title: Membrane/Water Partition Coefficients of Bile Salts Determined Using Laurdan as a Fluorescent Probe.
abstract: The interaction of liposomal membranes composed of soybean phosphatidylcholine with the bile salts (BSs) cholate (Ch), glycocholate (GC), chenodeoxycholate (CDC), and glycochenodeoxycholate (GCDC) was studied. The BSs differed with regard to their lipophilicity, pKa values, and the size of their hydrophilic moiety. Their membrane interactions were investigated using Laurdan as a membrane-anchored fluorescent dye. The apparent membrane/water partition coefficient, D, at pH 7.4 was calculated from binding plots and compared with direct binding measurements using ultracentrifugation as a reference. The Laurdan-derived LogD values at pH 7.4 were found to be 2.10 and 2.25 for the trihydroxy BSs, i.e., Ch and GC, and 2.85 and 2.75 for the dihydroxy BSs, i.e., CDC and GCDC, respectively. For the membrane-associated glycine-conjugated GC and GCDC (pKavalues of ∼3.9), no differences in the Laurdan spectra of the respective BS were found at pH 6.8, 7.4, and 8.2. Unconjugated Ch and CDC (pKavalues of ∼5.0) showed pronounced differences at the three pH values. Furthermore, the kinetics of membrane adsorption and transbilayer movement differed between conjugated and unconjugated BSs as determined with Laurdan-labeled liposomes.
authors.affiliation: University of Freiburg, Freiburg, Germany.
authors.forename: Alice
authors.initials: A
authors.lastname: Strohmeier
authors.affiliation: University of Freiburg, Freiburg, Germany.
authors.forename: Gesche
authors.initials: G
authors.lastname: Först
authors.affiliation: University of Freiburg, Freiburg, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Tauber
authors.affiliation: University of Freiburg, Freiburg, Germany. Electronic address: rolf.schubert@pharmazie.uni-freiburg.de.
authors.forename: Rolf
authors.initials: R
authors.lastname: Schubert
mesh_terms: D015081:2-Naphthylamine / Q000031:analogs & derivatives* / Q000737:chemistry; D001647:Bile Acids and Salts / Q000737:chemistry* / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption; D007553:Isotope Labeling; D007700:Kinetics; D007848:Laurates / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D014867:Water / Q000737:chemistry*
chemical_list: D001647:Bile Acids and Salts; D005456:Fluorescent Dyes; D007848:Laurates; D008081:Liposomes; D014867:Water; D015081:2-Naphthylamine; C065580:laurdan