Inhibition of xanthine oxidase by Puerto Rican plant extracts

This study was conducted to search for xanthine oxidase inhibitors in natural products obtained from plants collected in Puerto Rico and to assess the influence of these extracts in the prevention of cataractogenesis.

Allopurinol is currently a xanthine oxidase inhibitor used in the treatment of gout. New alternatives with increased therapeutic activity and less side effects should be investigated. Preclusion of cataractogenesis in diabetic rats is also the focus of this investigation. Natural products in the form of plant extracts from Puerto Rico offer a rich and relatively untapped source for the discovery of new drugs that may address these kind of problems.

Nineteen collections of Myrtaceae plant extracts were screened for xanthine oxidase inhibition. A spectrophotometrical method was used employing allopurinol as positive control and a blank as negative control. A protocol of the assay with slight modifications was followed from the literature. Two extracts with the highest percentages of xanthine oxidase inhibition were evaluated for possible prevention of cataractogenesis in streptozotocin diabetic rats. The animals were given to drink these plant extracts ad libitum for three months while controls received water. The appearance of cataracts was assessed physically.

Two of the nineteen plant extracts showed high inhibition percentages of xanthine oxidase. Eucalyptus deglupta and Syzygium malaccense displayed 51% and 64% inhibitions (IC50 44.5 micrograms/ml and IC50 51 micrograms/ml), respectively. As for the cataractogenesis inhibition, laboratory animals that drank E. deglupta for three months did not develop cataracts.

Two plant extracts provided positive results with varying degrees of inhibition of xanthine oxidase. S. malaccense demonstrated the greatest xanthine oxidase inhibitory activity whereas E. deglupta presented the best finding for cataractogenesis prevention. The procedures used in this investigation are useful for the in vitro screening of xanthine oxidase inhibition and the in vivo evaluation of cataractogenesis prevention.