Glutamate neurotoxicity, oxidative stress and mitochondria

Role of glutamate transporters in redox homeostasis of the brain

Redox homeostasis is especially important in the brain where high oxygen consumption produces an abundance of harmful oxidative by-products. Glutathione (GSH) is a tripeptide non-protein thiol. It is the central nervous system's most abundant antioxidant and the master controller of brain redox homeostasis. The glutamate transporters, System xc(-) (SXC) and the Excitatory Amino Acid Transporters (EAAT), play important, synergistic roles in the synthesis of GSH. In glial cells, SXC mediates the uptake of cystine, which after intracellular reduction to cysteine, reacts with glutamate during the rate-limiting step of GSH synthesis. EAAT3 mediates direct cysteine uptake for neuronal GSH synthesis. SXC and EAAT work in concert in glial cells to provide two intracellular substrates for GSH synthesis, cystine and glutamate. Their cyclical basal function also prevents a buildup of extracellular glutamate, which SXC releases extracellularly in exchange for cystine uptake. Maintaining extracellular glutamate homeostasis is critical to prevent neuronal toxicity, as well as glutamate-mediated SXC inhibition, which could lead to a depletion of intracellular GSH and loss of cellular redox control. Many neurological diseases show evidence of GSH dysfunction, and increased GSH has been widely associated with chemotherapy and radiotherapy resistance of gliomas. We present evidence suggesting that gliomas expressing elevated levels of SXC are more reliant on GSH for growth and survival. They have an increased inherent radiation resistance, however, inhibition of SXC can increase tumor sensitivity at low radiation doses. GSH depletion through SXC inhibition may be a viable mechanism to enhance current glioma treatment strategies and make tumors more sensitive to radiation and chemotherapy protocols.

Anthocyanins protect against kainic acid-induced excitotoxicity and apoptosis via ROS-activated AMPK pathway in hippocampal neurons

INTRODUCTION

Excitotoxicity is an important mechanism involved in neurodegeneration. Kainic acid (KA)-induced excitotoxicity results an unfavorable stress, and we investigated the signaling pathways activated in such conditions.

AIMS

Here, we sought to determine the cellular and biochemical benefits of anthocyanins extracted from Korean black bean against KA-induced excitotoxicity and neuronal cell death.

METHODS AND RESULTS

Mouse hippocampal cell line (HT22) and primary prenatal rat hippocampal neurons were treated with KA to induce excitotoxicity. Incubation of the cells with KA alone significantly decreased cell viability, elevated intracellular Ca(2+) level, increased generation of reactive oxygen species (ROS) and loss of mitochondrial membrane potential (Δψ(M)). These events were accompanied by sustained phosphorylation and activation of AMP-activated protein kinase (AMPK). Kainic acid induced upregulation of Bax, decrease in Bcl-2, release of cytochrome-c, and activation of caspase-3 in both cell types. Anthocyanins attenuated KA-induced dysregulation of Ca(2+), ROS accumulation, activation of AMPK, and increase in percentage of apoptotic cells. Pretreatment of the cells with compound C, an inhibitor of AMPK, diminished the KA-induced activation of AMPK and caspase-3. The activation of AMPK through elevation of cellular ROS and Ca(2+) levels is required for KA-induced apoptosis in hippocampal neurons.

CONCLUSIONS

In summary, our data suggest that although anthocyanins have diverse activities, at least part of their beneficial effects against KA-induced hippocampal degeneration can be attributed to their well-recognized antioxidant properties.

Concentration-dependent opposite effects of 1-benzyl-1,2,3,4-tetrahydroisoquinoline on markers of apoptosis: in vitro and ex vivo studies

1-Benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ) was shown to be neurotoxic to the dopaminergic neurons, and thus it was proposed to be an endogenous risk factor leading to Parkinson’s disease. In order to better understand the molecular mechanisms of 1BnTIQ—produced toxicity, we examined the impact of different concentrations of 1BnTIQ (50, 100, and 500 μM) on glutamate-induced apoptotic pathway. We measured the markers of apoptosis, such as caspase-3 activity, lactate dehydrogenase release, and mitochondrial membrane potential. Molecular data were supported at the cellular level by calcein AM and Hoechst 33342 staining. The obtained data demonstrated concentration-dependent effects of 1BnTIQ opposing apoptosis, and evidenced that 1BnTIQ in a low concentration (50 μM) exhibited neuroprotective activity, whereas in 10 times higher concentration (500 μM) might be neurotoxic, and significantly intensified glutamate-induced increase in apoptosis markers. Additionally, using an ex vivo molecular study we indicated that both acute and chronic administration of 1BnTIQ did not affect the level of alpha synuclein and tyrosine hydroxylase protein in the rat substantia nigra. Summarizing the studies, we suggest that 1BnTIQ is a rather weak endogenous neurotoxin; however, it should be taken into account that in higher μmoles concentrations, it can initiate apoptosis in the central nervous system and may be involved in the etiopathology of neurodegenerative diseases.

Molecular mechanisms of retinal ganglion cell degeneration in glaucoma and future prospects for cell body and axonal protection

Glaucoma, which affects more than 70 million people worldwide, is a heterogeneous group of disorders with a resultant common denominator; optic neuropathy, eventually leading to irreversible blindness. The clinical manifestations of primary open-angle glaucoma (POAG), the most common subtype of glaucoma, include excavation of the optic disc and progressive loss of visual field. Axonal degeneration of retinal ganglion cells (RGCs) and apoptotic death of their cell bodies are observed in glaucoma, in which the reduction of intraocular pressure (IOP) is known to slow progression of the disease. A pattern of localized retinal nerve fiber layer (RNFL) defects in glaucoma patients indicates that axonal degeneration may precede RGC body death in this condition. The mechanisms of degeneration of neuronal cell bodies and their axons may differ. In this review, we addressed the molecular mechanisms of cell body death and axonal degeneration in glaucoma and proposed axonal protection in addition to cell body protection. The concept of axonal protection may become a new therapeutic strategy to prevent further axonal degeneration or revive dying axons in patients with preperimetric glaucoma. Further study will be needed to clarify whether the combination therapy of axonal protection and cell body protection will have greater protective effects in early or progressive glaucomatous optic neuropathy (GON).

Annatto prevents retinal degeneration induced by endoplasmic reticulum stress in vitro and in vivo

SCOPE

Annatto (Bixa orellana) seeds have been used as a colorant in butter and in a variety of other foods. In this study, we investigated the amelioration of retinal damage by an acetone extract of annatto (A-ext.), bixin (a main component of annatto), and four bixin derivatives (Bx-1, Bx-2, Bx-3, and Bx-4) that we have synthesized.

METHODS AND RESULTS

We used cultured retinal ganglion cells (RGC-5) to examine in vitro effects of A-ext. on stress pathways, focusing on intracellular oxidation induced by reactive oxygen species, expression of endoplasmic reticulum (ER) stress-related proteins, caspase-3 activation, and cell membrane damage. In vivo retinal damage in mice following intravitreous injection of tunicamycin was evaluated by counting the cell numbers in the ganglion cell layer (GCL) and measuring the thickness of outer nuclear layer (ONL). A-ext., bixin, and Bx-1 treatment inhibited both tunicamycin- and H₂O₂-induced cell death. Bixin derivatives also inhibited tunicamycin-induced cell death. Treatment with A-ext., bixin, and Bx-1 reduced tunicamycin-induced caspase-3 activity and inhibited the inversion of phosphatidylserine, an early apoptotic event without antioxidant effect or reduction of ER stress itself. A-ext., bixin, and Bx-1 significantly inhibited the tunicamycin-induced loss of cells from the GCL, and these materials also suppressed the tunicamycin-induced thinning of ONL.

CONCLUSION

A-ext., its main component bixin, and bixin derivatives may therefore be useful for preventive and therapeutic treatment of retinal-related diseases.

The role of non-synaptic extracellular glutamate

Although there are some mechanisms which allow the direct crossing of substances between the cytoplasm of adjacent cells (gap junctions), most substances use the extracellular space to diffuse between brain cells. The present work reviews the behavior and functions of extracellular glutamate (GLU). There are two extracellular pools of glutamate (GLU) in the brain, a synaptic pool whose functions in the excitatory neurotransmission has been widely studied and an extrasynaptic GLU pool although less known nonetheless is gaining attention among a growing number of researchers. Evidence accumulated over the last years shows a number of mechanisms capable of releasing glial GLU to the extracellular medium, thus modulating neurons, microglia and oligodendrocytes, and regulating the immune response, cerebral blood flow, neuronal synchronization and other brain functions. This new scenario is expanding present knowledge regarding the role of GLU in the brain under different physiological and pathological conditions. This article is part of a Special Issue entitled 'Extrasynaptic ionotropic receptors'.

Cannabinoids, multiple sclerosis and neuroprotection

The cannabinoid signaling system participates in the control of cell homeostasis in the CNS, which explains why, in different neurodegenerative diseases including multiple sclerosis (MS), alterations in this system have been found to serve both as a pathogenic factor (malfunctioning of this system has been found at early phases of these diseases) and as a therapeutic target (the management of this system has beneficial effects). MS is an autoimmune disease that affects the CNS and it is characterized by inflammation, demyelination, remyelination, gliosis and axonal damage. Although it has been considered mainly as an inflammatory disorder, recent studies have recognized the importance of axonal loss both in the progression of the disorder and in the appearance of neurological disability, even in early stages of the disease. In recent years, several laboratories have addressed the therapeutic potential of cannabinoids in MS, given the experience reported by some MS patients who self-medicated with marijuana. Most of these studies focused on the alleviation of symptoms (spasticity, tremor, anxiety and pain) or on the inflammatory component of the disease. However, recent data also revealed the important neuroprotective action that could be exerted by cannabinoids in this disorder. The present review will be precisely centered on this neuroprotective potential, which is based mainly on antioxidant, anti-inflammatory and anti-excitotoxic properties, exerted through the activation of CB1 or CB2 receptors or other unknown mechanisms.

Preparative isolation and purification of neuroprotective compounds from Rhus verniciflua by high speed counter-current chromatography

In the present study, extracts from Rhus verniciflua were demonstrated to significantly attenuate the negative effects of hydrogen peroxide (H(2)O(2)) on transformed retinal ganglion cell line (RGC-5 cells), indicating that they may be protective against oxidative stress-induced retinal degeneration. The inclusion of R. verniciflua in the culture was found to both reduce the levels of reactive oxygen species (ROS) present and lessen the up-regulation of apoptotic proteins such as cleaved poly(ADP-ribose) polymerase, cleaved caspase-3, and cleaved caspase-9. Active compounds were also successfully isolated from R. verniciflua using high-speed counter-current chromatography (HSCCC) with a two-phase solvent system composed of n-hexane-ethyl acetate-methanol-water (3.5:5:3.5:5, v/v). Using this method, we successfully separated 252.1 mg of fustin at a purity of over 93.09%, 51.2 mg of fisetin at a purity of over 95.45%, 39.7 mg of sulfuretin at a purity of over 95.17%, and 10.7 mg of butein at a purity of over 95.01% from 1.5 g of R. verniciflua extract. The chemical structures of these compounds were elucidated by chemical and spectral analyses. There isolated compounds also significantly attenuated the negative effects of H(2)O(2) on RGC-5 cells. Results therefore suggest that, due to its anti-oxidative and anti-apoptotic effects, R. verniciflua could be used as a lead substance for the treatment of retinal diseases such as glaucoma.

Neuroprotective effects of dehydroglyasperin C through activation of heme oxygenase-1 in mouse hippocampal cells

Licorice, the root of the Glycyrrhiza species ( Glycyrrhiza uralensis Fisher), is known to have antioxidant, anti-inflammatory, antiviral, and antitumor properties. The objective of this study is to explore the neuroprotective effect of dehydroglyasperin C (DGC) against glutamate-induced oxidative stress in mouse hippocampal HT22 cells. DGC significantly reduced cytotoxicity and reactive oxygen species (ROS) generation induced by glutamate in HT22 cells, whereas DGC did not restore glutathione depletion caused by glutamate. In addition, it was further investigated whether DGC affected the expression of heme oxygenase (HO)-1, one of the major cellular antioxidant defense systems, and it was found that DGC dose-dependently increased HO-1 expression. DGC-mediated cytoprotection of HT22 neuronal cells from glutamate insult was abrogated by either HO-1 inhibitor (Tin protoporphyrin, SnPP) or AKT inhibitor (LY294002). In conclusion, the present results demonstrate for the first time that DGC protects neuronal cells against glutamate-induced oxidative injury through the induction of HO-1 expression, which is, in turn, activated maybe through Nrf2-Keap1 and PI3K/AKT signaling pathways.

Paradox of schizophrenia genetics: is a paradigm shift occurring?

BACKGROUND

Genetic research of schizophrenia (SCZ) based on the nuclear genome model (NGM) has been one of the most active areas in psychiatry for the past two decades. Although this effort is ongoing, the current situation of the molecular genetics of SCZ seems disappointing or rather perplexing. Furthermore, a prominent discrepancy between persistence of the disease at a relatively high prevalence and a low reproductive fitness of patients creates a paradox. Heterozygote advantage works to sustain the frequency of a putative susceptibility gene in the mitochondrial genome model (MGM) but not in the NGM.

METHODS

We deduced a criterion that every nuclear susceptibility gene for SCZ should fulfill for the persistence of the disease under general assumptions of the multifactorial threshold model. SCZ-associated variants listed in the top 45 in the SZGene Database (the version of the 23rd December, 2011) were selected, and the distribution of the genes that could meet or do not meet the criterion was surveyed.

RESULTS

19 SCZ-associated variants that do not meet the criterion are located outside the regions where the SCZ-associated variants that could meet the criterion are located. Since a SCZ-associated variant that does not meet the criterion cannot be a susceptibility gene, but instead must be a protective gene, it should be linked to a susceptibility gene in the NGM, which is contrary to these results. On the other hand, every protective gene on any chromosome can be associated with SCZ in the MGM. Based on the MGM we propose a new hypothesis that assumes brain-specific antioxidant defenses in which trans-synaptic activations of dopamine- and N-methyl-d-aspartate-receptors are involved. Most of the ten predictions of this hypothesis seem to accord with the major epidemiological facts and the results of association studies to date.

CONCLUSION

The central paradox of SCZ genetics and the results of association studies to date argue against the NGM, and in its place the MGM is emerging as a viable option to account for genomic and pathophysiological research findings involving SCZ.

Asiatic acid, a pentacyclic triterpene in Centella asiatica, attenuates glutamate-induced cognitive deficits in mice and apoptosis in SH-SY5Y cells

AIM

To investigate whether asiatic acid (AA), a pentacyclic triterpene in Centella asiatica, exerted neuroprotective effects in vitro and in vivo, and to determine the underlying mechanisms.

METHODS

Human neuroblastoma SH-SY5Y cells were used for in vitro study. Cell viability was determined with the MTT assay. Hoechst 33342 staining and flow cytometry were used to examine the apoptosis. The mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) were measured using fluorescent dye. PGC-1α and Sirt1 levels were examined using Western blotting. Neonatal mice were given monosodium glutamate (2.5 mg/g) subcutaneously at the neck from postnatal day (PD) 7 to 13, and orally administered with AA on PD 14 daily for 30 d. The learning and memory of the mice were evaluated with the Morris water maze test. HE staining was used to analyze the pyramidal layer structure in the CA1 and CA3 regions.

RESULTS

Pretreatment of SH-SY5Y cells with AA (0.1-100 nmol/L) attenuated toxicity induced by 10 mmol/L glutamate in a concentration-dependent manner. AA 10 nmol/L significantly decreased apoptotic cell death and reduced reactive oxygen species (ROS), stabilized the mitochondrial membrane potential (MMP), and promoted the expression of PGC-1α and Sirt1. In the mice models, oral administration of AA (100 mg/kg) significantly attenuated cognitive deficits in the Morris water maze test, and restored lipid peroxidation and glutathione and the activity of SOD in the hippocampus and cortex to the control levels. AA (50 and 100 mg/kg) also attenuated neuronal damage of the pyramidal layer in the CA1 and CA3 regions.

CONCLUSION

AA attenuates glutamate-induced cognitive deficits of mice and protects SH-SY5Y cells against glutamate-induced apoptosis in vitro.

Redox balance- and radiation-mediated alteration in hippocampal neurogenesis

Changes in the intracellular and extracellular redox balance have been correlated with cell fate decisions in terms of proliferation versus differentiation, entering versus existing cell cycle and survival versus cell death. Adult hippocampal neurogenesis has been correlated with neuronal plasticity of learning and memory; however, the process is exquisitely sensitive to changes in redox balance. Cranial irradiation is an effective modality in treating brain tumours but often leads to deficits in hippocampus-related learning and memory, which is most likely due to sustained elevation of oxygen free radical production and suppression of hippocampal neurogenesis. The subcellular redox environment affecting hippocampal neurogenesis is largely unknown. Using mutant mice deficient in each one of the three superoxide dismutase (SOD, EC 1.15.1.1) isoforms, we have begun to determine the consequences of SOD deficiency in hippocampal neurogenesis and the related functions of learning and memory under normal condition and following cranial irradiation.

Oxidative stress and adult neurogenesis--effects of radiation and superoxide dismutase deficiency

Hippocampus plays an important role in learning and memory and in spatial navigation. Production of new neurons that are functionally integrated into the hippocampal neuronal network is important for the maintenance of functional plasticity. In adults, production of new neurons in the hippocampus takes place in the subgranular zone (SGZ) of dentate gyrus. Neural progenitor/stem cells go through processes of proliferation, differentiation, migration, and maturation. This process is exquisitely sensitive to oxidative stress, and perturbation in the redox balance in the neurogenic microenvironment can lead to reduced neurogenesis. Cranial irradiation is an effective treatment for primary and secondary brain tumors. However, even low doses of irradiation can lead to persistent elevation of oxidative stress and sustained suppression of hippocampal neurogenesis. Superoxide dismutases (SODs) are major antioxidant enzymes for the removal of superoxide radicals in different subcellular compartments. To identify the subcellular location where reactive oxygen species (ROS) are continuously generated after cranial irradiation, different SOD deficient mice have been used to determine the effects of irradiation on hippocampal neurogenesis. The study results suggest that, regardless of the subcellular location, SOD deficiency leads to a significant reduction in the production of new neurons in the SGZ of hippocampal dentate gyrus. In exchange, the generation of new glial cells was significantly increased. The SOD deficient condition, however, altered the tissue response to irradiation, and SOD deficient mice were able to maintain a similar level of neurogenesis after irradiation while wild type mice showed a significant reduction in the production of new neurons.

The Neuroprotective Effect of Picroside II from Hu-Huang-Lian against Oxidative Stress

Picroside II is an active constituent extracted from the traditional Chinese medicine (TCM) Hu-Huang-Lian. To evaluate the neuroprotective effect of picroside II, PC12 cells were treated with glutamate in vitro and male ICR mice were treated with AlCl 3in vivo. Pre-treatment of PC12 cells with picroside II could enhance the cell viability and decrease the level of intracellular reactive oxygen species (ROS) induced by glutamate. By DNA fragmentation and flow cytometry assay, picroside II (1.2 mg/ml) significantly prevented glutamate-induced cell apoptosis. In the animal study, amnesia was induced in mice by AlCl 3 (100 mg/kg/d, i.v.). Pricroside II, at the dose of 20 and 40 mg/kg/d (i.g.), markedly ameliorated AlCl 3-induced learning and memory dysfunctions and attenuated AlCl 3-induced histological changes. This was associated with the significant increased superoxide dismutase (SOD) activity in the brain of experimental mice. All these results indicated that picroside II possessed the therapeutic potential in protecting against neurological injuries damaged by oxidative stress.

Effects of antioxidant gene therapy on retinal neurons and oxidative stress in a model of retinal ischemia/reperfusion

Retinal ischemia/reperfusion (I/R) results in neuronal death and generation of reactive oxygen species. The aim of this study was to investigate the neuroprotective effect of manganese superoxide dismutase (SOD2) on retinal ganglion cells (RGCs) in an I/R-induced retinal injury model. One eye of each Wistar rat was pretreated with recombinant adeno-associated virus containing the SOD2 gene (AAV-SOD2) or recombinant AAV containing the GFP gene (AAV-GFP) by intravitreal injection 21 days before initiation of I/R injury. Retinal I/R injury was induced by elevating intraocular pressure for 1h, and reperfusion was established immediately afterward. The number of RGCs and the inner plexiform layer (IPL) thickness were measured by Fluorogold retrograde labeling and hematoxylin and eosin staining at 6 h, 24 h, 72 h, and 5 days after injury. Superoxide anion, the number of RGCs, IPL thickness, malondialdehyde (MDA) level, 8-hydroxy-2-deoxyguanosine (8-OHdG) level, MnSOD (manganese superoxide dismutase) activity, and nitrotyrosine level were measured by fluorescence staining, immunohistochemistry, and enzyme-linked immunosorbent analysis at 5 days after I/R injury. Severe RGC loss, reduced IPL thickness, reduced MnSOD activity, and increased superoxide ion, MDA, 8-OHdG, and nitrotyrosine production were observed after I/R injury. Administration of AAV-SOD2 significantly reduced the levels of superoxide ion, MDA, 8-OHdG, and nitrotyrosine and prevented the damage to RGCs and IPL. Delivery of the antioxidant gene inhibited I/R-induced RGC and IPL damage by reducing oxidative stress and nitrative stress, suggesting that MnSOD may be relevant for the neuroprotection of the inner retina from I/R-related diseases.

Alzheimer's disease: pathological mechanisms and the beneficial role of melatonin

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD.

New drug targets in depression: inflammatory, cell-mediated immune, oxidative and nitrosative stress, mitochondrial, antioxidant, and neuroprogressive pathways. And new drug candidates--Nrf2 activators and GSK-3 inhibitors

This paper reviews new drug targets in the treatment of depression and new drug candidates to treat depression. Depression is characterized by aberrations in six intertwined pathways: (1) inflammatory pathways as indicated by increased levels of proinflammatory cytokines, e.g. interleukin-1 (IL-1), IL-6, and tumour necrosis factor α. (2) Activation of cell-mediated immune pathways as indicated by an increased production of interferon γ and neopterin. (3) Increased reactive oxygen and nitrogen species and damage by oxidative and nitrosative stress (O&NS), including lipid peroxidation, damage to DNA, proteins and mitochondria. (4) Lowered levels of key antioxidants, such as coenzyme Q10, zinc, vitamin E, glutathione, and glutathione peroxidase. (5) Damage to mitochondria and mitochondrial DNA and reduced activity of respiratory chain enzymes and adenosine triphosphate production. (6) Neuroprogression, which is the progressive process of neurodegeneration, apoptosis, and reduced neurogenesis and neuronal plasticity, phenomena that are probably caused by inflammation and O&NS. Antidepressants tend to normalize the above six pathways. Targeting these pathways has the potential to yield antidepressant effects, e.g. using cytokine antagonists, minocycline, Cox-2 inhibitors, statins, acetylsalicylic acid, ketamine, ω3 poly-unsaturated fatty acids, antioxidants, and neurotrophic factors. These six pathways offer new, pathophysiologically guided drug targets suggesting that novel therapies could be developed that target these six pathways simultaneously. Both nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activators and glycogen synthase kinase-3 (GSK-3) inhibitors target the six above-mentioned pathways. GSK-3 inhibitors have antidepressant effects in animal models of depression. Nrf2 activators and GSK-3 inhibitors have the potential to be advanced to phase-2 clinical trials to examine whether they augment the efficacy of antidepressants or are useful as monotherapy.

Down-regulation of Homer1b/c attenuates glutamate-mediated excitotoxicity through endoplasmic reticulum and mitochondria pathways in rat cortical neurons

Glutamate-mediated excitotoxicity is involved in many acute and chronic brain diseases. Homer proteins, a new member of the postsynaptic scaffolding proteins, regulate glutamatergic signaling and intracellular calcium mobilization in the central nervous system. Here we investigated the effects of down-regulating Homer1b/c, a constitutively expressed long form of Homer proteins, on glutamate excitotoxicity-induced neuronal injury. In our in vitro excitotoxic models, we demonstrated that glutamate insults led to a dose-dependent neuronal injury, which was mediated by the intracellular calcium-dependent reactive oxygen species (ROS) production. We found that down-regulation of Homer1b/c with specific small interfering RNA (siRNA) improved neuronal survival, inhibited intracellular ROS production, and reduced apoptotic cell death after neurotoxicity. Homer1b/c knockdown decreased the intracellular calcium overload through inhibition of the group I metabotropic glutamate receptor (mGluR)/inositol 1,4,5-trisphosphate receptor (IP3R)-mediated Ca2+ release from the endoplasmic reticulum (ER) in injured neurons. In addition, Homer1b/c siRNA transfection attenuated the activation of eukaryotic initiation factor 2α (eIF2α), RNA-dependent protein kinase-like ER kinase (PERK) and caspase-12, and inhibited the up-regulation of glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP) after glutamate treatment. Homer1b/c knockdown also preserved the mitochondrial membrane potential (MMP), reduced cytochrome c (Cyt. c) release, and partly blocked the increase of capase-9 activity and Bax/Bcl-2 ratio. Taken together, these results suggest that down-regulation of Homer1b/c protects cortical neurons against glutamate-induced excitatory damage, and this neuroprotection may be dependent at least in part on the inhibition of calcium-dependent ROS production and the preservation of the ER and mitochondrial function.

Hydroalcoholic extract of Emblica officinalis protects against kainic acid-induced status epilepticus in rats: evidence for an antioxidant, anti-inflammatory, and neuroprotective intervention

CONTEXT

Emblica officinalis (Euphorbiaceae), commonly known as amla, is traditionally used for central nervous system (CNS) disorders.

OBJECTIVE

In the present study, the effect of standardized hydroalcoholic extract of E. officinalis fruit (HAEEO), an Indian medicinal plant with potent antioxidant activity, was studied against kainic acid (KA)-induced seizures, cognitive deficits and on markers of oxidative stress.

MATERIALS AND METHODS

Rats were administered KA (10 mg/kg, i.p.) and observed for behavioral changes, incidence, and latency of convulsions over 4 h. The rats were thereafter sacrificed for estimation of oxidative stress parameters: thiobarbituric acid-reactive substances (TBARS) and glutathione (GSH). The proinflammatory cytokine tumor necrosis factor alpha (TNF-α) was also determined in the rat brain.

RESULTS

Pretreatment with HAEEO (500 and 700 mg/kg, i.p.) significantly (P < 0.001) increased the latency of seizures as compared with the vehicle-treated KA group. HAEEO significantly prevented the increase in TBARS levels and ameliorated the fall in GSH. Furthermore, HAEEO dose-dependently attenuated the KA-induced increase in the TNF-α level in the brain. HAEEO also significantly improved the cognitive deficit induced by KA, as evidenced by increased latency in passive avoidance task.

DISCUSSION AND CONCLUSION

HAEEO at the dose of 700 mg/kg, i.p., was most effective in suppressing KA-induced seizures, cognitive decline, and oxidative stress in the brain. These neuroprotective effects may be due to the antioxidant and anti-inflammatory effects of HAEEO.

Handedness correlates with the dominant Parkinson side: a systematic review and meta-analysis

Parkinson's disease (PD) characteristically presents with asymmetrical symptoms, contralateral to the side of the most extensive cerebral affection. This intriguing asymmetry, even included in the definition for diagnosing PD, however, is still part of a mystery. The relation with handedness as a common indicator of cerebral asymmetry might provide a clue in the search for causal factors of asymmetrical symptom onset in PD. This possible relationship, however, is still under debate. The objective of this study was to establish whether a relation between handedness and dominant PD side exists. We searched for cross-sectional or cohort studies that registered handedness and onset side in PD patients in PubMed, EMBASE, and Web of Science from their first record until 14 February 2011. Data about handedness and dominant PD side was extracted. Authors who registered both but not described their relation were contacted for further information. Odds ratios (ORs) were analyzed with a fixed effect Mantel-Haenszel model. Heterogeneity and indications of publication bias were limited. Our electronic search identified 10 studies involving 4405 asymmetric PD patients. Of the right-handed patients, 2413 (59.5%) had right-dominant and 1644 (40.5%) had left-dominant PD symptoms. For the left-handed patients this relation was reversed, with 142 (40.8%) right-dominant and 206 (59.2%) left-dominant PD symptoms. Overall OR was 2.13 (95% confidence interval [CI], 1.71-2.66). Handedness and symptom dominance in PD are firmly related with each other in such a way that the PD symptoms emerge more often on the dominant hand-side. Possible causal factors are discussed.

Stress signaling from the endoplasmic reticulum: A central player in the pathogenesis of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by the misfolding and aggregation of distinct proteins in affected tissues, however, the pathogenic cause of disease remains unknown. Recent evidence indicates that endoplasmic reticulum (ER) stress plays a central role in ALS pathogenesis. ER stress activates the unfolded protein response (UPR), a homeostatic response to misfolded proteins. The UPR is initially protective by up-regulation of specific ER stress-regulated genes and inhibition of general protein translation. However, long-term ER stress leads to cell death via apoptotic signaling, thus providing a link to neurodegeneration. Activation of the UPR is one of the earliest events in affected motor neurons of transgenic rodent models expressing ALS-linked mutant superoxide dismutase 1 (SOD1). Recently, genetic manipulation of ER stress in several different SOD1 mouse models was shown to alter disease onset and progression, implicating an active role for the UPR in disease mechanisms. Furthermore, mutations to vesicle-associated membrane protein-associated protein B (VAPB), an ER transmembrane protein involved in ER stress regulation, also cause some cases of familial ALS. ER stress also occurs in spinal cord tissues of human sporadic ALS patients, and recent evidence suggests that perturbation of the ER could occur in ALS cases associated with TAR DNA binding protein 43 (TDP-43), fused in sarcoma (FUS) and valosin containing protein (VCP). Together these findings implicate ER stress as a potential upstream mechanism involved in both familial and sporadic forms of ALS.

Protective effects of catalase on retinal ischemia/reperfusion injury in rats

Retinal ischemia/reperfusion (I/R) injury causes profound tissue damage, especially retinal ganglion cell (RGC) death. The aims of the study were to investigate whether catalase (CAT) has a neuroprotective effect on RGC after I/R injury in rats, and to determine the possible antioxidant mechanism. Wistar female rats were randonmized into four groups: normal control group (Control group), retinal I/R with vehicle group (I/R with vehicle group), retinal I/R with AAV-CAT group (I/R with AAV-CAT group), and normal retina with AAV-CAT group (normal with AAV-CAT group). One eye of each rat was pretreated with recombinant adeno-associated virus containing catalase gene (I/R with AAV-CAT group or normal with AAV-CAT group) and recombinant adeno-associated virus containing GFP gene (I/R with vehicle group) by intravitreal injection 21 days before initiation of I/R injury. Retinal I/R injury was induced by elevating intraocular pressure to 100mmHg for 1h. The number of RGC and inner plexiform layer (IPL) thickness were measured by fluorogold retrograde labeling and hematoxylin and eosin staining at 6h, 24h, 72 h and 5d after injury. Hydrogen peroxide (H(2)O(2)), the number of RGC, IPL thickness, malondialdehyde(MDA), 8-hydroxy-2-deoxyguanosine (8-OHdG), CAT activity and nitrotyrosine were measured by fluorescence staining, immunohistochemistry and enzyme-linked immunosorbent assay analysis at 5 days after injury. Electroretinographic (ERG) evaluation was also used. Pretreatment of AAV-CAT significantly decreased the levels of H(2)O(2), MDA, 8-OHdG and nitrotyrosine, increased the catalase activity, and prevented the reduction of a- and b- waves in the I/R with AAV-CAT group compare with the I/R with vehicle group (p<0.01). Catalase attenuated the I/R-induced damage of RGC and IPL and retinal function. Therefore, catalase can protect the rat retina from I/R-induced injury by enhancing the antioxidative ability and reducing oxidative stress, which suggests that catalase may be relevant for the neuroprotection of inner retina from I/R-related diseases.

Bax and calpain mediate excitotoxic oligodendrocyte death induced by activation of both AMPA and kainate receptors

Sustained activation of AMPA and kainate receptors in rat oligodendrocytes induces cytosolic calcium overload, mitochondrial depolarization, and an increase of reactive oxygen species, resulting in cell death. Here, we provide evidence that Bax, a proapoptotic member of the Bcl-2 protein family, is involved in excitotoxic apoptotic death of oligodendrocytes and that calpain mediates Bax activation. Cultured Bax(-/-) oligodendrocytes, obtained from the optic nerve of Bax knock-out mice, were resistant to AMPA and kainate receptor-mediated insults. In turn, both mitochondrial calcium uptake and mitochondrial alterations after excitotoxic insults were diminished in Bax-null oligodendrocytes. Moreover, pretreatment with furosemide, a blocker of Bax translocation to mitochondria, significantly protected rat and mouse oligodendrocytes from AMPA- and kainate-induced damage; in contrast, bongkrekic acid, a blocker of the mitochondrial permeability transition pore, had no effect. Finally, we analyzed the participation of calpain, which cleaves Bax and is activated by AMPA and kainate, in oligodendrocyte death. Pretreatment with 3-(4-iodophenyl)-2-mercapto-(Z)-2-propenoic acid (PD150606), a broad cell-permeable calpain inhibitor, and two additional calpain inhibitors diminished Bax activation, inhibited its translocation to mitochondria, and attenuated all apoptotic events resulting from excitotoxic insults to rat oligodendrocytes. Together, these results indicate that Bax and calpain are essential intermediaries of the mitochondria-dependent death pathway, triggered by AMPA and kainate receptor activation in oligodendrocytes.

Early disruption of the actin cytoskeleton in cultured cerebellar granule neurons exposed to 3-morpholinosydnonimine-oxidative stress is linked to alterations of the cytosolic calcium concentration

Cytoskeleton damage is a frequent feature in neuronal cell death and one of the early events in oxidant-induced cell injury. This work addresses whether actin cytoskeleton reorganization is an early event of SIN-1-induced extracellular nitrosative/oxidative stress in cultured cerebellar granule neurons (CGN). The actin polymerization state, i.e. the relative levels of G-/F-actin, was quantitatively assessed by the ratio of the fluorescence intensities of microscopy images obtained from CGN double-labelled with Alexa594-DNase-I (for actin monomers) and Bodipy-FL-phallacidin (for actin filaments). Exposure of CGN to a flux of peroxynitrite as low as 0.5-1μM/min during 30min (achieved with 0.1mM SIN-1) was found to promote alterations of the actin cytoskeleton dynamics as it increases the G-actin/F-actin ratio. Because L-type voltage-operated Ca(2+) channels (L-VOCC) are primary targets in CGN exposed to SIN-1, the possible role of Ca(2+) dynamics on the perturbation of the actin cytoskeleton was also assessed from the cytosolic Ca(2+) concentration response to the L-VOCC's agonist FPL-64176 and to the L-VOCC's blocker nifedipine. The results showed that SIN-1 induced changes in the actin polymerization state correlated with its ability to decrease Ca(2+) influx through L-VOCC. Combined analysis of cytosolic Ca(2+) concentration and G-actin/F-actin ratio alterations by SIN-1, cytochalasin D, latrunculin B and jasplakinolide support that disruption of the actin cytoskeleton is linked to cytosolic calcium concentration changes.

Iron handling in hippocampal neurons: activity-dependent iron entry and mitochondria-mediated neurotoxicity

The characterization of iron handling in neurons is still lacking, with contradictory and incomplete results. In particular, the relevance of non-transferrin-bound iron (NTBI), under physiologic conditions, during aging and in neurodegenerative disorders, is undetermined. This study investigates the mechanisms underlying NTBI entry into primary hippocampal neurons and evaluates the consequence of iron elevation on neuronal viability. Fluorescence-based single cell analysis revealed that an increase in extracellular free Fe(2+) (the main component of NTBI pool) is sufficient to promote Fe(2+) entry and that activation of either N-methyl-d-aspartate receptors (NMDARs) or voltage operated calcium channels (VOCCs) significantly potentiates this pathway, independently of changes in intracellular Ca(2+) concentration ([Ca(2+) ](i) ). The enhancement of Fe(2+) influx was accompanied by a corresponding elevation of reactive oxygen species (ROS) production and higher susceptibility of neurons to death. Interestingly, iron vulnerability increased in aged cultures. Scavenging of mitochondrial ROS was the most powerful protective treatment against iron overload, being able to preserve the mitochondrial membrane potential and to safeguard the morphologic integrity of these organelles. Overall, we demonstrate for the first time that Fe(2+) and Ca(2+) compete for common routes (i.e. NMDARs and different types of VOCCs) to enter primary neurons. These iron entry pathways are not controlled by the intracellular iron level and can be harmful for neurons during aging and in conditions of elevated NTBI levels. Finally, our data draw the attention to mitochondria as a potential target for the treatment of the neurodegenerative processes induced by iron dysmetabolism.

Plasma selenium is positively related to performance in neurological tasks assessing coordination and motor speed

Parkinson's disease (PD) is a degenerative process affecting the striato nigral system (SN). Its etiology, although obscure, may involve oxidative damage. Selenium, an antioxidant, was shown to protect the SN in animal models. In the current study, we investigate the association between plasma selenium concentrations and the presence of "soft" neurological signs related to the SN. Plasma selenium concentration was assessed in participants of age ≥65 years in the InCHIANTI study, a population-based cohort study in Tuscany, Italy. PD was defined based on standard criteria. "Soft" neurological signs were ascertained by physical examination. A total of 1,012 participants were included. No association was found between the presence of PD and plasma selenium. There was, however, a strong association between plasma selenium and timed performance-based assessments. Lower levels of selenium were significantly associated withdecreased performance in neurological tests of coordination among older adults. Prospective studies are needed to further investigate the effects of selenium on SN dysfunction.

SUN N8075, a novel radical scavenger, protects against retinal cell death in mice

In this study, we examined the effect of SUN N8075, a radical scavenger with neuroprotective properties, on murine retinal damage induced by intravitreous injection of N-methyl-d-aspartate (NMDA) or high-intraocular pressure (IOP). In both models, systemic administration of SUN N8075 decreased the cell loss in the ganglion cell layer (GCL) after retinal damage occurred. Moreover, SUN N8075 reduced the number of apoptotic cells and the expression of an oxidative stress marker in GCL in the NMDA model. These findings suggest that SUN N8075 has a neuroprotective effect against retinal damage, presumably via the radical scavenging effect.

AT₁ receptor and NAD(P)H oxidase mediate angiotensin II-stimulated antioxidant enzymes and mitogen-activated protein kinase activity in the rat hypothalamus

INTRODUCTION

Angiotensin II (AngII) regulates blood pressure and water and electrolyte metabolism through the stimulation of NAD(P)H oxidase and production of reactive oxygen species (ROS) such as O₂⁻, which is metabolised by superoxide dismutase, catalase and glutathione peroxidase. We assessed the role of AT₁ and AT₂ receptors, NAD(P)H oxidase and protein kinase C (PKC) in Ang II-induced sodium and water excretion and their capacity to stimulate antioxidant enzymes in the rat hypothalamus, a brain structure known to express a high density of AngII receptors.

MATERIALS AND METHODS

Male Sprague-Dawley rats were intracerebroventricularly (ICV) injected with AngII and urinary sodium and water excretion was assessed. Urine sodium concentration was determined using flame photometry. After decapitation the hypothalamus was microdissected under stereomicroscopic control. Superoxide dismutase, catalase and glutathione peroxidase activity were determined spectrophotometrically and extracellular signal-regulated kinase (ERK1/2) activation was analysed by Western blot.

RESULTS

AngII-ICV resulted in antidiuresis and natriuresis. ICV administration of losartan, PD123319, apocynin and chelerythrine blunted natriuresis. In hypothalamus, AngII increased catalase, superoxide dismutase and glutation peroxidase activity and ERK1/2 phosphorylation. These actions were prevented by losartan, apocynin and chelerythrine, and increased by PD123319.

CONCLUSIONS

AT₁ and AT₂ receptors, NAD(P)H oxidase and PKC pathway are involved in the regulation of hydromineral metabolism and antioxidant enzyme activity induced by AngII.

Effects of the AMPA antagonist ZK 200775 on visual function: a randomized controlled trial

BACKGROUND

ZK 200775 is an antagonist at the alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor and had earned attention as a possible neuroprotective agent in cerebral ischemia. Probands receiving the agent within phase I trials reported on an alteration of visual perception. In this trial, the effects of ZK 200775 on the visual system were analyzed in detail.

METHODOLOGY

In a randomised controlled trial we examined eyes and vision before and after the intravenous administration of two different doses of ZK 200775 and placebo. There were 3 groups of 6 probands each: Group 1 recieved 0.03 mg/kg/h, group 2 0.75 mg/kg/h of ZK 200775, the control group received 0.9% sodium chloride solution. Probands were healthy males aged between 57 and 69 years. The following methods were applied: clinical examination, visual acuity, ophthalmoscopy, colour vision, rod absolute threshold, central visual field, pattern-reversal visual evoked potentials (pVEP), ON-OFF and full-field electroretinogram (ERG).

PRINCIPAL FINDINGS

No effect of ZK 200775 was seen on eye position or motility, stereopsis, pupillary function or central visual field testing. Visual acuity and dark vision deteriorated significantly in both treated groups. Color vision was most remarkably impaired. The dark-adapted ERG revealed a reduction of oscillatory potentials (OP) and partly of the a- and b-wave, furthermore an alteration of b-wave morphology and an insignificantly elevated b/a-ratio. Cone-ERG modalities showed decreased amplitudes and delayed implicit times. In the ON-OFF ERG the ON-answer amplitudes increased whereas the peak times of the OFF-answer were reduced. The pattern VEP exhibited lower amplitudes and prolonged peak times.

CONCLUSIONS

The AMPA receptor blockade led to a strong impairment of typical OFF-pathway functions like color vision and the cone ERG. On the other hand the ON-pathway as measured by dark vision and the scotopic ERG was affected as well. This further elucidates the interdependence of both pathways.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00999284.

Quantitative changes in the mitochondrial proteome from subjects with mild cognitive impairment, early stage, and late stage Alzheimer's disease

The major barrier to treating or preventing Alzheimer's disease (AD) is its unknown etiology and pathogenesis. Although increasing evidence supports a role for mitochondrial dysfunction in the pathogenesis of AD, there have been few studies that simultaneously evaluate changes in multiple mitochondrial proteins. To evaluate changes in sites of potentially interacting mitochondrial proteins, we applied 2-dimensional liquid chromatography coupled with tandem mass spectrometry and the isotope coded affinity tag method to identify and quantify proteins in mitochondrial enriched fractions isolated from short postmortem interval temporal pole specimens from subjects with mild cognitive impairment (4 subjects pooled), early AD (4 subjects pooled), late-stage AD (8 subjects pooled) and age-matched normal control (7 subjects pooled) subjects. A total of 112 unique, non-redundant proteins were identified and quantified in common to all three stages of disease progression. Overall, patterns of protein change suggest activation of mitochondrial pathways that include proteins responsible for transport and utilization of ATP. These proteins include adenine nucleotide translocase, voltage dependent anion channels, hexokinase, and creatine kinase. Comparison of protein changes throughout the progression of AD suggests the most pronounced changes occur in early AD mitochondria.

Enzymatic-nonenzymatic cellular antioxidant defense systems response and immunohistochemical detection of MDMA, VMAT2, HSP70, and apoptosis as biomarkers for MDMA (Ecstasy) neurotoxicity

3,4-Methylenedioxymethamphetamine (MDMA)-induced neurotoxicity leads to the formation of quinone metabolities and hydroxyl radicals and then to the production of reactive oxygen species (ROS). We evaluated the effect of a single dose of MDMA (20 mg/kg, i.p.) on the enzymatic and nonenzymatic cellular antioxidant defense system in different areas of rat brain in the early hours (<6 hr) of the administration itself, and we identified the morphological expressions of neurotoxicity induced by MDMA on the vulnerable brain areas in the first 24 hr. The acute administration of MDMA produces a decrease of reduced and oxidized glutathione ratio, and antioxidant enzyme activities were significantly reduced after 3 hr and after 6 hr in frontal cortex. Ascorbic acid levels strongly increased in striatum, hippocampus, and frontal cortex after 3 and 6 hr. High levels of malonaldehyde with respect to control were measured in striatum after 3 and 6 hr and in hippocampus and frontal cortex after 6 hr. An immunohistochemical investigation on the frontal, thalamic, hypothalamic, and striatal areas was performed. A strong positive reaction to the antivesicular monoamine transporter 2 was observed in the frontal section, in the basal ganglia and thalamus. Cortical positivity, located in the most superficial layer was revealed only for heat shock protein 70 after 24 hr.

Limonoids from Dictamnus dasycarpus protect against glutamate-induced toxicity in primary cultured rat cortical cells

In our previous report, four limonoids, obacunone, limonin, fraxinellone, and calodendrolide, isolated from Dictamnus dasycarpus showed significant neuroprotective activity against glutamate toxicity in primary cultured rat cortical cells. This study investigated neuroprotective mechanism of these compounds using the same in vitro culture system. These four compounds showed significant neuroprotective activity at the concentration of 0.1 muM. They effectively inhibited calcium influx and overproduction of cellular nitric oxide and reactive oxygen species accompanied by glutamate-induced neurotoxicity. In addition, these compounds significantly preserved mitochondrial membrane potential and activities of antioxidative enzymes. Our results showed that obacunone, limonin, fraxinellone, and calodendrolide significantly protect primary culture cortical cells against glutamate-induced toxicity by preserving the antioxidant defense system. These compounds might offer potential drug development candidate for various neurodegenerative diseases involved with glutamate.

Amyloid beta oligomers induce Ca2+ dysregulation and neuronal death through activation of ionotropic glutamate receptors

Amyloid beta (Abeta) oligomers accumulate in brain tissue of Alzheimer disease patients and are related to pathogenesis. The precise mechanisms by which Abeta oligomers cause neurotoxicity remain unresolved. In this study, we investigated the role of ionotropic glutamate receptors on the intracellular Ca2+ overload caused by Abeta. Using rat cortical neurons in culture and entorhinal-hippocampal organotypic slices, we found that Abeta oligomers significantly induced inward currents, intracellular Ca2+ increases and apoptotic cell death through a mechanism requiring NMDA and AMPA receptor activation. The massive entry of Ca2+ through NMDA and AMPA receptors induced by Abeta oligomers caused mitochondrial dysfunction as indicated by mitochondrial Ca2+ overload, oxidative stress and mitochondrial membrane depolarization. Importantly, chronic treatment with nanomolar concentration of Abeta oligomers also induced NMDA- and AMPA receptor-dependent cell death in entorhinal cortex and hippocampal slice cultures. Together, these results indicate that overactivation of NMDA and AMPA receptor, mitochondrial Ca2+ overload and mitochondrial damage underlie the neurotoxicity induced by Abeta oligomers. Hence, drugs that modulate these events can prevent from Abeta damage to neurons in Alzheimer's disease.

Gain-of-function variant in GLUD2 glutamate dehydrogenase modifies Parkinson's disease onset

Parkinson's disease (PD), a common neurodegenerative disorder characterized by progressive loss of dopaminergic neurons and their terminations in the basal ganglia, is thought to be related to genetic and environmental factors. Although the pathophysiology of PD neurodegeneration remains unclear, protein misfolding, mitochondrial abnormalities, glutamate dysfunction and/or oxidative stress have been implicated. In this study, we report that a rare T1492G variant in GLUD2, an X-linked gene encoding a glutamate dehydrogenase (a mitochondrial enzyme central to glutamate metabolism) that is expressed in brain (hGDH2), interacted significantly with age at PD onset in Caucasian populations. Individuals hemizygous for this GLUD2 coding change that results in substitution of Ala for Ser445 in the regulatory domain of hGDH2 developed PD 6-13 years earlier than did subjects with other genotypes in two independent Greek PD groups and one North American PD cohort. However, this effect was not present in female PD patients who were heterozygous for the DNA change. The variant enzyme, obtained by substitution of Ala for Ser445, showed an enhanced basal activity that was resistant to GTP inhibition but markedly sensitive to modification by estrogens. Thus, a gain-of-function rare polymorphism in hGDH2 hastens the onset of PD in hemizygous subjects, probably by damaging nigral cells through enhanced glutamate oxidative dehydrogenation. The lack of effect in female heterozygous PD patients could be related to a modification of the overactive variant enzyme by estrogens.

Endoplasmic reticulum Ca(2+) release through ryanodine and IP(3) receptors contributes to neuronal excitotoxicity

Overactivation of ionotropic glutamate receptors induces a Ca(2+) overload into the cytoplasm that leads neurons to excitotoxic death, a process that has been linked to several neurodegenerative disorders. While the role of mitochondria and its involvement in excitotoxicity have been widely studied, the contribution of endoplasmic reticulum (ER), another crucial intracellular store in maintaining Ca(2+) homeostasis, is not fully understood. In this study, we analyzed the contribution of ER-Ca(2+) release through ryanodine (RyR) and IP(3) (IP(3)R) receptors to a neuronal in vitro model of excitotoxicity. NMDA induced a dose-dependent neuronal death, which was significantly decreased by ER-Ca(2+) release inhibitors in cortical neurons as well as in organotypic slices. Furthermore, ryanodine and 2APB, RyR and IP(3)R inhibitors respectively, attenuated NMDA-triggered intracellular Ca(2+) increase and oxidative stress, whereas 2APB reduced mitochondrial membrane depolarization and caspase-3 cleavage. Consistent with ER-Ca(2+) homeostasis disruption, we observed that NMDA-induced ER stress, characterized here by eIF2alpha phosphorylation and over-expression of GRP chaperones which were regulated by ER-Ca(2+) release inhibitors. These results demonstrate that Ca(2+) release from ER contributes to neuronal death by both promoting mitochondrial dysfunction and inducing specific stress and apoptosis pathways during excitotoxicity.

Transient neurologic syndrome after spinal anesthesia with epidural steroid treatment

BACKGROUND

Transient neurologic syndrome (TNS) is a rare complication of spinal and epidural anesthesia. It is defined as paradoxic postoperative back pain radiating to the lower extremities with no neurologic deficits. Because it is a self-limited disease, the treatment is usually symptomatic and consists of NSAIDs and injections of a neuromuscular-blocking drug at the trigger points. The syndrome may be resistant to this treatment regimen and may last for several months, resulting in a long convalescence.

CASE SUMMARY

A 63-year-old Turkish woman (height, 165 cm; weight, 71 kg) underwent hemorrhoidectomy in the jackknife position using spinal anesthesia. No adverse events occurred during puncture or surgery or in the immediate postoperative recovery period. Recovery from the sensory and motor block was normal. Twenty-four hours after surgery, lower limb and plantar pain developed with no sensory or motor deficit. Neurologic examination revealed normal motor and sensory function. Electroneuromyography showed partial denervation potential of muscles innervated by the left sciatic nerve. The symptoms were suggestive of TNS. Combination oral NSAID treatment with amitriptyline (25 mg/d) and gabapentin (1200 mg/d) was initiated. Because the pain still persisted 6 weeks after surgery, epidural steroid injection with triamcinolone acetate (80 mg) with isotonic saline was administered, resulting in definite pain relief (visual analog scale score = 0).

CONCLUSIONS

Epidural steroid treatment was effective in this patient with TNS resistant to treatment with NSAIDs, amitriptyline, and gabapentin. Future studies are needed to evaluate this treatment.

Mangifera indica L. extract attenuates glutamate-induced neurotoxicity on rat cortical neurons

Overstimulation of ionotropic glutamate receptors causes excitotoxic neuronal death contributing to neurodegenerative disorders. Massive influx of calcium in excitotoxicity provokes alterations in the membrane potential of mitochondria and increases the production of reactive oxygen species. Here we report that Mangifera indica L. extracts (MiE) prevent glutamate-induced excitotoxicity in primary cultured neurons of the rat cerebral cortex. To evaluate the effects of MiE on excitotoxicity, cells were stimulated with L-glutamic acid (50 microM; 10 min) alone or in the presence of MiE. Maximal protection (56%) was obtained with 2.5 microg/mL of MiE. In turn, we measured the effects of MiE on excitotoxic-induced oxidative stress and mitochondrial depolarization by fluorimetry using 5,6-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate and tetramethylrhodamine, respectively. Both parameters were effectively reduced by MiE at concentrations which showed neuroprotection. Mangiferin, an antioxidant polyphenol which is a major component of MiE, was also effective in preventing neuronal death, oxidative stress and mitochondrial depolarization. Maximal protection (64%) was obtained at 12.5 microg/mL of mangiferin which also attenuated oxidative stress and mitochondrial depolarization at the neuroprotective concentrations. Together, these results indicate that MiE is an efficient neuroprotector of excitotoxic neuronal death, indicates that mangiferin carries a substantial part of the antioxidant and neuroprotective activity of MiE, and that this natural extract has therapeutic potential to treat neurodegenerative disorders.

Neuroprotective effects of R,R-tetrahydrochrysene against glutamate-induced cell death through anti-excitotoxic and antioxidant actions involving estrogen receptor-dependent and -independent pathways

Glutamate-induced neural cell death is mediated by excitotoxicity and oxidative stress. Treatment of glutamate toxicity with estrogen and its related compounds for neuroprotection remains controversial. In this study, we examined the effects of selective estrogen receptor (ER) ligands on glutamate toxicity and found that R,R-tetrahydrochrysene (R,R-THC), an antagonist of ERbeta and agonist of ERalpha, has neuroprotective effects against glutamate-induced death in primary rat cortical cells and mouse N29/4 hypothalamic cells. The protective effect of R,R-THC was dose-dependent and was maintained even when added several hours after the initial glutamate exposure. R,R-THC blocked glutamate-induced depletion of intracellular glutathione, increased superoxide dismutase activity, and protected cells from hydrogen peroxide-induced death. R,R-THC also prevented glutamate-induced nuclear translocation of apoptotic inducing factor and release of mitochondrial cytochrome c. The protective effect of R,R-THC was blocked by methyl-piperidino-pyrazole (MPP; an ERalpha antagonist) in glutamate-treated cortical cells, and pretreatment with MK-801 (an NMDA receptor antagonist) but not CNQX (an AMPA/kainate receptor antagonist) increased cell survival. On the other hand, MPP did not block the protective effect of R,R-THC in glutamate-treated N29/4 cells, and neither MK-801 nor CNQX conferred protection. Activation of ERalpha and/or ERbeta with 17beta-estradiol (E2), propyl-pyrazole-triol or diarylpropionitrile did not provide effective neuroprotection, and pretreatment with ICI 182,780 did not inhibit the protective effect of R,R-THC in either type of cell. These results suggest that the use of ER agonists (including E2) has limited beneficial effects when both excitotoxicity and oxidative stress occur. In contrast to agonists of ERs, R,R-THC, which possesses anti-excitotoxic and antioxidant actions via ER-dependent and -independent pathways, provides significant neuroprotection.

Role of oxidative stress in the natriuresis induced by central administration of angiotensin II

Introduction. Central administration of angiotensin II (Ang II) is known to reduce urinary volume and to increase sodium and potassium excretion. Recently, a novel signalling mechanism for Ang II in the periphery has been shown to involve reduced nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase-derived reactive oxygen species (ROS).Although ROS are now known to be involved in numerous Ang II-regulated processes in peripheral tissues, and are increasingly implicated in CNS neurodegenerative diseases, the role of ROS in central regulation of Ang II-induced hydromineral metabolism remains unexplored.The hypothesis that ROS are involved in central Ang II signalling and in Ang II-dependent antidiuresis, natriuresis and kaliuresis was tested by the use of selective antagonists of the NAD(P)H oxidase cascade. Materials and methods. In intracerebroventricular (ICV)-cannulated rats,Ang II was injected ICV and urinary sodium and potassium excretion was assessed at 1-, 3-, and 6-hour periods of urine collection. Urine sample was analysed for sodium and potassium concentration using a flame photometer. The role of NAD(P)H oxidase-dependent signalling cascade was evaluated using the selective NAD(P)H oxidase inhibitor, apocynin; the superoxide dismutase mimetic, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (tempol); and the protein kinase C inhibitor, chelerythrine. Results. ICV administration of Ang II to conscious hydrated rats resulted in a significant decrease in urinary volume in the first hour, and an increased sodium and potassium excretion during the 6-hour period of urine collection, which was most effective during the 3 and 6 h. Interference with the NAD(P)H oxidase signalling by central administration of apocynin, tempol or chelerythrine, blunted the natriuretic and kaliuretic effect induced by central administration of Ang II, without affecting its antidiuretic action.

Conclusion.This study demonstrates that increases of urinary sodium and potassium excretion elicited by central administration of Ang II are mediated by NAD(P)H oxidase- dependent production of superoxide and protein kinase C activation in conscious hydrated rats.