Association between cell-bound blood amyloid-β(1-40) levels and hippocampus volume

Plasma amyloid beta levels are associated with cerebral amyloid and tau deposition

Introduction

We investigated the relationship of plasma amyloid beta (Aβ) with cerebral deposition of Aβ and tau on positron emission tomography (PET).

Methods

Forty-four participants (18 cognitively normal older adults [CN], 10 mild cognitive impairment, 16 Alzheimer's disease [AD]) underwent amyloid PET and a blood draw. Free and total plasma Aβ40 and Aβ42 were assessed using a validated assay. Thirty-seven participants (17 CN, 8 mild cognitive impairment, 12 AD) also underwent a [¹⁸F]flortaucipir scan. Scans were preprocessed by standard techniques, and mean global and regional amyloid and tau values were extracted. Free Aβ42/Aβ40 (Aβ F42:F40) and total Aβ42/Aβ40 (Aβ T42:T40) were evaluated for differences by diagnosis and relation to PET Aβ positivity. Relationships between these measures and cerebral Aβ and tau on both regional and voxel-wise basis were also evaluated.

Results

Lower Aβ T42:T40 was associated with diagnosis and PET Aβ positivity. Lower plasma Aβ T42:T40 ratios predicted cerebral Aβ positivity, both across the full sample and in CN only. Finally, lower plasma Aβ T42:T40 ratios were associated with increased cortical Aβ and tau in AD-related regions on both regional and voxel-wise analyses.

Discussion

Plasma Aβ measures may be useful biomarkers for predicting cerebral Aβ and tau. Additional studies in larger samples are warranted.

Plasma biomarkers are associated with agitation and regional brain atrophy in Alzheimer's disease

This study investigated the relationships among plasma biomarkers, regional brain atrophy, and clinical symptoms in patients with Alzheimer's disease (AD; n = 177), mild cognitive impairment (MCI; N = 60) and controls (n = 108). The Mini-Mental Status Examination (MMSE), Clinical Dementia Rating (CDR), and Neuropsychiatric Inventory (NPI) subscales were administered to subjects. Magnetic resonance imaging was performed and medial temporal atrophy (MTA) and posterior atrophy (PA) were assessed visually. We examined associations among cognition, NPI score, plasma β-amyloid (Aβ) and clusterin levels, and regional brain atrophy in patients with AD by regression analysis. The mean MTA score was associated with the plasma Aβ1-42/Aβ1-40 ratio (r = 0.38, p = 0.01) and with MMSE scores (r = 0.43, p < 0.01). The plasma clusterin level was correlated with CDR sum of box and right-side PA scores (r = 0.28, p = 0.01 and r = 0.30, p = 0.03, respectively). Right-side PA scores were correlated significantly with NPI agitation/aggression (r = 0.30, p = 0.03) subscale scores. In conclusion, the plasma ratio of Aβ1-42/Aβ1-40 and clusterin level may be associated with different patterns of regional brain atrophy, which in turn may account for the clinical symptoms in patients with AD.

Neurovascular Alterations in Alzheimer's Disease: Transporter Expression Profiles and CNS Drug Access

Despite a century of steady and incremental progress toward understanding the underlying biochemical mechanisms, Alzheimer's disease (AD) remains a complicated and enigmatic disease, and greater insight will be necessary before substantive clinical success is realised. Over the last decade in particular, a large body of work has highlighted the cerebral microvasculature as an anatomical region with an increasingly apparent role in the pathogenesis of AD. The causative interplay and temporal cascade that manifest between the brain vasculature and the wider disease progression of AD are not yet fully understood, and further inquiry is required to properly characterise these relationships. The purpose of this review is to highlight the recent advancements in research implicating neurovascular factors in AD, at both the molecular and anatomical levels. We begin with a brief introduction of the biochemical and genetic aspects of AD, before reviewing the essential concepts of the blood-brain barrier (BBB) and the neurovascular unit (NVU). In detail, we then examine the evidence demonstrating involvement of BBB dysfunction in AD pathogenesis, highlighting the importance of neurovascular components in AD. Lastly, we include within this review research that focuses on how altered properties of the BBB in AD impact upon CNS exposure of therapeutic agents and the potential clinical impact that this may have on people with this disease.

Recent publications from the Alzheimer's Disease Neuroimaging Initiative: Reviewing progress toward improved AD clinical trials

INTRODUCTION

The Alzheimer's Disease Neuroimaging Initiative (ADNI) has continued development and standardization of methodologies for biomarkers and has provided an increased depth and breadth of data available to qualified researchers. This review summarizes the over 400 publications using ADNI data during 2014 and 2015.

METHODS

We used standard searches to find publications using ADNI data.

RESULTS

(1) Structural and functional changes, including subtle changes to hippocampal shape and texture, atrophy in areas outside of hippocampus, and disruption to functional networks, are detectable in presymptomatic subjects before hippocampal atrophy; (2) In subjects with abnormal β-amyloid deposition (Aβ+), biomarkers become abnormal in the order predicted by the amyloid cascade hypothesis; (3) Cognitive decline is more closely linked to tau than Aβ deposition; (4) Cerebrovascular risk factors may interact with Aβ to increase white-matter (WM) abnormalities which may accelerate Alzheimer's disease (AD) progression in conjunction with tau abnormalities; (5) Different patterns of atrophy are associated with impairment of memory and executive function and may underlie psychiatric symptoms; (6) Structural, functional, and metabolic network connectivities are disrupted as AD progresses. Models of prion-like spreading of Aβ pathology along WM tracts predict known patterns of cortical Aβ deposition and declines in glucose metabolism; (7) New AD risk and protective gene loci have been identified using biologically informed approaches; (8) Cognitively normal and mild cognitive impairment (MCI) subjects are heterogeneous and include groups typified not only by "classic" AD pathology but also by normal biomarkers, accelerated decline, and suspected non-Alzheimer's pathology; (9) Selection of subjects at risk of imminent decline on the basis of one or more pathologies improves the power of clinical trials; (10) Sensitivity of cognitive outcome measures to early changes in cognition has been improved and surrogate outcome measures using longitudinal structural magnetic resonance imaging may further reduce clinical trial cost and duration; (11) Advances in machine learning techniques such as neural networks have improved diagnostic and prognostic accuracy especially in challenges involving MCI subjects; and (12) Network connectivity measures and genetic variants show promise in multimodal classification and some classifiers using single modalities are rivaling multimodal classifiers.

DISCUSSION

Taken together, these studies fundamentally deepen our understanding of AD progression and its underlying genetic basis, which in turn informs and improves clinical trial design.

Blood-Based Proteomic Biomarkers of Alzheimer's Disease Pathology

The complexity of Alzheimer’s disease (AD) and its long prodromal phase poses challenges for early diagnosis and yet allows for the possibility of the development of disease modifying treatments for secondary prevention. It is, therefore, of importance to develop biomarkers, in particular, in the preclinical or early phases that reflect the pathological characteristics of the disease and, moreover, could be of utility in triaging subjects for preventative therapeutic clinical trials. Much research has sought biomarkers for diagnostic purposes by comparing affected people to unaffected controls. However, given that AD pathology precedes disease onset, a pathology endophenotype design for biomarker discovery creates the opportunity for detection of much earlier markers of disease. Blood-based biomarkers potentially provide a minimally invasive option for this purpose and research in the field has adopted various “omics” approaches in order to achieve this. This review will, therefore, examine the current literature regarding blood-based proteomic biomarkers of AD and its associated pathology.

Increased levels of plasma amyloid-beta are related to cortical thinning and cognitive decline in cognitively normal elderly subjects

Plasma levels of circulating amyloid-beta (Aβ) peptides are of particular interest in Alzheimer' disease, but little is known about cognitive and cortical correlates of peripheral Aβ levels in normal aging. Here, we compared cognitive functioning, vascular risk factors, and patterns of cortical thickness between cognitively intact elderly subjects with low (N = 60) and high (N = 60) plasma Aβ levels (cutoffs: 225 pg/mL and 23 pg/mL for Aβ1-40 and Aβ1-42, respectively). Overall, subjects with high Aβ levels showed lower cognitive performance and thinner cortex than those with low Aβ levels. More specifically, subjects with high Aβ1-40 showed bilateral thinning of the prefrontal cortex, poorer objective memory, slower processing speed, and lower nonverbal reasoning skills, whereas subjects with high Aβ1-42 had thinner temporal lobe, poorer everyday memory, and increased levels of homocysteine. Overall, these results suggest that high plasma Aβ levels in normal elderly subjects are associated with subclinical markers of vulnerable aging, which may be helpful at predicting different trajectories of aging in cognitively intact older adults.