Physicochemical properties of bile acids and their relationship to biological properties: an overview of the problem.

The hydrophobic-hydrophilic balance of bile salts. Inverse correlation between reverse-phase high performance liquid chromatographic mobilities and micellar cholesterol-solubilizing capacities.

High pressure liquid chromatographic analysis of conjugated bile acids in human bile: simultaneous resolution of sulfated and unsulfated lithocholyl amidates and the common conjugated bile acids.

Review of operating principle and applications of the charged aerosol detector.

The bile salts chenodeoxycholate (CDC) and its 7 beta-hydroxy epimer ursodeoxycholate (UDC) are administered therapeutically (as acids) to dissolve cholesterol gallstones in man Since their micellarr solutions and those of their physiological conjugates differ strikingly in their capacities to solubilize cholesterol, we studied the interfacial and micellar properties of the epimers by a number of complimentary physical--chemical methods and correlated these with their solubilizing capacities The critical micella concentrations (cmc) estimated by surface tension, dye titration, and turbidimetry were similar (1-5 mM), varying slightly with the bile salt species, the method employed, NaCl concentration (0-1 M), and temperature (10-50 degrees C) The weight-average aggregation number (number of monomers per micelle, nw) at the cmc, derived from Debye plots of conventional light-scattering data and from the mean hydrodynamic radii of the micelles obtained by quasi-elastic light-scattering spectroscopy, revealed no appreciable differences between the UDC-CDC epimers or between their conjugates From the mean hydrodynamic radii, the taurine conjugates were found to form larger micelles (nw = 15-17) than the glycine conjugates (nw = 13) which in turn were larger than the free species (n w = 5), respectively Consistent with previous experimental deductions, free and conjugated CDC micelles grew slightly in size with increases in total lipid concentration, but UDC micelles did not With solubilization of cholesterol monohydrate, the mean sizes of UDC (134 A) and of CDC (13 A) micelles in 10 g/dL solutions did not change appreciably, even as the cholesterol saturation limit was reached At the air-5 M NaCl (pH 2) interface, the glycine conjugates formed more expanded monomolecular films than the free acid, and both UDC and its glycine conjugate collapsed at surface pressures that were 10-20 mN m-1 lower than the collapse pressures of monolayers of CDC and its glycine conjugate Similarly, adsorbed monolayers of ionized UDC and its taurine conjugate lowered the surface tension of water approximately 5 mN m-1 less than equimolar concentrations of CDC and its taurine conjugate By employing high-performance reversed-phase liquid chromatography (HPLC), we measured the relative hydrophilic--hydrophobic properties of the bile salts and found a close correlation between HPLC mobility and cholesterol-solubilizing cpacity Assuming a single cholesterol binding site per micelle, we estimated from the nw values and bile salt/cholesterol saturation ratios that the magnitude of the cholesterol binding constant (K) was 57 X 10(6) L/mol for unconjugated CDC and 25 X 10(5) L/mol for unconjugated UDC at 30 degrees C These results suggest that the differences in cholesterol-solubilizing capacities of CDC and UDC and their conjugates are due to subtle differences in micellar structure, resulting from the axial or equatorial orientation of the 7-hydroxyl function and the various conjugating groups

Thermodynamic and molecular basis for dissimilar cholesterol-solubilizing capacities by micellar solutions of bile salts: cases of sodium chenodeoxycholate and sodium ursodeoxycholate and their glycine and taurine conjugates

Craig A. Bloch

Papers

Determination of conjugated bile acids in human bile and duodenal fluid by reverse-phase high-performance liquid chromatography.