Molecular mechanism of Thioflavin-T binding to amyloid fibrils.

Curcumin is a constituent (up to ∼5%) of the traditional medicine known as turmeric. Interest in the therapeutic use of turmeric and the relative ease of isolation of curcuminoids has led to their extensive investigation. Curcumin has recently been classified as both a PAINS (pan-assay interference compounds) and an IMPS (invalid metabolic panaceas) candidate. The likely false activity of curcumin in vitro and in vivo has resulted in >120 clinical trials of curcuminoids against several diseases. No double-blinded, placebo controlled clinical trial of curcumin has been successful. This manuscript reviews the essential medicinal chemistry of curcumin and provides evidence that curcumin is an unstable, reactive, nonbioavailable compound and, therefore, a highly improbable lead. On the basis of this in-depth evaluation, potential new directions for research on curcuminoids are discussed.

The Essential Medicinal Chemistry of Curcumin

Thioflavin T (ThT) dye fluorescence is used regularly to quantify the formation and inhibition of amyloid fibrils in the presence of anti-amyloidogenic compounds such as polyphenols. However, in this study, it was shown, using three polyphenolics (curcumin, quercetin and resveratrol), that ThT fluorescence should be used with caution in the presence of such exogenous compounds. The strong absorptive and fluorescent properties of quercetin and curcumin were found to significantly bias the ThT fluorescence readings in both in situ real-time ThT assays and single time-point dilution ThT-type assays. The presence of curcumin at concentrations as low as 0.01 and 1 mum was sufficient to interfere with the ThT fluorescence associated with fibrillar amyloid-beta(1-42) (0.5 mum) and fibrillar reduced and carboxymethylated kappa-casein (50 mum), respectively. The ThT fluorescence associated with fibrillar amyloid-beta(1-42) was also biased using higher concentrations of resveratrol, a polyphenol that is not spectroscopically active at the wavelengths of ThT fluorescence, implying that there can be direct interactions between ThT and the exogenous compound and/or competitive binding with ThT for the fibrils. Thus, in all cases where ThT is used in the presence of an exogenous compound, biases for amyloid-associated ThT fluorescence should be tested, regardless of whether the additive is spectroscopically active. Simple methods to conduct these tests were described. The Congo red spectral shift assay is demonstrated as a more viable spectrophotometric alternative to ThT, but allied methods, such as transmission electron microscopy, should also be used to assess fibril formation independently of dye-based assays. Structured digital abstract: * MINT-7259867: RCMkappa-CN (uniprotkb:P02668) and RCMkappa-CN (uniprotkb:P02668) bind (MI:0407) by electron microscopy (MI:0040) * MINT-7258930: RCMkappa-CN (uniprotkb:P02668) and RCMkappa-CN (uniprotkb:P02668) bind (MI:0407) by fluorescence technologies (MI:0051) * MINT-7259878: Amyloid beta (uniprotkb:P05067) and Amyloid beta (uniprotkb:P05067) bind (MI:0407) by fluorescence technologies (MI:0051).

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The thioflavin T fluorescence assay for amyloid fibril detection can be biased by the presence of exogenous compounds

Resveratrol Selectively Remodels Soluble Oligomers and Fibrils of Amyloid Aβ into Off-pathway Conformers

Inhibition of Amyloid Formation

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=1983&context=scipapers

Sean A. Hudson

Papers

The thioflavin T fluorescence assay for amyloid fibril detection can be biased by the presence of exogenous compounds

(−)-Epigallocatechin-3-Gallate (EGCG) Maintains κ-Casein in Its Pre-Fibrillar State without Redirecting Its Aggregation Pathway