Dec 1, 1992
Calcified Tissue International
Free radicals are fragments of molecules, or atoms with one or more unpaired electrons. They are involved in many biological reactions and in the last decade it has been suggested that they play an important role in the development of various diseases. Many molecules can be classified as free radicals. The most important from the point of view of involvement in disease processes are reported in Table [1, 2]. The most common reactions are in Table 2 . Agents opposing the oxidative effects of free radicals are known as antioxidants and are also very numerous [4, 5]. Some of them are reported in Table 3. The development of free radicals is far from being only a pathological event but participates widely in the modulation of many physiological functions. The problem has been likened to a balance which when it tips towards free radicals means disease and when it tips towards antioxidants, health . Although this is rather simplistic as a myriad of events may lie on both scales, the simile explains the basic concept that inadequately detoxified free radicals may react with various molecules producing tissue damage by denaturing proteins and peroxidizing lipids in the extracellular space and in cell structures. Five modes of free radical yielding deserve to be mentioned: hyperoxia, reactions to xenobiotics [6, 7], reactions during arachidonic acid metabolism [8, 9], burst activity during phagocytosis [10, 11], and reactions during ischemiareperfusion [12, 13-16]. Each of these mechanisms is involved in important pathological events such as oxidative hemolysis, brain and myocardial injury, and inflammatory damage. Although free radical release has been demonstrated in a wide range of diseases, their real importance in the initial stage of tissue damage is still unclear. Hence, it is worthwhile mentioning some of their effects on cell metabolism, such as that involving calcium.