1 research outputs found
Key Role for the 12-Hydroxy Group in the Negative Ion Fragmentation of Unconjugated C24 Bile Acids
Host-gut microbial
interactions contribute to human health and
disease states and an important manifestation resulting from this
cometabolism is a vast diversity of bile acids (BAs). There is increasing
interest in using BAs as biomarkers to assess the health status of
individuals and, therefore, an increased need for their accurate separation
and identification. In this study, the negative ion fragmentation
behaviors of C24 BAs were investigated by UPLC-ESI-QTOF-MS. The step-by-step
fragmentation analysis revealed a distinct fragmentation mechanism
for the unconjugated BAs containing a 12-hydroxyl group. The unconjugated
BAs lacking 12-hydroxylation fragmented via dehydration and dehydrogenation.
In contrast, the 12-hydroxylated ones, such as deoxycholic acid (DCA)
and cholic acid (CA), employed dissociation routes including dehydration,
loss of carbon monoxide or carbon dioxide, and dehydrogenation. All
fragmentations of the 12-hydroxylated unconjugated BAs, characterized
by means of stable isotope labeled standards, were associated with
the rotation of the carboxylate side chain and the subsequent rearrangements
accompanied by proton transfer between 12-hydroxyl and 24-carboxyl
groups. Compared to DCA, CA underwent further cleavages of the steroid
skeleton. Accordingly, the effects of stereochemistry on the fragmentation
pattern of CA were investigated using its stereoisomers. Based on
the knowledge gained from the fragmentation analysis, a novel BA,
3β,7β,12α-trihydroxy-5β-cholanic acid, was
identified in the postprandial urine samples of patients with nonalcoholic
steatohepatitis. The analyses used in this study may contribute to
a better understanding of the chemical diversity of BAs and the molecular
basis of human liver diseases that involve BA synthesis, transport,
and metabolism