Inhibition of amyloid fibrillation of γD-crystallin model peptide by the cochineal Carmine

gamma D-crystallin is among the most abundant gamma-crystallins in the human eye lens which are essential for preserving its transparency. Aging, and environmental changes, cause crystallins to lose their native soluble structure and aggregate, resulting in the formation of cataract. Current treatment of cataract is surgical removal which is costly. Pharmaceutical therapeutics of cataract is an unmet need. We report a screen for small molecules capable of inhibiting aggregation of human gamma D-crystallin. Using a highly amyloidogenic hexapeptide model (41)GCWMLY(46) derived from the full-length protein, we screened a library of 68 anthraquinone molecules using ThT fluorescence assay. A leading hit, the cochineal Carmine, effectively reduced aggregation of the model GDC6 peptide in dose dependent manner. Similar effect was observed toward aggregation of the full-length gamma D-crystallin. Transmission electron microscopy, intrinsic Tryptophan fluorescence and ANS fluorescence assays corroborated these results. Insights obtained from molecular docking suggested that Carmine interaction with monomeric GDC6 involved hydrogen bonding with Ace group, Cys, Met residues and hydrophobic contact with Trp residue. Carmine was non-toxic toward retinal cells in culture. It also reduced ex vivo the turbidity of human extracted cataract material. Collectively, our results indicate that Carmine could be used for developing new therapeutics to treat cataract. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Gamma D-crystallin is essential in maintaining the transparency of the human eye lens, with its aggregation leading to cataract formation. The study found that cochineal Carmine could effectively reduce aggregation of gamma D-crystallin, showing potential for developing new therapeutics for cataract treatment.