In Vitro and In Vivo Studies on Quercus acuta Thunb. (Fagaceae) Extract: Active Constituents, Serum Uric Acid Suppression, and Xanthine Oxidase Inhibitory Activity

Abstract

Quercus acuta Thunb. (Fagaceae) (QA) is cultivated as a dietary and ornamental plant in China, Japan, South Korea, and Taiwan. It has been widely used as the main ingredient of acorn tofu, a traditional food in China and South Korea. The aim of this study was to determine in vitro and in vivo xanthine oxidase (XO) inhibitory and antihyperuricemic activities of an ethyl acetate extract of QA leaf (QALE) and identify its active phytochemicals using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography (LC) systems. The QALE was found to possess potent in vitro antioxidant and XO inhibitory activities. In vivo study using hyperuricemic mice induced with potassium oxonate demonstrated that the QALE could inhibit hepatic XO activity at a relatively low oral dose (50 mg/kg) and significantly alleviate hyperuricemia to a similar extent as allopurinol. Several active compounds including vitamin E known to possess XO inhibitory activity were identified from the QALE. To the best of our knowledge, this is the first study that reports the active constituents and antihyperuricemic effect of QA, suggesting that it is feasible to use QALE as a food therapy or alternative medicine for alleviating hyperuricemia and gout.

Figure 1

In vitro xanthine oxidase (XO) inhibitory activity of QALE at various concentrations ranging from 0 to 1000 μg/mL; ^∗significantly different from the control group (QALE at a concentration of 0 μg/mL). The rectangular bars and their error bars represent the means and standard deviations, respectively (n = 5).

Figure 2

Serum uric acid levels after oral administration of saline in normal mice (normal) or after oral administration of saline (HU), allopurinol at a dose of 10 mg/kg (HU + ALP), or QALE at a dose of 50 (HU + QA50) or 250 mg/kg (HU + QA250) during 7 days prior to inducing hyperuricemia in mice. The rectangular bars and their error bars represent the means and standard deviations, respectively (n = 5); ^∗significantly different from the normal group; ^#significantly different from the HU group (p < 0.05, ANOVA a posteriori Tukey's multiple range test).

Figure 3

Hepatic xanthine oxidase (XO) activity after oral administration of saline in normal mice (normal) or after oral administration of saline (HU), allopurinol at a dose of 10 mg/kg (HU + ALP), or QALE at a dose of 50 (HU + QA50) or 250 mg/kg (HU + QA250) during 7 days prior to inducing hyperuricemia in mice. The rectangular bars and their error bars represent the means and standard deviations, respectively (n = 5); ^∗significantly different from the normal group; ^#significantly different from the HU group (p < 0.05, ANOVA a posteriori Tukey's multiple range test).

Figure 4

Serum xanthine oxidase (XO) activity after oral administration of saline in normal mice (normal) and after oral administration of saline (HU), allopurinol at a dose of 10 mg/kg (HU + ALP), or QALE at a dose of 50 (HU + QA50) or 250 mg/kg (HU + QA250) during 7 days prior to inducing hyperuricemia in mice. The rectangular bars and their error bars represent the means and standard deviations, respectively (n = 5); ^∗significantly different from the normal group; ^#significantly different from the HU group (p < 0.05, ANOVA a posteriori Tukey's multiple range test).

Figure 5

Representative GC-MS chromatogram to show bioactive constituent profiles of QALE.

Figure 6

Representative HPLC chromatogram to show bioactive constituent profiles of QALE (API: apigenin; LUT: luteolin; QCT: quercetin).