Recent advances in molecular imaging of atherosclerotic plaques and thrombosis

Progress in ultrasmall ferrite nanoparticles enhanced T1 magnetic resonance angiography

Contrast-enhanced magnetic resonance angiography (CE-MRA) plays a critical role in diagnosing and monitoring various vascular diseases. Achieving high-sensitivity detection of vascular abnormalities in CE-MRA depends on the properties of contrast agents. In contrast to clinically used gadolinium-based contrast agents (GBCAs), the new generation of ultrasmall ferrite nanoparticles-based contrast agents have high relaxivity, long blood circulation time, easy surface functionalization, and high biocompatibility, hence showing promising prospects in CE-MRA. This review aims to comprehensively summarize the advancements in ultrasmall ferrite nanoparticles-enhanced MRA for detecting vascular diseases. Additionally, this review also discusses the future clinical translational potential of ultrasmall ferrite nanoparticles-based contrast agents for vascular imaging. By investigating the current status of research and clinical applications, this review attempts to outline the progress, challenges, and future directions of using ultrasmall ferrite nanoparticles to drive the field of CE-MRA into a new frontier of accuracy and diagnostic efficacy.

Reactive oxygen species-responsive nano-platform with dual-targeting and fluorescent lipid-specific imaging capabilities for the management of atherosclerotic plaques

Atherosclerosis (AS), a pathological cause of cardiovascular disease, results from endothelial injury, local progressive inflammation, and excessive lipid accumulation. AS plaques rich in foam cells are prone to rupture and form thrombus, which can cause life-threatening complications. Therefore, the assessment of atherosclerotic plaque vulnerability and early intervention are crucial in reducing the mortality rates associated with cardiovascular disease. In this work, A fluorescent probe FC-TPA was synthesized, which switches the fluorescence state between protonated and non-protonated, reducing background fluorescence and enhancing imaging signal-to-noise ratio. On this basis, FC-TPA is loaded into cyclodextrin (CD) modified with phosphatidylserine targeting peptide (PTP) and coated with hyaluronic acid (HA) to construct the intelligent responsive diagnostic nanoplatform (HA@PCFT). HA@PCFT effectively targets atherosclerotic plaques, utilizing dual targeting mechanisms. HA binds strongly to CD44, while PTP binds to phosphatidylserine, enabling nanoparticle aggregation at the lesion site. ROS acts as a smart release switch for probes. Both in vitro and in vivo evaluations confirm impressive lipid-specific fluorescence imaging capabilities of HA@PCFT nanoparticles (NPs). The detection of lipid load in atherosclerotic plaque by fluorescence imaging will aid in assessing the vulnerability of atherosclerotic plaque. STATEMENT OF SIGNIFICANCE: Currently, numerous fluorescent probes have been developed for lipid imaging. However, some challenges including inadequate water solubility, nonspecific distribution patterns, and fluorescence background interference, have greatly limited their further applications in vivo. To overcome these limitations, a fluorescent molecule has been designed and synthesized, thoroughly investigating its photophysical properties through both theoretical and experimental approaches. Interestingly, this fluorescent molecule exhibits the reversible fluorescence switching capabilities, mediated by hydrogen bonds, which effectively mitigate background fluorescence interference. Additionally, the fluorescent molecules has been successfully loaded into nanocarriers functionalized with the active targeting abilities, which has significantly improved the solubility of the fluorescent molecules and reduced their nonspecific distribution in vivo for an efficient target imaging in atherosclerosis. This study provides a valuable reference for evaluating the performance of such fluorescent dyes, and offers a promising perspective on the design of the target delivery systems for atherosclerosis.

Progress of fluorescent probes for protein phosphorylation and glycosylation in atherosclerosis

Exploring the post-translational modification (PTM) of proteins in the course of atherosclerotic disease has important guiding significance for the early warning of atherosclerotic plaque, the development of targeted drugs and the treatment of disease. The advancement advanced detection and imaging methods for phosphorylated and glycosylated proteins is an important tool to further reveal the levels of protein phosphorylation and glycosylation during atherosclerotic plaque formation. We present research strategies for detecting protein phosphorylation and glycosylation from the perspective of fluorescent probes, and discuss the feasibility and future direction of the development of these methods for detecting and imaging phosphorylated and glycosylated proteins in atherosclerotic disease.

Tetrazine-Based Ratiometric Nitric Oxide Sensor Identifies Endogenous Nitric Oxide in Atherosclerosis Plaques by Riding Macrophages as a Smart Vehicle

Atherosclerosis (AS) is the formation of plaques in blood vessels, which leads to serious cardiovascular diseases. Current research has disclosed that the formation of AS plaques is highly related to the foaming of macrophages. However, there is a lack of detailed molecular biological mechanisms. We proposed a "live sensor" by grafting a tetrazine-based ratiometric NO probe within macrophages through metabolic and bio-orthogonal labeling. This "live sensor" was proved to target the AS plaques with a diameter of only tens of micrometers specifically and visualized endogenous NO at two lesion stages in the AS mouse model. The ratiometric signals from the probe confirmed the participation of NO during AS and indicated that the generation of endogenous NO increased significantly as the lesion progressed. Our proposal of this "live sensor" provided a native and smart strategy to target and deliver small molecular probes to the AS plaques at the in vivo level, which can be used as universal platforms for the detection of reactive molecules or microenvironmental factors in AS.

Detection and Imaging of Active Substances in Early Atherosclerotic Lesions Using Fluorescent Probes

Atherosclerosis (AS) is a vascular disease caused by chronic inflammation and lipids that is the main cause of myocardial infarction, stroke and other cardiovascular diseases. Atherosclerosis is often difficult to detect in its early stages due to the absence of clinically significant vascular stenosis. This is not conducive to early intervention or treatment of the disease. Over the past decade, researchers have developed various imaging methods for the detection and imaging of atherosclerosis. At the same time, more and more biomarkers are being found that can be used as targets for detecting atherosclerosis. Therefore, the development of a variety of imaging methods and a variety of targeted imaging probes is an important project to achieve early assessment and treatment of atherosclerosis. This paper provides a comprehensive review of the optical probes used to detect and target atherosclerosis imaging in recent years, and describes the current challenges and future development directions.

In Vivo NIR-II Fluorescence Lifetime Imaging of Whole-Body Vascular Using High Quantum Yield Lanthanide-Doped Nanoparticles

Second near infrared (NIR-II, 1000-1700 nm) fluorescence lifetime imaging is a powerful tool for biosensing, anti-counterfeiting, and multiplex imaging. However, the low photoluminescence quantum yield (PLQY) of fluorescence probes in NIR-II region limits its data collecting efficiency and accuracy, especially in multiplex molecular imaging in vivo. To solve this problem, lanthanide-doped nanoparticles (NPs) β-NaErF4 : 2%Ce@NaYbF4 @NaYF4 with high PLQY and tunable PL lifetime through multi-ion doping and core-shell structural design, are presented. The obtained internal PLQY can reach up to 50.1% in cyclohexane and 9.2% in water under excitation at 980 nm. Inspired by the above results, a fast NIR-II fluorescence lifetime imaging of whole-body vascular in mice is successfully performed by using the homebuilt fluorescence lifetime imaging system, which reveals a murine abdominal capillary network with low background. A further demonstration of fluorescence lifetime multiplex imaging is carried out in molecular imaging of atherosclerosis cells and different organs in vivo through NPs conjugating with specific peptides and different injection modalities, respectively. These results demonstrate that the high PLQY NPs combined with the homebuilt fluorescence lifetime imaging system can realize a fast and high signal-to-noise fluorescence lifetime imaging; thus, opening a road for multiplex molecular imaging of atherosclerosis.

Plexin D1 mediates disturbed flow-induced M1 macrophage polarization in atherosclerosis

Atherosclerosis preferentially develops at bifurcations exposed to disturbed flow. Plexin D1 (PLXND1) responds to mechanical forces and drives macrophage accumulation in atherosclerosis. Here, multiple strategies were used to identify the role of PLXND1 in site-specific atherosclerosis. Using computational fluid dynamics and three-dimensional light-sheet fluorescence-microscopy, the elevated PLXND1 in M1 macrophages was mainly distributed in disturbed flow area of ApoE^-/- carotid bifurcation lesions, and visualization of atherosclerosis in vivo was achieved by targeting PLXND1. Subsequently, to simulate the microenvironment of bifurcation lesions in vitro, we co-cultured oxidized low-density lipoprotein (oxLDL)-treated THP-1-derived macrophages with shear-treated human umbilical vein endothelial cells (HUVECs). We found that oscillatory shear induced the increase of PLXND1 in M1 macrophages, and knocking down PLXND1 inhibited M1 polarization. Semaphorin 3E, the ligand of PLXND1 which was highly expressed in plaques, strongly enhanced M1 macrophage polarization via PLXND1 in vitro. Our findings provide insights into pathogenesis in site-specific atherosclerosis that PLXND1 mediates disturbed flow-induced M1 macrophage polarization.

Scavenger receptor-AI targeted theranostic nanoparticles for regression of atherosclerotic plaques via ABCA1 modulation

ATP-binding cassette transporter A1 (ABCA1) plays a crucial role in atherosclerotic formation through mediated cholesterol efflux in macrophage-derived foam cells. In this study, a scavenger receptors AI (SR-AI) targeted theranostic nanoparticles was constructed for atherosclerosis regression via ABCA1 activation in foam cells. ABCA1-upregulator 5242331 and IR780 were encapsulated in PLGA-PEG micelles which were conjugated with SR-AI targeting peptide (PP1) to formulate the nanoparticles (SAU-NPs). Immunostaining revealed that SR-AI was highly expressed both in macrophage foam cells and in atherosclerotic plaque of ApoE^-/- mice. The SAU-NPs have shown more active targeting to plaque lesion with higher stability compared with non-SR-AI targeted nanoparticles. The transformation from macrophage to foam cells was inhibited by SAU-NPs carried 5242331. Cholesterol deposition was effectively reduced in foam cells by SAU-NPs through activating the LXRα-ABCA1/ABCG1/SR-BI pathway. In conclusion, theranostic SAU-NPs which carried ABCA1-upregulator 5242331 exert beneficial effects on atherosclerosis regression via LXRα activation.

CD40-targeting magnetic nanoparticles for MRI/optical dual-modality molecular imaging of vulnerable atherosclerotic plaques

BACKGROUND AND AIMS

Acute coronary syndrome caused by vulnerable plaque rupture or erosion is a leading cause of death worldwide. CD40 has been reported to be highly expressed in atherosclerotic plaques and closely related to plaque stability. Therefore, CD40 is expected to be a potential target for the molecular imaging of vulnerable plaques in atherosclerosis. We aimed to design a CD40-targeted magnetic resonance imaging (MRI)/optical multimodal molecular imaging probe and explore its ability to detect and target vulnerable atherosclerotic plaques.

METHODS

CD40-Cy5.5 superparamagnetic iron oxide nanoparticles (CD40-Cy5.5-SPIONs), which comprise a CD40-targeting multimodal imaging contrast agent, were constructed by conjugating CD40 antibody and Cy5.5-N-hydroxysuccinimide ester with SPIONs. During this in vitro study, we observed the binding ability of CD40-Cy5.5-SPIONs with RAW 264.7 cells and mouse aortic vascular smooth muscle cells (MOVAS) after different treatments, using confocal fluorescence microscopy and Prussian blue staining. An in vivo study involving ApoE^-/- mice fed a high-fat diet for 24-28 weeks was performed. 24 h after intravenous injection of CD40-Cy5.5-SPIONs, fluorescence imaging and MRI were performed.

RESULTS

CD40-Cy5.5-SPIONs bind specifically to tumor necrosis factor (TNF)-α-treated macrophages and smooth muscle cells. Fluorescence imaging results showed that, compared with the control group and the atherosclerosis group injected with non-specific bovine serum albumin (BSA)-Cy5.5-SPIONs, the atherosclerotic group injected with CD40-Cy5.5-SPIONs had a stronger fluorescence signal. T2-weighted images showed that the carotid arteries of atherosclerotic mice injected with CD40-Cy5.5-SPIONs had a significant substantial T2 contrast enhancement effect.

CONCLUSIONS

CD40-Cy5.5-SPIONs could potentially serve as an effective MRI/optical probe for vulnerable atherosclerotic plaques during non-invasive detection.

Assessing the Progression of Early Atherosclerosis Mice Using a Fluorescence Nanosensor for the Simultaneous Detection and Imaging of pH and Phosphorylation

The inflammatory microenvironment involves changes in pH and protein phosphorylation state and is closely related to the occurrence and development of atherosclerosis (AS). Herein, we constructed a dual-detection fluorescence nanosensor PCN-NP-HPZ based on post modification of MOFs, which realized the simultaneous detection and imaging of pH and phosphorylation through the pH-sensitive group piperazine and the Zr^IV node of the MOFs. The sensors were used to monitor changes in blood pH and phosphate levels at different time stages during atherosclerotic plaque formation. Two-photon fluorescence imaging was also performed in the vascular endothelium. Blood tests combined with two-photon fluorescence images indicated that in the early stage of AS, blood and tissue pH levels were lower than that of the normal mice, while phosphate and tissue phosphorylation levels were higher than that of the normal mice. The present study provides a new analysis method for the assessment of early atherosclerotic disease.

A Lipid Activatable Fluorescence Probe for Atherosclerosis Imaging

Lipid has been considered as a promising target for atherosclerosis diagnosis. However, there is still no available lipid imaging technology in clinic. Herein, we have prepared a fluorescence probe TPN for lipid-specific imaging in atherosclerosis. TPN exhibited extremely weak emission in water, while its emission was significantly enhanced in lipid environment at 666nm. Meanwhile, TPN has showed low cytotoxicity and great intracellular lipid-specific fluorescence imaging ability with high signal-to-noise ratio. Importantly, TPN could specifically stain the lipid in atherosclerotic plaque, which would be a potential candidate for the diagnosis of atherosclerosis.

Targeted Imaging in Atherosclerosis

Atherosclerosis is a chronic inflammatory disease involved in plaque rupture, stroke, thrombosis, and heart attack (myocardial infarction), which is a leading cause of sudden cardiovascular events. In the past decades, various imaging strategies have been designed and employed for the diagnosis of atherosclerosis. Targeted imaging can accurately distinguish pathological tissues from normal tissues and reliably reveal biological information in the occurrence and development of atherosclerosis. By taking advantage of versatile imaging techniques, rationally designed imaging probes targeting biomarkers overexpressed in plaque microenvironments and targeting activated cells by modifying specific ligands accumulated in lesion regions have attracted increasing attention. This Perspective elucidates comprehensively the targeted imaging strategies, current challenges, and future development directions for precise identification and diagnosis of atherosclerosis, which is beneficial to better understand the physiological and pathological progression and exploit novel imaging strategies.

Immune-Associated Gene Signatures and Subtypes to Predict the Progression of Atherosclerotic Plaques Based on Machine Learning

Objective: Experimental and clinical evidence suggests that atherosclerosis is a chronic inflammatory disease. Our study was conducted for uncovering the roles of immune-associated genes during atherosclerotic plaque progression.

Methods: Gene expression profiling of GSE28829, GSE43292, GSE41571, and GSE120521 datasets was retrieved from the GEO database. Three machine learning algorithms, least absolute shrinkage, and selection operator (LASSO), random forest, and support vector machine–recursive feature elimination (SVM-RFE) were utilized for screening characteristic genes among atherosclerotic plaque progression- and immune-associated genes. ROC curves were generated for estimating the diagnostic efficacy. Immune cell infiltrations were estimated via ssGSEA, and immune checkpoints were quantified. CMap analysis was implemented to screen potential small-molecule compounds. Atherosclerotic plaque specimens were classified using a consensus clustering approach.

Results: Seven characteristic genes (TNFSF13B, CCL5, CCL19, ITGAL, CD14, GZMB, and BTK) were identified, which enabled the prediction of progression of atherosclerotic plaques. Higher immune cell infiltrations and immune checkpoint expressions were found in advanced-stage than in early-stage atherosclerotic plaques and were positively linked to characteristic genes. Patients could clinically benefit from the characteristic gene-based nomogram. Several small molecular compounds were predicted based on the characteristic genes. Two subtypes, namely, C1 immune subtype and C2 non-immune subtype, were classified across atherosclerotic plaques. The characteristic genes presented higher expression in C1 than in C2 subtypes.

Conclusion: Our findings provide several promising atherosclerotic plaque progression- and immune-associated genes as well as immune subtypes, which might enable to assist the design of more accurately tailored cardiovascular immunotherapy.

Computational Study of Double Transition Metal Atom Anchored on Graphdiyne Monolayer for Nitrogen Electroreduction

Converting N₂ to NH₃ is an essential reaction but remains a great challenge for industries. Developing more efficient catalysts for N₂ reduction under mild conditions is of vital importance. In this work, double transition metal atoms (TM=Mo, W, Nb and Ru) anchored on graphdiyne monolayer (TM₂ @GDY) as electrocatalysts are designed, and the corresponding reaction mechanisms of N₂ electroreduction are systematically investigated by means of first-principles calculations. The results show that the double TM atoms can be strongly anchored on the acetylenic ring of GDY and Ru₂ @GDY exhibits the highest catalytic activity for NRR with a maximum free energy change of 0.55 eV through the enzymatic pathway. The significant charge transfer between the substrate and the adsorbed N₂ molecule is responsible for the superior catalytic activity. This work could provide a new approach for the rational design of double-atom catalysts for NRR and other related reduction reactions.

Coronary Atherosclerotic Plaque Regression: JACC State-of-the-Art Review

Over the last 3 decades there have been substantial improvements in treatments aimed at reducing cardiovascular (CV) events. As these treatments have been developed, there have been parallel improvements in coronary imaging modalities that can assess plaque volumes and composition, using both invasive and noninvasive techniques. Plaque progression can be seen to precede CV events, and therefore, many studies have longitudinally assessed changes in plaque characteristics in response to various treatments, aiming to demonstrate plaque regression and improvements in high-risk features, with the rationale being that this will reduce CV events. In the past, decisions surrounding treatments for atherosclerosis have been informed by population-based risk scores for initiation in primary prevention and low-density lipoprotein cholesterol levels for titration in secondary prevention. If outcome data linking plaque regression to reduced CV events emerge, it may become possible to directly image plaque treatment response to guide management decisions.

Near-Infrared Fluorescence Imaging of Carotid Plaques in an Atherosclerotic Murine Model

Successful imaging of atherosclerosis, one of the leading global causes of death, is crucial for diagnosis and intervention. Near-infrared fluorescence (NIRF) imaging has been widely adopted along with multimodal/hybrid imaging systems for plaque detection. We evaluate two macrophage-targeting fluorescent tracers for NIRF imaging (TLR4-ZW800-1C and Feraheme-Alexa Fluor 750) in an atherosclerotic murine cohort, where the left carotid artery (LCA) is ligated to cause stenosis, and the right carotid artery (RCA) is used as a control. Imaging performed on dissected tissues revealed that both tracers had high uptake in the diseased vessel compared to the control, which was readily visible even at short exposure times. In addition, ZW800-1C's renal clearance ability and Feraheme's FDA approval puts these two tracers in line with other NIRF tracers such as ICG. Continued investigation with these tracers using intravascular NIRF imaging and larger animal models is warranted for clinical translation.

Enzyme-activated probes in optical imaging: a focus on atherosclerosis

Enzyme-activated probes enable complex biological processes to be studied in real-time. A wide range of enzymes are modulated in diseases, including cancer, inflammatory diseases and cardiovascular disease, and have the potential to act as vital diagnostic and prognostic biomarkers to monitor and report on disease progression. In this perspective article, we discuss suitable design characteristics of enzyme-activated fluorescent probes for ex vivo and in vivo optical imaging applications. With a particular focus on atherosclerosis imaging, we highlight recent approaches to report on the activity of cathepsins (K and B), matrix metalloproteinases (MMP-2 and MMP-9), thrombin, heme oxygenase-1 (HO-1) and myeloperoxidase (MPO).

Ultrasmall superparamagnetic iron oxide nanoparticles: A next generation contrast agent for magnetic resonance imaging

As a research hotspot, the development of magnetic resonance imaging (MRI) contrast agents has attracted great attention over the past decades for improving the accuracy of diagnosis. Ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles with core diameter smaller than 5.0 nm are expected to become a next generation of contrast agents owing to their excellent MRI performance, long blood circulation time upon proper surface modification, renal clearance capacity, and remarkable biosafety profile. On top of these merits, USPIO nanoparticles are used for developing not only T₁ contrast agents, but also T₂ /T₁ switchable contrast agents via assembly/disassembly approaches. In recent years, as a new type of contrast agents, USPIO nanoparticles have shown considerable applications in the diagnosis of various diseases such as vascular pathological changes and inflammations apart from malignant tumors. In this review, we are focusing on the state-of-the-art developments and the latest applications of USPIO nanoparticles as MRI contrast agents to discuss their advantages and future prospects. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Molecular Imaging and Non-molecular Imaging of Atherosclerotic Plaque Thrombosis

Thrombosis in the context of atherosclerosis typically results in life-threatening consequences, including acute coronary events and ischemic stroke. As such, early detection and treatment of thrombosis in atherosclerosis patients is essential. Clinical diagnosis of thrombosis in these patients is typically based upon a combination of imaging approaches. However, conventional imaging modalities primarily focus on assessing the anatomical structure and physiological function, severely constraining their ability to detect early thrombus formation or the processes underlying such pathology. Recently, however, novel molecular and non-molecular imaging strategies have been developed to assess thrombus composition and activity at the molecular and cellular levels more accurately. These approaches have been successfully used to markedly reduce rates of atherothrombotic events in patients suffering from acute coronary syndrome (ACS) by facilitating simultaneous diagnosis and personalized treatment of thrombosis. Moreover, these modalities allow monitoring of plaque condition for preventing plaque rupture and associated adverse cardiovascular events in such patients. Sustained developments in molecular and non-molecular imaging technologies have enabled the increasingly specific and sensitive diagnosis of atherothrombosis in animal studies and clinical settings, making these technologies invaluable to patients' health in the future. In the present review, we discuss current progress regarding the non-molecular and molecular imaging of thrombosis in different animal studies and atherosclerotic patients.

In vivostudy of iron oxide-calcium phosphate composite nanoparticles for delivery to atherosclerosis

Atherosclerosis is a macrophage-related inflammatory disease that remains a leading cause of death worldwide. Magnetic iron oxide (IO) nanocrystals are clinically used as magnetic resonance imaging contrast agents and their application as a detection agent for macrophages in arterial lesions has been studied extensively. We recently fabricated heparin-modified calcium phosphate (CaP) nanoparticles loaded with a large number of IO nanocrystals via coprecipitation from a supersaturated CaP solution supplemented with heparin and ferucarbotran (IO nanocrystals coated with carboxydextran). In this study, we further increased the content of IO nanocrystals in the heparin-modified IO-CaP composite nanoparticles by increasing the ferucarbotran concentration in the supersaturated CaP solution. The increase in nanoparticle IO content caused a decrease in particle diameter without impairing its dispersibility; the nanoparticles remained dispersed in water for up to 2 h due to electrostatic repulsion between particles due to the surface modification with heparin. The nanoparticles were more effectively taken up by murine RAW264.7 macrophages compared to free ferucarbotran without showing significant cytotoxicity. A preliminaryin vivostudy showed that the nanoparticles injected intravenously into mice delivered more IO nanocrystals to macrophage-rich carotid arterial lesions than free ferucarbotran. Our nanoparticles have potential as a delivery agent of IO nanocrystals to macrophages in arterial lesions.

Near-infrared Fluorophores for Thrombosis Diagnosis and Therapy

Thrombosis is an adverse physiological event wherein the resulting thrombus and thrombus-induced diseases collectively result in high morbidity and mortality rates. Currently, nano-medicines that incorporate fluorophores emitting in the near-infrared-I (NIR-I, 700-900 nm) spectral region into their systems have been adopted to afford thrombosis theranostics. However, several unsolved problems such as limited penetration depth and image quality severely impede further applications of such nano-medicine systems. Fortunately, the ability to incorporate fluorophores emitting in the NIR-II (1000-1700 nm) window into nano-medicine systems can unambiguously identify biological processes with high signal-to-noise, deep tissue penetration depth, and high image resolution. Considering the inherently favorable properties of NIR-II fluorophores, we believe such have enormous potential to quickly become incorporated into nano-medicine systems for thrombosis theranostics. In this review, we i) discuss the development of NIR fluorescence as an imaging modality and fluorescent agents; ii) comprehensively summarize the recent development of NIR-I fluorophore-based nano-medicine systems for thrombosis theranostics; iii) highlight the state-of-the-art NIR-II fluorophores that have been designed for the specific purpose of affording thrombotic diagnosis; iv) speculate on possible forward avenues for the use of NIR-II fluorophores towards thrombosis diagnosis and therapy; and v) discuss the potential for their clinical translation.

An intelligent T1-T2 switchable MRI contrast agent for the non-invasive identification of vulnerable atherosclerotic plaques

Unlike stable atherosclerotic plaques, vulnerable plaques are very likely to cause serious cardio-cerebrovascular diseases. Meanwhile, how to non-invasively identify vulnerable plaques at early stages has been an urgent but challenging problem in clinical practices. Here, we propose a macrophage-targeted and in situ stimuli-triggered T₁-T₂ switchable magnetic resonance imaging (MRI) nanoprobe for the non-invasive diagnosis of vulnerable plaques. Precisely, single-dispersed iron oxide nanoparticles (IONPs) modified with hyaluronic acid (HA), denoted as IONP-HP, show macrophage targetability and T₁ MRI enhancement (r₂/r₁ = 3.415). Triggered by the low pH environment of macrophage lysosomes, the single-dispersed IONP-HP transforms into a cluster analogue, which exhibits T₂ MRI enhancement (r₂/r₁ = 13.326). Furthermore, an in vivo switch of T₁-T₂ enhancement modes shows that the vulnerable plaques exhibit strong T₁ enhancement after intravenous administration of the nanoprobe, followed by a switch to T₂ enhancement after 9 h. In contrast, stable plaques show only slight T₁ enhancement but without T₂ enhancement. It is therefore imperative that the intelligent and novel nanoplatform proposed in this study achieves a substantial non-invasive diagnosis of vulnerable plaques by means of a facile but effective T₁-T₂ switchable process, which will significantly contribute to the application of materials science in solving clinical problems.

Protein nanoparticles in molecular, cellular, and tissue imaging

The quest to develop ideal nanoparticles capable of molecular, cellular, and tissue level imaging is ongoing. Since certain imaging probes and nanoparticles face drawbacks such as low aqueous solubility, increased ROS generation leading to DNA damage, apoptosis, and high cellular/organ toxicities, the development of versatile and biocompatible nanocarriers becomes necessary. Protein nanoparticles (PNPs) are one such promising class of nanocarriers that possess most of the desirable properties of an ideal nanocarrier for bioimaging applications. PNPs demonstrate high aqueous solubility, minimal cytotoxicity, and multi-cargo loading capacity. They are also amenable to surface-functionalization, as well as modulation of their hydrophobicity and hydrophilicity. The use of PNPs for bioimaging applications has made rapid advancements in the past two decades. Being comparatively less explored, the field opens up a plethora of opportunities and focus areas to engineer ideal bioimaging protein nanocarriers. The use of PNPs as carriers of their natural ligands as well as other heavy metals and fluorescent probes, along with drug molecules for combined theranostic applications has been reported. In addition, surface functionalization to impart specificity of targeting the PNPs has been shown to reduce nonspecific cellular interactions, thus reducing systemic toxicity. PNPs have been explored for their application in imaging of numerous cancers, cardiovascular diseases as well as imaging of the brain using near infrared fluorescence (NIRF) imaging, magnetic resonance imaging (MRI), X-ray computed tomography (CT), positron emission tomography (PET), single-photon emission computed tomography (SPECT), ultrasound (US), and photoacoustic (PA) imaging. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Treatment of atherosclerosis through transplantation of endothelial progenitor cells overexpressing dimethylarginine dimethylaminohydrolase (DDAH) in rabbits

BACKGROUND

Endothelial dysfunction is a key event in the development of vascular diseases, including atherosclerosis. Endothelial progenitor cells (EPCs) play an important role in vascular repair. Decreased dimethylarginine dimethylaminohydrolase (DDAH) activity is observed in several pathological conditions, and it is associated with an increased risk of vascular disease. We hypothesized that bone marrow-derived EPCs and combination therapy with DDAH2-EPCs could reduce plaque size and ameliorate endothelial dysfunction in an atherosclerosis rabbit model.

METHOD

Four groups of rabbits (n = 8 per group) were subjected to a hyperlipidemic diet for a month. After establishing the atherosclerosis model, rabbits received 4 × 10⁶ EPC, EPCs expressing DDAH2, through femoral vein injection, or saline (the control group with basic food and the untreated group). One month after transplantation, plaque thickness, endothelial function, oxidative stress, and inflammatory mRNAs, DDAH, and eNOS function were assessed.

RESULTS

DDAH2-EPCs transplantation (p < 0.05) and EPCs transplantation (p < 0.05) were both associated with a reduction in plaque size compared to the control saline injection. The antiproliferative and antiatherogenic effects of EPCs were further enhanced by the overexpression of DDAH2 (p < 0.05, DDAH2-EPCs vs. EPCs). Furthermore, DDAH2-EPCs transplantation significantly increased endothelium integrity compared to the EPCs transplantation.

CONCLUSION

Transplantation of EPCs overexpressing DDAH2 may enhance the repair of injured endothelium by reducing inflammation and restoring endothelial function. Therefore, pCMV6-mediated DDAH2 gene-transfected EPCs are a potentially valuable tool for the treatment of atherosclerosis.

Recent advances in improving tumor-targeted delivery of imaging nanoprobes

Tumor-targeted delivery of imaging nanoprobes provides a promising approach for the precision imaging diagnosis of cancers. Nanoprobes with desired bio-nano interface properties can preferably enter tumor tissues through the vascular endothelium, penetrate into deep tissues, and detect target lesions. Surface engineering of nanoparticles offers a critical strategy to improve tumor-targeting capacities of nanoprobes. Improvements to the efficacy of targeted nanoprobes have been intensively explored and much of this work centers on the selection of suitable targeting ligands. Herein, in this review, various recent strategies based on different targeting ligands to improve tumor-targeting of imaging nanoprobes have been developed, ranging from small molecule ligands to biomimetic coatings, with highlights on emerging coating techniques using cell membranes and dual-targeting ligands. In particular, construction and surface modification methods, targeting capacities, and imaging/theranostic performance with key issues and potential questions have been described and discussed together with considerations for future development and innovations.