Oxidative stress in the brain: novel cellular targets that govern survival during neurodegenerative disease

Clinical treatments for mitochondrial dysfunctions after brain injury

PURPOSE OF REVIEW

This review provides a comprehensive look at the evidence supporting the role of mitochondrial dysfunction in promoting neuronal death after acute brain injury, and critically discusses the most recent proposed therapies that could limit the deleterious effects of such a dysfunction on neurological outcome.

RECENT FINDINGS

Following acute brain injury, disruption of calcium homeostasis, overproduction of reactive oxygen species, and opening of the mitochondrial permeability transition pore, are key factors in promoting mitochondrial dysfunction, with ensuing activation of either necrotic or apoptotic cell death pathways. Growing interest has been focused on developing new therapeutic strategies able to oppose these mechanisms. Several pharmacological agents are currently under investigation, including novel calcium channel blockers and antioxidants, uncoupling proteins and mitochondrial permeability transition pore inhibitors. Although a 'magic bullet' has not yet been identified, the results of both preclinical and clinical studies are encouraging.

SUMMARY

Therapeutic interventions directly targeting processes and mechanisms responsible for mitochondrial dysfunction, may offer neuroprotection in brain-injured patients. The multifactorial cause of mitochondrial dysfunction suggests, however, the need for further studies aimed at clarifying optimal dose and time for drug administration, as well as the logical combination/sequence of those approaches that may ultimately achieve improvement in neurological outcome.

Microglial integrity is maintained by erythropoietin through integration of Akt and its substrates of glycogen synthase kinase-3beta, beta-catenin, and nuclear factor-kappaB

Recognized as a robust cytoprotectant for multiple tissues of the hematopoietic, vascular, cardiac, and nervous systems, erythropoietin (EPO) also is considered to be an attractive therapeutic candidate to modulate inflammatory cell function and survival during neurodegenerative disorders. To this end, microglia of the central nervous system serve a complex function not only to dispense of foreign organisms and injured cells of the brain, but also to foster tissue repair and reorganization during neuronal and vascular cell insults. We therefore examined the ability of EPO to modulate microglial cell survival and the underlying signal transduction pathways that govern microglial integrity during oxygen-glucose deprivation (OGD)--induced oxidative stress. We demonstrate in the microglial cell line EOC 2 that EPO provides direct microglial protection against early and late apoptotic programs of membrane phosphatidylserine exposure and genomic DNA degradation. Furthermore, expression and activation of Akt1 is vital to the cytoprotective capacity of EPO, since pharmacological inhibition of the PI 3-K pathway or gene silencing of Akt1 expression eliminates the ability of EPO to protect microglial cells. Through Akt1 dependent mechanisms that can be abrogated through the gene silencing of Akt1, maintenance of microglial cell integrity during OGD by EPO is closely integrated with the phosphorylation and inhibition of glycogen synthase kinase-3beta activity as well as the intracellular trafficking of beta-catenin and nuclear factor-kappaB. Further work that continues to elucidate the ability of EPO to target the intricate pathways that determine inflammatory cell function and integrity may lay the ground work for new therapeutic avenues for neurodegenerative disease.

Programmed cell death in African trypanosomes

Until recently it had generally been assumed that apoptosis and other forms of programmed cell death evolved during evolution of the metazoans to regulate growth and development in these multicellular organisms. However, recent research is adding strength to the original phenotypic observations described almost a decade ago which indicated that some parasitic protozoa may have evolved a cell death pathway analogous to the process described as apoptosis in metazoa. Here we explore the implications of a programmed cell death pathway in the African tsetse-transmitted trypanosomes.

Insulin restores metabolic function in cultured cortical neurons subjected to oxidative stress

We previously demonstrated that insulin has a neuroprotective role against oxidative stress, a deleterious condition associated with diabetes, ischemia, and age-related neurodegenerative diseases. In this study, we investigated the effect of insulin on neuronal glucose uptake and metabolism after oxidative stress in rat primary cortical neurons. On oxidative stress, insulin stimulates neuronal glucose uptake and subsequent metabolism into pyruvate, restoring intracellular ATP and phosphocreatine. Insulin also increases intracellular and decreases extracellular adenosine, counteracting the effect of oxidative stress. Insulin effects are apparently mediated by phosphatidylinositol 3-K and extracellular signal-regulated kinase signaling pathways. Extracellular adenosine under oxidative stress is largely inhibited after blockade of ecto-5'-nucleotidase, suggesting that extracellular adenosine results preferentially from ATP release and catabolism. Moreover, insulin appears to interfere with the ATP release induced by oxidative stress, regulating extracellular adenosine levels. In conclusion, insulin neuroprotection against oxidative stress-mediated damage involves 1) stimulation of glucose uptake and metabolism, increasing energy levels and intracellular adenosine and, ultimately, uric acid formation and 2) a decrease in extracellular adenosine, which may reduce the facilitatory activity of adenosine receptors.

Attempted cell cycle induction in post-mitotic neurons occurs in early and late apoptotic programs through Rb, E2F1, and caspase 3

Either the absence or dysfunction of a number of critical pathways, such as those that involve the nuclear retinoblastoma protein (Rb) and the transcription factor E2F1, may account for the aberrant induction of the cell cycle in post-mitotic neurons that can be responsible for oxidative stress-induced apoptotic cellular destruction. Yet, it is unclear whether early programs of apoptotic injury that involve membrane phosphatidylserine (PS) exposure and calreticulin expression as well as later phases of apoptotic injury with nuclear DNA injury require the critical modulation of Rb and E2F1. We demonstrate that both the post-translational of phosphorylation of Rb to prevent E2F1 transcription as well as the protein integrity of Rb are closely aligned with the modulation of cell cycle induction in post mitotic neurons during oxidative stress. More importantly, we illustrate that both the initial onset of apoptosis with either membrane PS exposure or calreticulin analysis as well as the more terminal phases of apoptosis that involve nuclear DNA degradation proceed concurrently in the same neuronal cells with cell cycle induction. Progression of attempted cell cycle induction is closely associated with the phosphorylation of Rb, its inability to bind to E2F1, and the degradation of the Rb protein. Inhibition of Rb phosphorylation using cyclin dependent kinase inhibitors maintains the integrity of the E2F1/Rb complex and is neuroprotective during free radical exposure. Furthermore, maintenance of the integrity of the Rb protein is specifically dependent upon caspase 3-like activity, since caspase 3 can cleave Rb during free radical activity and this degradation of Rb can be blocked during the inhibition of caspase 3 activity. Our studies not only highlight the critical role of attempted cell cycle induction during oxidative stress-induced neuronal apoptotic injury, but also bring to light the significant impact of the Rb and E2F1 pathways upon early apoptotic programs that can directly influence both intrinsic cell survival as well as extrinsic inflammatory cell activation.

Effects of inhaled manganese on biomarkers of oxidative stress in the rat brain

Manganese (Mn) is a ubiquitous and essential element that can be toxic at high doses. In individuals exposed to high levels of this metal, Mn can accumulate in various brain regions, leading to neurotoxicity. In particular, Mn accumulation in the mid-brain structures, such as the globus pallidus and striatum, can lead to a Parkinson's-like movement disorder known as manganism. While the mechanism of this toxicity is currently unknown, it has been postulated that Mn may be involved in the generation of reactive oxygen species (ROS) through interaction with intracellular molecules, such as superoxide and hydrogen peroxide, produced within mitochondria. Conversely, Mn is a required component of an important antioxidant enzyme, Mn superoxide dismutase (MnSOD), while glutamine synthetase (GS), a Mn-containing astrocyte-specific enzyme, is exquisitely sensitive to oxidative stress. To investigate the possible role of oxidative stress in Mn-induced neurotoxicity, a series of inhalation studies was performed in neonatal and adult male and female rats as well as senescent male rats exposed to various levels of airborne-Mn for periods of time ranging from 14 to 90 days. Oxidative stress was then indirectly assessed by measuring glutathione (GSH), metallothionein (MT), and GS levels in several brain regions. MT and GS mRNA levels and regional brain Mn concentrations were also determined. The collective results of these studies argue against extensive involvement of ROS in Mn neurotoxicity in rats of differing genders and ages. There are, however, instances of changes in individual endpoints consistent with oxidative stress in certain brain tissues.

Cytoglobin is a stress-responsive hemoprotein expressed in the developing and adult brain

Cytoglobin (Cygb) is a novel tissue hemoprotein relatively similar to myoglobin (Mb). Because Cygb shares several structural features with Mb, we hypothesized that Cygb functions in the modulation of oxygen and nitric oxide metabolism or in scavenging free radicals within a cell. In the present study we examined the spatial and temporal expression pattern of Cygb during murine embryogenesis. Using in situ hybridization, RT-PCR, and Northern blot analyses, limited Cygb expression was observed during embryogenesis compared with Mb expression. Cygb expression was primarily restricted to the central nervous system and neural crest derivatives during the latter stages of development. In the adult mouse, Cygb is expressed in distinct regions of the brain as compared with neuroglobin (Ngb), another globin protein, and these regions are responsive to oxidative stress (i.e., hippocampus, thalamus, and hypothalamus). In contrast to Ngb, Cygb expression in the brain is induced in response to chronic hypoxia (10% oxygen). These results support the hypothesis that Cygb is an oxygen-responsive tissue hemoglobin expressed in distinct regions of thenormoxic and hypoxic brain and may play a key role in the response of the brain to ahypoxic insult.

Chitotriosidase and inflammatory mediator levels in Alzheimer's disease and cerebrovascular dementia

Inflammation has been reported to be involved in the pathogenesis of cerebrovascular dementias (CvDs). This study investigated the involvement of Chitotriosidase (ChT), a chinolitic enzyme mainly produced by activated macrophages, in the pathophysiology of Alzheimer's disease (AD) and ischemic CvD. In addition, the levels of interleukin (IL)-16, IL-18, transforming growth factor (TGF)-beta1 and superoxide anion (O2(-)) were determined to evaluate the relationship between ChT levels, these cytokines and oxidative stress in both AD and ischemic CvD patients. The levels of ChT and IL-16, IL-18, and TGF-beta1 mRNA were investigated using quantitative real-time polymerase chain reaction on macrophages of peripheral blood of 40 patients with AD, 40 patients with ischemic CvD and 40 non-demented age-matched subjects. The results show that ChT, IL-16 and O2(-) levels significantly increased in ischemic CvD patients compared with AD patients and were significantly and positively correlated with IL-18 and O2(-). The production of IL-18 was increased in both AD and ischemic CvD patients. TGF-beta1 expression was higher in AD patients and was inversely correlated with the expression of ChT, IL-16 and IL-18, respectively. In non-demented age-matched subjects no significant changes in ChT and IL-16, IL-18, and TGF-beta1 expression were found. Our results indicate that ChT, IL-16, IL-18 and TGF-beta1 are increased in ischemic CvD and AD, confirming that the immune system may play an important role in the development and progression of neurodegenerative disorders. In addition, the present findings suggest that ChT could also play a crucial role in pathological conditions such as CvD in which the inflammatory process is activated.

Comparative Proteomics in Neurodegenerative and Non-neurodegenerative Diseases Suggest Nodal Point Proteins in Regulatory Networking

Neurodegenerative disorders (ND) encompass clinically and genetically heterogeneous diseases with considerable overlap of their clinical, neuropathological and molecular phenotype. Various causes of neurodegeneration in disease may affect eventually the same proteins within protein networks. To identify common changes in ND, we compared brain protein changes detected by 2-D electrophoresis in four mouse models for ND: (i) Parkinson's disease, (ii) Huntington's disease, (iii) prion disease Scrapie, and (iv) a model for impaired synaptic transmission. To determine specificity of these changes for ND, we extended the scope of our investigation to three neurological conditions that do not result in neurodegeneration (non-ND). We detected 12 to 216 consistent qualitative or quantitative protein changes in individual ND and non-ND models when compared to controls. Up to 36% of these proteins were found to be altered in multiple disease states (at least three) and were therefore termed nodal point proteins. Alterations in alpha B-Crystallin and splicing factor 3b (subunit 4) occurred in at least three ND but not in non-ND. In contrast, alterations in peroxiredoxin 1 and 3, astrocytic phosphoprotein PEA15, complexin 2 and aminoacylase 1 were common to both ND and non-ND. Finally, we investigated the expression pattern of the nodal point proteins in three inbred mouse strains and found different protein abundance (expression polymorphisms) in all cases. Nodal point proteins showing expression polymorphisms may be candidate proteins for disease associated modifiers.

Group I metabotropic receptor neuroprotection requires Akt and its substrates that govern FOXO3a, Bim, and beta-catenin during oxidative stress

Metabotropic glutamate receptors are expressed throughout the nervous system, but their function as well as their ability to promote neuronal survival rests heavily upon the intracellular mechanisms governed by this family of G-proteins. In this regard, we examined one of the primary pathways that can oversee cell survival, namely protein kinase B (Akt1), and its functional integration with some of its substrates that may work in concert with group I metabotropic glutamate receptor (mGluRI) activation to protect primary hippocampal neurons during oxidative stress. We demonstrate that neuroprotection against free radical injury through mGluRI activation with DHPG requires the activation of Akt1, since loss of Akt1 activity assessed through its GSK-3alpha/beta substrate by pharmacological blockade of the phosphatidylinositide-3-kinase pathway or the gene silencing of Akt1 expression prevents neuronal protection during mGluRI activation. Closely coupled to the robust neuroprotection by mGluRI activation are the inhibitory phosphorylation and prevention of caspase 3 cleavage of the Forkhead transcription factor FOXO3a, the down-regulation of Bim expression, and the protection of beta-catenin by Akt1 against phosphorylation and degradation to promote its translocation from the cytoplasm to the nucleus and allow it to assist with a "pro-survival" cellular program. Further insight into the cellular mechanisms that determine neuronal protection by the metabotropic glutamate system will foster the successful therapeutic development of mGluRs for neurodegenerative disorders.

A conserved MST-FOXO signaling pathway mediates oxidative-stress responses and extends life span

Oxidative stress influences cell survival and homeostasis, but the mechanisms underlying the biological effects of oxidative stress remain to be elucidated. Here, we demonstrate that the protein kinase MST1 mediates oxidative-stress-induced cell death in primary mammalian neurons by directly activating the FOXO transcription factors. MST1 phosphorylates FOXO proteins at a conserved site within the forkhead domain that disrupts their interaction with 14-3-3 proteins, promotes FOXO nuclear translocation, and thereby induces cell death in neurons. We also extend the MST-FOXO signaling link to nematodes. Knockdown of the C. elegans MST1 ortholog CST-1 shortens life span and accelerates tissue aging, while overexpression of cst-1 promotes life span and delays aging. The cst-1-induced life-span extension occurs in a daf-16-dependent manner. The identification of the FOXO transcription factors as major and evolutionarily conserved targets of MST1 suggests that MST kinases play important roles in diverse biological processes including cellular responses to oxidative stress and longevity.

Antioxidant pyrrolidine dithiocarbamate activates Akt-GSK signaling and is neuroprotective in neonatal hypoxia-ischemia

Pyrrolidine dithiocarbamate (PDTC), an antioxidant and inhibitor of transcription factor nuclear factor kappa-B (NF-kappaB), has been reported to reduce inflammation and apoptosis. Because PDTC was recently found to protect in various models of adult brain ischemia with a wide therapeutic time window, we tested the effect of PDTC in a rodent model of neonatal hypoxia-ischemia (HI) brain injury. T2-weighed magnetic resonance imaging (T2-MRI) 7 days after the insult showed that a single PDTC (50 mg/kg) injection 2.5 h after the HI reduced the mean brain infarct size by 59%. PDTC reduced the HI-induced dephosphorylation of Akt and glycogen synthase kinase-3beta (GSK-3beta), expression of cleaved caspase-3, and nuclear translocation of NF-kappaB in the neonatal brain. PDTC targeted directly neurons, as PDTC reduced hypoxia-reoxygenation-induced cell death in pure hippocampal neuronal cultures. It is suggested that in addition to the previously indicated NF-kappaB inhibition as a protective mechanism of PDTC treatment, PDTC may reduce HI-induced brain injury at least partially by acting as an antioxidant, which reduces the Akt-GSK-3beta pathway of apoptotic cell death. The clinically approved PDTC and its analogues may be beneficial after HI insults with a reasonable time window.

Creatine supplementation affords cytoprotection in oxidatively injured cultured mammalian cells via direct antioxidant activity

A growing body of evidence suggests that creatine (Cr) might exert protective effects in a variety of pathologies where oxidative stress plays a concausal etiologic role; furthermore, it has been recently reported that Cr displays direct antioxidant activity in a cell-free setting. However, at present, no research has been specifically aimed to directly test the antioxidant potential of Cr on oxidatively injured cultured cells. Here, the effects of Cr were studied using cultured human promonocytic (U937) and endothelial (HUVEC) cells, and murine myoblasts (C2C12) exposed to H(2)O(2), tert-butylhydroperoxide (tB-OOH) and, in the case of U937 cells, peroxynitrite. Cr (0.1-10 mM) attenuated the cytotoxic effects caused by the oxidants in all the cell lines; under our conditions, cytoprotection was invariably associated with elevation of the intracellular fraction of Cr but it seemed to be unrelated to the levels of Cr phosphate (CrP); Cr did not affect the activity of catalase (CAT) and glutathione peroxidase (GpX), but it prevented H(2)O(2)- or tB-OOH-induced consumption of the nonprotein sulfhydryl (NPSH) pool in U937 and HUVEC cells; mass spectrometry experiments showed that a 136 MW molecule, which is likely to represent an oxidation by-product of Cr, formed in reaction buffers containing Cr and H(2)O(2) as well as in cellular extracts from H(2)O(2)- or tB-OOH- treated Cr-preloaded U937 cells; finally, Cr cytoprotection appeared to be unrelated to chelation of Fe(2+). In conclusion, it is suggested that Cr exerts a mild, although significant, antioxidant activity in living cells, via a mechanism depending on direct scavenging of reactive oxygen (in particular hydroxyl radical) and nitrogen species.

Vital elements of the Wnt-Frizzled signaling pathway in the nervous system

Wnt proteins are cysteine-rich glycosylated proteins named after the Drosophilia Wingless (Wg) and the mouse Int-1 genes that play a role in embryonic cell patterning, proliferation, differentiation, orientation, adhesion, survival, and programmed cell death (PCD). Wnt proteins involve at least two intracellular signaling pathways. One pathway controls target gene transcription through beta-catenin, generally referred to as the canonical pathway and a second pathway pertains to intracellular calcium (Ca(2+)) release which is termed the non-canonical or Wnt/ Ca(2+) pathway. The majority of Wnt proteins activate gene transcription through the canonical signaling pathway regulated by pathways that include the Frizzled transmembrane receptor and the co-receptor LRP-5/6, Dishevelled, glycogen synthase kinase-3beta (GSK-3beta), adenomatous polyposis coli (APC), and beta-catenin. In contrast, the non-canonical Wnt signaling pathway has two intracellular signaling cascades that consist of the Wnt/ Ca(2+) pathway with protein kinase C (PKC) and the Wnt/PCP pathway involving Rho/Rac small GTPase and Jun N-terminal kinase (JNK). Through a series of signaling pathways, Wnt proteins modulate cell development, proliferation, and cell fate. In regards to cell survival and fate through PCD, Wnt may be critical for the prevention of tissue pathology that involves cytokine and growth factor control during disorders such as neuropsychiatric disease, retinal disease, and Alzheimer's disease. Elucidation of the vital elements that shape and control the Wnt-Frizzled signaling pathway may provide significant prospects for the treatment of disorders of the nervous system.

Post-injury treatment with a new antioxidant compound H-290/51 attenuates spinal cord trauma-induced c-fos expression, motor dysfunction, edema formation, and cell injury in the rat

The neuroprotective efficacy of post-injury treatment with the antioxidant compound H-290/51 (10, 30, and 60 minutes after trauma) on immediate early gene expression (c-fos), blood-spinal cord barrier (BSCB) permeability, edema formation, and motor dysfunction was examined in a rat model of spinal cord injury (SCI). SCI was produced by a longitudinal incision into the right dorsal horn of the T10-11 segment under Equithesin anesthesia. Focal SCI in control rats resulted in profound up-regulation of c-fos expression, BSCB dysfunction, edema formation, and cell damage in the adjacent T9 and T12 segments at 5 hours. Pronounced motor dysfunction was present at this time as assessed using the Tarlov scale and the inclined plane test. Treatment with H-290/51 (50 mg/kg, p.o.) 10 and 30 minutes after SCI (but not after 60 minutes) markedly attenuated c-fos expression and motor dysfunction. In these groups, BSCB permeability, edema formation, and cell injuries were mildly but significantly reduced. These observations suggest that (i) antioxidants are capable of attenuating cellular and molecular events following trauma, and (ii) have the capacity to induce neuroprotection and improve motor function if administered during the early phase of SCI, a novel finding.

Erythropoietin requires NF-kappaB and its nuclear translocation to prevent early and late apoptotic neuronal injury during beta-amyloid toxicity

No longer considered exclusive for the function of the hematopoietic system, erythropoietin (EPO) is now considered as a viable agent to address central nervous system injury in a variety of cellular systems that involve neuronal, vascular, and inflammatory cells. Yet, it remains unclear whether the protective capacity of EPO may be effective for chronic neurodegenerative disorders such as Alzheimer's disease (AD) that involve beta-amyloid (Abeta) apoptotic injury to hippocampal neurons. We therefore investigated whether EPO could prevent both early and late apoptotic injury during Abeta exposure in primary hippocampal neurons and assessed potential cellular pathways responsible for this protection. Primary hippocampal neuronal injury was evaluated by trypan blue dye exclusion, DNA fragmentation, membrane phosphatidylserine (PS) exposure, and nuclear factor-kappaB (NF-kappaB) expression with subcellular translocation. We show that EPO, in a concentration specific manner, is able to prevent the loss of both apoptotic genomic DNA integrity and cellular membrane asymmetry during Abeta exposure. This blockade of Abeta generated neuronal apoptosis by EPO is both necessary and sufficient, since protection by EPO is completely abolished by co-treatment with an anti-EPO neutralizing antibody. Furthermore, neuroprotection by EPO is closely linked to the expression of NF-kappaB p65 by preventing the degradation of this protein by Abeta and fostering the subcellular translocation of NF-kappaB p65 from the cytoplasm to the nucleus to allow the initiation of an anti-apoptotic program. In addition, EPO intimately relies upon NF-kappaB p65 to promote neuronal survival, since gene silencing of NF-kappaB p65 by RNA interference removes the protective capacity of EPO during Abeta exposure. Our work illustrates that EPO is an effective entity at the neuronal cellular level against Abeta toxicity and requires the close modulation of the NF-kappaB p65 pathway, suggesting that either EPO or NF-kappaB may be used as future potential therapeutic strategies for the management of chronic neurodegenerative disorders, such as AD.

Driving cellular plasticity and survival through the signal transduction pathways of metabotropic glutamate receptors

Metabotropic glutamate receptors (mGluRs) share a common molecular morphology with other G protein-linked receptors, but there expression throughout the mammalian nervous system places these receptors as essential mediators not only for the initial development of an organism, but also for the vital determination of a cell's fate during many disorders in the nervous system that include amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease, Multiple Sclerosis, epilepsy, trauma, and stroke. Given the ubiquitous distribution of these receptors, the mGluR system impacts upon neuronal, vascular, and glial cell function and is activated by a wide variety of stimuli that includes neurotransmitters, peptides, hormones, growth factors, ions, lipids, and light. Employing signal transduction pathways that can modulate both excitatory and inhibitory responses, the mGluR system drives a spectrum of cellular pathways that involve protein kinases, endonucleases, cellular acidity, energy metabolism, mitochondrial membrane potential, caspases, and specific mitogen-activated protein kinases. Ultimately these pathways can converge to regulate genomic DNA degradation, membrane phosphatidylserine (PS) residue exposure, and inflammatory microglial activation. As we continue to push the envelope for our understanding of this complex and critical family of metabotropic receptors, we should be able to reap enormous benefits for both clinical disease as well as our understanding of basic biology in the nervous system.

Hyperactive striatal neurons in symptomatic Huntington R6/2 mice: variations with behavioral state and repeated ascorbate treatment

Membrane and morphological abnormalities occur in the striatum of R6/2 transgenics, a widely used mouse model of Huntington's disease. To assess changes in behavior-related neuronal activity, we implanted micro-wire bundles in the striatum of symptomatic R6/2 mice and wild-type controls. Unit activity was recorded in an open-field arena once weekly for the next several weeks. For each recording session, firing rate was monitored before, during, and after a period of light anesthesia to assess the influence of behavioral arousal. Because low ascorbate in striatal extracellular fluid may contribute to Huntington's disease symptoms, all animals received an injection of either 300 mg/kg sodium ascorbate or vehicle for three consecutive days prior to each recording session. In R6/2 mice, regardless of treatment, striatal unit activity was significantly faster than in wild-type controls. The difference in mean (+/-S.E.M.) firing was most apparent during wakefulness (6.4+/-0.8 vs. 3.5+/-0.3 spikes/s) but also persisted during anesthesia (2.0+/-0.3 vs. 0.7+/-0.1 spikes/s). Assessment of treatment duration indicated that R6/2 mean waking discharge rate was significantly slower after three weeks than after one week of ascorbate treatment (3.1+/-0.6 vs. 10.2+/-2.7 spikes/s). Vehicle-treated R6/2s showed no such decline in striatal activity ruling out an age- or injection-related effect. Slow-scan voltammetry in separate animals confirmed that ascorbate-injections returned the level of striatal extracellular ascorbate in R6/2 mice to that of wild-type controls. Our results indicate that although striatal neurons modulate firing in relation to behavioral state, impulse activity is consistently elevated in transgenic relative to wild-type mice. Restoring extracellular ascorbate to the wild-type level reverses this effect suggesting a role for ascorbate in normalizing neuronal function in Huntington's disease striatum.

T-817MA, a novel neurotrophic agent, improves sodium nitroprusside-induced mitochondrial dysfunction in cortical neurons

1-{3-[2-(1-Benzothiophen-5-yl)ethoxy]propyl}-3-azetidinol maleate (T-817MA), a novel neurotrophic agent, protects against amyloid-beta peptide- or hydrogen peroxide-induced neuronal death. The exact mechanism of the neuroprotection is not known. This study examines the effects of T-817MA on oxidative stress-induced cytotoxicity in primary rat cortical neurons. Treatment with the NO donor sodium nitoroprusside (SNP) at 300microM decreased cell viability and induced apoptotic cell death. SNP-induced neuronal toxicity was accompanied by a decrease in mitochondrial transmembrane potential without an increase in the expression of CHOP and GRP78 mRNAs, endoplasmic reticulum stress makers. T-817MA at 0.1 and 1microM attenuated the neurotoxicity in a dose-dependent way and the protective effect required pretreatment for more than 8h. T-817MA attenuated SNP-induced decrease in mitochondrial transmembrane potential. In addition, the agent reduced SNP-induced increase in mitochondrial reactive oxygen species (ROS) production. The effects of T-817MA on SNP-induced decrease in cell viability and SNP-induced increase in mitochondrial ROS production were blocked by cycloheximide. These results suggest that T-817MA improves SNP-induced mitochondrial dysfunction in cortical neurons in a newly synthesized protein-mediated mechanism and this effect contributes to its neuroprotective effect.

The sirtuin inhibitor nicotinamide enhances neuronal cell survival during acute anoxic injury through AKT, BAD, PARP, and mitochondrial associated "anti-apoptotic" pathways

Understanding the role of nicotinamide (NIC) in different cell systems represents a significant challenge in several respects. Recently, NIC has been reported to have diverse roles during cell biology. In the absence of NIC, sirtuin protein activity is enhanced and pyrazinamidase/nicotinamidase 1 (PNC1) expression, an enzyme that deaminates NIC to convert NIC into nicotinic acid, is increased to lead to lifespan extension during calorie restriction, at least in yeast. Yet, NIC may be critical for cell survival as well as the modulation of inflammatory injury during both experimental models as well as in clinical studies. We therefore investigated some of the underlying signal transduction pathways that could be critical for the determination of the neuroprotective properties of NIC. We examined neuronal injury by trypan blue exclusion, DNA fragmentation, phosphatidylserine (PS) exposure, Akt1 phosphorylation, Bad phosphorylation, mitochondrial membrane potential, caspase activity, cleavage of poly(ADP-ribose) polymerase (PARP), and mitogen-activated protein kinases (MAPKs) phosphorylation. Application of NIC (12.5 mM) significantly increased neuronal survival from 38 -/+ 3% of anoxia treated alone to 68 +/- 3%, decreased DNA fragmentation and membrane PS exposure from 67 -/+ 4% and 61 -/+ 5% of anoxia treated alone to 30 +/- 4% and 26 +/- 4% respectively. We further demonstrate that NIC functions through Akt1 activation, Bad phosphorylation, and the downstream modulation of mitochrondrial membrane potential, cytochrome c release, caspase 1, 3, and 8 - like activities, and PARP integrity to prevent genomic DNA degradation and PS externalization during anoxia. Yet, NIC does not alter the activity of either the MAPKs p38 or JNK, suggesting that protection by NIC during anoxia is independent of the p38 and JNK pathways. Additional investigations targeted to elucidate the cellular pathways responsible for the ability of NIC to modulate both lifespan extension and cytoprotection may offer critical insight for the development of new therapies for nervous system disorders.