Dement Neurocogn Disord.  2020 Mar;19(1):1-18. 10.12779/dnd.2020.19.1.1.

Alzheimer's Disease Diagnosis Using Misfolding Proteins in Blood

• Lee H
• Ugay D
• Hong S
• Kim Y

• KMID: 2471931
• DOI: http://doi.org/10.12779/dnd.2020.19.1.1

Abstract

Alzheimer's disease (AD) is pathologically characterized by a long progressive phase of neuronal changes, including accumulation of extracellular amyloid-β (Aβ) and intracellular neurofibrillary tangles, before the onset of observable symptoms. Many efforts have been made to develop a blood-based diagnostic method for AD by incorporating Aβ and tau as plasma biomarkers. As blood tests have the advantages of being highly accessible and low cost, clinical implementation of AD blood tests would provide preventative screening to presymptomatic individuals, facilitating early identification of AD patients and, thus, treatment development in clinical research. However, the low concentration of AD biomarkers in the plasma has posed difficulties for accurate detection, hindering the development of a reliable blood test. In this review, we introduce three AD blood test technologies emerging in South Korea, which have distinctive methods of heightening detection sensitivity of specific plasma biomarkers. We discuss in detail the multimer detection system, the self-standard analysis of Aβ biomarkers quantified by interdigitated microelectrodes, and a biomarker ratio analysis comprising Aβ and tau.

Keyword

tau Proteins; Plasma; Diagnostic Techniques and Procedures; Biomarkers; Amyloid-beta Peptides; Alzheimer's Disease

MeSH Terms

Alzheimer Disease*
Biomarkers
Diagnosis*
Diagnostic Techniques and Procedures
Hematologic Tests
Humans
Korea
Mass Screening
Methods
Microelectrodes
Neurofibrillary Tangles
Neurons
Plasma
tau Proteins
Biomarkers
tau Proteins

Figure

• 

  Fig. 1 OAβ Test via Multimer Detection System. (1) Blood sample is collected and centrifuged. (2) Isolated plasma is spiked with synthetic Aβ42 (10 ng/mL) and incubated at 37°C for 144 hours. (3) Spiked Aβ42 induces Aβ oligomerization, thereby changing the levels of plasma Aβ oligomers. (4) The sample is added to wells that have been precoated by mouse monoclonal antibody 6E10 (capture antibody), which captures Aβ at residues 3-8. (5) FF51-horseradish peroxidase antibody (detection antibody) binds to Aβ residues 1–4. (6) Addition of a chemiluminescent substrate solution results in the formation of a colored product, which can be detected and quantified using a spectrophotometer.Aβ: amyloid-β, MDS: multimer detection system.

• 

  Fig. 2 Comparing levels of Aβ by self-standard analysis via IME sensors. (1) Blood sample is collected and centrifuged. (2) Isolated plasma is divided into 2 aliquots. (3) Sample 1 is a control (no additional reagent), and Sample 2 is treated with 100 mM EPPS and incubated at room temperature for 30 minutes, which results in monomerization of plasma Aβ oligomers. (4) Both samples are applied to an IME sensor chip, which is composed of 2 PDMS microfluidic channels for simultaneous loading and 4 sensors with a sensing zone fabricated with immobilized 6E10 antibodies between each pair of electrodes. (5) The interaction between Aβ monomers and detection antibodies results in the impedance change, thus, allowing to determine the concentration of Aβ monomers in each sample. The self-standard ratio is calculated by dividing the concentration of homogenized Aβ monomers by the concentration of heterogeneous Aβ monomers in the untreated sample.Aβ: amyloid-β, IME: interdigitated microelectrode, EPPS: 4-(2-hydroxyethyl)-1-piperazinepropanesulphonic acid, PDMS: polydimethylsiloxane.

• 

  Fig. 3 Quantification of plasma tau using Simoa HD-I analyzer. (1) Blood sample is collected and centrifuged. (2) Paramagnetic microbeads coupled to detection antibodies (supplied along with Simoa Human tau immunoassay kit) are added to the plasma sample, preceding the addition of standard ELISA reagents. (3) If hyperphosphorylated tau protein is present (the target of the immunoassay) in the plasma sample, the formation sandwich immunocomplex will occur. (4) The microbeads are then concentrated by magnetic separation and loaded onto the arrays of femtomolar-wells, each capable of fitting a single immunocomplex. The arrays are located on the Simoa disk composed of 24 arrays. (5) After adding a fluorogenic substrate and sealing the wells using an oil solution, a single-binding event is detected and quantified by the instrument.ELISA: enzyme-linked immunosorbent assay.

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