Brandy Garzel1, Tao Hu1, Linhao Li1, Yuanfu Lu2, Scott Heyward3, James Polli1, Lei Zhang4, Shiew-Mei Huang4, Jean-Pierre Raufman5,6, Hongbing Wang7. 1. Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, 20 Penn Street, Baltimore, Maryland, 21201, USA. 2. Key Laboratory of Pharmacology of Ministry of Education, Zunyi Medical University, Zunyi, China. 3. BioIVT, 1450 S Rolling Road, Baltimore, Maryland, 21227, USA. 4. Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland, 20993, USA. 5. Division of Gastroenterology and Hepatology, University of Maryland School of Medicine, 22 South Greene Street, Baltimore, Maryland, 21201, USA. 6. VA Maryland Health Care System, 10 N. Greene Street, Baltimore, Maryland, 21201, USA. 7. Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, 20 Penn Street, Baltimore, Maryland, 21201, USA. hongbing.wang@rx.umaryland.edu.
Abstract
PURPOSE: The bile salt export pump (BSEP), a key player in hepatic bile acid clearance, has been the center of research on drug-induced cholestasis. However, such studies focus primarily on the direct inhibition of BSEP, often overlooking the potential impact of transcriptional repression. This work aims to explore the disruption of bile acid efflux caused by drug-induced BSEP repression. METHODS: BSEP activity was analyzed in human primary hepatocytes (HPH) using a traditional biliary-clearance experiment and a modified efflux assay, which includes a 72-h pretreatment prior to efflux measurement. Relative mRNA and protein expressions were examined by RT-PCR and Western blotting, respectively. RESULTS: Metformin concentration-dependently repressed BSEP expression in HPH. Although metformin did not directly inhibit BSEP activity, longer metformin exposure reduced BSEP transport function in HPH by down-regulating BSEP expression. BSEP repression by metformin was found to be AMP-activated protein kinase-independent. Additional screening of 10 reported cholestatic non-BSEP inhibitors revealed that the anti-cancer drug tamoxifen also markedly repressed BSEP expression and reduced BSEP activity in HPH. CONCLUSIONS: Repression of BSEP alone is sufficient to disrupt hepatic bile acid efflux. Metformin and tamoxifen appear to be prototypes of a class of BSEP repressors that may cause drug-induced cholestasis through gene repression instead of direct BSEP inhibition.
PURPOSE: The bile salt export pump (BSEP), a key player in hepatic bile acid clearance, has been the center of research on drug-induced cholestasis. However, such studies focus primarily on the direct inhibition of BSEP, often overlooking the potential impact of transcriptional repression. This work aims to explore the disruption of bile acid efflux caused by drug-induced BSEP repression. METHODS:BSEP activity was analyzed in human primary hepatocytes (HPH) using a traditional biliary-clearance experiment and a modified efflux assay, which includes a 72-h pretreatment prior to efflux measurement. Relative mRNA and protein expressions were examined by RT-PCR and Western blotting, respectively. RESULTS:Metformin concentration-dependently repressed BSEP expression in HPH. Although metformin did not directly inhibit BSEP activity, longer metformin exposure reduced BSEP transport function in HPH by down-regulating BSEP expression. BSEP repression by metformin was found to be AMP-activated protein kinase-independent. Additional screening of 10 reported cholestatic non-BSEP inhibitors revealed that the anti-cancer drug tamoxifen also markedly repressed BSEP expression and reduced BSEP activity in HPH. CONCLUSIONS: Repression of BSEP alone is sufficient to disrupt hepatic bile acid efflux. Metformin and tamoxifen appear to be prototypes of a class of BSEP repressors that may cause drug-induced cholestasis through gene repression instead of direct BSEP inhibition.
Authors: Brandy Garzel; Hui Yang; Lei Zhang; Shiew-Mei Huang; James E Polli; Hongbing Wang Journal: Drug Metab Dispos Date: 2013-12-12 Impact factor: 3.922
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