title: Xanthine oxidase inhibitory activity and hypouricemic effect of aspalathin from unfermented rooibos.
abstract: Rooibos is rich in flavonoids such as aspalathin, which is a unique C-glycosyl dihydrochalcone, that is used as a traditional herbal tea. This study was designed to evaluate the in vitro xanthine oxidase (XOD) inhibitory activity of the aspalathin-rich fraction (ARF) and purified aspalathin from rooibos. The hypouricemic effects of the ARF and aspalathin on hyperuricemic mice were also assessed. The ARF was prepared from aqueous extract of unfermented rooibos leaves and stems, and it was collected by column chromatography; the aspalathin content in this fraction was 21.4%. The ARF and aspalathin inhibited XOD in a dose-dependent manner. The concentrations of the ARF and aspalathin required to inhibit XOD at 50% (IC50 ) were 20.4 μg/mL (4.4 μg/mL aspalathin equivalents) and 4.5 μg/mL, respectively. Lineweaver-Burk plot analysis indicated that aspalathin was a competitive inhibitor of XOD, and the inhibition constant (Ki) was 3.1 μM. In hyperuricemic mice induced by inosine-5'-monophosphate, treatment with the ARF and aspalathin significantly suppressed the increased plasma uric acid level in a dose-dependent manner. The suppressed plasma uric acid level in mice could be attributed to the XOD inhibitory activity of the ARF and aspalathin. Further study is required to determine the effect of aspalathin or its metabolites on XOD activity in vivo.
authors.affiliation: Graduate School of Bioresources, Mie Univ., Tsu, Mie 514-8507, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Kondo
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Hirano
authors.forename: Masahiro
authors.initials: M
authors.lastname: Nishio
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Furuya
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Nakamura
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Watanabe
mesh_terms: D000818:Animals; D036903:Aspalathus / Q000737:chemistry*; D001628:Beverages / Q000032:analysis; D047188:Chalcones / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005419:Flavonoids / Q000032:analysis; D020128:Inhibitory Concentration 50; D008297:Male; D051379:Mice; D010936:Plant Extracts / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry; D014969:Xanthine Oxidase / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D047188:Chalcones; D004791:Enzyme Inhibitors; D005419:Flavonoids; D010936:Plant Extracts; C517016:aspalathin; D014969:Xanthine Oxidase
keywords: aspalathin; hypouricemic effect; rooibos; xanthine oxidase