Diagnostic Values of Cerebrospinal Fluid T-Tau and Aβ₄₂ using Meso Scale Discovery Assays for Alzheimer's Disease

How far is the goal of applying β-amyloid in cerebrospinal fluid for clinical diagnosis of Alzheimer's disease with standardization of measurements?

Cerebrospinal fluid (CSF) β-amyloid (Aβ) is important for early diagnosis of Alzheimer's disease (AD). However, the cohort distributions and cut-off values have large variation across different analytical assays, kits, and laboratories. In this review, we summarize the cut-off values and diagnostic performance for CSF Aβ1-42 and Aβ1-42/Aβ1-40, and explore the important effect factors. Based on the Alzheimer's Association external quality control program (AAQC program), the peer group coefficient of variation of manual ELISA assays for CSF Aβ1-42 was unsatisfied (>20%). Fully automated platforms with better performance have recently been developed, but still not widely applied. In 2020, the certified reference material (CRM) for CSF Aβ1-42 was launched; however, the AAQC 2021-round results did not show effective improvements. Thus, further development and popularization of CRM for CSF Aβ1-42 and Aβ1-40 are urgently required. Standardizing the diagnostic procedures of AD and related status and the pre-analytical protocols of CSF samples, improving detection performance of analytical assays, and popularizing the application of fully automated platforms are also important for the establishment of uniform cut-off values. Moreover, each laboratory should verify the applicability of uniform cut-off values, and evaluate whether it is necessary to establish its own population- and assay-specific cut-off values.

The small HDL particle hypothesis of Alzheimer's disease

We propose the hypothesis that small high-density lipoprotein (HDL) particles reduce the risk of Alzheimer's disease (AD) by virtue of their capacity to exchange lipids, affecting neuronal membrane composition and vascular and synaptic functions. Concentrations of small HDLs in cerebrospinal fluid (CSF) and plasma were measured in 180 individuals ≥60 years of age using ion mobility methodology. Small HDL concentrations in CSF were positively associated with performance in three domains of cognitive function independent of apolipoprotein E (APOE) ε4 status, age, sex, and years of education. Moreover, there was a significant correlation between levels of small HDLs in CSF and plasma. Further studies will be aimed at determining whether specific components of small HDL exchange across the blood, brain, and CSF barriers, and developing approaches to exploit small HDLs for therapeutic purposes.

Passage of exogeneous fine particles from the lung into the brain in humans and animals

Addressing the knowledge gaps regarding the access to and harmful effects of airborne fine particles on the central nervous system is critical. Various exogenous fine particles were found in human cerebrospinal fluids, including commonly found particles and others that have not been reported previously. Animal experiments provided mechanistic explanations and verifications of the translocation of inhaled particles into the brain. Moreover, retention of particles in the brain for longer durations than in other organs was demonstrated through isotope labeling–based biodistribution studies in mice, suggesting possible long-term effects on the brain. This work unravels indications and associations between inhalation and particle transport and adds evidence on the relationship between air pollution and detrimental effects of exogenous particles on the brain.

There are still significant knowledge gaps in understanding the intrusion and retention of exogeneous particles into the central nervous system (CNS). Here, we uncovered various exogeneous fine particles in human cerebrospinal fluids (CSFs) and identified the ambient environmental or occupational exposure sources of these particles, including commonly found particles (e.g., Fe- and Ca-containing ones) and other compositions that have not been reported previously (such as malayaite and anatase TiO₂), by mapping their chemical and structural fingerprints. Furthermore, using mouse and in vitro models, we unveiled a possible translocation pathway of various inhaled fine particles from the lung to the brain through blood circulation (via dedicated biodistribution and mechanistic studies). Importantly, with the aid of isotope labeling, we obtained the retention kinetics of inhaled fine particles in mice, indicating a much slower clearance rate of localized exogenous particles from the brain than from other main metabolic organs. Collectively, our results provide a piece of evidence on the intrusion of exogeneous particles into the CNS and support the association between the inhalation of exogenous particles and their transport into the brain tissues. This work thus provides additional insights for the continued investigation of the adverse effects of air pollution on the brain.

Alpha desynchronization during Stroop test unmasks cognitively healthy individuals with abnormal CSF Amyloid/Tau

Synaptic dysfunctions precede cognitive decline in Alzheimer's disease by decades, affect executive functions, and can be detected by quantitative electroencephalography (qEEG). We used quantitative electroencephalography combined with Stroop testing to identify changes of inhibitory controls in cognitively healthy individuals with an abnormal versus normal ratio of cerebrospinal fluid (CSF) amyloid/total-tau. We studied two groups of participants (60-94 years) with either normal (CH-NAT or controls, n = 20) or abnormal (CH-PAT, n = 21) CSF amyloid/tau ratio. We compared: alpha event-related desynchronization (ERD), alpha spectral entropy (SE), and their relationships with estimated cognitive reserve. CH-PATs had more negative occipital alpha ERD, and higher frontal and occipital alpha SE during low load congruent trials, indicating hyperactivity. CH-PATs demonstrated fewer frontal SE changes with higher load, incongruent Stroop testing. Correlations of alpha ERD with estimated cognitive reserve were significant in CH-PATs but not in CH-NATs. These results suggested compensatory hyperactivity in CH-PATs compared to CH-NATs. We did not find differences in alpha ERD comparisons with individual CSF amyloid(A), p-tau(T), total-tau(N) biomarkers.

An Association Between Saturated Fatty Acid-Containing Phosphatidylcholine in Cerebrospinal Fluid with Tau Phosphorylation

Background: Mechanistic studies in animal models implicate a role for saturated fatty acids in neurodegeneration, but validation of this finding in human studies is still lacking. Objective: We investigated how cerebrospinal levels of sphingomyelins (SM) and phosphatidylcholine (PC)-containing saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids associate with total tau and phosphorylated tau (p-tau). Methods: Cerebrospinal fluid (CSF) lipids were measured in two cohorts, a discovery and a confirmation cohort of older non-demented individuals from University of Southern California and Huntington Medical Research Institutes cohorts. Lipid analysis was performed using hydrophilic interaction liquid chromatography, and individual PC and SM lipid species were measured using tandem mass spectrometry. In addition, CSF levels of Aβ 42, total tau, and p-tau-181 were measured using an MSD multiplex assay. Results: The discovery cohort (n = 47) consisted of older individuals and more females compared to the confirmation cohort (n = 46). Notwithstanding the age and gender differences, and a higher p-tau, Aβ 42, and LDL-cholesterol in the discovery cohort, CSF concentrations of dipalmitoyl-PC (PC32a:0) were significantly associated with p-tau in both cohorts. Similarly, total saturated PC but not mono or polyunsaturated PCs correlated with p-tau concentrations in both cohorts. Conclusion: Saturated PC species in CSF associate with early markers of neurodegeneration and are potential early disease progression biomarkers. We propose mechanisms by which saturated PC may promote tau hyperphosphorylation.

Blood-brain barrier link to human cognitive impairment and Alzheimer's Disease

Vascular dysfunction is frequently seen in disorders associated with cognitive impairment, dementia and Alzheimer's disease (AD). Recent advances in neuroimaging and fluid biomarkers suggest that vascular dysfunction is not an innocent bystander only accompanying neuronal dysfunction. Loss of cerebrovascular integrity, often referred to as breakdown in the blood-brain barrier (BBB), has recently shown to be an early biomarker of human cognitive dysfunction and possibly underlying mechanism of age-related cognitive decline. Damage to the BBB may initiate or further invoke a range of tissue injuries causing synaptic and neuronal dysfunction and cognitive impairment that may contribute to AD. Therefore, better understanding of how vascular dysfunction caused by BBB breakdown interacts with amyloid-β and tau AD biomarkers to confer cognitive impairment may lead to new ways of thinking about pathogenesis, and possibly treatment and prevention of early cognitive impairment, dementia and AD, for which we still do not have effective therapies.

Fine Particulate Matter Exposure and Cerebrospinal Fluid Markers of Vascular Injury

BACKGROUND

Cerebrovascular diseases play an important role in dementia. Air pollution is associated with cardiovascular disease, with growing links to neurodegeneration. Prior studies demonstrate associations between fine particulate matter (PM2.5) and biomarkers of endothelial injury in the blood; however, no studies have evaluated these biomarkers in cerebrospinal fluid (CSF).

OBJECTIVE

We evaluate associations between short-term and long-term PM2.5 exposure with CSF vascular cell adhesion molecule-1 (VCAM-1) and e-selectin in cognitively normal and mild cognitive impairment (MCI)/Alzheimer's disease (AD) individuals.

METHODS

We collected CSF from 133 community volunteers at VA Puget Sound between 2001-2012. We assigned short-term PM2.5 from central monitors and long-term PM2.5 based on annual average exposure predictions linked to participant addresses. We performed analyses stratified by cognitive status and adjusted for key covariates with tiered models. Our primary exposure windows for the short-term and long-term analyses were 7-day and 1-year averages, respectively.

RESULTS

Among cognitively normal individuals, a 5 μg/m3 increase in 7-day and 1-year average PM2.5 was associated with elevated VCAM-1 (7-day: 35.4 (9.7, 61.1) ng/ml; 1-year: 51.8 (6.5, 97.1) ng/ml). A 5 μg/m3 increase in 1-year average PM2.5, but not 7-day average, was associated with elevated e-selectin (53.3 (11.0, 95.5) pg/ml). We found no consistent associations among MCI/AD individuals.

CONCLUSIONS

We report associations between short-term and long term PM2.5 and CSF biomarkers of vascular damage in cognitively normal adults. These results are aligned with prior research linking PM2.5 to vascular damage in other biofluids as well as emerging evidence of the role of PM2.5 in neurodegeneration.

Significance of Blood and Cerebrospinal Fluid Biomarkers for Alzheimer's Disease: Sensitivity, Specificity and Potential for Clinical Use

Alzheimer's disease (AD) is the most common type of dementia, affecting more than 5 million Americans, with steadily increasing mortality and incredible socio-economic burden. Not only have therapeutic efforts so far failed to reach significant efficacy, but the real pathogenesis of the disease is still obscure. The current theories are based on pathological findings of amyloid plaques and tau neurofibrillary tangles that accumulate in the brain parenchyma of affected patients. These findings have defined, together with the extensive neurodegeneration, the diagnostic criteria of the disease. The ability to detect changes in the levels of amyloid and tau in cerebrospinal fluid (CSF) first, and more recently in blood, has allowed us to use these biomarkers for the specific in-vivo diagnosis of AD in humans. Furthermore, other pathological elements of AD, such as the loss of neurons, inflammation and metabolic derangement, have translated to the definition of other CSF and blood biomarkers, which are not specific of the disease but, when combined with amyloid and tau, correlate with the progression from mild cognitive impairment to AD dementia, or identify patients who will develop AD pathology. In this review, we discuss the role of current and hypothetical biomarkers of Alzheimer's disease, their specificity, and the caveats of current high-sensitivity platforms for their peripheral detection.

Validation of MicroRNA Biomarkers for Alzheimer's Disease in Human Cerebrospinal Fluid

We previously discovered microRNAs (miRNAs) in cerebrospinal fluid (CSF) that differentiate Alzheimer's disease (AD) patients from Controls. Here we examined the performance of 37 candidate AD miRNA biomarkers in a new and independent cohort of CSF from 47 AD patients and 71 Controls on custom TaqMan arrays. We employed a consensus ranking approach to provide an overall priority score for each miRNA, then used multimarker models to assess the relative contributions of the top-ranking miRNAs to differentiate AD from Controls. We assessed classification performance of the top-ranking miRNAs when combined with apolipoprotein E4 (APOE4) genotype status or CSF amyloid-β42 (Aβ42):total tau (T-tau) measures. We also assessed whether miRNAs that ranked higher as AD markers correlate with Mini-Mental State Examination (MMSE) scores. We show that of 37 miRNAs brought forth from the discovery study, 26 miRNAs remained viable as candidate biomarkers for AD in the validation study. We found that combinations of 6-7 miRNAs work better to identify AD than subsets of fewer miRNAs. Of 26 miRNAs that contribute most to the multimarker models, 14 have higher potential than the others to predict AD. Addition of these 14 miRNAs to APOE4 status or CSF Aβ42:T-tau measures significantly improved classification performance for AD. We further show that individual miRNAs that ranked higher as AD markers correlate more strongly with changes in MMSE scores. Our studies validate that a set of CSF miRNAs serve as biomarkers for AD, and support their advancement toward development as biomarkers in the clinical setting.

APOE4 leads to blood-brain barrier dysfunction predicting cognitive decline

Vascular contributions to dementia and Alzheimer's disease are increasingly recognized1-6. Recent studies have suggested that breakdown of the blood-brain barrier (BBB) is an early biomarker of human cognitive dysfunction7, including the early clinical stages of Alzheimer's disease5,8-10. The E4 variant of apolipoprotein E (APOE4), the main susceptibility gene for Alzheimer's disease11-14, leads to accelerated breakdown of the BBB and degeneration of brain capillary pericytes15-19, which maintain BBB integrity20-22. It is unclear, however, whether the cerebrovascular effects of APOE4 contribute to cognitive impairment. Here we show that individuals bearing APOE4 (with the ε3/ε4 or ε4/ε4 alleles) are distinguished from those without APOE4 (ε3/ε3) by breakdown of the BBB in the hippocampus and medial temporal lobe. This finding is apparent in cognitively unimpaired APOE4 carriers and more severe in those with cognitive impairment, but is not related to amyloid-β or tau pathology measured in cerebrospinal fluid or by positron emission tomography23. High baseline levels of the BBB pericyte injury biomarker soluble PDGFRβ7,8 in the cerebrospinal fluid predicted future cognitive decline in APOE4 carriers but not in non-carriers, even after controlling for amyloid-β and tau status, and were correlated with increased activity of the BBB-degrading cyclophilin A-matrix metalloproteinase-9 pathway19 in cerebrospinal fluid. Our findings suggest that breakdown of the BBB contributes to APOE4-associated cognitive decline independently of Alzheimer's disease pathology, and might be a therapeutic target in APOE4 carriers.

Plasma tau/amyloid-β1-42 ratio predicts brain tau deposition and neurodegeneration in Alzheimer's disease

One of the hallmarks of Alzheimer's disease is abnormal deposition of tau proteins in the brain. Although plasma tau has been proposed as a potential biomarker for Alzheimer's disease, a direct link to brain deposition of tau is limited. Here, we estimated the amount of in vivo tau deposition in the brain by PET imaging and measured plasma levels of total tau (t-tau), phosphorylated tau (p-tau, T181) and amyloid-β1-42. We found significant correlations of plasma p-tau, t-tau, p-tau/amyloid-β1-42, and t-tau/amyloid-β1-42 with brain tau deposition in cross-sectional and longitudinal manners. In particular, t-tau/amyloid-β1-42 in plasma was highly predictive of brain tau deposition, exhibiting 80% sensitivity and 91% specificity. Interestingly, the brain regions where plasma t-tau/amyloid-β1-42 correlated with brain tau were similar to the typical deposition sites of neurofibrillary tangles in Alzheimer's disease. Furthermore, the longitudinal changes in cerebral amyloid deposition, brain glucose metabolism, and hippocampal volume change were also highly associated with plasma t-tau/amyloid-β1-42. These results indicate that combination of plasma tau and amyloid-β1-42 levels might be potential biomarkers for predicting brain tau pathology and neurodegeneration.

A Sensitive and Cost-Effective Chemiluminescence ELISA for Measurement of Amyloid-β 1-42 Peptide in Human Plasma

BACKGROUND

Amyloid-β42 (Aβ42) is associated with plaque formation in the brain of patients with Alzheimer's disease (AD). Studies have suggested the potential utility of plasma Aβ42 levels in the diagnosis, and in longitudinal study of AD pathology. Conventional ELISAs are used to measure Aβ42 levels in plasma but are not sensitive enough to quantitate low levels. Although ultrasensitive assays like single molecule array or immunoprecipitation-mass spectrometry have been developed to quantitate plasma Aβ42 levels, the high cost of instruments and reagents limit their use.

OBJECTIVE

We hypothesized that a sensitive and cost-effective chemiluminescence (CL) immunoassay could be developed to detect low Aβ42 levels in human plasma.

METHODS

We developed a sandwich ELISA using high affinity rabbit monoclonal antibody specific to Aβ42. The sensitivity of the assay was increased using CL substrate to quantitate low levels of Aβ42 in plasma. We examined the levels in plasma from 13 AD, 25 Down syndrome (DS), and 50 elderly controls.

RESULTS

The measurement range of the assay was 0.25 to 500 pg/ml. The limit of detection was 1 pg/ml. All AD, DS, and 45 of 50 control plasma showed measurable Aβ42 levels.

CONCLUSION

This assay detects low levels of Aβ42 in plasma and does not need any expensive equipment or reagents. It offers a preferred alternative to ultrasensitive assays. Since the antibodies, peptide, and substrate are commercially available, the assay is well suited for academic or diagnostic laboratories, and has a potential for the diagnosis of AD or in clinical trials.

Approaches to the discovery of non-invasive urinary biomarkers of prostate cancer

Prostate cancer (PCa) continues to be one of the most common cancers in men worldwide. Prostate specific antigen (PSA) measured in blood has been used for decades as an aid for physicians to detect the presence of prostate cancer. However, the PSA test has limited sensitivity and specificity, leading to unnecessary biopsies, overdiagnosis and overtreatment of patients. For these reasons, there is an urgent need for more accurate PCa biomarkers that can detect PCa with high sensitivity and specificity. Urine is a unique source of potential protein biomarkers that can be measured in a non-invasive way. This review comprehensively summarizes state of the art approaches used in the discovery and validation of urinary biomarkers for PCa. Numerous strategies are currently being used in the discovery of urinary biomarkers for prostate cancer including gel-based separation techniques, mass spectrometry, activity-based proteomic assays and software approaches. Antibody-based approaches remain preferred method for validation of candidate biomarkers with rapidly advancing multiplex immunoassays and MS-based targeted approaches. In the last decade, there has been a dramatic acceleration in the development of new techniques and approaches in the discovery of protein biomarkers for prostate cancer including computational, statistical and data mining methods. Many urinary-based protein biomarkers have been identified and have shown significant promise in initial studies. Examples of these potential biomarkers and the methods utilized in their discovery are also discussed in this review.

The technical reliability and biotemporal stability of cerebrospinal fluid biomarkers for profiling multiple pathophysiologies in Alzheimer's disease

OBJECTIVE

Alzheimer's disease (AD) is a complex neurodegenerative disease driven by multiple interacting pathophysiological processes that ultimately results in synaptic loss, neuronal death, and dementia. We implemented a fit-for-purpose modeled approach to qualify a broad selection of commercially available immunoassays and evaluate the biotemporal stability of analytes across five pathophysiological domains of interest in AD, including core amyloid-β (Aβ) and tau AD biomarkers, neurodegeneration, inflammation/immune modulation, neurovascular injury, and metabolism/oxidative stress.

METHODS

Paired baseline and eight-week CSFs from twenty participants in a clinical drug trial for mild cognitive impairment (MCI) or mild dementia due to AD were used to evaluate sensitivity, intra-assay precision, inter-assay replicability, and eight-week biotemporal stability for sixty unique analytes measured with commercially available single- and multi-plex ELISA assays. Coefficients of variation (CV) were calculated, and intraclass correlation and Wilcoxon signed rank tests were applied.

RESULTS

We identified 32 biomarker candidates with good to excellent performance characteristics according to assay technical performance and CSF analyte biotemporal stability cut-off criteria. These included: 1) the core AD biomarkers Aβ1-42, Aβ1-40, Aβ1-38, and total tau; 2) non-Aβ, non-tau neurodegeneration markers NfL and FABP3; 3) inflammation/immune modulation markers IL-6, IL-7, IL-8, IL-12/23p40, IL-15, IL-16, MCP-1, MDC, MIP-1β, and YKL-40; 4) neurovascular markers Flt-1, ICAM-1, MMP-1, MMP-2, MMP-3, MMP-10, PlGF, VCAM-1, VEGF, VEGF-C, and VEGF-D; and 5) metabolism/oxidative stress markers 24-OHC, adiponectin, leptin, soluble insulin receptor, and 8-OHdG.

CONCLUSIONS

Assays for these CSF analytes demonstrate consistent sensitivity, reliability, and biotemporally stability for use in a multiple pathophysiological CSF biomarker panel to profile AD. Their qualification enables further investigation for use in AD diagnosis, staging and progression, disease mechanism profiling, and clinical trials.

The use of cerebrospinal fluid in biomarker studies

Cerebrospinal fluid (CSF) is an extremely useful matrix for biomarker research for several purposes, such as diagnosis, prognosis, monitoring, and identification of prominent leads in pathways of neurologic diseases. Such biomarkers can be identified based on a priori hypotheses around prominent protein changes, but also by applying -omics technologies. Proteomics is widely used, but metabolomics and transcriptomics are rapidly revealing their potential for CSF studies. The basis of such studies is the availability of high-quality biobanks. Furthermore, profound knowledge and consequent optimization of all aspects in biomarker development are needed. Here we discuss current knowledge and recently developed protocols for successful biomarker studies, from collection of CSF by lumbar puncture, processing, and biobanking protocols, preanalytic confounding factors, and cost-efficient development and validation of assays for implementation into clinical practice or research.

Effects of Meditation and Music-Listening on Blood Biomarkers of Cellular Aging and Alzheimer's Disease in Adults with Subjective Cognitive Decline: An Exploratory Randomized Clinical Trial

BACKGROUND

Telomere length (TL), telomerase activity (TA), and plasma amyloid-β (Aβ) levels have emerged as possible predictors of cognitive decline and dementia.

OBJECTIVE

To assess the: 1) effects of two 12-week relaxation programs on TL, TA, and Aβ levels in adults with subjective cognitive decline; and 2) relationship of biomarker changes to those in cognitive function, psychosocial status, and quality of life (QOL).

METHODS

Participants were randomized to a 12-week Kirtan Kriya meditation (KK) or music listening (ML) program and asked to practice 12 minutes/day. Plasma Aβ(38/40/42) and peripheral blood mononuclear cell TL and TA were measured at baseline and 3 months. Cognition, stress, sleep, mood, and QOL were assessed at baseline, 3 months, and 6 months.

RESULTS

Baseline blood samples were available for 53 participants (25 KK, 28 ML). The KK group showed significantly greater increases in Aβ40 than the ML group. TA rose in both groups, although increases were significant only among those with higher practice adherence and lower baseline TA. Changes in both TL and TA varied by their baseline values, with greater increases among participants with values ≤50th percentile (ps-interaction <0.006). Both groups improved in cognitive and psychosocial status (ps ≤0.05), with improvements in stress, mood, and QOL greater in the KK group. Rising Aβ levels were correlated with gains in cognitive function, mood, sleep, and QOL at both 3 and 6 months, associations that were particularly pronounced in the KK group. Increases in TL and TA were also correlated with improvements in certain cognitive and psychosocial measures.

CONCLUSION

Practice of simple mind-body therapies may alter plasma Aβ levels, TL, and TA. Biomarker increases were associated with improvements in cognitive function, sleep, mood, and QOL, suggesting potential functional relationships.

Concordance Between Different Amyloid Immunoassays and Visual Amyloid Positron Emission Tomographic Assessment

Importance

Visual assessment of amyloid positron emission tomographic (PET) images has been approved by regulatory authorities for clinical use. Several immunoassays have been developed to measure β-amyloid (Aβ) 42 in cerebrospinal fluid (CSF). The agreement between CSF Aβ42 measures from different immunoassays and visual PET readings may influence the use of CSF biomarkers and/or amyloid PET assessment in clinical practice and trials.

Objective

To determine the concordance between CSF Aβ42 levels measured using 5 different immunoassays and visual amyloid PET analysis.

Design, Setting, and Participants

The study included 262 patients with mild cognitive impairment or subjective cognitive decline from the Swedish BioFINDER (Biomarkers for Identifying Neurodegenerative Disorders Early and Reliably) cohort (recruited from September 1, 2010, through December 31, 2014) who had undergone flutemetamol F 18 ([18F]flutemetamol)-labeled PET. Levels of CSF Aβ42 were analyzed using the classic INNOTEST and the newer modified INNOTEST, fully automated Lumipulse (FL), EUROIMMUN (EI), and Meso Scale Discovery (MSD) assays. Concentrations of CSF Aβ were assessed using an antibody-independent mass spectrometry-based reference measurement procedure.

Main Outcomes and Measures

The concordance of CSF Aβ42 levels and Aβ42:Aβ40 and Aβ42:tau ratios with visual [18F]flutemetamol PET status.

Results

Of 262 participants (mean [SD] age, 70.9 [5.5] years), 108 were women (41.2%) and 154 were men (58.8%). The mass spectrometry-derived Aβ42 values showed higher correlations with the modified Aβ42-INNOTEST (r = 0.97), Aβ42-FL (r = 0.93), Aβ42-EI (r = 0.93), and Aβ42-MSD (r = 0.95) assays compared with the classic Aβ42-INNOTEST assay (r = 0.88; P ≤ .01). The signal in the classic Aβ42-INNOTEST assay was partly quenched by recombinant Aβ1-40 peptide. However, the classic Aβ42-INNOTEST assay showed better concordance with visual [18F]flutemetamol PET status (area under the receiver operating characteristic curve [AUC], 0.92) compared with the newer assays (AUCs, 0.87-0.89; P ≤ .01). The accuracies of the newer assays improved significantly when Aβ42:Aβ40 (AUCs, 0.93-0.95; P ≤ .01), Aβ42 to total tau (T-tau) (AUCs, 0.94; P ≤ .05), or Aβ42 to phosphorylated tau (P-tau) (AUCs, 0.94-0.95; P ≤ .001) ratios were used. A combination of the Aβ42:Aβ40 ratio and T-tau or P-tau level did not improve the accuracy compared with the ratio alone.

Conclusions and Relevance

Concentrations of CSF Aβ42 derived from the new immunoassays (modified INNOTEST, FL, EI, and MSD) may correlate better with the antibody-independent mass spectrometry-based reference measurement procedure and may show improved agreement with visual [18F]flutemetamol PET assessment when using the Aβ42:Aβ40 or Aβ42:tau ratios. These findings suggest the benefit of implementing the CSF Aβ42:Aβ40 or Aβ42:tau ratios as a biomarker of amyloid deposition in clinical practice and trials.

Cerebrospinal fluid biomarkers for Alzheimer's and vascular disease vary by age, gender, and APOE genotype in cognitively normal adults

BACKGROUND

This study sought to evaluate gender and APOE genotype-related differences in the concentrations of cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease (AD) and cerebrovascular injury across the life span of cognitively normal adults.

METHODS

CSF amyloid beta_1-42 (Aβ₄₂), phospho-tau-181 (p-tau₁₈₁), and total tau were measured in 331 participants who were between the ages of 21 and 100. CSF E-selectin and vascular cell adhesion protein 1 (VCAM1) were measured in 249 participants who were between the ages of 50 and 100.

RESULTS

CSF total tau and p-tau₁₈₁ increased with age over the adult life span (p < 0.01) with no gender differences in those increases. CSF Aβ₄₂ concentration varied according to age, gender, and APOE genotype (interaction of age × gender × ε4, p = 0.047). CSF VCAM1, but not E-selectin, increased with age (p < 0.01), but both were elevated in men compared to women (p < 0.01).

CONCLUSIONS

Female APOE-ε4 carriers appear at higher risk for AD after age 50. In contrast, men may experience a relatively higher rate of cerebrovascular injury in middle and early old age.

Genome-wide association and interaction studies of CSF T-tau/Aβ42 ratio in ADNI cohort

The pathogenic relevance in Alzheimer's disease (AD) presents a decrease of cerebrospinal fluid amyloid-ß₄₂ (Aß₄₂) burden and an increase in cerebrospinal fluid total tau (T-tau) levels. In this work, we performed genome-wide association study (GWAS) and genome-wide interaction study of T-tau/Aß₄₂ ratio as an AD imaging quantitative trait on 843 subjects and 563,980 single-nucleotide polymorphisms (SNPs) in ADNI cohort. We aim to identify not only SNPs with significant main effects but also SNPs with interaction effects to help explain "missing heritability". Linear regression method was used to detect SNP-SNP interactions among SNPs with uncorrected p-value ≤0.01 from the GWAS. Age, gender, and diagnosis were considered as covariates in both studies. The GWAS results replicated the previously reported AD-related genes APOE, APOC1, and TOMM40, as well as identified 14 novel genes, which showed genome-wide statistical significance. Genome-wide interaction study revealed 7 pairs of SNPs meeting the cell-size criteria and with bonferroni-corrected p-value ≤0.05. As we expect, these interaction pairs all had marginal main effects but explained a relatively high-level variance of T-tau/Aß₄₂, demonstrating their potential association with AD pathology.

Validation of α-Synuclein as a CSF Biomarker for Sporadic Creutzfeldt-Jakob Disease

The analysis of cerebrospinal fluid (CSF) biomarkers gains importance in the differential diagnosis of prion diseases. However, no single diagnostic tool or combination of them can unequivocally confirm prion disease diagnosis. Electrochemiluminescence (ECL)-based immunoassays have demonstrated to achieve high diagnostic accuracy in a variety of sample types due to their high sensitivity and dynamic range. Quantification of CSF α-synuclein (a-syn) by an in-house ECL-based ELISA assay has been recently reported as an excellent approach for the diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD), the most prevalent form of human prion disease. In the present study, we validated a commercially available ECL-based a-syn ELISA platform as a diagnostic test for correct classification of sCJD cases. CSF a-syn was analysed in 203 sCJD cases with definite diagnosis and in 445 non-CJD cases. We investigated reproducibility and stability of CSF a-syn and made recommendations for its analysis in the sCJD diagnostic workup. A sensitivity of 98% and a specificity of 97% were achieved when using an optimal cut-off of 820 pg/mL a-syn. Moreover, we were able to show a negative correlation between a-syn levels and disease duration suggesting that CSF a-syn may be a good prognostic marker for sCJD patients. The present study validates the use of a-syn as a CSF biomarker of sCJD and establishes the clinical and pre-analytical parameters for its use in differential diagnosis in clinical routine. Additionally, the current test presents some advantages compared to other diagnostic approaches: it is fast, economic, requires minimal amount of CSF and a-syn levels are stable along disease progression.

Mass-Spectrometry-Based Method To Quantify in Parallel Tau and Amyloid β 1-42 in CSF for the Diagnosis of Alzheimer's Disease

Alzheimer's disease (AD), the most common form of dementia, afflicts about 50 million people worldwide. Currently, AD diagnosis is primarily based on psychological evaluation and can only be confirmed post-mortem. Reliable and objective biomarkers for prognosis and diagnosis have been sought for years. Together, tau and amyloid β 1-42 (Aβ₄₂) in cerebrospinal fluid (CSF) have been shown to provide good diagnostic sensitivity and specificity. Additionally, phosphorylated forms of tau, such as tau pS181, have also shown promising results. However, the measurement of such markers currently relies on antibody-based immunoassays that have shown variability, leading to discrepant results across laboratories. To date, mass spectrometry methods developed to evaluate CSF tau and Aβ₄₂ are not compatible. We present in this article the development of a mass-spectrometry-based method of quantification for CSF tau and Aβ₄₂ in parallel. The absolute concentrations of tau and Aβ₄₂ we measured are on average 50 ng/mL (7-130 ng/mL) and 7.1 ng/mL (3-13 ng/mL), respectively. Analyses of CSF tau and Aβ₄₂, in a cohort of patients with AD, mild cognitive impairment, and healthy controls (30 subjects), provide significant group differences evaluated with ROC curves (AUC_(control-AD) and AUC_{(control-MCI)} = 1, AUC_(MCI-AD) = 0.76), with at least equivalent diagnostic utility to immunoassay measurements in the same sample set. Finally, a significant and negative correlation was found between the tau and Aβ peptides ratio and the disease severity.

Increased CSF E-Selectin in Clinical Alzheimer's Disease without Altered CSF Aβ42 and Tau

Clinically diagnosed Alzheimer's disease (AD) is pathologically heterogeneous. In this multicenter cohort of 215 clinically diagnosed AD patients and 249 controls, E-selectin and vascular cell adhesion molecule 1 (VACM-1) were measured along with amyloid-β peptide 1-42 (Aβ42) and tau. We discovered that E-selectin, a biomarker of endothelial function/vascular injury, was inversely correlated with cerebrospinal fluid (CSF) tau/Aβ42 ratio and significantly elevated in clinical AD patients without the typical AD CSF biomarker signature (i.e., low tau/Aβ42 ratio) compared to those with the signature. These findings suggest that E-selectin may be an objective biomarker related to vascular mechanisms contributing to dementia.

A First Tetraplex Assay for the Simultaneous Quantification of Total α-Synuclein, Tau, β-Amyloid42 and DJ-1 in Human Cerebrospinal Fluid

The quantification of four distinct proteins (α-synuclein, β-amyloid_1-42, DJ-1, and total tau) in cerebrospinal fluid (CSF) has been proposed as a laboratory-based platform for the diagnosis of Parkinson’s disease (PD) and Alzheimer’s disease (AD). While there is some clinical utility in measuring these markers individually, their usage in routine clinical testing remains challenging, in part due to substantial overlap of concentrations between healthy controls and diseased subjects. In contrast, measurement of different analytes in a single sample from individual patients in parallel appears to considerably improve the accuracy of AD or PD diagnosis. Here, we report the development and initial characterization of a first, electrochemiluminescence-based multiplex immunoassay for the simultaneous quantification of all four proteins (‘tetraplex’) in as little as 50 μl of CSF. In analytical performance experiments, we assessed its sensitivity, spike-recovery rate, parallelism and dilution linearity as well as the intra- and inter-assay variability. Using our in-house calibrators, we recorded a lower limit of detection for α-synuclein, β-amyloid₄₂, DJ-1, and t-tau of 1.95, 1.24, 5.63, and 4.05 pg/ml, respectively. The corresponding, linear concentration range covered >3 orders of magnitude. In diluted CSF samples (up to 1:4), spike-recovery rates ranged from a low of 55% for β-amyloid₄₂ to a high of 98% for DJ-1. Hillslopes ranged from 1.03 to 1.30, and inter-assay variability demonstrated very high reproducibility. Our newly established tetraplex assay represents a significant technical advance for fluid-based biomarker studies in neurodegenerative disorders allowing the simultaneous measurement of four pivotal makers in single CSF specimens. It provides exceptional sensitivity, accuracy and speed.