Elevation of glutathione as a therapeutic strategy in Alzheimer disease.

Oxidative stress has been associated with the onset and progression of mild cognitive impairment (MCI) and Alzheimer disease (AD). AD and MCI brain and plasma display extensive oxidative stress as indexed by protein oxidation, lipid peroxidation, free radical formation, DNA oxidation, and decreased antioxidants. The most abundant endogenous antioxidant, glutathione, plays a significant role in combating oxidative stress. The ratio of oxidized to reduced glutathione is utilized as a measure of intensity of oxidative stress. Antioxidants have long been considered as an approach to slow down AD progression. In this review, we focus on the elevation on glutathione through N-acetyl-cysteine (NAC) and γ-glutamylcysteine ethyl ester (GCEE) as a potential therapeutic approach for Alzheimer disease. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Protective effects of NIM811 in transient focal cerebral ischemia suggest involvement of the mitochondrial permeability transition.

Cerebral ischemia followed by reperfusion activates numerous pathways that lead to cell death. One such pathway involves the release of large quantities of the excitatory amino acid glutamate into the synapse and activation of N-methyl-D-aspartate receptors. This causes an increase in mitochondrial calcium levels ([Ca(2+)](m)) and a production of reactive oxygen species (ROS), both of which may induce the mitochondrial permeability transition (MPT). As a consequence, there is eventual mitochondrial failure culminating in either apoptotic or necrotic cell death. Thus, agents that inhibit MPT might prove useful as therapeutic interventions in cerebral ischemia. In this study, we have investigated the neuroprotective efficacy of the novel compound NIM811. Similar in structure of its parent compound cyclosporin A, NIM811 is a potent inhibitor of the MPT. Unlike cyclosporin A, however, it is essentially void of immunosuppressive actions, allowing the role of MPT to be clarified in ischemia/reperfusion injury. The results of these studies demonstrate that NIM811 provides almost 40% protection in a model of transient focal cerebral ischemia. This was associated with a nearly 10% reduction in mitochondrial reactive species formation and 34% and 38% reduction of cytochrome c release in core and penumbra, respectively. Treatment with NIM811 also increased calcium retention capacity by approximately 20%. Interestingly, NIM811 failed to improve ischemia-induced impairment of bioenergetics. The neuroprotective effects of NIM811 were not due to drug-induced alterations in cerebral perfusion after ischemia. Activation of MPT appears to be an important process in ischemia/reperfusion injury and may be a therapeutic target.

Oxidative stress and therapeutic approaches in HIV dementia.

Despite the rapidly increasing incidence of HIV infection worldwide and the increasing prevalence of HIVassociated cognitive impairment, even in patients adequately treated with antiretroviral therapy, currently no effective treatment exists for HIV dementia. A broad range of studies using either brain or cerebrospinal fluid (CSF) tissues from well-characterized patients with HIV dementia, animal models, and in vitro studies from several laboratories using HIV-infected cells or HIV proteins provide overwhelming evidence for oxidative stress in mediating neuronal injury in this patient population. These studies also suggest that patients with apolipoprotein E (ApoE) 4 allele are more susceptible to such oxidative damage. In this review, we provide a critical analysis of these studies, including the few clinical trials that have used antioxidants to treat HIV dementia. We also discuss several novel agents with potent antioxidative properties and provide a rationale for combination antioxidant and neuroprotective therapy.

HIV-dementia, Tat-induced oxidative stress, and antioxidant therapeutic considerations.

Oxidative stress is thought to play a role in the onset of dementia. HIV-dementia has recently been demonstrated to be associated with oxidative stress as indexed by increased protein and lipid peroxidation in the brain and cerebrospinal fluid compared to HIV non-demented patients. The HIV protein Tat induces neurotoxicity, and, more recently, Tat was found to induce oxidative stress directly and indirectly. The role of Tat in HIV-dementia and possible therapeutic strategies involving endogenous and exogenous antioxidants are discussed.

Proteomic analysis of oxidatively modified proteins induced by the mitochondrial toxin 3-nitropropionic acid in human astrocytes expressing the HIV protein tat.

The human immunodeficiency virus (HIV)-Tat protein has been implicated in the neuropathogenesis of HIV infection. However, its role in modulating astroglial function is poorly understood. Astrocyte infection with HIV has been associated with rapid progression of dementia. Intracellularly expressed Tat is not toxic to astrocytes. In fact, intracellularly expressed Tat offers protection against oxidative stress-related toxins such as the mitochondrial toxin 3-nitroproprionic acid (3-NP). In the current study, human astrocytes expressing Tat (SVGA-Tat) and vector controls (SVGA-pcDNA) were each treated with the irreversible mitochondrial complex II inhibitor 3-NP. Proteomics analysis was utilized to identify changes in protein expression levels. By coupling 2D fingerprinting and identification of proteins by mass spectrometry, actin, heat shock protein 90, and mitochondrial single-stranded DNA binding protein were identified as proteins with increased expression, while lactate dehydrogenase had decreased protein expression levels in SVGA-Tat cells treated with 3-NP compared to SVGA-pcDNA cells treated with 3-NP. Oxidative damage can lead to several events including loss in specific protein function, abnormal protein clearance, depletion of the cellular redox-balance and interference with the cell cycle, ultimately leading to neuronal death. Identification of specific proteins protected from oxidation is a crucial step in understanding the interaction of Tat with astrocytes. In the current study, proteomics also was used to identify proteins that were specifically oxidized in SVGA-pcDNA cells treated with 3-NP compared to SVGA-Tat cells treated with 3-NP. We found beta-actin, calreticulin precursor protein, and synovial sarcoma X breakpoint 5 isoform A to have increased oxidation in control SVGA-pcDNA cells treated with 3-NP compared to SVGA-Tat cells treated with 3-NP. These results are discussed with reference to potential involvement of these proteins in HIV dementia and protection of astrocytes against oxidative stress by the HIV virus, a prerequisite for survival of a viral host cell.

Proteomics analysis of human astrocytes expressing the HIV protein Tat.

Astrocyte infection in HIV has been associated with rapid progression of dementia in a subset of HIV/AIDS patients. Astrogliosis and microglial activation are observed in areas of axonal and dendritic damage in HIVD. In HIV-infected astrocytes, the regulatory gene tat is over expressed and mRNA levels for Tat are elevated in brain extracts from individuals with HIV-1 dementia. Tat can be detected in HIV-infected astrocytes in vivo. The HIV-1 protein Tat transactivates viral and cellular gene expression, is actively secreted mainly from astrocytes, microglia and macrophages, into the extracellular environment, and is taken up by neighboring uninfected cells such as neurons. The HIV-1 protein Tat released from astrocytes reportedly produces trimming of neurites, mitochondrial dysfunction and cell death in neurons, while protecting its host, the astrocyte. We utilized proteomics to investigate protein expression changes in human astrocytes intracellularly expressing Tat (SVGA-Tat). By coupling 2D fingerprinting and identification of proteins by mass spectrometry, we identified phosphatase 2A, isocitrate dehydrogenase, nuclear ribonucleoprotein A1, Rho GDP dissociation inhibitor alpha, beta-tubulin, crocalbin like protein/calumenin, and vimentin/alpha-tubulin to have decreased protein expression levels in SVGA-Tat cells compared to the SVGA-pcDNA cells. Heat shock protein 70, heme oxygenase-1, and inducible nitric oxide synthase were found to have increased protein expression in SVGA-Tat cells compared to controls by slotblot technique. These findings are discussed with reference to astrocytes serving as a reservoir for the HIV virus and how Tat promotes survival of the astrocytic host.

Effects of apolipoprotein E on the human immunodeficiency virus protein Tat in neuronal cultures and synaptosomes.

Human immunodeficiency virus type 1 (HIV-1)-associated dementia is observed in 20-30% of patients with acquired immunodeficiency syndrome (AIDS). The epsilon4 allele of the apolipoprotein E (APOE) gene currently is thought to play a role as a risk factor for the development of HIV dementia. The HIV protein Tat is neurotoxic and binds to the same receptor as apoE, the low-density lipoprotein receptor-related protein (LRP). In this study, we investigated the role apoE plays in Tat toxicity. Synaptosomes from wild-type mice treated with Tat had increased reactive oxygen species (ROS), increased lipid and protein oxidation, and decreased mitochondrial membrane potential. Synaptosomes from APOE-knockout mice also had increased ROS, increased protein oxidation, and decreased mitochondrial membrane potential, but to a significantly lesser degree. Treatment of synaptosomes with heparinase and Tat increased Tat-induced oxidative stress, consistent with the notion of Tat requiring interaction with neuronal membranes to induce oxidative damage. Human lipidated apoE3 greatly protected neurons from Tat-induced toxicity, whereas human lipidated apoE4 showed no protection. We demonstrated that human apoE3 has antioxidant properties against Tat-induced toxicity. Taken together, the data suggest that murine apoE and human apoE4 act similarly and do not protect the cell from Tat-induced toxicity. This would allow excess Tat to remain outside the cell and interact with synaptosomal membranes, leading to oxidative stress and neurotoxicity, which could contribute to dementia associated with HIV. We show that the antioxidant properties of apoE3 greatly outweigh the competition for clearance in deterring Tat-induced oxidative stress.

Striatal damage and oxidative stress induced by the mitochondrial toxin malonate are reduced in clorgyline-treated rats and MAO-A deficient mice.

Intrastriatal administration of the succinate dehydrogenase (SDH) inhibitor malonate produces neuronal injury by a "secondary excitotoxic" mechanism involving the generation of reactive oxygen species (ROS). Recent evidence indicates dopamine may contribute to malonate-induced striatal neurodegeneration; infusion of malonate causes a pronounced increase in extracellular dopamine and dopamine deafferentation attenuates malonate toxicity. Inhibition of the catabolic enzyme monoamine oxidase (MAO) also attenuates striatal lesions induced by malonate. In addition to forming 3,4-dihydroxyphenylacetic acid, metabolism of dopamine by MAO generates H2O2, suggesting that dopamine metabolism may be a source of ROS in malonate toxicity. There are two isoforms of MAO, MAO-A and MAO-B. In this study, we have investigated the role of each isozyme in malonate-induced striatal injury using both pharmacological and genetic approaches. In rats treated with either of the specific MAO-A or -B inhibitors, clorgyline or deprenyl, respectively, malonate lesion volumes were reduced by 30% compared to controls. In knock-out mice lacking the MAO-A isoform, malonate-induced lesions were reduced by 50% and protein carbonyls, an index ROS formation, were reduced by 11%, compared to wild-type animals. In contrast, mice deficient in MAO-B showed highly variable susceptibility to malonate toxicity precluding us from determining the precise role of MAO-B in this form of brain damage. These findings indicate that normal levels of MAO-A participate in expression of malonate toxicity by a mechanism involving oxidative stress.

The glutamatergic system and Alzheimer's disease: therapeutic implications.

Alzheimer's disease affects nearly 5 million Americans currently and, as a result of the baby boomer cohort, is predicted to affect 14 million Americans and 22 million persons totally worldwide in just a few decades. Alzheimer's disease is present in nearly half of individuals aged 85 years. The main symptom of Alzheimer's disease is a gradual loss of cognitive function. Glutamatergic neurotransmission, an important process in learning and memory, is severely disrupted in patients with Alzheimer's disease. Loss of glutamatergic function in Alzheimer's disease may be related to the increase in oxidative stress associated with the amyloid beta-peptide that is found in the brains of individuals who have the disease. Therefore, therapeutic strategies directed at the glutamatergic system may hold promise. Therapies addressing oxidative stress induced by hyperactivity of glutamate receptors include supplementation with estrogen and antioxidants such as tocopherol (vitamin E) and acetylcysteine (N-acetylcysteine). Therapy for hypoactivity of glutamate receptors is aimed at inducing the NMDA receptor with glycine and cycloserine (D-cycloserine). Recently, memantine, an NMDA receptor antagonist that addresses the hyperactivity of these receptors, has been approved in some countries for use in Alzheimer's disease.

Intracellular human immunodeficiency virus Tat expression in astrocytes promotes astrocyte survival but induces potent neurotoxicity at distant sites via axonal transport.

The human immunodeficiency virus (HIV)-Tat protein has been implicated in the neuropathogenesis of HIV infection. However, its role in modulating astroglial-neuronal relationships is poorly understood. Astrocyte infection with HIV has been associated with rapid progression of dementia. We thus initially transfected astrocytes with HIV proviral DNA and confirmed Tat production in these cells. Subsequently, using stably Tat-producing asytocyte cell lines, we observed that Tat promoted astrocyte survival by causing a prominent antioxidant effect and resistance to cell injury in these cells. Tat was released extracellularly where it could be taken up by other cells. Tat remained functionally active following uptake and caused long terminal repeat (LTR) transactivation in lymphocytic and astrocytic cell lines. Tat released from astrocytes caused mitochondrial dysfunction, trimming of neurites, and cell death in neurons. Tat neurotoxicity was attenuated by anti-Tat antibodies, kynurenate or heparan sulfate. The neurotoxic effects of Tat were caused at concentrations lower than that needed to cause LTR transactivation. When Tat-expressing cells were injected into the rat dentate gyrus, Tat was taken up by granule cells and transported along neuronal pathways to the CA3 region where it caused glial cell activation and neurotoxicity. The arginine-rich domain of Tat was essential for both the LTR transactivation and the neurotoxic properties of Tat. Thus HIV-Tat is a potent neurotoxin that may act at distant sites while at the same time it assures its production by preventing cell death in astrocytes where it is produced.

Acrolein inhibits NADH-linked mitochondrial enzyme activity: implications for Alzheimer's disease.

In Alzheimer's disease (AD) brain increased lipid peroxidation and decreased energy utilization are found. Mitochondria membranes contain a significant amount of arachidonic and linoleic acids, precursors of lipid peroxidation products, 4-hydroxynonenal (HNE) and 2-propen-1-al (acrolein), that are extremely reactive. Both alkenals are increased in AD brain. In this study, we examined the effects of nanomolar levels of acrolein on the activities of pyruvate dehydrogenase (PDH) and Alpha-ketoglutarate dehydrogenase (KGDH), both reduced nicotinamide adenine dinucleotide (NADH)-linked mitochondrial enzymes. Acrolein decreased PDH and KGDH activities significantly in a dose-dependent manner. Using high performance liquid chromatography coupled to mass spectrometry (HPLC-MS), acrolein was found to bind lipoic acid, a component in both the PDH and KGDH complexes, most likely explaining the loss of enzyme activity. Acrolein also interacted with oxidized nicotinamide adenine dinucleotide (NAD(+)) in such a way as to decrease the production of NADH. Acrolein, which is increased in AD brain, may be partially responsible for the dysfunction of mitochondria and loss of energy found in AD brain by inhibition of PDH and KGDH activities, potentially contributing to the neurodegeneration in this disorder.

Nutritional approaches to combat oxidative stress in Alzheimer's disease.

Alzheimer's disease (AD) brains are characterized by extensive oxidative stress. Additionally, large depositions of amyloid beta-peptide (Abeta) are observed, and many researchers opine that Abeta is central to the pathogenesis of AD. Our laboratory combined these two observations in a comprehensive model for neurodegeneration in AD brains centered around Abeta-induced oxidative stress. Given the oxidative stress in AD and its potentially important role in neurodegeneration, considerable research has been conducted on the use of antioxidants to slow or reverse the pathology and course of AD. One source of antioxidants is the diet. This review examines the literature of the effects of endogenous and exogenous, nutritionally-derived antioxidants in relation to AD. In particular, studies of glutathione and other SH-containing antioxidants, vitamins, and polyphenolic compounds and their use in AD and modulation of Abeta-induced oxidative stress and neurotoxicity are reviewed.