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Abstract
Reactive oxygen species (ROS) is a term which encompasses all highly reactive, oxygen-containing molecules, including free radicals. Types of ROS include the hydroxyl radical, the super oxide anion radical, hydrogen peroxide, singlet oxygen, nitric oxide radical, hypochlorite radical, and various lipid peroxides. All are capable of reacting with membrane lipids, nucleic acids, proteins and enzymes, and other small molecules, resulting in cellular damage.
To protect the cells and organ systems of the body against reactive oxygen species, humans have evolved a highly sophisticated and complex antioxidant protection system. It involves a variety of components, both endogenous and exogenous in origin, that function interactively and synergistically to neutralize free radicals.
These components include:
• Nutrient-derived antioxidants like ascorbic acid (vitamin C), tocopherols and tocotrienols (vitamin E), carotenoids, and other low molecular weight compounds such as glutathione and lipoic acid.
• Antioxidant enzymes, e.g., superoxide dismutase, glutathione peroxidase, and glutathione reductase, which catalyze free radical quenching reactions.
• Metal binding proteins, such as ferritin, lactoferrin, albumin, and ceruloplasmin that sequester free iron and copper ions that are capable of catalyzing oxidative reactions.
• Numerous other antioxidant phytonutrients present in a wide variety of plant foods.
Free radical production occurs continuously in all cells as a by-product of cell metabolism. In tandem, the human body has developed endogenous antioxidant systems as well as taken advantage of dietary exogenous antioxidants to process and detoxify free radicals appropriately. However, certain conditions may increase free radical production beyond the body’s endogenous and exogenous antioxidant systems. The neonatal period is a vulnerable time for free radical damage and injury, particularly for preterm infants whose antioxidant defense systems have not fully matured. Endogenous and passively acquired exogenous antioxidant defense systems do not accelerate in maturation until late in the third trimester.