[Oxidizing agents and free radicals in biomedicine]

The reactions which involve oxidants and free radicals species have played an essential role at the beginning of aerobic life, and they are an intrinsic part in the regulation of the cellular processes. However, as a result of the derived toxic effects of these oxidative processes, antioxidants molecules appeared in the very early stages of the evolution and they are able to control the production of these reactants and their dangerous effects. Oxidants and antioxidants have a clear function in the cellular physiology. When this delicate balance change many biochemical and cellular reactions are altered, and that may cause different pathologic diseases. In addition, free radicals of oxygen are thought to play a growing role in the biological process of ageing (1). It is not unusual to find papers about these reactants in every topic of the biomedicine. The main oxidants and free radicals in the organisms are oxygen-related agents, which are globally called reactive oxygen intermediates (ROI). These unavoidable, useful and dangerous biological oxidants are well characterized, although the recent implications they received in some pathologies deserve, in our opinion, a general review.