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Molecular Imaging |
1 From Laboratoire d’Imagerie Moléculaire et Fonctionnelle, Équipes de Recherche Technologique, Centre National de la Recherche Scientifique (C.B., O.H., C.T.W.M., N.G.), Institut National de la Santé et de la Recherche Médicale E362 (A.D., J. Rosenbaum), and Centre National de la Recherche Scientifique, Formation de Recherche en Évolution 2617 (A.S., C.G., Z.I., J. Ripoche), Univ Victor Segalen Bordeaux-2, 146 rue Leo Saignat, Case 117, 33076 Bordeaux, France; Institut National de la Santé et de la Recherche Médicale U 441, Pessac, France (Y.D., I.D., C.C.); Etablissement Français du Sang Aquitaine-Limousin, Bordeaux, France (Z.I.); Laboratoire d’Hématopoïèse, Univ de Tours, Tours, France (P.C.); and Inst for Cell Engineering and Dept of Radiology and Radiological Science, Johns Hopkins Univ School of Medicine, Baltimore, Md (J.W.M.B.). Received Oct 23, 2003; revision requested Jan 13, 2004; revision received Feb 29; accepted Mar 29. Address correspondence to C.B. (e-mail: clemens@imf.u-bordeaux2.fr).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: This study was conducted in accordance with French law governing animal research and met guidelines for animal care and use. Rat MSCs were labeled with SPIO and transfection agent. Relaxation rates at 1.5 T, cell viability, proliferation, differentiation capacity, and labeling stability were assessed in vitro as a function of SPIO concentration. MSCs were injected into renal arteries of healthy rats (labeled cells in four, unlabeled cells in two) and portal veins of rats treated with carbon tetrachloride to induce centrolobular liver necrosis (labeled cells and unlabeled cells in two each). Follow-up serial T2*-weighted gradient-echo MR imaging and R2* mapping were performed. MR imaging findings were compared histologically.
RESULTS: SPIO labeling caused a strong R2* effect that increased linearly with iron dose; R2* increase for cells labeled for 48 hours with 50 µg of iron per milliliter was 50 sec–1 per million cells per milliliter. R2* was proportional to iron load of cells. SPIO labeling did not affect cell viability (P > .27). Labeled cells were able to differentiate into adipocytes and osteocytes. Proliferation was substantially limited for MSCs labeled with 100 µg Fe/mL or greater. Label half-life was longer than 11 days. In normal kidneys, labeled MSCs caused signal intensity loss in renal cortex. After labeled MSC injection, diseased liver had diffuse granular appearance. Cells were detected for up to 7 days in kidney and 12 days in liver. Signal intensity loss and fading over time were confirmed with serial R2* mapping. At histologic analysis, signal intensity loss correlated with iron-loaded cells, primarily in renal glomeruli and hepatic sinusoids; immunohistochemical analysis results confirmed these cells were MSCs.
CONCLUSION: MR imaging can aid in monitoring of intravascularly administered SPIO-labeled MSCs in vivo in kidney and liver.
© RSNA, 2004
Index terms: Kidney, MR, 81.121411, 81.121412 • Liver, MR, 761.121411, 761.121412 • Stem cells
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MSCs can be isolated, notably from bone marrow, by using established protocols (8). They easily can be expanded in vitro (9) and can colonize many organs, such as the liver and the kidney, after grafting (10). In addition, there is a high likelihood that they could differentiate into hepatic stellate and renal mesangial cells that are cells of mesenchymal origin, although this process has not been fully demonstrated, to our knowledge (11,12). It is thus noteworthy that mesangial cells were found to arise from donor cells after bone marrow transplantation (13,14). Therefore, MSCs are potentially important vectors for cell and gene therapy in the liver or the kidneys.
In the heart and central nervous system, cells have been implanted locally and have provided a high concentration of labeled cells; this high concentration is reflected at T2- or T2*-weighted magnetic resonance (MR) imaging as a low-signal-intensity spot within an otherwise unaffected signal intensity of the receiving tissue. The combination of magnetic cell labeling and MR imaging has allowed demonstration of cell migration away from the injection site; an account of the migration of embryonic stem cells and neural progenitor cells after local implantation was given by Hoehn et al (5) and Bulte et al (3), respectively. Yet, cell migration was limited to a few millimeters per week, and this limitation rendered cell therapy of an entire organ problematic.
Intravascular administration of stem cells would be attractive to achieve distribution in a whole organ, which is an important aspect of cell therapy applications in diffuse diseases, especially for diseases of organs such as the kidney or the liver that are clinically accessible through the intravascular route. To our knowledge, no studies of tracking by using MR imaging of intravascularly injected SPIO-labeled stem cells in the liver or the kidneys have been performed. Thus, the purpose of our study was to evaluate in vivo MR imaging with a conventional 1.5-T MR imaging unit for depiction and tracking of SPIO-labeled MSCs after local intravascular injection.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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-Eagle minimum essential medium (Invitrogen, Cergy Pontoise, France) and penicillin, streptomycin, and glutamine (Gibco-Invitrogen, Cergy-Pontoise, France), with 10% fetal calf serum (Hyclone, Logan, Utah). Membranous antigen expression on MSCs was determined by using fluorescence-activated cell sorter analysis with a flow cytometer equipped with software (EPICS XL with Expo 32 analysis software; Coulter, Villepinte, France). Cells were harvested with a combination of trypsin and ethylenediaminetetraacetic acid and stained for CD45 and CD90 by using mouse antirat CD45 or CD90 antibodies (BD Biosciences Pharmingen, Le Pont de Claix, France) or an isotype-matched control, followed by fluorescein isothiocyanate–conjugated goat antimouse immunoglobulin. SH3 expression was assessed by using phycoerythrin-conjugated anti-SH3 antibody (BD Biosciences Pharmingen) or an isotype-matched phycoerythrin-conjugated antibody.
Multipotency was assessed by inducing osteogenic and adipogenic differentiation, as described previously (8,15). Briefly, MSCs were plated in six-well chamber slides. For osteogenic assays, cells were plated at 3000 cells per square centimeter. From the day following plating (day 0), cells were subsequently grown without (control) or with osteogenic supplements (dexamethasone, 10–7 mol/L; sodium ß-glycerophosphate, 10 mmol/L; and L-ascorbic acid-2-phosphate, 0.05 mmol/L [Sigma Aldrich, St Quentin Fallavier, France]). Medium was changed twice a week, and at day 14, cultures were assayed for osteogenic differentiation. Alkaline phosphatase enzyme activity was detected by using an alkaline phosphatase detection kit (Sigma Aldrich). Mineralization was visualized by means of von Kossa staining after cell fixation in methanol. Osteopontin expression was assessed by using immunoperoxidase staining with goat polyclonal antibody (clone P-18; Santa Cruz, Santa Cruz, Calif). For adipogenic assays, induction medium that contained 0.5 mmol/L of methyl-isobutylxanthine, 10–6 mol/L of dexamethasone, 100 µmol/L of indomethacin, and 100 ng/mL of insulin (Sigma Aldrich) was added to standard MSC medium; adipogenic maintenance medium contained only 100 ng/mL of insulin. When cells reached confluence, induction was made by using standard MSC medium for 3 days, adipogenic maintenance medium for 1 day, standard MSC medium for another 3 days, and finally adipogenic maintenance medium for 7 days, before fixation at day 14. Lipid vacuoles were stained with oil red O after fixation in methanol. Nuclear antigen peroxisome-proliferator-activated receptor gamma detection was performed after formalin fixation by using immunoperoxidase staining with mouse monoclonal antibody (clone E-8; Santa Cruz).
In Vitro Cell Labeling
First, the effect of SPIO concentration on labeling efficiency, cell viability, and proliferation was studied. Cells were labeled by using a protocol adapted from Frank et al (16). Cells were grown to confluence in six 25-cm2 flat-bottom flasks and labeled by means of incubation for 48 hours with a combination of an SPIO preparation (Endorem; Guerbet Group, Aulnay-sous-Bois, France) and a dendrimer transfection agent (Superfect; Qiagen, Hilden, Germany). Iron concentration varied with a range of 0–200 µg of iron per milliliter. After labeling, cells were counted, and cell viability was checked by means of trypan blue stain exclusion. A clear suspension of about 2.5 x 106 labeled cells was made in 1 mL of 2% wt/wt gelatin for MR imaging relaxation measurements. Then, the gel contents of the six flasks were liquefied and diluted 10-fold for determination of the iron content of the cells in picograms per cell by using inductively coupled plasma optical emission spectrometry (150 AX Turbo; Varian, Palo Alto, Calif).
To assess the effect of iron loading on cell proliferation, labeled cells were replated at 6 x 105 cells per 25-cm2 flask, and cells were counted after 6 days of culturing. Labeling efficiency was assessed with determination of the percentage of Perls Prussian blue stain–positive cells, after cells were labeled at 25, 50, and 100 µg Fe/mL. Finally, the location of the SPIO particles within the cells was examined with an 80-kV electron microscope (Tecnai CM10; FEI, Eindhoven, the Netherlands) in cells labeled with 50 µg Fe/mL.
For a study of labeling stability, cells were labeled by means of incubation with 50 µg Fe/mL and 0.01% transfection agent for 48 hours. Twelve aliquots of 105 cells were used, two of which were prepared for immediate MR imaging. The other samples were replated in duplicate in 25-cm2 flat-bottom flasks. After 1, 2, 4, 7, and 11 days, cells were washed three times, treated with trypsin, and counted, and membrane integrity was verified with trypan blue stain exclusion. After centrifugation, all cells were then suspended in gelatin for MR relaxation measurements. Here, we used the premise that we were operating in the static dephasing regimen and R2* was a measure of the total iron content of the sample (17).
To verify differentiation ability after SPIO labeling, control medium or differentiation-inducing medium was used for unlabeled cells and cells that had been labeled with 50 µg Fe/mL and 0.01% transfection agent for 48 hours.
Animal Experiments
This study was conducted in accordance with the French law governing animal research and met the guidelines for animal care and use. For all manipulations, rats were anesthetized with an intraperitoneal injection of 0.5 mL of chloral hydrate (Sigma Aldrich) at 8% wt/wt per 100 g body weight.
Cells were prepared for injection by labeling with the transfection agent (0.01%) and SPIO at 50 µg Fe/mL for 48 hours. Then cells were washed three times with phosphate-buffered saline, treated with trypsin, washed twice by using centrifugation at 300g for 5 minutes, and counted. Finally, cells were spun down and suspended in phosphate-buffered saline for injection.
Cells were injected by teams of two investigators. For cell grafting in the kidney, one team (Y.D., A.D.) injected (5–6) x 105 labeled (n = 4) or unlabeled (n = 2) cells diluted in 300–400 µL phosphate-buffered saline into the left renal artery in healthy 300-g Lewis 1A rats (n = 6). The left renal artery was accessed through a 2-cm lateral incision in the abdominal wall, and the renal vascular pedicle was exposed by lifting the kidney out of the abdominal cavity. Cells were injected by using a 30-gauge needle and magnifying binoculars. Rats were imaged before MSC injection and immediately after MSC injection. Initially, a 4-, 8-, and 12-day imaging follow-up schedule was foreseen, but results in the first animal made us resort to a tighter 2-, 4-, and 7-day schedule. Rats were sacrificed after 7 days or sooner when the fading of the signal intensity decrease on T2*-weighted MR images made the kidney indistinguishable from the kidney observed on the baseline image. The kidneys were then prepared for ex vivo imaging.
For cell grafting in the liver, the other team (A.D., J. Ripoche) administered carbon tetrachloride in olive oil (375 µL/kg body weight) orally to 180-g Lewis 1A rats (n = 4) to induce hepatocyte necrosis and inflammation around centrolobular veins. After 2 days, the rats received an injection of 5 x 106 labeled (n = 2) or unlabeled (n = 2) MSCs in 300–500 µL of phosphate-buffered saline. The abdomen of the rats was opened, and cells were injected into the portal vein with a 30-gauge needle. Rats underwent MR imaging of the liver immediately before and after MSC injection and at 4, 8, and 12 days after MSC injection. After 12 days, rats were sacrificed, and the liver was prepared for ex vivo MR imaging.
For ex vivo MR imaging and histologic analysis, organs of interest were thoroughly perfused with phosphate-buffered saline, to remove circulating cells, and then perfusion with 4% paraformaldehyde in phosphate-buffered saline was performed. The kidneys or the liver was then removed, and MR imaging was performed. All samples were fixed in 4% paraformaldehyde and embedded in paraffin.
Relaxation Measurements and MR Imaging
All MR imaging experiments were performed with a 1.5-T clinical unit (Gyroscan Intera; Philips, Best, the Netherlands). The R2 (or 1/T2) of the embedded cell samples was determined by using a multiple spin-echo sequence, with 32 echoes and echo spacing of 7 msec. The R2* (or 1/T2*) was determined by using a multiple gradient-echo sequence, with repetition time of 500 msec, flip angle of 30°, and 25 echoes acquired with an echo spacing of 2.5 msec starting at 2.8 msec.
In rats, baseline and serial follow-up MR imaging were performed. The in vivo MR imaging protocol consisted of a fat-suppressed T2*-weighted multisection gradient-echo sequence, a T2*-weighted three-dimensional gradient-echo sequence, and a quantitative multisection multiple gradient-echo technique for R2* mapping. Rats that received an injection in the left renal artery were imaged in the decubitus position, with the left kidney on a 47-mm surface coil and saturation slabs placed cranially and caudally to the imaging volume to reduce motion artifacts. The ex vivo imaging protocol included acquisition of a single T2*-weighted three-dimensional volume image, with a 23-mm surface coil for signal reception. Further details about the imaging parameters can be found in the Table.
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Image Analysis
The multisection multiple-echo quantitative R2 and R2* data were evaluated by using software (IDL; RSI, Boulder, CO). R2* (or R2) was determined by fitting an exponential decay to the magnitude of the signal intensity. Regions of interest (30–130 pixels in the renal cortex, 250–1000 pixels per liver lobe) were placed in consensus during a reading by a radiologist and an MR imaging physicist (N.G., C.B.). They placed these regions while trying to avoid those that were overtly affected by large-scale susceptibility effects that arose from air-tissue interfaces in the bowels and the lungs. The overall R2* was then obtained by determining the weighted (with respect to the number of pixels) average of the R2* values in the individual sections. For kidney, R2* values were determined in the renal cortex, renal medulla, and dorsal muscle. For liver, R2* values were determined in the median and right lobe of the liver.
Histologic Analysis
Analyses were performed by two authors (Y.D., A.D.), who had 5 and 15 years of experience, respectively, with histologic analysis and immunohistochemical analysis. Sections were stained with hematoxylin-eosin for routine histologic analysis. To assess MSC localization, paraffin-embedded serial microsections were used for Perls Prussian blue staining and subsequent immunostaining. In the kidney, expression of smooth muscle–-actin was assessed with a monoclonal antibody (clone 1A4; Sigma Aldrich). In the liver sections, CD90 antigen expression was evaluated by using immunoperoxidase analysis with an anti-CD90 antibody (BD Biosciences Pharmingen).
Statistical Analysis
In the dose-effect and proliferation experiment, cell numbers were determined as the average of four counts plus or minus the standard deviation. Cell counts for labeled cells were compared with those for unlabeled cells by using a two-tailed t test. A P value of less than .05 was considered to indicate a significant difference. Coefficients of determination (R2) were calculated with linear regression analysis to characterize the relationships among R2* per cell per milliliter, iron concentration in the medium during labeling, and iron load per cell.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Observations after in Vitro Cell Labeling
Immediately after SPIO labeling, we did not observe any significant differences in the number of cells (P > .39) or in cell viability (P > .27) between the iron-loaded cells and control cells for iron concentrations up to 200 µg/mL. The R2* effect was about 30 times stronger than was the R2 effect, and it in-creased linearly (R2 = 0.996, P < .001) with the iron concentration in the medium (Fig 1a). Relaxation effects were also proportional (R2 = 0.971, P < .001) to the iron load of the cells, as measured with inductively coupled plasma optical emission spectrometry. For 25, 50, and 100 µg/mL after 48 hours, there were, respectively, an average 91.5 ± 4.1 (standard deviation), 98.4 ± 2.4, and 99.1 ± 1.8 Perls Prussian blue stain–positive cells per 100 cells. The replating experiment resulted in a moderately reduced cell proliferation rate after labeling at 50 µg/mL (P < .002) (Fig 1b). At higher iron concentrations, this reduction became important, which indicated that iron concentration should preferably remain less than 100 µg/mL. On the basis of these results, we adopted a labeling protocol with an iron concentration of 50 µg/mL that had given an iron load of 1.5 pg per cell and an R2 change of 50 sec–1 per million cells per milliliter. Findings in studies of the stability of SPIO labeling showed that after 11 days of culturing, the samples retained greater than 50% of their relaxation effect (Fig 1c). At day 11, the number of cells had increased 16-fold; thus, per cell, the label was considerably diluted. Electron microscopy showed the SPIO to be present in endosomal vesicles (Fig 2).
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-actin immunoperoxidase staining confirmed that these cells were labeled MSCs: the cells that were positive for smooth muscle–-actin had a distribution pattern that was identical to that of the Perls Prussian blue stain–positive cells on an adjacent microsection (Fig 5, B). The only cells that are positive for smooth muscle–-actin in the normal kidney are vascular smooth muscle cells, whereas glomerular tufts are negative for this antigen (18). Since MSCs express smooth muscle–-actin constitutively (19,20), cells positive for smooth muscle–-actin seen in glomeruli are grafted MSCs. Most MSCs were localized in the glomeruli, but some were also observed in the interstitial tissue and under the renal capsule in the injected territory. The noninjected vascular territory and contralateral kidney did not show any Perls Prussian blue stain–positive cells in the parenchyma or cells positive for smooth muscle–-actin in the glomeruli.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The results of in vitro labeling of rat MSCs agree with those of other studies that show the usefulness of iron oxide preparations to label lymphocytes (16,21–24), neural progenitor cells (3,4,22,25), hematopoietic progenitor cells (22,26,27), tumor cells (4,16), embryonic stem cells (5), and human and swine MSCs (4,6,7,16) for noninvasive visualization of cells with MR imaging. The iron load per cell was lower than that achieved by Frank et al (16) for human MSCs with use of the same transfection agent–SPIO combination, and this finding may be related to the higher dose of transfection agent used in that study (1:1250 dilution [Frank et al] vs 1:10 000 dilution [our study]).
Labeled MSCs were able to differentiate, as also was reported recently by Hill et al (7) in their study about swine MSCs. Differentiation potential, either in vitro or in vivo, after iron oxide labeling has also been reported for other types of stem cells, hematopoietic progenitors (22), neural stem cells (4), and embryonic stem cells (5). Since MSCs are to be used in cell therapy protocols, where they are expected to differentiate in order to regenerate damaged tissues, conservation of differentiation capacities is essential. Furthermore, SPIO labeling can be performed without alteration of the proliferation capacities of the MSCs, and incorporation of the SPIO within the endosomal compartment is relatively stable over time.
To our knowledge, for the first time the local intravascular route for cell grafting allowed visualization of SPIO-labeled MSCs within kidney and liver parenchyma with in vivo MR imaging. For future cell therapy purposes, local vascular administration is attractive because a large number of cells are directly delivered to the target organ and can be distributed throughout the organ with a single injection. The selective distribution of MSCs within the rat kidney, in our study, was related to the injection downstream of the renal artery trunk. The use of interventional radiology techniques can provide minimally invasive access to the renal artery and to the portal vein, as well as radiologic control of the injection, and would thus allow a diffuse and homogeneous delivery of cells to these organs.
Alternatively, we may inject cells intravenously and then rely on cell homing to accumulate cells where they are needed, such as in the kidney. Visualization at MR imaging of intravenously injected cells by using magnetically labeled mouse T lymphocytes both ex vivo (24) and in vivo (23) has been reported. Only recently has in vivo MR imaging of homing of MSCs to the heart been demonstrated in a rat model of myocardial ischemia (28).
So far, in most studies about MR imaging of grafted stem cells, the cells were locally implanted into the rat brain and spine (3–5,29) and the porcine heart (6,7). After implantation, cells are concentrated in a small volume rather than being dispersed throughout the target organ, as occurs after intravascular injection. In the weeks after implantation, cells were observed to migrate (3–5), but only at a rate of a few millimeters a week, and treatment of an entire organ would require many injections (6,7). This invasive approach seems more appropriate for localized diseases within an organ, and mostly if perfusion of these areas is compromised, as in myocardial or brain ischemia.
Several approaches have been proposed to label cells for visualization at MR imaging. Most authors describe the use of custom-made or commercially available iron oxide particles that locally disturb the magnetic field and at high field strength have a negligible R1 but a strong R2 and R2* effect (3–7,16,22,24,25,29–31). For clusters of iron oxide particles, such as those that occur in cell suspensions, the R2* effect becomes much stronger than the R2 effect (17): R2* was 30 times higher than was R2 in our study. Therefore, we used R2*-based imaging methods that depict accumulated cells as a pronounced local signal intensity loss. The susceptibility effect of the iron oxide label extends well outside the volume occupied by the cell, and this extension augments its detectability. T2*-weighted imaging, however, is sensitive to susceptibility artifacts from air-tissue interfaces, and the negative contrast may confound other causes of low signal intensity. Nevertheless, the typical granular appearance of rat kidney and liver on the T2*-weighted images allowed us to reliably distinguish MSCs from these confounding effects. To obtain T1-based positive contrast by labeling with paramagnetic ions, the protons are required to be in close proximity to the cell, and this requirement limits the volume affected (26). Still, particles that carry many thousands of gadolinium atoms and that can detect molecules in nanomolar range concentrations have been conceived, but their utility for cell labeling remains to be determined (32).
R2* quantitation provides a measure independent of image windowing to demonstrate the presence of MSCs. Bowen et al (17) demonstrated that a simple linear relationship exists between the iron concentration and R2* change in vitro for cell suspensions where the magnetic material is distributed in clusters that are large with respect to the diffusion length of the surrounding water. In our study, the R2* increase measured in the liver was of the right order to correspond to the number of MSCs injected in the portal vein. However, R2*-based quantification of the number of cells in vivo remains complicated, especially in longitudinal studies. First, the R2* measurement is influenced by the position of air-tissue interfaces with respect to the organ studied and by respiratory and bowel motion. Precision of the R2* measurement is limited by random noise. Second, the iron load of cells after labeling is variable, and, once in the animal, cells divide and die; moreover, this behavior has a yet unknown effect on the iron load per cell. Finally, baseline R2 and R2* may change as a consequence of disease, healing, and iron metabolism.
For kidneys, MSCs were found preferentially within glomeruli. This might be related to cells being mechanically trapped in the normal glomerular tuft. Therefore, it is tempting to speculate that, in cortical renal diseases, this prolonged trapping could help in getting MSCs attracted through the endothelial barrier to reach the target zones. However, this cortical trapping could limit the use of this technique for cellular repair within the medulla; the observed absence of MSCs within this compartment is probably related to its postcapillary (portal type) vascularization.
After injection into the portal vein, MSCs were observed to be diffusely distributed in the liver. However, MSCs were particularly present along sinusoids where the cells could be mechanically trapped, and this trapping is similar to what happens in glomerular capillary tuft. Isolated and/or small groups of cells were observed in portal tracts and close to centrolobular veins. Hence, intraportal injection for MSC grafting in the liver would be appropriate for cell therapy for sinusoidal diseases and, maybe to a lesser extent, for diseases that affect the portal tract.
There were some limitations to this study. First, the number of animals in this study was small. The number was sufficient, however, to achieve our main objective; that is, with the number, we were able to demonstrate that the presence of SPIO-labeled MSCs can be confidently confirmed after intravascular grafting. Evaluation of differences of cell grafting between normal and diseased organs was beyond the scope of these experiments and would require larger experimental groups. Second, the follow-up was limited to 7 or 12 days. Therefore, the fate of the cells and the SPIO label in the long term is not known, in particular if correspondence between signal intensity loss and MSCs is maintained. Third, only the target organs were imaged because of coil sensitivity constraints. Additional imaging of, for example, the spleen and the liver might shed light on the destination of iron cells that are leaving the target organs, as witnessed by the R2* measurements. Fourth, the reproducibility of the iron load per cell of the labeling protocol was not systematically examined. This is essential as soon as quantification of the number of cells from R2* effects is attempted.
Practical application: Intravascular administration of cells is a viable way to seed cells throughout a target organ, and this process holds potential for application in future cell therapy protocols. Iron labeling of MSCs and visualization at MR imaging have utility for development and evaluation of the transplantation procedures used for cell therapy, since the success of cell therapy will depend on the local availability of stem cells for tissue regeneration or transgene expression (1,2). The combination of the techniques provides a means to deliver cells and immediately verify whether the cells have indeed grafted within the target organ. Possibly, MR imaging may allow an estimation of the number of cells that were seeded. Finally, sequential MR imaging may allow assessment of the permanence of the grafted cells over time.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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See also Science to Practice in this issue.
Authors stated no financial relationship to disclose.
Author contributions: Guarantors of integrity of entire study, C.B., Y.D., J. Ripoche; study concepts, all authors; study design, C.B., Y.D., J. Ripoche, N.G., C.T.W.M., C.C., A.D.; literature research, C.B., Y.D., A.D.; experimental studies, C.B., Y.D., A.D., A.S., Z.I., I.D., O.H., J. Ripoche; data acquisition, C.B., Y.D., J. Ripoche, N.G., A.D., A.S.; data analysis/interpretation, C.B., Y.D., A.D., J. Ripoche, N.G.; manuscript preparation, C.B., Y.D., A.D., J. Ripoche; manuscript definition of intellectual content, C.B., Y.D., A.D., J. Ripoche, N.G., A.S., C.C., C.T.W.M., J. Rosenbaum; manuscript editing, C.B., Y.D., J. Ripoche, N.G.; manuscript revision/review, C.B., Y.D., N.G.; manuscript final version approval, all authors.
C.B. and Y.D. contributed equally to this work.
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U. Mahmood Can MR Imaging Be Used to Track Delivery of Intravascularly Administered Stem Cells? Radiology, December 1, 2004; 233(3): 625 - 626. [Full Text] [PDF]
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