Quantitative profiling of bile acids in blood, adipose tissue, intestine, and gall bladder samples using ultra high performance liquid chromatography-tandem mass spectrometry

Plasma bile acid profile analysis by liquid chromatography-tandem mass spectrometry and its application in healthy subjects and IBD patients

Bile acids (BAs), not only promote the absorption of fat-soluble nutrients and regulate the metabolism of multiple substances but also have a potential role as diagnostic and prognostic indicators in a variety of diseases such as cholestasis, hepatocellular carcinoma, and diabetes mellitus. Here, a rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantification of 50 BAs was developed and validated. Sample preparation included internal standard spiking, followed by protein precipitation, centrifugation, solvent evaporation, and reconstitution. Baseline separation of all isobaric BA species was achieved on an Ultimate XS-C18 column (5 μm, 150 mm × 4.6 mm). The method showed good linearity with high regression coefficients (>0.990) with acceptable accuracy and precision for intra-day and inter-day analyses and achieved good recovery rates for representative analytes. No apparent carryover or matrix effect was observed. The analytical method was successfully applied to the determination of the plasma BA profile in healthy subjects and patients with inflammatory bowel disease (IBD). The routine instrumentation, low sample volume, simple pretreatment, wide range of BAs, and good separation make this LC-MS/MS method suitable for use as a BA profile assay in clinical and basic research studies. This method could be poised to identify possible BA biomarkers for non-invasive early diagnosis and therapeutic evaluation of IBD.

Optimization of saliva sampling methods for analysis of bile acids by UHPLC-MS

This study investigated methods for sampling bile acids in saliva, a potential non-invasive diagnostic biofluid. Bile acids have been implicated in causing damage and permanent changes to the esophageal mucosa and increasing the risk of developing Barrett's esophagus, a condition that can potentially progress to esophageal cancer. Three saliva collection methods were compared: spitting, Salivette® swabs, and Salivette Cortisol® swabs. Spitting emerged as the superior method with the highest recoveries and the least interference, likely due to Salivette swabs retaining bile acids or introducing unknown interferences. All saliva samples were analyzed by UHPLC-MS/MS using the Zorbax RRHD Eclipse Plus C18 column (3 × 50 mm, 1.8 µm) in gradient elution of 0.1 % formic acid in water and methanol. Saliva sample stability was assessed over 14 days, reflecting typical storage times. The levels of detected bile acids were stable for the measured period (RSD ≤ 22 %) and no degradation was observed. Bile acid levels in saliva fluctuated throughout the day, with the greatest changes observed for glycine-conjugated bile acids after meals. To minimize sampling variability, saliva collection by spitting after overnight fasting is recommended for future studies. Our findings are applicable for standardized bile acid sampling and are currently applied in a large clinical study evaluating bile acids as potential susceptibility markers for Barrett's esophagus diagnostics.

Bile acid profiles and mRNA abundance of bile acid-related genes in adipose tissue of dairy cows with high versus normal body condition

Besides their lipid-digestive role, bile acids (BA) influence overall energy homeostasis, such as glucose and lipid metabolism. We hypothesized that BA along with their receptors, regulatory enzymes, and transporters are present in subcutaneous adipose tissue (scAT). In addition, we hypothesized that their mRNA abundance varies with the body condition of dairy cows around calving. Therefore, we analyzed BA in serum and scAT as well as the mRNA abundance of BA-related enzymes, transporters, and receptors in scAT during the transition period in cows with different body conditions around calving. In a previously established animal model, 38 German Holstein cows were divided into either a high (HBCS; n = 19) or normal BCS (NBCS; n = 19) group based on their BCS and back-fat thickness (BFT). Cows were fed different diets to achieve the targeted differences in BCS and BFT (NBCS: BCS <3.5, BFT <1.2 cm; HBCS: BCS >3.75, BFT >1.4 cm) until dry-off at 7 wk antepartum. During the dry period and subsequent lactation, both groups were fed the same diets according to their energy demands. Using a targeted metabolomics approach via liquid chromatography-electrospray ionization-MS /MS, BA were analyzed in serum and scAT at wk -7, 1, 3, and 12 relative to parturition. In serum, 15 BA were observed: cholic acid (CA), chenodeoxycholic acid (CDCA), glycocholic acid (GCA), taurocholic acid (TCA), glycochenodeoxycholic acid (GCDCA), taurochenodeoxycholic acid, deoxycholic acid (DCA), lithocholic acid, glycodeoxycholic acid (GDCA), glycolithocholic acid, taurodeoxycholic acid, taurolithocholic acid, β-muricholic acid, tauromuricholic acid (sum of α and β), and glycoursodeoxycholic acid, whereas in scAT 7 BA were detected: CA, GCA, TCA, GCDCA, taurochenodeoxycholic acid, GDCA, and taurodeoxycholic acid. In serum and scAT samples, the primary BA CA and its conjugate GCA were predominantly detected. Increasing serum concentrations of CA, CDCA, TCA, GCA, GCDCA, DCA, and β-muricholic acid with the onset of lactation might be related to the increasing DMI after parturition. Furthermore, serum concentrations of CA, CDCA, GCA, DCA, GCDCA, TCA, lithocholic acid, and GDCA were lower in HBCS cows compared with NBCS cows, concomitant with increased lipolysis in HBCS cows. The correlation between CA in serum and scAT may point to the transport of CA across cell membranes. Overall, the findings of the present study suggest a potential role of BA in lipid metabolism depending on the body condition of periparturient dairy cows.

Comparative profiling of serum, urine, and feces bile acids in humans, rats, and mice

Bile acids (BAs) play important pathophysiological roles in both humans and mammalian animals. Laboratory rats and mice are widely used animal models for assessing pharmacological effects and their underlying molecular mechanisms. However, substantial physiological differences exist in BA composition between humans and murine rodents. Here, we comprehensively compare BA profiles, including primary and secondary BAs, along with their amino acid conjugates, and sulfated metabolites in serum, urine, and feces between humans and two murine rodents. We further analyze the capabilities in gut microbial transform BAs among three species and compare sex-dependent variations within each species. As a result, BAs undergo amidation predominately with glycine in humans and taurine in mice but are primarily unamidated in rats. BA sulfation is a unique characteristic in humans, whereas rats and mice primarily perform multiple hydroxylations during BA synthesis and metabolism. For gut microbial transformed BA capabilities, humans are comparable to those of rats, stronger than those of mice in deconjugation and 7α-dehydroxylation, while humans are weak than those of rats or mice in oxidation and epimerization. Such differences enhance our understanding of the divergent experimental outcomes observed in humans and murine rodents, necessitating caution when translating findings from these rodent species to humans.

Bile acid signaling in the regulation of whole body metabolic and immunological homeostasis

Bile acids (BAs) play a crucial role in nutrient absorption and act as key regulators of lipid and glucose metabolism and immune homeostasis. Through the enterohepatic circulation, BAs are synthesized, metabolized, and reabsorbed, with a portion entering the vascular circulation and distributing systemically. This allows BAs to interact with receptors in all major organs, leading to organ-organ interactions that regulate both local and global metabolic processes, as well as the immune system. This review focuses on the whole-body effects of BA-mediated metabolic and immunological regulation, including in the brain, heart, liver, intestine, eyes, skin, adipose tissue, and muscle. Targeting BA synthesis and receptor signaling is a promising strategy for the development of novel therapies for various diseases throughout the body.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Separation of bile acid isomer plays a pivotal role in bioequivalence evaluation of ursodeoxycholic acid

Based on our experiences in bile acid profiling, this work developed and validated a liquid chromatography electrospray ionization tandem mass spectrometry method to separate endogenous bile acid isomers and quantitatively determine ursodeoxycholic acid (UDCA), glycoursodeoxycholic acid (GUDCA) and tauroursodeoxycholic acid (TUDCA) in human plasma. The separation was performed on a CORTECS C18 column with the mobile phase consisting of 1.0 mM ammonium acetate and acetonitrile-methanol (80:20, v/v). UDCA, GUDCA and TUDCA were detected in the negative mode on a triple-quadrupole mass spectrometer at the ion transitions of m/z 391 > 391, m/z 448 > 74, m/z 498 > 80, respectively. Phosphate buffer was employed as the surrogate matrix to establish the isotope internal standard corrected calibration curves of analytes. The background-method with a linearity range of 10-200 ng/mL was partially validated to determine the endogenous levels of analytes in blank human plasma, which was incorporated into the validation of bioequivalence-method with a linearity range of 50-10000 ng/mL. The bioequivalence (BE)-method was fully validated with special focus on matrix effects, which have been critically evaluated using the precision and accuracy of quality control samples prepared from the blank human plasma of 12 individuals. It is disclosed for the first time that the BE results of UDCA formulation may yield false results when the method is insufficient to separate UDCA from isoursodeoxycholic acid, a microbial metabolite of both endogenous and exogenous UDCA. The present method has established a milestone for the evaluation of UDCA formulations and is expected to provide a valuable reference for the bioanalytical development of endogenous medicinal products.

Molecular Biomarkers in Cholangiocarcinoma: Focus on Bile

Hepatobiliary system cancers have demonstrated an increasing incidence rate in the past years. Without the presence of early symptoms, the majority of such cancers manifest with a set of similar symptoms, such as cholestasis resulting in posthepatic icterus. Differential diagnosis of hepatobiliary cancers is required for the therapy selection, however, the similarity of the symptoms complicates diagnostics. Thus, the search for molecular markers is of high interest for such patients. Cholangiocarcinoma (CCA) is characterized by a poor prognosis due to a low resectability rate, which occurs because this disease is frequently beyond the limits of surgical therapy at the time of diagnosis. The CCA is diagnosed by the combination of clinical/biochemical features, radiological methods, and non-specific serum tumor biomarkers, although invasive examination is still needed. The main disadvantage is limited specificity and sensitivity, which complicates early diagnostics. Therefore, prognostic and predictive biomarkers are still lacking and urgently needed for early diagnosis. In contrast to serum, bile is more accessible to identify biliary disease due to its simpler composition. Moreover, bile can contain higher concentrations of tumor biomarkers due to its direct contact with the tumor. It is known that the composition of the main bile component - bile acids, may vary during different diseases of the biliary tract. This review summarizes the recent developments in the current research on the diagnostic biomarkers for CCA in serum and bile and provides an overview of the methods of bile acids analysis.

Simultaneous determination of UDCA and its major metabolites in human plasma with surrogate matrix by a rapid and specific LC-MS/MS method

A rapid, convenient, and specific liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous quantification of ursodeoxycholic acid (UDCA), and its major metabolites, glycoursodeoxycholic acid (GUDCA) and tauroursodeoxycholic acid (TUDCA) in human plasma. Methanol was chosen as surrogate matrix for preparation the calibrators to establish calibration curves. Isotope internal standard was used for each analyte. After plasma samples were deproteinized with methanol, the post-treatment samples were analyzed on a ZORBAX SB-C18 column (2.1 × 50 mm, 1.8 μm) with 2 mM ammonium acetate and acetonitrile as mobile phase at a flow rate of 0.5 mL/min. Detection was performed on a triple quadrupole mass spectrometer operating in multiple reaction monitoring (MRM) employing negative ESI interface using API5500 triple quadrupole tandem mass spectrometer system, with the transitions set at m/z 391.4 → m/z 391.4, m/z 448.3 → m/z 73.9, m/z 498.4 → m/z 80.1, m/z 395.3 → m/z 395.3, m/z 453.3 → m/z 74.0, and m/z 503.2 → m/z 79.9 for UDCA, GUDCA, TUDCA, UDCA-d4, GUDCA-d5, and TUDCA-d5, respectively. The calibration curve ranges were 5.00-2500 ng/mL for UDCA and GUDCA and 0.500-250 ng/mL for TUDCA. The intra- and inter-day precision was within 7.00% in terms of relative standard deviation (RSD%) and the accuracy within 11.75% in terms of relative error. The selectivity, sensitivity, extraction recovery, matrix effect, dilution reliability, and stability were within the acceptable range. The method was successfully applied to a pharmacokinetic study in 12 healthy Chinese volunteers after oral administration of 250 mg UDCA.

Dysregulation of secondary bile acid metabolism precedes islet autoimmunity and type 1 diabetes

The gut microbiota is crucial in the regulation of bile acid (BA) metabolism. However, not much is known about the regulation of BAs during progression to type 1 diabetes (T1D). Here, we analyzed serum and stool BAs in longitudinal samples collected at 3, 6, 12, 18, 24, and 36 months of age from children who developed a single islet autoantibody (AAb) (P1Ab; n = 23) or multiple islet AAbs (P2Ab; n = 13) and controls (CTRs; n = 38) who remained AAb negative. We also analyzed the stool microbiome in a subgroup of these children. Factor analysis showed that age had the strongest impact on both BA and microbiome profiles. We found that at an early age, systemic BAs and microbial secondary BA pathways were altered in the P2Ab group compared with the P1Ab and CTR groups. Our findings thus suggest that dysregulated BA metabolism in early life may contribute to the risk and pathogenesis of T1D.

A dynamic multiple reaction monitoring strategy to develop and optimize targeted metabolomics methods: Analyzing bile acids in capecitabine-induced diarrhea

OBJECTIVE

We sought to develop and optimize a targeted bile acids (BAs) metabolomics method based on a dynamic multiple reaction monitoring (dMRM) strategy and explored the dynamic alterations of BAs in diarrhea induced by capecitabine in a mouse model.

METHOD

The targeted metabolomics method was developed using an Agilent 6460A triple quadrupole mass spectrometer, and 41 types of BAs were monitored in negative ionization mode. The mass spectrometer detection was optimized using dMRM to enhance the responses, separation, and peak shape and to shorten the analysis time. A mouse model of diarrhea was established by multiple administration of capecitabine, and plasma samples were collected at baseline and the end of drug administration for subsequent BAs analysis.

RESULTS

The targeted BA metabolomics method achieved shorter chromatographic separation time (10 min) for 41 BAs, with good peak shapes and response increases of 3- to 10-fold after application of dMRM. The mouse model of capecitabine-induced diarrhea was established, and the three BAs 23-norcholic acid, isolithocholic acid, and isodeoxycholic acid in the baseline samples contributed the most to differentiating mice with diarrhea from those without diarrhea. For mice that ultimately developed diarrhea, apocholic acid, isodeoxycholic acid, and 7-ketodeoxycholic acid exhibited the largest change in concentrations compared with their baseline concentrations.

CONCLUSION

The dMRM strategy has obvious advantages compared with common MRM. The results in model mice showed that a differentiated profile of BAs in the baseline may indicate biomarkers of diarrhea induced by capecitabine, and disturbed homeostasis may explain the metabolomic mechanism of diarrhea occurrence.

Cannabidiol-Treated Ovariectomized Mice Show Improved Glucose, Energy, and Bone Metabolism With a Bloom in Lactobacillus

Loss of ovarian 17β-estradiol (E2) in postmenopause is associated with gut dysbiosis, inflammation, and increased risk of cardiometabolic disease and osteoporosis. The risk-benefit profile of hormone replacement therapy is not favorable in postmenopausal women therefore better treatment options are needed. Cannabidiol (CBD), a non-psychotropic phytocannabinoid extracted from hemp, has shown pharmacological activities suggesting it has therapeutic value for postmenopause, which can be modeled in ovariectomized (OVX) mice. We evaluated the efficacy of cannabidiol (25 mg/kg) administered perorally to OVX and sham surgery mice for 18 weeks. Compared to VEH-treated OVX mice, CBD-treated OVX mice had improved oral glucose tolerance, increased energy expenditure, improved whole body areal bone mineral density (aBMD) and bone mineral content as well as increased femoral bone volume fraction, trabecular thickness, and volumetric bone mineral density. Compared to VEH-treated OVX mice, CBD-treated OVX mice had increased relative abundance of fecal Lactobacillus species and several gene expression changes in the intestine and femur consistent with reduced inflammation and less bone resorption. These data provide preclinical evidence supporting further investigation of CBD as a therapeutic for postmenopause-related disorders.

Chiral nematic liquid crystal droplets as a basis for sensor systems

For a series of phospholipid coated calamitic nematic liquid crystal droplets (5CB, 6CB, 7CB, E7 and MLC7023) of diameter ∼18 μm, the addition of chiral dopant leaves the sign of surface anchoring unchanged. Herein we report that for these chiral nematic droplets an analyte induced transition from a Frank-Pryce structure (with planar anchoring) to a nested-cup structure (with perpendicular anchoring) is accompanied by changes in the intensity of reflected light. We propose this system as both a general scheme for understanding director fields in chiral nematic liquid crystal droplets with perpendicular anchoring and as an ideal candidate to be utilised as the basis for developing cheap, single use LC-based sensor devices.

Recent Trends of Microbiota-Based Microbial Metabolites Metabolism in Liver Disease

The gut microbiome and microbial metabolomic influences on liver diseases and their diagnosis, prognosis, and treatment are still controversial. Research studies have provocatively claimed that the gut microbiome, metabolomics understanding, and microbial metabolite screening are key approaches to understanding liver cancer and liver diseases. An advance of logical innovations in metabolomics profiling, the metabolome inclusion, challenges, and the reproducibility of the investigations at every stage are devoted to this domain to link the common molecules across multiple liver diseases, such as fatty liver, hepatitis, and cirrhosis. These molecules are not immediately recognizable because of the huge underlying and synthetic variety present inside the liver cellular metabolome. This review focuses on microenvironmental metabolic stimuli in the gut-liver axis. Microbial small-molecule profiling (i.e., semiquantitative monitoring, metabolic discrimination, target profiling, and untargeted profiling) in biological fluids has been incompletely addressed. Here, we have reviewed the differential expression of the metabolome of short-chain fatty acids (SCFAs), tryptophan, one-carbon metabolism and bile acid, and the gut microbiota effects are summarized and discussed. We further present proof-of-evidence for gut microbiota-based metabolomics that manipulates the host's gut or liver microbes, mechanosensitive metabolite reactions and potential metabolic pathways. We conclude with a forward-looking perspective on future attention to the “dark matter” of the gut microbiota and microbial metabolomics.

Identification and Spatial Visualization of Dysregulated Bile Acid Metabolism in High-Fat Diet-Fed Mice by Mass Spectral Imaging

Changes in overall bile acid (BA) levels and specific BA metabolites are involved in metabolic diseases, gastrointestinal, and liver cancer. BAs have become established as important signaling molecules that enable fine-tuned inter-tissue communication within the enterohepatic circulation. The liver, BAs site of production, displayed physiological and functional zonal differences in the periportal zone versus the centrilobular zone. In addition, BA metabolism shows regional differences in the intestinal tract. However, there is no available method to detect the spatial distribution and molecular profiling of BAs within the enterohepatic circulation. Herein, we demonstrated the application in mass spectrometry imaging (MSI) with a high spatial resolution (3 μm) plus mass accuracy matrix-assisted laser desorption ionization (MALDI) to imaging BAs and N-1-naphthylphthalamic acid (NPA). Our results could clearly determine the zonation patterns and regional difference characteristics of BAs on mouse liver, ileum, and colon tissue sections, and the relative content of BAs based on NPA could also be ascertained. In conclusion, our method promoted the accessibility of spatial localization and quantitative study of BAs on gastrointestinal tissue sections and demonstrated that MALDI-MSI was a valuable tool to investigate and locate several BA molecules in different tissue types leading to a better understanding of the role of BAs behind the gastrointestinal diseases.

The role of bile acids in carcinogenesis

Bile acids are soluble derivatives of cholesterol produced in the liver that subsequently undergo bacterial transformation yielding a diverse array of metabolites. The bulk of bile acid synthesis takes place in the liver yielding primary bile acids; however, other tissues have also the capacity to generate bile acids (e.g. ovaries). Hepatic bile acids are then transported to bile and are subsequently released into the intestines. In the large intestine, a fraction of primary bile acids is converted to secondary bile acids by gut bacteria. The majority of the intestinal bile acids undergo reuptake and return to the liver. A small fraction of secondary and primary bile acids remains in the circulation and exert receptor-mediated and pure chemical effects (e.g. acidic bile in oesophageal cancer) on cancer cells. In this review, we assess how changes to bile acid biosynthesis, bile acid flux and local bile acid concentration modulate the behavior of different cancers. Here, we present in-depth the involvement of bile acids in oesophageal, gastric, hepatocellular, pancreatic, colorectal, breast, prostate, ovarian cancer. Previous studies often used bile acids in supraphysiological concentration, sometimes in concentrations 1000 times higher than the highest reported tissue or serum concentrations likely eliciting unspecific effects, a practice that we advocate against in this review. Furthermore, we show that, although bile acids were classically considered as pro-carcinogenic agents (e.g. oesophageal cancer), the dogma that switch, as lower concentrations of bile acids that correspond to their serum or tissue reference concentration possess anticancer activity in a subset of cancers. Differences in the response of cancers to bile acids lie in the differential expression of bile acid receptors between cancers (e.g. FXR vs. TGR5). UDCA, a bile acid that is sold as a generic medication against cholestasis or biliary surge, and its conjugates were identified with almost purely anticancer features suggesting a possibility for drug repurposing. Taken together, bile acids were considered as tumor inducers or tumor promoter molecules; nevertheless, in certain cancers, like breast cancer, bile acids in their reference concentrations may act as tumor suppressors suggesting a Janus-faced nature of bile acids in carcinogenesis.

BAFinder: A Software for Unknown Bile Acid Identification Using Accurate Mass LC-MS/MS in Positive and Negative Modes

Most LC-MS based bile acid analyses target common bile acids. The identification of unknown bile acids remains challenging in untargeted experiments. Here, a software named BAFinder was developed to improve the identification of unknown bile acids from accurate mass LC-MS/MS data in both the positive and negative ESI modes. A wide variety of bile acid structures were covered in BAFinder, including oxidized bile acids and sugar conjugates that were often ignored. The annotation of unknown bile acids was based on a thorough investigation of MS/MS fragmentation patterns of 84 bile acid reference standards in both modes. Specifically, BAFinder took the peak alignment result and MS/MS spectra, grouped candidate features in positive and negative modes, searched their representative MS/MS spectra against a MS/MS library, and used characteristic product ions and neutral losses to annotate bile acids not covered in the library. Finally, the number of hydroxyl groups and double bonds, conjugation, and isomer information of bile acids were reported with four different levels of annotation confidence. The use of BAFinder was demonstrated through successful application to the analysis of human plasma and urine samples, in which a total of 112 and 244 bile acids were annotated and 75 and 111 of them were confirmed with standards or synthesized compounds, respectively. The software is freely available at https://bafinder.github.io/.

Bile Acid Detection Techniques and Bile Acid-Related Diseases

Bile acid is a derivative of cholinergic acid (steroidal parent nucleus) that plays an important role in digestion, absorption, and metabolism. In recent years, bile acids have been identified as signaling molecules that regulate self-metabolism, lipid metabolism, energy balance, and glucose metabolism. The detection of fine changes in bile acids caused by metabolism, disease, or individual differences has become a research hotspot. At present, there are many related techniques, such as enzyme analysis, immunoassays, and chromatography, that are used for bile acid detection. These methods have been applied in clinical practice and laboratory research to varying degrees. However, mainstream detection technology is constantly updated and replaced with the passage of time, proffering new detection technologies. Previously, gas chromatography (GS) and gas chromatography-mass spectrometry (GC-MS) were the most commonly used for bile acid detection. In recent years, high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) has developed rapidly and has gradually become the mainstream bile acid sample separation and detection technology. In this review, the basic principles, development and progress of technology, applicability, advantages, and disadvantages of various detection techniques are discussed and the changes in bile acids caused by related diseases are summarized.

Identification cholesterol metabolites altered before the onset of nonalcoholic steatohepatitis by targeted metabolomics

Nonalcoholic steatohepatitis (NASH) is a disease with symptoms similar to those of alcoholic liver inflammation without alcohol intake. As an effective treatment strategy has not been established for this disease, a detailed understanding of the pathological progression mechanism is required. We focused on cholesterol metabolites, which are suspected to regulate NASH pathology, and investigated their relationship with the pathological progression in the early stages of NASH. First, the LC/MS/MS methods for bile acids and sterols were optimized and validated. Next, NASH model mice were established by feeding a choline-deficient, methionine-reduced high-fat diet, and the levels of hepatic cholesterol metabolites were measured. As a result, before the onset of NASH, desmosterol, 4β-hydroxycholesterol, campesterol, sitosterol, secondary bile acids such as taurodeoxycholic acid significantly decreased by up to 1/38 of NASH model group. Autoxidation-generated sterols significantly increased 2- to 5-fold, and various primary bile acids such as conjugated β-muricholic acids and cholic acids significantly increased 2- to 7-fold. In this study, the levels of cholesterol metabolites changed in the before the onset of NASH. These metabolic alterations involved in inflammation induction and detoxification for NASH may help the discovery of early diagnostic biomarkers in the future.

Symposium review: Adipose tissue endocrinology in the periparturient period of dairy cows

The involvement of adipose tissue (AT) in metabolism is not limited to energy storage but turned out to be much more complex. We now know that in addition to lipid metabolism, AT is important in glucose homeostasis and AA metabolism and also has a role in inflammatory processes. With the discovery of leptin in 1994, the concept of AT being able to secrete messenger molecules collectively termed as adipokines, and acting in an endo-, para-, and autocrine manner emerged. Moreover, based on its asset of receptors, many stimuli from other tissues reaching AT via the bloodstream can also elicit distinct responses and thus integrate AT as a control element in the regulatory circuits of the whole body's functions. The protein secretome of human differentiated adipocytes was described to comprise more than 400 different proteins. However, in dairy cows, the characterization of the physiological time course of adipokines in AT during the transition from pregnancy to lactation is largely limited to the mRNA level; for the protein level, the analytical methods are limited and available assays often lack sound validation. In addition to proteinaceous adipokines, small compounds such as steroids can also be secreted from AT. Due to the lipophilic nature of steroids, they are stored in AT, but during the past years, AT became also known as being able to metabolize and even to generate steroid hormones de novo. In high-yielding dairy cows, AT is substantially mobilized due to increased energy requirements related to lactation. As to whether the steroidogenic system in AT is affected and may change during the common loss of body fat is largely unknown. Moreover, most research about AT in transition dairy cows is based on subcutaneous AT, whereas other depots have scarcely been investigated. This contribution aims to review the changes in adipokine mRNA and-where available-protein expression with time relative to calving in high-yielding dairy cows at different conditions, including parity, body condition, diet, specific feed supplements, and health disorders. In addition, the review provides insights into steroidogenic pathways in dairy cows AT, and addresses differences between fat depots where possible.

Predictive value of liver cirrhosis using metabolite biomarkers of bile acid in the blood: A protocol for systematic review and meta-analysis

BACKGROUND

Previous studies have indicated that the changes of bile acids are associated with liver cirrhosis. The objective of our study is to perform a systematic review to explore the relationship between bile acids and the pathologic process of cirrhosis, and to find minimally invasive, accurate and reliable potential biomarkers for predicting cirrhosis.

METHODS

EMBASE, the Cochrane Library, PubMed, Web of Science, WanFang Data and Chinese National Knowledge Infrastructure (CNKI) will be searched, using the search strategy of liver cirrhosis, bile acids and metabolomic. The screening process will be conducted strictly based on inclusion and exclusion criteria. Clinical studies based on human including randomized controlled trial, cohort study and case control study will be included without restriction of time. Cochrane collaboration's tool for assessing risk of bias and Newcastle-Ottawa Scale (NOS) will be applied to assess the risk of bias to randomized controlled trial and observational study, respectively. The bile acids and their concentrate which are different between liver cirrhosis and control group will be the mainly outcome. A qualitative analysis will be performed to profile the trajectory change of bile acids, then the meta-analysis will be done for quantitative analysis.

RESULTS

The bile acids profile of liver cirrhosis that has potential predictive value for cirrhosis will be identified.

CONCLUSION

The conclusion of this systematic review will finding potential biomarkers for predicting cirrhosis.

ETHICS AND DISSEMINATION

This systematic review is based on published researches, so there is no ethical approval required. We intend to disseminate our findings in a peer-reviewed journal.

Conjugated C-6 hydroxylated bile acids in serum relate to human metabolic health and gut Clostridia species

Knowledge about in vivo effects of human circulating C-6 hydroxylated bile acids (BAs), also called muricholic acids, is sparse. It is unsettled if the gut microbiome might contribute to their biosynthesis. Here, we measured a range of serum BAs and related them to markers of human metabolic health and the gut microbiome. We examined 283 non-obese and obese Danish adults from the MetaHit study. Fasting concentrations of serum BAs were quantified using ultra-performance liquid chromatography-tandem mass-spectrometry. The gut microbiome was characterized with shotgun metagenomic sequencing and genome-scale metabolic modeling. We find that tauro- and glycohyocholic acid correlated inversely with body mass index (P = 4.1e-03, P = 1.9e-05, respectively), waist circumference (P = 0.017, P = 1.1e-04, respectively), body fat percentage (P = 2.5e-03, P = 2.3e-06, respectively), insulin resistance (P = 0.051, P = 4.6e-4, respectively), fasting concentrations of triglycerides (P = 0.06, P = 9.2e-4, respectively) and leptin (P = 0.067, P = 9.2e-4). Tauro- and glycohyocholic acids, and tauro-a-muricholic acid were directly linked with a distinct gut microbial community primarily composed of Clostridia species (P = 0.037, P = 0.013, P = 0.027, respectively). We conclude that serum conjugated C-6-hydroxylated BAs associate with measures of human metabolic health and gut communities of Clostridia species. The findings merit preclinical interventions and human feasibility studies to explore the therapeutic potential of these BAs in obesity and type 2 diabetes.

Analytical challenges in human exposome analysis with focus on environmental analysis combined with metabolomics

Environmental factors, such as chemical exposures, are likely to play a crucial role in the development of several human chronic diseases. However, how the specific exposures contribute to the onset and progress of various diseases is still poorly understood. In part, this is because comprehensive characterization of the chemical exposome is a highly challenging task, both due to its complex dynamic nature as well as due to the analytical challenges. Herein, the analytical challenges in the field of exposome research are reviewed, with specific emphasis on the sampling, sample preparation, and analysis, as well as challenges in the compound identification. The primary focus is on the human chemical exposome, that is, exposures to mixtures of environmental chemicals and its impact on human metabolome. In order to highlight the recent progress in the exposome research in relation to human health and disease, selected examples of human exposome studies are presented.

Bileome: The bile acid metabolome of rat

Bile acids (BA) play a vital physiological role in vivo. They are not only detergent of dietary lipids and nutrients, but also important hormones or nutrient signaling molecules in metabolic regulation process. Recent studies have also shown BA involvement in various cancers and diseases such as Parkinson's and Alzheimer's and liver diseases. However, majority of the reported literature about BA is restricted to enterohepatic circulation. Hitherto, there has been no comprehensive study of the BA profile in all the major tissue and biofluids in rat has been reported. In this first bileomics study, BA profile of 14 different rat biological specimens (liver, serum, kidney, heart, stomach, ovary, mammary, uterus, small intestine, big intestine, spleen, brain, feces and urine) were studied by ultra-performance liquid chromatography (UPLC)-tandem mass spectrometry (MS/MS). Here I report the comprehensive identification and measurements of bile acids, the bileome, in rat. PCA analysis show distinct separate clusters of tissues as well as biofluids based on BA composition profile. Furthermore, we found that BA profiles of the organs that are involved in enterohepatic circulation were different than the other organs. Most of BA in brain, spleen, heart, ovary, urine, feces and uterus were in the unamidated form, and LCA and MOCA are the most abundant BAs in these organs. Whereas, most of BAs in liver, serum, mammary, large intestine, small intestine, stomach and kidney existed in amidated form, and TCA and T-β-MCA are primary BAs. Finally, first time, BAs are found and measured in kidney, heart, stomach, ovary, mammary, uterus, and spleen of rats.

Analysis of bile acids in human biological samples by microcolumn separation techniques: A review

Bile acids are a group of compounds essential for lipid digestion and absorption with a steroid skeleton and a carboxylate side chain usually conjugated to glycine or taurine. Bile acids are regulatory molecules for a number of metabolic processes and can be used as biomarkers of various disorders. Since the middle of the twentieth century, the detection of bile acids has evolved from simple qualitative analysis to accurate quantification in complicated mixtures. Advanced methods are required to characterize and quantify individual bile acids in these mixtures. This article overviews the literature from the last two decades (2000-2020) and focuses on bile acid analysis in various human biological samples. The methods for sample preparation, including the sample treatment of conventional (blood plasma, blood serum, and urine) and unconventional samples (bile, saliva, duodenal/gastric juice, feces, etc.) are shortly discussed. Eventually, the focus is on novel analytical approaches and methods for each particular biological sample, providing an overview of the microcolumn separation techniques, such as high-performance liquid chromatography, gas chromatography, and capillary electrophoresis, used in their analysis. This is followed by a discussion on selected clinical applications.

Untargeted Profiling of Bile Acids and Lysophospholipids Identifies the Lipid Signature Associated with Glycemic Outcome in an Obese Non-Diabetic Clinical Cohort

The development of high throughput assays for assessing lipid metabolism in metabolic disorders, especially in diabetes research, nonalcoholic fatty liver disease (NAFLD), and nonalcoholic steatohepatitis (NASH), provides a reliable tool for identifying and characterizing potential biomarkers in human plasma for early diagnosis or prognosis of the disease and/or responses to a specific treatment. Predicting the outcome of weight loss or weight management programs is a challenging yet important aspect of such a program’s success. The characterization of potential biomarkers of metabolic disorders, such as lysophospholipids and bile acids, in large human clinical cohorts could provide a useful tool for successful predictions. In this study, we validated an LC-MS method combining the targeted and untargeted detection of these lipid species. Its potential for biomarker discovery was demonstrated in a well-characterized overweight/obese cohort subjected to a low-caloric diet intervention, followed by a weight maintenance phase. Relevant markers predicting successful responses to the low-caloric diet intervention for both weight loss and glycemic control improvements were identified. The response to a controlled weight loss intervention could be best predicted using the baseline concentration of three lysophospholipids (PC(22:4/0:0), PE(17:1/0:0), and PC(22:5/0:0)). Insulin resistance on the other hand could be best predicted using clinical parameters and levels of circulating lysophospholipids and bile acids. Our approach provides a robust tool not only for research purposes, but also for clinical practice, as well as designing new clinical interventions or assessing responses to specific treatment. Considering this, it presents a step toward personalized medicine.

Simultaneous determination of perfluoroalkyl substances and bile acids in human serum using ultra-high-performance liquid chromatography-tandem mass spectrometry

There is evidence of a positive association between per- and polyfluoroalkyl substances (PFASs) and cholesterol levels in human plasma, which may be due to common reabsorption of PFASs and bile acids (BAs) in the gut. Here we report development and validation of a method that allows simultaneous, quantitative determination of PFASs and BAs in plasma, using 150 μL or 20 μL of sample. The method involves protein precipitation using 96-well plates. The instrumental analysis was performed with ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS), using reverse-phase chromatography, with the ion source operated in negative electrospray mode. The mass spectrometry analysis was carried out using multiple reaction monitoring mode. The method proved to be sensitive, robust, and with sufficient linear range to allow reliable determination of both PFASs and BAs. The method detection limits were between 0.01 and 0.06 ng mL-1 for PFASs and between 0.002 and 0.152 ng mL-1 for BAs, with the exception of glycochenodeoxycholic acid (0.56 ng mL-1). The PFAS measured showed excellent agreement with certified plasma PFAS concentrations in NIST SRM 1957 reference serum. The method was tested on serum samples from 20 healthy individuals. In this proof-of-concept study, we identified significant associations between plasma PFAS and BA levels, which suggests that PFAS may alter the synthesis and/or uptake of BAs. Graphical Abstract.

Bile acids in glucose metabolism and insulin signalling - mechanisms and research needs

Of all the novel glucoregulatory molecules discovered in the past 20 years, bile acids (BAs) are notable for the fact that they were hiding in plain sight. BAs were well known for their requirement in dietary lipid absorption and biliary cholesterol secretion, due to their micelle-forming properties. However, it was not until 1999 that BAs were discovered to be endogenous ligands for the nuclear receptor FXR. Since that time, BAs have been shown to act through multiple receptors (PXR, VDR, TGR5 and S1PR2), as well as to have receptor-independent mechanisms (membrane dynamics, allosteric modulation of N-acyl phosphatidylethanolamine phospholipase D). We now also have an appreciation of the range of physiological, pathophysiological and therapeutic conditions in which endogenous BAs are altered, raising the possibility that BAs contribute to the effects of these conditions on glycaemia. In this Review, we highlight the mechanisms by which BAs regulate glucose homeostasis and the settings in which endogenous BAs are altered, and provide suggestions for future research.

Metabolomics for Investigating Physiological and Pathophysiological Processes

Metabolomics uses advanced analytical chemistry techniques to enable the high-throughput characterization of metabolites from cells, organs, tissues, or biofluids. The rapid growth in metabolomics is leading to a renewed interest in metabolism and the role that small molecule metabolites play in many biological processes. As a result, traditional views of metabolites as being simply the "bricks and mortar" of cells or just the fuel for cellular energetics are being upended. Indeed, metabolites appear to have much more varied and far more important roles as signaling molecules, immune modulators, endogenous toxins, and environmental sensors. This review explores how metabolomics is yielding important new insights into a number of important biological and physiological processes. In particular, a major focus is on illustrating how metabolomics and discoveries made through metabolomics are improving our understanding of both normal physiology and the pathophysiology of many diseases. These discoveries are yielding new insights into how metabolites influence organ function, immune function, nutrient sensing, and gut physiology. Collectively, this work is leading to a much more unified and system-wide perspective of biology wherein metabolites, proteins, and genes are understood to interact synergistically to modify the actions and functions of organelles, organs, and organisms.

Bile acid changes after metabolic surgery are linked to improvement in insulin sensitivity

Background

Metabolic surgery is associated with a prompt improvement in insulin resistance, although the mechanism of action remains unknown. The literature on bile acid changes after metabolic surgery is conflicting, and insulin sensitivity is generally assessed by indirect methods. The aim of this study was to investigate the relationship between improvement in insulin sensitivity and concentration of circulating bile acids after biliopancreatic diversion (BPD) and Roux‐en‐Y gastric bypass (RYGB).

Methods

This was a prospective observational study of nine patients who underwent BPD and six who had RYGB. Inclusion criteria for participation were a BMI in excess of 40 kg/m², no previous diagnosis of type 2 diabetes and willingness to participate. Exclusion criteria were major endocrine diseases, malignancies and liver cirrhosis. Follow‐up visits were carried out after a mean(s.d.) of 185·3(72·9) days. Fasting plasma bile acids were assessed by ultra‐high‐performance liquid chromatography coupled with a triple quadrupole mass spectrometer, and insulin sensitivity was measured by means of a hyperinsulinaemic–euglycaemic clamp.

Results

A significant increase in all bile acids, as well as an amelioration of insulin sensitivity, was observed after metabolic surgery. An increase in conjugated secondary bile acids was significantly associated with an increase in insulin sensitivity. Only the increase in glycodeoxycholic acid was significantly associated with an increase in insulin sensitivity in analysis of individual conjugated secondary bile acids.

Conclusion

Glycodeoxycholic acid might drive the improved insulin sensitivity after metabolic surgery.

Analysis of human C24 bile acids metabolome in serum and urine based on enzyme digestion of conjugated bile acids and LC-MS determination of unconjugated bile acids

Host-gut microbiota metabolic interactions are closely associated with health and disease. A manifestation of such co-metabolism is the vast structural diversity of bile acids (BAs) involving both oxidative stereochemistry and conjugation. Herein, we describe the development and validation of a LC-MS-based method for the analysis of human C24 BA metabolome in serum and urine. The method has high throughput covering the discrimination of oxidative stereochemistry of unconjugated species in a 15-min analytical cycle. The validated quantitative performance provided an indirect way to ascertain the conjugation patterns of BAs via enzyme-digestion protocols that incorporated the enzymes, sulfatase, β-glucuronidase, and choloylglycine hydrolase. Application of the method has led to the detection of at least 70 unconjugated BAs including 27 known species and 43 newly found species in the post-prandial serum and urine samples from 7 nonalcoholic steatohepatitis patients and 13 healthy volunteers. Newly identified unconjugated BAs included 3α, 12β-dihydroxy-5β-cholan-24-oic acid, 12α-hydroxy-3-oxo-5β-cholan-24-oic acid, and 3α, 7α, 12β-trihydroxy-5β-cholan-24-oic acid. High-definition negative fragment spectra of the other major unknown species were acquired to facilitate future identification endeavors. An extensive conjugation pattern is the major reason for the "invisibility" of the newly found BAs to other common analytical methods. Metabolomic analysis of the total unconjugated BA profile in combination with analysis of their conjugation patterns and urinary excretion tendencies have provided substantial insights into the interconnected roles of host and gut microbiota in maintaining BA homeostasis. It was proposed that the urinary total BA profile may serve as an ideal footprint for the functional status of the host-gut microbial BA co-metabolism. In summary, this work provided a powerful tool for human C24 BA metabolome analysis that bridges the gap between GC-MS techniques in the past age and LC-MS techniques currently prevailing in biomedical researches. Further applications of the present method in clinical, translational research, and other biomedical explorations will continue to boost the construction of a host-gut microbial co-metabolism network of BAs and thus facilitate the decryption of BA-mediated host-gut microbiota crosstalk in health and diseases. Graphical abstract ᅟ.

Detection technologies and metabolic profiling of bile acids: a comprehensive review

Bile acids (BAs) are important regulatory factors of life activities, which are involved in the regulation of glucose, lipid and energy metabolisms, and closely associated with intestinal hormones, microbiotas and energy balance. BAs abnormalities easily lead to inflammation and metabolic diseases, in turn, the progress of diseases could influence characteristics of BAs. Therefore, accurate detection of BAs contents is of great significance to disease prevention, diagnosis and treatment. At present, the most widely used enzymatic method in clinical practice is applicable to the detection of total bile acid (TBA). In laboratory research, different types of BAs can be accurately separated and quantified by liquid chromatography-mass spectrometry (LC-MS). The metabolic profiling of BAs based on detection technologies can completely and accurately monitor their types and contents, playing a crucial role in disease prevention, diagnosis and treatment. We herein reviewed the main detection technologies of BAs and the application of metabolic profiling in related diseases in recent years.

MALDI Mass Spectral Imaging of Bile Acids Observed as Deprotonated Molecules and Proton-Bound Dimers from Mouse Liver Sections

Bile acids (BAs) play two vital roles in living organisms, as they are involved in (1) the secretion of cholesterol from liver, and (2) the lipid digestion/absorption in the intestine. Abnormal bile acid synthesis or secretion can lead to severe liver disorders. Even though there is extensive literature on the mass spectrometric determination of BAs in biofluids and tissue homogenates, there are no reports on the spatial distribution in the biliary network of the liver. Here, we demonstrate the application of high mass resolution/mass accuracy matrix-assisted laser desorption/ionization (MALDI)-Fourier-transform ion cyclotron resonance (FTICR) to MS imaging (MSI) of BAs at high spatial resolutions (pixel size, 25 μm). The results show chemical heterogeneity of the mouse liver sections with a number of branching biliary and blood ducts. In addition to ion signals from deprotonation of the BA molecules, MALDI-MSI generated several further intense signals at larger m/z for the BAs. These signals were spatially co-localized with the deprotonated molecules and easily misinterpreted as additional products of BA biotransformations. In-depth analysis of accurate mass shifts and additional electrospray ionization and MALDI-FTICR experiments, however, confirmed them as proton-bound dimers. Interestingly, dimers of bile acids, but also unusual mixed dimers of different taurine-conjugated bile acids and free taurine, were identified. Since formation of these complexes will negatively influence signal intensities of the desired [M - H]^- ions and significantly complicate mass spectral interpretations, two simple broadband techniques were proposed for non-selective dissociation of dimers that lead to increased signals for the deprotonated BAs. Graphical Abstract ᅟ.

Metformin impacts cecal bile acid profiles in mice

Bile acids (BAs) are major components of bile synthesized from cholesterol and take part in the digestion of dietary lipids, as well as having signaling functions. They undergo extensive microbial metabolism inside the gastrointestinal tract. Here, we present a method of ultra-high pressure liquid chromatography coupled to ion trap mass spectrometry for quantification of 45 BAs in mouse cecum. The system was validated in regard to sensitivity with limits of detection and quantification (0.6-24.9 nM), interday accuracy (102.4%), interday precision (15.2%), recovery rate (74.7%), matrix effect (98.2%) and carry-over effect (<1.1%). Afterwards, we applied our method to investigate the effect of metformin on BA profiles. Diabetic mice were treated with metformin for 1 day or 14 days. One day of treatment resulted in a significant increase of total BA concentration (2.7-fold increase; db/db metformin 5.32 μmol/g, db/db control mice 1.95 μmol/g), most notable in levels of 7-oxodeoxycholic, 3-dehydrocholic and cholic acid. We observed only minor impact on BA metabolism after 14 days of metformin treatment, compared to the single treatment. Furthermore, healthy wild type mice had elevated concentrations of allocholic and ω-muricholic acid compared to diabetic mice. Our method proved the applicability of profiling BAs in cecum to investigate intestinal BA metabolism in diabetes and pharmacological applications.

Bile Acid Recognition by Mouse Ileal Bile Acid Binding Protein

Ileal bile acid binding protein (I-BABP, gene name FABP6) is a component of the bile acid recycling system, expressed in the ileal enterocyte. The physiological role of I-BABP has been hypothesized to be either an intracellular buffering agent to protect against excess intracellular bile acids or separately as a modulator of bile acid controlled transcription. We investigated mouse I-BABP (mI-BABP) to understand the function of this protein family. Here, we studied energetics and site selectivity of binding with physiological bile acids using a combination of isothermal calorimetric analysis and NMR spectroscopy. We found that the most abundant bile acid in the mouse (β-muricholic acid) binds with weak affinity individually and in combination with other bile acids. Further analysis showed that mI-BABP like human I-BABP (hI-BABP) specifically recognizes the conjugated form of cholic acid:chenodeoxycholic acid (CA:CDCA) in a site-selective manner, displaying the highest affinity of any bile acid combination tested. These results indicate that I-BABP specifically recognizes the ligand combination of CDCA and CA, even in a species such as the mouse where CDCA only represents a trace component of the physiological pool. Specific and conserved recognition of the CDCA and CA ligand combination suggests that I-BABP may play a critical role in the regulation of bile acid signaling in addition to its proposed role as a buffering agent.

Western Diet Deregulates Bile Acid Homeostasis, Cell Proliferation, and Tumorigenesis in Colon

Western-style diets (WD) high in fat and scarce in fiber and vitamin D increase risks of colorectal cancer. Here, we performed a long-term diet study in mice to follow tumorigenesis and characterize structural and metabolic changes in colon mucosa associated with WD and predisposition to colorectal cancer. WD increased colon tumor numbers, and mucosa proteomic analysis indicated severe deregulation of intracellular bile acid (BA) homeostasis and activation of cell proliferation. WD also increased crypt depth and colon cell proliferation. Despite increased luminal BA, colonocytes from WD-fed mice exhibited decreased expression of the BA transporters FABP6, OSTβ, and ASBT and decreased concentrations of secondary BA deoxycholic acid and lithocholic acid, indicating reduced activity of the nuclear BA receptor FXR. Overall, our results suggest that WD increases cancer risk by FXR inactivation, leading to BA deregulation and increased colon cell proliferation. Cancer Res; 77(12); 3352-63. ©2017 AACR.

Role of steroid sulfatase in steroid homeostasis and characterization of the sulfated steroid pathway: Evidence from steroid sulfatase deficiency

The impact of steroid sulfatase (STS) activity in the circulating levels of both sulfated and unconjugated steroids is only partially known. In addition, the sulfated steroid pathway, a parallel pathway to the one for unconjugated steroids, which uses the same enzymes, has never been characterized in detail before. Patients with steroid sulfatase deficiency (STSD) are unable to enzymatically convert sulfated steroids into their unconjugated forms, and are a good model to elucidate how STS affects steroid biosynthesis and to study the metabolism of sulfated steroids. We quantified unconjugated and sulfated steroids in STSD serum, and compared these results with data obtained from serum of healthy controls. Most sulfated steroids were increased in STSD. However, androstenediol-3-sulfate and epiandrosterone sulfate showed similar levels in both groups, and the concentrations of androsterone sulfate were notably lower. Hydroxylated forms of DHEAS and of pregnenolone sulfate were found to be increased in STSD, suggesting a mechanism to improve the excretion of sulfated steroids. STSD testosterone concentrations were normal, but cholesterol and DHEA were significantly decreased. Additionally, serum bile acids were three-fold higher in STSD. Correlations between concentrations of steroids in each group indicate that 17α-hydroxy-pregnenolone-3-sulfate in men is mainly biosynthesized from the precursor pregnenolone sulfate and androstenediol-3-sulfate from DHEAS. These findings confirm the coexistence of two steroidogenic pathways: one for unconjugated steroids and another one for sulfated steroids. Each pathway is responsible for the synthesis of specific steroids. The equal levels of testosterone, and the reduced level of unconjugated precursors in STSD, support that testosterone is primarily synthesized from sulfated steroids. In consequence, testosterone synthesis in STSD relies on an enzyme with sulfatase activity other than STS. This study reveals that STS is a key player of steroid biosynthesis regulating the availability of circulating cholesterol.

Rapid analysis of bile acids in different biological matrices using LC-ESI-MS/MS for the investigation of bile acid transformation by mammalian gut bacteria

Bile acids are important signaling molecules that regulate cholesterol, glucose, and energy homoeostasis and have thus been implicated in the development of metabolic disorders. Their bioavailability is strongly modulated by the gut microbiota, which contributes to generation of complex individual-specific bile acid profiles. Hence, it is important to have accurate methods at hand for precise measurement of these important metabolites. Here, a rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous identification and quantitation of primary and secondary bile acids as well as their taurine and glycine conjugates was developed and validated. Applicability of the method was demonstrated for mammalian tissues, biofluids, and cell culture media. The analytical approach mainly consists of a simple and rapid liquid-liquid extraction procedure in presence of deuterium-labeled internal standards. Baseline separation of all isobaric bile acid species was achieved and a linear correlation over a broad concentration range was observed. The method showed acceptable accuracy and precision on intra-day (1.42-11.07 %) and inter-day (2.11-12.71 %) analyses and achieved good recovery rates for representative analytes (83.7-107.1 %). As a proof of concept, the analytical method was applied to mouse tissues and biofluids, but especially to samples from in vitro fermentations with gut bacteria of the family Coriobacteriaceae. The developed method revealed that the species Eggerthella lenta and Collinsella aerofaciens possess bile salt hydrolase activity, and for the first time that the species Enterorhabdus mucosicola is able to deconjugate and dehydrogenate primary bile acids in vitro.

Profiling of bile acids in bovine follicular fluid by fused-core-LC-MS/MS

Bile acids (BAs) are present in follicular fluid (FF) from humans and cattle. This fact has triggered an interest on the role BAs might play in folliculogenesis and their possible association with fertility. To achieve a better understanding about this subject, new methods are needed to provide reliable information about concentrations of the most important BAs in FF. In this context, liquid chromatography-tandem mass spectrometry (LC-MS/MS) offers high specificity with a relatively simple sample workup. We developed and validated a new assay for the quick profiling of the 9 most abundant BAs in follicular fluid from cattle. The method uses 200μl of FF and can quantify cholic acid (CA), chenodeoxycholic acid (CDCA), deoxycholic acid (DCA) and their glycine (G) and taurine (T) conjugates. Lithocholic acid (LCA), its conjugates GLCA and TLCA, and sulfated forms, were present in some samples, but their concentration was low compared to other BAs (in average, below 60ng/ml for LCA, GLCA or TLCA and below 20ng/ml for their corresponding sulfates). Method performance was studied at three quality controls for each compound in consonance with their physiological concentration. Excellent linearity and recovery were found for all compounds at every control level. Intra-day and between-day precisions (%CV) and accuracies (relative errors) were below 15% for all the compounds. Matrix effects were negligible for most of the analytes. Samples undergoing freeze-thaw showed no degradation of their BAs. The method makes use of a fused-core phenyl column coupled to a triple quadrupole tandem mass spectrometer to achieve chromatographic separation within 5min. We quantified BAs grouped in four different follicle sizes (3-5mm, 6-8mm, 9-14mm, >15mm), obtaining a similar relative BA profile for all the sizes, with CA always in higher concentration, ranging between 1600 and 18000ng/ml, approximately, followed by its conjugate glycocholic acid, GCA, which ranged between 800 and 9000ng/ml. The highest concentration in CA, DCA or CDCA was always detected in FF stemming from follicles of 6-8mm. To our knowledge, this is the first report in which BAs subspecies have been detected and quantified in bovine follicular fluid.

Association between serum bile acid profiles and gestational diabetes mellitus: A targeted metabolomics study

BACKGROUND

Given the potential influence of aberrant bile acid metabolism on glucose homeostasis, we hypothesized that serum bile acid metabolism is altered in gestational diabetes mellitus (GDM). We characterized the metabolic profiling changes of serum bile acids in GDM and to find the potential biomarkers for the diagnosis and differential diagnosis of GDM.

METHODS

Based on ultrahigh performance liquid chromatography/hybrid quadrupole time-of-flight mass spectrometry, a targeted metabolomics study that involved targeted and untargeted screening techniques was performed to explore the changes in serum bile acid metabolism of GDM cases, intrahepatic cholestasis of pregnancy (ICP) cases and healthy controls.

RESULTS

There were 3 significantly different profiling of serum bile acids for GDM, ICP and controls. Compared to the controls, GDM individuals demonstrated significant increases in 8 bile acid species, including 2 dihydroxy conjugated, 1 trihydroxy unconjugated and 5 sulfated bile acids. β-muricholic acid (β-MCA) and di-2 were well-suited to use as the metabolic markers for the diagnosis and differential diagnosis of GDM, respectively.

CONCLUSIONS

These preliminary findings revealed the protective effect of body against cytotoxicity via elimination of increased sulfated bile acids and aberrant enzyme activity participated in the cycle β-MCA→hyodeoxycholic acid (HDCA) of the bile acid metabolism pathway for the women with GDM, which gave us further insights into the etiology and pathophysiology of GDM.