Dietary antioxidants as inhibitors of the heme-induced peroxidation of linoleic acid: Mechanism of action and synergism

In this work, a quantitative kinetic model for investigating the heme-induced peroxidation of linoleic acid and its inhibition by two important dietary antioxidants, quercetin and a-tocopherol, is developed. The main conclusions of this work are: (1) The time dependence of the lipid hydroperoxide concentration is critically dependent on the rate constant for lipid hydroperoxide cleavage, initial fraction of lipid hydroperoxides among the pool of conjugated dienes, and rate of heme degradation. (2) The lipophilic antioxidant a-tocopherol acts as a chain-breaking antioxidant that quickly reduces 1-2 eq of lipid peroxyl radicals (inhibition of propagation), whereas the more hydrophilic antioxidant quercetin is only marginally chain-breaking but capable of reducing 4-5 eq of iron-oxo initiator (inhibition of initiation). (3) Based on comparisons between experimental peroxidation curves and simulated curves assuming additivity, it can be concluded that combinations of a-tocopherol and quercetin are generally synergistic. The kinetic analysis and HPLC titrations of the antioxidants both suggest that synergism mainly arises from a capacity of a-tocopherol to regenerate some quercetin oxidation products still endowed with a reducing activity. (c) 2007 Elsevier Inc. All rights reserved.