Inhibition of Lysozyme Amyloid Fibrillation by Silybin Diastereoisomers: The Effects of Stereochemistry

Silybin is a flavonoid lignin compound consisting of two diastereomers with nearly equal molar ratios. It has been reported that silybin can effectively inhibit the aggregation of amyloid protein, but the difference between the two silybin diastereomers has been rarely studied. In this work, the inhibitory ability of silybin to hen egg-white lysozyme (HEWL) was demonstrated, and the difference of kinetic parameters of two diastereomers was analyzed. Fluorescence quenching titration was utilized to analyze the binding differences to native HEWL between the diastereomers, and transmission electron microscopy (TEM) was utilized to analyze the characteristics of the surface of various samples. The differences between hydrophobicity and the secondary structure among several HEWL samples were measured by the 8-anilino-1-naphthalene sulfonic (ANS) acid fluorescence probe, Raman spectra, and far-UV circular dichroism. Moreover, the differences in the binding energy of these two diastereomers with HEWL were analyzed by molecular docking. Also, we have investigated the effect of silybin diastereomers on HEWL fibril-induced cytotoxicity in SH-SY5Y cells. Results show that silybin has a certain inhibitory effect on the HEWL fibrillogenesis process, while silybin B (SB) has a more significant inhibitory effect than silybin A (SA), especially at high concentrations. This work provides some insights into the screening of amyloid inhibitors from complicated natural products and indicates that SB has the prospect of further development as an amyloid inhibitor.