Free radicals in cell biology.

In aerobic cells, free radicals are constantly produced mostly as reactive oxygen species. Once produced, free radicals are removed by antioxidant defenses including enzyme catalase, glutathione peroxidase, and superoxide dismutase. Reactive oxygen species, including nitric oxide and related species, commonly exert a series of useful physiological effects. However, imbalance between prooxidant and antioxidant defenses in favor of prooxidants results in oxidative stress associated with the oxidative modification of biomolecules such as lipids, proteins, and nucleic acids. Alone or in combination with primary ethiological factors, free radicals are involved in a pathogenesis of more than a hundred diseases. This chapter reviews the basic science of some of the potential sources and characteristics of free radicals, as well as antioxidant enzymes. Special attention is paid to the role of free radicals in the pathogenesis of atherosclerosis and immunology-mediated inflammatory reaction.