Plasma Levels of Aβ42 and Tau Identified Probable Alzheimer's Dementia: Findings in Two Cohorts

Evaluating the diagnostic performance of six plasma biomarkers for Alzheimer's disease and other neurodegenerative dementias in a large Chinese cohort

BACKGROUND

Ethnic variations and detection methods may lead to differences in diagnostic biomarkers of dementia, and few comparative studies have evaluated the six plasma biomarkers of Alzheimer's disease (AD) and other neurodegenerative dementias in the Chinese population.

METHODS

A cross-sectional cohort of 668 participants were enrolled, including 245 amnesic mild cognitive impairment (aMCI) or AD patients with Aβ positive pathology, 67 with frontotemporal dementia (FTD), 100 with progressive supranuclear palsy (PSP), 72 with dementia with Lewy bodies (DLB) and 184 healthy controls. Additionally, a longitudinal subset of 19 aMCI and 30 AD patients was followed for an average period of 1 year. Plasma biomarkers, including p-tau181, p-tau217, p-tau231, NfL, GFAP, and α-synuclein, were simultaneously measured using a novel single molecular array method. Aβ42 and p-tau181 levels in CSF, amyloid PET and structural MRI were measured.

RESULTS

Plasma p-tau217 and p-tau231 were most effective in diagnosing aMCI/AD (AUC = 0.95 and 0.93, respectively), while p-tau217, p-tau231 and p-tau181 presented the best differential diagnosis for AD from PSP, FTD and DLB respectively (AUC = 0.84, 0.81 and 0.83). α-synuclein was presented as the best biomarker for PSP variant and behavior variant FTD subtypes (AUC = 0.81 and 0.74, respectively). Among them, p-tau217, p-tau231, GFAP and a-synuclein were negatively correlated with CSF Aβ42/40, while p-tau217 and GFAP were positively correlated with CSF p-tau181. Besides, p-tau181, p-tau217, and GFAP were associated with temporal lobe volume, while p-tau231 and GFAP were associated with frontal lobe volume. Longitudinal analysis showed the higher p-tau181 could predict the cognitive decline progression.

CONCLUSIONS

This study validate the practicality of blood biomarkers in the Chinese Han population using a novel single molecule immune detection method. Through the clinical performance study for several biomarkers, we found the plasma p-tau217 was the most effective biomarker in AD diagnosis, and p-tau showed high accuracy for differential diagnosis of AD from other dementia, GFAP is associated with multiple aspects of AD pathology, and frontal and temporal lobe volume, and p-tau181 can reflect the dynamic cognitive decline of AD.

Ultrasensitive Assays Detect Different Conformations of Plasma β Amyloids

With the developments of ultrasensitive technologies such as immunomagnetic reduction (IMR) assay, single molecule array (SIMOA) assay, electrochemiluminescence immunoassay (ECLIA), the assay of blood-based amyloid 1-42 (Aβ1-42) becomes possible. However, the changes in measured plasma Aβ1-42 concentrations in Alzheimer's disease (AD) compared to cognitively unimpaired subjects (CU) are inconsistent. A possible reason for the inconsistency regarding various conformations of Aβ1-42 in plasma is explored in this study. Three samples with equal amounts of Aβ1-42 but different proportions of monomers and oligomers of Aβ1-42 were prepared. The Aβ1-42 composition of monomers and oligomers in samples was analyzed with Western blot. Identically diluted versions of these three samples were assayed with IMR and SIMOA for Aβ1-42 concentrations. The three diluted samples showed similar levels of Aβ1-42 assayed with IMR, whereas much lower levels for samples with more oligomers assayed with SIOMA. The results imply that IMR detects both monomers and oligomers of Aβ1-42. The measured levels of Aβ1-42 are independent of the proportions of monomer or oligomer Aβ1-42 but depend on the total amounts of Aβ1-42. In the case of SIMOA, monomers of Aβ1-42 are the primary target measured. By comparing Aβ1-42 concentrations of the plasma using IMR and SIMOA, the significant difference in plasma Aβ1-42 levels using IMR in AD compared to CU is mainly due to the formations of oligomeric Aβ1-42. Therefore, if the target molecules are monomers of Aβ1-42, SIMOA is the method of choice. Still, if the target molecules should include monomers, small and large oligomers, IMR would be an optimal consideration. In the future, the clinical implications of the proportion of oligomeric Aβ1-42 need to be elucidated.

Mediating role of obstructive sleep apnea in altering slow-wave activity and elevating Alzheimer's disease risk: Pilot study from a northern Taiwan cohort

OBJECTIVES

Obstructive sleep apnea is associated with alterations in slow-wave activity during sleep, potentially increasing the risk of Alzheimer's disease. This study investigated the associations between obstructive sleep apnea manifestations such as respiratory events, hypoxia, arousal, slow-wave patterns, and neurochemical biomarker levels.

METHODS

Individuals with suspected obstructive sleep apnea underwent polysomnography. Sleep disorder indices, oxygen metrics, and slow-wave activity data were obtained from the polysomnography, and blood samples were taken the following morning to determine the plasma levels of total tau (T-Tau) and amyloid beta-peptide 42 (Aβ42) by using an ultrasensitive immunomagnetic reduction assay. Subsequently, the participants were categorized into groups with low and high Alzheimer's disease risk on the basis of their computed product Aβ42 × T-Tau. Intergroup differences and the associations and mediation effects between sleep-related parameters and neurochemical biomarkers were analyzed.

RESULTS

Forty-two participants were enrolled, with 21 assigned to each of the low- and high-risk groups. High-risk individuals had a higher apnea-hypopnea index, oxygen desaturation index (≥3%, ODI-3%), fraction of total sleep time with oxygen desaturation (SpO2-90% TST), and arousal index and greater peak-to-peak amplitude and slope in slow-wave activity, with a correspondingly shorter duration, than did low-risk individuals. Furthermore, indices such as the apnea-hypopnea index, ODI-3% and SpO2-90% TST were found to indirectly affect slow-wave activity, thereby raising the Aβ42 × T-Tau level.

CONCLUSIONS

Obstructive sleep apnea manifestations, such as respiratory events and hypoxia, may influence slow-wave sleep activity (functioning as intermediaries) and may be linked to elevated neurochemical biomarker levels. However, a longitudinal study is necessary to determine causal relationships among these factors.

STATEMENT OF SIGNIFICANCE

This research aims to bridge gaps in understanding how obstructive sleep apnea is associated with an elevated risk of Alzheimer's disease, providing valuable knowledge for sleep and cognitive health.

Application of blood-based biomarkers of Alzheimer's disease in clinical practice: Recommendations from Taiwan Dementia Society

Blood-based biomarkers (BBM) are potentially powerful tools that assist in the biological diagnosis of Alzheimer's disease (AD) in vivo with minimal invasiveness, relatively low cost, and good accessibility. This review summarizes current evidence for using BBMs in AD, focusing on amyloid, tau, and biomarkers for neurodegeneration. Blood-based phosphorylated tau and the Aβ42/Aβ40 ratio showed consistent concordance with brain pathology measured by CSF or PET in the research setting. In addition, glial fibrillary acidic protein (GFAP) and neurofilament light chain (NfL) are neurodegenerative biomarkers that show the potential to assist in the differential diagnosis of AD. Other pathology-specific biomarkers, such as α-synuclein and TAR DNA-binding protein 43 (TDP-43), can potentially detect AD concurrent pathology. Based on current evidence, the working group from the Taiwan Dementia Society (TDS) achieved consensus recommendations on the appropriate use of BBMs for AD in clinical practice. BBMs may assist clinical diagnosis and prognosis in AD subjects with cognitive symptoms; however, the results should be interpreted by dementia specialists and combining biochemical, neuropsychological, and neuroimaging information. Further studies are needed to evaluate BBMs' real-world performance and potential impact on clinical decision-making.

The Inflammasome Adaptor Protein ASC in Plasma as a Biomarker of Early Cognitive Changes

Dementia is a group of symptoms including memory loss, language difficulties, and other types of cognitive and functional impairments that affects 57 million people worldwide, with the incidence expected to double by 2040. Therefore, there is an unmet need to develop reliable biomarkers to diagnose early brain impairments so that emerging interventions can be applied before brain degeneration. Here, we performed biomarker analyses for apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), and amyloid-β 42/40 (Aβ42/40) ratio in the plasma of older adults. Participants had blood drawn at baseline and underwent two annual clinical and cognitive evaluations. The groups tested either cognitively normal on both evaluations (NN), cognitively normal year 1 but cognitively impaired year 2 (NI), or cognitively impaired on both evaluations (II). ASC was elevated in the plasma of the NI group compared to the NN and II groups. Additionally, Aβ42 was increased in the plasma in the NI and II groups compared to the NN group. Importantly, the area under the curve (AUC) for ASC in participants older than 70 years old in NN vs. NI groups was 0.81, indicating that ASC is a promising plasma biomarker for early detection of cognitive decline.

Longitudinal assessment of plasma biomarkers for early detection of cognitive changes in subjective cognitive decline

Background

Individuals experiencing subjective cognitive decline (SCD) are at an increased risk of developing mild cognitive impairment and dementia. Early identification of SCD and neurodegenerative diseases using biomarkers may help clinical decision-making and improve prognosis. However, few cross-sectional and longitudinal studies have explored plasma biomarkers in individuals with SCD using immunomagnetic reduction.

Objective

To identify plasma biomarkers for SCD.

Methods

Fifty-two participants [38 with SCD, 14 healthy controls (HCs)] underwent baseline assessments, including measurements of plasma Aβ42, Aβ40, t-tau, p-tau, and α-synuclein using immunomagnetic reduction (IMR) assays, cognitive tests and the Mini-Mental State Examination (MMSE). Following initial cross-sectional analysis, 39 individuals (29 with SCD, 10 HCs) entered a longitudinal phase for reassessment of these biomarkers and the MMSE. Biomarker outcomes across different individual categories were primarily assessed using the area under the receiver operating characteristic (ROC) curve. The SCD subgroup with an MMSE decline over one point was compared to those without such a decline.

Results

Higher baseline plasma Aβ1-42 levels significantly discriminated participants with SCD from HCs, with an acceptable area under the ROC curve (AUC) of 67.5% [95% confidence interval (CI), 52.7-80.0%]. However, follow-up and changes in MMSE and IMR data did not significantly differ between the SCD and HC groups (p > 0.05). Furthermore, lower baseline plasma Aβ1-42 levels were able to discriminate SCD subgroups with and without cognitive decline with a satisfied performance (AUC, 75.0%; 95% CI, 55.6-89.1%). At last, the changes in t-tau and Aβ42 × t-tau could differentiate between the two SCD subgroups (p < 0.05).

Conclusion

Baseline plasma Aβ42 may help identify people with SCD and predict SCD progression. The role of plasma Aβ42 levels as well as their upward trends from baseline in cases of SCD that progress to mild cognitive impairment and Alzheimer's disease require further investigation.

The free plasma amyloid Aβ1-42/Aβ1-40 ratio predicts conversion to dementia for subjects with mild cognitive impairment with performance equivalent to that of the total plasma Aβ1-42/Aβ1-40 ratio. The BALTAZAR study

BACKGROUND AND PURPOSE

Blood-based biomarkers are a non-invasive solution to predict the risk of conversion of mild cognitive impairment (MCI) to dementia. The utility of free plasma amyloid peptides (not bound to plasma proteins and/or cells) as an early indicator of conversion to dementia is still debated, as the results of studies have been contradictory. In this context, we investigated whether plasma levels of the free amyloid peptides Aβ1-42 and Aβ1-40 and the free plasma Aβ1-42/Aβ1-40 ratio are associated with the conversion of MCI to dementia, in particular AD, over three years of follow-up in a subgroup of the BALTAZAR cohort. We also compared their predictive value to that of total plasma Aβ1-42 and Aβ1-40 levels and the total plasma Aβ1-42/Aβ1-40 ratio.

METHODS

The plasma Aβ1-42 and Aβ1-40 peptide assay was performed using the INNO-BIA kit (Fujirebio Europe). Free amyloid levels (defined by the amyloid fraction directly accessible to antibodies of the assay) were obtained with the undiluted plasma, whereas total amyloid levels were obtained after the dilution of plasma (1/3) with a denaturing buffer. Free and total Aβ1-42 and Aβ1-40 levels were measured at inclusion for a subgroup of participants (N = 106) with mild cognitive impairment (MCI) from the BALTAZAR study (a large-scale longitudinal multicenter cohort with a three-year follow-up). Associations between conversion and the free/total plasma Aβ1-42 and Aβ1-40 levels and Aβ1-42/Aβ1-40 ratio were analyzed using logistic and Cox Proportional Hazards models. Demographic, clinical, cognitive (MMSE, ADL and IADL), APOE, and MRI characteristics (relative hippocampal volume) were compared using non-parametric (Mann-Whitney) or parametric (Student) tests for quantitative variables and Chi-square or Fisher exact tests for qualitative variables.

RESULTS

The risk of conversion to dementia was lower for patients in the highest quartile of free plasma Aβ1-42/Aβ1-40 (≥ 25.8%) than those in the three lower quartiles: hazard ratio = 0.36 (95% confidence interval [0.15-0.87]), after adjustment for age, sex, education, and APOE ε4 (p-value = 0.022). This was comparable to the risk of conversion in the highest quartile of total plasma Aβ1-42/Aβ1-40: hazard ratio = 0.37 (95% confidence interval [0.16-0.89], p-value = 0.027). However, while patients in the highest quartile of total plasma Aβ1-42/Aβ1-40 showed higher MMSE scores and a higher hippocampal volume than patients in the three lowest quartiles of total plasma Aβ1-42/Aβ1-40, as well as normal CSF biomarker levels, the patients in the highest quartile of free plasma Aβ1-42/Aβ1-40 did not show any significant differences in MMSE scores, hippocampal volume, or CSF biomarker levels relative to the three lowest quartiles of free plasma Aβ1-42/Aβ1-40.

CONCLUSION

The free plasma Aβ1-42/Aβ1-40 ratio is associated with a risk of conversion from MCI to dementia within three years, with performance comparable to that of the total plasma Aβ1-42/Aβ1-40 ratio. Threshold levels of the free and total plasma Aβ1-42/Aβ1-40 ratio could be determined, with a 60% lower risk of conversion for patients above the threshold than those below.

Polydopamine-coated hexagonal boron nitride-based electrochemical immunosensing of T-Tau as a marker of Alzheimer's disease

Alzheimer's disease (AD) is a complex pathological process that is one of the leading causes of dementia globally. The demand for diagnostic tools that are minimally invasive, timely, and accurate is on the rise. Total tau (T-Tau) protein in blood serum is a promising biomarker for predicting early-stage AD diagnosis. In this study, the hexagonal boron nitride (HBN) based immunosensor platform was developed to detect T-Tau in artificial blood serum. After the exfoliation of HBN, its surface was coated with polydopamine (PDA) in alkaline conditions. The Anti-T-Tau was immobilized on a hydrophilic nanocomposite surface using PDA's reactive catechol and quinone groups, eliminating the need for extra crosslinkers. The working electrode surface of the screen-printed carbon electrode (SPCE) was coated with HBN-PDA nanocomposite using the drop-casting method. The biofunctional surface was created by directly immobilizing Anti-T-Tau on the HBN-PDA nanocomposite-modified SPCE. The analytical performance of the HBN-PDA/Anti-T-Tau/T-Tau immunosensor in the presence of T-Tau isoforms was determined through electrochemical measurements. The linear detection range was 1-30 pg/mL with a detection limit of 0.42 pg/mL for T-Tau, which is suitable for detecting T-Tau in the blood serum.

Protein aggregation and neurodegenerative disease: Structural outlook for the novel therapeutics

Before the controversial approval of humanized monoclonal antibody lecanemab, which binds to the soluble amyloid-β protofibrils, all the treatments available earlier, for Alzheimer's disease (AD) were symptomatic. The researchers are still struggling to find a breakthrough in AD therapeutic medicine, which is partially attributable to lack in understanding of the structural information associated with the intrinsically disordered proteins and amyloids. One of the major challenges in this area of research is to understand the structural diversity of intrinsically disordered proteins under in vitro conditions. Therefore, in this review, we have summarized the in vitro applications of biophysical methods, which are aimed to shed some light on the heterogeneity, pathogenicity, structures and mechanisms of the intrinsically disordered protein aggregates associated with proteinopathies including AD. This review will also rationalize some of the strategies in modulating disease-relevant pathogenic protein entities by small molecules using structural biology approaches and biophysical characterization. We have also highlighted tools and techniques to simulate the in vivo conditions for native and cytotoxic tau/amyloids assemblies, urge new chemical approaches to replicate tau/amyloids assemblies similar to those in vivo conditions, in addition to designing novel potential drugs.

Plasma levels of phosphorylated tau and neurofilament light chain as potential biomarkers for Alzheimer's disease: A biochemical analysis in Pakistani population

The National Institute on Aging-Alzheimer's Association's research framework in 2018 proposed a molecular construct for the diagnosis of Alzheimer's disease (AD). Nonetheless, the clinical exclusionary strategy is still the mainstay of AD diagnosis in Pakistan. We looked at the plasma levels of amyloid beta-42 (Aβ-42), phosphorylated tau (P-tau), and neurofilament light (NFL) in patients with Alzheimer's clinical syndrome (ACS) and healthy controls (HC) from the Pakistani population to keep pace with the global efforts towards establishing accessible and affordable biochemical diagnostic markers for AD in Pakistan. Consultant neurologists screened patients who presented with cognitive impairment to three large tertiary care hospitals in Karachi, and after receiving informed consent, recruited participants with ACS and HC from the same facilities. We collected 5cc of blood in EDTA tubes along with demographic and lifestyle information of the subjects. Plasma aliquots were stored at -80°C after centrifugation. For analysis it was thawed at 4℃ and levels of the three proteins were measured through ELISA. Data from 28 ACS patients and 28 age matched healthy controls were evaluated. Among demographic factors, education and depression were related with health status (p = 0.03 and 0.003, respectively). NFL and P-tau mean values demonstrated a significant difference between the ACS and control groups (p = 0.003 and 0.006), however Aβ42 did not (p = 0.114). ROC analysis showed that plasma P-tau and NFL, with AUCs of 0.717 and 0.735, respectively, could substantially distinguish ACS from the HC group (p = 0.007 and 0.003, respectively). Both plasma P-tau (r = -0.389; p = 0.004) and NFL (r = -0.424; p = 0.001) levels were significantly and negatively correlated with individuals' MMSE scores. NFL and plasma P-tau show promise in differentiating AD patients from healthy individuals. However, similar larger studies are needed to validate our findings.

Early Diagnosis of Alzheimer's Disease with Blood Test; Tempting but Challenging

The increasing prevalence of Alzheimer's disease (AD) has led to a health crisis. According to official statistics, more than 55 million people globally have AD or other types of dementia, making it the sixth leading cause of death. It is still difficult to diagnose AD and there is no definitive diagnosis yet; post-mortem autopsy is still the only definite method. Moreover, clinical manifestations occur very late in the course of disease progression; therefore, profound irreversible changes have already occurred when the disease manifests. Studies have shown that in the preclinical stage of AD, changes in some biomarkers are measurable prior to any neurological damage or other symptoms. Hence, creating a reliable, fast, and affordable method capable of detecting AD in early stage has attracted the most attention. Seeking clinically applicable, inexpensive, less invasive, and much more easily accessible biomarkers for early diagnosis of AD, blood-based biomarkers (BBBs) seem to be an ideal option. This review is an inclusive report of BBBs that have been shown to be altered in the course of AD progression. The aim of this report is to provide comprehensive insight into the research status of early detection of AD based on BBBs.

Machine Learning-Based Classification of Subjective Cognitive Decline, Mild Cognitive Impairment, and Alzheimer's Dementia Using Neuroimage and Plasma Biomarkers

Alzheimer's disease (AD) progresses relentlessly from the preclinical to the dementia stage. The process begins decades before the diagnosis of dementia. Therefore, it is crucial to detect early manifestations to prevent cognitive decline. Recent advances in artificial intelligence help tackle the complex high-dimensional data encountered in clinical decision-making. In total, we recruited 206 subjects, including 69 cognitively unimpaired, 40 subjective cognitive decline (SCD), 34 mild cognitive impairment (MCI), and 63 AD dementia (ADD). We included 3 demographic, 1 clinical, 18 brain-image, and 3 plasma biomarker (Aß_1-42, Aß_1-40, and tau protein) features. We employed the linear discriminant analysis method for feature extraction to make data more distinguishable after dimension reduction. The sequential forward selection method was used for feature selection to identify the 12 best features for machine learning classifiers. We used both random forest and support vector machine as classifiers. The area under the receiver operative curve (AUROC) was close to 0.9 between diseased (combining ADD and MCI) and the controls. AUROC was higher than 0.85 between SCD and controls, 0.90 between MCI and SCD, and above 0.85 between ADD and MCI. We can differentiate between adjacent phases of the AD spectrum with blood biomarkers and brain MR images with the help of machine learning algorithms.

Plasma amyloid beta predicts conversion to dementia in subjects with mild cognitive impairment: The BALTAZAR study

INTRODUCTION

Blood-based biomarkers are the next challenge for Alzheimer's disease (AD) diagnosis and prognosis.

METHODS

Mild cognitive impairment (MCI) participants (N = 485) of the BALTAZAR study, a large-scale longitudinal multicenter cohort, were followed-up for 3 years. A total of 165 of them converted to dementia (95% AD). Associations of conversion and plasma amyloid beta (Aβ)_1-42 , Aβ_1-40 , Aβ_1-42 /Aβ_1-40 ratio were analyzed with logistic and Cox models.

RESULTS

Converters to dementia had lower level of plasma Aβ_1-42 (37.1 pg/mL [12.5] vs. 39.2 [11.1] , P value = .03) and lower Aβ_1-42 /Aβ_1-40 ratio than non-converters (0.148 [0.125] vs. 0.154 [0.076], P value = .02). MCI participants in the highest quartile of Aβ_1-42 /Aβ_1-40 ratio (>0.169) had a significant lower risk of conversion (hazard ratio adjusted for age, sex, education, apolipoprotein E ε4, hippocampus atrophy = 0.52 (95% confidence interval [0.31-0.86], P value = .01).

DISCUSSION

In this large cohort of MCI subjects we identified a threshold for plasma Aβ_1-42 /Aβ_1-40 ratio that may detect patients with a low risk of conversion to dementia within 3 years.

Associations between risk of Alzheimer's disease and obstructive sleep apnea, intermittent hypoxia, and arousal responses: A pilot study

OBJECTIVES

Obstructive sleep apnea (OSA) may increase the risk of Alzheimer's disease (AD). However, potential associations among sleep-disordered breathing, hypoxia, and OSA-induced arousal responses should be investigated. This study determined differences in sleep parameters and investigated the relationship between such parameters and the risk of AD.

METHODS

Patients with suspected OSA were recruited and underwent in-lab polysomnography (PSG). Subsequently, blood samples were collected from participants. Patients' plasma levels of total tau (T-Tau) and amyloid beta-peptide 42 (Aβ42) were measured using an ultrasensitive immunomagnetic reduction assay. Next, the participants were categorized into low- and high-risk groups on the basis of the computed product (Aβ42 × T-Tau, the cutoff for AD risk). PSG parameters were analyzed and compared.

RESULTS

We included 36 patients in this study, of whom 18 and 18 were assigned to the low- and high-risk groups, respectively. The average apnea-hypopnea index (AHI), apnea, hypopnea index [during rapid eye movement (REM) and non-REM (NREM) sleep], and oxygen desaturation index (≥3%, ODI-3%) values of the high-risk group were significantly higher than those of the low-risk group. Similarly, the mean arousal index and respiratory arousal index (R-ArI) of the high-risk group were significantly higher than those of the low-risk group. Sleep-disordered breathing indices, oxygen desaturation, and arousal responses were significantly associated with an increased risk of AD. Positive associations were observed among the AHI, ODI-3%, R-ArI, and computed product.

CONCLUSIONS

Recurrent sleep-disordered breathing, intermittent hypoxia, and arousal responses, including those occurring during the NREM stage, were associated with AD risk. However, a longitudinal study should be conducted to investigate the causal relationships among these factors.

Sera miR-34a, miR-29b and miR-181c as potential novel diagnostic biomarker panel for Alzheimers in the Egyptian population

BACKGROUND

Till date, there is an obvious obscurity of specific and early diagnostic biomarkers for Alzheimer's disease (AD). The promising diagnostic potential of serum miRNAs is increasingly emerging; however, rare miRNAs data originates from middle and low-income countries to provide proper validation in these highly affected populations. This study evaluated the diagnostic value of serum miR-34a, miR-29b and miR-181c in Egyptian AD patients.

METHODS

Expression levels of serum miR-34a, miR-29b and miR-181c were determined using quantitative real time PCR in AD patients versus healthy controls. Amyloid Beta 42 (Aβ42), Phosphorylated Tau (p-Tau) and TNF-α levels were also detected as distinctive AD markers. We further explored the correlation between miRNAs levels and Mini mental state examination (MMSE) scores. Finally, we conducted logistic regression and ROC curve analyses to evaluate the diagnostic values of the measured parameters.

RESULTS

Sera miR-34a, miR-29b and miR-181c were significantly downregulated in AD patients and this decrease was associated with cognitive decline. AD patients manifested significant elevation of Aβ42, pTau and TNF-α levels. The measured miRNAs showed good AD diagnostic value solely and when used together (AUC = 0.77, 95 % C·I. 0.62-0.93 at p < 0.01). Interestingly, combining miRNAs panel with Aβ42, TNF-α and pTau levels remarkably increased the diagnostic power (AUC = 0.97, 95 % C·I. 0.94-1.00 at p < 0.001) achieving sensitivity 88.2 % and specificity 91.4 %.

CONCLUSION

This study spots for the first time the diagnostic potential of serum miR-34a, miR-29b and miR-181c as minimally invasive AD biomarker panel in Egyptian patients and highlights their contribution in AD pathogenesis.

Relevance of plasma biomarkers to pathologies in Alzheimer's disease, Parkinson's disease and frontotemporal dementia

Amyloid plaques and tau tangles are pathological hallmarks of Alzheimer's disease (AD). Parkinson's disease (PD) results from the accumulation of α-synuclein. TAR DNA-binding protein (TDP-43) and total tau protein (T-Tau) play roles in FTD pathology. All of the pathological evidence was found in the biopsy. However, it is impossible to perform stein examinations in clinical practice. Assays of biomarkers in plasma would be convenient. It would be better to investigate the combinations of various biomarkers in AD, PD and FTD. Ninety-one subjects without neurodegenerative diseases, 76 patients with amnesic mild cognitive impairment (aMCI) or AD dementia, combined as AD family, were enrolled. One hundred and nine PD patients with normal cognition (PD-NC) or dementia (PDD), combined as PD family, were enrolled. Twenty-five FTD patients were enrolled for assays of plasma amyloid β 1-40 (Aβ_1-40), Aβ_1-42, T-Tau, α-synuclein and TDP-43 using immunomagnetic reduction (IMR). The results show that Aβs and T-Tau are major domains in AD family. α-synuclein is highly dominant in PD family. FTD is closely associated with TDP-43 and T-Tau. The dominant plasma biomarkers in AD family, PD family and FTD are consistent with pathology. This implies that plasma biomarkers are promising for precise and differential assessments of AD, PD and FTD in clinical practice.

Associations between blood-based biomarkers of Alzheimer's disease with cognition in motoric cognitive risk syndrome: A pilot study using plasma Aβ42 and total tau

Background

Motoric cognitive risk (MCR) syndrome is a conceptual construct that combines slow gait speed with subjective cognitive complaints and has been shown to be associated with an increased risk of developing dementia. However, the relationships between the pathology of Alzheimer's disease (AD) and MCR syndrome remain uncertain. Therefore, the purpose of this study was to determine the levels of plasma AD biomarkers (Aβ42 and total tau) and their relationships with cognition in individuals with MCR.

Materials and methods

This was a cross-sectional pilot study that enrolled 25 individuals with normal cognition (NC), 27 with MCR, and 16 with AD. Plasma Aβ42 and total tau (t-tau) levels were measured using immunomagnetic reduction (IMR) assays. A comprehensive neuropsychological assessment was also performed.

Results

The levels of plasma t-tau proteins did not differ significantly between the MCR and AD groups, but that of plasma t-tau was significantly increased in the MCR and AD groups, compared to the NC group. Visuospatial performance was significantly lower in the MCR group than in the NC group. The levels of plasma t-tau correlated significantly with the Montreal Cognitive Assessment (MoCA) and Boston naming test scores in the MCR group.

Conclusion

In this pilot study, we found significantly increased plasma t-tau proteins in the MCR and AD groups, compared with the NC group. The plasma t-tau levels were also significantly correlated with the cognitive function of older adults with MCR. These results implied that MCR and AD may share similar pathology. However, these findings need further confirmation in longitudinal studies.

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.

Elevated tau and β-amyloid in the serum of fibromyalgia patients

OBJECTIVE

Fibromyalgia (FM) is a chronic widespread pain syndrome. Although its mechanism remains relatively unknown, accelerated neurodegeneration in the brain has been reported in patients with FM. Sleep disturbance can increase the risk of neurocognitive disorders, which are associated with tau and beta-amyloid (Aβ) protein accumulation. We hypothesize neurodegeneration in patients with FM may be associated with sleep disturbance.

METHODS

In this case-control study, we analyzed serum tau and Aβ levels and their association with symptom profiles for patients with FM, by recruiting 22 patients with FM and 22 age-matched healthy participants. The visual analog scale, Fibromyalgia Impact Questionnaire, pressure pain threshold test, Pittsburgh Sleep Quality Index (PSQI), Beck Depression Inventory-II, Beck Anxiety Inventory, and serum tau and beta-amyloid-42 (Aβ-42) levels were recorded. The Mann-Whitney test was conducted to compare questionnaire and protein level results between the groups. Pearson correlation test was conducted to investigate the correlation of questionnaire scores with tau and Aβ-42 levels in patients with FM. The significance level was set at P < .05.

RESULTS

Serum tau and Aβ-42 levels were significantly higher in patients with FM than in controls. A positive correlation between serum tau levels and PSQI scores was observed in patients with FM (r = 0.476, P = .025). We found that only sleep disturbance in patients with FM was significantly associated with higher serum tau levels among all symptom scores.

CONCLUSIONS

We suggest sleep disturbance may play a vital role in the pathomechanism of accelerated neurodegeneration in FM.

Correlation Between Brain Structure Atrophy and Plasma Amyloid-β and Phosphorylated Tau in Patients With Alzheimer’s Disease and Amnestic Mild Cognitive Impairment Explored by Surface-Based Morphometry

Objective

To investigate the changes in the cortical thickness of the region of interest (ROI) and plasma Aβ40, Aβ42, and phosphorylated Tau (P-Tau) concentrations in patients with Alzheimer’s disease (AD) and amnestic mild cognitive impairment (aMCI) as the disease progressed with surface-based morphometry (SBM), to analyze the correlation between ROI cortical thickness and measured plasma indexes and neuropsychological scales, and to explore the clinical value of ROI cortical thickness combined with plasma Aβ40, Aβ42, and P-Tau in the early recognition and diagnosis of AD.

Methods

This study enrolled 33 patients with AD, 48 patients with aMCI, and 33 healthy controls (normal control, NC). Concentration changes in plasma Aβ42, Aβ40, and P-Tau collected in each group were analyzed. Meanwhile, the whole brain T1 structure images (T1WI-3D-MPRAGE) of each group of patients were collected, and T1 image in AD-aMCI, AD-NC, and aMCI-NC group were analyzed and processed by SBM technology to obtain brain regions with statistical differences as clusters, and the cortical thickness of each cluster was extracted. Multivariate ordered logistic regression analysis was used to screen out the measured plasma indexes and the indexes with independent risk factors in the cortical thickness of each cluster. Three comparative receiver operating characteristic (ROC) curves of AD-aMCI, AD-NC, and aMCI-NC groups were plotted, respectively, to explore the diagnostic value of multi-factor combined prediction for cognitive impairment. The relationship between cortical thickness and plasma indexes, and between cortical thickness and Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) scores were clarified by Pearson correlation analysis.

Results

Plasma Aβ40, Aβ42, and P-Tau proteins in the NC, aMCI, and AD groups increased with the progression of AD (P &lt; 0.01); cortical thickness reductions in the AD-aMCI groups and AD-NC groups mainly involved the bilateral superior temporal gyrus, transverse temporal gyrus, superior marginal gyrus, insula, right entorhinal cortex, right fusiform gyrus, and cingulate gyrus. However, there were no statistical significances in cortical thickness reductions in the aMCI and NC groups. The cortical thickness of the ROI was negatively correlated with plasma Aβ40, Aβ42, and P-Tau concentrations (P &lt; 0.05), and the cortical thickness of the ROI was positively correlated with MMSE and MoCA scores. Independent risk factors such as Aβ40, Aβ42, P-Tau, and AD-NC cluster 1R (right superior temporal gyrus, temporal pole, entorhinal cortex, transverse temporal gyrus, fusiform gyrus, superior marginal gyrus, middle temporal gyrus, and inferior temporal gyrus) were combined to plot ROC curves. The diagnostic efficiency of plasma indexes was higher than that of cortical thickness indexes, the diagnostic efficiency of ROC curves after the combination of cortical thickness and plasma indexes was higher than that of cortical thickness or plasma indexes alone.

Conclusion

Plasma Aβ40, Aβ42, and P-Tau may be potential biomarkers for early prediction of AD. As the disease progressed, AD patients developed cortical atrophy characterized by atrophy of the medial temporal lobe. The combined prediction of these region and plasma Aβ40, Aβ42, and P-Tau had a higher diagnostic value than single-factor prediction for cognitive decline.

Blood-Based Biomarkers for Alzheimer's Disease Diagnosis and Progression: An Overview

Alzheimer's Disease (AD) is a progressive neurodegenerative disease characterized by amyloid-β (Aβ) plaque deposition and neurofibrillary tangle accumulation in the brain. Although several studies have been conducted to unravel the complex and interconnected pathophysiology of AD, clinical trial failure rates have been high, and no disease-modifying therapies are presently available. Fluid biomarker discovery for AD is a rapidly expanding field of research aimed at anticipating disease diagnosis and following disease progression over time. Currently, Aβ1-42, phosphorylated tau, and total tau levels in the cerebrospinal fluid are the best-studied fluid biomarkers for AD, but the need for novel, cheap, less-invasive, easily detectable, and more-accessible markers has recently led to the search for new blood-based molecules. However, despite considerable research activity, a comprehensive and up-to-date overview of the main blood-based biomarker candidates is still lacking. In this narrative review, we discuss the role of proteins, lipids, metabolites, oxidative-stress-related molecules, and cytokines as possible disease biomarkers. Furthermore, we highlight the potential of the emerging miRNAs and long non-coding RNAs (lncRNAs) as diagnostic tools, and we briefly present the role of vitamins and gut-microbiome-related molecules as novel candidates for AD detection and monitoring, thus offering new insights into the diagnosis and progression of this devastating disease.

Novel Ultrasensitive Detection Technologies for the Identification of Early and Minimally Invasive Alzheimer's Disease Blood Biomarkers

BACKGROUND

Single molecule array (SIMOA) and other ultrasensitive detection technologies have allowed the determination of blood-based biomarkers of Alzheimer's disease (AD) for diagnosis and monitoring, thereby opening up a promising field of research.

OBJECTIVE

To review the published bibliography on plasma biomarkers in AD using new ultrasensitive techniques.

METHODS

A systematic review of the PubMed database was carried out to identify reports on the use of blood-based ultrasensitive technology to identify biomarkers for AD.

RESULTS

Based on this search, 86 works were included and classified according to the biomarker determined. First, plasma amyloid-β showed satisfactory accuracy as an AD biomarker in patients with a high risk of developing dementia. Second, plasma t-Tau displayed good sensitivity in detecting different neurodegenerative diseases. Third, plasma p-Tau was highly specific for AD. Fourth, plasma NfL was highly sensitive for distinguishing between patients with neurodegenerative diseases and healthy controls. In general, the simultaneous determination of several biomarkers facilitated greater accuracy in diagnosing AD (Aβ42/Aβ40, p-Tau181/217).

CONCLUSION

The recent development of ultrasensitive technology allows the determination of blood-based biomarkers with high sensitivity, thus facilitating the early detection of AD through the analysis of easily obtained biological samples. In short, as a result of this knowledge, pre-symptomatic and early AD diagnosis may be possible, and the recruitment process for future clinical trials could be more precise. However, further studies are necessary to standardize levels of blood-based biomarkers in the general population and thus achieve reproducible results among different laboratories.

Biomarkers used in Alzheimer's disease diagnosis, treatment, and prevention

Alzheimer's disease (AD), being the number one in terms of dementia burden, is an insidious age-related neurodegenerative disease and is presently considered a global public health threat. Its main histological hallmarks are the Aβ senile plaques and the P-tau neurofibrillary tangles, while clinically it is marked by a progressive cognitive decline that reflects the underlying synaptic loss and neurodegeneration. Many of the drug therapies targeting the two pathological hallmarks namely Aβ and P-tau have been proven futile. This is probably attributed to the initiation of therapy at a stage where cognitive alterations are already obvious. In other words, the underlying neuropathological changes are at a stage where these drugs lack any therapeutic value in reversing the damage. Therefore, there is an urgent need to start treatment in the very early stage where these changes can be reversed, and hence, early diagnosis is of primordial importance. To this aim, the use of robust and informative biomarkers that could provide accurate diagnosis preferably at an earlier phase of the disease is of the essence. To date, several biomarkers have been established that, to a different extent, allow researchers and clinicians to evaluate, diagnose, and more specially exclude other related pathologies. In this study, we extensively reviewed data on the currently explored biomarkers in terms of AD pathology-specific and non-specific biomarkers and highlighted the recent developments in the diagnostic and theragnostic domains. In the end, we have presented a separate elaboration on aspects of future perspectives and concluding remarks.

Analysis of plasma proteins using 2D gels and novel fluorescent probes: in search of blood based biomarkers for Alzheimer's disease

BACKGROUND

The Australian Imaging and Biomarker Lifestyle (AIBL) study of aging is designed to aid the discovery of biomarkers. The current study aimed to discover differentially expressed plasma proteins that could yield a blood-based screening tool for Alzheimer's disease.

METHODS

The concentration of proteins in plasma covers a vast range of 12 orders of magnitude. Therefore, to search for medium to low abundant biomarkers and elucidate mechanisms of AD, we immuno-depleted the most abundant plasma proteins and pre-fractionated the remaining proteins by HPLC, prior to two-dimensional gel electrophoresis. The relative levels of approximately 3400 protein species resolved on the 2D gels were compared using in-gel differential analysis with spectrally resolved fluorescent protein detection dyes (Zdyes™). Here we report on analysis of pooled plasma samples from an initial screen of a sex-matched cohort of 72 probable AD patients and 72 healthy controls from the baseline time point of AIBL.

RESULTS

We report significant changes in variants of apolipoprotein E, haptoglobin, α1 anti-trypsin, inter-α trypsin inhibitor, histidine-rich glycoprotein, and a protein of unknown identity. α1 anti-trypsin and α1 anti-chymotrypsin demonstrated plasma concentrations that were dependent on APOE ε4 allele dose. Our analysis also identified an association with the level of Vitamin D binding protein fragments and complement factor I with sex. We then conducted a preliminary validation study, on unique individual samples compared to the discovery cohort, using a targeted LC-MS/MS assay on a subset of discovered biomarkers. We found that targets that displayed a high degree of isoform specific changes in the 2D gels were not changed in the targeted MS assay which reports on the total level of the biomarker.

CONCLUSIONS

This demonstrates that further development of mass spectrometry assays is needed to capture the isoform complexity that exists in theses biological samples. However, this study indicates that a peripheral protein signature has potential to aid in the characterization of AD.

Evidence of plasma biomarkers indicating high risk of dementia in cognitively normal subjects

Subjects with comorbidities are at risk for neurodegeneration. There is a lack of a direct relationship between comorbidities and neurodegeneration. In this study, immunomagnetic reduction (IMR) assays were utilized to assay plasma Aβ_1-42 and total tau protein (T-Tau) levels in poststroke (PS, n = 27), family history of Alzheimer's disease (ADFH, n = 35), diabetes (n = 21), end-stage renal disease (ESRD, n = 41), obstructive sleep apnea (OSA, n = 20), Alzheimer's disease (AD, n = 65). Thirty-seven healthy controls (HCs) were enrolled. The measured concentrations of plasma Aβ_1-42 were 14.26 ± 1.42, 15.43 ± 1.76, 15.52 ± 1.60, 16.15 ± 1.05, 16.52 ± 0.59, 15.97 ± 0.54 and 20.06 ± 3.09 pg/mL in HC, PS, ADFH, diabetes, ESRD, OSA and AD groups, respectively. The corresponding concentrations of plasma T-Tau were 15.13 ± 3.62, 19.29 ± 8.01, 17.93 ± 6.26, 19.74 ± 2.92, 21.54 ± 2.72, 20.17 ± 2.77 and 41.24 ± 14.64 pg/mL. The plasma levels of Aβ_1-42 and T-Tau in were significantly higher in the PS, ADFH, diabetes, ESRD and OSA groups than controls (Aβ_1-42 in PS: 15.43 ± 1.76 pg/mL vs. 14.26 ± 1.42 pg/mL, p < 0.005; T-Tau in PS: 19.29 ± 8.01 vs. 15.13 ± 3.62 pg/mL, p < 0.005, Aβ_1-42 in ADFH: 15.52 ± 1.60 pg/mL vs. 14.26 ± 1.42 pg/mL, p < 0.001; T-Tau in ADFH: 17.93 ± 6.26 vs. 15.13 ± 3.62 pg/mL, p < 0.005, Aβ_1-42 in diabetes: 16.15 ± 1.05 pg/mL vs. 14.26 ± 1.42 pg/mL, p < 0.001; T-Tau in diabetes: 19.74 ± 2.92 vs. 15.13 ± 3.62 pg/mL, p < 0.001, Aβ_1-42 in ESRD: 16.52 ± 0.59 pg/mL vs. 14.26 ± 1.42 pg/mL, p < 0.001; T-Tau in ESRD: 21.54 ± 2.72 vs. 15.13 ± 3.62 pg/mL, p < 0.001, Aβ_1-42 in OSA: 15.97 ± 0.54 pg/mL vs. 14.26 ± 1.42 pg/mL, p < 0.001; T-Tau in OSA: 20.17 ± 2.77 vs. 15.13 ± 3.62 pg/mL, p < 0.001). This evidence indicates the high risk for dementia in these groups from the perspective of plasma biomarkers.

The impact of uremic toxins on Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia, pathologically characterized by accumulation of senile plaques and neurofibrillary tangles. Chronic kidney disease (CKD) is highly prevalent in elderly population closely associated with occurrence of dementia. Recent epidemiological and experimental studies suggest a potential association of CKD with AD. Both diseases share a panel of identical risk factors, such as type 2 diabetes; and hypertension. However, the relationship between CKD and AD is unclear. Lower clearance of a panel of uremic toxin including cystatin-C, guanidine, and adiponectin due to CKD is implied to contribute to AD pathogenesis. In this review we summarize the current evidence from epidemiological, experimental and clinical studies on the potential contribution of uremic toxins to AD pathogenesis. We describe outstanding questions and propose an outlook on the link between uremic toxins and AD.

Acoustofluidic multimodal diagnostic system for Alzheimer's disease

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative brain disorder that affects tens of millions of older adults worldwide and has significant economic and societal impacts. Despite its prevalence and severity, early diagnosis of AD remains a considerable challenge. Here we report an integrated acoustofluidics-based diagnostic system (ADx), which combines triple functions of acoustics, microfluidics, and orthogonal biosensors for clinically accurate, sensitive, and rapid detection of AD biomarkers from human plasma. We design and fabricate a surface acoustic wave-based acoustofluidic separation device to isolate and purify AD biomarkers to increase the signal-to-noise ratio. Multimodal biosensors within the integrated ADx are fabricated by in-situ patterning of the ZnO nanorod array and deposition of Ag nanoparticles onto the ZnO nanorods for surface-enhanced Raman scattering (SERS) and electrochemical immunosensors. We obtain the label-free detections of SERS and electrochemical immunoassay of clinical plasma samples from AD patients and healthy controls with high sensitivity and specificity. We believe that this efficient integration provides promising solutions for the early diagnosis of AD.

Association Plasma Aβ42 Levels with Alzheimer's Disease and Its Influencing Factors in Chinese Elderly Population

BACKGROUND AND PURPOSE

Intracerebral Aβ protein deposition is an important pathological mechanism of Alzheimer's disease (AD) and is one of the indicators of early diagnosis of AD. However, invasive lumbar puncture and Aβ PET are difficult to perform in primary units, resulting delays in early diagnosis of AD. In recent years, it has been found that plasma Aβ can reflect the pathological state of AD in early stage, but the results are not consistent. The objective of this study was to explore the association between plasma Aβ42 levels and AD cognitive impairment and its influencing factors in Chinese elderly population, so as to provide guidance for the clinical application of plasma Aβ42 as a blood biomarker of AD.

METHODS

This is a cross-sectional study based on the community population. Plasma samples were collected from 604 healthy controls (HC), 508 mild cognitive impairment (MCI) and 202 dementia with Alzheimer's type (DAT) patients from three cities. We analyzed the correlation between plasma Aβ42 levels and cognitive function and the influence of confounding factors on the relationship between plasma Aβ42 levels and AD. The independent influencing factors of plasma Aβ42 levels were determined by covariance and linear regression analysis.

RESULTS

Our results suggest that there is a special linear relationship between plasma Aβ42 and cognitive impairment of AD in Chinese elderly population, with Aβ42 levels slightly decreased in early AD and significantly increased in moderate-to-severe AD (P<0.01). There are many factors influencing the association between plasma Aβ42 levels and AD cognitive impairment, and sample source, gender and BMI are independent influencing factors of plasma Aβ42.

CONCLUSION

This indentifies that plasma Aβ42 may be a peripheral biomarker for AD screening in Chinese elderly population, but it is necessary to establish standardized detection methods and establish different demarcation criteria for various influencing factors.

Neurodegeneration and Vascular Burden on Cognition After Midlife: A Plasma and Neuroimaging Biomarker Study

Background and Objectives: Neurodegeneration and vascular burden are the two most common causes of post-stroke cognitive impairment. However, the interrelationship between the plasma beta-amyloid (Aβ) and tau protein, cortical atrophy and brain amyloid accumulation on PET imaging in stroke patients is undetermined. We aimed to explore: (1) the relationships of cortical thickness and amyloid burden on PET with plasma Aβ40, Aβ42, tau protein and their composite scores in stroke patients; and (2) the associations of post-stroke cognitive presentations with these plasma and neuroimaging biomarkers.

Methods: The prospective project recruited first-ever ischemic stroke patients around 3 months after stroke onset. The plasma Aβ40, Aβ42, and total tau protein were measured with the immunomagnetic reduction method. Cortical thickness was evaluated on MRI, and cortical amyloid plaque deposition was evaluated by ¹⁸F-florbetapir PET. Cognition was evaluated with Mini-Mental State Examination (MMSE), Geriatric Depression Scale (GDS), Dementia Rating Scale-2 (DRS-2).

Results: The study recruited 24 stroke patients and 13 normal controls. The plasma tau and tau*Aβ42 levels were correlated with mean cortical thickness after age adjustment. The Aβ42/Aβ40 ratio was correlated with global cortical ¹⁸F-florbetapir uptake value. The DRS-2 and GDS scores were associated with mean cortical thickness and plasma biomarkers, including Aβ42/Aβ40, tau, tau*Aβ42, tau/Aβ42, and tau/Aβ40 levels, in stroke patients.

Conclusion: Plasma Aβ, tau, and their composite scores were associated with cognitive performance 3 months after stroke, and these plasma biomarkers were correlated with corresponding imaging biomarkers of neurodegeneration. Further longitudinal studies with a larger sample size are warranted to replicate the study results.

Serum Glycoproteomics and Identification of Potential Mechanisms Underlying Alzheimer’s Disease

Objectives. This study compares glycoproteomes in Thai Alzheimer’s disease (AD) patients with those of cognitively normal individuals. Methods. Study participants included outpatients with clinically diagnosed AD ( $N=136$ ) and healthy controls without cognitive impairment ( $N=183$ ). Blood samples were collected from all participants for biochemical analysis and for $\text{Apolipoprotein}\text{E}$ (APOE) genotyping by real-time TaqMan PCR assays. Comparative serum glycoproteomic profiling by liquid chromatography-tandem mass spectrometry was then performed to identify differentially abundant proteins with functional relevance. Results. Statistical differences in age, educational level, and APOE ɛ3/ɛ4 and ɛ4/ɛ4 haplotype frequencies were found between the AD and control groups. The frequency of the APOE ɛ4 allele was significantly higher in the AD group than in the control group. In total, 871 glycoproteins were identified, including 266 and 259 unique proteins in control and AD groups, respectively. There were 49 and 297 upregulated and downregulated glycoproteins, respectively, in AD samples compared with the controls. Unique AD glycoproteins were associated with numerous pathways, including Alzheimer’s disease-presenilin pathway (16.6%), inflammation pathway mediated by chemokine and cytokine signaling (9.2%), Wnt signaling pathway (8.2%), and apoptosis signaling pathway (6.7%). Conclusion. Functions and pathways associated with protein-protein interactions were identified in AD. Significant changes in these proteins can indicate the molecular mechanisms involved in the pathogenesis of AD, and they have the potential to serve as AD biomarkers. Such findings could allow us to better understand AD pathology.

Assessment of High Risk for Alzheimer's Disease Using Plasma Biomarkers in Subjects with Normal Cognition in Taiwan: A Preliminary Study

Background

In Alzheimer's disease (AD), cognitive impairment begins 10-15 years later than neurodegeneration in the brain. Plasma biomarkers are promising candidates for assessing neurodegeneration in people with normal cognition. It has been reported that subjects with the concentration of plasma amyloid-β 1-42×total tau protein higher than 455 pg²/ml² are assessed as having a high risk of amnesic mild impairment or AD, denoted as high risk of AD (HRAD).

Objective

The prevalence of high-risk for dementia in cognitively normal controls is explored by assaying plasma biomarkers.

Methods

422 subjects with normal cognition were enrolled around Taiwan. Plasma Aβ_1-40, Aβ_1-42, and T-Tau levels were assayed using immunomagnetic reduction to assess the risk of dementia.

Results

The results showed that 4.6% of young adults (age: 20-44 years), 8.5% of middle-aged adults (age: 45-64 years), and 7.3% of elderly adults (age: 65-90 years) had HRAD. The percentage of individuals with HRAD dramatically increased in middle-aged and elderly adults compared to young adults.

Conclusion

The percentage of HRAD in cognitively normal subjects are approximately 10%, which reveals that the potentially public-health problem of AD in normal population. Although the subject having abnormal levels of Aβ or tau is not definitely going on to develop cognitive declines or AD, the risk of suffering cognitive impairment in future is relatively high. Suitable managements are suggested for these high-risk cognitively normal population. Worth noting, attention should be paid to preventing cognitive impairment due to AD, not only in elderly adults but also middle-aged adults.

Performance of Plasma Amyloid β, Total Tau, and Neurofilament Light Chain in the Identification of Probable Alzheimer's Disease in South China

Background: Alzheimer's disease (AD) is the most common type of dementia and has no effective treatment to date. It is essential to develop a minimally invasive blood-based biomarker as a tool for screening the general population, but the efficacy remains controversial. This cross-sectional study aimed to evaluate the ability of plasma biomarkers, including amyloid β (Aβ), total tau (t-tau), and neurofilament light chain (NfL), to detect probable AD in the South Chinese population.

Methods: A total of 277 patients with a clinical diagnosis of probable AD and 153 healthy controls with normal cognitive function (CN) were enrolled in this study. The levels of plasma Aβ42, Aβ40, t-tau, and NfL were detected using ultra-sensitive immune-based assays (SIMOA). Lumbar puncture was conducted in 89 patients with AD to detect Aβ42, Aβ40, t-tau, and phosphorylated (p)-tau levels in the cerebrospinal fluid (CSF) and to evaluate the consistency between plasma and CSF biomarkers through correlation analysis. Finally, the diagnostic value of plasma biomarkers was further assessed by constructing a receiver operating characteristic (ROC) curve.

Results: After adjusting for age, sex, and the apolipoprotein E (APOE) alleles, compared to the CN group, the plasma t-tau, and NfL were significantly increased in the AD group (p < 0.01, Bonferroni correction). Correlation analysis showed that only the plasma t-tau level was positively correlated with the CSF t-tau levels (r = 0.319, p = 0.003). The diagnostic model combining plasma t-tau and NfL levels, and age, sex, and APOE alleles, showed the best performance for the identification of probable AD [area under the curve (AUC) = 0.89, sensitivity = 82.31%, specificity = 83.66%].

Conclusion: Blood biomarkers can effectively distinguish patients with probable AD from controls and may be a non-invasive and efficient method for AD pre-screening.

Association Between Plasma Amyloid-β and Neuropsychological Performance in Patients With Cognitive Decline

Objective: To investigate the association between plasma amyloid-β (Aβ) levels and neuropsychological performance in patients with cognitive decline using a highly sensitive nano-biosensing platform.

Methods: We prospectively recruited 44 patients with cognitive decline who underwent plasma Aβ analysis, amyloid positron emission tomography (PET) scanning, and detailed neuropsychological tests. Patients were classified into a normal control (NC, n = 25) or Alzheimer’s disease (AD, n = 19) group based on amyloid PET positivity. Multiple linear regression was performed to determine whether plasma Aβ (Aβ₄₀, Aβ₄₂, and Aβ_42/40) levels were associated with neuropsychological test results.

Results: The plasma levels of Aβ_42/40 were significantly different between the NC and AD groups and were the best predictor of amyloid PET positivity by receiver operating characteristic curve analysis [area under the curve of 0.952 (95% confidence interval, 0.892–1.000)]. Although there were significant differences in the neuropsychological performance of cognitive domains (language, visuospatial, verbal/visual memory, and frontal/executive functions) between the NC and AD groups, higher levels of plasma Aβ_42/40 were negatively correlated only with verbal and visual memory performance.

Conclusion: Our results demonstrated that plasma Aβ analysis using a nano-biosensing platform could be a useful tool for diagnosing AD and assessing memory performance in patients with cognitive decline.

Bias-generating factors in biofluid amyloid-β measurements for Alzheimer's disease diagnosis

Alzheimer's disease (AD) is the most prevalent cause of dementia worldwide, yet the dearth of readily accessible diagnostic biomarkers is a substantial hindrance towards progressing to effective preventive and therapeutic approaches. Due to a long delay between cerebral amyloid-β (Aβ) accumulation and the onset of cognitive impairments, biomarkers that reflect Aβ pathology and enable routine screening for disease progression are of urgent need for application in the clinical diagnosis of AD. According to accumulating evidences, cerebrospinal fluid (CSF) and plasma offer windows to the brain as they allow monitoring of biochemical changes in the brain. Considering the high availability and accuracy in depicting Aβ deposition in the brain, Aβ levels in CSF and plasma are regarded as promising fluid biomarkers for the diagnosis of AD patients at an early stage. However, clinical data with intra- and interindividual variations in the concentrations of CSF and plasma Aβ implicate the need to reevaluate current Aβ detection methods and establish a standardized operating procedure. Therefore, this review introduces three bias-generating factors in biofluid Aβ measurement that may hamper the accurate Aβ quantification and how such complications can be overcome for the widespread implementation of fluid Aβ detection in clinical practice.

Blood-Based ATN Biomarkers of Alzheimer's Disease: A Meta-Analysis

BACKGROUND

The Amyloid Tau Neurodegeneration (ATN) framework was proposed to define the biological state underpinning Alzheimer's disease (AD). Blood-based biomarkers offer a scalable alternative to the costly and invasive currently available biomarkers.

OBJECTIVE

In this meta-analysis we sought to assess the diagnostic performance of plasma amyloid (Aβ40, Aβ42, Aβ42/40 ratio), tangle (p-tau181), and neurodegeneration (total tau [t-tau], neurofilament light [NfL]) biomarkers.

METHODS

Electronic databases were screened for studies reporting biomarker concentrations for AD and control cohorts. Biomarker performance was examined by random-effect meta-analyses based on the ratio between biomarker concentrations in patients and controls.

RESULTS

83 studies published between 1996 and 2020 were included in the analyses. Aβ42/40 ratio as well as Aβ42 discriminated AD patients from controls when using novel platforms such as immunomagnetic reduction (IMR). We found significant differences in ptau-181 concentration for studies based on single molecule array (Simoa), but not for studies based on IMR or ELISA. T-tau was significantly different between AD patients and control in IMR and Simoa but not in ELISA-based studies. In contrast, NfL differentiated between groups across platforms. Exosome studies showed strong separation between patients and controls for Aβ42, t-tau, and p-tau181.

CONCLUSION

Currently available assays for sampling plasma ATN biomarkers appear to differentiate between AD patients and controls. Novel assay methodologies have given the field a significant boost for testing these biomarkers, such as IMR for Aβ, Simoa for p-tau181. Enriching samples through extracellular vesicles shows promise but requires further validation.

Investigation of the Number of Tests Required for Assaying Plasma Biomarkers Associated with Alzheimer's Disease Using Immunomagnetic Reduction

INTRODUCTION

Concentrations of plasma biomarkers associated with Alzheimer's disease have been reported to be as low as several tens of picograms/milliliter (pg/ml). However, in assays measuring these biomarkers, it is likely that repeated measurements are necessary to obtain reliable values.

METHODS

We performed assays as a single test or as duplicate, quadruplicate, fivefold and tenfold repeated tests, on samples spiked with different concentrations of amyloid β 1-40 (Aβ_1-40; 1-1000 pg/ml), Aβ_1-42 (1-30,000 pg/ml) and total Tau protein (T-Tau; 0.1-1000 pg/ml), with the aim to to calculate the coefficients of variation (CVs).

RESULTS

The results demonstrated common changes in the CVs with changes in the number of tests for a given sample: the CVs decreased with increases in the number of tests from one to ten. All CV values were distributed within the range of 0.35 to 15.5%; as such, the CV values were all lower than the acceptable value of 20%.

CONCLUSION

Based on this study, a single assay of Aβ_1-40, Aβ_1-42 and T-Tau, respectively, provides reliable results in terms of the measurement of that plasma biomarker.

Ultrasensitive techniques and protein misfolding amplification assays for biomarker-guided reconceptualization of Alzheimer's and other neurodegenerative diseases

INTRODUCTION

The clinical validation and qualification of biomarkers reflecting the complex pathophysiology of neurodegenerative diseases (NDDs) is a fundamental challenge for current drug discovery and development and next-generation clinical practice. Novel ultrasensitive detection techniques and protein misfolding amplification assays hold the potential to optimize and accelerate this process.

AREAS COVERED

Here we perform a PubMed-based state of the art review and perspective report on blood-based ultrasensitive detection techniques and protein misfolding amplification assays for biomarkers discovery and development in NDDs.

EXPERT OPINION

Ultrasensitive assays represent innovative solutions for blood-based assessments during the entire Alzheimer's disease (AD) biological and clinical continuum, for contexts of use (COU) such as prediction, detection, early diagnosis, and prognosis of AD. Moreover, cerebrospinal fluid (CSF)-based misfolding amplification assays show encouraging performance in detecting α-synucleinopathies in prodromal or at-high-risk individuals and may serve as tools for patients' stratification by the presence of α-synuclein pathology. Further clinical research will help overcome current methodological limitations, also through exploring multiple accessible bodily matrices. Eventually, integrative longitudinal studies will support precise definitions for appropriate COU across NDDs.

Towards point-of-care diagnosis of Alzheimer's disease: Multi-analyte based portable chemiresistive platform for simultaneous detection of β-amyloid (1-40) and (1-42) in plasma

Label-free simultaneous detection of Alzheimer's disease (AD) specific biomarkers Aβ40 and Aβ42 peptides on a single platform using polypyrrole nanoparticle-based chemiresistive biosensors is reported here. The proposed interdigitated-microelectrode based inexpensive multisensor-platform can concurrently detect Aβ40 and Aβ42 in spiked-plasma in the range of 10-14 - 10-6 g/mL (with LoDs being 5.71 and 9.09 fg/mL, respectively), enabling the estimation of diagnostically significant Aβ42/Aβ40 ratio. A detailed study has been undertaken here to record the individual sensor responses against spiked-plasma samples with varying amounts and proportions of the two target peptides, towards enabling disease-progression monitoring using the Aβ-ratio. As compared to the existing cost-ineffective brain-imaging techniques such as PET and MRI, and the high-risk CSF based invasive AD biomarkers detecting procedures, the proposed approach offers a viable alternative for affordable point-of-care AD diagnostics, with possible usage in performance evaluation of therapeutic drugs. Towards point-of-care applications, the portable readout used in this work was conjugated with an android-based mobile app for data-acquisition and analysis.

The Role of Plasma Neurofilament Light Protein for Assessing Cognitive Impairment in Patients With End-Stage Renal Disease

Introduction: End-stage renal disease (ESRD) is defined as the irreversible loss of renal function, necessitating renal replacement therapy. Patients with ESRD tend to have more risk factors for cognitive impairment than the general population, including hypertension, accumulative uremic toxin, anemia, and old age. The association between these risk factors and the pathologic protein was lacking. Blood-based assays for detecting pathologic protein, such as amyloid beta (Aβ), total tau protein, and neurofilament light chain (NfL), have the advantages of being less invasive and more cost-effective for diagnosing patients with cognitive impairment. The aim of the study is to validate if the common neurologic biomarkers were different in ESRD patients and to differentiate if the specific biomarkers could correlate with specific correctable risk factors. Methods: In total, 67 participants aged >45 years were enrolled. The definition of ESRD was receiving maintenance hemodialysis for >3 months. Cognitive impairment was defined as a Mini-Mental State Examination score of <24. The participants were divided into groups for ESRD with and without cognitive impairment. The blood-based biomarkers (tau protein, Aβ1/40, Aβ1/42, and NfL) were analyzed through immunomagnetic reduction assay. Other biochemical and hematologic data were obtained simultaneously. Summary of results: The study enrolled 43 patients with ESRD who did not have cognitive impairment and 24 patients with ESRD who had cognitive impairment [Mini-Mental State Examination (MMSE): 27.60 ± 1.80 vs. 16.84 ± 6.40, p < 0.05]. Among the blood-based biomarkers, NfL was marginally higher in the ESRD with cognitive impairment group than in the ESRD without cognitive impairment group (10.41 ± 3.26 vs. 8.74 ± 2.81 pg/mL, p = 0.037). The concentrations of tau protein, amyloid β 1/42, and amyloid β 1/40 (p = 0.504, 0.393, and 0.952, respectively) were similar between the two groups. The area under the curve of NfL to distinguish cognitively impaired and unimpaired ESRD patients was 0.687 (95% confidence interval: 0.548-0.825, p = 0.034). There was no correlation between the concentration of NfL and MMSE among total population (r = -0.153, p = 0.277), patients with (r = 0.137, p = 0.583) or without cognitive impairment (r = 0.155, p = 0.333). Conclusion: Patients with ESRD who had cognitive impairment had marginally higher plasma NfL concentrations. NfL concentration was not correlated with the biochemical parameters, total MMSE among total population or individual groups with or without cognitive impairment. The concentrations of Aβ1/40, Aβ1/42, and tau were similar between the groups.

Potential of FTIR Spectroscopy Applied to Exosomes for Alzheimer's Disease Discrimination: A Pilot Study

Alzheimer's disease (AD) diagnosis is based on psychological and imaging tests but can also include monitoring cerebrospinal fluid (CSF) biomarkers. However, CSF based-neurochemical approaches are expensive and invasive, limiting their use to well-equipped settings. In contrast, blood-based biomarkers are minimally invasive, cost-effective, and a widely accessible alternative. Blood-derived exosomes have recently emerged as a reliable AD biomarker source, carrying disease-specific cargo. Fourier-transformed infrared (FTIR) spectroscopy meets the criteria for an ideal diagnostic methodology since it is rapid, easy to implement, and has high reproducibility. This metabolome-based technique is useful for diagnosing a broad range of diseases, although to our knowledge, no reports for FTIR spectroscopy applied to exosomes in AD exist. In this ground-breaking pilot study, FTIR spectra of serum and serum-derived exosomes from two independent cohorts were acquired and analyzed using multivariate analysis. The regional UA-cohort includes 9 individuals, clinically diagnosed with AD, mean age of 78.7 years old; and the UMG-cohort comprises 12 individuals, clinically diagnosed with AD (based on molecular and/or imaging data), mean age of 73.2 years old. Unsupervised principal component analysis of FTIR spectra of serum-derived exosomes revealed higher discriminatory value for AD cases when compared to serum as a whole. Consistently, the partial least-squares analysis revealed that serum-derived exosomes present higher correlations than serum. In addition, the second derivative peak area calculation also revealed significant differences among Controls and AD cases. The results obtained suggest that this methodology can discriminate cases from Controls and thus be potential useful to assist in AD clinical diagnosis.

Safety and efficacy of sargramostim (GM-CSF) in the treatment of Alzheimer's disease

INTRODUCTION

Inflammatory markers have long been observed in the brain, cerebrospinal fluid (CSF), and plasma of Alzheimer's disease (AD) patients, suggesting that inflammation contributes to AD and might be a therapeutic target. However, non-steroidal anti-inflammatory drug trials in AD and mild cognitive impairment (MCI) failed to show benefit. Our previous work seeking to understand why people with the inflammatory disease rheumatoid arthritis are protected from AD found that short-term treatment of transgenic AD mice with the pro-inflammatory cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) led to an increase in activated microglia, a 50% reduction in amyloid load, an increase in synaptic area, and improvement in spatial memory to normal. These results called into question the consensus view that inflammation is solely detrimental in AD. Here, we tested our hypothesis that modulation of the innate immune system might similarly be used to treat AD in humans by investigating the ability of GM-CSF/sargramostim to safely ameliorate AD symptoms/pathology.

METHODS

A randomized, double-blind, placebo-controlled trial was conducted in mild-to-moderate AD participants (NCT01409915). Treatments (20 participants/group) occurred 5 days/week for 3 weeks plus two follow-up (FU) visits (FU1 at 45 days and FU2 at 90 days) with neurological, neuropsychological, blood biomarker, and imaging assessments.

RESULTS

Sargramostim treatment expectedly changed innate immune system markers, with no drug-related serious adverse events or amyloid-related imaging abnormalities. At end of treatment (EOT), the Mini-Mental State Examination score of the sargramostim group increased compared to baseline (P = .0074) and compared to placebo (P = .0370); the treatment effect persisted at FU1 (P = .0272). Plasma markers of amyloid beta (Aβ40 [decreased in AD]) increased 10% (P = .0105); plasma markers of neurodegeneration (total tau and UCH-L1) decreased 24% (P = .0174) and 42% (P = .0019), respectively, after sargramostim treatment compared to placebo.

DISCUSSION

The innate immune system is a viable target for therapeutic intervention in AD. An extended treatment trial testing the long-term safety and efficacy of GM-CSF/sargramostim in AD is warranted.

Ultrasensitive assays for detection of plasma tau and phosphorylated tau 181 in Alzheimer's disease: a systematic review and meta-analysis

A lack of convenient and reliable biomarkers for diagnosis and prognosis is a common challenge for neurodegenerative diseases such as Alzheimer's disease (AD). Recent advancement in ultrasensitive protein assays has allowed the quantification of tau and phosphorylated tau proteins in peripheral plasma. Here we identified 66 eligible studies reporting quantification of plasma tau and phosphorylated tau 181 (ptau181) using four ultrasensitive methods. Meta-analysis of these studies confirmed that the AD patients had significantly higher plasma tau and ptau181 levels compared with controls, and that the plasma tau and ptau181 could predict AD with high-accuracy area under curve of the Receiver Operating Characteristic. Therefore, plasma tau and plasma ptau181 can be considered as biomarkers for AD diagnosis.

Progress regarding the context-of-use of tau as biomarker of Alzheimer's disease and other neurodegenerative diseases

Introduction: Tau protein misfolding and accumulation in toxic species is a critical pathophysiological process of Alzheimer's disease (AD) and other neurodegenerative disorders (NDDs). Tau biomarkers, namely cerebrospinal fluid (CSF) total-tau (t-tau), 181-phosphorylated tau (p-tau), and tau-PET tracers, have been recently embedded in the diagnostic criteria for AD. Nevertheless, the role of tau as a diagnostic and prognostic biomarker for other NDDs remains controversial.Areas covered: We performed a systematical PubMed-based review of the most recent advances in tau-related biomarkers for NDDs. We focused on papers published from 2015 to 2020 assessing the diagnostic or prognostic value of each biomarker.Expert opinion: The assessment of tau biomarkers in alternative easily accessible matrices, through the development of ultrasensitive techniques, represents the most significant perspective for AD-biomarker research. In NDDs, novel tau isoforms (e.g. p-tau217) or proteolytic fragments (e.g. N-terminal fragments) may represent candidate diagnostic and prognostic biomarkers and may help monitoring disease progression. Protein misfolding amplification assays, allowing the identification of different tau strains (e.g. 3 R- vs. 4 R-tau) in CSF, may constitute a breakthrough for the in vivo stratification of NDDs. Tau-PET may help tracking the spatial-temporal evolution of tau pathophysiology in AD but its application outside the AD-spectrum deserves further studies.

A cross-sectional examination of a family history of Alzheimer's disease and ApoE epsilon 4 on physical fitness, molecular biomarkers, and neurocognitive performance

PURPOSE

The present study examined whether the ɛ4 allele of the apolipoprotein E (ApoE) gene impacts molecular biomarkers and neurocognitive performance among individuals at genetic risk for developing Alzheimer's disease (AD). The correlations between physical fitness and molecular/neurocognitive indices were also explored.

METHODS

Fasting blood samples were collected from 162 individuals with a family history of AD (ADFH). There were twenty-two carriers of the ApoE-4 variant (ApoE-4 group). For comparison purposes we randomly selected 22 non-ɛ4 carriers (non-ApoE-4 group) from the ADFH individuals. Circulating inflammatory cytokines (e.g., TNF-α, IL-1β, IL-6, IL-8, and IL-15), neuroprotective growth factors (e.g., BDNF, IGF-1, IGF-2, VEGF, and FGF-2), and Amyloid-β peptides (e.g., Aβ1-40 and Aβ1-42), neurocognitive performance [e.g., behavior and brain even-related potentials (ERP)] during a task-switching paradigm, as well as physical fitness scores were measured.

RESULTS

The ApoE-4 group relative to the non-ApoE-4 group was similar with respect to molecular biomarkers, physical fitness, and most measures of neurocognitive performance. However, ADFH individuals that were ɛ4 carriers exhibited significantly higher local switching accuracy costs, worse accuracy as well as smaller ERP P3 amplitudes for the memory-switching condition. Importantly, cardiorespiratory fitness levels were significantly correlated with accuracy for most task-switching conditions, and levels of BDNF, Aβ1-40, and Aβ1-42 collapsed across the two groups even when controlling for the age co-variable, while the ApoE-4 group revealed similar pattern of results.

CONCLUSIONS

These data suggest that individuals with ADFH that were carriers of the ApoE-4 variant performed worse on the task-switching paradigm and that this could be due to compromised task-set and memory updating processes. Physical exercise interventions aimed to enhance cardiorespiratory fitness levels could be a potential AD prevention strategy for ameliorating cognitive function and reducing the accumulation of the Aβ peptides in this high risk group.

Age and sex impact plasma NFL and t-Tau trajectories in individuals with subjective memory complaints: a 3-year follow-up study

Background

Plasma neurofilament light (NFL) and total Tau (t-Tau) proteins are candidate biomarkers for early stages of Alzheimer’s disease (AD). The impact of biological factors on their plasma concentrations in individuals with subjective memory complaints (SMC) has been poorly explored. We longitudinally investigate the effect of sex, age, APOE ε4 allele, comorbidities, brain amyloid-β (Aβ) burden, and cognitive scores on plasma NFL and t-Tau concentrations in cognitively healthy individuals with SMC, a condition associated with AD development.

Methods

Three hundred sixteen and 79 individuals, respectively, have baseline and three-time point assessments (at baseline, 1-year, and 3-year follow-up) of the two biomarkers. Plasma biomarkers were measured with an ultrasensitive assay in a mono-center cohort (INSIGHT-preAD study).

Results

We show an effect of age on plasma NFL, with women having a higher increase of plasma t-Tau concentrations compared to men, over time. The APOE ε4 allele does not affect the biomarker concentrations while plasma vitamin B12 deficiency is associated with higher plasma t-Tau concentrations. Both biomarkers are correlated and increase over time. Baseline NFL is related to the rate of Aβ deposition at 2-year follow-up in the left-posterior cingulate and the inferior parietal gyri. Baseline plasma NFL and the rate of change of plasma t-Tau are inversely associated with cognitive score.

Conclusion

We find that plasma NFL and t-Tau longitudinal trajectories are affected by age and female sex, respectively, in SMC individuals. Exploring the influence of biological variables on AD biomarkers is crucial for their clinical validation in blood.

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

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

Circulating levels of Irisin in obese individuals at genetic risk for Alzheimer's disease: Correlations with amyloid-β, metabolic, and neurocognitive indices

Irisin is involved in various metabolic pathways and is suggested to be a potential agent capable of preventing onset of Alzheimer's disease (AD) and ameliorating AD neuropathology and cognitive deficits. In the present study, the serum levels of Irisin and Amyloid-β (Aβ) peptides and the neurocognitive performance among obese individuals at genetic risk for AD were investigated. The correlations between Irisin and AD-related neuropathological and neurocognitive indices were also explored. Thirty-two individuals with a family history of AD (ADFH) and obesity (ADFH-obesity group) and 32 controls (ADFH-non-obesity group) were recruited. Circulating levels of Irisin, Aβ peptides, and metabolic biomarkers, as well as neurocognitive performance [e.g., behavior and brain even-related potentials (ERP)] were measured during a visuospatial working memory task. Although the ADFH-obesity group exhibited comparable reaction times, ERP N2 latency and amplitudes, and P3 latency as compared to the ADFH-non-obesity group when performing the cognitive task, they exhibited significantly lower rates of accuracy and smaller P3 amplitudes in the higher memory-load condition, even when controlling for the blood pressure and cardiorespiratory fitness co-variables. The serum levels of leptin, insulin, and glucose, and HOMA-IR were significantly higher in the ADFH-obesity group relative to the ADFH-non-obesity group, but this was not the case for the levels of Aβ1-40 and Aβ1-42. The Irisin levels approached between-group significance. Partial correlations adjusting for cardiorespiratory fitness and blood pressure showed that Irisin levels were positively associated with neurophysiological (i.e., P3 amplitude) performance in the ADFH-obesity group. The Irisin levels were not significantly correlated with the levels of Aβ1-40 and Aβ1-42. The present findings suggest that ADFH individuals with obesity exhibited neurocognitive deficits when performing the visuospatial working memory task, and serum Irisin levels could be one of the influencing factors. However, the relationship between the circulating levels of Irisin and Aβ peptides needs more evidence to support this assumption.

Immunomagnetic Reduction Detects Plasma Aβ1-42 Levels as a Potential Dominant Indicator Predicting Cognitive Decline

Although the concentrations of Alzheimer’s disease (AD) biomarkers Aβ_1–40, Aβ_1–42 and tau protein are very low in human plasma, ultrasensitive assays such as immunomagnetic reduction (IMR) are able to precisely quantify them. Review articles have described the detailed working mechanism of IMR and revealed the feasibility of detecting early-stage AD by assaying these plasma biomarkers with IMR. In this review, we aimed to compare the significance of these plasma biomarkers in predicting cognitive decline in patients with Down syndrome, stroke, or amnestic mild cognitive impairment based on findings in the literature. We found that plasma Aβ_1–42 might play the predominant role in predicting cognitive decline in these patients.

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.