INTRODUCTION Oxygen is an indispensable element for life. Oxidative property of oxygen plays a vital role in various biological phenomena; being essential for life, oxygen can also aggravate the damage within the cell by oxidative events. Oxygen is used by the cell to generate energy and free radicals are formed as a consequence of ATP (adenosine triphosphate) production by the mitochondria. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the by-products resulting from t...