indicaxanthin and 2-2--azobis(2-4-dimethylvaleronitrile)

The reaction of the phytochemical indicaxanthin with lipoperoxyl radicals generated in methyl linoleate methanol solution by 2,2'-azobis(2,4-dimethylvaleronitrile), and in aqueous soybean phosphatidylcholine unilamellar liposomes by 2,2'-azobis(2-amidinopropane)hydrochloride, was studied. The molecule acts as a chain-terminating lipoperoxyl radical scavenger in solution, with a calculated inhibition constant of 3.63 x 10(5) M(-1) s(-1), and a stoichiometric factor approaching 2. Indicaxanthin incorporated in liposomes prevented lipid oxidation, inducing clear-cut lag periods and decrease of the propagation 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 longer the time-interval during which it remained in its native state. Indicaxanthin and alpha-tocopherol, simultaneously incorporated in liposomes, exhibited cooperative antioxidant effects and reciprocal protective interactions. The extent of synergism decreased at the increase of the ratio (indicaxanthin)/(alpha-tocopherol). A potential antioxidant mechanism of indicaxanthin is discussed in the context of the chemistry of the molecule, and of the possible reactivity of a short-lived intermediate.

Topics: 1,2-Dipalmitoylphosphatidylcholine; alpha-Tocopherol; Amidines; Antioxidants; Azo Compounds; Betaxanthins; Dose-Response Relationship, Drug; Drug Synergism; Free Radical Scavengers; In Vitro Techniques; Kinetics; Linoleic Acids; Lipid Bilayers; Lipid Peroxidation; Lipid Peroxides; Liposomes; Methanol; Molecular Structure; Nitriles; Oxidation-Reduction; Phosphatidylcholines; Pyridines; Solutions; Solvents; Suspensions