Raffay Khan

Ventricular Assist Device Implantation Corrects Myocardial Lipotoxicity, Reverses Insulin Resistance, and Normalizes Cardiac Metabolism in Patients With Advanced Heart Failure

Background— Heart failure is associated with impaired myocardial metabolism with a shift from fatty acids to glucose use for ATP generation. We hypothesized that cardiac accumulation of toxic lipid intermediates inhibits insulin signaling in advanced heart failure and that mechanical unloading of the failing myocardium corrects impaired cardiac metabolism. Methods and Results— We analyzed the myocardium and serum of 61 patients with heart failure (body mass index, 26.5±5.1 kg/m2; age, 51±12 years) obtained during left ventricular assist device implantation and at explantation (mean duration, 185±156 days) and from 9 control subjects. Systemic insulin resistance in heart failure was accompanied by decreased myocardial triglyceride and overall fatty acid content but increased toxic lipid intermediates, diacylglycerol, and ceramide. Increased membrane localization of protein kinase C isoforms, inhibitors of insulin signaling, and decreased activity of insulin signaling molecules Akt and Foxo were detectable in heart failure compared with control subjects. Left ventricular assist device implantation improved whole-body insulin resistance (homeostatic model of analysis–insulin resistance, 4.5±0.6–3.2±0.5; P<0.05) and decreased myocardial levels of diacylglycerol and ceramide, whereas triglyceride and fatty acid content remained unchanged. Improved activation of the insulin/phosphatidylinositol-3 kinase/Akt signaling cascade after left ventricular assist device implantation was confirmed by increased phosphorylation of Akt and Foxo, which was accompanied by decreased membrane localization of protein kinase C isoforms after left ventricular assist device implantation. Conclusions— Mechanical unloading after left ventricular assist device implantation corrects systemic and local metabolic derangements in advanced heart failure, leading to reduced myocardial levels of toxic lipid intermediates and improved cardiac insulin signaling.

Adipose Tissue Inflammation and Adiponectin Resistance in Patients with Advanced Heart Failure: Correction after Ventricular Assist Device Implantation

Background— Heart failure (HF) is characterized by inflammation, insulin resistance, and progressive catabolism. We hypothesized that patients with advanced HF also develop adipose tissue inflammation associated with impaired adipokine signaling and that hemodynamic correction through implantation of ventricular assist devices (VADs) would reverse adipocyte activation and correct adipokine signaling in advanced HF. Methods and Results— Circulating insulin, adiponectin, leptin, and resistin levels were measured in 36 patients with advanced HF before and after VAD implantation and 10 healthy control subjects. Serum adiponectin was higher in HF patients before VAD implantation compared with control subjects (13.3±4.9 versus 6.4±2.1 &mgr;g/mL, P=0.02). VAD implantation (mean, 129±99 days) reduced serum adiponectin (7.4±3.4 &mgr;g/mL, P<0.05) and improved insulin resistance (Homeostasis Assessment Model of insulin resistance: 6.3±5.8–3.6±2.9; P<0.05). Adiponectin expression in adipose tissue decreased after VAD implantation (−65%; P<0.03). Adiponectin receptor expression was suppressed in the failing myocardium compared with control subjects and increased after mechanical unloading. Histomorphometric analysis of adipose tissue specimens revealed reduced adipocyte size in patients with advanced HF compared with control subjects (1999±24 &mgr;m2 versus 5583±142 &mgr;m2 in control subjects; P<0.05), which increased after VAD placement. Of note, macrophage infiltration in adipose tissue was higher in advanced HF patients compared with control subjects (+25%; P<0.01), which normalized after VAD implantation. Conclusions— Adipose tissue inflammation and adiponectin resistance develop in advanced HF. Mechanical unloading of the failing myocardium reverses adipose tissue macrophage infiltration, inflammation, and adiponectin resistance in patients with advanced HF.

DGAT1 deficiency decreases PPAR expression and does not lead to lipotoxicity in cardiac and skeletal muscle

Diacylglycerol (DAG) acyl transferase 1 (Dgat1) knockout (−/−) mice are resistant to high-fat-induced obesity and insulin resistance, but the reasons are unclear. Dgat1−/− mice had reduced mRNA levels of all three Ppar genes and genes involved in fatty acid oxidation in the myocardium of Dgat1−/− mice. Although DGAT1 converts DAG to triglyceride (TG), tissue levels of DAG were not increased in Dgat1−/− mice. Hearts of chow-diet Dgat1−/− mice were larger than those of wild-type (WT) mice, but cardiac function was normal. Skeletal muscles from Dgat1−/− mice were also larger. Muscle hypertrophy factors phospho-AKT and phospho-mTOR were increased in Dgat1−/− cardiac and skeletal muscle. In contrast to muscle, liver from Dgat1−/− mice had no reduction in mRNA levels of genes mediating fatty acid oxidation. Glucose uptake was increased in cardiac and skeletal muscle in Dgat1−/− mice. Treatment with an inhibitor specific for DGAT1 led to similarly striking reductions in mRNA levels of genes mediating fatty acid oxidation in cardiac and skeletal muscle. These changes were reproduced in cultured myocytes with the DGAT1 inhibitor, which also blocked the increase in mRNA levels of Ppar genes and their targets induced by palmitic acid. Thus, loss of DGAT1 activity in muscles decreases mRNA levels of genes involved in lipid uptake and oxidation.

Cardiomyocyte lipids impair β-adrenergic receptor function via PKC activation.

Normal hearts have increased contractility in response to catecholamines. Because several lipids activate PKCs, we hypothesized that excess cellular lipids would inhibit cardiomyocyte responsiveness to adrenergic stimuli. Cardiomyocytes treated with saturated free fatty acids, ceramide, and diacylglycerol had reduced cellular cAMP response to isoproterenol. This was associated with increased PKC activation and reduction of β-adrenergic receptor (β-AR) density. Pharmacological and genetic PKC inhibition prevented both palmitate-induced β-AR insensitivity and the accompanying reduction in cell surface β-ARs. Mice with excess lipid uptake due to either cardiac-specific overexpression of anchored lipoprotein lipase, PPARγ, or acyl-CoA synthetase-1 or high-fat diet showed reduced inotropic responsiveness to dobutamine. This was associated with activation of protein kinase C (PKC)α or PKCδ. Thus, several lipids that are increased in the setting of lipotoxicity can produce abnormalities in β-AR responsiveness. This can be attributed to PKC activation and reduced β-AR levels.

Cardiomyocyte Specific Deficiency of Serine Palmitoyltransferase Subunit 2 Reduces Ceramide but Leads to Cardiac Dysfunction

Background: The importance of de novo ceramide biosynthesis in maintaining cardiac function is unknown. Results: Deletion of serine palmitoyltransferase subunit Sptlc2 reduced cardiac ceramide and caused cardiac dysfunction associated with activation of ER stress. Conclusion: Reduced ceramide content by Sptlc2 deficiency does not protect against lipid toxicity associated with increased saturated acyl CoAs. Significance: Development of disease by lipotoxicity is caused by a number of changes in lipidome. The role of serine palmitoyltransferase (SPT) and de novo ceramide biosynthesis in cardiac ceramide and sphingomyelin metabolism is unclear. To determine whether the de novo synthetic pathways, rather than ceramide uptake from circulating lipoproteins, is important for heart ceramide levels, we created cardiomyocyte-specific deficiency of Sptlc2, a subunit of SPT. Heart-specific Sptlc2-deficient (hSptlc2 KO) mice had a >35% reduction in ceramide, which was limited to C18:0 and very long chain ceramides. Sphingomyelinase expression, and levels of sphingomyelin and diacylglycerol were unchanged. But surprisingly phospholipids and acyl CoAs contained increased saturated long chain fatty acids. hSptlc2 KO mice had decreased fractional shortening and thinning of the cardiac wall. While the genes regulating glucose and fatty acid metabolism were not changed, expression of cardiac failure markers and the genes involved in the formation of extracellular matrices were up-regulated in hSptlc2 KO hearts. In addition, ER-stress markers were up-regulated leading to increased apoptosis. These results suggest that Sptlc2-mediated de novo ceramide synthesis is an essential source of C18:0 and very long chain, but not of shorter chain, ceramides in the heart. Changes in heart lipids other than ceramide levels lead to cardiac toxicity.

Inhibition of c-Jun-N-terminal Kinase Increases Cardiac Peroxisome Proliferator-activated Receptor α Expression and Fatty Acid Oxidation and Prevents Lipopolysaccharide-induced Heart Dysfunction

Septic shock results from bacterial infection and is associated with multi-organ failure, high mortality, and cardiac dysfunction. Sepsis causes both myocardial inflammation and energy depletion. We hypothesized that reduced cardiac energy production is a primary cause of ventricular dysfunction in sepsis. The JNK pathway is activated in sepsis and has also been implicated in impaired fatty acid oxidation in several tissues. Therefore, we tested whether JNK activation inhibits cardiac fatty acid oxidation and whether blocking JNK would restore fatty acid oxidation during LPS treatment. LPS treatment of C57BL/6 mice and adenovirus-mediated activation of the JNK pathway in cardiomyocytes inhibited peroxisome proliferator-activated receptor α expression and fatty acid oxidation. Surprisingly, none of the adaptive responses that have been described in other types of heart failure, such as increased glucose utilization, reduced αMHC:βMHC ratio or induction of certain microRNAs, occurred in LPS-treated mice. Treatment of C57BL/6 mice with a general JNK inhibitor (SP600125) increased fatty acid oxidation in mice and a cardiomyocyte-derived cell line. JNK inhibition also prevented LPS-mediated reduction in fatty acid oxidation and cardiac dysfunction. Inflammation was not alleviated in LPS-treated mice that received the JNK inhibitor. We conclude that activation of JNK signaling reduces fatty acid oxidation and prevents the peroxisome proliferator-activated receptor α down-regulation that occurs with LPS.

Peroxisome Proliferator–Activated Receptor-γ Activation Prevents Sepsis-Related Cardiac Dysfunction and Mortality In Mice

Impaired cardiac contractility contributes to the hypotension and increased mortality that occur with sepsis1. A possible cause of sepsis-mediated cardiac dysfunction is reduced energy production due in part to compromised fatty acid oxidation (FAO)2-5 and glucose catabolism3, 6. Thus, it is likely that sepsis compromises cardiac energy production, which might be the major cause of cardiac dysfunction. Alternatively, sepsis induces the production of inflammatory cytokines, such as tumor necrosis factor (TNF) α, interleukin (IL)-1 and IL-6, and these might directly alter heart function7-9. Intraperitoneal (i.p.) injection of lipopolysaccharide (LPS) has been extensively used to model many of the clinical features of sepsis, including elevated inflammation and cardiac dysfunction10. LPS leads to production of inflammatory cytokines7-9, 11 and also reduces cardiac energy utilization2, 3, 12. Nuclear receptors, particularly peroxisomal proliferator-activated receptors (PPARs), regulate cardiac FAO. The PPAR family consists of three members, PPARα, PPARδ and PPARγ. PPARα increases FA storage in triglycerides13 and FAO in heart14 and induces expression of peroxisomal and mitochondrial enzymes. Besides PPARα, cardiac FAO can be increased by activation of PPARγ15 or PPARδ16. Cardiomyocyte-specific overexpression of PPARα14 or PPARγ17 leads to cardiac lipid accumulation, an indication that lipid uptake exceeds FAO. PPARγ-coactivator-1 (PGC-1) α and β18 enhance FAO and mitochondrial biogenesis19. Both PPARα and PGC-1 mRNA levels are markedly reduced in the heart by LPS administration2, 3, 12, 20, while PPARγ is not affected2. Our group showed that maintenance of normal cardiac FAO via c-Jun-N-terminal kinase (JNK) inhibitor-mediated prevention of PPARα downregulation rescued cardiac function in septic mice despite elevated expression of cardiac inflammatory markers. In a similar context constitutive cardiac expression of PGC-1β prevented cardiac dysfunction that was caused by LPS-mediated sepsis3, an observation that was proposed to be due to improvement in cardiac FAO and attenuation of reactive oxygen species production. In the current study we show that constitutive cardiomyocyte-specific expression of PPARγ or systemic administration of the PPARγ agonist, rosiglitazone, increased cardiac FAO and prevented cardiac dysfunction in mice with LPS-induced sepsis, despite increased expression of cardiac inflammatory markers. In addition, we show that rosiglitazone-mediated activation of PPARγ prevents the loss of cardiac mitochondria that occurs in sepsis. Moreover, we show that restoration of cardiac FAO by rosiglitazone not only prevents but also treats LPS-induced heart dysfunction and improves survival. Thus the use of rosiglitazone is proposed as a potential treatment for septic cardiac dysfunction.Background—Cardiac dysfunction with sepsis is associated with both inflammation and reduced fatty acid oxidation. We hypothesized that energy deprivation accounts for sepsis-related cardiac dysfunction. Methods and Results—Escherichia coli lipopolysaccharide (LPS) administered to C57BL/6 mice (wild type) induced cardiac dysfunction and reduced fatty acid oxidation and mRNA levels of peroxisome proliferator–activated receptor (PPAR)-&agr; and its downstream targets within 6–8 hours. Transgenic mice in which cardiomyocyte-specific expression of PPAR&ggr; is driven by the &agr;-myosin heavy chain promoter (&agr;MHC-PPAR&ggr;) were protected from LPS-induced cardiac dysfunction. Despite a reduction in PPAR&agr;, fatty acid oxidation and associated genes were not decreased in hearts of LPS-treated &agr;MHC-PPAR&ggr; mice. LPS treatment, however, continued to induce inflammation-related genes, such as interleukin-1&agr;, interleukin-1&bgr;, interleukin-6, and tumor necrosis factor-&agr; in hearts of &agr;MHC-PPAR&ggr; mice. Treatment of wild-type mice with LPS and the PPAR&ggr; agonist, rosiglitazone, but not the PPAR&agr; agonist (WY-14643), increased fatty acid oxidation, prevented LPS-mediated reduction of mitochondria, and treated cardiac dysfunction, as well as it improved survival, despite continued increases in the expression of cardiac inflammatory markers. Conclusions—Activation of PPAR&ggr; in LPS-treated mice prevented cardiac dysfunction and mortality, despite development of cardiac inflammation and PPAR&agr; downregulation.

Diacylglycerol acyl transferase 1 overexpression detoxifies cardiac lipids in PPARγ transgenic mice

Accumulation of excess lipids is associated with heart failure. The effects of transgenic expression of diacylglycerol acyl transferase 1 (DGAT1) in cardiomyocytes is controversial. We explored whether mice expressing DGAT1 via the myosin heavy chain (MHC) promoter develop heart dysfunction with aging or after crossing with mice over expressing peroxisome proliferator-activated receptor γ (PPARγ) in the heart. MHC-DGAT1 transgenic mice had increased heart triglyceride but no evidence of heart dysfunction, even up to age 12 months. The MHC-DGAT1 transgene improved heart dysfunction and survival of MHC-PPARγ-expressing transgenic mice. Both diacylglycerol and ceramide levels in the heart were reduced by this cross, as were the levels of several mRNAs of genes involved in lipid metabolism. There were fewer large lipid droplets in MHC-DGAT1×MHC-PPARγ mice compared with MHC-PPARγ, but total lipid content was not changed. Therefore, overexpression of DGAT1 is not toxic to the heart but reduces levels of toxic lipids and improves lipotoxic cardiomyopathy. Moreover, the beneficial effects of DGAT1 illustrate the interrelationship of several lipid metabolic pathways and the difficulty of assigning benefit to an isolated change in one potentially toxic lipid species.

Mice With Cardiac Overexpression of Peroxisome Proliferator–Activated Receptor γ Have Impaired Repolarization and Spontaneous Fatal Ventricular Arrhythmias

Background— Diabetes mellitus and obesity, which confer an increased risk of sudden cardiac death, are associated with cardiomyocyte lipid accumulation and altered cardiac electric properties, manifested by prolongation of the QRS duration and QT interval. It is difficult to distinguish the contribution of cardiomyocyte lipid accumulation from the contribution of global metabolic defects to the increased incidence of sudden death and electric abnormalities. Methods and Results— In order to study the effects of metabolic abnormalities on arrhythmias without the complex systemic effects of diabetes mellitus and obesity, we studied transgenic mice with cardiac-specific overexpression of peroxisome proliferator–activated receptor &ggr; 1 (PPAR&ggr;1) via the cardiac &agr;-myosin heavy-chain promoter. The PPAR&ggr; transgenic mice develop abnormal accumulation of intracellular lipids and die as young adults before any significant reduction in systolic function. Using implantable ECG telemeters, we found that these mice have prolongation of the QRS and QT intervals and spontaneous ventricular arrhythmias, including polymorphic ventricular tachycardia and ventricular fibrillation. Isolated cardiomyocytes demonstrated prolonged action potential duration caused by reduced expression and function of the potassium channels responsible for repolarization. Short-term exposure to pioglitazone, a PPAR&ggr; agonist, had no effect on mortality or rhythm in WT mice but further exacerbated the arrhythmic phenotype and increased the mortality in the PPAR&ggr; transgenic mice. Conclusions— Our findings support an important link between PPAR&ggr; activation, cardiomyocyte lipid accumulation, ion channel remodeling, and increased cardiac mortality.Background Diabetes and obesity, which confer an increased risk of sudden cardiac death, are associated with cardiomyocyte lipid accumulation and altered cardiac electrical properties, manifested by prolongation of the QRS duration and QT interval. It is difficult to distinguish the contribution of cardiomyocyte lipid accumulation versus the contribution of global metabolic defects to the increased incidence of sudden death and electrical abnormalities.

Creating and curing fatty hearts.

Purpose of reviewDiseases associated with ectopic disposition of lipids are becoming an increasingly important medical problem as the incidence of type 2 diabetes and obesity increases. One of the organs affected by lipotoxicity is the heart and this review presents an update on human and animal studies of this problem. Recent findingsHuman studies have clearly correlated heart dysfunction with the content of triglyceride. More recently human heart samples have been used to assess gene changes associated with altered lipid accumulation. Genetically altered mice have been created that develop lipotoxic cardiomyopathies and newer investigations are attempting to delineate curative therapies. SummaryHuman studies will confirm the metabolic changes associated with lipotoxic cardiomyopathy and, hopefully, animal studies will guide treatment options.