Green tea leaf constituents inhibit the formation of lysozyme amyloid aggregates: An effect of mutual interactions.

Amyloidoses represent a group of pathological conditions characterized by amyloid fibrils accumulating in the form of deposits in intra- or extracellular space, leading to tissue damage. The lysozyme from hen egg-white (HEWL) is often used as a universal model protein to study the anti-amyloid effects of small molecules. The in vitro anti-amyloid activity and mutual interactions of green tea leaf constituents: (-)-epigallocatechin gallate (EGCG), (-)-epicatechin (EC), gallic acid (GA), caffeine (CF) and their equimolar mixtures were studied. The inhibition of HEWL amyloid aggregation was monitored by a Thioflavin T fluorescence assay and atomic force microscopy (AFM). The interactions of the analyzed molecules with HEWL were interpreted by ATR-FTIR and protein-small ligand docking studies. EGCG was the only substance efficiently inhibiting amyloid formation (IC50 ∼193 μM), slowing the aggregation process, reducing the number of fibrils and partially stabilizing the secondary structure of HEWL. Compared to EGCG alone, EGCG-containing mixtures displayed lower overall anti-amyloid efficacy. The decrease in efficiency results from (a) the spatial interference of GA, CF and EC with EGCG while binding to HEWL, (b) the propensity of CF to form a less active adduct with EGCG, which participates in interactions with HEWL in parallel with pure EGCG. This study confirms the importance of interaction studies, revealing the possible antagonistic behavior of molecules when combined.