Magnetic resonance imaging overestimates ferumoxide-labeled stem cell survival after transplantation in the heart

Spatial and temporal tracking of multi-layered cells sheet using reporter gene imaging with human sodium iodide symporter: a preclinical study using a rat model of myocardial infarction

PURPOSE

This study aimed to evaluate a novel technique for cell tracking by visualising the activity of the human sodium/iodide symporter (hNIS) after transplantation of hNIS-expressing multilayered cell sheets in a rat model of chronic myocardial infarction.

METHODS

Triple-layered cell sheets were generated from mouse embryonic fibroblasts (MEFs) derived from mice overexpressing hNIS (hNIS-Tg). Myocardial infarction was induced by permanent ligation of the left anterior descending coronary artery in F344 athymic rats, and a triple-layered MEFs sheets were transplanted to the infarcted area two weeks after surgery. To validate the temporal tracking and kinetic analysis of the transplanted MEFs sheets, sequential cardiac single-photon emission computed tomography (SPECT) examinations with a 99mTcO4- injection were performed. The cell sheets generated using MEFs of wild-type mice (WT) served as controls.

RESULTS

A significantly higher amount of 99mTcO4- was taken into the hNIS-Tg MEFs than into WT MEFs (146.1 ± 30.9-fold). The obvious accumulation of 99mTcO4- was observed in agreement with the region where hNIS-Tg MEFs were transplanted, and these radioactivities peaked 40-60 min after 99mTcO4- administration. The volume of distribution of the hNIS-Tg MEF sheets declined gradually after transplantation, implying cellular malfunction and a loss in the number of transplanted cells.

CONCLUSION

The reporter gene imaging with hNIS enables the serial tracking and quantitative kinetic analysis of cell sheets transplanted to infarcted hearts.

Bright ferritin for long-term MR imaging of human embryonic stem cells

BACKGROUND

A non-invasive imaging technology that can monitor cell viability, retention, distribution, and interaction with host tissue after transplantation is needed for optimizing and translating stem cell-based therapies. Current cell imaging approaches are limited in sensitivity or specificity, or both, for in vivo cell tracking. The objective of this study was to apply a novel ferritin-based magnetic resonance imaging (MRI) platform to longitudinal tracking of human embryonic stem cells (hESCs) in vivo.

METHODS

Human embryonic stem cells (hESCs) were genetically modified to stably overexpress ferritin using the CRISPR-Cas9 system. Cellular toxicity associated with ferritin overexpression and manganese (Mn) supplementation were assessed based on cell viability, proliferation, and metabolic activity. Ferritin-overexpressing hESCs were characterized based on stem cell pluripotency and cardiac-lineage differentiation capability. Cells were supplemented with Mn and imaged in vitro as cell pellets on a preclinical 3 T MR scanner. T1-weighted images and T1 relaxation times were analyzed to assess contrast. For in vivo study, three million cells were injected into the leg muscle of non-obese diabetic severe combined immunodeficiency (NOD SCID) mice. Mn was administrated subcutaneously. T1-weighted sequences and T1 mapping were used to image the animals for longitudinal in vivo cell tracking. Cell survival, proliferation, and teratoma formation were non-invasively monitored by MRI. Histological analysis was used to validate MRI results.

RESULTS

Ferritin-overexpressing hESCs labeled with 0.1 mM MnCl2 provided significant T1-induced bright contrast on in vitro MRI, with no adverse effect on cell viability, proliferation, pluripotency, and differentiation into cardiomyocytes. Transplanted hESCs displayed significant bright contrast on MRI 24 h after Mn administration, with contrast persisting for 5 days. Bright contrast was recalled at 4-6 weeks with early teratoma outgrowth.

CONCLUSIONS

The bright-ferritin platform provides the first demonstration of longitudinal cell tracking with signal recall, opening a window on the massive cell death that hESCs undergo in the weeks following transplantation before the surviving cell fraction proliferates to form teratomas.

In vivo tracking of unlabelled mesenchymal stromal cells by mannose-weighted chemical exchange saturation transfer MRI

The tracking of the in vivo biodistribution of transplanted human mesenchymal stromal cells (hMSCs) relies on reporter genes or on the addition of exogenous imaging agents. However, reporter genes and exogenous labels may require bespoke manufacturing and regulatory processes if used in cell therapies, and the labels may alter the cells' properties and are diluted on cellular division. Here we show that high-mannose N-linked glycans, which are abundantly expressed on the surface of hMSCs, can serve as a biomarker for the label-free tracking of transplanted hMSCs by mannose-weighted chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI). For live mice with luciferase-transfected hMSCs transplanted into their brains, post-mortem fluorescence staining with a mannose-specific lectin showed that increases in the CEST MRI signal, which correlated well with the bioluminescence intensity of viable hMSCs for 14 days, corresponded to the presence of mannose. In vitro, osteogenically differentiated hMSCs led to lower CEST MRI signal intensities owing to the concomitantly reduced expression of mannose. The label-free imaging of hMSCs may facilitate the development and testing of cell therapies.

Ferromagnetic Vortex Iron Oxide Nanorings Modified with Integrin β1 Antibody for Targeted MRI Tracking of Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) have demonstrated great potential for tissue engineering and regenerative medicine applications. Noninvasive and real-term tracking of transplanted MSCs in vivo is crucial for studying the distribution and migration of MSCs, and their role in tissue injury repair. This study reports on the use of ferrimagnetic vortex iron oxide (FVIO) nanorings modified with anti-human integrin β1 for specific recognition and magnetic resonance imaging (MRI) tracking of human MSCs (hMSCs). Integrin β1 is highly expressed at all stem cell proliferation and differentiation stages. Therefore, the anti-integrin β1 antibody (Ab) introduced in FVIO targets integrin β1, thus enabling FVIO to target stem cells at any stage. This is unlike the traditional MRI-based monitoring of transplanted stem cells, which usually requires pre-labeling the stem cells with tracers before injection. Because of the ability to recognize hMSCs, the Ab-modified FVIO nanotracers (FVIO-Ab) have the advantage of not requiring pre-labeling before stem cell transplantation. Furthermore, the FVIO-Ab nanotracers have high T^*₂ contrast resulting from the unique magnetic properties of FVIO which can improve the MRI tracking efficiency of stem cells. This work may provide a new way for stem cell labeling and in vivo MRI tracking, thus reducing the risks associated with stem cell transplantation and promoting clinical translation.

Nanomagnet-facilitated pharmaco-compatibility for cancer diagnostics: Underlying risks and the emergence of ultrasmall nanomagnets

Cancer therapy is a fast-emerging biomedical paradigm that elevates the diagnostic and therapeutic potential of a nanovector for identification, monitoring, targeting, and post-treatment response analysis. Nanovectors of superparamagnetic iron oxide nanoparticles (SPION) are of tremendous significance in cancer therapy because of their inherited high surface area, high reactivity, biocompatibility, superior contrast, and magnetic and photo-inducibility properties. In addition to a brief introduction, we summarize various progressive aspects of nanomagnets pertaining to their production with an emphasis on sustainable biomimetic approaches. Post-synthesis particulate and surface alterations in terms of pharmaco-affinity, liquid accessibility, and biocompatibility to facilitate cancer therapy are highlighted. SPION parameters including particle contrast, core-fusions, surface area, reactivity, photosensitivity, photodynamics, and photothermal properties, which facilitate diverse cancer diagnostics, are discussed. We also elaborate on the concept of magnetism to selectively focus chemotherapeutics on tumors, cell sorting, purification of bioentities, and elimination of toxins. Finally, while addressing the toxicity of nanomaterials, the advent of ultrasmall nanomagnets as a healthier alternative with superior properties and compatible cellular interactions is reviewed. In summary, these discussions spotlight the versatility and integration of multi-tasking nanomagnets and ultrasmall nanomagnets for diverse cancer theragnostics.

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SPION synthesis with ascribed prominence on sustainable procedures.

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Particulate species, composition, and surface alteration-enabled theragnostics are highlighted.

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Inherent properties of SPIONs facilitating cancer diagnostics are elaborated.

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Magnetism-based “chemotherapeutics,” cell-sorting, and bioentity purification are emphasized.

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Emergence of ultrasmall SPIONs as a healthier option is summarized.

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.

Options for imaging cellular therapeutics in vivo: a multi-stakeholder perspective

Cell-based therapies have been making great advances toward clinical reality. Despite the increase in trial activity, few therapies have successfully navigated late-phase clinical trials and received market authorization. One possible explanation for this is that additional tools and technologies to enable their development have only recently become available. To support the safety evaluation of cell therapies, the Health and Environmental Sciences Institute Cell Therapy-Tracking, Circulation and Safety Committee, a multisector collaborative committee, polled the attendees of the 2017 International Society for Cell & Gene Therapy conference in London, UK, to understand the gaps and needs that cell therapy developers have encountered regarding safety evaluations in vivo. The goal of the survey was to collect information to inform stakeholders of areas of interest that can help ensure the safe use of cellular therapeutics in the clinic. This review is a response to the cellular imaging interests of those respondents. The authors offer a brief overview of available technologies and then highlight the areas of interest from the survey by describing how imaging technologies can meet those needs. The areas of interest include imaging of cells over time, sensitivity of imaging modalities, ability to quantify cells, imaging cellular survival and differentiation and safety concerns around adding imaging agents to cellular therapy protocols. The Health and Environmental Sciences Institute Cell Therapy-Tracking, Circulation and Safety Committee believes that the ability to understand therapeutic cell fate is vital for determining and understanding cell therapy efficacy and safety and offers this review to aid in those needs. An aim of this article is to share the available imaging technologies with the cell therapy community to demonstrate how these technologies can accomplish unmet needs throughout the translational process and strengthen the understanding of cellular therapeutics.

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.

Long-Term Tri-Modal In Vivo Tracking of Engrafted Cartilage-Derived Stem/Progenitor Cells Based on Upconversion Nanoparticles

Cartilage-derived stem/progenitor cells (CSPCs) are a potential choice for seed cells in osteal and chondral regeneration, and the outcomes of their survival and position distribution in vivo form the basis for the investigation of their mechanism. However, the current use of in vivo stem cell tracing techniques in laboratories is relatively limited, owing to their high operating costs and cytotoxicity. Herein, we performed tri-modal in vivo imaging of CSPCs during subcutaneous chondrogenesis using upconversion nanoparticles (UCNPs) for 28 days. Distinctive signals at accurate positions were acquired without signal noise from X-ray computed tomography, magnetic resonance imaging, and upconversion luminescence. The measured intensities were all significantly proportional to the cell numbers, thereby enabling real-time in vivo quantification of the implanted cells. However, limitations of the detectable range of cell numbers were also observed, owing to the imaging shortcomings of UCNPs, which requires further improvement of the nanoparticles. Our study explores the application value of upconversion nanomaterials in the tri-modal monitoring of implanted stem cells and provides new perspectives for future clinical translation.

Mitochondrial Transplantation: A Critical Analysis

"Mitochondrial transplantation" refers to a procedure for introducing isolated mitochondria into a damaged area of a heart or other organ. A considerable amount of data has been accumulated on the therapeutic effects of "mitochondrial transplantation" in animals with ischemic heart damage. In 2017, the first attempts were made to apply this procedure in a clinic. The authors of the method suggest that exogenous mitochondria penetrate into cardiomyocytes, retaining functional activity, and compensate for impaired energy output of endogenous mitochondria. This hypothesis contradicts the well-known fact of loss of mitochondrial functions in the presence of high concentrations of Ca2+, which are characteristic of the extracellular medium. This review critically considers the possible mechanisms of the therapeutic effect of "mitochondrial transplantation".

Nanotechnology shaping stem cell therapy: Recent advances, application, challenges, and future outlook

Currently, stem cell nanotechnology is one of the novel and exciting fields. Certain experimental studies conducted on the interaction of stem cells with nanostructures or nanomaterials have made significant progress. The significance of nanostructures, nanotechnology, and nanomaterials in the development of stem cell-based therapies for degenerative diseases and injuries has been well established. Specifically, the structure and properties of nanomaterials affecting the propagation and differentiation of stem cells have become a new interdisciplinary frontier in material science and regeneration medicines. In the current review, we highlight the recent major progress in this field, explore the application prospects, and discuss the issues, approaches, and challenges, to improve the applications of nanotechnology in the research and development of stem cells.

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.

Tissue-Specific Ferritin- and GFP-Based Genetic Vectors Visualize Neurons by MRI in the Intact and Post-Ischemic Rat Brain

(1) Background: Neurogenesis is considered to be a potential brain repair mechanism and is enhanced in stroke. It is difficult to reconstruct the neurogenesis process only from the histological sections taken from different animals at different stages of brain damage and restoration. Study of neurogenesis would greatly benefit from development of tissue-specific visualization probes. (2) Purpose: The study aimed to explore if overexpression of ferritin, a nontoxic iron-binding protein, under a doublecortin promoter can be used for non-invasive visualization of neurogenesis using magnetic resonance imaging (MRI). (3) Methods: Ferritin heavy chain (FerrH) was expressed in the adeno-associated viral backbone (AAV) under the doublecortin promoter (pDCX), specific for young neurons, in the viral construct AAV-pDCX-FerrH. Expression of the enhanced green fluorescent protein (eGFP) was used as an expression control (AAV-pDCX-eGFP). The viral vectors or phosphate-buffered saline (PBS) were injected intracerebrally into 18 adult male Sprague–Dawley rats. Three days before injection, rats underwent transient middle-cerebral-artery occlusion or sham operation. Animals were subjected to In vivo MRI study before surgery and on days 7, 14, 21, and 28 days after injection using a Bruker BioSpec 11.7 T scanner. Brain sections obtained on day 28 after injection were immunostained for ferritin, young (DCX) and mature (NeuN) neurons, and activated microglia/macrophages (CD68). Additionally, RT-PCR was performed to confirm ferritin expression. (4) Results: T2* images in post-ischemic brains of animals injected with AAV-pDCX-FerrH showed two distinct zones of MRI signal hypointensity in the ipsilesioned hemisphere starting from 14 days after viral injection—in the ischemic lesion and near the lateral ventricle and subventricular zone (SVZ). In sham-operated animals, only one zone of hypointensity near the lateral ventricle and SVZ was revealed. Immunochemistry showed that ferritin-expressing cells in ischemic lesions were macrophages (88.1%), while ferritin-expressing cells near the lateral ventricle in animals both after ischemia and sham operation were mostly mature (55.7% and 61.8%, respectively) and young (30.6% and 7.1%, respectively) neurons. RT-PCR confirmed upregulated expression of ferritin in the caudoputamen and corpus callosum. Surprisingly, in animals injected with AAV-pDCX-eGFP we similarly observed two zones of hypointensity on T2* images. Cellular studies also showed the presence of mature (81.5%) and young neurons (6.1%) near the lateral ventricle in both postischemic and sham-operated animals, while macrophages in ischemic lesions were ferritin-positive (98.2%). (5) Conclusion: Ferritin overexpression induced by injection of AAV-pDCX-FerrH was detected by MRI using T2*-weighted images, which was confirmed by immunochemistry showing ferritin in young and mature neurons. Expression of eGFP also caused a comparable reduced MR signal intensity in T2*-weighted images. Additional studies are needed to investigate the potential and tissue-specific features of the use of eGFP and ferritin expression in MRI studies.

Organ-specific toxicity of magnetic iron oxide-based nanoparticles

The unique properties of magnetic iron oxide nanoparticles determined their widespread use in medical applications, the food industry, textile industry, which in turn led to environmental pollution. These factors determine the long-term nature of the effect of iron oxide nanoparticles on the body. However, studies in the field of chronic nanotoxicology of magnetic iron particles are insufficient and scattered. Studies show that toxicity may be increased depending on oral and inhalation routes of administration rather than injection. The sensory nerve pathway can produce a number of specific effects not seen with other routes of administration. Organ systems showing potential toxic effects when injected with iron oxide nanoparticles include the nervous system, heart and lungs, the thyroid gland, and organs of the mononuclear phagocytic system (MPS). A special place is occupied by the reproductive system and the effect of nanoparticles on the health of the first and second generations of individuals exposed to the toxic effects of iron oxide nanoparticles. This knowledge should be taken into account for subsequent studies of the toxicity of iron oxide nanoparticles. Particular attention should be paid to tests conducted on animals with pathologies representing human chronic socially significant diseases. This part of preclinical studies is almost in its infancy but of great importance for further medical translation on nanomaterials to practice.

Magnetic resonance imaging of human neural stem cells in rodent and primate brain

Stem cell transplantation therapies are currently under investigation for central nervous system disorders. Although preclinical models show benefit, clinical translation is somewhat limited by the absence of reliable noninvasive methods to confirm targeting and monitor transplanted cells in vivo. Here, we assess a novel magnetic resonance imaging (MRI) contrast agent derived from magnetotactic bacteria, magneto‐endosymbionts (MEs), as a translatable methodology for in vivo tracking of stem cells after intracranial transplantation. We show that ME labeling provides robust MRI contrast without impairment of cell viability or other important therapeutic features. Labeled cells were visualized immediately post‐transplantation and over time by serial MRI in nonhuman primate and mouse brain. Postmortem tissue analysis confirmed on‐target grft location, and linear correlations were observed between MRI signal, cell engraftment, and tissue ME levels, suggesting that MEs may be useful for determining graft survival or rejection. Overall, these findings indicate that MEs are an effective tool for in vivo tracking and monitoring of cell transplantation therapies with potential relevance to many cellular therapy applications.

Non-viral reprogramming and induced pluripotent stem cells for cardiovascular therapy

Despite significant effort devoted to developing new treatments and procedures, cardiac disease is still one of the leading causes of death in the world. The loss of myocytes due to ischemic injury remains a major therapeutic challenge. However, cell-based therapy to repair the injured heart has shown significant promise in basic and translation research and in clinical trials. Embryonic stem cells have been successfully used to improve cardiac outcomes. Unfortunately, treatment with these cells is complicated by ethical and legal issues. Recent progress in developing induced pluripotent stem cells (iPSCs) using non-viral vectors has made it possible to derive cardiomyocytes for therapy. This review will focus on these non-integration-based approaches for reprogramming and their therapeutic advantages for cardiovascular medicine.

In Vivo MRI Tracking of Mesenchymal Stromal Cells Labeled with Ultrasmall Paramagnetic Iron Oxide Particles after Intramyocardial Transplantation in Patients with Chronic Ischemic Heart Disease

Background

While regenerative stem cell therapy for ischemic heart disease has moved into phase 3 studies, little is still known about retention and migration of cell posttransplantation. In human studies, the ability to track transplanted cells has been limited to labeling with radioisotopes and tracking using nuclear imaging. This method is limited by low resolution and short half-lives of available radioisotopes. Longitudinal tracking using magnetic resonance imaging (MRI) of myocardial injected cells labeled with iron oxide nanoparticles has shown promising results in numerous preclinical studies but has yet to be evaluated in human studies. We aimed to evaluate MRI tracking of mesenchymal stromal cells (MSCs) labeled with ultrasmall paramagnetic iron oxide (USPIO) nanoparticles after intramyocardial transplantation in patients with ischemic heart disease (IHD).

Methods

Five no-option patients with chronic symptomatic IHD underwent NOGA-guided intramyocardial transplantation of USPIO-labeled MSCs. Serial MRI scans were performed to track labeled cells both visually and using semiautomated T2∗ relaxation time analysis. For safety, we followed symptoms, quality of life, and myocardial function for 6 months.

Results

USPIO-labeled MSCs were tracked for up to 14 days after transplantation at injection sites both visually and using semiautomated regional T2∗ relaxation time analysis. Labeling of MSCs did not impair long-term safety of treatment.

Conclusion

This was a first-in-man clinical experience aimed at evaluating the utility of MRI tracking of USPIO-labeled bone marrow-derived autologous MSCs after intramyocardial injection in patients with chronic IHD. The treatment was safe, and cells were detectable at injection sites up to 14 days after transplantation. Further studies are needed to clarify if MSCs migrate out of the injection area into other areas of the myocardium or if injected cells are washed out into the peripheral circulation. The trial is registered with ClinicalTrials.gov NCT03651791.

Nanoscale Technologies for Prevention and Treatment of Heart Failure: Challenges and Opportunities

The adult myocardium has a limited regenerative capacity following heart injury, and the lost cells are primarily replaced by fibrotic scar tissue. Suboptimal efficiency of current clinical therapies to resurrect the infarcted heart results in injured heart enlargement and remodeling to maintain its physiological functions. These remodeling processes ultimately leads to ischemic cardiomyopathy and heart failure (HF). Recent therapeutic approaches (e.g., regenerative and nanomedicine) have shown promise to prevent HF postmyocardial infarction in animal models. However, these preclinical, clinical, and technological advancements have yet to yield substantial enhancements in the survival rate and quality of life of patients with severe ischemic injuries. This could be attributed largely to the considerable gap in knowledge between clinicians and nanobioengineers. Development of highly effective cardiac regenerative therapies requires connecting and coordinating multiple fields, including cardiology, cellular and molecular biology, biochemistry and chemistry, and mechanical and materials sciences, among others. This review is particularly intended to bridge the knowledge gap between cardiologists and regenerative nanomedicine experts. Establishing this multidisciplinary knowledge base may help pave the way for developing novel, safer, and more effective approaches that will enable the medical community to reduce morbidity and mortality in HF patients.

Albumin nanocomposites with MnO2/Gd2O3 motifs for precise MR imaging of acute myocardial infarction in rabbit models

The severe mortality and morbidity of myocardial infarction requests appropriate and accurate detection. Considering pathological profile of the acidic myocardial infarction microenvironments, herein, the low pH-sensitive albumin nanocomposites with MnO₂ motifs (MnO₂@BSA) have been engineered for T₁-weighted MR imaging of myocardial infarction, while using non-pH-responsive Gd₂O₃@BSA nanocomposites as control. The nanocomposites were 20-30 nm in diameter with spheroid morphology. Besides, the MnO₂@BSA have exhibited pH-triggered releasing of Mn²⁺, demonstrating approximately 38-fold and 55-fold increased molecular relaxivity at acute myocardial infarction-mimicking pH 6.5 (13.08 mM^-1s^-1) and macrophage intracellular pH 5.0 (18.76 mM^-1s^-1) compared to the extremely low relaxivity (0.34 mM^-1s^-1) at normal physiological conditions (pH 7.4). However, the Gd₂O₃@BSA with molecular relaxivity approximately 10 mM^-1s^-1 were without pH-sensitive properties. Furthermore, the MnO₂@BSA have demonstrated high accumulation in the acute myocardial infarction regions and fast metabolism from the body after systemic injection, accounting high contrast enhancement for accurate MR imaging of acute myocardial infarction in rabbit models, demonstrating better diagnostic performance over the controls.

Iron Oxide Labeling and Tracking of Extracellular Vesicles

Extracellular vesicles (EVs) are essential tools for conveying biological information and modulating functions of recipient cells. Implantation of isolated or modulated EVs can be innovative therapeutics for various diseases. Furthermore, EVs could be a biocompatible drug delivery vehicle to carry both endogenous and exogenous biologics. Tracking EVs should play essential roles in understanding the functions of EVs and advancing EV therapeutics. EVs have the characteristic structures consisting of the lipid bilayer and specific membrane proteins, through which they can be labeled efficiently. EVs can be labeled either directly using probes or indirectly by transfection of reporter genes. Optical imaging (fluorescent imaging and bioluminescent imaging), single-photon emission computed tomography (SPECT)/positron emission tomography (PET), and magnetic resonance imaging (MRI) are currently used for imaging EVs. Labeling EVs with superparamagnetic iron oxide (SPIO) nanoparticles for MRI tracking is a promising method that can be translated into clinic. SPIO can be internalized by most of the cell types and then released as SPIO containing EVs, which can be visualized on T2*-weighted imaging. However, this method has limitations in real-time imaging because of the life cycle of SPIO after EV degradation. Further studies will be needed to validate SPIO labeling by other imaging modalities in preclinical studies. The emerging technologies of labeling and imaging EVs with SPIO in comparison with other imaging modalities are reviewed in this paper.

Gadolinium-Labelled Cell Scaffolds to Follow-up Cell Transplantation by Magnetic Resonance Imaging

Cell scaffolds are often used in cell transplantation as they provide a solid structural support to implanted cells and can be bioengineered to mimic the native extracellular matrix. Gadolinium fluoride nanoparticles (Gd-NPs) as a contrast agent for Magnetic Resonance Imaging (MRI) were incorporated into poly(lactide-co-glycolide)/chitosan scaffolds to obtain Imaging Labelled Cell Scaffolds (ILCSs), having the shape of hollow spherical/ellipsoidal particles (200-600 μm diameter and 50-80 μm shell thickness). While Gd-NPs incorporated into microparticles do not provide any contrast enhancement in T1-weighted (T1w) MR images, ILCSs can release Gd-NPs in a controlled manner, thus activating MRI contrast. ILCSs seeded with human mesenchymal stromal cells (hMSCs) were xenografted subcutaneously into either immunocompromised and immunocompetent mice without any immunosuppressant treatments, and the transplants were followed-up in vivo by MRI for 18 days. Immunocompromised mice showed a progressive activation of MRI contrast within the implants due to the release of Gd-NPs in the extracellular matrix. Instead, immunocompetent mice showed poor activation of MRI contrast due to the encapsulation of ILCSs within fibrotic capsules and to the scavenging of released Gd-NPs by phagocytic cells. In conclusion, the MRI follow-up of cell xenografts can report the host cell response to the xenograft. However, it does not strictly report on the viability of transplanted hMSCs.

Clinical Tracking of Cell Transfer and Cell Transplantation: Trials and Tribulations

Cell therapy has provided unprecedented opportunities for tissue repair and cancer therapy. Imaging tools for in vivo tracking of therapeutic cells have entered the clinic to evaluate therapeutic cell delivery and retention in patients. Thus far, clinical cell tracking studies have been a mere proof of principle of the feasibility of cell detection. This review centers around the main clinical queries associated with cell therapy: Have cells been delivered correctly at the targeted site of injection? Are cells still alive, and, if so, how many? Are cells being rejected by the host, and, if so, how severe is the immune response? For stem cell therapeutics, have cells differentiated into downstream cell lineages? Is there cell proliferation including tumor formation? At present, clinical cell tracking trials have only provided information on immediate cell delivery and short-term cell retention. The next big question is if these cell tracking tools can improve the clinical management of the patients and, if so, by how much, for how many, and for whom; in addition, it must be determined whether tracking therapeutic cells in every patient is needed. To become clinically relevant, it must now be demonstrated how cell tracking techniques can inform patient treatment and affect clinical outcomes.

Transplantation of human mobilized mononuclear cells improved diabetic neuropathy

Rodent stem cells demonstrated regenerative effects in diabetic neuropathy via improvement in nerve perfusion. As a pre-clinical step, we explored if human mobilized mononuclear cells (hMNC) would have the same effects in rats. hMNC were injected into Rt. hind-limb muscles of streptozotocin-induced diabetic nude rats, and the grafts were monitored using with MRI. After 4 weeks, the effects were compared with those in the vehicle-injected Lt. hind limbs. Nerve conduction, muscle perfusion and gene expression of sciatic nerves were assessed. Induction of diabetes decreased nerve function and expression of Mpz and Met in the sciatic nerves, which are related with myelination. hMNC injection significantly improved the amplitude of compound muscle action potentials along with muscle perfusion and sciatic nerve Mpz expression. On MRI, hypointense signals were observed for 4 weeks at the graft site, but their correlation with the presence of hMNC was detectable for only 1 week. To evaluate paracrine effects of hMNC, IMS32 cells were tested with hepatocyte growth factor (HGF), which had been reported as a myelination-related factor from stem cells. We could observe that HGF enhanced Mpz expression in the IMS32 cells. Because hMNC secreted HGF, IMS32 cells were co-cultured with hMNC, and the expression of Mpz increased along with morphologic maturation. The hMNC-induced Mpz expression was abrogated by treatment of anti-HGF. These results suggest that hMNC could improve diabetic neuropathy, possibly through enhancement of myelination as well as perfusion. According to in vitro studies, HGF was involved in the hMNC-induced myelination activity, at least in part.

Evaluation of different routes of administration and biodistribution of human amnion epithelial cells in mice

Placenta is a non-controversial and promising source of cells for the treatment of several liver diseases. We previously reported that transplanted human amnion epithelial cells (hAECs) differentiate into hepatocyte-like cells, resulting in correction of mouse models of metabolic liver disease or acute hepatic failure. As part of preclinical safety studies, we investigated the distribution of hAECs using two routes of administration to efficiently deliver hAECs to the liver. Optical imaging is commonly used because it can provide fast, high-throughput, whole-body imaging, thus DiR-labeled hAECs were injected into immunodeficient mice, via the spleen or the tail vein. The cell distribution was monitored using an in vivo imaging system over the next 24 h. After splenic injection, the DiR signal was detected in liver and spleen at 1, 3 and 24 h post-transplant. The distribution was confirmed by analysis of human DNA content at 24 h post-transplant and human-specific cytokeratin 8/18 staining. Tail vein infusion resulted in cell engraftment mainly in the lungs, with minimal detection in the liver. Delivery of cells to the portal vein, via the spleen, resulted in efficient delivery of hAECs to the liver, with minimal, off-target distribution to lungs or other organs.

Impaired adhesion of induced pluripotent stem cell-derived cardiac progenitor cells (iPSC-CPCs) to isolated extracellular matrix from failing hearts

We tested the hypothesis that induced pluripotent stem cell-derived cardiac progenitor cells (iPSC-CPCs) are less able to adhere to the extracellular matrix (ECM) derived from failing human hearts with dilated cardiomyopathy compared to nonfailing human heart ECM. We also hypothesized that morphological development, cell beating rates, and mRNA levels of Nkx2.5 and cardiac troponin T would be altered after culturing the iPSC-CPCs on the failing heart ECM under cardiomyocyte differentiation conditions. We used microscopy to distinguish between adhered and unadhered cells, and to determine morphological development and cell beating. We used qPCR to determine mRNA levels. iPSC-CPCs show a significantly reduced ability to adhere to the ECM of failing hearts and higher expression of Nkx2.5 mRNA. However, morphological development, cell beating rates, and cardiac troponin T levels were not significantly altered in the cells cultured on the failing heart ECM. Our study shows that the failing heart ECM from patients with dilated cardiomyopathy impairs initial iPSC-CPC adhesion and may have a modest effect on the ability of the cells to transdifferentiate into cardiomyocytes.

Contribution of macrophages in the contrast loss in iron oxide-based MRI cancer cell tracking studies

Magnetic resonance imaging (MRI) cell tracking of cancer cells labeled with superparamagnetic iron oxides (SPIO) allows visualizing metastatic cells in preclinical models. However, previous works showed that the signal void induced by SPIO on T₂(*)-weighted images decreased over time. Here, we aim at characterizing the fate of iron oxide nanoparticles used in cell tracking studies and the role of macrophages in SPIO metabolism.

In vivo MRI cell tracking of SPIO positive 4T1 breast cancer cells revealed a quick loss of T₂* contrast after injection. We next took advantage of electron paramagnetic resonance (EPR) spectroscopy and inductively coupled plasma mass spectroscopy (ICP-MS) for characterizing the evolution of superparamagnetic and non-superparamagnetic iron pools in 4T1 breast cancer cells and J774 macrophages after SPIO labeling. These in vitro experiments and histology studies performed on 4T1 tumors highlighted the quick degradation of iron oxides by macrophages in SPIO-based cell tracking experiments.

In conclusion, the release of SPIO by dying cancer cells and the subsequent uptake of iron oxides by tumor macrophages are limiting factors in MRI cell tracking experiments that plead for the use of (MR) reporter-gene based imaging methods for the long-term tracking of metastatic cells.

Cell-assembled nanoclusters of MSC-targeting Gd-DOTA-peptide as a T2 contrast agent for MRI cell tracking

A cyclic peptide CC9 that targets cell membrane of mesenchymal stem cells (MSCs) is coupled with Gd-DOTA to yield a Gd-DOTA-CC9 complex as MRI contrast agent. It is used to label human MSCs (hMSCs) via electroporation. Electroporation-labeling of hMSCs with Gd-DOTA-CC9 induces cell-assembly of Gd-DOTA-CC9 nanoclusters in the cytoplasm, significantly promotes cell-labeling efficacy and intracellular retention time of the agent. In vitro MRI of labeled hMSCs exhibits significant signal reduction under T₂ -weighted MRI, which can allow long-term tracking of labeled cell transplants in in vivo migration. The labeling strategy is safe in cytotoxicity and differentiation potential.

In Vivo magnetic resonance imaging of xenografted tumors using FTH1 reporter gene expression controlled by a tet-on switch

As a promising magnetic resonance imaging (MRI) reporter, ferritin has been used to track cells in vivo; however, its continuous overexpression can be cytotoxic, which restricts its application. In this study, we aimed to develop a switch to turn this genetic reporter “on” or “off” while monitoring cell grafts via MRI. To accomplish this, we genetically modified the ferritin heavy chain (FTH1) with a Tet-On switch and assessed the expression of FTH1 in transduced neuroblastoma cells (SK-N-SH) in vitro and in xenografted tumors in vivo. We found that FTH1 expression induced by doxycycline (Dox) in SK-N-SH-FTH1 cells depended on treatment dose and duration. We successfully detected T₂-weighted MRI contrast in cell grafts after switching “on” the reporter gene using Dox, and this contrast disappeared when we switched it “off”. The genetic reporter FTH1 can thus be switched “on” or “off” throughout longitudinal monitoring of cell grafts, limiting expression to when MRI contrast is needed. The controllable imaging system we have developed minimizes risks from constitutive reporter gene overexpression and facilitates tumor cell monitoring in vitro and in vivo.

Stem cell tracking using effective self-assembled peptide-modified superparamagnetic nanoparticles

Peptide modified superparamagnetic iron oxide nanoparticles (SPIONs) have been developed as excellent magnetic resonance imaging (MRI) contrast agents for stem cell labeling and tracking due to their biocompatibility.

Liposome-Indocyanine Green Nanoprobes for Optical Labeling and Tracking of Human Mesenchymal Stem Cells Post-Transplantation In Vivo

Direct labeling of human mesenchymal stem cells (hMSC) prior to transplantation provides a means to track cells after administration and it is a powerful tool for the assessment of new cell-based therapies. Biocompatible nanoprobes consisting of liposome-indocyanine green hybrid vesicles (liposome-ICG) are used to safely label hMSC. Labeled hMSC recapitulating a 3D cellular environment is transplanted as spheroids subcutaneously and intracranially in athymic nude mice. Cells emit a strong NIR signal used for tracking post-transplantation with the IVIS imaging system up to 2 weeks (subcutaneous) and 1 week (intracranial). The transplanted stem cells are imaged in situ after engraftment deep in the brain up to 1 week in living animals using optical imaging techniques and without the need to genetically modify the cells. This method is proposed for efficient, nontoxic direct cell labeling for the preclinical assessment of cell-based therapies and the design of clinical trials, and potentially for localization of the cell engraftment after transplantation into patients.

In vivo tracking of the tropism of mesenchymal stem cells to malignant gliomas using reporter gene-based MR imaging

Mesenchymal stem cells (MSCs) have emerged as a promising cellular vehicle for gene therapy of malignant gliomas due to their property of tumor tropism. However, MSCs may show bidirectional and divergent effects on tumor growth. Therefore, a robust surveillance system with a capacity for noninvasive monitoring of the homing, distribution and fate of stem cells in vivo is highly desired for developing stem cell-based gene therapies for tumors. In this study, we used ferritin gene-based magnetic resonance imaging (MRI) to track the tumor tropism of MSCs in a rat orthotopic xenograft model of malignant glioma. MSCs were transduced with lentiviral vectors expressing ferritin heavy chain (FTH) and enhanced green fluorescent protein (eGFP). Intra-arterial, intravenous and intertumoral injections of these FTH transgenic MSCs (FTH-MSCs) were performed in rats bearing intracranial orthotopic C6 gliomas. The FTH-MSCs were detected as hypointense signals on T2- and T2*-weighted images on a 3.0 T clinical MRI. After intra-arterial injection, 17% of FTH-MSCs migrated toward the tumor and gradually diffused throughout the orthotopic glioma. This dynamic process could be tracked in vivo by MRI up to 10 days of follow-up, as confirmed by histology. Moreover, the tumor tropism of MSCs showed no appreciable impact on the progression of the tumor. These results suggest that FTH reporter gene-based MRI can be used to reliably track the tropism and fate of MSCs after their systemic transplantation in orthotopic gliomas. This real-time in vivo tracking system will facilitate the future development of stem cell-based therapies for malignant gliomas.

In vivo monitoring of magnetically labeled mesenchymal stem cells homing to rabbit hepatic VX2 tumors using magnetic resonance imaging

Although mesenchymal stem cells (MSCs) have been demonstrated to possess a tumor‑homing feature, their tropism to liver tumors has not been delineated in a visible manner. The aim of the present study was to evaluate the tumor‑homing capacity of MSCs and to investigate the spatial and temporal distributions of MSCs in liver tumors using magnetic resonance imaging (MRI). MSCs were colabeled with superparamagnetic iron oxide (SPIO) particles and 4',6‑diamidino‑2‑phenylindole (DAPI), and then transplanted into rabbits with VX2 liver tumors through intravenous injections. The rabbits were subjected to MRI before and at 3, 7 and 14 days after cell transplantation using a clinical 1.5‑T MRI system. Immediately after the MRI examination, histological analyses were performed using fluorescence and Prussian blue staining. At 3 days after injection with labeled MSCs, heterogeneous hypointensity was detected on the MRI images of the tumor. At 7 days after transplantation, the tumor exhibited anisointense MRI signal, whereas a hypointense ring was detected at the border of the tumor. At 14 days after transplantation, the MRI signal recovered the hyperintensity. As demonstrated in the histological analyses, the distribution of the iron particles visualized with Prussian blue staining was consistent with the DAPI‑stained bright fluorescent nuclei, and the particles corresponded to the hypointense region on the MR images. Thus, systemically administered MSCs could localize to liver tumors with high specificity and possessed a migration feature with active tumor growth. These results demonstrated that the targeting and distribution of the magnetically labeled stem cells in the tumor could be tracked for 7 days in vivo using a clinical 1.5‑T MRI scanner.

Molecular imaging in stem cell-based therapies of cardiac diseases

In the past 15years, despite that regenerative medicine has shown great potential for cardiovascular diseases, the outcome and safety of stem cell transplantation has shown controversial results in the published literature. Medical imaging might be useful for monitoring and quantifying transplanted cells within the heart and to serially characterize the effects of stem cell therapy of the myocardium. From the multiple available noninvasive imaging techniques, magnetic resonance imaging and nuclear imaging by positron (PET) or single photon emission computer tomography (SPECT) are the most used clinical approaches to follow the fate of transplanted stem cells in vivo. In this article, we provide a review on the role of different noninvasive imaging modalities and discuss their advantages and disadvantages. We focus on the different in-vivo labeling and reporter gene imaging strategies for stem cell tracking as well as the concept and reliability to use imaging parameters as noninvasive surrogate endpoints for the evaluation of the post-therapeutic outcome.

The long-term fate of mesenchymal stem cells labeled with magnetic resonance imaging-visible polymersomes in cerebral ischemia

Understanding the long-term fate and potential mechanisms of mesenchymal stem cells (MSCs) after transplantation is essential for improving functional benefits of stem cell-based stroke treatment. Magnetic resonance imaging (MRI) is considered an attractive and clinically translatable tool for longitudinal tracking of stem cells, but certain controversies have arisen in this regard. In this study, we used SPION-loaded cationic polymersomes to label green fluorescent protein (GFP)-expressing MSCs to determine whether MRI can accurately reflect survival, long-term fate, and potential mechanisms of MSCs in ischemic stroke therapy. Our results showed that MSCs could improve the functional outcome and reduce the infarct volume of stroke in the brain. In vivo MRI can verify the biodistribution and migration of grafted cells when pre-labeled with SPION-loaded polymersome. The dynamic change of low signal volume on MRI can reflect the tendency of cell survival and apoptosis, but may overestimate long-term survival owing to the presence of iron-laden macrophages around cell graft. Only a small fraction of grafted cells survived up to 8 weeks after transplantation. A minority of these surviving cells were differentiated into astrocytes, but not into neurons. MSCs might exert their therapeutic effect via secreting paracrine factors rather than directing cell replacement through differentiation into neuronal and/or glial phenotypes.

Multiscale technologies for treatment of ischemic cardiomyopathy

The adult mammalian heart possesses only limited capacity for innate regeneration and the response to severe injury is dominated by the formation of scar tissue. Current therapy to replace damaged cardiac tissue is limited to cardiac transplantation and thus many patients suffer progressive decay in the heart's pumping capacity to the point of heart failure. Nanostructured systems have the potential to revolutionize both preventive and therapeutic approaches for treating cardiovascular disease. Here, we outline recent advancements in nanotechnology that could be exploited to overcome the major obstacles in the prevention of and therapy for heart disease. We also discuss emerging trends in nanotechnology affecting the cardiovascular field that may offer new hope for patients suffering massive heart attacks.

Direct Cell Labeling to Image Transplanted Stem Cells in Real Time Using a Dual-Contrast MRI Technique

Exogenous direct cell labeling with superparamagnetic iron oxide nanoparticles (SPIONs) is currently the most employed cell-labeling technique for tracking transplanted cells using magnetic resonance imaging (MRI). Although SPION-based cell labeling is effective for monitoring cell delivery and migration, monitoring cell survival is still a challenge. This unit describes an MRI technique that permits detection of the delivery, migration, and death of transplanted cells. This dual-contrast technique involves labeling cells with two different classes of MRI contrast agents, possessing different diffusion coefficients: SPIONs (T₂ /T₂^* contrast agents, with lower diffusion coefficients) and gadolinium chelates (T₁ contrast agents, with higher diffusion coefficients). In live cells, where both agents are in close proximity, the T₂ /T₂^* contrast predominates and the T₁ contrast is quenched. In dead cells, where the cell membrane is breached, gadolinium chelates diffuse from the SPIONs and generate a signature T₁ contrast enhancement in the vicinity of dead cells. © 2017 by John Wiley & Sons, Inc.

Two novel direct SPIO labels and in vivo MRI detection of labeled cells after acute myocardial infarct

BACKGROUND

Acute myocardial infarction (AMI) is a leading cause of morbidity and mortality worldwide. Cellular decay due hypoxia requires rapid and validated methods for possible therapeutic cell transplantation.

PURPOSE

To develop direct and rapid superparamagnetic iron oxide (SPIO) cell label for a large-animal model and to assess in vivo cell targeting by magnetic resonance imaging (MRI) in an experimental AMI model.

MATERIAL AND METHODS

Bone marrow mononuclear cells (BMMNCs) were labeled with SPIO particles using two novel direct labeling methods (rotating incubation method and electroporation). Labeling, iron incorporation in cells and label distribution, cellular viability, and proliferation were validated in vitro. An AMI porcine model was used to evaluate the direct labeling method (rotating incubation method) by examining targeting of labeled BMMNCs using MRI and histology.

RESULTS

Labeling (1 h) did not alter either cellular differentiation potential or viability of cells in vitro. Cellular relaxation values at 9.4 T correlated with label concentration and MRI at 1.5 T showing 89 ± 4% signal reduction compared with non-labeled cells in vitro. In vivo, a high spatial correlation between MRI and histology was observed. The extent of macroscopic pathological myocardial changes (hemorrhage) correlated with altered function detected on MRI.

CONCLUSION

We demonstrated two novel direct SPIO labeling methods and demonstrated the feasibility of clinical MRI for monitoring targeting of the labeled cells in animal models of AMI.

MRI reveals slow clearance of dead cell transplants in mouse forelimb muscles

A small molecule tetraazacyclododecane-1,4,7,10-tetraacetic acid (Gd-DOTA)₄-TPP agent is used to label human mesenchymal stem cells (hMSCs) via electroporation (EP). The present study assessed the cytotoxicity of cell labeling, in addition to its effect on cell differentiation potential. There were no significant adverse effects on cell viability or differentiation induced by either EP or cellular uptake of (Gd-DOTA)₄-TPP. Labeled live and dead hMSCs were transplanted into mouse forelimb muscles. T₂-weighted magnetic resonance imaging (MRI) was used to track the in vivo fate of the cell transplants. The labeling and imaging strategy allowed long term tracking of the cell transplants and unambiguous distinguishing of the cell transplants from their surrounding tissues. Cell migration was observed for live hMSCs injected into subcutaneous tissues, however not for either live or dead hMSCS injected into limb muscles. A slow clearance process occurred of the dead cell transplants in the limb muscular tissue. The MRI results therefore reveal that the fate and physiological activities of cell transplants depend on the nature of their host tissue.

Detection of intramyocardially injected DiR-labeled mesenchymal stem cells by optical and optoacoustic tomography

The distribution of intramyocardially injected rabbit MSCs, labeled with the near-infrared dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbo-cyanine-iodide (DiR) using hybrid Fluorescence Molecular Tomography-X-ray Computed Tomography (FMT-XCT) and Multispectral Optoacoustic Tomography (MSOT) imaging technologies, was investigated. Viability and induction of apoptosis of DiR labeled MSCs were assessed by XTT- and Caspase-3/-7-testing in vitro. 2 × 10⁶, 2 × 10⁵ and 2 × 10⁴ MSCs labeled with 5 and 10 μg DiR/ml were injected into fresh frozen rabbit hearts. FMT-XCT, MSOT and fluorescence cryosection imaging were performed. Concentrations up to 10 μg DiR/ml did not cause apoptosis in vitro (p > 0.05). FMT and MSOT imaging of labeled MSCs led to a strong signal. The imaging modalities highlighted a difference in cell distribution and concentration correlated to the number of injected cells. Ex-vivo cryosectioning confirmed the molecular fluorescence signal. FMT and MSOT are sensitive imaging techniques offering high-anatomic resolution in terms of detection and distribution of intramyocardially injected stem cells in a rabbit model.

Superparamagnetic Iron Oxide Nanoparticles-Complexed Cationic Amylose for In Vivo Magnetic Resonance Imaging Tracking of Transplanted Stem Cells in Stroke

Cell-based therapy with mesenchymal stem cells (MSCs) is a promising strategy for acute ischemic stroke. In vivo tracking of therapeutic stem cells with magnetic resonance imaging (MRI) is imperative for better understanding cellular survival and migrational dynamics over time. In this study, we develop a novel biocompatible nanocomplex (ASP-SPIONs) based on cationic amylose, by introducing spermine and the image label, ultrasmall superparamagnetic iron oxide nanoparticles (SPIONs), to label MSCs. The capacity, efficiency, and cytotoxicity of the nanocomplex in transferring SPIONs into green fluorescence protein-modified MSCs were tested; and the performance of in vivo MRI tracking of the transplanted cells in acute ischemic stroke was determined. The results demonstrated that the new class of SPIONs-complexed nanoparticles based on biodegradable amylose can serve as a highly effective and safe carrier to transfer magnetic label into stem cells. A reliable tracking of transplanted stem cells in stroke was achieved by MRI up to 6 weeks, with the desirable therapeutic benefit of stem cells on stroke retained. With the advantages of a relatively low SPIONs concentration and a short labeling period, the biocompatible complex of cationic amylose with SPIONs is highly translatable for clinical application. It holds great promise in efficient, rapid, and safe labeling of stem cells for subsequent cellular MRI tracking in regenerative medicine.

Intramyocardial fate and effect of iron nanoparticles co-injected with MACS® purified stem cell products

BACKGROUND

Magnetic activated cell sorting (MACS^®) is routinely used to isolate stem cell subpopulations intended for the treatment of cardiovascular diseases. In strong contrast, studies examining the amount, effect and intramyocardial distribution of iron nanoparticles used for magnetic cell labelling are missing, although iron excess can cause functional disorders in the heart.

METHODS AND RESULTS

CD133⁺ haematopoietic and CD271⁺ mesenchymal stem cells were purified from bone marrow using automatically and manually MACS^® based systems. Flow cytometric measurements demonstrated a rapid loss of MACS^® MicroBeads from cells under culture conditions, while storage under hypothermic conditions decelerated their detachment. Moreover, an average loading of ∼11 fg iron/cell caused by magnetic labelling was determined in magnetic particle spectroscopy. Importantly, hemodynamic measurements as well as histological examinations using a myocardial ischemia/reperfusion mouse model showed no influence of MACS^® MicroBeads on cardiac regeneration, while the transplantation of stem cells caused a significant improvement. Furthermore, immunostainings demonstrated the clearance of co-injected iron nanoparticles from stem cells and the surrounding heart tissue within 48 h post transplantation.

CONCLUSIONS

Our results indicate that iron amounts typically co-injected with MACS^® purified stem cells do not harm cardiac functions and are cleared from heart tissue within a few hours. Therefore, we conclude that MACS^® MicroBeads exhibit a good compatibility in the cardiac environment.

Vectorized nanodelivery systems for ischemic stroke: a concept and a need

Neurological diseases of diverse aetiologies have significant effects on the quality of life of patients. The limited self-repairing capacity of the brain is considered to be the origin of the irreversible and progressive nature of many neurological diseases. Therefore, neuroprotection is an important goal shared by many clinical neurologists and neuroscientists. In this review, we discuss the main obstacles that have prevented the implementation of experimental neuroprotective strategies in humans and propose alternative avenues for the use of neuroprotection as a feasible therapeutic approach. Special attention is devoted to nanotechnology, which is a new approach for developing highly specific and localized biomedical solutions for the study of the multiple mechanisms involved in stroke. Nanotechnology is contributing to personalized neuroprotection by allowing us to identify mechanisms, determine optimal therapeutic windows, and protect patients from brain damage. In summary, multiple aspects of these new players in biomedicine should be considered in future in vivo and in vitro studies with the aim of improving their applicability to clinical studies.