Uric acid, antioxidant properties

A large number of nonenzymatic compounds, including tocopherols, caroti-noids, vitamins C and D, steroids, ubiquinones, thiols, uric acid, bilirubin, ino-sine, taurine, pyruvate, CRP, and so on, demonstrate qualitative antioxidant properties under experimental conditions. However, the quantitative relevance of most findings remains unclear. 

Other antioxidant species are synthesized by cells like uric acid, ubiquinol or thiols (cystein, homocystein, etc.). In addition, many compounds found in food display antioxidant properties retinol (vitamin A) and its precursor /(-carotene, and polyphenols (flavonoids, etc.). Figure 8.2 shows the apparent standard potential of some LMWA and ROS explaining the spontaneous oxido-reduction reactions at the origin of the antioxidant protection system. 

The composition of a concentrated base for nonalcoholic drinks is described, which includes aboveground parts of Jerusalem artichoke. The proposed concentrated base is claimed to exhibit antioxidant properties, normalize withdrawal of excess of uric and oxalic acids, and enable rheumatism prophylaxis. 

The lung also possesses nonenzymatic antioxidants such as vitamin E, beta-carotene, vitamin C, and uric acid. Vitamin E is lipid-soluble and partitions into lipid membranes, where it is positioned optimally for maximal antioxidant effectiveness. Vitamin E converts superoxide anion, hydroxyl radical, and lipid peroxyl radicals to less reactive oxygen metabolites. Beta-carotene also accumulates in cell membranes and is a metabolic precursor to vitamin A. Furthermore, it can scavenge superoxide anion and react directly with peroxyl-free radicals, thereby serving as an additional lipid-soluble antioxidant. Vitamin C is widely available in both extracellular and intracellular spaces where it can participate in redox reactions. Vitamin C can directly scavenge superoxide and hydroxyl radical. Uric acid formed by the catabolism of purines also has antioxidant properties and primarily scavenges hydroxyl radical and peroxyl radicals from lipid peroxidation. 

Uric acid in very low concentrations, very strongly absorbs UV radiation and for this reason, has been used to protect various FD C colors against fading when they will be probably exposed to direct sunlight (112). Uric acid has been found to enhance the photostability of solutions of colchicine (70) and FD C Blue No. 2 (82,113). Sodium urate, the neutral salt of uric acid, has a photoprotective effect on solutions of metronidazole (68), doxorubicin hydrochloride (77), and physostigmine sulfate (108). In addition to its photon-absorbing property, uric acid has been reported to also possess antioxidant quality (114). 

Abstract Low molecular weight antioxidants are an important part of the antioxidative defense mechanisms of cells and organisms. This chapter gives a short overview of the actions of the main antioxidants, including uric acid, ubichinones,lipoic acid, vitamins C and E, carotenoids, and phenolic compounds. The antioxidative properties of these endogeous and nutritional compounds are discussed in this chapter. However, it is critically discussed whether the antioxidative properties of some of these compounds are really important in vivo. 

Using the appropriate reagents (kits) (ABCD GmbH, Germany www. minilum.de) to determine the activity of fat- and water-soluble antioxidants, antioxidant parameters caused antiradical properties of uric (UA) and ascorbic (ASC) acids and high protein (ARAP - anti-radical ability of proteins) were measured. 

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