Abstract
This work characterized for the first time the binding of acidic, neutral, and basic drugs to human intestinal fatty acid binding protein (IFABP) and, for comparison, to bovine serum albumin (BSA). In addition, the study investigated whether IFABP can substitute for BSA as a constituent in incubations of human liver microsomes (HLMs) in in vitro-in vivo extrapolation (IV-IVE) studies. Each molecule of purified IFABP bound a single molecule of the fluorescent probe 1-anilino-8-naphthalene sulfonate or arachidonic acid with Kd values similar to those reported for rat IFABP. Basic drugs bound negligibly to IFABP. Based on fraction unbound (fu) at a protein concentration of 0.5% (w/v), binding of acidic and neutral drugs ranged from minor (fu > 0.8) to moderate (fu 0.5–0.8). Of the compounds screened, highest binding to IFABP was observed for sulfinpyrazone (an acid) and β-estradiol (a neutral compound). However, binding to IFABP was lower than to BSA for all the drugs investigated. To determine the potential suitability of IFABP as an alternative to BSA for enhancing the prediction accuracy of IV-IVE based on human liver microsomal kinetic data, the kinetics of zidovudine (AZT) glucuronidation by HLM were characterized in the absence and presence of BSA and IFABP (0.5–2.5%, w/v). Each protein reduced the Km for AZT glucuronidation in a concentration-dependent manner, although a higher content of IFABP in incubations (2.5 versus 1–1.5% for BSA) was necessary for a 10-fold reduction in this parameter. The results indicate that IFABP is likely to have advantages over BSA in microsomal kinetic studies with drugs that bind extensively to albumin.
Footnotes
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This work was supported by a grant from the National Health and Medical Research Council of Australia.
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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.109.027656.
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ABBREVIATIONS: FABP, fatty acid binding protein; IFABP, intestinal fatty acid binding protein; LFABP, liver fatty acid binding protein; IV-IVE, in vitro-in vivo extrapolation; CLint, intrinsic clearance; CLH, hepatic clearance; UGT, UDP-glucuronosyltransferase; P450, cytochrome P450; HLM, human liver microsome; BSA, bovine serum albumin; HSA-FAF, essentially fatty acid free human serum albumin; AZT, zidovudine; ANS, 1-anilino-8-naphthalene sulfonate; HPLC, high-performance liquid chromatography; fu, fraction unbound.
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↵ The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.
- Accepted April 23, 2009.
- Received March 19, 2009.
- The American Society for Pharmacology and Experimental Therapeutics
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