Advances in Blood Biomarkers for Alzheimer's Disease: Ultra-Sensitive Detection Technologies and Impact on Clinical Diagnosis

Abstract

Alzheimer's disease has escalated into a critical public health concern, marked by its neurodegenerative nature that progressively diminishes cognitive abilities. Recognized as a continuously advancing and presently incurable condition, AD underscores the necessity for early-stage diagnosis and interventions aimed at delaying the decline in mental function. Despite the proven efficacy of cerebrospinal fluid and positron emission tomography in diagnosing AD, their broader utility is constrained by significant costs and the invasive nature of these procedures. Consequently, the innovation of blood biomarkers such as Amyloid-beta, phosphorylated-tau, total-tau et al, distinguished by their high sensitivity, minimal invasiveness, accessibility, and cost-efficiency, emerges as a promising avenue for AD diagnosis. The advent of ultra-sensitive detection methodologies, including single-molecule enzyme-linked immunosorbent assay and immunoprecipitation-mass spectrometry, has revolutionized the detection of AD plasma biomarkers, supplanting previous low-sensitivity techniques. This rapid advancement in detection technology facilitates the more accurate quantification of pathological brain proteins and AD-associated biomarkers in the bloodstream. This manuscript meticulously reviews the landscape of current research on immunological markers for AD, anchored in the National Institute on Aging-Alzheimer's Association AT(N) research framework. It highlights a selection of forefront ultra-sensitive detection technologies now integral to assessing AD blood immunological markers. Additionally, this review examines the crucial pre-analytical processing steps for AD blood samples that significantly impact research outcomes and addresses the practical challenges faced during clinical testing. These discussions are crucial for enhancing our comprehension and refining the diagnostic precision of AD using blood-based biomarkers. The review aims to shed light on potential avenues for innovation and improvement in the techniques employed for detecting and investigating AD, thereby contributing to the broader field of neurodegenerative disease research.

Keywords: Alzheimer’s disease; biomarkers; blood; detection technologies; pre-analytical.

Figure 1

Single Molecule Array (Simoa) technology is a highly sensitive bio-detection method used to detect extremely low concentrations of biomarkers associated with Alzheimer’s Disease (AD). Prepare samples containing target AD biomarkers, like blood or cerebrospinal fluid, and employ Simoa chips or kits equipped with highly specific antibodies to capture and detect specific proteins within the samples. Enhance the signal of the antibodies bound to these proteins using signal amplification techniques, such as enzyme labeling or fluorescent tagging, allowing for the detection of proteins at the single-molecule level. Use the Simoa analyzer to read and analyze the samples, providing quantitative data on biomarker concentrations. By Figdraw.

Figure 2

Differentiate beads by size and fluorescence and conjugate with specific antibodies. Mix bead panel with target analyte sample, bind, then wash. Add biotinylated detection antibodies to form bead-analyte-antibody complexes. Add Streptavidin-phycoerythrin (SA-PE) for fluorescence. Use flow cytometry to segregate and quantify bead populations. Determine analyte concentrations using the assay’s standard curve. By Figdraw.

Figure 3

This detection method predates the high-specificity binding between select antibodies or antigens and target biomolecules. Under an applied alternating magnetic field, these magnetic particles rotate, leading to variations in the magnetic signal. The binding of target biomolecules reduces the number of magnetic particles that can rotate, thus diminishing the magnetic signal (magnetic reduction). The extent of magnetic reduction is directly proportional to the concentration of biomolecules in the sample, allowing for the quantitative analysis of biomolecules by measuring the reduction in the magnetic reagent’s signal. The functionalities of the analyzer include generating an alternating magnetic field and detecting changes in the magnetic signal to ascertain the concentration of biomolecules. By Figdraw.