Reactive oxygen species as mediators of tissue protection and injury

Extensive research efforts during the last three decades resulted in a larg e body of experimental evidence that suggests an important role of the disb alance between generation and elimination of the oxygen and xenobiotic deri ved free radicals in physiological and pathological processes. Reactive oxy gen species (ROS) are generated in many metabolic pathways, and are enterin g the organisms from exogenous sources, dominantly via airways and gut. ROS induced injuries, e.g. thermal, chemical, radiation, ischaemia/reperfusion , inflammation, hyperoxia, etc., result in diseases like atherosclerosis, u lcerative colitis, autoimmune diseases, asthma, etc. The current paper is d esigned to provide an overview of the effects ROS may exert in various tiss ues. Because of the effective defense systems, the tolerance of viable huma n cells to ROS is relatively high. The oxidant stress induced dysfunction o f various systems, such as the gut, airways, nervous, cardiovascular system , etc., involve both direct and indirect mechanisms. Understanding of these molecular mechanisms is essential for a rational antioxidant therapy.