The effects of novel vasodilator long chain acyl carnitine esters in the isolated perfused heart of the rat

Long-chain acylcarnitine 18:1 acutely increases human atrial myocardial contractility and arrhythmia susceptibility

Long-chain acylcarnitines (LCACs) are known to directly alter cardiac contractility and electrophysiology. However, the acute effect of LCACs on human cardiac function is unknown. We aimed to determine the effect of LCAC 18:1, which has been associated with cardiovascular disease, on the contractility and arrhythmia susceptibility of human atrial myocardium. Additionally, we aimed to assess how LCAC 18:1 alters Ca²⁺ influx and spontaneous Ca²⁺ release in vitro. Human right atrial trabeculae (n = 32) stimulated at 1 Hz were treated with LCAC 18:1 at a range of concentrations (1-25 µM) for a 45-min period. Exposure to the LCAC induced a dose-dependent positive inotropic effect on myocardial contractility (maximal 1.5-fold increase vs. control). At the 25 µM dose (n = 8), this was paralleled by an enhanced propensity for spontaneous contractions (50% increase). Furthermore, all LCAC 18:1 effects on myocardial function were reversed following LCAC 18:1 washout. In fluo-4-AM-loaded HEK293 cells, LCAC 18:1 dose dependently increased cytosolic Ca²⁺ influx relative to vehicle controls and the short-chain acylcarnitine C3. In HEK293 cells expressing ryanodine receptor (RyR2), this increased Ca²⁺ influx was linked to an increased propensity for RyR2-mediated spontaneous Ca²⁺ release events. Our study is the first to show that LCAC 18:1 directly and acutely alters human myocardial function and in vitro Ca²⁺ handling. The metabolite promotes proarrhythmic muscle contractions and increases contractility. The exploratory findings in vitro suggest that LCAC 18:1 increases proarrhythmic RyR2-mediated spontaneous Ca²⁺ release propensity. The direct effects of metabolites on human myocardial function are essential to understand cardiometabolic dysfunction.NEW & NOTEWORTHY For the first time, the fatty acid metabolite, long-chain acylcarnitine 18:1, is shown to acutely increase the arrhythmia susceptibility and contractility of human atrial myocardium. In vitro, this was linked to an influx of Ca²⁺ and an enhanced propensity for spontaneous RyR2-mediated Ca²⁺ release.

Long-Chain Acylcarnitines and Monounsaturated Fatty Acids Discriminate Heart Failure Patients According to Pulmonary Hypertension Status

Defects in fatty acid (FA) utilization have been well described in group 1 pulmonary hypertension (PH) and in heart failure (HF), yet poorly studied in group 2 PH. This study was to assess whether the metabolomic profile of patients with pulmonary hypertension (PH) due HF, classified as group 2 PH, differs from those without PH. We conducted a proof-of-principle cross-sectional analysis of 60 patients with chronic HF with reduced ejection fraction and 72 healthy controls in which the circulating level of 71 energy-related metabolites was measured using various methods. Echocardiography was used to classify HF patients as noPH-HF (n = 27; mean pulmonary artery pressure [mPAP] 21 mmHg) and PH-HF (n = 33; mPAP 35 mmHg). The profile of circulating metabolites among groups was compared using principal component analysis (PCA), analysis of covariance (ANCOVA), and Pearson’s correlation tests. Patients with noPH-HF and PH-HF were aged 64 ± 11 and 68 ± 10 years, respectively, with baseline left ventricular ejection fractions of 27 ± 7% and 26 ± 7%. Principal component analysis segregated groups, more markedly for PH-HF, with long-chain acylcarnitines, acetylcarnitine, and monounsaturated FA carrying the highest loading scores. After adjustment for age, sex, kidney function, insulin resistance, and N-terminal pro-brain natriuretic peptide (NT-proBNP), 5/15 and 8/15 lipid-related metabolite levels were significantly different from controls in noPH-HF and PH-HF subjects, respectively. All metabolites for which circulating levels interacted between group and NT-proBNP significantly correlated with NT-proBNP in HF-PH, but none with HF-noPH. FA-related metabolites were differently affected in HF with or without PH, and may convey adverse outcomes given their distinct correlation with NT-proBNP in the setting of PH.

Long-Chain Acylcarnitines and Cardiac Excitation-Contraction Coupling: Links to Arrhythmias

A growing number of metabolomic studies have associated high circulating levels of the amphiphilic fatty acid metabolites, long-chain acylcarnitines (LCACs), with cardiovascular disease (CVD) risk. These studies show that plasma LCAC levels can be correlated with the stage and severity of CVD and with indices of cardiac hypertrophy and ventricular function. Complementing these recent clinical associations is an extensive body of basic research that stems mostly from the twentieth century. These works, performed in cardiomyocyte and multicellular preparations from animal and cell models, highlight stereotypical derangements in cardiac electrophysiology induced by exogenous LCAC treatment that promote arrhythmic muscle behavior. In many cases, this is coupled with acute inotropic modulation; however, whether LCACs increase or decrease contractility is inconclusive. Linked to the electromechanical alterations induced by LCAC exposure is an array of effects on cardiac excitation-contraction coupling mechanisms that overload the cardiomyocyte cytosol with Na⁺ and Ca²⁺ ions. The aim of this review is to revisit this age-old literature and collate it with recent findings to provide a pathophysiological context for the growing body of metabolomic association studies that link circulating LCACs with CVD.

Metabolic cardiomyopathies

The energy needed by cardiac muscle to maintain proper function is supplied by adenosine Ariphosphate primarily (ATP) production through breakdown of fatty acids. Metabolic cardiomyopathies can be caused by disturbances in metabolism, for example diabetes mellitus, hypertrophy and heart failure or alcoholic cardiomyopathy. Deficiency in enzymes of the mitochondrial beta-oxidation show a varying degree of cardiac manifestation. Aberrations of mitochondrial DNA lead to a wide variety of cardiac disorders, without any obvious correlation between genotype and phenotype. A completely different pathogenetic model comprises cardiac manifestation of systemic metabolic diseases caused by deficiencies of various enzymes in a variety of metabolic pathways. Examples of these disorders are glycogen storage diseases (e.g. glycogenosis type II and III), lysosomal storage diseases (e.g. Niemann-Pick disease, Gaucher disease, I-cell disease, various types of mucopolysaccharidoses, GM1 gangliosidosis, galactosialidosis, carbohydrate-deficient glycoprotein syndromes and Sandhoff's disease). There are some systemic diseases which can also affect the heart, for example triosephosphate isomerase deficiency, hereditary haemochromatosis, CD 36 defect or propionic acidaemia.

Effects of Palmitoyl Carnitine on Perfused Heart and Papillary Muscle

BACKGROUND: Palmitoyl carnitine accumulation during ischemia causes profound electrophysiological changes, resulting in arrhythmias. We studied the electrophysiological and contractile effects of palmitoyl carnitine. METHODS AND RESULTS: Extracellular recordings made by using the endocardial unipolar paced evoked response (PER) in isolated perfused rabbit hearts were compared with action potentials (AP) recorded from septal artery perfused rabbit papillary muscle. Left ventricular pressure was monitored in isolated hearts. In perfused hearts palmitoyl carnitine (30 µmol/L, 30 minutes) significantly (P <.001) increased the latency of activation (St-R interval) by 58% +/- 8% and reduced repolarization time (R-E interval) by 39% +/- 4%. PER duration (St-E interval), was reduced by 30% +/- 3%. Palmitoyl carnitine (30 µmol/L) significantly (P <.001) decreased resting membrane potential (19 +/- 2 mV) of AP, reduced peak amplitude (33.5 +/- 8 mV) and rate of rise of phase 0 (41 +/- 8 V/s). Significant reductions (P <.001) in the action potential duration 50% (129.4 +/- 28 ms) and 90% (139.8 +/- 32 ms) were also observed. An initial positive inotropic effect, which declined as irreversible contracture developed, was also observed. Verapamil (1 µmol/L), nifedipine (1 µmol/L), and caffeine (10 mmol/L) failed to abolish the positive inotropy. CONCLUSIONS: We suggest that palmitoyl carnitine disrupts intracellular calcium homeostasis leading to disturbances in electrical and contractile activity. Its accumulation during myocardial ischemia could contribute to calcium overloading and initiate lethal arrhythmias.

Fatal carnitine palmitoyltransferase II deficiency in a newborn: new phenotypic features

We describe the term male infant of asymptomatic, healthy nonconsanguineous parents presenting on the first day of life with nonketotic hypoglycemia, seizures, hepatomegaly, cardiomegaly with biventricular hypertrophy, and ventricular arrhythmias. Cranial ultrasound revealed cystic dysplasia with several foci of hyperechogenicity within the right basal ganglia. Free carnitine was markedly decreased in the urine and plasma with a pronounced elevation of plasma long-chain acylcarnitines. Fibroblast carnitine palmitoyltransferase II activity was reduced to 26% and 38% in the father and mother, respectively. The infant expired on day 5 of life from malignant ventricular tachy-arrhythmias. Diffuse lipid accumulation was evident at autopsy, including in the liver, heart, kidney, adrenal cortex, skeletal muscle, and lungs. This new case of infantile CPT-II deficiency illustrates the severity of the early onset form of CPT-II deficiency.

Structure-activity relationships of some novel coronary dilator derivatives of palmitoyl carnitine in the rat isolated heart

The structure-activity relationships of some novel coronary dilator derivatives of palmitoyl carnitine in the rat isolated perfused heart are described. It has been shown previously that esterification of palmitoyl carnitine changes the activity of the compound from a coronary constrictor to a coronary dilator. In this study, it was found that the ester group is not a necessary requirement for coronary dilator activity, but only the absence of the negatively charged carboxylic acid group of palmitoyl carnitine, as compounds containing an ethyl group in place of the ester group were also active coronary dilators. Furthermore, substituting the methyl groups attached to the nitrogen atom of the molecule profoundly altered coronary dilator activity. A quaternary ammonium group was a necessary requirement for potent coronary dilator activity.

Vasodilator action of the isopropyl ester of palmitoyl carnitine in the rat coronary circulation and mesenteric vascular bed

The vasodilator action of the isopropyl ester of palmitoyl carnitine (P1Pi) has been examined in perfused rat hearts and mesenteric vessels. The coronary vasodilator effect P1Pi was not significantly inhibited by flurbiprofen (10 microM), BW755C (10 microM), glibenclamide (10 microM) or the bradykinin B2 receptor antagonist D-Arg0[Hyp3,Thi5,8,D-Phe7]bradykinin (1 microM), indicating that the action of P1Pi is not mediated via arachidonic acid metabolites, ATP-dependent K+ channels or bradykinin B2 receptors. L-NG-Nitro arginine (100 microM) did not inhibit the vasodilator action of P1Pi whilst superoxide dismutase (20 and 50 U.ml-1) attenuated its vasodilator action. Methylene blue (10 microM) caused inhibition in three out of four hearts, while haemoglobin (1 microM) caused an irreversible inhibition of the action of P1Pi which was associated with a depression of myocardial contractility. In air-damaged mesenteric vascular beds the vasodilator action of P1Pi was not attenuated, whilst that of acetylcholine was abolished. In K(+)-depolarised mesenteric vascular beds the constrictor action of Ca2+ was attenuated by P1Pi. Therefore the vasodilator effect of P1Pi appears to be the result of a direct effect on smooth muscle.

Palmitoyl-DL-carnitine has calcium-dependent effects on cultured neurones from rat dorsal root ganglia

1. The effects of palmitoyl-DL-carnitine (0.01 to 1 mM) on whole cell voltage-activated calcium channel currents carried by calcium or barium and Ca(2+)-activated chloride currents were studied in cultured neurones from rat dorsal root ganglia. 2. Palmitoyl-DL-carnitine applied to the extracellular environment or intracellularly via the patch solution reduced Ca2+ currents activated over a wide voltage range from a holding potential of -90 mV. Inhibition of high voltage activated Ca2+ channel currents was dependent on intracellular Ca2+ buffering and was reduced by increasing the EGTA concentration from 2 to 10 mM in the patch solution. Barium currents were significantly less sensitive to palmitoyl-DL-carnitine than Ca2+ currents. 3. The amplitude of Ca(2+)-activated Cl- tail currents was reduced by palmitoyl-DL-carnitine. However, the duration of these Cl- currents was greatly prolonged by palmitoyl-DL-carnitine, suggesting slower removal of free Ca2+ from the cytoplasm following Ca2+ entry through voltage-activated channels. 4. Palmitoyl-DL-carnitine evoked Ca(2+)-dependent inward currents which could be promoted by activation of the residual voltage-activated Ca2+ currents and attenuated by intracellular application of EGTA. 5. We conclude that palmitoyl-DL-carnitine reduced the efficiency of intracellular Ca2+ handling in cultured dorsal root ganglion neurones and resulted in enhancement of Ca(2+)-dependent events including inactivation of voltage-activated Ca2+ currents. The activation of inward currents by palmitolyl-DL-carnitine may involve Ca(2+)-induced Ca2+ release from intracellular stores, or direct interaction of palmitoyl-DL-carnitine with Ca2+ stores.

The synthesis, and structure-activity relationships of some long chain acyl carnitine esters on the coronary circulation of the rat isolated heart

The synthesis of the isopropyl ester of carnitine and a series of fatty acid derivatives with fatty acid lengths C8-C30 is described. Bolus doses of these compounds (0.03-300 nmol) showed coronary vasodilator activity in the rat isolated heart. Increasing fatty acid chain length from C8 to C16 resulted in an increased vasodilator potency. Longer lasting vasodilation was observed with the C20 compound. Increasing fatty acid chain length to C30 was associated with a small dilator response preceded by vasoconstriction.