Poly(N,N-dimethylacrylamide)-coated maghemite nanoparticles for stem cell labeling.

Maghemite (gamma-Fe2O3) nanoparticles were obtained by the coprecipitation of Fe(II) and Fe (III) salts with ammonium hydroxide followed by oxidation with sodium hypochlorite. Solution radical polymerization of N,N-dimethylacrylamide(DMAAm) in the presence of maghemite nanoparticles yielded poly(N,N-dimethylacrylamide)(PDMAAm)-coated maghemite nanoparticles. The presence of PDMAAm on the maghemite particle surface was confirmed by elemental analysis and ATR FTIR spectroscopy. Other methods of nanoparticle characterization involved scanning and transmission electron microscopy, atomic adsorption spectroscopy (AAS), and dynamic light scattering (DLS). The conversion of DMAAm during polymerization and the molecular weight of PDMAAmbound to maghemite were determined by using gas and size-exclusion chromatography, respectively. The effect of ionic 4,4'-azobis(4-cyanovaleric acid) (ACVA) initiator on nanoparticle morphology was elucidated. The nanoparticles exhibited long-term colloidal stability in water or physiological buffer. Rat and human bone marrow mesenchymal stem cells (MSCs) were labeled with uncoated and PDMAAm-coated maghemite nanoparticles and with Endorem as a control. Uptake of the nanoparticles was evaluated by Prussian Blue staining, transmission electron microscopy, T(2)-MR relaxometry, and iron content analysis. Significant differences in labeling efficiency were found for human and rat cells. PDMAAm-modified nanoparticles demonstrated a higher efficiency of intracellular uptake into human cells in comparison with that of dextran-modified (Endorem) and unmodified nanoparticles. In gelatin, even a small number of labeled cells changed the contrast in MR images. PDMAAmcoatednanoparticles provided the highest T(2) relaxivity of all the investigated particles. In vivo MR imaging ofPDMAAm-modified iron oxide-labeled rMSCs implanted in a rat brain confirmed their better resolution compared with Endorem-labeled cells.

Poly(L-lysine)-modified iron oxide nanoparticles for stem cell labeling.

New surface-modified iron oxide nanoparticles were developed by precipitation of Fe(II) and Fe(III) salts with ammonium hydroxide and oxidation of the resulting magnetite with sodium hypochlorite, followed by the addition of poly( L-lysine) (PLL) solution. PLL of several molecular weights ranging from 146 ( L-lysine) to 579 000 was tested as a coating to boost the intracellular uptake of the nanoparticles. The nanoparticles were characterized by TEM, dynamic light scattering, FTIR, and ultrasonic spectrometry. TEM revealed that the particles were ca. 6 nm in diameter, while FTIR showed that their surfaces were well-coated with PLL. The interaction of PLL-modified iron oxide nanoparticles with DMEM culture medium was verified by UV-vis spectroscopy. Rat bone marrow stromal cells (rMSCs) and human mesenchymal stem cells (hMSC) were labeled with PLL-modified iron oxide nanoparticles or with Endorem (control). Optical microscopy and TEM confirmed the presence of PLL-modified iron oxide nanoparticles inside the cells. Cellular uptake was very high (more than 92%) for PLL-modified nanoparticles that were coated with PLL (molecular weight 388 00) at a concentration of 0.02 mg PLL per milliliter of colloid. The cellular uptake of PLL-modified iron oxide was facilitated by its interaction with the negatively charged cell surface and subsequent endosomolytic uptake. The relaxivity of rMSCs labeled with PLL-modified iron oxide and the amount of iron in the cells were determined. PLL-modified iron oxide-labeled rMSCs were imaged in vitro and in vivo after intracerebral grafting into the contralateral hemisphere of the adult rat brain. The implanted cells were visible on magnetic resonance (MR) images as a hypointense area at the injection site and in the lesion. In comparison with Endorem, nanoparticles modified with PLL of an optimum molecular weight demonstrated a higher efficiency of intracellular uptake by MSC cells.

Transplantation of bone marrow stem cells as well as mobilization by granulocyte-colony stimulating factor promotes recovery after spinal cord injury in rats.

Emerging clinical studies of treating brain and spinal cord injury (SCI) with autologous adult stem cells led us to compare the effect of an intravenous injection of mesenchymal stem cells (MSCs), an injection of a freshly prepared mononuclear fraction of bone marrow cells (BMCs) or bone marrow cell mobilization induced by granulocyte colony stimulating factor (G-CSF) in rats with a balloon- induced spinal cord compression lesion. MSCs were isolated from rat bone marrow by their adherence to plastic, labeled with iron-oxide nanoparticles and expanded in vitro. Seven days after injury, rats received an intravenous injection of MSCs or BMCs or a subcutaneous injection of GCSF (from day 7 to 11 post-injury). Functional status was assessed weekly for 5 weeks after SCI, using the Basso-Beattie-Bresnehan (BBB) locomotor rating score and the plantar test. Animals with SCI treated with MSCs, BMCs, or G-CSF had higher BBB scores and better recovery of hind limb sensitivity than controls injected with saline. Morphometric measurements showed an increase in the spared white matter. MR images of the spinal cords were taken ex vivo 5 weeks after SCI using a Bruker 4.7-T spectrometer. The lesions populated by grafted MSCs appeared as dark hypointense areas. Histology confirmed a large number of iron-containing and PKH 26-positive cells in the lesion site. We conclude that treatment with three different bone marrow cell populations had a positive effect on behavioral outcome and histopathological assessment after SCI, which was most pronounced after MSC injection.

Transplantation of embryonic neuroectodermal progenitor cells into the site of a photochemical lesion: immunohistochemical and electrophysiological analysis.

GFP labeled/NE-4C neural progenitor cells cloned from primary neuroectodermal cultures of p53- mouse embryos give rise to neurons when exposed to retinoic acid in vitro. To study their survival and differentiation in vivo, cells were transplanted into the cortex of 6-week-old rats, 1 week after the induction of a photochemical lesion or into noninjured cortex. The electrophysiological properties of GFP/NE-4C cells were studied in vitro (8-10 days after differentiation induction) and 4 weeks after transplantation using the whole-cell patch-clamp technique, and immunohistochemical analyses were carried out. After transplantation into a photochemical lesion, a large number of cells survived, some of which expressed the astrocytic marker GFAP. GFP/GFAP-positive cells, with an average resting membrane potential (Vrest) of -71.9 mV, displayed passive time- and voltage-independent K+ currents and, additionally, voltage-dependent A-type K+ currents (KA) and/or delayed outwardly rectifying K+ currents (KDR). Numerous GFP-positive cells expressed NeuN, betaIII-tubulin, or 68 kD neurofilaments. GFP/betaIII-tubulin-positive cells, with an average Vrest of -61.6 mV, were characterized by the expression of KA and KDR currents and tetrodotoxin-sensitive Na+ currents. GFP/NE-4C cells also gave rise to oligodendrocytes, based on the detection of oligodendrocyte-specific markers. Our results indicate that GFP/NE-4C neural progenitors transplanted into the site of a photochemical lesion give rise to neurons and astrocytes with membrane properties comparable to those transplanted into noninjured cortex. Therefore, GFP/NE-4C cells provide a suitable model for studying neuro- and gliogenesis in vivo. Further, our results suggest that embryonic neuroectodermal progenitor cells may hold considerable promise for the repair of ischemic brain lesions.

Magnetic resonance tracking of human CD34+ progenitor cells separated by means of immunomagnetic selection and transplanted into injured rat brain.

Magnetic resonance imaging (MRI) provides a noninvasive method for studying the fate of transplanted cells in vivo. We studied whether superparamagnetic nanoparticles (CD34 microbeads), used clinically for specific magnetic sorting, can be used as a magnetic cell label for in vivo cell visualization. Human cells from peripheral blood were selected by CliniMACS CD34 Selection Technology (Miltenyi). Purified CD34+ cells were implanted into rats with a cortical photochemical lesion, contralaterally to the lesion. Twenty-four hours after grafting, the implanted cells were detected in the contralateral hemisphere as a hypointense spot on T2 weighted images; the hypointensity of the implant decreased during the first week. At the lesion site we observed a hypointensive signal 10 days after grafting that persisted for the next 3 weeks, until the end of the experiment. Prussian blue and anti-human nuclei staining confirmed the presence of magnetically labeled human cells in the corpus callosum and in the lesion 4 weeks after grafting. CD34+ cells were also found in the subventricular zone (SVZ). Human DNA (a human-specific 850 base pair fragment of alpha-satellite DNA from human chromosome 17) was detected in brain tissue sections from the lesion using PCR, confirming the presence of human cells. Our results show that CD34 microbeads superparamagnetic nanoparticles can be used as a magnetic cell label for in vivo cell visualization. The fact that microbeads coated with different commercially available antibodies can bind to specific cell types opens extensive possibilities for cell tracking in vivo.

Changes in sialylation in homozygous Sp2H mouse mutant embryos.

BACKGROUND: The splotch (Sp(2H)), Pax-3 mutant mice are characterized by neurulation defects, neural crest deficiencies, and altered somitogenesis. A link connecting all morphological abnormalities in the Pax-3 homozygous embryos is the composition of extracellular matrix and misexpression of cell adhesion molecules. The neural cell adhesion molecule (NCAM) is one of the Pax-3 target genes. Its adhesive properties depend on the attached polysialic acid (PSA). We have studied whether NCAM sialylation has been affected in the Pax-3 mutant embryos. METHODS: Genotyping of embryos was determined using polymerase chain reaction. The periodate-resorcinol method was used for quantitative determination of sialic acid. Immunoblotting was used to detect sialylated NCAM isoforms and sialic acids on the blot. This antibody was also used to detect PSA-NCAM spatial expression. RESULTS: Quantitative determination of sialic acid at days 10.5-13.5 showed decreased sialic acid content in Sp(2H) homozygotes. The results of both techniques used in evaluating the expression of PSA-NCAM isoforms in our study indicate that the 180-kDa isoform is decreased in homozygous Splotch (Sp(2H)) embryos. Immunohistochemistry showed decreased staining in the neural tube, ganglion VIII, (day 13.5), frontal lobe, olfactory bulb, and neuroblastic retinal cells (day 18.5). CONCLUSIONS: PSA-NCAM is present in Sp(2H) embryos of all genotypes, starting on developmental day 9.5. Sialylation of the 180-kDa NCAM isoform begins to decrease on day 12.5 in Sp(2H) homozygotes. Reduced NCAM sialylation could contribute to the decreased migration of cells in the sensory organs.

Magnetic resonance tracking of transplanted bone marrow and embryonic stem cells labeled by iron oxide nanoparticles in rat brain and spinal cord.

Nuclear magnetic resonance (MR) imaging provides a noninvasive method for studying the fate of transplanted cells in vivo. We studied, in animals with a cortical photochemical lesion or with a balloon-induced spinal cord compression lesion, the fate of implanted rat bone marrow stromal cells (MSCs) and mouse embryonic stem cells (ESCs) labeled with superparamagnetic iron oxide nanoparticles (Endorem). MSCs were colabeled with bromodeoxyuridine (BrdU), and ESCs were transfected with pEGFP-C1 (eGFP ESCs). Cells were either grafted intracerebrally into the contralateral hemisphere of the adult rat brain or injected intravenously. In vivo MR imaging was used to track their fate; Prussian blue staining and electron microscopy confirmed the presence of iron oxide nanoparticles inside the cells. During the first week postimplantation, grafted cells migrated to the lesion site and populated the border zone of the lesion. Less than 3% of MSCs differentiated into neurons and none into astrocytes; 5% of eGFP ESCs differentiated into neurons, whereas 70% of eGFP ESCs became astrocytes. The implanted cells were visible on MR images as a hypointense area at the injection site, in the corpus callosum and in the lesion. The hypointense signal persisted for more than 50 days. The presence of GFP-positive or BrdU-positive and nanoparticle-labeled cells was confirmed by histological staining. Our study demonstrates that both grafted MSCs and eGFP ESCs labeled with a contrast agent based on iron oxide nanoparticles migrate into the injured CNS. Iron oxide nanoparticles can therefore be used as a marker for the long-term noninvasive MR tracking of implanted stem cells.

Imaging the fate of implanted bone marrow stromal cells labeled with superparamagnetic nanoparticles.

Bone marrow stromal cells (MSCs) are pluripotent progenitor cells that have the capacity to migrate toward lesions and induce or facilitate site-dependent differentiation in response to environmental signals. In animals with a cortical photochemical lesion, the fate of rat MSCs colabeled with magnetic iron-oxide nanoparticles (Endorem) and bromodeoxyuridine (BrdU) was studied. MSCs were either grafted intracerebrally into the contralateral hemisphere of adult rat brain or injected intravenously. In vivo MRI was used to track their fate; Prussian blue staining and transmission electron microscopy (TEM) confirmed the presence of iron-oxide nanoparticles inside the cells. During the first week posttransplantation, the transplanted cells migrated to the lesion site and populated the border zone of the damaged cortical tissue. The implanted cells were visible on MR images as a hypointense area at the injection site and in the lesion. The hypointense signal persisted for more than 50 days. The presence of BrdU-positive and iron-containing cells was confirmed by subsequent histological staining. Three to 4 weeks after injection, <3% of MSCs around the lesion expressed the neuronal marker NeuN. Our study demonstrates that a commercially available contrast agent can be used as a marker for the long-term noninvasive MR tracking of implanted cells.