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Enzymatic methods may underestimate the total serum bile acid concentration.

ABSTRACT: Enzymatic assays based on bacterial 3?-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 ?-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.

SUBMITTER: Zizalova K

PROVIDER: S-EPMC7380613 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Enzymatic methods may underestimate the total serum bile acid concentration.

Žížalová Kateřina K Vecka Marek M Vítek Libor L Leníček Martin M

PloS one 20200724 7

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. Addition ...[more]

PMID: 32706797

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Project description:Regular exercise has profound metabolic influence on the liver, but effects on bile acid (BA) metabolism are less well known. BAs are synthesized exclusively in the liver from cholesterol via the rate-limiting enzyme cholesterol 7 alpha-hydroxylase (CYP7A1). BAs contribute to the solubilization and absorption of lipids and serve as important signaling molecules, capable of systemic endocrine function. Circulating BAs increase with obesity and insulin resistance, but effects following exercise and diet-induced weight loss are unknown. To test if improvements in fitness and weight loss as a result of exercise training enhance BA metabolism, we measured serum concentrations of total BAs (conjugated and unconjugated primary and secondary BAs) in sedentary, obese, insulin-resistant women (N = 11) before (PRE) and after (POST) a ∼14-wk exercise and diet-induced weight loss intervention. BAs were measured in serum collected after an overnight fast and during an oral glucose tolerance test (OGTT). Serum fibroblast growth factor 19 (FGF19; a regulator of BA synthesis) and 7-alpha-hydroxy-cholesten-3-one (C4, a marker of CYP7A1 enzymatic activity) also were measured. Using linear mixed-model analyses and the change in V̇O2peak (mL/min/kg) as a covariate, we observed that exercise and weight loss intervention decreased total fasting serum BA by ∼30% (P = 0.001) and increased fasting serum C4 concentrations by 55% (P = 0.004). C4 was significantly correlated with serum total BAs only in the POST condition, whereas serum FGF19 was unchanged. These data indicate that a fitness and weight loss intervention modifies BA metabolism in obese women and suggest that improved metabolic health associates with higher postabsorptive (fasting) BA synthesis. Furthermore, pre- vs. postintervention patterns of serum C4 following an OGTT support the hypothesis that responsiveness of BA synthesis to postprandial inhibition is improved after exercise and weight loss.NEW & NOTEWORTHY Exercise and weight loss in previously sedentary, insulin-resistant women facilitates a significant improvement in insulin sensitivity and fitness that may be linked to changes in bile acid metabolism. Diet-induced weight loss plus exercise-induced increases in fitness promote greater postabsorptive bile acid synthesis while also sensitizing the bile acid metabolic system to feedback inhibition during a glucose challenge when glucose and insulin are elevated.

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Enzymatic methods may underestimate the total serum bile acid concentration.

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Enzymatic methods may underestimate the total serum bile acid concentration.

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