Kinetics of the lipoperoxyl radical-scavenging activity of indicaxanthin in solution and unilamellar liposomes

AbstractThe reaction of the phytochemical indicaxanthin with lipoperoxyl radicals generated in methyl linoleate methanol solution by2,20-azobis(2,4-dimethylvaleronitrile), and in aqueous soybean phosphatidylcholine unilamellar liposomes by 2,20-azobis(2-amidinopropane)hydrochloride, was studied. The molecule acts as a chain-terminating lipoperoxyl radical scavengerin solution, with a calculated inhibition constant of 3.63 £ 105M21 s21, and a stoichiometric factor approaching 2.Indicaxanthin incorporated in liposomes prevented lipid oxidation, inducing clear-cut lag periods and decrease of thepropagation rate. Both effects were concentration-dependent, but not linearly related to the phytochemical concentration.The consumption of indicaxanthin during liposome oxidation was remarkably delayed, the lower the concentration the longerthe time-interval during which it remained in its native state. Indicaxanthin and a-tocopherol, simultaneously incorporated inliposomes, exhibited cooperative antioxidant effects and reciprocal protective interactions. The extent of synergism decreasedat the increase of the ratio (indicaxanthin)/(a-tocopherol). A potential antioxidant mechanism of indicaxanthin is discussed inthe context of the chemistry of the molecule, and of the possible reactivity of a short-lived intermediate.Keywords: Indicaxanthin, phytochemical, lipid oxidation, nutritional value