Binding of cytochrome P450 monooxygenase and lipoxygenase pathway products by heart fatty acid-binding protein

Arachidonic acid metabolism by lipoxygenases and cytochrome P350 monooxygenases produces regioisomeric hydroperoxyeicosatetraenoic acids (HPETEs), hydroxyeicosatetranoic acids (HETEs), epoxyeicosatrienoic acids (EETs), and dihydroxyeicosatrienoic acids (DHETs), which serve as components of cell signaling cascades. Intracellular fatty acid-binding proteins (FABPs) may differentially bind these nonprostanoid oxygenated fatty acids, thus modulating their metabolism and activities. Vascular cells, which express heart FABP (H-FABP), utilize oxygenated fatty acids for regulation of vascular tone. Therefore, the relative affinities of H-FABP for several isomeric series of these compounds were measured by fluorescent displacement of 1-anilinonaphthalene-8-sulfonic acid (ANS). In general, H-FABP rank order affinities (arachidonic acid > EETs > HETEs > DHETs) paralleled reversed-phase high-performance liquid chromatography retention times, indicating that the differences in H-FABP affinity were determined largely by polarity. H-FABP displayed a similar rank order of affinity for compounds derived from linoleic acid. H-FABP affinity for 20-HETE [apparent dissociation constant (K-d') of 0.44 muM] was much greater than expected from its polarity, indicating unique binding interactions for this HETE, H-FABP affinity for 5,6-EET and 11,12-EET (K-d' Of similar to0.4 muM) was similar to 20-fold greater than for DHETs (K-d' of similar to8 muM). The homologous proteins, liver FABP and intestinal FABP, also displayed selective affinity for EET versus DHET. Thus, FABP binding of EETs may facilitate their intracellular retention whereas the lack of FABP affinity for DHETs may partially explain their release from cells. The affinity of H-FABP for EETs suggests that this family of intracellular proteins may modulate the metabolism, activities, and targeting of these potent eicosanoid biomediators.