Tracking cell fate with noninvasive imaging

A Three-Dimensional Imaging Method for the Quantification and Localization of Dynamic Cell Tracking Posttransplantation

Cell transplantation has been proposed as a promising therapeutic strategy for curing the diseases requiring tissue repairing and functional restoration. A preclinical method to systematically evaluate the fates of donor cells in recipients, spatially and temporally, is demanded for judging therapeutic potentials for the particularly designed cell transplantation. Yet, the dynamic cell tracking methodology for tracing transplanted cells in vivo is still at its early phase. Here, we created a practical protocol for dynamically tracking cell via a three-dimensional (3D) technique which enabled us to localize, quantify, and overall evaluate the transplanted hepatocytes within a liver failure mouse model. First, the capacity of 3D bioluminescence imaging for quantifying transplanted hepatocytes was defined. Images obtained from the 3D bioluminescence imaging module were then combined with the CT scanner to reconstruct structure images of host mice. With those reconstructed images, precise locations of transplanted hepatocytes in the liver of the recipient were dynamically monitored. Immunohistochemistry staining of transplanted cells, and the serology assay of liver panel of the host mice were applied to verify the successful engraftment of donor cells in the host livers. Our protocol was practical for evaluating the engraftment efficiency of donor cells at their preclinical phases, which is also applicable as a referable standard for studying the fates of other transplanted cells, such as stem cell-derived cell types, during preclinical studies with cell transplantation therapy.

Dextran-coated iron oxide nanoparticle-induced nanotoxicity in neuron cultures

Recent technological advances have introduced diverse engineered nanoparticles (ENPs) into our air, water, medicine, cosmetics, clothing, and food. However, the health and environmental effects of these increasingly common ENPs are still not well understood. In particular, potential neurological effects are one of the most poorly understood areas of nanoparticle toxicology (nanotoxicology), in that low-to-moderate neurotoxicity can be subtle and difficult to measure. Culturing primary neuron explants on planar microelectrode arrays (MEAs) has emerged as one of the most promising in vitro techniques with which to study neuro-nanotoxicology, as MEAs enable the fluorescent tracking of nanoparticles together with neuronal electrical activity recording at the submillisecond time scale, enabling the resolution of individual action potentials. Here we examine the dose-dependent neurotoxicity of dextran-coated iron oxide nanoparticles (dIONPs), a common type of functionalized ENP used in biomedical applications, on cultured primary neurons harvested from postnatal day 0-1 mouse brains. A range of dIONP concentrations (5-40 µg/ml) were added to neuron cultures, and cells were plated either onto well plates for live cell, fluorescent reactive oxidative species (ROS) and viability observations, or onto planar microelectrode arrays (MEAs) for electrophysiological measurements. Below 10 µg/ml, there were no dose-dependent cellular ROS increases or effects in MEA bursting behavior at sub-lethal dosages. However, above 20 µg/ml, cell death was obvious and widespread. Our findings demonstrate a significant dIONP toxicity in cultured neurons at concentrations previously reported to be safe for stem cells and other non-neuronal cell types.

Tracking and Quantification of Magnetically Labeled Stem Cells using Magnetic Resonance Imaging

Stem cell based therapies have critical impacts on treatments and cures of diseases such as neurodegenerative or cardiovascular disease. In vivo tracking of stem cells labeled with magnetic contrast agents is of particular interest and importance as it allows for monitoring of the cells' bio-distribution, viability, and physiological responses. Herein, recent advances are introduced in tracking and quantification of super-paramagnetic iron oxide (SPIO) nanoparticles-labeled cells with magnetic resonance imaging, a noninvasive approach that can longitudinally monitor transplanted cells. This is followed by recent translational research on human stem cells that are dual-labeled with green fluorescence protein (GFP) and SPIO nanoparticles, then transplanted and tracked in a chicken embryo model. Cell labeling efficiency, viability, and cell differentiation are also presented.

Evaluation of the autologous bone marrow mononuclear therapy and functional restoration in the scarred myocardium by imaging analysis

A 62-year-old male patient with previous history of myocardial infarction, akinetic myocardial segments, and an ejection fraction of 31% with the NYHA class III category was selected for the autologous bone marrow (ABM)-derived mononuclear cell fraction injection during CABG surgery. Nitrate augmented myocardial tracer uptake was imaged by ECG gated SPECT pre- and 1 year post-ABM therapy, using radiotracer Tc99m Sestamibi. The baseline gated SPECT demonstrated full thickness infarct in 40% area of LAD territory. Bone marrow aspirate of 20.0 ml from sternum yielding a mono nuclear cell fraction of 4.5 × 10⁷ cells/ml was suspended in 2.0 ml of sterile normal saline to be injected at eight sites of the injured myocardium. There were no apparent side effects due to the procedure, i.e., life threatening events, major bleeds, reaction, or shock. The case was followed at the end of 1, 3, 6 months by ECG and Holter monitor and ECG gated SPECT at the end of 12 months. The gated SPECT images demonstrated mild but definitely improved tracer uptake within part of the infarcted segments along with improvement in ejection fraction to 45%, and a clinical change in the NYHA Class to II. Cell-based therapy may offer benefits of induction of normal tissue microenvironment.

Determining the fate of seeded cells in venous tissue-engineered vascular grafts using serial MRI

A major limitation of tissue engineering research is the lack of noninvasive monitoring techniques for observations of dynamic changes in single tissue-engineered constructs. We use cellular magnetic resonance imaging (MRI) to track the fate of cells seeded onto functional tissue-engineered vascular grafts (TEVGs) through serial imaging. After in vitro optimization, murine macrophages were labeled with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles and seeded onto scaffolds that were surgically implanted as inferior vena cava interposition grafts in SCID/bg mice. Serial MRI showed the transverse relaxation times (T(2)) were significantly lower immediately following implantation of USPIO-labeled scaffolds (T(2) = 44 ± 6.8 vs. 71 ± 10.2 ms) but increased rapidly at 2 h to values identical to control implants seeded with unlabeled macrophages (T(2) = 63 ± 12 vs. 63 ± 14 ms). This strongly indicates the rapid loss of seeded cells from the scaffolds, a finding verified using Prussian blue staining for iron containing macrophages on explanted TEVGs. Our results support a novel paradigm where seeded cells are rapidly lost from implanted scaffolds instead of developing into cells of the neovessel, as traditionally thought. Our findings confirm and validate this paradigm shift while demonstrating the first successful application of noninvasive MRI for serial study of cellular-level processes in tissue engineering.

Tracking stem cells using magnetic nanoparticles

Stem cell therapies offer great promise for many diseases, especially those without current effective treatments. It is believed that noninvasive imaging techniques, which offer the ability to track the status of cells after transplantation, will expedite progress in this field and help to achieve maximized therapeutic effect. Today's biomedical imaging technology allows for real-time, noninvasive monitoring of grafted stem cells including their biodistribution, migration, survival, and differentiation, with magnetic resonance imaging (MRI) of nanoparticle-labeled cells being one of the most commonly used techniques. Among the advantages of MR cell tracking are its high spatial resolution, no exposure to ionizing radiation, and clinical applicability. In order to track cells by MRI, the cells need to be labeled with magnetic nanoparticles, for which many types exist. There are several cellular labeling techniques available, including simple incubation, use of transfection agents, magnetoelectroporation, and magnetosonoporation. In this overview article, we will review the use of different magnetic nanoparticles and discuss how these particles can be used to track the distribution of transplanted cells in different organ systems. Caveats and limitations inherent to the tracking of nanoparticle-labeled stem cells are also discussed.