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.
Key laboratory of Drug Targeting and Drug Delivery System, Ministry of Education, West China School of Pharmacy, Sichuan University , Chengdu 610041, China.|Metabolomics Shared Resource, University of Hawaii Cancer Center , Honolulu, Hawaii 96813, United States.
Ke
K
Lan
Metabolomics Shared Resource, University of Hawaii Cancer Center , Honolulu, Hawaii 96813, United States.
Mingming
M
Su
Metabolomics Shared Resource, University of Hawaii Cancer Center , Honolulu, Hawaii 96813, United States.
Guoxiang
G
Xie
UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599-7569, United States.
Brian C
BC
Ferslew
UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599-7569, United States.
Kim L R
KL
Brouwer
Metabolomics Shared Resource, University of Hawaii Cancer Center , Honolulu, Hawaii 96813, United States.
Cynthia
C
Rajani
State Key Laboratory of Drug Delivery Technology and Pharmacokinetics, Tianjin Institute of Pharmaceutical Research , Tianjin 300193, China.
Changxiao
C
Liu
Metabolomics Shared Resource, University of Hawaii Cancer Center , Honolulu, Hawaii 96813, United States.
Wei
W
Jia
D000328:Adult; D000438:Alcohols / Q000737:chemistry* / Q000652:urine; D001647:Bile Acids and Salts / Q000737:chemistry* / Q000652:urine; D005260:Female; D006801:Humans; D008297:Male; D013058:Mass Spectrometry; D015394:Molecular Structure; D013237:Stereoisomerism
D000438:Alcohols; D001647:Bile Acids and Salts