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Zinc boosts EGCG's hIAPP amyloid Inhibition both in solution and membrane

Lee, Young-Ho, Lin, Yuxi, Cox, Sarah J., Kinoshita, Misaki, Sahoo, Bikash R., Ivanova, Magdalena, Ramamoorthy, Ayyalusamy
Biochimica et biophysica acta 2019 v.1867 no.5 pp. 529-536
amyloid, cell death, circular dichroism spectroscopy, cytotoxicity, epigallocatechin gallate, fluorescence, humans, insulin, lipids, magnetism, noninsulin-dependent diabetes mellitus, polypeptides, titration, transmission electron microscopy, zinc
Amyloid aggregation of human islet amyloid polypeptide (hIAPP) is linked to insulin-producing islet cell death in type II diabetes. Previous studies have shown that zinc (Zn(II)) and insulin, co-secreted with hIAPP, have an inhibition effect on hIAPP aggregation. Lipid membranes have also been shown to significantly influence the aggregation kinetics of hIAPP. An increasing number of studies report the importance of developing small molecule inhibitors to suppress the hIAPP's aggregation and subsequent toxicity. The ability of epigallocatechin-gallate (EGCG) to inhibit aggregation of a variety of amyloid peptide/proteins initiated numerous studies as well as the development of derivative compounds to potentially treat amyloid diseases. In this study, a combination of Thioflavin-T fluorescence kinetics, transmission electron microscopy, isothermal titration calorimetery, circular dicrosim and nucelar magnetic resonance experiments were used to demonstrate a significant enhancement in EGCG's efficiency when complexed with Zn(II). We demonstrate that the Zn-EGCG complex is able to significantly suppress hIAPP's amyloid aggregation both in presence and absence of lipid membrane. Circular dichroism experiments indicate the formation and stabilization of a helical structure of hIAPP in presence of the EGCG:Zn(II) complex. Our results also reveal the ability of EGCG or EGCG:Zn(II) to efficiently suppress hIAPP's cellular toxicity. We believe that the reported results could be useful to develop strategies to trap hIAPP intermediates for further biophysical and structural studies, and also to devise approaches to abolish amyloid aggregation and cellular toxicity.