ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the inhibitory effect of Gnaphalium affine extracts on xanthine oxidase (XO) activity in vitro and to analyze the mechanism of this effect.</p><p><b>METHODS</b>In this in vitro study, Kinetic measurements were performed in 4 different inhibitor concentrations and 5 different xanthine concentrations (60, 100, 200, 300, 400 Μmol/L). Dixon and Lineweaver-Burk plot analysis were used to determine Ki values and the inhibition mode for the compounds isolated from Gnaphalium affine extract.</p><p><b>RESULTS</b>Four potent xanthine oxidase inhibitors were found in 95% ethanolic (v/v) Gnaphalium affine extract. Among them, the flavone Eupatilin exhibited the strongest inhibitory effect on XO with a inhibition constant (Ki) of 0.37 Μmol/L, lower than the Ki of allopurinol (4.56 mol/L), a known synthetic XO inhibitor. Apigenin (Ki of 0.56 Μmol/L, a proportion of 0.0053‰ in Gnaphalium affine), luteolin (Ki of 2.63 Μmol/L, 0.0032‰ in Gnaphalium affine) and 5-hydroxy-6,7,3',4'-tetramethoxyflavone (Ki of 3.15 Μmol/L, 0.0043‰ in Gnaphalium affine) also contributed to the inhibitory effect of Gnaphalium affine extract on XO activity.</p><p><b>CONCLUSIONS</b>These results suggest that the use of Gnaphalium affine in the treatment of gout could be attributed to its inhibitory effect on XO. This study provides a rational basis for the traditional use of Gnaphalium affine against gout.</p>