Inhibitory Effect of Phenolic Compounds on Amyloid Fibrillation of Insulin

More than 20 human diseases are considered to be associated with amyloid fibrillation in polypeptides. Polyphenolic compounds have been demonstrated to disrupt amyloid structures and attenuate cytotoxicity of amyloid fibrils. In the present study, the inhibitory effects of four phenolic compounds on amyloid formation were investigated using bovine insulin as a model peptide. The results indicated that catechol and hydroquinone inhibited insulin fibrillation and bonded to the peptide chains with quinone moieties, showing a similar effect to benzoquinone. In contrast, phenol and resorcinol did not modify insulin with a quinone moiety, showing no effect on amyloid fibrillation. Furthermore, catechol and hydroquinone were less effective as an inhibitor of insulin fibrillation under anaerobic conditions, suggested that the formation of quinone intermediates via oxidation and subsequently transform insulin into quinopeptide were prerequisites for a phenolic compound to inhibit amyloid fibrillation. The results show that quinone intermediates are the active form for phenolic compounds to inhibit insulin amyloid fibrillation.