Analytical evaluation of three enzymatic assays for measuring total bile acids in plasma using a fully-automated clinical chemistry platform

Application of AI on cholangiocarcinoma

Cholangiocarcinoma, classified as intrahepatic, perihilar, and extrahepatic, is considered a deadly malignancy of the hepatobiliary system. Most cases of cholangiocarcinoma are asymptomatic. Therefore, early detection of cholangiocarcinoma is significant but still challenging. The routine screening of a tumor lacks specificity and accuracy. With the application of AI, high-risk patients can be easily found by analyzing their clinical characteristics, serum biomarkers, and medical images. Moreover, AI can be used to predict the prognosis including recurrence risk and metastasis. Although they have some limitations, AI algorithms will still significantly improve many aspects of cholangiocarcinoma in the medical field with the development of computing power and technology.

A simple and reliable bile acid assay in human serum by LC-MS/MS

Background

Bile acids, as important signaling molecules and regulatory factors acting on glucose, lipid, and energy metabolism, are always involved in liver, biliary, and intestinal diseases. Development and validation of a simple liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method for determination of bile acids is significant for the routine clinical testing.

Methods

Fifty microlitre of serum was mixed with 10 μl of the internal standard working solution and then 140 μl of methanol for protein precipitation. After centrifuged, the supernatant was directly used for LC‐MS/MS analysis.

Results

Good separation of all bile acid species was achieved. The method was validated with consistent linearity for individual bile acids, good recovery, low carryover, satisfactory sample stability, and analytical specificity against hemolysis, lipemia, and bilirubinemia. The intra‐day and the inter‐day imprecision values were in the range of 1.53%–10.63% and 3.01%–13.98%, respectively. No obvious matrix effect was observed. The reference intervals of bile acids in adults have been established for the clinical testing.

Conclusions

The low sample volume, simple sample preparation, good separation of all species, and satisfying validation results make this LC‐MS/MS approach suitable for usage as a high‐throughput assay in routine clinical laboratories.

Increased circulating butyrate and ursodeoxycholate during probiotic intervention in humans with type 2 diabetes

Background

An increasing body of evidence implicates the resident gut microbiota as playing a critical role in type 2 diabetes (T2D) pathogenesis. We previously reported significant improvement in postprandial glucose control in human participants with T2D following 12-week administration of a 5-strain novel probiotic formulation (‘WBF-011’) in a double-blind, randomized, placebo controlled setting (NCT03893422). While the clinical endpoints were encouraging, additional exploratory measurements were needed in order to link the motivating mechanistic hypothesis - increased short-chain fatty acids - with markers of disease.

Results

Here we report targeted and untargeted metabolomic measurements on fasting plasma (n = 104) collected at baseline and end of intervention. Butyrate and ursodeoxycholate increased among participants randomized to WBF-011, along with compelling trends between butyrate and glycated haemoglobin (HbA1c). In vitro monoculture experiments demonstrated that the formulation’s C. butyricum strain efficiently synthesizes ursodeoxycholate from the primary bile acid chenodeoxycholate during butyrogenic growth. Untargeted metabolomics also revealed coordinated decreases in intermediates of fatty acid oxidation and bilirubin, potential secondary signatures for metabolic improvement. Finally, improvement in HbA1c was limited almost entirely to participants not using sulfonylurea drugs. We show that these drugs can inhibit growth of formulation strains in vitro.

Conclusion

To our knowledge, this is the first description of an increase in circulating butyrate or ursodeoxycholate following a probiotic intervention in humans with T2D, adding support for the possibility of a targeted microbiome-based approach to assist in the management of T2D. The efficient synthesis of UDCA by C. butyricum is also likely of interest to investigators of its use as a probiotic in other disease settings. The potential for inhibitory interaction between sulfonylurea drugs and gut microbiota should be considered carefully in the design of future studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02415-8.

Targeted profiling of 24 sulfated and non-sulfated bile acids in urine using two-dimensional isotope dilution UHPLC-MS/MS

OBJECTIVES

Bile acids serve as biomarkers for liver function and are indicators for cholestatic and hepatobiliary diseases like hepatitis, cirrhosis, and intrahepatic cholestasis of pregnancy (ICP). Sulfation and renal excretion of bile acids are important elimination steps. The power of ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) allows specific profiling of primary and secondary bile acids as well as their sulfated counterparts.

METHODS

Twenty-four sulfated and non-sulfated primary and secondary bile acids were quantified in urine with 15 corresponding stable isotope labeled internal standards by using two-dimensional UHPLC-MS/MS. The sample preparation was based on a simple dilution with a methanolic zinc sulfate solution followed by an automated online solid phase extraction clean up.

RESULTS

The validation results of the method fulfilled the criteria of the European Medicine Agency (EMA) "Guideline on bioanalytical method validation". To verify fitness for purpose, 40 urine samples were analyzed which showed an average of 86% sulfation, 9.1% taurine-conjugation, 14% non-conjugation, and 77% glycine-conjugation rates.

CONCLUSIONS

Lossless one-pot sample preparation, automated sample purification, and high number of internal standards are major innovations of the presented profiling method, which may allow diagnostic application of BA profiling in the future.

The BACH project protocol: an international multicentre total Bile Acid Comparison and Harmonisation project and sub-study of the TURRIFIC randomised trial

OBJECTIVES

Multicentre international trials relying on diagnoses derived from biochemical results may overlook the importance of assay standardisation from the participating laboratories. Here we describe a study protocol aimed at harmonising results from total bile acid determinations within the context of an international randomised controlled Trial of two treatments, URsodeoxycholic acid and RIFampicin, for women with severe early onset Intrahepatic Cholestasis of pregnancy (TURRIFIC), referred to as the Bile Acid Comparison and Harmonisation (BACH) study, with the aims of reducing inter-laboratory heterogeneity in total bile acid assays.

METHODS

We have simulated laboratory data to determine the feasibility of total bile acid recalibration using a reference set of patient samples with a consensus value approach and subsequently used regression-based techniques to transform the data.

RESULTS

From these simulations, we have demonstrated that mathematical recalibration of total bile acid results is plausible, with a high probability of successfully harmonising results across participating laboratories.

CONCLUSIONS

Standardisation of bile acid results facilitates the commutability of laboratory results and collation for statistical analysis. It may provide the momentum for broader application of the described techniques in the setting of large-scale multinational clinical trials dependent on results from non-standardised assays.

Effect of Fasting on Total Bile Acid Levels in Pregnancy

OBJECTIVE

To evaluate differences between fasting and nonfasting bile acid levels in asymptomatic and symptomatic pregnant women.

METHODS

This is a report of two prospective cohort studies describing bile acid levels in the fasting and nonfasting state in pregnancy. The first cohort included asymptomatic women with singleton pregnancies. Women with a diagnosis of cholestasis, symptoms of cholestasis, or intolerance to components of a standardized meal were excluded. Bile acid levels were measured during the second and third trimesters after fasting and again 2 hours after a standardized meal. The second cohort included symptomatic women with singleton pregnancies in whom fasting and nonfasting bile acid levels were measured at the time of symptom evaluation. A cutoff of 10 micromoles/L was used for diagnosis.

RESULTS

A total of 27 women were included in the asymptomatic cohort. Median [interquartile range] fasting bile acid levels were significantly lower than nonfasting levels in both the second trimester (4.65 micromoles/L [1.02-29.57] vs 13.62 micromoles/L [2.03-40.26]; P<.001) and third trimester (8.31 micromoles/L [1.14-51.26] vs 17.35 micromoles/L [1.77-62.93]; P<.001). Bile acid levels exceeded 10 micromoles/L in 21% of the fasting samples and in 58% of the nonfasting samples in the third trimester. A total of 26 women were included in the symptomatic cohort. Median [interquartile range] fasting bile acid levels were significantly lower than nonfasting values (11.5 micromoles/L [7-56] vs 13.5 micromoles/L [9-142]; P<.001). Six patients in the symptomatic cohort (23%) had nonfasting bile acid levels greater than 10 micromoles/L that dropped below 10 micromoles/L when fasting.

CONCLUSION

Fasting bile acid levels are significantly lower when compared with nonfasting values in both asymptomatic and symptomatic pregnant women. In asymptomatic women, nonfasting bile acid levels often exceeded 10 micromoles/L whereas fasting values did not. In symptomatic women, fasting bile acid levels resulted in 23% fewer diagnoses of cholestasis when compared with nonfasting values. These findings suggest that fasting evaluation of bile acid levels or a higher threshold for diagnosis of cholestasis should be considered.

Rapid determination of 20 bile acids in human serum by ultra performance liquid chromatography-tandem mass spectrometry

A method was established for the simultaneous determination of 20 kinds of bile acids in human serum employing ultraperformance liquid chromatography-tandem mass spectrometry. Chromatographic conditions and sample preparation were optimized to achieve good separation and maximum sensitivity for these analytes. The linearity, accuracy and repeatability of the development method were validated with a series of experiments. Under the optimum conditions, good linearities were achieved in the quantitative range for each bile acid with the correlation coefficients (r² ) >0.9901. The limit of detections (signal-noise ratio 3) of the method were in a range from 0.02 to 0.57 nmol/L. The recoveries were in the range of 88.1-109.9%, RSD < 6.12%. This method was successfully applied for the determination of bile acids in a human serum sample with simple operation, high sensitivity and good accuracy, and provides a reference for the clinical determination of bile acid content.

Analytical performance and method comparison of a quantitative point-of-care immunoassay for measurement of bile acids in cats and dogs

Point-of-care analyzers (POCAs) for quantitative assessment of bile acids (BAs) are scarce in veterinary medicine. We evaluated the Fuji Dri-Chem Immuno AU10V analyzer and v-BA test kit (Fujifilm) for detection of feline and canine total serum BA concentration. Results were compared with a 5th-generation assay as reference method and a 3rd-generation assay, both run on a bench-top analyzer. Analytical performance was assessed at 3 different concentration ranges, and with interferences. For method comparison, samples of 60 healthy and diseased cats and 64 dogs were included. Linearity was demonstrated for a BA concentration up to 130 µmol/L in cats (r = 0.99) and 110 µmol/L in dogs (r = 0.99). The analyzer showed high precision near the lower limit of quantification of 2 µmol/L reported by the manufacturer. Intra- and inter-assay coefficients of variation were < 5% for both species and all concentrations. Interferences were observed for bilirubin (800 mg/L) and lipid (4 g/L). There was excellent correlation with the reference method for feline (rs = 0.98) and canine samples (rs = 0.97), with proportional biases of 6.7% and -1.3%, respectively. However, a large bias (44.1%) was noted when the POCA was compared to the 3rd-generation assay. Total observed error was less than total allowable error at the 3 concentrations. The POCA reliably detected feline and canine BA in clinically relevant concentrations.

Machine Learning Model Comparison in the Screening of Cholangiocarcinoma Using Plasma Bile Acids Profiles

Bile acids (BAs) assessments are garnering increasing interest for their potential involvement in development and progression of cholangiocarcinoma (CCA). Since machine learning (ML) algorithms are increasingly used for exploring metabolomic profiles, we evaluated performance of some ML models for dissecting patients with CCA or benign biliary diseases according to their plasma BAs profiles. We used ultra-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) for assessing plasma BAs profile in 112 patients (70 CCA, 42 benign biliary diseases). Twelve normalisation procedures were applied, and performance of six ML algorithms were evaluated (logistic regression, k-nearest neighbors, naïve bayes, RBF SVM, random forest, extreme gradient boosting). Naïve bayes, using direct bilirubin concentration for normalisation of BAs, was the ML model displaying better performance in the holdout set, with an Area Under Curve (AUC) of 0.95, 0.79 sensitivity, 1.00 specificity. This model, also characterised by 1.00 positive predictive value and 0.73 negative predictive value, displayed a globally excellent accuracy (86.4%). The accuracy of the other five models was lower, and AUCs ranged 0.75–0.95. Preliminary results of this study show that application of ML to BAs profile analysis can provide a valuable contribution for characterising bile duct diseases and identifying patients with higher likelihood of having malignant pathologies.

Enzymatic methods may underestimate the total serum bile acid concentration

Enzymatic assays based on bacterial 3α-hydroxysteroid dehydrogenase are the method of choice for quantification of total bile acids (BAs) in serum. Although non-specific, it is generally considered precise and robust. The aim of this study was to investigate how changes in the BA spectrum might affect the reliability of the method. We measured standard solutions of twenty-three human and murine BAs using a commercial enzymatic assay and compared the measured vs. expected concentrations. Additionally, total BA concentrations in rat and human cholestatic samples with an abnormal BA spectrum were measured using an enzymatic assay, and a more specific LC-MS/MS method. We observed a great variability in the response of individual BAs in the enzymatic assay. Relative signal intensities ranged from 100% in glycocholic acid (reference) to only 20% in α-muricholic acid. The enzymatic assay markedly underestimated the BA concentrations in both human and rat cholestatic sera when compared to the LC-MS/MS assay. Our study indicated that the performance of an enzymatic assay largely depends on the BA spectrum, and the total concentration of BAs can be markedly underestimated. Samples with an atypical BA spectrum (viz. in rodents) should preferably be measured by other methods.

Bile Acids Quantification by Liquid Chromatography-Tandem Mass Spectrometry: Method Validation, Reference Range, and Interference Study

Bile acids (BA) play a pivotal role in cholesterol metabolism. Their blood concentration has also been proposed as new prognostic and diagnostic indicator of hepatobiliary, intestinal, and cardiovascular disease. Liquid chromatography tandem mass spectrometry (LC-MS/MS) currently represents the gold standard for analysis of BA profile in biological samples. We report here development and validation of a LC-MS/MS technique for simultaneously quantifying 15 BA species in serum samples. We also established a reference range for adult healthy subjects (n = 130) and performed a preliminary evaluation of in vitro and in vivo interference. The method displayed good linearity, with high regression coefficients (>0.99) over a range of 5 ng/mL (lower limit of quantification, LLOQ) and 5000 ng/mL for all analytes tested. The accuracies were between 85-115%. Both intra- and inter-assay imprecision was <10%. The recoveries ranged between 92-110%. Each of the tested BA species (assessed on three concentrations) were stable for 15 days at room temperature, 4 °C, and -20 °C. The in vitro study did not reveal any interference from triglycerides, bilirubin, or cell-free hemoglobin. The in vivo interference study showed that pools obtained from hyper-cholesterolemic patients and hyper-bilirubinemic patients due to post-hepatic jaundice for benign cholestasis, cholangiocarcinoma and pancreatic head tumors had clearly distinct patterns of BA concentrations compared with a pool obtained from samples of healthy subjects. In conclusion, this study proposes a new suitable candidate method for identification and quantitation of BA in biological samples and provides new insight into a number of variables that should be taken into account when investigating pathophysiological changes of BA in human diseases.

The association of serum total bile acid with non-alcoholic fatty liver disease in Chinese adults: a cross sectional study

Background

Non-alcoholic fatty liver disease (NAFLD) is currently the major cause of chronic liver disease globally. Bile acids (BAs) have emerged as relevant signaling molecules that are associated with NAFLD development. This study was aimed to examine the association of serum total bile acids (TBAs) with NAFLD in a large population of Chinese subjects.

Methods

This cross sectional study recruited 152,336 participants from the Second Xiangya Hospital, China. NAFLD was diagnosed based on the presence of hepatic steatosis on ultrasonography, without significant alcohol consumption and other known causes for chronic liver disease. A multivariate logistic regression model was used to test for the association of serum TBAs with NAFLD, adjusting for conventional risk factors of NAFLD.

Results

A total of 27.4% of the participants had NAFLD. Patients with NAFLD had slightly higher TBA levels than those without, 3.4 vs. 3.0 μmol/L (p < 0.001). However, TBA levels were not associated with NAFLD in the multivariate logistic regression model, which adjusted for age, gender and other acknowledged risk factors for NAFLD (OR = 1.00. 95% CI: 1.00–1.00, p = 0.797).

Conclusions

We found that the serum TBA levels were not associated with NAFLD. Future studies in a large population, focusing on serum BA composition may improve the understating of the role of BAs in NAFLD.

Serum Bile Acids in Patients With Primary Open-angle Glaucoma

PURPOSE

To measure the serum bile acids (SBA) in patients with primary open-angle glaucoma (POAG) and to compare with nonglaucomatous controls.

PATIENTS AND METHODS

A hospital-based case control study of 90 patients above the age of 40 years was conducted. Patients with POAG formed the study group and individuals without glaucoma in the same age group formed the control group. SBA estimation was done using ELISA kit enzymatic assay technique and the median value was compared between the 2 groups.

RESULTS

The median of SBA level was found to be more in POAG patients when compared with the control group. The difference was statistically significant (P<0.001). Median SBA level was not affected by the age or sex of the participants in the study.

CONCLUSIONS

"Bile acids" may have a role in the oxidative stress and apoptosis involved in the pathophysiology of POAG.

A review of analytical platforms for accurate bile acid measurement

Bile acids are acidic steroids which help in lipid absorption, act as signaling molecules, and are key intermediate molecules between host and gut microbial metabolism. Perturbations in the circulating bile acid pool can lead to dysregulated metabolic and immunological function which may be associated with liver and intestinal disease. Bile acids have chemically diverse structures and are present in a broad range of concentrations in a wide variety of samples with complex biological matrices. Advanced analytical methods are therefore required to identify and accurately quantify individual bile acids. Though enzymatic determination of total bile acid is most popular in clinical laboratories, these methods provide limited information about individual bile acids. Advanced analytical methods such as gas chromatography- and liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy are highly informative techniques which help in identification and quantification of individual bile acids in complex biological matrices. Here, we review the detection technologies currently used for bile acid identification and quantification. We further discuss the advantages and disadvantages of these analytical techniques with respect to sensitivity, specificity, robustness, and ease of use. Graphical abstract.

LC-MS/MS Analysis of Bile Acids in In Vitro Samples

Over the last decade, liquid chromatography-tandem mass spectrometry (LC-MS/MS) has become the method of choice for the quantification of bile acids (BA) and their conjugates in different matrices, such as plasma, blood, urine, and cell lysates. Numerous reports have indeed been published describing methods for quantitative determination of bile acids in plasma samples obtained during in vivo studies. However, information on bioanalytical methods suitable for determination of bile acids in in vitro samples remained scarce. Therefore, we presently report a simple and accurate LC-MS/MS method for the quantification of BA in cells (e.g., cultured human hepatocytes) and corresponding cell culture medium, obtained during in vitro experiments.

Divergent effects of resistance and endurance exercise on plasma bile acids, FGF19, and FGF21 in humans

BACKGROUND

Exercise has profound pleiotropic health benefits, yet the underlying mechanisms remain incompletely understood. Endocrine FGF21, bile acids (BAs), and BA-induced FGF19 have emerged as metabolic signaling molecules. Here, we investigated if dissimilar modes of exercise, resistance exercise (RE) and endurance exercise (EE), regulate plasma BAs, FGF19, and FGF21 in humans.

METHODS

Ten healthy, moderately trained males were enrolled in a randomized crossover study of 1 hour of bicycling at 70% of VO2peak (EE) and 1 hour of high-volume RE. Hormones and metabolites were measured in venous blood and sampled before and after exercise and at 15, 30, 60, 90, 120, and 180 minutes after exercise.

RESULTS

We observed exercise mode-specific changes in plasma concentrations of FGF19 and FGF21. Whereas FGF19 decreased following RE (P < 0.001), FGF21 increased in response to EE (P < 0.001). Total plasma BAs decreased exclusively following RE (P < 0.05), but the composition of BAs changed in response to both types of exercise. Notably, circulating levels of the potent TGR5 receptor agonist, lithocholic acid, increased with both types of exercise (P < 0.001).

CONCLUSION

This study reveals divergent effects of EE and RE on circulating concentrations of the BA species, FGF19, and FGF21. We identify temporal relationships between decreased BA and FGF19 following RE and a sharp disparity in FGF21 concentrations, with EE eliciting a clear increase parallel to that of glucagon.

FUNDING

The Novo Nordisk Foundation (NNF17OC0026114) and the Lundbeck Foundation (R238-2016-2859).