Quantification of Alzheimer DiseaseAmyloid β Peptide 43 in Human BrainWith a Newly Developed Enzyme-LinkedImmunosorbent Assay (ELISA)

Abstract: A 20 weeks project at Karolinska Institutet (KI), Huddinge, Sweden is in this master thesis summarized. Alzheimer’s disease is the most common form of dementia in the world. One of the pathological hallmarks seen in AD patients consists of amyloid plaques assembled of beta amyloid (Aβ) peptide aggregates. A lot of research has been done on Aβ40 and Aβ42 but not on the longer variant with 43 residues. An earlier study by Welander et al, quantified the Aβ43 peptide from amyloid plaque cores with high-performance liquid chromatography coupled to mass-spectrometry (HPLC-MS/MS)1. Here, I present the initial development of an enzyme-linked immunosorbent assay (ELISA) with the goal to quantify Aβ43 peptides in soluble fractions of human brain tissue. An ELISA method with the possibility to quantify Aβ43 peptides from cerebral spinal fluid might have the prospect to serve as a diagnostic tool for AD in the future. Commercial ELISA kits coated with antibodies against all Aβ species was not suitable for detecting Aβ43 in soluble brain tissue from human AD patients. This is due to the high amount of Aβ40 (and in some extent Aβ42) in the samples, which will bind to the same epitope as Aβ43 on the capturing antibody. These shorter Aβ species will be in excess and bind to the capturing antibody thereby ousting Aβ43 from binding in. A better way for quantifying Aβ43 with ELISA might instead be to coat a polystyrene plate with α-Aβ43 antibodies, which are c-terminal specific to Aβ43. This will abolish the competition between the different Aβ species and function as an immunoprecipitation of unwanted species. This yielded adequate quantification of Aβ43 (2.64 pM) from tris-buffer saline (TBS) fractions from a human brain sample from AD.