Models of β-amyloid induced Tau-pathology: the long and "folded" road to understand the mechanism

Innovative pathological network-based multitarget approaches for Alzheimer's disease treatment

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease and is a major health threat globally. Its prevalence is forecasted to exponentially increase during the next 30 years due to the global aging population. Currently, approved drugs are merely symptomatic, being ineffective in delaying or blocking the relentless disease advance. Intensive AD research describes this disease as a highly complex multifactorial disease. Disclosure of novel pathological pathways and their interconnections has had a major impact on medicinal chemistry drug development for AD over the last two decades. The complex network of pathological events involved in the onset of the disease has prompted the development of multitarget drugs. These chemical entities combine pharmacological activities toward two or more drug targets of interest. These multitarget-directed ligands are proposed to modify different nodes in the pathological network aiming to delay or even stop disease progression. Here, we review the multitarget drug development strategy for AD during the last decade.

A systematic review of the efficacy and safety of anti-amyloid beta monoclonal antibodies in treatment of Alzheimer's disease

INTRODUCTION

Alzheimer's disease can cause dementia through brain matter degradation. This study investigates the monoclonal antibody usage for AD treatment, following PRISMA 2020 guidelines, and aims to discern the monoclonal antibody that offers the optimal balance of efficacy and safety for individuals with AD.

METHODS

A systematic search was conducted across databases such as PubMed, Cochrane Library, and clinical trial registries for randomized controlled trials. The quality of studies was assessed using the Cochrane risk of bias 2 tool. Cognitive function and daily activities were evaluated using MMSE, ADAS-Cog, and CDR-SB test data.

RESULTS

According to CDR-SB measurements, lecanemab showed effectiveness in reducing brain amyloid and cognitive decline, with a change from baseline of 1.21. Aducanumab resulted in a decrease of -0.39 (-22%). Bapineuzumab showed no significant benefit, with scores of 2.4 (2.8). Gantenerumab, scoring 1.69 (1.37, 2.01), reduces amyloid, particularly in early Alzheimer's stages. Crenezumab was ineffective, with a score of 3.61.

CONCLUSION

The findings provide various perspectives. Lecanemab showed the most promise in brain amyloid reduction and decelerating cognitive decline compared to the other therapies. Further research is needed, highlighting the necessity of AD therapeutic research to alter AD's trajectory and provide reliable treatment.

PROTOCOL REGISTRATION

www.crd.york.ac.uk/prospero identifier is CRD42024504358.

β-amyloid's neurotoxic mechanisms as defined by in vitro microelectrode arrays: a review

Alzheimer's disease is characterised by the aggregation of β-amyloid, a pathological feature believed to drive the neuronal loss and cognitive decline commonly seen in the disease. Given the growing prevalence of this progressive neurodegenerative disease, understanding the exact mechanisms underlying this process has become a top priority. Microelectrode arrays are commonly used for chronic, non-invasive recording of both spontaneous and evoked neuronal activity from diverse in vitro disease models and to evaluate therapeutic or toxic compounds. To date, microelectrode arrays have been used to investigate β-amyloids' toxic effects, β-amyloids role in specific pathological features and to assess pharmacological approaches to treat Alzheimer's disease. The versatility of microelectrode arrays means these studies use a variety of methods and investigate different disease models and brain regions. This review provides an overview of these studies, highlighting their disparities and presenting the status of the current literature. Despite methodological differences, the current literature indicates that β-amyloid has an inhibitory effect on synaptic plasticity and induces network connectivity disruptions. β-amyloid's effect on spontaneous neuronal activity appears more complex. Overall, the literature corroborates the theory that β-amyloid induces neurotoxicity, having a progressive deleterious effect on neuronal signalling and plasticity. These studies also confirm that microelectrode arrays are valuable tools for investigating β-amyloid pathology from a functional perspective, helping to bridge the gap between cellular and network pathology and disease symptoms. The use of microelectrode arrays provides a functional insight into Alzheimer's disease pathology which will aid in the development of novel therapeutic interventions.

Exploring pathological link between antimicrobial and amyloid peptides

Amyloid peptides (AMYs) and antimicrobial peptides (AMPs) are considered as the two distinct families of peptides, characterized by their unique sequences, structures, biological functions, and specific pathological targets. However, accumulating evidence has revealed intriguing pathological connections between these peptide families in the context of microbial infection and neurodegenerative diseases. Some AMYs and AMPs share certain structural and functional characteristics, including the ability to self-assemble, the presence of β-sheet-rich structures, and membrane-disrupting mechanisms. These shared features enable AMYs to possess antimicrobial activity and AMPs to acquire amyloidogenic properties. Despite limited studies on AMYs-AMPs systems, the cross-seeding phenomenon between AMYs and AMPs has emerged as a crucial factor in the bidirectional communication between the pathogenesis of neurodegenerative diseases and host defense against microbial infections. In this review, we examine recent developments in the potential interplay between AMYs and AMPs, as well as their pathological implications for both infectious and neurodegenerative diseases. By discussing the current progress and challenges in this emerging field, this account aims to inspire further research and investments to enhance our understanding of the intricate molecular crosstalk between AMYs and AMPs. This knowledge holds great promise for the development of innovative therapies to combat both microbial infections and neurodegenerative disorders.

Neuronal APOE4-induced Early Hippocampal Network Hyperexcitability in Alzheimer's Disease Pathogenesis

The full impact of apolipoprotein E4 (APOE4), the strongest genetic risk factor for Alzheimer's disease (AD), on neuronal and network function remains unclear. We found hippocampal region-specific network hyperexcitability in young APOE4 knock-in (E4-KI) mice which predicted cognitive deficits at old age. Network hyperexcitability in young E4-KI mice was mediated by hippocampal region-specific subpopulations of smaller and hyperexcitable neurons that were eliminated by selective removal of neuronal APOE4. Aged E4-KI mice exhibited hyperexcitable granule cells, a progressive inhibitory deficit, and E/I imbalance in the dentate gyrus, exacerbating hippocampal hyperexcitability. Single-nucleus RNA-sequencing revealed neuronal cell type-specific and age-dependent transcriptomic changes, including Nell2 overexpression in E4-KI mice. Reducing Nell2 expression in specific neuronal types of E4-KI mice with CRISPRi rescued their abnormal excitability phenotypes, implicating Nell2 overexpression as a cause of APOE4-induced hyperexcitability. These findings highlight the early transcriptomic and electrophysiological alterations underlying APOE4-induced hippocampal network dysfunction and its contribution to AD pathogenesis with aging.

FGFR3 drives Aβ-induced tau uptake

The amyloid cascade hypothesis suggests that amyloid beta (Aβ) contributes to initiating subsequent tau pathology in Alzheimer's disease (AD). However, the underlying mechanisms through which Aβ contributes to tau uptake and propagation remain poorly understood. Here, we show that preexisting amyloid pathology accelerates the uptake of extracellular tau into neurons. Using quantitative proteomic analysis of endocytic vesicles, we reveal that Aβ induces the internalization of fibroblast growth factor receptor 3 (FGFR3). Extracellular tau binds to the extracellular domain of FGFR3 and is internalized by the FGFR3 ligand, fibroblast growth factor 2 (FGF2). Aβ accelerates FGF2 secretion from neurons, thereby inducing the internalization of tau-attached FGFR3. Knockdown of FGFR3 in the hippocampus reduces tau aggregation by decreasing tau uptake and improving memory function in AD model mice. These data suggest FGFR3 in neurons as a novel tau receptor and a key mediator of Aβ-induced tau uptake in AD.

Alkaloids as drug leads in Alzheimer's treatment: Mechanistic and therapeutic insights

Alzheimer's disease (AD) has few effective treatment options and continues to be a major global health concern. AD is a neurodegenerative disease that typically affects elderly people. Alkaloids have potential sources for novel drug discovery due to their diverse chemical structures and pharmacological activities. Alkaloids, natural products with heterocyclic nitrogen-containing structures, are considered potential treatments for AD. This review explores the neuroprotective properties of alkaloids in AD, focusing on their ability to regulate pathways such as amyloid-beta aggregation, oxidative stress, synaptic dysfunction, tau hyperphosphorylation, and neuroinflammation. The FDA has approved alkaloids such as acetylcholinesterase inhibitors like galantamine and rivastigmine. This article explores AD's origins, current market medications, and clinical applications of alkaloids in AD therapy. This review explores the development of alkaloid-based drugs for AD, focusing on pharmacokinetics, blood-brain barrier penetration, and potential adverse effects. Future research should focus on the clinical evaluation of promising alkaloids, developing recently discovered alkaloids, and the ongoing search for novel alkaloids for medical treatment. A pharmaceutical option containing an alkaloid may potentially slow down the progression of AD while enhancing its symptoms. This review highlights the potential of alkaloids as valuable drug leads in treating AD, providing a comprehensive understanding of their mechanisms of action and therapeutic implications.

Native PLGA nanoparticles attenuate Aβ-seed induced tau aggregation under in vitro conditions: potential implication in Alzheimer's disease pathology

Evidence suggests that beta-amyloid (Aβ)-induced phosphorylation/aggregation of tau protein plays a critical role in the degeneration of neurons and development of Alzheimer's disease (AD), the most common cause of dementia affecting the elderly population. Many studies have pursued a variety of small molecules, including nanoparticles conjugated with drugs to interfere with Aβ and/or tau aggregation/toxicity as an effective strategy for AD treatment. We reported earlier that FDA approved PLGA nanoparticles without any drug can attenuate Aβ aggregation/toxicity in cellular/animal models of AD. In this study, we evaluated the effects of native PLGA on Aβ seed-induced aggregation of tau protein using a variety of biophysical, structural and spectroscopic approaches. Our results show that Aβ1-42 seeds enhanced aggregation of tau protein in the presence and absence of heparin and the effect was attenuated by native PLGA nanoparticles. Interestingly, PLGA inhibited aggregation of both 4R and 3R tau isoforms involved in the formation of neurofibrillary tangles in AD brains. Furthermore, Aβ seed-induced tau aggregation in the presence of arachidonic acid was suppressed by native PLGA. Collectively, our results suggest that native PLGA nanoparticles can inhibit the Aβ seed-induced aggregation of different tau protein isoforms highlighting their therapeutic implication in the treatment of AD.

Signalling Pathways Involved in Microglial Activation in Alzheimer's Disease and Potential Neuroprotective Role of Phytoconstituents

Alzheimer's disease (AD) is a commonly reported neurodegenerative disorder associated with dementia and cognitive impairment. The pathophysiology of AD comprises Aβ, hyperphosphorylated tau protein formation, abrupt cholinergic cascade, oxidative stress, neuronal apoptosis, and neuroinflammation. Recent findings have established the profound role of immunological dysfunction and microglial activation in the pathogenesis of AD. Microglial activation is a multifactorial cascade encompassing various signalling molecules and pathways such as Nrf2/NLRP3/NF-kB/p38 MAPKs/ GSK-3β. Additionally, deposited Aβ or tau protein triggers microglial activation and accelerates its pathogenesis. Currently, the FDA-approved therapeutic regimens are based on the modulation of the cholinergic system, and recently, one more drug, aducanumab, has been approved by the FDA. On the one hand, these drugs only offer symptomatic relief and not a cure for AD. Additionally, no targetedbased microglial medicines are available for treating and managing AD. On the other hand, various natural products have been explored for the possible anti-Alzheimer effect via targeting microglial activation or different targets of microglial activation. Therefore, the present review focuses on exploring the mechanism and associated signalling related to microglial activation and a detailed description of various natural products that have previously been reported with anti-Alzheimer's effect via mitigation of microglial activation. Additionally, we have discussed the various patents and clinical trials related to managing and treating AD.

A systematic review for the development of Alzheimer's disease in in vitro models: a focus on different inducing agents

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease and is associated with dementia. Presently, various chemical and environmental agents are used to induce in-vitro models of Alzheimer disease to investigate the efficacy of different therapeutic drugs. We screened literature from databases such as PubMed, ScienceDirect, and Google scholar, emphasizing the diverse targeting mechanisms of neuro degeneration explored in in-vitro models. The results revealed studies in which different types of chemicals and environmental agents were used for in-vitro development of Alzheimer-targeting mechanisms of neurodegeneration. Studies using chemically induced in-vitro AD models included in this systematic review will contribute to a deeper understanding of AD. However, none of these models can reproduce all the characteristics of disease progression seen in the majority of Alzheimer's disease subtypes. Additional modifications would be required to replicate the complex conditions of human AD in an exact manner. In-vitro models of Alzheimer's disease developed using chemicals and environmental agents are instrumental in providing insights into the disease's pathophysiology; therefore, chemical-induced in-vitro AD models will continue to play vital role in future AD research. This systematic screening revealed the pivotal role of chemical-induced in-vitro AD models in advancing our understanding of AD pathophysiology and is therefore important to understand the potential of these chemicals in AD pathogenesis.

Potential use of iPSCs for disease modeling, drug screening, and cell-based therapy for Alzheimer's disease

Alzheimer's disease (AD) is a chronic illness marked by increasing cognitive decline and nervous system deterioration. At this time, there is no known medication that will stop the course of Alzheimer's disease; instead, most symptoms are treated. Clinical trial failure rates for new drugs remain high, highlighting the urgent need for improved AD modeling for improving understanding of the underlying pathophysiology of disease and improving drug development. The development of induced pluripotent stem cells (iPSCs) has made it possible to model neurological diseases like AD, giving access to an infinite number of patient-derived cells capable of differentiating neuronal fates. This advance will accelerate Alzheimer's disease research and provide an opportunity to create more accurate patient-specific models of Alzheimer's disease to support pathophysiological research, drug development, and the potential application of stem cell-based therapeutics. This review article provides a complete summary of research done to date on the potential use of iPSCs from AD patients for disease modeling, drug discovery, and cell-based therapeutics. Current technological developments in AD research including 3D modeling, genome editing, gene therapy for AD, and research on familial (FAD) and sporadic (SAD) forms of the disease are discussed. Finally, we outline the issues that need to be elucidated and future directions for iPSC modeling in AD.

Polyherbal and Multimodal Treatments: Kaempferol- and Quercetin-Rich Herbs Alleviate Symptoms of Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder impairing cognition and memory in the elderly. This disorder has a complex etiology, including senile plaque and neurofibrillary tangle formation, neuroinflammation, oxidative stress, and damaged neuroplasticity. Current treatment options are limited, so alternative treatments such as herbal medicine could suppress symptoms while slowing cognitive decline. We followed PRISMA guidelines to identify potential herbal treatments, their associated medicinal phytochemicals, and the potential mechanisms of these treatments. Common herbs, including Ginkgo biloba, Camellia sinensis, Glycyrrhiza uralensis, Cyperus rotundus, and Buplerum falcatum, produced promising pre-clinical results. These herbs are rich in kaempferol and quercetin, flavonoids with a polyphenolic structure that facilitate multiple mechanisms of action. These mechanisms include the inhibition of Aβ plaque formation, a reduction in tau hyperphosphorylation, the suppression of oxidative stress, and the modulation of BDNF and PI3K/AKT pathways. Using pre-clinical findings from quercetin research and the comparatively limited data on kaempferol, we proposed that kaempferol ameliorates the neuroinflammatory state, maintains proper cellular function, and restores pro-neuroplastic signaling. In this review, we discuss the anti-AD mechanisms of quercetin and kaempferol and their limitations, and we suggest a potential alternative treatment for AD. Our findings lead us to conclude that a polyherbal kaempferol- and quercetin-rich cocktail could treat AD-related brain damage.

CSF biomarker analysis of ABCA7 mutation carriers suggests altered APP processing and reduced inflammatory response

BACKGROUND

The Alzheimer's disease (AD) risk gene ABCA7 has suggested functions in lipid metabolism and the immune system. Rare premature termination codon (PTC) mutations and an expansion of a variable number of tandem repeats (VNTR) polymorphism in the gene, both likely cause a lower ABCA7 expression and hereby increased risk for AD. However, the exact mechanism of action remains unclear. By studying CSF biomarkers reflecting different types of AD-related pathological processes, we aim to get a better insight in those processes and establish a biomarker profile of mutation carriers.

METHODS

The study population consisted of 229 AD patients for whom CSF was available and ABCA7 sequencing and VNTR genotyping had been performed. This included 28 PTC mutation and 16 pathogenic expansion carriers. CSF levels of Aβ1-42, Aβ1-40, P-tau181, T-tau, sAPPα, sAPPβ, YKL-40, and hFABP were determined using ELISA and Meso Scale Discovery assays. We compared differences in levels of these biomarkers and the Aβ ratio between AD patients with or without an ABCA7 PTC mutation or expansion using linear regression on INT-transformed data with APOE-status, age and sex as covariates.

RESULTS

Carriers of ABCA7 expansion mutations had significantly lower Aβ1-42 levels (P = 0.022) compared with non-carrier patients. The effect of the presence of ABCA7 mutations on CSF levels was especially pronounced in APOE ε4-negative carriers. In addition, VNTR expansion carriers had reduced Aβ1-40 (P = 0.023), sAPPα (P = 0.047), sAPPβ (P = 0.016), and YKL-40 (P = 0.0036) levels.

CONCLUSIONS

Our results are suggestive for an effect on APP processing by repeat expansions given the changes in the amyloid-related CSF biomarkers that were found in carriers. The decrease in YKL-40 levels in expansion carriers moreover suggests that these patients potentially have a reduced inflammatory response to AD damage. Moreover, our findings suggest the existence of a mechanism, independent of lowered expression, affecting neuropathology in expansion carriers.

Research progress of plant-derived natural alkaloids in central nervous system diseases

Central nervous system (CNS) disease is one of the most important causes of human death. Because of their complex pathogenesis, more and more attention has been paid to them. At present, drug treatment of the CNS is the main means; however, most drugs only relieve symptoms, and some have certain toxicity and side effects. Natural compounds derived from plants can provide safer and more effective alternatives. Alkaloids are common nitrogenous basic organic compounds found in nature, which exist widely in many kinds of plants and have unique application value in modern medicine. For example, Galantamine and Huperzine A from medicinal plants are widely used drugs on the market to treat Alzheimer's disease. Therefore, the main purpose of this review is to provide the available information on natural alkaloids with the activity of treating central nervous system diseases in order to explore the trends and perspectives for the further study of central nervous system drugs. In this paper, 120 alkaloids with the potential effect of treating central nervous system diseases are summarized from the aspects of sources, structure types, mechanism of action and structure-activity relationship.

Neuroprotective effect of nose-to-brain delivery of Asiatic acid in solid lipid nanoparticles and its mechanisms against memory dysfunction induced by Amyloid Beta1-42 in mice

BACKGROUND

Amyloid-β1-42 (Aβ1-42) plays an essential role in the development of the early stage of Alzheimer's disease (AD). Asiatic acid (AA), an active compound in Centella asiatica L, exhibit neuroprotective properties in previous studies. Due to its low bioavailability, the nose-to-brain delivery technique was used to enhance AA penetration in the brain. In this study, AA was also loaded in solid lipid nanoparticles (SLNs) as a strategy to increase its absorption in the nasal cavity.

METHODS

Memory impairment was induced via direct intracerebroventricular injection of Aβ1-42 oligomer into mouse brain. The neuroprotective effect and potential underlying mechanisms were investigated using several memory behavioral examinations and molecular techniques.

RESULTS

The intranasal administration of AA in SLNs attenuated learning and memory impairment induced by Aβ1-42 in Morris water maze and novel object recognition tests. AA significantly inhibited tau hyperphosphorylation of pTau-S396 and pTau-T231 and prevented astrocyte reactivity and microglial activation in the hippocampus of Aβ1-42-treated mice. It is also decreased the high levels of IL-1β, TNF-α, and malondialdehyde (MDA) in mouse brain.

CONCLUSIONS

These results suggested that nose-to-brain delivery of AA in SLNs could be a promising strategy to treat the early stage of AD.

Cholinergic-like neurons and cerebral spheroids bearing the PSEN1 p.Ile416Thr variant mirror Alzheimer's disease neuropathology

Familial Alzheimer's disease (FAD) is a complex neurodegenerative disorder for which there are no therapeutics to date. Several mutations in presenilin 1 (PSEN 1), which is the catalytic component of γ-secretase complex, are causal of FAD. Recently, the p.Ile416Thr (I416T) PSEN 1 mutation has been reported in large kindred in Colombia. However, cell and molecular information from I416T mutation is scarce. Here, we demonstrate that menstrual stromal cells (MenSCs)-derived planar (2D) PSEN 1 I416T cholinergic-like cells (ChLNS) and (3D) cerebral spheroids (CSs) reproduce the typical neuropathological markers of FAD in 4 post-transdifferentiating or 11 days of transdifferentiating, respectively. The models produce intracellular aggregation of APPβ fragments (at day 4 and 11) and phosphorylated protein TAU at residue Ser202/Thr205 (at day 11) suggesting that iAPPβ fragments precede p-TAU. Mutant ChLNs and CSs displayed DJ-1 Cys106-SO3 (sulfonic acid), failure of mitochondria membrane potential (ΔΨm), and activation of transcription factor c-JUN and p53, expression of pro-apoptotic protein PUMA, and activation of executer protein caspase 3 (CASP3), all markers of cell death by apoptosis. Moreover, we found that both mutant ChLNs and CSs produced high amounts of extracellular eAβ42. The I416T ChLNs and CSs were irresponsive to acetylcholine induced Ca2+ influx compared to WT. The I416T PSEN 1 mutation might work as dominant-negative PSEN1 mutation. These findings might help to understanding the recurring failures of clinical trials of anti-eAβ42, and support the view that FAD is triggered by the accumulation of other intracellular AβPP metabolites, rather than eAβ42.

Voltage-Gated Na+ Channels in Alzheimer's Disease: Physiological Roles and Therapeutic Potential

Alzheimer's disease (AD) is the most common cause of dementia and is classically characterized by two major histopathological abnormalities: extracellular plaques composed of amyloid beta (Aβ) and intracellular hyperphosphorylated tau. Due to the progressive nature of the disease, it is of the utmost importance to develop disease-modifying therapeutics that tackle AD pathology in its early stages. Attenuation of hippocampal hyperactivity, one of the earliest neuronal abnormalities observed in AD brains, has emerged as a promising strategy to ameliorate cognitive deficits and abate the spread of neurotoxic species. This aberrant hyperactivity has been attributed in part to the dysfunction of voltage-gated Na+ (Nav) channels, which are central mediators of neuronal excitability. Therefore, targeting Nav channels is a promising strategy for developing disease-modifying therapeutics that can correct aberrant neuronal phenotypes in early-stage AD. This review will explore the role of Nav channels in neuronal function, their connections to AD pathology, and their potential as therapeutic targets.

Unbiased proteomics and multivariable regularized regression techniques identify SMOC1, NOG, APCS, and NTN1 in an Alzheimer's disease brain proteomic signature

Advancements in omics methodologies have generated a wealth of high-dimensional Alzheimer's disease (AD) datasets, creating significant opportunities and challenges for data interpretation. In this study, we utilized multivariable regularized regression techniques to identify a reduced set of proteins that could discriminate between AD and cognitively normal (CN) brain samples. Utilizing eNetXplorer, an R package that tests the accuracy and significance of a family of elastic net generalized linear models, we identified 4 proteins (SMOC1, NOG, APCS, NTN1) that accurately discriminated between AD (n = 31) and CN (n = 22) middle frontal gyrus (MFG) tissue samples from Religious Orders Study participants with 83 percent accuracy. We then validated this signature in MFG samples from Baltimore Longitudinal Study of Aging participants using leave-one-out logistic regression cross-validation, finding that the signature again accurately discriminated AD (n = 31) and CN (n = 19) participants with a receiver operating characteristic curve area under the curve of 0.863. These proteins were strongly correlated with the burden of neurofibrillary tangle and amyloid pathology in both study cohorts. We additionally tested whether these proteins differed between AD and CN inferior temporal gyrus (ITG) samples and blood serum samples at the time of AD diagnosis in ROS and BLSA, finding that the proteins differed between AD and CN ITG samples but not in blood serum samples. The identified proteins may provide mechanistic insights into the pathophysiology of AD, and the methods utilized in this study may serve as the basis for further work with additional high-dimensional datasets in AD.

A simple genetic stratification method for lower cost, more expedient clinical trials in early Alzheimer's disease: A preliminary study of tau PET and cognitive outcomes

INTRODUCTION

Identifying individuals who are most likely to accumulate tau and exhibit cognitive decline is critical for Alzheimer's disease (AD) clinical trials.

METHODS

Participants (N = 235) who were cognitively normal or with mild cognitive impairment from the Alzheimer's Disease Neuroimaging Initiative were stratified by a cutoff on the polygenic hazard score (PHS) at 65th percentile (above as high-risk group and below as low-risk group). We evaluated the associations between the PHS risk groups and tau positron emission tomography and cognitive decline, respectively. Power analyses estimated the sample size needed for clinical trials to detect differences in tau accumulation or cognitive change.

RESULTS

The high-risk group showed faster tau accumulation and cognitive decline. Clinical trials using the high-risk group would require a fraction of the sample size as trials without this inclusion criterion.

DISCUSSION

Incorporating a PHS inclusion criterion represents a low-cost and accessible way to identify potential participants for AD clinical trials.

Alzheimer's Disease and Its Possible Evolutionary Origin: Hypothesis

The enormous, 2-3-million-year evolutionary expansion of hominin neocortices to the current enormity enabled humans to take over the planet. However, there appears to have been a glitch, and it occurred without a compensatory expansion of the entorhinal cortical (EC) gateway to the hippocampal memory-encoding system needed to manage the processing of the increasing volume of neocortical data converging on it. The resulting age-dependent connectopathic glitch was unnoticed by the early short-lived populations. It has now surfaced as Alzheimer's disease (AD) in today's long-lived populations. With advancing age, processing of the converging neocortical data by the neurons of the relatively small lateral entorhinal cortex (LEC) inflicts persistent strain and high energy costs on these cells. This may result in their hyper-release of harmless Aβ1-42 monomers into the interstitial fluid, where they seed the formation of toxic amyloid-β oligomers (AβOs) that initiate AD. At the core of connectopathic AD are the postsynaptic cellular prion protein (PrPC). Electrostatic binding of the negatively charged AβOs to the positively charged N-terminus of PrPC induces hyperphosphorylation of tau that destroys synapses. The spread of these accumulating AβOs from ground zero is supported by Aβ's own production mediated by target cells' Ca2+-sensing receptors (CaSRs). These data suggest that an early administration of a strongly positively charged, AβOs-interacting peptide or protein, plus an inhibitor of CaSR, might be an effective AD-arresting therapeutic combination.

Molecular Insights into Cell Type-specific Roles in Alzheimer's Disease: Human Induced Pluripotent Stem Cell-based Disease Modelling

Alzheimer's disease (AD) is the most common cause of dementia resulting in widespread degeneration of the central nervous system with severe cognitive impairment. Despite the devastating toll of AD, the incomplete understanding of the complex molecular mechanisms hinders the expeditious development of effective cures. Emerging evidence from animal studies has shown that different brain cell types play distinct roles in the pathogenesis of AD. Glutamatergic neurons are preferentially affected in AD and pronounced gliosis contributes to the progression of AD in both a cell-autonomous and a non-cell-autonomous manner. Much has been discovered through genetically modified animal models, yet frequently failed translational attempts to clinical applications call for better disease models. Emerging evidence supports the significance of human-induced pluripotent stem cell (iPSC) derived brain cells in modeling disease development and progression, opening new avenues for the discovery of molecular mechanisms. This review summarizes the function of different cell types in the pathogenesis of AD, such as neurons, microglia, and astrocytes, and recognizes the potential of utilizing the rapidly growing iPSC technology in modeling AD.

Structural and molecular insights into tacrine-benzofuran hybrid induced inhibition of amyloid-β peptide aggregation and BACE1 activity

Amyloid-β (Aβ) aggregation and β-amyloid precursor protein cleaving enzyme 1 (BACE1) are the potential therapeutic drug targets for Alzheimer's disease (AD). A recent study highlighted that tacrine-benzofuran hybrid C1 displayed anti-aggregation activity against Aβ42 peptide and inhibit BACE1 activity. However, the inhibition mechanism of C1 against Aβ42 aggregation and BACE1 activity remains unclear. Thus, molecular dynamics (MD) simulations of Aβ42 monomer and BACE1 with and without C1 were performed to inspect the inhibitory mechanism of C1 against Aβ42 aggregation and BACE1 activity. In addition, a ligand-based virtual screening followed by MD simulations was employed to explore potent new small-molecule dual inhibitors of Aβ42 aggregation and BACE1 activity. MD simulations highlighted that C1 promotes the non aggregating helical conformation in Aβ42 and destabilizes D23-K28 salt bridge that plays a vital role in the self-aggregation of Aβ42. C1 displays a favourable binding free energy (-50.7 ± 7.3 kcal/mol) with Aβ42 monomer and preferentially binds to the central hydrophobic core (CHC) residues. MD simulations highlighted that C1 strongly interacted with the BACE1 active site (Asp32 and Asp228) and active pockets. The scrutiny of interatomic distances among key residues of BACE1 highlighted the close flap (non-active) position in BACE1 on the incorporation of C1. The MD simulations explain the observed high inhibitory activity of C1 against Aβ aggregation and BACE1 in the in vitro studies. The ligand-based virtual screening followed by MD simulations identified CHEMBL2019027 (C2) as a promising dual inhibitor of Aβ42 aggregation and BACE1 activity.Communicated by Ramaswamy H. Sarma.

Complement protein levels in serum astrocyte-derived exosomes are associated with cognitive impairment in obstructive sleep apnea

STUDY OBJECTIVES

An association between neuroinflammation and cognitive decline has been established. The complement system regulates neuroinflammation. Dysregulation, impairment, or inadvertent activation of complement components contribute to preclinical Alzheimer's disease. The astrocyte-derived exosome (ADE) complement proteins, including C3b and C5b-9, may be predictive biomarkers of mild cognitive impairment conversion to Alzheimer's disease dementia. We hypothesized that complement proteins might be involved in cognitive impairment during obstructive sleep apnea (OSA). The aim of our study was to explore the correlation between the complement system and mild cognitive impairment (MCI) in patients with OSA.

METHODS

All participants with subjective snoring complaints from the Sleep Medicine Center underwent polysomnography. OSA was defined as apnea-hypopnea index ≥ 5 events/h. MCI was defined as the Montreal Cognitive Assessment < 26 and met the criteria: (1) a subjective cognitive impairment; (2) an objective impairment in 1 or more cognitive domains; (3) complex instrumental daily abilities can be slightly impaired but independent daily living abilities are maintained; and (4) no dementia. The ADEs were isolated immunochemically for enzyme-linked immunosorbent assay quantification of complement proteins, including C3b, C5b-9, and CD55. The participants who received continuous positive airway pressure were followed up and their complement protein levels were reassessed after 1 year of treatment.

RESULTS

A total of 212 participants (66.98% males; mean age of 56.71 ± 10.10 years) were divided into the OSA+MCI group (n = 90), OSA-MCI group (n = 79), and controls (normal cognitive state without OSA) (n = 43). The ADE levels of C3b and C5b-9 in the OSA+MCI group were higher than those in the OSA-MCI and control groups. The C3b and C5b-9 were independently associated with cognitive impairment in patients with OSA. The relationship between apnea-hypopnea index and Montreal Cognitive Assessment scores was mediated by C3b and C5b-9. We found no linear correlation between the complement proteins and the severity of OSA. The complement proteins were negatively correlated with global cognitive performance and cognitive subdomains. The complement protein levels significantly decreased after continuous positive airway pressure treatment.

CONCLUSIONS

Complement proteins were implicated in cognitive impairment in patients with OSA and may be promising biomarkers for predicting cognitive impairment in patients with OSA.

CLINICAL TRIAL REGISTRATION

Registry: Chinese Clinical Trial Registry; Name: Study on early diagnostic markers in patients with dementia and mild cognitive impairment; URL: https://www.chictr.org.cn/; Identifier: ChiCTR1900021544.

CITATION

Li M, Sun C, Xue S, et al. Complement proteins levels in serum astrocyte-derived exosomes are associated with cognitive impairment in obstructive sleep apnea. J Clin Sleep Med. 2023;19(4):727-739.

Molecular Tweezers: Supramolecular Hosts with Broad-Spectrum Biological Applications

Lysine-selective molecular tweezers (MTs) are supramolecular host molecules displaying a remarkably broad spectrum of biologic activities. MTs act as inhibitors of the self-assembly and toxicity of amyloidogenic proteins using a unique mechanism. They destroy viral membranes and inhibit infection by enveloped viruses, such as HIV-1 and SARS-CoV-2, by mechanisms unrelated to their action on protein self-assembly. They also disrupt biofilm of Gram-positive bacteria. The efficacy and safety of MTs have been demonstrated in vitro, in cell culture, and in vivo, suggesting that these versatile compounds are attractive therapeutic candidates for various diseases, infections, and injuries. A lead compound called CLR01 has been shown to inhibit the aggregation of various amyloidogenic proteins, facilitate their clearance in vivo, prevent infection by multiple viruses, display potent anti-biofilm activity, and have a high safety margin in animal models. The inhibitory effect of CLR01 against amyloidogenic proteins is highly specific to abnormal self-assembly of amyloidogenic proteins with no disruption of normal mammalian biologic processes at the doses needed for inhibition. Therapeutic effects of CLR01 have been demonstrated in animal models of proteinopathies, lysosomal-storage diseases, and spinal-cord injury. Here we review the activity and mechanisms of action of these intriguing compounds and discuss future research directions. SIGNIFICANCE STATEMENT: Molecular tweezers are supramolecular host molecules with broad biological applications, including inhibition of abnormal protein aggregation, facilitation of lysosomal clearance of toxic aggregates, disruption of viral membranes, and interference of biofilm formation by Gram-positive bacteria. This review discusses the molecular and cellular mechanisms of action of the molecular tweezers, including the discovery of distinct mechanisms acting in vitro and in vivo, and the application of these compounds in multiple preclinical disease models.

The Nerve Growth Factor Receptor (NGFR/p75NTR): A Major Player in Alzheimer's Disease

Alzheimer's disease (AD) represents the most prevalent type of dementia in elderly people, primarily characterized by brain accumulation of beta-amyloid (Aβ) peptides, derived from Amyloid Precursor Protein (APP), in the extracellular space (amyloid plaques) and intracellular deposits of the hyperphosphorylated form of the protein tau (p-tau; tangles or neurofibrillary aggregates). The Nerve growth factor receptor (NGFR/p75^NTR) represents a low-affinity receptor for all known mammalians neurotrophins (i.e., proNGF, NGF, BDNF, NT-3 e NT-4/5) and it is involved in pathways that determine both survival and death of neurons. Interestingly, also Aβ peptides can blind to NGFR/p75^NTR making it the "ideal" candidate in mediating Aβ-induced neuropathology. In addition to pathogenesis and neuropathology, several data indicated that NGFR/p75^NTR could play a key role in AD also from a genetic perspective. Other studies suggested that NGFR/p75^NTR could represent a good diagnostic tool, as well as a promising therapeutic target for AD. Here, we comprehensively summarize and review the current experimental evidence on this topic.

Identification of a Novel Wnt Antagonist Based Therapeutic and Diagnostic Target for Alzheimer's Disease Using a Stem Cell-Derived Model

Currently, all the existing treatments for Alzheimer's disease (AD) fail to stall progression due to longer duration of time between onset of the symptoms and diagnosis of the disease, raising the necessity of effective diagnostics and novel treatment. Specific molecular regulation of the onset and progression of disease is not yet elucidated. This warranted investigation of the role of Wnt signaling regulators which are thought to be involved in neurogenesis. The AD model was established using amyloid beta (Aβ) in human mesenchymal stem cells derived from amniotic membranes which were differentiated into neuronal cell types. In vivo studies were carried out with Aβ or a Wnt antagonist, AD201, belonging to the sFRP family. We further created an AD201-knockdown in vitro model to determine the role of Wnt antagonism. BACE1 upregulation, ChAT and α7nAChR downregulation with synapse and functionality loss with increases in ROS confirmed the neurodegeneration. Reduced β-catenin and increased AD201 expression indicated Wnt/canonical pathway inhibition. Similar results were exhibited in the in vivo study along with AD-associated behavioural and molecular changes. AD201-knockdown rescued neurons from Aβ-induced toxicity. We demonstrated for the first time a role of AD201 in Alzheimer's disease manifestation, which indicates a promising disease target and biomarker.

Lipoprotein Metabolism, Protein Aggregation, and Alzheimer's Disease: A Literature Review

Alzheimer's disease (AD) is the most common form of dementia. The physiopathology of AD is well described by the presence of two neuropathological features: amyloid plaques and tau neurofibrillary tangles. In the last decade, neuroinflammation and cellular stress have gained importance as key factors in the development and pathology of AD. Chronic cellular stress occurs in degenerating neurons. Stress Granules (SGs) are nonmembranous organelles formed as a response to stress, with a protective role; however, SGs have been noted to turn into pathological and neurotoxic features when stress is chronic, and they are related to an increased tau aggregation. On the other hand, correct lipid metabolism is essential to good function of the brain; apolipoproteins are highly associated with risk of AD, and impaired cholesterol efflux and lipid transport are associated with an increased risk of AD. In this review, we provide an insight into the relationship between cellular stress, SGs, protein aggregation, and lipid metabolism in AD.

Magnoflorine-Loaded Chitosan Collagen Nanocapsules Ameliorate Cognitive Deficit in Scopolamine-Induced Alzheimer's Disease-like Conditions in a Rat Model by Downregulating IL-1β, IL-6, TNF-α, and Oxidative Stress and Upregulating Brain-Derived Neurotrophic Factor and DCX Expressions

Dementia or the loss of cognitive functioning is one of the major health issues in elderly people. Alzheimer's disease (AD) is one of the common forms of dementia. Treatment chiefly involves the use of acetylcholinesterase (AChE) inhibitors in AD. However, oxidative stress has also been found to be involved in the proliferation of the disease. Magnoflorine is one of the active compounds of Coptidis Rhizoma and has high anti-oxidative properties. Active principle-loaded nanoparticles have shown increased efficiency for neurodegenerative diseases due to their ability to cross the blood-brain barrier more easily. An in vitro study involving magnoflorine-loaded chitosan collagen nanocapsules (MF-CCNc) has shown them to possess inhibitory effects against oxidative stress and to some extent on AChE as well. In the current study, both nootropic and anti-amnesic effects of magnoflorine and MF-CCNc on scopolamine-induced amnesia in rats were evaluated. The treatment was done intraperitoneally (i.p.) once daily for 17 consecutive days with MF-CCNc (0.25, 0.5, and 1 mg), magnoflorine (1 mg), and donepezil (1 mg). To induce amnesia, hence, cognitive deficit rats were induced with scopolamine (1 mg/kg) daily for the last 9 days. Novel object recognition (NOR) and elevated plus maze (EPM) behavioral analysis were done to assess memory functioning. Hippocampal tissues were extracted to study the effect on biochemicals (AChE, MDA, SOD, and CAT), pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), and immunohistochemistry (brain-derived neurotrophic factor (BDNF) and DCX). MF-CCNc showed memory-enhancing effects in nootropic as well as chronic scopolamine-treated rats in NOR and an increase in inflexion ratio in EPM. MF-CCNc reduced the levels of AChE and MDA while increasing SOD and CAT levels in the hippocampus. MF-CCNc further lowered the levels of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α. These nanocapsules further increased the expression of BDNF and DCX that are necessary for adult neurogenesis. From the research findings, it can be concluded that MF-CCNc has high anti-amnesic properties and could be a promising candidate for the treatment of AD.

Current Naturopathy to Combat Alzheimer's Disease

Neurodegeneration is the progressive loss of structure or function of neurons, which may ultimately involve cell death. The most common neurodegenerative disorder in the brain happens with Alzheimer's disease (AD), the most common cause of dementia. It ultimately leads to neuronal death, thereby impairing the normal functionality of the central or peripheral nervous system. The onset and prevalence of AD involve heterogeneous etiology, either in terms of genetic predisposition, neurometabolomic malfunctioning, or lifestyle. The worldwide relevancies are estimated to be over 45 million people. The rapid increase in AD has led to a concomitant increase in the research work directed towards discovering a lucrative cure for AD. The neuropathology of AD comprises the deficiency in the availability of neurotransmitters and important neurotrophic factors in the brain, extracellular betaamyloid plaque depositions, and intracellular neurofibrillary tangles of hyperphosphorylated tau protein. Current pharmaceutical interventions utilizing synthetic drugs have manifested resistance and toxicity problems. This has led to the quest for new pharmacotherapeutic candidates naturally prevalent in phytochemicals. This review aims to provide an elaborative description of promising Phyto component entities having activities against various potential AD targets. Therefore, naturopathy may combine with synthetic chemotherapeutics to longer the survival of the patients.

The effects of microglia on tauopathy progression can be quantified using Nexopathy in silico (Nexis) models

The prion-like transsynaptic propagation of misfolded tau along the brain's connectome has previously been modeled using connectome-based network diffusion models. In addition to the connectome, interactions between the general neurological "milieu" in the neurodegenerative brain and proteinopathic species can also contribute to pathology propagation. Such a molecular nexopathy framework posits that the distinct characteristics of neurodegenerative disorders stem from interactions between the network and surrounding molecular players. However, the effects of these modulators remain unquantified. Here, we present Nexopathy in silico ("Nexis"), a quantitative model of tau progression augmenting earlier models by including parameters of pathology propagation defined by the molecular modulators of connectome-based spread. Our Nexis:microglia model provides the first quantitative characterization of this effect on the whole brain by expanding previous models of neuropathology progression by incorporating microglial influence. We show that Trem2, but not microglial homeostasis genes, significantly improved the model's predictive power. Trem2 appears to reduce tau accumulation rate while increasing its interregional spread from the hippocampal seed area, causing higher tau burden in the striatum, pallidum, and contralateral hippocampus. Nexis provides an improved understanding and quantification of microglial contribution to tau propagation and can be flexibly modified to include other modulators of progressive neurodegeneration.

Synthetic, Cell-Derived, Brain-Derived, and Recombinant β-Amyloid: Modelling Alzheimer's Disease for Research and Drug Development

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, characterised by the accumulation of senile plaques and tau tangles, neurodegeneration, and neuroinflammation in the brain. The development of AD is a pathological cascade starting according to the amyloid hypothesis with the accumulation and aggregation of the β-amyloid peptide (Aβ), which induces hyperphosphorylation of tau and promotes the pro-inflammatory activation of microglia leading to synaptic loss and, ultimately, neuronal death. Modelling AD-related processes is important for both studying the molecular basis of the disease and the development of novel therapeutics. The replication of these processes is often achieved with the use of a purified Aβ peptide. However, Aβ preparations obtained from different sources can have strikingly different properties. This review aims to compare the structure and biological effects of Aβ oligomers and aggregates of a higher order: synthetic, recombinant, purified from cell culture, or extracted from brain tissue. The authors summarise the applicability of Aβ preparations for modelling Aβ aggregation, neurotoxicity, cytoskeleton damage, receptor toxicity in vitro and cerebral amyloidosis, synaptic plasticity disruption, and cognitive impairment in vivo and ex vivo. Further, the paper discusses the causes of the reported differences in the effect of Aβ obtained from the sources mentioned above. This review points to the importance of the source of Aβ for AD modelling and could help researchers to choose the optimal way to model the Aβ-induced abnormalities.

Misfolded protein oligomers induce an increase of intracellular Ca2+ causing an escalation of reactive oxidative species

Alzheimer's disease is characterized by the accumulation in the brain of the amyloid β (Aβ) peptide in the form of senile plaques. According to the amyloid hypothesis, the aggregation process of Aβ also generates smaller soluble misfolded oligomers that contribute to disease progression. One of the mechanisms of Aβ oligomer cytotoxicity is the aberrant interaction of these species with the phospholipid bilayer of cell membranes, with a consequent increase in cytosolic Ca²⁺ levels, flowing from the extracellular space, and production of reactive oxygen species (ROS). Here we investigated the relationship between the increase in Ca²⁺ and ROS levels immediately after the exposure to misfolded protein oligomers, asking whether they are simultaneous or instead one precedes the other. Using Aβ₄₂-derived diffusible ligands (ADDLs) and type A HypF-N model oligomers (OAs), we followed the kinetics of ROS production and Ca²⁺ influx in human neuroblastoma SH-SY5Y cells and rat primary cortical neurons in a variety of conditions. In all cases we found a faster increase of intracellular Ca²⁺ than ROS levels, and a lag phase in the latter process. A Ca²⁺-deprived cell medium prevented the increase of intracellular Ca²⁺ ions and abolished ROS production. By contrast, treatment with antioxidant agents prevented ROS formation, did not prevent the initial Ca²⁺ flux, but allowed the cells to react to the initial calcium dyshomeostasis, restoring later the normal levels of the ions. These results reveal a mechanism in which the entry of Ca²⁺ causes the production of ROS in cells challenged by aberrant protein oligomers.

Symptomatic and Disease-Modifying Therapy Pipeline for Alzheimer's Disease: Towards a Personalized Polypharmacology Patient-Centered Approach

Since 1906, when Dr. Alois Alzheimer first described in a patient "a peculiar severe disease process of the cerebral cortex", people suffering from this pathology have been waiting for a breakthrough therapy. Alzheimer's disease (AD) is an irreversible, progressive neurodegenerative brain disorder and the most common form of dementia in the elderly with a long presymptomatic phase. Worldwide, approximately 50 million people are living with dementia, with AD comprising 60-70% of cases. Pathologically, AD is characterized by the deposition of amyloid β-peptide (Aβ) in the neuropil (neuritic plaques) and blood vessels (amyloid angiopathy), and by the accumulation of hyperphosphorylated tau in neurons (neurofibrillary tangles) in the brain, with associated loss of synapses and neurons, together with glial activation, and neuroinflammation, resulting in cognitive deficits and eventually dementia. The current competitive landscape in AD consists of symptomatic treatments, of which there are currently six approved medications: three AChEIs (donepezil, rivastigmine, and galantamine), one NMDA-R antagonist (memantine), one combination therapy (memantine/donepezil), and GV-971 (sodium oligomannate, a mixture of oligosaccharides derived from algae) only approved in China. Improvements to the approved therapies, such as easier routes of administration and reduced dosing frequencies, along with the developments of new strategies and combined treatments are expected to occur within the next decade and will positively impact the way the disease is managed. Recently, Aducanumab, the first disease-modifying therapy (DMT) has been approved for AD, and several DMTs are in advanced stages of clinical development or regulatory review. Small molecules, mAbs, or multimodal strategies showing promise in animal studies have not confirmed that promise in the clinic (where small to moderate changes in clinical efficacy have been observed), and therefore, there is a significant unmet need for a better understanding of the AD pathogenesis and the exploration of alternative etiologies and therapeutic effective disease-modifying therapies strategies for AD. Therefore, a critical review of the disease-modifying therapy pipeline for Alzheimer's disease is needed.

Wolframin is a novel regulator of tau pathology and neurodegeneration

Selective neuronal vulnerability to protein aggregation is found in many neurodegenerative diseases including Alzheimer's disease (AD). Understanding the molecular origins of this selective vulnerability is, therefore, of fundamental importance. Tau protein aggregates have been found in Wolframin (WFS1)-expressing excitatory neurons in the entorhinal cortex, one of the earliest affected regions in AD. The role of WFS1 in Tauopathies and its levels in tau pathology-associated neurodegeneration, however, is largely unknown. Here we report that WFS1 deficiency is associated with increased tau pathology and neurodegeneration, whereas overexpression of WFS1 reduces those changes. We also find that WFS1 interacts with tau protein and controls the susceptibility to tau pathology. Furthermore, chronic ER stress and autophagy-lysosome pathway (ALP)-associated genes are enriched in WFS1-high excitatory neurons in human AD at early Braak stages. The protein levels of ER stress and autophagy-lysosome pathway (ALP)-associated proteins are changed in tau transgenic mice with WFS1 deficiency, while overexpression of WFS1 reverses those changes. This work demonstrates a possible role for WFS1 in the regulation of tau pathology and neurodegeneration via chronic ER stress and the downstream ALP. Our findings provide insights into mechanisms that underpin selective neuronal vulnerability, and for developing new therapeutics to protect vulnerable neurons in AD.

History in Perspective: The Prime Pathological Players and Role of Phytochemicals in Alzheimer’s Disease

Alzheimer's disease is a steadily progressive, irreversible neurological disorder that is most frequently categorized under the umbrella term "neurodegeneration". Several attempts are underway to clarify the pathogenic mechanisms, identify the aetiologies, and determine a pathway by which the therapeutic steps can be implemented. Oxidative stress is one of the pathogenic processes, which is commonly believed to be associated with neurodegenerative diseases. Accumulation of extracellular amyloid-β protein (Aβ), hyperphosphorylation of tau, initiation of neurometabolic reactions characterized by the loss of neuronal function and synaptic failure, and decreased or lost learning capability and memory function are the most central neuropathological characteristics of AD. According to the amyloid cascade hypothesis, the enhanced deposition of Aβ deposits and neurofibrillary tangles due to hyperphosphorylation of Tau activates the cascade reactions in the brain. These reactions affect the synaptic activity and activation of microglia, which results in neuroinflammation due to enhanced immune function. Plant-based phytochemicals have also been used long ago against several diseases. Phytoconstituents play a significant neuroprotective property by preventing the pathophysiology of the disease. In this review, we have discussed the formation and crosstalk between amyloid and tau pathologies as well as the effect of neuroinflammation on the progression of AD. We have specifically focused on the formation of NFT, β-amyloids, inflammation, and pathophysiology of AD and the role of phytochemicals in the prevention of AD.

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AD is an insidious, slowly progressive, and neurodegenerative disorder.

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Common symptoms are memory loss, difficulty in recalling, and understanding.

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β-amyloids and Neurofibrillary tangles are the main factors in AD pathogenesis.

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Activated microglia and oxidative stress have different effects on AD progression.

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Phytochemicals show a key role against AD by inhibiting several pathways.

Tau Toxicity in Neurodegeneration

Tau is a microtubule-associated protein widely distributed in the central nervous system (CNS). The main function of tau is to promote the assembly of microtubules and stabilize their structure. After a long period of research on neurodegenerative diseases, the function and dysfunction of the microtubule-associated protein tau in neurodegenerative diseases and tau neurotoxicity have attracted increasing attention. Tauopathies are a series of progressive neurodegenerative diseases caused by pathological changes in tau, such as abnormal phosphorylation. The pathological features of tauopathies are the deposition of abnormally phosphorylated tau proteins and the aggregation of tau proteins in neurons. This article first describes the normal physiological function and dysfunction of tau proteins and then discusses the enzymes and proteins involved in tau phosphorylation and dephosphorylation, the role of tau in cell dysfunction, and the relationships between tau and several neurodegenerative diseases. The study of tau neurotoxicity provides new directions for the treatment of tauopathies.

Mechanistic insight into the role of metformin in Alzheimer's disease

Alzheimer's disease (AD), a type of dementia, is characterized by progressive memory decline and cognition impairment. Despite the considerable body of evidence regarding AD pathophysiology, current therapies merely slow down the disease progression, and a comprehensive therapeutic approach is unavailable. Accordingly, finding an efficient multifunctional remedy is necessary to blunt the increasing rate of AD incidence in the upcoming years. AD shares pathophysiological similarities (e.g., impairment of cognitive functions, insulin sensitivity, and brain glucose metabolism) with noninsulin-dependent diabetes mellitus (NIDDM), which offers the utilization of metformin, a biguanide hypoglycemic agent, as an alternative therapeutic approach in AD therapy. Emerging evidence has revealed the impact of metformin in patients suffering from AD. It has been described that metformin employs multiple mechanisms to improve cognition and memory impairment in pre-clinical AD models, including reduction of hippocampal amyloid-beta (Aβ) plaque and neurofibrillary tangles (NFTs) load, suppression of inflammation, amelioration of mitochondrial dysfunction and oxidative stress, restriction of apoptotic neuronal death, and induction of neurogenesis. This review discusses the pre-clinical evidence, which may shed light on the role of metformin in AD and provide a more comprehensive mechanistic insight for future studies in this area of research.

A new strategy to reconcile amyloid cross-seeding and amyloid prevention in a binary system of α-synuclein fragmental peptide and hIAPP

Amyloid cross-seeding and amyloid inhibition are two different research subjects being studied separately for different pathological purposes, in which amyloid cross-seeding targets to study the co-aggregation of different amyloid proteins and potential molecular links between different neurodegenerative diseases, while amyloid inhibition aims to design different molecules for preventing amyloid aggregation. While both amyloid cross-seeding and amyloid inhibition are critical for better understanding the pathological causes of different neurodegenerative diseases including Parkinson disease (PD) and Type 2 diabetes (T2D), less efforts have been made to reconcile the two phenomena. Herein, we proposed a new preventive strategy to demonstrate (a) the cross-seeding of octapeptide TKEQVTNV from α-synuclein (associated with PD) with hIAPP (associated with T2D) and (b) the cross-seeding-promoted hIAPP fibrillization and cross-seeding-reduced hIAPP toxicity. Collective results confirmed that TKEQVTNV can indeed cross-seed with hIAPP monomers and oligomers, not protofibrils, to form β-structure-rich fibrils and to accelerate hIAPP fibrillization. Moreover, such cross-seeding-induced promotion effect by TKEQVTNV also rescued the pancreatic cells from hIAPP-induced cytotoxicity by increasing cell viability and reducing cell apoptosis simultaneously. This work provides a new angle to discover amyloid fragments and use them as amyloid modulators (inhibitors or promotors) to interfere with amyloid aggregation of other amyloid proteins, as well as sequence/structure basis to explore the amyloid cross-seeding between different amyloid proteins that may help explain a potential molecular talk between different neurodegenerative diseases.

Repurposing of intestinal defensins as multi-target, dual-function amyloid inhibitors via cross-seeding

Amyloid formation and microbial infection are the two common pathological causes of neurogenerative diseases, including Alzheimer's disease (AD), type II diabetes (T2D), and medullary thyroid carcinoma (MTC). While significant efforts have been made to develop different prevention strategies and preclinical hits for these diseases, conventional design strategies of amyloid inhibitors are mostly limited to either a single prevention mechanism (amyloid cascade vs. microbial infection) or a single amyloid protein (Aβ, hIAPP, or hCT), which has prevented the launch of any successful drug on the market. Here, we propose and demonstrate a new “anti-amyloid and anti-bacteria” strategy to repurpose two intestinal defensins, human α-defensin 6 (HD-6) and human β-defensin 1 (HBD-1), as multiple-target, dual-function, amyloid inhibitors. Both HD-6 and HBD-1 can cross-seed with three amyloid peptides, Aβ (associated with AD), hIAPP (associated with T2D), and hCT (associated with MTC), to prevent their aggregation towards amyloid fibrils from monomers and oligomers, rescue SH-SY5Y and RIN-m5F cells from amyloid-induced cytotoxicity, and retain their original antimicrobial activity against four common bacterial strains at sub-stoichiometric concentrations. Such sequence-independent anti-amyloid and anti-bacterial functions of intestinal defensins mainly stem from their cross-interactions with amyloid proteins through amyloid-like mimicry of β-sheet associations. In a broader view, this work provides a new out-of-the-box thinking to search and repurpose a huge source of antimicrobial peptides as amyloid inhibitors, allowing the blocking of the two interlinked pathological pathways and bidirectional communication between the central nervous system and intestines via the gut–brain axis associated with neurodegenerative diseases.

Amyloid formation and microbial infection are the two common pathological causes of neurogenerative diseases. Here, we proposed a new “anti-amyloid and anti-bacteria” strategy to repurpose two intestinal defensins as multiple-target, dual-function amyloid inhibitors.

Conformational-Specific Self-Assembled Peptides as Dual-Mode, Multi-target Inhibitors and Detectors for Different Amyloid Pro-teins

Prevention and detection of misfolded amyloid proteins and their β-structure-rich aggregates are the two promising but differ-ent (pre)clinical strategies to treat and diagnose neurodegenerative diseases including Alzheimer’s diseases (AD) and...

A mechanistic survey of Alzheimer's disease

Alzheimer's disease (AD) is the most common, age-dependent neurodegenerative disorder. While AD has been intensively studied from different aspects, there is no effective cure for AD, largely due to a lack of a clear mechanistic understanding of AD. In this mini-review, we mainly focus on the discussion and summary of mechanistic causes of Alzheimer's disease (AD). While different AD mechanisms illustrate different molecular and cellular pathways in AD pathogenesis, they do not necessarily exclude each other. Instead, some of them could work together to initiate, trigger, and promote the onset and development of AD. In a broader viewpoint, some AD mechanisms (e.g., amyloid aggregation mechanism, microbial infection/neuroinflammation mechanism, and amyloid cross-seeding mechanism) could also be applicable to other amyloid diseases including type II diabetes, Parkinson's disease, and prion disease. Such common mechanisms for AD and other amyloid diseases explain not only the pathogenesis of individual amyloid diseases, but also the spreading of pathologies between these diseases, which will inspire new strategies for therapeutic intervention and prevention for AD.

Arginine and Arginine-Rich Peptides as Modulators of Protein Aggregation and Cytotoxicity Associated With Alzheimer's Disease

A substantial body of evidence indicates cationic, arginine-rich peptides (CARPs) are effective therapeutic compounds for a range of neurodegenerative pathologies, with beneficial effects including the reduction of excitotoxic cell death and mitochondrial dysfunction. CARPs, therefore, represent an emergent class of promising neurotherapeutics with multimodal mechanisms of action. Arginine itself is a known chaotrope, able to prevent misfolding and aggregation of proteins. The putative role of proteopathies in chronic neurodegenerative diseases such as Alzheimer's disease (AD) warrants investigation into whether CARPs could also prevent the aggregation and cytotoxicity of amyloidogenic proteins, particularly amyloid-beta and tau. While monomeric arginine is well-established as an inhibitor of protein aggregation in solution, no studies have comprehensively discussed the anti-aggregatory properties of arginine and CARPs on proteins associated with neurodegenerative disease. Here, we review the structural, physicochemical, and self-associative properties of arginine and the guanidinium moiety, to explore the mechanisms underlying the modulation of protein aggregation by monomeric and multimeric arginine molecules. Arginine-rich peptide-based inhibitors of amyloid-beta and tau aggregation are discussed, as well as further modulatory roles which could reduce proteopathic cytotoxicity, in the context of therapeutic development for AD.

Amyloid-Driven Tau Accumulation on Mitochondria Potentially Leads to Cognitive Deterioration in Alzheimer's Disease

Despite the well-accepted role of the two main neuropathological markers (β-amyloid and tau) in the progression of Alzheimer’s disease, the interaction and specific contribution of each of them is not fully elucidated. To address this question, in the present study, an adeno-associated virus (AAV9) carrying the mutant P301L form of human tau, was injected into the dorsal hippocampi of APP/PS1 transgenic mice or wild type mice (WT). Three months after injections, memory tasks, biochemical and immunohistochemical analysis were performed. We found that the overexpression of hTauP301L accelerates memory deficits in APP/PS1 mice, but it did not affect memory function of WT mice. Likewise, biochemical assays showed that only in the case of APP/PS1-hTauP301L injected mice, an important accumulation of tau was observed in the insoluble urea fraction. Similarly, electron microscopy images revealed that numerous clusters of tau immunoparticles appear at the dendrites of APP/PS1 injected mice and not in WT animals, suggesting that the presence of amyloid is necessary to induce tau aggregation. Interestingly, these tau immunoparticles accumulate in dendritic mitochondria in the APP/PS1 mice, whereas most of mitochondria in WT injected mice remain free of tau immunoparticles. Taken together, it seems that amyloid induces tau aggregation and accumulation in the dendritic mitochondria and subsequently may alter synapse function, thus, contributing to accelerate cognitive decline in APP/PS1 mice.

Mesenchymal Stem Cell-Derived Extracellular Vesicle-Based Therapy for Alzheimer's Disease: Progress and Opportunity

Alzheimer's disease (AD), as a neurodegenerative disorder, is characterized by mass neuronal and synaptic loss and, currently, there are no successful curative therapies. Extracellular vesicles (EVs) are an emerging approach to intercellular communication via transferring cellular materials such as proteins, lipids, mRNAs, and miRNAs from parental cells to recipient cells, leading to the reprogramming of the molecular machinery. Numerous studies have suggested the therapeutic potential of EVs derived from mesenchymal stem cells (MSCs) in the treatment of AD, based on the neuroprotective, regenerative and immunomodulatory effects as effective as MSCs. In this review, we focus on the biology and function of EVs, the potential of MSC-derived EVs for AD therapy in preclinical and clinical studies, as well as the potent mechanisms of MSC-derived EVs actions. Finally, we highlight the modification strategies and diagnosis utilities in order to make advance in this field.

Microglia Mediate the Occurrence and Development of Alzheimer's Disease Through Ligand-Receptor Axis Communication

Alzheimer's disease (AD) is a common neurodegenerative disease. Its onset is insidious and its progression is slow, making diagnosis difficult. In addition, its underlying molecular and cellular mechanisms remain unclear. In this study, clustering analysis was performed on single-cell RNA sequencing (scRNA-seq) data from the prefrontal cortex of 48 AD patients. Each sample module was identified to be a specific AD cell type, eight main brain cell types were identified, and the dysfunctional evolution of each cell type was further explored by pseudo-time analysis. Correlation analysis was then used to explore the relationship between AD cell types and pathological characteristics. In particular, intercellular communication between neurons and glial cells in AD patients was investigated by cell communication analysis. In patients, neuronal cells and glial cells significantly correlated with pathological features, and glial cells appear to play a key role in the development of AD through ligand-receptor axis communication. Marker genes involved in communication between these two cell types were identified using five types of modeling: logistic regression, multivariate logistic regression, least absolute shrinkage and selection operator (LASSO) and support vector machine (SVM). LASSO modeling identified CXCR4, EGFR, MAP4K4, and IGF1R as key genes in this communication. Our results support the idea that microglia play a role in the occurrence and development of AD through ligand-receptor axis communication. In particular, our analyses identify CXCR4, EGFR, MAP4K4, and IGF1R as potential biomarkers and therapeutic targets in AD.

Role of Neuron and Glia in Alzheimer's Disease and Associated Vascular Dysfunction

Amyloidogenicity and vascular dysfunction are the key players in the pathogenesis of Alzheimer’s disease (AD), involving dysregulated cellular interactions. An intricate balance between neurons, astrocytes, microglia, oligodendrocytes and vascular cells sustains the normal neuronal circuits. Conversely, cerebrovascular diseases overlap neuropathologically with AD, and glial dyshomeostasis promotes AD-associated neurodegenerative cascade. While pathological hallmarks of AD primarily include amyloid-β (Aβ) plaques and neurofibrillary tangles, microvascular disorders, altered cerebral blood flow (CBF), and blood-brain barrier (BBB) permeability induce neuronal loss and synaptic atrophy. Accordingly, microglia-mediated inflammation and astrogliosis disrupt the homeostasis of the neuro-vascular unit and stimulate infiltration of circulating leukocytes into the brain. Large-scale genetic and epidemiological studies demonstrate a critical role of cellular crosstalk for altered immune response, metabolism, and vasculature in AD. The glia associated genetic risk factors include APOE, TREM2, CD33, PGRN, CR1, and NLRP3, which correlate with the deposition and altered phagocytosis of Aβ. Moreover, aging-dependent downregulation of astrocyte and microglial Aβ-degrading enzymes limits the neurotrophic and neurogenic role of glial cells and inhibits lysosomal degradation and clearance of Aβ. Microglial cells secrete IGF-1, and neurons show a reduced responsiveness to the neurotrophic IGF-1R/IRS-2/PI3K signaling pathway, generating amyloidogenic and vascular dyshomeostasis in AD. Glial signals connect to neural stem cells, and a shift in glial phenotype over the AD trajectory even affects adult neurogenesis and the neurovascular niche. Overall, the current review informs about the interaction of neuronal and glial cell types in AD pathogenesis and its critical association with cerebrovascular dysfunction.

Tacrolimus Protects against Age-Associated Microstructural Changes in the Beagle Brain

The overexpression of calcineurin leads to astrocyte hyperactivation, neuronal death, and inflammation, which are characteristics often associated with pathologic aging and Alzheimer's disease. In this study, we tested the hypothesis that tacrolimus, a calcineurin inhibitor, prevents age-associated microstructural atrophy, which we measured using higher-order diffusion MRI, in the middle-aged beagle brain (n = 30, male and female). We find that tacrolimus reduces hippocampal (p = 0.001) and parahippocampal (p = 0.002) neurite density index, as well as protects against an age-associated increase in the parahippocampal (p = 0.007) orientation dispersion index. Tacrolimus also protects against an age-related decrease in fractional anisotropy in the prefrontal cortex (p < 0.0001). We also show that these microstructural alterations precede cognitive decline and gross atrophy. These results support the idea that calcineurin inhibitors may have the potential to prevent aging-related pathology if administered at middle age.SIGNIFICANCE STATEMENT Hyperactive calcineurin signaling causes neuroinflammation and other neurobiological changes often associated with pathologic aging and Alzheimer's disease (AD). Controlling the expression of calcineurin before gross cognitive deficits are observable might serve as a promising avenue for preventing AD pathology. In this study, we show that the administration of the calcineurin inhibitor, tacrolimus, over 1 year prevents age- and AD-associated microstructural changes in the hippocampus, parahippocampal cortex, and prefrontal cortex of the middle-aged beagle brain, with no noticeable adverse effects. Tacrolimus is already approved by the Food and Drug Administration for use in humans to prevent solid organ transplant rejection, and our results bolster the promise of this drug to prevent AD and aging-related pathology.