Carotenoids are degraded by free radicals but do not affect lipid peroxidation in unilamellar liposomes under different oxygen tensions

It has been questioned whether carotenoids can act as antioxidants in biolo gical membranes. Biological membranes can be modeled for studies of lipid p eroxidation using unilamellar liposomes. Both carotenoid depletion and lipi d peroxidation were increased with increasing oxygen tension in unilamellar liposomes. Carotenoids in such liposomes. were found to be very sensitive to degradation by free radicals generated from iron and 2,2'-azobis(2-amidi nopropane) dihydro chloride, but they were not protective against lipid per oxidation. Lycopene and beta -carotene were more sensitive to free radical attack than lutein, zeaxanthin, and beta -cryptoxanthin. (C) 2001 Federatio n of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.