Isolation of myocardial membrane long-chain fatty acid-binding protein: homology with a rat membrane protein implicated in the binding or transport of long-chain fatty acids

CD36 as a gatekeeper of myocardial lipid metabolism and therapeutic target for metabolic disease

The multifunctional membrane glycoprotein CD36 is expressed in different types of cells and plays a key regulatory role in cellular lipid metabolism, especially in cardiac muscle. CD36 facilitates the cellular uptake of long-chain fatty acids, mediates lipid signaling, and regulates storage and oxidation of lipids in various tissues with active lipid metabolism. CD36 deficiency leads to marked impairments in peripheral lipid metabolism, which consequently impact on the cellular utilization of multiple different fuels because of the integrated nature of metabolism. The functional presence of CD36 at the plasma membrane is regulated by its reversible subcellular recycling from and to endosomes and is under the control of mechanical, hormonal, and nutritional factors. Aberrations in this dynamic role of CD36 are causally associated with various metabolic diseases, in particular insulin resistance, diabetic cardiomyopathy, and cardiac hypertrophy. Recent research in cardiac muscle has disclosed the endosomal proton pump vacuolar-type H+-ATPase (v-ATPase) as a key enzyme regulating subcellular CD36 recycling and being the site of interaction between various substrates to determine cellular substrate preference. In addition, evidence is accumulating that interventions targeting CD36 directly or modulating its subcellular recycling are effective for the treatment of metabolic diseases. In conclusion, subcellular CD36 localization is the major adaptive regulator of cellular uptake and metabolism of long-chain fatty acids and appears a suitable target for metabolic modulation therapy to mend failing hearts.

Endothelial Cell Receptors in Tissue Lipid Uptake and Metabolism

Lipid uptake and metabolism are central to the function of organs such as heart, skeletal muscle, and adipose tissue. Although most heart energy derives from fatty acids (FAs), excess lipid accumulation can cause cardiomyopathy. Similarly, high delivery of cholesterol can initiate coronary artery atherosclerosis. Hearts and arteries-unlike liver and adrenals-have nonfenestrated capillaries and lipid accumulation in both health and disease requires lipid movement from the circulation across the endothelial barrier. This review summarizes recent in vitro and in vivo findings on the importance of endothelial cell receptors and uptake pathways in regulating FAs and cholesterol uptake in normal physiology and cardiovascular disease. We highlight clinical and experimental data on the roles of ECs in lipid supply to tissues, heart, and arterial wall in particular, and how this affects organ metabolism and function. Models of FA uptake into ECs suggest that receptor-mediated uptake predominates at low FA concentrations, such as during fasting, whereas FA uptake during lipolysis of chylomicrons may involve paracellular movement. Similarly, in the setting of an intact arterial endothelial layer, recent and historic data support a role for receptor-mediated processes in the movement of lipoproteins into the subarterial space. We conclude with thoughts on the need to better understand endothelial lipid transfer for fuller comprehension of the pathophysiology of hyperlipidemia, and lipotoxic diseases such as some forms of cardiomyopathy and atherosclerosis.

The ‘Goldilocks zone’ of fatty acid metabolism; to ensure that the relationship with cardiac function is just right

Fatty acids (FA) are the main fuel used by the healthy heart to power contraction, supplying 60–70% of the ATP required. FA generate more ATP per carbon molecule than glucose, but require more oxygen to produce the ATP, making them a more energy dense but less oxygen efficient fuel compared with glucose. The pathways involved in myocardial FA metabolism are regulated at various subcellular levels, and can be divided into sarcolemmal FA uptake, cytosolic activation and storage, mitochondrial uptake and β-oxidation. An understanding of the critical involvement of each of these steps has been amassed from genetic mouse models, where forcing the heart to metabolize too much or too little fat was accompanied by cardiac contractile dysfunction and hypertrophy. In cardiac pathologies, such as heart disease and diabetes, aberrations in FA metabolism occur concomitantly with changes in cardiac function. In heart failure, FA oxidation is decreased, correlating with systolic dysfunction and hypertrophy. In contrast, in type 2 diabetes, FA oxidation and triglyceride storage are increased, and correlate with diastolic dysfunction and insulin resistance. Therefore, too much FA metabolism is as detrimental as too little FA metabolism in these settings. Therapeutic compounds that rebalance FA metabolism may provide a mechanism to improve cardiac function in disease. Just like Goldilocks and her porridge, the heart needs to maintain FA metabolism in a zone that is ‘just right’ to support contractile function.

Palmitoylation of CD36/FAT regulates the rate of its post-transcriptional processing in the endoplasmic reticulum

CD36/FAT is a transmembrane glycoprotein that functions in the cellular uptake of long-chain fatty acids and also as a scavenger receptor. As such it plays an important role in lipid homeostasis and, pathophysiologically, in the progression of type 2 diabetes and atherosclerosis. CD36 expression is tightly regulated at the levels of both transcription and translation. Here we show that its expression and location are also regulated post-translationally, by palmitoylation. Although palmitoylation of CD36 was not required for receptor maturation and cell surface expression, inhibition of palmitoylation either pharmacologically with cerulenin or by mutation of the relevant cysteines delayed processing at the ER and trafficking through the secretory pathway. The absence of palmitoylation also reduced the half life of the CD36 protein. Additionally, the CD36 palmitoylation mutant did not incorporate efficiently into lipid rafts, a site known to be required for its function of fatty acid uptake, and this reduced the efficiency of uptake of oxidized low density lipoprotein. These findings provide an added level of sophistication where translocation of CD36 to the plasma membrane may be physiologically regulated by palmitoylation.

Myocardial fatty acid metabolism in health and disease

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

Purification, immunochemical quantification and localization in rat heart of putative fatty acid translocase (FAT/CD36)

Evidence is accumulating that the heavily glycosylated integral membrane protein fatty acid translocase (FAT/CD36) is involved in the transport of long-chain fatty acids across the sarcolemma of heart muscle cells. The aim of this study was to analyse the distribution between FAT/CD36 present in cardiac myocytes and endothelial cells. We therefore developed a method to purify FAT/CD36 from total rat heart and isolated cardiomyocytes, and used the proteins as standards in an immunochemical assay. Two steps, chromatography on wheat germ agglutinin-agarose and anion-exchange chromatography on Q-Sepharose fast flow, were sufficient for obtaining the protein in a > 95% pure form. When used to isolate FAT/CD36 from total heart tissue, the FAT/CD36 yield of the method was 9% and the purification factor was 64. Purifying FAT/CD36 from isolated cardiomyocytes yielded the same 88 kDa protein band on SDS-PAGE gels and reactivity of this band on western blots was comparable to that of the FAT/CD36 isolated from total hearts. Quantifying FAT/CD36 contents by western blotting showed that the amounts of FAT/CD36 that are present in isolated cardiomyocytes (10 +/- 3 microg/mg protein) and total hearts (14 +/- 4 microg/mg protein) are of comparable magnitude. Immunofluorescence labelling showed that at least a part of the FAT/CD36 present in the cardiomyocyte is associated with the sarcolemma. This study established that FAT/CD36 is a relatively abundant protein in the cardiomyocyte. In addition, the further developed purification procedure is the first method for isolating FAT/CD36 from rat heart and cardiomyocyte FAT/CD36.

Identification of fatty acid translocase on human skeletal muscle mitochondrial membranes: essential role in fatty acid oxidation

Fatty acid translocase (FAT/CD36) is a transport protein with a high affinity for long-chain fatty acids (LCFA). It was recently identified on rat skeletal muscle mitochondrial membranes and found to be required for palmitate uptake and oxidation. Our aim was to identify the presence and elucidate the role of FAT/CD36 on human skeletal muscle mitochondrial membranes. We demonstrate that FAT/CD36 is present in highly purified human skeletal mitochondria. Blocking of human muscle mitochondrial FAT/CD36 with the specific inhibitor sulfo-N-succimidyl-oleate (SSO) decreased palmitate oxidation in a dose-dependent manner. At maximal SSO concentrations (200 muM) palmitate oxidation was decreased by 95% (P<0.01), suggesting an important role for FAT/CD36 in LCFA transport across the mitochondrial membranes. SSO treatment of mitochondria did not affect mitochondrial octanoate oxidation and had no effect on maximal and submaximal carnitine palmitoyltransferase I (CPT I) activity. However, SSO treatment did inhibit palmitoylcarnitine oxidation by 92% (P<0.001), suggesting that FAT/CD36 may be playing a role downstream of CPT I activity, possibly in the transfer of palmitoylcarnitine from CPT I to carnitine-acylcarnitine translocase. These data provide new insight regarding human skeletal muscle mitochondrial fatty acid (FA) transport, and suggest that FAT/CD36 could be involved in the cellular and mitochondrial adaptations resulting in improved and/or impaired states of FA oxidation.

Metabolic Imaging With β-Methyl- p -[ 123 I]-Iodophenyl-Pentadecanoic Acid Identifies Ischemic Memory After Demand Ischemia

Background— After myocardial ischemia, prolonged suppression of fatty acid metabolism may persist despite restoration of blood flow, which is called metabolic stunning. We hypothesized that a branched-chain fatty acid, β-methyl- p -[ 123 I]-iodophenyl-pentadecanoic acid (BMIPP), might identify the presence of myocardial ischemia late after demand ischemia at rest up to 30 hours later.

Methods and Results— In 32 patients with exercise-induced ischemia on thallium SPECT, BMIPP was injected at rest within 30 hours of ischemia. SPECT images were acquired beginning 10 minutes after injection (early) and again 30 minutes after injection (delayed). Thallium and BMIPP SPECT data were read separately by 3 observers blinded to other imaging and clinical data. Agreement between BMIPP and thallium data for the presence of an abnormality on the patient level was 91% (95% CI, 75 to 98) for the early BMIPP data and 94% (95% CI, 79 to 99) for the delayed BMIPP data. Agreement between delayed BMIPP and thallium was 95% among 21 patients studied on the same day, a mean of 6.2±1.4 hours after exercise-induced ischemia, and 91% among the 11 patients studied on the next calendar day, a mean of 24.9±2.6 hours after ischemia ( P =NS). The magnitude of resting BMIPP metabolic defect by semiquantitative visual analysis was correlated to the magnitude of exercise-induced thallium perfusion defect ( r =0.6, P <0.001 for early BMIPP; r =0.5, P =0.005 for delayed BMIPP).

Conclusions— Metabolic imaging with BMIPP identifies patients with recent exercise-induced myocardial ischemia. These findings support the concept that BMIPP imaging can successfully demonstrate the metabolic imprint of a stress-induced ischemic episode, also known as ischemic memory.

Microarray analysis reveals novel gene expression changes associated with erectile dysfunction in diabetic rats

To investigate the full range of molecular changes associated with erectile dysfunction (ED) in Type 1 diabetes, we examined alterations in penile gene expression in streptozotocin-induced diabetic rats and littermate controls. With the use of Affymetrix GeneChip arrays and statistical filtering, 529 genes/transcripts were considered to be differentially expressed in the diabetic rat cavernosum compared with control. Gene Ontology (GO) classification indicated that there was a decrease in numerous extracellular matrix genes (e.g., collagen and elastin related) and an increase in oxidative stress-associated genes in the diabetic rat cavernosum. In addition, PubMatrix literature mining identified differentially expressed genes previously shown to mediate vascular dysfunction [e.g., ceruloplasmin (Cp), lipoprotein lipase, and Cd36] as well as genes involved in the modulation of the smooth muscle phenotype (e.g., Kruppel-like factor 5 and chemokine C-X3-C motif ligand 1). Real-time PCR was used to confirm changes in expression for 23 relevant genes. Further validation of Cp expression in the diabetic rat cavernosum demonstrated increased mRNA levels of the secreted and anchored splice variants of Cp. CP protein levels showed a 1.9-fold increase in tissues from diabetic rats versus controls. Immunohistochemistry demonstrated localization of CP protein in cavernosal sinusoids of control and diabetic animals, including endothelial and smooth muscle layers. Overall, this study broadens the scope of candidate genes and pathways that may be relevant to the pathophysiology of diabetes-induced ED as well as highlights the potential complexity of this disorder.

A novel function for fatty acid translocase (FAT)/CD36: involvement in long chain fatty acid transfer into the mitochondria

Fatty acid translocase (FAT)/CD36 is a long chain fatty acid transporter present at the plasma membrane, as well as in intracellular pools of skeletal muscle. In this study, we assessed the unexpected presence of FAT/CD36 in both subsarcolemmal and intermyofibril fractions of highly purified mitochondria. Functional assessments demonstrated that the mitochondria could bind (14)C-labeled palmitate, but could only oxidize it in the presence of carnitine. However, the addition of sulfo-N-succinimidyl oleate, a known inhibitor of FAT/CD36, resulted in an 87 and 85% reduction of palmitate oxidation in subsarcolemmal and intermyofibril fractions, respectively. Further studies revealed that maximal carnitine palmitoyltransferase I (CPTI) activity in vitro was inhibited by succinimidyl oleate (42 and 48% reduction). Interestingly, CPTI immunoprecipitated with FAT/CD36, indicating a physical pairing. Tissue differences in mitochondrial FAT/CD36 protein follow the same pattern as the capacity for fatty acid oxidation (heart >> red muscle > white muscle). Additionally, chronic stimulation of hindlimb muscles (7 days) increased FAT/CD36 expression and also resulted in a concomitant increase in mitochondrial FAT/CD36 content (46 and 47% increase). Interestingly, with acute electrical stimulation of hindlimb muscles (30 min), FAT/CD36 expression was not altered, but there was an increase in the mitochondrial content of FAT/CD36 compared with the non-stimulated control limb (35 and 37% increase). Together, these data suggest a role for FAT/CD36 in mitochondrial long chain fatty acid uptake and demonstrate system flexibility to match FAT/CD36 mitochondrial content with an increased capacity for fatty acid oxidation, possibly involving translocation of FAT/CD36 to the mitochondria.

Regulation of myocardial triacylglycerol synthesis and metabolism

Studies showing a correlation of excess myocardial triacylglycerol stores with apoptosis, fibrosis, and contractile dysfunction indicate that dysregulation of triacylglycerol metabolism may contribute to cardiac disease. This review covers the regulation of heart triacylglycerol accumulation at the critical control points of fatty acid uptake, enzymes of triacylglycerol synthesis, lipolysis, and lipoprotein secretion. These pathways are discussed in the context of the central role myocardial triacylglycerol plays in cardiac energy metabolism and heart disease.

CD36 genotype and long-chain fatty acid uptake in the heart

Homozygous or compound heterozygous mutation of the CD36 gene (CD36-/-) in humans results in severe defects of the uptake of long-chain fatty acids (LCFAs) in the heart. Because the effect of a single mutation of this gene (CD36+/-) on the LCFA uptake is not known, it was evaluated in 29 subjects with the CD36 wild-type gene (WT) (6 healthy subjects, 10 patients with heart disease), CD36+/- (4 healthy subjects, 5 patients) and CD36-/- (4 patients). The CD36 genotype was identified in the coding region of genomic DNA, and the expression of CD36 protein was examined by flow cytometry after staining with monoclonal anti-CD36 antibody. The LCFA uptake in the heart was assessed as the radioactivity accumulation ratio of heart to mediastinum after intravenous administration of iodine-123 15-(p-iodophenyl)-3-R, S-methylpentadecanoic acid (H/M ratio). The H/M ratios in WT, CD36+/- and CD36-/- were 2.28 +/- 0.10, 1.90 +/- 0.06 and 1.40 +/- 0.11, respectively (p < 0.0001, among groups). The H/M ratio between healthy subjects and patients with heart disease for WT and CD36+/- did not differ significantly (ie, those of WT and CD36+/- in healthy subjects and patients were 2.29 +/- 0.08 vs 2.27 +/- 0.12 and 1.90+/- 0.07 vs 1.89 +/- 0.05, respectively). Not only CD36-/- but also CD36+/- resulted in a significant reduction of the LCFA uptake in the heart independent of heart disease, suggesting genotype dependency and that CD36 might be a fundamental determinant of myocardial LCFA uptake.

Evidence in favor of a facilitated transport system for FA uptake in cultured L6 cells

In this manuscript we report a study of the transport of FA in L6 muscle cells. Cultured L6 cells took up labeled FA (C10 to C20) as a linear function of time up to 15 min. Thereafter, the rate of uptake gradually declined although it persisted for at least 12 h after the addition of the substrate. Kinetic parameters (Km, Vm, and k(o)) were determined from a fitted Michaelis-Menten-type equation modified by a term for a saturable (linear) component of the measured total uptake. Vm values were different for some of the FA studied, and Km data showed significant differences between saturated and unsaturated FA. The maximal rate of uptake was observed at pH 7.40 for decanoate, palmitate, and eicosatrienoate. Uptake was significantly influenced when the pH of the incubation medium was changed. Experiments designed to study the influence of FA/albumin molar ratio indicated that Vm was dependent on the total (bound and free) concentration of the FA. A concentrative uptake was demonstrated in short-term experiments with an apparent plateau of 20 and 40 microM for palmitate and eicosatrienoate, respectively. A competitive inhibition was also observed between palmitate as substrate and the other FA. From our results we can postulate that the uptake of FA in L6 cells is the sum of passive diffusion plus a saturable component and that the rate of uptake is dependent on one (or more) protein structures, although their precise characteristics and functions remain to be elucidated.

CD36 mRNA and Protein Expression Levels Are Significantly Increased in the Heart and Testis of apoE Deficient Mice in Comparison to Wild Type (C57BL/6)

CD36, an 88kd-adhesion molecule, plays a major role as a scavenging receptor implicated in cellular lipid metabolism. Secretory mammary epithelium, microvasculature endothelium, adipocytes, smooth muscle cells, and platelets express CD36. In addition, CD36 expression is significantly enhanced in macrophages differentiating into foam cells. The effect of pathological levels of cholesterol, as observed in apoE(-/-), on vascular CD36 expression is, at this stage, not known. In this study, a quantitative analysis of CD36 transcription and protein expression levels, present in tissues of male C57BL/6 and apolipoprotein-E (apoE) deficient mice was carried out by Northern and Western blots. Four-week-old animals were fed a chow diet over different periods of time (0, 6, 16, or 20 weeks). Immunohistochemistry was used to localize CD36 protein expression in the heart and testis. Results indicate that CD36 transcription is increased in hearts of apoE deficient animals (100% higher at 6 weeks, and 30% higher at 16 and 20 weeks) in comparison to wild type. This was confirmed at the protein level, which showed an increase of at least 100% at 6 weeks, and between 40% to 50% increase at 16 and 20 weeks of apoE(-/-) mice compared to controls. In addition, CD36 transcription levels were significantly increased in testis of apoE animals (at least 100% at 6, 16, and 20 weeks) compared to C57BL/6 wild type. Such an increase was also confirmed at the protein level (65% increase at 16 weeks in apoE mice compared to control). Finally, localization of CD36 protein expression by immunohistochemistry showed that it was expressed in the capillaries of heart and testis endothelial cells and also at the head of spermatozoid during spermatogenesis. These results indicate that high circulating cholesterol levels, in apoE deficient mice, significantly enhance the expression of CD36 in the heart and testis. Such enhanced CD36 expression might lead to organ remodeling and/or dysfunction.

Improvement in cardiac function and free fatty acid metabolism in a case of dilated cardiomyopathy with CD36 deficiency

A 27-year-old man diagnosed as having dilated cardiomyopathy (DCM) without myocardial accumulation of 123I-beta-methyl-iodophenylpentadecanoic acid, and he was found to have type I CD36 deficiency. This abnormality of cardiac free fatty acid metabolism was also confirmed by other methods: 18F-fluoro-2-deoxyglucose positron emission tomography, measurements of myocardial respiratory quotient and cardiac fatty acid uptake. Although the type I CD36 deficiency was reconfirmed after 3 months, the abnormal free fatty acid metabolism improved after carvedilol therapy and was accompanied by improved cardiac function. Apart from a cause-and-effect relationship, carvedilol can improve cardiac function and increase free fatty acid metabolism in patients with both DCM and CD36 deficiency.

PS-liposome and ox-LDL bind to different sites of the immunodominant domain (#155-183) of CD36: a study with GS95, a new anti-CD36 monoclonal antibody

CD36, a multifunctional adhesive receptor on a variety of cells such as monocytes and platelets, has been implicated in clearance of modified LDL and in the removal of apoptotic or senescent cells. We recently developed a new anti-CD36 monoclonal antibody, GS95. We determined the binding site of phosphatidylserine (PS)-liposome on CD36 by flow cytometric analysis of competitive bindings between phospholipid-liposomes or synthetic CD36 peptides and FITC-labeled anti-CD36 antibodies (GS95, OKM5, and FA6-152). The epitope of GS95 was mapped to the amino acid sequence #162-183 of CD36 that was partially overlapped with, but distinct from, #155-183, which has been reported as the epitopes of two commercially available antibodies, OKM5 and FA6-152. Oxidized-LDL dose-dependently inhibited bindings of both GS95 and OKM5 antibodies to platelet CD36, while PS-liposome inhibited the binding of GS95 but not OKM5 or FA6-152. These results indicate that the binding site of PS-liposome on platelet CD36 is not identical to that of oxidized-LDL and may be located in the amino acid sequence #162-183.

Scintigraphic evidence for a specific long-chain fatty acid transporting system deficit and the genetic background in a patient with hypertrophic cardiomyopathy

The mechanism of cardiac uptake of long-chain free fatty acids has not been fully determined. We encountered a hypertrophic cardiomyopathy patient who showed a lack of cardiac uptake of 2 different types of long-chain fatty acid analogues on the scintigraphic images. Flow cytometric analysis revealed no platelet or monocyte CD36 molecule expression (type I CD36 deficiency) and his CD36 gene showed homozygous mutation for 478C to T substitution, leading to an abnormal CD36 amino acid sequence. These findings strongly suggest that a specific transporting system rather than a simple diffusion is commonly involved in the cardiac uptake of long-chain free fatty acids in humans, and that the CD36 protein is the most likely candidate for the specific transporter and to explain scintigraphic defects on fatty acid imaging.

Basic kinetics of 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) in canine myocardium

BMIPP is a radioiodinated fatty acid analogue used for myocardial single photon emission CT (SPECT) imaging based on high cardiac fatty acid metabolism. In normal dogs, 74% of the injected BMIPP was instantly extracted and was then retained in 65.3%. The washout of the retained radioactivity was low, and most of the washout was alpha- and beta-oxidation metabolites. ATP concentration plays an important role in the myocardial uptake and retention of BMIPP. The ATP-dependent BMIPP uptake at the TG pool was strongly regulated by etomoxir with modifying mitochondrial beta-oxidation and subsequent ATP production. Thus, myocardial viability was reflected on the BMIPP uptake in acute ischemia. In spite of insignificant changes in early extraction and retention. BMIPP back diffusion (r = -0.92) and full-oxidation metabolite (r = 0.78) were correlated with the severity of ischemia. Mismatched region of BMIPP with flow (Tl-201) showed decreased metabolic enzymes such as citrate synthase and 3-hydroxyacyl-CoA dehydrogenase. These data suggest that BMIPP would be feasible for detecting cellular energy state from lipid metabolism.

Future aspects of BMIPP

Iodinated fatty acid compounds have an important role in early detection of myocardial abnormalities and provide insights into pathological states in the heart. Among them, 15-(p-iodophenyl)-3R,S-methyl pentadecanoic acid (BMIPP) has been most widely used providing excellent images of the left ventricular myocardium due to high myocardial uptake and long retention. The previous chapters have focused on the basic characters and clinical applications of this compound. However, the precise mechanisms of myocardial kinetics should be further investigated under various conditions. Most of the studies showed reduced BMIPP uptake relative to perfusion in a variety of myocardial disorders, whereas an increase in BMIPP uptake relative to perfusion is often reported. The potential mechanisms of such conflicting results are discussed, but basic studies should be performed to clarify such results in detail. There are a number of clinical values of this compound. Since alteration of fatty acid is observed in the repetitive ischemia, BMIPP can be used for detecting severe ischemic episodes. The concept of 'ischemic memory' imaging can be applied for patients with unstable or vasospastic angina at rest and for those with acute myocardial infarction with successful revascularization to identify the risk area. The discordant decrease in BMIPP uptake relative to perfusion is often seen in ischemic but viable myocardium, and therefore, the combined imaging of BMIPP and perfusion can be used for assessment of tissue viability. Furthermore, abnormal BMIPP uptake is most often observed in hypertrophic cardiomyopathy, and thus, this compound can be used for an early detection and differential diagnosis of the cardiomyopathy. Although BMIPP imaging seems to be quite promising in many fields, the number of patient data remain limited. In this respect, a multicenter study with a vast majority of patients is warranted to confirm these important values of BMIPP. In addition, this attractive tracer should be available all over the world to confirm its clinical value in the near future.

CD36 abnormality and impaired myocardial long-chain fatty acid uptake in patients with hypertrophic cardiomyopathy

Some patients with hypertrophic cardiomyopathy (HCM) demonstrate abnormal myocardial long-chain fatty acid (LCFA) metabolism. However, the exact mechanism involved is unknown. Recently, it was proposed that myocardial cells take up LCFAs via a specific mechanism, in which the CD36 molecule has been implicated as a possible candidate molecule. In addition, a high prevalence of CD36 deficiency was also found in a small number of HCM patients. Accordingly, the investigation of abnormality of the CD36 molecule in a large number of HCM patients may be useful in finding the possible cause of HCM. Moreover, the analysis of myocardial LCFA uptake in patients with molecular abnormalities may be helpful in understanding the possible function of this molecule. In this study, in order to discover the relationship between HCM and the CD36 molecular abnormality, the expression level of platelet CD36 and CD36 cDNA in 55 HCM patients was analyzed. Twelve patients showed negligible (<5%) CD36 expression on their platelets. Among them, one was found to be homozygous for the C-478-->T substitution and 6 were heterozygous for the C-478-->T substitution. In 9 patients, CD36 was expressed by less than 50% of the platelets. One of them was found to be heterozygous for the C-478-->T substitution. Two other patients were also found to be heterozygous for this point mutation, although their platelets expressed CD36. Thus, 23 out of 55 (41.8%) HCM patients had negligible (<5%) or reduced (<50%) levels of CD36 expression on platelets, or had a point mutation of CD36 cDNA. These 55 HCM patients were also evaluated with myocardial scintigraphy both for LCFA uptake and perfusion, which showed a moderate to severe discrepancy between myocardial LCFA accumulation and myocardial perfusion in 95.5% of the patients (21/23). On the other hand, 70% of the patients with normal (>90%) CD36 expression (14/20) did not show any severe discrepancies between myocardial LCFA accumulation and myocardial perfusion. These data could suggest that abnormal myocardial LCFA metabolism seen in HCM patients may be related to abnormality of the CD36 molecule, and that abnormalities of this molecule may be linked to the cause of some types of HCM.

Perinatal changes in myocardial supply and flux of fatty acids, carbohydrates, and ketone bodies in lambs

No information is available on perinatal changes in myocardial metabolism in vivo. We measured myocardial supply and flux of fatty acids, carbohydrates, and ketone bodies in chronically instrumented fetal, newborn (1-4 days), and juvenile (7 wk) lambs, by measuring aorta-coronary sinus concentration differences and blood flow. In the fetal lambs, myocardial supply and flux of fatty acids were zero. In the newborn lambs, the supply of fatty acids increased tenfold, but there was no flux of fatty acids. Carbohydrates were the major energy source in fetal and newborn lambs, accounting for 89 and 69% of myocardial oxygen consumption, respectively. In the juvenile lambs, the flux of fatty acids was increased threefold. The supply and flux of carbohydrates were decreased (by 31 and 82%, respectively). The supply and flux of ketone bodies gradually increased with age. We show that the myocardium of the lamb in vivo does not switch immediately after birth from carbohydrates to fatty acids. The mechanisms involved in the development of myocardial fatty acid oxidation remain to be elucidated.

Absent myocardial accumulation of two different radioiodinated pentadecanoic acids

This article presents two cases with preserved myocardial 201Tl uptake and absent uptake of two kinds of radioiodinated fatty acids: iodine-123-labeled 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (BMIPP) and iodine-123-labeled 15-(p-iodophenyl)-9-(R,S)-methylpentadecanoic acid (9MPA). Although coronary angiography showed no stenotic lesion and left ventriculography revealed no wall motion abnormality, no myocardial uptake of BMIPP and 9MPA was observed in the first case. In the second case, no myocardial accumulation was recognized even in the initial phase of dynamic SPECT acquired soon after the injection of 9MPA. The results suggest that the non-visualized myocardium was not specific for BMIPP imaging and that rather than the early back diffusion of the tracers from the myocardium, abnormality of the myocardial cell membrane was a possible mechanism accounting for the phenomenon.

Do repolarization abnormalities in hypertrophic cardiomyopathy represent impaired fatty acid utilization? An observation with QRST isointegral maps

To identify the clinical significance of the isointegral body surface map of the QRST interval (QRST map) and the occurrence of repolarization abnormalities in patients with hypertrophic cardiomyopathy (HCM), the QRST map and signal-averaged electrocardiogram were evaluated in 50 patients with HCM, in 33 of whom the results were compared with nuclear images both for radioiodine-labeled fatty acid metabolism and for radiothallium perfusion. The QRST departure map was used to determine two parameters of difference between patient and control recordings: the subnormal area (the number of lead points at which the departure index values were negative and lay more than 2 SDs from the mean of the normal control group) and the subnormal minimum (the absolute value of the minimum in the departure map). Late potentials were detected in 6 (12%) of the 50 patients; they were observed in 3 of the 5 patients with dilated-phase HCM but in only 3 (7%) of the other 45 patients. The subnormal area and minimum values were lower in nonobstructive HCM than in dilated-phase HCM. Of the 33 patients examined by myocardial imaging, 28 (33%) had a filling defect or decreased uptake, as shown on fatty acid metabolic images, and 10 of the 28 also showed abnormal myocardial perfusion images, while the 18 others showed normal perfusion images. These 28 patients showed significantly larger values of the subnormal area and minimum than patients with normal results in both image tests, regardless of whether or not myocardial perfusion imaging abnormalities were present. The localization of filling defects or of decreased uptake presented in fatty acid metabolic images corresponded to the position of the minimum on the QRST departure map. These results suggest that the QRST map is useful for detection of repolarization abnormalities in HCM and that these abnormalities are highly related to impaired fatty acid utilization of the myocardium.

Covalent complexes between serum albumin and 7-hydroxycoumarin-4-acetic acid: synthesis and applications in the spectrophotometric detection of long-chain fatty acids

Using a hydrophobic 8-aminooctanoic acid cross-linker, the pH-indicator dye 7-hydroxycoumarin-4-acetic acid (7-HCA) is covalently bound to bovine serum albumin (BSA) at the positions of reactive amino groups. A highly stable and water-soluble complex (BSA-HCA) with a 1:4 molar stoichiometry is synthesized. Appearance of a strong absorption band at gamma max = 372 nm is associated to ionization of the 7-HCA chromophore when it is transferred from water into a basic microenvironment on the BSA surface. This particular surface site is related to the region(s) for high-affinity binding of long-chain fatty acids (FA). BSA-HCA responds to binding of FA (14-20 carbons) with immediate spectral changes and a decrease in 372 nm absorption. BSA-HCA provides an indicator-protein having a range of practical applications for the quantitative determination of long-chain FA in biochemical studies. The lower detection limit in a spectrophotometric method is approximately 1 microM FA. BSA-HCA is usable both in various buffers and in the presence of detergents such as n-octylglucoside, Triton X-100 and CHAPS. A novel method for continuous assay of phospholipase A2 activity with BSA-HCA and a mixed phosphatidylcholine/CHAPS micellar substrate is reported.

Absent myocardial I-123 BMIPP uptake in a family

A 72-year-old woman with hypertension showed no sign of myocardial accumulation of 123I-BMIPP, and 201Tl and 123I-MIBG scintigraphy demonstrated normal findings. Electrocardiography showed left axis deviation with inverted T waves in leads I, aVL, V2-6 and QT prolongation. Coronary arteriography, two dimensional echo cardiography and laboratory data showed no abnormality. Her 66-year-old sister with non-insulin-dependent diabetes mellitus also had no myocardial BMIPP uptake, but had normal 201Tl finding. ECG and chest film findings were normal. Laboratory data indicated slightly high fasted blood glucose, triglyceride and total cholesterol. Four sons of a 72-year-old woman also underwent BMIPP scintigraphy. No BMIPP uptake was also observed in her 2nd son (49 years old) and his electrocardiogram showed QT prolongation. Since these rare findings indicating no myocardial BMIPP uptake were seen in a family, we suspected that a hereditary myocardial metabolic abnormality accounted for them.

Effect of sulfo-N-succinimidyl palmitate on the rat heart: myocardial long-chain fatty acid uptake and cardiac hypertrophy

Abnormal long-chain fatty acid metabolism has been suggested as having a role in the genesis of certain cardiac diseases, and depressed myocardial long-chain fatty acid uptake has been clinically demonstrated in some patients with hypertrophic cardiomyopathy. However, the site where long-chain fatty acid metabolism is affected in cardiomyopathy remains unclear. Although cardiac hypertrophy is reported to be induced in rats by a fat-free diet, little is known of the consequences of depressed myocardial long-chain fatty acid uptake. Sulfo-N-succinimidyl derivatives of long-chain fatty acids have been shown to irreversibly inhibit long-chain fatty acid transport. To investigate the possible linkage of abnormal long-chain fatty acid uptake with cardiac hypertrophy, myocardial long-chain fatty acid uptake was blocked in rats using a sulfo-N-succinimidyl derivative of palmitate (SSP). SSP was intraperitoneally administered to rats for 12 weeks, and its effects on physiological parameters, and cardiac morphology were studied, SSP treatment (20 mg/kg) caused a 12% increase in heart weight (663.7 +/- 33.6 mg in controls v 741.2 +/- 26.5 mg after SSP treatment) and an 11% increase in the heart weight to body weight ratio (2.46 +/- 0.10 in controls v 2.72 +/- 0.17 after SSP) without any significant change of body weight. No significant differences were observed in blood pressure, heart rate, and serum hormones (insulin and triiodothyronine) between the control and SSP-treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)