Abstract
IntroductionAmyloid β-protein oligomers play a key role in Alzheimer’s disease (AD), but well-validated assays that routinely detect them in cerebrospinal fluid (CSF) are just emerging. We sought to confirm and extend a recent study using the Singulex Erenna platform that reported increased mean CSF oligomer levels in AD.MethodsWe tested four antibody pairs and chose one pair that was particularly sensitive, using 1C22, our new oligomer-selective monoclonal antibody, for capture. We applied this new assay to extracts of human brain and CSF.ResultsA combination of 1C22 for capture and 3D6 for detection yielded an Erenna immunoassay with a lower limit of quantification of approximately 0.15 pg/ml that was highly selective for oligomers over monomers and detected a wide size-range of oligomers. Most CSFs we tested had detectable oligomer levels but with a large overlap between AD and controls and a trend for higher mean levels in mild cognitive impairment (MCI) than controls.ConclusionAβ oligomers are detectable in most human CSFs, but AD and controls overlap. MCI CSFs may have a modest elevation in mean value by this assay.Electronic supplementary materialThe online version of this article (doi:10.1186/s13195-015-0100-y) contains supplementary material, which is available to authorized users.
Highlights
Amyloid β-protein oligomers play a key role in Alzheimer’s disease (AD), but well-validated assays that routinely detect them in cerebrospinal fluid (CSF) are just emerging
Antibodies Monoclonal antibody 3D6 is highly specific for the extreme N-terminus of amyloid beta (Aβ) [11] and was kindly provided by Dr Guriq Basi and Dr Dale Schenk (Elan, plc, South San Francisco, CA, USA). mAb 3B3 was generated by immunizing mice with an Aβ1–42 preparation known as amyloid-beta-derived diffusible ligand (ADDL) and was provided by Dr Bill Goure (Acumen Inc., Beverly Hills, CA, USA) [8]. 3B3 is the murine precursor of the humanized 19.3 mAb used by Savage and colleagues and has the same complementary determining regions, and it demonstrates similar relative preferences to amyloid-beta oligomers (oAβ) as assessed by surface plasmon resonance and KinExA (Sapidyne Instruments Inc., Boise, ID, USA)
Developing an Aβ oligomer-selective immunoassay with improved sensitivity In an attempt to achieve an assay that can sensitively detect soluble oAβ in human biological fluids, we systematically evaluated several mAbs and two detection platforms
Summary
Amyloid β-protein oligomers play a key role in Alzheimer’s disease (AD), but well-validated assays that routinely detect them in cerebrospinal fluid (CSF) are just emerging. While natural oAβ can be readily identified in aqueous extracts of AD brain tissue, attempts to detect soluble oAβ in cerebrospinal fluid (CSF) have led to mixed results, with a few laboratories reporting their ready detection but others concluding that their levels are very low or virtually undetectable (discussed in [3]). All five found considerable overlap between the levels of oligomers detected in AD and control CSF, but four studies reported higher mean levels of soluble oligomers in AD than control subjects. Holtta and colleagues found that AD patients with mild and moderate AD had significantly higher mean levels of oAβ than controls, whereas patients with severe AD did not differ significantly from the control group [5]. Most of the groups describing positive detection of natural oligomers did
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