High Selectivity and Sensitivity of Oligomeric p-Phenylene Ethynylenes for Detecting Fibrillar and Prefibrillar Amyloid Protein Aggregates

Misfolding and aggregation of amyloid proteins into fibrillar aggregates is a central pathogenic event in neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's diseases (PD). Currently, there is a lack of reliable sensors for detecting the range of protein aggregates involved in disease etiology, particularly the prefibrillar aggregate conformations that are more neurotoxic. In this study, the fluorescent sensing of two novel oligomeric p-phenylene ethynylenes (OPEs), anionic OPE1- and cationic OPE2+, for detecting prefibrillar and fibrillar aggregates of AD-associated amyloid-beta (A beta 40 and A beta 42) and PD-associated alpha-synuclein proteins (wildtype, and single mutants A30P, E35K, and AS3T) over their monomeric counterparts, were tested. Furthermore, the performance of OPEs was evaluated and compared to thioflavin T (ThT), the most widely used fibril dye. Our results show that OPE1 and OPE2+ exhibited aggregate-specific binding inducing large fluorescence turn-on and spectral shifts based on a combination of backbone planarization, hydrophobic unquenching, and superluminescent OPE complex formation sensing modes. OPEs exhibited higher selectivity, higher binding affinity, and comparable limits of detection for A beta 40 fibrils compared to ThT. OPE2+ exhibited the largest fluorescence turn-on and highest sensitivity. Significantly, OPEs detected prefibrillar aggregates of A beta 42 and alpha-synuclein that ThT failed to detect. The superior sensing performance, the nonprotein specific detection, and the ability to selectively detect fibrillar and prefibrillar amyloid protein aggregates point to the potential of OPEs to overcome the limitations of existing probes and promise significant advancement in the detection of the myriad of protein aggregates involved in the early stages of AD and PD.