Abeta mediated diminution of MTT reduction--an artefact of single cell culture?

FRET-based assay for intracellular evaluation of α-synuclein aggregation inhibitors

Aggregation of small neuronal protein α-synuclein (αSyn) in amyloid fibrils is considered to be one of the main causes of Parkinson's disease. Inhibition of this aggregation is a promising approach for disease treatment. Dozens of compounds able to inhibit αSyn fibrillization in solution were developed during the last decade. However, the applicability of most of them in the cellular environment was not established because of the absence of a suitable cell-based assay. In this work, we developed an assay for testing αSyn aggregation inhibitors in cells that is based on fluorescence resonance energy transfer (FRET) between labeled αSyn molecules in fibrils. The assay directly reports the amount of fibrillized αSyn and is more reliable than the assays based on cell viability. Moreover, we showed that cell viability decline does not always correlate with the amount of misfolded αSyn. The developed FRET-based assay does not interfere with the aggregation process and is suitable for high-throughput testing of αSyn aggregation inhibitors. Its application can sort out non-specific inhibitors and thus significantly facilitate the development of drugs for Parkinson`s disease.

Cross-Seeded Fibrillation Induced by Pyroglutamate-3 and Truncated Aβ40 Variants Leads to Aβ40 Structural Polymorphism Modulation and Elevated Toxicity

The pathological amyloid plaques in Alzheimer's disease (AD) patients contain not only the wild-type β-amyloid (wt-Aβ) peptide sequences but also a variety of post-translationally modified variants. The pyroglutamate-3 Aβ (pyroE3-Aβ), which is generated from its truncated precursors ΔE3-Aβ, shows the highest abundance among all modified Aβ variants. Previous works have shown that pyroE3-Aβ and/or ΔE3-Aβ, compared with the wild-type sequences, led to a more rapid fibrillation process and final fibrils with higher neuronal cytotoxicity levels. However, much less is known about how the formation of pyroE3/ΔE3-Aβ fibrils would affect the amyloid deposition of wt-Aβ peptides, which are the main pathological events in AD. We show in the present work that the pyroE3/ΔE3-Aβ₄₀ fibrils differ significantly from the wt-Aβ₄₀ fibrils in terms of their molecular structures. When added into monomeric wt-Aβ₄₀ peptides, these variant fibrils can cross-seed the formation of wt-Aβ₄₀ fibrils with fibrillation kinetics that are greater than the self-seeded fibrillation of wt-Aβ₄₀. Furthermore, the cross-seeding process modulates the molecular structures of the yielded wt-Aβ₄₀ fibrils, which show similar features as their variant seeds. The cross-seeded fibrillation process also induces higher cytotoxicity levels compared with the self-seeded fibrillation of wt-Aβ₄₀. Overall, our results support the hypothesis that pyroE3 and ΔE3-Aβ₄₀ variants may serve as triggering factors of the pathological amyloid aggregation of wt-Aβ₄₀ and may underlie the pathological significance of pyroE3/ΔE3-Aβ₄₀ variants on the structural polymorphism of Aβ deposits.

Activation of Microbiota Sensing - Free Fatty Acid Receptor 2 Signaling Ameliorates Amyloid-β Induced Neurotoxicity by Modulating Proteolysis-Senescence Axis

Multiple emerging evidence indicates that the gut microbiota contributes to the pathology of Alzheimer's disease (AD)-a debilitating public health problem in older adults. However, strategies to beneficially modulate gut microbiota and its sensing signaling pathways remain largely unknown. Here, we screened, validated, and established the agonists of free fatty acid receptor 2 (FFAR2) signaling, which senses beneficial signals from short chain fatty acids (SCFAs) produced by microbiota. The abundance of SCFAs, is often low in the gut of older adults with AD. We demonstrated that inhibition of FFAR2 signaling increases amyloid-beta (Aβ) stimulated neuronal toxicity. Thus, we screened FFAR2 agonists using an in-silico library of more than 144,000 natural compounds and selected 15 of them based on binding with FFAR2-agonist active sites. Fenchol (a natural compound commonly present in basil) was recognized as a potential FFAR2 stimulator in neuronal cells and demonstrated protective effects against Aβ-stimulated neurodegeneration in an FFAR2-dependent manner. In addition, Fenchol reduced AD-like phenotypes, such as Aβ-accumulation, and impaired chemotaxis behavior in Caenorhabditis (C.) elegans and mice models, by increasing Aβ-clearance via the promotion of proteolysis and reduced senescence in neuronal cells. These results suggest that the inhibition of FFAR2 signaling promotes Aβ-induced neurodegeneration, while the activation of FFAR2 by Fenchol ameliorates these abnormalities by promoting proteolytic Aβ-clearance and reducing cellular senescence. Thus, stimulation of FFAR2 signaling by Fenchol as a natural compound can be a therapeutic approach to ameliorate AD pathology.

Bushen-Huatan-Yizhi formula reduces spatial learning and memory challenges through inhibition of the GSK-3β/CREB pathway in AD-like model rats

BACKGROUND

There is an increase in cases of Alzheimer's disease (AD) stemming from a globally ageing population demographic. Although substantial research efforts were performed for the scope of prophylaxis and therapeutic measure development against AD, based on its pathogenesis, most were unsuccessful. Bushen-Huatan-Yizhi formula (BSHTYZ) is extensively implemented to manage dementia. However, few studies have been carried out to understand how BSHTYZ enhances recovery of spatial learning and memory and how it modulates relevant molecular interplays in order to achieve this.

PURPOSE

To investigate neuroprotective function, ameliorating learning/memory capacity of BSHTYZ via GSK-3β / CREB signaling pathway in rat AD models influenced through Aβ1-42.

METHODS

A total of 60 male SD rats (3 months old) were randomized into six groups and treated with 2.6 μg/μl Aβ1-42 (5 μl) into the lateral ventricle, though the control group (Con) was administered an equivalent volume of vehicle. Consequently, the rat cohorts were administered either BSHTYZ or donepezil hydrochloride or normal saline, by intragastric administration, for four weeks. Spatial learning / memory were detected through the Morris water maze, and possible mechanisms detected by histomorphological examination and Western blot in the rat AD models induced by Aβ1-42.

RESULTS

Spatial learning/memory issues were monitored after Aβ1-42 infusion in rats. Simultaneously, neuron loss in cornuammonis1 (CA1) / dentate gyrus (DG) within hippocampus region were identified, together with enhanced black granule staining within the hippocampus and hyperphosphorylated tau within Ser202 and Ser396 sites. It was also elucidated that Aβ1-42 had the capacity to up-regulate glycogen synthase kinase-3β (GSK-3β) and down-regulate cAMP response element binding protein (CREB). BSHTYZ was found to reverse such molecular interplays.

CONCLUSION

The study suggested BSHTYZ could possibly provide neuroprotective role against learning / memory impairment, which provided a potential therapeutic tool delaying the progression of AD molecular interplays that includes the GSK-3β / CREB signaling pathway.

Acute Effects of Two Different Species of Amyloid-β on Oscillatory Activity and Synaptic Plasticity in the Commissural CA3-CA1 Circuit of the Hippocampus

Recent evidence indicates that soluble amyloid-β (Aβ) species induce imbalances in excitatory and inhibitory transmission, resulting in neural network functional impairment and cognitive deficits during early stages of Alzheimer's disease (AD). To evaluate the in vivo effects of two soluble Aβ species (Aβ_25-35 and Aβ_1-40) on commissural CA3-to-CA1 (cCA3-to-CA1) synaptic transmission and plasticity, and CA1 oscillatory activity, we used acute intrahippocampal microinjections in adult anaesthetized male Wistar rats. Soluble Aβ microinjection increased cCA3-to-CA1 synaptic variability without significant changes in synaptic efficiency. High-frequency CA3 stimulation was rendered inefficient by soluble Aβ intrahippocampal injection to induce long-term potentiation and to enhance synaptic variability in CA1, contrasting with what was observed in vehicle-injected subjects. Although soluble Aβ microinjection significantly increased the relative power of γ-band and ripple oscillations and significantly shifted the average vector of θ-to-γ phase-amplitude coupling (PAC) in CA1, it prevented θ-to-γ PAC shift induced by high-frequency CA3 stimulation, opposite to what was observed in vehicle-injected animals. These results provide further evidence that soluble Aβ species induce synaptic dysfunction causing abnormal synaptic variability, impaired long-term plasticity, and deviant oscillatory activity, leading to network activity derailment in the hippocampus.

N-Terminal Modified Aβ Variants Enable Modulations to the Structures and Cytotoxicity Levels of Wild-Type Aβ Fibrils through Cross-Seeding

Post-translational modifications (PTMs) of β-amyloid (Aβ) peptides are considered as triggering factors in sporadic Alzheimer's disease. However, studies to show the influence of pre-existing PTM-Aβ fibrils on wild-type Aβ peptides, which directly mimic the triggering scenarios, are rare. Here we show that three types of pathologically relevant PTM-Aβ variants with modifications in a particular segment (from D7 to V12) of the primary sequence lead to distinct impacts on the fibrillization of wild-type Aβ peptides. In general, the triggering effects are observed through cross-seeding between the PTM-Aβ seeds and wild-type peptides, which consequently induce modulations in the resultant wild-type fibril structures and elevations in the fibrillar cytotoxicity levels. Modifications with a similar chemical nature, such as the S8-phosphorylation and Y10-nitration, both of which introduce additional side-chain negative charges, show comparable structural-modulation and cytotoxicity-elevation effects. The results imply the biological influences of PTM-Aβ variants on the formation of amyloid deposits through cross-seeded fibrillization.

Structural Interaction of Apolipoprotein A-I Mimetic Peptide with Amyloid-β Generates Toxic Hetero-oligomers

Apolipoproteins are involved in pathological conditions of Alzheimer's disease (AD), and it has been reported that truncated apolipoprotein fragments and β-amyloid (Aβ) peptides coexist as neurotoxic heteromers within the plaques. Therefore, it is important to investigate these complexes at the molecular level to better understand their properties and roles in the pathology of AD. Here, we present a mechanistic insight into such heteromerization using a structurally homologue apolipoprotein fragment of apoA-I (4F) complexed with Aβ(M1-42) and characterize their toxicity. The 4F peptide slows down the aggregation kinetics of Aβ(M1-42) by constraining its structural plasticity. NMR and CD experiments identified 4F-Aβ(M1-42) heteromers comprised of unstructured Aβ(M1-42) and helical 4F. A uniform two-fold reduction in ¹⁵N/¹H NMR signal intensities of Aβ(M1-42) with no observable chemical shift perturbation indicated the formation of a large complex, which was further confirmed by diffusion NMR experiments. Microsecond-scale atomistic molecular dynamics simulations showed that 4F interaction with Aβ(M1-42) is electrostatically driven and induces unfolding of Aβ(M1-42). Neurotoxicity profiling of Aβ(M1-42) complexed with 4F confirms a significant reduction in cell viability and neurite growth. Thus, the molecular architecture of heteromerization between 4F and Aβ(M1-42) discovered in this study provides evidence toward our understanding of the role of apolipoproteins or their truncated fragments in exacerbating AD pathology.

Diminished amyloid-β uptake by mouse microglia upon treatment with quantum dots, silver or cerium oxide nanoparticles: Nanoparticles and amyloid-β uptake by microglia

Alzheimer’s disease (AD) is a chronic neurodegenerative disease leading to progressive dementia in elderly people. The disease is characterized, among others, by formation of amyloid- β (A β) polypeptide plaques in the brain. Although etiology of the disease is not fully understood, recent research suggest that nanomaterials may affect AD development. Here, we described the consequences of exposure of mouse BV-2 microglia to silver nanoparticles (AgNPs, 50 µg/mL), cerium oxide nanoparticles (CeO2NPs, 100 µg/mL), and cadmium telluride quantum dots (CdTeQDs, 3 or 10 µg/mL) in the context of its ability to clear A β plaques. The brain microglial cells play an important role in removing A β plaques from the brain. Cell viability and cycle progression were assessed by trypan blue test and propidium iodide binding, respectively. The uptake of A β and NPs was measured by flow cytometry. Secretion of proinflammatory cytokines was measured with the use of cytometric bead array. A β (0.1 μM) did not affect viability, whereas NPs decreased microglia growth by arresting the cells in G1 phase (CdTeQDs) or in S phase (AgNPs and CeO2NPs) of cell cycle. The uptake of A β was significantly reduced in the presence of AgNPs and CeO2NPs. In addition, the least toxic CeO2NPs induced the release of proinflammatory cytokine, tumor necrosis factor α. In summary, each of the NPs tested affected either the microglia phagocytic activity (AgNPs and CeO2NPs) and/or its viability (AgNPs and CdTeQDs) that may favor the occurrence of AD and accelerate its development.

Effects of Acetylcholine on β-Amyloid-Induced cPLA2 Activation in the TB Neuroectodermal Cell Line: Implications for the Pathogenesis of Alzheimer's Disease

The role of β-amyloid (Aβ) in the pathogenesis of Alzheimer's disease (AD) is still considered crucial. The state of Aβ aggregation is critical in promoting neuronal loss and neuronal function impairment. Recently, we demonstrated that Acetylcholine (ACh) is neuroprotective against the toxic effects of Aβ in the cholinergic LAN-2 cells. In biophysical experiments, ACh promotes the soluble Aβ peptide conformation rather than the aggregation-prone β-sheet conformation. In order to better understand the biological role of ACh in AD, we studied the effect of Aβ on the phosphorylation of the cytosolic phospholipase A2 (cPLA2) in the TB neuroectodermal cell line, which differentiates toward a neuronal phenotype when cultured in the presence of retinoic acid (RA). We chose the phosphorylated form of cPLA2 (Ser505, Phospho-cPLA2) as a biomarker to test the influence of ACh on the effects of Aβ in both undifferentiated and RA-differentiated TB cells. Our results show that TB cells are responsive to Aβ. Moreover, in undifferentiated cells 1 h treatment with Aβ induces a 2.5-fold increase of the Phospho-cPLA2 level compared to the control after 24 h in vitro, while no significant difference is observed between Aβ-treated and non-treated cells after 4 and 7 days in vitro. The RA-differentiated cells are not sensitive to Aβ. In TB cell line ACh is able to blunt the effects of Aβ. The ability of ACh to protect non-cholinergic cells against Aβ reinforces the hypothesis that, in addition to its role in cholinergic transmission, ACh could also act as a neuroprotective agent.

Effects of Ranolazine on Astrocytes and Neurons in Primary Culture

Ranolazine (Rn) is an antianginal agent used for the treatment of chronic angina pectoris when angina is not adequately controlled by other drugs. Rn also acts in the central nervous system and it has been proposed for the treatment of pain and epileptic disorders. Under the hypothesis that ranolazine could act as a neuroprotective drug, we studied its effects on astrocytes and neurons in primary culture. We incubated rat astrocytes and neurons in primary cultures for 24 hours with Rn (10-7, 10-6 and 10-5 M). Cell viability and proliferation were measured using trypan blue exclusion assay, MTT conversion assay and LDH release assay. Apoptosis was determined by Caspase 3 activity assay. The effects of Rn on pro-inflammatory mediators IL-β and TNF-α was determined by ELISA technique, and protein expression levels of Smac/Diablo, PPAR-γ, Mn-SOD and Cu/Zn-SOD by western blot technique. In cultured astrocytes, Rn significantly increased cell viability and proliferation at any concentration tested, and decreased LDH leakage, Smac/Diablo expression and Caspase 3 activity indicating less cell death. Rn also increased anti-inflammatory PPAR-γ protein expression and reduced pro-inflammatory proteins IL-1 β and TNFα levels. Furthermore, antioxidant proteins Cu/Zn-SOD and Mn-SOD significantly increased after Rn addition in cultured astrocytes. Conversely, Rn did not exert any effect on cultured neurons. In conclusion, Rn could act as a neuroprotective drug in the central nervous system by promoting astrocyte viability, preventing necrosis and apoptosis, inhibiting inflammatory phenomena and inducing anti-inflammatory and antioxidant agents.

WIN 55,212-2, agonist of cannabinoid receptors, prevents amyloid β1-42 effects on astrocytes in primary culture

Alzheimer´s disease (AD), a neurodegenerative illness involving synaptic dysfunction with extracellular accumulation of Aβ_1-42 toxic peptide, glial activation, inflammatory response and oxidative stress, can lead to neuronal death. Endogenous cannabinoid system is implicated in physiological and physiopathological events in central nervous system (CNS), and changes in this system are related to many human diseases, including AD. However, studies on the effects of cannabinoids on astrocytes functions are scarce. In primary cultured astrocytes we studied cellular viability using MTT assay. Inflammatory and oxidative stress mediators were determined by ELISA and Western-blot techniques both in the presence and absence of Aβ_1-42 peptide. Effects of WIN 55,212-2 (a synthetic cannabinoid) on cell viability, inflammatory mediators and oxidative stress were also determined. Aβ_1-42 diminished astrocytes viability, increased TNF-α and IL-1β levels and p-65, COX-2 and iNOS protein expression while decreased PPAR-γ and antioxidant enzyme Cu/Zn SOD. WIN 55,212-2 pretreatment prevents all effects elicited by Aβ_1-42. Furthermore, cannabinoid WIN 55,212-2 also increased cell viability and PPAR-γ expression in control astrocytes. In conclusion cannabinoid WIN 55,212-2 increases cell viability and anti-inflammatory response in cultured astrocytes. Moreover, WIN 55,212-2 increases expression of anti-oxidant Cu/Zn SOD and is able to prevent inflammation induced by Aβ_1-42 in cultured astrocytes. Further studies would be needed to assess the possible beneficial effects of cannabinoids in Alzheimer's disease patients.

Alzheimer's therapeutics targeting amyloid beta 1-42 oligomers I: Abeta 42 oligomer binding to specific neuronal receptors is displaced by drug candidates that improve cognitive deficits

Synaptic dysfunction and loss caused by age-dependent accumulation of synaptotoxic beta amyloid (Abeta) 1-42 oligomers is proposed to underlie cognitive decline in Alzheimer's disease (AD). Alterations in membrane trafficking induced by Abeta oligomers mediates reduction in neuronal surface receptor expression that is the basis for inhibition of electrophysiological measures of synaptic plasticity and thus learning and memory. We have utilized phenotypic screens in mature, in vitro cultures of rat brain cells to identify small molecules which block or prevent the binding and effects of Abeta oligomers. Synthetic Abeta oligomers bind saturably to a single site on neuronal synapses and induce deficits in membrane trafficking in neuronal cultures with an EC50 that corresponds to its binding affinity. The therapeutic lead compounds we have found are pharmacological antagonists of Abeta oligomers, reducing the binding of Abeta oligomers to neurons in vitro, preventing spine loss in neurons and preventing and treating oligomer-induced deficits in membrane trafficking. These molecules are highly brain penetrant and prevent and restore cognitive deficits in mouse models of Alzheimer's disease. Counter-screening these compounds against a broad panel of potential CNS targets revealed they are highly potent and specific ligands of the sigma-2/PGRMC1 receptor. Brain concentrations of the compounds corresponding to greater than 80% receptor occupancy at the sigma-2/PGRMC1 receptor restore cognitive function in transgenic hAPP Swe/Ldn mice. These studies demonstrate that synthetic and human-derived Abeta oligomers act as pharmacologically-behaved ligands at neuronal receptors--i.e. they exhibit saturable binding to a target, they exert a functional effect related to their binding and their displacement by small molecule antagonists blocks their functional effect. The first-in-class small molecule receptor antagonists described here restore memory to normal in multiple AD models and sustain improvement long-term, representing a novel mechanism of action for disease-modifying Alzheimer's therapeutics.

β-Amyloid inhibits E-S potentiation through suppression of cannabinoid receptor 1-dependent synaptic disinhibition

It has been widely reported that β-amyloid peptide (Aβ) blocks long-term potentiation (LTP) of hippocampal synapses. Here, we show evidence that Aβ more potently blocks the potentiation of excitatory postsynaptic potential (EPSP)-spike coupling (E-S potentiation). This occurs, not by direct effect on excitatory synapses or postsynaptic neurons, but rather through an indirect mechanism: reduction of endocannabinoid-mediated peritetanic disinhibition. During high-frequency (tetanic) stimulation, somatic synaptic inhibition is suppressed by endocannabinoids. We find that Aβ prevents this endocannabinoid-mediated disinhibition, thus leaving synaptic inhibition more intact during tetanic stimulation. This intact inhibition opposes the normal depolarization of hippocampal pyramidal neurons that occurs during tetanus, thus opposing the induction of synaptic plasticity. Thus, a pathway through which Aβ can act to modulate neural activity is identified, relevant to learning and memory and how it may mediate aspects of the cognitive decline seen in Alzheimer's disease.

Targeting the proper amyloid-beta neuronal toxins: a path forward for Alzheimer's disease immunotherapeutics

Levels of amyloid-beta monomer and deposited amyloid-beta in the Alzheimer’s disease brain are orders of magnitude greater than soluble amyloid-beta oligomer levels. Monomeric amyloid-beta has no known direct toxicity. Insoluble fibrillar amyloid-beta has been proposed to be an in vivo mechanism for removal of soluble amyloid-beta and exhibits relatively low toxicity. In contrast, soluble amyloid-beta oligomers are widely reported to be the most toxic amyloid-beta form, both causing acute synaptotoxicity and inducing neurodegenerative processes. None of the amyloid-beta immunotherapies currently in clinical development selectively target soluble amyloid-beta oligomers, and their lack of efficacy is not unexpected considering their selectivity for monomeric or fibrillar amyloid-beta (or both) rather than soluble amyloid-beta oligomers. Because they exhibit acute, memory-compromising synaptic toxicity and induce chronic neurodegenerative toxicity and because they exist at very low in vivo levels in the Alzheimer’s disease brain, soluble amyloid-beta oligomers constitute an optimal immunotherapeutic target that should be pursued more aggressively.

Oligomer-targeting with a conformational antibody fragment promotes toxicity in Aβ-expressing flies

Introduction

The self-assembly of Aβ peptides into a range of conformationally heterogeneous amyloid states represents a fundamental event in Alzheimer’s disease. Within these structures oligomeric intermediates are considered to be particularly pathogenic. To test this hypothesis we have used a conformational targeting approach where particular conformational states, such as oligomers or fibrils, are recognized in vivo by state-specific antibody fragments.

Results

We show that oligomer targeting with the KW1 antibody fragment, but not fibril targeting with the B10 antibody fragment, affects toxicity in Aβ-expressing Drosophila melanogaster. The effect of KW1 is observed to occur selectively with flies expressing Aβ(1–40) and not with those expressing Aβ(1–42) or the arctic variant of Aβ(1–42) This finding is consistent with the binding preference of KW1 for Aβ(1–40) oligomers that has been established in vitro. Strikingly, and in contrast to the previously demonstrated in vitro ability of this antibody fragment to block oligomeric toxicity in long-term potentiation measurements, KW1 promotes toxicity in the flies rather than preventing it. This result shows the crucial importance of the environment in determining the influence of antibody binding on the nature and consequences of the protein misfolding and aggregation.

Conclusions

While our data support to the pathological relevance of oligomers, they highlight the issues to be addressed when developing inhibitory strategies that aim to neutralize these states by means of antagonistic binding agents.

Axon degeneration is key component of neuronal death in amyloid-β toxicity

Depending upon the stimulus, neuronal cell death can either be triggered from the cell body (soma) or the axon. We investigated the origin of the degeneration signal in amyloid β (Aβ) induced neuronal cell death in cultured in vitro hippocampal neurons. We discovered that Aβ1-42 toxicity-induced axon degeneration precedes cell death in hippocampal neurons. Overexpression of Bcl-xl inhibited both axonal and cell body degeneration in the Aβ-42 treated neurons. Nicotinamide mononucleotide adenylyltransferase 1 (Nmnat1) blocks axon degeneration in a variety of paradigms, but it cannot block neuronal cell body death. Therefore, if the neuronal death signals in Aβ1-42 toxicity originate from degenerating axons, we should be able to block neuronal death by inhibiting axon degeneration. To explore this possibility we over-expressed Nmnat1 in hippocampal neurons. We found that inhibition of axon degeneration in Aβ1-42 treated neurons prevented neuronal cell death. Thus, we conclude that axon degeneration is the key component of Aβ1-42 induced neuronal degeneration, and therapies targeting axonal protection can be important in finding a treatment for Alzheimer's disease.

A structure-toxicity study of Aß42 reveals a new anti-parallel aggregation pathway

Amyloid beta (Aβ) peptides produced by APP cleavage are central to the pathology of Alzheimer’s disease. Despite widespread interest in this issue, the relationship between the auto-assembly and toxicity of these peptides remains controversial. One intriguing feature stems from their capacity to form anti-parallel ß-sheet oligomeric intermediates that can be converted into a parallel topology to allow the formation of protofibrillar and fibrillar Aβ. Here, we present a novel approach to determining the molecular aspects of Aß assembly that is responsible for its in vivo toxicity. We selected Aß mutants with varying intracellular toxicities. In vitro, only toxic Aß (including wild-type Aß₄₂) formed urea-resistant oligomers. These oligomers were able to assemble into fibrils that are rich in anti-parallel ß-sheet structures. Our results support the existence of a new pathway that depends on the folding capacity of Aß .

Amyloid Beta peptides differentially affect hippocampal theta rhythms in vitro

Soluble amyloid beta peptide (A β ) is responsible for the early cognitive dysfunction observed in Alzheimer's disease. Both cholinergically and glutamatergically induced hippocampal theta rhythms are related to learning and memory, spatial navigation, and spatial memory. However, these two types of theta rhythms are not identical; they are associated with different behaviors and can be differentially modulated by diverse experimental conditions. Therefore, in this study, we aimed to investigate whether or not application of soluble A β alters the two types of theta frequency oscillatory network activity generated in rat hippocampal slices by application of the cholinergic and glutamatergic agonists carbachol or DHPG, respectively. Due to previous evidence that oscillatory activity can be differentially affected by different A β peptides, we also compared Aβ 25-35 and Aβ 1-42 for their effects on theta rhythms in vitro at similar concentrations (0.5 to 1.0  μ M). We found that Aβ 25-35 reduces, with less potency than Aβ 1-42, carbachol-induced population theta oscillatory activity. In contrast, DHPG-induced oscillatory activity was not affected by a high concentration of Aβ 25-35 but was reduced by Aβ 1-42. Our results support the idea that different amyloid peptides might alter specific cellular mechanisms related to the generation of specific neuronal network activities, instead of exerting a generalized inhibitory effect on neuronal network function.

Therapeutic Effect of Yi-Chi-Tsung-Ming-Tang on Amyloid β-Induced Alzheimer's Disease-Like Phenotype via an Increase of Acetylcholine and Decrease of Amyloid β

Alzheimer's disease (AD) is an irreversible neurodegenerative disorder characterized by amyloid accumulation, neuronal death, and cognitive impairments. Yi-Chi-Tsung-Ming-Tang (YCTMT) is a traditional Chinese medicine and has never been used to enhance cognitive function and treat neurodegenerative disorders such as senile dementia. Whether YCTMT has a beneficial role in improving learning and memory in AD patients remains unclear. The present study showed that oral administration of YCTMT ameliorated amyloid-β- (Aβ₁₋₄₀) injection-induced learning and memory impairments in rats, examined using passive avoidance and Morris water-maze tests. Immunostaining and Western Blot results showed that continuous Aβ₁₋₄₀ infusion caused amyloid accumulation and decreased acetylcholine level in hippocampus. Oral administration of medium and high dose of YCTMT 7 days after the Aβ₁₋₄₀ infusion decreased amyloid accumulation area and reversed acetylcholine decline in the Aβ₁₋₄₀-injected hippocampus, suggesting that YCTMT might inhibit Aβ plague accumulation and rescue reduced acetylcholine expression. This study has provided evidence on the beneficial role of YCTMT in ameliorating amyloid-induced AD-like symptom, indicating that YCTMT may offer an alternative strategy for treating AD.

Phenolic compounds prevent amyloid β-protein oligomerization and synaptic dysfunction by site-specific binding

Cerebral deposition of amyloid β protein (Aβ) is an invariant feature of Alzheimer disease (AD), and epidemiological evidence suggests that moderate consumption of foods enriched with phenolic compounds reduce the incidence of AD. We reported previously that the phenolic compounds myricetin (Myr) and rosmarinic acid (RA) inhibited Aβ aggregation in vitro and in vivo. To elucidate a mechanistic basis for these results, we analyzed the effects of five phenolic compounds in the Aβ aggregation process and in oligomer-induced synaptic toxicities. We now report that the phenolic compounds blocked Aβ oligomerization, and Myr promoted significant NMR chemical shift changes of monomeric Aβ. Both Myr and RA reduced cellular toxicity and synaptic dysfunction of the Aβ oligomers. These results suggest that Myr and RA may play key roles in blocking the toxicity and early assembly processes associated with Aβ through different binding.

Oligomeric intermediates in amyloid formation: structure determination and mechanisms of toxicity

Oligomeric intermediates are non-fibrillar polypeptide assemblies that occur during amyloid fibril formation and that are thought to underlie the aetiology of amyloid diseases, such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Focusing primarily on the oligomeric states formed from Alzheimer's disease β-amyloid (Aβ) peptide, this review will make references to other polypeptide systems, highlighting common principles or sequence-specific differences. The covered topics include the structural properties and polymorphism of oligomers, the biophysical mechanism of peptide self-assembly and its role for pathogenicity in amyloid disease. Oligomer-dependent toxicity mechanisms will be explained along with recently emerging possibilities of interference.

Beta-like hippocampal network activity is differentially affected by amyloid beta peptides

Alzheimer disease (AD) patients show alterations in both neuronal network oscillations and the cognitive processes associated to them. Related to this clinical observation, it has been found that amyloid beta protein (Abeta) differentially affects some hippocampal network activities, reducing theta and gamma oscillations, without affecting sharp waves and ripples. Beta-like oscillations is another cognitive-related network activity that can be evoked in hippocampal slices by several experimental manipulations, including bath application of kainate and increasing extracellular potassium. Here, we tested whether or not different Abeta peptides differentially affect beta-like oscillatory patterns. We specifically tested the effects of fresh dissolved Abeta(25-35) and oligomerized Abeta(1-42) and found that kainate-induced oscillatory network activity was affected, in a slightly concentration dependent-manner, by both fresh dissolved (mostly monomeric) Abeta(25-35) and oligomeric Abeta(1-42). In contrast, potassium-induced oscillatory activity, which is reduced by oligomeric Abeta(1-42), is not affected by monomeric Abeta(25-35) at any of the concentrations tested. Our results support the idea that different amyloid peptides might alter specific cellular mechanisms related to the generation of specific neuronal network activities, instead of a generalized inhibitory effect of Abeta peptides on neuronal network function.

Effects of the English (H6R) and Tottori (D7N) familial Alzheimer disease mutations on amyloid beta-protein assembly and toxicity

Mutations in the amyloid beta-protein (Abeta) precursor gene cause autosomal dominant Alzheimer disease in a number of kindreds. In two such kindreds, the English and the Tottori, the mutations produce amyloid beta-proteins containing amino acid substitutions, H6R and D7N, respectively, at the peptide N terminus. To elucidate the structural and biological effects of the mutations, we began by examining monomer conformational dynamics and oligomerization. Relative to their wild type homologues, and in both the Abeta40 and Abeta42 systems, the English and Tottori substitutions accelerated the kinetics of secondary structure change from statistical coil --> alpha/beta --> beta and produced oligomer size distributions skewed to higher order. This skewing was reflected in increases in average oligomer size, as measured using electron microscopy and atomic force microscopy. Stabilization of peptide oligomers using in situ chemical cross-linking allowed detailed study of their properties. Each substitution produced an oligomer that displayed substantial beta-strand (H6R) or alpha/beta (D7N) structure, in contrast to the predominately statistical coil structure of wild type Abeta oligomers. Mutant oligomers functioned as fibril seeds, and with efficiencies significantly higher than those of their wild type homologues. Importantly, the mutant forms of both native and chemically stabilized oligomers were significantly more toxic in assays of cell physiology and death. The results show that the English and Tottori mutations alter Abeta assembly at its earliest stages, monomer folding and oligomerization, and produce oligomers that are more toxic to cultured neuronal cells than are wild type oligomers.

Oligomerisation differentially affects the acute and chronic actions of amyloid-beta in vitro

Key neuropathological hallmarks of Alzheimer's disease include the accumulation of amyloid-beta (Abeta), disruption of Ca(2+) homeostasis and neurodegeneration. However, the physical nature of the toxic Abeta species is controversial. Here, we examined the effect of aging on acute and chronic actions of Abeta peptides: changes in intracellular Ca(2+) and toxic responses, respectively. Acute application of Abeta(1-42) to PC12 cells potentiated KCl-evoked increases in Ca(2+), while chronic application decreased mitochondrial function with concomitant perturbation of membrane integrity and activation of apoptosis in PC12 cells, and reduced neurite length and synaptogenesis in rat cortical neurons. Both the acute and chronic effects of Abeta(1-42) were prevented by the anti-oligomerisation peptide D-KLVFFA, implicating oligomeric structures. The generation of a range of oligomeric species by aging Abeta(1-42) at 37 degrees C for different times was supported by thioflavin T fluorescence and atomic force microscopy. Abeta(1-42) aged for 24 h maximally potentiated KCl-evoked increases in Ca(2+), and this correlated with oligomers composed of 3-6 monomers, as judged by size exclusion filtration. Aging for 72 or 96 h, which generated fibrillar structures, was less efficacious. The Abeta(25-35) fragment that lacks the self-recognition element targeted by D-KLVFFA failed to potentiate KCl-evoked increases in Ca(2+). However, Abeta(25-35) was more efficacious than Abeta(1-42) at decreasing cellular functions when applied chronically. The acute and chronic effects of Abeta(1-42) also showed differential sensitivity to blockade of voltage operated Ca(2+) channels. These results suggest that the acute effects of Abeta(1-42) on Ca(2+) signals do not underpin the toxic responses measured, although both acute and chronic effects are promoted by small oligomeric species.