The Interaction of Lipophilic Drugs with Intestinal Fatty Acid-binding Protein

Abstract

Intestinal fatty acid-binding protein (I-FABP) is a small protein that binds long-chain dietary fatty acids in the cytosol of the columnar absorptive epithelial cells (enterocytes) of the intestine. The binding cavity of I-FABP is much larger than is necessary to bind a fatty acid molecule, which suggests that the protein may be able to bind other hydrophobic and amphipathic ligands such as lipophilic drugs. Herein we describe the binding of three structurally diverse lipophilic drugs, bezafibrate, ibuprofen (both R- and S-isomers) and nitrazepam to I-FABP. The rank order of affinity for I-FABP determined for these compounds was found to be R-ibuprofen approximately bezafibrate > S-ibuprofen >> nitrazepam. The binding affinities were not directly related to aqueous solubility or partition coefficient of the compounds; however, the freely water-soluble drug diltiazem showed no affinity for I-FABP. Drug-I-FABP interaction interfaces were defined by analysis of chemical shift perturbations in NMR spectra, which revealed that the drugs bound within the central fatty acid binding cavity. Each drug participated in a different set of interactions within the cavity; however, a number of common contacts were observed with residues also involved in fatty acid binding. These data suggest that the binding of non-fatty acid lipophilic drugs to I-FABP may increase the cytosolic solubility of these compounds and thereby facilitate drug transport from the intestinal lumen across the enterocyte to sites of distribution and metabolism.

Characterization of the Binding of Drugs to Human Intestinal Fatty Acid Binding Protein (IFABP): Potential Role of IFABP as an Alternative to Albumin for in Vitro-in Vivo Extrapolation of Drug Kinetic Parameters

“…In contrast, K d values and capacities for the binding of phenytoin to BSA and IFABP were of a similar order (Table 3). The observation of two modes for the binding of phenytoin to IFABP is consistent with the docking of ibuprofen and bezafibrate into the binding cavity of the rat IFABP X-ray crystal structure, which suggests that, unlike fatty acids, some acidic drugs may bind to IFABP in two orientations (Velkov et al, 2005). It should be noted that the molecular masses of IFABP (Ϸ15 kDa) and albumin (Ϸ66 kDa) differ.…”

“…3B), which was best fit to the single binding site equation. The derived K d value for arachidonic acid binding to IFABP was 122 nM, which is within the range reported for the binding of saturated and unsaturated longchain fatty acids to rat IFABP (Richieri et al, 1994;Velkov et al, 2005).…”

“…The carboxylate head group of the fatty acid is deeply buried in the ligand binding site, where it hydrogen-bonds with Arg106 (Hamilton, 2004). Although it is known that rat IFABP and liver FABP (LFABP) bind a number of acidic and neutral drugs with varying affinities (Velkov et al, 2005(Velkov et al, , 2007Chuang et al, 2008), the binding of drugs to human IFABP has not been characterized.…”

Interaction of perfluoroalkyl acids with human liver fatty acid-binding protein

“…Fluorometric titrations of 1,8-ANS into hL-FABP and PFAAs displacement were performed as described previously (Carbone and Velkov 2013;Velkov et al 2005), with an adjustment in protein concentration (0.25 μM). All data modeling operations were performed as previously described using GraphPad Prism V5.0 (GraphPad software, San Diego, CA, USA).…”

Fatty Acid-binding Proteins 1 and 2 Differentially Modulate the Activation of Peroxisome Proliferator-activated Receptor α in a Ligand-selective Manner

“…Intracellular lipid-binding proteins (iLBPs) are small, soluble proteins that include the sterol carrier proteins, retinol-binding proteins, and cytosolic fatty acid-binding proteins (FABPs). iLBPs bind a range of molecules, including lipids, vitamins, and other poorly water-soluble ligands (7,8), and can facilitate the cellular and nuclear transport of endogenous PPAR activators. For example, FABP1 expression increases fatty acid delivery to the nucleus (9 -11) and enhances ligandmediated transactivation of PPAR␣ in COS-7 and HepG2 cells (12); cellular retinoic acid-binding protein II translocates to the nucleus on binding retinoic acid, associates directly with the retinoic acid receptor, and thereby facilitates delivery of retinoic acid to its receptor (13)(14)(15); adipocyte-fatty acid-binding protein (A-FABP or FABP4) binds the PPAR␥ agonist troglitazone, promoting nuclear localization and PPAR␥ activation.…”