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

A primer on in vivo cell tracking using MRI

Cell tracking by in vivo magnetic resonance imaging (MRI) offers a collection of multiple advantages over other imaging modalities, including high spatial resolution, unlimited depth penetration, 3D visualization, lack of ionizing radiation, and the potential for long-term cell monitoring. Three decades of innovation in both contrast agent chemistry and imaging physics have built an expansive array of probes and methods to track cells non-invasively across a diverse range of applications. In this review, we describe both established and emerging MRI cell tracking approaches and the variety of mechanisms available for contrast generation. Emphasis is given to the advantages, practical limitations, and persistent challenges of each approach, incorporating quantitative comparisons where possible. Toward the end of this review, we take a deeper dive into three key application areas - tracking cancer metastasis, immunotherapy for cancer, and stem cell regeneration - and discuss the cell tracking techniques most suitable to each.

Stem Cell Tracing Through MR Molecular Imaging

Stem cell therapy opens a new window in medicine to overcome several diseases that remain incurable. It appears such diseases as cardiovascular disorders, brain injury, multiple sclerosis, urinary system diseases, cartilage lesions and diabetes are curable with stem cell transplantation. However, some questions related to stem cell therapy have remained unanswered. Stem cell imaging allows approval of appropriated strategies such as selection of the type and dose of stem cell, and also mode of cell delivery before being tested in clinical trials. MRI as a non-invasive imaging modality provides proper conditions for this aim. So far, different contrast agents such as superparamagnetic or paramagnetic nanoparticles, ultrasmall superparamagnetic nanoparticles, fluorine, gadolinium and some types of reporter genes have been used for imaging of stem cells. The core subject of these studies is to investigate the survival and differentiation of stem cells, contrast agent's toxicity and long term following of transplanted cells. The promising results of in vivo and some clinical trial studies may raise hope for clinical stem cells imaging with MRI.

Gadospin F-enhanced magnetic resonance imaging for diagnosis and monitoring of atherosclerosis: validation with transmission electron microscopy and x-ray fluorescence imaging in the apolipoprotein e-deficient mouse

The aim of this study was to investigate the feasibility of noninvasive monitoring of plaque burden in apolipoprotein E-deficient (ApoE-/-) mice by Gadospin F (GDF)-enhanced magnetic resonance imaging (MRI). Gadolinium uptake in plaques was controlled using transmission electron microscopy (TEM) and x-ray fluorescence (XRF) microscopy. To monitor the progression of atherosclerosis, ApoE-/- (n  =  5) and wild-type (n  =  2) mice were fed a Western diet and imaged at 5, 10, 15, and 20 weeks. Contrast-enhanced MRI was performed at 7 T Clinscan (Bruker, Ettlingen, Germany) before and 2 hours after intravenous injection of GDF (100 μmol/kg) to determine the blood clearance. Plaque size and contrast to noise ratio (CNR) were calculated for each time point using region of interest measurements to evaluate plaque progression. Following MRI, aortas were excised and GDF uptake was cross-validated by TEM and XRF microscopy. The best signal enhancement in aortic plaque was achieved 2 hours after application of GDF. No signal differences between pre- and postcontrast MRI were detectable in wild-type mice. We observed a gradual and considerable increase in plaque CNR and size for the different disease stages. TEM and XRF microscopy confirmed the localization of GDF within the plaque. GDF-enhanced MRI allows noninvasive and reliable estimation of plaque burden and monitoring of atherosclerotic progression in vivo.

Superparamagnetic iron oxide nanoparticles as a means to track mesenchymal stem cells in a large animal model of tendon injury

The goal of this study was to establish an SPIO-based cell-tracking method in an ovine model of tendonitis and to determine if this method may be useful for further study of cellular therapies in tendonitis in vivo. Functional assays were performed on labeled and unlabeled cells to ensure that no significant changes were induced by intracellular SPIOs. Following biosafety validation, tendon lesions were mechanically (n = 4) or chemically (n = 4) induced in four sheep and scanned ex vivo at 7 and 14 days to determine the presence and distribution of intralesional cells. Ovine MSCs labeled with 50 µg SPIOs/mL remained viable, proliferate, and undergo tri-lineage differentiation (p < 0.05). Labeled ovine MSCs remained detectable in vitro in concentrated cell numbers as low as 10 000 and in volumetric distributions as low as 100 000 cells/mL. Cells remained detectable by MRI at 7 days, as confirmed by correlative histology for dually labeled SPIO+/GFP+ cells. Histological evidence at 14 days suggested that SPIO particles remained embedded in tissue, providing MRI signal, although cells were no longer present. SPIO labeling has proven to be an effective method for cell tracking for a large animal model of tendon injury for up to 7 days post-injection. The data obtained in this study justify further investigation into the effects of MSC survival and migration on overall tendon healing and tissue regeneration.

Double labelling of human umbilical cord mesenchymal stem cells with Gd-DTPA and PKH26 and the influence on biological characteristics of hUCMSCs

The aim of this study was to determine whether double labelling of human umbilical cord mesenchymal stem cells (hUCMSCs) with gadolinium-diethylene triamine penta-acetic acid (Gd-DTPA) and PKH26 influences their biological characteristics. A tissue adherence technique was used to separate and purify the hUCMSCs and flow cytometry was performed to detect the surface markers expressed on them. Gd-DTPA and PKH26 were used to label the stem cells and MRI and fluorescence microscopy were used to detect the double-labelled hUCMSCs. A MTT assay was used to delineate the growth curve. Transmission electron microscopy (TEM) and atomic force microscopy were used to demonstrate the ultrastructural features of the hUCMSCs. Flow cytometry showed that hUCMSCs highly expressed CD29, CD90, CD44 and CD105. No expression of CD31, CD34 and CD45 was detected. Very low expression of HLA-DR and CD40 was detected. Atomic force microscopy showed these cells were long, spindle shaped, and the cytoplasm and nucleus had clear boundaries. After double labelling, TEM showed Gd particles aggregated in the cytoplasm in a cluster pattern. The proliferation activity, cell cycle, apoptosis and differentiation of the stem cells were not influenced by double labelling. Thus a tissue adherence technique is helpful to separate and purify hUCMSCs effectively; and Gd-DTPA and PKH26 are promising tracers in the investigation of migration and distribution of hUCMSCs in vivo.

Tracking of mesenchymal stem cells labeled with gadolinium diethylenetriamine pentaacetic acid by 7T magnetic resonance imaging in a model of cerebral ischemia

Progress in the development of stem cell and gene therapy requires repeatable and non-invasive techniques to monitor the survival and integration of stem cells in vivo with a high temporal and spatial resolution. The purpose of the present study was to examine the feasibility of using the standard contrast agent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) to label rat mesenchymal stem cells (MSCs) for stem cell tracking. MSCs, obtained from the bilateral femora of rats, were cultured and propagated. The non-liposomal lipid transfection reagent effectene was then used to induce the intracellular uptake of Gd-DTPA. Electron microscopy was used to detect the distribution of Gd-DTPA particles in the MSCs. The labeling efficiency of the Gd-DTPA particles in the MSCs was determined using spectrophotometry, and MTT and trypan blue exclusion assays were used to evaluate the viability and proliferation of the labeled MSCs. T1-weighted magnetic resonance imaging (MRI) was used to observe the labeled cells in vitro and in the rat brain. Gd-DTPA particles were detected inside the MSCs using transmission electron microscopy and a high labeling efficiency was observed. No difference was observed in cell viability or proliferation between the labeled and unlabeled MSCs (P>0.05). In the in vitro T1-weighted MRI and in the rat brain, a high signal intensity was observed in the labeled MSCs. The T1-weighted imaging of the labeled cells revealed a significantly higher signal intensity compared with that of the unlabeled cells (P<0.05) and the T1 values were significantly lower. The function of the labeled MSCs demonstrated no change following Gd-DTPA labeling, with no evident adverse effect on cell viability or proliferation. Therefore, a change in MR signal intensity was detected in vitro and in vivo, suggesting Gd-DTPA can be used to label MSCs for MRI tracking.

Multimodal cell tracking of a spontaneous metastasis model: comparison between MRI, electron paramagnetic resonance and bioluminescence

MRI cell tracking is a promising technique for tracking various cell types in living animals. Usually, cells are incubated with iron oxides so that the particles are taken up before the cells are injected in vivo. In the present study, we aimed to monitor migration of luciferase-expressing mouse renal cancer cells (RENCA-luc) after intrarenal or intrasplenic injection. These cells were labelled using Molday Ion Rhodamine B (MIRB) fluorescent superparamagnetic iron oxide particles. Their fate after injection was first assessed using ex vivo X-band electron paramagnetic resonance (EPR) spectroscopy. This biodistribution study showed that RENCA-luc cells quickly colonized the lungs and the liver after intrarenal and intrasplenic injection, respectively. Bioluminescence imaging (BLI) studies confirmed that this cell line preferentially metastasized to these organs. Early tracking of labelled RENCA-luc cells in the liver using high-field MRI (11.7 T) was not feasible because of a lack of sensitivity. MRI of MIRB-labelled RENCA-luc cells after injection in the left kidney was then performed. T2 - and T2 *-weighted images showed that the labelled cells induced hypointense signals at the injection site. Nevertheless, the hypointense regions tended to disappear after several days, mainly owing to dilution of the MIRB iron oxides with cell proliferation. In conclusion, EPR is well adapted to ex vivo analysis of tissues after cell tracking experiments and allows short-term monitoring of metastasizing cells. MRI is a suitable tool for checking labelled cells at their injection site, but dilution of the iron oxides owing to cell division remains a major limitation. BLI remains the most suitable technique for long-term monitoring of metastatic cells.

Functional investigations on embryonic stem cells labeled with clinically translatable iron oxide nanoparticles

Stem cell based therapies offer significant potential in the field of regenerative medicine. The development of superparamagnetic iron oxide (SPIO) nanoparticle labeling and magnetic resonance imaging (MRI) have been increasingly used to track the transplanted cells, enabling in vivo determination of cell fate. However, the impact of SPIO-labeling on the cell phenotype and differentiation capacity of embryonic stem cells (ESCs) remains unclear. In this study, we wrapped SPIO nanoparticles with stearic acid grafted PEI600, termed as Stearic-LWPEI-SPIO, to generate efficient and non-toxic ESC labeling tools. Our results showed that efficient labeling of ESCs at an optimized low dosage of Stearic-LWPEI-SPIO nanoparticles did not alter the differentiation and self-renewal properties of ESCs. The localization of the transplanted ESCs observed by MRI correlated well with histological studies. These findings demonstrate that Stearic-LWPEI-SPIO nanoparticles have potential to be clinically translatable MRI probes and may enable non-invasive in vivo tracking of ESCs in experimental and clinical settings during cell-based therapies.

Analysis of feasibility of in vitro nuclear magnetic resonance tracking human umbilical cord mesenchymal stem cells by Gd-DTPA labeled

OBJECTIVE

Three different kinds of transfection reagents were used to mediate the transfection of gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA) into human umbilical-cord-derived mesenchymal stem cells (hUCMSCs). The efficacy of different transfection reagents and the feasibility of NMR tracer in vitro of magnetized stem cells were estimated.

METHODS

After purification by tissue explants adherent method, the biological characteristics of hUCMSCs in vitro were identified by subculture and amplification. Calcium phosphate, Effectene and liposome2000 were used to transfect Gd-DTPA-labeled hUCMSCs respectively, and cell counting was used to mediate the transfection of Gd-DTPA into hUCMSCs, which were then induced to lipoblast and osteoblast in vitro. The determination of the transfection activities of the transfection reagents was conducted by measuring the magnetic resonance imaging (MRI) signal intensity of the Gd-DTPA-labeled cells and the concentration of gadolinium ion in the cells. Furthermore, the relationship between the signal intensity of Gd-DTPA-labeled hUCMSCsMRI, cell subculture and generations was studied.

RESULTS

Primary cells were obtained by tissue explants adherent for two weeks. The cells displayed a long spindle form and grew in swirl. After two passage generations, the cellular morphology became more homogeneous. The result detected by the flow cytometer showed that CD29C, D44, CD90, and CD105 were highly expressed, while no CD45, CD40, and HLA-DR expression was detected in the third generation cells. Directional induction in vitro caused the differentiation into lipoblast and osteoblast. After transfected by calcium phosphate, Effectene and liposome 2000, the signal intensity of stem cells was 2281.2±118.8, 2031.9±59.7 and 1887.4±40.8 measured by MRI. Differences between these three groups were statistically significant (P<0.05). The concentrations of gadolinium ion in three groups of stem cells were 0.178±0.009mg/L, 0.158±0.003mg/L and 0.120±0.002mg/L respectively, examined by inductively coupled plasma atomic emission spectrometry. No significant differences were found among these three groups (P<0.05). The proliferation and differentiation abilities of the Gd-DTPA-labeled stem cells were not affected. A minimum 5×10(4) Gd-DTPA-labeled stem cells could be traced with MRI in vitro and presented in high signal. The trace duration time in vitro was about 12days.

CONCLUSIONS

Tissue explants adherent method can be availably applied to purify hUCMSCs. The Effectene method was proved to have the best transfection effect. The proliferation ability and differentiation potency of Gd-DTPA-labeled hUCMSCs were not affected, and the NMR of labeled stem cells in vitro was proved to be feasible.

Biologic properties of gadolinium diethylenetriaminepentaacetic acid-labeled and PKH26-labeled human umbilical cord mesenchymal stromal cells

BACKGROUND AIMS

This study was conducted to characterize gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA)-labeled and PKH26-labeled human umbilical cord mesenchymal stromal cells (HuMSCs) and to track them with magnetic resonance imaging (MRI) in vitro and in vivo.

METHODS

HuMSCs were isolated from umbilical cords and expanded in vitro. Cells were sequentially labeled with Gd-DTPA and PKH26. The labeling efficiency was determined by spectrophotometry measurements, and the longevity of Gd-DTPA maintenance was measured with MRI. The influence of double labeling on cellular biologic properties was assessed by cell proliferation, viability, differentiation, cycle and apoptosis. Transplantation of double-labeled HuMSCs or placebo was performed in 39 female Sprague-Dawley rats. Leak point pressure and maximal bladder capacity were measured in animals 6 weeks after injection.

RESULTS

The T1 values and signal intensity on T1-weighted imaging of labeled cells were significantly higher than the control group (P < 0.05). The signal intensity on T1-weighted imaging of labeled cells was retained >14 days in vitro and in vivo. There was no significant difference in the cell cycle, cell apoptosis, cell proliferation and cell viability between labeled and unlabeled HuMSCs (P > 0.05). After double labeling, HuMSCs were still capable of differentiating into osteoblasts and adipocytes. Periurethrally injected HuMSCs in the rats significantly improved leak point pressure and maximal bladder capacity.

CONCLUSIONS

HuMSCs were successfully labeled with Gd-DTPA and PKH26. This labeling method is reliable and efficient and can be applied for tracking cells in vitro and in vivo without altering cellular biologic properties.

Cell transplantation for spinal cord injury: a systematic review

Cell transplantation, as a therapeutic intervention for spinal cord injury (SCI), has been extensively studied by researchers in recent years. A number of different kinds of stem cells, neural progenitors, and glial cells have been tested in basic research, and most have been excluded from clinical studies because of a variety of reasons, including safety and efficacy. The signaling pathways, protein interactions, cellular behavior, and the differentiated fates of experimental cells have been studied in vitro in detail. Furthermore, the survival, proliferation, differentiation, and effects on promoting functional recovery of transplanted cells have also been examined in different animal SCI models. However, despite significant progress, a "bench to bedside" gap still exists. In this paper, we comprehensively cover publications in the field from the last years. The most commonly utilized cell lineages were covered in this paper and specific areas covered include survival of grafted cells, axonal regeneration and remyelination, sensory and motor functional recovery, and electrophysiological improvements. Finally we also review the literature on the in vivo tracking techniques for transplanted cells.

Electron paramagnetic resonance as a sensitive tool to assess the iron oxide content in cells for MRI cell labeling studies

MRI cell tracking is a promising technique to track various cell types (stem cells, tumor cells, etc.) in living animals. Usually, cells are incubated with iron oxides (T(2) contrast agent) in order to take up the particles before being injected in vivo. Iron oxide quantification is important in such studies for validating the labeling protocols and assessing the dilution of the particles with cell proliferation. We here propose to implement electron paramagnetic resonance (EPR) as a very sensitive method to quantify iron oxide concentration in cells. Iron oxide particles exhibit a unique EPR spectrum, which directly reflects the number of particles in a sample. In order to compare EPR with existing methods (Perls's Prussian blue reaction, ICP-MS and fluorimetry), we labeled tumor cells (melanoma and renal adenocarcinoma cell lines) and fibroblasts with fluorescent iron oxide particles, and determined the limits of detection of the different techniques. We show that EPR is a very sensitive technique and is specific for iron oxide quantification as measurements are not affected by endogenous iron. As a consequence, EPR is well adapted to perform ex vivo analysis of tissues after cell tracking experiments in order to confirm MRI results.

Transplanted neural stem cells promote nerve regeneration in acute peripheral nerve traction injury: assessment using MRI

OBJECTIVE

The purpose of our study was to monitor neural stem cells (NSCs) transplanted in acute peripheral nerve traction injury and to use MRI to assess the ability of NSCs to promote nerve regeneration.

MATERIALS AND METHODS

After labeling with gadolinium-diethylene triamine pentaacetic acid (gadopentetate dimeglumine) and fluorescent dye (PKH26), 5 × 10(5) NSCs were grafted to acutely distracted sciatic nerves in 21 New Zealand White rabbits. In addition, 5 × 10(5) unlabeled NSCs (n = 21) and vehicle alone (n = 21) subjects were injected as a control. Serial MRI was performed with a 1.5-T scanner to determine the distribution of grafted cells. Sequential T1 and T2 values of the nerves and functional recovery were measured over a 70-day follow-up period, with histologic assessments performed at regular intervals.

RESULTS

The distribution and migration of labeled NSCs could be tracked with MRI until 10 days after transplantation. Compared with vehicle control, nerves grafted with labeled or unlabeled NSCs had better functional recovery and showed improved nerve regeneration but exhibited a sustained increase of T1 and T2 values during the phase of regeneration.

CONCLUSION

Gadopentetate dimeglumine-based labeling allowed short-term in vivo MRI tracking of NSCs grafted in injured nerves. NSCs transplantation could promote nerve regeneration in acute peripheral nerve traction injury as shown by a prolonged increase of nerve T1 and T2 values.