In Silico Molecular Docking Studies and Xanthine Oxidase Inhibitory Activity of Abies kawakamii Leaf Extract and Its Constituent

Gout is a metabolic disorder associated with abnormal purine metabolism and persistent hyperuricaemia, which promotes formation and deposition of monosodium urate crystal in joints, leading to acute arthritis and impaired quality of life. This study aimed to evaluate the xanthine oxidase inhibitory activity of ethanolic leaf extract of Abies kawakamii and its fractions. The protocol of bioassay-guided fractionation was employed to isolate active compounds from leaf extract. Maltol was identified as the major active compound from the ethyl acetate fraction (EAF). Maltol inhibited xanthine oxidase with IC50 values of 33.18 and 26.67 μg/mL against xanthine and hypoxanthine, respectively, significantly lower than the crude extract (152.04 and 136.57 μg/mL) and EAF (66.70 and 48.76 μg/mL). Enzyme kinetic analyses further showed that EAF inhibited xanthine oxidase through a competitive inhibition mechanism toward both substrates. Molecular docking analysis suggested that maltol may interact with the active-site region of xanthine oxidase, showing a binding affinity of −6.5 kcal/mol, slightly weaker than that of allopurinol, with no predicted hepatotoxicity based on in silico analysis. Our findings indicate that A. kawakamii leaf extract and its constituent, maltol, could be further explored as a natural approach for gout management.