Roles of peroxisome proliferator-activated receptor gamma in cardiovascular disease

Clerodendrum volubile Ethanol Leaf Extract: A Potential Antidote to Doxorubicin-Induced Cardiotoxicity in Rats

Doxorubicin is widely applied in hematological and solid tumor treatment but limited by its off-target cardiotoxicity. Thus, cardioprotective potential and mechanism(s) of CVE in DOX-induced cardiotoxicity were investigated using cardiac and oxidative stress markers and histopathological endpoints. 50–400 mg/kg/day CVE in 5% DMSO in distilled water were investigated in Wistar rats intraperitoneally injected with 2.5 mg/kg DOX on alternate days for 14 days, using serum troponin I and LDH, complete lipid profile, cardiac tissue oxidative stress marker assays, and histopathological examination of DOX-treated cardiac tissue. Preliminary qualitative and quantitative assays of CVE's secondary metabolites were also conducted. Phytochemical analyses revealed the presence of flavonoids (34.79 ± 0.37 mg/100 mg dry extract), alkaloids (36.73 ± 0.27 mg/100 mg dry extract), reducing sugars (07.78 ± 0.09 mg/100 mg dry extract), and cardiac glycosides (24.55 ± 0.12 mg/100 mg dry extract). 50–400 mg/kg/day CVE significantly attenuated increases in the serum LDH and troponin I levels. Similarly, the CVE dose unrelatedly decreased serum TG and VLDL-c levels without significant alterations in the serum TC, HDL-c, and LDL-c levels. Also, CVE profoundly attenuated alterations in the cardiac tissue oxidative stress markers' activities while improving DOX-associated cardiac histological lesions that were possibly mediated via free radical scavenging and/or antioxidant mechanisms. Overall, CVE may play a significant therapeutic role in the management of DOX-induced cardiotoxicity in humans.

Collaborative Power of Nrf2 and PPARγ Activators against Metabolic and Drug-Induced Oxidative Injury

Mammalian cells have evolved a unique strategy to protect themselves against oxidative damage induced by reactive oxygen species (ROS). Especially, two transcription factors, nuclear factor erythroid 2p45-related factor 2 (Nrf2) and peroxisome proliferator-activated receptor γ (PPARγ), have been shown to play key roles in establishing this cellular antioxidative defense system. Recently, several researchers reported ameliorating effects of pharmacological activators for these Nrf2 and PPARγ pathways on the progression of various metabolic disorders and drug-induced organ injuries by oxidative stress. In this review, general features of Nrf2 and PPARγ pathways in the context of oxidative protection will be summarized first. Then, a number of successful applications of natural and synthetic Nrf2 and PPARγ activators to the alleviation of pathological and drug-related oxidative damage will be discussed later.

Differential Effects of Peroxisome Proliferator Activator Receptor-α and γ Ligands on Intimal Hyperplasia After Balloon Catheter-Induced Vascular Injury in Zucker Rats

Background: Patients with type 2 diabetes mellitus have a higher rate of restenosis following angioplasty. Peroxisome proliferator activator receptor-x (PPAR) and y ligands such as fenofibrate and rosiglitazone, respectively, have been shown to have protective effects on the vessel wall. We studied the effect of fenofibrate and rosiglitazone on intimal hyperplasia in the Zucker rat, a model for insulin resistance and type 2 diabetes mellitus, following balloon catheter-induced injury.

Methods and Results: Three groups of 13-week-old female fatty Zucker rats were administered an aqueous suspension of either 3 mg/kg/d rosiglitazone (n = 7) or 150 mg/kg/d fenofibrate (n = 6) by gavage, or served as controls (n = 9). In addition, two groups of 13-week-old female lean Zucker rats were either administered 3 mg/kg/d rosiglitazone (n = 6) or served as controls (n = 6). Carotid balloon injury was induced 1 week after the drugs were started. The drug administration was continued for 3 weeks. A 2-mm balloon catheter was introduced through the femoral artery to the left carotid. The balloon was inflated to 4 atmospheres for 20 seconds and then was deflated to 2 atmospheres and dragged down to the aorta. The rats were killed 3 weeks after the injury. The carotid intima/media ratio was calculated. Intimal hyperplasia after carotid balloon-induced injury in the fatty Zucker rats was significantly reduced in the group treated with rosiglitazone (0.18 ± 0.29) compared with the untreated group (0.97 ± 0.13; P < .01). Plasma glucose, triglyceride, and insulin levels were elevated, indicative of the presence of insulin resistance; rosiglitazone treatment significantly reduced insulin and triglyceride levels without decreasing glucose. Rosiglitazone treatment also reduced, but to a lesser extent, the intimal hyperplasia in the lean Zucker rats (0.57 ± 0.10 vs 1.06 ± 0.12 treated and untreated, respectively; P < .01); however, it had no effect on insulin, triglyceride, or glucose levels in this group. The intimal hyperplasia in the fatty Zucker rats treated with fenofibrate was not reduced compared with controls (0.84 ± 0.26 vs 0.97 ± 0.13, respectively); fenofibrate reduced insulin and triglyceride, but not glucose levels, in these animals.

Conclusions: The PPAR-y ligand rosiglitazone, but not the PPAR-x ligand fenofibrate, decreases intimal hyperplasia following balloon injury in both fatty and lean Zucker rats. This effect of the PPAR-y ligand was independent of glycemia, insulin, and lipid levels, and was more pronounced in insulin-resistant rats.

Association between PRO12ALA polymorphism of the PPAR-γ2 gene and type 2 diabetes mellitus in Iranian patients

BACKGROUND:

Peroxisome proliferator-activated receptor (PPARs) have been identified as ligand-activated transcription factors that belong to the nuclear receptor superfamily. It has been shown that an association exists between Proline 12 alanine (Pro12Ala) polymorphism of PPAR-GAMMA2 (PPAR-γ2) gene and increased risk of type 2 diabetes mellitus (T2DM) in different populations. Therefore, the present study was designed to investigate the association between Pro12Ala polymorphism of PPAR-γ2 gene and T2DM in an Iranian population.

MATERIALS AND METHODS:

Two hundred unrelated people, including 100 healthy controls and 100 diabetic patients were recruited diagnosed based on American Diabetes Association criteria. Blood samples were used for isolation of genomic deoxyribonucleic acid (DNA). Having extracted the genomic DNA from human blood leukocytes by means of High Pure polymerase chain reaction (PCR) Template preparation kit, we carried out polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) on each blood sample. Then, Genomic DNA was digested by BstU-I restriction enzyme. Thereafter, restriction products were analyzed by means of Polyacrylamide gel electrophoresis and stained by Ethidium Bromide.

RESULTS:

We found that the frequency of Ala allele in healthy subjects was significantly higher than in diabetic subjects (P = 0003). Moreover, the genotype frequency of Ala/Ala in healthy subjects was significantly higher than in diabetic subjects (P < 0.001). However, the genotype frequency of Ala/Pro in diabetic subjects was significantly higher than in healthy subjects (P < 0.001).

CONCLUSION:

The present study suggests that polymorphism of PPAR-γ2 gene is associated with T2DM. Furthermore, Ala allele is significantly found in non-diabetic individual’s Iranian population.

An analysis of peroxisome proliferator-activated receptor gamma (PPAR-gamma 2) Pro12Ala polymorphism distribution and prevalence of type 2 diabetes mellitus (T2DM) in world populations in relation to dietary habits

BACKGROUND AND AIM

The human peroxisome proliferator-activated receptor gamma (PPAR-gamma) is involved in lipid storage, glucose homeostasis and adipocyte differentiation. The Ala allele of the Pro12Ala polymorphism has been associated with a protective effect against T2DM. Ala allele frequencies are known for many populations, but data are absent for other interesting human groups.

METHODS AND RESULTS

We examined samples from Ethiopia, Benin, Ecuador and Italy. In addition, we performed an analysis of the Pro12Ala polymorphism distribution in world populations, also in relation to T2DM prevalence and the diet lipid content. In the European populations, the Ala allele frequencies are distributed according to a latitudinal trend, with the highest in the northern and central European populations and the lowest in the Mediterranean populations. Considering the world populations, a significant inverse relationship between Ala frequency and T2DM prevalence was observed mainly in populations where energy from lipids exceeded 30% of the total energy intake.

CONCLUSION

Northern Europe's cold climate has been hypothesised to have played a role in contributing to the present pattern. Moreover our analysis appears to confirm, at a population level, the protective effect of Ala allele against T2DM, already observed in case-control studies, but only in populations with a diet rich in lipids.

Thiazolidinediones and vascular damage

PURPOSE OF REVIEW

Although the thiazolidinediones were introduced for the treatment of hyperglycemia in type 2 diabetes, it became quickly apparent that these agents modulated many pathways related to vascular physiology and pathophysiology. Given the fact that cardiovascular disease is the leading cause of death in diabetes, it has become important to know whether these agents have vasculoprotective effects and if so whether these are associated with the prevention of cardiovascular disease.

RECENT FINDINGS

The thiazolidinedione class improves endothelial vasomotion, inhibits inflammatory and procoagulant processes and has powerful antiproliferative and antioxidant effects. Experimentally these agents retard atherosclerosis development in predisposed animals. Clinical studies demonstrate that they increase HDL cholesterol and LDL size, and may lower triglyceride levels. They modestly lower blood pressure, reduce microalbuminuria, arterial stiffness and reduce carotid wall thickening. These effects are generally independent of glucose lowering and in many instances have been shown to occur in nondiabetic subjects. A single clinical endpoint intervention trial of add-on pioglitazone treatment in type 2 diabetic patients with cardiovascular disease suggested on secondary analyses that the agent reduced cardiovascular events.

SUMMARY

The weight of the experimental, subclinical and clinical assessments of the effects of these agents supports the contention that they are vasculoprotective. In the final analysis their use in clinical practice to prevent cardiovascular disease will mostly depend on whether clinical trials consistently demonstrate that they reduced cardiovascular events.

A role for the peroxisome proliferator-activated receptor α in T-cell physiology and ageing immunobiology

Peroxisome proliferator-activated receptor (PPAR) α represents an important member of the nuclear hormone receptor superfamily that can be activated by a variety of natural fatty acids, some of their metabolites and by commonly-used anti-lipidaemic drugs. We recently demonstrated PPARα expression in T lymphocytes, where it controls the initiation of transcription of T-box expressed in T-cells (T-bet) independent of added agonist. T-bet is an activation-inducible transcription factor regulator of interleukin 2 (suppression) and interferon γ (stimulation) synthesis. A suppressed ability to produce interleukin 2 and an enhanced production of interferon γ occurs in activated T-cells from PPARα-/- mice, as well as in T-cells from wild-type aged animals whose lymphocytes express lowered basal levels of PPARα. The dysregulated expression and/or function of cytokines, glucocorticoids or leptin that occurs with advanced age could all be responsible for the reduced expression of PPARα. Dietary supplementation of aged mice with vitamin E, or supplementation with known agonists of PPARα, was associated with elevation of lymphocyte expression of this nuclear hormone receptor, restoration of control over T-bet expression and elimination of the dysregulated production of interleukin 2 and interferon γ following lymphocyte activation. Interleukin 2 and interferon γ play very important roles in the initiation and/or regulation of immune, inflammatory and autoimmune disease states. Thus, the mechanisms that control the timing, magnitude and duration of specific cytokine production by activated T lymphocytes need clarification before appropriate nutritional or therapeutic strategies can be devised to treat disease conditions where cytokine expression and/or activities are deemed to be dysregulated and responsible.

The peroxisome proliferator-activated receptor gamma (PPAR-γ2) Pro12Ala polymorphism is associated with higher risk for Alzheimer's disease in octogenarians

Recent observations support the hypothesis that inflammatory processes at the brain level may contribute to the pathogenesis of Alzheimer's disease (AD). Peroxisome proliferator-activated receptor gamma (PPAR-gamma) is involved in such processes, so we thought it interesting to study the Pro12Ala polymorphism in exon 2 of the gene in a sample of late-onset AD patients. We found that Ala genotypes were significantly overrepresented among octogenarian patients compared to controls (p=0.034). Using logistic regression we observed that carrying the Ala allele significantly increased by nearly two-fold the risk of developing AD in subjects 80 years or older (OR=1.98; 95% CI 1.03-3.80, p=0.04). Though this difference was borderline significant after correction for multiple comparisons, our results suggest a possible involvement of the PPAR-gamma gene in susceptibility to late-onset AD in octogenarians.

Genetic variants in peroxisome proliferator-activated receptor gamma influence insulin resistance and testosterone levels in normal women, but not those with polycystic ovary syndrome

OBJECTIVE

To investigate the relationship of the peroxisome proliferator-activated receptor gamma (PPARG) Pro12Ala and silent exon 6 (His447His) polymorphisms with the clinical features of polycystic ovary syndrome (PCOS).

DESIGN

Patients with PCOS and control subjects were genotyped for Pro12Ala and His447His. Associations between genotype, diagnosis, and hormonal/metabolic parameters were assessed.

SETTING

Subjects were recruited from the reproductive endocrinology clinic at the University of Alabama at Birmingham, Birmingham, Alabama. Control subjects were recruited from the surrounding community. Genotyping was performed at the Cedars-Sinai Medical Center in Los Angeles, California.

PATIENT(S)

Participants included 285 white women with PCOS and 187 controls.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The Pro12Ala and His447His genotypes, and hormonal and metabolic phenotypes.

RESULT(S)

The Pro12Ala and His447His genotypes did not influence risk of PCOS or its component phenotypes in patients with PCOS. In controls, Pro12Ala did not influence measures of insulin resistance or androgen production. However, carriers of the His447His T-allele had significantly decreased free and total T levels, and a significantly decreased homeostasis model assessment index of insulin resistance. Furthermore, haplotypes in controls bearing the His447His T-allele were also associated with decreased T.

CONCLUSION(S)

Peroxisome proliferator-activated receptor gamma does not appear to be an important modifier gene in PCOS. In controls, however, the His447His T-allele may be in linkage disequilibrium with a functional variant that influences insulin resistance and T production.

Thiazolidinediones

Our knowledge and understanding of the role played by peroxisome proliferator-activated gamma receptors in physiology and pathophysiology has expanded dramatically over the past 5 years. Originally described as having important functions in adipogenesis and glucose homeostasis, their pharmacologic agonists, the thiazolidinediones, were introduced as antihyperglycemic, insulin-sensitizing agents for the management of type 2 diabetes mellitus. However, it was to some degree inevitable that the thiazolidinediones would be rapidly recognized as having vasculoprotective properties beyond glycemic control that might also be beneficial. First, diabetic complications are vascular in nature, the earliest feature of these is endothelial dysfunction. Second, it is being increasingly appreciated that these complications develop through inflammatory and procoagulant pathways in which increased oxidative stress is considered a major etiologic mechanism, and which are closely linked to the presence of insulin resistance, visceral obesity, and hyperglycemia. Early appreciation that the thiazolidinediones have antioxidant, anti-inflammatory, anti-procoagulant, and antiproliferative properties in addition to their insulin-sensitizing, anti-lipotoxic properties created a marriage of investigative pathways that has not only led to a very large body of literature on the pleiotropic effects of thiazolidinediones, but also to the development of new understandings of the connections between insulin resistance, obesity, and hyperglycemia and the onset of vascular disease. Understandably, most of the focus has been directed at the macrovascular complications of diabetes, since these are the major causes of morbidity and mortality in this population. However, there is evidence that these agents may have benefits for the microvascular complications as well, and their potential role for cardiovascular disease prevention in non-diabetic patients with the metabolic syndrome is a logical extension of the work performed in diabetes. The recently reported results of the effects of pioglitazone versus placebo on cardiovascular events in patients with type 2 diabetes support the contention that these agents have vasculoprotective effects.

Quercetin protects against linoleic acid-induced porcine endothelial cell dysfunction

Consumption of plant phenolics, such as quercetin, may be associated with decreased risk of cardiovascular disease by stabilizing and protecting vascular endothelial cells against oxidative and proinflammatory insults. The present study focused on the effect of quercetin on linoleic acid-induced oxidative stress and the inflammatory pathways of nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1). Because the transcription factor peroxisome proliferator activated receptor gamma (PPARgamma) was reported to downregulate inflammatory pathways, we further investigated the effect of quercetin on PPARgamma. Porcine pulmonary-arterial endothelial cells were activated with linoleic acid in the presence or absence of quercetin. Oxidative stress was markedly induced by endothelial cell exposure to linoleic acid and diminished by treatment with quercetin as measured via the oxidation of 2',7'-dichlorofluorescin. Quercetin reduced linoleic acid-mediated binding activity of NF-kappaB and AP-1 and mRNA levels of inflammatory genes such as interleukin-6 (IL-6) and vascular cell adhesion molecule-1 (VCAM-1). Cotreatment of linoleic acid plus quercetin or vitamin E also decreased linoleic acid-induced binding activity of PPARgamma. These data suggest that quercetin has potent antioxidative and anti-inflammatory properties and protects endothelial cells against linoleic acid-mediated cell dysfunction.

Quantitative analysis of peroxisome proliferator-activated receptor gamma (PPARγ) expression in arteries and hearts of patients with ischaemic or dilated cardiomyopathy

PPARgamma, a nuclear transcription factor, is expressed in various cells within the vasculature and in cardiomyocytes. It has been suggested that PPARgamma is involved in atherogenesis and in cardiac hypertrophy. Therefore, we sought to quantify PPARgamma mRNA in coronary arteries, the aorta and left ventricular specimens from patients with ischaemic (CHD) and dilated cardiomyopathy (CMP). Using real-time PCR, we were able to demonstrate the expression of PPARgamma in all of the human specimens. The lowest expression of PPARgamma was detected in the aorta specimens of both groups (this was set to one). In comparison, the expression in coronary arteries was 2.32-fold in CHD- and 3.78-fold in CMP specimens and in the left ventricle specimens, 2.12-fold in CHD- and 3.51-fold in CMP. Samples from CHD patients showed a higher expression of PPARgamma in all of the samples compared to those from CMP patients (aorta: 1.99-fold; coronary arteries: 1.35; left ventricles: 1.23). PPARgamma levels were not significantly correlated to CD 36 expression values in any group, suggesting that higher levels of PPARgamma are not principally due to increased PPARgamma expression in macrophages. This was confirmed by immunohistochemical analysis, which showed that PPARgamma is also located in the smooth muscle layer and in cardiomyocytes. In conclusion, our observations of increased PPAR mRNA expression in the coronary arteries and left ventricles from CHD and CMP patients suggest an important function of this nuclear receptor in the pathogenesis of heart disease.

Rosiglitazone activates renal sodium- and water-reabsorptive pathways and lowers blood pressure in normal rats

Synthetic agonists of the peroxisomal proliferator-activated receptor subtype gamma (PPAR-gamma) are highly beneficial in the treatment of type II diabetes. However, they are also associated with fluid retention and edema, potentially serious side effects of unknown origin. These studies were designed to test the hypothesis that rosiglitazone (RGZ, PPAR-gamma agonist) may activate sodium- and water-reabsorptive processes in the kidney, possibly in response to a drop in mean arterial blood pressure (MAP), as well as directly through PPAR-gamma. Targeted proteomics of the major renal sodium and water transporters and channel proteins was used to identify potentially regulated sites of renal sodium and water reabsorption. RGZ (47 or 94 mg/kg diet) was fed to male, Sprague-Dawley rats (approximately 270g) for 3 days. MAP, measured by radiotelemetry, was decreased significantly in rats fed either level of RGZ, relative to control rats. Delta MAP from baseline was -3.2 +/- 1.2 mm Hg in rats fed high-dose RGZ versus + 3.4 +/- 0.8 for rats fed control diet. RGZ did not affect feed or water intake, but rats treated with high-dose RGZ had decreased urine volume (by 22%), sodium excretion (44%), kidney weight (9%), and creatinine clearance (35%). RGZ increased whole kidney protein abundance of the alpha-1 subunit of Na-K-ATPase, the bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2), the sodium hydrogen exchanger (NHE3), the aquaporins 2 and 3, and endothelial nitric-oxide synthase. We conclude that both increases in renal tubule transporter abundance and a decrease in glomerular filtration rate likely contribute to the RGZ-induced sodium retention.

Peroxisome proliferator-activated receptor γ C161T polymorphisms and survival of Japanese patients with immunoglobulin A nephropathy

Peroxisome proliferator-activated receptor gamma (PPAR gamma) plays an important role in lipid metabolism, insulin sensitivity, atherogenesis, and immune regulation. A genetic polymorphism (C161T) at exon 6 of PPAR gamma gene (PPARG) was reported to be associated with the onset of coronary artery disease. However, there has been no report of an association with renal disease. Genomic DNAs were isolated from 225 Japanese patients with histologically confirmed immunoglobulin A nephropathy (IgAN). The PPARG C161T genotype was determined by polymerase chain reaction-restriction fragment length polymorphism. The association of the polymorphism with renal prognosis in IgAN patients was analyzed using the Kaplan-Meier method and Cox proportional hazard regression model. The PPARG polymorphism was not associated with the renal survival rate. However, when patients were stratified into those either with or without hypertension at the time of diagnosis, the renal survival of the CT/TT genotypes was significantly better in those without hypertension than those with the CC genotype. We report that the PPARG C161T polymorphism is associated with the survival of IgAN patients without hypertension. The T allele of the polymorphism might have a protective effect on the progression of IgAN.

Inhibitory molecules in signal transduction pathways of cardiac hypertrophy

Cardiac hypertrophy is induced by a variety of diseases, such as hypertension, valvular diseases, myocardial infarction, and endocrine disorders. Although cardiac hypertrophy may initially be a beneficial response that normalizes wall stress and maintains normal cardiac function, prolonged hypertrophy is a leading cause of heart failure and sudden death. A number of studies have elucidated molecules responsible for the development of cardiac hypertrophy, including the mitogen-activated protein (MAP) kinases pathway, Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, and calcium/calmodulin-dependent protein phosphatase calcineurin pathway. These molecules may be targets for therapies designed to prevent the progression of cardiac hypertrophy. Numerous studies have focused on characterization of the intracellular signal transduction molecules that promote cardiac hypertrophy in order to clarify the molecular mechanisms, but there have been only a few reports on the inhibitory regulators of hypertrophic response. Recently, several molecules have attracted much attention as endogenous inhibitory regulators of cardiac hypertrophy. Enhancement of these inhibitory regulators would also seem to be a potential approach for the pharmacological treatment of hypertrophy. In this review, we summarize the inhibitory molecules of cardiac hypertrophy.