MRI detection of single particles for cellular imaging

Lipid nanoparticles encapsulating curcumin for imaging and stabilization of vulnerable atherosclerotic plaques via phagocytic "eat-me" signals

Curcumin potentiates the stabilization of atherosclerotic plaques by polarizing macrophages, but its non-specific targeting hinders its clinical application. We aim to harness multifunctional lipid nanoparticles (MLNPs) to facilitate the imaging and targeted delivery of curcumin specifically to inflammatory macrophages, counteracting vulnerable plaques and mitigating the risk of ischemic events. Cholesteryl-9-carboxynonanoate-(125I‑iron oxide nanoparticle/Curcumin)-lipid-coated nanoparticles [9-CCN-(125I-ION/Cur)-LNPs], namely MLNPs, are designed to carry hybrid imaging agents. These agents combine 125I-ION with lipids containing phagocytic 'eat-me' signals, inducing macrophages to engulf the MLNPs. Our research demonstrates that the designed MLNPs accurately accumulate at unstable plaques and are precisely visualized and highlighted by both SPECT and MRI. Furthermore, MLNPs achieve high efficiency in delivering 125I-ION and curcumin to macrophages, ultimately leading to significant M1-to-M2 macrophage polarization. These real-time imaging and polarization capabilities of plaques have immediate clinical applicability and may pave the way for novel therapies to stabilize unstable atherosclerotic plaques.

Immuno-MRI for Stroke Diagnosis and Prognosis

Following a stroke, an inflammatory response occurs, characterized by an increased blood-brain barrier permeability, expression of endothelial trafficking molecules, and infiltration of immune cells. Adhesion molecules expressed on activated brain endothelial cells are potential biomarkers of intraparenchymal inflammation. However, in current clinical practice, it is not possible to measure endothelial activation using clinically available imaging. Using targeted micro-sized particles of iron oxide (MPIO), immuno-MRI enables the detection of endothelial adhesion molecules at high resolution and, consequently, facilitates the detection of stroke-induced brain inflammation. In this review, we highlight the most recent studies that used immuno-MRI in models of neurovascular disorders, including transient ischemic attack, ischemic stroke, intracranial hemorrhage, and subarachnoid hemorrhage. We also discuss the potential of immuno-MRI in clinical practice and the necessary next steps for its implementation in patients.

Multimodal MRI reveals brainstem connections that sustain wakefulness in human consciousness

Consciousness is composed of arousal (i.e., wakefulness) and awareness. Substantial progress has been made in mapping the cortical networks that underlie awareness in the human brain, but knowledge about the subcortical networks that sustain arousal in humans is incomplete. Here, we aimed to map the connectivity of a proposed subcortical arousal network that sustains wakefulness in the human brain, analogous to the cortical default mode network (DMN) that has been shown to contribute to awareness. We integrated data from ex vivo diffusion magnetic resonance imaging (MRI) of three human brains, obtained at autopsy from neurologically normal individuals, with immunohistochemical staining of subcortical brain sections. We identified nodes of the proposed default ascending arousal network (dAAN) in the brainstem, hypothalamus, thalamus, and basal forebrain. Deterministic and probabilistic tractography analyses of the ex vivo diffusion MRI data revealed projection, association, and commissural pathways linking dAAN nodes with one another and with DMN nodes. Complementary analyses of in vivo 7-tesla resting-state functional MRI data from the Human Connectome Project identified the dopaminergic ventral tegmental area in the midbrain as a widely connected hub node at the nexus of the subcortical arousal and cortical awareness networks. Our network-based autopsy methods and connectivity data provide a putative neuroanatomic architecture for the integration of arousal and awareness in human consciousness.

MRI-Based Cell Tracking of OATP-Expressing Cell Transplants by Pre-Labeling with Gd-EOB-DTPA

PURPOSE

A critical step in cell-based therapies is determining the exact position of transplanted cells immediately post-transplant. Here, we devised a method to detect cell transplants immediately post-transplant, using a clinical gadolinium-based contrast agent. These cells were detected as hyperintense signals using a clinically familiar T1-weighted MRI protocol.

PROCEDURES

HEK293 cells were stably transduced to express human OATP1B3, a hepatic organic anion transporting polypeptide that transports Gd-EOB-DTPA into cells that express the transporters, the intracellular accumulation of which cells causes signal enhancement on T1-weighted MRI. Cells were pre-labeled prior to injection in media containing Gd-EOB-DTPA for MRI evaluation and indocyanine green for cryofluorescence tomography validation. Labeled cells were injected into chicken hearts, in vitro, after which MRI and cryofluorescence tomography were performed in sequence.

RESULTS

OATP1B3-expressing cells had substantially reduced T1 following labeling with Gd-EOB-DTPA in culture. Following their implantation into chicken heart, these cells were robustly identified in T1-weighted MRI, with image-derived injection volumes of cells commensurate with intended injection volumes. Cryofluorescence tomography showed that the areas of signal enhancement in MRI overlapped with areas of indocyanine green signal, indicating that MRI signal enhancement was due to the transplanted cells.

CONCLUSIONS

OATP1B3-expressing cells can be pre-labeled with Gd-EOB-DTPA prior to injection into tissue, affording the use of clinically familiar T1-weighted MRI to robustly detect cell transplants immediately after transplant. This procedure is easily generalizable and has potential advantages over the use of iron oxide based cell labeling agents and imaging procedures.

Exploration of sialic acid receptors as a potential target for cancer treatment: A comprehensive review

The potential to target anticancer drugs directly to cancer cells is the most difficult challenge in the current scenario. Progressive works are being done on multifarious receptors and are on the horizon, expected to facilitate tailored treatment for cancer. Among several receptors, one is the sialic acid (SA) receptor by which cancer cells can be targeted directly as hyper sialylation is one of the most distinguishing characteristics of cancer cells. SA receptors have shown tremendous potential for tumor targeting because of their elevated expression in a range of human malignancies including prostate, breast, gastric cells, myeloid leukemia, liver, etc. This article reviews the overexpression of SA receptors in various tumors and diverse strategies for targeting these receptors to deliver drugs, enzymes, and genes for therapeutic applications. It also summarizes the diagnostic applications of SA-grafted nanoparticles for imaging various SA-overexpressing cancer cells and technological advances that are propelling sialic acid to the forefront of cancer therapy.

Medical Imaging Technology for Micro/Nanorobots

Due to their enormous potential to be navigated through complex biological media or narrow capillaries, microrobots have demonstrated their potential in a variety of biomedical applications, such as assisted fertilization, targeted drug delivery, tissue repair, and regeneration. Numerous initial studies have been conducted to demonstrate the biomedical applications in test tubes and in vitro environments. Microrobots can reach human areas that are difficult to reach by existing medical devices through precise navigation. Medical imaging technology is essential for locating and tracking this small treatment machine for evaluation. This article discusses the progress of imaging in tracking the imaging of micro and nano robots in vivo and analyzes the current status of imaging technology for microrobots. The working principle and imaging parameters (temporal resolution, spatial resolution, and penetration depth) of each imaging technology are discussed in depth.

Cell specificity of Manganese-enhanced MRI signal in the cerebellum

Magnetic Resonance Imaging (MRI) resolution continues to improve, making it important to understand the cellular basis for different MRI contrast mechanisms. Manganese-enhanced MRI (MEMRI) produces layer-specific contrast throughout the brain enabling in vivo visualization of cellular cytoarchitecture, particularly in the cerebellum. Due to the unique geometry of the cerebellum, especially near the midline, 2D MEMRI images can be acquired from a relatively thick slice by averaging through areas of uniform morphology and cytoarchitecture to produce very high-resolution visualization of sagittal planes. In such images, MEMRI hyperintensity is uniform in thickness throughout the anterior-posterior axis of sagittal sections and is centrally located in the cerebellar cortex. These signal features suggested that the Purkinje cell layer, which houses the cell bodies of the Purkinje cells and the Bergmann glia, is the source of hyperintensity. Despite this circumstantial evidence, the cellular source of MRI contrast has been difficult to define. In this study, we quantified the effects of selective ablation of Purkinje cells or Bergmann glia on cerebellar MEMRI signal to determine whether signal could be assigned to one cell type. We found that the Purkinje cells, not the Bergmann glia, are the primary of source of the enhancement in the Purkinje cell layer. This cell-ablation strategy should be useful for determining the cell specificity of other MRI contrast mechanisms.

Multinuclear MRI Reveals Early Efficacy of Stem Cell Therapy in Stroke

Compromised adult human mesenchymal stem cells (hMSC) can impair cell therapy efficacy and further reverse ischemic recovery. However, in vitro assays require extended passage to characterize cells, limiting rapid assessment for therapeutic potency. Multinuclear magnetic resonance imaging and spectroscopy (MRI/S) provides near real-time feedback on disease progression and tissue recovery. Applied to ischemic stroke, 23Na MRI evaluates treatment efficacy within 24 h after middle cerebral artery occlusion, showing recovery of sodium homeostasis and lesion reduction in specimens treated with hMSC while 1H MRS identifies reduction in lactate levels. This combined metric was confirmed by evaluating treatment groups receiving healthy or compromised hMSC versus vehicle (sham saline injection) over 21 days. Behavioral tests to assess functional recovery and cell analysis for immunomodulatory and macrophage activity to detect hMSC potency confirm MR findings. Clinically, these MR metrics may prove critical to early evaluations of therapeutic efficacy and overall stroke recovery.

Sustaining wakefulness: Brainstem connectivity in human consciousness

Consciousness is comprised of arousal (i.e., wakefulness) and awareness. Substantial progress has been made in mapping the cortical networks that modulate awareness in the human brain, but knowledge about the subcortical networks that sustain arousal is lacking. We integrated data from ex vivo diffusion MRI, immunohistochemistry, and in vivo 7 Tesla functional MRI to map the connectivity of a subcortical arousal network that we postulate sustains wakefulness in the resting, conscious human brain, analogous to the cortical default mode network (DMN) that is believed to sustain self-awareness. We identified nodes of the proposed default ascending arousal network (dAAN) in the brainstem, hypothalamus, thalamus, and basal forebrain by correlating ex vivo diffusion MRI with immunohistochemistry in three human brain specimens from neurologically normal individuals scanned at 600-750 μm resolution. We performed deterministic and probabilistic tractography analyses of the diffusion MRI data to map dAAN intra-network connections and dAAN-DMN internetwork connections. Using a newly developed network-based autopsy of the human brain that integrates ex vivo MRI and histopathology, we identified projection, association, and commissural pathways linking dAAN nodes with one another and with cortical DMN nodes, providing a structural architecture for the integration of arousal and awareness in human consciousness. We release the ex vivo diffusion MRI data, corresponding immunohistochemistry data, network-based autopsy methods, and a new brainstem dAAN atlas to support efforts to map the connectivity of human consciousness.

Dual Labeling of Primary Cells with Fluorescent Gadolinium Oxide Nanoparticles

The interest in mesenchymal stromal cells as a therapy option is increasing rapidly. To improve their implementation, location, and distribution, the properties of these must be investigated. Therefore, cells can be labeled with nanoparticles as a dual contrast agent for fluorescence and magnetic resonance imaging (MRI). In this study, a more efficient protocol for an easy synthesis of rose bengal-dextran-coated gadolinium oxide (Gd₂O₃-dex-RB) nanoparticles within only 4 h was established. Nanoparticles were characterized by zeta potential measurements, photometric measurements, fluorescence and transmission electron microscopy, and MRI. In vitro cell experiments with SK-MEL-28 and primary adipose-derived mesenchymal stromal cells (ASC), nanoparticle internalization, fluorescence and MRI properties, and cell proliferation were performed. The synthesis of Gd₂O₃-dex-RB nanoparticles was successful, and they were proven to show adequate signaling in fluorescence microscopy and MRI. Nanoparticles were internalized into SK-MEL-28 and ASC via endocytosis. Labeled cells showed sufficient fluorescence and MRI signal. Labeling concentrations of up to 4 mM and 8 mM for ASC and SK-MEL-28, respectively, did not interfere with cell viability and proliferation. Gd₂O₃-dex-RB nanoparticles are a feasible contrast agent to track cells via fluorescence microscopy and MRI. Fluorescence microscopy is a suitable method to track cells in in vitro experiments with smaller samples.

Cellular 1H MR Relaxation Times in Healthy and Cancer Three-Dimensional (3D) Breast Cell Culture

Noninvasive measurements of 1H Magnetic Resonance Imaging (MR) relaxation times in a three-dimensional (3D) cell culture construct are presented. Trastuzumab was used as a pharmacological component delivered to the cells in vitro. The purpose of this study was to evaluate the Trastuzumab delivery by relaxation times in 3D cell cultures. The bioreactor has been designed and used for 3D cell cultures. Four bioreactors were prepared, two with normal cells and two with breast cancer cells. The relaxation times of HTB-125 and CRL 2314 cell cultures were determined. An immunohistochemistry (IHC) test was performed before MRI measurements to confirm the amount of HER2 protein in the CRL-2314 cancer cells. The results showed that the relaxation time of CRL2314 cells is lower than normal HTB-125 cells in both cases, before and after treatment. An analysis of the results showed that 3D culture studies have potential in evaluating treatment efficacy using relaxation times measurements with a field of 1.5 Tesla. The use 1H MRI relaxation times allows for the visualization of cell viability in response to treatment.

Intelligent Micro-/Nanorobots for Cancer Theragnostic

Cancer is one of the most intractable diseases owing to its high mortality rate and lack of effective diagnostic and treatment tools. Advancements in micro-/nanorobot (MNR)-assisted sensing, imaging, and therapeutics offer unprecedented opportunities to develop MNR-based cancer theragnostic platforms. Unlike ordinary nanoparticles, which exhibit Brownian motion in biofluids, MNRs overcome viscous resistance in an ultralow Reynolds number (Re << 1) environment by effective self-propulsion. This unique locomotion property has motivated the advanced design and functionalization of MNRs as a basis for next-generation cancer-therapy platforms, which offer the potential for precise distribution and improved permeation of therapeutic agents. Enhanced barrier penetration, imaging-guided operation, and biosensing are additionally studied to enable the promising cancer-related applications of MNRs. Herein, the recent advances in MNR-based cancer therapy are comprehensively addresses, including actuation engines, diagnostics, medical imaging, and targeted drug delivery; promising research opportunities that can have a profound impact on cancer therapy over the next decade is highlighted.

Biocompatible Iron Oxide Nanoring-Labeled Mesenchymal Stem Cells: An Innovative Magnetothermal Approach for Cell Tracking and Targeted Stroke Therapy

Labeling stem cells with magnetic nanoparticles is a promising technique for in vivo tracking and magnetic targeting of transplanted stem cells, which is critical for improving the therapeutic efficacy of cell therapy. However, conventional endocytic labeling with relatively poor labeling efficiency and a short labeling lifetime has hindered the implementation of these innovative enhancements in stem-cell-mediated regenerative medicine. Herein, we describe an advanced magnetothermal approach to label mesenchymal stem cells (MSCs) efficiently by local induction of heat-enhanced membrane permeability for magnetic resonance imaging (MRI) tracking and targeted therapy of stroke, where biocompatible γ-phase, ferrimagnetic vortex-domain iron oxide nanorings (γ-FVIOs) with superior magnetoresponsive properties were used as a tracer. This approach facilitates a safe and efficient labeling of γ-FVIOs as high as 150 pg of Fe per cell without affecting the MSCs proliferation and differentiation, which is 3.44-fold higher than that by endocytosis labeling. Such a high labeling efficiency not only enables the ultrasensitive magnetic resonance imaging (MRI) detection of sub-10 cells and long-term tracking of transplanted MSCs over 10 weeks but also endows transplanted MSCs with a magnetic manipulation ability in vivo. A proof-of-concept study using a rat stroke model showed that the labeled MSCs facilitated MRI tracking and magnetic targeting for efficient replacement therapy with a significantly reduced dosage of 5 × 10⁴ transplanted cells. The findings in this study have demonstrated the great potential of the magnetothermal approach as an efficient labeling technique for future clinical usage.

In vivo molecular and single cell imaging

Molecular imaging is used to improve the disease diagnosis, prognosis, monitoring of treatment in living subjects. Numerous molecular targets have been developed for various cellular and molecular processes in genetic, metabolic, proteomic, and cellular biologic level. Molecular imaging modalities such as Optical Imaging, Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), and Computed Tomography (CT) can be used to visualize anatomic, genetic, biochemical, and physiologic changes in vivo. For in vivo cell imaging, certain cells such as cancer cells, immune cells, stem cells could be labeled by direct and indirect labeling methods to monitor cell migration, cell activity, and cell effects in cell-based therapy. In case of cancer, it could be used to investigate biological processes such as cancer metastasis and to analyze the drug treatment process. In addition, transplanted stem cells and immune cells in cell-based therapy could be visualized and tracked to confirm the fate, activity, and function of cells. In conventional molecular imaging, cells can be monitored in vivo in bulk non-invasively with optical imaging, MRI, PET, and SPECT imaging. However, single cell imaging in vivo has been a great challenge due to an extremely high sensitive detection of single cell. Recently, there has been great attention for in vivo single cell imaging due to the development of single cell study. In vivo single imaging could analyze the survival or death, movement direction, and characteristics of a single cell in live subjects. In this article, we reviewed basic principle of in vivo molecular imaging and introduced recent studies for in vivo single cell imaging based on the concept of in vivo molecular imaging.

Early detection of cerebrovascular pathology and protective antiviral immunity by MRI

Central nervous system (CNS) infections are a major cause of human morbidity and mortality worldwide. Even patients that survive CNS infections can have lasting neurological dysfunction resulting from immune and pathogen induced pathology. Developing approaches to noninvasively track pathology and immunity in the infected CNS is crucial for patient management and development of new therapeutics. Here, we develop novel MRI-based approaches to monitor virus-specific CD8+ T cells and their relationship to cerebrovascular pathology in the living brain. We studied a relevant murine model in which a neurotropic virus (vesicular stomatitis virus) was introduced intranasally and then entered the brain via olfactory sensory neurons - a route exploited by many pathogens in humans. Using T2*-weighted high-resolution MRI, we identified small cerebral microbleeds as an early form of pathology associated with viral entry into the brain. Mechanistically, these microbleeds occurred in the absence of peripheral immune cells and were associated with infection of vascular endothelial cells. We monitored the adaptive response to this infection by developing methods to iron label and track individual virus specific CD8+ T cells by MRI. Transferred antiviral T cells were detected in the brain within a day of infection and were able to reduce cerebral microbleeds. These data demonstrate the utility of MRI in detecting the earliest pathological events in the virally infected CNS as well as the therapeutic potential of antiviral T cells in mitigating this pathology.

In vivo MRI tracking and therapeutic efficacy of transplanted mesenchymal stem cells labeled with ferrimagnetic vortex iron oxide nanorings for liver fibrosis repair

Mesenchymal stem cells (MSCs) have showed promising effects in the treatment of liver fibrosis. Long-term and noninvasive in vivo tracking of transplanted MSCs is essential for understanding the therapeutic mechanism of MSCs during the therapy of liver fibrosis. In this study, we report the development of a ferrimagnetic vortex iron oxide nanoring (FVIO)-based nanotracer for the long-term visualization of transplanted human MSCs (hMSCs) by magnetic resonance imaging (MRI). The FVIOs were prepared by a hydrothermal reaction followed by hydrogen reduction. To endow the FVIOs with biocompatibility, polyethylene glycol amine (mPEG-NH₂) was covalently coupled on the surface of FVIOs, forming FVIO@PEG nanotracers with high contrast enhancement and intracellular uptake. The hMSCs labeled with FVIO@PEG nanotracers exhibited enhanced MRI contrast than those labeled with a commercial contrast agent, and could be continuously monitored by MRI in liver fibrosis mice for 28 days after transplantation, clearly clarifying the migration behavior of hMSCs in vivo. Moreover, we explored the therapeutic mechanism of the FVIO@PEG labeled hMSCs in the amelioration of liver fibrosis, including the reduction in inflammation and oxidative stress, the inhibition of hepatic fibrosis-caused histopathological damage, as well as the down-regulation of the expression of relevant cytokines. The results obtained in this work may deepen our understanding of the behavior and role of hMSCs in the treatment of liver fibrosis, which is key to the clinical application of stem cells in the therapy of liver diseases.

Magnetic particle imaging: tracer development and the biomedical applications of a radiation-free, sensitive, and quantitative imaging modality

Magnetic particle imaging (MPI) is an emerging tracer-based modality that enables real-time three-dimensional imaging of the non-linear magnetisation produced by superparamagnetic iron oxide nanoparticles (SPIONs), in the presence of an external oscillating magnetic field. As a technique, it produces highly sensitive radiation-free tomographic images with absolute quantitation. Coupled with a high contrast, as well as zero signal attenuation at-depth, there are essentially no limitations to where that can be imaged within the body. These characteristics enable various biomedical applications of clinical interest. In the opening sections of this review, the principles of image generation are introduced, along with a detailed comparison of the fundamental properties of this technique with other common imaging modalities. The main feature is a presentation on the up-to-date literature for the development of SPIONs tailored for improved imaging performance, and developments in the current and promising biomedical applications of this emerging technique, with a specific focus on theranostics, cell tracking and perfusion imaging. Finally, we will discuss recent progress in the clinical translation of MPI. As signal detection in MPI is almost entirely dependent on the properties of the SPION employed, this work emphasises the importance of tailoring the synthetic process to produce SPIONs demonstrating specific properties and how this impacts imaging in particular applications and MPI's overall performance.

A novel magnetophoretic-based device for magnetometry and separation of single magnetic particles and magnetized cells

The use of magnetic micro- and nanoparticles in medicine and biology is expanding. One important example is the transport of magnetic microparticles and magnetized cells in lab-on-a-chip systems. The magnetic susceptibility of the particles is a key factor in determining their response to the externally applied magnetic field. Typically, to measure this parameter, their magnetophoretic mobility is studied. However, the particle tracking system for accurately determining the traveled distance in a certain time may be too complicated. Here, we introduce a lithographically fabricated chip composed of an array of thin magnetic micro-disks for evaluating the magnetic susceptibility of numerous individual magnetic particles simultaneously. The proposed novel magnetometer works based on the phase change in the trajectory of microparticles circulating around the disks in a rotating in-plane magnetic field. We explain that the easily detectable transition between the "phase-locked" and the "phase-slipping" regimes and the frequency at which it happens are appropriate parameters for measuring the magnetic susceptibility of the magnetic particles at the single-particle level. We show that this high-throughput (i.e., ∼ten thousand particles on a 1 cm² area) single-particle magnetometry method has various crucial applications, including i) magnetic characterization of magnetic beads as well as magnetically labeled living cells, ii) determining the magnetization rate of the cells taking up magnetic nanoparticles with respect to time, iii) evaluating the rate of degradation of magnetic nanoparticles in cells over time, iv) detecting the number of target cells in a sample, and v) separating particles based on their size and magnetic susceptibility.

Recent Trends in Fascinating Applications of Nanotechnology in Allied Health Sciences

The increased advancement in nanosciences in recent times has led to fascinating innovations. It has potential applications for altering the structural, surface, and physicochemical properties of nano-ranged metamaterials. The adaptable optical, structural, and surface characteristics of the nanoscopic regimes enhance the quality of integrated nanodevices and sensors. These are further used in optoelectronics, biomedicines, and catalysis. The use of nanomaterials for constructing nano-biosensors and various other organic and inorganic functional nanomaterials is quite promising. They have excellent electronic and surface-to-volume reactivity. Their various applications include metal and metal-oxides-based nanoparticles, clusters, wires, and 2D nanosheets as carbon nanotubes. More recently, hybrid nanomaterials are being developed to regulate sensing functionalities in the field of nanomedicine and the pharmaceutical industry. They are used as nano-markers, templates, and targeted agents. Moreover, the mechanical strength, chemical stability, durability, and flexibility of the hybrid nanomaterials make them appropriate for developing a healthy life for humans. This consists of a variety of applications, such as drug delivery, antimicrobial impacts, nutrition, orthopedics, dentistry, and fluorescence fabrics. This review article caters to the essential importance of nanoscience for biomedical applications and information for health science and research. The fundamental characteristics and functionalities of nanomaterials for particular biomedical uses are specifically addressed here.

Resolving immune cells with patrolling behaviour by magnetic resonance time-lapse single cell tracking

BACKGROUND

Immune cells show distinct motion patterns that change upon inflammatory stimuli. Monocytes patrol the vasculature to screen for pathogens, thereby exerting an early task of innate immunity. Here, we aimed to non-invasively analyse single patrolling monocyte behaviour upon inflammatory stimuli.

METHODS

We used time-lapse Magnetic Resonance Imaging (MRI) of the murine brain to dynamically track single patrolling monocytes within the circulation distant to the actual site of inflammation in different inflammatory conditions, ranging from a subcutaneous pellet model to severe peritonitis and bacteraemia.

FINDINGS

Single patrolling immune cells with a velocity of <1 µm/s could be detected and followed dynamically using time-lapse MRI. We show, that due to local and systemic stimuli the slowly patrolling behaviour of monocytes is altered systemically and differs with type, duration and strength of the underlying stimulus.

INTERPRETATION

Using time-lapse MRI, it is now possible to investigate the behaviour of single circulating monocytes over the course of the systemic immune response. Monocyte patrolling behaviour is altered systemically even before the onset of clinical symptoms distant to and depending on the underlying inflammatory stimulus.

FUNDING

This study was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - CRC 1009 - 194468054 to AZ, CF and - CRC 1450 - 431460824 to MM, SN, HB, AZ, CF, the Joachim Herz Foundation (Add-on Fellowship for Interdisciplinary Life Sciences to MM), the Interdisciplinary Centre for Clinical Research (IZKF, core unit PIX) and the Medical Faculty of the University of Muenster (MEDK fellowship to FF and IF).

In vivo Cell Tracking Using Non-invasive Imaging of Iron Oxide-Based Particles with Particular Relevance for Stem Cell-Based Treatments of Neurological and Cardiac Disease

Stem cell-based therapeutics is a rapidly developing field associated with a number of clinical challenges. One such challenge lies in the implementation of methods to track stem cells and stem cell-derived cells in experimental animal models and in the living patient. Here, we provide an overview of cell tracking in the context of cardiac and neurological disease, focusing on the use of iron oxide-based particles (IOPs) visualized in vivo using magnetic resonance imaging (MRI). We discuss the types of IOPs available for such tracking, their advantages and limitations, approaches for labeling cells with IOPs, biological interactions and effects of IOPs at the molecular and cellular levels, and MRI-based and associated approaches for in vivo and histological visualization. We conclude with reviews of the literature on IOP-based cell tracking in cardiac and neurological disease, covering both preclinical and clinical studies.

Iron Oxide Nanoparticles as Theranostic Agents in Cancer Immunotherapy

Starting from the mid-1990s, several iron oxide nanoparticles (NPs) were developed as MRI contrast agents. Since their sizes fall in the tenths of a nanometer range, after i.v. injection these NPs are preferentially captured by the reticuloendothelial system of the liver. They have therefore been proposed as liver-specific contrast agents. Even though their unfavorable cost/benefit ratio has led to their withdrawal from the market, innovative applications have recently prompted a renewal of interest in these NPs. One important and innovative application is as diagnostic agents in cancer immunotherapy, thanks to their ability to track tumor-associated macrophages (TAMs) in vivo. It is worth noting that iron oxide NPs may also have a therapeutic role, given their ability to alter macrophage polarization. This review is devoted to the most recent advances in applications of iron oxide NPs in tumor diagnosis and therapy. The intrinsic therapeutic effect of these NPs on tumor growth, their capability to alter macrophage polarization and their diagnostic potential are examined. Innovative strategies for NP-based drug delivery in tumors (e.g., magnetic resonance targeting) will also be described. Finally, the review looks at their role as tracers for innovative, and very promising, imaging techniques (magnetic particle imaging-MPI).

Tractography-Pathology Correlations in Traumatic Brain Injury: A TRACK-TBI Study

Diffusion tractography magnetic resonance imaging (MRI) can infer changes in network connectivity in patients with traumatic brain injury (TBI), but the pathological substrates of disconnected tracts have not been well defined because of a lack of high-resolution imaging with histopathological validation. We developed an ex vivo MRI protocol to analyze tract terminations at 750-μm isotropic resolution, followed by histopathological evaluation of white matter pathology, and applied these methods to a 60-year-old man who died 26 days after TBI. Analysis of 74 cerebral hemispheric white matter regions revealed a heterogeneous distribution of tract disruptions. Associated histopathology identified variable white matter injury with patchy deposition of amyloid precursor protein (APP), loss of neurofilament-positive axonal processes, myelin dissolution, astrogliosis, microgliosis, and perivascular hemosiderin-laden macrophages. Multiple linear regression revealed that tract disruption strongly correlated with the density of APP-positive axonal swellings and neurofilament loss. Ex vivo diffusion MRI can detect tract disruptions in the human brain that reflect axonal injury.

One-pot synthesis of carboxymethyl-dextran coated iron oxide nanoparticles (CION) for preclinical fMRI and MRA applications

Superparamagnetic iron-oxide nanoparticles are robust contrast agents for magnetic resonance imaging (MRI) used for sensitive structural and functional mapping of the cerebral blood volume (CBV) when administered intravenously. To date, many CBV-MRI studies are conducted with Feraheme, manufactured for the clinical treatment of iron-deficiency. Unfortunately, Feraheme is currently not available outside the United States due to commercial and regulatory constraints, making CBV-MRI methods either inaccessible or very costly to achieve. To address this barrier, we developed a simple, one-pot recipe to synthesize Carboxymethyl-dextran coated Iron Oxide Nanoparticles, namely, “CION”, suitable for preclinical CBV-MRI applications. Here we disseminate a step-by-step instruction of our one-pot synthesis protocol, which allows CION to be produced in laboratories with minimal cost. We also characterized different CION-conjugations by manipulating polymer to metal stoichiometric ratio in terms of their size, surface chemistry, and chemical composition, and shifts in MR relaxivity and pharmacokinetics. We performed several proof-of-concept experiments in vivo, demonstrating the utility of CION for functional and structural MRI applications, including hypercapnic CO₂ challenge, visual stimulation, targeted optogenetic stimulation, and microangiography. We also present evidence that CION can serve as a cross-modality research platform by showing concurrent in vivo optical and MRI measurement of CBV using fluorescent-labeled CION. The simplicity and cost-effectiveness of our one-pot synthesis method should allow researchers to reproduce CION and tailor the relaxivity and pharmacokinetics according to their imaging needs. It is our hope that this work makes CBV-MRI more openly available and affordable for a variety of research applications.

Assembly and Function of a Bioengineered Human Liver for Transplantation Generated Solely from Induced Pluripotent Stem Cells

The availability of an autologous transplantable auxiliary liver would dramatically affect the treatment of liver disease. Assembly and function in vivo of a bioengineered human liver derived from induced pluripotent stem cells (iPSCs) has not been previously described. By improving methods for liver decellularization, recellularization, and differentiation of different liver cellular lineages of human iPSCs in an organ-like environment, we generated functional engineered human mini livers and performed transplantation in a rat model. Whereas previous studies recellularized liver scaffolds largely with rodent hepatocytes, we repopulated not only the parenchyma with human iPSC-hepatocytes but also the vascular system with human iPS-endothelial cells, and the bile duct network with human iPSC-biliary epithelial cells. The regenerated human iPSC-derived mini liver containing multiple cell types was tested in vivo and remained functional for 4 days after auxiliary liver transplantation in immunocompromised, engineered (IL2rg^-/-) rats.

Effects of labeling human mesenchymal stem cells with superparamagnetic zinc-nickel ferrite nanoparticles on cellular characteristics and adipogenesis/osteogenesis differentiation

OBJECTIVE

An attractive cell source for stem cell-based therapy are WJ-MSCs. Hence, tracking WJ-MSCs using non-invasive imaging procedures (such as MRI) and contrast agents (Zn0.5Ni0.5Fe2O4, NFNPs) are required to evaluate cell distribution, migration, and differentiation.

RESULTS

Results showed that the bare and dextrin-coated NFNPs were internalized inside the WJ-MSCs and had no effect on the cell viability, proliferation, apoptosis, karyotyping, and morphology of WJ-MSCs up to 125 µg/mL. Besides, treated WJ-MSCs were differentiated into osteo/adipocyte-like cells. The expression of RUNX 2, SPP 1 (P < 0.05), and OCN (P > 0.05) genes in the WJ-MSCs treated with dextrin-coated NFNPs was higher than the untreated WJ-MSCs; and the expression of CFD, LPL, and PPAR-γ genes was reduced in WJ-MSCs treated with both NFNPs in comparison with the untreated WJ-MSCs (P > 0.05).

CONCLUSION

Overall, results showed that dextrin-coated NFNPs had no adverse effect on the cellular characteristics, proliferation, and differentiation of WJ-MSCs, and suggesting their potential clinical efficacy.

Engineering Nano-Therapeutics to Boost Adoptive Cell Therapy for Cancer Treatment

Although adoptive transfer of therapeutic cells to cancer patients is demonstrated with great success and fortunately approved for the treatment of leukemia and B-cell lymphoma, potential issues, including the unclear mechanism, complicated procedures, unfavorable therapeutic efficacy for solid tumors, and side effects, still hinder its extensive applications. The explosion of nanotechnology recently has led to advanced development of novel strategies to address these challenges, facilitating the design of nano-therapeutics to improve adoptive cell therapy (ACT) for cancer treatment. In this review, the emerging nano-enabled approaches, that design multiscale artificial antigen-presenting cells for cell proliferation and stimulation in vitro, promote the transducing efficiency of tumor-targeting domains, engineer therapeutic cells for in vivo imaging, tumor infiltration, and in vivo functional sustainability, as well as generate tumoricidal T cells in vivo, are summarized. Meanwhile, the current challenges and future perspectives of the nanostrategy-based ACT for cancer treatment are also discussed in the end.

A hierarchy of manganese competition and entry in organotypic hippocampal slice cultures

Contrast agents improve clinical and basic research MRI. The manganese ion (Mn²⁺ ) is an essential, endogenous metal found in cells and it enhances MRI contrast because of its paramagnetic properties. Manganese-enhanced MRI (MEMRI) has been widely used to image healthy and diseased states of the body and the brain in a variety of animal models. There has also been some work in translating the useful properties of MEMRI to humans. Mn²⁺ accumulates in brain regions with high neural activity and enters cells via voltage-dependent channels that flux calcium (Ca²⁺ ). In addition, metal transporters for zinc (Zn²⁺ ) and iron (Fe²⁺ ) can also transport Mn²⁺ . There is also transfer through channels specific for Mn²⁺ . Although Mn²⁺ accumulates in many tissues including brain, the mechanisms and preferences of its mode of entry into cells are not well characterized. The current study used MRI on living organotypic hippocampal slice cultures to detect which transport mechanisms are preferentially used by Mn²⁺ to enter cells. The use of slice culture overcomes the presence of the blood brain barrier, which limits inferences made with studies of the intact brain in vivo. A range of Mn²⁺ concentrations were used and their effects on neural activity were assessed to avoid using interfering doses of Mn²⁺ . Zn²⁺ and Fe²⁺ were the most efficient competitors for Mn²⁺ uptake into the cultured slices, while the presence of Ca²⁺ or Ca²⁺ channel antagonists had a more moderate effect. Reducing slice activity via excitatory receptor antagonists was also effective at lowering Mn²⁺ uptake. In conclusion, a hierarchy of those agents which influence Mn²⁺ uptake was established to enhance understanding of how Mn²⁺ enters cells in a cultured slice preparation.

Superparamagnetic cobalt ferrite nanoparticles as T2 contrast agent in MRI: in vitro study

Superparamagnetic cobalt ferrite nanoparticles (CoFe₂O₄) possess favourite advantages for theranostic applications. Most of previous studies reported that CoFe₂O₄ magnetic nanoparticles (MNPs) are suitable candidates for induction of hyperthermia and transfection agents for drug delivery. The present study synthesized and investigated the potential use of CoFe₂O₄ as a contrast agent in magnetic resonance imaging (MRI) by using a conventional MRI system. The CoFe₂O₄ were synthesized using co-precipitation method and characterized by TEM, XRD, FTIR, EDX and VSM techniques. Relaxivities r₁ and r₂ of CoFe₂O₄ were then calculated using a 1.5 Tesla clinical magnetic field. The cytotoxicity of CoFe₂O₄ was evaluated by the MTT assay. Finally, the optimal concentrations of MNPs for MRI uses were calculated through the analysis of T₂ weighted imaging cell phantoms. The superparamagnetic CoFe2O4 NPs with an average stable size of 10.45 nm were synthesized. Relaxivity r₁,₂ calculations resulted in suitable r₂ and r₂/ r₁ with values of 58.6 and 51 that confirmed the size dependency on relaxivity values. The optimal concentration of MNPs for MR image acquisition was calculated as 0.154 mM. Conclusion: CoFe₂O₄ synthesized in this study could be considered as a suitable T₂ weighted contrast agent because of its high r₂/r₁ value.

Micron-sized iron oxide particles for both MRI cell tracking and magnetic fluid hyperthermia treatment

Iron oxide particles (IOP) are commonly used for Cellular Magnetic Resonance Imaging (MRI) and in combination with several treatments, like Magnetic Fluid Hyperthermia (MFH), due to the rise in temperature they provoke under an Alternating Magnetic Field (AMF). Micrometric IOP have a high sensitivity of detection. Nevertheless, little is known about their internalization processes or their potential heat power. Two micrometric commercial IOP (from Bangs Laboratories and Chemicell) were characterized by Transmission Electron Microscopy (TEM) and their endocytic pathways into glioma cells were analyzed. Their Specific Absorption Rate (SAR) and cytotoxicity were evaluated using a commercial AMF inductor. T2-weighted imaging was used to monitor tumor growth in vivo after MFH treatment in mice. The two micron-sized IOP had similar structures and r2 relaxivities (100 mM-1 s-1) but involved different endocytic pathways. Only ScreenMAG particles generated a significant rise in temperature following AMF (SAR = 113 W g-1 Fe). After 1 h of AMF exposure, 60% of ScreenMAG-labeled cells died. Translated to a glioma model, 89% of mice responded to the treatment with smaller tumor volume 42 days post-implantation. Micrometric particles were investigated from their characterization to their intracellular internalization pathways and applied in one in vivo cancer treatment, i.e. MFH.

Naphthalene-facilitated self-assembly of a Gd-chelate as a novel T2 MRI contrast agent for visualization of stem cell transplants

Naphthalene is coupled with DOTA via a peptide sequence to yield an amphipathic MRI probe Nap-CFGKTG-DOTA-Gd (Nap-Gd) that can self-assemble into nanofibers. Incubation of NSCs, hMSCs and L929 cells in the presence of Nap-Gd in the μM level can introduce a significant amount of Nap-Gd into the cells as nanoclusters or nanofibers. The resultant intracellular Gd content is 10-60 times that achieved by incubation with Dotarem at the same concentration. The labelled cells exhibit a significant hyperintensive effect under T1-weighted MRI and a significant hypointensive effect under T2-weighted MRI. The hypointensive effect is more persistent than the hyperintensive effect, which allows in vivo tracking of labelled hMSCs for over 12 days under T2-weighted MRI. A comprehensive interpretation of the MRI signal intensity and the associated relaxation times reveals the structure-function relationship between the binding status of Nap-Gd in cells (structure) and the magnetic relaxation processes (function) toward a full understanding of the observed hyperintensive and hypointensive effects.

Cardiac MRI Assessment of Mouse Myocardial Infarction and Regeneration

Small animal models are indispensable for cardiac regeneration research. Studies in mouse and rat models have provided important insights into the etiology and mechanisms of cardiovascular diseases and accelerated the development of therapeutic strategies. It is vitally important to be able to evaluate the therapeutic efficacy and have reliable surrogate markers for therapeutic development for cardiac regeneration research. Magnetic resonance imaging (MRI), a versatile and noninvasive imaging modality with excellent penetration depth, tissue coverage, and soft-tissue contrast, is becoming a more important tool in both clinical settings and research arenas. Cardiac MRI (CMR) is versatile, noninvasive, and capable of measuring many different aspects of cardiac functions, and, thus, is ideally suited to evaluate therapeutic efficacy for cardiac regeneration. CMR applications include assessment of cardiac anatomy, regional wall motion, myocardial perfusion, myocardial viability, cardiac function assessment, assessment of myocardial infarction, and myocardial injury. Myocardial infarction models in mice are commonly used model systems for cardiac regeneration research. In this chapter, we discuss various CMR applications to evaluate cardiac functions and inflammation after myocardial infarction.

VCAM-1 Target in Non-Invasive Imaging for the Detection of Atherosclerotic Plaques

Simple Summary

Cardiovascular diseases are the first cause of morbimortality worldwide. They are mainly caused by atherosclerosis, with progressive plaque formation in the arterial wall. In this context, several imaging techniques have been developed to screen, detect and quantify atherosclerosis. Early screening improves primary prevention and promotes the prescription of adequate medication before adverse clinical events. In this review, we focus on the imaging of vascular cell adhesion molecule-1, an adhesion molecule involved in the first stages of the development of atherosclerosis. This molecule could therefore be a promising target to detect early atherosclerosis non-invasively. Potential clinical applications are critically discussed.

Abstract

Atherosclerosis is a progressive chronic arterial disease characterised by atheromatous plaque formation in the intima of the arterial wall. Several invasive and non-invasive imaging techniques have been developed to detect and characterise atherosclerosis in the vessel wall: anatomic/structural imaging, functional imaging and molecular imaging. In molecular imaging, vascular cell adhesion molecule-1 (VCAM-1) is a promising target for the non-invasive detection of atherosclerosis and for the assessment of novel antiatherogenic treatments. VCAM-1 is an adhesion molecule expressed on the activated endothelial surface that binds leucocyte ligands and therefore promotes leucocyte adhesion and transendothelial migration. Hence, for several years, there has been an increase in molecular imaging methods for detecting VCAM-1 in MRI, PET, SPECT, optical imaging and ultrasound. The use of microparticles of iron oxide (MPIO), ultrasmall superparamagnetic iron oxide (USPIO), microbubbles, echogenic immunoliposomes, peptides, nanobodies and other nanoparticles has been described. However, these approaches have been tested in animal models, and the remaining challenge is bench-to-bedside development and clinical applicability.

Inducing Defects in 19F-Nanocrystals Provides Paramagnetic-free Relaxation Enhancement for Improved In Vivo Hotspot MRI

Paramagnetic relaxation enhancement (PRE) is the current strategy of choice for enhancing magnetic resonance imaging (MRI) contrast and for accelerating MRI acquisition schemes. Yet, debates regarding lanthanides' biocompatibility and PRE-effect on MRI signal quantification have raised the need for alternative strategies for relaxation enhancement. Herein, we show an approach for shortening the spin-lattice relaxation time (T₁) of fluoride-based nanocrystals (NCs) that are used for in vivo ¹⁹F-MRI, by inducing crystal defects in their solid-crystal core. By utilizing a phosphate-based rather than a carboxylate-based capping ligand for the synthesis of CaF₂ NCs, we were able to induce grain boundary defects in the NC lattice. The obtained defects led to a 10-fold shorter T₁ of the NCs' fluorides. Such paramagnetic-free relaxation enhancement of CaF₂ NCs, gained without affecting either their size or their colloidal characteristics, improved 4-fold the obtained ¹⁹F-MRI signal-to-noise ratio, allowing their use, in vivo, with enhanced hotspot MRI sensitivity.

Medical Imaging of Microrobots: Toward In Vivo Applications

Medical microrobots (MRs) have been demonstrated for a variety of non-invasive biomedical applications, such as tissue engineering, drug delivery, and assisted fertilization, among others. However, most of these demonstrations have been carried out in in vitro settings and under optical microscopy, being significantly different from the clinical practice. Thus, medical imaging techniques are required for localizing and tracking such tiny therapeutic machines when used in medical-relevant applications. This review aims at analyzing the state of the art of microrobots imaging by critically discussing the potentialities and limitations of the techniques employed in this field. Moreover, the physics and the working principle behind each analyzed imaging strategy, the spatiotemporal resolution, and the penetration depth are thoroughly discussed. The paper deals with the suitability of each imaging technique for tracking single or swarms of MRs and discusses the scenarios where contrast or imaging agent's inclusion is required, either to absorb, emit, or reflect a determined physical signal detected by an external system. Finally, the review highlights the existing challenges and perspective solutions which could be promising for future in vivo applications.

Tuning the size and composition of manganese oxide nanoparticles through varying temperature ramp and aging time

Manganese oxide (MnO) nanoparticles (NPs) can serve as robust pH-sensitive contrast agents for magnetic resonance imaging (MRI) due to Mn2+ release at low pH, which generates a ~30 fold change in T1 relaxivity. Strategies to control NP size, composition, and Mn2+ dissolution rates are essential to improve diagnostic performance of pH-responsive MnO NPs. We are the first to demonstrate that MnO NP size and composition can be tuned by the temperature ramping rate and aging time used during thermal decomposition of manganese(II) acetylacetonate. Two different temperature ramping rates (10°C/min and 20°C/min) were applied to reach 300°C and NPs were aged at that temperature for 5, 15, or 30 min. A faster ramping rate and shorter aging time produced the smallest NPs of ~23 nm. Shorter aging times created a mixture of MnO and Mn3O4 NPs, whereas longer aging times formed MnO. Our results indicate that a 20°C/min ramp rate with an aging time of 30 min was the ideal temperature condition to form the smallest pure MnO NPs of ~32 nm. However, Mn2+ dissolution rates at low pH were unaffected by synthesis conditions. Although Mn2+ production was high at pH 5 mimicking endosomes inside cells, minimal Mn2+ was released at pH 6.5 and 7.4, which mimic the tumor extracellular space and blood, respectively. To further elucidate the effects of NP composition and size on Mn2+ release and MRI contrast, the ideal MnO NP formulation (~32 nm) was compared with smaller MnO and Mn3O4 NPs. Small MnO NPs produced the highest amount of Mn2+ at acidic pH with maximum T1 MRI signal; Mn3O4 NPs generated the lowest MRI signal. MnO NPs encapsulated within poly(lactide-co-glycolide) (PLGA) retained significantly higher Mn2+ release and MRI signal compared to PLGA Mn3O4 NPs. Therefore, MnO instead of Mn3O4 should be targeted intracellularly to maximize MRI contrast.

Multifield and inverse-contrast switching of magnetocaloric high contrast ratio MRI labels

PURPOSE

Demonstrating multifield and inverse contrast switching of magnetocaloric high contrast ratio MRI labels that either have increasing or decreasing moment versus temperature slopes depending on the material at physiological temperatures and different MRI magnetic field strengths.

METHODS

Two iron-rhodium samples of different purity (99% and 99.9%) and a lanthanum-iron-silicon sample were obtained from commercial vendors. Temperature and magnetic field-dependent magnetic moment measurements of the samples were performed on a vibrating sample magnetometer. Temperature-dependent MRI of different iron-rhodium and lanthanum-iron-silicon samples were performed on 3 different MRI scanners at 1 Tesla (T), 4.7T, and 7T.

RESULTS

Sharp, first-order magnetic phase transition of each iron-rhodium sample at a physiologically relevant temperature (~37°C) but at different MRI magnetic fields (1T, 4.7T, and 7T, depending on the sample) showed clear image contrast changes in temperature-dependent MRI. Iron-rhodium and lanthanum-iron-silicon samples with sharp, first-order magnetic phase transitions at the same MRI field of 1T and physiological temperature of 37°C, but with positive and negative slope of magnetization versus temperature, respectively, showed clear inverse contrast image changes. Temperature-dependent MRI on individual microparticle samples of lanthanum-iron-silicon also showed sharp image contrast changes.

CONCLUSION

Magnetocaloric materials of different purity and composition were demonstrated to act as diverse high contrast ratio switchable MRI contrast agents. Thus, we show that a range of magnetocaloric materials can be optimized for unique image contrast response under MRI-appropriate conditions at physiological temperatures and be controllably switched in situ.

Ultra Short Echo Time MRI of Iron-Labelled Mesenchymal Stem Cells in an Ovine Osteochondral Defect Model

Multipotent Mesenchymal Stem/Stromal Cells (MSCs) are widely used in cellular therapy for joint repair. However, the use of MSC therapies is complicated by a lack of understanding of the behaviour of cells and repair within the joint. Current methods of MSC tracking include labelling the cells with Super Paramagnetic Iron Oxide nanoparticles (SPIOs). However, standard acquisition sequences (T2 and T2*) give poor anatomical definition in the presence of SPIOs. To avoid anatomical compromise in the presence of SPIOs, we have investigated the use of Ultra-short Echo Time (UTE) MRI, using a 3D cones acquisition trajectory. This method was used to track SPIO labelled MSC injected into joints containing osteochondral defects in experimental sheep. This study demonstrates that multiple echo times from UTE with 3 T MRI can provide excellent anatomical detail of osteochondral defects and demonstrate similar features to histology. This work also monitors the location of SPIO-labelled cells for regenerative medicine of the knee with MRI, histology, and Prussian blue staining. With these methods, we show that the SPIOs do not hone to the site of defect but instead aggregate in the location of injection, which suggests that any repair mechanism with this disease model must trigger a secondary process.

Controlled Synthesis and Characterization of Micrometric Single Crystalline Magnetite With Superparamagnetic Behavior and Cytocompatibility/Cytotoxicity Assessments

A new class of magnetite (Fe₃O₄) particles, coined as “Single Crystalline Micrometric Iron Oxide Particles” (SCMIOPs), were obtained by hydrothermal synthesis. Both the single Fe₃O₄ phase content and the particle sizes range, from 1 µm to 30 µm, can be controlled by synthesis. The notable finding states that these particles exhibit vanishing remanent magnetization (σr=0.28 emu/g) and coercive force (Hc=1.5 Oe), which indicate a superparamagnetic-like behavior (unexpected at micrometric particles size), and remarkably high saturation magnetization (σs=95.5 emu/g), what ensures strong magnetic response, and the lack of agglomeration after the magnetic field removal. These qualities make such particles candidates for biomedical applications, to be used instead of magnetic nanoparticles which inevitably involve some drawbacks like aglommeration and insufficient magnetic response. In this sense, cytocompatibility/cytotoxicity tests were performed on human cells, and the results have clearly indicated that SCMIOPs are cytocompatible for healthy cell lines HaCaT (human keratinocytes) and HEMa (primary epidermal melanocytes) and cytotoxic for neoplastic cell lines A375 (human melanoma) and B164A5 (murine melanoma) in a dose-dependent manner.

Nano-immunoimaging

Immunoimaging is a rapidly growing field stoked in large part by the intriguing triumphs of immunotherapy. On the heels of immunotherapy's successes, there exists a growing need to evaluate tumor response to therapy particularly immunotherapy, stratify patients into responders vs. non-responders, identify inflammation, and better understand the fundamental roles of immune system components to improve both immunoimaging and immunotherapy. Innovative nanomaterials have begun to provide novel opportunities for immunoimaging, in part due to their sensitivity, modularity, capacity for many potentially varied ligands (high avidity), and potential for multifunctionality/multimodality imaging. This review strives to comprehensively summarize the integration of nanotechnology and immunoimaging, and the field's potential for clinical applications.

Methods of Granulocyte Isolation from Human Blood and Labeling with Multimodal Superparamagnetic Iron Oxide Nanoparticles

This in vitro study aimed to find the best method of granulocyte isolation for subsequent labeling with multimodal nanoparticles (magnetic and fluorescent properties) to enable detection by optical and magnetic resonance imaging (MRI) techniques. The granulocytes were obtained from venous blood samples from 12 healthy volunteers. To achieve high purity and yield, four different methods of granulocyte isolation were evaluated. The isolated granulocytes were labeled with multimodal superparamagnetic iron oxide nanoparticles (M-SPIONs) coated with dextran, and the iron load was evaluated qualitatively and quantitatively by MRI, near-infrared fluorescence (NIRF) and inductively coupled plasma mass spectrometry (ICP-MS). The best method of granulocyte isolation was Percoll with Ficoll, which showed 95.92% purity and 94% viability. After labeling with M-SPIONs, the granulocytes showed 98.0% purity with a yield of 3.5 × 10⁶ cells/mL and more than 98.6% viability. The iron-loading value in the labeled granulocytes, as obtained by MRI, was 6.40 ± 0.18 pg/cell. Similar values were found with the ICP-MS and NIRF imaging techniques. Therefore, our study shows that it is possible to isolate granulocytes with high purity and yield and labeling with M-SPIONs provides a high internalized iron load and low toxicity to cells. Therefore, these M-SPION-labeled granulocytes could be a promising candidate for future use in inflammation/infection detection by optical and MRI techniques.

Introducing Specificity to Iron Oxide Nanoparticle Imaging by Combining 57Fe-Based MRI and Mass Spectrometry

Iron oxide nanoparticles (ION) are highly sensitive probes for magnetic resonance imaging (MRI) that have previously been used for in vivo cell tracking and have enabled implementation of several diagnostic tools to detect and monitor disease. However, the in vivo MRI signal of ION can overlap with the signal from endogenous iron, resulting in a lack of detection specificity. Therefore, the long-term fate of administered ION remains largely unknown, and possible tissue deposition of iron cannot be assessed with established methods. Herein, we combine nonradioactive ⁵⁷Fe-ION MRI with ex vivo laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging, enabling unambiguous differentiation between endogenous iron (⁵⁶Fe) and iron originating from applied ION in mice. We establish ⁵⁷Fe-ION as an in vivo MRI sensor for cell tracking in a mouse model of subcutaneous inflammation and for assessing the long-term fate of ⁵⁷Fe-ION. Our approach resolves the lack of detection specificity in ION imaging by unambiguously recording a ⁵⁷Fe signature.

Comparison of incremental concentrations of micron-sized superparamagnetic iron oxide for labelling articular cartilage derived chondroprogenitors

INTRODUCTION

In vivo tracking of labelled cells can provide valuable information about cellular behavior in the microenvironment, migration and contribution of transplanted cells toward tissue regeneration. Articular cartilage derived chondroprogenitors (CPs) show promise as a candidate for cell-based therapy as they have been classified as mesenchymal stem cells with inherent chondrogenic potential. Iron oxide labelling is known to withstand harsh processing techniques known to be associated with staining of osteochondral specimens.

AIM AND METHODS

The aim of our study was to investigate the feasibility of labelling CPs with micron-sized super paramagnetic iron oxide (M-SPIO) particles and to study the effects of this approach on the labelling efficiency, viability, maintenance of phenotype and potential for differentiation. Human CPs were isolated using fibronectin adhesion assay, passage 2 cells were labelled using three concentrations of M-SPIO (12.75 μg/ml, 25.5 μg/ml and 38.25 μg/ml). At sub confluence, cells were assessed for a) iron uptake by Prussian blue stain and colorimetry b) viability using 7-amino actinomycin D, c) MSC marker expression by flow cytometric analysis and d) trilineage differentiation potential.

RESULTS AND CONCLUSION

Iron uptake was higher with increase in M-SPIO concentration whereas CD73, CD90 marker expression significantly decreased and chondrogenic potential appreciably reduced with increase in M-SPIO concentration. In conclusion, 12.75 μg/ml M-SPIO can successfully label human articular cartilage derived chondroprogenitors with minimal effect on cellular viability, MSC marker expression and potential for differentiation.

Cellular magnetic resonance imaging: in vivo tracking of gastric cancer cells and detecting of lymph node metastases using microparticles of iron oxide in mice

Background

Monitoring the fate of implanted cells over time in an experimental animal may provide a new way to track the metastatic process. Lymph node metastase is of extremely importance for the prognostic prediction of gastric carcinoma. The aim of this study was to assess the feasibility of magnetic resonance imaging (MRI), using micron-sized superparamagnetic iron oxide particles (MPIO), for monitoring of the fate of gastric cancer cells and detecting the migration of gastric cancer cells through the lymphatic system in a mouse model.

Methods

SGC-7901 gastric cancer cells were labeled with green fluorescent MPIO. The cells were monitored in vitro at multiple time points by staining for iron-labeled cells and by flow cytometric detection of the fluorescent MPIO. MPIO-labeled cells were implanted subcutaneously into nude mice, and cellular MRI was performed at different time points until 35 days postinjection.

Results

The potential for retention of the iron particles in vitro was evaluated. Our results showed that the labeling and uptake efficiency of MPIO reached 90.0% after 24 hrs of incubation, and a small percentage of cells that retained MPIO could be examined until 16 days after labeling. In vivo MRI-based tracking over several weeks in mice revealed regions of signal loss in the primary tumors for up to 5 weeks. Furthermore, small regions of signal void were detected in images of the inguinal lymph nodes in three mice at day 28 postinjection or later, and histological assays confirmed the presence of iron-labeled cancer cells.

Conclusion

This study supports MPIO-based cell tracking is a useful tool for monitoring the fate of gastric cancer cells in mice over time, which may facilitate progress in understanding the mechanisms of early regional lymph node micrometastases.

Determination of portal vein tumor thrombus blood supply using in vivo cellular magnetic resonance imaging in a rabbit model

Objective: This study aimed to investigate the anatomic configuration of the blood vessels that contribute to portal vein tumor thrombus (PVTT), a common complication of hepatocellular carcinoma, in VX2 rabbits.

Materials and methods: Peripheral blood mononuclear cells (MNCs) were isolated and labeled using superparamagnetic iron oxide particles in vitro. Twenty-four rabbits were injected with the VX2 tumor via the portal vein to establish the PVTT model. The rabbits (n=6/treatment group) were randomly assigned into four groups. Rabbits of groups A, B and C received an infusion of iron-labeled MNCs via the hepatic artery, the portal vein or the auricular vein, respectively, whereas rabbits of group D received an injection of normal saline via the auricular vein 7 days after the injection of VX2 tumors. MRI was performed, and the signal intensity (SI) of the PVTTs was measured on T2-weighted images (T2WIs) 1 day after the transfusion of iron-labeled cells.

Results: The SI of PVTTs, as measured on T2WIs, in rabbits of groups A, B, C and D was 241.400 (172.350, 364.825), 221.150 (203.775, 318.225), 590.200 (363.325, 728.875) and 568.050 (474.725, 705.150), respectively. Our data showed a significant decrease in the SI of PVTTs in rabbits of groups A and B compared with rabbits of groups C and D (group A vs group C, U=4.000, p=0.025; group A vs group D, U=2.000, p=0.010; group B vs group C, U=4.000, p=0.025; group B vs group D, U=1.000, p=0.006). There was no significant difference in the SI of PVTTs in rabbits of group A and B.

Conclusion: Our results indicated that the portal vein and the hepatic artery supplied blood flow to the PVTT in rabbits.

Normalized averaged range (nAR), a robust quantification method for MPIO-content

Micron-sized paramagnetic iron oxide particles (MPIO) are commonly used as contrast agents in magnetic resonance imaging (MRI) that produce negative contrast enhancement, i.e. darkening, on T2^*-weighted images. However, estimation and quantification of MPIO in vivo is still challenging. This limitation mainly arises from smearing and displacement of the negative contrast of the MPIO, so-called blooming, potentially leading to false-positive detection. Further, the bias field induced by the MR coils also hinders visualization and quantification of the MPIO. To mitigate these drawbacks, a positive contrast image can be generated, for example by using a frequency offset technique, which can significantly improve the accuracy of quantification methods. In this research, we introduce the normalized average range (nAR) as a new way to quantify the relative MPIO content within a study. The method compares the average value of test ROIs to that of a control ROI in range filtered images. The nAR can be used on both positive and negative contrast images. The nAR was tested on agar phantoms containing various MPIO concentrations, and on a rostral migration model for MPIO labeled stem cells in mice. The amount of MPIO was quantified for biased and unbiased data, and both for positive and negative contrast images. In addition, the presence of MPIOs in the olfactory bulb was verified by histology. The results show the nAR can indicate the presence and relative content of MPIO for both negative and positive images. However, the nAR showed slightly higher sensitivity in optimized positive contrast images compared to negative contrast images. In all cases, the bias field played a minor role in the quantification, making debiasing less of a concern. The dependency of the nAR values on the MPIO content in the ROI was further validated histologically. Thus, the nAR provides a robust and reliable tool for quantification of MPIO in mice.

Magnetic Resonance Imaging for Characterization of a Chick Embryo Model of Cancer Cell Metastases

Metastasis is the most common cause of death for patients with cancer. To fully understand the steps involved in metastatic dissemination, in vivo models are required, of which murine ones are the most common. Therefore, preclinical imaging methods such as magnetic resonance imaging (MRI) have mainly been developed for small mammals and their potential to monitor cancer growth and metastasis in nonmammalian models is not fully harnessed. We have here used MRI to measure primary neuroblastoma tumor size and metastasis in a chick embryo model. We compared its sensitivity and accuracy to end-point fluorescence detection upon dissection. Human neuroblastoma cells labeled with green fluorescent protein (GFP) and micron-sized iron particles were implanted on the extraembryonic chorioallantoic membrane of the chick at E7. T₂ RARE, T₂-weighted fast low angle shot (FLASH) as well as time-of-flight MR angiography imaging were applied at E14. Micron-sized iron particle labeling of neuroblastoma cells allowed in ovo observation of the primary tumor and tumor volume measurement noninvasively. Moreover, T₂ weighted and FLASH imaging permitted the detection of small metastatic deposits in the chick embryo, thereby reinforcing the potential of this convenient, 3R compliant, in vivo model for cancer research.