Effects of palmitoyl CoA and palmitoyl carnitine on the membrane potential and Mg2+ content of rat heart mitochondria

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

Long-chain acylcarnitines determine ischaemia/reperfusion-induced damage in heart mitochondria

The accumulation of long-chain fatty acids (FAs) and their CoA and carnitine esters is observed in the ischaemic myocardium after acute ischaemia/reperfusion. The aim of the present study was to identify harmful FA intermediates and their detrimental mechanisms of action in mitochondria and the ischaemic myocardium. In the present study, we found that the long-chain acyl-CoA and acylcarnitine content is increased in mitochondria isolated from an ischaemic area of the myocardium. In analysing the FA derivative content, we discovered that long-chain acylcarnitines, but not acyl-CoAs, accumulate at concentrations that are harmful to mitochondria. Acylcarnitine accumulation in the mitochondrial intermembrane space is a result of increased carnitine palmitoyltransferase 1 (CPT1) and decreased carnitine palmitoyltransferase 2 (CPT2) activity in ischaemic myocardium and it leads to inhibition of oxidative phosphorylation, which in turn induces mitochondrial membrane hyperpolarization and stimulates the production of reactive oxygen species (ROS) in cardiac mitochondria. Thanks to protection mediated by acyl-CoA-binding protein (ACBP), the heart is much better guarded against the damaging effects of acyl-CoAs than against acylcarnitines. Supplementation of perfusion buffer with palmitoylcarnitine (PC) before occlusion resulted in a 2-fold increase in the acylcarnitine content of the heart and increased the infarct size (IS) by 33%. A pharmacologically induced decrease in the mitochondrial acylcarnitine content reduced the IS by 44%. Long-chain acylcarnitines are harmful FA intermediates, accumulating in ischaemic heart mitochondria and inducing inhibition of oxidative phosphorylation. Therefore, decreasing the acylcarnitine content via cardioprotective drugs may represent a novel treatment strategy.

Screening of medicinal and edible plants in Okinawa, Japan, for enhanced proliferative and collagen synthesis activities in NB1RGB human skin fibroblast cells

To identify plants with bioactive potential for skin care, methanol extracts of 56 plant parts from 47 medical and edible plants cultivated in Okinawa were tested for their proliferative effects on NB1RGB skin fibroblast cells. Extracts from six plants, Bischofia javanica, Colocasia esculenta, Melaleuca alternifolia, Piper angustifolia, Jasminum sambac, and Curcuma longa, showed higher NB1RGB cell proliferation activity (>10%) than the control, at various concentrations. Among the six extracts, only the C. longa extract caused an increase in collagen synthesis in NB1RGB cells, as compared to treatment with the positive control, ascorbic acid (AsA). Expression of the collagen synthesis marker, transforming growth factor-β1, was higher after treatment with the C. longa extract than with AsA.

Different effects of palmitoyl-L-carnitine and palmitoyl-CoA on mitochondrial function in rat ventricular myocytes

Although mitochondrial oxidative catabolism of fatty acid (FA) is a major energy source for the adult mammalian heart, cardiac lipotoxity resulting from elevated serum FA and enhanced FA use has been implicated in the pathogenesis of heart failure. To investigate the effects of intermediates of FA metabolism [palmitoyl-l-carnitine (Pal-car) and palmitoyl-CoA (Pal-CoA)] on mitochondrial function, we measured membrane potential (DeltaPsi(m)), opening of the mitochondrial permeability transition pore (mPTP), and the production of ROS in saponin-treated rat ventricular myocytes with a laser scanning confocal microscope. Our results revealed that 1) lower concentrations of Pal-car (1 and 5 muM) caused a slight hyperpolarization of DeltaPsi(m) [tetramethylrhodamine ethyl ester (TMRE) intensity increased to 115.5 +/- 5.4% and 110.7 +/- 1.6% of baseline, respectively, P < 0.05] but did not open the mPTP, 2) a higher concentration of Pal-car (10 microM) depolarized DeltaPsi(m) (TMRE intensity decreased to 61.9 +/- 12.2% of baseline, P < 0.01) and opened the mPTP (calcein intensity decreased to 70.7 +/- 2.8% of baseline, P < 0.01), 3) Pal-CoA depolarized DeltaPsi(m) without opening the mPTP, and 4) only the higher concentration of Pal-car (10 muM) increased ROS generation (2',7'-dichlorofluorescein diacetate intensity increased to 3.4 +/- 0.3-fold of baseline). We concluded that excessive exogenous intermediates of long-chain saturated FA may disturb mitochondrial function in different ways between Pal-car and Pal-CoA. The distinct mechanisms of the deteriorating effects of long-chain FA on mitochondrial function are important for our understanding of the development of cardiac diseases in systemic metabolic disorders.

Characterization and bioavailability of liposomes containing a ukon extract

In order to use liposomes as an efficient carrier of functional food materials, liposomes encapsulating a ukon extract (LUE) were prepared by the mechanochemical method under different conditions, and were physico-chemically and biochemically characterized. After a homogenization treatment, the size of LUE decreased with decreasing concentration of the extract from 10 to 2.5 wt %, but did not decrease below 570 nm. LUE were thus subjected to microfluidization. The LUE solutions obtained from less than 5 wt % of the extract remained well dispersed for at least 14 d, whereas those from 10 wt % showed phase separation. With 5 wt % of the extract, the size of LUE obtained at an inlet pressure of 100 MPa was smaller than that obtained at 20 MPa, and reached below 180 nm. Under optimal conditions, resulting LUE was confirmed to be small unilamellar vesicles (SUV) with a diameter of approximately 100 nm by freeze-fracture electron microscopy (FFEM). When used for treating simulated gastric and intestinal fluids, LUE obtained by microfluidization showed a 2-fold higher residual rate of curcumin than the uncapsuled extract itself. The bioactivity of LUE was further examined for its suppressive effect on carbon tetrachloride (CCl(4))-induced liver injury by using mice. Orally administrated LUE at a dose of 10 mg/kg as the extract had a much higher suppressive effect on the serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, compared to the uncapsuled extract at a dose of 33 mg/kg.

Eugenol [2-methoxy-4-(2-propenyl)phenol] prevents 6-hydroxydopamine-induced dopamine depression and lipid peroxidation inductivity in mouse striatum

As superoxide (.O2-) and hydroxyl radical (.OH) have been implicated in the pathogenesis of Parkinson disease, free radical scavenging and antioxidants have attracted attention as way to prevent progression of this disease. We examined the effects of eugenol, an essential oil extracted from cloves, on 6-hydroxydopamine (6-OHDA)-induced dopamine (DA) reduction in the mouse striatum. Eugenol administration 3 d before and 7 more days following one intracerebroventricular 6-OHDA injection prevented the reduction of striatal DA and its metabolites. Eugenol administration for 3 d reduced the increase of thiobarbituric acid-reactive substances (an indicator of lipid peroxidation) induced by ferric ion and increased glutathione (GSH) and L-ascorbate (Asc) in the striatum. Eugenol did not change the levels of catalase, glutathione peroxidase, or superoxide dismutase-like activities. Eugenol is known to have .O2- and .OH scavenging activities in vitro. These results suggest that eugenol prevents 6-OHDA-induced DA depression by preventing lipid peroxidation directly and indirectly (via stimulation of GSH and Asc generating systems). Furthermore, increased GSH may protect cell death by conjugating with p-quinone produced in 6-OHDA auto-oxidation. The effects of eugenol treatment in this model suggest its possible usefulness for the treatment of Parkinson disease.

Studies on the Critical Micellar Concentration and Phase Transitions of Stearoylcarnitine

The critical micellar concentration (CMC) of stearoylcarnitine was determined at different pH values at room temperature by fluorescence spectroscopy, monitoring the spectral changes of 8-anilinonaphthalene-1-sulfonate (ANS). The CMC was found to vary with pH, increasing from about 10 μM at pH 3.0 to ca. 25 μM at pH 7.0, but decreasing slightly with further increase in pH to approximately 19 μM at pH 10.0. Differential scanning calorimetry (DSC) shows that stearoylcarnitine dispersed in water at low concentration undergoes a broad thermotropic phase transition at 44.5°C, with a transition enthalpy of 15.0 kcal/mol. The transition temperature (Tt) shifts to ca. 50.5°C in the presence of 1 mM EDTA or when the concentration is increased significantly. The turbidity of aqueous dispersions of stearoylcarnitine was found to be considerably high at low temperatures, which decreases quite abruptly over a short temperature range, indicating that a transition occurs from a phase of large aggregates to one of much smaller aggregates, most likely micelles. The phase transition temperature was determined as 29.1°C at pH 3.0, which increased with increasing pH up to a value of 55.3°C at pH 8.6 and remains nearly constant thereafter up to pH 11.2. The pH dependence of CMC and Ttsuggest that the pKa of the carboxyl group of long chain acylcarnitines shifts to higher temperatures upon aggregation (micelles or bilayer membranes).

Mitochondrial energy dissipation by fatty acids. Mechanisms and implications for cell death

For most cell types, fatty acids are excellent respiratory substrates. After being transported across the outer and inner mitochondrial membranes they undergo beta-oxidation in the matrix and feed electrons into the mitochondrial energy-conserving respiratory chain. On the other hand, fatty acids also physically interact with mitochondrial membranes, and possess the potential to alter their permeability. This occurs according to two mechanisms: an increase in proton conductance of the inner mitochondrial membrane and the opening of the permeability transition pore, an inner membrane high-conductance channel that may be involved in the release of apoptogenic proteins into the cytosol. This article addresses in some detail the mechanisms through which fatty acids exert their protonophoric action and how they modulate the permeability transition pore and discusses the cellular effects of fatty acids, with specific emphasis on their role as potential mitochondrial mediators of apoptotic signaling.

Roles of long chain fatty acids and carnitine in mitochondrial membrane permeability transition

Palmitoyl-CoA (Pal-CoA) lowered the respiratory control ratio (RCR), and induced mitochondrial membrane permeability transition (MPT) and cytochrome c (Cyt. c) release from isolated rat liver mitochondria. L-Carnitine suppressed the Pal-CoA-induced dysfunction, MPT, and Cyt. c release of isolated mitochondria. This suppression was inhibited by cephaloridine, an inhibitor of carnitine uptake into mitochondria. Cyclosporin A (CsA), an inhibitor of MPT, and BSA also suppressed the Pal-CoA-induced MPT. In the presence of inorganic phosphate (P(i)), Ca2+-induced MPT was suppressed by BSA, L-carnitine, and chlorpromazine, an inhibitor of phospholipase A2. In the presence of a low concentration of Ca2+, 3,3',5-triiodothyronine, long chain fatty acids, salicylic acid, and diclofenac induced MPT by a mechanism that was suppressed by BSA, L-carnitine, or chlorpromazine. During the incubation of mitochondria on ice, their respiratory competence decreased; L-carnitine and BSA also prevented this decrease. Mitochondrial depolarization in pheochromocytoma PC12 cells was induced by either serum deprivation or arachidonic acid by a mechanism that was suppressed by acetyl-L-carnitine. These results indicate that some MPTs may be regulated by fatty acid metabolism and that the Pal-CoA-induced MPT plays an important role in the induction of apoptosis.

Role of acylCoA binding protein in acylCoA transport, metabolism and cell signaling

Long chain acylCoA esters (LCAs) act both as substrates and intermediates in intermediary metabolism and as regulators in various intracellular functions. AcylCoA binding protein (ACBP) binds LCAs with high affinity and is believed to play an important role in intracellular acylCoA transport and pool formation and therefore also for the function of LCAs as metabolites and regulators of cellular functions [1]. The major factors controlling the free concentration of cytosol long chain acylCoA ester (LCA) include ACBP [2], sterol carrier protein 2 (SCP2) [3] and fatty acid binding protein (FABP) [4]. Additional factors affecting the concentration of free LCA include feed back inhibition of the acylCoA synthetase [5], binding to acylCoA receptors (LCA-regulated molecules and enzymes), binding to membranes and the activity of acylCoA hydrolases [6].

Two mechanisms by which ATP depletion potentiates induction of the mitochondrial permeability transition

The present and a previous study [J. W. Snyder, J. G. Pastorino, A. M. Attie, and J. L. Farber, Am. J. Physiol. 264 (Cell Physiol. 33): C709-C714, 1993] define two mechanisms whereby ATP depletion promotes liver cell death. ATP depletion and cell death are linked by the mitochondrial permeability transition (MPT). Mitochondrial deenergization promotes the MPT, and ATP maintains a membrane potential by reversal of ATP synthase. With an increased influx of Ca2+ induced by the ionophore A-23187, oligomycin depleted the cells of ATP without loss of the mitochondrial membrane potential and further elevated the intracellular Ca2+ concentration. Cyclosporin A (CyA) prevented the accompanying cell killing. Fructose also preserved the viability of the cells. With the increased cytosolic Ca2+ imposed by A-23187, viability is maintained by ATP-dependent processes. Upon depletion of ATP, Ca2+ homeostasis cannot be maintained, and the MPT is induced. Rotenone also depleted the cells of ATP, and A-23187 accelerated the loss of the mitochondrial membrane potential occurring with rotenone alone. CyA and fructose prevented the cell killing with rotenone and A-23187. Oligomycin did not prevent this action of fructose. We conclude that ATP is needed to maintain Ca2+ homeostasis to prevent the MPT and the resultant liver cell death. ATP is also needed to maintain mitochondrial energization when electron transport is inhibited.

Palmitoylcarnitine, a surface-active metabolite

Palmitoylcarnitine is a well-known intermediate in mitochondrial fatty acid oxidation. Less known are its properties as a surfactant, with a capacity to solubilize biological membranes similar to that of many synthetic detergents used in the biochemical laboratory. Some of the physico-chemical properties of palmitoylcarnitine may help to explain the need for coenzyme A-carnitine-coenzyme A acyl exchange during mitochondrial fatty acid import. The amphiphilic character of palmitoylcarnitine may also explain its proposed involvement in the pathogenesis of myocardial ischemia.

The membrane-perturbing properties of palmitoyl-coenzyme A and palmitoylcarnitine. A comparative study

Fatty acyl-coenzyme A's are temporarily converted into fatty acylcarnitines while transferred across the inner mitochondrial membrane, in their catabolic pathway. In search of an explanation for the need of this coenzyme exchange, the present work describes comparatively the abilities of both kinds of fatty acyl derivatives (represented by palmitoyl-coenzyme A and palmitoylcarnitine) in binding to and perturbing the structure of phosphatidylcholine bilayers in the form of large unilamellar vesicles. Both palmitoyl-coenzyme A and palmitoylcarnitine partition preferentially into the bilayer lipids, so that their free concentration in water is in practice negligible. However, palmitoylcarnitine is able to disrupt the membrane barrier to solutes, leading to vesicle leakage, and, at higher concentrations, it produces complete membrane solubilization, while palmitoyl-coenzyme A produces neither leakage nor solubilization. Palmitoylcarnitine has the properties of many commonly used biochemical detergents. The different behavior of both fatty acyl derivatives helps to explain the need for the transitory coenzyme A/carnitine exchange, and provides a pathogenic mechanism for some genetic defects of mitochondrial fatty acid transport. Other pathophysiological processes in which palmitoylcarnitine has been putatively involved are examined in light of the above results.

Substrate competition in postischemic myocardium. Effect of substrate availability during reperfusion on metabolic and contractile recovery in isolated rat hearts

Normal myocardium can derive energy for contraction and relaxation from oxidative metabolism of a variety of substrates. This investigation examined the influence of substrate availability early during reperfusion on the substrate pattern of oxidative metabolism and recovery of contractile function. For this purpose, isovolumically beating isolated rat hearts, perfused retrogradely with erythrocyte-supplemented buffer containing 0.4 mmol/L palmitate and 11 mmol/L glucose, were subjected to 40 minutes of no-flow ischemia. Hearts were reperfused with medium containing selected concentrations of palmitate and glucose. The substrate pattern for oxidative metabolism was determined on the basis of myocardial release of 14CO2 after equilibration of the hearts during the initial 15 minutes of reperfusion with either [1-14C]palmitate or [U-14C]glucose. In continuously perfused control hearts, glucose oxidation was largely inhibited by palmitate. During postischemic reperfusion, oxidation of glucose was increased by 59% (P < .05) and 467% (P <.01) in hearts reperfused after the ischemic period with 11 mmol/L glucose plus 0.4 or 1.2 mmol/L palmitate, respectively. Oxidation of palmitate was concomitantly reduced during reperfusion at low (0.4 mmol/L) but not at high (1.2 mmol/L) palmitate concentration. Compared with hearts reperfused with medium containing 0.4 mmol/L palmitate as sole substrate, hearts reperfused with medium containing 11 mmol/L glucose with 0.4 mmol/L palmitate exhibited lower left ventricular diastolic pressure (69 +/- 5 versus 90 +/- 3 mm Hg [mean +/- SEM], P < .05), less release of creatine kinase (31 +/- 5 versus 59 +/- 7 U/g wet wt, P < .05), and better recovery of left ventricular pressure development (26 +/- 9 versus 6 +/- 4 mm Hg, P < .05). Omission of palmitate or increasing the palmitate concentration to 1.2 mmol/L did not significantly alter postischemic myocardial contracture and enzyme release. The findings support the view that glucose oxidation early during reperfusion may be crucial for functional recovery. The results further indicate that interaction of substrates of oxidative metabolism is altered in severely injured postischemic myocardium. Inhibition of glucose oxidation by fatty acids was partially reversed during reperfusion.