Molecular oxygen is an excellent acceptor of electrons and is therefore employed by nature for a wide variety of highly important biochemical reactions. The chemical reactivity of oxygen, however, also leads to the formation of oxygen radicals as by-products of metabolism. These radicals result in a condition that is commonly referred to as oxidative stress, in which the formation of reactive oxygen species represents a functional challenge, or even endangers survival of a cell or organism. Oxidative stress can arise from increased production of reactive oxygen species, from exposure to an oxidant. or from decreased function of antioxidant systems or oxidant repair systems. Important examples for the involvement of reactive oxygen species in pathological conditions are inflammatory diseases, ischemia/reperfusion injuries, and many n euro degenerative disorders.
