Comparison of iron oxide labeling properties of hematopoietic progenitor cells from umbilical cord blood and from peripheral blood for subsequent in vivo tracking in a xenotransplant mouse model XXX

Labeling Human Melanoma Cells With SPIO: In Vitro Observations

Objectives:

To use the superparamagnetic iron oxide (SPIO) contrast agent Resovist (±transfection agent) to label human melanoma cells and determine its effects on cellular viability, microstructure, iron quantity, and magnetic resonance imaging (MRI) detectability.

Materials and Methods:

Human SK-Mel28 melanoma cells were incubated with Resovist (±liposomal transfection agent DOSPER). The cellular iron content was measured, and labeled cells were examined at 1.5 T and 3.0 T. The intracellular and extracellular distributions of the contrast agent were assessed by light and electron microscopy.

Results:

The incubation of melanoma cells with SPIO does not interfere with cell viability or proliferation. The iron is located both intracellularly and extracellularly as iron clusters associated with the exterior of the cell membrane. Despite thorough washing, the extracellular SPIO remained associated with the cell membrane. The liposomal transfection agent does not change the maximum achievable cellular iron content but promotes a faster iron uptake. The MRI detectability persists for at least 7 days.

Conclusion:

The transfection agent DOSPER facilitates the efficient labeling of human metastatic melanoma cells with Resovist. Our findings raise the possibility that other Resovist-labeled cells may collect associated extracellular nanoparticles. The SPIO may be available to other iron-handling cells and not completely compartmentalized during the labeling procedure.

Manganese-impregnated mesoporous silica nanoparticles for signal enhancement in MRI cell labelling studies

Mesoporous silica nanoparticles (MSNs) are used in drug delivery and cell tracking applications. As Mn(2+) is already implemented as a "positive" cell contrast agent in preclinical imaging procedures (in the form of MnCl2 for neurological studies), the introduction of Mn in the porous network of MSNs would allow labelling cells and tracking them using MRI. These particles are in general internalized in endosomes, an acidic environment with high saline concentration. In addition, the available MSN porosity could also serve as a carrier to deliver medical/therapeutic substances through the labelled cells. In the present study, manganese oxide was introduced in the porous network of MCM-48 silica nanoparticles (Mn-M48SNs). The particles exhibit a narrow size distribution (~140 nm diam.) and high porosity (~60% vol.), which was validated after insertion of Mn. The resulting Mn-M48SNs were characterized by TEM, N2 physisorption, and XRD. Evidence was found with H2-TPR, and XPS characterization, that Mn(II) is the main oxidation state of the paramagnetic species after suspension in water, most probably in the form of Mn-OOH. The colloidal stability as a function of time was confirmed by DLS in water, acetate buffer and cell culture medium. In NMR data, no significant evidence of Mn(2+) leaching was found in Mn-M48SNs in acidic water (pH 6), up to 96 hours after suspension. High longitudinal relaxivity values of r1 = 8.4 mM(-1) s(-1) were measured at 60 MHz and 37 °C, with the lowest relaxometric ratios (r2/r1 = 2) reported to date for a Mn-MSN system. Leukaemia cells (P388) were labelled with Mn-M48SNs and nanoparticle cell internalization was confirmed by TEM. Finally, MRI contrast enhancement provided by cell labelling with escalated incubation concentrations of Mn-M48SNs was quantified at 1 T. This study confirmed the possibility of efficiently confining Mn into M48SNs using incipient wetness, while maintaining an open porosity and relatively high pore volume. Because these Mn-labelled M48SNs express strong "positive" contrast media properties at low concentrations, they are potentially applicable for cell tracking and drug delivery methodologies.

The therapeutic potential of umbilical cord mesenchymal stem cells in mice premature ovarian failure

Mesenchymal stem cells, which are poorly immunogenic and have potent immunosuppressive activities, have emerged as promising cellular therapeutics for the treatment of several diseases. Mesenchymal-like cells derived from Wharton's Jelly, called umbilical cord matrix stem cells (UCMSCs), reportedly secrete a variety of cytokines and growth factors, acting as trophic suppliers. Here, we used UCMSCs to treat premature ovarian failure (POF). Ovarian function was evaluated by ovulation and the number of follicles. Apoptosis of the granulosa cells (GC) was analyzed by TUNEL staining. We found that after transplantation of the UCMSCs, apoptosis of cumulus cells in the ovarian damage model was reduced and the function of the ovary had been recovered. The sex hormone level was significantly elevated in mice treated with UCMSCs. The number of follicles in the treated group was higher than in the control group. Our results demonstrate that UCMSCs can effectively restore ovary functionality and reduce apoptosis of granulosa cells. We compared the RNA expression of the UCMSCs treated group with the POF model and wild-type control group and found that the UCMSC group is most similar to the wild-type group. Our experiments provide new information regarding the treatment of ovarian function failure.

MnO-labeled cells: positive contrast enhancement in MRI

Manganese oxide (MnO) nanoparticles have been suggested as a promising "positive" MRI contrast agent for cellular and molecular studies. Mn-based contrast agents could enable T(1)-weighted quantitative cell tracking procedures in vivo based on signal enhancement. In this study, ultrasmall MnO particles were synthesized and coated with thiolated molecules (DMSA) and polyethylene glycol (PEG) to allow enhanced cell labeling properties and colloidal stability. This coating allowed the fabrication of individual ultrasmall nanoparticles of MnO (USPMnO) as well as of nanoaggregates of the same material (SPMnO). Particle size was measured by TEM and DLS. Physico-chemical properties were characterized by XPS and FTIR. The relaxometric properties of these aqueous suspensions were measured at various magnetic fields. The suspensions provided strong positive contrast enhancement in T(1)-weighted imaging due to high longitudinal relaxivities (r(1)) and low r(2)/r(1) ratios (USPMnO: r(1) = 3.4 ± 0.1 mM(-1)s(-1), r(2)/r(1) = 3.2; SPMnO: r(1) = 17.0 ± 0.5 mM(-1)s(-1), r(2)/r(1) = 4.0, at 1.41T). HT-1080 cancer cells incubated with the contrast agents were clearly visualized in MRI for Mn contents >1.1 pg Mn/cell. The viability of cells was not affected, contrarily to cells labeled with an equivalent concentration of Mn(2+) ions. A higher signal per cell was found for SPMnO-labeled compared with USPMnO-labeled cells, due to the higher relaxometric properties of the agglomerates. As a result, the "positive" signal enhancement effect is not significantly affected upon agglomeration of MnO particles in endosomes. This is a major requirement in the development of reliable cell tracking procedures using T(1)-weighted imaging sequences. This study confirms the potential of SPMnO and USPMnO to establish more quantitative cell tracking procedures with MRI.

Efficient and rapid uptake of magnetic carbon nanotubes into human monocytic cells: implications for cell-based cancer gene therapy

Monocyte-based gene therapies in cancer have been hampered by either the resistance of these cells to non-viral molecular delivery methods or their poor trafficking to the tumor site after their ex vivo manipulations. Magnetic nanoparticles (MNP)-loaded genetically engineered monocytes can efficiently delivered to tumor site by external magnetic field, but they are not ideal delivery tools due to their spherical shape. Hence, we have investigated the cellular uptake efficiency and cytotoxicity of fluorescein isothiocyanate (FITC)-labelled magnetic carbon nanotubes (FITC-mCNT) in human monocytic leukemia cell line THP-1 for application in cell-based gene therapy against cancer. Uptake of FITC-mCNT into THP-1 cells reached 100% only 1 h after the delivery. Confocal imaging confirmed that FITC-mCNT entered the cell cytoplasm and even into the nucleus. FITC-mCNT uptake did not compromise cell viability. This delivery system might therefore enhance cell-based cancer gene therapies.

Magnetic resonance imaging of ferumoxide-labeled mesenchymal stem cells in cartilage defects: in vitro and in vivo investigations

The purpose of this study was to (1) compare three different techniques for ferumoxide labeling of mesenchymal stem cells (MSCs), (2) evaluate if ferumoxide labeling allows in vivo tracking of matrix-associated stem cell implants (MASIs) in an animal model, and (3) compare the magnetic resonance imaging (MRI) characteristics of ferumoxide-labeled viable and apoptotic MSCs. MSCs labeled with ferumoxide by simple incubation, protamine transfection, or Lipofectin transfection were evaluated with MRI and histopathology. Ferumoxide-labeled and unlabeled viable and apoptotic MSCs in osteochondral defects of rat knee joints were evaluated over 12 weeks with MRI. Signal to noise ratios (SNRs) of viable and apoptotic labeled MASIs were tested for significant differences using t-tests. A simple incubation labeling protocol demonstrated the best compromise between significant magnetic resonance signal effects and preserved cell viability and potential for immediate clinical translation. Labeled viable and apoptotic MASIs did not show significant differences in SNR. Labeled viable but not apoptotic MSCs demonstrated an increasing area of T2 signal loss over time, which correlated to stem cell proliferation at the transplantation site. Histopathology confirmed successful engraftment of viable MSCs. The engraftment of iron oxide-labeled MASIs by simple incubation can be monitored over several weeks with MRI. Viable and apoptotic MASIs can be distinguished via imaging signs of cell proliferation at the transplantation site.

Ultra-fast method to synthesize mesoporous magnetite nanoclusters as highly sensitive magnetic resonance probe

An ultra-fast method to synthesize mesoporous magnetite (Fe(3)O(4)) nanoclusters is reported. These mesoporous magnetite can be used as a highly sensitive magnetic resonance imaging (MRI) probe. The nanoclusters were synthesized by reducing iron (III) acetylacetonate with hydrazine in ethylene glycol under microwave irradiation and only 5 min was needed in the synthesis. The diameter of the nanoclusters could be controlled effectively between 75 nm and 115 nm by increasing the amount of iron (III) acetylacetonate. Brunauer-Emmett-Teller (BET) results reveal a mesoporous structure and a large surface area of 72.3 m(2) g(-1). Cytotoxicity test performed in HepG2 cell line indicated that the as-prepared nanoclusters were non-cytotoxic. The nanoclusters exhibited an enhanced T(2) relaxivity value of 417.4±29.9 s(-1) mM(-1). In vitro and in vivo MRI confirmed the high sensitivity of the magnetite nanoclusters as MRI probe. The biodistribution of the nanoclusters in rat liver and spleen after intravenous injection was also investigated.

Umbilical cord blood mononuclear cell transplantation for neonatal hypoxic-ischemic encephalopathy

Despite recent advances in the treatment of neonatal hypoxic-ischemic encephalopathy (HIE) using therapeutic hypothermia, at least 30% of the cooled infants will die or have moderate/severe neurological disability. Umbilical cord blood cells (UCBCs), which are readily available at birth, have been shown to reduce sensorimotor and/or cognitive impairments in several models of brain damage, representing a promising option for the treatment of neurological diseases. In this review, we discuss recent preclinical studies that assessed the effects of UCBC transplantation in the Rice-Vannucci animal model of HIE. We also review the possible cell types and mechanisms involved in the therapeutic effect of UCBC transplantation, including neuroprotection, immunomodulation, and stimulation of neural plasticity and regeneration. In addition, we discuss how neuroimaging methods, such as bioluminescence imaging, nuclear-medicine imaging, or magnetic resonance imaging, could be used to evaluate the biodistribution of UCBCs in both preclinical and clinical studies.

Magnetic resonance cell-tracking studies: spectrophotometry-based method for the quantification of cellular iron content after loading with superparamagnetic iron oxide nanoparticles

The purpose of this article is to present a user-friendly tool for quantifying the iron content of superparamagnetic labeled cells before cell tracking by magnetic resonance imaging (MRI). Iron quantification was evaluated by using Prussian blue staining and spectrophotometry. White blood cells were labeled with superparamagnetic iron oxide (SPIO) nanoparticles. Labeling was confirmed by light microscopy. Subsequently, the cells were embedded in a phantom and scanned on a 3 T magnetic resonance tomography (MRT) whole-body system. Mean peak wavelengths λ(peak) was determined at A(720 nm) (range 719-722 nm). Linearity was proven for the measuring range 0.5 to 10 μg Fe/mL (r  =  .9958; p  =  2.2 × 10(-12)). The limit of detection was 0.01 μg Fe/mL (0.1785 mM), and the limit of quantification was 0.04 μg Fe/mL (0.714 mM). Accuracy was demonstrated by comparison with atomic absorption spectrometry. Precision and robustness were also proven. On T(2)-weighted images, signal intensity varied according to the iron concentration of SPIO-labeled cells. Absorption spectrophotometry is both a highly sensitive and user-friendly technique that is feasible for quantifying the iron content of magnetically labeled cells. The presented data suggest that spectrophotometry is a promising tool for promoting the implementation of magnetic resonance-based cell tracking in routine clinical applications (from bench to bedside).

Efficient in vitro labeling rabbit neural stem cell with paramagnetic Gd-DTPA and fluorescent substance

OBJECTIVES

The aim of this study is to label rabbit neural stem cells (NSCs) by using standard contrast agents (Gd-DTPA) in combination with PKH26 and in vitro track them with MR imaging.

MATERIALS AND METHODS

NSCs from prenatal brains of rabbits were cultured and propagated. Intracellular uptake of Gd-DTPA was achieved by using a non-liposomal lipid transfection reagent (Effectene) as the transfection agent. After labeling with Gd-DTPA, cells were incubated with cellular membrane fluorescent dye PKH26. The labeling effectiveness and the longevity of Gd-DTPA maintenance were measured on a 1.5T MR scanner. The influence of labeling on the cellular biological behaviors was assessed by cellular viability, proliferation and differentiation assessment.

RESULTS

The labeling efficiency of Gd-DTPA was up to 90%. The signal intensity on T1-weighted imaging and T1 values of labeled cells were significantly higher than those of unlabeled cells (P<0.05). The minimal number of detectable cells for T1-weighted imaging was 5×10(3). Cellular uptake of Gd-DTPA was maintained until 15 days after initially labeling. There was no significant difference in the cellular viability and proliferation between the labeled and unlabeled NSCs (P>0.05). Normal glial and neuronal differentiation remained in labeled NSCs like unlabeled NSCs.

CONCLUSION

Highly efficient labeling NSCs with Gd-DTPA could be achieved by using Effectene. This method of labeling NSCs allows for tracking cells with MR imaging, and without alterations of cellular biological behaviors.

lacZ as a genetic reporter for real-time MRI

Molecular imaging based on MRI is currently hampered by the lack of genetic reporters for in vivo imaging. We determined that the commercially available substrate S-Gal can be used to detect genetically engineered beta-galactosidase expressing cells by MRI. The effect and specificity of the reaction between beta-galactosidase and S-Gal on MRI contrast were determined both in vitro and in vivo. beta-galactosidase activity in the presence of S-Gal resulted in enhanced T(2) and T*(2) MR-contrast, which was amplified with increasing magnetic field strengths (4.7-17.6 T) in phantom studies. Using both lacZ(+) transgenic animals and lacZ(+) tissue transplants, we were able to detect labeled cells in live animals in real time. Similar to phantom studies, detection of the labeled cells/tissues in vivo was enhanced at high magnetic fields. These results demonstrate that the genetic reporter, lacZ, can be used as an in vivo marker gene using high-field-strength MRI.

Magnetic carbon nanotube labelling for haematopoietic stem/progenitor cell tracking

Haematopoietic stem and progenitor cell (HSPC) research has significantly contributed to the understanding and harnessing of haematopoiesis for regenerative medicine. However, the methodology for real-time tracking HSPC in vivo is still lacking, which seriously restricts the progress of research. Recently, magnetic carbon nanotubes (mCNT) have generated great excitement because they have been successfully used as vehicles to deliver a lot of biomolecules into various cells. There is, however, no report about mCNT being used for tracking HSPC. In this paper, we investigated the uptake efficiency of fluorescein-isothiocyanate-labelled mCNT (FITC-mCNT) into HSPC and their effect on the cytotoxicity and differentiation of HSPC. We found that cellular uptake of FITC-mCNT was concentration-and time-dependent. The uptake of FITC-mCNT into HSPC reached up to 100% with the highest mean fluorescence (MF). More importantly, efficient FITC-mCNT uptake has no adverse effect on the cell viability, cytotoxicity and differentiation of HSPC as confirmed by colony-forming unit assay (CFU). In conclusion, the results reported here suggest the further tailoring of mCNT for their use in HSPC labelling/tracking in vivo or gene delivery into HSPC.

Accelerated stem cell labeling with ferucarbotran and protamine

OBJECTIVE

To develop and characterize a clinically applicable, fast and efficient method for stem cell labeling with ferucarbotran and protamine for depiction with clinical MRI.

METHODS

The hydrodynamic diameter, zeta potential and relaxivities of ferucarbotran and varying concentrations of protamine were measured. Once the optimized ratio was found, human mesenchymal stem cells (MSCs) were labeled at varying incubation times (1-24 h). Viability was assessed via Trypan blue exclusion testing. 150,000 labeled cells in Ficoll solution were imaged with T1-, T2- and T2*-weighted sequences at 3 T, and relaxation rates were calculated.

RESULTS

Varying the concentrations of protamine allows for easy modification of the physicochemical properties. Simple incubation with ferucarbotran alone resulted in efficient labeling after 24 h of incubation while assisted labeling with protamine resulted in similar results after only 1 h. Cell viability remained unaffected. R2 and R2* relaxation rates were drastically increased. Electron microscopy confirmed intracellular iron oxide uptake in lysosomes. Relaxation times correlated with results from ICP-AES.

CONCLUSION

Our results show internalization of ferucarbotran can be accelerated in MSCs with protamine, an approved heparin antagonist and potentially clinically applicable uptake-enhancing agent.

Imaging circulating cells and lymphoid tissues with iron oxide nanoparticles

The use of nanometer-sized iron oxide nanoparticles and micron-sized iron oxide particles as magnetic resonance (MR) contrast agents has garnered a high degree of interest in diverse areas of biology and medicine. Applications such as cell tracking, molecular imaging, gene detection, and lymphography are being explored to provide insight into disease mechanisms, monitor therapeutic efficacy, and facilitate diagnostic imaging. What makes iron oxide so appealing is a number of favorable properties including high detectability by MR, biodegradability and low toxicity. Here we describe the recent progress on the use of magnetic nanoparticles in imaging circulating cells and lymphoid tissues. The study of the lymph system and the biodistribution of various circulating immune cells is important in the diagnosis, prognosis, and treatment of a wide range of diseases and is expected to have a profound effect on patient outcome.

Stem cell therapy: MRI guidance and monitoring

With the recent advances in magnetic resonance (MR) labeling of cellular therapeutics, it is natural that interventional MRI techniques for targeting would be developed. This review provides an overview of the current methods of stem cell labeling and the challenges that are created with respect to interventional MRI administration. In particular, stem cell therapies will require specialized, MR-compatible devices as well as integration of graphical user interfaces with pulse sequences designed for interactive, real-time delivery in many organs. Specific applications that are being developed will be reviewed as well as strategies for future translation to the clinical realm.

In vivo imaging of transplanted hepatocytes with a 1.5-T clinical MRI system--initial experience in mice

The feasibility of in vitro mature mouse hepatocyte labeling with a novel iron oxide particle was assessed and the ability of 1.5-T magnetic resonance imaging (MRI) to track labeled mouse hepatocytes in syngenic recipient livers following intraportal cell transplantation was tested. Mouse hepatocytes were incubated with anionic iron oxide nanoparticles at various iron concentrations. Cell viability was assessed and iron oxide particle uptake quantified. Labeled hepatocytes were intraportally injected into 20 mice, while unlabeled hepatocytes were injected into two mice. Liver T2 values, spleen-to-muscle relative signal intensity (RI( spleen/muscle )), and liver-to-muscle relative signal intensity (RI( liver/muscle )) on gradient-echo T2-weighted imaging after injection of either labeled or unlabeled hepatocytes were compared with an ANOVA test followed by Fisher's a posteriori PLSD test. Livers, spleens and lungs were collected for histological analysis. Iron oxide particle uptake was saturable with a maximum iron content of 20 pg per cell and without viability alteration after 3 days of culture. Following labeled-cell transplantation, recipient livers showed well-defined nodular foci of low signal intensity on MRI--consistent with clusters of labeled hepatocytes on pathological analysis--combined with a significant decrease in both liver T2 values and liver-to-muscle RI( liver/muscle ) (P = 0.01) with minimal T2 values demonstrated 8 days after transplantation. Conventional MRI can demonstrate the presence of transplanted iron-labeled mature hepatocytes in mouse liver.

Fluorophore-conjugated iron oxide nanoparticle labeling and analysis of engrafting human hematopoietic stem cells

The use of nanometer-sized iron oxide particles combined with molecular imaging techniques enables dynamic studies of homing and trafficking of human hematopoietic stem cells (HSC). Identifying clinically applicable strategies for loading nanoparticles into primitive HSC requires strictly defined culture conditions to maintain viability without inducing terminal differentiation. In the current study, fluorescent molecules were covalently linked to dextran-coated iron oxide nanoparticles (Feridex) to characterize human HSC labeling to monitor the engraftment process. Conjugating fluorophores to the dextran coat for fluorescence-activated cell sorting purification eliminated spurious signals from nonsequestered nanoparticle contaminants. A short-term defined incubation strategy was developed that allowed efficient labeling of both quiescent and cycling HSC, with no discernable toxicity in vitro or in vivo. Transplantation of purified primary human cord blood lineage-depleted and CD34(+) cells into immunodeficient mice allowed detection of labeled human HSC in the recipient bones. Flow cytometry was used to precisely quantitate the cell populations that had sequestered the nanoparticles and to follow their fate post-transplantation. Flow cytometry endpoint analysis confirmed the presence of nanoparticle-labeled human stem cells in the marrow. The use of fluorophore-labeled iron oxide nanoparticles for fluorescence imaging in combination with flow cytometry allows evaluation of labeling efficiencies and homing capabilities of defined human HSC subsets.

MRI of intravenously injected bone marrow cells homing to the site of injured arteries

The aim of this study was to test the feasibility of using MRI to detect magnetically labeled, intravenously injected bone marrow (BM) cells homing to injured arteries. In the first phase, BM cells from LacZ-transgenic or green fluorescent protein (GFP)-transgenic mice were transplanted into eight recipient mice. The left femoral arteries of recipient mice were injured using a cuff-constriction or endothelium-damage approach, and the right femoral arteries were uninjured to serve as controls. The location and distribution of migrated LacZ-BM or GFP-BM cells were confirmed with histology. In the second phase, BM-derived cells from LacZ-transgenic mice were labeled with superparamagnetic iron oxide (Feridex) and then transplanted into eight recipient mice with cuff-induced injuries in the left femoral arteries. Migrated Feridex/LacZ-BM cells were monitored in vivo using a 4.7 T MR scanner. Subsequently, high-resolution ex vivo MRI was performed on 9.4 T and 11.7 T. LacZ-positive or GFP-positive cells in the thickened adventitia of the injured arteries were evident on histology. Both in vivo and ex vivo MRI showed larger regions of hypointensity with Feridex-labeled cells at the sites of the injured arteries compared with control arteries (P < 0.01). This study provides initial evidence that may support the potential use of MRI to detect homing of intravenously injected BM cells to injured arteries.

Abdominal magnetic resonance imaging in small rodents using a clinical 1.5 T MR scanner

Because of superior soft-tissue contrast compared to other imaging techniques, non-invasive abdominal magnetic resonance imaging (MRI) is ideal for monitoring organ regeneration, tissue repair, cancer stage, and treatment effects in a wide variety of experimental animal models. Currently, sophisticated MR protocols, including technically demanding procedures for motion artefact compensation, achieve an MRI resolution limit of < 100 microm under ideal conditions. However, such a high spatial resolution is not required for most experimental rodent studies. This article describes both a detailed imaging protocol for MR data acquisition in a ubiquitously and commercially available 1.5 T MR unit and 3-dimensional volumetry of organs, tissue components, or tumors. Future developments in MR technology will allow in vivo investigation of physiological and pathological processes at the cellular and even the molecular levels. Experimental MRI is crucial for non-invasive monitoring of a broad range of biological processes and will further our general understanding of physiology and disease.

In vivo MR imaging of bone marrow cells trafficking to atherosclerotic plaques

PURPOSE

To develop a magnetic resonance imaging (MRI)-based method to monitor in vivo trafficking of bone marrow (BM) cells to atherosclerotic lesions.

MATERIALS AND METHODS

BM cells from LacZ-transgenic mice were labeled with a superparamagnetic iron oxide (Feridex) and then transplanted into ApoE(-/-) recipient mice that were fed an atherogenic diet. Twenty-four ApoE(-/-) mice were divided into three study groups: 1) group I with Feridex-labeled BM transplantation (BMT) cells (N = 9), 2) group II with unlabeled BMT cells (N = 10), and 3) group III with no BMT cells (N = 5). Migrated Feridex/LacZ-BM cells to atherosclerotic aortic walls were monitored in vivo using a 4.7T MR scanner and correlated with histopathological findings.

RESULTS

In group I with Feridex-BMT cells, histology examination displayed plaques in five of nine animals. In four of these five animals, in vivo MRI showed large MR signal voids of the aorta walls (due to the "blooming" effect of migrated Feridex-BM cells in plaques), which were correlated with Feridex- and/or LacZ-positive cells detected in the atherosclerotic lesions. No signal voids could be visualized in the two control animal groups (groups II and III).

CONCLUSION

This study demonstrates the potential use of in vivo MRI to monitor the trafficking of magnetically labeled BM cells to atherosclerotic lesions.

Quantification of superparamagnetic iron oxide (SPIO)-labeled cells using MRI

PURPOSE

To show the feasibility of using magnetic resonance imaging (MRI) to quantify superparamagnetic iron oxide (SPIO)-labeled cells.

MATERIALS AND METHODS

Lymphocytes and 9L rat gliosarcoma cells were labeled with ferumoxides-protamine sulfate complex (FE-PRO). The cells were labeled efficiently (more than 95%) and the iron concentration inside each cell was measured by spectrophotometry (4.77-30.21 pg). Phantom tubes containing different numbers of labeled or unlabeled cells, as well as different concentrations of FE-PRO, were made. In addition, labeled and unlabeled cells were injected into fresh and fixed rat brains.

RESULTS

Cellular viability and proliferation of labeled and unlabeled cells were shown to be similar. T2-weighted images were acquired using 7T and 3T MRI systems, and R2 maps of the tubes containing cells, free FE-PRO, and brains were made. There was a strong linear correlation between R2 values and labeled cell numbers, but the regression lines were different for the lymphocytes and gliosarcoma cells. Similarly, there was strong correlation between R2 values and free iron. However, free iron had higher R2 values than the labeled cells for the same concentration of iron.

CONCLUSION

Our data indicate that in vivo quantification of labeled cells can be done by careful consideration of different factors and specific control groups.

R2 and R2* mapping for sensing cell-bound superparamagnetic nanoparticles: in vitro and murine in vivo testing

PURPOSE

To prospectively determine the cellular iron uptake by using R2 and R2* mapping with multiecho readout gradient-echo and spin-echo sequences.

MATERIALS AND METHODS

All experiments were approved by the institutional animal care committee. Lung carcinoma cells were lipofected with superparamagnetic iron oxides (SPIOs). Agarose gel phantoms containing (a) 1 x 10(5) CCL-185 cells per milliliter of agarose gel with increasing SPIO load (0.01-5.00 mg of iron per milliliter in the medium), (b) different amounts (5.0 x 10(3) to 2.5 x 10(5) cells per milliliter of agarose gel) of identically loaded cells, and (c) free (non-cell-bound) SPIOs at the iron concentrations described for (b) were analyzed with 3.0-T R2 and R2* relaxometry. Iron uptake was analyzed with light microscopy, quantified with atomic emission spectroscopy (AES), and compared with MR data. For in vivo relaxometry, agarose gel pellets containing SPIO-labeled cells, free SPIO, unlabeled control cells, and pure agarose gel were injected into three nude mice each. Linear and nonlinear regression analyses were performed.

RESULTS

Light microscopy and AES revealed efficient SPIO particle uptake (mean uptake: 0.22 pg of iron per cell +/- 0.1 [standard deviation] for unlabeled cells, 31.17 pg of iron per cell +/- 4.63 for cells incubated with 0.5 mg/mL iron). R2 and R2* values were linearly correlated with cellular iron load, number of iron-loaded cells, and content of freely dissolved iron (r(2) range, 0.92-0.99; P < .001). For cell-bound SPIO, R2* effects were significantly greater than R2 effects (P < .01); for free SPIO, R2 and R2* effects were similar. In vivo relaxometry enabled accurate prediction of the number of labeled cells. R2' (R2* - R2) mapping enabled differentiation between cell-bound and free iron in vitro and in vivo.

CONCLUSION

Quantitative R2 and R2* mapping enables noninvasive estimations of cellular iron load and number of iron-labeled cells. Cell-bound SPIOs can be differentiated from free SPIOs with R2' imaging.

Current issues and perspectives in small rodent magnetic resonance imaging using clinical MRI scanners

Small rodents such as mice and rats are frequently used in animal experiments for several reasons. In the past, animal experiments were frequently associated with invasive methods and groups of animals had to be killed to perform longitudinal studies. Today's modern imaging techniques such as magnetic resonance imaging (MRI) allow non-invasive longitudinal monitoring of multiple parameters. Although only a few institutions have access to dedicated small animal MR scanners, most institutions carrying out animal experiments have access to clinical MR scanners. Technological advances and the increasing field strength of clinical scanners make MRI a broadly available and viable technique in preclinical in vivo research. This review provides an overview of current concepts, limitations, and recent studies dealing with small animal imaging using clinical MR scanners.

MR-based imaging of neural stem cells

The efficacy of therapies based on neural stem cells (NSC) has been demonstrated in preclinical models of several central nervous system (CNS) diseases. Before any potential human application of such promising therapies can be envisaged, there are some important issues that need to be solved. The most relevant one is the requirement for a noninvasive technique capable of monitoring NSC delivery, homing to target sites and trafficking. Knowledge of the location and temporospatial migration of either transplanted or genetically modified NSC is of the utmost importance in analyzing mechanisms of correction and cell distribution. Further, such a technique may represent a crucial step toward clinical application of NSC-based approaches in humans, for both designing successful protocols and monitoring their outcome. Among the diverse imaging approaches available for noninvasive cell tracking, such as nuclear medicine techniques, fluorescence and bioluminescence, magnetic resonance imaging (MRI) has unique advantages. Its high temporospatial resolution, high sensitivity and specificity render MRI one of the most promising imaging modalities available, since it allows dynamic visualization of migration of transplanted cells in animal models and patients during clinically useful time periods. Different cellular and molecular labeling approaches for MRI depiction of NSC are described and discussed in this review, as well as the most relevant issues to be considered in optimizing molecular imaging techniques for clinical application.

Cell labeling with the positive MR contrast agent Gadofluorine M

The purpose of this study was to label human monocytes with Gadofluorine M by simple incubation for subsequent cell depiction at 1.5 and 3 T. Gadofluorine M displays a high r(1) relaxivity and is spontaneously phagocytosed by macrophages. Human monocytes were incubated with Gadofluorine M-Cy at varying concentrations and incubation times and underwent MR imaging at 1.5 and 3 T at increasing time intervals after the labeling procedure. R1-relaxation rates and r1 relaxivities of the labeled cells and non-labeled controls were determined. Cellular contrast agent uptake was examined by fluorescence microscopy and quantified by ICP-AES. Efficient cell labeling was achieved after incubation of the cells with 25 mM Gd Gadofluorine M for 12 h, resulting in a maximal uptake of 0.3 fmol Gd/cell without impairment of cell viability. Fluorescence microscopy confirmed internalization of the fluorescent contrast agent by monocytes. The r1 relaxivity of the labeled cells was 137 mM(-1)s(-1) at 1.5 T and 80.46 mM(-1)s(-1) at 3 T. Imaging studies showed stable labeling for at least 7 days. Human monocytes can be effectively labeled for MR imaging with Gadofluorine M. Potential in vivo cell-tracking applications include targeting of inflammatory processes with Gadofluorine-labeled leukocytes or monitoring of stem cell therapies for the treatment of arthritis.

Sensitivity of magnetic resonance imaging of dendritic cells for in vivo tracking of cellular cancer vaccines

Success of immunotherapy with dendritic cells (DC) to treat cancer is highly dependent on their interaction with and activation of antigen specific T cells. To maximize DC-T cell contact accurate delivery of the therapeutic cells into the lymph node, or efficient trafficking of DC to the lymph nodes of the patient is essential. Since responses are seen in some patients but not in others, monitoring of the injected cells may be of major importance. Tracking of cells with magnetic resonance (MR) imaging is a non-invasive method that provides detailed anatomical information and is therefore more informative for the evaluation of the localization of therapeutic cells after injection than e.g. scintigraphic imaging. To challenge the sensitivity of this novel technique, we investigated the minimum amount of label and the number of cells required for MR imaging and the effect of labeling on DC function. DC were labeled with different concentrations of a clinically approved MR contrast agent consisting of superparamagnetic iron oxide particles and were imaged at both 3 and 7 T. Our results demonstrate the following: (i) When loaded with 30 (+/-4) pg Fe/cell, cell numbers as low as 1,000 cells/mm3 at 3 T and 500 cells/mm3 at 7 T could be readily imaged; (ii) Labeling does not affect cell viability and function; (iii) Because of its high spatial resolution and sensitivity, MRI is ideally suited to track therapeutic cells in vivo.

Expression of transferrin receptor and ferritin following ferumoxides-protamine sulfate labeling of cells: implications for cellular magnetic resonance imaging

Ferumoxides-protamine sulfate (FE-Pro) complexes are used for intracellular magnetic labeling of cells to non-invasively monitor cell trafficking by in vivo MRI. FE-Pro labeling is non-toxic to cells; however, the effects of FE-Pro labeling on cellular expression of transferrin receptor (TfR-1) and ferritin, proteins involved in iron transport and storage, has not been reported. FE-Pro-labeled human mesenchymal stem cells (MSCs), HeLa cells and primary macrophages were cultured from 1 week to 2 months and evaluated for TfR-1 and ferritin gene expression by RT-PCR and protein levels were determined using Western blots. MTT (proliferation assay) and reactive oxygen species (ROS) analysis were performed. FE-Pro labeling of HeLa and MSCs resulted in a transient decrease in TfR-1 mRNA and protein levels. In contrast, Fe-Pro labeling of primary macrophages resulted in an increase in TfR-1 mRNA but not in TfR-1 protein levels. Ferritin mRNA and protein levels increased transiently in labeled HeLa and macrophages but were sustained in MSCs. No changes in MTT and ROS analysis were noted. In conclusion, FE-Pro labeling elicited physiological changes of iron metabolism or storage, validating the safety of this procedure for cellular tracking by MRI.

T1 and T2 relaxivity of intracellular and extracellular USPIO at 1.5T and 3T clinical MR scanning

In this study we evaluated the effects of intracellular compartmentalization of the ultrasmall superparamagnetic iron oxide (USPIO) ferumoxtran-10 on its proton T1 and T2 relaxivities at 1.5 and 3T. Monocytes were labeled with ferumoxtran-10 by simple incubation. Decreasing quantities of ferumoxtran-10-labeled cells (2.5x10(7)-0.3x10(7) cells/ml) and decreasing concentrations of free ferumoxtran-10 (without cells) in Ficoll solution were evaluated with 1.5 and 3T clinical magnetic resonance (MR) scanners. Pulse sequences comprised axial spin echo (SE) sequences with multiple TRs and fixed TE and SE sequences with fixed TR and increasing TEs. Signal intensity measurements were used to calculate T1 and T2 relaxation times of all samples, assuming a monoexponential signal decay. The iron content in all samples was determined by inductively coupled plasma atomic emission spectrometry and used for calculating relaxivities. Measurements at 1.5T and 3T showed higher T1 and T2 relaxivity values of free extracellular ferumoxtran-10 as opposed to intracellularly compartmentalized ferumoxtran-10, under the evaluated conditions of homogeneously dispersed contrast agents/cells in Ficoll solution and a cell density of up to 2.5x10(7) cells/ml. At 3T, differences in T1-relaxivities between intra- and extracellular USPIO were smaller, while differences in USPIO T2-relaxivities were similar compared with 1.5T. In conclusion, cellular compartmentalization of ferumoxtran-10 changes proton relaxivity.