Polyphenolic Gallotannins 1,3,6-Tri-O-galloyl-β-d-glucose and Corilagin Attenuate IAPP Amyloid Formation and Cytotoxicity by Primarily Targeting Secondary Nucleation

Protein misfolding and subsequent aggregation into insoluble amyloid deposits are associated with various diseases, including Alzheimer's disease, systemic amyloidosis, and type 2 diabetes mellitus (T2DM). In T2DM, the peptide hormone islet amyloid polypeptide (IAPP), which regulates glucose homeostasis, aggregates in the pancreas, forming soluble cytotoxic aggregates and amyloid fibrils that contribute to β-cell dysfunction and death. Thus, the inhibition of IAPP aggregation consists of a promising strategy for treating T2DM. Natural gallotannins are potential amyloid modulators, though their effects on amyloid self-assembly are not fully understood. This study examines two gallotannins, 1,3,6-tri-O-galloyl-β-d-glucose (β-TGG) and corilagin, and their inhibitory effects on IAPP aggregation. Using thioflavin T fluorescence, atomic force microscopy, and circular dichroism, it was found that the gallotannins delay IAPP self-assembly and reduce the length and quantity of amyloid fibrils. Despite structural similarity, corilagin exhibited markedly higher antiaggregative activity at lower concentrations compared to β-TGG. Peptide monomer-gallotannin interactions were further investigated using all-atom explicit solvent molecular dynamics simulations, providing valuable insight into the binding of both gallotannins to monomeric IAPP. Furthermore, corilagin provided significant cytoprotective effects against IAPP-induced cytotoxicity and membrane damage in pancreatic β-cells. Mechanistic analysis revealed that corilagin exerts its effects primarily by inhibiting secondary nucleation and facilitating off-pathway aggregation into cytocompatible proteospecies. Together, these findings highlight the potential of both gallotannins in inhibiting amyloid self-assembly and inspiring the development of antiaggregative agents.