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Cell labeling by superparamagnetic iron oxide particles (SPIO) has emerged as a potentially powerful tool to monitor trafficking of transplanted cells by magnetic resonance tomography, e.g., in studies for tissue repair. However, intracellular labeling is mostly achieved by transfection agents not approved for clinical use. In this work, the feasibility and efficiency of labeling human mesenchymal stem cells (MSC) and HeLa cells with two commercially available SPIOs (Resovist and Feridex) without transfection agents was evaluated. In both cell types, Resovist without a transfection agent was more efficiently taken up than Feridex. Increasing the concentration of Resovist can yield similar amounts of iron in cells as SPIOs with transfection agents. This offers the opportunity to omit transfection agents from the labeling protocol when Resovist is used. Intracellular localization of the contrast agents is found by light microscopy and confirmed by electron microscopy. Coagulation of the SPIO nanoparticles, which is problematic for the quantification of the intracellular iron content, was observed and analyzed with a fluorescent activated cell sorter. As Resovist consists of a carboxydextran shell in contrast to Feridex which is composed of a dextran shell, we synthesized fluorescent polymeric nanoparticles as model systems with different amounts of carboxyl groups on the surface by the miniemulsion process. A steady increase in uptake of nanoparticles was detected with a higher density of carboxyl groups showing the relevance of charged groups as in the case of Resovist. Aggregation of these polymeric nanoparticles was not found.
Mol Imaging Biol
PMID:Carboxylated superparamagnetic iron oxide particles label cells intracellularly without transfection agents. 1829 65

Small particles of iron oxide (SPIO) and ultrasmall particles of iron oxide (USPIO), inducing a strong negative contrast on T(2) and T(2)*-weighted MR images, are the most commonly used systems for the magnetic labeling of cultured cells and their subsequent detection by magnetic resonance imaging (MRI). The purpose of this work is to study the influence of iron incubation concentration, nanoparticle size and nanoparticle coating on the magnetic labeling and the viability of non-phagocytic adherent cells in culture. The magnetic labeling of 3T6 fibroblasts was studied by T(2)-weighted MRI at 4.7 T and by dosing-or cytochemical revealing-of iron through methods based on Perl's Prussian blue staining. Cells were incubated for 48 h with increasing iron concentrations of SPIO (25-1000 microg Fe/ml Endorem. Sinerem, a USPIO (20-40 nm) coated with neutral dextran, and Resovist (65 nm), a SPIO bearing an anionic carboxydextran coating, were compared with Endorem (dextran-coated, 80-150 nm) as magnetic tags. The iron loading of marrow stromal cell primary cultures (MSCs) isolated from rat femurs was compared with that of 3T6 fibroblasts. The SPIO-labeling of cells with Endorem was found to be dependent on the iron incubation concentration. MSCs, more sparsely distributed in the culture, exhibited higher iron contents than more densely populated 3T6 fibroblast cultures. A larger iron loading was achieved with Resovist than with Endorem, which in turn was more efficient than Sinerem as a magnetic tag. The magnetic labeling of cultured non-phagocytic adherent cells with iron oxide nanoparticles was thus found to be dependent on the relative concentration of the magnetic tag and of the cells in culture, on the nanoparticle size, and on the coating type. The viability of cells, estimated by methods assessing cell membrane permeability, was not affected by magnetic labeling in the conditions used in this work.
Contrast Media Mol Imaging
PMID:Magnetic labeling of non-phagocytic adherent cells with iron oxide nanoparticles: a comprehensive study. 1907 71

The aim of the work was to compare in vivo MRI visualization of pancreatic islets labeled with clinical-grade superparamagnetic iron oxide (SPIOs) contrast agents with ex vivo examination of liver tissue in an experimental model of marginal mass transplantation in rats. Seven hundred IEq (Islet Equivalent) from Wistar rats, labeled by incubation with Endorem or Resovist, were transplanted into Sprague-Dawley rats through the portal vein. Liver MR images of recipient rats were acquired at different time points (3-42 days) after transplantation. Animals were sacrificed during this period and their livers were excised and prepared for histology and electron microscopy. Hypointense spots originating from iron particles were observed in MR images. The number of separate spots was counted. Three days after transplantation one spot for every three or four transplanted islets was observed. Seven days after transplantation, histological sections showed the presence of iron within pancreatic islets. The time course of MR images showed a decrease in the number of spots, at 42 days, amounting to 65 and 22% of the initial value, for Resovist and Endorem respectively, while no immunopositive endocrine cells were detected in histological slices. The present work shows that pancreatic islets can be labeled using clinically approved SPIO contrast agents and visualized using in vivo MRI with high sensitivity, consistently with findings in the literature. Differently from reports in the literature, our findings indicate that iron particles could last in the liver for long periods, independently of the presence of intact pancreatic islets.
Contrast Media Mol Imaging
PMID:In vivo visualization of transplanted pancreatic islets by MRI: comparison between in vivo, histological and electron microscopy findings. 1948 41

Superparamagnetic iron oxide (SPIO) nanoparticles are emerging as ideal probes for noninvasive cell tracking. In this study, poly-L-lysine (PLL) was mixed with Resovist to form the PLL-Resovist complexes and the control of the complexes formed by PLL and Resovist and their subsequent properties was easily achievable. MSCs could be safely and efficiently labeled for MR imaging using PLL-Resovist complexes (w/w 0.01:1) and the labeled MSCs could be detected to have definite decreased signal intensity on T(2)-weight imaging until 20 days with standard 1.5 T MR equipment. This study describes a simple protocol to label MSCs using PLL-Resovist complexes and the results presented in our study can provide a basis for the application of PLL-Resovist complexes cell labeling.
Contrast Media Mol Imaging
PMID:MR imaging for the longevity of mesenchymal stem cells labeled with poly-L-lysine-Resovist complexes. 2023 46

Superparamagnetic iron-oxide particles (SPIO) are used in different ways as contrast agents for magnetic resonance imaging (MRI): Particles with high nonspecific uptake are required for unspecific labeling of phagocytic cells whereas those that target specific molecules need to have very low unspecific cellular uptake. We compared iron-oxide particles with different core materials (magnetite, maghemite), different coatings (none, dextran, carboxydextran, polystyrene) and different hydrodynamic diameters (20-850 nm) for internalization kinetics, release of internalized particles, toxicity, localization of particles and ability to generate contrast in MRI. Particle uptake was investigated with U118 glioma cells und human umbilical vein endothelial cells (HUVEC), which exhibit different phagocytic properties. In both cell types, the contrast agents Resovist, B102, non-coated Fe(3)O(4) particles and microspheres were better internalized than dextran-coated Nanomag particles. SPIO uptake into the cells increased with particle/iron concentrations. Maximum intracellular accumulation of iron particles was observed between 24 h to 36 h of exposure. Most particles were retained in the cells for at least two weeks, were deeply internalized, and only few remained adsorbed at the cell surface. Internalized particles clustered in the cytosol of the cells. Furthermore, all particles showed a low toxicity. By MRI, monolayers consisting of 5000 Resovist-labeled cells could easily be visualized. Thus, for unspecific cell labeling, Resovist and microspheres show the highest potential, whereas Nanomag particles are promising contrast agents for target-specific labeling.
Int J Mol Sci 2010 Dec 23
PMID:Biological properties of iron oxide nanoparticles for cellular and molecular magnetic resonance imaging. 2133 73