MRI of iron-oxide labelled transplanted hepatocytes in mice: effect of treatment with cyclophosphamide

Novel alternative transplantation therapy for orthotopic liver transplantation in liver failure: A systematic review

BACKGROUND

Orthotopic liver transplantation (OLT) is the only treatment for end-stage liver failure; however, graft shortage impedes its applicability. Therefore, studies investigating alternative therapies are plenty. Nevertheless, no study has comprehensively analyzed these therapies from different perspectives.

AIM

To summarize the current status of alternative transplantation therapies for OLT and to support future research.

METHODS

A systematic literature search was performed using PubMed, Cochrane Library and EMBASE for articles published between January 2010 and 2018, using the following MeSH terms: [(liver transplantation) AND cell] OR [(liver transplantation) AND differentiation] OR [(liver transplantation) AND organoid] OR [(liver transplantation) AND xenotransplantation]. Various types of studies describing therapies to replace OLT were retrieved for full-text evaluation. Among them, we selected articles including in vivo transplantation.

RESULTS

A total of 89 studies were selected. There are three principle forms of treatment for liver failure: Xeno-organ transplantation, scaffold-based transplantation, and cell transplantation. Xeno-organ transplantation was covered in 14 articles, scaffold-based transplantation was discussed in 22 articles, and cell transplantation was discussed in 53 articles. Various types of alternative therapies were discussed: Organ liver, 25 articles; adult hepatocytes, 31 articles; fetal hepatocytes, three articles; mesenchymal stem cells (MSCs), 25 articles; embryonic stem cells, one article; and induced pluripotent stem cells, three articles and other sources. Clinical applications were discussed in 12 studies: Cell transplantation using hepatocytes in four studies, five studies using umbilical cord-derived MSCs, three studies using bone marrow-derived MSCs, and two studies using hematopoietic stem cells.

CONCLUSION

The clinical applications are present only for cell transplantation. Scaffold-based transplantation is a comprehensive treatment combining organ and cell transplantations, which warrants future research to find relevant clinical applications.

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.

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.

Current status of hepatocyte transplantation

Hepatocyte transplantation (HT) has been performed in patients with liver-based metabolic disease and acute liver failure as a potential alternative to liver transplantation. The results are encouraging in genetic liver conditions where HT can replace the missing enzyme or protein. However, there are limitations to the technique, which need to be overcome. Unused donor livers to isolate hepatocytes are in short supply and are often steatotic, although addition of N-acetylcysteine improves the quality of the cells obtained. Hepatocytes are cryopreserved for later use and this is detrimental to metabolic function on thawing. There are improved cryopreservation protocols, but these need further refinement. Hepatocytes are usually infused into the hepatic portal vein with many cells rapidly cleared by the innate immune system, which needs to be prevented. It is difficult to detect engraftment of donor cells in the liver, and methods to track cells labeled with iron oxide magnetic resonance imaging contrast agents are being developed. Methods to increase cell engraftment based on portal embolization or irradiation of the liver are being assessed for clinical application. Encapsulation of hepatocytes allows cells to be transplanted intraperitoneally in acute liver failure with the advantage of avoiding immunosuppression. Alternative sources of hepatocytes, which could be derived from stem cells, are needed. Mesenchymal stem cells are currently being investigated particularly for their hepatotropic effects. Other sources of cells may be better if the potential for tumor formation can be avoided. With a greater supply of hepatocytes, wider use of HT and evaluation in different liver conditions should be possible.