Formation of ROS is a normal consequence of essential biochemical processes. Low levels of ROS are harmless and necessary in several processes such as intracellular messaging, immunity and defence against microorganisms. In contrast, growing evidence indicates that ROS may lead to a variety of biological responses, including the induction of apoptosis, cell cycle arrest and formation of DNA mutations, which are associated with the pathogenesis of several diseases, including cancer (25-27). Therefore, the balance between ROS production and antioxidant defenses appears to one of the most significant physiological factors for cell transformation.