INHIBITION BY BETA-CAROTENE AND ASTAXANTHIN OF NADPH-DEPENDENT MICROSOMAL PHOSPHOLIPID PEROXIDATION

To evaluate the antioxidant effects of beta-carotene and astaxanthin, rat liver microsomes were exposed to a mixture of chelated iron (Fe3+/ ADP) and NADPH. The carotenoids (190 pmol/mg protein) were incorporate d into some of these microsomal membranes, and phospholipid hydroperox ides (PLOOH), thiobarbituric acid reactive substances (TEARS) and endo genous alpha-tocopherol content were measured over time after the init iation of oxidant stress, In control microsomes, oxidant stress led to accumulation of 1,865 (+/-371) pmol PLOOH/mg protein during the initi al 10-min peroxidation reaction, followed by a more gradual increase d uring the subsequent 20-min of reaction. PLOOH accumulation during the initial 10-min reaction period was reduced to 588 (+/-169) pmol/mg pr otein with beta-carotene present and 800 (+/-288) pmol/mg protein with astaxanthin present. During the following 20-min of incubation, PLOOH levels declined in the carotenoid-supplemented microsomes but continu ed to increase at a slower rate in control preparations. TEARS did not show such large accumulation as observed in PLOOH during the initial 10-min incubation in any microsomal sample. The presence of carotenoid s in the microsomal membrane partially inhibited the loss of alpha-toc opherol, especially during the later phase of oxidant stress. When lip id peroxidation is generated by membrane-bound cyt-P450, the specific measurement of PLOOH clearly demonstrates that the presence of caroten oids provides antioxidant protection.