Membrane-associated and cytoplasmic fatty acid-binding proteins

Association between the FABP2 Ala54Thr and CRP+1059C/G polymorphisms and small dense LDL level in patients with atherosclerosis: a case-control study

BACKGROUND

The polymorphisms of fatty acid-binding protein 2 (FABP2) and C-reactive protein (CRP) might act as genetic risk factors for atherosclerosis. The study aimed to investigate the relationship between FABP2 Ala54Thr and CRP+1059C/G polymorphisms and atherosclerosis as well as the association of Small dense-LDL (sd-LDL).

METHODS

A total of 255 subjects (125 controls and 130 patients) were included. The FABP2 and CRP polymorphisms were determined by PCR-RFLP and AS-PCR methods, respectively. Sd-LDL was measured based on Hirano et al method.

RESULTS

There were no significant distinctions between the patient and control groups concerning FABP2 and CRP polymorphisms (p > .05). No significant relationship was observed between studied polymorphisms and sd-LDL level in the patient group (p > .05). However, patients group had higher level of sd-LDL compared to controls (p < .05).

CONCLUSION

FABP2 Ala54Thr and CRP+1059G/C polymorphisms were not associated with atherosclerosis and sd-LDL level. However, the increased sd-LDL level was known as a risk factor for atherosclerosis.

High-fat diet induces aberrant hepatic lipid secretion in blunt snout bream by activating endoplasmic reticulum stress-associated IRE1/XBP1 pathway

This study was conducted to understand the effect of high-fat diet challenge on lipid transport and endoplasmic reticulum stress in blunt snout bream. Ninety fish (average weight: 41.84 ± 0.07 g) were randomly fed a control diet (6% fat) or a high-fat diet (11% fat) for 9 weeks. The growth performance and feed utilization efficiency were evaluated at the end of the trial. The liver samples of both groups were harvested for molecular analysis and histological evaluation. Compared to the Control group, the high-fat diet group showed no effects on either growth performance or energy intake in blunt snout bream. However, high-fat diet resulted in a massive accumulation of lipid and pathological structural alternations, and disrupted expression of lipid transport-related genes and endoplasmic reticulum stress in the liver of the fish. In vitro, after exposure of the isolated primary hepatocytes from blunt snout bream to oleic acid, the cells showed increased intracellular TG accumulation, decreased VLDL secretion, which was attributed to altered expression levels of lipid transport-related genes through the activated IRE1/XBP1 signaling. The oleic acid-induced detrimental effects were alleviated by co-incubating the cells with an IER1 inhibitor, 4μ8c. In conclusion, high-fat diet could lead to aberrant lipid secretion by activating the ER stress-associated IRE1/XBP1 pathway. Inhibiting the activity of IRE1 represents a promising target to rescue the side-effects of high-fat diet on the liver function of blunt snout bream.

Exploring and Expanding the Fatty-Acid-Binding Protein Superfamily in Fasciola Species

The liver flukes Fasciola hepatica and F. gigantica infect livestock worldwide and threaten food security with climate change and problematic control measures spreading disease. Fascioliasis is also a foodborne disease with up to 17 million humans infected. In the absence of vaccines, treatment depends on triclabendazole (TCBZ), and overuse has led to widespread resistance, compromising future TCBZ control. Reductionist biology from many laboratories has predicted new therapeutic targets. To this end, the fatty-acid-binding protein (FABP) superfamily has proposed multifunctional roles, including functions intersecting vaccine and drug therapy, such as immune modulation and anthelmintic sequestration. Research is hindered by a lack of understanding of the full FABP superfamily complement. Although discovery studies predicted FABPs as promising vaccine candidates, it is unclear if uncharacterized FABPs are more relevant for vaccine formulations. We have coupled genome, transcriptome, and EST data mining with proteomics and phylogenetics to reveal a liver fluke FABP superfamily of seven clades: previously identified clades I-III and newly identified clades IV-VII. All new clade FABPs were analyzed using bioinformatics and cloned from both liver flukes. The extended FABP data set will provide new study tools to research the role of FABPs in parasite biology and as therapy targets.

High FABP5 Versus CRABPII Expression Ratio in Recurrent Craniopharyngiomas: Implications for Future Treatment

BACKGROUND AND OBJECTIVE

Recurrence is a major problem in craniopharyngioma (CP) management. Recent study shows that high FABP5/CRABPII may be related to tumor growth and that all-trans retinoic acid (ATRA) may suppress primary CP growth. We studied the expression profile of FABP5 and CRABPII in recurrent CP tissue and the effect of ATRA on recurrent CP cells.

METHODS

Fifty cases of patients with CP were enrolled in the retrospective study. Among them, 15 were recurrent. Fresh specimens were collected for immunohistochemistry, reverse transcription polymerase chain reaction, and western blotting analysis of FABP5 and CRABPII. Fresh specimens from 6 primary and recurrent CPs were collected and subjected to cell culture using an explants method. ATRA at various concentrations was applied to recurrent CP cell culture, and cell growth was recorded and analyzed.

RESULTS

Immunohistochemistry, reverse transcription polymerase chain reaction, and western blot study showed that FABP5 was expressed significantly higher in recurrent tumors, whereas CRABPII was expressed significantly higher in primary tumors. The FABP5/CRABPII ratio was significantly higher in recurrent rather than primary tumors. Recurrent CP cells grew faster than primary cells, and ATRA induced cellular apoptosis and inhibited CP cell growth in a dose-dependent manner.

CONCLUSIONS

A high expression ratio between FABP5 and CRABPII may be related to CP tumor recurrence and ATRA could be a potential therapeutic agent for CP chemotherapy.

Absorption of resveratrol by vascular endothelial cells through passive diffusion and an SGLT1-mediated pathway

Resveratrol is a natural polyphenol that exerts potent effects to suppress atherosclerosis. However, its low concentration in plasma has placed this role in doubt. Thus, resveratrol effects might be dependent on its transport into vascular endothelium, a question not previously addressed in spite of its obvious and fundamental importance. Via high-performance liquid chromatography and liquid chromatography/mass spectrometry, we found that resveratrol was absorbed by human umbilical vein endothelial cells in a temperature-, concentration- and time-dependent manner, suggesting the involvement of passive diffusion and active transport. As determined by confocal laser scanning microscopy, resveratrol primarily distributed throughout the cytoplasm. Furthermore, resveratrol absorption was modulated by serum proteins and sodium-dependent glucose transporter 1 (SGLT1) yet inhibited by glucose (an SGLT1 substrate) and phlorizin (an SGLT1 selective inhibitor), as well as SGLT1 siRNA transfection. Additionally, Sprague-Dawley rats were intragastrically administrated with 100mg/kg of resveratrol and the concentration of resveratrol in blood vessels declined more slowly up to 24h compared to that in the blood. Our results suggested that resveratrol uptake by vascular endothelial cells involved both passive diffusion and an SGLT1-mediated process, at least partially. Moreover, the intracellular resveratrol pool may be more important than the serum level in vivo. These provide new insights into the cardiovascular benefits of resveratrol.

Arachidonic acid and its COX1/2 metabolites inhibit interferon-γ mediated induction of indoleamine-2,3 dioxygenase in THP-1 cells and human monocytes

Using human acute monocytic leukaemic THP-1 cells and human primary monocytes, this study examined the ability of arachidonic acid (AA) to modulate the activity of the IFNγ signalling cascade and its downstream effector indoleamine 2,3-dioxygenase (IDO). We established that AA inhibited IDO enzyme activity with an IC(50) of 20 μM in THP-1 cells and 12 μM in monocytes, and this was due to reduced expression of INDO1 mRNA and reduced level of IDO protein. Further mechanistic analysis revealed that AA interfered with the transcriptional function of the IFNγ signalling pathway by reducing phosphorylation of signal transducer and activator of transcription (STAT1) on tyrosine 701. The importance of AA metabolism via the COX and LOX pathways was investigated using inhibitors. Indomethacin, but not nordihydroguaiaretic acid, prevented the AA-mediated inhibition of STAT1 phosphorylation and thereby IDO enzymatic activity in THP-1 cells and monocytes. This is the first study to demonstrate that AA inhibits the IFNγ/STAT/IDO pathway, and this function is mediated by COX1/2 produced metabolites of AA. We now have evidence demonstrating that the AA metabolites, prostaglandins A(2) and D(2,) were highly inhibitory towards the IFNγ pathway, while prostaglandin E(2) had no effect. Together, these results indicate that the fatty acid AA has the potential to modulate the immunosuppressive activity of IDO and may form the basis of novel inhibitory compounds.

Metabolic syndrome and ALA54THR polymorphism of fatty acid-binding protein 2 in obese patients

The prevalence of metabolic syndrome (MS) has been estimated to be approximately 25% of the population at large. A transition G to A at codon 54 of fatty acid-binding protein 2 (FABP2) results in an amino acid substitution (ala54 to Thr54), and this polymorphism was associated with some cardiovascular risk factors. The aim of our study was to investigate the relationship between MS and Thr54 polymorphism in the FABP2 gene in obese patients. A population of 750 (body mass index >30) obese patients was analyzed in cross-sectional survey. Bioimpedance, blood pressure, and serial assessment of nutritional intake with 3-day written food records and biochemical analysis were performed. The statistical analysis was performed for the combined Ala54/Thr54 and Thr54/Thr54 as a mutant group and wild-type Ala54/Ala54 as second group. Prevalence of MS with Adult Treatment Panel III definition was 49.7% (373 patients; 24.9% male and 75.1% female), and 50.3% of the patients had no MS (n = 377; 34.2% male and 65.8% female). Prevalence of FABP genotypes was similar in patients with MS (55.5% wild genotype and 44.5% mutant genotype) and without MS (54.6% wild genotype and 45.4% mutant genotype). Prevalence of each criteria of MS was calculated in wild- and mutant-type genotypes, without statistical differences. No differences in anthropometric and biochemical parameters were detected between genotypes in the same group of MS. The finding of our study is the lack of association of the Thr54/Ala54 and Thr54/Thr54 FABP2 genotypes with MS.

Fatty acid-binding protein-2 genotype influences lipid and lipoprotein response to eicosapentaenoic acid supplementation in hypertriglyceridemic subjects

OBJECTIVE

The blood lipid-lowering effects of eicosapentaenoic acid (EPA) on hypertriglyceridemic subjects with different fatty acid-binding protein-2 (FABP2) genotypes have not, to our knowledge, been previously studied.

METHODS

Twenty-three FABP2 Ala54 and 23 Thr54 carriers with hypertriglyceridemia (triacylglycerol level >200mg/dL) were enrolled in this study. Participants took 2g of pure EPA daily for 8 wk. Fasting blood lipid and lipoprotein profiles were determined and changes from baseline were measured.

RESULTS

Blood lipids and lipoprotein responses of the FABP2 genotypes differed after EPA supplementation. Changes from baseline for triacylglycerol (19.2% decrease for Ala54 and 60.5% for Thr54, P<0.001), very low-density lipoprotein (20.0% decrease for Ala54 and 60.5% for Thr54, P<0.001), apolipoprotein CIII (22.8% decrease for Ala54 and 36.4% for Thr54, P<0.01), and high-density lipoprotein cholesterol (17.6% increase for Ala54 and 30.7% for Thr54, P<0.01) differed significantly between the two carrier groups. However, changes in total cholesterol, low-density lipoprotein cholesterol, and apolipoprotein B were not significant. EPA supplementation increased plasma EPA in Ala54 and Thr54 carriers. Although EPA supplementation increased the level of plasma EPA in both carrier groups, this effect was more pronounced in the Thr54 carriers.

CONCLUSION

Therefore, EPA consumption has more favorable effects on blood lipids of hypertriglyceridemics with Thr54 genotype rather than those with Ala54. The level of plasma EPA increases after EPA supplementation. Because the FABP2 Thr54 polymorphism appears to be prevalent in hypertriglyceridemic subjects, increasing EPA intake in these subjects could be an effective strategy for reducing blood triacylglycerol concentration.

Characterisation of a fatty acid and retinol binding protein orthologue from the hookworm Ancylostoma ceylanicum

Hookworms, bloodfeeding intestinal nematodes, infect nearly one billion people in resource limited countries and are a leading cause of anaemia and malnutrition. Like other nematodes, hookworms lack the capacity to synthesise essential fatty acids de novo and therefore must acquire those from exogenous sources. The cDNA corresponding to a putative Ancylostoma ceylanicum fatty acid and retinol binding protein-1 (AceFAR-1) was amplified from adult hookworm mRNA. Studies using quantitative reverse transcriptase real-time PCR demonstrate that AceFAR-1 transcripts are most abundant in the earliest developmental stages of the parasite, and greater in females than males. Using in vitro assays, the recombinant AceFAR-1 (rAceFAR-1) was shown to bind individual fatty acids with equilibrium dissociation constants in the low micromolar range. The pattern of fatty acid uptake by live adult worms cultured ex vivo was similar to the in vitro binding profile of rAceFAR-1, raising the possibility that the native protein may be involved in acquisition of fatty acids by A. ceylanicum. Animals vaccinated orally with rAceFAR-1 and the mucosal adjuvant cholera toxin exhibited a statistically significant (40-47%) reduction in intestinal worm burden compared with controls immunized with antigen or adjuvant alone. Together, these data suggest a potential role for AceFAR-1 in hookworm biology, making it a potentially valuable target for drug and vaccine development.

Influence of Ala54Thr polymorphism of fatty acid-binding protein 2 on weight loss and insulin levels secondary to two hypocaloric diets: a randomized clinical trial

OBJECTIVE

A transition G to A at codon 54 of FABP2 was associated with high insulin resistance and different dietary response. The aim of our study was to investigate the influence of this polymorphism on weight loss and metabolic changes secondary to two hypocaloric diets.

SUBJECTS AND METHODS

A sample of 204 obesity patients was analyzed. Before and after 2 months of hypocaloric diet, a nutritional evaluation was performed. Patients were randomly allocated to diet I (low-fat diet) or II (low carbohydrate diet).

RESULTS

With diet Type I and in the wild group (Ala54/Ala54), BMI, weight, fat mass, waist circumference, waist to hip ratio, systolic and diastolic blood pressures, total cholesterol, triglyceride and insulin levels decreased. In the mutant group (Ala54/Thr54 and Thr54/Thr54), BMI, weight, waist circumference and fat mass decreased. In the wild group with diet Type II, the same parameters that group I decreased and glucose levels, too. In the mutant group, BMI, weight, waist circumference and fat mass decreased. Only leptin levels have a significant decrease in the wild group with both diets (diet I: 30.7%; p<0.05 and diet II: 15.85%; p<0.05).

CONCLUSION

Similar weight loss is associated with different changes, depending on the FABP genotype with both diets. Weight loss is associated with a more deep decrease in serum leptin concentration with low-fat diet.

Influence of Ala54Thr polymorphism of fatty acid-binding protein-2 on clinical results of biliopancreatic diversion

OBJECTIVE

Bariatric surgery is the most effective long-term treatment for morbid obesity, reducing obesity-associated comorbidities. The purpose of the present study was to evaluate the fatty acid-binding protein-2 Ala54Thr polymorphism outcomes 1 y after biliopancreatic diversion in morbidly obese patients.

METHODS

A sample of 41 morbidly obese patients (body mass index >40 kg/m(2)) were operated upon from December 2004 to December 2006. Weight, fat mass, blood pressure, basal glucose, triacylglycerides, total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were measured at the basal visit and at each visit. The frequency of patients with diabetes mellitus, hypertension, and hyperlipidemia was recorded at each visit.

RESULTS

Twenty-three patients (56.1%) had genotype Ala54/Ala54 (wild group) and 18 patients had genotype Ala54/Thr54 (15 patients, 36.5%) or Thr54/Thr54 (3 patients, 7.4%; mutant group). In the wild group, body mass index, weight, fat mass, systolic blood pressure, glucose, total cholesterol, low-density lipoprotein cholesterol, and triacylglycerol concentrations decreased. Diastolic blood pressure remained unchanged. In the mutant group, the same parameters improved, without statistical differences from the wild group. Initial excess weight percent loss at 1 y of follow-up was similar in both genotype groups (61.8% versus 61.9%, NS).

CONCLUSION

Polymorphism Ala54Thr of fatty acid-binding protein did not have an effect on weight loss or clinical outcomes after bariatric surgery.

Genes, diet and type 2 diabetes mellitus: a review

Diabetes mellitus is widely recognized as one of the leading causes of death and disability. While insulin insensitivity is an early phenomenon partly related to obesity, pancreatic beta-cell function declines gradually over time even before the onset of clinical hyperglycemia. Several mechanisms have been proposed to be responsible for insulin resistance, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction, as well as glucotoxicity, lipotoxicity, and amyloid formation for beta-cell dysfunction. Moreover, the disease has a strong genetic component, although only a handful of genes have been identified so far. Diabetic management includes diet, exercise and combinations of antihyperglycemic drug treatment with lipid-lowering, antihypertensive, and antiplatelet therapy. Since many persons with type 2 diabetes are insulin resistant and overweight, nutrition therapy often begins with lifestyle strategies to reduce energy intake and increase energy expenditure through physical activity. These strategies should be implemented as soon as diabetes or impaired glucose homoeostasis (pre-diabetes) is diagnosed.

Influence of ALA54THR Polymorphism of Fatty Acid Binding Protein 2 on Lifestyle Modification Response in Obese Subjects

BACKGROUND/AIM

It has been found that the expression of fatty acid binding protein 2 (FABP2) mRNA is under dietary control. A G-to-A transition at codon 54 of FABP2 results in an amino acid substitution (from Ala 54 to Thr 54). This polymorphism was associated with high insulin resistance and high fasting insulin concentrations. The aim of our study was to investigate the influence of Thr54 polymorphism in the FABP2 protein on the response to a lifestyle modification (Mediterranean hypocaloric diet and exercise) in obese patients.

METHODS

A population of 69 obese (body mass index > 30) nondiabetic outpatients was analyzed in a prospective way. Before and after 3 months of the lifestyle modification program, indirect calorimetry, tetrapolar electrical bioimpedance measurement, blood pressure recording, serial assessment of the nutritional intake (3 days of written food records), and biochemical analysis were performed. The lifestyle modification program consisted of a hypocaloric diet (1,520 kcal; 52% carbohydrates, 25% lipids, and 23% proteins). The exercise program consisted of aerobic exercise for at least three times/week (60 min each). Statistical analysis was performed for combined Ala54/Thr54 and Thr54/Thr54 as a mutant group and wild-type Ala54/Ala54 as second group.

RESULTS

The mean age was 45.5 +/- 16.7 years, the mean body mass index was 34.1 +/- 5.1, and there were 14 males (20.3%) and 55 females (79.7%) with a weight loss of 3.17 +/- 3.5 kg (3.5%). Thirty-seven patients (53.6%) had the genotype Ala54/Ala54 (wild-type group) and 32 (46.4%) patients either the genotype Ala54/Thr54 (26 patients, 30.2%) or the genotype Thr54/Thr54 (6 patients, 16.2%). The percentage of responders (weight loss) was similar in both groups (89.2 vs. 90.6%). In the wild-type group, body mass index, weight, fat mass, low-density lipoprotein cholesterol level, and waist circumference decreased, whereas the VO2 (oxygen consumption) increased. In the mutant group, glucose, body mass index, weight, waist circumference, and systolic blood pressure decreased, and VO2 increased. No differences were detected between basal values in both groups. Only the leptin levels showed a significant decrease in the wild-type group (23.85%; p < 0.05), with no statistically significant difference in the mutant group (2.59%; NS). Resistin, tumor necrosis factor alpha, interleukin 6, insulin, and C-reactive protein remained without changes in both groups.

CONCLUSIONS

Weight loss is associated with different changes, depending on the FABP2 genotype. Carriers of the Thr54 allele have a different response than wild-type obese subjects, with a significant decrease of systolic blood pressure and glucose levels in Thr54 carriers and a significant decrease in fat mass, low-density lipoprotein cholesterol, and leptin in wild-type patients.

Membrane binding proteins are the major determinants for the hepatocellular transmembrane flux of long-chain fatty acids bound to albumin

PURPOSE

The hepatic transmembrane flux of long-chain fatty acids (LCFA) occurs through passive and fatty acid transport protein facilitated processes from blood. The extent that these transport processes can be related to the unbound and protein-bound fractions of LCFA in blood is not clear.

METHODS

We used hepatocyte suspensions, hepatoma monolayers, and perfused rat livers to quantitate the transport of purified [(3)H]palmitate ([(3)H]PA) and 12-(N-methyl)-N-[(7-nitrobenz-2oxa-1,3-diazol-4yl-)amino]octadecanoicacid (12-NBDS) from solutions with a constant unbound LCFA concentration with varying bovine serum albumin (BSA) concentrations and in the presence and absence of antisera raised against cytosolic liver fatty acid binding protein (L-FABP).

RESULTS

In the absence of L-FABP antisera, using an unbound ligand concentration that was adjusted to remain constant at each BSA concentration, hepatocyte [(3)H]PA and 12-NBDS uptake rates increased linearly with an increase in BSA concentration (p < 0.0001). In the presence of L-FABP antisera, [(3)H]PA uptake showed a greater reduction in the presence of 100 muM BSA than 5 muM BSA. The calculated permeability surface area product (PS) confirmed that both unbound and bound fractions of LCFA contributed to the overall flux, but only the PS for the protein-bound fraction was reduced in the presence of L-FABP antisera. In situ rat liver perfusion studies showed that the only rate process for the disposition of [(3)H]PA in the liver inhibited by L-FABP antisera was that for influx, as defined by PS, and that it reduced PS in the perfused liver by 42%.

CONCLUSION

These results suggest that, at physiological albumin concentrations, most of the LCFA uptake is mediated from that bound to albumin by a hepatocyte basolateral membrane transport protein, and uptake of unbound LCFA occurring by passive diffusion contributes a minor component.

The immunomodulatory effects of novel beta-oxa, beta-thia, and gamma-thia polyunsaturated fatty acids on human T lymphocyte proliferation, cytokine production, and activation of protein kinase C and MAPKs

We have recently demonstrated that a novel n-3 long chain polyunsaturated fatty acid (PUFA) (beta-oxa 21:3n-3) was a more potent and more selective anti-inflammatory agent than n-3 PUFA. To gain further insights into this technology, we synthesized other novel PUFA consisting of beta-oxa, beta-thia, and gamma-thia compounds. All three types displayed anti-inflammatory activity. Each of the unsaturated beta-oxa fatty acids showed similar inhibition of PHA-PMA-induced T cell proliferation with a parallel inhibition of TNF-beta production. However, beta-oxa 25:6n-3 and beta-oxa 21:4n-3 displayed lower inhibitory action on IFN-gamma production. Surprisingly, beta-oxa 23:4n-6 and beta-oxa 21:3n-6 had marginal effect on IL-2 production. Thus, structural variation can generate selectivity for different immunological parameters. The beta-thia compounds 23:4n-6, 21:3n-6, and 21:3n-3 were highly effective in inhibiting all immunological responses. Of the two gamma-thia PUFA tested, gamma-thia 24:4n-6 was a strong inhibitor of all responses apart from IL-2, but gamma-thia 22:3n-6 had very little inhibitory effect. Two of the most active compounds, beta-thia 23:4n-6 and beta-thia 21:3n-6, were studied in more detail and shown to have an IC(50) of 1-2 muM under optimal conditions. Thus, these PUFA retain the immunosuppressive properties of the n-3 PUFAs, 20:5n-3 and 22:6n-3, but not the neutrophil-stimulating properties. Their action on T lymphocytes is independent of cyclooxygenase or lipoxygenase activity, and they act at a postreceptor-binding level by inhibiting the activation of protein kinase C and ERK1/ERK2 kinases.

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Placental regulation of fatty acid delivery and its effect on fetal growth--a review

More than 90 per cent of the fat deposition in the fetus occurs in the last 10 weeks of pregnancy during which it increases exponentially to reach a rate of accretion of around 7 g/day close to term. All of the n -3 and n -6 fatty acid structure acquired by the fetus has to cross the placenta and fetal blood is enriched in long chain polyunsaturated fatty acids (LCPUFA) relative to the maternal supply. The placenta may regulate its own fatty acid substrate supply via the action of placental leptin on maternal adipose tissue. Fatty acids cross the microvillous and basal membranes by simple diffusion and via the action of membrane bound and cytosolic fatty acid binding proteins (FABPs). The direction and magnitude of fatty acid flux is mainly dictated by the relative abundance of available binding sites. The fatty acid mix delivered to the fetus is largely determined by the fatty acid composition of the maternal blood although the placenta is able to preferentially transfer the important PUFA to the fetus as a result of selective uptake by the syncytiotrophoblast, intracellular metabolic channelling of individual fatty acids, and selective export to the fetal circulation. Placental FABP polymorphisms may affect these processes. There is little evidence to suggest that placental delivery of fatty acids limits normal fetal growth although the importance of the in utero supply may be to support post-natal development as most of the LCPUFA accumulated by the fetus is stored in the adipose tissue for use in early post-natal life.

Structural and functional characterization of the mouse fatty acid translocase promoter: activation during adipose differentiation

Fatty acid translocase (FAT/CD36) is a cell-surface glycoprotein that functions as a receptor/transporter for long-chain fatty acids (LCFAs), and interacts with other protein and lipid ligands. FAT/CD36 is expressed by various cell types, including platelets, monocytes/macrophages and endothelial cells, and tissues with an active LCFA metabolism, such as adipose, small intestine and heart. FAT/CD36 expression is induced during adipose cell differentiation and is transcriptionally up-regulated by LCFAs and thiazolidinediones in pre-adipocytes via a peroxisome-proliferator-activated receptor (PPAR)-mediated process. We isolated and analysed the murine FAT/CD36 promoter employing C(2)C(12)N cells directed to differentiate to either adipose or muscle. Transient transfection studies revealed that the 309 bp upstream from the start of exon 1 confer adipose specific activity. Sequence analysis of this DNA fragment revealed the presence of two imperfect direct repeat-1 elements. Electrophoretic mobility-shift assay demonstrated that these elements were peroxisome-proliferator-responsive elements (PPREs). Mutagenesis and transfection experiments indicated that both PPREs co-operate to drive strong promoter activity in adipose cells. We conclude that murine FAT/CD36 expression in adipose tissue is dependent upon transcriptional activation via PPARs through binding to two PPREs located at -245 to -233 bp and -120 to -108 bp from the transcription start site.

Induction and axonal localization of epithelial/epidermal fatty acid-binding protein in retinal ganglion cells are associated with axon development and regeneration

Epithelial/epidermal fatty acid-binding protein (E-FABP) is induced in peripheral neurons during nerve regeneration and is found at high levels in central neurons during neuronal migration and development. Furthermore, E-FABP expression is required for normal neurite outgrowth in PC12 cells treated with nerve growth factor (NGF). The present study examined whether E-FABP plays a role in retinal ganglion cell (RGC) differentiation and axon growth. Rat retinal tissues from embryonic (E) and postnatal (P) development through adulthood were examined using immunocytochemical labeling with E-FABP and growth-associated protein 43 (GAP-43) antibodies. E-FABP colocalized with GAP-43 at E14 through P10. At E14, E-FABP immunoreactivity was confined to the somas of GAP-43-positive cells in the ganglion cell layer, but it was localized to their axons by E15. The axons in the optic nerve were GAP-43-positive and E-FABP-negative on E15, but the two proteins were colocalized by E18. Retinal cultures at E15 confirmed that E-FABP and GAP-43 colocalize in RGCs. Postnatally, labeling was present between P1 and P10 but decreased at older ages and was minimally present or absent in adult animals. Western immunoblotting revealed that at E18, P1, and P10 E-FABP levels were at least fourfold greater than those in the adult. By P15, protein levels were only twofold greater, with adult levels reached by P31. Furthermore, E-FABP could be reinduced during axon regeneration. Dissociated P15 retinal cells cultured in the presence of brain-derived neurotrophic factor, ciliary neurotrophic factor, and basic fibroblast growth factor exhibited sixfold more GAP-43 and E-FABP double-positive RGCs (cell body and axons) than controls. Moreover, all GAP-43-immunoreactive RGCs were also positive for E-FABP. Taken together, these results indicate the following: 1) E-FABP is expressed in RGCs as they reached the ganglion cell layer and 2) E-FABP plays a functional role in the elaboration of RGC axons in both development and regeneration.

A surface-associated retinol- and fatty acid-binding protein (Gp-FAR-1) from the potato cyst nematode Globodera pallida: lipid binding activities, structural analysis and expression pattern

Parasitic nematodes produce at least two structurally novel classes of small helix-rich retinol- and fatty-acid-binding proteins that have no counterparts in their plant or animal hosts and thus represent potential targets for new nematicides. Here we describe a protein (Gp-FAR-1) from the plant-parasitic nematode Globodera pallida, which is a member of the nematode-specific fatty-acid- and retinol-binding (FAR) family of proteins but localizes to the surface of this species, placing it in a strategic position for interaction with the host. Recombinant Gp-FAR-1 was found to bind retinol, cis-parinaric acid and the fluorophore-tagged lipids 11-(dansylamino)undecanoic acid and dansyl-D,L-alpha-amino-octanoic acid. The fluorescence emission characteristics of the dansylated analogues indicated that the entire ligand enters the binding cavity. Fluorescence competition experiments showed that Gp-FAR-1 binds fatty acids in the range C(11) to C(24), with optimal binding at C(15). Intrinsic fluorescence analysis of a mutant protein into which a tryptophan residue had been inserted supported computer-based predictions of the position of this residue at the protein's interior and possibly also at the binding site. Of direct relevance to plant defence systems was the observation that Gp-FAR-1 binds two lipids (linolenic and linoleic acids) that are precursors of plant defence compounds and the jasmonic acid signalling pathway. Moreover, Gp-FAR-1 was found to inhibit the lipoxygenase-mediated modification of these substrates in vitro. Thus not only does Gp-FAR-1 function as a broad-spectrum retinol- and fatty-acid-binding protein, the results are consistent with the idea that Gp-FAR-1 is involved in the evasion of primary host plant defence systems.

Transport of fatty acids and metabolites across the peroxisomal membrane

The peroxisomal membrane forms a permeability barrier for a wide variety of metabolites required for and formed during fatty acid beta-oxidation. To communicate with the cytoplasm and mitochondria, peroxisomes need dedicated proteins to transport such hydrophilic molecules across their membranes. Genetic and biochemical studies in the yeast Saccharomyces cerevisiae have identified enzymes for redox shuttles as well as the first peroxisomal membrane transporter. This peroxisomal ATP-binding cassette transporter (Pat) is highly homologous to the gene mutated in X-linked adrenoleukodystrophy (X-ALD). The yeast Pat is required for import of activated fatty acids into peroxisomes suggesting that this is the primary defect in X-ALD.

Fatty acid import into mitochondria

The mitochondrial carnitine system plays an obligatory role in beta-oxidation of long-chain fatty acids by catalyzing their transport into the mitochondrial matrix. This transport system consists of the malonyl-CoA sensitive carnitine palmitoyltransferase I (CPT-I) localized in the mitochondrial outer membrane, the carnitine:acylcarnitine translocase, an integral inner membrane protein, and carnitine palmitoyltransferase II localized on the matrix side of the inner membrane. Carnitine palmitoyltransferase I is subject to regulation at the transcriptional level and to acute control by malonyl-CoA. The N-terminal domain of CPT-I is essential for malonyl-CoA inhibition. In liver CPT-I activity is also regulated by changes in the enzyme's sensitivity to malonyl-CoA. As fluctuations in tissue malonyl-CoA content are parallel with changes in acetyl-CoA carboxylase activity, which in turn is under the control of 5'-AMP-activated protein kinase, the CPT-I/malonyl-CoA system is part of a fuel sensing gauge, turning off and on fatty acid oxidation depending on the tissue's energy demand. Additional mechanism(s) of short-term control of CPT-I activity are emerging. One proposed mechanism involves phosphorylation/dephosphorylation dependent direct interaction of cytoskeletal components with the mitochondrial outer membrane or CPT-I. We have proposed that contact sites between the outer and inner mitochondrial membranes form a microenvironment which facilitates the carnitine transport system. In addition, this system includes the long-chain acyl-CoA synthetase and porin as components.

Reduced hepatic fatty acid oxidation in fasting PPARalpha null mice is due to impaired mitochondrial hydroxymethylglutaryl-CoA synthase gene expression

Glucose and fatty acid metabolism (oxidation versus esterification) has been measured in hepatocytes isolated from 24 h starved peroxisome proliferator-activated receptor-alpha (PPARalpha) null and wild-type mice. In PPARalpha null mice, the development of hypoglycemia during starvation was due to a reduced capacity for hepatic gluconeogenesis secondary to a 70% lower rate of fatty acid oxidation. This was not due to inappropriate expression of the hepatic CPT I gene, which was similar in both genotypes, but to impaired mitochondrial hydroxymethylglutaryl-CoA synthase gene expression in the PPARalpha null mouse liver. We also demonstrate that hepatic steatosis of fasting PPARalpha null mice was not due to enhanced triglyceride synthesis.

Transport mechanisms for long-chain polyunsaturated fatty acids in the human placenta

To understand the placental role in the processes responsible for the preferential accumulation of maternal long-chain polyunsaturated fatty acids (LCPUFAs) in the fetus, we investigated fatty acid uptake and metabolism in the human placenta. A preference for LCPUFAs over nonessential fatty acids has been observed in isolated human placental membranes as well as in BeWo cells, a human placental choriocarcinoma cell line. A placental plasma membrane fatty acid binding protein (p-FABP(pm)) with a molecular mass of approximately 40 kDa was identified. The purified p-FABP(pm) preferentially bound with essential fatty acids (EFAs) and LCPUFAs over nonessential fatty acids. Oleic acid was taken up least and docosahexaenoic acid (DHA) most by BeWo cells, whereas no such discrimination was observed in HepG2 liver cells. Studies on the distribution of radiolabeled fatty acids in the cellular lipids of BeWo cells showed that DHA is incorporated mainly into the triacylglycerol fraction, followed by the phospholipid fraction; the reverse is true for arachidonic acid (AA). The greater cellular uptake of DHA and its preferential incorporation into the triacylglycerol fraction suggests that both uptake and transport modes of DHA by the placenta to the fetus are different from those of AA. p-FABP(pm) antiserum preferentially decreased the uptake of LCPUFAs and EFAs by BeWo cells compared with preimmune serum. Together, these results show the preferential uptake of LCPUFAs by the placenta that is most probably mediated via the p-FABP(pm).

Genetic predictors of plasma lipid response to diet intervention

There is a growing interest in determining the genetic predictors of plasma lipid response to diet intervention. Several candidate gene loci, namely, apolipoprotein (APO) A1, APOA4, APOC3, APOB, APOE, CETP, LPL, and FABP2, have been shown to explain a significant, but still rather small, proportion of the interindividual variability in dietary response. Other gene loci code for products that play a relevant role in lipoprotein metabolism and are prime candidates for future studies (ie, CYP7). Future progress in this complex area will come from experiments carried out using animal models and from carefully controlled dietary protocols in humans.

Co-expression in rat heart and skeletal muscle of four genes coding for proteins implicated in long-chain fatty acid uptake

It has been suggested that specific membrane-associated and cytoplasmic proteins cooperate in the uptake of long-chain fatty acids by cardiac and skeletal muscle cells. A prerequisite for this hypothesis would be the co-occurrence of these proteins in muscle. Thus, we studied the possible co-expression in rat muscles of the genes coding for the integral membrane proteins fatty acid transport protein (FATP) and fatty acid translocase (FAT), the membrane-associated plasmalemmal fatty acid-binding protein (FABPpm) and the cytoplasmic heart-type fatty acid-binding protein (H-FABPc). The transcripts of the four proteins were assessed in heart and skeletal muscles of adult Wistar rats, in isolated cells and cell lines from rat heart and also in rat heart during development and upon streptozotocin-induced diabetes. All four genes showed high expression levels in heart, somewhat lower in red skeletal muscle (soleus) and appreciably lower in white skeletal muscle (extensor digitorum longus). FATP, FAT and H-FABPc showed a 3- to 5-fold increase in mRNA expression during maturational growth of the heart, while the FABPpm expression remained virtually constant. In the heart, streptozotocin-diabetes induced a slight, but statistically not significant, increase in the expression of all four genes. In conclusion, this study shows the co-expression of FATP, FAT, FABPpm and H-FABPc in rat muscles. This finding supports the possible cooperation of these proteins in the uptake of long-chain fatty acids by muscle cells.

Detection and cellular localization of plasma membrane-associated and cytoplasmic fatty acid-binding proteins in human placenta

The aim of this study was to investigate location and the types of membrane-associated and cytoplasmic fatty acid-binding proteins in human placental trophoblasts using monospecific polyclonal antibodies. Western blot analysis demonstrated the presence of multiple membrane and cytoplasmic fatty acid transport/binding proteins in human placenta. In addition to previously reported placental membrane fatty acid-binding (p-FABPpm, 40 kDa), fatty acid translocase (FAT, 88 kDa) and fatty acid transport protein (FATP, 62 kDa) were detected in both microvillous and basal membranes of the human placenta. Among the cytoplasmic proteins, heart (H) and liver (L) type FABP were detected in the cytosol of the human placental primary trophoblasts as well as in human placental choriocarcinoma (BeWo) cells. The immunoreactivity of epidermal type (E)-FABP was not detected in trophoblasts or BeWo cells despite its presence in human placental cytosol. Location of FAT and FATP on the both sides of the bipolar placental cells may favour transport of free fatty acids (FFA) pool in both directions i.e. from the mother to the fetus and vice versa. However, p-FABPpm, because of its exclusive location on the microvillous membranes, may favour the unidirectional flow of maternal plasma long-chain polyunsaturated fatty acids present in the FFA pool to the fetus, due to binding specificity for these fatty acids. Although the roles of these proteins in placental fatty acid uptake and metabolism are yet to be understood fully, their complex interaction may be involved in the uptake of maternal FFA by the placenta for delivery to the fetus.

Fatty acid-binding proteins in the heart

Long-chain fatty acids are important fuel molecules for the heart, their oxidation in mitochondria providing the bulk of energy required for cardiac functioning. The low solubility of fatty acids in aqueous solutions impairs their cellular transport. However, cardiac tissue contains several proteins capable of binding fatty acids non-covalently. These fatty acid-binding proteins (FABPs) are thought to facilitate both cellular uptake and intracellular transport of fatty acids. The majority of fatty acids taken up by the heart seems to pass the sarcolemma through a carrier-mediated translocation mechanism consisting of one or more membrane-associated FABPs. Intracellular transport of fatty acids towards sites of metabolic conversion is most likely accomplished by cytoplasmic FABPs. In this review, the roles of membrane-associated and cytoplasmic FABPs in cardiac fatty acid metabolism under (patho)physiological circumstances are discussed.

Oxidant-induced arachidonic acid release and impairment of fatty acid acylation in vascular smooth muscle cells

Oxidative damage, which plays a major role in the early stages of atherosclerosis, is associated with arachidonic acid (AA) release in vascular smooth muscle cells (VSMC) as in other cell types. In this study, H2O2 was used to investigate mechanisms of AA release from VSMC on oxidative stress. Cell treatment with H2O2 inhibited AA incorporation in an inverse relationship to prolonged H2O2-induced AA release. Identical kinetics of inhibition of AA incorporation and AA release were observed after cell treatment with AlF4-, a process not involving phospholipase A2 (PLA2) activation as recently described (A. Cane, M. Breton, G. Béréziat, and O. Colard. Biochem. Pharmacol. 53: 327-337, 1997). AA release was not specific, since oleic acid also increased in the extracellular medium of cells treated with H2O2 or AlF4- as measured by gas chromatography-mass spectrometry. In contrast, AA and oleic acid cell content decreased after cell treatment. Oleoyl and arachidonoyl acyl-CoA synthases and acyltransferases, assayed using a cell-free system, were not significantly modified. In contrast, a good correlation was observed between decreases in AA acylation and cell ATP content. The decrease in ATP content is only partially accounted for by mitochondrial damage as assayed by rhodamine 123 assay. We conclude that oxidant-induced arachidonate release results from impairment of fatty acid esterification and that ATP availability is probably responsible for free AA accumulation on oxidative stress by preventing its reesterification and/or transmembrane transport.

Molecular mechanism of cellular uptake and intracellular translocation of fatty acids

The molecular mechanism of the transport of long-chain fatty acids across cellular membranes and the necessity and precise functioning of specific proteins in this process are still unclear. Various alternative mechanisms have been proposed. Studies with artificial phospholipid bilayers support the concept that fatty acids may enter and traverse the plasma membrane without the involvement of proteins. On the other hand, a number of membrane-associated fatty acid-binding proteins (FABPs) have been described which putatively function as acceptors for fatty acids released from albumin or from lipoproteins. Albumin binding proteins located at the outer cell surface could play an additional role in the delivery of fatty acids. The subsequent transmembrane translocation of fatty acids could take place by a membrane protein acting as a translocase, or by simple diffusion of fatty acids through either the phospholipid bilayer or a pore or channel formed by one or more membrane fatty acid transporters. At the inner side of the plasma membrane, the fatty acid is bound to a cytoplasmic FABP, which serves to buffer the intracellular aqueous fatty acid concentration. The direction of fatty acid migration through the plasma membrane most likely is governed by the transmembrane gradient of fatty acid concentration, assisted to some extent and in selected tissues by co-transport of sodium ions. The intracellular transport of fatty acids from the plasma membrane to the sites of metabolic conversion (oxidation, esterification) or subcellular target (signal transduction) is greatly facilitated by cytoplasmic FABPs. In conclusion, cellular uptake and intracellular translocation of long-chain fatty acids is a multi-step process that is facilitated by various membrane-associated and soluble proteins. The mechanism of cellular uptake of fatty acids probably involves both a passive and carrier-mediated transmembrane translocation.

Regulation of FAT/CD36 gene expression: further evidence in support of a role of the protein in fatty acid binding/transport

Much biochemical evidence has implicated rat adipocyte CD36 (FAT) in membrane binding and transport of long-chain fatty acids (FA). Expression of the mRNA favored tissues with active FA metabolism and was upregulated in vivo with diabetes and with high fat feeding. In culture, CD36 mRNA was a strong marker of preadipocyte differentiation and was modulated by the same factors effective on mRNAs coding for other proteins involved in FA metabolism. In preadipocytes, long-chain FA or 2-bromopalmitate but not short-chain FA strongly induced CD36 mRNA within 8 h to an optimum within 24 h. Removal of the FA resulted in a decay of CD36 mRNA with a half life of about 12 h. In differentiated adipocytes, levels of CD36 mRNA were downregulated by the 3': 5'-cyclic adenosine monophosphate, cAMP, analog, 8-(4-chlorophenylthio) adenosine, 8-CPT, at concentrations of 1-100 microM. The effect, observed within 6 h, was optimal after 18 h and independent of the action of 8-CPT to mobilize FA. Regulation of CD36 expression by factors effective on expression of other proteins implicated in FA metabolism is consistent with its role in membrane FA transport.

Dramatic enhancement of the specific expression of the heart-type fatty acid binding protein in rat brown adipose tissue by cold exposure

To understand the difference in energy metabolisms in brown (BAT) and white (WAT) adipose tissues, we examined the steady-state transcript levels of the heart-type and adipose-type fatty acid binding proteins (H-FABP and A-FABP, respectively) by Northern blot analysis. The transcript of H-FABP in rat BAT was increased about 100-fold by cold exposure, whereas that in WAT was negligible, and was increased only slightly by cold exposure. The transcript of A-FABP was observed in both BAT and WAT, the level being slightly greater in WAT. However, its transcript level was not affected by cold exposure in either adipose tissue. In addition, on treatment with norepinephrine (NE), transcript level of H-FABP was elevated markedly but that of A-FABP was not changed in rat brown adipocytes. Therefore, the stimulatory effect of cold exposure on the transcript of H-FABP in BAT was concluded to be mediated by NE, like that of the uncoupling protein (UCP). Thus, the expressions of H-FABP and UCP may be controlled by the same mechanism.