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Abstract: Numerous phenolic compounds have been reported to have an inhibitory role on amyloid formation of proteins. The present study, utilizing lysozyme as a model system, examined the anti-amyloidogenic effects of phenol and three diphenol epimers. The results indicated that catechol and hydroquinone dose-dependently inhibited lysozyme fibrillation and covalently bound to the peptide chains to form quinoproteins, showing a similar effect to benzoquinone. In contrast, phenol and resorcinol did not modify the peptide with a quinone moiety, showing no effect on lysozyme fibrillation. We suggest that quinone intermediates are the active form for a phenolic compound to inhibit lysozyme fibrillation. The modification of lysozyme with quinone moieties alters the interacting forces between peptide chains and consequently interrupts the process of lysozyme fibrillation. Structured summary of protein interactions: Lysozyme and Lysozyme bind by fluorescence technology (View interaction). Lysozyme and Lysozyme bind by transmission electron microscopy (View interaction). [Copyright &y& Elsevier]

Ascorbic acid (AsA) is an important antioxidant and enzyme cofactor in many biochemical processes. Most biological activities of AsA are closely related to its redox properties. Recent investigations have demonstrated that AsA is associated with amyloid-related diseases and can inhibit amyloid aggregation of polypeptides. In the present study, we determined the kinetics of AsA degradation and investigated the anti-amyloidogenic activities of AsA and its degradation products by utilizing insulin as a model polypeptide. The results showed that the half-life of AsA varied with the pH of the medium and the incubation temperature. The degradation products of AsA inhibited insulin fibrillation, with an activity positively correlated to the degree of AsA degradation. The degradation species, compared with intact AsA, also showed a stronger disruptive effect on mature amyloid fibrils and significantly decreased fibrillar cytotoxicity. Dehydroascorbic acid and diketogulonic acid, two key intermediates in AsA degradation, had similar anti-amyloidogenic activity toward the degradation species of AsA. The results of this work indicate that degradation of natural antioxidants must be considered when evaluating their anti-amyloidogenic effects. These insights into the action of AsA may also provide a novel route to understand its physiological/pharmacological roles in amyloid-related diseases. [ABSTRACT FROM AUTHOR]

Abstract: Growing interest and research efforts have recently been focused on elucidating the molecular mechanism of amyloid formation and the screening of effective inhibitors to interrupt amyloid structures. In the present study, the anti-amyloidogenic effects of quercetin were investigated in vitro using bovine insulin as a model protein. The results demonstrated that quercetin dose-dependently inhibited amyloid formation of insulin. Moreover, quercetin destabilized the preformed insulin fibrils and transformed the fibrils into amorphous aggregates. Hemolysis was observed when human erythrocytes were co-incubated with insulin fibrils. Quercetin inhibited fibril-induced hemolysis in a dose-dependent manner. SDS–PAGE showed that insulin fibrils induced the aggregation of cytoskeletal proteins of erythrocyte membranes and that quercetin attenuated this fibril-induced cytoskeletal aggregation. The results of the present work suggest that quercetin may serve as a lead structure for the design of novel anti-amyloidogenic drugs. [Copyright &y& Elsevier]