Journal of Lipid Research, Vol 35, 1795-1800, Copyright © 1994 by Lipid Research, Inc.
Bile acid synthesis in HepG2 cells: effect of cyclosporin
J Levy, K Budai and NB Javitt
Division of Hepatic Diseases, New York University Medical Center, NY 10016.
The hypothesis that cyclosporin specifically affects the pathway of bile
acid synthesis that begins with 27-hydroxylation of cholesterol was
evaluated in HepG2 cells, which synthesize chenodeoxycholic acid and cholic
acid from endogenous 7 alpha-hydroxycholesterol. At a concentration in the
medium of 8.3 microM cyclosporin, the proportion of cholic acid increased
from 29 +/- 7% to 44 +/- 6% (P < 0.001) with no major change in total
bile acid production. Chenodeoxycholic acid synthesis was enhanced by the
addition of either 7 alpha- hydroxycholesterol or 5 beta-cholestane-3
alpha,7 alpha-diol to the medium and cholic acid synthesis was enhanced by
the addition of 5 beta- cholestane-3 alpha,7 alpha,12 alpha-triol to the
medium. Cyclosporin significantly inhibited only enhanced chenodeoxycholic
acid synthesis, indicating a selective interference in mitochondrial side
chain oxidation of less polar intermediates in bile acid synthesis derived
from either initial 7 alpha- or initial 27-hydroxylation of cholesterol.
The increase in the proportion of cholic acid that occurs in the presence
of cyclosporin mimics that occurring in genetically determined sterol
27-hydroxylase deficiency (cerebrotendinous xanthomatosis). Cyclosporin is
useful for dissecting the subcellular pathways of bile acid synthesis.