Iron-oxide labeling and outcome of transplanted mesenchymal stem cells in the infarcted myocardium

Advancing MRI with magnetic nanoparticles: a comprehensive review of translational research and clinical trials

The nexus of advanced technology and medical therapeutics has ushered in a transformative epoch in contemporary medicine. Within this arena, Magnetic Resonance Imaging (MRI) emerges as a paramount tool, intertwining the advancements of technology with the art of healing. MRI's pivotal role is evident in its broad applicability, spanning from neurological diseases, soft-tissue and tumour characterization, to many more applications. Though already foundational, aspirations remain to further enhance MRI's capabilities. A significant avenue under exploration is the incorporation of innovative nanotechnological contrast agents. Forefront among these are Superparamagnetic Iron Oxide Nanoparticles (SPIONs), recognized for their adaptability and safety profile. SPION's intrinsic malleability allows them to be tailored for improved biocompatibility, while their functionality is further broadened when equipped with specific targeting molecules. Yet, the path to optimization is not devoid of challenges, from renal clearance concerns to potential side effects stemming from iron overload. This review endeavors to map the intricate journey of SPIONs as MRI contrast agents, offering a chronological perspective of their evolution and deployment. We provide an in-depth current outline of the most representative and impactful pre-clinical and clinical studies centered on the integration of SPIONs in MRI, tracing their trajectory from foundational research to contemporary applications.

In vivo tracking transplanted cardiomyocytes derived from human induced pluripotent stem cells using nuclear medicine imaging

Introduction

Transplantation of human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) is a promising treatment for heart failure. Information on long-term cell engraftment after transplantation is clinically important. However, clinically applicable evaluation methods have not yet been established.

Methods

In this study, to noninvasively assess transplanted cell engraftment, human SLC5A5, which encodes a sodium/iodide symporter (NIS) that transports radioactive tracers such as 125I, 18F-tetrafluoroborate (TFB), and 99mTc-pertechnetate (99mTcO4-), was transduced into human induced pluripotent stem cells (iPSCs), and nuclear medicine imaging was used to track engrafted human iPSC-CMs.

Results

To evaluate the pluripotency of NIS-expressing human iPSCs, they were subcutaneously transplanted into immunodeficient rats. Teratomas were detected by 99mTcO4- single photon emission computed tomography (SPECT/CT) imaging. NIS expression and the uptake ability of 125I were maintained in purified human iPSC-CMs. NIS-expressing human iPSC-CMs transplanted into immunodeficient rats could be detected over time using 99mTcO4- SPECT/CT imaging. Unexpectedly, NIS expression affected cell proliferation of human iPSCs and iPSC-derived cells.

Discussion

Such functionally designed iPSC-CMs have potential clinical applications as a noninvasive method of grafted cell evaluation, but further studies are needed to determine the effects of NIS transduction on cellular characteristics and functions.

A primer on in vivo cell tracking using MRI

Cell tracking by in vivo magnetic resonance imaging (MRI) offers a collection of multiple advantages over other imaging modalities, including high spatial resolution, unlimited depth penetration, 3D visualization, lack of ionizing radiation, and the potential for long-term cell monitoring. Three decades of innovation in both contrast agent chemistry and imaging physics have built an expansive array of probes and methods to track cells non-invasively across a diverse range of applications. In this review, we describe both established and emerging MRI cell tracking approaches and the variety of mechanisms available for contrast generation. Emphasis is given to the advantages, practical limitations, and persistent challenges of each approach, incorporating quantitative comparisons where possible. Toward the end of this review, we take a deeper dive into three key application areas - tracking cancer metastasis, immunotherapy for cancer, and stem cell regeneration - and discuss the cell tracking techniques most suitable to each.

CRISPR-Cas9 editing of TLR4 to improve the outcome of cardiac cell therapy

Inflammation and fibrosis limit the reparative properties of human mesenchymal stromal cells (hMSCs). We hypothesized that disrupting the toll-like receptor 4 (TLR4) gene would switch hMSCs toward a reparative phenotype and improve the outcome of cell therapy for infarct repair. We developed and optimized an improved electroporation protocol for CRISPR-Cas9 gene editing. This protocol achieved a 68% success rate when applied to isolated hMSCs from the heart and epicardial fat of patients with ischemic heart disease. While cell editing lowered TLR4 expression in hMSCs, it did not affect classical markers of hMSCs, proliferation, and migration rate. Protein mass spectrometry analysis revealed that edited cells secreted fewer proteins involved in inflammation. Analysis of biological processes revealed that TLR4 editing reduced processes linked to inflammation and extracellular organization. Furthermore, edited cells expressed less NF-ƙB and secreted lower amounts of extracellular vesicles and pro-inflammatory and pro-fibrotic cytokines than unedited hMSCs. Cell therapy with both edited and unedited hMSCs improved survival, left ventricular remodeling, and cardiac function after myocardial infarction (MI) in mice. Postmortem histologic analysis revealed clusters of edited cells that survived in the scar tissue 28 days after MI. Morphometric analysis showed that implantation of edited cells increased the area of myocardial islands in the scar tissue, reduced the occurrence of transmural scar, increased scar thickness, and decreased expansion index. We show, for the first time, that CRISPR-Cas9-based disruption of the TLR4-gene reduces pro-inflammatory polarization of hMSCs and improves infarct healing and remodeling in mice. Our results provide a new approach to improving the outcomes of cell therapy for cardiovascular diseases.

Dual Magnetic Particle Imaging and Akaluc Bioluminescence Imaging for Tracking Cancer Cell Metastasis

Magnetic particle imaging (MPI) provides hotspot tracking and direct quantification of superparamagnetic iron oxide nanoparticle (SPIO)-labelled cells. Bioluminescence imaging (BLI) with the luciferase reporter gene Akaluc can provide complementary information on cell viability. Thus, we explored combining these technologies to provide a more holistic view of cancer cell fate in mice. Akaluc-expressing 4T1Br5 cells were labelled with the SPIO Synomag-D and injected into the mammary fat pads (MFP) of four nude mice. BLI was performed on days 0, 6 and 13, and MPI was performed on days 1, 8 and 14. Ex vivo histology and fluorescence microscopy of MFP and a potential metastatic site was conducted. The BLI signal in the MFP increased significantly from day 0 to day 13 (p < 0.05), mirroring tumor growth. The MPI signal significantly decreased from day 1 to day 14 (p < 0.05) due to SPIO dilution in proliferating cells. Both modalities detected secondary metastases; however, they were visualized in different anatomical regions. Akaluc BLI complemented MPI cell tracking, allowing for longitudinal measures of cell viability and sensitive detection of distant metastases at different locations. We predict this multimodal imaging approach will help to evaluate novel therapeutics and give a better understanding of metastatic mechanisms.

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

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

Recent achievements in nano-based technologies for ocular disease diagnosis and treatment, review and update

Ocular drug delivery is one of the most challenging endeavors among the various available drug delivery systems. Despite having suitable drugs for the treatment of ophthalmic disease, we have not yet succeeded in achieving a proper drug delivery approach with the least adverse effects. Nanotechnology offers great opportunities to overwhelm the restrictions of common ocular delivery systems, including low therapeutic effects and adverse effects because of invasive surgery or systemic exposure. The present review is dedicated to highlighting and updating the recent achievements of nano-based technologies for ocular disease diagnosis and treatment. While further effort remains, the progress illustrated here might pave the way to new and very useful ocular nanomedicines.

Molecular imaging nanoprobes for theranostic applications

As a non-invasive imaging monitoring method, molecular imaging can provide the location and expression level of disease signature biomolecules in vivo, leading to early diagnosis of relevant diseases, improved treatment strategies, and accurate assessment of treating efficacy. In recent years, a variety of nanosized imaging probes have been developed and intensively investigated in fundamental/translational research and clinical practice. Meanwhile, as an interdisciplinary discipline, this field combines many subjects of chemistry, medicine, biology, radiology, and material science, etc. The successful molecular imaging not only requires advanced imaging equipment, but also the synthesis of efficient imaging probes. However, limited summary has been reported for recent advances of nanoprobes. In this paper, we summarized the recent progress of three common and main types of nanosized molecular imaging probes, including ultrasound (US) imaging nanoprobes, magnetic resonance imaging (MRI) nanoprobes, and computed tomography (CT) imaging nanoprobes. The applications of molecular imaging nanoprobes were discussed in details. Finally, we provided an outlook on the development of next generation molecular imaging nanoprobes.

Cardiac Mesenchymal Stem Cells Promote Fibrosis and Remodeling in Heart Failure: Role of PDGF Signaling

Heart failure (HF) is characterized by progressive fibrosis. Both fibroblasts and mesenchymal stem cells (MSCs) can differentiate into pro-fibrotic myofibroblasts. MSCs secrete and express platelet-derived growth factor (PDGF) and its receptors. We hypothesized that PDGF signaling in cardiac MSCs (cMSCs) promotes their myofibroblast differentiation and aggravates post-myocardial infarction left ventricular remodeling and fibrosis. We show that cMSCs from failing hearts post-myocardial infarction exhibit an altered phenotype. Inhibition of PDGF signaling in vitro inhibited cMSC-myofibroblast differentiation, whereas in vivo inhibition during established ischemic HF alleviated left ventricular remodeling and function, and decreased myocardial fibrosis, hypertrophy, and inflammation. Modulating cMSC PDGF receptor expression may thus represent a novel approach to limit pathologic cardiac fibrosis in HF.

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.

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.

Magnetic Particle Imaging: Current and Future Applications, Magnetic Nanoparticle Synthesis Methods and Safety Measures

Magnetic nanoparticles (MNPs) have a wide range of applications; an area of particular interest is magnetic particle imaging (MPI). MPI is an imaging modality that utilizes superparamagnetic iron oxide particles (SPIONs) as tracer particles to produce highly sensitive and specific images in a broad range of applications, including cardiovascular, neuroimaging, tumor imaging, magnetic hyperthermia and cellular tracking. While there are hurdles to overcome, including accessibility of products, and an understanding of safety and toxicity profiles, MPI has the potential to revolutionize research and clinical biomedical imaging. This review will explore a brief history of MPI, MNP synthesis methods, current and future applications, and safety concerns associated with this newly emerging imaging modality.

Rapamycin-Preactivated Autophagy Enhances Survival and Differentiation of Mesenchymal Stem Cells After Transplantation into Infarcted Myocardium

Stem cell transplantation has been limited by poor survival of the engrafted cells in hostile microenvironment of the infarcted myocardium. This study investigated cytoprotective effect of rapamycin-preactivated autophagy on survival of the transplanted mesemchymal stem cells (MSCs). MSCs isolated from rat bone marrow were treated with 50 nmol/L rapamycin for 2 h, and then the cytoprotective effect of rapamycin was examined. After intramyocardial transplantation in rat ischemia/reperfusion models, the survival and differentiation of the rapamycin-pretreated calls were accessed. After treatment with rapamycin, autophagic activities and lysososme production of the cells were increased significantly. In the condition of short-term or long-term hypoxia and serum deprivation, the apoptotic cells in rapamycin-pretreated cells were less, and secretion of HGF, IGF-1, SCF, SDF-1 and VEGF was increased. After transplantation of rapamycin-pretreated cells, repair of the infarcted myocardium and restoration of cardial function were enhanced dramatically. Expression of HGF, IGF-1, SCF, SDF-1, VEGF, HIF-1α and IL-10 in the myocardium was upregulated, while expression of IL-1β and TNF-α was downregulated. Tracing of GFP and Sry gene showed that the survival of rapamycin-pretreated cells was increased. Cardiomyogenesis and angiogenesis in the infarcted myocardium were strengthened. Some rapamycin-pretreated cells differentiated into cardiomyocytes or endothelial cells. These results demonstrate that moderate preactivation of autophagy with rapamycin enhances the survival and differentiation of the transplanted MSCs. Rapamycin-primed MSCs can promote repair of the infarcted myocardium and improvement of cardiac function effectively.

Macrophages and Stem Cells-Two to Tango for Tissue Repair?

Macrophages (MCs) are present in all tissues, not only supporting homeostasis, but also playing an important role in organogenesis, post-injury regeneration, and diseases. They are a heterogeneous cell population due to their origin, tissue specificity, and polarization in response to aggression factors, depending on environmental cues. Thus, as pro-inflammatory M1 phagocytic MCs, they contribute to tissue damage and even fibrosis, but the anti-inflammatory M2 phenotype participates in repairing processes and wound healing through a molecular interplay with most cells in adult stem cell niches. In this review, we emphasize MC phenotypic heterogeneity in health and disease, highlighting their systemic and systematic contribution to tissue homeostasis and repair. Unraveling the intervention of both resident and migrated MCs on the behavior of stem cells and the regulation of the stem cell niche is crucial for opening new perspectives for novel therapeutic strategies in different diseases.

Mesenchymal stem/stromal cells as a valuable source for the treatment of immune-mediated disorders

Over recent years, mesenchymal stem/stromal cells (MSCs) and their potential biomedical applications have received much attention from the global scientific community in an increasing manner. Firstly, MSCs were successfully isolated from human bone marrow (BM), but in the next steps, they were also extracted from other sources, mostly from the umbilical cord (UC) and adipose tissue (AT). The International Society for Cellular Therapy (ISCT) has suggested minimum criteria to identify and characterize MSCs as follows: plastic adherence, surface expression of CD73, D90, CD105 in the lack of expression of CD14, CD34, CD45, and human leucocyte antigen-DR (HLA-DR), and also the capability to differentiate to multiple cell types including adipocyte, chondrocyte, or osteoblast in vitro depends on culture conditions. However, these distinct properties, including self-renewability, multipotency, and easy accessibility are just one side of the coin; another side is their huge secretome which is comprised of hundreds of mediators, cytokines, and signaling molecules and can effectively modulate the inflammatory responses and control the infiltration process that finally leads to a regulated tissue repair/healing or regeneration process. MSC-mediated immunomodulation is a direct result of a harmonic synergy of MSC-released signaling molecules (i.e., mediators, cytokines, and chemokines), the reaction of immune cells and other target cells to those molecules, and also feedback in the MSC-molecule-target cell axis. These features make MSCs a respectable and eligible therapeutic candidate to be evaluated in immune-mediated disorders, such as graft versus host diseases (GVHD), multiple sclerosis (MS), Crohn's disease (CD), and osteoarthritis (OA), and even in immune-dysregulating infectious diseases such as the novel coronavirus disease 2019 (COVID-19). This paper discussed the therapeutic applications of MSC secretome and its biomedical aspects related to immune-mediated conditions. Sources for MSC extraction, their migration and homing properties, therapeutic molecules released by MSCs, and the pathways and molecular mechanisms possibly involved in the exceptional immunoregulatory competence of MSCs were discussed. Besides, the novel discoveries and recent findings on immunomodulatory plasticity of MSCs, clinical applications, and the methods required for their use as an effective therapeutic option in patients with immune-mediated/immune-dysregulating diseases were highlighted.

Hybrid PET/MR imaging in myocardial inflammation post-myocardial infarction

Hybrid PET/MR imaging is an emerging imaging modality combining positron emission tomography (PET) and magnetic resonance imaging (MRI) in the same system. Since the introduction of clinical PET/MRI in 2011, it has had some impact (e.g., imaging the components of inflammation in myocardial infarction), but its role could be much greater. Many opportunities remain unexplored and will be highlighted in this review. The inflammatory process post-myocardial infarction has many facets at a cellular level which may affect the outcome of the patient, specifically the effects on adverse left ventricular remodeling, and ultimately prognosis. The goal of inflammation imaging is to track the process non-invasively and quantitatively to determine the best therapeutic options for intervention and to monitor those therapies. While PET and MRI, acquired separately, can image aspects of inflammation, hybrid PET/MRI has the potential to advance imaging of myocardial inflammation. This review contains a description of hybrid PET/MRI, its application to inflammation imaging in myocardial infarction and the challenges, constraints, and opportunities in designing data collection protocols. Finally, this review explores opportunities in PET/MRI: improved registration, partial volume correction, machine learning, new approaches in the development of PET and MRI pulse sequences, and the use of novel injection strategies.

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.

Current Status of Stem Cell-Derived Therapies for Parkinson's Disease: From Cell Assessment and Imaging Modalities to Clinical Trials

Curative therapies or treatments reversing the progression of Parkinson’s disease (PD) have attracted considerable interest in the last few decades. PD is characterized by the gradual loss of dopaminergic (DA) neurons and decreased striatal dopamine levels. Current challenges include optimizing neuroprotective strategies, developing personalized drug therapy, and minimizing side effects from the long-term prescription of pharmacological drugs used to relieve short-term motor symptoms. Transplantation of DA cells into PD patients’ brains to replace degenerated DA has the potential to change the treatment paradigm. Herein, we provide updates on current progress in stem cell-derived DA neuron transplantation as a therapeutic alternative for PD. We briefly highlight cell sources for transplantation and focus on cell assessment methods such as identification of genetic markers, single-cell sequencing, and imaging modalities used to access cell survival and function. More importantly, we summarize clinical reports of patients who have undergone cell-derived transplantation in PD to better perceive lessons that can be drawn from past and present clinical outcomes. Modifying factors include (1) source of the stem cells, (2) quality of the stem cells, (3) age of the patient, (4) stage of disease progression at the time of cell therapy, (5) surgical technique/practices, and (6) the use of immunosuppression. We await the outcomes of joint efforts in clinical trials around the world such as NYSTEM and CiRA to further guide us in the selection of the most suitable parameters for cell-based neurotransplantation in PD.

A Translational Porcine Model for Human Cell-Based Therapies in the Treatment of Posttraumatic Osteoarthritis After Anterior Cruciate Ligament Injury

BACKGROUND

There is a high incidence of posttraumatic osteoarthritis (PTOA) after anterior cruciate ligament (ACL) injury, and these injuries represent an enormous health care economic burden. In an effort to address this unmet clinical need, there has been increasing interest in cell-based therapies.

PURPOSE

To establish a translational large animal model of PTOA and demonstrate the feasibility of intra-articular human cell-based interventions.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Nine Yucatan mini-pigs underwent unilateral ACL transection and were monitored for up to 12 weeks after injury. Interleukin 1 beta (IL-1β) levels and collagen breakdown were evaluated longitudinally using enzyme-linked immunosorbent assays of synovial fluid, serum, and urine. Animals were euthanized at 4 weeks (n = 3) or 12 weeks (n = 3) after injury, and injured and uninjured limbs underwent magnetic resonance imaging (MRI) and histologic analysis. At 2 days after ACL injury, an additional 3 animals received an intra-articular injection of 10⁷ human bone marrow-derived mesenchymal stem cells (hBM-MSCs) combined with a fibrin carrier. These cells were labeled with the luciferase reporter gene (hBM-MSCs-Luc) as well as fluorescent markers and intracellular iron nanoparticles. These animals were euthanized on day 0 (n = 1) or day 14 (n = 2) after injection. hBM-MSC-Luc viability and localization were assessed using ex vivo bioluminescence imaging, fluorescence imaging, and MRI.

RESULTS

PTOA was detected as early as 4 weeks after injury. At 12 weeks after injury, osteoarthritis could be detected grossly as well as on histologic analysis. Synovial fluid analysis showed elevation of IL-1β shortly after ACL injury, with subsequent resolution by 2 weeks after injury. Collagen type II protein fragments were elevated in the synovial fluid and serum after injury. hBM-MSCs-Luc were detected immediately after injection and at 2 weeks after injection using fluorescence imaging, MRI, and bioluminescence imaging.

CONCLUSION

This study demonstrates the feasibility of reproducing the chondral changes, intra-articular cytokine alterations, and body fluid biomarker findings consistent with PTOA after ACL injury in a large animal model. Furthermore, we have demonstrated the ability of hBM-MSCs to survive and express transgene within the knee joint of porcine hosts without immunosuppression for at least 2 weeks.

CLINICAL RELEVANCE

This model holds great potential to significantly contribute to investigations focused on the development of cell-based therapies for human ACL injury-associated PTOA in the future (see Appendix Figure A1, available online).

Decellularized Aortic Scaffold Alleviates H2O2-Induced Inflammation and Apoptosis in CD34+ Progenitor Cells While Driving Neovasculogenesis

Bone marrow-derived stem/progenitor cells have been utilized for cardiac or vascular repair after ischemic injury, but they are subject to apoptosis and immune rejection in the ischemic site. Multiple scaffolds were used as delivery tools to transplant stem/progenitor cells; however, these scaffolds did not show intrinsically antiapoptotic or anti-inflammatory properties. Decellularized aortic scaffolds that facilitate cell delivery and tissue repair were prepared by removing cells of patient-derived aortic tissues. Scanning electron microscopy (SEM) showed cells attached well to the scaffold after culturing for 5 days. Live/dead staining showed most seeded cells survived at day 7 on a decellularized aortic scaffold. Ki67 staining demonstrated that decellularized aortic scaffold promoted proliferation of bone marrow-derived CD34+ progenitor cells. Apoptosis of CD34+ progenitor cells induced by H₂O₂ at high concentration was significantly alleviated in the presence of decellularized aortic scaffolds, demonstrating a protective effect against oxidative stress-induced apoptosis. Furthermore, decellularized aortic scaffolds significantly reduced the expression of proinflammatory cytokines (IL-8, GM-CSF, MIP-1β, GRO-α, Entoxin, and GRO) concurrently with an increase in anti-inflammatory cytokines (IL-2 and TGF-β) released from CD34+ progenitor cells when exposed to H₂O₂ at low concentration. Finally, neovascularization was observed by H&E and immunohistochemical staining 14 days after the decellularized aortic scaffolds were subcutaneously implanted in nude mice. This preclinical study demonstrates that the use of a decellularized aortic scaffold possessing antiapoptotic and anti-inflammatory properties may represent a promising strategy for cardiovascular repair after ischemic injury.

Finite element analysis reveals an important role for cell morphology in response to mechanical compression

Mechanical loading naturally controls cell phenotype, development, motility and various other biological functions; however, prolonged or substantial loading can cause cell damage and eventual death. Loading-induced mechanobiological and mechanostructural responses of different cell types affect their morphology and the internal architecture and the mechanics of the cellular components. Using single, mesenchymal stem cells, we have developed a cell-specific three-dimensional finite-element model; cell models were developed from phase-contrast microscopy images. This allowed us to evaluate the mechanostructural response of the naturally occurring variety of cell morphologies to increase sustained compressive loading. We focus on the morphology of the cytoplasm and the nucleus, as the main mechanically responsive elements, and evaluate formation of tensional strains and area changes in cells undergoing increasing uniaxial compressions. Here, we study mesenchymal stem cells as a model, due to their important role in tissue engineering and regenerative medicine; the method and findings are, however, applicable to any cell type. We observe variability in the cell responses to compression, which correlate directly with the morphology of the cells. Specifically, in cells with or without elongated protrusions (i.e., lamellipodia) tensional strains were, respectively, distributed mostly in the thin extensions or concentrated around the stiff nucleus. Thus, through cell-specific computational modeling of mechanical loading we have identified an underlying cause for stiffening (by actin recruitment) along the length of lamellipodia as well as a role for cell morphology in inducing cell-to-cell variability in mechanostructural response to loading.

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.

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

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

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.

Labeling Stem Cells with a New Hybrid Bismuth/Carbon Nanotube Contrast Agent for X-Ray Imaging

The poor retention and survival of cells after transplantation to solid tissue represent a major obstacle for the effectiveness of stem cell-based therapies. The ability to track stem cells in vivo can lead to a better understanding of the biodistribution of transplanted cells, in addition to improving the analysis of stem cell therapies' outcomes. Here, we described the use of a carbon nanotube-based contrast agent (CA) for X-ray computed tomography (CT) imaging as an intracellular CA to label bone marrow-derived mesenchymal stem cells (MSCs). Porcine MSCs were labeled without observed cytotoxicity. The CA consists of a hybrid material containing ultra-short single-walled carbon nanotubes (20-80 nm in length, US-tubes) and Bi(III) oxo-salicylate clusters which contain four Bi³⁺ ions per cluster (Bi₄C). The CA is thus abbreviated as Bi₄C@US-tubes.

In vivo MRI assessment of bioactive magnetic iron oxide/human serum albumin nanoparticle delivery into the posterior segment of the eye in a rat model of retinal degeneration

Background

Retinal degeneration diseases affect millions of patients worldwide and lead to incurable vision loss. These diseases are caused by pathologies in the retina and underlying choroid, located in the back of the eye. One of the major challenges in the development of treatments for these blinding diseases is the safe and efficient delivery of therapeutics into the back of the eye. Previous studies demonstrated that narrow size distribution core–shell near infra-red fluorescent iron oxide (IO) nanoparticles (NPs) coated with human serum albumin (HSA, IO/HSA NPs) increase the half-life of conjugated therapeutic factors, suggesting they may be used for sustained release of therapeutics. In the present study, the in vivo tracking by MRI and the long term safety of IO/HSA NPs delivery into the suprachoroid of a rat model of retinal degeneration were assessed.

Results

Twenty-five Royal College of Surgeons (RCS) pigmented rats received suprachoroidal injection of 20-nm IO/HSA NPs into the right eye. The left eye was not injected and used as control. Animals were examined by magnetic resonance imaging (MRI), electroretinogram (ERG) and histology up to 30 weeks following injection. IO/HSA NPs were detected in the back part of the rats’ eyes up to 30 weeks following injection by MRI, and up to 6 weeks by histology. No significant differences in retinal structure and function were observed between injected and non-injected eyes. There was no significant difference in the weight of IO/HSA NP-injected animals compared to non-injected rats.

Conclusions

MRI could track the nanoparticles in the posterior segment of the injected eyes demonstrating their long-term persistence, and highlighting the possible use of MRI for translational studies in animals and in future clinical studies. Suprachoroidal injection of IO/HSA NPs showed no sign of adverse effects on retinal structure and function in a rat model of retinal degeneration, suggesting that suprachoroidal delivery of IO/HSA NPs is safe and that these NPs may be used in future translational and clinical studies for extended release drug delivery at the back of the eye.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0438-y) contains supplementary material, which is available to authorized users.

Characterization of Magneto-Endosymbionts as MRI Cell Labeling and Tracking Agents

PURPOSE

Magneto-endosymbionts (MEs) show promise as living magnetic resonance imaging (MRI) contrast agents for in vivo cell tracking. Here we characterize the biomedical imaging properties of ME contrast agents, in vitro and in vivo.

PROCEDURES

By adapting and engineering magnetotactic bacteria to the intracellular niche, we are creating magneto-endosymbionts (MEs) that offer advantages relative to passive iron-based contrast agents (superparamagnetic iron oxides, SPIOs) for cell tracking. This work presents a biomedical imaging characterization of MEs including: MRI transverse relaxivity (r ₂) for MEs and ME-labeled cells (compared to a commercially available iron oxide nanoparticle); microscopic validation of labeling efficiency and subcellular locations; and in vivo imaging of a MDA-MB-231BR (231BR) human breast cancer cells in a mouse brain.

RESULTS

At 7T, r ₂ relaxivity of bare MEs was higher (250 s^-1 mM^-1) than that of conventional SPIO (178 s^-1 mM^-1). Optimized in vitro loading of MEs into 231BR cells yielded 1-4 pg iron/cell (compared to 5-10 pg iron/cell for conventional SPIO). r ₂ relaxivity dropped by a factor of ~3 upon loading into cells, and was on the same order of magnitude for ME-loaded cells compared to SPIO-loaded cells. In vivo, ME-labeled cells exhibited strong MR contrast, allowing as few as 100 cells to be detected in mice using an optimized 3D SPGR gradient-echo sequence.

CONCLUSIONS

Our results demonstrate the potential of magneto-endosymbionts as living MR contrast agents. They have r ₂ relaxivity values comparable to traditional iron oxide nanoparticle contrast agents, and provide strong MR contrast when loaded into cells and implanted in tissue.

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.

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.

The effects of superparamagnetic iron oxide nanoparticles-labeled mesenchymal stem cells in the presence of a magnetic field on attenuation of injury after heart failure

Migration of stem cells after transplantation reduces their therapeutic effects. In this study, we hypothesized that superparamagnetic iron oxide nanoparticles (SPION)-labeled mesenchymal stem cells (MSCs) in the presence of magnetic field may have a capability to increase regenerative ability after heart failure (HF). A rat model of ISO (isoproterenol)-HF was established to investigate the effects of SPION-labeled MSCs on tissue regeneration in the presence and absence of magnetic field. Hydrodynamic size, shape, and formation of chemical bonds between SPION and polyethylene glycol (PEG) were measured using dynamic light scattering (DLS), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). The MRI was used to monitor SPION-labeled MSCs in vivo. Cell and tissue uptake of nanoparticles were determined by Prussian blue staining, atomic absorption spectroscopy (AAS), and inductively coupled plasma spectroscopy (ICP). Purity of the MSCs, heart function, myocardial fibrosis, and histologic damage were evaluated using flow-cytometry, echocardiography, Masson's trichrome, and H&E staining respectively. Various spectroscopic and microscopic analyses revealed that hydrodynamic size of SPION was 40 ± 2 and their shape was spherical. FTIR confirmed the presence of PEG on the surface of nanoparticles. The presence of magnetic field significantly increased cell homing. Highly purified MSCs population was detected by flow-cytometry. Using SPION-labeled MSCs in the presence of magnetic field markedly improved heart function and myocardial hypertrophy and reduced fibrosis (p < 0.05). Collectively, our results demonstrated that SPION-labeled MSCs in the presence of magnetic field might contribute to regeneration after HF.

Nanoparticles for diagnosis and therapy of atherosclerosis and myocardial infarction: evolution toward prospective theranostic approaches

Cardiovascular diseases are the leading cause of death worldwide. Despite preventive efforts, early detection of atherosclerosis, the common pathophysiological mechanism underlying cardiovascular diseases remains elusive, and overt coronary artery disease or myocardial infarction is often the first clinical manifestation. Nanoparticles represent a novel strategy for prevention, diagnosis, and treatment of atherosclerosis, and new multifunctional nanoparticles with combined diagnostic and therapeutic capacities hold the promise for theranostic approaches to this disease. This review focuses on the development of nanosystems for therapy and diagnosis of subclinical atherosclerosis, coronary artery disease, and myocardial infarction and the evolution of nanosystems as theranostic tools. We also discuss the use of nanoparticles in noninvasive imaging, targeted drug delivery, photothermal therapies together with the challenges faced by nanosystems during clinical translation.

Using tyrosinase as a tri-modality reporter gene to monitor transplanted stem cells in acute myocardial infarction

The study aimed to investigate the feasibility of noninvasive monitoring of bone marrow mesenchymal stem cells (MSCs) transduced with the tyrosinase reporter gene for acute myocardial infarction (AMI) with photoacoustic imaging (PAI), magnetic resonance imaging (MRI), and positron emission tomography (PET) in vitro and in vivo. MSCs were transduced with a lentivirus carrying a tyrosinase reporter gene. After transduction, the rate of ¹⁸F-5-fluoro-N-(2-[diethylamino]ethyl)picolinamide (¹⁸F-5-FPN) uptake was measured. PAI and MRI of stable cell lines expressing tyrosinase (TYR-MSCs) were performed in vitro. An AMI model was induced and verified. TYR-MSCs and MSCs were injected into the margins of the infarcted areas, and PAI, MRI, and PET images were acquired 1, 7, 14, 21, and 28 days after cell injection. Sham-operated models without injection were used as the control group. TYR-MSCs showed noticeably higher uptake of ¹⁸F-5-FPN and stronger signals in T1-weighted MRI and PAI than non-transduced MSCs. In vivo studies revealed prominent signals in the injected area of the infarcted myocardium on PAI/MRI/PET images, whereas no signal could be seen in rats injected with non-transduced MSCs or sham-operated rats. The uptake values of ¹⁸F-5-FPN in vivo showed a slight decrease over 28 days, whereas MRI and PAI signal intensity decreased dramatically. MSCs stably transduced with the tyrosinase reporter gene could be monitored in vivo in myocardial infarction models by PET, MRI, and PAI, providing a feasible and reliable method for checking the viability, location, and dwell time of transplanted stem cells.

Developing stem cell treatments for heart disease could be aided by adding the gene for tyrosinase, an enzyme that can reveal the location and activity of the cells. Transplanting stem cells derived from bone marrow into injured hearts shows promise for repairing the damage caused by heart attacks. Developing the treatment is hampered by limitations of existing methods for monitoring the fate of the transplanted stem cells. Researchers in China led by Xiaoli Lan at Huazhong University of Science and Technology tackled this limitation by adding the gene for tyrosinase into the stem cells. The enzyme produces the pigment melanin which both directly and by binding to other chemicals generates signals which can be identified by photoacoustic imaging, magnetic resonance imaging and positron emission tomography. Tests in cultured cells and rats confirm the procedure’s potential.

Multimodality reporter gene imaging: Construction strategies and application

Molecular imaging has played an important role in the noninvasive exploration of multiple biological processes. Reporter gene imaging is a key part of molecular imaging. By combining with a reporter probe, a reporter protein can induce the accumulation of specific signals that are detectable by an imaging device to provide indirect information of reporter gene expression in living subjects. There are many types of reporter genes and each corresponding imaging technique has its own advantages and drawbacks. Fused reporter genes or single reporter genes with products detectable by multiple imaging modalities can compensate for the disadvantages and potentiate the advantages of each modality. Reporter gene multimodality imaging could be applied to trace implanted cells, monitor gene therapy, assess endogenous molecular events, screen drugs, etc. Although several types of multimodality imaging apparatus and multimodality reporter genes are available, more sophisticated detectors and multimodality reporter gene systems are needed.

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.

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.

Iron oxide labeling does not affect differentiation potential of human bone marrow mesenchymal stem cells exhibited by their differentiation into cardiac and neuronal cells

Mesenchymal stem cells (MSCs) have shown promising outcomes in cardiac and neuronal diseases. Efficient and noninvasive tracking of MSCs is essential to harness their therapeutic potential. Iron oxide nanoparticles (IONPs) have emerged as effective means to label stem cells and visualize them using magnetic resonance imaging (MRI). It is known that IONPs do not affect viability and cell proliferation of stem cells. However, very few studies have demonstrated differentiation potential of iron oxide-labeled MSCs and their differentiation into specific lineages that can contribute to cellular therapies. The differentiation of IONP-labeled human bone marrow mesenchymal stem cells (hBM-MSCs) into cardiac and neuronal lineages has never been studied. In this study, we have shown that IONP-labeled hBM-MSCs retain their differentiation potential to cardiac and neuronal cell lineages. We also confirmed that labeling hBM-MSCs with IONP does not affect their characteristic properties such as viability, cellular proliferation rate, surface marker profiling, and trilineage differentiation capacity. This study shows that IONP can be efficiently tracked, and its labeling does not alter stemness and differentiation potential of hBM-MSCs. Thus, the labeled hBM-MSCs can be used in clinical therapies and regenerative medicine.

Immunoprivileged no more: measuring the immunogenicity of allogeneic adult mesenchymal stem cells

Background

Autologous and allogeneic adult mesenchymal stem/stromal cells (MSCs) are increasingly being investigated for treating a wide range of clinical diseases. Allogeneic MSCs are especially attractive due to their potential to provide immediate care at the time of tissue injury or disease diagnosis. The prevailing dogma has been that allogeneic MSCs are immune privileged, but there have been very few studies that control for matched or mismatched major histocompatibility complex (MHC) molecule expression and that examine immunogenicity in vivo. Studies that control for MHC expression have reported both cell-mediated and humoral immune responses to MHC-mismatched MSCs. The clinical implications of immune responses to MHC-mismatched MSCs are still unknown. Pre-clinical and clinical studies that document the MHC haplotype of donors and recipients and measure immune responses following MSC treatment are necessary to answer this critical question.

Conclusions

This review details what is currently known about the immunogenicity of allogeneic MSCs and suggests contemporary assays that could be utilized in future studies to appropriately identify and measure immune responses to MHC-mismatched MSCs.

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.

Stem Cell Tracking Technologies for Neurological Regenerative Medicine Purposes

The growing field of stem cell therapy is moving toward clinical trials in a variety of applications, particularly for neurological diseases. However, this translation of cell therapies into humans has prompted a need to create innovative and breakthrough methods for stem cell tracing, to explore the migration routes and its reciprocity with microenvironment targets in the body, to monitor and track the outcome after stem cell transplantation therapy, and to track the distribution and cell viability of transplanted cells noninvasively and longitudinally. Recently, a larger number of cell tracking methods in vivo were developed and applied in animals and humans, including magnetic resonance imaging, nuclear medicine imaging, and optical imaging. This review has been intended to summarize the current use of those imaging tools in tracking stem cells, detailing their main features and drawbacks, including image resolution, tissue penetrating depth, and biosafety aspects. Finally, we address that multimodality imaging method will be a more potential tracking tool in the future clinical application.

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.

Mechanisms of stem cell based cardiac repair-gap junctional signaling promotes the cardiac lineage specification of mesenchymal stem cells

Different subtypes of bone marrow-derived stem cells are characterized by varying functionality and activity after transplantation into the infarcted heart. Improvement of stem cell therapeutics requires deep knowledge about the mechanisms that mediate the benefits of stem cell treatment. Here, we demonstrated that co-transplantation of mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) led to enhanced synergistic effects on cardiac remodeling. While HSCs were associated with blood vessel formation, MSCs were found to possess transdifferentiation capacity. This cardiomyogenic plasticity of MSCs was strongly promoted by a gap junction-dependent crosstalk between myocytes and stem cells. The inhibition of cell-cell coupling significantly reduced the expression of the cardiac specific transcription factors NKX2.5 and GATA4. Interestingly, we observed that small non-coding RNAs are exchanged between MSCs and cardiomyocytes in a GJ-dependent manner that might contribute to the transdifferentiation process of MSCs within a cardiac environment. Our results suggest that the predominant mechanism of HSCs contribution to cardiac regeneration is based on their ability to regulate angiogenesis. In contrast, transplanted MSCs have the capability for intercellular communication with surrounding cardiomyocytes, which triggers the intrinsic program of cardiogenic lineage specification of MSCs by providing cardiomyocyte-derived cues.

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.

Bone marrow mesenchymal stem cell-derived vascular endothelial growth factor attenuates cardiac apoptosis via regulation of cardiac miRNA-23a and miRNA-92a in a rat model of myocardial infarction

Bone marrow-mesenchymal stem cell (BM-MSC) therapy improves the recovery of cardiac function after myocardial infarction (MI); however, the underlying molecular mechanisms are not completely understood. Recent studies have shown that microRNAs (miRNAs) modulate the pathophysiology of cardiovascular diseases. Here, we investigated the mechanisms underlying the effects of BM-MSC-derived paracrine factors and cardiac miRNAs on myocardial regeneration after MI. In our study, MI was induced by permanent ligation of the left anterior descending (LAD) coronary artery. BM-MSCs transplanted in infarcted rats significantly downregulated the expression of miRNA-23a and miRNA-92a and inhibited apoptosis in the myocardium. An in vitro experiment showed that supernatant from BM-MSCs cultured under hypoxia contained higher levels of vascular endothelial growth factor (VEGF) than that from BM-MSCs under normoxia. In addition, inhibition of miRNA-23a and miRNA-92a reduced cardiac apoptosis. Moreover, the VEGF-containing BM-MSC supernatant inhibited miRNA-23a and miRNA-92a expression and reduced apoptotic signaling in cardiomyocytes under hypoxia. These effects were inhibited when the supernatant was treated with neutralizing antibodies against VEGF. Our results indicate that the paracrine factor, VEGF, derived from transplanted BM-MSCs, regulated the expression of miRNAs such as miRNA-23a and miRNA-92a and exerted anti-apoptotic effects in cardiomyocytes after MI.

Magnetic Resonance Imaging of Myocardial Function Following Intracoronary and Intramyocardial Stem Cell Injection

Stem cell-based therapy is a new therapeutic option that can be used in patients with cardiac diseases caused by myocardial injury. Cardiac magnetic resonance imaging (MRI) is a new noninvasive imaging method with an increasingly widespread indication. The aim of this review was to evaluate the role of cardiac MRI in patients with myocardial infarction undergoing stem cell therapy. We studied the role of MRI in the assessment of myocardial viability, stem cell tracking, assessment of cell survival rate, and monitoring of the long-term effects of stem cell therapy. Based on the current knowledge in this field, this noninvasive, in vivo cardiac imaging technique has a large indication in this group of patients and plays an important role in all stages of stem cell therapy, from the indication to the long-term follow-up of patients.