Chemoselective Bioconjugation of Amyloidogenic Protein Antigens to PEGylated Microspheres Enables Detection of α-Synuclein Autoantibodies in Human Plasma

Abstract

The misfolding and subsequent aggregation of amyloidogenic proteins is a classic pathological hallmark of neurodegenerative diseases. Aggregates of the α-synuclein protein (αS) are implicated in Parkinson's disease (PD) pathogenesis, and naturally occurring autoantibodies to these aggregates are proposed to be potential early-stage biomarkers to facilitate the diagnosis of PD. However, upon misfolding, αS forms a multitude of quaternary structures of varying functions that are unstable ex vivo. Thus, when used as a capture agent in enzyme-linked immunosorbent assays (ELISAs), significant variance among laboratories has prevented the development of these valuable diagnostic tests. We reasoned that those conflicting results arise due to the high nonspecific binding and amyloid nucleation that are typical of ELISA platforms. In this work, we describe a multiplexed, easy-to-operate immunoassay that is generally applicable to quantify the levels of amyloid proteins and their binding partners, named Oxaziridine-Assisted Solid-phase Immunosorbent (OASIS) assay. The assay is built on a hydrophilic poly(ethylene glycol) scaffold that inhibits aggregate nucleation, which we show reduces assay variance when compared to similar ELISA measurements. To validate our OASIS assay in patient-derived samples, we measured the levels of naturally occurring antibodies against the αS monomer and oligomers in a cohort of donor plasma from patients diagnosed with PD. Using OASIS assays, we observed significantly higher titers of immunoglobulin G antibody recognizing αS oligomers in PD patients compared to those in healthy controls, while there was no significant difference in naturally occurring antibodies against the αS monomer. In addition to its development into a blood test to potentially predict or monitor PD, we anticipate that the OASIS assay will be of high utility for studies aimed at understanding protein misfolding, its pathology and symptomology in PD, and other neurodegenerative diseases.