A highly sensitive novel immunoassay specifically detects low levels of soluble Aβ oligomers in human cerebrospinal fluid

Single-Molecule Maps of Membrane Insertion by Amyloid-β Oligomers Predict Their Toxicity

The interaction of small Amyloid-β (Aβ) oligomers with the lipid membrane is an important component of the pathomechanism of Alzheimer's disease (AD). However, oligomers are heterogeneous in size. How each type of oligomer incorporates into the membrane, and how that relates to their toxicity, is unknown. Here, we employ a single molecule technique called Q-SLIP (Quencher-induced Step Length Increase in Photobleaching) to measure the membrane insertion of each monomeric unit of individual oligomers of Aβ42, Aβ40, and Aβ40-F19-Cyclohexyl alanine (Aβ40-F19Cha), and correlate it with their toxicity. We observe that the N-terminus of Aβ42 inserts close to the center of the bilayer, the less toxic Aβ40 inserts to a shallower depth, and the least toxic Aβ40-F19Cha has no specific distribution. This oligomer-specific map provides a mechanistic representation of membrane-mediated Aβ toxicity and should be a valuable tool for AD research.

Recent Advancements in Biosensors for the Detection and Characterization of Amyloids: A Review

Modern medicine has increased the human lifespan. However, with an increase in average lifespan risk of amyloidosis increases. Amyloidosis is a condition characterized by protein misfolding and aggregation. Early detection of amyloidosis is crucial, yet conventional diagnostic methods are costly and lack precision, necessitating innovative tools. This review explores recent advancements in diverse amyloid detection methodologies, highlighting the need for interdisciplinary research to develop a miniaturized electrochemical biosensor leveraging nanotechnology. However, the diagnostics industry faces obstacles such as skilled labor shortages, standardized selection processes, and concurrent multi-analyte identification challenges. Research efforts are focused on integrating electrochemical techniques into clinical applications and diagnostics, with the successful transition of miniaturized technologies from development to testing posing a significant hurdle. Label-free transduction techniques like voltammetry and electrochemical impedance spectroscopy (EIS) have gained traction due to their rapid, cost-effective, and user-friendly nature.

Performance of SOBA-AD blood test in discriminating Alzheimer's disease patients from cognitively unimpaired controls in two independent cohorts

Amyloid-beta (Aβ) toxic oligomers are critical early players in the molecular pathology of Alzheimer's disease (AD). We have developed a Soluble Oligomer Binding Assay (SOBA-AD) for detection of these Aβ oligomers that contain α-sheet secondary structure that discriminates plasma samples from patients on the AD continuum from non-AD controls. We tested 265 plasma samples from two independent cohorts to investigate the performance of SOBA-AD. Testing was performed at two different sites, with different personnel, reagents, and instrumentation. Across two cohorts, SOBA-AD discriminated AD patients from cognitively unimpaired (CU) subjects with 100% sensitivity, > 95% specificity, and > 98% area under the curve (AUC) (95% CI 0.95-1.00). A SOBA-AD positive readout, reflecting α-sheet toxic oligomer burden, was found in AD patients, and not in controls, providing separation of the two populations, aside from 5 SOBA-AD positive controls. Based on an earlier SOBA-AD study, the Aβ oligomers detected in these CU subjects may represent preclinical cases of AD. The results presented here support the value of SOBA-AD as a promising blood-based tool for the detection and confirmation of AD.

Aβ oligomers peak in early stages of Alzheimer's disease preceding tau pathology

INTRODUCTION

Soluble amyloid beta (Aβ) oligomers have been suggested as initiating Aβ related neuropathologic change in Alzheimer's disease (AD) but their quantitative distribution and chronological sequence within the AD continuum remain unclear.

METHODS

A total of 526 participants in early clinical stages of AD and controls from a longitudinal cohort were neurobiologically classified for amyloid and tau pathology applying the AT(N) system. Aβ and tau oligomers in the quantified cerebrospinal fluid (CSF) were measured using surface-based fluorescence intensity distribution analysis (sFIDA) technology.

RESULTS

Across groups, highest Aβ oligomer levels were found in A+ with subjective cognitive decline and mild cognitive impairment. Aβ oligomers were significantly higher in A+T- compared to A-T- and A+T+. APOE ε4 allele carriers showed significantly higher Aβ oligomer levels. No differences in tau oligomers were detected.

DISCUSSION

The accumulation of Aβ oligomers in the CSF peaks early within the AD continuum, preceding tau pathology. Disease-modifying treatments targeting Aβ oligomers might have the highest therapeutic effect in these disease stages.

Highlights

Using surface-based fluorescence intensity distribution analysis (sFIDA) technology, we quantified Aβ oligomers in cerebrospinal fluid (CSF) samples of the DZNE-Longitudinal Cognitive Impairment and Dementia (DELCODE) cohortAβ oligomers were significantly elevated in mild cognitive impairment (MCI)Amyloid-positive subjects in the subjective cognitive decline (SCD) group increased compared to the amyloid-negative control groupInterestingly, levels of Aβ oligomers decrease at advanced stages of the disease (A+T+), which might be explained by altered clearing mechanisms.

A single-domain antibody detects and neutralises toxic Aβ42 oligomers in the Alzheimer's disease CSF

BACKGROUND

Amyloid-β42 (Aβ42) aggregation consists of a complex chain of nucleation events producing soluble oligomeric intermediates, which are considered the major neurotoxic agents in Alzheimer's disease (AD). Cerebral lesions in the brain of AD patients start to develop 20 years before symptom onset; however, no preventive strategies, effective treatments, or specific and sensitive diagnostic tests to identify people with early-stage AD are currently available. In addition, the isolation and characterisation of neurotoxic Aβ42 oligomers are particularly difficult because of their transient and heterogeneous nature. To overcome this challenge, a rationally designed method generated a single-domain antibody (sdAb), named DesAb-O, targeting Aβ42 oligomers.

METHODS

We investigated the ability of DesAb-O to selectively detect preformed Aβ42 oligomers both in vitro and in cultured neuronal cells, by using dot-blot, ELISA immunoassay and super-resolution STED microscopy, and to counteract the toxicity induced by the oligomers, monitoring their interaction with neuronal membrane and the resulting mitochondrial impairment. We then applied this approach to CSF samples (CSFs) from AD patients as compared to age-matched control subjects.

RESULTS

DesAb-O was found to selectively detect synthetic Aβ42 oligomers both in vitro and in cultured cells, and to neutralise their associated neuronal dysfunction. DesAb-O can also identify Aβ42 oligomers present in the CSFs of AD patients with respect to healthy individuals, and completely prevent cell dysfunction induced by the administration of CSFs to neuronal cells.

CONCLUSIONS

Taken together, our data indicate a promising method for the improvement of an early diagnosis of AD and for the generation of novel therapeutic approaches based on sdAbs for the treatment of AD and other devastating neurodegenerative conditions.

Real-time monitoring of the amyloid β1-42 monomer-to-oligomer channel transition using a lipid bilayer system

This study describes the observation of the transformation of monomeric amyloid β1-42 (Aβ42) into oligomers in a lipid membrane utilizing a lipid bilayer system for electrophysiological measurement. The relevance of oligomers and protofibrils in Alzheimer's disease (AD) is underscored given their significant neurotoxicity. By closely monitoring the shift of Aβ42 from its monomeric state to forming oligomeric channels in phospholipid membranes, we noted that this transformation transpired within a 2-h frame. We manipulated the lipid membrane's constitution with components such as glycerophospholipid, porcine brain total lipid extract, sphingomyelin (SM), and cholesterol (Chol.) to effectively imitate nerve cell membranes. Interesting findings showcased Chol.'s ability to foster stable oligomeric channel formation in the lipid membrane, with SM and GM1 lipids potentially enhancing channel formation as well. Additionally, the study identified the potential of a catechin derivative, epigallocatechin gallate (EGCG), in obstructing oligomerization. With EGCG present in the outer solution of the Aβ42-infused membrane, a noteworthy reduction in channel current was observed, suggesting the successful inhibition of oligomerization. This conclusion held true in both, prior and subsequent, stages of oligomerization. Our findings shed light on the toxicity of oligomers, promising invaluable information for future advancements in AD treatment strategies.

Abundant Aβ fibrils in ultracentrifugal supernatants of aqueous extracts from Alzheimer's disease brains

Soluble oligomers of amyloid β-protein (Aβ) have been defined as aggregates in supernatants following ultracentrifugation of aqueous extracts from Alzheimer's disease (AD) brains and are believed to be upstream initiators of synaptic dysfunction, but little is known about their structures. We now report the unexpected presence of Aβ fibrils in synaptotoxic high-speed supernatants from AD brains extracted by soaking in an aqueous buffer. The fibrils did not appear to form during preparation, and their counts by EM correlated with Aβ ELISA quantification. Cryo-EM structures of aqueous Aβ fibrils were identical to those from sarkosyl-insoluble homogenates. The fibrils in aqueous extracts were labeled by lecanemab, an Aβ aggregate-directed antibody reported to improve AD cognitive outcomes. Lecanemab provided protection against aqueous fibril synaptotoxicity. We conclude that fibrils are abundant in aqueous extracts from AD brains and have the same structures as those from plaques. These findings have implications for AD pathogenesis and drug design.

Learnings about Aβ from human brain recommend the use of a live-neuron bioassay for the discovery of next generation Alzheimer's disease immunotherapeutics

Despite ongoing debate, the amyloid β-protein (Aβ) remains the prime therapeutic target for the treatment of Alzheimer's disease (AD). However, rational drug design has been hampered by a lack of knowledge about neuroactive Aβ. To help address this deficit, we developed live-cell imaging of iPSC-derived human neurons (iNs) to study the effects of the most disease relevant form of Aβ-oligomeric assemblies (oAβ) extracted from AD brain. Of ten brains studied, extracts from nine caused neuritotoxicity, and in eight cases this was abrogated by Aβ immunodepletion. Here we show that activity in this bioassay agrees relatively well with disruption of hippocampal long-term potentiation, a correlate of learning and memory, and that measurement of neurotoxic oAβ can be obscured by more abundant non-toxic forms of Aβ. These findings indicate that the development of novel Aβ targeting therapeutics may benefit from unbiased activity-based discovery. To test this principle, we directly compared 5 clinical antibodies (aducanumab, bapineuzumab,  BAN2401, gantenerumab, and SAR228810) together with an in-house aggregate-preferring antibody (1C22) and established relative EC50s in protecting human neurons from human Aβ. The results yielded objective numerical data on the potency of each antibody in neutralizing human oAβ neuritotoxicity. Their relative efficacies in this morphological assay were paralleled by their functional ability to rescue oAβ-induced inhibition of hippocampal synaptic plasticity. This novel paradigm provides an unbiased, all-human system for selecting candidate antibodies for advancement to human immunotherapy.

Site-Specific Phospho-Tau Aggregation-Based Biomarker Discovery for AD Diagnosis and Differentiation

Tau aggregates are present in multiple neurodegenerative diseases known as "tauopathies," including Alzheimer's disease (AD), Pick's disease (PiD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). Such misfolded tau aggregates are therefore potential sources for tauopathy biomarker discovery. Using the tau antibody screening approach targeting high-molecular-weight misfolded tau aggregates, we tested several tau antibodies and a comprehensive set of site-specific phospho-tau (p-tau) antibodies targeting tau phosphorylation sites showing high frequencies in AD subjects. Our screens revealed that site-specific p-tau antibodies can not only differentiate AD from non-AD brains, but also discriminate AD from rare tauopathies PiD, PSP, and CBD brains. Differential detection of tau aggregates identified several novel p-tau sites as potential new biomarkers. As a proof-of-principle example, we showed that p-tau198 is a novel promising AD biomarker with sensitivity and specificity comparable with the existing biomarkers p-tau181 and p-tau217. Our results demonstrated that p-tau198 detection can not only differentiate AD from non-AD controls, but also diagnose AD from related 4R tauopathies PSP and CBD with AUCs of 0.96-0.99 (95% CI ranges from 0.90 to 1.00). Promisingly, p-tau198 was able to discriminate mild cognitive impairment from cognitively normal brains with an AUC of 0.75 (95% CI = 0.58-0.92). Our work provides a new avenue for developing diagnosis and differentiation tools for AD and related tauopathies.

Adaptable toolbox to characterize Alzheimer's disease pathology in mouse models

Here, we describe a highly adaptable toolbox for characterizing and analyzing molecular and histopathological changes in Alzheimer's disease (AD) mouse models. We detail optimized and streamlined approaches from sample preparation to image analysis to facilitate reproducible analyses. We also describe the extraction and measurement of the soluble Aβ level by sandwich ELISA in the cortex and hippocampus of AD mouse models before and after plaque deposition. Finally, we outline the steps for image quantification and analysis using Imaris and ImageJ. For complete details on the use and execution of this protocol, please refer to Huang et al. (2021).¹.

Development of Alkaline Phosphatase-Fused Mouse Prion Protein and Its Application in Toxic Aβ Oligomer Detection

Amyloid β (Aβ) oligomers play a key role in the progression of Alzheimer's disease (AD). Multiple forms of Aβ assemblies have been identified by in vitro and in vivo analyses; however, it is uncertain which oligomer is highly neurotoxic. Thus, understanding the pathogenesis of AD by detecting toxic Aβ oligomers is crucial. In this study, we report a fusion protein of cellular prion protein (PrPc) and alkaline phosphatase (ALP) from Escherichia coli as a sensing element for toxic Aβ oligomers. Since the N-terminus domain of PrPc (residue 23-111) derived from mice is known to bind to toxic Aβ oligomers in vitro, we genetically fused PrPc_23-111 to ALP. The developed fusion protein, PrP-ALP, retained both the binding ability of PrPc and enzymatic activity of ALP. We showed that PrP-ALP strongly bound to high molecular weight (HMW) oligomers but showed little or no affinity toward monomers. The observation that PrP-ALP neutralized the toxic effect of Aβ oligomers indicated an interaction between PrP-ALP and toxic HMW oligomers. Based on ALP activity, we succeeded in detecting Aβ oligomers. PrP-ALP may serve as a powerful tool for detecting toxic Aβ oligomers that may be related to AD progression.

Dual-emitting Iridium nanorods combining dual-regulating coreaction accelerator Ag nanoparticles for electrochemiluminescence ratio determination of amyloid-β oligomers

Iridium(III) complexes have been developed as eminent electrochemiluminescence (ECL) luminophores, but their current applications are only limited to anodic ECL emission because of weak cathodic ECL emission. This work explored poly(styrene-co-maleicanhydride) (PSMA) as functional reagent to modulate iridium(III) complexes to simultaneously emit bipolar ECL signals. The prepared iridium(III) nanorods (Ir NRs) were detected strong bipolar ECL emissions at +0.9 V and -2.0 V with N,N-diisopropylethylenediamine (DPEA) and persulfate (S₂O₈^2-) as coreactant, respectively. Meanwhile, Ag nanoparticles (Ag NPs) were developed as dual-regulating coreaction accelerator to boost the bipolar emissions of Ir NRs simultaneously. The dual-emitting Ir NRs coupled with dual-regulating coreaction accelerator Ag NPs facilitated the construction of mono-luminophore-based ECL ratio strategy for detecting amyloid-β oligomers (AβO). When the target AβO appeared, the Mg²⁺-dependent DNAzyme-powered biped walkers were unlocked to cleave single-stranded S1 immobilized on the surface of magnetic beads (MBs), resulting in the production of massive single-stranded ST. Then, the output ST cleaved hairpin H1 captured by Ir NRs modified electrode to produce numerous single strands, which could initiate the hybridization chain reaction (HCR) between Ag NPs-labeled H2 and Ag NPs-labeled H3 to introduce abundant Ag NPs onto the electrode surface. Due to the enhancement effect of Ag NPs on the bipolar ECL emissions from Ir NRs, the ECL ratio detection of AβO was achieved with the detection limit of 0.62 pM. The unique dual-emitting properties of Ir NRs coupled with dual-regulating effect of Ag NPs provided an interesting mono-luminophore-based ECL ratio sensing platform for biological analysis.

Mechanistic Models of Protein Aggregation Across Length-Scales and Time-Scales: From the Test Tube to Neurodegenerative Disease

Through advances in the past decades, the central role of aberrant protein aggregation has been established in many neurodegenerative diseases. Crucially, however, the molecular mechanisms that underlie aggregate proliferation in the brains of affected individuals are still only poorly understood. Under controlled in vitro conditions, significant progress has been made in elucidating the molecular mechanisms that take place during the assembly of purified protein molecules, through advances in both experimental methods and the theories used to analyse the resulting data. The determination of the aggregation mechanism for a variety of proteins revealed the importance of intermediate oligomeric species and of the interactions with promotors and inhibitors. Such mechanistic insights, if they can be achieved in a disease-relevant system, provide invaluable information to guide the design of potential cures to these devastating disorders. However, as experimental systems approach the situation present in real disease, their complexity increases substantially. Timescales increase from hours an aggregation reaction takes in vitro, to decades over which the process takes place in disease, and length-scales increase to the dimension of a human brain. Thus, molecular level mechanistic studies, like those that successfully determined mechanisms in vitro, have only been applied in a handful of living systems to date. If their application can be extended to further systems, including patient data, they promise powerful new insights. Here we present a review of the existing strategies to gain mechanistic insights into the molecular steps driving protein aggregation and discuss the obstacles and potential paths to achieving their application in disease. First, we review the experimental approaches and analysis techniques that are used to establish the aggregation mechanisms in vitro and the insights that have been gained from them. We then discuss how these approaches must be modified and adapted to be applicable in vivo and review the existing works that have successfully applied mechanistic analysis of protein aggregation in living systems. Finally, we present a broad mechanistic classification of in vivo systems and discuss what will be required to further our understanding of aggregate formation in living systems.

OUP accepted manuscript

Aqueously soluble oligomers of amyloid-β peptide may be the principal neurotoxic forms of amyloid-β in Alzheimer’s disease, initiating downstream events that include tau hyperphosphorylation, neuritic/synaptic injury, microgliosis and neuron loss. Synthetic oligomeric amyloid-β has been studied extensively, but little is known about the biochemistry of natural oligomeric amyloid-β in human brain, even though it is more potent than simple synthetic peptides and comprises truncated and modified amyloid-β monomers. We hypothesized that monoclonal antibodies specific to neurotoxic oligomeric amyloid-β could be used to isolate it for further study.

Here we report a unique human monoclonal antibody (B24) raised against synthetic oligomeric amyloid-β that potently prevents Alzheimer’s disease brain oligomeric amyloid-β-induced impairment of hippocampal long-term potentiation. B24 binds natural and synthetic oligomeric amyloid-β and a subset of amyloid plaques, but only in the presence of Ca²⁺. The amyloid-β N terminus is required for B24 binding. Hydroxyapatite chromatography revealed that natural oligomeric amyloid-β is highly avid for Ca²⁺. We took advantage of the reversible Ca²⁺-dependence of B24 binding to perform non-denaturing immunoaffinity isolation of oligomeric amyloid-β from Alzheimer’s disease brain-soluble extracts.

Unexpectedly, the immunopurified material contained amyloid fibrils visualized by electron microscopy and amenable to further structural characterization. B24-purified human oligomeric amyloid-β inhibited mouse hippocampal long-term potentiation. These findings identify a calcium-dependent method for purifying bioactive brain oligomeric amyloid-β, at least some of which appears fibrillar.

Development of three-dimensional semi-solid hydrogel matrices for ratiometric fluorescence sensing of Amyloid β peptide and imaging in SH-SY5 cells: Improvement of point of care diagnosis of Alzheimer's disease biomarker

Alzheimer's is a neurodegenerative disease with high morbidity and mortality in the elderly, so, detection of its biomarker for definite diagnosis of Alzheimer's in the early stage of disease is a challenge. Amyloid beta peptide (Aβ) chosen as an Alzheimer's biomarker. Here, we developed novel, semi-solid, three-dimensional hydrogel matrices for ratiometric fluorescence detection of Aβ. This assay's great performance stems from the employment of a hybrid conjugate composed of Rhodamine B (RB), Carbon dots (CDs), and an Aβ probe entrapped in Polyvinyl alcohol (PVA), and then detection of fluorescence resonance energy transfer (FRET) that occurs in the presence of AuNP/target-Aβ, as a result of hybridization. The RB-CDs' fluorescence (at 582 nm and 675 nm under 430 nm excitation) is quenched in the presence of AuNPs, while the ratio of fluorescence (I₅₈₂/I₆₇₅) is increased by the addition of Aβ target, and shows a linear relationship in the range of 75 pM-250 nM, with a detection limit of 0.5 pM. Furthermore, the assay possesses strong selectivity for Aβ compared to other proteins, and different quantities of a human serum sample successfully analyzed with excellent sensitivity, satisfactory precision, and reliability. Due to distribution of Aβ in SH-SY5 human neuroblastoma cells, extending this UV-Vis-NIR full-range responsive CDs bio-probe to imaging of Aβ in cells. In both fixed and living SH-SY5 cells, the nanoprobe delivers a clear signal to the Aβ target. Because of its high sensitivity, selectivity, biocompatibility and affordability, this nanoprobe is a good option for early Alzheimer's disease diagnosis.

The Amyloid-β Pathway in Alzheimer's Disease

Breakthroughs in molecular medicine have positioned the amyloid-β (Aβ) pathway at the center of Alzheimer's disease (AD) pathophysiology. While the detailed molecular mechanisms of the pathway and the spatial-temporal dynamics leading to synaptic failure, neurodegeneration, and clinical onset are still under intense investigation, the established biochemical alterations of the Aβ cycle remain the core biological hallmark of AD and are promising targets for the development of disease-modifying therapies. Here, we systematically review and update the vast state-of-the-art literature of Aβ science with evidence from basic research studies to human genetic and multi-modal biomarker investigations, which supports a crucial role of Aβ pathway dyshomeostasis in AD pathophysiological dynamics. We discuss the evidence highlighting a differentiated interaction of distinct Aβ species with other AD-related biological mechanisms, such as tau-mediated, neuroimmune and inflammatory changes, as well as a neurochemical imbalance. Through the lens of the latest development of multimodal in vivo biomarkers of AD, this cross-disciplinary review examines the compelling hypothesis- and data-driven rationale for Aβ-targeting therapeutic strategies in development for the early treatment of AD.

An ultra-sensitive immunoassay detects and quantifies soluble Aβ oligomers in human plasma

INTRODUCTION

Evidence strongly suggests that soluble oligomers of amyloid beta protein (oAβ) help initiate the pathogenic cascade of Alzheimer's disease (AD). To date, there have been no validated assays specific for detecting and quantifying oAβ in human blood.

METHODS

We developed an ultrasensitive oAβ immunoassay using a novel capture antibody (71A1) with N-terminal antibody 3D6 for detection that specifically quantifies soluble oAβ in the human brain, cerebrospinal fluid (CSF), and plasma.

RESULTS

Two new antibodies (71A1; 1G5) are oAβ-selective, label Aβ plaques in non-fixed AD brain sections, and potently neutralize the synaptotoxicity of AD brain-derived oAβ. The 71A1/3D6 assay showed excellent dilution linearity in CSF and plasma without matrix effects, good spike recovery, and specific immunodepletion.

DISCUSSION

We have created a sensitive, high throughput, and inexpensive method to quantify synaptotoxic oAβ in human plasma for analyzing large cohorts of aged and AD subjects to assess the dynamics of this key pathogenic species and response to therapy.

Detection of Amyloid β Oligomers by a Fluorescence Ratio Strategy Based on Optically Trapped Highly Doped Upconversion Nanoparticles-SiO2@Metal-Organic Framework Microspheres

Alzheimer's disease (AD), known as a progressive neurodegenerative disorder, has had a terrible impact on the health of aged people. Due to its severity, early diagnosis of AD is significant to retard the progress and provide timely treatment. Here, we report a fluorescence ratio detection of AD biomarker amyloid β oligomers (AβOs) by combining highly doped upconversion nanoparticles-SiO₂@metal-organic framework/black hole quencher (H-USM/BHQ-1) microspheres with optical tweezer (OT) microscopic imaging. Optical trapping a single microsphere not only avoids the interference of fluid viscosity but also provides a high power density laser source to efficiently stimulate upconversion luminescence (UCL) of highly doped upconversion nanoparticles (H-UCNPs). Under this condition, H-UCNPs show stronger UCL and greater power-dependent properties compared to low-doped ones. Moreover, the closely packed quenching molecules BHQ-1 on a metal-organic framework (ZIF-8) exhibit excellent quenching efficiency for upconversion 525 and 540 nm emission. Also, the luminescent resonance energy transfer efficiency reaches 89.58%. When different concentrations of AβOs are present, the UCL₅₄₀ recovers due to the decomposition of ZIF-8 and the release of BHQ-1. Using 540 and 654 nm emission ratio of highly doped UCNPs as reporters, the limit of detection reaches 28.4 pM for the quantitative determination of AβOs. Besides, this strategy is able to selectively quantify the AβO concentration. Therefore, we demonstrated the combination of optical trapping and highly doped UCNPs which is applied for the detection of AβOs with high sensitivity and specificity.

Mapping the binding site topology of amyloid protein aggregates using multivalent ligands

A key process in the development of neurodegenerative diseases such as Alzheimer's and Parkinson's diseases is the aggregation of proteins to produce fibrillary aggregates with a cross β-sheet structure, amyloid. The development of reagents that can bind these aggregates with high affinity and selectivity has potential for early disease diagnosis. By linking two benzothiazole aniline (BTA) head groups with different length polyethylene glycol (PEG) spacers, fluorescent probes that bind amyloid fibrils with low nanomolar affinity have been obtained. Dissociation constants measured for interaction with Aβ, α-synuclein and tau fibrils show that the length of the linker determines binding affinity and selectivity. These compounds were successfully used to image α-synuclein aggregates in vitro and in the post-mortem brain tissue of patients with Parkinson's disease. The results demonstrate that multivalent ligands offer a powerful approach to obtain high affinity, selective reagents to bind the fibrillary aggregates that form in neurodegenerative disease.

Multivalent ligands offer a powerful approach to obtain high affinity reagents to bind the aggregates that form in neurodegenerative disease. Selectivity for different proteins was achieved by using different linkers to connect the head groups.

Quantifying misfolded protein oligomers as drug targets and biomarkers in Alzheimer and Parkinson diseases

Protein misfolding and aggregation are characteristic of a wide range of neurodegenerative disorders, including Alzheimer and Parkinson diseases. A hallmark of these diseases is the aggregation of otherwise soluble and functional proteins into amyloid aggregates. Although for many decades such amyloid deposits have been thought to be responsible for disease progression, it is now increasingly recognized that the misfolded protein oligomers formed during aggregation are, instead, the main agents causing pathological processes. These oligomers are transient and heterogeneous, which makes it difficult to detect and quantify them, generating confusion about their exact role in disease. The lack of suitable methods to address these challenges has hampered efforts to investigate the molecular mechanisms of oligomer toxicity and to develop oligomer-based diagnostic and therapeutic tools to combat protein misfolding diseases. In this Review, we describe methods to quantify misfolded protein oligomers, with particular emphasis on diagnostic applications as disease biomarkers and on therapeutic applications as target biomarkers. The development of these methods is ongoing, and we discuss the challenges that remain to be addressed to establish measurement tools capable of overcoming existing limitations and to meet present needs.

Emerging Technologies and Platforms for the Immunodetection of Multiple Biochemical Markers in Osteoarthritis Research and Therapy

Biomarkers, especially biochemical markers, are important in osteoarthritis (OA) research, clinical trials, and drug development and have potential for more extensive use in therapeutic monitoring. However, they have not yet had any significant impact on disease diagnosis and follow-up in a clinical context. Nevertheless, the development of immunoassays for the detection and measurement of biochemical markers in OA research and therapy is an active area of research and development. The evaluation of biochemical markers representing low-grade inflammation or extracellular matrix turnover may permit OA prognosis and expedite the development of personalized treatment tailored to fit particular disease severities. However, currently detection methods have failed to overcome specific hurdles such as low biochemical marker concentrations, patient-specific variation, and limited utility of single biochemical markers for definitive characterization of disease status. These challenges require new and innovative approaches for development of detection and quantification systems that incorporate clinically relevant biochemical marker panels. Emerging platforms and technologies that are already on the way to implementation in routine diagnostics and monitoring of other diseases could potentially serve as good technological and strategic examples for better assessment of OA. State-of-the-art technologies such as advanced multiplex assays, enhanced immunoassays, and biosensors ensure simultaneous screening of a range of biochemical marker targets, the expansion of detection limits, low costs, and rapid analysis. This paper explores the implementation of such technologies in OA research and therapy. Application of novel immunoassay-based technologies may shed light on poorly understood mechanisms in disease pathogenesis and lead to the development of clinically relevant biochemical marker panels. More sensitive and specific biochemical marker immunodetection will complement imaging biomarkers and ensure evidence-based comparisons of intervention efficacy. We discuss the challenges hindering the development, testing, and implementation of new OA biochemical marker assays utilizing emerging multiplexing technologies and biosensors.

β-Secretase1 biological markers for Alzheimer's disease: state-of-art of validation and qualification

β-Secretase1 (BACE1) protein concentrations and rates of enzyme activity, analyzed in human bodily fluids, are promising candidate biological markers for guidance in clinical trials investigating BACE1 inhibitors to halt or delay the dysregulation of the amyloid-β pathway in Alzheimer's disease (AD). A robust body of evidence demonstrates an association between cerebrospinal fluid/blood BACE1 biomarkers and core pathophysiological mechanisms of AD, such as brain protein misfolding and aggregration, neurodegeneration, and synaptic dysfunction.In pharmacological trials, BACE1 candidate biomarkers may be applied to a wide set of contexts of use (CoU), including proof of mechanism, dose-finding, response and toxicity dose estimation. For clinical CoU, BACE1 biomarkers show good performance for prognosis and disease prediction.The roadmap toward validation and qualification of BACE1 biomarkers requires standardized pre-analytical and analytical protocols to reduce inter-site variance that may have contributed to inconsistent results.BACE1 biomarker-drug co-development programs, including biomarker-guided outcomes and endpoints, may support the identification of sub-populations with a higher probability to benefit from BACE1 inhibitors with a reduced risk of adverse effects, in line with the evolving precision medicine paradigm.

Peripheral cytokine and fatty acid associations with neuroinflammation in AD and aMCI patients: An exploratory study

Neuroinflammation is thought to be important in the progression of Alzheimer's disease (AD). To evaluate cerebral inflammation radioligands that target TSPO, a translocator protein strongly expressed in microglia and macrophages during inflammation, can be used in conjunction with positron emission tomography (PET) imaging. In AD patients, neuroinflammation is up-regulated compared to both healthy volunteers as well as to subjects with amnestic Mild Cognitive Impairment. Peripheral biomarkers, such as serum cytokines and total fatty acids (FAs), can also be indicative of the inflammatory state of subjects with neurodegenerative disorders. To understand whether peripheral biomarkers are predictive of neuroinflammation we conducted a secondary exploratory analysis of two TSPO imaging studies conducted in subjects with AD, aMCI and aged matched healthy volunteers. We examined the association between candidate peripheral biomarkers (including amyloid beta, cytokines and serum total fatty acids) with brain TSPO levels. Our results showed that serum IL-6 and IL-10 are higher in AD compared to the aMCI and healthy volunteers while levels of some fatty acids are modulated during the disease. A limited number of associations were observed between region-specific inflammation and fatty acids in aMCI patients, and between amyloid beta 42 and brain inflammation in AD, however no associations were present with systemic cytokines. Our study suggests that while TSPO binding and systemic IL-6 and IL-10 were elevated in AD, serum amyloid beta, cytokines and fatty acids were generally not predictive of the disease nor correlated with neuroinflammation.

DNAzyme-Powered Three-Dimensional DNA Walker Nanoprobe for Detection Amyloid β-Peptide Oligomer in Living Cells and in Vivo

Amyloid β-peptide oligomer (AβO) is widely acknowledged as the promising biomarker for the diagnosis of Alzheimer's disease (AD). In this work, we designed a three-dimensional (3D) DNA walker nanoprobe for AβO detection and real-time imaging in living cells and in vivo. The presence of AβO triggered the DNAzyme walking strand to cleave the fluorophore (TAMRA)-labeled substrate strand modified on the gold nanoparticle (AuNP) surface and release TAMRA-labeled DNA fragment, resulting in the recovery of fluorescent signal. The entire process was autonomous and continuous, without external fuel strands or protease, and finally produced plenty of TAMRA fluorescence, achieving signal amplification effect. The nanoprobe enabled the quantitative detection of AβO in vitro, and the limit of detection was 22.3 pM. Given the good biocompatibility of 3D DNA walker nanoprobe, we extended this enzyme-free signal amplification method to real-time imaging of AβO. Under the microscope, nanoprobe accurately located and visualized the distribution of AβO in living cells. Moreover, in vivo imaging results showed that our nanoprobe could be used to effectively distinguish the AD mice from the wild-type mice. This nanoprobe with the advantages of great sensitivity, high specificity, and convenience, provides an outstanding prospect for AD's early diagnosis development.

Rationally Designed Antibodies as Research Tools to Study the Structure-Toxicity Relationship of Amyloid-β Oligomers

Alzheimer's disease is associated with the aggregation of the amyloid-β peptide (Aβ), resulting in the deposition of amyloid plaques in brain tissue. Recent scrutiny of the mechanisms by which Aβ aggregates induce neuronal dysfunction has highlighted the importance of the Aβ oligomers of this protein fragment. Because of the transient and heterogeneous nature of these oligomers, however, it has been challenging to investigate the detailed mechanisms by which these species exert cytotoxicity. To address this problem, we demonstrate here the use of rationally designed single-domain antibodies (DesAbs) to characterize the structure-toxicity relationship of Aβ oligomers. For this purpose, we use Zn2+-stabilized oligomers of the 40-residue form of Aβ (Aβ40) as models of brain Aβ oligomers and two single-domain antibodies (DesAb18-24 and DesAb34-40), designed to bind to epitopes at residues 18-24 and 34-40 of Aβ40, respectively. We found that the DesAbs induce a change in structure of the Zn2+-stabilized Aβ40 oligomers, generating a simultaneous increase in their size and solvent-exposed hydrophobicity. We then observed that these increments in both the size and hydrophobicity of the oligomers neutralize each other in terms of their effects on cytotoxicity, as predicted by a recently proposed general structure-toxicity relationship, and observed experimentally. These results illustrate the use of the DesAbs as research tools to investigate the biophysical and cytotoxicity properties of Aβ oligomers.

A mechanistic hypothesis for the impairment of synaptic plasticity by soluble Aβ oligomers from Alzheimer's brain

It is increasingly accepted that early cognitive impairment in Alzheimer's disease results in considerable part from synaptic dysfunction caused by the accumulation of a range of oligomeric assemblies of amyloid β-protein (Aβ). Most studies have used synthetic Aβ peptides to explore the mechanisms of memory deficits in rodent models, but recent work suggests that Aβ assemblies isolated from human (AD) brain tissue are far more potent and disease-relevant. Although reductionist experiments show Aβ oligomers to impair synaptic plasticity and neuronal viability, the responsible mechanisms are only partly understood. Glutamatergic receptors, GABAergic receptors, nicotinic receptors, insulin receptors, the cellular prion protein, inflammatory mediators, and diverse signaling pathways have all been suggested. Studies using AD brain-derived soluble Aβ oligomers suggest that only certain bioactive forms (principally small, diffusible oligomers) can disrupt synaptic plasticity, including by binding to plasma membranes and changing excitatory-inhibitory balance, perturbing mGluR, PrP, and other neuronal surface proteins, down-regulating glutamate transporters, causing glutamate spillover, and activating extrasynaptic GluN2B-containing NMDA receptors. We synthesize these emerging data into a mechanistic hypothesis for synaptic failure in Alzheimer's disease that can be modified as new knowledge is added and specific therapeutics are developed.

The path forward in Alzheimer's disease therapeutics: Reevaluating the amyloid cascade hypothesis

Development of disease-modifying treatments for Alzheimer's disease (AD) has been challenging, with no drugs approved to date. The failures of several amyloid-targeted programs have led many to dismiss the amyloid beta (Aβ) hypothesis of AD. An antiamyloid antibody aducanumab recently showed modest but significant efficacy in a phase 3 trial, providing important validation of amyloid as a therapeutic target. However, the inconsistent results observed with aducanumab may be explained by the limited brain penetration and lack of selectivity for the soluble Aβ oligomers, which are implicated as upstream drivers of neurodegeneration by multiple studies. Development of agents that can effectively inhibit Aβ oligomer formation or block their toxicity is therefore warranted. An ideal drug would cross the blood-brain barrier efficiently and achieve sustained brain levels that can continuously prevent oligomer formation or inhibit their toxicity. A late-stage candidate with these attributes is ALZ-801, an oral drug with a favorable safety profile and high brain penetration that can robustly inhibit Aβ oligomer formation. An upcoming phase 3 trial with ALZ-801 in APOE4/4 homozygous patients with early AD will effectively test this amyloid oligomer hypothesis.

Serum levels and mutual correlations of amyloid β in patients with depression

AIM

Epidemiological studies have shown that depression is a risk factor for Alzheimer's disease (AD). Although the biological mechanism underlying the link between depression and AD is unclear, altered amyloid β (Aβ) metabolism in patients with depression has been suggested as a potential mechanism. Results from previous studies of Aβ metabolism in patients with depression have been inconsistent, and Aβ polymerization, which is a crucial process in AD pathology, has not previously been assessed.

METHODS

Serum levels of Aβ40, Aβ42 and Aβ oligomers were evaluated in 104 inpatients with major depressive disorder (MDD) and 132 healthy control individuals.

RESULTS

Lower serum Aβ42 levels were observed in patients with MDD, but there was no difference in serum Aβ oligomer levels between the MDD group and the healthy control group, even in older adults. Interestingly, serum Aβ oligomer levels in patients with MDD were dependent on serum Aβ42 levels, regardless of age, and this relationship was not observed in the control group.

CONCLUSIONS

These results suggest that Aβ42 is more prone to aggregation and polymerization in patients with depression than in healthy individuals, suggesting a possible mechanism underlying the transition from depression to AD. Geriatr Gerontol Int 2020; 20: 125-129.

NMR-based site-resolved profiling of β-amyloid misfolding reveals structural transitions from pathologically relevant spherical oligomer to fibril

Increasing evidence highlights the central role of neurotoxic oligomers of the 42-residue-long β-amyloid (Aβ42) in Alzheimer's disease (AD). However, very limited information is available on the structural transition from oligomer to fibril, particularly for pathologically relevant amyloids. To the best of our knowledge, we present here the first site-specific structural characterization of Aβ42 misfolding, from toxic oligomeric assembly yielding a similar conformation to an AD-associated Aβ42 oligomer, into a fibril. Transmission EM (TEM) analysis revealed that a spherical amyloid assembly (SPA) of Aβ42 with a 15.6 ± 2.1-nm diameter forms in a ∼30-μm Aβ42 solution after a ∼10-h incubation at 4 °C, followed by a slow conversion into fibril at ∼180 h. Immunological analysis suggested that the SPA has a surface structure similar to that of amylospheroid (ASPD), a patient-derived toxic Aβ oligomer, which had a diameter of 10-15 nm in negative-stain TEM. Solid-state NMR analyses indicated that the SPA structure involves a β-loop-β motif, which significantly differed from the triple-β motif observed for the Aβ42 fibril. The comparison of the ¹³C chemical shifts of SPA with those of the fibril prepared in the above conditions and interstrand distance measurements suggested a large conformational change involving rearrangements of intermolecular β-sheet into in-register parallel β-sheet during the misfolding. A comparison of the SPA and ASPD ¹³C chemical shifts indicated that SPA is structurally similar to the ASPD relevant to AD. These observations provide insights into the architecture and key structural transitions of amyloid oligomers relevant for AD pathology.

The Beta Amyloid Dysfunction (BAD) Hypothesis for Alzheimer's Disease

Beta amyloid, Aβ 1–42, originally named as Amyloid A4 protein, is one of the most investigated peptides in neuroscience and has attracted substantial interest since its discovery as the main insoluble fibril-type protein in cerebrovascular amyloid angiopathy (Glenner and Wong, 1984; Masters et al., 1985) of Alzheimer’s disease (AD). From the very beginning, Aβ was regarded per se as a “bad molecule,” triggering the so-called “beta amyloid cascade hypothesis” (Hardy and Higgins, 1992). This hypothesis ignored any physiological function for in situ generated Aβ monomer with normal production and turnover rate (Bateman et al., 2006). Accordingly, pan-Aβ-related therapeutic approaches were designed to eliminate or lower the three structural isoforms in parallel: (1) the pre-amyloid monomer, (2) the misfolded oligomer, and (3) the final fibril. While we already knew about poor correlations between plaques and cognitive decline quite early (Terry et al., 1991), data for an essential benign physiological role for Aβ monomer at low concentrations were also not considered to be relevant. Here, a different Beta Amyloid hypothesis is described, the so-called “Beta Amyloid Dysfunction hypothesis,” which, in contrast to the “Beta Amyloid Cascade hypothesis,” builds on the homeostasis of essential Aβ monomer in the synaptic vesicle cycle (SVC). Disease-relevant early pathology emerges through disturbance of the Aβ homeostasis by so far unknown factors leading to the formation of misfolded Aβ oligomers. These early species interfere with the synaptic physiological Aβ monomer regulation and exert their neurotoxicity via various receptors for sticky oligomer-type Aβ aggregates. The Beta Amyloid Dysfunction (BAD) hypothesis is introduced and shown to explain negative clinical results of Gamma-secretase and Beta-secretase (BACE) inhibitors as well as pan-Aβ isotype unselective immunotherapies. This hypothesis gives guidance to what needs to be done therapeutically to revive successful clinical testing in AD for this highly validated target. The BAD hypothesis will need further refinement in particular through more detailed exploration for the role of physiological Aβ monomer.

Reappraisal of Aβ40 and Aβ42 Peptides Measurements in Cerebrospinal Fluid of Patients with Alzheimer's Disease

Cerebrospinal fluid (CSF) biomarkers are currently included in the diagnostic criteria for Alzheimer's disease (AD), in particular, decreased concentrations of amyloid-β peptide 1-42 (Aβ42) in the CSF, coupled with increased levels of tau and phosphorylated tau proteins, are supportive of AD diagnosis. To date, the quantification of Aβ42 levels with antibody-dependent immunoassay shows a marked variability among different laboratories and is also affected by different pre-analytical factors, suggesting that part of Aβ42 peptides might be aggregated and thus undetected by antibodies. To bypass an antibody-dependent measurement, we determined the Aβ40 and Aβ42 levels by immunoblot. We analyzed CSF samples from 35 patients with clinical diagnosis of probable AD and from 15 age-matched normal controls; CSF Aβ levels were determined by two different ELISA kits and by immunoblot analysis. Aβ40 levels measured by ELISA were comparable to those obtained by immunoblot, whereas CSF concentrations of Aβ42 measured by ELISA were significantly lower compared to values obtained by immunoblot quantification. Biochemical analysis, following 1D- and 2D-PAGE analysis, showed that the qualitative composition of Aβ peptides in the CSF is similar in AD and controls but different from that of AD brain tissues. Moreover, sedimentation velocity in sucrose gradient of CSF and brain homogenate from AD demonstrated that Aβ42 in CSF is different from Aβ42 in brain in terms of solubility and aggregation state.

Target engagement in an alzheimer trial: Crenezumab lowers amyloid β oligomers in cerebrospinal fluid

OBJECTIVE

Oligomeric forms of amyloid β protein (oAβ) are believed to be principally responsible for neurotoxicity in Alzheimer disease (AD), but it is not known whether anti-Aβ antibodies are capable of lowering oAβ levels in humans.

METHODS

We developed an ultrasensitive immunoassay and used it to measure oAβ in cerebrospinal fluid (CSF) from 104 AD subjects participating in the ABBY and BLAZE phase 2 trials of the anti-Aβ antibody crenezumab. Patients received subcutaneous (SC) crenezumab (300mg) or placebo every 2 weeks, or intravenous (IV) crenezumab (15mg/kg) or placebo every 4 weeks for 68 weeks. Ninety-eight of the 104 patients had measurable baseline oAβ levels, and these were compared to levels at week 69 in placebo (n = 28), SC (n = 35), and IV (n = 35) treated patients.

RESULTS

Among those receiving crenezumab, 89% of SC and 86% of IV patients had lower levels of oAβ at week 69 versus baseline. The difference in the proportion of patients with decreasing levels was significant for both treatment arms: p = 0.0035 for SC and p = 0.01 for IV crenezumab versus placebo. The median percentage change was -48% in the SC arm and -43% in the IV arm. No systematic change was observed in the placebo group, with a median change of -13% and equivalent portions with negative and positive change.

INTERPRETATION

Crenezumab lowered CSF oAβ levels in the large majority of treated patients tested. These results support engagement of the principal pathobiological target in AD and identify CSF oAβ as a novel pharmacodynamic biomarker for use in trials of anti-Aβ agents. ANN NEUROL 2019;86:215-224.

Long Non-coding RNA BACE1-AS May Serve as an Alzheimer's Disease Blood-Based Biomarker

Circulating long noncoding RNAs (lncRNAs) might serve as biomarkers for different pathological conditions. BACE1-AS lncRNA upregulates in the brain of people with Alzheimer's disease (AD) and might be detected in the bloodstream. To reveal if lncRNA BACE1-AS may serve as a blood-based biomarker for AD, we compared its levels in plasma and plasma-derived exosomes between AD (n = 45) and healthy people (n = 36). Exosomes were purified from plasma by Invitrogen™ Total Exosome Isolation Kit and characterized by scanning electron microscopy (SEM) and dynamic light scattering (DLS). Total RNA was extracted from whole plasma, and plasma-derived exosomes using TRIzol® LS or TRIzol® Reagents respectively were then reverse transcribed to the cDNA using PrimeScript II cDNA synthesis kit. The BACE1-AS levels were quantified by real-time PCR, and their biomarker potencies were evaluated using ROC curve analysis. Results obtained verified the presence of BACE1-AS in the plasma samples of both AD and healthy controls. We did not observe any significant differences between the levels of BACE1-AS in the plasma or plasma-derived exosomes of AD and control people. However, there were significant differences between AD subgroups and control in the whole plasma samples. The BACE1-AS level was low in pre-AD subgroup but it was high in full-AD people compared to the healthy controls. Moreover, ROC curve analysis revealed that lncRNA BACE1-AS may discriminate pre-AD and healthy control (75% sensitivity and 100% specificity), full-AD and healthy control (68% sensitivity and 100% specificity), and pre-AD and full-AD subgroups (78% sensitivity and 100% specificity), highlighting its potential as a biomarker for AD development. In conclusion, plasma BACE1-AS level may serve as a potent blood-based biomarker for Alzheimer's disease.

Clusterin accumulates in synapses in Alzheimer's disease and is increased in apolipoprotein E4 carriers

One of the major challenges in developing effective therapeutic strategies for Alzheimer’s disease is understanding how genetic risk factors contribute to neurodegeneration. The apolipoprotein epsilon 4 isoform (APOE4) and variants in the Clusterin (CLU) gene (also known as apolipoprotein J) are associated with increased risk of developing Alzheimer’s. Our previous work demonstrated that APOE4 exacerbates synapse degeneration and synaptic accumulation of toxic oligomeric amyloid beta in human Alzheimer’s and mouse models of disease. Here, we observe clusterin in synapses in human Alzheimer's disease brain. The percentage of synapses containing clusterin is higher in APOE4 carriers than APOE3 carriers. Furthermore, we observe oligomeric amyloid beta accumulation within synapses containing clusterin which is also higher in APOE4 carriers. These data link two genetic risk factors with synapse degeneration in Alzheimer’s and support a potential role for clusterin working with APOE in causing synaptic damage.

Aβ(M1-40) and Wild-Type Aβ40 Self-Assemble into Oligomers with Distinct Quaternary Structures

Amyloid-β oligomers (AβOs) self-assemble into polymorphic species with diverse biological activities that are implicated causally to Alzheimer’s disease (AD). Synaptotoxicity of AβO species is dependent on their quaternary structure, however, low-abundance and environmental sensitivity of AβOs in vivo have impeded a thorough assessment of structure–function relationships. We developed a simple biochemical assay to quantify the relative abundance and morphology of cross-linked AβOs. We compared oligomers derived from synthetic Aβ40 (wild-type (WT) Aβ40) and a recombinant source, called Aβ(M1–40). Both peptides assemble into oligomers with common sizes and morphology, however, the predominant quaternary structures of Aβ(M1–40) oligomeric states were more diverse in terms of dispersity and morphology. We identified self-assembly conditions that stabilize high-molecular weight oligomers of Aβ(M1–40) with apparent molecular weights greater than 36 kDa. Given that mixtures of AβOs derived from both peptides have been shown to be potent neurotoxins that disrupt long-term potentiation, we anticipate that the diverse quaternary structures reported for Aβ(M1–40) oligomers using the assays reported here will facilitate research efforts aimed at isolating and identifying common toxic species that contribute to synaptic dysfunction.

The Amyloid-β Oligomer Hypothesis: Beginning of the Third Decade

The amyloid-β oligomer (AβO) hypothesis was introduced in 1998. It proposed that the brain damage leading to Alzheimer’s disease (AD) was instigated by soluble, ligand-like AβOs. This hypothesis was based on the discovery that fibril-free synthetic preparations of AβOs were potent CNS neurotoxins that rapidly inhibited long-term potentiation and, with time, caused selective nerve cell death (Lambert et al., 1998). The mechanism was attributed to disrupted signaling involving the tyrosine-protein kinase Fyn, mediated by an unknown toxin receptor. Over 4,000 articles concerning AβOs have been published since then, including more than 400 reviews. AβOs have been shown to accumulate in an AD-dependent manner in human and animal model brain tissue and, experimentally, to impair learning and memory and instigate major facets of AD neuropathology, including tau pathology, synapse deterioration and loss, inflammation, and oxidative damage. As reviewed by Hayden and Teplow in 2013, the AβO hypothesis “has all but supplanted the amyloid cascade.” Despite the emerging understanding of the role played by AβOs in AD pathogenesis, AβOs have not yet received the clinical attention given to amyloid plaques, which have been at the core of major attempts at therapeutics and diagnostics but are no longer regarded as the most pathogenic form of Aβ. However, if the momentum of AβO research continues, particularly efforts to elucidate key aspects of structure, a clear path to a successful disease modifying therapy can be envisioned. Ensuring that lessons learned from recent, late-stage clinical failures are applied appropriately throughout therapeutic development will further enable the likelihood of a successful therapy in the near-term.

Innovative Biomarkers for Alzheimer's Disease: Focus on the Hidden Disease Biomarkers

The criteria for the clinical diagnosis of AD include the analysis of biomarkers of the underlying brain disease pathology; a set of cerebrospinal fluid (CSF) tests, amyloid-β1-42 (Aβ42), total-tau (t-tau), and phosphorylated tau (p-tau), are available and their performance in a clinical setting has been assessed in several studies. Thus, in dementia research, great advances have been made in the discovery of putative biomarkers; however, disappointingly, few of them have been translated into clinically applicable assays. To find biomarkers able to reliably detect AD pathology already at prodromal stages and in blood is even more important. Recent technical breakthroughs have provided ultrasensitive methods that allow the detection of brain-specific proteins in blood. In the present review, we will focus on the usefulness of ultrasensitive technologies for biomarker discovery and trace elements detection; moreover, we will review studies on circulating nano-compartments, a promising novel source of material for molecular diagnostics.

Opposing Roles of apolipoprotein E in aging and neurodegeneration

Apolipoprotein E (APOE) effects on brain function remain controversial. Removal of APOE not only impairs cognitive functions but also reduces neuritic amyloid plaques in mouse models of Alzheimer's disease (AD). Can APOE simultaneously protect and impair neural circuits? Here, we dissociated the role of APOE in AD versus aging to determine its effects on neuronal function and synaptic integrity. Using two-photon calcium imaging in awake mice to record visually evoked responses, we found that genetic removal of APOE improved neuronal responses in adult APP/PSEN1 mice (8-10 mo). These animals also exhibited fewer neuritic plaques with less surrounding synapse loss, fewer neuritic dystrophies, and reactive glia. Surprisingly, the lack of APOE in aged mice (18-20 mo), even in the absence of amyloid, disrupted visually evoked responses. These results suggest a dissociation in APOE's role in AD versus aging: APOE may be neurotoxic during early stages of amyloid deposition, although being neuroprotective in latter stages of aging.

Current state of Alzheimer's fluid biomarkers

Alzheimer’s disease (AD) is a progressive neurodegenerative disease with a complex and heterogeneous pathophysiology. The number of people living with AD is predicted to increase; however, there are no disease-modifying therapies currently available and none have been successful in late-stage clinical trials. Fluid biomarkers measured in cerebrospinal fluid (CSF) or blood hold promise for enabling more effective drug development and establishing a more personalized medicine approach for AD diagnosis and treatment. Biomarkers used in drug development programmes should be qualified for a specific context of use (COU). These COUs include, but are not limited to, subject/patient selection, assessment of disease state and/or prognosis, assessment of mechanism of action, dose optimization, drug response monitoring, efficacy maximization, and toxicity/adverse reactions identification and minimization. The core AD CSF biomarkers Aβ42, t-tau, and p-tau are recognized by research guidelines for their diagnostic utility and are being considered for qualification for subject selection in clinical trials. However, there is a need to better understand their potential for other COUs, as well as identify additional fluid biomarkers reflecting other aspects of AD pathophysiology. Several novel fluid biomarkers have been proposed, but their role in AD pathology and their use as AD biomarkers have yet to be validated. In this review, we summarize some of the pathological mechanisms implicated in the sporadic AD and highlight the data for several established and novel fluid biomarkers (including BACE1, TREM2, YKL-40, IP-10, neurogranin, SNAP-25, synaptotagmin, α-synuclein, TDP-43, ferritin, VILIP-1, and NF-L) associated with each mechanism. We discuss the potential COUs for each biomarker.

SAR228810: an antibody for protofibrillar amyloid β peptide designed to reduce the risk of amyloid-related imaging abnormalities (ARIA)

BACKGROUND

Anti-amyloid β (Aβ) immunotherapy represents a major area of drug development for Alzheimer's disease (AD). However, Aβ peptide adopts multiple conformations and the pathological forms to be specifically targeted have not been identified. Aβ immunotherapy-related vasogenic edema has also been severely dose limiting for antibodies with effector functions binding vascular amyloid such as bapineuzumab. These two factors might have contributed to the limited efficacy demonstrated so far in clinical studies.

METHODS

To address these limitations, we have engineered SAR228810, a humanized monoclonal antibody (mAb) with limited Fc effector functions that binds specifically to soluble protofibrillar and fibrillar forms of Aβ peptide and we tested it together with its murine precursor SAR255952 in vitro and in vivo.

RESULTS

Unlike gantenerumab and BAN2401, SAR228810 and SAR255952 do not bind to Aβ monomers, low molecular weight Aβ oligomers or, in human brain sections, to Aβ diffuse deposits which are not specific of AD pathology. Both antibodies prevent Aβ42 oligomer neurotoxicity in primary neuronal cultures. In vivo, SAR255952, a mouse aglycosylated IgG1, dose-dependently prevented brain amyloid plaque formation and plaque-related inflammation with a minimal active dose of 3 mg/kg/week by the intraperitoneal route. No increase in plasma Aβ levels was observed with SAR255952 treatment, in line with its lack of affinity for monomeric Aβ. The effects of SAR255952 translated into synaptic functional improvement in ex-vivo hippocampal slices. Brain penetration and decoration of cerebral amyloid plaques was documented in live animals and postmortem. SAR255952 (up to 50 mg/kg/week intravenously) did not increase brain microhemorrhages and/or microscopic changes in meningeal and cerebral arteries in old APPSL mice while 3D6, the murine version of bapineuzumab, did. In immunotolerized mice, the clinical candidate SAR228810 demonstrated the same level of efficacy as the murine SAR255952.

CONCLUSION

Based on the improved efficacy/safety profile in non-clinical models of SAR228810, a first-in-man single and multiple dose administration clinical study has been initiated in AD patients.

Decoding the synaptic dysfunction of bioactive human AD brain soluble Aβ to inspire novel therapeutic avenues for Alzheimer's disease

Pathologic, biochemical and genetic evidence indicates that accumulation and aggregation of amyloid β-proteins (Aβ) is a critical factor in the pathogenesis of Alzheimer's disease (AD). Several therapeutic interventions attempting to lower Aβ have failed to ameliorate cognitive decline in patients with clinical AD significantly, but most such approaches target only one or two facets of Aβ production/clearance/toxicity and do not consider the heterogeneity of human Aβ species. As synaptic dysfunction may be among the earliest deficits in AD, we used hippocampal long-term potentiation (LTP) as a sensitive indicator of the early neurotoxic effects of Aβ species. Here we confirmed prior findings that soluble Aβ oligomers, much more than fibrillar amyloid plaque cores or Aβ monomers, disrupt synaptic function. Interestingly, not all (84%) human AD brain extracts are able to inhibit LTP and the degree of LTP impairment by AD brain extracts does not correlate with Aβ levels detected by standard ELISAs. Bioactive AD brain extracts also induce neurotoxicity in iPSC-derived human neurons. Shorter forms of Aβ (including Aβ_1-37, Aβ_1-38, Aβ_1-39), pre-Aβ APP fragments (- 30 to - 1) and N-terminally extended Aβs (- 30 to + 40) each showed much less synaptotoxicity than longer Aβs (Aβ_1-42 - Aβ_1-46). We found that antibodies which target the N-terminus, not the C-terminus, efficiently rescued Aβ oligomer-impaired LTP and oligomer-facilitated LTD. Our data suggest that preventing soluble Aβ oligomer formation and targeting their N-terminal residues with antibodies could be an attractive combined therapeutic approach.

Inhibiting the Ca2+ Influx Induced by Human CSF

One potential therapeutic strategy for Alzheimer’s disease (AD) is to use antibodies that bind to small soluble protein aggregates to reduce their toxic effects. However, these therapies are rarely tested in human CSF before clinical trials because of the lack of sensitive methods that enable the measurement of aggregate-induced toxicity at low concentrations. We have developed highly sensitive single vesicle and single-cell-based assays that detect the Ca²⁺ influx caused by the CSF of individuals affected with AD and healthy controls, and we have found comparable effects for both types of samples. We also show that an extracellular chaperone clusterin; a nanobody specific to the amyloid-β peptide (Aβ); and bapineuzumab, a humanized monoclonal antibody raised against Aβ, could all reduce the Ca²⁺ influx caused by synthetic Aβ oligomers but are less effective in CSF. These assays could be used to characterize potential therapeutic agents in CSF before clinical trials.

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Human cerebrospinal fluid (CSF) can permeabilize membranes and induce Ca²⁺ influx

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CSF of control individuals and those with Alzheimer’s disease show similar Ca²⁺ influx

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An extracellular chaperone clusterin and a nanobody Nb3 can inhibit Ca²⁺ influx

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Bapineuzumab reduces Aβ-aggregate-induced Ca²⁺ influx but is less effective in CSF

Diffusible, highly bioactive oligomers represent a critical minority of soluble Aβ in Alzheimer's disease brain

Significant data suggest that soluble Aβ oligomers play an important role in Alzheimer's disease (AD), but there is great confusion over what exactly constitutes an Aβ oligomer and which oligomers are toxic. Most studies have utilized synthetic Aβ peptides, but the relevance of these test tube experiments to the conditions that prevail in AD is uncertain. A few groups have studied Aβ extracted from human brain, but they employed vigorous tissue homogenization which is likely to release insoluble Aβ that was sequestered in plaques during life. Several studies have found such extracts to possess disease-relevant activity and considerable efforts are being made to purify and better understand the forms of Aβ therein. Here, we compared the abundance of Aβ in AD extracts prepared by traditional homogenization versus using a far gentler extraction, and assessed their bioactivity via real-time imaging of iPSC-derived human neurons plus the sensitive functional assay of long-term potentiation. Surprisingly, the amount of Aβ retrieved by gentle extraction constituted only a small portion of that released by traditional homogenization, but this readily diffusible fraction retained all of the Aβ-dependent neurotoxic activity. Thus, the bulk of Aβ extractable from AD brain was innocuous, and only the small portion that was aqueously diffusible caused toxicity. This unexpected finding predicts that generic anti-oligomer therapies, including Aβ antibodies now in trials, may be bound up by the large pool of inactive oligomers, whereas agents that specifically target the small pool of diffusible, bioactive Aβ would be more useful. Furthermore, our results indicate that efforts to purify and target toxic Aβ must employ assays of disease-relevant activity. The approaches described here should enable these efforts, and may assist the study of other disease-associated aggregation-prone proteins.

An acute functional screen identifies an effective antibody targeting amyloid-β oligomers based on calcium imaging

Soluble amyloid β oligomers (AβOs) are widely recognized neurotoxins that trigger aberrant signaling in specific subsets of neurons, leading to accumulated neuronal damage and memory disorders in Alzheimer's disease (AD). One of the profound downstream consequences of AβO-triggered events is dysregulation of cytosolic calcium concentration ([Ca2+]i), which has been implicated in synaptic failure, cytoskeletal abnormalities, and eventually neuronal death. We have developed an in vitro/in vivo drug screening assay to evaluate putative AβO-blocking candidates by measuring AβO-induced real-time changes in [Ca2+]i. Our screening assay demonstrated that the anti-AβO monoclonal antibody ACU3B3 exhibits potent blocking capability against a broad size range of AβOs. We showed that picomolar concentrations of AβOs were capable of increasing [Ca2+]i in primary neuronal cultures, an effect prevented by ACU3B3. Topical application of 5 nM AβOs onto exposed cortical surfaces also elicited significant calcium elevations in vivo, which was completely abolished by pre-treatment of the brain with 1 ng/mL (6.67 pM) ACU3B3. Our results provide strong support for the utility of this functional screening assay in identifying and confirming the efficacy of AβO-blocking drug candidates such as the human homolog of ACU3B3, which may emerge as the first experimental AD therapeutic to validate the amyloid oligomer hypothesis.

Methods for the Specific Detection and Quantitation of Amyloid-β Oligomers in Cerebrospinal Fluid

Protein misfolding and aggregation are fundamental features of the majority of neurodegenerative diseases, like Alzheimer's disease (AD), Parkinson's disease, frontotemporal dementia, and prion diseases. Proteinaceous deposits in the brain of the patient, e.g., amyloid plaques consisting of the amyloid-β (Aβ) peptide and tangles composed of tau protein, are the hallmarks of AD. Soluble oligomers of Aβ and tau play a fundamental role in disease progression, and specific detection and quantification of the respective oligomeric proteins in cerebrospinal fluid may provide presymptomatically detectable biomarkers, paving the way for early diagnosis or even prognosis. Several studies on the development of techniques for the specific detection of Aβ oligomers were published, but some of the existing tools do not yet seem to be satisfactory, and the study results are contradicting. The detection of oligomers is challenging due to their polymorphous and unstable nature, their low concentration, and the presence of competing proteins and Aβ monomers in body fluids. Here, we present an overview of the current state of the development of methods for Aβ oligomer specific detection and quantitation. The methods are divided in the three subgroups: (i) enzyme linked immunosorbent assays (ELISA), (ii) methods for single oligomer detection, and (iii) others, which are mainly biosensor based methods.

Non-Fibrillar Oligomeric Amyloid-β within Synapses

Alzheimer's disease (AD) is characterized by memory loss, insidious cognitive decline, profound neurodegeneration, and the extracellular accumulation of amyloid-β (Aβ) peptide in senile plaques and intracellular accumulation of tau in neurofibrillary tangles. Loss and dysfunction of synapses are believed to underlie the devastating cognitive decline in AD. A large amount of evidence suggests that oligomeric forms of Aβ associated with senile plaques are toxic to synapses, but the precise sub-synaptic localization of Aβ and which forms are synaptotoxic remain unknown. Here, we characterize the sub-synaptic localization of Aβ oligomers using three high-resolution imaging techniques, stochastic optical reconstruction microscopy, immunogold electron microscopy, and Förster resonance energy transfer in a plaque-bearing mouse model of AD. With all three techniques, we observe oligomeric Aβ inside synaptic terminals. Further, we tested a panel of Aβ antibodies using the relatively high-throughput array tomography technique to determine which forms are present in synapses. Our results show that different oligomeric Aβ species are present in synapses and highlight the potential of array tomography for rapid testing of aggregation state specific Aβ antibodies in brain tissue.

Production and Use of Recombinant Aβ for Aggregation Studies

The amyloid β-protein (Aβ) is believed to play a central role in Alzheimer's disease (AD) pathogenesis and there is great interest in understanding the process of Aβ aggregation, its underlying mechanism and the species generated during aggregation and their biological activity. Although Aβ has been studied for more than 30 years, analysis of its aggregation has been hampered by structural and chemical impurities. Here we provide a detailed protocol for the expression and purification of chemically and structurally homogeneous Aβ monomer. We also describe a method to produce covalent Aβ dimers linked by phenolic coupling of tyrosine residues.