Brazilin inhibits the Zn2 +-mediated aggregation of amyloid β-protein and alleviates cytotoxicity

Abstract

Interactions of Zn2+ with amyloid β-protein (Aβ) and the subsequent induction of Aβ aggregation have been implicated in the pathogenesis of Alzheimer's disease (AD). The development of small-compound inhibitors against Zn2+-mediated Aβ aggregation is therefore greatly desired. In this study, brazilin was used to inhibit Zn2+-mediated Aβ aggregation and alleviate its cytotoxicity. The binding properties of brazilin and Zn2+ were first probed using Fourier transform infrared (FTIR) spectroscopy and isothermal titration calorimetry (ITC) assays. Both the FTIR and ITC results have shown that brazilin is able to bind Zn2+ in a physiologically suitable range of concentrations. The dissociation constant (Kd) between brazilin and Zn2+ was about 46.0±6.8μM, which makes brazilin a potential drug model for the chelation of free Zn2+. Moreover, the higher affinity of brazilin for Aβ42 (Kd=2.5±1.6μM) than that of Zn2+ (Kd=6.2±0. 9μM), enables brazilin to sequester Zn2+ from the Aβ42-Zn2+ complex. In addition, the inhibitory effects of brazilin on Zn2+-mediated Aβ aggregation were examined using the Thioflavin T fluorescence assay, transmission electron microscopy and cytotoxicity assays. It was found that brazilin showed remarkable inhibitory capability against Zn2+-induced aggregation of Aβ42. Furthermore, the Zn2+-mediated cytotoxicity of Aβ42 was also largely mitigated under the influence of brazilin. This study therefore provides further insights into the role of Zn2+ in the Aβ42 aggregation pathway, indicating potential new strategies for the design of small compounds with therapeutic potential for AD.