Distribution of Abeta peptide in whole blood

Biofluid Biomarkers of Alzheimer’s Disease: Progress, Problems, and Perspectives

Since the establishment of the biomarker-based A-T-N (Amyloid/Tau/Neurodegeneration) framework in Alzheimer’s disease (AD), the diagnosis of AD has become more precise, and cerebrospinal fluid tests and positron emission tomography examinations based on this framework have become widely accepted. However, the A-T-N framework does not encompass the whole spectrum of AD pathologies, and problems with invasiveness and high cost limit the application of the above diagnostic methods aimed at the central nervous system. Therefore, we suggest the addition of an “X” to the A-T-N framework and a focus on peripheral biomarkers in the diagnosis of AD. In this review, we retrospectively describe the recent progress in biomarkers based on the A-T-N-X framework, analyze the problems, and present our perspectives on the diagnosis of AD.

A new methodology for simultaneous quantification of total-Aβ, Aβx-38, Aβx-40, and Aβx-42 by column-switching LC/MS/MS

This article details the development of a novel method that overcomes the drawbacks of sandwich ELISA (sELISA) and allows reliable evaluation of simultaneous quantification of the amyloid (Aβ)-peptides, total-Aβ, Aβx-38, Aβx-40, and Aβx-42, in rat brain by optimized sample purification and column-switching liquid chromatographic-tandem mass spectrometry (LC/MS/MS). This method provides accurate analyses of total-Aβ, Aβx-38, Aβx-40, and Aβx-42 with a linear calibration range between 0.05 and 45 ng/mL. Verification for accuracy and precision of biological samples were determined by a standard addition and recovery test, spiked with synthetic Aβ1-38, Aβ1-40, and Aβ1-42 into the rat brain homogenate. This method showed <20% relative error and relative standard deviation, indicating high reproducibility and reliability. The brain concentrations of total-Aβ, Aβx-38, Aβx-40, and Aβx-42 after oral administration of flurbiprofen in rats were measured by this method. Aβx-42 concentrations (4.57 ± 0.69 ng/g) in rats administered flurbiprofen were lower than those in untreated rats (6.48 ± 0.93 ng/g). This was consistent with several reports demonstrating that NSAIDs reduced the generation of Aβ. We report here a method that allows not only the quantification of specific molecular species of Aβ but also simultaneous quantification of total-Aβ, Aβx-38, Aβx-40, and Aβx-42, thus overcoming the drawbacks of sELISA.

Monitoring the amyloid beta-peptide in vivo--caveat emptor

As a wave of 'disease modifying' (DM) therapies for Alzheimer's disease (AD) progresses towards the later stages of clinical development, an evaluation of our ability to measure relevant pharmacodynamic effects of such therapies is warranted. Reducing accumulation of amyloid beta (Abeta)-peptide in the brain parenchyma is the primary objective of most current DM approaches. Although a number of methods are available to measure Abeta in blood, cerebrospinal fluid (CSF) and the cerebrum, putative DM-induced changes in the levels of the peptides may not be fully captured, and the reasons for any such changes are not fully understood. Additional candidate biofluid (tau and isoprostanes) and imaging (MRI, FDG-PET) measures may provide alternative supporting evidence of drug activity and subsequent clinical efficacy in patient populations.

Maximizing the potential of plasma amyloid-beta as a diagnostic biomarker for Alzheimer's disease

Amyloid plaques are composed primarily of amyloid-beta (Abeta) peptides derived from proteolytic cleavage of amyloid precursor protein (APP) and are considered to play a pivotal role in Alzheimer's disease (AD) pathogenesis. Presently, AD is diagnosed after the onset of clinical manifestations. With the arrival of novel therapeutic agents for treatment of AD, there is an urgent need for biomarkers to detect early stages of AD. Measurement of plasma Abeta has been suggested as an inexpensive and non-invasive tool to diagnose AD and to monitor Abeta modifying therapies. However, the majority of cross-sectional studies on plasma Abeta levels in humans have not shown differences between individuals with AD compared to controls. Similarly, cross-sectional studies of mouse plasma Abeta have yielded inconsistent trends in different mouse models. However, longitudinal studies appear to be more promising in humans. Recently, efforts to modify plasma Abeta levels using modulators have shown some promise. In this review, we will summarize the present data on plasma Abeta in humans and mouse models of AD. We will discuss the potential of modulators of Abeta levels in plasma, including antibodies and insulin, and the challenges associated with measuring plasma Abeta. Modulators of plasma Abeta may provide an important tool to optimize plasma Abeta levels and may improve the diagnostic potential of this approach.

Solid-phase extraction enhances detection of beta-amyloid peptides in plasma and enables Abeta quantification following passive immunization with Abeta antibodies

We have previously developed a solid-phase extraction (SPE) procedure to enable the detection of beta-amyloid (Abeta) peptides in brain tissue from non-transgenic animals. We have now adapted these methods to enrich the Abeta fraction in cerebrospinal fluid (CSF) and plasma. Human CSF and plasma and Tg2576 mouse plasma were subjected to guanidine denaturation followed by SPE in 96-well cassettes. The resulting eluates could be concentrated significantly to enhance detection of low-abundance Abeta peptides by immunoassay. The concentrated eluates diluted in a linear fashion with consistent recovery between SPE columns. This technique was therefore used to facilitate quantification of Abeta1-X, 1-40, 1-42, and 1-38 peptides in normal human CSF and plasma samples. SPE sample preparation was also applied to the plasma of mice dosed peripherally with a monoclonal antibody raised against Abeta. When such samples were assayed directly, the presence of the systemically administered antibody interfered with the subsequent immunoassay, by preventing detection of antibody-bound Abeta. After subjecting plasma from antibody-treated animals to denaturation and SPE, the antibody-antigen complex was disrupted, and the Abeta fraction could be isolated from the antibody-containing fraction. Application of this method allowed for detection of a 100-fold increase in plasma Abeta1-40 following treatment of Tg2576 mice or wild type littermate control mice with Abeta40-specific monoclonal antibody 9TL. Given the availability of a variety of SPE matrices, we hypothesize that these methods could facilitate plasma antigen retrieval using multiple therapeutic antibody approaches.