Proton magnetic resonance assay of total and taurine-conjugated bile acids in bile

Abstract

Biliary bile acids, coexisting with phospholipid and cholesterol, are partly conjugated with taurine. In the present report we show that total and taurine-conjugated bile acids in bile can be simultaneously and quantitatively measured by high-resolution 1H-nuclear magnetic resonance (1H-NMR) spectroscopy. We used a 7.05-Tesla NMR spectrometer to obtain the 1H-NMR spectra of model and biological biles. Only addition of trimethylsilyl-3-propionic acid sodium salt-D4 (TSP) to each sample as an internal standard was required in preparation for 1H-NMR measurement. In 1H-NMR spectra of rat bile, peaks of C-18 methyl protons of bile acids and of C-25 methylene protons on the taurine moiety of taurine-conjugated bile acids were detected at 0.7 ppm and 3.1 ppm, respectively. Peak areas, of C-18 and C-25 peaks, increased in proportion to the concentrations of bile acids or taurine-conjugated bile acids, even in the presence of phospholipid and cholesterol. The accuracy of NMR measurement of total and taurine-conjugated bile acids was confirmed by comparing the results of NMR with those of enzyme-fluorimetry. The results clearly demonstrate that 1H-NMR spectroscopy can be applied to the quantitative determination of total and taurine-conjugated bile acids in bile without troublesome preparative steps.—Ishikawa, H., T. Nakashima, K. Inaba, H. Mitsuyoshi, Y. Nakajima, Y. Sakamoto, T. Okanoue, K. Kashima, and Y. Seo. Proton magnetic resonance assay of total and taurine-conjugated bile acids in bile. J. Lipid Res. 1999. 40: 1920–1924.

Keywords

• 1H-NMR
• cholic acid
• phospholipid
• cholesterol