Lipid Effects of Peroxisome Proliferator-Activated Receptor-Δ Agonist GW501516 in Subjects With Low High-Density Lipoprotein Cholesterol

Activation of PPARδ in bone marrow endothelial progenitor cells improves their hematopoiesis-supporting ability after myelosuppressive injury

Dysfunctional bone marrow (BM) endothelial progenitor cells (EPCs) with high levels of reactive oxygen species (ROS) are responsible for defective hematopoiesis in poor graft function (PGF) patients with acute leukemia or myelodysplastic neoplasms post-allotransplant. However, the underlying mechanism by which BM EPCs regulate their intracellular ROS levels and the capacity to support hematopoiesis have not been well clarified. Herein, we demonstrated decreased levels of peroxisome proliferator-activated receptor delta (PPARδ), a lipid-activated nuclear receptor, in BM EPCs of PGF patients compared with those with good graft function (GGF). In vitro assays further identified that PPARδ knockdown contributed to reduced and dysfunctional BM EPCs, characterized by the impaired ability to support hematopoiesis, which were restored by PPARδ overexpression. Moreover, GW501516, an agonist of PPARδ, repaired the damaged BM EPCs triggered by 5-fluorouracil (5FU) in vitro and in vivo. Clinically, activation of PPARδ by GW501516 benefited the damaged BM EPCs from PGF patients or acute leukemia patients in complete remission (CR) post-chemotherapy. Mechanistically, we found that increased expression of NADPH oxidases (NOXs), the main ROS-generating enzymes, may lead to elevated ROS level in BM EPCs, and insufficient PPARδ may trigger BM EPC damage via ROS/p53 pathway. Collectively, we found that defective PPARδ contributes to BM EPC dysfunction, whereas activation of PPARδ in BM EPCs improves their hematopoiesis-supporting ability after myelosuppressive therapy, which may provide a potential therapeutic target not only for patients with leukemia but also for those with other cancers.

PPARβ/δ as a promising molecular drug target for liver diseases: A focused review

Various liver diseases pose great threats to humans. Although the etiologies of these liver diseases are quite diverse, they share similar pathologic phenotypes and molecular mechanisms such as oxidative stress, lipid and glucose metabolism disturbance, hepatic Kupffer cell (KC) proinflammatory polarization and inflammation, insulin resistance, and hepatic stellate cell (HSC) activation and proliferation. Peroxisome proliferator-activated receptor β/δ (PPARβ/δ) is expressed in various types of liver cells with relatively higher expression in KCs and HSCs. Accumulating evidence has revealed the versatile functions of PPARβ/δ such as controlling lipid homeostasis, inhibiting inflammation, regulating glucose metabolism, and restoring insulin sensitivity, suggesting that PPARβ/δ may serve as a potential molecular drug target for various liver diseases. This article aims to provide a concise review of the structure, expression pattern and biological functions of PPARβ/δ in the liver and its roles in various liver diseases, and to discuss potential future research perspectives.

Macrophage fatty acid oxidation in atherosclerosis

Atherosclerosis significantly contributes to the development of cardiovascular diseases (CVD) and is characterized by lipid retention and inflammation within the artery wall. Multiple immune cell types are implicated in the pathogenesis of atherosclerosis, macrophages play a central role as the primary source of inflammatory effectors in this pathogenic process. The metabolic influences of lipids on macrophage function and fatty acid β-oxidation (FAO) have similarly drawn attention due to its relevance as an immunometabolic hub. This review discusses recent findings regarding the impact of mitochondrial-dependent FAO in the phenotype and function of macrophages, as well as transcriptional regulation of FAO within macrophages. Finally, the therapeutic strategy of macrophage FAO in atherosclerosis is highlighted.

Discovery and structure-activity relationship study of 2-piperazinyl-benzothiazole derivatives as potent and selective PPARδ agonists

Peroxisome proliferator-activated receptor δ (PPARδ) is considered to be a target for treating metabolic syndrome, whereas there is no PPARδ agonist in clinical use. Previously, we have reported the discovery of 2-(1-piperidinyl)-1,3-benzothiazole derivatives as a new series of PPARδ agonists using docking-based virtual screening techniques. In this study, we performed the further optimization study of the lead compound 1 focusing on improvement of hydrophobic interactions in the binding site to enhance agonist efficacy for PPARδ and subtype selectivity, thereby discovering a novel PPARδ agonist 5g which exhibited high in vitro agonist activity (hPPARδ, EC₅₀ = 4.1 nM) and sufficiently high selectivity ratio over PPARα and PPARγ. Moreover, 5g revealed a significant upregulation of high-density lipoprotein cholesterol level in vivo.

Targeted therapeutics and novel signaling pathways in non-alcohol-associated fatty liver/steatohepatitis (NAFL/NASH)

Non-alcohol-associated fatty liver/steatohepatitis (NAFL/NASH) has become the leading cause of liver disease worldwide. NASH, an advanced form of NAFL, can be progressive and more susceptible to developing cirrhosis and hepatocellular carcinoma. Currently, lifestyle interventions are the most essential and effective strategies for preventing and controlling NAFL without the development of fibrosis. While there are still limited appropriate drugs specifically to treat NAFL/NASH, growing progress is being seen in elucidating the pathogenesis and identifying therapeutic targets. In this review, we discussed recent developments in etiology and prospective therapeutic targets, as well as pharmacological candidates in pre/clinical trials and patents, with a focus on diabetes, hepatic lipid metabolism, inflammation, and fibrosis. Importantly, growing evidence elucidates that the disruption of the gut-liver axis and microbe-derived metabolites drive the pathogenesis of NAFL/NASH. Extracellular vesicles (EVs) act as a signaling mediator, resulting in lipid accumulation, macrophage and hepatic stellate cell activation, further promoting inflammation and liver fibrosis progression during the development of NAFL/NASH. Targeting gut microbiota or EVs may serve as new strategies for the treatment of NAFL/NASH. Finally, other mechanisms, such as cell therapy and genetic approaches, also have enormous therapeutic potential. Incorporating drugs with different mechanisms and personalized medicine may improve the efficacy to better benefit patients with NAFL/NASH.

Abnormal Metabolism in the Progression of Nonalcoholic Fatty Liver Disease to Hepatocellular Carcinoma: Mechanistic Insights to Chemoprevention

Nonalcoholic fatty liver disease (NAFLD) is on the rise and becoming a major contributor to the development of hepatocellular carcinoma (HCC). Reasons for this include the rise in obesity and metabolic syndrome in contrast to the marked advances in prevention and treatment strategies of viral HCC. These shifts are expected to rapidly propel this trend even further in the coming decades, with NAFLD on course to become the leading etiology of end-stage liver disease and HCC. No Food and Drug Administration (FDA)-approved medications are currently available for the treatment of NAFLD, and advances are desperately needed. Numerous medications with varying mechanisms of action targeting liver steatosis and fibrosis are being investigated including peroxisome proliferator-activated receptor (PPAR) agonists and farnesoid X receptor (FXR) agonists. Additionally, drugs targeting components of metabolic syndrome, such as antihyperglycemics, have been found to affect NAFLD progression and are now being considered in the treatment of these patients. As NAFLD drug discovery continues, special attention should be given to their relationship to HCC. Several mechanisms in the pathogenesis of NAFLD have been implicated in hepatocarcinogenesis, and therapies aimed at NAFLD may additionally harbor independent antitumorigenic potential. This approach may provide novel prevention and treatment strategies.

Targeting Energy Expenditure-Drugs for Obesity Treatment

Obesity and overweight are associated with lethal diseases. In this context, obese and overweight individuals infected by COVID-19 are at greater risk of dying. Obesity is treated by three main pharmaceutical approaches, namely suppressing appetite, reducing energy intake by impairing absorption, and increasing energy expenditure. Most compounds used for the latter were first envisaged for other medical uses. However, several candidates are now being developed explicitly for targeting obesity by increasing energy expenditure. This review analyzes the compounds that show anti-obesity activity exerted through the energy expenditure pathway. They are classified on the basis of their development status: FDA-approved, Withdrawn, Clinical Trials, and Under Development. The chemical nature, target, mechanisms of action, and description of the current stage of development are described for each one.

Co-Incubation with PPARβ/δ Agonists and Antagonists Modeled Using Computational Chemistry: Effect on LPS Induced Inflammatory Markers in Pulmonary Artery

Peroxisome proliferator activated receptor beta/delta (PPARβ/δ) is a nuclear receptor ubiquitously expressed in cells, whose signaling controls inflammation. There are large discrepancies in understanding the complex role of PPARβ/δ in disease, having both anti- and pro-effects on inflammation. After ligand activation, PPARβ/δ regulates genes by two different mechanisms; induction and transrepression, the effects of which are difficult to differentiate directly. We studied the PPARβ/δ-regulation of lipopolysaccharide (LPS) induced inflammation (indicated by release of nitrite and IL-6) of rat pulmonary artery, using different combinations of agonists (GW0742 or L-165402) and antagonists (GSK3787 or GSK0660). LPS induced release of NO and IL-6 is not significantly reduced by incubation with PPARβ/δ ligands (either agonist or antagonist), however, co-incubation with an agonist and antagonist significantly reduces LPS-induced nitrite production and Nos2 mRNA expression. In contrast, incubation with LPS and PPARβ/δ agonists leads to a significant increase in Pdk-4 and Angptl-4 mRNA expression, which is significantly decreased in the presence of PPARβ/δ antagonists. Docking using computational chemistry methods indicates that PPARβ/δ agonists form polar bonds with His287, His413 and Tyr437, while antagonists are more promiscuous about which amino acids they bind to, although they are very prone to bind Thr252 and Asn307. Dual binding in the PPARβ/δ binding pocket indicates the ligands retain similar binding energies, which suggests that co-incubation with both agonist and antagonist does not prevent the specific binding of each other to the large PPARβ/δ binding pocket. To our knowledge, this is the first time that the possibility of binding two ligands simultaneously into the PPARβ/δ binding pocket has been explored. Agonist binding followed by antagonist simultaneously switches the PPARβ/δ mode of action from induction to transrepression, which is linked with an increase in Nos2 mRNA expression and nitrite production.

Nutritional strategies to modulate inflammation pathways via regulation of peroxisome proliferator-activated receptor β/δ

The peroxisome proliferator-activated receptor (PPAR) β/δ has an important role in multiple inflammatory conditions, including obesity, hypertension, cancer, cardiovascular disease, diabetes mellitus, and autoimmune diseases. PPARβ/δ forms a heterodimer with the retinoic acid receptor and binds to peroxisome proliferator response elements to initiate transcription of its target genes. PPARβ/δ is also able to suppress the activities of several transcription factors, including nuclear factor κB, and activator protein 1, thus regulating anti-inflammatory cellular responses and playing a protective role in several diseases. Recent studies have shown that nutritional compounds, including nutrients and bioactive compounds, can regulate PPARβ/δ expression. This review discusses key nutritional compounds that are known to modulate PPARβ/δ and are likely to affect human health.

Exploration and Development of PPAR Modulators in Health and Disease: An Update of Clinical Evidence

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that govern the expression of genes responsible for energy metabolism, cellular development, and differentiation. Their crucial biological roles dictate the significance of PPAR-targeting synthetic ligands in medical research and drug discovery. Clinical implications of PPAR agonists span across a wide range of health conditions, including metabolic diseases, chronic inflammatory diseases, infections, autoimmune diseases, neurological and psychiatric disorders, and malignancies. In this review we aim to consolidate existing clinical evidence of PPAR modulators, highlighting their clinical prospects and challenges. Findings from clinical trials revealed that different agonists of the same PPAR subtype could present different safety profiles and clinical outcomes in a disease-dependent manner. Pemafibrate, due to its high selectivity, is likely to replace other PPARα agonists for dyslipidemia and cardiovascular diseases. PPARγ agonist pioglitazone showed tremendous promises in many non-metabolic disorders like chronic kidney disease, depression, inflammation, and autoimmune diseases. The clinical niche of PPARβ/δ agonists is less well-explored. Interestingly, dual- or pan-PPAR agonists, namely chiglitazar, saroglitazar, elafibranor, and lanifibranor, are gaining momentum with their optimistic outcomes in many diseases including type 2 diabetes, dyslipidemia, non-alcoholic fatty liver disease, and primary biliary cholangitis. Notably, the preclinical and clinical development for PPAR antagonists remains unacceptably deficient. We anticipate the future design of better PPAR modulators with minimal off-target effects, high selectivity, superior bioavailability, and pharmacokinetics. This will open new possibilities for PPAR ligands in medicine.

PPARs as Nuclear Receptors for Nutrient and Energy Metabolism

It has been more than 36 years since peroxisome proliferator-activated receptors (PPARs) were first recognized as enhancers of peroxisome proliferation. Consequently, many studies in different fields have illustrated that PPARs are nuclear receptors that participate in nutrient and energy metabolism and regulate cellular and whole-body energy homeostasis during lipid and carbohydrate metabolism, cell growth, cancer development, and so on. With increasing challenges to human health, PPARs have attracted much attention for their ability to ameliorate metabolic syndromes. In our previous studies, we found that the complex functions of PPARs may be used as future targets in obesity and atherosclerosis treatments. Here, we review three types of PPARs that play overlapping but distinct roles in nutrient and energy metabolism during different metabolic states and in different organs. Furthermore, research has emerged showing that PPARs also play many other roles in inflammation, central nervous system-related diseases, and cancer. Increasingly, drug development has been based on the use of several selective PPARs as modulators to diminish the adverse effects of the PPAR agonists previously used in clinical practice. In conclusion, the complex roles of PPARs in metabolic networks keep these factors in the forefront of research because it is hoped that they will have potential therapeutic effects in future applications.

Comparative Evaluation of Gemcabene and Peroxisome Proliferator-Activated Receptor Ligands in Transcriptional Assays of Peroxisome Proliferator-Activated Receptors: Implication for the Treatment of Hyperlipidemia and Cardiovascular Disease

Gemcabene, a late-stage clinical candidate, has shown efficacy for LDL-C, non-HDL cholesterol, apoB, triglycerides, and hsCRP reduction, all risk factors for cardiovascular disease. In rodents, gemcabene showed changes in targets, including apoC-III, apoA-I, peroxisomal enzymes, considered regulated through peroxisome proliferator-activated receptor (PPAR) gene activation, suggesting a PPAR-mediated mechanism of action for the observed hypolipidemic effects observed in rodents and humans. In the current study, the gemcabene agonist activity against PPAR subtypes of human, rat, and mouse were compared with known lipid lowering PPAR activators. Surprisingly, gemcabene showed no or little PPAR-α transactivation compared with reference agonists, which showed concentration-dependent transactivation against human PPAR-α of 2.4- to 30-fold (fenofibric acid), 17-fold (GW590735), and 2.3- to 25-fold (WY-14643). These agents also showed robust transactivation of mouse and rat PPAR-α in a concentration-dependent manner. The known PPAR-δ agonists, GW1516, L165041, and GW0742, showed potent agonist activity against human, mouse, and rat receptors (ranging from 165- to 396-fold). By contrast, gemcabene at the highest concentration tested (300 μM) showed no response in mouse and rat and a marginal response against human PPAR-δ receptors (3.2-fold). For PPAR-γ, gemcabene showed no agonist activity against all 3 species at 100 μM and marginal activity (3.6- to 5-fold) at 300 μM. By contrast, the known agonists, rosiglitazone, indomethacin, and muraglitazar showed strong activation against the mouse, rat, and human PPAR-γ receptors. No clear antagonist activity was observed with gemcabene against any PPAR subtypes for all 3 species over a wide range of concentrations. In summary, the transactivation studies rule out gemcabene as a direct agonist or antagonist of PPAR-α, PPAR-γ, and PPAR-δ receptors of these 3 species. These data suggest that the peroxisomal effects observed in rodents and the lipid regulating effects observed in rodents and humans are not related to a direct activation of PPAR receptors by gemcabene.

The association between peroxisome proliferator-activated receptor Δ rs3777744, rs3798343, and rs6922548 and coronary artery disease

Objective: The aim of the present study is to investigate the association between the single nucleotide polymorphism (SNP) sites of peroxisome proliferator-activated receptor Δ (PPARD) and the risk of coronary artery disease (CAD). To this end, a prospective observational single-center study of the clinical data from 880 subjects in a Chinese population was conducted. Methods: A total of 880 subjects, including 609 CAD patients and 271 control subjects, were selected for the present study. All inpatients had 4 ml of venous blood drawn after 12 h of fasting, and then clinical tests were conducted to obtain the biochemical parameters. CAD patients and Controls were distinguished by coronary angiography. Statistical analysis was conducted with SPSS software (ver 16.0). Results: A significant association between the G-alleles of PPARD rs3777744 and rs3798343 and a decreased risk for CAD was found. Moreover, we found an interaction between high fasting high-density lipoprotein cholesterol (HDL-C) serum levels, low serum glucose levels and their genotypes, ultimately decreasing the risk of CAD. Haplotype analysis was conducted on the three SNP sites, rs3777744 and rs3798343 to form a block [r² = 0.79, D′ = 0.99). The A-C haplotypes were associated with an increased risk of CAD (odds ratio (OR), 95% confidence interval (CI): 1.321 (1.060–1.647), P=0.013], and the G-G haplotypes were associated with a decreased risk [OR, 95% CI: 0.714 (0.567–0.849), P=0.004]. Conclusions: Our study indicates a significant association between the G-alleles of PPARD rs3777744 and rs3798343 and a decreased CAD risk. In addition, genotypes interact with high serum HDL-C levels and low serum glucose levels, resulting in decreased prevalence of CAD.

Ginsenoside Rg1 augments oxidative metabolism and anabolic response of skeletal muscle in mice

Background

The ginsenoside Rg1 has been shown to exert various pharmacological activities with health benefits. Previously, we have reported that Rg1 promoted myogenic differentiation and myotube growth in C2C12 myoblasts. In this study, the in vivo effect of Rg1 on fiber-type composition and oxidative metabolism in skeletal muscle was examined.

Methods

To examine the effect of Rg1 on skeletal muscle, 3-month-old mice were treated with Rg1 for 5 weeks. To assess muscle strength, grip strength tests were performed, and the lower hind limb muscles were harvested, followed by various detailed analysis, such as histological staining, immunoblotting, immunostaining, and real-time quantitative reverse transcription polymerase chain reaction. In addition, to verify the in vivo data, primary myoblasts isolated from mice were treated with Rg1, and the Rg1 effect on myotube growth was examined by immunoblotting and immunostaining analysis.

Results

Rg1 treatment increased the expression of myosin heavy chain isoforms characteristic for both oxidative and glycolytic muscle fibers; increased myofiber sizes were accompanied by enhanced muscle strength. Rg1 treatment also enhanced oxidative muscle metabolism with elevated oxidative phosphorylation proteins. Furthermore, Rg1-treated muscles exhibited increased levels of anabolic S6 kinase signaling.

Conclusion

Rg1 improves muscle functionality via enhancing muscle gene expression and oxidative muscle metabolism in mice.

PPARβ/δ: A Key Therapeutic Target in Metabolic Disorders

Research in recent years on peroxisome proliferator-activated receptor (PPAR)β/δ indicates that it plays a key role in the maintenance of energy homeostasis, both at the cellular level and within the organism as a whole. PPARβ/δ activation might help prevent the development of metabolic disorders, including obesity, dyslipidaemia, type 2 diabetes mellitus and non-alcoholic fatty liver disease. This review highlights research findings on the PPARβ/δ regulation of energy metabolism and the development of diseases related to altered cellular and body metabolism. It also describes the potential of the pharmacological activation of PPARβ/δ as a treatment for human metabolic disorders.

The selective peroxisome proliferator-activated receptor-delta agonist seladelpar reverses nonalcoholic steatohepatitis pathology by abrogating lipotoxicity in diabetic obese mice

Lipotoxicity associated with insulin resistance is central to nonalcoholic steatohepatitis (NASH) pathogenesis. To date, only weight loss fully reverses NASH pathology, but mixed peroxisome proliferator–activated receptor‐alpha/delta (PPAR‐α/δ) agonists show some efficacy. Seladelpar (MBX‐8025), a selective PPAR‐δ agonist, improves atherogenic dyslipidemia. We therefore used this agent to test whether selective PPAR‐δ activation can reverse hepatic lipotoxicity and NASH in an obese, dyslipidemic, and diabetic mouse model. From weaning, female Alms1 mutant (foz/foz) mice and wild‐type littermates were fed an atherogenic diet for 16 weeks; groups (n = 8‐12) were then randomized to receive MBX‐8025 (10 mg/kg) or vehicle (1% methylcellulose) by gavage for 8 weeks. Despite minimally altering body weight, MBX‐8025 normalized hyperglycemia, hyperinsulinemia, and glucose disposal in foz/foz mice. Serum alanine aminotransferase ranged 300‐600 U/L in vehicle‐treated foz/foz mice; MBX‐8025 reduced alanine aminotransferase by 50%. In addition, MBX‐8025 normalized serum lipids and hepatic levels of free cholesterol and other lipotoxic lipids that were increased in vehicle‐treated foz/foz versus wild‐type mice. This abolished hepatocyte ballooning and apoptosis, substantially reduced steatosis and liver inflammation, and improved liver fibrosis. In vehicle‐treated foz/foz mice, the mean nonalcoholic fatty liver disease activity score was 6.9, indicating NASH; MBX‐8025 reversed NASH in all foz/foz mice (nonalcoholic fatty liver disease activity score 3.13). Conclusion: Seladelpar improves insulin sensitivity and reverses dyslipidemia and hepatic storage of lipotoxic lipids to improve NASH pathology in atherogenic diet–fed obese diabetic mice. Selective PPAR‐δ agonists act independently of weight reduction, but counter lipotoxicity related to insulin resistance, thereby providing a novel therapy for NASH. (Hepatology Communications 2017;1:663–674)

Intestinal PPARδ protects against diet-induced obesity, insulin resistance and dyslipidemia

Peroxisome proliferator-activated receptor δ (PPARδ) is a ligand-activated transcription factor that has an important role in lipid metabolism. Activation of PPARδ stimulates fatty acid oxidation in adipose tissue and skeletal muscle and improves dyslipidemia in mice and humans. PPARδ is highly expressed in the intestinal tract but its physiological function in this organ is not known. Using mice with an intestinal epithelial cell-specific deletion of PPARδ, we show that intestinal PPARδ protects against diet-induced obesity, insulin resistance and dyslipidemia. Furthermore, absence of intestinal PPARδ abolished the ability of PPARδ agonist GW501516 to increase plasma levels of HDL-cholesterol. Together, our findings show that intestinal PPARδ is important in maintaining metabolic homeostasis and suggest that intestinal-specific activation of PPARδ could be a therapeutic approach for treatment of the metabolic syndrome and dyslipidemia, while avoiding systemic toxicity.

PPARs in obesity-induced T2DM, dyslipidaemia and NAFLD

Obesity is a worldwide epidemic that predisposes individuals to cardiometabolic complications, such as type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD), which are all related to inappropriate ectopic lipid deposition. Identification of the pathogenic molecular mechanisms and effective therapeutic approaches are highly needed. The peroxisome proliferator-activated receptors (PPARs) modulate several biological processes that are perturbed in obesity, including inflammation, lipid and glucose metabolism and overall energy homeostasis. Here, we review how PPARs regulate the functions of adipose tissues, such as adipogenesis, lipid storage and adaptive thermogenesis, under healthy and pathological conditions. We also discuss the clinical use and mechanism of PPAR agonists in the treatment of obesity comorbidities such as dyslipidaemia, T2DM and NAFLD. First generation PPAR agonists, primarily those acting on PPARγ, are associated with adverse effects that outweigh their clinical benefits, which led to the discontinuation of their development. An improved understanding of the physiological roles of PPARs might, therefore, enable the development of safe, new PPAR agonists with improved therapeutic potential.

Antihypertensive effects of peroxisome proliferator-activated receptor-β/δ activation

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors, which is composed of three members encoded by distinct genes: PPARα, PPARβ/δ, and PPARγ. The biological actions of PPARα and PPARγ and their potential as a cardiovascular therapeutic target have been extensively reviewed, whereas the biological actions of PPARβ/δ and its effectiveness as a therapeutic target in the treatment of hypertension remain less investigated. Preclinical studies suggest that pharmacological PPARβ/δ activation induces antihypertensive effects in direct [spontaneously hypertensive rat (SHR), ANG II, and DOCA-salt] and indirect (dyslipemic and gestational) models of hypertension, associated with end-organ damage protection. This review summarizes mechanistic insights into the antihypertensive effects of PPARβ/δ activators, including molecular and functional mechanisms. Pharmacological PPARβ/δ activation induces genomic actions including the increase of regulators of G protein-coupled signaling (RGS), acute nongenomic vasodilator effects, as well as the ability to improve the endothelial dysfunction, reduce vascular inflammation, vasoconstrictor responses, and sympathetic outflow from central nervous system. Evidence from clinical trials is also examined. These preclinical and clinical outcomes of PPARβ/δ ligands may provide a basis for the development of therapies in combating hypertension.

Apoptotic effect of the selective PPARβ/δ agonist GW501516 in invasive bladder cancer cells

GW501516 is a selective and high-affinity synthetic agonist of peroxisome proliferator-activated receptor β/δ (PPARβ/δ). This molecule promoted the inhibition of proliferation and apoptosis in few cancer cell lines, but its anticancer action has never been investigated in bladder tumor cells. Thus, this study was undertaken to determine whether GW501516 had antiproliferative and/or apoptotic effects on RT4 and T24 urothelial cancer cells and to explore the molecular mechanisms involved. Our results indicated that, in RT4 cells (derived from a low-grade papillary tumor), GW501516 did not induce cell death. On the other hand, in T24 cells (derived from an undifferentiated high-grade carcinoma), this PPARβ/δ agonist induced cytotoxic effects including cell morphological changes, a decrease of cell viability, a G2/M cell cycle arrest, and the cell death as evidenced by the increase of the sub-G1 cell population. Furthermore, GW501516 triggered T24 cell apoptosis in a caspase-dependent manner including both extrinsic and intrinsic apoptotic pathways through Bid cleavage. In addition, the drug led to an increase of the Bax/Bcl-2 ratio, a mitochondrial dysfunction associated with the dissipation of ΔΨm, and the release of cytochrome c from the mitochondria to the cytosol. GW501516 induced also ROS generation which was not responsible for T24 cell death since NAC did not rescue cells upon PPARβ/δ agonist exposure. For the first time, our data highlight the capacity of GW501516 to induce apoptosis in invasive bladder cancer cells. This molecule could be relevant as a therapeutic drug for high-grade urothelial cancers.

Vascular smooth muscle cell dysfunction in diabetes: nuclear receptors channel to relaxation

Endothelial dysfunction and impaired vascular relaxation represent a common cause of microvascular disease in patients with diabetes. Although multiple mechanisms underlying altered endothelial cell function in diabetes have been described, there is currently no specific and approved pharmacological treatment. In this edition of Clinical Science, Morales-Cano et al. characterize voltage-dependent K+ (Kv) channels as genes regulated by pharmacological activation of peroxisome proliferator-activated receptor-b/d (PPARb/d). Diabetes altered Kv channel function leading to impaired coronary artery relaxation, which was prevented by pharmacological activation of PPARb/d. These studies highlight an important mechanism of vascular dysfunction in diabetes and point to a potential approach for therapy, particularly considering that PPARb/d ligands have been developed and tested in small clinical trials.

Interaction Between Peroxisome Proliferator Activated Receptor δ and Epithelial Membrane Protein 2 Polymorphisms Influences HDL-C Levels in the Chinese Population

Peroxisome proliferator activated receptors (PPARs) are transcription factors involved in the regulation of key metabolic pathways. Numerous in vivo and in vitro studies have established their important roles in lipid metabolism. A few SNPs in PPAR genes have been reported to be associated with lipid levels. In this study, we aimed to investigate the interactive effects between single nucleotide polymorphisms (SNPs) in three PPAR isoforms α/δ/γ and other genetic variants across the genome on plasma high-density lipoprotein-cholesterol (HDL-C) levels. Study subjects (N = 2003) were genotyped using Illumina HumanOmniZhongHua-8 Beadchip. Fifty-three tag SNPs ± 100 kb of PPAR α, δ, and γ (r(2) < 0.2) were selected. The effect of interactions between PPAR SNPs and those across the genome on HDL-C was tested using linear regression models. One statistically significant interaction influencing HDL-C was detected between PPARδ SNP rs2267668 and epithelial membrane protein 2 (EMP2) downstream SNP rs7191411 (N = 1993, β = 0.74, adjusted P = 0.022). This interaction was successfully replicated in the meta-analysis of two additional Chinese cohorts (N = 3948, P = 0.01). The present study showed a novel SNP × SNP interaction between rs2267668 in PPARδ and rs7191411 in EMP2 that has significant impact on circulating HDL-C levels in the Singaporean Chinese population.

Activation of Peroxisome Proliferator–Activated Receptor-δ as Novel Therapeutic Strategy to Prevent In-Stent Restenosis and Stent Thrombosis

Objective—

Drug-eluting coronary stents reduce restenosis rate and late lumen loss compared with bare-metal stents; however, drug-eluting coronary stents may delay vascular healing and increase late stent thrombosis. The peroxisome proliferator–activated receptor-delta (PPARδ) exhibits actions that could favorably influence outcomes after drug-eluting coronary stents placement.

Approach and Results—

Here, we report that PPARδ ligand–coated stents strongly reduce the development of neointima and luminal narrowing in a rabbit model of experimental atherosclerosis. Inhibition of inflammatory gene expression and vascular smooth muscle cell (VSMC) proliferation and migration, prevention of thrombocyte activation and aggregation, and proproliferative effects on endothelial cells were identified as key mechanisms for the prevention of restenosis. Using normal and PPARδ-depleted VSMCs, we show that the observed effects of PPARδ ligand GW0742 on VSMCs and thrombocytes are PPARδ receptor dependent. PPARδ ligand treatment induces expression of pyruvate dehydrogenase kinase isozyme 4 and downregulates the glucose transporter 1 in VSMCs, thus impairing the ability of VSMCs to provide the increased energy demands required for growth factor–stimulated proliferation and migration.

Conclusions—

In contrast to commonly used drugs for stent coating, PPARδ ligands not only inhibit inflammatory response and proliferation of VSMCs but also prevent thrombocyte activation and support vessel re-endothelialization. Thus, pharmacological PPARδ activation could be a promising novel strategy to improve drug-eluting coronary stents outcomes.

Nuclear receptors and AMPK: can exercise mimetics cure diabetes?

Endurance exercise can lead to systemic improvements in insulin sensitivity and metabolic homeostasis, and is an effective approach to combat metabolic diseases. Pharmacological compounds that recapitulate the beneficial effects of exercise, also known as 'exercise mimetics', have the potential to improve disease symptoms of metabolic syndrome. These drugs, which can increase energy expenditure, suppress hepatic gluconeogenesis, and induce insulin sensitization, have accordingly been highly scrutinized for their utility in treating metabolic diseases including diabetes. Nevertheless, the identity of an efficacious exercise mimetic still remains elusive. In this review, we highlight several nuclear receptors and cofactors that are putative molecular targets for exercise mimetics, and review recent studies that provide advancements in our mechanistic understanding of how exercise mimetics exert their beneficial effects. We also discuss evidence from clinical trials using these compounds in human subjects to evaluate their efficacy in treating diabetes.

Unraveling the Effects of PPARβ/δ on Insulin Resistance and Cardiovascular Disease

Insulin resistance precedes dyslipidemia and type 2 diabetes mellitus (T2DM) development. Preclinical evidence suggests that peroxisome proliferator-activated receptor (PPAR) β/δ activators may prevent and treat obesity-induced insulin resistance and T2DM, while clinical trials highlight their potential utility in dyslipidemia. This review summarizes recent mechanistic insights into the antidiabetic effects of PPARβ/δ activators, including their anti-inflammatory actions, their ability to inhibit endoplasmic reticulum (ER) stress and hepatic lipogenesis, and to improve atherogenesis and insulin sensitivity, as well as their capacity to activate pathways that are also stimulated by exercise. Findings from clinical trials are also examined. Dissecting the effects of PPARβ/δ ligands on insulin sensitivity and atherogenesis may provide a basis for the development of therapies for the prevention and treatment of T2DM and cardiovascular disease (CVD).

A selective peroxisome proliferator-activated receptor δ agonist PYPEP suppresses atherosclerosis in association with improvement of the serum lipoprotein profiles in human apolipoprotein B100 and cholesteryl ester transfer protein double transgenic mice

OBJECTIVE

Although peroxisome proliferator-activated receptor (PPAR) δ agonists have been shown to improve the serum lipoprotein profiles in humans, the impact of the changes in these lipoprotein profiles on atherosclerosis remains to be elucidated. The aim of this study was to investigate the relationship between the selective PPARδ agonist-induced alterations of serum lipoprotein profiles and the development of atherosclerosis in human apolipoprotein B100 and cholesterol ester transfer protein double transgenic (hApoB100/hCETP-dTg) mice with human-like hypercholesterolemic dyslipidemia.

METHODS

hApoB100/hCETP-dTg mice fed an atherogenic diet received a novel PPARδ agonist (PYPEP) or vehicle for 18 weeks, followed by evaluation of atherosclerosis. Serum samples were collected during the treatment period at least at 3-week intervals to determine the lipoprotein levels and the levels of an inflammatory marker, macrophage chemotactic protein-1 (MCP-1), and to analyze the lipoprotein profile by fast protein liquid chromatography. The cholesterol efflux capacity of high-density lipoprotein (HDL) was examined using [(3)H]-cholesterol labeled macrophages.

RESULTS

Compared with vehicle treatment, PYPEP treatment caused increases in the serum levels of HDL cholesterol and apolipoprotein A-I (ApoA-I), as well as reductions in the serum non-HDL cholesterol and MCP-1 levels. The HDL fraction from the PYPEP-treated group maintained its cholesterol efflux capacity and showed an increased population of smaller HDL particles. PYPEP substantially suppressed atherosclerotic lesion progression, and the lesion areas had significant correlations with non-HDL cholesterol, HDL cholesterol, ApoA-I and MCP-1 by Pearson's correlation analysis. A multiple regression analysis revealed that non-HDL cholesterol and ApoA-I were significantly associated with the atherosclerotic lesion area.

CONCLUSION

A novel PPARδ agonist, PYPEP, suppressed atherosclerotic lesion progression by improving the serum lipoprotein profiles, including increased levels of ApoA-I and functional HDL particles, as well as a reduced non-HDL cholesterol level, in hApoB100/hCETP-dTg mice with human-like hypercholesterolemic dyslipidemia.

In silico modelling of prostacyclin and other lipid mediators to nuclear receptors reveal novel thyroid hormone receptor antagonist properties

Prostacyclin (PGI2) is a key mediator involved in cardiovascular homeostasis, acting predominantly on two receptor types; cell surface IP receptor and cytosolic peroxisome proliferator activated receptor (PPAR) β/δ. Having a very short half-life, direct methods to determine its long term effects on cells is difficult, and little is known of its interactions with nuclear receptors. Here we used computational chemistry methods to investigate the potential for PGI2, beraprost (IP receptor agonist), and GW0742 (PPARβ/δ agonist), to bind to nuclear receptors, confirmed with pharmacological methods. In silico screening predicted that PGI2, beraprost, and GW0742 have the potential to bind to different nuclear receptors, in particular thyroid hormone β receptor (TRβ) and thyroid hormone α receptor (TRα). Docking analysis predicts a binding profile to residues thought to have allosteric control on the TR ligand binding site. Luciferase reporter assays confirmed that beraprost and GW0742 display TRβ and TRα antagonistic properties; beraprost IC50 6.3 × 10(-5)mol/L and GW0742 IC50 4.9 × 10(-6) mol/L. Changes to triiodothyronine (T3) induced vasodilation of rat mesenteric arteries measured on the wire myograph were measured in the presence of the TR antagonist MLS000389544 (10(-5) mol/L), beraprost (10(-5) mol/L) and GW0742 (10(-5) mol/L); all significantly inhibited T3 induced vasodilation compared to controls. We have shown that both beraprost and GW0742 exhibit TRβ and TRα antagonist behaviour, and suggests that PGI2 has the ability to affect the long term function of cells through binding to and inactivating thyroid hormone receptors.

Novel investigational drugs mimicking exercise for the treatment of cachexia

INTRODUCTION

Cachexia is a syndrome characterized by body weight loss, muscle wasting and metabolic abnormalities, that frequently complicates the management of people affected by chronic diseases. No effective therapy is actually available, although several drugs are under clinical evaluation. Altered energy metabolism markedly contributes to the pathogenesis of cachexia; it can be improved by exercise, which is able to both induce anabolism and inhibit catabolism.

AREAS COVERED

This review focuses on exercise mimetics and their potential inclusion in combined protocols to treat cachexia. The authors pay with particular reference to the cancer-associated cachexia.

EXPERT OPINION

Even though exercise improves muscle phenotype, most patients retain sedentary habits which are quite difficult to disrupt. Moreover, they frequently present with chronic fatigue and comorbidities that reduce exercise tolerance. For these reasons, drugs mimicking exercise could be beneficial to those who are unable to comply with the practice of physical activity. Since some exercise mimetics may exert serious side effects, further investigations should focus on treatments which maintain their effectiveness on muscle phenotype while remaining tolerable at the same time.

Combinatorial therapeutic activation with heparin and AICAR stimulates additive effects on utrophin A expression in dystrophic muscles

Upregulation of utrophin A is an attractive therapeutic strategy for treating Duchenne muscular dystrophy (DMD). Over the years, several studies revealed that utrophin A is regulated by multiple transcriptional and post-transcriptional mechanisms, and that pharmacological modulation of these pathways stimulates utrophin A expression in dystrophic muscle. In particular, we recently showed that activation of p38 signaling causes an increase in the levels of utrophin A mRNAs and protein by decreasing the functional availability of the destabilizing RNA-binding protein called K-homology splicing regulatory protein, thereby resulting in increases in the stability of existing mRNAs. Here, we treated 6-week-old mdx mice for 4 weeks with the clinically used anticoagulant drug heparin known to activate p38 mitogen-activated protein kinase, and determined the impact of this pharmacological intervention on the dystrophic phenotype. Our results show that heparin treatment of mdx mice caused a significant ∼1.5- to 3-fold increase in utrophin A expression in diaphragm, extensor digitorum longus and tibialis anterior (TA) muscles. In agreement with these findings, heparin-treated diaphragm and TA muscle fibers showed an accumulation of utrophin A and β-dystroglycan along their sarcolemma and displayed improved morphology and structural integrity. Moreover, combinatorial drug treatment using both heparin and 5-amino-4-imidazolecarboxamide riboside (AICAR), the latter targeting 5' adenosine monophosphate-activated protein kinase and the transcriptional activation of utrophin A, caused an additive effect on utrophin A expression in dystrophic muscle. These findings establish that heparin is a relevant therapeutic agent for treating DMD, and illustrate that combinatorial treatment of heparin with AICAR may serve as an effective strategy to further increase utrophin A expression in dystrophic muscle via activation of distinct signaling pathways.

Association and interaction of PPARα, δ, and γ gene polymorphisms with low-density lipoprotein-cholesterol in a Chinese Han population

AIMS

Elevated low-density lipoprotein-cholesterol (LDL-C) is regarded as one of major risks of cardiovascular diseases and atherosclerotic events. It has been previously reported that peroxisome proliferator-activated receptors (PPARs) play an important role in the regulation of lipid metabolism. In this study, we aimed to investigate the influence of PPARα/δ/γ gene polymorphisms on LDL-C level. Eight hundred twenty unrelated participants were recruited. Ten single-nucleotide polymorphisms (SNPs) were genotyped to analyze the gene-gene interactions among these polymorphisms using the generalized multifactor dimensionality reduction (GMDR) method.

RESULTS

The results of single-locus analyses indicated that the genotypes with minor allele variants at the rs1800206, rs9794, rs1805192, rs709158, and rs3856806 loci are associated with higher LDL-C levels (p<0.05) after adjusting for covariates. In contrast, individuals that were homozygous for the major allele (CC) of rs10865710 had significantly higher LDL-C than those with either one or more minor type alleles (CG+GG, mean difference: -0.21 mM; 95% confidence interval [CI]: -0.37 to -0.04 mM; p=0.013). Significant gene-gene interactions among PPAR gene polymorphisms on LDL-C were identified by a generalized multifactor dimensionality reduction (GMDR) approach in 2- to 8-locus models (p<0.05).

CONCLUSION

Our results provide evidence that multiple PPARα/δ/γ gene polymorphisms are individually associated with increased LDL-C, and that interactions, among these alleles result in additional increased risk suggesting that PPAR genes may contribute substantially to the risk of cardiovascular diseases and atherosclerosis.

In vitro evaluation of dual agonists for PPARγ/β from the flower of Edgeworthia gardneri (wall.) Meisn

ETHNOPHARMACOLOGICAL RELEVANCE

In Tibet, the flower of Edgeworthia gardneri (Wall.) Meisn., locally named "Lvluohua, [symbols: see text]", has been traditionally used to treat diabetes mellitus for many years.

AIM OF THIS STUDY

To evaluate the activity of dual agonists for PPARγ/β from the flower of E.gardneri in vitro.

MATERIALS AND METHODS

HeLa cells were transiently co-transfected with the re-constructed plasmids of pBIND-PPARγ-LBD or pBIND-PPARβ-LBD and rL4.35. The activities of crude extracts, secondary fractions and compounds from the flower of E.gardneri were evaluated with the transfected cells. Rosiglitazone (at 0.5 μg/mL) and L-165041 (at 0.5 μg/mL) were used as the positive controls for PPARγ and PPARβ respectively.

RESULTS

The results demonstrated that n-hexane, ethyl acetate and n-butanol extracts from the flower of E.gardneri were able to significantly activate PPARγ and PPARβ respectively, and the activity of ethyl acetate extract was much better. We further observed that, among the 11 secondary fractions of ethyl acetate extract, the fr. 9 could activate PPARγ and PPARβ significantly. Moreover, umbelliferone (from fr.9) and pentadecanoic acid could activate PPARγ and PPARβ at the same time.

CONCLUSIONS

The extracts from the flower of E.gardneri could significantly activate PPARγ and PPARβ. Besides, umbelliferone and pentadecanoic acid isolated from the flower of E.gardneri were the new agonists for PPARγ and PPARβ.

Minireview: nuclear receptor regulation of osteoclast and bone remodeling

Osteoclasts are bone-resorbing cells essential for skeletal remodeling and regeneration. However, excessive osteoclasts often contribute to prevalent bone degenerative diseases such as osteoporosis, arthritis, and cancer bone metastasis. Osteoclast dysregulation is also associated with rare disorders such as osteopetrosis, pycnodysostosis, Paget's disease, and Gorham-Stout syndrome. The nuclear receptor (NR) family of transcription factors functions as metabolic sensors that control a variety of physiological processes including skeletal homeostasis and serves as attractive therapeutic targets for many diseases. In this review, we highlight recent findings on the new players and the new mechanisms for how NRs regulate osteoclast differentiation and bone resorption. An enhanced understanding of NR functions in osteoclastogenesis will facilitate the development of not only novel osteoprotective medicine but also prudent strategies to minimize the adverse skeletal effects of certain NR-targeting drugs for a better treatment of cancer and metabolic diseases.

Turn up the power - pharmacological activation of mitochondrial biogenesis in mouse models

The oxidative phosphorylation (OXPHOS) system in mitochondria is responsible for the generation of the majority of cellular energy in the form of ATP. Patients with genetic OXPHOS disorders form the largest group of inborn errors of metabolism. Unfortunately, there is still a lack of efficient therapies for these disorders other than management of symptoms. Developing therapies has been complicated because, although the total group of OXPHOS patients is relatively large, there is enormous clinical and genetic heterogeneity within this patient population. Thus there has been a lot of interest in generating relevant mouse models for the different kinds of OXPHOS disorders. The most common treatment strategies tested in these mouse models have aimed to up-regulate mitochondrial biogenesis, in order to increase the residual OXPHOS activity present in affected animals and thereby to ameliorate the energy deficiency. Drugs such as bezafibrate, resveratrol and AICAR target the master regulator of mitochondrial biogenesis PGC-1α either directly or indirectly to manipulate mitochondrial metabolism. This review will summarize the outcome of preclinical treatment trials with these drugs in mouse models of OXPHOS disorders and discuss similar treatments in a number of mouse models of common diseases in which pathology is closely linked to mitochondrial dysfunction. In the majority of these studies the pharmacological activation of the PGC-1α axis shows true potential as therapy; however, other effects besides mitochondrial biogenesis may be contributing to this as well.

Mechanisms governing the health and performance benefits of exercise

Humans are considered among the greatest if not the greatest endurance land animals. Over the last 50 years, as the population has become more sedentary, rates of cardiovascular disease and its associated risk factors such as obesity, type 2 diabetes and hypertension have all increased. Aerobic fitness is considered protective for all-cause mortality, cardiovascular disease, a variety of cancers, joint disease and depression. Here, I will review the emerging mechanisms that underlie the response to exercise, focusing on the major target organ the skeletal muscle system. Understanding the mechanisms of action of exercise will allow us to develop new therapies that mimic the protective actions of exercise.

Peroxisome proliferator-activated receptor agonists (PPARs): a promising prospect in the treatment of psoriasis and psoriatic arthritis

Psoriasis is a polygenic, inflammatory and progressive disease, characterized by an abnormal differentiation and hyperproliferation of keratinocytes, associated with impaired immunologic activation and systemic disorders, while psoriatic arthritis is a chronic inflammatory articular disease. Pathophysiology of psoriasis comprises a dysfunction of the immune system cells with an interactive network between cells and cytokines supporting the initiation and perpetuation of disease and leading to inflammation of skin, enthesis and joints. Recent studies have shown an important role of systemic inflammation in the development of atherosclerosis. Corroborating these findings, patients with severe Psoriasis have marked incidence of psoriatic arthritis, cardiovascular diseases, hypertension, dyslipidemia, obesity and diabetes mellitus, showing an increased risk for acute myocardial infarction, which suggests that the condition is not restricted to the skin. Nuclear receptors are ligand-dependent transcription factors, whose activation affects genes that control vital processes. Among them the peroxisome proliferator-activated receptor is responsible for establishing the relationship between lipids, metabolic diseases and innate immunity. In the skin, peroxisome proliferator-activated receptors have an important effect in keratinocyte homeostasis, suggesting a role in diseases such as psoriasis. The peroxisome proliferator-activated receptors agonists represent a relevant source of research in the treatment of skin conditions, however more clinical studies are needed to define the potential response of these drugs in patients with psoriasis and psoriatic arthritis.

New peroxisome proliferator-activated receptor agonists: potential treatments for atherogenic dyslipidemia and non-alcoholic fatty liver disease

INTRODUCTION

Novel peroxisome proliferator-activated receptor (PPAR) modulators (selective PPAR modulators [SPPARMs]) and dual PPAR agonists may have an important role in the treatment of cardiometabolic disorders owing to lipid-modifying, insulin-sensitizing and anti-inflammatory effects.

AREAS COVERED

This review summarizes the efficacy of new PPAR agonists and SPPARMs that are under development for the treatment of atherogenic dyslipidemia and non-alcoholic fatty liver disease (NAFLD).

EXPERT OPINION

ABT-335 is a new formulation of fenofibrate that has been approved for concomitant use with statins. K-877, a SPPARM-α with encouraging preliminary results in modulating atherogenic dyslipidemia, and INT131, a SPPARM-γ with predominantly insulin-sensitizing actions, may also have favorable lipid-modifying effects. Although the development of dual PPAR-α/γ agonists (glitazars) and the SPPARM-δ GW501516 has been abandoned because of safety issues, another SPPARM-δ (MBX-8025) and a dual PPAR-α/δ agonist (GFT-505) have shown promising efficacy in decreasing plasma triglyceride and increasing high-density lipoprotein cholesterol concentrations, as well as improving insulin sensitivity and liver function. The beneficial effects of GFT-505 are complemented by preclinical findings that indicate reduction of hepatic fat accumulation, inflammation and fibrosis, making it a promising candidate for the treatment of NAFLD/nonalcoholic steatohepatitis (NASH). Long-term trials are required to test the efficacy and safety of these new PPAR agonists in reducing cardiovascular outcomes and treating NAFLD/NASH.

The therapeutic potential of skeletal muscle plasticity in Duchenne muscular dystrophy: phenotypic modifiers as pharmacologic targets

Duchenne muscular dystrophy (DMD) is a life-limiting, neuromuscular disorder that causes progressive, severe muscle wasting in boys and young men. Although there is no cure, scientists and clinicians can leverage the fact that slower, more oxidative skeletal muscle fibers possess an enhanced degree of resistance to the dystrophic pathology relative to their faster, more glycolytic counterparts, and can thus use this knowledge when investigating novel therapeutic avenues. Several factors have been identified as powerful regulators of muscle plasticity. Some proteins, such as calcineurin, peroxisome proliferator-activated receptor (PPAR) γ coactivator 1α (PGC-1α), PPARβ/δ, and AMP-activated protein kinase (AMPK), when chronically stimulated in animal models, remodel skeletal muscle toward the slow, oxidative myogenic program, whereas others, such as receptor-interacting protein 140 (RIP140) and E2F transcription factor 1 (E2F1), repress this phenotype. Recent studies demonstrating that pharmacologic and physiological activation of targets that shift dystrophic muscle toward the slow, oxidative myogenic program provide appreciable molecular and functional benefits. This review surveys the rationale behind, and evidence for, the study of skeletal muscle plasticity in preclinical models of DMD and highlights the potential therapeutic opportunities in advancing a strategy focused on remodeling skeletal muscle in patients with DMD toward the slow, oxidative phenotype.

Pleiotropic effects of peroxisome proliferator-activated receptor γ and δ in vascular diseases

Peroxisome proliferator-activated receptors gamma (PPARγ) and delta (PPARδ) are nuclear receptors that have significant physiological effects on glucose and lipid metabolism. Experimental studies in animal models of metabolic disease have demonstrated their effects on improving lipid profile, insulin sensitivity, and reducing inflammatory responses. PPARγ and -δ are also expressed in the vasculature and their beneficial effects have been examined in various cardiovascular disease models such as atherosclerosis, hypertension, diabetic vascular complications, etc. using pharmacological ligands or genetic tools including viral vectors and transgenic mice. These studies suggest that PPARγ and δ are antiinflammatory, antiatherogenic, antioxidant, and antifibrotic against vascular diseases. Several signaling pathways, effector molecules, as well as coactivators/repressors have been identified as responsible for the protective effects of PPARγ and -δ in the vasculature. We discuss the pleiotropic effect of PPARγ and δ in vascular dysfunction, including atherosclerosis, hypertension, vascular remodeling, vascular injury, and diabetic vasculopathy, in various animal models, and the major underlying mechanisms. We also compare the phenotypes of several endothelial cell/vascular smooth muscle-specific PPARγ and -δ knockout and overexpressing transgenic mice in various disease models, and the implications underlying the functional importance of vascular PPARγ and δ in regulating whole-body homeostasis.

Peroxisome proliferator-activated receptor delta and cardiovascular disease

Recent reports have shown that peroxisome proliferator-activated receptor delta (PPARD) plays an important role in different vascular processes suggesting that PPARD is a significant modulator of cardiovascular disease. This review will focus on PPARD in relation to cardiovascular risk factors based on cell, animal and human data. Mouse studies suggest that Ppard is an important metabolic modulator that may have implications for cardiovascular disease (CVD). Specific human PPARD gene variants show no clear association with CVD but interactions between variants and lifestyle factors might influence disease risk. During recent years, development of specific and potent PPARD agonists has also made it possible to study the effects of PPARD activation in humans. PPARD agonists seem to exert beneficial effects on dyslipidemia and insulin-resistant syndromes but safety issues have been raised due to the role that PPARD plays in cell proliferation. Thus, large long term outcome as well as detailed safety and tolerability studies are needed to evaluate whether PPARD agonists could be used to treat CVD in humans.

PPARδ binding to heme oxygenase 1 promoter prevents angiotensin II-induced adipocyte dysfunction in Goldblatt hypertensive rats

Objective:

Renin–angiotensin system (RAS) regulates adipogenic response with adipocyte hypertrophy by increasing oxidative stress. Recent studies have shown the role of peroxisome proliferator-activated receptor-δ (PPARδ) agonist in attenuation of angiotensin II-induced oxidative stress. The aim of this study was to explore a potential mechanistic link between PPARδ and the cytoprotective enzyme heme oxygenase-1 (HO-1) and to elucidate the contribution of HO-1 to the adipocyte regulatory effects of PPARδ agonism in an animal model of enhanced RAS, the Goldblatt 2 kidney 1 clip (2K1C) model.

Method:

We first established a direct stimulatory effect of the PPARδ agonist (GW 501516) on the HO-1 gene by demonstrating increased luciferase activity in COS-7 cells transfected with a luciferase-HO-1 promoter construct. Sprague-Dawley rats were divided into four groups: sham-operated animals, 2K1C rats and 2K1C rats treated with GW 501516, in the absence or presence of the HO activity inhibitor, stannous mesoporphyrin (SnMP).

Results:

2K1C animals had increased visceral adiposity, adipocyte hypertrophy, increased inflammatory cytokines, increased circulatory and adipose tisssue levels of renin and Ang II along with increased adipose tissue gp91 phox expression (P<0.05) when compared with sham-operated animals. Treatment with GW 501516 increased adipose tissue HO-1 and adiponectin levels (P<0.01) along with enhancement of Wnt10b and β-catenin expression. HO-1 induction was accompanied by the decreased expression of Wnt5b, mesoderm specific transcript (mest) and C/EBPα levels and an increased number of small adipocytes (P<0.05). These effects of GW501516 were reversed in 2K1C animals exposed to SnMP (P<0.05).

Conclusion:

Taken together, our study demonstrates, for the first time, that increased levels of Ang II contribute towards adipose tissue dysregulation, which is abated by PPARδ-mediated upregulation of the heme-HO system. These findings highlight the pivotal role and symbiotic relationship of HO-1, adiponectin and PPARδ in the regulation of metabolic homeostasis in adipose tissues.