Bile acids and polyphenols inhibit succinic anhydride-induced protein succinylation and amyloid aggregation: Mechanistic insights.

Lysine succinylation is a major post-translational modification affecting diverse proteins, and its excessive occurrence can lead to protein misfolding and aggregation-hallmarks of various proteinopathies, such as amyloid-β and Tau tangle formation in Alzheimer's disease and islet amyloid polypeptide aggregation in type 2 diabetes. Here, we investigated the inhibitory effects of bile acid metabolites (deoxycholic acid, glycocholic acid, and taurocholic acid sodium) and natural polyphenols (anthocyanin and salidroside) on succinylation and succinylation-induced amyloid aggregation. Succinylation levels were evaluated using the ninhydrin assay before and after treatment, and aggregation behavior and structural alterations were characterized by SDS-PAGE, inverted fluorescence microscopy, and intrinsic fluorescence spectroscopy. Additionally, fluorescence quenching and molecular docking were used to explore the underlying mechanisms. All five small molecules significantly reduced succinylation in a concentration-dependent manner (p < 0.05). Among bile acids, taurocholic acid sodium exhibited the strongest suppression of aggregation (40.99 %), followed by glycocholic acid (28.32 %) and deoxycholic acid (27.94 %). Anthocyanin showed greater inhibition (33.81 %) than salidroside (26.54 %) (all p < 0.05). The results suggest that these small molecules inhibit succinylation-induced aggregation potentially by interacting with proteins and altering their conformations, thereby preventing excessive succinylation at lysine residues. This study provides new insight into the interplay between bile acid metabolism and protein homeostasis and highlights the therapeutic potential of natural compounds in preventing protein aggregation-related diseases.