P-glycoprotein function and expression during obstructive cholestasis in rats

Area of Science:

• Pharmacology
• Hepatology
• Nephrology

Background:

• Bile duct obstruction (BDO) in rats induces acute and chronic cholestasis.
• P-glycoprotein (P-gp) is a key transporter involved in drug excretion.
• Rhodamine 123 (Rho123) is a known P-gp substrate used to study transporter function.

Purpose of the Study:

• To evaluate the in vivo biliary and renal excretion of Rho123 in rats with cholestasis.
• To assess the correlation between P-gp expression and Rho123 clearance during cholestasis.
• To understand the impact of cholestasis on the elimination of P-gp substrates.

Main Methods:

• Rats underwent bile duct obstruction (BDO) for 1 day (BDO1) or 7 days (BDO7).
• Rho123 clearance was measured in bile and urine after achieving steady-state plasma concentrations.
• P-gp expression in liver and kidney tissues was quantified using immunohistochemistry and immunoblotting.

Main Results:

• Liver P-gp expression was significantly upregulated in both acute and chronic cholestasis, with altered localization.
• Kidney P-gp expression increased after 1 day of BDO but decreased by 7 days.
• Biliary and renal clearances of Rho123 did not directly mirror P-gp expression changes; biliary clearance decreased then recovered, while renal clearance was preserved then reduced.
• Conjugated bilirubin excretion was significantly reduced in both cholestatic groups.

Conclusions:

• Extrahepatic cholestasis induces time-dependent alterations in Rho123 elimination that do not precisely reflect P-gp expression changes in rat liver and kidney.
• These findings suggest a potential mechanism for impaired P-gp substrate elimination in clinical cholestasis.
• The study highlights the complex relationship between transporter expression and function during cholestatic conditions.