Pathophysiology of oligodendroglial excitotoxicity

Oligodendrocyte-like cells (OLD) derived from the rat oligodendroglial precursor line, CG-4, express Ca²⁺-permeable non-methyl-D-aspartate glutamate receptor channels (GluR). Exposure to kainate, an L-glutamate analogue, markedly elevates OLC Ca²⁺ influx and cytosolic [Ca²⁺], and results in damage to both OLC plasma membrane and OLC nuclear DNA. Two observations indicate that kainate-induced OLC internucleosomal DNA nicking is not simply a delayed consequence of cell necrosis: 1) there is no temporal lag between onset of plasma membrane injury and of DNA nicking; and 2) aurintricarboxylic acid, an endonuclease inhibitor, blocks kainate-induced damage to the plasma membrane. N-acetyl-L-cysteine also inhibits OLC kainate injury, suggesting that reactive oxygen species participate in OLC excitotoxicity. Kainate-induced OLC Ca²⁺ influx and excitotoxicity are blocked by α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), indicating that these kainate effects are mediated by AMPA-GluR. AMPA and L-glutamate fail to elicit OLC damage unless cyclothiazide, an AMPA-GluR desensitization blocker, is present. OLC express both the “flip” and “flop” forms of GluR2, GluR3, and GluR4 mRNAs, but neither flip nor flop GluR1 mRNA. These data, together with the restriction of the desensitization-blocking activity of cyclothiazide to GluR containing flip-encoded GluR subunits, and the sharply diminished Ca²⁺ permeability of GluR containing edited GluR2, suggest OLC excitotoxicity is mediated by AMPA-GluR that contain flip GluR3 and/or flip GluR4 protein subunits, but neither flip nor flop GluR2 protein subunits. Rapid desensitization of these GluR is likely to be important in protecting cells of the oligodendroglial lineage from excitotoxicity. © 1996 Wiley-Liss, Inc.     

Neuroprotective effects of erythropoietin posttreatment against kainate-induced excitotoxicity in mixed spinal cultures

Although the neuroprotective effects of erythropoietin (EPO) preconditioning are well known, the potential of postapplied EPO to protect neurons against excitotoxic injury has not been clearly established. Here we show that kainate (KA)-induced excitotoxicity, which plays a key role in secondary spinal cord injury, decreased neuron survival, inhibited neurite extension, and significantly reduced the expression of erythropoietin receptors (EpoR) in cultured spinal neurons. Posttreatment with EPO for 48 hr protected neurons against KA-induced injury, opposing KA-induced apoptosis and promoting regrowth of motoneuron neurites. These neuroprotective effects were paralleled by a restoration of EpoR expression. The importance of the EpoR signaling pathway was demonstrated using an EpoR blocking antibody, which neutralized the neuroprotective action of EPO posttreatment and prevented EPO-induced increases in EpoR expression. We also found that up-regulated EpoR stimulated the Janus kinase 2 (JAK2) pathway, which is known to facilitate neuronal growth and neurite regeneration. Although EPO posttreatment modestly attenuated KA-induced reactive gliosis in mixed neuron-glial cultures, blocking EpoR activity did not alter glial fibrillary acidic protein expression or astrocyte proliferation. In conclusion, 48 hr treatment with EPO following KA exposure induced EpoR-dependent protection against excitotoxic injury, demonstrating that preconditioning is not a prerequisite for neuroprotection by EPO. The neuroprotective effects of EPO posttreatment were mediated by an EpoR-dependent signaling pathway that possibly involves JAK2. The neuroprotective effect of EPO posttreatment against KA excitotoxicity appears to reflect direct effects on neurons and not indirect effects mediated by astrocytes.     

Neuroprotective properties and mechanisms of erythropoietin in in vitro and in vivo experimental models for hypoxia/ischemia

Besides its established function in erythropoiesis, erythropoietin (EPO) is currently also appreciated for its neuroprotective effects. The detrimental sequelae of prolonged cerebral hypoxia and ischemia have been shown to attenuate by EPO treatment. After binding to the EPO receptor, EPO is capable of initiating a cascade of events which--via different pathways--may lead to neuroprotection. The circumstances that determine which specific signalling route(s) are activated by EPO are largely unknown. We aim to provide the reader with a timely overview on the use of EPO in models of stroke and hypoxia-ischemia and to discuss the molecular events that underlie its neuroprotection.     

Neuroprotective effects of lithium in cultured cells and animal models of diseases

Lithium, the major drug used to treat manic depressive illness, robustly protects cultured rat brain neurons from glutamate excitotoxicity mediated by N-methyl-D-aspartate (NMDA) receptors. The lithium neuroprotection against glutamate excitotoxiciy is long-lasting, requires long-term pretreatment and occurs at therapeutic concentrations of this drug. The neuroprotective mechanisms involve inactivation of NMDA receptors, decreased expression of pro-apoptotic proteins, p53 and Bax, enhanced expression of the cytoprotective protein, Bcl-2, and activation of the cell survival kinase, Akt. In addition, lithium pretreatment suppresses glutamate-induced loss of the activities of Akt, cyclic AMP-response element binding protein (CREB), c-Jun – N-terminal kinase (JNK) and p38 kinase. Lithium also reduces brain damage in animal models of neurodegenerative diseases in which excitotoxicity has been implicated. In the rat model of stroke using middle cerebral artery occlusion, lithium markedly reduces neurologic deficits and decreases brain infarct volume even when administered after the onset of ischemia. In a rat Huntington's disease model, lithium significantly reduces brain lesions resulting from intrastriatal infusion of quinolinic acid, an excitotoxin. Our results suggest that lithium might have utility in the treatment of neurodegenerative disorders in addition to its common use for the treatment of bipolar depressive patients.     

Neuroprotective effects of nicotinamide and 1-methylnicotinamide in acute excitotoxicity in vitro

Nicotinamide (NAM), an important cofactor in many metabolic pathways, exhibits at high doses neuroprotective abilities of an unclear mechanism. In the present study we evaluated the unknown protective capability of its immediate metabolite 1-methylnicotinamide (MNA) in comparison to NAM in primary cultures of rat cerebellar granule cells (CGC) submitted to acute excitotoxicity. Neurotoxicity was evaluated with propidium iodide staining 24 h after 30 min exposure to glutamate (GLU) and NMDA. NAM and MNA reduced NMDA toxicity only at 25 mM concentration, while neurotoxicity of 0.5 mM GLU was slightly diminished only by 25 mM NAM. Both compounds at 25 mM reduced GLU-induced 45Ca uptake and dose-dependently inhibited NMDA-induced 45Ca accumulation. Neither NAM nor MNA interfered with GLU-evoked intracellular calcium transients evaluated with calcium orange fluorescent probe or inhibited [3H]MK-801 binding to rat cortical membranes. NAM and MNA failed to change GLU-evoked decrease in mitochondrial membrane potential monitored using the fluorescent dye rhodamine 123. Analysis with a hydroperoxide-sensitive fluorescent probe demonstrated significant reduction by 20 and 25 mM MNA, but not NAM, of oxidative stress in cultures after 1 h treatment with GLU. CGC accumulated radiolabelled NAM and MNA in a time and concentration dependent manner, NAM being transported more rapidly. These findings demonstrate that weak neuroprotective ability of MNA in excitotoxicity, accompanied by incomplete stabilization of calcium imbalance and lessening of oxidative stress, is not connected with direct inhibition of NMDA receptors. The exact mechanisms of these effects require further investigation.     

Randomized controlled trial of memantine in dementia associated with Parkinson's disease

The objective of this study is to investigate the safety and tolerability of memantine, a glutamatergic modulator, in patients suffering from dementia associated with Parkinson's disease (PDD), an increasingly common complication of PD. This was a 22‐week trial of 25 participants with a DSM‐IV diagnosis of PDD who were randomized to either placebo or 20 mg/day of memantine. Memantine was well tolerated by participants at 20 mg/day dosing. No participant was withdrawn due to memantine‐related adverse events. Six weeks after drug withdrawal, a significantly greater proportion (P = 0.04) of memantine‐treated participants deteriorated globally compared with those treated with placebo. These findings suggest that continued treatment with memantine may be needed to maintain global level of functioning over time. Based on the findings of this pilot study, memantine is safe and very well‐tolerated in PDD. © 2009 Movement Disorder Society     

盐酸美金刚治疗阿尔茨海默病的疗效观察

目的 评估盐酸美金刚片(美金刚)治疗中、重度(MMSE<20)阿尔茨海默病(Alzheimer's disease,AD)的临床疗效和安全性.方法 30例经GDS评分3~6分的可能或很可能中、重度AD 患者接受美金刚治疗20周,每周随访1次,评估采用简易智能状态检查量表(MMSE)、Blessed-Roth 量表和全面衰退量表(GDS).结果 自身前后比较差别有统计学意义,不良反应率为6.7%.结论 美金刚能显著改善轻、中度AD 患者的认知功能、日常生活能力和人格情感障碍,且具有较好的安全性.     

美金胺对脑缺氧缺血新生大鼠热休克蛋白70基因表达的影响

近来报道非竞争性NMDA受体拮抗剂美金胺（Memantine)对缺氧缺血损伤（HI）具有脑保护作用。在对HI新生大鼠先行进行了HSP70基因表达的研究基础上,对新生大鼠在HI前后对照应用美金胺,通过观察HSP70基因表达的变化,进一步从分子水平评估美金胺的脑保护效果。结果,HSP70mRNA在正常情况下仅有极微弱表达,HI后可引起其表达明显增加。应用美金胺后,其HSP70基因表达虽较正常对照组增高,但显著弱于HI组,提示美金胺的应用具有一定的脑保护作用,可能减轻了HI的脑损伤,因而使作为一种敏感的脑缺氧缺血标志的HSP70基因的表达降低。数据显示美金胺在HI前应用较之HI后应用似有更明显的脑保护效果,尽管统计显示其差异无显著性意义。结合已完成的脑病理研究和病理量化评分,初步证实美金胺作为较安全有效的NMDA受体离子通道非竞争性拮抗剂,对由NMDA受体所介导的神经兴奋毒作用有一定疗效。     

Novel regimen through combination of memantine and tea polyphenol for neuroprotection against brain excitotoxicity

NMDA receptors are abundant, ubiquitously distributed throughout the brain, fundamental to excitatory neurotransmission, and critical for normal CNS function. However, excessive glutamate overstimulates NMDA receptors, leading to increased intracellular calcium and excitotoxicity. Mitochondrial dysfunction associated with loss of Ca(2+)homeostasis and enhanced cellular oxidative stress has long been recognized to play a major role in cell damage associated with excitotoxicity. In this experiment, we attempted to explore whether treatment with memantine (an NMDA receptor antagonist) and tea polyphenol (an antioxidant and anti-inflammatory agent), either alone or in combination, is effective in neuroprotection in a mouse excitotoxic injury model. Memantine (10 mg/kg/day), tea polyphenol (60 mg/kg/day), or a combination (memantine 5 mg/kg/day plus tea polyphenol 30 mg/kg/day) was administered by oral gavage for 2 consecutive days before causing excitotoxic injury. Mice received a 0.3-microL NMDA [335 mM (pH 7.2)] injection into the left striatum. Locomotor activity was assessed 24 hr before and after excitotoxic injury. Brain synaptosomes were harvested 24 hr after excitotoxic injury for assessment of Na(+), K(+)-ATPase and Mg(2+)-ATPase activity, reactive oxygen species production, mitochondrial membrane potential (Delta Psi m), mitochondrial reductase activity (MTT test), and Ca(2+)concentration. The results showed that treatment with memantine could significantly rescue mitochondrial function by attenuating the decreased mitochondrial membrane potential (Delta Psi m) and mitochondrial reductase activity in mouse excitotoxic injury. Treatment with tea polyphenol could significantly decrease the increased production of synaptosomal reactive oxygen species (ROS) and thus reduced the deteriorative ROS-sensitive Na(+), K(+)-ATPase and Mg(2+)-ATPase activity. However, neither memantine nor tea polyphenol alone could significantly improve the impaired locomotor activity unless treatment was combined. Combined treatment with memantine and tea polyphenol could significantly protect mice against excitotoxic injury by reducing the increased synaptosomal ROS production, attenuating the decreased Na(+), K(+)-ATPase and Mg(2+)-ATPase activity, the mitochondrial membrane potential (Delta Psi m), the mitochondrial reductase activity, and the increased synaptosomal Ca(2+)concentration. In addition, the impairment in locomotor activity was also significantly improved. Therefore, the combined treatment of memantine and tea polyphenol is more effective in neuroprotection than either memantine or tea polyphenol alone in mouse excitotoxic injury. These findings provide useful information about the potential application of memantine and tea polyphenols in preventing clinical excitotoxic injury such as brain trauma, brain ischemia, epilepsy, and Alzheimer's disease.     

Effect of memantine on CBF and CMRO2 in patients with early Parkinson's disease

Objectives –  Parkinson's disease (PD) may be associated with increased energy metabolism in overactive regions of the basal ganglia. Therefore, we hypothesized that treatment with the N -methyl- d -aspartate receptor (NMDAR) antagonist memantine would decrease regional cerebral blood flow (rCBF) and oxygen metabolism in the basal ganglia of patients with early-stage PD.
Methods –  Quantitative positron emission tomography (PET) recordings were obtained with [¹⁵O]water and [¹⁵O]oxygen in 10 patients, scanned first in a baseline condition, and again 6 weeks after treatment with a daily dose of 20 mg memantine. Dynamic PET data were analyzed using volume of interest and voxel-based approaches.
Results –  The treatment evoked rCBF decreases in basal ganglia, and in several frontal cortical areas. The regional cerebral metabolic rate of oxygen (rCMRO₂) did not decrease in any of the a priori defined regions, and consequently the oxygen extraction fraction was increased in these regions. Two peaks of significantly decreased rCMRO₂ were detected near the frontal poles in both hemispheres, using a posteriori voxel-based analysis.
Conclusions –  Although we did not find the predicted decrease in basal ganglia oxygen consumption, our data suggest that treatment with memantine actively modulates neuronal activity and/or hemodynamic response in basal ganglia of PD patients. This finding may be relevant to the putative neuroprotective properties of NMDAR antagonists.     

A double-blind, placebo-controlled trial of memantine in age-associated memory impairment (memantine in AAMI)

OBJECTIVES: To determine the safety and efficacy of memantine in treating Age-Associated Memory Impairment (AAMI). METHODS: Sixty adults between 50-79 years of age meeting diagnostic requirements for AAMI were randomly assigned to either memantine (titrated to 20 mg) or a matched placebo and treated for 90 days. An extensive battery of computerized cognitive tests was administered at screening, baseline and, thereafter, at monthly intervals. RESULTS AND CONCLUSION: Study results suggest that the primary cognitive effects of memantine in this population are on attention and information processing speed, rather than on memory. There were no differences in adverse events between memantine and placebo.     

Cellular origin and regulation of D- and L-serine in in vitro and in vivo models of cerebral ischemia

D-Serine is known to be essential for the activation of the N-methyl-D-aspartate (NMDA) receptor in the excitation of glutamatergic neurons, which have critical roles in long-term potentiation and memory formation. D-Serine is also thought to be involved in NMDA receptor-mediated neurotoxicity. The deletion of serine racemase (SRR), which synthesizes D-serine from L-serine, was recently reported to improve ischemic damage in mouse middle cerebral artery occlusion model. However, the cell type in which this phenomenon originates and the regulatory mechanism for D-/L-serine remain elusive. The D-/L-serine content in ischemic brain increased until 20 hours after recanalization and then leveled off gradually. The results of in vitro experiments using cultured cells suggested that D-serine is derived from neurons, while L-serine seems to be released from astroglia. Immunohistochemistry studies of brain tissue after cerebral ischemia showed that SRR is expressed in neurons, and 3-phosphoglycerate dehydrogenase (3-PGDH), which synthesizes L-serine from 3-phosphoglycerate, is located in astrocytes, supporting the results of the in vitro experiments. A western blot analysis showed that neither SRR nor 3-PGDH was upregulated after cerebral ischemia. Therefore, the increase in D-/L-serine was not related to an increase in SRR or 3-PGDH, but to an increase in the substrates of SRR and 3-PGDH.     

Self-induced accumulation of glutamate in striatal astrocytes and basal ganglia excitotoxicity

Excitotoxicity induced by high levels of extracellular glutamate (GLU) has been proposed as a cause of cell degeneration in basal ganglia disorders. This phenomenon is normally prevented by the astrocytic GLU‐uptake and the GLU‐catabolization to less dangerous molecules. However, high‐GLU can induce reactive gliosis which could change the neuroprotective role of astrocytes. The striatal astrocyte response to high GLU was studied here in an in vivo rat preparation. The transient striatal perfusion of GLU (1 h) by reverse microdialysis induced complex reactive gliosis which persisted for weeks and which was different for radial‐like glia, protoplasmic astrocytes and fibrous astrocytes. This gliosis was accompanied by a persistent cytosolic accumulation of GLU (immunofluorescence quantified by confocal microscope), which persisted for weeks (self‐induced glutamate accumulation), and which was associated to a selective decrease of glutamine synthetase activity. This massive and persistent self‐induced glutamate accumulation in striatal astrocytes could be an additional factor for the GLU‐induced excitotoxicity, which has been implicated in the progression of different basal ganglia disorders. © 2012 Wiley Periodicals, Inc.     

Effects of memantine on behavioural symptoms in Alzheimer's disease patients: an analysis of the Neuropsychiatric Inventory (NPI) data of two randomised, controlled studies

INTRODUCTION: Behavioural symptoms are common in moderate to severe Alzheimer's disease (AD). We have analysed the databases of two randomised studies with regard to the effects of memantine treatment on behavioural symptoms, measured using the 12-item version of the Neuropsychiatric Inventory (NPI). SUBJECTS: The monotherapy study (memantine only) reported by Reisberg et al. (2003) involved 252 patients with baseline MMSE total score of between 3 and 14, whereas the combination study (memantine and donepezil) reported by Tariot et al. (2004) comprised 404 patients with MMSE scores of between 5 and 14. In both studies, patients received 10 mg memantine b.i.d. or matching placebo, and lived in the community. METHODS: For both studies NPI total and individual domains scores were analysed in the ITT population. For the monotherapy study a dichotomised analysis was performed separately for patients who had behavioural symptoms at baseline and for those without pre-existing symptoms. Furthermore, a factor analysis was used to identify any behavioural clusters within the patient population. RESULTS: In both studies, the change in NPI total scores at endpoint was consistently in favour of memantine treatment, reaching statistical significance in the combination study (p = 0.002). Memantine treatment showed a significant beneficial effect in comparison to placebo treatment in the NPI agitation/aggression domain in both studies (p = 0.008; p = 0.001).The dichotomised analysis of the monotherapy study showed that there was significantly less agitation/aggression emerging in the memantine-treated group compared to placebo (p = 0.003). Factor analysis showed that hyperactivity accounted for 27% of the data variance. CONCLUSIONS: Memantine has a beneficial effect on the behavioural symptoms of patients with moderate to severe AD, with the most pronounced effect on agitation/aggression.     

Tachykinins and excitotoxicity in cerebellar granule cells

The tachykinins represent an important group of neuropeptides that are widely distributed both in the central and peripheral nervous system where they perform several functions connected with neuronal modulation, often in synergy with glutamate excitatory transmission. While a great deal of data is available on their distribution and many studies have been performed by molecular, biochemical, and immunohistochemical techniques, much less is known about their physiological role, in particular in the cerebellum. This review is an attempt to summarize the diverse evidence suggesting a role for tachykinins in cerebellar granule neurons.     

氯氮平联合美金刚治疗精神分裂症阴性症状对照研究

目的:探讨氯氮平联合美金刚治疗精神分裂症阴性症状的疗效及安全性. 方法:将64例以阴性症状为主的慢性精神分裂症患者随机分成两组,每组32例,两组在服用原有抗精神病药(氯氮平)的基础上,研究组联合美金刚治疗,对照组联合安慰剂治疗,观察12周.于治疗前、治疗8周及12周采用阳性与阴性症状量表(PANSS)、阴性症状量表(SANS)评定临床疗效. 结果:治疗8周及12周时研究组和对照组PANSS总分、阴性因子分及SANS总分较治疗前显著下降(P＜0.05或P＜0.01)),研究组较对照组下降更为显著(P＜0.05或P＜0.01). 结论:氯氮平联合美金刚治疗与单用氯氮平相比,可显著缓解精神分裂症患者的阴性症状.     

beta-Amyloid neurotoxicity is exacerbated during glycolysis inhibition and mitochondrial impairment in the rat hippocampus in vivo and in isolated nerve terminals: implications for Alzheimer's disease

Senile plaques composed mainly by beta-amyloid (Abeta) protein are one of the pathological hallmarks of Alzheimer's disease (AD). In vitro, Abeta and its active fragment 25-35 have been shown either to be directly neurotoxic or to exacerbate the damaging effect of other neurotoxic insults. However, the attempts to replicate Abeta neurotoxicity in vivo have yielded conflicting results. One of the most consistent alterations in AD is a reduced resting glucose utilization. Important evidence suggests that impairment of brain energy metabolism can lead to neuronal damage or facilitate the deleterious effects of some neurotoxic agents. In the present study we have investigated the influence of glycolysis inhibition induced by iodoacetate, and mitochondrial impairment induced by 3-nitropropionic acid (3-NP), in the toxicity of Abeta. We have studied Abeta neurotoxicity during energy deficiency both in vivo in the dentate gyrus of the hippocampal formation and in presynaptic terminals isolated from neocortex and hippocampus. Results show that during metabolic inhibition an enhanced vulnerability of hippocampal neurons to Abeta peptide toxicity occurs, probably resulting from decreased glucose metabolism and mitochondrial ATP production. Synaptosomal response to energy impairment and Abeta toxicity was evaluated by the MTT assay. Results suggest that synapses may be particularly sensitive to metabolic perturbation, which in turn exacerbates Abeta toxicity. The present data provide experimental support to the hypothesis that certain risk factors such as metabolic dysfunction and amyloid accumulation may interact to exacerbate AD, and that metabolic substrates such as pyruvate may play a role as a therapeutic tool.     

NGF-PBCA-NP的制备与性能评价及其对体外AD细胞模型的保护作用

目的 制备神经生长因子-聚氰基丙烯酸丁酯纳米粒(NGF-PBCA-NP)并评价其性能,检测其对Aβ1-40诱导的大鼠肾上腺嗜铬细胞瘤细胞(PC12细胞)增殖抑制和细胞凋亡的作用. 方法 采用乳化聚合法制备NGF-PBCA-NP,透射电镜观察形态,紫外分光光度法检测包封率和载药量.PC12细胞用10μg/mL的Aβ1-40处理,制备体外AD细胞模型后,用NGF (NGF对照组)和NGF-PBCA-NP(NGF-PBCA-NP组)分别作用于细胞,MTT法检测细胞增殖率,流式细胞术检测细胞凋亡率. 结果 NGF-PBCA-NP呈圆球形,包封率为80.87％,载药量为19.88％.与NGF对照组相比,NGF-PBCA-NP组细胞增殖抑制程度减轻,细胞凋亡率下降,差异有统计学意义(P＜0.05).其中50 μg/L NGF-PBCA-NP处理后细胞增殖比达峰值. 结论 乳化聚合法制备的NGF-PBCA-NP,形态一致,包封率和载药量较高,性能稳定,在体外具有一定的神经细胞保护和修复作用.