RESUMEN
In eukaryotes, carnitine is best known for its ability to shuttle esterified fatty acids across mitochondrial membranes for ß-oxidation. It also returns to the cytoplasm, in the form of acetyl-L-carnitine (LAC), some of the resulting acetyl groups for posttranslational protein modification and lipid biosynthesis. While dietary LAC supplementation has been clinically investigated, its effects on cellular metabolism are not well understood. To explain how exogenous LAC influences mammalian cell metabolism, we synthesized isotope-labeled forms of LAC and its analogs. In cultures of glucose-limited U87MG glioma cells, exogenous LAC contributed more robustly to intracellular acetyl-CoA pools than did ß-hydroxybutyrate, the predominant circulating ketone body in mammals. The fact that most LAC-derived acetyl-CoA is cytosolic is evident from strong labeling of fatty acids in U87MG cells by exogenous 13C2-acetyl-L-carnitine. We found that the addition of d3-acetyl-L-carnitine increases the supply of acetyl-CoA for cytosolic posttranslational modifications due to its strong kinetic isotope effect on acetyl-CoA carboxylase, the first committed step in fatty acid biosynthesis. Surprisingly, whereas cytosolic carnitine acetyltransferase is believed to catalyze acetyl group transfer from LAC to coenzyme A, CRAT-/- U87MG cells were unimpaired in their ability to assimilate exogenous LAC into acetyl-CoA. We identified carnitine octanoyltransferase as the key enzyme in this process, implicating a role for peroxisomes in efficient LAC utilization. Our work has opened the door to further biochemical investigations of a new pathway for supplying acetyl-CoA to certain glucose-starved cells.
Asunto(s)
Acetilcoenzima A , Acetilcarnitina , Carnitina Aciltransferasas , Carnitina , Acetilcoenzima A/metabolismo , Acetilcarnitina/farmacología , Carnitina/metabolismo , Carnitina Aciltransferasas/metabolismo , Carnitina O-Acetiltransferasa/genética , Carnitina O-Acetiltransferasa/metabolismo , Ácidos Grasos/metabolismo , Glucosa/metabolismo , Oxidación-Reducción , Humanos , Línea Celular TumoralRESUMEN
Circulating tumor cells are the key link between a primary tumor and distant metastases, but once in the bloodstream, loss of adhesion induces cell death. To identify the mechanisms relevant for melanoma circulating tumor cell survival, we performed RNA sequencing and discovered that detached melanoma cells and isolated melanoma circulating tumor cells rewire lipid metabolism by upregulating fatty acid (FA) transport and FA beta-oxidationârelated genes. In patients with melanoma, high expression of FA transporters and FA beta-oxidation enzymes significantly correlates with reduced progression-free and overall survival. Among the highest expressed regulators in melanoma circulating tumor cells were the carnitine transferases carnitine O-octanoyltransferase and carnitine acetyltransferase, which control the shuttle of peroxisome-derived medium-chain FAs toward mitochondria to fuel mitochondrial FA beta-oxidation. Knockdown of carnitine O-octanoyltransferase or carnitine acetyltransferase and short-term treatment with peroxisomal or mitochondrial FA beta-oxidation inhibitors thioridazine or ranolazine suppressed melanoma metastasis in mice. Carnitine O-octanoyltransferase and carnitine acetyltransferase depletion could be rescued by medium-chain FA supplementation, indicating that the peroxisomal supply of FAs is crucial for the survival of nonadherent melanoma cells. Our study identifies targeting the FA-based cross-talk between peroxisomes and mitochondria as a potential therapeutic opportunity to challenge melanoma progression. Moreover, the discovery of the antimetastatic activity of the Food and Drug Administrationâapproved drug ranolazine carries translational potential.
Asunto(s)
Melanoma , Células Neoplásicas Circulantes , Ratones , Animales , Carnitina O-Acetiltransferasa/genética , Carnitina O-Acetiltransferasa/metabolismo , Carnitina Aciltransferasas/genética , Carnitina Aciltransferasas/metabolismo , Ranolazina , Oxidación-Reducción , Ácidos Grasos/metabolismo , Melanoma/tratamiento farmacológico , Carnitina/metabolismoRESUMEN
Carnitine acyl-carnitine translocase deficiency (CACTD) is a rare autosomal recessive disorder of mitochondrial long-chain fatty-acid transport. Most patients present in the first 2 days of life, with hypoketotic hypoglycaemia, hyperammonaemia, cardiomyopathy or arrhythmia, hepatomegaly and elevated liver enzymes. Multi-centre international retrospective chart review of clinical presentation, biochemistry, treatment modalities including diet, subsequent complications, and mode of death of all patients. Twenty-three patients from nine tertiary metabolic units were identified. Seven attenuated patients of Pakistani heritage, six of these homozygous c.82G>T, had later onset manifestations and long-term survival without chronic hyperammonemia. Of the 16 classical cases, 15 had cardiac involvement at presentation comprising cardiac arrhythmias (9/15), cardiac arrest (7/15), and cardiac hypertrophy (9/15). Where recorded, ammonia levels were elevated in all but one severe case (13/14 measured) and 14/16 had hypoglycaemia. Nine classical patients survived longer-term-most with feeding difficulties and cognitive delay. Hyperammonaemia appears refractory to ammonia scavenger treatment and carglumic acid, but responds well to high glucose delivery during acute metabolic crises. High-energy intake seems necessary to prevent decompensation. Anaplerosis utilising therapeutic d,l-3-hydroxybutyrate, Triheptanoin and increased protein intake, appeared to improve chronic hyperammonemia and metabolic stability where trialled in individual cases. CACTD is a rare disorder of fatty acid oxidation with a preponderance to severe cardiac dysfunction. Long-term survival is possible in classical early-onset cases with long-chain fat restriction, judicious use of glucose infusions, and medium chain triglyceride supplementation. Adjunctive therapies supporting anaplerosis may improve longer-term outcomes.
Asunto(s)
Carnitina Aciltransferasas/deficiencia , Carnitina/uso terapéutico , Dieta con Restricción de Grasas , Errores Innatos del Metabolismo Lipídico/dietoterapia , Errores Innatos del Metabolismo Lipídico/tratamiento farmacológico , Suplementos Dietéticos , Humanos , Recién Nacido , Internacionalidad , Estudios Retrospectivos , Tasa de SupervivenciaRESUMEN
Inhibition of lipid accumulation is the key step to prevent nonalcoholic fatty liver (NAFL) progressing to nonalcoholic steatohepatitis. We aimed to study the effect of low-molecular-weight citrus pectin (LCP) against lipid accumulation and the underlying mechanism. Oleic acid (OA)-induced lipid deposition in HepG2 cells was applied to mimic in vitro model of lipid accumulation. Oil Red O (ORO) stain result showed lipid accumulation was significantly reduced, and levels of adipose triglyceride lipase (ATGL) and carnitine palmitoyltransferase-1 (CPT-1), involved in triacylglycerol catabolism and fatty acid ß-oxidation, detected by RT-qPCR were increased after OA-stimulated HepG2 cells treated with LCP. RNA sequencing analysis identified 740 differentially expressed genes (DEGs) in OA-stimulated HepG2 cells treated with the LCP group (OA+LCP group), and bioinformatics analysis indicated that some DEGs were enriched in lipid metabolism-related processes and pathways. The expression of the top 8 known DEGs in the OA+LCP group was then verified by RT-qPCR, which showed that fold change (abs) of METTL7B was the highest among the 8 candidates. In addition, overexpression of METTL7B in HepG2 cells significantly inhibited the lipid accumulation and enhanced levels of ATGL and CPT-1. In conclusion, LCP inhibited lipid accumulation through the upregulation of METTL7B, and further enhancement of ATGL and CPT-1 levels. LCP is expected to develop as a promising agent to ameliorate fat accumulation in NAFL.
Asunto(s)
Proteínas Portadoras/metabolismo , Pectinas/farmacología , Carnitina Aciltransferasas/metabolismo , Proteínas Portadoras/genética , Biología Computacional , Células Hep G2 , Humanos , Lipasa/metabolismo , Metabolismo de los Lípidos/efectos de los fármacosRESUMEN
Alterations in muscle fatty acid metabolism have been implicated in mediating the severity of insulin resistance. In the insulin resistant heart fatty acids are favored as an energy source over glucose, which is thus associated with increased fatty acid oxidation, and an overall decrease in glycolysis and glucose oxidation. In addition, excessive uptake and beta-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. In animal studies, mice fed a high fat diet (HFD) show cardiac insulin resistance in which the accumulation of intra-myocardial diacylglycerol has been implicated, likely involving parallel signaling pathways. A HFD also results in accumulation of fatty acid oxidation byproducts in muscle, further contributing to insulin resistance. Carnitine acetyltransferase (CrAT) has an essential role in the cardiomyocyte because of its need for large amounts of carnitine. In the cardiomyocyte, carnitine switches energy substrate preference in the heart from fatty acid oxidation to glucose oxidation. This carnitine-induced switch in fatty acid oxidation to glucose oxidation is due to the presence of cytosolic CrAT and reverse CrAT activity. Accordingly, inhibition of fatty acid oxidation, or stimulation of CrAT, may be a novel approach to treatment of insulin resistance.
Asunto(s)
Carnitina Aciltransferasas/metabolismo , Carnitina/metabolismo , Diabetes Mellitus/metabolismo , Ácidos Grasos no Esterificados/metabolismo , Resistencia a la Insulina , Miocardio/metabolismo , Obesidad/metabolismo , Animales , Carnitina/deficiencia , Carnitina/uso terapéutico , Carnitina Aciltransferasas/química , Enfermedades Carenciales/dietoterapia , Enfermedades Carenciales/metabolismo , Enfermedades Carenciales/fisiopatología , Enfermedades Carenciales/prevención & control , Diabetes Mellitus/dietoterapia , Diabetes Mellitus/etiología , Diabetes Mellitus/fisiopatología , Dieta Alta en Grasa/efectos adversos , Suplementos Dietéticos , Diglicéridos/metabolismo , Corazón/fisiopatología , Humanos , Músculos/enzimología , Músculos/metabolismo , Miocardio/enzimología , Obesidad/dietoterapia , Obesidad/etiología , Obesidad/fisiopatología , Oxidación-Reducción , Disfunción Ventricular/etiología , Disfunción Ventricular/prevención & controlRESUMEN
The metabolic roles of carnitine have been greatly clarified over the past 50 years, and it is now well established that carnitine is a key player in mitochondrial generation of energy and metabolism of acetyl coenzyme A. A therapeutic role for carnitine in treatment of nutritional deficiencies in infants and children was first demonstrated in 1958, and since that time it has been used to treat a number of inborn errors of metabolism. Carnitine was approved by the US Food and Drug Administration in 1985 for treatment of 'primary carnitine deficiency', and later in 1992 for treatment of 'secondary carnitine deficiency', a definition that included the majority of relevant metabolic disorders associated with low or abnormal plasma carnitine levels. Today, carnitine treatment of inborn errors of metabolism is a safe and integral part of many treatment protocols, and a growing interest in carnitine has resulted in greater recognition of many causes of carnitine depletion. Notwithstanding, there is still a lack of data from randomized clinical trials, even on the use of carnitine in inborn errors of metabolism, although ethical issues may be a contributing factor in this regard.
Asunto(s)
Cardiomiopatías/prevención & control , Carnitina/deficiencia , Carnitina/uso terapéutico , Ciencias de la Nutrición del Niño/historia , Enfermedades Carenciales/prevención & control , Suplementos Dietéticos , Hiperamonemia/prevención & control , Errores Innatos del Metabolismo/dietoterapia , Enfermedades Musculares/prevención & control , Ciencias de la Nutrición/historia , Administración Intravenosa , Adulto , Cardiomiopatías/dietoterapia , Cardiomiopatías/historia , Cardiomiopatías/fisiopatología , Carnitina/administración & dosificación , Carnitina/efectos adversos , Carnitina/historia , Carnitina Aciltransferasas/deficiencia , Carnitina Aciltransferasas/historia , Niño , Ensayos Clínicos como Asunto , Enfermedades Carenciales/dietoterapia , Enfermedades Carenciales/historia , Enfermedades Carenciales/fisiopatología , Suplementos Dietéticos/efectos adversos , Metabolismo Energético , Historia del Siglo XX , Historia del Siglo XXI , Humanos , Hiperamonemia/dietoterapia , Hiperamonemia/historia , Hiperamonemia/fisiopatología , Lactante , Errores Innatos del Metabolismo Lipídico/dietoterapia , Errores Innatos del Metabolismo Lipídico/tratamiento farmacológico , Errores Innatos del Metabolismo Lipídico/historia , Errores Innatos del Metabolismo Lipídico/fisiopatología , Errores Innatos del Metabolismo/tratamiento farmacológico , Errores Innatos del Metabolismo/historia , Errores Innatos del Metabolismo/fisiopatología , Enfermedades Musculares/dietoterapia , Enfermedades Musculares/historia , Enfermedades Musculares/fisiopatología , Producción de Medicamentos sin Interés Comercial/historiaRESUMEN
Obesity has become a public health concern due to its positive association with the incidence of many diseases, and coffee components including chlorogenic acid (CGA) and caffeine have been demonstrated to play roles in the suppression of fat accumulation. To investigate the mechanism by which CGA and caffeine regulate lipid metabolism, in the present study, forty mice were randomly assigned to four groups and fed diets containing no CGA or caffeine, CGA, caffeine, or CGA+caffeine for 24 weeks. Body weight, intraperitoneal adipose tissue (IPAT) weight, and serum biochemical parameters were measured, and the activities and mRNA and protein expression of lipid metabolism-related enzymes were analysed. There was a decrease in the body weight and IPAT weight of mice fed the CGA+caffeine diet. There was a significant decrease in the serum and hepatic concentrations of total cholesterol, TAG and leptin of mice fed the CGA+caffeine diet. The activities of carnitine acyltransferase (CAT) and acyl-CoA oxidase (ACO) were increased in mice fed the caffeine and CGA+caffeine diets, while the activity of fatty acid synthase (FAS) was suppressed in those fed the CGA+caffeine diet. The mRNA expression levels of AMP-activated protein kinase (AMPK), CAT and ACO were considerably up-regulated in mice fed the CGA+caffeine diet, while those of PPARγ2 were down-regulated. The protein expression levels of AMPK were increased and those of FAS were decreased in mice fed the CGA+caffeine diet. These results indicate that CGA+caffeine suppresses fat accumulation and body weight gain by regulating the activities and mRNA and protein expression levels of hepatic lipid metabolism-related enzymes and that these effects are stronger than those exerted by CGA and caffeine individually.
Asunto(s)
Cafeína/uso terapéutico , Ácido Clorogénico/uso terapéutico , Suplementos Dietéticos , Hígado Graso/prevención & control , Regulación Enzimológica de la Expresión Génica , Hígado/metabolismo , Acil-CoA Oxidasa/química , Acil-CoA Oxidasa/genética , Acil-CoA Oxidasa/metabolismo , Adiposidad , Animales , Carnitina Aciltransferasas/química , Carnitina Aciltransferasas/genética , Carnitina Aciltransferasas/metabolismo , Inducción Enzimática , Represión Enzimática , Ácido Graso Sintasas/antagonistas & inhibidores , Ácido Graso Sintasas/genética , Ácido Graso Sintasas/metabolismo , Hígado Graso/metabolismo , Hígado Graso/patología , Femenino , Hiperlipidemias/prevención & control , Grasa Intraabdominal/metabolismo , Grasa Intraabdominal/patología , Leptina/sangre , Leptina/metabolismo , Metabolismo de los Lípidos , Hígado/enzimología , Hígado/patología , Ratones , Ratones Endogámicos ICR , Tamaño de los Órganos , Distribución AleatoriaRESUMEN
The carnitine/acylcarnitine translocase (CACT), an integral protein of the mitochondrial inner membrane, belongs to the carnitine-dependent system of fatty acid transport into mitochondria, where beta-oxidation occurs. CACT exchanges cytosolic acylcarnitine or free carnitine for carnitine in the mitochondrial matrix. The object of this study was to investigate in rat liver the effect, if any, of diets enriched with saturated fatty acids (beef tallow, BT, the control), n-3 polyunsaturated fatty acids (PUFA) (fish oil, FO), n-6 PUFA (safflower oil, SO), and mono-unsaturated fatty acids (MUFA) (olive oil, OO) on the activity and expression of CACT. Translocase exchange rates increased, in parallel with CACT mRNA abundance, upon FO-feeding, whereas OO-dietary treatment induced a decrease in both CACT activity and expression. No changes were observed upon SO-feeding. Nuclear run-on assay revealed that FO-treatment increased the transcriptional rate of CACT mRNA. On the other hand, only in the nuclei of hepatocytes from OO-fed rats splicing of the last intron of CACT pre-mRNA and the rate of formation of the 3'-end were affected. Overall, these findings suggest that compared to the BT-enriched diet, the SO-enriched diet did not influence CACT activity and expression, whereas FO- and OO-feeding alters CACT activity in an opposite fashion, i.e. modulating its expression at transcriptional and post-transcriptional levels, respectively.
Asunto(s)
Carnitina Aciltransferasas/metabolismo , Grasas de la Dieta/farmacología , Mitocondrias Hepáticas/enzimología , Animales , Carnitina Aciltransferasas/análisis , Carnitina Aciltransferasas/genética , Masculino , Lípidos de la Membrana/análisis , Estabilidad del ARN , ARN Mensajero/análisis , Ratas , Ratas WistarRESUMEN
OBJETIVO: Apresentar a resposta cardiovascular à L-carnitina de um paciente com insuficiência cardíaca congestiva decorrente de miocardiopatia dilatada pelo vírus da imunodeficiência humana. DESCRIÇÃO DO CASO: Criança com quadro clínico de insuficiência cardíaca congestiva grave devido à miocardiopatia dilatada pela síndrome de imunodeficiência adquirida. O tratamento para as manifestações clínicas foi instituído, com pouca resposta clínica. Com objetivo de melhorar o desempenho energético/metabólico dos cardiomiócitos, foi instituída terapia com L-carnitina. Observou-se significativa melhora clínica do paciente, em relação ao desempenho cardíaco, mesmo antes do início do tratamento com os fármacos antirretrovirais. COMENTÁRIOS: A L-carnitina é um composto que facilita o transporte dos ácidos graxos de cadeia longa para dentro da mitocôndria. Nesse caso, o uso da L-carnitina parece ser clinica e bioquimicamente justificado.
OBJECTIVE: To present the cardiovascular response to L-carnitine of a patient with congestive heart failure caused by dilated cardiomyopathy and human immunodeficiency virus. CASE DESCRIPTION: Child with a clinical history of severe congestive heart failure due to dilated cardiomyopathy caused by acquired immunodeficiency syndrome. The treatment for the symptoms resulted in a poor clinical response. In order to improve the energetic performance/metabolism of cardiomyocytes, therapy with L-carnitine was established. There was significant clinical improvement of the cardiac performance of the patient, even before starting the treatment with antiretroviral drugs. COMMENTS: L-carnitine is a compound that facilitates the transport of long-chain fatty acids into the mitochondria. In this case the administration of L-carnitine appears to be clinically and biochemical justified.
Asunto(s)
Humanos , Masculino , Preescolar , Cardiomiopatía Dilatada/tratamiento farmacológico , Carnitina Aciltransferasas/uso terapéutico , Síndrome de Inmunodeficiencia Adquirida/complicacionesRESUMEN
Riboflavin, commonly known as vitamin B2, is the precursor of flavin cofactors. It is present in our typical diet, and inside the cells it is metabolized to FMN and FAD. As a result of their rather unique and flexible chemical properties these flavins are among the most important redox cofactors present in a large series of different enzymes. A problem in riboflavin metabolism or a low intake of this vitamin will have consequences on the level of FAD and FMN in the cell, resulting in disorders associated with riboflavin deficiency. In a few number of cases, riboflavin deficiency is associated with impaired oxidative folding, cell damage and impaired heme biosynthesis. More relevant are several studies referring reduced activity of enzymes such as dehydrogenases involved in oxidative reactions, respiratory complexes and enzymes from the fatty acid ß-oxidation pathway. The role of this vitamin in mitochondrial metabolism, and in particular in fatty acid oxidation, will be discussed in this review. The basic aspects concerning riboflavin and flavin metabolism and deficiency will be addressed, as well as an overview of the role of the different flavoenzymes and flavin chemistry in fatty acid ß-oxidation, merging clinical, cellular and biochemical perspectives. A number of recent studies shedding new light on the cellular processes and biological effects of riboflavin supplementation in metabolic disease will also be overviewed. Overall, a deeper understanding of these emerging roles of riboflavin intake is essential to design better therapies.
Asunto(s)
Mitocondrias/metabolismo , Riboflavina/fisiología , Carnitina Aciltransferasas/metabolismo , Humanos , Deficiencia Múltiple de Acil Coenzima A Deshidrogenasa/metabolismo , Oxidación-Reducción , Oxidorreductasas actuantes sobre Donantes de Grupo CH-CH/metabolismo , Riboflavina/metabolismoRESUMEN
Carnitine-acylcarnitine translocase (CACT) deficiency (McKusick 212138) is a rare life threatening disorder characterized by hypoketotic hypoglycemia, hyperammonemia, encephalopathy, cardiomyopathy hepatopathy, and myopathy. Here, we present a detailed clinical course of 3 Saudi siblings with a severe phenotype. The third patient was described in more detail. Early medical intervention in the form of 25% dextrose intravenous infusion and carnitine supplement followed by a gradual introduction of a high carbohydrate low fat special formula resulted in a good clinical and biochemical response to the treatment in our patient. However, early nephrocalcinosis, severe hypotonia, and subsequently intravascular cerebral accident could not be prevented. He died at 18 months of age as a result of metabolic decompensation. This suggests that CACT deficiency is still a lethal disorder even with an early and aggressive medical intervention.
Asunto(s)
Carnitina Aciltransferasas/deficiencia , Humanos , Recién Nacido , FenotipoRESUMEN
The mitochondrial carnitine/acylcarnitine carrier (CAC) is characterized by the presence of a distinct motif, RXXPANAAXF, within its sixth transmembrane alpha-helix. In this study, we analysed the role of the amino acids of this motif in the structure-function relationships of the human CAC by using two complementary approaches. First, we performed functional analysis in the model fungus Aspergillus nidulans of selected mutations with structural and functional relevance. Second, similar mutant human CACs were biochemically characterized after their reconstitution into liposomes. Both analyses have provided relevant information on the importance and role of the CAC motif residues in the activity and metabolic function of CAC. Only the two adjacent alanines, Ala281 and Ala282 in the human CAC, have been found not to be crucial for transport activity and in vivo function. Results obtained from amino acid substitutions of residues Arg275, Asn280 and Phe284 of human CAC together with structural analysis using molecular modelling of the carrier suggest that R275, N280 and F284 are involved in substrate binding during acylcarnitine/carnitine translocation. Furthermore, functional analysis of mutations of residues Pro278 and Ala279 in A. nidulans, together with kinetic data in reconstituted liposomes, suggest a predominant structural role for these amino acids.
Asunto(s)
Aminoácidos/metabolismo , Carnitina Aciltransferasas/química , Carnitina Aciltransferasas/metabolismo , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Aspergillus nidulans/enzimología , Aspergillus nidulans/crecimiento & desarrollo , Transporte Biológico , Calorimetría , Carnitina/metabolismo , Humanos , Cinética , Liposomas/metabolismo , Modelos Moleculares , Datos de Secuencia Molecular , Proteínas Mutantes/química , Proteínas Mutantes/metabolismo , Estructura Secundaria de Proteína , Proteínas Recombinantes/metabolismo , Relación Estructura-Actividad , Factores de Tiempo , Transformación Genética , Tritio/metabolismoRESUMEN
Peroxisomes metabolize a variety of lipids, acting as a chain-shortening system that produces acyl-CoAs of varying chain lengths, including acetyl-CoA and propionyl-CoA. It is, however, still largely unknown how beta-oxidation products exit peroxisomes and where they are further metabolized. Peroxisomes contain carnitine acetyltransferase (CRAT) and carnitine octanoyltransferase (CROT) that produce carnitine esters for transport out of peroxisomes, together with recently characterized acyl-CoA thioesterases (ACOTs) that produce free fatty acids. Here we have performed tissue expression profiling of the short- and medium-chain carnitine acyltransferases Crat, Crot and the short- and medium-chain thioesterases (Acot12) and (Acot5), and show that they are largely expressed in different tissues, suggesting that they do not compete for the same substrates but rather provide complementary systems for transport of metabolites across the peroxisomal membrane. These data also explain earlier observed tissue differences in peroxisomal production of acetyl-CoA/acetyl-carnitine/acetate and underscores the differences in peroxisome function in various organs.
Asunto(s)
Carnitina Aciltransferasas/metabolismo , Peroxisomas/metabolismo , Tioléster Hidrolasas/metabolismo , Empalme Alternativo/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Transporte Biológico , Carnitina Aciltransferasas/química , Carnitina Aciltransferasas/genética , Catalasa/metabolismo , Regulación Enzimológica de la Expresión Génica , Isoenzimas/química , Isoenzimas/genética , Isoenzimas/metabolismo , Masculino , Ratones , Mitocondrias/enzimología , Datos de Secuencia Molecular , Especificidad de Órganos , Oxidación-Reducción , Alineación de SecuenciaRESUMEN
Carnitine-acylcarnitine translocase (CACT) deficiency is a rare disorder that results in long-chain fatty acids being unavailable for mitochondrial beta-oxidation and ketogenesis. It can present in the neonatal period or infancy with a severe clinical form, typically with convulsions, hypothermia, encephalopathy, cardiomyopathy and liver dysfunction, or with a milder phenotype with episodes of hypoglycaemia and hyperammonaemia during intercurrent illness. Investigations show hypoketonaemia, intermittent dicarboxyluria and hypocarnitinaemia with grossly elevated acylcarnitines. Enzyme assay or DNA analysis confirms the diagnosis. The severe phenotype results in severe disability or death. The less severe phenotype can also cause significant disability secondary to hypoglycaemia and/or hyperammonaemia at presentation. We report the outcome of two siblings with CACT deficiency. The index patient presented at the age of 2 months during a respiratory illness with hypoglycaemia, hyperammonaemia and cardiorespiratory collapse. Acylcarnitine profiles showed decreased free carnitine but striking elevations of long-chain acylcarnitines. Urine organic acids showed dicarboxylic aciduria. Fatty acid oxidation studies showed reduced oleate and myristate oxidation. His acylcarnitine profile normalized after he was started on a medium-chain triglyceride (MCT) low-fat diet and carnitine supplementation. Low CACT activity on enzyme assay confirmed the diagnosis. He has resulting profound developmental delay and epilepsy. The sibling was prospectively treated with a low-fat MCT diet and carnitine supplementation. Acylcarnitine profile at birth also showed elevated long-chain acylcarnitines. Fatty acid oxidation studies confirmed the diagnosis. To date he has normal development and has not had any significant periods of hypoglycaemia or hyperammonaemia.
Asunto(s)
Carnitina Aciltransferasas/deficiencia , Carnitina/uso terapéutico , Dieta con Restricción de Grasas , Suplementos Dietéticos , Proteínas de Transporte de Membrana/deficiencia , Errores Innatos del Metabolismo/dietoterapia , Errores Innatos del Metabolismo/tratamiento farmacológico , Carnitina/análogos & derivados , Carnitina/sangre , Ácidos Dicarboxílicos/orina , Ácidos Grasos/metabolismo , Humanos , Hiperamonemia/etiología , Hiperamonemia/prevención & control , Hipoglucemia/etiología , Hipoglucemia/prevención & control , Lactante , Masculino , Errores Innatos del Metabolismo/complicaciones , Errores Innatos del Metabolismo/diagnóstico , Errores Innatos del Metabolismo/metabolismo , Oxidación-Reducción , Linaje , Fenotipo , Índice de Severidad de la Enfermedad , Resultado del TratamientoRESUMEN
The carnitine-acylcarnitine translocase (CACT) is one of the components of the carnitine cycle. The carnitine cycle is necessary to shuttle long-chain fatty acids from the cytosol into the intramitochondrial space where mitochondrial beta-oxidation of fatty acids takes place. The oxidation of fatty acids yields acetyl-coenzyme A (CoA) units, which may either be degraded to CO(2) and H(2)O in the citric acid cycle to produce ATP or converted into ketone bodies which occurs in liver and kidneys. Metabolic consequences of a defective CACT are hypoketotic hypoglycaemia under fasting conditions, hyperammonemia, elevated creatine kinase and transaminases, dicarboxylic aciduria, very low free carnitine and an abnormal acylcarnitine profile with marked elevation of the long-chain acylcarnitines. Clinical signs and symptoms in CACT deficient patients, are a combination of energy depletion and endogenous toxicity. The predominantly affected organs are brain, heart and skeletal muscle, and liver, leading to neurological abnormalities, cardiomyopathy and arrythmias, skeletal muscle damage and liver dysfunction. Most patients become symptomatic in the neonatal period with a rapidly progressive deterioration and a high mortality rate. However, presentations at a later age with a milder phenotype have also been reported. The therapeutic approach is the same as in other long-chain fatty acid disorders and includes intravenous glucose (+/- insulin) administration to maximally inhibit lipolysis and subsequent fatty acid oxidation during the acute deterioration, along with other measures such as ammonia detoxification, depending on the clinical features. Long-term strategy consists of avoidance of fasting with frequent meals and a special diet with restriction of long-chain fatty acids. Due to the extremely low free carnitine concentrations, carnitine supplementation is often needed. Acylcarnitine profiling in plasma is the assay of choice for the diagnosis at a metabolite level. However, since the acylcarnitine profile observed in CACT-deficient patients is identical to that in CPT2-deficient patients, definitive identification of CACT-deficiency in a certain patient requires determination of the activity of CACT. Subsequently, mutational analysis of the CACT gene can be performed. So far, 9 different mutations have been identified in the CACT gene.
Asunto(s)
Carnitina Aciltransferasas/deficiencia , Carnitina Aciltransferasas/metabolismo , Animales , Carnitina/metabolismo , Carnitina Aciltransferasas/genética , Homeostasis , Humanos , Mitocondrias/enzimología , Mitocondrias/metabolismo , Mutación/genéticaRESUMEN
Cells contain limited and sequestered pools of Coenzyme A (CoA) that are essential for activating carboxylate metabolites. Some acyl-CoA esters have high metabolic and signalling impact, so control of CoA ester concentrations is important. This and transfer of the activated acyl moieties between cell compartments without wasting energy on futile cycles of hydrolysis and resynthesis is achieved through the carnitine system. The location, properties of and deficiencies in the carnitine acyltransferases are described in relation to their influence on the CoA pools in the cell and, hence, on metabolism. The protection of free CoA pools in disease states is achieved by excretion of acyl-carnitine so that carnitine supplementation is required where unwanted acyl groups build up, such as in some inherited disorders of fatty acid oxidation. Acetyl-carnitine improves cognition in the brain and propionyl-carnitine improves cardiac performance in heart disease and diabetes. The therapeutic effects of carnitine and its esters are discussed in relation to the integrative influence of the carnitine system across CoA pools. Recent evidence for sequestered pools of activated acetate for synthesis of malonyl-CoA, for the synthesis of polyunsaturated fatty acids and for the inhibition of carnitine palmitoyltransferase 1 to regulate fatty acid oxidation is reviewed.
Asunto(s)
Carnitina Aciltransferasas/metabolismo , Coenzima A/metabolismo , Enfermedad , Salud , Animales , Carnitina/química , Carnitina/metabolismo , Carnitina/uso terapéutico , Humanos , Mitocondrias/metabolismoRESUMEN
Deficiency of carnitine/acylcarnitine translocase (CACT) is an autosomal recessive disorder of the carnitine cycle resulting in the inability to transfer fatty acids across the inner mitochondrial membrane. Only a limited number of affected patients have been reported and the effect of therapy on this condition is still not well defined. Here, we report a new patient with this disorder and follow the response to therapy. Our patient was the product of a consanguineous marriage. He presented shortly after birth with cardiac myopathy and arrhythmia coupled with severe non-ketotic hypoglycemia. Initial metabolic studies indicated severe non-ketotic C6-C10 dicarboxylic aciduria, plasma carnitine deficiency, and a characteristic elevation of plasma C:16:0, C18:1, and C18:2 acylcarnitine species. Enzyme assay confirmed deficiency of CACT activity. Molecular studies indicated that this child was homozygous, and both parents heterozygous, for a single bp change converting glutamine 238 to arginine (Q238R). Therapy with a formula providing most of the fat via medium chain triglycerides (MCT) and carnitine supplementation reduced the concentration of long-chain acylcarnitines and reversed cardiac symptoms and the hypoglycemia. These results suggest that carnitine and MCT may be effective in treating this defect of long-chain fatty acid oxidation.
Asunto(s)
Carnitina Aciltransferasas/deficiencia , Carnitina Aciltransferasas/genética , Dietoterapia , Mutación Missense , Acetilcarnitina/sangre , Carnitina/administración & dosificación , Carnitina/uso terapéutico , Preescolar , Consanguinidad , Análisis Mutacional de ADN , Ácidos Dicarboxílicos/orina , Fibroblastos/enzimología , Humanos , Errores Innatos del Metabolismo Lipídico , Masculino , Modelos Biológicos , Linaje , Valores de Referencia , Arabia Saudita/etnología , Resultado del Tratamiento , Triglicéridos/administración & dosificaciónRESUMEN
The carnitine-dependent transport of long-chain fatty acids is essential for fatty acid catabolism. In this system, the fatty acid moiety of acyl-CoA is transferred enzymatically to carnitine, and the resultant product, acylcarnitine, is imported into the mitochondrial matrix through a transporter named carnitine-acylcarnitine translocase (CACT). Here we report a novel mammalian protein homologous to CACT. The protein, designated as CACL (CACT-like), is localized to the mitochondria and has palmitoylcarnitine transporting activity. The tissue distribution of CACL is similar to that of CACT; both are expressed at a higher level in tissues using fatty acids as fuels, except in the brain, where only CACL is expressed. In addition, CACL is induced by partial hepatectomy or fasting. Thus, CACL may play an important role cooperatively with its homologue CACT in a stress-induced change of lipid metabolism, and may be specialized for the metabolism of a distinct class of fatty acids involved in brain function.
Asunto(s)
Carnitina Aciltransferasas/química , Carnitina Aciltransferasas/metabolismo , Carnitina Aciltransferasas/farmacología , Carnitina/análogos & derivados , Hígado/fisiología , Mitocondrias/enzimología , Proteínas Mitocondriales/farmacología , Células 3T3 , Secuencia de Aminoácidos , Animales , Transporte Biológico , Northern Blotting , Western Blotting , Encéfalo/fisiología , Carnitina/química , ADN Complementario/metabolismo , Escherichia coli/metabolismo , Ácidos Grasos/metabolismo , Privación de Alimentos , Prueba de Complementación Genética , Humanos , Inmunohistoquímica , Metabolismo de los Lípidos , Hígado/metabolismo , Ratones , Ratones Endogámicos C57BL , Mitocondrias/metabolismo , Proteínas Mitocondriales/química , Datos de Secuencia Molecular , Palmitoilcarnitina/química , Plásmidos/metabolismo , Saccharomyces cerevisiae/metabolismo , Homología de Secuencia de Aminoácido , Factores de Tiempo , Distribución TisularRESUMEN
In this study, we examined the effects of sesamin and vegetable oil on the concentrations of polyunsaturated fatty acid (PUFA) and lipids (triacylglycerol, free cholesterol, and phospholipid), and beta-oxidation enzyme activities in the rat liver. Rats were fed a diet containing 5% (low-fat diet) or 20% (high-fat diet) salad oil (rapeseed oil: soybean oil, 7:3) with or without sesamin (0.5% w/w) for 4 wk. As a result, the concentrations of linoleic acid (LA, n-6), alpha-linolenic acid (ALA, n-3), and total PUFA in the liver increased significantly as the result of the high-fat diet. In the high-fat diet groups, sesamin administration decreased the concentrations of LA, ALA, and total PUFA to almost the same level as the low-fat diet group, while it increased the concentrations of dihomo-gamma-linolenic acid (DGLA, n-6) and arachidonic acid (AA, n-6). The activities of carnitine acyltransferase and acyl-CoA dehydrogenase in liver mitochondria were enhanced by the intake of the high-fat diet, and were further enhanced by the administration of sesamin. Peroxisomal acyl-CoA oxidase activity was also enhanced by sesamin, while it was not affected by the dietary fat level. These results suggest that sesamin suppressed the increase of hepatic PUFA concentration caused by feeding the high-fat diet through enhancing the enzyme activities of fatty acid beta-oxidation and PUFA metabolism from LA and ALA.
Asunto(s)
Grasas de la Dieta/administración & dosificación , Dioxoles/administración & dosificación , Ácidos Grasos Insaturados/metabolismo , Lignanos/administración & dosificación , Ácido 8,11,14-Eicosatrienoico/análisis , Acil-CoA Deshidrogenasa/metabolismo , Animales , Ácido Araquidónico/análisis , Carnitina Aciltransferasas/metabolismo , Ácidos Grasos Monoinsaturados , Ácidos Grasos Insaturados/análisis , Ácido Linoleico/análisis , Hígado/química , Hígado/efectos de los fármacos , Masculino , Mitocondrias Hepáticas/enzimología , Aceites de Plantas/administración & dosificación , Aceite de Brassica napus , Ratas , Ratas Wistar , Aceite de Soja/administración & dosificación , Ácido alfa-Linolénico/análisisRESUMEN
Rat peroxisomal carnitine octanoyltransferase (COT), which facilitates the transport of medium-chain fatty acids through the peroxisomal membrane, is irreversibly inhibited by the hypoglycaemia-inducing drug etomoxir. To identify the molecular basis of this inhibition, cDNAs encoding full-length wild-type COT, two different variant point mutants and one variant double mutant from rat peroxisomal COT were expressed in Saccharomyces cerevisiae, an organism devoid of endogenous COT activity. The recombinant mutated enzymes showed activity towards both carnitine and decanoyl-CoA in the same range as the wild type. Whereas the wild-type version expressed in yeast was inhibited by etomoxir in an identical manner to COT from rat liver peroxisomes, the activity of the enzyme containing the double mutation H131A/H340A was completely insensitive to etomoxir. Individual point mutations H131A and H340A also drastically reduced sensitivity to etomoxir. Taken together, these results indicate that the two histidine residues, H131 and H340, are the sites responsible for inhibition by etomoxir and that the full inhibitory properties of the drug will be shown only if both histidines are intact at the same time. Our data demonstrate that both etomoxir and malonyl-CoA inhibit COT by interacting with the same sites.