DISTRIBUTIONS OF CAROTENOIDS AND ALPHA-TOCOPHEROL AMONG LIPOPROTEINS DO NOT CHANGE WHEN HUMAN PLASMA IS INCUBATED IN-VITRO

Carotenoids and cr-tocopherol are dietary, lipophilic antioxidants whi ch may protect plasma iipoproteins from oxidation, a process believed to contribute to atherogenesis. In this study, the quantities and dist ributions of carotenoids, alpha-tocopherol and major lipids in the pla sma and lipoproteins of seven normolipidemic humans were determined. E xperiments were also conducted to determine if these antioxidants redi stribute among lipoproteins when plasma is incubated in vitro. Virtual ly ail of the total carotenoid in plasma associated with lipoproteins, primarily LDL [73 +/- 10% (mean +/- sD)], as did the more non-polar i ndividual carotenoids, beta-cryptoxanthin (68 +/- 9%), lycopene (79 +/ - 9%), and beta-carotene (72 +/- 12%), in patterns which closely resem bled the distribution of total cholesterol. Xanthophyll, the most pola r carotenoid examined, distributed equally between LDL (44 +/- 11%) an d HDL (38 +/- 14%), whereas alpha-tocopherol associated with LDL (43 /- 12%), HDL (26 +/- 10%), and VLDL (27 +/- 13%), These patterns close ly resembled that of phospholipid. Approximately four carotenoid molec ules associated with each VLDL and one with each LDL particle, whereas only 25 of every 1000 HDL particles contained carotenoid. Approximate ly 145 molecules of alpha-tocopherol associated with VLDL, 12 with LDL , and one with each HDL particle. Unlike triglyceride and cholesteryl ester, known to transfer among lipoproteins through the action of chol esteryl ester transfer protein, net transfer of carotenoids and alpha- tocopherol among lipoproteins did not occur, While these results sugge st that the relative polarities of these antioxidants influence their distributions among lipoproteins, the extent to which carotenoids and alpha-tocopherol associate with specific lipoproteins does not appear to be governed by some of the mechanisms which lead to the establishme nt of major lipid distributions.