ABSTRACT
The evolution of life on Earth traces an anaerobic environment to an aerobic environment. The consequences of living in an oxygen-rich atmosphere, ca. 21% O2, result in some negative outcomes, especially in terms of oxidation or the generation of free radicals. For example, free radical damage is believed to be involved in or responsible for a number of diseases, including cancer, cardiovascular disease, Parkinson’s disease, Alzheimer’s disease, cataracts, and diseases of the immune system. In biological species, the onset of free radical damage occurs when free radicals are produced in the healthy cell. This results in molecular damage to cellular components, such as lipids, proteins, and DNA, eventually leading to a damaged cell and, finally, disease state or cell death. Free radical damage in tissues can be caused by exposure to ultraviolet (UV) radiation, ozone, smoke, and certain drugs. As the outermost protective organ of the body, the skin continuously finds itself in contact with such dangerous elements. In addition, there are many processes that occur in mammalian biology that produce free radicals. Two endogenous examples of free radical sources consist of the mitochondrial electron transport chain and the inflammatory process, which is part of our immune response to ward off foreign pathogens. Chemically, the formation of free radicals may occur as the result of covalent bond scission, an electron transfer reaction (Fe, Cu, Mn, etc.), or lipid peroxidation. This chapter will explore the various topics related to free radical mechanisms that occur in biological systems. In particular, the various radical species that an organism may encounter, the sources of radicals, and the types of reactions they are likely to be involved in will be thoroughly reviewed.
