Hydration Shell of PEO–PPO–PEO Block Copolymer Assembly Controls the Modulation of Protein Aggregation: Synergistic Inhibition of Fibrillation Using Trehalose and Protection from Cu 2+ -Induced Fibrillation

Amyloid aggregation is a key process involved in many neurodegenerative diseases including Alzheimer's disease. It affects the brain and peripheral tissues, where different types of protein aggregates are accumulated. Pluronic PEO-PPO-PEO block copolymer self-assemblies are widely used as nanocarriers for the brain-targeted delivery of therapeutic agents. Elucidating protein aggregation at these polymer interfaces can provide critical insights into how macromolecular crowding and protein-polymer interactions influence the kinetics of protein aggregation. Here, we investigate the roles of two pluronic copolymers, namely, P123 and F127, which have a similar size of hydrophobic PPO block but different PEO block length on protein aggregation using hen egg white lysozyme (HEWL) as a model protein. Our study reveals that the more hydrated F127 self-assemblies with thicker PEO hydration shells accelerate the onset of protein-aggregation yet moderately retard the extent of overall fibril formation. On the other hand, the less hydrated P123 self-assemblies with compact hydration shells significantly delay the onset of protein aggregation and efficiently inhibit fibril formation. The binding of protein within the hydrated and longer PEO corona of F127 micelles favors accelerated kinetics of β-rich oligomers and fibril formation without a delay phase through soft-chemical interactions. For the less hydrated P123 micellar assemblies, the hydrophobic interactions and strong excluded volume effects probably contribute to stabilization of the protein. The addition of the widely used osmolyte trehalose further delays the protein aggregation and significantly retards the fibril formation through the synergistic inhibitory effects of trehalose and polymer assemblies. The trehalose-bearing pluronic micelles can, therefore, emerge as a potentially efficient inhibitor with great promise in therapeutic applications. The pluronic self-assemblies are also found to be highly effective in protecting the protein from toxicity associated with Cu2+ induced enhanced amyloid fibrillation. The binding of Cu2+ within the hydrated PEO corona makes them inaccessible to protein interactions and fibril formation.