Magnetic resonance imaging of cells in experimental disease models

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.

Cytosolic delivery of gadolinium via photoporation enables improved in vivo magnetic resonance imaging of cancer cells

Longitudinal in vivo monitoring of transplanted cells is crucial to perform cancer research or to assess the treatment outcome of cell-based therapies. While several bio-imaging techniques can be used, magnetic resonance imaging (MRI) clearly stands out in terms of high spatial resolution and excellent soft-tissue contrast. However, MRI suffers from low sensitivity, requiring cells to be labeled with high concentrations of contrast agents. An interesting option is to label cells with clinically approved gadolinium chelates which generate a hyperintense MR signal. However, spontaneous uptake of the label via pinocytosis results in its endosomal sequestration, leading to quenching of the T₁-weighted relaxation. To avoid this quenching effect, delivery of gadolinium chelates directly into the cytosol via electroporation or hypotonic cell swelling have been proposed. However, these methods are also accompanied by several drawbacks such as a high cytotoxicity, and changes in gene expression and phenotype. Here, we demonstrate that nanoparticle-sensitized laser induced photoporation forms an attractive alternative to efficiently deliver the contrast agent gadobutrol into the cytosol of both HeLa and SK-OV-3 IP1 cells. After intracellular delivery by photoporation the quenching effect is clearly avoided, leading to a strong increase in the hyperintense T₁-weighted MR signal. Moreover, when compared to nucleofection as a state-of-the-art electroporation platform, photoporation has much less impact on cell viability, which is extremely important for reliable cell tracking studies. Additional experiments confirm that photoporation does not induce any change in the long-term viability or the migratory capacity of the cells. Finally, we show that gadolinium 'labeled' SK-OV-3 IP1 cells can be imaged in vivo by MRI with high soft-tissue contrast and spatial resolution, revealing indications of potential tumor invasion or angiogenesis.

Preclinical Applications of Magnetic Resonance Imaging in Oncology

The evolving possibilities of molecular imaging (MI) are fundamentally changing the way we look at cancer, with imaging paradigms now shifting away from basic morphological measures toward the longitudinal assessment of functional, metabolic, cellular, and molecular information in vivo. Recent developments of imaging methodology and probe molecules utilizing the vast number of novel animal models of human cancers have enhanced our ability to non-invasively characterize neoplastic tissue and follow anticancer treatments. While preclinical molecular imaging offers a whole palette of excellent methodology to choose from, we will focus on magnetic resonance imaging (MRI) techniques, since they provide excellent molecular imaging capabilities and bear high potential for clinical translation. Prerequisites and consequences of using animal models as surrogates of human cancers in preclinical molecular imaging are outlined. We present physical principles, values, and limitations of MRI as molecular imaging modality and comment on its high potential to non-invasively assess information on metabolism, hypoxia, angiogenesis, and cell trafficking in preclinical cancer research.

An Efficient T 1 Contrast Agent for Labeling and Tracking Human Embryonic Stem Cells on MRI

Noninvasive cell tracking in vivo has the potential to advance stem cell-based therapies into the clinic. Magnetic resonance imaging (MRI) provides an excellent image-guidance platform; however, existing MR cell labeling agents are fraught with limited specificity. To address this unmet need, we developed a highly efficient manganese porphyrin contrast agent, MnEtP, using a two-step synthesis. In vitro MRI at 3 Tesla on human embryonic stem cells (hESCs) demonstrated high labeling efficiency at a very low dose of 10 µM MnEtP, resulting in a four-fold lower T₁ relaxation time. This extraordinarily low dose is ideal for labeling large cell numbers required for large animals and humans. Cell viability and differentiation capacity were unaffected. Cellular manganese quantification corroborated MRI findings, and the agent localized primarily on the cell membrane. In vivo MRI of transplanted hESCs in a rat demonstrated excellent sensitivity and specificity of MnEtP for noninvasive stem cell tracking.

The application of Magnetic Resonance Imaging (mri) to the examination of plant tissues and water barriers

The aim of the present study is to extend the applicability of MRI measurements similar to those used in human diagnostics to the examination of water barriers in living plants, thus broadening their use in natural sciences. The cucumber, Cucumis sativus, and Phillyrea angustifolia, or false olive, were chosen as test plants. The MRI measurements were carried out on three samples of each plant in the same position vis-a-vis the MRI apparatus using a Siemens Avanto MRI scanner. Two different relaxation times were employed, T₁, capable of histological mapping, and T₂, used for the examination of water content. In the course of the analysis, it was found that certain histological formations and branching cause modifications to the intensity detected with relaxation time T₂. Furthermore, these positions can also be found in T1 measurements. A monotonic correlation (cucumber: ρ = 0.829; false olive: ρ = -0.84) was observed between the T₁ and T₂ measurements. In the course of the statistical analysis of the signal intensities of the xylems it was concluded that they cannot be regarded as independent in a statistical sense; these changes rather depend on the anatomic structure of the plant, as the intensity profile is modified by nodes, leaves and branches. This serves as a demonstration of the applicability of MRI to the measurement of well know plant physiological processes. The special parametrization required for this equipment, which is usually used in human diagnostics, is also documented in the present study.

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.

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.

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.

An enzyme-activatable and cell-permeable MnIII-porphyrin as a highly efficient T1 MRI contrast agent for cell labeling

Magnetic resonance imaging (MRI) is a preferred technique for noninvasively monitoring the fate of implanted cells, such as stem cells and immune cells in vivo. Cellular MRI requires contrast agents (CAs) to label the cells of interest. Despite promising progress made in this emerging field, highly sensitive, stable and biocompatible T1 CAs with high cell permeability and specificity remains an unmet challenge. To address this need, a novel MnIII-porphyrin, MnAMP was designed and synthesized based on the modification of MnIIItetra(carboxy-porphyrin) (MnTCP), a small and highly stable non-Gd extracellular CA with good biocompatibility and high T1 relaxivity (r1 = 7.9 mM-1 s-1) at clinical field of 3 Tesla (T). Cell permeability was achieved by masking the polar carboxylates of MnTCP with acetoxymethyl-ester (AM) groups, which are susceptible to hydrolysis by intracellular esterases. The enzymatic cleavage of AM groups led to disaggregation of the hydrophobic MnAMP, releasing activated MnTCP with significant increase in T1 relaxivity. Cell uptake of MnAMP is highly efficient as tested on two non-phagocytic human cell lines with no side effects observed on cell viability. MRI of labeled cells exhibited significant contrast enhancement with a short T1 of 161 ms at 3 T, even though a relatively low concentration of MnAMP and short incubation time was applied for cell labeling. Overall, MnAMP is among the most efficient T1 cell labeling agents developed for cellular MRI.

Magnetic nanoparticles for oligodendrocyte precursor cell transplantation therapies: progress and challenges

Oligodendrocyte precursor cells (OPCs) have shown high promise as a transplant population to promote regeneration in the central nervous system, specifically, for the production of myelin - the protective sheath around nerve fibers. While clinical trials for these cells have commenced in some areas, there are currently key barriers to the translation of neural cell therapies. These include the ability to (a) image transplant populations in vivo; (b) genetically engineer transplant cells to augment their repair potential; and (c) safely target cells to sites of pathology. Here, we review the evidence that magnetic nanoparticles (MNPs) are a 'multifunctional nanoplatform' that can aid in safely addressing these translational challenges in neural cell/OPC therapy: by facilitating real-time and post-mortem assessment of transplant cell biodistribution, and biomolecule delivery to transplant cells, as well as non-invasive 'magnetic cell targeting' to injury sites by application of high gradient fields. We identify key issues relating to the standardization and reporting of physicochemical and biological data in the field; we consider that it will be essential to systematically address these issues in order to fully evaluate the utility of the MNP platform for neural cell transplantation, and to develop efficacious neurocompatible particles for translational applications.

Magnetic nanoparticles for oligodendrocyte precursor cell transplantation therapies: progress and challenges

Oligodendrocyte precursor cells (OPCs) have shown high promise as a transplant population to promote regeneration in the central nervous system, specifically, for the production of myelin – the protective sheath around nerve fibers. While clinical trials for these cells have commenced in some areas, there are currently key barriers to the translation of neural cell therapies. These include the ability to (a) image transplant populations in vivo; (b) genetically engineer transplant cells to augment their repair potential; and (c) safely target cells to sites of pathology. Here, we review the evidence that magnetic nanoparticles (MNPs) are a ‘multifunctional nanoplatform’ that can aid in safely addressing these translational challenges in neural cell/OPC therapy: by facilitating real-time and post-mortem assessment of transplant cell biodistribution, and biomolecule delivery to transplant cells, as well as non-invasive ‘magnetic cell targeting’ to injury sites by application of high gradient fields. We identify key issues relating to the standardization and reporting of physicochemical and biological data in the field; we consider that it will be essential to systematically address these issues in order to fully evaluate the utility of the MNP platform for neural cell transplantation, and to develop efficacious neurocompatible particles for translational applications.

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.

Could magnetic resonance provide in vivo histology?

The diagnosis of a suspected tumor lesion faces two basic problems: detection and identification of the specific type of tumor. Radiological techniques are commonly used for the detection and localization of solid tumors. Prerequisite is a high intrinsic or enhanced contrast between normal and neoplastic tissue. Identification of the tumor type is still based on histological analysis. The result depends critically on the sampling sites, which given the inherent heterogeneity of tumors, constitutes a major limitation. Non-invasive in vivo imaging might overcome this limitation providing comprehensive three-dimensional morphological, physiological, and metabolic information as well as the possibility for longitudinal studies. In this context, magnetic resonance based techniques are quite attractive since offer at the same time high spatial resolution, unique soft tissue contrast, good temporal resolution to study dynamic processes and high chemical specificity. The goal of this paper is to review the role of magnetic resonance techniques in characterizing tumor tissue in vivo both at morphological and physiological levels. The first part of this review covers methods, which provide information on specific aspects of tumor phenotypes, considered as indicators of malignancy. These comprise measurements of the inflammatory status, neo-vascular physiology, acidosis, tumor oxygenation, and metabolism together with tissue morphology. Even if the spatial resolution is not sufficient to characterize the tumor phenotype at a cellular level, this multiparametric information might potentially be used for classification of tumors. The second part discusses mathematical tools, which allow characterizing tissue based on the acquired three-dimensional data set. In particular, methods addressing tumor heterogeneity will be highlighted. Finally, we address the potential and limitation of using MRI as a tool to provide in vivo tissue characterization.

Differences in magnetic particle uptake by CNS neuroglial subclasses: implications for neural tissue engineering

Aim: To analyze magnetic particle uptake and intracellular processing by the four main non-neuronal subclasses of the CNS: oligodendrocyte precursor cells; oligodendrocytes; astrocytes; and microglia. Materials & methods: Magnetic particle uptake and processing were studied in rat oligodendrocyte precursor cells and oligodendrocytes using fluorescence and transmission electron microscopy, and the results collated with previous data from rat microglia and astrocyte studies. All cells were derived from primary mixed glial cultures. Results: Significant intercellular differences were observed between glial subtypes: microglia demonstrate the most rapid/extensive particle uptake, followed by astrocytes, with oligodendrocyte precursor cells and oligodendrocytes showing significantly lower uptake. Ultrastructural analyses suggest that magnetic particles are extensively degraded in microglia, but relatively stable in other cells. Conclusion: Intercellular differences in particle uptake and handling exist between the major neuroglial subtypes. This has important implications for the utility of the magnetic particle platform for neurobiological applications including genetic modification, transplant cell labeling and biomolecule delivery to mixed CNS cell populations.

Original submitted 23 March 2012; Revised submitted 24 July 2012; Published online 22 November 2012

Sugar/gadolinium-loaded gold nanoparticles for labelling and imaging cells by magnetic resonance imaging

Targeted magnetic resonance imaging (MRI) probes for selective cell labelling and tracking are highly desired. We here present biocompatible sugar-coated paramagnetic Gd-based gold nanoparticles (Gd-GNPs) and test them as MRI T₁ reporters in different cellular lines at a high magnetic field (11.7 T). With an average number of 20 Gd atoms per nanoparticle, Gd-GNPs show relaxivity values r₁ ranging from 7 to 18 mM^-1 s^-1 at 1.41 T. The multivalent presentation of carbohydrates on the Gd-GNPs enhances the avidity of sugars for carbohydrate-binding receptors at the cell surface and increases the local concentration of the probes. A large reduction in longitudinal relaxation times T₁ is achieved with both fixed cells and live cells. Differences in cellular labelling are obtained by changing the type of sugar on the gold surface, indicating that simple monosaccharides and disaccharides are able to modulate the cellular uptake. These results stress the benefits of using sugars to produce nanoparticles for cellular labelling. To the best of our knowledge this is the first report on labelling and imaging cells with Gd-based gold nanoparticles which use simple sugars as receptor reporters.

Preclinical molecular imaging using PET and MRI

Molecular imaging fundamentally changes the way we look at cancer. Imaging paradigms are now shifting away from classical morphological measures towards the assessment of functional, metabolic, cellular, and molecular information in vivo. Interdisciplinary driven developments of imaging methodology and probe molecules utilizing animal models of human cancers have enhanced our ability to non-invasively characterize neoplastic tissue and follow anti-cancer treatments. Preclinical molecular imaging offers a whole palette of excellent methodology to choose from. We will focus on positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques, since they provide excellent and complementary molecular imaging capabilities and bear high potential for clinical translation. Prerequisites and consequences of using animal models as surrogates of human cancers in preclinical molecular imaging are outlined. We present physical principles, values and limitations of PET and MRI as molecular imaging modalities and comment on their high potential to non-invasively assess information on hypoxia, angiogenesis, apoptosis, gene expression, metabolism, and cell trafficking in preclinical cancer research.

Personalized nanomedicine advancements for stem cell tracking

Recent technological developments in biomedicine have facilitated the generation of data on the anatomical, physiological and molecular level for individual patients and thus introduces opportunity for therapy to be personalized in an unprecedented fashion. Generation of patient-specific stem cells exemplifies the efforts toward this new approach. Cell-based therapy is a highly promising treatment paradigm; however, due to the lack of consistent and unbiased data about the fate of stem cells in vivo, interpretation of therapeutic effects remains challenging hampering the progress in this field. The advent of nanotechnology with a wide palette of inorganic and organic nanostructures has expanded the arsenal of methods for tracking transplanted stem cells. The diversity of nanomaterials has revolutionized personalized nanomedicine and enables individualized tailoring of stem cell labeling materials for the specific needs of each patient. The successful implementation of stem cell tracking will likely be a significant driving force that will contribute to the further development of nanotheranostics. The purpose of this review is to emphasize the role of cell tracking using currently available nanoparticles.

Molecular imaging of microglia/macrophages in the brain

Neuroinflammation perpetuates neuronal damage in many neurological disorders. Activation of resident microglia and infiltration of monocytes/macrophages contributes to neuronal injury and synaptic damage. Noninvasive imaging of these cells in vivo provides a means to monitor progression of disease as well as assess efficacies of potential therapeutics. This review provides an overview of positron emission tomography (PET) and magnetic resonance (MR) imaging of microglia/macrophages in the brain. We describe the rationale behind PET imaging of microglia/macrophages with ligands that bind to translocator protein-18 kDa (TSPO). We discuss the prototype TSPO radioligand [(11)C]PK11195, its limitations, and the development of newer TSPO ligands as PET imaging agents. PET imaging agents for targets other than TSPO are emerging, and we outline the potential of these agents for imaging brain microglia/macrophage activity in vivo. Finally, we briefly summarize advances in MR imaging of microglia/macrophages using iron oxide nanoparticles and ultra-small super paramagnetic particles that are phagocytosed. Despite many technical advances, more sensitive agents are required to be useful indicators of neuroinflammation in brain.

ICV-transplanted human glial precursor cells are short-lived yet exert immunomodulatory effects in mice with EAE

Human glial precursor cells (hGPs) have potential for remyelinating lesions and are an attractive cell source for cell therapy of multiple sclerosis (MS). To investigate whether transplanted hGPs can affect the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of MS, we evaluated the therapeutic effects of transplanted hGPs together with the in vivo fate of these cells using magnetic resonance imaging (MRI) and bioluminescence imaging (BLI). At 14 days post-EAE induction, mice (n = 19) were intracerebroventricularly (ICV) injected with 5 × 10(5) hGPs that were magnetically labeled with superparamagnetic iron oxide (SPIO) particles as MR contrast agent and transduced with firefly luciferase for BLI of cell survival. Control mice (n = 18) received phosphate buffered saline (PBS) vehicle only. The severity of EAE clinical disability in the hGP-transplanted group was significantly suppressed (P < 0.05) with concomitant inhibition of ConA and MOG-specific T cell proliferation in the spleen. Astrogliosis was reduced and a lower activity of macrophages and/or microglia was observed in the spinal cord (P < 0.05). On MRI, SPIO signal was detected within the lateral ventricle from 1 day post-transplantation and remained there for up to 34 days. BLI indicated that most cells did not survive beyond 5-10 days, consistent with the lack of detectable migration into the brain parenchyma and the histological presence of an abundance of apoptotic cells. Transplanted hGPs could not be detected in the spleen. We conclude that ICV transplantation of short-lived hGPs can have a remote therapeutic effect through immunomodulation from within the ventricle, without cells directly participating in remyelination.

Automated detection and characterization of SPIO-labeled cells and capsules using magnetic field perturbations

Understanding how individual cells behave inside living systems will help enable new diagnostic tools and cellular therapies. Superparamagnetic iron oxide particles can be used to label cells and theranostic capsules for noninvasive tracking using MRI. Contrast changes from superparamagnetic iron oxide are often subtle relative to intrinsic sources of contrast, presenting a detection challenge. Here, we describe a versatile postprocessing method, called Phase map cross-correlation Detection and Quantification (PDQ), that automatically identifies localized deposits of superparamagnetic iron oxide, estimating their volume magnetic susceptibility and magnetic moment. To demonstrate applicability, PDQ was used to detect and characterize superparamagnetic iron oxide-labeled magnetocapsules implanted in porcine liver and suspended in agarose gel. PDQ was also applied to mouse brains infiltrated by MPIO-labeled macrophages following traumatic brain injury; longitudinal, in vivo studies tracked individual MPIO clusters over 3 days, and tracked clusters were corroborated in ex vivo brain scans. Additionally, we applied PDQ to rat hearts infiltrated by MPIO-labeled macrophages in a transplant model of organ rejection. PDQ magnetic measurements were signal-to-noise ratio invariant for images with signal-to-noise ratio > 11. PDQ can be used with conventional gradient-echo pulse sequences, requiring no extra scan time. The method is useful for visualizing biodistribution of cells and theranostic magnetocapsules and for measuring their relative iron content.

Ultra-small particles of iron oxide as peroxidase for immunohistochemical detection

Dimercaptosuccinic acid (DMSA) modified ultra-small particles of iron oxide (USPIO) were synthesized through a two-step process. The first step: oleic acid (OA) capped Fe(3)O(4) (OA-USPIO) were synthesized by a novel oxidation coprecipitation method in H(2)O/DMSO mixing system, where DMSO acts as an oxidant simultaneously. The second step: OA was replaced by DMSA to obtain water-soluble nanoparticles. The as-synthesized nanoparticles were characterized by TEM, FTIR, TGA, VSM, DLS, EDS and UV-vis. Hydrodynamic sizes and Peroxidase-like catalytic activity of the nanoparticles were investigated. The hydrodynamic sizes of the nanoparticles (around 24.4 nm) were well suited to developing stable nanoprobes for bio-detection. The kinetic studies were performed to quantitatively evaluate the catalytic ability of the peroxidase-like nanoparticles. The calculated kinetic parameters indicated that the DMSA-USPIO possesses high catalytic activity. Based on the high activity, immunohistochemical experiments were established: using low-cost nanoparticles as the enzyme instead of expensive HRP, Nimotuzumab was conjugated onto the surface of the nanoparticles to construct a kind of ultra-small nanoprobe which was employed to detect epidermal growth factor receptor (EGFR) over-expressed on the membrane of esophageal cancer cell. The proper sizes of the probes and the result of membranous immunohistochemical staining suggest that the probes can be served as a useful diagnostic reagent for bio-detection.

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.

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.

MPI Cell Tracking: What Can We Learn from MRI?

Magnetic resonance imaging (MRI) cell tracking has become an important non-invasive technique to interrogate the fate of cells upon transplantation. At least 6 clinical trials have been published at the end of 2010, all of which have shown that real-time monitoring of the injection procedure, initial engraftment, and short-term biodistribution of cells is critical to further advance the field of cellular therapeutics. In MRI cell tracking, cells are loaded with superparamagnetic iron oxide (SPIO) particles that provide an MRI contrast effect through microscopic magnetic field disturbances and dephasing of protons. Magnetic particle imaging (MPI) has recently emerged as a potential cellular imaging technique that promises to have several advantages over MRI, primarily linear quantification of cells, a higher sensitivity, and "hot spot" tracer identification without confounding background signal. Although probably not fully optimized, SPIO particles that are currently used as MRI contrast agent can be employed as MPI tracer. Initial studies have shown that cells loaded with SPIO particles can give a detectable MPI signal, encouraging further development of MPI cell tracking.

Neural precursors exhibit distinctly different patterns of cell migration upon transplantation during either the acute or chronic phase of EAE: a serial MR imaging study

As the complex pathogenesis of multiple sclerosis contributes to spatiotemporal variations in the trophic micromilieu of the central nervous system, the optimal intervention period for cell-replacement therapy must be systematically defined. We applied serial, 3D high-resolution magnetic resonance imaging to transplanted neural precursor cells (NPCs) labeled with superparamagnetic iron oxide nanoparticles and 5-bromo-2-deoxyuridine, and compared the migration pattern of NPCs in acute inflamed (n = 10) versus chronic demyelinated (n = 9) brains of mice induced with experimental allergic encephalomyelitis (EAE). Serial in vivo and ex-vivo 3D magnetic resonance imaging revealed that NPCs migrated 2.5 ± 1.3 mm along the corpus callosum in acute EAE. In chronic EAE, cell migration was slightly reduced (2.3 ± 1.3 mm) and only occurred in the lateral side of transplantation. Surprisingly, in 6/10 acute EAE brains, NPCs were found to migrate in a radial pattern along RECA-1(+) cortical blood vessels, in a pattern hitherto only reported for migrating glioblastoma cells. This striking radial biodistribution pattern was not detected in either chronic EAE or disease-free control brains. In both acute and chronic EAE brain, Iba1(+) microglia/macrophage number was significantly higher in central nervous system regions containing migrating NPCs. The existence of differential NPC migration patterns is an important consideration for implementing future translational studies in multiple sclerosis patients with variable disease.

Concise review: Nanoparticles and cellular carriers-allies in cancer imaging and cellular gene therapy?

Ineffective treatment and poor patient management continue to plague the arena of clinical oncology. The crucial issues include inadequate treatment efficacy due to ineffective targeting of cancer deposits, systemic toxicities, suboptimal cancer detection and disease monitoring. This has led to the quest for clinically relevant, innovative multifaceted solutions such as development of targeted and traceable therapies. Mesenchymal stem cells (MSCs) have the intrinsic ability to "home" to growing tumors and are hypoimmunogenic. Therefore, these can be used as (a) "Trojan Horses" to deliver gene therapy directly into the tumors and (b) carriers of nanoparticles to allow cell tracking and simultaneous cancer detection. The camouflage of MSC carriers can potentially tackle the issues of safety, vector, and/or transgene immunogenicity as well as nanoparticle clearance and toxicity. The versatility of the nanotechnology platform could allow cellular tracking using single or multimodal imaging modalities. Toward that end, noninvasive magnetic resonance imaging (MRI) is fast becoming a clinical favorite, though there is scope for improvement in its accuracy and sensitivity. In that, use of superparamagnetic iron-oxide nanoparticles (SPION) as MRI contrast enhancers may be the best option for tracking therapeutic MSC. The prospects and consequences of synergistic approaches using MSC carriers, gene therapy, and SPION in developing cancer diagnostics and therapeutics are discussed.

In vivo MRI cell tracking: clinical studies

OBJECTIVE

The purpose of this review is to describe the principles of MRI cell tracking with superparamagnetic iron oxides and the four clinical trials that have been performed.

CONCLUSION

Clinical MRI cell tracking is likely to become an important tool at the bedside once (stem) cell therapy becomes mainstream. The most prominent role of this technique probably will be verification of accurate cell delivery with MRI-guided injection, in which interventional radiologists will play a role in the near future. All clinical studies described as of this writing have been performed outside the United States.