ABSTRACT
Under normal and pathological conditions, cellular metabolism generates substantial amounts of free radicals, i.e., atoms and molecules with one or more unpaired electrons (1). By virtue of this electron imbalance, free radicals are unstable and prone to snatch electrons from neighboring atoms and molecules, whereby they inflict oxidative damage. The classical view is that free radicalinduced oxidative damage of biological compounds such as DNA,proteins, and lipids may cause serious cellular derangement and ultimately even cell death. Of note, not all atoms or molecules that can cause oxidative damage are free radicals because they do not have unpaired electrons (e.g., singlet oxygen, hydrogen peroxide). Therefore, those species that either have or do not have unpaired electrons and are all mainly oxygen-centered we refer to as reactive oxygen species (ROS).
