Xanthine oxidase inhibitory activity of Vietnamese medicinal plants

Among 288 extracts, prepared from 96 medicinal plants used in Vietnamese traditional medicine to treat gout and related symptoms, 188 demonstrated xanthine oxidase (XO) inhibitory activity at 100 μg/ml, with 46 having greater than 50% inhibition. At 50 μg/ml, 168 of the extracts were active, with 21 possessing more than 50% inhibition. At 25 μg/ml, 146 extracts exhibited inhibitory activity, with 8 showing over 50% inhibition, while 126 extracts presented activity at 10 μg/ml, with 2 having greater than 50% inhibition. The MeOH extracts of Artemisia vulgaris, Caesalpinia sappan (collected at the Seven-Mountain area), Blumea balsamifera (collected in Lam Dong province), Chrysanthemum sinense and MeOH-H₂O extract of Tetracera scandens (Khanh Hoa province) exhibited strong XO inhibitory activity with IC₅₀ values less than 20 μg/ml. The most active extract was the MeOH extract of the flower of C. sinense with an IC₅₀ value of 5.1 μg/ml. Activity-guided fractionation of the MeOH extract led to the isolation of caffeic acid (1), luteolin (2), eriodictyol (3), and 1,5-di-O-caffeoylquinic acid (4). All these compounds showed significant XO inhibitory activity in a concentration-dependent manner, and the activity of 2 was more potent (IC₅₀ 1.3 μM) than the clinically used drug, allopurinol (IC₅₀ 2.5 μM).