Biosynthesis of Nanoparticles with Green Tea for Inhibition of β-Amyloid Fibrillation Coupled with Ligands Analysis

Background

Inhibition of amyloid β protein fragment (Aβ) aggregation is considered to be one of the most effective strategies for the treatment of Alzheimer's disease. (-)-Epigallocatechin-3-gallate (EGCG) has been found to be effective in this regard; however, owing to its low bioavailability, nanodelivery is recommended for practical applications. Compared to chemical reduction methods, biosynthesis avoids possible biotoxicity and cumbersome preparation processes.

Materials and Methods

The interaction between EGCG and Aβ42 was simulated by molecular docking, and green tea-conjugated gold nanoparticles (GT-Au NPs) and EGCG-Au NPs were synthesized using EGCG-enriched green tea and EGCG solutions, respectively. Surface active molecules of the particles were identified and analyzed using various liquid chromatography-tandem triple quadrupole mass spectrometry methods. ThT fluorescence assay, circular dichroism, and TEM were used to investigate the effect of synthesized particles on the inhibition of Aβ42 aggregation.

Results

EGCG as well as apigenin, quercetin, baicalin, and glutathione were identified as capping ligands stabilized on the surface of GT-Au NPs. They more or less inhibited Aβ42 aggregation or promoted fibril disaggregation, with EGCG being the most effective, which bound to Aβ42 through hydrogen bonding, hydrophobic interactions, etc. resulting in 39.86% and 88.50% inhibition of aggregation and disaggregation effects, respectively. EGCG-Au NPs were not as effective as free EGCG, whereas multiple thiols and polyphenols in green tea accelerated and optimized heavy metal detoxification. The synthesized GT-Au NPs conferred the efficacy of diverse ligands to the particles, with inhibition of aggregation and disaggregation effects of 54.69% and 88.75%, respectively, while increasing the yield, enhancing water solubility, and decreasing cost.

Conclusion

Biosynthesis of nanoparticles using green tea is a promising simple and economical drug-carrying approach to confer multiple pharmacophore molecules to Au NPs. This could be used to design new drug candidates to treat Alzheimer's disease.

An NMR Toolkit to Probe Amyloid Oligomer Inhibition in Neurodegenerative Diseases: From Ligand Screening to Dissecting Binding Topology and Mechanisms of Action

The aggregation of amyloid peptides and proteins into toxic oligomers is a hallmark of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Machado-Joseph's disease, and transmissible spongiform encephalopathies. Inhibition of amyloid oligomers formation and interactions with biological counterparts, as well as the triggering of non-toxic amorphous aggregates, are strategies towards preventive interventions against these pathologies. NMR spectroscopy addresses the need for structural characterization of amyloid proteins and their aggregates, their binding to inhibitors, and rapid screening of compound libraries for ligand identification. Here we briefly discuss the solution experiments constituting the NMR spectroscopist's toolkit and provide examples of their application.

Cell-Free and In Vivo Characterization of the Inhibitory Activity of Lavado Cocoa Flavanols on the Amyloid Protein Ataxin-3: Toward New Approaches against Spinocerebellar Ataxia Type 3

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disorder characterized by ataxia and other neurological manifestations, with a poor prognosis and a lack of effective therapies. The amyloid aggregation of the ataxin-3 protein is a hallmark of SCA3 and one of the main biochemical events prompting its onset, making it a prominent target for the development of preventive and therapeutic interventions. Here, we tested the efficacy of an aqueous Lavado cocoa extract and its polyphenolic components against ataxin-3 aggregation and neurotoxicity. The combination of biochemical assays and atomic force microscopy morphological analysis provided clear evidence of cocoa flavanols' ability to hinder ATX3 amyloid aggregation through direct physical interaction, as assessed by NMR spectroscopy. The chemical identity of the flavanols was investigated by ultraperformance liquid chromatography-high-resolution mass spectrometry. The use of the preclinical model Caenorhabditis elegans allowed us to demonstrate cocoa flavanols' ability to ameliorate ataxic phenotypes in vivo. To the best of our knowledge, Lavado cocoa is the first natural source whose extract is able to directly interfere with ATX3 aggregation, leading to the formation of off-pathway species.

In-depth analyses of lncRNA and circRNA expression in the hippocampus of LPS-induced AD mice by Byu d Mar 25

Byu d Mar 25 (BM25) has been verified to have neuroprotective effects in Alzheimer's disease (AD) mice. However, the molecular mechanism remains unclear. We aimed to investigate the expression profiling of lncRNAs and circRNAs by microarray analysis. Six hippocampus from LPS-mediated AD mice model treated with (normal saline (NS) (n = 3) and AD mice model treated with BM25 (n = 3) were selected. Microarray analysis was performed to detect the expression profiles of lncRNAs and circRNAs in hippocampus. Differentially expressed (DE) lncRNAs, mRNAs and circRNAs were identified through scatter plot and volcano plot filtering with a threshold of fold-change ≥2 and P  ≤ 0.05. Co-expression network is analyzed by Circos software. Cis - and Trans - regulation were analyzed using RIsearch-2.0 and FEELNC softwares. LncRNA-transcription factors (TFs) and LncRNA-Target-TFs network were analyzed by Clusterprofiler software. The prediction of miRNAs bind to circRNAs were performed with miRNAbase. A total of 113 DElncRNAs, 117 DEmRNAs, and 4 DEcircRNAs were detected. The pathway analysis showed the mRNAs that correlated with lncRNAs were involved in apoptosis, inflammatory mediator regulation of TRP channels, NF-kappa B and PI3K-Akt signaling pathway. The lncRNA-TFs network analysis suggested the lncRNAs were mostly regulated by Ncoa1, Phf5a, Klf6, Lmx1b, and Pax3. Additionally, lncRNA-target-TFs network analysis indicated the GATA6, Junb, Smad1, Twist1, and Mafb mostly regulate the same lncRNAs: XR_001783430.1 and NR_051982.1. Furthermore, 480 miRNAs were predicted binding to 4 identified circRNAs. The BM25 may affect AD by regulating the expression of lncRNAs and circRNAs, which could regulate the expressions of mRNAs or miRNAs by LncRNA-Target-TFs network.

Targeting gut-brain axis by dietary flavonoids ameliorate aging-related cognition decline: Evidences and mechanisms

Aging-related cognitive impairment, mainly Alzheimer's disease (AD), has been widely studied. However, effective prevention and treatment methods are still lacking. In recent years, researchers have observed beneficial effects of plant-based supplements, such as flavonoids, on cognitive protection. This provides a new clue for the prevention of cognitive dysfunction. Studies have shown that dietary flavonoids have neuroprotective effects, but the mechanism is not clear. In this review, we systematically reviewed the research progress on the effects of dietary flavonoids on gut microbes and their metabolites, and concluded that flavonoids could improve cognitive function through the gut-brain axis. Flavonoids can be absorbed through the intestine, cross the blood-brain barrier, and enter the brain tissue. Flavonoids can inhibit the expression and secretion of inflammatory factors in brain tissue, reduce the damage caused by oxidative stress, clear neural damage proteins and inhibit neuronal apoptosis, thereby ameliorating age-related cognitive disorders. Future work will continue to explore the gut-brain axis and target genes regulated by flavonoids. In addition, clinical research and its mechanisms need to be further explored to provide solutions or advise for patients with cognitive impairment.

Structural fingerprinting of pleiotropic flavonoids for multifaceted Alzheimer's disease

Alzheimer's disease has emerged as one of the most challenging neurodegenerative diseases associated with dementia, loss of cognitive functioning and memory impairment. Despite enormous efforts to identify disease modifying technologies, the repertoire of currently approved drugs consists of a few symptomatic candidates that are not capable of halting disease progression. Moreover, these single mechanism drugs target only a small part of the pathological cascade and do not address most of the etiological basis of the disease. Development of therapies that are able to simultaneously tackle all the multiple interlinked causative factors such as amyloid protein aggregation, tau hyperphosphorylation, cholinergic deficit, oxidative stress, metal dyshomeostasis and neuro-inflammation has become the focus of intensive research in this domain. Flavonoids are natural phytochemicals that have demonstrated immense potential as medicinal agents due to their multiple beneficial therapeutic effects. The polypharmacological profile of flavonoids aligns well with the multifactorial pathological landscape of Alzheimer's disease, making them promising candidates to overcome the challenges of this neurodegenerative disorder. This review presents a detailed overview of the pleiotropic biology of flavonoids favourable for Alzheimer therapeutics and the structural basis for these effects. Structure activity trends for several flavonoid classes such as flavones, flavonols, flavanones, isoflavones, flavanols and anthocyanins are comprehensively analyzed in detail and presented.

Alzheimer's Disease Prevention through Natural Compounds: Cell-Free, In Vitro, and In Vivo Dissection of Hop (Humulus lupulus L.) Multitarget Activity

The relevant social and economic costs associated with aging and neurodegenerative diseases, particularly Alzheimer's disease (AD), entail considerable efforts to develop effective preventive and therapeutic strategies. The search for natural compounds, whose intake through diet can help prevent the main biochemical mechanisms responsible for AD onset, led us to screen hops, one of the main ingredients of beer. To explore the chemical variability of hops, we characterized four hop varieties, i.e., Cascade, Saaz, Tettnang, and Summit. We investigated the potential multitarget hop activity, in particular its ability to hinder Aβ1-42 peptide aggregation and cytotoxicity, its antioxidant properties, and its ability to enhance autophagy, promoting the clearance of misfolded and aggregated proteins in a human neuroblastoma SH-SY5Y cell line. Moreover, we provided evidence of in vivo hop efficacy using the transgenic CL2006Caenorhabditis elegans strain expressing the Aβ3-42 peptide. By combining cell-free and in vitro assays with nuclear magnetic resonance (NMR) and MS-based metabolomics, NMR molecular recognition studies, and atomic force microscopy, we identified feruloyl and p-coumaroylquinic acids flavan-3-ol glycosides and procyanidins as the main anti-Aβ components of hop.

Insights into Molecular Mechanisms of EGCG and Apigenin on Disrupting Amyloid-Beta Protofibrils Based on Molecular Dynamics Simulations

The fibrillization and deposition of amyloid-beta (Aβ) protofibrils are one of the important factors leading to Alzheimer's disease. Molecular dynamics simulations can offer information on intermolecular interaction mechanisms between Aβ protofibrils and Aβ fibrillization inhibitors. Here, in this work, we explore the early molecular mechanisms of (-)-epigallocatechin-3-gallate (EGCG) and apigenin on disrupting Aβ42 protofibrils based on molecular simulations. The binding modes of EGCG and apigenin with the Aβ42 protofibril are obtained. Furthermore, we compare the behavioral mechanisms of EGCG and apigenin on disturbing the Aβ42 protofibril. Both EGCG and apigenin are able to decrease the proportion of the β-sheet and bend structures of the Aβ42 protofibril while inducing random coil structures. The results of hydrogen bonds and D23-K28 salt bridges illustrate that EGCG and apigenin have the ability of destabilizing the Aβ42 protofibril. Meanwhile, the van der Waals interactions between the EGCG and Aβ42 protofibril are shown to be larger than that of apigenin with the Aβ42 protofibril, but the electrostatic interactions between apigenin and the Aβ42 protofibril are dominant in the binding affinity. Our findings may help in designing effective drug candidates for disordering the Aβ protofibril and impeding Aβ fibrillization.

Neuroprotective Effect of Artichoke-Based Nanoformulation in Sporadic Alzheimer’s Disease Mouse Model: Focus on Antioxidant, Anti-Inflammatory, and Amyloidogenic Pathways

The vast socio-economic impact of Alzheimer’s disease (AD) has prompted the search for new neuroprotective agents with good tolerability and safety profile. With its outstanding role as antioxidant and anti-inflammatory, alongside its anti-acetylcholinesterase activity, the artichoke can be implemented in a multi-targeted approach in AD therapy. Moreover, artichoke agricultural wastes can represent according to the current United Nations Sustainable Development goals an opportunity to produce medicinally valuable phenolic-rich extracts. In this context, the UPLC-ESI-MS/MS phytochemical characterization of artichoke bracts extract revealed the presence of mono- and di-caffeoylquinic acids and apigenin, luteolin, and kaempferol O-glycosides with remarkable total phenolics and flavonoids contents. A broad antioxidant spectrum was established in vitro. Artichoke-loaded, chitosan-coated, solid lipid nanoparticles (SLNs) were prepared and characterized for their size, zeta potential, morphology, entrapment efficiency, release, and ex vivo permeation and showed suitable colloidal characteristics, a controlled release profile, and promising ex vivo permeation, indicating possibly better physicochemical and biopharmaceutical parameters than free artichoke extract. The anti-Alzheimer potential of the extract and prepared SLNs was assessed in vivo in streptozotocin-induced sporadic Alzheimer mice. A great improvement in cognitive functions and spatial memory recovery, in addition to a marked reduction of the inflammatory biomarker TNF-α, β-amyloid, and tau protein levels, were observed. Significant neuroprotective efficacy in dentate Gyrus sub-regions was achieved in mice treated with free artichoke extract and to a significantly higher extent with artichoke-loaded SLNs. The results clarify the strong potential of artichoke bracts extract as a botanical anti-AD drug and will contribute to altering the future medicinal outlook of artichoke bracts previously regarded as agro-industrial waste.

Beneficial effects of apigenin on the transgenic Drosophila model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. The available drugs improve the symptoms but do not play role in modifying disease effects. Currently, the treatment strategies focus on inhibiting the production of Aβ-42 aggregates and tau filaments. In this context the natural plant products could act as a potent candidate. Therefore, we decided to study the effect of apigenin on the transgenic Drosophila model of AD i.e., expressing Aβ-42 in the neurons. The AD flies were allowed to feed on the diet having 25, 50, 75 and 100μM of apigenin for 30 days. The exposure of AD flies to apigenin showed a dose dependent significant decrease in the oxidative stress and delay in the loss of climbing ability. Apigenin also inhibits the activity of acetylcholinesterase. The immunostaining and molecular docking studies suggest that apigenin inhibits the formation of Aβ-42 aggregates. Apigenin is potent in reducing the AD symptoms being mimicked in the transgenic Drosophila model of AD.

NMR-Driven Identification of Cinnamon Bud and Bark Components With Anti-Aβ Activity

The anti-Alzheimer disease (AD) activity reported for an aqueous cinnamon bark extract prompted us to investigate and compare the anti-amyloidogenic properties of cinnamon extracts obtained from both bark and bud, the latter being a very little explored matrix. We prepared the extracts with different procedures (alcoholic, hydroalcoholic, or aqueous extractions). An efficient protocol for the rapid analysis of NMR spectra of cinnamon bud and bark extracts was set up, enabling the automatic identification and quantification of metabolites. Moreover, we exploited preparative reverse-phase (RP) chromatography to prepare fractions enriched in polyphenols, further characterized by UPLC-HR-MS. Then, we combined NMR-based molecular recognition studies, atomic force microscopy, and in vitro biochemical and cellular assays to investigate the anti-amyloidogenic activity of our extracts. Both bud and bark extracts showed a potent anti-amyloidogenic activity. Flavanols, particularly procyanidins, and cinnamaldehydes, are the chemical components of cinnamon hindering Aβ peptide on-pathway aggregation and toxicity in a human neuroblastoma SH-SY5Y cell line. Together with the previously reported ability to hinder tau aggregation and filament formation, these data indicate cinnamon polyphenols as natural products possessing multitarget anti-AD activity. Since cinnamon is a spice increasingly present in the human diet, our results support its use to prepare nutraceuticals useful in preventing AD through an active contrast to the biochemical processes that underlie the onset of this disease. Moreover, the structures of cinnamon components responsible for cinnamon anti-AD activities represent molecular templates for designing and synthesizing new anti-amyloidogenic drugs.

Eugenitol ameliorates memory impairments in 5XFAD mice by reducing Aβ plaques and neuroinflammation

Alzheimer's disease (AD) is caused by various pathological mechanisms; therefore, it is necessary to develop drugs that simultaneously act on multiple targets. In this study, we investigated the effects of eugenitol, which has anti-amyloid β (Aβ) and anti-neuroinflammatory effects, in an AD mouse model. We found that eugenitol potently inhibited Aβ plaque and oligomer formation. Moreover, eugenitol dissociated the preformed Aβ plaques and reduced Aβ-induced nero2a cell death. An in silico docking simulation study showed that eugenitol may interact with Aβ1-42 monomers and fibrils. Eugenitol showed radical scavenging effects and potently reduced the release of proinflammatory cytokines from lipopolysaccharide-treated BV2 cells. Systemic administration of eugenitol blocked Aβ aggregate-induced memory impairment in the Morris water maze test in a dose-dependent manner. In 5XFAD mice, prolonged administration of eugenitol ameliorated memory and hippocampal long-term potentiation impairment. Moreover, eugenitol significantly reduced Aβ deposits and neuroinflammation in the hippocampus of 5XFAD mice. These results suggest that eugenitol, which has anti-Aβ aggregation, Aβ fibril dissociation, and anti-inflammatory effects, potently modulates AD-like pathologies in 5XFAD mice, and could be a promising candidate for AD therapy.

Glycosides and Their Corresponding Small Molecules Inhibit Aggregation and Alleviate Cytotoxicity of Aβ40

Polyphenols are the class of naturally synthesized compounds in the secondary metabolism of plants, which are widely distributed in fruits and vegetables. Their potential health treatment strategies have attracted wide attention in the scientific community. The abnormal aggregation of Aβ to form mature fibrils is pathologically related to Alzheimer's disease (AD). Therefore, inhibiting Aβ40 fibrillogenesis was considered to be the major method for the intervention and therapy of AD. Glycosides, as a cluster of natural phenolic compounds, are widely distributed in Chinese herbs, fruits, and vegetables. The inhibitory effect of glycosides (phloridzin, salidroside, polydatin, geniposide, and gastrodin) and their corresponding small molecules (phloretin, 4-hydroxyphenyl ethanol, resveratrol, genipin, and 4-hydroxybenzyl alcohol) on Aβ40 aggregation and fibrils prolongation, disaggregation against mature fibrils, and the resulting cytotoxicity were studied by systematical biochemical, cell biology and molecular docking techniques, respectively. As a result, all inhibitors were observed against Aβ40 aggregation and fibrils prolongation and disaggregated mature Aβ40 fibrils in a dose-dependent manner. Besides, the cell validity experiments also showed that all inhibitors could effectively alleviate the cytotoxicity induced by Aβ40 aggregates, and the glycoside groups played important roles in this inhibiting process. Finally, molecular docking was performed to study the interactions between these inhibitors and Aβ40. Docking showed that all inhibitors were bound to the similar region of Aβ40, and glycoside group formed hydrogen bonds with the pivotal residues Lys16. These results indicated that the glycoside groups could increase the inhibitory effects and reduce cytotoxicity. Glycosides have tremendous potential to be developed as an innovative type of aggregation inhibitor to control and treat neurodegenerative diseases.

Protective effect of olive leaves phenolic compounds against neurodegenerative disorders: Promising alternative for Alzheimer and Parkinson diseases modulation

The main objective of this work was to review literature on compounds extracted from olive tree leaves, such as simple phenols (hydroxytyrosol) and flavonoids (Apigenin, apigenin-7-O-glucoside, luteolin.) and their diverse pharmacological activities as antioxidant, antimicrobial, anti-viral, anti-obesity, anti-inflammatory and neuroprotective properties. In addition, the study discussed the key mechanisms underlying their neuroprotective effects. This study adopted an approach of collecting data through the databases provided by ScienceDirect, SCOPUS, MEDLINE, PubMed and Google Scholar. This review revealed that there was an agreement on the great impact of olive tree leaves phenolic compounds on many metabolic syndromes as well as on the most prevalent neurodegenerative diseases such as Alzheimer and Parkinson. These findings would be of great importance for the use of olive tree leaves extracts as a food supplement and/or a source of drugs for many diseases. In addition, this review would of great help to beginning researchers in the field since it would offer them a general overview of the studies undertaken in the last two decades on the topic.

On-cell saturation transfer difference NMR for the identification of FimH ligands and inhibitors

We describe the development of an on-cell NMR method for the rapid screening of FimH ligands and the structural identification of ligand binding epitopes. FimH is a mannose-binding bacterial adhesin expressed at the apical end of type 1 pili of uropathogenic bacterial strains and responsible for their d-mannose sensitive adhesion to host mammalian epithelial cells. Because of these properties, FimH is a key virulence factor and an attractive therapeutic target for urinary tract infection. We prepared synthetic d-mannose decorated dendrimers, we tested their ability to prevent the FimH-mediated yeast agglutination, and thus we used the compounds showing the best inhibitory activity as models of FimH multivalent ligands to set up our NMR methodology. Our experimental protocol, based on on-cell STD NMR techniques, is a suitable tool for the screening and the epitope mapping of FimH ligands aimed at the development of new antiadhesive and diagnostic tools against urinary tract infection pathogens. Notably, the study is carried out in a physiological environment, i.e. at the surface of living pathogen cells expressing FimH.

Flavonoid-Based Nanomedicines in Alzheimer's Disease Therapeutics: Promises Made, a Long Way To Go

Alzheimer's disease (AD) is characterized by the continuous decline of the cognitive abilities manifested due to the accumulation of large aggregates of amyloid-beta 42 (Aβ42), the formation of neurofibrillary tangles of hyper-phosphorylated forms of microtubule-associated tau protein, which may lead to many alterations at the cellular and systemic level. The current therapeutic strategies primarily focus on alleviating pathological symptoms rather than providing a possible cure. AD is one of the highly studied but least understood neurological problems and remains an unresolved condition of human brain degeneration. Over the years, multiple naturally derived small molecules, including plant products, microbial isolates, and some metabolic byproducts, have been projected as supplements reducing the risk or possible treatment of the disease. However, unfortunately, none has met the expected success. One major challenge for most medications is their ability to cross the blood-brain barrier (BBB). In past decades, nanotechnology-based interventions have offered an alternative platform to address the problem of the successful delivery of the drugs to the specific targets. Interestingly, the exciting interface of natural products and nanomedicine is delivering promising results in AD treatment. The potential applications of flavonoids, the plant-derived compounds best known for their antioxidant activities, and their amalgamation with nanomedicinal approaches may lead to highly effective therapeutic strategies for treating well-known neurodegenerative diseases. In the present review, we explore the possibilities and recent developments on an exciting combination of flavonoids and nanoparticles in AD.

Flavonoids as an Intervention for Alzheimer's Disease: Progress and Hurdles Towards Defining a Mechanism of Action

Attempts to develop a disease modifying intervention for Alzheimer’s disease (AD) through targeting amyloid β (Aβ) have so far been unsuccessful. There is, therefore, a need for novel therapeutics against alternative targets coupled with approaches which may be suitable for early and sustained use likely required for AD prevention. Numerous in vitro and in vivo studies have shown that flavonoids can act within processes and pathways relevant to AD, such as Aβ and tau pathology, increases in BDNF, inflammation, oxidative stress and neurogenesis. However, the therapeutic development of flavonoids has been hindered by an ongoing lack of clear mechanistic data that fully takes into consideration metabolism and bioavailability of flavonoids in vivo. With a focus on studies that incorporate these considerations into their experimental design, this review will evaluate the evidence for developing specific flavonoids as therapeutics for AD. Given the current lack of success of anti-Aβ targeting therapeutics, particular attention will be given to flavonoid-mediated regulation of tau phosphorylation and aggregation, where there is a comparable lack of study. Reflecting on this evidence, the obstacles that prevent therapeutic development of flavonoids will be examined. Finally, the significance of recent advances in flavonoid metabolomics, modifications and influence of the microbiome on the therapeutic capacity of flavonoids in AD are explored. By highlighting the potential of flavonoids to target multiple aspects of AD pathology, as well as considering the hurdles, this review aims to promote the efficient and effective identification of flavonoid-based approaches that have potential as therapeutic interventions for AD.

Recent Research on Flavonoids and their Biomedical Applications

Flavonoids, commonly found in various plants, are a class of polyphenolic compounds having a basic structural unit of 2-phenylchromone. Flavonoid compounds have attracted much attention due to their wide biological applications. In order to facilitate further research on the biomedical application of flavonoids, we surveyed the literature published on the use of flavonoids in medicine during the past decade, documented the commonly found structures in natural flavonoids, and summarized their pharmacological activities as well as associated mechanisms of action against a variety of health disorders including chronic inflammation, cancer, cardiovascular complications and hypoglycemia. In this mini-review, we provide suggestions for further research on the biomedical applications of flavonoids.

Natural Compounds as Inhibitors of Aβ Peptide Aggregation: Chemical Requirements and Molecular Mechanisms

Alzheimer’s disease (AD) is one of the most common neurodegenerative disorders, with no cure and preventive therapy. Misfolding and extracellular aggregation of Amyloid-β (Aβ) peptides are recognized as the main cause of AD progression, leading to the formation of toxic Aβ oligomers and to the deposition of β-amyloid plaques in the brain, representing the hallmarks of AD. Given the urgent need to provide alternative therapies, natural products serve as vital resources for novel drugs. In recent years, several natural compounds with different chemical structures, such as polyphenols, alkaloids, terpenes, flavonoids, tannins, saponins and vitamins from plants have received attention for their role against the neurodegenerative pathological processes. However, only for a small subset of them experimental evidences are provided on their mechanism of action. This review focuses on those natural compounds shown to interfere with Aβ aggregation by direct interaction with Aβ peptide and whose inhibitory mechanism has been investigated by means of biophysical and structural biology experimental approaches. In few cases, the combination of approaches offering a macroscopic characterization of the oligomers, such as TEM, AFM, fluorescence, together with high-resolution methods could shed light on the complex mechanism of inhibition. In particular, solution NMR spectroscopy, through peptide-based and ligand-based observation, was successfully employed to investigate the interactions of the natural compounds with both soluble NMR-visible (monomer and low molecular weight oligomers) and NMR-invisible (high molecular weight oligomers and protofibrils) species. The molecular determinants of the interaction of promising natural compounds are here compared to infer the chemical requirements of the inhibitors and the common mechanisms of inhibition. Most of the data converge to indicate that the Aβ regions relevant to perturb the aggregation cascade and regulate the toxicity of the stabilized oligomers, are the N-term and β1 region. The ability of the natural aggregation inhibitors to cross the brain blood barrier, together with the tactics to improve their low bioavailability are discussed. The analysis of the data ensemble can provide a rationale for the selection of natural compounds as molecular scaffolds for the design of new therapeutic strategies against the progression of early and late stages of AD.

NMR-based Lavado cocoa chemical characterization and comparison with fermented cocoa varieties: Insights on cocoa's anti-amyloidogenic activity

The metabolic profile of Lavado cocoa was characterized for the first time by NMR spectroscopy, then compared with the profiles of fermented and processed varieties, Natural and commercial cocoa. The significant difference in the contents of theobromine and flavanols prompted us to examine the cocoa varieties to seek correlations between these metabolite concentrations and the anti-amyloidogenic activity reported for cocoa in the literature. We combined NMR spectroscopy, preparative reversed-phase (RP) chromatography, atomic force microscopy, in vitro biochemical and cell assays, to investigate and compare the anti-amyloidogenic properties of extracts and fractions enriched in different metabolite classes. Lavado variety was the most active and the catechins and theobromine were the chemical components of cocoa hindering Aβ peptide on-pathway aggregation and toxicity in a human neuroblastoma SH-SY5Y cell line.

Molecular Insight into the Therapeutic Promise of Flavonoids against Alzheimer's Disease

Alzheimer’s disease (AD) is one of the utmost chronic neurodegenerative disorders, which is characterized from a neuropathological point of view by the aggregates of amyloid beta (Aβ) peptides that are deposited as senile plaques and tau proteins which form neurofibrillary tangles (NFTs). Even though advancement has been observed in order to understand AD pathogenesis, currently available therapeutic methods can only deliver modest symptomatic relief. Interestingly, naturally occurring dietary flavonoids have gained substantial attention due to their antioxidative, anti-inflammatory, and anti-amyloidogenic properties as alternative candidates for AD therapy. Experimental proof provides support to the idea that some flavonoids might protect AD by interfering with the production and aggregation of Aβ peptides and/or decreasing the aggregation of tau. Flavonoids have the ability to promote clearance of Aβ peptides and inhibit tau phosphorylation by the mTOR/autophagy signaling pathway. Moreover, due to their cholinesterase inhibitory potential, flavonoids can represent promising symptomatic anti-Alzheimer agents. Several processes have been suggested for the aptitude of flavonoids to slow down the advancement or to avert the onset of Alzheimer’s pathogenesis. To enhance cognitive performance and to prevent the onset and progress of AD, the interaction of flavonoids with various signaling pathways is proposed to exert their therapeutic potential. Therefore, this review elaborates on the probable therapeutic approaches of flavonoids aimed at averting or slowing the progression of the AD pathogenesis.

A novel rhamnoside derivative PL402 up-regulates matrix metalloproteinase 3/9 to promote Aβ degradation and alleviates Alzheimer's-like pathology

The accumulation of amyloid-β (Aβ), considered as the major cause of Alzheimer’s disease (AD) pathogenesis, relays on the rate of its biosynthesis and degradation. Aβ degradation is a common overture to late-onset AD and targeting the impairment of Aβ degradation has gained attention in the recent years. In this study, we demonstrated a rhamnoside derivative PL402 suppressed Aβ level in cell models without changing the expression or activity of Aβ generation-related secretases. However, the levels of matrix metalloproteinase (MMP) 3 and 9, belonging to amyloid-degrading enzymes (ADEs), were up-regulated by PL402. The inhibition or the knockdown of these two enzymes abolished the effect of PL402, indicating that PL402 may reduce Aβ via MMP3/9-mediated Aβ degradation. Notably, administration of PL402 significantly attenuated Aβ pathology and cognitive defects in APP/PS1 transgenic mice with the consistent promotion of ADEs expression. Thus, our study suggests that targeting Aβ degradation could be an effective strategy against AD and the rhamnoside derivatives may have therapeutic effects.

Inhibitory Effects of Novel 7-Substituted 6-iodo-3-O-Flavonol Glycosides against Cholinesterases and β-secretase Activities, and Evaluation for Potential Antioxidant Properties

A series of 7-halogeno- (X = F, Cl, Br) and 7-methoxy-substituted acetylated 6-iodo-3-O-flavonol glycosides were prepared, and evaluated for inhibitory effect in vitro against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities. 7-Bromo-2-(4-chlorophenyl)-6-iodo-4H-chromen-4-one-3-O-2,3,4,6-O-tetraacetyl-β-d-glucopyranoside (2k) and 7-bromo-6-iodo-2-(4-methoxyphenyl)-4H-chromen-4-one-3-O-2,3,4,6-O-tetraacetyl-β-d-glucopyranoside (2l) exhibited significant inhibitory effect against AChE activity when compared to the activity of the reference standard, donepezil. Compound 2k was found to be selective against AChE and to exhibit reduced inhibitory effect against BChE activity. 6-Iodo-7-methoxy-2-(4-methoxyphenyl)-4H-chromen-4-one-3-O-2,3,4,6-O-tetraacetyl-β-d-glucopyranoside (2p) was found to exhibit increased activity against BChE, more so than the activity of donepezil. The most active compounds were also evaluated for inhibitory effect against β-secretase activity and for potential radical scavenging activities. The experimental data were complemented with molecular docking (in silico) studies of the most active compounds into the active sites of these enzymes.

Neuroprotective and Anti-Amyloid β Effect and Main Chemical Profiles of White Tea: Comparison Against Green, Oolong and Black Tea

White tea (WT) is one of six tea types originally derived from Fujian Province, China. White tea is known for its health-promoting properties. However, the neuroprotective and anti-aggregatory properties of WT against the hallmark toxic Alzheimer's protein, Aβ have not been investigated. In this study, WT, green tea (GT), oolong tea (OT) and black tea (BT) were manufactured using tea leaves from the cultivar Camellia sinensis (Jin Guanyin). The protective effects of these tea extracts were then studied under oxidative stress conditions via t-bhp and H₂O₂ exposure, in addition to Aβ treatment using a PC-12 cell model. Each tea type failed to rescue PC-12 cells from either t-bhp or H₂O₂-mediated toxicity, however each extract exerted significant protection against Aβ-evoked neurotoxicity. Results of the Thioflavin T Kinetic (ThT) and TEM assay showed that Aβ aggregate formation was inhibited by each tea type. Additionally, TEM also supported the different anti-aggregatory effect of WT by modifying Aβ into an amorphous and punctate aggregate morphology. Higher accumulated precedent or potential neuroprotective compounds in WT, including ECG''3Me, 8-C-ascorbyl-EGCG, GABA and Gln, in addition to flavonol or flavone glycosides detected by using UPLC-QTOF-MS and UPLC-QqQ-MS, may contribute to a favourable anti-aggregative and neuroprotective effect of WT against Aβ.

Epigallocatechin-3-gallate and related phenol compounds redirect the amyloidogenic aggregation pathway of ataxin-3 towards non-toxic aggregates and prevent toxicity in neural cells and Caenorhabditis elegans animal model

The protein ataxin-3 (ATX3) triggers an amyloid-related neurodegenerative disease when its polyglutamine stretch is expanded beyond a critical threshold. We formerly demonstrated that the polyphenol epigallocatechin-3-gallate (EGCG) could redirect amyloid aggregation of a full-length, expanded ATX3 (ATX3-Q55) towards non-toxic, soluble, SDS-resistant aggregates. Here, we have characterized other related phenol compounds, although smaller in size, i.e. (-)-epigallocatechin gallate (EGC), and gallic acid (GA). We analysed the aggregation pattern of ATX3-Q55 and of the N-terminal globular Josephin domain (JD) by assessing the time course of the soluble protein, as well its structural features by FTIR and AFM, in the presence and the absence of the mentioned compounds. All of them redirected the aggregation pattern towards soluble, SDS-resistant aggregates. They also prevented the appearance of ordered side-chain hydrogen bonding in ATX3-Q55, which is the hallmark of polyQ-related amyloids. Molecular docking analyses on the JD highlighted three interacting regions, including the central, aggregation-prone one. All three compounds bound to each of them, although with different patterns. This might account for their capability to prevent amyloidogenesis. Saturation transfer difference NMR experiments also confirmed EGCG and EGC binding to monomeric JD. ATX3-Q55 pre-incubation with any of the three compounds prevented its calcium-influx-mediated cytotoxicity towards neural cells. Finally, all the phenols significantly reduced toxicity in a transgenic Caenorhabditis elegans strain expressing an expanded ATX3. Overall, our results show that the three polyphenols act in a substantially similar manner. GA, however, might be more suitable for antiamyloid treatments due to its simpler structure and higher chemical stability.

Molecular Mechanism for the (-)-Epigallocatechin Gallate-Induced Toxic to Nontoxic Remodeling of Aβ Oligomers

(-)-Epigallocatechin gallate (EGCG) effectively reduces the cytotoxicity of the Alzheimer's disease β-amyloid peptide (Aβ) by remodeling seeding-competent Aβ oligomers into off-pathway seeding-incompetent Aβ assemblies. However, the mechanism of EGCG-induced remodeling is not fully understood. Here we combine ¹⁵N and ¹H dark-state exchange saturation transfer (DEST), relaxation, and chemical shift projection NMR analyses with fluorescence, dynamic light scattering, and electron microscopy to elucidate how EGCG remodels Aβ oligomers. We show that the remodeling adheres to a Hill-Scatchard model whereby the Aβ(1-40) self-association occurs cooperatively and generates Aβ(1-40) oligomers with multiple independent binding sites for EGCG with a K_d ∼10-fold lower than that for the Aβ(1-40) monomers. Upon binding to EGCG, the Aβ(1-40) oligomers become less solvent exposed, and the β-regions, which are involved in direct monomer-protofibril contacts in the absence of EGCG, undergo a direct-to-tethered contact shift. This switch toward less engaged monomer-protofibril contacts explains the seeding incompetency observed upon EGCG remodeling and suggests that EGCG interferes with secondary nucleation events known to generate toxic Aβ assemblies. Unexpectedly, the N-terminal residues experience an opposite EGCG-induced shift from tethered to direct contacts, explaining why EGCG remodeling occurs without release of Aβ(1-40) monomers. We also show that upon binding Aβ(1-40) oligomers the relative positions of the EGCG B and D rings change with respect to that of ring A. These distinct structural changes occurring in both Aβ(1-40) oligomers and EGCG during remodeling offer a foundation for understanding the molecular mechanism of EGCG as a neurotoxicity inhibitor. Furthermore, the results reported here illustrate the effectiveness of DEST-based NMR approaches in investigating the mechanism of low-molecular-weight amyloid inhibitors.