Molecular MRI of atherosclerosis

Targeted Diagnosis, Therapeutic Monitoring, and Assessment of Atherosclerosis Based on Mesoporous Silica Nanoparticles Coated with cRGD-Platelets

Objective

The off-target effects and severe side effects of PPARα and LXRα agonists greatly limit their application in atherosclerosis (AS). Therefore, this study intended to use mesoporous silica nanoparticles as carriers to generate MnO nanoparticles in situ with T1WI-MRI in mesoporous pores and simultaneously load PPARα and LXRα agonists. Afterward, cRGD-chelated platelet membranes can be used for coating to construct a new nanotheranostic agent.

Methods

cRGD-platelet@MnO/MSN@PPARα/LXRα nanoparticles were synthesized by a chemical method. Dynamic light scattering (DLS) was utilized to detect the size distribution and polydispersity index (PDI) of the nanoparticles. The safety of the nanoparticles was detected by CCK8 in vitro and HE staining and kidney function in vivo. Cell apoptosis was detected by flow cytometry detection and TUNEL staining. Oxidative stress responses (ROS, SOD, MDA, and NOX levels) were tested via a DCFH-DA assay and commercial kits. Immunofluorescence and phagocytosis experiments were used to detect the targeting of nanoparticles. Magnetic resonance imaging (MRI) was used to detect the imaging performance of cRGD-platelet@MnO/MSN@PPARα/LXRα nanoparticles. Using western blotting, the expression changes in LXRα and ABCA1 were identified.

Results

cRGD-platelet@MnO/MSN@PPARα/LXRα nanoparticles were successfully established, with a particle size of approximately 150 nm and PDI less than 0.3, and showed high safety both in vitro and in vivo. cRGD-platelet@MnO/MSN@PPARα/LXRα nanoparticles showed good targeting properties and better MRI imaging performance in AS. cRGD-platelet@MnO/MSN@PPARα/LXRα nanoparticles showed better antioxidative capacities, MRI imaging performance, and diagnostic and therapeutic effects on AS by regulating the expression of LXRα and ABCA1.

Conclusion

In the present study, cRGD-platelet@MnO/MSN@PPARα/LXRα nanoparticles with high safety and the capacity to target vulnerable plaques of AS were successfully established. They showed better performance on MRI images and treatment effects on AS by promoting cholesterol efflux through the regulation of ABCA1. These findings might address the problems of off-target effects and side effects of nanoparticle-mediated drug delivery, which will enhance the efficiency of AS treatment and provide new ideas for the clinical treatment of AS.

Whole-Body Atherosclerosis Imaging by Positron Emission Tomography/Magnetic Resonance Imaging: From Mice to Nonhuman Primates

Cardiovascular disease due to atherosclerosis is still the main cause of morbidity and mortality worldwide. This disease is a complex systemic disorder arising from a network of pathological processes within the arterial vessel wall, and, outside of the vasculature, in the hematopoietic system and organs involved in metabolism. Recent years have seen tremendous efforts in the development and validation of quantitative imaging technologies for the noninvasive evaluation of patients with atherosclerotic cardiovascular disease. Specifically, the advent of combined positron emission tomography and magnetic resonance imaging scanners has opened new exciting opportunities in cardiovascular imaging. In this review, we will describe how combined positron emission tomography/magnetic resonance imaging scanners can be leveraged to evaluate atherosclerotic cardiovascular disease at the whole-body level, with specific focus on preclinical animal models of disease, from mouse to nonhuman primates. We will broadly describe 3 major areas of application: (1) vascular imaging, for advanced atherosclerotic plaque phenotyping and evaluation of novel imaging tracers or therapeutic interventions; (2) assessment of the ischemic heart and brain; and (3) whole-body imaging of the hematopoietic system. Finally, we will provide insights on potential novel technical developments which may further increase the relevance of integrated positron emission tomography/magnetic resonance imaging in preclinical atherosclerosis studies.

Molecular and Nonmolecular Magnetic Resonance Coronary and Carotid Imaging

Atherosclerosis is the leading cause of cardiovascular morbidity and mortality. Over the past 2 decades, increasing research attention is converging on the early detection and monitoring of atherosclerotic plaque. Among several invasive and noninvasive imaging modalities, magnetic resonance imaging (MRI) is emerging as a promising option. Advantages include its versatility, excellent soft tissue contrast for plaque characterization and lack of ionizing radiation. In this review, we will explore the recent advances in multicontrast and multiparametric imaging sequences that are bringing the aspiration of simultaneous arterial lumen, vessel wall, and plaque characterization closer to clinical feasibility. We also discuss the latest advances in molecular magnetic resonance and multimodal atherosclerosis imaging.

Activatable magnetic resonance nanosensor as a potential imaging agent for detecting and discriminating thrombosis

The early detection and accurate characterization of life-threatening diseases such as cardiovascular disease and cancer are critical to the design of treatment. Knowing whether or not a thrombus in a blood vessel is new (fresh) or old (constituted) is very important for physicians to decide a treatment protocol. We have designed smart MRI nano-sensors that can detect, sense and report the stage or progression of cardiovascular diseases such as thrombosis. The nanosensors were functionalized with fibrin-binding peptide to specifically target thrombus and were also labelled with fluorescent dye to enable optical imaging. We have demonstrated that our nanosensors were able to switch between the T1 and T2 signal depending on thrombus age or the presence or absence of thrombin at the thrombus site. The developed nanosensors appeared to be non-toxic when tested with Chinese Hamster Ovarian cells within the tested concentrations. The working principle demonstrated in this study can be applied to many other diseases such as cancer.

The Growing Field of Imaging of Atherosclerosis in Peripheral Arteries

In the past decades, peripheral arteries have represented a model for the comprehension of atherosclerosis as well as for the development of new diagnostic imaging modalities and therapeutic strategies. Peripheral arteries may represent a window to study atherosclerosis. Pathology has prominently contributed to move the clinical and research attention from the arterial lumen stenosis and angiography to morphological and functional imaging techniques. Evidence from large and prospective cohort or randomized controlled studies is still modest. Nevertheless, several emerging imaging investigations represent a potential tool for a comprehensive "in vivo" evaluation of the entire natural history of peripheral atherosclerosis. This constitutes a demanding assignment, as it would be desirable to obtain both single-lesion focused and extensive arterial system views to achieve the most accurate prognostic information. Our narrative review rests upon the fundamental pathological evidence, summarizing the rapidly growing field of imaging of atherosclerosis in peripheral arteries and presenting a selection of both currently available and emerging imaging techniques.

Recent Advances in Managing Atherosclerosis via Nanomedicine

Atherosclerosis, driven by chronic inflammation of the arteries and lipid accumulation on the blood vessel wall, underpins many cardiovascular diseases with high mortality rates globally, such as stroke and ischemic heart disease. Engineered bio-nanomaterials are now under active investigation as carriers of therapeutic and/or imaging agents to atherosclerotic plaques. This Review summarizes the latest bio-nanomaterial-based strategies for managing atherosclerosis published over the past five years, a period marked by a rapid surge in preclinical applications of bio-nanomaterials for imaging and/or treating atherosclerosis. To start, the biomarkers exploited by emerging bio-nanomaterials for targeting various components of atherosclerotic plaques are outlined. In addition, recent efforts to rationally design and screen for bio-nanomaterials with the optimal physicochemical properties for targeting plaques are presented. Moreover, the latest preclinical applications of bio-nanomaterials as carriers of imaging, therapeutic, or theranostic agents to atherosclerotic plaques are discussed. Finally, a mechanistic understanding of the interactions between bio-nanomaterials and the plaque ("athero-nano" interactions) is suggested, the opportunities and challenges in the clinical translation of bio-nanomaterials for managing atherosclerosis are discussed, and recent clinical trials for atherosclerotic nanomedicines are introduced.

A review of molecular imaging of atherosclerosis and the potential application of dendrimer in imaging of plaque

Despite the fact that technological advancements have been made in diagnosis and treatment, cardiovascular diseases (CVDs) remain the leading cause of mortality and morbidity worldwide. Early detection of atherosclerosis (AS), especially vulnerable plaques, plays a crucial role in the prevention of acute coronary syndrome (ACS). Targeting the critical cytokines and molecules that are upregulated during the biological process of AS by in vivo molecular imaging has been widely used in plaque imaging. With their three-dimensional architecture, composition, and abundant terminal functional groups, dendrimers provide a platform for multitargeting and multimodal imaging. Thus, modified dendrimers with the key molecules upregulated in AS plaques will be an innovative attempt to achieve targeted imaging of AS plaques specifically and efficiently. This review was aimed to address some recent works on imaging of AS plaques using various types of image technology and further discuss the applications of dendrimers, an innovative yet seldom used method in imaging of AS plaques due to some limitations and challenges, and we highlight the bright future of the modified dendrimers in characterizing AS plaques.

Noninvasive Molecular Imaging of Mouse Atherosclerosis

Molecular imaging offers great potential for noninvasive visualization and quantitation of the cellular and molecular components involved in atherosclerotic plaque stability. In this chapter, we review emerging molecular imaging modalities and approaches for quantitative, noninvasive detection of early biological processes in atherogenesis, including vascular endothelial permeability, endothelial adhesion molecule up-regulation, and macrophage accumulation, with special emphasis on mouse models. We also highlight a number of targeted imaging nanomaterials for assessment of advanced atherosclerotic plaques, including extracellular matrix degradation, proteolytic enzyme activity, and activated platelets using mouse models of atherosclerosis. The potential for clinical translation of molecular imaging nanomaterials for assessment of atherosclerotic plaque biology, together with multimodal approaches is also discussed.

Preclinical models of atherosclerosis. The future of Hybrid PET/MR technology for the early detection of vulnerable plaque

Cardiovascular diseases are the leading cause of death in developed countries. The aetiology is currently multifactorial, thus making them very difficult to prevent. Preclinical models of atherothrombotic diseases, including vulnerable plaque-associated complications, are now providing significant insights into pathologies like atherosclerosis, and in combination with the most recent advances in new non-invasive imaging technologies, they have become essential tools to evaluate new therapeutic strategies, with which can forecast and prevent plaque rupture. Positron emission tomography (PET)/computed tomography imaging is currently used for plaque visualisation in clinical and pre-clinical cardiovascular research, albeit with significant limitations. However, the combination of PET and magnetic resonance imaging (MRI) technologies is still the best option available today, as combined PET/MRI scans provide simultaneous data acquisition together with high quality anatomical information, sensitivity and lower radiation exposure for the patient. The coming years may represent a new era for the implementation of PET/MRI in clinical practice, but first, clinically efficient attenuation correction algorithms and research towards multimodal reagents and safety issues should be validated at the preclinical level.

In vivo MR and Fluorescence Dual-modality Imaging of Atherosclerosis Characteristics in Mice Using Profilin-1 Targeted Magnetic Nanoparticles

Aims: This study aims to explore non-invasive imaging of atherosclerotic plaque through magnetic resonance imaging (MRI) and near-infrared fluorescence (NIRF) by using profilin-1 targeted magnetic iron oxide nanoparticles (PF₁-Cy5.5-DMSA-Fe₃O₄-NPs, denoted as PC-NPs) as multimodality molecular imaging probe in murine model of atherosclerosis. Methods and Results: PC-NPs were constructed by conjugating polyclonal profilin-1 antibody and NHS-Cy5.5 fluorescent dye to the surface of DMSA-Fe₃O₄-nanoparticles via condensation reaction. Murine atherosclerosis model was induced in apoE^-/- mice by high fat and cholesterol diet (HFD) for 16 weeks. The plaque areas in aortic artery were detected with Oil Red O staining. Immunofluorescent staining and Western blot analysis were applied respectively to investigate profilin-1 expression. CCK-8 assay and transwell migration experiment were performed to detect vascular smooth muscle cells (VSMCs) proliferation. In vivo MRI and NIRF imaging of atherosclerotic plaque were carried out before and 36 h after intravenous injection of PC-NPs. Oil Red O staining showed that the plaque area was significantly increased in HFD group (p<0.05). Immunofluorescence staining revealed that profilin-1 protein was highly abundant within plaque in HFD group and co-localized with α-smooth muscle actin. Profilin-1 siRNA intervention could inhibit VSMCs proliferation and migration elicited by ox-LDL (p<0.05). In vivo MRI and NIRF imaging revealed that PC-NPs accumulated in atherosclerotic plaque of carotid artery. There was a good correlation between the signals of MRI and ex vivo fluorescence intensities of NIRF imaging in animals with PC-NPs injection. Conclusion: PC-NPs is a promising dual modality imaging probe, which may improve molecular diagnosis of plaque characteristics and evaluation of pharmaceutical interventions for atherosclerosis.

A perspective on structural and computational work on collagen

Collagen is the single most abundant protein in the extracellular matrix in the animal kingdom, with remarkable structural and functional diversity and regarded one of the most useful biomaterials.

Nanoparticle uptake by macrophages in vulnerable plaques for atherosclerosis diagnosis

The composition of atherosclerotic (AS) plaques is crucial concerning rupture, thrombosis and clinical events. Two plaque types are distinguished: stable and vulnerable plaques. Vulnerable plaques are rich in inflammatory cells, mostly only M1 macrophages, and are highly susceptible to rupture. These plaques represent a high risk particularly with the standard invasive diagnosis by coronary angiography. So far there are no non-invasive low-risk clinical approaches available to detect and distinguish AS plaque types in vivo. The perspective review introduces a whole work-flow for a novel approach for non-invasive detection and classification of AS plaques using the diffusion reflection method with gold nanoparticle loaded macrophages in combination with flow and image cytometric analysis for quality assurance. Classical biophotonic methods for AS diagnosis are summarized. Phenotyping of monocytes and macrophages are discussed for specific subset labelling by nanomaterials, as well as existing studies and first experimental proofs of concept for the novel approach are shown. In vitro and in vivo detection of NP loaded macrophages (MΦ). Different ways of MΦ labelling include (1) in vitro labelling in suspension (whole blood or buffy coat) or (2) labelling of short-term MΦ cultures with re-injection of MΦ-NP into the animal to detect migration of the cells in the plaques and (3) in vivo injection of NP into the organism.

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.

MRI-based assessment of endothelial function in mice in vivo

While a healthy endothelium serves to maintain vascular haemostasis, a malfunctioning endothelium leads to various cardiovascular diseases, including atherothrombosis. Endothelial dysfunction is characterized by increased vascular permeability, impaired endothelium-dependent responses and various pro-inflammatory and pro-thrombotic changes in endothelial phenotype, all of which could provide the basis for an in vivo diagnosis of endothelial dysfunction. In the present review, we briefly summarize the magnetic resonance imaging (MRI)-based methods available for assessing endothelial function in animal models, especially in mice. These methods are aimed to assess biochemical phenotype using molecular imaging, endothelium-dependent responses or changes in endothelial permeability. All these approaches provide a complementary insight into the endothelial dysfunction in vivo and may offer a unique opportunity to study endothelium-based mechanisms of diseases and endothelial response to treatment.

Coronary artery wall imaging

Like X-Ray contrast angiography, MR coronary angiograms show the vessel lumens rather than the vessels themselves. Consequently, outward remodeling of the vessel wall, which occurs in subclinical coronary disease before luminal narrowing, cannot be seen. The current gold standard for assessing the coronary vessel wall is intravascular ultrasound, and more recently, optical coherence tomography, both of which are invasive and use ionizing radiation. A noninvasive, low-risk technique for assessing the vessel wall would be beneficial to cardiologists interested in the early detection of preclinical disease and for the safe monitoring of the progression or regression of disease in longitudinal studies. In this review article, the current state of the art in MR coronary vessel wall imaging is discussed, together with validation studies and recent developments.