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Book/Book Chapter 
Oxidative stress and antioxidants in aging 
Ozben, T 
In accordance with the present state of scientific knowledge, the excessive production of free radicals in the organism, and the imbalance between the concentrations of these and the antioxidant defenses, may be related to processes such as aging and several diseases. Aging is associated with changes in physical characteristics and decline of many physiological functions. The aging process has been described by - various theories, in particular the free radical theory of aging has received widespread attention. It has been proposed that the oxidative stress or damage induced by free radicals is related to aging. Oxidants and antioxidants have a clear function in the cellular physiology. When this delicate balance changes, many biochemical and cellular reactions are altered. The free radical hypothesis of aging proposes that deleterious actions of oxygen-derived radicals are responsible for the functional deterioration associated with aging. Modification of membrane lipids by the radicals has been produced to play a major role in the process of aging. Although. the relationship between lipid peroxidation and aging has been investigated extensively. the studies have produced conflicting results. To investigate the correlation between the oxidative stress and aging, we have determined the levels of lipid peroxidation expressed as thiobarbituric acid reactive substances and conjugated dien: oxidative protein damage as indicated by carbonyl content and activities of antioxidant enzymes including superoxide dismutase(SOD), catalase (CAT) and glutathione peroxidase(GPx) in a sample of 100 healthy men and women ranging in age from 20 to 70 years. In addition, vitamin E, C levels, reduced glutathione and sulfhydryl content were determined. The oxidation end product of nitric oxide (nitrate) was also studied to investigate any role of nitrogen radicals in aging. Our data shows that there is an age related increase in the concentration of lipid peroxides expressed as MDA and oxidative protein damage as indicated by carbonyl content. We found that aging is not linked to a decline in antioxidant enzymes except GPx. Our data suggests that the level of oxidative stress increase cannot be entirely attributed to a decrease in the activities of antioxidant defense system and probably various factors may contribute to this process.