Implantation of a carotid cuff for triggering shear-stress induced atherosclerosis in mice

Translational Molecular Imaging Tool of Vulnerable Carotid Plaque: Evaluate Effects of Statin Therapy on Plaque Inflammation and American Heart Association-Defined Risk Levels in Cuff-Implanted Apolipoprotein E-Deficient Mice

Identification of high-risk carotid plaques in asymptomatic patients remains a challenging but crucial step in stroke prevention. The challenge is to accurately monitor the development of high-risk carotid plaques and promptly identify patients, who are unresponsive to best medical therapy, and hence targeted for carotid surgical interventions to prevent stroke. Inflammation is a key operator in destabilisation of plaques prior to clinical sequelae. Currently, there is a lack of imaging tool in routine clinical practice, which allows assessment of inflammatory activity within the atherosclerotic plaque. Herein, we have used a periarterial cuff to generate a progressive carotid atherosclerosis model in apolipoprotein E-deficient mice. This model produced clinically relevant plaques with different levels of risk, fulfilling American Heart Association (AHA) classification, at specific timepoints and locations, along the same carotid artery. Exploiting this platform, we have developed smart molecular magnetic resonance imaging (MRI) probes consisting of dual-targeted microparticles of iron oxide (DT-MPIO) against VCAM-1 and P-selectin, to evaluate the anti-inflammatory effect of statin therapy on progressive carotid atherosclerosis. We demonstrated that in vivo DT-MPIO-enhanced MRI can (i) quantitatively track plaque inflammation from early to advanced stage; (ii) identify and characterise high-risk inflamed, vulnerable plaques; and (iii) monitor the response to statin therapy longitudinally. Moreover, this molecular imaging-defined therapeutic response was validated using AHA classification of human plaques, a clinically relevant parameter, approximating the clinical translation of this tool. Further development and translation of this molecular imaging tool into the clinical arena may potentially facilitate more accurate risk stratification, permitting timely identification of the high-risk patients for prophylactic carotid intervention, affording early opportunities for stroke prevention in the future.

Flow-induced reprogramming of endothelial cells in atherosclerosis

Atherosclerotic diseases such as myocardial infarction, ischaemic stroke and peripheral artery disease continue to be leading causes of death worldwide despite the success of treatments with cholesterol-lowering drugs and drug-eluting stents, raising the need to identify additional therapeutic targets. Interestingly, atherosclerosis preferentially develops in curved and branching arterial regions, where endothelial cells are exposed to disturbed blood flow with characteristic low-magnitude oscillatory shear stress. By contrast, straight arterial regions exposed to stable flow, which is associated with high-magnitude, unidirectional shear stress, are relatively well protected from the disease through shear-dependent, atheroprotective endothelial cell responses. Flow potently regulates structural, functional, transcriptomic, epigenomic and metabolic changes in endothelial cells through mechanosensors and mechanosignal transduction pathways. A study using single-cell RNA sequencing and chromatin accessibility analysis in a mouse model of flow-induced atherosclerosis demonstrated that disturbed flow reprogrammes arterial endothelial cells in situ from healthy phenotypes to diseased ones characterized by endothelial inflammation, endothelial-to-mesenchymal transition, endothelial-to-immune cell-like transition and metabolic changes. In this Review, we discuss this emerging concept of disturbed-flow-induced reprogramming of endothelial cells (FIRE) as a potential pro-atherogenic mechanism. Defining the flow-induced mechanisms through which endothelial cells are reprogrammed to promote atherosclerosis is a crucial area of research that could lead to the identification of novel therapeutic targets to combat the high prevalence of atherosclerotic disease.

Development of Molecular Magnetic Resonance Imaging Tools for Longitudinal Tracking of Carotid Atherosclerotic Disease Using Fast Imaging with Steady-State Precession

Identification of patients with high-risk asymptomatic carotid plaques remains a challenging but essential step in stroke prevention. Current selection criteria for intervention in carotid disease are still determined by symptomatology and degree of luminal stenosis. This strategy has been less effective in identifying the high-risk asymptomatic individual patients. Inflammation is the key factor that drives plaque instability causing clinical sequelae. Currently, there is no imaging tool in routine clinical practice to assess the inflammatory status within atherosclerotic plaques. Herein we describe the development of a novel molecular magnetic resonance imaging (MRI) strategy to interrogate plaque inflammation, and hence its vulnerability in vivo, using dual-targeted iron particle-based probes and fast imaging with steady-state precession (FISP) sequence, adding further prognostic information to luminal stenosis alone. A periarterial cuff was used to generate high-risk plaques at specific timepoints and location of the carotid artery in an apolipoprotein-E-deficient mouse model. Using this platform, we demonstrated that in vivo dual-targeted iron particles with enhanced FISP can (i) target and characterise high-risk vulnerable plaques and (ii) quantitatively report and track the inflammatory activity within carotid plaques longitudinally. This molecular imaging tool may permit (i) accurate monitoring of the risk of carotid plaques and (ii) timely identification of high-risk asymptomatic patients for prophylactic carotid intervention, achieving early stroke prevention.

Animal Models of Neointimal Hyperplasia and Restenosis: Species-Specific Differences and Implications for Translational Research

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Neointimal hyperplasia is the major factor contributing to restenosis after angioplasty procedures.

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Multiple animal models exist to study basic and translational aspects of restenosis formation.

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Animal models differ substantially, and species-specific differences have major impact on the pathophysiology of the model.

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Genetic, dietary, and mechanical interventions determine the translational potential of the animal model used and have to be considered when choosing the model.

The process of restenosis is based on the interplay of various mechanical and biological processes triggered by angioplasty-induced vascular trauma. Early arterial recoil, negative vascular remodeling, and neointimal formation therefore limit the long-term patency of interventional recanalization procedures. The most serious of these processes is neointimal hyperplasia, which can be traced back to 4 main mechanisms: endothelial damage and activation; monocyte accumulation in the subintimal space; fibroblast migration; and the transformation of vascular smooth muscle cells. A wide variety of animal models exists to investigate the underlying pathophysiology. Although mouse models, with their ease of genetic manipulation, enable cell- and molecular-focused fundamental research, and rats provide the opportunity to use stent and balloon models with high throughput, both rodents lack a lipid metabolism comparable to humans. Rabbits instead build a bridge to close the gap between basic and clinical research due to their human-like lipid metabolism, as well as their size being accessible for clinical angioplasty procedures. Every different combination of animal, dietary, and injury model has various advantages and disadvantages, and the decision for a proper model requires awareness of species-specific biological properties reaching from vessel morphology to distinct cellular and molecular features.

Development of Molecular Magnetic Resonance Imaging Tools for Risk Stratification of Carotid Atherosclerotic Disease Using Dual-Targeted Microparticles of Iron Oxide

Identification of patients with high-risk asymptomatic carotid plaques remains a challenging but crucial step in stroke prevention. Inflammation is the key factor that drives plaque instability. Currently, there is no imaging tool in routine clinical practice to assess the inflammatory status within atherosclerotic plaques. We have developed a molecular magnetic resonance imaging (MRI) tool to quantitatively report the inflammatory activity in atherosclerosis using dual-targeted microparticles of iron oxide (DT-MPIO) against P-selectin and VCAM-1 as a smart MRI probe. A periarterial cuff was used to generate plaques with varying degree of phenotypes, inflammation and risk levels at specific locations along the same single carotid artery in an Apolipoprotein-E-deficient mouse model. Using this platform, we demonstrated that in vivo DT-MPIO-enhanced MRI can (i) target high-risk vulnerable plaques, (ii) differentiate the heterogeneity (i.e. high vs intermediate vs low-risk plaques) within the asymptomatic plaque population and (iii) quantitatively report the inflammatory activity of local plaques in carotid artery. This novel molecular MRI tool may allow characterisation of plaque vulnerability and quantitative reporting of inflammatory status in atherosclerosis. This would permit accurate risk stratification by identifying high-risk asymptomatic individual patients for prophylactic carotid intervention, expediting early stroke prevention and paving the way for personalised management of carotid atherosclerotic disease.

Biomechanical Forces and Atherosclerosis: From Mechanism to Diagnosis and Treatment

The article provides an overview of current views on the role of biomechanical forces in the pathogenesis of atherosclerosis. The importance of biomechanical forces in maintaining vascular homeostasis is considered. We provide descriptions of mechanosensing and mechanotransduction. The roles of wall shear stress and circumferential wall stress in the initiation, progression and destabilization of atherosclerotic plaque are described. The data on the possibilities of assessing biomechanical factors in clinical practice and the clinical significance of this approach are presented. The article concludes with a discussion on current therapeutic approaches based on the modulation of biomechanical forces.

[Expression of connexin 43 in peripheral blood monocytes from patients with acute coronary syndrome]

OBJECTIVE

To investigate the expression of connexin 43 (Cx43) in peripheral blood monocytes (PBMCs) from patients with acute coronary syndrome (ACS) and its clinical implications.

METHODS

We prospectively collected the clinical data from 40 patients with ACS including 20 with unstable angina pectoris (UAP) and 20 with acute myocardial infarction (AMI) admitted in our department between January, 2018 and June, 2018, with 20 healthy subjects undergoing routine physical examinations serving as the control group. Peripheral blood samples were obtained from all the participants and plasma and PBMCs were separated. Enzyme-linked immunosorbent assay (ELISA) and turbidimetric inhibition immunoassay (TIIA) were used for analysis of plasma levels of interleukin (IL)-1β and high sensitive C-reactive protein (hs-CRP), respectively; real-time quantitative RT-PCR and Western blotting were used to detect the mRNA and protein levels of Cx43 in the PBMCs.

RESULTS

Compared with the control group, the patients with UAP showed significantly increased plasma levels of IL-1β and hs-CRP (P < 0.001) and obviously elevated expressions of Cx43 at both mRNA and protein levels in the PBMCs (P < 0.001). Compared with the patients with UAP, the patients with AMI had significantly higher plasma IL-1β and hs-CRP levels (P < 0.001 and P < 0.01) but lower expression levels of Cx43 in the PBMCs (P < 0.05).

CONCLUSIONS

Patients with UAP and AMI have activated inflammatory responses and reverse changes in Cx43 expression in the PBMCs, suggesting the different roles of Cx43 in the pathogenic mechanisms of different types of ACS.

Molecular imaging of MMP activity discriminates unstable from stable plaque phenotypes in shear-stress induced murine atherosclerosis

Purpose

As atherosclerotic plaque ruptures are the primary cause of ischaemic events, their preventive identification by imaging remains a clinical challenge. Matrix metalloproteinases (MMP) are involved in plaque progression and destabilisation and are therefore promising targets to characterize rupture-prone unstable plaques. This study aims at evaluating MMP imaging to discriminate unstable from stable plaque phenotypes.

Methods

ApoE deficient mice (ApoE^-/-) on a high cholesterol diet underwent implantation of a tapered cuff around the right common carotid artery (CCA) inducing a highly inflamed atherosclerotic plaque upstream (US) and a more stable plaque phenotype downstream (DS) of the cuff. 8 weeks after surgery, the MMP inhibitor-based photoprobe Cy5.5-AF443 was administered i.v. 3h prior to in situ and ex vivo fluorescence reflectance imaging of the CCAs. Thereafter, CCAs were analysed regarding plaque size, presence of macrophages, and MMP-2 and MMP-9 concentrations by immunohistochemistry and ELISA.

Results

We found a significantly higher uptake of Cy5.5-AF443 in US as compared to DS plaques in situ (1.29 vs. 1.06 plaque-to-background ratio; p<0.001), which was confirmed by ex vivo measurements. Immunohistochemistry revealed a higher presence of macrophages, MMP-2 and MMP-9 in US compared to DS plaques. Accordingly, MMP-2 concentrations were significantly higher in US plaques (47.2±7.6 vs. 29.6±4.6 ng/mg; p<0.05).

Conclusions

In the ApoE^-/- cuff model MMP-2 and MMP-9 activities are significantly higher in upstream low shear stress-induced unstable atherosclerotic plaques as compared to downstream more stable plaque phenotypes. MMP inhibitor-based fluorescence molecular imaging allows visualization of these differences in shear stress-induced atherosclerosis.

Bilateral Implantation of Shear Stress Modifier in ApoE Knockout Mouse Induces Cognitive Impairment and Tau Abnormalities

Vascular cognitive impairment (VCI) encompasses all causes of cerebrovascular disease that lead to cognitive decline, or overt dementia, atherosclerotic disease being the most common contributor. However, few rodent models that mimic the pathology of VCI replicated the clinical cerebrovascular atherosclerosis. Here we aimed to investigate the mechanism underlying VCI in an Apolipoprotein E knockout (ApoE-KO) mouse model fed with western style food with implantation of bilateral shear stress modifiers. We established a cognitive decline in spatial learning and memory developed in the bilateral modifier treated mice. Brain imaging and pathological examinations demonstrated reduced glucose intake and neuronal loss in hippocampus. Although no amyloid plaques or neurofibrillary tangles (NFTs) were observed, tau pathology including hyperphosphorylation, paired helical filament formation and pathologic truncation were found at considerable higher extent in the bilateral modifier group 8 weeks post the procedure. In addition, gliosis and microglia activation were confirmed in corpus callosum (CC) and ventral striatum. Thus, this ApoE-KO mouse model faithfully replicates the stenosis of common carotid artery (CCA) and cognitive impairment following atherosclerotic deposition and global cerebral hypoperfusion. The close correlation of cognitive decline and tau pathology indicates the toxic tau species could be at least partially responsible for the neurodegenerative changes induced by the chronic hypoxia/ischemia.

Local Delivery of miR-21 Stabilizes Fibrous Caps in Vulnerable Atherosclerotic Lesions

miRNAs are potential regulators of carotid artery stenosis and concordant vulnerable atherosclerotic plaques. Hence, we analyzed miRNA expression in laser captured micro-dissected fibrous caps of either ruptured or stable plaques (n = 10 each), discovering that miR-21 was significantly downregulated in unstable lesions. To functionally evaluate miR-21 in plaque vulnerability, miR-21 and miR-21/apolipoprotein-E double-deficient mice (Apoe-/-miR-21-/-) were assessed. miR-21-/- mice lacked sufficient smooth muscle cell proliferation in response to carotid ligation injury. When exposing Apoe-/-miR-21-/- mice to an inducible plaque rupture model, they presented with more atherothrombotic events (93%) compared with miR-21+/+Apoe-/- mice (57%). We discovered that smooth muscle cell fate in experimentally induced advanced lesions is steered via a REST-miR-21-REST feedback signaling pathway. Furthermore, Apoe-/-miR-21-/- mice presented with more pronounced atherosclerotic lesions, greater foam cell formation, and substantially higher levels of arterial macrophage infiltration. Local delivery of a miR-21 mimic using ultrasound-targeted microbubbles into carotid plaques rescued the vulnerable plaque rupture phenotype. In the present study, we identify miR-21 as a key modulator of pathologic processes in advanced atherosclerosis. Targeted, lesion site-specific overexpression of miR-21 can stabilize vulnerable plaques.

CD80 Is Upregulated in a Mouse Model with Shear Stress-Induced Atherosclerosis and Allows for Evaluating CD80-Targeting PET Tracers

PURPOSE

A shear stress-induced atherosclerosis mouse model was characterized for its expression of inflammation markers with focus on CD80. With this model, we evaluated two positron emission tomography (PET) radiotracers targeting CD80 as well as 2-deoxy-2-[¹⁸F]fluoro-D-mannose ([¹⁸F]FDM) in comparison with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG).

PROCEDURE

A flow constrictive cuff implanted around the common carotid artery in apolipoprotein E knockout mice resulted in plaque formation. CD80 expression levels and plaque histopathology were evaluated. Serial PET/X-ray computed tomography scans were performed to follow inflammation.

RESULTS

Plaque formation with increased levels of CD80 was observed. Histologically, plaques presented macrophage-rich and large necrotic areas covered by a thin fibrous cap. Of the CD80-specific tracers, one displayed an increased uptake in plaques by PET. Both [¹⁸F]FDG and [¹⁸F]FDM accumulated in atherosclerotic plaques.

CONCLUSION

This mouse model presented, similar to humans, an increased expression of CD80 which renders it suitable for non-invasively targeting CD80-positive immune cells and evaluating CD80-specific radiotracers.

Contrast-enhanced micro-CT imaging in murine carotid arteries: a new protocol for computing wall shear stress

BACKGROUND

Wall shear stress (WSS) is involved in the pathophysiology of atherosclerosis. The correlation between WSS and atherosclerosis can be investigated over time using a WSS-manipulated atherosclerotic mouse model. To determine WSS in vivo, detailed 3D geometry of the vessel network is required. However, a protocol to reconstruct 3D murine vasculature using this animal model is lacking. In this project, we evaluated the adequacy of eXIA 160, a small animal contrast agent, for assessing murine vascular network on micro-CT. Also, a protocol was established for vessel geometry segmentation and WSS analysis.

METHODS

A tapering cast was placed around the right common carotid artery (RCCA) of ApoE-/- mice (n = 8). Contrast-enhanced micro-CT was performed using eXIA 160. An innovative local threshold-based segmentation procedure was implemented to reconstruct 3D geometry of the RCCA. The reconstructed RCCA was compared to the vessel geometry using a global threshold-based segmentation method. Computational fluid dynamics was applied to compute the velocity field and WSS distribution along the RCCA.

RESULTS

eXIA 160-enhanced micro-CT allowed clear visualization and assessment of the RCCA in all eight animals. No adverse biological effects were observed from the use of eXIA 160. Segmentation using local threshold values generated more accurate RCCA geometry than the global threshold-based approach. Mouse-specific velocity data and the RCCA geometry generated 3D WSS maps with high resolution, enabling quantitative analysis of WSS. In all animals, we observed low WSS upstream of the cast. Downstream of the cast, asymmetric WSS patterns were revealed with variation in size and location between animals.

CONCLUSIONS

eXIA 160 provided good contrast to reconstruct 3D vessel geometry and determine WSS patterns in the RCCA of the atherosclerotic mouse model. We established a novel local threshold-based segmentation protocol for RCCA reconstruction and WSS computation. The observed differences between animals indicate the necessity to use mouse-specific data for WSS analysis. For our future work, our protocol makes it possible to study in vivo WSS longitudinally over a growing plaque.

Preclinical imaging of the co-stimulatory molecules CD80 and CD86 with indium-111-labeled belatacept in atherosclerosis

Background

The inflammatory nature of atherosclerosis provides a broad range of potential molecular targets for atherosclerosis imaging. Growing interest is focused on targets related to plaque vulnerability such as the co-stimulatory molecules CD80 and CD86. We investigated in this preclinical proof-of-concept study the applicability of the CD80/CD86-binding fusion protein belatacept as a probe for atherosclerosis imaging.

Methods

Belatacept was labeled with indium-111, and the binding affinity was determined with CD80/CD86-positive Raji cells. In vivo distribution was investigated in Raji xenograft-bearing mice in single-photon emission computed tomography (SPECT)/CT scans, biodistribution, and ex vivo autoradiography studies. Ex vivo SPECT/CT experiments were performed with aortas and carotids of ApoE KO mice. Accumulation in human carotid atherosclerotic plaques was investigated by in vitro autoradiography.

Results

¹¹¹In-DOTA-belatacept was obtained in >70 % yield, >99 % radiochemical purity, and ~40 GBq/μmol specific activity. The labeled belatacept bound with high affinity to Raji cells. In vivo, ¹¹¹In-DOTA-belatacept accumulated specifically in Raji xenografts, lymph nodes, and salivary glands. Ex vivo SPECT experiments revealed displaceable accumulation in atherosclerotic plaques of ApoE KO mice fed an atherosclerosis-promoting diet. In human plaques, binding correlated with the infiltration by immune cells and the presence of a large lipid and necrotic core.

Conclusions

¹¹¹In-DOTA-belatacept accumulates in CD80/CD86-positive tissues in vivo and in vitro rendering it a research tool for the assessment of inflammatory activity in atherosclerosis and possibly other diseases. The tracer is suitable for preclinical imaging of co-stimulatory molecules of both human and murine origin. Radiolabeled belatacept could serve as a benchmark for future CD80/CD86-specific imaging agents.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-015-0157-4) contains supplementary material, which is available to authorized users.

Small animal cardiovascular MR imaging and spectroscopy

The use of MR imaging and spectroscopy for studying cardiovascular disease processes in small animals has increased tremendously over the past decade. This is the result of the remarkable advances in MR technologies and the increased availability of genetically modified mice. MR techniques provide a window on the entire timeline of cardiovascular disease development, ranging from subtle early changes in myocardial metabolism that often mark disease onset to severe myocardial dysfunction associated with end-stage heart failure. MR imaging and spectroscopy techniques play an important role in basic cardiovascular research and in cardiovascular disease diagnosis and therapy follow-up. This is due to the broad range of functional, structural and metabolic parameters that can be quantified by MR under in vivo conditions non-invasively. This review describes the spectrum of MR techniques that are employed in small animal cardiovascular disease research and how the technological challenges resulting from the small dimensions of heart and blood vessels as well as high heart and respiratory rates, particularly in mice, are tackled.

Murine model of femoral artery wire injury with implantation of a perivascular drug delivery patch

Percutaneous interventions including balloon angioplasty and stenting have been used to restore blood flow in vessels with occlusive vascular disease. While these therapies lead to the rapid restoration of blood flow, these technologies remain limited by restenosis in the case of bare metal stents and angioplasty, or reduced healing and possibly enhanced risk of thrombosis in the case of drug eluting stents. A key pathophysiological mechanism in the formation of restenosis is intimal hyperplasia caused by the activation of vascular smooth muscle cells and inflammation due to arterial stretch and injury. Surgeries that induce arterial injury in genetically modified mice are useful for the mechanistic study of the vascular response to injury but are often technically challenging to perform in mouse models due to the their small size and lack of appropriate sized devices. We describe two approaches for a surgical technique that induces endothelial denudation and arterial stretch in the femoral artery of mice to produce robust neointimal hyperplasia. The first approach creates an arteriotomy in the muscular branch of the femoral artery to obtain vascular access. Following wire injury this arterial branch is ligated to close the arteriotomy. A second approach creates an arteriotomy in the main femoral artery that is later closed through localized cautery. This method allows for vascular access through a larger vessel and, consequently, provides a less technically demanding procedure that can be used in smaller mice. Following either method of arterial injury, a degradable drug delivery patch can be placed over or around the injured artery to deliver therapeutic agents.

Experimental Rat and Mouse Carotid Artery Surgery: Injury & Remodeling Studies

In cardiovascular research, translation of benchtop findings to the whole body environment is often critical in order to gain a more thorough and comprehensive clinical evaluation of the data with direct extrapolation to the human condition. In particular, developmental and/or pathophysiologic vascular growth studies often employ in vitro approaches such as cultured cells or tissue explant models in order to analyze specific cellular, molecular, genetic and/or biochemical signaling factors under pristine controlled conditions. However, validation of in vitro data in a whole body setting complete with neural, endocrine and other systemic contributions provides essential proof-of-concept from a clinical perspective. Several well-characterized experimental in vivo models exist that provide excellent proof-of-concept tools with which to examine vascular growth and remodeling in the whole body. This article will examine the rat carotid artery balloon injury model, the mouse carotid artery wire denudation injury model, and rat and mouse carotid artery ligation models with particular emphasis on minimally invasive surgical access to the site of intervention. Discussion will include key scientific and technical details as well as caveats, limitations, and considerations for practical use for each of these valuable experimental models.