Action of ascorbic acid as a scavenger of active and stable oxygen radicals.

Free radicals attack lipids, proteins, enzymes, and DNA to cause pathological events and cancer. Ascorbic acid is one of the strongest reductants and radical scavengers and reduces stable oxygen, nitrogen, and thyl radical and acts as a primary defense against aqueous radicals in the blood. When radicals were formed in aqueous suspensions of erythrocytes or low-density lipoprotein (LDL), ascorbic acid scavenged radicals before they reached membranes and LDL. Although ascorbic acid cannot scavenge lipophilic radicals within the lipid compartment by itself, it acts as a synergist with tocopherol for the reduction of lipid peroxyl radicals within the lipid compartment by reacting with tocopheroxyl radical and regenerating active tocopherol. Ascorbic acid may act as a prooxidant in vitro in the presence of metal, but this effect is unlikely to be important in vivo where metal ions are sequestered and other reductants are present.