Measuring Amyloid-β Peptide Concentrations in Murine Brain with Improved ELISA Assay

The amyloid-β (Aβ) peptides of 40 and 42 amino acids that are implicated in Alzheimer's disease may potentially aggregate into toxic oligomers and form neuritic plaques. The enzyme-linked immunosorbent assay (ELISA) is a facile method used for the determination of Aβ concentrations in biological matrices, namely plasma, cerebrospinal fluid, and brain. The method is mostly used for the measurement of Aβ concentrations in transgenic mice, but it is unknown whether the ELISA method is suitable for measuring low, endogenous levels of Aβ in the brains of wild-type mice. The Aβ ELISA kit manufacturer recommends use of 5 M guanidine hydrochloride (GuHCl), a protein-denaturing agent, for homogenization of the brain tissue, followed by dilution back down to 0.1 M to avoid quenching by GuHCl. Components of brain matrices and GuHCl that could interfere with the quantitation have not been investigated. In this article, we describe an improved method involving homogenization of mouse brain with 1 M instead of 5 M GuHCl, reducing the dilution factor by 5× to provide a higher sensitivity. The modified ELISA assay is improved for the quantitation of brain Aβ peptides in wild-type mice, where Aβ peptide levels are much lower than those in transgenic mouse models. © 2021 Wiley Periodicals LLC.