INTERACTIONS BETWEEN FLAVONOIDS, VITAMIN C AND VITAMIN E IN PROTECTING MEMBRANES AGAINST OXIDATIVE STRESS
Vitamin C, as a water-soluble antioxidant and vitamin E being the major lipid-soluble antioxidant, play vital roles in preventing oxidative damage. Flavonoids are a class of plant secondary metabolites well known for antioxidant activities that due to their amphiphilicity may interact with both vitamin C and vitamin E. This research investigates their cooperation with vitamin C and vitamin E on oxidative status in vitro using artificial liposomes and isolated rat liver mitochondrial membranes. Vitamin C induced pro-oxidant effects in both systems and the oxidative stress was positively correlated with its concentration. The presence of vitamin E in liposomes inhibited the pro-oxidant effect of ascorbic acid, and the flavonoid quercetin inhibited this effect in vitamin E-free liposomes. Experiments with added tert-butyl hydroperoxide were used to test for a possible cooperation between vitamin C, flavonoids, and vitamin E in inhibiting lipid peroxidation. While most of the conditions did not reveal cooperation, evidence for cooperation involving quercetin was observed in liposomes at the lowest level of vitamin E tested. In measurements of vitamin E (α-tocopherol) content in mitochondria using HPLC and mass spectrometry, the combination of vitamin C and quercetin was able to synergistically regenerate the α-tocopherol in the presence of hydroperoxide while the regeneration did not happen with either vitamin C or quercetin alone. However, the recovery of vitamin E did not relate to the TBARS measurement, indicating that the α-tocopherol concentration was not directly correlated to the TBARS formation. Based on this research, acorbate has pro-oxidative effects on both systems, which can be suppressed by quercetin but not completely by vitamin E. Among the tested flavonoids, only quercetin was observed to synergistically interact with acorbate to regenerate α- tocopherol, although under this condition the interaction did not rescue the mitochondria from oxidative damage.
Vitamin C, Vitamin E, flavonoids, oxidative stress, synergism
Master of Science (M.Sc.)
Pharmacy and Nutrition