Multicomponent analysis of bile acids in faeces by anion exchange and capillary column gas-liquid chromatography: application in oxytetracycline treated subjects

Abstract

A method is described for the multicomponent analysis of bile acids in faeces. Following homogenization and extraction, bile acids are separated into several groups according to their mode of conjugation by anion exchange chromatography on DEAE-Sephadex A-25 in the acetate form. The different conjugate groups are then processed separately and quantified using capillary column gas-liquid chromatography (GC), the identity of the individual bile acid components being established by gas chromatography-mass spectrometry (GC-MS). The method permits the quantitative determination, with good precision, of unconjugated bile acids, their saponifiable derivatives, and their glycine-, taurine- and sulfated conjugates. In five healthy men the mean daily excretion of bile acids was 472 +/- 21.8 mumol (SEM) and the mean faecal concentration 7.74 +/- 1.07 mumol (SEM)/g dry weight. Free bile acids constituted 74.8% +/- 5.8% (SEM), saponifiable conjugates 23.5% +/- 5.8% (SEM) glycine-conjugates 0.7% +/- 0.2% (SEM), taurine-conjugates 0.2% +/- 0.07% (SEM), and their sulfated conjugates 0.8% +/- 0.1% (SEM) of total faecal bile acids. In addition to a detailed description of the methodology the effect of antibiotics on faecal bile acid profiles is presented. Oxytetracycline consistently decreased faecal concentrations of saponifiable derivatives of bile acids while increasing the taurine- and sulfated conjugates. The concentrations of the primary bile acids, cholic- and chenodeoxycholic acid, were higher during the course of oxytetracycline.