The Aβ oligomer hypothesis for synapse failure and memory loss in Alzheimer's disease

Evolution of Alzheimer's Disease Therapeutics: From Conventional Drugs to Medicinal Plants, Immunotherapy, Microbiotherapy and Nanotherapy

Alzheimer's disease (AD) represents an escalating global health crisis, constituting the leading cause of dementia among the elderly and profoundly impairing their quality of life. Current FDA-approved drugs, such as rivastigmine, donepezil, galantamine, and memantine, offer only modest symptomatic relief and are frequently associated with significant adverse effects. Faced with this challenge and in line with advances in the understanding of the pathophysiology of this neurodegenerative condition, various innovative therapeutic strategies have been explored. Here, we review novel approaches inspired by advanced knowledge of the underlying pathophysiological mechanisms of the disease. Among the therapeutic alternatives, immunotherapy stands out, employing monoclonal antibodies to specifically target and eliminate toxic proteins implicated in AD. Additionally, the use of medicinal plants is examined, as their synergistic effects among components may confer neuroprotective properties. The modulation of the gut microbiota is also addressed as a peripheral strategy that could influence neuroinflammatory and degenerative processes in the brain. Furthermore, the therapeutic potential of emerging approaches, such as the use of microRNAs to regulate key cellular processes and nanotherapy, which enables precise drug delivery to the central nervous system, is analyzed. Despite promising advances in these strategies, the incidence of Alzheimer's disease continues to rise. Therefore, it is proposed that achieving effective treatment in the future may require the integration of combined approaches, maximizing the synergistic effects of different therapeutic interventions.

Mitochondria-targeting by small molecules against Alzheimer's disease: A mechanistic perspective

Alzheimer's disease (AD) poses a considerable worldwide health obstacle, marked by gradual cognitive deterioration and neuronal loss. While the molecular mechanisms underlying AD pathology have been elucidated to some extent, therapeutic options remain limited. Mitochondrial dysfunction has become recognized as a significant factor in the development of AD, with oxidative stress and disrupted energy metabolism being critical elements. This review explores the mechanistic aspects of small molecule targeting of mitochondria as a potential therapeutic approach for AD. The review explores the role of mitochondrial dysfunction in AD, including its involvement in the accumulation of β-amyloid plaques and neurofibrillary tangles, synaptic dysfunction, and neuronal death. Furthermore, the effects of oxidative stress on mitochondrial function were investigated, including the resulting damage to mitochondrial components. Mitochondrial-targeted therapies have attracted attention for their potential to restore mitochondrial function and reduce AD pathology. The review outlines the latest preclinical and clinical evidence supporting the effectiveness of small molecules in targeting mitochondrial dysfunction in AD. Additionally, it discusses the molecular pathways involved in mitochondrial dysfunction and examines how small molecules can intervene to address these abnormalities. By providing a comprehensive overview of the latest research in this field, this review aims to shed light on the therapeutic potential of small molecule targeting of mitochondria in AD and stimulate further research in this promising area of drug development.

Proteomic insights into early-stage Alzheimer's disease: Identifying key neuronal proteins impacted by amyloid beta oligomers in an in vitro model

Alzheimer's disease (AD) remains a pressing global health concern, necessitating comprehensive investigations into its underlying molecular mechanisms. While the late-stage pathophysiology of this disease is well understood, it is crucial to examine the role of amyloid beta oligomers (Aβo), which form in the brain during the early stages of disease development. These toxic oligomers could affect neuronal viability and generate oxidative stress in the brain. In this study, we exposed SHSY-5Y cells to Aβo. The increase in intracellular reactive oxygen species and apoptosis observed in Aβo-treated cells mimics the early stages of AD. Comprehensive proteomic profiling identified 2966 differentially expressed proteins, with 123 significantly modulated. Utilizing the NeuroPro database, we identified 80 confirmed AD-related proteins and 43 novel candidates. Seven AD-related proteins with a NeuroPro score ≥ 5 were shortlisted. Furthermore, these proteins are found to be associated with Aβ plaques in AD brains. VGF, LTF, PARP1, and MAOA have been implicated in various mechanisms underlying AD, including synaptic plasticity, iron homeostasis, DNA repair, and neurotransmitter degradation. Our study also revealed the involvement of less-explored proteins like MYH9, CISD1, and SNRNP70, which play critical roles in cytoskeletal dynamics, mitochondrial function, and RNA splicing, respectively. These findings underscore the complex pathophysiology of AD, highlighting potential biomarkers and therapeutic targets for early intervention. The present study advances the understanding of Aβo-induced oxidative stress and neuronal damage, providing a foundation for future research into early-stage AD diagnosis and subsequent treatment strategies.

Sexual dimorphism, altered hippocampal glutamatergic neurotransmission, and cognitive impairment in APP knock-in mice

BACKGROUND

It is well established that glutamatergic neurotransmission plays an essential role in learning and memory. Previous studies indicate that glutamate dynamics shift with Alzheimer's disease (AD) progression, contributing to negative cognitive outcomes.

OBJECTIVE

In this study, we characterized hippocampal glutamatergic signaling with age and disease progression in a knock-in mouse model of AD (APPNL-F/NL--F).

METHODS

At 2-4 and 18+ months old, male and female APPNL/NL, APPNL-F/NL-F, and C57BL/6 mice underwent cognitive assessment using Morris water maze (MWM) and Novel Object Recognition (NOR). Then, basal and 70 mM KCl stimulus-evoked glutamate release was measured in the dentate gyrus (DG), CA3, and CA1 regions of the hippocampus using a glutamate-selective microelectrode in anesthetized mice.

RESULTS

Glutamate recordings support elevated stimulus-evoked glutamate release in the DG and CA3 of young APPNL-F/NL-F male mice that declined with age compared to age-matched control mice. Young female APPNL-F/NL-F mice exhibited increased glutamate clearance in the CA1 that slowed with age compared to age-matched control mice. Male and female APPNL-F/NL-F mice exhibited decreased CA1 basal glutamate levels, while males also showed depletion in the CA3. Cognitive assessment demonstrated impaired spatial cognition in aged male and female APPNL-F/NL-F mice, but only aged females displayed recognition memory deficits compared to age-matched control mice.

CONCLUSIONS

These findings confirm a sex-dependent hyper-to-hypoactivation glutamatergic paradigm in APPNL-F/NL-F mice. Further, data illustrate a sexually dimorphic biological aging process resulting in a more severe cognitive phenotype for female APPNL-F/NL-F mice than their male counterparts. Research outcomes mirror that of human AD pathology and provide further evidence of divergent AD pathogenesis between sexes.

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

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

A small TAT-TrkB peptide prevents BDNF receptor cleavage and restores synaptic physiology in Alzheimer's disease

In Alzheimer's disease (AD), amyloid β (Aβ)-triggered cleavage of TrkB-FL impairs brain-derived neurotrophic factor (BDNF) signaling, thereby compromising neuronal survival, differentiation, and synaptic transmission and plasticity. Using cerebrospinal fluid and postmortem human brain samples, we show that TrkB-FL cleavage occurs from the early stages of the disease and increases as a function of pathology severity. To explore the therapeutic potential of this disease mechanism, we designed small TAT-fused peptides and screened their ability to prevent TrkB-FL receptor cleavage. Among these, a TAT-TrkB peptide with a lysine-lysine linker prevented TrkB-FL cleavage both in vitro and in vivo and rescued synaptic deficits induced by oligomeric Aβ in hippocampal slices. Furthermore, this TAT-TrkB peptide improved the cognitive performance, ameliorated synaptic plasticity deficits and prevented Tau pathology progression in vivo in the 5XFAD mouse model of AD. No evidence of liver or kidney toxicity was found. We provide proof-of-concept evidence for the efficacy and safety of this therapeutic strategy and anticipate that this TAT-TrkB peptide has the potential to be a disease-modifying drug that can prevent and/or reverse cognitive deficits in patients with AD.

Histone deacetylase inhibition mitigates cognitive deficits and astrocyte dysfunction induced by amyloid-β (Aβ) oligomers

BACKGROUND AND PURPOSE

Inhibitors of histone deacetylases (iHDACs) are promising drugs for neurodegenerative diseases. We have evaluated the therapeutic potential of the new iHDAC LASSBio-1911 in Aβ oligomer (AβO) toxicity models and astrocytes, key players in neuroinflammation and Alzheimer's disease (AD).

EXPERIMENTAL APPROACH

Astrocyte phenotype and synapse density were evaluated by flow cytometry, Western blotting, immunofluorescence and qPCR, in vitro and in mice. Cognitive function was evaluated by behavioural assays using a mouse model of intracerebroventricular infusion of AβO.

KEY RESULTS

LASSBio-1911 modulates reactivity and synaptogenic potential of cultured astrocytes and improves synaptic markers in cultured neurons and in mice. It prevents AβO-triggered astrocytic reactivity in mice and enhances the neuroprotective potential of astrocytes. LASSBio-1911 improves behavioural performance and rescues synaptic and memory function in AβO-infused mice.

CONCLUSION AND IMPLICATIONS

These results contribute to unveiling the mechanisms underlying astrocyte role in AD and provide the rationale for using astrocytes as targets to new drugs for AD.

Insulin Resistance, a Risk Factor for Alzheimer's Disease: Pathological Mechanisms and a New Proposal for a Preventive Therapeutic Approach

Peripheral insulin resistance (IR) is a well-documented, independent risk factor for the development of type 2 diabetes, cardiovascular disease, cancer and cellular senescence. Recently, the brain has also been identified as an insulin-responsive region, where insulin acts as regulator of the brain metabolism. Despite the clear link between IR and the brain, the exact mechanisms underlying this relationship remain unclear. Therapeutic intervention in patients showing symptoms of neurodegenerative diseases has produced little or no results. It has been demonstrated that insulin resistance plays a significant role in the pathogenesis of neurodegenerative diseases, particularly cognitive decline. Peripheral and brain IR may represent a modifiable state that could be used to prevent major brain disorders. In this review, we will analyse the scientific literature supporting IR as a risk factor for Alzheimer's disease and suggest some therapeutic strategies to provide a new proposal for the prevention of brain IR and its consequences.

Revolutionizing Alzheimer's treatment: Harnessing human serum albumin for targeted drug delivery and therapy advancements

Alzheimer's disease (AD) is a neurodegenerative disorder initiated by amyloid-beta (Aβ) accumulation, leading to impaired cognitive function. Several delivery approaches have been improved for AD management. Among them, human serum albumin (HSA) is broadly employed for drug delivery and targeting the Aβ in AD owing to its biocompatibility, Aβ inhibitory effect, and nanoform, which showed blood-brain barrier (BBB) crossing ability via glycoprotein 60 (gp60) receptor and secreted protein acidic and rich in cysteine (SPARC) protein to transfer the drug molecules in the brain. Thus far, there is no previous review focusing on HSA and its drug delivery system in AD. Hence, the reviewed article aimed to critically compile the HSA therapeutic as well as drug delivery role in AD management. It also delivers information on how HSA-incorporated nanoparticles with surfaced embedded ligands such as TAT, GM1, and so on, not only improve BBB permeability but also increase neuron cell targetability in AD brain. Additionally, Aβ and tau pathology, including various metabolic markers likely BACE1 and BACE2, etc., are discussed. Besides, the molecular interaction of HSA with Aβ and its distinctive forms are critically reviewed that HSA can segregate Zn(II) and Cu(II) metal ions from Aβ owing to high affinity. Furthermore, the BBB drug delivery challenges in AD are addressed. Finally, the clinical formulation of HSA for the management of AD is critically discussed on how the HSA inhibits Aβ oligomer and fibril, while glycated HSA participates in amyloid plaque formation, i.e., β-structure sheet formation. This review report provides theoretical background on HSA-based AD drug delivery and makes suggestions for future prospect-related work.

The ketamine metabolite (2R,6R)-hydroxynorketamine rescues hippocampal mRNA translation, synaptic plasticity and memory in mouse models of Alzheimer's disease

INTRODUCTION

Impaired brain protein synthesis, synaptic plasticity, and memory are major hallmarks of Alzheimer's disease (AD). The ketamine metabolite (2R,6R)-hydroxynorketamine (HNK) has been shown to modulate protein synthesis, but its effects on memory in AD models remain elusive.

METHODS

We investigated the effects of HNK on hippocampal protein synthesis, long-term potentiation (LTP), and memory in AD mouse models.

RESULTS

HNK activated extracellular signal-regulated kinase 1/2 (ERK1/2), mechanistic target of rapamycin (mTOR), and p70S6 kinase 1 (S6K1)/ribosomal protein S6 signaling pathways. Treatment with HNK rescued hippocampal LTP and memory deficits in amyloid-β oligomers (AβO)-infused mice in an ERK1/2-dependent manner. Treatment with HNK further corrected aberrant transcription, LTP and memory in aged APP/PS1 mice.

DISCUSSION

Our findings demonstrate that HNK induces signaling and transcriptional responses that correct synaptic and memory deficits in AD mice. These results raise the prospect that HNK could serve as a therapeutic approach in AD.

HIGHLIGHTS

The ketamine metabolite HNK activates hippocampal ERK/mTOR/S6 signaling pathways. HNK corrects hippocampal synaptic and memory defects in two mouse models of AD. Rescue of synaptic and memory impairments by HNK depends on ERK signaling. HNK corrects aberrant transcriptional signatures in APP/PS1 mice.

Characterization of Olive Oil Phenolic Extracts and Their Effects on the Aggregation of the Alzheimer's Amyloid-β Peptide and Tau

The dietary consumption of extra virgin olive oil (EVOO) is believed to slow the progression of Alzheimer's disease (AD) symptoms. Its protective mechanisms are unclear, but specific EVOO phenolic compounds can individually impede the aggregation of amyloid-β (Aβ) peptides and the microtubule-associated protein tau, two important pathological manifestations of AD. It is unknown, however, whether the numerous and variable phenolic compounds that are consumed in dietary EVOO can collectively alter tau and Aβ aggregation as effectively as the individual compounds. The activity of these complex mixtures against Aβ and tau may be moderated by competition between active and nonactive phenolic components and by extensive derivatizations and isomerization. Here, phenolic mixtures extracted from two different EVOO sources are characterized and tested for how they modulate the aggregation of Aβ40 peptide and tau peptides in vitro. The chromatographic and NMR analysis of Greek and Saudi Arabian EVOO phenolic extracts reveals that they have different concentration profiles, and over 30 compounds are identified. Thioflavin T fluorescence and circular dichroism measurements show that relatively low concentrations (<20 μg/mL) of the Greek and Saudi extracts reduce the rate of Aβ40 aggregation and fibril mass, despite the extracts having different phenolic profiles. By contrast, the Greek extract reduces the rate of tau aggregation only at very high phenolic concentrations (>100 μg/mL). Most compounds in the extracts bind to preformed Aβ40 fibrils and release soluble Aβ oligomers that are mildly toxic to SH-SY5Y cells. Much higher (500 μg/mL) extract concentrations are required to remodel tau filaments into oligomers, and a minimal binding of phenolic compounds to the preformed filaments is observed. It is concluded that EVOO extracts having different phenol profiles are similarly capable of modulating Aβ40 aggregation and fibril morphology in vitro at relatively low concentrations but are less efficient at modulating tau aggregation. Over 2 M tonnes of EVOO are consumed globally each year as part of the Mediterranean diet, and the results here provide motivation for further clinical interrogation of the antiaggregation properties of EVOO as a potential protective mechanism against AD.

Chemically Driven Clearance of Amyloid Aggregates by Polyfunctionalized Furo[2,3-b:4,5-b']dipyridine-Chalcone Hybrids to Ameliorate Memory in an Alzheimer Mouse Model

The aberrant assembly of amyloid-β (Aβ) is implicated in Alzheimer's disease (AD). Recent clinical outcomes of Aβ-targeted immunotherapy reinforce the notion that clearing Aβ burden is a potential therapeutic approach for AD. Herein, to develop drug candidates for chemically driven clearance of Aβ aggregates, we synthesized 51 novel polyfunctionalized furo[2,3-b:4,5-b']dipyridine-chalcone hybrid compounds. After conducting two types of cell-free anti-Aβ functional assays, Aβ aggregation prevention and Aβ aggregate clearance, we selected YIAD-0336, (E)-8-((1H-pyrrol-2-yl)methylene)-10-(4-chlorophenyl)-2,4-dimethyl-7,8-dihydropyrido[3',2':4,5]furo[3,2-b]quinolin-9(6H)-one, for further in vivo investigations. As YIAD-0336 exhibited a low blood-brain barrier penetration profile, it was injected along with aggregated Aβ directly into the intracerebroventricular region of ICR mice and ameliorated spatial memory in Y-maze tests. Next, YIAD-0336 was orally administered to 5XFAD transgenic mice with intravenous injections of mannitol, and YIAD-0336 significantly removed Aβ plaques from the brains of 5XFAD mice. Collectively, YIAD-0336 dissociated toxic aggregates in the mouse brain and hence alleviated cognitive deterioration. Our findings indicate that chemically driven clearance of Aβ aggregates is a promising therapeutic approach for AD.

Development of an anti-tauopathy mucosal vaccine specifically targeting pathologic conformers

Alzheimer's disease (AD) and related tauopathies are associated with pathological tau protein aggregation, which plays an important role in neurofibrillary degeneration and dementia. Targeted immunotherapy to eliminate pathological tau aggregates is known to improve cognitive deficits in AD animal models. The tau repeat domain (TauRD) plays a pivotal role in tau-microtubule interactions and is critically involved in the aggregation of hyperphosphorylated tau proteins. Because TauRD forms the structural core of tau aggregates, the development of immunotherapies that selectively target TauRD-induced pathological aggregates holds great promise for the modulation of tauopathies. In this study, we generated recombinant TauRD polypeptide that form neurofibrillary tangle-like structures and evaluated TauRD-specific immune responses following intranasal immunization in combination with the mucosal adjuvant FlaB. In BALB/C mice, repeated immunizations at one-week intervals induced robust TauRD-specific antibody responses in a TLR5-dependent manner. Notably, the resulting antiserum recognized only the aggregated form of TauRD, while ignoring monomeric TauRD. The antiserum effectively inhibited TauRD filament formation and promoted the phagocytic degradation of TauRD aggregate fragments by microglia. The antiserum also specifically recognized pathological tau conformers in the human AD brain. Based on these results, we engineered a built-in flagellin-adjuvanted TauRD (FlaB-TauRD) vaccine and tested its efficacy in a P301S transgenic mouse model. Mucosal immunization with FlaB-TauRD improved quality of life, as indicated by the amelioration of memory deficits, and alleviated tauopathy progression. Notably, the survival of the vaccinated mice was dramatically extended. In conclusion, we developed a mucosal vaccine that exclusively targets pathological tau conformers and prevents disease progression.

Sexual Dimorphism, Altered Hippocampal Glutamatergic Neurotransmission and Cognitive Impairment in APP Knock-In Mice

Background

It is well established that glutamatergic neurotransmission plays an essential role in learning and memory. Previous studies indicate that glutamate dynamics shift with Alzheimer's disease (AD) progression, contributing to negative cognitive outcomes.

Objective

In this study, we characterized hippocampal glutamatergic signaling with age and disease progression in a knock-in mouse model of AD (APPNL-F/NL-F).

Methods

At 2-4 and 18+ months old, male and female APPNL/NL, APPNL-F/NL-F, and C57BL/6 mice underwent cognitive assessment using Morris water maze (MWM) and Novel Object Recognition (NOR). Then, basal and 70 mM KCl stimulus-evoked glutamate release was measured in the dentate gyrus (DG), CA3, and CA1 regions of the hippocampus using a glutamate-selective microelectrode in anesthetized mice.

Results

Glutamate recordings support elevated stimulus-evoked glutamate release in the DG and CA3 of young APPNL-F/NL-F male mice that declined with age compared to age-matched control mice. Young female APPNL-F/NL-F mice exhibited increased glutamate clearance in the CA1 that slowed with age compared to age-matched control mice. Male and female APPNL-F/NL-F mice exhibited decreased CA1 basal glutamate levels, while males also showed depletion in the CA3. Cognitive assessment demonstrated impaired spatial cognition in aged male and female APPNL-F/NL-F mice, but only aged females displayed recognition memory deficits compared to age-matched control mice. Conclusions: These findings confirm a sex-dependent hyper-to-hypoactivation glutamatergic paradigm in APPNL-F/NL-F mice. Further, data illustrate a sexually dimorphic biological aging process resulting in a more severe cognitive phenotype for female APPNL-F/NL-F mice than their male counterparts. Research outcomes mirror that of human AD pathology and provide further evidence of divergent AD pathogenesis between sexes.

Iterative Design of Near-Infrared Fluorescent Probes for Early Diagnosis of Alzheimer's Disease by Targeting Aβ Oligomers

Amyloid-β oligomers (AβOs), crucial toxic proteins in early Alzheimer's disease (AD), precede the formation of Aβ plaques and cognitive impairment. In this context, we present our iterative process for developing novel near-infrared fluorescent (NIRF) probes specifically targeting AβOs, aimed at early AD diagnosis. An initial screening identified compound 18 as being highly selective for AβOs. Subsequent analysis revealed that compound 20 improved serum stability while retaining affinity for AβOs. The most promising iteration, compound 37, demonstrated exceptional qualities: a high affinity for AβOs, emission in the near-infrared region, and good biocompatibility. Significantly, ex vivo double staining indicated that compound 37 detected AβOs in AD mouse brain and in vivo imaging experiments showed that compound 37 could differentiate between 4-month-old AD mice and age-matched wild-type mice. Therefore, compound 37 has emerged as a valuable NIRF probe for early detection of AD and a useful tool in exploring AD's pathological mechanisms.

Cacao consumption improves passive avoidance memory impairment in a rat model of Alzheimer's disease: the role of hippocampal synaptic plasticity and oxidative stress

Introduction: Alzheimer's disease (AD) causes progressive loss of cognitive function and synaptic plasticity, which is the most common form of dementia. The present study was designed to scrutinize the effects of cacao on passive avoidance memory function and to identify the roles of hippocampal synaptic plasticity and oxidative stress in an AD rat model induced by unilateral intracerebroventricular (UICV) injection of amyloid-beta (Aβ). Methods: Oral administration of cacao (500 mg/kg/ day) was given for 2 consecutive months. A memory retention test was conducted 24 h after passive avoidance training was completed. Subsequently, the amplitude of population spike (PS) and slope of field excitatory postsynaptic potentials (fEPSPs) were assessed at hippocampal long-term potentiation (LTP) in perforant pathway-dentate gyrus (PP-DG) synapses. Moreover, total thiol group (TTG) and malondialdehyde (MDA) concentrations were evaluated in the plasma. Furthermore, compact Aβ plaques were detected in the hippocampal DG by performing Congo red staining. Results: As a result of AD induction, passive avoidance memory was impaired; also, reduced fEPSP slopes, PS amplitudes, and content of TTG, and increase in MDA levels in the rats were observed. In contrast, cacao treatment ameliorated passive avoidance memory impairment, improved hippocampal LTP impairment, modulated oxidative-antioxidative status, and delayed Aβ plaques production in AD rats. Disscussion: Conclusively, cacao alleviates Aβ-induced cognitive deficit, probably by the amelioration of hippocampal LTP impairment, modulation of oxidative-antioxidative status, and inhibition of Aβ plaque accumulation.

Combination strategy employing BACE1 inhibitor and memantine to boost cognitive benefits in Alzheimer's disease therapy

RATIONALE

The β-secretase BACE1 initiates amyloid-β (Aβ) generation and represents a long-standing prime therapeutic target for the treatment of Alzheimer's disease (AD). However, BACE1 inhibitors tested to date in clinical trials have yielded no beneficial outcomes. In fact, prior BACE1 inhibitor trials targeted at ~ 50-90% Aβ reductions in symptomatic or prodromal AD stages have ended in the discontinuation due to futility and/or side effects, including cognitive worsening rather than expected improvement at the highest dose.

OBJECTIVES

We tested whether a combination strategy with the selective BACE1 inhibitor GRL-8234 and the FDA-approved symptomatic drug memantine may provide synergistic cognitive benefits within their safe dose range.

METHODS

The drug effects were evaluated in the advanced symptomatic stage of 5XFAD mice that developed extensive cerebral Aβ deposition.

RESULTS

Chronic combination treatment with 33.4-mg/kg GRL-8234 and 10-mg/kg memantine, but not either drug alone, rescued cognitive deficits in 5XFAD mice at 12 months of age (the endpoint after 60-day drug treatment), as assessed by the contextual fear conditioning, spontaneous alternation Y-maze and nest building tasks. Intact baseline performances of wild-type control mice on three cognitive paradigms demonstrated that combination treatment did not augment potential cognitive side effects of individual drugs. Biochemical and immunohistochemical examination showed that combination treatment did not synergistically reduce the β-amyloidogenic processing of amyloid precursor protein or Aβ levels in 5XFAD mouse brains.

CONCLUSIONS

A combination strategy with BACE1 inhibitors and memantine may be able to increase the effectiveness of individual drugs within their safe dose range in AD therapy.

Binding mechanism of full-length Aβ40 peptide to a mixed lipid bilayer

The destructive effect of Aβ peptides on membranes is an important source of its cytotoxicity in the pathogenesis of Alzheimer's disease. We have investigated the binding mechanism between the Aβ42 peptide and bilayer in our former work. However, as another abundant form of Aβ peptides in the physiological environment, the binding mechanism between Aβ40 peptide and the lipid bilayer still remains ambiguous. Hence, we performed all-atom simulations on the Aβ40 peptides with the lipid bilayer herein using replica exchange with the solute tempering 2 method. We obtained four major binding models with the hydrophobic C-terminus as the most preferable binding region. Hydrophobic residues and positively charged residues are the principal residues involved in the peptide-bilayer interactions. Aβ40 peptides in our simulation mainly adopt a β-rich conformation in both bound and unbound states. Besides, we determined peptide-water interactions and found that bound peptides prefer forming hydrogen bonds with water molecules than unbound peptides. Our findings herein may provide new insights for the in-depth understanding of the membrane-destructive mechanism of Aβ peptides.

Akt activation ameliorates deficits in hippocampal-dependent memory and activity-dependent synaptic protein synthesis in an Alzheimer's disease mouse model

Protein kinase-B (Akt) and the mechanistic target of rapamycin (mTOR) signaling pathways are implicated in Alzheimer's disease (AD) pathology. Akt/mTOR signaling pathways, activated by external inputs, enable new protein synthesis at the synapse and synaptic plasticity. The molecular mechanisms impeding new protein synthesis at the synapse in AD pathogenesis remain elusive. Here, we aimed to understand the molecular mechanisms prior to the manifestation of histopathological hallmarks by characterizing Akt1/mTOR signaling cascades and new protein synthesis in the hippocampus of WT and amyloid precursor protein/presenilin-1 (APP/PS1) male mice. Intriguingly, compared to those in WT mice, we found significant decreases in pAkt1, pGSK3β, pmTOR, pS6 ribosomal protein, and p4E-BP1 levels in both post nuclear supernatant and synaptosomes isolated from the hippocampus of one-month-old (presymptomatic) APP/PS1 mice. In synaptoneurosomes prepared from the hippocampus of presymptomatic APP/PS1 mice, activity-dependent protein synthesis at the synapse was impaired and this deficit was sustained in young adults. In hippocampal neurons from C57BL/6 mice, downregulation of Akt1 precluded synaptic activity-dependent protein synthesis at the dendrites but not in the soma. In three-month-old APP/PS1 mice, Akt activator (SC79) administration restored deficits in memory recall and activity-dependent synaptic protein synthesis. C57BL/6 mice administered with an Akt inhibitor (MK2206) resulted in memory recall deficits compared to those treated with vehicle. We conclude that dysregulation of Akt1/mTOR and its downstream signaling molecules in the hippocampus contribute to memory recall deficits and loss of activity-dependent synaptic protein synthesis. In AD mice, however, Akt activation ameliorates deficits in memory recall and activity-dependent synaptic protein synthesis.

Stabilization and Reduced Cytotoxicity of Amyloid Beta Aggregates in the Presence of Catechol Neurotransmitters

Oligomeric aggregates of the amyloid-beta (Aβ) peptide have been implicated as the toxic species for Alzheimer's disease by contributing to oxidative cytotoxicity and physical disruption in cell membranes in the brain. Recent evidence points to the ability of the catecholamine neurotransmitter dopamine in the presence of copper ions to both stabilize oligomers and decrease the toxic effects of these oligomers. Based on these results, physical characterization of aggregates and subsequent cell studies with a neuroblastoma line were performed that show both dopamine and the related neurotransmitter, norepinephrine, can stabilize oligomers and decrease toxicity of Aβ aggregates without copper present. To investigate this reduction of toxicity, structural characterization of oligomers in the presence of neurotransmitters was compared to aggregates formed with Aβ alone. Gel electrophoresis and transmission electron microscopy show higher levels of oligomers in the presence of dopamine and norepinephrine, yet the oligomer structure is largely amorphous. Aβ aggregated alone forms the predicted highly organized fibrillar species, with increased levels of dityrosine covalent linkages, which are largely absent in the presence of the neurotransmitters. A proposed mechanism for the observed decrease in cell death by Aβ in the presence of dopamine and norepinephrine suggests the neurotransmitters both block the formation of organized oligomer structures and dityrosine stabilizing linkages while also behaving as antioxidants, providing a dual mechanism for increased cell viability.

Mitophagy in Alzheimer's Disease: A Bibliometric Analysis from 2007 to 2022

Background

The investigation of mitophagy in Alzheimer's disease (AD) remains relatively underexplored in bibliometric analysis.

Objective

To delve into the progress of mitophagy, offering a comprehensive overview of research trends and frontiers for researchers.

Methods

Basic bibliometric information, targets, and target-drug-clinical trial-disease extracted from publications identified in the Web of Science Core Collection from 2007 to 2022 were assessed using bibliometric software.

Results

The study encompassed 5,146 publications, displaying a consistent 16-year upward trajectory. The United States emerged as the foremost contributor in publications, with the Journal of Alzheimer's Disease being the most prolific journal. P. Hemachandra Reddy, George Perry, and Xiongwei Zhu are the top 3 most prolific authors. PINK1 and Parkin exhibited an upward trend in the last 6 years. Keywords (e.g., insulin, aging, epilepsy, tauopathy, and mitochondrial quality control) have recently emerged as focal points of interest within the past 3 years. "Mitochondrial dysfunction" is among the top terms in disease clustering. The top 10 drugs/molecules (e.g., curcumin, insulin, and melatonin) were summarized, accompanied by their clinical trials and related targets.

Conclusions

This study presents a comprehensive overview of the mitophagy research landscape in AD over the past 16 years, underscoring mitophagy as an emerging molecular mechanism and a crucial focal point for potential drug in AD. This study pioneers the inclusion of targets and their correlations with drugs, clinical trials, and diseases in bibliometric analysis, providing valuable insights and inspiration for scholars and readers of JADR interested in understanding the potential mechanisms and clinical trials in AD.

Research Mechanism and Progress of the Natural Compound Curcumin in Treating Alzheimer´s Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. AD patients usually present symptoms, such as cognitive dysfunction, progressive memory loss, and other manifestations. With the increasing number of AD cases worldwide, there is an urgent need to develop effective drug treatments. Currently, drugs targeting AD symptoms may not change or prevent the progression of the disease. Curcumin, a polyphenol extracted from the turmeric herb, has been used for the treatment of AD. In this review, we summarized both cellular and animal studies and described the mechanism of action of curcumin in altering the pathological features of AD. Curcumin attenuates the formation of amyloid-β plaques and promotes its decomposition, reduces the phosphorylation of tau, improves its clearance rate, and binds with copper to reduce cholesterol. It changes the activity of microglia, suppresses acetylcholinesterase, regulates insulin signal transduction, and exhibits antioxidant properties. Studies have found that curcumin can promote nerve repair and has a significant effect on AD. However, the low bioavailability of curcumin may hinder its use as a therapeutic agent. If this limitation can be overcome, curcumin may emerge as a promising drug for the treatment of AD.

Alzheimer's disease brain-derived extracellular vesicles reveal altered synapse-related proteome and induce cognitive impairment in mice

INTRODUCTION

Extracellular vesicles (EVs) have been implicated in the spread of neuropathology in Alzheimer's disease (AD), but their involvement in behavioral outcomes linked to AD remains to be determined.

METHODS

EVs isolated from post mortem brain tissue from control, AD, or frontotemporal dementia (FTD) donors, as well as from APP/PS1 mice, were injected into the hippocampi of wild-type (WT) or a humanized Tau mouse model (hTau/mTauKO). Memory tests were carried out. Differentially expressed proteins in EVs were assessed by proteomics.

RESULTS

Both AD-EVs and APP/PS1-EVs trigger memory impairment in WT mice. We further demonstrate that AD-EVs and FTD-EVs carry Tau protein, present altered protein composition associated with synapse regulation and transmission, and trigger memory impairment in hTau/mTauKO mice.

DISCUSSION

Results demonstrate that AD-EVs and FTD-EVs have negative impacts on memory in mice and suggest that, in addition to spreading pathology, EVs may contribute to memory impairment in AD and FTD.

HIGHLIGHTS

Aβ was detected in EVs from post mortem AD brain tissue and APP/PS1 mice. Tau was enriched in EVs from post mortem AD, PSP and FTD brain tissue. AD-derived EVs and APP/PS1-EVs induce cognitive impairment in wild-type (WT) mice. AD- and FTD-derived EVs induce cognitive impairment in humanized Tau mice. Proteomics findings associate EVs with synapse dysregulation in tauopathies.

Administration of amyloid-β oligomer to the buccal ganglia may reduce food intake and cholinergic synaptic responses within the feeding neural circuit in Aplysia kurodai

Anorexia is a behavioral change caused by functional brain disorders in patients with Alzheimer's disease (AD). Amyloid-β (1-42) oligomers (o-Aβ) are possible causative agents of AD that impair signaling via synaptic dysfunction. In this study, we used Aplysia kurodai to study functional disorders of the brain through o-Aβ. Administration of o-Aβ to the buccal ganglia (feeding brain for oral movements) by surgical treatment significantly reduced food intake for at least five days. Furthermore, we explored the effects of o-Aβ on the synaptic function in the feeding neural circuit, focusing on a specific inhibitory synaptic response in jaw-closing motor neurons produced by cholinergic buccal multi-action neurons because we recently found that this cholinergic response decreases with aging, which is consistent with the cholinergic hypothesis for aging. Administration of o-Aβ to the buccal ganglia significantly reduced the synaptic response within minutes, whereas administration of amyloid-β (1-42) monomers did not. These results suggest that o-Aβ may impair the cholinergic synapses, even in Aplysia, which is consistent with the cholinergic hypothesis for AD.

The Role of Oxytocin in Alzheimer's Disease and Its Relationship with Social Interaction

Alzheimer's disease (AD)-the most common cause of dementia in the elderly-is characterized by progressive memory loss and β-amyloid protein (Aβ) accumulation in the brain. Recently, loneliness was found to be a high risk factor for AD, and social isolation has become a major cause of AD. AD. Oxytocin (OXT), the main hormone involved in social bonding, has been implicated in social interactions, notably in building trust and relationships. Moreover, social isolation or social enrichment modulates the activation of neurons related to OXT. Recently, we reported that OXT reverses learning and memory impairment in AD animal models. Based on the limited number of studies currently available, OXT might be a therapeutic target for AD. Further studies are necessary in order to better understand the role of oxytocin in AD. In this review, we described the relationships between OXT, AD, and social interaction.

Aquaporin-4 Mediated Aggregation of Alzheimer's Amyloid β-Peptide

Clearance of Alzheimer's amyloid oligomers from the brain is crucial for preventing cell toxicity. Dementia complications arise as a result of apoptosis, which is caused by peptide plaques on the lipid surface of cells. Here, we employed all-atom and coarse-grained molecular dynamics simulations to investigate the aggregation of amyloid peptides at the lipid surface and the role of aquaporin-4 (AQP4) in facilitating peptide clearance from astrocytes. The network of protein-protein interactions through text mining revealed that the expression of AQP4 and amyloid aggregation were strongly correlated. It has also been revealed that the role of aquaporins in the etiology of Alzheimer's disease involves several interconnected proteins and pathways. The nature of aggregation at the surface of the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayer was revealed by the interaction of amyloid oligomers. The membrane-bound pore region of AQP4 interacts with the peptide and slows its aggregation. This interaction maintains the helical content of the peptide while lowering its toxicity at the lipid surface. The hydrophobicity of the peptide also decreased because of these interactions, which may help in the removal of the peptide from astrocytes. Long-term coarse-grained MD simulations demonstrated different features of oligomer aggregation at the surface and strong oligomer attraction to AQP4, which inhibited aggregation. Additionally, the water dynamics of aquaporins demonstrate how the selectivity filter is broken to disrupt water flow. Our findings also provide insight into the physiological alterations in brain tissue associated with Alzheimer's disease, including water retention and increased water flow in the CSF. Furthermore, in vitro thioflavin fluorescence spectroscopy revealed a slower aggregation of the peptide in the presence of AQP4.

American Ginseng for the Treatment of Alzheimer's Disease: A Review

Alzheimer's disease (AD) is a prevalent degenerative condition that is increasingly affecting populations globally. American ginseng (AG) has anti-AD bioactivity, and ginsenosides, as the main active components of AG, have shown strong anti-AD effects in both in vitro and in vivo studies. It has been reported that ginsenosides can inhibit amyloid β-protein (Aβ) production and deposition, tau phosphorylation, apoptosis and cytotoxicity, as well as possess anti-oxidant and anti-inflammatory properties, thus suppressing the progression of AD. In this review, we aim to provide a comprehensive overview of the pathogenesis of AD, the potential anti-AD effects of ginsenosides found in AG, and the underlying molecular mechanisms associated with these effects. Additionally, we will discuss the potential use of AG in the treatment of AD, and how ginsenosides in AG may exert more potent anti-AD effects in vivo may be a direction for further research.

Alzheimer's Disease and Its Possible Evolutionary Origin: Hypothesis

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

Aβ Oligomer Toxicity-Reducing Therapy for the Prevention of Alzheimer's Disease: Importance of the Nrf2 and PPARγ Pathways

Recent studies have revealed that soluble amyloid-β oligomers (AβOs) play a pathogenetic role in Alzheimer's disease (AD). Indeed, AβOs induce neurotoxic and synaptotoxic effects and are also critically involved in neuroinflammation. Oxidative stress appears to be a crucial event underlying these pathological effects of AβOs. From a therapeutic standpoint, new drugs for AD designed to remove AβOs or inhibit the formation of AβOs are currently being developed. However, it is also worth considering strategies for preventing AβO toxicity itself. In particular, small molecules with AβO toxicity-reducing activity have potential as drug candidates. Among such small molecules, those that can enhance Nrf2 and/or PPARγ activity can effectively inhibit AβO toxicity. In this review, I summarize studies on the small molecules that counteract AβO toxicity and are capable of activating Nrf2 and/or PPARγ. I also discuss how these interrelated pathways are involved in the mechanisms by which these small molecules prevent AβO-induced neurotoxicity and neuroinflammation. I propose that AβO toxicity-reducing therapy, designated ATR-T, could be a beneficial, complementary strategy for the prevention and treatment of AD.

The Protective Effects of Policosanol on Learning and Memory Impairments in a Male Rat Model of Alzheimer's Disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by a progressive decline in cognitive performance and memory formation. The present study was designed to investigate the effect of policosanol (PCO) on cognitive function, oxidative-antioxidative status, and amyloid-beta (Aβ) plaque formation in an AD rat model induced by intracerebroventricular (ICV) injection of Aβ_1-40. Healthy adult male Wistar rats were randomly divided into seven groups: control, sham (5 μL, ICV injection of phosphate-buffered saline), AD model (5 μL, ICV injection of Aβ), acacia gum (50 mg/kg, 8 weeks, gavage), PCO (50 mg/kg, 8 weeks, gavage), AD + acacia gum (50 mg/kg, 8 weeks, gavage), and AD + PCO (50 mg/kg, 8 weeks, gavage). During the ninth and tenth weeks of the study, the cognitive function of the rats was assessed by commonly used behavioral paradigms. Subsequently, oxidative-antioxidative status was examined in the serum. Moreover, compact Aβ plaques were detected by Congo red staining. The results showed that injection of Aβ impaired recognition memory in the novel object recognition test, reduced the spatial cognitive ability in the Morris water maze, and alleviated retention and recall capability in the passive avoidance task. Additionally, injection of Aβ resulted in increased total oxidant status, decreased total antioxidant capacity, and enhanced Aβ plaque formation in the rats. Intriguingly, PCO treatment improved all the above-mentioned neuropathological changes in the Aβ-induced AD rats. The results suggest that PCO improves Aβ-induced cognitive decline, possibly through modulation of oxidative-antioxidative status and inhibition of Aβ plaque formation.

Pioglitazone use increases risk of Alzheimer's disease in patients with type 2 diabetes receiving insulin

Pioglitazone is an insulin resistance inhibitor widely used as monotherapy or combined with metformin or insulin in treating type 2 diabetes mellitus (T2DM). This study further investigated the relationship between pioglitazone use and the risk of developing Alzheimer's disease (AD) in patients newly diagnosed with T2DM, and examined the potential impact of insulin use on this association. Data were extracted from the National Health Insurance Research Database (NHIRD) of Taiwan. Our data exhibited that the risk of developing AD in the pioglitazone group was 1.584-fold (aHR = 1.584, 95% CI 1.203-1.967, p < 0.05) higher than that in the non-pioglitazone controls. Compared to patients without both insulin and pioglitazone, higher cumulative risk of developing AD was found in patients receiving both insulin and pioglitazone (aHR = 2.004, 95% CI = 1.702-2.498), pioglitazone alone (aHR = 1.596, 95% CI = 1.398-1.803), and insulin alone (aHR = 1.365, 95% CI = 1.125-1.572), respectively (all p < 0.05). A similar observation also found in the evaluation the use of diabetic drugs with a cumulative defined daily dose (cDDD). No interaction between pioglitazone and major risk factors (comorbidities) of AD was observed. In conclusion, alternative drug therapies may be an effective strategy for reducing risk of developing AD in T2DM patients.

Mid-Adulthood Cognitive Training Improves Performance in a Spatial Task but Does Not Ameliorate Hippocampal Pathology in a Mouse Model of Alzheimer's Disease

BACKGROUND

Prior experience in early life has been shown to improve performance in aging and mice with Alzheimer's disease (AD) pathology. However, whether cognitive training at a later life stage would benefit subsequent cognition and reduce pathology in AD mice needs to be better understood.

OBJECTIVE

This study aimed to verify if behavioral training in mid-adulthood would improve subsequent cognition and reduce AD pathology and astrogliosis.

METHODS

Mixed-sex APP/PS1 and wildtype littermate mice received a battery of behavioral training, composed of spontaneous alternation in the Y-maze, novel object recognition and location tasks, and spatial training in the water maze, or handling only at 7 months of age. The impact of AD genotype and prior training on subsequent learning and memory of aforementioned tasks were assessed at 9 months.

RESULTS

APP/PS1 mice made more errors than wildtype littermates in the radial-arm water maze (RAWM) task. Prior training prevented this impairment in APP/PS1 mice. Prior training also contributed to better efficiency in finding the escape platform in both APP/PS1 mice and wildtype littermates. Short-term and long-term memory of this RAWM task, of a reversal task, and of a transfer task were comparable among APP/PS1 and wildtype mice, with or without prior training. Amyloid pathology and astrogliosis in the hippocampus were also comparable between the APP/PS1 groups.

CONCLUSION

These data suggest that cognitive training in mid-adulthood improves subsequent accuracy in AD mice and efficiency in all mice in the spatial task. Cognitive training in mid-adulthood provides no clear benefit on memory or on amyloid pathology in midlife.

Investigation of Cyclo-Z Therapeutic Effect on Insulin Pathway in Alzheimer's Rat Model: Biochemical and Electrophysiological Parameters

Cyclo (his-pro-CHP) plus zinc (Zn⁺²) (Cyclo-Z) is the only known chemical that increases the production of insulin-degrading enzyme (IDE) and decreases the number of inactive insulin fragments in cells. The aim of the present study was to systematically characterize the effects of Cyclo-Z on the insulin pathway, memory functions, and brain oscillations in the Alzheimer's disease (AD) rat model. The rat model of AD was established by bilateral injection of Aβ42 oligomer (2,5nmol/10μl) into the lateral ventricles. Cyclo-Z (10mg Zn+2/kg and 0.2mg CHP/kg) gavage treatment started seven days after Aβ injection and lasted for 21 days. At the end of the experimental period, memory tests and electrophysiological recordings were performed, which were followed by the biochemical analysis. Aβ42 oligomers led to a significant increase in fasting blood glucose, serum insulin, Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) and phospho-tau-Ser356 levels. Moreover, Aβ42 oligomers caused a significant decrement in body weight, hippocampal insulin, brain insulin receptor substrate (IRS-Ser612), and glycogen synthase kinase-3 beta (GSK-3β) levels. Also, Aβ42 oligomers resulted in a significant reduction in memory. The Cyclo-Z treatment prevented the observed alterations in the ADZ group except for phospho-tau levels and attenuated the increased Aβ42 oligomer levels in the ADZ group. We also found that the Aβ42 oligomer decreased the left temporal spindle and delta power during ketamine anesthesia. Cyclo-Z treatment reversed the Aβ42 oligomer-related alterations in the left temporal spindle power. Cyclo-Z prevents Aβ oligomer-induced changes in the insulin pathway and amyloid toxicity, and may contribute to the improvement of memory deficits and neural network dynamics in this rat model.

Policosanol protects against Alzheimer's disease-associated spatial cognitive decline in male rats: possible involved mechanisms

RATIONALE

Alzheimer's disease (AD) is a chronic neurodegenerative disorder characterized by cognitive decline and synaptic failure.

OBJECTIVE

The present study was designed to explore the possible protective effects of policosanol (PCO) on spatial cognitive capacity, long-term potentiation (LTP) induction, oxidant/antioxidant status, and Aβ plaques formation in an AD rat model induced by intracerebroventricular (ICV) injection of Aβ_1-40.

METHODS

Healthy adult male Wistar rats were randomly divided into control, sham (ICV injection of 5 µl phosphate-buffered saline), AG (50 mg/kg; P.O., as PCO vehicle), PCO (50 mg/kg; P.O.), AD model (ICV injection of 5 µl Aβ), AD + AG (50 mg/kg; P.O.), and AD + PCO (50 mg/kg; P.O.). Treatments were performed for eight consecutive weeks. At the end of the treatment course, spatial learning and memory functions, hippocampal long-term potentiation (LTP) induction, malondialdehyde (MDA), and total thiol group (TTG) levels, as well as the formation of Aβ plaques, were examined.

RESULTS

The results showed that injection of Aβ reduced spatial learning and memory abilities in the Barnes maze test, which was accompanied by decreases in field excitatory postsynaptic potential (fEPSP) slope, population spike (PS) amplitude, and TTG level and increases in Aβ plaque accumulation and MDA content. In contrast, PCO treatment improved all the above-mentioned changes in the Aβ-infused rats.

CONCLUSIONS

The results suggest that amelioration of hippocampal synaptic plasticity impairment, modulation of oxidant/antioxidant status, and inhibition of Aβ plaque formation by PCO may be the mechanisms behind its protective effect against AD-associated spatial cognitive decline.

Insulin‐like growth factor‐2 is a promising candidate for the treatment and prevention of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. Current AD treatments slow the rate of cognitive decline, but do not restore lost function. One reason for the low efficacy of current treatments is that they fail to target neurotrophic processes, which are thought to be essential for functional recovery. Bolstering neurotrophic processes may also be a viable strategy for preventative treatment, since structural losses are thought to underlie cognitive decline in AD. The challenge of identifying presymptomatic patients who might benefit from preventative treatment means that any such treatment must meet a high standard of safety and tolerability. The neurotrophic peptide insulin-like growth factor-2 (IGF2) is a promising candidate for both treating and preventing AD-induced cognitive decline. Brain IGF2 expression declines in AD patients. In rodent models of AD, exogenous IGF2 modulates multiple aspects of AD pathology, resulting in (1) improved cognitive function; (2) stimulation of neurogenesis and synaptogenesis; and, (3) neuroprotection against cholinergic dysfunction and beta amyloid-induced neurotoxicity. Preclinical evidence suggests that IGF2 is likely to be safe and tolerable at therapeutic doses. In the preventative treatment context, the intranasal route of administration is likely to be the preferred method for achieving the therapeutic effect without risking adverse side effects. For patients already experiencing AD dementia, routes of administration that deliver IGF2 directly access the CNS may be necessary. Finally, we discuss several strategies for improving the translational validity of animal models used to study the therapeutic potential of IGF2.

Purinergic signaling in cognitive impairment and neuropsychiatric symptoms of Alzheimer's disease

About 10 million new cases of dementia develop worldwide each year, of which up to 70% are attributable to Alzheimer's disease (AD). In addition to the widely known symptoms of memory loss and cognitive impairment, AD patients frequently develop non-cognitive symptoms, referred to as behavioral and psychological symptoms of dementia (BPSDs). Sleep disorders are often associated with AD, but mood alterations, notably depression and apathy, comprise the most frequent class of BPSDs. BPSDs negatively affect the lives of AD patients and their caregivers, and have a significant impact on public health systems and the economy. Because treatments currently available for AD are not disease-modifying and mainly aim to ameliorate some of the cognitive symptoms, elucidating the mechanisms underlying mood alterations and other BPSDs in AD may reveal novel avenues for progress in AD therapy. Purinergic signaling is implicated in the pathophysiology of several central nervous system (CNS) disorders, such as AD, depression and sleep disorders. Here, we review recent findings indicating that purinergic receptors, mainly the A₁, A_2A, and P2X7 subtypes, are associated with the development/progression of AD. Current evidence suggests that targeting purinergic signaling may represent a promising therapeutic approach in AD and related conditions. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Effects of Terahertz Radiation on the Aggregation of Alzheimer's Aβ42 Peptide

The pathophysiology of Alzheimer's disease is thought to be directly linked to the abnormal aggregation of β-amyloid (Aβ) in the nervous system as a common neurodegenerative disease. Consequently, researchers in many areas are actively looking for factors that affect Aβ aggregation. Numerous investigations have demonstrated that, in addition to chemical induction of Aβ aggregation, electromagnetic radiation may also affect Aβ aggregation. Terahertz waves are an emerging form of non-ionizing radiation that has the potential to affect the secondary bonding networks of biological systems, which in turn could affect the course of biochemical reactions by altering the conformation of biological macromolecules. As the primary radiation target in this investigation, the in vitro modeled Aβ42 aggregation system was examined using fluorescence spectrophotometry, supplemented by cellular simulations and transmission electron microscopy, to see how it responded to 3.1 THz radiation in various aggregation phases. The results demonstrated that in the nucleation aggregation stage, 3.1 THz electromagnetic waves promote Aβ42 monomer aggregation and that this promoting effect gradually diminishes with the exacerbation of the degree of aggregation. However, by the stage of oligomer aggregation into the original fiber, 3.1 THz electromagnetic waves exhibited an inhibitory effect. This leads us to the conclusion that terahertz radiation has an impact on the stability of the Aβ42 secondary structure, which in turn affects how Aβ42 molecules are recognized during the aggregation process and causes a seemingly aberrant biochemical response. Molecular dynamics simulation was employed to support the theory based on the aforementioned experimental observations and inferences.

Cerebrospinal fluid biomarkers of axonal and synaptic degeneration in a population-based sample

BACKGROUND

Neurofilament light (NfL) and neurogranin (Ng) are promising candidate AD biomarkers, reflecting axonal and synaptic damage, respectively. Since there is a need to understand the synaptic and axonal damage in preclinical Alzheimer's disease (AD), we aimed to determine the cerebrospinal fluid (CSF) levels of NfL and Ng in cognitively unimpaired elderly from the Gothenburg H70 Birth Cohort Studies classified according to the amyloid/tau/neurodegeneration (A/T/N) system.

METHODS

The sample consisted of 258 cognitively unimpaired older adults (age 70, 129 women and 129 men) from the Gothenburg Birth Cohort Studies. We compared CSF NfL and Ng concentrations in A/T/N groups using Student's T-test and ANCOVA.

RESULTS

CSF NfL concentration was higher in the A-T-N+ group (p=0.001) and the A-T+N+ group (p=0.006) compared with A-T-N-. CSF Ng concentration was higher in the A-T-N+, A-T+N+, A+T-N+, and A+T+N+ groups (p<0.0001) compared with A-T-N-. We found no difference in NfL or Ng concentration in A+ compared with A- (disregarding T- and N- status), whereas those with N+ had higher concentrations of NfL and Ng compared with N- (p<0.0001) (disregarding A- and T- status).

CONCLUSIONS

CSF NfL and Ng concentrations are increased in cognitively normal older adults with biomarker evidence of tau pathology and neurodegeneration.

Non-competitive AMPA glutamate receptors antagonism by perampanel as a strategy to counteract hippocampal hyper-excitability and cognitive deficits in cerebral amyloidosis

Pathological accumulation of Aβ oligomers has been linked to neuronal networks hyperexcitability, potentially underpinned by glutamatergic AMPA receptors (AMPARs) dysfunction. We aimed to investigate whether the non-competitive block of AMPARs was able to counteract the alteration of hippocampal epileptic threshold, and of synaptic plasticity linked to Aβ oligomers accumulation, being this glutamate receptor a valuable specific therapeutic target. In this work, we showed that the non-competitive AMPARs antagonist perampanel (PER) which, per se, did not affect physiological synaptic transmission, was able to counteract Aβ-induced hyperexcitability. Moreover, AMPAR antagonism was able to counteract Aβ-induced hippocampal LTP impairment and hippocampal-based cognitive deficits in Aβ oligomers-injected mice, while retaining antiseizure efficacy. Beside this, AMPAR antagonism was also able to reduce the increased expression of proinflammatory cytokines in this mice model, also suggesting the presence of an anti-inflammatory activity. Thus, targeting AMPARs might be a valuable strategy to reduce both hippocampal networks hyperexcitability and synaptic plasticity deficits induced by Aβ oligomers accumulation.

Defective proteostasis in Alzheimer's disease

The homeostasis of cellular proteins, or proteostasis, is critical for neuronal function and for brain processes, including learning and memory. Increasing evidence indicates that defective proteostasis contributes to the progression of neurodegenerative disorders, including Alzheimer's disease (AD), the most prevalent form of dementia in the elderly. Proteostasis comprises a set of cellular mechanisms that control protein synthesis, folding, post-translational modification and degradation, all of which are deregulated in AD. Importantly, deregulation of proteostasis plays a key role in synapse dysfunction and in memory impairment, the major clinical manifestation of AD. Here, we discuss molecular pathways involved in protein synthesis and degradation that are altered in AD, and possible pharmacological approaches to correct these defects.

AAV-mediated neuronal expression of an scFv antibody selective for Aβ oligomers protects synapses and rescues memory in Alzheimer models

The accumulation of soluble oligomers of the amyloid-β peptide (AβOs) in the brain has been implicated in synapse failure and memory impairment in Alzheimer's disease. Here, we initially show that treatment with NUsc1, a single-chain variable-fragment antibody (scFv) that selectively targets a subpopulation of AβOs and shows minimal reactivity to Aβ monomers and fibrils, prevents the inhibition of long-term potentiation in hippocampal slices and memory impairment induced by AβOs in mice. As a therapeutic approach for intracerebral antibody delivery, we developed an adeno-associated virus vector to drive neuronal expression of NUsc1 (AAV-NUsc1) within the brain. Transduction by AAV-NUsc1 induced NUsc1 expression and secretion in adult human brain slices and inhibited AβO binding to neurons and AβO-induced loss of dendritic spines in primary rat hippocampal cultures. Treatment of mice with AAV-NUsc1 prevented memory impairment induced by AβOs and, remarkably, reversed memory deficits in aged APPswe/PS1ΔE9 Alzheimer's disease model mice. These results support the feasibility of immunotherapy using viral vector-mediated gene delivery of NUsc1 or other AβO-specific single-chain antibodies as a potential therapeutic approach in Alzheimer's disease.

The Anaesthetics Isoflurane and Xenon Reverse the Synaptotoxic Effects of Aβ1-42 on Megf10-Dependent Astrocytic Synapse Elimination and Spine Density in Ex Vivo Hippocampal Brain Slices

It has been hypothesised that inhalational anaesthetics such as isoflurane (Iso) may trigger the pathogenesis of Alzheimer's disease (AD), while the gaseous anaesthetic xenon (Xe) exhibits many features of a putative neuroprotective agent. Loss of synapses is regarded as one key cause of dementia in AD. Multiple EGF-like domains 10 (MEGF10) is one of the phagocytic receptors which assists the elimination of synapses by astrocytes. Here, we investigated how β-amyloid peptide 1-42 (Aβ_1-42), Iso and Xe interact with MEGF10-dependent synapse elimination. Murine cultured astrocytes as well as cortical and hippocampal ex vivo brain slices were treated with either Aβ_1-42, Iso or Xe and the combination of Aβ_1-42 with either Iso or Xe. We quantified MEGF10 expression in astrocytes and dendritic spine density (DSD) in slices. In brain slices of wild type and AAV-induced MEGF10 knock-down mice, antibodies against astrocytes (GFAP), pre- (synaptophysin) and postsynaptic (PSD95) components were used for co-localization analyses by means of immunofluorescence-imaging and 3D rendering techniques. Aβ_1-42 elevated pre- and postsynaptic components inside astrocytes and decreased DSD. The combined application with either Iso or Xe reversed these effects. In the presence of Aβ_1-42 both anaesthetics decreased MEGF10 expression. AAV-induced knock-down of MEGF10 reduced the pre- and postsynaptic marker inside astrocytes. The presented data suggest Iso and Xe are able to reverse the Aβ_1-42-induced enhancement of synaptic elimination in ex vivo hippocampal brain slices, presumably through MEGF10 downregulation.

Hypoglycemic medicines in the treatment of Alzheimer's disease: Pathophysiological links between AD and glucose metabolism

Alzheimer's Disease (AD) is a global chronic disease in adults with beta-amyloid (Aβ) deposits and hyperphosphorylated tau protein as the pathologic characteristics. Although the exact etiology of AD is still not fully elucidated, aberrant metabolism including insulin signaling and mitochondria dysfunction plays an important role in the development of AD. Binding to insulin receptor substrates, insulin can transport through the blood-brain barrier (BBB), thus mediating insulin signaling pathways to regulate physiological functions. Impaired insulin signaling pathways, including PI3K/Akt/GSK3β and MAPK pathways, could cause damage to the brain in the pathogenesis of AD. Mitochondrial dysfunction and overexpression of TXNIP could also be causative links between AD and DM. Some antidiabetic medicines may have benefits in the treatment of AD. Metformin can be beneficial for cognition improvement in AD patients, although results from clinical trials were inconsistent. Exendin-4 may affect AD in animal models but there is a lack of clinical trials. Liraglutide and dulaglutide could also benefit AD patients in adequate clinical studies but not semaglutide. Dipeptidyl peptidase IV inhibitors (DPP4is) such as saxagliptin, vildagliptin, linagliptin, and sitagliptin could boost cognitive function in animal models. And SGLT2 inhibitors such as empagliflozin and dapagliflozin were also considerably protective against new-onset dementia in T2DM patients. Insulin therapy is a promising therapy but some studies indicated that it may increase the risk of AD. Herbal medicines are helpful for cognitive function and neuroprotection in the brain. For example, polyphenols, alkaloids, glycosides, and flavonoids have protective benefits in cognition function and glucose metabolism. Focusing on glucose metabolism, we summarized the pharmacological mechanism of hypoglycemic drugs and herbal medicines. New treatment approaches including antidiabetic synthesized drugs and herbal medicines would be provided to patients with AD. More clinical trials are needed to produce definite evidence for the effectiveness of hypoglycemic medications.

Lung inflammation induced by silica particles triggers hippocampal inflammation, synapse damage and memory impairment in mice

BACKGROUND

Considerable evidence indicates that a signaling crosstalk between the brain and periphery plays important roles in neurological disorders, and that both acute and chronic peripheral inflammation can produce brain changes leading to cognitive impairments. Recent clinical and epidemiological studies have revealed an increased risk of cognitive impairment and dementia in individuals with impaired pulmonary function. However, the mechanistic underpinnings of this association remain unknown. Exposure to SiO₂ (silica) particles triggers lung inflammation, including infiltration by peripheral immune cells and upregulation of pro-inflammatory cytokines. We here utilized a mouse model of lung silicosis to investigate the crosstalk between lung inflammation and memory.

METHODS

Silicosis was induced by intratracheal administration of a single dose of 2.5 mg SiO₂/kg in mice_. Molecular and behavioral measurements were conducted 24 h and 15 days after silica administration. Lung and hippocampal inflammation were investigated by histological analysis and by determination of pro-inflammatory cytokines. Hippocampal synapse damage, amyloid-β (Aβ) peptide content and phosphorylation of Akt, a proxy of hippocampal insulin signaling, were investigated by Western blotting and ELISA. Memory was assessed using the open field and novel object recognition tests.

RESULTS

Administration of silica induced alveolar collapse, lung infiltration by polymorphonuclear (PMN) cells, and increased lung pro-inflammatory cytokines. Lung inflammation was followed by upregulation of hippocampal pro-inflammatory cytokines, synapse damage, accumulation of the Aβ peptide, and memory impairment in mice.

CONCLUSION

The current study identified a crosstalk between lung and brain inflammatory responses leading to hippocampal synapse damage and memory impairment after exposure to a single low dose of silica in mice.

Sex-Specific Multiparameter Blood Test for the Early Diagnosis of Alzheimer's Disease

Blood-based biomarkers are needed for the early diagnosis of Alzheimer's disease (AD). We analyzed longitudinal human plasma samples from AD and control cases to identify biomarkers for the early diagnosis of AD. Plasma samples were grouped based on clinical diagnosis at the time of collection: AD, mild cognitive impairment (MCI), and pre-symptomatic (preMCI). Samples were analyzed by ELISA using a panel of reagents against nine different AD-related amyloid-β (Aβ), tau, or TDP-43 variants. Receiver operating characteristic (ROC) curves of different biomarker panels for different diagnostic sample groups were determined. Analysis of all of the samples gave a sensitivity of 92% and specificity of 76% for the diagnosis of AD. Early-stage diagnosis of AD, utilizing only the preMCI and MCI samples, identified 88% of AD cases. Using sex-biased biomarker panels, early diagnosis of AD cases improved to 96%. Using the sex-biased panels, we also identified 6 of the 25 control group cases as being at high risk of AD, which is consistent with what is expected given the advanced age of the control cases. Specific AD-associated protein variants are effective blood-based biomarkers for the early diagnosis of AD. Notably, significant differences were observed in biomarker profiles for the early detection of male and female AD cases.

Exploring the potential anti-Alzheimer disease mechanisms of Alpiniae Oxyphyliae Fructus by network pharmacology study and molecular docking

Alpiniae Oxyphyliae Fructus (AOF) (yizhi) is a frequently medicated Chinese herb for Alzheimer disease (AD) treatment. The present study investigated the components and potential mechanisms of AOF through network pharmacology analysis and molecular docking. The results showed that AOF contains at least 20 active ingredients and involves 184 target genes. A total of 301 AD-related genes were obtained from the DisGeNET, GeneCards, GEO, OMIM, and Alzheimer Disease: Genes databases. A total of 41 key targets were identified from the topology analysis of the AOF-AD target network. These key targets are involved in 105 signal pathways, such as the PI3K-Akt, HIF-1, and MAPK pathways, and can regulate gene transcription, cell death, cell proliferation, drug response, and protein phosphorylation. AOF's active ingredients, Chrysin, Isocyperol, Izalpinin, Linolenic acid, CHEMBL489541, Oxyphyllenone A, Oxyphyllenone B, and Oxyphyllol C, show high affinity to targets, including PPARG, ESR1, and AKT1. These findings provide a new basis for AOF application and anti-AD study.

Type 2 Diabetes Mellitus and Alzheimer's Disease: Shared Molecular Mechanisms and Potential Common Therapeutic Targets

The global prevalence of diabetes mellitus and Alzheimer's disease is increasing alarmingly with the aging of the population. Numerous epidemiological data suggest that there is a strong association between type 2 diabetes and an increased risk of dementia. These diseases are both degenerative and progressive and share common risk factors. The amyloid cascade plays a key role in the pathophysiology of Alzheimer's disease. The accumulation of amyloid beta peptides gradually leads to the hyperphosphorylation of tau proteins, which then form neurofibrillary tangles, resulting in neurodegeneration and cerebral atrophy. In Alzheimer's disease, apart from these processes, the alteration of glucose metabolism and insulin signaling in the brain seems to induce early neuronal loss and the impairment of synaptic plasticity, years before the clinical manifestation of the disease. The large amount of evidence on the existence of insulin resistance in the brain during Alzheimer's disease has led to the description of this disease as "type 3 diabetes". Available animal models have been valuable in the understanding of the relationships between type 2 diabetes and Alzheimer's disease, but to date, the mechanistical links are poorly understood. In this non-exhaustive review, we describe the main molecular mechanisms that may link these two diseases, with an emphasis on impaired insulin and IGF-1 signaling. We also focus on GSK3β and DYRK1A, markers of Alzheimer's disease, which are also closely associated with pancreatic β-cell dysfunction and type 2 diabetes, and thus may represent common therapeutic targets for both diseases.

Beta-amyloid Deposition in Biliary Atresia Reduces Liver Regeneration by Inhibiting Energy Metabolism and Mammalian Target of Rapamycin Signaling

INTRODUCTION

Biliary atresia (BA) is a devastating obstructive bile duct disease found in newborns. This study aims to investigate the roles and involved mechanisms of beta-amyloid (Aβ) in the pathogenesis of BA.

METHODS

We examined the distribution of Aβ protein and its precursor in the livers of patients with BA. A murine liver organoid and a zebrafish model were established to investigate the exact roles of Aβ in liver regeneration for BA.

RESULTS

Both Aβ mRNA and protein significantly increased in livers of infants with BA and deposited around the central vein. In the plasma, Aβ elevated significantly in patients with BA and positively correlated with liver injury progression. In vitro , Aβ treatment induced abnormal morphology and caused impaired growth in liver organoids. Energy metabolism analysis demonstrated Aβ increased aerobic glycolysis and reduced ATP synthase in organoids, in which the mammalian target of rapamycin signaling was suppressed. In vivo , Aβ42 exposure caused liver degeneration in zebrafish larvae.

DISCUSSION

Aβ depositing in livers of infants with BA reduced the liver regeneration through attenuating mitochondrial respiration and mammalian target of rapamycin signaling.

SIRT1 deficiency increases O-GlcNAcylation of tau, mediating synaptic tauopathy

Hyperphosphorylation of the microtubule associated protein tau is associated with several neurodegenerative diseases including Alzheimer's Disease (AD), collectively referred to as tauopathies. However, the mechanisms by which tau is linked to synaptic dysfunction and memory impairment remain unclear. To address this question, we constructed a mouse model with brain-specific deficiency of SIRT1 (SIRT1 flox/Cre + ). Here, we show that increase of site-specific phosphorylation of tau is coupled with the strengthened O-GlcNAcylation of tau triggered by reduced O-GlcNAcase (OGA) and increased O-GlcNAc transferase (OGT) protein level in the brain of SIRT1 flox/Cre+ mice. SIRT1 deletion in mice brain changes the synaptosomal distribution of site-specific phospho-tau. Learning and memory deficiency induced by dendritic spine deficits and synaptic dysfunction are revealed via SIRT1 flox/Cre+ mice. Our results provide evidence for SIRT1 as a potential therapeutic target in clinical tauopathies.