Oxidative Stress-Induced Carcinogenesis

Abstract

Oxygen is a blessing for the existence of all the aerobic organisms on earth. Nevertheless, it plays an adverse role in biological systems by involving the phenomenon of oxidative stress. In biological systems, oxygen constantly undergoes metabolic reactions to generate oxygen-derived free radicals in the form of superoxide (O²⁻), hydroxyl (OH), alkoxyl (RO), and peroxyl (RO2) plus non-radicals in the form of hydrogen peroxide (H₂O₂), peroxynitrite (ONOO–), hypochlorous acid (HOCl), and hypobromous acid (HOBr). Reactive species are divided into four groups depending on the main atom involved: ROS, reactive nitrogen species (RNS), reactive sulfur species (RSS), and reactive chloride species (RClS); their half-lives vary from a few nanoseconds to hours depending on the stability of the molecule. During intracellular metabolic processes like electron transport chain, ROS and RNS are also produced. Normal physiological state in a living system is achieved by a proper equilibrium between the generation and neutralization of ROS and does not lead to any oxidative damage (Roberts et al. 2009). A group of researchers illustrated that an imbalance between the generation of ROS (prooxidant) and antioxidant defense system leads to oxidative stress.