Ameliorative Effect of Combination of Fenofibrate and Rosiglitazone in Pressure Overload-Induced Cardiac Hypertrophy in Rats

Mechanistic insights to the cardioprotective effect of blueberry nutraceutical extract in isoprenaline-induced cardiac hypertrophy

BACKGROUND

Lowbush blueberry extract (Vaccinium angustifolium) is abundant with polyphenols (such as chlorogenic acid) with high antioxidant profile. It has received great interest due to its protective role in many disorders such as heart diseases and neurological disorders.

HYPOTHESIS

We hypothesized that blueberry leaf extract might have a protective effect against cardiac hypertrophy via suppressing oxidative stress, inflammation and fibrosis.

METHOD

Blueberry leaf nutraceutical extract was administered orally to male albino rats at three different doses (25, 50 and 100 mg/kg/day of the extract, equivalent to 3.4, 6.8 and 13.6 mg of chlorogenic acid, respectively) once daily for 28 consecutive days against a dose of isoprenaline (ISO) (5 mg/kg) for 14 days.

RESULTS

The results indicated that isoprenaline induced significant myocardial damage, characterized by conduction abnormalities, increased heart-to-body weight ratio, increased serum CKMB, AST, c-TnI and LDH. Pretreatment with blueberry extract at a dose of 50 mg/kg/day (equivalent to 6.8 mg chlorogenic acid) protected against ISO-induced ECG changes, leakage of cardiac enzymes and histopathological changes. Also, ISO caused significant glutathione depletion, lipid peroxidation and reduction in activities of antioxidant catalase enzyme. These effects were prevented by pretreatment with blueberry extract. Additionally, ISO elicited inflammatory effects by increasing the expression of NF-κB, COX-2, TNF-α and IL-6 while pretreatment with blueberry extract significantly inhibited these inflammatory responses. Furthermore, ISO induced fibrosis by increasing the level of TGF-β while pretreatment with blueberry extract significantly reduced it.

CONCLUSION

These findings indicate that blueberry leaf extract possessed a potent protective effect against ISO-induced cardiac hypertrophy via suppressing oxidative stress, inflammation and fibrosis.

PPAR-γ is involved in the protective effect of 2,3,4',5-tetrahydroxystilbene-2-O-beta-D-glucoside against cardiac fibrosis in pressure-overloaded rats

2, 3, 4', 5-tetrahydroxystilbene-2-0-β-D glucoside (TSG) could inhibit cardiac remodeling in response to pressure overload. Peroxisome proliferator-activated receptor gamma (PPAR-γ) has been recognized as a potent, endogenous antifibrotic factor and maintaining a proper expression level in myocardium is necessary for assuring that structure and function of heart adapt to pressure overload stress. The aim of the present study was to investigate whether PPAR-γ is involved in the beneficial effect of TSG on pressure overload-induced cardiac fibrosis. TSG (120mg/kg/day) or TSG (120mg/kg/day) plus the PPAR-γ antagonist GW9662 (1mg/kg/day) was administered to rats with pressure overload induced by abdominal aortic banding. 30 days later, pressure overload-induced hypertension, cardiac dysfunction and fibrosis were significantly inhibited by TSG. TSG also significantly reduced collagen I, collagen III, fibronectin and plasminogen activator inhibitor (PAI)-1 expression, as makers of myocardial fibrosis. Theses anti-fibrotic effects of TSG in pressure overloaded hearts could be abrogated by co-treatment with GW9662. Accordingly, upregulated PPAR-γ protein expression by TSG in pressure overloaded hearts was also reversed by co-treatment with GW9662. Additionally, the inhibitory effects of TSG on angiotensin II induced cardiac fibroblasts proliferation, differentiation and expression of collagen I and III, fibronectin and PAI-1 were abrogated by PPAR-γ antagonist GW9662 and PPAR-γ silencing. Furthermore, TSG directly increased PPAR-γ gene expression at gene promoter, mRNA and protein level in angiotensin II-treated cardiac fibroblats in vitro. Our results suggested that upregualtion of endogenous PPAR-γ expression by TSG may be involved in its beneficial effect on pressure overload-induced cardiac fibrosis.

Fenofibrate plus Metformin Produces Cardioprotection in a Type 2 Diabetes and Acute Myocardial Infarction Model

We investigated whether fenofibrate, metformin, and their combination generate cardioprotection in a rat model of type 2 diabetes (T2D) and acute myocardial infarction (AMI). Streptozotocin-induced diabetic- (DB-) rats received 14 days of either vehicle, fenofibrate, metformin, or their combination and immediately after underwent myocardial ischemia/reperfusion (I/R). Fenofibrate plus metformin generated cardioprotection in a DBI/R model, reported as decreased coronary vascular resistance, compared to DBI/R-Vehicle, smaller infarct size, and increased cardiac work. The subchronic treatment with fenofibrate plus metformin increased, compared with DBI/R-Vehicle, total antioxidant capacity, manganese-dependent superoxide dismutase activity (MnSOD), guanosine triphosphate cyclohydrolase I (GTPCH-I) expression, tetrahydrobiopterin : dihydrobiopterin (BH₄ : BH₂) ratio, endothelial nitric oxide synthase (eNOS) activity, nitric oxide (NO) bioavailability, and decreased inducible NOS (iNOS) activity. These findings suggest that PPARα activation by fenofibrate + metformin, at low doses, generates cardioprotection in a rat model of T2D and AMI and may represent a novel treatment strategy to limit I/R injury in patients with T2D.

Rapid effects of aldosterone in primary cultures of cardiomyocytes - do they suggest the existence of a membrane-bound receptor?

Aldosterone acts on its target tissue through a classical mechanism or through the rapid pathway through a putative membrane-bound receptor. Our goal here was to better understand the molecular and biochemical rapid mechanisms responsible for aldosterone-induced cardiomyocyte hypertrophy. We have evaluated the hypertrophic process through the levels of ANP, which was confirmed by the analysis of the superficial area of cardiomyocytes. Aldosterone increased the levels of ANP and the cellular area of the cardiomyocytes; spironolactone reduced the aldosterone-increased ANP level and cellular area of cardiomyocytes. Aldosterone or spironolactone alone did not increase the level of cyclic 3',5'-adenosine monophosphate (cAMP), but aldosterone plus spironolactone led to increased cAMP level; the treatment with aldosterone + spironolactone + BAPTA-AM reduced the levels of cAMP. These data suggest that aldosterone-induced cAMP increase is independent of mineralocorticoid receptor (MR) and dependent on Ca(2+). Next, we have evaluated the role of A-kinase anchor proteins (AKAP) in the aldosterone-induced hypertrophic response. We have found that St-Ht31 (AKAP inhibitor) reduced the increased level of ANP which was induced by aldosterone; in addition, we have found an increase on protein kinase C (PKC) and extracellular signal-regulated kinase 5 (ERK5) activity when cells were treated with aldosterone alone, spironolactone alone and with a combination of both. Our data suggest that PKC could be responsible for ERK5 aldosterone-induced phosphorylation. Our study suggests that the aldosterone through its rapid effects promotes a hypertrophic response in cardiomyocytes that is controlled by an AKAP, being dependent on ERK5 and PKC, but not on cAMP/cAMP-dependent protein kinase signaling pathways. Lastly, we provide evidence that the targeting of AKAPs could be relevant in patients with aldosterone-induced cardiac hypertrophy and heart failure.

PPARs: Protectors or Opponents of Myocardial Function?

Over 5 million people in the United States suffer from the complications of heart failure (HF), which is a rapidly expanding health complication. Disorders that contribute to HF include ischemic cardiac disease, cardiomyopathies, and hypertension. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family. There are three PPAR isoforms: PPARα, PPARγ, and PPARδ. They can be activated by endogenous ligands, such as fatty acids, as well as by pharmacologic agents. Activators of PPARs are used for treating several metabolic complications, such as diabetes and hyperlipidemia that are directly or indirectly associated with HF. However, some of these drugs have adverse effects that compromise cardiac function. This review article aims to summarize the current basic and clinical research findings of the beneficial or detrimental effects of PPAR biology on myocardial function.

Fenofibrate ameliorates cardiac hypertrophy by activation of peroxisome proliferator-activated receptor-α partly via preventing p65-NFκB binding to NFATc4

Fenofibrate, a specific peroxisome proliferator-activated receptor alpha (PPAR-α) agonist, was reported to inhibit cardiac hypertrophy. However, the detailed molecular mechanisms and particularly the transcriptional components that are decisive in this process remain to be elucidated. Here we found that fenofibrate ameliorated cardiac hypertrophy in vitro and in vivo. Fenofibrate prevented nuclear translocation of nuclear factor of activated T-cells c4 (NFATc4) and p65 subunit of nuclear factor-kappa B (p65-NFκB) induced by pressure overload or angiotensinII (AngII). Moreover, fenofibrate increased the association of PPAR-α with NFATc4 in nucleus, which inhibited the interaction of NFATc4 with p65-NFκB. Our results suggested that the anti-hypertrophic effect of fenofibrate may be partially attributed to activation of PPAR-α, which decreases the binding of p65-NFκB to NFATc4 and thereby inhibits transactivation of NFATc4.

Antidiabetic effects of Corni Fructus extract in streptozotocin-induced diabetic rats

PURPOSE

Diabetes is the leading cause of end-stage renal failure. The present study was undertaken to characterize the effects of Corni Fructus on diabetic nephropathy in streptozotocin-induced diabetic rats and their mechanisms.

MATERIALS AND METHODS

Streptozotocin-diabetic rats were orally administrated with Corni Fructus at a dose of 100, 200 or 400 mg/kg body mass for 40 days.

RESULTS

Corni Fructus-treated diabetic rats showed significant decreases of blood glucose, urinary protein levels and water consumption. Corni Fructus also reduced serum total cholesterol, total triglyceride and low-density lipoprotein cholesterol levels, and showed a tendency of enhancing high-density lipoprotein cholesterol level. Levels of serum albumin and creatinine in diabetic rats were also significantly reduced by Corni Fructus administration at a dose of 200 and 400 mg/kg body mass compared with non-treated diabetic rats. Corni Fructus increased catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidose (GSH-px) activities in the kidneys of diabetic rats. Furthermore, Corni Fructus treatment enhanced renal peroxisome proliferator-activated receptor-γ (PPARγ) expression in diabetic rats.

CONCLUSION

These results demonstrated that Corni Fructus may have the potential to protect the animals from diabetic nephropathy by amelioration of oxidative stress and stimulation of PPARγ expression.

Transforming growth factor-β inhibits myocardial PPARγ expression in pressure overload-induced cardiac fibrosis and remodeling in mice

OBJECTIVES

Pharmacological activation of peroxisome proliferator-activated receptor gamma (PPARγ) has been shown to attenuate pressure overload-induced cardiac fibrosis, suggesting that PPARγ has an antifibrotic effect. This study tested the hypothesis that there is a functional interaction between transforming growth factor-β (TGF-β) signaling and endogenous PPARγ expression in cardiac fibroblasts and pressure overloaded heart.

METHODS AND RESULTS

We observed that, in response to pressure overload induced by transverse aortic constriction, left-ventricular PPARγ protein levels were decreased in wild-type mice, but increased in mice with an inducible overexpression of dominant negative mutation of the human TGF-β type II receptor (DnTGFβRII), in which TGF-β signaling is blocked. In isolated mouse cardiac fibroblasts, we demonstrated that TGF-β1 treatment decreased steady state PPARγ mRNA (-34%) and protein (-52%) levels, as well as PPARγ transcriptional activity (-53%). Chromatin immunoprecipitation analysis showed that TGF-β1 treatment increased binding of Smad2/3, Smad4 and histone deacetylase 1, and decreased binding of acetylated histone 3 to the PPARγ promoter in cardiac fibroblasts. Both pharmacological activation and overexpression of PPARγ significantly inhibited TGF-β1-induced extracellular matrix molecule expression in isolated cardiac fibroblasts, whereas treatment with the PPARγ agonist rosiglitazone inhibited, and treatment with the PPARγ antagonist T0070907 exacerbated chronic pressure overload-induced cardiac fibrosis and remodeling in wild-type mice in vivo.

CONCLUSION

These data provide strong evidence that TGF-β1 directly suppresses PPARγ expression in cardiac fibroblasts via a transcriptional mechanism and suggest that the down-regulation of endogenous PPARγ expression by TGF-β may be involved in pressure overload-induced cardiac fibrosis.

Impact of obesity on hypertension-induced cardiac remodeling: role of oxidative stress and its modulation by gemfibrozil treatment in rats

This study investigated the possible synergistic role of obesity in hypertension-induced cardiac remodeling and its modulation by gemfibrozil treatment in rats. Male Wistar rats were fed a high-fat diet (HFD) for 90 days. Normal rats were subjected to hypertension by partial abdominal aortic constriction (PAAC) for 28 days. In the HFD+PAAC control group, rats on HFD were subjected to PAAC on the 62nd day and were sacrificed on the 90th day. HFD and PAAC individually resulted in significant cardiac hypertrophy and fibrosis along with increased oxidative stress and mean arterial blood pressure (MABP) in rats as evidenced by various morphological, biochemical, and histological parameters. Moreover, the HFD + PAAC control group showed marked cardiac remodeling compared to rats subjected to HFD or PAAC alone. The HFD+gemfibrozil and HFD+PAAC+gemfibrozil groups showed significant reduction in cardiac remodeling along with reduction in oxidative stress and MABP. Hence, it may be concluded that oxidative stress plays a key role in obesity-mediated synergistic effects on induction and progression of PAAC-induced cardiac remodeling, and its deleterious effects could be reversed by gemfibrozil treatment in rats through its antioxidant activity.

Ameliorative role of rosiglitazone in hyperhomocysteinemia-induced experimental cardiac hypertrophy

The present study has been designed to explore the beneficial effect of rosiglitazone, a peroxisome proliferator activated receptor-gamma agonist, in hyperhomocysteinemia-induced cardiac hypertrophy in rats. The hyperhomocysteinemia was induced in rats by feeding L-methionine (1.7 g/kg per day orally) for 8 weeks. The development of cardiac hypertrophy was assessed by measuring ratio of left ventricular weight to body weight, left ventricular wall thickness, cardiomyocyte diameter, and mean arterial blood pressure. The extent of fibrosis was checked by biochemical and histological assessment of collagen deposition. Moreover, the oxidative stress in heart was measured in terms of an increase in thiobarbituric acid reactive substances, superoxide anion generation, and decrease in reduced glutathione levels. The treatment with rosiglitazone (5 and 10 mg/kg per day orally) started from the first day of administration of L-methionine significantly abolished hyperhomocysteinemia-induced increase in left ventricular weight to body weight ratio, left ventricular wall thickness, cardiomyocyte diameter, collagen deposition, and oxidative stress without affecting serum homocysteine levels in rats. At high dose, rosiglitazone markedly reduced mean arterial blood pressure but at low dose, a significant reduction in mean arterial blood pressure was not observed in hyperhomocysteinemic rats. Hence, our results suggest that rosiglitazone provides benefit in hyperhomocysteinemia-induced cardiac hypertrophy and fibrosis in a dose-dependent manner and its protective action is independent of change in mean arterial blood pressure and serum homocysteine levels in rats.

PPARalpha and PPARgamma are co-expressed, functional and show positive interactions in the rat urinary bladder urothelium

Some dual-acting PPARalpha + gamma agonists cause cancer in the rat urinary bladder, in some cases overrepresented in males, by a mechanism suggested to involve chronic stimulation of PPARalpha and PPARgamma, i.e. exaggerated pharmacology. By western blotting, we found that the rat urinary bladder urothelium expressed PPARalpha at higher levels than the liver and heart, and comparable to kidney. Urothelial expression of PPARgamma was above that of fat, heart, skeletal muscle and kidney. Male rats exhibited a higher PPARalpha/PPARgamma expression balance in the bladder urothelium than did female rats. Rats were treated by gastric gavage with rosiglitazone (PPARgamma agonist), fenofibrate (PPARalpha agonist) or a combination of rosiglitazone and fenofibrate for 7 days. In the urothelium, the transcription factor Egr-1 was induced to significantly higher levels in rats co-administered rosiglitazone and fenofibrate than in rats administered either rosiglitazone or fenofibrate alone. Egr-1 was also induced in the heart and liver of rats treated with fenofibrate, but a positive interaction between rosiglitazone and fenofibrate with regards to Egr-1 induction was only seen in the urothelium. Thus, in the rat urinary bladder urothelium, PPARalpha and PPARgamma were expressed at high levels, were functional and exhibited positive interactions. Interestingly, fenofibrate induced the peroxisome membrane protein PMP70 not only in liver, but also in the bladder urothelium, opening the possibility that oxidative stress may contribute to rat urothelial carcinogenesis by dual-acting PPARalpha + gamma agonists.

Minireview: Won't get fooled again: the nonmetabolic roles of peroxisome proliferator-activated receptors (PPARs) in the heart

The peroxisome proliferator-activated receptor (PPAR) transcription factors are nuclear receptors initially identified for their key role in regulating metabolic processes. Recent studies designed to identify the role of PPARalpha, -beta, and -gamma in vivo uncovered extrametabolic roles that may be less well known in the heart. In this review, we describe what is known about these extrametabolic roles of PPARs, including regulation of cardiac inflammation, extracellular matrix remodeling, oxidative stress, and regulation of cardiac hypertrophy. Lastly, we discuss the emerging role of PPARs in cell cycle regulation and angiogenesis in noncardiac systems that may be applicable to heart biology. Although this review primarily discusses the extrametabolic role of PPARalpha, the most studied PPAR isoform in the heart, we highlight where possible what is known about the unique and overlapping roles of the PPAR isoforms in terms of metabolic function.

The effect of tanshinone IIA upon the TGF-beta1/Smads signaling pathway in hypertrophic myocardium of hypertensive rats

To investigate the molecular mechanism by which Tanshinone IIA (TSN IIA) prevents left ventricular hypertrophy (LVH), we examined the expression of AT1R, TGF-beta1 and Smads gene in the hypertrophic myocardium of hypertensive rats with abdominal aorta constriction. LVH model was established by creating abdominal aorta constriction. Four weeks later, animals were randomly divided into 4 groups with 8 animals in each. One group was used as model control, the other three groups were treated with TSN IIA (20 mg/kg), TSN IIA (10 mg/kg) and valsartan (10 mg/kg), respectively. Another 8 SD rats were subjected to sham surgery and served as blank control. After 8-week treatment, the caudal artery pressure of the animals was measured. The tissues of left ventricle were taken for the measurement of the left ventricular mass index (LVMI) and pathological sectioning and HE-staining were used for determining the myocardial fiber dimension (MFD). The mRNA expression of AT1R, protein expression of TGF-beta1 and activity of Smad-2, 4, 7 were detected by RT-PCR and Western blotting, respectively. Our results showed that (1) the blood pressure of rats treated with TSN IIA, either at high or low dose, was significantly higher than those in the control and valsartan-treated group (P<0.01, P<0.05); (2) LVMI and MFD in TSN IIA and valsartan-treated rats were higher than those in the control group (P<0.05) but significantly lower than those in the model control (P<0.01); (3) the high doses of TSN IIA and valsartan significantly down-regulated the mRNA expression of AT1R and protein expression of TGF-beta1 and Smad-3 in the hypertrophic myocardium (P<0.01), and TGF-beta1 in valsartan-treated animals was more significantly lower than that in rats treated with TSN IIA; (4) the two doses of TSN IIA and valsartan significantly up-regulated the protein expression of Smad-7 in the hypertrophic myocardium (P<0.01), and Smad-7 in the animals treated with high-dose TSN IIA was significantly higher than that in rats treated with valsartan. It is concluded that inhibition of myocardial hypertrophy induced by TSN IIA independent of blood pressure. The underlying mechanism might be the down-regulated expression of AT1R mRNA and Smad-3, increased production of Smad-7, and blocking effect of TSN IIA on TGF beta1/Smads signal pathway in local myocardium.

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) agonist, AVE8134, attenuates the progression of heart failure and increases survival in rats

AIM

To investigate the efficacy of the peroxisome proliferator-activated receptor-alpha (PPARalpha) agonist, AVE8134, in cellular and experimental models of cardiac dysfunction and heart failure.

METHODS

In Sprague Dawley rats with permanent ligation of the left coronary artery (post-MI), AVE8134 was compared to the PPARgamma agonist rosiglitazone and in a second study to the ACE inhibitor ramipril. In DOCA-salt sensitive rats, efficacy of AVE8134 on cardiac hypertrophy and fibrosis was investigated. Finally, AVE8134 was administered to old spontaneously hypertensive rats (SHR) at a non-blood pressure lowering dose with survival as endpoint. In cellular models, we studied AVE8134 on hypertrophy in rat cardiomyocytes, nitric oxide signaling in human endothelial cells (HUVEC) and LDL-uptake in human MonoMac-6 cells.

RESULTS

In post-MI rats, AVE8134 dose-dependently improved cardiac output, myocardial contractility and relaxation and reduced lung and left ventricular weight and fibrosis. In contrast, rosiglitazone exacerbated cardiac dysfunction. Treatment at AVE8134 decreased plasma proBNP and arginine and increased plasma citrulline and urinary NOx/creatinine ratio. In DOCA rats, AVE8134 prevented development of high blood pressure, myocardial hypertrophy and cardiac fibrosis, and ameliorated endothelial dysfunction. Compound treatment increased cardiac protein expression and phosphorylation of eNOS. In old SHR, treatment with a low dose of AVE8134 improved cardiac and vascular function and increased life expectancy without lowering blood pressure. AVE8134 reduced phenylephrine-induced hypertrophy in adult rat cardiomyocytes. In HUVEC, Ser-1177-eNOS phosphorylation but not eNOS expression was increased. In monocytes, AVE8134 increased the expression of CD36 and the macrophage scavenger receptor 1, resulting in enhanced uptake of oxidized LDL.

CONCLUSION

The PPARalpha agonist AVE8134 prevents post-MI myocardial hypertrophy, fibrosis and cardiac dysfunction. AVE8134 has beneficial effects against hypertension-induced organ damages, resulting in decreased mortality. The compound exerts its protective properties by a direct effect on cardiomyocyte hypertrophy, but also indirectly via monocyte signaling and increased endothelial NO production.Acta Pharmacologica Sinica (2009) 30: 935-946; doi: 10.1038/aps.2009.58; published online 8 June 2009.

Defective peroxisomal proliferators activated receptor gamma activity due to dominant-negative mutation synergizes with hypertension to accelerate cardiac fibrosis in mice

Aims

Humans with inactivating mutations in peroxisomal proliferators activated receptor gamma (PPARγ) typically develop a complex metabolic syndrome characterized by insulin resistance, diabetes, lipodystrophy, hypertension, and dyslipidaemia which is likely to increase their cardiovascular risk. Despite evidence that the activation of PPARγ may prevent cardiac fibrosis and hypertrophy, recent evidence has suggested that pharmacological activation of PPARγ causes increased cardiovascular mortality. In this study, we investigated the effects of defective PPARγ function on the development of cardiac fibrosis and hypertrophy in a murine model carrying a human dominant-negative mutation in PPARγ.

Methods and results

Mice with a dominant-negative point mutation in PPARγ (P465L) and their wild-type (WT) littermates were treated with either subcutaneous angiotensin II (AngII) infusion or saline for 2 weeks. Heterozygous P465L and WT mice developed a similar increase in systolic blood pressure, but the mutant mice developed significantly more severe cardiac fibrosis to AngII that correlated with increased expression of profibrotic genes. Both groups similarly increased the heart weight to body weight ratio compared with saline-treated controls. There were no differences in fibrosis between saline-treated WT and P465L mice.

Conclusion

These results show synergistic pathogenic effects between the presence of defective PPARγ and AngII-induced hypertension and suggest that patients with PPARγ mutation and hypertension may need more aggressive therapeutic measures to reduce the risk of accelerated cardiac fibrosis.

Rat Urinary Bladder Carcinogenesis by Dual-Acting PPARalpha + gamma Agonists

Despite clinical promise, dual-acting activators of PPARalpha and gamma (here termed PPARalpha+gamma agonists) have experienced high attrition rates in preclinical and early clinical development, due to toxicity. In some cases, discontinuation was due to carcinogenic effect in the rat urothelium, the epithelial layer lining the urinary bladder, ureters, and kidney pelvis. Chronic pharmacological activation of PPARalpha is invariably associated with cancer in rats and mice. Chronic pharmacological activation of PPARgamma can in some cases also cause cancer in rats and mice. Urothelial cells coexpress PPARalpha as well as PPARgamma, making it plausible that the urothelial carcinogenicity of PPARalpha+gamma agonists may be caused by receptor-mediated effects (exaggerated pharmacology). Based on previously published mode of action data for the PPARalpha+gamma agonist ragaglitazar, and the available literature about the role of PPARalpha and gamma in rodent carcinogenesis, we propose a mode of action hypothesis for the carcinogenic effect of PPARalpha+gamma agonists in the rat urothelium, which combines receptor-mediated and off-target cytotoxic effects. The proposed mode of action hypothesis is being explored in our laboratories, towards understanding the human relevance of the rat cancer findings, and developing rapid in vitro or short-term in vivo screening approaches to faciliate development of new dual-acting PPAR agonist compounds.

Peroxisome proliferator-activated receptors and inflammation: take it to heart

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors acting as key regulators of lipid metabolism as well as modulators of inflammation. The role of PPARalpha and PPARgamma in cardiac ischaemia-reperfusion injury, infarct healing and hypertrophy is the subject of intense research. Due to the later development of PPARdelta-specific ligands, the role of this PPAR isoform in cardiac disease remains to be established. Although many studies point to salutatory effects of PPAR ligands in cardiac disease, the exact molecular mechanism is still largely unsolved. Both the metabolic (via transactivation) and the more recently discovered anti-inflammatory (via transrepression) effects of PPARs are likely to play a role. In this review the reported, and sometimes contradictory, effects of PPAR ligands on ischaemia-reperfusion, infarct healing and cardiac hypertrophy are critically evaluated. In particular the role of inflammation in these disease processes, the ability of PPARs to interfere with pro-inflammatory processes, and the mechanisms of transrepression are discussed. Currently, the significance of PPARs as therapeutic targets in cardiovascular disease is receiving widespread attention. Accordingly, detailed understanding of the mechanisms controlling the activity of these nuclear hormone receptors is essential.

Peroxisome proliferator-activated receptor alpha agonists enhance cardiomyogenesis of mouse ES cells by utilization of a reactive oxygen species-dependent mechanism

Peroxisome proliferator-activated receptors (PPARalpha, -beta and -gamma) are nuclear receptors involved in transcriptional regulation of lipid and energy metabolism. Since the energy demand increases when cardiac progenitor cells are developing rhythmic contractile activity, PPAR activation may play a critical role during cardiomyogenesis of embryonic stem (ES) cells. It is shown that ES cells express PPARalpha, -beta, and -gamma mRNA during differentiation of ES cells towards cardiac cells. Treatment with PPARalpha agonists (WY14643, GW7647, and ciprofibrate) significantly increased cardiomyogenesis and expression of the cardiac genes MLC2a, ANP, MHC-beta, MLC2v, and cardiac alpha-actin. Furthermore, WY14643 increased PPARalpha gene expression and the expression of the cardiogenic transcription factors GATA-4, Nkx2.5, DTEF-1, and MEF 2C. In contrast, the PPARalpha antagonist MK886 decreased cardiomyogenesis, whereas the PPARbeta agonist L-165,041 as well as the PPARgamma agonist GW1929 were without effects. Treatment with PPARalpha, but not PPARbeta, and PPARgamma agonists and MK886, resulted in generation of reactive oxygen species (ROS), which was inhibited in the presence of the NADPH oxidase inhibitors diphenylen iodonium (DPI) and apocynin and the free radical scavengers vitamin E and N-(2-mercapto-propionyl)-glycine (NMPG), whereas the mitochondrial complex I inhibitor rotenone was without effects. The effect of PPARalpha agonists on cardiomyogenesis of ES cells was abolished upon preincubation with free radical scavengers and NADPH oxidase inhibitors, indicating involvement of ROS in PPARalpha, mediated cardiac differentiation. In summary, our data indicate that stimulation of PPARalpha but not PPARbeta and -gamma enhances cardiomyogenesis in ES cells using a pathway that involves ROS and NADPH oxidase activity.