Polyphenols in combination with β-cyclodextrin can inhibit and disaggregate α-synuclein amyloids under cell mimicking conditions: A promising therapeutic alternative Saurabh Gautam a , Sandip Karmakar a , Radhika Batra a , Pankaj Sharma b , Prashant Pradhan b , Jasdeep Singh b , Bishwajit Kundu b, ⁎, Pramit K. Chowdhury a, ⁎ a Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India b Kusuma School of Biological Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India abstract article info Article history: Received 25 July 2016 Received in revised form 17 February 2017 Accepted 22 February 2017 Available online 24 February 2017 Parkinson's disease is characterized by the presence of insoluble and neurotoxic aggregates (amyloid fibrils) of an intrinsically disordered protein α-synuclein. In this study we have examined the effects of four naturally occur- ring polyphenols in combination with β-cyclodextrin (β-CD) on the aggregation of α-synuclein in the presence of macromolecular crowding agents. Our results reveal that even at sub-stoichiometric concentrations of the in- dividual components, the polyphenol–β-CD combination(s) not only inhibited the aggregation of the proteins but was also effective in disaggregating preformed fibrils. Curcumin was found to be the most efficient, followed by baicalein with (-)-epigallocatechin gallate and resveratrol coming in next, the latter two exhibiting very sim- ilar effects. Our results suggest that the efficiency of curcumin results from a balanced composition of the phenolic \\ OH groups, benzene rings and flexibility. The latter ensures proper positioning of the functional groups to max- imize the underlying interactions with both the monomeric form of α-synuclein and its aggregates. The unique- ness of β-CD was reinforced by the observation that none of the other cyclodextrin variants [α-CD and HP-β-CD] used was as effective, in spite of these possessing better water solubility. Moreover, the fact that the combinations remained effective under conditions of macromolecular crowding suggests that these have the potential to be de- veloped into viable drug compositions in the near future. MTT assays on cell viability independently confirmed this hypothesis wherein these combinations (and the polyphenols alone too) appreciably impeded the toxicity of the prefibrillar α-synuclein aggregates on the mouse neuroblastoma cell lines (N2a cells). © 2017 Elsevier B.V. All rights reserved. Keywords: α-Synuclein β-cyclodextrin Polyphenols Amyloid inhibition and disaggregation Parkinson's disease 1. Introduction A number of human pathological diseases such as Alzheimer's dis- ease, type 2 diabetes, Parkinson's disease, Amyotrophic lateral sclerosis (ALS), the prion diseases, and Huntington disease arise from the un- wanted misfolding, oligomerization and aggregation of proteins [1]. Most of these diseases are characterized by the deposition of amyloid fi- brils in body tissues. Among them Parkinson's disease is one of the most common diseases with 7–10 million people worldwide suffering from it. Parkinson's disease and dementia (due to synucleinopathies) are characterized by the presence of macroscopic amyloid deposits of the protein α-synuclein known as Lewy neuritis and Lewy bodies in brain tissues [2]. α-Synuclein is copiously present in human brain tissues and also in some other tissues such as red blood cells [2]. It is an intrinsically disor- dered protein, composed of 140 amino acid residues that can be struc- turally divided into three distinct segments (Fig. S1, Supporting Information) namely: (a) N-terminal amphipathic segment (1–60 amino acid residues), (b) a hydrophobic central region (61–95 residues) and (c) C-terminal acidic region (96–140 residues) [3]. The N-terminal region shares homology with lipoproteins (with amphipathic α-heli- ces) and contains a characteristic consensus hexameric sequence (KTKEGV) which is repeated about four times. The central hydrophobic region is known to be responsible for the aggregation of α-synuclein, without which the protein loses its propensity to form amyloids. The carboxy terminus region is highly acidic in nature and has been found to interfere in the formation of aggregates due to its role as an Biochimica et Biophysica Acta 1865 (2017) 589–603 Abbreviations: β-CD, β-cyclodextrin; CR, congo red; EGCG, (-)-epigallocatechin gallate; HP-β-CD, (2-Hydroxypropyl)-β-cyclodextrin; IPTG, isopropyl β-D- thiogalactopyranoside; SEC, size exclusion chromatography; TEM, transmission electron microscopy; ThT, Thioflavin T. ⁎ Corresponding authors. E-mail addresses: bkundu@bioschool.iitd.ac.in (B. Kundu), pramitc@chemistry.iitd.ac.in (P.K. Chowdhury). http://dx.doi.org/10.1016/j.bbapap.2017.02.014 1570-9639/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Biochimica et Biophysica Acta journal homepage: www.elsevier.com/locate/bbapap