title: Influence of charge and steric bulk in the C-24 region on the interaction of bile acids with human apical sodium-dependent bile acid transporter.
abstract: The human apical sodium-dependent bile acid transporter (hASBT) is a potential target for drug delivery, but an understanding of hASBT substrate requirements is limited. The objective of this study was to evaluate the influence of ionic character and steric bulk in the C-24 region of bile acid conjugates in governing interaction with hASBT. Ionic character was studied using chenodeoxycholate (CDCA) conjugates of glutamic acid and lysine, which varied in charge (monoanionic, dianionic, cationic, neutral, and zwitterionic) and location of charge (proximal or distal to C-24). Steric effects were evaluated using ester conjugates that varied in ester substituent size (methyl, benzyl, and tert-butyl) and location (proximal and/or distal). Conjugate interaction with hASBT was assessed via transport and inhibition studies, using a hASBT-MDCK monolayer. Monoanionic, cationic, and neutral conjugates of CDCA exhibited high inhibitory potency (Ki<10 microM). High inhibition potency of neutral and cationic conjugates indicated that a negative charge is not essential for hASBT binding. Dianionic conjugates exhibited low inhibition potency (Ki>100 microM). Conjugates with a single bulky ester substituent proximal or distal to the C-24 region exhibited high inhibition potency. However, two bulky substituents practically abolished interaction. In transport studies, monoanionic conjugates were high affinity hASBT substrates. Meanwhile, cationic and zwitterionic conjugates were not substrates for hASBT. Overall, C-24 ionic character influenced interaction with hASBT. Although the presence of a single negative charge was not essential for interaction with hASBT, monoanionic conjugates were favored for hASBT-mediated transport compared to cationic and zwitterionic conjugates.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Maryland 21201, USA.
authors.forename: Anand
authors.initials: A
authors.lastname: Balakrishnan
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Wring
authors.forename: Andrew
authors.initials: A
authors.lastname: Coop
authors.forename: James E
authors.initials: JE
authors.lastname: Polli
mesh_terms: D001647:Bile Acids and Salts / Q000737:chemistry* / Q000378:metabolism*; D001693:Biological Transport, Active; D002478:Cells, Cultured; D002635:Chenodeoxycholic Acid / Q000737:chemistry; D015195:Drug Design; D006801:Humans; D007477:Ions / Q000378:metabolism; D008968:Molecular Conformation; D029363:Organic Anion Transporters, Sodium-Dependent / Q000737:chemistry* / Q000378:metabolism*; D027981:Symporters / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D001647:Bile Acids and Salts; D007477:Ions; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; D002635:Chenodeoxycholic Acid; C071908:sodium-bile acid cotransporter