After challenged by intra- and extracellular environmental factors, such as nitric oxide, calcium and pathogenic organisms, the balance between oxidative and antioxidant defense systems in human and animal cells is broken, which results in the accumulation of reactive oxygen species （ ROS ） within cells, and finally oxidative stress occurs. Oxidative stress can cause DNA damage, such as DNA strand breaks, point mutations, aberrant DNA cross-linking, and mutations in proto-oncogenes and tumor suppressor genes; meanwhile, when challenged by phy...
