中文摘要
高尿酸血症是指成年男性的血中尿酸值高於7.0 mg/dL，而成年女性則是高於6.0 mg/dL。尿酸是人體代謝嘌呤類的最終產物，由於人類不像其他哺乳類(如老鼠、狗)可以產生尿酸酶(uricase)將尿酸轉化成為小分子的尿囊素(allantoin)排出。所以當尿酸堆積在血液中的濃度過高時，便會產生高尿酸血症，也可能引起其他疾病如痛風、腎結石等進而引起腎炎。黃嘌呤氧化酶在嘌呤類代謝的路徑中扮演著極為重要的角色，同時也是治療高尿酸血症的重要的標靶酵素。
葉下珠又稱作真珠草、珠仔草，學名是Phyllanthus urinaria Linn. 屬於大戟科葉下珠屬，生長於世界熱帶至亞熱帶地區，如台灣、中國大陸南部、日本、印度及中南半島等地。 在我們的實驗中發現，葉下珠乙醇萃取物可以抑制黃嘌呤氧化酶產生尿酸，不過其抑制率不高，IC50 大約為452.58 μg/ml。 因此，我們將葉下珠的萃取物，再以有機溶劑乙酸乙酯做萃取，而後將得到的次級萃取物做酵素抑制的實驗。 結果發現次級萃取物的IC50 大約為22.36 μg/ml (相較於異嘌呤的IC50 約為1.17 μg/ml)。接著分別取200mg/kg以及300mg/kg的次級萃取物溶於食鹽水中，早晚餵食七天。 在第七天時以腹腔注射氧嗪酸鉀來引發大鼠的高尿酸血症，於引發後的第一、二、四以及六小時抽取血液，再分析血清中的尿酸值。 我們發現葉下珠的乙酸乙酯萃取物中確實可以降低大鼠體內血液中的約60%尿酸值。

ABSTRACT
Hyperuricemia is defined as a serum uric acid level greater than 7.0 mg/dL for males and 6.0 mg/dL for females. In the human body, uric acid is the final product in purine degradation, and xanthine oxidase is the key enzyme in the pathway. In other words, xanthine oxidase is the main enzyme in the pathogenesis of hyperuricemia which may cause gout and other serious diseases such as urolithiasis and nephritis. Phyllanthus urinaria L. (Euphorbiaceae), is widely distributed in tropical and subtropical countries including Taiwan. The plant has been widely used as anti-inflammatory, anti-diarrheal, and hepatoprotective medicines in Asian countries particular in India, China, and Thailand. In our research, P. urinaria extract was used to inhibit xanthine oxidase and control hyperuricemia. The result showed that the ethyl acetate fraction of P. urinaria. extract can efficiently inhibit xanthine oxidase and prevent hypoxanthine from being oxidized to xanthine and further to uric acid. The IC50 of P. urinaria ethyl acetate fraction extract is 22.36 μg/ml (Allopurinol is 1.17 μg/ml). After enzyme inhibition assay, the P. urinaria extract was experimented in an animal model to observe whether it can reduce the serum uric acid or not. After the rats were fed with the extract for 7 days, an anti-hyperuricemia activity in rats which were induced uric acid by subcutaneous injecting the potassium oxonate could be observed.
According to the result in animal model, we may consider P. urinaria as a potential treatment for hyperuricemia. Hopefully, we can identify the active ingredient in P. urinaria and obtain the higher efficacy in the animal model.

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