Biofluid‐based biomarker panels toward personalized medicine in dementia diagnostics

Abstract

Alzheimer's & Dementia publishes a set of papers exploring the diagnostic and prognostic capabilities of a novel cutting‐edge multiplexed biomarker measurement technology across neurodegenerative dementias.

1. INTRODUCTION

During recent years, we have seen an enormous development of blood‐based biomarkers for amyloid beta (Aβ) and tau pathologies, as well as neurodegeneration, in Alzheimer's disease (AD) and related disorders, and these biomarkers have been validated against neuropathology, and gold standard cerebrospinal fluid (CSF) and imaging biomarkers. ¹ The hypothesis that blood‐based biomarkers for brain diseases would be too challenging to quantify due to the blood–brain barrier and dilution in the complex blood matrix has been falsified thanks to analytical methods that have grown increasingly sensitive and precise by the day. This development took off with the advent of the single molecule array (Simoa) technology in 2010, ² which allowed for the reliable quantification of tau, neurofilament light chain (NfL), and Aβ proteins in plasma using a sandwich enzyme‐linked immunosorbent assay (ELISA) principle with a twist. Compartmentalization of the detection reaction using antibody‐conjugated nanobeads capturing the enzyme‐labeled immunocomplex in microwells allowing for single molecule counting did the trick, and Simoa assays paved the way for the optimization of fully automated clinical chemistry tests that could achieve ultra‐sensitivity by other means (high precision, in addition to really great antibodies). Now assays for certain forms of phosphorylated tau (p‐tau217 in particular) on multiple platforms can detect AD pathophysiology almost as accurately as CSF and positron emission tomography (PET) biomarkers at a much lower cost and with higher availability and less burden for the patients than the imaging and CSF methods. ¹

Neurodegenerative diseases are typically characterized by multiple pathogenic processes, ³ which makes multiplexed measurement of biomarkers in the same sample an attractive concept. Color‐coding of the capture beads in Simoa made low‐n multiplexing possible, and there are now assays that quantify, for example, NfL, glial fibrillary acidic protein (GFAP), and Aβ peptides, in the same reaction.

Higher multiplexing complexity could be obtained by the proximity extension assay (PEA) technology by Olink. ⁴ The PEA technology combines antibody‐ and DNA‐based methods to measure protein levels in body fluids. Each target protein is detected by two antibodies that are coupled to unique DNA oligonucleotide sequences, specific for each target protein. Upon binding of both antibodies to the target, these DNA oligonucleotide sequences are in close enough proximity to hybridize, forming a template that can be quantified by real‐time polymerase chain reaction or next‐generation sequencing. For one reason or another, diagnostically accurate p‐tau biomarkers have not been available using Olink, and there has been a lack of multiplexed assays detecting a broader range of biomarkers of relevance to neurodegeneration.

This changed in 2023 with the advent of the nucleic acid‐linked immuno‐sandwich assay (NULISA), which is a novel method to measure many molecules in the blood proteome at attomolar concentrations. The technology uses a PEA‐like approach but with additional wash steps, which reduces the background and improves the analytical sensitivity. ⁵ The technology has been validated in oncology and immunology, and, in collaboration with neuroscience researchers, Alamar has developed a central nervous system–directed panel that analyzes 120 proteins associated with diverse neurodegenerative processes in a few microliters of plasma. Comparing the performance of NULISA with known high‐performing biomarker assays, for example, for p‐tau217, the high performance of the NULISA technology was demonstrated. ⁶ In addition to the classical amyloid, tau, and neurodegeneration (ATN) biomarkers, the panel measures several novel biomarker candidates of unknown potential in neurodegenerative dementias. In this issue of Alzheimer's & Dementia, we publish a collection of papers examining the performance of the NULISA technology to detect processes of relevance to neurodegeneration, which hopefully will inspire the development and validation of targeted biomarker panels that in the future could be useful to neurologists and memory clinic specialists when they see their patients.

CONFLICT OF INTEREST STATEMENT

The author declares no conflicts of interest. Author disclosure is available in the supporting information.

Supporting information

Supporting Information