Novel Antioxidative Activity of Astaxanthin and Its Synergistic Effect with Vitamin E

Astaxanthin (Asx) is known to be a potent quencher of singlet oxygen and an efficient scavenger of superoxide anion. However, the scavenging activity of Asx toward the hydroxyl radical was currently unclear because the high lipophilicity of Asx prevents analysis of such activity in water. Liposomes containing Asx (Asx-lipo) were previously shown to be dispersed in water. Analysis of the hydroxyl radical scavenging activity of Asx-lipo demonstrated a dose-dependence in water, with the effect of Asx being more potent than the vitamin E α-tocopherol (α-T). Furthermore, liposomes co-encapsulating Asx and vitamin E derivatives, namely tocotrienols (T3), showed a synergistic elimination effect on singlet oxygen and hydroxyl radical, although the antioxidative activity of liposomes co-encapsulating Asx and α-T was lower than the calculated additive value of each independent activity. A calculation of the most stable structure of Asx in the presence of α-T or T3, suggested that only T3 was able to hydrogen bond with Asx, and the Asx polyene chain partially interacting with the α-T3 triene chain, which could explain the synergistic effect between Asx and T3, but not Asx and α-T. This review introduces the hydroxyl radical scavenging activity of Asx, and its synergistic effect with T3.