Koychev I, Jansen K, Dette A, Shi L and Holling H

J Alzheimers Dis. 2020 Nov 24

DOI: 10.3233/JAD-200900

Abstract

Background: The Amyloid Tau Neurodegeneration (ATN) framework was proposed to define the biological state underpinning Alzheimer’s disease (AD). Blood-based biomarkers offer a scalable alternative to the costly and invasive currently available biomarkers. Objective:In this meta-analysis we sought to assess the diagnostic performance of plasma amyloid (Aβ 40, Aβ 42, Aβ 42/40 ratio), tangle (p-tau181), and neurodegeneration (total tau [t-tau], neurofilament light [NfL]) biomarkers.

Methods: Electronic databases were screened for studies reporting biomarker concentrations for AD and control cohorts. Biomarker performance was examined by random-effect meta-analyses based on the ratio between biomarker concentrations in patients and controls.

Results: 83 studies published between 1996 and 2020 were included in the analyses. Aβ 42/40 ratio as well as Aβ 42 discriminated AD patients from controls when using novel platforms such as immunomagnetic reduction (IMR). We found significant differences in ptau-181 concentration for studies based on single molecule array (Simoa), but not for studies based on IMR or ELISA. T-tau was significantly different between AD patients and control in IMR and Simoa but not in ELISA-based studies. In contrast, NfL differentiated between groups across platforms. Exosome studies showed strong separation between patients and controls for Aβ 42, t-tau, and p-tau181.

Conclusion: Currently available assays for sampling plasma ATN biomarkers appear to differentiate between AD patients and controls. Novel assay methodologies have given the field a significant boost for testing these biomarkers, such as IMR for Aβ, Simoa for p-tau181. Enriching samples through extracellular vesicles shows promise but requires further validation.