The Gastrointestinal System by Po Sing Leung

Author:Po Sing Leung
Language: eng
Format: epub, pdf
Publisher: Springer Netherlands, Dordrecht

2.5 Cholesterol Esterification, Incorporation into Lipoproteins, and Secretion

Within the enterocyte, 70–90 % of the absorbed cholesterol is esterified with fatty acids. Various lipid binding proteins may be involved in directing the absorbed cholesterol to the endoplasmic reticulum. The principal enzyme responsible for cholesterol esterification is acyl CoA:cholesterol acyl transferase 2 (ACAT2 ) that is present in the endoplasmic reticulum. Sitosterol and other plant sterols are less effective substrates for ACAT2 than cholesterol. The microsomal triglyceride transfer protein (MTTP) transfers cholesteryl esters to the nascent chylomicron particle, and chylomicrons are the principal lipoprotein delivering cholesterol into the circulation. Within chylomicrons and other intestinal lipoproteins, cholesteryl esters are incorporated into the oily lipoprotein core, whereas free cholesterol is present on the surface of the particle.

Another route of cholesterol exit from the enterocyte may be via incorporation into HDL. A basolateral cholesterol efflux pump ABCA1 facilitates the transfer of cholesterol to an apolipoprotein A-I acceptor molecule forming discoidal HDL particles (Fig. 8.1). The amount of cholesterol absorbed via this pathway appears to be small, but ABCA1 may be a key role in HDL production. Patients with Tangier disease with mutations in ABCA1 have virtual absence of plasma HDL and increased enterocyte cholesterol content. ABCA1 is regulated by the transcriptional factor LXRα.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.