ADDITION OF LUTEIN, LYCOPENE, OR BETA-CAROTENE TO LDL OR SERUM IN-VITRO - EFFECTS ON CAROTENOID DISTRIBUTION, LDL COMPOSITION, AND LDL OXIDATION

Carotenoids are dietary antioxidants transported with plasma lipoprote ins, primarily low-density lipoprotein (LDL). In this study in vitro m ethods were used to increase the amounts of specific, individual carot enoids in LDL. By addition of carotenoid to isolated LDL or serum, fol lowed by (re)isolation of the lipoproteins, samples of LDL were enrich ed 4- to 150-fold with lutein, 2- to 15-fold with lycopene, or 3- to 2 5-fold with beta-carotene. Enrichment with specific carotenoids was ac hieved without affecting the electrophoretic mobility of the lipoprote in, its cholesterol to protein ratio, or the levels of other carotenoi ds or alpha-tocopherol. The distributions among lipoproteins of carote noid added to serum were similar, but not identical, to the distributi ons of the endogenous carotenoids. In particular, for added lutein, a greater proportion was found in HDL, and for added beta-carotene, more was found in very low-density lipoprotein (VLDL). We then studied the effect of enriching LDL with specific carotenoids on its susceptibili ty to oxidation by copper ions. Lutein, beta-cryptoxanthin, lycopene, and beta-carotene, the four major plasma carotenoids, and alpha-tocoph erol were destroyed before the formation of lipid peroxidation product s. The rates of destruction of the individual carotenoids differed; ly copene was destroyed most rapidly and lutein most slowly. Upon oxidati on of beta-carotene-enriched LDL, the rates of destruction of beta-car otene, lycopene, and lutein were slowed and the lag times before the i nitiation of lipid peroxidation increased from 19 to 65 min. Neither e ffect was observed in LDL enriched with lutein or lycopene. Thus, beta -carotene was unique among the carotenoids studied in having a small, but significant effect on LDL oxidation in vitro. (C) Elsevier Science Inc. 1997.