Oxygen radicals, generation from lipids

Exposure of protein amino groups to MDA (formed by the degradation of lipid peroxides) or to oxygen radicals directly, generated by transition metals and hydrogen peroxide, induce fluorescence indistinguishable from that attributed to Amadori-adduct formation (Chio and Tappel, 1969), and leads to the formation of cross-links (Lunec a al., 1985). 

Lipid hydroperoxides are also generated in singlet molecular oxygen mediated oxidations and by the action of enzymes such as lipoxygenases and cyclooxygenases. Chemiluminescence (CL) arising from lipid peroxidation has been used as a sensitive detector of oxidative stress both in vitro and in vivo . Several authors have attributed ultra-weak CL associated with lipid peroxidation to the radiative deactivation of O2 and to triplet-excited carbonyls (63, 72) (equations 35 and 36) " . It has been proposed that the latter emitters arise from the thermolysis of dioxetane intermediates (61, 62) (equation 35), endoperoxide (73) (equation 37) and annihilation of aUtoxyl, as well as peroxyl radicals ... 

Arachidonic acid metabolism through eicosanoid biosynthesis is accompanied by the generation and subsequent utilization of oxygen-derived free radicals. Arachidonic acid, released from lipids as a result... 

Several mechanisms of antioxidant action have been proposed. The presence of antioxidants may result in the decreased formation of the reactive oxygen and nitrogen species in the first place. Antioxidants may also scavenge the reactive species or their precursors. Vitamin E is an example of this latter behavior in its inhibition of lipid oxidation by reaction with radical intermediates generated from polyunsaturated fatty acids. Some antioxidants can bind the metal ions needed to catalyze the formation of the reactive oxidants. Other antioxidants can repair oxidative damage to biomolecules or can influence enzymes that catalyze repair mechanisms. 

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