Autoxidation Enhances Anti-Amyloid Potential of Flavone Derivatives

Abstract

The increasing prevalence of amyloid-related disorders, such as Alzheimer’s or Parkinson’s disease, raises the need for effective anti-amyloid drugs. It has been shown on numerous occasions that flavones, a group of naturally occurring anti-oxidants, can impact the aggregation process of several amyloidogenic proteins and peptides, including amyloid-beta. Due to flavone autoxidation at neutral pH, it is uncertain if the effective inhibitor is the initial molecule or a product of this reaction, as many anti-amyloid assays attempt to mimic physiological conditions. In this work, we examine the aggregation-inhibiting properties of flavones before and after they are oxidized. The oxidation of flavones was monitored by measuring the UV-vis absorbance spectrum change over time. The protein aggregation kinetics were followed by measuring the amyloidophilic dye thioflavin-T (ThT) fluorescence intensity change. Atomic force microscopy was employed to image the aggregates formed with the most prominent inhibitors. We demonstrate that flavones, which undergo autoxidation, have a far greater potency at inhibiting the aggregation of both the disease-related amyloid-beta, as well as a model amyloidogenic protein—insulin. Oxidized 6,2′,3′-trihydroxyflavone was the most potent inhibitor affecting both insulin (7-fold inhibition) and amyloid-beta (2-fold inhibition). We also show that this tendency to autoxidize is related to the positions of the flavone hydroxyl groups.

Exploring the Formation of Polymers with Anti-Amyloid Properties within the 2′3′-Dihydroxyflavone Autoxidation Process

“…Purification of recombinant Aβ42. The Aβ42 peptide was expressed in E. coli BL-21Star TM (DE3) (Invitrogen, Carlsbad, CA, USA) and purified similarly as previously described [ 21 ]. In brief, the cell culture was grown for 15 h in a ZYM-5052 medium containing ampicillin (100 µg/mL).…”

“…Flavones belong to a group of natural anti-oxidants that are found in nature in fruits, herbs, spices, and vegetables [ 15 , 16 ]. Besides their anti-microbial, anti-HIV, anti-cancer, anti-platelet, neuroprotective, anti-mutagenic, anti-allergic and anti-inflammatory characteristics [ 17 , 18 , 19 ], they were also shown in multiple reports to possess anti-amyloid properties [ 20 , 21 , 22 ]. A large number of flavone derivatives are described as acetylcholinesterase (AChE) inhibitors which makes them appealing candidates for the symptomatic treatment of AD [ 23 , 24 ].…”

“…However, the stability of flavones is questionable. The derivatives possessing neighboring hydroxyl groups are very likely to autoxidize at neutral or basic pH, completely changing the nature of these molecules [ 21 ]. Nevertheless, autoxidation improves the inhibitory effect against Aβ and insulin aggregation [ 20 , 22 ].…”

“…In order to identify the inhibitory molecules in the flavone oxidation mixture, we selected oxidized 2′,3′-dihydroxyflavone, which has previously been shown to possess the highest inhibitory potential among number of tested flavones against Aβ aggregation [ 21 ]. The 2′,3′-dihydroxyflavone has a C2-C3 double bond catechol moiety and the absence of 3-hydroxyl group that should favor the stabilization of the o-quinone and the oxidation coupling [ 30 ].…”

Neuroprotective Properties of Food-Borne Polyphenols in Neurodegenerative Diseases

“…Ribeiro et al [ 1 ] proposed the use of a new enzymatic biosensor to determine the antioxidant activity of commercially available teas, as well as the level of ascorbic acid in effervescent products, which can also be used to detect the real level of antioxidants in samples and depict the validity of “antioxidant” labeling in the product information. Using flavone derivatives, Sakalauskas et al [ 2 ] further explored the potential of polyphenols to prevent amyloid aggregation, an important hallmark of Alzheimer’s disease (AD) as well as other amyloid-related disorders. They demonstrated that after oxidation, flavones, particularly oxidized 6,2′,3′-trihydroxyflavone, not only keep but even increase their anti-amyloid properties, which might be a relevant addition to the discussion relating to whether, after physiologic metabolization, polyphenol derivatives still keep their beneficial properties.…”