Evaluation of Xanthine Oxidase Inhibitory Potential and In vivo Hypouricemic Activity of Dimocarpus longan Lour. Extracts.
BACKGROUND
Longan is a fruit tree known to contain many phenolic components, which are capable of protecting people from oxidative damage through an anti-inflammatory mechanism. It may be also worthwhile to study the effect on lowering uric acid activity.


METHODS
This study investigates the lowering of uric acid using longan extracts, including flowers, pericarps, seeds, leaves, and twigs, on potassium-oxonate-induced hyperuricemia mice and its inhibitory actions against xanthine oxidase (XO) activities.


RESULTS
The findings revealed that ethyl acetate fraction of longan extracts exhibited strong XO-inhibitory activity, and the flower extracts (IC50 = 115.8 μg/mL) revealed more potent XO-inhibitory activity to those of pericarps (118.9 μg/mL), twigs (125.3 μg/mL), seeds (262.5 μg/mL), and leaves (331.1 μg/mL) in vitro. In addition, different dosages of longan extract (50-100 mg/kg) were administered to hyperuricemic mice. The lowering effect of longan extracts on uric acid at 75 mg/kg markedly reduced plasma uric acid levels in decreasing order: Flowers (80%) > seeds (72%) > pericarps (64%) > twigs (59%) > leaves (41%), compared with allopurinol (89%). Finally, 10 isolated phytochemicals from longan flowers were then examined in vitro. The results indicated that proanthocyanidin A2 and acetonylgeraniin A significantly inhibited XO activity in vitro. This is the first report providing new insights into the urate-reducing effect of phenolic dimer and hydrolyzable tannin, which can be developed to potential hypouricemic agents.


CONCLUSIONS
Longan flower extracts possess more potent XO-inhibitory activity than pericarps, twigs, seeds, and leaves in vitroThe lowering effect of longan flowers and seeds extracts markedly reduced plasma uric acid levels as compared to allopurinol in vivoThe extract proanthocyanidin A2 and acetonylgeraniin A were demonstrated potent XO inhibitory activity in vitro Abbreviations used: PO: Potassium-oxonate, XO: xanthine oxidase, HE: n-hexane, EA: ethyl acetate, i.p.: intraperitoneal, PBS: phosphate-buffered saline, AP: allopurinol, PUA: plasma uric acid.
School of Medicine, Chung Shan Medical University, Taichung Branch, Taiwan; Department of Integrated Chinese and Western Medicine, Chung Shan Medical University Hospital, Taichung Branch, Taiwan; Department of Occupational Therapy, Asia University, Taichung Branch, Taiwan.
Shi-Yuan
SY
Sheu
Department of Chinese Medicine, Buddhist Tzu Chi General Hospital, Taichung Branch, Taiwan; School of Post-Baccalaureate Chinese Medicine, Tzu Chi University, Taiwan.
Yuan-Tsung
YT
Fu
Department of Agronomy, National Taiwan University, Taiwan.
Wen-Dar
WD
Huang
School of Veterinary Medicine, National Taiwan University, Taiwan.
Yung-Ann
YA
Chen
School of Veterinary Medicine, National Taiwan University, Taiwan.
Yi-Chih
YC
Lei
School of Chinese Medicine, China Medical University, Taiwan; Department of Biomedical Imaging and Radiological Science, China Medical University, Taiwan; Department of Biomedical Informatics, Asia University, Taiwan.
Chun-Hsu
CH
Yao
College of Pharmacy, School of Pharmacy, Taipei Medical University, Taiwan; Graduate Institute of Pharmacognosy, Taipei Medical University, Taiwan.
Feng-Lin
FL
Hsu
School of Veterinary Medicine, National Taiwan University, Taiwan; Department of Post-Baccalaureate Veterinary Medicine, Asia University, Taiwan.
Tzong-Fu
TF
Kuo
Dimocarpus longan Lour; hypouricemic effect; xanthine oxidase inhibition