Vivo Magnetic Resonance Imaging Research Articles

In Vivo MRI Assessment of Hepatic and Splenic Disease in a Murine Model of Schistosomiasis [corrected

BackgroundSchistosomiasis (or bilharzia), a major parasitic disease, affects more than 260 million people worldwide. In chronic cases of intestinal schistosomiasis caused by trematodes of the Schistosoma genus, hepatic fibrosis develops as a host immune response to the helminth eggs, followed by potentially lethal portal hypertension. In this study, we characterized hepatic and splenic features of a murine model of intestinal schistosomiasis using in vivo magnetic resonance imaging (MRI) and evaluated the transverse relaxation time T2 as a non-invasive imaging biomarker for monitoring hepatic fibrogenesis.Methodology/Principal FindingsCBA/J mice were imaged at 11.75T two, six and ten weeks after percutaneous infection with Schistosoma mansoni. In vivo imaging studies were completed with histology at the last two time points. Anatomical MRI allowed detection of typical manifestations of the intestinal disease such as significant hepato- and splenomegaly, and dilation of the portal vein as early as six weeks, with further aggravation at 10 weeks after infection. Liver multifocal lesions observed by MRI in infected animals at 10 weeks post infection corresponded to granulomatous inflammation and intergranulomatous fibrosis with METAVIR scores up to A2F2. While most healthy hepatic tissue showed T2 values below 14 ms, these lesions were characterized by a T2 greater than 16 ms. The area fraction of increased T2 correlated (rS = 0.83) with the area fraction of Sirius Red stained collagen in histological sections. A continuous liver T2* decrease was also measured while brown pigments in macrophages were detected at histology. These findings suggest accumulation of hematin in infected livers.Conclusions/SignificanceOur multiparametric MRI approach confirms that this murine model replicates hepatic and splenic manifestations of human intestinal schistosomiasis. Quantitative T2 mapping proved sensitive to assess liver fibrogenesis non-invasively and may therefore constitute an objective imaging biomarker for treatment monitoring in diseases involving hepatic fibrosis.

In Vivo MRI Evidence that Neuropathology is Attenuated by Cognitive Enrichment in the Yac128 Huntington's Disease Mouse Model.

Environmental enrichment has been shown to improve symptoms and reduce neuropathology in mouse models of Huntington's disease (HD); however results are limited to ex vivo techniques with associated shortcomings. In-vivo magnetic resonance imaging (MRI) can overcome some of the shortcomings and is applied for the first time here to assess the effect of a cognitive intervention in a mouse model of HD. We aimed to investigate whether in-vivo high-field MRI can detect a disease-modifying effect in tissue macrostructure following a cognitive enrichment regime. YAC128 transgenic and wild type mice were exposed to cognitive enrichment throughout their lifetime. At 20-months old, mice were scanned with a T2-weighted MRI sequence and a region-of-interest (ROI) approach was used to examine structural changes. Locomotor activity and performance on the rotarod and serial discrimination watermaze task were assessed to measure motor and cognitive function respectively. Mice exposed to cognitive enrichment were more active and able to stay on a rotating rod longer compared to control mice, with comparable rotarod performance between HD enriched mice and wild-type mice. YAC128 mice demonstrated cognitive impairments which were not improved by cognitive enrichment. In-vivo MRI revealed a reduction in the degree of caudate-putamen atrophy in the enriched HD mice. We provide in vivo evidence of a beneficial effect of environmental enrichment on neuropathology and motor function in a HD mouse model. This demonstrates the efficacy of MRI in a model of HD and provides the basis for an in-vivo non-destructive outcome measure necessary for longitudinal study designs to understand the effect of enrichment with disease progression.

In vivo PET imaging of the α4β2 nicotinic acetylcholine receptor as a marker for brain inflammation after cerebral ischemia.

PET imaging of nicotinic acetylcholine receptors (nAChRs) could become an effective tool for the diagnosis and therapy evaluation of neurologic diseases. Despite this, the role of nAChRs α4β2 receptors after brain diseases such as cerebral ischemia and its involvement in inflammatory reaction is still largely unknown. To investigate this, we performed in parallel in vivo magnetic resonance imaging (MRI) and positron emission tomography (PET) with 2[(18)F]-fluoro-A85380 and [(11)C]PK11195 at 1, 3, 7, 14, 21, and 28 d after middle cerebral artery occlusion (MCAO) in rats. In the ischemic territory, PET with 2[(18)F]-fluoro-A85380 and [(11)C]PK11195 showed a progressive binding increase from days 3-7, followed by a progressive decrease from days 14-28 after cerebral ischemia onset. Ex vivo immunohistochemistry for the nicotinic α4β2 receptor and the mitochondrial translocator protein (18 kDa) (TSPO) confirmed the PET findings and demonstrated the overexpression of α4β2 receptors in both microglia/macrophages and astrocytes from days 7-28 after experimental ischemic stroke. Likewise, the role played by α4β2 receptors on neuroinflammation was supported by the increase of [(11)C]PK11195 binding in ischemic rats treated with the α4β2 antagonist dihydro-β-erythroidine hydrobromide (DHBE) at day 7 after MCAO. Finally, both functional and behavioral testing showed major impaired outcome at day 1 after ischemia onset, followed by a recovery of the sensorimotor function and dexterity from days 21-28 after experimental stroke. Together, these results suggest that the nicotinic α4β2 receptor could have a key role in the inflammatory reaction underlying cerebral ischemia in rats.

Spatially Resolved Quantification of Gadolinium(III)‐Based Magnetic Resonance Agents in Tissue by MALDI Imaging Mass Spectrometry after In Vivo MRI

AbstractGadolinium(III)‐based contrast agents improve the sensitivity and specificity of magnetic resonance imaging (MRI), especially when targeted contrast agents are applied. Because of nonlinear correlation between the contrast agent concentration in tissue and the MRI signal obtained in vivo, quantification of certain biological or pathophysiological processes by MRI remains a challenge. Up to now, no technology has been able to provide a spatially resolved quantification of MRI agents directly within the tissue, which would allow a more precise verification of in vivo imaging results. MALDI imaging mass spectrometry for spatially resolved in situ quantification of gadolinium(III) agents, in correlation to in vivo MRI, were evaluated. Enhanced kinetics of Gadofluorine M were determined dynamically over time in a mouse model of myocardial infarction. MALDI imaging was able to corroborate the in vivo imaging MRI signals and enabled in situ quantification of the gadolinium probe with high spatial resolution.

In Vivo Magnetic Resonance Imaging Detection of Paramagnetic Liposomes Loaded with Amphiphilic Gadolinium(III) Complexes: Impact of Molecular Structure on Relaxivity and Excretion Efficiency.

The magnetic resonance imaging (MRI) performance of two liposome formulations incorporating amphiphilic 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-like GdIII complexes has been investigated both in vitro and in vivo. The complexes differ in one donor group of the coordination cage (carboxylate versus carboxoamide), and in the length (C12 versus C18 ) and the point of attachment of the aliphatic chains to the chelators. The in vitro 1 H relaxometric characterisation of the systems, performed with a newly developed relaxation model that takes into account the contributions of the GdIII chelates pointing in- and outwards of the liposome, indicates that their efficacy is optimal in the range 0.5-1.5 T. The tetracarboxylic C12 -containing liposomes (LIPO-GdDOTA(GAC12 )2 ; GA=glutaric acid) are four-fold more efficient than the monoamide C18 -based analogue (LIPO-GdDOTAMA(C18 )2 ). Such a difference is also found in vivo at 1 T in a melanoma tumour model on mice. A few hours after intravenous injection, the T1 contrast enhancement in the organs where the nanovesicles typically distribute (liver, spleen, kidneys and tumour) is much higher for LIPO-GdDOTA(GAC12 )2 . Interestingly, after about 7 h post-injection the contrast enhancement observed for the more efficient liposomes decreases rapidly and becomes lower than for LIPO-GdDOTAMA(C18 )2 . The relaxometric data and the quantification of the GdIII complexes in the organs, determined ex vivo by inductively coupled plasma mass spectrometry, indicate that: 1) the differences in the contrast enhancement can be attributed to the different rate of water exchange and rotational dynamics of the Gd complexes, and 2) the rapid contrast decrease is caused by a faster clearance of GdDOTA(GAC12 )2 from the organs. This is also confirmed by using a newly synthesised amphiphilic cyanine-based fluorescent probe (Cy5-(C16 )2 ). As one of the main limitations for the clinical translation of liposomes incorporating amphiphilic imaging agents is related to their very long persistence in the body, the results reported herein suggest that the clearance of the probes can be accelerated, without compromising their role, by a proper selection of the lipophilic portion of the incorporated compound as well as of the ligand site at which the aliphatic tails are linked. Then, GdDOTA(GAC12 )2 complex may represent a good candidate for the development of improved MRI protocols based on paramagnetically labelled lipidic nanoparticles.

Bacteria tracking by in vivomagnetic resonance imaging

BackgroundDifferent non-invasive real-time imaging techniques have been developed over the last decades to study bacterial pathogenic mechanisms in mouse models by following infections over a time course. In vivo investigations of bacterial infections previously relied mostly on bioluminescence imaging (BLI), which is able to localize metabolically active bacteria, but provides no data on the status of the involved organs in the infected host organism. In this study we established an in vivo imaging platform by magnetic resonance imaging (MRI) for tracking bacteria in mouse models of infection to study infection biology of clinically relevant bacteria.ResultsWe have developed a method to label Gram-positive and Gram-negative bacteria with iron oxide nano particles and detected and pursued these with MRI. The key step for successful labeling was to manipulate the bacterial surface charge by producing electro-competent cells enabling charge interactions between the iron particles and the cell wall. Different particle sizes and coatings were tested for their ability to attach to the cell wall and possible labeling mechanisms were elaborated by comparing Gram-positive and -negative bacterial characteristics. With 5-nm citrate-coated particles an iron load of 0.015 ± 0.002 pg Fe/bacterial cell was achieved for Staphylococcus aureus. In both a subcutaneous and a systemic infection model induced by iron-labeled S. aureus bacteria, high resolution MR images allowed for bacterial tracking and provided information on the morphology of organs and the inflammatory response.ConclusionLabeled with iron oxide particles, in vivo detection of small S. aureus colonies in infection models is feasible by MRI and provides a versatile tool to follow bacterial infections in vivo. The established cell labeling strategy can easily be transferred to other bacterial species and thus provides a conceptual advance in the field of molecular MRI.

Anti–IL-17A Treatment Reduces Clinical Score and VCAM-1 Expression Detected by in Vivo Magnetic Resonance Imaging in Chronic Relapsing EAE ABH Mice

IL-17 is argued to play an important role in the multiple sclerosis-like disease experimental autoimmune encephalitis (EAE). We investigated the therapeutic effects of anti-IL-17A in a chronic relapsing EAE ABH mouse model using conventional scoring, quantitative behavioral outcomes, and a novel vascular cell adhesion molecule 1 (VCAM-1)-targeted magnetic resonance imaging (MRI) contrast agent [anti-VCAM-microparticles of iron oxide (MPIO)] to identify conventionally undetectable neuropathology. Mice were administered prophylactic or treatment regimens of anti-IL-17A or IgG and two injections ofanti-VCAM-MPIO before undergoing T2*-weighted three-dimensional and gadolinium-diethylenetriamine pentaacetic acid T1-weighted MRI. Rotarod, inverted screen, and open field motor function tests were performed, conventional clinical scores calculated, and central IL-17A mRNA expression quantified during acute disease, remission, and relapse. Prophylactic anti-IL-17A prevents acute disease and relapse and is associated with reduced clinical and functional severity. Treatment regimens delay relapse, improve functional scores, and are associated with reduced VCAM-MPIO lesions during remission. No significant alteration was detectable in levels of gadolinium-diethylenetriamine pentaacetic acid- or VCAM-MPIO-positive lesions during relapse. Prophylactic and treatment anti-IL-17A were therapeutically effective in chronic relapsing EAE, improving clinical and quantifiable functional outcomes. IL-17A expression seems significant during acute disease but less important chronically. Disease-related immunoneuropathology is more sensitively detected using VCAM-MPIO MRI, which may, therefore, be used to monitor therapy meaningfully.

Optimal Labeling Dose, Labeling Time, and Magnetic Resonance Imaging Detection Limits of Ultrasmall Superparamagnetic Iron-Oxide Nanoparticle Labeled Mesenchymal Stromal Cells

Background. Regenerative therapy is an emerging treatment modality. To determine migration and retention of implanted cells, it is crucial to develop noninvasive tracking methods. The aim was to determine ex vivo magnetic resonance imaging (MRI) detection limits of ultrasmall superparamagnetic iron-oxide (USPIO) labeled mesenchymal stromal cells (MSCs). Materials and Methods. 248 gel-phantoms were constructed and scanned on a 1.5T MRI-scanner. Phantoms contained human MSCs preincubated with USPIO nanoparticles for 2, 6, or 21 hours using 5 or 10 μg USPIO/105 MSCs. In addition, porcine hearts were scanned after injection of USPIO labeled MSCs. Results. Using 21 h incubation time and 10 μg USPIO/105 MSCs, labeled cells were clearly separated from unlabeled cells on MRI using 250.000 (P < 0.001), 500.000 (P = 0.007), and 1.000.000 MSCs (P = 0.008). At lower incubation times and doses, neither labeled nor unlabeled cells could be separated. In porcine hearts labeled, but not unlabeled, MSCs were identified on MRI. Conclusions. As few as 250.000 MSCs can be detected on MRI using 21 h incubation time and 10 μg USPIO/105 MSCs. At lower incubation times and doses, several million cells are needed for MRI detection. USPIO labeled cells can be visualized by MRI in porcine myocardial tissue.

Therapeutic Testosterone Administration Preserves Excitatory Synaptic Transmission in the Hippocampus during Autoimmune Demyelinating Disease

Over 50% of multiple sclerosis (MS) patients experience cognitive deficits, and hippocampal-dependent memory impairment has been reported in >30% of these patients. While postmortem pathology studies and in vivo magnetic resonance imaging demonstrate that the hippocampus is targeted in MS, the neuropathology underlying hippocampal dysfunction remains unknown. Furthermore, there are no treatments available to date to effectively prevent neurodegeneration and associated cognitive dysfunction in MS. We have recently demonstrated that the hippocampus is also targeted in experimental autoimmune encephalomyelitis (EAE), the most widely used animal model of MS. The objective of this study was to assess whether a candidate treatment (testosterone) could prevent hippocampal synaptic dysfunction and underlying pathology when administered in either a preventative or a therapeutic (postdisease induction) manner. Electrophysiological studies revealed impairments in basal excitatory synaptic transmission that involved both AMPA receptor-mediated changes in synaptic currents, and faster decay rates of NMDA receptor-mediated currents in mice with EAE. Neuropathology revealed atrophy of the pyramidal and dendritic layers of hippocampal CA1, decreased presynaptic (Synapsin-1) and postsynaptic (postsynaptic density 95; PSD-95) staining, diffuse demyelination, and microglial activation. Testosterone treatment administered either before or after disease induction restores excitatory synaptic transmission as well as presynaptic and postsynaptic protein levels within the hippocampus. Furthermore, cross-modality correlations demonstrate that fluctuations in EPSPs are significantly correlated to changes in postsynaptic protein levels and suggest that PSD-95 is a neuropathological substrate to impaired synaptic transmission in the hippocampus during EAE. This is the first report demonstrating that testosterone is a viable therapeutic treatment option that can restore both hippocampal function and disease-associated pathology that occur during autoimmune disease.

In Vivo Magnetic Resonance Imaging of Transgenic Mice Expressing Human Ferritin

This study aims to produce the transgenic mice (TG) engineered for magnetic resonance imaging (MRI) studies based on the ubiquitous expression of ferritin MRI reporter gene in diverse tissues. Transgenic mice (TG) expressing myc-tagged human heavy chain ferritin (myc-hFTH) under the control of a ubiquitous CAG promoter were produced. The expression of myc-hFTH in diverse tissues of the myc-hFTH TG was assessed by RT-PCR, Western blotting, and immunohistochemistry. The iron accumulation and the deposition of ferritin aggregates in tissues of myc-hFTH TG and WT were analyzed by Prussian blue staining and transmission electron microscopy. The myc-hFTH TG (n = 9) and wild-type mice (WT) (n = 4) were subjected to MRI on 9.4 T MR scanner. An eight-point T(2)* mapping was performed using a multiple gradient echo sequence, and T(2)* value was estimated pixel by pixel by using a routine least-squares fitting algorithm. We generated the myc-hFTH TG expressing myc-hFTH in brain, heart, liver, lung, spleen, pancreas, kidney, and intestine. The myc-hFTH TG showed no apparent pathological symptoms and no histological changes compared to WT. The expression of myc-hFTH in the brain and liver tissues of myc-hFTH TG led to a significant decrease in T(2)* values, as shown by noninvasive MRI, compared to WT (P < 0.05, TG vs. WT). This study demonstrates that the novel myc-hFTH TG, which expresses an MRI reporter in many tissues, would be a valuable animal model of FTH-based molecular imaging in which to study potential therapies for cell and tissue grafting using an MRI technique. These mice could also serve to study disease related with iron metabolism.

In Vivo Magnetic Resonance Imaging for Investigating the Development and Distribution of Experimental Brain Metastases due to Breast Cancer

INTRODUCTION: The overall goal of this study was to assess the utility of three-dimensional magnetic resonance imaging (MRI) for monitoring the temporal and spatial development of experimental brain metastasis in mice. MATERIALS AND METHODS: Brain metastatic human breast cancer cells (231-BR or 231-BR-HER2) were injected intracardially in nude mice for delivery to the brain. Mouse brains were imaged in vivo at different time points using a balanced steady-state-free precession (bSSFP) pulse sequence at 1.5 T. Brains were categorized into four regions: cortex, central brain, olfactory, and posterior. The number of metastases and their volumes were quantified for both cell lines. RESULTS: There was no difference in the mean number of metastases for either cell line. The volumes of metastases in mice injected with 231-BR-HER2 cells were significantly larger than those for mice injected with 231-BR cells. The growth rate for 231-BR-HER2 metastases was 67.5% compared with 54.4% for the 231-BR metastases. More than 50% of metastases were located in the cortex and 25% to 30% of metastases were identified in the central brain for each time point and for mice injected with either cell line. The volumes of metastases were significantly larger in mice with fewer metastases at end point. SIGNIFICANT CONCLUSIONS: MRI provided a comprehensive accounting of the number and size of experimental brain metastases in the whole mouse brain at multiple time points. This approach has provided new information about the temporal and spatial development of metastases in the brain not possible by other histopathologic or imaging methods.

Fabrication and Packaging of Flexible Polymeric Microantennae for in Vivo Magnetic Resonance Imaging

In this paper, we detail how microantennae dedicated to Magnetic Resonance Imaging (MRI) can benefit from the advantages offered by polymer substrates, especially flexibility and dielectric properties. We present a monolithic and wireless design based on the transmission lines between conductor windings on both sides of a dielectric substrate and its fabrication process. This last one requires specific plasma treatments to improve polymer/metal adhesion. We have led a comparative study on the effects of the ageing time on the wettability and the metal adhesion to Kapton and Teflon surfaces. Correlation between wettability (water contact angle) and adhesion (tensile strength) has been established. Then, the use of PolyDiMethylSiloxane (PDMS) as biocompatible packaging material and the optimization of its thickness allows us to conserve suitable f0 and Q values in a conducting environment such as the biological tissues. These studies allow us to perform 7 Tesla in vivo MRI of the rat brain with a high spatial resolution of 100 x 100 x 200 µm3 and a Signal to Noise Ratio of 80.

The sound of one-hand clapping: handedness and perisylvian neural correlates of a communicative gesture in chimpanzees

Whether lateralization of communicative signalling in non-human primates might constitute prerequisites of hemispheric specialization for language is unclear. In the present study, we examined (i) hand preference for a communicative gesture (clapping in 94 captive chimpanzees from two research facilities) and (ii) the in vivo magnetic resonance imaging brain scans of 40 of these individuals. The preferred hand for clapping was defined as the one in the upper position when the two hands came together. Using computer manual tracing of regions of interest, we measured the neuroanatomical asymmetries for the homologues of key language areas, including the inferior frontal gyrus (IFG) and planum temporale (PT). When considering the entire sample, there was a predominance of right-handedness for clapping and the distribution of right- and left-handed individuals did not differ between the two facilities. The direction of hand preference (right- versus left-handed subjects) for clapping explained a significant portion of variability in asymmetries of the PT and IFG. The results are consistent with the view that gestural communication in the common ancestor may have been a precursor of language and its cerebral substrates in modern humans.

Facilitating Tumor Functional Assessment by Spatially Relating 3D Tumor Histology and In Vivo MRI: Image Registration Approach

BackgroundMagnetic resonance imaging (MRI), together with histology, is widely used to diagnose and to monitor treatment in oncology. Spatial correspondence between these modalities provides information about the ability of MRI to characterize cancerous tissue. However, registration is complicated by deformations during pathological processing, and differences in scale and information content.Methodology/Principal FindingsThis study proposes a methodology for establishing an accurate 3D relation between histological sections and high resolution in vivo MRI tumor data. The key features of the methodology are: 1) standardized acquisition and processing, 2) use of an intermediate ex vivo MRI, 3) use of a reference cutting plane, 4) dense histological sampling, 5) elastic registration, and 6) use of complete 3D data sets. Five rat pancreatic tumors imaged by T2*-w MRI were used to evaluate the proposed methodology. The registration accuracy was assessed by root mean squared (RMS) distances between manually annotated landmark points in both modalities. After elastic registration the average RMS distance decreased from 1.4 to 0.7 mm. The intermediate ex vivo MRI and the reference cutting plane shared by all three 3D images (in vivo MRI, ex vivo MRI, and 3D histology data) were found to be crucial for the accurate co-registration between the 3D histological data set and in vivo MRI. The MR intensity in necrotic regions, as manually annotated in 3D histology, was significantly different from other histologically confirmed regions (i.e., viable and hemorrhagic). However, the viable and the hemorrhagic regions showed a large overlap in T2*-w MRI signal intensity.ConclusionsThe established 3D correspondence between tumor histology and in vivo MRI enables extraction of MRI characteristics for histologically confirmed regions. The proposed methodology allows the creation of a tumor database of spatially registered multi-spectral MR images and multi-stained 3D histology.

In Vivo Magnetic Resonance Imaging to Detect Biliary Excretion of 19F-Labeled Drug in Mice

Isoflurane is an inhaled halogenated hydrocarbon anesthetic commonly used for animal research. In our quest to develop a method for measuring bile acid transport in live animals using (19)F magnetic resonance (MR) imaging, it occurred to us that isoflurane, which contains five fluorines per molecule and is probably widely distributed, would provide an excellent test drug to evaluate the merits of this approach. Experiments in 20- to 28-g male C57BL/6 mice were performed using a horizontal bore scanner with a 30-mm (19)F/(1)H dual-tuned surface coil used to transmit and receive radiofrequency signals at 300.28 MHz for (1)H and 282.55 MHz for (19)F nuclei. Proton MR imaging was used to identify the mouse gallbladder in vivo, which was verified by anatomical dissection. Subsequent experiments in mice inhaling 1.5% isoflurane for 1 to 2 h revealed robust (19)F signals from the gallbladder, verified by overlying (1)H and (19)F signals. No (19)F signal was detected in mice anesthetized with nonhalogenated anesthetics. The presence of isoflurane in gallbladder bile of isoflurane-treated mice was verified using liquid chromatography-mass spectrometry. Gallbladder bile isoflurane content ranged from 3.2 to 4.7 μg. The data presented here provide proof of concept that this novel approach can be used for in vivo measurement of biliary excretion of both existing and novel (19)F-labeled drugs.

Combined Small Interfering RNA Therapy and In Vivo Magnetic Resonance Imaging in Islet Transplantation

OBJECTIVERecent advances in human islet transplantation are hampered by significant graft loss shortly after transplantation and inability to follow islet fate directly. Both issues were addressed by utilizing a dual-purpose therapy/imaging small interfering RNA (siRNA)-nanoparticle probe targeting apoptotic-related gene caspase-3. We expect that treatment with the probe would result in significantly better survival of transplanted islets, which could be monitored by in vivo magnetic resonance imaging (MRI).RESEARCH DESIGN AND METHODSWe synthesized a probe consisting of therapeutic (siRNA to human caspase-3) and imaging (magnetic iron oxide nanoparticles, MN) moieties. In vitro testing of the probe included serum starvation of the islets followed by treatment with the probe. Caspase-3 gene silencing and protein expression were determined by RT-PCR and Western blot, respectively. In vivo studies included serial MRI of NOD-SCID mice transplanted with MN-small interfering (si)Caspase-3–labeled human islets under the left kidney capsule and MN-treated islets under the right kidney capsule.RESULTSTreatment with MN-siCaspase-3 probe resulted in decrease of mRNA and protein expression in serum-starved islets compared with controls. In vivo MRI showed that there were significant differences in the relative volume change between MN-siCaspase-3–treated grafts and MN-labeled grafts. Histology revealed decreased caspase-3 expression and cell apoptosis in MN-siCaspase-3–treated grafts compared with the control side.CONCLUSIONSOur data show the feasibility of combining siRNA therapy and in vivo monitoring of transplanted islets in mice. We observed a protective effect of MN-siCaspase-3 in treated islets both in vitro and in vivo. This study could potentially aid in increasing the success of clinical islet transplantation.

In Vivo Magnetic Resonance Imaging and Optical Imaging Comparison of Viable and Nonviable Mesenchymal Stem Cells with a Bifunctional Label

The purpose of this study was to compare viable and nonviable bilabeled mesenchymal stem cells (MSCs) in arthritic joints with magnetic resonance imaging (MRI) and optical imaging (OI). MSCs were labeled with ferucarbotran and DiD. MRI and OI of bilabeled cells were compared with controls. Six rats with arthritis received intra-articular injections of bilabeled viable MSCs into the right knee and nonviable MSCs into the left knee. Animals underwent MRI and OI preinjection and at 4, 24, 48, and 72 hours postinjection. The results were analyzed with a mixed random effects model and Fisher probability. Bilabeled MSCs showed increased MRI and OI signals compared to unlabeled controls (p < .0001). After intra-articular injection, bilabeled MSCs caused significant T2 and T2* effect on MRI and fluorescence on OI up to 72 hours postinjection (p < .05). There was no significant difference between viable and nonviable MSC signal in the knee joints; however, some of the viable cells migrated to an adjacent inflamed ankle joint (p < .05). Immunohistochemistry confirmed viable MSCs in right knee and ankle joints and nonviable MSCs in the left knee. Viable and nonviable cells could not be differentiated with MRI or OI signal intensity but were differentiated based on their ability to migrate in vivo.

In Vivo MRI Tracking of Cell Invasion and Migration in a Rat Glioma Model

Malignant brain tumors are characterized by extensive infiltration into the normal brain tissue. Tumor migration is a complicated process which results from the interplay of a number of mechanisms, and the extent to which anatomic structure determined the migration pattern has not been extensively addressed. In the present study, we labeled C6 glioma cells with iron oxide nanoparticles and monitored the fate of the cells in vivo with magnetic resonance imaging (MRI). C6 glioma cells were labeled with ferumoxide-poly-L-lysine complexes and their migration in the brains of rats tracked by T2-weighted MRI. The same amount of iron-laden cells were implanted into the caudate nucleus (CN) and at the vicinity of anterior commissure (AC), respectively, and MRI was performed during the course of 20-day monitoring period to track tumor growth and migration. A clear tendency of tumor migration along the white matter fiber tracts was observed in the AC group, which is consistent with the previous reports; by contrast, tumor expanded to but remained confined within the boundary of right hemisphere in the CN group. We successfully demonstrated the ability of MRI to investigate the impact of anatomical structure on the glioma migration pathway in vivo.

In Vivo Magnetic Resonance Imaging of Injected Endothelial Progenitor Cells after Myocardial Infarction in Rats

The purpose of this study was to detect and follow transplanted superparamagnetic iron oxide (SPIO)-labeled endothelial progenitor cells (EPCs) by magnetic resonance imaging (MRI). Infarcted rats were randomized to injections of SPIO-labeled EPCs, unlabeled EPCs, or saline. From 1day to 8weeks, in vivo serial MRI was performed for cell tracking. Labeled cells were visualized as hypointense areas by MRI. The presence of labeled EPCs at 10days and disappearance of these cells by 8weeks was confirmed by iron and 4',6-diamidino-2-phenylindole. Co-staining for iron and ED-1 showed that the iron-positive cells were macrophages. EPC implantation significantly elevated vascular endothelial growth factor expression, accompanied by increased capillary and arteriole density in the ischemic myocardium. At 8weeks, the transplanted EPCs were not present and the enhanced MRI signals arose from macrophages. However, both EPCs enhanced cardiac function. The major mechanism of cardiac improvement appears to be paracrine pathways of the engrafted EPCs.

In Vivo MRI Stem Cell Tracking Requires Balancing of Detection Limit and Cell Viability

Cell-based therapy using adult mesenchymal stem cells (MSCs) has already been the subject of clinical trials, but for further development and optimization the distribution and integration of the engrafted cells into host tissues have to be monitored. Today, for this purpose magnetic resonance imaging (MRI) is the most suitable technique, and micron-sized iron oxide particles (MPIOs) used for labeling are favorable due to their low detection limit. However, constitutional data concerning labeling efficiency, cell viability, and function are lacking. We demonstrate that cell viability and migratory potential of bone marrow mesenchymal stromal cells (BMSCs) are negatively correlated with incorporated MPIOs, presumably due to interference with the actin cytoskeleton. Nevertheless, labeling of BMSCs with low amounts of MPIOs results in maintained cellular function and sufficient contrast for in vivo observation of single cells by MRI in a rat glioma model. Conclusively, though careful titration is indicated, MPIOs are a promising tool for in vivo cell tracking and evaluation of cell-based therapies.