Meta-analysis of plasma amyloid-β levels in Alzheimer's disease

Poly-Adenine Assisted Signaling Displaced Probe Ratiometric Electrochemical Aptasensor for Accurate Detection of Alzheimer's Disease Aβ Biomarkers

Alzheimer's disease (AD) is a widely prevalent neurodegenerative condition globally, arousing significant interest in the noninvasive early detection of the disease. The concentration of amyloid β (Aβ) biomarkers in the blood is closely linked to the progression of AD, emphasizing the importance of developing a precise method for detecting these biomarkers in blood samples for early diagnosis. In this study, we developed a ratiometric electrochemical aptamer-based (EAB) biosensor for accurate detection of Aβ42 and Aβ40. The ratiometric biosensor utilizes a gold nanoparticle (AuNPs) modified electrode through an electrochemical deposition assay and a self-assembled poly-A based U-shaped structure to achieve signal changes through competitive binding of target molecules. Importantly, using the calibration of the clipping reference probe, the proposed biosensor displayed accurate detection ability for Aβ42 and Aβ40, with detection limits of 59 and 21 pM, respectively. It also has great stability and anti-interference ability in complex biological samples. Furthermore, it demonstrated satisfactory performance in detecting the Aβ peptides in a 20% FBS sample, with recoveries ranging from 96.7% to 102.2% in serum samples, and relative standard deviations (RSD) ranging from 3.3% to 8.9%. Moreover, the proposed method is expected to directly quantify the Aβ42/Aβ40 ratio by introducing a suitable reference probe, providing a potential and effective tool for the early diagnosis of AD.

Chemical-Driven Amyloid Clearance for Therapeutics and Diagnostics of Alzheimer's Disease

ConspectusA century ago, German neurologist Alois Alzheimer documented the first case of Alzheimer's disease (AD), illuminating cognitive impairments associated with the presence of abnormal protein clusters, including amyloid plaques and tau tangles, within the brain. In a typical physiological state, the equilibrium of amyloid-β (Aβ) levels is maintained, but aging can precipitate disruptions in the homeostasis of Aβ due to its overproduction, impaired clearance, and other factors, ultimately leading to its accumulation. Although the link between Aβ aggregates and neurodegeneration has long made Aβ a promising target for AD, decades without successful drug development targeting Aβ have generated skepticism regarding the efficacy of this strategy for AD therapy. However, recent approvals of anti-Aβ antibody drugs by the FDA, including aducanumab (Aduhelm), lecanemab (Leqembi), and donanemab (Kisunla), have prompted a re-evaluation of this perspective. These therapies have demonstrated efficacy in reducing brain Aβ levels, thereby decelerating disease progression and reaffirming Aβ as a key target. Despite advancements, immunotherapies are accompanied by considerable disadvantages, including adverse effects, high costs, and cumbersome administration. To address these limitations, our research has focused on developing small molecules that can mitigate the challenges of antibody treatments while offering practical and accessible options. We identified 4-(2-hydroxyethyl)-1-piperazine propanesulfonic acid (EPPS) as a promising compound that significantly reduces aggregated Aβ in the brain and enhances behavior in AD rodent models. Following administration, EPPS penetrates the blood-brain barrier (BBB) and binds to toxic Aβ aggregates, subsequently breaking them down into nontoxic monomers. This leads to two significant outcomes: a reduction of Aβ aggregates in the brain and a subsequent increase in Aβ monomers in blood. The monomeric Aβ, unlike its aggregated form, can now traverse the BBB and enter the bloodstream. This mechanism provides an innovative approach to AD treatment and diagnosis. By detaching cerebral Aβ aggregates, EPPS facilitates Aβ clearance and addresses a key pathological feature of AD. Concurrently, the increase in blood Aβ levels offers a potential biomarker for monitoring treatment efficacy and disease progression, thereby revolutionizing both AD treatment and diagnosis. Investigating the detailed mode of action of drug candidates requires structural information about a target protein. Unfortunately, the unstable and heterogeneous nature of Aβ aggregates, which form larger clusters, complicates the identification of these structures. Therefore, we developed new tools for screening small molecules by immobilizing monomeric Aβ and its fragments on plates. This allows us not only to identify novel compounds that target Aβ but also to elucidate their mechanisms of action, enabling the development of Aβ-targeting therapeutic avenues in AD. We believe that our work on chemical-driven amyloid clearance through small molecules represents an advance in AD research, offering chemical diversity and straightforward, economical development processes. In clinical practice, we anticipate that these findings will contribute to the development of patient-friendly therapeutic and diagnostic interventions, including self-administered and orally available options, thereby enhancing disease management and overall quality of life for individuals with AD. Furthermore, this research extends beyond AD, potentially offering insights into other neurodegenerative diseases characterized by protein aggregation.

Elevated C-Reactive Protein in Older Men With Chronic Pain: Association With Plasma Amyloid Levels and Hippocampal Volume

BACKGROUND

Chronic pain leads to tau accumulation and hippocampal atrophy, which may be moderated through inflammation. In older men, we examined associations of chronic pain with Alzheimer's disease (AD)-related plasma biomarkers and hippocampal volume as moderated by systemic inflammation.

METHODS

Participants were men without dementia. Chronic pain was defined as moderate-to-severe pain in 2+ study waves at average ages 56, 62, and 68. At age 68, we measured plasma amyloid-beta (Aβ42, n = 871), Aβ40 (n = 887), total tau (t-tau, n = 841), and neurofilament light chain (NfL, n = 915), and serum high-sensitivity C-reactive protein (hs-CRP, n = 968), a marker of systemic inflammation. A subgroup underwent structural MRI to measure hippocampal volume (n = 385). Analyses adjusted for medical morbidities, depressive symptoms, and opioid use.

RESULTS

Chronic pain was related to higher Aβ40 (β = 0.25, p = .009), but hs-CRP was unrelated to AD-related biomarkers (ps > .05). There was a significant interaction such that older men with both chronic pain and higher levels of hs-CRP had higher levels of Aβ42 (β = 0.36, p = .001) and Aβ40 (β = 0.29, p = .003). Chronic pain and hs-CRP did not interact to predict levels of Aβ42/Aβ40, t-tau, or NfL. Furthermore, there were significant interactions such that Aβ42 and Aβ40 were associated with lower hippocampal volume, particularly when levels of hs-CRP were elevated (hs-CRP × Aβ42: β = -0.19, p = .002; hs-CRP × Aβ40: β = -0.21, p = .001), regardless of chronic pain status.

CONCLUSIONS

Chronic pain was associated with higher plasma Aβ, especially when hs-CRP was also elevated. Higher hs-CRP and Aβ levels were both related to smaller hippocampal volumes. Chronic pain, when accompanied by systemic inflammation, may elevate the risk of neurodegeneration in AD-vulnerable regions.

Chemically Self-Assembled Monolayer Semiconducting Single-Walled Carbon Nanotube-Based Biosensor Platform for Amyloid-β Detection

This paper presents a platform for amyloid-β (Aβ) biosensors, employing nearly monolayer semiconducting single-walled carbon nanotubes (sc-SWNTs) via click reaction. A high-purity sc-SWNT ink was obtained by employing a conjugated polymer wrapping method with the addition of silica gel. Aβ detection involved monitoring the electrical resistances of the sc-SWNT layers. Electrical resistances increased rapidly corresponding to the concentration of amyloid-β 1-42 (Aβ1-42) peptides. Furthermore, we introduced Aβ peptides onto the 1-pyrenebutanoic acid succinimidyl ester (PBASE) linker, confirming that only the chemical adsorption of the peptide by the antibody-antigen reaction yielded a significant change in electrical resistance. The optimized sensor exhibited a high sensitivity of 29% for Aβ at a concentration of 10 pM. Notably, the biosensor platform featuring chemically immobilized sc-SWNT networks can be customized by incorporating various bioreceptors beyond Aβ antibodies.

Osteoporosis and Alzheimer´s disease (or Alzheimer´s disease and Osteoporosis)

Alzheimer's disease (AD) and osteoporosis are two diseases that mainly affect elderly people, with increases in the occurrence of cases due to a longer life expectancy. Several epidemiological studies have shown a reciprocal association between both diseases, finding an increase in incidence of osteoporosis in patients with AD, and a higher burden of AD in osteoporotic patients. This epidemiological relationship has motivated the search for molecules, genes, signaling pathways and mechanisms that are related to both pathologies. The mechanisms found in these studies can serve to improve treatments and establish better patient care protocols.

Advances in Blood Biomarkers for Alzheimer's Disease: Ultra-Sensitive Detection Technologies and Impact on Clinical Diagnosis

Alzheimer's disease has escalated into a critical public health concern, marked by its neurodegenerative nature that progressively diminishes cognitive abilities. Recognized as a continuously advancing and presently incurable condition, AD underscores the necessity for early-stage diagnosis and interventions aimed at delaying the decline in mental function. Despite the proven efficacy of cerebrospinal fluid and positron emission tomography in diagnosing AD, their broader utility is constrained by significant costs and the invasive nature of these procedures. Consequently, the innovation of blood biomarkers such as Amyloid-beta, phosphorylated-tau, total-tau et al, distinguished by their high sensitivity, minimal invasiveness, accessibility, and cost-efficiency, emerges as a promising avenue for AD diagnosis. The advent of ultra-sensitive detection methodologies, including single-molecule enzyme-linked immunosorbent assay and immunoprecipitation-mass spectrometry, has revolutionized the detection of AD plasma biomarkers, supplanting previous low-sensitivity techniques. This rapid advancement in detection technology facilitates the more accurate quantification of pathological brain proteins and AD-associated biomarkers in the bloodstream. This manuscript meticulously reviews the landscape of current research on immunological markers for AD, anchored in the National Institute on Aging-Alzheimer's Association AT(N) research framework. It highlights a selection of forefront ultra-sensitive detection technologies now integral to assessing AD blood immunological markers. Additionally, this review examines the crucial pre-analytical processing steps for AD blood samples that significantly impact research outcomes and addresses the practical challenges faced during clinical testing. These discussions are crucial for enhancing our comprehension and refining the diagnostic precision of AD using blood-based biomarkers. The review aims to shed light on potential avenues for innovation and improvement in the techniques employed for detecting and investigating AD, thereby contributing to the broader field of neurodegenerative disease research.

Probable chronic pain, brain structure, and Alzheimer's plasma biomarkers in older men

Chronic pain leads to tau accumulation and hippocampal atrophy in mice. In this study, we provide one of the first assessments in humans, examining the associations of probable chronic pain with hippocampal volume, integrity of the locus coeruleus (LC)-an upstream site of tau deposition-and Alzheimer's Disease-related plasma biomarkers. Participants were mostly cognitively unimpaired men. Probable chronic pain was defined as moderate-to-severe pain in 2+ study waves at average ages 56, 62, and 68. At age 68, 424 participants underwent structural magnestic resonance imaging (MRI) of hippocampal volume and LC-sensitive MRI providing an index of LC integrity (LC contrast-to-noise ratio). Analyses adjusted for confounders including major health conditions, depressive symptoms, and opioid use. Models showed that men with probable chronic pain had smaller hippocampal volume and lower rostral-middle-but not caudal-LC contrast-to-noise ratio compared to men without probable chronic pain. Men with probable chronic pain also had higher levels of plasma total tau, beta-amyloid-42, and beta-amyloid-40 compared to men without probable chronic pain. These findings suggest that probable chronic pain is associated with tau accumulation and reduced structural brain integrity in regions affected early in the development of Alzheimer's Disease. PERSPECTIVE: Probable chronic pain was associated with plasma biomarkers and brain regions that are affected early in Alzheimer's disease (AD). Reducing pain in midlife and elucidating biological mechanisms may help to reduce the risk of AD in older adults.

Heart rate and breathing effects on attention and memory (HeartBEAM): study protocol for a randomized controlled trial in older adults

BACKGROUND

In healthy people, the "fight-or-flight" sympathetic system is counterbalanced by the "rest-and-digest" parasympathetic system. As we grow older, the parasympathetic system declines as the sympathetic system becomes hyperactive. In our prior heart rate variability biofeedback and emotion regulation (HRV-ER) clinical trial, we found that increasing parasympathetic activity through daily practice of slow-paced breathing significantly decreased plasma amyloid-β (Aβ) in healthy younger and older adults. In healthy adults, higher plasma Aβ is associated with greater risk of Alzheimer's disease (AD). Our primary goal of this trial is to reproduce and extend our initial findings regarding effects of slow-paced breathing on Aβ. Our secondary objectives are to examine the effects of daily slow-paced breathing on brain structure and the rate of learning.

METHODS

Adults aged 50-70 have been randomized to practice one of two breathing protocols twice daily for 9 weeks: (1) "slow-paced breathing condition" involving daily cognitive training followed by slow-paced breathing designed to maximize heart rate oscillations or (2) "random-paced breathing condition" involving daily cognitive training followed by random-paced breathing to avoid increasing heart rate oscillations. The primary outcomes are plasma Aβ40 and Aβ42 levels and plasma Aβ42/40 ratio. The secondary outcomes are brain perivascular space volume, hippocampal volume, and learning rates measured by cognitive training performance. Other pre-registered outcomes include plasma pTau-181/tTau ratio and urine Aβ42. Recruitment began in January 2023. Interventions are ongoing and will be completed by the end of 2023.

DISCUSSION

Our HRV-ER trial was groundbreaking in demonstrating that a behavioral intervention can reduce plasma Aβ levels relative to a randomized control group. We aim to reproduce these findings while testing effects on brain clearance pathways and cognition.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05602220. Registered on January 12, 2023.

Plasma neurofilament light chain in association to late-life depression in the general population

AIM

Investigating what is underlying late-life depression is becoming increasingly important with the rapidly growing elderly population. Yet, the associations between plasma biomarkers of neuroaxonal damage and late-life depression remain largely unclear. Therefore, we determined cross-sectional and longitudinal associations of neurofilament light chain (NfL) with depression in middle-aged and elderly individuals, and total tau, β-amyloid 40 and 42 for comparison.

METHODS

We included 3,895 participants (71.78 years [SD = 7.37], 53.4% women) from the population-based Rotterdam Study. Between 2002 and 2005, NfL, total tau, β-amyloid 40 and β-amyloid 42 were determined in blood and depressive symptoms were measured with the Center for Epidemiologic Studies Depression scale (CES-D). Incident depressive events (clinically relevant depressive symptoms, depressive syndromes, major depressive disorders) were measured prospectively with the Center for Epidemiologic Studies Depression, a clinical interview and follow-up of medical records over a median follow-up of 7.0 years (interquartile range 1.80). We used linear and Cox proportional hazard regression models.

RESULTS

Each log2 pg./mL increase in NfL was cross-sectionally associated with more depressive symptoms (adjusted mean difference: 0.32, 95% CI 0.05-0.58), as well as with an increased risk of any incident depressive event over time (hazard ratio: 1.22, 95% CI 1.01-1.47). Further, more amyloid-β 40 was cross-sectionally associated with more depressive symptoms (adjusted mean difference: 0.70, 95% CI 0.15-1.25).

CONCLUSION

Higher levels of NfL are cross-sectionally associated with more depressive symptoms and a higher risk of incident depressive events longitudinally. The association was stronger for NfL compared to other plasma biomarkers, suggesting a potential role of neuroaxonal damage in developing late-life depression.

High-Performance Plasma Biomarker Panel for Alzheimer's Disease Screening Using a Femtomolar-Level Label-Free Biosensing System

Alzheimer's disease (AD) is the most common cause of dementia in older people. However, diagnosing AD through noncognitive methods, such as invasive cerebrospinal fluid sampling or radioactive positron emission tomography, has limited applications. Herein, the femtomolar levels of AD biomarkers amyloid β 40 (Aβ40), amyloid β 42 (Aβ42), phosphorylated tau 181 (P-tau181), phosphorylated tau 217 (P-tau217), and neurofilament light chain (NfL) were determined in human plasma in multicenter clinical cohorts using an ultrasensitive graphene field-effect transistor sensor. A machine-learning algorithm was also used to assemble these plasma biomarkers and optimize their performance in discriminating individual stages of Alzheimer's dementia progression. The "composite-info" biomarker panel, which combines these biomarkers and clinical information, considerably improved the staging performance in AD progression. It achieved an area under the curve of >0.94 in the receiver operator characteristic (ROC) curve. In addition, the panel demonstrated an advantage in the individual-based stage assessment compared with that of the Mini-Mental State Examination/Montreal Cognitive Assessment and nuclear magnetic resonance imaging. This study provides a composite biomarker panel for the screening and early diagnosis of AD using a rapid detection system.

Lithography-free interdigitated electrodes by trench-filling patterning on polymer substrate for Alzheimer's disease detection

Microelectrodes have played a crucial role in electrochemistry for the last few decades. However, the conventional lithographic processes, the key players in fabrication, are nonetheless technologically challenging, pricey, and lack reproducibility. In this work has developed a novel and low-cost patterned-replication fabrication technology for interdigitated electrode array (IDA) electrodes on the polymer substrate. Conventional UV-lithography has been utilized to fabricate the nickel IDA electrode pattern as a master mold on the stainless-steel substrate, which was replicated onto the polymer substrate by the hot-emboss technique. Then, gold was deposited on the replicated wafer by electron beam evaporation, and finally adhesive tape lift-off was used to obtain the gold IDA electrode. The fabricated IDA electrode was applied for electrochemical detection of various p-aminophenol (PAP) concentrations as a representative biomarker with a detection limit of 0.01 nM. Finally, different levels of amyloid beta 42 (Aß42) and amyloid beta aggregated (Aß Agg.), two Alzheimer's disease (AD) biomarkers, were measured using the developed IDA electrode via e-ELISA using enzyme by-products PAP. While quantified, the proposed IDA electrode successfully detects Aß42 and Aß Agg. with the lower detection limit (LOD) of 3.9 and 7.81 pg/ml, respectively.

A systematic review with meta-analysis to assess Alzheimer's disease biomarkers in adults with or without obstructive sleep apnoea

INTRODUCTION

The aim was to design a meta-analysis evaluating the positron emission tomography (PET) uptake and cerebrospinal fluid (CSF), circulating levels of amyloid-β (Aβ), and tau proteins OSA group versus control group, as well as the association of these biomarkers with the severity of OSA.

MATERIAL AND METHODS

Four databases were searched until April 17, 2023, without any restrictions. The effect sizes were the standardized mean difference (SMD) along with a 95% confidence interval (CI).

RESULTS

A total of 21 articles were entered into the meta-analysis. The pooled SMDs of the CSF levels in OSA adults compared to controls were: -0.82 (P=0.004) for Aβ42, -1.13 (P<0.001) for Aβ40, 0.17 (P=0.23) for p-tau, 0.04 (P=0.65) for t-tau, 0.08 (P=0.89) for Aβ42/Aβ40 ratio, and 0.81 (P=0.001) for t-tau/Aβ42 ratio. The pooled SMD for the PET uptake of Aβ burden in OSA adults compared to controls was 0.30 (P=0.03). The pooled SMDs of the circulating levels in OSA adults compared to controls were: 0.67 (P=0.002) for Aβ42, 0.11 (P=0.82) for Aβ40, 0.35 (P=0.06) for p-tau, and 1.41(P=0.005) for t-tau. The pooled SMDs for levels of Aβ42, Aβ40, total Aβ, p-tau, t-tau, and Aβ42/Aβ40 ratio in severe OSA adults compared to mild/moderate OSA adults were -0.15 (P=0.33), 0.25 (P=35), 0.04 (P=87), -2.53 (P=0.24), -0.24 (P=0.52), and -0.28 (P=0.30), respectively.

CONCLUSIONS

The results indicated that CSF levels of Aβ42 and Aβ40 in OSA adults were significantly lower, but the CSF level of t-tau/Aβ42 ratio and PET Aβ burden uptake in OSA adults significantly were higher than in controls.

Amyloid beta and postoperative delirium: partners in crime or strangers in the dark?

Postoperative delirium is a particularly debilitating complication of surgery and perioperative care. Although the aetiology of postoperative delirium is not entirely understood, recent evidence suggests that Alzheimer's disease and related dementias pathology plays an important role in the development of postoperative delirium. A recent study evaluating postoperative changes in plasma beta amyloid (Aβ) levels found increased Aβ across the postoperative period, but the association with postoperative delirium incidence and severity was variable. These findings support the idea that Alzheimer's disease and related dementias pathology in combination with blood-brain barrier dysfunction and neuroinflammation may impart risk for postoperative delirium.

Ultrasensitive FET biosensor chip based on self-assembled organic nanoporous membrane for femtomolar detection of Amyloid-β

Early diagnosis of Alzheimer's disease (AD) is critical for preventing disease progression, however, the diagnosis of AD remains challenging for most patients due to limitations of current sensing technologies. A common pathological feature found in AD-affected brains is the accumulation of Amyloid-β (Aβ) polypeptides, which lead to neurofibrillary tangles and neuroinflammatory plaques. Here, we developed a portable ultrasensitive FET biosensor chip based on a self-assembled nanoporous membrane for ultrasensitive detection of Aβ protein in complex environments. The microscale semiconductor channel was covered with a self-assembled organic nanoporous membrane modified by antibody molecules to pick up and amplify the Aβ protein signal. The nanoporous structure helps protect the sensitive channel from non-target proteins and improves its stability since no chemical functionalization process involved, largely reduces background noise of the sensing platform. When a bio-gated target is captured, the doping state of the polymer bulk could be tuned and amplified the strength of the weak signal, achieving ultrasensitive detecting performance (enabling the device to detect target protein less than 1 fg/ml in 1 µl sample). Moreover, the device simplifies the circuit connection by integrating all the connections on a 2 cm × 2 cm chip, avoiding expensive and complex manufacturing processes, and makes it usable for portable prognosis. We believe that this ultrasensitive, portable, low-cost Aβ sensor chip shows the great potential in the early diagnosis of AD and large-scale population screening applications.

The association of obstructive sleep apnea with blood and cerebrospinal fluid biomarkers of Alzheimer's dementia - A systematic review and meta-analysis

Alzheimer's disease (AD) is the most common type of dementia and is characterized by the aggregation of extracellular amyloid-beta and intracellular hyperphosphorylation of tau proteins. Obstructive Sleep Apnea (OSA) is associated with increased AD risk. We hypothesize that OSA is associated with higher levels of AD biomarkers. The study aims to conduct a systematic review and meta-analysis of the association between OSA and levels of blood and cerebrospinal fluid biomarkers of AD. Two authors independently searched PubMed, Embase, and Cochrane Library for studies comparing blood and cerebrospinal fluid levels of dementia biomarkers between patients with OSA and healthy controls. Meta-analyses of the standardized mean difference were conducted using random-effects models. From 18 studies with 2804 patients, meta-analysis found that cerebrospinal fluid amyloid beta-40 (SMD:-1.13, 95%CI:-1.65 to -0.60), blood total amyloid beta (SMD:0.68, 95%CI: 0.40 to 0.96), blood amyloid beta-40 (SMD:0.60, 95%CI: 0.35 to 0.85), blood amyloid beta-42 (SMD:0.80, 95%CI: 0.38 to 1.23) and blood total-tau (SMD: 0.664, 95% CI: 0.257 to 1.072, I² = 82, p<0.01, 7 studies) were significantly higher in OSA patients compared with healthy controls. These findings suggest that OSA is associated with an elevation of some biomarkers of AD.

Plasma Biomarkers of Alzheimer's Disease: A Review of Available Assays, Recent Developments, and Implications for Clinical Practice

Recently, low-sensitive plasma assays have been replaced by new ultra-sensitive assays such as single molecule enzyme-linked immunosorbent assay (Simoa), the Mesoscale Discovery (MSD) platform, and immunoprecipitation-mass spectrometry (IP-MS) with higher accuracy in the determination of plasma biomarkers of Alzheimer's disease (AD). Despite the significant variability, many studies have established in-house cut-off values for the most promising available biomarkers. We first reviewed the most used laboratory methods and assays to measure plasma AD biomarkers. Next, we review studies focused on the diagnostic performance of these biomarkers to identify AD cases, predict cognitive decline in pre-clinical AD cases, and differentiate AD cases from other dementia. We summarized data from studies published until January 2023. A combination of plasma Aβ_42/40 ratio, age, and APOE status showed the best accuracy in diagnosing brain amyloidosis with a liquid chromatography-mass spectrometry (LC-MS) assay. Plasma p-tau217 has shown the best accuracy in distinguishing Aβ-PET+ from Aβ-PET-even in cognitively unimpaired individuals. We also summarized the different cut-off values for each biomarker when available. Recently developed assays for plasma biomarkers have undeniable importance in AD research, with improved analytical and diagnostic performance. Some biomarkers have been extensively used in clinical trials and are now clinically available. Nonetheless, several challenges remain to their widespread use in clinical practice.

Modulating heart rate oscillation affects plasma amyloid beta and tau levels in younger and older adults

Slow paced breathing via heart rate variability (HRV) biofeedback stimulates vagus-nerve pathways that counter noradrenergic stress and arousal pathways that can influence production and clearance of Alzheimer's disease (AD)-related proteins. Thus, we examined whether HRV biofeedback intervention affects plasma Αβ40, Αβ42, total tau (tTau), and phosphorylated tau-181 (pTau-181) levels. We randomized healthy adults (N = 108) to use slow-paced breathing with HRV biofeedback to increase heart rate oscillations (Osc+) or to use personalized strategies with HRV biofeedback to decrease heart rate oscillations (Osc-). They practiced 20-40 min daily. Four weeks of practicing the Osc+ and Osc- conditions produced large effect size differences in change in plasma Aβ40 and Aβ42 levels. The Osc+ condition decreased plasma Αβ while the Osc- condition increased Αβ. Decreases in Αβ were associated with decreases in gene transcription indicators of β-adrenergic signaling, linking effects to the noradrenergic system. There were also opposing effects of the Osc+ and Osc- interventions on tTau for younger adults and pTau-181 for older adults. These results provide novel data supporting a causal role of autonomic activity in modulating plasma AD-related biomarkers.Trial registration: NCT03458910 (ClinicalTrials.gov); first posted on 03/08/2018.

Precise profiling of exosomal biomarkers via programmable curved plasmonic nanoarchitecture-based biosensor for clinical diagnosis of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease of complex pathogenesis, with overt symptoms following disease progression. Early AD diagnosis is challenging due to the lack of robust biomarkers and limited patient access to diagnostics via neuroimaging and cerebrospinal fluid (CSF) tests. Exosomes present in body fluids are attracting attention as diagnostic biomarkers that directly reflect neuropathological features within the brain. In particular, exosomal miRNAs (exomiRs) signatures are involved in AD pathogenesis, showing a different expression between patients and the healthy controls (HCs). However, low yield and high homologous nature impede the accuracy and reproducibility of exosome blood-based AD diagnostics. Here, we developed a programmable curved plasmonic nanoarchitecture-based biosensor to analyze exomiRs in clinical serum samples for accurate AD diagnosis. To allow the detection of exomiRs in serum at attomolar levels, nanospaces (e.g., nanocrevice and nanocavity) were introduced into the nanostructures to dramatically increase the spectral sensitivity by adjusting the bending angle of the plasmonic nanostructure through sodium chloride concentration control. The developed biosensor classifies individuals into AD, mild cognitive impairment (MCI) patients, and HCs through profiling and quantifying exomiRs. Furthermore, integrating analysis expression patterns of multiple exosomal biomarkers improved serum-based diagnostic performance (average accuracy of 98.22%). Therefore, precise, highly sensitive serum-derived exosomal biomarker detection-based plasmonic biosensor has a robust capacity to predict the molecular pathologic of neurodegenerative disease, progression of cognitive decline, MCI/AD conversion, as well as early diagnosis and treatment.

Air pollution and plasma amyloid beta in a cohort of older adults: Evidence from the Ginkgo Evaluation of Memory study

Air pollution has been linked to Alzheimer's disease and related dementias (ADRD), but the mechanisms connecting air pollution to ADRD have not been firmly established. Air pollution may cause oxidative stress and neuroinflammation and contribute to the deposition of amyloid beta (Aβ) in the brain. We examined the association between fine particulate matter<2.5 μm in diameter (PM2.5), particulate matter<10 μm in diameter (PM10), nitrogen dioxide (NO2), and plasma based measures of Aβ1-40, Aβ1-42 and Aβ1-42/Aβ1-40 using data from 3044 dementia-free participants of the Ginkgo Evaluation of Memory Study (GEMS). Air pollution exposures were estimated at residential addresses that incorporated address histories dating back to 1980, resulting in one-, five-, 10- and 20- year exposure averages. Aβ was measured at baseline (2000-2002) and then again at the end of the study (2007-2008) allowing for linear regression models to assess cross-sectional associations and linear random effects models to evaluate repeated measures. After adjustment for socio-demographic and behavioral covariates, we found small positive associations between each air pollutant and Aβ1-40 but no association with Aβ1-42 or the ratio measures in cross sectional analysis. In repeat measures analysis, we found larger positive associations between each air pollutant and all three outcomes. We observed a 4.43% (95% CI 3.26%, 5.60%) higher Aβ1-40 level, 9.73% (6.20%, 13.38%) higher Aβ1-42 and 1.57% (95% CI: 0.94%, 2.20%) higher Aβ1-42/Aβ1-40 ratio associated with a 2 µg/m3 higher 20-year average PM2.5. Associations with other air pollutants were similar. Our study contributes to the broader evidence base on air pollution and ADRD biomarkers by evaluating longer air pollution exposure averaging periods to better mimic disease progression and provides a modifiable target for ADRD prevention.

Prefrontal EEG slowing, synchronization, and ERP peak latency in association with predementia stages of Alzheimer's disease

Background

Early screening of elderly individuals who are at risk of dementia allows timely medical interventions to prevent disease progression. The portable and low-cost electroencephalography (EEG) technique has the potential to serve it.

Objective

We examined prefrontal EEG and event-related potential (ERP) variables in association with the predementia stages of Alzheimer's disease (AD).

Methods

One hundred elderly individuals were recruited from the GARD cohort. The participants were classified into four groups according to their amyloid beta deposition (A+ or A-) and neurodegeneration status (N+ or N-): cognitively normal (CN; A-N-, n = 27), asymptomatic AD (aAD; A + N-, n = 15), mild cognitive impairment (MCI) with AD pathology (pAD; A+N+, n = 16), and MCI with non-AD pathology (MCI(-); A-N+, n = 42). Prefrontal resting-state eyes-closed EEG measurements were recorded for five minutes and auditory ERP measurements were recorded for 8 min. Three variables of median frequency (MDF), spectrum triangular index (STI), and positive-peak latency (PPL) were employed to reflect EEG slowing, temporal synchrony, and ERP latency, respectively.

Results

Decreasing prefrontal MDF and increasing PPL were observed in the MCI with AD pathology. Interestingly, after controlling for age, sex, and education, we found a significant negative association between MDF and the aAD and pAD stages with an odds ratio (OR) of 0.58. Similarly, PPL exhibited a significant positive association with these AD stages with an OR of 2.36. Additionally, compared with the MCI(-) group, significant negative associations were demonstrated by the aAD group with STI and those in the pAD group with MDF with ORs of 0.30 and 0.42, respectively.

Conclusion

Slow intrinsic EEG oscillation is associated with MCI due to AD, and a delayed ERP peak latency is likely associated with general cognitive impairment. MCI individuals without AD pathology exhibited better cortical temporal synchronization and faster EEG oscillations than those with aAD or pAD.

Significance

The EEG/ERP variables obtained from prefrontal EEG techniques are associated with early cognitive impairment due to AD and non-AD pathology. This result suggests that prefrontal EEG/ERP metrics may serve as useful indicators to screen elderly individuals' early stages on the AD continuum as well as overall cognitive impairment.

A Review of Application of Aβ42/40 Ratio in Diagnosis and Prognosis of Alzheimer’s Disease

The number of patients with Alzheimer’s disease (AD) and non-Alzheimer’s disease (non-AD) has drastically increased over recent decades. The amyloid cascade hypothesis attributes a vital role to amyloid-β protein (Aβ) in the pathogenesis of AD. As the main pathological hallmark of AD, amyloid plaques consist of merely the 42 and 40 amino acid variants of Aβ (Aβ 42 and Aβ 40). The cerebrospinal fluid (CSF) biomarker Aβ 42/40 has been extensively investigated and eventually integrated into important diagnostic tools to support the clinical diagnosis of AD. With the development of highly sensitive assays and technologies, blood-based Aβ 42/40, which was obtained using a minimally invasive and cost-effective method, has been proven to be abnormal in synchrony with CSF biomarker values. This paper presents the recent progress of the CSF Aβ 42/40 ratio and plasma Aβ 42/40 for AD as well as their potential clinical application as diagnostic markers or screening tools for dementia.

Circulating Amyloid-β and Methionine-Related Metabolites to Predict the Risk of Mild Cognitive Impairment: A Nested Case-Control Study

Background: The high cost, limited availability, and perceived invasiveness of amyloid PET and cerebrospinal fluid biomarkers limit their use for the diagnosis of Alzheimer’s disease. Objective: The present study aimed to assess the associations of mild cognitive impairment (MCI) with circulating amyloid-β (Aβ), methionine circulating metabolites (MCMs), and their downstream products, and to develop a nomogram based on these easily accessible blood indexes for the individualized prediction of MCI risk in older adults. Methods: In this nested case-control study, we recruited 74 MCI patients and, for each, 3 matched controls (n = 222) within the context of the Tianjin Elderly Nutrition and Cognition (TENC) cohort, a population-based prospective study in China. Concentrations of Aβ, MCMs, and their circulating downstream factors (i.e., leukocyte telomere length and inflammatory cytokines) were evaluated in fasting blood sample using standard procedures. We constructed a nomogram for MCI harnessed multivariable logistic models incorporating variables selected in the Lasso regression. Results: Among the many biomarkers examined, the final prediction nomogram retained only 3 factors: Aβ 42/Aβ 40 ratio, Hcy, and SAM/SAH ratio. The model achieved favorable discrimination, with a C-statistic of 0.75 (95% confidence interval 0.69–0.81) in internal validation after adjustment of optimism. The calibration accuracy was satisfactory; the Brier score of the model was 0.161 in internal validation after adjustment of optimism. Conclusion: his study presents an individualized prediction nomogram incorporating only three blood biomarkers (i.e., Aβ 42/Aβ 40 ratio, Hcy, and SAM/SAH ratio), which can be conveniently utilized to facilitate early identification and the development of high-risk prevention strategies for MCI in older adults.

Plasma biomarkers and their correlation in adult children of parents with Alzheimer’s disease

Family history (FH) of late-onset Alzheimer’s disease (AD) is associated with changes in several cerebrospinal fluid (CSF) biomarkers in cognitively normal individuals. However, potential changes in plasma biomarkers remain unknown. This study aimed to evaluate potential plasma biomarkers and their correlation in cognitively normal adult children (AC) and to compare this data with their AD parents and unrelated non-demented controls (NC). Participants with dementia due to AD, their AC and NC were recruited. Plasma samples were assessed for amyloid beta (Aβ)_1–42, Aβ_1–40, total tau (T-tau) and phosphorylated tau (P-tau). Kruskal–Wallis test was used for the comparison of this data between the three groups. Spearman rank correlation was used for evaluation of the correlations between Aβ_1–40 and Aβ_1–42, and T-tau and P-tau in the AD and AC groups. A total of 99 subjects completed the assessment (30 had AD; 38 were AC group; and 31 were NC). Compared with the NC group, there were significantly higher levels of Aβ_1–40, P-tau, and P-tau/T-tau ratio, and lower levels of Aβ_1–42 and Aβ_1–42/Aβ_1–40 ratio in the AD and AC groups. The correlation between the level of Aβ_1–42 and Aβ_1–40 and level of T-tau and P-tau was only observed in the AC but not in the AD group. AC of AD parents demonstrate some indicators of AD like their parents. Disruption to the correlation between Aβ and tau in AD may be a biomarker for the development of AD in AC, which should be examined in a longitudinal cohort.

Aptamer-Functionalized Carbon Nanotube Field-Effect Transistor Biosensors for Alzheimer's Disease Serum Biomarker Detection

Blood-biomarker-based tests are highly important for the early clinical diagnosis of Alzheimer's disease (AD) and the treatment and care of AD patients, but the complex serum environment and extremely low abundance of AD blood protein biomarkers present challenges. Nanomaterials are promising for constructing highly sensitive transistor-based biosensors due to their small size. However, such biosensors are difficult to fabricate on a large scale and suffer from the lack of combined optimization of reproducibility and sensitivity in complex physiological fluids. In this work, field-effect transistor (FET) biosensors based on highly uniform semiconducting carbon nanotube (CNT) thin films are mass produced to achieve highly sensitive and selective detection of the AD core blood biomarkers of β-amyloid (Aβ). The combination of the mass-produced CNT FET sensors and oligonucleotide aptamers as efficient bioreceptors enables reliable and reproducible sub-femtomolar detection in full human serum for Aβ₄₂ and Aβ₄₀ peptides and has outperformed other methods reported to date. The adsorption of biological substrates to the sensor was significantly reduced by multiple blocking steps, resulting in selectivity ratios of up to 730% (Aβ₄₀) and 800% (Aβ₄₂). The aptamer-functionalized CNT FET biosensor exhibits a large dynamic range (>10⁴), rapid response time (several minutes), and low variation (<10%) and can be delivered as a low-cost and rapid clinical detection technology for the early diagnosis and mass screening of AD. This platform will help bring complex laboratory-based and expensive diagnostic tools to the point of care.

Combination of gut microbiota and plasma amyloid-β as a potential index for identifying preclinical Alzheimer's disease: a cross-sectional analysis from the SILCODE study

Background

Plasma amyloid-β (Aβ) may facilitate identification of individuals with brain amyloidosis. Gut microbial dysbiosis in Alzheimer’s disease (AD) is increasingly being recognized. However, knowledge about alterations of gut microbiota in preclinical AD, as well as whether the combination of plasma Aβ and gut microbiota could identify preclinical AD, remains largely unknown.

Methods

This study recruited 34 Aβ-negative cognitively normal (CN−) participants, 32 Aβ-positive cognitively normal (CN+) participants, and 22 patients with cognitive impairment (CI), including 11 patients with mild cognitive impairment (MCI) and 11 AD dementia patients. All participants underwent neuropsychological assessments and fecal microbiota analysis through 16S ribosomal RNA (rRNA) Illumina Miseq sequencing technique. Meso Scale Discovery (MSD) kits were used to quantify the plasma Aβ₄₀, Aβ₄₂, and Aβ₄₂/Aβ₄₀ in CN− and CN+ participants. Using Spearman’s correlation analysis, the associations of global standard uptake value rate (SUVR) with altered gut microbiota and plasma Aβ markers were separately evaluated. Furthermore, the discriminative power of the combination of gut microbiota and plasma Aβ markers for identifying CN+ individuals was investigated.

Results

Compared with the CN− group, the CN+ group showed significantly reduced plasma Aβ₄₂ (p = 0.011) and Aβ₄₂/Aβ₄₀ (p = 0.003). The relative abundance of phylum Bacteroidetes was significantly enriched, whereas phylum Firmicutes and class Deltaproteobacteria were significantly decreased in CN+ individuals in comparison with that in CN− individuals. Particularly, the relative abundance of phylum Firmicutes and its corresponding SCFA-producing bacteria exhibited a progressive decline tendency from CN− to CN+ and CI. Besides, the global brain Aβ burden was negatively associated with the plasma Aβ₄₂/Aβ₄₀ (r = −0.298, p = 0.015), family Desulfovibrionaceae (r = −0.331, p = 0.007), genus Bilophila (r = −0.247, p = 0.046), and genus Faecalibacterium (r = −0.291, p = 0.018) for all CN participants. Finally, the combination of plasma Aβ markers, altered gut microbiota, and cognitive performance reached a relatively good discriminative power in identifying individuals with CN+ from CN− (AUC = 0.869, 95% CI 0.782 ~ 0.955).

Conclusions

This study provided the evidence that the gut microbial composition was altered in preclinical AD. The combination of plasma Aβ and gut microbiota may serve as a non-invasive, cost-effective diagnostic tool for early AD screening. Targeting the gut microbiota may be a novel therapeutic strategy for AD.

Trial registration

This study has been registered in ClinicalTrials.gov (NCT03370744, https://www.clinicaltrials.gov) in November 15, 2017.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-00977-x.

Distance-based β-amyloid protein detection on PADs for the scanning and subsequent follow-up of Alzheimer's disease in human urine samples

We report on the first development of a simple distance-based β-amyloid (Aβ) protein quantification using a paper-based device (dPAD) to screen for Alzheimer's disease (AD) and to subsequently follow up on its influence, i.e., clinical dementia. This sensor method is based on the transformation of a free acid form and its binding with a basic form of bromocresol purple (BCP) through its electrostatic interaction with an Aβ protein. This sensor can measure the length of color change from yellow to blue-green on a paper strip, with this change proportional to the amount of Aβ protein level. We found that the linearity for Aβ protein monitoring was in the range from 0.50 to 10.0 ng mL^-1, and the subsequent naked-eye detection limit for Aβ was 0.20 ng mL^-1. This system also provided high reproducibility and with no apparent interference effect for Aβ protein analysis in human urine samples. Furthermore, our developed dPAD constituted an accurate and effective device to precisely determine an Aβ protein concentration in real samples, with percentage recoveries in the range of 97-103%, and with the highest relative standard deviation of 5.41%. Subsequently, the validation of our assay was assessed by comparison with a commercial ELISA approach, with favorable results. Finally, the proposed dPAD was successfully applied to the determination of an Aβ protein in human urine samples and showed more benefits for the unskilled user, such as cost-efficiency, simplicity, low reagent usage, and low time consumption. It is also suitable for point-of-care monitoring.

Out with the old, in with the new: Could plasma exchange be used to fill a therapeutic gap in neurology?

The global tally of neurological disorders is exponentially rising and yet effective therapies for most remain evasive. There is a great deal of research into novel small molecules, immunotherapies and gene therapies to fill this therapeutic gap. We believe greater focus on plasma exchange as a research and clinical tool may provide useful insight into pathological mechanisms and effective treatment strategies. Plasma exchange has been traditionally used to treat antibody-mediated neurological diseases, such as myasthenia gravis and neuromyelitis optica, but there could be much wider future potential uses in neurology. Plasma exchange is not antibody specific, as it also removes a variety of other plasma-soluble factors, including age-related and disease-associated neurotoxic proteins, such as fibrinogen and amyloid. As research develops into the role of blood-brain barrier and immunological alterations in diseases not typically regarded as immune-driven, interest in neurotoxic plasma proteins grows. Here, we highlight that plasma exchange may have uses outside of antibody-mediated neurological diseases, by removing neurotoxic proteins from the systemic circulation.

Blood-based biomarkers for Alzheimer's disease

Neurodegenerative disorders such as Alzheimer's disease (AD) represent a mounting public health challenge. As these diseases are difficult to diagnose clinically, biomarkers of underlying pathophysiology are playing an ever-increasing role in research, clinical trials, and in the clinical work-up of patients. Though cerebrospinal fluid (CSF) and positron emission tomography (PET)-based measures are available, their use is not widespread due to limitations, including high costs and perceived invasiveness. As a result of rapid advances in the development of ultra-sensitive assays, the levels of pathological brain- and AD-related proteins can now be measured in blood, with recent work showing promising results. Plasma P-tau appears to be the best candidate marker during symptomatic AD (i.e., prodromal AD and AD dementia) and preclinical AD when combined with Aβ42/Aβ40. Though not AD-specific, blood NfL appears promising for the detection of neurodegeneration and could potentially be used to detect the effects of disease-modifying therapies. This review provides an overview of the progress achieved thus far using AD blood-based biomarkers, highlighting key areas of application and unmet challenges.

Controllable signal molecule release from Au NP-gated MSNs for photocathodic detection of ultralow level AβO

By integrating a target-responsive MSN-based controlled release system with a sensitization-SPR co-enhanced thionine/MoS₂ QDs/Cu NWs photocathode, a highly sensitive split-type PEC aptasensing platform for AβO detection in blood is constructed. Ultralow detection limit (2.1 fM) and high selectivity show great potential in early AD diagnosis.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Cobalt induces neurodegenerative damages through Pin1 inactivation in mice and human neuroglioma cells

Cobalt is a hazardous material that has harmful effects on neurotoxicity. Excessive exposure to cobalt or inactivation of the unique proline isomerase Pin1 contributes to age-dependent neurodegeneration. However, nothing is known about the role of Pin1 in cobalt-induced neurodegeneration. Here we find that out of several hazardous materials, only cobalt dose-dependently decreased Pin1 expression and alterations in its substrates, including cis and trans phosphorylated Tau in human neuronal cells, concomitant with neurotoxicity. Cobalt-induced neurotoxicity was aggravated by Pin1 genetic or chemical inhibition, but rescued by Pin1 upregulation. Furthermore, less than 4 μg/l of blood cobalt induced dose- and age-dependent Pin1 downregulation in murine brains, ensuing neurodegenerative changes. These defects were corroborated by changes in Pin1 substrates, including cis and trans phosphorylated Tau, amyloid precursor protein, β amyloid and GSK3β. Moreover, blood Pin1 was downregulated in human hip replacement patients with median blood cobalt level of 2.514 μg/l, which is significantly less than the safety threshold of 10 μg/l, suggesting an early role Pin1 played in neurodegenerative damages. Thus, Pin1 inactivation by cobalt contributes to age-dependent neurodegeneration, revealing that cobalt is a hazardous material triggering AD-like neurodegenerative damages.

The Role of Age on Beta-Amyloid1-42 Plasma Levels in Healthy Subjects

Beta-amyloid (Aβ) plaques have been observed in the brain of healthy elderlies with frequencies strongly influenced by age. The aim of the study is to evaluate the role of age and other biochemical and hematological parameters on Aβ_1–42 plasma levels in cognitively and neurologically normal individuals. Two-hundred and seventy-five normal subjects stratified by age groups (<35 years, 35–65 years, and >65 years) were included in the study. Aβ_1–42 plasma levels significantly correlated with age (r_s = 0.27; p < 0.0001) in the whole sample, inversely correlated with age in the first age group (r_s = −0.25, p = 0.01), positively correlated in the second group (r_s = 0.22, p = 0.03), while there was no significant correlation in the older group (r_s = 0.02, p = 0.86). Both age (β-estimate = 0.08; p < 0.001) and cholesterol (β-estimate = 0.03; p = 0.009) were significantly associated with Aβ_1–42 plasma level in multivariable analysis. However, only the association with age survived post hoc adjustment for multiple comparisons. The different effects of age on the Aβ level across age groups should be explored in further studies to better understand the age-dependent variability. This could better define the value of plasma Aβ as a biomarker of the Alzheimer neuropathology.

The validation status of blood biomarkers of amyloid and phospho-tau assessed with the 5-phase development framework for AD biomarkers

PURPOSE

The development of blood biomarkers that reflect Alzheimer's disease (AD) pathophysiology (phosphorylated tau and amyloid-β) has offered potential as scalable tests for dementia differential diagnosis and early detection. In 2019, the Geneva AD Biomarker Roadmap Initiative included blood biomarkers in the systematic validation of AD biomarkers.

METHODS

A panel of experts convened in November 2019 at a two-day workshop in Geneva. The level of maturity (fully achieved, partly achieved, preliminary evidence, not achieved, unsuccessful) of blood biomarkers was assessed based on the Biomarker Roadmap methodology and discussed fully during the workshop which also evaluated cerebrospinal fluid (CSF) and positron emission tomography (PET) biomarkers.

RESULTS

Plasma p-tau has shown analytical validity (phase 2 primary aim 1) and first evidence of clinical validity (phase 3 primary aim 1), whereas the maturity level for Aβ remains to be partially achieved. Full and partial achievement has been assigned to p-tau and Aβ, respectively, in their associations to ante-mortem measures (phase 2 secondary aim 2). However, only preliminary evidence exists for the influence of covariates, assay comparison and cut-off criteria.

CONCLUSIONS

Despite the relative infancy of blood biomarkers, in comparison to CSF biomarkers, much has already been achieved for phases 1 through 3 - with p-tau having greater success in detecting AD and predicting disease progression. However, sufficient data about the effect of covariates on the biomarker measurement is lacking. No phase 4 (real-world performance) or phase 5 (assessment of impact/cost) aim has been tested, thus not achieved.

Plasma Amyloid Concentration in Alzheimer's Disease: Performance of a High-Throughput Amyloid Assay in Distinguishing Alzheimer's Disease Cases from Controls

Background:

Collection of cerebrospinal fluid (CSF) for measurement of amyloid-β (Aβ) species is a gold standard in Alzheimer’s disease (AD) diagnosis, but has risks. Thus, establishing a low-risk blood Aβ test with high AD sensitivity and specificity is of outmost interest.

Objective:

We evaluated the ability of a commercially available plasma Aβ assay to distinguish AD patients from biomarker-healthy controls.

Method:

In a case-control design, we examined plasma samples from 44 AD patients (A + N+) and 49 controls (A–N–) from a memory clinic. AD was diagnosed using a combination of neuropsychological examination, CSF biomarker analysis and brain imaging. Total Aβ₄₀ and total Aβ₄₂ in plasma were measured through enzyme-linked immunosorbent assay (ELISA) technology using ABtest40 and ABtest42 test kits (Araclon Biotech Ltd.). Receiver operating characteristic (ROC) analyses with outcome AD were performed, and sensitivity and specificity were calculated.

Results:

Plasma Aβ_42/40 was weakly positively correlated with CSF Aβ_42/40 (Spearman’s rho 0.22; p = 0.037). Plasma Aβ_42/40 alone was not able to statistically significantly distinguish between AD patients and controls (AUC 0.58; 95% CI 0.46, 0.70). At a cut-point of 0.076 maximizing sensitivity and specificity, plasma Aβ_42/40 had a sensitivity of 61.2% and a specificity of 63.6%.

Conclusion:

In this sample, the high-throughput blood Aβ assay was not able to distinguish well between AD patients and controls. Whether or not the assay may be useful in large-scale epidemiological settings remains to be seen.

Biomarkers of Alzheimer Disease

BACKGROUND

Alzheimer disease (AD) was once a clinical diagnosis confirmed by postmortem autopsy. Today, with the development of AD biomarkers, laboratory assays to detect AD pathology are able to complement clinical diagnosis in symptomatic individuals with uncertain diagnosis. A variety of commercially available assays are performed as laboratory-developed tests, and many more are in development for both clinical and research purposes.

CONTENT

The role of laboratory medicine in diagnosing and managing AD is expanding; thus, it is important for laboratory professionals and ordering physicians to understand the strengths and limitations of both existing and emerging AD biomarker assays. In this review, we will provide an overview of the diagnosis of AD, discuss existing laboratory assays for AD and their recommended use, and examine the clinical performance of emerging AD biomarkers.

SUMMARY

The field of AD biomarker discovery and assay development is rapidly evolving, with recent studies promising to improve both the diagnosis of symptomatic individuals and enrollment and monitoring of asymptomatic individuals in research studies. However, care must be taken to ensure proper use and interpretation of these assays. For clinical purposes, these assays are meant to aid in diagnosis but are not themselves diagnostic. For individuals without symptoms, AD biomarker tests are still only appropriate for research purposes. Additionally, there are analytical challenges that require careful attention, especially for longitudinal use of AD tests.

Change in the plasma proteome associated with canine cognitive dysfunction syndrome (CCDS) in Thailand

BACKGROUND

Canine cognitive dysfunction syndrome (CCDS) is a progressive neurodegenerative disorder found in senior dogs. Due to the lack of biological markers, CCDS is commonly underdiagnosed. The aim of this study was to identify potential plasma biomarkers using proteomics techniques and to increase our understanding of the pathogenic mechanism of the disease. Plasma amyloid beta 42 (Aβ42) has been seen to be a controversial biomarker for CCDS. Proteomics analysis was performed for protein identification and quantification.

RESULTS

Within CCDS, ageing, and adult dogs, 87 proteins were identified specific to Canis spp. in the plasma samples. Of 87 proteins, 48 and 41 proteins were changed in the ageing and adult groups, respectively. Several distinctly expressed plasma proteins identified in CCDS were involved in complement and coagulation cascades and the apolipoprotein metabolism pathway. Plasma Aβ42 levels considerably overlapped within the CCDS and ageing groups. In the adult group, the Aβ42 level was low compared with that in the other groups. Nevertheless, plasma Aβ42 did not show a correlation with the Canine Cognitive Dysfunction Rating scale (CCDR) score in the CCDS group (p = 0.131, R2 = 0.261).

CONCLUSIONS

Our present findings suggest that plasma Aβ42 does not show potential for use as a diagnostic biomarker in CCDS. The nano-LC-MS/MS data revealed that the predictive underlying mechanism of CCDS was the co-occurrence of inflammation-mediated acute phase response proteins and complement and coagulation cascades that partly functioned by apolipoproteins and lipid metabolism. Some of the differentially expressed proteins may serve as potential predictor biomarkers along with Aβ42 in plasma for improved CCDS diagnosis. Further study in larger population-based cohort study is required in validation to define the correlation between protein expression and the pathogenesis of CCDS.

Functional nanoassemblies for the diagnosis and therapy of Alzheimer's diseases

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects populations around the world. Many therapeutics have been investigated for AD diagnosis and/or therapy, but the efficacy is largely limited by the poor bioavailability of drugs and by the presence of the blood-brain barrier. Recently, the development of nanomedicines enables efficient drug delivery to the brain, but the complex pathological mechanism of AD prevents them from successful treatment. As a type of advanced nanomedicine, multifunctional nanoassemblies self-assembled from nanoscale imaging or therapeutic agents can simultaneously target multiple pathological factors, showing great potential in the diagnosis and therapy of AD. To help readers better understand this emerging field, in this review, we first introduce the pathological mechanisms and the potential drug candidates of AD, as well as the design strategies of nanoassemblies for improving AD targeting efficiency. Moreover, the progress of dynamic nanoassemblies that can diagnose and/or treat AD in response to the endogenous or exogenous stimuli will be described. Finally, we conclude with our perspectives on the future development in this field. The objective of this review is to outline the latest progress of using nanoassemblies to overcome the complex pathological environment of AD for improved diagnosis and therapy, in hopes of accelerating the future development of intelligent AD nanomedicines. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

A Workshop on Cognitive Aging and Impairment in the 9/11-Exposed Population

The terrorist attacks on 11 September 2001 potentially exposed more than 400,000 responders, workers, and residents to psychological and physical stressors, and numerous hazardous pollutants. In 2011, the World Trade Center Health Program (WTCHP) was mandated to monitor and treat persons with 9/11-related adverse health conditions and conduct research on physical and mental health conditions related to the attacks. Emerging evidence suggests that persons exposed to 9/11 may be at increased risk of developing mild cognitive impairment. To investigate further, the WTCHP convened a scientific workshop that examined the natural history of cognitive aging and impairment, biomarkers in the pathway of neurodegenerative diseases, the neuropathological changes associated with hazardous exposures, and the evidence of cognitive decline and impairment in the 9/11-exposed population. Invited participants included scientists actively involved in health-effects research of 9/11-exposed persons and other at-risk populations. Attendees shared relevant research results from their respective programs and discussed several options for enhancements to research and surveillance activities, including the development of a multi-institutional collaborative research network. The goal of this report is to outline the meeting's agenda and provide an overview of the presentation materials and group discussion.

Kynurenic Acid Electrochemical Immunosensor: Blood-Based Diagnosis of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by a functional deterioration of the brain. Currently, there are selected biomarkers for its diagnosis in cerebrospinal fluid. However, its extraction has several disadvantages for the patient. Therefore, there is an urgent need for a detection method using sensitive and selective blood-based biomarkers. Kynurenic acid (KYNA) is a potential biomarker candidate for this purpose. The alteration of the KYNA levels in blood has been related with inflammatory processes in the brain, produced as a protective function when neurons are damaged. This paper describes a novel electrochemical immunosensor for KYNA detection, based on successive functionalization multi-electrode array. The resultant sensor was characterized by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The proposed biosensor detects KYNA within a linear calibration range from 10 pM to 100 nM using CA and EIS, obtaining a limit of detection (LOD) of 16.9 pM and 37.6 pM in buffer, respectively, being the lowest reported LOD for this biomarker. Moreover, to assess our device closer to the real application, the developed immunosensor was also tested under human serum matrix, obtaining an LOD of 391.71 pM for CA and 278.8 pM for EIS with diluted serum.

Evaluation of plasma amyloid peptides Aβ1-40 and Aβ1-42 as diagnostic biomarker of alzheimer's disease, its association with different grades of clinical severity and 18f-fluorodeoxyglucose positron emission tomography Z score in the Indian population: A case-control study

Background:

We estimated plasma amyloid-peptides levels (Aβ_1-42 and Aβ_1-40) as diagnostic biomarker of Alzheimer's disease (AD) and evaluated its association with clinical severity and 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) Z score of the different brain regions in the Indian population.

Patients and Methods:

A case-control study was conducted. Diagnostic and statistical manual-IV, Dubois, and NIA-AA criteria were used for the diagnosis of AD. The plasma Aβ_1-42 and Aβ_1-40 concentration and 18F-FDG PET Z score were estimated for different brain regions.

Results:

Forty-seven cognitive impairment patients (AD = 29, mild cognitive impairment = 18) and 33 age-matched controls were enrolled. Plasma Aβ_1-42 level was significantly higher in the AD group compared to controls (P = 0.046) and a cut-off >5.7 ng/mL has a specificity of 96.9%, sensitivity of 27.6%, positive predictive value 88.9%, and negative predictive value 60.4% for differentiating AD patients from controls. Significant correlation was seen between Aβ_1-40/Aβ_1-42 ratio and 18F-FDG PET Z score in the bilateral-parietal, temporal, frontal-association area, and posterior-cingulate areas.

Conclusion:

As a diagnostic biomarker of AD, plasma Aβ_1-42 level showed good specificity but low sensitivity in the Indian population.

Alzheimer's Disease and Vascular Aging: JACC Focus Seminar

Alzheimer’s disease, the leading cause of dementia in the elderly, is a neurodegenerative condition characterized by accumulation of amyloid plaques and neurofibrillary tangles in the brain. However, age-related vascular changes accompany or even precede the development of Alzheimer’s pathology, raising the possibility that they may have a pathogenic role. This review provides an appraisal of the alterations in cerebral and systemic vasculature, the heart, and hemostasis that occur in Alzheimer’s disease and their relationships to cognitive impairment. Although the molecular pathogenesis of these alterations remains to be defined, amyloid-β is a likely contributor in the brain as in the heart. Collectively, the evidence suggests that vascular pathology is a likely pathogenic contributor to age-related dementia, including Alzheimer’s disease, inextricably linked to disease onset and progression. Consequently, the contribution of vascular factors should be considered in preventive, diagnostic, and therapeutic approaches to address one of the major health challenges of our time.

Assessment of Plasma Amyloid-β42/40 and Cognitive Decline Among Community-Dwelling Older Adults

IMPORTANCE

Plasma measurement of amyloid-β (Aβ) peptides has been associated with cognitive function, but evidence of its ability to identify cognitive decline is still scarce.

OBJECTIVE

To investigate the associations between plasma Aβ42/40 and cognitive decline over time among community-dwelling older adults with subjective memory concerns.

DESIGN, SETTING, AND PARTICIPANTS

This multicenter cohort study used data from volunteers in the 5-year study Multidomain Alzheimer Preventive Trial (MAPT). Participants were aged 70 years or older and observed for a median (interquartile range) of 3.9 (2.0-4.0) years. Recruitment of participants started in May 2008 and ended in February 2011. Follow-up ended in April 2016. Data analysis was conducted from April to October 2020.

EXPOSURE

Plasma Aβ42 and Aβ40 were measured at 12 months for 448 participants (92.8%) and at 24 months for the rest. The moment of Aβ assessment was defined as the baseline for this study.

MAIN OUTCOMES AND MEASURES

Cognitive function was assessed at 12, 24, 36, 48, and 60 months by a composite cognitive score based on 4 tests; Mini Mental State Examination (MMSE); Clinical Dementia Rating, sum of boxes; and Alzheimer Disease Cooperative Study-Activities of Daily Living. Mixed-effect linear regressions were performed.

RESULTS

A total of 483 participants (median [IQR] age, 76.0 [73.0-80.0]; 286 [59.2%] women) were analyzed. Of them, 161 (33.3%) were classified as low plasma Aβ42/40 (≤0.107). After adjusting for age, sex, education, body mass index, Geriatric Depression Scale score, apolipoprotein E ε4 genotype, and MAPT intervention groups, low plasma Aβ42/40 was associated with more pronounced decline in composite cognitive score (adjusted between-group mean difference: -0.20, 95% CI, -0.34 to -0.07; P = .004) and decline in MMSE score (adjusted between-group mean difference: -0.59; 95% CI, -1.07 to -0.11; P = .02) during the follow-up period compared with the group with an Aβ42/40 ratio greater than 0.107.

CONCLUSIONS AND RELEVANCE

In this study, low plasma Aβ42/40 was associated with more pronounced decline in cognitive function (measured by multiple outcomes) over time. Findings suggest that plasma Aβ42/40 may be used to identify people at risk of cognitive decline, being an alternative to more complex and expensive measures, such as positron emission tomography imaging or cerebrospinal fluid measurement.

Peripheral Glycolysis in Neurodegenerative Diseases

Neurodegenerative diseases are a group of nervous system conditions characterised pathologically by the abnormal deposition of protein throughout the brain and spinal cord. One common pathophysiological change seen in all neurodegenerative disease is a change to the metabolic function of nervous system and peripheral cells. Glycolysis is the conversion of glucose to pyruvate or lactate which results in the generation of ATP and has been shown to be abnormal in peripheral cells in Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis. Changes to the glycolytic pathway are seen early in neurodegenerative disease and highlight how in multiple neurodegenerative conditions pathology is not always confined to the nervous system. In this paper, we review the abnormalities described in glycolysis in the three most common neurodegenerative diseases. We show that in all three diseases glycolytic changes are seen in fibroblasts, and red blood cells, and that liver, kidney, muscle and white blood cells have abnormal glycolysis in certain diseases. We highlight there is potential for peripheral glycolysis to be developed into multiple types of disease biomarker, but large-scale bio sampling and deciphering how glycolysis is inherently altered in neurodegenerative disease in multiple patients' needs to be accomplished first to meet this aim.

Indicators of rapid cognitive decline in amnestic mild cognitive impairment: The role of plasma biomarkers using magnetically labeled immunoassays

Plasma levels of biomarkers change with the progression of Alzheimer's disease (AD), which involves the accumulation of pathological amyloid β (Aβ) and Tau protein tangles. However, few studies have investigated the association between plasma biomarkers and rapid cognitive decline in patients with amnestic mild cognitive impairment (aMCI) and AD. A total of 10 healthy controls, 24 patients with aMCI, and 19 patients with AD were enrolled. All participants underwent twice Mini-Mental State Examination (MMSE), with a mean 1.2 year interval. Immunomagnetic reduction was utilized to evaluate levels of plasma biomarkers, including amyloid β 1-40 (Aβ_1-40), Aβ_1-42, total Tau protein, phosphorylated Tau protein (Threonine 181), and α-synuclein (α-Syn). The correlations between plasma levels of biomarkers and MMSE change were examined. Our analysis reveals that current higher plasma levels of Aβ_1-42 and α-Syn with the cut-off value of plasma Aβ_1-42 >17.26 pg/mL and α-Syn >105 fg/mL had a moderate-to-high discriminatory capacity (area under the curve >0.70) for identifying cognitive deterioration in patients with aMCI. Our results thus suggest that plasma levels of Aβ_1-42 and α-Syn may be considered as useful markers to assess the severity of global cognitive decline in patients with aMCI.

Multiplexed femtomolar detection of Alzheimer's disease biomarkers in biofluids using a reduced graphene oxide field-effect transistor

Alzheimer's disease (AD) is a neurodegenerative disease that accounts for 70% of all dementia. Early stage diagnosis of AD is essential as there is no certain treatment after the lesion has progressed in the late stage. Nevertheless, there are still limitations of early diagnosis of AD using neuroimaging and psychological memory assessments. Here, we demonstrate ultrasensitive and multiplexed detection of pivotal AD biomarkers (Aβ_1-42 and t-Tau) in biofluids using a reduced graphene oxide field-effect transistor (gFET). The proposed approach provides a wide logarithmically linear range of detection from 10^-1-10⁵ pg mL^-1 and a femtomolar-level limit of detection in biofluids (human plasma and artificial cerebrospinal fluid) as well as phosphate-buffered saline (PBS). Furthermore, as these core biomarkers have different surface charges in physiological conditions based on the isoelectric point (pI), we achieved a distinctive output signal for each biomarker. The gFET biosensor platform presented in this paper has great potential and can be used for early diagnosis of AD in clinical practice as well as accurate analysis based on the surface charge of the analytes.

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

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

Chronic Administration of Scopolamine Increased GSK3βP9, Beta Secretase, Amyloid Beta, and Oxidative Stress in the Hippocampus of Wistar Rats

The increase of amyloid beta (Aβ) release and hyperphosphorylation of Tau protein represents the main events related to Alzheimer's disease (AD). Furthermore, the sporadic type represents the most common form of AD. Therefore, the establishment of a non-transgenic animal model that resembles the characteristics of the disease is of particular importance. Scopolamine has been linked to increases in both Aβ production and oxidative stress in rat and mice brains. Thus, the purpose of the present work was to identify changes in biomarkers that are related to AD after chronic administration of scopolamine (2 mg/kg i.p., during 6 and 12 weeks) to male Wistar rats. The results showed increased Aβ deposition at rat hippocampus which could be due to an increase of β-site amyloid-β-protein precursor cleaving enzyme 1 (BACE1) expression and activity. These findings could be related to the increase of glycogen synthase kinase 3 phosphorylated (GSK3βP9) expression. Finally, the establishment of a state of oxidative stress in groups treated with scopolamine was demonstrated by an increase in free radical content and MDA levels. The present study facilitates our understanding of the changes that occur in biomolecules related to AD in Wistar rats after the chronic administration of scopolamine.

Proteomics as a reliable approach for discovery of blood-based Alzheimer's disease biomarkers: A systematic review and meta-analysis

In order to gauge the impact of proteomics in discovery of Alzheimer's disease (AD) blood-based biomarkers, this study had systematically reviewed articles published between 1984-2019. Articles that fulfilled the inclusion criteria were assessed for risk of bias. A meta-analysis was performed for replicable candidate biomarkers (CB). Of the 1651 articles that were identified, 17 case-control and two cohort studies, as well as three combined case-control and longitudinal designs were shortlisted. A total of 207 AD and mild cognitive impairment (MCI) CB were discovered, with 48 reported in >2 studies. This review highlights six CB, namely alpha-2-macroglobulin (α2M)_ps, pancreatic polypeptide (PP)_ps, apolipoprotein A-1 (ApoA-1)_ps, afamin_p, insulin growth factor binding protein-2 (IGFBP-2)_ps and fibrinogen-γ-chain_p, all of which exhibited consistent pattern of regulation in >three independent cohorts. They are involved in AD pathogenesis via amyloid-beta (Aβ), neurofibrillary tangles, diabetes and cardiovascular diseases (CVD). Meta-analysis indicated that ApoA-1_ps was significantly downregulated in AD (SMD = -1.52, 95% CI: -1.89, -1.16, p < 0.00001), with low inter-study heterogeneity (I² = 0%, p = 0.59). α2M_ps was significantly upregulated in AD (SMD = 0.83, 95% CI: 0.05, 1.62, p = 0.04), with moderate inter-study heterogeneity (I² = 41%, p = 0.19). Both CB are involved in Aβ formation. These findings provide important insights into blood-based AD biomarkers discovery via proteomics.