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PubMed2006

Vectorial transport of unconjugated and conjugated bile salts by monolayers of LLC-PK1 cells doubly transfected with human NTCP and BSEP or with rat Ntcp and Bsep.

Na(+)-taurocholate-cotransporting peptide (NTCP)/SLC10A1 and bile salt export pump (BSEP)/ABCB11 synergistically play an important role in the transport of bile salts by the hepatocyte. In this study, we transfected human NTCP and BSEP or rat Ntcp and Bsep into LLC-PK1 cells, a cell line devoid of bile salts transporters. Transport by these cells was characterized with a focus on substrate specificity between rats and humans. The basal to apical flux of taurocholate across NTCP- and BSEP-expressing LLC-PK1 monolayers was 10 times higher than that in the opposite direction, whereas the flux across the monolayer of control and NTCP or BSEP single-expressing cells did not show any vectorial transport. The basal to apical flux of taurocholate was saturated with a K(m) value of 20 microM. Vectorial transcellular transport was also observed for cholate, chenodeoxycholate, ursodeoxycholate, their taurine and glycine conjugates, and taurodeoxycholate and glycodeoxycholate, whereas no transport of lithocholate was detected. To evaluate the respective functions of NTCP and BSEP and to compare them with those of rat Ntcp and Bsep, we calculated the clearance by each transporter in this system. A good correlation in the clearance of the examined bile salts (cholate, chenodeoxycholate, ursodeoxycholate, and their taurine or glycine conjugates) was observed between transport by human and that of rat transporters in terms of their rank order: for NTCP, taurine conjugates > glycine conjugates > unconjugated bile salts, and for BSEP, unconjugated bile salts and glycine conjugates > taurine conjugates. In conclusion, the substrate specificity of human and rat NTCP and BSEP appear to be very similar at least for monovalent bile salts under physiological conditions.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2002

Bile salt aggregates in the gas phase: an electrospray ionization mass spectrometric study.

Helical and ordered structures have previously been identified by X-ray diffraction analysis in crystals and fibers of bile salts, and proposed as models of the micellar aggregates formed by trimeric or dimeric units of dihydroxy and trihydroxy salts, respectively. These models were supported by the results of studies of micellar bile salt solutions performed with different experimental techniques. The study has now been extended to the gas phase by utilizing electrospray ionization mass spectrometry (ESIMS) to investigate the formation and the composition of aggregates stabilized by noncovalent interactions, including polar (ion-ion, ion-dipole, dipole-dipole, hydrogen bonding etc.) and apolar (van der Waals and repulsive) interactions. The positive and negative ESIMS spectra of sodium glycodeoxycholate (NaGDC), taurodeoxycholate (NaTDC), glycocholate (NaGC), and taurocholate (NaTC) aqueous solutions, recorded under different experimental conditions, show in the first place that aggregates analogous to those present in micellar solutions do also exist in the gas phase. Furthermore, consistently with the condensed-phase model, the positive-ion spectra show that the trimers are the most stable oligomers among the aggregates of dihydroxy salts (NaGDC and NaTDC) whilst the dimers are the most stable among the aggregates of trihydroxy salts (NaGC and NaTC). Moreover, the binding energy of the constituent glycocholate salt units in most gaseous oligomers exceeds that of the corresponding taurocholate units. The ESIMS evidence has been confirmed by vapor-pressure measurements performed on NaGC and NaTC crystals and NaGDC and NaTDC fibers, the results of which show that the evaporation enthalpy of glycocholate exceeds that of taurocholate by some 50 kJ mol(-1).

Algorithms↗

PubMed1990

Comparison of bile salt perturbation of duodenal and jejunal isolated brush-border membranes.

Rabbit duodenal and jejunal brush-border membrane vesicle integrity, fluidity and passive proton permeability were studied after in vitro exposure to deoxycholate, glycodeoxycholate or taurodeoxycholate. Duodenal and jejunal membrane mean vesicle volume [0.54 (0.05) and 0.54 (0.03) microliters/mg, mean values with SE in parentheses], and proton permeability [6.30 (0.02) x 10(-4) and 5.59 (0.17) x 10(-4) cm.S-1] were similar, while membrane fluidity was slightly, but significantly, greater in jejunal membranes [diphenylhexatriene fluorescence anisotropy, (r0/r)-1 = 0.499 (0.013) and 0.572 (0.012)]. The three bile salts (0.1-5.0 mM) caused concentration-related decreases in vesicle integrity as assessed by [14C]glucose retention at equilibrium. Jejunal membranes were more sensitive at low bile salt concentrations, 0.1 and 0.5 mM. With high concentrations of bile salts, 5 mM, above their critical micelle concentrations, less than 10% of jejunal or duodenal vesicles remained. The bile salts caused concentration-related increases in jejunal membrane fluidity over the range 0.1-1.0 mM bile salt, but duodenal membrane fluidity was only increased at the highest concentration of bile salt. Proton permeability (Pnet) of the membranes was increased by the bile salts (0.1-1.0 mM), and again the jejunal membranes were more sensitive; Pnet increased by approximately 120, 150 and 170 in duodenal, and 150, 220 and 380% in jejunal membranes, with deoxycholate at 0.1, 0.5 and 1.0 mM, respectively. There were no consistent differences in the potency of the unconjugated and conjugated bile salts. The three variables were only significantly correlated for duodenal membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2005

Bile salts inhibit growth and induce apoptosis of culture human normal esophageal mucosal epithelial cells.

AIM: To investigate the effect of six bile salts: glycocholate (GC), glycochenodeoxycholate (GCDC), glycodeoxycholate (GDC), taurocholate (TC), taurochenodeoxycholate (TCDC), taurodeoxycholate (TDC), and their mixture on cultured human normal esophageal mucosal epithelial cells. METHODS: Human normal esophageal mucosal epithelial cells were cultured with serum-free keratinocyte medium.3-[4,5-Dimethylthiaolyl]-2,5-diphenyl-tetrazolium bromide assay was applied to the detection of cell proliferation. Apoptotic morphology was observed by phase-contrast video microscopy and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. Sub-G1 DNA fragmentations and early apoptotic cells were assayed by flow cytometry (FCM) with propidium iodide (PI) staining and annexin V-FITC conjugated with PI staining. Apoptotic DNA ladders on agarose gel electrophoresis were observed. RESULTS: Except for GC, GCDC, GDC, TC, TCDC, TDC and their mixture could initiate growth inhibition of esophageal mucosal epithelial cells in a dose- and time-dependent manner. TUNEL and FCM assays demonstrated that the bile salts at 500 mumol/L and their mixture at 1 500 micromol/L induced apoptosis except for GC. The percentage of sub-G1 detected by FCM with PI staining was 83.5% in cells treated with 500 micromol/L TC for 2 h, and 19.8%, 20.4%, 25.6%, 13.5%, and 75.8% in cells treated with 500 micromol/L GCDC, TCDC, GDC, TDC, and 1 500 micromol/L mixture for 24 h, respectively, which were higher than that of the control (1.5%). The percentage was 1.4% in cells with 500 micromol/L GC for 24 h. DNA ladders on agarose gel electrophoresis were seen in cells treated with 500 micromol/L TC for 2 h and 1 500 micromol/L mixture for 24 h. CONCLUSION: All GCDC, GDC, TC, TCDC, TDC and their mixture can inhibit growth and induce apoptosis of cultured human normal esophageal mucosal epithelial cells, but GC is well tolerated by the cells.

Apoptosis↗