beta-carotene and 12-(1-pyrene)dodecanoic-acid

The rate constants (ks) of 1O2 scavenging for alpha-tocopherol (alpha-Toc) and beta-carotene (beta-Car) were measured in liposome membranes, and compared with those in EtOH solution. 1O2 was site-specifically generated by photoirradiation using two photosensitizers, water-soluble Rose bengal (RB) and lipid-soluble 12-(1-pyrene)-dodecanoic acid (PDA). The ks value for beta-Car in EtOH solution was 1.3 x 10(10) M-1 s-1, which was 36 times that for alpha-Toc (3.6 x 10(8) M-1 s-1), but there was no difference between their ks values in liposomes (1.8 x 10(7) M-1 s-1 for beta-Car and 1.2 x 10(7) M-1 s-1 for alpha-Toc). In the liposomes, the ks value for alpha-Toc was affected by the membrane site where 1O2 was generated, which depended on the localization of the photosensitizer, being high at the membrane surface in the RB-system and low in the inner region of the membrane in the PDA-system. In contrast, the ks value for beta-Car was not affected by the 1O2-generating site. These differences were supposed to be caused by differences in the relative concentrations of 1O2 and active sites of alpha-Toc and beta-Car in the membranes. alpha-Toc and beta-Car inhibited 1O2-dependent peroxidation of egg yolk phosphatidylcholine (egg PC). The concentrations of alpha-Toc required for 50% inhibition of lipid peroxidation (IC50) were higher than those of beta-Car, being more than 6 times higher in EtOH solution and less than 2 times higher in liposomes. The ratio of the antioxidant activity of beta-Car to that of alpha-Toc was more in EtOH solution than in liposomes, and was well correlated with the ratio of their 1O2 scavenging rate constants.

Topics: beta Carotene; Electrochemistry; Ethanol; Free Radical Scavengers; Kinetics; Lauric Acids; Light; Liposomes; Oxidation-Reduction; Oxygen; Phosphatidylcholines; Phospholipids; Photosensitizing Agents; Rose Bengal; Singlet Oxygen; Solutions; Vitamin E

Large unilamellar liposomes comprising of egg yolk phosphatidylcholine (PC) was exposed to photoirradiation in the presence of methylene blue (water-soluble photosensitizer) or 12-(1-pyrene)dodecanoic acid (P-12, lipid-soluble photosensitizer) to estimate the inhibitory effect of beta-carotene and astaxanthin on photosensitized oxidation of phospholipid bilayers. Without sensitizers, astaxanthin decreased much slower than beta-carotene and other hydrocarbon carotenoids (lycopene, alpha-carotene). Astaxanthin lasted longer than beta-carotene even in the presence of methylene blue or P-12. Decrease of astaxanthin was also much slower than that of beta-carotene when egg yolk PC was replaced by dimyristoyl PC. However, inhibitory effect of astaxanthin was lower than beta-carotene in the case of P-12 sensitized photooxidation. These results suggest that effectiveness of carotenoids as antioxidants on photosensitized oxidation (Type II) in phospholipid bilayers depends on the site of singlet oxygen to be generated, as well as their stability on photoirradiation.

Topics: beta Carotene; Carotenoids; Lauric Acids; Lipid Bilayers; Lipid Peroxidation; Liposomes; Methylene Blue; Oxidation-Reduction; Phosphatidylcholines; Photosensitizing Agents; Vitamin E; Xanthophylls

Human plasma and plasma low-density lipoprotein (LDL) were exposed to photoirradiation in the presence of methylene blue (water-soluble photosensitizer) or 12-(1-pyrene)dodecanoic acid (P-12, lipid-soluble photosensitizer). In methylene-blue-sensitized photooxidation of human plasma and LDL, endogenous carotenoids and tocopherols were consumed with the accumulation of cholesteryl ester hydroperoxides (CE-OOH). Xanthophylls (zeaxanthin and lutein) decreased faster than lycopene and carotenes in the case of human plasma. In P-12-sensitized photooxidation of human plasma and LDL, the decrease rate of xanthophylls was slower than that of lycopene and carotenes. A lower level of beta-carotene exerted the effective inhibition of lipid peroxidation and retarded the oxidative loss of alpha-tocopherol, when the phosphatidylcholine liposomes containing these two lipid-soluble antioxidants were subjected to methylene blue- or P-12-sensitized photooxidation. These results suggest that antioxidant activity of carotenoids in photosensitized oxidation (Type II) of human plasma LDL depends on the site of singlet oxygen (1O2) to be generated and that carotenoids can protect tocopherols from the oxidative loss by 1O2 in the plasma.

Topics: beta Carotene; Carotenoids; Cholesterol Esters; Free Radicals; Humans; Hydrogen Peroxide; Kinetics; Lauric Acids; Light; Lipid Peroxidation; Lipoproteins, LDL; Liposomes; Lutein; Lycopene; Methylene Blue; Oxidation-Reduction; Phosphatidylcholines; Photochemistry; Vitamin E; Xanthophylls; Zeaxanthins