Clearance of amyloid-beta in Alzheimer's disease: progress, problems and perspectives

Promoting Alzheimer's disease research and therapy with stem cell technology

BACKGROUND

Alzheimer's disease (AD) is a prevalent form of dementia leading to memory loss, reduced cognitive and linguistic abilities, and decreased self-care. Current AD treatments aim to relieve symptoms and slow disease progression, but a cure is elusive due to limited understanding of the underlying disease mechanisms.

MAIN CONTENT

Stem cell technology has the potential to revolutionize AD research. With the ability to self-renew and differentiate into various cell types, stem cells are valuable tools for disease modeling, drug screening, and cell therapy. Recent advances have broadened our understanding beyond the deposition of amyloidβ (Aβ) or tau proteins in AD to encompass risk genes, immune system disorders, and neuron-glia mis-communication, relying heavily on stem cell-derived disease models. These stem cell-based models (e.g., organoids and microfluidic chips) simulate in vivo pathological processes with extraordinary spatial and temporal resolution. Stem cell technologies have the potential to alleviate AD pathology through various pathways, including immunomodulation, replacement of damaged neurons, and neurotrophic support. In recent years, transplantation of glial cells like oligodendrocytes and the infusion of exosomes have become hot research topics.

CONCLUSION

Although stem cell-based models and therapies for AD face several challenges, such as extended culture time and low differentiation efficiency, they still show considerable potential for AD treatment and are likely to become preferred tools for AD research.

Alzheimer's disease cerebrospinal fluid biomarkers and kidney function in normal and cognitively impaired older adults

INTRODUCTION

Recent Alzheimer's disease (AD) clinical trials have used cerebrospinal fluid (CSF) biomarker levels for screening and enrollment. Preliminary evidence suggests that AD risk is related to impaired renal function. The impact of kidney function on commonly used AD biomarkers remains unknown.

METHODS

Participants in studies conducted at the Goizueta Alzheimer's Disease Research Center (N = 973) had measurements of serum creatinine and CSF AD biomarkers. General linear models and individual data were used to assess the relationships between biomarkers and eGFR.

RESULTS

Lower estimated glomerular filtration rate (eGFR) was associated with lower amyloid beta (Aβ)42/tau ratio (p < 0.0001) and Aβ42 (p = 0.002) and higher tau (p < 0.0001) and p-tau (p = 0.0002). The impact of eGFR on AD biomarker levels was more robust in individuals with cognitive impairment (all p-values were < 0.005).

DISCUSSION

The association between eGFR and CSF AD biomarkers has a significant impact that varies by cognitive status. Future studies exploring this impact on the pathogenesis of AD and related biomarkers are needed.

Highlights

There is a significant association between Alzheimer's disease (AD) cerebrospinal fluid (CSF) biomarkers and both estimated glomerular filtration rate (eGFR) and mild cognitive impairment (MCI).Kidney function influences CSF biomarker levels in individuals with normal cognitive function and those with MCI.The impact of kidney function on AD biomarker levels is more pronounced in individuals with cognitive impairment.The variation in CSF tau levels is independent of cardiovascular factors and is likely directly related to kidney function.Tau may have a possible role in both kidney and cognitive function.

Covalent immobilization of human serum albumin on cellulose acetate membrane for scavenging amyloid beta - A stepping extracorporeal strategy for ameliorating Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by interrupted neurocognitive functions and impaired mental development presumably caused by the accumulation of amyloid beta (Aβ) in the form of plaques. Targeting Aβ has been considered a promising approach for treating AD. In the current study, human serum albumin (HSA), a natural Aβ binder, is covalently immobilized onto the surface of a cellulose acetate (CA) membrane to devise an extracorporeal Aβ sequester. The immobilization of HSA at 3.06 ± 0.22 μg/mm2 of the CA membrane was found to be active functionally, as evidenced by the esterase-like activity converting p-nitrophenyl acetate into p-nitrophenol. The green fluorescent protein-Aβ (GFP-Aβ) fusion protein, recombinantly produced as a model ligand, exhibited characteristics of native Aβ. These features include the propensity to form aggregates or fibrils and an affinity for HSA with a dissociation constant (KD) of 0.91 μM. The HSA on the CA membrane showed concentration-dependent sequestration of GFP-Aβ in the 1-10-μM range. Moreover, it had a greater binding capacity than HSA immobilized on a commercial amine-binding plate. Results suggest that the covalent immobilization of HSA on the CA surface can be used as a potential platform for sequestering Aβ to alleviate AD.

Levels of Alzheimer's disease blood biomarkers are altered after food intake-A pilot intervention study in healthy adults

INTRODUCTION

Blood biomarkers accurately identify Alzheimer's disease (AD) pathophysiology and axonal injury. We investigated the influence of food intake on AD-related biomarkers in cognitively healthy, obese adults at high metabolic risk.

METHODS

One-hundred eleven participants underwent repeated blood sampling during 3 h after a standardized meal (postprandial group, PG). For comparison, blood was sampled from a fasting subgroup over 3 h (fasting group, FG). Plasma neurofilament light (NfL), glial fibrillary acidic protein (GFAP), amyloid-beta (Aβ) 42/40, phosphorylated tau (p-tau) 181 and 231, and total-tau were measured via single molecule array assays.

RESULTS

Significant differences were found for NfL, GFAP, Aβ42/40, p-tau181, and p-tau231 between FG and PG. The greatest change to baseline occurred for GFAP and p-tau181 (120 min postprandially, p < 0.0001).

CONCLUSION

Our data suggest that AD-related biomarkers are altered by food intake. Further studies are needed to verify whether blood biomarker sampling should be performed in the fasting state.

HIGHLIGHTS

Acute food intake alters plasma biomarkers of Alzheimer's disease in obese, otherwise healthy adults. We also found dynamic fluctuations in plasma biomarkers concentration in the fasting state suggesting physiological diurnal variations. Further investigations are highly needed to verify if biomarker measurements should be performed in the fasting state and at a standardized time of day to improve the diagnostic accuracy.

Physiological Roles of β-amyloid in Regulating Synaptic Function: Implications for AD Pathophysiology

The physiological functions of endogenous amyloid-β (Aβ), which plays important role in the pathology of Alzheimer's disease (AD), have not been paid enough attention. Here, we review the multiple physiological effects of Aβ, particularly in regulating synaptic transmission, and the possible mechanisms, in order to decipher the real characters of Aβ under both physiological and pathological conditions. Some worthy studies have shown that the deprivation of endogenous Aβ gives rise to synaptic dysfunction and cognitive deficiency, while the moderate elevation of this peptide enhances long term potentiation and leads to neuronal hyperexcitability. In this review, we provide a new view for understanding the role of Aβ in AD pathophysiology from the perspective of physiological meaning.

MemophenolTM Prevents Amyloid-β Deposition and Attenuates Inflammation and Oxidative Stress in the Brain of an Alzheimer's Disease Rat

Alzheimer's disease (AD) is the most common cause of dementia, and its prevalence rises with age. Inflammation and altered antioxidant systems play essential roles in the genesis of neurodegenerative diseases. In this work, we looked at the effects of Memophenol^TM, a compound rich in polyphenols derived from French grape (Vitis vinifera L.) and wild North American blueberry (Vaccinium angustifolium A.) extracts, in a rat model of AD. Methods: For 60 days, the animals were administered with AlCl₃ (100 mg/kg, orally) and D-galactose (60 mg/kg, intraperitoneally), while from day 30, Memophenol^TM (15 mg/kg) was supplied orally for 30 consecutive days. AlCl₃ accumulates mainly in the hippocampus, the main part of the brain involved in memory and learning. Behavioral tests were performed the day before the sacrifice when brains were collected for analysis. Results: Memophenol^TM decreased behavioral alterations and hippocampus neuronal degeneration. It also lowered phosphorylated Tau (p-Tau) levels, amyloid precursor protein (APP) overexpression, and β-amyloid (Aβ) buildup. Furthermore, Memophenol^TM reduced the pro-oxidative and pro-inflammatory hippocampus changes caused by AD. Our finding, relevant to AD pathogenesis and therapeutics, suggests that Memophenol^TM, by modulating oxidative and inflammatory pathways and by regulating cellular brain stress response mechanisms, protects against the behavioral and histopathological changes associated with AD.

How Can Insulin Resistance Cause Alzheimer's Disease?

Alzheimer's disease (AD) is a neurodegenerative disorder associated with cognitive decline. Despite worldwide efforts to find a cure, no proper treatment has been developed yet, and the only effective countermeasure is to prevent the disease progression by early diagnosis. The reason why new drug candidates fail to show therapeutic effects in clinical studies may be due to misunderstanding the cause of AD. Regarding the cause of AD, the most widely known is the amyloid cascade hypothesis, in which the deposition of amyloid beta and hyperphosphorylated tau is the cause. However, many new hypotheses were suggested. Among them, based on preclinical and clinical evidence supporting a connection between AD and diabetes, insulin resistance has been pointed out as an important factor in the development of AD. Therefore, by reviewing the pathophysiological background of brain metabolic insufficiency and insulin insufficiency leading to AD pathology, we will discuss how can insulin resistance cause AD.

Impaired autophagy in amyloid-beta pathology: A traditional review of recent Alzheimer's research

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder. The major pathological changes in AD progression are the generation and accumulation of amyloid-beta (Aβ) peptides as well as the presence of abnormally hyperphosphorylated tau proteins in the brain. Autophagy is a conserved degradation pathway that eliminates abnormal protein aggregates and damaged organelles. Previous studies have suggested that autophagy plays a key role in the production and clearance of Aβ peptides to maintain a steady-state of Aβ peptides levels. However, a growing body of evidence suggests that autophagy is significantly impaired in the pathogenesis of AD, especially in Aβ metabolism. Therefore, this article reviews the latest studies concerning the mechanisms of autophagy, the metabolism of Aβ peptides, and the defective autophagy in the production and clearance of Aβ peptides. Here, we also summarize the established and new strategies for targeting autophagy in vivo and through clinical AD trials to identify gaps in our knowledge and to generate further questions.

Octadecaneuropeptide Ameliorates Cognitive Impairments Through Inhibiting Oxidative Stress in Alzheimer's Disease Models

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by amyloid-β peptide (Aβ) deposition. Aβ accumulation induces oxidative stress, leading to mitochondrial dysfunction, apoptosis, and so forth. Octadecaneuropeptide (ODN), a diazepam-binding inhibitor (DBI)-derived peptide, has been reported to have antioxidant properties. However, it is unclear whether ODN has neuroprotective effects in AD.

OBJECTIVE

To profile the potential effects of ODN on AD.

METHODS

We established a mouse model of AD via microinjection of Aβ in the lateral ventricle. Utilizing a combination of western blotting assays, electrophysiological recordings, and behavioral tests, we investigated the neuroprotective effects of ODN on AD.

RESULTS

DBI expression was decreased in AD model mice and cells. Meanwhile, ODN decreased Aβ generation by downregulating amyloidogenic AβPP processing in HEK-293 cells stably expressing human Swedish mutant APP695 and BACE1 (2EB2). Moreover, ODN could inhibit Aβ-induced oxidative stress in primary cultured cells and mice, as reflected by a dramatic increase in antioxidants and a decrease in pro-oxidants. We also found that ODN could reduce oxidative stress-induced apoptosis by restoring mitochondrial membrane potential, intracellular Ca2+ and cleaved caspase-3 levels in Aβ-treated primary cultured cells and mice. More importantly, intracerebroventricular injection of ODN attenuated cognitive impairments as well as long-term potentiation in Aβ-treated mice.

CONCLUSION

These results suggest that ODN may exert a potent neuroprotective effect against Aβ-induced neurotoxicity and memory decline via its antioxidant effects, indicating that ODN may be a potential therapeutic agent for AD.

The Role of ERK1/2 Pathway in the Pathophysiology of Alzheimer's Disease: An Overview and Update on New Developments

Alzheimer's disease (AD) is the most common neurodegenerative disorder worldwide. Several findings suggest that correcting the dysregulated signaling pathways may offer a potential therapeutic approach in this disease. Extracellular signal-regulated kinase 1/2 (ERK1/2), a member of the mitogen-activated protein kinase family, plays a major role in regulation of cell proliferation, autophagy process, and protein synthesis. The available literature suggests dysregulated ERK1/2 in AD patients with potential implications in the multifaceted underlying pathologies of AD, including amyloid-β plaque formation, tau phosphorylation, and neuroinflammation. In this regard, in the current review, we aim to summarize the reports on the potential roles of ERK1/2 in AD pathophysiology.

Excretion of Amyloid-β in the Gastrointestinal Tract and Regulation by the Gut Microbiota

Background: Amyloid-β (Aβ) is important in the etiology of Alzheimer’s disease (AD). Removal of Aβ from the brain is a major strategy for the prevention and treatment of AD. Objective: To clarify whether Aβ 42 can be cleared by intestinal excretion and whether the gut microbiota (GM) can affect the excretory clearance of Aβ 42 in the peripheral blood and intestines. Methods: Male 8-month-old C57BL6 mice were maintained on either normal chow or received broad-spectrum antibiotics in their drinking water for one week. Sterile saline, fluorescein isothiocyanate (FITC), or FITC-Aβ 42 (fluorescein isothiocyanate-labeled amyloid-β 42 peptides) was injected 1 h before FITC, or FITC-Aβ 42 was injected 1 h before sampling. Related changes of Aβ 42 before and after injection were evaluated. Results: FITC-Aβ 42 was injected into mice through the tail vein and could later be detected in feces. Furthermore, the fecal concentrations of FITC-Aβ 42 were higher in mice that had been fed antibiotics to alter their GM than in normal mice. However, the FITC-Aβ 42 concentrations in blood showed the opposite pattern. Conclusion: Aβ 42 can be excreted into the intestinal lumen and is regulated by the GM.

N-terminally truncated Aβ4-x proteoforms and their relevance for Alzheimer's pathophysiology

Background

The molecular heterogeneity of Alzheimer’s amyloid-β (Aβ) deposits extends well beyond the classic Aβ1-40/Aβ1-42 dichotomy, substantially expanded by multiple post-translational modifications that increase the proteome diversity. Numerous truncated fragments consistently populate the brain Aβ peptidome, and their homeostatic regulation and potential contribution to disease pathogenesis are largely unknown. Aβ4-x peptides have been reported as major components of plaque cores and the limited studies available indicate their relative abundance in Alzheimer’s disease (AD).

Methods

Immunohistochemistry was used to assess the topographic distribution of Aβ4-x species in well-characterized AD cases using custom-generated monoclonal antibody 18H6—specific for Aβ4-x species and blind for full-length Aβ1-40/Aβ1-42—in conjunction with thioflavin-S and antibodies recognizing Aβx-40 and Aβx-42 proteoforms. Circular dichroism, thioflavin-T binding, and electron microscopy evaluated the biophysical and aggregation/oligomerization properties of full-length and truncated synthetic homologues, whereas stereotaxic intracerebral injections of monomeric and oligomeric radiolabeled homologues in wild-type mice were used to evaluate their brain clearance characteristics.

Results

All types of amyloid deposits contained the probed Aβ epitopes, albeit expressed in different proportions. Aβ4-x species showed preferential localization within thioflavin-S-positive cerebral amyloid angiopathy and cored plaques, strongly suggesting poor clearance characteristics and consistent with the reduced solubility and enhanced oligomerization of their synthetic homologues. In vivo clearance studies demonstrated a fast brain efflux of N-terminally truncated and full-length monomeric forms whereas their oligomeric counterparts—particularly of Aβ4-40 and Aβ4-42—consistently exhibited enhanced brain retention.

Conclusions

The persistence of aggregation-prone Aβ4-x proteoforms likely contributes to the process of amyloid formation, self-perpetuating the amyloidogenic loop and exacerbating amyloid-mediated pathogenic pathways.

Oleuropein-Rich Olive Leaf Extract Attenuates Neuroinflammation in the Alzheimer's Disease Mouse Model

Alzheimer's disease (AD) is the most common form of dementia among several neurodegenerative disorders afflicting the elderly. AD is characterized by the deposition of extracellular amyloid-β (Aβ) plaques, disrupted blood-brain barrier (BBB), and neuroinflammation. Several studies have demonstrated the health benefits of olive oil and olive leaf extract (OLE) due to their polyphenolic content. The main phenolic compound in OLE is glycosylated oleuropein (OLG), while the aglycon form of oleuropein (OLA) exists in much lower amounts. This work aimed to evaluate the effect of a low dose of OLG-rich OLE and the mechanism(s) that contributed to the observed beneficial effects against Aβ pathology in the homozygous 5xFAD mouse model. Mice were fed with OLE-enriched diet (695 μg/kg body weight/day) for 3 months, starting at 3 months old. Overall findings demonstrated that OLE reduced neuroinflammation by inhibiting the NF-κB pathway and suppressing the activation of NLRP3 inflammasomes and RAGE/HMGB1 pathways. In addition, OLE reduced total Aβ brain levels due to increased clearance and reduced production of Aβ and enhanced BBB integrity and function, which collectively improved the memory function. Thus, the consumption of OLE as a dietary supplement is expected to stop and/or slow the progression of AD.

The impact of uremic toxins on Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia, pathologically characterized by accumulation of senile plaques and neurofibrillary tangles. Chronic kidney disease (CKD) is highly prevalent in elderly population closely associated with occurrence of dementia. Recent epidemiological and experimental studies suggest a potential association of CKD with AD. Both diseases share a panel of identical risk factors, such as type 2 diabetes; and hypertension. However, the relationship between CKD and AD is unclear. Lower clearance of a panel of uremic toxin including cystatin-C, guanidine, and adiponectin due to CKD is implied to contribute to AD pathogenesis. In this review we summarize the current evidence from epidemiological, experimental and clinical studies on the potential contribution of uremic toxins to AD pathogenesis. We describe outstanding questions and propose an outlook on the link between uremic toxins and AD.

The Function and Expression of ATP-Binding Cassette Transporters Proteins in the Alzheimer's Disease

Despite many years of research, radical treatment of Alzheimer's disease (AD) has still not been found. Amyloid-β (Aβ) peptide is known to play an important role in the pathogenesis of this disease. AD is characterized by three main changes occurring in the central nervous system: (1) Aβ plaque accumulation that prevents synaptic communication, (2) the accumulation of hyperphosphorylated tau proteins that inhibit the transport of molecules inside neurons, and (3) neuronal cell loss of the limbic system. Mechanisms leading to Aβ accumulation in AD are excessive Aβ production as a result of mutations in amyloid precursor protein or genes, and impairment of clearance of Aβ due to changes in Aβ aggregation properties and/or Aβ removal processes. Human ATP-binding cassette (ABC) transporters are expressed in astrocyte, microglia, neuron, brain capillary endothelial cell, choroid plexus, choroid plexus epithelial cell, and ventricular ependymal cell. ABC transporters have essential detoxification and neuroprotective roles in the brain. The expression and functional changes in ABC transporters contribute to the accumulation of Aβ peptide. In conclusion, the review was aimed to summarize and highlight accumulated evidence in the literature focusing on the changing functions of human ABC transporter members, in AD pathogenesis and progression.

Diagnostic accuracy of blood biomarkers for Alzheimer's disease and amnestic mild cognitive impairment: A meta-analysis

OBJECTIVE

To examine the diagnostic accuracy of blood-based biomarkers for detecting Alzheimer's disease (AD) and amnestic mild cognitive impairment (aMCI).

METHODS

Seven electronic databases were comprehensively searched for studies evaluating the diagnostic accuracy of blood-based biomarkers for detecting AD or aMCI up to July 31, 2020. The pooled sensitivity, specificity, and the diagnostic odds ratio (DOR) were calculated using a hierarchical summary receiver operating characteristic model.

RESULTS

A total of 17 studies (n = 2,083) were included. In differentiating patients with AD from the controls, the DOR was 32.2 for the plasma Aβ42 (sensitivity = 88 %, specificity = 81 %), 29.1 for the plasma Aβ oligomer (sensitivity = 80 %, specificity = 88 %), and 52.1 for the plasma tau (sensitivity = 90 %, specificity = 87 %). For differentiating aMCI from the controls, the DOR was 60.4 for the plasma Aβ42 (sensitivity = 86 %, specificity = 90 %) and 49.1 for the plasma tau (sensitivity = 79 %, specificity = 94 %). The use of ultra-high sensitive technology explained the heterogeneity in the diagnostic performance of blood-based biomarkers (P =  .01).

CONCLUSIONS

We suggest that blood-based biomarkers are minimally invasive and cost-effective tools for detecting AD; however, the evidence for detecting aMCI was still limited.

Dynamic Changes in the Levels of Amyloid-β42 Species in the Brain and Periphery of APP/PS1 Mice and Their Significance for Alzheimer's Disease

Although amyloid-β₄₂ (Aβ₄₂) has been used as one of the core biomarkers for Alzheimer’s disease (AD) diagnosis, the dynamic changes of its different forms in the brain, blood, and even intestines and its correlation with the progression of AD disease remain obscure. Herein, we screened Aβ₄₂-specific preferred antibody pairs 1F12/1F12 and 1F12/2C6 to accurately detect Aβ₄₂ types using sandwich ELISA, including total Aβ₄₂, Aβ₄₂ oligomers (Aβ₄₂Os), and Aβ₄₂ monomers (Aβ₄₂Ms). The levels of Aβ₄₂ species in the brain, blood, and intestines of different aged APP/PS1 mice were quantified to study their correlation with AD progression. Total Aβ₄₂ levels in the blood were not correlated with AD progression, but Aβ₄₂Ms level in the blood of 9-month-old APP/PS1 mice was significantly reduced, and Aβ₄₂Os level in the brain was significantly elevated compared to 3-month-old APP/PS1, demonstrating that the levels of Aβ₄₂Ms and Aβ₄₂Os in the blood and brain were correlated with AD progression. Interestingly, in 9-month-old APP/PS1 mice, the level of Aβ₄₂ in the intestine was higher than that in 3-month-old APP/PS1 mice, indicating that the increased level of Aβ₄₂ in the gastrointestinal organs may also be related to the progression of AD. Meanwhile, changes in the gut microbiota composition of APP/PS1 mice with age were also observed. Therefore, the increase in Aβ derived from intestinal tissues and changes in microbiome composition can be used as a potential early diagnosis tool for AD, and further used as an indicator of drug intervention to reduce brain amyloid.

Cardiometabolic Modification of Amyloid Beta in Alzheimer's Disease Pathology

In recent years, several studies have suggested that cardiometabolic disorders, such as diabetes, obesity, hypertension, and dyslipidemia, share strong connections with the onset of neurodegenerative disorders such as Parkinson’s and Alzheimer’s disease (AD). However, establishing a definitive link between medical disorders with coincident pathophysiologies is difficult due to etiological heterogeneity and underlying comorbidities. For this reason, amyloid β (Aβ), a physiological peptide derived from the sequential proteolysis of amyloid precursor protein (APP), serves as a crucial link that bridges the gap between cardiometabolic and neurodegenerative disorders. Aβ normally regulates neuronal synaptic function and repair; however, the intracellular accumulation of Aβ within the brain has been observed to play a critical role in AD pathology. A portion of Aβ is believed to originate from the brain itself and can readily cross the blood-brain barrier, while the rest resides in peripheral tissues that express APP required for Aβ generation such as the liver, pancreas, kidney, spleen, skin, and lungs. Consequently, numerous organs contribute to the body pool of total circulating Aβ, which can accumulate in the brain and facilitate neurodegeneration. Although the accumulation of Aβ corresponds with the onset of neurodegenerative disorders, the direct function of periphery born Aβ in AD pathophysiology is currently unknown. This review will highlight the contributions of individual cardiometabolic diseases including cardiovascular disease (CVD), type 2 diabetes (T2D), obesity, and non-alcoholic fatty liver disease (NAFLD) in elevating concentrations of circulating Aβ within the brain, as well as discuss the comorbid association of Aβ with AD pathology.

Effect of High Cholesterol Regulation of LRP1 and RAGE on Aβ Transport Across the Blood-Brain Barrier in Alzheimer's Disease

BACKGROUND

High cholesterol aggravates the risk development of Alzheimer's disease (AD). AD is closely related to the transport impairment of Amyloid-β (Aβ) in the blood-brain barrier. It is unclear whether high cholesterol affects the risk of cognitive impairment in AD by affecting Aβ transport. The purpose of the study is to investigate whether high cholesterol regulates Aβ transport through low-density Lipoprotein Receptor-Related Protein 1 (LRP1) and Receptor for Advanced Glycation End products (RAGE) in the risk development of AD.

METHODS

We established high cholesterol AD mice model. The learning and memory functions were evaluated by Morris Water Maze (MWM). Cerebral microvascular endothelial cells were isolated, cultured, and observed. The expression levels of LRP1 and RAGE of endothelial cells and their effect on Aβ transport in vivo were observed. The expression level of LRP1 and RAGE was detected in cultured microvessels after using Wnt inhibitor DKK-1 and β-catenin inhibitor XAV-939.

RESULTS

Hypercholesterolemia exacerbated spatial learning and memory impairment. Hypercholesterolemia increased serum Aβ40 level, while serum Aβ42 level did not change significantly. Hypercholesterolemia decreased LRP1 expression and increased RAGE expression in cerebral microvascular endothelial cells. Hypercholesterolemia increased brain apoptosis in AD mice. In in vitro experiment, high cholesterol decreased LRP1 expression and increased RAGE expression, increased Aβ40 expression in cerebral microvascular endothelial cells. High cholesterol regulated the expressions of LRP1 and RAGE and transcriptional activity of LRP1 and RAGE promoters by the Wnt/β-catenin signaling pathway.

CONCLUSION

High cholesterol decreased LRP1 expression and increased RAGE expression in cerebral microvascular endothelial cells, which led to Aβ transport disorder in the blood-brain barrier. Increased Aβ deposition in the brain aggravated apoptosis in the brain, resulting to cognitive impairment of AD mice.

Relationship Between Amyloid-β Deposition and Blood-Brain Barrier Dysfunction in Alzheimer's Disease

Amyloid-β (Aβ) is the predominant pathologic protein in Alzheimer's disease (AD). The production and deposition of Aβ are important factors affecting AD progression and prognosis. The deposition of neurotoxic Aβ contributes to damage of the blood-brain barrier. However, the BBB is also crucial in maintaining the normal metabolism of Aβ, and dysfunction of the BBB aggravates Aβ deposition. This review characterizes Aβ deposition and BBB damage in AD, summarizes their interactions, and details their respective mechanisms.

β-Amyloid Targeting with Two-Dimensional Covalent Organic Frameworks: Multi-Scale In-Silico Dissection of Nano-Biointerface

Cytotoxic aggregation of misfolded β-amyloid (Aβ) proteins is the main culprit suspected to be behind the development of Alzheimer's disease (AD). In this study, Aβ interactions with the novel two-dimensional (2D) covalent organic frameworks (COFs) as therapeutic options for avoiding β-amyloid aggregation have been investigated. The results from multi-scale atomistic simulations suggest that amine-functionalized COFs with a large surface area (more than 1000 m2 /gr) have the potential to prevent Aβ aggregation. Gibb's free energy analysis confirmed that COFs could prevent protofibril self-assembly in addition to inhibiting β-amyloid aggregation. Additionally, it was observed that the amine functional group and high contact area could improve the inhibitory effect of COFs on Aβ aggregation and enhance the diffusivity of COFs through the blood-brain barrier (BBB). In addition, microsecond coarse-grained (CG) simulations with three hundred amyloids reveal that the presence of COFs creates instability in the structure of amyloids and consequently prevents the fibrillation. These results suggest promising applications of engineered COFs in the treatment of AD and provide a new perspective on future experimental research.

Peptidomimetic-Based Vesicles Inhibit Amyloid-β Fibrillation and Attenuate Cytotoxicity

An interruption in Aβ homeostasis leads to the deposit of neurotoxic amyloid plaques and is associated with Alzheimer's disease. A supramolecular strategy based on the assembly of peptidomimetic agents into functional vesicles has been conceived for the simultaneous inhibition of Aβ₄₂ fibrillation and expedited clearance of Aβ₄₂ aggregates. Tris-pyrrolamide peptidomimetic, ADH-353, contains one hydrophobic N-butyl and two hydrophilic N-propylamine side chains and readily forms vesicles under physiological conditions. These vesicles completely rescue both mouse neuroblastoma N2a and human neuroblastoma SH-SY5Y cells from the cytotoxicity that follows from Aβ₄₂ misfolding likely in mitochondria. Biophysical studies, including confocal imaging, demonstrate the biocompatibility and selectivity of the approach toward this aberrant protein assembly in cellular milieu.

Changes of blood-brain-barrier function and transfer of amyloid beta in rats with collagen-induced arthritis

Background

Rheumatoid arthritis (RA) is characterized by synovial inflammation, cartilage damage, and systemic inflammation. RA is also associated with the occurrence of neuroinflammation and neurodegenerative diseases. In this study, the impacts of RA on the function of the blood-brain barrier (BBB) and the disposition of amyloid beta (Aβ), including BBB transport and peripheral clearance of Aβ, were investigated in rats with collagen-induced arthritis (CIA), an animal model with similarity to clinical and pathological features of human RA.

Methods

CIA was induced in female Lewis rats. In addition to neuroinflammation, the integrity and function of the BBB were examined. The expression of Aβ-transporting proteins at brain blood vessels was measured. Blood-to-brain influx and plasma clearance of Aβ were determined.

Results

Both microgliosis and astrogliosis were significantly increased in the brain of CIA rats, compared with controls. In terms of BBB function, the BBB permeability of sodium fluorescein, a marker compound for BBB integrity, was significantly increased in CIA rats. Moreover, increased expression of matrix metalloproteinase-3 (MMP-3) and MMP-9 and decreased expression of tight junction proteins, zonula occludens-1 (ZO-1) and occludin, were observed in brain microvessels of CIA rats. In related to BBB transport of Aβ, protein expression of the receptor of advanced glycation end product (RAGE) and P-glycoprotein (P-gp) was significantly increased in brain microvessels of CIA rats. Notably, much higher expression of RAGE was identified at the arterioles of the hippocampus of CIA rats. Following an intravenous injection of human Aβ, significant higher brain influx of Aβ was observed in the hippocampus of CIA rats.

Conclusions

Neuroinflammation and the changes of BBB function were observed in CIA rats. The increased RAGE expression at cerebral blood vessels and enhanced blood-to-brain influx of Aβ indicate the imbalanced BBB clearance of Aβ in RA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02086-2.

Nutraceutical based SIRT3 activators as therapeutic targets in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, and its incidence is increasing worldwide with increased lifespan. Currently, there is no effective treatment to cure or prevent the progression of AD, which indicates the need to develop novel therapeutic targets and agents. Sirtuins, especially SIRT3, a mitochondrial deacetylase, are NAD-dependent histone deacetylases involved in aging and longevity. Accumulating evidence indicates that SIRT3 dysfunction is strongly associated with pathologies of AD, hence, therapeutic modulation of SIRT3 activity may be a novel application to ameliorate the pathologies of AD. Natural products commonly used in traditional medicine have wide utility and appear to have therapeutic benefits for the treatment of neurodegenerative diseases such as AD. The present review summarizes the currently available natural SIRT3 activators and their potentially neuroprotective molecular mechanisms of action that make them a promising agent in the treatment and management of neurodegenerative diseases such as AD.

Disaggregation of Amyloid-β Plaques by a Local Electric Field Generated by a Vertical Nanowire Electrode Array

The aggregation and accumulation of amyloid-β (Aβ) peptides is a characteristic pathology for Alzheimer's disease (AD). Although noninvasive therapies involving stimulation by electric field (EF) have been reported, the efficiency of Aβ disaggregation needs to be further improved for this strategy to be used in clinical settings. In this study, we show that an electrode based on a vertical nanowire electrode array (VNEA) is far more superior to a typical flat-type electrode in disaggregating Aβ plaques. The enhanced disaggregation efficiency of VNEA is due to the formation of high-strength local EF between the nanowires, as verified by in silico and empirical evidence. Compared with those of the flat electrode, the simulation data revealed that 19.8-fold and 8.8-fold higher EFs are generated above and between the nanowires, respectively. Moreover, empirical cyclic voltammetry data demonstrated that VNEA had a 2.7-fold higher charge capacity than the flat electrode; this is associated with the higher surface area of VNEA. The conformational transition of Aβ peptides between the β-sheet and α-helix could be sensitively monitored in real time by the newly designed in situ circular dichroism instrument. This highly efficient EF-configuration of VNEA will lower the stimulation power for disaggregating the Aβ plaques, compared to that of other existing field-mediated modulation systems. Considering the complementary metal-oxide-semiconductor-compatibility and biocompatible strength of the EF for perturbing the Aβ aggregation, our study could pave the way for the potential use of electric stimulation devices for in vivo therapeutic application as well as scientific studies for AD.

The Interplay of ABC Transporters in Aβ Translocation and Cholesterol Metabolism: Implicating Their Roles in Alzheimer's Disease

The occurrence of Alzheimer's disease (AD) worldwide has been progressively accelerating at an alarming rate, without any successful therapeutic strategy for the disease mitigation. The complexity of AD pathogenesis needs to be targeted with an alternative approach, as provided by the superfamily of ATP-binding cassette (ABC) transporters, which constitutes an extensive range of proteins, capable of transporting molecular entities across biological membranes. These protein moieties have been implicated in AD, based upon their potential in lipid transportation, resulting in maintenance of cholesterol homeostasis. These transporters have been reported to target the primary hallmark of AD pathogenesis, namely, beta-amyloid hypothesis, which is associated with accumulation of beta-amyloid (Aβ) plaques in AD patients. The ABC transporters have been observed to be localized to the capillary endothelial cells of the blood-brain barrier and neural parenchymal cells, where they exhibit different roles, consequently influencing the neuronal expression of Aβ peptides. The review highlights different families of ABC transporters, ABCB1 (P-glycoprotein), ABCA (ABCA1, ABCA2, and ABCA7), ABCG2 (BCRP; breast cancer resistance protein), ABCG1 and ABCG4, as well as ABCC1 (MRP; multidrug resistance protein) in the CNS, and their interplay in regulating cholesterol metabolism and Aβ peptide load in the brain, simultaneously exerting protective effects against neurotoxic substrates and xenobiotics. The authors aim to establish the significance of this alternative approach as a novel therapeutic target in AD, to provide the researchers an opportunity to evaluate the potential aspects of ABC transporters in AD treatment.

"What Doesn't Kill You Makes You Stronger": Future Applications of Amyloid Aggregates in Biomedicine

Amyloid proteins are linked to the pathogenesis of several diseases including Alzheimer's disease, but at the same time a range of functional amyloids are physiologically important in humans. Although the disease pathogenies have been associated with protein aggregation, the mechanisms and factors that lead to protein aggregation are not completely understood. Paradoxically, unique characteristics of amyloids provide new opportunities for engineering innovative materials with biomedical applications. In this review, we discuss not only outstanding advances in biomedical applications of amyloid peptides, but also the mechanism of amyloid aggregation, factors affecting the process, and core sequences driving the aggregation. We aim with this review to provide a useful manual for those who engineer amyloids for innovative medicine solutions.

Impaired Peripheral Lymphatic Function and Cerebrospinal Fluid Outflow in a Mouse Model of Alzheimer's Disease

Cerebrospinal fluid (CSF) outflow from the brain occurs through absorption into the arachnoid villi and, more predominantly, through meningeal and olfactory lymphatics that ultimately drain into the peripheral lymphatics. Impaired CSF outflow has been postulated as a contributing mechanism in Alzheimer's disease (AD). Herein we conducted near-infrared fluorescence imaging of CSF outflow into the peripheral lymph nodes (LNs) and of peripheral lymphatic function in a transgenic mouse model of AD (5XFAD) and wild-type (WT) littermates. CSF outflow was assessed from change in fluorescence intensity in the submandibular LNs as a function of time following bolus, an intrathecal injection of indocyanine green (ICG). Peripheral lymphatic function was measured by assessing lymphangion contractile function in lymphatics draining into the popliteal LN following intradermal ICG injection in the dorsal aspect of the hind paw. The results show 1) significantly impaired CSF outflow into the submandibular LNs of 5XFAD mice and 2) reduced contractile frequency in the peripheral lymphatics as compared to WT mice. Impaired CSF clearance was also evidenced by reduction of fluorescence on ventral surfaces of extracted brains of 5XFAD mice at euthanasia. These results support the hypothesis that lymphatic congestion caused by reduced peripheral lymphatic function could limit CSF outflow and may contribute to the cause and/or progression of AD.

Mesenchymal Stem Cell Therapy and Alzheimer's Disease: Current Status and Future Perspectives

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease worldwide, but its cause remains unclear. Although a few drugs can provide temporary and partial relief of symptoms in some patients, no curative treatment is available. Therefore, attention has been focused on research using stem cells to treat AD. Among stem cells, mesenchymal stem cells (MSCs) have been used to treat the related pathologies in animal models of AD, and other neurodegenerative disease. This review describes latest research trends on the use of MSC-based therapies in AD and its action of mechanism. MSCs have several beneficial effects. They would be specified as the reduction of neuroinflammation, the elimination of amyloid-β, neurofibrillary tangles, and abnormal protein degradation, the promotion of autophagy-associated and blood-brain barrier recoveries, the upregulation of acetylcholine levels, improved cognition, and the recovery of mitochondrial transport. Therefore, this review describes the latest research trends in MSC-based therapy for AD by demonstrating the importance of MSC-based therapy and understanding of its mechanisms in AD and discusses the limitations and perspectives of stem cell therapy in AD.

Study of Biomolecular Interactions of Mitochondrial Proteins Related to Alzheimer's Disease: Toward Multi-Interaction Biomolecular Processes

Progressive mitochondrial dysfunction due to the accumulation of amyloid beta (Aβ) peptide within the mitochondrial matrix represents one of the key characteristics of Alzheimer's disease (AD) and appears already in its early stages. Inside the mitochondria, Aβ interacts with a number of biomolecules, including cyclophilin D (cypD) and 17β-hydroxysteroid dehydrogenase type 10 (17β-HSD10), and affects their physiological functions. However, despite intensive ongoing research, the exact mechanisms through which Aβ impairs mitochondrial functions remain to be explained. In this work, we studied the interactions of Aβ with cypD and 17β-HSD10 in vitro using the surface plasmon resonance (SPR) method and determined the kinetic parameters (association and dissociation rates) of these interactions. This is the first work which determines all these parameters under the same conditions, thus, enabling direct comparison of relative affinities of Aβ to its mitochondrial binding partners. Moreover, we used the determined characteristics of the individual interactions to simulate the concurrent interactions of Aβ with cypD and 17β-HSD10 in different model situations associated with the progression of AD. This study not only advances the understanding of Aβ-induced processes in mitochondria during AD, but it also provides a new perspective on research into complex multi-interaction biomolecular processes in general.

Modulation of SPARC/Hevin Proteins in Alzheimer's Disease Brain Injury

Alzheimer’s disease (AD) is an age-related progressive form of dementia that features neuronal loss, intracellular tau, and extracellular amyloid-β (Aβ) protein deposition. Neurodegeneration is accompanied by neuroinflammation mainly involving microglia, the resident innate immune cell population of the brain. During AD progression, microglia shift their phenotype, and it has been suggested that they express matricellular proteins such as secreted protein acidic and rich in cysteine (SPARC) and Hevin protein, which facilitate the migration of other immune cells, such as blood-derived dendritic cells. We have detected both SPARC and Hevin in postmortem AD brain tissues and confirmed significant alterations in transcript expression using real-time qPCR. We suggest that an infiltration of myeloid-derived immune cells occurs in the areas of diseased tissue. SPARC is highly expressed in AD brain and collocates to Aβ protein deposits, thus contributing actively to cerebral inflammation and subsequent tissue repair, and Hevin may be downregulated in the diseased state. However, further research is needed to reveal the exact roles of SPARC and Hevin proteins and associated signaling pathways in AD-related neuroinflammation. Nevertheless, normalizing SPARC/Hevin protein expression such as interdicting heightened SPARC protein expression may confer a novel therapeutic opportunity for modulating AD progression.

Blood-Based Biomarkers for Predictive Diagnosis of Cognitive Impairment in a Pakistani Population

Numerous studies have identified an association between age-related cognitive impairment (CI) and oxidative damage, accumulation of metals, amyloid levels, tau, and deranged lipid profile. There is a concerted effort to establish the reliability of these blood-based biomarkers for predictive diagnosis of CI and its progression. We assessed the serum levels of high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, total cholesterol, selected metals (Cu, Al, Zn, Pb, Mn, Cad), and total-tau and amyloid beta-42 protein in mild (n = 71), moderate (n = 86) and severe (n = 25) cognitively impaired patients and compared them with age-matched healthy controls (n = 90) from Pakistan. We found that a decrease in HDL cholesterol (correlation coefficient r = 0.467) and amyloid beta-42 (r = 0.451) were associated with increased severity of CI. On the other hand, an increase in cholesterol ratio (r = -0.562), LDL cholesterol (r = -0.428), triglycerides, and total-tau (r = -0.443) were associated with increased severity of CI. Increases in cholesterol ratio showed the strongest association and correlated with increases in tau concentration (r = 0.368), and increased triglycerides were associated with decreased amyloid beta-42 (r = -0.345). Increased Cu levels showed the strongest association with tau increase and increased Zn and Pb levels showed the strongest association with reduced amyloid beta-42 levels. Receiver Operating Characteristic (ROC) showed the cutoff values of blood metals (Al, Pb, Cu, Cad, Zn, and Mn), total-tau, and amyloid beta-42 with sensitivity and specificity. Our data show for the first time that blood lipids, metals (particularly Cu, Zn, Pb, and Al), serum amyloid-beta-42/tau proteins modulate each other's levels and can be collectively used as a predictive marker for CI.

Microglia Do Not Take Up Soluble Amyloid-beta Peptides, But Partially Degrade Them by Secreting Insulin-degrading Enzyme

Microglia play important roles in the pathogenesis of Alzheimer's disease (AD), in part, by affecting the clearance of amyloid-β (Aβ) peptides. Most studies, however, used synthetic soluble Aβ (sAβ) at higher concentrations. The exact mechanisms underlying microglia-mediated clearance of physiological sAβ at very low concentrations remain unclear. Here we reported that there were much more Iba-1- and CD68-positive microglia and significantly less sAβ left in the brain of adult mice 5 days after the surgery of sAβ microinjection compared to 2 h after the surgery (p < 0.05). However, very few Iba-1- and CD68-positive microglia co-localized with microinjected fluorescently labeled sAβ (FLsAβ₄₂) 5 days after the surgery. Also, there was no co-localization of FLsAβ₄₂ with a lysosomal marker (LAMP-1) 5 days after the surgery. There was no significant difference in the percentage of Aβ⁺/PE-CD11b⁺/APC-CD45^low microglia between the control group and the group microinjected with TBS-soluble Aβ extracted from the brains of AD patients (p > 0.05). The degradation of physiological sAβ was prevented by a highly selective insulin-degrading enzyme inhibitor (Ii1) but not by a phagocytosis inhibitor (polyinosinic acid) or pinocytosis inhibitor (cytochalasin B) in vitro. Furthermore, the reduction of synthetic and physiological sAβ in the brain was partially prevented by the co-injection of Ii1 in vivo (p < 0.05). Our results demonstrate that microglia do not take up synthetic or physiological sAβ, but partially degrade it via the secretion of insulin-degrading enzyme, which will be beneficial for understanding how sAβ is removed from the brain by microglia.

Revisiting the role of brain and peripheral Aβ in the pathogenesis of Alzheimer's disease

Amyloid beta (Aβ) is an intricate molecule that interacts with several biomolecules and/or produces insoluble assemblies and eventually the nonphysiological depositions of its alternate with normal neuronal conditions leading to Alzheimer's disease (AD). Aβ is formed through the proteolytic cleavage of the amyloid precursor protein (APP). Significant efforts are being made to explore the exact role of Aβ in AD pathogenesis. It is believed that the deposition of Aβ in the brain takes place from Aβ components which are derived from the brain itself. However, recent evidence suggests that Aβ derived also from the periphery and hence the Aβ circulating in the blood is capable of penetrating the blood-brain barrier (BBB) and the role of Aβ derived from the periphery is largely unknown so far. Therefore, Aβ origin determination and the underlying mechanisms of its pathological effects are of considerable interest in exploring effective therapeutic strategies. The purpose of this review is to provide a novel insight into AD pathogenesis based on Aβ in both the brain and periphery and highlight new therapeutic avenues to combat AD pathogenesis.

Interplay of curcumin and its liver metabolism on the level of Aβ in the brain of APPswe/PS1dE9 mice before AD onset

BACKGROUND

An increasing number of studies have shown that Alzheimer's disease (AD) is a systemic disease characterized by brain dysfunction. In this study, we aimed to investigate the effects of curcumin on the liver, an important metabolic organ, and on the brain in APP_swe/PS1_dE9 (APP/PS1) mice, and the interaction between these effects.

METHODS

Curcumin was administered to 5-month-old APP/PS1 transgenic mice for 7 consecutive days using the intragastric (ig) and intracerebroventricular (icv) administration routes, respectively. The object recognition test (ORT) and open field test (OFT) were conducted to evaluate long-term recognition memory and anxiety after curcumin administration. Levels of β-amyloid (Aβ), Aβ_42, and interleukin-1β (IL-1β) in the brain and liver were measured.

RESULTS

In the ig group, curcumin ameliorated anxiety-like behavior and suppressed the level of Aβ₄₂ in the liver and the total Aβ in the brain. In the icv group, curcumin treatment affected the distribution of Aβ₄₂ and IL-1β in the brain compared to the liver. There was a significant treatment-region interaction in Aβ₄₂ level for the icv group (F(1, 24) = 17.7, p < 0.001), but no interaction effect for the ig group.

CONCLUSION

Our findings show that curcumin administration before Aβ deposition shows promise for preventing AD, and further that curcumin may play an important role in the clearance of Aβ₄₂ from the brain to the peripheral circulation.

Cornel iridoid glycoside ameliorates cognitive deficits in APP/PS1/tau triple transgenic mice by attenuating amyloid-beta, tau hyperphosphorylation and neurotrophic dysfunction

Background

Targeted proteinopathy is involved in creating pharmacological agents that protect against Alzheimer disease (AD). Cornel iridoid glycoside (CIG) is an effective component derived from Cornus officinalis. The present study aimed to determine the effects of CIG on β-amyloid (Aβ) and tau pathology and the underlying mechanisms in APP/PS1/tau triple transgenic (3×Tg) model mice.

Methods

We intragastrically administered 16-month-old 3×Tg mice with CIG (100 and 200 mg/kg) daily for two months. Learning and memory abilities were determined using the Morris water maze (MWM) and object recognition tests (ORT). Amyloid plaques and Aβ40/42 and the expression of related proteins in the cerebral cortex and hippocampus of mice was determined by western blotting

Results

CIG improved learning and memory impairment in 3×Tg model mice, decreased amyloid plaque deposition, Aβ40/42 and the expression of full-length amyloid precursor protein, and increased levels of ADAM-10 (α-secretase), neprilysin (NEP), and insulin degrading enzyme (IDE) in the brains of the model mice. CIG also reduced tau hyperphosphorylation, and elevated phosphorylation level of GSK-3β at Ser9 and methylation of PP2A catalytic subunit C in the model mice. Moreover, CIG increased the expression of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and phosphorylated cAMP-responsive element binding protein (p-CREB) in the brain of 3×Tg mice.

Conclusions

CIG ameliorated learning and memory deficit via reducing Aβ content and, tau hyperphosphorylation and increasing neurotrophic factors in the brain of 3×Tg mice. These results suggest that CIG may be beneficial for AD therapy.

Extracellular Vesicles as a Neprilysin Delivery System Memory Improvement in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative brain disorder which has no effective treatment yet due to the blood barrier in the brain that limits the drugs with the potential of disease improvement. Extracellular vesicles (EVs) are biocompatible nanoparticles with a lipid membrane. These vesicles are secreted from various cells such as mesenchymal stem cells (MSCs) and can pass through biological barriers for transfer of information such as signals or be used as carriers for various proteins like Neprilysin (NEP). NEP is an active enzyme in the clearance of abnormal aggregated beta-amyloid sheets in the brain. In the present study, we used EVs to carry NEP for memory improvement in Alzheimer's disease. For this purpose, bone marrow MSCs were isolated from rat femur. Stemness evaluation of established cells was characterized by differentiation potency and specific markers with flowcytometry. EVs were isolated from MSCs supernatant by ultracentrifugation and analyzed by scanning electron microscopy (SEM), dynamic light scattering (DLS) and western blotting. EVs were loaded with NEP by freeze-thaw cycle and then administrated intranasally in a rat model of the AD for 14 days. Our findings showed EV-loaded NEP caused a decrease in IL-1beta and also BAX but an increase in BCL2 expression level in the rat brain. Altogether, these data showed that EV-loaded NEP can improve brain-related behavioural function which may be mediated through the regulation of inflammation and apoptosis. These findings suggest that EV-loaded NEP can be considered as a potential drug delivery system for the improvement of AD.

Combining Chalcones with Donepezil to Inhibit Both Cholinesterases and Aβ Fibril Assembly

The fact that the number of people with Alzheimer's disease is increasing, combined with the limited availability of drugs for its treatment, emphasize the need for the development of novel effective therapeutics for treating this brain disorder. Herein, we focus on generating 12 chalcone-donepezil hybrids, with the goal of simultaneously targeting amyloid-β (Aβ) peptides as well as cholinesterases (i.e., acetylcholinesterase (AChE) and butyrylcholinesterase (BChE)). We present the design, synthesis, and biochemical evaluation of these two series of novel 1,3-chalcone-donepezil (15a-15f) or 1,4-chalcone-donepezil (16a-16f) hybrids. We evaluate the relationship between their structures and their ability to inhibit AChE/BChE activity as well as their ability to bind Aβ peptides. We show that several of these novel chalcone-donepezil hybrids can successfully inhibit AChE/BChE as well as the assembly of N-biotinylated Aβ(1-42) oligomers. We also demonstrate that the Aβ binding site of these hybrids differs from that of Pittsburgh Compound B (PIB).

Liver Dysfunction as a Novel Player in Alzheimer's Progression: Looking Outside the Brain

Alzheimer's disease (AD) afflicts an estimated 20 million people worldwide and is the fourth-leading cause of death in the developed world. The most common cause of dementia in older individuals, AD is characterized by neuropathologies including synaptic and neuronal degeneration, amyloid plaques, and neurofibrillary tangles (NTFs). Amyloid plaques are primarily composed of amyloid-beta peptide (Aβ), which accumulates in the brains of patients with AD. Further, small aggregates termed Aβ oligomers are implicated in the synaptic loss and neuronal degeneration underlying early cognitive impairments. Whether Aβ accumulates in part because of dysregulated clearance from the brain remains unclear. The flow of substances (e.g., nutrients, drugs, toxins) in and out of the brain is mediated by the blood-brain-barrier (BBB). The BBB exhibits impairment in AD patients and animal models. The effect of BBB impairment on Aβ, and whether BBB function is affected by non-neurological pathologies that impair peripheral clearance requires further investigation. In particular, impaired peripheral clearance is a feature of nonalcoholic fatty liver disease (NAFLD), a spectrum of liver disorders characterized by accumulation of fat in the liver accompanied by varying degrees of inflammation and hepatocyte injury. NAFLD has reached epidemic proportions, with an estimated prevalence between 20% and 30% of the general population. This chronic condition may influence AD pathogenesis. This review article summarizes the current state of the literature linking NAFLD and AD, highlighting the role of the major Aβ efflux and clearance protein, the LRP-1 receptor, which is abundantly expressed in liver, brain, and vasculature.

Liraglutide and its Neuroprotective Properties-Focus on Possible Biochemical Mechanisms in Alzheimer's Disease and Cerebral Ischemic Events

Liraglutide is a GLP-1 analog (glucagon like peptide-1) used primarily in the treatment of diabetes mellitus type 2 (DM2) and obesity. The literature starts to suggest that liraglutide may reduce the effects of ischemic stroke by activating anti-apoptotic pathways, as well as limiting the harmful effects of free radicals. The GLP-1R expression has been reported in the cerebral cortex, especially occipital and frontal lobes, the hypothalamus, and the thalamus. Liraglutide reduced the area of ischemia caused by MCAO (middle cerebral artery occlusion), limited neurological deficits, decreased hyperglycemia caused by stress, and presented anti-apoptotic effects by increasing the expression of Bcl-2 and Bcl-xl proteins and reduction of Bax and Bad protein expression. The pharmaceutical managed to decrease concentrations of proapoptotic factors, such as NF-κB (Nuclear Factor-kappa β), ICAM-1 (Intercellular Adhesion Molecule 1), caspase-3, and reduced the level of TUNEL-positive cells. Liraglutide was able to reduce the level of free radicals by decreasing the level of malondialdehyde (MDA), and increasing the superoxide dismutase level (SOD), glutathione (GSH), and catalase. Liraglutide may affect the neurovascular unit causing its remodeling, which seems to be crucial for recovery after stroke. Liraglutide may stabilize atherosclerotic plaque, as well as counteract its early formation and further development. Liraglutide, through its binding to GLP-1R (glucagon like peptide-1 receptor) and consequent activation of PI3K/MAPK (Phosphoinositide 3-kinase/mitogen associated protein kinase) dependent pathways, may have a positive impact on Aβ (amyloid beta) trafficking and clearance by increasing the presence of Aβ transporters in cerebrospinal fluid. Liraglutide seems to affect tau pathology. It is possible that liraglutide may have some stem cell stimulating properties. The effects may be connected with PKA (phosphorylase kinase A) activation. This paper presents potential mechanisms of liraglutide activity in conditions connected with neuronal damage, with special emphasis on Alzheimer's disease and cerebral ischemia.

Genetic Analyses of Alzheimer's Disease in China: Achievements and Perspectives

Since 2010, the Chinese have become one of the most aged populations in the world, leading to a severe burden of neurodegenerative disorders. Alzheimer's disease (AD) is the most prevalent neurodegenerative disease and has a high genetic heritability. In the past two decades, numerous genetic analyses, from linkage analyses and candidate gene studies to genome-wide association studies (GWASs) and next-generation sequencing studies, have identified dozens of AD susceptibility or causal genes. These studies have provided a comprehensive genetic view and contributed to the understanding of the pathological and molecular mechanisms of the disease. However, most of the recognized AD genetic risk factors have been reported in studies based on European populations or populations of European ancestry, and data about the genetics of AD from other populations has been very limited. As China has the largest AD population in the world and because of the remarkable genetic differences between the East and the West, deciphering the genetic basis and molecular mechanism in Chinese patients with AD may add key points to the full characterization of AD. In this review, we present an overview of the current state of AD genetic research in China, with an emphasis on genome-level studies. We also describe the challenges and opportunities for future advances, especially for in-depth collaborations, brain bank construction, and primate animal modeling. There is an urgent need to promote public awareness and increase our collaborations and data sharing.

Lentiviral vector-mediated overexpression of Klotho in the brain improves Alzheimer's disease-like pathology and cognitive deficits in mice

Alzheimer's disease (AD) is the most common type of senile dementia. The antiaging gene Klotho is reported to decline in the brain of patients and animals with AD. However, the role of Klotho in the progression of AD remains elusive. The present study explored the effects and underlying mechanism of Klotho in a mouse model of AD. The upregulation of cerebral Klotho expression was mediated by an intracerebroventricular injection of a lentiviral vector that encoded Klotho (LV-KL) in 7-month-old amyloid precursor protein/presenilin 1 transgenic mice. Three months later, LV-KL significantly induced Klotho overexpression in the brain and effectively ameliorated cognitive deficit and AD-like pathology in amyloid precursor protein/presenilin 1 mice. LV-KL induced autophagy activation and protein kinase B/mammalian target of rapamycin inhibition both in AD mice and BV2 murine microglia. These results suggest that the upregulation of Klotho expression in the brain may promote the autophagic clearance of amyloid beta and protect against cognitive deficits in AD mice. These findings highlight the preventive and therapeutic potential of Klotho for the treatment of AD.

Vulnerability and resilience to Alzheimer's disease: early life conditions modulate neuropathology and determine cognitive reserve

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with a high prevalence among the elderly and a huge personal and societal impact. Recent epidemiological studies have indicated that the incidence and age of onset of sporadic AD can be modified by lifestyle factors such as education, exercise, and (early) stress exposure. Early life adversity is known to promote cognitive decline at a later age and to accelerate aging, which are both primary risk factors for AD. In rodent models, exposure to 'negative' or 'positive' early life experiences was recently found to modulate various measures of AD neuropathology, such as amyloid-beta levels and cognition at later ages. Although there is emerging interest in understanding whether experiences during early postnatal life also modulate AD risk in humans, the mechanisms and possible substrates underlying these long-lasting effects remain elusive.

METHODS

We review literature and discuss the role of early life experiences in determining later age and AD-related processes from a brain and cognitive 'reserve' perspective. We focus on rodent studies and the identification of possible early determinants of later AD vulnerability or resilience in relation to early life adversity/enrichment.

RESULTS

Potential substrates and mediators of early life experiences that may influence the development of AD pathology and cognitive decline are: programming of the hypothalamic-pituitary-adrenal axis, priming of the neuroinflammatory response, dendritic and synaptic complexity and function, overall brain plasticity, and proteins such as early growth response protein 1 (EGR1), activity regulated cytoskeleton-associated protein (Arc), and repressor element-1 silencing transcription factor (REST).

CONCLUSIONS

We conclude from these rodent studies that the early postnatal period is an important and sensitive phase that influences the vulnerability to develop AD pathology. Yet translational studies are required to investigate whether early life experiences also modify AD development in human studies, and whether similar molecular mediators can be identified in the sensitivity to develop AD in humans.

Self-Assembly Molecular Chaperone to Concurrently Inhibit the Production and Aggregation of Amyloid β Peptide Associated with Alzheimer's Disease

Amyloid β peptide (Aβ) plays a crucial role in the pathogenesis of Alzheimer's disease (AD). Currently, decreasing Aβ production and preventing Aβ aggregation are thought to be important strategies in anti-AD therapy. However, inhibiting Aβ production or aggregation in isolation is not sufficient to reverse the neurodegenerative process of AD patients in clinical testing. Here, a self-assembly molecular chaperone (SAMC) consisting of γ-secretase inhibitor DAPT and mixed-shell polymeric micelles is devised, serving as a bifunctional suppressor of AD. This two-in-one combinational system can simultaneously inhibit Aβ production and aggregation, which would contribute to enhancing the therapeutic effect by decreasing Aβ levels. Decorating a neuron-specific RVG29 peptide onto the surface, the DAPT-incorporated SAMC can specifically target neuronal cells and, thus, will relieve the strong side effect of DAPT on normal cells. Therefore, this combination strategy holds great potential to open up an avenue for AD treatment.

Tongluo Xingnao effervescent tablet reverses memory deficit and reduces plaque load in APPswe/PS1dE9 mice

Alzheimer's disease (AD) is the most common type of dementia. Amyloid-β (Aβ)-induced neurodegeneration is hypothesized to be the primary pathological mechanism of AD. Tongluo Xingnao effervescent tablets (TXET), based on the traditional Chinese formula Qionggui Tang, have been used to treat AD and other types of dementia in China for decades. In the present study, the effects of TXET on cognition deficit, amyloid-β production, amyloid precursor protein procession and β-secretase expression were investigated in the APPswe/PS1dE9 mouse model of AD. As expected, APPswe/PS1dE9 mice exhibited cognitive decline and higher levels of Aβ and plaques in the brain compared with normal mice; however, these changes were attenuated following TXET treatment. Levels of C-terminal fragment (CTF)-β protein were decreased following treatment with TXET; however, CTF-α levels were unaffected. Furthermore, TXET treatment did not decrease γ-secretase activity or levels of presenilin-1 (PS1), neprilysin or insulin-degrading enzyme. These results indicate that TXET may regulate Aβ metabolism by downregulating the expression of β-secretase. The results of the present study have laid the foundation for the development of a Chinese medicinal compound with a β-secretase inhibitor as the target for the treatment of AD.