glycodeoxycholic-acid and ursodoxicoltaurine

Topics: Bile; Bile Acids and Salts; Cholecystectomy; Gallbladder; Glycochenodeoxycholic Acid; Glycodeoxycholic Acid; Humans; Hydrogen; Magnetic Resonance Spectroscopy; Micelles; Phospholipids; Taurochenodeoxycholic Acid; Taurocholic Acid; Ursodeoxycholic Acid

Bile salts have been hypothesized to mediate cytotoxicity by increasing membrane permeability to aqueous solutes. We examined whether submicellar bile salt concentrations affect model and native membrane permeability to small uncharged molecules such as water, urea, and ammonia. Osmotic water permeability (Pf) and urea permeability were measured in large unilamellar vesicles composed with egg yolk phosphatidylcholine (EYPC) +/- cholesterol (Ch) or rat liver microsomal membranes by monitoring self-quenching of entrapped carboxyfluorescein (CF). Ammonia permeability was determined utilizing the pH dependence of CF fluorescence. Submicellar bile salt concentrations did not significantly alter Pf of EYPC +/- Ch or rat liver microsomal membranes. At taurodeoxycholate (TDC) or tauroursodeoxycholate concentrations approaching those that solubilized membrane lipids, CF leakage occurred from vesicles, but Pf remained unchanged. Higher bile salt concentrations (0.5-2 mM TDC) did not alter Pf of equimolar EYPC/Ch membranes. The activation energy for transmembrane water flux was unchanged (12.1 +/- 1.2 kcal/mol for EYPC) despite the presence of bile salts in one or both membrane hemileaflets, suggesting strongly that bile salts do not form transmembrane pores that facilitate water flux. Furthermore, submicellar bile salt concentrations did not increase membrane permeability to urea or ammonia. We conclude that at submicellar concentrations, bile salts do not form nonselective convective channels that facilitate transmembrane transport of small uncharged molecules. These results suggest that bile salt-mediated transport of specific substrates, rather than nonselective enhancement of membrane permeability, underlies bile salt cytotoxicity for enterocytes and hepatocytes.

Topics: Ammonia; Animals; Bile Acids and Salts; Calorimetry; Dose-Response Relationship, Drug; Glycodeoxycholic Acid; Intracellular Membranes; Kinetics; Light; Liposomes; Male; Micelles; Microsomes, Liver; Models, Biological; Molecular Weight; Permeability; Phosphatidylcholines; Rats; Rats, Sprague-Dawley; Scattering, Radiation; Solutions; Taurochenodeoxycholic Acid; Taurodeoxycholic Acid; Urea

Separation of the glycine and taurine conjugates of ursodeoxycholic acid from those of lithocholic acid, chenodeoxycholic acid, deoxycholic acid, and cholic acid by thin-layer chromatography is described. Thus, on running a silica gel G plate first in a solvent system of n-butanol-water 20:3 and then in a second solvent system of chloroform-isopropanol-acetic acid-water 30:20:4:1, all the above-mentioned conjugated bile acids are separated from one another. The application of this method to study the change in the biliary bile acid conjugation pattern in ursodeoxycholic acid-fed gallstone patients is described.

Topics: Chenodeoxycholic Acid; Chromatography, Thin Layer; Deoxycholic Acid; Glycine; Glycochenodeoxycholic Acid; Glycocholic Acid; Glycodeoxycholic Acid; Lithocholic Acid; Taurochenodeoxycholic Acid; Taurocholic Acid; Taurodeoxycholic Acid; Taurolithocholic Acid; Ursodeoxycholic Acid