The Amyloid Cascade Hypothesis in Alzheimer's Disease: It's Time to Change Our Mind

BACE-1 Inhibitors Targeting Alzheimer's Disease

The accumulation of amyloid-β (Aβ) is the main event related to Alzheimer's disease (AD) progression. Over the years, several disease-modulating approaches have been reported, but without clinical success. The amyloid cascade hypothesis evolved and proposed essential targets such as tau protein aggregation and modulation of β-secretase (β-site amyloid precursor protein cleaving enzyme 1 - BACE-1) and γ-secretase proteases. BACE-1 cuts the amyloid precursor protein (APP) to release the C99 fragment, giving rise to several Aβ peptide species during the subsequent γ-secretase cleavage. In this way, BACE-1 has emerged as a clinically validated and attractive target in medicinal chemistry, as it plays a crucial role in the rate of Aβ generation. In this review, we report the main results of candidates in clinical trials such as E2609, MK8931, and AZD-3293, in addition to highlighting the pharmacokinetic and pharmacodynamic-related effects of the inhibitors already reported. The current status of developing new peptidomimetic, non-peptidomimetic, naturally occurring, and other class inhibitors are demonstrated, considering their main limitations and lessons learned. The goal is to provide a broad and complete approach to the subject, exploring new chemical classes and perspectives.

Systems Pharmacology and Pharmacokinetics Strategy to Decode Bioactive Ingredients and Molecular Mechanisms from Zingiber officinale as Phyto-therapeutics against Neurological Diseases

BACKGROUND

The bioactive constituents from Zingiber officinale (Z. officinale) have shown a positive effect on neurodegenerative diseases like Alzheimer's disease (AD), which manifests as progressive memory loss and cognitive impairment.

OBJECTIVE

This study investigates the binding ability and the pharmaco-therapeutic potential of Z. officinale with AD disease targets by molecular docking and molecular dynamic (MD) simulation approaches.

METHODS

By coupling enormous available phytochemical data and advanced computational technologies, the possible molecular mechanism of action of these bioactive compounds was deciphered by evaluating phytochemicals, target fishing, and network biological analysis.

RESULTS

As a result, 175 bioactive compounds and 264 human target proteins were identified. The gene ontology and Kyoto Encyclopaedia of Genes and Genomes pathway enrichment analysis and molecular docking were used to predict the basis of vital bioactive compounds and biomolecular mechanisms involved in the treatment of AD. Amongst selected bioactive compounds, 10- Gingerdione and 1-dehydro-[8]-gingerdione exhibited significant anti-neurological properties against AD targeting amyloid precursor protein with docking energy of -6.0 and -5.6, respectively.

CONCLUSION

This study suggests that 10-Gingerdione and 1-dehydro-[8]-gingerdione strongly modulates the anti-neurological activity and are associated with pathological features like amyloid-β plaques and hyperphosphorylated tau protein are found to be critically regulated by these two target proteins. This comprehensive analysis provides a clue for further investigation of these natural compounds' inhibitory activity in drug discovery for AD treatment.

The Anti-Amyloid Monoclonal Antibody Lecanemab: 16 Cautionary Notes

After the CLARITY-AD clinical trial results of lecanemab were interpreted as positive, and supporting the amyloid hypothesis, the drug received accelerated Food and Drug Administration approval. However, we argue that benefits of lecanemab treatment are uncertain and may yield net harm for some patients, and that the data do not support the amyloid hypothesis. We note potential biases from inclusion, unblinding, dropouts, and other issues. Given substantial adverse effects and subgroup heterogeneity, we conclude that lecanemab's efficacy is not clinically meaningful, consistent with numerous analyses suggesting that amyloid-β and its derivatives are not the main causative agents of Alzheimer's disease dementia.

Pharmacotherapy Evolution in Alzheimer's Disease: Current Framework and Relevant Directions

Alzheimer's disease (AD), once considered a rare disease, is now the most common form of dementia in the elderly population. Current drugs (cholinesterase inhibitors and glutamate antagonists) are safe but of limited benefit to most patients, offering symptomatic relief without successful cure of the disease. Since the last several decades, there has been a great need for the development of a treatment that might cure the underlying causes of AD and thereby slow its progression in vulnerable individuals. That is why phase I, II, and III studies that act on several fronts, such as cognitive improvement, symptom reduction, and enhancing the basic biology of AD, are imperative to stop the disease. This review discusses current treatment strategies, summarizing the clinical features and pharmacological properties, along with molecular docking analyses of the existing medications.

Natural Carotenoids as Neuroprotective Agents for Alzheimer's Disease: An Evidence-Based Comprehensive Review

Alzheimer's disease (AD) is a neurodegenerative disorder of an ever-increasing aging population with various pathological features such as β-amyloid (Aβ) aggregation, oxidative stress, an impaired cholinergic system, and neuroinflammation. Several therapeutic drugs have been introduced to slow the progression of AD by targeting the above-mentioned pathways. In addition, emerging evidence suggests that naturally occurring compounds have the potential to serve as adjuvant therapies to alleviate AD symptoms. Carotenoids, a group of natural pigments with antioxidative and anti-inflammatory properties, are proposed to be implicated in neuroprotection. To obtain a comprehensive picture of the effect of carotenoids on AD prevention and development, we critically reviewed and discussed recent evidence from in silico, in vitro, in vivo, and human studies in databases including PubMed, Web of Science, Google Scholar, and Cochrane (CENTRAL). After analyzing the existing evidence, we found that high-quality randomized controlled trials (RCTs) are lacking to explore the neuroprotective role of carotenoids in AD pathogenesis and symptoms, especially carotenoids with solid preclinical evidence such as astaxanthin, fucoxanthin, macular carotenoids, and crocin, in order to develop effective preventive dietary supplements for AD patients to ameliorate the symptoms. This review points out directions for future studies to advance the knowledge in this field.

Mechanistic Insights into the Neuroprotective Potential of Sacred Ficus Trees

Ficus religiosa (Bo tree or sacred fig) and Ficus benghalensis (Indian banyan) are of immense spiritual and therapeutic importance. Various parts of these trees have been investigated for their antioxidant, antimicrobial, anticonvulsant, antidiabetic, anti-inflammatory, analgesic, hepatoprotective, dermoprotective, and nephroprotective properties. Previous reviews of Ficus mostly discussed traditional usages, photochemistry, and pharmacological activities, though comprehensive reviews of the neuroprotective potential of these Ficus species extracts and/or their important phytocompounds are lacking. The interesting phytocompounds from these trees include many bengalenosides, carotenoids, flavonoids (leucopelargonidin-3-O-β-d-glucopyranoside, leucopelargonidin-3-O-α-l-rhamnopyranoside, lupeol, cetyl behenate, and α-amyrin acetate), flavonols (kaempferol, quercetin, myricetin), leucocyanidin, phytosterols (bergapten, bergaptol, lanosterol, β-sitosterol, stigmasterol), terpenes (α-thujene, α-pinene, β-pinene, α-terpinene, limonene, β-ocimene, β-bourbonene, β-caryophyllene, α-trans-bergamotene, α-copaene, aromadendrene, α-humulene, alloaromadendrene, germacrene, γ-cadinene, and δ-cadinene), and diverse polyphenols (tannin, wax, saponin, leucoanthocyanin), contributing significantly to their pharmacological effects, ranging from antimicrobial action to neuroprotection. This review presents extensive mechanistic insights into the neuroprotective potential, especially important phytochemicals from F. religiosa and F. benghalensis. Owing to the complex pathophysiology of neurodegenerative disorders (NDDs), the currently existing drugs merely alleviate the symptoms. Hence, bioactive compounds with potent neuroprotective effects through a multitarget approach would be of great interest in developing pharmacophores for the treatment of NDDs.

Characterization of microtubule-associated protein tau isoforms and Alzheimer's disease-like pathology in normal sheep (Ovis aries): relevance to their potential as a model of Alzheimer's disease

Alzheimer's disease is a chronic neurodegenerative disease that accounts for up to 80% of all dementias. Characterised by deteriorations of memory and cognitive function, the key neuropathological features are accumulations of β-amyloid and hyperphosphorylated tau, as 'plaques' and 'tangles', respectively. Despite extensive study, however, the exact mechanism underlying aggregate formation in Alzheimer's disease remains elusive, as does the contribution of these aggregates to disease progression. Importantly, a recent evaluation of current Alzheimer's disease animal models suggested that rodent models are not able to fully recapitulate the pathological intricacies of the disease as it occurs in humans. Therefore, increasing attention is being paid to species that might make good alternatives to rodents for studying the molecular pathology of Alzheimer's disease. The sheep (Ovis aries) is one such species, although to date, there have been few molecular studies relating to Alzheimer's disease in sheep. Here, we investigated the Alzheimer's disease relevant histopathological characteristics of 22 sheep, using anti-β-amyloid (Abcam 12267 and mOC64) and phosphorylation specific anti-tau (AT8 and S396) antibodies. We identified numerous intraneuronal aggregates of both β-amyloid and tau that are consistent with early Alzheimer's disease-like pathology. We confirmed the expression of two 3-repeat (1N3R, 2N3R) and two 4-repeat (1N4R, 2N4R) tau isoforms in the ovine brain, which result from the alternative splicing of two tau exons. Finally, we investigated the phosphorylation status of the serine396 residue in 30 sheep, and report that the phosphorylation of this residue begins in sheep aged as young as 2 years. Together, these data show that sheep exhibit naturally occurring β-amyloid and tau pathologies, that reflect those that occur in the early stages of Alzheimer's disease. This is an important step towards the validation of the sheep as a feasible large animal species in which to model Alzheimer's disease.

Targeting Alzheimer's Disease: The Critical Crosstalk between the Liver and Brain

Alzheimer's disease (AD), an age-related neurodegenerative disorder, is currently incurable. Imbalanced amyloid-beta (Aβ) generation and clearance are thought to play a pivotal role in the pathogenesis of AD. Historically, strategies targeting Aβ clearance have typically focused on central clearance, but with limited clinical success. Recently, the contribution of peripheral systems, particularly the liver, to Aβ clearance has sparked an increased interest. In addition, AD presents pathological features similar to those of metabolic syndrome, and the critical involvement of brain energy metabolic disturbances in this disease has been recognized. More importantly, the liver may be a key regulator in these abnormalities, far beyond our past understanding. Here, we review recent animal and clinical findings indicating that liver dysfunction represents an early event in AD pathophysiology. We further propose that compromised peripheral Aβ clearance by the liver and aberrant hepatic physiological processes may contribute to AD neurodegeneration. The role of a hepatic synthesis product, fibroblast growth factor 21 (FGF21), in the management of AD is also discussed. A deeper understanding of the communication between the liver and brain may lead to new opportunities for the early diagnosis and treatment of AD.

Sticker-and-spacer model for amyloid beta condensation and fibrillation

A major pathogenic hallmark of Alzheimer's disease is the presence of neurotoxic plaques composed of amyloid beta (Aβ) peptides in patients' brains. The pathway of plaque formation remains elusive, though some clues appear to lie in the dominant presence of Aβ_{1 − 42} in these plaques despite Aβ₁₋₄₀ making up approximately 90% of the Aβ pool. We hypothesize that this asymmetry is driven by the hydrophobicity of the two extra amino acids that are incorporated in Aβ₁₋₄₂. To investigate this hypothesis at the level of single molecules, we have developed a molecular “sticker-and-spacer lattice model” of unfolded Aβ. The model protein has a single sticker that may reversibly dimerise and elongate into semi-flexible linear chains. The growth is hampered by excluded-volume interactions that are encoded by the hydrophilic spacers but are rendered cooperative by the attractive interactions of hydrophobic spacers. For sufficiently strong hydrophobicity, the chains undergo liquid-liquid phase-separation (LLPS) into condensates that facilitate the nucleation of fibers. We find that a small fraction of Aβ₁₋₄₀ in a mixture of Aβ₁₋₄₀ and Aβ₁₋₄₂ shifts the critical concentration for LLPS to lower values. This study provides theoretical support for the hypothesis that LLPS condensates act as a precursor for aggregation and provides an explanation for the Aβ₁₋₄₂-enrichment of aggregates in terms of hydrophobic interactions.

Mining on Alzheimer's diseases related knowledge graph to identity potential AD-related semantic triples for drug repurposing

BACKGROUND

To date, there are no effective treatments for most neurodegenerative diseases. Knowledge graphs can provide comprehensive and semantic representation for heterogeneous data, and have been successfully leveraged in many biomedical applications including drug repurposing. Our objective is to construct a knowledge graph from literature to study the relations between Alzheimer's disease (AD) and chemicals, drugs and dietary supplements in order to identify opportunities to prevent or delay neurodegenerative progression. We collected biomedical annotations and extracted their relations using SemRep via SemMedDB. We used both a BERT-based classifier and rule-based methods during data preprocessing to exclude noise while preserving most AD-related semantic triples. The 1,672,110 filtered triples were used to train with knowledge graph completion algorithms (i.e., TransE, DistMult, and ComplEx) to predict candidates that might be helpful for AD treatment or prevention.

RESULTS

Among three knowledge graph completion models, TransE outperformed the other two (MR = 10.53, Hits@1 = 0.28). We leveraged the time-slicing technique to further evaluate the prediction results. We found supporting evidence for most highly ranked candidates predicted by our model which indicates that our approach can inform reliable new knowledge.

CONCLUSION

This paper shows that our graph mining model can predict reliable new relationships between AD and other entities (i.e., dietary supplements, chemicals, and drugs). The knowledge graph constructed can facilitate data-driven knowledge discoveries and the generation of novel hypotheses.

Neuroinflammation represents a common theme amongst genetic and environmental risk factors for Alzheimer and Parkinson diseases

Multifactorial diseases are characterized by inter-individual variation in etiology, age of onset, and penetrance. These diseases tend to be relatively common and arise from the combined action of genetic and environmental factors; however, parsing the convoluted mechanisms underlying these gene-by-environment interactions presents a significant challenge to their study and management. For neurodegenerative disorders, resolving this challenge is imperative, given the enormous health and societal burdens they impose. The mechanisms by which genetic and environmental effects may act in concert to destabilize homeostasis and elevate risk has become a major research focus in the study of common disease. Emphasis is further being placed on determining the extent to which a unifying biological principle may account for the progressively diminishing capacity of a system to buffer disease phenotypes, as risk for disease increases. Data emerging from studies of common, neurodegenerative diseases are providing insights to pragmatically connect mechanisms of genetic and environmental risk that previously seemed disparate. In this review, we discuss evidence positing inflammation as a unifying biological principle of homeostatic destabilization affecting the risk, onset, and progression of neurodegenerative diseases. Specifically, we discuss how genetic variation associated with Alzheimer disease and Parkinson disease may contribute to pro-inflammatory responses, how such underlying predisposition may be exacerbated by environmental insults, and how this common theme is being leveraged in the ongoing search for effective therapeutic interventions.

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.

All roads lead to heterogeneity: The complex involvement of astrocytes and microglia in the pathogenesis of Alzheimer’s disease

In recent years, glial cells have been acknowledged as key players in the pathogenesis of Alzheimer’s disease (AD), a neurodegenerative condition in which an accumulation of intracellular neurofibrillary tangles and extracellular fibrillar amyloid beta is notably observed in the central nervous system. Genome-wide association studies have shown, both in microglia and astrocytes, an increase in gene variants associated with a higher risk of developing late-onset AD. Microglia, the resident innate immune cells of the brain, and astrocytes, glial cells crucial for vascular integrity and neuronal support, both agglomerate near amyloid beta plaques and dystrophic neurites where they participate in the elimination of these harmful parenchymal elements. However, their role in AD pathogenesis has been challenging to resolve due to the highly heterogeneous nature of these cell populations, i.e., their molecular, morphological, and ultrastructural diversity, together with their ever-changing responsiveness and functions throughout the pathological course of AD. With the recent expansions in the field of glial heterogeneity through innovative advances in state-of-the-art microscopy and -omics techniques, novel concepts and questions arose, notably pertaining to how the diverse microglial and astrocytic states interact with each other and with the AD hallmarks, and how their concerted efforts/actions impact the progression of the disease. In this review, we discuss the recent advances and findings on the topic of glial heterogeneity, particularly focusing on the relationships of these cells with AD hallmarks (e.g., amyloid beta plaques, neurofibrillary tangles, synaptic loss, and dystrophic neurites) in murine models of AD pathology and post-mortem brain samples of patients with AD.

Design, synthesis, extra-precision docking, and molecular dynamics simulation studies of pyrrolidin-2-one derivatives as potential acetylcholinesterase inhibitors

Inhibition of acetylcholinesterase (AChE) has been widely explored to develop novel molecules for management of Alzheimer's disease. In past research finding reported molecule 3-(4-(4-fluorobenzoyl)piperidin-1-yl)-1-(4-methoxybenzyl)pyrrolidin-2-one displayed a spectrum of anti-Alzheimer's properties herein, we report a library of 18 novel molecules that were rationally designed and synthesized employing known literature to mimic and explore the novel chemical space around the lead compound 6e and donepezil. All the compounds were docked in extra-precision mode with AChE (PDB ID 4EY7) using the Glide module. Molecular dynamics (MD) simulation studies were carried out for 100 ns along with MM-PBSA studies of the trajectory frames generated post-MD simulations. Docking and MD simulation studies suggested that the synthesized compounds showed a good binding affinity with AChE. and might form stable complexes. 3-(4-(benzyl(methyl)amino)piperidin-1-yl)-1-(3,4-dimethoxybenzyl)pyrrolidin-2-one (14a; docking score: -18.59) and 1-(3,4-dimethoxybenzyl)-3-(4-(methyl(thiazol-2-ylmethyl)amino)piperidin-1-yl)pyrrolidin-2-one (14d; docking score: -18.057) showed higher docking score than donepezil (docking score: -17.257) while most of the compounds had docking score >-10.0. ADMET study predicted these compounds to be CNS active and most of the compounds were drug-like molecules with no HERG blockade and good to excellent oral absorption. We developed an atom-based 3 D-QSAR model with R^2 and Q^2 values of 0.9639 and 0.8779 to predict the activity of the synthesized compounds. The model predicted these compounds to be potent AChE inhibitors with IC₅₀ values in the lower micromolar range. Based on the in silico findings, we report these newly synthesized compounds 3-(4-(benzyl(methyl)amino)piperidin-1-yl)-1-(3,4-dimethoxybenzyl)pyrrolidin-2-one (14a) and 7-(2,6-difluorobenzyl)-2-(4-methoxybenzyl)-2,7-diazaspiro[4.5]decan-1-one (20 b) as potential AChE inhibitors.Communicated by Ramaswamy H. Sarma.

Model scenarios for cell cycle re-entry in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease. Aberrant production and aggregation of amyloid beta (Aβ) peptide into plaques is a frequent feature of AD, but therapeutic approaches targeting Aβ accumulation fail to inhibit disease progression. The approved cholinesterase inhibitor drugs are symptomatic treatments. During human brain development, the progenitor cells differentiate into neurons and switch to a postmitotic state. However, cell cycle re-entry often precedes loss of neurons. We developed mathematical models of multiple routes leading to cell cycle re-entry in neurons that incorporate the crosstalk between cell cycle, neuronal, and apoptotic signaling mechanisms. We show that the integration of multiple feedback loops influences disease severity making the switch to pathological state irreversible. We observe that the transcriptional changes associated with this transition are also characteristics of the AD brain. We propose that targeting multiple arms of the feedback loop may bring about disease-modifying effects in AD.

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Developed mathematical models of cell cycle re-entry in Alzheimer's disease (AD)

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Integration of multiple feedback loops drives irreversible transition to AD

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Predicted transcriptional dysregulation is validated using AD gene expression data

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Inhibition of self-amplifying feedback loops brings about disease-modifying effects

Dysfunction of Mitochondria in Alzheimer’s Disease: ANT and VDAC Interact with Toxic Proteins and Aid to Determine the Fate of Brain Cells

Alzheimer’s disease (AD), certainly the most widespread proteinopathy, has as classical neuropathological hallmarks, two groups of protein aggregates: senile plaques and neurofibrillary tangles. However, the research interest is rapidly gaining ground in a better understanding of other pathological features, first, of all the mitochondrial dysfunctions. Several pieces of evidence support the hypothesis that abnormal mitochondrial function may trigger aberrant processing of amyloid progenitor protein or tau and thus neurodegeneration. Here, our aim is to emphasize the role played by two ‘bioenergetic’ proteins inserted in the mitochondrial membranes, inner and outer, respectively, that is, the adenine nucleotide translocator (ANT) and the voltage-dependent anion channel (VDAC), in the progression of AD. To perform this, we will magnify the ANT and VDAC defects, which are measurable hallmarks of mitochondrial dysfunction, and collect all the existing information on their interaction with toxic Alzheimer’s proteins. The pathological convergence of tau and amyloid β-peptide (Aβ) on mitochondria may finally explain why the therapeutic strategies used against the toxic forms of Aβ or tau have not given promising results separately. Furthermore, the crucial role of ANT-1 and VDAC impairment in the onset/progression of AD opens a window for new therapeutic strategies aimed at preserving/improving mitochondrial function, which is suspected to be the driving force leading to plaque and tangle deposition in AD.

A New Bistable Switch Model of Alzheimer’s Disease Pathogenesis

We propose a model to explain the pathogenesis of Alzheimer’s disease (AD) based on the theory that any disease affecting a healthy organism originates from a bistable feedback loop that shifts the system from a physiological to a pathological condition. We focused on the known double inhibitory loop involving the cellular prion protein (PrPC) and the enzyme BACE1 that produces amyloid-beta (Aβ) peptides. BACE1 is inhibited by PrPC, but its inhibitory activity is lost when PrPC binds to Aβ oligomers (Aβo). Excessive Aβo formation would switch the loop to a pathogenic condition involving the Aβo-PrPC-mGluR5 complex, Fyn kinase activation, tau, and NMDAR phosphorylation, ultimately leading to neurodegeneration. Based on the emerging role of cyclic nucleotides in Aβ production, and thereby in synaptic plasticity and cognitive processes, cAMP and cGMP can be considered as modulatory factors capable of inducing the transition from a physiological steady state to a pathogenic one. This would imply that critical pharmacological targets for AD treatment lie within pathways that lead to an imbalance of cyclic nucleotides in neurons. If this hypothesis is confirmed, it will provide precise indications for the development of preventive or therapeutic treatments for the disease.

The Interplay between cGMP and Calcium Signaling in Alzheimer’s Disease

Cyclic guanosine monophosphate (cGMP) is a ubiquitous second messenger and a key molecule in many important signaling cascades in the body and brain, including phototransduction, olfaction, vasodilation, and functional hyperemia. Additionally, cGMP is involved in long-term potentiation (LTP), a cellular correlate of learning and memory, and recent studies have identified the cGMP-increasing drug Sildenafil as a potential risk modifier in Alzheimer’s disease (AD). AD development is accompanied by a net increase in the expression of nitric oxide (NO) synthases but a decreased activity of soluble guanylate cyclases, so the exact sign and extent of AD-mediated imbalance remain unclear. Moreover, human patients and mouse models of the disease present with entangled deregulation of both cGMP and Ca²⁺ signaling, e.g., causing changes in cGMP-mediated Ca²⁺ release from the intracellular stores as well as Ca²⁺-mediated cGMP production. Still, the mechanisms governing such interplay are poorly understood. Here, we review the recent data on mechanisms underlying the brain cGMP signaling and its interconnection with Ca²⁺ signaling. We also discuss the recent evidence stressing the importance of such interplay for normal brain function as well as in Alzheimer’s disease.

Therapeutic nanotechnologies for Alzheimer's disease: a critical analysis of recent trends and findings

Alzheimer's Disease (AD) is an irreversible neurodegenerative disease for which no disease modifying therapies are presently available. Besides the identification of pathological targets, AD presents numerous clinical and pharmacological challenges such as efficient active delivery to the central nervous system, cell targeting, and long-term dosing. Nanoparticles have been explored to overcome some of these challenges as drug delivery vehicles or drugs themselves. However, early promises have failed to materialize as no nanotechnology-based product has been able to reach the market and very few have moved past preclinical stages. In this review, we perform a critical analysis of the past decade's research on nanomedicine-based therapies for AD at the preclinical and clinical stages. The main obstacles to nanotechnology products and the most promising approaches were also identified, including renewed promise with gene editing, gene modulation, and vaccines.

Dysregulated Ca2+ Homeostasis as a Central Theme in Neurodegeneration: Lessons from Alzheimer's Disease and Wolfram Syndrome

Calcium ions (Ca²⁺) operate as important messengers in the cell, indispensable for signaling the underlying numerous cellular processes in all of the cell types in the human body. In neurons, Ca²⁺ signaling is crucial for regulating synaptic transmission and for the processes of learning and memory formation. Hence, the dysregulation of intracellular Ca²⁺ homeostasis results in a broad range of disorders, including cancer and neurodegeneration. A major source for intracellular Ca²⁺ is the endoplasmic reticulum (ER), which has close contacts with other organelles, including mitochondria. In this review, we focus on the emerging role of Ca²⁺ signaling at the ER–mitochondrial interface in two different neurodegenerative diseases, namely Alzheimer’s disease and Wolfram syndrome. Both of these diseases share some common hallmarks in the early stages, including alterations in the ER and mitochondrial Ca²⁺ handling, mitochondrial dysfunction and increased Reactive oxygen species (ROS) production. This indicates that similar mechanisms may underly these two disease pathologies and suggests that both research topics might benefit from complementary research.

Association of Aortic Stiffness and Pressure Pulsatility With Global Amyloid-β and Regional Tau Burden Among Framingham Heart Study Participants Without Dementia

Importance

Aortic stiffness is associated with clinical hallmarks of Alzheimer disease and related dementias and could be a modifiable target for disease prevention.

Objective

To assess associations of aortic stiffness and pressure pulsatility with global amyloid-β plaques and regional tau burden in the brain of middle-aged and older adults without dementia.

Design, Setting, and Participants

The sample for this cross-sectional study was drawn from the Framingham Heart Study Third Generation Cohort at examination 3 (N = 3171; 2016-2019), of whom 3092 successfully underwent comprehensive hemodynamic evaluations. In a supplemental visit (2015-2021), a subset of 270 participants without dementia who represented the spectrum of vascular risk also underwent positron emission tomography. Thirteen participants were excluded for missing covariate data. The final sample size was 257 participants.

Exposures

Three measures of aortic stiffness and pressure pulsatility (carotid-femoral pulse wave velocity, central pulse pressure [CPP], and forward wave amplitude [FWA]) were evaluated using arterial tonometry.

Main Outcomes and Measures

Global amyloid-β plaques and regional tau were assessed using 11C-Pittsburgh compound B and 18F-flortaucipir positron emission tomography tracers, respectively.

Results

The mean (SD) age of the 257 participants was 54 (8) years, and 126 were women (49%). All participants were White Western European race. In multivariable models, higher CPP (β per SD = 0.17; 95% CI, 0.00-0.35; P = .045) and FWA (β per SD = 0.16; 95% CI, 0.00-0.31; P = .04) were associated with greater entorhinal tau burden. In similar models, higher CPP (β per SD = 0.19; 95% CI, 0.02-0.36; P = .03) and FWA (β per SD = 0.17; 95% CI, 0.01-0.32; P = .03) were associated with greater rhinal tau burden. Aortic stiffness and pressure pulsatility measures were not associated with amygdala, inferior temporal, precuneus tau burden, or global amyloid-β plaques. Associations for entorhinal and rhinal tau outcomes were more prominent in older participants (≥60 years). For example, higher levels of all aortic stiffness and pressure pulsatility measures (β per SD = 0.40-0.92; P = .001-.02) were associated with higher entorhinal tau burden among older but not younger participants in stratified analyses.

Conclusions and Relevance

In this cross-sectional study, abnormal central vascular hemodynamics were associated with higher tau burden in specific brain regions. Findings suggest that aortic stiffness, which is potentially modifiable, may be a probable independent target for prevention of tau-related pathologies.

Toxic SOD1 trimers are off-pathway in the formation of amyloid-like fibrils in ALS

Accumulation of insoluble amyloid fibrils is widely studied as a critical factor in the pathology of multiple neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease. Misfolded Cu, Zn superoxide dismutase (SOD1) was the first protein linked to ALS, and non-native SOD1 trimeric oligomers were recently linked to cytotoxicity, while larger oligomers were protective to cells. The balance between trimers and larger aggregates in the process of SOD1 aggregation is, thus, a critical determinant of potential therapeutic approaches to treat ALS. Yet, it is unknown whether these trimeric oligomers are a necessary intermediate for larger aggregate formation or a distinct off-pathway species competing with fibril formation. Depending on the on- or off-pathway scenario of trimer formation, we expect drastically different therapeutic approaches. Here, we show that the toxic SOD1 trimer is an off-pathway intermediate competing with protective fibril formation. We design mutant SOD1 constructs that remain in a trimeric state (super stable trimers) and show that stabilizing the trimeric SOD1 prevents formation of fibrils in vitro and in a motor neuron like cell model (NSC-34). Using size exclusion chromatography, we track the aggregation kinetics of purified SOD1 and show direct competition of trimeric SOD1 with larger oligomer and fibril formation. Finally, we show the trimer is structurally independent of both larger soluble oligomers and insoluble fibrils using circular dichroism spectroscopy and limited proteolysis.

Targeting brain Renin-Angiotensin System for the prevention and treatment of Alzheimer's disease: Past, present and future

Alzheimer's disease (AD) is a well-known neurodegenerative disease characterized by the presence of two main hallmarks - Tau hyperphosphorylation and Aβ deposits. Notwithstanding, in the last few years the scientific evidence about the drivers of AD have been changing and nowadays age-related vascular alterations and several cardiovascular risk factors have been shown to trigger the development of AD. In this context, drugs targeting the Renin Angiotensin System (RAS), commonly used for the treatment of hypertension, are evidencing a high potential to delay AD development due to their action on brain RAS. Indeed, the ACE 1/Ang II/AT1R axis is believed to be upregulated in AD and to be responsible for deleterious effects such as increased oxidative stress, neuroinflammation, blood-brain barrier (BBB) hyperpermeability, astrocytes dysfunction and a decrease in cerebral blood flow. In contrast, the alternative axis - ACE 1/Ang II/AT2R; ACE 2/Ang (1-7)/MasR; Ang IV/ AT4R(IRAP) - seems to counterbalance the deleterious effects of the principal axis and to exert beneficial effects on memory and cognition. Accordingly, retrospective studies demonstrate a reduced risk of developing AD among people taking RAS medication as well as several in vitro and in vivo pre-clinical studies as it is herein critically reviewed. In this review, we first revise, at a glance, the pathophysiology of AD focused on its classic hallmarks. Secondly, an overview about the impact of the RAS on the pathophysiology of AD is also provided, focused on their four essential axes ACE 1/Ang II/AT2R; ACE 2/Ang (1-7)/MasR; Ang IV/ AT4R(IRAP) and ACE 1/Ang II/AT1R. Finally, the therapeutic potential of available drugs targeting RAS on AD, namely angiotensin II receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs), is highlighted and data supporting this hope will be presented, from in vitro and in vivo pre-clinical to clinical studies.

Physiological Roles of Monomeric Amyloid-β and Implications for Alzheimer's Disease Therapeutics

Alzheimer's disease (AD) progressively inflicts impairment of synaptic functions with notable deposition of amyloid-β (Aβ) as senile plaques within the extracellular space of the brain. Accordingly, therapeutic directions for AD have focused on clearing Aβ plaques or preventing amyloidogenesis based on the amyloid cascade hypothesis. However, the emerging evidence suggests that Aβ serves biological roles, which include suppressing microbial infections, regulating synaptic plasticity, promoting recovery after brain injury, sealing leaks in the blood-brain barrier, and possibly inhibiting the proliferation of cancer cells. More importantly, these functions were found in in vitro and in vivo investigations in a hormetic manner, that is to be neuroprotective at low concentrations and pathological at high concentrations. We herein summarize the physiological roles of monomeric Aβ and current Aβ-directed therapies in clinical trials. Based on the evidence, we propose that novel therapeutics targeting Aβ should selectively target Aβ in neurotoxic forms such as oligomers while retaining monomeric Aβ in order to preserve the physiological functions of Aβ monomers.

Autophagy Modulation in Aggresome Formation: Emerging Implications and Treatments of Alzheimer's Disease

Alzheimer's disease (AD) is one of the most prevailing neurodegenerative diseases in the world, which is characterized by memory dysfunction and the formation of tau and amyloid β (Aβ) aggregates in multiple brain regions, including the hippocampus and cortex. The formation of senile plaques involving tau hyperphosphorylation, fibrillar Aβ, and neurofibrillary tangles (NFTs) is used as a pathological marker of AD and eventually produces aggregation or misfolded protein. Importantly, it has been found that the failure to degrade these aggregate-prone proteins leads to pathological consequences, such as synaptic impairment, cytotoxicity, neuronal atrophy, and memory deficits associated with AD. Recently, increasing evidence has suggested that the autophagy pathway plays a role as a central cellular protection system to prevent the toxicity induced by aggregation or misfolded proteins. Moreover, it has also been revealed that AD-related protein aggresomes could be selectively degraded by autophagosome and lysosomal fusion through the autophagy pathway, which is known as aggrephagy. Therefore, the regulation of autophagy serve as a useful approach to modulate the formation of aggresomes associated with AD. This review focuses on the recent improvements in the application of natural compounds and small molecules as a potential therapeutic approach for AD prevention and treatment via aggrephagy.

Post-translational Modifications of the p53 Protein and the Impact in Alzheimer’s Disease: A Review of the Literature

Our understanding of Alzheimer’s disease (AD) pathogenesis has developed with several hypotheses over the last 40 years, including the Amyloid and Tau hypotheses. More recently, the p53 protein, well-known as a genome guardian, has gained attention for its potential role in the early evolution of AD. This is due to the central involvement of p53’s in the control of oxidative stress and potential involvement in the Amyloid and Tau pathways. p53 is commonly regulated by post-translational modifications (PTMs), which affect its conformation, increasing its capacity to adopt multiple structural and functional states, including those that can affect brain processes, thus contributing to AD development. The following review will explore the impact of p53 PTMs on its function and consequential involvement in AD pathogenesis. The greater understanding of the role of p53 in the pathogenesis of AD could result in more targeted therapies benefiting the many patients of this debilitating disease.

Amyloid-β Induces Cdh1-Mediated Rock2 Stabilization Causing Neurodegeneration

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline, which is causally related to the accumulation of abnormally folded amyloid-β (Aβ) peptide and hyperphosphorylated tau protein aggregates. The dendritic spine regulator Rho protein kinase 2 (Rock2) accumulates in the brain at the earliest stages of AD and remains increased during disease progression. However, the molecular mechanism that upregulates Rock2 in AD, and its role in the disease progression, are unknown. Here, we found that oligomers of the amyloidogenic fragment 25–35 of the Aβ peptide (Aβ25-35) trigger Rock2 accumulation and activation in mouse cortical neurons in primary culture and in mouse hippocampus in vivo. Neuronal apoptotic death and memory impairment caused by Aβ25-35 administration were rescued by genetic and pharmacological inhibition of Rock2 activity. Mechanistically, Aβ25-35 elicited cyclin dependent kinase-5 (Cdk5)-mediated phosphorylation of Cdh1, a cofactor that is essential for the activity of the E3 ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C) in neurons. Notably, phosphorylated Cdh1 was disassembled from the APC/C complex, causing its inactivation and subsequent Rock2 protein stabilization and activation. Moreover, Aβ25-35-induced neuronal apoptosis was prevented by expressing a phosphodefective form of Cdh1, but not by a phosphomimetic Cdh1. Finally, Cdh1 inactivation, using both genetic and pharmacological approaches, enhanced Aβ25-35-mediated neuronal death through a mechanism that was prevented by inhibition of Rock2 activity. These results indicate that the Cdk5-Cdh1 signaling pathway accounts for the increased Rock2 activity by amyloidogenic Aβ peptides and that this mechanism may contribute to neurodegeneration and memory loss in AD.

Neuroproteomics Chip-Based Mass Spectrometry and Other Techniques for Alzheimer´S Disease Biomarkers – Update

Background:

Alzheimer's disease (AD) is a progressive neurodegenerative disease of growing interest given that there is cognitive damage and symptom onset acceleration. Therefore, it is important to find AD biomarkers for early diagnosis, disease progression, and discrimination of AD and other diseases.

Objective:

To update the relevance of mass spectrometry for the identification of peptides and proteins involved in AD useful as discriminating biomarkers.

Methods:

Proteomics and peptidomics technologies that show the highest possible specificity and selectivity for AD biomarkers are analyzed, together with the biological fluids used. In addition to positron emission tomography and magnetic resonance imaging, MALDI-TOF mass spectrometry is widely used to identify proteins and peptides involved in AD. The use of protein chips in SELDI technology and electroblotting chips for peptides makes feasible small amounts (L) of samples for analysis.

Results:

Suitable biomarkers are related to AD pathology, such as intracellular neurofibrillary tangles; extraneuronal senile plaques; neuronal and axonal degeneration; inflammation and oxidative stress. Recently, peptides were added to the candidate list, which are not amyloid-b or tau fragments, but are related to coagulation, brain plasticity, and complement/neuroinflammation systems involving the neurovascular unit.

Conclusion:

The progress made in the application of mass spectrometry and recent chip techniques is promising for discriminating between AD, mild cognitive impairment, and matched healthy controls. The application of this technique to blood samples from patients with AD has shown to be less invasive and fast enough to determine the diagnosis, stage of the disease, prognosis, and follow-up of the therapeutic response.

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.

Brain-Penetration and Neuron-Targeting DNA Nanoflowers Co-Delivering miR-124 and Rutin for Synergistic Therapy of Alzheimer's Disease

Alzheimer disease (AD) is the leading cause of dementia that affects millions of old people. Despite significant advances in the understanding of AD pathobiology, no disease modifying treatment is available. MicroRNA-124 (miR-124) is the most abundant miRNA in the normal brain with great potency to ameliorate AD-like pathology, while it is deficient in AD brain. Herein, the authors develop a DNA nanoflowers (DFs)-based delivery system to realize exogenous supplementation of miR-124 for AD therapy. The DFs with well-controlled size and morphology are prepared, and a miR-124 chimera is attached via hybridization. The DFs are further modified with RVG29 peptide to simultaneously realize brain-blood barrier (BBB) penetration and neuron targeting. Meanwhile, Rutin, a small molecular ancillary drug, is co-loaded into the DFs structure via its intercalation into the double stranded DNA region. Interestingly, Rutin could synergize miR-124 to suppress the expression of both BACE1 and APP, thus achieving a robust inhibition of amyloid β generation. The nanosystem could pro-long miR-124 circulation in vivo, promote its BBB penetration and neuron targeting, resulting in a significant increase of miR-124 in the hippocampus of APP/PS1 mice and robust therapeutic efficacy in vivo. Such a bio-derived therapeutic system shows promise as a biocompatible nanomedicine for AD therapy.

Dysmetabolism and Neurodegeneration: Trick or Treat?

Accumulating evidence suggests the existence of a strong link between metabolic syndrome and neurodegeneration. Indeed, epidemiologic studies have described solid associations between metabolic syndrome and neurodegeneration, whereas animal models contributed for the clarification of the mechanistic underlying the complex relationships between these conditions, having the development of an insulin resistance state a pivotal role in this relationship. Herein, we review in a concise manner the association between metabolic syndrome and neurodegeneration. We start by providing concepts regarding the role of insulin and insulin signaling pathways as well as the pathophysiological mechanisms that are in the genesis of metabolic diseases. Then, we focus on the role of insulin in the brain, with special attention to its function in the regulation of brain glucose metabolism, feeding, and cognition. Moreover, we extensively report on the association between neurodegeneration and metabolic diseases, with a particular emphasis on the evidence observed in animal models of dysmetabolism induced by hypercaloric diets. We also debate on strategies to prevent and/or delay neurodegeneration through the normalization of whole-body glucose homeostasis, particularly via the modulation of the carotid bodies, organs known to be key in connecting the periphery with the brain.

Alzheimer's Disease: Key Insights from Two Decades of Clinical Trial Failures

Given the acknowledged lack of success in Alzheimer’s disease (AD) drug development over the past two decades, the objective of this review was to derive key insights from the myriad failures to inform future drug development. A systematic and exhaustive review was performed on all failed AD compounds for dementia (interventional phase II and III clinical trials from ClinicalTrials.gov) from 2004 to the present. Starting with the initial ∼2,700 AD clinical trials, ∼550 trials met our initial criteria, from which 98 unique phase II and III compounds with various mechanisms of action met our criteria of a failed compound. The two recent reported phase III successes of aducanumab and oligomannate are very encouraging; however, we are awaiting real-world validation of their effectiveness. These two successes against the 98 failures gives a 2.0% phase II and III success rate since 2003, when the previous novel compound was approved. Potential contributing methodological factors for the clinical trial failures were categorized into 1) insufficient evidence to initiate the pivotal trials, and 2) pivotal trial design shortcomings. Our evaluation found that rational drug development principles were not always followed for AD therapeutics development, and the question remains whether some of the failed compounds may have shown efficacy if the principles were better adhered to. Several recommendations are made for future AD therapeutic development. The whole database of the 98 failed compounds is presented in the Supplementary Material.

Commercial and Instant Coffees Effectively Lower Aβ1-40 and Aβ1-42 in N2a/APPswe Cells

Background

Alzheimer's disease (AD) is a multifactorial neurological disease with neurofibrillary tangles and neuritic plaques as histopathological markers. Due to this, although AD is the leading cause of dementia worldwide, clinical AD dementia cannot be certainly diagnosed until neuropathological post-mortem evaluation. Coffee has been reported to have neurologically protective factors, particularly against AD, but coffee brand and type have not been taken into consideration in previous studies. We examined the discrepancies among popular commercial and instant coffees in limiting the development and progression through Aβ1-40 and Aβ1-42 production, and hypothesized that coffee consumption, regardless of brand or type, is beneficial for stalling the progression and development of Aβ-related AD.

Methods

Coffee samples from four commercial coffee brands and four instant coffees were purchased or prepared following given instructions and filtered for the study. 5, 2.5, and 1.25% concentrations of each coffee were used to treat N2a/APPswe cell lines. MTT assay was used to assess cell viability for coffee concentrations, as well as pure caffeine concentrations. Sandwich ELISA assay was used to determine Aβ concentration for Aβ1-40 and Aβ1-42 peptides of coffee-treated cells.

Results

Caffeine concentrations were significantly varied among all coffees (DC vs. MDC, PC, SB, NIN, MIN p < 0.05). There was no correlation between caffeine concentration and cell toxicity among brands and types of coffee, with no toxicity at 0.5 mg/ml caffeine and lower. Most coffees were toxic to N2a/APPswe cells at 5% (p < 0.05), but not at 2.5%. Most coffees at a 2.5% concentration reduced Aβ1-40 and Aβ1-42 production, with comparable results between commercial and instant coffees.

Conclusion

All coffees tested have beneficial health effects for AD through lowering Aβ1-40 and Aβ1-42 production, with Dunkin' Donuts® medium roast coffee demonstrating the most consistent and optimal cell survival rates and Aβ concentration. On the other hand, Starbucks® coffee exhibited the highest cell toxicity rates among the tested coffees.

Diagnostic Accuracy of Blood-Based Biomarker Panels: A Systematic Review

Background

Because of high prevalence of Alzheimer's disease (AD) in low- and middle-income countries (LMICs), there is an urgent need for inexpensive and minimally invasive diagnostic tests to detect biomarkers in the earliest and asymptomatic stages of the disease. Blood-based biomarkers are predicted to have the most impact for use as a screening tool and predict the onset of AD, especially in LMICs. Furthermore, it has been suggested that panels of markers may perform better than single protein candidates.

Methods

Medline/Pubmed was searched to identify current relevant studies published from January 2016 to December 2020. We included all full-text articles examining blood-based biomarkers as a set of protein markers or panels to aid in AD's early diagnosis, prognosis, and characterization.

Results

Seventy-six articles met the inclusion criteria for systematic review. Majority of the studies reported plasma and serum as the main source for biomarker determination in blood. Protein-based biomarker panels were reported to aid in AD diagnosis and prognosis with better accuracy than individual biomarkers. Conventional (amyloid-beta and tau) and neuroinflammatory biomarkers, such as amyloid beta-42, amyloid beta-40, total tau, phosphorylated tau-181, and other tau isoforms, were the most represented. We found the combination of amyloid beta-42/amyloid beta-40 ratio and APOEε4 status to be most represented with high accuracy for predicting amyloid beta-positron emission tomography status.

Conclusion

Assessment of Alzheimer's disease biomarkers in blood as a non-invasive and cost-effective alternative will potentially contribute to early diagnosis and improvement of therapeutic interventions. Given the heterogeneous nature of AD, combination of markers seems to perform better in the diagnosis and prognosis of the disease than individual biomarkers.

Drosophila Model for Studying Gut Microbiota in Behaviors and Neurodegenerative Diseases

Mounting evidence indicates that the gut microbiota is linked to several physiological processes and disease development in mammals; however, the underlying mechanisms remained unexplored mostly due to the complexity of the mammalian gut microbiome. The fruit fly, Drosophila melanogaster, is a valuable animal model for studying host-gut microbiota interactions in translational aspects. The availability of powerful genetic tools and resources in Drosophila allowed the scientists to unravel the mechanisms by which the gut microbes affect fitness, health, and behavior of their hosts. Drosophila models have been extensively used not only to study animal behaviors (i.e., courtship, aggression, sleep, and learning & memory), but also some human related neurodegenerative diseases (i.e., Alzheimer’s disease and Parkinson’s disease) in the past. This review comprehensively summarizes the current understanding of the gut microbiota of Drosophila and its impact on fly behavior, physiology, and neurodegenerative diseases.

The Multifaceted Role of Neuroprotective Plants in Alzheimer’s Disease Treatment

Alzheimer’s disease (AD) is an age-related, progressive neurodegenerative disorder characterized by impaired cognition, memory loss, and altered personality. Many of the available pharmaceutical treatments do not alter the onset of disease progression. Recently, alternatives to developed drug candidates have been explored including medicinal plants and herbal treatments for the treatment of AD. This article examines the role of herbal plant extracts and the neuroprotective effects as alternative modes of intervention for AD progression. These extracts contain key metabolites that culminate alterations in AD progression. The traditional plant extracts explored in this article induce a variety of beneficial properties, including antioxidants, anti-inflammatory, and enhanced cognition, while also inducing activity on AD drug targets such as Aβ degradation. While these neuroprotective aspects for AD are relatively recent, there is great potential in the drug discovery aspect of these plant extracts for future use in AD treatment.

Sporadic Alzheimer's Disease- and Neurotoxicity-Related microRNAs Affecting Key Events of Tau-Driven Adverse Outcome Pathway Toward Memory Loss

BACKGROUND

A complex network of aging-related homeostatic pathways that are sensitive to further deterioration in the presence of genetic, systemic, and environmental risk factors, and lifestyle, is implicated in the pathogenesis of progressive neurodegenerative diseases, such as sporadic (late-onset) Alzheimer's disease (sAD).

OBJECTIVE

Since sAD pathology and neurotoxicity share microRNAs (miRs) regulating common as well as overlapping pathological processes, environmental neurotoxic compounds are hypothesized to exert a risk for sAD initiation and progression.

METHODS

Literature search for miRs associated with human sAD and environmental neurotoxic compounds was conducted. Functional miR analysis using PathDip was performed to create miR-target interaction networks.

RESULTS

The identified miRs were successfully linked to the hypothetical starting point and key events of the earlier proposed tau-driven adverse outcome pathway toward memory loss. Functional miR analysis confirmed most of the findings retrieved from literature and revealed some interesting findings. The analysis identified 40 miRs involved in both sAD and neurotoxicity that dysregulated processes governing the plausible adverse outcome pathway for memory loss.

CONCLUSION

Creating miR-target interaction networks related to pathological processes involved in sAD initiation and progression, and environmental chemical-induced neurotoxicity, respectively, provided overlapping miR-target interaction networks. This overlap offered an opportunity to create an alternative picture of the mechanisms underlying sAD initiation and early progression. Looking at initiation and progression of sAD from this new angle may open for new biomarkers and novel drug targets for sAD before the appearance of the first clinical symptoms.

Recent Advancements in Strategies for Abnormal Protein Clearance in Alzheimer's Disease

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Alzheimer's disease (AD) is a intricate neurodegenerative disease with chronic and progressive development whose typical neuropathological features encompasses senile plaques and neurofibrillary tangles respectively formed by the extracellular deposition of amyloid-beta (Aβ) and the intracellular accumulation of hyperphosphorylated tau protein in the brain, particularly in limbic and cortical regions. The pathological changes are considered to be caused by the loss of Aβ and tau protein clearance mechanisms under pathological conditions, which leads to an imbalance between the rates of clearance and production. Consequently, the main strategies for treating AD aim to reduce the production of Aβ and hyperphosphorylated tau protein in the brain, inhibit their accumulation, or accelerate their clearance. Although drugs utilizing these therapeutic strategies have been studied successively, their therapeutic effects have generally been less than ideal. Fortunately, recent advances have been made in clearance strategies for these abnormally expressed proteins, including immunotherapies and nanomedicines targeting Aβ or tau, which could represent an important breakthrough for treating AD. Here, we review recent development of the strategies for the removal of abnormal proteins and provide new ideas and methods for treating AD.

Pathogenesis of sporadic Alzheimer's disease by deficiency of NMDA receptor subunit GluN3A

The Ca²⁺ hypothesis for Alzheimer's disease (AD) conceives Ca²⁺ dyshomeostasis as a common mechanism of AD; the cause of Ca²⁺ dysregulation, however, is obscure. Meanwhile, hyperactivities of N-Methyl-D-aspartate receptors (NMDARs), the primary mediator of Ca²⁺ influx, are reported in AD. GluN3A (NR3A) is an NMDAR inhibitory subunit. We hypothesize that GluN3A is critical for sustained Ca²⁺ homeostasis and its deficiency is pathogenic for AD. Cellular, molecular, and functional changes were examined in adult/aging GluN3A knockout (KO) mice. The GluN3A KO mouse brain displayed age-dependent moderate but persistent neuronal hyperactivity, elevated intracellular Ca²⁺ , neuroinflammation, impaired synaptic integrity/plasticity, and neuronal loss. GluN3A KO mice developed olfactory dysfunction followed by psychological/cognitive deficits prior to amyloid-β/tau pathology. Memantine at preclinical stage prevented/attenuated AD syndromes. AD patients' brains show reduced GluN3A expression. We propose that chronic "degenerative excitotoxicity" leads to sporadic AD, while GluN3A represents a primary pathogenic factor, an early biomarker, and an amyloid-independent therapeutic target.

Decoding Conformational Imprint of Convoluted Molecular Interactions Between Prenylflavonoids and Aggregated Amyloid-Beta42 Peptide Causing Alzheimer's Disease

Protein misfolding occurs due to the loss of native protein structure and adopts an abnormal structure, wherein the misfolded proteins accumulate and form aggregates, which result in the formation of amyloid fibrils that are associated with neurodegenerative diseases. Amyloid beta (Aβ42) aggregation or amyloidosis is contemplated as a unique hallmark characteristic of Alzheimer’s disease (AD). Due to aberrant accrual and aggregation of Aβ42 in extracellular space, the formation of senile plaques is found in AD patients. These senile plaques occur usually in the cognitive and memory region of the brain, enfeebles neurodegeneration, hinders the signaling between synapse, and disrupts neuronal functioning. In recent years, herbal compounds are identified and characterized for their potential as Aβ42 inhibitors. Thus, understanding their structure and molecular mechanics can provide an incredible finding in AD therapeutics. To describe the structure-based molecular studies in the rational designing of drugs against amyloid fibrils, we examined various herbal compounds that belong to prenylflavonoids. The present study characterizes the trends we identified at molecular docking studies and dynamics simulation where we observed stronger binding orientation of bavachalcone, bavachin, and neobavaisoflavone with the amyloid-beta (Aβ42) fibril structure. Hence, we could postulate that these herbal compounds could be potential inhibitors of Aβ42 fibrils; these anti-aggregation agents need to be considered in treating AD.

Disrupting Neurons and Glial Cells Oneness in the Brain-The Possible Causal Role of Herpes Simplex Virus Type 1 (HSV-1) in Alzheimer's Disease

Current data strongly suggest herpes simplex virus type 1 (HSV-1) infection in the brain as a contributing factor to Alzheimer's disease (AD). The consequences of HSV-1 brain infection are multilateral, not only are neurons and glial cells damaged, but modifications also occur in their environment, preventing the transmission of signals and fulfillment of homeostatic and immune functions, which can greatly contribute to the development of disease. In this review, we discuss the pathological alterations in the central nervous system (CNS) cells that occur, following HSV-1 infection. We describe the changes in neurons, astrocytes, microglia, and oligodendrocytes related to the production of inflammatory factors, transition of glial cells into a reactive state, oxidative damage, Aβ secretion, tau hyperphosphorylation, apoptosis, and autophagy. Further, HSV-1 infection can affect processes observed during brain aging, and advanced age favors HSV-1 reactivation as well as the entry of the virus into the brain. The host activates pattern recognition receptors (PRRs) for an effective antiviral response during HSV-1 brain infection, which primarily engages type I interferons (IFNs). Future studies regarding the influence of innate immune deficits on AD development, as well as supporting the neuroprotective properties of glial cells, would reveal valuable information on how to harness cytotoxic inflammatory milieu to counter AD initiation and progression.

Association of CSF Aβ38 Levels With Risk of Alzheimer Disease-Related Decline

OBJECTIVE

Experimental studies suggest that the balance between short and long Aβ species might modulate the toxic effects of Aβ in Alzheimer's disease (AD) but clinical evidence is lacking. We studied whether Aβ38 levels in cerebrospinal fluid (CSF) relate to risk of AD dementia and cognitive decline.

METHODS

CSF Aβ38 levels were measured in 656 individuals across two clinical cohorts - the Swedish BioFINDER study and the Alzheimer's Disease Neuroimaging Initiative (ADNI). Cox regression models were used to evaluate the association between baseline Aβ38 levels and risk of AD dementia in AD-biomarker positive individuals (AD+; determined by CSF P-tau/Aβ42 ratio) with subjective cognitive decline (SCD) or mild cognitive impairment (MCI). Linear mixed effects models were used to evaluate the association between baseline Aβ38 levels and cognitive decline as measured by the Mini-Mental State Examination (MMSE) in AD+ participants with SCD, MCI or AD dementia.

RESULTS

In the BioFINDER cohort, high Aβ38 levels were associated with slower decline in MMSE (β = 0.30 points / sd., P = 0.001) and with lower risk of conversion to AD dementia (HR = 0.83 per sd., P = 0.03). In the ADNI cohort, higher Aβ38 levels were associated with less decline in MMSE (β = 0.27, P = 0.01), but not risk of conversion to AD dementia (P = 0.66). Aβ38 levels in both cohorts were significantly associated with both cognitive and clinical outcomes when further adjusted for CSF P-tau or CSF Aβ42 levels.

INTERPRETATION

Higher CSF Aβ38 levels are associated with lower risk of AD-related changes in two independent clinical cohorts. These findings suggest that γ-secretase modulators could be effective as disease-altering therapy.

Prostaglandin EP2 receptor antagonist ameliorates neuroinflammation in a two-hit mouse model of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) causes substantial medical and societal burden with no therapies ameliorating cognitive deficits. Centralized pathologies involving amyloids, neurofibrillary tangles, and neuroinflammatory pathways are being investigated to identify disease-modifying targets for AD. Cyclooxygenase-2 (COX-2) is one of the potential neuroinflammatory agents involved in AD progression. However, chronic use of COX-2 inhibitors in patients produced adverse cardiovascular effects. We asked whether inhibition of EP2 receptors, downstream of the COX-2 signaling pathway, can ameliorate neuroinflammation in AD brains in presence or absence of a secondary inflammatory stimuli.

METHODS

We treated 5xFAD mice and their non-transgenic (nTg) littermates in presence or absence of lipopolysaccharide (LPS) with an EP2 antagonist (TG11-77.HCl). In cohort 1, nTg (no-hit) or 5xFAD (single-hit-genetic) mice were treated with vehicle or TG11-77.HCl for 12 weeks. In cohort 2, nTg (single-hit-environmental) and 5xFAD mice (two-hit) were administered LPS (0.5 mg/kg/week) and treated with vehicle or TG11-77.HCl for 8 weeks.

RESULTS

Complete blood count analysis showed that LPS induced anemia of inflammation in both groups in cohort 2. There was no adverse effect of LPS or EP2 antagonist on body weight throughout the treatment. In the neocortex isolated from the two-hit cohort of females, but not males, the elevated mRNA levels of proinflammatory mediators (IL-1β, TNF, IL-6, CCL2, EP2), glial markers (IBA1, GFAP, CD11b, S110B), and glial proteins were significantly reduced by EP2 antagonist treatment. Intriguingly, the EP2 antagonist had no effect on either of the single-hit cohorts. There was a modest increase in amyloid-plaque deposition upon EP2 antagonist treatment in the two-hit female brains, but not in the single-hit genetic female cohort.

CONCLUSION

These results reveal a potential neuroinflammatory role for EP2 in the two-hit 5xFAD mouse model. A selective EP2 antagonist reduces inflammation only in female AD mice subjected to a second inflammatory insult.

A potential biomarker of preclinical Alzheimer's disease: The olfactory dysfunction and its pathogenesis-based neural circuitry impairments

The olfactory dysfunction can signal and act as a potential biomarker of preclinical AD. However, the precise regulatory mechanism of olfactory function on the neural pathogenesis of AD is still unclear. The impairment of neural networks in olfaction system has been shown to be tightly associated with AD. As key brain regions of the olfactory system, the olfactory bulb (OB) and the piriform cortex (PCx) have a profound influence on the olfactory function. Therefore, this review will explore the mechanism of olfactory dysfunction in preclinical AD in the perspective of abnormal neural networks in the OB and PCx and their associated brain regions, especially from two aspects of aberrant oscillations and synaptic plasticity damages, which help better understand the underlying mechanism of olfactory neural network damages related to 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.