Screening of effective xanthine oxidase inhibitors in dietary anthocyanins from purple sweet potato (Ipomoea batatas L. Cultivar Eshu No.8) and deciphering of the underlying mechanisms in vitro

- Highly-acylated anthocyanins from purple sweet potato are effective XO inhibitors.
- Inhibition of anthocyanins on XO is reversible and mixed.
- Anthocyanins can insert into the hydrophobic pocket of XO.
- Anthocyanins can occupy the catalytic center of XO by competing with xanthine.
- The formation of anthocyanin-XO complex changes the secondary structure of XO.

This study was aimed to screen the effective xanthine oxidase (XO) inhibitors in dietary anthocyanins from purple sweet potato and decipher the underlying mechanisms in vitro. Inhibition kinetics demonstrated that anthocyanin-rich purple sweet potato extract (APSPE) has reversible and mixed inhibitory effect on XO. Among the four fractions purified from APSPE, the fraction with highly-acylated anthocyanins showed the most powerful inhibition on XO. Molecular docking results suggested that the inhibition mechanism is the insertion of anthocyanins into the hydrophobic pocket of XO by interacting with some amino acid residues. Fluorescence and CD spectroscopy results showed that the formation of anthocyanin-XO complex is the possible quenching mechanism, which changes the secondary structure of XO. The reaction is entropy-driven and endothermic, with hydrophobic interaction being the major driving force. This study indicates that the highly-acylated dietary anthocyanins of purple sweet potato would be a promising XO inhibitor in clinical treatment.