Plasma Aβ analysis using magnetically-labeled immunoassays and PET 18F-florbetapir binding in non-demented patients with major depressive disorder

Differential neuropsychiatric associations of plasma biomarkers in older adults with major depression and subjective cognitive decline

Older adults with major depressive disorder (MDD) or early cognitive decline during the subjective cognitive decline (SCD) stage may exhibit neuropsychiatric symptoms such as anxiety, depression, and subtle cognitive impairment. The clinicopathological features and biological mechanisms of MDD differ from those of SCD among older adults; these conditions thus require different treatment strategies. This study enrolled 82 participants above 50 years old with normal cognitive levels from the communities to examine biomarker-behavior correlations between MDD (n = 23) and SCD (n = 23) relative to a normal control (NC) group (n = 36). Multidomain assessments were performed for all participants, including immunomagnetic reduction tests to detect plasma beta-amyloid (Aβ), total tau (Tau), phosphorylated tau-181 (p-Tau181), neurofilament light chain, and glial fibrillary acidic protein (GFAP). This study observed that depressive symptoms in MDD were associated with amyloid pathology (plasma Aβ40 vs. HADS-D: R = 0.45, p = 0.031; Aβ42/Aβ40 vs. HADS-D: R = -0.47, p = 0.024), which was not observed in the NC (group difference p < 0.05). Moreover, cognitive decline in MDD was distinguished by a mixed neurodegenerative process involving amyloid (plasma Aβ42 vs. facial memory test: R = 0.48, p = 0.025), tau (Tau/Aβ42 vs. digit symbol substitution test (DSST): R = -0.53, p = 0.01), and astrocytic injury (plasma GFAP vs. Montreal cognitive assessment score: R = -0.44, p = 0.038; plasma GFAP vs. DSST: R = -0.52, p = 0.014), findings that did not apply to the NC (group difference p < 0.05). Moreover, this study revealed different biomarker-behavior correlations between individuals with SCD and the NC. Compared with the NC, cognitive decline in the SCD group might be unrelated to amyloid pathology and instead might be early manifestations of tau pathology. This study underscores the difference in clinicopathological features between MDD and SCD among older adults, which differ from those of the NC. These findings enhance our understanding of the mechanisms underlying MDD and SCD in older individuals.

Can platelet activation result in increased plasma Aβ levels and contribute to the pathogenesis of Alzheimer's disease?

One of the central lesions in the brain of subjects with Alzheimer's disease (AD) is represented by aggregates of β-amyloid (Aβ), a peptide of 40-42 amino acids derived from the amyloid precursor protein (APP). The reasons why Aβ accumulates in the brain of individuals with sporadic forms of AD are unknown. Platelets are the primary source of circulating APP and, upon activation, can secrete significant amounts of Aβ into the blood which can be actively transported to the brain across the blood-brain barrier and promote amyloid deposition. Increased platelet activity can stimulate platelet adhesion to endothelial cells, trigger the recruitment of leukocytes into the vascular wall and cause perivascular inflammation, which can spread inflammation in the brain. Neuroinflammation is fueled by activated microglial cells and reactive astrocytes that release neurotoxic cytokines and chemokines. Platelet activation is also associated with the progression of carotid artery disease resulting in an increased risk of cerebral hypoperfusion which may also contribute to the AD neurodegenerative process. Platelet activation may thus be a pathophysiological mechanism of AD and for the strong link between AD and cerebrovascular diseases. Interfering with platelet activation may represent a promising potential adjunct therapeutic approach for AD.

Mental Illness and Amyloid: A Scoping Review of Scientific Evidence over the Last 10 Years (2011 to 2021)

Amyloid precursor protein and its derivates represent a central factor in the process of neurodegeneration in Alzheimer’s disease (AD). Since mental illnesses share with AD cognitive impairment, amyloid indicators have been used to explore the unknown pathophysiologic mechanisms underlining psychiatric illness. This work aims to compare the role of amyloid markers, together with tau proteins, among various mental disorders evaluating the possible role of altered amyloid metabolism in the onset and in the course of psychiatric diseases, considering the relationship with cognitive impairment in dementia. This review includes articles written in English, published between 1 January 2011 and 31 January 2021, which evaluated amyloid and tau proteins in psychiatric patients. After screening, 31 studies were included in the review. Results suggest that amyloid metabolism is altered in major psychiatric disorders and that it could be a marker of cognitive impairment. Nevertheless, the role of amyloid in mental diseases seems to be related to neurodevelopmental alteration as well as neurodegeneration processes, like in AD. The role of amyloid in the pathogenesis of mental disorders is still unknown. Amyloid should not be only considered as a marker of cognitive impairment in mental illness, but also for altered neurodevelopment.

Different Sides of Depression in the Elderly: An In-depth View on the Role of Aβ Peptides

BACKGROUND

Late-onset depression (LOD) is the most common neuropsychiatric disorder associated with Alzheimer's disease (AD), often associated with structural and functional brain changes, neuropsychological impairments and negative family history for affective disorders. LOD could be a risk factor or a prodromal phase of AD; this has led to the investigation of the link between depression and amyloid-β (Aβ) peptides by measuring Aβ levels in plasma, cerebrospinal fluid (CSF) and brains of elderly depressed subjects.

OBJECTIVE

Clarify the complex relationship between depression, Aβ peptides and AD.

METHOD

We evaluated all articles published up to 2019 in PubMed in which Aβ was measured in serum (or plasma), CSF or brain in elderly with Major Depressive Disorder or depressive symptoms evaluated with standard scales.

RESULTS

Low plasma Aβ42 levels are strongly associated with depression severity. Plasma Aβ40 levels are higher in younger depressed, drug-resistant and those with more severe symptoms. CSF Aβ42 levels are lower in depressed than controls. PET-detected global and region-specific increases in Aβ deposition are sometimes associated with LOD, cognitive impairment, anxiety but not with Cardiovascular Diseases (CVDs)/CVD risk factors. Elderly depressed with CVDs/CVD risk factors have more frequently high plasma Aβ40 levels and drug-resistance; those without these co-morbidities have low plasma Aβ42 levels and a greater cognitive impairment.

CONCLUSION

Two specific Aβ profiles emerge in elderly depressed. One is associated with Aβ42 reductions in plasma and CSF, possibly reflecting increased brain amyloid deposition and prodromal AD. The other one is characterized by high plasma Aβ40 levels, cerebrovascular disease and clinically associated with increased AD risk.

Certification of Amyloid-Beta (Aβ) Certified Reference Materials by Amino Acid-Based Isotope Dilution High-Performance Liquid Chromatography Mass Spectrometry and Sulfur-Based High-Performance Liquid Chromatography Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

The use of amyloid-beta (Aβ) biomarkers could contribute to an early diagnosis of Alzheimer's disease (AD); however, there are still large variations among results from different assays. This variability can be overcome by standardization of those assays through the use of certified reference materials (CRMs) and the establishment of a traceability chain. In this study, Aβ₄₀ (GBW09874) and Aβ₄₂ (GBW09875) solution CRMs with the certified values and uncertainties of 7.58 ± 0.30 and 7.62 ± 0.30 μg g^-1 were developed with high-purity Aβ as raw materials. For the first time, isotope dilution high-performance liquid chromatography mass spectrometry (ID-LC-MS) and high-performance liquid chromatography isotope dilution inductively coupled plasma mass spectrometry (HPLC-ID-ICP-MS) strategies were employed to certify the candidate Aβ solution CRMs. The two candidate CRMs showed good homogeneity, and good stability was also demonstrated for at least 5 days at -20 °C and 14 months at -70 °C. These CRMs are primarily intended to be used for value assignment to secondary calibrators or CRMs with a clinical matrix, which will help in early diagnosis of AD.

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.