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, biliary excretion index (BEI), and unbound intrinsic biliary clearance (intrinsic 
) 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 
of these compounds. Surprisingly, BSA-FAF decreased both BEI and intrinsic 
for digoxin and pravastatin, which represent low and moderately bound compounds, respectively. The BEI and intrinsic 
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 retention. Neither the addition of physiological concentrations of calcium nor the addition of fatty acids to BSA-FAF was able to restore the BEI or intrinsic 
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.
Footnotes
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This work was supported by National Institutes of Health Grant GM41935. K.K.W. was supported by a postdoctoral fellowship from GlaxoSmithKline Inc. Data were presented at the American Association of Pharmaceutical Scientists Annual Meeting and Exposition in San Diego, CA, November 2007.
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K.L.R.B. is cofounder and Chair of the Scientific Advisory Board for Qualyst, Inc., which has exclusively licensed the sandwich-cultured hepatocyte technology for quantification of biliary excretion (B-CLEAR).
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.108.020842.
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ABBREVIATIONS: BSA, bovine serum albumin; UGT, UDP-glucuronosyltransferase; BSA-FAF, essentially fatty acid-free bovine serum albumin; BEI, biliary excretion index; fu, unbound fraction; DMEM, Dulbecco's modified Eagle's medium; MEM, minimal essential medium; CDFDA, 5 (and 6)-carboxy-2′,7′-dichlorofluorescein diacetate; HBSS, Hanks' balanced salt solution; BCA, bicinchoninic acid; LC/MS/MS, liquid chromatography with detection by tandem mass spectrometry; CDF, 5 (and 6)-carboxy-2′,7′-dichlorofluorescein; intrinsic
, unbound intrinsic biliary clearance; Ntcp, sodium-taurocholate cotransporting polypeptide; Oatp/OATP, organic anion-transporting polypeptide. - Received February 6, 2008.
- Accepted July 22, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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Effect of Albumin on the Biliary Clearance of Compounds in Sandwich-Cultured Rat Hepatocytes
