The Roles of the Amyloid Beta Monomers in Physiological and Pathological Conditions

Delving into the crucial role of the initial structure in the dynamic and self-assembly of amyloid beta

Alzheimer's disease involves the accumulation of amyloid beta (Aβ) monomers that form oligomers and fibrils in the brain. Studying the Aβ monomer is critical for understanding Aβ assembly and peptide behavior and has implications for drug design. Choosing a starting structure with a higher aggregation tendency for cost-effective MD studies and drug design is crucial. Previous studies have utilized distinct initial conformations, leading to varying results. Hence, this study was conducted to compare different initial conformations using the same MD simulation protocol to investigate the behavior and oligomerization propensity of different starting structures of Aβ during 1μs. The behavior of the monomers and their self-assembly systems were studied thoroughly, and the results revealed that highly helical Aβ monomers which used as starting structures retain high helix content during the simulation, and their tautomerization states did not cause significant changes in the structure. On the other hand, the Aβ extended and S-shaped monomers displayed the fingerprints of the fibril structure, which is believed to be more favorable for self-assembly. Self-assembly behaviors were seen for three S-shaped and three Aβ extended peptides. However, both conformations did not show stable β-sheet intermolecular interaction. For the Aβ16-22 monomer as a fragment of the Aβ that can assemble into fibrils, the impacts of capping and uncapping on the initial structure were also investigated. The results displayed that capped and uncapped structures can form oligomers with β-sheet at termini. However, in the capped state, β-sheet interactions were more stable and remained relatively longer than uncapped.

Conformationally adaptive therapeutic peptides for diseases caused by intrinsically disordered proteins (IDPs). New paradigm for drug discovery: Target the target, not the arrow

The traditional model of protein structure determined by the amino acid sequence is today seriously challenged by the fact that approximately half of the human proteome is made up of proteins that do not have a stable 3D structure, either partially or in totality. These proteins, called intrinsically disordered proteins (IDPs), are involved in numerous physiological functions and are associated with severe pathologies, e.g. Alzheimer, Parkinson, Creutzfeldt-Jakob, amyotrophic lateral sclerosis (ALS), and type 2 diabetes. Targeting these proteins is challenging for two reasons: i) we need to preserve their physiological functions, and ii) drug design by molecular docking is not possible due to the lack of reliable starting conditions. Faced with this challenge, the solutions proposed by artificial intelligence (AI) such as AlphaFold are clearly unsuitable. Instead, we suggest an innovative approach consisting of mimicking, in short synthetic peptides, the conformational flexibility of IDPs. These peptides, which we call adaptive peptides, are derived from the domains of IDPs that become structured after interacting with a ligand. Adaptive peptides are designed with the aim of selectively antagonizing the harmful effects of IDPs, without targeting them directly but through selected ligands, without affecting their physiological properties. This "target the target, not the arrow" strategy is promised to open a new route to drug discovery for currently undruggable proteins.

Alzheimer's Disease: Exploring Pathophysiological Hypotheses and the Role of Machine Learning in Drug Discovery

Alzheimer's disease (AD) is a major neurodegenerative dementia, with its complex pathophysiology challenging current treatments. Recent advancements have shifted the focus from the traditionally dominant amyloid hypothesis toward a multifactorial understanding of the disease. Emerging evidence suggests that while amyloid-beta (Aβ) accumulation is central to AD, it may not be the primary driver but rather part of a broader pathogenic process. Novel hypotheses have been proposed, including the role of tau protein abnormalities, mitochondrial dysfunction, and chronic neuroinflammation. Additionally, the gut-brain axis and epigenetic modifications have gained attention as potential contributors to AD progression. The limitations of existing therapies underscore the need for innovative strategies. This study explores the integration of machine learning (ML) in drug discovery to accelerate the identification of novel targets and drug candidates. ML offers the ability to navigate AD's complexity, enabling rapid analysis of extensive datasets and optimizing clinical trial design. The synergy between these themes presents a promising future for more effective AD treatments.

Therapeutic potential of chrysin in regulation of interleukin-17 signaling in a repeated intranasal amyloid-beta-induced Alzheimer's disease model

Objective: The aim of the current study was to study the therapeutic potential of chrysin against repeated intranasal amyloid-beta (Aβ)-induced interleukin-17 (IL-17) signaling in a mouse model of AD. Methods: Male BALB/c mice were daily exposed to intranasal Aβ1-42 (10 μg/10 μL) for seven consecutive days. Chrysin was orally administered at doses of 25, 50 and 100 mg kg-1 in 0.5% sodium carboxy methyl cellulose suspension from day 5 of Aβ1-42 administration for seven days. Following the treatment, the memory of the animals was appraised using Morris water maze, novel object recognition and passive avoidance tests. Further, the effects of chrysin on Aβ1-42-induced IL-17 signaling and redox levels were evaluated in the cortex and hippocampus regions of the mouse brain through western blot and immunohistochemistry. Results: The exposure to Aβ1-42 through the intranasal route induced a significant decline in the spatial, learning and cognitive memory of the animals, and most interestingly, exposure to Aβ1-42 triggered IL-17-mediated signaling, which resulted in a significant increase in the expression of IL-17RA, Act1 and TRAF6. Furthermore, Aβ1-42 impaired the tissue redox level and inflammatory cytokines in the mouse brain. Alternatively, treatment with chrysin at 25, 50 and 100 mg kg-1 oral doses alleviated Aβ1-42-mediated memory decline, impaired redox levels and inflammation. Specifically, chrysin downregulated the expression of IL-17 and mediated signaling in the brain regions of the mice. Conclusion: Chrysin was evidenced to be a potent antioxidant and anti-inflammatory agent, clearly showing a protective role against Aβ1-42-induced IL-17-mediated inflammation in the brain of the mice.

The effects of nitric oxide in Alzheimer's disease

Alzheimer's disease (AD), the most prevalent cause of dementia, is a progressive neurodegenerative condition that commences subtly and inexorably worsens over time. Despite considerable research, a specific drug that can fully cure or effectively halt the progression of AD remains elusive. Nitric oxide (NO), a crucial signaling molecule in the nervous system, is intimately associated with hallmark pathological changes in AD, such as amyloid-beta deposition and tau phosphorylation. Several therapeutic strategies for AD operate through the nitric oxide synthase/NO system. However, the potential neurotoxicity of NO introduces an element of controversy regarding its therapeutic utility in AD. This review focuses on research findings concerning NO's role in experimental AD and its underlying mechanisms. Furthermore, we have proposed directions for future research based on our current comprehension of this critical area.

Nose to brain strategy coupled to nano vesicular system for natural products delivery: Focus on synaptic plasticity in Alzheimer's disease

A wide number of natural molecules demonstrated neuroprotective effects on synaptic plasticity defects induced by amyloid-β (Aβ) in ex vivo and in vivo Alzheimer's disease (AD) models, suggesting a possible use in the treatment of this neurodegenerative disorder. However, several compounds, administered parenterally and orally, are unable to reach the brain due to the presence of the blood-brain barrier (BBB) which prevents the passage of external substances, such as proteins, peptides, or phytocompounds, representing a limit to the development of treatment for neurodegenerative diseases, such as AD. The combination of nano vesicular systems, as colloidal systems, and nose to brain (NtB) delivery depicts a new nanotechnological strategy to overtake this limit and to develop new treatment approaches for brain diseases, including the use of natural molecules in combination therapy for AD. Herein, we will provide an updated overview, examining the literature of the last 20 years and using specific keywords that provide evidence on natural products with the ability to restore synaptic plasticity alterations in AD models, and the possible application using safe and non-invasive strategies focusing on nano vesicular systems for NtB delivery.

Reversibility of cognitive worsening observed with BACE inhibitor umibecestat in the Alzheimer's Prevention Initiative (API) Generation Studies

INTRODUCTION

The Alzheimer's Prevention Initiative (API) Generation Studies evaluated the BACE inhibitor umibecestat for Alzheimer's disease (AD) prevention. The studies were terminated early, and the reversibility of umibecestat's side effects was assessed.

METHODS

Cognitively unimpaired 60- to 75-year-old apolipoprotein E (APOE) ε4 homozygotes and heterozygotes (the latter with elevated brain amyloid deposition) (n = 1556) received umibecestat (50 or 15 mg daily) or placebo for 7 months on average and were followed for a median (interquartile range) of 4 (3 to 6) months after washout.

RESULTS

Compared to placebo, umibecestat-treated participants had small, non-progressive, but statistically significant decline in performance on certain cognitive batteries including Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and API Preclinical Composite Cognitive test, but not Clinical Dementia Rating-Sum of Boxes. RBANS differences were no longer significant at the end of follow-up.

DISCUSSION

In people at genetic risk for AD, high-dose beta-site amyloid precursor protein cleaving enzyme (BACE) inhibition was associated with early mild cognitive worsening, which reversed shortly after washout, suggesting a symptomatic side effect not associated with neurodegeneration. Fully anonymized data, images, and samples are available upon request for further research on BACE inhibition.

HIGHLIGHTS

This is the first trial with blinded assessment of reversibility of BACE inhibitor side effects. Umibecestat was tested in cognitively unimpaired persons at genetic risk for AD. Umibecestat led to early mild cognitive decline that reversed shortly after washout. This suggests a potentially manageable effect not associated with neurodegeneration. Further research may determine the future of BACE inhibition in AD prevention.

The relationship between adult hippocampal neurogenesis and cognitive impairment in Alzheimer's disease

Neurogenesis persists throughout adulthood in the hippocampus and contributes to specific cognitive functions. In Alzheimer's disease (AD), the hippocampus is affected by pathology and functional impairment early in the disease. Human AD patients have reduced adult hippocampal neurogenesis (AHN) levels compared to age-matched healthy controls. Similarly, rodent AD models show a decrease in AHN before the onset of the classical hallmarks of AD pathology. Conversely, enhancement of AHN can protect against AD pathology and ameliorate memory deficits in both rodents and humans. Therefore, impaired AHN may be a contributing factor of AD-associated cognitive decline, rather than an effect of it. In this review we outline the regulation and function of AHN in healthy individuals, and highlight the relationship between AHN dysfunction and cognitive impairments in AD. The existence of AHN in humans and its relevance in AD patients will also be discussed, with an outlook toward future research directions. HIGHLIGHTS: Adult hippocampal neurogenesis occurs in the brains of mammals including humans. Adult hippocampal neurogenesis is reduced in Alzheimer's disease in humans and animal models.

Strategies for measuring concentrations and forms of amyloid-β peptides

Alzheimer's disease (AD) is affecting more and more people worldwide without the effective treatment, while the existed pathological mechanism has been confirmed barely useful in the treatment. Amyloid-β peptide (Aβ), a main component of senile plaque, is regarded as the most promising target in AD treatment. Aβ clearance from AD brain seems to be a reliably therapeutic strategy, as the two exited drugs, GV-971 and aducanumab, are both developed based on it. However, doubt still exists. To exhaustive expound on the pathological mechanism of Aβ, rigorous analyses on the concentrations and aggregation forms are essential. Thus, it is attracting broad attention these years. However, most of the sensors have not been used in pathological studies, as the lack of the bridge between analytical chemist and pathologists. In this review, we made a brief introduce on Aβ-related pathological mechanism included in β-amyloid hypothesis to elucidate the detection conditions of sensor methods. Furthermore, a summary of the sensor methods was made, which were based on Aβ concentrations and form detections that have been developed in the past 10 years. As the greatest number of the sensors were built on fluorescent spectroscopy, electrochemistry, and Roman spectroscopy, detailed elucidation on them was made. Notably, the aggregation process is another important factor in revealing the progress of AD and developing the treatment methods, so the sensors on monitoring Aβ aggregation processes were also summarized.

Diversity of amyloid beta peptide actions

Fibril formation by amyloidogenic proteins and peptides is considered the cause of a number of incurable diseases. One of the most known amyloid diseases is Alzheimer's disease (AD). Traditionally, amyloidogenic beta peptides Aβ40 and Aβ42 (Aβs) are considered as main causes of AD and the foremost targets in AD fight. The main efforts in pharmacology are aimed at reducing Aβs concentration to prevent their accumulation, aggregation, formation of senile plaques, neuronal death, and neurodegeneration. However, a number of publications have demonstrated certain beneficial physiological effects of Aβs. Simultaneously, it is indicated that the effects of Aβs turn into pathological due to the development of certain diseases in the body. The accumulation of C- and N-terminal truncated Aβs under diverse conditions is supposed to play a role in AD development. The significance of transformation of glutamate residue at positions 3 or 11 of Aβs catalyzed by glutaminyl cyclase making them more degradation resistant, hydrophobic, and prone to aggregation, as well as the participation of dipeptidyl peptidase IV in these transformations are discussed. The experimental data presented confirm the maintenance of physiological, nonaggregated state of Aβs by plant preparations. In conclusion, this review suggests that in the fight against AD, instead of removing Aβs, preference should be given to the treatment of common diseases. Glutaminyl cyclase and dipeptidyl peptidase IV can be considered as targets in AD treatment. Flavonoids and plant preparations that possess antiamyloidogenic propensity are proposed as beneficial neuroprotective, anticancer, and antidiabetic food additives.

Ultrasensitive and Multiple Biomarker Discrimination for Alzheimer's Disease via Plasmonic & Microfluidic Sensing Technologies

As the population ages, the worldwide prevalence of Alzheimer's disease (AD) as the most common dementia in the elderly is increasing dramatically. However, a long-term challenge is to achieve rapid and accurate early diagnosis of AD by detecting hallmarks such as amyloid beta (Aβ42). Here, a multi-channel microfluidic-based plasmonic fiber-optic biosensing platform is established for simultaneous detection and differentiation of multiple AD biomarkers. The platform is based on a gold-coated, highly-tilted fiber Bragg grating (TFBG) and a custom-developed microfluidics. TFBG excites a high-density, narrow-cladding-mode spectral comb that overlaps with the broad absorption of surface plasmons for high-precision interrogation, enabling ultrasensitive monitoring of analytes. In situ detection and in-parallel discrimination of different forms of Aβ42 in cerebrospinal fluid (CSF) are successfully demonstrated with a detection of limit in the range of ≈30-170 pg mL-1, which is one order of magnitude below the clinical cut-off level in AD onset, providing high detection sensitivity for early diagnosis of AD. The integration of the TFBG sensor with multi-channel microfluidics enables simultaneous detection of multiple biomarkers using sub-µL sample volumes, as well as combining initial binding rate and real-time response time to differentiate between multiple biomarkers in terms of binding kinetics. With the advantages of multi-parameter, low consumption, and highly sensitive detection, the sensor represents an urgently needed potentials for large-scale diagnosis of diseases at early stage.

Passive Anti-Amyloid Beta Immunotherapies in Alzheimer's Disease: From Mechanisms to Therapeutic Impact

Alzheimer's disease, the most common type of dementia worldwide, lacks effective disease-modifying therapies despite significant research efforts. Passive anti-amyloid immunotherapies represent a promising avenue for Alzheimer's disease treatment by targeting the amyloid-beta peptide, a key pathological hallmark of the disease. This approach utilizes monoclonal antibodies designed to specifically bind amyloid beta, facilitating its clearance from the brain. This review offers an original and critical analysis of anti-amyloid immunotherapies by exploring several aspects. Firstly, the mechanisms of action of these therapies are reviewed, focusing on their ability to promote Aβ degradation and enhance its efflux from the central nervous system. Subsequently, the extensive history of clinical trials involving anti-amyloid antibodies is presented, from initial efforts using first-generation molecules leading to mixed results to recent clinically approved drugs. Along with undeniable progress, the authors also highlight the pitfalls of this approach to offer a balanced perspective on this topic. Finally, based on its potential and limitations, the future directions of this promising therapeutic strategy for Alzheimer's disease are emphasized.

Specific Binding of Alzheimer's Aβ Peptides to Extracellular Vesicles

Alzheimer's disease (AD) is the fifth leading cause of death among adults aged 65 and older, yet the onset and progression of the disease is poorly understood. What is known is that the presence of amyloid, particularly polymerized Aβ42, defines when people are on the AD continuum. Interestingly, as AD progresses, less Aβ42 is detectable in the plasma, a phenomenon thought to result from Aβ becoming more aggregated in the brain and less Aβ42 and Aβ40 being transported from the brain to the plasma via the CSF. We propose that extracellular vesicles (EVs) play a role in this transport. EVs are found in bodily fluids such as blood, urine, and cerebrospinal fluid and carry diverse "cargos" of bioactive molecules (e.g., proteins, nucleic acids, lipids, metabolites) that dynamically reflect changes in the cells from which they are secreted. While Aβ42 and Aβ40 have been reported to be present in EVs, it is not known whether this interaction is specific for these peptides and thus whether amyloid-carrying EVs play a role in AD and/or serve as brain-specific biomarkers of the AD process. To determine if there is a specific interaction between Aβ and EVs, we used isothermal titration calorimetry (ITC) and discovered that Aβ42 and Aβ40 bind to EVs in a manner that is sequence specific, saturable, and endothermic. In addition, Aβ incubation with EVs overnight yielded larger amounts of bound Aβ peptide that was fibrillar in structure. These findings point to a specific amyloid-EV interaction, a potential role for EVs in the transport of amyloid from the brain to the blood, and a role for this amyloid pool in the AD process.

Amyloid-α Peptide Formed through Alternative Processing of the Amyloid Precursor Protein Attenuates Alzheimer's Amyloid-β Toxicity via Cross-Chaperoning

Amyloid aggregation is a key feature of Alzheimer's disease (AD) and a primary target for past and present therapeutic efforts. Recent research is making it increasingly clear that the heterogeneity of amyloid deposits, extending past the commonly targeted amyloid-β (Aβ), must be considered for successful therapy. We recently demonstrated that amyloid-α (Aα or p3), a C-terminal peptidic fragment of Aβ, aggregates rapidly to form amyloids and can expedite the aggregation of Aβ through seeding. Here, we advance the understanding of Aα biophysics and biology in several important ways. We report the first cryogenic electron microscopy (cryo-EM) structure of an Aα amyloid fibril, proving unambiguously that the peptide is fibrillogenic. We demonstrate that Aα induces Aβ to form amyloid aggregates that are less toxic than pure Aβ aggregates and use nuclear magnetic resonance spectroscopy (NMR) to provide insights into specific interactions between Aα and Aβ in solution. This is the first evidence that Aα can coassemble with Aβ and alter its biological effects at relatively low concentrations. Based on the above, we urge researchers in the field to re-examine the significance of Aα in AD.