Palmitoyl-L-carnitine modifies the myocardial levels of high-energy phosphates and free fatty acids

Role of ranolazine in heart failure: From cellular to clinic perspective

Ranolazine was approved by the US Food and Drug Administration as an antianginal drug in 2006, and has been used since in certain groups of patients with stable angina. The therapeutic action of ranolazine was initially attributed to inhibitory effects on fatty acids metabolism. As investigations went on, however, it developed that the main beneficial effects of ranolazine arise from its action on the late sodium current in the heart. Since late sodium currents were discovered to be involved in various heart pathologies such as ischemia, arrhythmias, systolic and diastolic dysfunctions, and all these conditions are associated with heart failure, ranolazine has in some way been tested either directly or indirectly on heart failure in numerous experimental and clinical studies. As the heart continuously remodels following any sort of severe injury, the inhibition by ranolazine of the underlying mechanisms of cardiac remodeling including ion disturbances, oxidative stress, inflammation, apoptosis, fibrosis, metabolic dysregulation, and neurohormonal impairment are discussed, along with unresolved issues. A projection of pathologies targeted by ranolazine from cellular level to clinical is provided in this review.

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 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.

Acylcarnitines--old actors auditioning for new roles in metabolic physiology

Perturbations in metabolic pathways can cause substantial increases in plasma and tissue concentrations of long-chain acylcarnitines (LCACs). For example, the levels of LCACs and other acylcarnitines rise in the blood and muscle during exercise, as changes in tissue pools of acyl-coenzyme A reflect accelerated fuel flux that is incompletely coupled to mitochondrial energy demand and capacity of the tricarboxylic acid cycle. This natural ebb and flow of acylcarnitine generation and accumulation contrasts with that of inherited fatty acid oxidation disorders (FAODs), cardiac ischaemia or type 2 diabetes mellitus. These conditions are characterized by very high (FAODs, ischaemia) or modestly increased (type 2 diabetes mellitus) tissue and blood levels of LCACs. Although specific plasma concentrations of LCACs and chain-lengths are widely used as diagnostic markers of FAODs, research into the potential effects of excessive LCAC accumulation or the roles of acylcarnitines as physiological modulators of cell metabolism is lacking. Nevertheless, a growing body of evidence has highlighted possible effects of LCACs on disparate aspects of pathophysiology, such as cardiac ischaemia outcomes, insulin sensitivity and inflammation. This Review, therefore, aims to provide a theoretical framework for the potential consequences of tissue build-up of LCACs among individuals with metabolic disorders.

Heart metabolic disturbances in cardiovascular diseases

Myocardial function depends on adenosine triphosphate (ATP) supplied by oxidation of several substrates. In the adult heart, this energy is obtained primarily from fatty acid oxidation through oxidative phosphorylation. However, the energy source may change depending on several factors such as substrate availability, energy demands, oxygen supply, and metabolic condition of the individual. Surprisingly, the role of energy metabolism in development of cardiac diseases has not been extensively studied. For instance, alterations in glucose oxidation and transport developed in diabetic heart may compromise myocardial performance under conditions in which ATP provided by glycolysis is relevant, such as in ischemia and reperfusion. In some cardiac diseases such as ischemic cardiomyopathy, heart failure, hypertrophy, and dilated cardiomyopathy, ATP generation is diminished by derangement of fatty acid delivery to mitochondria and by alteration of certain key enzymes of energy metabolism. Shortage of some co-factors such as L-carnitine and creatine also leads to energy depletion. Creatine kinase system and other mitochondrial enzymes are also affected. Initial attempts to modulate cardiac energy metabolism by use of drugs or supplements as a therapeutic approach to heart disease are described.

Propionyl-L-carnitine prevents renal function deterioration due to ischemia/reperfusion

BACKGROUND

Ischemia-reperfusion injury after organ transplantation is a major cause of delayed graft function. Prevention of post-transplant ischemia acute renal failure is still elusive.

METHODS

The present study was designed to examine whether propionyl-l-carnitine, an acyl derivative of carnitine involved in fatty acid oxidation pathway and adenosine 5'-triphosphate (ATP) generation of mitochondria, prevented renal function deterioration and structural injury induced by ischemia-reperfusion in an ex vivo rat model of isolated perfused kidney (IPK) preparation and in vivo in a model of syngeneic kidney transplantation.

RESULTS

In the model of ischemia (20 or 40 min)/reperfusion (90 or 70 min) in IPK, untreated kidneys showed a marked reduction of glomerular filtration rate (GFR) and renal perfusate flow (RPF) as compared to baseline, when perfusion was established by restoring effective perfusion pressure to 100 mm Hg. Exposure of kidneys to propionyl-l-carnitine before establishing the ischemia insult to tissue, largely prevented renal function impairment. Pre-exposure of ischemic kidneys to propionyl-l-carnitine largely reduced the percent of lactate dehydrogenase (LDH), a cell injury marker, released into the perfusate after reperfusion as compared to untreated ischemic kidneys. Histologic findings showed very mild post-ischemic lesions in kidneys exposed to propionyl-l-carnitine as compared to untreated ischemic kidneys. Immunohistochemical detection of 4-hydroxynonenal protein adduct, a major product of lipid peroxidation, was very low in kidney infused with propionyl-l-carnitine and exposed to ischemia/reperfusion as compared to untreated ischemic kidneys. ATP levels were not affected by propionyl-l-carnitine treatment. Renal function of kidneys exposed for four hours to cold Belzer UW solution added with propionyl-l-carnitine and transplanted to binephrectomized recipients was largely preserved as compared to untreated ischemic grafts. Propionyl-l-carnitine almost completely prevented polymorphonuclear cell graft infiltration and reduced tubular injury at 16 hours post-transplant.

CONCLUSIONS

These data indicate that propionyl-l-carnitine is of value in preventing decline of renal function that occurs during ischemia-reperfusion. The beneficial effect of propionyl-l-carnitine possibly relates to lowering lipid peroxidation and free radical generation that eventually results in the preservation of tubular cell structure. The efficacy of propionyl-l-carnitine to modulate ischemia-reperfusion injury in these models opens new perspectives for preventing post-transplant delayed graft function.

Differences in protective profiles of diltiazem isomers in ischemic and reperfused guinea pig hearts

The effects of L-cis and D-cis diltiazem on the extracellular potassium concentration ([K(+)]e), pH and cardiac function were compared in ischemic guinea pig hearts. Before inducing ischemia, L-cis diltiazem (10 and 30 microM) reduced the left ventricular developed pressure (LVDP) with a marginal inhibition of heart rate (HR), whereas lower doses of the D-cis isomer decreased both LVDP and HR. L-cis Diltiazem only slightly inhibited the increase in [K(+)]e and the decrease in pH but significantly inhibited ischemic contractures in contrast to the marked inhibition of these parameters produced by even low doses of the D-cis isomer. Notably, at equipotent doses for the ischemic parameters, L-cis diltiazem restored the left ventricular end-diastolic pressure (LVEDP) and HR after reperfusion to a greater extent than the D-cis isomer. These results suggest that the L-cis isomer may specifically improve postischemic function, in addition to the modest action on [K(+)]e and pH, in guinea pig hearts.

Ranolazine attenuates palmitoyl-L-carnitine-induced mechanical and metabolic derangement in the isolated, perfused rat heart

The effect of ranolazine, a novel anti-ischaemic drug that stimulates the activity of pyruvate dehydrogenase, on palmitoyl-L-carnitine-induced mechanical dysfunction and metabolic derangement in isolated perfused rat hearts has been studied and compared with the effect of dichloroacetate, an activator of pyruvate dehydrogenase. Rat hearts paced electrically were perfused aerobically at constant flow by the Langendorff technique. Palmitoyl-L-carnitine (4 microM) increased left ventricular end-diastolic pressure and reduced left ventricular developed pressure (i.e. induced mechanical dysfunction); it also reduced tissue levels of adenosine triphosphate and increased tissue levels of adenosine monophosphate (i.e. induced metabolic derangement). These functional and metabolic alterations induced by palmitoyl-L-carnitine were attenuated by ranolazine (5, 10, and 20 microM) in a concentration-dependent manner. In contrast, dichloroacetate (1 and 10 mM) did not attenuate palmitoyl-L-carnitine-induced mechanical and metabolic derangement. In the normal (palmitoyl-L-carnitine-untreated) heart, however, ranolazine did not modify mechanical function and energy metabolism. These results suggest that ranolazine attenuates palmitoyl-L-carnitine-induced mechanical and metabolic derangement in the rat heart, and that the beneficial action of ranolazine is not because of the energy-sparing effect or activation of pyruvate dehydrogenase.

L-cis diltiazem attenuates intracellular Ca(2+) overload by metabolic inhibition in guinea pig myocytes

We have previously demonstrated that treatment with L-cis diltiazem reduced cardiac infarct size in vivo. To examine the effect of L-cis diltiazem on Ca(2+) overload induced by ischemia/reperfusion, we used a model for Ca(2+) overload produced by metabolic inhibition in isolated guinea pig myocytes. Intracellular Ca(2+) concentration ([Ca(2+)](i)) was quantified by fura-2 fluorescence microscopy and Ca(2+) overload was induced by inclusion of 1 microM of carbonyl cyanide m-chrolophenylhydrazone (CCCP) for 40 min treatment followed by washout for 30 min. This treatment caused a large [Ca(2+)](i) elevation as well as a sustained contracture of the cardiomyocytes. The increase was suppressed by 10 microM of 2-[2-[4-(4-nitrobenzyloxy) phenyl] ethyl] isothiourea methanesulphonate (KB-R7943), a specific inhibitor of the Na(+)/Ca(2+) exchanger, but not by nitrendipine (10 microM). L-cis Diltiazem (10 microM) attenuated the [Ca(2+)](i) increase, suggesting that L-cis diltiazem elicits a cardioprotective effect via attenuation of the [Ca(2+)](i) increase induced by metabolic inhibition and energy repletion.

Treatment with l-cis diltiazem before reperfusion reduces infarct size in the ischemic rabbit heart in vivo

l-cis Diltiazem, an optical isomer of diltiazem, protects against myocardial dysfunction in vitro, whereas its Ca2+ channel blocking activity is about 100 times less potent than that of diltiazem. However, there is no evidence that l-cis diltiazem actually protects against ischemia/reperfusion injury in vivo. To assess this, we employed an anesthetized rabbit model, where the left circumflex artery was occluded for 15 min and reperfused for 360 min. Treatment with diltiazem before and during ischemia (bolus 200 microg/kg and 15 microg/kg per minute for 25 min, i.v.; 575 microg/kg total) showed slightly depressed hemodynamic parameters, while l-cis diltiazem (1150 microg/kg) had no effect. Treatment with l-cis diltiazem produced a high recovery of the thickening fraction and limited the infarct size in a dose-dependent manner. Furthermore, the treatment with l-cis diltiazem (1150 microg/kg) or diltiazem (575 microg/kg) 5 min before reperfusion also limited the infarct size, but not after reperfusion. These results suggest that l-cis diltiazem affects some events in the onset of reperfusion, independently of Ca2+-channel-blocking action. Our observations are the first to show that l-cis diltiazem demonstrated its cardioprotective action in the ischemic rabbit heart in vivo.

Both D-cis- and L-cis-diltiazem attenuate hydrogen peroxide-induced derangements in rat hearts

The effects of D-cis- and L-cis-diltiazem on the hydrogen peroxide (H2O2)-induced derangements of mechanical function and energy metabolism, and accumulation of intracellular Na+ were studied in isolated rat hearts. The intracellular concentration of Na+ ([Na+]i) in the myocardium was measured using a nuclear magnetic resonance technique. H2O2 (600 microM) increased the left ventricular end-diastolic pressure, decreased the tissue level of ATP, and increased the release of lactate dehydrogenase from the myocardium. These alterations induced by H2O2 were significantly attenuated by D-cis-diltiazem (15 microM) or L-cis-diltiazem (15 microM). H2O2 (1 mM) produced a marked increase in the myocardial [Na+]i, which was effectively inhibited by tetrodotoxin (3 microM), D-cis-diltiazem (15 microM) or L-cis-diltiazem (15 microM). These results suggest that both D-cis- and L-cis-diltiazem protect the myocardium against the H2O2-induced derangements in the isolated, perfused rat heart. The protective action of D-cis- and L-cis-diltiazem may be due to their ability to inhibit the H2O2-induced increase in [Na+]i, at least in part.

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.