[Free radicals in medicine and biology]

Free radicals have long been well known by physicists but have only interested biologists since 1969 when Fridovich showed that O2 was produced during an enzymatic oxidation. O2 and related radicals are highly toxic. This implies that, in all aerobic cells, mechanisms exist which inactivate free radicals as soon as they are produced by oxidative metabolism. O2 radicals are eliminated by a family of enzymes called superoxide dismutases (SOD). These SOD are present in the cytosol (CuSOD) and in the mitochondria (MnSOD). Overproduction of free radicals, originating in molecular oxygen, may explain the lesions which result from inflammation, ischemia, and radiation exposure. Free radicals can cause damage to membranes, macromolecules, and DNA. Whether free radical production is mainly intracellular or extracellular may determine to a degree which kind of damage will occur.