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

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.

Type 1 cluster of differentiation 36 deficiency-related cardiomyopathy accelerates heart failure with co-existing mitral valve prolapse: a case report

Background

Free fatty acid is a major energy source in the healthy heart and cluster of differentiation 36 (CD36) partially regulates the rate of myocardial fatty acid uptake. Here, we report a case of CD36 deficiency-related cardiomyopathy with a unique pathophysiology. Heart failure was accelerated by co-existing mitral valve prolapse (MVP) without a distinct phenotype of hypertrophic or dilated cardiomyopathy.

Case summary

A middle-aged man was aware of dyspnoea and hospitalized for heart failure with MVP. Cluster of differentiation 36 deficiency was found based on the absence of myocardial ¹²³l-15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid (BMIPP) uptake by myocardial scintigraphy. Type I CD36 deficiency was further diagnosed by the lack of CD36 in both platelets and monocytes by flow cytometry. Left ventricular muscle was obtained intraoperatively, and a histological examination reflected compensative hypertrophy of cardiomyocytes with myofibrillar loss and reactive fibrosis. The microvascular structure around the cardiomyocytes was highlighted by immunohistochemical staining for CD31, while CD36 expression was absent. He had an operation of mitral valve replacement and improved heart failure.

Discussion

Cluster of differentiation 36 deficiency potentially mediates various pathological conditions in the heart. Incidental CD36 deficiency-related cardiomyopathy may accelerate heart failure in the presence of co-existing heart diseases. BMIPP scintigraphy might be helpful for predicting CD36 deficiency.

Pressure Overload Impairs Cardiac Function in Long-Chain Fatty Acid Transporter CD36-Knockout Mice

CD36 is one of the important transporters of long-chain fatty acids (LCFAs) in the myocardium. We previously reported that CD36-deficient patients demonstrate a marked reduction of myocardial uptake of LCFA, while myocardial glucose uptake shows a compensatory increase, and are often accompanied by cardiomyopathy. However, the molecular mechanisms and functional role of CD36 in the myocardium remain unknown.The current study aimed to explore the pathophysiological role of CD36 in the heart. Methods: Using wild type (WT) and knockout (KO) mice, we generated pressure overload by transverse aortic constriction (TAC) and analyzed cardiac functions by echocardiography. To assess cardiac hypertrophy and fibrosis, histological and molecular analyses and measurement of ATP concentration in mouse hearts were performed.By applying TAC, the survival rate was significantly lower in KO than that in WT mice. After TAC, KO mice showed significantly higher heart weight-to-tibial length ratio and larger cross-sectional area of cardiomyocytes than those of WT. Although left ventricular (LV) wall thickness in the KO mice was similar to that in the WT mice, the KO mice showed a significant enlargement of LV cavity and reduced LV fractional shortening compared to the WT mice with TAC. A tendency for decreased myocardial ATP concentration was observed in the KO mice compared to the WT mice after TAC operation.These data suggest that the LCFA transporter CD36 is required for the maintenance of energy provision, systolic function, and myocardial structure.

STAT3-activated CD36 facilitates fatty acid uptake in chronic lymphocytic leukemia cells

Although several studies established that unlike normal B cells chronic lymphocytic leukemia (CLL) cells metabolize fatty acids (FA), how CLL cells internalize FA is poorly understood. Because in various cell types CD36 facilitates FA uptake, we wondered whether a similar mechanism is operative CLL. We found that CD36 levels are higher in CLL cells than in normal B cells, and that small interfering RNA, CD36 neutralizing antibodies or sulfosuccinimidyl oleate (SSO) that inhibits CD36 significantly reduced the oxygen consumption of CLL cells incubated with FA. Because CD36 is oeverexpressed and STAT3 is constitutively activated in CLL cells, we wondered whether STAT3 induces CD36 expression. Sequence analysis identified putative STAT3 binding sites in the CD36 gene promoter. Chromatin immunoprecipitation and an electrophoretic mobility shift assay revealed that STAT3 binds to the CD36 gene promoter. A luciferase assay and STAT3-small hairpin RNA, that significantly decreased the levels of CD36 in CLL cells, established that STAT3 activates the transcription of the CD36 gene. Furthermore, SSO induced a dose-dependent apoptosis of CLL cells. Taken together, our data suggest that STAT3 activates CD36 and that CD36 facilitates FA uptake in CLL cells. Whether CD36 inhibition would provide clinical benefits in CLL remains to be determined.

Potentiation of Ecstasy-induced hyperthermia and FAT/CD36 expression in chronically exercised animals

Fatal hyperthermia as a result of 3,4-methylenedioxymethamphetamine (MDMA) use involves non-esterified free fatty acids (NEFA) and the activation of mitochondrial uncoupling proteins (UCP). NEFA gain access into skeletal muscle via specific transport proteins, including fatty acid translocase (FAT/CD36). FAT/CD36 expression is known to increase following chronic exercise. Previous studies have demonstrated the essential role of NEFA and UCP3 in MDMA-induced hyperthermia. The aims of the present study were to use a chronic exercise model (swimming for two consecutive hours per day, five days per wk for six wk) to increase FAT/CD36 expression in order to: 1) determine the contribution of FAT/CD36 in MDMA (20 mg/kg, s.c.)-mediated hyperthermia; and 2) examine the effects of the FAT/CD36 inhibitor, SSO (sulfo-N-succinimidyl oleate), on MDMA-induced hyperthermia in chronic exercise and sedentary control rats. MDMA administration resulted in hyperthermia in both sedentary and chronic exercise animals. However, MDMA-induced hyperthermia was significantly potentiated in the chronic exercise animals compared to sedentary animals. Additionally, chronic exercise significantly reduced body weight, increased FAT/CD36 protein expression levels and reduced plasma NEFA levels. The FAT/CD36 inhibitor, SSO (40 mg/kg, ip), significantly attenuated the hyperthermia mediated by MDMA in chronic exercised but not sedentary animals. Plasma NEFA levels were elevated in sedentary and exercised animals treated with SSO prior to MDMA suggesting attenuation of NEFA uptake into skeletal muscle. Chronic exercise did not alter skeletal muscle UCP3 protein expression levels. In conclusion, chronic exercise potentiates MDMA-mediated hyperthermia in a FAT/CD36 dependent fashion.

Myocardial energy provision is preserved by increased utilization of glucose and ketone bodies in CD36 knockout mice

AIMS

CD36 is an important transporter of long-chain fatty acids (LCFAs) in the myocardium. As we have reported previously, CD36-deficient patients demonstrate a marked reduction in myocardial uptake of (123)I-15-(p-iodophenyl)-(R, S)-methyl pentadecanoic acid (BMIPP), which is an analog of LCFAs, while myocardial (18)F-fluorodeoxy-glucose (FDG) uptake is increased. However, it has not been clarified whether energy provision is preserved in patients with CD36 deficiency. The aims of the current study were to investigate the myocardial uptake of glucose and alterations in myocardial metabolites in wild-type (WT) and CD36 knockout (KO) mice.

METHODS AND RESULTS

High-resolution positron emission tomography (PET) demonstrated markedly enhanced glucose uptake in KO mouse hearts compared with those of WT mice in real-time. The myocardial protein expression of glucose transporter protein 1 (GLUT1) was significantly enhanced in KO mice compared to WT mice, whereas that of GLUT4 was not altered. While the myocardial expression of genes involved in fatty acid metabolism did not increase in KO mice, that of genes related to glucose utilization compensatorily increased in KO mice. The metabolomic analysis of cardiac tissues revealed that the myocardial concentrations of ATP and phosphocreatine were maintained, even in KO mice. The concentration of 3-hydroxybutyric acid and mRNA expression of hydroxybutyrate dehydrogenase in the heart were significantly higher in KO than in WT mice.

CONCLUSION

These data suggest that high-energy phosphate might be preserved by the increased utilization of glucose and ketone bodies in CD36KO mouse hearts under conditions of deficient LCFA uptake.

Metabolic impairment in heart failure: the myocardial and systemic perspective

Although bioenergetic starvation is not a new concept in heart failure (HF), recent research has led to a growing appreciation of the complexity of metabolic aspects of HF pathophysiology. All steps of energy extraction, transfer, and utilization are affected, and structural metabolism is impaired, leading to compromised functional integrity of tissues. Not only the myocardium, but also peripheral tissues and organs are affected by metabolic failure, resulting in a global imbalance between catabolic and anabolic signals, leading to tissue wasting and, ultimately, to cachexia. Metabolic feedback signals from muscle and fat actively contribute to further myocardial strain, promoting disease progression. The prolonged survival of patients with stable, compensated HF will increasingly bring chronic metabolic complications of HF to the fore and gradually shift its clinical presentation. This paper reviews recent evidence on myocardial and systemic metabolic impairment in HF and summarizes current and emerging therapeutic concepts with specific metabolic targets.

AMPK signalling and the control of substrate use in the heart

All mammalian cells rely on adenosine triphosphate (ATP) to maintain function and for survival. The heart has the highest basal ATP demand of any organ due to the necessity for continuous contraction. As such, the ability of the cardiomyocyte to monitor cellular energy status and adapt the supply of substrates to match the energy demand is crucial. One important serine/threonine protein kinase that monitors cellular energy status in the heart is adenosine monophosphate activated protein kinase (AMPK). AMPK is also a key enzyme that controls multiple catabolic and anabolic biochemical pathways in the heart and indirectly plays a crucial role in regulating cardiac function in both physiological and pathophysiological conditions. Herein, we review the involvement of AMPK in myocardial fatty acid and glucose transport and utilization, as it relates to basal cardiac function. We also assess the literature amassed on cardiac AMPK and discuss the controversies surrounding the role of AMPK in physiological and pathophysiological processes in the heart. The work reviewed herein also emphasizes areas that require further investigation for the purpose of eventually translating this information into improved patient care.

CD36 inhibition prevents lipid accumulation and contractile dysfunction in rat cardiomyocytes

An increased cardiac fatty acid supply and increased sarcolemmal presence of the long-chain fatty acid transporter CD36 are associated with and contribute to impaired cardiac insulin sensitivity and function. In the present study we aimed at preventing the development of insulin resistance and contractile dysfunction in cardiomyocytes by blocking CD36-mediated palmitate uptake. Insulin resistance and contractile dysfunction were induced in primary cardiomyocytes by 48 h incubation in media containing either 100 nM insulin (high insulin; HI) or 200 μM palmitate (high palmitate; HP). Under both culture conditions, insulin-stimulated glucose uptake and Akt phosphorylation were abrogated or markedly reduced. Furthermore, cardiomyocytes cultured in each medium displayed elevated sarcolemmal CD36 content, increased basal palmitate uptake, lipid accumulation and decreased sarcomere shortening. Immunochemical CD36 inhibition enhanced basal glucose uptake and prevented elevated basal palmitate uptake, triacylglycerol accumulation and contractile dysfunction in cardiomyocytes cultured in either medium. Additionally, CD36 inhibition prevented loss of insulin signalling in cells cultured in HP, but not in HI medium. In conclusion, CD36 inhibition prevents lipid accumulation and lipid-induced contractile dysfunction in cardiomyocytes, but probably independently of effects on insulin signalling. Nonetheless, pharmacological CD36 inhibition may be considered as a treatment strategy to counteract impaired functioning of the lipid-loaded heart.

CD36 as a target to prevent cardiac lipotoxicity and insulin resistance

The fatty acid transporter and scavenger receptor CD36 is increasingly being implicated in the pathogenesis of insulin resistance and its progression towards type 2 diabetes and associated cardiovascular complications. The redistribution of CD36 from intracellular stores to the plasma membrane is one of the earliest changes occurring in the heart during diet induced obesity and insulin resistance. This elicits an increased rate of fatty acid uptake and enhanced incorporation into triacylglycerol stores and lipid intermediates to subsequently interfere with insulin-induced GLUT4 recruitment (i.e., insulin resistance). In the present paper we discuss the potential of CD36 to serve as a target to rectify abnormal myocardial fatty acid uptake rates in cardiac lipotoxic diseases. Two approaches are described: (i) immunochemical inhibition of CD36 present at the sarcolemma and (ii) interference with the subcellular recycling of CD36. Using in vitro model systems of high-fat diet induced insulin resistance, the results indicate the feasibility of using CD36 as a target for adaptation of cardiac metabolic substrate utilization. In conclusion, CD36 deserves further attention as a promising therapeutic target to redirect fatty acid fluxes in the body.

Multiphasic triacylglycerol dynamics in the intact heart during acute in vivo overexpression of CD36

Cardiac triacylglycerol (TAG) stores buffer the intracellular availability of long chain fatty acid (LCFA) that act as nuclear receptor ligands, substrate for lipotoxic derivatives, and high energy-yield fuel. The kinetic characteristics of TAG turnover and homeostatic mechanisms linking uptake and storage dynamics in hearts have until now remained elusive. This work examines TAG pool dynamics in the intact beating heart, under normal conditions and in response to acute gene expression-induced changes in CD36. Dynamic mode (13)C NMR elucidated multiple kinetic processes in (13)C-palmitate incorporation into TAG: an initial, saturable exponential component and a slower linear rate. Although previous work indicates the linear component to reflect TAG turnover, we hypothesized the saturable exponential to reflect transport of LCFA across the sarcolemma. Thus, we overexpressed the LCFA transporter CD36 through cardiac-specific adenoviral infection in vivo. Within 72 h, CD36 expression was increased 40% in intact hearts, accelerating the exponential phase relative to PBS-infused hearts. TAG turnover also increased with elevations in adipose triglyceride lipase (ATGL) and a modest increase in diacylglycerol acyltransferase 1 (DGAT1), without a significant expansion of the intracellular lipid pools. The results demonstrate a dynamic system of reciprocal gene regulation that couples saturable LCFA uptake across the sarcolemma to TAG synthesis/lipolysis rates.

Membrane Fatty Acid Transporters as Regulators of Lipid Metabolism: Implications for Metabolic Disease

Long-chain fatty acids and lipids serve a wide variety of functions in mammalian homeostasis, particularly in the formation and dynamic properties of biological membranes and as fuels for energy production in tissues such as heart and skeletal muscle. On the other hand, long-chain fatty acid metabolites may exert toxic effects on cellular functions and cause cell injury. Therefore, fatty acid uptake into the cell and intracellular handling need to be carefully controlled. In the last few years, our knowledge of the regulation of cellular fatty acid uptake has dramatically increased. Notably, fatty acid uptake was found to occur by a mechanism that resembles that of cellular glucose uptake. Thus, following an acute stimulus, particularly insulin or muscle contraction, specific fatty acid transporters translocate from intracellular stores to the plasma membrane to facilitate fatty acid uptake, just as these same stimuli recruit glucose transporters to increase glucose uptake. This regulatory mechanism is important to clear lipids from the circulation postprandially and to rapidly facilitate substrate provision when the metabolic demands of heart and muscle are increased by contractile activity. Studies in both humans and animal models have implicated fatty acid transporters in the pathogenesis of diseases such as the progression of obesity to insulin resistance and type 2 diabetes. As a result, membrane fatty acid transporters are now being regarded as a promising therapeutic target to redirect lipid fluxes in the body in an organ-specific fashion.

Regulation of sarcolemmal glucose and fatty acid transporters in cardiac disease

Circulating long-chain fatty acids (LCFA) and glucose are the main sources for energy production in the heart. In the healthy heart the ratio of glucose and LCFA oxidation is sensitively balanced and chronic alterations in this substrate mix are closely associated with cardiac dysfunction. While it has been accepted for several years that cardiac glucose uptake is mediated by facilitated transport, i.e. by means of the glucose transport proteins GLUT1 and GLUT4, only in the last few years it has become clear that proteins with high-affinity binding sites to LCFA, referred to as LCFA transporters, are responsible for bulk LCFA uptake. Similar to the GLUTs, the LCFA transporters CD36 and FABP(pm) can be recruited from an intracellular storage compartment to the sarcolemma to increase the rate of substrate uptake. Permanent relocation of LCFA transporters, mainly CD36, from intracellular stores to the sarcolemma is accompanied by accumulation of lipids and lipid metabolites in the heart. As a consequence, insulin signalling and glucose utilization are impaired, leading to decreased contractile activity of the heart. These observations underline the particular role and interplay of substrate carriers for glucose and LCFA in modulating cardiac metabolism, and the development of heart failure. The signalling and trafficking pathways and subcellular machinery regulating translocation of glucose and LCFA transporters are beginning to be unravelled. More knowledge on substrate transporter recycling, especially the similarities and differences between glucose and LCFA transporters, is expected to enable novel therapies aimed at changing the subcellular distribution of glucose and LCFA transporters, thereby manipulating the substrate preference of the diseased heart to help restore cardiac function.

PPARγ agonist induced cardiac enlargement is associated with reduced fatty acid and increased glucose utilization in myocardium of Wistar rats

In toxicological studies, high doses of peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists cause cardiac enlargement. To investigate whether this could be explained by a large shift from free fatty acid to glucose utilization by the heart, Wistar rats were treated for 2-3 weeks with a potent, selective PPARgamma agonist (X334, 3 micromol/kg/d), or vehicle. X334 treatment increased body-weight gain and ventricular mass. Treatment lowered plasma triglycerides by 61%, free fatty acid levels by 72%, insulin levels by 45%, and reduced total plasma protein concentration by 7% (indicating plasma volume expansion) compared to vehicle animals. Fasting plasma glucose levels were unaltered. To assess cardiac free fatty acid and glucose utilization in vivo we used simultaneous infusions of non-beta-oxidizable free fatty acid analogue, [9,10-(3)H](R)-2-bromopalmitate and [U-(14)C]2-deoxy-d-glucose tracers, which yield indices of local free fatty acid and glucose utilization. In anesthetized, 7 h fasted animals, left ventricular glucose utilization was increased to 182% while free fatty acid utilization was reduced by 28% (P<0.05) compared to vehicle. In separate studies we attempted to prevent the X334-induced hypolipidemia. Various dietary fat supplements were unsuccessful. By contrast, restricting the time during which the treated animals had access to food (promoting endogenous lipolysis), restored plasma free fatty acid from 27% to 72% of vehicle control levels and prevented the cardiac enlargement. Body-weight gain in these treated-food restricted rats was not different from vehicle controls. In conclusion, the cardiac enlargement caused by intense PPARgamma activation in normal animals is associated with marked changes in free fatty acid/glucose utilization and the enlargement can be prevented by restoring free fatty acid availability.

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.

Gene-environment interactions in wet beriberi: effects of thiamine depletion in CD36-defect rats

Selective vulnerability to thiamine deficiency is known to occur between individuals and within different tissues. However, no comprehensive explanation for this has been found, and there are no reports that reproduce the cardiovascular manifestations of human wet beriberi in animals. We hypothesized that the distinction of substrate reliance, namely, the primary dependency on glucose as substrate, could be an underlying factor in the selective vulnerability of thiamine deficiency. In the setting of impaired fatty acid entry, which occurs in CD36-defect rats, substrate reliance shifts from fatty acid to glucose, which would be expected to lead to a susceptibility to thiamine deficiency. Genomic DNA was analyzed for CD36 defects in three cognate strains of rats [spontaneously hypertensive rats (SHR)/NCrj, SHR/Izm, and Wistar-Kyoto (WKY)/NCrj], which identified the presence of a CD36 defect in SHR/NCrj rats but not in SHR/Izm and WKY/NCrj rats. Treatment with 2 wk of thiamine-depleted chow on 4-wk-old rats of each of these strains resulted in increased body and lung weight in the SHR/NCrj rats but not in the SHR/Izm and WKY/NCrj rats. The increased lung weight in the SHR/NCrj rats was accompanied with histological changes of congestive vasculopathy, which were not observed in either the SHR/Izm or the WKY/NCrj rats. Thiamine-deficient 12-wk-old SHR/NCrj rats demonstrated increased body weight (305.6 +/- 6.2 g in thiamine-deficient rats vs. 280.8 +/- 9.1 g in control; P < 0.0001), lactic acidemia (pH, 7.322 +/- 0.026 in thiamine-deficient rats vs. 7.443 +/- 0.016 in control; P < 0.0001; lactate, 2.42 +/- 0.28 mM in thiamine-deficient rats vs. 1.20 +/- 0.11 mM in control; P < 0.0001) and reduced systemic vascular resistance (4.61 +/- 0.42 x 104 dyn.s.cm-5 in thiamine-deficient rats vs. 6.55 +/- 1.36 x 104 dyn.s.cm-5 in control; P < 0.0001) with high cardiac output (186.0 +/- 24.7 ml in thiamine-deficient rats vs. 135.4 +/- 27.2 ml in control; P < 0.0019). In conclusion, SHR/NCrj rats harboring a genetic defect of long-chain fatty acid uptake present the relevant clinical cardiovascular signs of human wet beriberi, strongly indicating a close gene-environment interaction in wet beriberi.

CD36 deficiency and absent myocardial iodine-123-(R,S)-15-(p-iodophenyl)-3-methylpentadecanoic acid uptake in a girl with cardiomyopathy

A 10-year-old girl presented left ventricular failure 1 month after the onset of hemolytic uremic syndrome (HUS) caused by an Escherichia coli O157 infection and was diagnosed as having dilated cardiomyopathy. Thallium myocardial scintigraphy showed normal perfusion, but no myocardial uptake of iodine-123-( R, S)-15-( p-iodophenyl)-3-methylpentadecanoic acid ((123)I-BMIPP) was observed. We analyzed the CD36 expression in platelets and monocytes by using a flowcytometer, and she turned out to have CD36 deficiency type I.

CONCLUSION

Some patients may be predisposed to myocardial damage in the presence of CD36 deficiency. It is necessary to clarify the etiological significance of the relationship between cardiac impairment and CD36 deficiency in children.

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.

Requirement for the heart-type fatty acid binding protein in cardiac fatty acid utilization

Nonenzymatic cytosolic fatty acid binding proteins (FABPs) are abundantly expressed in many animal tissues with high rates of fatty acid metabolism. No physiological role has been demonstrated for any FABP, although these proteins have been implicated in transport of free long-chain fatty acids (LCFAs) and protection against LCFA toxicity. We report here that mice lacking heart-type FABP (H-FABP) exhibit a severe defect of peripheral (nonhepatic, non-fat) LCFA utilization. In these mice, the heart is unable to efficiently take up plasma LCFAs, which are normally its main fuel, and switches to glucose usage. Altered plasma levels of LCFAs, glucose, lactate and beta-hydroxybutyrate are consistent with depressed peripheral LCFA utilization, intensified carbohydrate usage, and increased hepatic LCFA oxidation; these changes are most pronounced under conditions favoring LCFA oxidation. H-FABP deficiency is only incompletely compensated, however, causing acute exercise intolerance and, at old age, a localized cardiac hypertrophy. These data establish a requirement for H-FABP in cardiac intracellular lipid transport and fuel selection and a major role in metabolic homeostasis. This new animal model should be particularly useful for investigating the significance of peripheral LCFA utilization for heart function, insulin sensitivity, and blood pressure.

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.

Myocardial CD36 expression and fatty acid accumulation in patients with type I and II CD36 deficiency

Long-chain fatty acids (LCFA) are one of the major cardiac energy substrates, so understanding LCFA metabolism may help in elucidating the mechanisms of various heart diseases. CD36 is a multifunctional membrane glycoprotein that acts not only as a receptor for thrombospondin, collagen and oxidized low density lipoprotein but also as a receptor for LCFA. We investigated the relationship between CD36 expression in myocardial capillary endothelial cells and myocardial LCFA uptake in patients with CD36 deficiency. We analyzed CD36 expression in blood cells from 250 patients with heart diseases by means of a flow cytometer. In 218 patients, myocardial LCFA scintigraphy was performed with 123I-beta-methyl-p-iodophenyl pentadecanoic acid (BMIPP). In 5 patients, myocardial capillary endothelial cells were examined immunohistochemically for CD36 expression. Eleven patients (4%) showed signs of type I CD36 deficiency (neither platelets nor monocytes expressed CD36). Twenty patients (8%) had type II CD36 deficiency (monocytes expressed CD36 but platelets did not). In all 11 patients with type I CD36 deficiency, no BMIPP accumulation was observed in the heart, but in 13 patients with type II CD36 deficiency, BMIPP accumulation in the heart was focally reduced, but there were no patients without BMIPP accumulation in the heart. Although the myocardial capillary endothelial cells from two CD36-positive patients expressed CD36, those from two patients with type I CD36 deficiency did not. In a patient with type II CD36 deficiency, some capillary endothelial cells displayed patchy CD36 expression. CD36 deficiency was documented in 31 (12%) patients with heart diseases. Because CD36 was not expressed in the myocardial capillary endothelial cells in patients with type I CD36 deficiency, type I CD36 deficiency is closely related to lack of myocardial LCFA accumulation and metabolism in the myocardium.

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.

Long-term effects of fatty acids on cell viability and gene expression of neonatal cardiac myocytes

Fatty acids are the most important source of energy for the adult heart. However, cardiac substrate preference changes during development and alters in pathophysiological states. Fatty acids have also been shown to be involved in signal transduction pathways, thereby affecting gene expression in various cell systems. In the present paper the significance of changes in substrate preference and the potential role of fatty acids in signal transduction in the cardiomyocyte are briefly reviewed. Furthermore, the development of a cellular model system, useful in exploring the long-term effects of fatty acids on the normal and hypertrophic cardiomyocyte, is described. Some aspects of this model system are illustrated by showing the effects of different fatty acid species on cell viability and the effects of fatty acids on the expression of heart type fatty acid-binding protein (H-FABP), a 15 kDa protein thought to be involved in intracellular trafficking of fatty acids. To this end primary cultures of rat neonatal ventricular myocytes were kept in defined medium containing various (combinations of) substrates for up to 48 h. First, the effects of prolonged exposure to different fatty acid species, complexed to BSA, on cell viability were investigated. Exposure of the cells to saturated fatty acids (C16:0 or C18:0), but not mono-unsaturated (C16:1 or C18:1) fatty acids, resulted in cell death, as evidenced by the release of intracellular proteins like lactate dehydrogenase. The detrimental effects of saturated fatty acids were nullified by the co-addition of mono-unsaturated fatty acids. Accordingly, the combination of C16:0/C18:1 was used to examine the effects of fatty acids on the expression of H-FABP. Therefore, the cells were incubated with either (i) glucose only, (ii) fatty acids only, or (iii) glucose plus fatty acids. Incubation with fatty acids (with or without glucose) resulted in a nearly four-fold increase of the H-FABP mRNA level. Similarly, at the protein level the cellular H-FABP/LDH ratio increased almost two-fold. In hypertrophic cardiomyocytes (stimulated with the alpha1-adrenergic agonist phenylephrine) the stimulatory effect of fatty acids on H-FABP expression was mitigated. These findings strongly suggest that fatty acids are able to modulate gene expression in the context of the cardiac muscle cell.

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.