Brain Aβ Levels Research Articles

Low Density Lipoprotein Receptor-related Protein 2 Expression and Function in Cultured Astrocytes and Microglia.

Activation of glial cells, astrocytes and microglia, has been observed in neurodegenerative diseases including Alzheimer's disease (AD). Amyloid β (Aβ), which is aggregated and the aggregation is detected as characteristic pathology in AD brain, is known to be produced by neurons and to activate glial cells. Clearance of Aβ from the brain via active transport system is important to prevent the accumulation and aggregation. Low density lipoprotein receptor-related protein 2 (LRP2/megalin) is an Aβ transporter. However, expression and contribution of LRP2 in astrocytes and microglia remain to be clarified. In the present study, we examined the expression of LRP2 and its roles in cultured astrocytes prepared from rat embryonic brain cortex and mouse microglial cell line BV-2. Both cultured rat astrocytes and BV-2 cells expressed LRP2 mRNA detected by RT-PCR. When lipopolysaccharide (LPS) or all-trans retinoic acid (ATRA) were added to BV-2 cells, LRP2 mRNA expression and uptake of microbeads, Aβ and insulin were increased. On the other hand, LPS decreased LRP2 expression and uptake of Aβ and insulin in cultured astrocytes. Knockdown of LRP2 using siRNA attenuated the LPS- or ATRA-increased uptake of microbeads, Aβ and insulin in BV-2 cells. These results suggest that LRP2 was expressed in both astrocytes and microglia and might be involved in endocytosis activities. Adequate control of LRP2 expression and function in astrocytes and microglia might regulate Aβ and insulin levels in brain and would be a potential target in AD pathology.

Amyloid-Beta Peptides 40 and 42 Employ Distinct Molecular Pathways for Cell Entry and Intracellular Transit at the Blood-Brain Barrier Endothelium.

The blood-brain barrier (BBB) plays a critical role in maintaining the equilibrium between amyloid beta (Aβ) levels in blood and the brain by regulating Aβ transport. Our previous publications demonstrated that BBB trafficking of Aβ42 and Aβ40 is distinct and is disrupted under various pathophysiological conditions. However, the intracellular mechanisms that allow BBB endothelium to differentially handle Aβ40 and Aβ42 have not been clearly elucidated. In this study, we identified mechanisms of Aβ endocytosis in polarized human cerebral microvascular endothelial cell monolayers. Our studies demonstrated that Aβ peptides with fluorescent label (F-Aβ) were internalized by BBB endothelial cells via energy, dynamin, and actin-dependent endocytosis. Interestingly, endocytosis of F-Aβ40 but not F-Aβ42 was substantially reduced by clathrin inhibition, whereas F-Aβ42 but not F-Aβ40 endocytosis was reduced by half after inhibiting the caveolae-mediated pathway. Following endocytosis, both isoforms were sorted by the endo-lysosomal system. Although Aβ42 was shown to accumulate more in the lysosomes, which could lead to its higher degradation and/or aggregation at lower lysosomal pH, Aβ40 demonstrated robust accumulation in recycling endosomes, which may facilitate its exocytosis by the endothelial cells. These results provide a mechanistic insight into the selective ability of BBB endothelium to transport Aβ40 versus Aβ42. This knowledge contributes to the understanding of molecular pathways underlying Aβ accumulation in the BBB endothelium and associated BBB dysfunction. Moreover, it allows us to establish mechanistic rationale for altered Aβ40:Aβ42 ratios and anomalous amyloid deposition in the cerebral vasculature as well as brain parenchyma during Alzheimer's disease progression. SIGNIFICANCE STATEMENT: Differential interaction of Aβ40 and Aβ42 isoforms with the blood-brain barrier (BBB) endothelium may contribute to perturbation in Aβ42:Aβ40 ratio, which is associated with Alzheimer's disease (AD) progression and severity. The current study identified distinct molecular pathways by which Aβ40 and Aβ42 are trafficked at the BBB, which regulates equilibrium between blood and brain Aβ levels. These findings provide molecular insights into mechanisms that engender BBB dysfunction and promote Aβ accumulation in AD brain.

Cu(ATSM) Increases P-Glycoprotein Expression and Function at the Blood-Brain Barrier in C57BL6/J Mice.

P-glycoprotein (P-gp), expressed at the blood-brain barrier (BBB), is critical in preventing brain access to substrate drugs and effluxing amyloid beta (Aβ), a contributor to Alzheimer's disease (AD). Strategies to regulate P-gp expression therefore may impact central nervous system (CNS) drug delivery and brain Aβ levels. As we have demonstrated that the copper complex copper diacetyl bis(4-methyl-3-thiosemicarbazone) (Cu(ATSM)) increases P-gp expression and function in human brain endothelial cells, the present study assessed the impact of Cu(ATSM) on expression and function of P-gp in mouse brain endothelial cells (mBECs) and capillaries in vivo, as well as in peripheral organs. Isolated mBECs treated with Cu(ATSM) (100 nM for 24 h) exhibited a 1.6-fold increase in P-gp expression and a 20% reduction in accumulation of the P-gp substrate rhodamine 123. Oral administration of Cu(ATSM) (30 mg/kg/day) for 28 days led to a 1.5 & 1.3-fold increase in brain microvascular and hepatic expression of P-gp, respectively, and a 20% reduction in BBB transport of [3H]-digoxin. A metallomic analysis showed a 3.5 and 19.9-fold increase in Cu levels in brain microvessels and livers of Cu(ATSM)-treated mice. Our findings demonstrate that Cu(ATSM) increases P-gp expression and function at the BBB in vivo, with implications for CNS drug delivery and clearance of Aβ in AD.

Tranexamic acid in a mouse model of cerebral amyloid angiopathy: setting the stage for a novel stroke treatment approach

BackgroundSymptomatic intracerebral hemorrhage (sICH) commonly occurs in patients with cerebral amyloid angiopathy (CAA). Amyloid also initiates plasminogen activation and might promote sICH. ObjectivesAs amyloid-driven plasmin formation can be blocked by tranexamic acid (TXA), we aimed to evaluate the biodistribution and long-term consequences of TXA on brain amyloid-beta (Aβ) levels, inflammation, and neurologic function in APP/PS1 mice. MethodsAPP/PS1 mice overexpressing the mutant human amyloid precursor protein and wild-type littermates were randomized to TXA (20 mg/mL) or placebo in the drinking water for 6 months. TXA in plasma and various organs was determined by liquid chromatography-mass spectrometry. Plasmin activity assays were performed to evaluate changes in fibrinolytic activity. Neurologic function was evaluated by Y-maze and parallel rod floor testing. Proximity ligation–based immunoassays were used to quantitate changes of 92 biomarkers of inflammation. Brain Aβ levels were assessed by immunohistochemistry. ResultsLong-term oral TXA administration inhibited fibrinolysis. TXA accumulated in the kidney (19.4 ± 11.2 μg/g) with 2- to 5-fold lower levels seen in the lung, spleen, and liver. TXA levels were lowest in the brain (0.28 ± 0.01 μg/g). Over 6 months, TXA had no discernible effect on motor coordination, novelty preference, or brain Aβ levels. TXA reduced plasma levels of epithelial cell adhesion molecule and increased CCL20. ConclusionLong-term TXA treatment does not alter brain Aβ levels or impact neurologic behavior in mice predisposed to amyloid deposition and had minor effects on the levels of inflammatory mediators. This finding supports the safety of TXA and lays the foundation for TXA as a novel treatment to reduce sICH in patients with CAA.

Reduced slow-wave activity and autonomic dysfunction during sleep precede cognitive deficits in Alzheimer’s disease transgenic mice

Occurrence of amyloid-β (Aβ) aggregation in brain begins before the clinical onset of Alzheimer’s disease (AD), as preclinical AD. Studies have reported that sleep problems and autonomic dysfunction associate closely with AD. However, whether they, especially the interaction between sleep and autonomic function, play critical roles in preclinical AD are unclear. Therefore, we investigated how sleep patterns and autonomic regulation at different sleep–wake stages changed and whether they were related to cognitive performance in pathogenesis of AD mice. Polysomnographic recordings in freely-moving APP/PS1 and wild-type (WT) littermates were collected to study sleep patterns and autonomic function at 4 (early disease stage) and 8 months of age (advanced disease stage), cognitive tasks including novel object recognition and Morris water maze were performed, and Aβ levels in brain were measured. APP/PS1 mice at early stage of AD pathology with Aβ aggregation but without significant differences in cognitive performance had frequent sleep–wake transitions, lower sleep-related delta power percentage, lower overall autonomic activity, and lower parasympathetic activity mainly during sleep compared with WT mice. The same phenomenon was observed in advanced-stage APP/PS1 mice with significant cognitive deficits. In mice at both disease stages, sleep-related delta power percentage correlated positively with memory performance. At early stage, memory performance correlated positively with sympathetic activity during wakefulness; at advanced stage, memory performance correlated positively with parasympathetic activity during both wakefulness and sleep. In conclusion, sleep quality and distinction between wake- and sleep-related autonomic function may be biomarkers for early AD detection.

Germinated brown rice extract reduces brain lipid peroxidation and Aβ levels via regulations of BACE1, RAGE, IDE and LRP1 expressions in high fat/cholesterol diet-fed rats

A strong association presents between excessive amyloid-β (Aβ) buildup and oxidative stress with Alzheimer’s disease (AD). In view of the multifaceted neuroprotective effects of some dietary elements, the beneficial effect of germinated brown rice was investigated using a high fat/cholesterol diet (HFCD)-induced sporadic rat model of AD. Seven groups, including normal control, HFCD, and HFCD treated with Donepezil, Simvastatin, Probucol, and germinated brown rice ethyl acetate extract (GBR-EA; 100 and 200 mg/kg bw) were included in the present study. Biochemical assays, brain lipid peroxidation, mRNA and protein levels involved in Aβ processing and metabolism pathways were analyzed. HFCD-fed rats exhibited increased brain lipid peroxidation and Aβ levels, as well as altered expressions of proteins involved in Aβ generation, degradation and clearance. GBR-EA treatment groups showed significant reduction in lipid peroxidation and Aβ levels when compared to HFCD group. The effects of GBR-EA on Aβ levels are likely through the modulation of BACE1 and Presenilins, as well as induction of Aβ clearance and degradation. The findings revealed the potential use of germinated brown rice to attenuate HFCD diet-induced neurodegenerative alterations, likely due to reduced brain inflammation, as well as modulation of Aβ processing and metabolism pathways.

Alcohol as a Modifiable Risk Factor for Alzheimer's Disease-Evidence from Experimental Studies.

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by cognitive impairment and memory loss. Epidemiological evidence suggests that heavy alcohol consumption aggravates AD pathology, whereas low alcohol intake may be protective. However, these observations have been inconsistent, and because of methodological discrepancies, the findings remain controversial. Alcohol-feeding studies in AD mice support the notion that high alcohol intake promotes AD, while also hinting that low alcohol doses may be protective against AD. Chronic alcohol feeding to AD mice that delivers alcohol doses sufficient to cause liver injury largely promotes and accelerates AD pathology. The mechanisms by which alcohol can modulate cerebral AD pathology include Toll-like receptors, protein kinase-B (Akt)/mammalian target of rapamycin (mTOR) pathway, cyclic adenosine monophosphate (cAMP) response element-binding protein phosphorylation pathway, glycogen synthase kinase 3-β, cyclin-dependent kinase-5, insulin-like growth factor type-1 receptor, modulation of β-amyloid (Aβ) synthesis and clearance, microglial mediated, and brain endothelial alterations. Besides these brain-centric pathways, alcohol-mediated liver injury may significantly affect brain Aβ levels through alterations in the peripheral-to-central Aβ homeostasis. This article reviews published experimental studies (cell culture and AD rodent models) to summarize the scientific evidence and probable mechanisms (both cerebral and hepatic) by which alcohol promotes or protects against AD progression.

The amyloid-β pathway in Alzheimer's disease: a plain language summary.

This plain language summary of an article published in Molecular Psychiatry, reviews the evidence supporting the role of the amyloid-β (Aβ) pathway and its dysregulation in Alzheimer's disease (AD), and highlights the rationale for drugs targeting the Aβ pathway in the early stages of the disease. Aβ is a protein fragment (or peptide) that exists in several forms distinguished by their size, shape/structure, degree of solubility and disease relevance. The accumulation of Aβ plaques is a hallmark of AD. However, smaller, soluble aggregates of Aβ - including Aβ protofibrils - also play a role in the disease. Because Aβ-related disease mechanisms are complex, the diagnosis, treatment and management of AD should be reflective of and guided by up-to-date scientific knowledge and research findings in this area. This article describes the Aβ protein and its role in AD, summarizing the evidence showing that altered Aβ clearance from the brain may lead to the imbalance, toxic buildup and misfolding of the protein - triggering a cascade of cellular, molecular and systematic events that ultimately lead to AD. The physiological balance of brain Aβ levels in the context of AD is complex. Despite many unanswered questions, mounting evidence indicates that Aβ has a central role in driving AD progression. A better understanding of the Aβ pathway biology will help identify the best therapeutic targets for AD and inform treatment approaches.

Physiological β-amyloid clearance by the liver and its therapeutic potential for Alzheimer’s disease

Cerebral amyloid-β (Aβ) accumulation due to impaired Aβ clearance is a pivotal event in the pathogenesis of Alzheimer's disease (AD). Considerable brain-derived Aβ is cleared via transporting to the periphery. The liver is the largest organ responsible for the clearance of metabolites in the periphery. Whether the liver physiologically clears circulating Aβ and its therapeutic potential for AD remains unclear. Here, we found that about 13.9% of Aβ42 and 8.9% of Aβ40 were removed from the blood when flowing through the liver, and this capacity was decreased with Aβ receptor LRP-1 expression down-regulated in hepatocytes in the aged animals. Partial blockage of hepatic blood flow increased Aβ levels in both blood and brain interstitial fluid. The chronic decline in hepatic Aβ clearance via LRP-1 knockdown specific in hepatocytes aggravated cerebral Aβ burden and cognitive deficits, while enhancing hepatic Aβ clearance via LRP-1 overexpression attenuated cerebral Aβ deposition and cognitive impairments in APP/PS1 mice. Our findings demonstrate that the liver physiologically clears blood Aβ and regulates brain Aβ levels, suggesting that a decline of hepatic Aβ clearance during aging could be involved in AD development, and hepatic Aβ clearance is a novel therapeutic approach for AD.

Blood-brain barrier integrity impacts the use of plasma amyloid-β as a proxy of brain amyloid-β pathology.

Amyloid-β (Aβ) and tau can be quantified in blood. However, biological factors can influence the levels of brain-derived proteins in the blood. The blood-brain barrier (BBB) regulates protein transport between cerebrospinal fluid (CSF) and blood. BBB altered permeability might affect the relationship between brain and blood biomarkers. We assessed 224 participants in research (TRIAD, n=96) and clinical (BIODEGMAR, n=128) cohorts with plasma and CSF/positron emission tomography Aβ, p-tau, and albumin measures. Plasma Aβ42/40 better identified CSF Aβ42/40 and Aβ-PET positivity in individuals with high BBB permeability. An interaction between plasma Aβ42/40 and BBB permeability on CSF Aβ42/40 was observed. Voxel-wise models estimated that the association of positron emission tomography (PET), with plasma Aβ was most affected by BBB permeability in AD-related brain regions. BBB permeability did not significantly impact the relationship between brain and plasma p-tau levels. These findings suggest that BBB integrity may influence the performance of plasma Aβ, but not p-tau, biomarkers in research and clinical settings. BBB permeability affects the association between brain and plasma Aβ levels. BBB integrity does not affect the association between brain and plasma p-tau levels. Plasma Aβ was most affected by BBB permeability in AD-related brain regions. BBB permeability increases with age but not according to cognitive status.

Association of plasma phosphor-tau181 with Aβ levels may vary by APOE ε4 status and sex among non-demented old adults

BackgroundTo evaluate the relationship between blood tau phosphorylated at threonine 181 (p-tau181) levels and β-amyloid (Aβ) levels, this study took the potential role of sex differences and apolipoprotein E (APOE)-ε4 status into account. MethodsWe examined 620 participants with normal cognition (n = 178) and mild cognitive impairment (n = 442). Three-way interactions between sex, APOE ε4 status, and the levels of plasma p-tau181 were examined with linear regression models for Aβ levels adjusting for age, education, and diagnosis. The correlation analysis was performed to detect the association of the levels of plasma p-tau181 with brain Aβ stratified for APOE status and sex. ResultsBlood p-tau181 levels were higher in APOE ε4+ participants as compared to APOE ε4 – participants (p < 0.001). A comparison of APOE ε4 status within each gender showed that APOE ε4 carriers had higher levels of plasma p-tau181 and amyloid-β than APOE ε4 noncarriers in both men and women (p < 0.001). In sex/APOE-stratified analyses, individuals with the APOE ε4 allele showed stronger correlations between plasma p-tau181 and brain Aβ levels in both females (r = 0.49, p < 0.001 for APOE ε4 carriers vs r = 0.28, p < 0.001 for APOE ε4 noncarrier.) and males (r = 0.34, p < 0.001 for APOE ε4 carriers vs r = 0.21, p = 0.04 for APOE ε4 noncarriers.). In interactive analysis, the association of plasma p-tau181 and Aβ levels was significant in the female APOE ε4 carriers (p < 0.003). DiscussionAPOE ε4 status and female sex interact to impact the correlation between plasma p-tau181 and Aβ levels. Although the APOE ε4 genotype is one of the most important risky genes for AD, sex differences may also modify the degree of risk at critical times among non-demented older adults.

Experimental approaches for altering the expression of Abeta-degrading enzymes.

Cerebral clearance of amyloid β-protein (Aβ) is decreased in early-onset and late-onset Alzheimer's disease (AD). Aβ is cleared from the brain by enzymatic degradation and by transport out of the brain. More than 20 Aβ-degrading enzymes have been described. Increasing the degradation of Aβ offers an opportunity to decrease brain Aβ levels in AD patients. This review discusses the direct and indirect approaches which have been used in experimental systems to alter the expression and/or activity of Aβ-degrading enzymes. Also discussed are the enzymes' regulatory mechanisms, the conformations of Aβ they degrade, where in the scheme of Aβ production, extracellular release, cellular uptake, and intracellular degradation they exert their activities, and changes in their expression and/or activity in AD and its animal models. Most of the experimental approaches require further confirmation. Based upon each enzyme's effects on Aβ (some of the enzymes also possess β-secretase activity and may therefore promote Aβ production), its direction of change in AD and/or its animal models, and the Aβ conformation(s) it degrades, investigating the effects of increasing the expression of neprilysin in AD patients would be of particular interest. Increasing the expression of insulin-degrading enzyme, endothelin-converting enzyme-1, endothelin-converting enzyme-2, tissue plasminogen activator, angiotensin-converting enzyme, and presequence peptidase would also be of interest. Increasing matrix metalloproteinase-2, matrix metalloproteinase-9, cathepsin-B, and cathepsin-D expression would be problematic because of possible damage by the metalloproteinases to the blood brain barrier and the cathepsins' β-secretase activity. Many interventions which increase the enzymatic degradation of Aβ have been shown to decrease AD-type pathology in experimental models. If a safe approach can be found to increase the expression or activity of selected Aβ-degrading enzymes in human subjects, then the possibility that this approach could slow the AD progression should be examined in clinical trials.

Comparison of Oleocanthal-Low EVOO and Oleocanthal against Amyloid-β and Related Pathology in a Mouse Model of Alzheimer's Disease.

Alzheimer's disease (AD) is characterized by several pathological hallmarks, including the deposition of amyloid-β (Aβ) plaques, neurofibrillary tangles, blood-brain barrier (BBB) dysfunction, and neuroinflammation. Growing evidence support the neuroprotective effects of extra-virgin olive oil (EVOO) and oleocanthal (OC). In this work, we aimed to evaluate and compare the beneficial effects of equivalent doses of OC-low EVOO (0.5 mg total phenolic content/kg) and OC (0.5 mg OC/kg) on Aβ and related pathology and to assess their effect on neuroinflammation in a 5xFAD mouse model with advanced pathology. Homozygous 5xFAD mice were fed with refined olive oil (ROO), OC-low EVOO, or OC for 3 months starting at the age of 3 months. Our findings demonstrated that a low dose of 0.5 mg/kg EVOO-phenols and OC reduced brain Aβ levels and neuroinflammation by suppressing the nuclear factor-κB (NF-κB) pathway and reducing the activation of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasomes. On the other hand, only OC suppressed the receptor for advanced glycation endproducts/high-mobility group box 1 (RAGE/HMGB1) pathway. In conclusion, our results indicated that while OC-low EVOO demonstrated a beneficial effect against Aβ-related pathology in 5xFAD mice, EVOO rich with OC could provide a higher anti-inflammatory effect by targeting multiple mechanisms. Collectively, diet supplementation with EVOO or OC could prevent, halt progression, and treat AD.

Accumulation of amyloid-β in the brain of mouse models of Alzheimer's disease is modified by altered gene expression in the presence of human apoE isoforms during aging

Apolipoprotein E4 (apoE4) is a risk factor for Alzheimer's disease (AD). Here, we investigated brain amyloid-β (Aβ) accumulation throughout the aging process in an amyloid precursor protein (APP) knock-in (KI) mouse model of AD that expresses human APPNL-G-F with or without human apoE4 or apoE3. Brain Aβ42 levels were significantly lower in 9-month-old mice that express human isoforms of apoE than in age-matched APP-KI control mice. Linear accumulation of Aβ42 began in 5-month-old apoE4 mice, and a strong increase in Aβ42 levels was observed in 21-month-old apoE3 mice. Aβ42 levels in cerebroventricular fluid were higher in apoE3 than in apoE4 mice at 6–7 months of age, suggesting that apoE3 is more efficient at clearing Aβ42 than apoE4 at these ages. However, apoE3 protein levels were lower than apoE4 protein levels in the brains of 21-month-old apoE3 and apoE4 mice, respectively, which may explain the rapid increase in brain Aβ42 burden in apoE3 mice. We identified genes that were downregulated in a human apoE-dependent (apoE4 > apoE3) and age-dependent (apoE3 = apoE4) manner, which may regulate brain Aβ burden and/or AD progression. Analysis of gene expression in AD mouse models helps identify molecular mechanisms of pleiotropy by the human APOE gene during aging.

Targeting Substance P Pathway as an Emerging Novel Therapeutic Mechanism for Modulating Amyloid Beta in APP/PS1 Mouse Model

AbstractBackgroundNeurodegeneration associated with Alzheimer’s disease (AD) is well established to be mediated by amyloid β (Aβ) plaques and neurofibrillary tangles (NFTs) of Tau protein in the brain. However, there are a multitude of underlying processes that individually contribute to the development of these aberrant Aβ aggregations and NFTs over time that are still being elucidated. The substance P/neurokinin‐1 receptor signaling pathways play an important role in regulating neuroinflammation and have recently been demonstrated to also influence mechanisms responsible for Aβ amyloidogenesis and toxicity1,2,3. Accordingly, HT‐ALZ is under development as a novel AD therapeutic to target the SP/NK1R pathway.MethodUsing microdialysis, Aβ levels in the interstitial fluid (ISF) of the hippocampus were measured in male and female APP/PS1 mice (3‐4 months old). ISF samples were collected every hour for 6 hours prior to treatment to establish a baseline, HT‐ALZ or vehicle was administered via oral gavage, and samples were collected continuously for 12‐15 hours following treatment. Aβ levels were measured using ELISA and changes from baseline were calculated for each mouse.ResultWe observed a significant change from baseline in mice treated with HT‐ALZ, but not in vehicle treated mice. Mice treated with HT‐ALZ show a decrease in average ISF Aβ following treatment.ConclusionResults of our microdialysis study indicate targeting the SP/NK1R pathway has a beneficial effect on circulating Aβ levels in the mouse brain, which may lead to lower plaque load with longer term treatment. We are currently investigating the impact of HT‐ALZ on the cognitive and behavioral impairments in APP/PS1 mice; the results of these studies will be provided at the time of presentation.

An oligomer‐directed Aβ antibody decreases synaptotoxic oligomeric Aβ in brain and improves behavioral abnormality in humanized APP knock‐in mice

AbstractBackgroundThere is strong evidence that soluble oligomers of amyloid beta protein (oAβ) help initiate the pathogenic cascade of Alzheimer’s disease (AD), which suggests therapeutic strategies targeting oAβ over monomeric or fibrillar Aβ. A new antibody, 71A1, is 1∼00‐fold more sensitive for oAβ than synthetic monomers. The material that 71A1 specifically immunoprecipitates from AD soluble brain extracts impairs synaptic function as much as does the full extract. In accord, pre‐incubating brain extracts with 71A1 neutralizes its synaptotoxicity. 71A1 has potentially unique activities against disease‐relevant oAβ, making it a novel candidate for treating AD.Methods15 mg/kg 71A1 or anti‐KLH (negative control) was administered i.p. to 45 humanized APP knock‐in mice (APPNLGF/NLGF) weekly from 8 to 20 weeks of age. Cognition was assessed by spontaneous alternation (Y‐maze). Brains were harvested at age 21‐wk for biochemical, electrophysiological and immunohistochemical analyses. Diffusible (“soaking”) extracts of the brains were prepared to measure monomeric and oligomeric Aβ using homebrew ultra‐sensitive assays. Aliquots of the same soaking extracts were used to treat wild‐type mouse hippocampal slices and measure long‐term potentiation (LTP) to assess synaptotoxicity in the APPNLGF/NLGF brains post‐treatment.Results71A1 recognized oAβ and neutralized its synaptotoxicity in APPNLGF/NLGF mouse brain extracts. 71A1 effectively treated male APPNLGF/NLGF mice, which improved cognition significantly. The antibody reduced brain Aβ (1‐42) and oAβ levels with a trend toward statistical significance. Mouse brains with less oAβ had less synaptotoxicity as assessed by LTP.ConclusionsThese results demonstrate 71A1 is an oligomer‐preferring monoclonal antibody as a therapeutic candidate for AD, decreasing brain oAβ and oAβ‐induced synaptotoxicity. We believe this provides the first proof‐of‐concept mouse trial using an antibody that has been carefully characterized as oAβ‐preferring. We observed 1) a correlation between oAβ concentration and its synaptotoxicity; and 2) that 71A1 ameliorated aspects of cognitive impairment in APPNLGF/NLGF mice by targeting oAβ.

Erythropoietin signaling in peripheral macrophages is required for systemic β-amyloid clearance.

Impaired clearance of beta-amyloid (Aβ) is a primary cause of sporadic Alzheimer's disease (AD). Aβ clearance in the periphery contributes to reducing brain Aβ levels and preventing Alzheimer's disease pathogenesis. We show here that erythropoietin (EPO) increases phagocytic activity, levels of Aβ-degrading enzymes, and Aβ clearance in peripheral macrophages via PPARγ. Erythropoietin is also shown to suppress Aβ-induced inflammatory responses. Deletion of EPO receptor in peripheral macrophages leads to increased peripheral and brain Aβ levels and exacerbates Alzheimer's-associated brain pathologies and behavioral deficits in AD-model mice. Moreover, erythropoietin signaling is impaired in peripheral macrophages of old AD-model mice. Exogenous erythropoietin normalizes impaired EPO signaling and dysregulated functions of peripheral macrophages in old AD-model mice, promotes systemic Aβ clearance, and alleviates disease progression. Erythropoietin treatment may represent a potential therapeutic approach for Alzheimer's disease.

Review of Advanced Drug Trials Focusing on the Reduction of Brain Beta-Amyloid to Prevent and Treat Dementia.

Alzheimer disease (AD) is the most common neurodegenerative disease and typically affects patients older than age 65. Around this age, the number of neurons begins to gradually decrease in healthy brains, but brains of patients with AD show a marked increase in neuron death, often resulting in a significant loss of cognitive abilities. Cognitive skills affected include information retention, recognition capabilities, and language skills. At present, AD can be definitively diagnosed only through postmortem brain biopsies via the detection of extracellular amyloid beta (Aβ) plaques and intracellular hyperphosphorylated tau neurofibrillary tangles. Because the levels of both Aβ plaques and tau tangles are increased, these 2 proteins are thought to be related to disease progression. Although relatively little is known about the cause of AD and its exact pathobiological development, many forms of treatment have been investigated to determine an effective method for managing AD symptoms by targeting Aβ. These treatments include but are not limited to using small molecules to alter the interactions of Aβ monomers, reducing hyperactivation of neuronal circuits altering Aβ's molecular pathway of synthesis, improving degradation of Aβ, employing passive immunity approaches, and stimulating patients' active immunity to target Aβ. This review summarizes the current therapeutic interventions in Phase II/III of clinical development or higher that are capable of reducing abnormal brain Aβ levels to determine which treatments show the greatest likelihood of clinical efficacy. We conclude that, in the near future, the most promising therapeutic interventions for brain Aβ pathology will likely be passive immunotherapies, with aducanumab and donanemab leading the way, and that these drugs may be combined with antidepressants and acetylcholine esterase inhibitors, which can modulate Aβ synthesis.

Temporal Pattern of Neuroinflammation Associated with a Low Glycemic Index Diet in the 5xFAD Mouse Model of Alzheimer’s Disease

Alzheimer’s disease (AD) is associated with brain amyloid‐β (Aβ) peptide accumulation and neuroinflammation. Currants, a low glycemic index dried fruit, and their components display pleiotropic neuroprotective effects in AD. We examined how diet containing 5% Corinthian currant paste (CurD) administered in 1-month-old 5xFAD mice for 1, 3, and 6 months affects Aβ levels and neuroinflammation in comparison to control diet (ConD) or sugar-matched diet containing 3.5% glucose/fructose (GFD). No change in serum glucose or insulin levels was observed among the three groups. CurD administered for 3 months reduced brain Aβ42 levels in male mice as compared to ConD and GFD, but after 6 months, Aβ42 levels were increased in mice both on CurD and GFD compared to ConD. CurD for 3 months also reduced TNFα and IL-1β levels in male and female mouse cortex homogenates compared to ConD and GFD. However, after 6 months, TNFα levels were increased in cortex homogenates of mice both on CurD and GFD as compared to ConD. A similar pattern was observed for TNFα-expressing cells, mostly co-expressing the microglial marker CD11b, in mouse hippocampus. IL-1β levels were similarly increased in the brain of all groups after 6 months. Furthermore, a time dependent decrease of secreted TNFα levels was found in BV2 microglial cells treated with currant phenolic extract as compared to glucose/fructose solution. Overall, our findings suggest that a short-term currant consumption reduces neuroinflammation in 5xFAD mice as compared to sugar-matched or control diet, but longer-term intake of currant or sugar-matched diet enhances neuroinflammation.

In-Depth Characterization of Endo-Lysosomal Aβ in Intact Neurons.

Amyloid-beta (Aβ) peptides are produced within neurons. Some peptides are released into the brain parenchyma, while others are retained inside the neurons. However, the detection of intracellular Aβ remains a challenge since antibodies against Aβ capture Aβ and its precursor proteins (i.e., APP and C99). To overcome this drawback, we recently developed 1) the C99 720-670 biosensor for recording γ-secretase activity and 2) a unique multiplexed immunostaining platform that enables the selective detection of intracellular Aβ with subcellular resolution. Using these new assays, we showed that C99 is predominantly processed by γ-secretase in late endosomes and lysosomes, and intracellular Aβ is enriched in the same subcellular loci in intact neurons. However, the detailed properties of Aβ in the acidic compartments remain unclear. Here, we report using fluorescent lifetime imaging microscopy (FLIM) that intracellular Aβ includes both long Aβ intermediates bound to γ-secretase and short peptides dissociated from the protease complex. Surprisingly, our results also suggest that the dissociated Aβ is bound to the glycoproteins on the inner membrane of lysosomes. Furthermore, we show striking cell-to-cell heterogeneity in intracellular Aβ levels in primary neurons and APP transgenic mouse brains. These findings provide a basis for the further investigation of the role(s) of intracellular Aβ and its relevance to Alzheimer’s disease (AD).