Hyperuricemia is the hallmark of gout. Pathogenic mechanisms of hyperuricemia include uric acid overproduction in the liver or underexcretion in the kidney. Current antihyperuricemic agents include xanthine oxidase inhibitors in which allopurinol is the most often prescribed. Inhibitors of renal urate reabsorption such as probenecid and benzbromarone are also employed. However, these existing antihyperuricemic agents possess some undesirable effects such as hypersensitivity towards allopurinol and hepatotoxicity associated with benzbromarone. Therefore, search for alternative antihyperuricemic agents with a more favorable toxicological profile or via mechanisms other than the above two mentioned is highly warranted. / The present project represents such an effort. Four in vitro experimental models were developed for the screening of new antihyperuricemic agents. The effects of the potential compounds from natural sources on the activities of phosphoribosyl pyrophosphate synthetase, hypoxanthine-guanine phosphoribosyl transferase and xanthine oxidase, as well as the uptake of urate through rat renal brush border membrane vesicles were investigated. Several compounds emerged with strong urate uptake inhibitory activities in which morin (3, 5, 7, 2', 4'-pentahydroxyflavone) was the most potent. Interestingly some of these compounds including morin were also demonstrated to be xanthine oxidase inhibitors. The subsequent in vivo experiment showed that morin indeed exhibited hypouricemic and uricosuric actions in an acute oxonate-induced hyperuricemic rat model. The uricosuric action of morin was hirther studied in transfected HEK293 cells expressing the human urate anion transporter 1 (hURATI) which is believed to regulate blood urate level by mediating urate reabsorption. In hURAT1-expressing HEK293 cells, urate uptake was significantly increased as compared to the non-transfected parental cells. Incorporation of morin into the uptake buffer could dose-dependently inhibit urate uptake in the transfected cells. Taken together our data indicated that morin is a potentially useful antihyperuricemic agent which acts by inhibiting xanthine oxidase and inhibiting urate reabsorption. In addition, the favorable safety profile of this natural compound makes it a potential candidate worthy of further investigations. / Yu Zhifeng. / "June 2006." / Advisers: Christopher H. K. Cheng; Wing Ping Fong. / Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1584. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 155-169). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Lam Rosanna Yen Yen. / Thesis submitted in: September 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 142-154). / Abstracts in English and Chinese. / Abstract --- p.i / Chinese Abstract --- p.iii / Acknowledgements --- p.v / Table of Contents --- p.vi / List of Abbreviations --- p.xii / List of Figures --- p.xv / List of Tables --- p.xix / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Reactive oxygen species --- p.1 / Chapter 1.1.1 --- Intracellular sources of ROS --- p.1 / Chapter 1.1.2 --- Extracellular sources of ROS --- p.2 / Chapter 1.1.3 --- Superoxide anion radicals --- p.2 / Chapter 1.1.4 --- Hydrogen peroxide --- p.3 / Chapter 1.1.5 --- Hydroxyl radicals --- p.3 / Chapter 1.1.6 --- Singlet oxygen --- p.4 / Chapter 1.1.7 --- Peroxyl radicals and peroxides --- p.4 / Chapter 1.1.8 --- Damage of cellular structures by ROS --- p.5 / Chapter 1.2 --- Antioxidative defence in the body --- p.6 / Chapter 1.2.1 --- Antioxidant proteins --- p.6 / Chapter 1.2.2 --- Antioxidant enzymes --- p.6 / Chapter 1.2.3 --- Antioxidant compounds --- p.7 / Chapter 1.2.3.1 --- Vitamin E --- p.8 / Chapter 1.2.3.2 --- Vitamin C --- p.9 / Chapter 1.2.3.3 --- Glutathione --- p.9 / Chapter 1.2.3.4 --- Urate --- p.9 / Chapter 1.2.3.4.1 --- Purine metabolism --- p.10 / Chapter 1.2.3.4.2 --- Xanthine oxidase --- p.12 / Chapter 1.2.4 --- Oxidative stress and antioxidant defence mechanisms in RBC --- p.12 / Chapter 1.2.5 --- Oxidative stress and antioxidant defence mechanisms in LDL --- p.16 / Chapter 1.3 --- Human diseases originated from pro-oxidant conditions --- p.16 / Chapter 1.3.1 --- Atherosclerosis --- p.17 / Chapter 1.3.2 --- Ischemia /reperfusion injury --- p.17 / Chapter 1.3.3 --- Glucose-6-phosphate dehydrogenase deficiency --- p.18 / Chapter 1.3.4 --- DNA mutation --- p.18 / Chapter 1.3.5 --- Other pro-oxidant state related diseases --- p.19 / Chapter 1.4 --- Hyperuricemia and gout: diseases originated from an extreme antioxidant condition --- p.19 / Chapter 1.4.1 --- Inhibition of XOD as a treatment method for hyperuricemia --- p.20 / Chapter 1.4.2 --- Relationship between ROS injury and hyperuricemia --- p.22 / Chapter 1.5 --- Antioxidants in human nutrition --- p.23 / Chapter 1.6 --- Chinese medicinal therapeutics --- p.23 / Chapter 1.6.1 --- Rhubarb --- p.25 / Chapter 1.6.2 --- Aloe --- p.26 / Chapter 1.6.3 --- Ginger --- p.27 / Chapter 1.6.4 --- Objectives of the project --- p.30 / Chapter 1.6.5 --- Strategies applied to achieve the objectives of the present project --- p.30 / Chapter Chapter 2 --- Materials and methods --- p.31 / Chapter 2.1 --- XOD inhibition assay --- p.31 / Chapter 2.1.1 --- Assay development --- p.31 / Chapter 2.1.2 --- Dose-dependent study --- p.32 / Chapter 2.1.3 --- Reversibility of the enzyme inhibition --- p.32 / Chapter 2.1.4 --- Lineweaver-Burk plots --- p.33 / Chapter 2.2 --- Lipid peroxidation inhibition assay of mouse liver microsomes --- p.34 / Chapter 2.2.1 --- Preparation of mouse liver microsomes --- p.34 / Chapter 2.2.2 --- Basis of assay --- p.34 / Chapter 2.2.3 --- Assay procedures --- p.35 / Chapter 2.3 --- AAPH-induced hemolysis inhibition assay --- p.36 / Chapter 2.3.1 --- Preparation of RBC --- p.36 / Chapter 2.3.2 --- Basis of assay --- p.36 / Chapter 2.3.3 --- Assay procedures --- p.37 / Chapter 2.4 --- Lipid peroxidation inhibition assay of RBC membrane --- p.38 / Chapter 2.4.1 --- Preparation of RBC membrane --- p.38 / Chapter 2.4.2 --- Basis of assay --- p.39 / Chapter 2.4.3 --- Assay procedures --- p.40 / Chapter 2.5 --- ATPase protection assay --- p.41 / Chapter 2.5.1 --- Preparation of RBC membrane --- p.41 / Chapter 2.5.2 --- Preparation of malachite green (MG) reagent --- p.41 / Chapter 2.5.3 --- Basis of assay --- p.41 / Chapter 2.5.4 --- Assay procedures --- p.42 / Chapter 2.5.5 --- Determination of ATPase activities --- p.43 / Chapter 2.5.6 --- Assay buffers --- p.43 / Chapter 2.6 --- Sulfhydryl group protection assay --- p.44 / Chapter 2.6.1 --- Preparation of RBC membrane --- p.44 / Chapter 2.6.2 --- Basis of assay --- p.45 / Chapter 2.6.3 --- Assay procedures --- p.45 / Chapter 2.7 --- Lipid peroxidation inhibition assay of LDL by the AAPH method --- p.46 / Chapter 2.7.1 --- Basis of assay --- p.46 / Chapter 2.7.2 --- Assay procedures --- p.46 / Chapter 2.8 --- Lipid peroxidation inhibition assay of LDL by the hemin method --- p.47 / Chapter 2.8.1 --- Basis of assay --- p.47 / Chapter 2.8.2 --- Assay procedures --- p.47 / Chapter 2.9 --- Protein assay --- p.48 / Chapter 2.10 --- Statistical analysis --- p.48 / Chapter 2.11 --- Test compounds --- p.48 / Chapter Chapter 3 --- Xanthine oxidase inhibition assay: results and discussion --- p.49 / Chapter 3.1 --- Introduction --- p.49 / Chapter 3.2 --- Results --- p.54 / Chapter 3.3 --- Discussion --- p.59 / Chapter Chapter 4 --- Lipid peroxidation inhibition in mouse liver microsomes: results and discussion --- p.64 / Chapter 4.1 --- Introduction --- p.64 / Chapter 4.2 --- Results --- p.64 / Chapter 4.3 --- Discussion --- p.69 / Chapter Chapter 5 --- Assays on protection of RBC from oxidative damage: results and discussion --- p.71 / Chapter 5.1 --- Introduction --- p.71 / Chapter 5.2 --- Results --- p.75 / Chapter 5.2.1 --- AAPH-induced hemolysis inhibition assay --- p.75 / Chapter 5.2.2 --- Lipid peroxidation inhibition assay of RBC membranes --- p.82 / Chapter 5.2.3 --- Ca2+-ATPase protection assay --- p.88 / Chapter 5.2.4 --- Na+/K+-ATPase protection assay --- p.95 / Chapter 5.2.5 --- Sulfhydryl group protection assay --- p.100 / Chapter 5.3 --- Discussion --- p.110 / Chapter 5.3.1 --- AAPH-induced hemolysis inhibition assay --- p.110 / Chapter 5.3.2 --- Lipid peroxidation inhibition assay of RBC membranes --- p.111 / Chapter 5.3.3 --- Ca2+-ATPase protection assay --- p.113 / Chapter 5.3.4 --- Na+/K+-ATPase protection assay --- p.114 / Chapter 5.3.5 --- Sulfhydryl group protection assay --- p.115 / Chapter 5.3.6 --- Chapter summary --- p.117 / Chapter Chapter 6 --- Lipid peroxidation inhibition assay of LDL: results and discussion --- p.118 / Chapter 6.1 --- Introduction --- p.118 / Chapter 6.2 --- Results --- p.118 / Chapter 6.3 --- Discussion --- p.134 / Chapter Chapter 7 --- General discussion --- p.137 / References --- p.142