whether the activation of IR-A by the two ligands differentially activate post-receptor molecular mechanisms, we studied gene expression in response to IR-A activation by either insulin or IGF-II, using microarray technology. To avoid the interfering effect of the IGF-IR, IGF-II binding to the IR-A was studied in IGF-IR-deficient murine fibroblasts (R- cells) transfected with the human IR-A cDNA (R-/IR-A cells). Gene expression was studied at 0.5, 3, and 8 h. We found that 214 transcripts were similarly regulated by insulin and IGF-II, whereas 45 genes were differentially transcribed. Eighteen of these differentially regulated genes were responsive to only one of the two ligands (12 to insulin and 6 to IGF-II). Twenty-seven transcripts were regulated by both insulin and IGF-II, but a significant difference between the two ligands was present at least in one time point. Interestingly, IGF-II was a more potent and/or persistent regulator than insulin for these genes. Results were validated by measuring the expression of 12 genes by quantitative real-time reverse transcriptase-PCR. In conclusion, we show that insulin and IGF-II, acting via the same receptor, may differentially affect gene expression in cells. These studies provide a molecular basis for understanding some of the biological differences between the two ligands and may help to clarify the biological role of IR-A in embryonic/fetal growth and the selective biological advantage that malignant cells producing IGF-II may acquire via IR-A overexpression.

Protective effects of Wuyaoshunqisan against H2O2-induced apoptosis on hippocampal cell line HiB5

Oxidative stress has been implicated in the pathogenesis of different neurodegenerative disorders. To investigate the protective effects of Wuyaoshunqisan against H2O2-induced apoptosis in the central nervous system, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) method, flow cytometric analysis, and the DNA fragmentation assay were performed on cells of the hippocampal cell line HiB5. Through the morphological and biochemical analyses, it was shown that HiB5 cells treated with H2O2 exhibit classical apoptotic features, while the occurrence of such changes is reduced in cells pre-treated with Wuyaoshunqisan prior to H2O2 exposure.

Flavonoids of Inula britannica protect cultured cortical cells from necrotic cell death induced by glutamate

We previously reported 12 antioxidative flavonoids isolated from the n-BuOH extract of Inula britannica (Asteraceae). This prompted us to investigate further whether these flavonoids also showed antioxidative activity upon live cells grown in a culture system. Among the 12 flavonoids tested, only patuletin, nepetin, and axillarin protected primary cultures of rat cortical cells from oxidative stress induced by glutamate. These flavonoids exerted significant neuroprotective activity when they were administered either before or after the glutamate insult. Treatment with these flavonoids maintained the activities of such antioxidant enzymes as catalase, glutathione-peroxidase, and glutathione reductase, all of which play important roles in the antioxidative defense mechanism. Moreover, these three flavonoids also attenuated significant drops in glutathione induced by glutamate which is a routine concomitant of oxidative stress by inhibiting glutathione diminution. Accordingly, these flavonoids did not stimulate the synthesis of glutathione. With regard to structure-activity relationships, our results indicated that the 6-methoxyl group in the A ring and the 3', 4'-hydroxyl groups in the B ring are crucial for the protection against the oxidative stress; glycosylation greatly reduced their protective activities. Collectively, these results indicated that patuletin, nepetin, and axillarin strongly protect primary cultured neurons against glutamate-induced oxidative stress.

Protective effect of serotonin on 6-hydroxydopamine- and dopamine-induced oxidative damage of brain mitochondria and synaptosomes and PC12 cells

The present study elucidated the effects of indoleamines (serotonin, melatonin, and tryptophan) on oxidative damage of brain mitochondria and synaptosomes induced either by 6-hydroxydopamine (6-OHDA) or by iron plus ascorbate and on viability loss in dopamine-treated PC12 cells. Serotonin (1-100 microM), melatonin (100 microM), and antioxidant enzymes attenuated the effects of 6-OHDA, iron plus ascorbate, or 1-methyl-4-phenylpyridinium on mitochondrial swelling and membrane potential formation. Serotonin and melatonin decreased the attenuation of synaptosomal Ca(2+) uptake induced by either 6-OHDA alone or iron plus ascorbate. Serotonin and melatonin inhibited the production of reactive oxygen species, formation of malondialdehyde and carbonyls, and thiol oxidation in mitochondria and synaptosomes and decreased degradation of 2-deoxy-D-ribose. Unlike serotonin, melatonin did not reduce the iron plus ascorbate-induced thiol oxidation. Tryptophan decreased thiol oxidation and 2-deoxy-D-ribose degradation but did not inhibit the production of reactive oxygen species and formation of oxidation products in the brain tissues. Serotonin and melatonin attenuated the dopamine-induced viability loss, including apoptosis, in PC12 cells. The results suggest that serotonin may attenuate the oxidative damage of mitochondria and synaptosomes and the dopamine-induced viability loss in PC12 cells by a decomposing action on reactive oxygen species and inhibition of thiol oxidation and shows the effect comparable to melatonin. Serotonin may show a prominent protective effect on the iron-mediated neuronal damage.

Methylmercury neurotoxicity in cultures of human neurons, astrocytes, neuroblastoma cells

Neurotoxic effects of methylmercury, were investigated in vitro in primary cultures of human neurons and astrocytes isolatedfrom human fetal brain and in the human neuroblastoma cell line SH-SY5Y. The protection provided by agents with antioxidant properties was tested in these cultures to examine the oxidative stress mechanism of methylmercury poisoning. After 24 h of exposure to methylmercury, LC50 values were 6.5, 8.1 and 6.9 microM for human neurons, astrocytes and neuroblastoma cells, respectively, and the degree of cell damage increased at longer exposure times. Depletion of the cellular pool of reduced glutathione (GSH) by treatment with buthionine sulfoximine potentiated methylmercury cytotoxicity in all three cell types; neuroblastoma cells were the most sensitive. Addition of GSH extracellularly blocked methylmercury neurotoxicity in all cell types. The major beneficial effect of GSH could be attributed to its capacity to form conjugates with methylmercury, which reduces the availability of these organometallic molecules to the cells and facilitates their efflux. Cysteine protected astrocytes and neuroblastoma cells from methylmercury neurotoxicity, while selenite, Vitamin E and catalase produced some minor protective effects in three cell types, particularly in neurons. The present study showed that the human neural cells tested had differential responses to methylmercury: astrocytes were resistant to methylmercury neurotoxicity and neurons were more most responsive to protection afforded by antioxidants among the three cell types.

Caspase 3 inhibition attenuates hydrogen peroxide-induced DNA fragmentation but not cell death in neuronal PC12 cells

Exposure of neurons to H(2)O(2) results in both necrosis and apoptosis. Caspases play a pivotal role in apoptosis, but exactly how they are involved in H(2)O(2)-mediated cell death is unknown. We examined H(2)O(2)-induced toxicity in neuronal PC12 cells and the effects of inducible overexpression of the H(2)O(2)-scavenging enzyme catalase on this process. H(2)O(2) caused cell death in a time- and concentration-dependent manner. Cell death induced by H(2)O(2) was found to be mediated in part through an apoptotic pathway as H(2)O(2)-treated cells exhibited cell shrinkage, nuclear condensation and marked DNA fragmentation. H(2)O(2) also triggered activation of caspase 3. Genetic up-regulation of catalase not only significantly reduced cell death but also suppressed caspase 3 activity and DNA fragmentation. While the caspase 3 inhibitor DEVD inhibited both caspase 3 activity and DNA fragmentation induced by H(2)O(2) it did not prevent cell death. Treatment with the general caspase inhibitor ZVAD, however, resulted in complete attenuation of H(2)O(2)-mediated cellular toxicity. These results suggest that DNA fragmentation induced by H(2)O(2) is attributable to caspase 3 activation and that H(2)O(2) may be critical for signaling leading to apoptosis. However, unlike inducibly increased catalase expression and general caspase inhibition both of which protect cells from cytotoxicity, caspase 3 inhibition alone did not improve cell survival suggesting that prevention of DNA fragmentation is insufficient to prevent H(2)O(2)-mediated cell death.

Preferential resistance of dopaminergic neurons to the toxicity of glutathione depletion is independent of cellular glutathione peroxidase and is mediated by tetrahydrobiopterin

Depletion of glutathione in the substantia nigra is one of the earliest changes observed in Parkinson's disease (PD) and could initiate dopaminergic neuronal degeneration. Nevertheless, experimental glutathione depletion does not result in preferential toxicity to dopaminergic neurons either in vivo or in vitro. Moreover, dopaminergic neurons in culture are preferentially resistant to the toxicity of glutathione depletion, possibly owing to differences in cellular glutathione peroxidase (GPx1) function. However, mesencephalic cultures from GPx1-knockout and wild-type mice were equally susceptible to the toxicity of glutathione depletion, indicating that glutathione also has GPx1-independent functions in neuronal survival. In addition, dopaminergic neurons were more resistant to the toxicity of both glutathione depletion and treatment with peroxides than nondopaminergic neurons regardless of their GPx1 status. To explain this enhanced antioxidant capacity, we hypothesized that tetrahydrobiopterin (BH(4)) may function as an antioxidant in dopaminergic neurons. In agreement, inhibition of BH(4) synthesis increased the susceptibility of dopaminergic neurons to the toxicity of glutathione depletion, whereas increasing BH(4) levels completely protected nondopaminergic neurons against it. Our results suggest that BH(4) functions as a complementary antioxidant to the glutathione/glutathione peroxidase system and that changes in BH(4) levels may contribute to the pathogenesis of PD.

Role of antioxidant enzymes in brain tumours

Erythrocyte antioxidant enzymes were analysed in 100 patients with intracranial neoplasm and in 47 controls. There was a significant decrease in RBC glutathione reductase (GRx) and superoxide dismutase (SOD) activity in most types of brain tumor cases. Patients with acoustic neurinoma showed a significant reduction in selenium-dependent glutathione peroxidase (Se-GPx) activity. A decrease in catalase (CT) activity was seen in most of the brain tumor patients but remained statistically insignificant when compared to controls. A significant increase in plasma ceruloplasmin concentration was observed in patients with glioma. These enzymes were also studied in 27 post-treatment cases. GRx activity returned to normal levels in these patients. RBC SOD and plasma ceruloplasmin levels showed a tendency to return to normal. Hence, a marked decrease in the antioxidant enzymes may have a role in the genesis of considerable oxidative stress in patients with brain tumors.

Possible mechanism(s) of arachidonic acid-induced intracellular acidosis in rat cardiac myocytes

Arachidonic acid (AA) and other nonesterified fatty acids (FAs) have been shown to exert harmful effects during cardiac ischemia. By continuously measuring intracellular pH (pH(i)) changes in neonatal and adult cardiac myocytes, we have found, for the first time, that 10 micromol/L AA induces a substantial intracellular acidosis (0.3 to 0.4 pH units). We have ruled out the possibilities that the AA-induced acidosis is caused by (1) inhibition or stimulation of the pH(i) regulators, (2) protein kinase C activation or the generation of AA metabolites or free radicals, or (3) activation of NADPH oxidase or an inward H(+) current. The AA-induced acidosis fits to a simple diffusion mechanism, as proposed by Kamp and Hamilton (flip-flop model) for artificial phospholipid bilayers. The important properties found in the cardiac myocyte are that (1) the initial rate of acid flux (J(H)) increases with the AA concentration (2 to 50 micromol/L), (2) FAs with a (-)COOH group (eg, AA, oleic acid, and linoleic acid) induce intracellular acidification, but FAs with a (-)COOCH(3) group (eg, AA methyl ester) have little effect on the pH(i), (3) tetradecylamine (FA amine) induces intracellular alkalosis, and, most importantly, (4) both the AA- and tetradecylamine-induced pH(i) changes can be reversed by 0.3% BSA. Because a low concentration of AA (10 micromol/L) can induce a substantial acidosis, the possible involvement of the FA-evoked acidosis in the negative inotropic effect during cardiac ischemia is discussed. The full text of this article is available at http://www. circresaha.org.

Cynandione A from Cynanchum wilfordii protects cultured cortical neurons from toxicity induced by H2O2, L-glutamate, and kainate

Oxidative stress has been implicated as a primary cause of neuronal death in certain neurodegenerative disorders and in aging brains. Natural products have been used in Asian societies for centuries for treating such neurodegenerative disorders as senile dementia. In an effort to identify active neuroprotective compounds from these products, we have employed cultures of rat cortical neurons as our screening system. A methanolic extract from dried roots of Cynanchum wilfordii Hemsley (Asclepiadaceae) significantly mitigated the neurotoxicity induced by H2O2 in this screening system. Activity-guided fractionation using several chromatographic techniques resulted in the isolation of the neuroprotective compound, cynandione A, a biacetophenone. At a concentration of 50 microM, cynandione A significantly reduced neurotoxicity induced by H2O2. Cynandione A significantly attenuated decreases in levels of glutathione, superoxide dismutase, and other enzymes that participate in the cellular defense against oxidative stress. Furthermore, cynandione A alleviated neurotoxicity induced by the excitotoxic neurotransmitter, L-glutamate, the neurotoxicity induced by kainate, but not that mediated by N-methyl-D-aspartate. Cynandione A was demonstrated to be a natural antioxidant as it facilitated the breakdown of hydrogen peroxide in vitro; however, no mechanism was uncovered to explain its neuroprotectant effects against glutamate and kainate. Therefore, cynandione A may be efficacious in protecting neurons from oxidative stress mediated via activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate/kainate receptors since it exerted significant neuroprotective effects on cultured cortical neurons.

Prion protein-deficient neurons reveal lower glutathione reductase activity and increased susceptibility to hydrogen peroxide toxicity

The prion protein (PrP) has a central role in the pathogenesis of transmissible spongiform encephalopathies (TSE). Accumulating evidence suggests that normal cellular PrP (PrP(c)) may be involved in copper homeostasis and modulation of copper/zinc superoxide dismutase (Cu/ZnSOD) activity in neurons. Hydrogen peroxide (H(2)O(2)) is a toxic reactive oxygen species generated through normal cellular respiration, and neurons contain two important peroxide detoxifying systems (glutathione pathway and catalase). To determine whether PrP expression affects neuronal resistance to H(2)O(2), we exposed primary cerebellar granule neuron cultures derived from PrP knockout (PrP(-/-)) and wild-type (WT) mice to H(2)O(2) for 3, 6, and 24 hours. The PrP(-/-) neurons were significantly more susceptible to H(2)O(2) toxicity than WT neurons after 6 and 24 hours' exposure. The increased H(2)O(2) toxicity may be related to a significant decrease in glutathione reductase activity measured in PrP(-/-) neurons both in vitro and in vivo. This was supported by the finding that inhibition of GR activity with 1,3-bis(2-chloroethyl)-1-nitrosurea (BCNU) increased H(2)O(2) toxicity in WT neurons over the same exposure period. The PrP toxic peptide PrP106-126 significantly reduced neuronal glutathione reductase activity and increased susceptibility to H(2)O(2) toxicity in neuronal cultures suggesting that PrP toxicity in vivo may involve altered glutathione reductase activity. Our results suggest the pathophysiology of prion diseases may involve perturbed PrP(c) function with increased vulnerability to peroxidative stress.

Microinjection of catalase cDNA prevents hydrogen peroxide-induced motoneuron death

Oxidative stress is believed to play a central role in the pathogenesis of amyotrophic lateral sclerosis (ALS). We investigated the protective effects of overexpression of catalase in primary cultures of rat spinal motoneurons against the oxidative stress of hydrogen peroxide. Using microinjection, catalase-encoding cDNA was transferred into the motoneurons. In another approach, motoneurons were injected with a catalase solution. Both procedures elevated the intracellular antioxidant status of the cultured motoneurons as evidenced by a significant protection against H2O2 toxicity. We conclude that modulating the expression of enzymes involved in cellular defense against oxidative stress can render cells more resistant to oxidant toxicity.

Exacerbation of copper toxicity in primary neuronal cultures depleted of cellular glutathione

Perturbations to glutathione (GSH) metabolism may play an important role in neurodegenerative disorders such as Alzheimer's, Parkinson's, and prion diseases. A primary function of GSH is to prevent the toxic interaction between free radicals and reactive transition metals such as copper (Cu). Due to the potential role of Cu in neurodegeneration, we examined the effect of GSH depletion on Cu toxicity in murine primary neuronal cultures. Depletion of cellular GSH with L-buthionine-[S,R]-sulfoximine resulted in a dramatic potentiation of Cu toxicity in neurons without effect on iron (Fe) toxicity. Similarly, inhibition of glutathione reductase (GR) activity with 1,3-bis(2-chloroethyl)-1-nitrosurea also increased Cu toxicity in neurons. To determine if the Alzheimer's amyloid-beta (Abeta) peptide can affect neuronal resistance to transition metal toxicity, we exposed cultures to nontoxic concentrations of Abeta25-35 in the presence or absence of Cu or Fe. Abeta25-35 pretreatment was found to deplete neuronal GSH and increase GR activity, confirming the ability of Abeta to perturb neuronal GSH homeostasis. Abeta25-35 pretreatment potently increased Cu toxicity but had no effect on Fe toxicity. These studies demonstrate an important role for neuronal GSH homeostasis in selective protection against Cu toxicity, a finding with widespread implications for neurodegenerative disorders.

Direct evidence for glutathione as mediator of apoptosis in neuronal cells

Recent evidence has focused attention on the role of oxidative stress in various acute and chronic neurodegenerative diseases. Particularly, a decrease in the level of the powerful antioxidant glutathione (GSH) and death of dopaminergic neurons in substantia nigra are prominent features in Parkinson's disease. The mode of neuronal death is uncertain; however, apoptosis has been hypothesized to be mediated through the induction of free radicals via oxidative pathways. An approach to determine the role of GSH depletion in neurodegeneration and apoptosis was to create a selective modulation of this antioxidant by metabolic manipulations in a clonal cell line of neuronal origin (mouse neuroblastoma NS20Y). Intracellular GSH levels was lowered by inhibiting its biosynthesis with L-buthionine-(S,R)-sulfoximine (BSO), a specific inhibitor of gamma-glutamylcysteine synthetase. This treatment led to a GSH depletion of 50% after 1 h and 98% after 24 h. A direct cause/effect relationship between GSH depletion and apoptosis was evidenced in this neuronal cell type. GSH depletion induced the death of NS20Y and promoted nuclear alterations of apoptosis as demonstrated by the in situ staining of DNA fragmentation after 5 days of BSO treatment (by terminal-deoxynucleotide transferase-mediated dUTP-nick end labeling), and the appearance of DNA laddering on agarose gel. These results suggested that redox desequilibrium induced by GSH depletion may serve as a general trigger for apoptosis in neuronal cells, and are consistent with the hypothesis that GSH depletion contribute to neuronal death in Parkinson's disease.

Toxic effect of hemoglobin on spinal cord neurons in culture

The vulnerability of spinal cord neurons to hemoglobin was quantitatively assessed in primary cultures derived from fetal mice. Exposure to hemoglobin for 28 h in a serum-free medium resulted in concentration-dependent neuronal death, with an EC50 of 0.9 microM; glia were not injured. Neuronal death was decreased by the ferric iron chelator deferoxamine, the alpha-tocopherol analogue Trolox C, ascorbate, and exogenous catalase, but was potentiated by superoxide dismutase. Neuronal death was also increased by depletion of cellular glutathione with the gamma-glutamylcysteine synthetase inhibitor buthionine sulfoxamine; inhibition of endogenous catalase with 3-amino-1,2,4-triazole had no significant effect. These results suggest that hemoglobin is toxic to spinal neurons via an iron-dependent, oxidative mechanism involving a hydrogen peroxide intermediate, and support the hypothesis that hemoglobin release may contribute to neuronal loss after spinal cord trauma.

Characterization of t-butyl hydroperoxide toxicity in cultured rat cortical neurones and astrocytes

The present study investigates the toxicity of t-butyl hydroperoxide (t-BuOOH) in cultured rat cortical neurones and astrocytes. Both neurones and astrocytes were destroyed by exposure to t-BuOOH in a time- and concentration-dependent manner. Astrocytes were more resistant to destruction by hydrogen peroxide (H2O2) than neurones, but there was no difference in susceptibility to t-BuOOH between neurones and astrocytes. The toxic effect of t-BuOOH was significantly blocked by antioxidants, propyl gallate and trolox, but not by superoxide dismutase nor by H2O2-scavengers, catalase and 4-nitrophenylglyoxylic acid. These results suggest that t-BuOOH toxicity is caused by oxidative stress unrelated to superoxide and H2O2. In addition, the toxic effect of t-BuOOH was attenuated by the presence of iron chelators, deferoxamine and N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, indicating the requirement of endogenous iron for t-BuOOH toxicity.

Glucocorticoids may alter antioxidant enzyme capacity in the brain: kainic acid studies

Glucocorticoids (GCs) predispose hippocampal neurons to damage during metabolic stressors. One component of hippocampal GC-endangerment may be changes in neuronal defenses against oxidative challenge. Previous experiments showed a decrease in basal levels of copper/zinc superoxide dismutase (Cu/Zn SOD) and glutathione peroxidase (GSPx) in the brain of rats treated with GCs [L. McIntosh, K. Hong, R. Sapolsky, Glucocorticoids may alter antioxidant enzyme capacity in the brain: baseline studies, 1997.]. In this study we administered the excitotoxin kainic acid (KA) to generate reactive oxygen species (ROS) in the brain, and monitored the activity of four antioxidant enzymes over 24 h in GC-free and GC-supplemented rats. We tested the response pattern in three regions of the brain (hippocampus, cortex, cerebellum) and the liver as a peripheral control. In the hippocampus, KA induced Cu/Zn SOD and catalase, but GCs prevented the induction of catalase and maintained the lowered GSPx activity seen previously in the baseline studies. In the cortex, KA induced Cu/Zn SOD, Mn SOD and catalase activity, but there was no significant GC effect. There was no response to KA in the cerebellum, but GCs decreased GSPx activity. In the liver, KA produced a rise in Cu/Zn SOD and catalase activity, and GC-treated animals showed a slower return to baseline. These experiments indicate that the impairment of antioxidant enzyme defenses, particularly the hippocampal peroxidases, could be a component of GC-mediated neuroendangerment.

Glucocorticoids may alter antioxidant enzyme capacity in the brain: baseline studies

Glucocorticoids (GCs), the adrenal steroids secreted during stress, have been shown to increase the vulnerability of hippocampal neurons to metabolic insults, potentially by altering the neuronal defense capacity against oxidative damage. These experiments assessed the effect of long term in vivo GC supplementation on basal activity of the antioxidant enzymes copper/zinc superoxide dismutase (Cu/Zn SOD), manganese superoxide dismutase (Mn SOD), catalase, and glutathione peroxidase (GSPx). Kinetic enzyme studies were done using brain tissue from the hippocampus, cortex, cerebellum, and also from liver as a peripheral control. Cu/Zn SOD activity was significantly lower in all brain regions of GC-treated rats, but higher in the liver. Mn SOD activity was unaffected by treatment. Catalase in the brain appeared largely unaffected by GC treatment, although liver catalase was significantly decreased. GSPx activity was significantly decreased by GCs at high peroxide levels in all tissues. These results indicate that the presence of GCs may lower the antioxidant capacity of tissues in a region-specific manner, and that the deficit may not appear until the tissue is challenged with supranormal levels of oxidative products (as seen with GSPx).

Overexpression of superoxide dismutase and catalase in immortalized neural cells: toxic effects of hydrogen peroxide

Hydrogen peroxide (H2O2) is a known toxicant which causes its damage via the production of hydroxyl radicals. It has been reported to cause both necrotic and apoptotic cell death. The present study was undertaken to evaluate the mode of H2O2-induced cell death and to assess if overexpression of catalase could protect against its toxicity. H2O2 causes cell death of immortalized CSM 14.1 neural cells in a dose-dependent manner. H2O2-induced death was associated with DNA laddering as shown by agarose gel electrophoresis. Stable overexpression of catalase by transfection of a vector containing human cDNA into these cells markedly attenuated H2O2-induced toxic effects. Transfection of a vector containing a SOD cDNA afforded no protection. These results indicate that H2O2 can lead to the activation of endonuclease enzyme that breaks DNA into oligosomes. These cells which overexpress catalase or SOD will help to determine the specific role of H2O2 or O2- in the deleterious effects of a number of toxins.

Involvement of glutathione peroxidase and catalase in the disposal of exogenous hydrogen peroxide by cultured astroglial cells

The ability of astroglial cells to detoxify exogenously applied hydrogen peroxide (H2O2) was tested using astroglia-rich primary cultures derived from the brains of newborn rats. Incubation of astroglial cells with 100 microM H2O2 in the absence of glucose led to a 66% oxidation of the cellular glutathione within 30 s. Under these conditions, the cells were unable to re-establish the original high ratio of GSH/GSSG within 30 min of incubation. In contrast, if glucose was present the amount of GSSG produced on incubation with H2O2 was smaller (45% of total glutathione after 30 s) and the original ratio of GSH/GSSG was almost completely re-established within 10 min. If 100 microM H2O2 was applied, H2O2 disappeared from the incubation buffer with an apparent half-life of approximately 4 min. After 15 min of incubation, no H2O2 was detectable any more. The apparent half-life of H2O2 in the incubation buffer increased slightly but significantly with increasing concentration of H2O2 or when the cells were starved of glucose. A small reduction in the capacity of the cells to detoxify H2O2 was also observed after depletion of the glutathione content to 14% of control level by a 24 h pre-incubation of the cells in culture medium containing buthionine sulfoximine, an inhibitor of glutathione synthesis. Incubation of astroglial cells with mercaptosuccinate or 3-aminotriazole, inhibitors of glutathione peroxidase and catalase, respectively, only marginally reduced the rate of disappearance of H2O2 from the incubation buffer. In contrast, the rate of H2O2 clearance was strongly reduced in the presence of both inhibitors. These results demonstrate that glutathione peroxidase and catalase are involved in the detoxification of H2O2 by astroglial cells and that both enzymes are able to substitute for each other in the detoxification of H2O2.

Genetic elevation of monoamine oxidase levels in dopaminergic PC12 cells results in increased free radical damage and sensitivity to MPTP

Production of hydrogen peroxide as a by-product of the breakdown of catecholamines by the enzyme monoamine oxidase (MAO) has been hypothesized to contribute to the increased proclivity of dopaminergic neurons for oxidative injury. We established clonal dopaminergic PC12 cell lines which have elevated MAO activity levels resulting from transgenic expression of the B isoform of the enzyme. Both MAO-A and MAO-B have relatively equivalent affinities for dopamine, and since PC12 primarily express the A and not the B form of the enzyme, this allowed us to distinguish the transgenic MAO activity in these cells from endogenous using the MAO-B specific substrate PEA. Elevation of MAO activity levels in the MAO-B+ cells resulted in higher levels of both free radicals and free radical damage compared with controls. In addition, increased MAO-B levels within PC12 cells caused a dose-dependent increase in sensitivity to the toxin MPTP. Our data suggests that oxidation of catecholamines by MAO can contribute to free radical damage in catecholaminergic neurons and that the low MAO-B activity levels found endogenously in these cells likely accounts for their relative resistance to MPTP toxicity.

Cellular responses of cultured cerebellar astrocytes to ethacrynic acid-induced perturbation of subcellular glutathione homeostasis

Glutathione (GSH) and glutathione-related enzyme systems in astrocytes play an important role in cellular defense against oxidative stress in the nervous system. The present study was designed to characterize the cellular responses of cultured astrocytes to chemically-induced perturbations of mitochondrial and cytosolic GSH homeostasis. Treatment of astrocytes in culture with ethacrynic acid (EA), a mitochondrion-penetrating thiol reagent, induced rapid and extensive depletion of both cytosolic and mitochondrial pools of GSH. Concomitant with the effects of EA on cellular GSH were significant and concentration-dependent increases in intracellular generation of reactive oxygen species (ROS) as indicated by the oxidation of preloaded 2',7'-dichlorofluorescein diacetate. Significant elevation of intracellular ROS occurred by 15 min following exposure to 100 microM EA and reached peak levels by 30 min which were approximately 7-fold higher than corresponding control levels. Ethacrynic acid-induced GSH depletion and intracellular ROS elevation was followed by marked decreases in glutathione reductase (GR) activity in mitochondria, and to a lesser extent, in cytosolic fractions of cultured astrocytes. This inhibitory effect was time- and concentration-dependent, and other GSH-related enzymes, glutathione peroxidase and glutathione S-transferase, were not or only slightly affected. Kinetic studies showed that EA markedly diminished V(max) values of both mitochondrial and cytosolic GR without affecting K(m), suggesting noncompetitive inhibition of this thiol-dependent enzyme. Another thiol-dependent enzyme glyceraldehyde-3-phosphate dehydrogenase was also markedly inhibited by EA in a time-dependent fashion. Subsequent decline of mitochondrial transmembrane potential (rhodamine 123 uptake) and cellular ATP production following EA treatment occurred prior to the onset of loss of cell viability as indicated by lactate dehydrogenase leakage. These results suggest that the loss of mitochondrial GSH may render the astrocytes unable to combat the pathological sequelae of endogenous oxidative stress, leading to perturbations of thiol-dependent enzyme activities, mitochondrial function and energy metabolism.

Oxybenzone oxidation following solar irradiation of skin: photoprotection versus antioxidant inactivation

We used noninvasive Fourier transform (FT) Raman spectroscopy to follow the fate of the broadly used ultraviolet UVA sun blocker, oxybenzone, after topical application to the skin. Our results showed that oxybenzone is rapidly photo-oxidized, yielding oxybenzone semiquinone, a potent electrophile, which reacts with thiol groups on important anti-oxidant enzymes and substrates, such as thioredoxin reductase and reduced glutathione, respectively. Although oxybenzone is an excellent broad spectrum UVA filter, its rapid oxidation followed by the inactivation of important antioxidant systems indicates that this substance may be rather harmful to the homeostasis of the epidermis. Furthermore, these results demonstrate that FT-Raman spectroscopy is a useful method for studying the transport and metabolism of active ingredients in topical preparations.

Oxidative events in neuronal and glial cell-enriched fractions of rat cerebral cortex

The aim of this work was to investigate how neurons and glial cells separated from rat brain cortex respond to "in vitro" oxidative stress induced by incubation of the cellular fractions in the presence of prooxidant mixtures; in addition, the endogenous enzymatic antioxidant capacity of the purified fractions was investigated. Neuronal and glial cell-enriched fractions were obtained from rat cerebral cortex following passages of the tissue through meshes and centrifugations. The following parameters were evaluated: antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSHPx), and glucose-6-phosphate dehydrogenase (G6PDH); lipid peroxidation products (TBARS) prior to (basal) and after (iron-stimulated) incubation with a mixture of iron and ascorbic acid; intracellular production of reactive oxygen species (ROS) using a fluorescent probe, dichlorofluorescin-diacetate, in basal, iron-stimulated, and menadione stimulated conditions. SOD and GSHPx activities showed no significant changes between neurons and glia, whereas CAT and G6PDH activities were found to be significantly lower in glia than in neurons. TBARS levels were significantly lower in the glial fraction than in neurons, both in basal and iron-stimulated conditions. ROS production showed no differences between neurons and glia in both basal and menadione-stimulated conditions. Iron-stimulation produced a marked increase in ROS production, limited to the neuronal fraction, with the glial values being similar to the basal ones. Our conclusion is that glia and neurons isolated from rat cerebral cortex show a similar pattern of the most important antioxidant enzymes and of their basal ROS production, whereas glia is more resistant in "oxidative stress" conditions.

Effect of a spinal cord photolesion injury on catalase

Ischemic injury to the spinal cord results in cell and tissue damage. Oxygen free radicals have been implicated in post-ischemic cell injury and death while free radical scavengers like superoxide dismutase and catalase are associated with an amelioration of ischemic injury. Measurement of catalase enzyme activity or protein in ischemic tissue presents mechanical problems due to extensive tissue destruction. Therefore, we looked at the effects of a photochemical lesion (which reproduces ischemic injury) on the levels of catalase mRNA in the spinal cord tissues of rodents under various experimental conditions. A significant depletion in the levels of catalase mRNA was observed in the spinal cord tissues of rats that received a severe lesion and were sacrificed 6 days post-lesion, while levels of catalase mRNA in the spinal cord tissues of similarly lesioned rats sacrificed 14 days post-lesion showed a return to control values.

Thermosensitive phenotype of transgenic mice overproducing human glutathione peroxidases

Exposure of humans and other mammals to hyperthermic conditions elicits many physiological responses to stress in various tissues leading to profound injuries, which eventually result in death. It has been suggested that hyperthermia may increase oxidative stress in tissues to form reactive oxygen species harmful to cellular functions. By using transgenic mice with human antioxidant genes, we demonstrate that the overproduction of glutathione peroxidase (GP, both extracellular and intracellular) leads to a thermosensitive phenotype, whereas the overproduction of Cu,Zn-superoxide dismutase has no effect on the thermosensitivity of transgenic mice. Induction of HSP70 in brain, lung, and muscle in GP transgenic mice at elevated temperature was significantly inhibited in comparison to normal animals. Measurement of peroxide production in regions normally displaying induction of HSP70 under hyperthermia revealed high levels of peroxides in normal mice and low levels in GP transgenic mice. There was also a significant difference between normal and intracellular GP transgenic mice in level of prostaglandin E2 in hypothalamus and cerebellum. These data suggest direct participation of peroxides in induction of cytoprotective proteins (HSP70) and cellular mechanisms regulating body temperature. GP transgenic mice provide a model for studying thermoregulation and processes involving actions of hydroxy and lipid peroxides in mammals.