The Flavanol (−)-Epigallocatechin 3-Gallate Inhibits Amyloid Formation by Islet Amyloid Polypeptide, Disaggregates Amyloid Fibrils, and Protects Cultured Cells against IAPP-Induced Toxicity

摘要

Islet amyloid polypeptide (IAPP, amylin) is the major protein component of the islet amyloidndeposits associated with type 2 diabetes. The polypeptide lacks a well-defined structure in itsmonomeric statenbut readily assembles to form amyloid. Amyloid fibrils formed from IAPP, intermediates generated in thenassembly of IAPP amyloid, or both are toxic to β-cells, suggesting that islet amyloid formationmay contributento the pathology of type 2 diabetes. There are relatively few reported inhibitors of amyloid formation bynIAPP. Here we show that the tea-derived flavanol, (-)-epigallocatechin 3-gallate [(2R,3R)-5,7-dihydroxy-n2-(3,4,5-trihydroxyphenyl)-3,4-dihydro-2H-1-benzopyran-3-yl 3,4,5-trihydroxybenzoate] (EGCG), is anneffective inhibitor of in vitro IAPP amyloid formation and disaggregates preformed amyloid fibrils derivednfromIAPP. The compound is thus one of a very small set ofmolecules which have been shown to disaggregatenIAPP amyloid fibrils. Fluorescence-detected thioflavin-T binding assays and transmission electron micro-nscopy confirm that the compound inhibits unseeded amyloid fibril formation as well as disaggregates IAPPnamyloid. Seeding studies showthat the complex formed by IAPP and EGCGdoes not seed amyloid formationnby IAPP. In this regard, the behavior of IAPP is similar to the reported interactions of Aβ and R-synucleinnwith EGCG.Alamar blue assays and lightmicroscopy indicate that the compound protects cultured rat INS-1ncells against IAPP-induced toxicity. Thus, EGCG offers an interesting lead structure for further developmentnof inhibitors of IAPP amyloid formation and compounds that disaggregate IAPP amyloid.