New ELISAs with high specificity for soluble oligomers of amyloid β-protein detect natural Aβ oligomers in human brain but not CSF.

TLDR: There is a great need for assays that quantify Aß oligomers with high specificity and sensitivity in order to understand the mechanisms behind synaptic dysfunction, tau alteration, and neuritic dystrophy in AD and mouse models.

Abstract: Background Soluble oligomers of amyloid s-protein (As) have been increasingly linked to synaptic dysfunction, tau alteration, and neuritic dystrophy in Alzheimer's disease (AD) and mouse models. There is a great need for assays that quantify As oligomers with high specificity and sensitivity. Methods We designed and validated two oligomer-specific (o-) enzyme-linked immunoassays (ELISAs) using either an As aggregate-selective monoclonal for capture and a monoclonal to the free N-terminus for detection, or the latter antibody for both capture and detection. Results The o-ELISAs specifically quantified pure oligomers of synthetic As with sizes from dimers up to much larger assemblies and over a wide dynamic range of concentrations, whereas As monomers were undetectable. Natural As oligomers of similarly wide size and concentration ranges were measured in extracts of AD and control brains, revealing >1000-fold higher concentrations of As oligomers than monomers in the soluble fraction of AD cortex. The assays quantified the age-related rise in oligomers in hAPP transgenic mice. Unexpectedly, none of 90 human cerebrospinal fluid (CSF) samples gave a specific signal in either o-ELISA. Conclusions These new o-ELISAs with rigorously confirmed specificity can quantify oligomer burden in human and mouse brains for diagnostic and mechanistic studies and for AD biomarker development. However, our data raise the likelihood that the hydrophobicity of As oligomers makes them very low in number or absent in aqueous CSF.