PubMed · 2649359
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M Färkkilä. 1989. [Bile acids].. https://pubmed.ncbi.nlm.nih.gov/2649359/
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Clostridium scindens is a keystone bacterial species in the mammalian gut that, while low in abundance, has a significant impact on bile acid and steroid metabolism. Numerous studies indicate that the two most studied strains of C. scindens (i.e. ATCC 35704 and VPI 12708) are important for a myriad of physiological processes in the host. We focus on both historical and current microbiological and molecular biology work on the Hylemon-Björkhem pathway and the steroid-17,20-desmolase pathway that were first discovered in C. scindens. Our most recent analysis now calls into question whether strains currently defined as C. scindens represent two separate taxonomic groups. Future directions include developing genetic tools to further explore the physiological role of bile acid and steroid metabolism by strains of C. scindens and the causal role of these pathways in host physiology and disease.
Cholesterol crystallization is a key step in gallstone formation and is influenced by numerous factors. Human bile contains various bile salts having different hydrophobicity and micelle-forming capacities, but the importance of lipid composition to bile metastability remains unclear. This study investigated the effect of bile salts on cholesterol crystallization in model bile (MB) systems. Supersaturated MB systems were prepared with an identical composition on a molar basis (taurocholate/phosphatidylcholine/cholesterol, 152 mM:38 mM: 24 mM), except for partial replacement of taurocholate (10, 20, and 30%) with various taurine-conjugated bile salts. Cholesterol crystallization was quantitatively estimated by spectrophotometrically measuring crystal-related turbidity and morphologically scanned by video-enhanced microscopy. After partial replacement of taurocholate with hydrophobic bile salts, cholesterol crystallization increased dose-dependently without changing the size of vesicles or crystal morphology and the rank order of crystallization was deoxycholate>chenodeoxycholate>cholate (control MB). All of the hydrophilic bile salts (ursodeoxycholate, ursocholate and beta-muricholate) inhibited cholesterol precipitation by forming a stable liquid-crystal phase, and there were no significant differences among the hydrophilic bile-salt species. Cholesterol crystallization was markedly altered by partial replacement of bile salts with a different hydrophobicity. Thus minimal changes in bile-salt composition may dramatically alter bile lipid metastability.
A supercritical fluid extraction (SFE) method for the extraction of bile acids from faeces is described. HPLC with pulsed amperometric detection was used to examine and confirm the recovery of bile acids. The analytes were extracted within a period of 75 min using supercritical carbon dioxide at a pressure of 34.5 MPa and a temperature of 90 degrees C. In developing this method the following parameters were investigated: temperature, pressure, and extraction time. Two alternative methods of sample preparation were also investigated with a view to reducing the overall analysis time. The method was validated for the major primary and secondary bile acids found in faeces. It was found that the overall mean +/- SD recoveries were 102.1+/-7.92%, 111.6+/-9.91%, 112.1+/-9.92% and 113.7+/-9.92% for dry samples and 108.5+/-15.77%, 110.0+/-7.22%, 115.9+/-11.11% and 106.6+/-9.16% for wet samples with respect to cholic, deoxycholic, chenodeoxycholic and lithocholic acid. The SFE is an alternative to the traditional methods available. The extraction is relatively easy to conduct and does not utilise as much glassware, solvents or time.