Regenerative cell therapy for the treatment of hyperbilirubinemic Gunn rats with fresh and frozen human induced pluripotent stem cells-derived hepatic stem cells.

Pluripotent stem cells have been investigated as a renewable source of therapeutic hepatic cells, in order to overcome the lack of transplantable donor hepatocytes. Whereas different studies were able to correct hepatic defects in animal models, they focused on the most mature phenotype of hepatocyte-like cells (HLCs) derived from pluripotent stem cells and needed freshly prepared cells, which limits clinical applications of HLCs. Here, we report the production of hepatic stem cells (pHSCs) from human-induced pluripotent stem cells (hiPSCs) in xeno-free, feeder-free, and chemically defined conditions using as extracellular matrix a recombinant laminin instead of Matrigel, an undefined animal-derived matrix. Freshly prepared and frozen pHSCs were transplanted via splenic injection in Gunn rats, the animal model for Crigler-Najjar syndrome. Following cell transplantation and daily immunosuppression treatment, bilirubinemia was significantly decreased (around 30% decrease, P < .05) and remained stable throughout the 6-month study. The transplanted pHSCs underwent maturation in vivo to restore the deficient metabolic hepatic function (bilirubin glucuronidation by UGT1A1). In conclusion, we demonstrate for the first time the differentiation of hiPSCs into pHSCs that (a) are produced using a differentiation protocol compatible with Good Manufacturing Practices, (b) can be frozen, and (c) are sufficient to demonstrate in vivo therapeutic efficacy to significantly lower hyperbilirubinemia in a model of inherited liver disease, despite their immature phenotype. Thus, our approach provides major advances toward future clinical applications and would facilitate cell therapy manufacturing from human pluripotent stem cells.

Human hepatocytes derived from pluripotent stem cells: a promising cell model for drug hepatotoxicity screening.

Drug-induced liver injury (DILI) is a frequent cause of failure in both clinical and post-approval stages of drug development, and poses a key challenge to the pharmaceutical industry. Current animal models offer poor prediction of human DILI. Although several human cell-based models have been proposed for the detection of human DILI, human primary hepatocytes remain the gold standard for preclinical toxicological screening. However, their use is hindered by their limited availability, variability and phenotypic instability. In contrast, pluripotent stem cells, which include embryonic and induced pluripotent stem cells (iPSCs), proliferate extensively in vitro and can be differentiated into hepatocytes by the addition of soluble factors. This provides a stable source of hepatocytes for multiple applications, including early preclinical hepatotoxicity screening. In addition, iPSCs also have the potential to establish genotype-specific cells from different individuals, which would increase the predictivity of toxicity assays allowing more successful clinical trials. Therefore, the generation of human hepatocyte-like cells derived from pluripotent stem cells seems to be promising for overcoming limitations of hepatocyte preparations, and it is expected to have a substantial repercussion in preclinical hepatotoxicity risk assessment in early drug development stages.

Human neonatal hepatocyte transplantation induces long-term rescue of unconjugated hyperbilirubinemia in the Gunn rat.

Crigler-Najjar type 1 disease is a rare inherited metabolic disease characterized by high levels of unconjugated bilirubin due to the complete absence of hepatic uridine diphosphoglucuronate-glucuronosyltransferase activity. Hepatocyte transplantation (HT) has been proposed as an alternative treatment for Crigler-Najjar syndrome, but it is still limited by the quality and the low engraftment and repopulation ability of the cells used. Because of their attachment capability and expression of adhesion molecules as well as the higher proportion of hepatic progenitor cells, neonatal hepatocytes may have an advantage over adult cells. Adult or neonatal hepatocytes were transplanted into Gunn rats, a model for Crigler-Najjar disease. Engraftment and repopulation were studied and compared by immunofluorescence (IF). Additionally, the serum bilirubin levels, the presence of bilirubin conjugates in rat serum, and the expression of uridine diphosphate glucuronosyltransferase 1 family polypeptide A1 (UGT1A1) in rat liver samples were also analyzed. Here we show that neonatal HT results in long-term correction in Gunn rats. In comparison with adult cells, neonatal cells showed better engraftment and repopulation capability 3 days and 6 months after transplantation, respectively. Bilirubinemia decreased in the transplanted animals during the whole experimental follow-up (6 months). Bilirubin conjugates were also present in the serum of the transplanted animals. Western blots and IF confirmed the presence and expression of UGT1A1 in the liver. This work is the first to demonstrate the advantage of using neonatal hepatocytes for the treatment of Crigler-Najjar in vivo.

In vitro/in vivo screening of oxidative homeostasis and damage to DNA, protein, and lipids using UPLC/MS-MS.

Multiple analytical methods are required to comprehensively assess oxidative homeostasis and specific damage to macromolecules. Our aim was to develop a straightforward strategy for the fast assessment of global oxidative status and specific damage to DNA, proteins, and lipids. To this end, an analytical method, based on ultra-performance liquid chromatography coupled to mass spectrometry (UPLC-MS/MS), was developed and validated for the quantification of 16 oxidative stress (OS) biomarkers. Some of these markers were unstable; thus, an easy sample treatment procedure, including fractionation and derivatization, was set up. The method was validated according to Food and Drug Administration (FDA) guidelines, and it provided good results in terms of intra- and inter-day precision (≤17.2 and 16 %, respectively), accuracy (relative error measurement between -16.6 and 19.8 %), and linearity (R (2) > 0.994). The approach was applied to determine the oxidative insult provoked to cultured rat hepatocytes by cumene hydroperoxide and to analyze the liver and serum samples from patients diagnosed with nonalcoholic steatohepatitis. In both studies, significant differences were found if compared to the corresponding control groups; interestingly, ophthalmic acid was shown as an OS biomarker in both models for the first time. A key advantage of the novel approach in comparison with former multi-method approaches is that now a single method is applied to assess the 16 OS biomarkers. Its comprehensive capacity to profile oxidative homeostasis and damage in both in vitro and clinical samples has been illustrated, which indicates that the proposed approach is a good choice to evaluate whether OS is involved in physiological signals, diseases, or toxic events and to what extent.

miR-133a regulates vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1), a key protein in the vitamin K cycle.

Regulation of key proteins by microRNAs (miRNAs) is an emergent field in biomedicine. Vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) is a relevant molecule for cardiovascular diseases, since it is the target of oral anticoagulant drugs and plays a role in soft tissue calcification. The objective of this study was to determine the influence of miRNAs on the expression of VKORC1. Potential miRNAs targeting VKORC1 mRNA were searched by using online algorithms. Validation studies were carried out in HepG2 cells by using miRNA precursors; direct miRNA interaction was investigated with reporter assays. In silico studies identified two putative conserved binding sites for miR-133a and miR-137 on VKORC1 mRNA. Ex vivo studies showed that only miR-133a was expressed in liver; transfection of miRNA precursors of miR-133a in HepG2 cells reduced VKORC1 mRNA expression in a dose-dependent manner, as assessed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) as well as protein expression. Reporter assays in HEK293T cells showed that miR-133a interacts with the 3'UTR of VKORC1. Additionally, miR-133a levels correlated inversely with VKORC1 mRNA levels in 23 liver samples from healthy subjects. In conclusion, miR-133a appears to have a direct regulatory effect on expression of VKORC1 in humans; this regulation may have potential importance for anticoagulant therapy or aortic calcification.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME.

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Liver cell culture techniques.

Different sources of hepatic tissue, including whole or split livers from organ donors or from cadavers, waste liver from therapeutic hepatectomies or small-sized surgical biopsies, can be successfully used to prepare human hepatocytes cultures. The two-step collagenase perfusion remains the most effective way to isolate high yields of viable hepatocytes from human liver samples that express many typical hepatic functions, among them drug-metabolising (detoxification) enzymes, when placed in primary culture. Once isolated, human hepatocytes cultured in monolayer in chemically defined conditions (serum-free) survive for limited periods of time gradually losing their differentiated phenotype, in particular the drug-metabolising enzymes. Supplementation of chemically defined media with growth factors, hormones and other specific additives has been used with variable success to extend hepatocyte survival and functionality in culture. Other culture improvements include the use of extracellular components to coat plates or to entrap cells. Conditions for short-term monolayer cultures, allowing the maintenance of liver-specific functions for approximately 1 week, are now well established. Cultures on plastic dishes coated with extracellular matrix components (i.e. Matrigel(TM), collagen, fibronectin or mixture of collagen and fibronectin) do meet many of the requirements for short-term incubation experiments, without adding too much complexity to the system. Practical details on how to carry out these cultures and to assess their functionality (CYP activity and ureogenesis) are discussed in this chapter.

Low-density lipoprotein receptor-deficient hepatocytes differentiated from induced pluripotent stem cells allow familial hypercholesterolemia modeling, CRISPR/Cas-mediated genetic correction, and productive hepatitis C virus infection.

BACKGROUND: Familial hypercholesterolemia type IIA (FH) is due to mutations in the low-density lipoprotein receptor (LDLR) resulting in elevated levels of low-density lipoprotein cholesterol (LDL-c) in plasma and in premature cardiovascular diseases. As hepatocytes are the only cells capable of metabolizing cholesterol, they are therefore the target cells for cell/gene therapy approaches in the treatment of lipid metabolism disorders. Furthermore, the LDLR has been reported to be involved in hepatitis C virus (HCV) entry into hepatocytes; however, its role in the virus infection cycle is still disputed. METHODS: We generated induced pluripotent stem cells (iPSCs) from a homozygous LDLR-null FH-patient (FH-iPSCs). We constructed a correction cassette bearing LDLR cDNA under the control of human hepatic apolipoprotein A2 promoter that targets the adeno-associated virus integration site AAVS1. We differentiated both FH-iPSCs and corrected FH-iPSCs (corr-FH-iPSCs) into hepatocytes to study statin-mediated regulation of genes involved in cholesterol metabolism. Upon HCV particle inoculation, viral replication and production were quantified in these cells. RESULTS: We showed that FH-iPSCs displayed the disease phenotype. Using homologous recombination mediated by the CRISPR/Cas9 system, FH-iPSCs were genetically corrected by the targeted integration of a correction cassette at the AAVS1 locus. Both FH-iPSCs and corr-FH-iPSCs were then differentiated into functional polarized hepatocytes using a stepwise differentiation approach (FH-iHeps and corr-FH-iHeps). The correct insertion and expression of the correction cassette resulted in restoration of LDLR expression and function (LDL-c uptake) in corr-FH-iHeps. We next demonstrated that pravastatin treatment increased the expression of genes involved in cholesterol metabolism in both cell models. Moreover, LDLR expression and function were also enhanced in corr-FH-iHeps after pravastatin treatment. Finally, we demonstrated that both FH-iHeps and corr-FH-iHeps were as permissive to viral infection as primary human hepatocytes but that virus production in FH-iHeps was significantly decreased compared to corr-FH-iHeps, suggesting a role of the LDLR in HCV morphogenesis. CONCLUSIONS: Our work provides the first LDLR-null FH cell model and its corrected counterpart to study the regulation of cholesterol metabolism and host determinants of HCV life cycle, and a platform to screen drugs for treating dyslipidemia and HCV infection.

Identification of apoptotic drugs: multiparametric evaluation in cultured hepatocytes.

It is now recognized that necrosis is not the only mechanism responsible for chemically-induced cell death. It is believed that apoptosis could be the major form of cell death induced by toxicants and that necrosis is associated only with circumstances of gross cell injury. The liver is a key target organ for drug toxicity and an important effort in drug-discovery deals with the identification of molecules with hepatotoxic potential. The importance of apoptosis in toxicology has been underestimated given the difficulty of identifying apoptotic cells in in vitro models when apoptosis normally degenerates to secondary necrosis. Nowadays, the central role played by apoptosis in the toxicity of many xenobiotics and P450-generated metabolites is recognized. The detection of drug-induced apoptosis constitutes one of the highest priorities of the pharmaceutical industry. Different markers aimed at identifying apoptotic compounds irrespectively of the pathway of how cell apoptosis was initiated have been proposed. The aim of the present paper is to review the utility of some available in vitro strategies for studying drug-induced liver apoptosis. The evaluation of apoptotic or anti-apoptotic effects of chemicals in hepatocytes is illustrated by several examples including model apoptotic compounds, pharmaceutical drugs which have been shown to induce apoptosis as an adverse effect; and drugs preventing apoptosis. By combining appropriated markers, apoptosis can be detected in hepatocytes long before cell necrosis, at sub-cytotoxic concentrations of the drugs. The possibility of using small amounts of cells cultured in multiwell formats and automation has notably contributed to develop reproducible, reliable, sensitive, easy-to-handle and rapid multiparametric assays that are ideally amenable to high throughput screening (HTS).

Evaluation of drug-metabolizing and functional competence of human hepatocytes incubated under hypothermia in different media for clinical infusion.

Hepatocyte transplantation has been proposed as a method to support patients with liver insufficiency. Key factors for clinical cell transplantation to progress is to prevent hepatocyte damage, loss of viability and cell functionality, factors that depend on the nature of the tissue used for isolation to a large extent. The main sources of tissue for hepatocyte isolation are marginal livers that are unsuitable for transplantation, and segments from reduced cadaveric grafts. Hepatocellular transplantation requires infusing human hepatocytes in suspension over a period of minutes to hours. The beneficial effect of hypothermic preservation of hepatocytes in infusion medium has been reported, but how critical issues towards the success of cell transplantation, such as the composition of infusion medium and duration of hepatocyte storage will affect hepatocyte quality for clinical cell infusion has not been systematically investigated. Infusion media composition is phosphate-buffered saline containing anticoagulants and human serum albumin. The supplementation of infusion media with glucose or N-acetyl-cystein, or with both components at the same time, has been investigated. After isolation, hepatocytes were suspended in each infusion medium and a sample at the 0 time point was harvested for cell viability and functional assessment. Thereafter, cells were incubated in different infusion media agitated on a rocker platform to simulate the clinical infusion technique. The time course of hepatocyte viability, funtionality (drug-metabolizing enzymes, ureogenic capability, ATP, glycogen, and GSH levels), apoptosis (caspase-3 activation), and attachment and monolayer formation were analyzed. The optimal preservation of cell viability, attaching capacity, and functionality, particularly GSH and glycogen levels, as well as drug-metabolizing cytochrome P450 enzymes, was found in infusion media supplemented with 2 mM N-acetyl-cystein and 15 mM glucose.

Functional assessment of the quality of human hepatocyte preparations for cell transplantation.

Hepatocyte transplantation is an alternative therapy to orthotopic liver transplantation for the treatment of liver diseases. Good quality freshly isolated or cryopreserved human hepatocytes are needed for clinical transplantation. However, isolation, cryopreservation, and thawing processes can seriously impair hepatocyte viability and functionality. The aim of the present study was to develop a fast and sensitive procedure to estimate the quality of hepatocyte preparations prior to clinical cell infusion. To this end, cell viability, attachment efficiency, and metabolic competence (urea synthesis and drug-metabolizing P450 activities) were selected as objective criteria. Viability of hepatocyte suspension was estimated by trypan blue staining. DNA content of attached cells 50 min after hepatocyte platting to fibronectin/collagen-coated dishes was quantified to estimate adherence capacity. Urea production was determined after incubating hepatocyte suspensions with 2 mM C1NH4 for 30 min. The cytochrome P450 function was assayed by a 30-min incubation of hepatocyte suspension with a cocktail mixture containing selective substrates for seven individual P450 activities (CYP1A2, 2A6, 2C9, 2C19, 2D6, 2E1, and 3A4). The assay can be applied to both freshly isolated and cryopreserved hepatocyte suspensions, and the results are available within 1 h, which could help to make short-term decisions: 1) to assess the suitability for cell transplantation of a preparation of freshly isolated hepatocytes or a particular batch of thawed cells, or 2) to estimate the convenience of banking a particular cell preparation.

An update on metabolism studies using human hepatocytes in primary culture.

BACKGROUND: Cultured human hepatocytes are the closest in vitro model to human liver and constitute a very predictive model for drug metabolism in vivo. The variability observed in human hepatocytes reflects the existing phenotypic heterogeneity of cytochrome P450 expression in human liver. OBJECTIVES: As drug metabolism is the major source of pharmacokinetic variability in human beings, the main areas of current drug metabolism research in human hepatocytes are reviewed. METHODS: To speed up the selection of drug candidates, the evaluation of metabolic stability, metabolite profiling and identification, and drug-drug interaction potential are key issues in drug development. RESULTS/CONCLUSION: In vitro drug metabolism studies, which are inexpensive and readily carried out, serve as an adequate screening mechanism to characterize drug metabolites, elucidate their pathways, and make suggestions for further in vivo testing.

[Adipose tissue-derived stem cells: hepatic plasticity]. / Células madre del tejido adiposo: plasticidad hepática.

Currently, the only effective treatment for end-stage liver disease is liver transplantation. The number of patients on the waiting list increases considerably each year, giving rise to a wide imbalance between supply and demand for healthy livers. Knowledge of stem cells and their possible use have awakened great interest in the field of hepatology, these cells being one of the most promising short-term alternatives. Hepatic stem cell therapy consists of the implantation of healthy cells capable of performing the functions that damaged cells are unable to carry out. Recent observations indicate that several stem cells can differentiate into distinct cell lineages. Hepatic differentiation of adult stem cells from several origins has yielded highly promising results. Adipose tissue in adults contains a reservoir of stem cells that can be induced and differentiated into different types of cells, showing a high degree of plasticity. Because of its abundance and easy access, adipose tissue is a promising source of adult stem cells for hepatic stem cell therapy. The present article reviews the progress made in the differentiation of adult stem cells from adipose tissue into cells with hepatic phenotype. We also discuss the potential application of this technique as a therapy for temporary metabolic support in patients with 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 treatment in patients with genetic metabolic defects in vital liver functions.

Overexpression of SND p102, a rat homologue of p100 coactivator, promotes the secretion of lipoprotein phospholipids in primary hepatocytes.

SND p102 belongs to an evolutionarily conserved family of proteins first described as transcriptional coactivators, whose biological function has not yet been defined. High expression levels of homologues of SND p102 in non-nuclear compartments of lipid secretory tissues and in murine liver endoplasmic reticulum suggest a role for SND p102 in lipoprotein secretion in hepatocytes. To address this issue, after ascribing by confocal microscopy and Western blotting a non-nuclear localization of SND p102 in rat hepatocytes, we cloned its full-length cDNA, developed adenoviral vectors encoding the cDNA or a specific antisense sequence, and characterized the lipoprotein particles created and released for 24 h by transfected rat hepatocytes. The cellular ability to secrete apoB and apoA-I was not affected by SND p102 differential expression, nor was that of lipoproteins-triglyceride, -cholesterol and -cholesteryl esters. However, cells overexpressing SND p102 secreted phospholipid-rich lipoproteins. Compared with hepatocytes with basal or attenuated SND p102 expression, they secreted approximately 45% and 80% more phospholipid in d<1.015 g/mL and 1.015

Hepatocytes--the choice to investigate drug metabolism and toxicity in man: in vitro variability as a reflection of in vivo.

The pharmaceutical industry is committed to marketing safer drugs with fewer side effects, predictable pharmacokinetic properties and quantifiable drug-drug interactions. Drug metabolism is a major determinant of drug clearance and interindividual pharmacokinetic differences, and an indirect determinant of the clinical efficacy and toxicity of drugs. Progressive advances in the knowledge of metabolic routes and enzymes responsible for drug biotransformation have contributed to understanding the great metabolic variations existing in human beings. Phenotypic as well genotypic differences in the expression of the enzymes involved in drug metabolism are the main causes of this variability. However, only a minor part of phenotypic variability in man is attributable to gene polymorphisms, thus making the definition of a normal liver complex. At present, the use of human in vitro hepatic models at early preclinical stages means that the process of selecting drug candidates is becoming much more rational. Cultured human hepatocytes are considered to be the closest model to human liver. However, the fact that hepatocytes are located in a microenvironment that differs from that of the cell in the liver raises the question: to what extent does drug metabolism variability observed in vitro actually reflect that of the liver in vivo? By comparing the metabolism of a model compound both in vitro and in vivo in the same individual, a good correlation between the in vitro and in vivo relative abundance of oxidized metabolites and the hydrolysis of the compound was observed. Thus, it is reasonable to consider that the variability observed in human hepatocytes reflects the existing phenotypic heterogeneity of the P450 expression in human liver.

A human hepatocellular in vitro model to investigate steatosis.

The present study was designed to define an experimental model of hepatocellular steatosis with a fat overaccumulation profile in which the metabolic and cytotoxic/apoptotic effects could be separated. This was accomplished by defining the experimental conditions of lipid exposure that lead to significant intracellular fat accumulation in the absence of overt cytotoxicity, therefore allowing to differentiate between cytotoxic and apoptotic effects. Palmitic (C16:0) and oleic (C18:1) acids are the most abundant fatty acids (FFAs) in liver triglycerides in both normal subjects and patients with nonalcoholic fatty liver disease (NAFLD). Therefore, human hepatocytes and HepG2 cells were incubated with a mixture of different proportions of saturated (palmitate) and unsaturated (oleate) FFAs to induce fat-overloading. Similar intracellular levels of lipid accumulation as in the human steatotic liver were achieved. Individual FFAs have a distinct inherent toxic potential. Fat accumulation, cytotoxicity and apoptosis in cells exposed to the FFA mixtures were investigated. The FFA mixture containing a low proportion of palmitic acid (oleate/palmitate, 2:1 ratio) is associated with minor toxic and apoptotic effects, thus representing a cellular model of steatosis that mimics benign chronic steatosis. On the other hand, a high proportion of palmitic acid (oleate/palmitate, 0:3 ratio) might represent a cellular model of steatosis in which saturated FFAs promote an acute harmful effect of fat overaccumulation in the liver. These hepatic cellular models are apparently suitable to experimentally investigate the impact of fat overaccumulation in the liver excluding other factors that could influence hepatocyte behaviour.

Using high-content screening technology for studying drug-induced hepatotoxicity in preclinical studies.

INTRODUCTION: The need for alternatives to animal experimentation and traditional testing methods has been widely discussed in recent years. This has led scientists and regulatory authorities to investigate alternative methods for toxicity testing. High-content screening (HCS) has emerged as a powerful tool in predictive toxicology since it permits molecular, cellular and tissue-based toxicity assessments. HCS allows automated image acquisition and analysis, and provides information on multiple properties of individual cells loaded simultaneously with fluorescent dyes, which is used for drug safety evaluations. Areas covered: Herein, the authors review the principles of HCS technology and some of the most widely used HCS assays for studying drug-induced hepatotoxicity in preclinical studies in general and in the pharmaceutical industry in particular. Expert opinion: The widespread acceptation of HCS by pharmaceutical companies and academic researchers highlights the potential usefulness of this technology as a prioritization tool in drug development. The improvement of different key points such as fluorescent probes or bioinformatics tools will consolidate HCS in drug discovery.

Alternative Cell Sources to Adult Hepatocytes for Hepatic Cell Therapy.

Adult hepatocyte transplantation is limited by scarce availability of suitable donor liver tissue for hepatocyte isolation. New cell-based therapies are being developed to supplement whole-organ liver transplantation, to reduce the waiting-list mortality rate, and to obtain more sustained and significant metabolic correction. Fetal livers and unsuitable neonatal livers for organ transplantation have been proposed as potential useful sources of hepatic cells for cell therapy. However, the major challenge is to use alternative cell sources for transplantation that can be derived from reproducible methods. Different types of stem cells with hepatic differentiation potential are eligible for generating large numbers of functional hepatocytes for liver cell therapy to treat degenerative disorders, inborn hepatic metabolic diseases, and organ failure. Clinical trials are designed to fully establish the safety profile of such therapies and to define target patient groups and standardized protocols.

Hepatogenic differentiation of human mesenchymal stem cells from adipose tissue in comparison with bone marrow mesenchymal stem cells.

AIM: To investigate and compare the hepatogenic transdifferentiation of adipose tissue-derived stem cells (ADSC) and bone marrow-derived mesenchymal stem cells (BMSC) in vitro. Transdifferentiation of BMSC into hepatic cells in vivo has been described. Adipose tissue represents an accessible source of ADSC, with similar characteristics to BMSC. METHODS: BMSCs were obtained from patients undergoing total hip arthroplasty and ADSC from human adipose tissue obtained from lipectomy. Cells were grown in medium containing 15% human serum. Cultures were serum deprived for 2 d before cultivating under similar pro-hepatogenic conditions to those of liver development using a 2-step protocol with sequential addition of growth factors, cytokines and hormones. Hepatic differentiation was RT-PCR-assessed and liver-marker genes were immunohistochemically analysed. RESULTS: BMSC and ADSC exhibited a fibroblastic morphology that changed to a polygonal shape when cells differentiated. Expression of stem cell marker Thy1 decreased in differentiated ADSC and BMSC. However, the expression of the hepatic markers, albumin and CYPs increased to a similar extent in differentiated BMSC and ADSC. Hepatic gene activation could be attributed to increased liver-enriched transcription factors (C/EBPbeta and HNF4alpha), as demonstrated by adenoviral expression vectors. CONCLUSION: Mesenchymal stem cells can be induced to hepatogenic transdifferentiation in vitro. ADSCs have a similar hepatogenic differentiation potential to BMSC, but a longer culture period and higher proliferation capacity. Therefore, adipose tissue may be an ideal source of large amounts of autologous stem cells, and may become an alternative for hepatocyte regeneration, liver cell transplantation or preclinical drug testing.

Hepatocyte cell lines: their use, scope and limitations in drug metabolism studies.

Gaining knowledge on the metabolism of a drug, the enzymes involved and its inhibition or induction potential is a necessary step in pharmaceutical development of new compounds. Primary human hepatocytes are considered a cellular model of reference, as they express the majority of drug-metabolising enzymes, respond to enzyme inducers and are capable of generating in vitro a metabolic profile similar to what is found in vivo. However, hepatocytes show phenotypic instability and have a restricted accessibility. Different alternatives have been explored in the past recent years to overcome the limitations of primary hepatocytes. These include immortalisation of adult or fetal human hepatic cells by means of transforming tumour virus genes, oncogenes, conditionally immortalised hepatocytes, and cell fusion. New strategies are currently being used to upregulate the expression of drug-metabolising enzymes in cell lines or to derive hepatocytes from progenitor cells. This paper reviews the features of liver-derived cell lines, their suitability for drug metabolism studies as well as the state-of-the-art of the strategies pursued in order to generate metabolically competent hepatic cell lines.