Mitochondrial glutathione protects against cell death induced by oxidative and nitrative stress in astrocytes

Copper induces neuron-sparing, ferredoxin 1-independent astrocyte toxicity mediated by oxidative stress

Copper is an essential enzyme cofactor in oxidative metabolism, anti-oxidant defenses, and neurotransmitter synthesis. However, intracellular copper, when improperly buffered, can also lead to cell death. Given the growing interest in the use of copper in the presence of the ionophore elesclomol (CuES) for the treatment of gliomas, we investigated the effect of this compound on the surround parenchyma-namely neurons and astrocytes in vitro. Here, we show that astrocytes were highly sensitive to CuES toxicity while neurons were surprisingly resistant, a vulnerability profile that is opposite of what has been described for zinc and other toxins. Bolstering these findings, a human astrocytic cell line was similarly sensitive to CuES. Modifications of cellular metabolic pathways implicated in cuproptosis, a form of copper-regulated cell death, such as inhibition of mitochondrial respiration or knock-down of ferredoxin 1 (FDX1), did not block CuES toxicity to astrocytes. CuES toxicity was also unaffected by inhibitors of apoptosis, necrosis or ferroptosis. However, we did detect the presence of lipid peroxidation products in CuES-treated astrocytes, indicating that oxidative stress is a mediator of CuES-induced glial toxicity. Indeed, treatment with anti-oxidants mitigated CuES-induced cell death in astrocytes indicating that oxidative stress is a mediator of CuES-induced glial toxicity. Lastly, prior induction of metallothioneins 1 and 2 in astrocytes with zinc plus pyrithione was strikingly protective against CuES toxicity. As neurons express high levels of metallothioneins basally, these results may partially account for their resistance to CuES toxicity. These results demonstrate a unique toxic response to copper in glial cells which contrasts with the cell selectivity profile of zinc, another biologically relevant metal.

Brain Energy Metabolism in Ischemic Stroke: Effects of Smoking and Diabetes

Proper regulation of energy metabolism in the brain is crucial for maintaining brain activity in physiological and different pathophysiological conditions. Ischemic stroke has a complex pathophysiology which includes perturbations in the brain energy metabolism processes which can contribute to worsening of brain injury and stroke outcome. Smoking and diabetes are common risk factors and comorbid conditions for ischemic stroke which have also been associated with disruptions in brain energy metabolism. Simultaneous presence of these conditions may further alter energy metabolism in the brain leading to a poor clinical prognosis after an ischemic stroke event. In this review, we discuss the possible effects of smoking and/or diabetes on brain glucose utilization and mitochondrial energy metabolism which, when present concurrently, may exacerbate energy metabolism in the ischemic brain. More research is needed to investigate brain glucose utilization and mitochondrial oxidative metabolism in ischemic stroke in the presence of smoking and/or diabetes, which would provide further insights on the pathophysiology of these comorbid conditions and facilitate the development of therapeutic interventions.

Glutathione in the Nervous System as a Potential Therapeutic Target to Control the Development and Progression of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a rare neurological disorder that affects the motor neurons responsible for regulating muscle movement. However, the molecular pathogenic mechanisms of ALS remain poorly understood. A deficiency in the antioxidant tripeptide glutathione (GSH) in the nervous system appears to be involved in several neurodegenerative diseases characterized by the loss of neuronal cells. Impaired antioxidant defense systems, and the accumulation of oxidative damage due to increased dysfunction in GSH homeostasis are known to be involved in the development and progression of ALS. Aberrant GSH metabolism and redox status following oxidative damage are also associated with various cellular organelles, including the mitochondria and nucleus, and are crucial factors in neuronal toxicity induced by ALS. In this review, we provide an overview of the implications of imbalanced GSH homeostasis and its molecular characteristics in various experimental models of ALS.

Metabolic Dysregulation Contributes to the Progression of Alzheimer's Disease

Alzheimer's disease (AD) is an incurable neurodegenerative disease. Numerous studies have demonstrated a critical role for dysregulated glucose metabolism in its pathogenesis. In this review, we summarize metabolic alterations in aging brain and AD-related metabolic deficits associated with glucose metabolism dysregulation, glycolysis dysfunction, tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS) deficits, and pentose phosphate pathway impairment. Additionally, we discuss recent treatment strategies targeting metabolic defects in AD, including their limitations, in an effort to encourage the development of novel therapeutic strategies.

Mitochondrial Glutathione: Recent Insights and Role in Disease

Mitochondria are the main source of reactive oxygen species (ROS), most of them deriving from the mitochondrial respiratory chain. Among the numerous enzymatic and non-enzymatic antioxidant systems present in mitochondria, mitochondrial glutathione (mGSH) emerges as the main line of defense for maintaining the appropriate mitochondrial redox environment. mGSH’s ability to act directly or as a co-factor in reactions catalyzed by other mitochondrial enzymes makes its presence essential to avoid or to repair oxidative modifications that can lead to mitochondrial dysfunction and subsequently to cell death. Since mitochondrial redox disorders play a central part in many diseases, harboring optimal levels of mGSH is vitally important. In this review, we will highlight the participation of mGSH as a contributor to disease progression in pathologies as diverse as Alzheimer’s disease, alcoholic and non-alcoholic steatohepatitis, or diabetic nephropathy. Furthermore, the involvement of mitochondrial ROS in the signaling of new prescribed drugs and in other pathologies (or in other unmet medical needs, such as gender differences or coronavirus disease of 2019 (COVID-19) treatment) is still being revealed; guaranteeing that research on mGSH will be an interesting topic for years to come.

Glutathione monoethyl ester prevents TDP-43 pathology in motor neuronal NSC-34 cells

Oxidative stress is recognised as central in a range of neurological diseases including Amyotrophic lateral sclerosis (ALS), a disease characterised by fast progressing death of motor neurons in the brain and spinal cord. Cellular pathology includes cytosolic protein aggregates in motor neurons and glia of which potentially cytotoxic hyper-phosphorylated fragments of the Transactive response DNA Binding Protein 43 kDa (TDP-43) constitute a major component. This is closely associated with an additional loss of nuclear TDP-43 expression indicating a "loss of function" mechanism, accelerating motor neuron (MN) loss. Furthermore, mutations in TDP-43 cause familial ALS and ALS-like disease in animal models. In this study, we investigated the role of glutathione (GSH) in modulating oxidative stress responses in TDP-43 pathology in motor neuron NSC-34 cells. Results demonstrate that depletion of GSH produces pathology similar to that of mutant TDP-43, including occurrence of cytosolic aggregates, TDP-43 phosphorylation and nuclear clearing of endogenous TDP-43. We also demonstrate that introduction of mutant TDP-43^A315T and silencing of endogenous TDP-43, but not overexpression of wild-type TDP-43, result in similar pathology, including depletion of intracellular GSH, possibly resulting from a decreased expression of a regulatory subunit of ɣ-glutamylcysteine ligase (GCLM), a rate limiting enzyme in GSH synthesis. Importantly, treatment of mutant cells with GSH monoethyl ester (GSHe) that directly increases intracellular GSH and bypasses the need for GSH synthesis, protected against mutant-induced TDP-43 pathology, including reducing aggregate formation, nuclear clearance, reactive oxygen species (ROS) production and cell death. Our data strongly suggest that oxidative stress is central to TDP-43 pathology and may result from a loss of function affecting GSH synthesis and that treatments directly aimed at restoring cellular GSH content may be beneficial in preventing cell death in TDP-43-mediated ALS.

Resveratrol prevents ammonia-induced mitochondrial dysfunction and cellular redox imbalance in C6 astroglial cells

BACKGROUND

Resveratrol is a polyphenolic compound that presents several protective effects in the central nervous system, including gliotoxicity associated to hyperammonemia, a key element for the development of hepatic encephalopathy. In this condition, mitochondrial dysfunction leads to a reactive oxygen species (ROS) overproduction, which, in turn, exacerbates mitochondrial failure and causes cellular damage.

OBJECTIVE

This study sought to determine whether prevention of mitochondrial dysfunction and the maintenance of cellular redox status by resveratrol contribute to its protective action toward ammonia toxicity.

METHODS

C6 astrocyte cell line was pre-incubated in the presence or absence of resveratrol (100 μM) for 1 hour. After pre-incubation, resveratrol was maintained and 5 mM ammonia was added for 24 hours, followed by the evaluation of ROS production, mitochondrial functionality, antioxidant enzymatic and non-enzymatic defenses, energy metabolic parameters, and genotoxicity.

RESULTS

We showed that resveratrol prevented the increase in ROS production, the decrease of mitochondrial membrane potential (ΔΨ_m), and bioenergetics deficit caused by ammonia in C6 astroglial cells. In addition, resveratrol avoided the ammonia-induced upregulation of NOX activity and impairment in enzymatic and non-enzymatic antioxidant defenses. Ammonia also induced DNA damage that was prevented by resveratrol, indicating its genoprotective effect.

CONCLUSIONS

In summary, our study demonstrates that resveratrol prevents ammonia-induced cytotoxicity, as well as supports the role of resveratrol on mitochondrial/cellular redox functionality.

Passive regeneration of glutathione: Glutathione reductase regulation from the freeze-tolerant North American wood frog, Rana sylvatica

Wood frogs inhabit a broad range across North America, extending from the southern tip of the Appalachian Mountains to the northern boreal forest. Remarkably they can survive the winter in a frozen state, where as much as 70% of their body water is converted into ice. During the frozen state, their hearts cease to pump blood, causing their cells to experience ischemia which can dramatically increase the production of reactive oxygen species produced within the cell. To overcome this, wood frogs have elevated levels of glutathione, a primary antioxidant. We examined the regulation of glutathione reductase, the enzyme involved in recycling glutathione, in both the frozen and unfrozen state (control). Glutathione reductase activity from both the control and frozen state showed dramatic reduction in substrate specificity (Km) for oxidized glutathione (50%) when measured in the presence of glucose (300mM) and a increase (157%) when measured in the presence of levels of urea (75mM) encountered in the frozen state. However, when we tested the synergistic effect of urea and glucose simultaneously, we observed a substantial reduction in the Km for oxidized glutathione (43%) to a value similar to that of glucose alone. In fact, we found no observable differences in the kinetic and structural properties of glutathione reductase between the two states. Therefore, a significant increase in the affinity for oxidized glutathione in the presence of endogenous levels of glucose, suggests that increased glutathione recycling may result due to passive regulation of glutathione reductase by rising levels of glucose during freezing.

Energy metabolism and inflammation in brain aging and Alzheimer's disease

The high energy demand of the brain renders it sensitive to changes in energy fuel supply and mitochondrial function. Deficits in glucose availability and mitochondrial function are well-known hallmarks of brain aging and are particularly accentuated in neurodegenerative disorders such as Alzheimer's disease. As important cellular sources of H₂O₂, mitochondrial dysfunction is usually associated with altered redox status. Bioenergetic deficits and chronic oxidative stress are both major contributors to cognitive decline associated with brain aging and Alzheimer's disease. Neuroinflammatory changes, including microglial activation and production of inflammatory cytokines, are observed in neurodegenerative diseases and normal aging. The bioenergetic hypothesis advocates for sequential events from metabolic deficits to propagation of neuronal dysfunction, to aging, and to neurodegeneration, while the inflammatory hypothesis supports microglia activation as the driving force for neuroinflammation. Nevertheless, growing evidence suggests that these diverse mechanisms have redox dysregulation as a common denominator and connector. An independent view of the mechanisms underlying brain aging and neurodegeneration is being replaced by one that entails multiple mechanisms coordinating and interacting with each other. This review focuses on the alterations in energy metabolism and inflammatory responses and their connection via redox regulation in normal brain aging and Alzheimer's disease. Interaction of these systems is reviewed based on basic research and clinical studies.

Neuronal Glutathione Content and Antioxidant Capacity can be Normalized In Situ by N-acetyl Cysteine Concentrations Attained in Human Cerebrospinal Fluid

N-acetyl cysteine (NAC) supports the synthesis of glutathione (GSH), an essential substrate for fast, enzymatically catalyzed oxidant scavenging and protein repair processes. NAC is entering clinical trials for adrenoleukodystrophy, Parkinson's disease, schizophrenia, and other disorders in which oxidative stress may contribute to disease progression. However, these trials are hampered by uncertainty about the dose of NAC required to achieve biological effects in human brain. Here we describe an approach to this issue in which mice are used to establish the levels of NAC in cerebrospinal fluid (CSF) required to affect brain neurons. NAC dosing in humans can then be calibrated to achieve these NAC levels in human CSF. The mice were treated with NAC over a range of doses, followed by assessments of neuronal GSH levels and neuronal antioxidant capacity in ex vivo brain slices. Neuronal GSH levels and antioxidant capacity were augmented at NAC doses that produced peak CSF NAC concentrations of ≥50 nM. Oral NAC administration to humans produced CSF concentrations of up to 10 μM, thus demonstrating that oral NAC administration can surpass the levels required for biological activity in brain. Variations of this approach may similarly facilitate and rationalize drug dosing for other agents targeting central nervous system disorders.

Administration of a CXCL12 Analog in Endotoxemia Is Associated with Anti-Inflammatory, Anti-Oxidative and Cytoprotective Effects In Vivo

Background

The chemokine receptor CXCR4 is a multifunctional receptor which is activated by its natural ligand C-X-C motif chemokine 12 (CXCL12). As CXCR4 is part of the lipopolysaccharide sensing complex and CXCL12 analogs are not well characterized in inflammation, we aimed to uncover the systemic effects of a CXCL12 analog in severe systemic inflammation and to evaluate its impact on endotoxin induced organ damages by using a sublethal LPS dose.

Methods

The plasma stable CXCL12 analog CTCE-0214D was synthesized and administered subcutaneously shortly before LPS treatment. After 24 hours, mice were sacrificed and blood was obtained for TNF alpha, IFN gamma and blood glucose evaluation. Oxidative stress in the liver and spleen was assessed and liver biotransformation capacity was determined. Finally, CXCR4, CXCL12 and TLR4 expression patterns in liver, spleen and thymus tissue as well as the presence of different markers for apoptosis and oxidative stress were determined by means of immunohistochemistry.

Results

CTCE-0214D distinctly reduced the LPS mediated effects on TNF alpha, IFN gamma, ALAT and blood glucose levels. It attenuated oxidative stress in the liver and spleen tissue and enhanced liver biotransformation capacity unambiguously. Furthermore, in all three organs investigated, CTCE-0214D diminished the LPS induced expression of CXCR4, CXCL12, TLR4, NF-κB, cleaved caspase-3 and gp91 phox, whereas heme oxygenase 1 expression and activity was induced above average. Additionally, TUNEL staining revealed anti-apoptotic effects of CTCE-0214D.

Conclusions

In summary, CTCE-0214D displayed anti-inflammatory, anti-oxidative and cytoprotective features. It attenuated reactive oxygen species, induced heme oxygenase 1 activity and mitigated apoptosis. Thus, the CXCR4/CXCL12 axis seems to be a promising target in the treatment of acute systemic inflammation, especially when accompanied by a hepatic dysfunction and an excessive production of free radicals.

Assessment at the single-cell level identifies neuronal glutathione depletion as both a cause and effect of ischemia-reperfusion oxidative stress

Oxidative stress contributes to neuronal death in brain ischemia-reperfusion. Tissue levels of the endogenous antioxidant glutathione (GSH) are depleted during ischemia-reperfusion, but it is unknown whether this depletion is a cause or an effect of oxidative stress, and whether it occurs in neurons or other cell types. We used immunohistochemical methods to evaluate glutathione, superoxide, and oxidative stress in mouse hippocampal neurons after transient forebrain ischemia. GSH levels in CA1 pyramidal neurons were normally high relative to surrounding neuropil, and exhibited a time-dependent decrease during the first few hours of reperfusion. Colabeling for superoxide in the neurons showed a concurrent increase in detectable superoxide over this interval. To identify cause-effect relationships between these changes, we independently manipulated superoxide production and GSH metabolism during reperfusion. Mice in which NADPH oxidase activity was blocked to prevent superoxide production showed preservation of neuronal GSH content, thus demonstrating that neuronal GSH depletion is result of oxidative stress. Conversely, mice in which neuronal GSH levels were maintained by N-acetyl cysteine treatment during reperfusion showed less neuronal superoxide signal, oxidative stress, and neuronal death. At 3 d following ischemia, GSH content in reactive astrocytes and microglia was increased in the hippocampal CA1 relative to surviving neurons. Results of these studies demonstrate that neuronal GSH depletion is both a result and a cause of neuronal oxidative stress after ischemia-reperfusion, and that postischemic restoration of neuronal GSH levels can be neuroprotective.

Aqueous Extract of Agaricus blazei Murrill Prevents Age-Related Changes in the Myenteric Plexus of the Jejunum in Rats

This study evaluated the effects of the supplementation with aqueous extract of Agaricus blazei Murrill (ABM) on biometric and blood parameters and quantitative morphology of the myenteric plexus and jejunal wall in aging Wistar rats. The animals were euthanized at 7 (C7), 12 (C12 and CA12), and 23 months of age (C23 and CA23). The CA12 and CA23 groups received a daily dose of ABM extract (26 mg/animal) via gavage, beginning at 7 months of age. A reduction in food intake was observed with aging, with increases in the Lee index, retroperitoneal fat, intestinal length, and levels of total cholesterol and total proteins. Aging led to a reduction of the total wall thickness, mucosa tunic, villus height, crypt depth, and number of goblet cells. In the myenteric plexus, aging quantitatively decreased the population of HuC/D(+) neuronal and S100(+) glial cells, with maintenance of the nNOS(+) nitrergic subpopulation and increase in the cell body area of these populations. Supplementation with the ABM extract preserved the myenteric plexus in old animals, in which no differences were detected in the density and cell body profile of neurons and glial cells in the CA12 and CA23 groups, compared with C7 group. The supplementation with the aqueous extract of ABM efficiently maintained myenteric plexus homeostasis, which positively influenced the physiology and prevented the death of the neurons and glial cells.

Changes in the mitochondrial antioxidant systems in neurodegenerative diseases and acute brain disorders

Oxidative and nitrosative stress (ONS) contributes to the pathogenesis of most brain maladies, and the magnitude of ONS is related to the ability of cellular antioxidants to neutralize the accumulating reactive oxygen and nitrogen species (ROS/RNS). While the major ROS/RNS scavengers and regenerators of bio-oxidized molecules, superoxide dysmutases (SODs), glutathione (GSH), thioredoxin (Trx) and peroxiredoxin (Prx), are distributed in all cellular compartments. This review specifically focuses on the role of the systems operating in mitochondria. There is a growing consensus that the mitochondrial SOD isoform - SOD2 and GSH are critical for the cellular antioxidant defense. Variable changes of the expression or activities of one or more of the mitochondrial antioxidant systems have been documented in the brains derived from human patients and/or in animal models of neurodegenerative diseases (Alzheimer's disease, Parkinson's disease), cerebral ischemia, toxic brain cell damage associated with overexposure to mercury or excitotoxins, or hepatic encephalopathy. In many cases, ambiguity of the responses of the different antioxidant systems in one and the same disease needs to be more conclusively evaluated before the balance of the changes is viewed as beneficial or detrimental. Modulation of the mitochondrial antioxidant systems may in the future become a target of antioxidant therapy.

Antioxidant and anti-inflammatory effects of N-acetylcysteine against malathion-induced liver damages and immunotoxicity in rats

AIMS

Occupational exposure to organophosphate pesticides is becoming a common and increasingly alarming world-wide phenomenon. The present study is designed to investigate the preventive effect of N-acetylcysteine on malathion-induced hepatic injury and inflammation in rats.

MAIN METHODS

Adult male Wistar rats of body weight 200-230 g were used for the study. Malathion (200mg/kg b.w./day) was administered to rats by oral intubation and N-acetylcysteine (2g/l) in drinking water for 28 days. Rats were sacrificed on the 28th day, 2h after the last administration. Markers of liver injury (aspartate transaminase, alanine transaminase, alkaline phosphatase and lactate desyhdogenase), inflammation (leukocyte counts, myeloperoxidase, immunophenotyping of CD4(+) and CD8(+), interleukin-1β, interleukin-6 and interferon-γ expression) and oxidative stress (lipid peroxidation, reduced glutathione and antioxidant status) were assessed.

KEY FINDINGS

Malathion induced an increase in activities of hepatocellular enzymes in plasma, lipid peroxidation index, CD3(+)/CD4(+) and CD3(+)/CD4(+) percent and pro-inflammatory cytokines, when decreased antioxidant status in liver was noted. When malathion-treated rats were compared to NAC supplemented rats, leukocytosis, T cell count and IL-1β, IL-6, INF-γ expression were reduced. Furthermore, NAC restored liver enzyme activities and oxidative stress markers.

SIGNIFICANCE

Malathion induces hepatotoxicity, oxidative stress and liver inflammation. N-acetylcysteine showed therapeutic effects against malathion toxicity.

Stable over-expression of the 2-oxoglutarate carrier enhances neuronal cell resistance to oxidative stress via Bcl-2-dependent mitochondrial GSH transport

Mitochondrial glutathione (GSH) is a key endogenous antioxidant and its maintenance is critical for cell survival. Here, we generated stable NSC34 motor neuron-like cell lines over-expressing the mitochondrial GSH transporter, the 2-oxoglutarate carrier (OGC), to further elucidate the importance of mitochondrial GSH transport in determining neuronal resistance to oxidative stress. Two stable OGC cell lines displayed specific increases in mitochondrial GSH content and resistance to oxidative and nitrosative stressors, but not staurosporine. Inhibition of transport through OGC reduced levels of mitochondrial GSH and resensitized the stable cell lines to oxidative stress. The stable OGC cell lines displayed significant up-regulation of the anti-apoptotic protein, B cell lymphoma 2 (Bcl-2). This result was reproduced in parental NSC34 cells by chronic treatment with GSH monoethylester, which specifically increased mitochondrial GSH levels. Knockdown of Bcl-2 expression decreased mitochondrial GSH and resensitized the stable OGC cells to oxidative stress. Finally, endogenous OGC was co-immunoprecipitated with Bcl-2 from rat brain lysates in a GSH-dependent manner. These data are the first to show that increased mitochondrial GSH transport is sufficient to enhance neuronal resistance to oxidative stress. Moreover, sustained and specific enhancement of mitochondrial GSH leads to increased Bcl-2 expression, a required mechanism for the maintenance of increased mitochondrial GSH levels. Stable over-expression of the 2-oxoglutarate carrier (OGC) in a motor neuronal cell line induced a specific increase in mitochondrial GSH and markedly enhanced resistance to oxidative stress. Over-expression of OGC also induced Bcl-2 expression which was owing to the specific increase in mitochondrial GSH. Intriguingly, enhanced expression of Bcl-2 was required to sustain OGC-dependent GSH transport into the mitochondria. Thus, OGC and Bcl-2 work in a concerted manner to maintain the mitochondrial GSH pool which is crucial for neuronal survival.

Mitochondrial dysfunction in amyotrophic lateral sclerosis - a valid pharmacological target?

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by the selective death of upper and lower motor neurons which ultimately leads to paralysis and ultimately death. Pathological changes in ALS are closely associated with pronounced and progressive changes in mitochondrial morphology, bioenergetics and calcium homeostasis. Converging evidence suggests that impaired mitochondrial function could be pivotal in the rapid neurodegeneration of this condition. In this review, we provide an update of recent advances in understanding mitochondrial biology in the pathogenesis of ALS and highlight the therapeutic value of pharmacologically targeting mitochondrial biology to slow disease progression.

Inhibition of glutathione synthesis distinctly alters mitochondrial and cytosolic redox poise

The glutathione couple GSH/GSSG is the most abundant cellular redox buffer and is not at equilibrium among intracellular compartments. Perturbation of glutathione poise has been associated with tumorigenesis; however, due to analytical limitations, the underlying mechanisms behind this relationship are poorly understood. In this regard, we have implemented a ratiometric, genetically encoded redox-sensitive green fluorescent protein fused to human glutaredoxin (Grx1-roGFP2) to monitor real-time glutathione redox potentials in the cytosol and mitochondrial matrix of tumorigenic and non-tumorigenic cells. First, we demonstrated that recovery time in both compartments depended upon the length of exposure to oxidative challenge with diamide, a thiol-oxidizing agent. We then monitored changes in glutathione poise in cytosolic and mitochondrial matrices following inhibition of glutathione (GSH) synthesis with L-buthionine sulphoximine (BSO). The mitochondrial matrix showed higher oxidation in the BSO-treated cells indicating distinct compartmental alterations in redox poise. Finally, the contributory role of the p53 protein in supporting cytosolic redox poise was demonstrated. Inactivation of the p53 pathway by expression of a dominant-negative p53 protein sensitized the cytosol to oxidation in BSO-treated tumor cells. As a result, both compartments of PF161-T+p53(DD) cells were equally oxidized ≈20 mV by inhibition of GSH synthesis. Conversely, mitochondrial oxidation was independent of p53 status in GSH-deficient tumor cells. Taken together, these findings indicate different redox requirements for the glutathione thiol/disulfide redox couple within the cytosol and mitochondria of resting cells and reveal distinct regulation of their redox poise in response to inhibition of glutathione biosynthesis.

Neuroprotection against neuroblastoma cell death induced by depletion of mitochondrial glutathione

Mitochondrial glutathione pool is vital in protecting cells against oxidative stress as the majority of the cellular reactive oxygen species are generated in mitochondria. Oxidative stress is implicated as a causative factor in neuronal death in neurodegenerative disorders. We hypothesized that depletion of mitochondrial glutathione leads to mitochondrial dysfunction and apoptotic death of SK-N-SH (human neuroblastoma) cells and investigated the neuroprotective strategies against GSH depletion. SK-N-SH cells were treated with two distinct inhibitors of glutathione metabolism: L-buthionine-(S, R)-sulfoximine (BSO) and ethacrynic acid (EA). EA treatment caused depletion of both the total and mitochondrial glutathione (while BSO had no effect on mitochondrial glutathione), enhanced rotenone-induced ROS production, and reduced the viability of SK-N-SH cells. Glutathione depletion by BSO or EA demonstrated positive features of mitochondria-mediated apoptosis in neuroblastoma cell death. Prevention of apoptosis by Bcl2 overexpression or use of antioxidant ebselen did not confer neuroprotection. Co-culture with U-87 (human glioblastoma) cells protected SK-N-SH cells from the cell death. Our data suggest that depletion of mitochondrial glutathione leads to mitochondrial dysfunction and apoptosis. The study indicates that preventing mitochondrial glutathione depletion could become a novel strategy for the development of neuroprotective therapeutics in neurodegenerative disorders.

Mitochondrial glutathione transport is a key determinant of neuronal susceptibility to oxidative and nitrosative stress

Mitochondrial oxidative stress significantly contributes to the underlying pathology of several devastating neurodegenerative disorders. Mitochondria are highly sensitive to the damaging effects of reactive oxygen and nitrogen species; therefore, these organelles are equipped with a number of free radical scavenging systems. In particular, the mitochondrial glutathione (GSH) pool is a critical antioxidant reserve that is derived entirely from the larger cytosolic pool via facilitated transport. The mechanism of mitochondrial GSH transport has not been extensively studied in the brain. However, the dicarboxylate (DIC) and 2-oxoglutarate (OGC) carriers localized to the inner mitochondrial membrane have been established as GSH transporters in liver and kidney. Here, we investigated the role of these carriers in protecting neurons from oxidative and nitrosative stress. Immunoblot analysis of DIC and OGC in primary cultures of rat cerebellar granule neurons (CGNs) and cerebellar astrocytes showed differential expression of these carriers, with CGNs expressing only DIC and astrocytes expressing both DIC and OGC. Consistent with these findings, butylmalonate specifically reduced mitochondrial GSH in CGNs, whereas both butylmalonate and phenylsuccinate diminished mitochondrial GSH in astrocytes. Moreover, preincubation with butylmalonate but not phenylsuccinate significantly enhanced susceptibility of CGNs to oxidative and nitrosative stressors. This increased vulnerability was largely prevented by incubation with cell-permeable GSH monoethylester but not malate. Finally, knockdown of DIC with adenoviral siRNA also rendered CGNs more susceptible to oxidative stress. These findings demonstrate that maintenance of the mitochondrial GSH pool via sustained mitochondrial GSH transport is essential to protect neurons from oxidative and nitrosative stress.

Mitochondrial thiols in the regulation of cell death pathways

SIGNIFICANCE

Regulation of mitochondrial H(2)O(2) homeostasis and its involvement in the regulation of redox-sensitive signaling and transcriptional pathways is the consequence of the concerted activities of the mitochondrial energy- and redox systems.

RECENT ADVANCES

The energy component of this mitochondrial energy-redox axis entails the formation of reducing equivalents and their flow through the respiratory chain with the consequent electron leak to generate [Formula: see text] and H(2)O(2). The mitochondrial redox component entails the thiol-based antioxidant system, largely accounted for by glutathione- and thioredoxin-based systems that support the activities of glutathione peroxidases, peroxiredoxins, and methionine sulfoxide reductase. The ultimate reductant for these systems is NADPH: mitochondrial sources of NADPH are the nicotinamide nucleotide transhydrogenase, isocitrate dehydrogenase-2, and malic enzyme. NADPH also supports the glutaredoxin activity that regulates the extent of S-glutathionylation of mitochondrial proteins in response to altered redox status.

CRITICAL ISSUES

The integrated network of these mitochondrial thiols constitute a regulatory device involved in the maintenance of steady-state levels of H(2)O(2), mitochondrial and cellular redox and metabolic homeostasis, as well as the modulation of cytosolic redox-sensitive signaling; disturbances of this regulatory device affects transcription, growth, and ultimately influences cell survival/death.

FUTURE DIRECTIONS

The modulation of key mitochondrial thiol proteins, which participate in redox signaling, maintenance of the bioenergetic machinery, oxidative stress responses, and cell death programming, provides a pivotal direction in developing new therapies towards the prevention and treatment of several diseases.

Mitochondrial glutathione: features, regulation and role in disease

BACKGROUND

Mitochondria are the powerhouse of mammalian cells and the main source of reactive oxygen species (ROS) associated with oxygen consumption. In addition, they also play a strategic role in controlling the fate of cells through regulation of death pathways. Mitochondrial ROS production fulfills a signaling role through regulation of redox pathways, but also contributes to mitochondrial damage in a number of pathological states.

SCOPE OF REVIEW

Mitochondria are exposed to the constant generation of oxidant species, and yet the organelle remains functional due to the existence of an armamentarium of antioxidant defense systems aimed to repair oxidative damage, of which mitochondrial glutathione (mGSH) is of particular relevance. Thus, the aim of the review is to cover the regulation of mGSH and its role in disease.

MAJOR CONCLUSIONS

Cumulating evidence over recent years has demonstrated the essential role for mGSH in mitochondrial physiology and disease. Despite its high concentration in the mitochondrial matrix, mitochondria lack the enzymes to synthesize GSH de novo, so that mGSH originates from cytosolic GSH via transport through specific mitochondrial carriers, which exhibit sensitivity to membrane dynamics. Depletion of mGSH sensitizes cells to stimuli leading to oxidative stress such as TNF, hypoxia or amyloid β-peptide, thereby contributing to disease pathogenesis.

GENERAL SIGNIFICANCE

Understanding the regulation of mGSH may provide novel insights to disease pathogenesis and toxicity and the opportunity to design therapeutic targets of intervention in cell death susceptibility and disease. This article is part of a Special Issue entitled Cellular functions of glutathione.

Deficiency of αB crystallin augments ER stress-induced apoptosis by enhancing mitochondrial dysfunction

Endoplasmic reticulum (ER) stress is linked to several pathological conditions including age-related macular degeneration. Excessive ER stress initiates cell death cascades which are mediated, in part, through mitochondrial dysfunction. Here, we identify αB crystallin as an important regulator of ER stress-induced cell death. Retinal pigment epithelial (RPE) cells from αB crystallin (-/-) mice, and human RPE cells transfected with αB crystallin siRNA, are more vulnerable to ER stress induced by tunicamycin. ER stress-mediated cell death is associated with increased levels of reactive oxygen species, depletion of glutathione in mitochondria, decreased superoxide dismutase activity, increased release of cytochrome c, and activation of caspases 3 and 4. The ER stress signaling inhibitors, salubrinal and 4-(2-aminoethyl) benzenesulfonyl fluoride, decrease mitochondrial damage and reduce RPE apoptosis induced by ER stress. Prolonged ER stress decreases levels of αB crystallin, thus exacerbating mitochondrial dysfunction. Overexpression of αB crystallin protects RPE cells from ER stress-induced apoptosis by attenuating increases in Bax, CHOP, mitochondrial permeability transition, and cleaved caspase 3. Thus, these data collectively demonstrate that αB crystallin provides critical protection of mitochondrial function during ER stress-induced RPE apoptosis.

The mitochondrial T1095C mutation increases gentamicin-mediated apoptosis

We have previously reported a heteroplasmic mtDNA mutation (T1095C) in the 12SrRNA gene of an Italian family with features of maternally-inherited parkinsonism, antibiotic-mediated deafness and peripheral neuropathy. In the present study, we demonstrate that a transmitochondrial cybrid line derived from the proband of this family shows selective depletion of mitochondrial glutathione and decreases in the activity of complex II/III. Moreover, when exposed to an aminoglycoside antibiotic these cells responded with a ten-fold increase in the number of apoptotic cells compared to controls. These results support a pathogenic role for the T1095C mutation and indicate that the mutation increases the risk for aminoglycoside-induced toxicity.

Decreased oxidative stress during glycolytic inhibition enables maintenance of ATP production and astrocytic survival

Depressed energy metabolism and oxidative stress are common features in many pathological situations in the brain, including stroke. In order to investigate astrocytic responses to such stress, we induced metabolic depression in cultured rat astrocytes. Iodoacetate (IA), an inhibitor of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used and resulted in a rapid inhibition of GAPDH activity. After 1h of GAPDH inhibition the ATP levels started to decrease and were completely abolished at 4h. In parallel, the activity of reactive oxygen species (ROS) was significantly increased, followed by extensive cell death involving flipping of phosphatidylserine and translocation of apoptosis-inducing factor, but not caspase-3 activation. When IA was combined with azide, a respiratory chain complex IV inhibitor, the ATP levels decreased immediately. Interestingly, with azide present, the ROS activity remained low and the astrocytes remained viable even at very low ATP levels. Addition of exogenous ROS-scavengers prevented the IA-induced ROS activity, the ATP levels were maintained and cell death was prevented. Similar protection could be obtained when astrocytes, prior to addition of IA, were incubated with substances known to activate the nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated endogenous antioxidant system. When IA was washed out, after a relatively moderate ATP depression, massive cell death occurred. This was efficiently prevented by addition of azide or ROS scavengers during the IA treatment or by pre-activation of the Nrf2 system. Our results demonstrate that astrocytes in culture can endure and recover from glycolytic inhibition if the ROS activity remained at a low level and suggest that oxidative stress can be an important component for astrocytic cell death following metabolic stress.

Neuroprotective effects of anthocyanins on apoptosis induced by mitochondrial oxidative stress

OBJECTIVES

Mitochondrial oxidative stress (MOS) is a major factor in the underlying pathology of many neurodegenerative diseases. Here, we investigated the neuroprotective effects of a unique class of nutraceutical antioxidants, anthocyanins, against MOS-induced death of cultured cerebellar granule neurons (CGNs). Callistephin and kuromanin are anthocyanins derived from strawberries and black rice, respectively, whose neuroprotective properties have yet to be examined in detail.

METHODS

Glutathione (GSH)-sensitive MOS and intrinsic apoptosis were induced in CGNs by incubation with the Bcl-2 inhibitor, HA14-1. The effects of anthocyanin co-incubation on CGN survival were assessed.

RESULTS

The anthocyanins demonstrated significant protection from MOS-induced apoptosis which was equivalent to that provided by the green tea polyphenol, epigallocatechin 3-gallate; however, neither anthocyanin was as effective as GSH at rescuing CGNs. Inhibition of Bcl-2 caused a significant reduction of mitochondrial GSH which was prevented by the anthocyanins. Furthermore, the anthocyanins inhibited iron-induced lipid peroxidation in rat brain homogenates and prevented cardiolipin oxidation induced by MOS in CGNs. MOS-induced mitochondrial fragmentation and proteolytic cleavage of the optic atrophy 1 (OPA1) fusion GTPase were also attenuated by the anthocyanins. Finally, the anthocyanins significantly enhanced GSH peroxidase activity in a cell-free assay.

DISCUSSION

These data show that anthocyanins suppress MOS-induced apoptosis by preserving mitochondrial GSH and inhibiting cardiolipin oxidation and mitochondrial fragmentation. These nutraceutical antioxidants warrant further study as potential therapeutic agents for neurodegenerative diseases caused by MOS.

Bcl-2 is a novel interacting partner for the 2-oxoglutarate carrier and a key regulator of mitochondrial glutathione

Despite making up only a minor fraction of the total cellular glutathione, recent studies indicate that the mitochondrial glutathione pool is essential for cell survival. Selective depletion of mitochondrial glutathione is sufficient to sensitize cells to mitochondrial oxidative stress (MOS) and intrinsic apoptosis. Glutathione is synthesized exclusively in the cytoplasm and must be actively transported into mitochondria. Therefore, regulation of mitochondrial glutathione transport is a key factor in maintaining the antioxidant status of mitochondria. Bcl-2 resides in the outer mitochondrial membrane where it acts as a central regulator of the intrinsic apoptotic cascade. In addition, Bcl-2 displays an antioxidant-like function that has been linked experimentally to the regulation of cellular glutathione content. We have previously demonstrated a novel interaction between recombinant Bcl-2 and reduced glutathione (GSH), which was antagonized by either Bcl-2 homology-3 domain (BH3) mimetics or a BH3-only protein, recombinant Bim. These previous findings prompted us to investigate if this novel Bcl-2/GSH interaction might play a role in regulating mitochondrial glutathione transport. Incubation of primary cultures of cerebellar granule neurons (CGNs) with the BH3 mimetic HA14-1 induced MOS and caused specific depletion of the mitochondrial glutathione pool. Bcl-2 was coimmunoprecipitated with GSH after chemical cross-linking in CGNs and this Bcl-2/GSH interaction was antagonized by preincubation with HA14-1. Moreover, both HA14-1 and recombinant Bim inhibited GSH transport into isolated rat brain mitochondria. To further investigate a possible link between Bcl-2 function and mitochondrial glutathione transport, we next examined if Bcl-2 associated with the 2-oxoglutarate carrier (OGC), an inner mitochondrial membrane protein known to transport glutathione in liver and kidney. After cotransfection of CHO cells, Bcl-2 was coimmunoprecipitated with OGC and this novel interaction was significantly enhanced by glutathione monoethyl ester. Similarly, recombinant Bcl-2 interacted with recombinant OGC in the presence of GSH. Bcl-2 and OGC cotransfection in CHO cells significantly increased the mitochondrial glutathione pool. Finally, the ability of Bcl-2 to protect CHO cells from apoptosis induced by hydrogen peroxide was significantly attenuated by the OGC inhibitor phenylsuccinate. These data suggest that GSH binding by Bcl-2 enhances its affinity for the OGC. Bcl-2 and OGC appear to act in a coordinated manner to increase the mitochondrial glutathione pool and enhance resistance of cells to oxidative stress. We conclude that regulation of mitochondrial glutathione transport is a principal mechanism by which Bcl-2 suppresses MOS.

Erythrocyte antioxidant defenses as a potential biomarker of liver mitochondrial status in different oxidative conditions

The need for minimally invasive biomarkers to predict the progression of non-alcoholic fatty liver disease to non-alcoholic steatohepatitis is a priority. Oxidative stress and mitochondrial dysfunction contribute in this physiopathological process. The aim of this study was to analyze the potential role of erythrocytes as surrogate biomarkers of hepatic mitochondrial oxidative status in an animal model under different dietary oxidative conditions. Interestingly, we found that erythrocyte antioxidant status correlated with triglyceride content (p < 0.05-p < 0.001), thiobarbituric acid reactive species levels (p < 0.001) and with liver mitochondrial antioxidant levels (p < 0.001). These data suggest that erythrocyte antioxidant defenses could be used as sensitive and minimally invasive biomarkers of mitochondrial status in diverse oxidative conditions.

Rotenone enhances the antifungal properties of staurosporine

We studied staurosporine-induced cell death in the filamentous fungus Neurospora crassa. The generation of reactive oxygen species during the process appears to be an important signaling event, since addition of the antioxidant glutathione prevents the effects of staurosporine on fungal growth. Selected mutants with mutations in respiratory chain complex I are extremely sensitive to the drug, stressing the involvement of complex I in programmed cell death. Following this finding, we determined that the complex I-specific inhibitor rotenone used in combination with staurosporine results in a synergistic and specific antifungal activity, likely through a concerted action on intracellular glutathione depletion. Paradoxically, the synergistic antifungal activity of rotenone and staurosporine is observed in N. crassa complex I mutants and in Saccharomyces cerevisiae, which lacks complex I. In addition, it is not observed when other complex I inhibitors are used instead of rotenone. These results indicate that the rotenone effect is independent of complex I inhibition. The combination of rotenone and staurosporine is effective against N. crassa as well as against the common pathogens Aspergillus fumigatus and Candida albicans, pointing to its usefulness as an antifungal agent.

Copper accumulation by cultured astrocytes

To study copper transport in brain astrocytes, we have used astrocyte-rich primary cultures as model system. Cells in these cultures contained a basal copper content of 1.1+/-0.4 nmol per mg protein. The cellular copper content increased strongly after application of copper chloride in a time and concentration-dependent manner. Analysis of the linear copper accumulation during the first 5 min of copper exposure revealed that cultured astrocytes accumulated copper with saturable kinetics with apparent K(M)- and V(max)-values of 9.4+/-1.8 microM and 0.76+/-0.13 nmol/(min x mg protein), respectively. In contrast, incubation of astrocytes with copper in the presence of ascorbate caused a linear increase of the copper accumulation rates for copper concentrations of up to 30 microM. In addition, copper accumulation was strongly inhibited by the presence of an excess of zinc or of various other divalent metal ions. The presence of mRNA and of immunoreactivity of the copper transport protein Ctr1 in astrocyte cultures suggests that Ctr1 contributes to the observed copper accumulation. However, since some characteristics of the observed copper accumulation are not consistent with Ctr1-mediated copper transport, additional Ctr1-independent mechanism(s) are likely to be involved in astrocytic copper accumulation.

Apoptosis and glutathione: beyond an antioxidant

Apoptosis is a conserved homeostatic process critical for organ and tissue morphogenesis, development, and senescence. This form of programmed cell death also participates in the etiology of several human diseases including cancer, neurodegenerative, and autoimmune disorders. Although the signaling pathways leading to the progression of apoptosis have been extensively characterized, recent studies highlight the regulatory role of changes in the intracellular milieu (permissive apoptotic environment) in the efficient activation of the cell death machinery. In particular, glutathione (GSH) depletion is a common feature of apoptotic cell death triggered by a wide variety of stimuli including activation of death receptors, stress, environmental agents, and cytotoxic drugs. Although initial studies suggested that GSH depletion was only a byproduct of oxidative stress generated during cell death, recent discoveries suggest that GSH depletion and post-translational modifications of proteins through glutathionylation are critical regulators of apoptosis. Here, we reformulate these emerging paradigms into our current understanding of cell death mechanisms.

Mitochondria, oxidative metabolism and cell death in stroke

Stroke most commonly results from occlusion of a major artery in the brain and typically leads to the death of all cells within the affected tissue. Mitochondria are centrally involved in the development of this tissue injury due to modifications of their major role in supplying ATP and to changes in their properties that can contribute to the development of apoptotic and necrotic cell death. In animal models of stroke, the limited availability of glucose and oxygen directly impairs oxidative metabolism in severely ischemic regions of the affected tissue and leads to rapid changes in ATP and other energy-related metabolites. In the less-severely ischemic "penumbral" tissue, more moderate alterations develop in these metabolites, associated with near normal glucose use but impaired oxidative metabolism. This tissue remains potentially salvageable for at least the first few hours following stroke onset. Early restoration of blood flow can result in substantial recovery of energy-related metabolites throughout the affected tissue. However, glucose oxidation is markedly decreased due both to lower energy requirements in the post-ischemic tissue and limitations on the mitochondrial oxidation of pyruvate. A secondary deterioration of mitochondrial function subsequently develops that may contribute to progression to cell loss. Mitochondrial release of multiple apoptogenic proteins has been identified in ischemic and post-ischemic brain, mostly in neurons. Pharmacological interventions and genetic modifications in rodent models strongly implicate caspase-dependent and caspase-independent apoptosis and the mitochondrial permeability transition as important contributors to tissue damage, particularly when induced by short periods of temporary focal ischemia.

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

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

The mitochondrial permeability transition, and oxidative and nitrosative stress in the mechanism of copper toxicity in cultured neurons and astrocytes

Copper is an essential element and an integral component of various enzymes. However, excess copper is neurotoxic and has been implicated in the pathogenesis of Wilson's disease, Alzheimer's disease, prion conditions, and other disorders. Although mechanisms of copper neurotoxicity are not fully understood, copper is known to cause oxidative stress and mitochondrial dysfunction. As oxidative stress is an important factor in the induction of the mitochondrial permeability transition (mPT), we determined whether mPT plays a role in copper-induced neural cell injury. Cultured astrocytes and neurons were treated with 20 microM copper and mPT was measured by changes in the cyclosporin A (CsA)-sensitive inner mitochondrial membrane potential (Delta Psi m), employing the potentiometric dye TMRE. In astrocytes, copper caused a 36% decrease in the Delta Psi m at 12 h, which decreased further to 48% by 24 h and remained at that level for at least 72 h. Cobalt quenching of calcein fluorescence as a measure of mPT similarly displayed a 45% decrease at 24 h. Pretreatment with antioxidants significantly blocked the copper-induced mPT by 48-75%. Copper (24 h) also caused a 30% reduction in ATP in astrocytes, which was completely blocked by CsA. Copper caused death (42%) in astrocytes by 48 h, which was reduced by antioxidants (35-60%) and CsA (41%). In contrast to astrocytes, copper did not induce mPT in neurons. Instead, it caused early and extensive death with a concomitant reduction (63%) in ATP by 14 h. Neuronal death was prevented by antioxidants and nitric oxide synthase inhibitors but not by CsA. Copper increased protein tyrosine nitration in both astrocytes and neurons. These studies indicate that mPT, and oxidative and nitrosative stress represent major factors in copper-induced toxicity in astrocytes, whereas oxidative and nitrosative stress appears to play a major role in neuronal injury.

Neuroprotective immunity: T cell-derived glutamate endows astrocytes with a neuroprotective phenotype

A well-controlled T cell response to CNS injury may result in increased neuronal survival. However, the precise mechanism of T cell-induced neuroprotection is unknown. In this study, we report the unexpected finding that during culture of T cells, high levels of glutamate accumulate, which are efficiently cleared if T cells are cocultured with astrocytes. The T cell-derived glutamate elicits in turn, the release of neuroprotective thiols (cysteine, glutathione, and cysteinyl-glycine) and lactate from astrocytes. Media obtained from astrocytes conditioned in the presence of T cells reduce neuronal apoptosis induced by oxidative stress in primary neuronal cultures from 48 +/- 14 to 9 +/- 4% (p < 0.001). Inhibition of glutamate-dependent signaling during astrocyte-T cell cocultivation by a glutamate uptake inhibitor, l-aspartic acid beta-hydroxamate, abolishes this neuroprotective effect. The ability of astrocytes to clear extracellular glutamate is impaired under conditions of oxidative stress. We demonstrate that T cells, via secreted cytokines, restore glutamate clearance capacity of astrocytes under oxidative conditions. Furthermore, under normoxic conditions, glutamate-buffering capacity of astrocytes is increased upon cocultivation with T cells. It is known that, following CNS injury, astrocytes can respond with beneficial or destructive effects on neurons. However, the context and signaling mechanisms for this dual astrocytic response are unknown. Our results implicate T cells as potential determinants of the context that elicits a protective role for astrocytes in the damaged CNS.

Protection of respiratory chain enzymes from ischaemic damage in adult rat brain slices

The effect of aglycaemic hypoxia (AH) on the activity of the mitochondrial respiratory chain complexes was measured in superfused adult cortical brain slices. After 15 min of AH the activity of complex II-III was significantly reduced (by 45%) with no change in complex I or IV. Following 30 min of reperfusion the activities of complex II-III and IV were significantly reduced (by 45% and 20% respectively). These reductions in enzyme activity were abolished by removing the external calcium or by the addition of N omega-nitro-L-arginine (LNNA) or an analogue of superoxide dismutase (SOD) manganese [III] tetrakis 4-benzoic acid porphyrin (Mn-TBAP). These data suggest that a reactive oxygen species (ROS) such as peroxynitrite is involved in the reduction of mitochondrial complex activities following AH.