Structural studies of amyloid-β peptides: Unlocking the mechanism of aggregation and the associated toxicity

Helix-to-sheet transition of the Aβ42 peptide revealed using an enhanced sampling strategy and Markov state model

The self-assembly of Aβ peptides into toxic oligomers and fibrils is the primary cause of Alzheimer's disease. Moreover, the conformational transition from helix to sheet is considered a crucial step in the aggregation of Aβ peptides. However, the structural details of this process still remain unclear due to the heterogeneity and transient nature of the Aβ peptides. In this study, we developed an enhanced sampling strategy that combines artificial neural networks (ANN) with metadynamics to explore the conformational space of the Aβ42 peptides. The strategy consists of two parts: applying ANN to optimize CVs and conducting metadynamics based on the resulting CVs to sample conformations. The results showed that this strategy achieved better sampling performance in terms of the distribution of sampled conformations. The sampling efficiency is increased by 10-fold compared to our previous Hamiltonian Exchange Molecular Dynamics (MD) and by 1000-fold compared to ordinary MD. Based on the sampled conformations, we constructed a Markov state model to understand the detailed transition process. The intermediate states in this process are identified, and the connecting paths are analyzed. The conformational transitions in D23-K28 and M35-V40 are proven to be crucial for aggregation. These results are helpful in clarifying the mechanism and process of Aβ42 peptide aggregation. D23-K28 and M35-V40 can be identified as potential targets for screening and designing inhibitors of Aβ peptide aggregation.

Harnessing the Therapeutic Potential of Peptides for Synergistic Treatment of Alzheimer's Disease by Targeting Aβ Aggregation, Metal-Mediated Aβ Aggregation, Cholinesterase, Tau Degradation, and Oxidative Stress

Alzheimer's disease (AD) is a progressive multifaceted neurodegenerative disease and remains a formidable global health challenge. The current medication for AD gives symptomatic relief and, thus, urges us to look for alternative disease-modifying therapies based on a multitarget directed approach. Looking at the remarkable progress made in peptide drug development in the last decade and the benefits associated with peptides, they offer valuable chemotypes [multitarget directed ligands (MTDLs)] as AD therapeutics. This review recapitulates the current developments made in harnessing peptides as MTDLs in combating AD by targeting multiple key pathways involved in the disease's progression. The peptides hold immense potential and represent a convincing avenue in the pursuit of novel AD therapeutics. While hurdles remain, ongoing research offers hope that peptides may eventually provide a multifaceted approach to combat AD.

A turn for the worse: Aβ β-hairpins in Alzheimer's disease

Amyloid-β (Aβ) oligomers are a cause of neurodegeneration in Alzheimer's disease (AD). These soluble aggregates of the Aβ peptide have proven difficult to study due to their inherent metastability and heterogeneity. Strategies to isolate and stabilize homogenous Aβ oligomer populations have emerged such as mutations, covalent cross-linking, and protein fusions. These strategies along with molecular dynamics simulations have provided a variety of proposed structures of Aβ oligomers, many of which consist of molecules of Aβ in β-hairpin conformations. β-Hairpins are intramolecular antiparallel β-sheets composed of two β-strands connected by a loop or turn. Three decades of research suggests that Aβ peptides form several different β-hairpin conformations, some of which are building blocks of toxic Aβ oligomers. The insights from these studies are currently being used to design anti-Aβ antibodies and vaccines to treat AD. Research suggests that antibody therapies designed to target oligomeric Aβ may be more successful at treating AD than antibodies designed to target linear epitopes of Aβ or fibrillar Aβ. Aβ β-hairpins are good epitopes to use in antibody development to selectively target oligomeric Aβ. This review summarizes the research on β-hairpins in Aβ peptides and discusses the relevance of this conformation in AD pathogenesis and drug development.

Protective Effects of Heat-Killed Ruminococcus albus against β-Amyloid-Induced Apoptosis on SH-SY5Y Cells

A high level of β-amyloid (Aβ) in the brains of patients with Alzheimer's disease (AD) generates reactive oxygen species that induce neuronal death and DNA damage. The interaction between the gut microbiota and brain health has attracted attention in recent years. Heat-killed Ruminococcus albus (hkRA) reportedly protects neurons against damage induced by oxidative stress. However, whether hkRA can inhibit Aβ-induced apoptosis and thus alleviate AD remains unclear. Hence, we aimed to evaluate the protective effects of hkRA against Aβ-induced apoptosis on the human neuroblastoma SH-SY5Y cell. HkRA treatment (108 cells/ml) significantly decreased the Aβ-induced cytotoxicity and DNA damage in the SH-SY5Y cells. It also showed a significant increase of the bax/bcl-2 ratio in the Aβ-treated SH-SY5Y cells. Moreover, hkRA treatment stimulated the expression of antioxidation-related genes HO-1, Nrf2, and PKC-δ and increased the expression of brain-derived neurotrophic factor (BDNF). Meanwhile, it significantly decreased the activity of caspase-3 and protein expression of cleaved caspase-3 in the Aβ-treated SH-SY5Y cells. Additionally, the protein levels of mitochondrial and cytosolic cytochrome c increased and decreased, respectively, in the cells. These results suggest that hkRA protects human neuroblastoma cells from Aβ-induced apoptosis and oxidative stress. Thus, hkRA may be developed into a health-promoting paraprobiotic (the inactivated microbial cells of probiotics) for patients with AD.

A Novel Aggregation-Induced Emission Fluorescent Probe for Detection of β-Amyloid Based on Pyridinyltriphenylamine and Quinoline-Malononitrile

β-amyloid is an important pathological feature of Alzheimer's disease. Its abnormal production and aggregation in the patient's brain is an important basis for the early diagnosis and confirmation of Alzheimer's disease. In this study, a novel aggregation-induced emission fluorescent probe, PTPA-QM, was designed and synthesized based on pyridinyltriphenylamine and quinoline-malononitrile. These molecules exhibit a donor-donor-π-acceptor structure with a distorted intramolecular charge transfer feature. PTPA-QM displayed the advantages of good selectivity toward viscosity. The fluorescence intensity of PTPA-QM in 99% glycerol solution was 22-fold higher than that in pure DMSO. PTPA-QM has been confirmed to have excellent membrane permeability and low toxicity. More importantly, PTPA-QM exhibits a high affinity towards β-amyloid in brain sections of 5XFAD mice and classical inflammatory cognitive impairment mice. In conclusion, our work provides a promising tool for the detection of β-amyloid.

Chaperone Activity and Protective Effect against Aβ-Induced Cytotoxicity of Artocarpus camansi Blanco and Amaranthus dubius Mart. ex Thell Seed Protein Extracts

Alzheimer's disease (AD) is the most common type of dementia and is listed as the sixth-leading cause of death in the United States. Recent findings have linked AD to the aggregation of amyloid beta peptides (Aβ), a proteolytic fragment of 39-43 amino acid residues derived from the amyloid precursor protein. AD has no cure; thus, new therapies to stop the progression of this deadly disease are constantly being searched for. In recent years, chaperone-based medications from medicinal plants have gained significant interest as an anti-AD therapy. Chaperones are responsible for maintaining the three-dimensional shape of proteins and play an important role against neurotoxicity induced by the aggregation of misfolded proteins. Therefore, we hypothesized that proteins extracted from the seeds of Artocarpus camansi Blanco (A. camansi) and Amaranthus dubius Mart. ex Thell (A. dubius) could possess chaperone activity and consequently may exhibit a protective effect against Aβ_1-40-induced cytotoxicity. To test this hypothesis, the chaperone activity of these protein extracts was measured using the enzymatic reaction of citrate synthase (CS) under stress conditions. Then, their ability to inhibit the aggregation of Aβ_1-40 using a thioflavin T (ThT) fluorescence assay and DLS measurements was determined. Finally, the neuroprotective effect against Aβ_1-40 in SH-SY5Y neuroblastoma cells was evaluated. Our results demonstrated that A. camansi and A. dubius protein extracts exhibited chaperone activity and inhibited Aβ_1-40 fibril formation, with A. dubius showing the highest chaperone activity and inhibition at the concentration assessed. Additionally, both protein extracts showed neuroprotective effects against Aβ_1-40-induced toxicity. Overall, our data demonstrated that the plant-based proteins studied in this research work can effectively overcome one of the most important characteristics of AD.

Protein Self-Assembly at the Liquid-Surface Interface. Surface-Mediated Aggregation Catalysis

Protein self-assembly into aggregates of various morphologies is a ubiquitous phenomenon in physical chemistry and biophysics. The critical role of amyloid assemblies in the development of diseases, neurodegenerative diseases especially, highlights the importance of understanding the mechanistic picture of the self-assembly process. The translation of this knowledge to the development of efficient preventions and treatments for diseases requires designing experiments at conditions mimicking those in vivo. This Perspective reviews data satisfying two major requirements: membrane environment and physiologically low concentrations of proteins. Recent progress in experiments and computational modeling resulted in a novel model for the amyloid aggregation process at the membrane-liquid interface. The self-assembly under such conditions has a number of critical features, further understanding of which can lead to the development of efficient preventive means and treatments for Alzheimer's and other devastating neurodegenerative disorders.

Stability of the Aβ42 Peptide in Mixed Solutions of Denaturants and Proline

Amyloid β-peptide (Aβ) is responsible for the neuronal damage and death of a patient with Alzheimer's disease (AD). Aβ42 oligomeric forms are dominant neurotoxins and are related to neurodegeneration. Their different forms are related to various pathological conditions in the brain. We investigated Aβ42 peptides in different environments of proline, urea, and GdmCl solutions (in pure and mixed binary forms) through atomistic molecular dynamics simulations. Preferential exclusion from the protein surface and facile formation of a large number of weak molecular interactions are the driving forces for the osmolyte's action. We have focused on these interactions between peptide monomers and pure/mixed osmolytes and denaturants. Urea, as usual, denatures the peptide strongly compared to the GdmCl by accumulation around the peptide. GdmCl shows lesser build-up around protein in contrast to urea but is involved in destabilizing the salt bridge formation of Asp23 and Lys28. Proline as an osmolyte protects the peptide from aggregation when mixed with urea and GdmCl solutions. In mixed solutions of two denaturants and osmolyte plus denaturant, the peptide shows enhanced stability as compared to pure denaturant urea solution. The enhanced stability of peptides in proline may be attributed to its exclusion from the peptide surface and favoring salt bridge formation.

Monitoring the Conformational Changes of the Aβ(25-35) Peptide in SDS Micelles: A Matter of Time

Alzheimer's disease is a neurodegenerative disease characterized by the formation of amyloid plaques constituted prevalently by amyloid peptides. Due to the well-known challenges related to the study in solution of these peptides, several membrane-mimicking systems such as micelle constituted by detergent-i.e., DPC and SDS-have been deeply investigated. Additionally, the strategy of studying short fragments instead of the full-length peptide turned out to be advantageous in exploring the structural properties of the different moieties in Aβ in order to reproduce its pathologic effects. Several studies reveal that among Aβ fragments, Aβ(25-35) is the shortest fragment able to reproduce the aggregation process. To enrich the structural data currently available, in the present work we decided to evaluate the conformational changes adopted by Aβ(25-35) in SDS combining CD and NMR spectroscopies at different times. From the solved structures, it emerges that Aβ(25-35) passes from an unordered conformation at the time of the constitution of the system to a more ordered and energetically favorable secondary structure at day 7, which is kept for 2 weeks. These preliminary data suggest that a relatively long time affects the kinetic in the aggregation process of Aβ(25-35) in a micellar system, favoring the stabilization and the formation of a soluble helix conformation.

Mechanisms Underlying Neurodegenerative Disorders and Potential Neuroprotective Activity of Agrifood By-Products

Neurodegenerative diseases, characterized by progressive loss in selected areas of the nervous system, are becoming increasingly prevalent worldwide due to an aging population. Despite their diverse clinical manifestations, neurodegenerative diseases are multifactorial disorders with standard features and mechanisms such as abnormal protein aggregation, mitochondrial dysfunction, oxidative stress and inflammation. As there are no effective treatments to counteract neurodegenerative diseases, increasing interest has been directed to the potential neuroprotective activities of plant-derived compounds found abundantly in food and in agrifood by-products. Food waste has an extremely negative impact on the environment, and recycling is needed to promote their disposal and overcome this problem. Many studies have been carried out to develop green and effective strategies to extract bioactive compounds from food by-products, such as peel, leaves, seeds, bran, kernel, pomace, and oil cake, and to investigate their biological activity. In this review, we focused on the potential neuroprotective activity of agrifood wastes obtained by common products widely produced and consumed in Italy, such as grapes, coffee, tomatoes, olives, chestnuts, onions, apples, and pomegranates.

Bioinformatics tools and data resources for assay development of fluid protein biomarkers

Fluid protein biomarkers are important tools in clinical research and health care to support diagnosis and to monitor patients. Especially within the field of dementia, novel biomarkers could address the current challenges of providing an early diagnosis and of selecting trial participants. While the great potential of fluid biomarkers is recognized, their implementation in routine clinical use has been slow. One major obstacle is the often unsuccessful translation of biomarker candidates from explorative high-throughput techniques to sensitive antibody-based immunoassays. In this review, we propose the incorporation of bioinformatics into the workflow of novel immunoassay development to overcome this bottleneck and thus facilitate the development of novel biomarkers towards clinical laboratory practice. Due to the rapid progress within the field of bioinformatics many freely available and easy-to-use tools and data resources exist which can aid the researcher at various stages. Current prediction methods and databases can support the selection of suitable biomarker candidates, as well as the choice of appropriate commercial affinity reagents. Additionally, we examine methods that can determine or predict the epitope - an antibody’s binding region on its antigen - and can help to make an informed choice on the immunogenic peptide used for novel antibody production. Selected use cases for biomarker candidates help illustrate the application and interpretation of the introduced tools.

Proteinopathies: Deciphering Physiology and Mechanisms to Develop Effective Therapies for Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are a cluster of diseases marked by progressive neuronal loss, axonal transport blockage, mitochondrial dysfunction, oxidative stress, neuroinflammation, and aggregation of misfolded proteins. NDs are more prevalent beyond the age of 50, and their symptoms often include motor and cognitive impairment. Even though various proteins are involved in different NDs, the mechanisms of protein misfolding and aggregation are very similar. Recently, several studies have discovered that, like prions, these misfolded proteins have the inherent capability of translocation from one neuron to another, thus having far-reaching implications for understanding the processes involved in the onset and progression of NDs, as well as the development of innovative therapy and diagnostic options. These misfolded proteins can also influence the transcription of other proteins and form aggregates, tangles, plaques, and inclusion bodies, which then accumulate in the CNS, leading to neuronal dysfunction and neurodegeneration. This review demonstrates protein misfolding and aggregation in NDs, and similarities and differences between different protein aggregates have been discussed. Furthermore, we have also reviewed the disposal of protein aggregates, the various molecular machinery involved in the process, their regulation, and how these molecular mechanisms are targeted to build innovative therapeutic and diagnostic procedures. In addition, the landscape of various therapeutic interventions for targeting protein aggregation for the effective prevention or treatment of NDs has also been discussed.

Half-integer-spin quadrupolar nuclei in magic-angle spinning paramagnetic NMR: The case of NaMnO2

A combination of solid-state NMR methods for the extraction of ²³Na shift and quadrupolar parameters in the as-synthesized, structurally complex NaMnO₂ Na-ion cathode material, under magic-angle spinning (MAS) is presented. We show that the integration of the Magic-Angle Turning experiment with Rotor-Assisted Population transfer (RAPT) can be used both to identify shifts and to extract a range of magnitudes for their quadrupolar couplings. We also demonstrate the applicability of the two-dimensional one pulse (TOP) based double-sheared Satellite Transition Magic-Angle Spinning (TOP-STMAS) showing how it can yield a spectrum with separated shift and second-order quadrupolar anisotropies, which in turn can be used to analyze a quadrupolar lineshape free of anisotropic bulk magnetic susceptibility (ABMS) induced shift dispersion and determine both isotropic shift and quadrupolar products. Combining all these experiments, the shift and quadrupolar parameters for all observed Na environments were extracted and yielded excellent agreement with the density functional theory (DFT) based models that were reported in previous literature. We expect these methods to open the door for new possibilities for solid-state NMR to probe half-integer quadrupolar nuclei in paramagnetic materials and other systems exhibiting large shift dispersion.

Molecular packing of lipid membranes and action mechanisms of membrane-active peptides

Biomembranes are involved in diverse cellular activities. How membranes and proteins interact in the activities might hinge on the former's physical characteristics, which in turn are influenced by packing of lipid molecules. Yet, the validity of this understanding and its mechanism are unclear. By varying chain saturation of membranes, we explored correlations between lipid packing and peptide-mediated membrane disruption for the antimicrobial peptide, melittin, and amyloidogenic peptide, β-amyloid (1-42). Remarkably, reducing molecular packing flexibility enhanced the membrane disruption, possibly due to a shift from membrane perforation to micellization. A theoretical analysis suggested the energetic basis of this shift. This mechanistically shows that a peptide's mechanism might be dictated not only by its intrinsic properties but also by physical characteristics of membranes.

Revisiting APP secretases: an overview on the holistic effects of retinoic acid receptor stimulation in APP processing

Alzheimer's disease (AD) is the leading cause of dementia worldwide and is characterized by the accumulation of the β-amyloid peptide (Aβ) in the brain, along with profound alterations in phosphorylation-related events and regulatory pathways. The production of the neurotoxic Aβ peptide via amyloid precursor protein (APP) proteolysis is a crucial step in AD development. APP is highly expressed in the brain and is complexly metabolized by a series of sequential secretases, commonly denoted the α-, β-, and γ-cleavages. The toxicity of resulting fragments is a direct consequence of the first cleaving event. β-secretase (BACE1) induces amyloidogenic cleavages, while α-secretases (ADAM10 and ADAM17) result in less pathological peptides. Hence this first cleavage event is a prime therapeutic target for preventing or reverting initial biochemical events involved in AD. The subsequent cleavage by γ-secretase has a reduced impact on Aβ formation but affects the peptides' aggregating capacity. An array of therapeutic strategies are being explored, among them targeting Retinoic Acid (RA) signalling, which has long been associated with neuronal health. Additionally, several studies have described altered RA levels in AD patients, reinforcing RA Receptor (RAR) signalling as a promising therapeutic strategy. In this review we provide a holistic approach focussing on the effects of isoform-specific RAR modulation with respect to APP secretases and discuss its advantages and drawbacks in subcellular AD related events.

Pharmacological implications of ipriflavone against environmental metal-induced neurodegeneration and dementia in rats

Long-term exposure to environmental neurotoxic metals is implicated in the induction of dementia and cognitive decline. The present study aims to illustrate the therapeutic role of ipriflavone as a synthetic isoflavone against environmental metal-induced cognitive impairment in rats. Dementia was induced by a mixture of aluminum, cadmium, and fluoride for 90 days followed by ipriflavone for a further 30 days.  Metal-treated animals exhibited abnormal behaviors in the Morris water maze task. Neuropathological biomarkers including oxidative stress (TBARS, NO, SOD, GPX, GST, and GSH), inflammation (TNF- α, IL-6, and IL-1β), neurotransmission (AChE and MAO), and insulin resistance (insulin, insulin receptor, and insulin-degrading enzyme) were altered, which consequently elevated the level of amyloid-β42 and tau protein in the hippocampus tissues inducing neuronal injury. Ipriflavone significantly (P < 0.05) ameliorated the neurobehavioral abnormalities and the cognitive dysfunction biomarkers via antioxidant/anti-inflammatory mechanism. Moreover, ipriflavone downregulated the mRNA expression level of amyloid precursor protein and tau protein, preventing amyloid plaques and neurofibrillary tangle aggregation at P < 0.05. A molecular docking study revealed that ipriflavone has a potent binding affinity towards AChE more than donepezil and acts as a strong AChE inhibitor. Our data concluded that the therapeutic potential of ipriflavone against dementia could provide a new strategy in AD treatment.

Biological and methodological complexities of beta-amyloid peptide: Implications for Alzheimer's disease research

Although controversial, the amyloid cascade hypothesis remains central to the Alzheimer's disease (AD) field and posits amyloid-beta (Aβ) as the central factor initiating disease onset. In recent years, there has been an increase in emphasis on studying the role of low molecular weight aggregates, such as oligomers, which are suggested to be more neurotoxic than fibrillary Aβ. Other Aβ isoforms, such as truncated Aβ, have also been implicated in disease. However, developing a clear understanding of AD pathogenesis has been hampered by the complexity of Aβ biochemistry in vitro and in vivo. This review explores factors contributing to the lack of consistency in experimental approaches taken to model Aβ aggregation and toxicity and provides an overview of the different techniques available to analyse Aβ, such as electron and atomic force microscopy, nuclear magnetic resonance spectroscopy, dye-based assays, size exclusion chromatography, mass spectrometry and SDS-PAGE. The review also explores how different types of Aβ can influence Aβ aggregation and toxicity, leading to variation in experimental outcomes, further highlighting the need for standardisation in Aβ preparations and methods used in current research.

Separation of quadrupolar and paramagnetic shift interactions in high-resolution nuclear magnetic resonance of spinning powders

Separation and correlation of the shift anisotropy and the first-order quadrupolar interaction of spin I = 1 nuclei under magic-angle spinning (MAS) are achieved by the phase-adjusted spinning sideband (PASS) nuclear magnetic resonance (NMR) experiment. Compared to methods for static samples, this approach has the benefit of higher sensitivity and resolution. Moreover, the PASS experiment has the advantage over previous MAS sequences in the ability to completely separate the shift anisotropy and first-order quadrupolar interactions. However, the main drawback of the pulse sequence is the lower excitation bandwidth. The sequence is comprehensively evaluated using theoretical calculations and numerical simulations and applied experimentally to the ²H NMR of a range of paramagnetic systems: deuterated nickel(II) acetate tetrahydrate, deuterated copper(II) chloride dihydrate, and two forms of deuterated oxyhydride ion conductor BaTiO_3-xH_y. Our results show that despite the issue with broadband excitation, the extracted shift and quadrupolar interaction tensors and the Euler angles relating the two tensors match well with the NMR parameters obtained with static NMR methods. Therefore, the new application of the PASS experiment is an excellent addition to the arsenal of NMR experiments for ²H and potentially ¹⁴N in paramagnetic solids.

Amyloids: The History of Toxicity and Functionality

Proteins can perform their specific function due to their molecular structure. Partial or complete unfolding of the polypeptide chain may lead to the misfolding and aggregation of proteins in turn, resulting in the formation of different structures such as amyloid aggregates. Amyloids are rigid protein aggregates with the cross-β structure, resistant to most solvents and proteases. Because of their resistance to proteolysis, amyloid aggregates formed in the organism accumulate in tissues, promoting the development of various diseases called amyloidosis, for instance Alzheimer's diseases (AD). According to the main hypothesis, it is considered that the cause of AD is the formation and accumulation of amyloid plaques of Aβ. That is why Aβ-amyloid is the most studied representative of amyloids. Therefore, in this review, special attention is paid to the history of Aβ-amyloid toxicity. We note the main problems with anti-amyloid therapy and write about new views on amyloids that can play positive roles in the different organisms including humans.

Effects of Ions and Small Compounds on the Structure of Aβ42 Monomers

Aggregation of amyloid-β (Aβ) proteins in the brain is a hallmark of Alzheimer's disease. This phenomenon can be promoted or inhibited by adding small molecules to the solution where Aβ is embedded. These molecules affect the ensemble of conformations sampled by Aβ monomers even before aggregation starts. Here, we perform extensive all-atom replica exchange molecular dynamics (REMD) simulations to provide a comparative study of the ensemble of conformations sampled by Aβ₄₂ monomers in solutions that promote (i.e., aqueous solution containing NaCl) and inhibit (i.e., aqueous solutions containing scyllo-inositol or 4-aminophenol) aggregation. Simulations performed in pure water are used as our reference. We find that secondary-structure content is only affected in an antagonistic manner by promoters and inhibitors at the C-terminus and the central hydrophilic core. Moreover, the end of the C-terminus binds more favorably to the central hydrophobic core region of Aβ₄₂ in NaCl adopting a type of strand-loop-strand structure that is disfavored by inhibitors. Nonpolar residues that form the dry core of larger aggregates of Aβ₄₂ (e.g., PDB ID 2BEG) are found at close proximity in these strand-loop-strand structures, suggesting that their formation could play an important role in initiating nucleation. In the presence of inhibitors, the C-terminus binds the central hydrophilic core with a higher probability than in our reference simulation. This sensitivity of the C-terminus, which is affected in an antagonistic manner by inhibitors and promoters, provides evidence for its critical role in accounting for aggregation.

Emerging Promise of Immunotherapy for Alzheimer's Disease: A New Hope for the Development of Alzheimer's Vaccine

BACKGROUND

Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the characteristics of this devastating disorder include the progressive and disabling deficits in the cognitive functions including reasoning, attention, judgment, comprehension, memory, and language.

OBJECTIVE

In this article, we have focused on the recent progress that has been achieved in the development of an effective AD vaccine.

SUMMARY

Currently, available treatment options of AD are limited to deliver short-term symptomatic relief only. A number of strategies targeting amyloid-beta (Aβ) have been developed in order to treat or prevent AD. In order to exert an effective immune response, an AD vaccine should contain adjuvants that can induce an effective anti-inflammatory T helper 2 (Th2) immune response. AD vaccines should also possess the immunogens which have the capacity to stimulate a protective immune response against various cytotoxic Aβ conformers. The induction of an effective vaccine's immune response would necessitate the parallel delivery of immunogen to dendritic cells (DCs) and their priming to stimulate a Th2-polarized response. The aforesaid immune response is likely to mediate the generation of neutralizing antibodies against the neurotoxic Aβ oligomers (AβOs) and also anti-inflammatory cytokines, thus preventing the AD-related inflammation.

CONCLUSION

Since there is an age-related decline in the immune functions, therefore vaccines are more likely to prevent AD instead of providing treatment. AD vaccines might be an effective and convenient approach to avoid the treatment-related huge expense.

The membrane axis of Alzheimer's nanomedicine

Alzheimer's disease (AD) is a major neurological disorder impairing its carrier's cognitive function, memory and lifespan. While the development of AD nanomedicine is still nascent, the field is evolving into a new scientific frontier driven by the diverse physicochemical properties and theranostic potential of nanomaterials and nanocomposites. Characteristic to the AD pathology is the deposition of amyloid plaques and tangles of amyloid beta (Aβ) and tau, whose aggregation kinetics may be curbed by nanoparticle inhibitors via sequence-specific targeting or nonspecific interactions with the amyloidogenic proteins. As literature implicates cell membrane as a culprit in AD pathogenesis, here we summarize the membrane axis of AD nanomedicine and present a new rationale that the field development may greatly benefit from harnessing our existing knowledge of Aβ-membrane interaction, nanoparticle-membrane interaction and Aβ-nanoparticle interaction.

The Impact of Halogenated Phenylalanine Derivatives on NFGAIL Amyloid Formation

The hexapeptide hIAPP22-27 (NFGAIL) is known as a crucial amyloid core sequence of the human islet amyloid polypeptide (hIAPP) whose aggregates can be used to better understand the wild-type hIAPP's toxicity to β-cell death. In amyloid research, the role of hydrophobic and aromatic-aromatic interactions as potential driving forces during the aggregation process is controversially discussed not only in case of NFGAIL, but also for amyloidogenic peptides in general. We have used halogenation of the aromatic residue as a strategy to modulate hydrophobic and aromatic-aromatic interactions and prepared a library of NFGAIL variants containing fluorinated and iodinated phenylalanine analogues. We used thioflavin T staining, transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) to study the impact of side-chain halogenation on NFGAIL amyloid formation kinetics. Our data revealed a synergy between aggregation behavior and hydrophobicity of the phenylalanine residue. This study introduces systematic fluorination as a toolbox to further investigate the nature of the amyloid self-assembly process.

Molecular and cellular mechanisms underlying the pathogenesis of Alzheimer's disease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder seen in age-dependent dementia. There is currently no effective treatment for AD, which may be attributed in part to lack of a clear underlying mechanism. Studies within the last few decades provide growing evidence for a central role of amyloid β (Aβ) and tau, as well as glial contributions to various molecular and cellular pathways in AD pathogenesis. Herein, we review recent progress with respect to Aβ- and tau-associated mechanisms, and discuss glial dysfunction in AD with emphasis on neuronal and glial receptors that mediate Aβ-induced toxicity. We also discuss other critical factors that may affect AD pathogenesis, including genetics, aging, variables related to environment, lifestyle habits, and describe the potential role of apolipoprotein E (APOE), viral and bacterial infection, sleep, and microbiota. Although we have gained much towards understanding various aspects underlying this devastating neurodegenerative disorder, greater commitment towards research in molecular mechanism, diagnostics and treatment will be needed in future AD research.

Interaction of Aβ42 with Membranes Triggers the Self-Assembly into Oligomers

The self-assembly of amyloid β (Aβ) proteins into oligomers is the major pathogenic event leading to Alzheimer’s disease (AD). Typical in vitro experiments require high protein concentrations, whereas the physiological concentration of Aβ is in the picomolar to low nanomolar range. This complicates the translation of results obtained in vitro to understanding the aggregation process in vivo. Here, we demonstrate that Aβ42 self-assembles into aggregates on membrane bilayers at low nanomolar concentrations - a pathway in which the membrane plays the role of a catalyst. Additionally, physiological ionic conditions (150 mM NaCl) significantly enhance on-membrane aggregation, leading to the rapid formation of oligomers. The self-assembly process is reversible, so assembled aggregates can dissociate from the membrane surface into the bulk solution to further participate in the aggregation process. Molecular dynamics simulations demonstrate that the transient membrane-Aβ interaction dramatically changes the protein conformation, facilitating the assembly of dimers. The results indicate peptide–membrane interaction is the critical step towards oligomer formation at physiologically low protein concentrations.

Aggregation Mechanism of Alzheimer's Amyloid β-Peptide Mediated by α-Strand/α-Sheet Structure

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases and a widespread form of dementia. Aggregated forms of the amyloid β-peptide (Aβ) are identified as a toxic species responsible for neuronal damage in AD. Extensive research has been conducted to reveal the aggregation mechanism of Aβ. However, the structure of pathological aggregates and the mechanism of aggregation are not well understood. Recently, experimental studies have confirmed that the α-sheet structure in Aβ drives aggregation and toxicity in AD. However, how the α-sheet structure is formed in Aβ and how it contributes to Aβ aggregation remains elusive. In the present study, molecular dynamics simulations suggest that Aβ adopts the α-strand conformation by peptide-plane flipping. Multiple α-strands interact through hydrogen bonding to form α-sheets. This structure acts as a nucleus that initiates and promotes aggregation and fibrillation of Aβ. Our findings are supported by previous experimental as well as theoretical studies. This study provides valuable structural insights for the design of anti-AD drugs exploiting the α-strand/α-sheet structure.

The Clustering of mApoE Anti-Amyloidogenic Peptide on Nanoparticle Surface Does Not Alter Its Performance in Controlling Beta-Amyloid Aggregation

The deposition of amyloid-β (Aβ) plaques in the brain is a significant pathological signature of Alzheimer’s disease, correlating with synaptic dysfunction and neurodegeneration. Several compounds, peptides, or drugs have been designed to redirect or stop Aβ aggregation. Among them, the trideca-peptide CWG-LRKLRKRLLR (mApoE), which is derived from the receptor binding sequence of apolipoprotein E, is effectively able to inhibit Aβ aggregation and to promote fibril disaggregation. Taking advantage of Atomic Force Microscopy (AFM) imaging and fluorescence techniques, we investigate if the clustering of mApoE on gold nanoparticles (AuNP) surface may affect its performance in controlling Aβ aggregation/disaggregation processes. The results showed that the ability of free mApoE to destroy preformed Aβ fibrils or to hinder the Aβ aggregation process is preserved after its clustering on AuNP. This allows the possibility to design multifunctional drug delivery systems with clustering of anti-amyloidogenic molecules on any NP surface without affecting their performance in controlling Aβ aggregation processes.

High-yield Production of Amyloid-β Peptide Enabled by a Customized Spider Silk Domain

During storage in the silk gland, the N-terminal domain (NT) of spider silk proteins (spidroins) keeps the aggregation-prone repetitive region in solution at extreme concentrations. We observe that NTs from different spidroins have co-evolved with their respective repeat region, and now use an NT that is distantly related to previously used NTs, for efficient recombinant production of the amyloid-β peptide (Aβ) implicated in Alzheimer’s disease. A designed variant of NT from Nephila clavipes flagelliform spidroin, which in nature allows production and storage of β-hairpin repeat segments, gives exceptionally high yields of different human Aβ variants as a solubility tag. This tool enables efficient production of target peptides also in minimal medium and gives up to 10 times more isotope-labeled monomeric Aβ peptides per liter bacterial culture than previously reported.

Brain-Blood Partition Coefficient and Cerebral Blood Flow in Canines Using Calibrated Short TR Recovery (CaSTRR) Correction Method

The brain–blood partition coefficient (BBPC) is necessary for quantifying cerebral blood flow (CBF) when using tracer based techniques like arterial spin labeling (ASL). A recent improvement to traditional MRI measurements of BBPC, called calibrated short TR recovery (CaSTRR), has demonstrated a significant reduction in acquisition time for BBPC maps in mice. In this study CaSTRR is applied to a cohort of healthy canines (n = 17, age = 5.0 – 8.0 years) using a protocol suited for application in humans at 3T. The imaging protocol included CaSTRR for BBPC maps, pseudo-continuous ASL for CBF maps, and high resolution anatomical images. The standard CaSTRR method of normalizing BBPC to gadolinium-doped deuterium oxide phantoms was also compared to normalization using hematocrit (Hct) as a proxy value for blood water content. The results show that CaSTRR is able to produce high quality BBPC maps with a 4 min acquisition time. The BBPC maps demonstrate significantly higher BBPC in gray matter (0.83 ± 0.05 mL/g) than in white matter (0.78 ± 0.04 mL/g, p = 0.006). Maps of CBF acquired with pCASL demonstrate a negative correlation between gray matter perfusion and age (p = 0.003). Voxel-wise correction for BBPC is also shown to improve contrast to noise ratio between gray and white matter in CBF maps. A novel aspect of the study was to show that that BBPC measurements can be calculated based on the known Hct of the blood sample placed in scanner. We found a strong correlation (R² = 0.81 in gray matter, R² = 0.59 in white matter) established between BBPC maps normalized to the doped phantoms and BBPC maps normalized using Hct. This obviates the need for doped water phantoms which simplifies both the acquisition protocol and the post-processing methods. Together this suggests that CaSTRR represents a feasible, rapid method to account for BBPC variability when quantifying CBF. As canines have been used widely for aging and Alzheimer’s disease studies, the CaSTRR method established in the animals may further improve CBF measurements and advance our understanding of cerebrovascular changes in aging and neurodegeneration.

The basis of cellular and regional vulnerability in Alzheimer's disease

Alzheimer's disease (AD) differentially and specifically affects brain regions and neuronal cell types in a predictable pattern. Damage to the brain appears to spread and worsens with time, taking over more regions and activating multiple stressors that can converge to promote vulnerability of certain cell types. At the same time, other cell types and brain regions remain intact in the face of this onslaught of neuropathology. Although neuropathologic descriptions of AD have been extensively expanded and mapped over the last several decades, our understanding of the mechanisms underlying how certain regions and cell populations are specifically vulnerable or resistant has lagged behind. In this review, we detail what is known about the selectivity of local initiation of AD pathology in the hippocampus, its proposed spread via synaptic connections, and the diversity of clinical phenotypes and brain atrophy patterns that may arise from different fibrillar strains of pathologic proteins or genetic predispositions. We summarize accumulated and emerging knowledge of the cellular and molecular basis for neuroanatomic selectivity, consider potential disease-relevant differences between vulnerable and resistant neuronal cell types and isolate molecular markers to identify them.

Molecular insights into the surface-catalyzed secondary nucleation of amyloid-β40 (Aβ40) by the peptide fragment Aβ16-22

Understanding the structural mechanism by which proteins and peptides aggregate is crucial, given the role of fibrillar aggregates in debilitating amyloid diseases and bioinspired materials. Yet, this is a major challenge as the assembly involves multiple heterogeneous and transient intermediates. Here, we analyze the co-aggregation of Aβ₄₀ and Aβ_16-22, two widely studied peptide fragments of Aβ₄₂ implicated in Alzheimer's disease. We demonstrate that Aβ_16-22 increases the aggregation rate of Aβ₄₀ through a surface-catalyzed secondary nucleation mechanism. Discontinuous molecular dynamics simulations allowed aggregation to be tracked from the initial random coil monomer to the catalysis of nucleation on the fibril surface. Together, the results provide insight into how dynamic interactions between Aβ₄₀ monomers/oligomers on the surface of preformed Aβ_16-22 fibrils nucleate Aβ₄₀ amyloid assembly. This new understanding may facilitate development of surfaces designed to enhance or suppress secondary nucleation and hence to control the rates and products of fibril assembly.

Promising Results from Alzheimer's Disease Passive Immunotherapy Support the Development of a Preventive Vaccine

The apparently near-term effects of the monoclonal antibody BAN2401 in slowing the progression of prodromal Alzheimer's disease (AD) has created cautious optimism about the therapeutic use of antibodies that neutralize cytotoxic soluble amyloid-β aggregates, rather than removing plaque. Plaque being protective, as it immobilizes cytotoxic amyloid-β, rather than AD's causative agent. The presence of natural antibodies against cytotoxic amyloid-β implies the existence of a protective anti-AD immunity. Hence, for vaccines to induce a similar immunoresponse that prevents and/or delays the onset of AD, they must have adjuvants that stimulate a sole anti-inflammatory Th2 immunity, plus immunogens that induce a protective immunoresponse against diverse cytotoxic amyloid-β conformers. Indeed, amyloid-β pleomorphism may explain the lack of long-term protection by monoclonal antibodies that neutralize single conformers, like aducanumab. A situation that would allow new cytotoxic conformers to escape neutralization by previously effective monoclonal antibodies. Stimulation of a vaccine's effective immunoresponse would require the concurrent delivery of immunogen to dendritic cells and their priming, to induce a polarized Th2 immunity. An immunoresponse that would produce besides neutralizing antibodies against neurotoxic amyloid-β oligomers, anti-inflammatory cytokines; preventing inflammation that aggravates AD. Because of age-linked immune decline, vaccines would be significantly more effective in preventing, rather than treating AD. Considering the amyloid-β's role in tau's pathological hyperphosphorylation and their synergism in AD, the development of preventive vaccines against both amyloid-β and tau should be considered. Due to convenience and cost, vaccines may be the only option available to many countries to forestall the impending AD epidemic.

Modulation of Disordered Proteins with a Focus on Neurodegenerative Diseases and Other Pathologies

Intrinsically disordered proteins (IDPs) do not have rigid 3D structures, showing changes in their folding depending on the environment or ligands. Intrinsically disordered proteins are widely spread in eukaryotic genomes, and these proteins participate in many cell regulatory metabolism processes. Some IDPs, when aberrantly folded, can be the cause of some diseases such as Alzheimer′s, Parkinson′s, and prionic, among others. In these diseases, there are modifications in parts of the protein or in its entirety. A common conformational variation of these IDPs is misfolding and aggregation, forming, for instance, neurotoxic amyloid plaques. In this review, we discuss some IDPs that are involved in neurodegenerative diseases (such as beta amyloid, alpha synuclein, tau, and the “IDP-like” PrP), cancer (p53, c-Myc), and diabetes (amylin), focusing on the structural changes of these IDPs that are linked to such pathologies. We also present the IDP modulation mechanisms that can be explored in new strategies for drug design. Lastly, we show some candidate drugs that can be used in the future for the treatment of diseases caused by misfolded IDPs, considering that cancer therapy has more advanced research in comparison to other diseases, while also discussing recent and future developments in this area of research. Therefore, we aim to provide support to the study of IDPs and their modulation mechanisms as promising approaches to combat such severe diseases.

Computational insights into the role of α-strand/sheet in aggregation of α-synuclein

The α-synuclein is a major component of amyloid fibrils found in Lewy bodies, the characteristic intracellular proteinaceous deposits which are pathological hallmarks of neurodegenerative diseases such as Parkinson’s disease (PD) and dementia. It is an intrinsically disordered protein that may undergo dramatic structural changes to form amyloid fibrils. Aggregation process from α-synuclein monomers to amyloid fibrils through oligomeric intermediates is considered as the disease-causative toxic mechanism. However, mechanism underlying aggregation is not well-known despite several attempts. To characterize the mechanism, we have explored the effects of pH and temperature on the structural properties of wild-type and mutant α-synuclein using molecular dynamics (MD) simulation technique. MD studies suggested that amyloid fibrils can grow by monomer. Conformational transformation of the natively unfolded protein into partially folded intermediate could be accountable for aggregation and fibrillation. An intermediate α-strand was observed in the hydrophobic non-amyloid-β component (NAC) region of α-synuclein that could proceed to α-sheet and initiate early assembly events. Water network around the intermediate was analyzed to determine its influence on the α-strand structure. Findings of this study provide novel insights into possible mechanism of α-synuclein aggregation and promising neuroprotective strategy that could aid alleviate PD and its symptoms.

Insight into the internal structure of amyloid-β oligomers by isotope-edited Fourier transform infrared spectroscopy

Isotope-edited infrared spectroscopy reveals the structural unit of amyloid-β oligomers.

Amyloid Aggregation of Bacillus circulans Xylanase under Native Conditions and its Modulation by β-Amyloid-Derived Peptide Fragments

The aggregation of intrinsically disordered proteins into fibrils is implicated in many neurodegenerative diseases. Amyloid aggregation is a generic property of proteins as evidenced by globular proteins that often form amyloid aggregates under partially denaturing conditions. Recently, multiple lines of evidence have suggested that the amyloid aggregation of globular proteins can also occur under native conditions. Unfortunately, amyloid aggregation under native conditions has been demonstrated in only a handful of cases. Engineering a globular protein's amyloid aggregation might benefit from its fusion to an amyloid-derived fragment with reduced aggregation propensity. Unfortunately, the impacts of such fragments on the amyloid aggregation under native conditions have yet to be examined. In this study, we show that a globular protein, Bacillus circulans xylanase (BCX), can aggregate to form amyloid fibrils under native conditions. When BCX was mixed with or fused to the non-self-aggregating fragments, KLVFWAK and ELVFWAE-which were derived from β-amyloid (Aβ)-they modulated the BCX amyloid aggregation to differing extents. This study also provides insight into a correlation between the kinetic stability and amyloid aggregation of BCX, and supports a view that Aβ-derived fragments can be useful for the modulating amyloid aggregation of some, though not all, proteins.

Novel antibody against oligomeric amyloid-β: Insight into factors for effectively reducing the aggregation and cytotoxicity of amyloid-β aggregates

Amyloid-beta 42 (Aβ42) aggregates represent a prominent histopathological feature in Alzheimer's disease (AD); thus, immunotherapy against oligomeric Aβ42 aggregates is considered to be a potentially safe and specific therapeutic strategy. In this study, we identified an anti-oligomeric Aβ42 aggregate single-chain variable fragment (scFv) antibody, HT6, that is capable of efficiently binding to medium-sized Aβ42 aggregates (mainly 18-45 kDa) in vitro with an equilibrium dissociation constant (K_D) of 3.0 × 10^-6 M, whether they were derived from Aβ42 monomer, larger Aβ42 oligomers, or even fibrils. This ability allowed scFv HT6 to induce the gradual disassembly of large Aβ42 aggregates into small Aβ42 oligomers while simultaneously effectively inhibiting the further development of Aβ42 aggregates. Moreover, the scFv HT6-targeted conformational region on Aβ42 aggregates was found to be more local and relatively close to the N-terminus of Aβ42; thus, scFv HT6 significantly delayed or even prevented the aggregation of Aβ42 protofibrils, while significantly reducing the cytotoxicity of Aβ42 oligomers. Overall, this study demonstrate that even though the decrease in the cytotoxicity of Aβ42 aggregates might be closely related to the reduction in Aβ42 aggregates and vice versa, the reduction in Aβ42 aggregates might not necessarily be accompanied by or followed by the reduction or even elimination of the cytotoxicity of Aβ42 aggregates. This insight enriches the diversity of anti-oligomeric Aβ42 antibodies, further providing a new understanding into the relationship between their binding pattern to Aβ42 aggregates and the efficacy against their formation, offering a therapeutic strategy to delay the progression of AD.

Visual Features in Alzheimer's Disease: From Basic Mechanisms to Clinical Overview

Alzheimer's disease (AD) is the leading cause of dementia worldwide. It compromises patients' daily activities owing to progressive cognitive deterioration, which has elevated direct and indirect costs. Although AD has several risk factors, aging is considered the most important. Unfortunately, clinical diagnosis is usually performed at an advanced disease stage when dementia is established, making implementation of successful therapeutic interventions difficult. Current biomarkers tend to be expensive, insufficient, or invasive, raising the need for novel, improved tools aimed at early disease detection. AD is characterized by brain atrophy due to neuronal and synaptic loss, extracellular amyloid plaques composed of amyloid-beta peptide (Aβ), and neurofibrillary tangles of hyperphosphorylated tau protein. The visual system and central nervous system share many functional components. Thus, it is plausible that damage induced by Aβ, tau, and neuroinflammation may be observed in visual components such as the retina, even at an early disease stage. This underscores the importance of implementing ophthalmological examinations, less invasive and expensive than other biomarkers, as useful measures to assess disease progression and severity in individuals with or at risk of AD. Here, we review functional and morphological changes of the retina and visual pathway in AD from pathophysiological and clinical perspectives.

The concerted amyloid-beta clearance of LRP1 and ABCB1/P-gp across the blood-brain barrier is linked by PICALM

The accumulation of neurotoxic amyloid-beta (Aβ) in the brain is a characteristic hallmark of Alzheimer's disease (AD). The blood-brain barrier (BBB) provides a large surface area and has been shown to be an important mediator for removal of brain Aβ. Both, the ABC transporter P-glycoprotein (ABCB1/P-gp) and the receptor low-density lipoprotein receptor-related protein 1 (LRP1) have been implicated to play crucial roles in Aβ efflux from brain. Here, with immunoprecipitation experiments, co-immunostainings and dual inhibition of ABCB1/P-gp and LRP1, we show that both proteins are functionally linked, mediating a concerted transcytosis of Aβ through endothelial cells. Late-onset AD risk factor Phosphatidylinositol binding clathrin assembly protein (PICALM) is associated with both ABCB1/P-gp and LRP1 representing a functional link and guiding both proteins through the brain endothelium. Together, our results give more mechanistic insight on Aβ transport across the BBB and show that the functional interplay of different clearance proteins is needed for the rapid removal of Aβ from the brain.

Mutations of Histidine 13 to Arginine and Arginine 5 to Glycine Are Responsible for Different Coordination Sites of Zinc(II) to Human and Murine Peptides

Because mice and rats do not naturally develop Alzheimer's disease, genetically modified animals are required to study this pathology. This striking difference in terms of disease onset could be due to three alterations in the murine sequence (R5G, Y10F and H13R) of the amyloid-β peptide with respect to the human counterpart. Whether the metal-ion binding properties of the murine peptide are at the origin of such different amyloidogenicity of the two peptides is still an open question. Herein, the main zinc binding site to the murine amyloid-β at physiological pH has been determined through the combination of several spectroscopic and analytical methods applied to a series of six peptides with one or two of the key mutations. These results have been compared with the zinc binding site encountered in the human peptide. A coordination mechanism that demonstrates the importance of the H13R and R5G mutations in the different zinc environments present in the murine and human peptides is proposed. The nature of the minor zinc species present at physiological pH is also suggested for both peptides. Finally, the biological relevance and fallouts of the differences determined in zinc binding to human versus murine amyloid-β are also discussed.

Search of Neuroprotective Polyphenols Using the "Overlay" Isolation Method

Previous studies of the neuroprotective activity of polyphenols have used ununiform culture systems, making it difficult to compare their neuroprotective potency. We have established a new and simple method for preparing differentiated PC12 cells by removing the toxic coating step. Cells were induced to differentiate with the nerve growth factor (NGF) in a serum-free medium, without a medium change, but with a one-time overlay supplementation of NGF. The optimal inoculation density of the cells was 6–12 × 10³ cells/cm², and the presence of serum inhibited the differentiation. Neuroprotective activity could be quantified by the specific index (SI) value, that is, the ratio of the 50% cytotoxic concentration to the 50% effective concentration. Alkaline extract from the leaves of Sasa senanensis Rehder (SE), having had hormetic growth stimulation, showed the highest SI value, followed by epigallocatechin gallate. The SI value of curcumin and resveratrol was much lower. This simple overly method, that can prepare massive differentiated neuronal cells, may be applicable for the study of the differentiation-associated changes in intracellular metabolites, and the interaction between neuronal cells and physiological factors.

Fasudil in Combination With Bone Marrow Stromal Cells (BMSCs) Attenuates Alzheimer's Disease-Related Changes Through the Regulation of the Peripheral Immune System

Alzheimer’s disease (AD) is a chronic progressive neurodegenerative disease. Its mechanism is still not clear. Majority of research focused on the central nervous system (CNS) changes, while few studies emphasize on peripheral immune system modulation. Our study aimed to investigate the regulation of the peripheral immune system and its relationship to the severity of the disease after treatment in an AD model of APPswe/PSEN1dE9 transgenic (APP/PS1 Tg) mice. APP/PS1 Tg mice (8 months old) were treated with the ROCK-II inhibitor 1-(5-isoquinolinesulfonyl)-homo-piperazine (Fasudil) (intraperitoneal (i.p.) injections, 25 mg/kg/day), bone marrow stromal cells (BMSCs; caudal vein injections, 1 × 10⁶ BMSCs /time/mouse), Fasudil combined with BMSCs, or saline (i.p., control) for 2 months. Morris water maze (MWM) test was used to evaluate learning and memory. The mononuclear cells (MNCs) of spleens of APP/PS1 Tg mice were analyzed using flow cytometry for CD4+ T-cells, macrophages, and the pro-inflammatory and anti-inflammatory molecules of the macrophages. Immunohistochemical staining was used to examine the expression of ROCK-II in the spleens of APP/PS1 Tg mice. The MWM test showed improved spatial learning ability in APP/PS1 Tg mice treated with Fasudil or BMSCs alone or in combination, compared to untreated APP/PS1 Tg mice. Fasudil combined with BMSCs intervention significantly promoted the proliferation of CD4+/CD25+ and CD4+/ IL-10 lymphocytes, induced the release of cytokine factors, and regulated the balance of the immune system to work functionally. It also shifted M1 (MHC-II, CD86) to M2 (IL-10, CD206) phenotype of macrophages of CD11b and significantly enhanced the anti-inflammatory and phagocytic abilities (CD16/32) of macrophages of CD11b. Immunohistochemical staining showed significantly decreased expression of ROCK-II in mice treated with combination of Fasudil with BMSCs as compared to saline control. Fasudil in combination of BMSCs improved cognition of APP/PS1 Tg mice through the regulation of the peripheral immune system, including reduction of ROCK-II expression and increased proportion of anti-inflammatory M2 mononuclear phenotype and phagocytic macrophages in the spleen of the peripheral immune system. The latter was achieved through the communication between brain and spleen to improve the immunoregulation of CNS and AD disease conditions.

Targeting mTORs by omega-3 fatty acids: A possible novel therapeutic strategy for neurodegeneration?

Neurodegenerative diseases (NDs) such as Parkinson's (PD), Alzheimer's (AD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) cause significant world-wide morbidity and mortality. To date, there is no drug of cure for these, mostly age-related diseases, although approaches in delaying the pathology and/or giving patients some symptomatic relief have been adopted for the last few decades. Various studies in recent years have shown the beneficial effects of omega-3 poly unsaturated fatty acids (PUFAs) through diverse mechanisms including anti-inflammatory effects. This review now assesses the potential of this class of compounds in NDs therapy through specific action against the mammalian target of rapamycin (mTOR) signaling pathway. The role of mTOR in neurodegenerative diseases and targeted therapies by PUFAs are discussed.

Modulation of Amyloidogenesis Controlled by the C-Terminal Domain of Islet Amyloid Polypeptide Shows New Functions on Hepatocyte Cholesterol Metabolism

The islet amyloid polypeptide (IAPP) or amylin maintains a key role in metabolism. This 37-residues-peptide could form pancreatic amyloids, which are a characteristic feature of diabetes mellitus type 2. However, some species do not form amyloid fibril structures. By employing a biomimetic approach, we generated an extensive panel of optimized sequences of IAPP, which could drastically reduce aggregation propensity. A structural and cellular characterization analysis was performed on the C-terminal domain with the highest aggregation propensity. This allowed the observation of an aggregative phenomenon dependent of the lipid environment. Evaluation of the new F₂₃R variant demonstrated inhibition of β-sheet structure and, therefore, amyloid formation on the native C-terminal, phenomenon that was associated with functional optimization in calcium and cholesterol management coupled with the optimization of insulin secretion by beta cells. When F₂₃R variant was evaluated in microglia cells, a model of amyloidosis, cytotoxic conditions were not registered. In addition, it was found that C-terminal sequences of IAPP could modulate cholesterol metabolism in hepatocytes through regulation of SREBP-2, apoA-1, ABCA1, and LDLR, mechanism that may represent a new function of IAPP on the metabolism of cholesterol, increasing the LDL endocytosis in hepatocytes. Optimized sequences with only one residue modification in the C-terminal core aggregation could diminish β-sheet formation and represent a novel strategy adaptable to other pharmacological targets. Our data suggest a new IAPP function associated with rearrangements on metabolism of cholesterol in hepatocytes.

Eicosanoyl-5-hydroxytryptamide (EHT) prevents Alzheimer's disease-related cognitive and electrophysiological impairments in mice exposed to elevated concentrations of oligomeric beta-amyloid

Soluble forms of oligomeric beta-amyloid (Aβ) are thought to play a central role in Alzheimer's disease (AD). Transgenic manipulation of methylation of the serine/threonine protein phosphatase, PP2A, was recently shown to alter the sensitivity of mice to AD-related impairments resulting from acute exposure to elevated levels of Aβ. In addition, eicosanoyl-5-hydroxytryptamide (EHT), a naturally occurring component from coffee beans that modulates PP2A methylation, was shown to confer therapeutic benefits in rodent models of AD and Parkinson's disease. Here, we tested the hypothesis that EHT protects animals from the pathological effects of exposure to elevated levels of soluble oligomeric Aβ. We treated mice with EHT-containing food at two different doses and assessed the sensitivity of these animals to Aβ-induced behavioral and electrophysiological impairments. We found that EHT administration protected animals from Aβ-induced cognitive impairments in both a radial-arm water maze and contextual fear conditioning task. We also found that both chronic and acute EHT administration prevented Aβ-induced impairments in long-term potentiation. These data add to the accumulating evidence suggesting that interventions with pharmacological agents, such as EHT, that target PP2A activity may be therapeutically beneficial for AD and other neurological conditions.