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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 10 Schematic representation of the formation of an atherosclerotic plaque. (1) LDL<br />

enters the intimal layer <strong>and</strong> can be oxidized by several factors, such as lipoxygenase or<br />

reactive oxygen species. (2) Oxidized LDL is cytotoxic <strong>and</strong> causes endothelial damage, (3)<br />

which results in the expression of adhesive glycoproteins to which monocytes <strong>and</strong> T lymphocytes<br />

attach. (4) The damaged endothelial cells excrete chemoattractants, which causes a<br />

continuous recruitment of monocytes <strong>and</strong> T lymphocytes. (5) These cells pass the endothelial<br />

cell layer <strong>and</strong> monocytes may become macrophages. (6) Oxidized LDL prevents return of<br />

macrophages back to the lumen <strong>and</strong> (7) the arrested macrophages absorb large amounts of<br />

oxidized LDL via the scavenger receptors <strong>and</strong> become foam cells, which may eventually lead<br />

to the formation atherosclerotic plaques.<br />

mation of conjugated dienes, products formed after oxidation of the polyunsaturated<br />

fatty acids from the LDL particle. After LDL isolation, copper is added to the test<br />

tube to initiate the oxidation process <strong>and</strong> the formation of conjugated dienes is then<br />

quantified by measuring the change in absorbance at 234 nm (Fig. 11). This curve<br />

can be divided into three consecutive phases: the lag phase, the propagation phase,<br />

<strong>and</strong> the decomposition phase.<br />

During the lag phase, LDL-bound lipophilic antioxidants protect the polyunsaturated<br />

fatty acids from oxidation. Tocopherols <strong>and</strong> �-carotene, for example, scavenge<br />

lipid peroxide radicals, thereby breaking the chain reaction. The antioxidant<br />

has now become a relatively stable radical, which does not induce lipid peroxidation<br />

but is also not regenerated, as in vivo may happen. Addition of the water-soluble<br />

ascorbic acid (vitamin C) that is lost during LDL isolation leads to an increase in<br />

the lag phase because this antioxidant can regenerate tocopherols. Thus, at a certain<br />

stage the LDL particle becomes depleted of antioxidants; at this point, the peroxi-<br />

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

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