Blood Amyloid-β Oligomerization as a Biomarker of Alzheimer's Disease: A Blinded Validation Study

Synthesis of fluorinated curcumin derivatives for detecting amyloid plaques by 19F-MRI

The most prominent pathophysiological hallmark of Alzheimer's disease is the aggregation of amyloid-β (Aβ) peptides into senile plaques. Curcumin and its derivatives exhibit a high affinity for binding to Aβ fibrils, effectively inhibiting their growth. This property holds promise for both therapeutic applications and diagnostic molecular imaging. In this study, curcumin was functionalized with perfluoro-tert-butyl groups to create candidate molecular probes specifically targeted to Aβ fibrils for use in 19F-magnetic resonance imaging. Two types of fluorinated derivatives were considered: mono-substituted (containing nine fluorine atoms per molecule) and disubstituted (containing eighteen fluorine atoms). The linker connecting the perfluoro moiety with the curcumin scaffold was evaluated for its impact on binding affinity and water solubility. All mono-substituted compounds and one disubstituted compound exhibited a binding affinity toward Aβ fibrils on the same order of magnitude as reference curcumin. The insertion of a charged carboxylate group into the linker enhanced the water solubility of the probes. Compound Curc-Glu-F9 (with one L-glutamyl moiety and a perfluoro-tert-butyl group), showed the best properties in terms of binding affinity towards Aβ fibrils, water solubility, and intensity of the 19F-NMR signal in the Aβ oligomer bound form.

Nanoscale flow cytometry-based quantification of blood-based extracellular vesicle biomarkers distinguishes MCI and Alzheimer's disease

INTRODUCTION

Accurate testing for Alzheimer's disease (AD) represents a crucial step for therapeutic advancement. Currently, tests are expensive and require invasive sampling or radiation exposure.

METHODS

We developed a nanoscale flow cytometry (nFC)-based assay of extracellular vesicles (EVs) to screen biomarkers in plasma from mild cognitive impairment (MCI), AD, or controls.

RESULTS

Circulating amyloid beta (Aβ), tau, phosphorylated tau (p-tau)181, p-tau231, p-tau217, p-tauS235, ubiquitin, and lysosomal-associated membrane protein 1-positive EVs distinguished AD samples. p-tau181, p-tau217, p-tauS235, and ubiquitin-positive EVs distinguished MCI samples. The most sensitive marker for AD distinction was p-tau231, with an area under the receiver operating characteristic curve (AUC) of 0.96 (sensitivity 0.95/specificity 1.0) improving to an AUC of 0.989 when combined with p-tauS235.

DISCUSSION

This nFC-based assay accurately distinguishes MCI and AD plasma without EV isolation, offering a rapid approach requiring minute sample volumes. Incorporating nFC-based measurements in larger populations and comparison to "gold standard" biomarkers is an exciting next step for developing AD diagnostic tools.

HIGHLIGHTS

Extracellular vesicles represent promising biomarkers of Alzheimer's disease (AD) that can be measured in the peripheral circulation. This study demonstrates the utility of nanoscale flow cytometry for the measurement of circulating extracellular vesicles (EVs) in AD blood samples. Multiple markers including amyloid beta, tau, phosphorylated tau (p-tau)181, p-tau231, p-tau217, and p-tauS235 accurately distinguished AD samples from healthy controls. Future studies should expand blood and cerebrospinal fluid-based EV biomarker development using nanoflow cytometry approaches.

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.

PSEN1 His214Asn Mutation in a Korean Patient with Familial EOAD and the Importance of Histidine-Tryptophan Interactions in TM-4 Stability

A pathogenic mutation in presenilin-1 (PSEN1), His214Asn, was found in a male patient with memory decline at the age of 41 in Korea for the first time. The proband patient was associated with a positive family history from his father, paternal aunt, and paternal grandmother without genetic testing. He was diagnosed with early onset Alzheimer's disease (EOAD). PSEN1 His214Asn was initially reported in an Italian family, where the patient developed phenotypes similar to the current proband patient. Magnetic resonance imaging (MRI) scans revealed a mild hippocampal atrophy. The amyloid positron emission tomography (amyloid-PET) was positive, along with the positive test results of the increased amyloid ß (Aβ) oligomerization tendency with blood. The PSEN1 His214 amino acid position plays a significant role in the gamma-secretase function, especially from three additional reported mutations in this residue: His214Asp, His214Tyr, and His214Arg. The structure prediction model revealed that PSEN1 protein His214 may interact with Trp215 of His-Trp cation-π interaction, and the mutations of His214 would destroy this interaction. The His-Trp cation-π interaction between His214 and Trp215 would play a crucial structural role in stabilizing the 4th transmembrane domain of PSEN1 protein, especially when aromatic residues were often reported in the membrane interface of the lipid-extracellular region of alpha helices or beta sheets. The His214Asn would alter the cleavage dynamics of gamma-secretase from the disappeared interactions between His214 and Trp215 inside of the helix, resulting in elevated amyloid production. Hence, the increased Aβ was reflected in the increased Aβ oligomerization tendency and the accumulations of Aβ in the brain from amyloid-PET, leading to EOAD.

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.

Patient with PSEN1 Glu318Gly and Other Possible Disease Risk Mutations, Diagnosed with Early Onset Alzheimer's Disease

In this manuscript, we introduced a French EOAD patient in Korea who carried the presenilin-1 (PSEN1) Glu318Gly mutations with four possible risk variants, including sortilin-related receptor 1 (SORL1) Glu270Lys, ATP-binding cassette subfamily A member 7 (ABCA7) Val1946Met, translocase of outer mitochondrial membrane 40 (TOMM40) Arg239Trp, and granulin (GRN) Ala505Gly. The patient started to present memory decline and behavioral dysfunction in his early 60s. His brain imaging presented amyloid deposits by positron emission tomography (PET-CT). The multimer detection system (MDS) screening test for plasma for amyloid oligomers was also positive, which supported the AD diagnosis. It was verified that PSEN1 Glu318Gly itself may not impact amyloid production. However, additional variants were found in other AD and non-AD risk genes, as follows: SORL1 Glu270Lys was suggested as a risk mutation for AD and could increase amyloid peptide production and impair endosome functions. ABCA7 Val1946Met was a novel variant that was predicted to be damaging. The GRN Ala505Gly was a variant with uncertain significance; however, it may reduce the granulin levels in the plasma of dementia patients. Pathway analysis revealed that PSEN1 Glu318Gly may work as a risk factor along with the SORL1 and ABCA7 variants since pathway analysis revealed that PSEN1 could directly interact with them through amyloid-related and lipid metabolism pathways. TOMM40 and PSEN1 could have common mechanisms through mitochondrial dysfunction. It may be possible that PSEN1 Glu318Gly and GRN Ala505Gly would impact disease by impairing immune-related pathways, including microglia and astrocyte development, or NFkB-related pathways. Taken together, the five risk factors may contribute to disease-related pathways, including amyloid and lipid metabolism, or impair immune mechanisms.

Neuroplastic and Pro-cognitive Effects of Granulocyte Colony Stimulating Factor in Healthy Adults: A Pilot Study

OBJECTIVE

Granulocyte colony-stimulating factor (G-CSF) is a growth factor used to regulate the mobilization of bone marrow progenitor cells and has been shown to promote brain repair and reduce inflammation. This study aimed to investigate the pro-cognitive and neuroplastic effects of G-CSF in healthy adults.

METHODS

Sixteen healthy adults or donors of hematopoietic stem cell transplantation received G-CSF injections for 5 consecutive days, and their blood samples were collected before, immediately after, and 3 weeks after the G-CSF injections. Twelve subjects underwent neuropsychological testing before and 12 weeks after the G-CSF injections.

RESULTS

The study found that G-CSF administration resulted in significant improvements in cognitive function, as measured by the Rey- Osterrieth Complex Figure test for immediate recall, delayed recall, and recognition score at 12 weeks after the injections. The blood levels of brain-derived neurotrophic factor, interleukin-4, and interleukin-8 were significantly increased immediately after the injections and returned to baseline levels after 3 weeks. There was no significant change in the plasma level of Multimer Detection System-oligomerized amyloid beta.

CONCLUSION

Our results might suggest that G-CSF has neuroplastic and pro-cognitive effects in healthy adults. However, further study containing a larger sample size is needed to confirm our findings.

Overview of the blood biomarkers in Alzheimer's disease: Promises and challenges

The increasing number of people with advanced Alzheimer's disease (AD) represents a significant psychological and financial cost to the world population. Accurate detection of the earliest phase of preclinical AD is of major importance for the success of preventive and therapeutic strategies (Cullen et al., 2021). Advances in analytical techniques have been essential for the development of sensitive, specific and reliable diagnostic tests for AD biomarkers in biological fluids (cerebrospinal fluid and blood). Blood biomarkers hold promising potential for early and minimally invasive detection of AD, but also for differential diagnosis of dementia and for monitoring the course of the disease. The aim of this review is to provide an overview of current blood biomarkers of AD, from tau proteins and amyloid peptides to biomarkers of neuronal degeneration and inflammation, reactive and metabolic factors. We thus discuss the informative value of currently candidate blood biomarkers and their potential to be integrated into clinical practice for the management of AD in the near future.

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..

Detection of plasma Aβ seeding activity by a newly developed analyzer for diagnosis of Alzheimer’s disease

Objective

To evaluate the diagnostic value of plasma β-amyloid (Aβ) seeding activity measured using a newly developed instrument to distinguish Alzheimer’s disease (AD) from other forms of dementia.

Methods

Seventy-nine AD patients, 64 non-AD dementia (NADD) patients, and 75 cognitively normal (NC) subjects were recruited in the study. To measure the levels of Aβ seeding activity in the plasma samples, we have developed an AD-seeds protein analyzer. We used receiver operating characteristic (ROC) curves to quantify the ability of plasma Aβ seeding activity to distinguish between AD and NADD or NC individuals. Spearman’s correlation was used to examine the associations between plasma Aβ seeding activity and global cognitive function or conventional AD biomarkers.

Results

The Aβ seeding activities were 0.83 (0.58–1.16) A.U. in AD, 0.42 (0.04–0.74) A.U. in NADD and 0.42 (0.09–0.69) A.U. in NC, respectively. The Aβ seeding activity was able to identify AD patients and distinguish them from NC or NADD with high accuracy (AUC = 0.85–0.86). In addition, the plasma Aβ seeding activity showed a strong correlation with cognitive performance (mini-mental state examination, r = − 0.188; Montreal cognitive assessment, r = − 0.189; clinical dementia rating, r = 0.205) and conventional biomarkers (cerebrospinal fluid [CSF] Aβ42/40, r = -0.227; CSF T-tau/Aβ42, r = 0.239; CSF P-tau/Aβ42, r = 0.259).

Conclusion

Our results confirmed that plasma Aβ seeding activity is an antibody-free and low-cost biomarker for the diagnosis of AD.

Trial registration

Trial registration number NCT04850053

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.

Plasma amyloid-beta oligomer is related to subjective cognitive decline and brain amyloid status

Background

Subjective cognitive decline (SCD) is a target for Alzheimer’s disease prediction. Plasma amyloid-beta oligomer (AβO), the pathogenic form of Aβ in blood, has recently been proposed as a novel blood-based biomarker of AD prediction by representing brain Aβ deposition. The relationship between plasma AβO, brain Aβ deposition, and SCD in individuals with normal objective cognition has not been investigated.

Methods

In this cross-sectional study, we analyzed 126 participants with normal objective cognition. More SCD symptoms were expressed as higher scores of the Subjective Cognitive Decline Questionnaire (SCDQ) and Memory Age-associated Complaint Questionnaire (MACQ). The plasma AβO level of each participant was measured twice for validation and expressed as a concentration (ng/mL) and a ratio relative to the mean value of two internal standards. Brain Aβ deposition was assessed by [¹⁸F] flutemetamol positron emission tomography (PET) and expressed as standard uptake value ratio (SUVR). Associations of SCDQ and MACQ with plasma AβO levels or SUVR were analyzed in multiple linear regression models. The association between plasma AβO level and flutemetamol PET positivity was assessed in logistic regression and receiver operative characteristic analyses.

Results

Overall, participants were 73.3 years old with female predominance (69.0%). After adjustment for confounders, high SCDQ and MACQ scores were associated with the high plasma AβO levels as both concentrations and ratios (ratios: standardized coefficient = 0.246 and p = 0.023 for SCDQ, standardized coefficient = 0.209 and p = 0.029 for MACQ; concentrations: standardized coefficient = 0.257 and p = 0.015 for SCDQ, standardized coefficient = 0.217 and p = 0.021 for MACQ). In contrast, SCDQ and MACQ were not significantly associated with SUVRs (p = 0.134 for SCDQ, p = 0.079 for MACQ). High plasma AβO levels were associated with flutemetamol PET (+) with an area under the curve of 0.694 (ratio) or 0.662 (concentration). Combined with APOE e4, plasma AβO presented area under the curves of 0.789 (ratio) and 0.783 (concentration).

Conclusions

Our findings indicate that the high plasma AβO level could serve as a potential surrogate biomarker of severe SCD and the presence of brain Aβ deposition in individuals with normal objective cognition.

Fluorescent aptasensor based on conformational switch-induced hybridization for facile detection of β-amyloid oligomers

Aβ oligomers (AβO) are a dominant biomarker for early Alzheimer's disease diagnosis. A fluorescent aptasensor coupled with conformational switch-induced hybridization was established to detect AβO. The fluorescent aptasensor is based on the interaction of fluorophore-labeled AβO-specific aptamer (FAM-Apt) against its partly complementary DNA sequence on the surface of magnetic beads (cDNA-MBs). Once the FAM-Apt binds to AβO, the conformational switch of FAM-Apt increases the tendency to be captured by cDNA-MBs. This causes a descending fluorescence of supernatant, which can be utilized to determine the levels of AβO. Thus, the base-pair matching above 12 between FAM-Apt and cDNA-MBs with increasing hybridizing free energies reached the ascending fluorescent signal equilibrium. The optimized aptasensor showed linearity from 1.7 ng mL^-1 to 85.1 (R = 0.9977) with good recoveries (79.27-109.17%) in plasma. Furthermore, the established aptasensor possesses rational selectivity in the presence of monomeric Aβ, fibrotic Aβ, and interferences. Therefore, the developed aptasensor is capable of quantifying AβO in human plasma and possesses the potential to apply in clinical cases.

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).

Biofluid Biomarkers of Alzheimer’s Disease: Progress, Problems, and Perspectives

Since the establishment of the biomarker-based A-T-N (Amyloid/Tau/Neurodegeneration) framework in Alzheimer’s disease (AD), the diagnosis of AD has become more precise, and cerebrospinal fluid tests and positron emission tomography examinations based on this framework have become widely accepted. However, the A-T-N framework does not encompass the whole spectrum of AD pathologies, and problems with invasiveness and high cost limit the application of the above diagnostic methods aimed at the central nervous system. Therefore, we suggest the addition of an “X” to the A-T-N framework and a focus on peripheral biomarkers in the diagnosis of AD. In this review, we retrospectively describe the recent progress in biomarkers based on the A-T-N-X framework, analyze the problems, and present our perspectives on the diagnosis of AD.

Diagnostic Accuracy of Blood-Based Biomarker Panels: A Systematic Review

Background

Because of high prevalence of Alzheimer's disease (AD) in low- and middle-income countries (LMICs), there is an urgent need for inexpensive and minimally invasive diagnostic tests to detect biomarkers in the earliest and asymptomatic stages of the disease. Blood-based biomarkers are predicted to have the most impact for use as a screening tool and predict the onset of AD, especially in LMICs. Furthermore, it has been suggested that panels of markers may perform better than single protein candidates.

Methods

Medline/Pubmed was searched to identify current relevant studies published from January 2016 to December 2020. We included all full-text articles examining blood-based biomarkers as a set of protein markers or panels to aid in AD's early diagnosis, prognosis, and characterization.

Results

Seventy-six articles met the inclusion criteria for systematic review. Majority of the studies reported plasma and serum as the main source for biomarker determination in blood. Protein-based biomarker panels were reported to aid in AD diagnosis and prognosis with better accuracy than individual biomarkers. Conventional (amyloid-beta and tau) and neuroinflammatory biomarkers, such as amyloid beta-42, amyloid beta-40, total tau, phosphorylated tau-181, and other tau isoforms, were the most represented. We found the combination of amyloid beta-42/amyloid beta-40 ratio and APOEε4 status to be most represented with high accuracy for predicting amyloid beta-positron emission tomography status.

Conclusion

Assessment of Alzheimer's disease biomarkers in blood as a non-invasive and cost-effective alternative will potentially contribute to early diagnosis and improvement of therapeutic interventions. Given the heterogeneous nature of AD, combination of markers seems to perform better in the diagnosis and prognosis of the disease than individual biomarkers.

Beta-Amyloid Instigates Dysfunction of Mitochondria in Cardiac Cells

Alzheimer's disease (AD) includes the formation of extracellular deposits comprising aggregated β-amyloid (Aβ) fibers associated with oxidative stress, inflammation, mitochondrial abnormalities, and neuronal loss. There is an associative link between AD and cardiac diseases; however, the mechanisms underlying the potential role of AD, particularly Aβ in cardiac cells, remain unknown. Here, we investigated the role of mitochondria in mediating the effects of Aβ1-40 and Aβ1-42 in cultured cardiomyocytes and primary coronary endothelial cells. Our results demonstrated that Aβ1-40 and Aβ1-42 are differently accumulated in cardiomyocytes and coronary endothelial cells. Aβ1-42 had more adverse effects than Aβ1-40 on cell viability and mitochondrial function in both types of cells. Mitochondrial and cellular ROS were significantly increased, whereas mitochondrial membrane potential and calcium retention capacity decreased in both types of cells in response to Aβ1-42. Mitochondrial dysfunction induced by Aβ was associated with apoptosis of the cells. The effects of Aβ1-42 on mitochondria and cell death were more evident in coronary endothelial cells. In addition, Aβ1-40 and Aβ1-42 significantly increased Ca2+ -induced swelling in mitochondria isolated from the intact rat hearts. In conclusion, this study demonstrates the toxic effects of Aβ on cell survival and mitochondria function in cardiac cells.

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.

Study Design and Baseline Results in a Cohort Study to Identify Predictors for the Clinical Progression to Mild Cognitive Impairment or Dementia From Subjective Cognitive Decline (CoSCo) Study

Background and Purpose

Subjective cognitive decline (SCD) refers to the self-perception of cognitive decline with normal performance on objective neuropsychological tests. SCD, which is the first help-seeking stage and the last stage before the clinical disease stage, can be considered to be the most appropriate time for prevention and treatment. This study aimed to compare characteristics between the amyloid positive and amyloid negative groups of SCD patients.

Methods

A cohort study to identify predictors for the clinical progression to mild cognitive impairment (MCI) or dementia from subjective cognitive decline (CoSCo) study is a multicenter, prospective observational study conducted in the Republic of Korea. In total, 120 people aged 60 years or above who presented with a complaint of persistent cognitive decline were selected, and various risk factors were measured among these participants. Continuous variables were analyzed using the Wilcoxon rank-sum test, and categorical variables were analyzed using the χ² test or Fisher’s exact test. Logistic regression models were used to assess the predictors of amyloid positivity.

Results

The multivariate logistic regression model indicated that amyloid positivity on PET was related to a lack of hypertension, atrophy of the left temporal lateral and entorhinal cortex, low body mass index, low waist circumference, less body and visceral fat, fast gait speed, and the presence of the apolipoprotein E ε4 allele in amnestic SCD patients.

Conclusions

The CoSCo study is still in progress, and the authors aim to identify the risk factors that are related to the progression of MCI or dementia in amnestic SCD patients through a two-year follow-up longitudinal study.

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.

Development of molecular tools for diagnosis of Alzheimer's disease that are based on detection of amyloidogenic proteins

Alzheimer's disease (AD) is the most common form of dementia that usually occurs among older people. AD results from neuronal degeneration that leads to the cognitive impairment and death. AD is incurable, typically develops over the course of many years and is accompanied by a loss of functional autonomy, making a patient completely dependent on family members and/or healthcare workers. Critical features of AD are pathological polymerization of Aβ peptide and microtubule-associated protein tau, accompanied by alterations of their conformations and resulting in accumulation of cross-β fibrils (amyloids) in human brains. AD apparently progresses asymptomatically for years or even decades before the appearance of symptoms. Therefore, development of the early AD diagnosis at a pre-symptomatic stage is essential for potential therapies. This review is focused on current and potential molecular tools (including non-invasive methods) that are based on detection of amyloidogenic proteins and can be applicable to early diagnosis of AD.Abbreviations: Aβ - amyloid-β peptide; AβO - amyloid-β oligomers; AD - Alzheimer's disease; ADRDA - Alzheimer's Disease and Related Disorders Association; APH1 - anterior pharynx defective 1; APP - amyloid precursor protein; BACE1 - β-site APP-cleaving enzyme 1; BBB - brain blood barrier; CJD - Creutzfeldt-Jakob disease; CRM - certified reference material; CSF - cerebrospinal fluid; ELISA - enzyme-linked immunosorbent assay; FGD - 18F-fluorodesoxyglucose (2-deoxy-2-[18F]fluoro-D-glucose); IP-MS - immunoprecipitation-mass spectrometry assay; MCI - mild cognitive impairment; MDS - multimer detection system; MRI - magnetic resonance imaging; NIA-AA - National Institute on Ageing and Alzheimer's Association; NINCDS - National Institute of Neurological and Communicative Disorders and Stroke; PEN2 - presenilin enhancer 2; PET - positron emission tomography; PiB - Pittsburgh Compound B; PiB-SUVR - PIB standardized uptake value ratio; PMCA - Protein Misfolding Cycling Amplification; PrP - Prion Protein; P-tau - hyperphosphorylated tau protein; RMP - reference measurement procedure; RT-QuIC - real-time quaking-induced conversion; SiMoA - single-molecule array; ThT - thioflavin T; TSEs - Transmissible Spongiform Encephslopathies; T-tau - total tau protein.

Novel blood test for early biomarkers of preeclampsia and Alzheimer's disease

A non-invasive and sensitive blood test has long been a goal for early stage disease diagnosis and treatment for Alzheimer's disease (AD) and other proteinopathy diseases. We previously reported that preeclampsia (PE), a severe pregnancy complication, is another proteinopathy disorder with impaired autophagy. We hypothesized that induced autophagy deficiency would promote accumulation of pathologic protein aggregates. Here, we describe a novel, sensitive assay that detects serum protein aggregates from patients with PE (n = 33 early onset and 33 late onset) and gestational age-matched controls (n = 77) as well as AD in both dementia and prodromal mild cognitive impairment (MCI, n = 24) stages with age-matched controls (n = 19). The assay employs exposure of genetically engineered, autophagy-deficient human trophoblasts (ADTs) to serum from patients. The aggregated protein complexes and their individual components, including transthyretin, amyloid β-42, α-synuclein, and phosphorylated tau231, can be detected and quantified by co-staining with ProteoStat, a rotor dye with affinity to aggregated proteins, and respective antibodies. Detection of protein aggregates in ADTs was not dependent on transcriptional upregulation of these biomarkers. The ROC curve analysis validated the robustness of the assay for its specificity and sensitivity (PE; AUC: 1, CI: 0.949-1.00; AD; AUC: 0.986, CI: 0.832-1.00). In conclusion, we have developed a novel, noninvasive diagnostic and predictive assay for AD, MCI and PE.

Reference interval and the role of plasma oligomeric beta amyloid in screening of risk groups for cognitive dysfunction at health checkups

BACKGROUND

Alzheimer's disease (AD) has a prolonged preclinical stage characterized by cognitive dysfunction. Simple, reliable, and noninvasive biomarkers reflecting the pathogenesis of AD are needed for screening cognitive dysfunction in primary health care. The aims of this study were to determine (1) the potential utility of the Multimer Detection System-Oligomeric Amyloid-β (MDS-OAβ) value in cognitive assessments and (2) the reference interval (RI) of plasma MDS-OAβ values in the general population.

METHODS

This prospective study consecutively recruited 1,594 participants who underwent health checkups including cognitive function examination at 16 health-promotion centers in Korea between December 2020 and January 2021. The inBlood^TM OAβ test (PeopleBio, Gyeonggi-do, Republic of Korea) was utilized to quantify MDS-OAβ values in plasma. The reference subjects were obtained among those with normal general cognition on cognitive screening tools. RIs were established according to the CLSI C28-A3 guidelines.

RESULTS

The median MDS-OAβ value was higher in subjects with Korean Dementia Screening Questionnaire-Cognition (KDSQ-C) scores ≥8 than in those with KDSQ-C scores of 6-7 (P = 0.013). The median MDS-OAβ value was higher in subjects with Mini-Mental State Examination for Dementia Screening (MMSE-DS) scores of 21-26 than in those with MMSE-DS scores ≥27 (P = 0.011). The RI (one-side upper 95th percentile) of the MDS-OAβ value was 0.80 ng/mL (95% confidence interval = 0.78-0.82) in those aged ≥50 years.

CONCLUSIONS

The plasma MDS-OAβ value reflects cognitive function as assessed using the KDSQ-C and MMSE-DS. RIs obtained from a large and cognitively healthy community-based sample are presented.

The fluid biomarkers of Alzheimer’s disease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder. However, it still has no available disease‐modifying therapies. Its pathology cascade begins decades before symptomatic presentation. For these reasons, highly sensitive and highly specific fluid biomarkers should be developed for the early diagnosis of AD. In this study, the well‐established and emerging fluid biomarkers of AD are summarized, and recent advances on their role in early diagnosis and progression monitoring as well as their correlations with AD pathology are highlighted. Future prospects and related research directions are also discussed.

Distinct responses of human peripheral blood cells to different misfolded protein oligomers

Increasing evidence indicates that peripheral immune cells play a prominent role in neurodegeneration connected to protein misfolding, which are associated with formation of aberrant aggregates, including soluble protein misfolded oligomers. The precise links, however, between the physicochemical features of diverse oligomers and their effects on the immune system, particularly on adaptive immunity, remain currently unexplored, due partly to the transient and heterogeneous nature of the oligomers themselves. To overcome these limitations, we took advantage of two stable and well‐characterized types of model oligomers (A and B), formed by HypF‐N bacterial protein, type B oligomers displaying lower solvent‐exposed hydrophobicity. Exposure to oligomers of human peripheral blood mononuclear cells (PBMCs) revealed differential effects, with type B, but not type A, oligomers leading to a reduction in CD4⁺ cells. Type A oligomers promoted enhanced differentiation towards CD4⁺CD25^HighFoxP3⁺ Tregs and displayed a higher suppressive effect on lymphocyte proliferation than Tregs treated with oligomers B or untreated cells. Moreover, our results reveal Th1 and Th17 lymphocyte differentiation mediated by type A oligomers and a differential balance of TGF‐β, IL‐6, IL‐23, IFN‐γ and IL‐10 mediators. These results indicate that type B oligomers recapitulate some of the biological responses associated with Parkinson's disease in peripheral immunocompetent cells, while type A oligomers resemble responses associated with Alzheimer's disease. We anticipate that further studies characterizing the differential effects of protein misfolded oligomers on the peripheral immune system may lead to the development of blood‐based diagnostics, which could report on the type and properties of oligomers present in patients.

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.

Plasma Amyloid-β Oligomerization Tendency Predicts Amyloid PET Positivity

Purpose

Among other emerging amyloid-targeting blood-based biomarkers, Multimer Detection System-Oligomeric Amyloid-β (MDS-OAβ) measures dynamic changes in concentration of oligomeric amyloid-β (OAβ), which is considered the main pathogenic culprit of Alzheimer’s disease (AD), in plasma after spiking with synthetic amyloid-β (Aβ). We aimed to investigate the predictability of MDS-OAβ on amyloid positron emission tomography (PET) positivity.

Patients and Methods

A total of 96 subjects who visited Seoul National University Bundang Hospital for medical check-up complaining of cognitive decline and had undergone extensive medical assessment were recruited. Amyloid statuses were dichotomized into positive or negative based on visual assessment of amyloid PET. Plasma OAβ concentration was measured by MDS-OAβ. In the previous validation study, 0.78ng/mL was established as the cut-off value and the plasma OAβ concentration higher than or equal to the cut-off value was defined as MDS-OAβ positive.

Results

MDS-OAβ positivity could discriminate amyloid PET positivity with the AUC value of 0.855 (95% CI 0.776–0.933). Adding MDS-OAβ positivity to prediction models including age, MMSE score, and APOE ε4 status improved performance up to the AUC value of 0.926 (95% CI 0.871–0.980).

Conclusion

The Aβ oligomerization tendency in plasma could predict amyloid PET positivity with high performance, and, when it is combined with age, MMSE score, and APOE ε4 status, predictability was improved substantially. This suggests the potential of MDS-OAβ as a useful initial stage test in the clinical and research fields of AD.

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.

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.