Mise en évidence de plusieurs transcrits de la γ-butyrobétaine hydroxylase

Ghrelin reduces hepatic mitochondrial fatty acid beta oxidation.

Ghrelin is a 28-amino-acid peptide secreted during starvation by gastric cells. Ghrelin physiologically induces food intake and seems to alter lipid and glucid metabolism in several tissues such as adipose tissue and liver. Liver has a key position in lipid metabolism as it allows the metabolic orientation of fatty acids between oxidation and esterification. We investigated the effects of peripheral ghrelin administration on 2 crucial parameters of fatty acid oxidation: the levocarnitine (L-carnitine)-dependent entry of the fatty acids in the mitochondria and the mitochondrial fatty acid oxidation. Ghrelin was either given to rats prior to the hepatocyte preparation and culture or used to t…

Autism and carnitine: A possible link

Patients with autism spectrum disorders (ASD) present deficits in social interactions and communication, they also show limited and stereotypical patterns of behaviors and interests. The pathophysiological bases of ASD have not been defined yet. Many factors seem to be involved in the onset of this disorder. These include genetic and environmental factors, but autism is not linked to a single origin, only. Autism onset can be connected with various factors such as metabolic disorders: including carnitine deficiency. Carnitine is a derivative of two amino acid lysine and methionine. Carnitine is a cofactor for a large family of enzymes: the carnitine acyltransferases. Through their action th…

Carnitine et performance physique

Resume Objectif. – L’objectif de cette publication est de preciser l’implication de la carnitine dans le fonctionnement normal de la cellule musculaire et d’evaluer l’interet que pourrait representer pour les performances physiques une supplementation en carnitine. Actualites. – Recemment, de nouvelles informations concernant la voie de la biosynthese de la carnitine ainsi que de son transport dans les cellules musculaires ont ete publiees. Les bases moleculaires des deficiences en carnitine ont notamment ete identifiees permettant ainsi de mieux comprendre les mecanismes controlant l’utilisation de la carnitine dans ces cellules. Une analyse aussi exhaustive que possible a ete menee afin d…

Cardiolipin content controls mitochondrial coupling and energetic efficiency in muscle

Decreasing mitochondrial energy-production efficiency in skeletal muscle can confer protection against diet-induced obesity.

Characteristics of l-carnitine import into heart cells

Abstract l -carnitine is an essential cofactor for the transport of fatty acids across the mitochondrial membranes. l -carnitine can be provided by food products or biosynthesized in the liver. After intestinal absorption or hepatic biosynthesis, l -carnitine is transferred to organs whose metabolism is dependent upon fatty acid oxidation, such as the skeletal muscle and the heart. The intracellular transport of l -carnitine into the cell requires specific transporters and today, several of these have been characterized. Most of them belong to the solute carrier family. Heart is one of the major target for carnitine transport and use, however basic properties of carnitine uptake by heart ce…

Effets sanitaires liés aux rayonnements électromagnétiques basses fréquences en milieu de travail

Introduction L’Anses presente un etat des connaissances sur les dangers lies aux champs electromagnetiques basses frequences (CEM-BF) et les resultats de son expertise collective concernant les risques pour la sante lies aux expositions en milieu professionnel. Materiel et methodes Ce travail est fonde sur l’analyse des donnees de la litterature scientifique. Pour chaque effet sanitaire etudie, le niveau de preuve apporte par les donnees scientifiques a ete evalue en s’appuyant sur une methode adaptee au contexte des champs electromagnetiques. Resultats Toutes les professions peuvent etre exposees a des CEM-BF, mais a des intensites tres diverses. Ainsi, un photocopieur genere un champ magn…

Hormonal and nutritional control of L‐carnitine uptake in myoblastic C2C12 cells

L-Carnitine plays an important role in skeletal muscle bioenergetics, and its bioavailability and thus its import may be crucial for muscle function. We studied the effect of thyroid hormone, insulin, and iron overload, hormones and nutrients known to alter muscle metabolism, on L-carnitine import into C2C12 cells. We report here L-carnitine uptake is increased by thyroid hormones and decreased by iron. Insulin was found to be ineffective in altering the L-carnitine uptake.

Molecular cloning and characterization of the cDNA encoding the rat liver gamma-butyrobetaine hydroxylase

Carnitine biosynthesis from lysine and methionine involves five enzymatic reactions. gamma-butyrobetaine hydroxylase (BBH; EC 1.14. 11.1) is the last enzyme of this pathway. It catalyzes the reaction of hydroxylation of gamma-butyrobetaine to carnitine. The cDNA encoding this enzyme has been isolated and characterized. The cDNA contained an open reading frame of 1161 bp encoding a protein of 387 amino acids with a deduced molecular weight of 44.5 kDa. The sequence of the cDNA showed an important homology with the human cDNA recently isolated. Northern analysis showed gamma-butyrobetaine hydroxylase expression in the liver and in some extend in the testis and the epididymis. During this stud…

Changes in carnitine octanoyltransferase activity induce alteration in fatty acid metabolism

The peroxisomal beta oxidation of very long chain fatty acids (VLCFA) leads to the formation of medium chain acyl-CoAs such as octanoyl-CoA. Today, it seems clear that the exit of shortened fatty acids produced by the peroxisomal beta oxidation requires their conversion into acyl-carnitine and the presence of the carnitine octanoyltransferase (CROT). Here, we describe the consequences of an overexpression and a knock down of the CROT gene in terms of mitochondrial and peroxisomal fatty acids metabolism in a model of hepatic cells. Our experiments showed that an increase in CROT activity induced a decrease in MCFA and VLCFA levels in the cell. These changes are accompanied by an increase in …

Extracellular ATP Increases <i>L</i>-Carnitine Transport and Content in C2C12 Cells

Extracellular ATP regulates cell proliferation, muscle contraction and myoblast differentiation. ATP present in the muscle interstitium can be released from contracting skeletal muscle cells. <i>L</i>-Carnitine is a key element in muscle cell metabolism, as it serves as a carrier for fatty acid through mitochondrial membranes, controlling oxidation and energy production. Treatment of C2C12 cells with 1 mmol/l of ATP induced a marked increase in <i>L</i>-carnitine uptake that was associated with an increase in <i>L</i>-carnitine content in these cells. These effects were found to be dependent on the density of the cultured cells and on the dose of ATP. The…

Of dogs, mice and cells: role of HACD1 in muscle development and physiology

Potential Roles of Peroxisomes in Alzheimer's Disease and in Dementia of the Alzheimer's Type

In Alzheimer's disease (AD) and dementia of the Alzheimer's type (DAT), the role played by peroxisomes is not well known. Peroxisomes are present in all eukaryotic cells, with the exception of erythrocytes. They are involved in the β-oxidation process of long-chain fatty acids, very-long-chain fatty acids, and branched-chain fatty acids. They participate in the α-oxidation of phytanic acid, the biosynthesis of bile acids, and the breakdown of eicosanoids. Peroxisomes are also involved in the synthesis of specific fatty acids such as docosahexaenoic acid (DHA), which is essential for the brain and retina, and plasmalogens (PLGN), which play crucial roles in neural cells and are essential com…

Meat adulteration: The use of PCR

Crosstalk between mitochondria and peroxisomes

Mitochondria and peroxisomes are small ubiquitous organelles. They both play major roles in cell metabolism, especially in terms of fatty acid metabolism, reactive oxygen species (ROS) production, and ROS scavenging, and it is now clear that they metabolically interact with each other. These two organelles share some properties, such as great plasticity and high potency to adapt their form and number according to cell requirements. Their functions are connected, and any alteration in the function of mitochondria may induce changes in peroxisomal physiology. The objective of this paper was to highlight the interconnection and the crosstalk existing between mitochondria and peroxisomes. Speci…

l ‐carnitine: Structure and Function

l-carnitine is found in nearly all living cells. l-carnitine present in human body can be either provided by a biosynthetic pathway or by food. Carnitine plays a major role in lipid and energy metabolism. In the human body, the primary role of l-carnitine is to shuttle long-chain fatty acids into the mitochondria where they are used to produce energy. l-carnitine is also involved in the peroxisomal oxidative metabolism and serves as a cofactor for various enzymatic reactions. Several reports suggest that l-carnitine may act as an anti-oxidant agent and limit the deleterious effects of free radicals. Many studies have estimated the role and the potential effectiveness of l-carnitine in vario…

Hypolipidaemic effects of fenofibrate are not altered by mildronate-mediated normalization of carnitine concentration in rat liver.

The five-fold higher carnitine content in the liver of fenofibrate-treated rats addresses the question about the possible role of this enhancement in the hypolipidaemic effect of the drug and the underlying mechanisms. When fenofibrate was administered with mildronate (a gamma-butyrobetaine hydroxylase inhibitor) in suitable amount, the content in carnitine was found to be normalized in liver. However, triglyceride contents of liver and serum were then at least as low as in rats treated by fenofibrate only. When carnitine concentration was lowered by mildronate to the third of the normal value, a marked increase in triglycerides occurred both in liver and serum, while the five-fold increase…

Exploration of lipid metabolism in relation with plasma membrane properties of Duchenne muscular dystrophy cells: influence of L-carnitine.

Duchenne muscular dystrophy (DMD) arises as a consequence of mutations in the dystrophin gene. Dystrophin is a membrane-spanning protein that connects the cytoskeleton and the basal lamina. The most distinctive features of DMD are a progressive muscular dystrophy, a myofiber degeneration with fibrosis and metabolic alterations such as fatty infiltration, however, little is known on lipid metabolism changes arising in Duchenne patient cells. Our goal was to identify metabolic changes occurring in Duchenne patient cells especially in terms of L-carnitine homeostasis, fatty acid metabolism both at the mitochondrial and peroxisomal level and the consequences on the membrane structure and functi…

HACD1, a regulator of membrane composition and fluidity, promotes myoblast fusion and skeletal muscle growth

International audience; The reduced diameter of skeletal myofibres is a hallmark of several congenital myopathies, yet the underlying cellular and molecular mechanisms remain elusive. In this study, we investigate the role of HACD1/PTPLA, which is involved in the elongation of the very long chain fatty acids, in muscle fibre formation. In humans and dogs, HACD1 deficiency leads to a congenital myopathy with fibre size disproportion associated with a generalized muscle weakness. Through analysis of HACD1-deficient Labradors, Hacd1-knockout mice, and Hacd1-deficient myoblasts, we provide evidence that HACD1 promotes myoblast fusion during muscle development and regeneration. We further demons…

A high-fat diet increases l-carnitine synthesis through a differential maturation of the Bbox1 mRNAs.

International audience; l-carnitine is a key molecule in both mitochondrial and peroxisomal lipid metabolisms. l-carnitine is biosynthesized from gamma-butyrobetaine by a reaction catalyzed by the gamma-butyrobetaine hydroxylase (Bbox1). The aim of this work was to identify molecular mechanisms involved in the regulation of l-carnitine biosynthesis and availability. Using 3' RACE, we identified four alternatively polyadenylated Bbox1 mRNAs in rat liver. We utilized a combination of in vitro experiments using hybrid constructs containing the Bbox1 3' UTR and in vivo experiments on rat liver mRNAs to reveal specificities in the different Bbox1 mRNA isoforms, especially in terms of polyadenyla…

Carnitine transport into muscular cells. inhibition of transport and cell growth by mildronate

Carnitine is involved in the transfer of fatty acids across mitochondrial membranes. Carnitine is found in dairy and meat products, but is also biosynthesized from lysine and methionine via a process that, in rat, takes place essentially in the liver. After intestinal absorption or hepatic biosynthesis, carnitine is transferred to organs whose metabolism is dependent on fatty acid oxidation, such as heart and skeletal muscle. In skeletal muscle, carnitine concentration was found to be 50 times higher than in the plasma, implicating an active transport system for carnitine. In this study, we characterized this transport in isolated rat myotubes, established mouse C2C12 myoblastic cells, and …

Regulation of argininosuccinate synthetase level by corticosteroid and pancreatic hormones during perinatal period.

The urea cycle takes place in the hepatocyte of ureothelic animals. The conversion of ammonia into urea involves five reactions. The first 2 take place in the matrix of the mitochondria, the last 2 occur in the cytosol. Argininosuccinate synthetase (AS) is the third reaction of the urea cycle. It catalyses the condensation of citrulline and aspartate into arginonosuccinate. We have previously reported that rat AS activity was present in the cytosol and the outer membrane of the mitochondria. We have shown that, at the activity level, the colocation of AS was changing during fetal and neonatal development and was under the control of corticosteroid and pancreatic hormones. However, an unreso…

L-carnitine protects C2C12 cells against mitochondrial superoxide overproduction and cell death.

International audience; AIMTo identify and characterize the protective effect that L-carnitine exerted against an oxidative stress in C2C12 cells.METHODSMyoblastic C2C12 cells were treated with menadione, a vitamin K analog that engenders oxidative stress, and the protective effect of L-carnitine (a nutrient involved in fatty acid metabolism and the control of the oxidative process), was assessed by monitoring various parameters related to the oxidative stress, autophagy and cell death.RESULTSAssociated with its physiological function, a muscle cell metabolism is highly dependent on oxygen and may produce reactive oxygen species (ROS), especially under pathological conditions. High levels o…

Enhancement of activities relative to fatty acid oxidation in the liver of rats depleted of l-carnitine by d-carnitine and a γ-butyrobetaine hydroxylase inhibitor

Abstract This study was designed to examine whether the depletion of l -carnitine may induce compensatory mechanisms allowing higher fatty acid oxidative activities in liver, particularly with regard to mitochondrial carnitine palmitoyltransferase I activity and peroxisomal fatty acid oxidation. Wistar rats received d -carnitine for 2 days and 3-(2,2,2-trimethylhydrazinium)propionate (mildronate), a non-competitive inhibitor of γ-butyrobetaine hydroxylase, for 10 days. They were starved for 20 hr before being sacrificed. A dramatic reduction in carnitine concentration was observed in heart, skeletal muscles and kidneys, and to a lesser extent, in liver. Triacylglycerol content was found to …

Beneficial effects of l-carnitine in myoblastic C2C12 cells

L-Carnitine is a key molecule in the transfer of fatty acid across mitochondrial membranes. Bioavailable L-carnitine is either provided by an endogeneous biosynthesis or after intestinal absorption of dietary items containing L-carnitine. After intestinal absorption or hepatic biosynthesis, L-carnitine is transferred to organs whose metabolism is dependent upon fatty acid oxidation, such as skeletal muscle. To cross the muscle plasma membrane, there are several transporters involved. Among those transporters, OCTN2 is actually the only one to have been clearly characterized. Zidovudine is a commonly used inhibitor of human immunodeficiency virus (HIV) replication. Zidovudine has many side e…

Polyunsaturated n-3 and n-6 fatty acids at a low level in the diet alter mitochondrial outer membrane parameters in Wistar rat liver

Abstract This study was designed to examine whether n-3 and n-6 polyunsaturated fatty acids (PUFA) at a very low level in the diet (about 0.2%) may alter the fatty acid composition of mitochondrial outer membranes and the characteristics of carnitine palmitoyltransferase I (CPTI) activity in the liver of normal Wistar rats. The animals were fed diets containing different oil mixtures (5% wt/wt) with the same ratio of n-6 n-3 fatty acids supplied either as fish oil or arachidonic acid concentrate. The cholesterol content of the mitochondrial outer membranes from liver was similar for all diets, while the percentage of 22:6n-3 and 20:4n-6 in phospholipids was enhanced with the diets containin…

L-Carnitine Supplementation and Physical Exercise Restore Age-Associated Decline in Some Mitochondrial Functions in the Rat

In mammals, during the aging process, an atrophy of the muscle fibers, an increase in body fat mass, and a decrease in skeletal muscle oxidative capacities occur. Compounds and activities that interact with lipid oxidative metabolism may be useful in limiting damages that occur in aging muscle. In this study, we evaluated the effect of L-carnitine and physical exercise on several parameters related to muscle physiology. We described that supplementing old rats with L-carnitine at 30 mg/kg body weight for 12 weeks (a) allowed the restoration of L-carnitine level in muscle cells, (b) restored muscle oxidative activity in the soleus, and (c) induced positive changes in body composition: a decr…

Radioisotopic determination of l-carnitine content in foods commonly eaten in Western countries

Abstract l -Carnitine is a vitamin-like nutrient essential for energy production and lipid metabolism in many organs and tissues such as skeletal muscle and heart. Even if l -carnitine can be synthesized, most of the carnitine present in human body is provided by food. Until now, no large study has been conducted where the content in l -carnitine of various foods was analyzed. The objective of this study was to determine the level of free l -carnitine present in food commonly consumed in Western countries. A radioisotopic assay was used to estimate l -carnitine content in raw and processed foods. From this study, it clearly appeared that meat products were the best sources for l -carnitine.…

Thyroid hormone controls carnitine status through modifications of gamma-butyrobetaine hydroxylase activity and gene expression.

The carnitine system plays a key role in beta-oxidation of long-chain fatty acids by permitting their transport into the mitochondrial matrix. The effects of hypothyroidism and hyperthyroidism were studied on gamma-butyrobetaine hydroxylase (BBH), the enzyme responsible for carnitine biosynthesis in the rat. In rat liver, BBH activity was decreased in the hypothyroid state and increased in hyperthyroid animals. The modifications in BBH activity correlated with changes in the enzyme Vmax values. These changes were shown to be related to hepatic BBH mRNA abundance. Thyroid hormones are known to interact with lipid metabolism, in particular by increasing long-chain fatty acid oxidation through…

Interaction between peroxisomes and mitochondria in fatty acid metabolism

Peroxisomes and mitochondria are ubiquitously found organelles. They both are dynamic structures able to divide, to fuse and to undergo autophagic processes. Their activities are dependent on proteins that are, for most (mitochondria) or all (peroxisome) of them, synthesized in the cytosol from the nuclear genome. Nevertheless, the membrane structures and the DNA content differ between these two organelles. Mitochondria possess a small circular genome while peroxisomes don’t. The control of their dynamic is dependent on specific factors even if some of those are able to affect both. These two organelles are metabolically connected: they are both involved in lipid metabolism. They are both a…