Oxidative stress is the state of imbalance between the level of antioxidant
defense system and production of oxygen-derived species (ODS) which are inevitably
produced as by-products of normal aerobic metabolism. Increased O2 concentration
and production of oxygen-derived species, e.g. superoxide anion (O2
•-), hydroxyl
(OH•
), and hydrogen peroxide (H2O2) radicals can accelerate oxidative stress. The
ground-state oxygen (O2) molecule is gained a single unpaired electron, and becomes
O2
•-, O2
•- which rapidly reacts with different metabolic enzymes as well as cations
(Dhalla, Temsah and Netticadan, 2000). In additional H2O2 is product from reduction of oxygen and it is easily diffusible within and between cells. Since the O-O bond is
relatively weak, H2O2 readily decomposes to give the hydroxyl radical (OH•
). OH•
is
the most reactive species that induces significant damage to the cell by converting
guanine into 8-hydroxy guanine