Je. Romanchik et al., DISTRIBUTIONS OF CAROTENOIDS AND ALPHA-TOCOPHEROL AMONG LIPOPROTEINS DO NOT CHANGE WHEN HUMAN PLASMA IS INCUBATED IN-VITRO, The Journal of nutrition, 125(10), 1995, pp. 2610-2617
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.