Treatment of liver failure in rats with end-stage cirrhosis by transplantation of immortalized hepatocytes

A Novel Sprague-Dawley Rat Model Presents Improved NASH/NAFLD Symptoms with PEG Coated Vitexin Liposomes

Chronic liver disease (CLD) is a global threat to the human population, with manifestations resulting from alcohol-related liver disease (ALD) and non-alcohol fatty liver disease (NAFLD). NAFLD, if not treated, may progress to non-alcoholic steatohepatitis (NASH). Furthermore, inflammation leads to liver fibrosis, cirrhosis, and hepatocellular carcinoma. Vitexin, a natural flavonoid, has been recently reported for inhibiting NAFLD. It is a lipogenesis inhibitor and activates lipolysis and fatty acid oxidation. In addition, owing to its antioxidant properties, it appeared as a hepatoprotective candidate. However, it exhibits low bioavailability and low efficacy due to its hydrophobic nature. A novel rat model for liver cirrhosis was developed by CCL4/Urethane co-administration. Vitexin encapsulated liposomes were synthesized by the ‘thin-film hydration’ method. Polyethylene glycol (PEG) was coated on liposomes to enhance stability and stealth effect. The diseased rats were then treated with vitexin and PEGylated vitexin liposomes, administered intravenously and orally. Results ascertained the liposomal encapsulation of vitexin and subsequent PEG coating to be a substantial strategy for treating liver cirrhosis through oral drug delivery.

Current and Emerging Approaches for Hepatic Fibrosis Treatment

Liver fibrosis resulting from chronic liver injury is a key factor to develop liver cirrhosis and risk of hepatocellular carcinoma (HCC) which are major health burden worldwide. Therefore, it is necessary for antifibrotic therapies to prevent chronic liver disease progression and HCC development. There has been tremendous progress in understanding the mechanisms of liver fibrosis in the last decade, which has created new opportunities for the treatment of this condition. In this review, we aim to make an overview on information of different potential therapies (drug treatment, cell therapy, and liver transplantation) for the liver fibrosis and hope to provide the therapeutic options available for the treatment of liver fibrosis and discuss novel approaches.

Mechanisms Underlying Cell Therapy in Liver Fibrosis: An Overview

Fibrosis is a common feature in most pathogenetic processes in the liver, and usually results from a chronic insult that depletes the regenerative capacity of hepatocytes and activates multiple inflammatory pathways, recruiting resident and circulating immune cells, endothelial cells, non-parenchymal hepatic stellate cells, and fibroblasts, which become activated and lead to excessive extracellular matrix accumulation. The ongoing development of liver fibrosis results in a clinically silent and progressive loss of hepatocyte function, demanding the constant need for liver transplantation in clinical practice, and motivating the search for other treatments as the chances of obtaining compatible viable livers become scarcer. Although initially cell therapy has emerged as a plausible alternative to organ transplantation, many factors still challenge the establishment of this technique as a main or even additional therapeutic tool. Herein, the authors discuss the most recent advances and point out the corners and some controversies over several protocols and models that have shown promising results as potential candidates for cell therapy for liver fibrosis, presenting the respective mechanisms proposed for liver regeneration in each case.

Fetal liver stem cell transplantation for liver diseases

Stem cell transplantation exhibited a promising lifesaving therapy for various end-stage liver diseases and could serve as a salvaging bridge until curative methods can be performed. In past decades, mature hepatocytes, liver progenitor cells, mesenchymal stem cells and induced pluripotent stem cells have been practiced in above settings. However, long-term survival rates and continuous proliferation ability of these cells in vivo are unsatisfactory, whereas, fetal liver stem cells (FLSCs), given their unique superiority, may be the best candidate for stem cell transplantation technique. Recent studies have revealed that FLSCs could be used as an attractive genetic therapy or regenerative treatments for inherited metabolic or other hepatic disorders. In this study, we reviewed current status and advancements of FLSCs-based treatment.

Genetic Modification of Hepatocytes towards Hepatocyte Transplantation and Liver Tissue Engineering

Cell-based therapies, including liver tissue engineering following hepatocyte transplantation, have therapeutic potential for several types of liver diseases. Modifications in the methodology to manipulate the donor hepatocytes in a more simple and timely manner prior to transplantation would enhance the therapeutic efficacy of this procedure. Conventional approach for vector-mediated gene transduction to the isolated hepatocytes has been performed under primary culture conditions that routinely require several days to complete. In our study, we have established a clinically feasible approach that requires only 1 h of infection time with an adenoviral vector system that results in an extremely efficient transduction efficiency (>80%). To optimize transduction efficiency and sustain normal cellular function, we determined that the isolated hepatocytes should be maintained in UW solution as a suspension medium and infected with adenoviral vectors (Ad) for no more than 1 h at a MOI of 1. To establish if the isolated hepatocytes could be used as a source for cell-based therapies, we transplanted the Ad-transduced hepatocytes into the liver or under the kidney capsule. When the cells were transplanted into the liver, Ad-transduced hepatocytes cultured in suspension conditions were found to have a significantly higher survival rate (p < 0.01) than Ad-transduced hepatocytes cultured under standard conditions. We also confirmed that these Ad-transduced hepatocytes have ability to survive long term and were able to engineer a biologically active hepatic tissue under the kidney capsule. Finally, we obtained high level of transduction into canine, porcine, and human isolated hepatocytes in a suspension solution mixed with Ad. In conclusion, the present studies demonstrate that isolated hepatocytes could be genetically modified using Ad when kept in a suspension solution. For this reason, this cell-modified technique could be used for the treatment of liver-targeted diseases and/or disorders.

Cryopreserved Fetal Liver Cell Transplants Support the Chronic Failing Liver in Rats with CCl4-Induced Cirrhosis

Hepatocyte transplantation is a promising method for supporting hepatic function in a broad spectrum of liver diseases. The aim of this work was to test the efficacy of human fetal liver cells to support the chronic failing liver in an experimental model of carbon tetrachloride (CCl4)-induced cirrhosis in rats. Liver cirrhosis was induced by intraperitoneal administration of CCl4 at a dose of 0.2 ml (50% v/v solution)/100 g body weight, twice a week for 3 months in rats. Ten days after stopping CCl4 administration (experimental day 0), rats received intrasplenic injection of cryopreserved fetal liver cells (FLC, 1 × 107 cells in 0.3 ml medium). As a cirrhotic control group, CCl4-induced cirrhotic rats were used with intrasplenic injection of an equal volume of medium alone. Animals were sacrificed on experimental day 15. Human fetal liver cell transplantation almost completely prevented the death of cirrhotic animals during the 2 weeks after treatment, while high ongoing mortality was seen in the cirrhotic control group. Cell transplantation into the spleen normalized total bilirubin and TBARSs levels and increased albumin levels in blood serum, as well as restoring mitochondrial function and liver detoxification function (assessed by cytochrome P450 contents and activity) compared with the activities seen in the cirrhosis control group. In parallel with this restoration of biochemical and functional liver indices, morphological patterns of liver recovery or regeneration after liver cell transplantation were demonstrated in day 15 samples by light microscopy. These were absent in the group that had received only medium alone.

Strategies for immortalization of primary hepatocytes

The liver has the unique capacity to regenerate in response to a damaging event. Liver regeneration is hereby largely driven by hepatocyte proliferation, which in turn relies on cell cycling. The hepatocyte cell cycle is a complex process that is tightly regulated by several well-established mechanisms. In vitro, isolated hepatocytes do not longer retain this proliferative capacity. However, in vitro cell growth can be boosted by immortalization of hepatocytes. Well-defined immortalization genes can be artificially overexpressed in hepatocytes or the cells can be conditionally immortalized leading to controlled cell proliferation. This paper discusses the current immortalization techniques and provides a state-of-the-art overview of the actually available immortalized hepatocyte-derived cell lines and their applications.

Cell and tissue engineering for liver disease

Despite the tremendous hurdles presented by the complexity of the liver's structure and function, advances in liver physiology, stem cell biology and reprogramming, and the engineering of tissues and devices are accelerating the development of cell-based therapies for treating liver disease and liver failure. This State of the Art Review discusses both the near- and long-term prospects for such cell-based therapies and the unique challenges for clinical translation.

Hepatocyte transplants improve liver function and encephalopathy in portacaval shunted rats

AIM

Rats with portacaval shunt (PCS) are useful experimental models of human hepatic encephalopathy in chronic liver dysfunction. We have previously shown that PCS modifies amine neurotransmitter systems in the CNS and increases voluntary alcohol intake by rats. Hepatocyte transplantation, used in acute liver failure, has recently also been applied to chronic liver diseases, which prompted us to investigate whether the altered brain amine system and the drinking behavior in long-term shunted rats could be normalized by hepatocyte transplants.

METHODS

Hepatocytes, isolated from syngeneic donors by collagenase digestion, were injected (3 × 10(6) cells/rat) into the pancreatic tail region, 6 months after PCS. Hepatic function was evaluated by measuring urine urea and plasma L-histidine concentrations. A free choice test with two bottles (tap water and 10% ethyl alcohol) was performed for 3 days to assess the rats' preference for alcohol. The rats were euthanized 2 months posttransplantation. Brain histamine and 5-hydroxyindoleacetic acid (5-HIAA) levels were measured by radioenzymatic assay and by HPLC-EC, respectively, N-tele-methylhistamine by GC/MS while MAOA and MAOB activities by isotopic procedures.

RESULTS

Portacaval shunt rats with hepatocyte transplants gave more urea than before transplantation, with lower plasma L-His levels and higher body weight versus the PCS counterparts. Also, those rats consumed less alcohol. The CNS amines and 5-HIAA concentrations, as well as MAO-B activity, being abnormally high in untreated PCS rats, significantly reduced after PCS hepatocyte treatment.

CONCLUSIONS

The results support the therapeutic values of hepatocyte transplants in chronic liver diseases and the temporary character of PCS-exerted CNS dysfunctions.

Blood-derived stem cells (BDSCs) plasticity: in vitro hepatic differentiation

The limited availability of hepatic tissue suitable for the treatment of liver disease and drug research encourages the generation of hepatic-like cells from alternative sources as support for the regenerative medicine. Human blood derived stem cells (BDSCs) express surface markers and genes characteristic of pluripotent stem cells and have the ability to differentiate into different cell types, including tissues of endodermal origin (i.e., liver). Therefore they can represent a valuable source of hepatocytes for medicine. In this investigation, we exploited a fast hepatic differentiation protocol to generate hepatocyte-like cells from human BDSCs using only hepatocyte growth factor (HGF) and fibroblast growth factor-4 (FGF-4) as growth factors. The resulting cell population exhibited hepatic cell-like morphology and it was characterized with a variety of biological endpoint analyses. Here, we demonstrate how human BDSCs can be reprogrammed in hepatocyte-like cells by morphological, functional analysis, reverse transcriptase (RT)-PCR, and Western Blot assay. This study defines a fast and easy reprogramming strategy that facilitates the differentiation of human BDSCs along a hepatic lineage and provides a framework for a helpful source in the stem cells therapy and liver disorders.

Functional random effect time-varying coefficient model for longitudinal data

We propose a functional random effect time-varying coefficient model to establish the dynamic relationship between the response and predictor variables in longitudinal data. This model allows us not only to interpret time-varying covariate effects, but also to depict random effects via time-varying profiles that are characterized by functional principal components. We develop the functional profiling-backfitting method to estimate model components, which includes the profiling and backfitting procedures via a set of least squares type estimating equations. Asymptotic properties of the resulting estimator are obtained. Furthermore, we investigate the finite sample performance of the proposed method through simulation studies and present an application to primary biliary cirrhosis data.

Cell therapeutic options in liver diseases: cell types, medical devices and regulatory issues

Although significant progress has been made in the field of orthotopic liver transplantation, cell-based therapies seem to be a promising alternative to whole-organ transplantation. The reasons are manifold but organ shortage is the main cause for this approach. However, many problems such as the question which cell type should be used or which application site is best for transplantation have been raised. In addition, some clinicians have had success by cultivating liver cells in bioreactors for temporary life support. Besides answering the question which cell type, which injection site or even which culture form should be used for liver support recent international harmonization of legal requirements is needed to be addressed by clinicians, scientists and companies dealing with cellular therapies. We here briefly summarize the possible cell types used to partially or temporarily correct liver diseases, the most recent development of bioreactor technology and important regulatory issues.

Hepatic differentiation of amniotic epithelial cells

Hepatocyte transplantation to treat liver disease is largely limited by the availability of useful cells. Human amniotic epithelial cells (hAECs) from term placenta express surface markers and gene characteristics of embryonic stem cells and have the ability to differentiate into all three germ layers, including tissues of endodermal origin (i.e., liver). Thus, hAECs could provide a source of stem cell-derived hepatocytes for transplantation. We investigated the differentiation of hAECs in vitro and after transplantation into the livers of severe combined immunodeficient (SCID)/beige mice. Moreover, we tested the ability of rat amniotic epithelial cells (rAECs) to replicate and differentiate upon transplantation into a syngenic model of liver repopulation. In vitro results indicate that the presence of extracellular matrix proteins together with a mixture of growth factors, cytokines, and hormones are required for differentiation of hAECs into hepatocyte-like cells. Differentiated hAECs expressed hepatocyte markers at levels comparable to those of fetal hepatocytes. They were able to metabolize ammonia, testosterone, and 17α-hydroxyprogesterone caproate, and expressed inducible fetal cytochromes. After transplantation into the liver of retrorsine (RS)-treated SCID/beige mice, naïve hAECs differentiated into hepatocyte-like cells that expressed mature liver genes such as cytochromes, plasma proteins, transporters, and other hepatic enzymes at levels equal to adult liver tissue. When transplanted in a syngenic animal pretreated with RS, rAECs were able to engraft and generate a progeny of cells with morphology and protein expression typical of mature hepatocytes.

CONCLUSION

Amniotic epithelial cells possess the ability to differentiate into cells with characteristics of functional hepatocytes both in vitro and in vivo, thus representing a useful and noncontroversial source of cells for transplantation.

Transplanted human amniotic membrane-derived mesenchymal stem cells ameliorate carbon tetrachloride-induced liver cirrhosis in mouse

Background

Human amniotic membrane-derived mesenchymal stem cells (hAMCs) have the potential to reduce heart and lung fibrosis, but whether could reduce liver fibrosis remains largely unknown.

Methodology/Principal Findings

Hepatic cirrhosis model was established by infusion of CCl₄ (1 ml/kg body weight twice a week for 8 weeks) in immunocompetent C57Bl/6J mice. hAMCs, isolated from term delivered placenta, were infused into the spleen at 4 weeks after mice were challenged with CCl₄. Control mice received only saline infusion. Animals were sacrificed at 4 weeks post-transplantation. Blood analysis was performed to evaluate alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Histological analysis of the livers for fibrosis, hepatic stellate cells activation, hepatocyte apoptosis, proliferation and senescence were performed. The donor cell engraftment was assessed using immunofluorescence and polymerase chain reaction. The areas of hepatic fibrosis were reduced (6.2%±2.1 vs. control 9.6%±1.7, p<0.05) and liver function parameters (ALT 539.6±545.1 U/dl, AST 589.7±342.8 U/dl,vs. control ALT 139.1±138.3 U/dl, p<0.05 and AST 212.3±110.7 U/dl, p<0.01) were markedly ameliorated in the hAMCs group compared to control group. The transplantation of hAMCs into liver-fibrotic mice suppressed activation of hepatic stellate cells, decreased hepatocyte apoptosis and promoted liver regeneration. More interesting, hepatocyte senescence was depressed significantly in hAMCs group compared to control group. Immunofluorescence and polymerase chain reaction revealed that hAMCs engraftment into host livers and expressed the hepatocyte-specific markers, human albumin and α-fetoproteinran.

Conclusions/Significance

The transplantation of hAMCs significantly decreased the fibrosis formation and progression of CCl₄-induced cirrhosis, providing a new approach for the treatment of fibrotic liver disease.

Labeling and tracking human amniotic epithelial cells with green fluorescent protein in an adeno-associated virus vector

Human amniotic epithelial cells (hAECs) are a recently identified type of stem cell. Thanks to their ready availability and the lower risk of teratoma formation, hAECs have been studied and tested for a variety of human disease treatments and tissue reconstruction efforts. This aim of this study was to establish a stable tracking system to further monitor hAECs in vivo after transplantation. hAECs were isolated from the placentas of patients who visited the Hunan Province Maternity and Child Care Hospitals between Jan 2008 and Jan 2009. Using the classic transfection/infection technique, we successfully introduced green fluorescent protein (GFP) into cultured hAECs with an adeno-associated virus (AAV) vector. The initial preparation of the AAV-GFP virus stock was titrated using HT1081 cells, and further used for the infection of hAECs. GFP(+) hAECs preserve the capacity of differentiation into hepatocyte-like cells with the expression of cytokeratin-18 (CK18) and albumin (ALB). AAV-GFP virus-infected hAECs were transplanted through the spleen into severe combined immune deficiency (SCID) mice via hepatectomy. Four weeks later, the GFP and human albumin expressions were examined in multiple organs through immunofluorescence staining. In culture, over 50% of the hAECs were GFP-positive 3 days after infection. Following transplantation, AAV-GFP-infected hAECs survived and continued to express GFP in the host for up to 4 weeks. These cells were primarily found in the spleen and liver, expressing human albumin. This study provides a feasible and stable system to track hAECs. It may prove useful to further identify their biological characteristics after transplantation and to elucidate their beneficial roles for therapeutic purposes.

Human hepatocyte transplantation

Over the last decade the interest in hepatocyte transplantation has been growing continuously and this treatment may represent an alternative clinical approach for patients with acute liver failure and life-threatening liver-based metabolic disorders. The technology also serves as the proof of concept and reference for future development in stem cell technology. This chapter reviews the field of hepatocyte transplantation from bench to bedside.

Genetic modification of donor hepatocytes improves therapeutic efficacy for hemophilia B in mice

Hepatocyte transplantation (Tx) holds promise for curing genetic liver diseases. However, a limited number of donor hepatocytes can be transplanted into the host liver. Recipient preconditioning and donor cell engineering are under investigation to improve cell engraftment. In theory, genetically engineered cells secreting therapeutic proteins with superior function could compensate for poor engraftment efficiency. We have generated a bioengineered human coagulation factor IX (FIX) with augmented specific activity (named FIX-Triple). The aim of this study was to evaluate therapeutic efficacy of cell therapy using hemophilia B (HB) as a disease model by transplanting FIX-Triple-secreting hepatocytes. The donor hepatocytes were isolated from FIX-Triple knock-in (KI) or FIX-WT (wild-type) KI mice and transplanted intrasplenically into FIX knock-out (KO) mice. FIX-Triple KI recipients exhibited fourfold higher plasma FIX clotting activity than FIX-WT KI recipients. By repeated Txs, the clotting activity of FIX-Triple KI recipients even increased to more than 10% of normal mouse plasma. The engraftment and FIX production efficiencies of transplanted cells were equivalent between the FIX-WT KI and FIX-Triple KI donors. A hemostatic function assay showed that FIX-Triple KI recipients with repeated Txs had more enhanced clot kinetics and a greater maximum rate of thrombus generation than those with a single Tx. Moreover, FIX inhibitors in these recipients rarely developed. In conclusion, hepatocyte Tx with genetically engineered donor cells is an effective therapeutic strategy for HB.

Human hepatocyte transplantation: state of the art

Hepatocyte transplantation is making its transition from bench to bedside for liver-based metabolic disorders and acute liver failure. Over eighty patients have now been transplanted world wide and the safety of the procedure together with medium-term success has been established. A major limiting factor in the field is the availability of good quality cells as hepatocytes are derived from grafts that are deemed unsuitable for transplantation. Alternative sources of cell, including stem cells may provide a sustainable equivalent to primary hepatocytes. There is also a need to develop techniques that will improve the engraftment, survival and function of transplanted hepatocytes. Such developments may allow hepatocyte transplantation to become an accepted and practical alternative to liver transplantation in the near future.

Suppression of carbon tetrachloride-induced liver fibrosis by transplantation of a clonal mesenchymal stem cell line derived from rat bone marrow

Transplantation of hepatocytes or bone marrow-derived cells has been shown to ameliorate liver fibrosis in animal models, but no direct comparison of relative efficiency has been made. The aim of this study was to compare the efficiency of a bone marrow-derived clonal mesenchymal stem cell line established by us (rBM25/S3) with that of its adipogenic or hepatogenic differentiation derivative for suppression of rat liver fibrosis. After induction of differentiation of rBM25/S3 cells into adipogenic or hepatogenic cells in culture, we intrasplenically transplanted the three types of cells into rats (3 x 10(7) cells/rat) before and 4 weeks after initiation of carbon tetrachloride treatment (1 ml/kg body weight twice a week for 8 weeks) to induce liver fibrosis. Undifferentiated rBM25/S3 cells were the most effective for suppression of liver fibrosis, followed by the adipogenic cells and hepatogenic cells. Expression levels of MMP-2 and MMP-9 were also highest in undifferentiated rBM25/S3 cells. These results indicate that bone marrow-derived clonal mesenchymal stem cell lines are useful for further mechanistic studies on cell-mediated suppression of liver fibrosis and that such cell lines will provide information on an appropriate cell source for transplantation therapy for cirrhosis.

Hepatocyte transplantation in animal models

More than 30 years after the first hepatocyte transplant to treat the Gunn rat, the animal model for Crigler-Najjar syndrome, there are still a number of impediments to hepatocyte transplantation. Numerous animal models are still used in work aimed at improving hepatocyte engraftment and/or long-term function. Although other cell sources, particularly hepatic and extrahepatic stem cells, are being explored, adult hepatocytes remain the cells of choice for the treatment of liver diseases by cell therapy. In recent years, diverse approaches have been developed in various animal models to enhance hepatocyte transduction and amplification in vitro and cell engraftment and functionality in vivo. They have led to significant progress in hepatocyte transplantation for the treatment of patients with metabolic diseases and for bridging patients with acute injury until their own livers regenerate. This review presents and considers the results of this work with a special emphasis on procedures that might be clinically applicable.

Human hepatocyte transplantation overview

The interest in hepatocyte transplantation has been growing continuously in recent years and this treatment may represent an alternative clinical approach for patients with acute liver failure and liver-based metabolic disorders. This chapter presents an overview of liver cell transplantation, from the basic research to human experience. It summarizes the pre-clinical studies and present status of clinical hepatocyte transplantation and identifies some possible areas of future research in this area.

Review of hepatocyte transplantation

BACKGROUND

Hepatocyte transplantation is a promising treatment for several liver diseases and can also be used as a "bridge" to liver transplantation in cases of liver failure. Although the first animal experiments with this technique began in 1967, it was first applied in humans only in 1992. Unfortunately, unequivocal evidence of transplanted human hepatocyte function has been obtained in only one patient with Crigler-Najjar syndrome type I and, even then, the amount of bilirubin-UDP-glucuronosyltransferase enzyme activity derived from the transplanted cells was not sufficient to eliminate the patient's eventual need for organ transplantation.

METHODS

A literature review was carried out using MEDLINE and library searches.

RESULTS

This review considers the following: (1) alternatives or bridges to orthotopic liver transplantation (OLT); (2) solutions to the shortage of organs-the shortage of organ donors has impeded the development of human hepatocyte transplantation, and immortalized hepatocytes in particular could provide an unlimited supply of transplantable cells in a nearly future; (3) future directions. We review these efforts along with hepatocyte transplantation over the last 13 years.

Cellular Transplantation for Liver Diseases

Presently, the orthotropic liver transplantation (OLT) is still the most effective therapeutic for patients with acute or chronic hepatic failure. However, due to the shortage of donor livers, the number of patients benefited from this approach is limited. Therefore, some alternative modalities have been paid attention for restoring the liver function. The cell transplantation is one of the promising modalities to realize this purpose. The types of cells used in the cell transplantation include syngeneic hepatocytes, allogeneic hepatocytes, immortalized hepatocytes, and stem cells derived heptocytes. The stem cells, especially the adult stem cells from bone marrow, are shown as a promising cell source for liver repopulation. The mesenchymal bone marrow stem cells and embryonic stem cells can be induced to differentiate into the hepatic lineage and might be used in the cell transplantation for liver diseases. Compared to OLT, the advantages of cell-based therapy for liver disease are, but not limited to, less invasive, less expensive, easy manipulated, easy expansion of cells in vitro. Cells can be stored in a cell bank for future use. Though most of the current studies are experimental and animal based, the cellular therapy for liver disease is expected to be an effective alternative in clinical settings in near future.

Hepatic repopulation with stably transduced conditionally immortalized hepatocytes in the Gunn rat

BACKGROUND/AIMS

Conditionally immortalized hepatocytes offer a renewable source of hepatocytes, but although preparative maneuvers have been developed for hepatic repopulation with primary hepatocytes, extensive proliferation of transplanted immortalized hepatocytes has not been accomplished heretofore. Our aim was to achieve ex vivo gene therapy of uridinediphosphoglucuronate glucuronosyltransferase-1A1 (UGT1A1)-deficient jaundiced Gunn rats (model of Crigler-Najjar syndrome type-1) by hepatic repopulation with genetically modified and conditionally immortalized hepatocytes.

METHODS

Gunn rat hepatocytes were conditionally immortalized by stable transduction with a thermolabile mutant simian virus 40 T-antigen ((ts)Tag(A58)) and further transduced with UGT1A1. These hepatocytes proliferate at 33 degrees C, but at 37 degrees C the (ts)Tag(A58) is degraded and the cells become quiescent. The cells were transplanted into Gunn rat livers after preparative hepatic irradiation (50 Gy) and 66% hepatectomy.

RESULTS

The engrafted UGT1A1-positive immortalized hepatocytes replaced approximately 80% of the host hepatocytes in 20 weeks, leading to normalization of hyperbilirubinemia. Liver histology, and serum albumin and alanine aminotransferase levels remained normal.

CONCLUSIONS

We achieved complete cure of hyperbilirubinemia in Gunn rats by ex vivo gene therapy via genetically modified and conditionally immortalized hepatocytes.

Systemic and local release of inflammatory cytokines regulates hepatobiliary excretion of 99mTc-mebrofenin

OBJECTIVES

Imaging agents capable of providing cell compartment-specific information will facilitate studies of pathophysiological mechanisms, natural history of diseases, and therapeutic development. To demonstrate the effects of liver injury on the disposal of the organic anion mebrofenin, we performed animal studies.

METHODS

Acute liver injury was induced in Fischer 344 rats with 0.25-1 ml/kg single doses of carbon tetrachloride followed by studies of animals over 4 weeks. The liver injury was analyzed by blood tests and histological grading. Additional rats were treated with lipopolysaccharide, interleukin-6 or tumor necrosis factor-alpha to activate inflammatory events. Hepatic clearance of Tc-mebrofenin was studied with dynamic imaging and fractional retention after 60 min of peak hepatic mebrofenin activity was determined.

RESULTS

In healthy rats, only 24+/-2% of peak mebrofenin activity was retained in the liver after 60 min. By contrast, 24 h after carbon tetrachloride, virtually all mebrofenin activity was retained in the liver (P<0.001). Three weeks were required for mebrofenin excretion to become normal after carbon tetrachloride administration. In this situation, we found that Kupffer cell activity was increased. In addition, the abnormality in mebrofenin excretion was reproduced by lipopolysaccharide, which activates Kupffer cells. Moreover, mebrofenin excretion was highly sensitive to interleukin-6 and/or tumor necrosis factor-alpha, which help mediate the Kupffer cell response.

CONCLUSION

Hepatobiliary excretion of mebrofenin was affected rapidly and over an extended period by inflammatory cytokines released after liver injury. The remarkable sensitivity of mebrofenin excretion to cytokines suggests that Tc-mebrofenin imaging will be helpful for assessing cytokine-mediated liver inflammation.

Protective effects of total flavonoids of Bidens pilosa L. (TFB) on animal liver injury and liver fibrosis

The hepatoprotective effects of total flavonoids of Bidens pilosa L. (TFB), a traditional Chinese medicine were evaluated in carbon tetrachloride (CCl(4))-induced liver injury in mice and rats. Total flavonoids of Bidens pilosa L. (25, 50 and 100mg/kg) were administered via gavage daily for 10 days to CCl(4)-treated mice as well as TFB (30, 60 and 90mg/kg) administered for 6 weeks to CCl(4)-treated rats. Liver index (liver weight/body weight), serum levels of transaminases (alanine aminotransferase, ALT and aspartate aminotransferase, AST), hepatic malondialdehyde (MDA) content, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were evaluated following the 10 days treatment in mice. In addition histopathologic changes and nuclear factor-kappaB (NF-kappaB) expression of the liver were detected with hematoxylin-eosin (HE) and immunohistochemistry methods, respectively. The results showed that TFB (50 and 100mg/kg) effectively reduced the CCl(4)-induced elevated liver index, serum ALT, AST levels, hepatic MDA content, and restored hepatic SOD, GSH-Px activities in acute liver injury mice. TFB (60 and 90mg/kg) treatment significantly inhibited NF-kappaB activation in liver fibrosis of rats. The histopathological analysis suggested that TFB reduced the degree of liver injury in mice and severity of liver fibrosis in rats. These results suggested that TFB had a protective and therapeutic effect on animal liver injury, which might be associated with its antioxidant properties and inhibition of NF-kappaB activation.

Liver cirrhosis

Cirrhosis is defined as the histological development of regenerative nodules surrounded by fibrous bands in response to chronic liver injury, which leads to portal hypertension and end-stage liver disease. Recent advances in the understanding of the natural history and pathophysiology of cirrhosis, and in treatment of its complications, have resulted in improved management, quality of life, and life expectancy of patients. Liver transplantation remains the only curative option for a selected group of patients, but pharmacological treatments that can halt progression to decompensated cirrhosis or even reverse cirrhosis are currently being developed. This Seminar focuses on the diagnosis, complications, and management of cirrhosis, and new clinical and scientific developments.

Liver cirrhosis

Cirrhosis is defined as the histological development of regenerative nodules surrounded by fibrous bands in response to chronic liver injury, which leads to portal hypertension and end-stage liver disease. Recent advances in the understanding of the natural history and pathophysiology of cirrhosis, and in treatment of its complications, have resulted in improved management, quality of life, and life expectancy of patients. Liver transplantation remains the only curative option for a selected group of patients, but pharmacological treatments that can halt progression to decompensated cirrhosis or even reverse cirrhosis are currently being developed. This Seminar focuses on the diagnosis, complications, and management of cirrhosis, and new clinical and scientific developments.

Prevention of hepatocyte allograft rejection in rats by transferring adenoviral early region 3 genes into donor cells

Hepatocyte transplantation is being evaluated as an alternative to liver transplantation for metabolic support during liver failure and for definitive treatment of inherited liver diseases. However, as with liver transplantation, transplantation of allogeneic hepatocytes requires prolonged immunosuppression with its associated untoward effects. Therefore, we explored strategies for the genetic modification of donor hepatocytes that could eliminate allograft rejection, obviating the need for immunosuppression. Products of early region 3 (AdE3) of the adenoviral genome are known to protect infected cells from immune recognition and destruction. In the present study we showed that immortalized rat hepatocytes that had been stably transduced with AdE3 before transplantation into fully MHC-mismatched rats are protected from allograft rejection. Quantitative real-time PCR analysis showed that a similar number of engrafted AdE3-transfected hepatocytes had survived in syngeneic and allogeneic recipients. AdE3 expression did not reduce expression of MHC class I on the surfaces of donor hepatocytes. Consistent with this, the in vivo cytotoxic cell-mediated alloresponse was attenuated but not abolished in recipients of AdE3-transfected allogeneic hepatocytes. In contrast, graft survival correlated with a marked reduction in cell-surface localization of Fas receptor in the transplanted cells and inhibition of Fas-mediated apoptosis, which are related to the antiapoptotic functions of the AdE3 proteins.

CONCLUSION

AdE3 gene products prevent hepatocyte allograft rejection mainly by protecting the cells from the effector limb of the host immune response and could be used as a tool to facilitate allogeneic hepatocyte transplantation.

Prolonged survival of porcine hepatocytes in cynomolgus monkeys

BACKGROUND & AIMS

Management of patients with liver failure can be a significant medical challenge, and transplantation of the liver is the only definitive therapy. Whole liver allotransplantation is limited by a shortage of human donors and the risks of the surgery in those most ill. Transplants consisting of xenogeneic hepatocytes might overcome these problems, and work in rodents indicates that such transplants can correct some metabolic deficiencies and can prevent the complications and mortality associated with hepatic failure. As a prelude to clinical application, we tested the feasibility of hepatocyte xenotransplantation in nonhuman primates.

METHODS

One to 2 billion hepatocytes from outbred swine were transplanted into the spleens of cynomolgus monkeys using conventional immunosuppression to control rejection. Duration of graft function was determined based on assay for porcine albumin.

RESULTS

Following a single infusion, xenogeneic hepatocytes functioned for more than 80 days and, following re-transplantation, for more than 253 days. Engraftment in the spleen was confirmed 40 days after transplantation by asialoglycoprotein receptor-directed nuclear scanning. The humoral immune response to the transplanted porcine cells had no discernible impact on the survival of the grafts.

CONCLUSIONS

Xenotransplantation of hepatocytes should be explored as a readily available, minimally invasive form of therapy for hepatic failure.

Historical aspects of hepatocyte transplantation

Hepatocyte transplantation has been used for temporary metabolic support of patients in end-stage liver failure awaiting whole organ transplantation as a method to support liver function and facilitate regeneration of the native liver in cases of fulminant hepatic failure and as a "cellular therapy" for patients with genetic defects in vital liver functions. The aim of this paper was to discuss the basic research that led to clinical hepatocyte transplantation, the published clinical experience with this experimental technique, and some possible future uses of hepatocyte transplantation.

Hepatic Stem Cells: In Search of

The field of stem cell biology has exploded with the study of a wide range of cellular populations involving endodermal, mesenchymal, and ectodermal organs. One area of extensive study has included the identification of hepatic stem and progenitor cell subpopulations. Liver stem cells provide insights into the potential pathways involving liver regeneration that are independent of mature hepatocytes. Hepatic progenitor cells are either bipotent or multipotent and capable of multiple rounds of replication. They have been identified in fetal as well as adult liver. Various injury models have been used to expand this cellular compartment. The nomenclature, origin, and function of the hepatic progenitor cell populations are areas of ongoing debate. In this review, we will discuss the different definitions and functions of hepatic progenitor cells as well as the current research efforts examining their therapeutic potential.

Hepatocyte transplantation: clinical experience and potential for future use

Hepatocyte transplantation has been proposed as a method to support patients with liver insufficiency. There are three main areas where the transplantation of isolated hepatocytes has been proposed and used for clinical therapy. Cell transplantation has been used: 1) for temporary metabolic support of patients in end-stage liver failure awaiting whole organ transplantation, 2) as a method to support liver function and facilitate regeneration of the native liver in cases of fulminant hepatic failure, and 3) in a manner similar to gene therapy, as a "cellular therapy" for patients with genetic defects in vital liver functions. We will briefly review the basic research that leads to clinical hepatocyte transplantation, the published clinical experience with this experimental technique, and some possible future uses of hepatocyte transplantation.

Study of hepatocyte differentiation using embryonic stem cells

The liver has many crucial functions including metabolizing dietary molecules, detoxifying compounds, and storing glycogen. The hepatocytes, comprising most of the liver organ, progressively modify their gene expression profile during the fetal development according to their roles in the different phases of development. Embryonic stem (ES) cells serve as a major tool in understanding liver development. These cells may also serve as a source of hepatic cells for cellular therapy. In this review, we aim to summarize the research that has been performed in the field of hepatocyte differentiation from mouse and human ES cells. We discuss the various methodologies for the differentiation of ES cells towards hepatic cells using either spontaneous or directed differentiation protocols. Although many protocols for differentiating ES cells to hepatic cells have been developed, the analysis of their status is not trivial and can lead to various conclusions. Hence, we discuss the issues of analyzing hepatocytes by means of the specificity of the markers for hepatocytes and the status of the cells as fetal or adult hepatocytes.

Present status and perspectives of cell-based therapies for liver diseases

In recent years the interest in liver cell therapy has been increasing continuously, since the demand for whole liver transplantations in human beings far outweighs the supply. From the clinical point of view, transplantation of hepatocytes or hepatocyte-like cells may represent an alternative to orthotopic liver transplants in acute liver failure, for the correction of genetic disorders resulting in metabolically deficient states, and for late stage liver disease such as cirrhosis. Although the concept of cell therapy for various diseases of the liver is widely accepted, the practical approach in humans often remains difficult. An international expert panel critically discussed the recent published data on clinical and experimental hepatocyte transplantation and the possible role of stem cells in liver tissue repair. This paper aims to summarise the present status of cell based therapies for liver diseases and to identify areas of future preclinical and clinical research.

Treatment of acetaminophen-induced acute liver failure in the mouse with conditionally immortalized human hepatocytes

BACKGROUND/AIMS

Liver failure is a life threatening condition currently treated by palliative measures and, when applicable, organ transplantation. The use of a bioartificial organ capable of fulfilling the main functions of the liver would represent an attractive alternative. However, the shortage of suitable donor cells, and their limited growth ability have impeded the development of this strategy. We investigated whether lentiviral vectors allow for conditional immortalization of human hepatocytes and whether these immortalized hepatocytes could reverse lethal acute liver failure.

METHODS

We exposed primary human hepatocytes to Cre-excisable lentiviral vectors coding for SV40T Antigen, telomerase, and/or Bmi-1 and tested the functionality of the resulting cell lines. Therapeutic potential of immortalized hepatocytes were tested in a murine model of acetaminophen-induced hepatic injury.

RESULTS

The immortalized hepatocytes grew continuously yet were non-tumorigenic, stopped proliferating when exposed to Cre recombinase, and conserved defining properties of primary hepatocytes, including the ability to secrete liver-specific proteins and to detoxify drugs. The implantation of encapsulated immortalized human hepatocytes rescued mice from lethal doses of acetaminophen.

CONCLUSIONS

Lentiviral vectors represent tools of choice for immortalization of non-dividing primary cells, and lentivirally immortalized human hepatocytes are promising reagents for cell-based therapy of acute liver failure.

Characteristics of hepatocytes derived from early ES cells and treatment of surgically induced liver failure rats by transplantation

BACKGROUND

Although liver transplantation has become a standard therapy for diseases such as fulminant hepatitis and cirrhosis, the lack of donor organs remains a major problem. One solution is the development of transplantable hepatocytes. The metabolic characteristics as well as function and adaptation of hepatocytes (R-EES-hep cell) derived from rat early embryonic stem cells were examined after transplantation into rats with surgically induced liver failure.

METHODS

Rat hepatocyte cell lines were established from early embryonic stem cells cultured in the presence of embryotrophic factors by colony cloning methods. The cell lines were established from two cell embryos taken from spontaneous dwarf rats using the novel method of Ishiwata et al. Morphologic differentiation as well as albumin and bilirubin production were observed by immunostaining. R-EES-hep cells were transplanted into the spleens of 90% hepatectomized, surgically induced liver failure rats to analyze survival rates.

RESULTS

When cultured in type I collagen gel the cells formed cordlike structures resembling the liver. Both albumin and bilirubin production were observed when transplanted; the spleen was converted into a liver-like structure with prolonged survival of the 90% hepatectomized rats for up to 3 months up to the time of killing.

CONCLUSIONS

R-EES-hep cells showed many of the distinctive metabolic characteristics of the liver. These cells may be efficient for further research and application for hepatic cell transplantation to treat liver insufficiency patients and as biologic artificial organs.

The newly established human hepatocyte cell line: application for the bioartificial liver

BACKGROUND/AIMS

Human hepatocyte cell lines are reported to lose many of their biochemical functions in a hybrid artificial liver support system (HALSS). Differentiation therapy is useful to up-regulate liver function.

METHODS

The human hepatoblastoma cell line HepG2 was transfected with HSV/tk gene. Albumin synthesis and ammonia removal activity were evaluated when HepG2/tk was cultured with histone deacetylase inhibitor (FR228) and peroxisome proliferator activated receptor-gamma ligand (pioglitazone). To investigate the function of HepG2/tk in vivo, cell transplantation for 90% hepatectonized rats was conducted.

RESULTS

We established stable cell lines which expressed HSV/tk and were sensitive to gancyclovir in vitro and in vivo. Both albumin synthesis rate and ammonia removal rate improved for HepG2/tk incubated with FR228 and pioglitazone for 3 days, which induced nuclear transport of p21. Rats with intrasplenic injection of HepG2/tk precultured for 3 days with FR228 and pioglitazone survived significantly longer than the control rats. The ammonia and total bilirubin concentrations were significantly lower in the test group than in the control group. The injection of gancyclovir inhibited the prolonged survival of the rats with precultured HepG2/tk.

CONCLUSIONS

HepG2/tk is safe as well as enhancing high levels of liver function. It will be a potential cell source for HALLS in the future.

Toward the survival and function of xenogeneic hepatocyte grafts

Xenogeneic hepatocyte transplantation might offer an unobtrusive alternative to whole liver allotransplantation. Having previously found that the immune response to such grafts can be controlled by immunosuppression, we sought approaches to collection and delivery that would optimize survival and function after transplantation. Porcine hepatocytes were isolated by a 2-step collagenase technique and then: 1) used immediately; 2) stored in University of Wisconsin (UW) solution at 4 degrees C; 3) cultured in supplemented Williams E medium; or 4) cryopreserved in UW solution with 10% dimethyl sulfoxide (DMSO). The fate and function of the hepatocytes was determined after they were injected into the spleens of immunodeficient mice. Freshly isolated hepatocytes had better viability (92.2 +/- 1.9%) than hepatocytes cultured for 24 hours (78.4 +/- 6.3%), hypothermically preserved in UW solution for 24 hours (85.8 +/- 3.1%), or cryopreserved (65.0 +/- 2.6%). Freshly isolated hepatocytes secreted more albumin after transplantation than hepatocytes that were cultured, hypothermically stored, or cryopreserved. In conclusion, culture and storage profoundly compromises the function of isolated hepatocytes after transplantation. Freshly isolated hepatocytes are the preferred source for transplantation.

Hepatocytes cultured in alginate microspheres: an optimized technique to study enzyme induction

An important application of hepatocyte cultures is identification of drugs acting as inducers of biotransformation enzymes that alter metabolic clearance of other therapeutic agents. In the present study we optimized an in vitro system with hepatocytes cultured in alginate microspheres that allow studies of enzyme induction with excellent sensitivity. Induction factors obtained with standard inducers, such as 3-methylcholanthrene or phenobarbital, were higher compared to those with conventional hepatocyte co-cultures on collagen coated dishes. This is illustrated by activities of 7-ethoxyresorufin-O-deethylase (EROD) after incubation with 5 microM 3-methylcholanthrene (3-MC), a standard inducer for cytochrome P4501A1 and 1A2. Mean activities for solvent controls and 3-MC exposed cells were 2.99 and 449 pmol/min/mg protein (induction factor: 150) for hepatocytes cultured in microspheres compared to 2.72 and 80.6 pmol/min/mg (induction factor: 29.6) for hepatocytes on collagen coated dishes. To compare these in vitro data to the in vivo situation male Sprague Dawley rats, the same strain that was used also for the in vitro studies, were exposed to 3-MC in vivo using a protocol that guarantees maximal induction. Activities were 29.2 and 1656 pmol/min/mg in liver homogenate of solvent and 3-MC treated animals (induction factor: 56.7). Thus, the absolute activities of 3-MC exposed hepatocytes in microspheres are lower compared to the in vivo situation. However, the induction factor in vitro was even higher compared to the in vivo situation (150-fold versus 56.7-fold). A similar scenario was observed using phenobarbital (0.75 mM) for induction of CYP2B and 3A isoenzymes: induction factors for testosterone hydroxylation in position 16beta were 127.5- and 50.4-fold for hepatocytes in microspheres and conventionally cultured hepatocytes, respectively. The new in vitro system with hepatocytes embedded in solid alginate microspheres offers several technical advantages: (i) the solid alginate microspheres can be liquefied within 60s, allowing a fast and complete harvest of hepatocytes; (ii) alginate capsules are stable allowing transport and mechanical stress; (iii) high numbers of hepatocytes can be encapsulated in short periods; (iv) defined cell numbers between 600 hepatocytes, the approximate number of cells in one capsule, and 18 x 10(6) hepatocytes, the number of hepatocytes in 6 ml alginate, can be transferred to a culture dish or flask. Thus, encapsulated hepatocytes allow a flexible organization of experiments with respect to cell number. In conclusion, we optimized a technique for encapsulation of hepatocytes in alginate microspheres that allows identification of enzyme induction with an improved sensitivity compared to existing systems.

Hepatocyte transplantation

Isolated hepatocyte transplantation has long been recognized as a potential treatment for life-threatening liver disease. The basis for proceeding with clinical trials has been established by the extensive laboratory work in animal models. Human hepatocyte transplantation has been applied in individual cases and very small, uncontrolled series. Data, although sparse, demonstrate the safety and feasibility of this approach and are supportive, if less than conclusive, of effectiveness. The experience of hepatocyte transplantation in the laboratory and clinical arenas is reviewed and discussion will examine what is believed to be the primary cause for the slow growth of this technology in the clinical setting, namely a severe shortage of usable primary human hepatocytes. The potential of isolated hepatocyte transplantation remains largely untapped and awaits alternate sources of cells for transplantation other than those from discarded human cadaveric livers.

Hepatocyte transplantation

Numerous laboratory studies have shown that hepatocyte transplantation may serve as an alternative to organ transplantation for patients with life-threatening liver disease. Because of the successes of experimental hepatocyte transplantation, institutions have attempted to use this therapy in the clinic for the treatment of a variety of hepatic diseases. Unfortunately, unequivocal evidence of transplanted human hepatocyte function has been obtained in only one patient with Crigler-Najjar syndrome type I, and, even then, the amount of bilirubin-UGT enzyme activity derived from the transplanted cells was not sufficient to eliminate the patient's eventual need for organ transplantation. A roadmap for improving patient outcome following hepatocyte transplantation can be obtained by a re-examination of previous animal research. A better understanding of the factors that allow hepatocyte integration and survival in the liver and spleen is needed to help reduce the need for repeated cell infusions and multiple donors. Although clinical evidence of hepatocyte function can be used to indicate function of transplanted hepatocytes, definitive histologic evidence is difficult to obtain. In order to assess whether rejection is taking place in a timely fashion, a reliable way of detecting donor hepatocytes will be needed. The most important issue affecting transplantation, however, relates to donor availability. Alternatives to the transplantation of allogeneic human hepatocytes include transplantation of hepatocytes derived from fetal, adult or embryonic stem cells, engineered immortalized cells, or hepatocytes derived from other animal species.