(567o) Effect of Solid/Liquid Interfaces On the Formation of Amyloid Deposits –Insulin as a Case Study

Amyloid fibrils are proteinaceous deposits associated with a variety of human diseases like Alzheimer, islet amyloidosis, type two diabetes, systemic amyloidosis, transmissible spongiform encephalopathy, Parkinson disease, familial amyloid polyneuropathy, etc. Amyloid diseases are apparently unconnected; however, intermolecular secondary structure (mostly â-sheets) is present in all amyloid aggregates. Although the proteins involved in the different types of fibers lack homology, the morphology of the deposits is remarkable similar. Some experimental findings support the universality of amyloid fibrils formation whereas others contradict it. In spite of the large amount of published material, the effect of surfaces on the formation of the deposits remains obscure. The concentration of amyloid peptides in healthy or sick tissue is of the order of a few nano-moles. Therefore, the presence of a liquid/solid interface may serve as a crowding agent that ?catalyses? the formation of the aggregates. We studied the rate and extent of aggregation of bovine insulin in bulk and in the presence of different solid/liquid interfaces. The chemistry of surfaces was chosen to mimic those surfaces found in cells. Two types of surfaces were used: polystyrene latexes with different surface chemistry and negatively and positively charged liposomes. The rate and extent of aggregation was followed by dynamic light scattering, which was used to monitor the size of the aggregates as a function of time. Congo Red assays were performed to confirm if the aggregates were amyloidic and selected samples were inspected by atomic force microscopy. The results were rationalized by using experimentally determined (using static light scattering) second and third (osmotic) virial coefficients. Our results show that the crowding effect provided by the presence of a solid/liquid interface allows the formation of fibrils at conditions that are closer to biological ones (in contrast with the very harsh conditions that are needed to make fibrils with insulin in bulk).