Table 1: Reactive Oxygen Species (ROS), Sources, and Defense Mechanisms [1719, 22, 26].

ROS
 Superoxide (O2•−)
 Hydrogen peroxide (H2O2)
 Hydroxyl radical (OH)
 Peroxyl radicals (ROO)
 Alkoxyl radicals (RO)
 Organic hydroperoxides (ROOR')
 Hypochlorous acid (HOCl)
 Peroxynitrite (ONOO−)
 Singlet oxygen (1O2)
ROS sources
Endogenous
 Mitochondria (byproducts of electron transport)
 oxidases (Oxidase-catalyzed reactions)
 Inflammation (neutrophils, macrophages)
 Cytochrome P450 reactions
 Arginine metabolism
 Peroxisomal fatty acid metabolism (peroxisomes, lipoxygenases)
Exogenous
 Ionizing radiation (X–, γ−, UV)
 Chemotherapeutics
 Inflammatory cytokines (macrophages, neutrophils)
 Environmental toxins
Antioxidant defense mechanisms
Enzymatic systems
 Catalase (CAT)
 Superoxide dismutase (SOD)
 Glutathione peroxidase (GPx)
Nonenzymatic systems
 DNA repair mechanisms
 Glutathione
 Vitamins (A,C, and E)
 Carotenes