Ligands of the peroxisome proliferator-activated receptors (PPAR-gamma and PPAR-alpha) reduce myocardial infarct size

The current approach into signaling pathways in pulmonary arterial hypertension and their implication in novel therapeutic strategies

Many mediators and signaling pathways, with their downstream effectors, have been implicated in the pathogenesis of pulmonary hypertension. Currently approved drugs, representing an option of specific therapy, target NO, prostacyclin or ET-1 pathways and provide a significant improvement in the symptomatic status of patients and a slower rate of clinical deterioration. However, despite such improvements in the treatment, PAH remains a chronic disease without a cure, the mortality associated with PAH remains high and effective therapeutic regimens are still required. Knowledge about the role of the pathways involved in PAH and their interactions provides a better understanding of the pathogenesis of the disease and may highlight directions for novel therapeutic strategies for PAH. This paper reviews some novel, promising PAH-associated signaling pathways, such as RAAS, RhoA/ROCK, PDGF, PPAR, and TGF, focusing also on their possible interactions with well-established ones such as NO, ET-1 and prostacyclin pathways.

15-deoxy-Δ¹²,¹⁴-PGJ₂ promotes inflammation and apoptosis in cardiomyocytes via the DP2/MAPK/TNFα axis

Background

Prostaglandins (PGs), lipid autacoids derived from arachidonic acid, play a pivotal role during inflammation. PGD₂ synthase is abundantly expressed in heart tissue and PGD₂ has recently been found to induce cardiomyocyte apoptosis. PGD₂ is an unstable prostanoid metabolite; therefore the objective of the present study was to elucidate whether its final dehydration product, 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂, present at high levels in ischemic myocardium) might cause cardiomyocyte damage.

Methods and results

Using specific (ant)agonists we show that 15d-PGJ₂ induced formation of intracellular reactive oxygen species (ROS) and phosphorylation of p38 and p42/44 MAPKs via the PGD₂ receptor DP2 (but not DP1 or PPARγ) in the murine atrial cardiomyocyte HL-1 cell line. Activation of the DP2-ROS-MAPK axis by 15d-PGJ₂ enhanced transcription and translation of TNFα and induced apoptosis in HL-1 cardiomyocytes. Silencing of TNFα significantly attenuated the extrinsic (caspase-8) and intrinsic apoptotic pathways (bax and caspase-9), caspase-3 activation and downstream PARP cleavage and γH2AX activation. The apoptotic machinery was unaffected by intracellular calcium, transcription factor NF-κB and its downstream target p53. Of note, 9,10-dihydro-15d-PGJ₂ (lacking the electrophilic carbon atom in the cyclopentenone ring) did not activate cellular responses. Selected experiments performed in primary murine cardiomyocytes confirmed data obtained in HL-1 cells namely that the intrinsic and extrinsic apoptotic cascades are activated via DP2/MAPK/TNFα signaling.

Conclusions

We conclude that the reactive α,β-unsaturated carbonyl group of 15d-PGJ₂ is responsible for the pronounced upregulation of TNFα promoting cardiomyocyte apoptosis. We propose that inhibition of DP2 receptors could provide a possibility to modulate 15d-PGJ₂-induced myocardial injury.

Redox-dependent anti-inflammatory signaling actions of unsaturated fatty acids

Unsaturated fatty acids are metabolized to reactive products that can act as pro- or anti-inflammatory signaling mediators. Electrophilic fatty acid species, including nitro- and oxo-containing fatty acids, display salutary anti-inflammatory and metabolic actions. Electrophilicity can be conferred by both enzymatic and oxidative reactions, via the homolytic addition of nitrogen dioxide to a double bond or via the formation of α,β-unsaturated carbonyl and epoxide substituents. The endogenous formation of electrophilic fatty acids is significant and influenced by diet, metabolic, and inflammatory reactions. Transcriptional regulatory proteins and enzymes can sense the redox status of the surrounding environment upon electrophilic fatty acid adduction of functionally significant, nucleophilic cysteines. Through this covalent and often reversible posttranslational modification, gene expression and metabolic responses are induced. At low concentrations, the pleiotropic signaling actions that are regulated by these protein targets suggest that some classes of electrophilic lipids may be useful for treating metabolic and inflammatory diseases.

Delayed cardioprotective effects of WY-14643 are associated with inhibition of MMP-2 and modulation of Bcl-2 family proteins through PPAR-α activation in rat hearts subjected to global ischaemia–reperfusion

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors regulating cardiac lipid metabolism and energy homeostasis. Although the activation of PPARs has been implicated in cardioprotection, the molecular mechanisms are largely unexplored. In this study, we aimed to investigate the effect of the PPAR-α agonist WY-14643 (WY), mimicking a delayed effect of preconditioning in rat hearts exposed to acute ischaemia–reperfusion (I/R) 24 h later, and to define whether antioxidative and antiapoptotic mechanisms are involved. Treatment with WY markedly attenuated post-ischaemic contractile dysfunction (as evidenced by the reduced infarct size), the higher left ventricular developed pressure (LVDP) recovery, and the decreased occurrence of arrhythmias. These effects were abolished in the presence of the PPAR-α antagonist MK886. Heme oxygenase-1, a key antioxidative enzyme implicated in cytoprotection, was upregulated in response to WY at baseline, but was markedly reduced after I/R, indicating reduced oxidative stress. WY treatment was also associated with decreased mRNA levels and enzymatic activity of matrix metalloproteinase-2, and increased ratios of Bcl-2:Bax proteins. These results indicate that PPAR-α activation by its selective ligand WY may confer delayed preconditioning-like protection in rat hearts subjected to I/R by modulating oxidative stress, activation of matrix metalloproteinase-2, and expression of Bcl-2 and Bax.

The impact of lifestyle-related risk factors on cardiac response to ischemia and possibilities to restore impaired ischemic tolerance

Risk factors (RF) of cardiovascular diseases associated with modern lifestyle, such as stress, chronically increased blood pressure, hyperglycemia and dyslipidemia have a negative impact on the heart exposed to ischemia: they may facilitate its lethal injury (myocardial infarction) and occurrence of sudden death due to ventricular arrhythmias. On the other hand, some stressful stimuli related to RF including reactive oxygen species, transient episodes of ischemia (hypoxia), high glucose and other may play a dual role in the pathogenesis of ischemia/reperfusion (I/R) injury (IRI). Besides their deleterious effects, these factors may trigger adaptive processes in the heart resulting in greater resistance against IRI, which is also a characteristic feature of the female myocardium. However, sensitivity to ischemia is increasing with age in both genders. Current research indicates that comorbidity related to lifestyle may impair the cardiac response to acute ischemia not only by interference with pathophysiological mechanisms of IRI per se, but via suppression of intrinsic protective mechanisms in the heart and its ability to tolerate the ischemic challenges, although the role of RF has not been unequivocally proven. Moreover, even pathologically altered myocardium need not completely lose its adaptive potential. In addition, increased ischemic tolerance can be induced by the pleiotropic (independent of the primary) effects of some hypolipidemic and antidiabetic drugs, even in the diseased myocardium. This review addresses the issue of the impact of RF on cellular cardioprotective mechanisms and the possibilities to restore adaptive potential in subjects challenged with several RF. Reactivation of adaptive processes in the myocardium taking into consideration gender and age can contribute to optimalization of antiischemic therapy.

Peroxisome-proliferator-activated receptors regulate redox signaling in the cardiovascular system

Peroxisome-proliferator-activated receptors (PPARs) comprise three subtypes (PPARα, δ and γ) to form a nuclear receptor superfamily. PPARs act as key transcriptional regulators of lipid metabolism, mitochondrial biogenesis, and anti-oxidant defense. While their roles in regulating lipid metabolism have been well established, the role of PPARs in regulating redox activity remains incompletely understood. Since redox activity is an integral part of oxidative metabolism, it is not surprising that changes in PPAR signaling in a specific cell or tissue will lead to alteration of redox state. The effects of PPAR signaling are directly related to PPAR expression, protein activities and PPAR interactions with their coregulators. The three subtypes of PPARs regulate cellular lipid and energy metabolism in most tissues in the body with overlapping and preferential effects on different metabolic steps depending on a specific tissue. Adding to the complexity, specific ligands of each PPAR subtype may also display different potencies and specificities of their role on regulating the redox pathways. Moreover, the intensity and extension of redox regulation by each PPAR subtype are varied depending on different tissues and cell types. Both beneficial and adverse effects of PPAR ligands against cardiovascular disorders have been extensively studied by many groups. The purpose of the review is to summarize the effects of each PPAR on regulating redox and the underlying mechanisms, as well as to discuss the implications in the cardiovascular system.

The impact of current and novel anti-diabetic therapies on cardiovascular risk

Type 2 diabetes mellitus (T2DM) has become an overwhelming health condition that is no longer just a threat to developed nations, but to undeveloped nations as well. Current therapies for T2DM are relatively effective in controlling hyperglycemia; examples include metformin, thiazolidinediones, sulfonylurea derivatives, α-glucosidase inhibitors, glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors. Despite their efficacy in controlling hyperglycemia, due to recent findings of increased cardiovascular risk following treatment with either rosiglitazone or intensive glucose lowering, new guidelines from the US FDA recommend that new therapies for diabetes not only improve glycemia, but exert no adverse cardiovascular effects. Based on cardiovascular risk profiles, metformin appears to be the superior anti-diabetic therapy, although studies in humans with glucagon-like peptide-1 receptor agonists are encouraging. As patients with T2DM also often have cardiovascular disease, the increased rigor in drug development should ultimately reduce the health burden of both of these conditions.

MiRNA-711-SP1-collagen-I pathway is involved in the anti-fibrotic effect of pioglitazone in myocardial infarction

Although microRNAs (miRNAs) have been intensively studied in cardiac fibrosis, their roles in drug-mediated anti-fibrotic therapy are still unknown. Previously, Pioglitazone attenuated cardiac fibrosis and increased miR-711 experimentally. We aimed to explore the role and mechanism of miR-711 in pioglitazone-treated myocardial infarction in rats. Our results showed that pioglitazone significantly reduced collagen-I levels and increased miR-711 expression in myocardial infarction heart. Pioglitazone increased the expression of miR-711 in cardiac fibroblasts, and overexpression of miR-711 suppressed collagen-I levels in angiotensin II (Ang II)-treated or untreated cells. Transfection with antagomir-711 correspondingly abolished the pioglitazone-induced reduction in collagen-I levels. Bioinformatics analysis identified SP1, which directly promotes collagen-I synthesis, as the putative target of miR-711. This was confirmed by luciferase assay and western blot analysis. Additionally, increased SP1 expression was attenuated by pioglitazone in myocardial infarction heart. Furthermore, transfection of antagomir-711 attenuated pioglitazone-reduced SP1 expression in cardiac fibroblasts with or without Ang II stimulation. We conclude that pioglitazone up-regulated miR-711 to reduce collagen-I levels in rats with myocardial infarction. The miR-711-SP1-collagen-I pathway may be involved in the anti-fibrotic effects of pioglitazone. Our findings may provide new strategies for miRNA-based anti-fibrotic drug research.

PPAR agonist-induced reduction of Mcp1 in atherosclerotic plaques of obese, insulin-resistant mice depends on adiponectin-induced Irak3 expression

Synthetic peroxisome proliferator-activated receptor (PPAR) agonists are used to treat dyslipidemia and insulin resistance. In this study, we examined molecular mechanisms that explain differential effects of a PPARα agonist (fenofibrate) and a PPARγ agonist (rosiglitazone) on macrophages during obesity-induced atherogenesis. Twelve-week-old mice with combined leptin and LDL-receptor deficiency (DKO) were treated with fenofibrate, rosiglitazone or placebo for 12 weeks. Only rosiglitazone improved adipocyte function, restored insulin sensitivity, and inhibited atherosclerosis by decreasing lipid-loaded macrophages. In addition, it increased interleukin-1 receptor-associated kinase-3 (Irak3) and decreased monocyte chemoattractant protein-1 (Mcp1) expressions, indicative of a switch from M1 to M2 macrophages. The differences between fenofibrate and rosiglitazone were independent of Pparγ expression. In bone marrow-derived macrophages (BMDM), we identified the rosiglitazone-associated increase in adiponectin as cause of the increase in Irak3. Interestingly, the deletion of Irak3 in BMDM (IRAK3^−/− BMDM) resulted in activation of the canonical NFκB signaling pathway and increased Mcp1 protein secretion. Rosiglitazone could not decrease the elevated Mcp1 secretion in IRAK3^−/− BMDM directly and fenofibrate even increased the secretion, possibly due to increased mitochondrial reactive oxygen species production. Furthermore, aortic extracts of high-fat insulin-resistant LDL-receptor deficient mice, with lower adiponectin and Irak3 and higher Mcp1, showed accelerated atherosclerosis. In aggregate, our results emphasize an interaction between PPAR agonist-mediated increase in adiponectin and macrophage-associated Irak3 in the protection against atherosclerosis by PPAR agonists.

Clofibrate PPARα activation reduces oxidative stress and improves ultrastructure and ventricular hemodynamics in no-flow myocardial ischemia

Peroxisome proliferator-activated receptors (PPAR) play a critical physiological role in energy homeostasis, in inflammation, and a protective role in cardiovascular function. We assessed the antioxidant effect of clofibrate-induced Peroxisome proliferator-activated receptor alpha (PPARα) stimulation on ischemic myocardium on myocardial morphology and hemodynamics. Male Wistar rats (300 g) were distributed into the following groups: (1) Sham, (2) myocardial ischemia vehicle treated (MI-V), and (3) myocardial ischemia clofibrate [100 mg/kg/ intraperitoneally) treated (MI-C). Reactive oxygen species (ROS) and lipid peroxidation increased in MI-V, whereas clofibrate prevented this effect. Superoxide dismutase (SOD)-1 and SOD-2 expression increased 4 times upon PPARα stimulation. SOD-1, SOD-2, and catalase activity also increased in response to clofibrate. eNOS mRNA and tetrahydrobiopterin increased in the MI-C group. Clofibrate was able to decrease Angiotensin II (AngII), AngII AT1-receptor, whereas Ang-(1-7) and AngII AT2-receptor expression increased. Assessment of myocardial morphology and cardiac function show that clofibrate improved histological features and hemodynamic parameters. Our results suggest that PPARα stimulation by clofibrate increases the antioxidant defense, leading to improved cardiac function.

Diabetes, perioperative ischaemia and volatile anaesthetics: consequences of derangements in myocardial substrate metabolism

Volatile anaesthetics exert protective effects on the heart against perioperative ischaemic injury. However, there is growing evidence that these cardioprotective properties are reduced in case of type 2 diabetes mellitus. A strong predictor of postoperative cardiac function is myocardial substrate metabolism. In the type 2 diabetic heart, substrate metabolism is shifted from glucose utilisation to fatty acid oxidation, resulting in metabolic inflexibility and cardiac dysfunction. The ischaemic heart also loses its metabolic flexibility and can switch to glucose or fatty acid oxidation as its preferential state, which may deteriorate cardiac function even further in case of type 2 diabetes mellitus.Recent experimental studies suggest that the cardioprotective properties of volatile anaesthetics partly rely on changing myocardial substrate metabolism. Interventions that target at restoration of metabolic derangements, like lifestyle and pharmacological interventions, may therefore be an interesting candidate to reduce perioperative complications. This review will focus on the current knowledge regarding myocardial substrate metabolism during volatile anaesthesia in the obese and type 2 diabetic heart during perioperative ischaemia.

Uremic cardiomyopathy is characterized by loss of the cardioprotective effects of insulin

Chronic kidney disease is associated with a unique cardiomyopathy, characterized by a combination of structural and cellular remodeling, and an enhanced susceptibility to ischemia-reperfusion injury. This may represent dysfunction of the reperfusion injury salvage kinase pathway due to insulin resistance. The susceptibility of the uremic heart to ischemia-reperfusion injury and the cardioprotective effects of insulin and rosiglitazone were investigated. Uremia was induced in Sprague-Dawley rats by subtotal nephrectomy. Functional recovery from ischemia was investigated in vitro in control and uremic hearts ± insulin ± rosiglitazone. The response of myocardial oxidative metabolism to insulin was determined by13C-NMR spectroscopy. Activation of reperfusion injury salvage kinase pathway intermediates (Akt and GSK3β) were assessed by SDS-PAGE and immunoprecipitation. Insulin improved postischemic rate pressure product in control but not uremic hearts, [recovered rate pressure product (%), control 59.6 ± 10.7 vs. 88.9 ± 8.5, P < 0.05; uremic 19.3 ± 4.6 vs. 28.5 ± 10.4, P = ns]. Rosiglitazone resensitized uremic hearts to insulin-mediated cardioprotection [recovered rate pressure product (%) 12.7 ± 7.0 vs. 61.8 ± 15.9, P < 0.05]. Myocardial carbohydrate metabolism remained responsive to insulin in uremic hearts. Uremia was associated with increased phosphorylation of Akt (1.00 ± 0.08 vs. 1.31 ± 0.11, P < 0.05) in normoxia, but no change in postischemic phosphorylation of Akt or GSK3β. Akt2 isoform expression was decreased postischemia in uremic hearts ( P < 0.05). Uremia is associated with enhanced susceptibility to ischemia-reperfusion injury and a loss of insulin-mediated cardioprotection, which can be restored by administration of rosiglitazone. Altered Akt2 expression in uremic hearts post-ischemia-reperfusion and impaired activation of the reperfusion injury salvage kinase pathway may underlie these findings.

The effects of PPAR-γ agonist pioglitazone on renal ischemia/reperfusion injury in rats

BACKGROUND

Acute renal failure due to renal ischemia/reperfusion (IR) injury is a significant clinical problem in cardiovascular surgery. Reactive oxygen species and inflammation play essential roles in the pathophysiology of IR injury. Matrix metalloproteinases (MMPs) are enzymes that play important roles in inflammation and mediate extracellular matrix degradation. It is known that peroxisome proliferator-activated receptor-γ agonists have antiinflammatory and antioxidant effects. In the present study, we aimed to investigate the effects of pioglitazone, a synthetic peroxisome proliferator-activated receptor-γ agonist, on MMPs and oxidative stress in a renal IR injury model in rats.

MATERIALS AND METHODS

Male Wistar albino rats were divided into three groups: control (n = 7), placebo (n = 7; saline/p.o.), and pioglitazone (n = 7; 5 mg/kg/day/p.o.). In the control group, a right nephrectomy was conducted without left renal IR injury. In the placebo and pioglitazone groups, pretreatments were started 3 d before operation. In both groups, left renal pedicles were clamped for 60 min and then reperfused for 60 min. Paraffinized renal sections were evaluated histopathologically. Furthermore, expressions of MMP-2, MMP-9, tissue inhibitor of metalloproteinase (TIMP)-2, superoxide dismutase 1 (SOD1), and p47-phox/p67-phox subunits of NADPH oxidase were determined by immunostaining and scoring.

RESULTS

In the placebo group, renal IR injury induced diffuse tubular necrosis and intense acute inflammation, but pioglitazone inhibited these effects. MMP-2, MMP-9, and TIMP-2 expression increased in the placebo group. However, while MMP-2 and -9 expression decreased, TIMP-2 expression did not change in the pioglitazone group. p47-phox/p67-phox expression increased in the placebo group, but SOD1 expression did not change. Pioglitazone diminished p47-phox/p67-phox expression, whereas it enhanced SOD1 expression.

CONCLUSION

Our results suggest that pioglitazone might be helpful to reduce renal IR injury because of its antiinflammatory and antioxidant effects.

PPAR-alpha activation as a preconditioning-like intervention in rats in vivo confers myocardial protection against acute ischaemia–reperfusion injury: involvement of PI3K–Akt

Peroxisome proliferator-activated receptors (PPAR) regulate the expression of genes involved in lipid metabolism, energy production, and inflammation. Their role in ischaemia–reperfusion (I/R) is less clear, although research indicates involvement of PPARs in some forms of preconditioning. This study aimed to explore the effects of PPAR-α activation on the I/R injury and potential cardioprotective downstream mechanisms involved. Langendorff-perfused hearts of rats pretreated with the selective PPAR-α agonist WY-14643 (WY, pirinixic acid; 3 mg·(kg body mass)·day–1; 5 days) were subjected to 30 min ischaemia – 2 h reperfusion with or without the phosphatidylinositol 3-kinase (PI3K)–Akt inhibitor wortmannin for the evaluation of functional (left ventricular developed pressure, LVDP) recovery, infarct size (IS), and reperfusion-induced arrhythmias. A 2-fold increase in baseline PPAR-α mRNA levels (qPCR) in the WY-treated group and higher post-I/R PPAR-α levels compared with those in untreated controls were accompanied by similar changes in the expression of PPAR-α target genes PDK4 and mCPT-1, regulating glucose and fatty acid metabolism, and by enhanced Akt phosphorylation. Post-ischaemic LVDP restoration in WY-treated hearts reached 60% ± 9% of the pre-ischaemic values compared with 24% ± 3% in the control hearts (P < 0.05), coupled with reduced IS and incidence of ventricular fibrillation that was blunted by wortmannin. Results indicate that PPAR-α up-regulation may confer preconditioning-like protection via metabolic effects. Downstream mechanisms of PPAR-α-mediated cardioprotection may involve PI3K–Akt activation.

Cardioprotection from oxidative stress in the newborn heart by activation of PPARγ is mediated by catalase

Regulation of catalase (CAT) by peroxisome proliferator-activated receptor-γ (PPARγ) was investigated to determine if PPARγ activation provides cardioprotection from oxidative stress caused by hydrogen peroxide (H(2)O(2)) in an age-dependent manner. Left ventricular developed pressure (LVDP) was measured in Langendorff perfused newborn or adult rabbit hearts, exposed to 200μM H(2)O(2), with perfusion of rosiglitazone (RGZ) or pioglitazone (PGZ), PPARγ agonists. We found: (1) H(2)O(2) significantly decreased sarcomere shortening in newborn ventricular cells but not in adult cells. Lactate dehydrogenase (LDH) release occurred earlier in newborn than in adult heart, which may be due, in part, to the lower expression of CAT in newborn heart. (2) RGZ increased CAT mRNA and protein as well as activity in newborn but not in adult heart. GW9662 (PPARγ blocker) eliminated the increased CAT mRNA by RGZ. (3) In newborn heart, RGZ and PGZ treatment inhibited release of LDH in response to H(2)O(2) compared to H(2)O(2) alone. GW9662 decreased this inhibition. (4) LVDP was significantly higher in both RGZ+H(2)O(2) and PGZ+H(2)O(2) groups than in the H(2)O(2) group. Block of PPARγ abolished this effect. In contrast, there was no effect of RGZ in adult. (5) The cardioprotective effects of RGZ were abolished by inhibition of CAT. In conclusion, PPARγ activation is cardioprotective to H(2)O(2)-induced stress in the newborn heart by upregulation of catalase. These data suggest that PPARγ activation may be an effective therapy for the young cardiac patient.

Prenatal rosiglitazone administration to neonatal rat pups does not alter the adult metabolic phenotype

Prenatally administered rosiglitazone (RGZ) is effective in enhancing lung maturity; however, its long-term safety remains unknown. This study aimed to determine the effects of prenatally administered RGZ on the metabolic phenotype of adult rats. Methods. Pregnant Sprague-Dawley rat dams were administered either placebo or RGZ at embryonic days 18 and 19. Between 12 and 20 weeks of age, the rats underwent glucose and insulin tolerance tests and de novo fatty acid synthesis assays. The lungs, liver, skeletal muscle, and fat tissue were processed by Western hybridization for peroxisome proliferator-activated receptor (PPAR)γ, adipose differentiation-related protein (ADRP), and surfactant proteins B (SPB) and C (SPC). Plasma was assayed for triglycerides, cholesterol, insulin, glucagon, and troponin-I levels. Lungs were also morphometrically analyzed. Results. Insulin and glucose challenges, de novo fatty acid synthesis, and all serum assays revealed no differences among all groups. Western hybridization for PPARγ, ADRP, SPB, and SPC in lung, liver, muscle, and fat tissue showed equal levels. Histologic analyses showed a similar number of alveoli and septal thickness in all experimental groups. Conclusions. When administered prenatally, RGZ does not affect long-term fetal programming and may be safe for enhancing fetal lung maturation.

Enhancing the metabolic substrate: PPAR-alpha agonists in heart failure

The prognosis for patients diagnosed with heart failure has significantly improved over the past three decades; however, the disease still confers a high degree of morbidity and mortality. Current treatments for chronic heart failure have focused primarily on blocking neurohormonal signaling and optimizing hemodynamic parameters. Although significant resources have been devoted toward the development of new pharmaceutical therapies for heart failure, few new drugs have been designed to target myocardial metabolic pathways despite growing evidence that on a fundamental level chronic heart failure can be characterized as an imbalance between myocardial energy demand and supply. Disruptions in myocardial energy pathways are evident as the myocardium is unable to generate sufficient amounts of ATP with advancing stages of heart failure. Down-regulation of fatty acid oxidation likely contributes to the phenotype of the "energy starved" heart. Fibrates are small molecule agonists of PPARα pathways that have been used to treat dyslipidemia. Although never used therapeutically in clinical heart failure, PPARα agonists have been shown to enhance fatty acid oxidation, improve endothelial cell function, and decrease myocardial fibrosis and hypertrophy in animal models of heart failure. In light of their excellent clinical safety profile, PPARα agonists may improve outcomes in patients suffering from systolic heart failure by augmenting myocardial ATP production in addition to targeting maladaptive hypertrophic pathways.

Hyperbaric oxygen preconditioning protects cortical neurons against oxygen-glucose deprivation injury: role of peroxisome proliferator-activated receptor-gamma

Ischemic stroke is one of the leading causes of mortality and disability worldwide. Our previous studies have shown that hyperbaric oxygen (HBO) preconditioning can afford significant neuroprotection against cerebral ischemia-reperfusion (I/R) injury in rats. However, it is still unknown whether HBO preconditioning can directly protect primary cultured cortical neurons against oxygen-glucose deprivation (OGD). Peroxisome proliferator-activated receptor-gamma (PPAR γ) plays a central role in the regulation of apoptosis, oxidative stress and inflammation as well as affords significant neuroprotection against cerebral I/R injury. 15-deoxy-∆(12,14)-prostaglandin J(2) (15d-PGJ(2)) is an endogenous ligand with a high affinity for PPAR γ. Recently, some studies demonstrate that activation of PPAR γ mediates lipopolysaccharide and anesthetic preconditioning. In the present study, we firstly found that OGD exposure caused the significant damage of cultured cortical neurons evaluated by cell viability, lactate dehydrogenase (LDH) release and caspase-3 activity, which were significantly ameliorated by HBO preconditioning. Furthermore, HBO preconditioning significantly increased the levels of PPAR γ mRNA and protein, PPAR γ DNA binding activity, 15d-PGJ(2) and antioxidant enzymatic activities in primary cultured cortical neurons with OGD exposure. Moreover, PPAR γ antagonist GW9662 dose-dependently abolished the protection of HBO preconditioning in OGD-exposed neurons. GW9662 blocked the increase of PPAR γ DNA binding activity and antioxidant enzymatic activities, but did not influence the 15d-PGJ(2) level in OGD-exposed neurons with HBO preconditioning. However, the cyclooxygenase (COX)-2 inhibitor NS-398 blocked the production of 15d-PGJ(2) in OGD-exposed neurons with HBO preconditioning. In addition, 15d-PGJ(2) preconditioning could also protect cultured neurons against OGD injury. These results demonstrate that HBO preconditioning has directly beneficial effects on ODG-exposed cortical neurons by the activation of PPAR γ subsequent to the production of 15d-PGJ(2), which in turn increases the downstream antioxidant enzymatic activities.

Postischemic cardiac recovery in heme oxygenase-1 transgenic ischemic/reperfused mouse myocardium

Heme oxygenase-1 (HO-1) transgenic mice (Tg) were created using a rat HO-1 genomic transgene. Transgene expression was detected by RT-PCR and Western blots in the left ventricle (LV), right ventricle (RV) and septum (S) in mouse hearts, and its function was demonstrated by the elevated HO enzyme activity. Tg and non-transgenic (NTg) mouse hearts were isolated and subjected to ischemia/reperfusion. Significant post-ischemic recovery in coronary flow (CF), aortic flow (AF), aortic pressure (AOP) and first derivative of AOP (AOPdp/dt) were detected in the HO-1 Tg group compared to the NTg values. In HO-1 Tg hearts treated with 50 μmol/kg of tin protoporphyrin IX (SnPPIX), an HO enzyme inhibitor, abolished the post-ischemic cardiac recovery. HO-1 related carbon monoxide (CO) production was detected in NTg, HO-1 Tg and HO-1 Tg + SnPPIX treated groups, and a substantial increase in CO production was observed in the HO-1 Tg hearts subjected to ischemia/reperfusion. Moreover, in ischemia/reperfusion-induced tissue Na⁺ and Ca²⁺ gains were reduced in HO-1 Tg group in comparison with the NTg and HO-1 Tg + SnPPIX treated groups; furthermore K⁺ loss was reduced in the HO-1 Tg group. The infarct size was markedly reduced from its NTg control value of 37 ± 4% to 20 ± 6% (P < 0.05) in the HO-1 Tg group, and was increased to 47 ± 5% (P < 0.05) in the HO-1 knockout (KO) hearts. Parallel to the infarct size reduction, the incidence of total and sustained ventricular fibrillation were also reduced from their NTg control values of 92% and 83% to 25% (P < 0.05) and 8% (P < 0.05) in the HO-1 Tg group, and were increased to 100% and 100% in HO-1 KO^−/− hearts. Immunohistochemical staining of HO-1 was intensified in HO-1 Tg compared to the NTg myocardium. Thus, the HO-1 Tg mouse model suggests a valuable therapeutic approach in the treatment of ischemic myocardium.

Postnatal rosiglitazone administration to neonatal rat pups does not alter the young adult metabolic phenotype

BACKGROUND

Rosiglitazone (RGZ), a peroxisome proliferator-activated receptor-γ (PPARγ) agonist, significantly enhances lung maturation without affecting blood biochemical and metabolic profiles in the newborn period. However, whether this exposure to RGZ in neonatal life alters the adult metabolic phenotype is not known.

OBJECTIVE

To determine the effects of early postnatal administration of RGZ on the young adult metabolic phenotype.

METHODS

Newborn rat pups were administered either saline or RGZ for the first 7 days of life. At 11-14 weeks, glucose and insulin tolerance tests and deuterium labeling were performed. Blood and tissues were analyzed for various metabolic parameters.

RESULTS

Overall, there was no effect of early postnatal RGZ administration on young adult body weight, glucose and insulin tolerance, plasma cholesterol and triglyceride profiles, insulin, glucagon, cardiac troponin, fatty acid synthesis, or tissue adipogenic differentiation.

CONCLUSIONS

Treatment with RGZ in early neonatal life does not alter later developmental metabolic programming or lead to an altered metabolic phenotype in the young adult, further re-enforcing the safety of PPARγ agonists as a novel lung-protective strategy.

Rosiglitazone regulates c-reactive protein-induced inflammatory responses via glucocorticoid receptor-mediated inhibition of p38 mitogen-activated protein kinase-toll-like receptor 4 signal pathway in vascular smooth muscle cells

C-reactive protein (CRP) activates toll-like receptor 4 (TLR4) to initiate inflammatory response involved in the pathogenesis of atherosclerosis through mitogen-activated protein kinase (MAPK) signal pathways. Rosiglitazone, a synthetic peroxisome proliferator-activated receptor γ (PPARγ) agonist, is considered to be an important inhibitor of the inflammatory response. The present study was to explore the effect of rosiglitazone on the CRP-induced inflammatory responses and the related signal pathway in vascular smooth muscle cells (VSMCs). The results showed that rosiglitazone reduced the expressions of proinflammatory cytokines, such as vascular endothelial growth factor-A and inducible nitric oxide synthase, and enhanced the expression or activation of anti-inflammatory transcription factors including PPARγ and glucocorticoid receptor (GR) in VSMCs in response to CRP. The further investigations indicated that rosiglitazone inhibited CRP-induced TLR4 expression and p38 MAPK phosphorylation in VSMCs, and TLR4 knockdown potentiated the inhibitory effects of rosiglitazone on vascular endothelial growth factor-A and inducible nitric oxide synthase expressions. In addition, GR antagonist RU486 but not PPARγ inhibitor GW9662 remarkably weakened the inhibitory effects of rosiglitazone on CRP-induced TLR4 expression and p38 phosphorylation in VSMCs. But GW9662 did not affect rosiglitazone-induced GR phosphorylation. These suggest that rosiglitazone exerts its anti-inflammatory effect through activating GR and subsequently inhibiting p38 MAPK-TLR4 signaling pathway in CRP-stimulated VSMCs.

The potential effects of anti-diabetic medications on myocardial ischemia-reperfusion injury

Heart disease and stroke account for 65% of the deaths in people with diabetes mellitus (DM). DM and hyperglycemia cause systemic inflammation, endothelial dysfunction, a hypercoagulable state with impaired fibrinolysis and increased platelet degranulation, and reduced coronary collateral blood flow. DM also interferes with myocardial protection afforded by preconditioning and postconditioning. Newer anti-diabetic agents should not only reduce serum glucose and HbA1c levels, but also improve cardiovascular outcomes. The older sulfonylurea agent, glyburide, abolishes the benefits of ischemic and pharmacologic preconditioning, but newer sulfonylurea agents, such as glimepiride, may not interfere with preconditioning. GLP-1 analogs and sitagliptin, an oral dipeptidyl peptidase IV inhibitor, limit myocardial infarct size in animal models by increasing intracellular cAMP levels and activating protein kinase A, whereas metformin protects the heart by activating AMP-activated protein kinase. Both thiazolidinediones (rosiglitazone and pioglitazone) limit infarct size in animal models. The protective effect of pioglitazone is dependent on downstream activation of cytosolic phospholipase A(2) and cyclooxygenase-2 with subsequent increased production of 15-epi-lipoxin A(4), prostacyclin and 15-d-PGJ(2). We conclude that agents used to treat DM have additional actions that have been shown to affect the ability of the heart to protect itself against ischemia-reperfusion injury in preclinical models. However, the effects of these agents in doses used in the clinical setting to minimize ischemia-reperfusion injury and to affect clinical outcomes in patients with DM have yet to be shown. The clinical implications as well as the mechanisms of protection should be further studied.

The contribution of prostaglandins versus prostacyclin in ventricular remodeling during heart failure

Although the role of Cox-2 in the heart's response to physiologic stress remains controversial (i.e. expression in myocytes versus other resident myocardial cells) the ever expanding role of prostanoids in multiple models of heart failure cannot be denied. Due to the fact that prostanoids are metabolized rather quickly (half life of seconds to minutes) it is believed these signaling mediators act in a paracrine fashion at the site of production. Evidence to date is quite convincing that these bioactive lipid derivatives are involved in physiologic homeostatic regulation as well as beneficial and maladaptive ventricular remodeling in heart failure. Thus, this review will assess the direct contribution of each PG on remodeling in the left ventricle (e.g. hypertrophy, functional effects, and fibrosis).

15-Deoxy-Δ¹²,¹⁴-prostaglandin J₂, an electrophilic lipid mediator of anti-inflammatory and pro-resolving signaling

15-deoxy-Δ(12,14)-prostagandin J(2) (15d-PGJ2) is produced in the inflamed cells and tissues as a consequence of upregulation of cyclooxygenase-2 (COX-2). 15d-PGJ2 is known to be the endogenous ligand of peroxisome proliferator-activated receptor gamma (PPARγ) with multiple physiological properties. Though one of the terminal products of the COX-2-catalyzed reactions, this cyclopentenone prostaglandin exerts potent anti-inflammatory actions, in part, by antagonizing the activities of pro-inflammatory transcription factors, such as NF-κB, STAT3, and AP-1, while stimulating the anti-inflammatory transcription factor Nrf2. These effects are not necessarily dependent on its activation of PPARγ, but often involves direct interaction with the above signaling molecules and their regulators. The locally produced 15d-PGJ2 is also involved in the resolution of inflammatory responses. Thus, 15d-PGJ2, especially formed during the late phase of inflammation, might inhibit cytokine secretion and other events by antigen-presenting cells like dendritic cells or macrophages. 15d-PGJ2 can also affect the priming and effector functions of T lymphocytes and induce their apoptotic cell death. These represent a negative feedback explaining how once-initiated immunologic and inflammatory responses are switched off and terminated. In this context, 15d-PGJ2 and its synthetic derivatives have therapeutic potential for the treatment of inflammatory disorders.

To Live or to Die: Prosurvival Activity of PPARgamma in Cancers

The role of PPARγ in tumorigenesis is controversial. In this article, we review and analyze literature from the past decade that highlights the potential proneoplastic activity of PPARγ. We discuss the following five aspects of the nuclear hormone receptor and its agonists: (1) relative expression of PPARγ in human tumor versus normal tissues; (2) receptor-dependent proneoplastic effects; (3) impact of PPARγ and its agonists on tumors in animal models; (4) clinical trials of thiazolidinediones (TZDs) in human malignancies; (5) TZDs as chemopreventive agents in epidemiology studies. The focus is placed on the most relevant in vivo animal models and human data. In vitro cell line studies are included only when the effects are shown to be dependent on the PPARγ receptor.

Telmisartan, a dual ARB/partial PPAR-γ agonist, protects myocardium from ischaemic reperfusion injury in experimental diabetes

AIM

Apart from its angiotensin receptor blocker (ARB) activity, telmisartan is also a partial agonist of peroxisome proliferator-activated receptor gamma (PPAR-γ). Therefore, we assessed whether telmisartan treatment attenuates myocardial ischaemia/reperfusion (I/R) injury in diabetic rats through PPAR-γ pathway.

METHODS

Diabetic rats were randomized to receive vehicle (sham and I/R), telmisartan (10 mg/kg/day, orally), PPAR-γ antagonist GW9662 (1 mg/kg/day, intraperitoneally) or both for 14 days. On 15th day, excluding sham group, left anterior descending coronary artery occlusion was performed for 45 min followed by 1 h of reperfusion. Haemodynamic, biochemical, histopathological, ultrastructural, immunohistochemical (Bax and Bcl-2 protein), TUNEL positivity, infarct size and western blot studies were performed.

RESULTS

Telmisartan treatment significantly improved cardiac function by normalizing mean arterial pressure, left ventricular pressure (±LVdP/dt(max) , a marker of myocardial contraction and relaxation), by decreasing left ventricular end-diastolic pressure (a marker of preload, 3.7 ± 0.41 vs. 7.3 ± 0.89, p < 0.001) and percent infarct area (37.52 ± 5.83 vs. 46.27 ± 3.20, p < 0.01) as compared to diabetic I/R group. Interestingly, GW9662 worsens the I/R injury (percent infarct area, 54.38 ± 6.48 vs. 46.27 ± 3.20, p < 0.01), whereas telmisartan with GW9662 (percent infarct area, 41.16 ± 8.23 vs. 46.27 ± 3.20, p < 0.05) showed lesser significant results as compared to telmisartan alone. Additionally, telmisartan significantly ameliorates activities of endogenous antioxidants, creatine kinase-MB isoenzyme, lactate dehydrogenase and prevented the increase of tumour necrosis factor-alpha and malondialdehyde in myocardium. Furthermore, telmisartan also decreased Bax expression (4.45 ± 1.24% vs. 10.25 ± 0.96%, p < 0.01), number of TUNEL-positive cells (6.2 ± 0.98% vs. 13.0 ± 1.6, p < 0.01), inflammation, myonecrosis and increased Bcl-2 expression (5.45 ± 0.15% vs. 1.24 ± 0.3%, p < 0.01). On the other hand, GW9662 treatment alone increased the Bax expression, TUNEL positivity and decreased Bcl-2 expression. Telmisartan protective effects were partially attenuated by a co-administration with GW9662. Western blot analysis showed that telmisartan treatment enhanced PPAR-γ expression, whereas GW9662 decreased it in myocardium.

CONCLUSIONS

In addition to the class effect of ARBs, telmisartan has a beneficial effect in I/R injury in diabetic rats in part because of activation of PPAR-γ.

Mediterranean diet and cardioprotection: the role of nitrite, polyunsaturated fatty acids, and polyphenols

The continually increasing rate of myocardial infarction (MI) in the Western world at least partly can be explained by a poor diet lacking in green vegetables, fruits, and fish and enriched in food that contains saturated fat. In contrast, a number of epidemiologic studies provide strong evidence highlighting the cardioprotective benefits of the Mediterranean diet enriched in green vegetables, fruits, fish, and grape wine. Regular consumption of these products leads to an accumulation of nitrate/nitrite/NO, polyunsaturated fatty acids (PUFA), and polyphenolic compounds, such as resveratrol, in the human body. Studies have confirmed that these constituents are bioactive exogenous mediators, which induce strong protection against MI. The aim of this review is to provide a critical, in-depth analysis of the cardioprotective pathways mediated by nitrite/NO, PUFA, and phenolic compounds of grape wines discovered in the recent years, including cross-talk between different mechanisms and compounds. Overall, these findings may facilitate the design and synthesis of novel therapeutic tools for the treatment of MI.

Management of cardiac fibrosis in diabetic rats; the role of peroxisome proliferator activated receptor gamma (PPAR-gamma) and calcium channel blockers (CCBs)

BACKGROUND

Diabetes mellitus (DM) and hypertension (HTN) are accused of being responsible for the development of the cardiac fibrosis due to severe cardiomyopathy.

METHODS

Blood glucose (BG) test was carried out, lipid concentrations, tumor necrosis factor alpha (TNF-α), transforming growth factor beta (TGF-β), matrix metalloproteinase (MMP-2), collagen-I and collagen-III were measured in male Albino rats weighing 179-219 g. The rats were divided into five groups, kept on either control diet or high fat diet (HFD), and simultaneously treated with rosiglitazone (PPAR-gamma) only for one group with 3 mg/kg/day via oral route for 30 days, and with rosiglitazone and felodipine combination for another group with 3 mg/kg/day and 5 mg/kg/day, respectively via oral route for 30 days.

RESULTS

Diabetic hypertensive (DH) rats which fed on a HFD, injected with streptozotocin (STZ) (i.p.) and obstruction for its right kidney was occurred develop hyperglycemia, hypertension, cardiac fibrosis, hypertriglyceridemia, hypercholesterolemia, increased TNF-α, increased TGF-β, decreased MMP-2, increased collagen-I and increased collagen-III, when compared to rats fed on control diet. Treating the DH rats with rosiglitazone only causes a significant decrease for BG levels by 52.79%, triglycerides (TGs) by 24.05%, total cholesterol (T-Chol) by 30.23%, low density lipoprotein cholesterol (LDL-C) by 40.53%, TNF-α by 20.81%, TGF-β by 46.54%, collagen-I by 48.11% and collagen-III by 53.85% but causes a significant increase for MMP-2 by 272.73%. Moreover, Treating the DH rats with rosiglitazone and felodipine combination causes a significant decrease for BG levels by 61.08%, blood pressure (BP) by 16.78%, TGs by 23.80%, T-Chol by 33.27%, LDL-C by 45.18%, TNF-α by 22.82%, TGF-β by 49.31%, collagen-I by 64.15% and collagen-III by 53.85% but causes a significant increase for MMP-2 by 290.91%. Rosiglitazone alone failed to decrease the BP in DH rats in the current dosage and duration.

CONCLUSION

Our results indicate that the co-existence of diabetes and hypertension could induce cardiomyopathy which could further result in cardiac fibrosis, and that combination treatment with rosiglitazone and felodipine has a great protective role against the metabolic abnormalities, meanwhile, the treatment with rosiglitazone alone has a protective role with a minimal effect against these abnormalities and has no effect on decreasing BP in these cases which may lead to coronary artery diseases (CADs) in future.

PPARs as therapeutic targets in cardiovascular disease

IMPORTANCE OF THE FIELD

The role of peroxisome proliferator-activated receptors PPARα, PPARδ and PPARγ in cardiovascular disease is receiving widespread attention. As ligand-activated nuclear receptors, they play a role in regulation of lipid and glucose metabolism. This feature of the PPARs has been successfully exploited to treat systemic metabolic diseases, like hyperlipidemia and type-2 diabetes. Indirectly, their lipid lowering effect also leads to a reduction of the risk for cardiovascular diseases, primarily atherosclerosis.

AREAS COVERED IN THIS REVIEW

The pleiotropic effects of each of the PPAR isotypes on vascular and cardiac disease are discussed, with special emphasis on the molecular mechanism of action and on preclinical observations. The mechanism underlying the beneficial effect of PPARs is not confined to whole body metabolism, but also includes modulation of other vital processes, such as inflammation and cell fate (proliferation, differentiation, apoptosis).

WHAT THE READER WILL GAIN

A large body of preclinical studies indicates that, in addition to their effect on atherogenesis, PPAR ligands also impact on ischemic heart disease and the development of cardiac failure. It remains to be established to what extent these intriguing observations can be translated into clinical practice.

TAKE HOME MESSAGE

The versatile mechanism of action extends the potential therapeutic profile of the PPARs enormously. Conversely, this versatility makes it harder to attain a specific therapeutic effect, without increasing the risk of undesirable side effects. The future challenge will be to design PPAR-based therapeutic strategies that minimize the detrimental side effects.

Pioglitazone limits myocardial infarct size, activates Akt, and upregulates cPLA2 and COX-2 in a PPAR-γ-independent manner

Pioglitazone (PIO), a PPAR-γ agonist, limits myocardial infarct size by activating Akt and upregulating cytosolic phospholipase A(2) (cPLA(2)) and cyclooxygenase (COX)-2. However, PIO has several PPAR-γ-independent effects. We assessed whether PIO limits myocardial infarct size in PPAR-γ-knockout mice, attenuates hypoxia-reoxygenation injury and upregulates P-Akt, cPLA(2), and COX-2 expression in PPAR-γ-knockout cardiomyocytes. Cardiac-specific inducible PPAR-γ knockout mice were generated by crossing αMHC-Cre mice to PPAR-γ(loxp/loxp) mice. PPAR-γ deletion was achieved after 7 days of intraperitoneal tamoxifen (20 mg/kg/day) administration. Mice received PIO (10 mg/kg/day), or vehicle, for 3 days and underwent coronary occlusion (30 min) followed by reperfusion (4 h). We assessed the area at risk by blue dye and infarct size by TTC. Cultured adult cardiomyocytes of PPAR-γ(loxp/loxp/cre) mice without or with pretreatment with tamoxifen were incubated with or without PIO and subjected to 2 h hypoxia/2 h reoxygenation. Cardiac-specific PPAR-γ knockout significantly increased infarct size. PIO reduced infarct size by 51% in PPAR-γ knockout mice and by 55% in mice with intact PPAR-γ. Deleting the PPAR-γ gene increased cell death in vitro. PIO reduced cell death in cells with and without intact PPAR-γ. PIO similarly increased myocardial Ser-473 P-Akt, cPLA(2), and COX-2 levels after hypoxia/reoxygenation in cells with and without intact PPAR-γ. PIO limited infarct size in mice in a PPAR-γ-independent manner. PIO activated Akt, increased the expression of cPLA(2) and COX-2, and protected adult cardiomyocytes against the effects of hypoxia/reoxygenation independent of PPAR-γ activation.

Bardoxolone methyl (BARD) ameliorates ischemic AKI and increases expression of protective genes Nrf2, PPARγ, and HO-1

Ischemic acute kidney injury (AKI) triggers expression of adaptive (protective) and maladaptive genes. Agents that increase expression of protective genes should provide a therapeutic benefit. We now report that bardoxolone methyl (BARD) ameliorates ischemic murine AKI as assessed by both renal function and pathology. BARD may exert its beneficial effect by increasing expression of genes previously shown to protect against ischemic AKI, NF-E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor-γ (PPARγ), and heme oxygenase 1 (HO-1). Although we found that BARD alone or ischemia-reperfusion alone increased expression of these genes, the greatest increase occurred after the combination of both ischemia-reperfusion and BARD. BARD had a different mode of action than other agents that regulate PPARγ and Nrf2. Thus we report that BARD regulates PPARγ, not by acting as a ligand but by increasing the amount of PPARγ mRNA and protein. This should increase ligand-independent effects of PPARγ. Similarly, BARD increased Nrf2 mRNA; this increased Nrf2 protein by mechanisms in addition to the prolongation of Nrf2 protein half-life previously reported. Finally, we localized expression of these protective genes after ischemia and BARD treatment. Using double-immunofluorescence staining for CD31 and Nrf2 or PPARγ, we found increased Nrf2 and PPARγ on glomerular endothelia in the cortex; Nrf2 was also present on cortical peritubular capillaries. In contrast, HO-1 was localized to different cells, i.e., tubules and interstitial leukocytes. Although Nrf2-dependent increases in HO-1 have been described, our data suggest that BARD's effects on tubular and leukocyte HO-1 during ischemic AKI may be Nrf2 independent. We also found that BARD ameliorated cisplatin nephrotoxicity.

Targeting fatty acid and carbohydrate oxidation--a novel therapeutic intervention in the ischemic and failing heart

Cardiac ischemia and its consequences including heart failure, which itself has emerged as the leading cause of morbidity and mortality in developed countries are accompanied by complex alterations in myocardial energy substrate metabolism. In contrast to the normal heart, where fatty acid and glucose metabolism are tightly regulated, the dynamic relationship between fatty acid β-oxidation and glucose oxidation is perturbed in ischemic and ischemic-reperfused hearts, as well as in the failing heart. These metabolic alterations negatively impact both cardiac efficiency and function. Specifically there is an increased reliance on glycolysis during ischemia and fatty acid β-oxidation during reperfusion following ischemia as sources of adenosine triphosphate (ATP) production. Depending on the severity of heart failure, the contribution of overall myocardial oxidative metabolism (fatty acid β-oxidation and glucose oxidation) to adenosine triphosphate production can be depressed, while that of glycolysis can be increased. Nonetheless, the balance between fatty acid β-oxidation and glucose oxidation is amenable to pharmacological intervention at multiple levels of each metabolic pathway. This review will focus on the pathways of cardiac fatty acid and glucose metabolism, and the metabolic phenotypes of ischemic and ischemic/reperfused hearts, as well as the metabolic phenotype of the failing heart. Furthermore, as energy substrate metabolism has emerged as a novel therapeutic intervention in these cardiac pathologies, this review will describe the mechanistic bases and rationale for the use of pharmacological agents that modify energy substrate metabolism to improve cardiac function in the ischemic and failing heart. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

Fish oil decreases inflammation and reduces cardiac remodeling in rosiglitazone treated aging mice

Clinical studies suggest that rosiglitazone (RSG) treatment may increase the incidence of heart failure in diabetic patients. In this study, we examined whether a high corn oil diet with RSG treatment in insulin resistant aging mice exerted metabolic and pro-inflammatory effects that stimulate cardiac dysfunction. We also evaluated whether fish oil attenuated these effects. Female C57BL/6J mice (13 months old) were divided into 5 groups: (1) lean control (LC), (2) corn oil, (3) fish oil, (4) corn oil+RSG and (5) fish oil+RSG. Mice fed a corn oil enriched diet and RSG developed hypertrophy of the left ventricle (LV) and decreased fractional shortening, despite a significant increase in total body lean mass. In contrast, LV hypertrophy was prevented in RSG treated mice fed a fish oil enriched diet. Importantly, hyperglycemia was controlled in both RSG groups. Further, fish oil+RSG decreased LV expression of atrial and brain natriuretic peptides, fibronectin and the pro-inflammatory cytokines interleukin-6 and tumor necrosis factor-α, concomitant with increased interleukin-10 and adiponectin levels compared to the corn oil+RSG group. Fish oil+RSG treatment suppressed inflammation, increased serum adiponectin, and improved fractional shortening, attenuating the cardiac remodeling seen in the corn oil+RSG diet fed C57BL/6J insulin resistant aging mice. Our results suggest that RSG treatment has context-dependent effects on cardiac remodeling and serves a negative cardiac role when given with a corn oil enriched diet.

Activation of peroxisome-proliferator-activated receptors α and γ mediates remote ischemic preconditioning against myocardial infarction in vivo

Remote ischemic preconditioning (remote IPC) elicits a protective cardiac phenotype against myocardial ischemic injury. The remote stimulus has been hypothesized to act on major signaling pathways; however, its molecular targets remain largely undefined. We hypothesized that remote IPC exerts its effects by activating the peroxisome-proliferator-activated receptors (PPARs) α and γ, which have been previously implicated in cardioprotective signaling. Male New Zealand white rabbits (n = 78) were subjected to a 30-min coronary artery occlusion followed by three hours of reperfusion. Three cycles of remote IPC consisting of 10-min renal ischemia/reperfusion were performed. The animals either received the PPARα-antagonist GW6471 or the PPARγ-antagonist GW9662 alone or combined with remote IPC. Infarct size was determined gravimetrically. Tissue levels of 15d-prostaglandin J(2) (15d-PGJ(2)), as well as the PPAR DNA binding were measured using specific assays. Reverse transcriptase polymerase chain reaction was used to analyze changes in endothelial nitric oxide synthase or inducible nitric oxide synthase (iNOS) mRNA expression in relative quantity (RQ). Data are mean ± SD. As a result, remote IPC significantly reduced the myocardial infarct size (42.2 ± 4.9%* versus 61 ± 1.9%), accompanied by an increased PPAR DNA-binding (189.6 ± 19.8RLU* versus 44.4 ± 9RLU), increased iNOS expression (3.5 ± 1RQ* versus 1RQ), as well as 15d-PGJ(2) levels (179.7 ± 7.9 pg/mL* versus 127.9 ± 7.6 pg/mL). The protective response elicited by remote IPC, as well as the accompanying molecular changes were abolished by inhibiting PPARα (56.8 ± 4.7%; 61.1 ± 14.2RLU; and 1.91 ± 0.96RQ, respectively) or PPARγ (57.4 ± 3.3%; 52.7 ± 16.9RLU; and 1.54 ± 0.25RQ, respectively). (*Significantly different from control P < 0.05). In conclusion, the obtained results indicate that both PPARα and PPARγ play an essential role in remote IPC against myocardial infarction, impinging on the transcriptional control of iNOS expression.

Redox regulation of soluble epoxide hydrolase by 15-deoxy-delta-prostaglandin J2 controls coronary hypoxic vasodilation

RATIONALE

15-Deoxy-Δ-prostaglandin (15d-PG)J(2) is an electrophilic oxidant that dilates the coronary vasculature. This lipid can adduct to redox active protein thiols to induce oxidative posttranslational modifications that modulate protein and tissue function.

OBJECTIVE

To investigate the role of oxidative protein modifications in 15d-PGJ(2)-mediated coronary vasodilation and define the distal signaling pathways leading to enhanced perfusion.

METHODS AND RESULTS

Proteomic screening with biotinylated 15d-PGJ(2) identified novel vascular targets to which it adducts, most notably soluble epoxide hydrolase (sEH). 15d-PGJ(2) inhibited sEH by specifically adducting to a highly conserved thiol (Cys521) adjacent to the catalytic center of the hydrolase. Indeed a Cys521Ser sEH "redox-dead" mutant was resistant to 15d-PGJ(2)-induced hydrolase inhibition. 15d-PGJ(2) dilated coronary vessels and a role for hydrolase inhibition was supported by 2 structurally different sEH antagonists each independently inducing vasorelaxation. Furthermore, 15d-PGJ(2) and sEH antagonists also increased coronary effluent epoxyeicosatrienoic acids consistent with their vasodilatory actions. Indeed 14,15-EET alone induced relaxation and 15d-PGJ(2)-mediated vasodilation was blocked by the EET receptor antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE). Additionally, the coronary vasculature of sEH-null mice was basally dilated compared to wild-type controls and failed to vasodilate in response to 15d-PGJ(2). Coronary vasodilation to hypoxia in wild-types was accompanied by 15d-PGJ(2) adduction to and inhibition of sEH. Consistent with the importance of hydrolase inhibition, sEH-null mice failed to vasodilate during hypoxia.

CONCLUSION

This represents a new paradigm for the regulation of sEH by an endogenous lipid, which is integral to the fundamental physiological response of coronary hypoxic vasodilation.

Peroxisome-proliferator-activated receptor γ mediates the second window of anaesthetic-induced preconditioning

The second window of anaesthetic-induced preconditioning (APC) is afforded by the interplay of multiple signalling pathways, whereas a similar protective response is mediated by peroxisome-proliferator-activated receptor γ (PPARγ) agonists. However, a possible role of this nuclear receptor during APC has not been studied to date. We investigated the hypothesis that the second window of APC is mediated by the activation of PPARγ. New Zealand White rabbits (n = 48) were subjected to 30 min of coronary artery occlusion followed by 3 h of reperfusion. The animals received desflurane (1.0 minimal alveolar concentration), the PPARγ antagonist GW9662, as well as the combined application of both, respectively, 24 h prior to coronary artery occlusion. Infarct size was determined gravimetrically; tissue levels of 15-deoxy-(12,14)-prostaglandin J(2) (15d-PGJ(2)) and nitrite/nitrate (NO(x)), as well as PPAR DNA binding were measured using specific assays. Data are presented as means ± s.e.m. Desflurane led to a reduced myocardial infarct size (41.7 ± 2.5 versus 61.8 ± 2.8%, P < 0.05), accompanied by significantly increased PPAR DNA binding (289.9 ± 33 versus 102.9 ± 18 relative light units, P < 0.05), as well as elevated tissue levels of 15d-PGJ(2) (224.4 ± 10.2 versus 116.9 ± 14.2 pg ml(-1), P < 0.05) and NO(x) (14.9 ± 0.7 versus 5.4 ± 0.7 μm, P < 0.05). Pharmacological inhibition of PPARγ abolished these protective effects, resetting the infarct size (56.5 ± 2.9%), as well as PPAR DNA-binding activity (91.2 ± 31 relative light units) and NO(x) tissue levels (5.9 ± 0.9 μm) back to control levels. Desflurane governs a second window of APC by increasing the production of 15d-PGJ(2), subsequently activating PPARγ, resulting in a diminished myocardial infarct size by increasing the downstream availability of NO.

Activation of peroxisome proliferator-activated receptor-beta/delta attenuates myocardial ischemia/reperfusion injury in the rat

Peroxisome proliferator-activated receptor-beta/delta (PPAR-beta/delta) is a transcription factor that belongs to the PPAR nuclear hormone receptor family. There is little information about the effects of the immediate administration of specific ligands of PPAR-beta/delta (e.g., GW0742) in animal models of myocardial I/R injury. Using a rat model of regional myocardial I/R in vivo, we have investigated the effects of immediate administration of GW0742 on myocardial infarct size. Male Wistar rats were subjected to 25 min of regional ischemia followed by 2 h of reperfusion and treated with GW0742 (3, 30, or 300microg/kg i.v. given at 30 min before ischemia and again at the start of reperfusion). Higher doses (30 or 300 microg/kg i.v.) of GW0742 caused a reduction in infarct size, whereas the lowest dose used was not effective. The degree of cardioprotection was similar when GW0742 (30 microg/kg i.v.) was given on reperfusion alone. The reduction in infarct size afforded by GW0742 was not reduced by the competitive irreversible PPAR-alpha antagonist GW6471 (1 mg/kg i.v., 15 min before ischemia). GW0742 (30 microg/kg i.v.) reduced the I/R-induced (a) decrease in the phosphorylation of Akt and glycogen synthase kinase-3beta, (b) nuclear translocation of the p65 subunit of nuclear factor-kappaB (activation of nuclear factor-kappaB), and (c) increase in the expression of iNOS and cyclooxygenase-2. Thus, immediate administration of the PPAR-beta/delta ligand GW0742 during reperfusion reduces myocardial infarct size in the rat by a mechanism that may involve inhibition of the activity of glycogen synthase kinase-3beta secondary to activation of the Akt pathway.