ANTIOXIDANT AND PROOXIDANT EFFECTS OF ASCORBIC-ACID, DEHYDROASCORBIC ACID AND FLAVONOIDS ON LDL SUBMITTED TO DIFFERENT DEGREES OF OXIDATION

Although a high intake of antioxidants may decrease the risk of develo ping cardiovascular diseases, under certain circunstances they may pro mote free radical generation and lipid peroxidation. The objectives of the present study were to determine the antioxidant effects of ascorb ic acid (AA), dehydroascorbic acid (DHA) and flavonoids on LDL submitt ed to different degrees of oxidation. LDL was submitted to oxidation w ith CuCl2 (2.4 mu M). Before or at different times after the propagati on of the oxidation process, 28 mu M (5 mu g/ml) of either AA or DHA o r 5 mu g/mL flavonoids extract were added. Alpha-tocopherol, conjugate d diones, thiobarbituric acid, reacting substances (TBARS) and LDL ele ctrophoretic mobility were determined as indices of LDL oxidation. The presence of any of the three antioxidants from the onset of the incub ation 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-tocophe rol was consumed. Nevertheless, it also accelerated LDL oxidation when added during the propagation phase of the oxidation process. In concl usion: although AA, DHA and flavonoids delay LDL oxidation when added before the initiation of the process, they accelerate the process if a dded to minimally oxidized LDL.