Alzheimer's & Dementia

Introduction: Participant- and study partner-reported Cognitive Function Index scores may provide complementary information, but it remains unclear whether Alzheimer's disease biomarkers are associated with CFI scores across reporters, reporter-specific imbalance, or both. Methods: Using A4/LEARN screening data (screening sample, N = 1,686; primary dyadic analytic sample, N = 1,682; CDR global score = 0), we jointly modeled participant-reported (CFI-PT) and study partner-reported (CFI-SP) scores in long format to evaluate biomarker associations with CFI scores and biomarker x reporter interactions. As a secondary analysis, we compared tau PET with plasma p-tau217. Results: In an A4/LEARN-adapted regional extent model, reporter balance varied across amyloid regional extent categories, with the largest participant-leading contrast observed in the exploratory restricted early cortical subgroup. Tau PET was associated with higher CFI scores, but this association did not differ detectably between reporters. Plasma p-tau217 showed no clear CFI association or reporter-specific interaction in the A4-derived, amyloid-enriched subset. Discussion: Amyloid regional extent and tau PET were associated with different features of dyadic CFI data: reporter balance and CFI burden across reporters, respectively. Joint interpretation of CFI-PT and CFI-SP may support biomarker-informed interpretation of the instrument, although the cross-sectional findings require replication and longitudinal validation.

INTRODUCTIONThe growing number of assay platforms measuring blood-based biomarkers (BBMs) for Alzheimers disease (AD) has introduced challenges in interpretability and comparability across assays. Differences across studies also limit comparability of data. To address these challenges, a systematic evaluation of harmonization methods is needed to support BBM data integration within or across studies. METHODSTwo multisite studies, Alzheimers Disease Neuroimaging Initiative (ADNI, n = 219) and Human Connectome Project (HCP, n = 111), were used to evaluate harmonization methods for mitigating assay and cohort effects in plasma p-tau217 measurements. Methods includes various normalization, regression, and standardization approaches, including the recently developed CentiMarker. Assay effects were evaluated using repeated-measures data across assay platforms within each cohort, whereas cohort effects were assessed using pooled ADNI and HCP data. Harmonization performance was evaluated using distributional statistics and downstream modeling of p-tau217. RESULTSQuantile normalization and quantile mapping methods were most effective for mitigating assay effects, whereas conditional quantile mapping performed best for pooled multi-cohort data. These methods also preserved biological variability. In contrast, simple means adjustment and reference-based z-score standardization were least effective for mitigating assay effects, while simple means adjustment, z-score standardization, and quantile normalization were least effective for mitigating cohort effects. CentiMarker had minimal impact on assay or cohort effects. DISCUSSIONBased on our evaluation, we recommend (conditional) quantile mapping for p-tau217 studies integrating data across multiple assays or cohorts. In contrast, we caution against using CentiMarker and z-score-based methods, as they limit comparability and do not effectively mitigate technical variability.

INTRODUCTION: Brain resilience to tau has been mainly studied in relation to grey matter, while its role in white matter remains unclear in Alzheimer's disease (AD). Sex may moderate associations between brain resilience and cognition. METHODS: We analyzed medial temporal lobe tau PET SUVR, entorhinal cortical thickness, cingulum-hippocampal mean diffusivity, and cognition in 205 amyloid-positive individuals from ADNI. Associations between grey- and white-matter resilience to tau and cognitive performance or decline were examined using linear and mixed-effects models, including sex interactions and stratified analyses. RESULTS: Higher grey-matter resilience to tau related to better cross-sectional memory and language performance (p<0.005), whereas higher white-matter resilience related to slower decline in these domains (p<0.03). These associations were seen in men but not women. DISCUSSION: White-matter resilience may better capture early cognitive changes in AD. Sex differences suggest greater sensitivity of cognition to brain resilience in men.

Background: Blood-based biomarkers are increasingly used to identify Alzheimer's disease (AD)-related pathology, but differences in p217tau assay methodology, training cohorts, and model-development context can substantially influence machine-learning (ML) predictions. Whether emerging biomarker platforms preserve biologically meaningful AD-related information across independently developed ML frameworks remains incompletely understood. Objective: To evaluate the biological coherence and translational consistency of plasma biomarker measurements generated using the 5ADCSI platform by applying multiple externally trained ML frameworks and developing a consensus-risk approach that integrates framework predictions while quantifying prediction uncertainty. Methods: Plasma biomarker measurements from 472 participants in the Louisville Twins Study were analyzed using three independently trained ML frameworks: an A4-derived model using the Lilly p217tau MSD assay and two ADNI-derived models using Quanterix Simoa p217tau measured with either the AlzPath or Janssen antibody. Framework-specific predictions of amyloid positivity probability and predicted centiloid burden were integrated into consensus amyloid risk, consensus centiloid burden, and composite consensus AD-risk scores. Prediction uncertainty and rank instability were used to characterize framework agreement and participant-level classification stability. Results: All three frameworks recognized biologically coherent AD-related signal despite differences in training cohort and assay methodology. Agreement was strongest between the A4-MSD and ADNI-AlzPath frameworks, whereas agreement involving the ADNI-Jan framework was weaker. Consensus-risk modeling identified a reproducibly high-risk subgroup characterized by elevated consensus-risk scores, low prediction uncertainty, and low rank instability. Participants prioritized by the consensus framework were enriched for APOE {varepsilon}4 burden, p-tau217, p-tau217/A{beta}42, and GFAP, while discordant high-risk participants exhibited substantially greater framework disagreement. Conclusions: Plasma biomarker measurements generated using the 5ADCSI platform preserve biologically meaningful AD-related information that is consistently recognized across multiple independent ML frameworks. Consensus-risk modeling provides a practical strategy for integrating complementary information from external biological reference models while explicitly characterizing prediction uncertainty, thereby supporting evaluation of emerging blood-based biomarker platforms when direct pathological validation is unavailable.

Background: Plasma phosphorylated tau-217 (pTau-217) measurements for use in Alzheimer disease (AD) identification require thresholds to define positivity and there exist different approaches to operationally defining the boundary. We compared amyloid {beta} (AB) PET-anchored and distribution-based positivity cut-off values and explored how these mapped onto latent biomarker states. Methods: We analysed plasma pTau-217 measured in the Bio-Hermes-001 cohort (N = 990) using an immunoassay (Lilly) and mass spectrometry assay (University of Gothenburg). Gaussian mixture models were used to identify latent classes and thresholds were derived in two ways: achieving 90% specificity for AB PET positivity and exceeding the mean + 2SDs of the lowest latent class. We explore classes in reference to AB PET status and clinical diagnosis, as well as agreement between approaches using Cohen kappa for both assays. Results: In both assays, three latent biomarker classes were identified with monotonic increases in AD clinical diagnosis and AB PET positivity. PET-anchored thresholds showed lower specificity but higher sensitivity to amyloid positivity than distribution-based thresholds. Overall agreement between the approaches was acceptable (k = 0.678 for Lilly and 0.575 for University of Gothenburg), with disagreement concentrated in the intermediate latent class. Classes with the lowest and highest pTau-217 concentrations were classified consistently using both thresholds Discussion: The two thresholding approaches yielded similar classifications at both the negative and positive tail of the observed biomarker distribution, but classify intermediate concentrations differently. The boundary definition influenced pTau-217 positivity more than the analytical platform itself. Thresholding approaches may capture different pTau-217 biomarker states, therefore such methodological decisions should be grounded in the context of the intended application.

Introduction: Alzheimer's disease (AD) pathology accumulates decades before symptom onset, yet how the cumulative effect of genetic, familial, and modifiable lifestyle risk burden jointly affects plasma biomarker levels and trajectories in cognitively unimpaired older adults remains unknown. Methods: We analyzed data from 261 participants in the PREVENT-AD cohort. A composite risk score integrating APOE e4 status, polygenic score, family history, and modifiable/lifestyle risk was examined against six plasma biomarkers using linear regression and linear mixed-effects models. Results: APOE e4 was the strongest predictor of plasma biomarker levels. Higher composite risk burden was associated with elevated ptau181, ptau217, ptau217/Ab42, and GFAP levels, and lower Ab42/40 levels. A higher risk burden was predictive of accelerated ptau181 accumulation. Discussion: Cumulative AD risk burden is broadly associated with plasma biomarker levels and specifically predicts accelerated ptau181 accumulation in cognitively unimpaired older adults, supporting structured composite risk profiling as a framework for AD risk stratification.

Alzheimer's disease is clinically and biologically heterogeneous. We asked whether plasma proteomics separates patients into discrete molecular subtypes or instead reflects continuous biological variation. We studied 5,895 Global Neurodegeneration Proteomics Consortium (GNPC) participants with Alzheimer's disease or mild cognitive impairment using protein coexpression networks, clustering, and continuous molecular-axis analysis. External analyses used Stanford Alzheimer's Disease Research Center (ADRC) biomarker/imaging data and UK Biobank proteomics.Four continuous axes captured 81.5% of module-level proteomic variation. Although a two-cluster solution was reproducible, separation was weak and added little clinical information beyond the continuous axes. Stanford ADRC analyses showed selected fluid biomarker associations, but imaging and PET results did not provide consistent support. In UK Biobank, projected axes were more strongly related to APOE genotype and systemic hematologic, renal, lipid, inflammatory, and hepatic traits than to clear dementia-risk replication. Plasma proteomics did not support robust Alzheimer's disease subtypes. Continuous molecular coordinates better describe plasma proteomic heterogeneity and may guide future biological stratification.

Background: Plasma brain-derived pTau217(BD-pTau217) may provide a Alzheimers disease-specific plasma tau measure than total pTau217, but its prognostic value is unclear. We compared BD-pTau217 and total plasma pTau217 for predicting clinical and amyloid PET progression in cognitively unimpaired (CU) ADNI participants. Methods: Plasma NULISAseq biomarkers were measured in 1,427 ADNI participants, including 529 CU individuals. Amyloid PET progression was assessed in baseline CU amyloid-negative participants (Centiloid [&ge;] 24.1) with longitudinal PET imaging; clinical progression was assessed in all baseline CU participants. Associations were evaluated using Cox models and time-dependent AUC. Results: BD-pTau217 did not clearly outperform total pTau217 for predicting progression to mild cognitive impairment or dementia. However, among baseline amyloid-negative participants (N=175), BD-pTau217 better predicted amyloid PET positivity at 2.5 years (tdAUC 0.82 vs 0.69; HR=10.54, p=0.00015) and 4 years (tdAUC 0.77 vs 0.64; HR=7.03, p=0.00055). Conclusion: BD-pTau217 improved prediction of near-term amyloid PET progression, with less clear advantage for clinical progression.

Background: Up to 30% of individuals harboring core Alzheimer's disease (AD) neuropathology, amyloid-beta (Abeta; A) and tau (T)-remain cognitively unimpaired. Objective: We examine whether MRI measures of cerebral blood flow (CBF) and white matter hyperintensities (WMH) differentiate cognitively impaired (AD or mild cognitive impairment (MCI);AD+MCI) from non-demented individuals with (NDAN) and without (Controls) core AD neuropathology. Methods: A retrospective cohort study (2018-2023) using data from The Wisconsin Registry for Alzheimer's Prevention and Wisconsin Alzheimer's Disease Research Center studies employed linear models comparing group differences in regional gray matter (GM) CBF and whole brain WMH volume. Participants (N=500) underwent 3T MRI, amyloid- (11C-Pittsburgh Compound B) and tau- (18F-MK6240) PET, and neuropsychological assessments. We categorized participants based on PET and cognitive status as Controls (n=416; cognitively unimpaired, A-T-), NDAN (n=38; cognitively unimpaired, A+T+), or AD+MCI (n=46; cognitively impaired, A+T+). Results: Participants were 67 years old (mean), 68% female, and 37% APOE 4+. NDAN, like Controls, had significantly higher CBF than AD+MCI in GM regions susceptible to neurofibrillary tangle formation in early AD (frontal and temporal cortices, and limbic regions (ps<0.05)). Largest CBF differences (22-34%) were observed in GM regions that accumulate amyloid early but remain largely tangle-free during early AD progression, namely the occipital and parietal cortices. WMH volume differentiated AD+MCI from Controls (p=0.002) but not NDAN (p=0.16). Conclusion: CBF differentiated NDAN from AD+MCI, highlighting vascular contributions to cognitive resilience. Most pronounced CBF preservation in NDAN was observed in parietal and occipital cortices, regions typically free of tau until late stages of AD progression.

INTRODUCTION: The Clinical Dementia Rating Sum of Boxes (CDR-SB), a primary outcome in anti-amyloid therapy (AAT) trials, integrates information from participants and study partners. CDR-SB scores may vary by study partner characteristics, but their impact on 18-month change interpretation remains unclear. METHODS: Using the NACC Uniform Data Set, we fitted linear mixed-effects calibration models in an Alzheimer's disease (AD)-primary early symptomatic cohort and propagated study partner-associated coefficients through Monte Carlo simulations. We estimated components of 18-month CDR-SB change under observed profile changes, simulated follow-up imbalance in a common female living-with profile, and tipping-point scenarios. Analyses were repeated in amyloid-positive and trial-like cohorts. RESULTS: The AD-primary cohort included 15,061 participants and 7,683 baseline-to-18-month pairs. Observed profile changes generated a negligible cohort-level component (mean 0.0014 points, 95% simulation interval 0.0006 to 0.0022). Simulated follow-up imbalance generated differences of 0.014 to 0.071 points across 10% to 50% reassignment. Under the primary calibration model, generating a 0.45-point difference, equal to the reported Clarity AD CDR-SB group difference, required median net imbalance >100% and was feasible in 48% of iterations. Amyloid-positive and trial-like cohorts had lower median tipping points but wider intervals, reflecting coefficient imprecision. DISCUSSION: In the large AD-primary cohort, observed study partner profile changes and simulated follow-up imbalance generated CDR-SB differences that were small relative to the 0.45-point Clarity AD benchmark. Biomarker-confirmed estimates were less stable because of coefficient imprecision. These findings suggest limited impact under typical AD-primary conditions but support systematic study partner profile collection and sensitivity analyses in observational and external-comparator CDR-SB studies for AAT evaluation.

Background: Plasma phosphorylated tau at threonine 217 (p-Tau217) is a leading blood-based biomarker for Alzheimer's disease (AD). Robust analytical characterization on high-throughput platforms is essential for research use and clinical translation. Objective: To evaluate the analytical performance of an automated plasma p-Tau217 immunoassay and characterize its discrimination of PET-defined amyloid status. Methods: We performed analytical validation of the Access Research Use Only (RUO) plasma p-Tau217 immunoassay on the Beckman Coulter DxI 9000 Access Immunoassay Analyzer and evaluated biomarker discrimination of PET-defined amyloid pathology in a subset of the Bio-Hermes-001 cohort spanning the symptomatic cognitive continuum (mild cognitive impairment or mild AD dementia; cognitively unimpaired participants excluded; n = 449). Analytical precision, sensitivity, linearity, specificity, interference, and sample stability were assessed per Clinical and Laboratory Standards Institute guidelines. Discrimination of PET-defined amyloid status was evaluated using receiver operating characteristic curve and indeterminate zone analyses. Results: The assay demonstrated high precision (within-laboratory CV </=7.1%), excellent sensitivity (limit of detection 0.018-0.021 pg/mL), linearity across the analytical measuring range (R-squared > 0.99), strong epitope specificity (</=1.0% cross-reactivity with other tau phosphoisoforms), and minimal interference from over 60 endogenous and exogenous substances. In 449 research participants plasma p-Tau217 showed strong discrimination between amyloid-positive and amyloid-negative groups (AUC 0.881; 95% CI 0.846-0.915). Application of indeterminate zones systematically improved classification metrics at the cost of fewer definitive classifications. Conclusions: These findings support the Access p-Tau217 (RUO) assay as a robust, high-throughput assay for plasma biomarker-based discrimination of PET-defined amyloid pathology in AD applications.

Detection and characterisation of dementia and Mild Cognitive Impairment (MCI) is essential for diagnosis and to support recruitment of patients into trials of disease-targeted therapies. Computerised systems offer a means of improving detection in community and primary care settings in a scalable way. This study presents further validation of the self-test PROTECT Cognitive Test System of eight assessments of memory, attention and executive function in 36,941 participants (35,822 healthy, 1046 MCI, 73 dementia). PROTECT shows robust separation of dementia and non-dementia participants (p < 0.001), and good discriminative ability for dementia (Area Under the Curve = 0.966) with 90.90% sensitivity and 87.80% specificity. An optimised detection algorithm robustly identified MCI (P<0.001) and predicted 24-month decline across cognitive domains in both amnestic MCI and non-amnestic MCI phenotypes compared with healthy controls. PROTECT cognitive data also correlated strongly with the plasma biomarkers p-tau217 and Neurofilament Light (n = 46). The system provides a means of improving dementia and MCI detection using self-testing, offering a scalable triage and monitoring tool for clinical pathways and trials.

ABSTRACT Importance: The biological mechanisms underlying the associations of social isolation and loneliness with dementia risk are not well understood. Objective: To evaluate the relationship of prospectively measured social isolation and loneliness with AD/ADRD blood-based biomarkers. Design: Observational study using the U.S. Health and Retirement Study (2010-2016). Venous blood draws were conducted in 2016 and AD/ADRD biomarkers were released in 2025. We estimated associations of social isolation and loneliness patterns between 2012 and 2014 with continuous biomarkers using linear regressions, accounting for socio-demographic and health covariates. We evaluated effect modification by sex and APOE {varepsilon}4 carrier status. Setting: Population-based Participants: Community-dwelling HRS participants aged 50 years or older (n = 3862). Exposures: Primary exposures were four-category multi-wave variables of persistent, resolving, new-onset, or no social isolation/loneliness across the two exposure waves. Social isolation was classified as "severe" and "moderate-to-severe" based on a 5-item scale including marital status, household size, proximity to children, religious service attendance, and volunteering. Past-week loneliness was measured with a single-item question (yes/no). Main Outcomes and Measures: Neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), and the ratio of amyloid beta 42 to amyloid beta 40 (A{beta}42/40), measured in plasma via a Multiplex Simoa Assay and phosphorylated tau (p-tau181), measured in serum via a Simoa Assay. Results: At the analytic baseline, respondents were a mean age of 64 (9.5) years, 59% female, and 25% APOE {varepsilon}4 carriers. Across the two exposure waves, 4% experienced persistent severe social isolation, 16% experienced persistent moderate-to-severe social isolation, and 8% reported persistent loneliness. Multiple patterns of social isolation (vs. no social isolation) were associated with higher NfL, including persistent severe social isolation ({beta}: 0.31), new-onset moderate-to-severe social isolation ({beta}: 0.14), and resolving moderate-to-severe social isolation ({beta}: 0.20). Persistent severe social isolation was associated with lower GFAP ({beta}: -0.31) while persistent loneliness and, for men, new-onset loneliness were associated with higher GFAP ({beta}_persistent: 0.16; {beta}_(new onset_men): 0.25). New-onset severe social isolation was associated with a lower A{beta}42/40 ratio ({beta}: -0.25) while resolving moderate-to-severe social isolation and, for men, persistent severe social isolation were each associated with higher p-tau181 ({beta}_resolving: 0 .11; {beta}_(persistent_men): 0.41). There was some additional variation by APOE {varepsilon}4 carriership, although selective survival is a concern. Conclusions: Social isolation was associated with elevated blood-based biomarkers of neuronal injury, with variation by patterns of exposure over time. Associations between social isolation and loneliness with biomarkers related to astrocyte damage and Alzheimer's disease were less consistent, and varied in sign and magnitude by exposure and sex.

INTRODUCTION: Accurately identifying risk of Alzheimers Dementia (AD) is essential for supporting people living with symptoms in clinical settings, as well as recruiting adults in prospective medical research. Various algorithms have been created to calculate AD risk based on evidenced risk factors which are weighted toward a total score. As daily life conditions determining risk change at scale, it remains unclear how effective gold standard algorithms remain in modern cohorts. METHODS: In the Bio-Hermes-001 diverse cohort, we assessed algorithm discrimination and calibration in six outcomes: classifying AB PET binary outcome (negative N = 603, positive N = 342); phosphorylated tau-217 binary outcome (pTau-217 negative N = 166, positive N = 469); participants with Healthy Cognition (N = 417) from probable AD (N = 272); HC from Mild Cognitive Impairment (N = 312), HC from pooled MCI or AD; and MCI from AD. Approximately a third of the cohort are individuals from populations typically underrepresented in dementia research (HC: 19%; MCI: 24%; AD: 33%). RESULTS: Hosmer-Lemeshow tests and Brier score demonstrate acceptable calibration of all algorithms except the oldest algorithm. However, Receiver Operating Characteristic (ROC) curves and the associated area under the curve (AUC) estimates evidenced that in this cohort only the BDSI exceeded conventional thresholds for good discrimination (.8 AUC in HC-AD classification, with AUC approximately .7 in the other clinical, AB PET, and pTau-217 comparisons). When the functional item is removed from the BDSI score, it remains acceptably calibrated, but DeLong tests reflect statistically significant reduction in discriminatory performance for all group comparisons. The two earliest published algorithms were only chance-level accurate. DISCUSSION: In a contemporary, diverse cohort, most established dementia risk algorithms had limited power in discriminating amyloid positivity, pTau-217 positivity, and current cognitive status despite acceptable calibration. Including a functional measure markedly improved discrimination across both clinical and biomarker-defined outcomes, suggesting that proximal indicators of cognitive vulnerability are critical for identifying individuals with underlying AD-related pathology.

INTRODUCTION: Characterizing the prognostic utility of blood-based biomarkers for Alzheimer's disease (AD) in predicting longitudinal cognitive trajectories is essential; however, population-based evidence is needed. METHODS: We evaluated plasma phosphorylated tau at threonine 217 (p-tau217) and plasma neurofilament light chain (NfL) in 4,971 dementia-free individuals aged 70 years and older from the population-based Norwegian HUNT study. Predefined cut offs categorized biomarker ranges (p-tau217: low, intermediate, high; NfL: low, high), in addition to continuous biomarker analysis. RESULTS: Adjusted for other risk factors, higher baseline p-tau217 and NfL ranges indicated a significantly increased dementia risk after four years compared to low ranges (intermediate p-tau217: risk ratio [RR] 1.23, 95% CI 1.01-1.50; high p-tau217: RR 2.05, 95% CI 1.73-2.44; high NfL: RR 1.72, 95% CI 1.31-2.27; jointly high p-tau217 and NfL: RR 3.32, 95% CI 2.61-4.23). The estimated cumulative risk of all-cause dementia was 10.6% (95% CI 9.3-12.1) for low p-tau217, 16.9% (95% CI 14.6-19.5) for intermediate p-tau217, 33.0% (95% CI 29.9-36.1) for high p-tau217, 15.7% (95% CI 14.4-17.0) for low NfL, 35.4% (95% CI 30.6-40.5) for high NfL, and 47.8% (95% CI 40.7-55.0) for jointly high p-tau217 and NfL. The association of p-tau217 with incident dementia differed by sex. DISCUSSION: These findings support the use of blood-based biomarkers for population-level dementia risk stratification, underscore the value of combining markers to improve prognostic precision, and can aid clinicians using plasma p-tau217 or NfL in interpreting dementia risk.

Background: It remains unclear why biomarker-defined Alzheimers disease neuropathological change (ADNC) leads to cognitive decline and dementia in some individuals but not others. Multidomain lifestyle profiles may influence both pathology risk and clinical expression. Objectives: To determine whether multidomain lifestyle profiles are associated with (1) the risk of biomarker-defined ADNC and (2) the clinical expression of AD pathology, including longitudinal cognitive test score change and incident dementia. Design/Setting: Retrospective longitudinal population-based cohort study within the Trondelag Health Study (HUNT), Norway, including five waves over a 40-year follow-up period. Participants: The late-life source population comprises 9,956 HUNT4 70+ participants, of whom 5,729 participated in the Ageing in Trondelag (AiT) follow-up. Outcome measurements. ADNC is operationalized primarily using plasma phosphorylated tau at threonine 217 (p-tau217), with plasma neurofilament light (NfL) available as a complementary marker of neurodegeneration. In HUNT4 70+, participants aged 70 and older had a standardized cognitive diagnostic assessment, which was repeated at AiT four years later. Lifestyle Measurements: Multidomain lifestyle will be defined across five domains: nutrition, physical activity and skeletal muscle health, mental and social health, cardiovascular/metabolic status, and cognitive stimulation. Genetic susceptibility, including APOE and genome-wide/polygenic risk measures, and available multi-omics data will be examined as modifiers. Results: Analyses will examine the associations of multidomain lifestyle profiles and domain-specific exposures with both ADNC risk and clinical expression. Conclusions: This study will test whether multidomain lifestyle profiles are associated with both the risk of biomarker-defined ADNC and the clinical expression, informing risk stratification and modifiable prevention in AD.

Background: Alzheimer's disease (AD) involves complex molecular alterations in the cerebrospinal fluid (CSF) proteome, yet the links between these protein changes and hallmark AD pathology remain incompletely defined. We investigated the relationship between the CSF proteome with CSF biomarkers of Alzheimer's disease (AD). Methods: CSF was collected in 500 individuals of non-Hispanic white, African Americans, and Caribbean Hispanic individuals. CSF biomarkers of AD were measured including P-tau181, A{beta}40, A{beta}42, total-tau, neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP). CSF was depleted of abundant proteins followed by precipitation, cysteine reduction/alkylation, and proteolytic cleavage by trypsin. Peptides were measured using a Q-Exactive HF mass spectrometer (Thermo Scientific). Association of individual and co-abundant modules of proteins were tested using elevated CSF P-tau181 and reduced A{beta}42/A{beta}40 to confirm the diagnosis of AD. We validated results in CSF from 397 participants in the Accelerated Medicine Partnership-Alzheimer's Disease cohort. Associated proteins were functionally validated in postmortem human brains and zebrafish. Results: We detected 1030 proteins, yielding an overall data completeness value of 97%. CSF levels of 75 (7.3%) proteins were significantly associated with CSF P-tau181 levels after multiple testing correction. Notably phospholipase D3 (PLD3, p=2.41E-09), apoE (p=4.25e-08) and osteopontin (OPN p=1.4E-16) were increased and autotaxin (ATX/ENPP2, p= 8.39E-09) and ceruloplasmin (CP) (p=2.72E-07) were lower among individuals with high P-tau181 levels. These proteins were also associated with CSF A{beta}42/A{beta}40 ratio and total tau levels but not with NfL. OPN was also associated with CSF levels of GFAP (p=1.32e-05). Among proteins associated with P-tau181 levels, pathways related to axon development (p=2.4E-12), axonogenesis (p=1.45E-11) and regulation of axonogenesis (p=5.1E-09) were enriched. Immunostaining on postmortem human and zebrafish brain found that ENPP2 expression, the gene encoding ATX, was significantly reduced in AD brain and in the amyloidosis model in zebrafish. Reduced ENPP2 expression was consistent with reduced lysophosphatidic acid (LPA) levels in the CSF of individuals with AD. LPA administration into zebrafish CSF reduced the pathological changes in synapses and vasculature due to A{beta}42. Conclusion: Unbiased profiling of circulating CSF proteins among individuals with antemortem diagnosis of AD, identified key proteins PLD3, apoE, OPN, ATX, and ceruloplasmin. Validation in postmortem human brains and zebrafish models support potential roles in endosomal sorting and APP processing, inflammation, angiogenesis, lipid transport, and oxidative stress.

Introduction: Developing interventions for Alzheimer's disease (AD) requires an improved understanding of mechanisms linking biological pathology to the penetrance of, and resilience to, cognitive impairment. This research identifies blood metabolites that are associated with cognitive impairment adjusting for the presence of AD pathology. Methods: Mass spectrometry peaks (n=2,282) were screened using mutually conditioned models (N=154; cross-adjusting CSF-biomarker defined AD status and cognitive status). Peaks were then tested for multiplicative interactions (CSF biomarker x peak) against both endpoints using complete APOE-{varepsilon}4 and albumin CSF/serum quotient data (N=140). Results: The screen revealed two directional profiles: Profile I (negative with status; positive with cognition) and Profile II (positive with status; negative with cognition). Secondary interaction modeling identified four peaks with interactions significantly associated with AD, and two with cognitive impairment, including one annotated as cerebroside B. Discussion: These interaction patterns indicate peripheral features acting as context-dependent modulators of AD pathology and cognitive symptom penetrance rather than global risk indicators, improving clinical stratification.

Introduction: Neuropsychiatric symptoms in dementia (NPS) are common and among the most troubling aspects of living with dementia, yet their underlying mechanisms remain unclear. Here, we aimed to identify cerebrospinal fluid (CSF) proteins associated with NPS. Methods: Proteomes were profiled from CSF collected at baseline from participants of the Alzheimer's Disease Neuroimaging Initiative (ADNI) using mass spectrometry. Here, we included participants having positive AD CSF biomarkers (i.e., pTtau181 / Abeta42 ratio >0.025) and mild cognitive impairment or AD dementia (n=419). Eight NPS domains were assessed longitudinally with the Neuropsychiatric Symptom Inventory Questionnaire. Severity of cognitive impairment was evaluated using the CDR-SB. Proteome-wide differential expression analysis for each NPS domain at baseline was performed. Significant protein-NPS associations underwent mediation analysis to test whether they were mediated by cognitive impairment severity. Cox proportional hazard was modeled for baseline CSF proteins and incident NPS. Additionally, we tested whether candidate NPS causal proteins previously identified in brain are associated with NPS in CSF. Results: We identified 8 CSF proteins associated with apathy at baseline (FDR q<0.05) after adjusting for sex, age, and education - NTNG2, S100A1, FZD1, FSTL5, CDH7, CHODL, FBXO2, and CACNA2D2. Mediation analysis revealed these associations were independent of cognitive impairment severity in four proteins and only partially mediated by cognitive impairment severity in the remaining four proteins. Among the 10 NPS candidate causal proteins previously identified in brain and detected in CSF, the abundance of two proteins (CPD, GRN) in CSF was associated with baseline disinhibition and of two other proteins (PIK3IP1, PCMT1) with both baseline apathy and incident apathy after adjusting for sex, age, and education. Discussion: These findings suggest that proteomic alterations in apathy in MCI/AD encompass synaptic connectivity, calcium regulation, Wnt-signaling, and neuronal proteostasis, highlighting potential CSF biological processes and biomarker candidates for apathy.

Background: Alzheimer's disease (AD) is characterized by amyloid beta and tau accumulation accompanied by altered inflammatory responses. Sex is an important modifier of AD risk and pathology, however, its influence on relationships between peripheral inflammatory markers and cerebrospinal fluid (CSF) AD biomarkers remains unclear. The aim of this study was to determine whether sex modifies peripheral inflammatory biomarker relationships associated with AD pathology and clinical stage. Materials and Methods: Twelve CSF biomarkers and 41 plasma biomarkers spanning AD pathology, neurodegeneration, and inflammation were measured on the Luminex platform in a cross-sectional cohort of 261 participants from the Cleveland Clinic Lou Ruvo Center for Brain Health Biobank. Associations were evaluated in sex-adjusted, sex-interaction, and sex-stratified models, accounting for age, APOE4 carrier status, and diagnosis. Results: Plasma IL-5 was inversely associated with clinical stage, and 10 plasma inflammatory markers, including Flt-3L, MCP-1, soluble TREM2 (sTREM2), TNF, IL-8, IL-5, IL-12P40, IL-1RA, fractalkine, and G-CSF, were inversely associated with the CSF pTau181/A{beta}42 ratio in pooled models adjusted for sex. Although formal biomarker x sex interactions did not survive FDR correction, significant associations between the CSF pTau181/A{beta}42 ratio and plasma MCP-1 and IL-12P40 were observed in females but not males. Discussion: Our findings identify a group of peripheral inflammatory markers associated with AD pathology and suggest that some of these relationships may vary by sex, warranting larger studies to clarify the role of sex in AD pathobiology.