Macular pigments lutein and zeaxanthin as blue light filters studied in liposomes

Lutein and zeaxanthin are the predominant carotenoids in the human macula l utea. Epidemiological data suggest that an increased intake of a lutein-ric h diet correlates with a diminished risk for age-related macular degenerati on, a major cause of impaired vision in the elderly. Filtering of blue ligh t has been proposed as a possible mechanism of protection. Here, the blue l ight filter efficacy of carotenoids was investigated in unilamellar liposom es loaded in the hydrophilic core space with a fluorescent dye, Lucifer yel low, excitable by blue light. Carotenoids were incorporated into the lipoph ilic membrane. Fluorescence emission in carotenoid-containing liposomes was lower than in carotenoid-free controls when exposed to blue light, indicat ing a filter effect. Filter efficacy was in the order lutein > zeaxanthin > beta -carotene > lycopene. Some of the difference in blue light filter eff icacy of carotenoids is attributable to differences in extinction coefficie nts, and a major further contribution is suggested to be related to the ori entation of the incorporated molecules in the liposomal membrane. (C) 2001 Academic Press.