Cellular fatty acid-binding proteins: current concepts and future directions

Heart-type fatty acid binding protein predicts cardiovascular events in patients with stable coronary artery disease: a prospective cohort study

BACKGROUND

Heart-type fatty acid binding protein (H-FABP) has been reported to be a prognostic predictor for cardiovascular outcome in acute coronary syndrome (ACS). However, its prognostic utility in patients with stable coronary artery disease (CAD) has not been well established. The aim of this study was to assess the association between H-FABP with the severity of coronary disease and cardiovascular events (CVEs) in patients with stable CAD.

METHODS

A total of 4,370 angiography-proven CAD patients were consecutively enrolled. The severity of CAD was assessed by Gensini Score (GS) and the numbers of diseased vessels. The CVEs included cardiovascular death, myocardial infarction, stroke and coronary revascularization. Cox regression analysis with adjusted hazard ratios (HRs) and Kaplan-Meier analysis were used to evaluate the relation of H-FABP to CVEs in this cohort.

RESULTS

During a median follow-up of 51 months, 353 CVEs occurred. Overall, patients in the highest levels of H-FABP group had increased rate of multi-vessel stenosis and higher GS compared with those in the lowest group (P<0.05, respectively). Moreover, H-FABP levels were significantly higher in patients with events compared to those without (P<0.001). In Cox regression analysis, elevated H-FABP levels were found to be independently associated with a high risk of CVEs [adjusted HRs: 1.453; 95% confidence intervals (CIs): 1.040-2.029, P=0.028], especially with cardiovascular death (adjusted HRs: 2.865; 95% CI: 1.315-6.243, P=0.008).

CONCLUSIONS

Our results demonstrated that H-FABP was also a useful predictor for CVEs in patients with stable CAD, which needed to be verified by further studies.

A survey of proteins in midgut contents of the tick, Haemaphysalis flava, by proteome and transcriptome analysis

Tick blood meals are stored and digested in their midguts. Blood digestion is complex, and many proteins are involved. Study of the tick-derived proteins in the midgut content may aid in the discovery of active molecules that would be useful for anti-tick vaccines. We analyzed the midgut content proteomes of partially engorged female Haemaphysalis flava, fully engorged female H. flava, and hedgehog serum using liquid chromatography tandem-mass spectrometry and label-free quantitation. In this study, high-confidence protein profiling of tick midgut content was determined. Based on the search against our in-house transcriptome database, the 28 high-confidence proteins were identified. Of these, 17 were identified as tick-derived, and the rest were of unspecified origin (proteins that could not be differentiated as host-derived or tick-derived proteins). The function of these midgut content proteins identified here may involve nutrient transportation, anti-coagulation, erythrocyte lysis, detoxification, lipid metabolism, and immunization. The presence of hemoglobin suggested that the red blood cells were lysed in the gut lumen. The midgut contents contain a large amount of fibrinogen and it has the ability to clot immediately. The midgut contained mostly host-derived proteins, and these host proteins provide rich nutrients for tick development and reproduction. However, some intracellular proteins were also identified, suggesting the possibility of shedding of the midgut epithelium and ingestion of saliva during feeding. This finding advances our understanding of the digestive mechanism and will be useful in the screening of vaccine antigens.

Adipose-Specific Expression, Developmental and Nutritional Regulation of the Gene-Encoding Retinol-Binding Protein 7 in Pigs

Modulation of expression of adipose tissue-specific transcripts has been known to regulate adipogenesis and lipid metabolism. Recently, adipose-specific expression patterns and developmental regulation of the gene-encoding retinol-binding protein 7 (RBP7) was identified. However, its expression in adipose tissue of the porcine species has yet to be explored. In this study, adipose tissue-specific expression of porcine RBP7 was identified and conservation of the fatty acid-binding domains and evolutionary relationship of the RBP7 gene were verified comparatively across mammalian species. Our in vitro and in vivo analysis of gene expression revealed that RBP7 expression was significantly high in fat cell fraction compared to stromal vascular cells (p < 0.05) and increased during development (p < 0.05). The level of RBP7 expression was upregulated during a 24-h short-term fasting intervention and restored 6 h after refeeding (p < 0.05). Taken together, these studies provide insights into the role of RBP7 in adipose tissue of pigs during development and nutritional intervention and pave the way for future studies on the regulation of retinol homeostasis in porcine adipose tissue.

Novel Molecular Interactions of Acylcarnitines and Fatty Acids with Myoglobin

Previous research has indicated that long-chain fatty acids can bind myoglobin (Mb) in an oxygen-dependent manner. This suggests that oxy-Mb may play an important role in fuel delivery in Mb-rich muscle fibers (e.g. type I fibers and cardiomyocytes), and raises the possibility that Mb also serves as an acylcarnitine-binding protein. We report for the first time the putative interaction and affinity characteristics for different chain lengths of both fatty acids and acylcarnitines with oxy-Mb using molecular dynamic simulations and isothermal titration calorimetry experiments. We found that short- to medium-chain fatty acids or acylcarnitines (ranging from C2:0 to C10:0) fail to achieve a stable conformation with oxy-Mb. Furthermore, our results indicate that C12:0 is the minimum chain length essential for stable binding of either fatty acids or acylcarnitines with oxy-Mb. Importantly, the empirical lipid binding studies were consistent with structural modeling. These results reveal that: (i) the lipid binding affinity for oxy-Mb increases as the chain length increases (i.e. C12:0 to C18:1), (ii) the binding affinities of acylcarnitines are higher when compared with their respective fatty acid counterparts, and (iii) both fatty acids and acylcarnitines bind to oxy-Mb in 1:1 stoichiometry. Taken together, our results support a model in which oxy-Mb is a novel regulator of long-chain acylcarnitine and fatty acid pools in Mb-rich tissues. This has important implications for physiological fuel management during exercise, and relevance to pathophysiological conditions (e.g. fatty acid oxidation disorders and cardiac ischemia) where long-chain acylcarnitine accumulation is evident.

Reevaluation of cardiac risk scores and multiple biomarkers for the prediction of first major cardiovascular events and death in the drug-eluting stent era

BACKGROUND

Risk scores and cardiac biomarker tests allow clinicians to accurately diagnose acute coronary syndrome (ACS) and perform early risk stratification. However, few investigations have evaluated the use of these risk scores and biomarkers for predicting risk of cardiovascular events in drug-eluting stent (DES) era.

METHODS

This prospective cohort study included 861 patients with ACS. Three risk scores-Global Registry of Acute Coronary Events (GRACEs), Platelet glycoprotein IIb/IIIa in Unstable angina: Receptor Suppression Using Integrilin, and Thrombolysis In Myocardial Infarction-and levels of four biomarkers-N-terminal pro-B-type natriuretic peptide (NT pro-BNP), high-sensitivity troponin T, heart-fatty acid binding protein, and high-sensitivity C-reactive protein-were recorded on admission. Major adverse cardiac events (MACE) (death, cardiovascular events) were evaluated at 30-day and 1-year follow-up.

RESULTS

At 30-day follow-up, there were 23 (3.1%) deaths from cardiovascular events and 4 (0.5%) cerebral accidents. NT pro-BNP levels and GRACE score were strong MACE predictors, with adjusted odds ratios (ORs) (95% CI) of 2.90 (1.63-5.20) and 1.01 (1.00-1.02), respectively, in logistic model. The C-statistic of NT pro-BNP (0.77; 95% CI, 0.67-0.86) was similar to that of GRACE score (0.76; 95% CI, 0.66-0.87); however, the combined C-statistic was higher (0.81), yielding a net reclassification improvement of 13% (p<0.01). At 1-year follow-up, there were 51 (6.8%) deaths and 10 (1.3%) cerebral accidents.

CONCLUSION

In the DES era, GRACE score and biomarkers can still predict major cardiac events in patients with ACS for both acute and long-term prognoses.

Molecular dynamic simulations reveal the structural determinants of Fatty Acid binding to oxy-myoglobin

The mechanism(s) by which fatty acids are sequestered and transported in muscle have not been fully elucidated. A potential key player in this process is the protein myoglobin (Mb). Indeed, there is a catalogue of empirical evidence supporting direct interaction of globins with fatty acid metabolites; however, the binding pocket and regulation of the interaction remains to be established. In this study, we employed a computational strategy to elucidate the structural determinants of fatty acids (palmitic & oleic acid) binding to Mb. Sequence analysis and docking simulations with a horse (Equus caballus) structural Mb reference reveals a fatty acid-binding site in the hydrophobic cleft near the heme region in Mb. Both palmitic acid and oleic acid attain a "U" shaped structure similar to their conformation in pockets of other fatty acid-binding proteins. Specifically, we found that the carboxyl head group of palmitic acid coordinates with the amino group of Lys45, whereas the carboxyl group of oleic acid coordinates with both the amino groups of Lys45 and Lys63. The alkyl tails of both fatty acids are supported by surrounding hydrophobic residues Leu29, Leu32, Phe33, Phe43, Phe46, Val67, Val68 and Ile107. In the saturated palmitic acid, the hydrophobic tail moves freely and occasionally penetrates deeper inside the hydrophobic cleft, making additional contacts with Val28, Leu69, Leu72 and Ile111. Our simulations reveal a dynamic and stable binding pocket in which the oxygen molecule and heme group in Mb are required for additional hydrophobic interactions. Taken together, these findings support a mechanism in which Mb acts as a muscle transporter for fatty acid when it is in the oxygenated state and releases fatty acid when Mb converts to deoxygenated state.

The BRCA1 tumor suppressor binds to inositol 1,4,5-trisphosphate receptors to stimulate apoptotic calcium release

The inositol 1,4,5-trisphosphate receptor (IP3R) is a ubiquitously expressed endoplasmic reticulum (ER)-resident calcium channel. Calcium release mediated by IP3Rs influences many signaling pathways, including those regulating apoptosis. IP3R activity is regulated by protein-protein interactions, including binding to proto-oncogenes and tumor suppressors to regulate cell death. Here we show that the IP3R binds to the tumor suppressor BRCA1. BRCA1 binding directly sensitizes the IP3R to its ligand, IP3. BRCA1 is recruited to the ER during apoptosis in an IP3R-dependent manner, and, in addition, a pool of BRCA1 protein is constitutively associated with the ER under non-apoptotic conditions. This is likely mediated by a novel lipid binding activity of the first BRCA1 C terminus domain of BRCA1. These findings provide a mechanistic explanation by which BRCA1 can act as a proapoptotic protein.

Molecular cloning and functional analysis of the fatty acid-binding protein (Sp-FABP) gene in the mud crab (Scylla paramamosain)

Intracellular fatty acid-binding proteins (FABPs) are multifunctional cytosolic lipid-binding proteins found in vertebrates and invertebrates. In this work, we used RACE to obtain a full-length cDNA of Sp-FABP from the mud crab Scylla paramamosain. The open reading frame of the full length cDNA (886 bp) encoded a 136 amino acid polypeptide that showed high homology with related genes from other species. Real-time quantitative PCR identified variable levels of Sp-FABP transcripts in epidermis, eyestalk, gill, heart, hemocytes, hepatopancreas, muscle, ovary, stomach and thoracic ganglia. In ovaries, Sp-FABP expression increased gradually from stage I to stage IV of development and decreased in stage V. Sp-FABP transcripts in the hepatopancreas and hemocytes were up-regulated after a bacterial challenge with Vibrio alginnolyficus. These results suggest that Sp-FABP may be involved in the growth, reproduction and immunity of the mud crab.

Molecular cloning and tissue expression of the fatty acid-binding protein (Es-FABP) gene in female Chinese mitten crab (Eriocheir sinensis)

Background

Fatty acid-binding proteins (FABPs), small cytosolic proteins that function in the uptake and utilization of fatty acids, have been extensively studied in higher vertebrates while invertebrates have received little attention despite similar nutritional requirements during periods of reproductive activity.

Results

Therefore, a cDNA encoding Eriocheir sinensis FABP (Es-FABP) was cloned based upon EST analysis of a hepatopancreas cDNA library. The full length cDNA was 750 bp and encoded a 131 aa polypeptide that was highly homologous to related genes reported in shrimp. The 9108 bp Es-FABP gene contained four exons that were interrupted by three introns, a genomic organization common among FABP multigene family members in vertebrates. Gene expression analysis, as determined by RT-PCR, revealed the presence of Es-FABP transcripts in hepatopancreas, hemocytes, ovary, gills, muscle, thoracic ganglia, heart, and intestine, but not stomach or eyestalk. Real-time quantitative RT-PCR analysis revealed that Es-FABP expression in ovary, hemocytes, and hepatopancreas was dependent on the status of ovarian development, with peak expression observed in January.

Conclusions

Evidence provided in the present report supports a role of Es-FABP in lipid transport during the period of rapid ovarian growth in E. sinensis, and indirectly confirms the participation of the hepatopancreas, ovary, and hemocytes in lipid nutrient absorption and utilization processes.

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.

Prognostic utility of heart-type fatty acid binding protein in patients with acute coronary syndromes

BACKGROUND

Heart-type fatty acid binding protein (H-FABP) is a cytosolic protein that is released rapidly from the cardiomyocyte in response to myocardial injury. Although it has been investigated as an early marker of acute myocardial infarction, its prognostic utility in acute coronary syndromes has not been established.

METHODS AND RESULTS

We measured H-FABP in 2287 patients with acute coronary syndromes from the OPUS-TIMI 16 trial. H-FABP was elevated (> 8 ng/mL) in 332 patients (14.5%). Patients with an elevated H-FABP were more likely to suffer death (hazard ratio [HR], 4.1; 95% CI, 2.6 to 6.5), recurrent myocardial infarction (HR, 1.6; 95% CI, 1.0 to 2.5), congestive heart failure (HR, 4.5; 95% CI, 2.6 to 7.8), or the composite of these end points (HR, 2.6; 95% CI, 1.9 to 3.5) through the 10-month follow-up period. H-FABP predicted the risk of the composite end point both in patients who were troponin I negative (HR, 2.1; 95% CI, 1.3 to 3.4) and in those who were troponin I positive (HR, 3.3; 95% CI, 2.0 to 5.3). In a Cox proportional-hazards model that adjusted for baseline variables, including demographics, clinical characteristics, creatinine clearance, ST deviation, index diagnosis, and troponin I, elevated H-FABP remained a significant predictor of the composite end point (HR, 1.9; 95% CI, 1.3 to 2.7), as well as the individual end points of death (HR, 2.7; 95% CI, 1.5 to 4.9) and CHF (HR, 2.4; 95% CI, 1.2 to 5.0). In a multimarker approach, H-FABP, troponin I, and B-type natriuretic peptide provided complementary information.

CONCLUSIONS

Elevation of H-FABP is associated with an increased risk of death and major cardiac events in patients presenting across the spectrum of acute coronary syndromes and is independent of other established clinical risk predictors and biomarkers.

FABP3 and FABP10 in Atlantic salmon (Salmo salar L.)--general effects of dietary fatty acid composition and life cycle variations

The increased use of dietary plant oil supplementation combined with high dietary lipid loads challenges the lipid transport systems of cultivated fish species. Fatty acid binding proteins (FABPs) have been thoroughly studied as intracellular fatty acid transporters in vertebrates, but no data have been reported in Atlantic salmon. In the present study, comparative characterizations were performed, and dietary influence of plant oil supplementation on FABP3 and FABP10 expression was studied for several tissues in two separate dietary trials. In trial I, groups (6 fish each) were fed diets for 42 weeks (body mass 142+/-1 to 1463+/-83 g) (mean+/-S.D.), containing graded levels of rapeseed oil substituting for fish oil using a linear regression design. In trial II, groups (3 fish each) were fed 100% fish oil or 100% plant oil for 22 months (0.160+/-0.052 to 2523+/-590 g) (mean+/-S.D.) and sampled at regular intervals. Liver and muscle tissues appeared to express several FABPs possibly linked to different metabolic functions. FABPs mRNA expression did not change with dietary inclusion of 75% rapeseed oil, whereas FABP3 protein expression seemed to be affected by dietary rapeseed oil inclusion. Significant changes in red muscle FABP3 mRNA expression correlate to significant changes in total beta-oxidation capacity during the energy consuming process of smoltification.

Proteomic approach to the diagnosis of acute coronary syndrome: Preliminary results

BACKGROUND

Cardiac multimarker strategy is recommended by the IFCC, ESC and the ACC for an early risk stratification in non-ST-segment elevation (NSTE) ECG patients with chest pain. A new approach, based on protein biochip array technology, performs simultaneously: cTnI, CK-MB, myoglobin, CAIII, GFBB and FABP using a single chip.

METHODS

We evaluated the analytical performance of the Randox-Evidence Investigator -biochip cardiac panel according to IFCC recommendations and NCCLS guidelines; a preliminary clinical evaluation was carried out on chest pain NSTE ECG patients, to evaluate the accuracy of the multimarker approach in an early diagnosis of AMI, related to the final diagnosis (ACC/ESC criteria).

RESULTS

Troponin, CK-MB and FABP methods provide reproducible within-run and between-day results (total % CVs from 5.9% to 9.7%), and myoglobin and CAIII methods showed the total % CVs from 16.4% to 25.8%. Our preliminary clinical data suggests that FABP had a better diagnostic performance (sensibility = 100%) than myoglobin (sensibility = 75%) to detect AMI in the first hours after the onset of the chest pain and myoglobin/CAIII ratio (specificity = 92.9%) improved the myoglobin specificity.

CONCLUSIONS

Cardiac markers have different diagnostic roles and, in this contest, biochip technology could be an interesting approach supporting clinical expectations.

Heart fatty acid binding protein in the rapid evaluation of myocardial damage following valve replacement surgery

BACKGROUND

Myocardial damage occurs following valve replacement surgery. We estimated the value of heart fatty acid binding protein (H-FABP) in these patients.

METHODS

Sixty elected patients were enrolled and distributed into single (group A) and double (group B) valve replacement groups. The clinical data were outlined and blood samples were collected perioperatively for determination of plasma levels of H-FABP, cardiac troponin-I (cTn-I), and CK-MB in both groups.

RESULTS

56 patients completed the study and no significant difference of clinical data was observed except CPB time and ACC time between groups. H-FABP level elevated quickly after reperfusion and peaked significantly earlier than cTn-I and CK-MB, it also declined rapidly but did not return to baseline at 24 h after reperfusion. Three markers' levels were all higher in group B than in group A after reperfusion with significant differences at their peaks and thereafter. Patients with postoperative complications had significantly higher H-FABP levels than usual. H-FABP peak level associated well with the length of CPB and ACC as well as with other 2 markers' peak levels in both groups.

CONCLUSION

Compared with cTn-I and CK-MB, H-FABP is an earlier and potentially useful marker in the rapid evaluation of myocardial damage following valve replacement surgery with CPB.

Humoral immune response against Fasciola gigantica fatty acid binding protein

Recombinant fatty acid binding protein of Fasciola gigantica was expressed in Escherichia coli and purified by nickel chelating affinity chromatography. The recombinant protein along with native fatty acid binding protein (FABP) isolated from the parasite were evaluated for their potential in the diagnosis of F. gigantica infection in sheep, cattle and buffaloes, both by ELISA and western blotting. Results of this study indicate that there is no humoral immune response generated against this protein in the experimental infection of these ruminants with F. gigantica, thereby limiting the usefulness of this antigen in the early diagnosis of fasciolosis in these animals. Also, the paper discusses the probable reasons for the failure of this protein in detecting humoral response in these animals by ELISA and immunoblotting.

Microvascular and biochemical compensation during ventricular hypertrophy in male rainbow trout

We investigated whether there are compensatory changes in the coronary microvasculature, cardiac lipid metabolism, and myocyte ultrastructure associated with ventricular enlargement in male rainbow trout. Epicardial tissue was sampled at different stages of sexual maturation, and we estimated arterial capillary density, intercapillary diffusion distance, and applied a diffusion model to predict PO(2) at different workloads. We also measured biochemical indices of lipid metabolism and estimated fractional volumes of mitochondria and myofibrils in myocytes. Immature fish with nonenlarged ventricles had the highest capillary length densities (1620+/-158 mm mm(-3)). Maturing trout with moderate ventricular hypertrophy had lower capillary length densities (1103+/-58 mm mm(-3)) and similar diffusion distances (13.9+/-0.7 microm) compared with immature fish (11.7+/-0.9 microm). The largest ventricles had intermediate capillary length densities (1457+/-288 mm mm(-3)) and diffusion distances (12.8+/-0.8 microm). Modelling predicted that enlarged ventricles would not become anoxic even at maximal workloads. Biochemical markers of fatty acid metabolism and aerobic capacity were unchanged with hypertrophy. Volume densities of mitochondria and myofibrils were also not influenced by cardiac growth. In summary, ventricle hypertrophy results in expansion of the coronary capillary bed and the maintenance of the epicardial capacities for fat and oxidative metabolism.

Gene cloning, expression and vaccine testing of Schistosoma japonicum SjFABP

A 600 bp DNA fragment was amplified by PCR from an adult Schistosoma japonicum cDNA library. Sequence analysis confirmed that this fragment contained an S. japonicum Chinese mainland strain fatty acid binding protein (Sj14FABP) gene. This gene was subsequently expressed in Escherichia coli (E. coli) and in Baculovirus/silkworm systems. The recombinant protein from E. coli was a 41 kDa GST fusion protein (rSj14/GST), which could be purified by glutathione agarose affinity chromatography, with a yield of 25 mg/L E. coli culture. The recombinant protein from the Baculovirus/silkworm system was an 18 kDa fusion protein (rSj14/His), which could be purified by Ni-NTA resin chromatography column with a yield of 3.5 mg per silkworm larva. Both rSj14/GST and rSj14/His could be recognized by S. japonicum-infected mouse sera and anti-rSj14/GST mouse sera in Western blotting. The purified recombinant protein was immunogenic in mice, rats and sheep, and 34.3%, 31.9% and 59.2% worm reductions, respectively, were obtained in vaccinated Kunming mice, Wistar rats and sheep vaccinated with Sj14/GST, compared to non-vaccinated control groups. Worm reductions of 48.8% and 49.0% were recorded in Balb/c mice immunized with Sj14/His, compared to non-vaccinated and BCG-vaccinated groups, respectively. These results indicate that rSj14FABP is a promising candidate vaccine for schistosomiasis japonica, particularly as in the rat and sheep vaccination experiments, no adjuvant was used.

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.

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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.

Adipose differentiation related protein: expression, purification of recombinant protein in Escherichia coli and characterization of its fatty acid binding properties

Adipose differentiation related protein (ADRP) is a 53 kDa protein encoded by a cDNA originally cloned by differential hybridization from murine adipocytes. ADRP is induced during the early onset of the adipose differentiation program and is expressed at high level in mature adipocytes. We have demonstrated that ADRP stimulated the uptake of fatty acids thereby providing evidence for a functional role of ADRP in lipid metabolism. In the present paper, the murine ADRP has been expressed as a recombinant histidine-tagged protein in Escherichia coli, and purified from expressing cultures in order to examine its biochemical properties. We report here that the purified recombinant ADRP binds fatty acids and exhibits stoichiometric saturable binding of NBD-stearic acid with a K(d)=0.145+/-0.003 microM and a B(max)=0.99+/-0.05. Analysis of fluorescence emission spectra indicates that the polarity of the ADRP binding site is near epsilon approximately 23, close to that observed for fatty acid binding sites in other lipid binding proteins such as the liver fatty acid binding protein. The data presented here provide evidence that isolated ADRP purified in the experimental conditions described here can be used for functional studies.

Heart-type fatty acid binding protein as a marker of reperfusion after thrombolytic therapy

Accurate, rapid, and simple noninvasive measures of infarct-related artery (IRA) patency are needed to identify patients with failed coronary reperfusion for rescue percutaneous coronary intervention (PCI). Heart-type Fatty Acid Binding Protein (H-FABP) is a small, cytosolic protein found in high concentrations in the myocardium. We evaluated the efficacy of H-FABP as a marker for successful reperfusion after thrombolysis. Fifty-eight subjects from the TIMI 14 trial had H-FABP and myoglobin concentrations measured at baseline (immediately prior to thrombolysis) and 60, 90, and 180 min after thrombolysis. All patients underwent coronary angiography at 90 min. By 60 min after thrombolysis, median concentrations of H-FABP and myoglobin were significantly higher in patients with a patent IRA than in those with an occluded IRA (P<0.01 for each). Similarly, the 60 and 90 min/baseline H-FABP and myoglobin ratios were significantly higher among patients with a patent IRA (P<0.01 for each). There were no significant differences in marker concentrations or ratios between patients with TIMI grade 2 and TIMI grade 3 flow. The area under the ROC curve tended to be greater for the 60 and 90 min/baseline myoglobin ratios than for similar ratios of H-FABP (0.71 and 0.73 vs. 0.64 and 0.62; P=ns). In conclusion, successful reperfusion can be detected within the first 60 min after thrombolysis with either H-FABP or myoglobin. Despite a favorable kinetic profile, however, H-FABP does not appear to represent a significant advance over myoglobin in the noninvasive detection of reperfusion after thrombolysis.

Liver and intestinal fatty acid-binding protein expression increases phospholipid content and alters phospholipid fatty acid composition in L-cell fibroblasts

Although fatty acid-binding proteins (FABP) differentially affect fatty acid uptake, nothing is known regarding their role(s) in determining cellular phospholipid levels and phospholipid fatty acid composition. The effects of liver (L)- and intestinal (I)-FABP expression on these parameters were determined using stably transfected L-cells. Expression of L- and I-FABP increased cellular total phospholipid mass (nmol/mg protein) 1.7- and 1.3-fold relative to controls, respectively. L-FABP expression increased the masses of choline glycerophospholipids (ChoGpl) 1.5-fold, phosphatidylserine (PtdSer) 5.6-fold, ethanolamine glycerophospholipids 1.4-fold, sphingomyelin 1.7-fold, and phosphatidylinositol 2.6-fold. In contrast, I-FABP expression only increased the masses of ChoGpl and PtdSer, 1.2- and 3.1-fold, respectively. Surprisingly, both L- and I-FABP expression increased ethanolamine plasmalogen mass 1.6- and 1.1-fold, respectively, while choline plasmalogen mass was increased 2.3- and 1.7-fold, respectively. The increase in phospholipid levels resulted in dramatic 48 and 33% decreases in the cholesterol-to-phospholipid ratio in L- and I-FABP expressing cells, respectively. L-FABP expression generally increased polyunsaturated fatty acids, primarily by increasing 20:4n-6 and 22:6n-3, while decreasing 18:1n-9 and 16:1n-7. I-FABP expression generally increased only 20:4n-6 proportions. Hence, expression of both I- and L-FABP differentially affected phospholipid mass, class composition, and acyl chain composition. Although both proteins enhanced phospholipid synthesis, the effect of L-FABP was much greater, consistent with previous work suggesting that these two FABP differentially affect lipid metabolism.

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.

cDNA sequence and tissue-specific expression of a basic liver-type fatty acid binding protein in adult zebrafish (Danio rerio)

We have determined the nucleotide sequence for a cDNA clone derived from zebrafish (Danio rerio) that codes for a fatty acid binding protein (FABP). Amino acid sequence similarity of the zebrafish FABP was highest to FABPs isolated from the livers of catfish, chicken, salamander and iguana. The open-reading frame of the zebrafish FABP cDNA codes for a protein of 14.0 kDa with a calculated isoelectric point of 8.8. The zebrafish liver-type FABP (L-FABP) cDNA hybridized to single restriction fragments of total zebrafish genomic DNA digested with the restriction endonucleases HaeIII or EcoRI suggesting that a single copy of the L-FABP gene is present in the zebrafish genome. Northern blot analysis demonstrated that the zebrafish L-FABP cDNA hybridized to a transcript of 700 nucleotides in total zebrafish RNA. In situ hybridization and emulsion autoradiography revealed that the L-FABP was expressed exclusively in the liver of the adult zebrafish. Based on amino acid sequence similarity, the isoelectric point and its tissue-specific pattern of expression, we conclude that this zebrafish FABP belongs to the basic liver-type FABPs only found, thus far, in non-mammalian vertebrates.

Nucleotide sequence of a cDNA clone coding for an intestinal-type fatty acid binding protein and its tissue-specific expression in zebrafish (Danio rerio)

We have cloned a cDNA from zebrafish (Danio rerio) that contains an open-reading frame of 132 amino acids coding for a fatty acid binding protein (FABP) of approximately 15 kDa. Multiple sequence alignment revealed extensive amino acid identity between this zebrafish FABP and intestinal-like FABPs (I-FABP) from other species. The zebrafish I-FABP cDNA hybridized to single restriction fragments of total zebrafish genomic DNA digested with the restriction endonucleases PstI Bg/II or EcoRI suggesting that a single copy of the I-FABP gene is present in the zebrafish genome. An oligonucleotide probe complementary to the zebrafish I-FABP mRNA hybridized to an mRNA of approximately 800 bases in Northern blot analysis. In situ hybridization revealed that the I-FABP mRNA was expressed exclusively in the intestine of the adult zebrafish.

Intestinal fatty acid binding protein may favor differential apical fatty acid binding in the intestine

The intestinal mucosa metabolizes fatty acids differently when presented to the lumenal or basolateral membrane. Expression of both liver and intestinal fatty acid binding proteins (L- and I-FABPs) uniquely in the enterocyte offers a possible explanation of this phenomenon. An organ explant system was used to analyze the relative binding of fatty acids to each protein. More fatty acid was bound to L-FABP than to I-FABPs (28% vs. 6% of cytosolic radioactivity), no matter on which side the fatty acid was added. However, a 2-3-fold increase in fatty acid binding to the intestinal paralog was noted after apical addition of palmitic or oleic acid in mucosa from chow fed rats. When oleic acid was added apically, a 1.4-fold increase in binding to I-FABP was observed in mucosa derived from chronically fat fed rats, consistent with the previously observed 50% increase in the content of that protein. Immunocytochemical localization of both FABPs in vivo demonstrated an apical cytoplasmic localization in the fasting state, and redistribution to the entire cytoplasm after fat feeding. These data are consistent with the hypothesis that I-FABP may contribute to the metabolic compartmentalization of apically presented fatty acids in the intestine.

Down-regulation of liver and heart specific fatty acid binding proteins by endotoxin and cytokines in vivo

Fatty acid binding proteins (FABPs) are abundantly present in tissues that actively metabolize fatty acids (FA). While their precise physiological function is not known, FABPs have been shown to play a role in the uptake and/or utilization of FA within the cell. FA metabolism is markedly altered during the host response to infection and inflammation. Previous studies have demonstrated that endotoxin or bacterial lipopolysaccharide (LPS) enhances hepatic FA synthesis and re-esterification while inhibiting FA oxidation in liver, heart and muscle. Now, we have examined the in vivo effects of LPS and cytokines on FABPs in liver (L-FABP), heart and muscle (H-FABP). Syrian hamsters were injected with LPS, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) and the mRNA and protein content for L-FABP and H-FABP were analyzed. 16 h after administration, LPS (100 microg/100 g body weight) produced a 72% decrease in L-FABP mRNA levels in liver and this effect was sustained for 24 h. LPS also produced a 41% decrease in the protein content of L-FABP in liver after 24 h of treatment. TNF-alpha and IL-1beta decreased L-FABP mRNA levels in liver by 30 and 45%, respectively. LPS decreased H-FABP mRNA levels in skeletal muscle by 60% and in heart by 65%. LPS also produced a 49% decrease in H-FABP protein content in muscle. Neither TNF-alpha nor IL-1beta had any significant effect on H-FABP mRNA expression in heart and muscle. Taken together, these results indicate that LPS decreases FABP mRNA and protein levels in liver, heart and muscle, tissues that normally utilize FA as their primary fuel, whereas the inhibitory effect of cytokines is limited to the liver. The LPS-induced decrease in L-FABP and H-FABP may be an additional mechanism contributing to the decrease in FA oxidation that is associated with the host response to infection and inflammation.

Determination of the secondary structural elements of chicken liver fatty acid binding protein by two-dimensional homonuclear NMR

A conformational study in solution of the fatty acid binding protein from chicken liver is presented. The nearly complete sequence-specific 1H resonance assignment was achieved from homonuclear two-dimensional nmr experiments using a sample of native protein. The principal elements of secondary structure were identified: 10 antiparallel beta-strands and one helical segment followed by a turn comprising 5 residues. These elements correspond closely with those of the crystal structure of the related protein, and two new secondary structural features obtained from the nmr data are the beta-sheet conformation between the first and the last beta-strand in the protein sequence, as well as a helical loop at the N-terminus of the polypeptide chain.

The role of mitochondria in the salvage and the injury of the ischemic myocardium

The relationships between mitochondrial derangements and cell necrosis are exemplified by the changes in the function and metabolism of mitochondria that occur in the ischemic heart. From a mitochondrial point of view, the evolution of ischemic damage can be divided into three phases. The first is associated with the onset of ischemia, and changes mitochondria from ATP producers into powerful ATP utilizers. During this phase, the inverse operation of F0F1 ATPase maintains the mitochondrial membrane potential by using the ATP made available by glycolysis. The second phase can be identified from the functional and structural alterations of mitochondria caused by prolongation of ischemia, such as decreased utilization of NAD-linked substrates, release of cytochrome c and involvement of mitochondrial channels. These events indicate that the relationship between ischemic damage and mitochondria is not limited to the failure in ATP production. Finally, the third phase links mitochondria to the destiny of the myocytes upon post-ischemic reperfusion. Indeed, depending on the duration and the severity of ischemia, not only is mitochondrial function necessary for cell recovery, but it can also exacerbate cell injury.

Immunolocalization of schistosome proteins

This review discusses some of the recent advances in the characterization of potential vaccine molecules against Schistosoma japonicum, utilizing microscopy and immunocytochemistry methods. Microscopy has demonstrated the stage-specific expression of the muscle protein paramyosin onto the parasite surface, an important consideration as a vaccine target. Other potential vaccine component proteins examined include glutathione S-transferase (GST) and fatty acid binding protein (FABP); although not associated with the adult parasite surface, their localization to internal structures such as lipid droplets and regions of the female reproductive system have provided valuable insights into the biology of the parasite. Localization of the transport protein SGTP (schistosome glucose transporter protein) has demonstrated that the protein is more prevalent in the juvenile stages of the parasite development. This further highlights the diversity of the parasite life cycle. Using both light microscopy and transmission electron microscopy, the localization of a number of schistosome proteins has demonstrated the functions and significance of these proteins within the parasite. Molecular localization studies are crucial in understanding how and when a vaccine may work against the organism and may provide insights into which can be used in the design of future vaccines.

Fatty acid binding protein, a major protein in the flight muscle of migrating western sandpipers

Migratory flight in birds is fueled primarily by fatty acid oxidation imposing a requirement for high rates of fatty acid: (a) transport; (b) uptake; and (c) delivery to intracellular sites of beta-oxidation. Muscle fatty acid binding protein (M-FABP) is a cytosolic protein involved in the intracellular transport of fatty acids. Its expression appears to be correlated with muscle fatty acid oxidation capacity. The M-FABP was isolated for the first time from a long distance migrant bird using: (i) size exclusion; (ii) anion exchange; and (iii) hydroxyapatite chromatography. M-FABP has a molecular weight of approximately 14,000 Da and an isoelectric point of pH 4.8. A partial amino acid sequence of the protein demonstrated homology to M-FABPs from other species (80% identical to human heart FABP). It was estimated that M-FABP comprises approximately 14 and 21% of total cytosolic protein of the pectoralis and heart, respectively; the highest values yet reported from any vertebrate muscle. The abundance of M-FABP in these tissues suggests that the protein may play a key role in fatty acid supply during endurance flight. Thus, it is proposed that a seasonal increase in M-FABP expression could be a component of physiological preparation for migration.

Simulations of fatty acid-binding proteins. II. Sites for discrimination of monounsaturated ligands

Fatty acid binding proteins (FABPs) can discriminate between saturated and unsaturated fatty acids via molecular mechanisms that are not understood. Molecular dynamics computer calculations are used to suggest the relationship between tertiary structure and binding specificity. Three separate 1-ns simulations, with explicit solvent, are presented: 1) oleic acid (C18:1 cis) bound to adipocyte FABP, 2) oleic acid bound to human muscle FABP, and 3) elaidic acid (C18:1 trans) bound to human muscle FABP. The average structural, dynamic, and energetic properties of the trajectory were analyzed, as were the motional correlations. The molecular dynamics trajectories reveal intriguing differences among all three systems. For example, the two proteins have different strengths of interaction energy with the ligand and different motional coupling, as seen with covariance analysis. This suggests distinctive molecular behavior of monounsaturated fatty acids in the two similar proteins. An importance scale, based on motional correlation and interaction energy between protein and ligand, is proposed, to help identify amino acids involved with the discrimination of ligand saturation state or geometric isomerization.

Accumulation of arachidonic acid in ischemic/reperfused cardiac tissue: possible causes and consequences

Under physiological conditions, the content of unesterified arachidonic acid in cardiac tissue is very low. The bulk of arachidonic acid is present in the membrane phospholipid pool. Incorporation of arachidonic acid into phospholipids (reacylation) and liberation of this fatty acid from the phospholipid pool (deacylation) are controlled by a set of finely tuned enzymes, including lysophospholipid acyltransferase and phospholipase A2. At present, at least three subtypes of phospholipase A2 have been identified in cardiac structures, i.e., a low molecular mass group II phospholipase A2, a cytoplasmic high molecular mass phospholipase A2 and a plasmalogen-specific phospholipase A2. Cessation of flow to the heart (ischemia) gives rise to net degradation of membrane phospholipids accompanied by accumulation of fatty acids, including (unesterified) arachidonic acid. Restoration of flow to the previously ischemic cells results in a continued accumulation of fatty acids. The mechanism(s) underlying net phospholipid degradation in ischemic/reperfused myocardial tissue is (are) incompletely understood. Impaired reacylation, enhanced hydrolysis of phospholipids, or a combination of both may be responsible for the phenomena observed. Elevated tissue levels of arachidonic acid may exert both direct and indirect effects on the affected myocardium and healthy cardiac cells adjacent to the injured cardiomyocytes. Indirect effects might be evoked by arachidonic acid metabolites, i.e., eicosanoids. Arachidonic acid may directly influence ion channel activity, substrate metabolism and signal transduction, thereby affecting the functional characteristics of the ischemic/reperfused myocardium.

Early detection of successful coronary reperfusion based on serum concentration of human heart-type cytoplasmic fatty acid-binding protein

Both human heart-type cytoplasmic fatty acid-binding protein (H-FABPc) and myoglobin are low molecular weight proteins that are abundant in the cytoplasm of myocardial cells. Unlike myoglobin, H-FABPc content in the skeletal muscle is less than in cardiac muscle. To investigate the usefulness of the serum concentration of H-FABPc in the early detection of successful coronary reperfusion, we measured serum concentrations of H-FABPc and myoglobin in 45 patients with acute myocardial infarction treated with intracoronary thrombolysis or direct percutaneous transluminal coronary angioplasty. Coronary angiography was performed every 5 min for reperfusion therapy to identify the onset of reperfusion. Reperfusion, defined as a TIMI grade 2 or 3, was achieved within 60 min of the initiation of reperfusion therapy in 30 patients (the reperfused group), but was not achieved in 15 patients (the non-reperfused group). Blood samples were obtained before initiation of treatment and 15, 30 and 60 min after initiation of treatment in the non-reperfused group. In the reperfused group, samples were obtained before reperfusion and 15, 30 and 60 min after reperfusion. The H-FABPc ratio (the ratio of value after to value before the initiation of treatment or reperfusion) increased sharply after the onset of reperfusion, peaking at 41 +/- 18 min, and decreased rapidly thereafter. The predictive accuracy of an H-FABPc ratio of > 1.8 for the detection of reperfusion within 60 min of the initiation of treatment was 93% at 15 min after reperfusion, 98% at 30 min, and 100% at 60 min. Similar rates of predictive accuracy were observed for a myoglobin ratio > 2.4. The H-FABPc ratio detected successful reperfusion as early as 15 min after the onset of reperfusion and was highly accurate in detecting reperfusion within 60 min of the onset of reperfusion. The predictive accuracy of the H-FABPc ratio was similar to that of the myoglobin ratio for the early detection of successful coronary reperfusion.

Fatty acid binding proteins reduce 15-lipoxygenase-induced oxygenation of linoleic acid and arachidonic acid

Free fatty acids in plasma and cells are mainly bound to membranes and proteins such as albumin and fatty acid binding proteins (FABP), which can regulate their biological activities and metabolic transformations. We have investigated the effect of FABP and albumin on the peroxidation of linoleic acid (18:2) and arachidonic acid (20:4) by 15-lipoxygenase (15-LO). Rabbit reticulocyte 15-LO produced a rapid conversion of [1-14C]18:2 to 13-hydroxyoctadecadienoic acid (13-HODE) and [3H]20:4 to 15-hydroxyeicosatetraenoic acid (15-HETE). 13-HODE formation was reduced when intestinal FABP (I-FABP). liver FABP (L-FABP) or albumin was added. The relative ability of these proteins to reduce 15-LO induced formation of 13-HODE and 15-HETE was BSA > L-FABP > I-FABP. Smaller reductions in activity were observed with 20:4 as compared to 18:2. The IC50-values of I-FABP and L-FABP, using either 18:2 (3.4 microM) or 20:4 (3.4 microM), were 4.6 +/- 0.6 and 1.9 +/- 0.2 microM, respectively, for reduction of 13-HODE and 6.8 +/- 0.3 and 3.1 +/- 0.2 microM, respectively, for reduction of 15-HETE formation. The smaller 15-HETE reduction correlated with decreased binding of 20:4 to the FABP. Titration calorimetry also showed that the I-FABP IC50 for 18:2, 0.25 microM, was lower then for 20:4, 0.6 microM. Thus the reduction in fatty acid lipid peroxidation relates to the binding capacity of each FABP. We also demonstrated that 18:2 rapidly diffuses (flip-flops) across the phospholipid bilayer of small unilamellar vesicles (SUV) and measured partitioning of 18:2 between proteins and SUV by the pyranin fluorescence method [Kamp, F. and Hamilton, J.A. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 11367-11370]. Addition of proteins to SUV in buffer resulted in a complete desorption of 18:2 from SUV with a relative effect of BSA > L-FABP > I-FABP. This suggests that the relative effects of these proteins on 18:2 peroxidation will not be altered by the presence of membranes. Our results indicate that FAPBs protect intracellular polyunsaturated fatty acids against peroxidation and, through differential binding of 18:2 and 20:4, they may modulate the availability of these polyunsaturated fatty acids to intracellular oxidative pathways.

Estimation of myocardial infarct size from plasma myoglobin or fatty acid-binding protein. Influence of renal function

Myoglobin (M(r) 18,000) and fatty acid-binding protein (M(r) 15,000), are low molecular mass cytoplasmic proteins that are considered useful biochemical markers for early detection or exclusion of acute myocardial infarction, and also for early estimation of infarct size. As each of these proteins shows renal clearance, we studied the influence of renal function on the estimation of infarct size from their plasma concentration curves. For this, infarct size estimated from plasma myoglobin or fatty acid-binding protein release curves was compared with that estimated with the established infarct size markers hydroxybutyrate dehydrogenase and creatine kinase, which are not influenced by changes in renal function. The discordance between infarct size estimates was related to renal function. Creatine kinase (EC 2.7.3.2), hydroxybutyrate dehydrogenase (EC 1.1.1.27), myoglobin, fatty acid-binding protein and creatinine were assayed serially in plasma samples obtained frequently and for at least 72 hours after the start of thrombolytic therapy in 20 patients with acute myocardial infarction. Cumulative release of the different cardiac markers was calculated by using a two-compartment model for circulating proteins. Mean tissue contents of 156 U/g for hydroxybutyrate dehydrogenase, 2163 U/g for creatine kinase, 2.79 mg/g for myoglobin and 0.57 mg/g wet weight for fatty acid-binding protein, were used to express infarct size in gram-equivalents of healthy myocardium per litre of plasma (g-eq/l). Mean plasma creatinine was obtained by averaging the creatinine concentrations measured in all plasma samples taken during the first 24 hours after acute myocardial infarction. A relation was found between the mean plasma creatinine concentration during the first 24 hours after acute myocardial infarction and the discordance between infarct size estimated from cumulative hydroxybutyrate dehydrogenase release, compared to infarct size estimated from cumulative myoglobin or fatty acid-binding protein release. For patients with mean plasma creatinine concentrations within the reference interval for creatinine (group 1, n = 15) a good agreement was found between infarct size estimated from myoglobin or fatty acid-binding protein plasma curves and that estimated with either hydroxybutyrate dehydrogenase or creatine kinase. However, for patients with a mean creatinine concentration above the upper reference limit (group 2, n = 5), infarct size calculated from plasma myoglobin or fatty acid-binding protein release curves was markedly overestimated, especially for larger infarcts. Estimation of infarct size from serial plasma myoglobin or fatty acid-binding protein concentrations is possible in the first 24 hours after the onset of symptoms, but only in patients with normal renal function, as estimated from plasma creatinine concentrations.

Progress in myocardial damage detection: new biochemical markers for clinicians

New clinical requirements for triaging chest pain patients challenge the abilities of the current cardiac markers. Serial measurements of myoglobin, creatine kinase (CK) isoenzyme MB (CKMB) mass, or CK isoforms in emergency rooms help to rapidly rule out acute myocardial infarction (AMI). However, within the first 3 to 4 h from chest pain onset, their sensitivities are too low to contribute significantly to AMI diagnosis during this period. CKMB and lactate dehydrogenase (LDH) isoenzyme 1 are not heart-specific, which hampers reliable diagnosis in patients with concomitant skeletal muscle damage. By contrast, the regulatory proteins troponin I and troponin T are expressed in three different isoforms: one for slow-twitch skeletal muscle fibers, one for fast-twitch skeletal muscle fibers, and one for cardiac muscle (cTnI, cTnT); cardiac-specific cTnI and cTnT assays are already available for routine use. cTnT and cTnI are the most promising markers for risk stratification in patients with unstable angina pectoris. Recent reports on increased cTnT in patients with renal failure or myopathy without evidence of myocardial injury and undetectable cTnI suggest that cTnT could be reexpressed similar to CKMB and LDH-1 in chronically damaged human skeletal muscle. Therefore, cTnI is probably the most heart-specific marker. Among the recently proposed new markers for early AMI diagnosis: glycogen phosphorylase isoenzyme BB (GPBB), fatty acid binding protein, phosphoglyceric acid mutase isoenzyme MB, enolase isoenzyme alpha beta, S100a0, and annexin V, GPBB is the most promising because it increases as early as 1 to 4 h from chest pain onset and its early release appears to be essentially dependent on ischemic myocardial injury.

Intestinal fatty acid-binding protein expression stimulates fibroblast fatty acid esterification

The effect of intestinal fatty acid binding protein (I-FABP) expression on cell growth and cell lipid content is not known. Therefore, mouse L-cell fibroblasts were transfected with the cDNA encoding for I-FABP. The high expression clones expressed 0.35% of the total cytosolic proteins as I-FABP. Mock transfected L-cells did not differ from control L-cells in any properties tested. Neither the growth rate, maximal cell density, nor [3H]oleic acid uptake differed in I-FABP expressing as compared to control cells. In contrast, I-FABP expression increased triacylglycerol and cholesteryl ester mass (nmol/mg protein) by 63% and 25%, respectively. Phospholipid mass was unchanged in I-FABP expressing cells. The initial [3H]oleic acid esterification into triacylglycerols and cholesteryl esters was increased 3.9- and 2.5-fold in I-FABP expressing cells. Although, the initial [3H]oleic acid esterification into total phospholipids was unchanged, within the phospholipid fraction the initial [3H]oleic acid esterification into phosphatidylethanolamine was increased 70% and decreased 50% in phosphatidylcholine in I-FABP expressing cells. These observed differences suggest a distinct role for I-FABP in stimulating net formation, and not just turnover, of triacylglycerides and cholesteryl esters in transfected L-cell fibroblasts.

Acyl-CoA binding proteins: multiplicity and function

The physiological role of long-chain fatty acyl-CoA is thought to be primarily in intermediary metabolism of fatty acids. However, recent data show that nM to microM levels of these lipophilic molecules are potent regulators of cell functions in vitro. Although long-chain fatty acyl-CoA are present at several hundred microM concentration in the cell, very little long-chain fatty acyl-CoA actually exists as free or unbound molecules, but rather is bound with high affinity to membrane lipids and/or proteins. Recently, there is growing awareness that cytosol contains nonenzymatic proteins also capable of binding long-chain fatty acyl-CoA with high affinity. Although the identity of the cytosolic long-chain fatty acyl-CoA binding protein(s) has been the subject of some controversy, there is growing evidence that several diverse nonenzymatic cytosolic proteins will bind long-chain fatty acyl-CoA. Not only does acyl-CoA binding protein specifically bind medium and long-chain fatty acyl-CoA (LCFA-CoA), but ubiquitous proteins with multiple ligand specificities such as the fatty acid binding proteins and sterol carrier protein-2 also bind LCFA-CoA with high affinity. The potential of these acyl-CoA binding proteins to influence the level of free LCFA-CoA and thereby the amount of LCFA-CoA bound to regulatory sites in proteins and enzymes is only now being examined in detail. The purpose of this article is to explore the identity, nature, function, and pathobiology of these fascinating newly discovered long-chain fatty acyl-CoA binding proteins. The relative contributions of these three different protein families to LCFA-CoA utilization and/or regulation of cellular activities are the focus of new directions in this field.

Discrimination between myocardial and skeletal muscle injury by assessment of the plasma ratio of myoglobin over fatty acid-binding protein

BACKGROUND

Myoglobin and fatty acid-binding protein (FABP) each are useful as early biochemical markers of muscle injury. We studied whether the ratio of myoglobin over FABP in plasma can be used to distinguish myocardial from skeletal muscle injury.

METHODS AND RESULTS

Myoglobin and FABP were assayed immunochemically in tissue samples of human heart and skeletal muscle and in serial plasma samples from 22 patients with acute myocardial infarction (AMI), from 9 patients undergoing aortic surgery (causing injury of skeletal muscles), and from 10 patients undergoing cardiac surgery. In human heart tissue, the myoglobin/FABP ratio was 4.5 and in skeletal muscles varied from 21 to 73. After AMI, the plasma concentrations of both proteins were elevated between approximately 1 and 15 to 20 hours after the onset of symptoms. In this period, the myoglobin/FABP ratio was constant both in subgroups of patients receiving and those not receiving thrombolytics and amounted to 5.3 +/- 1.2 (SD). In serum from aortic surgery patients, both proteins were elevated between 6 and 24 hours after surgery; the myoglobin/FABP ratio was 45 +/- 22 (SD), which is significantly different from plasma values in AMI patients (P < .001). In patients with cardiac surgery, the ratio increased from 11.3 +/- 4.7 to 32.1 +/- 13.6 (SD) during 24 hours after surgery, indicating more rapid release of protein from injured myocardium than from skeletal muscles.

CONCLUSIONS

The ratio of the concentrations of myoglobin over FABP in plasma from patients with muscle injury reflects the ratio found in the affected tissue. Since this ratio is different between heart (4.5) and skeletal muscle (20 to 70), its assessment in plasma allows the discrimination between myocardial and skeletal muscle injury in humans.

The DvA-1 polyprotein of the parasitic nematode Dictyocaulus viviparus. A small helix-rich lipid-binding protein

DNA encoding a single unit of the DvA-1 polyprotein of the parasitic nematode Dictyocaulus viviparus was isolated and the polypeptide ("rDvA-1L") expressed in Escherichia coli, to give a protein showing high binding affinity for fatty acids and retinoids. Fluorescent fatty acid probes show substantial changes in emission spectrum in the presence of rDvA-1L, which can be reversed by fatty acids (oleic, palmitic, stearic, arachidonic) and retinoids, but not by tryptophan, squalene, or cholesterol. Moreover, changes in intrinsic fluorescence of retinol or retinoic acid confirm a retinoid binding activity. Fluorescence titration experiments indicate stoichiometric binding to a single protein site per monomer unit with affinities (Kd) in the range 3 x 10(-8) M for 11-((5-dimethylaminonaphthalene-1-sulfonyl)amino)undecanoic acid, and by competition, 5 x 10(-8) M for oleic acid. The extreme blue shift of bound fluorescent fatty acid suggests an unusually low polarity for the protein binding site. The emission spectrum of the single tryptophan of rDvA-1L indicates that it is deeply buried in a nonpolar environment, and its spectrum is unaffected by ligand binding. Far UV circular dichroism of rDvA-1L reveals a high alpha-helix content (53%). Differential scanning calorimetry studies indicate that rDvA-1L is highly stable (T(m) approximately 98 degrees C), refolding efficiently following thermal denaturation. DvA-1 therefore represents an example of a new class of lipid binding protein, and is the first product of a polyprotein with this activity to be described.

Monoclonal antibodies to human heart fatty acid-binding protein

Heart-type fatty acid-binding protein (H-FABP), a 15 kDa non-enzymatic protein, which is abundantly present in heart and some skeletal muscles, was recently found to be a useful plasma marker for acute myocardial infarction. The BIAcore biosensor technology was used to raise and characterize a panel of 13 monoclonal antibodies against human H-FABP which did not crossreact with other FABP types of human origin. The kinetics of association and dissociation between FABP and the monoclonal antibodies was studied. By pairwise mapping several distinct epitopes could be identified.