Beyond the Controversy on Aβ Blood-Based Biomarkers.

Area of Science:

• Neurology
• Biochemistry
• Biomarker Discovery

Background:

• Central biomarkers for Alzheimer's disease (AD) show diagnostic and prognostic value.
• Current methods like amyloid PET and CSF collection have limitations for widespread clinical trials.
• Developing blood-based biomarkers as surrogates for amyloid positivity is crucial.

Purpose of the Study:

• To review studies on amyloid-beta (Aβ) plasma levels, specifically the Aβ42/Aβ40 ratio, as potential Alzheimer's disease (AD) biomarkers.
• To identify and address confounding factors in blood-based biomarker studies.
• To improve the design of future studies investigating the association between peripheral and central AD biomarkers.

Main Methods:

• Literature review focusing on studies examining Aβ plasma levels and their association with AD.
• Analysis of confounding factors including clinical gold standards, biomarker time-courses, and Aβ metabolism.
• Synthesis of existing data to propose a model for the relationship between blood and central Aβ biomarkers.

Main Results:

• Evidence suggests a controversial association between plasma Aβ levels (particularly Aβ42/Aβ40) and AD diagnosis.
• Confounding factors related to study design, biomarker timing, and Aβ metabolism may obscure this association.
• A proposed model suggests parallel but temporally displaced trajectories for blood and central Aβ biomarkers in early preclinical AD.

Conclusions:

• Blood Aβ levels, especially the Aβ42/Aβ40 ratio, show potential as AD biomarkers but require rigorous study design.
• Understanding the temporal dynamics and confounding factors is key to resolving controversy surrounding blood-based AD biomarkers.
• The proposed model offers a framework for future research into the relationship between peripheral and central AD pathology.