Biological variation of ascorbic acid and α-tocopherol

Biological variability of superoxide dismutase and glutathione peroxidase in blood

The enzymatic antioxidant defences of mammalian cells include copper-zinc superoxide dismutase (SOD)(Cu Zn-SOD; EC 1.15.1.1) which catalyses the dismutation of superoxide anions (O2(.-)) to hydrogen peroxide(H(2), O(2))and a seleno-dependent glutathione peroxidase (GSH-px) (GSH-px; EC 1.11.1.9) which catalyses the degradation of H(2)O(2) to H(2)O and O(2). The measurement of these enzyme activities is often used as a possible biological index of oxidative stress in various clinical conditions. Complete understanding of such information requires knowledge of the random biological fluctuation of the enzyme activity which occurs in each individual. In the present investigation we examined this normal variability in 12 healthy volunteers (four women and eight men) aged 23-45 years, over 6 months. The intra-individual coefficients of variation (estimated using analysis of variance techniques) were 15% (SOD) and 13% (GSH-px). The analytical goal for imprecision was achieved for both enzymes, i.e. it was less than one half of the measured intra-individual variation. Both enzymes showed marked individuality, indicating that an individual's reference values are more useful than population-based data. The critical difference required for significant changes in serial results is 45% for SOD and 40% for GSH-px.

Free radical scavenging reactions and antioxidant activities of silybin: mechanistic aspects and pulse radiolytic studies

Silybin (extracted from Silybum marianum) is the major active constituent of silymarin which possesses a wide range of medicinal properties. These properties may be, in part, due to the potent scavenging capacity of oxidizing free radicals. In this context, scavenging radicals (hydroxyl, azide, dibromide anion radicals, nitrite, carbonate, etc.) of silybin have been studied to understand the mechanistic aspects of its action against free radicals. The transients produced in these reactions have been assigned and the rate constants have been measured by pulse radiolysis techniques. Reduction potential determined both by cyclic voltammetry gave a value 0.62+/-0.02 V vs NHE at pH 9. Quantum chemical calculations have been performed to further confirm the different activities of individual hydroxyl groups with the difference of heat of formation. Moreover, silybin also protected plasmid pUC18 DNA from soft X-ray radiation which induced strand breaks. These results are expected to be helpful for a better understanding of the anti-oxidative properties of silybin.

In vivo non-enzymatic repair of DNA oxidative damage by polyphenols

The non-enzymatic repair of DNA oxidative damage can occur in a purely chemical system, but data show that it might also occur in cells. Human hepatoma cells (SMMC-7721) and human hepatocyte cells (LO2) were treated with 200microM H(2)O(2) for 30min to induce oxidative DNA damage quantified by amount of 8-OHdG and degree of DNA strand breaks, without inducing enzymatic repair. The dynamics of enzymatic repair activity quantified by unscheduled DNA synthesis, within 30min after removal of H(2)O(2) enzymatic repair mechanism has not been initiated. However, pre-incubation with low micromolar level polyphenols, quercetin or rutin can significantly attenuate DNA damage in both cell lines, indicating that the polyphenols did not work through an enzymatic mechanism. Unscheduled DNA synthesis after removal of H(2)O(2) was also markedly decreased by quercetin and rutin. Combined with our previous studies of fast reaction chemistry, the inhibitory effect of polyphenols have to be assigned to non-enzymatic repair mechanism rather than to enzymatic repair mechanism or antioxidant mechanism.