ubiquinone and methyl-linoleate

The mechanisms and dynamics of antioxidant action of ubiquinol have been studied. Ubiquinol scavenges peroxyl radical faster than alpha-tocopherol. However, it is autooxidized rapidly to give hydroperoxyl radical and/or superoxide and hence its antioxidant potency is smaller than that of alpha-tocopherol. The side chain of ubiquinol reduces the mobility between the membranes. It was concluded that ubiquinol acts as a potent antioxidant in combination with alpha-tocopherol.

Topics: Animals; Antioxidants; Ascorbic Acid; Drug Synergism; Humans; Linoleic Acids; Lipid Peroxidation; Oxidation-Reduction; Peroxides; Phenylenediamines; Reactive Oxygen Species; Ubiquinone; Vitamin E

The dynamics of action of ubiquinol as an antioxidant against lipid peroxidation was reinvestigated and compared with that of alpha-tocopherol. It was found that ubiquinol was 2.5 and 1.9 times more reactive than alpha-tocopherol toward phenoxyl and peroxyl radicals, respectively, at 25 degrees C in ethanol and that it was capable of donating two hydrogen atoms toward oxygen radicals but that the apparent stoichiometric number decreased in the inhibition of lipid peroxidation, to even smaller than 1, due to its autoxidation. The autoxidation of ubiquinol proceeded even in the micelles and liposomal membranes in aqueous dispersions as well as in organic homogeneous solution. The apparent antioxidant activity of ubiquinol was smaller than that of alpha-tocopherol against lipid peroxidation in organic solution as judged from either rate of oxidation or duration of inhibition period. They exerted similar antioxidant potency against lipid peroxidation in the membranes and micelles in aqueous dispersions. The combination of ubiquinol and alpha-tocopherol was suggested to be effective.

Topics: Antioxidants; Free Radicals; Kinetics; Linoleic Acids; Lipid Peroxidation; Models, Chemical; Ubiquinone; Vitamin E

Alpha-tocopheryl quinone is a metabolite of alpha-tocopherol (TOH) in vivo. The antioxidant action of its reduced form, alpha-tocopheryl hydroquinone (TQH2), has received much attention recently. In the present study, the antioxidative activity of TQH2 was studied in various systems in vitro and compared with that of ubiquinol-10 (UQH2) or TOH to obtain the basic information on the dynamics of the antioxidant action of TQH2. First, their hydrogen-donating abilities were investigated in the reaction with galvinoxyl, a stable phenoxyl radical, and TQH2 was found to possess greater second-order rate constant (1.0 x 10(4) M(-1) s(-1)) than UQH2 (6.0 x 10(3) M(-1) s(-1)) and TOH (2.4 x 10(3) M(-1) s(-1)) at 25 degrees C in ethanol. The stoichiometric numbers were obtained as 1.9, 2.0, and 1.0 for TQH2, UQH2, and TOH, respectively, in reducing galvinoxyl. Second, their relative reactivities toward peroxyl radicals were assessed in competition with N,N'-diphenyl-p-phenylenediamine (DPPD) and found to be 6.0 (TQH2), 1.9 (UQH2), and 1.0 (TOH). Third, their antioxidant efficacies were evaluated in the oxidation of methyl linoleate in organic solvents and in aqueous dispersions. The antioxidant potency decreased in the order TOH > UQH2 > TQH2, as assessed by either the extent of the reduction in the rate of oxidation or the duration of inhibition period. The reverse order of their reactivities toward radicals and their antioxidant efficacies was interpreted by the rapid autoxidation of TQH2 and UQH2, carried out by hydroperoxyl radicals. Although neither TQH2 nor UQH2 acted as a potent antioxidant by itself, they acted as potent antioxidants in combination with TOH. TQH2 and UQH2 reduced alpha-tocopheroxyl radical to spare TOH, whereas TOH suppressed the autoxidation of TQH2 and UQH2. In the micelle oxidation, the antioxidant activities of TQH2, UQH2, and TOH were similar, whereas 2,2,5,7,8-pentamethyl-6-chromanol exerted much more potent efficacy than TQH2, UQH2, or TOH. These results clearly show that the antioxidant potencies against lipid peroxidation are determined not only by their chemical reactivities toward radicals, but also by the fate of an antioxidant-derived radical and the mobility of the antioxidant at the microenvironment.

Topics: alpha-Tocopherol; Antioxidants; Benzhydryl Compounds; Free Radical Scavengers; Free Radicals; Kinetics; Linoleic Acids; Lipid Peroxidation; Luminescent Measurements; Micelles; Oxidation-Reduction; Ubiquinone; Vitamin E

The antioxidant activities of ubiquinol and ubiquinone were measured in the free radical-mediated oxidations of methyl linoleate in solution and phosphatidylcholine liposomes in aqueous dispersion. Ubiquinol-10 suppressed the oxidation of methyl linoleate in hexane, although its reactivity toward peroxyl radical was about 10 times less than that of alpha-tocopherol. Ubiquinone-10, on the contrary, did not show any antioxidant activity. On the other hand, ubiquinol-10 inhibited the oxidation of phosphatidylcholine liposomal membranes as efficiently as alpha-tocopherol. When both ubiquinol-10 and alpha-tocopherol were present, ubiquinol-10 decreased first and alpha-tocopherol decreased after all ubiquinol-10 was consumed in both solution and liposomes. These results and electron spin resonance (ESR) study suggest that ubiquinol-10 regenerates alpha-tocopherol by reducing alpha-tocopheroxyl radical.

Topics: Animals; Antioxidants; Free Radicals; Linoleic Acids; Lipid Peroxidation; Liposomes; Phosphatidylcholines; Solutions; Ubiquinone; Vitamin E