MR tracking of stem cells in living recipients

Iron Oxide Nanoparticles in Regenerative Medicine and Tissue Engineering

In recent years, many promising nanotechnological approaches to biomedical research have been developed in order to increase implementation of regenerative medicine and tissue engineering in clinical practice. In the meantime, the use of nanomaterials for the regeneration of diseased or injured tissues is considered advantageous in most areas of medicine. In particular, for the treatment of cardiovascular, osteochondral and neurological defects, but also for the recovery of functions of other organs such as kidney, liver, pancreas, bladder, urethra and for wound healing, nanomaterials are increasingly being developed that serve as scaffolds, mimic the extracellular matrix and promote adhesion or differentiation of cells. This review focuses on the latest developments in regenerative medicine, in which iron oxide nanoparticles (IONPs) play a crucial role for tissue engineering and cell therapy. IONPs are not only enabling the use of non-invasive observation methods to monitor the therapy, but can also accelerate and enhance regeneration, either thanks to their inherent magnetic properties or by functionalization with bioactive or therapeutic compounds, such as drugs, enzymes and growth factors. In addition, the presence of magnetic fields can direct IONP-labeled cells specifically to the site of action or induce cell differentiation into a specific cell type through mechanotransduction.

Aggrecan modulates the expression and phosphorylation of tau in a novel bigenic TauP301L - Acan mouse model

Selected types of neurons in the central nervous system are associated with a specialized form of extracellular matrix. These so-called perineuronal nets (PNs) are supramolecular structures surrounding neuronal somata, proximal dendrites and axon initial segments. PNs are involved in the regulation of plasticity and synaptic physiology. In addition, PNs were proposed to carry neuroprotective functions as PN-ensheathed neurons are mostly spared of tau pathology in brains of Alzheimer patients. Recently, the neuroprotective action of PNs was confirmed experimentally, demonstrating (i) that mainly aggrecan mediates the neuroprotective function of PNs and (ii) that aggrecan seems to generate an external shielding preventing the internalization of pathological forms of tau. In the present study, we aimed at extending these findings and hypothesized that aggrecan further provides an intracellular protection by preventing mutation-triggered formation of pathological forms of tau. We used crossbreds of TauP301L mice and heterozygous aggrecan mice which are characterized by spontaneous deletion of the aggrecan allele. We analysed the extent of tau pathology in dependence of aggrecan protein amount by applying immunohistochemistry, Western blotting and ELISA. The results clearly indicate that aggrecan has no significant impact on tau aggregation in the brainstem of our mouse model. Still, reduced aggrecan levels were accompanied by increased levels of tau protein and reduced number of Tau-1-positive neurons, which indicate an increase in phosphorylation of tau. In conclusion, these data demonstrate a correlation between aggrecan and P301L mutation-triggered tau expression and phosphorylation in our bigenic mouse model.

Stem cell homing, tracking and therapeutic efficiency evaluation for stroke treatment using nanoparticles: A systematic review

BACKGROUND

Stroke is the second leading cause of death worldwide. There is a real need to develop treatment strategies for reducing neurological deficits in stroke survivors, and stem cell (SC) therapeutics appear to be a promising alternative for stroke therapy that can be used in combination with approved thrombolytic or thrombectomy approaches. However, the efficacy of SC therapy depends on the SC homing ability and engraftment into the injury site over a long period of time. Nonetheless, tracking SCs from their niche to the target tissues is a complex process.

AIM

To evaluate SC migration homing, tracking and therapeutic efficacy in the treatment of stroke using nanoparticles

METHODS

A systematic literature search was performed to identify articles published prior to November 2019 that were indexed in PubMed and Scopus. The following inclusion criteria were used: (1) Studies that used in vivo models of stroke or ischemic brain lesions; (2) Studies of SCs labeled with some type of contrast agent for cell migration detection; and (3) Studies that involved in vivo cellular homing and tracking analysis.

RESULTS

A total of 82 articles were identified by indexing in Scopus and PubMed. After the inclusion criteria were applied, 35 studies were selected, and the articles were assessed for eligibility; ultimately, only 25 studies were included. Most of the selected studies used SCs from human and mouse bone marrow labeled with magnetic nanoparticles alone or combined with fluorophore dyes. These cells were administered in the stroke model (to treat middle cerebral artery occlusion in 74% of studies and for photothrombotic induction in 26% of studies). Fifty-three percent of studies used xenogeneic grafts for cell therapy, and the migration homing and tracking evaluation was performed by magnetic resonance imaging as well as other techniques, such as near-infrared fluorescence imaging (12%) or bioluminescence assays (12%).

CONCLUSION

Our systematic review provided an up-to-date evaluation of SC migration homing and the efficacy of cellular therapy for stroke treatment in terms of functional and structural improvements in the late stage.

The neuronal extracellular matrix restricts distribution and internalization of aggregated Tau-protein

Alzheimer's disease (AD) is a chronic degenerative disorder characterized by fibrillary aggregates of Aß and Tau-protein. Formation and progression of these pathological hallmarks throughout the brain follow a specific spatio-temporal pattern which provides the basis for neuropathological staging. Previously, we could demonstrate that cortical and subcortical neurons are less frequently affected by neurofibrillary degeneration if they are enwrapped by a specialized form of the hyaluronan-based extracellular matrix (ECM), the so called 'perineuronal net' (PN). PNs are composed of large aggregating chondroitin sulfate proteoglycans connected to a hyaluronan backbone, stabilized by link proteins and cross-linked via tenascin-R. Recently, PN-associated neurons were shown to be better protected against iron-induced neurodegeneration compared to neurons without PN, indicating a neuroprotective function. Here, we investigated the role of PNs in distribution and internalization of exogenous Tau-protein by using organotypic slice cultures of wildtype mice as well as mice lacking the ECM-components aggrecan, HAPLN1 or tenascin-R. We could demonstrate that PNs restrict both distribution and internalization of Tau. Accordingly, PN-ensheathed neurons were less frequently affected by Tau-internalization, than neurons without PN. Finally, the PNs as well as their three investigated components were shown to modulate the processes of distribution as well as internalization of Tau.

Chronic spinal cord injury treated with transplanted autologous bone marrow-derived mesenchymal stem cells tracked by magnetic resonance imaging: a case report

INTRODUCTION

Intrathecal transplantation is a minimally invasive method for the delivery of stem cells, however, whether the cells migrate from the lumbar to the injured cervical spinal cord has not been proved in humans. We describe an attempt to track bone marrow-derived mesenchymal stem cells in a patient with a chronic cervical spinal cord injury.

CASE PRESENTATION

A 33-year-old Thai man who sustained an incomplete spinal cord injury from the atlanto-axial subluxation was enrolled into a pilot study aiming to track bone marrow-derived mesenchymal stem cells, labeled with superparamagnetic iron oxide nanoparticles, from intrathecal transplantation in chronic cervical spinal cord injury. He had been dependent on respiratory support since 2005. There had been no improvement in his neurological function for the past 54 months. Bone marrow-derived mesenchymal stem cells were retrieved from his iliac crest and repopulated to the target number. One half of the total cells were labeled with superparamagnetic iron oxide nanoparticles before transplantation to the intrathecal space between L4 and L5. Magnetic resonance imaging studies were performed immediately after the transplantation and at 48 hours, two weeks, one month and seven months after the transplantation. His magnetic resonance imaging scan performed immediately after the transplantation showed hyposignal intensity of paramagnetic substance tagged stem cells in the subarachnoid space at the lumbar spine area. This phenomenon was observed at the surface around his cervical spinal cord at 48 hours. A focal hyposignal intensity of tagged bone marrow-derived stem cells was detected at his cervical spinal cord with magnetic resonance imaging at 48 hours, which faded after two weeks, and then disappeared after one month. No clinical improvement of the neurological function had occurred at the end of this study. However, at 48 hours after the transplantation, he presented with a fever, headache, myalgia and worsening of his motor function (by one grade of all key muscles by the American Spinal Injury Association impairment scale), which lasted for 48 hours.

CONCLUSION

Intrathecal injection of bone marrow-derived stem cells at the lumbar spine level could deliver the cells to the injured cervical spinal cord. Transient complications should be observed closely in the first 48 hours after transplantation. Further study should be carried out to evaluate the result of the treatment.

Whole body MRI and fluorescent microscopy for detection of stem cells labeled with superparamagnetic iron oxide (SPIO) nanoparticles and DiI following intramuscular and systemic delivery

Methods to monitor transplanted stem cells in vivo are of great importance for potential therapeutic applications. Of particular interest are methods allowing noninvasive detection of stem cells throughout the body. Magnetic resonance imaging (MRI) is a tool that would allow detection of cells in nearly any tissue in the body and is already commonly used in the clinic. MRI tracking of stem cells is therefore feasible and likely to be easily adapted to patients receiving donor cells. Patients with Duchenne muscular dystrophy are good candidates for stem cell therapy, given the naturally regenerative nature of skeletal muscle, which repairs damage by employing endogenous stem cells from the muscle interstitium to regenerate muscle fibers throughout adulthood. We describe methods for labeling stem cells with superparamagnetic iron oxide nanoparticles (SPIO) to enhance MRI contrast, injecting them locally into skeletal and cardiac muscle, or systemically in mouse models for Duchenne muscular dystrophy, and tracking them in muscle tissue of live mice following injection. We focus on the use of whole body MRI to detect stem cells, as this is necessary for conditions such as muscular dystrophy, in which affected tissues are present throughout the body and systemic delivery of stem cells may be necessary. Emphasis is placed on the development of an MRI coil that is field of view (FOV) adjustable and can be used for both whole body imaging to determine stem cell localization as well as subsequent focusing on smaller, local regions where stem cells are present to obtain high-resolution images. We discuss the coil design and its significance for stem cell tracking. We also describe methods for labeling stem cells with a fluorescent dye and for tracking them in postmortem tissue specimens with fluorescent microscopy to correlate, compare, and contrast with results of whole body MRI in preclinical studies.

Multimodal imaging of stem cell implantation in the central nervous system of mice

During the past decade, stem cell transplantation has gained increasing interest as primary or secondary therapeutic modality for a variety of diseases, both in preclinical and clinical studies. However, to date results regarding functional outcome and/or tissue regeneration following stem cell transplantation are quite diverse. Generally, a clinical benefit is observed without profound understanding of the underlying mechanism(s). Therefore, multiple efforts have led to the development of different molecular imaging modalities to monitor stem cell grafting with the ultimate aim to accurately evaluate survival, fate and physiology of grafted stem cells and/or their micro-environment. Changes observed in one or more parameters determined by molecular imaging might be related to the observed clinical effect. In this context, our studies focus on the combined use of bioluminescence imaging (BLI), magnetic resonance imaging (MRI) and histological analysis to evaluate stem cell grafting. BLI is commonly used to non-invasively perform cell tracking and monitor cell survival in time following transplantation, based on a biochemical reaction where cells expressing the Luciferase-reporter gene are able to emit light following interaction with its substrate (e.g. D-luciferin). MRI on the other hand is a non-invasive technique which is clinically applicable and can be used to precisely locate cellular grafts with very high resolution, although its sensitivity highly depends on the contrast generated after cell labeling with an MRI contrast agent. Finally, post-mortem histological analysis is the method of choice to validate research results obtained with non-invasive techniques with highest resolution and sensitivity. Moreover end-point histological analysis allows us to perform detailed phenotypic analysis of grafted cells and/or the surrounding tissue, based on the use of fluorescent reporter proteins and/or direct cell labeling with specific antibodies. In summary, we here visually demonstrate the complementarities of BLI, MRI and histology to unravel different stem cell- and/or environment-associated characteristics following stem cell grafting in the CNS of mice. As an example, bone marrow-derived stromal cells, genetically engineered to express the enhanced Green Fluorescent Protein (eGFP) and firefly Luciferase (fLuc), and labeled with blue fluorescent micron-sized iron oxide particles (MPIOs), will be grafted in the CNS of immune-competent mice and outcome will be monitored by BLI, MRI and histology (Figure 1).

Evaluation of intracellular labeling with micron-sized particles of iron oxide (MPIOs) as a general tool for in vitro and in vivo tracking of human stem and progenitor cells

Magnetic resonance imaging (MRI)-based tracking is increasingly attracting attention as a means of better understanding stem cell dynamics in vivo. Intracellular labeling with micrometer-sized particles of iron oxide (MPIOs) provides a practical MRI-based approach due to superior detectability relative to smaller iron oxide particles. However, insufficient information is available about the general utility across cell types and the effects on cell vitality of MPIO labeling of human stem cells. We labeled six human cell types from different sources: mesenchymal stem cells derived from bone marrow (MSCs), mesenchymal stem cells derived from adipose tissue (ASCs), presumptive adult neural stem cells (ad-NSCs), fetal neural progenitor cells (f-NPCs), a glioma cell line (U87), and glioblastoma tumor stem cells (GSCs), with two different sizes of MPIOs (0.9 and 2.84 µm). Labeling and uptake efficiencies were highly variable among cell types. Several parameters of general cell function were tested in vitro. Only minor differences were found between labeled and unlabeled cells with respect to proliferation rate, mitotic duration, random motility, and capacity for differentiation to specific phenotypes. In vivo behavior was tested in chicken embryos and severe combined immunodeficient (SCID) mice. Postmortem histology showed that labeled cells survived and could integrate into various tissues. MRI-based tracking over several weeks in the SCID mice showed that labeled GSCs and f-NPCs injected into the brain exhibited translocations similar to those seen for unlabeled cells and as expected from migratory behavior described in previous studies. The results support MPIO-based cell tracking as a generally useful tool for studies of human stem cell dynamics in vivo.

Labeling of Luciferase/eGFP-expressing bone marrow-derived stromal cells with fluorescent micron-sized iron oxide particles improves quantitative and qualitative multimodal imaging of cellular grafts in vivo

PURPOSE

Development of multimodal imaging strategies is currently of utmost importance for the validation of preclinical stem cell therapy studies.

PROCEDURES

We performed a combined labeling strategy for bone marrow-derived stromal cells (BMSC) based on genetic modification with the reporter genes Luciferase and eGFP (BMSC-Luc/eGFP) and physical labeling with blue fluorescent micron-sized iron oxide particles (MPIO) in order to unambiguously identify BMSC localization, survival, and differentiation following engraftment in the central nervous system of mice by in vivo bioluminescence (BLI) and magnetic resonance imaging and postmortem histological analysis.

RESULTS

Using this combination, a significant increase of in vivo BLI signal was observed for MPIO-labeled BMSC-Luc/eGFP. Moreover, MPIO labeling of BMSC-Luc/eGFP allows for the improved identification of implanted cells within host tissue during histological observation.

CONCLUSIONS

This study describes an optimized labeling strategy for multimodal stem cell imaging resulting in improved quantitative and qualitative detection of cellular grafts.

Formulation and in vitro characterization of composite biodegradable magnetic nanoparticles for magnetically guided cell delivery

PURPOSE

Cells modified with magnetically responsive nanoparticles (MNP) can provide the basis for novel targeted therapeutic strategies. However, improvements are required in the MNP design and cell treatment protocols to provide adequate magnetic properties in balance with acceptable cell viability and function. This study focused on select variables controlling the uptake and cell compatibility of biodegradable polymer-based MNP in cultured endothelial cells.

METHODS

Fluorescent-labeled MNP were formed using magnetite and polylactide as structural components. Their magnetically driven sedimentation and uptake were studied fluorimetrically relative to cell viability in comparison to non-magnetic control conditions. The utility of surface-activated MNP forming affinity complexes with replication-deficient adenovirus (Ad) for transduction achieved concomitantly with magnetic cell loading was examined using the green fluorescent protein reporter.

RESULTS

A high-gradient magnetic field was essential for sedimentation and cell binding of albumin-stabilized MNP, the latter being rate-limiting in the MNP loading process. Cell loading up to 160 pg iron oxide per cell was achievable with cell viability >90%. Magnetically driven uptake of MNP-Ad complexes can provide high levels of transgene expression potentially useful for a combined cell/gene therapy.

CONCLUSIONS

Magnetically responsive endothelial cells for targeted delivery applications can be obtained rapidly and efficiently using composite biodegradable MNP.

14.1 T whole body MRI for detection of mesoangioblast stem cells in a murine model of Duchenne muscular dystrophy

Noninvasive imaging procedures will be important for stem cell therapy for muscular dystrophy (MD). Mesoangioblasts regenerate muscle in animal models of muscular dystrophy. In this study, superparamagnetic iron oxide nanoparticles were used to visualize mesoangioblasts in vivo with MRI. Mesoangioblasts incorporated superparamagnetic iron oxide without transfection reagents, and cell differentiation was not negatively impacted. A custom-built radiofrequency coil with an adjustable field of view and 14.1 T magnet were used for whole-body MRI of mice. High-resolution images of mesoangioblasts in skeletal and cardiac muscle of Mdx mice were obtained following local delivery. Labeled cells were verified by Prussian blue staining and dystrophin expression, indicating that the wild-type mesoangioblasts survived and differentiated in muscle. Iron-labeled cells were detected with MRI in vivo 6 months following intracardiac injection but were determined to be activated macrophages. Iron-labeled cells were not detected by MRI following systemic delivery but were present in skeletal and cardiac muscle, visualized by Prussian blue staining. Systemically delivered mesoangioblasts were detected in lungs by Prussian blue staining and DiI but not by MRI in our study. MRI may be useful for short-term tracking of mesoangioblasts delivered locally but not for long-term monitoring or detection after systemic delivery.

Efficacy and Durability in Direct Labeling of Mesenchymal Stem Cells Using Ultrasmall Superparamagnetic Iron Oxide Nanoparticles with Organosilica, Dextran, and PEG Coatings

We herein report a comparative study of mesenchymal stem cell (MSC) labeling using spherical superparamagnetic iron oxide (SPIO) nanoparticles containing different coatings, namely, organosilica, dextran, and poly(ethylene glycol) (PEG). These nanomaterials possess a similar SPIO core size of 6–7 nm. Together with their coatings, the overall sizes are 10–15 nm for all SPIO@SiO₂, SPIO@dextran, and SPIO@PEG nanoparticles. These nanoparticles were investigated for their efficacies to be uptaken by rabbit bone marrow-derived MSCs without any transfecting agent. Experimentally, both SPIO@SiO₂ and SPIO@PEG nanoparticles could be successfully uptaken by MSCs while the SPIO@dextran nanoparticles demonstrated limited labeling efficiency. The labeling durability of SPIO@SiO₂ and SPIO@PEG nanoparticles in MSCs after three weeks of culture were compared by Prussian blue staining tests. SPIO@SiO₂ nanoparticles demonstrated more blue staining than SPIO@PEG nanoparticles, rendering them better materials for MSCs labeling by direct uptake when durable intracellullar retention of SPIO is desired.

A biological global positioning system: considerations for tracking stem cell behaviors in the whole body

Many recent research studies have proposed stem cell therapy as a treatment for cancer, spinal cord injuries, brain damage, cardiovascular disease, and other conditions. Some of these experimental therapies have been tested in small animals and, in rare cases, in humans. Medical researchers anticipate extensive clinical applications of stem cell therapy in the future. The lack of basic knowledge concerning basic stem cell biology-survival, migration, differentiation, integration in a real time manner when transplanted into damaged CNS remains an absolute bottleneck for attempt to design stem cell therapies for CNS diseases. A major challenge to the development of clinical applied stem cell therapy in medical practice remains the lack of efficient stem cell tracking methods. As a result, the fate of the vast majority of stem cells transplanted in the human central nervous system (CNS), particularly in the detrimental effects, remains unknown. The paucity of knowledge concerning basic stem cell biology--survival, migration, differentiation, integration in real-time when transplanted into damaged CNS remains a bottleneck in the attempt to design stem cell therapies for CNS diseases. Even though excellent histological techniques remain as the gold standard, no good in vivo techniques are currently available to assess the transplanted graft for migration, differentiation, or survival. To address these issues, herein we propose strategies to investigate the lineage fate determination of derived human embryonic stem cells (hESC) transplanted in vivo into the CNS. Here, we describe a comprehensive biological Global Positioning System (bGPS) to track transplanted stem cells. But, first, we review, four currently used standard methods for tracking stem cells in vivo: magnetic resonance imaging (MRI), bioluminescence imaging (BLI), positron emission tomography (PET) imaging and fluorescence imaging (FLI) with quantum dots. We summarize these modalities and propose criteria that can be employed to rank the practical usefulness for specific applications. Based on the results of this review, we argue that additional qualities are still needed to advance these modalities toward clinical applications. We then discuss an ideal procedure for labeling and tracking stem cells in vivo, finally, we present a novel imaging system based on our experiments.

Magnetic drug delivery and targeting: principles and applications

BACKGROUND

Nanomaterials are at the leading edge of the rapidly developing field of nanotechnology. Magnetic nanoparticles for cancer therapy and diagnosis have been developed on the basis of their unique physico-chemical properties not present in other materials. Their versatility is widely exploited in such diverse techniques as cell and macromolecule separation and purification, immunoassays, targeted drug delivery, controlled material release, electromagnetic hyperthermia, gene therapy, or magnetic resonance imaging. In this review we concentrate on the physical principles of magnetic drug targeting and biomedical applications of this technique.

METHODS AND RESULTS

We examined several databases, PubMed, ISI Web of Knowledge, and Scopus, for the period 1985-2009, with specific attention to studies that used targeting of magnetic nanoparticles especially in the therapy and diagnostics of tumors. We have also presented several of our own results on theoretical simulations of magnetic particle motion in external magnetic field.

CONCLUSIONS

We found growing number of published papers in this field of nanomedicine, showing the almost unlimited potential of magnetic nanoparticles in the field of experimental and clinical oncology.