Free Radical Theory

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Free radicals, acknowledged in chemistry since the birth of the 20th century, were originally used to describe common compounds in organic and inorganic chemistry, and several chemical definitions for them were suggested. Only in 1954 when the pioneering work of Daniel Gilbert and Rebecca Gersham was published (Gilbert DL (ed.), 1981) were these radicals proposed as important players in biological environments and responsible for destructive processes in the cell. After which, in 1956, Herman Denham (Harman D, 1956) suggested that these species might play an important role in physiological events especially in the aging process (Harman D, 1981). His hypothesis, the free-radical theory of aging, inspired various studies and research efforts…show more content…
Nowadays, we are again facing an increase in ROP due to the exposure of the extremely young and small infants, weighing less than 700 grams, to the minimal incubator-oxygen concentration required to sustain their lives. Today oxygen is said to be toxic to bacteria, plants, eukaryotic cells, and humans. A important advancement in scientific interest in the field of oxygen toxicity and free radicals occurred when McCord and Fridovich in 1969 (McCord JM, Fridovich I, 1969) discovered the role of the protein hemocuprein in the dismutation of superoxide radicals and described the existence of superoxide dismutase (SOD) in almost all aerobic cells (Fridovich I, 1995). This discovery led to the description of the superoxide theory of oxygen toxicity (Halliwell B, GutteridgeJM, 1999), which became the target of much research and debate associated with aging, development, diseases, and cell signalling (AmesBN, Shigenaga K, HagenTM, 1993). Oxygen is required by prokaryotic and eukaryotic cells for energy production, often via the electron transport chain in the mitochondria. In most event oxygen is consumed as dioxygen in the form of a diatomic molecule, the configuration that exists in the atmosphere (Halliwell B,…show more content…
In contrast, a substance that donates electrons is a reductant or reducing agent (Cao G, Prior RL, 1998). In general, a chemical reaction in which a substance gains electrons is defined as a reduction (SchaferFQ, BuettnerGR, 2001). Oxidation is a process in which a loss of electrons occurs. When a reductant donates its electrons, it causes another substance to be reduced, and, when an oxidant accepts electrons, it causes another substance to be oxidized (Hrbac J, Kohen R, 2000). In biology, a reducing agent acts via donation of electrons, usually by donation of hydrogen or removal of oxygen. An oxidation process is always accompanied by a reduction process in which there is usually a loss of oxygen, while in an oxidation process there is a gain in oxygen (Hrbac J, Kohen R, 2000). Such reactions, called redox reactions, are the base for numerous biochemical pathways and cellular chemistry, biosynthesis, and regulation (ShapiroM, 1972). They are also important for understanding biological oxidation and radical/antioxidant effects. While reductant and oxidant are chemical terms, in biological environments they should be termed antioxidant and pro-oxidant, respectively (Cao G, Prior RL,

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