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Adaptive changes in hepatobiliary transporter expression in primary biliary cirrhosis
Gernot Zollner1, Peter Fickert, Dagmar Silbert
1Division of Gastroenterology and Hepatology, Department of Medicine, Karl-Franzens University, Auenbruggerplatz 15, A-8036, Graz, Austria.
Journal of Hepatology
|May 24, 2003
Summary
In primary biliary cirrhosis (PBC), reduced uptake transporters (NTCP, OATP2) and increased efflux pumps (MDR1, MDR3, MRP3) may protect the liver from toxic bile acids. Canalicular pumps (BSEP, MRP2) remained functional.
Area of Science:
- Hepatology
- Molecular Biology
- Biochemistry
Background:
- Primary biliary cirrhosis (PBC) is a cholestatic liver disease characterized by progressive destruction of intrahepatic bile ducts.
- Understanding alterations in hepatobiliary transporter expression is crucial for elucidating PBC pathogenesis and cholestasis.
- This study focuses on advanced stages of PBC, investigating key transporters involved in bile salt, organic anion, and phospholipid transport.
Purpose of the Study:
- To determine the expression levels and localization of critical hepatobiliary transporters in liver tissue from patients with advanced PBC.
- To investigate the relationship between transporter expression and hepatic bile acid composition in PBC.
- To explore potential adaptive mechanisms in PBC-related cholestasis.
Main Methods:
- Quantitative assessment of transporter mRNA and protein using RT-PCR and Western blotting.
- Immunohistochemistry and immunofluorescence microscopy to evaluate transporter tissue distribution and localization.
- Gas chromatography-mass spectrometry for measuring hepatic bile acid profiles.
Main Results:
- Down-regulation of basolateral uptake transporters, including sodium/taurocholate cotransporter (NTCP) and organic anion transporting protein 2 (OATP2).
- Preserved expression and proper canalicular localization of canalicular efflux pumps, such as bile salt export pump (BSEP) and multidrug resistance-associated protein 2 (MRP2).
- Upregulation of canalicular P-glycoproteins (MDR1, MDR3) and basolateral efflux pump MRP3; inverse correlation of OATP2 and MRP2 with hydrophobic bile acids.
Conclusions:
- Reduced expression of basolateral uptake systems in PBC may limit the entry of potentially toxic substances into hepatocytes.
- Maintenance and upregulation of efflux pumps suggest an adaptive response to prevent the accumulation of harmful biliary constituents.
- These transporter alterations may contribute to the cholestatic phenotype in advanced PBC.