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Food Lipids: Chemistry, Nutrition, and Biotechnology

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the circulation as well as in the urine by gas chromatography/mass spectrometry<br />

(GC-MS) or an immunoassay.<br />

2. LDL Oxidation <strong>and</strong> Coronary Heart Disease<br />

Although causality has not yet been proved, it would be unwise to ignore a possible<br />

role of LDL oxidation in the genesis of CHD.<br />

Palinsky et al. [36] have demonstrated the existence of autoantibodies directed<br />

against MDA-LDL in the human circulation. Further, Ylä-Herttuala et al. [37] have<br />

shown that atherosclerotic lesions contain compounds that react with antibodies directed<br />

against MDA-modified LDL <strong>and</strong> 4-HNE-lysine, while those antibodies did<br />

not react with native LDL. In that same study it was found that LDL isolated from<br />

atherosclerotic lesions showed a substantial correspondence to the characteristics of<br />

in vitro–oxidized LDL, such as an increased amount of lysophosphatidylcholine <strong>and</strong><br />

a chemotactic activity for monocytes. Furthermore, patients with acute myocardial<br />

infarcts or with carotid atherosclerosis show significantly higher plasma concentrations<br />

of MDA-modified LDL than control subjects [38].<br />

Urinary immunoreactive F2-isoprostanes were higher in hypercholesterolemic<br />

patients than in controls. Moreover, urinary F2-isoprostanes were inversely related<br />

to serum LDL cholesterol concentrations <strong>and</strong> LDL vitamin E levels [40]. Also, in<br />

non-insulin-dependent diabetic patients urinary immunoreactive isoprostane levels<br />

were higher than in controls, which could be counteracted by vitamin E supplementation<br />

[41].<br />

Not only oxidation of polyunsaturated fatty acids but also certain oxidized<br />

forms of cholesterol (oxysterols) are atherogenic <strong>and</strong> may play a role in plaque<br />

development [42]. Especially 7�-hydroxycholesterol may be a good marker for free<br />

radical–related lipid peroxidation. Two separate studies have now shown that in<br />

humans 7�-OH-cholesterol is associated with the risk for atherosclerosis [43,44].<br />

Also feeding a mixture of various oxysterols to atherosclerosis-prone LDL receptor<br />

(�/�) <strong>and</strong> apoE (�/�) mice accelerated fatty streak lesion formation in comparison<br />

with cholesterol feeding alone [45]. For humans, however, so far no causal relation<br />

has been established between oxysteroids <strong>and</strong> lesion formation.<br />

3. Dietary Effects<br />

The fatty acid composition of the diet, <strong>and</strong> in particular the amount of polyunsaturated<br />

fatty acids, is reflected by the fatty acid composition of the LDL particle (Tables<br />

4 <strong>and</strong> 5). As polyunsaturated fatty acids are more easily oxidized than monounsaturated<br />

or saturated fatty acids, it can be envisaged that LDL oxidizability is influenced<br />

by changing the dietary fatty acid composition. However, when interpreting<br />

the results it should be realized that diet always induces multiple changes in the fatty<br />

acid composition of the LDL particle. For example, the proportion of linoleic acid<br />

in the LDL particle increases after enrichment of the diet with this fatty acid, whereas<br />

the proportion of oleic acid, arachidonic acid, palmitoleic acid, <strong>and</strong> palmitic acid<br />

decreases [46].<br />

a. Effects of Linoleate-Rich vs. Oleate-Rich Diets. Linoleic acid, an n-6 polyunsaturated<br />

fatty acid, contains more unsaturated bonds than oleic acid <strong>and</strong> is preferentially<br />

incorporated into tissue lipids. Accordingly, increasing the amount of linoleic<br />

acid in the diet at the expense of oleic acid leads to a higher proportion of<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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