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

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.

Curative role of natural PPARγ agonist in non-alcoholic fatty liver disease (NAFLD)

NAFLD is a condition that develops when the liver accumulates excess fat without alcohol consumption. This chronic liver ailment progresses along with insulin resistant and is typically not diagnosed until the patients have cirrhosis. Nuclear hormone receptor superfamily PPARs are essential for metabolism of fatty acids and glucose. In liver, lipid metabolism is regulated by nuclear receptors and PPARα, and PPARβ/δ encourages fatty acid β-oxidation. PPAR-γ, an energy-balanced receptor is a crucial regulator in NAFLD. The partial activation of PPAR-γ could lead to increased level of adiponectin and insulin sensitivity, thus improved NAFLD. Because of less side effects, natural compounds are emerged as potential therapeutic agents for NAFLD by PPARγ agonists. Although the results from preclinical studies are promising, further research is needed to determine the potential dosing and efficacy of mentioned compounds in human subjects. In this review, we summarize the effect of natural PPARγ agonist in the NAFLD.

Effects of telmisartan on metabolic syndrome components: a comprehensive review

Telmisartan is an antagonist of the angiotensin II receptor used in the management of hypertension (alone or in combination with other antihypertensive agents. It belongs to the drug class of angiotensin II receptor blockers (ARBs). Among drugs of this class, telmisartan shows particular pharmacologic properties, including a longer half-life than any other angiotensin II receptor blockers that bring higher and persistent antihypertensive activity. In hypertensive patients, telmisartan has superior efficacy than other antihypertensive drugs (losartan, valsartan, ramipril, atenolol, and perindopril) in controlling blood pressure, especially towards the end of the dosing interval. Telmisartan has a partial PPARγ-agonistic effect whilst does not have the safety concerns of full agonists of PPARγ receptors (thiazolidinediones). Moreover, telmisartan has an agonist activity on PPARα and PPARδ receptors and modulates the adipokine levels. Thus, telmisartan could be considered as a suitable alternative option, with multi-benefit for all components of metabolic syndrome including hypertension, diabetes mellitus, obesity, and hyperlipidemia. This review will highlight the role of telmisartan in metabolic syndrome and the main mechanisms of action of telmisartan are discussed and summarized. Many studies have demonstrated the useful properties of telmisartan in the prevention and improving of metabolic syndrome and this well-tolerated drug can be greatly proposed in the treatment of different components of metabolic syndrome. However, larger and long-duration studies are needed to confirm these findings in long-term observational studies and prospective trials and to determine the optimum dose of telmisartan in metabolic syndrome.

Adding SGLT2 Cotransporter Inhibitor to PPARγ Activator Does Not Provide an Additive Effect in the Management of Diabetes-Induced Vascular Dysfunction

INTRODUCTION

Endothelial dysfunction (ED) plays a key role in the pathogenesis of diabetic vascular complications. In monotherapy, dapagliflozin (Dapa) as well as pioglitazone (Pio) prevent the progression of target organ damage in both type 1 (T1DM) and type 2 diabetes. We investigated whether the simultaneous PPAR-γ activation and SGLT2 cotransporter inhibition significantly alleviate ED-related pathological processes and thus normalize vascular response in experimental T1DM.

METHODS

Experimental diabetes was induced by streptozotocin (STZ; 55 mg/kg, i.p.) in Wistar rats. Dapa (10 mg/kg), Pio (12 mg/kg), or their combination were administrated to the STZ rats orally. Six weeks after STZ administration, the aorta was excised for functional studies and real-time qPCR analysis.

RESULTS

In the aorta of diabetic rats, impaired endothelium-dependent and independent relaxation were accompanied by the imbalance between vasoactive factors (eNos, Et1) and overexpression of inflammation (Tnfα, Il1b, Il6, Icam, Vcam) and oxidative stress (Cybb) markers. Pio monotherapy normalized response to vasoactive substances and restored balance between Et1-eNos expression, while Dapa treatment was ineffective. Nevertheless, Dapa and Pio monotherapy significantly reverted inflammation and oxidative stress markers to normal values. The combination treatment exhibited an additive effect in modulating Il6 expression, reaching the effect of Pio monotherapy in other measured parameters.

CONCLUSION

Particularly, Pio exerts a vasoprotective character when used in monotherapy. When combined with Dapa, it does not exhibit an expected additive effect within modulating vasoreactivity or oxidative stress, though having a significant influence on IL6 downregulation.

Mechanistic insights into the beneficial effects of curcumin on insulin resistance: opportunities and challenges

The past couple of decades in particular have seen a rapid increase in the prevalence of type 2 diabetes mellitus (T2DM), a debilitating metabolic disorder characterised by insulin resistance. The insufficient efficacy of current management strategies for insulin resistance calls for additional therapeutic options. The preponderance of evidence suggests potential beneficial effects of curcumin on insulin resistance, while modern science provides a scientific basis for its potential applications against the disease. Curcumin combats insulin resistance by increasing the levels of circulating irisin and adiponectin, activating PPARγ, suppressing Notch1 signalling, and regulating SREBP target genes, among others. In this review, we bring together the diverse areas pertaining to our current understanding of the potential benefits of curcumin on insulin resistance, associated mechanistic insights, and new therapeutic possibilities. Teaser: Current approaches to manage insulin resistance are not highly efficacious, which necessitates additional therapeutic options; curcumin combats insulin resistance by improving the levels of circulating irisin and adiponectin, upregulating and activating PPARγ, and suppressing Notch‑1 signalling.

Tetrastigma polysaccharide reprogramming of tumor-associated macrophages via PPARγ signaling pathway to play antitumor activity in breast cancer

ETHNOPHARMACOLOGICAL RELEVANCE

Tetrastigma Hemsleyanum Diels et Gilg (SYQ) is a typical She ethnomedicine that has been used in anti-tumor treatment in Chinese folklore. The polysaccharide of SYQ (SYQ-PA) has been reported to have antioxidant and anti-inflammatory effects, but the effect and mechanism on antitumor is still unclear.

AIM OF THE STUDY

To investigate the activity and mechanism of SYQ-PA against breast cancer in vitro and in vivo.

MATERIALS AND METHODS

In this study, different stages of MMTV-PYMT mice, which at 4-week-old and 8-week-old representative the transition from hyperplasia to late carcinoma, were used to investigate the potential effect of SYQ-PA of breast cancer development in vivo. The mechanism was explored with IL4/13-induced peritoneal macrophages model. Flow cytometry assay was employed to analysis the change of tumor microenvironment and the macrophages typing. The inhibition of the condition medium from macrophages on breast cancer cells was detected with xCELLigence system detection. The inflammation factors were tested with cytometric bead array. Co-culture system was used to detect the cell migration and invasion. In addition, the underlying mechanism was investigated using RNAseq analysis, Q-PCR and Western blot, and the PPARγ inhibitor was used to verify the mechanism.

RESULTS

SYQ-PA significantly attenuated the process of breast primary tumor growth and reduced the infiltration of TAMs accompanied promoting the polarization of M1 phenotype in MMTV-PyMT mice. Then in vitro studies showed that SYQ-PA promoted macrophages polarization form IL4/13 induced M2 toward to the anti-tumor M1 phenotypes, and the conditioned medium (CM) from the induced macrophages inhibited the proliferation of breast cancer cells. At the same time, SYQ-PA treated macrophages inhibited the migration and invasion of 4T1 in the co-culture system. Further results indicated that SYQ-PA suppressed the release of anti-inflammatory factors and promoted the production of inflammatory cytokines which may induce M1 macrophage polarization and inhibit breast cancer cell proliferation. Subsequently, the underlying mechanism analysis based on RNAseq and molecular assays indicated that SYQ-PA inhibited PPARγ expression and regulated downstream NF-κB in macrophages. After treated with PPARγ inhibitor, T0070907, the effect of SYQ-PA was decreased, or even disappeared. As the downstream, the expression of β-catenin was also inhibited obviously, those above all contribute the process of SYQ-PA induced M1 macrophages polarization.

CONCLUSIONS

Collectively, SYQ-PA was observed inhibited breast cancer, at least in part, via PPARγ activation- and β-catenin-mediated M2 macrophages polarization. These data expound the antitumor effect and mechanism of SYQ-PA, and provide a possible that SYQ-PA can be used as an adjuvant drug for macrophage tumor immunotherapy in breast cancer.

Tripeptide IRW Improves AMPK/eNOS Signaling Pathway via Activating ACE2 in the Aorta of High-Fat-Diet-Fed C57BL/6 Mice

This study aims to investigate the effect of tripeptide IRW on the local renin–angiotensin system (RAS), particularly angiotensin-converting enzyme 2 (ACE2), and their association with signaling pathways in the aorta of a high-fat-diet (HFD)-induced insulin-resistant mouse model. C57BL/6 mice were fed HFD (45% of the total calories) for six weeks, and then IRW was added to the diet (45 mg/kg body weight (BW)) for another eight weeks. ACE2 mRNA expression and protein level(s) were increased (p < 0.05), while angiotensin II receptor (AT1R) and angiotensin-converting enzyme (ACE) protein abundance was significantly reduced (p < 0.05) in the aorta of HFD mice treated by IRW. IRW supplementation also improved glucose transporter 4 (GLUT4) abundance (p < 0.05) alongside AMP-activated protein kinase (AMPK) (p < 0.05), Sirtuin 1 (SIRT1) (p < 0.05), and endothelial nitric oxide synthase (eNOS) (p < 0.05) expression. IRW downregulated the levels of endothelin 1 (ET-1) and p38 mitogen-activated protein kinases (p38 MAPK, p < 0.05). Furthermore, the levels of AMPK and eNOS in vascular smooth muscle cells (VSMCs) were significantly reduced in ACE2 knockdown cells treated with or without IRW (p < 0.01). In conclusion, this study provided new evidence of the regulatory role of IRW on the aortic ACE2 against metabolic syndrome (MetS) in an HFD-induced insulin-resistant model.

Is the peroxisome proliferator-activated receptor gamma a putative target for epilepsy treatment? Current evidence and future perspectives

The peroxisome proliferator-activated receptor gamma (PPARγ), which belongs to the family of nuclear receptors, has been mainly studied as an important factor in metabolic disorders. However, in recent years the potential role of PPARγ in different neurological diseases has been increasingly investigated. Especially, in the search of therapeutic targets for patients with epilepsy the question of the involvement of PPARγ in seizure control has been raised. Epilepsy is a chronic neurological disorder causing a major impact on the psychological, social, and economic conditions of patients and their families, besides the problems of the disease itself. Considering that the world prevalence of epilepsy ranges between 0.5% - 1.0%, this condition is the fourth for importance among the other neurological disorders, following migraine, stroke, and dementia. Among others, temporal lobe epilepsy (TLE) is the most common form of epilepsy in adult patients. About 65% of individuals who receive antiseizure medications (ASMs) experience seizure independence. For those in whom seizures still recur, investigating PPARγ could lead to the development of novel ASMs. This review focuses on the most important findings from recent investigations about the potential intracellular PPARγ-dependent processes behind different compounds that exhibited anti-seizure effects. Additionally, recent clinical investigations are discussed along with the promising results found for PPARγ agonists and the ketogenic diet (KD) in various rodent models of epilepsy.

Cynarin inhibits PDGF-BB-induced proliferation and activation in hepatic stellate cells through PPARγ

Cynarin, a caffeoylquinic acid compound that was mainly extracted from Cynara scolymus L., displays various activities such as antioxidant, antibacterial, choleretic, and hepatoprotective functions. However, the target of cynarin and the mechanism of its hepatoprotective effect are still unclear. To find cynarin’s target, we performed molecular docking analysis, fluorescence-based ligand-binding assay, and reporter gene system assay. Our results indicated that cynarin was a partial agonist of peroxisome proliferator-activated receptor gamma (PPARγ). Further studies showed that cynarin significantly inhibited platelet-derived growth factor (PDGF)-BB-induced proliferation and activation of rat CFSC-8G hepatic stellate cells (HSCs). Our results also revealed that cynarin inhibited PDGF-BB-induced extracellular regulated protein kinase (ERK) and v-akt murine thymoma viral oncogene homolog (AKT) phosphorylation in HSCs. In addition, this inhibition effect was PPARγ dependent since the knockdown of PPARγ significantly attenuated the effects of cynarin on PDGF-BB-induced p-ERK, p-AKT, and α-smooth muscle actin (α-SMA) expressions. Therefore, this study suggests that cynarin is a promising antifibrotic lead compound that inhibits the activation of HSCs, and it works by targeting PPARγ.

A Unifying Perspective in Blunting the Limited Oral Bioavailability of Curcumin: A Succinct Look

BACKGROUND

Curcumin is a polyphenolic compound derived from rhizomes of Curcuma longa, the golden spice. Curcumin has drawn much attention in recent years of biomedical research owing to its wide variety of biologic and pharmacologic actions. It exerts antiproliferative, antifibrogenic, anti-inflammatory, and antioxidative effects, among various imperative pharmacologic actions. In spite of its well-documented efficacies against numerous disease conditions, the limited systemic bioavailability of curcumin is a continuing concern. Perhaps, the poor bioavailability of curcumin may have curtailed its significant development from kitchen to clinic as a potential therapeutic agent. Subsequently, there have been a considerable number of studies over decades researching the scientific basis of curcumin's reduced bioavailability and eventually improvement of its bioavailability employing a variety of therapeutic approaches, for instance, in combination with piperine, the bio-active constituent of black pepper. Piperine has remarkable potential to modulate the functional activity of metabolic enzymes and drug transporters, and thus there has been a great interest in the therapeutic application of this widely used spice as alternative medicine and bioavailability enhancer. Growing body of evidence supports the synergistic potential of curcumin against numerous pathologic conditions when administered with piperine.

CONCLUSION

In light of current challenges, the major concern pertaining to poor systemic bioavailability of curcumin, its improvement, especially in combination with piperine, and the necessity of additional research in this setting are together described in this review. Besides, the recent advances in the potential therapeutic rationale and efficacy of curcumin-piperine combination, a promising duo, against various pathologic conditions are delineated.

Tetrazoles as PPARγ ligands: A structural and computational investigation

Diabetes is an important chronic disease affecting about 10% of the adult population in the US and over 420 million people worldwide, resulting in 1.6 million deaths every year, according to the World Health Organization. The most common type of the disease, type 2 diabetes, can be pharmacologically managed using oral hypoglycemic agents or thiazolidinediones (TZDs), such as pioglitazone, which act by activating the Peroxisome Proliferated-Activated Receptor γ. Despite their beneficial effects in diabetes treatment, TZDs like rosiglitazone and troglitazone were withdrawn due to safety reasons, creating a void in the pharmacological options for the treatment of this important disease. Here, we explored a structure-based approach in the screening for new chemical probes for a deeper investigation of the effects of PPARγ activation. A class of tetrazole compounds was identified and the compounds named T1, T2 and T3 were purchased and evaluated for their ability to interact with the PPARγ ligand binding domain (LBD). The compounds were binders with micromolar range affinity, as determined by their IC₅₀ values. A Monte Carlo simulation of the compound T2 revealed that the tetrazole ring makes favorable interaction with the polar arm of the receptor binding pocket. Finally, the crystal structure of the PPARγ-LBD-T2 complex was solved at 2.3 Å, confirming the binding mode for this compound. The structure also revealed that, when the helix H12 is mispositioned, an alternative binding conformation is observed for the ligand suggesting an H12-dependent binding conformation for the tetrazole compound.

Rice Bran Extract Protected against LPS-Induced Neuroinflammation in Mice through Targeting PPAR-γ Nuclear Receptor

PPAR-γ anti-inflammatory functions have received significant attention since its agonists have been shown to exert a wide range of protective effects in many experimental models of neurologic diseases. Rice bran is very rich in polyunsaturated fatty acids, which are reported to act as PPAR-γ partial agonists. Herein, the anti-inflammatory effect of rice bran extract (RBE) through PPAR-γ activation was evaluated in LPS-induced neuroinflammatory mouse model in comparison to pioglitazone (PG) using 80 Swiss albino mice. RBE (100 mg/kg) and PG (30 mg/kg) were given orally for 21 days and LPS (0.25 mg/kg) was injected intraperitoneally for the last 7 days. TNF-α and COX-2 brain contents were evaluated by real-time PCR and immunohistochemical analysis. In addition, NFκB binding to its response element was evaluated alongside with the effect of treatments on IκB gene expression. Furthermore, PPAR-γ sumoylation was also studied. Finally, histopathological examination was performed for different brain areas. RBE administration was found to protect against the LPS-induced inflammatory effects by decreasing the inflammatory mediator expression in mice brains. It also decreased PPAR-γ sumoylation without significant effect on IκB expression or NFκB binding to its response element. The majority of the effects were attenuated in presence of PPAR-γ antagonist (GW9662). Level of significance was set to P < 0.05. Such findings highlight the agonistic effect of RBE component(s) on PPAR-γ and support the hypothesis of involvement of PPAR-γ activation in its neuroprotective effect.

Anti-Diabetic Effect of Telmisartan Through its Partial PPARγ-Agonistic Activity

Telmisartan is an angiotensin II receptor antagonist, which selectively inhibits the angiotensin II type 1 receptor. Thus, it is widely used for hypertension management. Nowadays, telmisartan's effect on peroxisome proliferator-activated receptors (PPARs) is gaining wider attention. PPARs are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. Telmisartan is reported to have a partial PPARγ-agonistic effect while avoiding the safety concerns found with full PPARγ agonists (thiazolidinediones). Telmisartan could be an alternative treatment option, with dual benefit for diabetes mellitus (DM) and hypertension. This review summarizes the anti-diabetic activity of telmisartan via its partial PPARγ-agonistic activity.

The Journey of Thiazolidinediones as Modulators of PPARs for the Management of Diabetes: A Current Perspective

Peroxisome Proliferator-Activated Receptors (PPARs) also known as glitazone receptors are a family of receptors that regulate the expression of genes and have an essential role in carbohydrate, lipid and protein metabolism apart from other functions. PPARs come in 3 sub-types: PPAR-α, PPAR-β/δ and PPAR-γ - with PPAR-γ having 2 isoforms - γ1 and γ2. Upon activation, the PPARs regulate the transcription of various genes involved in lipid and glucose metabolism, adipocyte differentiation, increasing insulin sensitivity, prevention of oxidative stress and to a certain extent, modulation of immune responses via macrophages that have been implicated in the pathogenesis of insulin resistance. Hence, PPARs are an attractive molecular target for designing new anti-diabetic drugs. This has led to a boost in the research efforts directed towards designing of PPAR ligands - particularly ones that can selectively and specifically activate one or more of the PPAR subtypes. Though, PPAR- γ full agonists such as Thiazolidinediones (TZDs) are well established agents for dyslipidemia and type 2 diabetes mellitus (T2D), the side effect profile associated with TZDs has potentiated an imminent need to come up with newer agents that act through this pathway. Several newer derivatives having TZD scaffold have been designed using structure based drug designing technique and computational tools and tested for their PPAR binding affinity and efficacy in combating T2D and some have shown promising activities. This review would focus on the role of PPARs in the management of T2D; recently reported TZD derivatives which acted as agonists of PPAR- γ and its subtypes and are potentially useful in the new drug discovery for the disease.

A Contemporary Overview of PPARα/γ Dual Agonists for the Management of Diabetic Dyslipidemia

Background:

Diabetes mellitus and concomitant dyslipidemia, being referred to as ‘diabetic dyslipidemia’, are the foremost detrimental factors documented to play a pivotal role in cardiovascular illness. Diabetic dyslipidemia is associated with insulin resistance, high plasma triglyceride levels, low HDL-cholesterol concentration and elevated small dense LDL-cholesterol particles. Maintaining an optimal glucose and lipid levels in patients afflicted with diabetic dyslipidemia could be a major task that might require a well-planned diet-management system and regular physical activity, or otherwise an intake of combined antidiabetic and antihyperlipidemic medications. Synchronized treatment which efficiently controls insulin resistance-associated diabetes mellitus and co-existing dyslipidemia could indeed be a fascinating therapeutic option in the management of diabetic dyslipidemia. Peroxisome proliferator-activated receptors α/γ (PPARα/γ) dual agonists are such kind of drugs which possess therapeutic potentials to treat diabetic dyslipidemia. Nevertheless, PPARα/γ dual agonists like muraglitazar, naveglitazar, tesaglitazar, ragaglitazar and aleglitazar have been reported to have undesirable adverse effects, and their developments have been halted at various stages. On the other hand, a recently introduced PPARα/γ dual agonist, saroglitazar is an emerging therapeutic agent of glitazar class approved in India for the management of diabetic dyslipidemia, and its treatment has been reported to be generally safe and well tolerated.

Conclusion:

Some additional and new compounds, at initial and preclinical stages, have been recently reported to possess PPARα/γ dual agonistic potentials with considerable therapeutic efficacy and reduced adverse profile. This review sheds light on the current status of various PPARα/γ dual agonists for the management of diabetic dyslipidemia.

Pigment Epithelial-Derived Factor Deficiency Accelerates Atherosclerosis Development via Promoting Endothelial Fatty Acid Uptake in Mice With Hyperlipidemia

Background

Endothelial cell injury, induced by dyslipidemia, is the initiation of atherosclerosis, resulting in an imbalance in endothelial fatty acid (FA) transport. Pigment epithelial‐derived factor (PEDF) is an important regulator in lipid metabolism. We hypothesized that PEDF is involved in endothelium‐mediated FA uptake under hyperlipidemic conditions.

Methods and Results

Circulating PEDF levels were higher in patients with atherosclerotic cardiovascular disease than in normal individuals. However, decreasing trends of serum PEDF levels were confirmed in both wild‐type and apolipoprotein E–deficient mice fed a long‐term high‐fat diet. Apolipoprotein E–deficient/PEDF‐deficient mice were generated by crossing PEDF‐deficient mice with apolipoprotein E–deficient mice, and then mice were fed with 24, 36, or 48 weeks of high‐fat diet. Greater increases in body fat and plasma lipids were displayed in PEDF‐deficient mice. In addition, PEDF deficiency in mice accelerated atherosclerosis, as evidenced by increased atherosclerotic plaques, pronounced vascular dysfunction, and increased lipid accumulation in peripheral tissues, whereas injection of adeno‐associated virus encoding PEDF exerted opposite effects. Mechanistically, PEDF inhibited the vascular endothelial growth factor B paracrine signaling by reducing secretion of protein vascular endothelial growth factor B in peripheral tissue cells and decreasing expression of its downstream targets in endothelial cells, including its receptors (namely, vascular endothelial growth factor receptor‐1 and neuropilin‐1), and FA transport proteins 3 and 4, to suppress endothelial FA uptake, whereas PEDF deletion in mice activated the vascular endothelial growth factor B signaling pathway, thus causing markedly increased lipid accumulation.

Conclusions

Decreasing expression of PEDF aggravates atherosclerosis by significantly impaired vascular function and enhanced endothelial FA uptake, thus exacerbating ectopic lipid deposition in peripheral tissues.

A potential role of the renin-angiotensin-aldosterone system in epithelial-to-mesenchymal transition-induced renal abnormalities: Mechanisms and therapeutic implications

Epithelial-to-mesenchymal transition (EMT) is an orchestrated event where epithelial cells progressively undergo biochemical changes and transition into mesenchymal-like cells by gradually losing their epithelial characteristics. EMT plays a crucial pathologic role in renal abnormalities, especially renal fibrosis. A number of bench studies suggest the potential involvement of renin-angiotensin-aldosterone system (RAAS) in renal EMT process and associated renal abnormalities. EMT appears to be an important pathologic mechanism for the deleterious renal effects of angiotensin II and aldosterone, the two major RAAS components. Mechanistically, the renal RAAS-TGF-β-Smad3 signalling pathway plays an important pathologic role in EMT-associated renal abnormalities. Intriguingly, the RAAS antagonists such as losartan, telmisartan, eplerenone, and spironolactone have the potential to prevent renal EMT in bench studies. This review describes the key mechanistic role of RAAS overactivation in EMT-induced renal abnormalities. Moreover, drugs interrupting the RAAS at different levels in the cascade ameliorating the EMT-associated renal abnormalities are described.

Cardiovascular protective effect of pioglitazone on oxidative stress in rats with metabolic syndrome

BACKGROUND

Although cardiovascular oxidative stress is examined in type 2 diabetes, there is relatively limited number of reports about the effect of pioglitazone, an insulin sensitizer, on cardiovascular oxidative stress in sucrose diet-induced metabolic syndrome (MetS). As a regulator of cardiovascular homeostasis, thioredoxin (TRX) has an important role in defense against oxidative stress in cardiovascular diseases. The purpose of this study is to investigate the role of pioglitazone on oxidative stress markers and TRX1 level in tissues of both heart and aorta from MetS rats.

METHODS

Male Wistar rats (200 to 250 g in weight) were divided into three groups: control group, MetS group receiving drinking water including 935 mM sucrose, and pioglitazone-treated MetS (MetS-P) group. Aspartate aminotransferase (AST), lactate dehydrogenase (LDH), total oxidant status (TOS), and total antioxidant status (TAS) levels were measured in serum and tissues using commercial kits. Malondialdehyde (MDA) and superoxide dismutase (SOD) were measured in serum and tissues for experimental groups. TRX1 protein level was measured by western blot.

RESULTS

The sucrose-fed rats exhibited several characteristics of MetS. In MetS group, AST, LDH, TOS, and MDA levels of heart and aorta tissues increased, whereas TAS and SOD levels of these tissues decreased. TRX1 protein level of heart and aorta tissues decreased in MetS group. Also, in the serum of experimental groups, AST, LDH, and TOS levels increased.

CONCLUSION

Pioglitazone treatment significantly increased TRX1 protein level in heart and aorta tissues in MetS group. Pioglitazone affected the TRX1 protein level via regulation of reactive oxygen intermediates. Pioglitazone reduced the elevated oxidative stress in heart and aorta of MetS rats.

Taurine improves low-level inorganic arsenic-induced insulin resistance by activating PPARγ-mTORC2 signalling and inhibiting hepatic autophagy

Inorganic arsenic (iAs) is reportedly associated with the increased incidence of type 2 diabetes in the population. Here, we found that iAs exposure significantly decreased the expression of glycolytic genes and glycogen content and increased gluconeogenesis gene levels in C57/BL6J mice. The expression of peroxisome proliferator-activated receptor γ (PPARγ), and mechanistic target of rapamycin complex 2 (mTORC2) were decreased in the livers of iAs-treated mice. Furthermore, in iAs-treated HepG2 cells, we found that PPARγ agonist rosiglitazone (RGS) increased the expression of mTORC2, inhibited autophagy, and improved glucose metabolism. mTORC2 agonist palmitic acid inhibited autophagy and improved glucose metabolism as well as the autophagosome formation inhibitor 3-methyladenine. Taurine, a natural compound, reversed impaired glucose metabolism and decreased expression of PPARγ and mTORC2 induced by iAs in mice liver and HepG2 cells. These data indicated that taurine administration could ameliorate iAs-induced insulin resistance through activating PPARγ-mTORC2 signalling and subsequently inhibiting hepatic autophagy.

Linc01230, transcriptionally regulated by PPARγ, is identified as a novel modifier in endothelial function

Evidence is growing that PPARγ could improve the bioavailability of NO in pathological conditions to maintain endothelial function by activating Akt/eNOS pathway. LincRNAs participate in regulating development of cardiovascular diseases. Although investigations have been made to delineate the function of PPARγ and lincRNAs, little is known about the regulation relationship between them, especially in endothelial cells. In this study, we not only verified that PPARγ could antagonize the adverse effects brought from ox-LDL, but also found a novel factor related to PPARγ, named linc01230. According to our study, PPARγ transcriptionally regulated linc01230 by specifically combining with two binding regions, which have superposition effect, in the upstream of linc01230 promoter. In addition, linc01230 reduced ox-LDL induced endothelial dysfunction and affected the phosphorylation of Akt. These results conclude linc01230 as a novel modifier in PPARγ-mediated activation of Akt in endothelial function.

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.

Electroacupuncture mitigates endothelial dysfunction via effects on the PI3K/Akt signalling pathway in high fat diet-induced insulin-resistant rats

OBJECTIVE

To investigate the effect of electroacupuncture (EA) on endothelial dysfunction related to high fat diet (HFD)-induced insulin resistance through the phosphatidylinositol 3-kinase (PI3K)-protein kinase B (Akt) signalling pathway.

METHODS

Twenty-four male Sprague-Dawley rats were fed a regular diet (Control group, n=8) or a HFD (n=16) for 12 weeks to induce an insulin resistance model. HFD-fed rats were divided into two groups that remained untreated (HFD group, n=8) or received electroacupuncture (HFD+EA group, n=8). EA was applied at PC6, ST36, SP6 and BL23. At the end of the experiment, fasting blood glucose (FBG), serum insulin (FINS), serum C-peptide (C-P) and homeostatic model assessment of insulin resistance (HOMA-IR) indices were determined. Pancreatic islet samples were subjected to histopathological examination. The thoracic aorta was immunostained with anti-rat insulin receptor substrate (IRS)-1, Akt and endothelial nitric oxide synthase (eNOS) antibodies. mRNA and protein expression of IRS-1, PI3K, Akt2 and eNOS in the vascular endothelium were determined by real-time PCR and Western blot analysis, respectively.

RESULTS

The bodyweight increase of the HFD+EA group was smaller than that of the untreated HFD group. Compared with the HFD group, the levels of FBG, FINS, C-P and HOMA-IR in the HFD+EA group decreased significantly (P<0.01). Histopathological evaluation indicated that EA improved pancreatic islet inflammation. The expression of endothelial markers, such as IRS-1, PI3K, Akt2 and eNOS, decreased in the HFD group, while EA treatment appeared to ameliorate the negative impact of diet.

CONCLUSION

EA may improve insulin resistance and attenuate endothelial dysfunction, and therefore could play a potential role in the prevention or treatment of diabetic complications and cardiovascular disease through the PI3K/Akt signalling pathway.

The Positive Regulation of eNOS Signaling by PPAR Agonists in Cardiovascular Diseases

Increasing evidence shows that activation of peroxisome proliferator-activated receptors (PPARs) plays an essential role in the regulation of vascular endothelial function through a range of mechanisms, including non-metabolic. Among these, the PPAR-mediated activation of endothelial nitric oxide synthase (eNOS) appears to be of considerable importance. The regulated and sustained bioavailability of nitric oxide (NO) in the endothelium is essential to avoid the development of cardiovascular diseases such as hypertension or atherosclerosis. Therefore, a deeper understanding of the different effects of specific PPAR ligands on NO bioavailability could be useful in the development of novel or multi-targeted PPAR agonists. In this review, we report the most meaningful and up-to-date in vitro and in vivo studies of the regulation of NO production performed by different PPAR agonists. Insights into the molecular mechanisms of PPAR-mediated eNOS activation are also provided. Although findings from animal studies in which the activation of PPARα, PPARβ/δ, or PPARγ have provided clear vasoprotective effects have been promising, several benefits from PPAR agonists are offset by unwanted outcomes. Therefore, new insights could be useful in the development of tissue-targeted PPAR agonists with more tolerable side effects to improve treatment options for cardiovascular diseases.

Hypaphorine Attenuates Lipopolysaccharide-Induced Endothelial Inflammation via Regulation of TLR4 and PPAR-γ Dependent on PI3K/Akt/mTOR Signal Pathway

Endothelial lesion response to injurious stimuli is a necessary step for initiating inflammatory cascades in blood vessels. Hypaphorine (Hy) from different marine sources is shown to exhibit anti-inflammatory properties. However, the potential roles and possible molecular mechanisms of Hy in endothelial inflammation have yet to be fully clarified. We showed that Hy significantly inhibited the positive effects of lipopolysaccharide (LPS) on pro-inflammatory cytokines expressions, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), monocyte chemoattractant protein 1 (MCP-1) and vascular cellular adhesion molecule-1 (VCAM-1), as well as induction of the phosphorylation of Akt and mTOR in HMEC-1 cells. The downregulated peroxisome proliferator-activated receptor γ (PPAR-γ) and upregulated toll-like receptor 4 (TLR4) expressions in LPS-challenged endothelial cells were prevented by Hy. Inhibition of both PI3K and mTOR reversed LPS-stimulated increases in TLR4 expressions and decreases in PPAR-γ levels. Genetic silencing of TLR4 or PPAR-γ agonist pioglitazone obviously abrogated the levels of pro-inflammatory cytokines in LPS-treated HMEC-1 cells. These results suggest that Hy may exert anti-inflammatory actions through the regulation of TLR4 and PPAR-γ dependent on PI3K/Akt/mTOR signal pathways. Hy may be considered as a therapeutic agent that can potentially relieve or ameliorate endothelial inflammation-associated diseases.

The effect of Chinese herbs and its effective components on coronary heart disease through PPARs-PGC1α pathway

Background

DanQi pill (DQP) is prescribed widely in China and has definite cardioprotective effect on coronary heart disease. Our previous studies proved that DQP could effectively regulate plasma levels of high density lipoprotein (HDL) and low density lipoprotein (LDL). However, the regulatory mechanisms of DQP and its major components Salvianolic acids and Panax notoginseng saponins (DS) on lipid metabolism disorders haven’t been comprehensively studied so far.

Methods

Rat model of coronary heart disease was induced by left anterior descending (LAD) artery ligation operations. Rats were divided into sham, model, DQP treated, DS treated and positive drug (clofibrate) treated groups. At 28 days after surgery, cardiac functions were assessed by echocardiography. Expressions of transcription factors and key molecules in energy metabolism pathway were measured by reverse transcriptase polymerase chain reaction or western blotting.

Results

In ischemic heart model, cardiac functions were severely injured but improved by treatments of DQP and DS. Expression of LPL was down-regulated in model group. Both DQP and DS could up-regulate the mRNA expression of LPL. Membrane proteins involved in lipid transport and uptake, such as FABP4 and CPT-1A, were down-regulated in ischemic heart tissues. Treatment with DQP and DS regulated lipid metabolisms by up-regulating expressions of FABP4 and CPT-1A. DQP and DS also suppressed expression of cytochrome P450. Furthermore, transcriptional factors, such as PPARα, PPARγ, RXRA and PGC-1α, were down-regulated in ischemic model group. DQP and DS could up-regulate expressions of these factors. However, DS showed a better efficacy than DQP on PGC-1α, a coactivator of PPARs. Key molecules in signaling pathways such as AKT1/2, ERK and PI3K were also regulated by DQP and DS simultaneously.

Conclusions

Salvianolic acids and Panax notoginseng are the major effective components of DanQi pill in improving lipid metabolism in ischemic heart model. The effects may be mediated by regulating transcriptional factors such as PPARs, RXRA and PGC-1α.

Does Thiazolidinedione therapy exacerbate fluid retention in congestive heart failure?

The ever-growing global burden of congestive heart failure (CHF) and type 2 diabetes mellitus (T2DM) as well as their co-existence necessitate that anti-diabetic pharmacotherapy will modulate the cardiovascular risk inherent to T2DM while complying with the accompanying restrictions imposed by CHF. The thiazolidinedione (TZD) family of peroxisome proliferator-activated receptor γ (PPARγ) agonists initially provided a promising therapeutic option in T2DM owing to anti-diabetic efficacy combined with pleiotropic beneficial cardiovascular effects. However, the utility of TZDs in T2DM has declined in the past decade, largely due to concomitant adverse effects of fluid retention and edema formation attributed to salt-retaining effects of PPARγ activation on the nephron. Presumably, the latter effects are potentially deleterious in the context of pre-existing fluid retention in CHF. However, despite a considerable body of evidence on mechanisms responsible for TZD-induced fluid retention suggesting that this class of drugs is rightfully prohibited from use in CHF patients, there is a paucity of experimental and clinical studies that investigate the effects of TZDs on salt and water homeostasis in the CHF setting. In an attempt to elucidate whether TZDs actually exacerbate the pre-existing fluid retention in CHF, our review summarizes the pathophysiology of fluid retention in CHF. Moreover, we thoroughly review the available data on TZD-induced fluid retention and proposed mechanisms in animals and patients. Finally, we will present recent studies challenging the common notion that TZDs worsen renal salt and water retention in CHF.

Drug repurposing for vascular dementia: overview and current developments

Antidementive drugs have made Alzheimer's disease a symptomatically treatable condition but have essentially bypassed vascular dementia. The complexity of its pathology, the variable pathognomonic manifestations, the absence of validated biomarkers and the continuum with Alzheimer's disease that makes vascular dementia a comparatively small market are the major contributing factors. This report discusses how drug repurposing can be harnessed to identify new therapeutic opportunities, where such efforts are already yielding promising results, and which ones must be considered failures. Most investigations address obvious aspects cerebral small vessel disease, but some early-stage developments attempt changes in gene expression or modulation of complex biological pathways. A stronger focus on the nature and dynamics of white matter lesions should yield additional molecular targets.

Current Advances in the Biochemical and Physiological Aspects of the Treatment of Type 2 Diabetes Mellitus with Thiazolidinediones

The present review summarizes the current advances in the biochemical and physiological aspects in the treatment of type 2 diabetes mellitus (DM2) with thiazolidinediones (TZDs). DM2 is a metabolic disorder characterized by hyperglycemia, triggering the abnormal activation of physiological pathways such as glucose autooxidation, polyol's pathway, formation of advance glycation end (AGE) products, and glycolysis, leading to the overproduction of reactive oxygen species (ROS) and proinflammatory cytokines, which are responsible for the micro- and macrovascular complications of the disease. The treatment of DM2 has been directed toward the reduction of hyperglycemia using different drugs such as insulin sensitizers, as the case of TZDs, which are able to lower blood glucose levels and circulating triglycerides by binding to the nuclear peroxisome proliferator-activated receptor gamma (PPARγ) as full agonists. When TZDs interact with PPARγ, the receptor regulates the transcription of different genes involved in glucose homeostasis, insulin resistance, and adipogenesis. However, TZDs exhibit some adverse effects such as fluid retention, weight gain, hepatotoxicity, plasma-volume expansion, hemodilution, edema, bone fractures, and congestive heart failure, which limits their use in DM2 patients.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

The bioflavonoid quercetin synergises with PPAR-γ agonist pioglitazone in reducing angiotensin-II contractile effect in fructose-streptozotocin induced diabetic rats

This study investigated the effects of combined minimal concentrations of quercetin and pioglitazone on angiotensin II-induced contraction of the aorta from fructose-streptozotocin (F-STZ)-induced type 2 diabetic rats and the possible role of superoxide anions (O2(-)) and nitric oxide (NO) in their potential therapeutic interaction. Contractile responses to Ang II of aortic rings from Sprague-Dawley (SD) and F-STZ rats were tested following pre-incubation of the tissues in the vehicle (DMSO; 0.05%), quercetin (Q, 0.1 μM), pioglitazone (P, 0.1 μM) or their combination (P + Q; 0.1 μM each). The amount of superoxide anion was evaluated by lucigenin-enhanced chemiluminescence and dihydroethidium fluorescence, and NO by assay of total nitrate/nitrite, and 4-Amino-5-Methylamino-2',7'-Difluorofluorescein (DAF-FM) diacetate. The synergistic reduction of Ang II-induced contraction of diabetic but not normal aorta with minimally effective concentrations of P + Q occurs through inhibiting O2(-) and increasing NO bioavailability. This finding opens the possibility of maximal vascular protective/antidiabetic effects with low dose pioglitazone combined with quercetin, thus minimizing the risk of adverse effects.

Rosiglitazone attenuates early brain injury after experimental subarachnoid hemorrhage in rats

Early brain injury (EBI) plays a crucial role in the pathological progress of subarachnoid hemorrhage (SAH). This study was designed to determine whether rosiglitazone protects the brain against EBI in rats, and discuss the role of the anti-apoptotic mechanism mediated by Bcl-2 family proteins in this neuroprotection. 86 male Sprague-Dawley rats were divided into the sham group, the SAH+ vehicle group and the SAH+ rosiglitazone group. SAH was induced via an endovascular perforation technique and rosiglitazone (3mg/kg) or vehicle was administered. Mortality, neurological scores, brain water content, Evans blue dye assay, TUNEL stain assay, Gelatin zymography, and western blot analysis were performed. Rosiglitazone significantly improved mortality, neurological scores, brain water content, blood brain barrier (BBB) and apoptosis compared with the vehicle group within 24h after SAH. The TUNEL staining assay demonstrated that apoptosis was ameliorated. Cleaved Caspase-3 and MMP-9 expression was reduced, whereas Bcl-2 and p-Bad was markedly preserved by rosiglitazone. A significant elevation of p-Akt was detected after rosiglitazone treatment. Our study demonstrated that rosiglitazone plays a neuroprotective role in EBI after SAH via attenuation of BBB disruption, brain edema and apoptosis.

A step ahead of PPARγ full agonists to PPARγ partial agonists: therapeutic perspectives in the management of diabetic insulin resistance

Described since long as a member of the nuclear receptor superfamily, peroxisome proliferator-activated receptors (PPARs) regulate the gene expression of proteins involved in glucose and lipid metabolism. PPARs indeed regulate several physiologic processes, including lipid homeostasis, adipogenesis, inflammation, and wound healing. PPARs bind natural or synthetic PPAR ligands can function as cellular sensors to regulate the gene transcription. Dyslipidemia, and type 2 diabetes mellitus (T2DM) with insulin resistance are treated using agonists of PPARα and PPARγ, respectively. The PPARγ is a key regulator of insulin sensitization and glucose metabolism, and therefore is considered as an imperative pharmacological target to combat diabetic metabolic disease and insulin resistance. Of note, currently available PPARγ full agonists like rosiglitazone display serious adverse effects such as fluid retention/oedema, weight gain, and increased incidence of cardiovascular events. On the other hand, PPARγ partial agonists are being suggested to devoid or having less incidence of these undesirable events, and are under developmental stages. Current research is on the way for the development of novel PPARγ partial agonists with enhanced therapeutic efficacy and reduced adverse effects. This review sheds lights on the current status of development of PPARγ partial agonists, for the management of T2DM, having comparatively less or no adverse effects to that of PPARγ full agonists.

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.

2-methoxyestradiol induces vasodilation by stimulating NO release via PPARγ/PI3K/Akt pathway

The endogenous estradiol metabolite 2-methoxyestradiol (2-ME) reduces atherosclerotic lesion formation, while the underlying mechanisms remain obscure. In this work, we investigated the vasodilatory effect of 2-ME and the role of nitric oxide (NO) involved. In vivo studies using noninvasive tail-cuff methods showed that 2-ME decreased blood pressure in Sprague Dawley rats. Furthermore, in vitro studies showed that cumulative addition of 2-ME to the aorta caused a dose- and endothelium-dependent vasodilation. This effect was unaffected by the pretreatment with the pure estrogen receptor antagonist ICI 182,780, but was largely impaired by endothelial nitric oxide synthase (eNOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) or by phosphoinositide 3-kinase (PI3K) inhibitor wortmannin (WM). Moreover, 2-ME（10^{−7 ∼}10⁻⁵ M）enhanced phosphorylation of Akt and eNOS and promoted NO release from cultured human umbilical endothelial cells (HUVECs). These effects were blocked by PI3K inhibitor WM, or by the transfection with Akt specific siRNA, indicating that endothelial Akt/eNOS/NO cascade plays a crucial role in 2-ME-induced vasodilation. The peroxisome proliferator-activated receptor γ (PPARγ) mRNA and protein expression were detected in HUVECs and the antagonist GW9662 or the transfection with specific PPARγ siRNA inhibited 2-ME-induced eNOS and Akt phosphorylation, leading to the impairment of NO production and vasodilation. In conclusion, 2-ME induces vasodilation by stimulating NO release. These actions may be mediated by PPARγ and the subsequent activation of Akt/eNOS cascade in vascular endothelial cells.

Activation of nuclear factor erythroid 2-related factor 2 coordinates dimethylarginine dimethylaminohydrolase/PPAR-γ/endothelial nitric oxide synthase pathways that enhance nitric oxide generation in human glomerular endothelial cells

Dimethylarginine dimethylaminohydrolase (DDAH) degrades asymmetric dimethylarginine, which inhibits nitric oxide (NO) synthase (NOS). Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcriptional factor that binds to antioxidant response elements and transcribes many antioxidant genes. Because the promoters of the human DDAH-1 and DDAH-2, endothelial NOS (eNOS) and PPAR-γ genes contain 2 to 3 putative antioxidant response elements, we hypothesized that they were regulated by Nrf2/antioxidant response element. Incubation of human renal glomerular endothelial cells with the Nrf2 activator tert-butylhydroquinone (20 μmol·L(-1)) significantly (P<0.05) increased NO and activities of NOS and DDAH and decreased asymmetric dimethylarginine. It upregulated genes for hemoxygenase-1, eNOS, DDAH-1, DDAH-2, and PPAR-γ and partitioned Nrf2 into the nucleus. Knockdown of Nrf2 abolished these effects. Nrf2 bound to one antioxidant response element on DDAH-1 and DDAH-2 and PPAR-γ promoters but not to the eNOS promoter. An increased eNOS and phosphorylated eNOS (P-eNOSser-1177) expression with tert-butylhydroquinone was prevented by knockdown of PPAR-γ. Expression of Nrf2 was reduced by knockdown of PPAR-γ, whereas PPAR-γ was reduced by knockdown of Nrf2, thereby demonstrating 2-way positive interactions. Thus, Nrf2 transcribes HO-1 and other genes to reduce reactive oxygen species, and DDAH-1 and DDAH-2 to reduce asymmetric dimethylarginine and PPAR-γ to increase eNOS and its phosphorylation and activity thereby coordinating 3 pathways that enhance endothelial NO generation.

Natural product agonists of peroxisome proliferator-activated receptor gamma (PPARγ): a review

Agonists of the nuclear receptor PPARγ are therapeutically used to combat hyperglycaemia associated with the metabolic syndrome and type 2 diabetes. In spite of being effective in normalization of blood glucose levels, the currently used PPARγ agonists from the thiazolidinedione type have serious side effects, making the discovery of novel ligands highly relevant. Natural products have proven historically to be a promising pool of structures for drug discovery, and a significant research effort has recently been undertaken to explore the PPARγ-activating potential of a wide range of natural products originating from traditionally used medicinal plants or dietary sources. The majority of identified compounds are selective PPARγ modulators (SPPARMs), transactivating the expression of PPARγ-dependent reporter genes as partial agonists. Those natural PPARγ ligands have different binding modes to the receptor in comparison to the full thiazolidinedione agonists, and on some occasions activate in addition PPARα (e.g. genistein, biochanin A, sargaquinoic acid, sargahydroquinoic acid, resveratrol, amorphastilbol) or the PPARγ-dimer partner retinoid X receptor (RXR; e.g. the neolignans magnolol and honokiol). A number of in vivo studies suggest that some of the natural product activators of PPARγ (e.g. honokiol, amorfrutin 1, amorfrutin B, amorphastilbol) improve metabolic parameters in diabetic animal models, partly with reduced side effects in comparison to full thiazolidinedione agonists. The bioactivity pattern as well as the dietary use of several of the identified active compounds and plant extracts warrants future research regarding their therapeutic potential and the possibility to modulate PPARγ activation by dietary interventions or food supplements.

Pioglitazone and Endothelial Dysfunction: Pleiotropic Effects and Possible Therapeutic Implications

The vascular endothelium has a central role in the modulation of vascular tone with associated antioxidant, anti-inflammatory, pro-fibrinolytic, anti-adhesive, and anticoagulant effects. This is primarily accomplished by the timely release of endothelial autacoids. On the other hand, endothelial dysfunction (ED) provoked by insulin resistance has been linked with reduced nitric oxide bioavailability, increased production of reactive oxygen species, and alterations of endothelial regeneration. Pioglitazone is classified as an insulin-sensitizing, anti-hyperglycemic agent. The mechanism of action associated with pioglitazone includes the activation of peroxisome proliferator-activated receptor-gamma with stable improvement in glycemic control in diabetic patients. Today, it is known that apart from the beneficial effects on glucose homeostasis, pioglitazone exerts several pleiotropic effects, including the improvement of ED. Thus, the aim of this article was to summarize the current knowledge related to signaling mechanisms of the pioglitazone-induced improvement or reversal of ED. The relevant clinical studies and possible therapeutic implications connected to pioglitazone-related action on the endothelium were analyzed too.

A century old renin-angiotensin system still grows with endless possibilities: AT1 receptor signaling cascades in cardiovascular physiopathology

Ang II, the primary effector pleiotropic hormone of the renin-angiotensin system (RAS) cascade, mediates physiological control of blood pressure and electrolyte balance through its action on vascular tone, aldosterone secretion, renal sodium absorption, water intake, sympathetic activity and vasopressin release. It affects the function of most of the organs far beyond blood pressure control including heart, blood vessels, kidney and brain, thus, causing both beneficial and deleterious effects. However, the protective axis of the RAS composed of ACE2, Ang (1-7), alamandine, and Mas and MargD receptors might oppose some harmful effects of Ang II and might promote beneficial cardiovascular effects. Newly identified RAS family peptides, Ang A and angioprotectin, further extend the complexities in understanding the cardiovascular physiopathology of RAS. Most of the diverse actions of Ang II are mediated by AT1 receptors, which couple to classical Gq/11 protein and activate multiple downstream signals, including PKC, ERK1/2, Raf, tyrosine kinases, receptor tyrosine kinases (EGFR, PDGF, insulin receptor), nuclear factor κB and reactive oxygen species (ROS). Receptor activation via G12/13 stimulates Rho-kinase, which causes vascular contraction and hypertrophy. The AT1 receptor activation also stimulates G protein-independent signaling pathways such as β-arrestin-mediated MAPK activation and Src-JAK/STAT. AT1 receptor-mediated activation of NADPH oxidase releases ROS, resulting in the activation of pro-inflammatory transcription factors and stimulation of small G proteins such as Ras, Rac and RhoA. The components of the RAS and the major Ang II-induced signaling cascades of AT1 receptors are reviewed.

A meta-analysis of randomized controlled trials of telmisartan for flow-mediated dilatation

There have been a number of small-sized underpowered randomized controlled trials to assess effects of telmisartan on flow-mediated dilatation (FMD). To determine whether telmisartan increases FMD, we performed a meta-analysis of these trials. MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials were searched through December 2013. Eligible studies were prospective randomized controlled trials of telmisartan reporting FMD as an outcome. Search terms included: telmisartan; endothelial function/dysfunction; flow-mediated dilation/dilatation/vasodilation/vasodilatation; and randomized, randomly or randomization. Included studies were reviewed to determine the number of patients randomized, mean duration of treatment and percent changes of FMD. Of 25 potentially relevant articles screened initially, seven reports of randomized trials enrolling a total of 398 patients were identified and included. A pooled analysis of the seven trials demonstrated a statistically significant increase in FMD by 48.7%, with telmisartan relative to control in the random-effects model (mean difference, 48.72%; 95% confidence interval, 15.37-82.08%; P for effect=0.004; P for heterogeneity <0.00001). Exclusion of any single trial from the analysis did not substantively alter the overall result of our analysis. There was no evidence of significant publication bias. In conclusion, the present meta-analysis of seven randomized controlled trials enrolling a total of 398 patients confirmed the evidence of a significant increase in FMD with telmisartan, which suggests that telmisartan may improve endothelial dysfunction.