Water-soluble Abeta (N-40, N-42) oligomers in normal and Alzheimer disease brains

Prevention of amyloid β fibril deposition on the synaptic membrane in the precuneus by ganglioside nanocluster-targeting inhibitors

Alzheimer's disease (AD), a progressive neurodegenerative condition, is one of the most common causes of dementia. Senile plaques, a hallmark of AD, are formed by the accumulation of amyloid β protein (Aβ), which starts to aggregate before the onset of the disease. Gangliosides, sialic acid-containing glycosphingolipids, play a key role in the formation of toxic Aβ aggregates. In membrane rafts, ganglioside-bound complexes (GAβ) act as nuclei for Aβ assembly, suggesting that GAβ is a promising target for AD therapy. The formation of GAβ-induced Aβ assemblies has been evaluated using reconstituted planar lipid membranes composed of synaptosomal plasma membrane (SPM) lipids extracted from human and mouse brains. Although the effects of gangliosides on Aβ accumulation in the precuneus have been established, effects on Aβ fibrils have not been determined. In this study, Aβ42 fibrils on reconstituted membranes composed of SPM lipids prepared from the precuneus cortex of human autopsied brains were evaluated by atomic force microscopy. In particular, Aβ42 accumulation, as well as the fibril number and size were higher for membranes with precuneus lipids than for membranes with calcarine cortex lipids. In addition, artificial peptide inhibitors targeting Aβ-sensitive ganglioside nanoclusters cleared Aβ assemblies on synaptic membranes in the brain, providing a novel therapeutic strategy for AD.

A Toxicogenic Interaction between Intracellular Amyloid-β and Apolipoprotein-E

Alzheimer's disease (AD) is associated with the aggregation of amyloid β (Aβ) and tau proteins. Why ApoE variants are significant genetic risk factors remains a major unsolved puzzle in understanding AD, although intracellular interactions with ApoE are suspected to play a role. Here, we show that specific changes in the fluorescence lifetime of fluorescently tagged small Aβ oligomers in rat brain cells correlate with the cellular ApoE content. An inhibitor of the Aβ-ApoE interaction suppresses these changes and concomitantly reduces Aβ toxicity in a dose-dependent manner. Single-molecule techniques show changes both in the conformation and in the stoichiometry of the oligomers. Neural stem cells derived from hiPSCs of Alzheimer's patients also exhibit these fluorescence lifetime changes. We infer that intracellular interaction with ApoE modifies the N-terminus of the Aβ oligomers, inducing changes in their stoichiometry, membrane affinity, and toxicity. These changes can be directly imaged in live cells and can potentially be used as a rapid and quantitative cellular assay for AD drug discovery.

Visualization of Amyloid Oligomers in the Brain of Patients with Alzheimer's Disease

In the pathogenesis of Alzheimer's disease (AD), highly neurotoxic amyloid-β (Aβ) oligomers appear early, they are thus considered to be deeply involved in the onset of Alzheimer's disease. However, Aβ oligomer visualization is challenging in human tissues due to their multiple forms (e.g., low- and high-molecular-weight oligomers, including protofibrils) as well as their tendency to rapidly change forms and aggregate. In this review, we present two visualization approaches for Aβ oligomers in tissues: an immunohistochemical (using the monoclonal antibody TxCo1 against toxic Aβ oligomer conformers) and imaging mass spectrometry using the small chemical Shiga-Y51 that specifically binds Aβ oligomers. TxCo1 immunohistochemistry revealed Aβ oligomer distributions in postmortem human brains with AD. Using Shiga-Y51, imaging mass spectrometry revealed Aβ oligomer distributions in the brain of a transgenic mouse model for AD. These two methods would potentially contribute to elucidating the pathological mechanisms underlying AD.

Cyclization of Peptides Enhances the Inhibitory Activity against Ganglioside-Induced Aβ Fibril Formation

Alzheimer's disease is a progressive neurodegenerative disease and is the most common cause of dementia. It has been reported that the assembly of amyloid β-protein (Aβ) on the cell membrane is induced by the interaction of the Aβ monomer with gangliosides such as GM1. The ganglioside-bound Aβ (GAβ) complex acts as a seed to promote the toxic assembly of the Aβ fibrils. In a previous study, we found that a GM1 cluster-binding peptide (GCBP) specifically recognizes Aβ-sensitive ganglioside nanoclusters and inhibits the assembly of Aβ on a GM1-containing lipid membrane. In this study, cysteine-substituted double mutants of GCBP were designed and cyclized by intramolecular disulfide bond formation. Affinity assays indicated that one of the cyclic peptides had a higher affinity to a GM1-containing membrane compared to that of GCBP. Furthermore, surface topography analysis indicated that this peptide recognizes GM1 nanoclusters on the lipid membrane. An evaluation of the inhibitory kinetics indicated that the cyclic peptide could inhibit the formation of Aβ fibrils with an IC50 value of 1.2 fM, which is 10,000-fold higher than that of GCBP. The cyclic peptide was also shown to have a clearance effect on Aβ fibrils deposited on the lipid membrane and suppressed the formation of toxic Aβ assemblies. Our results indicate that the cyclic peptide that binds to the Aβ-sensitive ganglioside nanocluster is a potential novel inhibitor of ganglioside-induced Aβ assembly.

IM-MS and ECD-MS/MS Provide Insight into Modulation of Amyloid Proteins Self-Assembly by Peptides and Small Molecules

Neurodegenerative proteinopathies are characterized by formation and deposition of misfolded, aggregated proteins in the nervous system leading to neuronal dysfunction and death. It is widely believed that metastable oligomers of the offending proteins, preceding the fibrillar aggregates found in the tissue, are the proximal neurotoxins. There are currently almost no disease-modifying therapies for these diseases despite an active pipeline of preclinical development and clinical trials for over two decades, largely because studying the metastable oligomers and their interaction with potential therapeutics is notoriously difficult. Mass spectrometry (MS) is a powerful analytical tool for structural investigation of proteins, including protein-protein and protein-ligand interactions. Specific MS tools have been useful in determining the composition and conformation of abnormal protein oligomers involved in proteinopathies and the way they interact with drug candidates. Here, we analyze critically the utilization of ion-mobility spectroscopy-MS (IM-MS) and electron-capture dissociation (ECD) MS/MS for analyzing the oligomerization and conformation of multiple amyloidogenic proteins. We also discuss IM-MS investigation of their interaction with two classes of compounds developed by our group over the last two decades: C-terminal fragments derived from the 42-residue form of amyloid β-protein (Aβ42) and molecular tweezers. Finally, we review the utilization of ECD-MS/MS for elucidating the binding sites of the ligands on multiple proteins. These approaches are readily applicable to future studies addressing similar questions and hold promise for facilitating the development of successful disease-modifying drugs against neurodegenerative proteinopathies.

Tau and Amyloid β Protein in Patient-Derived Aqueous Brain Extracts Act Concomitantly to Disrupt Long-Term Potentiation in Vivo

Amyloid β protein (Aβ) and tau, the two main proteins implicated in causing Alzheimer's disease (AD), are posited to trigger synaptic dysfunction long before significant synaptic loss occurs in vulnerable circuits. Whereas soluble Aβ aggregates from AD brain are well recognized potent synaptotoxins, less is known about the synaptotoxicity of soluble tau from AD or other tauopathy patient brains. Minimally manipulated patient-derived aqueous brain extracts contain the more diffusible native forms of these proteins. Here, we explore how intracerebral injection of Aβ and tau present in such aqueous extracts of patient brain contribute to disruption of synaptic plasticity in the CA1 area of the male rat hippocampus. Aqueous extracts of certain AD brains acutely inhibited long-term potentiation (LTP) of synaptic transmission in a manner that required both Aβ and tau. Tau-containing aqueous extracts of a brain from a patient with Pick's disease (PiD) also impaired LTP, and diffusible tau from either AD or PiD brain lowered the threshold for AD brain Aβ to inhibit LTP. Remarkably, the disruption of LTP persisted for at least 2 weeks after a single injection. These findings support a critical role for diffusible tau in causing rapid onset, persistent synaptic plasticity deficits, and promoting Aβ-mediated synaptic dysfunction.SIGNIFICANCE STATEMENT The microtubule-associated protein tau forms relatively insoluble fibrillar deposits in the brains of people with neurodegenerative diseases including Alzheimer's and Pick's diseases. More soluble aggregates of disease-associated tau may diffuse between cells and could cause damage to synapses in vulnerable circuits. We prepared aqueous extracts of diseased cerebral cortex and tested their ability to interfere with synaptic function in the brains of live rats. Tau in these extracts rapidly and persistently disrupted synaptic plasticity and facilitated impairments caused by amyloid β protein, the other major pathologic protein in Alzheimer's disease. These findings show that certain diffusible forms of tau can mediate synaptic dysfunction and may be a target for therapy.

Methods for the isolation and analysis of Aβ from postmortem brain

Amyloid β-protein (Aβ) plays an initiating role in Alzheimer's disease (AD), but only a small number of groups have studied Aβ extracted from human brain. Most prior studies have utilized synthetic Aβ peptides, but the relevance of these test tube experiments to the conditions that prevail in AD is uncertain. Here, we describe three distinct methods for studying Aβ from cortical tissue. Each method allows the analysis of different ranges of species thus enabling the examination of different questions. The first method allows the study of readily diffusible Aβ with a relatively high specific activity. The second enables the analysis of readily solubilized forms of Aβ the majority of which are inactive. The third details the isolation of true Aβ dimers which have disease-related activity. We also describe a bioassay to study the effects of Aβ on the neuritic integrity of iPSC-derived human neurons. The combined use of this bioassay and the described extraction procedures provides a platform to investigate the activity of different forms and mixtures of Aβ species, and offers a tractable system to identify strategies to mitigate Aβ mediated neurotoxicity.

Aβ42 oligomer-specific antibody ALZ-201 reduces the neurotoxicity of Alzheimer's disease brain extracts

BACKGROUND

In Alzheimer's disease (AD), amyloid-β 1-42 (Aβ42) neurotoxicity stems mostly from its soluble oligomeric aggregates. Studies of such aggregates have been hampered by the lack of oligomer-specific research tools and their intrinsic instability and heterogeneity. Here, we developed a monoclonal antibody with a unique oligomer-specific binding profile (ALZ-201) using oligomer-stabilising technology. Subsequently, we assessed the etiological relevance of the Aβ targeted by ALZ-201 on physiologically derived, toxic Aβ using extracts from post-mortem brains of AD patients and controls in primary mouse neuron cultures.

METHODS

Mice were immunised with stable oligomers derived from the Aβ42 peptide with A21C/A30C mutations (AβCC), and ALZ-201 was developed using hybridoma technology. Specificity for the oligomeric form of the Aβ42CC antigen and Aβ42 was confirmed using ELISA, and non-reactivity against plaques by immunohistochemistry (IHC). The antibody's potential for cross-protective activity against pathological Aβ was evaluated in brain tissue samples from 10 individuals confirmed as AD (n=7) and non-AD (n=3) with IHC staining for Aβ and phosphorylated tau (p-Tau) aggregates. Brain extracts were prepared and immunodepleted using the positive control 4G8 antibody, ALZ-201 or an isotype control to ALZ-201. Fractions were biochemically characterised, and toxicity assays were performed in primary mouse neuronal cultures using automated high-content microscopy.

RESULTS

AD brain extracts proved to be more toxic than controls as demonstrated by neuronal loss and morphological determinants (e.g. synapse density and measures of neurite complexity). Immunodepletion using 4G8 reduced Aβ levels in both AD and control samples compared to ALZ-201 or the isotype control, which showed no significant difference. Importantly, despite the differential effect on the total Aβ content, the neuroprotective effects of 4G8 and ALZ-201 immunodepletion were similar, whereas the isotype control showed no effect.

CONCLUSIONS

ALZ-201 depletes a toxic species in post-mortem AD brain extracts causing a positive physiological and protective impact on the integrity and morphology of mouse neurons. Its unique specificity indicates that a low-abundant, soluble Aβ42 oligomer may account for much of the neurotoxicity in AD. This critical attribute identifies the potential of ALZ-201 as a novel drug candidate for achieving a true, clinical therapeutic effect in AD.

Oligomeropathies, inflammation and prion protein binding

The central role of oligomers, small soluble aggregates of misfolded proteins, in the pathogenesis of neurodegenerative disorders is recognized in numerous experimental conditions and is compatible with clinical evidence. To underline this concept, some years ago we coined the term oligomeropathies to define the common mechanism of action of protein misfolding diseases like Alzheimer, Parkinson or prion diseases. Using simple experimental conditions, with direct application of synthetic β amyloid or α-synuclein oligomers intraventricularly at micromolar concentrations, we could detect differences and similarities in the biological consequences. The two oligomer species affected cognitive behavior, neuronal dysfunction and cerebral inflammatory reactions with distinct mechanisms. In these experimental conditions the proposed mediatory role of cellular prion protein in oligomer activities was not confirmed. Together with oligomers, inflammation at different levels can be important early in neurodegenerative disorders; both β amyloid and α-synuclein oligomers induce inflammation and its control strongly affects neuronal dysfunction. This review summarizes our studies with β-amyloid or α-synuclein oligomers, also considering the potential curative role of doxycycline, a well-known antibiotic with anti-amyloidogenic and anti-inflammatory activities. These actions are analyzed in terms of the therapeutic prospects.

Synaptic Disruption by Soluble Oligomers in Patients with Alzheimer's and Parkinson's Disease

Neurodegenerative diseases are the result of progressive dysfunction of the neuronal activity and subsequent neuronal death. Currently, the most prevalent neurodegenerative diseases are by far Alzheimer's (AD) and Parkinson's (PD) disease, affecting millions of people worldwide. Although amyloid plaques and neurofibrillary tangles are the neuropathological hallmarks for AD and Lewy bodies (LB) are the hallmark for PD, current evidence strongly suggests that oligomers seeding the neuropathological hallmarks are more toxic and disease-relevant in both pathologies. The presence of small soluble oligomers is the common bond between AD and PD: amyloid β oligomers (AβOs) and Tau oligomers (TauOs) in AD and α-synuclein oligomers (αSynOs) in PD. Such oligomers appear to be particularly increased during the early pathological stages, targeting synapses at vulnerable brain regions leading to synaptic plasticity disruption, synapse loss, inflammation, excitation to inhibition imbalance and cognitive impairment. Absence of TauOs at synapses in individuals with strong AD disease pathology but preserved cognition suggests that mechanisms of resilience may be dependent on the interactions between soluble oligomers and their synaptic targets. In this review, we will discuss the current knowledge about the interactions between soluble oligomers and synaptic dysfunction in patients diagnosed with AD and PD, how it affects excitatory and inhibitory synaptic transmission, and the potential mechanisms of synaptic resilience in humans.

A History of Senile Plaques: From Alzheimer to Amyloid Imaging

Senile plaques have been studied in postmortem brains for more than 120 years and the resultant knowledge has not only helped us understand the etiology and pathogenesis of Alzheimer disease (AD), but has also pointed to possible modes of prevention and treatment. Within the last 15 years, it has become possible to image plaques in living subjects. This is arguably the single greatest advance in AD research since the identification of the Aβ peptide as the major plaque constituent. The limitations and potentialities of amyloid imaging are still not completely clear but are perhaps best glimpsed through the perspective gained from the accumulated postmortem histological studies. The basic morphological classification of plaques into neuritic, cored and diffuse has been supplemented by sophisticated immunohistochemical and biochemical analyses and increasingly detailed mapping of plaque brain distribution. Changes in plaque classification and staging have in turn contributed to changes in the definition and diagnostic criteria for AD. All of this information continues to be tested by clinicopathological correlations and it is through the insights thereby gained that we will best be able to employ the powerful tool of amyloid imaging.

Recent Advances Towards Diagnosis and Therapeutic Fingerprinting for Alzheimer's Disease

Since the report of "a peculiar severe disease process of the cerebral cortex" by Alois Alzheimer in 1906, it was considered to be a rare condition characterized by loss of cognition, memory impairment, and pathological markers such as senile plaques or neurofibrillary tangles (NFTs). Later on, the report was published in the textbook "Psychiatrie" and the disease was named as Alzheimer's disease (AD) and was known to be the consequences of aging; however, owing to its complex etiology, there is no cure for the progressive neurodegenerative disorder. Our current understanding of the mechanisms involved in the pathogenesis of AD is still at the mechanistic level. The treatment strategies applied currently only alleviate the symptoms and co-morbidities. For instance, the available treatments such as the usage of acetylcholinesterase inhibitors and N-methyl D-aspartate antagonists have minimal impact on the disease progression and target the later aspects of the disease. The recent advancements in the last two decades have made us more clearly understand the pathophysiology of the disease which has led to the development of novel therapeutic strategies. This review gives a brief idea about the various facets of AD pathophysiology and its management through modern investigational therapies to give a new direction for development of targeted therapeutic measures.

Amyloid-β Oligomers: Multiple Moving Targets

Alzheimer’s Disease (AD) is a neurodegenerative disorder that is characterized clinically by progressive cognitive decline and pathologically by the β-sheet rich fibril plaque deposition of the amyloid-β (Aβ) peptide in the brain. While plaques are a hallmark of AD, plaque burden is not correlated with cognitive impairment. Instead, Aβ oligomers formed during the aggregation process represent the main agents of neurotoxicity, which occurs 10–20 years before patients begin to show symptoms. These oligomers are dynamic in nature and represented by a heterogeneous distribution of aggregates ranging from low- to high-molecular weight, some of which are toxic while others are not. A major difficulty in determining the pathological mechanism(s) of Aβ, developing reliable diagnostic markers for early-stage detection, as well as effective therapeutics for AD are the differentiation and characterization of oligomers formed throughout disease propagation based on their molecular features, effects on biological function, and relevance to disease propagation and pathology. Thus, it is critical to methodically identify the mechanisms of Aβ aggregation and toxicity, as well as describe the roles of different oligomers and aggregates in disease progression and molecular pathology. Here, we describe a variety of biophysical techniques used to isolate and characterize a range of Aβ oligomer populations, as well as discuss proposed mechanisms of toxicity and therapeutic interventions aimed at specific assemblies formed during the aggregation process. The approaches being used to map the misfolding and aggregation of Aβ are like what was done during the fundamental early studies, mapping protein folding pathways using combinations of biophysical techniques in concert with protein engineering. Such information is critical to the design and molecular engineering of future diagnostics and therapeutics for AD.

Proteasome activity modulates amyloid toxicity

Alzheimer's disease (AD) is responsible for 60%-80% of identified cases of dementia. While the generation and accumulation of amyloid precursor protein (APP) fragments is accepted as a key step in AD pathogenesis, the precise role of these fragments remains poorly understood. To overcome this deficit, we induced the expression of the soluble C-terminal fragment of APP (C99), the rate-limiting peptide for the generation of amyloid fragments, in yeast that contain thermosensitive mutations in genes encoding proteasome subunits. Our previous work with this system demonstrated that these proteasome-deficient yeast cells, expressing C99 when proteasome activity was blunted, generated amyloid fragments similar to those observed in AD patients. We now report the phenotypic repercussions of inducing C99 expression in proteasome-deficient cells. We show increased levels of protein aggregates, cellular stress and chaperone expression, electron-dense accumulations in the nuclear envelope/ER, abnormal DNA condensation, and an induction of apoptosis. Taken together, these findings suggest that the generation of C99 and its associated fragments in yeast cells with compromised proteasomal activity results in phenotypes that may be relevant to the neuropathological processes observed in AD patients. These data also suggest that this yeast model should be useful for testing therapeutics that target AD-associated amyloid, since it allows for the assessment of the reversal of the perturbed cellular physiology observed when degradation pathways are dysfunctional.

Mitochondrial defects: An emerging theranostic avenue towards Alzheimer's associated dysregulations

Mitochondria play a crucial role in expediting the energy homeostasis under varying environmental conditions. As mitochondria are controllers of both energy production and apoptotic pathways, they are also distinctively involved in controlling the neuronal cell survival and/or death. Numerous factors are responsible for mitochondria to get degraded with aging and huge functional failures in mitochondria are also found to be associated with the commencement of numerous neurodegenerative conditions, including Alzheimer's disease (AD). A large number of existing literatures promote the pivotal role of mitochondrial damage and oxidative impairment in the pathogenesis of AD. Numerous mitochondria associated processes such as mitochondrial biogenesis, fission, fusion, mitophagy, transportation and bioenergetics are crucial for proper functioning of mitochondria but are reported to be defective in AD patients. Though, the knowledge on the precise and in-depth mechanisms of these actions is still in infancy. Based upon the outcome of various significant studies, mitochondria are also being considered as therapeutic targets for AD. Here, we review the current status of mitochondrial defects in AD and also summarize the possible role of these defects in the pathogenesis of AD. The various approaches for developing the mitochondria-targeted therapies are also discussed here in detail. Consequently, it is suggested that improving mitochondrial activity via pharmacological and/or non-pharmacological interventions could postpone the onset and slow the development of AD. Further research and consequences of ongoing clinical trials should extend our understanding and help to validate conclusions regarding the causation of AD.

Distinct types of amyloid-β oligomers displaying diverse neurotoxicity mechanisms in Alzheimer's disease

Soluble oligomers of amyloid-β (Aβ) are recognized as key pernicious species in Alzheimer's disease (AD) that cause synaptic dysfunction and memory impairments. Numerous studies have identified various types of Aβ oligomers having heterogeneous peptide length, size distribution, structure, appearance, and toxicity. Here, we review the characteristics of soluble Aβ oligomers based on their morphology, size, and structural reactivity toward the conformation-specific antibodies and then describe their formation, localization, and cellular effects in AD brains, in vivo and in vitro. We also summarize the mechanistic pathways by which these soluble Aβ oligomers cause proteasomal impairment, calcium dyshomeostasis, inhibition of long-term potentiation, apoptosis, mitochondrial damage, and cognitive decline. These cellular events include three distinct molecular mechanisms: (i) high-affinity binding with the receptors for Aβ oligomers such as N-methyl- d-aspartate receptors, cellular prion protein, nerve growth factor, insulin receptors, and frizzled receptors; (ii) the interaction of Aβ oligomers with the lipid membranes; (iii) intraneuronal accumulation of Aβ by α7-nicotinic acetylcholine receptors, apolipoprotein E, and receptor for advanced glycation end products. These studies indicate that there is a pressing need to carefully examine the role of size, appearance, and the conformation of oligomers in identifying the specific mechanism of neurotoxicity that may uncover potential targets for designing AD therapeutics.

Nicotine prevents in vivo Aβ toxicity in Caenorhabditis elegans via SKN-1

OBJECTIVE

Nicotine, a main active compound in tobacco, has been shown to attenuate amyloid-β (Aβ) mediated neurotoxicity. However, the detailed underlying mechanisms remains to be elucidated. In this study, nematode Caenorhabditis elegans (C. elegans) had been chosen as the model animal for dissecting the role of nicotine in the prevention of Aβ-induced toxicity in vivo.

METHODS

CL2120 and CL4176 transgenic worms of Alzheimer's disease (AD) models were treated with different concentrations of nicotine, and worm paralysis was monitored. Next, the effects of nicotine on Aβ deposits, Aβ oligomers, reactive oxygen species (ROS) and the oxidative stress resistance in worms were measured. Moreover, the pathway responsible for nicotine alleviating Aβ-induced toxicity in vivo was explored by observing the oxidative stress resistance of skn-1 or daf-16 mutants in the presence of nicotine. Furthermore, the worm paralysis and Aβ deposits were further checked in CL4176 worms with skn-1 RNA interference under the condition of nicotine.

RESULTS

Nicotine (5 μM) attenuated AD-like symptoms of worm paralysis in CL2120 and CL4176 transgenic C. elegans. Nicotine did not inhibit Aβ aggregation in vitro, however it suppressed Aβ deposits and reduced the Aβ oligomers to alleviate the toxicity induced by Aβ overexpression in C. elegans. Although nicotine did not possess apparent intrinsic anti-oxidative activity, it decreased in vivo reactive oxygen species (ROS). Nicotine enhanced the oxidative stress resistance of C. elegans, which was mediated by SKN-1 but not DAF-16 signaling. Furthermore, skn-1 RNAi abrogated the effect of nicotine reducing Aβ deposits in vivo and completely blocked nicotine preventing Aβ induced worm paralysis.

CONCLUSIONS

Nicotine reduces Aβ oligomer formation and alleviates Aβ-induced paralysis of C. elegans, which is mediated by SKN-1 signaling.

Soluble amyloid beta-containing aggregates are present throughout the brain at early stages of Alzheimer's disease

Protein aggregation likely plays a key role in the initiation and spreading of Alzheimer's disease pathology through the brain. Soluble aggregates of amyloid beta are believed to play a key role in this process. However, the aggregates present in humans are still poorly characterized due to a lack of suitable methods required for characterizing the low concentration of heterogeneous aggregates present. We have used a variety of biophysical methods to characterize the aggregates present in human Alzheimer's disease brains at Braak stage III. We find soluble amyloid beta-containing aggregates in all regions of the brain up to 200 nm in length, capable of causing an inflammatory response. Rather than aggregates spreading through the brain as disease progresses, it appears that aggregation occurs all over the brain and that different brain regions are at earlier or later stages of the same process, with the later stages causing increased inflammation.

Effect of cholesterol on the dimerization of C99-A molecular modeling perspective

C99, a naturally occurring peptide, is a precursor of the amyloid β-peptide (Aβ) and plays an important role in the so-called amyloidogenic pathway of degradation of amyloid precursor protein. While the effect of C99's dimerization is not clearly determined, it has been hypothesized that the dimerization protects C99 from being cleaved further. Cholesterol (CHOL) is known to interact with C99 and its presence in high concentrations has been linked to an increase in the production of Aβ; however, to what extent this is correlated, and how, has not yet been determined. In this study, we systematically examine the effect of increasing cholesterol concentration on the homodimerization propensity of C99, combining unbiased atomistic molecular dynamics simulations with biased simulations using a coarse grained resolution. Through the use of umbrella sampling, we show how the presence of high levels of CHOL destabilizes the interaction between two C99 monomers. The interaction pattern between the two C99s has shifted several residues, from the N-terminal end of the transmembrane region toward the corresponding C-terminal in the presence of CHOL. The umbrella sampling shows that the presence of high levels of CHOL led to a decrease of the disassociation energy by approximately 3 kJ/mol. In conclusion, this suggests that increasing CHOL destabilizes the interaction between the two C99 monomers, which may possibly cause an increase in the production of Aβ₄₂.

Peripheral inflammation exacerbates α-synuclein toxicity and neuropathology in Parkinson's models

AIMS

Parkinson's disease and related disorders are devastating neurodegenerative pathologies. Since α-synuclein was identified as a main component of Lewy bodies and neurites, efforts have been made to clarify the pathogenic mechanisms of α-synuclein's detrimental effects. α-synuclein oligomers are the most harmful species and may recruit and activate glial cells. Inflammation is emerging as a bridge between genetic susceptibility and environmental factors co-fostering Parkinson's disease. However, direct evidence linking inflammation to the harmful activities of α-synuclein oligomers or to the Parkinson's disease behavioural phenotype is lacking.

METHODS

To clarify whether neuroinflammation influences Parkinson's disease pathogenesis, we developed: (i) a 'double-hit' approach in C57BL/6 naive mice where peripherally administered lipopolysaccharides were followed by intracerebroventricular injection of an inactive oligomer dose; (ii) a transgenic 'double-hit' model where lipopolysaccharides were given to A53T α-synuclein transgenic Parkinson's disease mice.

RESULTS

Lipopolysaccharides induced a long-lasting neuroinflammatory response which facilitated the detrimental cognitive activities of oligomers. LPS-activated microglia and astrocytes responded differently to the oligomers with microglia activating further and acquiring a pro-inflammatory M1 phenotype, while astrocytes atrophied. In the transgenic 'double-hit' A53T mouse model, lipopolysaccharides aggravated cognitive deficits and increased microgliosis. Again, astrocytes responded differently to the double challenge. These findings indicate that peripherally induced neuroinflammation potentiates the α-synuclein oligomer's actions and aggravates cognitive deficits in A53T mice.

CONCLUSIONS

The fine management of both peripheral and central inflammation may offer a promising therapeutic approach to prevent or slow down some behavioural aspects in α-synucleinopathies.

RAPGEF2 mediates oligomeric Aβ-induced synaptic loss and cognitive dysfunction in the 3xTg-AD mouse model of Alzheimer's disease

AIMS

Amyloid-β (Aβ) oligomers trigger synaptic degeneration that precedes plaque and tangle pathology. However, the signalling molecules that link Aβ oligomers to synaptic pathology remain unclear. Here, we addressed the potential role of RAPGEF2 as a novel signalling molecule in Aβ oligomer-induced synaptic and cognitive impairments in human-mutant amyloid precursor protein (APP) mouse models of Alzheimer's disease (AD).

METHODS

To investigate the role of RAPGEF2 in Aβ oligomer-induced synaptic and cognitive impairments, we utilised a combination of approaches including biochemistry, molecular cell biology, light and electron microscopy, behavioural tests with primary neuron cultures, multiple AD mouse models and post-mortem human AD brain tissue.

RESULTS

We found significantly elevated RAPGEF2 levels in the post-mortem human AD hippocampus. RAPGEF2 levels also increased in the transgenic AD mouse models, generating high levels of Aβ oligomers before exhibiting synaptic and cognitive impairment. RAPGEF2 upregulation activated the downstream effectors Rap2 and JNK. In cultured hippocampal neurons, oligomeric Aβ treatment increased the fluorescence intensity of RAPGEF2 and reduced the number of dendritic spines and the intensities of synaptic marker proteins, while silencing RAPGEF2 expression blocked Aβ oligomer-induced synapse loss. Additionally, the in vivo knockdown of RAPGEF2 expression in the AD hippocampus prevented cognitive deficits and the loss of excitatory synapses.

CONCLUSIONS

These findings demonstrate that the upregulation of RAPGEF2 levels mediates Aβ oligomer-induced synaptic and cognitive disturbances in the AD hippocampus. We propose that an early intervention regarding RAPGEF2 expression may have beneficial effects on early synaptic pathology and memory loss in AD.

Membrane affinity of individual toxic protein oligomers determined at the single-molecule level

Oligomers are the key suspects in protein aggregation-linked diseases, such as Alzheimer's and Type II diabetes, and most likely exert their toxicity by interacting with lipid membranes. However, the "which oligomer" question remains an obstacle in understanding the disease mechanism, as the exact identity of the toxic oligomer(s) is not yet known. Oligomers exist as a mixture of species of different sizes (i.e. as different 'n-mers') in a physiological solution, making it difficult to determine the properties of individual species. Here we demonstrate a method based on single-molecule photo-bleaching (smPB) which can provide an answer to the "which oligomer" question, at least as far as membrane affinity is concerned. We calculate the ratio of the oligomer size distribution of human Islet Amyloid Polypeptide (IAPP) in the aqueous phase and that on a coexisting artificial lipid bilayer, and this measures the relative membrane affinity of individual oligomeric species. A problem with smPB measurements is that they can be very sensitive to pre-measurement bleaching. Here we correct for pre-bleaching using a covalently linked multimeric peptide as a bleaching standard. We find that the order of membrane affinity for IAPP n-mers is trimer > dimer > tetramer ≫ monomer. Our results agree well with the average membrane affinity values of oligomeric and monomeric solutions previously measured with Fluorescence Correlation Spectroscopy. The "which oligomer" question, in the context of membrane affinity, can therefore, be solved quantitatively for any membrane-active toxic protein aggregate.

Behavioral and neural network abnormalities in human APP transgenic mice resemble those of App knock-in mice and are modulated by familial Alzheimer's disease mutations but not by inhibition of BACE1

BACKGROUND

Alzheimer's disease (AD) is the most frequent and costly neurodegenerative disorder. Although diverse lines of evidence suggest that the amyloid precursor protein (APP) is involved in its causation, the precise mechanisms remain unknown and no treatments are available to prevent or halt the disease. A favorite hypothesis has been that APP contributes to AD pathogenesis through the cerebral accumulation of the amyloid-β peptide (Aβ), which is derived from APP through sequential proteolytic cleavage by BACE1 and γ-secretase. However, inhibitors of these enzymes have failed in clinical trials despite clear evidence for target engagement.

METHODS

To further elucidate the roles of APP and its metabolites in AD pathogenesis, we analyzed transgenic mice overexpressing wildtype human APP (hAPP) or hAPP carrying mutations that cause autosomal dominant familial AD (FAD), as well as App knock-in mice that do not overexpress hAPP but have two mouse App alleles with FAD mutations and a humanized Aβ sequence.

RESULTS

Although these lines of mice had marked differences in cortical and hippocampal levels of APP, APP C-terminal fragments, soluble Aβ, Aβ oligomers and age-dependent amyloid deposition, they all developed cognitive deficits as well as non-convulsive epileptiform activity, a type of network dysfunction that also occurs in a substantive proportion of humans with AD. Pharmacological inhibition of BACE1 effectively reduced levels of amyloidogenic APP C-terminal fragments (C99), soluble Aβ, Aβ oligomers, and amyloid deposits in transgenic mice expressing FAD-mutant hAPP, but did not improve their network dysfunction and behavioral abnormalities, even when initiated at early stages before amyloid deposits were detectable.

CONCLUSIONS

hAPP transgenic and App knock-in mice develop similar pathophysiological alterations. APP and its metabolites contribute to AD-related functional alterations through complex combinatorial mechanisms that may be difficult to block with BACE inhibitors and, possibly, also with other anti-Aβ treatments.

BDMC protects AD in vitro via AMPK and SIRT1

Background

Alzheimer’s disease (AD) is a common neurodegenerative disorder without any satisfactory therapeutic approaches. AD is mainly characterized by the deposition of β-amyloid protein (Aβ) and extensive neuronal cell death. Curcumin, with anti-oxidative stress (OS) and cell apoptosis properties, plays essential roles in AD. However, whether bisdemethoxycurcumin (BDMC), a derivative of curcumin, can exert a neuroprotective effect in AD remains to be elucidated.

Methods

In this study, SK-N-SH cells were used to establish an in vitro model to investigate the effects of BDMC on the Aβ_1–42-induced neurotoxicity. SK-N-SH cells were pretreated with BDMC and with or without compound C and EX527 for 30 min after co-incubation with rotenone for 24 h. Subsequently, western blotting, cell viability assay and SOD and GSH activity measurement were performed.

Results

BDMC increased the cell survival, anti-OS ability, AMPK phosphorylation levels and SIRT1 in SK-N-SH cells treated with Aβ_1–42. However, after treatment with compound C, an AMPK inhibitor, and EX527, an SIRT1inhibitor, the neuroprotective roles of BDMC on SK-N-SH cells treated with Aβ_1–42 were inhibited.

Conclusion

These results suggest that BDMC exerts a neuroprotective role on SK-N-SH cells in vitro via AMPK/SIRT1 signaling, laying the foundation for the application of BDMC in the treatment of neurodegenerative diseases related to AMPK/SIRT1 signaling.

A Peptide-Based Nanocarrier for an Enhanced Delivery and Targeting of Flurbiprofen into the Brain for the Treatment of Alzheimer's Disease: An In Vitro Study

Alzheimer's disease (AD) is an age-related disease caused by abnormal accumulation of amyloid-β in the brain leading to progressive tissue degeneration. Flurbiprofen (FP), a drug used to mitigate the disease progression, has low efficacy due to its limited permeability across the blood-brain barrier (BBB). In a previous work, FP was coupled at the uppermost branching of an ε-lysine-based branched carrier, its root presenting a phenylalanine moiety able to increase the hydrophobicity of the complex and enhance the transport across the BBB by adsorptive-mediated transcytosis (AMT). The present study explores a different molecular design of the FP-peptide delivery system, whereby its root presents an ApoE-mimicking peptide, a targeting ligand that could enhance transport across the BBB by receptor-mediated transcytosis (RMT). The functionalised complex was synthesised using a solid-phase peptide synthesis and characterised by mass spectrometry and FTIR. Cytotoxicity and permeability of this complex across an in vitro BBB model were analysed. Moreover, its activity and degradation to release the drug were investigated. The results revealed successful synthesis and grafting of FP molecules at the uppermost molecular branches of the lysine terminal without observed cytotoxicity. When covalently linked to the nanocarrier, FP was still active on target cells, albeit with a reduced activity, and was released as a free drug upon hydrolysis in a lysosome-mimicking medium. Noticeably, this work shows the high efficiency of RMT-driven FP delivery over delivery systems relying on AMT.

AMBAR, an Encouraging Alzheimer's Trial That Raises Questions

Grifols' recent Alzheimer Management by Albumin Replacement (“AMBAR”) study investigated the effects of plasmapheresis with albumin replacement, plus intravenous immunoglobulin (IVIG) in some subjects, in patients with mild-to-moderate Alzheimer's disease (AD). AMBAR was a phase IIb trial in the United States and a phase III trial in Europe. There were three treatment groups (plasmapheresis with albumin replacement; plasmapheresis with low dose albumin and IVIG; plasmapheresis with high dose albumin and IVIG) and sham-treated controls. Disease progression in pooled treated patients was 66% less than control subjects based on ADAS-Cog scores (p = 0.06) and 52% less based on ADCS-ADL scores (p = 0.03). Moderate AD patients had 61% less progression, based on both ADAS-Cog and ADCS-ADL scores, than their sham-treated counterparts (p-values 0.05 and 0.002), and their CDR-Sb scores declined 53% less than their sham-treated counterparts. However, ADAS-Cog and ADCS-ADL scores were not significantly different between actively-treated and sham-treated mild AD patients, although CDR-Sb scores improved vs. baseline for treated mild AD patients. Patients administered both IVIG and albumin had less reduction in brain glucose metabolism than sham-treated patients. Questions raised by these findings include: what mechanism(s) contributed to slowing of disease progression? Is this approach as effective in mild AD as in moderate AD? Must IVIG be included in the protocol? Does age, sex, or ApoE genotype influence treatment response? Does the protocol increase the risk for amyloid-related imaging abnormalities? How long does disease progression remain slowed post-treatment? A further study should allow this approach to be optimized.

Clinical Trials in Alzheimer's Disease: A Hurdle in the Path of Remedy

Human clinical trials seek to ameliorate the disease states and symptomatic progression of illnesses that, as of yet, are largely untreatable according to clinical standards. Ideally, clinical trials test "disease-modifying drugs," i.e., therapeutic agents that specifically modify pathological features or molecular bases of the disease and would presumably have a large impact on disease progression. In the case of Alzheimer's disease (AD), however, this approach appears to have stalled progress in the successful development of clinically useful therapies. For the last 25 years, clinical trials involving AD have centered on beta-amyloid (Aβ) and the Aβ hypothesis of AD progression and pathology. According to this hypothesis, the progression of AD begins following an accumulation of Aβ peptide, leading to eventual synapse loss and neuronal cell death: the true overriding pathological feature of AD. Clinical trials arising from the Aβ hypothesis target causal steps in the pathway in order to reduce the formation of Aβ or enhance clearance, and though agents have been successful in this aim, they remain unsuccessful in rescuing cognitive function or slowing cognitive decline. As such, further use of resources in the development of treatment options for AD that target Aβ, its precursors, or its products should be reevaluated. The purpose of this review was to give an overview of how human clinical trials are conducted in the USA and to assess the results of recent failed trials involving AD, the majority of which were based on the Aβ hypothesis. Based on these current findings, it is suggested that lowering Aβ is an unproven strategy, and it may be time to refocus on other targets for the treatment of this disease including pathological forms of tau.

A novel near-infrared fluorescent probe for detection of early-stage Aβ protofibrils in Alzheimer's disease

Detection of Aβ protofibrils at the early stage of Alzheimer's disease was realized by a novel near-infrared probe (DCM-AN) based on dicyanomethylene-4H-pyran. This probe exhibits high affinity towards Aβ protofibrils in vitro and in brain sections of transgenic mouse models for Alzheimer's disease.

Stabilization Mechanism for a Nonfibrillar Amyloid β Oligomer Based on Formation of a Hydrophobic Core Determined by Dissipative Particle Dynamics

Neurotoxicity caused by nonfibrillar amyloid β (Aβ) oligomers in the brain is suggested to be associated with the onset of Alzheimer's disease (AD). Elucidating the structural features of Aβ oligomers is critical for promoting drug discovery research for AD. One of the Aβ oligomers, known as Aβ*56, is a dodecamer that impairs memory when injected into healthy rats, suggesting that Aβ*56 may contribute to cognitive deficits in AD patients. Another dodecamer structure, formed by 20-residue peptide segments derived from the Aβ peptide (Aβ_17-36), has been revealed by X-ray crystallography. The structure of the Aβ_17-36 dodecamer is composed of trimer units and shows the oligomer antibody A11 reactivity, which are characteristic of Aβ*56, indicating that Aβ*56 and the Aβ_17-36 dodecamer share a similar structure. However, the structure of the C-terminal regions (Aβ_37-42) remains unclear. The C-terminal region, which is abundant in hydrophobic residues, is thought to play a key role in stabilizing the oligomer structure by forming a hydrophobic core. In this study, we employed dissipative particle dynamics, a coarse-grained simulation method with soft core potentials, utilizing the crystal structure information to unravel Aβ dodecamer structures with C-terminal regions. The simulation results were validated by the reported experimental data. Hence, an analysis of the simulation results can provide structural insights into Aβ oligomers. Our simulations revealed the stabilization mechanism of the dodecamer structure at the molecular level. We showed that C-terminal regions spontaneously form a hydrophobic core in the central cavity, contributing to stabilizing the dodecamer structure. Furthermore, four consecutive hydrophobic residues in the C-terminal region (i.e., Val39-Ala42) are important for core formation.

The Erythrocytic Hypothesis of Brain Energy Crisis in Sporadic Alzheimer Disease: Possible Consequences and Supporting Evidence

Alzheimer’s disease (AD) is a fatal form of dementia of unknown etiology. Although amyloid plaque accumulation in the brain has been the subject of intensive research in disease pathogenesis and anti-amyloid drug development; the continued failures of the clinical trials suggest that amyloids are not a key cause of AD and new approaches to AD investigation and treatment are needed. We propose a new hypothesis of AD development based on metabolic abnormalities in circulating red blood cells (RBCs) that slow down oxygen release from RBCs into brain tissue which in turn leads to hypoxia-induced brain energy crisis; loss of neurons; and progressive atrophy preceding cognitive dysfunction. This review summarizes current evidence for the erythrocytic hypothesis of AD development and provides new insights into the causes of neurodegeneration offering an innovative way to diagnose and treat this systemic disease.

Different aspects of Alzheimer's disease-related amyloid β-peptide pathology and their relationship to amyloid positron emission tomography imaging and dementia

Alzheimer’s disease (AD)-related amyloid β-peptide (Aβ) pathology in the form of amyloid plaques and cerebral amyloid angiopathy (CAA) spreads in its topographical distribution, increases in quantity, and undergoes qualitative changes in its composition of modified Aβ species throughout the pathogenesis of AD. It is not clear which of these aspects of Aβ pathology contribute to AD progression and to what extent amyloid positron emission tomography (PET) reflects each of these aspects. To address these questions three cohorts of human autopsy cases (in total n = 271) were neuropathologically and biochemically examined for the topographical distribution of Aβ pathology (plaques and CAA), its quantity and its composition. These parameters were compared with neurofibrillary tangle (NFT) and neuritic plaque pathology, the degree of dementia and the results from [¹⁸F]flutemetamol amyloid PET imaging in cohort 3. All three aspects of Aβ pathology correlated with one another, the estimation of Aβ pathology by [¹⁸F]flutemetamol PET, AD-related NFT pathology, neuritic plaques, and with the degree of dementia. These results show that one aspect of Aβ pathology can be used to predict the other two, and correlates well with the development of dementia, advancing NFT and neuritic plaque pathology. Moreover, amyloid PET estimates all three aspects of Aβ pathology in-vivo. Accordingly, amyloid PET-based estimates for staging of amyloid pathology indicate the progression status of amyloid pathology in general and, in doing so, also of AD pathology. Only 7.75% of our cases deviated from this general association.

Examination of Adsorption Orientation of Amyloidogenic Peptides Over Nano-Gold Colloidal Particle Surfaces

The adsorption of amyloidogenic peptides, amyloid beta 1–40 (Aβ_1–40), alpha-synuclein (α-syn), and beta 2 microglobulin (β2m), was attempted over the surface of nano-gold colloidal particles, ranging from d = 10 to 100 nm in diameter (d). The spectroscopic inspection between pH 2 and pH 12 successfully extracted the critical pH point (pH_o) at which the color change of the amyloidogenic peptide-coated nano-gold colloids occurred due to aggregation of the nano-gold colloids. The change in surface property caused by the degree of peptide coverage was hypothesized to reflect the ΔpH_o, which is the difference in pH_o between bare gold colloids and peptide coated gold colloids. The coverage ratio (Θ) for all amyloidogenic peptides over gold colloid of different sizes was extracted by assuming Θ = 0 at ΔpH_o = 0. Remarkably, Θ was found to have a nano-gold colloidal size dependence, however, this nano-size dependence was not simply correlated with d. The geometric analysis and simulation of reproducing Θ was conducted by assuming a prolate shape of all amyloidogenic peptides. The simulation concluded that a spiking-out orientation of a prolate was required in order to reproduce the extracted Θ. The involvement of a secondary layer was suggested; this secondary layer was considered to be due to the networking of the peptides. An extracted average distance of networking between adjacent gold colloids supports the binding of peptides as if they are “entangled” and enclosed in an interfacial distance that was found to be approximately 2 nm. The complex nano-size dependence of Θ was explained by available spacing between adjacent prolates. When the secondary layer was formed, Aβ_1–40 and α-syn possessed a higher affinity to a partially negative nano-gold colloidal surface. However, β2m peptides tend to interact with each other. This difference was explained by the difference in partial charge distribution over a monomer. Both Aβ_1–40 and α-syn are considered to have a partial charge (especially δ+) distribution centering around the prolate axis. The β2m, however, possesses a distorted charge distribution. For a lower Θ (i.e., Θ <0.5), a prolate was assumed to conduct a gyration motion, maintaining the spiking-out orientation to fill in the unoccupied space with a tilting angle ranging between 5° and 58° depending on the nano-scale and peptide coated to the gold colloid.

Zn2+ Interaction with Amyloid-Β: Affinity and Speciation

Conflicting values, obtained by different techniques and often under different experimental conditions have been reported on the affinity of Zn²⁺ for amyloid-β, that is recognized as the major interaction responsible for Alzheimer’s disease. Here, we compare the approaches employed so far, i.e., the evaluation of K_d and the determination of the stability constants to quantitatively express the affinity of Zn²⁺ for the amyloid-β peptide, evidencing the pros and cons of the two approaches. We also comment on the different techniques and conditions employed that may lead to divergent data. Through the analysis of the species distribution obtained for two selected examples, we show the implications that the speciation, based on stoichiometric constants rather than on K_d, may have on data interpretation. The paper also demonstrates that the problem is further complicated by the occurrence of multiple equilibria over a relatively narrow pH range.

Mitigating Alzheimer’s Disease with Natural Polyphenols: A Review

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According to Alzheimer’s Disease International (ADI), nearly 50 million people worldwide were living with dementia in 2017, and this number is expected to triple by 2050. Despite years of research in this field, the root cause and mechanisms responsible for Alzheimer’s disease (AD) have not been fully elucidated yet. Moreover, promising preclinical results have repeatedly failed to translate into patient treatments. Until now, none of the molecules targeting AD has successfully passed the Phase III trial. Although natural molecules have been extensively studied, they normally require high concentrations to be effective; alternately, they are too large to cross the blood-brain barrier (BBB).

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In this review, we report AD treatment strategies, with a virtually exclusive focus on green chemistry (natural phenolic molecules). These include therapeutic strategies for decreasing amyloid-β (Aβ) production, preventing and/or altering Aβ aggregation, and reducing oligomers cytotoxicity such as curcumin, (-)-epigallocatechin-3-gallate (EGCG), morin, resveratrol, tannic acid, and other natural green molecules. We also examine whether consideration should be given to potential candidates used outside of medicine and nutrition, through a discussion of two intermediate-sized green molecules, with very similar molecular structures and key properties, which exhibit potential in mitigating Alzheimer’s disease.

ERβ promotes Aβ degradation via the modulation of autophagy

Alzheimer's Disease (AD) is the most common neurodegenerative disorder in the elderly. Beta-amyloid (Aβ) peptide accumulation is considered as a primary cause of AD pathogenesis, with defective autophagy in patients' brains. Enhanced autophagic activity has been reported to promote Aβ clearance in vitro and in vivo models. Meanwhile, there is growing evidence that estrogen receptor β (ERβ) is a viable therapeutic target that can ameliorate the pathological features associated with AD. Very little is known about the detailed molecular mechanisms underlying the relationship between ERβ, autophagy, and Aβ degradation in AD. This study aims to uncover whether ERβ participates in autophagy and promotes extracellular Aβ1-42 degradation through the autophagy-lysosome system. Here we find that overexpression of ERβ caused autophagic activation as seen by increased microtubule-associated protein 1 light chain 3-II (LC3-II), SQSTM1 (sequestosome 1) degradation, LC3 punctate distribution, autophagosome, and autolysosome accumulation. In addition, we show that ERβ could induce autophagy through direct protein-protein interaction with ATG7 (E1-like enzyme). Furthermore, ERβ-mediated decrease in Aβ1-42 was blocked by the autophagy inhibitor chloroquine (CQ) in SH-SY5Y cells and the HEK293T (AβPPsw) model. Aβ1-42 or CQ induced cytotoxicity was restored by a selective ERβ activator diarylpropionitrile (DPN). Collectively, these data indicate that overexpression of ERβ exerts a neuroprotective effect through interacting with ATG7 protein and further enhances autophagy-lysosomal activity for Aβ1-42 clearance at the cellular level.

Doxycycline for Alzheimer's Disease: Fighting β-Amyloid Oligomers and Neuroinflammation

Alzheimer's disease (AD) is the most widespread form of dementia, affecting about 45 million people worldwide. Although the β-amyloid peptide (Aβ) remains the most acknowledged culprit of AD, the multiple failures of Aβ-centric therapies call for alternative therapeutic approaches. Conceivably, the complexity of the AD neuropathological scenario cannot be solved with single-target therapies, so multiple-target approaches are needed. Core targets of AD to date are soluble oligomeric Aβ species and neuroinflammation, in an intimate detrimental dialogue. Aβ oligomers, the most neurotoxic species, appear to induce synaptic and cognitive dysfunction through the activation of glial cells. Anti-inflammatory drugs can prevent the action of Aβ oligomers. Neuroinflammation is a chronic event whose perpetuation leads to the continuous release of pro-inflammatory cytokines, promoting neuronal cell death and gross brain atrophy. Among the possible multi-target therapeutic alternatives, this review highlights the antibiotic tetracyclines, which besides antimicrobial activity also have pleiotropic action against amyloidosis, neuroinflammation, and oxidative stress. A particular focus will be on doxycycline (Doxy), a second-generation tetracycline that crosses the blood-brain barrier more easily and has a safer clinical profile. Doxy emerged as a promising preventive strategy in prion diseases and gave compelling pre-clinical results in mouse models of AD against Aβ oligomers and neuroinflammation. This strongly supports its therapeutic potential and calls for deciphering its exact mechanisms of action so as to maximize its effects in the clinic.

The amyloid cascade and Alzheimer's disease therapeutics: theory versus observation

The identification of amyloid-β precursor protein (APP) pathogenic mutations in familial early onset Alzheimer's disease (AD), along with knowledge that amyloid-β (Aβ) was the principle protein component of senile plaques, led to the establishment of the amyloid cascade hypothesis. Down syndrome substantiated the hypothesis, given an extra copy of the APP gene and invariable AD pathology hallmarks that occur by middle age. An abundance of support for the amyloid cascade hypothesis followed. Prion-like protein misfolding and non-Mendelian transmission of neurotoxicity are among recent areas of investigation. Aβ-targeted clinical trials have been disappointing, with negative results attributed to inadequacies in patient selection, challenges in pharmacology, and incomplete knowledge of the most appropriate target. There is evidence, however, that proof of concept has been achieved, i.e., clearance of Aβ during life, but with no significant changes in cognitive trajectory in AD. Whether the time, effort, and expense of Aβ-targeted therapy will prove valuable will be determined over time, as Aβ-centered clinical trials continue to dominate therapeutic strategies. It seems reasonable to hypothesize that the amyloid cascade is intimately involved in AD, in parallel with disease pathogenesis, but that removal of toxic Aβ is insufficient for an effective disease modification.

Luminex-based quantification of Alzheimer's disease neuropathologic change in formalin-fixed post-mortem human brain tissue

The vast majority of archived research and clinical pathological specimens are stored in the form of formalin fixed, paraffin-embedded (FFPE) tissues, but, unlike fresh frozen tissue samples, highly quantitative measures in FFPE tissues are limited to immunohistochemical and immunofluorescence thresholding image analysis studies, cell counting, and ordinal ranking systems. This poses a significant obstacle for clinical investigations that aim to correlate diagnostic markers of neurodegenerative diseases like Alzheimer's disease (AD) with parameters like age, gender, drug exposures, genotype, disease stage, co-morbidities, or environmental factors. To overcome this limitation, we have developed Luminex-based techniques and protocols for the quantification of amyloid β and hyperphosphorylated Tau in FFPE brain sections. We validated the Luminex assay in FFPE sections from prefrontal cortex, hippocampus, and neostriatum from 30 cases that underwent prior neuropathological diagnostic assessment of AD following the current NIA-AA recommendations for AD: 10 cases diagnosed as not or low, 10 cases as intermediate, and 10 cases as high AD neuropathologic change. Consistent with the neuropathologic assessment, Luminex assay detected high amounts of amyloid beta in the frontal cortex and striatum, and high amounts of hyperphosphorylated Tau in the frontal cortex and hippocampus, of cases with high AD neuropathologic change. This assay can be expanded to detect diverse antigenic targets of interest, as we show here with IBA1 and GFAP. This novel approach supports multiplexed highly quantitative, molecularly specific neuropathology measures to further explore mechanisms of neurodegeneration in AD.

Fluorescence Chemicals To Detect Insoluble and Soluble Amyloid-β Aggregates

Misfolded amyloid-β (Aβ) is the key biomarker of Alzheimer's disease (AD), and discoveries of fluorescence chemicals visualizing such Aβ aggregates in the brain have made major contributions in postmortem and antemortem diagnosis of the disorder. Insoluble senile plaques of Aβ in brain tissues are commonly stained with thioflavin and congo red dyes and observed through microscopy, while those in living patient brains are detected via radioisotope-labeled fluorescence chemicals for positron emission tomography. Clinical evidence strongly supports the view that plaques are well-associated with the onset but not with the progression of AD. Plaques could accumulate while cognitive functions of at-risk individuals are still intact, and thus, another biomarker is needed to monitor neurodegeneration. Soluble Aβ oligomers are considered to have strong correlation with neuronal loss and brain atrophy as they are the most neurotoxic forms of misfolded Aβ. However, oligomer-targeting probes encounter several major difficulties in development. There is a significant structural distinction between two Aβ species-plaques are β-sheet-rich while oligomers are unordered-and it is still difficult to isolate and stabilize the oligomeric forms of Aβ. Due to these challenges, soluble oligomer-detecting imaging probes are relatively rare compared to the plaque-targeting chemical probes. This Review describes biochemical and optical characteristics of up-to-date fluorescence chemicals targeting insoluble plaques and soluble oligomers of Aβ. We also highlight the contributions of Aβ fluorescence chemicals to the clinical diagnosis of AD and technical challenges in searching for enhanced imaging probes.

Unravelling protein aggregation as an ageing related process or a neuropathological response

Protein aggregation is normally associated with amyloidosis, namely motor neurone, Alzheimer's, Parkinson's or prion diseases. However, recent results have unveiled a concept of gradual increase of protein aggregation associated with the ageing process, apparently not necessarily associated with pathological conditions. Given that protein aggregation is sufficient to activate stress-response and inflammation, impairing protein synthesis and quality control mechanisms, the former is assumed to negatively affect cellular metabolism and behaviour. In this review the state of the art in protein aggregation research is discussed, namely the relationship between pathology and proteostasis. The role of pathology and ageing in overriding protein quality-control mechanisms, and consequently, the effect of these faulty cellular processes on pathological and healthy ageing, are also addressed.

Review: PrP 106-126 - 25 years after

A quarter of a century ago, we proposed an innovative approach to study the pathogenesis of prion disease, one of the most intriguing biomedical problems that remains unresolved. The synthesis of a peptide homologous to residues 106-126 of the human prion protein (PrP106-126), a sequence present in the PrP amyloid protein of Gerstmann-Sträussler-Scheinker syndrome patients, provided a tractable tool for investigating the mechanisms of neurotoxicity. Together with several other discoveries at the beginning of the 1990s, PrP106-126 contributed to underpin the role of amyloid in the pathogenesis of protein-misfolding neurodegenerative disorders. Later, the role of oligomers on one hand and of prion-like spreading of pathology on the other further clarified mechanisms shared by different neurodegenerative conditions. Our original report on PrP106-126 neurotoxicity also highlighted a role for programmed cell death in CNS diseases. In this review, we analyse the prion research context in which PrP106-126 first appeared and the advances in our understanding of prion disease pathogenesis and therapeutic perspectives 25 years later.

Amyloid-β immunotherapy for alzheimer disease: Is it now a long shot?

The amyloid-β (Aβ) cascade hypothesis of Alzheimer disease (AD) holds that brain accumulation of Aβ initiates the disease process. Accordingly, drug research has targeted Aβ production, clearance, and deposition as therapeutic strategies. Unfortunately, candidate drugs have failed to show clinical benefit in established, early, or prodromal disease, or in those with high AD risk. Currently, monoclonal antibodies specifically directed against the most neurotoxic Aβ forms are undergoing large-scale trials to confirm initially encouraging results. However, recent findings on the normal physiology of Aβ suggest that accumulation may be compensatory rather than the pathological initiator. If this is true, alternative strategies will be needed to defeat this devastating disease. ANN NEUROL 2019;85:303-315.

Antemortem-Postmortem Correlation of Florbetapir (18F) PET Amyloid Imaging with Quantitative Biochemical Measures of Aβ42 but not Aβ40

Amyloid imaging demonstrates the in vivo presence of amyloid-β (Aβ) deposits in the aging human brain but it is still unknown which structural forms and modifications of Aβ are detected. In Alzheimer's disease, most amyloid deposits are predominantly composed of Aβ ending at amino acid residues Val40 or Ala42. It has been reported that Aβ40 is largely restricted to neuritic plaques while Aβ42 may be deposited in amyloid plaques of all types, and is often the sole component of diffuse plaques. The distinction is important as it is mainly the neuritic plaques that correlate with cognitive impairment while diffuse plaques may be the initial type of Aβ deposited. Whether PET amyloid ligands such as florbetapir-18F (Amyvid) are partially or wholly selective for brain deposits of Aβ40 or Aβ42 is currently unknown. We compared antemortem florbetapir PET cortical/cerebellar signal intensity (SUVr) of 55 subjects with postmortem biochemical (ELISA) measurements employing specific antibodies against Aβ40 and Aβ42. Spearman's univariable correlations were significant for both Aβ40 and Aβ42, but were much stronger for Aβ42. Multiple linear regression showed significance only for Aβ42. These results suggest that florbetapir binds only weakly, if at all, to Aβ40. This may be in part due to the higher likelihood for Aβ42 to be present in a β-pleated sheet tertiary structure, or to differences between Aβ40 and Aβ42 in β-pleated sheet tertiary or quaternary structure.

Dendrimeric Poly(Epsilon-Lysine) Delivery Systems for the Enhanced Permeability of Flurbiprofen across the Blood-Brain Barrier in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive brain disorder and age-related disease characterised by abnormal accumulation of β-amyloid (Aβ). The development of drugs to combat AD is hampered by the lack of therapeutically-active molecules able to cross the blood-brain barrier (BBB). It is agreed that specifically-designed carriers, such as dendrimers, could support the drug penetration across the BBB. The aim of this study was to design biocompatible and biodegradable dendrimeric delivery systems able to carry Flurbiprofen (FP), as drug for AD treatment, across the BBB and liberate it at the target tissue. These dendrons were synthesised using solid-phase peptide synthesis method and characterised by mass spectrometry and fourier-transform infrared spectroscopy (FTIR). The results revealed successful synthesis of dendrons having FP been integrated during the synthesis at their branching ends. Cytotoxicity assays demonstrated the biocompatibility of the delivery systems, whereas HPLC analysis showed high percentages of permeability across an in vitro BBB model for FP-integrated dendrons. Results also revealed the efficiency of drug conjugates on the γ-secretase enzyme in target cells with evidence of eventual drug release by hydrolysis of the carrier. This study demonstrates that the coupling of FP to dendrimeric delivery systems can successfully be achieved during the synthesis of the poly(epsilon-lysine) macromolecules to improve the transport of the active drug across the BBB.

An in vitro paradigm to assess potential anti-Aβ antibodies for Alzheimer's disease

Although the amyloid β-protein (Aβ) is believed to play an initiating role in Alzheimer's disease (AD), the molecular characteristics of the key pathogenic Aβ forms are not well understood. As a result, it has proved difficult to identify optimal agents that target disease-relevant forms of Aβ. Here, we combined the use of Aβ-rich aqueous extracts of brain samples from AD patients as a source of human Aβ and live-cell imaging of iPSC-derived human neurons to develop a bioassay capable of quantifying the relative protective effects of multiple anti-Aβ antibodies. We report the characterization of 1C22, an aggregate-preferring murine anti-Aβ antibody, which better protects against forms of Aβ oligomers that are toxic to neurites than do the murine precursors of the clinical immunotherapeutics, bapineuzumab and solanezumab. These results suggest further examination of 1C22 is warranted, and that this bioassay maybe useful as a primary screen to identify yet more potent anti-Aβ therapeutics.