Journal of Lipid Research, Vol 25, 1246-1256, Copyright © 1984 by Lipid Research, Inc.
Epimerization of the four 3,7-dihydroxy bile acid epimers by human fecal microorganisms in anaerobic mixed cultures and in feces
T Setoguchi, S Higashi, S Tateno, K Yahiro and T Katsuki
The conversion of 3,7-dihydroxy bile acids by anaerobic mixed cultures of
intestinal microorganisms was studied in fecal samples from eight healthy
adult males. Incubations using substrate chenodeoxycholic acid (CDCA) and
ursodeoxycholic acid (UDCA) were performed simultaneously in separate
microbial suspensions from the same fecal samples. A time course study was
done on four samples, chosen randomly from the eight. In the incubation of
CDCA, substrate CDCA always decreased rapidly in amount; UDCA increased in
amount, as did 3 beta, 7 beta-dihydroxy-5 beta-cholanoic acid (3 beta, 7
beta) and 3 beta, 7 alpha-dihydroxy-5 beta-cholanoic acid (3 beta, 7
alpha). In the incubation of UDCA, UDCA gradually decreased in amount; (3
beta, 7 beta), CDCA, and (3 beta, 7 alpha) increased gradually in amount.
All reactions involved four epimers. After 48-72 hr UDCA was predominant
and the reactions appeared to have reached equilibrium. In cultures from
all eight samples, after 72-96 hr, a predominance of beta-hydroxy
configurations at 7-position and alpha-hydroxy configurations at 3-position
was observed. To compare these bile acid compositions to those in feces, an
in vivo study using nine subjects was carried out. Concurrent with the
collection of feces, transit time of food through the gut was measured. In
samples from five subjects, in which amounts of lithocholic acid (LCA) was
small, four 3,7-dihydroxy epimers were found. In samples from the other
four, however, CDCA, the predominant epimer in bile, had apparently been
converted to LCA by 7-dehydroxylation, and four epimers were not always
found. In contrast to the incubation study, UDCA was not always the
predominant 3,7-dihydroxy epimer in the fecal study. This may have been due
to the transit times, which averaged 26.4 +/- 8.9 SD hr, being much shorter
than the time it took for the incubation reactions to reach equilibrium.
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