Oxidative changes associated with beta-carotene and alpha-tocopherol enrichment of human low-density lipoproteins.
OBJECTIVE
To determine what effects enrichment of human low-density lipoprotein (LDL) with combinations of alpha-tocopherol and beta-carotene would exert on LDL oxidation and attempt to define the nature of the effects.


METHODS
Human plasma was pooled and alpha-tocopherol and beta-carotene was added in a four-by-four design resulting in the enrichment of LDL with alpha-tocopherol and beta-carotene in varying concentrations. Enriched and control LDL was oxidized in Cu2+ mediated oxidation system and resistance of LDL to oxidation was determined by lag time, thiobarbituric acid reactive substances (TBARS) activity, and rate of oxidation.


RESULTS
Increasing LDL alpha-tocopherol concentration had a linear relationship with lag time and a negative correlation with rate of oxidation. LDL beta-carotene concentration was linearly correlated with the rate of LDL oxidation and beta-carotene loss, and exponentially related to TBARS concentration.


CONCLUSIONS
These results support earlier findings for the protective effect of a-tocopherol against LDL oxidation, and suggest that beta-carotene participates as a prooxidant in the oxidative degradation of LDL under these conditions. Since high levels of alpha-tocopherol did not mitigate the prooxidative effect of beta-carotene, these result indicate that increased LDL beta-carotene may cancel the protective qualities of alpha-tocopherol.
Bowen
H T
HT
Department of Nutrition, University of Nevada, Reno 89557, USA.
Omaye
S T
ST
D000293:Adolescent; D000328:Adult; D000975:Antioxidants / Q000378:metabolism*; D003300:Copper / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000097:blood*; D010084:Oxidation-Reduction; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism; D014810:Vitamin E / Q000097:blood*; D019207:beta Carotene / Q000097:blood*
D000975:Antioxidants; D008077:Lipoproteins, LDL; D017392:Thiobarbituric Acid Reactive Substances; C099252:oxidized low density lipoprotein; D019207:beta Carotene; D014810:Vitamin E; D003300:Copper