Antioxidant activity of polar carotenoids including astaxanthin-β-glucoside from marine bacterium on PC liposomes

This study was aimed at evaluating the antioxidant activity of polar carotenoids (zea-xanthin, astaxanthin, and astaxanthin-beta -glucoside) in free radical-mediated oxidation of phosphatidylcholine (PC) liposomes. In 1-palmitoyl-2-linoleoyl-PC liposomes, astaxanthin-beta -glucoside was the most active, followed by astaxanthin, zeaxanthin, and beta -carotene, although there was no significant difference in the antioxidant activity of these carotenoids in chloroform solution. Thus, it is suggested that the different antioxidant activity of four kinds of carotenoids found in the PC liposomes would depend not on their ability to scavenge free radicals, but on other factors such as their location and orientation in PC liposome systems and the degree of their incorporation into PC bilayers. These physicochemical properties would be strongly correlated with the structural acceptability between the PC molecule and carotenoid molecule, especially between two polar groups of the PC bilayer and the carotenoid. Furthermore, two polar groups of the carotenoid can act as trans-bilayer rivets. The tightly packed conformation of PC bilayers caused by this function of the dipolar carotenoid would also be correlated with their antioxidant activity. This was suppported by the result that cholesterol, known as acting like a peg through one half of the bilayer, also increased the oxidative stability of PC liposomes.