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Vitamin C in Skin Care
By: Peter T. Pugliese, MD
Posted: June 2, 2009, from the June 2009 issue of Skin Inc. magazine.
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Since vitamin C is water-soluble, it is able to destroy free radicals before they can reach the cellular membrane. Vitamin E and glutathione (GSH) need vitamin C in order to be regenerated to their active forms. The relationship between vitamin C and GSH is unique because vitamin C reduces GSH back to its active form. Vitamin C can sequester the singlet oxygen radical and stabilize the hydroxyl radical, as well as regenerate vitamin E back to its active state. All of these functions are critical in preventing peroxidation of cellular lipid membranes.2 Now, on to free radicals.
First, free radicals need to be reviewed and named because there are many types of free radicals that can be formed in the body. For this article, they are limited to the oxygen-centered free radicals (ROS). The ROS include: the superoxide anion (O2-), the hydroxyl radical (OH ·), singlet oxygen (1O2), and hydrogen peroxide (H2O2).
Superoxide is formed when oxygen as O2 adds an additional electron. This results in the oxygen molecule having only one unpaired electron. One theory of aging is that, in the mitochondria, the O2- is constantly being formed and damaging the mitochondria.
Hydroxyl radicals are the most damaging radicals within the body, but they have a short life. Hydroxyl radical are formed from O2- and H2O2 via the Haber-Weiss reactionc. In the presence of H2O2, the metals copper and iron produce OH, and this is called the Fenton reaction. Hydrogen peroxide is produced in the body by many reactions, and since it can be converted to the highly damaging hydroxyl radical, it becomes dangerous. Catalase is the enzyme that destroys it so it can be excreted harmlessly as water. GSH peroxidase is an enzyme that converts GSH to oxidized GSH, during which H2O2 is converted to water. This is an important reaction because if H2O2 is not converted into water singlet oxygen, 1O2 is formed. Although singlet oxygen is not a free radical, it can be formed during radical reactions and cause further damaging reactions.
Check out the role of vitamin C in regenerating vitamin E. Figure 4 illustrates the reaction in which vitamin E donates an H+ to a peroxidated fat, and along comes vitamin C and donates an H+ to vitamin E to restore it to an active form.