Antioxidant and prooxidant effects of ascorbic acid, dehydroascorbic acid and flavonoids on LDL submitted to different degrees of oxidation.

Abstract

Although a high intake of antioxidants may decrease the risk of developing cardiovascular diseases, under certain circunstances they may promote free radical generation and lipid peroxidation. The objectives of the present study were to determine the antioxidant effects of ascorbic acid (AA), der.ydroascorbic acid (DHA) and flavonoidf. on LDL submitted to different degrees of oxidation. LDL was submitted to oxidation with CuCf2 (2.4 µM). Before or at different times after the propagation of the oxidation process, 28 µM (5 µg/ml) of either AA or DHA or 5 µg/mL flavonoids extract were added. Alpha-tocopherol, conjugated dienes, ·thiobarbituric acid reacting substances (TBARS) and LDL electrophoretic mobility were determined as indices of LDL oxidation. The presence of any of the three antioxidants from the onset of the incubation delayed the oxidation process. However, the addition of both DHA and flavonoids to the oxidation process when it was already initiated and alpha-tocopherol consumed, accelerated the oxidation. In contrast, AA delayed the oxidation process even when added after alpha-tocopherol was consumed. Nevertheless, it also accelerated LDL oxidation when added during the propagation phase of the oxidation process. In conclusion: although AA, DHA and flavonoids delay LDL oxidation when added before the initiation of the process, they accelerate the process if added to minimally oxidized LDL.