Antioxidant chain-breaking redox

If the inhibitor is able to destroy more than one radical (as described below for chain-breaking redox antioxidants) then the efficiency of inhibition will be increased by this ratio. 

In this reaction scheme, the steady-state concentration of peroxyl radicals will be a direa function of the concentration of the transition metal and lipid peroxide content of the LDL particle, and will increase as the reaction proceeds. Scheme 2.2 is a diagrammatic representation of the redox interactions between copper, lipid hydroperoxides and lipid in the presence of a chain-breaking antioxidant. For the sake of clarity, the reaction involving the regeneration of the oxidized form of copper (Reaction 2.9) has been omitted. The first step is the independent decomposition of the Upid hydroperoxide to form the peroxyl radical. This may be terminated by reaction with an antioxidant, AH, but the lipid peroxide formed will contribute to the peroxide pool. It is evident from this scheme that the efficacy of a chain-breaking antioxidant in this scheme will be highly dependent on the initial size of the peroxide pool. In the section describing the copper-dependent oxidation of LDL (Section 2.6.1), the implications of this idea will be pursued further. 

Both CoQ and ascorbate have been proposed to have a role as free radical chain-breaking antioxidants especially through their interaction with vitamin E, in protecting lipids from peroxidation (Buettner, 1993). This property could be due to redox reactions that reduce quinones in the membranes (Nakamura and Hayashi, 1994). 

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