Oxidative stress plays an important role in the pathogenesis of numerous chronic age-related free radical-induced diseases. Improved antioxidant status minimizes oxidative damage to DNA, proteins, lipids and other biomolecules. Diet-derived antioxidants such as vitamin C, vitamin E, carotenoids and related plant pigments are important in antioxidative defense and maintaining health. The results of long-term epidemiological and clinical studies suggest that protective vitamin C plasma concentration for minimum risk of free radical disease is higher than 50 μmol/l. Products of oxidative damage to DNA (DNA strand breaks with oxidized purines and pyrimidines), proteins (carbonyls) and lipids (conjugated dienes of fatty acids, malondialdehyde) were estimated in a group of apparently healthy adult non-smoking population in dependence on different vitamin C plasma concentrations. Under conditions of protective plasma vitamin C concentrations (>50 μmol/l) significantly lower values of DNA, protein and lipid oxidative damage were found in comparison with the vitamin C-deficient group (<50 μmol/l). The inhibitory effect of higher fruit and vegetable consumption (leading to higher vitamin C intake and higher vitamin C plasma concentrations) on oxidation of DNA, proteins and lipids is also expressed by an inverse significant correlation between plasma vitamin C and products of oxidative damage. The results suggest an important role of higher and frequent consumption of protective food (fruit, vegetables, vegetable oils, nuts, seeds and cereal grains) in prevention of free radical disease.
We compared the progression of lens opacification with the time course of oxidation of lens proteins under conditions of streptozotocin-induced experimental diabetes in rats. By the end of the 17th week, approx. 50 % of the diabetic animals developed mature cataracts. During the following month, 95 % of the eyes in the diabetic group became
cataractous. In the course of lens opacification we observed a time-dependent increase in the content of protein carbonyls and decrease in the concentration of protein sulfhydryls in the lenses of diabetic animals. Significantly higher protein carbonyl (p<0.01) and lower protein sulfhydryl (p<0.001) content was found in lenses with the advanced stage
of cataract when compared with the diabetic lenses still transparent. We showed that the values of protein carbonyls exceeding 1.2 nmol/mg protein and of sulfhydryls falling below 60 nmol/mg protein corresponded to an approximately 50 % incidence of mature cataract development. At the end of the 34th week, when all lenses of diabetic rats became cataractous, the corresponding values of protein carbonyls and sulfhydryls were 2.5 nmol/mg protein and 27 nmol/mg protein, respectively. The main finding of this study is the disclosure of quantitative relationship between the degree of protein oxidation and the rate of advanced cataract development in the widely used model of streptozotocin-induced experimental diabetes in rats.