Antioxidants oxidative damage

Both thermodynamic and kinetic factors are of importance for antioxidant capacity. The antioxidant has to be located in the right position at the right time in order to prevent oxidative damage to vital cell components and will need to be regenerated from the one-electron oxidised form in a recycling process ... 

Lafferty, J., Truscott, T.C., and Land, E.J., Electron transfer reactions involving chlorophylls a and b and carotenoids, J. Chem. Soc. Farad. Trans., lA, 2760, 1978. Burri, B.J., Clifford, A.J., and Dixon, Z.R., Beta-carotene depletion and oxidative damage in women, in Natural Antioxidants and Anticarcinogens in Nutrition, Health and Disease, Kumulainen, J.T. and Salonen, J.T., Eds., Royal Society of Chemistry, Stockholm, 1999, 231. 

Comprehensive reviews published by Snodderly and Beatty et al. " explore the evidence for a protective fnnction by the macular pigment against age-related macnlar diseases and the mechanisms by which it might act. The antioxidant properties of Intein and zeaxanthin recently reviewed by Young and Lowe may rednce the degree to which oxidative damage promotes these diseases. Otherwise, becanse these... 

Van Der Vliet, A., Smith, D., O Neill, C.A., Kaur, H., Darley-Usmar, V.M., Cross, C.E. and Halliwell, B. (1994). Interactions of peroxynitrite with human plasma and its constituents oxidative damage and antioxidant depletion. Biochem. J. 303, 295-301. 

Ascorbate is known to act as a water-soluble antioxidant, reacting rapidly with superoxide, hydroxyl and peroxyl radicals. However, reduced ascorbate can react non-enzymatically with molecular oxygen to produce dehydroascorbate and hydrogen peroxide. Also, ascorbate in the presence of light, hydrogen peroxide and riboflavin, or transition metals (e.g. Fe, Cu " ), can give rise to hydroxyl radicals (Delaye and Tardieu, 1983 Ueno et al., 1987). These phenomena may also be important in oxidative damage to the lens and subsequent cataract formation. 

Within the gut, oxidative damage may be prevented by phytic acid, obtained from cereals and vegetables (Graf et al., 1987), and by soluble non-starch polysaccharides like pectin (Kohen et al., 1993). The use of antioxidant vitamins in the treatment of inflammatory bowel disease has also been su ested (Evans et al., 1990). 

Moreover, carotenoids themselves are very susceptible to oxidative damage and their oxidation products include deleterious aldehydes (Failloux et al., 2003 Hurst et al., 2005 Rozanowski and Rozanowska, 2005 Siems et al., 2000, 2002 Sommerburg et al., 2003). Therefore it is of interest to find out how carotenoids can offer antioxidant protection in cellular systems, how stable the carotenoids are within cells, and what the fate of the carotenoid degradation products is. 

As mentioned previously, in the AMD retina iron metabolism is compromised (He et al., 2007 Wong et al., 2007). Thus, it is of interest to determine the effects of potential antioxidants in the presence of iron. In an in vitro study of ARPE-19 cells, addition of a lipophilic iron complex led to about a ninefold increase in the photosensitized yield of 7a,(3-cholesterol hydroperoxides (Wrona et al., 2004). In the presence of the iron, ascorbate exerted pro-oxidant effects, while the effects of a-tocopherol, zeaxanthin, or their combination were still protective (Wrona et al., 2004). Thus, it appears that the effects of potential antioxidants are strongly dependent on the sources of oxidative damage. The same antioxidant may be protective under certain conditions and exert deleterious effects when the conditions are changed. Therefore a detailed understanding of the sources of the oxidative damage is required in order to design an adequate antioxidant mixture. 

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