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Journal of Lipid Research, Vol. 43, 665-670, May 2002
Copyright © 2002 by Lipid Research, Inc.
25R,26-Hydroxycholesterol revisited: synthesis, metabolism, and biologic roles
Norman B. Javitt1
Department of Pediatrics and Medicine, NYU School of Medicine, New York, NY 10016
1 e-mail norman.javitt{at}med.nyu.edu
The CYP27 gene is expressed in arterial endothelium, macrophages, and other tissues. The gene product generates sterol intermediates that function as ligands for nuclear receptors prior to their transport to the liver for metabolism, mostly to bile acids. Most attention has been given to 27-hydroxycholesterol as a ligand for LXR activated receptors and to chenodeoxycholic acid as a ligand for farnesoid X activated receptors (FXRs). Expression of the pathway in macrophages is essential for normal reverse cholesterol transport. Thus, ABC transporter activity is upregulated, which enhances cholesterol efflux. Absence of these mechanisms probably accounts for the accelerated atherosclerosis that occurs in cerebrotendinous xanthomatosis. Accumulation of 27-hydroxycholesterol in human atheroma is puzzling and may reflect low levels of oxysterol 7 -hydroxylase activity in human macrophages. The same enzyme determines the proportion of mono-, di-, and tri-hydroxy bile acids synthesized in the liver. Oxysterol 7 -hydroxylase deficiency is a molecular basis for cholestatic liver disease. Chenodeoxycholic acid, the major normal end product, downregulates expression of cholesterol 7 -hydroxylase via the FXR/short heterodimer protein nuclear receptor and thus limits total bile acid production. The challenge is to quantify in a physiologic setting the magnitude of the pathway in different tissues and to further evaluate the biologic roles of all the intermediates that may function as ligands for orphan nuclear receptors or via other regulatory mechanisms.Javitt, N. B. 25R,26-Hydroxycholesterol revisited: synthesis, metabolism, and biologic roles. J. Lipid Res. 2002. 43: 665670.
Abbreviations: StAR, steroid acute response Supplementary key words CYP27 CYP7A CYP7B ABC transporter monohydroxy bile acids StAR cholestasis atheroma

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Copyright © 2002 by the American Society for Biochemistry and Molecular Biology.
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