High Selectivity And Sensitivity Of Oligomeric P-Phenylene Ethynylenes For Detecting Amyloid Proteins In-Vitro

A common pathological hallmark of neurodegenerative diseases such as Alzheimer's and Parkinson's diseases is the presence of extra- or intra-cellularly accumulated amyloid proteins. Importantly, as these protein deposits are believed to initiate a cascade of events culminating in neurodegeneration and cognitive decline before the onset of clinical symptoms, protein amyloids are ideal biomarkers for early disease detection and therapeutic intervention. A molecular probe that selectively detect these β-sheet rich amyloid deposits could lead to early disease detection and a better understanding of these diseases. We are developing a class of novel amyloid sensors based on the p-phenylene ethynylene (PPE) molecular scaffold. We have shown that oligomeric PPE compounds (OPEs) bind specifically to amyloid fibrils made of model proteins, insulin and lysozyme, which leads to fluorescence turn-on. In this study, we evaluate the capability of two probes, OPE1- and OPE2+, to detect amyloid fibrils formed from Alzheimer's disease-associated amyloid-β (Aβ) peptides and Parkinson's disease associated α-synuclein proteins. Selectivity and specificity of OPE1- and OPE2+ to detect the amyloid conformation of those proteins were quantified. We show that both OPE1- and OPE2+ had higher selectivity toward Aβ40 fibrils than the commonly used amyloid dye, Thioflavin-T (ThT) and that the OPE compounds detected Aβ40 fibrils at a concentration as low as 0.5 µM. However, OPE2+ also displayed a small fluorescence enhancement in presence of the monomeric protein, which could lead to false positives. Compared to ThT, OPE1- more sensitively detected fibrillar aggregates of α-synuclein proteins. Importantly, OPE1- also detected pre-fibrillar aggregates of α-synuclein proteins that ThT did not detect. The high selectivity and specificity of OPE1- for the detection of a wider range of amyloid protein aggregates makes it a promising probe for the early detection of neurodegenerative diseases.