09/11/2009

Mouse Bsep ATPase assay: a nonradioactive tool for assessment of the cholestatic potential of drugs

E. Kis, Z. Rajnai, E. Ioja, K. Herédi-Szabó, T. Nagy, D. Méhn and P. Krajcsi

J Biomol Screen. 2009 Jan;14(1):10-5. Epub 2008 Nov 21.

Abstract

The mouse ortholog of the human bile salt export pump (BSEP) transporter was expressed in a baculovirus-infected insect cell (Sf9) system to study the effect of membrane cholesterol content on the transporter function. The transport activity of cholesterol-loaded mouse Bsep-HAM-Sf9 vesicles was determined in a vesicular transport assay with taurochenodeoxycholate (TCDC), a known BSEP substrate. Mouse Bsep transports TCDC at a high rate that can be sensitively detected in the ATPase assay. Cholesterol upload of the Sf9 membrane potentiates both TCDC transport and TCDC-stimulated ATPase activities. Inhibitory effect of BSEP interactors on probe substrate transport was tested in both vesicular transport and ATPase assays using cholesterol-loaded membrane vesicles. A good rank order correlation was found between IC(50) values measured in TCDC-stimulated mBsep ATPase assay and in the human BSEP vesicular transport assay utilizing taurocholate (TC) as probe substrate. This upgraded form of the mouse Bsep-HAM ATPase assay is a user friendly, sensitive, nonradioactive method for early high-throughput screening of drugs with BSEP-related cholestatic potential. It may complement the human BSEP-mediated taurocholate vesicular transport inhibition assay.

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