The enzyme xanthine oxidase catalyses the oxidation of hypoxanthine to xanthine and
then to uric acid, which plays a crucial role in gout. A total of 122 traditional
Chinese medicinal plants, selected according to the clinical efficacy and prescription
frequency for the treatment of gout and other hyperuricemia-related disorders, have
been evaluated for the enzyme inhibitory activity. Among the 122 methanol extracts
derived from these species, 69 were shown to be inhibitory at 100 microg/ml, with
29 having greater than 50% inhibition. As to the equal amount of water extracts, 40
were disclosed to be active at 100 microg/ml, with 13 possessing more than 50% inhibition.
At 50 microg/ml, 58 methanol and 24 water extracts exhibited inhibitory activity,
with 15 of the former and two of the latter showing greater than 50% inhibition. The
most active was the methanol extract of the twig of Cinnamomum cassia (Lauraceae)
(IC(50), 18 microg/ml), which was followed immediately by those of the flower of Chrysanthemum
indicum (Asteraceae) (IC(50), 22 microg/ml) and the leaves of Lycopus europaeus (Lamiatae)
(IC(50), 26 microg/ml). Among the water extracts, the strongest inhibition of the
enzyme was observed with that of the rhizome of Polygonum cuspidatum (Polygonaceae)
(IC(50), 38 microg/ml). The IC(50) value of allopurinol used as a positive control
was 1.06 microg/ml. The study demonstrated that the effects for these medicinal plants
used for the gout treatment were based, at least in part, on the xanthine oxidase
inhibitory action.