Longitudinal blood biomarker trajectories in preclinical Alzheimer's disease

INTRODUCTION

Plasma biomarkers are altered years prior to Alzheimer's disease (AD) clinical onset.

METHODS

We measured longitudinal changes in plasma amyloid-beta (Aβ)42/40 ratio, pTau181, pTau231, neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) in a cohort of older adults at risk of AD (n = 373 total, n = 229 with Aβ and tau positron emission tomography [PET] scans) considering genetic and demographic factors as possible modifiers of these markers' progression.

RESULTS

Aβ42/40 ratio concentrations decreased, while NfL and GFAP values increased over the 4-year follow-up. Apolipoprotein E (APOE) ε4 carriers showed faster increase in plasma pTau181 than non-carriers. Older individuals showed a faster increase in plasma NfL, and females showed a faster increase in plasma GFAP values. In the PET subsample, individuals both Aβ-PET and tau-PET positive showed faster plasma pTau181 and GFAP increase compared to PET-negative individuals.

DISCUSSION

Plasma markers can track biological change over time, with plasma pTau181 and GFAP markers showing longitudinal change in individuals with preclinical AD.

HIGHLIGHTS

Longitudinal increase of plasma pTau181 and glial fibrillary acidic protein (GFAP) can be measured in the preclinical phase of AD. Apolipoprotein E ε4 carriers experience faster increase in plasma pTau181 over time than non-carriers. Female sex showed accelerated increase in plasma GFAP over time compared to males. Aβ42/40 and pTau231 values are already abnormal at baseline in individuals with both amyloid and tau PET burden.

Association of Serum Brain-Derived Tau With Clinical Outcome and Longitudinal Change in Patients With Severe Traumatic Brain Injury

Importance

Blood-based measurements of total tau (T-tau) are commonly used to examine neuronal injury in patients with traumatic brain injury (TBI), but current assays do not differentiate between brain-derived tau (BD-tau) and tau produced in peripheral tissues. A novel assay for BD-tau has recently been reported that selectively quantifies nonphosphorylated tau of central nervous system origin in blood samples.

Objectives

To examine the association of serum BD-tau with clinical outcomes in patients with severe TBI (sTBI) and its longitudinal changes over 1 year.

Design, Setting, and Participants

This prospective cohort study was conducted at the neurointensive unit at the Sahlgrenska University Hospital, Gothenburg, Sweden, between September 1, 2006, and July 1, 2015. The study included 39 patients with sTBI followed up for up to 1 year. Statistical analysis was performed between October and November 2021.

Exposures

Serum BD-tau, T-tau, phosphorylated tau231 (p-tau231), and neurofilament light chain (NfL) measured on days 0, 7, and 365 after injury.

Main Outcomes and Measures

Associations of serum biomarkers with clinical outcome and longitudinal change in sTBI. Severity of sTBI was evaluated using the Glasgow Coma Scale at hospital admission, while clinical outcome was assessed with the Glasgow Outcome Scale (GOS) at 1-year follow-up. Participants were classified as having a favorable outcome (GOS score, 4-5) or unfavorable outcome (GOS score, 1-3).

Results

Among the 39 patients (median age at admission, 36 years [IQR, 22-54 years]; 26 men [66.7%]) in the study on day 0, the mean (SD) serum BD-tau level was higher among patients with unfavorable outcomes vs those with favorable outcomes (191.4 [190.8] pg/mL vs 75.6 [60.3] pg/mL; mean difference, 115.9 pg/mL [95% CI, 25.7-206.1 pg/mL]), while the other markers had smaller between-group mean differences (serum T-tau, 60.3 pg/mL [95% CI, -22.0 to 142.7 pg/mL]; serum p-tau231, 8.3 pg/mL [95% CI, -6.4 to 23.0 pg/mL]; serum NfL, -5.4 pg/mL [95% CI, -99.0 to 88.3 pg/mL]). Similar results were recorded on day 7. Longitudinally, baseline serum BD-tau concentrations showed slower decreases in the whole cohort (42.2% on day 7 [from 138.6 to 80.1 pg/mL] and 93.0% on day 365 [from 138.6 to 9.7 pg/mL]) compared with serum T-tau (81.5% on day 7 [from 57.3 to 10.6 pg/mL] and 99.0% on day 365 [from 57.3 to 0.6 pg/mL]) and p-tau231 (92.5% on day 7 [from 20.1 to 1.5 pg/mL] and 95.0% on day 365 [from 20.1 to 1.0 pg/mL]). These results did not change when considering clinical outcome, where T-tau decreased twice as fast as BD-tau in both groups. Similar results were obtained for p-tau231. Furthermore, the biomarker levels on day 365 were lower, compared with day 7, for BD-tau but not T-tau or p-tau231. Serum NfL had a different trajectory to the tau biomarkers, with levels increasing by 255.9% on day 7 compared with day 0 (from 86.8 to 308.9 pg/mL) but decreasing by 97.0% by day 365 vs day 7 (from 308.9 to 9.2 pg/mL).

Conclusions and Relevance

This study suggests that serum BD-tau, T-tau, and p-tau231 have differential associations with clinical outcome and 1-year longitudinal change in patients with sTBI. Serum BD-tau demonstrated utility as a biomarker to monitor outcomes in sTBI and can provide valuable information regarding acute neuronal damage.

Subjective difficulty in a verbal recognition-based memory task: Exploring brain-behaviour relationships at the individual level in healthy young adults

The vast majority of fMRI studies of task-related brain activity utilize common levels of task demands and analyses that rely on the central tendencies of the data. This approach does not take into account perceived difficulty nor regional variations in brain activity between people. The results are findings of brain-behavior relationships that weaken as sample sizes increase. Participants of the current study included twenty-six healthy young adults evenly split between the sexes. The current work utilizes five parametrically modulated levels of memory load centered around each individual's predetermined working memory cognitive capacity. Principal components analyses (PCA) identified the group-level central tendency of the data. After removing the group effect from the data, PCA identified individual-level patterns of brain activity across the five levels of task demands. Expression of the group effect significantly differed between the sexes across all load levels. Expression of the individual level patterns demonstrated a significant load by sex interaction. Furthermore, expressions of the individual maps make better predictors of response time behavior than group-derived maps. We demonstrated that utilization of an individual's unique pattern of brain activity in response to increasing a task's perceived difficulty is a better predictor of brain-behavior relationships than study designs and analyses focused on identification of group effects. Furthermore, these methods facilitate exploration into how individual differences in patterns of brain activity relate to individual differences in behavior and cognition.

Plasma p-tau231, p-tau181, PET biomarkers and cognitive change in older adults

OBJECTIVE

To evaluate novel plasma p-tau231, p-tau181 as well as Aβ₄₀ and Aβ₄₂ assays as indicators of tau and Aβ pathologies measured with positron emission tomography (PET), and their association with cognitive change, in cognitively unimpaired older adults.

METHODS

In a cohort of 244 older adults at risk of AD owing to a family history of AD dementia, we measured single molecule array (Simoa)-based plasma tau biomarkers (p-tau231, p-tau181), Aβ₄₀ and Aβ₄₂ with immunoprecipitation mass spectrometry, and Simoa NfL. A subset of 129 participants underwent amyloid-β (¹⁸ F-NAV4694) and tau (¹⁸ F-flortaucipir) PET assessments. We investigated plasma biomarker associations with Aβ and tau PET at the global and voxel level and tested plasma biomarker combinations for improved detection of Aβ-PET positivity. We also investigated associations with 8-year cognitive change.

RESULTS

Plasma p-tau biomarkers correlated with flortaucipir binding in medial temporal, parietal and inferior temporal regions. P-tau231 showed further associations in lateral parietal and occipital cortices. Plasma Aβ_42/40 explained more variance in global Aβ-PET binding than Aβ₄₂ alone. P-tau231 also showed strong and widespread associations with cortical Aβ-PET binding. Combining Aβ_42/40 with p-tau231 or p-tau181 allowed for good distinction between Aβ-negative and -positive participants (AUC range 0.81-0.86). Individuals with low plasma Aβ_42/40 and high p-tau experienced faster cognitive decline.

INTERPRETATION

Plasma p-tau231 showed more robust associations with PET biomarkers than p-tau181 in pre-symptomatic individuals. The combination of p-tau and Aβ_42/40 biomarkers detected early AD pathology and cognitive decline. Such markers could be used as pre-screening tools to reduce the cost of prevention trials. This article is protected by copyright. All rights reserved.