Activation of peroxisome proliferator-activated receptor-α and -γ in auricular tissue from heart failure patients

Peroxisome Proliferator-Activated Receptor-γ Is Critical to Cardiac Fibrosis

Peroxisome proliferator-activated receptor-γ (PPARγ) is a ligand-activated transcription factor belonging to the nuclear receptor superfamily, which plays a central role in regulating lipid and glucose metabolism. However, accumulating evidence demonstrates that PPARγ agonists have potential to reduce inflammation, influence the balance of immune cells, suppress oxidative stress, and improve endothelial function, which are all involved in the cellular and molecular mechanisms of cardiac fibrosis. Thus, in this review we discuss the role of PPARγ in various cardiovascular conditions associated with cardiac fibrosis, including diabetes mellitus, hypertension, myocardial infarction, heart failure, ischemia/reperfusion injury, atrial fibrillation, and several other cardiovascular disease (CVD) conditions, and summarize the developmental status of PPARγ agonists for the clinical management of CVD.

The pathological roles of environmental and redox stresses in cardiovascular diseases

Oxidative stress and inflammation are implicated in cardiovascular diseases such as atherosclerosis, reperfusion injury, hypertension, and heart failure. High levels of oxidative stress resulting from increased cardiac generation of reactive oxygen species (ROS) is thought to contribute to contractile and endothelial dysfunction, apoptosis and necrosis of myocytes, and extracellular matrix remodeling in the heart. ROS activate several transcription factors known as redox-regulated transcription factors, and these transcription factors play important roles in the pathophysiology of cardiovascular diseases. This review focuses on the pathological roles of environmental and redox stresses in cardiovascular diseases, especially severe cardiac dysfunction and the transition from compensated hypertrophy to heart failure. The aryl hydrocarbon receptor (AHR) and NF-E2 p45-related factor (Nrf2) are transcription factors involved in the regulation of drug-metabolizing enzymes. AHR has been studied as a receptor for environmental contaminants and as a mediator of chemical toxicity. However, other roles for AHR in cardiac and vascular development have recently been described. Moreover, Nrf2 protects against oxidative stress by increasing the transcription of genes, including those for several antioxidant enzymes. The roles of these transcription factors, AHR and Nrf2 in angiogenesis are also discussed in this review.

Bilobetin ameliorates insulin resistance by PKA-mediated phosphorylation of PPARα in rats fed a high-fat diet

BACKGROUND AND PURPOSE

The amelioration of insulin resistance by bilobetin is closely related to its hypolipidaemic effect. The aim of the present study was to determine the insulin-sensitizing mechanism of bilobetin by elucidating its effect on lipid metabolism.

EXPERIMENTAL APPROACH

Rats fed a high-fat diet were treated with bilobetin for either 4 or 14 days before applying a hyperinsulinaemic-euglycaemic clamp. Triglyceride and fatty acids labelled with radioactive isotopes were used to track the transportation and the fate of lipids in tissues. The activity of lipid metabolism-related enzymes and β-oxidation rate were measured. Western blot was used to investigate the phosphorylation, translocation and expression of PPARα in several tissues and cultured cells. The location of amino acid residues subjected to phosphorylation in PPARα was also studied.

KEY RESULTS

Bilobetin ameliorated insulin resistance, increased the hepatic uptake and oxidation of lipids, reduced very-low-density lipoprotein triglyceride secretion and blood triglyceride levels, enhanced the expression and activity of enzymes involved in β-oxidation and attenuated the accumulation of triglycerides and their metabolites in tissues. Bilobetin also increased the phosphorylation, nuclear translocation and activity of PPARα accompanied by elevated cAMP level and PKA activity. Threonine-129-alanine and/or serine-163-alanine mutations on the PPARα genes and PKA inhibitors prevented the effects of bilobetin on PPARα. However, cells overexpressing PKA appeared to stimulate the phosphorylation, nuclear translocation and activity of PPARα.

CONCLUSIONS AND IMPLICATIONS

Bilobetin treatment ameliorates hyperlipidaemia, lipotoxicity and insulin resistance in rats by stimulating PPARα-mediated lipid catabolism. PKA activation is crucial for this process.

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 γ 1 (PPARγ1) via the cardiac α-myosin heavy-chain promoter. The PPARγ 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 PPARγ agonist, had no effect on mortality or rhythm in WT mice but further exacerbated the arrhythmic phenotype and increased the mortality in the PPARγ transgenic mice.

CONCLUSIONS

Our findings support an important link between PPARγ activation, cardiomyocyte lipid accumulation, ion channel remodeling, and increased cardiac mortality.

Rosuvastatin added to standard heart failure therapy improves cardiac remodelling in heart failure rats with preserved ejection fraction

AIMS

Although statins may provide potential therapeutic pathways for patients with heart failure with preserved ejection fraction (HFpEF), no studies have evaluated statins in combination with standard HF therapy, which would reflect clinical practice more closely. To address this question, we evaluated whether rosuvastatin added to a standard HF therapy provides additional improvement in cardiac structure and function in rats with hypertensive heart failure (SHHF).

METHODS AND RESULTS

Two-month-old SHHF rats were randomly assigned to four groups: (i) non-treated SHHF rats; (ii) rosuvastatin-treated SHHF rats; (iii) SHHF rats treated with quinapril plus torasemide plus carvedilol (considered as standard HF therapy); and (iv) SHHF rats treated with the combination of standard HF therapy and rosuvastatin. The administration of a standard anti-hypertensive HF therapy to SHHF rats for 17 months attenuated left ventricular (LV) chamber dilatation, cardiac hypertrophy, fibrosis, and inflammation compared with non-treated SHHF rats. Rosuvastatin alone prevented LV dilatation and cardiac inflammation similar to standard HF therapy-treated SHHF, despite being unable to normalize blood pressure (BP) or influence cardiac hypertrophy. However, and importantly, the addition of rosuvastatin to the standard HF therapy further prevented LV dilatation, preserved cardiac function, and normalized inflammation.

CONCLUSION

These data show that the use of rosuvastatin plus a standard HF therapy results in a significant additional improvement in HF and cardiac remodelling in a rat model of HFpEF. These beneficial effects were independent of BP and plasma lipid changes, and seem to be due, at least in part, to decreased myocardial inflammation.

A potential link between peroxisome proliferator-activated receptor signalling and the pathogenesis of arrhythmogenic right ventricular cardiomyopathy

AIMS

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by major fibro-fatty replacement of the right ventricle (RV). We hypothesized that changes in peroxisome proliferator-activated receptor (PPAR) signalling contributed to myocardium fatty accumulation and contractile dysfunction in ARVC.

METHODS AND RESULTS

Real-time quantitative reverse transcriptase-polymerase chain reaction and western blotting were used to assess cardiac expression of PPARalpha and gamma and two of their downstream target genes--medium-chain acyl-CoA dehydrogenase (MCAD) and phosphoenolpyruvate carboxykinase (PEPCK)--in both RV and left ventricle (LV) from five controls and five ARVC patients. In vitro motility assays were used to analyse functional properties of myosin. In the RV, sliding velocity was nearly two-fold lower in ARVC than in controls, whereas a 10% reduction in velocity values was noted between ARVC and non-failing myocardium in the LV. In controls, PPARalpha and MCAD mRNA and protein levels were higher in the RV compared with the LV. In ARVC, the expression of PPARalpha and MCAD mRNA and/or proteins was decreased in both RV and LV. RV from ARVC was also characterized by a dramatic activation of the PPARgamma pathway, as attested by the increase in PPARgamma mRNA and protein (500 and 270%, respectively, each P < 0.001) and by the induction of PEPCK gene. In contrast, the LV of ARVC heart exhibited no changes in the expression of the PPARgamma regulatory pathway compared with control.

CONCLUSION

ARVC is associated with major disturbances in the PPARalpha and PPARgamma signalling pathway in the RV that may contribute to intracellular lipid overload and severe myosin dysfunction.

Ezetimibe reduces plaque inflammation in a rabbit model of atherosclerosis and inhibits monocyte migration in addition to its lipid-lowering effect

BACKGROUND AND PURPOSE

Ezetimibe, a selective inhibitor of intestinal cholesterol absorption, might also suppress inflammatory components of atherogenesis. We have studied the effects of ezetimibe on two characteristics of atherosclerotic plaques (infiltrate and fibrosis) and on expression of inflammatory genes in a rabbit model of accelerated atherosclerosis.

EXPERIMENTAL APPROACH

Femoral atherosclerosis was induced by a combination of endothelial desiccation and atherogenic diet. Animals were randomized to ezetimibe (0.6 mg x kg(-1) x day(-1)), simvastatin (5 mg x kg(-1) x day(-1)), ezetimibe plus simvastatin or no treatment, still on atherogenic diet. A control group of rabbits received normolipidemic diet.

KEY RESULTS

Rabbits fed the normolipidemic diet showed normal plasma lipid levels. Either the normolipidemic diet or drug treatment reduced the intima/media ratio (normolipidemic diet: 22%, ezetimibe: 13%, simvastatin: 27%, ezetimibe + simvastatin: 28%), compared with rabbits with atherosclerosis. Ezetimibe also decreased macrophage content and monocyte chemoattractant protein-1 expression in atherosclerotic lesions. Furthermore, ezetimibe reduced the increased activity of nuclear factor kappaB in peripheral blood leucocytes and plasma C-reactive protein levels in rabbits with atherosclerosis. In THP-1 cells, ezetimibe decreased monocyte chemoattractant protein-1-induced monocyte migration. Importantly, the combination of ezetimibe with simvastatin was associated with a more significant reduction in plaque monocyte/macrophage content and some proinflammatory markers than observed with each drug alone.

CONCLUSIONS AND IMPLICATIONS

Ezetimibe had beneficial effects both on atherosclerosis progression and plaque stabilization and showed additional anti-atherogenic benefits when combined with simvastatin. Its effect on monocyte migration provides a potentially beneficial action, in addition to its effects on lipids.

PPAR-gamma expression in animals subjected to volume overload and chronic Urotensin II administration

Activation of PPAR-gamma through the administration of glitazones has shown promise in preserving function following cardiac injury, although recent evidence has suggested their use may be contraindicated in the case of severe heart failure. This study tested the hypothesis that PPAR-gamma expression increases in a time dependent manner in response to chronic volume overload (VO) induced heart failure. Additionally, we attempted to determine what effect 4 week administration of Urotensin II (UTII) may have on PPAR-gamma expression. VO induced heart failure was produced in Sprague-Dawley rats (n=32) by aorta-caval fistula. Animals were sacrificed at 1, 4, and 14 weeks following shunt creation. In a separate set of experiments, animals were administered 300 pmol/kg/h of UTII for 4 weeks, subjected to 4 weeks of volume overload, or given UTII+VO. Densitometric analysis of left ventricular (LV) protein demonstrated PPAR-gamma expression was significantly ((*)p<0.05) upregulated at 4 and 14 weeks (31.5% and 37%, respectively) post-fistula formation compared to control values. PPAR-gamma activation was decreased in the 4 and 14 week (39.16% and 42.4%, respectively), but not in the 1-week animals, and these changes did not correlate with NF-kappaB activity. Animals given UTII either with or without VO demonstrated increased expression of PPAR-gamma as did animals subjected to 4 week VO alone. Animals given UTII either with or without VO had decreased activity vs. control. These data suggest PPAR-gamma may play a role in the progression of heart failure, however, the exact nature has yet to be determined.