Received for publication February 6, 2008.
Revised June 7, 2008.
Accepted for publication July 22, 2008.

Effect of Albumin on the Biliary Clearance of Compounds in Sandwich-Cultured Rat Hepatocytes

Abstract

The purpose of the present study was to evaluate the effects of bovine serum albumin(BSA) and essentially fatty acid-free BSA (BSA-FAF) on the biliary clearance of compounds in sandwich-cultured rat hepatocytes. Unbound fraction (f_u), biliary excretion index (BEI), and unbound intrinsic biliary clearance (intrinsic Cl'_biliary) were determined for digoxin, pravastatin, and taurocholate in the absence or presence of BSA or BSA-FAF. BSA had little effect on the BEI or intrinsic Cl'_biliary of these compounds. Surprisingly, BSA-FAF decreased both BEI and intrinsic Cl'_biliary for digoxin and pravastatin, which represent low and moderately-bound compounds, respectively. The BEI and intrinsic Cl'_biliary of taurocholate, a highly-bound compound, were not altered significantly by BSA-FAF. Neither BSA nor BSA-FAF had a discernable effect on the bile canalicular networks, based on carboxydichlorofluorescein (CDF) retention. The addition of physiological concentrations of calcium, or the addition of fatty acids to BSA-FAF, was unable to restore the BEI or intrinsic Cl'_biliary of the model compounds to similar values in the absence or presence of BSA. Careful consideration is warranted when selecting the type of BSA for addition to in vitro systems such as sandwich-cultured rat hepatocytes.

Key words: biliary excretion, hepatobiliary disposition, hepatocytes, protein binding