Last update:
17-Mar-2007

A free radical is either an atom or a group of atoms with one or several unpaired electrons at least in an outer orbital. Biologically relevant free radicals include oxygen-carbon-nitrogen-and chlorine-centered radicals. Depending on the primarily involved cellural site of production, five primarily metabolic sources of free radicals are recognizable: plasmamembrane, mitochondria, peroxisomes, endoplasmic reticulum, and cytosol. Since free radical formation is dangerous for living organisms, under normal conditions this is kept under control by the antioxidant defense system. Oxidative stress is defined as a particular kind of chemical stress induced by the presence of exaggerated amounts of free radicals which results either from their overproduction or from a reduced inability of the antioxidant defense system to respond. The lung represents a unique tissue among organs for oxidant stress, because it is directly exposed to higher oxygen tensions. A variety of lung diseases seem to be related with free radicals, such as obstructive lung disease, interstitial lung disease, sarcoidosis and other granulomatous lung disorders, asbestosis and lung cancer. As far as lung cancer is concerned, it appears that reactive oxygen species are associated with both carcinogenesis and cancer progression, as numerous investigations have shown.

Key words: Antioxidant defense system, Free radicals, Oxidative stress, Pathogenesis of lung diseases.