Down-regulation of acyl-CoA oxidase gene expression and increased NF-kappaB activity in etomoxir-induced cardiac hypertrophy

Etomoxir-carnitine, a novel pharmaco-metabolite of etomoxir, inhibits phospholipases A2 and mitochondrial respiration

Mitochondrial fatty acid oxidation serves as an essential process for cellular survival, differentiation, proliferation, and energy metabolism. Numerous studies have utilized etomoxir (ETO) for the irreversible inhibition of carnitine palmitoylcarnitine transferase 1 (CPT1), which catalyzes the rate-limiting step for mitochondrial long-chain fatty acid β-oxidation to examine the bioenergetic roles of mitochondrial fatty acid metabolism in many tissues in multiple diverse disease states. Herein, we demonstrate that intact mitochondria robustly metabolize ETO to etomoxir-carnitine (ETO-carnitine) prior to nearly complete ETO-mediated inhibition of CPT1. The novel pharmaco-metabolite, ETO-carnitine, was conclusively identified by accurate mass, fragmentation patterns, and isotopic fine structure. On the basis of these data, ETO-carnitine was successfully differentiated from isobaric structures (e.g., 3-hydroxy-C18:0 carnitine and 3-hydroxy-C18:1 carnitine). Mechanistically, generation of ETO-carnitine from mitochondria required exogenous Mg2+, ATP or ADP, CoASH, and L-carnitine, indicating that thioesterification by long-chain acyl-CoA synthetase to form ETO-CoA precedes its conversion to ETO-carnitine by CPT1. CPT1-dependent generation of ETO-carnitine was substantiated by an orthogonal approach using ST1326 (a CPT1 inhibitor), which effectively inhibits mitochondrial ETO-carnitine production. Surprisingly, purified ETO-carnitine potently inhibited calcium-independent PLA2γ and PLA2β as well as mitochondrial respiration independent of CPT1. Robust production and release of ETO-carnitine from HepG2 cells incubated in the presence of ETO was also demonstrated. Collectively, this study identifies the chemical mechanism for the biosynthesis of a novel pharmaco-metabolite of ETO, ETO-carnitine, that is generated by CPT1 in mitochondria and likely impacts multiple downstream (non-CPT1 related) enzymes and processes in multiple subcellular compartments.

Metabolic Approaches for the Treatment of Dilated Cardiomyopathy

In dilated cardiomyopathy (DCM), where the heart muscle becomes stretched and thin, heart failure (HF) occurs, and the cardiomyocytes suffer from an energetic inefficiency caused by an abnormal cardiac metabolism. Although underappreciated as a potential therapeutic target, the optimal metabolic milieu of a failing heart is still largely unknown and subject to debate. Because glucose naturally has a lower P/O ratio (the ATP yield per oxygen atom), the previous studies using this strategy to increase glucose oxidation have produced some intriguing findings. In reality, the vast majority of small-scale pilot trials using trimetazidine, ranolazine, perhexiline, and etomoxir have demonstrated enhanced left ventricular (LV) function and, in some circumstances, myocardial energetics in chronic ischemic and non-ischemic HF with a reduced ejection fraction (EF). However, for unidentified reasons, none of these drugs has ever been tested in a clinical trial of sufficient size. Other pilot studies came to the conclusion that because the heart in severe dilated cardiomyopathy appears to be metabolically flexible and not limited by oxygen, the current rationale for increasing glucose oxidation as a therapeutic target is contradicted and increasing fatty acid oxidation is supported. As a result, treating metabolic dysfunction in HF may benefit from raising ketone body levels. Interestingly, treatment with sodium-glucose cotransporter-2 inhibitors (SGLT2i) improves cardiac function and outcomes in HF patients with or without type 2 diabetes mellitus (T2DM) through a variety of pleiotropic effects, such as elevated ketone body levels. The improvement in overall cardiac function seen in patients receiving SGLT2i could be explained by this increase, which appears to be a reflection of an adaptive process that optimizes cardiac energy metabolism. This review aims to identify the best metabolic therapeutic approach for DCM patients, to examine the drugs that directly affect cardiac metabolism, and to outline all the potential ancillary metabolic effects of the guideline-directed medical therapy. In addition, a special focus is placed on SGLT2i, which were first studied and prescribed to diabetic patients before being successfully incorporated into the pharmacological arsenal for HF patients.

Embryonic exposure to acetyl-L-carnitine protects against valproic acid-induced cardiac malformation in zebrafish model

Worldwide, estimated counts of about 7.9 million children are born with serious birth defects. In addition to genetic factors, prenatal exposure to drugs and environmental toxicants represents a major contributing factor to congenital malformations. In earlier investigation, we explored cardiac malformation caused by valproic acid (VPA) during early developing stages of zebrafish. Since heart depends on mitochondrial fatty acid oxidative metabolism for energy demands in which carnitine shuttle has a major role, the present study aimed to investigate the effect of acetyl-L-carnitine (AC) against VPA-induced cardiac malformation in developing zebrafish. Initially, AC was subjected to toxicological evaluation, and two micromolar concentrations (25 µM and 50 µM) were selected for evaluation. A sub-lethal concentration of VPA (50 µM) was selected to induce cardiac malformation. The embryos were grouped and the drug exposures were made at 2.5 h post-fertilization (hpf). The cardiac development and functioning was monitored. A progressive decline in cardiac functioning was noted in group exposed to VPA 50 µM. At 96 hpf and 120 hpf, the morphology of heart was severely affected with the chambers which became elongated and string-like accompanied by histological changes. Acridine orange staining showed accumulation of apoptotic cells. Group exposed to VPA 50 µM with AC 50 µM showed a significant reduction in pericardial sac edema with morphological, functional and histological recovery in developing heart. Moreover, reduced number of apoptotic cells was noted. The improvement with AC might be due to restoration of carnitine homeostasis for cardiac energy metabolism in developing heart.

Medium-Chain Acyl-CoA Dehydrogenase Protects Mitochondria from Lipid Peroxidation in Glioblastoma

Glioblastoma (GBM) is highly resistant to chemotherapies, immune-based therapies, and targeted inhibitors. To identify novel drug targets, we screened orthotopically implanted, patient-derived glioblastoma sphere-forming cells using an RNAi library to probe essential tumor cell metabolic programs. This identified high dependence on mitochondrial fatty acid metabolism. We focused on medium-chain acyl-CoA dehydrogenase (MCAD), which oxidizes medium-chain fatty acids (MCFA), due to its consistently high score and high expression among models and upregulation in GBM compared with normal brain. Beyond the expected energetics impairment, MCAD depletion in primary GBM models induced an irreversible cascade of detrimental metabolic effects characterized by accumulation of unmetabolized MCFAs, which induced lipid peroxidation and oxidative stress, irreversible mitochondrial damage, and apoptosis. Our data uncover a novel protective role for MCAD to clear lipid molecules that may cause lethal cell damage, suggesting that therapeutic targeting of MCFA catabolism may exploit a key metabolic feature of GBM. SIGNIFICANCE: MCAD exerts a protective role to prevent accumulation of toxic metabolic by-products in glioma cells, actively catabolizing lipid species that would otherwise affect mitochondrial integrity and induce cell death. This work represents a first demonstration of a nonenergetic role for dependence on fatty acid metabolism in cancer.This article is highlighted in the In This Issue feature, p. 2659.

Hepatic synthesis of triacylglycerols containing medium-chain fatty acids is dominated by diacylglycerol acyltransferase 1 and efficiently inhibited by etomoxir

Objective

Medium-chain fatty acids (MCFAs) play an increasing role in human nutrition. In the liver, one fraction is used for synthesis of MCFA-containing triacylglycerol (MCFA-TG), and the rest is used for oxidative energy production or ketogenesis. We investigated which enzymes catalyse the synthesis of MCFA-TG and how inhibition of MCFA-TG synthesis or fatty acid (FA) oxidation influences the metabolic fate of the MCFAs.

Methods

FA metabolism was followed by time-resolved tracing of alkyne-labelled FAs in freshly isolated mouse hepatocytes. Quantitative data were obtained by mass spectrometry of several hundred labelled lipid species. Wild-type hepatocytes and cells from diacylglycerol acyltransferase (DGAT)1^−/− mice were treated with inhibitors against DGAT1, DGAT2, or FA β-oxidation.

Results

Inhibition or deletion of DGAT1 resulted in a reduction of MCFA-TG synthesis by 70%, while long-chain (LC)FA-TG synthesis was reduced by 20%. In contrast, DGAT2 inhibition increased MCFA-TG formation by 50%, while LCFA-TG synthesis was reduced by 5–25%. Inhibition of β-oxidation by the specific inhibitor teglicar strongly increased MCFA-TG synthesis. In contrast, the widely used β-oxidation inhibitor etomoxir blocked MCFA-TG synthesis, phenocopying DGAT1 inhibition.

Conclusions

DGAT1 is the major enzyme for hepatic MCFA-TG synthesis. Its loss can only partially be compensated by DGAT2. Specific inhibition of β-oxidation leads to a compensatory increase in MCFA-TG synthesis, whereas etomoxir blocks both β-oxidation and MCFA-TG synthesis, indicating a strong off-target effect on DGAT1.

Carnitine Supplementation Attenuates Sunitinib-Induced Inhibition of AMP-Activated Protein Kinase Downstream Signals in Cardiac Tissues

This study has been initiated to investigate whether sunitinib (SUN) alters the expression of key genes engaged in mitochondrial transport and oxidation of long chain fatty acids (LCFA), and if so, whether these alterations should be viewed as a mechanism of SUN-induced cardiotoxicity, and to explore the molecular mechanisms whereby carnitine supplementation could attenuate SUN-induced cardiotoxicity. Adult male Wister albino rats were assigned to one of the four treatment groups: Rats in group 1 received no treatment but free access to tap water for 28 days. Rats in group 2 received L-carnitine (200 mg/kg/day) in drinking water for 28 days. Rats in group 3 received SUN (25 mg/kg/day) in drinking water for 28 days. Rats in group 4 received the same doses of L-carnitine and SUN in drinking water for 28 days. Treatment with SUN significantly increased heart weight, cardiac index, and cardiotoxicity enzymatic indices, as well as severe histopathological changes. Moreover, SUN significantly decreased level of adenosine monophosphate-activated protein kinase (AMPKα2), total carnitine, adenosine triphosphate (ATP) and carnitine palmitoyltransferase I (CPT I) expression and significantly increased acetyl-CoA carboxylase-2 (ACC2) expression and malonyl-CoA level in cardiac tissues. Interestingly, carnitine supplementation resulted in a complete reversal of all the biochemical, gene expression and histopathological changes-induced by SUN to the control values. In conclusion, data from this study suggest that SUN inhibits AMPK downstream signaling with the consequent inhibition of mitochondrial transport of LCFA and energy production in cardiac tissues. Carnitine supplementation attenuates SUN-induced cardiotoxicity.

Re-balancing cellular energy substrate metabolism to mend the failing heart

Fatty acids and glucose are the main substrates for myocardial energy provision. Under physiologic conditions, there is a distinct and finely tuned balance between the utilization of these substrates. Using the non-ischemic heart as an example, we discuss that upon stress this substrate balance is upset resulting in an over-reliance on either fatty acids or glucose, and that chronic fuel shifts towards a single type of substrate appear to be linked with cardiac dysfunction. These observations suggest that interventions aimed at re-balancing a tilted substrate preference towards an appropriate mix of substrates may result in restoration of cardiac contractile performance. Examples of manipulating cellular substrate uptake as a means to re-balance fuel supply, being associated with mended cardiac function underscore this concept. We also address the molecular mechanisms underlying the apparent need for a fatty acid-glucose fuel balance. We propose that re-balancing cellular fuel supply, in particular with respect to fatty acids and glucose, may be an effective strategy to treat the failing heart.

Dronedarone-Induced Cardiac Mitochondrial Dysfunction and Its Mitigation by Epoxyeicosatrienoic Acids

Dronedarone and amiodarone are structurally similar antiarrhythmic drugs. Dronedarone worsens cardiac adverse effects with unknown causes while amiodarone has no cardiac adversity. Dronedarone induces preclinical mitochondrial toxicity in rat liver and exhibits clinical hepatotoxicity. Here, we further investigated the relative potential of the antiarrhythmic drugs in causing mitochondrial injury in cardiomyocytes. Differentiated rat H9c2 cardiomyocytes were treated with dronedarone, amiodarone, and their respective metabolites namely N-desbutyldronedarone (NDBD) and N-desethylamiodarone (NDEA). Intracellular ATP content, mitochondrial membrane potential (Δψm), and inhibition of carnitine palmitoyltransferase I (CPT1) activity and arachidonic acid (AA) metabolism were measured in H9c2 cells. Inhibition of electron transport chain (ETC) activities and uncoupling of ETC were further studied in isolated rat heart mitochondria. Dronedarone, amiodarone, NDBD and NDEA decreased intracellular ATP content significantly (IC50 = 0.49, 1.84, 1.07, and 0.63 µM, respectively) and dissipated Δψm potently (IC50 = 0.5, 2.94, 12.8, and 7.38 µM, respectively). Dronedarone, NDBD, and NDEA weakly inhibited CPT1 activity while amiodarone (IC50 > 100 µM) yielded negligible inhibition. Only dronedarone inhibited AA metabolism to its regioisomeric epoxyeicosatrienoic acids (EETs) consistently and potently. NADH-supplemented ETC activity was inhibited by dronedarone, amiodarone, NDBD and NDEA (IC50 = 3.07, 5.24, 11.94, and 16.16 µM, respectively). Cytotoxicity, ATP decrease and Δψm disruption were ameliorated via exogenous pre-treatment of H9c2 cells with 11, 12-EET and 14, 15-EET. Our study confirmed that dronedarone causes mitochondrial injury in cardiomyocytes by perturbing Δψm, inhibiting mitochondrial complex I, uncoupling ETC and dysregulating AA-EET metabolism. We postulate that cardiac mitochondrial injury is one potential contributing factor to dronedarone-induced cardiac failure exacerbation.

Pharmacologic activation of peroxisome proliferator-activating receptor-α accelerates hepatic fatty acid oxidation in neonatal pigs

Up-regulation of peroxisome proliferator-activating receptor-α (PPARα) and increasing fatty acid oxidation are important for reducing pre-weaning mortality of pigs. We examined the time-dependent regulatory effects of PPARα activation via oral postnatal clofibrate administration (75 mg/(kg-BW·d) for up to 7 days) on mitochondrial and peroxisomal fatty acid oxidation in pigs, a species with limited hepatic fatty acid oxidative capacity due to low ketogenesis. Hepatic oxidation was increased by 44-147% (depending on fatty acid chain-length) and was attained after only 4 days of clofibrate treatment. Acyl-CoA oxidase (ACO) and carnitine palmitoyltransferase I (CPTI) activities accelerated in parallel. The increase in CPTI activity was accompanied by a rapid reduction in the sensitivity of CPTI to malonyl-CoA inhibition. The mRNA abundance of CPTI and ACO, as well as peroxisomal keto-acyl-CoA thiolase (KetoACoA) and mitochondrial malonyl-CoA decarboxylase (MCD), also were augmented greatly. However, the increase in ACO activity and MCD expression were different from CPTI, and significant interactions were observed between postnatal age and clofibrate administration. Furthermore, the expression of acetyl-CoA carboxylase β (ACCβ) decreased with postnatal age and clofibrate had no effect on its expression. Collectively these results demonstrate that the expression of PPARα target genes and the increase in fatty acid oxidation induced by clofibrate are time- and age-dependent in the liver of neonatal pigs. Although the induction patterns of CPTI, MCD, ACO, KetoACoA, and ACCβ are different during the early postnatal period, 4 days of exposure to clofibrate were sufficient to robustly accelerate fatty acid oxidation.

Identification and Characterization of Key Charged Residues in the Cofilin Protein Involved in Azole Susceptibility, Apoptosis, and Virulence of Aspergillus fumigatus

Through some specific amino acid residues, cofilin, a ubiquitous actin depolymerization factor, can significantly affect mitochondrial function related to drug resistance and apoptosis in Saccharomyces cerevisiae; however, this modulation in a major fungal pathogen, Aspergillus fumigatus, was still unclear. Hereby, it was found, first, that mutations on several charged residues in cofilin to alanine, D19A-R21A, E48A, and K36A, increased the formation of reactive oxygen species and induced apoptosis along with typical hallmarks, including mitochondrial membrane potential depolarization, cytochrome c release, upregulation of metacaspases, and DNA cleavage, in A. fumigatus Two of these mutations (D19A-R21A and K36A) increased acetyl coenzyme A and ATP concentrations by triggering fatty acid β-oxidation. The upregulated acetyl coenzyme A affected the ergosterol biosynthetic pathway, leading to overexpression of cyp51A and -B, while excess ATP fueled ATP-binding cassette transporters. Besides, both of these mutations reduced the susceptibility of A. fumigatus to azole drugs and enhanced the virulence of A. fumigatus in a Galleria mellonella infection model. Taken together, novel and key charged residues in cofilin were identified to be essential modules regulating the mitochondrial function involved in azole susceptibility, apoptosis, and virulence of A. fumigatus.

Biguanides sensitize leukemia cells to ABT-737-induced apoptosis by inhibiting mitochondrial electron transport

Metformin displays antileukemic effects partly due to activation of AMPK and subsequent inhibition of mTOR signaling. Nevertheless, Metformin also inhibits mitochondrial electron transport at complex I in an AMPK-independent manner, Here we report that Metformin and rotenone inhibit mitochondrial electron transport and increase triglyceride levels in leukemia cell lines, suggesting impairment of fatty acid oxidation (FAO). We also report that, like other FAO inhibitors, both agents and the related biguanide, Phenformin, increase sensitivity to apoptosis induction by the bcl-2 inhibitor ABT-737 supporting the notion that electron transport antagonizes activation of the intrinsic apoptosis pathway in leukemia cells. Both biguanides and rotenone induce superoxide generation in leukemia cells, indicating that oxidative damage may sensitize toABT-737 induced apoptosis. In addition, we demonstrate that Metformin sensitizes leukemia cells to the oligomerization of Bak, suggesting that the observed synergy with ABT-737 is mediated, at least in part, by enhanced outer mitochondrial membrane permeabilization. Notably, Phenformin was at least 10-fold more potent than Metformin in abrogating electron transport and increasing sensitivity to ABT-737, suggesting that this agent may be better suited for targeting hematological malignancies. Taken together, our results suggest that inhibition of mitochondrial metabolism by Metformin or Phenformin is associated with increased leukemia cell susceptibility to induction of intrinsic apoptosis, and provide a rationale for clinical studies exploring the efficacy of combining biguanides with the orally bioavailable derivative of ABT-737, Venetoclax.

Targeting immuno-metabolism to improve anti-cancer therapies

The immunology community has made significant strides in recent years in using the immune system to target and eliminate cancer. Therapies such as hematopoietic stem cell transplantation (HSCT) are the standard of care treatment for several malignancies, while therapies incorporating chimeric antigen receptor (CAR) T cells or checkpoint molecule blockade have been revolutionary. However, these approaches are not optimal for all cancers and in some cases, have failed outright. The greatest obstacle to making these therapies more effective may be rooted in one of the most basic concepts of cell biology, metabolism. Research over the last decade has revealed that T cell proliferation and differentiation is intimately linked to robust changes in metabolic activity, delineation of which may provide ways to manipulate the immuno-oncologic responses to our advantage. Here, we provide a basic overview of T cell metabolism, discuss what is known about metabolic regulation of T cells during allogeneic HSCT, point to evidence on the importance of T cell metabolism during CAR T cell and solid tumor therapies, and speculate about the role for compounds that might have dual-action on both immune cells and tumor cells simultaneously.

Emerging drugs for the treatment of angina pectoris

INTRODUCTION

Angina pectoris, or symptomatic myocardial ischaemia, reflects an impairment of coronary blood flow, and usually a deficiency of available myocardial energetics. Treatment options vary with the precise cause, which may vary with regards to the roles of increased myocardial oxygen demand versus reduced supply. Traditionally, organic nitrates, β-adrenoceptor antagonists, and non-dihydropyridine calcium antagonists were the only commonly used prophylactic anti-anginal agents. However, many patients failed to respond adequately to such therapy, and/or were unsuitable for their use. Areas covered: A number of 'new' agents have been shown to represent ancillary forms of prophylactic anti-anginal therapy and are particularly useful in patients who are relatively unsuitable for either percutaneous or surgical revascularisation. These include modulators of myocardial metabolic efficiency, such as perhexiline, trimetazidine and ranolazine, as well as high dose allopurinol, nicorandil and ivabradine. The advantages and disadvantages of these various agents are summarized. Expert opinion: 'Optimal' medical treatment of angina pectoris now includes use of agents primarily intended to reduce risk of infarction (e.g. statins, aspirin, ACE inhibitors). In patients whose angina persists despite the use of 'standard' anti-anginal therapy, and who are not ideal for invasive revascularization options, a number of emerging drugs offer prospects of symptomatic relief.

Fatty acid oxidation and carnitine palmitoyltransferase I: emerging therapeutic targets in cancer

Tumor cells exhibit unique metabolic adaptations that are increasingly viewed as potential targets for novel and specific cancer therapies. Among these targets, the carnitine palmitoyltransferase system is responsible for delivering the long-chain fatty acid (FA) from cytoplasm into mitochondria for oxidation, where carnitine palmitoyltransferase I (CPTI) catalyzes the rate-limiting step of fatty acid oxidation (FAO). With increasing understanding of the crucial role had by fatty acid oxidation in cancer, CPTI has received renewed attention as a pivotal mediator in cancer metabolic mechanism. CPTI activates FAO and fuels cancer growth via ATP and NADPH production, constituting an essential part of cancer metabolism adaptation. Moreover, CPTI also functionally intertwines with other key pathways and factors to regulate gene expression and apoptosis of cancer cell. Here, we summarize recent findings and update the current understanding of FAO and CPTI in cancer and provide theoretical basis for this enzyme as an emerging potential molecular target in cancer therapeutic intervention.

Lipid metabolism and signaling in cardiac lipotoxicity

The heart balances uptake, metabolism and oxidation of fatty acids (FAs) to maintain ATP production, membrane biosynthesis and lipid signaling. Under conditions where FA uptake outpaces FA oxidation and FA sequestration as triacylglycerols in lipid droplets, toxic FA metabolites such as ceramides, diacylglycerols, long-chain acyl-CoAs, and acylcarnitines can accumulate in cardiomyocytes and cause cardiomyopathy. Moreover, studies using mutant mice have shown that dysregulation of enzymes involved in triacylglycerol, phospholipid, and sphingolipid metabolism in the heart can lead to the excess deposition of toxic lipid species that adversely affect cardiomyocyte function. This review summarizes our current understanding of lipid uptake, metabolism and signaling pathways that have been implicated in the development of lipotoxic cardiomyopathy under conditions including obesity, diabetes, aging, and myocardial ischemia-reperfusion. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Deranged Cardiac Metabolism and the Pathogenesis of Heart Failure

Activation of the neuro-hormonal system is a pathophysiological consequence of heart failure. Neuro-hormonal activation promotes metabolic changes, such as insulin resistance, and determines an increased use of non-carbohydrate substrates for energy production. Fasting blood ketone bodies as well as fat oxidation are increased in patients with heart failure, yielding a state of metabolic inefficiency. The net result is additional depletion of myocardial adenosine triphosphate, phosphocreatine and creatine kinase levels with further decreased efficiency of mechanical work. In this context, manipulation of cardiac energy metabolism by modification of substrate use by the failing heart has produced positive clinical results. The results of current research support the concept that shifting the energy substrate preference away from fatty acid metabolism and towards glucose metabolism could be an effective adjunctive treatment in patients with heart failure. The additional use of drugs able to partially inhibit fatty acids oxidation in patients with heart failure may therefore yield a significant protective effect for clinical symptoms and cardiac function improvement, and simultaneously ameliorate left ventricular remodelling. Certainly, to clarify the exact therapeutic role of metabolic therapy in heart failure, a large multicentre, randomised controlled trial should be performed.

Inhibition of gene expression of carnitine palmitoyltransferase I and heart fatty acid binding protein in cyclophosphamide and ifosfamide-induced acute cardiotoxic rat models

This study investigated whether cyclophosphamide (CP) and ifosfamide (IFO) therapy alters the expression of the key genes engaged in long-chain fatty acid (LCFA) oxidation outside rat heart mitochondria, and if so, whether these alterations should be viewed as a mechanism during CP- and IFO-induced cardiotoxicity. Adult male Wistar albino rats were assigned to one of the six treatment groups: Rats in group 1 (control) and group 2 (L-carnitine) were injected intraperitoneal (i.p.) with normal saline and L-carnitine (200 mg/kg/day), respectively, for 10 successive days. Animals in group 3 (CP group) were injected i.p. with normal saline for 5 days before and 5 days after a single dose of CP (200 mg/kg, i.p.). Rats in group 4 (IFO group) received normal saline for 5 successive days followed by IFO (50 mg/kg/day, i.p.) for 5 successive days. Rats in group 5 (CP-carnitine supplemented) were given the same doses of L-carnitine as group 2 for 5 days before and 5 days after a single dose of CP as group 3. Rats in group 6 (IFO-carnitine supplemented) were given the same doses of L-carnitine as group 2 for 5 days before and 5 days concomitant with IFO as group 4. Immediately, after the last dose of the treatment protocol, blood samples were withdrawn and animals were killed for biochemical, histopathological and gene expression studies. Treatment with CP and IFO significantly decreased expression of heart fatty acid binding protein (H-FABP) and carnitine palmitoyltransferase I (CPT I) genes in cardiac tissues. Moreover, CP but not IFO significantly increased acetyl-CoA carboxylase2 mRNA expression. Conversely, IFO but not CP significantly decreased mRNA expression of malonyl-CoA decarboxylase. Both CP and IFO significantly increased serum lactate dehydrogenase, creatine kinase isoenzyme MB and malonyl-CoA content and histopathological lesions in cardiac tissues. Interestingly, carnitine supplementation completely reversed all the biochemical, histopathological and gene expression changes induced by CP and IFO to the control values, except CPT I mRNA, and protein expression remained inhibited by IFO. Data from the current study suggest, for the first time, that (1) CP and IFO therapy is associated with the inhibition of the expression of H-FABP and CPT I genes in cardiac tissues with the consequent inhibition of mitochondrial transport and oxidation of LCFA. (2) The progressive increase in cardiotoxicity enzymatic indices and the decrease in H-FABP and CPT I expression may point to the possible contribution of these genes to CP- and IFO-induced cardiotoxicity.

Inhibition of carnitine palymitoyltransferase1b induces cardiac hypertrophy and mortality in mice

Recent reports suggest that short-term pharmacological carnitine palmitoyltransferase 1 (Cpt1) inhibition improves skeletal muscle glucose tolerance and insulin sensitivity. Although this appears promising for the treatment of diabetes, these Cpt1 inhibitors are not specific to skeletal muscle and target multiple Cpt1 isoforms. To assess the effects of inhibiting the Cpt1b isoform we generated mice with a heart- and skeletal muscle-specific deletion of the Cpt1b, Cpt1b(HM-/-). These mice seem to develop normally with similar bodyweights as control mice. However, premature mortality was observed by 15 weeks of age in the Cpt1b(HM-/-) mice. The hearts of Cpt1b(HM-/-) mice were four times the size of controls. Cpt1b(HM-/-) mice were also subject to stress-induced seizures that accompanied an increased risk for premature mortality. Our data suggests that prolonged Cpt1b inhibition poses severe cardiac risk and emphasizes that attempts to improve insulin sensitivity by targeting Cpt1 with current inhibitors is not viable.

Carnitine palmitoyltransferase-1b deficiency aggravates pressure overload-induced cardiac hypertrophy caused by lipotoxicity

BACKGROUND

Carnitine palmitoyltransferase-1 (CPT1) is a rate-limiting step of mitochondrial β-oxidation by controlling the mitochondrial uptake of long-chain acyl-CoAs. The muscle isoform, CPT1b, is the predominant isoform expressed in the heart. It has been suggested that inhibiting CPT1 activity by specific CPT1 inhibitors exerts protective effects against cardiac hypertrophy and heart failure. However, clinical and animal studies have shown mixed results, thereby creating concerns about the safety of this class of drugs. Preclinical studies using genetically modified animal models should provide a better understanding of targeting CPT1 to evaluate it as a safe and effective therapeutic approach.

METHODS AND RESULTS

Heterozygous CPT1b knockout (CPT1b(+/-)) mice were subjected to transverse aorta constriction-induced pressure overload. These mice showed overtly normal cardiac structure/function under the basal condition. Under a severe pressure-overload condition induced by 2 weeks of transverse aorta constriction, CPT1b(+/-) mice were susceptible to premature death with congestive heart failure. Under a milder pressure-overload condition, CPT1b(+/-) mice exhibited exacerbated cardiac hypertrophy and remodeling compared with wild-type littermates. There were more pronounced impairments of cardiac contraction with greater eccentric cardiac hypertrophy in CPT1b(+/-) mice than in control mice. Moreover, the CPT1b(+/-) heart exhibited exacerbated mitochondrial abnormalities and myocardial lipid accumulation with elevated triglycerides and ceramide content, leading to greater cardiomyocyte apoptosis.

CONCLUSIONS

CPT1b deficiency can cause lipotoxicity in the heart under pathological stress, leading to exacerbation of cardiac pathology. Therefore, caution should be exercised in the clinical use of CPT1 inhibitors.

Altered glutathione homeostasis in heart augments cardiac lipotoxicity associated with diet-induced obesity in mice

Obesity-related cardiac lipid accumulation is associated with increased myocardial oxidative stress. The role of the antioxidant glutathione in cardiac lipotoxicity is unclear. Cystathionine β-synthase (Cbs) catalyzes the first step in the trans-sulfuration of homocysteine to cysteine, which is estimated to provide ∼50% of cysteine for hepatic glutathione biosynthesis. As cardiac glutathione is a reflection of the liver glutathione pool, we hypothesize that mice heterozygous for targeted disruption of Cbs (Cbs(+/-)) are more susceptible to obesity-related cardiolipotoxicity because of impaired liver glutathione synthesis. Cbs(+/+) and Cbs(+/-) mice were fed a high fat diet (60% energy) from weaning for 13 weeks to induce obesity and had similar increases in body weight and body fat. This was accompanied by increased hepatic triglyceride but no differences in hepatic glutathione levels compared with mice fed chow. However, Cbs(+/-) mice with diet-induced obesity had greater glucose intolerance and lower total and reduced glutathione levels in the heart, accompanied by lower plasma cysteine levels compared with Cbs(+/+) mice. Higher triglyceride concentrations, increased oxidative stress, and increased markers of apoptosis were also observed in heart from Cbs(+/-) mice with diet-induced obesity compared with Cbs(+/+) mice. This study suggests a novel role for Cbs in maintaining the cardiac glutathione pool and protecting against cardiac lipid accumulation and oxidative stress during diet-induced obesity in mice.

Trimetazidine reduces endogenous free fatty acid oxidation and improves myocardial efficiency in obese humans

INTRODUCTION

The metabolic modulator trimetazidine (TMZ) has been suggested to induce a metabolic shift from myocardial fatty acid oxidation (FAO) to glucose utilization, but this mechanism remains unproven in humans. The oxidation of plasma derived FA is commonly measured in humans, whereas the contribution of FA from triglycerides stored in the myocardium has been poorly characterized.

AIMS

To verify the hypothesis that TMZ induces a metabolic shift, we combined positron emission tomography (PET) and magnetic resonance spectroscopy ((1)H-MRS) to measure myocardial FAO from plasma and intracellular lipids, and myocardial glucose metabolism. Nine obese subjects were studied before and after 1 month of TMZ treatment. Myocardial glucose and FA metabolism were assessed by PET with (18)F-fluorodeoxyglucose and (11)C-palmitate. (1)H-MRS was used to measure myocardial lipids, the latter being integrated into the PET data analysis to quantify myocardial triglyceride turnover.

RESULTS

Myocardial FAO derived from intracellular lipids was at least equal to that of plasma FAs (P = NS). BMI and cardiac work were positively associated with the oxidation of plasma derived FA (P ≤ 0.01). TMZ halved total and triglyceride-derived myocardial FAO (32.7 ± 8.0 to 19.6 ± 4.0 μmol/min and 23.7 ± 7.5 to 10.3 ± 2.7 μmol/min, respectively; P ≤ 0.05). These changes were accompanied by increased cardiac efficiency since unchanged LV work (1.6 ± 0.2 to 1.6 ± 0.1 Watt/g × 10(2), NS) was associated with decreased work energy from the intramyocardial triglyceride oxidation (1.6 ± 0.5 to 0.4 ± 0.1 Watt/g × 10(2), P = 0.036).

CONCLUSIONS

In obese subjects, we demonstrate that myocardial intracellular triglyceride oxidation significantly provides FA-derived energy for mechanical work. TMZ reduced the oxidation of triglyceride-derived myocardial FAs improving myocardial efficiency.

Etomoxir-induced partial carnitine palmitoyltransferase-I (CPT-I) inhibition in vivo does not alter cardiac long-chain fatty acid uptake and oxidation rates

Although CPT-I (carnitine palmitoyltransferase-I) is generally regarded to present a major rate-controlling site in mitochondrial β-oxidation, it is incompletely understood whether CPT-I is rate-limiting in the overall LCFA (long-chain fatty acid) flux in the heart. Another important site of regulation of the LCFA flux in the heart is trans-sarcolemmal LCFA transport facilitated by CD36 and FABPpm (plasma membrane fatty acid-binding protein). Therefore, we explored to what extent a chronic pharmacological blockade of the LCFA flux at the level of mitochondrial entry of LCFA-CoA would affect sarcolemmal LCFA uptake. Rats were injected daily with saline or etomoxir, a specific CPT-I inhibitor, for 8 days at 20 mg/kg of body mass. Etomoxir-treated rats displayed a 44% reduced cardiac CPT-I activity. Sarcolemmal contents of CD36 and FABPpm, as well as the LCFA transport capacity, were not altered in the hearts of etomoxir-treated versus control rats. Furthermore, rates of LCFA uptake and oxidation, and glucose uptake by cardiac myocytes from etomoxir-treated rats were not different from control rats, neither under basal nor under acutely induced maximal metabolic demands. Finally, hearts from etomoxir-treated rats did not display triacylglycerol accumulation. Therefore CPT-I appears not to present a major rate-controlling site in total cardiac LCFA flux. It is likely that sarcolemmal LCFA entry rather than mitochondrial LCFA-CoA entry is a promising target for normalizing LCFA flux in cardiac metabolic diseases.

Characterization of hepatic mitochondrial injury induced by fatty acid oxidation inhibitors

Impairment of liver mitochondrial beta-oxidation is an important mechanism of drug-induced liver injury. Four inhibitors of fatty acid oxidation were compared in short-term rat in vivo studies in which the rats were administered one or four doses. The hepatocellular vacuolation represented ultra-structural mitochondrial changes. Urine nuclear magnetic resonance (NMR) spectroscopy revealed that both FOX988 and SDZ51-641 induced a persistent dicarboxylic aciduria, suggesting an inhibition of mitochondrial beta-oxidation and incomplete fatty acid metabolism. Etomoxir caused minimal mitochondrial ultrastructural changes and induced only transient dicarboxylic aciduria. CPI975 served as a negative control, in that there were no significant perturbations to the mitochondrial ultrastructural morphology or in the urine NMR composition; however, compound exposure was confirmed by the up-regulation of liver gene expression compared to vehicle control. The liver gene expression changes that were altered by the compounds were indicative of mitochondria, general and oxidative stress, and peroxisomal enzymes involved in beta-oxidation, suggestive of a compensatory response to the inhibition in the mitochondria. In addition, both FOX988 and SDZ51-641 up-regulated ribosomal genes associated with apoptosis, as well as p53 pathways linked with apoptosis. In summary, metabonomics and liver gene expression provided mechanistic information on mitochondrial dysfunction and impaired fatty acid oxidation to further define the clinical pathology and histopathology findings of hepatotoxicity.

Modulation of peroxisome proliferator-activated receptor-alpha activity by N-acetyl cysteine attenuates inhibition of oligodendrocyte development in lipopolysaccharide stimulated mixed glial cultures

Glial cells secrete proinflammatory mediators in the brain in response to exogenous stimuli such as infection and injury. Previously, we documented that systemic maternal lipopolysaccharide (LPS)-exposure at embryonic gestation day 18 causes oligodendrocyte (OL)-injury/hypomyelination in the developing brain which can be attenuated by N-acetyl cysteine (NAC; precursor of glutathione). The present study delineates the underlying mechanism of NAC-mediated attenuation of inhibition of OL development in LPS-stimulated mixed glial cultures. Factors released by LPS-stimulated mixed glial cultures inhibited OL development as shown by decrease in both proliferation 3bromo-deoxyuridine+/chondroitin sulfate proteoglycan-NG2+, hereafter BrdU+/NG+ and differentiation (O4+ and myelin basic protein+) of OL-progenitors. Correspondingly, an impairment of peroxisomal proliferation was shown by a decrease in the level of peroxisomal proteins in the developing OLs following exposure to LPS-conditioned media (LCM). Both NAC and WY14643, a peroxisome proliferator-activated receptor (PPAR)-alpha agonist attenuated these LCM-induced effects in OL-progenitors. Similar to WY14643, NAC attenuated LCM-induced inhibition of PPAR-alpha activity in developing OLs. Studies conducted with cytokines and diamide (a thiol-depleting agent) confirmed that cytokines are active agents in LCM which may be responsible for inhibition of OL development via peroxisomal dysfunction and induction of oxidative stress. These findings were further corroborated by similar treatment of developing OLs generated from PPAR-alpha(-/-) and wild-type mice or B12 oligodendroglial cells co-transfected with PPAR-alpha small interfering RNAs/pTK-PPREx3-Luc plasmids. Collectively, these data provide evidence that the modulation of PPAR-alpha activity, thus peroxisomal function by NAC attenuates LPS-induced glial factors-mediated inhibition of OL development suggesting new therapeutic interventions to prevent the devastating effects of maternal infections.

Lipopolysaccharide-induced peroxisomal dysfunction exacerbates cerebral white matter injury: attenuation by N-acetyl cysteine

Cerebral white matter injury during prenatal maternal infection characterized as periventricular leukomalacia is the main substrate for cerebral palsy (CP) in premature infants. Previously, we reported that maternal LPS exposure causes oligodendrocyte (OL)-injury/hypomyelination in the developing brain which can be attenuated by an antioxidant agent, N-acetyl cysteine (NAC). Herein, we elucidated the role of peroxisomes in LPS-induced neuroinflammation and cerebral white matter injury. Peroxisomes are important for detoxification of reactive oxidative species (ROS) and metabolism of myelin-lipids in OLs. Maternal LPS exposure induced selective depletion of developing OLs in the fetal brain which was associated with ROS generation, glutathione depletion and peroxisomal dysfunction. Likewise, hypomyelination in the postnatal brain was associated with decrease in peroxisomes and OLs after maternal LPS exposure. Conversely, NAC abolished these LPS-induced effects in the developing brain. CP brains imitated these observed changes in peroxisomal/myelin proteins in the postnatal brain after maternal LPS exposure. In vitro studies revealed that pro-inflammatory cytokines cause OL-injury via peroxisomal dysfunction and ROS generation. NAC or WY14643 (peroxisome proliferators activated receptor (PPAR)-alpha agonist) reverses these effects of pro-inflammatory cytokines in the wild-type OLs, but not in PPAR-alpha(-/-) OLs. Similarly treated B12 oligodenroglial cells co-transfected with PPAR-alpha siRNAs/pTK-PPREx3-Luc, and LPS exposed PPAR-alpha(-/-) pregnant mice treated with NAC or WY14643 further suggested that PPAR-alpha activity mediates NAC-induced protective effects. Collectively, these data provide unprecedented evidence that LPS-induced peroxisomal dysfunction exacerbates cerebral white matter injury and its attenuation by NAC via a PPAR-alpha dependent mechanism expands therapeutic avenues for CP and related demyelinating diseases.

The PPARalpha activator fenofibrate slows down the progression of the left ventricular dysfunction in porcine tachycardia-induced cardiomyopathy

It has been reported that high intramyocardial peroxisome proliferator-activated receptor alpha (PPARalpha) stimulation or overexpression altered cardiac contractile function in mouse models of cardiac hypertrophy and heart failure. Nevertheless, it has never been demonstrated that clinically relevant doses of drugs stimulating PPARalpha activity such as fenofibrate increase the risk to develop heart failure in humans. To determine if fenofibrate accelerates the development of heart failure in large mammals, we have tested its effects on the progression of left ventricular dysfunction in pacing-induced heart failure in pigs. Fenofibrate treatment blunted reduction in left ventricular ejection fraction, reduced cardiac hypertrophy, and attenuated clinical signs of heart failure. Fenofibrate impeded the increase in atrial natriuretic peptide, brain natriuretic peptide, and endothelin-1 plasma levels. The expression of PPARalpha, fatty acyl-CoA-oxidase, and carnitine palmitoyltransferase-Ibeta was reduced at mRNA levels in the left ventricle from untreated heart failure pigs but maintained near normal values with fenofibrate. Fenofibrate prevented heart failure-induced overexpression of TNFalpha mRNA and enhanced catalase activity in left ventricle compared to placebo. These data suggest that a clinically relevant dose of fenofibrate does not accelerate but slows down heart failure development in the model of pacing-induced heart failure in large mammals.

Glucose kinetics and exercise tolerance in mice lacking the GLUT4 glucose transporter

The absence of GLUT4 severely impairs basal glucose uptake in vivo, but does not alter glucose homeostasis or circulating insulin. Glucose uptake in isolated contracting skeletal muscle (MGU) is also impaired by the absence of GLUT4, and onset of muscle fatigue is hastened. Whether the body can compensate and preserve glucose homeostasis during exercise, as it does in the basal state, is unknown. One aim was to test the effectiveness of glucoregulatory compensation for the absence of GLUT4 in vivo. The absence of GLUT4 was also used to further define the role of hexokinase (HK) II, which catalyses glucose phosphorylation after it is transported in the cell. HK II increases MGU during exercise, as well as exercise endurance. In the absence of GLUT4, HK II expression will not affect MGU. A second aim was to test whether, in the absence of GLUT4, HK II retains its ability to increase exercise endurance. Wild-type (WT), GLUT4 null (GLUT4(-/-)), and GLUT4 null overexpressing HK II (GLUT4(-/-)HK(Tg)) mice were studied using a catheterized mouse model that allows blood sampling and isotope infusions during treadmill exercise. The impaired capacity of working muscle to take up glucose in GLUT4(-/-) is partially offset by an exaggerated increase in the glucagon: insulin ratio, increased liver glucose production, hyperglycaemia, and a greater capillary density in order to increase the delivery of glucose to the exercising muscle of GLUT4(-/-). Hearts of GLUT4(-/-) also exhibited a compensatory increase in HK II expression and a paradoxical increase in glucose uptake. Exercise tolerance was reduced in GLUT4(-/-) compared to WT. As expected, MGU in GLUT4(-/-)HK(Tg) was the same as in GLUT4(-/-). However, HK II overexpression retained its ability to increase exercise endurance. In conclusion, unlike the basal state where glucose homeostasis is preserved, hyperglycaemia results during exercise in GLUT4(-/-) due to a robust stimulation of liver glucose release in the face of severe impairments in MGU. Finally, studies in GLUT4(-/-)HK(Tg) show that HK II improves exercise tolerance, independent of its effects on MGU.

Inhibition of free fatty acids metabolism as a therapeutic target in patients with heart failure

Recent studies have evidenced that alterations of cardiac metabolism can be present in several cardiac syndromes. In heart failure, wasting of subcutaneous fat and skeletal muscle is relatively common and suggests an increased utilisation of non-carbohydrate substrates for energy production. In fact, fasting blood ketone bodies as well as fat oxidation during exercise have been shown to be increased in patients with heart failure. This metabolic shift determines a reduction of myocardial oxygen consumption efficiency. A direct approach to manipulate cardiac energy metabolism consists in modifying substrate utilisation by the heart. To date, the most effective metabolic treatments include several pharmacological agents that directly inhibit fatty acid oxidation. Clinical studies have shown that these agents can substantially increase the ischaemic threshold in patients with effort angina. However, the results of current research is also supporting the concept that shifting the energy substrate preference away from fatty acid metabolism and towards glucose metabolism could be an effective adjunctive treatment in patients with heart failure, in terms of left ventricular function and glucose metabolism improvement. In fact, these agents have also been shown to improve overall glucose metabolism in diabetic patients with left ventricular dysfunction. In this paper, the recent literature on the beneficial therapeutic effects of modulation of cardiac metabolic substrates utilisation in patients with heart failure is reviewed and discussed.

Expression of PPARalpha modifies fatty acid effects on insulin secretion in uncoupling protein-2 knockout mice

Aims/hypothesis

In uncoupling protein-2 (UCP2) knockout (KO) mice, protection of beta cells from fatty acid exposure is dependent upon transcriptional events mediated by peroxisome proliferator-activated receptor-α (PPARα).

Methods

PPARα expression was reduced in isolated islets from UCP2KO and wild-type (WT) mice with siRNA for PPARα (siPPARα) overnight. Some islets were also cultured with oleic or palmitic acid, then glucose stimulated insulin secretion (GSIS) was measured. Expression of genes was examined by quantitative RT-PCR or immunoblotting. PPARα activation was assessed by oligonucleotide consensus sequence binding.

Results

siPPARα treatment reduced PPARα protein expression in KO and WT islets by >85%. In siPPARα-treated UCP2KO islets, PA but not OA treatment significantly decreased the insulin response to 16.5 mM glucose. In WT islets, siPPARα treatment did not modify GSIS in PA and OA exposed groups. In WT islets, PA treatment significantly increased UCP2 mRNA and protein expression. Both PA and OA treatment significantly increased PPARα expression in UCP2KO and WT islets but OA treatment augmented PPARα protein expression only in UCP2KO islets (p < 0.05). PA treatment induced carnitine palmitoyltransferase I, acyl CoA oxidase and malonyl CoA decarboxylase mRNA in UCP2KO islets.

Conclusion

These data show that the negative effect of saturated fatty acid on GSIS is mediated by PPARα/UCP2. Knockout of UCP2 protects beta-cells from PA exposure. However, in the absence of both UCP2 and PPARα even a short exposure (24 h) to PA significantly impairs GSIS.

Etomoxir, a fatty acid oxidation inhibitor, increases food intake and reduces hepatic energy status in rats

Etomoxir, an inhibitor of fatty acid oxidation, increases food intake and reported hunger in humans. Work with animal models suggests that other inhibitors of fatty acid oxidation stimulate feeding behavior by acting on the liver. In the following study, we assessed whether etomoxir would increase food intake in rats and to what degree the effects of etomoxir on feeding were associated with changes in hepatic energy status. The effects of etomoxir on hepatic energy status were assessed by measuring liver ATP, ADP, phosphorylation potential, and glycogen content. Blood glucose, free fatty acids, and ketone bodies were also measured to determine the availability of circulating fuels following etomoxir treatment. Etomoxir and methyl palmoxirate (MP; another inhibitor of fatty acid oxidation) increased food intake. Etomoxir, like MP, also reduced hepatic ATP/ADP ratio and phosphorylation potential. In combination with 2,5-anhydro-D-mannitol (an analogue of fructose that produces an increase in feeding by action on the liver), etomoxir synergistically increased food intake and reduced hepatic ATP/ADP ratio. In summary, etomoxir increased food intake and decreased hepatic energy status in the rat. This suggests that etomoxir stimulates feeding by action on the liver.