P1‐022: The use of AlphaLISA in measurement of Aβ1–15/16 as a potential biomarker in neurodegenerative diseases

In progressive neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's disease (PD), cerebrospinal fluid (CSF) biomarkers reflect brain amyloid axonal pathology and neuronal death. In AD, the established CSF marker Aβ1–42 is reduced while the relative level of Aβ1–16 is increased. Furthermore, drug-induced γ-secretase inhibition enhances the relative levels of Aβ1–15 and Aβ1–16. Finding methods that are sensitive enough to quantify small soluble molecules in heterogeneous matrices such as CSF, has been a major challenge for a long time. Unlike the other AlphaLISA Aβ detection kits, the Aβ1–15/16 assay kit used fetal bovine serum (FBS) in its buffer system. Here, we investigate the effect of an FBS-containing AlphaLISA kit, for the benefit of measuring Aβ1–15/16 as a potential diagnostic marker. Different methodological set-ups such as time- and concentration-dependence and inhibitor studies were applied to evaluate different aspects of how the presence of FBS influences the measurements of Aβ1–15/16. Concentrations of Aβ1–15/16 using the AlphaLISA immunoassay were analyzed in two patient materials. First, we use CSF (n = 453) samples from controls, subjects with PD, PD with dementia (PDD), dementia with Lewy bodies (DLB), AD, progressive supranuclear palsy (PSP), multiple system atrophy (MSA) and corticobasal degeneration (CBD). Second, clinical de-identified CSF samples, controls and AD, collected from the routine workflow were also used. A combination of Aβ1–15 and Aβ1–16 is measured in the presence of FBS. A carboxypeptidase, which is present in the FBS, degrades Aβ1–16 to Aβ1–15 which is then detected by the AlphaLISA kit as reflected by higher measured concentrations in the presence of FBS. Significantly lower levels of Aβ1–15/16 were detected in PD and PDD compared to other neurodegenerative diseases. Using the AlphaLISA assay, both the CSF levels of Aβ1–15 and Aβ1–16 can be measured. They may provide valuable information as diagnostic markers in neurodegenerative disorders and may also function as pharmacodynamic markers in response to inhibition of γ-secretase in clinical trials.