Partial characterization of cytoprotective mechanisms of lecithin against bile salt-induced bile duct damage.
BACKGROUND
We recently demonstrated that cyclosporine A causes a disproportionate reduction of biliary lipid secretion, and this is inhibited by hydrophilic bile salts through the enhancing of biliary lecithin secretion. In the present study, the underlying mechanism of such a cytoprotective action of hydrophilic bile salts was determined with attention to the possible role of lecithin.


METHODS
Immortalized mouse cholangiocytes were cultured for 4 h with taurine conjugates of a hydrophobic bile salt (cholate [TC]), and hydrophilic bile salts (ursodeoxycholate [TUDC], betamuricholate [TbetaMC], and alphamuricholate [TalphaMC]), at 200 microM, in the presence or absence of lecithin (5, 10, 25, 50, 100, or 200 microM), followed by flow cytometric detection of apoptosis, using Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) staining. Cholangiocyte bile salt transporter mRNAs (apical sodium-dependent bile-salt transporter [Asbt] and multidrug resistance protein 3 [Mrp3]) were determined by reverse transcription-polymerase chain reaction (RT-PCR).


RESULTS
Apoptosis was induced by all of the bile salts (TC > TUDC, TbetaMC, and TalphaMC). Interestingly, bile salt-induced apoptosis was inhibited by lecithin in a concentration-dependent manner. Further, RT-PCR showed that the expressions of Asbt and Mrp3 mRNAs were enhanced by all the bile salts, whereas lecithin reduced Asbt expression, but enhanced Mrp3 expression.


CONCLUSIONS
These findings indicate that bile salts cause bile-duct cell damage through Asbt-mediated uptake, but that biliary lecithin physiologically inhibits such damage by reducing the expression of this transporter. In addition, the induction of Mrp3 expression by lecithin may play a role in inhibiting the accumulation of bile. Thus, the modulation of lecithin secretion into bile may be another important target for the treatment of biliary disorders.
Tsuboi
Kazuhiko
K
Department of Medicine and Molecular Science, Division of Frontier Medical Science Programs for Biomedical Research, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, 734-8551, Hiroshima, Japan.
Tazuma
Susumu
S
Nishioka
Tomoji
T
Chayama
Kazuaki
K
D000818:Animals; D017209:Apoptosis; D001647:Bile Acids and Salts / Q000494:pharmacology*; D001652:Bile Ducts / Q000166:cytology / Q000187:drug effects*; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D019610:Cytoprotection / Q000502:physiology*; D018432:Drug Resistance, Multiple; D051379:Mice; D008807:Mice, Inbred BALB C; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000502:physiology*; D029363:Organic Anion Transporters, Sodium-Dependent / Q000378:metabolism / Q000502:physiology*; D010713:Phosphatidylcholines / Q000502:physiology*; D027981:Symporters / Q000378:metabolism / Q000502:physiology*
D001647:Bile Acids and Salts; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D010713:Phosphatidylcholines; D027981:Symporters; C071908:sodium-bile acid cotransporter; C114462:multidrug resistance-associated protein 3