OXIDANTS AND ANTIOXIDANTS | Antioxidants, Enzymatic

Abstract

The lungs have the richest oxygen supply compared with other organs of the body. Therefore, lungs are always vulnerable to attack by free radicals and reactive oxygen species (ROS). Regulation of the oxidation/reduction (redox) state is critical for cell activation, proliferation and viability, and other organ functions. The ROS generated in the lungs are encountered and neutralized by a battery of protein and nonprotein molecules known as antioxidants. The lung antioxidant defense system is comprised of enzymatic antioxidants such as superoxide dismutases (three types that transform superoxide radicals into hydrogen peroxide), catalase (degrades hydrogen peroxide into water), glutathione peroxidases (mainly transform organic hydroperoxides into less toxic organic hydroxides with the help of glutathione), and other accessory enzymes such as thioredoxins, peroxiredoxins, and glutaredoxins. The nonenzymatic antioxidant defense system is chiefly comprised of low-molecular-weight compounds such as vitamins (vitamins C and E), thiols (mainly glutathione), uric acid, β-carotene, etc., either supplemented through dietary sources or synthesized in the body. In several inflammatory conditions of the lungs the levels of these antioxidants have been found to be reduced either due to impaired synthesis or inactivation. Since antioxidants are the main weapon for defense of the lungs, any impairment in their status would lead to several injurious and acute or chronic inflammatory lung conditions.