Effect of antioxidants on oxidative modification of LDL.
Human low density lipoprotein (LDL) with a molecular mass of 2.5 million contains on average 1300 molecules of polyunsaturated fatty acids (PUFAs) bound in the different lipid classes. The predominant antioxidant in LDL is alpha-tocopherol, with an average of 6 molecules in each LDL particle. The other substances with potential antioxidant activity are: gamma-tocopherol, beta-carotene, alpha-carotene, lycopene, cryptoxanthin, cantaxanthin, phytofluene and ubiquinol-10. Each is present in amounts of only 1/20th to 1/300th of that of alpha-tocopherol. If LDL is exposed to oxidative conditions (Cu++ ions, macrophages) a lag phase precedes the oxidation of PUFAs. During the lag phase the antioxidants disappear with alpha-tocopherol the first to go and beta-carotene the last. The lag phase, which can readily be determined, is an index of the oxidation resistance of LDL. If LDL is loaded with vitamin E in vitro its oxidation resistance increases linearly with its alpha-tocopherol content according to the equation, y = kx+a. The same relationship is applicable if the alpha-tocopherol content of LDL is increased by taking oral vitamin E. Daily doses of 150, 225, 800 and 1200 IU RRR-alpha-tocopherol increased the LDL alpha-tocopherol on average to 138%, 158%, 144% and 215% of the initial value, the oxidation resistance being increased to 118%, 156%, 135% and 175%, respectively. The efficiency of vitamin E-dependent (= k) and the vitamin independent (= a) oxidation resistance seem to be subject specific with strong individual variation.(ABSTRACT TRUNCATED AT 250 WORDS)
Esterbauer
H
H
Institute of Biochemistry, University of Graz, Austria.
Puhl
H
H
Dieber-Rotheneder
M
M
Waeg
G
G
Rabl
H
H
D000975:Antioxidants / Q000378:metabolism*; D001161:Arteriosclerosis / Q000188:drug therapy / Q000209:etiology*; D003300:Copper / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D006801:Humans; D015227:Lipid Peroxidation / Q000187:drug effects / Q000502:physiology; D008077:Lipoproteins, LDL / Q000378:metabolism*; D014810:Vitamin E / Q000378:metabolism / Q000627:therapeutic use
D000975:Antioxidants; D005231:Fatty Acids, Unsaturated; D008077:Lipoproteins, LDL; D014810:Vitamin E; D003300:Copper