Date Published: March 1, 2018
Publisher: Public Library of Science
Author(s): Peng-Li Hu, Ya-Hong Yuan, Tian-Li Yue, Chun-Feng Guo, Pratyoosh Shukla.
This study aimed to analyze the bile acid patterns in commercially available oxgall powders used for evaluation of the bile tolerance ability of probiotic bacteria. Qxgall powders purchased from Sigma-Aldrich, Oxoid and BD Difco were dissolved in distilled water, and analyzed. Conjugated bile acids were profiled by ion-pair high-performance liquid chromatography (HPLC), free bile acids were detected as their p-bromophenacyl ester derivatives using reversed-phase HPLC after extraction with acetic ether, and total bile acids were analyzed by enzymatic-colorimetric assay. The results showed that 9 individual bile acids (i.e., taurocholic acid, glycocholic acid, taurodeoxycholic acid, glycodeoxycholic acid, taurochenodeoxycholic acid, glycochenodeoxycholic acid, cholic acid, chenodeoxycholic acid, deoxycholic acid) were present in each of the oxgall powders tested. The content of total bile acid among the three oxgall powders was similar; however, the relative contents of the individual bile acids among these oxgall powders were significantly different (P < 0.001). The oxgall powder from Sigma-Aldrich was closer to human bile in the ratios of glycine-conjugated bile acids to taurine-conjugated bile acids, dihydroxy bile acids to trihydroxy bile acids, and free bile acids to conjugated bile acids than the other powders were. It was concluded that the oxgall powder from Sigma-Aldrich should be used instead of those from Oxoid and BD Difco to evaluate the bile tolerance ability of probiotic bacteria as human bile model.
Bile acids are synthesized from cholesterol in liver hepatocytes in humans and most animals, stored in the gallbladder, secreted into the small intestine after ingestion of a fatty meal, efficiently reabsorbed by the distal small intestine and returned to the liver via the portal vein . Bile acids are a digestive secretion that plays an important physiological role in the elimination of cholesterol from the body and in the intestinal solubilization and absorption of lipids .
The liquid chromatograms obtained from the analysis of the bile acid compositions of the three oxgall powders showed baseline separation and symmetrical sharp peaks for nearly all the conjugated bile acids (S1 Fig) and the free bile acids modified as p-bromophenacyl esters (S2 Fig) under the present chromatographic conditions. No severe peak tailing or leading was observed for any of the analytes. The major conjugated bile acids in the oxgall powders were identified as TCA, GCA, TDCA, GDCA, TCDCA and GCDCA, whereas the major free bile acids were characterized as CA, DCA and CDCA. The sum of the content of these individual bile acids in each of the oxgall powders exceeded 98% of total bile acids content determined with the enzymatic colorimetric method. The content of individual bile acids in the oxgall powders is summarized in Table 1. The content of the individual bile acids in each oxgall powder was significantly different (P < 0.05). In each oxgall powder, TCA was the most abundant conjugated bile acid, followed by GCA, TDCA, GDCA, TCDCA, and GCDCA, whereas CA was the most abundant free bile acid, followed by DCA and CDCA. Bile is a yellow-green aqueous solution whose major constituents include 70% bile salts, 22% phospholipids, 4% cholesterol, 3% proteins, and 0.3% bilirubin . The core antimicrobial constituents in bile are conjugated bile acids formed from cholesterol in the liver cells. In the gallbladder, duodenum, and the jejunum, bile acids are present almost exclusively as glycine or taurine derivatives . The human biliary bile acids consist mainly (~ 96%) of GCA, GCDCA, GDCA, TCA, TCDCA, and TDCA in a molar ratio of ~ 6:6:4:3:3:2 . Nine bile acids (i.e., TCA, GCA, TDCA, GDCA, TCDCA GCDCA, CA, CDCA, and DCA) were detected in all three oxgall powders from Sigma-Aldrich, Oxoid, and BD Difco. Although there was not considerable difference in the content of total bile acid among the three oxgall powders, significant difference was found in the relative content of the individual bile acids. Since the oxgall powder from Sigma-Aldrich was the most similar to human bile in the GCBA to TCBA, DHBA to THBA, and FBA to TBA ratios compared to those from Oxoid and BD Difco, it is the most suitable for evaluating the bile tolerance ability of probiotic bacteria instead of human bile. Source: http://doi.org/10.1371/journal.pone.0192964