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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Table 3 Some Major Apolipoprotein <strong>and</strong> Their Functions<br />

Apolipoprotein Lipoprotein Function<br />

ApoC-II Chylomicrons, VLDLs Activator of LPL<br />

ApoE Chylomicron remnants, VLDLs, IDLs Lig<strong>and</strong> for remnant <strong>and</strong><br />

LDL receptors<br />

ApoB-100 IDLs, LDLs Lig<strong>and</strong> for LDL receptor<br />

ApoA-I Chylomicron, HDLs Cofactor for LCAT<br />

B. Endogenous Pathway<br />

The liver excretes cholesterol <strong>and</strong> triacylglycerols into the circulation by the formation<br />

of VLDL particles. These lipoproteins also interact with LPL, triacylglycerols<br />

become hydrolyzed, <strong>and</strong> VLDL remnants (also called IDLs) are formed. A part of<br />

the IDL is taken up by the liver, while the remaining part is converted in the circulation<br />

into LDL. LDLs are nearly devoid of triacylglycerols <strong>and</strong> carry about 60–<br />

Figure 1 Overview of the metabolism of dietary fatty acids, dietary cholesterol, <strong>and</strong> plasma<br />

lipoproteins. Dietary triacylglycerols <strong>and</strong> cholesterol enter the blood circulation in chylomicrons<br />

(C). The triacylglycerols from the chylomicron core are hydrolyzed by lipoprotein lipase<br />

(LPL), <strong>and</strong> the so-formed chylomicron remnants (CR) are removed from the circulation by<br />

the hepatic remnant receptor. The liver excretes cholesterol <strong>and</strong> triacylglycerols into the circulation<br />

in VLDLs. These lipoproteins also interact with LPL, <strong>and</strong> VLDL remnants—also<br />

called IDLs—are formed, which are taken up by the liver or converted to LDL. Most of the<br />

LDL is removed from the circulation by the (hepatic) LDL receptor pathway, while a smaller<br />

part is removed via the scavenger pathway. HDL binds cholesterol from tissues, which can<br />

be transferred with the assistance of cholesterol ester transfer protein (CETP) to LDL. HDL<br />

particles may also be taken up in the liver by a putative HDL receptor, or lose a part of its<br />

content by the action of hepatic lipase <strong>and</strong> then reenter the circulation again (not drawn).<br />

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

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