Inhibitory Effect of Ruta graveolens L. Extract on Guinea Pig Liver and Bovine Milk Xanthine Oxidase

      Flavonoids could serve as potent inhibitors of xanthine oxidase (XO). In the present study, the effects of Ruta graveolens L. extract and its major isolated flavonoids, quercetin and rutin, on guinea pig liver XO have been investigated. The inhibitory effects of R. graveolens, quercetin and its glycoside form, rutin, were assayed spectrophotometrically. R. graveolens extract showed moderate inhibition on XO activity. Interestingly, bovine milk and guinea pig liver XO were inhibited significantly at different ranges by either the extract or its flavonoids, whereas allopurinol acted with almost the same potency on both enzymes. Rutin inhibited the enzymes in a competitive manner, while quercetin was found to be a competitive and mixed inhibitor of guinea pig liver and bovine milk XO, respectively. In conclusion, R. graveolens extract can act as a good inhibitor of XO. Interestingly, it was shown that the inhibitory effects of flavonoids on XO could be species dependent.