Xanthine oxidase inhibitory activity of medicinal plants and spices

Xanthine oxidase (XOD, EC 1.2.3.2) is the key enzyme of a human catabolic pathway of purine nucleotide metabolism. Its major function is to catalyze the oxidation of hypoxanthine to xanthine and later to uric acid. The overproduction of uric acid may lead to hyperuricemia and development of related symptoms such as gout. Therefore, inhibition of XOD is one of the most common therapeutic approaches. Traditionally, medicinal plants and herbal prescriptions have been used for gout treatment around the globe.

In our study, ethanolic and methanol-dichlormethane (1:1) extracts of 20 medicinal plants or spices with ethnobotanical indication such as gout treatment, anti-arthritic or antirheumatic usage were screened for XOD inhibitory activity, using a previously published spectrophotometrical method [1]. The assay mixture consisted of 100µg/ml of plant extract, 30µM xanthine and 0.15 units/ml of microbial XOD, diluted in 33 mM potassium phosphate buffer. Allopurinol at concentration of 100µg/ml was used as a positive control. Absorbance was measured after 3min at 295nm. All samples were assayed in triplicate. The inhibitory activity was expressed in per cent of absorbance reduction compared to blank sample.

More than 50% of extracts exhibited some degree of inhibitory activity ranging between 5–59%. Ethanolic extract of Thymus vulgaris was shown to be most effective, followed by methanol-dichlormethane extract of Matricaria chamomilla and ethanolic extract of Phylodendron evansii.

Acknowledgements: this work was supported by grant of the Czech Science Foundation GACR 525/08/P503

References: 1. Owen, P.L. and Johns, T. (1999)J Ethnopharmacol 64:149.