Imaging of stem cells using MRI

In Vivo Stem Cell Imaging Principles and Applications

Stem cells are the foundational cells for every organ and tissue in our body. Cell-based therapeutics using stem cells in regenerative medicine have received attracting attention as a possible treatment for various diseases caused by congenital defects. Stem cells such as induced pluripotent stem cells (iPSCs) as well as embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), and neuroprogenitors stem cells (NSCs) have recently been studied in various ways as a cell-based therapeutic agent. When various stem cells are transplanted into a living body, they can differentiate and perform complex functions. For stem cell transplantation, it is essential to determine the suitability of the stem cell-based treatment by evaluating the origin of stem, the route of administration, in vivo bio-distribution, transplanted cell survival, function, and mobility. Currently, these various stem cells are being imaged in vivo through various molecular imaging methods. Various imaging modalities such as optical imaging, magnetic resonance imaging (MRI), ultrasound (US), positron emission tomography (PET), and single-photon emission computed tomography (SPECT) have been introduced for the application of various stem cell imaging. In this review, we discuss the principles and recent advances of in vivo molecular imaging for application of stem cell research.

How can clinical safety and efficacy concerns in stem cell therapy for spinal cord injury be overcome?

INTRODUCTION

Spinal cord injury (SCI) can lead to severe neurological dysfunction. Despite scientific and medical advances, clinically effective regenerative therapies including stem cells are lacking for SCI.

AREAS COVERED

This paper discusses translational challenges related to the safe, effective use of stem cells for SCI, with a focus on mesenchymal stem cells (MSCs), neural stem cells (NSCs), Schwann cells (SCs), olfactory ensheathing cells (OECs), oligodendrocyte precursor cells (OPCs), embryonic stem cells (ESCs), and induced pluripotent stem cells (iPSCs). We discuss approaches to enhance the efficacy of cell-based strategies by i) addressing patient heterogeneity and enhancing patient selection; ii) selecting cell type, cell source, cell developmental stage, and delivery technique; iii) enhancing graft integration and mitigating immune-mediated graft rejection; and iv) ensuring availability of cells. Additionally, we review strategies to optimize outcomes including combinatorial use of rehabilitation and discuss ways to mitigate potential risks of tumor formation associated with stem cell-based strategies.

EXPERT OPINION

Basic science research will drive translational advances to develop stem cell-based therapies for SCI. Genetic, serological, and imaging biomarkers may enable individualization of cell-based treatments. Moreover, combinatorial strategies will be required to enhance graft survival, migration and functional integration, to enable precision-based intervention.

In vivo observation of multi-phase spatiotemporal cellular dynamics of transplanted HSPCs during early engraftment

Hematopoietic stem cell transplantation (HSCT) is commonly used to treat patients with various blood disorders, genetic and immunological diseases, and solid tumors. Several systemic complications following HSCT are critical limiting factors for achieving a successful outcome. These systemic complications are mainly due to the lack of initial engraftment after transplantation. However, the detailed underlying cellular dynamics of early engraftment have not been fully characterized yet. We performed in vivo longitudinal visualization of early engraftment characteristics of transplanted hematopoietic stem and progenitor cells (HSPCs) in the mouse calvarial bone marrow (BM). To achieve this, we utilized an in vivo laser-scanning confocal microscopy imaging system with a cranial BM imaging window and stereotaxic device. We observed two distinct cellular behaviors of HSPCs in vivo, cluster formation and cluster dissociation, early after transplantation. Furthermore, we successfully identified three cellular phases of engraftment with distinct cellular distances which are coordinated with cell proliferation and cell migration dynamics during initial engraftment.

Metabolic Labeling of Live Stem Cell for In Vitro Imaging and In Vivo Tracking

Stem cell therapy offers promising solutions to diseases and injuries that traditional medicines and therapies can't effectively cure. To get and explain their full therapeutic potentials, the survival, viability, integration, homing, and differentiation of stem cells after transplant must be clearly understood. To meet these urgent needs, noninvasive stem cell imaging and tracking technologies have been developed. Metabolic labeling technique is one of the most powerful tools for live cell imaging and tracking. In addition, it has many advantages for in vivo live cell imaging and tracking such as low background, correlation of survival, and very toxic and nontoxic by-products. Herein, we described the fundamental information and process of metabolic labeling techniques and suggested optimal condition for in vitro and in vivo imaging and tracking of human umbilical cord blood-derived endothelial progenitor cells (hUCB-EPCs). Based on this study, metabolic labeling techniques can be helpful for understanding the safety and effectiveness of stem cell-based therapy and determining the utility of stem cells in downstream experiments.

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.

IQF characterization of a cathepsin B-responsive nanoprobe for report of differentiation of HL60 cells into macrophages

Tracking of in vivo fates of exogenous cell transplants in terms of viability, migration, directional differentiation and function delivery by a suitable method of medical imaging is of great significance in the development and application of various cell therapies. In this contribution directional differentiation of HL60 cells into macrophages and granulocytes, and a difference in the associated expression level of cathepsin B (Cat B) among the parent and daughter cells is used as a model to guide and evaluate the development of a Cat B-responsive Abz-FRFK-Dnp@PLGA nanoprobe for an optical report of the differentiation process. A well-documented internally quenched fluorescence (IQF) pair coupled with a peptide substrate FRFK of Cat B was synthesized and imbedded in PLGA to form the nanoprobe. The nanoprobe is resistant to leakage when dispersed in water for 10 days. Degradation of the nanoprobe is dominated by Cat B. HL60 cells were then labelled with the Abz-FRFK-Dnp@PLGA nanoprobe to track the differentiation process. Differentiation of labelled HL60 cells into macrophages exhibited a significantly higher fluorescence relative to the granulocytes or the labelled parent cells. The fluorescence difference allows the differentiation process to be followed. The established characterization and assessment procedure is to be used for the development and evaluation of nanoprobes for other imaging modalities.

A Cat B-responsive Abz-FRFK-Dnp@PLGA nanoprobe for an optical report of the differentiation of HL60 cells into macrophages.

Multiparametric classification of sub-acute ischemic stroke recovery with ultrafast diffusion, 23 Na, and MPIO-labeled stem cell MRI at 21.1 T

MRI leverages multiple modes of contrast to characterize stroke. High-magnetic-field systems enhance the performance of these MRI measurements. Previously, we have demonstrated that individually sodium and stem cell tracking metrics are enhanced at ultrahigh field in a rat model of stroke, and we have developed robust single-scan diffusion-weighted imaging approaches that utilize spatiotemporal encoding (SPEN) of the apparent diffusion coefficient (ADC) for these challenging field strengths. Here, we performed a multiparametric study of middle cerebral artery occlusion (MCAO) biomarker evolution focusing on comparison of these MRI biomarkers for stroke assessment during sub-acute recovery in rat MCAO models at 21.1 T. T₂ -weighted MRI was used as the benchmark for identification of the ischemic lesion over the course of the study. The number of MPIO-induced voids measured by gradient-recalled echo, the SPEN measurement of ADC, and ²³ Na MRI values were determined in the ischemic area and contralateral hemisphere, and relative performances for stroke classification were compared by receiver operator characteristic analysis. These measurements were associated with unique time-dependent trajectories during stroke recovery that changed the sensitivity and specificity for stroke monitoring during its evolution. Advantages and limitations of these contrasts, and the use of ultrahigh field for multiparametric stroke assessment, are discussed.

Hyperpolarized 129 Xe imaging of embryonic stem cell-derived alveolar-like macrophages in rat lungs: proof-of-concept study using superparamagnetic iron oxide nanoparticles

PURPOSE

To measure regional changes in hyperpolarized ¹²⁹ Xe MRI signal and apparent transverse relaxation ( T 2 ∗ ) because of instillation of SPION-labeled alveolar-like macrophages (ALMs) in the lungs of rats and compare to histology.

METHODS

MRI was performed in 6 healthy mechanically ventilated rats before instillation, as well as 5 min and 1 h after instillation of 4 million SPION-labeled ALMs into either the left or right lung. T 2 ∗ maps were calculated from 2D multi-echo data at each time point and changes in T 2 ∗ were measured and compared to control rats receiving 4 million unlabeled ALMs. Histology of the ex vivo lungs was used to compare the regional MRI findings with the locations of the SPION-labeled ALMs.

RESULTS

Regions of signal loss were observed immediately after instillation of unlabeled and SPION-labeled ALMs and persisted at least 1 h in the case of the SPION-labeled ALMs. This was reflected in the measurements of T 2 ∗ . One hour after the instillation of SPION-labeled ALMs, the T 2 ∗ decreased to 54.0 ± 7.0% of the baseline, compared to a full recovery to baseline after the instillation of unlabeled ALMs. Histology confirmed the co-localization of SPION-labeled ALMs with regions of signal loss and T 2 ∗ decreases for each rat.

CONCLUSION

Hyperpolarized ¹²⁹ Xe MRI can detect the presence of SPION-labeled ALMs in the airways 1 h after instillation. This approach is promising for targeting and tracking of stem cells for the treatment of lung disease.

Peripheral artery disease: the new frontiers of imaging techniques to evaluate the evolution of regenerative medicine

Introduction: Stem cells (ESC, iPSC, MSC) are known to have intrinsic regenerative properties. In the last decades numerous findings have favored the development of innovative therapeutic protocols based on the use of stem cells (Regenerative Medicine/Cell Therapy) for the treatment of numerous diseases including PAD, with promising results in preclinical studies. So far, several clinical studies have shown a general improvement of the patient's clinical outcome, however they possess many critical issues caused by the non-randomized design of the limited number of patients examined, the type cells to be used, their dosage, the short duration of treatment and also their delivery strategy. Areas covered: In this context, the use of the most advanced molecular imaging techniques will allow the visualization of very important physio-pathological processes otherwise invisible with conventional techniques, such as angiogenesis, also providing important structural and functional data. Expert opinion: The new frontier of cell therapy applied to PAD, potentially able to stop or even the process that causes the disease, with particular emphasis on the clinical aspects that different types of cells involve and on the use of more innovative molecular imaging techniques now available.

Safe Harbor Targeted CRISPR-Cas9 Tools for Molecular-Genetic Imaging of Cells in Living Subjects

Noninvasive molecular-genetic imaging of cells expressing imaging reporter genes is an invaluable approach for longitudinal monitoring of the biodistribution and viability of cancer cells and cell-based therapies in preclinical models and patients. However, labeling cells with reporter genes often relies on using gene transfer methods that randomly integrate the reporter genes into the genome, which may cause unwanted and serious detrimental effects. To overcome this, we have developed CRISPR-Cas9 tools to edit cells at the adeno-associated virus site 1 (AAVS1) safe harbour with a large donor construct (∼6.3 kilobases) encoding an antibiotic resistance gene and reporter genes for bioluminescence (BLI) and fluorescence imaging. HEK293T cells were transfected with a dual plasmid system encoding the Cas9 endonuclease and an AAVS1-targeted guide RNA in one plasmid, and a donor plasmid encoding a puromycin resistance gene, tdTomato and firefly luciferase flanked by AAVS1 homology arms. Puromycin-resistant clonal cells were isolated and AAVS1 integration was confirmed via PCR and sequencing of the PCR product. In vitro BLI signal correlated well to cell number (R² = 0.9988; p < 0.05) and was stable over multiple passages. Engineered cells (2.5 × 10⁶) were injected into the left hind flank of nude mice and in vivo BLI was performed on days 0, 7, 14, 21, and 28. BLI signal trended down from day 0 to day 7, but significantly increased by day 28 due to cell growth (p < 0.05). This describes the first CRISPR-Cas9 system for AAVS1 integration of large gene constructs for molecular-genetic imaging of cells in vivo. With further development, including improving editing efficiency, use of clinically relevant reporters, and evaluation in other cell populations that can be readily expanded in culture (e.g., immortalized cells or T cells), this CRISPR-Cas9 reporter gene system could be broadly applied to a number of in vivo cell tracking studies.

Effects of labeling human mesenchymal stem cells with superparamagnetic iron oxides on cellular functions and magnetic resonance contrast in hypoxic environments and long-term monitoring

Ischemia, which involves decreased blood flow to a region and a corresponding deprivation of oxygen and nutrients, can be induced as a consequence of stroke or heart attack. A prevalent disease that affects many individuals worldwide, ischemic stroke results in functional and cognitive impairments, as neural cells in the brain receive inadequate nourishment and encounter inflammation and various other detrimental toxic factors that lead to their death. Given the scarce treatments for this disease in the clinic such as the administration of tissue plasminogen activator, which is only effective in a limited time window after the occurrence of stroke, it will be necessary to develop new strategies to ameliorate or prevent stroke-induced brain damage. Cell-based therapies appear to be a promising solution for treating ischemic stroke and many other ischemia-associated and neurodegenerative maladies. Particularly, human mesenchymal stem cells (hMSCs) are of interest for cell transplantation in stroke, given their multipotency, accessibility, and reparative abilities. To determine the fate and survival of hMSC, which will be imperative for successful transplantation therapies, these cells may be monitored using magnetic resonance imaging and transfected with superparamagnetic iron oxide (SPIO), a contrast agent that facilitates the detection of these hMSCs. This review encompasses pertinent research and findings to reveal the effects of SPIO on hMSC functions in the context of transplantation in ischemic environments and over extended time periods. This paper is a review article. Referred literature in this paper has been listed in the references section. The data sets supporting the conclusions of this article are available online by searching various databases, including PubMed. Some original points in this article come from the laboratory practice in our research center and the authors' experiences.

In Vivo Long-Term Tracking of Neural Stem Cells Transplanted into an Acute Ischemic Stroke model with Reporter Gene-Based Bimodal MR and Optical Imaging

Transplantation of neural stem cells (NSCs) is emerging as a new therapeutic approach for stroke. Real-time imaging of transplanted NSCs is essential for successful cell delivery, safety monitoring, tracking cell fate and function, and understanding the interactions of transplanted cells with the host environment. Magnetic resonance imaging (MRI) of magnetic nanoparticle-labeled cells has been the most widely used means to track stem cells in vivo. Nevertheless, it does not allow for the reliable discrimination between live and dead cells. Reporter gene-based MRI was considered as an alternative strategy to overcome this shortcoming. In this work, a class of lentiviral vector-encoding ferritin heavy chain (FTH) and enhanced green fluorescent protein (EGFP) was constructed to deliver reporter genes into NSCs. After these transgenic NSCs were transplanted into the contralateral hemisphere of rats with acute ischemic stroke, MRI and fluorescence imaging (FLI) were performed in vivo for tracking the fate of transplanted cells over a long period of 6 wk. The results demonstrated that the FTH and EGFP can be effectively and safely delivered to NSCs via the designed lentiviral vector. The distribution and migration of grafted stem cells could be monitored by bimodal MRI and FLI. FTH can be used as a robust MRI reporter for reliable reporting of the short-term viability of cell grafts, whereas its capacity for tracking the long-term viability of stem cells remains dependent on several confounding factors such as cell death and the concomitant reactive inflammation.

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.

Stem Cell Tracing Through MR Molecular Imaging

Stem cell therapy opens a new window in medicine to overcome several diseases that remain incurable. It appears such diseases as cardiovascular disorders, brain injury, multiple sclerosis, urinary system diseases, cartilage lesions and diabetes are curable with stem cell transplantation. However, some questions related to stem cell therapy have remained unanswered. Stem cell imaging allows approval of appropriated strategies such as selection of the type and dose of stem cell, and also mode of cell delivery before being tested in clinical trials. MRI as a non-invasive imaging modality provides proper conditions for this aim. So far, different contrast agents such as superparamagnetic or paramagnetic nanoparticles, ultrasmall superparamagnetic nanoparticles, fluorine, gadolinium and some types of reporter genes have been used for imaging of stem cells. The core subject of these studies is to investigate the survival and differentiation of stem cells, contrast agent's toxicity and long term following of transplanted cells. The promising results of in vivo and some clinical trial studies may raise hope for clinical stem cells imaging with MRI.

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.

Tracking mesenchymal stem cells using magnetic resonance imaging

Recent translational studies in the fields of tissue regeneration and cell therapy have characterized mesenchymal stem cells (MSCs) as a potentially effective and accessible measure for treating ischemic cerebral and neurodegenerative disorders such as stroke, Parkinson's disease, and amyotrophic lateral sclerosis. Developing more efficient cell tracking techniques bear the potential to optimize MSC transplantation therapies by providing a more accurate picture of the fate and area of effect of implanted cells. Currently, determining the location of transplanted MSCs involves a histological approach, but magnetic resonance imaging (MRI) presents a noninvasive paradigm that permits repeat evaluations. To visualize MSCs using MRI, the implanted cells must be treated with an intracellular contrast agent. These are commonly paramagnetic compounds, many of which are based on superparamagnetic iron oxide (SPIO) nanoparticles. Recent research has set out characterize the effects of SPIO-uptake on the cellular activity of in vitro human MSCs and the resultant influence that respective SPIO concentration has on MRI sensitivity. As these studies reveal, SPIO-uptake has no effect on the cellular processes of proliferation and differentiation while producing high contrast MRI signals. Moreover, transplantation of SPIO-labeled MSCs in animal models encouragingly showed no loss in MRI contrast, suggesting that SPIO labeling may be an appealing regime for lasting MRI detection. This study is a review article. Referred literature in this study has been listed in the reference part. The datasets supporting the conclusions of this article are available online by searching the PubMed. Some original points in this article come from the laboratory practice in our research centers and the authors’ experiences.

Noninvasive in-vivo tracing and imaging of transplanted stem cells for liver regeneration

Terminal liver disease is a major cause of death globally. The only ultimate therapeutic approach is orthotopic liver transplant. Because of the innate defects of organ transplantation, stem cell-based therapy has emerged as an effective alternative, based on the capacity of stem cells for multilineage differentiation and their homing to injured sites. However, the disease etiology, cell type, timing of cellular graft, therapeutic dose, delivery route, and choice of endpoints have varied between studies, leading to different, even divergent, results. In-vivo cell imaging could therefore help us better understand the fate and behaviors of stem cells to optimize cell-based therapy for liver regeneration. The primary imaging techniques in preclinical or clinical studies have consisted of optical imaging, magnetic resonance imaging, radionuclide imaging, reporter gene imaging, and Y chromosome-based fluorescence in-situ hybridization imaging. More attention has been focused on developing new or modified imaging methods for longitudinal and high-efficiency tracing. Herein, we provide a descriptive overview of imaging modalities and discuss recent advances in the field of molecular imaging of intrahepatic stem cell grafts.

Cardiac Chemical Exchange Saturation Transfer MR Imaging Tracking of Cell Survival or Rejection in Mouse Models of Cell Therapy

Purpose To examine whether cardiac chemical exchange saturation transfer (CEST) imaging can be serially and noninvasively used to probe cell survival or rejection after intramyocardial implantation in mice. Materials and Methods Experiments were compliant with the National Institutes of Health Guidelines on the Use of Laboratory Animals and approved by the Institutional Animal Care and Use Committee. One million C2C12 cells labeled with either europium (Eu) 10-(2-hydroxypropyl)-1,4,7-tetraazacyclododecane-1,4,7-triacetic acid (HP-DO3A) or saline via the hypotonic swelling technique were implanted into the anterior-lateral left ventricular wall in C57BL/6J (allogeneic model, n = 17) and C3H (syngeneic model, n = 13) mice. Imaging (frequency offsets of ±15 parts per million) was performed 1, 10, and 20 days after implantation, with the asymmetrical magnetization transfer ratio (MTR_asym) calculated from image pairs. Histologic examination was performed at the conclusion of imaging. Changes in MTR_asym over time and between mice were assessed by using two-way repeated-measures analysis of variance. Results MTR_asym was significantly higher in C3H and C57BL/6J mice in grafts of Eu-HP-DO3A-labeled cells (40.2% ± 5.0 vs 37.8% ± 7.0, respectively) compared with surrounding tissue (-0.67% ± 1.7 vs -1.8% ± 5.3, respectively; P < .001) and saline-labeled grafts (-0.4% ± 6.0 vs -1.2% ± 3.6, respectively; P < .001) at day 1. In C3H mice, MTR_asym remained increased (31.3% ± 9.2 on day 10, 28.7% ± 5.2 on day 20; P < .001 vs septum) in areas of in Eu-HP-DO3A-labeled cell grafts. In C57BL/6J mice, corresponding MTR_asym values (11.3% ± 8.1 on day 10, 5.1% ± 9.4 on day 20; P < .001 vs day 1) were similar to surrounding myocardium by day 20 (P = .409). Histologic findings confirmed cell rejection in C57BL/6J mice. Estimation of graft area was similar with cardiac CEST imaging and histologic examination (R² = 0.89). Conclusion Cardiac CEST imaging can be used to image cell survival and rejection in preclinical models of cell therapy. ^© RSNA, 2016 Online supplemental material is available for this article.

A preclinical murine model for the early detection of radiation-induced brain injury using magnetic resonance imaging and behavioral tests for learning and memory: with applications for the evaluation of possible stem cell imaging agents and therapies

Stem cell therapies are being developed for radiotherapy-induced brain injuries (RIBI). Magnetic resonance imaging (MRI) offers advantages for imaging transplanted stem cells. However, most MRI cell-tracking techniques employ superparamagnetic iron oxide particles (SPIOs), which are difficult to distinguish from hemorrhage. In current preclinical RIBI models, hemorrhage occurs concurrently with other injury markers. This makes the evaluation of the recruitment of transplanted SPIO-labeled stem cells to injury sites difficult. Here, we developed a RIBI model, with early injury markers reflective of hippocampal dysfunction, which can be detected noninvasively with MRI and behavioral tests. Lesions were generated by sub-hemispheric irradiation of mouse hippocampi with single X-ray beams of 80 Gy. Lesion formation was monitored with anatomical and contrast-enhanced MRI and changes in memory and learning were assessed with fear-conditioning tests. Early injury markers were detected 2 weeks after irradiation. These included an increase in the permeability of the blood-brain barrier, demonstrated by a 92 ± 20 % contrast enhancement of the irradiated versus the non-irradiated brain hemispheres, within 15 min of the administration of an MRI contrast agent. A change in short-term memory was also detected, as demonstrated by a 40.88 ± 5.03 % decrease in the freezing time measured during the short-term memory context test at this time point, compared to that before irradiation. SPIO-labeled stem cells transplanted contralateral to the lesion migrated toward the lesion at this time point. No hemorrhage was detected up to 10 weeks after irradiation. This model can be used to evaluate SPIO-based stem cell-tracking agents, short-term.

Advanced cardiac chemical exchange saturation transfer (cardioCEST) MRI for in vivo cell tracking and metabolic imaging

An improved pre-clinical cardiac chemical exchange saturation transfer (CEST) pulse sequence (cardioCEST) was used to selectively visualize paramagnetic CEST (paraCEST)-labeled cells following intramyocardial implantation. In addition, cardioCEST was used to examine the effect of diet-induced obesity upon myocardial creatine CEST contrast. CEST pulse sequences were designed from standard turbo-spin-echo and gradient-echo sequences, and a cardiorespiratory-gated steady-state cine gradient-echo sequence. In vitro validation studies performed in phantoms composed of 20 mM Eu-HPDO3A, 20 mM Yb-HPDO3A, or saline demonstrated similar CEST contrast by spin-echo and gradient-echo pulse sequences. Skeletal myoblast cells (C2C12) were labeled with either Eu-HPDO3A or saline using a hypotonic swelling procedure and implanted into the myocardium of C57B6/J mice. Inductively coupled plasma mass spectrometry confirmed cellular levels of Eu of 2.1 × 10(-3) ng/cell in Eu-HPDO3A-labeled cells and 2.3 × 10(-5) ng/cell in saline-labeled cells. In vivo cardioCEST imaging of labeled cells at ±15 ppm was performed 24 h after implantation and revealed significantly elevated asymmetric magnetization transfer ratio values in regions of Eu-HPDO3A-labeled cells when compared with surrounding myocardium or saline-labeled cells. We further utilized the cardioCEST pulse sequence to examine changes in myocardial creatine in response to diet-induced obesity by acquiring pairs of cardioCEST images at ±1.8 ppm. While ventricular geometry and function were unchanged between mice fed either a high-fat diet or a corresponding control low-fat diet for 14 weeks, myocardial creatine CEST contrast was significantly reduced in mice fed the high-fat diet. The selective visualization of paraCEST-labeled cells using cardioCEST imaging can enable investigation of cell fate processes in cardioregenerative medicine, or multiplex imaging of cell survival with imaging of cardiac structure and function and additional imaging of myocardial creatine.

Bone Marrow-Derived Cells as a Therapeutic Approach to Optic Nerve Diseases

Following optic nerve injury associated with acute or progressive diseases, retinal ganglion cells (RGCs) of adult mammals degenerate and undergo apoptosis. These diseases have limited therapeutic options, due to the low inherent capacity of RGCs to regenerate and due to the inhibitory milieu of the central nervous system. Among the numerous treatment approaches investigated to stimulate neuronal survival and axonal extension, cell transplantation emerges as a promising option. This review focuses on cell therapies with bone marrow mononuclear cells and bone marrow-derived mesenchymal stem cells, which have shown positive therapeutic effects in animal models of optic neuropathies. Different aspects of available preclinical studies are analyzed, including cell distribution, potential doses, routes of administration, and mechanisms of action. Finally, published and ongoing clinical trials are summarized.

Longitudinal Evaluation of Effects of Intra-Articular Mesenchymal Stromal Cell Administration for the Treatment of Osteoarthritis in an Ovine Model

In this study, the therapeutic effect of intra-articularly injected autologous mesenchymal stromal cells (MSCs) was evaluated in an ovine osteoarthritis (OA) model using consecutive magnetic resonance imaging (MRI), radiography, and macroscopic and histologic postmortem examination. In 12 sheep, OA was induced by bilateral, lateral meniscectomy. After 6 weeks, 20 × 106 bone marrow-derived MSCs (50% MSCs were superparamagnetic iron oxide particle labeled) were injected intra-articularly into one knee joint. The contralateral knee served as negative control. MR images were acquired before OA induction, immediately before and after MSC injection, and 1, 4, 8, and 12 weeks thereafter using a 0.5T unit and a T2* gradient echo sequence. Radiographs were obtained before OA induction, at MSC injection, and 12 weeks thereafter. The MRI scoring system included articular cartilage, bone, joint capsule, and synovial fluid evaluation. The radiographic scoring system included the joint space and bone. Postmortem evaluation entailed macroscopic and histologic assessment. Longitudinal MRI revealed a significant deceleration of OA progression in MSC-treated joints. However, at the conclusion of the study, there was no significant difference in the degree of OA detected by MRI, radiography, and postmortem evaluation between the treatment and control group. The degree of OA on MRI varied among the 12 animals at the time of injection, but there was no difference between the left and right limb. In conclusion, intra-articular MSCs decreased OA progression. However, no significant treatment effects were seen at the conclusion of the study at 12 weeks. This somewhat contradicts previously published results. Nevertheless, the choice of OA model, outcome measures, or lack of additional medication might explain the differences. Our results indicate that OA might benefit from intra-articular MSC injection, but further studies are needed to refine patient selection and injection parameters for a more substantially improved outcome.

Multimeric Near IR-MR Contrast Agent for Multimodal In Vivo Imaging

Multiple imaging modalities are often required for in vivo imaging applications that require both high probe sensitivity and excellent spatial and temporal resolution. In particular, MR and optical imaging are an attractive combination that can be used to determine both molecular and anatomical information. Herein, we describe the synthesis and in vivo testing of two multimeric NIR-MR contrast agents that contain three Gd(III) chelates and an IR-783 dye moiety. One agent contains a PEG linker and the other a short alkyl linker. These agents label cells with extraordinary efficacy and can be detected in vivo using both imaging modalities. Biodistribution of the PEGylated agent shows observable fluorescence in xenograft MCF7 tumors and renal clearance by MR imaging.

Seeing stem cells at work in vivo

Stem cell based-therapies are novel therapeutic strategies that hold key for developing new treatments for diseases conditions with very few or no cures. Although there has been an increase in the number of clinical trials involving stem cell-based therapies in the last few years, the long-term risks and benefits of these therapies are still unknown. Detailed in vivo studies are needed to monitor the fate of transplanted cells, including their distribution, differentiation, and longevity over time. Advancements in non-invasive cellular imaging techniques to track engrafted cells in real-time present a powerful tool for determining the efficacy of stem cell-based therapies. In this review, we describe the latest approaches to stem cell labeling and tracking using different imaging modalities.

Magnetic resonance imaging of transplanted stem cell fate in stroke

Nowadays, scientific findings in the field of regeneration of nervous system have revealed the possibility of stem cell based therapies for damaged brain tissue related disorders like stroke. Furthermore, to achieve desirable outcomes from cellular therapies, one needs to monitor the migration, engraftment, viability, and also functional fate of transplanted stem cells. Magnetic resonance imaging is an extremely versatile technique for this purpose, which has been broadly used to study stroke and assessment of therapeutic role of stem cells. In this review we searched in PubMed search engine by using following keywords; "Stem Cells", "Cell Tracking", "Stroke", "Stem Cell Transplantation", "Nanoparticles", and "Magnetic Resonance Imaging" as entry terms and based on the mentioned key words, the search period was set from 1976 to 2012. The main purpose of this article is describing various advantages of molecular and magnetic resonance imaging of stem cells, with focus on translation of stem cell research to clinical research.

Tracking of stem cells in vivo for cardiovascular applications

In the past ten years, the concept of injecting stem and progenitor cells to assist with rebuilding damaged blood vessels and myocardial tissue after injury in the heart and peripheral vasculature has moved from bench to bedside. Non-invasive imaging can not only provide a means to assess cardiac repair and, thereby, cellular therapy efficacy but also a means to confirm cell delivery and engraftment after administration. In this first of a two-part review, we will review the different types of cellular labeling techniques and the application of these techniques in cardiovascular magnetic resonance and ultrasound. In addition, we provide a synopsis of the cardiac cellular clinical trials that have been performed to-date.

Comparative Labeling of Equine and Ovine Multipotent Stromal Cells With Superparamagnetic Iron Oxide Particles for Magnetic Resonance Imaging In Vitro

The purpose of this study was to evaluate the use of three different superparamagnetic iron oxide (SPIO) particles for labeling of ovine and equine bone marrow (BM)-derived multipotent stromal cells (MSCs) in vitro. MSCs were obtained from five adult sheep and horses, respectively. After three passages (p3), cells were labeled with either 1) Molday ION Rhodamine B, 2) Endorem, 3) Resovist, or 4) remained unlabeled as control. Labeling efficiency, marker retention, and long-term detectability in MRI until p7 were evaluated. Further, proliferation capacity and trilineage differentiation as indicators for potential impact on stromal cell characteristics were assessed. MSCs of both species were successfully labeled with all three SPIO products. A high, exclusively intracellular, iron uptake was achieved by Molday ION Rhodamine B only. Labeling with Resovist led to prominent extracellular iron presence; labeling with Endorem was less efficient. During MRI, all labeled cells showed strong hypointense signals, contrary to unlabeled controls. Resovist induced the largest areas of hypointense signals, followed by Molday ION Rhodamine B and Endorem. MRI signal detectability decreased from p4 to p7. Proliferation, adipogenic, and osteogenic differentiation potential were not reduced by cell labeling compared to unlabeled cells. Chondrogenic differentiation capacity decreased with increasing amount of iron associated with the cells. Among the three products, Resovist and Molday were identified as promising labeling agents. While Resovist achieved superior results in most of the assessed parameters, Molday ION Rhodamine B ensured intracellular iron uptake without extracellular SPIO complexes and consistent hypointense signals on MRI.

Design of Biomimetic Vascular Grafts with Magnetic Endothelial Patterning

The development of small diameter vascular grafts with a controlled pluricellular organization is still needed for effective vascular tissue engineering. Here, we describe a technological approach combining a tubular scaffold and magnetically labeled cells to create a pluricellular and organized vascular graft, the endothelialization of which could be monitored by MRI prior to transplantation. A novel type of scaffold was developed with a tubular geometry and a porous bulk structure enabling the seeding of cells in the scaffold pores. A homogeneous distribution of human mesenchymal stem cells in the macroporous structure was obtained by seeding the freeze-dried scaffold with the cell suspension. The efficient covering of the luminal surface of the tube was then made possible thanks to the implementation of a magnetic-based patterning technique. Human endothelial cells or endothelial progenitors were magnetically labeled with iron oxide nanoparticles and successfully attracted to the 2-mm lumen where they attached and formed a continuous endothelium. The combination of imaging modalities [fluorescence imaging, histology, and 3D magnetic resonance imaging (MRI)] evidenced the integrity of the vascular construct. In particular, the observation of different cell organizations in a vascular scaffold within the range of resolution of single cells by 4.7 T MRI is reported.

Iron administration before stem cell harvest enables MR imaging tracking after transplantation

PURPOSE

To determine whether intravenous ferumoxytol can be used to effectively label mesenchymal stem cells (MSCs) in vivo and can be used for tracking of stem cell transplants.

MATERIALS AND METHODS

This study was approved by the institutional animal care and use committee. Sprague-Dawley rats (6-8 weeks old) were injected with ferumoxytol 48 hours prior to extraction of MSCs from bone marrow. Ferumoxytol uptake by these MSCs was evaluated with fluorescence, confocal, and electron microscopy and compared with results of traditional ex vivo-labeling procedures. The in vivo-labeled cells were subsequently transplanted in osteochondral defects of 14 knees of seven athymic rats and were evaluated with magnetic resonance (MR) imaging up to 4 weeks after transplantation. T2 relaxation times of in vivo-labeled MSC transplants and unlabeled control transplants were compared by using t tests. MR data were correlated with histopathologic results.

RESULTS

In vivo-labeled MSCs demonstrated significantly higher ferumoxytol uptake compared with ex vivo-labeled cells. With electron microscopy, iron oxide nanoparticles were localized in secondary lysosomes. In vivo-labeled cells demonstrated significant T2 shortening effects in vitro and in vivo when they were compared with unlabeled control cells (T2 in vivo, 15.4 vs 24.4 msec; P < .05) and could be tracked in osteochondral defects for 4 weeks. Histologic examination confirmed the presence of iron in labeled transplants and defect remodeling.

CONCLUSION

Intravenous ferumoxytol can be used to effectively label MSCs in vivo and can be used for tracking of stem cell transplants with MR imaging. This method eliminates risks of contamination and biologic alteration of MSCs associated with ex vivo-labeling procedures.

DiI labeling of human adipose-derived stem cells: evaluation of DNA damage, toxicity and functional impairment

INTRODUCTION

Adipose tissue-derived stem cells (ASCs) have become the primary focus of tissue engineering research. To understand their functions and behavior in in vitro and in vivo models, it is mandatory to track the implanted cells and distinguish them from the resident or host cells. A common labeling method is the use of fluorescent dyes, e.g. the lipophilic carbocyanine dye, DiI. This study aimed to analyze potential DNA damage, toxicity and impairment of the functional properties of human ASCs after labeling with DiI.

METHODS

Cytotoxicity was measured using the MTT assay and DNA damage was determined by means of the comet assay. Potential apoptotic effects were determined using the annexin V-propidium iodide test. Differentiation potential was evaluated by trilineage differentiation procedures in labeled and unlabeled ASCs. Proliferation as well as migration capability was analyzed, and the duration and stability of DiI labeling in ASCs during in vitro expansion was observed over a period of 35 days.

RESULTS

DiI labeling did not cause genotoxic effects 15, or 30 min or 24 h after the labeling procedure, and there were no cytotoxic effects until 72 h afterwards. No impairment of proliferation or migration capability or differentiation potential could be determined. However, after 35 days, only 37% of labeled cells could be detected using the fluorescence microscope, which indicates a decrease in staining stability during in vitro expansion.

CONCLUSION

DiI is a convenient method for ASCs labeling which causes no toxic effects and does not impair the proliferation, migration or differentiation potential of ASCs after the labeling procedure.

Nanotechnology and stem cell therapy for cardiovascular diseases: potential applications

The use of stem cell therapy for the treatment of cardiovascular diseases has generated significant interest in recent years. Limitations to the clinical application of this therapy center on issues of stem cell delivery, engraftment, and fate. Nanotechnology-based cell labeling and imaging techniques facilitate stem cell tracking and engraftment studies. Nanotechnology also brings exciting new opportunities to translational stem cell research as it enables the controlled engineering of nanoparticles and nanomaterials that can properly relate to the physical scale of cell-cell and cell-niche interactions. This review summarizes the most relevant potential applications of nanoscale technologies to the field of stem cell therapy for the treatment of cardiovascular diseases.

Electron paramagnetic resonance as a sensitive tool to assess the iron oxide content in cells for MRI cell labeling studies

MRI cell tracking is a promising technique to track various cell types (stem cells, tumor cells, etc.) in living animals. Usually, cells are incubated with iron oxides (T(2) contrast agent) in order to take up the particles before being injected in vivo. Iron oxide quantification is important in such studies for validating the labeling protocols and assessing the dilution of the particles with cell proliferation. We here propose to implement electron paramagnetic resonance (EPR) as a very sensitive method to quantify iron oxide concentration in cells. Iron oxide particles exhibit a unique EPR spectrum, which directly reflects the number of particles in a sample. In order to compare EPR with existing methods (Perls's Prussian blue reaction, ICP-MS and fluorimetry), we labeled tumor cells (melanoma and renal adenocarcinoma cell lines) and fibroblasts with fluorescent iron oxide particles, and determined the limits of detection of the different techniques. We show that EPR is a very sensitive technique and is specific for iron oxide quantification as measurements are not affected by endogenous iron. As a consequence, EPR is well adapted to perform ex vivo analysis of tissues after cell tracking experiments in order to confirm MRI results.

In vivo tracking techniques for cellular regeneration, replacement, and redirection

Cellular therapy can be defined as the transplantation of living cells for the treatment of medical conditions. Three main objectives of cellular therapy are regeneration of damaged tissue, replacement of function by secretion of biologically active molecules, and redirection of aberrant processes. Given the complex nature of these approaches, in vivo tracking of the transplanted cells is critical to evaluate their potential benefit and to optimize treatment strategies. Recent advances are reviewed that enable in vivo cell tracking as an important adjunct to implement cellular therapy in clinical practice.

Tracking mesenchymal stem cells with iron oxide nanoparticle loaded poly(lactide-co-glycolide) microparticles

Monitoring the location, distribution and long-term engraftment of administered cells is critical for demonstrating the success of a cell therapy. Among available imaging-based cell tracking tools, magnetic resonance imaging (MRI) is advantageous due to its noninvasiveness, deep penetration, and high spatial resolution. While tracking cells in preclinical models via internalized MRI contrast agents (iron oxide nanoparticles, IO-NPs) is a widely used method, IO-NPs suffer from low iron content per particle, low uptake in nonphagocytotic cell types (e.g., mesenchymal stem cells, MSCs), weak negative contrast, and decreased MRI signal due to cell proliferation and cellular exocytosis. Herein, we demonstrate that internalization of IO-NP (10 nm) loaded biodegradable poly(lactide-co-glycolide) microparticles (IO/PLGA-MPs, 0.4-3 μm) in MSCs enhances MR parameters such as the r(2) relaxivity (5-fold), residence time inside the cells (3-fold) and R(2) signal (2-fold) compared to IO-NPs alone. Intriguingly, in vitro and in vivo experiments demonstrate that internalization of IO/PLGA-MPs in MSCs does not compromise inherent cell properties such as viability, proliferation, migration and their ability to home to sites of inflammation.

Quantitative evaluation of MRI-based tracking of ferritin-labeled endogenous neural stem cell progeny in rodent brain

Endogenous neural stem cells have the potential to facilitate therapy for various neurodegenerative brain disorders. To increase our understanding of neural stem and progenitor cell biology in healthy and diseased brain, methods to label and visualize stem cells and their progeny in vivo are indispensable. Iron oxide particle based cell-labeling approaches enable cell tracking by MRI with high resolution and good soft tissue contrast in the brain. However, in addition to important concerns about unspecific labeling and low labeling efficiency, the dilution effect upon cell division is a major drawback for longitudinal follow-up of highly proliferating neural progenitor cells with MRI. Stable viral vector-mediated marking of endogenous stem cells and their progeny with a reporter gene for MRI could overcome these limitations. We stably and efficiently labeled endogenous neural stem/progenitor cells in the subventricular zone in situ by injecting a lentiviral vector expressing ferritin, a reporter for MRI. We developed an image analysis pipeline to quantify MRI signal changes at the level of the olfactory bulb as a result of migration of ferritin-labeled neuroblasts along the rostral migratory stream. We were able to detect ferritin-labeled endogenous neural stem cell progeny into the olfactory bulb of individual animals with ex vivo MRI at 30 weeks post injection, but could not demonstrate reliable in vivo detection and longitudinal tracking of neuroblast migration to the OB in individual animals. Therefore, although LV-mediated labeling of endogenous neural stem and progenitor cells resulted in efficient and stable ferritin-labeling of stem cell progeny in the OB, even with quantitative image analysis, sensitivity remains a limitation for in vivo applications.

Superparamagnetic iron oxide (SPIO) labeling efficiency and subsequent MRI tracking of native cell populations pertinent to pulmonary heart valve tissue engineering studies

The intimal and medial linings of the pulmonary artery consist largely of vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs), respectively. The migration of these cell types to a potential tissue-engineered pulmonary valve (TEPV) implant process is therefore of interest in understanding the valve remodeling process. Visualization and cell tracking by MRI, which employs hypointense contrast achievable through the use of superparamagnetic iron oxide (SPIO) microparticles to label cells, provides a method in which this can be studied. We investigated the SPIO labeling efficiency of human VECs and VSMCs, and used two- and three-dimensional gradient echo sequences to track the migration of these cells in agar gel constructs. Protamine sulfate (4.5 µg/mL) was used to enhance SPIO uptake and was found to have no influence on cell viability or proliferation. MRI experiments were initially performed using a 9.4-T scanner. The results demonstrated that the spatial positions of hypointense spots were relatively unchanged over 12 days. Subsequent MR experiments performed at 7 T demonstrated that three-dimensional imaging provided the best spatial resolution to assess cell fate. R(2)* maps were bright in SPIO cell-encapsulated gels in comparison with unlabeled counterparts. Signal voids were ruled out as hypointense regions owing to the smooth exponential decay of T(2)* in these voxels. As a next step, we intend to use the SPIO cell labeling and MR protocols established in this study to assess whether hemodynamic stresses will alter the vascular cell migratory patterns. These studies will shed light on the mechanisms of vascular remodeling after TEPV implantation.

Nanoparticle-based monitoring of cell therapy

Exogenous cell therapy aims to replace/repair diseased or dysfunctional cells and promises to revolutionize medicine by restoring tissue and organ function. To develop effective cell therapy, the location, distribution and long-term persistence of transplanted cells must be evaluated. Nanoparticle (NP) based imaging technologies have the potential to track transplanted cells non-invasively. Here we summarize the most recent advances in NP-based cell tracking with emphasis on (1) the design criteria for cell tracking NPs, (2) protocols for cell labeling, (3) a comparison of available imaging modalities and their corresponding contrast agents, (4) a summary of preclinical studies on NP-based cell tracking and finally (5) perspectives and future directions.

Fate and toxicity of metallic and metal-containing nanoparticles for biomedical applications

It is important to obtain a better understanding of the uptake, trafficking, pharmacokinetics, clearance, and role of nanomaterials in biological systems, so that their possible undesirable effects can be avoided. A number of metallic or metal-containing nanomaterials, such as gold nanoparticles and nanorods, quantum dots, iron oxides nanoparticles, and endohedral metallofullerenes, have already been or will soon become very promising for biomedical applications. This review presents a summary of currently available data on the fate and toxicity of these metallic or metal-containing nanoparticles based on animal studies. Several issues regarding the nanotoxicity assessment and future directions on the study of the fate of these nanoparticles are also proposed.

MRI stem cell tracking for therapy in experimental cerebral ischemia

Magnetic resonance has an established role in investigations on the evolution of stroke and the assessment of therapeutic strategies in experimental animals. Here we show that the technique has also an important place for the study of stem cell-mediated regenerative therapies after stroke. We review the literature by bridging from the methodological aspects of stem cell labeling via grafting and monitoring of cell dynamics after implantation into the brain all the way to MRI's role in analyzing the stem cell-mediated functional improvement. Thus, we have aimed at a view combining the focus on the monitoring of the cell activities with the aspect of lesion evolution while including also the essence of a potential functional improvement by the implantation of stem cells following stroke.

Emerging roles for integrated imaging modalities in cardiovascular cell-based therapeutics: a clinical perspective

Despite preclinical promise, the progress of cell-based therapy to clinical cardiovascular practice has been slowed by several challenges and uncertainties that have been highlighted by the conflicting results of human trials. Most telling has been the revelation that current strategies fall short of achieving sufficient retention and engraftment of cells to meet the ambitious objective of myocardial regeneration. This has sparked novel research into the refinement of cell biology and delivery to overcome these shortcomings. Within this context, molecular imaging has emerged as a valuable tool for providing noninvasive surveillance of cell fate in vivo. Direct and indirect labelling of cells can be coupled with clinically relevant imaging modalities, such as radionuclide single photon emission computed tomography and positron emission tomography, and magnetic resonance imaging, to assess their short- and long-term distributions, along with their viability, proliferation and functional interaction with the host myocardium. This review details the strengths and limitations of the different cell labelling and imaging techniques and their potential application to the clinical realm. We also consider the broader, multifaceted utility of imaging throughout the cell therapy process, providing a discussion of its considerable value during cell delivery and its importance during the evaluation of cardiac outcomes in clinical studies.

Tracking stem cells for cardiovascular applications in vivo: focus on imaging techniques

Despite rapid translation of stem cell therapy into clinical practice, the treatment of cardiovascular disease using embryonic stem cells, adult stem and progenitor cells or induced pluripotent stem cells has not yielded satisfactory results to date. Noninvasive stem cell imaging techniques could provide greater insight into not only the therapeutic benefit, but also the fundamental mechanisms underlying stem cell fate, migration, survival and engraftment in vivo. This information could also assist in the appropriate choice of stem cell type(s), delivery routes and dosing regimes in clinical cardiovascular stem cell trials. Multiple imaging modalities, such as MRI, PET, SPECT and CT, have emerged, offering the ability to localize, monitor and track stem cells in vivo. This article discusses stem cell labeling approaches and highlights the latest cardiac stem cell imaging techniques that may help clinicians, research scientists or other healthcare professionals select the best cellular therapeutics for cardiovascular disease management.

Ferritin as a reporter gene for in vivo tracking of stem cells by 1.5-T cardiac MRI in a rat model of myocardial infarction

The methods currently utilized to track stem cells by cardiac MRI are affected by important limitations, and new solutions are needed. We tested human ferritin heavy chain (hFTH) as a reporter gene for in vivo tracking of stem cells by cardiac MRI. Swine cardiac stem/progenitor cells were transduced with a lentiviral vector to overexpress hFTH and cultured to obtain cardiospheres (Cs). Myocardial infarction was induced in rats, and, after 45 min, the animals were subjected to intramyocardial injection of ∼200 hFTH-Cs or nontransduced Cs or saline solution in the border zone. By employing clinical standard 1.5-Tesla MRI scanner and a multiecho T2* gradient echo sequence, we localized iron-accumulating tissue only in hearts treated with hFTH-Cs. This signal was detectable at 1 wk after infarction, and its size did not change significantly after 4 wk (6.33 ± 3.05 vs. 4.41 ± 4.38 mm2). Cs transduction did not affect their cardioreparative potential, as indicated by the significantly better preserved left ventricular global and regional function and the 36% reduction in infarct size in both groups that received Cs compared with control infarcts. Prussian blue staining confirmed the presence of differentiated, iron-accumulating cells containing mitochondria of porcine origin. Cs-derived cells displayed CD31, α-smooth muscle, and α-sarcomeric actin antigens, indicating that the differentiation into endothelial, smooth muscle and cardiac muscle lineage was not affected by ferritin overexpression. In conclusion, hFTH can be used as a MRI reporter gene to track dividing/differentiating stem cells in the beating heart, while simultaneously monitoring cardiac morpho-functional changes.

Nanomedicine: application areas and development prospects

Nanotechnology, along with related concepts such as nanomaterials, nanostructures and nanoparticles, has become a priority area for scientific research and technological development. Nanotechnology, i.e., the creation and utilization of materials and devices at nanometer scale, already has multiple applications in electronics and other fields. However, the greatest expectations are for its application in biotechnology and health, with the direct impact these could have on the quality of health in future societies. The emerging discipline of nanomedicine brings nanotechnology and medicine together in order to develop novel therapies and improve existing treatments. In nanomedicine, atoms and molecules are manipulated to produce nanostructures of the same size as biomolecules for interaction with human cells. This procedure offers a range of new solutions for diagnoses and “smart” treatments by stimulating the body’s own repair mechanisms. It will enhance the early diagnosis and treatment of diseases such as cancer, diabetes, Alzheimer’s, Parkinson’s and cardiovascular diseases. Preventive medicine may then become a reality.

Ultra-high-field MRI real-time imaging of HSC engraftment of the bone marrow niche

The bone marrow (BM) undergoes extensive remodeling following irradiation damage. A crucial part of restoring homeostasis following irradiation is the ability of hematopoietic stem cells (HSCs) to home to and engraft specialized niches within the BM through a remodeling BM vascular system. Here we show that a combination of ultra-high-field strength magnetic resonance imaging (17.6 T, MRI) coupled with fluorescent microscopy (FLM) serves as a powerful tool for the in vivo imaging of cell homing within the BM. Ultra-high-field MRI can achieve high-resolution three-dimensional (3D) images (28 × 28 × 60 μm(3)) of the BM in live mice, sufficient to resolve anatomical changes in BM microstructures attributed to radiation damage. Following intra-arterial infusion with dsRed-expressing BM cells, labeled with superparamagnetic iron oxides, both FLM and MRI could be used to follow initial homing and engraftment of donor HSC to a limited number of preferred sites within a few cell diameters of the calcified bone-the endosteal niche. Subsequent histology confirmed the fidelity and accuracy of MRI to create non-invasive, high-resolution 3D images of donor cell engraftment of the BM in living animals at the level of single-cell detection.