OXYGEN-DERIVED SPECIES - THEIR RELATION TO HUMAN-DISEASE AND ENVIRONMENTAL-STRESS

Free radicals and other reactive oxygen species (ROS) are constantly f ormed in the human body, often for useful metabolic purposes. Antioxid ant defenses protect against them, but these defenses are not complete ly adequate, and systems that repair damage by ROS are also necessary. Mild oxidative stress often induces antioxidant defense enzymes, but severe stress can cause oxidative damage to lipids, proteins, and DNA within cells, leading to such events as DNA strand breakage and disrup tion of calcium ion metabolism. Oxidative stress can result from expos ure to toxic agents, and by the process of tissue injury itself. Ozone , oxides of nitrogen, and cigarette smoke can cause oxidative damage; but the molecular targets that they damage may not be the same.