Received for publication December 5, 2005.
Revised June 4, 2006.
Accepted for publication June 5, 2006.

Inhibition of bile acid transport across NTCP and BSEP co-expressing LLC-PK1 cells by cholestasis-inducing drugs

Abstract

Vectorial transport of bile acids across hepatocytes is a major driving force for bile flow, and bile acid retention in the liver causes hepatotoxicity. The basolateral and apical transporters for bile acids are thought to be targets of drugs that induce cholestasis. Previously, we constructed polarized LLC-PK1 cells that express both a major bile acid uptake transporter human NTCP and the bile acid efflux transporter human BSEP and showed that monolayers of such cells can be used to characterize vectorial transcellular transport of bile acids. In the present study, we investigated whether cholestasis-inducing drugs could inhibit bile acid transport in such cells. Because fluorescent substrates allow the development of a high throughput screening method, we examined the transport by NTCP and BSEP of fluorescent bile acids as well as taurocholate. The aminofluorescein-tagged bile acids, CDCGamF and CGamF, were substrates of both NTCP and BSEP, and their basal-to-apical transport rates across co-expressing cell monolayers were 4.3-4.5 times those of the vector control, although smaller than for taurocholate. The well-known cholestatic drugs, rifampicin, rifamycin SV, glibenclamide and cyclosporin A, reduced the basal-to-apical transport and the apical efflux clearance of taurocholate across NTCP and BSEP co-expressing cell monolayers. Further analysis indicated that the drugs inhibited both NTCP and BSEP. Our study suggests that such co-expressing cells can provide a useful system for the identification of inhibitors of these two transport systems, including potential drug candidates.

Key words: ABC transporters, biliary excretion, drug induced liver disease, drug toxicity, hepatic transport, hepatobiliary transport, hepatotoxicity, pharmacokinetics, transporters

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