Effect of Membrane Cholesterol on BSEP/Bsep Activity: Species Specificity Studies for Substrates and Inhibitors

• Published in: Drug metabolism and disposition Vol. 37; no. 9; pp. 1878 - 1886
• Main Authors: KIS, Emese, LOJA, Eniko, NAGY, Tunde, SZENTE, Lajos, HEREDI-SZABO, Krisztina, KRAJCSI, Péter
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Pharmacology and Experimental Therapeutics 01.09.2009
• Subjects: Animals; ATP Binding Cassette Subfamily B Member 11; ATP-Binding Cassette Transporters - antagonists & inhibitors; ATP-Binding Cassette Transporters - metabolism; Bile Acids and Salts - metabolism; Biological and medical sciences; Biological Transport, Active; Blotting, Western; Cell Line; Cell Membrane - metabolism; Cholesterol - pharmacology; Chromans - metabolism; Cyclosporine - metabolism; Electrophoresis, Polyacrylamide Gel; Glyburide - metabolism; Humans; Hypoglycemic Agents - metabolism; Immunosuppressive Agents - metabolism; Insecta - metabolism; Kinetics; Medical sciences; Mice; Pharmacology. Drug treatments; Rats; Species Specificity; Substrate Specificity; Thiazolidinediones - metabolism; Vesicular Transport Proteins - metabolism; Substrate; Lipids; Inhibitor; Species specificity; Biological activity; Cholesterol
• ISSN: 0090-9556; 1521-009X
• DOI: 10.1124/dmd.108.024778

The efflux transporter responsible for the canalicular elimination of bile salts from the hepatocytes is the bile salt export pump (BSEP, ABCB11). Absence or inhibition of this transporter leads to bile salt retention in the hepatocyte and in turn can lead to cholestatic liver disease. We expressed the BSEP/Bsep protein from three species (human, rat, and mouse) in a baculovirus-infected Sf9 system. Vesicles prepared from these cells were used to evaluate bile salt transport of four conjugated bile salts. Because the Sf9 system contains less membrane cholesterol than the liver canalicular membrane, the effect of added cholesterol on the kinetics of BSEP/Bsep-mediated bile salt transport was also investigated. Cholesterol treatment increased the V max values in all the species, with the most pronounced effect observed in the rat transporter. In contrast, K m values, with the exception of glycochenodeoxycholate, remained largely unchanged. The species-specific bile salt transport inhibition potential of three compounds known to cause clinical cholestasis was investigated in vesicles containing BSEP/Bsep. Troglitazone and glibenclamide inhibited the BSEP/Bsep-mediated transport of different bile salts with similar affinities, whereas the potential of cyclosporine A to inhibit bile salt transport showed species- and bile salt-specific variations. In conclusion, the cholesterol-loaded Sf9 vesicles overexpressing BSEP/Bsep seem to be a useful system for the identification of potential cholestatic compounds and can also be used for the investigation of species specificity. We observed greater differences in IC 50 values for inhibitors than in K m values for substrates between species.