In vivo detection limits of magnetically labeled embryonic stem cells in the rat brain using high-field (17.6 T) magnetic resonance imaging

Magnetic labeling of primary murine monocytes using very small superparamagnetic iron oxide nanoparticles

Due to their very small size, nanoparticles can interact with all cells in the central nervous system. One of the most promising nanoparticle subgroups are very small superparamagnetic iron oxide nanoparticles (VSOP) that are citrate coated for electrostatic stabilization. To determine their influence on murine blood-derived monocytes, which easily enter the injured central nervous system, we applied VSOP and carboxydextran-coated superparamagnetic iron oxide nanoparticles (Resovist). We assessed their impact on the viability, cytokine, and chemokine secretion, as well as iron uptake of murine blood-derived monocytes. We found that (1) the monocytes accumulated VSOP and Resovist, (2) this uptake seemed to be nanoparticle- and time-dependent, (3) the decrease of monocytes viability was treatment-related, (4) VSOP and Resovist incubation did not alter cytokine homeostasis, and (5) overall a 6-hour treatment with 0.75 mM VSOP-R1 was probably sufficient to effectively label monocytes for future experiments. Since homeostasis is not altered, it is safe to label blood-derived monocles with VSOP. VSOP labeled monocytes can be used to study injured central nervous system sites further, for example with drug-carrying VSOP.

Application of magnetic nanoparticles in cell therapy

Fe₃O₄ magnetic nanoparticles (MNPs) are biomedical materials that have been approved by the FDA. To date, MNPs have been developed rapidly in nanomedicine and are of great significance. Stem cells and secretory vesicles can be used for tissue regeneration and repair. In cell therapy, MNPs which interact with external magnetic field are introduced to achieve the purpose of cell directional enrichment, while MRI to monitor cell distribution and drug delivery. This paper reviews the size optimization, response in external magnetic field and biomedical application of MNPs in cell therapy and provides a comprehensive view.

Ophthalmic Magnetic Resonance Imaging: Where Are We (Heading To)?

Magnetic resonance imaging of the eye and orbit (MReye) is a cross-domain research field, combining (bio)physics, (bio)engineering, physiology, data sciences and ophthalmology. A growing number of reports document technical innovations of MReye and promote their application in preclinical research and clinical science. Realizing the progress and promises, this review outlines current trends in MReye. Examples of MReye strategies and their clinical relevance are demonstrated. Frontier applications in ocular oncology, refractive surgery, ocular muscle disorders and orbital inflammation are presented and their implications for explorations into ophthalmic diseases are provided. Substantial progress in anatomically detailed, high-spatial resolution MReye of the eye, orbit and optic nerve is demonstrated. Recent developments in MReye of ocular tumors are explored, and its value for personalized eye models derived from machine learning in the treatment planning of uveal melanoma and evaluation of retinoblastoma is highlighted. The potential of MReye for monitoring drug distribution and for improving treatment management and the assessment of individual responses is discussed. To open a window into the eye and into (patho)physiological processes that in the past have been largely inaccessible, advances in MReye at ultrahigh magnetic field strengths are discussed. A concluding section ventures a glance beyond the horizon and explores future directions of MReye across multiple scales, including in vivo electrolyte mapping of sodium and other nuclei. This review underscores the need for the (bio)medical imaging and ophthalmic communities to expand efforts to find solutions to the remaining unsolved problems and technical obstacles of MReye, with the objective to transfer methodological advancements driven by MR physics into genuine clinical value.

Fast field-cycling magnetic resonance detection of intracellular ultra-small iron oxide particles in vitro: Proof-of-concept

PURPOSE

Inflammation is central in disease pathophysiology and accurate methods for its detection and quantification are increasingly required to guide diagnosis and therapy. Here we explored the ability of Fast Field-Cycling Magnetic Resonance (FFC-MR) in quantifying the signal of ultra-small superparamagnetic iron oxide particles (USPIO) phagocytosed by J774 macrophage-like cells as a proof-of-principle.

METHODS

Relaxation rates were measured in suspensions of J774 macrophage-like cells loaded with USPIO (0-200 μg/ml Fe as ferumoxytol), using a 0.25 T FFC benchtop relaxometer and a human whole-body, in-house built 0.2 T FFC-MR prototype system with a custom test tube coil. Identical non-imaging, saturation recovery pulse sequence with 90° flip angle and 20 different evolution fields selected logarithmically between 80 μT and 0.2 T (3.4 kHz and 8.51 MHz proton Larmor frequency [PLF] respectively). Results were compared with imaging flow cytometry quantification of side scatter intensity and USPIO-occupied cell area. A reference colorimetric iron assay was used.

RESULTS

The T1 dispersion curves derived from FFC-MR were excellent in detecting USPIO at all concentrations examined (0-200 μg/ml Fe as ferumoxytol) vs. control cells, p ≤ 0.001. FFC-NMR was capable of reliably detecting cellular iron content as low as 1.12 ng/µg cell protein, validated using a colorimetric assay. FFC-MR was comparable to imaging flow cytometry quantification of side scatter intensity but superior to USPIO-occupied cell area, the latter being only sensitive at exposures ≥ 10 µg/ml USPIO.

CONCLUSIONS

We demonstrated for the first time that FFC-MR is capable of quantitative assessment of intra-cellular iron which will have important implications for the use of USPIO in a variety of biological applications, including the study of inflammation.

A Safe and Effective Magnetic Labeling Protocol for MRI-Based Tracking of Human Adult Neural Stem Cells

Magnetic resonance imaging (MRI) provides a unique tool for in vivo visualization and tracking of stem cells in the brain. This is of particular importance when assessing safety of experimental cell treatments in the preclinical or clinical setup. Yet, specific imaging requires an efficient and non-perturbing cellular magnetic labeling which precludes adverse effects of the tag, e.g., the impact of iron-oxide-nanoparticles on the critical differentiation and integration processes of the respective stem cell population investigated. In this study we investigated the effects of very small superparamagnetic iron oxide particle (VSOP) labeling on viability, stemness, and neuronal differentiation potential of primary human adult neural stem cells (haNSCs). Cytoplasmic VSOP incorporation massively reduced the transverse relaxation time T2, an important parameter determining MR contrast. Cells retained cytoplasmic label for at least a month, indicating stable incorporation, a necessity for long-term imaging. Using a clinical 3T MRI, 1 × 10³ haNSCs were visualized upon injection in a gel phantom, but detection limit was much lower (5 × 10⁴ cells) in layer phantoms and using an imaging protocol feasible in a clinical scenario. Transcriptional analysis and fluorescence immunocytochemistry did not reveal a detrimental impact of VSOP labeling on important parameters of cellular physiology with cellular viability, stemness and neuronal differentiation potential remaining unaffected. This represents a pivotal prerequisite with respect to clinical application of this method.

Application of nanomaterials in three-dimensional stem cell culture

Petri dish cultured cells have for long provided scientists an aperture to understanding cell's behavior both in normal and disease states as well as in vitro and in vivo. But recent advances have brought to light how the architecture and composite nature of the immediate environment within which the cell is proliferated can profoundly influence its phenotypic features and functions, thus making obvious, limitations of the conventional two-dimensional cell culture despite it cost effectiveness. Fortunately, the transition to three-dimensional (3D) cell culture has occurred concurrently with expanded knowledge of nanoscience and materials, thereby lending significant impetus for innovative research. This review is focused on the application of nanoparticles in 3D stem cell breeding, recent trends and developments in medical sciences for improved drug delivery, and treatment approaches to some human diseases. We also reviewed prevailing challenges and concerns of nanotoxicity as it continues to impede and delay clinical applications as well the ongoing concerted and multidisciplinary efforts to overcome them.

Gadolinium Doping Enhances the Photoacoustic Signal of Synthetic Melanin Nanoparticles: A Dual Modality Contrast Agent for Stem Cell Imaging

In this paper, we show that gadolinium-loaded synthetic melanin nanoparticles (Gd(III)-SMNPs) exhibit up to a 40-fold enhanced photoacoustic signal intensity relative to synthetic melanin alone and higher than other metal-chelated SMNPs. This property makes these materials useful as dual labeling agents because Gd(III)-SMNPs also behave as magnetic resonance imaging (MRI) contrast agents. As a proof-of-concept, we used these nanoparticles to label human mesenchymal stem cells. Cellular uptake was confirmed with bright-field optical and transmission electron microscopy. The Gd(III)-SMNP-labeled stem cells continued to express the stem cell surface markers CD73, CD90, and CD105 and proliferate. The labeled stem cells were subsequently injected intramyocardially in mice, and the tissue was observed by photoacoustic and MR imaging. We found that the photoacoustic signal increased as the cell number increased (R 2 = 0.96), indicating that such an approach could be employed to discriminate between stem cell populations with a limit of detection of 2.3 × 104 cells in in vitro tests. This multimodal photoacoustic/MRI approach combines the excellent temporal resolution of photoacoustics with the anatomic resolution of MRI.

Temporal window for detection of inflammatory disease using dynamic cell tracking with time-lapse MRI

Time-lapse MRI was implemented for dynamic non-invasive cell tracking of individual slowly moving intravascular immune cells. Repetitive MRI acquisition enabled dynamic observation of iron oxide nanoparticle (ION) labelled cells. Simulations of MRI contrast indicated that only cells moving slower than 1 µm/s were detectable. Time-lapse MRI of the brain was performed after either IONs or ION-labelled monocytes were injected intravenously into naïve and experimental autoimmune encephalomyelitis (EAE) bearing mice at a presymptomatic or symptomatic stage. EAE mice showed a reduced number of slow moving, i.e. patrolling cells before and after onset of symptoms as compared to naïve controls. This observation is consistent with the notion of altered cell dynamics, i.e. higher velocities of immune cells rolling along the endothelium in the inflamed condition. Thus, time-lapse MRI enables for assessing immune cell dynamics non-invasively in deep tissue and may serve as a tool for detection or monitoring of an inflammatory response.

Methodological aspects of MRI of transplanted superparamagnetic iron oxide-labeled mesenchymal stem cells in live rat brain

In vivo tracking of transplanted mesenchymal stem cells (MSCs) migration and homing is vital for understanding the mechanisms of beneficial effects of MSCs transplantation in animal models of diseases and in clinical trials. Transplanted cells can be labeled with superparamagnetic iron oxide (SPIO) particles and visualized in vivo using a number of iron sensitive MRI techniques. However, the applicability of those techniques for SPIO-labeled MSCs tracking in live brain has not been sufficiently investigated. The goal of this study was to estimate the efficiency of various MRI techniques of SPIO-labeled cell tracing in the brain. To achieve that goal, the precision and specificity of T2WI, T2*WI and SWI (Susceptibility-Weighted Imaging) techniques of SPIO-labeled MSCs tracing in vitro and in live rat brain were for the first time compared in the same experiment. We have shown that SWI presents the most sensitive pulse sequence for SPIO-labeled MSCs MR visualization. After intracerebral administration due to limitations caused by local micro-hemorrhages the visualization threshold was 10² cells, while after intra-arterial transplantation SWI permitted detection of several cells or even single cells. There is just one publication claiming detection of individual SPIO-labeled MSCs in live brain, while the other state much lower sensitivity, describe detection of different cell types or high resolution tracing of MSCs in other tissues. This study confirms the possibility of single cell tracing in live brain and outlines the necessary conditions. SWI is a method convenient for the detection of single SPIO labeled MSCs and small groups of SPIO labeled MSCs in brain tissue and can be appropriate for monitoring migration and homing of transplanted cells in basic and translational neuroscience.

Synthesis of europium-doped VSOP, customized enhancer solution and improved microscopy fluorescence methodology for unambiguous histological detection

Background

Intrinsic iron in biological tissues frequently precludes unambiguous the identification of iron oxide nanoparticles when iron-based detection methods are used. Here we report the full methodology for synthesizing very small iron oxide nanoparticles (VSOP) doped with europium (Eu) in their iron oxide core (Eu-VSOP) and their unambiguous qualitative and quantitative detection by fluorescence.

Methods and results

The resulting Eu-VSOP contained 0.7 to 2.7% Eu relative to iron, which was sufficient for fluorescent detection while not altering other important particle parameters such as size, surface charge, or relaxivity. A customized enhancer solution with high buffer capacity and nearly neutral pH was developed to provide an antenna system that allowed fluorescent detection of Eu-VSOP in cells and histologic tissue slices as well as in solutions even under acidic conditions as frequently obtained from dissolved organic material. This enhancer solution allowed detection of Eu-VSOP using a standard fluorescence spectrophotometer and a fluorescence microscope equipped with a custom filter set with an excitation wavelength (λ_ex) of 338 nm and an emission wavelength (λ_em) of 616 nm.

Conclusion

The fluorescent detection of Eu-doped very small iron oxide nanoparticles (Eu-VSOP) provides a straightforward tool to unambiguously characterize VSOP biodistribution and toxicology at tissue, and cellular levels, providing a sensitive analytical tool to detect Eu-doped IONP in dissolved organ tissue and biological fluids with fluorescence instruments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-017-0301-6) contains supplementary material, which is available to authorized users.

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.

Biocompatibility of very small superparamagnetic iron oxide nanoparticles in murine organotypic hippocampal slice cultures and the role of microglia

Superparamagnetic iron oxide nanoparticles (SPIO) are applied as contrast media for magnetic resonance imaging (MRI) and treatment of neurologic diseases despite the fact that important information concerning their local interactions is still lacking. Due to their small size, SPIO have great potential for magnetically labeling different cell populations, facilitating their MRI tracking in vivo. Before SPIO are applied, however, their effect on cell viability and tissue homoeostasis should be studied thoroughly. We have previously published data showing how citrate-coated very small superparamagnetic iron oxide particles (VSOP) affect primary microglia and neuron cell cultures as well as neuron-glia cocultures. To extend our knowledge of VSOP interactions on the three-dimensional multicellular level, we further examined the influence of two types of coated VSOP (R1 and R2) on murine organotypic hippocampal slice cultures. Our data show that 1) VSOP can penetrate deep tissue layers, 2) long-term VSOP-R2 treatment alters cell viability within the dentate gyrus, 3) during short-term incubation VSOP-R1 and VSOP-R2 comparably modify hippocampal cell viability, 4) VSOP treatment does not affect cytokine homeostasis, 5) microglial depletion decreases VSOP uptake, and 6) microglial depletion plus VSOP treatment increases hippocampal cell death during short-term incubation. These results are in line with our previous findings in cell coculture experiments regarding microglial protection of neurite branching. Thus, we have not only clarified the interaction between VSOP, slice culture, and microglia to a degree but also demonstrated that our model is a promising approach for screening nanoparticles to exclude potential cytotoxic effects.

Rationale for the Combination of Nuclear Medicine with Magnetic Resonance for Pre-clinical Imaging

Multi-modality combinations of SPECT/CT and PET/CT have proven to be highly successful in the clinic and small animal SPECT/CT and PET/CT are becoming the norm in the research and drug development setting. However, the use of ionizing radiation from a high-resolution CT scanner is undesirable in any setting and particularly in small animal imaging (SAI), in laboratory experiments where it can result in radiation doses of sufficient magnitude that the experimental results can be influenced by the organism's response to radiation. The alternative use of magnetic resonance (MR) would offer a high-resolution, non-ionizing method for anatomical imaging of laboratory animals. MR brings considerably more than its 3D anatomical capability, especially regarding the imaging of laboratory animals. Dynamic MR imaging techniques can facilitate studies of perfusion, oxygenation, and diffusion amongst others. Further, MR spectroscopy can provide images that can be related to the concentration of endogenous molecules in vivo. MR imaging of injected contrast agents extends MR into the domain of molecular imaging. In combination with nuclear medicine (NM) SPECT and PET modalities in small animal imaging, MR would facilitate studies of dynamic processes such as biodistribution, pharmacokinetics, and pharmacodynamics. However, the detectors for nearly all PET and SPECT systems are still based on vacuum tube technology, namely: photomultiplier tubes (PMT's) in which the signal is generated by transporting electrons over a substantial distance within an evacuated glass tube, making them inoperable in even small magnetic fields. Thus the combination of SPECT or PET with MR has not been practical until the recent availability of semiconductor detectors such as silicon avalanche photodiodes (APD's) for PET and CdZnTe (CZT) detectors for SPECT coupled with the availability of high-density low noise ASIC electronics to read out the semiconductor detectors. The strong advantage of these technologies over PMT's is their insensitivity to magnetic fields which makes their use in co-axial multi-modality nuclear medicine/magnetic resonance instrumentation possible.

Labeling of mesenchymal stem cells for MRI with single-cell sensitivity

Sensitive cell detection by magnetic resonance imaging (MRI) is an important tool for the development of cell therapies. However, clinically approved contrast agents that allow single-cell detection are currently not available. Therefore, we compared very small iron oxide nanoparticles (VSOP) and new multicore carboxymethyl dextran-coated iron oxide nanoparticles (multicore particles, MCP) designed by our department for magnetic particle imaging (MPI) with discontinued Resovist^® regarding their suitability for detection of single mesenchymal stem cells (MSC) by MRI. We achieved an average intracellular nanoparticle (NP) load of >10 pg Fe per cell without the use of transfection agents. NP loading did not lead to significantly different results in proliferation, colony formation, and multilineage in vitro differentiation assays in comparison to controls. MRI allowed single-cell detection using VSOP, MCP, and Resovist^® in conjunction with high-resolution T2*-weighted imaging at 7 T with postprocessing of phase images in agarose cell phantoms and in vivo after delivery of 2,000 NP-labeled MSC into mouse brains via the left carotid artery. With optimized labeling conditions, a detection rate of ~45% was achieved; however, the experiments were limited by nonhomogeneous NP loading of the MSC population. Attempts should be made to achieve better cell separation for homogeneous NP loading and to thus improve NP-uptake-dependent biocompatibility studies and cell detection by MRI and future MPI. Additionally, using a 7 T MR imager equipped with a cryocoil resulted in approximately two times higher detection. In conclusion, we established labeling conditions for new high-relaxivity MCP, VSOP, and Resovist^® for improved MRI of MSC with single-cell sensitivity.

Stem Cell Tracking with Nanoparticles for Regenerative Medicine Purposes: An Overview

Accurate and noninvasive stem cell tracking is one of the most important needs in regenerative medicine to determine both stem cell destinations and final differentiation fates, thus allowing a more detailed picture of the mechanisms involved in these therapies. Given the great importance and advances in the field of nanotechnology for stem cell imaging, currently, several nanoparticles have become standardized products and have been undergoing fast commercialization. This review has been intended to summarize the current use of different engineered nanoparticles in stem cell tracking for regenerative medicine purposes, in particular by detailing their main features and exploring their biosafety aspects, the first step for clinical application. Moreover, this review has summarized the advantages and applications of stem cell tracking with nanoparticles in experimental and preclinical studies and investigated present limitations for their employment in the clinical setting.

Novel bimodal iron oxide particles for efficient tracking of human neural stem cells in vivo

AIMS

We validated novel bimodal iron oxide particles as substitute of ferumoxides for efficient labeling of human neural stem cells (NSCs). The dextrane-coated FeraTrack Direct (FTD)-Vio particles have additional far-red fluorophores for microscopic cell analysis.

METHODS

MR relaxometry, spectrophotometric iron determination and microscopy are used for characterization in vitro and in vivo.

RESULTS

Efficient uptake is not transfection agent-dependent. FTD-Vio594 labeling had no influence on viability, proliferation, migration and differentiation capacity. It allows MRI-based tracking of engrafted NSCs in mouse brain up to 11 days, complemented by bioluminescence imaging of firefly luciferase expressed by the engrafted cells.

CONCLUSION

Our results highlight the FTD-Vio594 particles as safe and sensitive substitute of ferumoxides for longitudinal tracking of NSCs in preclinical studies.

Sensitivity of susceptibility-weighted imaging in detecting superparamagnetic iron oxide-labeled mesenchymal stem cells: a comparative study

Background:

Susceptibility-weighted imaging (SWI) is extremely sensitive in the detection of superparamagnetic iron oxide (SPIO) nanoparticle-labeled cells. However, no study has compared molecular imaging for stem cell detection using SWI and other MRI pulse sequences.

Objectives:

This study aims to assess the sensitivity of SWI in detecting SPIO nanoparticle-labeled, human bone marrow-derived mesenchymal stem cells (SPIO-hMSCs) compared with that of T₂- and T₂*-weighted imaging (T₂WI and T₂*WI, respectively) in a phantom and in vivo study in rats.

Materials and Methods:

A phantom was prepared with various cell concentrations. In one normal rat, SPIO-hMSCs were implanted directly through burr holes into both caudate putamens, while in three rats without and six rats with photothrombotic infarction, 2.5 × 10⁵/ml SPIO-hMSCs were infused into the ipsilateral internal carotid artery (ICA). T₂WI, T₂*WI, and SWI findings were compared for dark regions representing SPIO-hMSCs.

Results:

SWI and T₂*WI detected 15 µL of 13 SPIO-hMSCs/µL and 15 µL of 27 SPIO-hMSCs/µL in the phantom, respectively and 3 µL of 333 SPIO-hMSCs/µL and 3 µL of 167 SPIO-hMSCs/µL in the normal rat brain (direct implantation). In the normal rat brain (ICA infusion), one of the three cases showed numerous foci of dark regions dispersed throughout the brain on T₂*WI and SWI. Dark regions surrounded the infarcts in all six infracted rat brains. The dark region was most prominent on SWI, followed by T₂*WI and T₂WI in all six rats (P = 0.002). Implanted SPIO-hMSCs were confirmed using Prussian blue staining.

Conclusions:

SWI is the most sensitive in the detection of SPIO-hMSCs, with the dark regions representing SPIO-hMSCs being more prominent on SWI than on T₂*WI and T₂WI.

In vitro and in vivo experiments with iron oxide nanoparticles functionalized with DEXTRAN or polyethylene glycol for medical applications: magnetic targeting

In this research work, DEXTRAN- and polyethylene glycol (PEG)-coated iron-oxide superparamagnetic nanoparticles were synthetized and their cytotoxicity and biodistribution assessed. Well-crystalline hydrophobic Fe3 O4 SPIONs were formed by a thermal decomposition process with d = 18 nm and σ = 2 nm; finally, the character of SPIONs was changed to hydrophilic by a post-synthesis procedure with the functionalization of the SPIONs with PEG or DEXTRAN. The nanoparticles present high saturation magnetization and superparamagnetic behavior at room temperature, and the hydrodynamic diameters of DEXTRAN- and PEG-coated SPIONs were measured as 170 and 120 nm, respectively. PEG- and DEXTRAN-coated SPIONs have a Specific Power Absorption SPA of 320 and 400 W/g, respectively, in an ac magnetic field with amplitude of 13 kA/m and frequency of 256 kHz. In vitro studies using VERO and MDCK cell lineages were performed to study the cytotoxicity and cell uptake of the SPIONs. For both cell lineages, PEG- and DEXTRAN-coated nanoparticles presented high cell viability for concentrations as high as 200 μg/mL. In vivo studies were conducted using BALB/c mice inoculating the SPIONs intravenously and exposing them to the presence of an external magnet located over the tumour. It was observed that the amount of PEG-coated SPIONs in the tumor increased by up to 160% when using the external permanent magnetic as opposed to those animals that were not exposed to the external magnetic field.

Inflammatory modulation of stem cells by Magnetic Resonance Imaging (MRI)-detectable nanoparticles

Novel MRI-detectable PLGA nanoparticles can track hematopoietic stem cells and down-regulate the secretion of pro-inflammatory cytokines by interfering with TLRs.

Tracking stem cells in tissue-engineered organs using magnetic nanoparticles

The use of human stem cells (SCs) in tissue engineering holds promise in revolutionising the treatment of numerous diseases. There is a pressing need to comprehend the distribution, movement and role of SCs once implanted onto scaffolds. Nanotechnology has provided a platform to investigate this through the development of inorganic magnetic nanoparticles (MNPs). MNPs can be used to label and track SCs by magnetic resonance imaging (MRI) since this clinically available imaging modality has high spatial resolution. In this review, we highlight recent applications of iron oxide and gadolinium based MNPs in SC labelling and MRI; and offer novel considerations for their future development.

Imaging of VSOP labeled stem cells in agarose phantoms with susceptibility weighted and T2* weighted MR Imaging at 3T: determination of the detection limit

OBJECTIVES

This study aimed to evaluate the detectability of stem cells labeled with very small iron oxide particles (VSOP) at 3T with susceptibility weighted (SWI) and T2* weighted imaging as a methodological basis for subsequent examinations in a large animal stroke model (sheep).

MATERIALS AND METHODS

We examined ovine mesenchymal stem cells labeled with VSOP in agarose layer phantoms. The experiments were performed in 2 different groups, with quantities of 0-100,000 labeled cells per layer. 15 different SWI- and T2*-weighted sequences and 3 RF coils were used. All measurements were carried out on a clinical 3T MRI. Images of Group A were analyzed by four radiologists blinded for the number of cells, and rated for detectability according to a four-step scale. Images of Group B were subject to a ROI-based analysis of signal intensities. Signal deviations of more than the 0.95 confidence interval in cell containing layers as compared to the mean of the signal intensity of non cell bearing layers were considered significant.

RESULTS

GROUP A

500 or more labeled cells were judged as confidently visible when examined with a SWI-sequence with 0.15 mm slice thickness. Group B: 500 or more labeled cells showed a significant signal reduction in SWI sequences with a slice thickness of 0.25 mm. Slice thickness and cell number per layer had a significant influence on the amount of detected signal reduction.

CONCLUSION

500 VSOP labeled stem cells could be detected with SWI imaging at 3 Tesla using an experimental design suitable for large animal models.

Magnetic resonance imaging of Fe3O4@SiO2-labeled human mesenchymal stem cells in mice at 11.7 T

Fe(3)O(4)@SiO(2) core-shell nanoparticles were synthesized and used to label human mesenchymal stem cells (hMSCs) for in vitro and in vivo magnetic resonance imaging study. The diameter of the nanoparticles is 24-30 nm with a Fe(3)O(4) core of ∼8 nm and a SiO(2) shell of ~8 nm. Transverse relaxivity of the nanoparticles dispersed in water is measured to be ~106 mM(-1) s(-1). After incubation with hMSCs for 12 h at a concentration of 100 μg Fe/mL, cellular uptake of Fe(3)O(4)@SiO(2) is 20-100 pg Fe/cell, which are located predominantly in the cytoplasm of cells. This level of uptake exhibits no significant influence on hMSCs' viability and differentiation. In vitro imaging of Fe(3)O(4)@SiO(2)-labeled hMSCs evenly distributed in agarose gel yields single cell sensitivity at 11.7 T. In vivo imaging of Fe(3)O(4)@SiO(2)-labeled hMSCs injected into the left brain hemisphere of nude mice yields imaging sensitivity of ~130 hMSCs.

Magnetic Nanoclusters with Hydrophilic Spacing for Dual Drug Delivery and Sensitive Magnetic Resonance Imaging

Magnetic Block Ionomer Clusters (MBIClusters) with hydrophilic ionic cores and nonionic coronas have been prepared that have ultrahigh transverse NMR relaxivities together with capacities for incorporating high concentrations of polar antibiotic payloads. Magnetite-polymer nanoparticles were assembled by adsorbing the polyacrylate block of an aminofunctional poly(ethylene oxide-b-acrylate) (H2N-PEO-b-PAA) copolymer onto magnetite nanoparticles. The PEO blocks extended into aqueous media to keep the nanoparticles dispersed. Amines at the tips of the H2N-PEO corona were then linked through reaction with a PEO diacrylate oligomer to yield MBIClusters where the metal oxide in the precursor nanoparticles were distinctly separated by the hydrophilic polymer. The intensity average spacing between the magnetite nanoparticles within the clusters was estimated to be ~50 nm. These MBIClusters with hydrophilic intra-cluster space had transverse relaxivities (r2's) that increased from 190 to 604 s-1 mM Fe-1 measured at 1.4 T and 37 °C as their average sizes increased. The clusters were loaded with up to ~38 wt% of the multi-cationic drug gentamicin. MRI scans focused on the livers of mice demonstrated that these MBIClusters are sensitive contrast agents.

Intrahippocampal transplantation of mesenchymal stromal cells promotes neuroplasticity

BACKGROUND AIMS

Multipotent mesenchymal stromal cells (MSC) secrete soluble factors that stimulate the surrounding microenvironment. Such paracrine effects might underlie the potential benefits of many stem cell therapies. We tested the hypothesis that MSC are able to enhance intrinsic cellular plasticity in the adult rat hippocampus.

METHODS

Rat bone marrow-derived MSC were labeled with very small superparamagnetic iron oxide particles (VSOP), which allowed for non-invasive graft localization by magnetic resonance imaging (MRI). Moreover, MSC were transduced with lentiviral vectors to express the green fluorescent protein (GFP). The effects of bilateral MSC transplantation on hippocampal cellular plasticity were assessed using the thymidine analogs 5-bromo-2'-deoxyuridine (BrdU) and 5-iodo-2'-deoxyuridine (IdU). Behavioral testing was performed to examine the consequences of intrahippocampal MSC transplantation on locomotion, learning and memory, and anxiety-like and depression-like behavior.

RESULTS

We found that intrahippocampal transplantation of MSC resulted in enhanced neurogenesis despite short-term graft survival. In contrast, systemic administration of the selective serotonin re-uptake inhibitor citalopram increased cell survival but did not affect cell proliferation. Intrahippocampal transplantation of MSC did not impair behavioral functions in rats, but only citalopram exerted anti-depressant effects.

CONCLUSIONS

This is the first study to examine the effects of intrahippocampal transplantation of allogeneic MSC on hippocampal structural plasticity and behavioral functions in rats combined with non-invasive cell tracking by MRI. We found that iron oxide nanoparticles can be used to detect transplanted MSC in the brain. Although graft survival was short, intrahippocampal transplantation of MSC resulted in long-term changes in hippocampal plasticity. Our results suggest that MSC can be used to stimulate adult neurogenesis.

In vivo magnetic resonance imaging tracking of SPIO-labeled human umbilical cord mesenchymal stem cells

Human umbilical cord mesenchymal stem cells (hUC-MSCs) can be efficiently labeled by superparamagnetic iron oxide (SPIO) nanoparticles, which produces low signal intensity on magnetic resonance imaging (MRI) in vitro. This study was to evaluate the feasibility of in vivo tracking for hUC-MSCs labeled by SPIO with noninvasive MRI. SPIO was added to cultures at concentrations equivalent to 0, 7, 14, 28, and 56 µg Fe/ml (diluted with DMEM/F12) and incubated for 16 h. Prussian Blue staining was used to determinate the labeling efficiency. Rats were randomly divided into three groups, control group, hUC-MSCs group, and SPIO-labeled hUC-MSCs group. All groups were subjected to spinal cord injury (SCI) by weight drop device. Rats were examined for neurological function. In vivo MRI was used to track SPIO-labeled hUC-MSCs transplanted in rats spinal cord. Survival and migration of hUC-MSCs were also explored using immunofluorescence. Significant improvements in locomotion were observed in the hUC-MSCs groups. There was statistical significance compared with control group. In vivo MRI 1 and 3 weeks after injection showed a large reduction in signal intensity in the region transplanted with SPIO-labeled hUC-MSCs. The images from unlabeled hUC-MSCs showed a smaller reduction in signal intensity. Transplanted hUC-MSCs engrafted within the injured rats spinal cord and survived for at least 8 weeks. In conclusion, hUC-MSCs can survive and migrate in the host spinal cord after transplantation, which promote functional recovery after SCI. Noninvasive imaging of transplanted SPIO-labeled hUC-MSCs is feasible.

Biological applications of magnetic nanoparticles

In this review an overview about biological applications of magnetic colloidal nanoparticles will be given, which comprises their synthesis, characterization, and in vitro and in vivo applications. The potential future role of magnetic nanoparticles compared to other functional nanoparticles will be discussed by highlighting the possibility of integration with other nanostructures and with existing biotechnology as well as by pointing out the specific properties of magnetic colloids. Current limitations in the fabrication process and issues related with the outcome of the particles in the body will be also pointed out in order to address the remaining challenges for an extended application of magnetic nanoparticles in medicine.

Magnetic nanoparticles in magnetic resonance imaging and diagnostics

Magnetic nanoparticles are useful as contrast agents for magnetic resonance imaging (MRI). Paramagnetic contrast agents have been used for a long time, but more recently superparamagnetic iron oxide nanoparticles (SPIOs) have been discovered to influence MRI contrast as well. In contrast to paramagnetic contrast agents, SPIOs can be functionalized and size-tailored in order to adapt to various kinds of soft tissues. Although both types of contrast agents have a inducible magnetization, their mechanisms of influence on spin-spin and spin-lattice relaxation of protons are different. A special emphasis on the basic magnetism of nanoparticles and their structures as well as on the principle of nuclear magnetic resonance is made. Examples of different contrast-enhanced magnetic resonance images are given. The potential use of magnetic nanoparticles as diagnostic tracers is explored. Additionally, SPIOs can be used in diagnostic magnetic resonance, since the spin relaxation time of water protons differs, whether magnetic nanoparticles are bound to a target or not.

Electrostatically Stabilized Magnetic Nanoparticles - An Optimized Protocol to Label Murine T Cells for in vivo MRI

We present a novel highly efficient protocol to magnetically label T cells applying electrostatically stabilized very small superparamagnetic iron oxide particles (VSOP). Our long-term aim is to use magnetic resonance imaging (MRI) to investigate T cell dynamics in vivo during the course of neuroinflammatory disorders such as experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. Encephalitogenic T cells were co-incubated with VSOP, or with protamine-complexed VSOP (VProt), respectively, at different conditions, optimizing concentrations and incubation times. Labeling efficacy was determined by atomic absorption spectrometry as well as histologically, and evaluated on a 7 T MR system. Furthermore, we investigated possible alterations of T cell physiology caused by the labeling procedure. T cell co-incubation with VSOP resulted in an efficient cellular iron uptake. T2 times of labeled cells dropped significantly, resulting in prominent hypointensity on T2*-weighted scans. Optimal labeling efficacy was achieved by VProt (1 mM Fe/ml, 8 h incubation; T2 time shortening of ∼80% compared to untreated cells). Although VSOP promoted T cell proliferation and altered the ratio of T cell subpopulations toward a CD4⁺ phenotype, no effects on CD4 T cell proliferation or phenotypic stability were observed by labeling in vitro differentiated Th17 cells with VProt. Yet, high concentrations of intracellular iron oxide might induce alterations in T cell function, which should be considered in cell tagging studies. Moreover, we demonstrated that labeling of encephalitogenic T cells did not affect pathogenicity; labeled T cells were still capable of inducing EAE in susceptible recipient mice.

14.1 T whole body MRI for detection of mesoangioblast stem cells in a murine model of Duchenne muscular dystrophy

Noninvasive imaging procedures will be important for stem cell therapy for muscular dystrophy (MD). Mesoangioblasts regenerate muscle in animal models of muscular dystrophy. In this study, superparamagnetic iron oxide nanoparticles were used to visualize mesoangioblasts in vivo with MRI. Mesoangioblasts incorporated superparamagnetic iron oxide without transfection reagents, and cell differentiation was not negatively impacted. A custom-built radiofrequency coil with an adjustable field of view and 14.1 T magnet were used for whole-body MRI of mice. High-resolution images of mesoangioblasts in skeletal and cardiac muscle of Mdx mice were obtained following local delivery. Labeled cells were verified by Prussian blue staining and dystrophin expression, indicating that the wild-type mesoangioblasts survived and differentiated in muscle. Iron-labeled cells were detected with MRI in vivo 6 months following intracardiac injection but were determined to be activated macrophages. Iron-labeled cells were not detected by MRI following systemic delivery but were present in skeletal and cardiac muscle, visualized by Prussian blue staining. Systemically delivered mesoangioblasts were detected in lungs by Prussian blue staining and DiI but not by MRI in our study. MRI may be useful for short-term tracking of mesoangioblasts delivered locally but not for long-term monitoring or detection after systemic delivery.

Quantitative analysis of neural stem cell migration and tracer clearance in the rat brain by MRI

PURPOSE

This study describes a quantitative method to estimate the migratory capacity of neural stem cells (NSCs) using magnetic resonance imaging.

PROCEDURES

NSCs were labeled with ferumoxides and injected stereotaxically into the corpus callosum of the normal rat brain. Control subjects received either free ferumoxides or nonviable labeled cells. Subjects were scanned after initial injection and at 1 week. Image sets were coregistered, compared morphologically, and analyzed parametrically to determine migration speed.

RESULTS

Subjects receiving injections of viable cells had a significantly greater spread of the tracer after 1 week than either control group (p< 0.05). The speed of migration for viable NSCs was significantly higher than that of controls along the corpus callosum (p < 0.05). Migratory speeds estimated from histology and imaging were significantly correlated.

CONCLUSIONS

This study provides a quantitative assessment of posttransplantation neural stem cell migration that is clearly distinguishable from tracer clearance.

Nanotoxicology and nanoparticle safety in biomedical designs

Nanotechnology has wide applications in many fields, especially in the biological sciences and medicine. Nanomaterials are applied as coating materials or in treatment and diagnosis. Nanoparticles such as titania, zirconia, silver, diamonds, iron oxides, carbon nanotubes, and biodegradable polymers have been studied in diagnosis and treatment. Many of these nanoparticles may have toxic effects on cells. Many factors such as size, inherent properties, and surface chemistry may cause nanoparticle toxicity. There are methods for improving the performance and reducing toxicity of nanoparticles in medical design, such as biocompatible coating materials or biodegradable/biocompatible nanoparticles. Most metal oxide nanoparticles show toxic effects, but no toxic effects have been observed with biocompatible coatings. Biodegradable nanoparticles are also used in the efficient design of medical materials, which will be reviewed in this article.

High MR sensitive fluorescent magnetite nanocluster for stem cell tracking in ischemic mouse brain

Stem cells have shown a great potential to treat diseases and injuries, including ischemic brain injury. However, developing agents for the long-term tracking of stem cells with few side effects is still challenging. Our aim is to develop a novel fluorescent-magnetite-nanocluster (FMNC) with high MRI sensitivity and to examine its application in the labeling and tracking of mesenchymal stem cells (MSC). For this purpose, we developed FMNC by embedding individual magnetite nanoparticles (NPs) into a polystyrene scaffold coated with two layers of silica and a sandwiched layer of rhodamine. We examined the efficacy of FMNC in MSC labeling and the feasibility of tracking FMNC-labeled MSCs in the ischemic mouse brain. We found that FMNC has high cell-labeling efficiency with no adverse effects on MSCs. In a mouse middle cerebral artery occlusion model, FMNC-labeled MSCs migrated to and accumulated in the ischemic region after FMNC-labeled MSC transplantation. MRI findings highly correlated to immunohistochemistry results.

FROM THE CLINICAL EDITOR

In this study, the authors report a novel fluorescent-magnetite-nanocluster with high MRI sensitivity and to labeling and tracking of mesenchymal stem cells, and provide in vivo data utilizing a murine stroke model.

Long-term magnetic resonance imaging of stem cells in neonatal ischemic injury

OBJECTIVE

Quantitative magnetic resonance imaging (MRI) can serially and noninvasively assess the degree of injury in rat pup models of hypoxic ischemic injury (HII). It can also noninvasively monitor stem cell migration following iron oxide prelabeling. Reports have shown that neural stem cells (NSCs) may help mediate neuroprotection or stimulate neuroreparative responses in adult and neonatal models of ischemic injury. We investigated the ability of high-field MRI to monitor and noninvasively quantify the migration, proliferation, and location of iron oxide-labeled NSCs over very long time periods (58 weeks) in real time while contemporaneously correlating this activity with the evolving severity and extent of neural damage.

METHODS

Labeled clonal murine NSCs (mNSCs) were implanted 3 days after unilateral HII in 10-day-old rat pups into the contralateral striatum or ventricle. We developed methods for objectively quantifying key aspects of dynamic NSC behavior (eg, viability; extent, and speed of migration; degree of proliferation; extent of integration into host parenchyma). MRI images were validated with histological and immunohistochemical assessments.

RESULTS

mNSCs rapidly migrated (100 μm/day) to the lesion site. Chains of migrating NSCs were observed in the corpus callosum. In pups subjected to HII, though not in intact control animals, we observed a 273% increase in the MR-derived volume of mNSCs 4 weeks after implantation (correlating with the known proliferative behavior of endogenous and exogenous NSCs) that slowly declined over the 58-week time course, with no adverse consequences. Large numbers of now quiescent mNSCs remained at the site of injury, many retaining their iron oxide label.

INTERPRETATION

Our studies demonstrate that MRI can simultaneously monitor evolving neonatal cerebral injury as well as NSC migration and location. Most importantly, it can noninvasively monitor proliferation dynamically for prolonged time periods. To be able to pursue clinical trials in newborns using stem cell therapies it is axiomatic that safety be insured through the long-term real time monitoring of cell fate and activity, particularly with regard to observing unanticipated risks to the developing brain. This study supports the feasibility of reliably using MRI for this purpose.

Conserved fate and function of ferumoxides-labeled neural precursor cells in vitro and in vivo

Recent progress in cell therapy research for brain diseases has raised the need for non-invasive monitoring of transplanted cells. For therapeutic application in multiple sclerosis, transplanted cells need to be tracked both spatially and temporally, in order to assess their migration and survival in the host tissue. Magnetic resonance imaging (MRI) of superparamagnetic iron oxide-(SPIO)-labeled cells has been widely used for high resolution monitoring of the biodistribution of cells after transplantation into the central nervous system (CNS). Here we labeled mouse glial-committed neural precursor cells (NPCs) with the clinically approved SPIO contrast agent ferumoxides and examined their survival and differentiation in vitro, as well as their functional response to environmental signals present within the inflamed brain of experimental autoimmune encephalomyelitis (EAE) mice in vivo. We show that ferumoxides labeling does not affect NPC survival and pluripotency in vitro. Following intracerebroventricular (ICV) transplantation in EAE mice, ferumoxides-labeled NPCs responded to inflammatory cues in a similar fashion as unlabeled cells. Ferumoxides-labeled NPCs migrated over comparable distances in white matter tracts and differentiated equally into the glial lineages. Furthermore, ferumoxides-labeled NPCs inhibited lymph node cell proliferation in vitro, similarly to non-labeled cells, suggesting a preserved immunomodulatory function. These results demonstrate that ferumoxides-based MRI cell tracking is well suited for non-invasive monitoring of NPC transplantation.

Beyond blood brain barrier breakdown - in vivo detection of occult neuroinflammatory foci by magnetic nanoparticles in high field MRI

Background

Gadopentate dimeglumine (Gd-DTPA) enhanced magnetic resonance imaging (MRI) is widely applied for the visualization of blood brain barrier (BBB) breakdown in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). Recently, the potential of magnetic nanoparticles to detect macrophage infiltration by MRI was demonstrated. We here investigated a new class of very small superparamagnetic iron oxide particles (VSOP) as novel contrast medium in murine adoptive-transfer EAE.

Methods

EAE was induced in 17 mice via transfer of proteolipid protein specific T cells. MR images were obtained before and after application of Gd-DTPA and VSOP on a 7 Tesla rodent MR scanner. The enhancement pattern of the two contrast agents was compared, and correlated to histology, including Prussian Blue staining for VSOP detection and immunofluorescent staining against IBA-1 to identify macrophages/microglia.

Results

Both contrast media depicted BBB breakdown in 42 lesions, although differing in plaques appearances and shapes. Furthermore, 13 lesions could be exclusively visualized by VSOP. In the subsequent histological analysis, VSOP was localized to microglia/macrophages, and also diffusely dispersed within the extracellular matrix.

Conclusion

VSOP showed a higher sensitivity in detecting BBB alterations compared to Gd-DTPA enhanced MRI, providing complementary information of macrophage/microglia activity in inflammatory plaques that has not been visualized by conventional means.

New opportunities: the use of nanotechnologies to manipulate and track stem cells

Nanotechnologies are emerging platforms that could be useful in measuring, understanding, and manipulating stem cells. Examples include magnetic nanoparticles and quantum dots for stem cell labeling and in vivo tracking; nanoparticles, carbon nanotubes, and polyplexes for the intracellular delivery of genes/oligonucleotides and protein/peptides; and engineered nanometer-scale scaffolds for stem cell differentiation and transplantation. This review examines the use of nanotechnologies for stem cell tracking, differentiation, and transplantation. We further discuss their utility and the potential concerns regarding their cytotoxicity.

Impact of Magnetic Labeling on Human and Mouse Stem Cells and Their Long-Term Magnetic Resonance Tracking in a Rat Model of Parkinson Disease

Magnetic resonance imaging (MRI) of magnetically labeled stem cells has become a valuable tool in the understanding and evaluation of experimental stem cell–based therapies of degenerative central nervous system disorders. This comprehensive study assesses the impact of magnetic labeling of both human and rodent stem cell–containing populations on multiple biologic parameters as maintenance of stemness and oxidative stress levels. Cells were efficiently magnetically labeled with very small superparamagnetic iron oxide particles. Only under the condition of tailored labeling strategies can the impact of magnetic labeling on vitality, proliferation, pluripotency, and oxidative stress levels be minimized. In a rat model of Parkinson disease, magnetically labeled mouse embryonic stem cells were tracked by high-field MRI for 6 months. Significant interindividual differences concerning the spatial distribution of cells became evident. Histologically, transplanted green fluorescent protein–positive iron oxide–labeled cells were clearly identified. No significant increase in oxidative stress levels at the implantation site and no secondary uptake of magnetic label by host phagocytotic cells were observed. Our study strongly suggests that molecular MRI approaches must be carefully tailored to the respective cell population to exert minimal physiologic impact, ensuring the feasibility of this imaging approach for clinical applications.

Labeling of stem cells with monocrystalline iron oxide for tracking and localization by magnetic resonance imaging

Precise localization of exogenously delivered stem cells is critical to our understanding of their reparative response. Our current inability to determine the exact location of small numbers of cells may hinder optimal development of these cells for clinical use. We describe a method using magnetic resonance imaging to track and localize small numbers of stem cells following transplantation. Endothelial progenitor cells (EPC) were labeled with monocrystalline iron oxide nanoparticles (MIONs) which neither adversely altered their viability nor their ability to migrate in vitro and allowed successful detection of limited numbers of these cells in muscle. MION-labeled stem cells were also injected into the vitreous cavity of mice undergoing the model of choroidal neovascularization, laser rupture of Bruch's membrane. Migration of the MION-labeled cells from the injection site towards the laser burns was visualized by MRI. In conclusion, MION labeling of EPC provides a non-invasive means to define the location of small numbers of these cells. Localization of these cells following injection is critical to their optimization for therapy.

Nanomedicine: perspective and promises with ligand-directed molecular imaging

Molecular imaging and targeted drug delivery play an important role toward personalized medicine, which is the future of patient management. Of late, nanoparticle-based molecular imaging has emerged as an interdisciplinary area, which shows promises to understand the components, processes, dynamics and therapies of a disease at a molecular level. The unprecedented potential of nanoplatforms for early detection, diagnosis and personalized treatment of diseases, have found application in every biomedical imaging modality. Biological and biophysical barriers are overcome by the integration of targeting ligands, imaging agents and therapeutics into the nanoplatform which allow for theranostic applications. In this article, we have discussed the opportunities and potential of targeted molecular imaging with various modalities putting a particular emphasis on perfluorocarbon nanoemulsion-based platform technology.

Neuroimaging as a basis for rational stem cell therapy

Neonatal global or focal hypoxic-ischemic brain injury remains a frequent and devastating condition, with serious long-term sequelae. An important issue in any neonatal clinical trial of neuroprotective agents relates to developing accurate measures of injury severity and also suitable measures of the response to treatment. Advanced magnetic resonance imaging techniques can acquire serial and noninvasive data about brain structure, metabolic activity, and the response to injury or treatment. These imaging methods need validation in appropriate animal models for translational research studies in human newborns. This review describes several approaches that use imaging as well as proton magnetic resonance spectroscopy to assess the severity of ischemic injury (e.g., for possible candidate selection) and for monitoring the progression and evolution of injury over time and as an indicator of recovery or response to treatment. Preliminary data are presented on how imaging can be used after neural stem cell implantation to characterize the migration rate, the magnitude of stem cell proliferation, and their final location. Imaging has the potential to allow monitoring of many dimensions of neuroprotective treatments and can be expected to contribute to efficacy and safety when clinical trials using neural stem cells or other neuroprotective agents become available.

Cellular magnetic resonance imaging using superparamagnetic anionic iron oxide nanoparticles: applications to in vivo trafficking of lymphocytes and cell-based anticancer therapy

In current cancer research, the application of cytotoxic T lymphocytes with specificity to tumor antigens is regarded as a real therapeutic hope. The objective of imaging is to provide a follow-up of these killer cells in real time, in order to gain a better understanding of the mechanisms and action modes of lymphocytes on the tumor. Magnetic resonance imaging (MRI) has the advantage of the innocuousness of the applied magnetic field. Moreover, it has an exceptional spatial resolution allowing the visualization of anatomical areas without in-depth limitations. These features make MRI particularly adapted for cellular imaging. The use of " (ultrasmall) superparamagnetic iron oxide " particles [(U) SPIO] offers the adequate sensitivity required for cellular imaging. To promote a sufficient capture of these particles in nonphagocytic cells and make the cell of interest " detectable " by MRI after its injection, an important challenge in cellular imaging is to develop improved cell-labeling techniques. Superparamagnetic anionic nanoparticles (iron oxides of 10-nm diameter) are adsorbed in a nonspecific way on the membrane of the majority of cells, allowing their spontaneous internalization in intracellular vesicles. This pathway of cellular labeling confers a particular status to these nanoparticles as MRI contrast agents; the cells labeled in this manner possess magnetic and contrast properties that allow their in vivo detection and follow-up by MRI. This chapter describes the synthesis, the potential use, and the features of cellular labeling with these types of anionic nanoparticles. We also focus on the MRI contrast properties of the labeled cells, as well as on the feasibility of in vivo detection of immunizing circulating cells by MRI, with direct implications in cell-based anticancer therapy using lymphocytes.

Tracking of neural stem cells in rats with intracerebral hemorrhage by the use of 3T MRI

OBJECTIVE

To access the feasibility of clinically available 3T MRI to detect the migration of labeled neural stem cells (NSCs) in intracerebral hemorrhage (ICH) in a rat model.

MATERIALS AND METHODS

The ethics committee of our institution approved this study. ICH was induced by the injection of collagenase type IV into the right striatum of ten Sprague-Dawley rats. Human NSCs conjugated with Feridex (super-paramagnetic iron oxide: SPIO) were transplanted into the left striatum one week after ICH induction. MRI was performed on a 3T scanner during the first, second, third, fourth, and sixth weeks post-transplantation. MRI was obtained using coronal T2- and T2*-weighted sequences. Two rats were sacrificed every week after in vivo MRI in order to analyze the histological findings.

RESULTS

ICH in the right striatum was detected by MRI one and two weeks after transplantation without migration of the NSCs. There was no migration of the NSCs as seen on the histological findings one week after transplantation. The histological findings two weeks after transplantation showed a small number of NSCs along the corpus callosum. On MRI three weeks after transplantation, there was a hypointense line along the corpus callosum and decreased signal intensity in the right periventricular region. Histological findings three weeks after transplantation confirmed the presence of the hypointense line representing SPIO-labeled NSCs. MRI four and six weeks after transplantation showed a hypointense spot in the right periventricular region. The histological findings four and six weeks after transplantation showed the presence of prominent NSCs in the right periventricular region.

CONCLUSION

3T MRI can detect the migration of NSCs in rats with ICH along the corpus callosum. Therefore, 3T MRI could be feasible for detecting the migration of NSCs in the clinical setting of stem cell therapy.