The Interaction Of Lipophilic Drugs With Liver Fatty Acid Binding Protein

Liver fatty acid-binding protein(LFABP) is a small protein that binds long-chain dietary fatty acids in the cytosol of the liver cells(enterocytes).Its molecular weight is about 14-15KD.The binding cavity of LFABP is much larger than its 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.The relationship of LFABP with some small molecular has been investivigaed extensively,neitheless,very little is known about the binding of LFABP with lipophilic drugs.Herein we describe the binding of several structurally diverse lipophilic drugs: ketoprofen,ibuprofen(both R-and S-isomers) to LFABP by comparing the differation binding betteen wild type LFABP and mutant type LFABP.We found that the binding affnity of mutanty type LFABP is decessed significantly.The affnity of different drugs was analyzed by CD,fluorescence assay and NMR titration.The rank order of affinity for LFABP of these compounds was found to be Indomethacin＞ketoprofen＞S-Ketoprofen＞Ibuprofen＞S-Ibuprofen＞Diltiazem.The binding affinities were not directly related to aqueous solubility or partition coefficient of the compounds;however,the freely water soluble drug diltiazem showed lest affinity to LFABP.Drug-LFABP interaction interfaces were defined by analysis of the 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 LFABP may increase the cytosolic solubility of these compounds and thereby facilitate drug transport from the liver across the enterocyte to sites of distribution and metabolism.