Non-invasive imaging of atherosclerosis regression with magnetic resonance to guide drug development

Challenges and Opportunities for the Prevention and Treatment of Cardiovascular Disease Among Young Adults: Report From a National Heart, Lung, and Blood Institute Working Group

Improvements in cardiovascular disease (CVD) rates among young adults in the past 2 decades have been offset by increasing racial/ethnic and gender disparities, persistence of unhealthy lifestyle habits, overweight and obesity, and other CVD risk factors. To enhance the promotion of cardiovascular health among young adults 18 to 39 years old, the medical and broader public health community must understand the biological, interpersonal, and behavioral features of this life stage. Therefore, the National Heart, Lung, and Blood Institute, with support from the Office of Behavioral and Social Science Research, convened a 2-day workshop in Bethesda, Maryland, in September 2017 to identify research challenges and opportunities related to the cardiovascular health of young adults. The current generation of young adults live in an environment undergoing substantial economic, social, and technological transformations, differentiating them from prior research cohorts of young adults. Although the accumulation of clinical and behavioral risk factors for CVD begins early in life, and research suggests early risk is an important determinant of future events, few trials have studied prevention and treatment of CVD in participants <40 years old. Building an evidence base for CVD prevention in this population will require the engagement of young adults, who are often disconnected from the healthcare system and may not prioritize long-term health. These changes demand a repositioning of existing evidence-based treatments to accommodate new sociotechnical contexts. In this article, the authors review the recent literature and current research opportunities to advance the cardiovascular health of today's young adults.

Gd(DOTA)-grafted submicronic polysaccharide-based particles functionalized with fucoidan as potential MR contrast agent able to target human activated platelets

Early detection of thrombotic events remains a big medical challenge. Dextran-based submicronic particles bearing Gd(DOTA) groups and functionalized with fucoidan have been produced via a simple and green water-in-oil emulsification/co-crosslinking process. Their capacity to bind to human activated platelets was evidenced in vitro as well as their cytocompatibility with human endothelial cells. The presence of Gd(DOTA) moieties was confirmed by elemental analysis and total reflection X-ray fluorescence (TRXF) spectrometry. Detailed characterization of particles was performed in terms of size distribution, morphology, and relaxation rates. In particular, longitudinal and transversal proton relaxivities were respectively 1.7 and 5.0 times higher than those of DOTAREM. This study highlights their potential as an MRI diagnostic platform for atherothrombosis.

Improved Detection of Molecular Markers of Atherosclerotic Plaques Using Sub-Millimeter PET Imaging

Since atherosclerotic plaques are small and sparse, their non-invasive detection via PET imaging requires both highly specific radiotracers as well as imaging systems with high sensitivity and resolution. This study aimed to assess the targeting and biodistribution of a novel fluorine-18 anti-VCAM-1 Nanobody (Nb), and to investigate whether sub-millimetre resolution PET imaging could improve detectability of plaques in mice. The anti-VCAM-1 Nb functionalised with the novel restrained complexing agent (RESCA) chelator was labelled with [¹⁸F]AlF with a high radiochemical yield (>75%) and radiochemical purity (>99%). Subsequently, [¹⁸F]AlF(RESCA)-cAbVCAM1-5 was injected in ApoE^-/- mice, or co-injected with excess of unlabelled Nb (control group). Mice were imaged sequentially using a cross-over design on two different commercially available PET/CT systems and finally sacrificed for ex vivo analysis. Both the PET/CT images and ex vivo data showed specific uptake of [¹⁸F]AlF(RESCA)-cAbVCAM1-5 in atherosclerotic lesions. Non-specific bone uptake was also noticeable, most probably due to in vivo defluorination. Image analysis yielded higher target-to-heart and target-to-brain ratios with the β-CUBE (MOLECUBES) PET scanner, demonstrating that preclinical detection of atherosclerotic lesions could be improved using the latest PET technology.

Macrophages in Atherosclerosis Regression

Macrophages play a central role in the development of atherosclerotic cardiovascular disease (ASCVD), which encompasses coronary artery disease, peripheral artery disease, cerebrovascular disease, and aortic atherosclerosis. In each vascular bed, macrophages contribute to the maintenance of the local inflammatory response, propagate plaque development, and promote thrombosis. These central roles, coupled with their plasticity, makes macrophages attractive therapeutic targets in stemming the development of and stabilizing existing atherosclerosis. In the context of ASCVD, classically activated M1 macrophages initiate and sustain inflammation, and alternatively activated M2 macrophages resolve inflammation. However, this classification is now considered an oversimplification, and a greater understanding of plaque macrophage physiology in ASCVD is required to aid in the development of therapeutics to promote ASCVD regression. Reviewed herein are the macrophage phenotypes and molecular regulators characteristic of ASCVD regression, and the current murine models of ASCVD regression.

Regression of atherosclerosis: lessons learned from genetically modified mouse models

PURPOSE OF REVIEW

Regression, or reversal, of atherosclerosis has become an important clinical objective. The development of consistent models of murine atherosclerosis regression has accelerated this field of research. The purpose of this review is to highlight recent mouse studies that reveal molecular mechanisms as well as therapeutics targeted for regression.

RECENT FINDINGS

Atherosclerosis regression does not involve the same mechanisms as progression in reverse order. Distinct molecular processes within the plaque characterize regression. These processes remained elusive until the advent of murine regression models including aortic transplant, the Reversa mouse, gene complementation and dietary intervention. Studies revealed that depletion of plaque macrophages is a quintessential characteristic of regression, driven by reduced monocyte recruitment into plaques, increased egress of macrophages from plaques and reduced macrophage proliferation. In addition, regression results in polarization of remaining plaque macrophages towards an anti-inflammatory phenotype, smaller necrotic cores and promotion of an organized fibrous cap. Furthermore, type 1 diabetes hinders plaque regression, and several therapeutic interventions show promise in slowing plaque progression or inducing regression.

SUMMARY

Mouse models of atherosclerosis regression have accelerated our understanding of the molecular mechanisms governing lesion resolution. These insights will be valuable in identifying therapeutic targets aimed at atherosclerosis regression.

Is atherosclerosis imaging the most sensitive way to assess patients' risk and the best way to conduct future drug trials? A pros-and-cons debate

Atherosclerosis imaging has been the focus of intense debate and research for several decades. Among its primary applications are risk stratification of asymptomatic individuals and follow-up of atherosclerosis progression under a variety of treatments designed to retard or regress the development of arterial disease. Although endorsed and supported by many, this approach has been fiercely opposed by several key opinion leaders over the years. Similarly, regulatory agencies have raised a number of objections to resist the approval of new drugs and devices based on surrogate imaging markers. However, there is a large body of evidence in the medical literature that shows that risk stratification is improved with implementation of atherosclerosis imaging. Additionally, numerous lipid-modifying agents have been tested as far as their ability to affect progression of atherosclerosis, and in many cases the information obtained with imaging was in line with the outcome of subsequent clinical trials. This pros-and-cons debate was staged to bring up in a fun and provoking way the main arguments in favour or against the application of atherosclerosis imaging in the main settings described above.

The phenomenon of atherosclerosis reversal and regression: Lessons from animal models

Studies in non-rodent and murine models showed that atherosclerosis can be reversed. Atherosclerosis progression induced by high-fat or cholesterol-rich diet can be reduced and reversed to plaque regression after switching to a normal diet or through administration of lipid-lowering agents. The similar process should exist in humans after implementation of lipid-lowering therapy and as a result of targeting of small rupture-prone plaques that are major contributors for acute atherosclerotic complications. Lowering of low density lipoprotein (LDL) cholesterol and the activation of reverse cholesterol transport lead to a decline in foam cell content, to the depletion of plaque lipid reservoirs, a decrease in lesional macrophage numbers through the activation of macrophage emigration and, probably, apoptosis, dampening plaque inflammation, and the induction of anti-inflammatory macrophages involved in clearance of the necrotic core and plaque healing. By contrast, plaque regression is characterized by opposite events, leading to the retention of atherogenic LDL and oxidized LDL particles in the plaque, an increased flux of monocytes, the immobilization of macrophages in the intimal vascular tissues, and the propagation of intraplaque inflammation. Transfer of various apolipoprotein (apo) genes to spontaneously hypercholesterolemic mice deficient for either apoE or LDL receptor and, especially, the implementation of the transplantation murine model allowed studying molecular mechanisms of atherosclerotic regression, associated with the depletion of atherogenic lipids in the plaque, egress of macrophages and phenotypic switch of macrophages from the proinflammatory M1 to the anti-inflammatory M2.

The future of imaging in cardiovascular disease intervention trials: 2017 and beyond

PURPOSE OF REVIEW

As our understanding of cardiovascular disease has advanced over the past decades, multiple novel treatment strategies have been developed with the hope of reducing the global morbidity and mortality associated with this condition. Large-scale trials to test such novel therapies using clinical end points are expensive, leading to interest in phase II clinical trials with imaging-derived outcome measures.

RECENT FINDINGS

Noninvasive imaging techniques that assess changes in both atherosclerotic disease burden and plaque composition in response to therapy are well established. With the advent of molecular techniques and hybrid imaging, we now have the ability to assess disease activity alongside these standard anatomic assessments. This multifaceted approach has the potential to provide a more comprehensive assessment of the actions and efficacy of novel therapies in the carotids, aorta and coronary arteries.

SUMMARY

This review will examine how advanced noninvasive imaging strategies have been used to investigate drug efficacy in intervention trials to date, and crucially how these approaches are set to evolve and play a central role in developing the next generation of atherosclerotic medication.