Reverse cholesterol transport
Fig. 9.5 Forward and reverse cholesterol transport. Cholesterol is secreted by the liver in VLDL particles; these become LDL particles after hydrolysis of their triacylglycerol by lipoprotein lipase and hepatic lipase (see Fig. 9.3) and are taken up by tissues via the LDL receptor. A proportion of the particles will be taken up again by the liver. Cholesterol is removed from peripheral tissues by HDL particles via interaction with the receptor ABC-A1 (more details of HDL metabolism are in Fig. 9.4). This cholesterol is transferred to the liver by interaction with the receptor SR-BI and may be excreted in the bile. An alternative fate for the cholesterol in HDL particles is transfer via the action of cholesteryl ester transfer protein (CETP) to triacylglycerol-rich particles whose remnants thus become cholesterol-enriched. This is an alternative route for transfer of cholesterol to the liver. CE, cholesteryl ester; FC, free cholesterol.
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