Tr. Dugas et al., IMPACT OF LDL CAROTENOID AND ALPHA-TOCOPHEROL CONTENT ON LDL OXIDATION BY ENDOTHELIAL-CELLS IN CULTURE, Journal of lipid research, 39(5), 1998, pp. 999-1007
Carotenoids and alpha-tocopherol are dietary, lipophilic antioxidants
that may protect plasma lipoproteins from oxidation, a process believe
d to contribute to atherogenesis, Previous work demonstrated that afte
r the Cu(II)initiated oxidation of human low density lipoprotein (LDL)
in vitro, carotenoids and alpha-tocopherol were destroyed before sign
ificant lipid peroxidation took place, and that alpha-tocopherol was d
estroyed at a much faster rate than were the carotenoids, Additionally
, in vitro enrichment of LDL with beta-carotene, but not with lutein o
r lycopene, inhibited LDL oxidation, In the present studies the impact
of LDL carotenoid and alpha-tocopherol content on LDL oxidation by hu
man endothelial cells (EaHy-1) in culture was assessed. LDL isolated f
rom 11 individual donors was incubated at 0.25 mg protein/mL with EaHy
-1 cells in Ham's F-IO medium for up to 48 h., Formation of lipid hydr
operoxides was assessed by chemical analysis and the contents of lutei
n, beta-cryptoxanthin, lycopene, beta-carotene and alpha-tocopherol we
re determined by high performance liquid chromatography, The extent of
Lipid peroxidation correlated with the endogenous alpha-tocopherol co
ntent of the LDL but not with its content of carotenoids, As in the Cu
(II)-initiated system, carotenoids and alpha-tocopherol were destroyed
before significant peroxidation took place, but, in the cell-mediated
system, alpha-tocopherol and the carotenoids were destroyed at compar
able rates. Also, like the Cu(II)-initiated oxidation, enrichment of t
he LDL with beta-carotene protected it from oxidation by the endotheli
al cells, However, enrichment with either lutein or lycopene actually
enhanced the cell mediated oxidation of the LDL.ir Thus, the specific
content of carotenoids in low density lipoprotein (LDL) clearly modula
tes its susceptibility to oxidation, but individual carotenoids may ei
ther inhibit or promote LDL oxidation.