Superoxide lipid peroxidation

As strong antioxidants and scavengers of superoxide, hydroxyl and peroxyl radicals, tea flavonoids can suppress radical chain reactions and terminate lipid peroxidation (Kumamoto and Sonda, 1998, Yang and Wang, 1993). 

Not all oxidants formed biolc cally have the potential to promote lipid peroxidation. The free radicals superoxide and nitric oxide [or endothelium-derived relaxing aor (EDRF)] are known to be formed in ww but are not able to initiate the peroxidation of lipids (Moncada et tU., 1991). The protonated form of the superoxide radical, the hydroperoxy radical, is capable of initiating lipid peroxidation but its low pili of 4.5 effectively precludes a major contribution under most physiological conditions, although this has been suggested (Aikens and Dix, 1991). Interestingly, the reaction product between nitric oxide and superoxide forms the powerful oxidant peroxynitrite (Equation 2.6) at a rate that is essentially difiiision controlled (Beckman eta/., 1990 Huie and Padmaja, 1993). 

Kellogg, E.W. and Fridovich, I. (1975). Superoxide, hydrogen peroxide, and singlet oxygen in lipid peroxidation by a xanthine oxidase system. J. Biol. Chem 250, 8812-8817. 

Thomas, C.E., Morehouse, L.A. and Aust, S.D. (1985). Ferritin and superoxide dependent lipid peroxidation. J. Biol. Chem. 260, 3275-3280. 

Gutteridge, J.M.C., Richmond, R, and HaUiweU, B. (1979). Inhibition of the iron-catalysed formation of hydroxyl radicals from superoxide and of lipid peroxidation by desferrioxamine. Biochem. J. 184, 469-472. 

Elroy-Stein, D., Bernstein, Y. and Groner, Y. (1986). Overproduction of human Cu/Zn-superoxide dismutase in transfected cells extenuation of paraquat-mediated cytotoxicity and enhancement of lipid peroxidation. EMBO J. 5, 615-622. 

Patients in which oxidative damage may be an important aetiological factor cataract formation include those with Down s syndrome, since there is now evidence that they have increased indices of free-radical activity and lipid peroxidation. It has been su ested that this is due to the increased levels of Cu/Zn-SOD (carried on chromosome 21) generating increased concentrations of hydrogen peroxide (Bras etal., 1989). In the presence of superoxide radicals these produce highly reactive hydroxyl radicals. 

Nonaka, A., Manabe, T., Tamura, K., Asano, N., Imanishi, K. and Tobe, T. (1989b). Changes of xanthine oxidase, lipid peroxide and superoxide dismutase in mouse acute pancreatitis. Digestion 43, 41-46. 

Younes, M., Mohr, A., Schoenberg, M.H. and Schildbeig, F.W. (1987). Inhibition of lipid peroxidation by superoxide dismutase following regional intestinal ischaemia and reperfiision. Res. Exp. Med. 187, 9-17. 

Shaw, S. and Jayatilleke, E. (1987). Acetaldehyde-mediated lipid peroxidation role for superoxide and ferritin. Biochem. Biophys, Res. Commun. 143, 984-990. 

Lipid peroxidation (see Fig. 17.2) is a chain reaction that can be attacked in many ways. The chain reaction can be inhibited by use of radical scavengers (chain termination). Initiation of the chain reaction can be blocked by either inhibiting synthesis. of reactive oxygen species (ROS) or by use of antioxidant enzymes like superoxide dismutase (SOD), complexes of SOD and catalase. Finally, agents that chelate iron can remove free iron and thus reduce Flaber-Weiss-mediated iron/oxygen injury. 

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