A new blood‐based biomarker of Aβ clearance: The monocyte Aβ mid‐domain assay

Abstract

AbstractBackgroundDeficiency in cerebral Amyloid beta (Aβ) clearance is implicated in the pathogenesis of Alzheimer’s disease (AD), and Aβ clearance systems are potential therapeutic targets in AD. Clearance of Aβ is a complex process were phagocytosis and degradation of Aβ are two important components. Innate immune‐linked genetic risk factors contribute to AD, and innate immune cells; microglia in the brain and monocytes/macrophages in the peripheral blood (PB), phagocytose Aβ and contribute to clearance. Our objective was to develop an assay measuring Aβ mid‐domain peptides in relevant biological specimens. The intracellular concentration of peptides containing mid‐domain fragments may reflect phagocytic activity or Aβ degradation efficiency.MethodAn immunoassay on the Quanterix Single Molecule Array (Simoa) platform was developed against an Ab 20‐34 peptide using a proprietary anti‐mid‐domain sheep monoclonal antibody as capture antibody (2A9). The detector reagent consists of an anticomplex antibody using Bio‐Rad HuCAL technology (H3) ensuring the optimal Aβ mid‐domain peptide specificity and assay sensitivity. Monocytes were isolated from 8 ml blood samples using a combination of BD CPT blood sampling tubes and RosetteSep antibodies from StemCell.ResultThe 2A9/H3 immunoassay run on the Simoa platform detected Aβ mid‐domain containing peptides with a lower limit of quantification (LLOQ) of approximately 0,7 pg/ml resulting in measurable levels of the peptides in both CSF and monocyte lysates (figure 1 a).ConclusionAs shown in figure 1 b, the 2A9/H3 combination has a high specificity for mid‐domain restricted peptides. Here we show that as used in a sensitive Simoa‐assay, this assay detects Aβ mid‐domain containing peptides both in CSF and monocyte lysates, and may serve as a tool for PB measurement of Aβ catabolism in both disease progression studies and intervention studies. The PreADx ™ assay is an accurate and highly sensitive immunoassay for quantification of mid domain Aβ peptides in relevant biological fluids and cells. The assay demonstrates high precision with monocyte lysates and linearity in spiking and dilution experiments (not shown).