Use of magnetic resonance imaging contrast agents to detect transplanted liver cells

The Magnetic Field of Magnetic Resonance Imaging Systems Does Not Affect Cells Labeled with Micrometer-Sized Iron Oxide Particles

INTRODUCTION

Labeling using iron oxide particles enables cell tracking through magnetic resonance imaging (MRI). However, the magnetic field can affect the particle-labeled cells. Here, we investigated the effects of a clinical MRI system on primary human hepatocytes labeled using micrometer-sized iron oxide particles (MPIOs).

METHODS

HuH7 tumor cells were incubated with increasing concentrations of biocompatible, silica-based, micrometer-sized iron oxide-containing particles (sMPIOs; 40-160 particles/cell). Primary human hepatocytes were incubated with 100 sMPIOs/cell. The particle-labeled cells and the native cells were imaged using a clinical 3.0 T MRI system, whereas the control groups of the labeled and unlabeled cells were kept at room temperature without exposure to a magnetic field. Viability, formation of reactive oxygen species (ROS), aspartate aminotransferase leakage, and urea and albumin synthesis were assessed for a culture period of 5 days.

RESULTS

The dose finding study showed no adverse effects of the sMPIOs labeling on HuH7 cells. MRI had no adverse effects on the morphology of the sMPIO-labeled primary human hepatocytes. Imaging using the T1- and T2-weighted sequences did not affect the viability, transaminase leakage, formation of ROS, or metabolic activity of the sMPIO-labeled cells or the unlabeled, primary human hepatocytes.

CONCLUSION

sMPIOs did not induce adverse effects on the labeled cells under the conditions of the magnetic field of a clinical MRI system.

Clinical Hepatocyte Transplantation: Practical Limits and Possible Solutions

Since the first human hepatocyte transplants (HTx) in 1992, clinical studies have clearly established proof of principle for this therapy as a treatment for patients with acquired or inherited liver disease. Although major accomplishments have been made, there are still some specific limitations to this technology, which, if overcome, could greatly enhance the efficacy and implementation of this therapy. Here, we describe what in our view are the most significant obstacles to the clinical application of HTx and review the solutions currently proposed. The obstacles of significance include the limited number and quality of liver tissues as a cell source, the lack of clinical grade reagents, quality control evaluation of hepatocytes prior to transplantation, hypothermic storage of cells prior to transplantation, preconditioning treatments to enhance engraftment and proliferation of donor cells, tracking or monitoring cells after transplantation, and the optimal immunosuppression protocols for transplant recipients.

Considerations for the clinical use of contrast agents for cellular MRI in regenerative medicine

Advances in regenerative medicine are rapidly transforming healthcare. A cornerstone of regenerative medicine is the introduction of cells that were grown or manipulated in vitro. Key questions that arise after these cells are re-introduced are: whether these cells are localized in the appropriate site; whether cells survive; and whether these cells migrate. These questions predominantly relate to the safety of the therapeutic approach (i.e. tumorigenesis), but certain aspects can also influence the efficacy of the therapeutic approach (e.g. site of injection). The European Medicines Agency has indicated that suitable methods for stem cell tracking should be applied where these methods are available. We here discuss the European regulatory framework, as well as the scientific evidence, that should be considered to facilitate the potential clinical implementation of magnetic resonance imaging contrast media to track implanted/injected cells in human studies.

Liver support strategies: cutting-edge technologies

The treatment of end-stage liver disease and acute liver failure remains a clinically relevant issue. Although orthotopic liver transplantation is a well-established procedure, whole-organ transplantation is invasive and increasingly limited by the unavailability of suitable donor organs. Artificial and bioartificial liver support systems have been developed to provide an alternative to whole organ transplantation, but despite three decades of scientific efforts, the results are still not convincing with respect to clinical outcome. In this Review, conceptual limitations of clinically available liver support therapy systems are discussed. Furthermore, alternative concepts, such as hepatocyte transplantation, and cutting-edge developments in the field of liver support strategies, including the repopulation of decellularized organs and the biofabrication of entirely new organs by printing techniques or induced organogenesis are analysed with respect to clinical relevance. Whereas hepatocyte transplantation shows promising clinical results, at least for the temporary treatment of inborn metabolic diseases, so far data regarding implantation of engineered hepatic tissue have only emerged from preclinical experiments. However, the evolving techniques presented here raise hope for bioengineered liver support therapies in the future.

In vivo hepatocyte MR imaging using lactose functionalized magnetoliposomes

The aim of this study was to assess a novel lactose functionalized magnetoliposomes (MLs) as an MR contrast agent to target hepatocytes as well as to evaluate the targeting ability of MLs for in vivo applications. In the present work, 17 nm sized iron oxide cores functionalized with anionic MLs bearing lactose moieties were used for targeting the asialoglycoprotein receptor (ASGP-r), which is highly expressed in hepatocytes. Non-functionalized anionic MLs were tested as negative controls. The size distribution of lactose and anionic MLs was determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS). After intravenous administration of both MLs, contrast enhancement in the liver was observed by magnetic resonance imaging (MRI). Label retention was monitored non-invasively by MRI and validated with Prussian blue staining and TEM for up to eight days post MLs administration. Although the MRI signal intensity did not show significant differences between functionalized and non-functionalized particles, iron-specific Prussian blue staining and TEM analysis confirmed the uptake of lactose MLs mainly in hepatocytes. In contrast, non-functionalized anionic MLs were mainly taken up by Kupffer and sinusoidal cells. Target specificity was further confirmed by high-resolution MR imaging of phantoms containing isolated hepatocytes, Kupffer cell (KCs) and hepatic stellate cells (HSCs) fractions. Hypointense signal was observed for hepatocytes isolated from animals which received lactose MLs but not from animals which received anionic MLs. These data demonstrate that galactose-functionalized MLs can be used as a hepatocyte targeting MR contrast agent to potentially aid in the diagnosis of hepatic diseases if the non-specific uptake by KCs is taken into account.

Ex vivo magnetic resonance imaging of transplanted hepatocytes in a rat model of acute liver failure

Hepatocyte transplantation is being evaluated as an alternative to liver transplantation. However, the fate of hepatocytes after transplantation is not well defined. The aims of the study were to improve hepatocyte labeling in vitro using superparamagnetic iron oxide nanoparticles (SPIOs) and to perform in vivo experiments on tracking labeled cells by magnetic resonance imaging (MRI). Human and rat hepatocytes were labeled in vitro for 16 h with clinically approved SPIOs (12.5 µg Fe/ml) and protamine sulfate (3 µg/ml) as a transfection agent. Increased cellular iron uptake was obtained, and cell viability and function were shown not to be affected by labeling. Labeled cells (2,000/µl) could be detected on T2-weighted images in vitro using a 7T MR scanner. In a rat model of acute liver failure (ALF), female recipients received intrasplenic transplantation of 2 × 10(7) male rat hepatocytes 28-30 h after intraperitoneal injection of d-galactosamine (1.2 g/kg). There were four groups (n = 4 each): vehicle injection, injection of freshly isolated cells labeled with CM-DiI, injection of cultured cells labeled with CM-DiI, and injection of cultured cells labeled with both SPIOs and CM-DiI. Ex vivo T2*-weighted gradient-echo images at 7T MRI were acquired at day 7 post-ALF induction. Six days after transplantation, SPIOs were detected in the rat liver as a decrease in the MRI signal intensity in the surviving animals. Histologically, most of the SPIOs were located in Kupffer cells, indicating clearance of labeled hepatocytes. Furthermore, labeled cells could not be detected in the liver by the fluorescent dye or by PCR for the Y-chromosome (Sry-2 gene). In conclusion, optimum conditions to label human hepatocytes with SPIOs were established and did not affect cell viability or metabolic function and were sufficient for in vitro MRI detection. However, the clearance of hepatocytes after transplantation limits the value of MRI for assessing long-term hepatocyte engraftment.

Hepatocyte transplantation for inherited metabolic diseases of the liver

Inherited metabolic diseases of the liver are characterized by deficiency of a hepatic enzyme or protein often resulting in life-threatening disease. The remaining liver function is usually normal. For most patients, treatment consists of supportive therapy, and the only curative option is liver transplantation. Hepatocyte transplantation is a promising therapy for patients with inherited metabolic liver diseases, which offers a less invasive and fully reversible approach. Procedure-related complications are rare. Here, we review the experience of hepatocyte transplantation for metabolic liver diseases and discuss the major obstacles that need to be overcome to establish hepatocyte transplantation as a reliable treatment option in the clinic.

Impact of indium-111 oxine labelling on viability of human mesenchymal stem cells in vitro, and 3D cell-tracking using SPECT/CT in vivo

PURPOSE

This study investigates the effects of (111)In-oxine incorporation on human mesenchymal stem cells' (hMSC) biology and viability, and the applicability of (111)In-oxine for single-photon emission computed tomography/X-ray computed tomography (SPECT/CT) monitoring of hMSC in vivo.

PROCEDURES

HMSC were labelled with 10 Bq/cell. Cellular retention of radioactivity, cell survival, and migration were evaluated over 48 h. Metabolic activity was assessed over 14 days and the hMSC's stem cell character was evaluated. Serial SPECT/CT was performed after intra-osseous injection to athymic rats over 48 h.

RESULTS

Labelling efficiency was 25%, with 61% of incorporated (111)In remaining in the hMSC at 48 h. The radiolabelling was without effect on cell viability, stem cell character, and plasticity, whereas metabolic activity and migration were significantly reduced. Grafted cells could be imaged in situ with SPECT/CT.

CONCLUSIONS

(111)In-oxine labelling moderately impaired hMSC's functional integrity while preserving their stem cell character. Combined SPECT/CT imaging of (111)In-oxine-labelled hMSC opens the possibility for non-invasive sequential monitoring of therapeutic stem cells.

CARS microscopy for the visualization of micrometer-sized iron oxide MRI contrast agents in living cells

Micrometer-sized iron oxide particles (MPIOs) attract increasing interest as contrast agents for cellular tracking by clinical Magnetic Resonance Imaging (MRI). Despite the great potential of MPIOs for in vivo imaging of labeled cells, little is known on the intracellular localization of these particles following uptake due to the lack of techniques with the ability to monitor the particle uptake in vivo at single-cell level. Here, we show that coherent anti-Stokes Raman scattering (CARS) microscopy enables non-invasive, label-free imaging of MPIOs in living cells with sub-micron resolution in three dimensions. CARS allows simultaneous visualization of the cell framework and the MPIOs, where the particles can be readily distinguished from other cellular components of comparable dimensions, and localized inside the cell.

Use of a clinically approved iron oxide MRI contrast agent to label human hepatocytes

Reliable noninvasive methods are needed to monitor cell engraftment and graft survival after hepatocyte transplantation. Superparamagnetic iron oxide nanoparticles (SPIOs) have been shown to accumulate in various types of cells, and are currently the labeling agent of choice for cellular magnetic resonance imaging (MRI). However, for successful clinical translation to hepatocyte transplantation, it is important that hepatocytes maintain their viability and synthetic function after labeling. In this study, primary human hepatocytes were incubated with increasing concentrations of clinical grade SPIOs for different time intervals. SPIOs uptake was confirmed by light and fluorescence microscopy, and intracellular iron content quantified by a colorimetric ferrozine-based assay. Studies were performed to determine if labeling affected cell viability and function. Intracellular iron concentrations increased in a time- and dose-dependent manner after incubation with SPIOs. Labeling had minimal short-term effects on cell attachment and mitochondrial function. However, exposure of hepatocytes to SPIOs resulted in a dose- and time-dependent reduction in protein synthesis. Cell labeling for 16 h had no significant effect on hepatocyte-specific function, but longer periods of incubation resulted in a dose-dependent decrease in albumin production. Hepatocytes incorporated SPIOs at sufficient levels for in vitro detection on a 7-T MRI imaging system, with a minimum of 2,000 SPIO-labeled cells/μl detected by a decreased T2 relaxivity compared to controls. Intrasplenic transplantation of human hepatocytes labeled with 50 μg Fe/ml of SPIOs was performed in nonobese diabetic/severe combined immune deficiency (NOD-Scid) mice. Recipient livers showed a clear decrease in signal intensity on T2*-weighted MR images when compared to controls, allowing detection of hepatocytes. With further experiments to optimize the conditions for labeling human hepatocytes, it should be possible to apply this technique to track hepatocyte transplantation in patients with liver disease.

In vitro evaluation of magnetic resonance imaging contrast agents for labeling human liver cells: implications for clinical translation

PURPOSE

Magnetic resonance imaging (MRI) is a promising approach for non-invasive monitoring after liver cell transplantation. We compared in vitro labeling of human liver cells with nano-sized (SPIO) and micron-sized iron oxide particles (MPIO).

PROCEDURES

The cellular iron load was quantified and phantom studies were performed using 3.0-T MRI. Transferrin receptor and ferritin gene expression, reactive oxygen species (ROS) formation, transaminase leakage, and urea synthesis were investigated over 6 days.

RESULTS

Incubation with MPIO produced stronger signal extinctions in MRI at similar iron loads within shorter labeling time. MPIO had no negative effects on the cellular iron homeostasis or cell performance, whereas SPIO caused temporary ROS formation and non-physiologic activation of the iron metabolic pathway.

CONCLUSIONS

Our findings suggest that MPIO are suited for clinical translation of strategies for cellular imaging with MRI. Attention should be paid to iron release and oxidative stress caused by biodegradable contrast agents.