Oxygen Centered Radicals: The Price of Aerobic Adaptation

Oxygen is an indispensable element for life; however, the cellular biochemistry of oxygen is Janus-faced, as the good side includes numerous enzyme-catalyzed reactions that occur during normal cellular  etabolism, while the dark side encompasses deleterious effects of species derived from molecular oxygen. The present review highlights the formation of oxygen-centered radicals as a consequence of aerobic adaptation of the biological system. These are the byproducts of cellular aerobic metabolism, and can initiate conversion of molecules to reactive species and thereby, propagate the chain reactions. The oxygen-centered radicals are: produced during UV, X-rays and gamma rays irradiation; generated during transition metal-catalyzed reactions and by environmental pollutants; produced by neutrophils and macrophages during inflammation, and are byproducts of mitochondrial respiratory chain. Antioxidants are the natural antidotes against oxidative stress. Small fluctuations in steady-state concentration of oxygencentered radicals may actually play a role in intracellular signaling, however, when the physiologically permissible limits of oxygen centered radicals are exceeded, they indiscriminately target proteins, lipids, DNA and polysaccharides resulting in various pathological scenarios.