A highly sensitive novel immunoassay specifically detects low levels of soluble Aβ oligomers in human cerebrospinal fluid

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.

Methods for the Specific Detection and Quantitation of Amyloid-β Oligomers in Cerebrospinal Fluid

“…These reduced CSF A␤ 42 levels allowed an accurate prediction of development of AD in tested MCI subjects (sensitivity of 90%, specificity of 71%) [3,[17][18][19][20]. According to Jack and coworkers, the first biomarker change detectable with state-to-the-art methods is the decrease of CSF A␤ 42, which might reflect the formation of A␤ plaques, as suggested by the "sink hypothesis" [21]. Neuritic plaque formation can be visualized using PIB-PET [22].…”

“…Recent biomarker studies often include measurements of other core biomarkers of AD other than A␤ 42 (A␤ 40 , tau, phospho-tau), and the combination of results increased the current average sensitivity of AD biomarker detection slightly [17,20]. However, these assays did not significantly improve the predictive value over present clinical tests and therefore, other biomarkers are needed to monitor fundamental disease features.…”

“…Across a large number of studies, A␤ 42 monomer concentrations in cerebrospinal fluid (CSF) samples, determined by ELISA or similar methods, are consistently and significantly reduced by 50% in patients with AD compared to healthy controls. Sensitivity and specificity exceeded 80% in most of the studies, making CSF A␤ 42 one of the best established biochemical markers.…”

“…Sensitivity and specificity exceeded 80% in most of the studies, making CSF A␤ 42 one of the best established biochemical markers. It is shown that patients with mild cognitive impairment (MCI) and later conversion to AD have reduced CSF A␤ 42 levels as well.…”

“…A␤ is generated from the amyloid-␤ protein precursor (A␤PP) by subsequent enzymatic cleavage of the ␤-and ␥-secretase, respectively [7][8][9]. Several A␤ isoforms of various chain length are formed, but A␤ 42 has the highest propensity for aggregation and undergoes formation of oligomers and larger intermediate forms like protofibrils, insoluble fibrils, and plaques. A range of conformational subtypes, varying in number of monomers, secondary and tertiary structure, shape, size, and compactness has already been described in vitro and in vivo [10,11].…”