Alzheimer's disease, β-amyloid, glutamate, NMDA receptors and memantine--searching for the connections

Nanostructured Antagonist of Extrasynaptic NMDA Receptors

Glutamatergic cytotoxicity mediated by overactivation of N-methyl-d-aspartate receptors (NMDARs) is implicated in numerous neurological disorders. To be therapeutically viable, NMDAR antagonists must preserve physiological role of synaptic NMDARs (sNMDARs) in synaptic transmission and block only excessive pathological activation of NMDARs. Here we present a novel NMDAR antagonist that satisfies this two-fold requirement by exploiting spatial differences in NMDAR subcellular locations. Specifically, we designed a hybrid nanodrug (AuM) to be larger than the synaptic cleft by attaching memantine, NMDAR antagonist, via polymer linkers to a gold nanoparticle. We show that AuM efficiently and selectively inhibited extrasynaptic NMDARs (eNMDARs), while having no effect on sNMDARs and synaptic transmission. AuM exhibited neuroprotective properties both in vitro and ex vivo during such neurotoxic insults as NMDAR-mediated cytotoxicity in cerebrocortical cell culture and oxygen-glucose deprivation in acute hippocampal slices. Furthermore, AuM prevented dendritic spine loss triggered by Aβ oligomers in organotypic hippocampal slices and was more effective than free memantine. Using a novel rational design strategy, we demonstrate a proof of concept for a new class of neuroprotective drugs that might be beneficial for treatment of several neurological disorders.

A critical concentration of N-terminal pyroglutamylated amyloid beta drives the misfolding of Ab1-42 into more toxic aggregates

A wide consensus based on robust experimental evidence indicates pyroglutamylated amyloid-β isoform (AβpE3-42) as one of the most neurotoxic peptides involved in the onset of Alzheimer's disease. Furthermore, AβpE3-42 co-oligomerized with excess of Aβ1-42, produces oligomers and aggregates that are structurally distinct and far more cytotoxic than those made from Aβ1-42 alone. Here, we investigate quantitatively the influence of AβpE3-42 on biophysical properties and biological activity of Aβ1-42. We tested different ratios of AβpE3-42/Aβ1-42 mixtures finding a correlation between the biological activity and the structural conformation and morphology of the analyzed mixtures. We find that a mixture containing 5% AβpE3-42, induces the highest disruption of intracellular calcium homeostasis and the highest neuronal toxicity. These data correlate to an high content of relaxed antiparallel β-sheet structure and the coexistence of a population of big spheroidal aggregates together with short fibrils. Our experiments provide also evidence that AβpE3-42 causes template-induced misfolding of Aβ1-42 at ratios below 33%. This means that there exists a critical concentration required to have seeding on Aβ1-42 aggregation, above this threshold, the seed effect is not possible anymore and AβpE3-42 controls the total aggregation kinetics.

Towards understanding brain-gut-microbiome connections in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is complex, with genetic, epigenetic, and environmental factors contributing to disease susceptibility and progression. While significant progress has been made in understanding genetic, molecular, behavioral, and neurological aspects of AD, relatively little is known about which environmental factors are important in AD etiology and how they interact with genetic factors in the development of AD. Here, we propose a data-driven, hypotheses-free computational approach to characterize which and how human gut microbial metabolites, an important modifiable environmental factor, may contribute to various aspects of AD.

MATERIALS AND METHODS

We integrated vast amounts of complex and heterogeneous biomedical data, including disease genetics, chemical genetics, human microbial metabolites, protein-protein interactions, and genetic pathways. We developed a novel network-based approach to model the genetic interactions between all human microbial metabolites and genetic diseases. We identified metabolites that share significant genetic commonality with AD in humans. We developed signal prioritization algorithms to identify the co-regulated genetic pathways underlying the identified AD-metabolite (brain-gut) connections.

RESULTS

We validated our algorithms using known microbial metabolite-AD associations, namely AD-3,4-dihydroxybenzeneacetic acid, AD-mannitol, and AD-succinic acid. Our study provides supporting evidence that human gut microbial metabolites may be an important mechanistic link between environmental exposure and various aspects of AD. We identified metabolites that are significantly associated with various aspects in AD, including AD susceptibility, cognitive decline, biomarkers, age of onset, and the onset of AD. We identified common genetic pathways underlying AD biomarkers and its top one ranked metabolite trimethylamine N-oxide (TMAO), a gut microbial metabolite of dietary meat and fat. These coregulated pathways between TMAO-AD may provide insights into the mechanisms of how dietary meat and fat contribute to AD.

CONCLUSIONS

Employing an integrated computational approach, we provide intriguing and supporting evidence for a role of microbial metabolites, an important modifiable environmental factor, in AD etiology. Our study provides the foundations for subsequent hypothesis-driven biological and clinical studies of brain-gut-environment interactions in AD.

Toxicological Differences Between NMDA Receptor Antagonists and Cholinesterase Inhibitors

Cholinesterase inhibitors (ChEIs), represented by donepezil, rivastigmine, and galantamine, used to be the only approved class of drugs for the treatment of Alzheimer's disease. After the approval of memantine by the Food and Drug Administration (FDA), N-methyl-d-aspartic acid (NMDA) receptor antagonists have been recognized by authorities and broadly used in the treatment of Alzheimer's disease. Along with complementary mechanisms of action, NMDA antagonists and ChEIs differ not only in therapeutic effects but also in adverse reactions, which is an important consideration in clinical drug use. And the number of patients using NMDA antagonists and ChEIs concomitantly has increased, making the matter more complicated. Here we used the FDA Adverse Event Reporting System for statistical analysis , in order to compare the adverse events of memantine and ChEIs. In general, the clinical evidence confirmed the safety advantages of memantine over ChEIs, reiterating the precautions of clinical drug use and the future direction of antidementia drug development.

Dysfunction of NMDA receptors in Alzheimer's disease

N-methyl-D-aspartate receptors (NMDARs) play a pivotal role in the synaptic transmission and synaptic plasticity thought to underlie learning and memory. NMDARs activation has been recently implicated in Alzheimer's disease (AD) related to synaptic dysfunction. Synaptic NMDARs are neuroprotective, whereas overactivation of NMDARs located outside of the synapse cause loss of mitochondrial membrane potential and cell death. NMDARs dysfunction in the glutamatergic tripartite synapse, comprising presynaptic and postsynaptic neurons and glial cells, is directly involved in AD. This review discusses that both beta-amyloid (Aβ) and tau perturb synaptic functioning of the tripartite synapse, including alterations in glutamate release, astrocytic uptake, and receptor signaling. Particular emphasis is given to the role of NMDARs as a possible convergence point for Aβ and tau toxicity and possible reversible stages of the AD through preventive and/or disease-modifying therapeutic strategies.

Acute rosmarinic acid treatment enhances long-term potentiation, BDNF and GluR-2 protein expression, and cell survival rate against scopolamine challenge in rat organotypic hippocampal slice cultures

BACKGROUND

Rosmarinic acid (RA) is a polyphenolic ester of caffeic acid and is commonly found in the Nepetoideae subfamily of flowering mint plants. Because RA has previously exhibited antioxidant, neuroprotective, and antidepressant-like effects, we evaluated its influences on cellular functions in neuronal cultures.

OBJECTIVE

To elucidate possible mechanisms of RA, we investigated the influences of acute RA administration on long-term potentiation (LTP), plasticity-related protein expression, and scopolamine-induced cell death in organotypic hippocampal slice cultures.

METHODS

LTP analysis in organotypic hippocampal slice cultures (OHSCs) was carried out with various ion channel blockers, such as AP5 (10 μM), CNQX (10 μM), niflumic acid (100 μM), and scopolamine (300 μM) in response to RA (1, 10 or 100 μg/mL) treatment. Protein expression and cell death assays in the presence of scopolamine were examined to observe the effects of RA. For LTP analysis, baseline field excitatory postsynaptic potentials (fEPSPs) were recorded in CA1 by a 60-channel multielectrode array (MEA) every min for 40 min before 15 min of high-frequency stimulation (HFS) to the Schaffer collaterals and commissural pathways, followed by a successive 50 min of recording. For protein expression measurements, anti-BDNF and anti-GluR2 antibodies were used for Western blotting assays in whole-hippocampal tissue homogenate. Finally, for cell death assays, OHSCs were exposed to a culture medium containing propidium iodide (PI) for 24 or 48 h, followed by the assessment of cell death by fluorescent image analysis of PI uptake.

RESULTS

and discussion: Our results indicate that RA treatment enhances fEPSPs following HFS in CA1 synapses at 1 and 10 μg/ml RA, an effect that was inhibited by CNQX and NFA but not by AP5. RA treatment also increases the expression of BDNF and GluR-2 proteins and prevents cell death of scopolamine-exposed OHSCs. Our results suggest the possibility that rosmarinic acid can enhance neural plasticity by modulating glutamatergic signaling pathways, as well as providing neuroprotection with reduced cholinergic activity.

THE ROLE OF CYSTEINE PROTEASE IN ALZHEIMER DISEASE

INTRODUCTION

Cysteine protease are biological catalysts which play a pivotal role in numerous biological reactions in organism. Much of the literature is inscribed to their biochemical significance, distribution and mechanism of action. Many diseases, e.g. Alzheimer's disease, develop due to enzyme balance disruption. Understanding of cysteine protease's disbalance is therefor a key to unravel the new possibilities of treatment. Cysteine protease are one of the most important enzymes for protein disruption during programmed cell death. Whether protein disruption is part of cell deaths is not enough clear in any cases. Thereafter, any tissue disruption, including proteolysis, generate more or less inflammation appearance.

REVIEW

This review briefly summarizes the current knowledge about pathological mechanism's that results in AD, with significant reference to the role of cysteine protease in it. Based on the summary, new pharmacological approach and development of novel potent drugs with selective toxicity targeting cysteine protease will be a major challenge in years to come.

Effect of deoxyribonuclease I treatment for dementia in end-stage Alzheimer's disease: a case report

Background

Alzheimer's disease is the most common cause of dementia and is characterized by a progressive loss of brain tissue leading to amyloid-β accumulation and severe decline in cognitive function. The cause of Alzheimer’s disease is poorly understood, and available treatments are limited in their efficacy, particularly for patients with more severe symptoms.

Case presentation

We report the case of a 77-year-old Caucasian man with severe dementia and behavioral disturbance secondary to Alzheimer’s disease treated with memantine who began adjunct treatment with deoxyribonuclease I. Prior to initiation of deoxyribonuclease I treatment, our patient appeared to be in a stuporous state, with a Mini-Mental State Examination score of 3 and a Functional Assessment Staging Test score of 7. After obtaining informed consent from family members, we started administration of 120 mg of deoxyribonuclease I per day (1500 KU/mg) for treatment of severe cognitive impairment.

Conclusions

Our patient began to demonstrate rapid, considerable improvement in cognitive function 2 days following initiation of deoxyribonuclease I treatment. After 2 months of continued treatment, Mini-Mental State Examination and Functional Assessment Staging Test scores were 18 and 4, respectively.

Peripheral cytokines, C-X-C motif ligand10 and interleukin-13, are associated with Malaysian Alzheimer's disease

AIM

Cytokines released from chronically-activated microglia could result in neuroinflammation. An accurate profile of the relationship between cytokines and Alzheimer's disease (AD) pathogenesis, as well as the patterns of these inflammatory mediators in AD patients could lead to the identification of peripheral markers for the disease. The present study was undertaken to identify pro- and anti-inflammatory cytokines associated with AD in the Malaysian population.

METHODS

Further to informed consent from 39 healthy subjects and 39 probable AD patients, 8.5 mL of peripheral blood was collected and serum was extracted. The differential levels of 12 serum cytokines extracted from peripheral blood samples were measured using Procarta Multiplex Cytokine and enzyme-linked immunoassay kits. Concentrations of cytokines were measured at 615 nm using a fluorometer.

RESULTS

Except for tumor necrosis factor-α, all classical pro-inflammatory cytokines (interleukin [IL]-1β, IL-6, IL-12 and interferon-γ) were found to be significantly upregulated (P < 0.001) in AD patients. Three of the five non-classical pro-inflammatory cytokines (C-X-C motif ligand 10 [CXCL-10], monocyte chemoattractant protein-1 and macrophage inflammatory protein-1α) showed similar patterns. Both classical IL-10 and non-classical IL-13 anti-inflammatory cytokines were significantly downregulated (P < 0.001) in AD patients when compared with non-AD controls. Receiver operating characteristic curve analyses for both CXCL-10 (IP-10) and IL-13 showed a high level of diagnostic accuracy (area under curve = 1 [95% confidence interval]). Both CXCL-10 and IL-13 also showed sensitivity of 100% and specificity of 100% for diagnosis of AD (cut-off values >53.65 ρg/mL and <9.315 ρg/mL, respectively).

CONCLUSIONS

Both the non-classical pro-inflammatory CXCL-10 and anti-inflammatory IL-13 cytokines showed promising potential as blood-based cytokine biomarkers for AD. This is the first study of non-classical cytokine profiles of Malaysian AD patients. Geriatr Gerontol Int 2017; 17: 839-846.

Parishin C's prevention of Aβ 1-42-induced inhibition of long-term potentiation is related to NMDA receptors

The rhizome of Gastrodia elata (GE), a herb medicine, has been used for treatment of neuronal disorders in Eastern Asia for hundreds of years. Parishin C is a major ingredient of GE. In this study, the i.c.v. injection of soluble Aβ_1–42 oligomers model of LTP injury was used. We investigated the effects of parishin C on the improvement of LTP in soluble Aβ_1–42 oligomer–injected rats and the underlying electrophysiological mechanisms. Parishin C (i.p. or i.c.v.) significantly ameliorated LTP impairment induced by i.c.v. injection of soluble Aβ_1–42 oligomers. In cultured hippocampal neurons, soluble Aβ_1–42 oligomers significantly inhibited NMDAR currents while not affecting AMPAR currents and voltage-dependent currents. Pretreatment with parishin C protected NMDA receptor currents from the damage induced by Aβ. In summary, parishin C improved LTP deficits induced by soluble Aβ_1–42 oligomers. The protection by parishin C against Aβ-induced LTP damage might be related to NMDA receptors.

Exploring neuroprotective potential of Withania somnifera phytochemicals by inhibition of GluN2B-containing NMDA receptors: An in silico study

N-methyl-d-aspartate receptors (NMDARs) mediated excitotoxicity has been implicated in multi-neurodegenerative diseases. Due to lack of efficacy and adverse effects of NMDA receptor antagonists, search for herbal remedies that may act as therapeutic agents is an active area of research to combat these diseases. Withania somnifera (WS) is being used for centuries as a nerve tonic and Nootropic agents. The present study targets the in silico evaluation of the neuroprotective efficacy of W. somnifera phytochemicals by inhibition of NMDA receptor-mediated excitotoxicity through allosteric inhibition of the GluN2B containing NMDARs. We predict Blood Brain Barrier (BBB) penetration, mutagenicity, drug-likeness and Human Intestinal Absorption properties of 25 WS phytochemicals. Further, molecular docking was performed to know whether these phytochemicals inhibit the GluN2B containing NMDARs or not. The results suggest that Anaferine, Beta-Sitosterol, Withaferin A, Withanolide A, Withanolide B and Withanolide D inhibit GluN2B containing NMDARs through allosteric mode similar to the well-known selective antagonist Ifenprodil. These phytochemicals have potential as an essentially useful oral drug to counter NMDARs mediated excitotoxicity and to treat multi-neurodegenerative diseases.

Efficacy of memantine on neuropsychiatric symptoms associated with the severity of behavioral variant frontotemporal dementia: A six-month, open-label, self-controlled clinical trial

Previous studies have focused on the curative effects of memantine in patients with mild-to-moderate frontotemporal lobar degeneration (FTLD); however, its benefits in patients with moderate-to-severe FTLD have not been investigated. The present study explores the behavioral, cognitive and functional effects of memantine on behavioral variant frontotemporal dementia (bvFTD) in patients with mild and moderate-to-severe stage bvFTD. A total of 42 patients with bvFTD completed a 6-month treatment plan of 20 mg memantine daily in an open-label, self-controlled clinical trial. Patients were divided into two groups according to their Mini-Mental State Examination (MMSE) score: Mild (score, 21-26); and moderate-to-severe (score, 4-20). Primary endpoints included Neuropsychiatric Inventory Questionnaire (NPI-Q) and Clinic Dementia Rating (CDR) scores, and secondary endpoints comprised Neuropsychiatric Inventory Caregiver Distress Scale (NPI-D), MMSE, Montreal Cognitive Assessment (MoCA), Activity of Daily Life (ADL) and Hamilton Depression Rating Scale (HAMD) scores. Memantine treatment had no effect on overall NPI-Q scores, with the exception of the agitation subdomain in all patients with bvFTD. However, patients with moderate-to-severe bvFTD exhibited a better performance than patients with mild bvFTD, demonstrated by improved NPI-Q total scores and subscales of agitation, depression, apathy and disinhibition. In the moderate-to-severe group, CDR and HAMD scores remained stable, but MMSE, MoCA and ADL scores were reduced after 6 months of treatment. Memantine was well-tolerated in patients. In conclusion, patients with moderate-to-severe bvFTD responded significantly better to memantine in comparison to patients with mild bvFTD with regard to their neuropsychiatric scores, while memantine did not present any cognitive or functional benefits in patients with mild bvFTD. A randomized, double-blind, placebo-controlled clinical trial with a larger number of patients is required to verify these promising results for patients with moderate-to-severe bvFTD.

Zn(2+) at a cellular crossroads

Zinc is an essential micronutrient for cellular homeostasis. Initially proposed to only contribute to cellular viability through structural roles and non-redox catalysis, advances in quantifying changes in nM and pM quantities of Zn(2+) have elucidated increasing functions as an important signaling molecule. This includes Zn(2+)-mediated regulation of transcription factors and subsequent protein expression, storage and release of intracellular compartments of zinc quanta into the extracellular space which modulates plasma membrane protein function, as well as intracellular signaling pathways which contribute to the immune response. This review highlights some recent advances in our understanding of zinc signaling.

Preliminary evidence of altered steroidogenesis in women with Alzheimer's disease: Have the patients "OLDER" adrenal zona reticularis?

Alzheimer's disease (AD) represents more than half of total dementias. Various factors including altered steroid biosynthesis may participate in its pathophysiology. We investigated how the circulating steroids (measured by GC-MS and RIA) may be altered in the presence of AD. Sixteen women with AD and 22 age- and BMI-corresponding controls aged over 65 years were enrolled in the study. The steroid levels (47 steroids and steroid polar conjugates) and their ratios in AD female patients indicated increased CYP11A1 activity, weakened activity of the CYP17A1C17,20 lyase metabolic step and attenuated sulfotransferase SULT2A1 activity at higher activity of the CYP17A1 17-hydroxylase step. The patients showed diminished HSD3B2 activity for C21 steroids, abated conversion of 17-hydroxyprogesterone to cortisol, and significantly elevated cortisol. The women with AD had also attenuated steroid 7α-hydroxylation forming immunoprotective Δ(5)-C19 steroids, attenuated aromatase activity forming estradiol that induces autoimmunity and a shift from the 3β-hydroxy-5α/β-reduced C19 steroids to their neuroinhibitory and antiinflammatory GABAergic 3α-hydroxy- counterparts and showed higher levels of the 3α-hydroxy-5α/β-reduced C21 steroids and pregnenolone sulfate (improves cognitive abilities but may be both protective and excitotoxic). Our preliminary data indicated functioning of alternative "backdoor" pathway in women with AD showing higher levels of both 5α/β-reduced C21 steroids but reduced levels of both 5α/β-reduced C21 steroids, which implied that the alternative "backdoor" pathway might include both 5α- and 5β-reduced steroids. Our study suggested relationships between AD status in women based on the age of subjects and levels of 10 steroids measured by GC-MS.

Signaling pathways and posttranslational modifications of tau in Alzheimer's disease: the humanization of yeast cells

In the past decade, yeast have been frequently employed to study the molecular mechanisms of human neurodegenerative diseases, generally by means of heterologous expression of genes encoding the relevant hallmark proteins. However, it has become evident that substantial posttranslational modifications of many of these proteins are required for the development and progression of potentially disease relevant changes. This is exemplified by the neuronal tau proteins, which are critically involved in a class of neuro-degenerative diseases collectively called tauopathies and which includes Alz-heimer's disease (AD) as its most common representative. In the course of the disease, tau changes its phosphorylation state and becomes hyperphosphory-lated, gets truncated by proteolytic cleavage, is subject to O-glycosylation, sumoylation, ubiquitinylation, acetylation and some other modifications. This poses the important question, which of these posttranslational modifications are naturally occurring in the yeast model or can be reconstituted by heterol-ogous gene expression. Here, we present an overview on common modifica-tions as they occur in tau during AD, summarize their potential relevance with respect to disease mechanisms and refer to the native yeast enzyme orthologs capable to perform these modifications. We will also discuss potential approaches to humanize yeast in order to create modification patterns resembling the situation in mammalian cells, which could enhance the value of Saccharomyces cerevisiae and Kluyveromyces lactis as disease models.

Signaling pathways and posttranslational modifications of tau in Alzheimer's disease: the humanization of yeast cells

In the past decade, yeast have been frequently employed to study the molecular mechanisms of human neurodegenerative diseases, generally by means of heterologous expression of genes encoding the relevant hallmark proteins. However, it has become evident that substantial posttranslational modifications of many of these proteins are required for the development and progression of potentially disease relevant changes. This is exemplified by the neuronal tau proteins, which are critically involved in a class of neuro-degenerative diseases collectively called tauopathies and which includes Alz-heimer's disease (AD) as its most common representative. In the course of the disease, tau changes its phosphorylation state and becomes hyperphosphory-lated, gets truncated by proteolytic cleavage, is subject to O-glycosylation, sumoylation, ubiquitinylation, acetylation and some other modifications. This poses the important question, which of these posttranslational modifications are naturally occurring in the yeast model or can be reconstituted by heterol-ogous gene expression. Here, we present an overview on common modifica-tions as they occur in tau during AD, summarize their potential relevance with respect to disease mechanisms and refer to the native yeast enzyme orthologs capable to perform these modifications. We will also discuss potential approaches to humanize yeast in order to create modification patterns resembling the situation in mammalian cells, which could enhance the value of Saccharomyces cerevisiae and Kluyveromyces lactis as disease models.

An overview on therapeutics attenuating amyloid β level in Alzheimer's disease: targeting neurotransmission, inflammation, oxidative stress and enhanced cholesterol levels

Alzheimer's disease (AD) is the most common underlying cause of dementia, and novel drugs for its treatment are needed. Of the different theories explaining the development and progression of AD, "amyloid hypothesis" is the most supported by experimental data. This hypothesis states that the cleavage of amyloid precursor protein (APP) leads to the formation of amyloid beta (Aβ) peptides that congregate with formation and deposition of Aβ plaques in the frontal cortex and hippocampus. Risk factors including neurotransmitter modulation, chronic inflammation, metal-induced oxidative stress and elevated cholesterol levels are key contributors to the disease progress. Current therapeutic strategies abating AD progression are primarily based on anti-acetylcholinesterase (AChE) inhibitors as cognitive enhancers. The AChE inhibitor, donepezil, is proven to strengthen cognitive functions and appears effective in treating moderate to severe AD patients. N-Methyl-D-aspartate receptor antagonist, memantine, is also useful, and its combination with donepezil demonstrated a strong stabilizing effect in clinical studies on AD. Nonsteroidal anti-inflammatory drugs delayed the onset and progression of AD and attenuated cognitive dysfunction. Based upon epidemiological evidence and animal studies, antioxidants emerged as potential AD preventive agents; however, clinical trials revealed inconsistencies. Pharmacokinetic and pharmacodynamic profiling demonstrated pleiotropic functions of the hypolipidemic class of drugs, statins, potentially contributing towards the prevention of AD. In addition, targeting the APP processing pathways, stimulating neuroprotective signaling mechanisms, using the amyloid anti-aggregants and Aβ immunotherapy surfaced as well-tested strategies in reducing the AD-like pathology. Overall, this review covers mechanism of inducing the Aβ formation, key risk factors and major therapeutics prevalent in the AD treatment nowadays. It also delineates the need for novel screening approaches towards identifying drugs that may prevent or at least limit the progression of this devastating disease.

An integrative genome-wide transcriptome reveals that candesartan is neuroprotective and a candidate therapeutic for Alzheimer's disease

BACKGROUND

Alzheimer's disease is the most frequent age-related dementia, and is currently without treatment. To identify possible targets for early therapeutic intervention we focused on glutamate excitotoxicity, a major early pathogenic factor, and the effects of candesartan, an angiotensin receptor blocker of neuroprotective efficacy in cell cultures and rodent models of Alzheimer's disease. The overall goal of the study was to determine whether gene analysis of drug effects in a primary neuronal culture correlate with alterations in gene expression in Alzheimer's disease, thus providing further preclinical evidence of beneficial therapeutic effects.

METHODS

Primary neuronal cultures were treated with candesartan at neuroprotective concentrations followed by excitotoxic glutamate amounts. We performed genome-wide expression profile analysis and data evaluation by ingenuity pathway analysis and gene set enrichment analysis, compared with alterations in gene expression from two independent published datasets identified by microarray analysis of postmortem hippocampus from Alzheimer's disease patients. Preferential expression in cerebrovascular endothelial cells or neurons was analyzed by comparison to published gene expression in these cells isolated from human cortex by laser capture microdissection.

RESULTS

Candesartan prevented glutamate upregulation or downregulation of several hundred genes in our cultures. Ingenuity pathway analysis and gene set enrichment analysis revealed that inflammation, cardiovascular disease and diabetes signal transduction pathways and amyloid β metabolism were major components of the neuronal response to glutamate excitotoxicity. Further analysis showed associations of glutamate-induced changes in the expression of several hundred genes, normalized by candesartan, with similar alterations observed in hippocampus from Alzheimer's disease patients. Gene analysis of neurons and cerebrovascular endothelial cells obtained by laser capture microdissection revealed that genes up- and downregulated by glutamate were preferentially expressed in endothelial cells and neurons, respectively.

CONCLUSIONS

Our data may be interpreted as evidence of direct candesartan neuroprotection beyond its effects on blood pressure, revealing common and novel disease mechanisms that may underlie the in vitro gene alterations reported here and glutamate-induced cell injury in Alzheimer's disease. Our observations provide novel evidence for candesartan neuroprotection through early molecular mechanisms of injury in Alzheimer's disease, supporting testing this compound in controlled clinical studies in the early stages of the illness.

Neuroprotection of medial septal cholinergic neurons by memantine after intralateral septal injection of Aβ1-40

Alzheimer's disease (AD) is a progressive disorder of the brain that leads to memory loss, dementia, and death. Several lines of evidence suggest that the accumulation of amyloid-β (Aβ) peptides may trigger the dysfunction and degeneration observed in the AD brain. The basal forebrain, including the septal region, which regulates the excitability of the hippocampus and neocortex, is affected early in AD because its neurons are vulnerable to Aβ peptides. In addition, connections between lateral and medial septal regions (medial septum and diagonal band of Broca) have been demonstrated in previous studies. To demonstrate the involvement of excitotoxicity in Aβ-induced septal damage, we compared rats injected with Aβ1-40 into the lateral septal region structure with rats treated with memantine (a noncompetitive NMDA receptor antagonist), before, during, and after Aβ1-40 injection. Medial septal cholinergic neurons were immunochemically identified and their numbers were estimated using Image J cell count. Our results show that Aβ1-40-treated animals have a significantly low number of medial septum and diagonal band of Broca cholinergic neurons compared with the Aβ/memantine-treated group.

Altered Cortical Synaptic Plasticity in Response to 5-Hz Repetitive Transcranial Magnetic Stimulation as a New Electrophysiological Finding in Amnestic Mild Cognitive Impairment Converting to Alzheimer's Disease: Results from a 4-year Prospective Cohort Study

INTRODUCTION

To investigate cortical excitability and synaptic plasticity in amnestic mild cognitive impairment (aMCI) using 5 Hz repetitive transcranial magnetic stimulation (5 Hz-rTMS) and to assess whether specific TMS parameters predict conversion time to Alzheimer's disease (AD).

MATERIALS AND METHODS

Forty aMCI patients (single- and multi-domain) and 20 healthy controls underwent, at baseline, a neuropsychological examination and 5 Hz-rTMS delivered in trains of 10 stimuli and 120% of resting motor threshold (rMT) intensity over the dominant motor area. The rMT and the ratio between amplitude of the 1st and the 10th motor-evoked potential elicited by the train (X/I-MEP ratio) were calculated as measures of cortical excitability and synaptic plasticity, respectively. Patients were followed up annually over a period of 48 months. Analysis of variance for repeated measures was used to compare TMS parameters in patients with those in controls. Spearman's correlation was performed by considering demographic variables, aMCI subtype, neuropsychological test scores, TMS parameters, and conversion time.

RESULTS

Thirty-five aMCI subjects completed the study; 60% of these converted to AD. The baseline rMT and X/I-MEP ratio were significantly lower in patients than in controls (p = 0.04 and p = 0.01). Spearman's analysis showed that conversion time correlated with the rMT (0.40) and X/I-MEP ratio (0.51).

DISCUSSION

aMCI patients displayed cortical hyperexcitability and altered synaptic plasticity to 5 Hz-rTMS when compared with healthy subjects. The extent of these changes correlated with conversion time. These alterations, which have previously been observed in AD, are thus present in the early stages of disease and may be considered as potential neurophysiological markers of conversion from aMCI to AD.

A Mutation in DAOA Modifies the Age of Onset in PSEN1 E280A Alzheimer's Disease

We previously reported age of onset (AOO) modifier genes in the world's largest pedigree segregating early-onset Alzheimer's disease (AD), caused by the p.Glu280Ala (E280A) mutation in the PSEN1 gene. Here we report the results of a targeted analysis of functional exonic variants in those AOO modifier genes in sixty individuals with PSEN1 E280A AD who were whole-exome genotyped for ~250,000 variants. Standard quality control, filtering, and annotation for functional variants were applied, and common functional variants located in those previously reported as AOO modifier loci were selected. Multiloci linear mixed-effects models were used to test the association between these variants and AOO. An exonic missense mutation in the G72 (DAOA) gene (rs2391191, P = 1.94 × 10⁻⁴, P_FDR = 9.34 × 10⁻³) was found to modify AOO in PSEN1 E280A AD. Nominal associations of missense mutations in the CLUAP1 (rs9790, P = 7.63 × 10⁻³, P_FDR = 0.1832) and EXOC2 (rs17136239, P = 0.0325, P_FDR = 0.391) genes were also found. Previous studies have linked polymorphisms in the DAOA gene with the occurrence of neuropsychiatric symptoms such as depression, apathy, aggression, delusions, hallucinations, and psychosis in AD. Our findings strongly suggest that this new conspicuous functional AOO modifier within the G72 (DAOA) gene could be pivotal for understanding the genetic basis of AD.

Endogenous 24S-hydroxycholesterol modulates NMDAR-mediated function in hippocampal slices

N-methyl-D-aspartate receptors (NMDARs), a major subtype of glutamate receptors mediating excitatory transmission throughout the central nervous system (CNS), play critical roles in governing brain function and cognition. Because NMDAR dysfunction contributes to the etiology of neurological and psychiatric disorders including stroke and schizophrenia, NMDAR modulators are potential drug candidates. Our group recently demonstrated that the major brain cholesterol metabolite, 24S-hydroxycholesterol (24S-HC), positively modulates NMDARs when exogenously administered. Here, we studied whether endogenous 24S-HC regulates NMDAR activity in hippocampal slices. In CYP46A1(-/-) (knockout; KO) slices where endogenous 24S-HC is greatly reduced, NMDAR tone, measured as NMDAR-to-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) excitatory postsynaptic current (EPSC) ratio, was reduced. This difference translated into more NMDAR-driven spiking in wild-type (WT) slices compared with KO slices. Application of SGE-301, a 24S-HC analog, had comparable potentiating effects on NMDAR EPSCs in both WT and KO slices, suggesting that endogenous 24S-HC does not saturate its NMDAR modulatory site in ex vivo slices. KO slices did not differ from WT slices in either spontaneous neurotransmission or in neuronal intrinsic excitability, and exhibited LTP indistinguishable from WT slices. However, KO slices exhibited higher resistance to persistent NMDAR-dependent depression of synaptic transmission induced by oxygen-glucose deprivation (OGD), an effect restored by SGE-301. Together, our results suggest that loss of positive NMDAR tone does not elicit compensatory changes in excitability or transmission, but it protects transmission against NMDAR-mediated dysfunction. We expect that manipulating this endogenous NMDAR modulator may offer new treatment strategies for neuropsychiatric dysfunction.

Hypoxia and GABA shunt activation in the pathogenesis of Alzheimer's disease

We have previously observed that the conversion of mild cognitive impairment to definitive Alzheimer's disease (AD) is associated with a significant increase in the serum level of 2,4-dihydroxybutyrate (2,4-DHBA). The metabolic generation of 2,4-DHBA is linked to the activation of the γ-aminobutyric acid (GABA) shunt, an alternative energy production pathway activated during cellular stress, when the function of Krebs cycle is compromised. The GABA shunt can be triggered by local hypoperfusion and subsequent hypoxia in AD brains caused by cerebral amyloid angiopathy. Succinic semialdehyde dehydrogenase (SSADH) is a key enzyme in the GABA shunt, converting succinic semialdehyde (SSA) into succinate, a Krebs cycle intermediate. A deficiency of SSADH activity stimulates the conversion of SSA into γ-hydroxybutyrate (GHB), an alternative route from the GABA shunt. GHB can exert not only acute neuroprotective activities but unfortunately also chronic detrimental effects which may lead to cognitive impairment. Subsequently, GHB can be metabolized to 2,4-DHBA and secreted from the brain. Thus, the activation of the GABA shunt and the generation of GHB and 2,4-DHBA can have an important role in the early phase of AD pathogenesis.

Hippocampal plasticity during the progression of Alzheimer's disease

Neuroplasticity involves molecular and structural changes in central nervous system (CNS) throughout life. The concept of neural organization allows for remodeling as a compensatory mechanism to the early pathobiology of Alzheimer's disease (AD) in an attempt to maintain brain function and cognition during the onset of dementia. The hippocampus, a crucial component of the medial temporal lobe memory circuit, is affected early in AD and displays synaptic and intraneuronal molecular remodeling against a pathological background of extracellular amyloid-beta (Aβ) deposition and intracellular neurofibrillary tangle (NFT) formation in the early stages of AD. Here we discuss human clinical pathological findings supporting the concept that the hippocampus is capable of neural plasticity during mild cognitive impairment (MCI), a prodromal stage of AD and early stage AD.

Cerebrospinal Fluid Aβ42 Levels: When Physiological Become Pathological State

Impaired amyloid beta (Aβ) metabolism is currently considered central to understand the pathophysiology of Alzheimer's disease (AD). Measurements of cerebrospinal fluid Aβ levels remain the most useful marker for diagnostic purposes and to individuate people at risk for AD. Despite recent advances criticized the direct role in neurodegeneration of cortical neurons, Aβ is considered responsible for synaptopathy and impairment of neurotransmission and therefore remains the major trigger of AD and future pharmacological treatment remain Aβ oriented. However, experimental and clinical findings showed that Aβ peptides could have a wider range of action responsible for cell dysfunction and for appearance of clinico-pathological entities different from AD. Such findings may induce misunderstanding of the real role played by Aβ in AD and therefore strengthen criticism on its centrality and need for CSF measurements. Aim of this review is to discuss the role of CSF Aβ levels in light of experimental, clinical pathologic, and electrophysiological results in AD and other pathological entities to put in a correct frame the value of Aβ changes.

Effects and possible mechanisms of action of acacetin on the behavior and eye morphology of Drosophila models of Alzheimer's disease

The human β-amyloid (Aβ) cleaving enzyme (BACE-1) is a target for Alzheimer's disease (AD) treatments. This study was conducted to determine if acacetin extracted from the whole Agastache rugosa plant had anti-BACE-1 and behavioral activities in Drosophila melanogaster AD models and to determine acacetin's mechanism of action. Acacetin (100, 300, and 500 μM) rescued amyloid precursor protein (APP)/BACE1-expressing flies and kept them from developing both eye morphology (dark deposits, ommatidial collapse and fusion, and the absence of ommatidial bristles) and behavioral (motor abnormalities) defects. The reverse transcription polymerase chain reaction analysis revealed that acacetin reduced both the human APP and BACE-1 mRNA levels in the transgenic flies, suggesting that it plays an important role in the transcriptional regulation of human BACE-1 and APP. Western blot analysis revealed that acacetin reduced Aβ production by interfering with BACE-1 activity and APP synthesis, resulting in a decrease in the levels of the APP carboxy-terminal fragments and the APP intracellular domain. Therefore, the protective effect of acacetin on Aβ production is mediated by transcriptional regulation of BACE-1 and APP, resulting in decreased APP protein expression and BACE-1 activity. Acacetin also inhibited APP synthesis, resulting in a decrease in the number of amyloid plaques.

Tau-mediated synaptic damage in Alzheimer's disease

Synapses are the principal sites for chemical communication between neurons and are essential for performing the dynamic functions of the brain. In Alzheimer’s disease and related tauopathies, synapses are exposed to disease modified protein tau, which may cause the loss of synaptic contacts that culminate in dementia. In recent decades, structural, transcriptomic and proteomic studies suggest that Alzheimer’s disease represents a synaptic disorder. Tau neurofibrillary pathology and synaptic loss correlate well with cognitive impairment in these disorders. Moreover, regional distribution and the load of neurofibrillary lesions parallel the distribution of the synaptic loss. Several transgenic models of tauopathy expressing various forms of tau protein exhibit structural synaptic deficits. The pathological tau proteins cause the dysregulation of synaptic proteome and lead to the functional abnormalities of synaptic transmission. A large body of evidence suggests that tau protein plays a key role in the synaptic impairment of human tauopathies.

Mechanisms of Neuronal Protection against Excitotoxicity, Endoplasmic Reticulum Stress, and Mitochondrial Dysfunction in Stroke and Neurodegenerative Diseases

In stroke and neurodegenerative disease, neuronal excitotoxicity, caused by increased extracellular glutamate levels, is known to result in calcium overload and mitochondrial dysfunction. Mitochondrial deficits may involve a deficiency in energy supply as well as generation of high levels of oxidants which are key contributors to neuronal cell death through necrotic and apoptotic mechanisms. Excessive glutamate receptor stimulation also results in increased nitric oxide generation which can be detrimental to cells as nitric oxide interacts with superoxide to form the toxic molecule peroxynitrite. High level oxidant production elicits neuronal apoptosis through the actions of proapoptotic Bcl-2 family members resulting in mitochondrial permeability transition pore opening. In addition to apoptotic responses to severe stress, accumulation of misfolded proteins and high levels of oxidants can elicit endoplasmic reticulum (ER) stress pathways which may also contribute to induction of apoptosis. Two categories of therapeutics are discussed that impact major pro-death events that include induction of oxidants, calcium overload, and ER stress. The first category of therapeutic agent includes the amino acid taurine which prevents calcium overload and is also capable of preventing ER stress by inhibiting specific ER stress pathways. The second category involves N-methyl-D-aspartate receptor (NMDA receptor) partial antagonists illustrated by S-Methyl-N, N-diethyldithiocarbamate sulfoxide (DETC-MeSO), and memantine. DETC-MeSO is protective through preventing excitotoxicity and calcium overload and by blocking specific ER stress pathways. Another NMDA receptor partial antagonist is memantine which prevents excessive glutamate excitation but also remarkably allows maintenance of physiological neurotransmission. Targeting of these major sites of neuronal damage using pharmacological agents is discussed in terms of potential therapeutic approaches for neurological disorders.

Amyloid beta modulation of neuronal network activity in vitro

In vitro assays offer a means of screening potential therapeutics and accelerating the drug development process. Here, we utilized neuronal cultures on planar microelectrode arrays (MEA) as a functional assay to assess the neurotoxicity of amyloid-β 1-42 (Aβ42), a biomolecule implicated in the Alzheimer׳s disease (AD). In this approach, neurons harvested from embryonic mice were seeded on the substrate-integrated microelectrode arrays. The cultured neurons form a spontaneously active network, and the spiking activity as a functional endpoint could be detected via the MEA. Aβ42 oligomer, but not monomer, significantly reduced network spike rate. In addition, we demonstrated that the ionotropic glutamate receptors, NMDA and AMPA/kainate, play a role in the effects of Aβ42 on neuronal activity in vitro. To examine the utility of the MEA-based assay for AD drug discovery, we tested two model therapeutics for AD, methylene blue (MB) and memantine. Our results show an almost full recovery in the activity within 24h after administration of Aβ42 in the cultures pre-treated with either MB or memantine. Our findings suggest that cultured neuronal networks may be a useful platform in screening potential therapeutics for Aβ induced changes in neurological function.

Slowing the progression of Alzheimer's disease; what works?

Alzheimer's disease (AD) is an age-related progressive dementia, which is increasing in prevalence world-wide. Typically affecting short-term memory at onset, this devastating illness advances to impair all aspects of cognition, as well as non-cognitive domains. Although much effort has been made in recent years to develop disease-modifying treatments, medications which provided promising results in pre-clinical research have so far faltered in human clinical trials. Attention has recently shifted into trying to identify preventative measures that may delay the onset of the illness. Preventative factors include physical activity, proper diet, cognitive stimulation and the management of conditions such as hypertension, diabetes and obesity. However, it remains imperative to identify approaches that may help patients already diagnosed with the illness. Alongside pharmacological research, much work has been done on uncovering strategies which may slow down the progression of AD. This review aims to summarize evidence supporting or refuting methods impacting on the progression of the disease. AD remains a chronic and serious condition, therefore any intervention delaying the onset of moderate/severe symptoms will have a significant impact on patients and their families.

The role of proteases in regulating Eph/ephrin signaling

Proteases regulate a myriad of cell functions, both in normal and disease states. In addition to protein turnover, they regulate a range of signaling processes, including those mediated by Eph receptors and their ephrin ligands. A variety of proteases is reported to directly cleave Ephs and/or ephrins under different conditions, to promote receptor and/or ligand shedding, and regulate receptor/ligand internalisation and signaling. They also cleave other adhesion proteins in response to Eph-ephrin interactions, to indirectly facilitate Eph-mediated functions. Proteases thus contribute to Eph/ephrin mediated changes in cell-cell and cell-matrix interactions, in cell morphology and in cell migration and invasion, in a manner which appears to be tightly regulated by, and co-ordinated with, Eph signaling. This review summarizes the current literature describing the function and regulation of protease activities during Eph/ephrin-mediated cell signaling.

Na, K-ATPase α3 is a death target of Alzheimer patient amyloid-β assembly

Neurodegeneration correlates with Alzheimer's disease (AD) symptoms, but the molecular identities of pathogenic amyloid β-protein (Aβ) oligomers and their targets, leading to neurodegeneration, remain unclear. Amylospheroids (ASPD) are AD patient-derived 10- to 15-nm spherical Aβ oligomers that cause selective degeneration of mature neurons. Here, we show that the ASPD target is neuron-specific Na(+)/K(+)-ATPase α3 subunit (NAKα3). ASPD-binding to NAKα3 impaired NAKα3-specific activity, activated N-type voltage-gated calcium channels, and caused mitochondrial calcium dyshomeostasis, tau abnormalities, and neurodegeneration. NMR and molecular modeling studies suggested that spherical ASPD contain N-terminal-Aβ-derived "thorns" responsible for target binding, which are distinct from low molecular-weight oligomers and dodecamers. The fourth extracellular loop (Ex4) region of NAKα3 encompassing Asn(879) and Trp(880) is essential for ASPD-NAKα3 interaction, because tetrapeptides mimicking this Ex4 region bound to the ASPD surface and blocked ASPD neurotoxicity. Our findings open up new possibilities for knowledge-based design of peptidomimetics that inhibit neurodegeneration in AD by blocking aberrant ASPD-NAKα3 interaction.

Current and novel therapeutic molecules and targets in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder in which the death of brain cells causes memory loss and cognitive decline, i.e., dementia. The disease starts with mild symptoms and gradually becomes severe. AD is one of the leading causes of mortality worldwide. Several different hallmarks of the disease have been reported such as deposits of β-amyloid around neurons, hyperphosphorylated tau protein, oxidative stress, dyshomeostasis of bio-metals, low levels of acetylcholine, etc. AD is not simple to diagnose since there is no single diagnostic test for it. Pharmacotherapy for AD currently provides only symptomatic relief and mostly targets cognitive revival. Computational biology approaches have proved to be reliable tools for the selection of novel targets and therapeutic ligands. Molecular docking is a key tool in computer-assisted drug design and development. Docking has been utilized to perform virtual screening on large libraries of compounds, and propose structural hypotheses of how the ligands bind with the target with lead optimization. Another potential application of docking is optimization stages of the drug-discovery cycle. This review summarizes the known drug targets of AD, in vivo active agents against AD, state-of-the-art docking studies done in AD, and future prospects of the docking with particular emphasis on AD.

Aβ selectively impairs mGluR7 modulation of NMDA signaling in basal forebrain cholinergic neurons: implication in Alzheimer's disease

Degeneration of basal forebrain (BF) cholinergic neurons is one of the early pathological events in Alzheimer's disease (AD) and is thought to be responsible for the cholinergic and cognitive deficits in AD. The functions of this group of neurons are highly influenced by glutamatergic inputs from neocortex. We found that activation of metabotropic glutamate receptor 7 (mGluR7) decreased NMDAR-mediated currents and NR1 surface expression in rodent BF neurons via a mechanism involving cofilin-regulated actin dynamics. In BF cholinergic neurons, β-amyloid (Aβ) selectively impaired mGluR7 regulation of NMDARs by increasing p21-activated kinase activity and decreasing cofilin-mediated actin depolymerization through a p75(NTR)-dependent mechanism. Cell viability assays showed that activation of mGluR7 protected BF neurons from NMDA-induced excitotoxicity, which was selectively impaired by Aβ in BF cholinergic neurons. It provides a potential basis for the Aβ-induced disruption of calcium homeostasis that might contribute to the selective degeneration of BF cholinergic neurons in the early stage of AD.

The Chemistry of Neurodegeneration: Kinetic Data and Their Implications

We collected experimental kinetic rate constants for chemical processes responsible for the development and progress of neurodegeneration, focused on the enzymatic and non-enzymatic degradation of amine neurotransmitters and their reactive and neurotoxic metabolites. A gross scheme of neurodegeneration on the molecular level is based on two pathways. Firstly, reactive species oxidise heavy atom ions, which enhances the interaction with alpha-synuclein, thus promoting its folding to the beta form and giving rise to insoluble amyloid plaques. The latter prevents the function of vesicular transport leading to gradual neuronal death. In the second pathway, radical species, OH(·) in particular, react with the methylene groups of the apolar part of the lipid bilayer of either the cell or mitochondrial wall, resulting in membrane leakage followed by dyshomeostasis, loss of resting potential and neuron death. Unlike all other central neural system (CNS)-relevant biogenic amines, dopamine and noradrenaline are capable of a non-enzymatic auto-oxidative reaction, which produces hydrogen peroxide. This reaction is not limited to the mitochondrial membrane where scavenging enzymes, such as catalase, are located. On the other hand, dopamine and its metabolites, such as dopamine-o-quinone, dopaminechrome, 5,6-dihydroxyindole and indo-5,6-quinone, also interact directly with alpha-synuclein and reversibly inhibit plaque formation. We consider the role of the heavy metal ions, selected scavengers and scavenging enzymes, and discuss the relevance of certain foods and food supplements, including curcumin, garlic, N-acetyl cysteine, caffeine and red wine, as well as the long-term administration of non-steroid anti-inflammatory drugs and occasional tobacco smoking, that could all act toward preventing neurodegeneration. The current analysis can be employed in developing strategies for the prevention and treatment of neurodegeneration, and, hopefully, aid in the building of an overall kinetic molecular model of neurodegeneration itself.

Beta-amyloid oligomers induce early loss of presynaptic proteins in primary neurons by caspase-dependent and proteasome-dependent mechanisms

Beta-amyloid is a major pathogenic molecule for Alzheimer's disease (AD) and can be aggregated into a soluble oligomer, which is a toxic intermediate, before amyloid fibril formation. Beta-amyloid oligomers are associated closely with early synaptic loss in AD. However, it is still unknown which synaptic proteins are involved in the synaptotoxicity, and a direct comparison among the synaptic proteins should also be addressed. Here, we investigated changes in the expression of several presynaptic and postsynaptic proteins in primary neurons after treatment with a low-molecular weight and a high-molecular weight beta-amyloid oligomer. Both oligomers induced early neuronal dysfunction after 4 h and significantly reduced presynaptic protein (synaptophysin, syntaxin, synapsin, and synaptotagmin) expression. However, the expression of postsynaptic proteins (PSD95, NMDAR2A/B, and GluR2/3), except NMDAR1 was not reduced, and some protein expression levels were increased. Glutamate treatment, which is correlated with postsynaptic activation, showed more postsynaptic-specific protein loss compared with beta-amyloid oligomer treatment. Finally, the caspase inhibitor zVAD and the proteasomal inhibitor MG132 attenuated presynaptic protein loss. Thus, our data showed changes in synaptic proteins by beta-amyloid oligomers, which provides an understanding of early synaptotoxicity and suggests new approaches for AD treatment.

Protection of curcumin against amyloid-β-induced cell damage and death involves the prevention from NMDA receptor-mediated intracellular Ca2+ elevation

Alzheimer's disease (AD) is one of the common neurodegenerative diseases and amyloid-β (Aβ) is thought to be a key molecule contributing to AD pathology. Recently, curcumin is supposed to be beneficial to AD treatment. This study investigates the inhibitory effects of curcumin on Aβ-induced cell damage and death involving NMDA receptor-mediated intracellular Ca(2+) elevation in human neuroblastoma SH-SY5Y cells. Cells were impaired significantly in Aβ-damaged group compared with the control group, and cell viability was decreased while the released LDH from the cytosol was increased. Curcumin promotes cell growth and decreases cell impairment induced by Aβ. Curcmin attenuates Aβ-induced elevation of the ratio of cellular glutamate/γ-aminobutyric acid (GABA) with a concentration-dependent manner. Curcumin inhibits Aβ-induced increase of cellular Ca(2+) and depresses Aβ-induced phosphorylations of both NMDA receptor and cyclic AMP response element-binding protein (CREB) and activating transcription factor 1 (ATF-1). These results indicated that curcumin inhibits Aβ-induced neuronal damage and cell death involving the prevention from intracellular Ca(2+) elevation mediated by the NMDA receptor.

Relationship between Zinc (Zn (2+) ) and Glutamate Receptors in the Processes Underlying Neurodegeneration

The results from numerous studies have shown that an imbalance between particular neurotransmitters may lead to brain circuit dysfunction and development of many pathological states. The significance of glutamate pathways for the functioning of the nervous system is equivocal. On the one hand, glutamate transmission is necessary for neuroplasticity, synaptogenesis, or cell survival, but on the other hand an excessive and long-lasting increased level of glutamate in the synapse may lead to cell death. Under clinical conditions, hyperactivity of the glutamate system is associated with ischemia, epilepsy, and neurodegenerative diseases such as Alzheimer's, Huntington's, and many others. The achievement of glutamate activity in the physiological range requires efficient control by endogenous regulatory factors. Due to the fact that the free pool of ion Zn(2+) is a cotransmitter in some glutamate neurons; the role of this element in the pathophysiology of a neurodegenerative diseases has been intensively studied. There is a lot of evidence for Zn(2+) dyshomeostasis and glutamate system abnormalities in ischemic and neurodegenerative disorders. However, the precise interaction between Zn(2+) regulative function and the glutamate system is still not fully understood. This review describes the relationship between Zn(2+) and glutamate dependent signaling pathways under selected pathological central nervous system (CNS) conditions.

[Calpains and their endo- and exogenous regulators in various neurodegeneration models]

On the basis of experimental series with murine models there was obtained the evidence on calcium-dependent protease activity changes in rat brain at induced neurodegeneration. The properties of the proteolytic and regulatory components of calpain system under the effect of neurotoxic stimuli--amyloid beta-peptide or glutamate--were characterized; the basic endogenous regulatory mechanisms of calcium-dependent proteolysis modulation were determined as well. Neuroprotective properties of exogenous calpain regulators differing in the mechanisms of action (sex steroids, calcium regulators) were tested on studied neurodegeneration models.

Glutamate receptors in the kidney

l-Glutamate (l-Glu) plays an essential role in the central nervous system (CNS) as an excitatory neurotransmitter, and exerts its effects by acting on a large number of ionotropic and metabotropic receptors. These receptors are also expressed in several peripheral tissues, including the kidney. This review summarizes the general properties of ionotropic and metabotropic l-Glu receptors, focusing on N-methyl-d-aspartate (NMDA) and Group 1 metabotropic glutamate receptors (mGluRs). NMDA receptors are expressed in the renal cortex and medulla, and appear to play a role in the regulation of renal blood flow, glomerular filtration, proximal tubule reabsorption and urine concentration within medullary collecting ducts. Sustained activation of NMDA receptors induces Ca(2+) influx and oxidative stress, which can lead to glomerulosclerosis, for example in hyperhomocysteinemia. Group 1 mGluRs are expressed in podocytes and probably in other cell types. Mice in which these receptors are knocked out gradually develop albuminuria and glomerulosclerosis. Several endogenous agonists of l-Glu receptors, which include sulfur-containing amino acids derived from l-homocysteine, and quinolinic acid (QA), as well as the co-agonists glycine and d-serine, are present in the circulation at concentrations capable of robustly activating ionotropic and metabotropic l-Glu receptors. These endogenous agonists may also be secreted from renal parenchymal cells, or from cells that have migrated into the kidney, by exocytosis or by transporters such as system x(-)(c), or by transporters involved in ammonia secretion. l-Glu receptors may be useful targets for drug therapy, and many selective orally-active compounds exist for investigation of these receptors as potential drug targets for various kidney diseases.