Nanoparticle PET-CT detects rejection and immunomodulation in cardiac allografts

Functional Diversity in Radiolabeled Nanoceramics and Related Biomaterials for the Multimodal Imaging of Tumors

Nanotechnology advances have the potential to assist toward the earlier detection of diseases, giving increased accuracy for diagnosis and helping to personalize treatments, especially in the case of noncommunicative diseases (NCDs) such as cancer. The main advantage of nanoparticles, the scaffolds underpinning nanomedicine, is their potential to present multifunctionality: synthetic nanoplatforms for nanomedicines can be tailored to support a range of biomedical imaging modalities of relevance for clinical practice, such as, for example, optical imaging, computed tomography (CT), magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). A single nanoparticle has the potential to incorporate myriads of contrast agent units or imaging tracers, encapsulate, and/or be conjugated to different combinations of imaging tags, thus providing the means for multimodality diagnostic methods. These arrangements have been shown to provide significant improvements to the signal-to-noise ratios that may be obtained by molecular imaging techniques, for example, in PET diagnostic imaging with nanomaterials versus the cases when molecular species are involved as radiotracers. We surveyed some of the main discoveries in the simultaneous incorporation of nanoparticulate materials and imaging agents within highly kinetically stable radio-nanomaterials as potential tracers with (pre)clinical potential. Diversity in function and new developments toward synthesis, radiolabeling, and microscopy investigations are explored, and preclinical applications in molecular imaging are highlighted. The emphasis is on the biocompatible materials at the forefront of the main preclinical developments, e.g., nanoceramics and liposome-based constructs, which have driven the evolution of diagnostic radio-nanomedicines over the past decade.

Methods for Radiolabelling Nanoparticles: PET Use (Part 2)

The use of radiolabelled nanoparticles (NPs) is a promising nuclear medicine tool for diagnostic and therapeutic purposes. Thanks to the heterogeneity of their material (organic or inorganic) and their unique physical and chemical characteristics, they are highly versatile for their use in several medical applications. In particular, they have shown interesting results as radiolabelled probes for positron emission tomography (PET) imaging. The high variability of NP types and the possibility to use several isotopes in the radiolabelling process implies different radiolabelling methods that have been applied over the previous years. In this review, we compare and summarize the different methods for NP radiolabelling with the most frequently used PET isotopes.

The immunomodulatory effects of antihypertensive therapy: A review

Hypertension remains the leading preventable risk factor for stroke and coronary artery disease, significantly contributing to all-cause global mortality and predisposing patients to renal and heart failure, as well as peripheral vascular disease. Due to the widespread usage of antihypertensive drugs, global mean blood pressure has remained unchanged or even slightly decreased over the past four decades. However, considering the broad spectrum of mechanisms involved in the action of antihypertensive drugs and the prevalence of their target receptors on immune cells, possible immunomodulatory effects which may exert beneficial effects of lowering blood pressure but also potentially alter immune function should be considered. In this review, we attempt to assess the consequences to immune system function of administering the five most commonly prescribed groups of antihypertensive drugs and to explain the mechanisms behind those interactions. Finally, we show potential gaps in our understanding of the effects of antihypertensive drugs on patient health. With regard to the widespread use of these drugs in the adult population worldwide, the discussed results may be of vital importance to evidence-based decision-making in daily clinical practice.

Designer Functional Nanomedicine for Myocardial Repair by Regulating the Inflammatory Microenvironment

Acute myocardial infarction is a major global health problem, and the repair of damaged myocardium is still a major challenge. Myocardial injury triggers an inflammatory response: immune cells infiltrate into the myocardium while activating myofibroblasts and vascular endothelial cells, promoting tissue repair and scar formation. Fragments released by cardiomyocytes become endogenous “danger signals”, which are recognized by cardiac pattern recognition receptors, activate resident cardiac immune cells, release thrombin factors and inflammatory mediators, and trigger severe inflammatory responses. Inflammatory signaling plays an important role in the dilation and fibrosis remodeling of the infarcted heart, and is a key event driving the pathogenesis of post-infarct heart failure. At present, there is no effective way to reverse the inflammatory microenvironment in injured myocardium, so it is urgent to find new therapeutic and diagnostic strategies. Nanomedicine, the application of nanoparticles for the prevention, treatment, and imaging of disease, has produced a number of promising applications. This review discusses the treatment and challenges of myocardial injury and describes the advantages of functional nanoparticles in regulating the myocardial inflammatory microenvironment and overcoming side effects. In addition, the role of inflammatory signals in regulating the repair and remodeling of infarcted hearts is discussed, and specific therapeutic targets are identified to provide new therapeutic ideas for the treatment of myocardial injury.

Nanoparticles Targeting the Molecular Pathways of Heart Remodeling and Regeneration

Cardiovascular diseases are the main cause of death worldwide, a trend that will continue to grow over the next decade. The heart consists of a complex cellular network based mainly on cardiomyocytes, but also on endothelial cells, smooth muscle cells, fibroblasts, and pericytes, which closely communicate through paracrine factors and direct contact. These interactions serve as valuable targets in understanding the phenomenon of heart remodeling and regeneration. The advances in nanomedicine in the controlled delivery of active pharmacological agents are remarkable and may provide substantial contribution to the treatment of heart diseases. This review aims to summarize the main mechanisms involved in cardiac remodeling and regeneration and how they have been applied in nanomedicine.

Nanoscale Technologies for Prevention and Treatment of Heart Failure: Challenges and Opportunities

The adult myocardium has a limited regenerative capacity following heart injury, and the lost cells are primarily replaced by fibrotic scar tissue. Suboptimal efficiency of current clinical therapies to resurrect the infarcted heart results in injured heart enlargement and remodeling to maintain its physiological functions. These remodeling processes ultimately leads to ischemic cardiomyopathy and heart failure (HF). Recent therapeutic approaches (e.g., regenerative and nanomedicine) have shown promise to prevent HF postmyocardial infarction in animal models. However, these preclinical, clinical, and technological advancements have yet to yield substantial enhancements in the survival rate and quality of life of patients with severe ischemic injuries. This could be attributed largely to the considerable gap in knowledge between clinicians and nanobioengineers. Development of highly effective cardiac regenerative therapies requires connecting and coordinating multiple fields, including cardiology, cellular and molecular biology, biochemistry and chemistry, and mechanical and materials sciences, among others. This review is particularly intended to bridge the knowledge gap between cardiologists and regenerative nanomedicine experts. Establishing this multidisciplinary knowledge base may help pave the way for developing novel, safer, and more effective approaches that will enable the medical community to reduce morbidity and mortality in HF patients.

Molecular Imaging of the Heart

Multimodality cardiovascular imaging is routinely used to assess cardiac function, structure, and physiological parameters to facilitate the diagnosis, characterization, and phenotyping of numerous cardiovascular diseases (CVD), as well as allows for risk stratification and guidance in medical therapy decision-making. Although useful, these imaging strategies are unable to assess the underlying cellular and molecular processes that modulate pathophysiological changes. Over the last decade, there have been great advancements in imaging instrumentation and technology that have been paralleled by breakthroughs in probe development and image analysis. These advancements have been merged with discoveries in cellular/molecular cardiovascular biology to burgeon the field of cardiovascular molecular imaging. Cardiovascular molecular imaging aims to noninvasively detect and characterize underlying disease processes to facilitate early diagnosis, improve prognostication, and guide targeted therapy across the continuum of CVD. The most-widely used approaches for preclinical and clinical molecular imaging include radiotracers that allow for high-sensitivity in vivo detection and quantification of molecular processes with single photon emission computed tomography and positron emission tomography. This review will describe multimodality molecular imaging instrumentation along with established and novel molecular imaging targets and probes. We will highlight how molecular imaging has provided valuable insights in determining the underlying fundamental biology of a wide variety of CVDs, including: myocardial infarction, cardiac arrhythmias, and nonischemic and ischemic heart failure with reduced and preserved ejection fraction. In addition, the potential of molecular imaging to assist in the characterization and risk stratification of systemic diseases, such as amyloidosis and sarcoidosis will be discussed. © 2019 American Physiological Society. Compr Physiol 9:477-533, 2019.

Applications of nanoparticles in biomedical imaging

An urgent need for early detection and diagnosis of diseases continuously pushes the advancements of imaging modalities and contrast agents. Current challenges remain for fast and detailed imaging of tissue microstructures and lesion characterization that could be achieved via development of nontoxic contrast agents with longer circulation time. Nanoparticle technology offers this possibility. Here, we review nanoparticle-based contrast agents employed in most common biomedical imaging modalities, including fluorescence imaging, MRI, CT, US, PET and SPECT, addressing their structure related features, advantages and limitations. Furthermore, their applications in each imaging modality are also reviewed using commonly studied examples. Future research will investigate multifunctional nanoplatforms to address safety, efficacy and theranostic capabilities. Nanoparticles as imaging contrast agents have promise to greatly benefit clinical practice.

Quantitative Imaging of Tumor-Associated Macrophages and Their Response to Therapy Using 64Cu-Labeled Macrin

Tumor-associated macrophages (TAMs) are widely implicated in cancer progression, and TAM levels can influence drug responses, particularly to immunotherapy and nanomedicines. However, it has been difficult to quantify total TAM numbers and their dynamic spatiotemporal distribution in a non-invasive and translationally relevant manner. Here, we address this need by developing a pharmacokinetically optimized, ⁶⁴Cu-labeled polyglucose nanoparticle (Macrin) for quantitative positron emission tomography (PET) imaging of macrophages in tumors. By combining PET with high-resolution in vivo confocal microscopy and ex vivo imaging of optically cleared tissue, we found that Macrin was taken up by macrophages with >90% selectivity. Uptake correlated with the content of macrophages in both healthy tissue and tumors ( R² > 0.9) and showed striking heterogeneity in the TAM content of an orthotopic and immunocompetent mouse model of lung carcinoma. In a proof-of-principle application, we imaged Macrin to monitor the macrophage response to neo-adjuvant therapy, using a panel of chemotherapeutic and γ-irradiation regimens. Multiple treatments elicited 180-650% increase in TAMs. Imaging identified especially TAM-rich tumors thought to exhibit enhanced permeability and retention of nanotherapeutics. Indeed, these TAM-rich tumors accumulated >700% higher amounts of a model poly(d,l-lactic- co-glycolic acid)- b-polyethylene glycol (PLGA-PEG) therapeutic nanoparticle compared to TAM-deficient tumors, suggesting that imaging may guide patient selection into nanomedicine trials. In an orthotopic breast cancer model, chemoradiation enhanced TAM and Macrin accumulation in tumors, which corresponded to the improved delivery and efficacy of two model nanotherapies, PEGylated liposomal doxorubicin and a TAM-targeted nanoformulation of the toll-like receptor 7/8 agonist resiquimod (R848). Thus, Macrin imaging offers a selective and translational means to quantify TAMs and inform therapeutic decisions.

Application of animal and human PET in cardiac research

PURPOSE OF REVIEW

After a warm-up period of imaging research, several modalities of positron emission tomography (PET) are under development for evaluating ischemic heart disease.

RECENT FINDINGS

Several types of well-documented stem/progenitor PET imaging have been utilized for changes in myocardial blood flow and carbohydrate metabolism. Some recent experimental and human studies reported that these data may have beneficial effects on cardiac research.

SUMMARY

Although the role of PET in the pathology of ischemic heart disease has not been sufficiently elucidated, many studies attempting imaging research of myocardial metabolism and neural regulation have been reported. Further studies are needed to better evaluate the potential of PET in evaluating ischemic heart disease.

Iron Oxide Nanoradiomaterials: Combining Nanoscale Properties with Radioisotopes for Enhanced Molecular Imaging

The combination of the size-dependent properties of nanomaterials with radioisotopes is emerging as a novel tool for molecular imaging. There are numerous examples already showing how the controlled synthesis of nanoparticles and the incorporation of a radioisotope in the nanostructure offer new features beyond the simple addition of different components. Among the different nanomaterials, iron oxide-based nanoparticles are the most used in imaging because of their versatility. In this review, we will study the different radioisotopes for biomedical imaging, how to incorporate them within the nanoparticles, and what applications they can be used for. Our focus is directed towards what is new in this field, what the nanoparticles can offer to the field of nuclear imaging, and the radioisotopes hybridized with nanomaterials for use in molecular imaging.

Molecular Imaging of Acute Cardiac Transplant Rejection: Animal Experiments and Prospects

Acute rejection (AR) remains the biggest challenge during the first year after heart transplantation despite advances in immunosuppressive therapy. The early detection and curbing of AR are crucial to the survival of transplant recipients. However, as the criterion standard for AR, endomyocardial biopsy has several limitations because of its inherent invasiveness and morbidity. Traditional imaging techniques, such as echocardiography and cardiac magnetic resonance imaging, are of certain value for AR, but their diagnostic criteria and accuracy remain in question. Molecular imaging sheds new light on AR diagnosis because it can provide information about gene expression and the location of molecules and cells. This article reviews the latest research and applications of several typical modalities of molecular imaging used in AR and discusses their advantages and disadvantages.

Methotrexate associated to lipid core nanoparticles improves cardiac allograft vasculopathy and the inflammatory profile in a rabbit heart graft model

Coronary allograft vasculopathy is an inflammatory-proliferative process that compromises the long-term success of heart transplantation and has no effective treatment. A lipid nanoemulsion (LDE) can carry chemotherapeutic agents in the circulation and concentrates them in the heart graft. The aim of the study was to investigate the effects of methotrexate (MTX) associated to LDE. Rabbits fed a 0.5% cholesterol diet and submitted to heterotopic heart transplantation were treated with cyclosporine A (10 mg·kg^–1·day^–1 orally) and allocated to treatment with intravenous LDE-MTX (4 mg/kg, weekly, n=10) or with weekly intravenous saline solution (control group, n=10), beginning on the day of surgery. Animals were euthanized 6 weeks later. Compared to controls, grafts of LDE-MTX treated rabbits showed 20% reduction of coronary stenosis, with a four-fold increase in vessel lumen and 80% reduction of macrophage staining in grafts. Necrosis was attenuated by LDE-MTX. Native hearts of both LDE-MTX and Control groups were apparently normal. Gene expression of lipoprotein receptors was significantly greater in grafts compared to native hearts. In LDE-MTX group, gene expression of the pro-inflammatory factors tumor necrosis factor-α, monocyte chemoattractant protein-1, interleukin-18, vascular cell adhesion molecule-1, and matrix metalloproteinase-12 was strongly diminished whereas expression of anti-inflammatory interleukin-10 increased. LDE-MTX promoted improvement of the cardiac allograft vasculopathy and diminished inflammation in heart grafts.

Mechanisms of Myeloid Cell Modulation of Atherosclerosis

Inflammation furnishes a series of pathogenic pathways that couple the risk factors for atherosclerosis with altered behavior of the intrinsic cells of the arterial wall, endothelium, and smooth muscle and promote the disease and its complications. Myeloid cells participate critically in all phases of atherosclerosis from initiation through progression, and ultimately the thrombotic consequences of this disease. Foam cells, lipid-laden macrophages, constitute the hallmark of atheromata. Much of the recent expansion in knowledge of the roles of myeloid cells in atherosclerosis revolves around the functional contributions of subsets of monocytes, precursors of macrophages, the most abundant myeloid cells in the atheroma. Proinflammatory monocytes preferentially accumulate in nascent atherosclerotic plaques. The most dramatic manifestations of atherosclerosis result from blood clot formation. Myocardial infarction, ischemic stroke, and abrupt limb ischemia all arise primarily from thrombi that complicate atherosclerotic plaques. Myeloid cells contribute pivotally to triggering thrombosis, for example, by elaborating enzymes that degrade the plaque's protective extracellular matrix, rendering it fragile, and by producing the potent procoagulant tissue factor. While most attention has focused on mononuclear phagocytes, the participation of polymorphonuclear leukocytes may aggravate local thrombus formation. Existing therapies such as statins may exert some of their protective effects by altering the functions of myeloid cells. The pathways of innate immunity that involve myeloid cells provide a myriad of potential targets for modifying atherosclerosis and its complications, and provide a fertile field for future attempts to address the residual burden of this disease, whose global prevalence is on the rise.

Nanomaterials for In Vivo Imaging

In vivo imaging, which enables us to peer deeply within living subjects, is producing tremendous opportunities both for clinical diagnostics and as a research tool. Contrast material is often required to clearly visualize the functional architecture of physiological structures. Recent advances in nanomaterials are becoming pivotal to generate the high-resolution, high-contrast images needed for accurate, precision diagnostics. Nanomaterials are playing major roles in imaging by delivering large imaging payloads, yielding improved sensitivity, multiplexing capacity, and modularity of design. Indeed, for several imaging modalities, nanomaterials are now not simply ancillary contrast entities, but are instead the original and sole source of image signal that make possible the modality's existence. We address the physicochemical makeup/design of nanomaterials through the lens of the physical properties that produce contrast signal for the cognate imaging modality-we stratify nanomaterials on the basis of their (i) magnetic, (ii) optical, (iii) acoustic, and/or (iv) nuclear properties. We evaluate them for their ability to provide relevant information under preclinical and clinical circumstances, their in vivo safety profiles (which are being incorporated into their chemical design), their modularity in being fused to create multimodal nanomaterials (spanning multiple different physical imaging modalities and therapeutic/theranostic capabilities), their key properties, and critically their likelihood to be clinically translated.

Development of PET Imaging to Visualize Activated Macrophages Accumulated in the Transplanted iPSc-Derived Cardiac Myocytes of Allogeneic Origin for Detecting the Immune Rejection of Allogeneic Cell Transplants in Mice

Allogeneic transplantation (Tx) of induced pluripotent stem cells (iPSCs) is a promising tissue regeneration therapy. However, this inevitably induces macrophage-mediated immune response against the graft, limiting its therapeutic efficacy. Monitoring the magnitude of the immune response using imaging tools would be useful for prolonging graft survival and increasing the therapy longevity. Minimally invasive quantitative detection of activated macrophages by medical imaging technologies such as positron emission tomography (PET) imaging targets translocator protein (TSPO), which is highly expressed on mitochondrial membrane, especially in activated macrophage. N,N-diethyl-2-[4-(2-fluoroethoxy) phenyl]-5,7-dimethylpyrazolo[1,5-a]pyrimidine-3-acetamide (DPA-714) is known as a TSPO ligand used in clinical settings. We herein hypothesized that immune rejection of the transplanted iPSC-derived cardiomyocytes (iPSC-CMs) of allogeneic origin may be quantitated using 18F-DPA-714-PET imaging study. iPSC-CM cell-sheets of C57BL/6 mice origin were transplanted on the surface of the left ventricle (LV) of C57BL/6 mice as a syngeneic cell-transplant model (syngeneic Tx group), or Balb/c mice as an allogeneic model (allogeneic Tx group). 18F-DPA-714-PET was used to determine the uptake ratio, calculated as the maximum standardized uptake value in the anterior and septal wall of the LV. The uptake ratio was significantly higher in the allogeneic Tx group than in the syngeneic group or the sham group at days 7 and day 10 after the cell transplantation. In addition, the immunochemistry showed significant presence of CD68 and CD3-positive cells at day 7 and 10 in the transplanted graft of the allogeneic Tx group. The expression of TSPO, CD68, IL-1 beta, and MCP-1 was significantly higher in the allogeneic Tx group than in the syngeneic Tx and the sham groups at day 7. The 18F-DPA-714-PET imaging study enabled quantitative visualization of the macrophages-mediated immune rejection of the allogeneic iPSC-cardiac. This imaging tool may enable the understanding and monitoring host-immune response of the host, allogeneic cell transplantation therapy.

Recent advances in the preparation and application of multifunctional iron oxide and liposome-based nanosystems for multimodal diagnosis and therapy

Nowadays, thanks to the successful discoveries in the biomedical field achieved in the last two decades, a deeper understanding about the complexity of mechanistic aspects of different pathological processes has been obtained. As a consequence, even the standard therapeutic protocols have undergone a vast redesign. In fact, the awareness about the necessity to progress towards a combined multitherapy in order to potentially increase the final healing chances has become a reality. One of the crucial elements of this novel approach is that large amounts of detailed information are highly needed and in vivo imaging techniques represent one of the most powerful tools to visualize and monitor the pathological state of the patient. To this scope, due to their unique features, nanostructured materials have emerged as attractive elements for the development of multifunctional tools for diagnosis and therapy. Hence, in this review, the most recent and relevant advances achieved by applying multifunctional nanostructures in multimodal theranosis of different diseases will be discussed. In more detail, the preparation and application of single multifunctional nano-radiotracers based on iron oxides and enabling PET/MRI dual imaging will be firstly detailed. After that, especially considering their highly promising clinical potential, the preparation and application of multifunctional liposomes useful for multimodal imaging and therapy will be reviewed. In both cases, a special focus will be set on the application of such a multifunctional nanocarriers in cancer as well as cardiovascular diseases.

Emerging imaging techniques after cardiac transplantation

Improvements in survival after cardiac transplantation have in part been driven by improved graft surveillance. Graft surveillance relies mainly on 3 techniques: coronary angiography, endomyocardial biopsy and echocardiography. Developments in invasive and non-invasive imaging technology have revolutionized assessment of the heart in both health and disease, offering new insights into tissue composition and myocardial metabolism. Herein we aim to review the strengths and weaknesses of these techniques, and summarize the evidence in the following 5 fields of cardiac imaging after transplantation: cardiovascular magnetic resonance; computed tomography; positron emission tomography; single-photon emission computed tomography; and optical coherence tomography and molecular imaging techniques.

Subtumoral analysis of PRINT nanoparticle distribution reveals targeting variation based on cellular and particle properties

The biological activity of nanoparticle-directed therapies critically depends on cellular targeting. We examined the subtumoral fate of Particle Replication in Non-Wetting Templates (PRINT) nanoparticles in a xenografted melanoma tumor model by multi-color flow cytometry and in vivo confocal tumor imaging. These approaches were compared with the typical method of whole-organ quantification by radiolabeling. In contrast to radioactivity based detection which demonstrated a linear dose-dependent accumulation in the organ, flow cytometry revealed that particle association with cancer cells became dose-independent with increased particle doses and that the majority of the nanoparticles in the tumor were associated with cancer cells despite a low fractional association. In vivo imaging demonstrated an inverse relationship between tumor cell association and other immune cells, likely macrophages. Finally, variation in particle size nonuniformly affected subtumoral association. This study demonstrates the importance of subtumoral targeting when assessing nanoparticle activity within tumors.

FROM THE CLINICAL EDITOR

Particle Replication in Non-Wetting Templates (PRINT) technology allows the production of nanoparticles with uniform size. The authors in the study utilized PRINT-produced nanoparticles to investigate specific tumor uptake by multi-color flow cytometry and in vivo confocal tumor imaging. This approach allowed further in-depth correlation between nanoparticle properties and tumor cells and should improve future design.

Nanoparticles for Cardiovascular Imaging and Therapeutic Delivery, Part 2: Radiolabeled Probes

Nanoparticulate imaging agents and therapeutics have proven to be valuable tools in preclinical cardiovascular disease research. Because of their distinct properties and significant functional versatility, nanoparticulate imaging agents afford certain capabilities that are typically not provided by traditional small molecule agents. This review is the second in a two-part series covering nanoparticulate imaging agents and theranostics. It highlights current examples of radiolabeled nanoparticulate probes in preclinical cardiovascular research and demonstrates their utility in applications such as blood pool imaging and molecular imaging of ischemia, angiogenesis, atherosclerosis, and inflammation. These agents provide valuable insight into the molecular and cellular mechanisms of cardiovascular disease and illustrate both the limitations and the significant potential of nanoparticles in diagnostic and therapeutic applications. Further technologic development to improve performance, address safety concerns, and fulfil regulatory obligations is required for clinical translation of these emergent technologies.

Nanoparticles for Cardiovascular Imaging and Therapeutic Delivery, Part 1: Compositions and Features

Imaging agents made from nanoparticles are functionally versatile and have unique properties that may translate to clinical utility in several key cardiovascular imaging niches. Nanoparticles exhibit size-based circulation, biodistribution, and elimination properties different from those of small molecules and microparticles. In addition, nanoparticles provide versatile platforms that can be engineered to create both multimodal and multifunctional imaging agents with tunable properties. With these features, nanoparticulate imaging agents can facilitate fusion of high-sensitivity and high-resolution imaging modalities and selectively bind tissues for targeted molecular imaging and therapeutic delivery. Despite their intriguing attributes, nanoparticulate imaging agents have thus far achieved only limited clinical use. The reasons for this restricted advancement include an evolving scope of applications, the simplicity and effectiveness of existing small-molecule agents, pharmacokinetic limitations, safety concerns, and a complex regulatory environment. This review describes general features of nanoparticulate imaging agents and therapeutics and discusses challenges associated with clinical translation. A second, related review to appear in a subsequent issue of JNM highlights nuclear-based nanoparticulate probes in preclinical cardiovascular imaging.

Molecular imaging of macrophage enzyme activity in cardiac inflammation

Molecular imaging is highly advantageous as various insidious inflammatory events can be imaged in a serial and quantitative fashion. Combined with the conventional imaging modalities like computed tomography (CT), magnetic resonance (MR) and nuclear imaging, it helps us resolve the extent of ongoing pathology, quantify inflammation and predict outcome. Macrophages are increasingly gaining importance as an imaging biomarker in inflammatory cardiovascular diseases. Macrophages, recruited to the site of injury, internalize necrotic or foreign material. Along with phagocytosis, activated macrophages release proteolytic enzymes like matrix metalloproteinases (MMPs) and cathepsins into the extracellular environment. Pro-inflammatory monocytes and macrophages also induce tissue oxidative damage through the inflammatory enzyme myeloperoxidase (MPO). In this review we will highlight recent advances in molecular macrophage imaging. Particular stress will be given to macrophage functional and enzymatic activity imaging which targets phagocytosis, proteolysis and myeloperoxidase activity imaging.