Experimental Atherosclerotic Plaques Research Articles

Implication of miR-155-5p and miR-143-3p in the Vascular Insulin Resistance and Instability of Human and Experimental Atherosclerotic Plaque.

(1) Background: Cardiovascular diseases (CVDs) are the main cause of death in developed countries, being atherosclerosis, a recurring process underlying their apparition. MicroRNAs (miRNAs) modulate the expression of their targets and have emerged as key players in CVDs; (2) Methods: 18 miRNAs were selected (Pubmed and GEO database) for their possible role in promoting atherosclerosis and were analysed by RT-qPCR in the aorta from apolipoprotein E-deficient (ApoE−/−) mice. Afterwards, the altered miRNAs in the aorta from 18 weeks-ApoE−/− mice were studied in human aortic and carotid samples; (3) Results: miR-155-5p was overexpressed and miR-143-3p was downregulated in mouse and human atherosclerotic lesions. In addition, a significant decrease in protein kinase B (AKT), target of miR-155-5p, and an increase in insulin-like growth factor type II receptor (IGF-IIR), target of miR-143-3p, were noted in aortic roots from ApoE−/− mice and in carotid plaques from patients with advanced carotid atherosclerosis (ACA). Finally, the overexpression of miR-155-5p reduced AKT levels and its phosphorylation in vascular smooth muscle cells, while miR-143-3p overexpression decreased IGF-IIR reducing apoptosis in vascular cells; (4) Conclusions: Our results suggest that miR-155-5p and miR-143-3p may be implicated in insulin resistance and plaque instability by the modulation of their targets AKT and IGF-IIR, contributing to the progression of atherosclerosis.

P715Deletion of fibroblast activation protein decreases experimental atherosclerotic plaque formation and vulnerability

Abstract Background Fibroblast activation protein (FAP) is a serine protease that is upregulated in sites of tissue remodeling, including arthritis, tumors and atherosclerosis. We have reported that FAP degrades type I collagen in human thin-cap fibroatheromata; its expression is enhanced in advanced human plaques and induced by inflammation. However, the role of endogenous FAP in atherosclerosis remains unknown. Purpose To investigate the effects of constitutive Fap loss-of-function on atherosclerotic plaque formation and vulnerability. Methods and results Male 8-week-old Apoe−/− Fap+/+ and Apoe−/− Fap−/− mice were fed a high-cholesterol diet (1.25% chol) for 12 weeks. En face analyses of thoracoabdominal aortae using Oil Red O (ORO) revealed decreased plaques in Apoe−/− Fap−/− mice (5.7±0.5%; n=21) compared to Apoe−/− Fap+/+ mice (10.7±0.7%; n=24; p<0.0001). In parallel, ORO analyses of serial aortic root cross sections showed diminished plaques in Fap-deficient mice (18.4±3.4% vs 27.6±2.1%). As a surrogate of plaque vulnerability, fibrous cap thickness was increased in Apoe−/− Fap−/− mice (65±6 mm vs 35±3 mm; p<0.01), whereas necrotic core size, plaque macrophages (CD68) and T cells (CD3) accumulation, as well as VCAM1 expression did not differ. These changes were independent of plasma triglycerides, total and LDL-cholesterol levels. Plasma of Fap-deficient mice showed decreased FAP activity compared to Fap wildtype controls. Notably, second harmonics generation in cross sections of aortic root plaques showed that the deposition and density of fibrillar collagens was enhanced in Fap-deficient (25.5±4.4%) compared to control plaques (13.8±2.5%; p<0.05). Consistently, Fap deletion led to an accumulation of uncleaved pre-COL3A1, a proteolytic target of FAP. Conclusions Constitutive Fap deletion decreases experimental atherosclerosis and features of plaque vulnerability. Thus, inhibition of FAP expression or activity may be a promising therapeutic target in atherosclerosis. Acknowledgement/Funding Swiss National Science Foundation, Swiss Heart Foundation

Effects of Noradrenaline and Adenosine Triphosphate on the Degree on Contrast Enhancement in a Rabbit Model of Atherosclerosis during Contrast-Enhanced Ultrasonography

The aim of the study is to assess the effects of vasoactive agents on the degree of contrast enhancement in experimental atherosclerotic plaque during contrast-enhanced ultrasonography (CEUS). Abdominal aortic atherosclerosis was induced in 25 New Zealand white rabbits by a combination of cholesterol-rich diet and balloon endothelial denudation. Standard ultrasonography and CEUS were performed at baseline and during intravenous infusion of noradrenaline or adenosine triphosphate (ATP). The degree of contrast enhancement of the plaque after injection of contrast material was quantified by calculating the enhanced intensity in the plaque. The infusion of noradrenaline induced significant increase in systolic blood pressure (84 ± 13 mm Hg vs. 112 ± 20 mm Hg, p = 0.011) and significant decrease in the enhanced intensity in the plaque (7.52 ± 1.32 dB vs. 5.88 ± 1.33 dB, p < 0.001) during CEUS. The infusion of ATP resulted in the significant decrease in systolic blood pressure (80 ± 13 mm Hg vs. 65 ± 11 mm Hg, p = 0.005) and increase in the enhanced intensity in the plaque (7.52 ± 1.32 dB vs. 8.84 ± 1.55 dB, p < 0.001) during CEUS. The degree of contrast enhancement within an experimental atherosclerotic plaque during CEUS can be influenced by vasoactive agents and hemodynamic status.

Polymeric Nanoparticle PET/MR Imaging Allows Macrophage Detection in Atherosclerotic Plaques

Myeloid cell content in atherosclerotic plaques associates with rupture and thrombosis. Thus, imaging of lesional monocytes and macrophages could serve as a biomarker of disease progression and therapeutic intervention. To noninvasively assess plaque inflammation with dextran nanoparticle (DNP)-facilitated hybrid positron emission tomography/magnetic resonance imaging (PET/MRI). Using clinically approved building blocks, we systematically developed 13-nm polymeric nanoparticles consisting of cross-linked short chain dextrans, which were modified with desferoxamine for zirconium-89 radiolabeling ((89)Zr-DNP) and a near-infrared fluorochrome (VT680) for microscopic and cellular validation. Flow cytometry of cells isolated from excised aortas showed DNP uptake predominantly in monocytes and macrophages (76.7%) and lower signal originating from other leukocytes, such as neutrophils and lymphocytes (11.8% and 0.7%, P<0.05 versus monocytes and macrophages). DNP colocalized with the myeloid cell marker CD11b on immunohistochemistry. PET/MRI revealed high uptake of (89)Zr-DNP in the aortic root of apolipoprotein E knock out (ApoE(-/-)) mice (standard uptake value, ApoE(-/-) mice versus wild-type controls, 1.9±0.28 versus 1.3±0.03; P<0.05), corroborated by ex vivo scintillation counting and autoradiography. Therapeutic silencing of the monocyte-recruiting receptor C-C chemokine receptor type 2 with short-interfering RNA decreased (89)Zr-DNP plaque signal (P<0.05) and inflammatory gene expression (P<0.05). Hybrid PET/MRI with a 13-nm DNP enables noninvasive assessment of inflammation in experimental atherosclerotic plaques and reports on therapeutic efficacy of anti-inflammatory therapy.

Evaluation of recombinant endostatin in the treatment of atherosclerotic plaques and neovascularization in rabbits

Atherosclerotic plaques and neovascularization play an important role in the course of coronary atherosclerosis. This study evaluated the effect of recombinant endostatin on experimental atherosclerotic plaques and neovascularization in rabbits. Eighteen healthy male rabbits were divided into three groups: control group, atherosclerotic model group, and recombinant endostatin treated group. The atherosclerotic model was established via a high-cholesterol diet after balloon catheter injury. The subject weights, serum total cholesterol, creatine kinase-myocardial band fraction (CKMB), and matrix metalloproteinase-2 (MMP-2) were measured. Six weeks after treatment, the aortic roots were taken for pathological assay. The thickness ratio of the intima to media was measured by hematoxylin and eosin (HE) staining, and the number of neovessels was measured by immunohistochemistry via monoclonal antibody CD31 staining. The weight, plasma total cholesterol, and CKMB were not significantly different between the atherosclerotic model group and the recombinant endostatin treated group, but much higher than those of the control group (P<0.05). The thickness ratio of the intima to media in the recombinant endostatin treated group was distinctly less than that in the atherosclerotic model group (P<0.05). The number of neovessels decreased dramatically (P<0.05) and the content of MMP-2 decreased slightly without statistical difference (P>0.05) in the recombinant endostatin treated group, compared to the atherosclerotic model group. Recombinant endostatin is able to inhibit the growth of neovascularization in the atherosclerotic plaque and the development of plaque.

Mast Cells as Mediators and Modulators of Atherogenesis

The central role of inflammation in atherogenesis has gained broad acceptance and has revolutionized our understanding of this common disease. This recognition has heightened interest in identifying the specific mediators and mechanisms that contribute to the interplay between risk factors (traditional and emerging), inflammation, and the altered biology of the arterial wall that regulates plaque development and complication.1 In particular, leukocytes have come to occupy center stage as the major cellular effectors of inflammation. When these inflammatory cells join endothelial and smooth-muscle cells in the artery wall, they spur much of the biology that drives atherogenesis and plaque complication. Article p 2516 The list of leukocyte subtypes involved in arterial inflammation has entered a flourishing phase of refinement. Our understanding of leukocyte involvement in atherogenesis has gone through several strata of discovery and probing. During the initial descriptive phase, the use of rigorous molecular markers buttressed venerable morphological observations and verified the presence of various leukocyte classes within lesions.2 Later, a phase of experimental validation established the causal relationship between leukocyte accumulation in lesions and the aspects of atherogenesis.3–5 Next, continuing mechanistic exploration has probed the precise molecular pathways by which a given leukocyte population can promote or otherwise modify disease.6 Ultimately, the human relevance of in vitro and animal experiments requires observations in human tissues and in patients. The saga of the macrophage in atherosclerosis followed this pattern. Initial morphological observations supported an early role of monocyte recruitment in the formation of experimental atherosclerotic lesions in rabbits—observations that extend back to the middle of the last century.7 With the advent of rigorously characterized monoclonal antibodies, studies in the 1980s solidly documented the presence of mononuclear phagocytes in human and experimental atherosclerotic plaques.8–10 Subsequent studies in the closing decade of the last century highlighted …

Molecular imaging of vascular cell adhesion molecule-1 expression in experimental atherosclerotic plaques with radiolabelled B2702-p

VCAM-1 plays a major role in the chronic inflammatory processes present in vulnerable atherosclerotic plaques. The residues 75-84 (B2702-p) and 84-75/75-84 (B2702-rp) of the major histocompatibility complex-1 (MHC-1) molecule B2702 were previously shown to bind specifically to VCAM-1. We hypothesised that radiolabelled B2702-p and B2702-rp might have potential for the molecular imaging of vascular cell adhesion molecule-1 (VCAM-1) expression in atherosclerotic plaques. Preliminary biodistribution studies indicated that 125I-B2702-rp was unsuitable for in vivo imaging owing to extremely high lung uptake. 123I- or 99mTc-labelled B2702-p was injected intravenously to Watanabe heritable hyperlipidaemic rabbits (WHHL, n=6) and control animals (n=6). After 180 min, aortas were harvested for ex vivo autoradiographic imaging, gamma-well counting, VCAM-1 immunohistology and Sudan IV lipid staining. Robust VCAM-1 immunostaining was observed in Sudan IV-positive and to a lesser extent in Sudan IV-negative areas of WHHL animals, whereas no expression was detected in control animals. Significant 2.9-fold and 1.9-fold increases in 123I-B2702-p and 99mTc-B2702-p aortic-to-blood ratios, respectively, were observed between WHHL and control animals (p<0.05). Tracer uptake on ex vivo images co-localised with atherosclerotic plaques. Image quantification indicated a graded increase in 123I-B2702-p and 99mTc-B2702-p activities from control to Sudan IV-negative and to Sudan IV-positive areas, consistent with the observed pattern of VCAM-1 expression. Sudan IV-positive to control area tracer activity ratios were 17.0+/-9.0 and 5.9+/-1.8 for 123I-B2702-p and 99mTc-B2702-p, respectively. Radiolabelled B2702-p is a potentially useful radiotracer for the molecular imaging of VCAM-1 in atherosclerosis.

Magnetic resonance imaging of experimental atherosclerotic plaque: Comparison of two ultrasmall superparamagnetic particles of iron oxide

To evaluate a new ultrasmall superparamagnetic particles of iron oxide (USPIO) compound, ferumoxytol, as a marker of macrophage activity in atherosclerotic plaques and to compare it to ferumoxtran-10. Ten mature heritable hyperlipidemic (WHHL) female Watanabe rabbits served as the animal model for atherosclerosis, four coeval female New Zealand White (NZW) rabbits were the control group. Five WHHL and two NZW received a single intravenous injection (250 micromol/kg) of either ferumoxtran-10 or ferumoxytol and were subjected to daily MR examinations on a 1.5T whole body scanner for the next five days. Development of signal intensity changes and susceptibility effects was assessed. Statistical analysis was based on a nonparametric Wilcoxon-Mann-Whitney-U test by using a P value at the 0.05 significance level. On day 5, the rabbits were sacrificed and the aorta was referred to histopathology, distribution of iron particles in the vessel wall was analyzed. MRI was feasible in all animals. Three days after injection of ferumoxytol the highest luminal signal intensity measurements were observed in the ferumoxytol group; the highest measurements were five days after injection in the ferumoxtran-10 group (P < 0.05). In the WHHL, susceptibility effects presented as homogeneous dark lines parallel to the aortic wall after ferumoxytol and spotted areas void of signal after ferumoxtran-10. None of these findings were observed in the NZW control groups. Ferumoxtran-10 and ferumoxytol at a respective dose of 250 mumol/kg appear well suited for atherosclerotic plaque detection with MRI in experimental atherosclerosis. Ferumoxytol warrants further analysis in humans.

Evaluation of99mTc labeled diadenosine tetraphosphate as an atherosclerotic plaque imaging agent in experimental models

The potential of 99mTc labeled P1, P4-di (adenosine-5')-tetraphosphate (Ap4A) for imaging experimental atherosclerotic plaques was evaluated in New Zealand white (NZW) rabbits. To label the 99mTc to Ap4A, stannous tartrate solution was used. 99mTc-Ap4A was purified on a Sephadex G-25 column. The radiochemistry purities of 99mTc-Ap4A were 85% to 91%. Biodistribution study revealed 99mTc-Ap4A cleared from blood rapidly. Thirty min after 99mTc-Ap4A administrated on NZW atherosclerotic rabbits, lesion to blood (target/blood, T/B) ratio was 3.17 +/- 1.27, and lesions to normal (target/non-target, T/NT) ratio was 5.23 +/- 1.87. Shadows of atherosclerotic plaques were clearly visible on radioautographic film. Aortas with atherosclerotic plaques also could be seen on ex vivo gamma camera images. Atherosclerotic abdominal aortas were clearly visible on in vivo images 15 min to 3 h after 99mTc-Ap4A administration. 99mTc-labeled Ap4A can be used for rapid noninvasive detection of experimental atherosclerotic plaque.

Biodistribution and radioimmunopharmacokinetics of 131I-Ama monoclonal antibody in atherosclerotic rabbits

Monoclonal antibodies have been raised against Ama isolated from human and experimental atherosclerotic plaque. 131I-Ama-MoAb in the whole antibody form was injected into normal NZW rabbits and Watanabe hyperlipidemic rabbits. Biodistribution studies showed that atheromatous aortas had a significantly higher (5-7X) uptake of 131I-Ama-MoAb than that of normal aortas. However, 131I-Ama-MoAb was cleared very slowly from atherosclerotic rabbits. As a result, atheromas could not be identified by imaging because of the low target to non-target ratios.

Foam cells of the rabbit atherosclerotic plaque arrested in metaphase by colchicine show a macrophage phenotype

Proliferative activity of smooth muscle cells and foam cells characterizes experimental atherosclerotic plaques as they first appear. Immunohistochemical and ultrastructural methods were applied to cells arrested in metaphase by colchicine and the phenotype of cells in mitosis was detected. Most of the metaphase arrested FC found in aortic plaques of cholesterol fed New Zealand rabbits were positive to the anti-macrophage monoclonal antibody and negative to the anti-smooth muscle actin monoclonal antibody. Moreover, most of the metaphase blocked FC had the ultrastructural features of macrophages. These preliminary results further strengthen previous observations on rabbit plaques that the FC pool is mainly constituted by macrophages and show, for the first time, that the dimension of this pool depends not only on migration of circulating monocytcs but also on the in situ proliferation of macrophages.

Phosphorus metabolism in experimental atherosclerotic plaque reversal

Summary A study of phosphate components in experimental atherosclerotic plaque reversal of the rabbit aorta reveals a shorter half-life for total aortic phosphate, phospholipid phosphorus, and TCA-soluble phosphate in MgEDTA-treated animals compared to normal and atherosclerotic controls. In MgEDTA-treated animals these phosphorus components in absolute amounts lie well between that of the normal and untreated atherosclerotic animal.