Inhibition Activity and Mechanism Studies of Sulfonate Derivatives of Chrysin on Xanthine Oxidase

The water soluble chrysin-8-sulfonate acid sodium (Chas-8), chrysin-6-sulfonate acid sodium (Chas-6), chrysin-4'-sulfonate acid sodium (Chas-4') were investigated as potent xanthine oxidase (XO) inhibitors in vitro, and compared to that of patent chrysin. Among them, Chas-4'exhibited the most potential inhibition activity with IC(50 )values of 0.758 +/- 0.14 mu M. However, Chas-8 and Chas-6 on XO inhibition activities were very weak due to the IC50 values exceeding to 50 mu M. The Chas-4' could reversibly inhibit XO in a mixed-type competitive kinetics manner, and could quench the intrinsic fluorescence of XO by a static process with the quenching constant of 3.64 x10(4) L mol(-1) at 298 K. Synchronous fluorescence revealed that Chas-4'could bind to the active center of XO, and induce the conformation change of XO. Molecular docking also confirmed that Chas-4' interacted with several amino acid residues of XO. Moreover, the pi-pi stacking, hydrogen bond and hydrophobic interactions might play key roles in the formation of stable complex. The present studies on differences in inhibition activities of chrysin, Chas-8, Chas-6, and Chas-4' will enhance the understanding of structure-activity relationships, and also demonstrate that Chas-4' is a new lead drug for prevention and treatment gout.