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.

FSH Is Responsible for Androgen Deprivation Therapy-Associated Atherosclerosis in Mice by Exaggerating Endothelial Inflammation and Monocyte Adhesion

BACKGROUND

Androgen deprivation therapy (ADT) is the mainstay treatment for advanced prostate cancer. But ADTs with orchiectomy and gonadotropin-releasing hormone (GnRH) agonist are associated with increased risk of cardiovascular diseases, which appears less significant with GnRH antagonist. The difference of follicle-stimulating hormone (FSH) in ADT modalities is hypothesized to be responsible for ADT-associated cardiovascular diseases.

METHODS

We administered orchiectomy, GnRH agonist, or GnRH antagonist in male ApoE-/- mice fed with Western diet and manipulated FSH levels by testosterone and FSH supplementation or FSH antibody to investigate the role of FSH elevation on atherosclerosis. By combining lipidomics, in vitro study, and intraluminal FSHR (FSH receptor) inhibition, we delineated the effects of FSH on endothelium and monocytes and the underlying mechanisms.

RESULTS

Orchiectomy and GnRH agonist, but not GnRH antagonist, induced long- or short-term FSH elevation and significantly accelerated atherogenesis. In orchiectomized and testosterone-supplemented mice, FSH exposure increased atherosclerosis. In GnRH agonist-treated mice, blocking of short FSH surge by anti-FSHβ antibody greatly alleviated endothelial inflammation and delayed atherogenesis. In GnRH antagonist-treated mice, FSH supplementation aggravated atherogenesis. Mechanistically, FSH, synergizing with TNF-α (tumor necrosis factor alpha), exacerbated endothelial inflammation by elevating VCAM-1 (vascular cell adhesion protein 1) expression through the cAMP/PKA (protein kinase A)/CREB (cAMP response element-binding protein)/c-Jun and PI3K (phosphatidylinositol 3 kinase)/AKT (protein kinase B)/GSK-3β (glycogen synthase kinase 3 beta)/GATA-6 (GATA-binding protein 6) pathways. In monocytes, FSH upregulated CD29 (cluster of differentiation 29) expression via the PI3K/AKT/GSK-3β/SP1 (specificity protein 1) pathway and promoted monocyte-endothelial adhesion both in vitro and in vivo. Importantly, FSHR knockdown by shRNA in endothelium of carotid arteries markedly reduced GnRH agonist-induced endothelial inflammation and atherosclerosis in mice.

CONCLUSIONS

FSH is responsible for ADT-associated atherosclerosis by exaggerating endothelial inflammation and promoting monocyte-endothelial adhesion.

Renin-angiotensin-aldosterone system inhibitors as a risk factor for chronic subdural hematoma recurrence: A matter of debate

OBJECTIVES

Chronic subdural hematoma (cSDH) is a common central nervous system condition. Recent reports indicate that cSDH affects long-term prognosis; however, its definitive risk factors remain unknown. An antihypertensive drug, renin-angiotensin-aldosterone system inhibitors (RAASi), can affect vascular permeability and cell proliferation processes, which may suppress the recurrence of cSDH. However, several studies have reported negative results to this effect. Therefore, we aimed to evaluate antihypertensive drugs, including RAASi, as risk factors for recurrent cSDH.

MATERIALS AND METHODS

A total of 203 consecutive cases of surgically treated cSDH were retrospectively reviewed. Clinical and radiological parameters were compared between the groups with and without cSDH recurrence to identify risk factors.

RESULTS

Of the included cases, 68 (33.5%) used RAASi and 37 (18.2%) developed recurrence within 60 days of surgery. In the multiple logistic regression analysis adjusted by composite risk score, the odds ratios (95% confidence interval) of RAASi, calcium channel blockers, diuretics, β and α blockers, for the recurrent risk of cSDH after surgery were 2.49 (1.16, 5.42), 1.79 (0.84, 3.82), 1.83 (0.62, 4.87), 0.90 (0.28, 2.44), and 0.96 (0.21, 3.20), respectively. The Cox proportional hazard model also demonstrated that RAASi-use was an independent risk factor for cSDH recurrence.

CONCLUSIONS

Present series suggests RAASi-use as a risk factor for cSDH recurrence, although the role of RAASi-use in cSDH remains debatable. Further studies for deeper understanding of the microenvironment of hematoma and the surroundings are preferable. (235 words).

Endothelial tight junctions and their regulatory signaling pathways in vascular homeostasis and disease

Endothelial tight junctions (TJs) regulate the transport of water, ions, and molecules through the paracellular pathway, serving as an important barrier in blood vessels and maintaining vascular homeostasis. In endothelial cells (ECs), TJs are highly dynamic structures that respond to multiple external stimuli and pathological conditions. Alterations in the expression, distribution, and structure of endothelial TJs may lead to many related vascular diseases and pathologies. In this review, we provide an overview of the assessment methods used to evaluate endothelial TJ barrier function both in vitro and in vivo and describe the composition of endothelial TJs in diverse vascular systems and ECs. More importantly, the direct phosphorylation and dephosphorylation of TJ proteins by intracellular kinases and phosphatases, as well as the signaling pathways involved in the regulation of TJs, including and the protein kinase C (PKC), PKA, PKG, Ras homolog gene family member A (RhoA), mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/Akt, and Wnt/β-catenin pathways, are discussed. With great advances in this area, targeting endothelial TJs may provide novel treatment for TJ-related vascular pathologies.

Probiotic mixture VSL#3 reduce high fat diet induced vascular inflammation and atherosclerosis in ApoE(-/-) mice

Atherosclerosis results from chronic inflammation potentially caused by translocation of bacterial components from the oro-gastrointestinal tract to circulation. Specific probiotics have anti-inflammatory effects and may reduce bacterial translocation. We thereby tested whether a probiotic mixture with documented anti-inflammatory potential could reduce atherosclerosis. ApoE^−/− mice were fed high fat diet alone or with VSL#3 or a positive control treatment, telmisartan or both for 12 weeks. All treatments reduced atherosclerotic plaques significantly compared to high fat diet alone. VSL#3 significantly reduced proinflammatory adhesion molecules and risk factors of plaque rupture, reduced vascular inflammation and atherosclerosis to a comparable extent to telmisartan; and VSL#3 treated mice had the most distinctly different intestinal microbiota composition from the control groups. Combining the VSL#3 and telmisartan brought no further benefits. Our findings showed the therapeutic potential of VSL#3 in reducing atherosclerosis and vascular inflammation.

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.

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)

Chlorella 11-peptide inhibits the production of macrophage-induced adhesion molecules and reduces endothelin-1 expression and endothelial permeability

The inflammation process in large vessels involves the up-regulation of vascular adhesion molecules such as endothelial cell selectin (E-selectin), intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) which are also known as the markers of atherosclerosis. We have reported that Chlorella 11-peptide exhibited effective anti-inflammatory effects. This peptide with an amino sequence Val-Glu-Cys-Tyr-Gly-Pro-Asn-Arg-Pro-Gln-Phe was further examined for its potential in preventing atherosclerosis in this study. In particular, the roles of Chlorella 11-peptide in lowering the production of vascular adhesion molecules, monocyte chemoattractant protein (MCP-1) and expression of endothelin-1 (ET-1) from endothelia (SVEC4-10 cells) were studied. The production of E-selectin, ICAM-1, VCAM-1 and MCP-1 in SVEC4-10 cells was measured with ELISA. The mRNA expression of ET-1 was analyzed by RT-PCR and agarose gel. Results showed that Chlorella 11-peptide significantly suppressed the levels of E-selectin, ICAM, VCAM, MCP-1 as well as ET-1 gene expression. The inhibition of ICAM-1 and VCAM-1 production by Chlorella 11-peptide was reversed in the presence of protein kinase A inhibitor (H89) which suggests that the cAMP pathway was involved in the inhibitory cause of the peptide. In addition, this peptide was shown to reduce the extent of increased intercellular permeability induced by combination of 50% of lipopolysaccharide (LPS)-activated RAW 264.7 cells medium and 50% normal SEVC cell culture medium (referred to as 50% RAW-conditioned medium). These data demonstrate that Chlorella 11-peptide is a promising biomolecule in preventing chronic inflammatory-related vascular diseases.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Differential effects of short-term treatment with two AT1 receptor blockers on diameter of pial arterioles in SHR

Chronic treatment with angiotensin receptor blockers is largely accepted for protecting cerebral circulation during hypertension, but beneficial effects of short-term treatments are questionable, as highlighted by the recent SCAST trial. We compared the impact of 10 days treatment with candesartan (as SCAST) versus telmisartan (previously described to reverse arteriolar remodeling, chronic treatment) on pial arterioles of spontaneously hypertensive rats (SHR). We explored whether PPAR-gamma agonist activity or AT(1) receptor blockade are involved in their differential effects. In the first study, 4-month-old male SHR were treated with telmisartan (TELMI, 2 mg/kg per day) or candesartan cilexetil (CANDE, 10 mg/kg per day) and compared to vehicle treated SHR and normotensive WKY. In a second study, SHR were treated with CANDE, pioglitazone (a PPAR-gamma agonist, PIO 2.5 mg/kg per day) or CANDE+PIO, compared to TELMI. Internal diameter of pial arterioles (ID, cranial window) was measured at baseline, during hemorrhage-induced hypotension, or following suffusion of Ang II (10(-6) mol/L) or EDTA inactivation of smooth muscle cells (passive ID). PPAR-gamma and eNOS (target gene of PPAR-gamma) mRNA were evaluated in brain microvessels. For similar antihypertensive effects, TELMI (+44% versus SHR), but not CANDE, increased baseline ID. During hemorrhage, ID in TELMI group was similar to WKY, while ID in SHR and CANDE remained lower. In the second study, TELMI (+36%, versus SHR) and CANDE+PIO (+43%) increased baseline ID, but not CANDE or PIO alone. TELMI (-66%) and CANDE+PIO (-69%), but neither CANDE nor PIO alone, decreased Ang II-induced vasoconstriction. CANDE+PIO, but not CANDE, increased passive ID. In both studies, PPAR-gamma and eNOS expressions were higher in TELMI than CANDE. Short-term treatment with TELMI, but not with CANDE, reverses narrowing of pial arteriolar ID in SHR. This may involve PPAR-gamma related mechanisms, since CANDE+PIO treatment induced similar effects, and a better blockade of AT(1) receptors.

Telmisartan: just an antihypertensive agent? A literature review

INTRODUCTION

The modulation of the renin angiotensin aldosterone system (RAAS) is an important pathway in managing high blood pressure, and its overexpression plays a key role in target end-organ damage. Telmisartan is an angiotensin II receptor blocker (ARB) with unique pharmacologic properties, including the longest half-life among all ARBs; this leads to a significant and 24-h sustained reduction of blood pressure. Telmisartan has well-known antihypertensive properties, but there is also strong clinical evidence that it reduces left ventricular hypertrophy, arterial stiffness and the recurrence of atrial fibrillation, and confers renoprotection.

AREAS COVERED

This paper reviews telmisartan's pharmacological properties in terms of efficacy for hypertension control and, importantly, focuses on its new therapeutic indications and their clinical implications.

EXPERT OPINION

ONTARGET (ongoing telmisartan alone and in combination with ramipril global endpoint trial) demonstrated, that telmisartan confers cardiovascular protective effects similar to those of ramipril, but with a better tolerability. Moreover, recent investigations focused on the capability of telmisartan to modulate the peroxisome proliferator-activated receptor-gamma (PPAR-γ), an established target in the treatment of insulin resistance, diabetes and metabolic syndrome, whose activation is also correlated to anti-inflammatory and, finally, anti-atherosclerotic properties. Telmisartan shows peculiar features that go beyond blood pressure control. It presents promising and unique protective properties against target end-organ damage, potentially able to open a scenario of new therapeutic approaches to cardiovascular disease.

Antiviral effect of Bosentan and Valsartan during coxsackievirus B3 infection of human endothelial cells

In viral myocarditis, adeno- and enteroviruses have most commonly been implicated as causes of infection. Both viruses require the human coxsackie-adenovirus receptor (CAR) to infect the myocardium. Due to its crucial role for viral entry, CAR-downregulation may lead to novel approaches for treatment for viral myocarditis. In this study, we report on pharmaceutical drug influences on CAR levels in human umbilical vein endothelial cells (HUVEC) and cervical carcinoma cells (HeLa) detected by immunoblotting, quantitative real time-PCR and cellular susceptibility to the cardiotropic coxsackie-B3 virus strain Nancy (CVB3). Our results indicate, for the first time, a dose-dependent CAR mRNA and protein downregulation upon Valsartan and Bosentan treatment. Most interestingly, drug-induced CAR diminution significantly reduced the viral load in CVB3-infected HUVEC. In order to assess the regulatory effects of both drugs in detail, we knocked down their protein targets, the G-protein coupled receptors angiotensin-II type-1 receptor (AT1R) and endothelin-1 type-A and -B receptors (ETAR/ETBR) in HUVEC. Receptor-specific gene silencing indicates that CAR gene expression is regulated by agonistic and antagonistic binding to ETBR, but not ETAR. In addition, neither stimulation nor inhibition of AT1R seemed to be involved in CAR gene regulatory processes. Our study indicates that Valsartan and Bosentan protected human endothelial cells from CVB3-infection. Therefore, besides their well-known anti-hypertensive effects these drugs may also protect the myocardium and other tissues from coxsackie- and adenoviral infection.

Diesel exhaust particles modulate vascular endothelial cell permeability: implication of ZO-1 expression

Exposure to air pollutants increases the incidence of cardiovascular disease. Recent toxicity studies revealed that ultra-fine particles (UFP, d(p)<100-200 nm), the major portion of particulate matter (PM) by numbers in the atmosphere, induced atherosclerosis. In this study, we posited that variations in chemical composition in diesel exhausted particles (DEP) regulated endothelial cell permeability to a different extent. Human aortic endothelial cells (HAEC) were exposed to well-characterized DEP (d(p)<100 nm) emitted from a diesel engine in either idling mode (DEP1) or in urban dynamometer driving schedule (UDDS) (DEP2). Horse Radish Peroxidase-Streptavidin activity assay showed that DEP2 increased endothelial permeability to a greater extent than DEP1 (control=0.077+/-0.005, DEP1=0.175+/-0.003, DEP2=0.265+/-0.006, n=3, p<0.01). DEP2 also down-regulated tight junction protein, Zonular Occludin-1 (ZO-1), to a greater extent compared to DEP1. LDH and caspase-3 activities revealed that DEP-mediated increase in permeability was not due to direct cytotoxicity, and DEP-mediated ZO-1 down-regulation was not due to a decrease in ZO-1 mRNA. Hence, our findings suggest that DEP1 vs. DEP2 differentially influenced the extent of endothelial permeability at the post-translational level. This increase in endothelium permeability is implicated in inflammatory cell transmigration into subendothelial layers with relevance to the initiation of atherosclerosis.