Roles of PPARs on regulating myocardial energy and lipid homeostasis

Doxorubicin-Induced Cardiac Toxicity Is Mediated by Lowering of Peroxisome Proliferator-Activated Receptor δ Expression in Rats

The present study investigates the changes of peroxisome proliferator-activated receptors δ (PPARδ) expression and troponin phosphorylation in heart of rats which were treated with doxorubicin (DOX). Wistar rats which were treated with DOX according to a previous method. The protein levels of PPARδ and troponin phosphorylation were measured using Western blot. The PPARδ expression in heart was markedly reduced in DOX-treated rats showing a marked decrease in cardiac dP/dT and cardiac output. Also, cardiac troponin phosphorylation was lowered in DOX-treated rats. Meanwhile, combined treatment with the agonist of PPARδ (GW0742) reversed the decrease of cardiac dP/dT and cardiac output in DOX-treated rats. Then, primary cultured cardiomyocytes from neonatal rats were used to measure the changes of calcium concentration in cells. In addition to both decrease of PPARδ expression and troponin phosphorylation in neonatal cardiomyocytes by DOX, a marked decrease of calcium concentration was also observed. Our results suggest the mediation of cardiac PPARδ in DOX-induced cardiotoxicity in rats. Thus, activation of PPARδ may restore the expression of p-TnI and the cardiac performance in DOX-induced cardio toxicity in rats.

Increase of myocardial performance by Rhodiola-ethanol extract in diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Rhodiola rosea (also known as golden root or roseroot) is a perennial plant of the Crassulaceae family that grows in the Arctic and in the mountainous regions of Europe, Asia, and North America. The rhizome and roots of this plant have been long used as traditional medicine in Eastern Europe and Asia for enhancing physical and mental performance.

AIM OF THE STUDY

The present study is designed to investigate the cardiac action of Rhodiola-ethanol extract in streptozotocin-induced diabetic rats (STZ-diabetic rats) with heart failure.

MATERIALS AND METHODS

Diabetes was induced in Wistar rats by injection of streptozotocin. We measured the changes of body weight, water intake, and food intake in three groups of age-matched rats; the normal control received vehicle, STZ-diabetic rat received Rhodiola-ethanol extract or vehicle. Cardiac output, heart rate, blood pressure, and hemodynamic dP/dt in addition to plasma insulin and glucose level were also determined. The mRNA and protein levels of PPARδ were measured using real-time PCR and Western blotting, respectively.

RESULTS

Food intake, water intake and blood glucose were raised in STZ-diabetic rats showing lower body weight and plasma insulin, as compared with the control. Also, cardiac output, heart rate, blood pressure and hemodynamic dP/dt were markedly reduced in STZ-diabetic rats indicating the heart failure physiologically. After a 21-day treatment with Rhodiola-ethanol extract, cardiac output was raised in STZ-rats while the diabetic parameters were not modified. The PPARδ expression of both mRNA and protein was markedly elevated in the heart of STZ-rats receiving treatment with Rhodiola-ethanol extract. Also, the increased phosphorylation level of cardiac troponin-I was restored by this treatment with Rhodiola-ethanol extract. Otherwise, increase of cardiac output by Rhodiola-ethanol extract was blocked by antagonist of PPARδ in STZ-diabetic rats.

CONCLUSIONS

Our results suggest that ethanol extract of Rhodiola has an ability to increase the cardiac output in STZ-diabetic rats showing heart failure. Also, increase of PPAR-δ is responsible for this action of Rodiola-ethanol extract.

Mitochondrial function in vascular endothelial cell in diabetes

Micro- and macrovascular complications are commonly seen in diabetic patients and endothelial dysfunction contributes to the development and progression of the complications. Abnormal functions in endothelial cells lead to the increase in vascular tension and atherosclerosis, followed by systemic hypertension as well as increased incidence of ischemia and stroke in diabetic patients. Mitochondria are organelles serving as a source of energy production and as regulators of cell survival (e.g., apoptosis and cell development) and ion homeostasis (e.g., H(+), Ca(2+)). Endothelial mitochondria are mainly responsible for generation of reactive oxygen species (ROS) and maintaining the Ca(2+) concentration in the cytosol. There is increasing evidence that mitochondrial morphological and functional changes are implicated in vascular endothelial dysfunction. Enhanced mitochondrial fission and/or attenuated fusion lead to mitochondrial fragmentation and disrupt the endothelial physiological function. Abnormal mitochondrial biogenesis and disturbance of mitochondrial autophagy increase the accumulation of damaged mitochondria, such as irreversibly depolarized or leaky mitochondria, and facilitate cell death. Augmented mitochondrial ROS production and Ca(2+) overload in mitochondria not only cause the maladaptive effect on the endothelial function, but also are potentially detrimental to cell survival. In this article, we review the physiological and pathophysiological role of mitochondria in endothelial function with special focus on diabetes.

Reduction of rat cardiac hypertrophy by osthol is related to regulation of cardiac oxidative stress and lipid metabolism

The objective of this study was to examine the therapeutic effect of osthol, a coumarin compound isolated from the fruit of Cnidium monnieri (L.) Cusson, on cardiac hypertrophy in rats and investigate its potential mechanisms. The rats with cardiac hypertrophy induced by renovascular hypertension were given osthol orally by gavage for 4 weeks. The results showed that in the osthol 20 mg/kg group, the blood pressure, heart weight index and myocardial malondialdehyde content were lowered (p < 0.001, p = 0.002 and p = 0.025, respectively), the myocardial superoxide dismutase and glutathione peroxidase contents were increased (p < 0.001), and the elevated unesterified fatty acids and triacylglycerols in myocardial tissues were decreased (p = 0.017 and p = 0.004, respectively). At the same time, the myocardial peroxisome proliferator-activated receptor (PPAR)-α and carnitine palmitoyltransferase (CPT)-1a mRNA expressions were increased and the myocardial diacylglycerol acyltransferase (DGAT) mRNA expression was decreased in the osthol 20 mg/kg group (p < 0.001). Osthol treatment was associated with a decreased cross-sectional area of cardiomyocytes (p < 0.001). These findings suggest that osthol may exert a therapeutic effect on cardiac hypertrophy in rats, and its mechanisms may be related to the improvement of myocardial oxidative stress and lipid metabolism via regulation of PPARα-mediated target gene expressions including an increase in CPT-1a mRNA expression and a decrease in DGAT mRNA expression.

Sphingolipids, lipotoxic cardiomyopathy, and cardiac failure

In the setting of obesity and type 2 diabetes mellitus, the ectopic disposition of lipids may be a cause of heart failure. Clinical studies have clearly shown a correlation between the accumulation of triglycerides and heart dysfunction. In this process, it is likely that there are also changes in the contents of sphingolipids. Sphingolipids are important structural and signaling molecules. One specific sphingolipid, ceramide, may cause cardiac dysfunction, whereas another, sphingosine 1-phosphate, is cardioprotective. In this review, the authors focus on the role of sphingolipids in the development and prevention of cardiac failure.

Myocardial fatty acid metabolism and lipotoxicity in the setting of insulin resistance

Management of diabetes and insulin resistance in the setting of cardiovascular disease has become an important issue in an increasingly obese society. Besides the development of hypertension and buildup of atherosclerotic plaques, the derangement of fatty acid and lipid metabolism in the heart plays an important role in promoting cardiac dysfunction and oxidative stress. This review discusses the mechanisms by which metabolic inflexibility in the use of fatty acids as the preferred cardiac substrate in diabetes produces detrimental effects on mechanical efficiency, mitochondrial function, and recovery from ischemia. Lipid accumulation and the consequences of toxic lipid metabolites are also discussed.

Activation of β-adrenoceptors by dobutamine may induce a higher expression of peroxisome proliferator-activated receptors δ (PPARδ) in neonatal rat cardiomyocytes

Recent evidence showed the role of peroxisome proliferator-activated receptors (PPARs) in cardiac function. Cardiac contraction induced by various agents is critical in restoring the activity of peroxisome proliferator-activated receptors δ (PPARδ) in cardiac myopathy. Because dobutamine is an agent widely used to treat heart failure in emergency setting, this study is aimed to investigate the change of PPARδ in response to dobutamine. Neonatal rat cardiomyocytes were used to examine the effects of dobutamine on PPARδ expression levels and cardiac troponin I (cTnI) phosphorylation via Western blotting analysis. We show that treatment with dobutamine increased PPARδ expression and cTnI phosphorylation in a time- and dose-dependent manner in neonatal rat cardiomyocytes. These increases were blocked by the antagonist of β1-adrenoceptors. Also, the action of dobutamine was related to the increase of calcium ions and diminished by chelating intracellular calcium. Additionally, dobutamine-induced action was reduced by the inhibition of downstream messengers involved in this calcium-related pathway. Moreover, deletion of PPARδ using siRNA generated the reduction of cTnI phosphorylation in cardiomyocytes treated with dobutamine. Thus, we concluded that PPARδ is increased by dobutamine in cardiac cells.

Cardiac peroxisome-proliferator-activated receptor expression in hypertension co-existing with diabetes

Hypertension and DM (diabetes mellitus) are common chronic disorders that often co-exist. DM and PPAR (peroxisome-proliferator-activated receptor)-γ agonists may directly impair heart function. However, the effects of DM and PPAR-γ agonists on hypertensive myocardium are not known. Hence the aim of the present study was to investigate whether DM and a PPAR-γ agonist [RGZ (rosiglitazone)] modulated the effects of hypertension on myocardial expression of PPAR isoforms. Cardiac PPAR isoforms, TNF (tumour necrosis factor)-α and IL (interleukin)-6 were evaluated by real-time PCR and Western blotting in SHRs (spontaneously hypertensive rats), diabetic SHRs, diabetic SHRs treated with RGZ (5 mg/kg of body weight) and control WKY (Wistar-Kyoto) rats. Cardiac NADPH oxidase activity was quantified using a SOD (superoxide dismutase)-sensitive cytochrome c reduction assay. When compared with hearts from control WKY rats, hearts from SHRs had decreased PPAR-α and PPAR-δ mRNA and protein levels (39 and 44% respectively for PPAR-α, and 37 and 42% respectively for PPAR-δ), but had increased PPAR-γ mRNA and protein levels (1.9- and 1.4-fold respectively). The hypertension-induced changes in mRNA and protein of cardiac PPAR isoforms were enhanced in diabetic SHRs, which were attenuated in diabetic SHRs treated with RGZ. Cardiac TNF-α and IL-6 protein levels and NADPH oxidase activities were increased in SHRs and were increased further in diabetic SHRs. RGZ treatment decreased TNF-α and IL-6 protein levels and NADPH oxidase activities in hearts from diabetic SHRs. In conclusion, these findings suggest that DM and the PPAR-γ agonist modulated the hypertensive effects on cardiac PPAR isoform expression.

Characterization of the mechanisms of the increase in PPARδ expression induced by digoxin in the heart using the H9c2 cell line

BACKGROUND AND PURPOSE

Digoxin has been used as an inotropic agent in heart failure for a long time. Troponin I (TnI) phosphorylation is related to cardiac contractility, and the genes are regulated by peroxisome proliferator-activated receptors (PPARs). Our previous studies indicated that cardiac abnormality related to the depressed expression of PPARδ in the hearts of STZ rats is reversed by digoxin. However, the cellular mechanisms for this effect of digoxin have not been elucidated. The aim of the present study was to investigate possible mechanisms for this effect of digoxin using the H9c2 cell line cultured in high glucose (HG) conditions.

METHODS

The effects of digoxin on PPARδ expression, intracellular calcium and TnI phosphorylation were investigated in cultured H9c2 cells, maintained in a HG medium, by using Western blot analysis.

RESULTS

Digoxin increased PPARδ expression in H9c2 cells subjected to HG conditions, and increase the intracellular calcium concentration. This effect of digoxin was blocked by BAPTA-AM at concentrations sufficient to chelate calcium ions. In addition, the calcineurin inhibitor cyclosporine A and KN93, an inhibitor of calcium/calmodulin-dependent protein kinase, inhibited this action. Digoxin also increased TnI phosphorylation and this was inhibited when PPARδ was silenced by the addition of RNAi to the cells. Similar changes were observed on the contraction of H9c2 cells.

CONCLUSION

The results suggest that digoxin appears, through calcium-triggered signals, to reverse the reduced expression of PPARδ in H9c2 cells caused by HG treatment.

Cardiomyocyte-Restricted Deletion of PPARβ/δ in PPARα-Null Mice Causes Impaired Mitochondrial Biogenesis and Defense, but No Further Depression of Myocardial Fatty Acid Oxidation

It is well documented that PPARα and PPARβ/δ share overlapping functions in regulating myocardial lipid metabolism. However, previous studies demonstrated that cardiomyocyte-restricted PPARβ/δ deficiency in mice leads to severe cardiac pathological development, whereas global PPARα knockout shows a benign cardiac phenotype. It is unknown whether a PPARα-null background would alter the pathological development in mice with cardiomyocyte-restricted PPARβ/δ deficiency. In the present study, a mouse model with long-term PPARβ/δ deficiency in PPARα-null background showed a comparably reduced cardiac expression of lipid metabolism to those of single PPAR-deficient mouse models. The PPARα-null background did not rescue or aggravate the cardiac pathological development linked to cardiomyocyte-restricted PPARβ/δ deficiency. Moreover, PPARα-null did not alter the phenotypic development in adult mice with the short-term deletion of PPARβ/δ in their hearts, which showed mitochondrial abnormalities, depressed cardiac performance, and cardiac hypertrophy with attenuated expression of key factors in mitochondrial biogenesis and defense. The present study demonstrates that cardiomyocyte-restricted deletion of PPARβ/δ in PPARα-null mice causes impaired mitochondrial biogenesis and defense, but no further depression of fatty acid oxidation. Therefore, PPARβ/δ is essential for maintaining mitochondrial biogenesis and defense in cardiomyocytes independent of PPARα.

Anticancer Properties of PPARalpha-Effects on Cellular Metabolism and Inflammation

Peroxisome proliferator-activated receptors (PPARs) have lately attracted much attention as therapeutic targets. Previously, PPAR ligands were associated with the treatment of diabetes, hyperlipidemia and cardiovascular diseases, as they modulate the expression of genes regulating glucose and lipid metabolism. Recently, PPAR ligands have been also considered as potential anticancer agents, with relatively low systemic toxicity. The emerging evidence for antiproliferative, proapoptotic, antiinflammatory and potential antimetastatic properties of PPARα ligands prompted us to discuss possible roles of PPARα in tumor suppression. PPARα activation can target cancer cells energy balance by blocking fatty acid synthesis and by promoting fatty acid β-oxidation. In the state of limited nutrient availability, frequently presents in the tumor microenvironment, PPARα cooperates with AMP-dependent protein kinase in: (i) repressing oncogenic Akt activity, (ii) inhibiting cell proliferation, and (iii) forcing glycolysis-dependent cancer cells into “metabolic catastrophe.” Other potential anticancer effects of PPARα include suppression of inflammation, and upregulation of uncoupling proteins (UCPs), which attenuates mitochondrial reactive oxygen species production and cell proliferation. In conclusion, there are strong premises that the low-toxic and well-tolerated PPAR ligands should be considered as new therapeutic agents to fight disseminating cancer, which represents the major challenge for modern medicine and basic research.

Effect of Cheonggukjang supplementation upon hepatic acyl-CoA synthase, carnitine palmitoyltransferase I, acyl-CoA oxidase and uncoupling protein 2 mRNA levels in C57BL/6J mice fed with high fat diet

This study investigated the effect of Cheonggukjang on mRNA levels of hepatic acyl-CoA synthase (ACS), carnitine palmitoyltransferase I (CPT-I), acyl-CoA oxidase (ACO) and uncoupling protein 2 (UCP2), and on serum lipid profiles in C57BL/6J mice. Thirty male C57BL/6J mice were divided into three groups; normal diet (ND), high fat diet (HD) and high fat diet with 40% Cheonggukjang (HDC). Energy intake was significantly higher in the HDC group than in the ND and HD groups. The HDC group normalized in weight gain, epididymal and back fat (g/100 g) accumulation which are increased by high fat diet. Serum concentrations of triglyceride and total cholesterol in the HDC were significantly lower than those in the HD group. These results were confirmed by hepatic mRNA expression of enzymes and protein (ACS, CPT-1, ACO, UCP2) which is related with lipid metabolism by RT-PCR. Hepatic CPT-I, ACO and UCP2 mRNA expression was increased by Cheonggukjang supplementation. We demonstrated that Cheonggukjang supplement leads to increased mRNA expressions of enzymes and protein involved in fatty acid oxidation in liver, reduced accumulation of body fat and improvement of serum lipids in high fat diet fed mice.

Heart sphingolipids in health and disease

In recent years, the role of sphingolipids in physiology and pathophysiology of the heart attracted much attention. Ceramide was found to be involved in the pathogenesis of cardiac dysfunction in animal models of ischemia/reperfusion injury, Type 2 diabetes and lipotoxic cardiomyopathy. On the other hand, another member of this lipid family, namely sphingosine-1-phosphate, has been shown to possess potent cardioprotective properties. This chapter provides a review of the role of ceramide and other bioactive sphingolipids in physiology and pathophysiology of the heart. We describe the role of PPARs and exercise in regulation of myocardial sphingolipid metabolism. We also summarize the present state of knowledge on the involvement of ceramide and sphingosine-1-phosphate in the development and prevention of ischemia/reperfusion injury of the heart. In the last section of this chapter we discuss the evidence for a role of ceramide in myocardial lipotoxicity.

Peroxisome proliferator-activated receptors, metabolic syndrome and cardiovascular disease

Metabolic syndrome (MetS) is a constellation of risk factors including insulin resistance, central obesity, dyslipidemia and hypertension that markedly increase the risk of Type 2 diabetes (T2DM) and cardiovascular disease (CVD). The peroxisome proliferators-activated receptor (PPAR) isotypes, PPARα, PPARδ/ß and PPARγ are ligand-activated nuclear transcription factors, which modulate the expression of an array of genes that play a central role in regulating glucose, lipid and cholesterol metabolism, where imbalance can lead to obesity, T2DM and CVD. They are also drug targets, and currently, PPARα (fibrates) and PPARγ (thiazolodinediones) agonists are in clinical use for treating dyslipidemia and T2DM, respectively. These metabolic characteristics of the PPARs, coupled with their involvement in metabolic diseases, mean extensive efforts are underway worldwide to develop new and efficacious PPAR-based therapies for the treatment of additional maladies associated with the MetS. This article presents an overview of the functional characteristics of three PPAR isotypes, discusses recent advances in our understanding of the diverse biological actions of PPARs, particularly in the vascular system, and summarizes the developmental status of new single, dual, pan (multiple) and partial PPAR agonists for the clinical management of key components of MetS, T2DM and CVD. It also summarizes the clinical outcomes from various clinical trials aimed at evaluating the atheroprotective actions of currently used fibrates and thiazolodinediones.

Oxidative stress and inflammation modulate peroxisome proliferator-activated receptors with regional discrepancy in diabetic heart

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) play a pivotal role in myocardial lipid and glucose homeostasis. We investigated the effects of diabetes on PPAR isoforms in different cardiac regions and explored whether proinflammatory cytokines or oxidative stress modulate PPARs in diabetic hearts.

MATERIALS AND METHODS

Male Wistar rats were separated into control, diabetes and ascorbate-treated diabetes groups. Real-time PCR and Western blot analysis were performed on PPAR isoforms, tumour necrosis factor (TNF)-alpha and interleukin (IL)-6, from left and right atria and ventricles. Nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase activity was quantified through photometric measurements.

RESULTS

In control hearts, PPAR-alpha was most expressed, and PPAR-gamma least expressed in mRNA and protein levels. Diabetes decreased the protein and mRNA levels of PPAR-alpha and PPAR-delta. Ascorbate attenuated the diabetes-induced down-regulations of PPAR-alpha and PPAR-delta proteins in all cardiac regions and down-regulation of PPAR-alpha mRNA in the left atrium. In PPAR-gamma, the protein and mRNA levels were increased in diabetic atria and ventricles, which were decreased by ascorbate. Moreover, diabetes increased the TNF-alpha and IL-6 protein levels, and NAD(P)H oxidase activities in atria and ventricles. Ascorbate attenuated the increase of TNF-alpha, IL-6 protein levels and NAD(P)H oxidase activity in the atria, but only attenuated the increase of NAD(P)H oxidase activities in the ventricles.

CONCLUSIONS

Peroxisome proliferator-activated receptor isoforms are differentially expressed in the atria and ventricles. Diabetes can modulate PPARs through increased inflammatory cytokines and oxidative stress, which are attenuated by ascorbate treatment.

PPARs, Cardiovascular Metabolism, and Function: Near- or Far-from-Equilibrium Pathways

Peroxisome proliferator-activated receptors (PPAR α, β/δ and γ) play a key role in metabolic regulatory processes and gene regulation of cellular metabolism, particularly in the cardiovascular system. Moreover, PPARs have various extra metabolic roles, in circadian rhythms, inflammation and oxidative stress. In this review, we focus mainly on the effects of PPARs on some thermodynamic processes, which can behave either near equilibrium, or far-from-equilibrium. New functions of PPARs are reported in the arrhythmogenic right ventricular cardiomyopathy, a human genetic heart disease. It is now possible to link the genetic desmosomal abnormalitiy to the presence of fat in the right ventricle, partly due to an overexpression of PPARγ. Moreover, PPARs are directly or indirectly involved in cellular oscillatory processes such as the Wnt-b-catenin pathway, circadian rhythms of arterial blood pressure and cardiac frequency and glycolysis metabolic pathway. Dysfunction of clock genes and PPARγ may lead to hyperphagia, obesity, metabolic syndrome, myocardial infarction and sudden cardiac death, In pathological conditions, regulatory processes of the cardiovascular system may bifurcate towards new states, such as those encountered in hypertension, type 2 diabetes, and heart failure. Numerous of these oscillatory mechanisms, organized in time and space, behave far from equilibrium and are “dissipative structures”.

Myocardial fatty acid metabolism in health and disease

There is a constant high demand for energy to sustain the continuous contractile activity of the heart, which is met primarily by the beta-oxidation of long-chain fatty acids. The control of fatty acid beta-oxidation is complex and is aimed at ensuring that the supply and oxidation of the fatty acids is sufficient to meet the energy demands of the heart. The metabolism of fatty acids via beta-oxidation is not regulated in isolation; rather, it occurs in response to alterations in contractile work, the presence of competing substrates (i.e., glucose, lactate, ketones, amino acids), changes in hormonal milieu, and limitations in oxygen supply. Alterations in fatty acid metabolism can contribute to cardiac pathology. For instance, the excessive uptake and beta-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. Furthermore, alterations in fatty acid beta-oxidation both during and after ischemia and in the failing heart can also contribute to cardiac pathology. This paper reviews the regulation of myocardial fatty acid beta-oxidation and how alterations in fatty acid beta-oxidation can contribute to heart disease. The implications of inhibiting fatty acid beta-oxidation as a potential novel therapeutic approach for the treatment of various forms of heart disease are also discussed.

Peroxisome proliferator-activated receptor {delta} is an essential transcriptional regulator for mitochondrial protection and biogenesis in adult heart

RATIONALE

Peroxisome proliferator-activated receptors (PPARs) (alpha, gamma, and delta/beta) are nuclear hormone receptors and ligand-activated transcription factors that serve as key determinants of myocardial fatty acid metabolism. Long-term cardiomyocyte-restricted PPARdelta deficiency in mice leads to depressed myocardial fatty acid oxidation, bioenergetics, and premature death with lipotoxic cardiomyopathy.

OBJECTIVE

To explore the essential role of PPARdelta in the adult heart.

METHODS AND RESULTS

We investigated the consequences of inducible short-term PPARdelta knockout in the adult mouse heart. In addition to a substantial transcriptional downregulation of lipid metabolic proteins, short-term PPARdelta knockout in the adult mouse heart attenuated cardiac expression of both Cu/Zn superoxide dismutase and manganese superoxide dismutase, leading to increased oxidative damage to the heart. Moreover, expression of key mitochondrial biogenesis determinants such as PPARgamma coactivator-1 were substantially decreased in the short-term PPARdelta deficient heart, concomitant with a decreased mitochondrial DNA copy number. Rates of palmitate and glucose oxidation were markedly depressed in cardiomyocytes of PPARdelta knockout hearts. Consequently, PPARdelta deficiency in the adult heart led to depressed cardiac performance and cardiac hypertrophy.

CONCLUSIONS

PPARdelta is an essential regulator of cardiac mitochondrial protection and biogenesis and PPARdelta activation can be a potential therapeutic target for cardiac disorders.

Tie2-mediated loss of peroxisome proliferator-activated receptor-gamma in mice causes PDGF receptor-beta-dependent pulmonary arterial muscularization

Peroxisome proliferator-activated receptor (PPAR)-gamma is reduced in pulmonary arteries (PAs) of patients with PA hypertension (PAH), and we reported that deletion of PPARgamma in smooth muscle cells (SMCs) of transgenic mice results in PAH. However, the sequelae of loss of PPARgamma in PA endothelial cells (ECs) are unknown. Therefore, we bred Tie2-Cre mice with PPARgamma(flox/flox) mice to induce EC loss of PPARgamma (Tie2 PPARgamma(-/-)), and we assessed PAH by right ventricular systolic pressure (RVSP), RV hypertrophy (RVH), and muscularized distal PAs in room air (RA), after chronic hypoxia (CH), and after 4 wk of recovery in RA (Rec-RA). The Tie2 PPARgamma(-/-) mice developed spontaneous PAH in RA with increased RVSP, RVH, and muscularized PAs vs. wild type (WT); both genotypes exhibited a similar degree of PAH following chronic hypoxia, but Tie2 PPARgamma(-/-) mice had more residual PAH compared with WT mice after Rec-RA. The Tie2 PPARgamma(-/-) vs. WT mice in RA had increased platelet-derived growth factor receptor-beta (PDGF-Rbeta) expression and signaling, despite an elevation in the PPARgamma target apolipoprotein E, an inhibitor of PDGF signaling. Inhibition of PDGF-Rbeta signaling with imatinib, however, was sufficient to reverse the PAH observed in the Tie2 PPARgamma(-/-) mice. Thus the disruption of PPARgamma signaling in EC is sufficient to cause mild PAH and to impair recovery from CH-induced PAH. Inhibition of heightened PDGF-Rbeta signaling is sufficient to reverse PAH in this genetic model.

High-fat feeding in cardiomyocyte-restricted PPARdelta knockout mice leads to cardiac overexpression of lipid metabolic genes but fails to rescue cardiac phenotypes

Peroxisome proliferator-activated receptor delta (PPARdelta) is an essential determinant of basal myocardial fatty acid oxidation (FAO) and bioenergetics. We wished to determine whether increased lipid loading affects the PPARdelta deficient heart in transcriptional regulation of FAO and in the development of cardiac pathology. Cardiomyocyte-restricted PPARdelta knockout (CR-PPARdelta(-/-)) and control (alpha-MyHC-Cre) mice were subjected to 48 h of fasting and to a long-term maintenance on a (28 weeks) high-fat diet (HFD). The expression of key FAO proteins in heart was examined. Serum lipid profiles, cardiac pathology, and changes of various transduction signaling pathways were also examined. Mice subjected to fasting exhibited upregulated transcript expression of FAO genes in the CR-PPARdelta(-/-) hearts. Moreover, long-term HFD in CR-PPARdelta(-/-) mice induced a strikingly greater transcriptional response. After HFD, genes encoding key FAO enzymes were expressed remarkably more in CR-PPARdelta(-/-) hearts than in those of control mice. Despite the marked rise of FAO gene expression, corresponding protein expression remained low in the CR-PPARdelta(-/-) heart, accompanied by abnormalities in sarcomere structures and mitochondria that were similar to those of CR-PPARdelta(-/-) hearts with regular chow feeding. The CR-PPARdelta(-/-) mice displayed increased expression of PPARgamma co-activator-1alpha (PGC-1alpha) and PPARalpha in the heart with deactivated Akt and p42/44 MAPK signaling in response to HFD. We conclude that PPARdelta is an essential determinant of myocardial FAO. Increased lipid intake activates cardiac expression of FAO genes via PPARalpha/PGC-1alpha pathway, albeit it is not sufficient to improve cardiac pathology due to PPARdelta deficiency.

Proinflammatory cytokine and ligands modulate cardiac peroxisome proliferator-activated receptors

BACKGROUND

Peroxisome proliferator-activated receptors (PPAR) mediate inflammatory processes and alter cardiac function. However, it is not clear whether inflammatory cytokines or PPAR ligands regulate PPARs in the cardiomyocytes to modulate cardiac functions. We investigated the effects of tumour necrosis factor-alpha (TNF-alpha) and PPAR ligands on the expression of PPARs in HL-1 cardiomyocytes.

MATERIALS AND METHODS

HL-1 cardiomyocytes were incubated with and without TNF-alpha (1, 10, 25 and 50 ng mL(-1)) or PPAR ligands (rosiglitazone, pioglitazone and fenofibrate) at concentrations of 0.1, 1 and 10 microM for 24 h. The cells also received SN-50 (NF-kappaB inhibitor, 50 microg mL(-1)), ascorbic acid (100 microM) and coenzyme Q10 (10 microM) alone or combined with TNF-alpha.

RESULTS

Using reverse transcriptase-polymerase chain reaction and Western blot, we found that incubation of TNF-alpha (50 ng mL(-1)) for 24 h decreased PPAR-alpha, but increased PPAR-gamma without altering PPAR-delta. These effects were not changed by co-administration of SN-50. However, co-administration of ascorbic acid prevented the effect of TNF-alpha both on PPAR-alpha and PPAR-gamma. Coenzyme Q10 partially attenuated the effect of TNF-alpha on PPAR-gamma but did not alter its effect on PPAR-alpha. The administration of rosiglitazone (10 microM) and pioglitazone (10 microM) for 24 h increased PPAR-gamma mRNA, but did not alter PPAR-alpha or PPAR-delta. Moreover, fenofibrate (0.1, 1 and 10 microM) increased PPAR-gamma without any effects on PPAR-alpha or PPAR-delta.

CONCLUSIONS

Oxidative stress causes the regulations of PPAR-alpha and PPAR-gamma in the TNF-alpha-treated cardiomyocytes. The up-regulation of PPAR-gamma by PPAR ligands may contribute to their anti-inflammation effects.

Expression of renin-angiotensin system and peroxisome proliferator-activated receptors in alcoholic cardiomyopathy

BACKGROUND

Alcoholic cardiomyopathy (ACM) develops in response to chronic alcohol intake and it is hypothesized that activation of the renin-angiotensin system (RAS) and disorders in energy metabolism may play important roles in its onset. Given that the expression of peroxisome proliferator-activated receptors (PPARalpha and PPARgamma) changes with alterations in cardiac metabolism and myocardial remodeling, this study was designed to test the hypothesis that protein expression of PPARalpha and PPARgamma is correlated with RAS activation in ACM.

METHODS

For the first experiment, rats were divided into 3 groups: 30 received alcohol (intragastric administration with ad libitum drinking), 30 received alcohol and irbesartan (5 mg/kg/d, p.o.), and 30 served as controls. RAS activity and protein expression of PPARalpha and PPARgamma were evaluated in rats following 6 months of alcohol feeding using radioimmunoassay, reverse transcriptase PCR, and Western blot methods. For the second experiment, rats were divided into 4 groups: 10 rats received alcohol/irbesartan (5 mg/kg/d, p.o.)/PD98059 (methyl ethyl ketone [MEK]-1 inhibitor) (0.3 mg/kg/d, p.o.), 10 rats received alcohol/PD98059, 10 rats received alcohol/irbesartan, and 10 rats received alcohol alone. Myocardial PPARalpha and PPARgamma protein expression was detected following 6 months of alcohol feeding using Western blot method.

RESULTS

Compared with controls, myocardial angiotensin (Ang) I, Ang II, and renin levels were progressively increased at 2, 4, and 6 months of alcohol intake. mRNA expression of renin, angiotensinogen, angiotensin-converting enzyme (ACE), and AT1 was increased at 6 months. Moreover, activated RAS downregulated PPARalpha and upregulated PPARgamma protein expression as ACM progressed. Finally, extracellular signal regulated kinase 1 and 2 (ERK1/2) was shown to play a key role in the regulation of protein expression of PPARalpha and PPARgamma.

CONCLUSION

These results suggest that RAS is activated during the development of ACM. Moreover, ERK1/2 plays a key role in the regulation of protein expression of PPARalpha and PPARgamma by RAS in ACM.

Pioglitazone induces lipid accumulation in the rat heart despite concomitant reduction in plasma free fatty acid availability

Thiazolidinediones are insulin-sensitizing drugs which have been proved to be effective in the treatment of type 2 diabetes. However, the action of thiazolidinediones on myocardial metabolism is only poorly recognized. Therefore, the aim of our study was to investigate the effects of two-week pioglitazone treatment (3 mg/kg/d) on lipid and carbohydrate metabolism in the heart of rats fed on a standard chow or on a high-fat diet (HFD) for three weeks. High-fat feeding increased myocardial protein expression of all peroxisome proliferator-activated receptor (PPAR) isoforms. The greatest response was, however, noted in the case of PPARgamma. Surprisingly, administration of pioglitazone induced accumulation of free fatty acids (FFA) and diacylglycerol in the heart in both groups, despite concomitant reduction in plasma FFA concentration. The content of triacylglycerol was increased only in the HFD group. Pioglitazone treatment also shifted myocardial substrate utilization towards greater contribution of glucose in both groups, as evidenced by decreased rate of palmitate oxidation and higher 2-deoxyglucose uptake and elevated glycogen content. This could induce a mismatch between the rate of myocardial fatty acid uptake and oxidation leading to increased intracellular availability of fatty acids for non-oxidative metabolic pathways like synthesis of acylglycerols. Our data suggests that thiazolidinediones improve cardiac insulin sensitivity by mechanisms other than reduction in intramyocardial lipid content.

Salacia root, a unique Ayurvedic medicine, meets multiple targets in diabetes and obesity

In many traditional schools of medicine it is claimed that a balanced modulation of several targets can provide a superior therapeutic effect and decrease in side effect profile compared to a single action from a single selective ligand, especially in the treatment of certain chronic and complex diseases, such as diabetes and obesity. Diabetes and obesity have a multi-factorial basis involving both genetic and environmental risk factors. A wide array of medicinal plants and their active constituents play a role in the prevention and treatment of diabetes. Salacia roots have been used in Ayurvedic medicine for diabetes and obesity since antiquity, and have been extensively consumed in Japan, the United States and other countries as a food supplement for the prevention of obesity and diabetes. Recent pharmacological studies have demonstrated that Salacia roots modulate multiple targets: peroxisome proliferator-activated receptor-alpha-mediated lipogenic gene transcription, angiotensin II/angiotensin II type 1 receptor, alpha-glucosidase, aldose reductase and pancreatic lipase. These multi-target actions may mainly contribute to Salacia root-induced improvement of type 2 diabetes and obesity-associated hyperglycemia, dyslipidemia and related cardiovascular complications seen in humans and rodents. The results of bioassay-guided identification indicate that mangiferin, salacinol, kotalanol and kotalagenin 16-acetate are at least in part responsible for these multi-target regulatory activities of Salacia roots. The evidence suggests that this unique traditional medicine fulfills a multiple-target strategy in the prevention and treatment of diabetes and obesity. Although toxicological studies have suggested minimal adverse effects of the herbal medicine in rodents, a clinical trial is crucial to further confirm the safety of Salacia roots. In addition, further mechanistic studies are necessary in order to allow a better understanding of how use of Salacia root may interact with other therapeutic interventions.

Pharmacogenetics of the PPAR genes and cardiovascular disease

The goal of pharmacogenetics is to define the genetic determinants of individual drug responsiveness, and thereby provide personalized treatment to each individual. The peroxisome proliferator-activated receptors (PPARs) are polypeptide products of a set of related genes functioning to regulate several cellular processes that are central to cardiovascular health and disease. Given their pleiotropic roles in lipid and glucose homeostasis, cardiac energy balance and regulation of adipocyte release of circulating inflammatory factors, it is not surprising that PPARs represent an attractive target for clinical investigation and intervention in disease states, such as diabetes, obesity, atherosclerosis, cardiomyopathy, cardiac hypertrophy and heart failure. Research into the manipulation of PPAR function by pharmacologic agents has already resulted in important advances in the treatment of diabetes mellitus and cardiovascular disease. It follows that PPAR pharmacogenetics promises important advances in the personalized treatment of cardiovascular disease.