Fatty acid-binding capacity of cytosolic proteins of various rat tissues: effect of postnatal development, starvation, sex, clofibrate feeding and light cycle

Recent insights into the biological functions of liver fatty acid binding protein 1

Over four decades have passed since liver fatty acid binding protein (FABP)1 was first isolated. There are few protein families for which most of the complete tertiary structures, binding properties, and tissue occurrences are described in such detail and yet new functions are being uncovered for this protein. FABP1 is known to be critical for fatty acid uptake and intracellular transport and also has an important role in regulating lipid metabolism and cellular signaling pathways. FABP1 is an important endogenous cytoprotectant, minimizing hepatocyte oxidative damage and interfering with ischemia-reperfusion and other hepatic injuries. The protein may be targeted for metabolic activation through the cross-talk among many transcriptional factors and their activating ligands. Deficiency or malfunction of FABP1 has been reported in several diseases. FABP1 also influences cell proliferation during liver regeneration and may be considered as a prognostic factor for hepatic surgery. FABP1 binds and modulates the action of many molecules such as fatty acids, heme, and other metalloporphyrins. The ability to bind heme is another cytoprotective property and one that deserves closer investigation. The role of FABP1 in substrate availability and in protection from oxidative stress suggests that FABP1 plays a pivotal role during intracellular bacterial/viral infections by reducing inflammation and the adverse effects of starvation (energy deficiency).

Myocardial fatty acid metabolism in health and disease

There is a constant high demand for energy to sustain the continuous contractile activity of the heart, which is met primarily by the beta-oxidation of long-chain fatty acids. The control of fatty acid beta-oxidation is complex and is aimed at ensuring that the supply and oxidation of the fatty acids is sufficient to meet the energy demands of the heart. The metabolism of fatty acids via beta-oxidation is not regulated in isolation; rather, it occurs in response to alterations in contractile work, the presence of competing substrates (i.e., glucose, lactate, ketones, amino acids), changes in hormonal milieu, and limitations in oxygen supply. Alterations in fatty acid metabolism can contribute to cardiac pathology. For instance, the excessive uptake and beta-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. Furthermore, alterations in fatty acid beta-oxidation both during and after ischemia and in the failing heart can also contribute to cardiac pathology. This paper reviews the regulation of myocardial fatty acid beta-oxidation and how alterations in fatty acid beta-oxidation can contribute to heart disease. The implications of inhibiting fatty acid beta-oxidation as a potential novel therapeutic approach for the treatment of various forms of heart disease are also discussed.

Analysis of the fatty acid components in a perchloric acid-soluble protein

We had previously found that a perchloric acid-soluble protein (PSP1) occurs in rat liver, and that this novel protein inhibits protein synthesis in a rabbit reticulocyte lysate system (T. Oka, H. Tsuji, C. Noda, K. Sakai, Y.-H. Hong, I. Suzuki, S. Muñoz, Y. Natori, J. Biol. Chem. 270 (1995) 30060-30067). In the present study, we analyzed lipid components bound to PSP1. Native PSP1 was purified from rat liver using Sephadex G-75, DE-52 cellulose and IgGPSP-affinity chromatography, and the lipid components were extracted. The components obtained from the purified PSP1 were shown to be free fatty acids by thin-layer chromatography. By GC-MS, six major fatty acids were identified as 14:0, 16:0, 18:0, 18:1, 18:2 and 20:4. 1 mol of PSP1 contained 1.26 mol of total fatty acid components. The fatty acid-binding assay of PSP1 showed that the Bmax was 1.25 mol fatty acid/mol PSP1 and the Kd value for palmitic acid was 6.03 microM. The concentration of PSP1 mRNA in rat liver increased 2.3-fold by the administration of peroxisome proliferator, bezafibrate. These findings show that PSP1 is a fatty acid-binding protein-like protein, which is involved in the intracellular metabolism of fatty acid and is quite different from the known fatty acid-binding proteins.

Modulation of mitogenesis by liver fatty acid binding protein

Liver fatty acid binding protein (L-FABP), a cytoplasmic 14 kDa protein previously termed Z protein, is conventionally considered to be an intracellular carrier of fatty acids in rat hepatocytes. The following evidence now indicates that L-FABP is also a specific mediator of mitogenesis of rat hepatocytes: a. the synergy between the action of L-FABP and unsaturated fatty acids, especially linoleic acid, in the promotion of cell proliferation; b. the specific requirement for L-FABP in induction of mitogenesis by two classes of nongenotoxic hepatocarcinogenic peroxisome proliferators (amphipathic carboxylates and tetrazole-substituted acetophenones); c. the direct correlation between the binding avidities of different prostaglandins for L-FABP and their relative growth inhibitory activities toward cultured rat hepatocytes; d. the temporal coincidences between the covalent binding to L-FABP by chemically reactive metabolites of the genotoxic carcinogens, 2-acetylaminofluorene and aminoazo dyes, and their growth inhibitions of hepatocytes during liver carcinogenesis in rats; e. and f. the marked elevations of L-FABP in rat liver during mitosis in normal and regenerating hepatocytes, and during the entire cell cycle in the hyperplastic and malignant hepatocytes that are produced by the genotoxic carcinogens, 2-acetylaminofluorene and aminoazo dyes. These actions of L-FABP are consistent with those of a protein involved in regulation of hepatocyte multiplication. Discovery that L-FABP, the target protein of the two types of genotoxic carcinogens, is required for the mitogenesis induced by two classes of nongenotoxic carcinogens points to a common process by which both groups of carcinogens promote hepatocyte multiplication. The implication is that during tumor promotion of liver carcinogenesis, these genotoxic and nongenotoxic carcinogens modify the normal process by which L-FABP, functioning as a specific receptor of unsaturated fatty acids or their metabolites, promotes the multiplication of hepatocytes.

Effect of clofibric acid on the turnover of the fatty acid-binding protein identified in cultured endothelial cells from bovine aorta

Several types of fatty acid-binding proteins are found in mammalian cells. Cultured endothelial cells from bovine aorta were shown to contain exclusively the cardiac-type fatty acid-binding protein (cFABP) with a mean concentration of 90 ng cFABP/mg extract protein. Only small variations were observed from passage to passage. In pulse-chase labeling experiments with L-[35S]methionine, a half-life of 4.0 d was measured for cFABP which is about two times longer than the average half-life of the extracted proteins. These data imply that in aortic endothelial cells cFABP is not subject to short-term regulation. However, addition of clofibric acid to the culture medium led to a shortening of the half-life of cFABP, which was compensated for by an increase in its biosynthesis. The turnover of the bulk of extract proteins remained unchanged when the cells were challenged with clofibric acid.

Interaction of LY171883 and other peroxisome proliferators with fatty-acid-binding protein isolated from rat liver

Fatty-acid-binding protein (FABP) is a 14 kDa protein found in hepatic cytosol which binds and transports fatty acids and other hydrophobic ligands throughout the cell. The purpose of this investigation was to determine whether LY171883, a leukotriene D4 antagonist, and other peroxisome proliferators bind to FABP and displace an endogenous fatty acid. [3H]Oleic acid was used to monitor the elution of FABP during chromatographic purification. [14C]LY171883 had a similar elution profile when substituted in the purification, indicating a common interaction with FABP. LY171883 and its structural analogue, LY189585, as well as the hypolipidaemic peroxisome proliferators clofibric acid, ciprofibrate, bezafibrate and WY14,643, displaced [3H]oleic acid binding to FABP. Analogues of LY171883 that do not induce peroxisome proliferation only weakly displaced oleate binding. [3H]Ly171883 bound directly to FABP with a Kd of 10.8 microM, compared with a Kd of 0.96 microM for [3H]oleate. LY171883 binding was inhibited by LY189585, clofibric acid, ciprofibrate and bezafibrate. These findings demonstrate that peroxisome proliferators, presumably due to their structural similarity to fatty acids, are able to bind to FABP and displace an endogenous ligand from its binding site. Interaction of peroxisome proliferators with FABP may be involved in perturbations of fatty acid metabolism caused by these agents as well as in the development of the pleiotropic response of peroxisome proliferation.

Detection, tissue distribution and (sub)cellular localization of fatty acid-binding protein types

This overview of recent work on FABP types is focussed on their detection and expression in various tissues, their cellular and subcellular distribution and their binding properties. Besides the 3 well-known liver, heart and intestinal types, new types as the adipose tissue, myelin and (rat) renal FABPs have been described. Recent observations suggest the occurrence of more tissue-specific types, e.g. in placenta and adrenals. Heart FABP is widely distributed and present in skeletal muscles, kidney, lung, brain and endothelial cells. The cellular distribution of FABP types appears to be related to the function of the cells in liver, muscle and kidney. The presence of FABP in cellular organelles requires more evidence. The functional significance of the occurrence of more FABP types is unclear, in spite of the observed differences in their ligand-protein interaction.

Effects of linoleic and gamma-linolenic acids (efamol evening primrose oil) on fatty acid-binding proteins of rat liver

We have studied the effects of Efamol evening primrose oil (EPO) on fatty acid-binding proteins (L-FABP) of rat liver. EPO contains 72% cis-linoleic acid and 9% cis-gamma linolenic acid. EPO has been clinically used for treatment of a number of diseases in humans and animals. EPO is also known to lower cholesterol level in humans and animals. Feeding of an EPO supplemented diet to rats (n = 9) for 2 months decreases the oleate binding capacity of purified L-FABP of rat liver whereas the palmitate binding activity was increased by 38%. However, EPO feeding did not alter the L-FABP concentrations significantly as measured by using the fluorescence fatty acid probe, dansylamino undecanoic acid. Endogenous fatty acid analysis of L-FABPs revealed significant qualitative and quantitative changes in fatty acid pattern after EPO feeding. EPO feeding decreased the endogenous palmitate level by 53% and oleate level by 64% in L-FABPs and also EPO feeding decreased the total endogenous fatty acid content from 62 nanomole per mg of protein to 42 nanomole per mg of L-FABP (n = 3).

Fatty acid binding sites of rodent adipocyte and heart fatty acid binding proteins: characterization using fluorescent fatty acids

Murine adipocyte and rat heart fatty acid binding proteins (FABP) are closely related members of a family of cytosolic proteins which bind long-chain free fatty acids (ffa). The physical and chemical characteristics of the fatty acid binding sites of these proteins were studied using a series of fluorescent analogues of stearic acid (18:0) with an anthracene moiety covalently attached at seven different positions along the length of the hydrocarbon chain (AOffa). Previously, we used these probes to investigate the binding site of rat liver FABP (L-FABP) [Storch et al. (1989) J. Biol. Chem. 264, 8708-8713]. Here we extend those studies to adipocyte and heart FABP, two members of the FABP family which share a high degree of sequence homology with each other (62% identity) but which are less homologous with L-FABP (approximately 30%). The results show that the fluorescence emission spectra of AOffa bound to adipocyte FABP (A-FABP) are blue-shifted relative to heart FABP (H-FABP), indicating that AOffa bound to A-FABP are held in a more constrained configuration. For both proteins, constraint on the bound ffa probe is highest at the midportion of the acyl chain. Ffa are bound in a hydrophobic environment in both proteins. Excited-state lifetimes and fluorescence quantum yields suggest that the binding site of H-FABP is more hydrophobic than that of A-FABP. Nevertheless, acrylamide quenching experiments indicate that ffa bound to H-FABP are more accessible to the aqueous environment than are A-FABP-bound ffa.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunochemical quantitation of fatty acid-binding proteins. Tissue distribution of liver and heart FABP types in human and porcine tissues

1. Antisera against heart and liver fatty acid-binding proteins (FABPs) were used in enzyme-linked immunosorbent assay to study the cross-reactivity between these FABP types of man, pig and rat, and to assess their tissue distribution in man and pig. 2. No cross-reactivities were found of heart FABPs with anti-liver FABP sera and vice versa. With the liver FABPs, marked species differences were found, but the three proteins are clearly related. Human and pig heart FABP are immunochemically closer related to each other than to this protein from rat heart. 3. The tissue distribution of the heart and liver FABP types is similar in man, pig and rat. Liver FABP is only found in liver and intestine, and heart FABP is present in heart, skeletal muscle, kidney, lung, brain and placenta. 4. Cardiac FABP is also found in cultured human and rat endothelial cells. 5. The FABP content of human and pig liver is comparable to that of rat liver, but the tissue concentrations of heart FABP are lower in man and pig than in rat. When the latter values are expressed relative to the FABP content in heart, analogous distribution patterns are observed in man, pig and rat.

Influence of testosterone administration on the biosynthesis of unsaturated fatty acids in male and female rats

The in vivo effect of testosterone administration to male or female rats on the biosynthesis of unsaturated fatty acids of liver was studied. Twenty-four hours after injection of testosterone (260 micrograms/kg), delta 9 desaturase activity increased significantly, whereas the activities of delta 5 and delta 6 desaturases were strongly depressed. These effects were more pronounced in female than in male animals. The fatty acid composition of plasma and liver (homogenates, crude microsomes and cytosol) showed differences between the sexes. In males, the percentage of palmitic acid and the 18:1/18:0 ratio were higher whereas the 20:4(n-6)/18:2(n-6) ratio was lower than in female rats. The administration of testosterone significantly modified the fatty acid pattern in all fractions studied. Analytical data correlated with alterations in the fatty acid desaturase activities caused by the hormone. It is suggested that the mechanism by which testosterone exerts its effect on unsaturated fatty acid biosynthesis is different that that previously demonstrated by glucocorticoid action. The effects produced by testosterone may be of biological significance in atherosclerosis pathogenesis.

The fatty acid-binding protein from human skeletal muscle

Fatty acid-binding protein (FABP) was isolated from human skeletal muscle by gel filtration and anion- and cation-exchange chromatography. The isolation procedure, however, with rat and pig skeletal muscle gave mostly inactive preparations. Rat muscle FABP preparations contained parvalbumin as a contaminant. FABP from human muscle had a Mr of about 15 kDa, a pI value of 5.2, and a Kd value with oleic acid of 0.50 microM. Skeletal muscle and heart FABPs and their antisera showed a strong cross-reactivity on Western blots and in enzyme-linked immunosorbent assays (ELISA). No cross-reactivity was observed with liver FABP and its antiserum. On the basis of amino acid composition, electrophoretic behavior, fatty acid binding, and immunochemical properties, human skeletal muscle FABP must be similar or closely related to human heart FABP. The FABP content determined by ELISA was comparable in various human muscles and cultured muscle cells, but lower than that in rat muscles.

Glutathione transferases in the tapeworm Moniezia expansa

Four forms of GSH transferase were resolved from Moniezia expansa cytosol by GSH-Sepharose affinity chromatography and chromatofocusing in the range pH 6-4, and the presence of isoenzymes was further suggested by analytical isoelectric focusing. The four GSH transferase forms in the cestode showed no clear biochemical relationship to any one mammalian GSH transferase family. The N-terminal of the major GSH transferase form showed sequence homology with the Mu and Alpha family GSH transferases. The major GSH transferase appeared to bind a number of commercially available anthelmintics but did not appear to conjugate the compounds with GSH. The major GSH transferase efficiently conjugated members of the trans-alk-2-enal and trans,trans-alka-2,4-dienal series, established secondary products of lipid peroxidation.

The effect of dietary alpha-bromopalmitate on blood lipids in the rat

When alpha-bromopalmitate was fed to rats for 9-30 days, the level of serum triacylglycerol increased up to 2-fold over the concentration of controls. alpha-Bromopalmitate treatment had no effect on concentration of complex lipids in liver, while the triacylglycerol level in heart was significantly enhanced. From metabolic studies using isolated hepatocytes and liver microsomes, it is suggested that the increased serum triacylglycerol level after alpha-bromopalmitate feeding is mainly due to reduced fatty acid oxidation in both liver and peripheral tissues, and to a lesser extent, to inhibited fatty acid uptake and esterification.

The hepatocellular transport of sulfobromophthalein-glutathione by clofibrate treated, perfused rat liver

The hypolipidemic drug clofibrate is known to affect the hepatic transport of various organic anions including bilirubin, fatty acids and sulfobromophthalein. Changes in the rate of metabolism and/or intracellular transport have been claimed responsible for the effect. To evaluate these possibilities, the transport of sulfobromophthalein-glutathione, a model compound that does not require metabolism for biliary excretion, was studied in perfused livers isolated from clofibrate-treated and control rats. Cytosolic fatty acid binding protein and glutathione S-transferase activity were also measured. Clofibrate treatment significantly increased liver weight; as a result glutathione S-transferase activity (toward 1-chloro-2,4-dinitrobenzene) fell if expressed per gram of liver (4560 +/- 420 (SE) vs 7010 +/- 260 nmoles/min for clofibrate treated and controls respectively, p less than 0.002), but was unchanged when expressed per total liver (60.8 +/- 6.5 vs 64.6 +/- 3.5 mumoles/min for clofibrate and controls p greater than 0.5). Irrespective of how it was expressed fatty acid binding protein was significantly increased by the drug treatment. Steady state sulfobromophthalein-glutathione removal velocity was saturable with increasing concentrations of sulfobromophthalein-glutathione in both control and clofibrate-treated livers. Steady state extraction ratio, as well as Vmax and Km for removal, did not differ between the two groups. In keeping with other observations, these data collectively indicate that the hepatic steady state removal of nonmetabolized compounds is not affected by clofibrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary corn oil and salmon oil on the oxidation of fatty acids and prostaglandin E2 in rat gastric mucosa

The investigations previously carried out by Grataroli and colleagues (1) to elucidate the relationships between dietary fatty acids, lipid composition, prostaglandin E2 production and phospholipase A2 activity in the rat gastric mucosa are, here, extended. In the present investigations, fatty acid and prostaglandin E2 catabolizing enzymes were assayed in gastric mucosa from rats fed either a low fat diet (corn oil: 4.4% w/w) (referred as control group), a corn oil-enriched diet (17%) or a salmon oil-enriched diet (12.5%) supplemented with corn oil (4.5%) (referred as groups of treated animals) for eight weeks. Peroxisomal fatty acyl-CoA beta-oxidation was induced in the treated animals whereas the activities of catalase and mitochondrial tyramine oxidase were increased and normal, respectively. Mitochondrial acyl-CoA dehydrogenations occurred at higher rates and carnitine acyltransferase activities were enhanced. In addition, the induction of peroxisomal but not mitochondrial prostaglandoyl-E2-CoA beta-oxidation could be demonstrated. Induction of peroxisomal oxidation of fatty acids and prostaglandins is suggested to contribute to the decrease of prostaglandin E2 production in the treated animals, especially those receiving the salmon oil diet, that the above mentioned authors originally reported.

Immunochemical quantitation of fatty-acid-binding proteins. I. Tissue and intracellular distribution, postnatal development and influence of physiological conditions on rat heart and liver FABP

Antisera against rat heart and liver fatty acid-binding protein (FABP) were applied in Western blotting analysis and ELISA to assess their tissue and intracellular distribution, and the influence of development, physiological conditions and several agents on the FABP content of tissue cytosols. The data obtained are compared with the oleic acid-binding capacity. Heart FABP is found in high concentrations in heart, skeletal muscles, diaphragm and lung, and in lower concentrations in kidney, brain and spleen, whereas liver FABP is limited to liver and intestine. In heart and liver, FABP is only present in the cytosol. The FABP content of both heart and liver shows a progressive increase during the first weeks of postnatal development, in contrast to their constant oleic acid-binding capacity. The reciprocally declining alpha-fetoprotein content of both tissues may partially account for the complementary fraction of the fatty acid-binding capacity. The FABP content and the fatty acid-binding capacity of adult heart and liver were in good accordance under various physiological conditions. Addition of clofibrate to the diet induces an increase of liver FABP content, whereas feeding of cholesterol, cholestyramine, mevinolin or cholate caused a marked decrease. The significance of the combined determination of fatty acid-binding capacity and FABP content (by immunochemical quantitation and blotting analysis) is indicated.

The binding affinity of fatty acid-binding proteins from human, pig and rat liver for different fluorescent fatty acids and other ligands

1. Two forms of fatty acid-binding proteins (FABPs) were isolated from human, pig and rat liver cytosols by gelfiltration and anion-exchange chromatography. 2. Both forms did not show physicochemical or chemical differences. They had an Mr of about 14.5 kDa for all species. pI Values were 5.8 for both forms of human and pig liver FABP and 6.4 for both forms of rat liver FABP. In contrast to heart FABPs no tryptophan was present in liver FABPs. 3. Liver FABPs show a much higher enhancement of fluorescence at binding of 11-dansylaminoundecanoic acid, 16-anthroyloxy-palmitic acid and 1-pyrene-dodecanoic acid than heart FABPs and additionally a blue shift in excitation and emission wavelengths with the first fatty acid. 4. The bulky side-chain did not affect fatty acid binding since binding constants of liver FABPs were comparable for these fluorescent fatty acids and oleic acid (0.3-0.7 microM). 5. A 1:1 binding stoichiometry was obtained for oleic acid binding with heart and liver FABPs. 6. Liver FABPs have a high binding affinity for C16-C22 saturated and unsaturated fatty acids, palmitoyl-CoA, bromo-substituted fatty acids, POCA, tetradecylglycidic acid and flavaspidic acid. 7. Fatty acid binding could be reduced to less than 50% by arginine modification with 2,3-butadione or by enzymatic degradation of FABPs with trypsin or pronase.

Separation of fatty acid binding protein by high-performance mixed-mode chromatography

Fatty acid binding protein (FABP) (14 kDa), can regulate the levels of tissue free fatty acids by binding them with high affinity. Since free fatty acids are known to accumulate in the ischemic myocardium, it is likely that FABP has a significant role in regulating their concentration in ischemic heart. FABP has recently been purified from other proteins, but the method requires several hours and special techniques. In this report, we describe a rapid high-performance liquid chromatographic method for separating and isolating the FABP from myocardial tissue biopsies. About 25-50 micrograms of rat heart cytosol was incubated with 2 nmol of the potassium salt of [9,10-3H]oleate (25,000 cpm) for 10 min at 37 degrees C. This was then injected onto a Bio-Rad (Richmond, CA, U.S.A.) TSK-125 column. The sample was run using a low-salt isocratic mobile phase containing 10 mM potassium phosphate buffer (pH 7) and 1 mM dithiothreitol, and at a flow-rate of 0.8 ml/min. The heart cytosol, when incubated with isotopic oleate, was resolved into two radioactive peaks, one eluting in the area of serum albumin (retention time 9.6 min) and the other corresponding to a retention time of 12.9 min. The sodium dodecyl sulfate polyacrylamide gel electrophoretic profile of the later peak revealed a major protein band of ca. 14 kDa. Rat heart FABP purified by gel filtration and ion-exchange chromatography coeluted with the second radioactive peak.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acid binding protein of cardiac muscle in spontaneously hypertensive rats: effect of hypertrophy and its regression

To investigate the relationship between cardiac hypertrophy associated with hypertension, and the alterations in myocardial lipid metabolism, nicardipine (160 mg/kg/day), hydralazine (40 mg/kg/day), and enalapril (30 mg/kg/day) were administered to spontaneously hypertensive rats from 20 to 24 weeks of age. Drug administration significantly suppressed the increases in blood pressure and the ratio of left ventricular weight to body weight. A marked variation in the fatty acid binding capacities of the delipidated, dealbuminated heart cytosol obtained from these animals was observed in the 24-week-old rats (5.40 +/- 0.31 pmol/micrograms protein in non-treated rats; 4.73 +/- 0.34 pmol/mg protein in nicardipine-treated rats; 5.01 +/- 0.34 pmol/mg protein in hydralazine-treated rats; 4.61 +/- 0.26 pmol/mg protein in enalapril-treated rats) as compared to the 20-week-old non-treated rats (3.38 +/- 0.29 pmol/mg protein). The decrease in this capacity in the drug-treated groups closely correlated with the reduction of cardiac mass, suggesting that the factors governing regression may be closely related to those governing fatty acid binding capacity. It appears that fatty acid binding protein may play an important role in the hypertension-associated hypertrophic myocardium.

Characterization and binding properties of fatty acid-binding proteins from human, pig, and rat heart

Fatty acid-binding proteins (FABPs) were isolated from the cytosols of hearts of man, pig, and rat by gel filtration and anion-exchange chromatography. The heart FABPs had a Mr of about 15,000 (pig, rat) and 15,500 (man); pI values were 5.2, 4.9, and 5.0 for human, pig, and rat heart, respectively. In contrast to liver FABPs, tryptophan was present in the heart FABPs. Binding characteristics for long-chain fatty acids determined with the radiochemical Lipidex assay were comparable for all three proteins. Heart FABPs also bind palmitoyl-CoA and -carnitine with an affinity comparable to that for palmitic acid. Other ligands investigated, heme, bilirubin, cholesterol, retinoids, and prostaglandins, could not compete with oleic acid for binding by human heart FABP. Binding parameters of FABP for oleic acid from multilamellar liposomes were comparable to those from the Lipidex binding assay. Immunological interspecies cross-reactivity with antisera against the heart FABPs was much higher between man and pig than between rat and man or pig. None of the antisera reacted with liver FABPs. The IgG fraction of anti-human heart FABP serum inhibited fatty acid binding to human heart FABP.

Release of fatty acid-binding protein from isolated rat heart subjected to ischemia and reperfusion or to the calcium paradox

The release of cardiac fatty acid-binding protein (cFABP) and of fatty acids from isolated rat hearts was measured during both reperfusion following 60 min of ischemia and the calcium paradox (readmission of Ca2+ after a period of Ca2+-free perfusion). Total cFABP release was much more pronounced after Ca2+ readmission (over 50% of tissue content) than during post-ischemic reperfusion (on average, 3% of tissue content), but in both cases, it closely paralleled the release of lactate dehydrogenase. Only minor amounts of long-chain fatty acids, if any, were released from the heart. These observations are challenging the idea that cFABP plays a fatty acid-buffering role under the pathophysiological conditions studied.

Studies on fatty acid-binding proteins. The binding properties of rat liver fatty acid-binding protein

1. The fluorescent fatty acid probe 11-(dansylamino)undecanoic acid binds to rat liver fatty acid-binding protein with a 1:1 stoichiometry. 2. The binding of the fluorescent probe is competitive with long-chain fatty acids. 3. Binding displacement studies were performed with a wide range of fatty acids and other ligands and identified C16 and C18 fatty acids as the preferred fatty acids for rat liver fatty acid-binding protein. No preference was observed for unsaturated fatty acids within this group. 4. Fatty acyl-CoA binds less well than the corresponding fatty acid.

Sex-related differences in desaturation and chain elongation of essential fatty acids studied in isolated rat hepatocytes

When [14C]linoleic acid (18:2(n-6)) or [14C]dihomogammalinolenic acid (20:3(n-6)) was incubated with isolated liver cells from rats fed an essential fatty acid deficient diet, delta 6- and delta 5-desaturation, chain elongation and synthesis of 14C-labelled C14-C18 fatty acids (from [14C]acetate) were enhanced in female cells compared with male ones. No sex difference in total secretion of very low density lipoproteins (VLDL) was observed. However, VLDL secreted from female cells contained significantly more C16-C18 fatty acids than male cells. It is suggested that the observed sex differences, at least in part, may be related to the different content of fatty acid binding proteins in female cells compared with males.

Studies on fatty acid-binding proteins. Changes in the concentration of hepatic fatty acid-binding protein during development in the rat

The concentration of hepatic fatty acid-binding protein was determined in the livers of rats at various stages of development from foetus to young adult. Fatty acid-binding protein concentrations were determined by quantifying the fluorescence enhancement on the binding of the fluorescent probe 11-(dansylamino)-undecanoic acid. A 20-fold increase in the concentration of the protein was observed between the foetus and adult, and this increase was confirmed by immuno-blotting. No other protein in the 14,000-Mr range was observed in the foetus. Possible alternative fatty acid-binding proteins could not be detected in h.p.l.c.-fractionated foetal cytosol by the fluorescence-enhancement method.