| Summary: | 碩士 === 國立臺灣大學 === 獸醫學研究所 === 100 === Hyperuricemia results from over production or/and underexcretion of uric acid. Uric acid production is catalyzed by xanthine oxidase (XO) in the liver, which is a key enzyme in the oxidizing process of xanthine into uric acid. This study investigated anti-hyperuricemia bioactivity of Dimocarpus longan Lour. Longan pulp is a Chinese medicinal plant used for the treatment of amnesia and its flower is folklorically made into drinking tea to lower serum uric acid level. Therefore, the methanol extracts of the flower, seed, shell, stem and leaf of Longan were tested in vitro and in vivo to confirm its anti-hyperuricemic effect. Firstly, xanthine oxidase suppression rates were evaluated by the xanthine oxidase inhibition assay. The results showed that all Longan extracts reduced blood uric acid level as compared to the control group (p < 0.01). The flower extract exibited the best blood uric acid lowering effect and IC50 of XO inhibition was 115.76 μg/ml. 10 compounds have been previously isolated from Longan flower in other studies; in this study, we also examined them by the xanthine oxidase inhibition assay, revealing that proanthocyanidin A2 had the strongest inhibitory effect (70.67%). In the in vivo part of this study, the methanol extracts from 5 different Longan parts were orally administrated to different groups of mice at 50 mg/kg or 100 mg/kg 1 hour before oxonic acid was injected. The blood uric acid levels in mice were then detected 2 h later. Furthermore, we carried out the urine uric acid excretion test in rats to find out whether the Longan extracts could promote the excretion of uric acid; however no significant effect on the excretion of uric acid was observed. According to these results, the mechanism behind the antihyperuricemic effect of Longan methanol extracts was indicated to be associated with the inhibition of xanthine oxidase which results in decreased production of uric acid. This study not only revealed the existence of antihyperuricemic effect of of Dimocarpus longan, but also explored possible mechanisms. Our results showed that Dimocarpus longan has a great potential to be developed into novel therapeutic agents for the treatment of hyperuricemia.
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