Journal of Lipid Research, Vol 24, 841-853, Copyright © 1983 by Lipid Research, Inc.
Formation of ursodeoxycholic acid from chenodeoxycholic acid in the human colon: studies of the role of 7-ketolithocholic acid as an intermediate
H Fromm, RP Sarva and F Bazzoli
The formation of ursodeoxycholic acid from chenodeoxycholic acid and the
role of 7-ketolithocholic acid as an intermediate in this biotransformation
were studied in vitro in fecal incubations as well as in vivo in the human
colon. [24-14C]-Labeled 7-ketolithocholic and chenodeoxycholic acids were
studied at various concentrations, and the biotransformation products were
analyzed by thin-layer chromatography, gas-liquid chromatography, and mass
spectrometry. There was rapid colonic conversion of 7-ketolithocholic acid
to ursodeoxycholic acid and, to a lesser extent, to chenodeoxycholic acid.
The reduction of 7- ketolithocholic to ursodeoxycholic acid proceeded
significantly faster anaerobically and at acid pH than under aerobic and
alkaline conditions. When chenodeoxycholic acid was incubated in vitro or
instilled into the colon, various amounts of 7-ketolithocholic and
ursodeoxycholic acids were formed. The formation of 7-ketolithocholic acid
was favored by alkaline conditions. Isotope dilution studies, in which
trace amounts of labeled 7-ketolithocholic acid were incubated with
unlabeled chenodeoxycholic acid, indicate 7-ketolithocholic acid to be the
major intermediate in the intestinal bacterial conversion of
chenodeoxycholic to ursodeoxycholic acid.
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