Angiotensin receptor blockade with candesartan attenuates atherosclerosis, plaque disruption, and macrophage accumulation within the plaque in a rabbit model

Evaluation of Aortic Hemodynamics Using Four-Dimensional Flow of Magnetic Resonance Imaging in Rabbits with Liver Fibrosis

BACKGROUND

Liver fibrosis (LF) precipitates systemic hemodynamic alterations, however, its impact on the aorta remaining undefined.

PURPOSE

To assess aorta hemodynamics changes during LF development in a rabbit model.

STUDY TYPE

Prospective, experimental.

ANIMAL MODEL

Thirty 7-month-old male rabbits underwent bile duct ligation (BDL) to induce LF.

FIELD STRENGTH/SEQUENCE

Biweekly four-dimensional (4D) flow imaging incorporating a 3D gradient-echo at 3.0 T scanner for 14 weeks post-BDL.

ASSESSMENT

Histopathological exams for 2-5 rabbits were performed at each time point, following each MRI scan. LF was graded using the Metavir scale by a pathologist. 4D flow was analyzed by two radiologists using dedicated postprocessing software. They recorded 4D flow parameters at four aorta sections (aortic sinus, before and after bifurcation of aortic arch, and descending aorta).

STATISTICAL TESTS

The linear mixed model; Bonferroni correction; Pearson correlation coefficient (r); receiver operating characteristic (ROC) curve; Delong test. The level of significance was set at P < 0.05.

RESULTS

Following BDL, the wall shear stress (WSS) (0.23-0.32 Pa), energy loss (EL) (0.27-1.55 mW) of aorta significantly increased at the second week for each plane, peaking at the sixth week (WSS: 0.35-0.49 Pa, EL: 0.57-2.0 mW). So did the relative pressure difference (RPD) (second week: 1.67 ± 1.63 mmHg, sixth week: 2.43 ± 0.63 mmHg) in plane 2. Notably, the RPD in plane 2 at the second week displayed the highest area under ROC curve of 0.998 (specificity: 1, sensitivity: 0.967). LF were found at the second, fourth, and sixth week after BDL, with grade F2, F3, and F4, respectively. The RPD in plane 2 was most strongly correlated with the severity of LF (r = 0.86).

DATA CONCLUSIONS

The occurrence of LF could increase WSS, EL, and RPD of aorta as early as the second week following BDL.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 2.

Design, optimization, and in vivo evaluation of invasome-mediated candesartan for the control of diabetes-associated atherosclerosis

Atherosclerosis is an inflammatory disease characterized by the accumulation of arterial plaque. Diabetes mellitus stands out as a major risk factor for atherosclerosis. Candesartan is a potent angiotensin II receptor antagonist that enhances arterial blood flow and reduces insulin resistance. However, oral candesartan has limited activity because of its low bioavailability, water solubility, hepatic first-pass degradation, and efficacy. The current study aims to develop nasal candesartan-loaded invasome (CLI) drops to improve candesartan's permeation, release, and bioavailability as a potential treatment for diabetes-associated atherosclerosis. Design expert software was used to prepare various CLI formulations to determine the impact of the concentrations of ethanol, cineole, and phospholipid. The desirability index was used to estimate the optimized formulation composition to maximize entrapment efficiency and minimize vesicle size. The optimized formulation had a 1% ethanol concentration, a 1.5% cineole concentration, and a 2.32% phospholipid concentration. The selected optimized formulation was then tested in a rat model of diabetes and atherosclerosis to evaluate its activity. The results showed that nasal CLI drops significantly raised serum HDL levels by a ratio of 1.42 and lowered serum glucose, cholesterol, triglycerides, LDL, and VLDL levels by 69.70%, 72.22%, 36.52%, 58.0%, and 65.31%, respectively, compared with diabetic atherosclerotic rats, throwing an insight on the potential for promising anti-diabetic and anti-atherosclerotic activities. Additionally, atherosclerotic lesions were improved in rats treated with CLI, as shown in histopathology. In conclusion, the results of this investigation showed that treatment with nasal CSN-loaded invasome formulation drops prevented the initiation and progression of diabetes-associated atherosclerosis.

Fimasartan reduces neointimal formation and inflammation after carotid arterial injury in apolipoprotein E knockout mice

BACKGROUND

The beneficial effects of angiotensin II type 1 receptor blockers (ARBs) on atherosclerosis have been demonstrated in numerous studies. We investigated the effects of fimasartan on reducing neointimal formation and systemic inflammation after carotid artery (CA) injury in Apolipoprotein E knockout (ApoE KO) mice.

METHODS

ApoE KO mice were randomly allocated to Group I (without CA injury), Group II (without CA injury + Fimasartan), Group III (CA injury), and Group IV (CA injury + Fimasartan). Fimasartan was orally administered everyday starting 3 days before iatrogenic left CA injury.

RESULTS

At 28 days, neointimal hyperplasia and the inflammatory cytokines including TNFα, IL-6, ICAM, and MMP-9 in the peripheral blood were significantly reduced in Groups II and IV compared to Groups I and III, respectively. All fimasartan-administered groups revealed significant increases of CD4⁺CD25⁺Foxp3⁺ regulatory T (Treg) cells with increased plasma levels of IL-10 and TGFβ. In addition, increased CD8⁺ T cells by fimasartan were correlated with reduced smooth muscle cell (SMC) proliferation in the neointima in Groups II and IV. Furthermore, the populations of Treg and CD8⁺ T cells in total splenocytes were increased in Groups II and IV compared to Groups I and III, respectively. The enlargement of spleens due to CA injury in the Group III was attenuated by fimasartan, as shown in the Group IV. These data indicate that fimasartan significantly reduced SMC proliferation in neointima and increased Treg cells in ApoE KO CA injury mice.

CONCLUSIONS

This study suggests fimasartan could be an efficient strategy for reduction of atherosclerotic progression, with a decrease in immune response and systemic inflammation.

The role of monocyte chemotactic protein-induced protein 1 (MCPIP1) in angiotensin II-induced macrophage apoptosis and vulnerable plaque formation

Atherosclerotic plaque rupture is the main cause of acute coronary syndrome (ACS). Angiotensin II (Ang II) and macrophage apoptosis are involved in the pathogenesis of atherosclerosis. However, the underlying mechanisms remain unclear. We aimed to address the role of monocyte chemotactic protein-induced protein 1 (MCPIP1) in Ang II-induced macrophage apoptosis and vulnerable plaque formation. In mouse peritoneal macrophages, Ang II promoted endoplasmic reticulum (ER) stress-dependent macrophage apoptosis. Ang II markedly upregulated the expression of MCPIP1 via activating p38 mitogen-activated protein kinase (p38 MAPK). Treatment with MCPIP1 shRNA downregulated ER stress-related proteins and decreased macrophage apoptosis induced by Ang II. Ang II also activated the AMP-activated protein kinase (AMPK) signaling in macrophages. Inhibition of AMPK reduced macrophage apoptosis by inhibiting the p38 MAPK/MCPIP1/ER stress pathway. Furthermore, blocking the Ang II type 1 receptor (AT1R) with losartan effectively inhibited Ang II-induced macrophage apoptosis and AMPK/p38 MAPK/MCPIP1/ER pathway activation. In the atherosclerotic vulnerable plaque model in mice, losartan inhibited the progression of atherosclerosis and transformed vulnerable plaque into a more stable phenotype. Moreover, losartan markedly decreased the number of CD68⁺TUNEL⁺, CD68⁺MCPIP1⁺, CD68⁺p-eIF2α⁺ and CD68⁺CHOP⁺ cells in the lesion area. Taken together, Ang II promotes macrophage apoptosis via the AMPK/p38 MAPK/MCPIP1/ER stress pathway in macrophages via its receptor AT1R, which may contribute to vulnerable plaque formation. Our study clarifies a novel regulatory role of MCPIP1 in Ang II-induced macrophage apoptosis and plaque instability, providing a potential therapeutic target for prevention of ACS.

Prognostic Value and Therapeutic Perspectives of Coronary CT Angiography: A Literature Review

Coronary stenosis severity is both a powerful and a still debated predictor of prognosis in coronary artery disease. Coronary computed tomographic angiography (CCTA) has emerged as a noninvasive technique that enables anatomic visualization of coronary artery disease (CAD). CCTA with newer applications, plaque characterization and physiologic/functional evaluation, allows a comprehensive diagnostic and prognostic assessment of otherwise low-intermediate subjects for primary prevention. CCTA measures the overall plaque burden, differentiates plaque subtypes, and identifies high-risk plaque with good reproducibility. Research in this field may also advance towards an era of personalized risk prediction and individualized medical therapy. It has been demonstrated that statins may delay plaque progression and change some plaque features. The potential effects on plaque modifications induced by other medical therapies have also been investigated. Although it is not currently possible to recommend routinely serial scans to monitor the therapeutic efficacy of medical interventions, the plaque modulation, as a part of risk modification, appears a feasible strategy. In this review we summarize the current evidence regarding vulnerable plaque and effects of lipid lowering therapy on morphological features of CAD. We also discuss the potential ability of CCTA to characterize coronary atherosclerosis, stratify prognosis of asymptomatic subjects, and guide medical therapy.

The potential therapeutic use of renin-angiotensin system inhibitors in the treatment of inflammatory diseases

Inflammation is a normal part of the immune response to injury or infection but its dysregulation promotes the development of inflammatory diseases, which cause considerable human suffering. Nonsteroidal anti-inflammatory agents are the most commonly prescribed agents for the treatment of inflammatory diseases, but they are accompanied by a broad range of side effects, including gastrointestinal and cardiovascular events. The renin-angiotensin system (RAS) is traditionally known for its role in blood pressure regulation. However, there is increasing evidence that RAS signaling is also involved in the inflammatory response associated with several disease states. Angiotensin II increases blood pressure by binding to angiotensin type 1 (AT₁ ) receptor, and direct renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors and AT₁ receptor blockers (ARBs) are clinically used as antihypertensive agents. Recent data suggest that these drugs also have anti-inflammatory effects. Therefore, this review summarizes these recent findings for the efficacy of two of the most widely used antihypertensive drug classes, ACE inhibitors and ARBs, to reduce or treat inflammatory diseases such as atherosclerosis, arthritis, steatohepatitis, colitis, pancreatitis, and nephritis.

Leukocyte RhoA exchange factor Arhgef1 mediates vascular inflammation and atherosclerosis

Abnormal activity of the renin-angiotensin-aldosterone system plays a causal role in the development of hypertension, atherosclerosis, and associated cardiovascular events such as myocardial infarction, stroke, and heart failure. As both a vasoconstrictor and a proinflammatory mediator, angiotensin II (Ang II) is considered a potential link between hypertension and atherosclerosis. However, a role for Ang II-induced inflammation in atherosclerosis has not been clearly established, and the molecular mechanisms and intracellular signaling pathways involved are not known. Here, we demonstrated that the RhoA GEF Arhgef1 is essential for Ang II-induced inflammation. Specifically, we showed that deletion of Arhgef1 in a murine model prevents Ang II-induced integrin activation in leukocytes, thereby preventing Ang II-induced recruitment of leukocytes to the endothelium. Mice lacking both LDL receptor (LDLR) and Arhgef1 were protected from high-fat diet-induced atherosclerosis. Moreover, reconstitution of Ldlr-/- mice with Arhgef1-deficient BM prevented high-fat diet-induced atherosclerosis, while reconstitution of Ldlr-/- Arhgef1-/- with WT BM exacerbated atherosclerotic lesion formation, supporting Arhgef1 activation in leukocytes as causal in the development of atherosclerosis. Thus, our data highlight the importance of Arhgef1 in cardiovascular disease and suggest targeting Arhgef1 as a potential therapeutic strategy against atherosclerosis.

Angiotensin II prevents calcification in vascular smooth muscle cells by enhancing magnesium influx

BACKGROUND

Vascular calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD). Low magnesium levels are associated with VC, and recent in vitro studies confirm a protective role of magnesium, which is mediated by its entry into the VSMCs through the Transient Receptor Potential Melastatin 7 (TRPM7) channel. The role of Angiotensin II (Ang II) on VC is still unclear. As Ang II is able to stimulate TRPM7 activity, we hypothesize that it might prevent VC. Thus, the aim of this study was to dissect the direct effect of Ang II on VC.

MATERIALS AND METHODS

We worked with a model of high phosphate (HP)-induced calcification in human aortic smooth muscle cells, which resembles the CKD-related VC.

RESULTS

Addition of Ang II to cells growing in HP decreased calcification, which was associated with the upregulation of the osteogenic factors BMP2, Runx2/Cbfa1, Osterix and ALP. A reduction of magnesium entry into the HP-calcifying cells was found. The treatment with Ang II avoided this reduction, which was reversed by the cotreatment with the TRPM7-inhibitor 2-APB. The protective effect of Ang II was related to AT1R-induced ERK1/2 MAPKinase activation. HP-induced calcification was also associated with the upregulation of the canonical Wnt/beta-catenin pathway, while its downregulation was related to attenuation of calcification by Ang II.

CONCLUSION

As hypothesized, Ang II prevented phosphate-induced calcification in VSMCs, which appears mediated by the increase of magnesium influx and by the activation of the ERK1/2 and the inhibition of the canonical Wnt/beta-catenin signalling pathways.

Rapid stabilisation of atherosclerotic plaque with 5-aminolevulinic acid-mediated sonodynamic therapy

5-Aminolevulinic acid-mediated sonodynamic therapy (ALA-SDT) effectively induces the apoptosis of atherogenic macrophages, but whether it can stabilise atherosclerotic plaque in vivo is unclear. Here, we used an animal model to evaluate the effects of ALA-SDT on plaque stabilisation. Sixty rabbits were induced atherosclerotic plaques in the femoral artery with a combination of silastic tube placement with atherogenic diet, and randomly assigned into control (n = 12) and SDT (n = 48) groups. In the SDT group, after intravenous injected with ALA (60 mg/kg) animals underwent the treatment of ultrasound with intensities of 0.75, 1.00, 1.50 and 2.00 W/cm(²) (n = 12 for each intensity). Seven days after the treatment, the plaque disruption assay was performed to test plaque stability. We found that ALA-SDT with ultrasound intensity of 1.5 W/cm(²) showed the strongest efficacy to stabilise plaques. Under this condition, the frequency of plaque disruption decreased by 88% (p<0.01), positive area of macrophages reduced by 94% (p<0.001) and percentage content of lipids dropped by 60% (p < 0.001), while percentage content of collagens increased by 127% (p<0.001). We also found that the plaque stabilisation by ALA-SDT was associated with increased macrophage apoptosis and apoptotic cell clearance. Moreover, ALA-SDT decreased the contents and activities of matrix metalloproteinase-2,9 and increased the levels of tissue inhibitors of matrix metalloproteinase-1,2 in plaques. Our studies demonstrate that ALA-SDT promotes plaque stabilisation by inducing macrophage elimination and inhibiting matrix degradation. This method might be a promising regimen for atherosclerosis therapy.

Involvement of angiotensin II type 2 receptor (AT2R) signaling in human pancreatic ductal adenocarcinoma (PDAC): a novel AT2R agonist effectively attenuates growth of PDAC grafts in mice

We have recently discovered the potential involvement of angiotensin II type 2 receptor (AT2R) signaling in pancreatic cancer using AT2R deficient mice. To examine the involvement of AT2R expression in human PDAC, expressions of AT2R as well as the major angiotensin II receptor (type 1 receptor, AT1R) in human PDAC and adjacent normal tissue was evaluated by immunohistochemistry and real time PCR using surgically dissected human PDAC specimens. In immunohistochemical analysis, relatively strong AT1R expression was detected consistently in both normal pancreas and PDAC areas, whereas moderate AT2R expression was detected in 78.5% of PDAC specimens and 100% of normal area of the pancreas. AT1R, but not AT2R, mRNA levels were significantly higher in the PDAC area than in the normal pancreas. AT2R mRNA levels showed a negative correlation trend with overall survival. In cell cultures, treatment with a novel AT2R agonist significantly attenuated both murine and human PDAC cell growth with negligible cytotoxicity in normal epithelial cells. In a mouse study, administrations of the AT2R agonist in tumor surrounding connective tissue markedly attenuated growth of only AT2R expressing PAN02 murine PDAC grafts in syngeneic mice. The AT2R agonist treatment induced apoptosis primarily in tumor cells but not in stromal cells. Taken together, our findings offer clinical and preclinical evidence for the involvement of AT2R signaling in PDAC development and pinpoint that the novel AT2R agonist could serve as an effective therapeutic for PDAC treatment.

Antiatherosclerotic effects of the novel angiotensin receptor antagonist Fimasartan on plaque progression and stability in a rabbit model: a double-blind placebo-controlled trial

OBJECTIVES

To evaluate the effect of the novel angiotensin receptor blocker Fimasartan on the development of atherosclerosis and plaque stabilization in an animal model.

METHODS

Twenty-four rabbits received an aortic balloon injury from 30 cm to a level just above the aortic valve to the iliac bifurcation using 3 Fr Fogarty catheters on third day of the experiment, followed by a 1% cholesterol diet for 8 weeks. The rabbits were randomized to receive placebo or 3 or 6 mg · kg⁻¹ · d⁻¹ Fimasartan. The study was double blinded. The rabbits started receiving their medications 2 days before the aortic balloon injury and treatment continued. Atherosclerosis burden was determined by calculating the intima-media ratio of the infrarenal portion of the aorta because the bulk of the atherosclerotic burden was limited to the infrarenal region. The frequency of plaque disruption with thrombosis and the proportions of the plaques that were occupied by macrophages, smooth muscle cells, and collagen were determined.

RESULTS

Relative to the placebo group, the Fimasartan-treated rabbits had less atherosclerosis [intima-media ratio (mean ± SEM) of 1.14 ± 0.21 vs. 1.51 ± 0.26, P = 0.005], fewer disrupted plaques with thrombi (3 of 16 vs. 5 of 8, P = 0.047), lower proportion of macrophages (17.5% ± 2.5% vs. 26% ± 3.5%, P = 0.03), higher proportion of smooth muscle cells (43.5% ± 8.3% vs. 11.9% ± 2.1%, P = 0.001), and higher proportion of collagen (34.3% ± 6.4% vs. 19.7% ± 2.1%, P = 0.02).

CONCLUSIONS

These results show that the newly developed angiotensin receptor blocker, Fimasartan, attenuated atherosclerosis progression and reduced macrophage accumulation in the rabbit aortic plaques.

Atherosclerotic Plaque Destabilization

Understanding the pathophysiology of atherogenesis and the progression of atherosclerosis have been major goals of cardiovascular research during the previous decades. However, the complex molecular and cellular mechanisms underlying plaque destabilization remain largely obscure. Here, we review how lesional cells undergo cell death and how failed clearance exacerbates necrotic core formation. Advanced atherosclerotic lesions are further weakened by the pronounced local activity of matrix-degrading proteases as well as immature neovessels sprouting into the lesion. To stimulate translation of the current knowledge of molecular mechanisms of plaque destabilization into clinical studies, we further summarize available animal models of plaque destabilization. Based on the molecular mechanisms leading to plaque instability, we outline the current status of clinical and preclinical trials to induce plaque stability with a focus on induction of dead cell clearance, inhibition of protease activity, and dampening of inflammatory cell recruitment.

Contributions of leukocyte angiotensin-converting enzyme to development of atherosclerosis

OBJECTIVE

This study determined the role of angiotensin-converting enzyme (ACE) on the development of angiotensin I-induced atherosclerosis and the contribution of leukocyte-specific expression of this enzyme.

APPROACH AND RESULTS

To define the contribution of ACE-dependent activity to angiotensin II synthesis in atherosclerotic development, male low-density lipoprotein receptor(-/-) mice were fed a fat-enriched diet and infused with either angiotensin I or angiotensin II. The same infusion rate of these peptides had equivalent effects on atherosclerotic development. Coinfusion of an ACE inhibitor, enalapril, ablated angiotensin I-augmented atherosclerosis but had no effect on angiotensin II-induced lesion development. ACE protein was detected in several cell types in atherosclerotic lesions, with a predominance in macrophages. This cell type secreted angiotensin II, which was ablated by ACE inhibition. To study whether leukocyte ACE contributed to atherosclerosis, irradiated male low-density lipoprotein receptor(-/-) mice were repopulated with bone marrow-derived cells from either ACE(+/+) or ACE(-/-) mice and fed the fat-enriched diet for 12 weeks. Chimeric mice with ACE deficiency in bone marrow-derived cells had modestly reduced atherosclerotic lesions in aortic arches but had no effects in aortic roots.

CONCLUSIONS

ACE mediates angiotensin I-induced atherosclerosis, and ACE expression in leukocytes modestly contributes to atherosclerotic development in hypercholesterolemic mice.

Characterization of atherosclerotic plaque depositions by Raman and FTIR imaging

Spectroscopy-based imaging techniques can provide useful biochemical information about tissue samples. Here, we employ Raman and Fourier transform infrared (IR) imaging to characterize composition and constitution of atherosclerotic plaques of rabbits, fed with a high cholesterol diet. The results were compared with conventional light microscopy after staining with hematoxylin eosin, and elastica van Gieson. The spectral unmixing algorithm vertex component analysis was applied for data analysis and image reconstruction. IR microscopy allowed for differentiation between lipids and proteins in plaques of full aortic cross sections. Raman microscopy further discriminated cholesterol esters, cholesterol and triglycerides. FTIR and Raman images were recorded at a resolution near 20 micrometer per pixel for a large field of view. High resolution Raman images at 1 micrometer per pixel revealed structural details at selected regions of interest. The intima-media and the lipid-protein ratio were determined in five specimens for quantitation. These results correlate well with histopathology. The described method is a promising tool for easy and fast molecular imaging of atherosclerosis.

Plaque-stabilizing effect of angiotensin-converting enzyme inhibitor and/or angiotensin receptor blocker in a rabbit plaque model

AIM

Previous studies have revealed that blockade of the renin angiotensin system attenuates plaque vulnerability and reduces cardiovascular events; however, few studies have compared the effects of an angiotensin-converting enzyme inhibitor (ACEI) with an angiotensin receptor blocker (ARB) and evaluated combination therapy. The objective of this study was to compare the efficacy and mechanisms of plaque stabilization by ACEI or ARB and to determine the effects of combination therapy.

METHODS

Twenty-eight male Japanese white rabbits were fed a high-cholesterol diet after balloon injury of the carotid arteries, then separated into ACEI (n= 7; imidapril 0.5 mg/kg/day), ARB (n= 7; TA606 4.5 mg/kg/day), combination (n= 7; imidapril 0.5 mg/kg/day+TA606 4.5 mg/kg/day), and vehicle (n= 7) groups.

RESULTS

No difference in plaque volume was identified among the 4 groups. ACEI or ARB increased the thickness of the fibrous cap, collagen content and the number of smooth muscle cells in the intima (% smooth muscle cell in intima: ACEI, 36.3%; ARB, 36.4%; vehicle, 14.9%), and reduced the accumulation of macrophages (% macrophages in intima: ACEI, 20.1%; ARB, 24.0%; vehicle, 37.9%), suggesting the plaque-stabilizing effects of each drug. ACEI reduced matrix metalloproteinase (MMP)-9 expression and gelatinolytic activity in the intima. While ARB did not change gelatinolytic activity, accumulation ot T cell in the intima was suppressed. Combination therapy did not show additive effects.

CONCLUSION

These results suggest that ACEIs and ARBs have similar, but not additive, plaque-stabilizing effects. Each agent showed specific effects, with ACEIs decreasing gelatinolytic activity and ARBs suppressing T cell accumulation.

Comparative effects of different modes of renin angiotensin system inhibition on hypercholesterolaemia-induced atherosclerosis

BACKGROUND AND PURPOSE

Inhibition of the renin angiotensin system (RAS) has been consistently demonstrated to reduce atherosclerosis. However, there has been no direct comparison among the three available pharmacological modes of inhibiting the RAS, which are inhibitors of renin, ACE and angiotensin II type 1 receptor. The purpose of this study was to determine the relative effects of these three modes of pharmacological RAS inhibition in reducing atherosclerosis by determining the dose-response relationships.

EXPERIMENTAL APPROACH

Male LDL receptor -/- mice were administered either vehicle or any of three doses of aliskiren, enalapril or losartan through s.c. infusion for 12 weeks. All mice were fed a saturated fat-enriched diet during drug infusions. Systolic and diastolic BPs were measured during the study using a non-invasive tail-cuff system. Plasma cholesterol and renin concentrations, atherosclerotic lesions, and renal angiotensin II concentrations were determined at the termination of the study.

KEY RESULTS

Plasma renin concentrations were increased by all three drugs. None of the drugs changed plasma cholesterol concentrations. All drugs produced a dose-related decrease in BP. All three drugs also profoundly reduced atherosclerosis in a dose-dependent manner. The highest dose of each drug markedly attenuated lesion size, with no significant differences between the different drugs. The highest dose of each drug also similarly reduced renal angiotensin II concentrations.

CONCLUSION AND IMPLICATIONS

Drugs that inhibit the RAS, irrespective of their mode of inhibition, profoundly affect atherosclerotic lesion development in a dose-dependent manner.

The relation between carotid plaque echogenicity and oxidative stress marker 8-iso-prostaglandin F2α

Echolucent plaques are associated with high risk of ischemic cerebrovascular events. Oxidative stress has been implicated in the process of atherosclerotic plaque development from initiation to progression. We assessed the relation between carotid plaque echogenicity and urinary 8-iso-prostaglandin F2α, as an index of oxidative stress. This cross-sectional study was conducted prospectively on 290 consecutive outpatients. Each patient was evaluated for carotid plaque echogenicity using the gray-scale median at the maximal thickness plaque and urinary 8-iso-prostaglandin F2α using enzyme linked immunosorbent assay. By Pearson correlation analysis, we found significant negative linear relation between gray-scale median values and the urinary 8-iso-prostaglandin F2α levels (r = -0.133, p = 0.023). This correlation remained significant after adjustment for atherosclerotic risk factors, thickness of the maximal plaque and medication use (β = -0.137, p = 0.031). We herein show that higher levels of urinary 8-iso-prostaglandin F2α is associated with lower plaque echogenicity.

Angiotensin-converting enzyme 2 attenuates atherosclerotic lesions by targeting vascular cells

Angiotensin-converting enzyme 2 (ACE2) is a newly discovered homolog of ACE whose actions oppose those of angiotensin II (AngII). However, the underlying mechanisms by which ACE2 effectively suppresses early atherosclerotic lesions remain poorly understood. Here, we show, both in vitro and in vivo, that ACE2 inhibited the development of early atherosclerotic lesions by suppressing the growth of vascular smooth muscle cells (VSMCs) and improving endothelial function. In a relatively large cohort animal study (66 rabbits), aortic segments transfected by Ad-ACE2 showed significantly attenuated fatty streak formation, neointimal macrophage infiltration, and alleviation of impaired endothelial function. Segments also showed decreased expression of monocyte chemoattractant protein 1, lectin-like oxidized low-density lipoprotein receptor 1, and proliferating cell nuclear antigen, which led to the delayed onset of atherosclerotic lesions. At the cellular level, ACE2 significantly modulated AngII-induced growth and migration in human umbilical vein endothelial cells and VSMCs. The antiatherosclerotic effect of ACE2 involved down-regulation of the ERK-p38, JAK-STAT, and AngII-ROS-NF-kappaB signaling pathways and up-regulation of the PI3K-Akt pathway. These findings revealed the molecular mechanisms of the antiatherosclerotic activity of ACE2 and suggested that modulation of ACE2 could offer a therapeutic option for treating atherosclerosis.

AGEs increased migration and inflammatory responses of adventitial fibroblasts via RAGE, MAPK and NF-kappaB pathways

OBJECTIVE

Advanced glycation end products (AGEs) and vascular adventitial fibroblasts (AFs) are involved in diabetes-related vascular complications. However, the effect of AGEs on AFs remains unclear. The aim of this study was to observe the impact of AGEs on cell migration capacity and associated inflammatory responses of AFs.

METHODS AND RESULTS

Isolated vascular AFs of Sprague-Dawley rats were cultured, harvested after 24h synchronization and challenged with AGE-HSA. AGE-HSA upregulated the expression of receptor for advanced glycation end products (RAGE), significantly increased the migration capacity and inflammatory mediators MCP-1, IL-6, VCAM-1 expressions on AFs. These effects could be significantly attenuated by anti-RAGE neutralizing antibody, p38, ERK1/2 and JNK MAPK inhibitors as well as by candesartan. AGE-HAS also upregulated NF-kappaB transcriptional activity and I-kappaB-alpha phosphorylation, effect that was significantly inhibited by candesartan.

CONCLUSIONS

AGE-HSA increased the migration capacity and inflammatory responses of rat AFs via RAGE-MAPK-NF-kappaB pathways. Candesartan effectively inhibited these effects which might be a novel vascular protection mechanism of candesartan.

Resveratrol attenuates angiotensin II-induced interleukin-6 expression and perivascular fibrosis

Recent studies have shown that resveratrol (3,5,4'-trihydroxystilbene), a polyphenolic compound found in grapes and red wine, has various beneficial effects on cardiovascular diseases and prolongs the life span of mice fed a high-fat diet. We hypothesized that resveratrol may attenuate vascular inflammatory response induced by angiotensin (Ang) II. We examined the effect of resveratrol on Ang II-induced interleukin (IL)-6 expression in vascular smooth muscle cells (VSMCs). Resveratrol significantly attenuated Ang II-induced IL-6 mRNA expression and IL-6 protein in the supernatant of VSMC in a dose-dependent manner. Resveratrol suppressed the IL-6 gene promoter activity. Resveratrol inhibited the Ang II-induced cAMP-response element-binding protein and nuclear factor-kappa B activity, which are critical for Ang II-induced IL-6 gene activation. An increase in the serum concentration of IL-6 induced by Ang II infusion was attenuated by an oral administration of resveratrol. Resveratrol also inhibited Ang II-induced hypertension and perivascular fibrosis of the heart. Although hydralazine reduced blood pressure level equal to resveratrol, it did not reduce the Ang II-induced IL-6 production and perivascular fibrosis. These data suggest that the inhibition of Ang II-induced vascular inflammation and high blood pressure by resveratrol may contribute, at least in part, to the anti-atherogenic effects of resveratrol.

A robust rabbit model of human atherosclerosis and atherothrombosis

Disruption and thrombosis of atherosclerotic plaques cause most acute cardiovascular events, but their systematic study has been hampered by the lack of suitable animal models. To assess the value of a modified rabbit model of atherothrombosis, we performed detailed histology of rabbit aortic plaques. Atherosclerosis was induced with a high cholesterol diet fed 2 weeks prior to and 6 weeks after balloon injury of the aorta, followed by 4 weeks of normal diet. We found six out of eight types of plaques cataloged by the American Heart Association in the rabbit aorta. Vulnerable plaques were defined as those with attached platelet and fibrin-rich thrombi after pharmacological triggering with Russell's viper venom and histamine. Ruptured plaques had, as also described for human plaques: i) marked medial and adventitial changes, including neovascularization and inflammation; ii) cholesterol monohydrate crystals and liquid crystalline cholesterol esters in the intima and the fibrous cap; and iii) inflamed, thin fibrous caps. Increased cholesterol monohydrate area, internal elastic lamina area, positive remodeling, fibrous cap inflammation, adventitia breakdown, and inflammation were independent predictors of plaque disruption. Our findings reveal novel insights into plaque vulnerability and could guide the design of noninvasive imaging approaches for detecting and treating high-risk plaques.

Angiotensin II upregulates acyl-CoA:cholesterol acyltransferase-1 via the angiotensin II Type 1 receptor in human monocyte-macrophages

Angiotensin II (Ang II) is known to accelerate the progression of macrophage-driven atherosclerotic lesions. Acyl-CoA:cholesterol acyltransferase-1 (ACAT1) converts intracellular free cholesterol into cholesterol ester (CE) for storage in lipid droplets, and promotes foam cell formation in atherosclerotic lesions. The present study explored the effect of Ang II on ACAT1 expression as a molecular mechanism of foam cell formation in primary cultured human monocyte-macrophages. Ang II significantly increased ACAT1 protein expression in a time- or concentration-dependent manner. Application of an Ang II type 1 (AT(1)) receptor agonist (L162313), but not an Ang II type 2 (AT(2)) receptor agonist (CGP42112A), mimicked the effects of Ang II treatment in inducing ACAT1 protein expression. ACAT activity and ACAT1 mRNA levels were also significantly increased by Ang II. Two-fold increases in ACAT1 protein expression and ACAT activity with Ang II treatment were completely inhibited by AT(1) receptor antagonists (candesartan, [Sar(1),Ile(8)]-Ang II), but not by an AT(2) receptor antagonist (PD123319). Treatment with a G-protein inactivator (GDP-beta-S), a c-Src tyrosine kinase inhibitor (PP2), a protein kinase C (PKC) inhibitor (rottlerin), or a mitogen activated protein kinase (MAPK) kinase inhibitor (PD98059) significantly reduced Ang II-induced ACAT1 protein expression. Macrophage foam cell formation assessed using acetylated low-density lipoprotein (LDL)-induced CE accumulation was significantly enhanced by Ang II, which was completely inhibited by treatment with candesartan. These results suggested that Ang II enhances foam cell formation by upregulating ACAT1 expression predominantly through the actions of AT(1) receptor via the G protein/c-Src/PKC/MAPK pathway in human monocyte-macrophages.

The effect of quercetin on neointima formation in a rat artery balloon injury model

This study aimed at investigating the effect of quercetin on neointima hyperplasia in the abdominal aorta of rats after balloon injury and expressions of related growth factors. Fifty-four healthy male Sprague-Dawley rats were randomly divided into five groups: a sham-operation group (sham, n=6), a control group (control, n=12), and three quercetin-treated groups: Q50 group (50mg/kg body weight/day, n=12), Q100 group (100mg/kg body weight/day, n=12), and Q200 group (200mg/kg body weight/day, n=12) 3 days before balloon injury until the end of the experiment. Fourteen days after injury, rats were killed, and the abdominal aortas were harvested. Hematoxylin-eosin staining showed that quercetin significantly reduced the neointimal areas and the intimal to medial ratio in the Q100 and Q200 groups 14 days after injury. Immunohistochemical analysis showed that quercetin significantly inhibited PCNA, PDGF-BB, b-FGF, and TGF-beta1 expressions in the neointima. Masson's trichrome showed that quercetin significantly reduced collagen deposition in the neointima. We concluded that quercetin significantly inhibited neointimal hyperplasia in rat abdominal aorta 14 days after injury in relatively high doses. This effect of quercetin might be partially attributed to the suppression of PDGF-BB, b-FGF, and TGF-beta1 expressions.

In-Stent Restenosis of the Renal Artery in a Single Kidney Patient: The Role of ACEI in the Therapeutic Choice

Renal artery stenosis (RAS) caused by atherosclerotic changes of the renal arteries has become a concern as a cause of end-stage renal failure. Percutaneous balloon angioplasty with or without endovascular stenting is an increasingly accepted procedure at the expense of classical approaches such as aortorenal bypass and other types of surgery. Renal percutaneous transluminal angioplasty and stenting (RPTAS) represent the first therapeutic choice; however, there is doubt regarding the satisfactory long-term outcome for primary RPTAS. Currently, there is no clear evidence whether or not RPTAS prevents further progressive renal function decline because comparisons between interventional randomized studies and medical therapy are still lacking. Despite the fact that the use of angiotensin-converting enzyme inhibitors (ACEIs) may be a potential cause of acute renal failure, clinical data suggest that ACEI therapy is associated with better survival in patient with RAS. In our case, the use of ACEIs has been fundamental for the indirect evaluation of restenosis degree and RPTAS.

Attenuation of inflammation and expansive remodeling by Valsartan alone or in combination with Simvastatin in high-risk coronary atherosclerotic plaques

AIMS

We investigated the role of Valsartan (V) alone or in combination with Simvastatin (S) on coronary atherosclerosis and vascular remodeling, and tested the hypothesis that V or V/S attenuate the pro-inflammatory effect of low endothelial shear stress (ESS).

METHODS

Twenty-four diabetic, hyperlipidemic swine were allocated into Early (n=12) and Late (n=12) groups. In each group animals were treated with Placebo (n=4), V (n=4) and V/S (n=4) and followed for 8 weeks in the Early group and 30 weeks in the Late group. Blood pressure, serum cholesterol and glucose were similar across the treatment subgroups. ESS was calculated in plaque-free subsegments of interest (n=109) in the Late group at week 23. Coronary arteries of this group were harvested at week 30, and the subsegments of interest were identified, and analyzed histopathologically.

RESULTS

V alone or with S reduced the severity of inflammation in high-risk plaques. Both regimens attenuated the severity of enzymatic degradation of the arterial wall, reducing the severity of expansive remodeling. V alone or with S attenuated the pro-inflammatory effect of low ESS.

CONCLUSIONS

V alone or with S exerts a beneficial effect of reducing and stabilizing high-risk plaque characteristics independent of a blood pressure- and lipid-lowering effect.

The renin-angiotensin system and malignancy

The renin-angiotensin system (RAS) is usually associated with its systemic action on cardiovascular homoeostasis. However, recent studies suggest that at a local tissue level, the RAS influences tumour growth. The potential of the RAS as a target for cancer treatment and the suggested underlying mechanisms of its paracrine effects are reviewed here. These include modulation of angiogenesis, cellular proliferation, immune responses and extracellular matrix formation. Knowledge of the RAS has increased dramatically in recent years with the discovery of new enzymes, peptides and feedback mechanisms. The local RAS appears to influence tumour growth and metastases and there is evidence of tissue- and tumour-specific differences. Recent experimental studies provide strong evidence that drugs that inhibit the RAS have the potential to reduce cancer risk or retard tumour growth and metastases. Manipulation of the RAS may, therefore, provide a safe and inexpensive anticancer strategy.

In vivo optical coherence tomography of experimental thrombosis in a rabbit carotid model

Background:

Plaque rupture with subsequent thrombosis is recognised as the underlying pathophysiology of most acute coronary syndromes. Thus, direct thrombus visualisation in vivo may be beneficial for both diagnosis and guidance of therapy. We sought to test the feasibility of imaging acute thrombosis in vivo using optical coherence tomography (OCT) in an experimental thrombosis animal model.

Methods and results:

Nine male New Zealand White rabbits (weight ≈3.0 kg) were made atherosclerotic with a high-cholesterol diet after injury of the right carotid artery endothelium. Thrombus was then induced with the use of Russell’s viper venom (RVV) and histamine. Subsequently, OCT imaging of the right carotid artery was performed. Histology was performed on arterial regions that were injured by balloon. Six rabbits (67%) developed thrombus. Histological correlation confirmed all thrombi (100%) detected with OCT, with no other thrombi seen in the other regions of the right carotid artery. In the remaining three rabbits, no thrombus was observed by OCT or histology.

Conclusion:

We demonstrate the feasibility of OCT for the detection of acute thrombosis in vivo using an animal model of atherosclerosis and acute thrombosis. Potential clinical applications include thrombus detection in acute coronary syndromes.

Renal artery stenosis and accelerated atherosclerosis: which comes first?

Renal artery stenosis (RAS) is usually observed in hypertensive patients with extensive atherosclerosis. There is some evidence that in these patients the atherosclerotic process and the consequent target-organ damage is more severe than in hypertensive patients without RAS. In this review we will entertain the hypothesis that some of the humoral factors that are activated by RAS may contribute to accelerate the progression of atherosclerosis. Several studies identified RAS as a predictor of cardiovascular events in high-risk patients, although in most cases the contribution of blood pressure per se to the progression of vascular lesions could not be determined. As a result of experimental RAS, hypertension and increased oxidative stress are stimuli for atherosclerosis as well as cardiac and renal damage. In the presence of RAS, the renin-angiotensin system is stimulated, and it has been shown that angiotensin II exerts proinflammatory, pro-oxidant and procoagulant activities in experimental models and humans. The potential contribution of reactive oxygen species to the prohypertensive and proatherosclerotic effects of RAS is supported by evidence that nicotinamide adenine dinucleotide phosphate, reduced form oxidase is specifically stimulated by angiotensin II, an activity not shared by epinephrine. Moreover, angiotensin II triggers the release of aldosterone, endothelin 1, thromboxane A2 and other derivatives of the arachidonic acid metabolism, all of which can further and independently aggravate cardiovascular damage. Epidemiological and experimental evidence so far available suggests that accelerated atherosclerosis can be both the cause and the consequence of RAS.

Role of angiotensin II receptor blockers in atherosclerotic plaque stability

Several clinical trials have shown that agents blocking the renin-angiotensin system reduce the incidence of acute ischaemic events. This effect was independent from blood pressure reduction and was presumably related to plaque stabilisation. With the aim of investigating potential mechanisms underlying this effect, carotid plaques were analysed in a recent study from patients randomised to treatment with the angiotensin receptor blocker irbesartan, or the diuretic chlorthalidone for 4 months before carotid endarterectomy. It was found that irbesartan decreased inflammatory infiltration, increased collagen content and downregulated prostaglandin E2-dependent metalloproteases as a consequence of suppression of inducible COX-2/prostaglandin E synthase. This article reviews the results of this study and the most recent evidence that supports the possibility that angiotensin II receptor blockers represent a novel therapy for plaque stabilisation.

The effect of valsartan, captopril, or both on atherosclerotic events after acute myocardial infarction: an analysis of the Valsartan in Acute Myocardial Infarction Trial (VALIANT)

OBJECTIVES

We attempted to compare the effect of an angiotensin-converting enzyme (ACE) inhibitor and angiotensin receptor blocker (ARB) on atherosclerotic events.

BACKGROUND

Angiotensin-converting enzyme inhibitors and ARBs interrupt the renin-angiotensin system by distinct mechanisms. It is not clear whether ARBs reduce atherosclerotic events such as myocardial infarction (MI) like ACE inhibitors. This evidence gap may reflect the nature of the studies conducted, to date. Placebo-controlled studies enrolled cohorts at low risk of atherosclerotic events (e.g., patients with chronic heart failure, most treated with an ACE inhibitor). One of the main active controlled trials was confounded by a blood pressure difference between treatments.

METHODS

We compared the effects of captopril, valsartan, and their combination on atherosclerotic events in 14,703 patients randomized in the Valsartan in Acute Myocardial Infarction Trial (VALIANT).

RESULTS

The number of individuals adjudicated as having a fatal or non-fatal MI in the captopril group was 559 (total investigator reported events 798), 587 (796) in the valsartan group, and 554 (756) in the combination group; valsartan versus captopril, p = 0.651 (0.965); combination versus captopril, p = 0.187 (0.350). Overall, all atherosclerotic events examined occurred at a similar frequency in the captopril and valsartan groups.

CONCLUSIONS

Angiotensin receptor blockers appear to be as effective as ACE inhibitors in reducing atherosclerotic events, even when used in addition to other secondary preventive treatments. These data, although not conclusive, also support the hypothesis that adding an ARB to an ACE inhibitor may have a small additional anti-infarction effect, a possibility that needs to be prospectively tested.

Diabetes mellitus-associated atherosclerosis: mechanisms involved and potential for pharmacological invention

While diabetes mellitus is most often associated with hypertension, dyslipidemia, and obesity, these factors do not fully account for the increased burden of cardiovascular disease in patients with the disease. This strengthens the need for comprehensive studies investigating the underlying mechanisms mediating diabetic cardiovascular disease and, more specifically, diabetes-associated atherosclerosis. In addition to the recognized metabolic abnormalities associated with diabetes mellitus, upregulation of putative pathological pathways such as advanced glycation end products, the renin-angiotensin system, oxidative stress, and increased expression of growth factors and cytokines have been shown to play a causal role in atherosclerotic plaque formation and may explain the increased risk of macrovascular complications. This review discusses the methods used to assess the development of atherosclerosis in the clinic as well as addressing novel biomarkers of atherosclerosis, such as low-density lipoprotein receptor-1. Experimental models of diabetes-associated atherosclerosis are discussed, such as the streptozocin-induced diabetic apolipoprotein E knockout mouse. Results of major clinical trials with inhibitors of putative atherosclerotic pathways are presented. Other topics covered include the role of HMG-CoA reductase inhibitors and fibric acid derivatives with respect to their lipid-altering ability, as well as their emerging pleiotropic anti-atherogenic actions; the effect of inhibiting the renin-angiotensin system by either ACE inhibition or angiotensin II receptor antagonism; the effect of glycemic control and, in particular, the promising role of thiazolidinediones with respect to their direct anti-atherogenic actions; and newly emerging mediators of diabetes-associated atherosclerosis, such as advanced glycation end products, vascular endothelial growth factor and platelet-derived growth factor. Overall, this review aims to highlight the observation that various pathways, both independently and in concert, appear to contribute toward the pathology of diabetes-associated atherosclerosis. Furthermore, it reflects the need for combination therapy to combat this disease.

Impact of Angiotensin II Receptor Blockers on the Progression and Regression of Coronary Atherosclerosis An Intravascular Ultrasound Study

BACKGROUND

Although angiotensin II receptor blockers (ARB) have been found to reduce the coronary atherosclerotic plaque burden in animal models, it is unknown whether ARB have a similar effect on human coronary arteries.

METHODS AND RESULTS

Serial intravascular ultrasound (IVUS) studies of the left main (LM) coronary artery were performed in 64 patients at baseline and after 7-month follow-up. All patients were divided into 2 groups (ARB group: 23 patients; non-ARB group: 41 patients). Three-dimensional volumetric analysis was done throughout the LM coronary artery, and the volume index (VI; volume/length) was calculated for the vessel (VVI), lumen (LVI), and plaque (PVI). No significant difference was found between the 2 groups in baseline clinical characteristics, including age, gender, blood pressure levels, serum cholesterol levels, the presence of diabetes and smoking status. At baseline VVI, LVI and PVI were similar between the groups. In the non-ARB group, VVI, LVI, and PVI did not change between baseline and follow-up. In the ARB group, PVI significantly decreased during follow-up (9.9 +/-3.1 mm2 vs 9.1+/-2.7 mm2, p<0.01), whereas VVI and LVI were unaffected.

CONCLUSIONS

This preliminary IVUS study suggests that ARB could cause regression of coronary atherosclerosis in humans.

Cross-talk between dyslipidemia and renin-angiotensin system and the role of LOX-1 and MAPK in atherogenesis studies with the combined use of rosuvastatin and candesartan

There is increasing evidence of cross-talk between dyslipidemia and renin-angiotensin system (RAS) in atherogenesis. Both dyslipidemia and RAS activation enhance the expression of a newly described receptor for oxidized-low density lipoprotein (ox-LDL), lectin-like ox-LDL receptor-1 (LOX-1). We postulated that the blockade of dyslipidemia with rosuvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor and RAS with candesartan, an angiotensin II type 1 receptor blocker, would have a synergistic inhibitory effect on LOX-1 expression and atherogenesis. Apo-E knockout mice were fed a high-cholesterol diet (1% cholesterol, HC-diet) alone, or HC-diet with rosuvastatin (1mg/(kgd)), candesartan (1mg/(kgd)) or with both. Twelve weeks later the extent of atherosclerosis was determined by Sudan IV staining. Apo-E knockout mice on HC-diet had extensive atherosclerosis. Both rosuvastatin and candesartan decreased the extent of atherosclerosis (by 23 and 26%, respectively), despite the HC-diet; however, the combination of rosuvastatin and candesartan reduced atherosclerosis further (by 67%). Rosuvastatin decreased plasma levels of total cholesterol by over 50%, whereas candesartan had no effect. LOX-1 protein expression was found to be markedly up-regulated in HC-diet-fed apo-E knockout mice. While rosuvastatin and candesartan each had a small inhibitory effect on the expression of LOX-1 in the atherosclerotic tissues, the combination totally blocked the up-regulation of LOX-1. P38 mitogen-activated protein kinase (MAPK) expression and phosphorylation were increased in apo-E knockout mice, attenuated by rosuvastatin or candesartan alone, and completely blocked by the combination of the two agents. P44/42 MAPK expression and phosphorylation were not affected by the HC-diet, rosuvastatin, candesartan, or their combination. This study demonstrates the potent effect of rosuvastatin and candesartan on atherogenesis, as well as on the expression of LOX-1 and on the activation of p38 MAPK, but not p44/42 MAPK.