Recombinant HDL-like nanoparticles: a specific contrast agent for MRI of atherosclerotic plaques

Advances in Atherosclerosis Theranostics Harnessing Iron Oxide-Based Nanoparticles

Atherosclerosis, a multifaceted chronic inflammatory disease, has a profound impact on cardiovascular health. However, the critical limitations of atherosclerosis management include the delayed detection of advanced stages, the intricate assessment of plaque stability, and the absence of efficacious therapeutic strategies. Nanotheranostic based on nanotechnology offers a novel paradigm for addressing these challenges by amalgamating advanced imaging capabilities with targeted therapeutic interventions. Meanwhile, iron oxide nanoparticles have emerged as compelling candidates for theranostic applications in atherosclerosis due to their magnetic resonance imaging capability and biosafety. This review delineates the current state and prospects of iron oxide nanoparticle-based nanotheranostics in the realm of atherosclerosis, including pivotal aspects of atherosclerosis development, the pertinent targeting strategies involved in disease pathogenesis, and the diagnostic and therapeutic roles of iron oxide nanoparticles. Furthermore, this review provides a comprehensive overview of theranostic nanomedicine approaches employing iron oxide nanoparticles, encompassing chemical therapy, physical stimulation therapy, and biological therapy. Finally, this review proposes and discusses the challenges and prospects associated with translating these innovative strategies into clinically viable anti-atherosclerosis interventions. In conclusion, this review offers new insights into the future of atherosclerosis theranostic, showcasing the remarkable potential of iron oxide-based nanoparticles as versatile tools in the battle against atherosclerosis.

Oxidized Low-Density Lipoprotein (Ox-LDL)-Triggered Double-Lock Probe for Spatiotemporal Lipoprotein Oxidation and Atherosclerotic Plaque Imaging

Low-density lipoprotein (LDL), especially oxidative modified LDL (Ox-LDL), is the key risk factor for plaque accumulation and the development of cardiovascular disease. Herein, a highly specific Ox-LDL-triggered fluorogenic-colorimetric probe Pro-P1 is developed for visualizing the oxidation and aggregation progress of lipoproteins and plaque. A series of green fluorescent protein chromophores with modified donor-acceptor structures, containing carbazole as an electron donor and various substituents including pyridine-vinyl (P1), phenol-vinyl (P2), N, N-dimethylaniline-vinyl (P3), and thiophene-vinyl (P4), have been synthesized and evaluated. Emission spectroscopy and theoretical calculations of P1-P4 indicate that P1 shows enhanced green fluorescence (λem = 560 nm) by inhibiting its twisted intramolecular charge transfer in the presence of Ox-LDL. This feature allows the selection of P1 as a sensitive probe to directly visualize ferroptosis and Cu2+ -mediated LDL oxidative aggregation via in situ formation of fluorophore-bound Ox-LDL in living cells. The red-emissive probe Pro-P1 (λem = 660 nm) is prepared via borate protection of P1, which can be cleaved into P1 under high expression of HOCl and Ox-LDL condition at the lesion site, resulting in enhanced green emission. The plaque area and size with clear boundaries can be delineated by colorimetric fluorescence imaging and fluorescence lifetime imaging with precise differentiation.

Nanodiamond Decorated PEO Oxide Coatings on NiTi Alloy

Cardiovascular diseases (CVDs) remain a leading cause of death in the European population, primarily attributed to atherosclerosis and subsequent complications. Although statin drugs effectively prevent atherosclerosis, they fail to reduce plaque size and vascular stenosis. Bare metal stents (BMS) have shown promise in acute coronary disease treatment but are associated with restenosis in the stent. Drug-eluting stents (DES) have improved restenosis rates but present long-term complications. To overcome these limitations, nanomaterial-based modifications of the stent surfaces have been explored. This study focuses on the incorporation of detonation nanodiamonds (NDs) into a plasma electrolytic oxidation (PEO) coating on nitinol stents to enhance their performance. The functionalized ND showed a high surface-to-volume ratio and was incorporated into the oxide layer to mimic high-density lipoproteins (HDL) for reverse cholesterol transport (RCT). We provide substantial characterization of DND, including stability in two media (acetone and water), Fourier transmission infrared spectroscopy, and nanoparticle tracking analysis. The characterization of the modified ND revealed successful functionalization and adequate suspension stability. Scanning electron microscopy with EDX demonstrated successful incorporation of DND into the ceramic layer, but the formation of a porous surface is possible only in the high-voltage PEO. The biological assessment demonstrated the biocompatibility of the decorated nitinol surface with enhanced cell adhesion and proliferation. This study presents a novel approach to improving the performance of nitinol stents using ND-based surface modifications, providing a promising avenue for cardiovascular disease.

1821-2021: Contributions of physicians and researchers of Greek descent in the advancement of clinical and experimental cardiology and cardiac surgery

While the role of Greeks in the development of early western medicine is well-known and appreciated, the contributions of modern Greek medical practitioners are less known and often overlooked. On the occasion of the 200-year anniversary of the Greek War of Independence, this review article sheds light onto the achievements of modern scientists of Greek descent in the development of cardiology, cardiac surgery, and cardiovascular research, through a short history of the development of these fields and of the related institutions in Greece. In the last decades, the Greek cardiology and Cardiac Surgery communities have been active inside and outside Greece and have a remarkable presence internationally, particularly in the United States. This article highlights the ways in which Greek cardiology and cardiovascular research has been enriched by absorbing knowledge produced in international medical centers, academic institutes and pharmaceutical industries in which generations of Greek doctors and researchers trained prior to their return to the homeland; it also highlights the achievements of medical practitioners and researchers of Greek descent who excelled abroad, producing ground-breaking work that has left a permanent imprint on global medicine.

Recent advances on nanoparticle-based therapies for cardiovascular diseases

Nanoparticles are exclusively suitable for studying and developing potential therapies against cardiovascular diseases (CVD) because of their size, fine-tunable properties, and ability to incorporate therapeutic and imaging modalities. Recent advancements in nanomaterials open new avenues for treating CVD. In cardiology, the use of nanoparticles and nanocarriers has gathered significant consideration owing to characteristic features such as active and passive targeting to the cardiac tissues, greater target specificity, and sensitivity. It has been reported that through the use of nanotechnology, more than 50% of CVDs can be treated efficiently. Heart-targeted nano carrier-based drug delivery is an effective and efficient approach for treating cardiac-related disorders such as atherosclerosis, hypertension, and myocardial infarction. In this review, the authors focus on nanoparticle-based therapies used in CVD and provide an outline of essential knowledge and critical concerns on polymer-based nanomaterials in treating CVD.

Engineered rHDL Nanoparticles as a Suitable Platform for Theranostic Applications

Reconstituted high-density lipoproteins (rHDLs) can transport and specifically release drugs and imaging agents, mediated by the Scavenger Receptor Type B1 (SR-B1) present in a wide variety of tumor cells, providing convenient platforms for developing theranostic systems. Usually, phospholipids or Apo-A1 lipoproteins on the particle surfaces are the motifs used to conjugate molecules for the multifunctional purposes of the rHDL nanoparticles. Cholesterol has been less addressed as a region to bind molecules or functional groups to the rHDL surface. To maximize the efficacy and improve the radiolabeling of rHDL theranostic systems, we synthesized compounds with bifunctional agents covalently linked to cholesterol. This strategy means that the radionuclide was bound to the surface, while the therapeutic agent was encapsulated in the lipophilic core. In this research, HYNIC-S-(CH2)3-S-Cholesterol and DOTA-benzene-p-SC-NH-(CH2)2-NH-Cholesterol derivatives were synthesized to prepare nanoparticles (NPs) of HYNIC-rHDL and DOTA-rHDL, which can subsequently be linked to radionuclides for SPECT/PET imaging or targeted radiotherapy. HYNIC is used to complexing 99mTc and DOTA for labeling molecules with 111, 113mIn, 67, 68Ga, 177Lu, 161Tb, 225Ac, and 64Cu, among others. In vitro studies showed that the NPs of HYNIC-rHDL and DOTA-rHDL maintain specific recognition by SR-B1 and the ability to internalize and release, in the cytosol of cancer cells, the molecules carried in their core. The biodistribution in mice showed a similar behavior between rHDL (without surface modification) and HYNIC-rHDL, while DOTA-rHDL exhibited a different biodistribution pattern due to the significant reduction in the lipophilicity of the modified cholesterol molecule. Both systems demonstrated characteristics for the development of suitable theranostic platforms for personalized cancer treatment.

Effect of Chemically Modified Carbon-Coated Iron Nanoparticles on the Structure of Human Atherosclerotic Plaques Ex Vivo and on Adipose Tissue in Chronic Experiment In Vivo

The high mortality rate caused by atherosclerosis makes it necessary to constantly search for new and better treatments. In previous reports, chemically modified carbon-coated iron nanoparticles (Fe@C NPs) have been demonstrated a high biocompatibility and promising anti-plaque properties. To further investigate these effects, the interaction of these nanoparticles with the adipose tissue of Wistar rats (in vivo) and human atherosclerotic plaques (ex vivo) was studied. For the in vivo study, cobalt-chromium (CoCr) alloy tubes, which are used for coronary stent manufacturing, were prepared with a coating of polylactic acid (PLA) which contained either modified or non-modified Fe@C NPs in a 5% by weight concentration. The tubes were implanted into an area of subcutaneous fat in Wistar rats, where changes in the histological structure and functional properties of the surrounding tissue were observed in the case of coatings modified with Fe@C NPs. For the ex vivo study, freshly explanted human atherosclerotic plaques were treated in the physiological solution with doses of modified Fe@C NPs, with mass equal to 5% or 25% relative to the plaques. This treatment resulted in the release of cholesterol-like compounds from the surface of the plaques into the solution, thus proving a pronounced destructive effect on the plaque structure. Chemically modified Fe@C NPs, when used as an anti-atherosclerosis agent, were able to activate the activity of macrophages, which could lead to the destruction of atherosclerotic plaques structures. These findings could prove the fabrication of next-generation vascular stents with built-in anti-atherosclerotic agents.

Safe magnetic resonance imaging on biocompatible nanoformulations

Magnetic resonance imaging (MRI) holds promise for the early clinical diagnosis of various diseases, but most clinical MR techniques require the use of a contrast medium. Several nanomaterial (NM) mediated contrast agents (CAs) are widely used as T1- and T2-based MR contrast agents for clinical and non-clinical applications. Unfortunately, most NM-based CAs are toxic or non-biocompatible, restricting their practical/clinical applications. Therefore, the development of nontoxic and biocompatible CAs for clinical MRI diagnosis is highly desired. To this end, several biocompatible and biomimetic strategies have been developed to offer long blood circulation time, significant biocompatibility, in vivo biodistribution and high contrast ability for efficient imaging. However, detailed review reports on biocompatible NMs, specifically for MR imaging have not yet been summarized. Thus, in the present review we summarize  various surface coating strategies (such as polymers, proteins, cell membranes, etc.) to achieve biocompatible NPs, providing a detailed discussion of advances and future prospects for safe MRI imaging.

Nanoparticles in the diagnosis and treatment of vascular aging and related diseases

Aging-induced alternations of vasculature structures, phenotypes, and functions are key in the occurrence and development of vascular aging-related diseases. Multiple molecular and cellular events, such as oxidative stress, mitochondrial dysfunction, vascular inflammation, cellular senescence, and epigenetic alterations are highly associated with vascular aging physiopathology. Advances in nanoparticles and nanotechnology, which can realize sensitive diagnostic modalities, efficient medical treatment, and better prognosis as well as less adverse effects on non-target tissues, provide an amazing window in the field of vascular aging and related diseases. Throughout this review, we presented current knowledge on classification of nanoparticles and the relationship between vascular aging and related diseases. Importantly, we comprehensively summarized the potential of nanoparticles-based diagnostic and therapeutic techniques in vascular aging and related diseases, including cardiovascular diseases, cerebrovascular diseases, as well as chronic kidney diseases, and discussed the advantages and limitations of their clinical applications.

Nanomedicine in Neuroscience: An Application Towards the Treatment of Various Neurological Diseases

Absatract:

The effectiveness, cell viability, and selective delivery of medications and diagnostic substances to target organs, tissues, and organs are typical concerns in the care and prognosis of many illnesses. Neurological diseases pose complex challenges, as cerebral targeting represents a yet unresolved challenge in pharmacotherapy, owing to the blood-brain boundary, a densely com-pacted membrane of endothelial cells that prohibits undesired chemicals from reaching the brain. Engineered nanoparticles, with dimensions ranging from 1 to 100 nm, provide intriguing biomedi-cal techniques that may allow for resolving these issues, including the ability to cross the blood-brain barrier. It has substantially explored nanoparticles in the previous century, contributing to sub-stantial progress in biomedical studies and medical procedures. Using many synthesized nanoparti-cles on the molecular level has given many potential gains in various domains of regenerative medi-cine, such as illness detection, cascaded cell treatment, tissue regeneration, medication, and gene editing. This review will encapsulate the novel developments of nanostructured components used in neurological diseases with an emphasis on the most recent discoveries and forecasts for the future of varied biological nanoparticles for tissue repair, drug inventions, and the synthesizing of the deliv-ery mechanism.

Understanding the Exchange of Systemic HDL Particles Into the Brain and Vascular Cells Has Diagnostic and Therapeutic Implications for Neurodegenerative Diseases

High-density lipoproteins (HDLs) are complex, heterogenous lipoprotein particles, consisting of a large family of apolipoproteins, formed in subspecies of distinct shapes, sizes, and functions and are synthesized in both the brain and the periphery. HDL apolipoproteins are important determinants of Alzheimer’s disease (AD) pathology and vascular dementia, having both central and peripheral effects on brain amyloid-beta (Aβ) accumulation and vascular functions, however, the extent to which HDL particles (HLD-P) can exchange their protein and lipid components between the central nervous system (CNS) and the systemic circulation remains unclear. In this review, we delineate how HDL’s structure and composition enable exchange between the brain, cerebrospinal fluid (CSF) compartment, and vascular cells that ultimately affect brain amyloid metabolism and atherosclerosis. Accordingly, we then elucidate how modifications of HDL-P have diagnostic and therapeutic potential for brain vascular and neurodegenerative diseases.

Recent Advances in Gadolinium Based Contrast Agents for Bioimaging Applications

Gadolinium (Gd) based contrast agents (CAs) (Gd-CAs) represent one of the most advanced developments in the application of Gd for magnetic resonance imaging (MRI). Current challenges with existing CAs generated an urgent requirement to develop multimodal CAs with good biocompatibility, low toxicity, and prolonged circulation time. This review discussed the Gd-CAs used in bioimaging applications, addressing their advantages and limitations. Future research is required to establish the safety, efficacy and theragnostic capabilities of Gd-CAs. Nevertheless, these Gd-CAs offer extraordinary potential as imaging CAs and promise to benefit bioimaging applications significantly.

Nanoparticle theranostics in cardiovascular inflammation

Theranostics, literally derived from the combination of the words diagnostics and therapy, is an emerging field of clinical and preclinical research, where contrast agents, drugs and diagnostic techniques are combined to simultaneously diagnose and treat pathologies. Nanoparticles are extensively employed in theranostics due to their potential to target specific organs and their multifunctional capacity. In this review, we will discuss the current state of theranostic nanomedicine, providing key examples of its application in the imaging and treatment of cardiovascular inflammation.

Imaging cancer cells with nanostructures: Prospects of nanotechnology driven non-invasive cancer diagnosis

The application of nanostructured materials in medicine is a rapidly evolving area of research that includes both the diagnosis and treatment of various diseases. Metals, metal oxides and carbon-based nanomaterials have shown much promise in medical technological advancements due to their tunable physical, chemical and biological properties. The nanoscale properties, especially the size, shape, surface chemistry and stability makes them highly desirable for diagnosing and treating various diseases, including cancers. Major applications of nanomaterials in cancer diagnosis include in vivo bioimaging and molecular marker detection, mainly as image contrast agents using modalities such as radio, magnetic resonance, and ultrasound imaging. When a suitable targeting ligand is attached on the nanomaterial surface, it can help pinpoint the disease site during imaging. The application of nanostructured materials in cancer diagnosis can help in the early detection, treatment and patient follow-up . This review aims to gather and present the information regarding the application of nanotechnology in cancer diagnosis. We also discuss the challenges and prospects regarding the application of nanomaterials as cancer diagnostic tools.

Chemically Modified Biomimetic Carbon-Coated Iron Nanoparticles for Stent Coatings: In Vitro Cytocompatibility and In Vivo Structural Changes in Human Atherosclerotic Plaques

Atherosclerosis, a systematic degenerative disease related to the buildup of plaques in human vessels, remains the major cause of morbidity in the field of cardiovascular health problems, which are the number one cause of death globally. Novel atheroprotective HDL-mimicking chemically modified carbon-coated iron nanoparticles (Fe@C NPs) were produced by gas-phase synthesis and modified with organic functional groups of a lipophilic nature. Modified and non-modified Fe@C NPs, immobilized with polycaprolactone on stainless steel, showed high cytocompatibility in human endothelial cell culture. Furthermore, after ex vivo treatment of native atherosclerotic plaques obtained during open carotid endarterectomy surgery, Fe@C NPs penetrated the inner structures and caused structural changes of atherosclerotic plaques, depending on the period of implantation in Wistar rats, serving as a natural bioreactor. The high biocompatibility of the Fe@C NPs shows great potential in the treatment of atherosclerosis disease as an active substance of stent coatings to prevent restenosis and the formation of atherosclerotic plaques.

Bioprocessed Brewers' Spent Grain Improves Nutritional and Antioxidant Properties of Pasta

Brewers' spent grain (BSG), the by-product of brewing, was subjected to a xylanase treatment followed by fermentation with Lactiplantibacillus plantarum PU1. Bioprocessed BSG has been used as ingredient to obtain a fortified semolina pasta which can be labeled as "high fiber" and "source of protein" according to the European Community Regulation No. 1924/2006. Compared to native BSG, the use of bioprocessed BSG led to higher protein digestibility and quality indices (essential amino acid index, biological value, protein efficiency ratio, nutritional index), as well as lower predicted glycemic index. Bioprocessing also improved the technological properties of fortified pasta. Indeed, brightfield and confocal laser scanning microscopy revealed the formation of a more homogeneous protein network, resulting from the degradation of the arabinoxylan structure of BSG, and the release of the components entrapped into the cellular compartments. The extensive cell wall disruption contributed to the release of phenols, and conferred enhanced antioxidant activity to the fortified pasta. The persistence of the activity was demonstrated after in vitro-mimicked digestion, evaluating the protective effects of the digested pasta towards induced oxidative stress in Caco-2 cells cultures. The fortified pasta showed a peculiar sensory profile, markedly improved by the pre-treatment, thus confirming the great potential of bioprocessed BSG as health-promoting food ingredient.

(r)HDL in theranostics: how do we apply HDL's biology for precision medicine in atherosclerosis management?

High-density lipoproteins (HDL) are key players in cholesterol metabolism homeostasis since they are responsible for transporting excess cholesterol from peripheral tissues to the liver. Imbalance in this process, due to either excessive accumulation or impaired clearance, results in net cholesterol accumulation and increases the risk of cardiovascular disease (CVD). Therefore, significant effort has been focused on the development of therapeutic tools capable of either directly or indirectly enhancing HDL-guided reverse cholesterol transport (RCT). More recently, in light of the emergence of precision nanomedicine, there has been renewed research interest in attempting to take advantage of the development of advanced recombinant HDL (rHDL) for both therapeutic and diagnostic purposes. In this review, we provide an update on the different approaches that have been developed using rHDL, focusing on the rHDL production methodology and rHDL applications in theranostics. We also compile a series of examples highlighting potential future perspectives in the field.

A systematic review of the biodistribution of biomimetic high-density lipoproteins in mice

For the past two decades, biomimetic high-density lipoproteins (b-HDL) have been used for various drug delivery applications. The b-HDL mimic the endogenous HDL, and therefore possess many attractive features for drug delivery, including high biocompatibility, biodegradability, and ability to transport and deliver their cargo (e.g. drugs and/or imaging agents) to specific cells and tissues that are recognized by HDL. The b-HDL designs reported in the literature often differ in size, shape, composition, and type of incorporated cargo. However, there exists only limited insight into how the b-HDL design dictates their biodistribution. To fill this gap, we conducted a comprehensive systematic literature search of biodistribution studies using various designs of apolipoprotein A-I (apoA-I)-based b-HDL (i.e. b-HDL with apoA-I, apoA-I mutants, or apoA-I mimicking peptides). We carefully screened 679 papers (search hits) for b-HDL biodistribution studies in mice, and ended up with 24 relevant biodistribution profiles that we compared according to b-HDL design. We show similarities between b-HDL biodistribution studies irrespectively of the b-HDL design, whereas the biodistribution of the b-HDL components (lipids and scaffold) differ significantly. The b-HDL lipids primarily accumulate in liver, while the b-HDL scaffold primarily accumulates in the kidney. Furthermore, both b-HDL lipids and scaffold accumulate well in the tumor tissue in tumor-bearing mice. Finally, we present essential considerations and strategies for b-HDL labeling, and discuss how the b-HDL biodistribution can be tuned through particle design and administration route. Our meta-analysis and discussions provide a detailed overview of the fate of b-HDL in mice that is highly relevant when applying b-HDL for drug delivery or in vivo imaging applications.

LDL-mimetic lipid nanoparticles prepared by surface KAT ligation for in vivo MRI of atherosclerosis

Low-density lipoprotein (LDL)-mimetic lipid nanoparticles (LNPs), decorated with MRI contrast agents and fluorescent dyes, were prepared by the covalent attachment of apolipoprotein-mimetic peptide (P), Gd(iii)-chelate (Gd), and sulforhodamine B (R) moieties on the LNP surface. The functionalized LNPs were prepared using the amide-forming potassium acyltrifluoroborate (KAT) ligation reaction. The KAT groups on the surface of LNPs were allowed to react with the corresponding hydroxylamine (HA) derivatives of P and Gd to provide bi-functionalized LNPs (PGd-LNP). The reaction proceeded with excellent yields, as observed by ICP-MS (for B and Gd amounts) and MALDI-TOF-MS data, and did not alter the morphology of the LNPs (mean diameter: ca. 50 nm), as shown by DLS and cryoTEM analyses. With the help of the efficient KAT ligation, a high payload of Gd(iii)-chelate on the PGd-LNP surface (ca. 2800 Gd atoms per LNP) was successfully achieved and provided a high r₁ relaxivity (r₁ = 22.0 s⁻¹ mM⁻¹ at 1.4 T/60 MHz and 25 °C; r₁ = 8.2 s⁻¹ mM⁻¹ at 9.4 T/400 MHz and 37 °C). This bi-functionalized PGd-LNP was administered to three atherosclerotic apoE^−/− mice to reveal the clear enhancement of atherosclerotic plaques in the brachiocephalic artery (BA) by MRI, in good agreement with the high accumulation of Gd in the aortic arch as shown by ICP-MS. The parallel in vivo MRI and ex vivo studies of whole mouse cryo-imaging were performed using triply functionalized LNPs with P, Gd, and R (PGdR-LNP). The clear presence of atherosclerotic plaques in BA was observed by ex vivo bright field cryo-imaging, and they were also observed by high emission fluorescent imaging. These directly corresponded to the enhanced tissue in the in vivo MRI of the identical mouse.

LDL-mimetic lipid nanoparticles, decorated with MRI contrast agents and fluorescent dyes, were prepared by the covalent attachments of an apoB100-mimetic peptide, Gd(iii)-chelate, and rhodamine to enhance atherosclerosis in the in vivo imaging.

Reconfiguring Nature's Cholesterol Accepting Lipoproteins as Nanoparticle Platforms for Transport and Delivery of Therapeutic and Imaging Agents

Apolipoproteins are critical structural and functional components of lipoproteins, which are large supramolecular assemblies composed predominantly of lipids and proteins, and other biomolecules such as nucleic acids. A signature feature of apolipoproteins is the preponderance of amphipathic α-helical motifs that dictate their ability to make extensive non-covalent inter- or intra-molecular helix-helix interactions in lipid-free states or helix-lipid interactions with hydrophobic biomolecules in lipid-associated states. This review focuses on the latter ability of apolipoproteins, which has been capitalized on to reconstitute synthetic nanoscale binary/ternary lipoprotein complexes composed of apolipoproteins/peptides and lipids that mimic native high-density lipoproteins (HDLs) with the goal to transport drugs. It traces the historical development of our understanding of these nanostructures and how the cholesterol accepting property of HDL has been reconfigured to develop them as drug-loading platforms. The review provides the structural perspective of these platforms with different types of apolipoproteins and an overview of their synthesis. It also examines the cargo that have been loaded into the core for therapeutic and imaging purposes. Finally, it lays out the merits and challenges associated with apolipoprotein-based nanostructures with a future perspective calling for a need to develop "zip-code"-based delivery for therapeutic and diagnostic applications.

Squalene-based nanoparticles for the targeting of atherosclerotic lesions

Native low-density lipoproteins (LDL) naturally accumulate at atherosclerotic lesions and are thought to be among the main drivers of atherosclerosis progression. Numerous nanoparticular systems making use of recombinant lipoproteins have been developed for targeting atherosclerotic plaque. These innovative formulations often require complicated purification and synthesis procedures which limit their eventual translation to the clinics. Recently, squalenoylation has appeared as a simple and efficient technique for targeting agents to endogenous lipoproteins through a bioconjugation approach. In this study, we have developed a fluorescent squalene bioconjugate to evaluate the biodistribution of squalene-based nanoparticles in an ApoE^-/- model of atherosclerosis. By accumulating in LDL endogenous nanoparticles, the squalene bioconjugation could serve as an efficient targeting platform for atherosclerosis. Indeed, in this proof of concept, we show that our squalene-rhodamine (SQRho) nanoparticles, could accumulate in the aortas of atherosclerotic animals. Histological evaluation confirmed the presence of atherosclerotic lesions and the co-localization of SQRho bioconjugates at the lesion sites.

Dual-Targeted Synthetic Nanoparticles for Cardiovascular Diseases

Atherosclerosis is one of the world's most aggressive diseases, claiming over 17.5 million lives per year. This disease is usually caused by high amounts of lipoproteins circulating in the blood stream, which leads to plaque formation. Ultimately, these plaques can undergo thrombosis and lead to major heart damage. A major contributor to these vulnerable plaques is macrophage apoptosis. Development of nanovehicles that carry contrast and therapeutic agents to the mitochondria within these macrophages is attractive for the diagnosis and treatment of atherosclerosis. Here, we report the design and synthesis of a dual-targeted synthetic nanoparticle (NP) to perform the double duty of diagnosis and therapy in atherosclerosis treatment regime. A library of dual-targeted NPs with an encapsulated iron oxide NP, mito-magneto (MM), with a magnetic resonance imaging (MRI) contrast enhancement capability was elucidated. Relaxivity measurements revealed that there is a substantial enhancement in transverse relaxivities upon the encapsulation of MM inside the dual-targeted NPs, highlighting the MRI contrast-enhancing ability of these NPs. Successful in vivo imaging documenting the distribution of MM-encapsulated dual-targeted NPs in the heart and aorta in mice ensured the diagnostic potential. The presence of mannose receptor targeting ligands and the optimization of the NP composition facilitated its ability to perform therapeutic duty by targeting the macrophages at the plaque. These dual-targeted NPs with the encapsulated MM were able to show therapeutic potential and did not trigger any toxic immunogenic response.

High density lipoprotein mimicking nanoparticles for atherosclerosis

Atherosclerosis is a major contributor to many cardiovascular events, including myocardial infarction, ischemic stroke, and peripheral arterial disease, making it the leading cause of death worldwide. High-density lipoproteins (HDL), also known as "good cholesterol", have been shown to demonstrate anti-atherosclerotic efficacy through the removal of cholesterol from foam cells in atherosclerotic plaques. Because of the excellent anti-atherosclerotic properties of HDL, in the past several years, there has been tremendous attention in designing HDL mimicking nanoparticles (NPs) of varying functions to image, target, and treat atherosclerosis. In this review, we are summarizing the recent progress in the development of HDL mimicking NPs and their applications for atherosclerosis.

Artificial High Density Lipoprotein Nanoparticles in Cardiovascular Research

Lipoproteins are endogenous nanoparticles which are the major transporter of fats and cholesterol in the human body. They play a key role in the regulatory mechanisms of cardiovascular events. Lipoproteins can be modified and manipulated to act as drug delivery systems or nanocarriers for contrast agents. In particular, high density lipoproteins (HDL), which are the smallest class of lipoproteins, can be synthetically engineered either as nascent HDL nanodiscs or spherical HDL nanoparticles. Reconstituted HDL (rHDL) particles are formed by self-assembly of various lipids and apolipoprotein AI (apo-AI). A variety of substances including drugs, nucleic acids, signal emitting molecules, or dyes can be loaded, making them efficient nanocarriers for therapeutic applications or medical diagnostics. This review provides an overview about synthesis techniques, physicochemical properties of rHDL nanoparticles, and structural determinants for rHDL function. We discuss recent developments utilizing either apo-AI or apo-AI mimetic peptides for the design of pharmaceutical rHDL formulations. Advantages, limitations, challenges, and prospects for clinical translation are evaluated with a special focus on promising strategies for the treatment and diagnosis of atherosclerosis and cardiovascular diseases.

Covalent Surface Modification of Lipid Nanoparticles by Rapid Potassium Acyltrifluoroborate Amide Ligation

Because of the recent increasing demand for the synthetic biomimetic nanoparticles as in vivo carriers of drugs and imaging probes, it is very important to develop reliable, stable, and orthogonal methods for surface functionalization of the particles. To address these issues, in this study, a recently reported chemoselective amide-forming ligation reaction [potassium acyltrifluoroborate (KAT) ligation] was employed for the first time, as a mean to provide the surface functionalization of particles for creating covalent attachments of bioactive molecules. A KAT derivative of oleic acid (OA-KAT, 1) was added to a mixture of three lipid components (triolein, phosphatidyl choline, and cholesteryl oleate), which have been commonly used as substrates for lipid nanoparticles. After sonication and extrusion in a buffer, successfully obtained lipid nanoparticles containing OA-KAT (NP-KAT) resulted to be well-dispersed with mean diameters of about 40-70 nm by dynamic light scattering. After preliminary confirmation of the fast and efficient KAT ligation in a solution phase using the identical reaction substrates, the "on-surface (on-particle)" KAT ligation on the NP-KAT was tested with an N-hydroxylamine derivative of fluorescein 2. The ligation was carried out in a phosphate buffer (10 mM, pH 5.2) at room temperature with reactant concentration ranges of 250 μM. Reaction efficiency was evaluated based on the amount of boron (determined by inductively coupled plasma mass spectrometry) and fluorescein (determined by fluorescence emission) in the particles before and after the reaction. As a result, the reaction proceeded in a significantly efficient way with ca. 40-50% conversion of the OA-KAT incorporated in the particles. Taken together with the fact that KAT ligation does not require any additional coupling reagents, these results indicated that the "on-surface" chemical functionalization of nanoparticles by KAT ligation is a useful method and represents a powerful and potentially versatile tool for the production of nanoparticles with a variety of covalently functionalized biomolecules and probes.

Nanoparticles for diagnosis and therapy of atherosclerosis and myocardial infarction: evolution toward prospective theranostic approaches

Cardiovascular diseases are the leading cause of death worldwide. Despite preventive efforts, early detection of atherosclerosis, the common pathophysiological mechanism underlying cardiovascular diseases remains elusive, and overt coronary artery disease or myocardial infarction is often the first clinical manifestation. Nanoparticles represent a novel strategy for prevention, diagnosis, and treatment of atherosclerosis, and new multifunctional nanoparticles with combined diagnostic and therapeutic capacities hold the promise for theranostic approaches to this disease. This review focuses on the development of nanosystems for therapy and diagnosis of subclinical atherosclerosis, coronary artery disease, and myocardial infarction and the evolution of nanosystems as theranostic tools. We also discuss the use of nanoparticles in noninvasive imaging, targeted drug delivery, photothermal therapies together with the challenges faced by nanosystems during clinical translation.

Advances in gadolinium-based MRI contrast agent designs for monitoring biological processes in vivo

The gadolinium-based contrast agents widely used in diagnostic MRI exams for 30 years are all small molecule agents that distribute into all extracellular spaces in tissues without providing any specific biological information. Although many 'responsive agent' designs have been presented over the past 20 years or so, none have found use in clinical diagnostic medicine at this point. This review summarizes some recent approaches taken to enhance the sensitivity of such gadolinium-based agents, to target them to specific tissue components, and to create new systems for monitoring specific biological processes.

Theranostics and contrast agents for magnetic resonance imaging

BACKGROUND

Magnetic resonance imaging is one of the diagnostic tools that uses magnetic particles as contrast agents. It is noninvasive methodology which provides excellent spatial resolution. Although magnetic resonance imaging offers great temporal and spatial resolution and rapid in vivo images acquisition, it is less sensitive than other methodologies for small tissue lesions, molecular activity or cellular activities. Thus, there is a desire to develop contrast agents with higher efficiency. Contrast agents are known to shorten both T1 and T2. Gadolinium based contrast agents are examples of T1 agents and iron oxide contrast agents are examples of T2 agents. In order to develop high relaxivity agents, gadolinium or iron oxide-based contrast agents can be synthesized via conjugation with targeting ligands or functional moiety for specific interaction and achieve accumulation of contrast agents at disease sites.

MAIN BODY

This review discusses the principles of magnetic resonance imaging and recent efforts focused on specificity of contrast agents on specific organs such as liver, blood, lymph nodes, atherosclerotic plaque, and tumor. Furthermore, we will discuss the combination of theranostic such as contrast agent and drug, contrast agent and thermal therapy, contrast agent and photodynamic therapy, and neutron capture therapy, which can provide for cancer diagnosis and therapeutics.

CONCLUSION

These applications of magnetic resonance contrast agents demonstrate the usefulness of theranostic agents for diagnosis and treatment.

Surface impact on nanoparticle-based magnetic resonance imaging contrast agents

Magnetic resonance imaging (MRI) is one of the most widely used diagnostic tools in the clinic. To improve imaging quality, MRI contrast agents, which can modulate local T1 and T2 relaxation times, are often injected prior to or during MRI scans. However, clinically used contrast agents, including Gd3+-based chelates and iron oxide nanoparticles (IONPs), afford mediocre contrast abilities. To address this issue, there has been extensive research on developing alternative MRI contrast agents with superior r1 and r2 relaxivities. These efforts are facilitated by the fast progress in nanotechnology, which allows for preparation of magnetic nanoparticles (NPs) with varied size, shape, crystallinity, and composition. Studies suggest that surface coatings can also largely affect T1 and T2 relaxations and can be tailored in favor of a high r1 or r2. However, the surface impact of NPs has been less emphasized. Herein, we review recent progress on developing NP-based T1 and T2 contrast agents, with a focus on the surface impact.

Molecular engineering of lanthanide ion chelating phospholipids generating assemblies with a switched magnetic susceptibility

Lanthanide ion (Ln³⁺) chelating amphiphiles are powerful molecules for tailoring the magnetic response of polymolecular assemblies. Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA) complexed to Ln³⁺ deliver highly magnetically responsive bicelles. Their magnetic properties are readily tuned by changing the bicellar size or the magnetic susceptibility Δχ of the bilayer lipids. The former technique is intrinsically bound to the region of the phase diagram guarantying the formation of bicelles. Methods aiming towards manipulating the Δχ of the bilayer are comparatively more robust, flexible and lacking. Herein, we synthesized a new Ln³⁺ chelating phospholipid using glutamic acid as a backbone: DMPE-Glu-DTPA. The chelate polyhedron was specifically engineered to alter the Δχ, whilst remaining geometrically similar to DMPE-DTPA. Planar asymmetric assemblies hundreds of nanometers in size were achieved presenting unprecedented magnetic alignments. The DMPE-Glu-DTPA/Ln³⁺ complex switched the Δχ, achieving perpendicular alignment of assemblies containing Dy³⁺ and parallel alignment of those containing Tm³⁺. Moreover, samples with chelated Yb³⁺ were more alignable than the Tm³⁺ chelating counterparts. Such a possibility has never been demonstrated for planar Ln³⁺ chelating polymolecular assemblies. The physico-chemical properties of these novel assemblies were further studied by monitoring the alignment behavior at different temperatures and by including 16 mol% of cholesterol (Chol-OH) in the phospholipid bilayer. The DMPE-Glu-DTPA/Ln³⁺ complex and the resulting assemblies are promising candidates for applications in numerous fields including pharmaceutical technologies, structural characterization of membrane biomolecules by NMR spectroscopy, as contrasting agents for magnetic resonance imaging, and for the development of smart optical gels.

High-Density Lipoprotein Nanobiologics for Precision Medicine

Nature is an inspirational source for biomedical engineering developments. Particularly, numerous nanotechnological approaches have been derived from biological concepts. For example, among many different biological nanosized materials, viruses have been extensively studied and utilized, while exosome research has gained much traction in the 21st century. In our body, fat is transported by lipoproteins, intriguing supramolecular nanostructures that have important roles in cell function, lipid metabolism, and disease. Lipoproteins' main constituents are phospholipids and apolipoproteins, forming a corona that encloses a hydrophobic core of triglycerides and cholesterol esters. Within the lipoprotein family, high-density lipoprotein (HDL), primarily composed of apolipoprotein A1 (apoA-I) and phospholipids, measuring a mere 10 nm, is the smallest and densest particle. Its endogenous character makes HDL particularly suitable as a nanocarrier platform to target a range of inflammatory diseases. For a decade and a half, our laboratories have focused on HDL's exploitation, repurposing, and reengineering for diagnostic and therapeutic applications, generating versatile hybrid nanomaterials, referred to as nanobiologics, that are inherently biocompatible and biodegradable, efficiently cross different biological barriers, and intrinsically interact with immune cells. The latter is facilitated by HDL's intrinsic ability to interact with the ATP-binding cassette receptor A1 (ABCA1) and ABCG1, as well as scavenger receptor type B1 (SR-BI). In this Account, we will provide an up-to-date overview on the available methods for extraction, isolation, and purification of apoA-I from native HDL, as well as its recombinant production. ApoA-I's subsequent use for the reconstitution of HDL (rHDL) and other HDL-derived nanobiologics, including innovative microfluidic-based production methods, and their characterization will be discussed. The integration of different hydrophobic and amphiphilic imaging labels, including chelated radioisotopes and paramagnetic or fluorescent lipids, renders HDL nanobiologics suitable for diagnostic purposes. Nanoengineering also allows HDL reconstitution with core payloads, such as diagnostically active nanocrystals, as well as hydrophobic drugs or controlled release polymers for therapeutic purposes. The platform technology's specificity for inflammatory myeloid cells and methods to modulate specificity will be highlighted. This Account will build toward examples of in vivo studies in cardiovascular disease and cancer models, including diagnostic studies by magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography (PET). A translational success story about the escalation of zirconium-89 radiolabeled HDL (89Zr-HDL) PET imaging from atherosclerotic mice to rabbits and pigs and all the way to cardiovascular disease patients is highlighted. Finally, recent advances in nanobiologic-facilitated immunotherapy of inflammation are spotlighted. Lessons, success stories, and perspectives on the use of these nature-inspired HDL mimetics are an integral part of this Account.

SR-B1: A Unique Multifunctional Receptor for Cholesterol Influx and Efflux

The scavenger receptor, class B type 1 (SR-B1), is a multiligand membrane receptor protein that functions as a physiologically relevant high-density lipoprotein (HDL) receptor whose primary role is to mediate selective uptake or influx of HDL-derived cholesteryl esters into cells and tissues. SR-B1 also facilitates the efflux of cholesterol from peripheral tissues, including macrophages, back to liver. As a regulator of plasma membrane cholesterol content, SR-B1 promotes the uptake of lipid soluble vitamins as well as viral entry into host cells. These collective functions of SR-B1 ultimately affect programmed cell death, female fertility, platelet function, vasculature inflammation, and diet-induced atherosclerosis and myocardial infarction. SR-B1 has also been identified as a potential marker for cancer diagnosis and prognosis. Finally, the SR-B1-linked selective HDL-cholesteryl ester uptake pathway is now being evaluated as a gateway for the delivery of therapeutic and diagnostic agents. In this review, we focus on the regulation and functional significance of SR-B1 in mediating cholesterol movement into and out of cells.

Nanoparticles as Theranostic Vehicles in Experimental and Clinical Applications-Focus on Prostate and Breast Cancer

Prostate and breast cancer are the second most and most commonly diagnosed cancer in men and women worldwide, respectively. The American Cancer Society estimates that during 2016 in the USA around 430,000 individuals were diagnosed with one of these two types of cancers, and approximately 15% of them will die from the disease. In Europe, the rate of incidences and deaths are similar to those in the USA. Several different more or less successful diagnostic and therapeutic approaches have been developed and evaluated in order to tackle this issue and thereby decrease the death rates. By using nanoparticles as vehicles carrying both diagnostic and therapeutic molecular entities, individualized targeted theranostic nanomedicine has emerged as a promising option to increase the sensitivity and the specificity during diagnosis, as well as the likelihood of survival or prolonged survival after therapy. This article presents and discusses important and promising different kinds of nanoparticles, as well as imaging and therapy options, suitable for theranostic applications. The presentation of different nanoparticles and theranostic applications is quite general, but there is a special focus on prostate cancer. Some references and aspects regarding breast cancer are however also presented and discussed. Finally, the prostate cancer case is presented in more detail regarding diagnosis, staging, recurrence, metastases, and treatment options available today, followed by possible ways to move forward applying theranostics for both prostate and breast cancer based on promising experiments performed until today.

Effect of size and pegylation of liposomes and peptide-based synthetic lipoproteins on tumor targeting

Synthetic high-density lipoprotein nanoparticles (sHDL) are a valuable class of nanomedicines with established animal safety profile, clinical tolerability and therapeutic efficacy for cardiovascular applications. In this study we examined how the scavenger receptor B-I-mediated (SR-BI) tumor-targeting ability of sHDL, long plasma circulation half-life, and small particle size (9.6±0.2nm) impacted sHDL accumulation in SR-BI positive colorectal carcinoma cells, 3D tumor spheroids, and in vivo xenografts. We compared tumor accumulation of sHDL with that of liposomes (LIP, 130.7±0.8nm), pegylated liposomes (PEG-LIP, 101±2nm), and pegylated sHDL (12.1±0.1nm), all prepared with the same lipid components. sHDL penetrated deep (210μm) into tumor spheroids and exhibited 12- and 3-fold higher in vivo solid tumor accumulation, compared with LIP (p<0.01) and PEG-LIP (p<0.05), respectively. These results suggest that sHDL with established human safety possess promising intrinsic tumor-targeted properties.

Vascular targeting of nanoparticles for molecular imaging of diseased endothelium

This review seeks to highlight the enormous potential of targeted nanoparticles for molecular imaging applications. Being the closest point-of-contact, circulating nanoparticles can gain direct access to targetable molecular markers of disease that appear on the endothelium. Further, nanoparticles are ideally suitable to vascular targeting due to geometrically enhanced multivalent attachment on the vascular target. This natural synergy between nanoparticles, vascular targeting and molecular imaging can provide new avenues for diagnosis and prognosis of disease with quantitative precision. In addition to the obvious applications of targeting molecular signatures of vascular diseases (e.g., atherosclerosis), deep-tissue diseases often manifest themselves by continuously altering and remodeling their neighboring blood vessels (e.g., cancer). Thus, the remodeled endothelium provides a wide range of targets for nanoparticles and molecular imaging. To demonstrate the potential of molecular imaging, we present a variety of nanoparticles designed for molecular imaging of cancer or atherosclerosis using different imaging modalities.

Contrast agents for cardiovascular magnetic resonance imaging: an overview

Contrast agents for Cardiovascular Magnetic Resonance (CMR) play a major role in research and clinical cardiology.

Targeting the SR-B1 Receptor as a Gateway for Cancer Therapy and Imaging

Malignant tumors display remarkable heterogeneity to the extent that even at the same tissue site different types of cells with varying genetic background may be found. In contrast, a relatively consistent marker the scavenger receptor type B1 (SR-B1) has been found to be consistently overexpressed by most tumor cells. Scavenger Receptor Class B Type I (SR-BI) is a high density lipoprotein (HDL) receptor that facilitates the uptake of cholesterol esters from circulating lipoproteins. Additional findings suggest a critical role for SR-BI in cholesterol metabolism, signaling, motility, and proliferation of cancer cells and thus a potential major impact in carcinogenesis and metastasis. Recent findings indicate that the level of SR-BI expression correlate with aggressiveness and poor survival in breast and prostate cancer. Moreover, genomic data show that depending on the type of cancer, high or low SR-BI expression may promote poor survival. This review discusses the importance of SR-BI as a diagnostic as well as prognostic indicator of cancer to help elucidate the contributions of this protein to cancer development, progression, and survival. In addition, the SR-B1 receptor has been shown to serve as a potential gateway for the delivery of therapeutic agents when reconstituted high density lipoprotein nanoparticles are used for their transport to cancer cells and tumors. Opportunities for the development of new technologies, particularly in the areas of cancer therapy and tumor imaging are discussed.

Lipoproteins and lipoprotein mimetics for imaging and drug delivery

Lipoproteins are a set of natural nanoparticles whose main role is the transport of fats within the body. While much work has been done to develop synthetic nanocarriers to deliver drugs or contrast media, natural nanoparticles such as lipoproteins represent appealing alternatives. Lipoproteins are biocompatible, biodegradable, non-immunogenic and are naturally targeted to some disease sites. Lipoproteins can be modified to act as contrast agents in many ways, such as by insertion of gold cores to provide contrast for computed tomography. They can be loaded with drugs, nucleic acids, photosensitizers or boron to act as therapeutics. Attachment of ligands can re-route lipoproteins to new targets. These attributes render lipoproteins attractive and versatile delivery vehicles. In this review we will provide background on lipoproteins, then survey their roles as contrast agents, in drug and nucleic acid delivery, as well as in photodynamic therapy and boron neutron capture therapy.

Conformational Changes in High-Density Lipoprotein Nanoparticles Induced by High Payloads of Paramagnetic Lipids

High-density lipoprotein (HDL) nanoparticles doped with gadolinium lipids can be used as magnetic resonance imaging diagnostic agents for atherosclerosis. In this study, HDL nanoparticles with different molar fractions of gadolinium lipids (0 < x_Gd-lipids < 0.33) were prepared, and the MR relaxivity values (r1 and r2) for all compositions were measured. Both r1 and r2 parameters reached a maximal value at a molar fraction of approximately x_Gd-lipids = 0.2. Higher payloads of gadolinium did not significantly increase relaxivity values but induced changes in the structure of HDL, increasing the size of the particles from d_H = 8.2 ± 1.6 to 51.7 ± 7.3 nm. High payloads of gadolinium lipids trigger conformational changes in HDL, with potential effects on the in vivo behavior of the nanoparticles.

Lipoprotein-Related and Apolipoprotein-Mediated Delivery Systems for Drug Targeting and Imaging

The integration of lipoprotein-related or apolipoprotein-targeted nanoparticles as pharmaceutical carriers opens new therapeutic and diagnostic avenues in nanomedicine. The concept is to exploit the intrinsic characteristics of lipoprotein particles as being the natural transporter of apolar lipids and fat in human circulation. Discrete lipoprotein assemblies and lipoprotein-based biomimetics offer a versatile nanoparticle platform that can be manipulated and tuned for specific medical applications. This article reviews the possibilities for constructing drug loaded, reconstituted or artificial lipoprotein particles. The advantages and limitations of lipoproteinbased delivery systems are critically evaluated and potential future challenges, especially concerning targeting specificity, concepts for lipoprotein rerouting and design of innovative lipoprotein mimetic particles using apolipoprotein sequences as targeting moieties are discussed. Finally, the review highlights potential medical applications for lipoprotein-based nanoparticle systems in the fields of cardiovascular research, cancer therapy, gene delivery and brain targeting focusing on representative examples from literature.

Biomimetic strategies for targeted nanoparticle delivery

Nanoparticle‐based drug delivery and imaging platforms have become increasingly popular over the past several decades. Among different design parameters that can affect their performance, the incorporation of targeting functionality onto nanoparticle surfaces has been a widely studied subject. Targeted formulations have the ability to improve efficacy and function by positively modulating tissue localization. Many methods exist for creating targeted nanoformulations, including the use of custom biomolecules such as antibodies or aptamers. More recently, a great amount of focus has been placed on biomimetic targeting strategies that leverage targeting interactions found directly in nature. Such strategies, which have been painstakingly selected over time by the process of evolution to maximize functionality, oftentimes enable scientists to forgo the specialized discovery processes associated with many traditional ligands and help to accelerate development of novel nanoparticle formulations. In this review, we categorize and discuss in‐depth recent works in this growing field of bioinspired research.

In Vivo PET Imaging of HDL in Multiple Atherosclerosis Models

OBJECTIVES

The goal of this study was to develop and validate a noninvasive imaging tool to visualize the in vivo behavior of high-density lipoprotein (HDL) by using positron emission tomography (PET), with an emphasis on its plaque-targeting abilities.

BACKGROUND

HDL is a natural nanoparticle that interacts with atherosclerotic plaque macrophages to facilitate reverse cholesterol transport. HDL-cholesterol concentration in blood is inversely associated with risk of coronary heart disease and remains one of the strongest independent predictors of incident cardiovascular events.

METHODS

Discoidal HDL nanoparticles were prepared by reconstitution of its components apolipoprotein A-I (apo A-I) and the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine. For radiolabeling with zirconium-89 ((89)Zr), the chelator deferoxamine B was introduced by conjugation to apo A-I or as a phospholipid-chelator (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-deferoxamine B). Biodistribution and plaque targeting of radiolabeled HDL were studied in established murine, rabbit, and porcine atherosclerosis models by using PET combined with computed tomography (PET/CT) imaging or PET combined with magnetic resonance imaging. Ex vivo validation was conducted by radioactivity counting, autoradiography, and near-infrared fluorescence imaging. Flow cytometric assessment of cellular specificity in different tissues was performed in the murine model.

RESULTS

We observed distinct pharmacokinetic profiles for the two (89)Zr-HDL nanoparticles. Both apo A-I- and phospholipid-labeled HDL mainly accumulated in the kidneys, liver, and spleen, with some marked quantitative differences in radioactivity uptake values. Radioactivity concentrations in rabbit atherosclerotic aortas were 3- to 4-fold higher than in control animals at 5 days' post-injection for both (89)Zr-HDL nanoparticles. In the porcine model, increased accumulation of radioactivity was observed in lesions by using in vivo PET imaging. Irrespective of the radiolabel's location, HDL nanoparticles were able to preferentially target plaque macrophages and monocytes.

CONCLUSIONS

(89)Zr labeling of HDL allows study of its in vivo behavior by using noninvasive PET imaging, including visualization of its accumulation in advanced atherosclerotic lesions. The different labeling strategies provide insight on the pharmacokinetics and biodistribution of HDL's main components (i.e., phospholipids, apo A-I).

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.