Peroxisome proliferator-activated receptor gamma ligands increase release of nitric oxide from endothelial cells

PPARs in atherosclerosis: The spatial and temporal features from mechanism to druggable targets

BACKGROUND

Atherosclerosis is a chronic and complex disease caused by lipid disorder, inflammation, and other factors. It is closely related to cardiovascular diseases, the chief cause of death globally. Peroxisome proliferator-activated receptors (PPARs) are valuable anti-atherosclerosis targets that showcase multiple roles at different pathological stages of atherosclerosis and for cell types at different tissue sites.

AIM OF REVIEW

Considering the spatial and temporal characteristics of the pathological evolution of atherosclerosis, the roles and pharmacological and clinical studies of PPARs were summarized systematically and updated under different pathological stages and in different vascular cells of atherosclerosis. Moreover, selective PPAR modulators and PPAR-pan agonists can exert their synergistic effects meanwhile reducing the side effects, thereby providing novel insight into future drug development for precise spatial-temporal therapeutic strategy of anti-atherosclerosis targeting PPARs.

KEY SCIENTIFIC

Concepts of Review: Based on the spatial and temporal characteristics of atherosclerosis, we have proposed the importance of stage- and cell type-dependent precision therapy. Initially, PPARs improve endothelial cells' dysfunction by inhibiting inflammation and oxidative stress and then regulate macrophages' lipid metabolism and polarization to improve fatty streak. Finally, PPARs reduce fibrous cap formation by suppressing the proliferation and migration of vascular smooth muscle cells (VSMCs). Therefore, research on the cell type-specific mechanisms of PPARs can provide the foundation for space-time drug treatment. Moreover, pharmacological studies have demonstrated that several drugs or compounds can exert their effects by the activation of PPARs. Selective PPAR modulators (that specifically activate gene subsets of PPARs) can exert tissue and cell-specific effects. Furthermore, the dual- or pan-PPAR agonist could perform a better role in balancing efficacy and side effects. Therefore, research on cells/tissue-specific activation of PPARs and PPAR-pan agonists can provide the basis for precision therapy and drug development of PPARs.

PPARγ in Atherosclerotic Endothelial Dysfunction: Regulatory Compounds and PTMs

The formation of atherosclerotic plaques is one of the main sources of cardiovascular disease. In addition to known risk factors such as dyslipidemia, diabetes, obesity, and hypertension, endothelial dysfunction has been shown to play a key role in the formation and progression of atherosclerosis. Peroxisome proliferator-activated receptor-gamma (PPARγ), a transcription factor belonging to the steroid superfamily, is expressed in the aorta and plays a critical role in protecting endothelial function. It thereby serves as a target for treating both diabetes and atherosclerosis. Although many studies have examined endothelial cell disorders in atherosclerosis, the role of PPARγ in endothelial dysfunction is still not well understood. In this review, we summarize the possible mechanisms of action behind PPARγ regulatory compounds and post-translational modifications (PTMs) of PPARγ in the control of endothelial function. We also explore the potential use of endothelial PPARγ-targeted agents in the prevention and treatment of atherosclerosis.

Systemic and Airway Epigenetic Disruptions Are Associated with Health Status in COPD

Epigenetic modifications are common in chronic obstructive pulmonary disease (COPD); however, their clinical relevance is largely unknown. We hypothesized that epigenetic disruptions are associated with symptoms and health status in COPD. We profiled the blood (n = 57) and airways (n = 62) of COPD patients for DNA methylation (n = 55 paired). The patients' health status was assessed using the St. George's Respiratory Questionnaire (SGRQ). We conducted differential methylation analyses and identified pathways characterized by epigenetic disruptions associated with SGRQ scores and its individual domains. 29,211 and 5044 differentially methylated positions (DMPs) were associated with total SGRQ scores in blood and airway samples, respectively. The activity, impact, and symptom domains were associated with 9161, 25,689 and 17,293 DMPs in blood, respectively; and 4674, 3730 and 5063 DMPs in airways, respectively. There was a substantial overlap of DMPs between airway and blood. DMPs were enriched for pathways related to common co-morbidities of COPD (e.g., ageing, cancer and neurological) in both tissues. Health status in COPD is associated with airway and systemic epigenetic changes especially in pathways related to co-morbidities of COPD. There are more blood DMPs than in the airways suggesting that blood epigenome is a promising source to discover biomarkers for clinical outcomes in COPD.

Cumulative incidence and risk factors for radiation induced leukoencephalopathy in high grade glioma long term survivors

The incidence and risk factors associated with radiation-induced leukoencephalopathy (RIL) in long-term survivors of high-grade glioma (HGG) are still poorly investigated. We performed a retrospective research in our institutional database for patients with supratentorial HGG treated with focal radiotherapy, having a progression-free overall survival > 30 months and available germline DNA. We reviewed MRI scans for signs of leukoencephalopathy on T2/FLAIR sequences, and medical records for information on cerebrovascular risk factors and neurological symptoms. We investigated a panel of candidate single nucleotide polymorphisms (SNPs) to assess genetic risk. Eighty-one HGG patients (18 grade IV and 63 grade III, 50M/31F) were included in the study. The median age at the time of radiotherapy was 48 years old (range 18-69). The median follow-up after the completion of radiotherapy was 79 months. A total of 44 patients (44/81, 54.3%) developed RIL during follow-up. Twenty-nine of the 44 patients developed consistent symptoms such as subcortical dementia (n = 28), gait disturbances (n = 12), and urinary incontinence (n = 9). The cumulative incidence of RIL was 21% at 12 months, 42% at 36 months, and 48% at 60 months. Age > 60 years, smoking, and the germline SNP rs2120825 (PPARg locus) were associated with an increased risk of RIL. Our study identified potential risk factors for the development of RIL (age, smoking, and the germline SNP rs2120825) and established the rationale for testing PPARg agonists in the prevention and management of late-delayed radiation-induced neurotoxicity.

PPARγ Deacetylation Confers the Antiatherogenic Effect and Improves Endothelial Function in Diabetes Treatment

Cardiovascular disease (CVD) is the leading cause of death in patients with diabetes, and tight glycemic control fails to reduce the risk of developing CVD. Thiazolidinediones (TZDs), a class of peroxisome proliferator-activated receptor γ (PPARγ) agonists, are potent insulin sensitizers with antiatherogenic properties, but their clinical use is limited by side effects. PPARγ deacetylation on two lysine residues (K268 and K293) induces brown remodeling of white adipose tissue and uncouples the adverse effects of TZDs from insulin sensitization. Here we show that PPARγ deacetylation confers antiatherogenic properties and retains the insulin-sensitizing effects of TZD while circumventing its detriments. We generated mice homozygous with mice with deacetylation-mimetic PPARγ mutations K268R/K293R (2KR) on an LDL-receptor knockout (Ldlr ^-/- ) background. 2KR:Ldlr ^-/- mice showed smaller atherosclerotic lesion areas than Ldlr ^-/- mice, particularly in aortic arches. With rosiglitazone treatment, 2KR:Ldlr ^-/- mice demonstrated a residual antiatherogenic response and substantial protection against bone loss and fluid retention. The antiatherosclerotic effect of 2KR was attributed to the protection of endothelium, indicated by improved endothelium-dependent vasorelaxation and repressed expression of proatherogenic factors including inducible nitric oxide synthase, interleukin-6, and NADPH oxidase 2. Therefore, manipulating PPARγ acetylation is a promising therapeutic strategy to control risk of CVD in diabetes treatment.

PPARγ and RhoBTB1 in hypertension

PURPOSE OF REVIEW

This review provides an up-to-date understanding of how peroxisome proliferator activated receptor γ (PPARγ) exerts its cardioprotective effect in the vasculature through its activation of novel PPARγ target genes in endothelium and vascular smooth muscle.

RECENT FINDINGS

In vascular endothelial cells, PPARγ plays a protective role by increasing nitric oxide bioavailability and preventing oxidative stress. RBP7 is a PPARγ target gene enriched in vascular endothelial cells, which is likely to form a positive feedback loop with PPARγ. In vascular smooth muscle cells, PPARγ antagonizes the renin-angiotensin system, maintains vascular integrity, suppresses vasoconstriction, and promotes vasodilation through distinct pathways. Rho-related BTB domain containing protein 1 (RhoBTB1) is a novel PPARγ gene target in vascular smooth muscle cells that mediates the protective effect of PPARγ by serving as a substrate adaptor between the Cullin-3 RING ubiquitin ligase and phosphodiesterase 5, thus restraining its activity through ubiquitination and proteasomal degradation.

SUMMARY

In the vasculature, PPARγ exerts its cardioprotective effect through its transcriptional activity in endothelium and vascular smooth muscle. From the understanding of PPARγ's transcription targets in those pathways, novel hypertension therapy target(s) will emerge.

The impact of acute rosiglitazone on insulin pharmacokinetics at the blood-brain barrier

INTRODUCTION

CNS insulin levels are decreased and insulin receptor signalling is dampened in Alzheimer's disease (AD). Increasing CNS insulin levels through a variety of methods has been shown to improve memory. Indeed, medications routinely used to improve insulin resistance in type 2 diabetes are now being repurposed for memory enhancement. CNS insulin is primarily derived from the circulation, by an active transport system at the blood-brain barrier (BBB). The goal of this study was to determine whether rosiglitazone (RSG), a drug used to improve insulin sensitivity in type 2 diabetes, could enhance insulin transport at the BBB, as a potential therapeutic for improving memory.

METHODS

Using radioactively labelled insulin and the multiple-time regression analysis technique, we measured the rate of insulin BBB transport and level of vascular binding in mice pretreated with vehicle or 10 µg RSG in the presence or absence of an insulin receptor inhibitor.

RESULTS

Although we found acute RSG administration does not affect insulin transport at the BBB, it does restore BBB vascular binding of insulin in an insulin receptor-resistant state.

CONCLUSIONS

Acute RSG treatment does not alter insulin BBB transport in healthy mice but can restore insulin receptor binding at the BBB in an insulin-resistant state.

The impact of single and combined PPAR-α and PPAR-γ activation on the neurological outcomes following cerebral ischemia reperfusion

AIM

The neuronal damage and accompanied functional deficits induced by cerebral ischemia are among the most common causes of disabilities in adults. Activation of subtypes of peroxisome proliferator-activated receptors (PPARs); PPAR-α and PPAR-γ have shown neuroprotective effects in different neurodegenerative diseases including stroke. Thus, this study aimed to compare the effects of two different agonists: PPAR-α (fenofibrate) and PPAR-γ (pioglitazone) as well as the effect of their combination in ameliorating post-ischemia behavioral deficits.

METHODS

Male Wistar rats were either pretreated with vehicle, fenofibrate (100 mg/kg/day p.o), pioglitazone (10 mg/kg/day p.o) or their combination for 14 days prior to bilateral common carotid artery occlusion followed by reperfusion for 24 hoursh. The sensory motor functions of rats were assessed, then rats were sacrificed to determine infarct volume and histopathological changes as well as oxidative stress, inflammatory and apoptotic markers in the brain tissue.

KEY FINDINGS

Pre-treatment with fenofibrate and pioglitazone in addition to their combination improved neurobehavioral dysfunction, reduced cerebral infarct volume, attenuated inflammatory and apoptotic markers and ameliorated histopathological changes in I/R injured rats. The effect of pioglitazone in cerebral cortex was higher than its corresponding effect in fenofibrate while the combined administration of both drugs had additive neuroprotective effect and normalized inflammatory and apoptotic mediators in ischemic rats.

SIGNIFICANCE

The study compared the neuroprotective effects of PPAR-α and PPAR-γ agonists, and tested the impact of their combination. We concluded that no additional benefits on the functional outcomes might be gained upon their combination.

Redox Biology of Peroxisome Proliferator-Activated Receptor-γ in Pulmonary Hypertension

Significance: Peroxisome proliferator-activated receptor-gamma (PPARγ) maintains pulmonary vascular health through coordination of antioxidant defense systems, inflammation, and cellular metabolism. Insufficient PPARγ contributes to pulmonary hypertension (PH) pathogenesis, whereas therapeutic restoration of PPARγ activity attenuates PH in preclinical models. Recent Advances: Numerous studies in the past decade have elucidated the complex mechanisms by which PPARγ in the pulmonary vasculature and right ventricle (RV) protects against PH. The scope of PPARγ-interconnected pathways continues to expand and includes induction of antioxidant genes, transrepression of inflammatory signaling, regulation of mitochondrial biogenesis and bioenergetic integrity, control of cell cycle and proliferation, and regulation of vascular tone through interactions with nitric oxide and endogenous vasoactive molecules. Furthermore, PPARγ interacts with an extensive regulatory network of transcription factors and microRNAs leading to broad impact on cell signaling. Critical Issues: Abundant evidence suggests that targeting PPARγ exerts diverse salutary effects in PH and represents a novel and potentially translatable therapeutic strategy. However, progress has been slowed by an incomplete understanding of how specific PPARγ pathways are critically disrupted across PH disease subtypes and lack of optimal pharmacological ligands. Future Directions: Recent studies indicate that ligand-induced post-translational modifications of the PPARγ receptor differentially induce therapeutic benefits versus adverse side effects of PPARγ receptor activation. Strategies to selectively target PPARγ activity in diseased cells of pulmonary circulation and RV, coupled with development of ligands designed to specifically regulate post-translational PPARγ modifications, may unlock the full therapeutic potential of this versatile master transcriptional and metabolic regulator in PH.

Endothelial PPARγ Is Crucial for Averting Age-Related Vascular Dysfunction by Stalling Oxidative Stress and ROCK

Aging plays a significant role in the progression of vascular diseases and vascular dysfunction. Activation of the ADP-ribosylation factor 6 and small GTPases by inflammatory signals may cause vascular permeability and endothelial leakage. Pro-inflammatory molecules have a significant effect on smooth muscle cells (SMC). The migration and proliferation of SMC can be promoted by tumor necrosis factor alpha (TNF-α). TNF-α can also increase oxidative stress in SMCs, which has been identified to persuade DNA damage resulting in apoptosis and cellular senescence. Peroxisome proliferator-activated receptor (PPAR) acts as a ligand-dependent transcription factor and a member of the nuclear receptor superfamily. They play key roles in a wide range of biological processes, including cell differentiation and proliferation, bone formation, cell metabolism, tissue remodeling, insulin sensitivity, and eicosanoid signaling. The PPARγ activation regulates inflammatory responses, which can exert protective effects in the vasculature. In addition, loss of function of PPARγ enhances cardiovascular events and atherosclerosis in the vascular endothelium. This appraisal, therefore, discusses the critical linkage of PPARγ in the inflammatory process and highlights a crucial defensive role for endothelial PPARγ in vascular dysfunction and disease, as well as therapy for vascular aging.

The AGP-PPARγ axis promotes oxidative stress and diabetic endothelial cell dysfunction

Alkyl-glycerophosphate (AGP) accumulates in atherogenic oxidized-LDL and human atherosclerotic plaques and is a potent agonist of peroxisome-proliferator-activated receptor-gamma (PPARγ). Recent studies suggest a potential regulatory role for PPARγ in endothelial nitric oxide synthase (eNOS) expression/activation and nitrogen oxide (NO) generation in the vascular endothelium. Importantly, eNOS-induced NO and advanced glycation end-products (AGEs) are involved in blood-vessel damage, and diabetic patients exhibit high serum NO and AGE levels; however, the effect of AGP on NO- and AGE-mediated endothelium dysfunction remains unknown. Investigation of the AGP-specific effects on NO- and AGE-mediated dysfunction and the underlying molecular mechanisms revealed that AGP upregulated eNOS expression and NO production, and that eNOS silencing and PPARγ antagonism inhibited AGP-mediated eNOS upregulation and NO production. Moreover, AGP-PPARγ-axis-mediated NO production promoted the generation of reactive oxygen species and AGE formation. These results suggested that AGP plays a significant role in the initiation/progression of diabetes-related atherosclerosis through PPARγ activation.

Estradiol attenuates ischemia reperfusion-induced acute kidney injury through PPAR-γ stimulated eNOS activation in rats

We investigated the involvement of peroxisome proliferator activated receptor-γ (PPAR-γ)/endothelial nitric oxide synthase (eNOS) pathway in estradiol mediated protection against ischemia reperfusion (I/R)-induced acute kidney injury (AKI) in rats. To induce AKI, rats underwent 40 min of bilateral renal ischemia followed by 24 h of reperfusion. I/R-induced kidney damage was quantified by measuring serum creatinine, creatinine clearance, urea nitrogen, uric acid, potassium, fractional excretion of sodium, microproteinuria, and renal oxidative stress (thiobarbituric acid reactive substances, superoxide anion generation, and reduced glutathione). Hematoxylin eosin stain demonstrated renal histology, while renal expression of apoptotic markers (Bcl-2, Bax), PPAR-γ and eNOS were quantified by immunohistochemistry. Estradiol (1 mg/kg, i.p.) was administered 30 min before I/R in rats. In separate groups, PPAR-γ antagonist, BADGE (30 mg/kg, i.p.), and NOS inhibitor, L-NAME (20 mg/kg, i.p.) were administered prior to estradiol treatment, which was followed by I/R in rats. I/R caused significant renal damage as demonstrated by biochemical (serum/urine), renal oxidative stress and histological changes alongwith increased expression of Bax and decreased levels of Bcl-2, PPAR-γ and eNOS, which were prevented by estradiol. Pre-treatment with BADGE and L-NAME abolished estradiol mediated renoprotection. Notably, I/R + estradiol + BADGE group revealed decreased expression of PPAR-γ and eNOS in renal tissues. In I/R + estradiol + L-NAME group, eNOS expression was reduced while PPAR-γ levels remained unchanged. These results suggest that estradiol modulates PPAR-γ which consequently regulates eNOS expression in rat kidneys. We conclude that estradiol protects against I/R-induced AKI through PPAR-γ stimulated eNOS activation in rats.

Vascular smooth muscle cell peroxisome proliferator-activated receptor γ protects against endothelin-1-induced oxidative stress and inflammation

AIMS

Peroxisome proliferator-activated receptor γ (PPARγ) agonists reduce blood pressure and vascular injury in hypertensive rodents. Pparγ inactivation in vascular smooth muscle cells (VSMC) enhances vascular injury. Transgenic mice overexpressing endothelin (ET)-1 selectively in the endothelium (eET-1) exhibit endothelial dysfunction, increased oxidative stress and inflammation. We hypothesized that inactivation of the Pparγ gene in VSMC (smPparγ-/-) would exaggerate ET-1-induced vascular injury.

METHODS AND RESULTS

eET-1, smPparγ-/- and eET-1/smPparγ-/- mice were treated with tamoxifen for 5 days and studied 4 weeks later. SBP was higher in eET-1 and unaffected by smPparγ inactivation. Mesenteric artery vasodilatory responses to acetylcholine were impaired only in smPparγ-/-. N(omega)-Nitro-L-arginine methyl ester abrogated relaxation responses, and the Ednra/Ednrb mRNA ratio was decreased in eET-1/smPparγ-/-, which could indicate that nitric oxide production was enhanced by ET-1 stimulation of endothelin type B receptors. Mesenteric artery media/lumen was greater only in eET-1/smPparγ-/-. Mesenteric artery reactive oxygen species increased in smPparγ and were further enhanced in eET-1/smPparγ-/-. Perivascular fat monocyte/macrophage infiltration was higher in eET-1 and smPparγ and increased further in eET-1/smPparγ-/-. Spleen CD11b+ cells were increased in smPparγ-/- and further enhanced in eET-1/smPparγ-/-, whereas Ly-6C(hi) monocytes increased in eET-1 and smPparγ-/- but not in eET-1/smPparγ-/-. Spleen T regulatory lymphocytes increased in smPparγ and decreased in eET-1, and decreased further in eET-1/smPparγ-/-.

CONCLUSION

VSMC Pparγ inactivation exaggerates ET-1-induced vascular injury, supporting a protective role for PPARγ in hypertension through modulation of pro-oxidant and proinflammatory pathways. Paradoxically, ET-1 overexpression preserved endothelial function in smPparγ-/- mice, presumably by enhancing nitric oxide through stimulation of endothelin type B receptors.

Efficacy and safety of thiazolidinediones in diabetes patients with renal impairment: a systematic review and meta-analysis

We conducted a systematic review and meta-analysis to evaluate the efficacy and safety of TZDs in treatment of diabetes mellitus patients with renal impairment. We searched PubMed, EMBASE and Cochrane Central Register of Controlled Trials. Randomized controlled trials (RCTs), cohort studies, and case-control studies that investigated the effects of TZDs in patients with diabetes and renal impairment were eligible. Outcomes included glycosylated hemoglobin, fasting plasma glucose, serum lipids, and patient-important outcomes (i.e. hypoglycemia, weight, edema, cardiovascular events and mortality). 19 RCTs and 3 cohort studies involving 21,803 patients with diabetes and renal impairment were included. Meta-analysis of RCTs showed that TZDs could significantly reduce HbA1c (MD -0.64, 95%CI -0.93 to -0.35), FPG (MD -26.27, 95%CI -44.90 to -7.64) and increase HDL levels (MD 3.70, 95%CI 1.10, 6.29). TZDs could increase weight (MD 3.23, 95% CI 2.29 to 4.16) and risk of edema (RR 2.96, 95% CI 1.22 to 7.20). Their effects on risk of hypoglycemia (RR 1.46, 95% CI 0.65 to 3.29), heart failure (RR 0.64, 95% CI 0.15 to 2.66), angina (RR 1.45, 95% CI 0.23 to 8.95) and all-cause mortality (RR 0.40, 95% CI 0.08 to 2.01) are uncertain. Results from cohort studies were similar to RCTs.

Retinol-binding protein 7 is an endothelium-specific PPAR cofactor mediating an antioxidant response through adiponectin

Impaired PPARγ activity in endothelial cells causes oxidative stress and endothelial dysfunction which causes a predisposition to hypertension, but the identity of key PPARγ target genes that protect the endothelium remain unclear. Retinol-binding protein 7 (RBP7) is a PPARγ target gene that is essentially endothelium specific. Whereas RBP7-deficient mice exhibit normal endothelial function at baseline, they exhibit severe endothelial dysfunction in response to cardiovascular stressors, including high-fat diet and subpressor angiotensin II. Endothelial dysfunction was not due to differences in weight gain, impaired glucose homeostasis, or hepatosteatosis, but occurred through an oxidative stress-dependent mechanism which can be rescued by scavengers of superoxide. RNA sequencing revealed that RBP7 was required to mediate induction of a subset of PPARγ target genes by rosiglitazone in the endothelium including adiponectin. Adiponectin was selectively induced in the endothelium of control mice by high-fat diet and rosiglitazone, whereas RBP7 deficiency abolished this induction. Adiponectin inhibition caused endothelial dysfunction in control vessels, whereas adiponectin treatment of RBP7-deficient vessels improved endothelium-dependent relaxation and reduced oxidative stress. We conclude that RBP7 is required to mediate the protective effects of PPARγ in the endothelium through adiponectin, and RBP7 is an endothelium-specific PPARγ target and regulator of PPARγ activity.

The Role of PPARγ in Cardiovascular Diseases

The peroxisome proliferator-activated receptors (PPAR) belong to the nuclear superfamily of ligand-activated transcription factors. PPARγ acts as a nutrient sensor that regulates several homeostatic functions. Its disruption can lead to vascular pathologies, disorders of fatty acid/lipid metabolism and insulin resistance. PPARγ can modulate several signaling pathways connected with blood pressure regulation. Firstly, it affects the insulin signaling pathway and endothelial dysfunction by modulation of expression and/or phosphorylation of signaling molecules through the PI3K/Akt/eNOS or MAPK/ET-1 pathways. Secondly, it can modulate gene expression of the renin- angiotensin system – cascade proteins, which potentially slow down the progression of atherosclerosis and hypertension. Thirdly, it can modulate oxidative stress response either directly through PPAR or indirectly through Nrf2 activation. In this context, activation and functioning of PPARγ is very important in the regulation of several disorders such as diabetes mellitus, hypertension and/or metabolic syndrome.

Review: Vascular protective effects of peroxisome proliferator-activated receptor agonists

ardiovascular disease is significantly increased in patients with the metabolic syndrome and type 2 diabetes. A clustering of risk factors, including dyslipidaemia, insulin resistance, hypertension, inflammation and coagulation disorders are acting in concert to promote cardiovascular events in these patients. Peroxisome proliferator-activated receptors (PPARs) are transcription factors that influence vascular function by altering gene expression in vascular tissue and indirectly via effects on other tissues. Indeed, PPAR activation displays beneficial effects on glucose homeostasis and lipid metabolism, and also on endothelial function and vessel wall inflammation. Clinically used PPARα agonists, such as fibrates, and PPARγ agonists, such as insulin-sensitising thiazolidinediones, may consequently alter the process of atherosclerosis, especially in subjects with the metabolic syndrome and type 2 diabetes. The present review highlights emerging evidence for beneficial effects of PPAR α and PPARγ in the prevention and treatment of atherosclerosis in such high-risk patients.

Cardioprotective role of peroxisome proliferator-activated receptor-γ agonist, rosiglitazone in a unique murine model of diabetic cardiopathy

AIMS

Rosiglitazone (RSZ), a PPARγ agonist was potent efficacious insulin sensitizing blockbuster drug for treatment of Type 2 diabetes mellitus (T2DM) but the benefit of PPARγ activation in congestive heart failure (CHF) was controversial. The present work was planned to study the role of RSZ in diabetic cardiopathy.

MAIN METHODS

Zucker fa/fa rats, the genetic model of T2DM were subjected to constriction of suprarenal abdominal aorta so that they represent a combined model of diabetes and cardiopathy. The development cardiopathy was assessed biochemically (plasma BNP and aldosterone levels), using echocardiography and expression angiotensin II receptor type 1a gene in heart and Endothelin-1 gene in aorta. Rats were treated with RSZ and in combination with amiloride for four weeks and were assessed to evaluate the effect of RSZ or amiloride or its combination on antidiabetic activity, adverse or toxic effects and congestive heart failure status.

KEY FINDINGS

RSZ shows its anti-diabetic effect from 0.3mg/kg dose onwards and at 3mg/kg dose levels it caused beneficial effects (reduction of blood pressure) on cardiovascular system and at highest (30mg/kg) dose it starts showing adverse effects like body weight gain, edema, left ventricular hypertrophy. However, when highest dose of RSZ animals were treated with amiloride (ENaC inhibitor) at 2mg/kg the reversal of the adverse effects was evident, indicating the combination of RSZ and amiloride is beneficial in diabetic cardiopathy model.

SIGNIFICANCE

RSZ and amiloride combination appeared promising treatment in diabetic patients with cardiopathy without any side effect.

New thiazolidinediones affect endothelial cell activation and angiogenesis

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor-γ (PPARγ) agonists used in treating type 2 diabetes that may exhibit beneficial pleiotropic effects on endothelial cells. In this study, we characterized the effects of three new TZDs [GQ-32 (3-biphenyl-4-ylmethyl-5-(4-nitro-benzylidene)-thiazolidine-2,4-dione), GQ-169 (5-(4-chloro-benzylidene)-3-(2,6-dichloro-benzyl)-thiazolidine-2,4-dione), and LYSO-7 (5-(5-bromo-1H-indol-3-ylmethylene)-3-(4-chlorobenzyl)-thiazolidine-2,4-dione)] on endothelial cells. The effects of the new TZDs were evaluated on the production of nitric oxide (NO) and reactive oxygen species (ROS), cell migration, tube formation and the gene expression of adhesion molecules and angiogenic mediators in human umbilical vein endothelial cells (HUVECs). PPARγ activation by new TZDs was addressed with a reporter gene assay. The three new TZDs activated PPARγ and suppressed the tumor necrosis factor α-induced expression of vascular cell adhesion molecule 1 and intercellular adhesion molecule 1. GQ-169 and LYSO-7 also inhibited the glucose-induced ROS production. Although NO production assessed with 4-amino-5-methylamino-2',7'-difluorofluorescein-FM probe indicated that all tested TZDs enhanced intracellular levels of NO, only LYSO-7 treatment significantly increased the release of NO from HUVEC measured by chemiluminescence analysis of culture media. Additionally, GQ-32 and GQ-169 induced endothelial cell migration and tube formation by the up-regulation of angiogenic molecules expression, such as vascular endothelial growth factor A and interleukin 8. GQ-169 also increased the mRNA levels of basic fibroblast growth factor, and GQ-32 enhanced transforming growth factor-β expression. Together, the results of this study reveal that these new TZDs act as partial agonists of PPARγ and modulate endothelial cell activation and endothelial dysfunction besides to stimulate migration and tube formation.

Effects of a PPAR-gamma receptor agonist and an angiotensin receptor antagonist on aortic contractile responses to alpha receptor agonists in diabetic and/or hypertensive rats

Aim

The aim of this study was to investigate the effects of pioglitazone and losartan pre-treatment on the aortic contractile response to the alpha-1 agonist, phenylephrine, and the alpha-2 agonist, clonidine, in L-NAME-induced hypertensive, STZ-induced diabetic, and hypertensive diabetic rats.

Methods

Male Wistar rats were randomly allocated to four groups: control, diabetic (DM), hypertensive (HT) and hypertensive diabetic (HT + DM) groups. Three weeks after drug application, in vitro dose–response curves to phenylephrine (Phe) (10^-9–10^-5 M) and clonidine (Clo) (10^-9–10^-5 M) were recorded in aortic rings in the absence (control) and presence of pioglitazone (10 μM) and/or losartan (10 μM).

Results

Pioglitazone and losartan caused a shift to the right in contractile response to phenylephrine in all groups. The sensitivity of the aortic rings to phenylephrine was decreased in the presence of pioglitazone and/or losartan in all groups. The contractile response of clonidine decreased in the presence of pioglitazone and/or losartan in the control, HT and DM groups.

Conclusion

The sensitivity of aortic rings to alpha-1 and alpha-2 adrenoceptors was decreased in the presence of pioglitazone and/or losartan in diabetic and hypertensive rats. Concomitant use of PPAR-gamma agonists, thiazolidinediones, and angiotensin receptor blockers may be effective treatment for diabetes and hypertension.

Oxidative stress and early atherosclerosis: novel antioxidant treatment

Atherosclerotic lesions initiate in regions characterized by low shear stress and reduced activity of endothelial atheroprotective molecules such as nitric oxide, which is the key molecule managing vascular homeostasis. The generation of reactive oxygen species from the vascular endothelium is strongly related to various enzymes, such as xanthine oxidase, endothelial nitric oxide synthase and nicotinamide-adenine dinucleotide phosphate oxidase. Several pharmaceutical agents, including angiotensin converting enzyme inhibitors, angiotensin receptors blockers and statins, along with a variety of other agents, have demonstrated additional antioxidant properties beyond their principal role. Reports regarding the antioxidant role of vitamins present controversial results, especially those based on large scale studies. In addition, there is growing interest on the role of dietary flavonoids and their potential to improve endothelial function by modifying the oxidative stress status. However, the vascular-protective role of flavonoids and especially their antioxidant properties are still under investigation. Indeed, further research is required to establish the impact of the proposed new therapeutic strategies in atherosclerosis.

Interference with PPARγ in endothelium accelerates angiotensin II-induced endothelial dysfunction

The ligand activated nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) in the endothelium regulates vascular function and blood pressure (BP). We previously reported that transgenic mice (E-V290M) with selectively targeted endothelial-specific expression of dominant negative PPARγ exhibited endothelial dysfunction when treated with a high-fat diet, and exhibited an augmented pressor response to angiotensin II (ANG II). We hypothesize that interference with endothelial PPARγ would exacerbate ANG II-induced endothelial dysfunction. Endothelial function was examined in E-V290M mice infused with a subpressor dose of ANG II (120 ng·kg(-1)·min(-1)) or saline for 2 wk. ANG II infusion significantly impaired the responses to the endothelium-dependent agonist acetylcholine both in basilar and carotid arteries from E-V290M but not NT mice. This impairment was not due to increased BP, which was not significantly different in ANG II-infused E-V290M compared with NT mice. Superoxide levels, and expression of the pro-oxidant Nox2 gene was elevated, whereas expression of the anti-oxidant genes Catalase and SOD3 decreased in carotid arteries from ANG II-infused E-V290M mice. Increased p65 and decreased Iκ-Bα suggesting increased NF-κB activity was also observed in aorta from ANG II-infused E-V290M mice. The responses to acetylcholine were significantly improved both in basilar and carotid arteries after treatment with Tempol (1 mmol/l), a scavenger of superoxide. These findings provide evidence that interference with endothelial PPARγ accelerates ANG II-mediated endothelial dysfunction both in cerebral and conduit arteries through an oxidative stress-dependent mechanism, suggesting a role for endothelial PPARγ in protecting against ANG II-induced endothelial dysfunction.

Apocynin decreases AGEs-induced stimulation of NF-κB protein expression in vascular smooth muscle cells from GK rats

CONTEXT

Elevated oxidative stress plays a key role in diabetes-associated vascular disease. Excessive production of reactive oxygen species via advanced glycation end products (AGEs) activates peroxisome proliferator-activated receptor gamma (PPARγ) and the transcription factor nuclear factor-kB (NF-κB) in aortic vascular smooth muscle cells (VSMCs). Apocynin, a drug with an antioxidant effect, has also been proposed as a therapeutic agent for atherosclerotic disease.

OBJECTIVES

This work investigates the effects of apocynin on the PPARγ and NF-κB protein expression evoked by AGEs in cultured VSMCs from Goto-Kakisaki (GK) rats, a non-obese insulin model of both insulin resistance and type 2 diabetes.

MATERIALS AND METHODS

VSMCs, isolated from aortas of GK and non-diabetic rats, were cultured. The expression of proteins was evaluated by Western blot. The blood glucose concentration was measured with a blood glucose test meter. The diabetes of GK rats was controlled by blood glucose and insulin determinations (non-fasting values). The serum insulin concentration was determined by radioimmunoassay.

RESULTS

In VSMCs from non-diabetic and GK rats, apocynin (1 and 10 µM) abolished the protein overexpression of NF-κB induced by glycated bovine serum albumin (AGEs-BSA) incubation. However, apocynin (1 and 10 µM) enhanced the expression of PPARγ protein in the presence of AGEs-BSA (100 μg/mL) in VSMCs from non-diabetic, but not from GK rats.

CONCLUSION

These findings suggest that apocynin decreases the incidence of alterations in VSMCs induced by AGEs through the reduction of NF-κB and may represent an attractive therapeutic approach to treat diabetes mellitus.

MicroRNA-27b plays a role in pulmonary arterial hypertension by modulating peroxisome proliferator-activated receptor γ dependent Hsp90-eNOS signaling and nitric oxide production

Pulmonary artery endothelial dysfunction is associated with pulmonary arterial hypertension (PAH). Based on recent studies showing that microRNA (miR)-27b is aberrantly expressed in PAH, we hypothesized that miR-27b may contribute to pulmonary endothelial dysfunction and vascular remodeling in PAH. The effect of miR-27b on pulmonary endothelial dysfunction and the underlying mechanism were investigated in human pulmonary artery endothelial cells (HPAECs) in vitro and in a monocrotaline (MCT)-induced model of PAH in vivo. miR-27b expression was upregulated in MCT-induced PAH and inversely correlated with the levels of peroxisome proliferator-activated receptor (PPAR)-γ, and miR-27b inhibition attenuated MCT-induced endothelial dysfunction and remodeling and prevented PAH associated right ventricular hypertrophy and systolic pressure in rats. PPARγ was confirmed as a direct target of miR-27b in HPAECs and shown to mediate the effect of miR-27b on the disruption of endothelial nitric oxide synthase (eNOS) coupling to Hsp90 and the suppression of NO production associated with the PAH phenotype. We showed that miR-27b plays a role endothelial function and NO release and elucidated a potential mechanism by which miR-27b regulates Hsp90-eNOS and NO signaling by modulating PPARγ expression, providing potential therapeutic targets for the treatment of PAH.

Peroxisome proliferator-activated receptor gamma depletion stimulates Nox4 expression and human pulmonary artery smooth muscle cell proliferation

Hypoxia stimulates pulmonary hypertension (PH) in part by increasing the proliferation of pulmonary vascular wall cells. Recent evidence suggests that signaling events involved in hypoxia-induced cell proliferation include sustained nuclear factor-kappaB (NF-κB) activation, increased NADPH oxidase 4 (Nox4) expression, and downregulation of peroxisome proliferator-activated receptor gamma (PPARγ) levels. To further understand the role of reduced PPARγ levels associated with PH pathobiology, siRNA was employed to reduce PPARγ levels in human pulmonary artery smooth muscle cells (HPASMC) in vitro under normoxic conditions. PPARγ protein levels were reduced to levels comparable to those observed under hypoxic conditions. Depletion of PPARγ for 24-72 h activated mitogen-activated protein kinase, ERK 1/2, and NF-κB. Inhibition of ERK 1/2 prevented NF-κB activation caused by PPARγ depletion, indicating that ERK 1/2 lies upstream of NF-κB activation. Depletion of PPARγ for 72 h increased NF-κB-dependent Nox4 expression and H2O2 production. Inhibition of NF-κB or Nox4 attenuated PPARγ depletion-induced HPASMC proliferation. Degradation of PPARγ depletion-induced H2O2 by PEG-catalase prevented HPASMC proliferation and also ERK 1/2 and NF-κB activation and Nox4 expression, indicating that H2O2 participates in feed-forward activation of the above signaling events. Contrary to the effects of PPARγ depletion, HPASMC PPARγ overexpression reduced ERK 1/2 and NF-κB activation, Nox4 expression, and cell proliferation. Taken together these findings provide novel evidence that PPARγ plays a central role in the regulation of the ERK1/2-NF-κB-Nox4-H2O2 signaling axis in HPASMC. These results indicate that reductions in PPARγ caused by pathophysiological stimuli such as prolonged hypoxia exposure are sufficient to promote the proliferation of pulmonary vascular smooth muscle cells observed in PH pathobiology.

Endothelial PPAR-γ protects against vascular thrombosis by downregulating P-selectin expression

OBJECTIVE

We tested the hypothesis that endothelial peroxisome proliferator-activated receptor-γ protects against vascular thrombosis using a transgenic mouse model expressing a peroxisome proliferator-activated receptor-γ mutant (E-V290M) selectively in endothelium.

APPROACH AND RESULTS

The time to occlusive thrombosis of the carotid artery was significantly shortened in E-V290M mice compared with nontransgenic littermates after either chemical injury with ferric chloride (5.1 ± 0.2 versus 10.1 ± 3.3 minutes; P=0.01) or photochemical injury with rose bengal (48 ± 9 versus 74 ± 9 minutes; P=0.04). Gene set enrichment analysis demonstrated the upregulation of NF-κB target genes, including P-selectin, in aortic endothelial cells from E-V290M mice (P<0.001). Plasma P-selectin and carotid artery P-selectin mRNA were elevated in E-V290M mice (P<0.05). P-selectin-dependent leukocyte rolling on mesenteric venules was increased in E-V290M mice compared with nontransgenic mice (53 ± 8 versus 25 ± 7 per minute; P=0.02). The shortened time to arterial occlusion in E-V290M mice was reversed by administration of P-selectin-blocking antibodies or neutrophil-depleting antibodies (P=0.04 and P=0.02, respectively) before photochemical injury.

CONCLUSIONS

Endothelial peroxisome proliferator-activated receptor-γ protects against thrombosis through a mechanism that involves downregulation of P-selectin expression and diminished P-selectin-mediated leukocyte-endothelial interactions.

A protective role of ciglitazone in ox-LDL-induced rat microvascular endothelial cells via modulating PPARγ-dependent AMPK/eNOS pathway

Thiazolidinediones, the antidiabetic agents such as ciglitazone, has been proved to be effective in limiting atherosclerotic events. However, the underlying mechanism remains elucidative. Ox-LDL receptor-1 (LOX-1) plays a central role in ox-LDL-mediated atherosclerosis via endothelial nitric oxide synthase (eNOS) uncoupling and nitric oxide reduction. Therefore, we tested the hypothesis that ciglitazone, the PPARγ agonist, protected endothelial cells against ox-LDL through regulating eNOS activity and LOX-1 signalling. In the present study, rat microvascular endothelial cells (RMVECs) were stimulated by ox-LDL. The impact of ciglitazone on cell apoptosis and angiogenesis, eNOS expression and phosphorylation, nitric oxide synthesis and related AMPK, Akt and VEGF signalling pathway were observed. Our data showed that both eNOS and Akt phosphorylation, VEGF expression and nitric oxide production were significantly decreased, RMVECs ageing and apoptosis increased after ox-LDL induction for 24 hrs, all of which were effectively reversed by ciglitazone pre-treatment. Meanwhile, phosphorylation of AMP-activated protein kinase (AMPK) was suppressed by ox-LDL, which was also prevented by ciglitazone. Of interest, AMPK inhibition abolished ciglitazone-mediated eNOS function, nitric oxide synthesis and angiogenesis, and increased RMVECs ageing and apoptosis. Further experiments showed that inhibition of PPARγ significantly suppressed AMPK phosphorylation, eNOS expression and nitric oxide production. Ciglitazone-mediated angiogenesis and reduced cell ageing and apoptosis were reversed. Furthermore, LOX-1 protein expression in RMVECs was suppressed by ciglitazone, but re-enhanced by blocking PPARγ or AMPK. Ox-LDL-induced suppression of eNOS and nitric oxide synthesis were largely prevented by silencing LOX-1. Collectively, these data demonstrate that ciglitazone-mediated PPARγ activation suppresses LOX-1 and moderates AMPK/eNOS pathway, which contributes to endothelial cell survival and function preservation.

Synergistic effects of atorvastatin and rosiglitazone on endothelium protection in rats with dyslipidemia

Background

Endothelial dysfunction is implicated in the initiation and progression of atherosclerosis. Whether atorvastatin combined with rosiglitazone has synergistic effects on endothelial function improvement in the setting of dyslipidemia is unknown.

Methods

Dyslipidemia rat model was produced with high-fat and high-cholesterol diet administration. Thereafter, atorvastatin, rosiglitazone or atorvastatin combined with rosiglitazone were prescribed for 2 weeks. At baseline, 6 weeks of dyslipidemia model production, and 2 weeks of medical intervention, fasting blood was drawn for parameters of interest evaluation. At the end, myocardium was used for 15-deoxy-delta-12,14-PGJ₂ (15-d-PGJ₂) assessment.

Results

Initially, there was no significant difference of parameters between sham and dyslipidemia groups. With 6 weeks’ high-fat and high-cholesterol diet administration, as compared to sham group, serum levels of triglyceride (TG), total cholesterol (TC) and low density lipoprotein-cholesterol (LDL-C) were significantly increased. Additionally, nitric oxide (NO) production was reduced and serum levels of malondialdehyde (MDA), C-reactive protein (CRP) and asymmetric dimethylarginine (ADMA) were profoundly elevated in dyslipidemia group. After 2 weeks’ medical intervention, lipid profile was slightly improved in atorvastatin and combined groups as compared to control group. Nevertheless, in comparison to control group, NO production was profoundly increased and serum levels of MDA, CRP and ADMA were significantly decreased with atorvastatin or rosiglitazone therapy. 15-d-PGJ₂ expression of myocardium was also significantly elevated with atorvastatin or rosiglitazone treatment. Notably, these effects were further enhanced with combined therapy, suggesting that atorvastatin and rosiglitazone had synergistic effects on endothelial protection, and inflammation and oxidation amelioration.

Conclusion

Atorvastatin and rosiglitazone therapy had synergistic effects on endothelium protection as well as amelioration of oxidative stress and inflammatory reaction in rats with dyslipidemia.

Pulmonary hypertension and metabolic syndrome: Possible connection, PPARγ and Caveolin-1

A number of disparate diseases can lead to pulmonary hypertension (PH), a serious disorder with a high morbidity and mortality rate. Recent studies suggest that the associated metabolic dysregulation may be an important factor adversely impacting the prognosis of PH. Furthermore, metabolic syndrome is associated with vascular diseases including PH. Inflammation plays a significant role both in PH and metabolic syndrome. Adipose tissue modulates lipid and glucose metabolism, and also produces pro- and anti-inflammatory adipokines that modulate vascular function and angiogenesis, suggesting a close functional relationship between the adipose tissue and the vasculature. Both caveolin-1, a cell membrane scaffolding protein and peroxisome proliferator-activated receptor (PPAR) γ, a ligand-activated transcription factor are abundantly expressed in the endothelial cells and adipocytes. Both caveolin-1 and PPARγ modulate proliferative and anti-apoptotic pathways, cell migration, inflammation, vascular homeostasis, and participate in lipid transport, triacylglyceride synthesis and glucose metabolism. Caveolin-1 and PPARγ regulate the production of adipokines and in turn are modulated by them. This review article summarizes the roles and inter-relationships of caveolin-1, PPARγ and adipokines in PH and metabolic syndrome.

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many "distal" causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity-those that directly regulate energy metabolism or caloric intake-seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.

Thiazolidinedione-independent activation of peroxisome proliferator-activated receptor γ is a potential target for diabetic macrovascular complications

Macrovascular complications are responsible for the high morbidity and mortality in patients with diabetes. Peroxisome proliferator‐activated receptor γ (PPARγ) plays a central role in the process of adipocyte differentiation and insulin sensitization, and also possesses anti‐atherogenic effects. Recently, some statins, angiotensin II type 1 receptor blockers and calcium channel blockers have been reported to activate PPARγ. However, the impact of PPARγ activation on diabetic macrovascular complications is not fully understood. It has been reported that the activation of PPARγ by thiazolidinediones induces anti‐atherogenic effects in vascular cells, including monocytes/macrophages, endothelial cells and smooth muscle cells, in atherosclerotic animal models and in clinical studies. We have reported that hydroxymethylglutaryl coenzyme A reductase inhibitors (statins), which are used for treatment of hypercholesterolemia, activate PPARγ and mediate anti‐atherogenic effects through PPARγ activation in macrophages. Also, telmisartan, an angiotensin type I receptor blocker, has been reported to have anti‐atherogenic effects through PPARγ activation. Furthermore, we have reported that nifedipine, a dihydropyridine calcium channel blocker, can activate PPARγ, thereby mediating anti‐atherogenic effects in macrophages. Therefore, statin therapy and part of anti‐hypertensive therapy might produce beneficial effects through PPARγ activation in hypercholesterolemic and/or hypertensive patients with diabetes, and PPARγ might be a therapeutic target for diabetic macrovascular complications. In the present review, we focus on the anti‐atherogenic effects of PPARγ and suggest potential therapeutic approaches to prevent diabetic macrovascular complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00182.x, 2012)

Endothelial dysfunction in conduit arteries and in microcirculation. Novel therapeutic approaches

The vascular endothelium not only is a single monolayer of cells between the vessel lumen and the intimal wall, but also plays an important role by controlling vascular function and structure mainly via the production of nitric oxide (NO). The so called "cardiovascular risk factors" are associated with endothelial dysfunction, that reduces NO bioavailability, increases oxidative stress, and promotes inflammation contributing therefore to the development of atherosclerosis. The significant role of endothelial dysfunction in the development of atherosclerosis emphasizes the need for efficient therapeutic interventions. During the last years statins, angiotensin-converting enzyme inhibitors, angiotensin-receptor antagonists, antioxidants, beta-blockers and insulin sensitizers have been evaluated for their ability to restore endothelial function (Briasoulis et al., 2012). As there is not a straightforward relationship between therapeutic interventions and improvement of endothelial function but rather a complicated interrelationship between multiple cellular and sub-cellular targets, research has been focused on the understanding of the underlying mechanisms. Moreover, the development of novel diagnostic invasive and non-invasive methods has allowed the early detection of endothelial dysfunction expanding the role of therapeutic interventions and our knowledge. In the current review we present the available data concerning the contribution of endothelial dysfunction to atherogenesis and review the methods that assess endothelial function with a view to understand the multiple targets of therapeutic interventions. Finally we focus on the classic and novel therapeutic approaches aiming to improve endothelial dysfunction and the underlying mechanisms.

Nitrooleate mediates nitric oxide synthase activation in endothelial cells

Nitrated lipids such as nitrooleate (OLA-NO2) can act as endogenous peroxisome proliferator-activated receptor gamma (PPARγ) ligands to exert vascular protective effects. However, the molecular mechanisms regarding nitric oxide (NO) production and its regulation are not fully defined in the vasculature. Here, we show that OLA-NO2 increased endothelial NO release by modulating activation of endothelial nitric oxide synthase (eNOS) in endothelial cells. Treatment with OLA-NO2 (3 μM) increased NO release in a time-dependent manner. OLA-NO2 decreased protein expression of eNOS and caveolin-1 (Cav-1) but increased heat shock protein 90 (Hsp90) expression. Immunoprecipitation analysis confirmed that OLA-NO2 replaced eNOS/Cav-1 with eNOS/Hsp90 interaction, resulting in increasing eNOS activity. OLA-NO2 also induced eNOS phosphorylation at Ser633 and Ser1177 and eNOS dephosphorylation at Ser113 and Thr495. In addition, OLA-NO2 induced phosphorylation of Akt and extracellular signal-regulated protein kinase (ERK1/2), which might contribute to eNOS activation. Collectively, these results substantiate a new functional role for nitrated fatty acid, demonstrating that OLA-NO2 exerts vascular protective effects by increasing NO bioavailability through eNOS phosphorylation/dephosphorylation and interaction with associated proteins such as Hsp90 and Cav-1.

Differential metabolic actions of specific statins: clinical and therapeutic considerations

SIGNIFICANCE

Statins, the most widely prescribed drugs in clinical practice, mainly act by reducing the plasma level of low-density lipoprotein (LDL)-cholesterol. A shift in redox homeostasis to an imbalance between reactive oxygen species generation and endogenous antioxidant mechanisms results in oxidative stress that has been implicated in the pathogenesis of various diseases, including those of the cardiovascular system. Beyond their efficacy in lowering LDL cholesterol, statins modulate redox systems that are implicated in the development of atherosclerosis, cardiovascular morbidity, and mortality.

RECENT ADVANCES

Differences in specific statins or their dosages result in differential metabolic actions arising from off-target or unknown mechanisms of action that can have important implications for overall patient morbidity and mortality.

CRITICAL ISSUES

A recent meta-analysis and a combined analysis have suggested that high doses of statins increase the risk of developing type 2 diabetes mellitus, but reduce the risk of cardiovascular events. Thus, it is important to consider the cardiovascular and metabolic context and natural history of diseases when choosing a specific statin therapy for optimal individual patient health over the long term.

FUTURE DIRECTIONS

More information is needed regarding the metabolism of statins, and the off-target or unknown actions of statins in affecting insulin resistance and metabolic homeostasis. The differential metabolic effects of specific statins should be considered in formulating optimal therapeutic strategies to reduce not just cardiovascular-related but also overall patient morbidity and mortality.

Pioglitazone: an antidiabetic drug with cardiovascular therapeutic effects

The antidiabetic compound pioglitazone, an activator of the intracellular peroxisome proliferator-activated receptor-gamma, and decreases metabolic and vascular insulin resistance. The drug is well tolerated, and its metabolic effects include improvements in blood glucose and lipid control. Vascular effects consist of improvements in endothelial function and hypertension, and a reduction in surrogate markers of artherosclerosis. In a large, placebo-controlled, outcome study in secondary prevention, PROactive study, the use of pioglitazone in addition to an existing optimized macrovascular risk management resulted in a significant reduction of macrovascular endpoints within a short observation period that was comparable to the effect of statins and angiotensin converting enzyme inhibitors in other trials. These results underline the value of pioglitazone for managing the increased cardiovascular risk of patients with a metabolic syndrome or Type 2 diabetes mellitus.

Endothelin-1 decreases endothelial PPARγ signaling and impairs angiogenesis after chronic intrauterine pulmonary hypertension

Increased endothelin-1 (ET-1) disrupts angiogenesis in persistent pulmonary hypertension of the newborn (PPHN), but pathogenic mechanisms are unclear. Peroxisome proliferator activated receptor γ (PPARγ) is decreased in adult pulmonary hypertension, but whether ET-1-PPARγ interactions impair endothelial cell function and angiogenesis in PPHN remains unknown. We hypothesized that increased PPHN pulmonary artery endothelial cell (PAEC) ET-1 production decreases PPARγ signaling and impairs tube formation in vitro. Proximal PAECs were harvested from fetal sheep after partial ligation of the ductus arteriosus in utero (PPHN) and controls. PPARγ and phospho-PPARγ protein were compared between normal and PPHN PAECs ± ET-1 and bosentan (ETA/ETB receptor blocker). Tube formation was assessed in response to PPARγ agonists ± ET-1, N-nitro-l-arginine (LNA) (NOS inhibitor), and PPARγ siRNA. Endothelial NO synthase (eNOS), phospho-eNOS, and NO production were measured after exposure to PPARγ agonists and PPARγ siRNA. At baseline, PPHN PAECs demonstrate decreased tube formation and PPARγ protein expression and activity. PPARγ agonists restored PPHN tube formation to normal. ET-1 decreased normal and PPHN PAEC tube formation, which was rescued by PPARγ agonists. ET-1 decreased PPARγ protein and activity, which was prevented by bosentan. PPARγ agonists increased eNOS protein and activity and NO production in normal and PPHN PAECs. LNA inhibited the effect of PPARγ agonists on tube formation. PPARγ siRNA decreased eNOS protein and tube formation in normal PAECs. We conclude that ET-1 decreases PPARγ signaling and contributes to PAEC dysfunction and impaired angiogenesis in PPHN. We speculate that therapies aimed at decreasing ET-1 production will restore PPARγ signaling, preserve endothelial function, and improve angiogenesis in PPHN.

PPARgamma-Dependent Control of Renin Expression: Molecular Mechanisms and Pathophysiological Relevance

During the last years accumulating evidence demonstrated that the nuclear receptor peroxisome proliferator-activated receptor-gamma (PPARgamma) regulates the expression of renin gene and thus the overall renin production. This review summarizes the current knowledge of the transcriptional control of the renin gene by PPARgamma received from variety of models ranging from cell culture to transgenic animals. The molecular mechanisms of the PPARgamma action on renin are particularly interesting because they are featured by two newly described characteristics: one of them is the recently identified PPARgamma target sequence Pal3 which is specific for the human renin gene and mediates exceptionally high sensitivity to transactivation; the other is the potentiating effect of PPARgamma on the cAMP signaling in the renin-producing cells. Furthermore, I discuss the need for generating of additional transgenic animal models which are more appropriate with regard to the role of the PPARgamma-dependent regulation of the renin gene expression in human diseases such as arterial hypertension and metabolic syndrome.

The nuances of atherogenic dyslipidemia in diabetes: focus on triglycerides and current management strategies

Diabetes mellitus (DM) is a pandemic disease and an important cardiovascular (CV) risk factor. The atherogenic dyslipidemia in diabetes (ADD) is characterized by high serum triglycerides, high small dense LDL levels, low HDL levels and postprandial lipemia. Insulin resistance is a primary cause for ADD. Though statins are highly effective for CVD prevention in DM but a significant residual CV risk remains even after optimal statin therapy. Fibrates, niacin and omega-3 fatty acids are used in addition to statin for treatment of ADD (specifically hypertriglyceridemia). All these drugs have some limitations and they are far from being ideal companions of statins. Many newer drugs are in pipeline for management of ADD. Dual PPAR α/γ agonists are in most advanced stage of clinical development and they have a rational approach as they control blood glucose levels (by reducing insulin resistance, a primary factor for ADD) in addition to modulating ADD. Availability of dual PPAR α/γ agnosits and other drugs for ADD management may improve CV outcomes and decrease morbidity and mortality in diabetic patients in future.

Fish oil blunted nicotine-induced vascular endothelial abnormalities possibly via activation of PPARγ-eNOS-NO signals

Nicotine exposure is associated with an induction of vascular endothelial dysfunction (VED), a hallmark of various cardiovascular disorders. The present study investigated the effect of fish oil in nicotine-induced experimental VED. VED was assessed by employing isolated aortic ring preparation, estimating aortic and serum nitrite/nitrate, aortic superoxide anion generation, and serum TBARS, and carrying out electron microscopic and histological studies of thoracic aorta. Nicotine (2 mg/kg/day, i.p., 4 weeks) administration produced VED in rats by attenuating acetylcholine-induced endothelium-dependent relaxation in the isolated aortic ring preparation, decreasing aortic and serum nitrite/nitrate concentration, impairing endothelial integrity, and inducing vascular oxidative stress. Treatment with fish oil (2 mL/kg/day p.o., 4 weeks) markedly prevented nicotine-induced endothelial functional and structural abnormalities and oxidative stress. However, administration of GW9662, a selective inhibitor of PPARγ, to a significant degree attenuated fish oil-associated anti-oxidant action and vascular endothelial functional and structural improvements. Intriguingly, in vitro incubation of L-NAME (100 μM), an inhibitor of nitric oxide synthase (NOS), markedly attenuated fish oil-induced improvement in endothelium-dependent relaxation in the aorta of nicotine-administered rats. Nicotine administration altered the lipid profile by increasing serum total cholesterol, which was significantly prevented by fish oil treatment. The vascular protective potential of fish oil in preventing nicotine-induced VED may pertain to its additional properties (besides its lipid-lowering effect) such as activation of PPARγ and subsequent possible activation of endothelial NOS and generation of nitric oxide, and consequent reduction in oxidative stress.

Inhibition of PPARγ during rat pregnancy causes intrauterine growth restriction and attenuation of uterine vasodilation

Decreased peroxisome proliferator-activated receptor gamma (PPARγ) activity is thought to have a major role in preeclampsia through abnormal placental development. However, the role of PPARγ in adaptation of the uteroplacental vasculature that may lead to placental hypoperfusion and fetal growth restriction during pregnancy is not known. Here, pregnant Sprague-Dawley rats (n = 11/group) were treated during the second half of pregnancy with the PPARγ inhibitor GW9662 (10 mg/kg/day in food) or vehicle. Pregnancy outcome and PPARγ mRNA, vasodilation and structural remodeling were determined in maternal uterine and mesenteric arteries. PPARγ was expressed in uterine vascular tissue of both non-pregnant and pregnant rats with ~2-fold greater expression in radial vs. main uterine arteries. PPARγ mRNA levels were significantly higher in uterine compared to mesenteric arteries. GW9662 treatment during pregnancy did not affect maternal physiology (body weight, glucose, blood pressure), mesenteric artery vasodilation or structural remodeling of uterine and mesenteric vessels. Inhibition of PPARγ for the last 10 days of gestation caused decreased fetal weights on both day 20 and 21 of gestation that was associated with impaired vasodilation of radial uterine arteries in response to acetylcholine and sodium nitroprusside. These results define an essential role of PPARγ in the control of uteroplacental vasodilatory function during pregnancy, an important determinant of blood flow to the placenta and fetus. Strategies that target PPARγ activation in the uterine circulation could have important therapeutic potential in treatment of pregnancies complicated by hypertension, diabetes or preeclampsia.

Haplotype analysis of PPARγ C681G and intron CT variants. Positive association with essential hypertension

BACKGROUND

There is strong evidence suggesting an association between the peroxisome-activated receptor γ (PPARγ) gene and multimetabolic disorders. The association of PPARγ genetic variants with essential hypertension (EH) has not yet been investigated. The aim of this study was to investigate the association between the PPARγ gene (C681G and intron CT) and EH, examining the polymorphism and haplotype in a Han Chinese population.

METHODS

Participants were recruited within the framework of the PMMJS cohort population survey in an urban community of Jiangsu Province, China. Two single-nucleotide polymorphisms (SNPs) previously reported to be associated with multimetabolic disorders and the reasonable coverage of the PPARγ gene region were analyzed with TaqMan SNP genotyping assays.

RESULTS

C681G and intron CT were significantly associated with an increased risk of EH both in the codominant model and the dominant model after adjusting for potential nongenetic risk factors. Analysis of the haplotype association revealed that the risk of EH was significantly increased among individuals carrying the GC (odds ratio, 95 % CI: 1.60, 1.21-2.11), CT (1.45, 1.03-2.11), and GT haplotypes (1.95, 1.17-3.23) compared with those carrying the CC haplotype.

CONCLUSION

The polymorphisms of C681G and intron CT were significantly associated with the risk of EH, and the GC, CT, and GT haplotypes established by C681G and intron CT are likely to be genetic markers of EH in the Han Chinese population.

LC-MS-based method for the qualitative and quantitative analysis of the novel PPARγ agonist KR-62980

A sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for a novel peroxisome proliferator-activated receptor γ (PPARγ) agonist, KR-62980, in rat plasma. It involves liquid-liquid extraction (LLE) followed by HPLC separation and electrospray ionization tandem mass spectrometry. The linear ranges of the assay were 0.01-10 μg/mL with a correlation coefficient (R (2)) greater than 0.99 and the lower limit of quantification was 0.01 μg/mL. The average recovery was 90.1 and 98.4% from rat plasma for KR-62980 and imipramine, respectively. The coefficients of variation of intra- and inter-assay were 1.2-10.6% and the relative error was 0.8-13.2%. The method was validated and successfully applied to the pharmacokinetic study of KR-62980 in rat.

Rosiglitazone preserves pulmonary vascular function in lambs with increased pulmonary blood flow

BACKGROUND

Pulmonary vascular function is impaired with increased pulmonary blood flow (PBF). We hypothesized that a peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist would mitigate this effect.

METHODS

An aorta-to-pulmonary-artery shunt was placed in 11 fetal lambs. Lambs received the PPAR-γ agonist rosiglitazone (RG, 3 mg/kg/d, n = 6) or vehicle (n = 5) for 4 wk. Lung tissue from five normal 4-wk-old lambs was used for comparisons.

RESULTS

At 4 wk, pulmonary artery pressure (PAP) and vascular resistance (PVR) decreased with inhaled nitric oxide (NO) in RG- and vehicle-treated shunt lambs. PAP and PVR decreased with acetylcholine (Ach) in RG-treated, but not vehicle-treated, shunt lambs. In vehicle-treated shunt lambs, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, rac1, superoxide, and 3-nitrotyrosine (3-NT) levels were increased, and Ser1177 endothelial NO synthase (eNOS) protein was decreased as compared with normal lambs. In RG-treated shunt lambs, NOx, Ser1177 eNOS protein, and eNOS activity were increased, and NADPH activity, rac1, superoxide levels, and 3-NT levels were decreased, as compared with vehicle-treated shunt lambs. PPAR-γ protein expression was lower in vehicle-treated shunt lambs than in normal and RG-treated shunt lambs.

CONCLUSION

The PPAR-γ agonist RG prevents the loss of agonist-induced endothelium-dependent pulmonary vascular relaxation in lambs with increased PBF, in part, due to decreased oxidative stress and/or increased NO production.

Submaximal PPARγ activation and endothelial dysfunction: new perspectives for the management of cardiovascular disorders

PPARγ activation plays an important role in glucose metabolism by enhancing insulin sensitization. PPARγ is a primary target for thiazolidinedione-structured insulin sensitizers like pioglitazone and rosiglitazone employed for the treatment of type 2 diabetes mellitus. Additionally, PPARγ activation inhibits adhesion cascades and detrimental vascular inflammatory events. Importantly, activation of PPARγ plays a distinctive role in regulating the physiology and expression of endothelial nitric oxide synthase (eNOS) in the endothelium, resulting in enhanced generation of vascular nitric oxide. The PPARγ activation-mediated vascular anti-inflammatory and direct endothelial functional regulatory actions could, therefore, be beneficial in improving the vascular function in patients with atherosclerosis and hypertension with or without diabetes mellitus. Despite the disappointing cardiac side effect profile of rosiglitazone-like PPARγ full agonists, the therapeutic potential of novel pharmacological agents targeting PPARγ submaximally cannot be ruled out. This review discusses the potential regulatory role of PPARγ on eNOS expression and activation in improving the function of vascular endothelium. We argue that partial/submaximal activation of PPARγ could be a major target for vascular endothelial functional improvement. Interestingly, newly synthesized partial agonists of PPARγ such as balaglitazone, MBX-102, MK-0533, PAR-1622, PAM-1616, KR-62776 and SPPARγM5 are devoid of or have a reduced tendency to cause the adverse effects associated with full agonists of PPARγ. We propose that the vascular protective properties of pharmacological agents, which submaximally activate PPARγ, should be investigated. Moreover, the therapeutic opportunities of agents that submaximally activate PPARγ in preventing vascular endothelial dysfunction (VED) and VED-associated cardiovascular disorders are discussed.

Pkd2 mesenteric vessels exhibit a primary defect in endothelium-dependent vasodilatation restored by rosiglitazone

Patients with autosomal dominant polycystic kidney disease have a high prevalence of hypertension and structural vascular abnormalities, such as intracranial aneurysms. Hypertension can develop in childhood and often precedes a significant reduction in the glomerular filtration rate. The major aim of this study was to investigate whether a primary endothelial defect or a vascular smooth muscle (VSM) defect was present in murine polycystic kidney disease (Pkd)2 heterozygous mesenteric vessels before the development of renal failure or hypertension. Using pressure myography, we observed a marked defect in ACh-stimulated endothelium-dependent vasodilatation in Pkd2 arterioles. In contrast, Pkd2 vessels responded normally to sodium nitroprusside, phenylephrine, KCl, and pressure, indicating unaltered VSM-dependent responses. Pretreatment with the peroxisome proliferator-activated receptor-γ agonist rosiglitazone significantly restored ACh-dependent vasodilation in Pkd2 mice. Isolated heterozygous Pkd2 endothelial cells displayed normal ACh-stimulated Ca(2+) and nitric oxide production. However, isolated Pkd2 heterozygous VSM cells displayed basal increases in superoxide and sodium nitroprusside-stimulated peroxynitrite formation, which were both suppressed by rosiglitazone. Furthermore, we observed a defective response of Pkd2 mesenteric venules to ACh in vivo, which was more marked after ischemia-reperfusion injury. In conclusion, the results of our study suggest that the defect in vasodilatation in Pkd2 heterozygous vessels is primarily due to a reduction in nitric bioavailability secondary to increased vascular oxidative stress. The ability of rosiglitazone to correct this phenotype suggests that this defect is potentially reversible in patients with autosomal dominant polycystic kidney disease.