Deciphering the molecular basis of memory failure in Alzheimer's disease

Integrating in vitro and in silico approaches to evaluate the "dual functionality" of palmatine chloride in inhibiting and disassembling Tau-derived VQIVYK peptide fibrils

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disorder which is characterized by the deposits of intra-cellular tau protein and extra-cellular amyloid-β (Aβ) peptides in the human brain. Understanding the mechanism of protein aggregation and finding compounds that are capable of inhibiting its aggregation is considered to be highly important for disease therapy.

METHODS

We used an in vitro High-Throughput Screening for the identification of potent inhibitors of tau aggregation using a proxy model; a highly aggregation-prone hexapeptide fragment ³⁰⁶VQIVYK³¹¹ derived from tau. Using ThS fluorescence assay we screened a library of 2401 FDA approved, bio-active and natural compounds in attempt to find molecules which can efficiently modulate tau aggregation.

RESULTS

Among the screened compounds, palmatine chloride (PC) alkaloid was able to dramatically reduce the aggregation propensity of PHF6 at sub-molar concentrations. PC was also able to disassemble preformed aggregates of PHF6 and reduce the amyloid content in a dose-dependent manner. Insights obtained from MD simulation showed that PC interacted with the key residues of PHF6 responsible for β-sheet formation, which could likely be the mechanism of inhibition and disassembly. Furthermore, PC could effectively inhibit the aggregation of full-length tau and disassemble preformed aggregates.

CONCLUSIONS

We found that PC possesses "dual functionality" towards PHF6 and full-length tau, i.e. inhibit their aggregation and disassemble pre-formed fibrils.

GENERAL SIGNIFICANCE

The "dual functionality" of PC is valuable as a disease modifying strategy for AD, and other tauopathies, by inhibiting their progress and reducing the effect of fibrils already present in the brain.

Gastrointestinal hormones in regulation of memory

The connection between the gastrointestinal hormones and the brain has been established many years ago. This relation is termed the gut-brain axis (GBA). The GBA is a bidirectional communication which not only regulates gastrointestinal homeostasis but is also linked with higher emotional and cognitive functions. Hypothalamus plays a critical role in the regulation of energy metabolism, nutrient partitioning and control of feeding behaviors. Various gut hormones are released inside the gastrointestinal tract on food intake. These hormones act peripherally and influence the different responses of the tissues to the food intake, but do also have effects on the brain. The hypothalamus, in turn, integrates visceral function with limbic system structures such as hippocampus, amygdala, and cerebral cortex. The hippocampus has been known for its involvement in the cognitive function and the modulation of synaptic plasticity. This review aims to establish the role of various gut hormones in learning and memory, through the interaction of various receptors in the hippocampus. Understanding their role in memory can also aid in finding novel therapeutic strategies for the treatment of the neurological disorders associated with memory dysfunctions.

(-)-Epigallocatechin-3-gallate ameliorates memory impairment and rescues the abnormal synaptic protein levels in the frontal cortex and hippocampus in a mouse model of Alzheimer's disease

(-)-Epigallocatechin-3-gallate (EGCG) is the most abundant polyphenolic extract in green tea and it has attracted increasing attention for its multiple bioactive effects. However, the mechanisms by which EGCG exerts its neuroprotective actions in Alzheimer's disease (AD) are presently lacking. In the present study, a sporadic AD transgenic mouse model known as senescence-accelerated mouse prone 8 (SAMP8) was used to investigate whether oral administration of EGCG could improve recognition and memory function through reduction of amyloid β (Aβ) and tau hyperphosphorylation. We also investigated the effects of chronic EGCG treatment on the synaptic dysfunction in the frontal cortex (FC) and the hippocampus (Hip) of AD mice. The results showed that long-term oral consumption of EGCG at a relatively high dose (15 mg/kg) improved memory function in SAMP8 mice in the Y-maze and Morris water maze. The levels of Aβ1-42 and BACE-1 in FC and Hip were significantly reduced by EGCG treatment. EGCG treatment also prevented the hyperphosphorylation of tau and reversed the decreased synaptic protein marker synaptophysin and postsynaptic density protein 95 in FC and Hip of SAMP8 mice. The present study suggests that long-term oral consumption of EGCG ameliorates impairments in spatial learning and memory and rescues the reduction in synaptic proteins observed in an AD mouse model. Thus, EGCG may represent a novel candidate agent for the treatment of neurodegenerative diseases.

Neuroinflammation, Gut Microbiome, and Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that develops insidiously and causes dementia finally. There are also clinical complications in advanced dementia, such as eating problems, infections, which will lead to the decline of patients' life quality, and the rising cost of care for AD to our society. AD will be important public health challenge. Early detection of AD may be a key issue to prevent, delay, and stop the disease. Gut microbiome and neuroinflammation are closely related with nervous system diseases, although the specific mechanism is not clear. This review introduces the relationship between neuroinflammation, gut microbiome, and AD.

Dual GSK-3β/AChE Inhibitors as a New Strategy for Multitargeting Anti-Alzheimer's Disease Drug Discovery

Designing multitarget-directed ligands (MTDLs) is considered to be a promising approach to address complex and multifactorial maladies such as Alzheimer's disease (AD). The concurrent inhibition of the two crucial AD targets, glycogen synthase kinase-3β (GSK-3β) and human acetylcholinesterase (hAChE), might represent a breakthrough in the quest for clinical efficacy. Thus, a novel family of GSK-3β/AChE dual-target inhibitors was designed and synthesized. Among these hybrids, 2f showed the most promising profile as a nanomolar inhibitor on both hAChE (IC₅₀ = 6.5 nM) and hGSK-3β kinase activity (IC₅₀ = 66 nM). It also showed good inhibitory effect on β-amyloid self-aggregation (inhibitory rate = 46%) at 20 μM. Western blot analysis revealed that compound 2f inhibited hyperphosphorylation of tau protein in mouse neuroblastoma N2a-Tau cells. In vivo studies confirmed that 2f significantly ameliorated the cognitive disorders in scopolamine-treated ICR mice and less hepatotoxicity than tacrine. This study provides new leads for assessment of GSK-3β and AChE pathway dual inhibition as a promising strategy for AD treatment.

Protective effects of 7,8-dihydroxyflavone on neuropathological and neurochemical changes in a mouse model of Alzheimer's disease

Interest in brain-derived neurotrophic factor (BDNF) was greatly enhanced when it was recognized that its expression is reduced in neurodegenerative disorders, especially in Alzheimer's disease (AD). BDNF signaling through the TrkB receptor has a central role in promoting synaptic transmission, synaptogenesis, and facilitating synaptic plasticity making the BDNF-TrkB signaling pathway an attractive candidate for targeted therapies. Here we investigated the early effect of the small molecule TrkB agonist, 7,8 dihydroxyflavone (7,8-DHF), on AD-related pathology, dendritic arborization, synaptic density, and neurochemical changes in the 5xFAD mouse model of AD. We treated 5xFAD mice with 7,8-DHF for 2 months beginning at 1 month of age. We found that, in this model of AD, 7,8-DHF treatment decreased cortical Aβ plaque deposition and protected cortical neurons against reduced dendritic arbor complexity but had no significant impact on the density of dendritic spines. In addition 7,8-DHF treatment protected against hippocampal increase in the level of choline-containing compounds and glutamate loss, but had no significant impact on hippocampal neurogenesis.

Amyloid-Beta and Phosphorylated Tau Accumulations Cause Abnormalities at Synapses of Alzheimer's disease Neurons

Amyloid-beta (Aβ) and hyperphosphorylated tau are hallmark lesions of Alzheimer's disease (AD). However, the loss of synapses and dysfunctions of neurotransmission are more directly tied to disease severity. The role of these lesions in the pathoetiological progression of the disease remains contested. Biochemical, cellular, molecular, and pathological studies provided several lines of evidence and improved our understanding of how Aβ and hyperphosphorylated tau accumulation may directly harm synapses and alter neurotransmission. In vitro evidence suggests that Aβ and hyperphosphorylated tau have both direct and indirect cytotoxic effects that affect neurotransmission, axonal transport, signaling cascades, organelle function, and immune response in ways that lead to synaptic loss and dysfunctions in neurotransmitter release. Observations in preclinical models and autopsy studies support these findings, suggesting that while the pathoetiology of positive lesions remains elusive, their removal may reduce disease severity and progression. The purpose of this article is to highlight the need for further investigation of the role of tau in disease progression and its interactions with Aβ and neurotransmitters alike.

Amyloid Plaques Show Binding Capacity of Exogenous Injected Amyloid-β

Amyloid plaques, although inducing damage to the immediately surrounding neuropil, have been proposed to provide a relatively innocuous way to deposit toxic soluble amyloid-β (Aβ) species. Here we address this hypothesis by exploring spread and absorption of fluorescent Aβ to pre-existing amyloid plaques after local application in wild-type mice versus APP/PS1 transgenic mice with amyloid plaques. Local intracortical or intracerebroventricular injection of fluorescently-labeled Aβ in APP/PS1 mice with a high plaque density resulted in preferential accumulation of the peptide in amyloid plaques in both conventional postmortem histology and in live imaging using two-photon microscopy. These findings support the contention that amyloid plaques may act as buffers to protect neurons from the toxic effects of momentary high concentrations of soluble Aβ oligomers.

The ameliorative effects and underlying mechanisms of dopamine D1-like receptor agonist SKF38393 on Aβ1-42-induced cognitive impairment

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by extracellular amyloid plaques and intracellular neurofibrillary tangles. It is the most common form of human cognitive decline and dementia. In this study, we aim to systematically investigate the ameliorative effects of dopamine D1-like receptor agonist SKF38393 on cognitive dysfunction and explore its underlying mechanisms. The Aβ_1-42 was injected intracerebroventricularly to establish cognitive disorder model. Then, a series of behavior tests were used. In order to further study the mechanisms, some relevant protein was assessed by ELISA method and Western blot. The results in behavior tests revealed that SKF38393 significantly ameliorated all the test indexes compared with the model mice. Then SKF38393 increased phosphorylation of cAMP response element binding protein (CREB) and expression of Bcl-2 in Western blot analyses. Furthermore, in ELISA assay, SKF38393 significantly increased the brain-derived neurotrophic factor (BDNF) levels and reduced the β-site APP cleaving enzyme1 (BACE1) and Aβ_1-42 levels in hippocampus and cortex of mice. However, compared with SKF38393-H, all these results were significantly reversed by the dopamine D1 receptor antagonist SCH23390. These results indicated that SKF38393 could ameliorate Aβ_1-42-induced cognitive dysfunction in mice, which may be related to D1 receptor activation. It leads to the phosphorylation of CREB, which promote the expression of BDNF, Bcl-2 and decrease the expression of Aβ_1-42 of mice. Our findings suggest that dopamine D1-like receptor may be a potential target for the treatment of AD and its agonists may become a novel drug in the future.

Neurogenesis and morphological-neural alterations closely related to amyloid β-peptide (25-35)-induced memory impairment in male rats

Memory impairment by the Amyloid-β 25-35 (Aβ_25-35) peptide in animal models has provided an understanding of the causes behind the similar deterioration that occurs in Alzheimer's disease. However, it is uncertain if a decrease of dendritic spines and neurogenesis conduces to cognitive impairment by an impairment in the retrieval of stored memory. The aim of this study was to evaluate the consequences of impairment on spatial memory caused by the administration of the Aβ_25-35 peptide in the hippocampus, which is associated whit morphological changes and neurogenesis in the dentate gyrus (DG). The vehicle or Aβ_25-35 peptide (0.1μg/μL) were bilaterally administered in the CA1 subfield of the rat hippocampus. The animals were tested for spatial learning and memory in the Morris Water Maze. In the day's 11, 18 and 32 after administration of the Aβ_25-35 peptide were examined the morphological changes in the DG using a Golgi-Cox stain. In the day 32, the neurogenesis was evaluated by the immunoreactivity to 5-bromo-2'-deoxyuridine (BrdU; 100mg/kg, i.p.) that corresponding to cellular proliferation post damage, the neuronal specific nuclear protein (NeuN) and doublecortin (DCX). This study found a memory retrieval impairment occurring at day 17, a cognitive deficit which had increased significantly at day 31 after the administration of Aβ_25-35 peptide. These results are related to morphological changes in the granular cells of the DG, such as a shorter dendritic length and a decrease in the number of dendritic spines. In neurogenesis, the total number of cells positive to BrdU, NeuN and DCX in the hippocampal granule cell layer was found to have declined in animals treated with Aβ_25-35. The results suggest that the Aβ_25-35 peptide impairs memory retrieval by decreasing the number of dendritic spines and altering neurogenesis in the DG.

Peptides isolated from animal venom as a platform for new therapeutics for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that deeply affects patients, their family and society. Although scientists have made intense efforts in seeking the cure for AD, no drug available today is able to stop AD progression. In this context, compounds isolated from animal venom are potentially successful drugs for neuroprotection, since they selectively bind to nervous system targets. In this review, we presented different studies using peptides isolated from animal venom for the treatment of AD. This is a growing field that will be very helpful in understanding and even curing neurodegenerative diseases, especially AD.

A Novel Small Molecule Modulator of Amyloid Pathology

Because traditional approaches to drug development for Alzheimer's disease are becoming increasingly expensive and in many cases disappointingly unsuccessful, alternative approaches are required to shift the paradigm. Following leads from investigations of dihydropyridine calcium channel blockers, we observed unique properties from a class of functionalized naphthyridines and sought to develop these as novel therapeutics that minimize amyloid pathology without the adverse effects associated with current therapeutics. Our data show methyl 2,4-dimethyl-5-oxo-5,6-dihydrobenzo[c][2,7]naphthyridine-1-carboxylate (BNC-1) significantly decreases amyloid burden in a well-established mouse model of amyloid pathology through a unique mechanism mediated by Elk-1, a transcriptional repressor of presenilin-1. Additionally, BNC-1 treatment leads to increased levels of synaptophysin and synapsin, markers of synaptic integrity, but does not adversely impact presenilin-2 or processing of Notch-1, thus avoiding negative off target effects associated with pan-gamma secretase inhibition. Overall, our data show BNC-1 significantly decreases amyloid burden and improves markers of synaptic integrity in a well-established mouse model of amyloid deposition by promoting phosphorylation and activation of Elk-1, a transcriptional repressor of presenilin-1 but not presenilin-2. These data suggest BNC-1 might be a novel, disease-modifying therapeutic that will alter the pathogenesis of Alzheimer's disease.

Pharmacological Agents Targeting γ-Secretase Increase Risk of Cancer and Cognitive Decline in Alzheimer's Disease Patients: A Systematic Review and Meta-Analysis

BACKGROUND

Drugs targeting γ-secretase in Alzheimer's disease (AD) have failed to demonstrate efficacy in clinical trials.

OBJECTIVE

To perform a meta-analysis of randomized controlled trials (RCTs) to evaluate the efficacy and safety of drugs targeting γ-secretase in AD.

METHODS

Ten trials were identified involving 5,227 patients using electronic databases and manual review of reference lists. RCTs of at least two weeks duration involving a drug targeting γ-secretase were eligible. The main outcomes examined were adverse events and cognitive measures (ADAS-cog, MMSE, ADCS-ADL, and CDR-sb). A sub-group analysis was performed, excluding the γ-secretase modulator tarenflurbil, to evaluate the safety and efficacy of γ-secretase inhibitors only.

RESULTS

There was an increased risk of adverse events (Odds Ratio (OR) 1.38, 95% CI 1.09-1.73; p = 0.01), serious adverse events (OR 1.50, 95% CI 1.22-1.84; p < 0.001), and skin cancers (OR 4.77, 95% CI 2.83-8.06; p < 0.001). There was significantly increased risk of infections (OR 1.36, 95% CI 1.13-1.63; p < 0.001) in the subgroup analysis excluding tarenflurbil. Pooled results also revealed a worsening in ADAS-cog (difference in means 1.33, 95% CI 0.58-2.08; p < 0.001) and MMSE (difference in means -0.66, 95% CI -0.96 to 0.35; p < 0.001), but not ADCS-ADL or CDR-sb.

CONCLUSION

The use of γ-secretase inhibitors is associated with significantly increased risk of serious adverse events including skin cancers, and worsening in cognitive indicators. This evidence indicates that γ-secretase may not be an appropriate target for clinical treatment of AD.

Mechanistic insights into remodeled Tau-derived PHF6 peptide fibrils by Naphthoquinone-Tryptophan hybrids

Intra-cellular tau protein tangles and extra-cellular β-amyloid plaques are hallmarks of Alzheimer’s disease (AD), characterized by the conversion of natively unfolded monomeric protein/peptide into misfolded β-sheet rich aggregates. Therefore, inhibiting the aggregation cascade or disassembling the pre-formed aggregates becomes a pivotal event in disease treatment. In the present study, we show that Naphthoquinone-Tryptophan hybrids, i.e., NQTrp and Cl-NQTrp significantly disrupted the pre-formed fibrillar aggregates of Tau-derived PHF6 (VQIVYK) peptide and full-length tau protein in vitro, in a dose-dependent manner as evident from ThS assay, CD spectroscopy, and TEM. Molecular dynamics simulation of PHF6 oligomers and fibrils with the Naphthoquinone-Tryptophan hybrids provides a possible structure-function based mechanism-of-action, highlighting the role of hydrophobic interaction and hydrogen bond formation during fibril disassembly. These findings signify the effectiveness of NQTrp and Cl-NQTrp in disassembling fibrillar aggregates and may help in designing novel hybrid molecules for AD treatment.

Metabolic Abnormalities of Erythrocytes as a Risk Factor for Alzheimer's Disease

Alzheimer's disease (AD) is a slowly progressive, neurodegenerative disorder of uncertain etiology. According to the amyloid cascade hypothesis, accumulation of non-soluble amyloid β peptides (Aβ) in the Central Nervous System (CNS) is the primary cause initiating a pathogenic cascade leading to the complex multilayered pathology and clinical manifestation of the disease. It is, therefore, not surprising that the search for mechanisms underlying cognitive changes observed in AD has focused exclusively on the brain and Aβ-inducing synaptic and dendritic loss, oxidative stress, and neuronal death. However, since Aβ depositions were found in normal non-demented elderly people and in many other pathological conditions, the amyloid cascade hypothesis was modified to claim that intraneuronal accumulation of soluble Aβ oligomers, rather than monomer or insoluble amyloid fibrils, is the first step of a fatal cascade in AD. Since a characteristic reduction of cerebral perfusion and energy metabolism occurs in patients with AD it is suggested that capillary distortions commonly found in AD brain elicit hemodynamic changes that alter the delivery and transport of essential nutrients, particularly glucose and oxygen to neuronal and glial cells. Another important factor in tissue oxygenation is the ability of erythrocytes (red blood cells, RBC) to transport and deliver oxygen to tissues, which are first of all dependent on the RBC antioxidant and energy metabolism, which finally regulates the oxygen affinity of hemoglobin. In the present review, we consider the possibility that metabolic and antioxidant defense alterations in the circulating erythrocyte population can influence oxygen delivery to the brain, and that these changes might be a primary mechanism triggering the glucose metabolism disturbance resulting in neurobiological changes observed in the AD brain, possibly related to impaired cognitive function. We also discuss the possibility of using erythrocyte biochemical aberrations as potential tools that will help identify a risk factor for AD.

Design, synthesis and biological evaluation of LX2343 derivatives as neuroprotective agents for the treatment of Alzheimer's disease

A series of LX2343 derivatives were designed, synthesized and evaluated as neuroprotective agents for Alzheimer's disease (AD) in vitro. Most of the compounds displayed potent neuroprotective activities. Especially for compound A6, exhibited a remarkable EC₅₀ value of 0.22 μM. Further investigation demonstrated that compound A6 can significantly reduce Aβ production and increase Aβ clearance, and alleviate Tau hyperphosphorylation. Most importantly, compound A6 could ameliorate learning and memory impairments in APP/PS1 transgenic mice. The present study evidently showed that compound A6 is a potent neuroprotective agent and might serve as a promising lead candidate for the treatment of Alzheimer's disease.

Understanding the roles of mutations in the amyloid precursor protein in Alzheimer disease

Many models of disease progression in Alzheimer's disease (AD) have been proposed to help guide experimental design and aid the interpretation of results. Models focussing on the genetic evidence include the amyloid cascade (ACH) and presenilin (PSH) hypotheses and the amyloid precursor protein (APP) matrix approach (AMA), of which the ACH has held a dominant position for over two decades. However, the ACH has never been fully accepted and has not yet delivered on its therapeutic promise. We review the ACH, PSH and AMA in relation to levels of APP proteolytic fragments reported from AD-associated mutations in APP. Different APP mutations have diverse effects on the levels of APP proteolytic fragments. This evidence is consistent with at least three disease pathways that can differ between familial and sporadic AD and two pathways associated with cerebral amyloid angiopathy. We cannot fully evaluate the ACH, PSH and AMA in relation to the effects of mutations in APP as the APP proteolytic system has not been investigated systematically. The confounding effects of sequence homology, complexity of competing cleavages and antibody cross reactivities all illustrate limitations in our understanding of the roles these fragments and the APP proteolytic system as a whole in normal aging and disease play. Current experimental design should be refined to generate clearer evidence, addressing both aging and complex disorders with standardised reporting formats. A more flexible theoretical framework capable of accommodating the complexity of the APP proteolytic system is required to integrate available evidence.

Xanthoceraside attenuates amyloid β peptide1-42-induced memory impairments by reducing neuroinflammatory responses in mice

Xanthoceraside, a novel triterpenoid saponin extracted from the husks of Xanthoceras sorbifolia Bunge, has neuroprotective effects in vivo and anti-inflammatory properties in vitro. However, the exact mechanism of xanthoceraside on anti-amyloid beta (Aβ)-induced neuroinflammatory responses has not been elucidated. Therefore, we used intracerebroventricular injection of amyloid _1-42 (Aβ_1-42) to establish a mouse model to test the effects of xanthoceraside on Aβ-induced cognitive impairments and the TLR2/NF-κB and MAPK pathways. The mice received xanthoceraside (0.02, 0.08 or 0.32mg/kg) or vehicle from the day of Aβ_1-42 injection. The Morris water maze test was performed 4 days after Aβ_1-42 injection. The levels of inflammatory cytokines (interleukin (IL)-6 and IL-4) were measured by enzyme-linked immunosorbent assay (ELISA). The expression levels of glial fibrillary acidic protein (GFAP) and cluster of differentiation 11b (CD11b) in the hippocampus were determined with an immunohistochemistry assay. Inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) were analysed by Western blotting; iNOS, COX-2 and Toll-like receptor 2 (TLR2) mRNA expression levels were measured by reverse transcription-polymerase chain reaction (RT-PCR). Here, we observed that xanthoceraside at doses of 0.08 and 0.32mg/kg significantly improved learning and memory impairments and significantly inhibited GFAP and CD11b overexpression induced by Aβ_1-42 in mice. ELISA results revealed that xanthoceraside suppressed IL-6 release and increased IL-4 levels. Western blotting results showed that xanthoceraside reduced iNOS and COX-2 protein levels in hippocampus; xanthoceraside also inhibited translocation of NF-κB p50 and p65 into the nucleus and phosphorylation of extracellular signal-regulated kinase (ERK), Jun N-terminal kinase (JNK) and p38. RT-PCR confirmed that xanthoceraside decreased iNOS, COX-2 and TLR2 mRNA levels. These results suggest that xanthoceraside inhibition of the TLR2 pathway and down-regulation of MAPK and NF-κB activities may be related to the improvement in learning and memory impairments.

Design, synthesis and biological evaluation of tacrine-1,2,3-triazole derivatives as potent cholinesterase inhibitors

We report herein the design and synthesis of a series of 11 novel tacrine-1,2,3-triazole derivatives via a Cu(i)-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC) reaction. The newly synthesized compounds were evaluated for their inhibition activity against Electrophorus electricus acetylcholinesterase (AChE) and horse serum butyrylcholinesterase (BChE) as potential drug targets for Alzheimer's disease (AD). Among the designed compounds, compound 8a2 exhibited potent inhibition against AChE and BChE with IC₅₀ values of 4.89 μM and 3.61 μM, respectively. Further structure-activity relationship (SAR) and molecular modeling studies may provide valuable insights into the design of better tacrine-triazole analogues with potential therapeutic applications for AD.

Toward common mechanisms for risk factors in Alzheimer's syndrome

The global strategic goal of reducing health care cost, especially the prospects for massive increases due to expanding markets for health care services demanded by aging populations and/or people with a wide range of chronic disorders-disabilities, is a complex and formidable challenge with many facets. Current projections predict marked increases in the demand for health driven by both the exponential climb in the prevalence of chronic disabilities and the increases in the absolute numbers of people in need of some form of health care. Thus, the looming predicament for the economics of health care systems worldwide mandates the formulation of a strategic goal to foster significant expansion of global R&D efforts to discover and develop wide-ranging interventions to delay and/or prevent the onset of chronic disabling conditions. The rationale for adopting such a tactical objective is based on the premise that the costs and prevalence of chronic disabling conditions will be reduced by half even if a modest delay of 5 years in the onset of disability is obtained by a highly focused multinational research initiative. Because of the recent history of many failures in drug trials, the central thesis of this paper is to argue for the exploration-adoption of novel mechanistic ideas, theories, and paradigms for developing wide range and/or types of interventions. Although the primary focus of our discussion has been on biological approaches to therapy, we recognize the importance of emerging knowledge on nonpharmacological interventions and their potential impact in reducing health care costs. Although we may not find a drug to cure or prevent dementia for a long time, research is starting to demonstrate the potential contributes of nonpharmacological interventions toward the economics of health care in terms of rehabilitation, promoting autonomy, and potential to delay institutionalization, thus promoting healthy aging and reductions in the cost of care.

Bioactivity of Olive Oil Phenols in Neuroprotection

Neurological disorders such as stroke, Alzheimer’s and Parkinson’s diseases are associated with high morbidity and mortality, and few or no effective options are available for their treatment. These disorders share common pathological characteristics like the induction of oxidative stress, abnormal protein aggregation, perturbed Ca²⁺ homeostasis, excitotoxicity, inflammation and apoptosis. A large body of evidence supports the beneficial effects of the Mediterranean diet in preventing neurodegeneration. As the Mediterranean diet is characterized by a high consumption of extra-virgin olive oil it has been hypothesized that olive oil, and in particular its phenols, could be responsible for the beneficial effect of the Mediterranean diet. This review provides an updated vision of the beneficial properties of olive oil and olive oil phenols in preventing/counteracting both acute and chronic neurodegenerative diseases.

Single-Base Resolution Mapping of 5-Hydroxymethylcytosine Modifications in Hippocampus of Alzheimer's Disease Subjects

Epigenetic modifications to cytosine have been shown to regulate transcription in cancer, embryonic development, and recently neurodegeneration. While cytosine methylation studies are now common in neurodegenerative research, hydroxymethylation studies are rare, particularly genome-wide mapping studies. As an initial study to analyze 5-hydroxymethylcytosine (5-hmC) in the Alzheimer's disease (AD) genome, reduced representation hydroxymethylation profiling (RRHP) was used to analyze more than 2 million sites of possible modification in hippocampal DNA of sporadic AD and normal control subjects. Genes with differentially hydroxymethylated regions were filtered based on previously published microarray data for altered gene expression in hippocampal DNA of AD subjects. Our data show significant pathways for altered levels of 5-hmC in the hippocampus of AD subjects compared to age-matched normal controls involved in signaling, energy metabolism, cell function, gene expression, protein degradation, and cell structure and stabilization. Overall, our data suggest a possible role for the dysregulation of epigenetic modifications to cytosine in late stage AD.

Cassia tora Linn.: A boon to Alzheimer's disease for its anti-amyloidogenic and cholinergic activities

BACKGROUND

Drug discovery from natural products as alternatives for Alzheimer's disease (AD) is a current trend. For which plant is an alternative for searching potential molecule for treating AD. Availability of Cassia tora as weed and abundance in nature makes it as potential source. Many plants group under Leguminosae family has potential medicinal property of which Cassia tora is an appropriate choice, to know potency against AD. Etiology of AD is described by senile plaques and neurofibrillary tangles. The Aβ₄₂ has key major role in forming plaques by forming structures like protobirils, oligomers and final fibrilar like structures. Even at in vitro conditions, the peptides have a fibrilar like structure, which was exploited to preliminary screening of natural sources that may be effective in treating AD.

HYPOTHESIS/PURPOSE

The design of the study was to unravel the potential medicinal property of Cassia tora for its antioxidant, cholinergic and aggregation inhibition activity.

STUDY DESIGN

We evidenced that the methanol (MeOH), n-hexane (n-hex), petroleum ether (PE) and aqueous (aq) extracts from the leaves of Cassia tora (C. tora) were investigated for their inhibitory activity against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and anti-amyloidogenic assays. The antioxidant effect using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, total phenolic and flavonoid contents of the extracts were determined using Folin-Ciocaltaeu's and aluminum chloride (AlCl₃) reagents, respectively.

RESULTS

The methanol extract of C. tora exerted the highest inhibition against AChE (55.38 ± 2.28%) and BChE inhibition (50.02 ± 0.79%) at 100µg/ml concentration. The methanol extract was also found more active in the antioxidant test. The aggregation kinetics was monitored using thioflavin-T (ThT) assay and transmission electron microscopy (TEM) technique.

CONCLUSION

The results showed that C. tora methanol extract is able to inhibit the Aβ₄₂ aggregation from monomers and oligomers and also able to dis-aggregate the pre-formed fibrils. The study provides an insight on finding new natural products for AD therapeutics.

Interplay between protein glycosylation pathways in Alzheimer's disease

Deviations from the normal nucleoplasmic protein O-GlcNAcylation, as well as from normal protein sialylation and N-glycosylation in the secretory pathway, have been reported in Alzheimer's disease (AD). However, the interplay between the cytoplasmic protein O-GlcNAcylation and the secretory N-/O-glycosylation in AD has not been described. We present a comprehensive analysis of the N-, O-, and O-GlcNAc-glycomes in AD-affected brain regions as well as in AD patient serum. We detected marked differences in levels of glycan involved in both protein O-GlcNAcylation and N-/O-glycosylation between patients and healthy individuals and revealed brain region-specific glycosylation-related pathology in patients. These alterations are not general for other neurodegenerative conditions, such as frontotemporal dementia and corticobasal degeneration. The alterations in the AD glycome in the serum could potentially lead to novel glyco-based biomarkers for AD progression. Strikingly, negative interrelationship was found between the pathways of protein O-GlcNAcylation and N-/O-glycosylation, suggesting a novel intracellular cross-talk.

Aggregation of the Inflammatory S100A8 Precedes Aβ Plaque Formation in Transgenic APP Mice: Positive Feedback for S100A8 and Aβ Productions

Inflammation plays an important role in Alzheimer's disease (AD) and other neurodegenerative disorders. Although chronic inflammation in later stages of AD is well described, little is known about the inflammatory processes in preclinical or early stages of the disease prior to plaque deposition. In this study, we report that the inflammatory mediator S100A8 is increased with aging in the mouse brain. It is observed as extracellular aggregates, which do not correspond to corpora amylacea. S100A8 aggregation is enhanced in the hippocampi of two different mouse models for amyloid-β (Aβ) overproduction (Tg2576 and TgAPParctic mice). S100A8 aggregates are seen prior the formation of Aβ plaques and do not colocalize. In vitro treatment of glial cells from primary cultures with Aβ42 resulted in an increased production of S100A8. In parallel, treatment of a neuronal cell line with recombinant S100A8 protein resulted in enhanced Aβ42 and decreased Aβ40 production. Our results suggest that important inflammatory processes are occurring prior to Aβ deposition and the existence of a positive feedback between S100A8 and Aβ productions. The possible relevance of aging- or AD-dependent formation of S100A8 aggregates in the hippocampus thus affecting learning and memory processes is discussed.

LX2343 alleviates cognitive impairments in AD model rats by inhibiting oxidative stress-induced neuronal apoptosis and tauopathy

Alzheimer's disease (AD) is a progressive neurodegenerative disease leading to the irreversible loss of brain neurons and cognitive abilities, and the vicious interplay between oxidative stress (OS) and tauopathy is believed to be one of the major players in AD development. Here, we demonstrated the capability of the small molecule N-(1,3-benzodioxol-5-yl)-2-[5-chloro-2-methoxy(phenylsulfonyl)anilino]acetamide (LX2343) to ameliorate the cognitive dysfunction of AD model rats by inhibiting OS-induced neuronal apoptosis and tauopathy. Streptozotocin (STZ) was used to induce OS in neuronal cells in vitro and in AD model rats that were made by intracerebroventricular injection of STZ (3 mg/kg, bilaterally), and Morris water maze test was used to evaluate the cognitive dysfunction in ICV-STZ rats. Treatment with LX2343 (5-20 μmol/L) significantly attenuated STZ-induced apoptosis in SH-SY5Y cells and mouse primary cortical neurons by alleviating OS and inhibiting the JNK/p38 and pro-apoptotic pathways. LX2343 was able to restore the integrity of mitochondrial function and morphology, increase ATP biosynthesis, and reduce ROS accumulation in the neuronal cells. In addition, LX2343 was found to be a non-ATP competitive GSK-3β inhibitor with IC₅₀ of 1.84±0.07 μmol/L, and it potently inhibited tau hyperphosphorylation in the neuronal cells. In ICV-STZ rats, administration of LX2343 (7, 21 mg·kg^-1·d^-1, ip, for 5 weeks) efficiently improved their cognitive deficits. LX2343 ameliorates the cognitive dysfunction in the AD model rats by suppressing OS-induced neuronal apoptosis and tauopathy, thus highlighting the potential of LX2343 for the treatment of AD.

Enhanced neuroprotection of anthocyanin-loaded PEG-gold nanoparticles against Aβ1-42-induced neuroinflammation and neurodegeneration via the NF-KB /JNK/GSK3β signaling pathway

Amyloid-beta (Aβ_1-42) plaques and neurofibrillary tangles (NFTs) are the main hallmarks considered to be associated with neuroinflammation in Alzheimer's disease (AD). Recently, nanoparticle-based targeted drug delivery approaches have been found to be a useful tool in the neurotherapeutics field. Therefore, we examined and compared the neuroprotective effect of anthocyanins alone and anthocyanin-loaded poly (ethylene glycol)-gold nanoparticles (PEG-AuNPs) in Aβ_1-42-injected mouse and in vitro models of AD. We determined that anthocyanins alone or conjugated with PEG-AuNPs (AnPEG-AuNPs) reduced Aβ_1-42-induced neuroinflammatory and neuroapoptotic markers via inhibiting the p-JNK/NF-κB/p-GSK3β pathway in both in vivo and in vitro AD models. However, anthocyanins loaded with PEG-AuNPs were more effective compared to anthocyanins alone. Taken together, these results demonstrate that PEG-coated gold anthocyanins nanoparticles could be a new therapeutic agent in the field of nanomedicine to prevent neurodegenerative diseases such as AD.

Loss of clusterin shifts amyloid deposition to the cerebrovasculature via disruption of perivascular drainage pathways

Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) peptide deposition in brain parenchyma as plaques and in cerebral blood vessels as cerebral amyloid angiopathy (CAA). CAA deposition leads to several clinical complications, including intracerebral hemorrhage. The underlying molecular mechanisms that regulate plaque and CAA deposition in the vast majority of sporadic AD patients remain unclear. The clusterin (CLU) gene is genetically associated with AD and CLU has been shown to alter aggregation, toxicity, and blood-brain barrier transport of Aβ, suggesting it might play a key role in regulating the balance between Aβ deposition and clearance in both brain and blood vessels. Here, we investigated the effect of CLU on Aβ pathology using the amyloid precursor protein/presenilin 1 (APP/PS1) mouse model of AD amyloidosis on a Clu^+/+ or Clu^-/- background. We found a marked decrease in plaque deposition in the brain parenchyma but an equally striking increase in CAA within the cerebrovasculature of APP/PS1;Clu^-/- mice. Surprisingly, despite the several-fold increase in CAA levels, APP/PS1;Clu^-/- mice had significantly less hemorrhage and inflammation. Mice lacking CLU had impaired clearance of Aβ in vivo and exogenously added CLU significantly prevented Aβ binding to isolated vessels ex vivo. These findings suggest that in the absence of CLU, Aβ clearance shifts to perivascular drainage pathways, resulting in fewer parenchymal plaques but more CAA because of loss of CLU chaperone activity, complicating the potential therapeutic targeting of CLU for AD.

Hydroxytyrosol restores proper insulin signaling in an astrocytic model of Alzheimer's disease

Recent epidemiological evidence demonstrated that diabetes is a risk factor for AD onset and development. Indeed, meta-analyses of longitudinal epidemiologic studies show that diabetes increases AD risk by 50-100%, being insulin resistance (IR) the main binding link between diabetes and AD. Astrocytes are the foremost cerebral macroglial cells and are responsible for converting glucose into lactate and transfer it to neurons that use it as fuel, but Aβ(1-42) impairs insulin signaling and glycogen storage. Recent prospective studies showed that the Mediterranean diet is associated with lower incidence of AD. We hypothesized that hydroxytyrosol (HT, the preeminent polyphenol of olives and olive oil) could exert beneficial effects on IR associated with AD and investigated it mechanisms of action in an astrocytic model of AD. The astrocytic cell line C6 was exposed to Aβ(25-35) and co-incubated with HT for different periods. After treatment with Aβ(25-35), astrocytes' viability was significantly decreased as compared with controls; however, both pre- and post-treatment with HT prevented this effect. Mechanistically, we found that the preventive role of HT on Aβ(25-35)- induced cytotoxicity in astrocytes is moderated by an increased HT-induced activation of Akt, which is mediated by the insulin signaling pathway. In addition, we report that HT prevented the pronounced activation of mTOR, thereby restoring proper insulin signaling. In conclusion, we demonstrate that HT protects Aβ(25-35)-treated astrocytes by improving insulin sensitivity and restoring proper insulin-signaling. These data provide some mechanistic insight on the observed inverse association between olive oil consumption and prevalence of cognitive impairment. © 2017 BioFactors, 43(4):540-548, 2017.

Epigenetic mechanisms during ageing and neurogenesis as novel therapeutic avenues in human brain disorders

Ageing is the main risk factor for human neurological disorders. Among the diverse molecular pathways that govern ageing, epigenetics can guide age-associated decline in part by regulating gene expression and also through the modulation of genomic instability and high-order chromatin architecture. Epigenetic mechanisms are involved in the regulation of neural differentiation as well as in functional processes related to memory consolidation, learning or cognition during healthy lifespan. On the other side of the coin, many neurodegenerative diseases are associated with epigenetic dysregulation. The reversible nature of epigenetic factors and, especially, their role as mediators between the genome and the environment make them exciting candidates as therapeutic targets. Rather than providing a broad description of the pathways epigenetically deregulated in human neurological disorders, in this review, we have focused on the potential use of epigenetic enzymes as druggable targets to ameliorate neural decline during normal ageing and especially in neurological disorders. We will firstly discuss recent progress that supports a key role of epigenetic regulation during healthy ageing with an emphasis on the role of epigenetic regulation in adult neurogenesis. Then, we will focus on epigenetic alterations associated with ageing-related human disorders of the central nervous system. We will discuss examples in the context of psychiatric disorders, including schizophrenia and posttraumatic stress disorders, and also dementia or Alzheimer's disease as the most frequent neurodegenerative disease. Finally, methodological limitations and future perspectives are discussed.

Down-Regulation of KV4 Channel in Drosophila Mushroom Body Neurons Contributes to Aβ42-Induced Courtship Memory Deficits

Accumulation of amyloid-β (Aβ) is widely believed to be an early event in the pathogenesis of Alzheimer's disease (AD). K_v4 is an A-type K⁺ channel, and our previous report shows the degradation of K_v4, induced by the Aβ42 accumulation, may be a critical contributor to the hyperexcitability of neurons in a Drosophila AD model. Here, we used well-established courtship memory assay to investigate the contribution of the K_v4 channel to short-term memory (STM) deficits in the Aβ42-expressing AD model. We found that Aβ42 over-expression in Drosophila leads to age-dependent courtship STM loss, which can be also induced by driving acute Aβ42 expression post-developmentally. Interestingly, mutants with eliminated K_v4-mediated A-type K⁺ currents (I_A) by transgenically expressing dominant-negative subunit (DNK_v4) phenocopied Aβ42 flies in defective courtship STM. K_v4 channels in mushroom body (MB) and projection neurons (PNs) were found to be required for courtship STM. Furthermore, the STM phenotypes can be rescued, at least partially, by restoration of K_v4 expression in Aβ42 flies, indicating the STM deficits could be partially caused by K_v4 degradation. In addition, I_A is significantly decreased in MB neurons (MBNs) but not in PNs, suggesting K_v4 degradation in MBNs, in particular, plays a critical role in courtship STM loss in Aβ42 flies. These data highlight causal relationship between region-specific K_v4 degradation and age-dependent learning decline in the AD model, and provide a mechanism for the disturbed cognitive function in AD.

Genomics of Alzheimer Disease: A Review

IMPORTANCE

To provide a comprehensive review of knowledge of the genomics of Alzheimer disease (AD) and DNA amyloid β 42 (Aβ42) vaccination as a potential therapy.

OBSERVATIONS

Genotype-phenotype correlations of AD are presented to provide a comprehensive appreciation of the spectrum of disease causation. Alzheimer disease is caused in part by the overproduction and lack of clearance of Aβ protein. Oligomer Aβ, the most toxic species of Aβ, causes direct injury to neurons, accompanied by enhanced neuroinflammation, astrocytosis and gliosis, and eventually neuronal loss. The strongest genetic evidence supporting this hypothesis derives from mutations in the amyloid precursor protein (APP) gene. A detrimental APP mutation at the β-secretase cleavage site linked to early-onset AD found in a Swedish pedigree enhances Aβ production, in contrast to a beneficial mutation 2 residues away in APP that reduces Aβ production and protects against the onset of sporadic AD. A number of common variants associated with late-onset AD have been identified including apolipoprotein E, BIN1, ABC7, PICALM, MS4A4E/MS4A6A, CD2Ap, CD33, EPHA1, CLU, CR1, and SORL1. One or 2 copies of the apolipoprotein E ε4 allele are a major risk factor for late-onset AD. With DNA Aβ42 vaccination, a Th2-type noninflammatory immune response was achieved with a downregulation of Aβ42-specific effector (Th1, Th17, and Th2) cell responses at later immunization times. DNA Aβ42 vaccination upregulated T regulator cells (CD4+, CD25+, and FoxP3+) and its cytokine interleukin 10, resulting in downregulation of T effectors.

CONCLUSIONS AND RELEVANCE

Mutations in APP and PS-1 and PS-2 genes that are associated with early-onset, autosomal, dominantly inherited AD, in addition to the at-risk gene polymorphisms responsible for late-onset AD, all indicate a direct and early role of Aβ in the pathogenesis of AD. A translational result of genomic research has been Aβ-reducing therapies including DNA Aβ42 vaccination as a promising approach to delay or prevent this disease.

Metaplasticity mechanisms restore plasticity and associativity in an animal model of Alzheimer's disease

Dynamic regulation of plasticity thresholds in a neuronal population is critical for the formation of long-term plasticity and memory and is achieved by mechanisms such as metaplasticity. Metaplasticity tunes the synapses to undergo changes that are necessary prerequisites for memory storage under physiological and pathological conditions. Here we discovered that, in amyloid precursor protein (APP)/presenilin-1 (PS1) mice (age 3-4 mo), a prominent mouse model of Alzheimer's disease (AD), late long-term potentiation (LTP; L-LTP) and its associative plasticity mechanisms such as synaptic tagging and capture (STC) were impaired already in presymptomatic mice. Interestingly, late long-term depression (LTD; L-LTD) was not compromised, but the positive associative interaction of LTP and LTD, cross-capture, was altered in these mice. Metaplastic activation of ryanodine receptors (RyRs) in these neurons reestablished L-LTP and STC. We propose that RyR-mediated metaplastic mechanisms can be considered as a possible therapeutic target for counteracting synaptic impairments in the neuronal networks during the early progression of AD.