Free radicals: their history and current status in aging and disease.

Oxygen toxicity was first described in laboratory animals in 1878 and was further established in 1899. The first experiment regarding a free radical reaction was reported in 1894. However, it was not until the late 1940s to early 1950s that retrolental fibroplasia in premature newborns was recognized as being due to oxygen toxicity and not until the late 1960s to early 1970s that newborn bronchopulmonary dysplasia and adult respiratory distress syndrome were appreciated by the medical community. Moreover, the presence of free radicals in biological systems was not generally considered likely until the discovery of superoxide dismutase in 1969, although in the 1950s the basis of oxygen toxicity and X-irradiation was proposed to be by a common free radical mechanism and the radical theory of aging was hypothesized. Oxyradicals are now widely accepted as being very important, not only in the aging process but also in numerous human diseases/disorders where they have either a primary or secondary role. Currently, there are extensive global basic research efforts to define more clearly the role of free radicals and oxidative stress in these conditions. Continuing clinical research will lead to more reliable treatment and preventive measures for many of them. In this review, a short history is presented and the current status of free radicals and oxidative stress in aging and various diseases is discussed.