Intracellular fatty acid-binding proteins

Using the lymphatics to study nutrient absorption and the secretion of gastrointestinal hormones

The lymph fistula rat model has traditionally been used to study the intestinal absorption of nutrients, especially lipids, but recently this model has also been used for studying the secretion of incretin hormones by the small intestine. The small intestine is not only responsible for the digestion and transport of dietary triacylglycerol, through the formation of chylomicrons, but it also secretes the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) from enteroendocrine cells. Ultimately, both chylomicrons and incretins are found in lymph. Advantages of the lymph fistula rat model in studying chylomicron and incretin secretion are numerous and include: 1) the concentrations of incretin hormones are higher in lymph than in peripheral or portal plasma; 2) there is reduced degradation of incretin hormones by DPP-IV in the lymph compartment; 3) less dilution by the circulating fluid; 4) this model allows the continuous collection of lymph from conscious animals, eliminating any potential side effects on lymph flow and gastrointestinal function due to anesthesia; and finally, and perhaps most importantly, and 5) the concentration in the intestinal lymph provides a physiologically accurate representation of the hormonal milieu within the intestinal mucosa where incretins may interact with enteroendocrine and/or dendritic cells and signal through the enteric or autonomic neurons. The importance of GIP and GLP-1 in health and disease is becoming more apparent, especially as the prevalence of type 2 diabetes and other metabolic disorders increases. This review focuses on the use of the lymph fistula rat as a model to study the secretion of incretins, as well as dietary lipid.

Lymphatics in intestinal transport of nutrients and gastrointestinal hormones

The lymph fistula rat has been used for studying intestinal absorption of nutrients, especially lipids. Lipid absorption begins with the digestion of triacylglycerol (TAG) to form 2-monoacylglycerol (2-MAG) and fatty acids (FA), which are then incorporated in bile salt-mixed micelles. The mixed micelles deliver these digestion products to enterocytes for uptake. There, 2-MAG and FA are re-esterified to form TAG, which is then incorporated into chylomicrons (CMs) to be carried by the lymphatic system. Coincident with CMs' secretion into lymph, the small intestine also secretes incretin hormones. Advantages of the lymph fistula model in studying CMs and incretin secretion include the following: (1) the animal being conscious, (2) much less dilution of CMs and incretins than in portal blood, and (3) fewer degrading enzymes than portal blood, e.g., dipeptidyl peptidase-IV. Examples of the lymph fistula model being used for studying CMs' transport in normal and pathophysiologic states are presented. Recently, the lymph fistula rat has also been used for studying the secretion of incretins by the small intestine.

Liver fatty acid-binding protein and obesity

While low levels of unesterified long chain fatty acids (LCFAs) are normal metabolic intermediates of dietary and endogenous fat, LCFAs are also potent regulators of key receptors/enzymes and at high levels become toxic detergents within the cell. Elevated levels of LCFAs are associated with diabetes, obesity and metabolic syndrome. Consequently, mammals evolved fatty acid-binding proteins (FABPs) that bind/sequester these potentially toxic free fatty acids in the cytosol and present them for rapid removal in oxidative (mitochondria, peroxisomes) or storage (endoplasmic reticulum, lipid droplets) organelles. Mammals have a large (15-member) family of FABPs with multiple members occurring within a single cell type. The first described FABP, liver-FABP (L-FABP or FABP1), is expressed in very high levels (2-5% of cytosolic protein) in liver as well as in intestine and kidney. Since L-FABP facilitates uptake and metabolism of LCFAs in vitro and in cultured cells, it was expected that abnormal function or loss of L-FABP would reduce hepatic LCFA uptake/oxidation and thereby increase LCFAs available for oxidation in muscle and/or storage in adipose. This prediction was confirmed in vitro with isolated liver slices and cultured primary hepatocytes from L-FABP gene-ablated mice. Despite unaltered food consumption when fed a control diet ad libitum, the L-FABP null mice exhibited age- and sex-dependent weight gain and increased fat tissue mass. The obese phenotype was exacerbated in L-FABP null mice pair fed a high-fat diet. Taken together with other findings, these data suggest that L-FABP could have an important role in preventing age- or diet-induced obesity.

A novel polymorphism in the chicken adipocyte fatty acid-binding protein gene (FABP4) that alters ligand-binding and correlates with fatness

Similar to the mammalian FABP4 gene, the chicken (Gallus gallus) FABP4 gene consists of four exons separated by three introns and encodes a 132 amino acid protein termed the adipocyte fatty acid-binding protein (AFABP). In the current study, a novel G/A polymorphism in exon 3 of the chicken FABP4 gene was identified associated with different chicken breeds that leads to either Ser or Asn at amino acid 89 of the AFABP protein. The Baier chicken averages 0.89+/-0.12% abdominal fat and expresses the G allele (Ser 89 isoform) while the Broiler chicken typically has 3.74+/-0.23% abdominal fat and expresses the A allele (Asn 89 isoforms). cDNAs corresponding to the two AFABP isoforms were cloned and expressed in Escherichia coli as GST fusions, purified by using glutathione sepharose 4B chromatography and evaluated for lipid binding using the fluorescent surrogate ligand 1-anilinonaphthalene 8-sulphonic acid (1,8-ANS). The results showed that AFABP Ser89 exhibited a lower ligand-binding affinity with apparent dissociation constants (Kd) of 7.31+/-3.75 microM, while the AFABP Asn89 isoform bound 1,8-ANS with an apparent dissociation constant of 2.99+/-1.00 microM (P=0.02). These results suggest that the Ser89Asn polymorphism may influence chicken AFABP function and ultimately lipid deposition through changing the ligand-binding activity of AFABP.

Localization, function and regulation of the two intestinal fatty acid-binding protein types

Although intestinal (I) and liver (L) fatty acid binding proteins (FABP) have been widely studied, the physiological significance of the presence of the two FABP forms (I- and L-FABP) in absorptive cells remains unknown as do the differences related to their distribution along the crypt-villus axis, regional expression, ontogeny and regulation in the human intestine. Our morphological experiments supported the expression of I- and L-FABP as early as 13 weeks of gestation. Whereas cytoplasmic immunofluorescence staining of L-FABP was barely detectable in the lower half of the villus and in the crypt epithelial cells, I-FABP was visualized in epithelial cells of the crypt-villus axis in all intestinal segments until the adult period in which the staining was maximized in the upper part of the villus. Immunoelectron microscopy revealed more intense labeling of L-FABP compared with I-FABP, accompanied with a heterogeneous distribution in the cytoplasm, microvilli and basolateral membranes. By western blot analysis, I- and L-FABP at 15 weeks of gestation appeared predominant in jejunum compared with duodenum, ileum, proximal and distal colon. Exploration of the maturation aspect documented a rise in L-FABP in adult tissues. Permanent transfections of Caco-2 cells with I-FABP cDNA resulted in decreased lipid export, apolipoprotein (apo) biogenesis and chylomicron secretion. Additionally, supplementation of Caco-2 with insulin, hydrocortisone and epidermal growth factor differentially modulated the expression of I- and L-FABP, apo B-48 and microsomal triglyceride transfer protein (MTP), emphasizing that these key proteins do not exhibit a parallel modulation. Overall, our findings indicate that the two FABPs display differences in localization, regulation and developmental pattern.

Association between fatty acid binding protein 3 gene variants and essential hypertension in humans

BACKGROUND

We have earlier identified a quantitative trait locus (QTL) on rat chromosome 5 that appears to be primarily under the control of the sympathetic nervous system. Because sympathetic overactivity is related to both hypertension and insulin resistance, FABP3 is a candidate gene for the link between this QTL and blood pressure regulation. In this study, therefore, we explored the role of FABP3 genetic variations in essential hypertension (EH) in humans.

METHODS

We evaluated two single-nucleotide polymorphisms (SNPs) (rs2279885 and rs2271072) in 758 patients with EH and 726 controls. Polymorphism-related genotypes were determined using TaqMan assays, while haplotypes were estimated from the genotype data.

RESULTS

The frequencies of occurrence of the G allele of rs2279885 and the C allele of rs2271072 were significantly higher in subjects with EH than in normotensive (NT) subjects (P = 0.0339, P = 0.0209, respectively). However, the genotype distributions did not exhibit any significant differences.

CONCLUSION

We found an association between FABP3 gene polymorphisms and EH in a Japanese population, thereby suggesting that FABP3 is a susceptibility locus for EH.

Cloning and Characterization of Chicken Adipocyte Fatty Acid Binding Protein Gene

Fatty acid binding proteins (FABPs) are members of a superfamily of lipid-binding proteins and occur intracellularly in vertebrates and invertebrates. This study was designed to clone and characterize the adipocyte fatty acid binding protein (A-FABP) gene in the chicken. PCR primers were designed according to mammalian A-FABP gene sequence to amplify partial cDNA of A-FABP gene from chicken adipose tissues, and the full length of the gene was cloned by 5'RACE and 3'RACE. Analysis of sequence showed that the cDNA of the chicken A-FABP gene was 74 and 73% homologous with porcine and human A-FABP gene, respectively. The similarity was 77, 28, and 23% at the predicted amino acid level with human A-FABP, human L-FABP, and human I-FABP, respectively. RT-PCR and Northern blot analysis indicated that the chicken A-FABP gene, similar to that of the mammal, is only expressed in fat tissues. This is the first report to identify and characterize A-FABP gene in the chicken.

Tissue expression and association with fatness traits of liver fatty acid-binding protein gene in chicken

Fatty acid-binding proteins belong to a superfamily of lipid-binding proteins that exhibit a high affinity for long-chain fatty acids and appear to function in metabolism and intracellular transportation of lipids. The current study was designed to investigate expression characterization and association with growth and composition traits of the liver fatty acid-binding protein (L-FABP) gene in the chicken. Northern blot analysis indicated that the gene, similar to the mammal L-FABP gene, was expressed only in liver and intestinal tissues. The mRNA levels of the chicken L-FABP gene in liver and intestine had significant differences between the broilers and Baier layers. The China Agricultural University F(2) population was used in the present study. Body weight and body composition traits were measured in the populations. Primers for the coding region and 5' upstream region of the L-FABP gene were designed according to chicken genomic and cDNA sequence. Polymorphisms were detected by DNA sequencing, and the PCR single-strand conformation polymorphisms method was developed to genotype the F(2) population. The results indicated that the L-FABP gene polymorphisms were associated with abdominal fat weight and percentage of abdominal fat, and the L-FABP gene could be a candidate locus or linked to a major gene(s) that affects fatness traits in the chicken. The results of the current study provided basic molecular information for studying the role of the L-FABP gene in the regulation of lipid metabolism in avian species.

Heart fatty acid binding protein in the diagnosis of myocardial infarction: where do we stand today?

Heart fatty acid binding protein (hFABP) is a novel small cytosolic protein that is abundant in the heart. It is highly cardiac-specific (i.e. expressed primarily in cardiac tissue), but is also expressed at low concentrations in tissues outside the heart. After myocardial ischemic damage, hFABP can be detected in the blood as early as 1-3 h after onset of chest pain, with peak values reached at 6-8 h and plasma levels returning to normal within 24-30 h. hFABP's clinical diagnostic value is very limited in the presence of renal failure and skeletal muscle diseases as it is completely renally eliminated. In these conditions, the diagnosis of acute myocardial infarction (AMI) may be overestimated. The combination of initial hFABP release after symptom onset, rapid kidney clearance from the circulation and high cardiac specificity suggests great potential for clinical use. Serial measurements of hFABP in the first 24 h after onset of symptoms in AMI patients can: (a) identify patients who are susceptible to reperfusion strategies, (b) detect perioperative AMIs, (c) distinguish patients who reperfuse their infarct-related artery from those who do not, as early as 30 min after starting thrombolytic treatment, (d) detect re-infarction if it occurs within 10 h after symptom onset, and (e) permit an accurate estimation of myocardial infarct size providing important prognosis information.

Differential expression proteomics of human colon cancer

The focus of this study was to use differential protein expression to investigate operative pathways in early stages of human colon cancer. Colorectal cancer represents an ideal model system to study the development and progression of human tumors, and the proteomic approach avoids overlooking posttranslational modifications not detected by microarray analyses and the limited correlation between transcript and protein levels. Colon cancer samples, confined to the intestinal wall, were analyzed by expression proteomics and compared with matched samples from normal colon tissue. Samples were processed by two-dimensional gel electrophoresis, and spots differentially expressed and consistent across all patients were identified by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry analyses and by Western blot analyses. After differentially expressed proteins and their metabolic pathways were analyzed, the following main conclusions were achieved for tumor tissue: 1) a shift from beta-oxidation, as the main source of energy, to anaerobic glycolysis was observed owed to the alteration of nuclear- versus mitochondrial-encoded proteins and other proteins related to fatty acid and carbohydrate metabolism; 2) lower capacity for Na(+) and K(+) cycling; and 3) operativity of the apoptosis pathway, especially the mitochondrial one. This study of the human colon cancer proteome represents a step toward a better understanding of the metabolomics of colon cancer at early stages confined to the intestinal wall.

Identification of single nucleotide polymorphism of adipocyte fatty acid-binding protein gene and its association with fatness traits in the chicken

Fatty acid-binding proteins (FABP) belong to a superfamily of lipid binding proteins that exhibit a high affinity for long chain fatty acids and appear to function in metabolism and intracellular transportation of lipids. The current study was designed to investigate the effects of the adipocyte (A)-FABP gene on chicken growth and body composition traits. Two F2 resource populations were used in the current study. Body weight and body composition traits were measured in the populations. Primers for the coding region of the A-FABP gene were designed from chicken genomic and cDNA sequences. Polymorphism between parental lines was detected by DNA sequencing, and the PCR-RFLP method was developed to genotype the F2 populations. The results indicated that an A-FABP gene polymorphism was associated with abdominal fat weight and percentage of abdominal fat, and the A-FABP gene could be a candidate locus or linked to a major gene(s) that affects abdominal fat content in the chicken.

Cloning and tissue expression of chicken heart fatty acid-binding protein and intestine fatty acid-binding protein genes

Fatty acid-binding proteins (FABPs) are members of a superfamily of lipid-binding proteins, occurring intracellularly in invertebrates and vertebrates. This study was designed to clone and characterize the genes of heart fatty acid-binding protein and intestine fatty acid-binding protein in the chicken. PCR primers were designed according to the chicken EST sequences to amplify cDNA of H-FABP and I-FABP genes from chicken heart and intestinal tissues. Analysis of sequence showed that the cDNA of the chicken H-FABP gene is 75 to 77% homologues to human, mouse, and pig H-FABP genes, and the chicken I-FABP gene is 71 to 72% homologues to human, mouse, and pig I-FABP genes. In addition, Northern blot analysis indicated that of the two genes, similar to the copartner of the mammal, H-FABP gene was expressed in a wide variety of tissues, and I-FABP gene was expressed only in intestinal tissues. The expression levels of the chicken H-FABP mRNA in heart and I-FABP mRNA in intestine had significant differences between the broilers from fat line and Bai'er layers at six weeks of age. The results of this study provided basic molecular information for studying the role of two FABPs in the regulation of fatty acid metabolism in avian species.

Cloning and expression of Tsaiya duck liver fatty acid binding protein

Liver basic fatty acid (FA)-binding protein (Lb-FABP) cDNA was cloned from the livers of laying Tsaiya ducks and used to generate probes for quantification of the Lb-FABP mRNA in Tsaiya ducks. The full-length Lb-FABP cDNA of the Tsaiya duck was highly homologous with that of the mallard (99%), chicken (88%), and iguana (73%). The amino acid sequence was also highly homologous to Lb-FABP found in birds and reptiles, indicating a similar function of the Tsaiya duck Lb-FABP to those species. The calculated molecular weight for the cloned duck Lb-FABP was 14,043g/mol. The Lb-FABP was highly expressed in the liver of laying Tsaiya ducks and not detectable in heart, ovary, intestine, or adipose tissues. The expression of Tsaiya duck Lb-FABP in the skeletal muscle was also detected, and the sequence was confirmed. The greater expression of the hepatic Lb-FABP in the egg-laying Tsaiya ducks than the prelaying ducks paralleled the higher FA use by the laying ducks. These results suggest that hepatic Lb-FABP may be needed for egg production when FA metabolism is high for the ducks. Feeding laying Tsaiya ducks with diets enriched with 2% docosahexaenoic acid (DHA) oil for 2 wk significantly increased hepatic DHA content compared with in ducks fed a 2% butter basal diet. There was no effect of dietary DHA enrichment on the expression of Lb-FABP in the liver of Tsaiya ducks. The results suggest that even though the Lb-FABP may be involved in hepatic FA metabolism, the effect of individual FA on liver Lb-FABP in laying Tsaiya ducks needs to be further studied.

Urinary excretion of fatty acid-binding protein reflects stress overload on the proximal tubules

Urinary excretion of human liver-type fatty acid-binding protein (hL-FABP), which is expressed in human proximal tubules and engaged in free fatty acid (FFA) metabolism, was reported to reflect the clinical prognosis of chronic kidney disease. Here we have investigated the pathophysiological significance of hL-FABP in a model of protein overload nephropathy. Because L-FABP is not expressed in the wild-type mice, we generated hL-FABP chromosomal gene transgenic (Tg) mice. Tg mice were intraperitoneally injected with bovine serum albumin (BSA) replete with FFAs (r-BSA group) or FFA-depleted BSA (d-BSA group). The r-BSA group developed significantly more severe tubulointerstitial damage than did the d-BSA group. Renal expression of the hL-FABP gene was more up-regulated, and urinary excretion of hL-FABP was significantly higher, in the r-BSA group than in the d-BSA group. Furthermore, compared with their wild-type littermates injected with r-BSA, the number of infiltrated macrophages was significantly attenuated in Tg mice injected with it on day 28. In patients with kidney disease (n = 50), urinary hL-FABP was correlated with both urinary protein and the severity of tubulointerstitial injury. In conclusion, our experimental model suggests that urinary excretion of hL-FABP reflects stresses, such as urinary protein overload, on the proximal tubules. The clinical observations support this hypothesis.

Do we need additional markers of myocyte necrosis: the potential value of heart fatty-acid-binding protein

Heart fatty-acid-binding protein (FABP) is a small cytosolic protein that is abundant in the heart and has low concentrations in the blood and in tissues outside the heart. It appears in the blood as early as 1.5 h after onset of symptoms of infarction, peaks around 6 h and returns to baseline values in 24 h. These features of H-FABP make it an excellent potential candidate for the detection of acute myocardial infarction (AMI). We review the strengths and weaknesses of H-FABP as a clinically applicable marker of myocyte necrosis in the context of acute coronary syndromes.

Implementation of fatty acid carriers to skin irritation and the epidermal barrier

Acute perturbations are followed by barrier repair and enhanced lipid synthesis, as well as cellular fatty acid trafficking, yet irritation of the skin may be induced by repeat disturbance of barrier function. Recently, new insights in cellular fatty acid transport and metabolism have evolved with respect to skin irritation and barrier disturbances: (1) Employing sodium dodecyl sulfate, skin irritation is accompanied by the induction of an epidermal (E) cytosolic fatty acid binding protein (FABP) associated with enhanced barrier repair. Whether E-FABP contributes to the water barrier function in normal skin remains to be elucidated; (2) Cutaneous inflammation, as it occurs in irritant contact dermatitis, can be reduced by peroxisome proliferating activated receptor (PPAR) agonists, such as linoleic acid, with clinical effects comparable to that of glucocorticoids; (3) PPARalpha agonists accelerate barrier recovery and enhance lamellar body synthesis, neutral lipid synthesis, in particular that of ceramides and cholesterol; (4) PPARalpha agonists increase the minimal erythema dose in UVB-irradiated human skin. This review provides a brief overview of the current understanding of mammalian fatty acid (FA) metabolism with respect to epidermal barrier abrogation and repair, including new insights into cellular FA transport and metabolism.

The ontogeny of fatty acid-binding protein in turkey (Meleagridis gallopavo) intestine and yolk sac membrane during embryonic and early posthatch development

Experiments were conducted to confirm the existence and ontogeny of fatty acid binding protein (FABP) in the intestine and yolk sac membrane of turkey poults (Meleagridis gallopavo) during embryonic and early posthatch development. Intestinal (I-) FABP was measured using an immunoblot procedure incorporating anti-chick liver (L-)FABP antisera. FABP activity in both tissues was also confirmed with a ligand-binding assay incorporating 14C-oleic acid. I-FABP did not cross-react with chick L-FABP antisera until hatch, embryonic day 28 (ED 28), after which there was a 39% increase in I-FABP concentration through the first 3 d posthatch (PD 3). FABP concentration calculated on a total intestinal basis (ng/intestine), however, increased 10-fold through PD 6. Specific activity [disintegrations per minute (dpm)/ mg cytosolic protein] was greatest at hatch and decreased slightly thereafter, whereas specific activity of FABP in the yolk sac membrane peaked between ED 16 and ED 19 and then declined. Total yolk sac activity (dpm/yolk sac membrane), however, plateaued at ED 22 before declining to low levels by PD 3, coincident with the period of maximal lipid transfer out of the yolk.

The development of an immunoblotting assay for the quantification of liver fatty acid-binding protein during embryonic and early posthatch development of turkeys (Meleagridis gallopavo)

Turkey (Meleagridis gallopavo) liver cytosolic fatty acid binding protein (FABP) was purified and used as a standard for quantification. An immunoblotting procedure was developed to study the ontogeny of liver cytosolic FABP during embryonic and early posthatch development in turkey poults. Liver FABP activity was also determined indirectly through the use of gel filtration chromatography followed by a ligand-binding assay. The specific activity of liver FABP (ng/mg of cytosolic protein) increased with length of incubation, peaking initially at Day 22, declining between Days 22 and 25, and increasing again from hatch (Day 28) to 6 d posthatch. The specific activity of liver FABP increased 12-fold between Day 13 of incubation and 6 d posthatch compared with total activity, which increased from 946 to 1.01 x 10(6) ng/liver during the same period, a 1,067-fold increase. The results from both analytical procedures were similar, suggesting that the immunoblot method could be used to quantify liver FABP concentrations. The observed increases in FABP activity throughout the embryonic period and first days after hatching paralleled increases in liver lipid concentration. Therefore, liver FABP may be associated with hepatocyte fatty acid transport and metabolism during the latter stages of incubation and early posthatch period.

From interaction of lipidic vehicles with intestinal epithelial cell membranes to the formation and secretion of chylomicrons

Lipophilic drugs are carried by chylomicrons that are secreted by the small intestine and transported in lymph. This review discusses the digestion, uptake, and transport of dietary lipids and the impact that these processes have on the absorption of lipophilic drugs by the gastrointestinal tract. This chapter complements Dr. Chris Potter's chapter on the "pre-absorptive" events of drug processing and solubilization. This chapter reviews the digestion of lipids in the gastric and intestinal lumen and the role of bile salts in the solubilization of lipid digestion products for uptake by the gut. Both the passive and active uptake of lipid digestion products is discussed. How intestinal lipid transporters located at the brush border membrane may play a role in the uptake of lipids by the enterocytes is examined, as is the regulation of the absorption of cholesterol by the human ATP-binding cassette transporter-1 (ABC1). The intracellular trafficking and the resynthesis of complex lipids from lipid digestion products are explored, and the formation and secretion of chylomicrons are described.

Stimulatory effect of fatty acid treatment on glucose utilization in human erythrocytes

We previously reported that treatment of human erythrocytes with bee venom phospholipase A2 increased the rate of lactate production from glucose. This increase was suggested to be mediated through liberation of free fatty acids from membrane phospholipids. So, in the present study we examined the mechanism of stimulation of glycolysis by fatty acids. Treatment of intact erythrocytes with most of the 15 fatty acids tested resulted in stimulation of lactate production from glucose. Among the fatty acids tested, myristoleic acid showed the highest stimulatory activity. The ratio of moles of lactate produced to those of glucose utilized was about 1.9 in both myristoleic acid-treated and untreated cells. Treatment of erythrocytes with myristoleic acid did not affect the amount of 2,3-bisphosphoglycerate. Lactate production from D-glyceraldehyde, which is thought to be phosphorylated to D-glyceraldehyde 3-phosphate and then metabolized in the glycolytic pathway, was not at all affected by treatment of cells with myristoleic acid. The cross-over plot of glycolytic intermediates suggested that the enhancement of glycolysis was induced by activation of the 6-phosphofructokinase (PFK) step. Fatty acids incorporated into erythrocytes were found to be present predominantly in the cytoplasm rather than in the plasma membrane. The PFK activity, but not the hexokinase activity, in hemolysates was clearly increased by a set of fatty acids, and myristoleic acid was again the most potent. However, partially purified human erythrocyte PFK was not activated by the acid. We conclude that fatty acids stimulate glycolysis through activation of PFK in cooperation with some other component(s) in erythrocytes.

Time-resolved fluorescence of intestinal and liver fatty acid binding proteins: role of fatty acyl CoA and fatty acid

The effect of fatty acyl CoA and fatty acid on the solution structure and dynamics of two intestinal enterocyte fatty acid binding proteins, intestinal (I-FABP) and liver (L-FABP), was examined by time-resolved fluorescence of FABP aromatic amino acid residues. I-FABP Trp displayed two rotational correlation times, 6.6 and 0.4 ns. reflecting motion of the protein as a whole and segmental mobility of Trp. Neither oleoyl CoA, oleic acid, nor CoASH altered overall I-FABP rotational correlation time. However, oleic acid and CoASH increased I-FABP Trp segmental mobility, while oleoyl CoA and CoASH decreased I-FABP Trp limiting anisotropy (order). The angle of I-FABP Trp "wobbling in a cone" was increased by ligands in the order oleoyl CoA > CoASH > oleic acid. L-FABP Trp segmental mobility. L-FABP overall rotational motion, in contrast to that of I-FABP, was significantly increased by ligands in the order oleoyl CoA > oleic acid > CoASH. cis-Parinaric acid and cis-parinaroyl CoA bound to L-FABP also reflected overall L-FABP motion but yielded longer rotational correlation times, 8.2 and 10.7 ns, than the respective apo-FABPs. Such effects were not observed with I-FABP. Finally, both cis-parinaric acid and cis-parinaroyl CoA were much less ordered in the I-FABP ligand binding site than with L-FABP. These observations suggest that the rotational dynamics of L-FABP and its conformation are more sensitive to ligands than I-FABP. Further, ligands such as fatty acids, fatty acyl CoAs, and/or CoASH differentially modulate the I-FABP and L-FABP dynamics, and the ligand binding sites of these proteins differ in their ability to order the ligands.

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.

Carnitine palmitoyltransferase activities: effects of serum albumin, acyl-CoA binding protein and fatty acid binding protein

The carnitine palmitoyltransferase activity of various subcellular preparations measured with octanoyl-CoA as substrate was markedly increased by bovine serum albumin at low microM concentrations of octanoyl-CoA. However, even a large excess (500 microM) of this acyl-CoA did not inhibit the activity of the mitochondrial outer carnitine palmitoyltransferase, a carnitine palmitoyltransferase isoform that is particularly sensitive to inhibition by low microM concentrations of palmitoyl-CoA. This bovine serum albumin stimulation was independent of the salt activation of the carnitine palmitoyltransferase activity. The effects of acyl-CoA binding protein (ACBP) and the fatty acid binding protein were also examined with palmitoyl-CoA as substrate. The results were in line with the findings of stronger binding of acyl-CoA to ACBP but showed that fatty acid binding protein also binds acyl-CoA esters. Although the effects of these proteins on the outer mitochondrial carnitine palmitoyltransferase activity and its malonyl-CoA inhibition varied with the experimental conditions, they showed that the various carnitine palmitoyltransferase preparations are effectively able to use palmitoyl-CoA bound to ACBP in a near physiological molar ratio of 1:1 as well as that bound to the fatty acid binding protein. It is suggested that the three proteins mentioned above affect the carnitine palmitoyltransferase activities not only by binding of acyl-CoAs, preventing acyl-CoA inhibition, but also by facilitating the removal of the acylcarnitine product from carnitine palmitoyltransferase. These results support the possibility that the acyl-CoA binding ability of acyl-CoA binding protein and of fatty acid binding protein have a role in acyl-CoA metabolism in vivo.

Characterization and binding properties of human fetal lung fatty acid-binding proteins

When delipidated Mr > 10,000 cut-off human fetal lung cytosol was separated on gel filtration and ion-exchange chromatography on Auto-FPLC system, two fatty acid-binding proteins (FABPs) of pI 6.9 and pI 5.4 were purified to homogeneity. On Western blotting analysis with the anti-human fetal lung pI 6.9 FABP, these two proteins showed immunochemical cross reactivity with each other and with purified hepatic FABPs but not with cardiac or gut FABP. These two FABPs have identical molecular mass of 15.2 kDa, which is slightly higher than that of the hepatic proteins (14.2 kDa). Carbohydrate covalently linked to FABPs, that may substantially add to the molecular mass, was not detected in the purified protein preparations. Amino acid analysis revealed that both the proteins have same amino acid composition each containing one Trp residue that is lacking in hepatic FABP. Different isoforms of lung FABP exhibited different binding ability for their natural ligands. These proteins bind palmitoyl CoA with higher affinity than oleic acid. pI 6.9 FABP can more rapidly and efficiently transfer fatty acid than can pI 5.4 FABP from unilammelar liposomes. Thus these FABPs may play a critical role in fatty acid transport during human fetal lung development.

Two cytosolic protein families implicated in lipid-binding: main structural and functional features

1. According to the important biological role of fatty acids and phospholipids in cell membranes, two cytosolic proteins implicated in their binding and transport in brain were considered, namely: Fatty Acid-Binding Protein and basic 21 kDa protein. 2. They were reviewed as well as their related protein families. 3. Although the two protein groups do not present significant sequence homologies, they share several similar properties and might thus be implicated in common physiological functions.

Acyl-binding/lipid-transfer proteins from rape seedlings, a novel category of proteins interacting with lipids

From rape (Brassica napus) seedlings proteins able to bind fatty acids and their CoA-esters were purified by gel filtration and cation-exchange chromatography. Among the four proteins detected, one of them (peak IV) appeared purified to homogeneity. This protein is a monomer with a molecular mass of about 9 kDa, as estimated by gel filtration and by polyacrylamide gel electrophoresis. The isoelectric point of the rape protein was higher than 10.5 as determined by chromatofocusing. The pure rape protein appeared furthermore to be able to transfer several phospholipids (phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine) between membranes. The rape protein, having a multifunctional property, was thus called acyl-binding/lipid-transfer protein (AB-LTP). In order to compare this protein to plant lipid-transfer proteins (LTPs), its structure was determined. The amino acid analysis of the rape AB-LTP revealed a high amount of alanine, an absence of histidine and tryptophan and the presence of eight cysteine residues. The N-terminal amino acid sequence of the rape protein revealed a high homology to plant LTPs. These observations led us to propose that the rape AB-LTPs belong to a category of plant proteins interacting with lipids and playing a role in the fatty acid dynamics.

The binding of the fluorescent ATP analogue 2'(3')-trinitrophenyladenosine-5'-triphosphate to rat liver fatty acid-binding protein

The less polar fluorescent analogue of ATP, 2'(3')-trinitrophenyl-5'-triphosphate bound to rat liver fatty acid-binding protein with high affinity (Kd 6.3 x 10(-6) M) and 1:1 molar stoichiometry. This probe bound to the fatty acid binding site of the protein and was displaced by oleic acid and oleoyl CoA. High concentrations of ATP did not cause significant displacement of the fluorescent ATP analogue. Since the anionic part of this molecule is the triphosphate group it is difficult to envisage this group being accommodated at an anion binding site within the non-polar core of this protein as is the case with other fatty acid binding proteins. Therefore it is anticipated that the ligand must bind to liver fatty acid-binding protein with this triphosphate group surface exposed. Caution must be exercised when using the more hydrophobic fluorescent analogue of ATP to investigate the ATP binding properties of proteins.

Na pump and plasma membrane structure in L-cell fibroblasts expressing rat liver fatty acid binding protein

Although the intracellular fatty acid binding proteins have been investigated for nearly two decades and purified proteins are now available, little is known regarding the function of these proteins in intact cells. Therefore, L-cell fibroblasts transfected with cDNA encoding for rat liver fatty acid binding protein (L-FABP) were examined as to whether L-FABP expression in intact cells modifies plasma membrane enzyme activities, fluidity, and lipids. Plasma membrane Na/K-ATPase activity was 65.9 +/- 18.7 and 38.6 +/- 22.8 (P less than 0.001) nmol/mg protein x min for control and high-expression transfected cells, respectively. Consistent with this observation, [3H] ouabain binding to whole cells was significantly decreased from 3.7 +/- 0.3 to 2.0 +/- 0.8 pmol ouabain bound/mg cell protein in control and high-expression cells, respectively, whereas the cell's affinity for ouabain was not significantly altered. Unexpectedly, Western blot analysis indicated that transfected cells had higher levels of Na+, K(+)-ATPase protein; in contrast, the activities of 5'-nucleotidase and Mg-ATPase were unaltered. The effects of L-FABP expression on plasma membrane Na/K-ATPase function appeared to be mediated through alterations in plasma membrane lipids and/or structure. The plasma membrane cholesterol/phospholipid ratio decreased and the bulk plasma membrane fluidity increased in the high-expression cells. In conclusion, plasma membrane Na/K-ATPase activity in L cells may be regulated in part through expression of cytosolic L-FABP.

Rat brain fatty acid-binding protein during development

Cytosolic fatty acid-binding proteins (FABPs) have been described in rat and bovine whole brain. In the present study we investigated the distribution of FABP among white matter and gray matter as well as its changes during development. Fatty acid binding activity was similar in white and gray matter up to 40 days of age. In white matter it showed an age dependent increase thereafter, while in gray matter it remained constant throughout. Gel filtration (Sephadex G-75) of white matter cytosol of adult female rats resolved the fatty acid-binding activity in two peaks: A (Vo) and B (12-14 KDa; FABP). The specific binding activity in the FABP fraction was 10.4 pmol/micrograms of protein. The activity in peak A showed an age-dependent increase which paralleled myelin deposition. In contrast, the activity in the FABP fraction (peak B) remained undetectable up to 40 days of age, increasing thereafter. The differential distribution of cellular brain proteins with the capacity to bind fatty acids in gray matter and white matter suggests that this activity could be related to glial cells or to cell related structures such as myelin.

Inhibition of phospholipase A2 by cis-unsaturated fatty acids: evidence for the binding of fatty acid to enzyme

Calcium-dependent phospholipases A2 are markedly inhibited in vitro by cis-unsaturated fatty acids (CUFAs) and to a much lesser extent by trans-unsaturated or saturated fatty acids. Thus, CUFAs may function as endogenous suppressors of lipolysis. To better understand the mechanism of inhibition, kinetic analysis, fluorescence spectroscopy and gel permeation chromatography were employed to demonstrate that CUFAs interact with a highly purified Ca(2+)-dependent phospholipase A2 from Naja mossambica mossambica venom. Arachidonate inhibited hydrolysis of both [1-14C]oleate-labelled, autoclaved Escherichia coli and [1-14C]linoleate-labelled phosphatidylethanolamine in an apparent competitive manner. When subjected to gel permeation chromatography, [3H]arachidonate, but not [3H]palmitate, comigrated with the enzyme. Arachidonic and other CUFAs increased the fluorescence intensity of the enzyme almost 2-fold in a dose-dependent fashion (50 microM = 180% of control); methyl arachidonate was without effect. Saturated fatty acids had only a modest effect on enzyme fluorescence (50 microM = 122% of control). Concentrations of arachidonate that inhibited in vitro enzymatic activity by almost 80% did not alter binding of phospholipase A2 to the E. coli substrate. Collectively, these data demonstrate that, while CUFAs selectively bind to the enzyme, they do not influence phospholipase A2-substrate interaction. Inhibition of in vitro phospholipase A2 activity by CUFAs may be mediated by the formation of an enzymatically inactive enzyme-substrate-inhibitor complex.

Modulation of fatty-acid-binding protein content of rat heart and skeletal muscle by endurance training and testosterone treatment

The effects of training and/or testosterone treatment and its aromatization to oestradiol on fatty-acid-binding protein (FABP) content and cytochrome c oxidase activity in heart, soleus and extensor digitorum longus (EDL) muscles were studied in intact adult female rats. One group of rats remained sedentary, whereas the others were trained for 7 weeks. Thereafter the trained rats were divided into control and testosterone-treated groups, with or without an aromatase inhibitor. Testosterone was administered by a silastic implant. Training was continued for 2 weeks. In untreated sedentary rats the immunochemically assayed FABP contents were 497 +/- 28, 255 +/- 49 and 58 +/- 17 micrograms/g wet weight for the heart, soleus, and EDL respectively. In the heart the FABP content was increased after training (29%), testosterone treatment (33%) or both manipulations (53%). In soleus muscle FABP increased only after testosterone treatment (16%), whereas in EDL no changes were found. Inhibiting the aromatase enzyme complex abolished the testosterone-induced effect on FABP content in soleus (suggesting an oestradiol effect) but not in heart muscle. Among the three muscles studied the FABP content was found to be related to the cytochrome c oxidase activity in a non-linear way. In conclusion, it is shown that the FABP contents and mitochondrial activities of heart and skeletal muscle are affected by training and sex hormones and that these effects are different for heart and skeletal muscles.

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.