Blood amyloid-β oligomerization associated with neurodegeneration of Alzheimer's disease

Subsequent correlated changes in complement component 3 and amyloid beta oligomers in the blood of patients with Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) involves the complement cascade, with complement component 3 (C3) playing a key role. However, the relationship between C3 and amyloid beta (Aβ) in blood is limited.

METHODS

Plasma C3 and Aβ oligomerization tendency (AβOt) were measured in 35 AD patients and 62 healthy controls. Correlations with cerebrospinal fluid (CSF) biomarkers, cognitive impairment, and amyloid positron emission tomography (PET) were analyzed. Differences between biomarkers were compared in groups classified by concordances of biomarkers.

RESULTS

Plasma C3 and AβOt were elevated in AD patients and in CSF or amyloid PET-positive groups. Weak positive correlation was found between C3 and AβOt, while both had strong negative correlations with CSF Aβ42 and cognitive performance. Abnormalities were observed for AβOt and CSF Aβ42 followed by C3 changes.

DISCUSSION

Increased plasma C3 in AD are associated with amyloid pathology, possibly reflecting a defense response for Aβ clearance. Further studies on Aβ-binding proteins will enhance understanding of Aβ mechanisms in blood.

Plasma oligomer beta-amyloid is associated with disease severity and cerebral amyloid deposition in Alzheimer's disease spectrum

BACKGROUND

Multimer detection system-oligomeric amyloid-β (MDS-OAβ) is a measure of plasma OAβ, which is associated with Alzheimer's disease (AD) pathology. However, the relationship between MDS-OAβ and disease severity of AD is not clear. We aimed to investigate MDS-OAβ levels in different stages of AD and analyze the association between MDS-OAβ and cerebral Aβ deposition, cognitive function, and cortical thickness in subjects within the AD continuum.

METHODS

In this cross-sectional study, we analyzed a total 126 participants who underwent plasma MDS-OAβ, structural magnetic resonance image of brain, and neurocognitive measures using Korean version of the Consortium to Establish a Registry for Alzheimer's Disease, and cerebral Aβ deposition or amyloid positron emission tomography (A-PET) assessed by [18F] flutemetamol PET. Subjects were divided into 4 groups: N = 39 for normal control (NC), N = 31 for A-PET-negative mild cognitive impairment (MCI) patients, N = 30 for A-PET-positive MCI patients, and N = 22 for AD dementia patients. The severity of cerebral Aβ deposition was expressed as standard uptake value ratio (SUVR).

RESULTS

Compared to the NC (0.803 ± 0.27), MDS-OAβ level was higher in the A-PET-negative MCI group (0.946 ± 0.137) and highest in the A-PET-positive MCI group (1.07 ± 0.17). MDS-OAβ level in the AD dementia group was higher than in the NC, but it fell to that of the A-PET-negative MCI group level (0.958 ± 0.103). There were negative associations between MDS-OAβ and cognitive function and both global and regional cerebral Aβ deposition (SUVR). Cortical thickness of the left fusiform gyrus showed a negative association with MDS-OAβ when we excluded the AD dementia group.

CONCLUSIONS

These findings suggest that MDS-OAβ is not only associated with neurocognitive staging, but also with cerebral Aβ burden in patients along the AD continuum.

Early onset diagnosis in Alzheimer's disease patients via amyloid-β oligomers-sensing probe in cerebrospinal fluid

Amyloid-β (Aβ) oligomers are implicated in the onset of Alzheimer's disease (AD). Herein, quinoline-derived half-curcumin-dioxaborine (Q-OB) fluorescent probe was designed for detecting Aβ oligomers by finely tailoring the hydrophobicity of the biannulate donor motifs in donor-π-acceptor structure. Q-OB shows a great sensing potency in dynamically monitoring oligomerization of Aβ during amyloid fibrillogenesis in vitro. In addition, we applied this strategy to fluorometrically analyze Aβ self-assembly kinetics in the cerebrospinal fluids (CSF) of AD patients. The fluorescence intensity of Q-OB in AD patients' CSF revealed a marked change of log (I/I0) value of 0.34 ± 0.13 (cognitive normal), 0.15 ± 0.12 (mild cognitive impairment), and 0.14 ± 0.10 (AD dementia), guiding to distinguish a state of AD continuum for early diagnosis of AD. These studies demonstrate the potential of our approach can expand the currently available preclinical diagnostic platform for the early stages of AD, aiding in the disruption of pathological progression and the development of appropriate treatment strategies.

Association of plasma amyloid-β oligomerization with theta/beta ratio in older adults

Background

Oligomeric Aβ (OAβ) is a promising candidate marker for Alzheimer's disease (AD) diagnosis. Electroencephalography (EEG) is a potential tool for early detection of AD. Still, whether EEG power ratios, particularly the theta/alpha ratio (TAR) and theta/beta ratio (TBR), reflect Aβ burden-a primary mechanism underlying cognitive impairment and AD. This study investigated the association of TAR and TBR with amyloid burden in older adults based on MDS-OAβ levels.

Methods

529 individuals (aged ≥60 years) were recruited. All participants underwent EEG (MINDD SCAN, Ybrain Inc., South Korea) and AlzOn™ test (PeopleBio Inc., Gyeonggi-do, Republic of Korea) for quantifying MDS-OAβ values in the plasma. EEG variables were log-transformed to normalize the data distribution. Using the MDS-OAβ cutoff value (0.78 ng/mL), all participants were classified into two groups: high MDS-OAβ and low MDS-OAβ.

Results

Participants with high MDS-OAβ levels had significantly higher TARs and TBRs than those with low MDS-OAβ levels. The log-transformed TBRs in the central lobe (β = 0.161, p = 0.0026), frontal lobe (β = 0.145, p = 0.0044), parietal lobe (β = 0.166, p = 0.0028), occipital lobe (β = 0.158, p = 0.0058), and temporal lobe (beta = 0.162, p = 0.0042) were significantly and positively associated with increases in MDS-OAβ levels. After adjusting for the Bonferroni correction, the TBRs in all lobe regions, except the occipital lobe, were significantly associated with increased MDS-OAβ levels.

Conclusion

We found a significant association of MDS-OAβ with TBR in older adults. This finding indicates that an increase in amyloid burden may be associated with an increase in the low-frequency band and a decrease in the relatively high-frequency band.

Changes in Multiparametric Magnetic Resonance Imaging and Plasma Amyloid-Beta Protein in Subjective Cognitive Decline

The association between plasma amyloid-beta protein (Aβ) and subjective cognitive decline (SCD) remains controversial. We aimed to explore the correlation between neuroimaging findings, plasma Aβ, and neuropsychological scales using data from 53 SCD patients and 46 age- and sex-matched healthy controls (HCs). Magnetic resonance imaging (MRI) was used to obtain neuroimaging data for a whole-brain voxel-based morphometry analysis and cortical functional network topological features. The SCD group had slightly lower Montreal Cognitive Assessment (MoCA) scores than the HC group. The Aβ42 levels were significantly higher in the SCD group than in the HC group (p < 0.05). The SCD patients demonstrated reduced volumes in the left hippocampus, right rectal gyrus (REC.R), and right precentral gyrus (PreCG.R); an increased percentage fluctuation in the left thalamus (PerAF); and lower average small-world coefficient (aSigma) and average global efficiency (aEg) values. Correlation analyses with Aβ and neuropsychological scales revealed significant positive correlations between the volumes of the HIP.L, REC.R, PreCG.R, and MoCA scores. The HIP.L volume and Aβ42 were negatively correlated, as were the REC.R volume and Aβ42/40. PerAF and aSigma were negatively and positively correlated with the MoCA scores, respectively. The aEg was positively correlated with Aβ42/40. SCD patients may exhibit alterations in plasma biomarkers and multi-parameter MRI that resemble those observed in Alzheimer's disease, offering a theoretical foundation for early clinical intervention in SCD.

Progress in blood biomarkers of subjective cognitive decline in preclinical Alzheimer's disease

ABSTRACT

Alzheimer's disease (AD) is a neurodegenerative disease that gradually impairs cognitive functions. Recently, there has been a conceptual shift toward AD to view the disease as a continuum. Since AD is currently incurable, effective intervention to delay or prevent pathological cognitive decline may best target the early stages of symptomatic disease, such as subjective cognitive decline (SCD), in which cognitive function remains relatively intact. Diagnostic methods for identifying AD, such as cerebrospinal fluid biomarkers and positron emission tomography, are invasive and expensive. Therefore, it is imperative to develop blood biomarkers that are sensitive, less invasive, easier to access, and more cost effective for AD diagnosis. This review aimed to summarize the current data on whether individuals with SCD differ reliably and effectively in subjective and objective performances compared to cognitively normal elderly individuals, and to find one or more convenient and accessible blood biomarkers so that researchers can identify SCD patients with preclinical AD in the population as soon as possible. Owing to the heterogeneity and complicated pathogenesis of AD, it is difficult to make reliable diagnoses using only a single blood marker. This review provides an overview of the progress achieved to date with the use of SCD blood biomarkers in patients with preclinical AD, highlighting the key areas of application and current challenges.

Integration of amyloid-β oligomerization tendency as a plasma biomarker in Alzheimer's disease diagnosis

Introduction

There has been significant development in blood-based biomarkers targeting amyloidopathy of Alzheimer's disease (AD). However, the guidelines for integrating such biomarkers into AD diagnosis are still inadequate. Multimer Detection System-Oligomeric Amyloid-β (MDS-OAβ) as a plasma biomarker detecting oligomerization tendency is available in the clinical practice.

Main text

We suggest how to interpret the results of plasma biomarker for amyloidopathy using MDS-OAβ with neuropsychological test, brain magnetic resonance imaging (MRI), and amyloid PET for AD diagnosis. Combination of each test result differentiates various stages of AD, other neurodegenerative diseases, or cognitive impairment due to the causes other than neurodegeneration.

Discussion

A systematic interpretation strategy could support accurate diagnosis and staging of AD. Moreover, comprehensive use of biomarkers that target amyloidopathy such as amyloid PET on brain amyloid plaque and MDS-OAβ on amyloid-β oligomerization tendency can complement to gain advanced insights on amyloid-β dynamics in AD.

Follow-up Comparisons of Two Plasma Biomarkers of Alzheimer's Disease, Neurofilament Light Chain, and Oligomeric Aβ: A Pilot Study

BACKGROUND AND OBJECTIVE

Recent evidence suggests that blood-based biomarkers might be useful for Alzheimer's disease (AD). Among them, we intend to investigate whether neurofilament light (NfL) and multimer detection system-oligomeric Aβ (MDS-OAβ) values can be useful in screening, predicting, and monitoring disease progression and how the relationship between NfL and MDS-OAβ values changes.

METHODS

Eighty participants with probable AD dementia, 50 with mild cognitive impairment (MCI), and 19 with subjective cognitive decline (SCD) underwent baseline and follow-up evaluations of the Mini-Mental Status Examination (MMSE) and both plasma biomarkers.

RESULTS

Baseline MDS-OAß (p = 0.016) and NfL (p = 0.002) plasma concentrations differed significantly among groups, but only NfL correlated with baseline MMSE scores (r = -0.278, p = 0.001). In follow-up, neither correlated with MMSE changes overall. However, in SCD and MCI participants (n = 32), baseline MDS-OAß correlated with follow-up MMSE scores (r = 0.532, p = 0.041). Linear regression revealed a relationship between baseline MDS-OAβ and follow-up MMSE scores. In SCD and MCI participants, plasma NfL changes correlated with MMSE changes (r = 0.564, p = 0.028).

CONCLUSION

This study shows that only in participants with SCD and MCI, not including AD dementia, can MDS-OAß predict the longitudinal cognitive decline measured by follow-up MMSE. Changes of NfL, not MDS-OAß, parallel the changes of MMSE. Further studies with larger samples and longer durations could strengthen these results..

Prediction of amyloid PET positivity via machine learning algorithms trained with EDTA-based blood amyloid-β oligomerization data

Background

The tendency of amyloid-β to form oligomers in the blood as measured with Multimer Detection System-Oligomeric Amyloid-β (MDS-OAβ) is a valuable biomarker for Alzheimer’s disease and has been verified with heparin-based plasma. The objective of this study was to evaluate the performance of ethylenediaminetetraacetic acid (EDTA)-based MDS-OAβ and to develop machine learning algorithms to predict amyloid positron emission tomography (PET) positivity.

Methods

The performance of EDTA-based MDS-OAβ in predicting PET positivity was evaluated in 312 individuals with various machine learning models. The models with various combinations of features (i.e., MDS-OAβ level, age, apolipoprotein E4 alleles, and Mini-Mental Status Examination [MMSE] score) were tested 50 times on each dataset.

Results

The random forest model best-predicted amyloid PET positivity based on MDS-OAβ combined with other features with an accuracy of 77.14 ± 4.21% and an F1 of 85.44 ± 3.10%. The order of significance of predictive features was MDS-OAβ, MMSE, Age, and APOE. The Support Vector Machine using the MDS-OAβ value only showed an accuracy of 71.09 ± 3.27% and F−1 value of 80.18 ± 2.70%.

Conclusions

The Random Forest model using EDTA-based MDS-OAβ combined with the MMSE and apolipoprotein E status can be used to prescreen for amyloid PET positivity.

Is liquid biopsy mature enough for the diagnosis of Alzheimer’s disease?

The preclinical diagnosis and clinical practice for Alzheimer’s disease (AD) based on liquid biopsy have made great progress in recent years. As liquid biopsy is a fast, low-cost, and easy way to get the phase of AD, continual efforts from intense multidisciplinary studies have been made to move the research tools to routine clinical diagnostics. On one hand, technological breakthroughs have brought new detection methods to the outputs of liquid biopsy to stratify AD cases, resulting in higher accuracy and efficiency of diagnosis. On the other hand, diversiform biofluid biomarkers derived from cerebrospinal fluid (CSF), blood, urine, Saliva, and exosome were screened out and biologically verified. As a result, more detailed knowledge about the molecular pathogenesis of AD was discovered and elucidated. However, to date, how to weigh the reports derived from liquid biopsy for preclinical AD diagnosis is an ongoing question. In this review, we briefly introduce liquid biopsy and the role it plays in research and clinical practice. Then, we summarize the established fluid-based assays of the current state for AD diagnostic such as ELISA, single-molecule array (Simoa), Immunoprecipitation–Mass Spectrometry (IP–MS), liquid chromatography–MS, immunomagnetic reduction (IMR), multimer detection system (MDS). In addition, we give an updated list of fluid biomarkers in the AD research field. Lastly, the current outstanding challenges and the feasibility to use a stand-alone biomarker in the joint diagnostic strategy are discussed.

Correlation Between Plasma Oligomeric Amyloid-β and Performance on the Language Neutral Visual Cognitive Assessment Test in a Southeast Asian Population

Oligomeric amyloid-β (OAβ), an upstream driver of Alzheimer’s disease (AD) neuropathology, correlates with poor cognitive performance and brain volume reduction. Its effect on cognitive performance measured by the language neutral Visual Cognitive Assessment Test (VCAT) remains to be evaluated. We studied the correlation of plasma OAβ with VCAT scores and grey matter volume (GMV) in a Southeast Asian cohort with mild cognitive impairment. Higher plasma OAβ significantly correlated with lower; cognitive scores (VCAT, Mini-Mental State Examination) and GMV/intracranial volume ratio. Such findings reveal the clinical utility of plasma OAβ as a promising biomarker and support validation through longitudinal studies.

Multimer Detection System-Oligomerized Amyloid Beta (MDS-OAβ): A Plasma-Based Biomarker Differentiates Alzheimer's Disease from Other Etiologies of Dementia

With emerging amyloid therapies, documentation of the patient's amyloid status to confirm the etiology of a clinical diagnosis is warranted prior to instituting amyloid-based therapy. The Multimer Detection System-Oligomeric Amyloid-β (MDS-OAβ) is a noninvasive blood-based biomarker utilized to measure Aβ oligomerization tendency. We determined the difference in MDS-OAβ ratio across the groups: (a) no cognitive impairment or subjective cognitive impairment (NCI/SCI), (b) Alzheimer's disease (AD), (c) non-AD, and (d) mixed Alzheimer's disease-Vascular dementia (AD-VaD). MDS-OAβ level was not significantly different between AD and mixed AD-VaD, but both groups were significantly different from the NCI/SCI and from the non-AD group. An MDS-OAβ level of >1 could potentially indicate clinical variants of AD or mixed pathology (AD-VaD).

Ultrasensitive capacitance sensor to detect amyloid-beta 1-40 in human serum using supramolecular recognition of β-CD/RGO/ITO micro-disk electrode

In this paper, we developed a new ultrasensitive capacitance sensor for detection of amyloid beta 1-40 (aβ40) protein (one of Alzheimer's disease core biomarkers) in human serum based on the high supramolecular recognition of the β-cyclodextrin/reduced graphene oxide (β-CD/RGO) nanohybrid toward the anti-aβ40 antibody molecule. The sensor was established by immobilizing specific anti-aβ40 antibody onto the β-CD/RGO nanohybrid functionalized on indium tin oxide micro-disk electrode (anti-aβ40/β-CD/RGO/ITO). Detection of aβ40 in the human serum (HS) using the sensor anti-aβ40/β-CD/RGO/ITO is carried out by capacitance measurement without a redox probe to prevent protein denaturation, serving as a convenient strategy for point-of-care diagnosis. In comparison with other studies, the sensor shows a very low limit of detection of 0.69 fg mL^-1 in HS, demonstrating its ability for the ultrasensitive detection of aβ40. Using this sensor, the dissociation constant K_D of the binding interaction between anti-aβ40 and aβ40 in HS is found to be 2.9 × 10^-7 nM, indicating the high binding affinity of antibody-antigen and the suitability of the anti-aβ40/β-CD/RGO/ITO sensor for aβ40 protein detection. The good selectivity of the anti-aβ40/β-CD/RGO/ITO sensor in the presence of differential analytes was also performed in this paper.

Association of Plasma Oligomerized Amyloid-β and Cerebral White Matter Lesions in a Health Screening Population

BACKGROUND

Cerebral white matter lesions (WML) are related to a higher risk of vascular and Alzheimer's dementia. Moreover, oligomerized amyloid-β (OAβ) can be measured from blood for dementia screening.

OBJECTIVE

We aimed to investigate the relationship of plasma OAβ levels with clinical and radiological variables in a health screening population.

METHODS

WML, other volumetric parameters of magnetic resonance images, cognitive assessment, and plasma OAβ level were evaluated.

RESULTS

Ninety-two participants were analyzed. The majority of participants' clinical dementia rating was 0 or 0.5 (96.7%). White matter hyperintensities (WMH) increased with age, but OAβ levels did not (r2 = 0.19, p < 0.001, r2 = 0.03, p = 0.10, respectively). No volumetric data, including cortical thickness/hippocampal volume, showed any significant correlation with OAβ. Log-WMH volume was positively correlated with OAβ (r = 0.24, p = 0.02), and this association was significant in the periventricular area. White matter signal abnormalities from 3D-T1 images were also correlated with the OAβ in the periventricular area (p = 0.039). Multivariate linear regression showed that log-WMH values were independently associated with OAβ (B = 0.879 (95% confidence interval 0.098 -1.660, p = 0.028)). Higher tertiles of WMH showed higher OAβ levels than lower tertiles showed (p = 0.044). Using a cutoff of 0.78 ng/mL, the high OAβ group had a larger WMH volume, especially in the periventricular area, than the low OAβ group (p = 0.036).

CONCLUSION

Both WML and plasma OAβ levels can be early markers for neurodegeneration in the healthcare population. The lesions, especially in the periventricular area, might be related to amyloid pathogenesis, which strengthens the importance of WML in the predementia stage.

Current research status of blood biomarkers in Alzheimer's disease: Diagnosis and prognosis

Alzheimer's disease (AD), which mainly occurs in the elderly, is a neurodegenerative disease with a hidden onset, which leads to progressive cognitive and behavioral changes. The annually increasing prevalence rate and number of patients with AD exert great pressure on the society. No effective disease-modifying drug treatments are available; thus, there is no cure yet. The disease progression can only be delayed through early detection and drug assistance. Therefore, the importance of exploring associated biomarkers for the early diagnosis and prediction of the disease progress is highlighted. The National Institute on Aging- Alzheimer's Association (NIA-AA) proposed A/T/N diagnostic criteria in 2018, including Aβ42, p-tau, t-tau in cerebrospinal fluid (CSF), and positron emission tomography (PET). However, the invasiveness of lumbar puncture for CSF assessment and non-popularity of PET have prompted researchers to look for minimally invasive, easy to collect, and cost-effective biomarkers. Therefore, studies have largely focused on some novel molecules in the peripheral blood. This is an emerging research field, facing many obstacles and challenges while achieving some promising results.

Dysregulated expression levels of APH1B in peripheral blood are associated with brain atrophy and amyloid-β deposition in Alzheimer's disease

Background

The interaction between the brain and periphery might play a crucial role in the development of Alzheimer’s disease (AD).

Methods

Using blood transcriptomic profile data from two independent AD cohorts, we performed expression quantitative trait locus (cis-eQTL) analysis of 29 significant genetic loci from a recent large-scale genome-wide association study to investigate the effects of the AD genetic variants on gene expression levels and identify their potential target genes. We then performed differential gene expression analysis of identified AD target genes and linear regression analysis to evaluate the association of differentially expressed genes with neuroimaging biomarkers.

Results

A cis-eQTL analysis identified and replicated significant associations in seven genes (APH1B, BIN1, FCER1G, GATS, MS4A6A, RABEP1, TRIM4). APH1B expression levels in the blood increased in AD and were associated with entorhinal cortical thickness and global cortical amyloid-β deposition.

Conclusion

An integrative analysis of genetics, blood-based transcriptomic profiles, and imaging biomarkers suggests that APH1B expression levels in the blood might play a role in the pathogenesis of AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00919-z.

Plasma amyloid-β oligomerization assay as a pre-screening test for amyloid status

OBJECTIVE

We assessed the performance of plasma amyloid oligomerization tendency (OAβ) as a marker for abnormal amyloid status. Additionally, we examined long-term storage effects on plasma OAβ.

METHODS

We included 399 subjects regardless of clinical diagnosis from the Amsterdam Dementia Cohort and European Medical Information Framework for AD project (age, 63.8 ± 6.6; 44% female). Amyloid status was determined by visual read on positron emission tomography (PET; nabnormal = 206). Plasma OAβ was measured using the multimer detection system (MDS). Long-term storage effects on MDS-OAβ were assessed using general linear models. Associations between plasma MDS-OAβ and Aβ-PET status were assessed using logistic regression and receiver operating characteristics analyses. Correlations between plasma MDS-OAβ and CSF biomarker levels were evaluated using Pearson correlation analyses.

RESULTS

MDS-OAβ was higher in individuals with abnormal amyloid, and it identified abnormal Aβ-PET with an area under the curve (AUC) of 0.74 (95% CI, 0.67-0.81), especially in samples with a storage duration < 4 years. Combining APOEe4 and age with plasma MDS-OAβ revealed an AUC of 81% for abnormal amyloid PET status (95% CI, 74-87%). Plasma MDS-OAβ correlated negatively with MMSE (r = - 0.29, p < .01) and CSF Aβ42 (r = - 0.20, p < 0.05) and positively with CSF Tau (r = 0.20, p = 0.01).

CONCLUSIONS

Plasma MDS-OAβ combined with APOEe4 and age accurately identifies brain amyloidosis in a large Aβ-confirmed population. Using plasma MDS-OAβ as a screener reduced the costs and number of PET scans needed to screen for amyloidosis, which is relevant for clinical trials. Additionally, plasma MDS-OAβ levels appeared affected by long-term storage duration, which could be of interest for others measuring plasma Aβ biomarkers.

Detection of retinal and blood Aβ oligomers with nanobodies

Introduction

Abnormal retinal changes are increasingly recognized as an early pathological change in Alzheimer's disease (AD). Although amyloid beta oligomers (Aβo) have been shown to accumulate in the blood and retina of AD patients and animals, it is not known whether the early Aβo deposition precedes their accumulation in brain.

Methods and results

Using nanobodies targeting Aβ_1‐40 and Aβ_1‐42 oligomers we were able to detect Aβ oligomers in the retina and blood but not in the brain of 3‐month‐old APP/PS1 mice. Furthermore, Aβ plaques were detected in the brain but not the retina of 3‐month‐old APP/PS1 mice.

Conclusion

These results suggest that retinal accumulation of Aβo originates from peripheral blood and precedes cognitive decline and Aβo deposition in the brain. This provides a very strong basis to develop and implement an “eye test” for early detection of AD using nanobodies targeting retinal Aβ.

Relationship between Brain Tissue Changes and Blood Biomarkers of Cyclophilin A, Heme Oxygenase-1, and Inositol-Requiring Enzyme 1 in Patients with Alzheimer's Disease

Cyclophilin A (CypA), heme oxygenase-1 (HO-1), and inositol-requiring enzyme 1 (IRE1) are believed to be associated with Alzheimer's disease (AD). In this study, we investigated the association between gray matter volume (GMV) changes and blood levels of CypA, HO-1, and IRE1 in cognitively normal (CN) subjects and those with amnestic mild cognitive impairment (aMCI) and AD. Forty-five elderly CN, 34 aMCI, and 39 AD subjects were enrolled in this study. The results of voxel-based multiple regression analysis showed that blood levels of CypA, HO-1, and IRE1 were correlated with GMV on brain magnetic resonance imaging (MRI) in the entire population (p = 0.0005). The three serum protein levels were correlated with GMV of signature AD regions in the population as a whole. CypA values increased with increasing GMV in the occipital gyrus (r = 0.387, p < 0.0001) and posterior cingulate (r = 0.196, p = 0.034). HO-1 values increased with increasing GMV at the uncus (r = 0.307, p = 0.0008), lateral globus pallidus and putamen (r = 0.287, p = 0.002), and hippocampus (r = 0.197, p = 0.034). IRE1 values decreased with increasing GMV at the uncus (r = -0.239, p = 0.010) and lateral globus pallidus and putamen (r = -0.335, p = 0.0002). Associations between the three serum protein levels and regional GMV indicate that the blood levels of these biomarkers may reflect the pathological mechanism of AD in the brain.

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.

Is Korea Prepared for an Alzheimer's Disease-Modifying Therapy? Assessing the Korean Healthcare System Infrastructure and the Effect of Blood-Based Biomarker Tests

Background

With the rapid demographic change in Korea, Alzheimer’s disease has become a primary concern. Recent developments in disease-modifying therapies provide hope that therapy may become available soon. The high disease prevalence and complex evaluation process will create challenges for the healthcare system already burdened by the current pandemic. This study examined the preparedness of the South Korean healthcare system to identify and treat patients when such a therapy becomes available.

Methods

We used a Markov model to simulate a stylized patient’s journey. Based on national data and expert input, we presented projections of the diagnosis and treatment wait times and respective queues of patients under treatment and no-treatment scenarios and further simulated the possible option of adopting a blood-based biomarker test.

Results

Under the current system, we estimated a peak waiting time of 14 months when a treatment became available, largely because of the limited number of dementia specialists. Adopting a blood-based biomarker test dramatically reduced the initial wait times by more than half. A disease-modifying therapy was estimated to avert 575,000 incident cases in the first 10 years after the treatment entered the market, and a blood-based test further avoided 86,000 additional cases.

Conclusion

South Korea’s healthcare infrastructure requires more preparation for the introduction of a disease-modifying therapy, with the primary capacity limitation being the low number of dementia specialists. The utilization of a blood-based test for Alzheimer’s disease biomarkers may be an effective solution.

Plasma β-Amyloid Levels Associated With Structural Integrity Based on Diffusion Tensor Imaging in Subjective Cognitive Decline: The SILCODE Study

Background: Accumulating evidence has demonstrated that plasma β-amyloid (Aβ) levels are useful biomarkers to reflect brain amyloidosis and gray matter structure, but little is known about their correlation with subclinical white matter (WM) integrity in individuals at risk of Alzheimer's disease (AD). Here, we investigated the microstructural changes in WM between subjects with low and high plasma Aβ levels among individuals with subjective cognitive decline (SCD).

Methods: This study included 142 cognitively normal individuals with SCD who underwent a battery of neuropsychological tests, plasma Aβ measurements, and diffusion tensor imaging (DTI) based on the Sino Longitudinal Study on Cognitive Decline (SILCODE). Using tract-based spatial statistics (TBSS), we compared fractional anisotropy (FA), and mean diffusivity (MD) in WM between subjects with low (N = 71) and high (N = 71) plasma Aβ levels (cut-off: 761.45 pg/ml for Aβ40 and 10.74 pg/ml for Aβ42).

Results: We observed significantly decreased FA and increased MD in the high Aβ40 group compared to the low Aβ40 group in various regions, including the body, the genu, and the splenium of the corpus callosum; the superior longitudinal fasciculus; the corona radiata; the thalamic radiation; the external and internal capsules; the inferior fronto-occipital fasciculus; and the sagittal stratum [p < 0.05, familywise error (FWE) corrected]. Average FA values were associated with poor performance on executive and memory assessments. No significant differences were found in either MD or FA between the low and high Aβ42 groups.

Conclusion: Our results suggest that a correlation exists between WM integrity and plasma Aβ40 levels in individuals with SCD.

Endogenous Aβ peptide promote Aβ oligomerization tendency of spiked synthetic Aβ in Alzheimer's disease plasma

Alzheimer's disease (AD) is the most common form of age-associated dementia. Several studies have predicted that AD is caused by the production and deposition of the β-amyloid peptide (Aβ) in the brain, which is one of pathologic hallmarks of AD. In particular, Aβ oligomers are reportedly the most toxic and pathogenic of other peptide forms. We previously developed Multimer Detection System-Oligomeric Amyloid-β (MDS-OAβ), a technique for measuring Aβ oligomerization in plasma to diagnose AD. Here, we clarified the molecular sizes of oligomers that can be detected by the MDS and investigated differences in plasma spiking with a synthetic Aβ peptide in the plasma of AD patients and individuals with non-AD neurological conditions. To determine Aβ oligomer sizes detectable by MDS, size exclusion chromatography (SEC) was first performed on incubated samples of synthetic Aβ42 peptides. As a result, no MDS signals were observed for the Aβ42 monomer fractions, but strong signals were found for oligomers of 7-35-mers long. Also, an amplified luminescent proximity homogeneous assay-linked immunoassay (AlphaLISA) was used to confirm that synthetic Aβ peptides not only recruited endogenous Aβ in plasma but also induced significantly stronger seeding in AD plasma than in healthy control plasma. In addition, the absence of the MDS signals in Aβ-depleted plasma confirmed that the increased oligomerization tendency in AD plasma is dependent on the presence of endogenous Aβ in plasma. Therefore, the MDS-OAβ measurement of oligomerization differences in plasma after incubation with spiked synthetic Aβ peptides has significant potential in AD diagnosis.

Fluid Candidate Biomarkers for Alzheimer's Disease: A Precision Medicine Approach

A plethora of dynamic pathophysiological mechanisms underpins highly heterogeneous phenotypes in the field of dementia, particularly in Alzheimer's disease (AD). In such a faceted scenario, a biomarker-guided approach, through the implementation of specific fluid biomarkers individually reflecting distinct molecular pathways in the brain, may help establish a proper clinical diagnosis, even in its preclinical stages. Recently, ultrasensitive assays may detect different neurodegenerative mechanisms in blood earlier. ß-amyloid (Aß) peptides, phosphorylated-tau (p-tau), and neurofilament light chain (NFL) measured in blood are gaining momentum as candidate biomarkers for AD. P-tau is currently the more convincing plasma biomarker for the diagnostic workup of AD. The clinical role of plasma Aβ peptides should be better elucidated with further studies that also compare the accuracy of the different ultrasensitive techniques. Blood NFL is promising as a proxy of neurodegeneration process tout court. Protein misfolding amplification assays can accurately detect α-synuclein in cerebrospinal fluid (CSF), thus representing advancement in the pathologic stratification of AD. In CSF, neurogranin and YKL-40 are further candidate biomarkers tracking synaptic disruption and neuroinflammation, which are additional key pathophysiological pathways related to AD genesis. Advanced statistical analysis using clinical scores and biomarker data to bring together individuals with AD from large heterogeneous cohorts into consistent clusters may promote the discovery of pathophysiological causes and detection of tailored treatments.

Dynamic Blood Concentrations of Aβ1-40 and Aβ1-42 in Alzheimer's Disease

Amyloid-beta (Aβ) is produced by the cleavage of amyloid precursor proteins in the cell membrane by β-secretase and γ-secretase into a monomeric form with peptides of different lengths such as Aβ1-40 or Aβ1-42, which is then transformed into oligomeric and fibril forms and is considered to be one of the hallmarks of Alzheimer's disease (AD). The plasma concentrations of Aβ1-40 and Aβ1-42 are unstable after blood samples have been obtained. In order to examine the dynamic changes of plasma Aβ1-42 and Aβ1-40 in blood samples, we used fresh blood samples in ethylenediaminetetraacetic acid tubes from 32 clinically diagnosed AD patients. Each sample was subdivided into eight sub-samples, and levels of Aβ1-40 and Aβ1-42 were measured at 0 (baseline), 0.5, 1, 2, 3, 5, 8, and 24 h, respectively. All samples were incubated at 37°C before being measuring. The results showed that compared to baseline, 87.5 and 62.5% of the patients had higher plasma levels of Aβ1-42 and Aβ1-40 at 24 h, respectively. The patients with an increased amyloid level did not have a significantly different apo-lipoprotein E4 allele (APOE4) gene status for either Aβ1-40 (p = 0.422) or Aβ1-42 (p = 1.000). However, for plasma Aβ1-42, the APOE4 carriers had a significantly lower level than the non-carriers at baseline [31.2 ± 6.5 (mean ± SD) ng/ml vs. 50.4 ± 47.7 ng/ml, p = 0.031] and 0.5 h (37.5 ± 7.6 ng/ml vs. 51.9 ± 30.8 ng/ml, p = 0.043). There were no significant differences between the APOE4 carriers and non-carriers in plasma Aβ1-42 concentration at 1, 2, 3, 5, 8, and 24 h (p = 0.112, p = 0.086, p = 0.112, p = 0.263, p = 0.170 and p = 0.621, respectively). The Aβ1-40 level was related to disease severity as assessed using the clinical dementia rating (CDR) scale. Patients with advanced stages of dementia (CDR = 1 and CDR = 2) had a significantly higher Aβ1-40 level compared to those with very mild stage dementia (CDR = 0.5) at all time points (p < 0.05) except for 24 h (p = 0.059). Our findings illustrate the effects of APOE4 status on dynamic changes in plasma Aβ1-40 and Aβ1-42 levels, and significant associations between Aβ1-40 level and disease severity. Further studies are needed to investigate the exact mechanisms of how APOE4 affects the dynamic changes in plasma Aβ1-40 and Aβ1-42, and the association between Aβ1-40 and advanced dementia.

Amyloid-β oligomerization monitored by single-molecule stepwise photobleaching

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Method enables investigation of amyloid-β oligomer stoichiometry without requiring extrinsic fluorescent probes.

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Uses single-molecule stepwise photobleaching in vitro.

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Unveils heterogeneity within populations of oligomers.

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Assays oligomer-induced dysregulation of intracellular Ca²⁺ homeostasis in living cells.

A major hallmark of Alzheimer’s disease is the misfolding and aggregation of the amyloid- β peptide (Aβ). While early research pointed towards large fibrillar- and plaque-like aggregates as being the most toxic species, recent evidence now implicates small soluble Aβ oligomers as being orders of magnitude more harmful. Techniques capable of characterizing oligomer stoichiometry and assembly are thus critical for a deeper understanding of the earliest stages of neurodegeneration and for rationally testing next-generation oligomer inhibitors. While the fluorescence response of extrinsic fluorescent probes such as Thioflavin-T have become workhorse tools for characterizing large Aβ aggregates in solution, it is widely accepted that these methods suffer from many important drawbacks, including an insensitivity to oligomeric species. Here, we integrate several biophysics techniques to gain new insight into oligomer formation at the single-molecule level. We showcase single-molecule stepwise photobleaching of fluorescent dye molecules as a powerful method to bypass many of the traditional limitations, and provide a step-by-step guide to implementing the technique in vitro. By collecting fluorescence emission from single Aβ(1–42) peptides labelled at the N-terminal position with HiLyte Fluor 555 via wide-field total internal reflection fluorescence (TIRF) imaging, we demonstrate how to characterize the number of peptides per single immobile oligomer and reveal heterogeneity within sample populations. Importantly, fluorescence emerging from Aβ oligomers cannot be easily investigated using diffraction-limited optical microscopy tools. To assay oligomer activity, we also demonstrate the implementation of another biophysical method involving the ratiometric imaging of Fura-2-AM loaded cells which quantifies the rate of oligomer-induced dysregulation of intracellular Ca²⁺ homeostasis. We anticipate that the integrated single-molecule biophysics approaches highlighted here will develop further and in principle may be extended to the investigation of other protein aggregation systems under controlled experimental conditions.

Role of Body-Fluid Biomarkers in Alzheimer's Disease Diagnosis

Alzheimer’s disease (AD) is a complex neurodegenerative disease that requires extremely specific biomarkers for its diagnosis. For current diagnostics capable of identifying AD, the development and validation of early stage biomarkers is a top research priority. Body-fluid biomarkers might closely reflect synaptic dysfunction in the brain and, thereby, could contribute to improving diagnostic accuracy and monitoring disease progression, and serve as markers for assessing the response to disease-modifying therapies at early onset. Here, we highlight current advances in the research on the capabilities of body-fluid biomarkers and their role in AD pathology. Then, we describe and discuss current applications of the potential biomarkers in clinical diagnostics in AD.

Association of Plasma Oligomerized Beta Amyloid with Neurocognitive Battery Using Korean Version of Consortium to Establish a Registry for Alzheimer's Disease in Health Screening Population

The increasing prevalence of Alzheimer’s disease (AD) has become a global phenomenon presenting serious social and health challenges. For detecting early molecular changes in the disease, several techniques to measure varied species of amyloid beta in the peripheral blood have been recently developed, but the efforts to associate them with cognitive assessments have yet to produce sufficient data. We prospectively collected participants from the consecutive population who visited our center for brain health screening. In total, 97 participants (F:M = 58:39) aged 69.4 ± 7.52 were assessed. Participants performed the Korean version of the Consortium to Establish a Registry for Alzheimer’s disease (CERAD-K), the clinical dementia rating (CDR), plasma oligomeric amyloid-β (OAβ) level tests, routine blood tests, ApoE genotype, and brain MRI. Among total population, 55.7% had a CDR of 0, and 40.2% had a CDR of 0.5. The results showed that word memory and word recall, and the total scores of the CERAD-K were negatively correlated with the plasma OAβ level. With a cut-off value of 0.78 ng/mL for the OAβ level and a −1.5 standard deviation of age/sex/education adjusted norms for the CERAD-K; naming, word memory, word recall, word recognition, and total score were significantly correlated with the OAβ level. No correlation between the OAβ level and mini-mental status examination was found. Our results demonstrate that the level of plasma OAβ was well correlated with the measure of cognitive function through the CERAD-K in the field data collected from consecutive populations. Studies on longitudinal comparisons with large cohorts will further validate the diagnostic value of plasma OAβ as a useful biomarker for screening AD and predicting progression.

Hebbian and Homeostatic Synaptic Plasticity-Do Alterations of One Reflect Enhancement of the Other?

During the past 50 years, the cellular and molecular mechanisms of synaptic plasticity have been studied in great detail. A plethora of signaling pathways have been identified that account for synaptic changes based on positive and negative feedback mechanisms. Yet, the biological significance of Hebbian synaptic plasticity (= positive feedback) and homeostatic synaptic plasticity (= negative feedback) remains a matter of debate. Specifically, it is unclear how these opposing forms of plasticity, which share common downstream mechanisms, operate in the same networks, neurons, and synapses. Based on the observation that rapid and input-specific homeostatic mechanisms exist, we here discuss a model that is based on signaling pathways that may adjust a balance between Hebbian and homeostatic synaptic plasticity. Hence, “alterations” in Hebbian plasticity may, in fact, resemble “enhanced” homeostasis, which rapidly returns synaptic strength to baseline. In turn, long-lasting experience-dependent synaptic changes may require attenuation of homeostatic mechanisms or the adjustment of homeostatic setpoints at the single-synapse level. In this context, we propose a role for the proteolytic processing of the amyloid precursor protein (APP) in setting a balance between the ability of neurons to express Hebbian and homeostatic synaptic plasticity.

Alzheimer's Disease Diagnosis Using Misfolding Proteins in Blood

Alzheimer's disease (AD) is pathologically characterized by a long progressive phase of neuronal changes, including accumulation of extracellular amyloid-β (Aβ) and intracellular neurofibrillary tangles, before the onset of observable symptoms. Many efforts have been made to develop a blood-based diagnostic method for AD by incorporating Aβ and tau as plasma biomarkers. As blood tests have the advantages of being highly accessible and low cost, clinical implementation of AD blood tests would provide preventative screening to presymptomatic individuals, facilitating early identification of AD patients and, thus, treatment development in clinical research. However, the low concentration of AD biomarkers in the plasma has posed difficulties for accurate detection, hindering the development of a reliable blood test. In this review, we introduce three AD blood test technologies emerging in South Korea, which have distinctive methods of heightening detection sensitivity of specific plasma biomarkers. We discuss in detail the multimer detection system, the self-standard analysis of Aβ biomarkers quantified by interdigitated microelectrodes, and a biomarker ratio analysis comprising Aβ and tau.

Association between increased levels of amyloid-β oligomers in plasma and episodic memory loss in Alzheimer's disease

Objective

The objectives of this study were to investigate whether the plasma levels of oligomeric amyloid-β (OAβ) were affected in Alzheimer’s disease (AD) and to examine the associations (or possible correlations) between plasma OAβ levels and memory performance.

Method

Thirty subjects with AD and 28 cognitively normal controls were recruited in the study. The multimer detection system (MDS) was used to measure the levels of OAβ in the plasma. In addition to assessing the general cognitive function with the Mini-Mental State Examination (MMSE), Cognitive Abilities Screening Instrument (CASI), and Alzheimer’s Disease Assessment Scale–cognitive portion (ADAS-Cog), the common objects memory test (COMT) was used to examine the episodic memory performance. Pearson’s and partial correlation analyses were conducted to explore the associations between cognitive performance and OAβ levels in the plasma. A receiving operating curve (ROC) analysis was used to discriminate between the AD and control groups.

Results

The plasma OAβ levels in the AD group were significantly higher than those in the control group [1.88 (0.38) ng/ml vs 1.20 (0.40) ng/ml, p < 0.001]. The elevated levels of plasma OAβ showed a strong correlation with cognitive performance in patients with AD, including an inverse correlation with scores on the MMSE (r = − 0.43, p = 0.02), CASI (r = − 0.56, p < 0.01), and the immediate recall (r = − 0.45, p = 0.01), 5-min delayed recall (r = − 0.56, p < 0.01), and 30-min delayed recall (r = − 0.71, p < 0.001) tests of the COMT, and a positive correlation with the ADAS-Cog scores (r = 0.59, p < 0.001). The EDTA plasma Aβ oligomer optical density (OD) value measured using the MDS could discriminate between the AD and control groups with an area under the curve (AUC) of 0.89. The optimal sensitivity and specificity were 82.1% and 90.0%, respectively.

Conclusion

The elevated levels of OAβ in the plasma distinguished the AD and control groups and were associated with the severity of symptoms, especially memory performance, in patients with AD. Our results suggested that plasma OAβ could potentially be a simple and non-invasive blood-based biomarker for AD diagnosis. Furthermore, longitudinal studies are warranted to explore the application of plasma OAβ levels as a valid diagnostic biomarker in patients with AD.

Electronic supplementary material

The online version of this article (10.1186/s13195-019-0535-7) contains supplementary material, which is available to authorized users.

Novel amyloid precursor protein mutation, Val669Leu ("Seoul APP"), in a Korean patient with early-onset Alzheimer's disease

In this study, a novel mutation in APP gene, Val669Leu ("Seoul APP"), was reported in a Korean female patient with Alzheimer's disease. She developed cognitive decline at 56 years of age, and her memory declined rapidly over one-year period from her 1st visit to the hospital. Her Mini-Mental State Examination scores dropped from 25/30 to 13/30. Two years later, she developed parkinsonian features, myoclonic jerk, and generalized seizure. As the disease progressed, aggravated diffuse brain atrophy and small-vessel ischemic lesion was also observed, and she became mute and vegetative in 4 years from the symptom onset. Magnetic resonance imaging showed mild medial temporal lobe and hippocampal atrophy, and 18F-fluoro-deoxyglucose positron emission tomography showed bilateral temporoparietal hypometabolism. Plasma amyloid oligomer analysis revealed highly elevated Aβ oligomers levels in the proband patient. Family history revealed positive without biochemical confirmation because family members testified similar type of cognitive decline from the proband's mother and one of her aunt/uncle. Her half-siblings did not present any signs of memory impairment. Sanger sequencing of the proband patient revealed a novel mutation in APP gene, Val669Leu, but mutation was not found in her unaffected half-sisters. A designed algorithm by Guerreiro et al. on early-onset Alzheimer's disease-associated mutations suggested the mutation as possibly pathogenic mutation. On the other hand, PolyPhen2 and SIFT tools suggested as otherwise. Since the mutation was located nearby the β-secretase cleavage site of APP, right next to the Swedish APP (Lys,Met670/671Asn,Leu) mutation, it was named as "Seoul APP" mutation. 3D modeling revealed that this mutation could result in significant changes in loop orientation of APP and also its intramolecular interactions. Hence, a novel APP Val669Leu mutation could alter the binding interactions between APP and β-secretase, which may influence the Aβ40 and Aβ42 generations.